text:
\section{General Overview}

The \aipcls{} is a \LaTeXe{} document class for conference proceedings
of the American Institute of Physics and other documents with similar
layout requirements.  Your file will be used to reproduce
your paper as is, the only modifications done by the publisher are
adding appropriate page numbers and the copyright line. It is
therefore essential that you embed all fonts when saving your file.

This version of the guide explains all features of the class some of
which are only applicable to certain proceeding layouts.

The class provides essentially the same markup as implemented by
\LaTeX's standard
\texttt{article} class.  In addition to this it implements the
following:
\begin{itemize}
\item extended set of front matter commands,
\item automatic placement of floats into column or page areas
  including turning of table floats by 90\textdegree{} if necessary,
\item allows mixing column and page-wide floats without getting the
  numbering out of sync,
\item footnotes will appear below bottom floats,
\item extended set of citation commands if the \texttt{natbib} system
  is installed,
\item support for table notes,
\item support for textual page references like ``on the next page''.
\end{itemize}

Due to the extended functionality an article written for \LaTeX{}'s
standard article class might need adjustments in the following places
before it can be used with the \aipcls{}
(a more detailed description is given in later sections):
\begin{itemize}
\item
  In the preamble, since the \aipcls{} requires a |\layoutstyle|
  declaration.
\item
  In the front matter, since  the \aipcls{} uses an extended set of
  title/author declarations.
\item
  In the body of floats, since the \aipcls{} only allows a single
  |\caption| command and processes the body in horizontal mode.
\end{itemize}

\section{Checking your \LaTeX{} distribution}

To ensure that your installation of \LaTeX{} contains everything
necessary to successfully use the \aipcls{}, run the file
\texttt{aipcheck.tex} through \LaTeX, e.g.,
\begin{verbatim}
  latex aipcheck
\end{verbatim}
It will try to determine if everything
necessary is available and if not, will make recommendations what can
be done about it. In certain cases you might be able to use the class
if you follow the suggestions, in other cases the only solution is to
upgrade your \LaTeX{} installation.

Unfortunately it is impossible to check for all potential problems. If
\texttt{aipcheck.tex} claims everything is fine, but you nevertheless
have difficulties, consult the ``Frequently Asked Question''
(\texttt{FAQ.txt}) and the readme file in the distribution.

\section{Class details}

\subsection{Selecting the target layout}

The class supports different layouts. These are selected by
placing a |\layoutstyle| declaration in the preamble of the document.

\BDefC{layoutstyle}[m]{layout name}

This command is required.
With version 1.3 of the \aipcls{} the
following \Larg{layout name}s can be specified.
\begin{description}
\item[6x9]          Layout for the AIP Conference Proceedings with
  6 x 9 inches single column format (short name |6s|).
\item[8x11single] Layout for the AIP Conference Proceedings with
  8.5 x 11 inches single column format (short name |8s|).
\item[8x11double] Layout for the AIP Conference Proceedings with
  8.5 x 11 inches double column format (short name |8d|).
\item[arlo] Layout for the ``Acoustics Research Letters Online'' --- ARLO.
\end{description}
For example, the current guide was produced using the declaration
|\layoutstyle{|\texttt{\selectedlayoutstyle}|}|.

\subsection{Supported options}\label{suppopt}

As the class is based on the article class of standard \LaTeX{} all
reasonable\footnote{Reasonable means not conflicting with fixed
requirements for the AIP class, e.g., as this class requires 10pt body
size option \texttt{11pt} and \texttt{12pt} are ignored and produce a
warning.} options of this class are supported automatically.
In addition there are a number of options unique to the \aipcls.

\subsubsection{Paper selection}

Two options control the placement of the text on the physical
page. Choose the one that corresponds to your printer paper.
\begin{description}
\item[letterpaper] Directs the class to assume that the output is
printed on US letter sized paper (default).

\emph{Please note that the paper format is typically also specified in
the program that turns the \LaTeX{} output into PostScript. For
example, some \texttt{dvips} installations have A4 as their default
paper (typically those in Europe). In that case you have to call the
\texttt{dvips} program  with the option \texttt{-t letter} to ensure
that the resulting PostScript file has the correct margins!}

\item[4apaper] Directs the class to assume that the output is
printed on A4 sized paper.
\end{description}

\subsubsection{Font selection}

Five options control the selection of fonts in the document; use at
most one of them.
\begin{description}
\item[mathptmx] Directs the class to use PostScript Times and Symbol
  fonts (a few missing glyphs are taken from Computer Modern) for
  math by loading the \texttt{mathptmx} package.
  This option is the default.

  This option does not support the |\boldmath| command since there
  exists no PostScript Symbol font in bold. It is possible, however to
  use |\mathbf| which allows you to get at least a bold Latin
  Alphabet.

\item[mathptm] Directs the class to use PostScript Times and Symbol
  fonts but used the older package \texttt{mathptm} which has upright
  greek lowercase letters.

  This option does not support the |\boldmath| command since there
  exists no PostScript Symbol font in bold. It is possible, however to
  use |\mathbf| which allows you to get at least a bold Latin
  Alphabet.

\item[mathtime] Directs the class to use MathTime fonts for math by
  loading the \texttt{mathtime} package. These fonts are commercial so
  that this option will not work if you don't own them.
  If this option is chosen one can also use the options for this
  package as global options to the class.

\item[mtpro] Directs the class to use MathTime Professional fonts for math by
  loading the \texttt{mtpro} package. These fonts are commercial (the
  successors to the MathTime fonts from the previous option) so
  that this option will not work if you don't own them.
  If this option is chosen one can also use the options for this
  package as global options to the class.

\item[nomathfonts] Directs the class not to set up math fonts (which
  means using the installation default which is usually Computer
  Modern). This option is intended in case a special math font setup
  is loaded in the document preamble.

\item[cmfonts] Directs the class to use standard Computer Modern fonts
  for math and text. This does not conform to the specification for this
  class and is intended for draft preparation in environments where
  the required fonts are unavailable.
\end{description}

\subsubsection{Textual references}

The next options enable textual references; if this is desired select
one of them:
\begin{description}
\item[varioref] Loads the \texttt{varioref} package
  (see \cite[p.68ff]{A-W:MG04})
  allowing to produce textual page references. See section on
  Cross-references~\vpageref{xref} for details.
\item[nonvarioref] Disables the |\reftextvario| command so that the
  strings produced by \texttt{varioref} commands will not depend on
  the number of references seen so far. Implies the varioref option.
\end{description}

\subsubsection{Table note markers}

Notes to tables can be influenced as follows:
\begin{description}
\item[tnotealph] Produce raised lower case alphabetic marks to
  indicate table notes.
\item[tnotesymbol] Use footnote symbols to indicate table notes
  (default).
\end{description}

\subsubsection{Citation mode}

The citation mode can be influenced with the following two options:
\begin{description}
\item[numcites] Citations are typeset using numbers. Depending on the
  proceeding style these might appear raised or in brackets, etc.~(default).
\item[bibliocites] Citations are typeset using an author/year
  scheme. This requires the installation of the \texttt{natbib} system.
\end{description}
In some layout styles these options might be without effect.

\subsubsection{Heading numbers}

Heading numbers can be turned on or off with the following two options:
\begin{description}
\item[numberedheadings] Headings are numbered.
\item[unnumberedheadings] Headings are unnumbered (default).
\end{description}
In some layout styles these options might be without effect.

\subsubsection{Drafts}

Finally there is one standard \texttt{article} class option which has
its functionality extended:
\begin{description}
\item[draft] Allows |\tableofcontents| and similar commands to work
  without error message (during development of article). It marks
  overfull boxes and
  also provides page numbers in the printout.

  \textbf{Remove this option when producing the final paper.}
\end{description}

\subsection{Front matter}

The class supports an extended set of front matter commands. These
commands differ from those used by standard \LaTeX's \texttt{article}
class. Thus, if an article already written is adapted to be used with
the \aipcls{}, the front matter has to be modified somewhat.

Some of the commands below
are required only for certain proceedings. Declarations that are not
required will be silently ignored.

\BDefC{title}[om]{short title}{title text}
In standard \LaTeX{} this command has no optional argument. In the
\aipcls{} one can specify an abbreviated title text which is used,
for example, in the running footer in draft mode.

\BDefC{author}[mm]{author name}{author information}

In standard \LaTeX{} this command had only one argument containing
both author name and address information. In this class it has two
arguments and the second argument contains data structured using
key/value pairs separated by commas.

For example, the authors of this paper have been specified as:
\begin{verbatim}
\author{F. Mittelbach}{
  address={Zedernweg 62, Mainz},
 ,email=
{frank.mittelbach@latex-project.org}}
\author{D. P. Carlisle}{
  address={Willow House, Souldern},
 ,email={david@dcarlisle.demon.co.uk}}
\end{verbatim}
Supported keywords will be \texttt{address}, \texttt{email},
\texttt{altaddress}, \texttt{homepage},
and \texttt{thanks}.
(With release 1.3 of \aipcls{} only
\texttt{address}, \texttt{altaddress} and \texttt{email} should be used; support for the other
keywords will be added later.)
Depending on the layout of the target proceedings
some of the keys may get ignored!

\BDefC{classification}[m]{data}
Some proceedings require classification data, e.g., PACS numbers. If not,
this declaration is ignored.

\BDefC{keywords}[m]{data}
Some layouts require keyword data. If not, this declaration is
ignored.

\BDefC{copyrightholder}[m]{name}
Some layouts require copyright information.  Normally a default
is provided by the class. With this declaration the copyright holder
can be overwritten.

\BDefC{copyrightyear}[m]{year}
Some layouts require copyright data. With this declaration the
copyright year can be specified. (If such data is required the current
year is provided as default).

\BDefE{abstract}
In contrast to standard \LaTeX{} the abstract environment has to
appear before the |\maketitle| command.

\BDefC{maketitle}
This command inserts the actual front matter data. It has to follow the
above declarations.

\subsubsection{Multiple authors}

Multiple authors are entered by specifying one |\author| command per
author. Care needs to be taken when specifying shared addresses: they
have to be absolutely identical. Depending on the chosen layout the
class will merge such addresses but will recognize them only as
identical, if the input including spaces is the same!

The |\and| command as defined in the \texttt{article} class to
separate multiple authors is not supported.

\subsubsection{Dates}

\BDefC{received}[m]{date}
\BDefC{revised}[m]{date}
\BDefC{accepted}[m]{date}
Some layouts require specification of date of arrival, revision,
and/or acceptance. The above declarations provide a way to specify such
dates if necessary.

\BDefC{date}[m]{date}
The article class provides the |\date| command which is not used
by \aipcls. If supplied it will be ignored unless the \texttt{draft}
option is specified in which case it will show up in a footer line
together with the title and the page number to ease document
development.

\subsubsection{Other front matter commands}

The |\tableofcontents|, |\listoffigures|, and |\listoftables| commands
are provided but produce (beside output) an error message unless the
\texttt{draft} option was selected. This is done since the \aipcls{}
does not support page numbering and thus the above commands
essentially produce incorrect data.

\subsection{Headings}

The \aipcls{} officially supports three heading levels, i.e.,
|\section|, |\subsection|, and |\subsubsection|.

It also supports the commands |\paragraph| and |\subparagraph|
although the latter heading levels are not part of the \aipcls{}
specification and are therefore discouraged.

In some layouts |\section| headings are changed to UPPERCASE. Special care is
taken not to uppercase math material, but this support is only available if
the package |textcase| is part of the \LaTeX{} distribution.

\subsection{Cross-references}\label{xref}

Cross-references to page numbers are not possible with the \aipcls{}
as the page numbers are determined after production. For this reason
the |\pageref| command of \LaTeX{} is disabled by default.

Since headings in most layouts do not carry numbers they can't be
referenced either.

References to tables, figures, and equations are possible using
the \LaTeX{} commands |\label| and |\ref|.

However if the class option \texttt{varioref} or \texttt{nonvarioref}
is used, references to page numbers are possible again as they will
generate textual references of the form ``on the following page'' or
``on an earlier page'' etc. The produced strings are customizable as
described in detail in the \texttt{varioref} package documentation or
in \cite[p.68ff]{A-W:MG04}.

The class defaults are as follows and can be changed with
|\renewcommand| in the document preamble. The \texttt{varioref}
package normally distinguishes between reference to facing pages and
references to pages that need turning over using different strings in
these cases. However, since with \aipcls{} class page numbers are not
determined at the time of production no assumption can be made that
page $x$ and $x+1$ actually fall onto the same double spread. For this
reason the defaults used here do not produce strings containing the
word ``facing'' or ``opposite''.
\begin{verbatim}
 \renewcommand\reftextfaceafter
    {on the next page}
 \renewcommand\reftextfacebefore
    {on the \reftextvario{previous}
                  {preceding} page}
 \renewcommand\reftextafter
    {on the \reftextvario{next}
                  {following} page}
 \renewcommand\reftextbefore
    {on the \reftextvario{previous
                page}{page before}}
 \renewcommand\reftextcurrent
    {on \reftextvario{this}
                {the current} page}
\end{verbatim}
Normally, text for references which are ``far away'' are produced
using |\reftextfaraway| in \texttt{varioref}. However, to produce
textual references without referring to actual page numbers even in
this case, this command was hijacked in the \aipcls{} and redefined to
determine whether or not this is a reference to some earlier or later
page. So instead of changing this command the class provides the
following two commands for customization:
\begin{verbatim}
 \renewcommand\reftextearlier
    {\reftextvario{on an earlier
                 page}{earlier on}}
 \renewcommand\reftextlater
    {\reftextvario{later on}
                    {further down}}
\end{verbatim}
To illustrate the result of this package all references in this
document are made using |\vref| or |\vpageref|, e.g., references to
Figure~\vref{fig:b} and Figure~\vref{fig:a}. These commands work best
if used only for important references. Be careful when using them
several times close to each other as the automatically generated texts
then may sound strange (as they do in the example in this paragraph).

\BDefC{eqref}[m]{label}

For reference to equation numbers |\eqref| can be used instead of
the standard |\ref| command. The |\eqref| command will automatically add any
frills required by the layout style, while |\ref| will only typeset
the plain number.
For example, in the \texttt{arlo} style it will
print ``Eq.~(1)'' while |\ref| would result in ``1''.

\subsection{Lists}

The \aipcls{} supports all standard list environments like
\texttt{itemize}, \texttt{enumerate}, etc.

\subsection{Graphics support}

Support for including and manipulating graphics is provided as the
standard \LaTeX{} \texttt{graphicx} package is automatically loaded by
the \aipcls. For detailed descriptions of the commands made available
by this package see~\cite{A-W:GMR97} or the package documentation
coming with the \LaTeX{} release. A sufficient introduction is also
given by~\cite{A-W:LLa94} although there only the \texttt{graphics}
package (a subset of the \texttt{graphicx} package) is described.

A typical application is given in the following example where a
picture is resized to span 70\% of one column:
\begin{verbatim}
\begin{figure}[!b]
 \resizebox{.7\columnwidth}{!}
  {\includegraphics{escher}}
 \source{Guy Shaw}
 \caption{An illustration taken
          from~\cite{A-W:MG04}}
 \label{fig:a}
\end{figure}
\end{verbatim}
resulting in figure \vref{fig:a}.
\begin{figure}[!b]
 \resizebox{.7\columnwidth}{!}
  {\includegraphics[draft=false]{escher}}
 \source{Guy Shaw}
 \caption{An illustration taken
          from~\cite{A-W:MG04}}
 \label{fig:a}
\end{figure}

\subsection{Floats}

Floats are objects which do not have to stay in sync with the running
text but are allowed to move from their original place to some other
position where they fit better for page breaking reasons. Such objects
they are typically numbered so that they can be referenced from within
the running text.

\LaTeX{} by default supports two float types: figures and
tables. These float types are also supported by the \aipcls{} although
their internal implementation is quite different resulting in a number
of important differences in behavior:\footnote{There exist packages
that extend the number of float types. (This information is given as a
footnote to show that footnotes in this class come out below a bottom
float.)}
\begin{itemize}
\item The position of the float caption is determined automatically,
  independently of the placement of the |\caption| command within the
  float body.
\item
  Depending on its width the float automatically spans two
  columns.
  In case of a table the whole object (including its caption)
  might be rotated automatically if its exceeds |\textwidth|.
\item The body of the float environments are processed in L-R mode and
  not in paragraph mode as in standard \LaTeX. This is necessary for
  measuring its width. Thus if paragraph mode is needed one has to put
  a \texttt{minipage} environment of the appropriate width (e.g.,
  |\columnwidth|) into the body.
\item Only one |\caption| command per float is allowed.
\end{itemize}

\subsubsection{Figures}

\BDefE{figure}[o]{pos}

Like with standard \LaTeX{} the optional \Larg{pos} argument can be
used to specify into which float areas this float is allowed to
migrate (default is |tbp|).

The environment \texttt{figure*} is not supported as figures that need
to span both columns are automatically recognized in two column mode.

\BDefC{source}[m]{text}
Command to specify the origin of the picture shown. The \Larg{text}
will be printed in small italics below the illustration.

A typical example of a figure float would be
\begin{verbatim}
\begin{figure}
 \resizebox{.8\textwidth}{!}
           {\includegraphics{outline}}
 \caption{PostScript example taken
          from~\cite{A-W:MG04}}
 \label{fig:b}
 \source{F. Mittelbach}
\end{figure}
\end{verbatim}
The result is shown in Figure~\vref{fig:b}.

\begin{figure}
\resizebox{.8\textwidth}{!}{\includegraphics[draft=false]{outline}}
\caption{PostScript example taken from~\cite{A-W:MG04}}
\label{fig:b}
\source{F. Mittelbach}
\end{figure}

\BDefC{spaceforfigure}[mm]{horizontal}{vertical}
If the illustration is to be manually pasted into the final document
one can leave the right amount of space by using this command as
follows:
\begin{verbatim}
\begin{figure}
 \spaceforfigure{2in}{1cm}
 \caption{Caption for a figure to be
          pasted in later}
 \label{fig:3}
 \source{F. Mittelbach}
\end{figure}
\end{verbatim}
All standard \TeX{} units can be used to specify the space needed. The
above example make room for an illustration that is two inches wide and
one centimeter high. The result is shown as Figure~\vref{fig:3}.

\begin{figure}
 \spaceforfigure{2in}{1cm}
 \caption{Caption for a figure to be
          pasted in later}
 \label{fig:3}
 \source{F. Mittelbach}
\end{figure}

\subsubsection{Tables}

\BDefE{table}[o]{pos}

Like with standard \LaTeX{} the optional \Larg{pos} argument can be
used to specify into which float areas this float is allowed to
migrate (default is |tbp|).

The environment \texttt{table*} is not supported as tables that need
to span both columns are automatically recognized in two column mode.

Typically the body of the environment would consist of a
\texttt{tabular} environment responsible for producing the actual
table including the table and stub headers.

\BDefC{tablehead}[mmmm]{cols}{h-pos}{v-pos}{heading text}

To ease the production of tables the command |\tablehead| is provided
which is essentially and abbreviation for a |\multicolumn| command
that additionally boldens its text argument. I.e., \Larg{cols}
specifies the number of columns the \Larg{heading text} should span
and \Larg{h-pos} defines the horizontal positioning of the text of the
column(s), e.g., |l|, |r|, |c|, or |p{...}|.  In contrast to a simple
|\multicolumn| command the \Larg{heading text} can be split vertically
by using |\\| to denote the line breaks.  The \Larg{v-pos} argument
should contain either |t|, |c|, or |b| denoting the vertical placement
of the text in relation to other cells of that row. It is only
relevant if the \Larg{heading text} consists of more than one
line. See the example table \vpageref[below]{tab:source} that
demonstrates the use of this command.

\BDefC{source}[m]{text} Command to specify the origin of the data
given in the table. The \Larg{text} will be printed in small italics
below the table.

\BDefC{tablenote}[m]{text}

Command to produce a note to the table. It can only be used within a
\texttt{table} environment and should be used only at the right
end of a table cell. The command produces a raised footnote symbol at
the place used which sticks into the right margin. As far as \LaTeX{}
is concerned this symbol does not occupy any space. Thus is will not
modify the alignment of table columns. The \Larg{text} will appear
below the table.

In the current release notes to |\caption| or |\source| are not
possible.

\BDefC{tablenote*}[m]{text}
Like |\tablenote| but this time the raised footnote symbol will occupy
space. This version is intended to be used in the middle of cells.

An example showing the use of all commands described above is shown in
Table~\vref{tab:a}. It was produced by the following input:\label{tab:source}
\begin{verbatim}
\begin{table}
\begin{tabular}{lrrrr}
\hline
 &\tablehead{1}{r}{b}{Single\\outlet}
 &\tablehead{1}{r}{b}{Small\tablenote
       {2-9 retail outlets}\\multiple}
 &\tablehead{1}{r}{b}{Large\\multiple}
 &\tablehead{1}{r}{b}{Total}   \\
\hline
1982 & 98  & 129 & 620    & 847\\
1987 & 138 & 176 & 1000  & 1314\\
1991 & 173 & 248 & 1230  & 1651\\
1998\tablenote{predicted}
     & 200 & 300 & 1500  & 2000\\
\hline
\end{tabular}
\source{Central Statistical Office,
        UK}
\caption{Average turnover per shop: by
  type of retail organisation}
\label{tab:a}
\end{table}
\end{verbatim}

\begin{table}
\begin{tabular}{lrrrr}
\hline
  & \tablehead{1}{r}{b}{Single\\outlet}
  & \tablehead{1}{r}{b}{Small\tablenote{2-9 retail outlets}\\multiple}
  & \tablehead{1}{r}{b}{Large\\multiple}
  & \tablehead{1}{r}{b}{Total}   \\
\hline
1982 & 98 & 129 & 620    & 847\\
1987 & 138 & 176 & 1000  & 1314\\
1991 & 173 & 248 & 1230  & 1651\\
1998\tablenote{predicted} & 200 & 300 & 1500  & 2000\\
\hline
\end{tabular}
\source{Central Statistical Office, UK}
\caption{Average turnover per shop: by type
  of retail organisation}
\label{tab:a}
\end{table}

\BDefC{setlength}[mm]{\texttt{\upshape\string\hlinesep}}{value}

Vertical spacing between horizontal lines produced from |\hline|
inside a tabular environment is controlled by the length parameter
|\hlinesep| in this class. The default value (1pt) gives one point
extra space above such lines and three times as much (i.e. 3pt) extra
space below. This is done to implement the layout requirements for
tables in the AIP proceedings (which are not supposed to have vertical
lines in the tables). If tables with vertical lines are necessary for
some reason, then the value of this parameter should be set to
\texttt{0pt} either globally for the whole document or locally within
the \texttt{table} environment. Otherwise the vertical lines will have
strange gaps whenever a |\hline| command is used to produce a
horizontal line.

\subsubsection{Counters}

The |\alph| and |\fnsymbol| commands to represent counter values have
extended ranges. For example |\alph| will now count up to 52 (zz) and
the |\fnsymbol| command will produce the following symbols
\makeatletter
\@fnsymbol{1},
\@fnsymbol{2},
\@fnsymbol{3},
\@fnsymbol{4},
\@fnsymbol{5},
\@fnsymbol{6},
\@fnsymbol{7},
\@fnsymbol{8},
\@fnsymbol{9},
\@fnsymbol{10},
\@fnsymbol{11},
\@fnsymbol{12},
\@fnsymbol{13},
\@fnsymbol{14},
\@fnsymbol{15}, and
\@fnsymbol{16}.
\makeatother
This will allow for up to 16 table notes per table. For documents that
need a larger number of table notes select the option
\texttt{tnotealph} to switch to lower case alphabetic letters to mark
such notes.

\subsubsection{Long tables}

Tables which are longer than one page cannot be placed into a
\texttt{table} environment as floats cannot have a size larger than a
page. Such tables are supported by the standard \LaTeX{} package
\texttt{longtable} written by David Carlisle. However this package
only works in single column mode.

With two-column layouts, such as the one for the AIP 8x11 double
column proceedings, such tables can only be added at the end of the
paper by preceding the |longtable| environments with a |\onecolumn|
declaration.

The package is supported by the class in the sense that captions
within a \texttt{longtable} environment will be formatted using the
appropriate style; however in contrast to the \texttt{table}
environment it is the responsibility of the user to place the caption
at the top of the table. The commands |\source| and |\tablenote| are
not supported within this environment, but the |\tablehead| command
can be used to produce column heads if desired.

Refer to the \texttt{longtable} package documentation or to
\cite[p.122ff]{A-W:LLa94} for a detailed description of the syntax of
the \texttt{longtable} environment.

A possible alternative is the package \texttt{supertabular} written by
Johannes Braams; however in this case no attempt has been made to
ensure that a table produced with \texttt{supertabular} conforms to
the layout specification for the \aipcls{}. Be aware that this package
defines its own |\tablehead| command (with a completely different
function).

Refer to the package documentation for the syntax description. A
detailed comparison between \texttt{supertabular} and
\texttt{longtable} can be found in Chapter~5 of \cite{A-W:LLa94}.

\subsubsection{Building floats manually}

The original \LaTeX{} environments \texttt{figure} and \texttt{table}
as well as their star forms are still available under the names
\texttt{ltxfigure} and \texttt{ltxtable}. They should not be used in
normal circumstances but are provided in case the automatism of
the \aipcls{} needs overwriting.

Please note that if these environments are used the position of the
|\caption| command determines the placement of the caption within the
float body and that the special commands for figures and tables, e.g.,
|\tablenote|, etc.\ as provided by this class are not available within
these environments.

\begin{table}[!t]
\makeatletter
\if8\expandafter\@car\selectedlayoutstyle\@nil\relax
\else
  \fontsize{7}{8}\selectfont
\fi
\makeatother
\begin{tabular}{rrrp{.6\textwidth}}
\hline
  \tablehead{1}{r}{b}{File} &
  \tablehead{1}{c}{b}{Date} &
  \tablehead{1}{c}{b}{Version} &
  \tablehead{1}{c}{b}{Description} \\
\hline
 aipproc.cls &    2000/08/31 & v1.2a & AIP Proceedings (FMi) \\
fixltx2e.sty &    1999/12/01 & v1.0b & fixes to LaTeX \\
    calc.sty &    1998/07/07 & v4.1b & Infix arithmetic (KKT,FJ) \\
  ifthen.sty &    1999/09/10 & v1.1b & Standard LaTeX ifthen package (DPC) \\
graphicx.sty &    1999/02/16 & v1.0f & Enhanced LaTeX Graphics (DPC,SPQR) \\
  keyval.sty &    1999/03/16 & v1.13 & key=value parser (DPC) \\
graphics.sty &    1999/02/16 & v1.0l & Standard LaTeX Graphics (DPC,SPQR) \\
    trig.sty &    1999/03/16 & v1.09 & sin cos tan (DPC) \\
graphics.cfg & \\
   dvips.def &    1999/02/16 & v3.0i & Driver-dependant file (DPC,SPQR) \\
     url.sty &    1999/03/28 &  ver 1.5x  & Verb mode for urls, etc. \\
 article.cls &    2000/05/19 & v1.4b & Standard LaTeX document class \\
  size10.clo &    2000/05/19 & v1.4b & Standard LaTeX file (size option) \\
  aipxfm.sty & \\
 mathptm.sty &   2000/01/12 &PSNFSS-v8.1 &Times + math package (SPQR) \\
   times.sty &   2000/01/12 &PSNFSS-v8.1 &Times font as default roman(SPQR) \\
  ot1ptm.fd  &  2000/01/12  &PSNFSS-v8.1 & font definitions for OT1/ptm. \\
 fontenc.sty & \\
   t1enc.def &   2000/08/30 & v1.91 &Standard LaTeX file \\
   t1ptm.fd  &  2000/01/12  &PSNFSS-v8.1 & font definitions for T1/ptm. \\
textcomp.sty &   2000/08/30 &v1.91 &Standard LaTeX package \\
  ts1enc.def &   1998/06/12 & v3.0d & (jk/car/fm) Standard LaTeX file \\
varioref.sty &   1999/12/02 &v1.2c &package for extended references (FMi) \\
  aip-8s.clo & \\
ttct0001.sty & \\
shortvrb.sty &   2000/07/04  &v2.0m & Standard LaTeX documentation package
 (FMi) \\
hyperref.sty &   2000/05/08  &v6.70f & Hypertext links for LaTeX \\
  pd1enc.def &   2000/05/08  &v6.70f & Hyperref: PDFDocEncoding definition
 (HO) \\
hyperref.cfg & \\
  hdvips.def &   2000/05/08  &v6.70f & Hyperref driver for dvips \\
 pdfmark.def &   2000/05/08  &v6.70f & Hyperref definitions for pdfmark
 specials \\
  ts1cmr.fd  &  1999/05/25  &v2.5h & Standard LaTeX font definitions \\
 nameref.sty &   2000/05/08  &v2.18 & Cross-referencing by name of section \\
   t1pcr.fd  &  2000/01/12  &PSNFSS-v8.1 & font definitions for T1/pcr. \\
ot1ptmcm.fd  &  2000/01/03  &Fontinst v1.801 & font definitions for
 OT1/ptmcm. \\
omlptmcm.fd  &  2000/01/03  &Fontinst v1.801 & font definitions for
 OML/ptmcm. \\
omspzccm.fd  &  2000/01/03  &Fontinst v1.801 & font definitions for
 OMS/pzccm. \\
omxpsycm.fd  &  2000/01/03 & Fontinst v1.801  &font definitions for
 OMX/psycm. \\
  ts1ptm.fd  &  2000/01/12 & PSNFSS-v8.1  &font definitions for TS1/ptm. \\
  escher.eps &   &&  Graphic file (type eps) \\
 outline.eps &  & &  Graphic file (type eps)  \\
\hline
\end{tabular}
\caption{Files used by the \aipcls{}}
\label{tab:b}
\source{Output of \texttt{\string\listfiles} when processing
        \texttt{aipguide.tex}}

\end{table}

\subsection{Urls}

\BDefC{url}[m]{data}

For documenting URLs and related data the |\url| command is provided.
It allows breaking the URL in certain places and typesets it in an
adequate font and format. Instead of using curly brackets the argument
can be delimited by two identical characters not used in the argument.

\subsection{Bibliography}

Referring to other articles, books, etc.\ can be done using the |\cite|
command of standard \LaTeX{}. The list of references itself can
either be produced using standard \LaTeX{} methods or using
\textsc{Bib}\TeX.

If installed, the \aipcls{} class includes the \texttt{natbib} system
which offers an extended set of citation commands. These commands have
been originally developed to support author/year citation styles but
are also useful with numerical citation styles.

The \texttt{natbib} system has two basic citation commands, |\citet| and
|\citep| for \emph{textual} and \emph{parenthetical} citations, respectively.
There also exist the starred versions |\citet*| and |\citep*| that print
the full author list, and not just the abbreviated one.
All of these may take one or two optional arguments to add some text before
and after the citation. Table~\vref{tab:natbib} shows some examples.
\begin{table}
\begin{tabular}{@{}l@{\quad$\Rightarrow$\quad}l}
\hline
\multicolumn{2}{@{}l}{\bfseries Author/year style} \\
\hline
  |\citet{jon90}| & Jones et al. (1990)\\
  |\citet[chap.~2]{jon90}| & Jones et al. (1990, chap.~2)\\[0.5ex]
  |\citep{jon90}| & (Jones et al., 1990)\\
  |\citep[chap.~2]{jon90}| & (Jones et al., 1990, chap.~2)\\
  |\citep[see][]{jon90}| & (see Jones et al., 1990)\\
  |\citep[see][chap.~2]{jon90}| & (see Jones et al., 1990, chap.~2)\\[0.5ex]
  |\citet*{jon90}| & Jones, Baker, and Williams (1990)\\
  |\citep*{jon90}| & (Jones, Baker, and Williams, 1990) \\
\hline
\multicolumn{2}{@{}l}{\bfseries Numerical style} \\
\hline
  |\citet{jon90}| & Jones et al. [21]\\
  |\citet[chap.~2]{jon90}| & Jones et al. [21, chap.~2]\\[0.5ex]
  |\citep{jon90}| & [21]\\
  |\citep[chap.~2]{jon90}| & [21, chap.~2]\\
  |\citep[see][]{jon90}| & [see 21]\\
  |\citep[see][chap.~2]{jon90}| & [see 21, chap.~2]\\[0.5ex]
  |\citep{jon90a,jon90b}| & [21, 32]\\
\hline
\end{tabular}
\caption{Example of \texttt{natbib} commands and their results}
\label{tab:natbib}
\end{table}
There are many more commands and variants, see \cite{man:Daly99a} or
\cite{man:Daly99b} for further details.

\subsubsection{Bibliography produced manually}

\BDefE{thebibliography}[m]{widest-label}

Environment to hold the list of references.

\BDefC{bibitem}[m]{label}

Command to start a bibliographical entry having the label \Larg{label}
for use in |\cite| commands. Refer to the publishers manual, e.g.,
\cite{man:aipproceed}, for information on how to lay out individual
entries. For example:
\begin{verbatim}
\bibitem{Brown2000}
   M.~P. Brown and K. Austin,
  \emph{The New Physique},
  Publisher Name, Publisher City,
  2000, pp. 212--213.
\end{verbatim}

If commands from \texttt{natbib} (e.g., from table~\ref{tab:natbib})
should be usable, then additional information has to be passed to the
|\bibitem| via an optional argument.

\BDefC{bibitem}[om]{display-info}{label}

The optional argument \Larg{display-info} should then, and only then,
contain the author(s) name(s) followed by the year in parentheses
without any spaces, for example:
\begin{verbatim}
\bibitem[Brown and Austin(2000)]
        {Brown2000}
  ...
\end{verbatim}
The essential feature is that the label (the part in brackets) consists
of the author names, as they should appear in the citation, with the year
in parentheses following. There must be no space before the opening
parenthesis!
This will be automatically produced if \BibTeX{} is used.

\subsubsection{Bibliography produced using \textsc{Bib}\TeX}

The \aipcls{} is accompanied by \BibTeX{} style files which can be used
to produce compliant reference lists from \BibTeX{} database
files. To use \BibTeX{} one first has to run the source file through
\LaTeX{} then run \BibTeX{} and then rerun \LaTeX{} twice to get all
references resolved. \BibTeX{} is described in more detail in appendix
B of \cite{A-W:LLa94} and in chapter~13 of \cite{A-W:MG04}.

\BDefC{bibliographystyle}[m]{style-name}
This declaration specifies to \BibTeX{} that the style
\Larg{style-name} should be used. It can be placed anywhere within the
document but is usually positioned directly in front of the command
described below.

For a discussion which of the supplied \BibTeX{} styles should be used
for which proceedings see the section ``Special requirements\ldots''
below.

\BDefC{bibliography}[m]{bib-list}

This command denotes the position where the reference list produced by
\BibTeX{} will be included in the document. The \Larg{bib-list} is a
comma separated list of \BibTeX{} database files.

\section{General requirements and restrictions}

This class was designed to work with \LaTeXe{} release 1999/06/01 or a
later version. Earlier releases may work but have not been tested.

With the exception of the packages \texttt{natbib} and \texttt{url} it
only requires files which are part of a standard \LaTeX{}
distribution, i.e., it should work if your installation contains the
following components:
\texttt{base}, \texttt{tools}, \texttt{graphics}, and \texttt{psnfss},
see \vref{tab:b} for files used to produce this document.

The most recent \LaTeX{} distribution as well as \texttt{natbib} and
\texttt{url} can be obtained from CTAN sites (Comprehensive \TeX{}
Archive Network).

Refer to \url{http://www.tug.org} for more information on CTAN and
\TeX{} in general.

A ready to run \TeX{} system for various platforms which has
everything required is available on CD-ROM, look into
\url{http://www.tug.org/texlive.html}.

This \TeX{} implementation is also made available as an add-on to
several books on \LaTeX, e.g., \cite{A-W:KD04,A-W:MG04}.

For loading individual packages from a CTAN archive refer to
\url{http://www.ctan.org} and search for the package name. Please omit
extensions such as \texttt{.sty} when searching, e.g., search for
\texttt{natbib} rather than \texttt{natbib.sty}, as such packages are
often distributed in source form only, e.g., as a \texttt{.dtx} file.

It is also possible to download a complete \TeX/\LaTeX{} installation
from CTAN, e.g., Miktex + Winedit + Ghostview. Finally, it is also
possible to download a CD-ROM image of the \TeX-live CD from CTAN
(roughly 300MB): search for \texttt{texlive} (and make sure you select
a suitable mirror near you).

\section{Special requirements for individual layouts}

\subsection{AIP proceeding layout 6x9}

\begin{itemize}
\raggedright
\item
 The entire paper will be reduced 15\% in the printing process. Please
 make sure all figures as well as the text within the figures are
 large enough in the manuscript to be readable in the finished book.
\item
 The use of the |\source| command is discouraged.
\item
 Compliant \BibTeX{} styles are \texttt{aipproc} (for use with
 \texttt{natbib}) and  \texttt{aipprocl} (if \texttt{natbib} is
 missing at the site).
\item
 The options \texttt{bibliocites} and \texttt{numberedheadings} have
 no effect.
\end{itemize}

\subsection{AIP proceeding layout 8x11 single/double}

\begin{itemize}
\raggedright
\item
 The use of the |\source| command is discouraged.
\item
 Compliant \BibTeX{} styles are \texttt{aipproc} (for use with
 \texttt{natbib}) and  \texttt{aipprocl} (if \texttt{natbib} is
 missing at the site).
\item
 The options \texttt{bibliocites} and \texttt{numberedheadings} have
 no effect.
\end{itemize}

\subsection{ARLO}

Note: the ARLO layout is no longer supported.

\begin{itemize}
\raggedright
\item
A copyright year (|\copyrightyear|) needs to be provided.

\item
Pacs numbers should be provided (|\classification|).

\item
  The \texttt{arlo} layout offers one additional environment to specify
  multimedia files:
\begin{verbatim}
\begin{multimedia}
 \multimediauid{523}
 \multimediatype{gif}
 \multimediasize{1.2Mb}
 \multimediaurl{http://yorktown.%
       eng.yale.edu/test/msXXX/}
 \multimediacaption{Fancy video}
 \label{fv}
\end{multimedia}
\end{verbatim}
  References to a multimedia file can be made using |\label| and
  |\ref|. Instead of the latter command |\multimediaref| can be used
to automatically get the appropriate frills, e.g., `Mm.~2' instead of
just `2' as produced by |\ref|.

\item
  Select the \texttt{draft} option for the initial submission and the
  copy-editing stage. Replace it by the \texttt{final} option when
  producing the final paper, so that page numbers and other
  items are stripped away.

\item
  To conform to the layout specification for citations the
  \texttt{natbib} system has to be installed.

\item
 For ARLO two compliant \BibTeX{} styles are available:
 \texttt{arlonum} should be used together with the class option
 \texttt{numcites}, while \texttt{arlobib} should be used together with
 the option \texttt{bibliocites}.

\item
 The options \texttt{bibliocites} and \texttt{numberedheadings} can be
 used to switch to author/year citation scheme and numbered headings,
 respectively.
\end{itemize}

\section{Introduction}
Granular materials such as sand, rice, powders and coffee beans have surprising mechanical behavior. They are defined as collections of particles whose thermal energy is negligible, yet they can behave as liquids, solids and gases~\cite{1996_revmodphys_jaeger, 2008_annurevfluid_forterre}. Both packing fraction and shear stress have emerged as crucial variables necessary to describe the state of the granulate. One can cross the phase boundary between solid and liquid granular materials thus \emph{jamming} the granulate, either by shear~\cite{bi11} or compaction~\cite{2009_jphyscondmat_hecke}. Most of these effects have been observed in numerical simulations or quasi two dimensional experiments. However, experimental studies that explore the microstructure of granular materials in three dimensional systems are rare~\cite{brujic, saadatfar, hurley16}. Refractive index matched scanning (RIMS) has emerged as a useful tool to perform three dimensional imaging on dense granular samples. The technique has been perfected over the past decade to the extent it can now be applied in many different experimental contexts~\cite{DijksmanRSI12, budwig, wiederseiner}. In this review article, we explore how \textit{soft} transparent particles can be used for RIMS-based granular experiments. We focus in particular on hydrogel particles. Hydrogel particles can be index matched with watery solutions and are therefore particularly amenable to use with RIMS. Hydrogels, and soft particles in general, however present the experimentalist with technical challenges. For example: finding the right kind of solvent to index match watery porous gel particles requires careful considerations. The first part of this article is entirely devoted to such experimental considerations; it is an update of previous work~\cite{dijksman13}.\\
Another feature of experiments on soft particles is the need for finding the complete surface structure of particles in the packing. As the particles are soft, they deform under mechanical loading. The implication is that the usual assumption of particle sphericity breaks down. This has consequences for finding their position, as the center of mass now depends on the shape. However, measuring particle level deformations has significant benefits: obtaining shape information allows one to extract contact forces and contact networks~\cite{brodu}. In general, it allows one to extract particle level stress tensor information from packings of soft spheres. In addition the shape information of particles gives access to particle level anisotropy metrics, which are also relevant to understand the microscopic mechanics of granular packings~\cite{gerd}. The second part of this article is therefore devoted to a general discussion on how to extract particle shape information from three dimensional (3D) images. The algorithmic aspects described here are generic; they may also apply to 3D images obtained by means of confocal~\cite{brujic}, X-Ray~\cite{saadatfar} or magnetic resonance imaging methods.\\

\section{Using hydrogel spheres}

\begin{figure}
  \includegraphics[width=1\columnwidth,clip]{RSI_mech_v01_copy.pdf}
  \caption{Reproduced from AIP Conf. Proc. \textbf{1542}, 457 (2013) with the permission of AIP Publishing. (a) Typical growth dynamics of a single dried hydrogel sphere in demineralized water. The inset shows a dry and fully grown sphere. (b) Compression force as a function of strain for a single fully grown hydrogel sphere. Total cycle time is 100 seconds (blue) and 1000 seconds (dashed red). The inset shows the same data on double 10-logarithmic scale, with a power law of exponent 1.5 indicated. \label{fig:compresssphere}}
\end{figure}

Refractive index matching studies rely on combining particles and fluids with the same refractive index. Due to the simplicity of hard sphere suspensions and availability of materials, RIMS studies are mostly done with plastic or glass particles~\cite{DijksmanRSI12, budwig, wiederseiner}, index matched with viscous and/or expensive liquids. However, spherical particles made out of hydrogel (or polyacrylamide gel) have become commercially available~\cite{footnote1} and methods to custom produce them have been proposed~\cite{workamp}. Hydrogel as a material has the benefit that it is cheap, safe and easily index matched with a watery solution. In addition, hydrogel is soft, with a Young's modulus in the 10-100 kPa range, so it allows for the detection of contacts through its macroscopic deformation under modest forcing. The softness of the particles means that care should be taken to generalize findings in such a system to systems with hard, frictional grains. However, the easy deformability does gives an opportunity to probe the role of particle shape on granular packing mechanics. In this first part of this review, we describe experimental aspects of using hydrogel spheres in RIMS studies that make imaging of hydrogel particles practically possible.

\subsection{Swelling Dynamics}
Commercially available hydrogel spheres~\cite{footnote1} grow as indicated in Fig.~\ref{fig:compresssphere} when submersed in demineralized water. They are purchased as millimeter sized hard spheres; their final size depends on the properties of their chemical environment such as salinity, pH and temperature~\cite{muniz, shin, verneuil}. The swelling is reversible; upon drying, the particles revert to their dry spherical shape, althrough there is an asymmetry in the swelling/drying dynamics~\cite{thibault}. We describe the properties of these spheres throughout the paper unless otherwise noted. Note that hydrogel particles can be custom made with a droplet pinch-off technique~\cite{technote, patel, workamp} or by injection molding~\cite{bellani}.

\subsection{Mechanical Behavior}
To measure the response of a single sphere, we perform compression tests in a TA Instruments Micro Strain Analyzer III.  We compress a single hydrogel sphere vertically and uniaxially between two steel plates and measure the resultant force $F$ as a function of strain $\gamma$. We use a fully swollen hydrogel sphere with no liquids on its surface to minimize liquid bridge induced capillary forces. We perform experiments in an open container and hence evaporation is present. Typical experimental results are shown in Fig.~\ref{fig:compresssphere}. The force response $F(\gamma)$ is consistent with an exponent of $1.5$, in accordance with linear elasticity theory for compressed spheres. This Hertzian behavior is also observed for submersed spheres; see below. The prefactor $Y$ in $F = Y\gamma^{\alpha}$ is related to the Young's modulus of the hydrogel. Experimental results shown in Fig.~\ref{fig:compresssphere}b suggest that the Young's modulus for the hydrogel spheres grown in demineralized water is $\sim 20~kPa$. This is in line with literature values~\cite{muniz}, and also depends on the chemical environment (e.g. salinity or pH) of the spheres as they are grown~\cite{muniz, shin}; we always used demineralized water as growing environment.\\
The hydrogel spheres are made out of cross-linked polymers which form an elastic network. At any finite temperature however, the elastic network bonds can rearrange and the interstitial fluid can move around, allowing the gel to lower its internal stresses. The hydrogel network will therefore adjust to applied stresses~\cite{stressrelax1, stressrelax2, stressrelax3}. This is also visible in Fig.~\ref{fig:compresssphere} from the finite surface area of the force loop; during the compression cycle of the sphere, the porous polymer network evolves, leading to a different force response. The pressure adjustment is more noticeable when the compression loop is slowed. To characterize this relaxation more quantitatively, we compress a packing of $\sim$1000 spheres in a fixed volume and probe the pressure response over time. The packing is fully submersed to prevent evaporation of water in the hydrogel particles. Fig.~\ref{fig:relax}a shows the typical pressure response. At late times, an exponential relaxation can be observed, with a decay timescale of about 5.1 hours. Subtracting the late time behavior reveals an exponential early time relaxation process with a considerably faster decay timescale of about 0.5 hours. This double relaxation process is robust: it is also present as a background process when the packing is sheared quasi-statically. However, when the compression level is varied stepwise as in Ref.~\cite{brodu}, the relaxation disappears. We speculate that particle level contact evolution also can play a role.\\

\textit{Temperature dependence ---} The mechanical behavior of hydrogels is generally also temperature dependent. We perform uniaxial compression tests as mentioned above, but then with a $\sim$ 20mm swollen hydrogel particle submersed in a water bath of a specific temperature. Again we measure the expected $F \propto \gamma^{1.5}$ as shown in Fig.~\ref{fig:tempdepgel}. The prefactor in the proportionality was obtained by collapsing the experiments done at different temperatures onto a single master curve. Independent checks~\cite{brodu} had already confirmed that the modulus of the spheres is $23~kPA$ at 21$^{\circ}$ Celsius; this allowed us to determine the modulus of the colder particles by scaling (Fig.~\ref{fig:tempdepgel} inset). The submersed particle also shrinks somewhat during cooling: to quantify this effect, we repeat the same strain cycle at different temperatures and record the offset at which the contact between compressing plate and particle are established. We extract the contact point from the force-displacement data. An increase in the offset of the contact of contact here implies shrinking of the test particle. These offsets are shown in Fig.~\ref{fig:tempdepgel} (bottom right inset).

\begin{figure}
  \includegraphics[width=1\columnwidth]{RSI_time_v01_copy.pdf}
  \caption{Reproduced from AIP Conf. Proc. \textbf{1542}, 457 (2013) with the permission of AIP Publishing. (a) Pressure evolution of a packing of hydrogel spheres kept at constant volume (blue solid line). An exponential decay to zero at late times can be observed; the green dashed line is a best fit with time constant of 5.1 hours. (b) Subtracting the late time exponential decay, an early time exponential relaxation process with a different time constant is observed (blue solid line). The red dashed line is a fit with decay time of 0.5 hour. Note the different time scales in panel (a) and (b).\label{fig:relax}}
\end{figure}

\begin{figure}
  \includegraphics[width=1\columnwidth]{hydrogel_temp_copy.pdf}
  \caption{Main panel: force-displacement data from the compression of a submersed hydrogel sphere at $15,17,19,21~^{\circ}C$ (red $\circ$, blue $\triangle$, black $\square$, green $\lozenge$). The dashed line indicates slope 1.5. Vertical and horizontal offsets are removed to achieve a collapse of the data. Top inset: vertical offset from the data in the main panel provides the modulus as a function of temperature. Bottom inset: horizontal offset correction from data in main panel, representing the shrinking of the particle with lower temperature.   \label{fig:tempdepgel}}
\end{figure}

\subsection{Hydrogel Friction}
Hydrogels have been shown to have very low friction coefficient with glass or plastic substrates~\cite{slippery1, slippery2, slippery3}. Friction on hydrogels is however rich in phenomenology~\cite{slippery4} including non-Coulomb behavior and rate dependence. We can get an upper bound on the friction coefficient of a hydrogel-hydrogel (HH) contact by stacking two dyed hydrogel cubes (Educational Innovations) on top of each other in a demineralized water bath. The inclination angle at which the cubes start to slide gives us an upper bound for HH friction coefficient of $<0.03$.
The low friction in HH contacts have a beneficial consequence: since such contacts cannot support shear stresses, a deformation of the contact in a hydrogel sphere is only due to normal forces. Linear elasticity theory then provides a relationship between the contact deformation and the applied normal force. Thus, imaging the deformation of hydrogel spheres allows for the extraction of contact forces in granular packings in three dimensions to a high degree of accuracy.

\subsection{Density \& Index Matching}
Hydrogel spheres contain 80-99.5\% water by volume, depending on their chemical environment. Thus, the index of refraction of hydrogel spheres is higher, but close to that of water. To image a dense packing of particles, index matching of the fluid phase needs to be fine tuned to that of the spheres to image as many layers as possible~\cite{DijksmanRSI12}. Ordinarily, index matching is achieved by dissolving a second component in the fluid phase. In the case of hydrogel spheres, this approach can fail due to the porosity of the hydrogel. Any small water-soluble molecule, such as glycerol, will diffuse into the hydrogel polymer network, raising both the index of the fluid and the particle. There are two approaches to resolve this. Macromolecules above a particular size are physically too large to diffuse into the polymer network and stay in the fluid phase. We found that polyethyleneglycol (PEG) with a molecular weight of 40,000 diffused into the hydrogel spheres on a timescale of hours, but polyvinylpyrrolidone (PVP) with a molecular weight of 360,000 did not diffuse into the hydrogel over a timescale of weeks. Dynamic light scattering on dilute 360,000 PVP samples indicate that the equilibrium size of these macromolecules is about 20 nanometer.  Note that a concentration gradient of PVP creates an osmotic pressure on the hydrogel spheres, but this is not large enough to result in any visible size change. Adding macromolecules such as PVP to the index matching liquid will however affect the HH friction contact~\cite{ward}; in general the mixing of solvents for index matching can also create non-Newtonian suspensions, as is the case for certain Triton-water mixtures~\cite{beyer}.

In order to image the packing structure, an imaging contrast agent is required. In standard RIMS applications, this is a fluorescent dye that is dissolved in the fluid phase of the system. As mentioned above, the hydrogel spheres are permeable to small molecules, including all fluorescent dyes. A dye dissolved in the fluid phase will therefore also be able to penetrate the hydrogel. Yet, there are some fluorescent dyes that prefer to stay in the hydrogel network rather than in the fluid phase, perhaps due to hydrophobicity~\cite{zanetti}. Gel specific interactions also play a role, as we found that Nile Blue 690 (Exciton) works for commercial hydrogel spheres, but not for custom made hydrogels. For details, see~\citep{dijksman13}.

\section{Imaging and Image Analysis}

In this section, we discuss some image analysis aspects applicable to soft particles under compression. Soft here means that particles deform \emph{measurably} under mechanical load. This deformation leads to the emergence of asymmetric particles, whose location and contact force extraction require the extraction of their entire surface structure. This is in contrast with most particle tracking codes, which assume a specific (e.g. spherical, elliptical) particle shape. In this part of the article we provide background information on image processing, particle recognition and shape extraction algorithms.

\subsection{Distortion compensation in 3D}
The first step in imaging is to ensure the camera system presents no optical distortion. This is the case with cheap lenses, or by using a zoom lens at suboptimal settings. In order to estimate the distortion field of the camera system, we used the checkerboard method with implementation taken from OpenCV~\cite{opencv,opencv_library}. Images of the checkerboard in multiple 3D orientations are taken in order to estimate both the 3D projection model from the camera to the real world, together with the lens distortion parameters. In practice, for our camera / lens system, no noticeable distortion was observed.
The second step is to compensate for varying optical path lengths. This is done by measuring the position of each corner of the hydrogel container, in the image for each depth. We thus tag the positions of these corners in selected images at various depths, building a list of $(r,c,1)$ triplets for each corner (standing respectively for row, column, and a constant for homogeneous coordinates). Each of these triplets ideally corresponds to known coordinates $(x,y,z,1)$ in the container referencial. A least-squared error fit is performed~\cite{lourakis04LM} in order to estimate the $3\times 4$ projection matrix $M$ such that
\[
\left\|
\alpha\left[\begin{array}{cccc}
r_{1} & r_{2} &  & r_{n}\\
c_{1} & c_{2} & \ldots & c_{n}\\
1 & 1 &  & 1
\end{array}\right] - M\left[\begin{array}{cccc}
x_{1} & x_{2} &  & x_{n}\\
y_{1} & y_{2} & \ldots & y_{n}\\
z_{1} & z_{2} &  & z_{n}\\
1 & 1 &  & 1
\end{array}\right]
\right\|^2
\] is minimal, where $n$ is the number of observations and  $\alpha$ is a free coefficient for the homogeneous transform.
This method implicitly handles the rotation of the image so that the bottom of the tank appears horizontal. For each image, a robust sub-pixel position of the corners is obtained from the projection. These positions are then used to rescale and stack images into 3D. The net result is a properly scaled three dimensional image based on the (noisy) image slices. The next step is to denoise this 3D image volume.

\subsection{Image Denoising}

\begin{figure}
  \includegraphics[width=1\columnwidth]{raw_image_commented.pdf}
  \caption{Raw image with major sources of artifacts that needs to be processed.\label{fig:raw_image}}
\end{figure}

\begin{figure}
  \includegraphics[width=1\columnwidth]{processed_image_commented.pdf}
  \caption{Processed image after artifact removal, and edge detection.\label{fig:processed_image}}
\end{figure}
There are several types of noise in the slice images (shown in Fig.\ref{fig:raw_image}), which we deal with separately (see Fig.\ref{fig:processed_image}). \emph{Dust from particles} and turbidity or leftover dye in water generates noise with unknown characteristics, so we use NL-Means filtering~\cite{nlmeans} to adequately remove it. This step can in fact be performed on the raw images, before stacking them in 3D.\\
\emph{Refraction shadows:} These are due to a slight index mismatch, especially at the interface between grains. In the laser sheet plane, the grain cross-section appears as a disk. The deflection on each side of the grain surface produces a dark zone, starting tangentially to the disk, opposite the direction of the laser source. Call D that tangent deflection point. The dark zone starts at D: on the grain inner side the laser is deflected, outside it is not, so the in-between region appears as a thin triangle in the sheet plane. In the plane orthogonal to the laser sheet, but containing at least a laser ray, the geometry is the same and the dark zone has the same shape. In the third orthogonal plane, crossing each laser ray (thus, parallel to the box side opposite the laser source), the dark zones appear as circles. A specific denoising algorithm was created to fill these dark zones. The images are first stacked into 3D to make voxels. That algorithm starts by detecting lines making up the triangles dark zones in one of the first two planes, starting at one grain edge, with a Hough transform~\cite{HoughTransform}. It then fills voxel regions where lines were detected: voxels with the surrounding interstitial fluid ambient intensity are added along the line on the inner side of the dark region. The algorithm then alternates into the other orthogonal plane in order to detect more lines and fill more voxels, until convergence or a prescribed number of iterations were reached. The algorithm could be extended by using circle Hough transforms instead of linear ones and iterating in the third plane, but good results were reached already by alternating in the first two planes.\\
\emph{Reflection shadows} and laser light absorption: A local grey-level renormalization is performed. The image is split in overlapping sub-region chunks of $10\times 10$ pixels each. The empirical distribution of gray levels in these chunks is determined, together with its 90\% quantiles interval range. Then, the chunk intensity is renormalized within that range and outside values are clipped to the lower and upper quantile intensity values. This way, differences in intensities on each side of the box due to light absorption are compensated, and difference in illumination due to reflections on elements outside the container are also reduced.

\subsection{Border Voxels}

Finding border voxels at the edge of the grains is a challenge. Starting from the cleaned and preprocessed images, we followed the following steps, detailed hereafter.
\begin{itemize}
\item[-] Finding the grain edge transitions along each 3D axis.
\item[-] Assigning intervals for inner grain voxels between edges.
\item[-] Merging nearby segments to account for false edge detection within grains.
\end{itemize}

Edge transitions are found by using a smooth numerical differentiator filter~\cite{smoothdiff} on voxel intensities. These filters compute the large variations in intensity while being robust to noise. Fig.\ref{fig:raw_image} shows contiguous regions of intensity, with large variations betwen the grain interiors and exteriors. After this first step, a list of transition voxels is established. Most of these voxels lie on grain surfaces: the dye is concentrated within grains, so interior voxels have higher intensities than the surrounding fluid. Other voxels are outliers, for example due to fine particles in suspension that results in large local intensity variations and thus could not be reduced numerically.
The next step is to detect these outliers and orient the grain surface voxels by finding grain interiors. For this, we assume that differences in dye absorption are larger between different grains than between different parts of the same grain. With this assumption, a distribution of intensity levels is built along each segment between successive voxels on each 3D axis. Segments from within the same grain should thus sample the same intensity distribution, while segments between different grains should not. A standard Kolmogorov-Smirnov 2-sample test solves this problem, with a confidence threshold empirically determined from experimental data. Similar segments are merged, covering low-intensity regions within grains due to dye inhomogeneity that resulted in spurious transitions. False positives in the merger test may result in intervals larger than a grain diameter and these are discarded. Isolated edge voxels are also removed.

\subsection{Grain attribution and cleaning up voxels}

At this stage, only a small amount of false border outliers remains, small enough to have negligible influence on the grain identification. We then attribute border voxels to unique grain identifiers. In order to do this, a local tangent plane is fit at each voxel, using a Principal Component Analysis on neighbor voxels in order to find the main two directions of largest variation. The plane normal, oriented towards largest voxel intensities, determines the direction toward a rough estimate of the grain center. This proto-center is empirically placed at an average radius distance in this direction. There is one such proto-center per border voxel, and these are considered to be distributed around the true grain center. Assuming these are indeed samples of a probability distribution for the location of the true center, we estimate that distribution with a 3D kernel density estimation \citep{Epanechnikov69}. A simple gradient ascent on that probability distribution is initiated at each proto-center in order to find the local maxima. With a large enough kernel support, the distribution is smooth and only one maxima exists per grain. The location of that maximum is used as an estimate of the grain center.

All border voxels are attributed to the center estimate matching their associated proto-center. Border voxels that are too close or too far from a grain center are considered outliers and eliminated. A voxel reattribution step is then performed in order to deal with limit cases at the interface between two grains. Starting from the estimated grain centers, consider 3D angular sectors spanning all directions. The distribution of border voxels at each distance within the angular sector is estimated by another kernel density estimation. When that density has two peaks, the closest is assumed to point at the true grain surface, and the other to border voxels that were missatributed to this grain. The furthest away voxels are put into a pool of voxels to reassign. Once all grains have been processed, these extra voxels are then reattributed to nearby grain centers, or completely eliminated if that would lead to inconsistent results. This procedure may possibly eliminate a few valid pixels, but it ensures very few outliers or wrong attribution remain.

\subsection{Analytic grain surface estimation}

\begin{figure}
  \includegraphics[width=1\columnwidth]{border_voxels_and_surface.pdf}
  \caption{Border voxels with analytic surface fit.\label{fig:border_voxels_and_surface}}
\end{figure}
The goal of this step is to produce an analytic representation of the grain surface, represented as a function that can be evaluated outside border voxels. The process is similar to fitting a curve from measurements, but for a closed surface (shown in Fig.~\ref{fig:border_voxels_and_surface}). Starting from the grain center $G$, a unit vector $\overrightarrow{u}$ defines a direction. The location of the surface in that direction is given by a distance from the grain center $G+f(\overrightarrow{u})\overrightarrow{u}$. The analytic surface representation we choose to use is thus a function $f$  that takes as input a unit vector $\overrightarrow{u}$  in $S^2$, the unit sphere, and produces a positive scalar quantity $f(\overrightarrow{u})\in\mathbb{R}^+$. Triangular spherical B-splines~\cite{strisplines} are used in order to define a basis $B=(b_1,b_2,\ldots,b_n)$ of $n$ functions from $S^2$ to $\mathbb{R}^+$. We then express a grain surface as a set of coefficients in that function basis: $f=c_1b_1+c_2b_2+\ldots+c_nb_n$. The main advantage of this method is that there is no pole, no singularity on the sphere that would result for example from meshing with rectangular longitude/latitude coordinates (or with b-splines in Cartesian coordinates). A second advantage is the isotropy: The triangular spherical B-splines can evaluate any direction in space, but are themselves computed from a set of fixed points in space. These points are taken to be the vertices of a regular geode. The next step is to estimate the surface coefficients $c_{1..n}$ from border voxels  $X_{1..m}$ with $m$ the number of voxels. This is done by least squared error minimization between the border voxels and the estimated surface of the grain: $c_{1\ldots n}=\textrm{argmin}\sum_{i=1}^{m}\left\Vert \left(G+f(\overrightarrow{u})\overrightarrow{u}\right)-X_{i}\right\Vert ^{2}+R$.  A convexity criterion $R$ is used to regularize angular sectors without enough border voxels ( see Fig.~\ref{fig:border_voxels_and_surface}), or to avoid leftover outliers from having too much influence. This criterion stipulates that, for any direction $\overrightarrow{u}$ and directions from neighbor angular sectors $\overrightarrow{v_j}$,  $f(\overrightarrow{u})\overrightarrow{u}$ is within the convex hull of the $f(\overrightarrow{v_j})\overrightarrow{v_j}$ .  This makes the fitting problem non-linear, so we use the Levenberg-Marquardt algorithm~\cite{lourakis04LM}. Once the analytic grain surface is available, we can compute precise geometric parameters from the grain by numerical integration: center of mass, areas of contacts between adjacent grains, etc. In fact, we iteratively reprocess the data using the center of mass instead of the initial center estimate, until convergence for $G$.

\subsection{Computing Forces From Local Surface Structure}

We use the general theory of linear elasticity~\cite{LnL} in order to derive force values from grain deformations. Observed images correspond to deformed grains, so the first step is to derive the deformation $\delta$ from the undeformed surface. With all grains having the same Young's modulus, $\delta$ is split equally at each contact (Fig.~\ref{fig:computeforce}). Thanks to the analytic surface representation from the previous section, we know the position of the center of mass $G$ and of the center of the contact area $C$. Therefore, the undeformed radius of curvature is $r = d + \frac{1}{2}\delta$, with $d$ the distance between $G$ and $C$. The force is given both by $F = E_e r^{1/2}\delta^{3/2}$ and by $F = E_e\delta a$, with $E_e$ the effective Young's modulus, $\frac{1}{r_e} = \frac{1}{r_1} + \frac{1}{r_2}$ the effective contact radius and $a = \sqrt{A/\pi}$ the radius of the area of contact. The effective Young's modulus appears in both expressions and does not intervene for deriving $\delta$ from purely geometric measurements: $r^{1/2}\delta^{3/2}=\delta a$ is obtained by equating both force expressions. This leads to a cubic equation for $\delta$, which we solve at each contact. Once $\delta$ is found, we use an independent measurement of the Young's modulus, $E \sim 23~kPa$ for our particles, in order to convert $\delta$ into a force value. Assuming negligible friction, the 3D force vector points in the direction $G-C$ and is thus available at each contact.

\begin{figure}
  \includegraphics[width=1\columnwidth]{contact.pdf}
  \caption{\label{fig:computeforce} Reproduced with permission from Nature Comm. \textbf{6} 6361 (2015) under the Creative Commons Attribution 4.0 International License. Contact and grain geometries, sketched in a 2D plane orthogonal to the contact area. The surface of each grain (blue/green) is shown as solid lines, the hypothetical ``undeformed'' surface of the grains is shown as dashed lines. The deformation, $\delta$, for this contact is the unknown quantity that we infer from linear elasticity. We measure the area of contact $A$, the position of the contact centroid $C$ and its distance $d$ to \textbf{$G_i$}, the center of mass (CoM) of each grain. Note that $d$ (hence $r$) can vary for different contacts on the same particle, as particles are weakly non-spherical. The distance between grain centers $b$ depends mainly on the grain polydispersity and weakly on their non-sphericity so, on average, $\langle b \rangle \sim 2\langle d \rangle$. Our force inference algorithm uses the observed surfaces, without assuming sphericity, and provides experimental access to all the relevant quantities in order to reconstruct $\delta$.}
\end{figure}

\subsection{Coarse Graining the Stress Tensor}

The goal of this section is to validate our method and embedded assumptions, for example the use of Hertz' law for the contact force, by comparing the image-reconstructed global force value acting on a compressed and imaged packing with the force on the top plate that is compressing the imaged packing. This independent force measurement represents a third independent measurement, the first two being the 3D images themselves and the Young's modulus measurement on a single compressed sphere. Unfortunately, directly summing the force values of individual contacts on the top plate is not possible due to image processing inaccuracies at grain/plate boundaries. Finding the precise location of that top plate is difficult for the same reason.

The solution is to coarse-grain individual contacts between grains in order to get a continuous expression of the stress tensor, which is then integrated over the top plate in order to get the global force value to compare with the measurement. The stress tensor can indeed  be integrated over a plane at any height $h$  within the tank, leading to a force $F(h)$. We use the hydrostatic pressure gradient in order to find the precise location of the top plate within the tank referential, by selecting the $h$  for which $F(h)$  equals the measured force.

We compute the coarse-grained continuum stress tensor from the average balance equations of~\cite{Babic97}. Assuming no dynamic components, these simplify and can be computed purely from geometric properties of the grains, which are available as detailed in the previous sections. Spatially continuous values, outside contact points, are derived by applying a kernel density estimation~\cite{Epanechnikov69}. The coarse-graining scale, hence kernel bandwidth, is set to be one average grain diameter. We thus compute continuous expressions of the stress tensor at the scale of grains. This coarse graining correctly computes the force dynamics on a compressed particle packing; for the numerical evidence we refer the reader to Ref.~\cite{brodu}.

\subsection{Accuracy of Image Analysis}

\begin{figure}
  \includegraphics[width=1\columnwidth]{displacement_correlations.pdf}
  \caption{Probability of finding a CoM displacement in the $\textbf{x},\textbf{y}$-plane during $\textbf{z}$ compression. \label{fig:xydisp}}
\end{figure}

\textit{Displacement resolution} --- In order to quantify the accuracy of the image analysis methods we described above, we look at two different metrics. First, we probe the resolution of the center of mass (CoM) detection through measuring displacement fields in a uniaxially compressed packing of hydrogel spheres. If the compression direction is in the $\textbf{z}$ direction, the displacements of the CoMs of the particles in the packing in the $\textbf{x},\textbf{y}$ directions should be minimal and uncorrelated. We plot the distribution of these displacements in Fig.~\ref{fig:xydisp}. We can clearly see that the observed displacements in the $\textbf{x},\textbf{y}$ directions per $\textbf{z}$-compression step are mostly very small. The standard deviation of the distribution of both $\textbf{x}$ and $\textbf{y}$ displacements is within 50 micron. Moreover, the distribution has azimuthal symmetry, with only minor preferences for detecting displacements along the coordinate axes.\\

\textit{Angular resolution} --- The calculation of stress tensors from the microscopic information in the images involves a large number of dot products and other vectorial analyses. It is thus crucial to get a sense of the accuracy of angle measurements in the packing. To estimate the angular resolution of the microscopic data, we quantify the angle between the vector connecting the CoMs of two contacting particles and the branch vector to their contact,  so between \textbf{$G_i$}-\textbf{$G_j$} and \textbf{$G_i$}-\textbf{$C$} as indicated in Fig.~\ref{fig:computeforce}. This angle $\theta$ should in principle be zero for perfectly spherical particles, but will deviate due to inaccuracy in CoM determination and, at higher compression levels, perhaps due to pronounced asymmetry of particle shape. The angle inaccuracy due to noise in CoM location follows a modified Rayleigh distribution as follows: noise in an angle between vector $i$ and $j$ whose expected deviation is null can be quantified by expressing $j$ as $\epsilon_x,\epsilon_y$ components in the plane of which $i$ is the normal hence aligned with the \textbf{z}-axis. This leads to angle noise of $\cos(\theta) = 1/\sqrt{\epsilon_x^2 + \epsilon_y^2 + 1}$, assuming that $i$ is normalized, and the $j = \{\epsilon_x, \epsilon_y, 1\}$. For $\epsilon_{x,y}$ Gaussian variables, this produces a modified Rayleigh distribution. In Fig.~\ref{fig:anglenoise} we plot this distribution for a set of uncorrelated Gaussian distributed $\epsilon_{x,y}$ with a standard deviation of 30~micron (dashed line). This CoM location detection noise is consistent with the displacement noise shown in the same Fig.~\ref{fig:xydisp} and captures the experimental data on angle noise very well. Only at maximum compression can a small deviation be observed, perhaps due to pronounced asphericity of the particles at this compression levels. We conclude that vectorial angle noise is due to CoM and contact location detection noise.

\begin{figure}
  \includegraphics[width=1\columnwidth]{CoManglenoise-copy.pdf}
  \caption{(a) histogram of angles between CoM and CoB for a strain of $\sim 15\%$ (red $\lozenge$) and $\sim 3\%$: blue $\circ$ (during compression); green $\triangle$ (during decompression). The dashed line indicates a distribution of angles obtained with a location detection noise of 30~microns. (b) Same data on linear scale.}\label{fig:anglenoise}
\end{figure}

\section{Conclusions}
We discussed the use of hydrogel spheres for their use in index matched scanning experiments on the mechanics of three dimensional granular samples. We discussed both index matching aspects and image analysis techniques that allow one to extract the aspherical surface structure of compressed particles inside a mechanically deformed packing. The surface structure data so extracted gives access to the particle stress tensor and the moment of inertia of a particles, which are relevant microscopic ingredients for any micromechanically tested theory of granular media. The source code for the methodology described in this paper, together with the data, are available at http://nicolas.brodu.net/recherche/tomorim/. We thank Matthias Schr\"{o}ter and Thorsten P\"{o}schel for their hospitality during the Erlangen Spring School in April 2016.

\bibliographystyle{aipproc}

redpajama_set_name: RedPajamaArXiv


text:
<?php
namespace Donhang\Form;
use Zend\Form\Element;
use Zend\Form\Form;
class DonhangForm extends Form
{
	public function __construct($name=null)
	{
		parent::__construct('donhang');

		$this->setAttribute('method','post');

		$customers_id = new Element\Hidden('customers_id');
		$this->add($customers_id);

		$customers_name = new Element\Text('customers_name');
		$customers_name->setLabel("Họ tên");
		$this->add($customers_name);

		$address = new Element\Text('address');
		$address->setLabel("Địa chỉ");
		$this->add($address);

		$phone_number = new Element\Text('phone_number');
		$phone_number->setLabel('Điện thoại');
		$this->add($phone_number);

		$delivery_address = new Element\Text('delivery_address');
		$delivery_address->setLabel('Địa chỉ giao hàng');
		$this->add($delivery_address);

		$email = new Element\Text('email');
		$email->setLabel('Email');
		$this->add($email);

		$submit = new Element\Submit('submit');
		$submit->setLabel('Go');
		$submit->setAttributes(array('class'=>"art-button",'value'=>"Go"));
		$this->add($submit);
	}
}
?>

redpajama_set_name: RedPajamaGithub


text:
Steamer Lane and Some Surf History
Steamer Lane in January 2013. Photo: Julia Gaudinski/Mobile Ranger
In 2009, Surfer Magazine named Santa Cruz, California as the best surfing town and extolled Steamer Lane as a "world class right-hand reef-point." But do not call it "Steamer's Lane," because locals will get all huffy (although "Steamer's" is acceptable).
The name apparently originates from early surfers who watched for huge waves in the lane that steamships used to come in to the wharf. These days, unless it is extremely stormy, you'll probably see at least a few surfers in the water at Steamer's, but the ships are long gone.
Good surf at Steamer's, January 2013. Photo: Julia Gaudinski/Mobile Ranger
Surf Zones
Steamer Lane is divided into four zones: Indicators, Middle Peak, The Slot, and The Point. Total beginners should not surf here at all. They should go to Cowell Beach, instead. Difficulty increases from Indicators out to The Point, where you'd better be pretty good. Only experts surf out past the lane at Third Reef.
The surf zones at Steamer Lane. Image: Julia Gaudinski/Mobile Ranger with thanks to inspiration from map at shorelinesurf.com
Local Surfing Legend
It was here in the 1950s and '60s that Jack O'Neill developed the modern surfing wetsuit, which helped make surfing in cold-water locations possible around the world. In those days, his surf shop was at Cowell Beach where the Dream Inn now stands. Jack's son Pat has followed in his father's footsteps. In the 1970s, frustrated with having his board trashed on the rocks, he experimented with surfboard straps that led to the modern-day "leashes."
In 2011, the O'Neill Coldwater Classic, a huge event held here annually in some form since the 1980s, was upgraded to an Association of Surfing Professionals World Title event. It is usually held in early November.
A surfer jumping into the waves from "The Point." Photo: Julia Gaudinski/Mobile Ranger
A fraction of a second later. Photo: Julia Gaudinski/Mobile Ranger
A World Surfing Reserve
In February 2011, the nonprofit Save the Waves Coalition named Santa Cruz, from Natural Bridges to Opal Cliffs east of Pleasure Point, as one of only four surfing reserves worldwide. This designation is not only to help the community understand the value of the area as a great surf spot but also to recognize it as an important coastal ecosystem that merits protection. The other three spots are Ericeira (Portugal), Manly Beach (Australia), and Malibu (California).
Dead Surfer Memorial
The Dead Surfer Memorial at Steamer Lane. Photo: Julia Gaudinski/Mobile Ranger
Honoring those who have died while enjoying the ocean surf is a theme in the Lighthouse Point area. At the top of the staircase that goes down to Steamer Lane is the Dead Surfer's Memorial. You will see hand-carved wooden tributes, flowers, and other trinkets placed there to commemorate loved ones lost.
The Arch at Steamer Lane
In the late 1800s, there was a large natural bridge here. It was made of sandstone from the Purisima Formation and was often used by tourists of the day for photographs. It collapsed during a storm in 1888, leaving behind a sea stack (the vertical remnants of a bridge or arch). A small chunk of it remains today. Can you find it in the previous photos?
The arch at Steamer Lane circa 1887. Photo: Courtesy of Frank Perry
This piece is part of the West Cliff Drive Tour. Download the free app with many tours of the Santa Cruz area and beyond.
Lighthouse Point: Illuminating Santa Cruz, by Frank A. Perry. Topics in Monterey Bay History series. Santa Cruz, California: Otter B Books, 2002.
Best Surf Towns. No. 1: Santa Cruz, CA. Surfer. Surfer Magazine online, April 5, 2009.
"Save the Waves: Santa Cruz honored as one of four surfing reserves worldwide," Shanna McCord. Santa Cruz Sentinel, April 28, 2012.
Steamer Lane. Wikipedia, February 2016.
Steamer Lane History, by Ben Marcus. Surfline.com website.
Previous : Recent: Geologically Speaking
Next : Mitchell Cove: Home of the Outfall Pipeline
I really enjoy field trips. I love being in a cool place and having someone tell me about it. The problem is, you can't always find a professor or park ranger-type to tell you all they know about the local rocks, plants, and history. So I decided to combine my love of things natural with mobile technology.
Barbara Waldemar
The Streamer Lane Memorial Stairs were wooden stairs built and used for about 30 years until the City deemed them a possible reason for West Side Drive road deterioration and becoming unsafe due to age.
This is Real stairs meant in anything with Memorial Stairs see face book site I put up. These stairs were built by all local surfers. They were built of wood and removed in large piece by crane in Spring. 2003
They gave surfers another set of stairs to exit as enter the Lane safety. This is where all the initial placks were and made by my now deceased brother, Robert Wally Waldemar, Thanks
Barbara Waldemar- thanks for this great info. I may e-mail you with some more questions as I would love to flesh out this story.

redpajama_set_name: RedPajamaCommonCrawl


Karen Maitland, Queen of the Dark Ages, has created possibly some of the most wicked children in fiction. From Narigorm, the child rune reader with a penchant for death, from Company of Liars, to the scheming yet devastatingly beautiful Leonia in The Vanishing Witch, they revel in manipulating the world around them – and those foolish enough to cross them. In Wicked Children: Murderous Tales from History, Karen Maitland explores some of the real-life cases of dangerous and powerful children which have inspired her own young – but deadly – characters.


text:
Michael Cohen's Damning Portrayal of Trump as a Lying, Racist Crook
By root	 Last updated Mar 1, 2019
Michael Cohen's Damning Portrayal of Trump as a Lying Racist Crook
At 10:02 on Wednesday morning, Representative Elijah Cummings, the veteran Maryland Democrat who now heads the House Oversight Committee, called his colleagues to order. More than seven hours later, Michael Cohen was still answering questions from the twenty-four Democrats and eighteen Republicans on the panel. What did we learn from this long hearing, which some have compared to the Watergate hearings of 1973 and 1974?
One lesson was to be careful with historical comparisons. Donald Trump isn't Richard Nixon; Michael Cohen isn't John Dean, and today's Republican Party most certainly isn't the Republican Party of Howard Baker and Lowell Weicker, Jr., who were G.O.P. representatives on the Senate Watergate Committee. These days, the House G.O.P. membership is a right-wing rabble, and the nation's capital is a site of unremitting partisan warfare. From the very start of the hearing, Jim Jordan, the ranking Republican on the committee, and Mark Meadows, who heads up the Freedom Caucus, made clear that their only goal was to attack Cohen's credibility. Even if the witness had turned up with a copy of the Moscow pee tape and a signed agreement between Trump and Vladimir Putin, the Republican duo and most of their colleagues would have tried to spin it as a Democratic hit job concocted by Lanny Davis and Adam Schiff.
Cohen hadn't come to the hearing bearing explosives precisely of this nature. He told Representative Jamie Raskin that he had "no reason to believe that tape exists." At another point, he stated that he had seen no direct evidence of collusion between the Trump campaign and Russia. But he also added that he had his suspicions. "Mr. Trump's desire to win would have him work with anyone," he said. He claimed that during a July, 2016, meeting at Trump Tower, he witnessed Roger Stone calling in and telling Trump "that he had just gotten off the phone with Julian Assange and that Mr. Assange told Mr. Stone that, within a couple of days, there would be a massive dump of e-mails that would damage Hillary Clinton's campaign." (WikiLeaks subsequently put out a statement saying no such call took place between Stone and Assange, and Stone said in a statement that Cohen's testimony was "not true.")
Cohen also claimed that Trump engaged in criminal behavior from inside the White House relating to the Stormy Daniels payoffs, and this assertion he backed up with documents. After providing the committee with a signed thirty-five-thousand-dollar check from Trump, dated August 1st, 2017—more than six months into Trump's Presidency—Cohen calmly explained that it was meant "to reimburse me for the hush-money payments I made to cover up his affair with an adult-film star and prevent damage to this campaign."
To be sure, the U.S. Attorney's Office for the Southern District of New York essentially asserted, last December, that Trump had been involved in the payoff scheme when it said in a sentencing memorandum that Cohen acted at the direction of "Individual-1." But it was still instructive to see Cohen saying bluntly and on live television, "For the record: Individual-1 is Donald J. Trump." It was equally instructive when the California Democrat Katie Hill elicited from Cohen the revelation that, as recently as early last year, when the existence of the payoffs was revealed, Trump was involved in concocting a cover story that he knew nothing about them. "That's what was discussed to do between myself, Mr. Trump, and Allen Weisselberg," Cohen said. (Weisselberg is the chief financial officer of the Trump Organization.)
Cohen also claimed that he and Weisselberg discussed how to disguise the 2016 payoff to Daniels's lawyer—Cohen ended up using his own money—and that Donald Trump, Jr., on behalf of the Trump Organization, signed one of the checks that eventually reimbursed him. Late in the afternoon session, Ro Khanna, a Democrat who represents Silicon Valley, zeroed in on these payments. "This is nothing to do with collusion," he said. "This is garden-variety financial fraud." Khanna also asked Cohen directly if he was claiming that Trump directed these transactions with Weisselberg and Trump, Jr., as "part of a criminal conspiracy, a financial fraud." Cohen replied, "Yes."
If there has been a previous occasion when a President's personal lawyer has testified to Congress that his client is a common crook, it has been lost to the history books. But that wasn't the end of Cohen's damning testimony about the man he also described as "a racist," "a cheat," and "a con man." He provided more details about the extensive efforts, on the part of Trump and himself, to mislead the American public about how long the Trump Organization pursued the Trump Tower Moscow project. Trump has long denied that there was a Russia deal of any type in the works. Cohen, who spent years working assiduously with Felix Sater, another colorful Trump associate, to put together a deal to construct Europe's tallest building in the Russian capital, knew all along that this was a lie. "So to be clear, Mr. Trump knew of and directed the Trump-Moscow negotiations throughout the campaign and lied about it," Cohen said in his opening statement. "He lied about it, because he never expected to win."
In 2017, Cohen went on, he told congressional investigators, "We stopped negotiating in January, 2016. That was false—our negotiations continued for months during the campaign." Between January and June of 2016, Cohen added, Trump asked him at least six times about the progress of the Moscow project. And after Trump surprised everybody, himself included, by winning the election, he "did not directly tell me to lie to Congress. That's not how he operates. . . . He would look me in the eye and tell me there's no business in Russia, and then go out and lie to the American people by saying the same thing. In his way, he was telling me to lie."
For all Cohen's record of duplicity and lying, which he repeatedly fessed up to during the hearing, this statement had the ring of genuine insider knowledge. To be sure, this was a figure who acted as Trump's fixer and bruiser for more than ten years, and who recently pleaded guilty to tax evasion, making false statements to banks, engaging in campaign-finance violations, and lying to the last Congress. But the very things that made Cohen such a problematic witness—his closeness to Trump and his history of finagling on behalf of his boss and himself—are also what made him a compelling one. This was an account of the darkness, told from within.
A bit later in the hearing, Michigan's Justin Amash, about the only Republican to show a bit of independence, asked Cohen if he could talk some more about the way in which Trump sometimes communicated his directions indirectly. "Sure," Cohen replied. "It would be no different than if I said, 'That's the nicest-looking tie I've ever seen. Isn't it?' What are you going to do? Are you going to fight with him? The answer is no. So you say, 'Yeah, it's the nicest-looking tie I've ever seen.' That's how he speaks. He doesn't give you questions, he doesn't give you orders. He speaks in code. And I understand the code because I've been around him for decades."
During a subsequent exchange with Jim Cooper, a Tennessee Democrat, Cohen suggested that others around Trump are also in the know, and he appeared to allude directly to the Republicans on the panel who were busy doing the President's bidding even as he was eight thousand miles away, in Hanoi. "Everybody's job at the Trump Org was to protect Mr. Trump," he said. "Every day, most of us knew we were coming in and we were going to lie for him on something. And that's exactly what's happening right now in this country. It's exactly what's happening here in government." That statement, too, had the ring of authenticity.
Donald Trumphouse of representativesmichael cohenroger stonestormy danielswikileaks
From "Lock Her Up" to "Send Her Back": Trump in North Carolina
'Send Her Back!': Trump Supporters at His N.C. Rally
U.S. May Have to Consider a Norea Korea Weapons Freeze
Donald Trump holds Oval Office meeting with survivors of religious persecution