text:
This article was published on October 3, 2012
Tweetbot creator launches Netbot, a mature and polished App.net client for iPhone and iPad
October 3, 2012 - 6:01 pm
Matthew Panzarino
Matthew Panzarino was Managing Editor at TNW. He's no longer with the company, but you can follow him on Twitter. (show all) Matthew Panzarino was Managing Editor at TNW. He's no longer with the company, but you can follow him on Twitter.
Tapbots, the studio behind the popular Tweetbot client for Twitter, has brought its design prowess to the fledgeling communication platform App.net. The company's new app Netbot serves users with the same visual panache and sure hand that it has brought to its Twitter client and to a half-dozen other robot-themed apps.
We've taken a look at several other clients for App.net recently that have a unique feel, like Rivr for iPhone and Hooha for Android. But Netbot's familiarity to many Twitter users, along with its general level of polish, make it an instant contender for the best App.net client for a lot of people.
App.net, for the unfamiliar, is a communication platform that — at least for now — works a lot like Twitter does. There is a global stream of messages that offers a look at the messages coming from all 20,000+ current users as well as a personal feed of just the people you follow. Over the past few weeks, App.net's engineers, led by founder Dalton Caldwell, have been implementing many of the features that Twitter users have come to enjoy from a real-time web platform.
These included Replies, Mentions, Reposts (retweets), Stars (favorites), conversations and more. Netbot has gained support for each of these as they've become available in the API, which is evolving rapidly. Thankfully, Tapbots has shown a progressive attitude towards getting them in the app and getting them working right, at least over the course of my time testing it.
And, given their continuous support of the Twitter ecosystem over the years, buying into Netbot is unlikely to be a bad decision if you want to continue to be able to take advantages of the latest and greatest App.net features down the road.
Much of the interface remains unchanged from Tweetbot, aside from the icon, which features a darker Mirror Universe version of the infamous bird. Perhaps they should have given it a goatee. There are some new bits of visual flare, however. Visiting a profile page and pulling down will expand the profile image that a user has set:
If you look at the bottom of the profile page, you'll also see a little easter-eggy thing that tells you which # user of App.net a person is and when they joined the alpha. I believe that #18 is the earliest non-employee.
Another nice visual touch is the small popup that shows you whether a post has been reported or starred and how many times when you visit its detail view. And you can see a list of those who have reposted or starred one of your posts, which is kind of cool. Like a built-in semi-Favstar.
The gestures and pop-out drawer actions are all the same as Tweetbot, and allow you to swipe for detail views, tap a link or Avatar in the timeline or tap and hold any of them to get more options. You can also configure a triple-tap to reply, star, repost or translate a post.
Swiping right brings you into a conversation and left brings you to the detail view of a post.
When posting, you can choose to post from multiple accounts by tapping on the header of the post view. When you do, you can also choose to cross-post to Twitter as well. The Twitter posting mechanism uses iOS' universal sign-on, so you have to have it enabled in Settings.app. When you first launch the app, be sure to hit up the Search pane where you can search App.net for all of your Twitter friends who have profiles on the service too.
Just so you're aware, when you cross-post to Twitter, you'll end up with a message that ends in an App.net link. That link leads back to the post at alpha.app.net:
Reposting works very similar to Tweetbot as well, but you can repost from multiple accounts by tapping and holding the repost button. Muting is in, and you can mute either by keyword or by client used to post.
Some clients like Rivr post lots of hashtags for annotation features like 'moods' and music playing. Until the App.net API gets filtering by annotation support, some folks will appreciate the mute by client.
All of the normal posting services are here for media and link shortening as well, aside from Twitter's image services of course. CloudApp, Mobypicture and Droplr are in for images and video. And Instapaper, Pinboard, Readability and Pocket support for Read Later services.
There are no push notifications yet in Netbot for iOS, but they're definitely planned for future versions, Haddad told me. That all depends on when an official addition of push is made to the App.net API, though, so it's a waiting game. Since the API has been progressing fairly rapidly, I wouldn't think it would be too long, but there's no solid timeline yet. Other apps like Rivr are using their own polling system to generate notifications now, if that's an important factor for you.
There is also currently no private messaging built in to the App.net API, but when it's there, Netbot will implement it.
We spoke to Tapbots' Paul Haddad about the decision to launch an App.net client and his thoughts on developing for the platform:
TNW: Why create a client for App.net?
Paul: We're excited about where App.net is heading. They've got a really good team in place and have been making good progress on releasing new APIs. I think as the weeks progress and they get past the basics of a social networking site we're going to see some really unique opportunities with their architecture.
TNW: What has your experience been working with developing an app for the platform?
Paul: It's been overwhelmingly positive. The API is very straightforward and works as expected and the App.net guys have been very helpful in answering questions and adding requested features.
TNW: What are your thoughts on its future for developers, especially with regards to the incentive program
Paul: I think its too early to really tell how that program is going to work out, but I think its indicative of the value that App.net puts on its developer ecosystem.
Netbot is available in both iPad and iPhone versions, which are separate purchases, just like Tweetbot.
Netbot for iPhone $4.99
Netbot for iPad $4.99
Published October 3, 2012 - 6:01 pm UTC
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Operation Christmas Child Shoeboxes 2018 – Good News! Great Joy!
Martin Luther Church participated in Operation Christmas Child for their fourth year. This Mission Project was our focus for October to mid-November. Operation Christmas Child was started over 20 years ago by Samaritan's Purse – a nondenominational evangelical Christian organization led by Franklin Graham.
From our youngest to our oldest members, shoebox gifts were packed to be a blessing to children in need around the world. What's in a box? A "wow" item such as a doll, soccer ball with pump, stuffed animal, or a small toy. Hygiene items, school supplies, and wearable items such as flip-flops, t-shirts, hats, etc. fill up the box. It truly is astounding how many thoughtful items can be used to fill those boxes!
On November 13, 135 boxes were taken to our nearest collection point which was Tecumseh, Nebraska. From there they were taken to a processing center (Denver for our area) where thousands of volunteers prepare them for international shipping.
The shoeboxes will travel to children in over 100 countries. The transportation by volunteers is completed by various methods!
The shoebox distribution results in evangelism and discipleship. Pastors and trained volunteers host the shoebox distributions in places where people may not know Christ or as resources for outreach in orphanages and other at-risk areas. "The Greatest Gift" a Gospel story booklet developed for shoebox recipients by Samaritan's Purse is distributed with the shoeboxes. Boys and girls across the globe have an opportunity to learn about Jesus.
Kindness and caring at MLC – inspired by Jesus, our Lord – resulting in great joy!


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text:
Police recover 30 more looted tractors in Adamawa
By Onimisi Alao, Yola
The police in Adamawa State have recovered additional 30 tractors looted in the capital city of Yola.
Also recovered are 107 bags of fertilisers, 28 hand tractors and 29 cartons of agrochemicals looted by some hoodlums who hijacked the #EndSARS protest.
No fewer than 238 suspects were arrested, from whom 35 tractors, nine vehicles, over 600 bags of fertiliser, 50 hand tractors and hoes, and 18 bags of maize were earlier recovered.
Return my late father's judges' robes, Ndoma-Egba begs looters
Police spokesman, Suleiman Nguroje, said the additional recoveries were made possible with the cooperation of other security agencies.
He said: "The Command also arrested four female and one male suspect, who allegedly looted public, corporate and private warehouses during the protest.
"The Commissioner of Police, Olugbenga Adeyanju, thanks the people of Adamawa, especially those who volunteered information to the police leading to the recovery of the looted items,'' he stated.
The recovered tractors are said to belong to the Northeast Commodity Association (NECAS), a regional agricultural leasing and mechanisation intervention group based in Yola.
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redpajama_set_name: RedPajamaCommonCrawl


text:
\section{Introduction}
\label{sec:intro}

Stellar radial velocities of enhanced precision are required for applications such as the tracing
of stellar wobble caused by an exoplanet, motion against a binary companion, or velocity
relative to nearby stars in a moving cluster. The common method of interpreting wavelength
positions of spectral lines in terms of a Doppler shift caused by radial motion reaches a limit
when accuracies much better than $\sim$1~km\,s$^{-1}$ are required.  Even for objects with
well-defined and rich spectra, limits are set by spectral line asymmetries and displacements
caused by physical motions on the stellar surface and by gravitational redshifts.
One step towards an improved understanding of such effects and their eventual mitigation is to
measure stellar radial velocities also without the use of spectroscopy. With adequate accuracy
and sufficient baselines in time, such determinations are now enabled through space
astrometry.

Astrometric methods to determine the radial component of stellar motion include monitoring
the secular change of the annual parallax, measuring changes in proper motion, and assessing
the varying angular extent of moving clusters whose stars share the same space velocity
\citepads{1999A&A...348.1040D}. Among these methods, the moving-cluster one offered
the highest accuracy based on \textsc{Hipparcos} data \citepads{1997A&A...323L..49P},
and radial motions for stars in such clusters have been determined by
\citetads{2001A&A...367..111D}, \citetads{2019MNRAS.483.5026L},
\citetads{2000A&A...356.1119L}, and \citetads{2002A&A...381..446M}.
When combining astrometric data with spectroscopic data, it then becomes possible to search for
phenomena, other than the Doppler effect, that are displacing stellar spectral lines
(\citeads{2003A&A...401.1185L}; \citeads{2003A&A...411..581M}; \citeads{2021arXiv210201079M};
\citeads{2011A&A...526A.127P}; \citeads{2002A&A...386..280P}).
In solar-type stars, both convective blueshifts
and gravitational redshifts amount to $\sim$0.5 km\,s$^{-1}$, while the moving-cluster method
enables accuracies of the order of a few hundred m\,s$^{-1}$.  Such levels are comparable
to the modulation of apparent radial velocities by stellar magnetic activity
\citepads{2021arXiv210406072M}.

\section{Perspective change of proper motions}
\label{sec:propermotions}

In this paper we examine how perspective acceleration, measured as proper motions changing over time, permits the radial component of stellar motion to be determined. The potential of such astrometric observations was realised already long ago
(\citeads{1902Vierteljahrsschrift....37...242S}; \citeads{1917AJ.....30..137S};
\citeads{1900AN....154...65S}); however, except for a few stars of very large proper motion, they were not practical to apply until adequate observational precision was achieved by space astrometry.  By combining positions and proper motions from \textsc{Hipparcos} with old measurements from the {\textit{Carte du Ciel}} and its Astrographic Catalogue, \citetads{1999A&A...348.1040D}
obtained astrometric radial velocities for 16 stars with typical errors in the range of 30--40 km\,s$^{-1}$.  For one object, however, the data could be combined with the visual observations by Bessel from 1838, reducing the uncertainty to 11 km\,s$^{-1}$. Recent data releases from the \textit{Gaia} mission have enabled order-of-magnitude improvements over the past \textsc{Hipparcos} study, and they are the topic of this paper.

Proper motions of stars change gradually with time even if their space motions are strictly uniform relative to the solar system barycentre (SSB). This perspective (or secular) acceleration is proportional to the radial velocity of the star and therefore allows the line-of-sight
component of the space motion to be measured.  An assumption is that the space motion is not significantly accelerated by the gravitational pull of a companion body. Because the perspective effect is proportional to the parallax and proper motion of the star, the method is limited to
nearby single stars of high proper motion in practice. Contrary to the moving-cluster method, where the attainable precision is ultimately limited by internal motions in the cluster, the perspective acceleration method continues to improve for measurements accumulated over longer periods in time and, therefore, has a higher potential accuracy, albeit only for nearby, unperturbed stars.

\section{Method and data}
\label{sec:method}

We applied the method to a sample of \textsc{Hipparcos} stars that also appear in the
\textit{Gaia} Early Data Release~3 (EDR3; \citeads{2021A&A...649A...1G}). The nearly
25~year epoch difference between \textsc{Hipparcos} (J1991.25) and EDR3 (J2016.0) is
sufficient to give a potentially interesting precision of the astrometric radial velocity for
hundreds of stars, although for many of them the measured acceleration is dominated
by other effects.

Geometric effects cause the proper motion ($\mu$) and parallax ($\varpi$) of nearby
stars to change at the rates
\begin{equation}\label{eq04}
\dot{\mu}=-2\mu\varpi\vra/A \, , \quad \dot{\varpi}=-\varpi^2\vra/A \,
\end{equation}
(e.g.\ \citeads{1917AJ.....30..137S}; \citeads{1977VA.....21..289V};
\citeads{1999A&A...348.1040D}),
where $\vra$ is the radial velocity and $A$ is the astronomical unit.%
\footnote{With radial velocity expressed in km\,s$^{-1}$ and the astrometric quantities
in milliarcseconds (mas), mas per Julian year (yr), and mas\,yr$^{-2}$, we have
$A=(149597870.7~\text{km})\times(648000000/\pi~\text{mas\,rad}^{-1})
/(365.25\times 86400~\text{s\,yr}^{-1})=9.7779222168\text{\dots}
\times 10^8$~mas\,km\,yr\,s$^{-1}$.}
Following \citetads{2003A&A...401.1185L}, we use $\vra$ to designate the radial component
of the space motion and $\vrs$ for the (spectroscopic) radial velocity.
The perspective acceleration refers to the effect given by $\dot{\mu}$ in Eq.~(\ref{eq04}).
Propagated over the time interval $\Delta t$ ($=24.75$~yr in this case), the accumulated
change in proper motion is $-2\mu\varpi\vra\Delta t/A$, in position
$-\mu\varpi\vra\Delta t^2/A$, and in parallax $-\varpi^2\vra\Delta t/A$.
The largest changes are expected for Barnards's star (HIP~87937) owing to its sizeable
parallax ($\simeq 547$~mas), proper motion ($\simeq 10\,393$~mas\,yr$^{-1}$), and radial velocity
($\simeq -110$~km\,s$^{-1}$). For this star the perspective effects produce, over the 24.75~yr,
a position difference of about 393~mas, an increase in the parallax by 0.84~mas, and an increase
in the proper motion by about 32~mas\,yr$^{-1}$.

Our method to obtain an astrometric estimate of $\vra$ is simple in principle: for a given star,
the astrometric parameters, as given in EDR3 for the epoch J2016.0, are propagated back in time
to epoch J1991.25, where they are compared with the corresponding values in the \textsc{Hipparcos}
catalogue, yielding the differences
$\Delta\alpha\cos\delta$, $\Delta\delta$, $\Delta\varpi$, $\Delta\mu_{\alpha*}$, and
$\Delta\mu_{\alpha*}$ in the five astrometric parameters. The propagation depends on the assumed value of $\vra$ (at the epoch J2016.0), which is then adjusted for the best overall agreement with the data. We minimised the goodness-of-fit measure
\begin{equation}\label{eq06}
\chi^2(\vra) = \vec{\Delta}^\prime\left(\vec{C}_\text{H}+\vec{C}_\text{G}\right)^{-1}\vec{\Delta}\, ,
\end{equation}
where $\vec{\Delta}$ is the $5\times 1$ matrix of the parameter differences,
$\vec{C}_\text{H}$, $\vec{C}_\text{G}$ are the covariance matrices for the corresponding parameters in the \textsc{Hipparcos} catalogue and the (propagated) \textit{Gaia} data, and
$\vec{\Delta}^\prime$ is the transpose of $\vec{\Delta}$. Confidence intervals of the
estimated $\vra$ were obtained from the increase in $\chi^2(\vra)$ around the minimum value; in particular, the 68\% confidence interval ($\pm 1\sigma_\vra$) is where
$\smash{\chi^2(\vra) \le \chi^2_\text{min}+1}$ \citep{book:nr3}. For the \textsc{Hipparcos}
data, we used the re-reduction by \citetads{2007ASSL..350.....V}, with covariances computed as described in Appendix~B of \citetads{2014A&A...571A..85M}.

To identify \textsc{Hipparcos} stars in \textit{Gaia} EDR3, we used the cross-match table
\texttt{gaiaedr3.hipparcos2\_best\_neighbour} provided with the release; of the 99\,525 \textsc{Hipparcos} entries in that table, 98\,004 have valid positions and proper motions in both catalogues. However, it is not meaningful to attempt to estimate the radial velocity for all of them. As indicated by Eq.~(\ref{eq04}), the precision on $\vra$ mainly
depends on the size of the product $\mu\varpi$, and we therefore consider only the 13\,161 sources in this sample that have $\mu\varpi>1000$~mas$^2$\,yr$^{-1}$ in EDR3.

The practical implementation of the method to estimate $\vra$ is complicated by the need to use a very accurate algorithm for propagating the astrometric parameters and by possible systematic differences
between the \textit{Gaia} and \textsc{Hipparcos} data sets. We used the propagation formulae derived by \citetads{2014A&A...570A..62B}, which assume uniform rectilinear motion relative to the SSB and rigorously take light-time effects  into account in addition to the geometric effects in Eq.~(\ref{eq04}).

In \textit{Gaia} EDR3, there are known issues with the parallax zero point as well as with the reference
frame of the bright stars ($G\lesssim 13$, which includes all \textsc{Hipparcos} stars). Moreover,
the \textsc{Hipparcos} reference frame may differ systematically from the EDR3 frame even after
the latter has been corrected for the known issues (e.g.\ \citeads{2021arXiv210511662B}). All of this
could produce errors of the order of 1~mas and 0.2~mas\,yr$^{-1}$ in the calculated parameter
differences $\vec{\Delta}$ in Eq.~(\ref{eq06}), which would affect our estimation of $\vra$. In order
to minimise their impact, we used the following correction procedure in three steps.
In the first step, the EDR3 data were corrected by subtracting the parallax bias according to
\citetads{2021A&A...649A...4L} and the magnitude-dependent proper motion bias according to
\citetads{2021A&A...649A.124C}. The resulting EDR3 data are, to the best of our knowledge, absolute
and on a non-rotating reference frame for all magnitudes.

In the second step, we propagated the corrected EDR3 data to the \textsc{Hipparcos} epoch and
analysed the \textsc{Hipparcos}--\textit{Gaia} differences in position and proper motion in terms
of an orientation error ($\vec{\varepsilon}$) and spin ($\vec{\omega}$) of the \textsc{Hipparcos}
reference frame with respect to the (corrected) \textit{Gaia} frame. This used the equations
\begin{equation}
\begin{bmatrix} (\alpha_\text{H}-\alpha_\text{G})\cos\delta \\[6pt]
\delta_\text{H}-\delta_\text{G} \end{bmatrix} = \vec{M}\vec{\varepsilon}\, , \quad\quad
\begin{bmatrix} \mu_{\alpha*,\text{H}}-\mu_{\alpha*,\text{G}} \\[6pt]
\mu_{\delta,\text{H}}-\mu_{\delta,\text{G}} \end{bmatrix} = \vec{M}\vec{\omega}\, ,
\end{equation}
where the subscript H refers to the \textsc{Hipparcos} data as published by \citetads{2007ASSL..350.....V},
G refers to the corrected and propagated \textit{Gaia} data, and
\begin{equation}
\vec{M} = \begin{bmatrix}
-\sin\delta\cos\alpha & -\sin\delta\sin\alpha &\cos\delta\\
\phantom{+}\sin\alpha & \cos\alpha & \end{bmatrix}\, .
\end{equation}
Using least-squares solutions weighted by the inverse combined variances, as in
Eq.~(\ref{eq06}), this resulted in the estimates
\begin{equation}\label{eq:eps}
\vec{\varepsilon}(1991.25)=\begin{bmatrix} -0.574\pm 0.007\\
-0.888\pm 0.007\\ +0.243\pm 0.008 \end{bmatrix}~\text{mas}
\end{equation}
and
\begin{equation}\label{eq:ome}
\vec{\omega}=\begin{bmatrix} -0.094\pm 0.004\\
+0.198\pm 0.004\\ +0.080\pm 0.005 \end{bmatrix}~\text{mas\,yr$^{-1}$} \, .
\end{equation}
Initially the full set of 98\,004 sources was included; however, after iteratively removing sources
with significant residuals (mainly binaries), the final solutions used 86\,914 sources for
$\vec{\varepsilon}$ and 96\,400 sources for $\vec{\omega}$. The uncertainties were
estimated by bootstrap resampling. The offsets in Eqs.~(\ref{eq:eps}) and (\ref{eq:ome})
are consistent with the estimated uncertainties of the \textsc{Hipparcos} reference frame,
namely $\pm0.6$~mas for the components of $\vec{\varepsilon}(1991.25)$ and
$\pm0.25$~mas\,yr$^{-1}$ for the components of $\vec{\omega}$ \citepads{1997A&A...323..620K}.

In the third and final step, the \textsc{Hipparcos} data were transformed to the (corrected)
\textit{Gaia} reference frame by subtracting $\vec{M}\vec{\varepsilon}$ from the positions
and $\vec{M}\vec{\omega}$ from the proper motions. These were then used together with
corrected \textit{Gaia} data to compute the parameter differences $\vec{\Delta}$ in Eq.~(\ref{eq06}).

The various systematic corrections to the parallaxes and, in particular, the proper motions
have a small but not entirely negligible impact on the estimated values of $\vra$. However, if
none of the above corrections were applied, the resulting changes in $\vra$ would in most
cases be less than $\pm 0.3\sigma_{\vra}$.

We note that other researchers have used similar techniques of combining \textsc{Hipparcos}
and \textit{Gaia} data for the somewhat orthogonal purpose of identifying astrometric binaries and stars dynamically accelerated by faint companions. Investigations based on the second release (DR2) of \textit{Gaia} data include \citetads{2018ApJS..239...31B} and \citetads{2019A&A...623A..72K}, while
\citetads{2021arXiv210511662B} provides an update using EDR3. In these studies the perspective
effect was removed by adopting the spectroscopic radial velocity, when available, for the radial motion.
In principle, the resulting $\chi^2$ (or similar) then includes a contribution from a possible
difference between the astrometric and spectroscopic velocities; however, in general our method
tends to give a high $\chi^2_\text{min}$ for the same stars that are identified as accelerated in
these other studies.

\begin{figure}
\centering
  \includegraphics[width=\hsize]{hist_DeltaVr_R1.pdf}
    \caption{Distribution of the difference $\vra-\vrs$ between the astrometric and
    spectroscopic radial velocities for two samples of \textsc{Hipparcos} stars.
    \textit{Light blue:} 926 stars with $|\,\vra\,|<2000$~km\,s$^{-1}$, $\sigma_{\vra}<100$~km\,s$^{-1}$,
    and with radial velocities in SIMBAD. \textit{Dark blue:} Sub-sample of 852 stars that, in
    addition, have  $\chi^2_\text{min}<40$. The bin size is 50~km\,s$^{-1}$.}
    \label{fig:hist_DeltaVr}
\end{figure}

\begin{figure}
\centering
  \includegraphics[width=\hsize]{fig2_R1.pdf}
    \caption{Comparison of the astrometric and spectroscopic radial velocities. \textit{Top:}
    Astrometric versus spectroscopic values for the sample shown as the dark blue
    histogram in Fig.~\ref{fig:hist_DeltaVr} and colour-coded according to the formal uncertainty
    ($\sigma_{\vra}$) of the astrometric radial velocity estimate. The black line is the 1:1 relation.
There are 28 data points that fall outside the limits of this plot.
    \textit{Bottom:} Difference between the astrometric and spectroscopic velocities for the sub-sample
    with $\sigma_{\vra}<10$~km\,s$^{-1}$ (corresponding to Table~\ref{table1}), with error bars at
    $\pm\sigma_{\vra}$. There are 11 data points outside of this plot.}
    \label{fig:vr_vr_vrE}
\end{figure}

\begin{table*}
\caption{Estimated astrometric radial velocities for selected \textsc{Hipparcos} stars in order of
increasing formal uncertainty.
\label{table1}}
\small
\begin{tabular}{rllrrrl}
\hline\hline
\noalign{\smallskip}
HIP & Name & Sp
&$\vrs$\phantom{}
&\multicolumn{1}{c}{$\vra$}
& $\chi^2_\text{min}$
& Remark\\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
87937 &  Barnard's star & M4V & $-110.35$ & $ -110.92\pm 0.37$ &      7.3 & \\
114046 & HD 217987 & M2V & $  +8.82$ & $   +5.86\pm 0.50$ &      9.2 & \\
54035 & HD  95735 & M2+V & $ -84.69$ & $  -86.15\pm 0.68$ &     22.3 & \\
24186 & HD  33793 & M1VIp & $+245.23$ & $ +244.11\pm 0.70$ &      7.4 & Kapteyn's star\\
104217 &   61 Cyg B & K7V & $ -64.25$ & $  -80.86\pm 0.74$ &  29284.9 & see Table~\ref{table2}\\
70890 &  Proxima Centauri & M5.5Ve & $ -22.40$ & $  -23.20\pm 0.74$ &      7.6 & \\
57939 & HD 103095 & K1V\_Fe-1.5 & $ -98.01$ & $  -98.61\pm 0.99$ &     39.3 & Groombridge 1830\\
1475 & V GX And & M2V & $ +11.82$ & $  -57.57\pm 1.28$ &    391.7 & \\
54211 & BD+44  2051 & M1.0Ve & $ +68.75$ & $  +80.97\pm 1.85$ &     17.2 & \\
36208 & BD+05  1668 & M3.5V & $ +18.22$ & $  +15.08\pm 1.87$ &      5.1 & Luyten's star\\
105090 & V AX Mic & M1V & $ +20.56$ & $  +19.82\pm 1.91$ &     12.4 & \\
108870 & $\varepsilon$ Ind & K5V & $ -40.03$ & $  -64.19\pm 2.55$ &    464.1 & \\
49908 & HD  88230 & K6VeFe-1 & $ -25.92$ & $  -25.45\pm 2.75$ &     16.5 & \\
25878 & HD  36395 & M1.5Ve & $  +8.63$ & $  +20.63\pm 2.87$ &      6.8 & \\
67155 & HD 119850 & M2V & $ +15.81$ & $  +23.35\pm 3.61$ &      6.2 & \\
104214 &   61 Cyg A & K5V & $ -65.82$ & $  -47.32\pm 3.69$ &    248.9 & see Table~\ref{table2}\\
55360 & V SZ UMa & M2V & $ +60.43$ & $  +68.24\pm 4.28$ &      4.5 & \\
85295 & HD 157881 & K7V & $ -23.52$ & $  -28.96\pm 4.50$ &      3.0 & \\
84478 & V V2215 Oph & K5V & $  -0.09$ & $   +0.15\pm 4.57$ &     31.6 & \\
80824 & BD$-$12  4523 & M3V & $ -21.22$ & $  -34.11\pm 4.83$ &      0.5 & \\
57367 & LAWD 37 & DQ & -- & $  +28.05\pm 4.91$ &      1.1 & \\
91768 & HD 173739 & M3V & $  -0.77$ & $ +138.52\pm 5.28$ &    564.3 & see Table~\ref{table2}\\
76074 & CD$-$40  9712 & M2.5V & $ +21.46$ & $   +1.70\pm 5.51$ &      6.2 & \\
41926 & HD  72673 & K1V & $ +14.72$ & $  +15.98\pm 5.64$ &     10.2 & \\
114622 & HD 219134 & K3V & $ -18.48$ & $   -7.77\pm 5.79$ &     20.7 & \\
94761 & HD 180617 & M3-V & $ +35.88$ & $  +18.07\pm 5.95$ &      3.2 & \\
23311 & HD  32147 & K3+V & $ +21.62$ & $  +37.02\pm 6.09$ &     15.2 & \\
79537 & HD 145417 & K3VFe-1.7 & $  +8.73$ & $   -2.52\pm 6.46$ &      8.2 & \\
65859 & BD+11  2576 & M1.0Ve & $ +14.56$ & $  +31.01\pm 6.59$ &      2.2 & \\
117473 & V BR Psc & dM1 & $ -71.13$ & $  -66.57\pm 6.65$ &      6.4 & \\
86162 & BD+68   946 & M3.0V & $ -28.76$ & $  -17.96\pm 6.73$ &      3.1 & \\
85523 & CD$-$46 11540 & M3V & $  -2.90$ & $  -25.05\pm 6.85$ &      1.1 & \\
3829 & Wolf   28 & DZ7.5 & $+263$ & $  -11.74\pm 7.11$ &      1.7 & van Maanen 2\\
106440 & HD 204961 & M2/3V & $ +13.16$ & $ -127.25\pm 7.16$ &     33.8 & \\
57548 & Ross  128 & dM4 & $ -31.07$ & $  -30.13\pm 7.18$ &      3.0 & \\
73184 & HD 131977 & K4V & $ +26.99$ & $ +207.16\pm 7.34$ &    120.4 & \\
83591 & HD 154363 & K4/5V & $ +34.03$ & $  +33.34\pm 7.39$ &      8.7 & \\
58345 & HD 103932 & K4+V & $ +48.57$ & $  +63.16\pm 7.41$ &      3.8 & \\
8102 & $\tau$ Cet & G8V & $ -16.60$ & $  -32.31\pm 7.60$ &      5.4 & \\
4856 & Ross  318 & M3.0Ve & $  +1.52$ & $  +14.19\pm 7.65$ &      2.6 & \\
26857 & Ross   47 & M4V & $+105.88$ & $ +127.17\pm 7.92$ &      2.2 & \\
91772 & HD 173740 & M3.5V & $  +1.10$ & $ -209.03\pm 8.26$ &    956.5 & see Table~\ref{table2}\\
98792 & HD 190404 & K1V & $  -2.47$ & $  +28.73\pm 8.74$ &      7.5 & \\
104432 & Wolf  918 & M1V & $ -58.26$ & $  -66.01\pm 9.03$ &      2.9 & \\
86287 & BD+18  3421 & M1.5Ve & $  -9.51$ & $   +4.05\pm 9.03$ &      0.6 & \\
86990 & L  205$-$128 & M3.5V & $ -42.94$ & $  -56.77\pm 9.05$ &      3.1 & \\
74235 & HD 134439 & sd:K1Fe-1 & $+309.99$ & $ +318.52\pm 9.11$ &      2.3 & \\
82588 & HD 152391 & G8.5Vk: & $ +45.12$ & $  +27.75\pm 9.12$ &      9.4 & \\
21088 & G 175$-$34 & M4.0Ve & $ +28.80$ & $  +74.92\pm 9.18$ &    356.6 & \\
112460 & V EV Lac & M4.0V & $  +0.29$ & $  -31.82\pm 9.18$ &      3.4 & \\
10279 & BD+02   348 & M1V & $  -2.56$ & $   -1.46\pm 9.23$ &      1.7 & \\
67090 & BD+18  2776 & M1V & $ +18.90$ & $  +17.61\pm 9.42$ &     18.8 & \\
29295 & HD  42581 & M1V & $  +4.73$ & $-1011.33\pm 9.50$ &   4885.0 & \\
113020 & BD$-$15  6290 & M3.5V & $  -1.60$ & $  +17.33\pm 9.59$ &      3.8 & \\
60559 & Ross  695 & dM2.0 & $ +51.19$ & $  +47.33\pm 9.97$ &      0.6 & \\
\noalign{\smallskip}
\hline
\end{tabular}
\tablefoot{Column~1: \textsc{Hipparcos} identifier.
Columns~2--4: main identifier, spectral type, and (spectroscopic) radial velocity ($\vrs$ in
km\,s$^{-1}$) as given in SIMBAD.
Column~5: estimated astrometric radial velocity ($\vra$) at epoch J2016.0 and its formal uncertainty
($\pm\sigma_{\vra}$), both in km\,s$^{-1}$.
Column~6: goodness-of-fit in Eq.~(\ref{eq06}) for the estimated $\vra$
(4~degrees of freedom).
}
\end{table*}

\begin{table*}
\caption{Estimated systemic astrometric radial velocities and mass ratios for physical pairs.
\label{table2}}
\small
\begin{tabular}{lrrrrlr}
\hline\hline
\noalign{\smallskip}
System & HIP (A) & HIP (B) & $\vrs$ (CM) & \multicolumn{1}{c}{$\vra$ (CM)}
& \multicolumn{1}{c}{$q$}  & \multicolumn{1}{c}{$\chi^2_\text{min}$ (dof)} \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
GJ 338 AB & 45343 & 120005 & $  +11.51$ & $ +152.82\pm 32.00$ & $0.452\pm 0.092$ &   9.60 (3)\\
 &  &  & $  +11.67$ & $  +50.83\pm 20.76$ & $0.959$ &  26.41 (4)\\
\\
GJ 725 AB & 91768 & 91772 & $   -0.11$ & $  +16.71\pm  6.31$ & $0.544\pm 0.030$ &  49.90 (3)\\
 &  &  & $   +0.04$ & $  -11.27\pm  4.79$ & $0.766$ &  89.71 (4)\\
\\
61 Cyg AB & 104214 & 104217 & $  -65.14$ & $  -65.53\pm  2.25$ & $0.758\pm 0.049$ &   5.39 (3)\\
 &  &  & $  -65.09$ & $  -67.03\pm  2.03$ & $0.877$ &  11.29 (4)\\
\noalign{\smallskip}
\hline
\end{tabular}
\tablefoot{Column~1: name of the system.
Columns~2--3: \textsc{Hipparcos} identifiers of the components.
Column~4: spectroscopic radial velocity (in km\,s$^{-1}$) for the centre of mass (CM), using
component values from SIMBAD and the given mass ratio.
Column~5: estimated astrometric radial velocity of the centre of mass and its formal uncertainty
($\pm\sigma_{\vra}$), both in km\,s$^{-1}$.
Column~6: estimated or assumed mass ratio $q=M_\text{B}/M_\text{A}$.
Column~7: goodness-of-fit with the number of degrees of freedom in brackets. For each system, the first
line shows the result when both $\vra$ and $q$ are fitted, and the second shows the result when $q$ is
constrained to the value in the line (see text for references).
}
\end{table*}

\section{Determined radial velocities}
\label{sec:results}

When the algorithm outlined above is applied to the selected sample of \textsc{Hipparcos} stars,
most of them obtain physically unrealistic values of $\vra$ and/or very large formal uncertainties
$\sigma_{\vra}$. For 930~stars, we find $|\,\vra\,|<2000$~km\,s$^{-1}$ and $\sigma_{\vra}<100$~km\,s$^{-1}$
and in Table~\ref{table1} we give the results for the 55 entries among them
having $\sigma_{\vra}<10$~km\,s$^{-1}$. Of the 930 stars, all but four have spectroscopic radial
velocities ($\vrs$) in the SIMBAD database \citepads{2000A&AS..143....9W}, and in
Fig.~\ref{fig:hist_DeltaVr} we show the distribution of
$\vra-\vrs$ for these stars as the light-blue histogram. Their median $\vra-\vrs$ is
$+2.3$~km\,s$^{-1}$ and the interquartile range (IQR) is $101.3$~km\,s$^{-1}$.
The sub-sample of 852 stars that also have a reasonably good fit is shown in darker blue,
$\chi^2_\text{min}<40$, indicating that the stars are perhaps not strongly perturbed by a companion.
For these stars the median difference is $+1.2$~km\,s$^{-1}$ and the IQR is $95.5$~km\,s$^{-1}$.

For a number of the high-precision stars with small or moderate $\chi^2_\text{min}$, the agreement
between the astrometric and spectroscopic values is remarkable. This is illustrated in the top
panel of
Fig.~\ref{fig:vr_vr_vrE}, where the two quantities are plotted against each other for the sub-sample
with $\chi^2_\text{min}<40$. The correlation is especially clear for the high-precision points
shown in darker colours.
Excluding the outlier van~Maanen~2 (see Sect.~\ref{ssec:vanmaanen2}), a
least-squares fit to the remaining 851 data points, weighted by $\sigma_{\vra}^{-2}$, yields
\begin{equation}\label{eq07}
\vra = (-1.11\pm 0.65~\text{km\,s$^{-1}$}) + (0.9999\pm 0.0060)\,\vrs \, .
\end{equation}
The reduced chi-square of this fit is high, about 8.3, as can be expected from the presence of
a number of binaries in the sample. The closeness of Eq.~(\ref{eq07}) to the equality
relation $\vra=\vrs$, nevertheless, suggests that the binaries do not bias the population mean of
$\vra$. The lower panel in Fig.~\ref{fig:vr_vr_vrE} shows the velocity differences, with error bars,
for the sub-sample in Table~\ref{table1}.

The uncertainties of $\vra$ given in the table and diagrams are formal ones obtained as
described in Sect.~\ref{sec:method}, based on the astrometric uncertainties provided in the
\textsc{Hipparcos} and \textit{Gaia} EDR3 catalogues. From a comparison of these two
catalogues, \citetads{2021arXiv210511662B} conclude that the uncertainties in EDR3,
for these bright sources, are underestimated by a factor of 1.37.
If this is also the case for the
present high-precision sub-sample, the uncertainties in Table~\ref{table1} on
average should be multiplied by a factor $\simeq 1.2$, and $\chi^2_\text{min}$ by a factor
$\simeq 0.9$. It would however have a negligible impact on the estimated values of $\vra$.

Many entries in Table~\ref{table1} show a large discrepancy between $\vra$ and $\vrs$ (by many times
the formal uncertainty) combined with a large $\chi^2_\text{min}$. These may be components of physical
systems where the mutual perturbations cause dynamical accelerations that strongly bias the estimated
$\vra$. A prime example is the binary system 61~Cyg~AB (HIP~104214+104127), where the application of the
method in Sect.~\ref{sec:method} to the individual components gives $\chi^2_\text{min}$ of 249 and
29\,285, respectively.

For binaries such as this, the method should instead be applied to the centre of mass (CM) of the
system, yielding an estimate of the systemic $\vra$.  Given the mass ratio $q=M_\text{B}/M_\text{A}$,
the astrometric parameters ($\vec{a}$) of the CM in each catalogue can be computed as
$(\vec{a}_1+q\vec{a}_2)/(1+q)$, with covariance $(\vec{C}_1+q^2\vec{C}_2)/(1+q)^2$. Propagating these
parameters from EDR3 to the \textsc{Hipparcos} epoch and applying Eq.~(\ref{eq06}) yields a function
$\chi^2(\vra,q)$ from which it may be possible to estimate both the (systemic) $\vra$ and the mass
ratio $q$.

Because the mass ratio equals the inverse ratio of the dynamical accelerations (e.g.\ Eq.~(24) in \citeads{2019A&A...623A..72K}), it is only possible to determine the mass ratio when the measured accelerations are significantly different for the two components, leading to significantly different (and biased) estimates of $\vra$ when the dynamical contributions are neglected. In addition to 61~Cyg~AB (with $\Delta\vra\equiv\vra_\text{B}-\vra_\text{A} = -33.54\pm 3.76$~km\,s$^{-1}$), there are two other systems that fulfil this condition: HIP~91768+91772 ($\Delta\vra = -347.55\pm 9.80$~km\,s$^{-1}$) and HIP~45343+120005 ($\Delta\vra = -552.68\pm 41.26$~km\,s$^{-1}$).
Estimates of $q$ and the centre-of-mass $\vra$ for these systems are given in Table~\ref{table2}. For comparison, the table also gives the estimated $\vra$ and $\chi^2_\text{min}$ when the mass ratio is constrained to the value based on evolutionary models (for 61~Cyg, from  \citeads{2008A&A...488..667K}), or the absolute $K$ band magnitude (for GJ~338 and GJ725, from \citeads{2019A&A...623A..72K} using the calibration by \citeads{2015ApJ...804...64M}). The $q$ values used in the constrained solutions are given without error limits in the second line of each object in Table~\ref{table2}. For a separate discussion of 61~Cyg~AB, see Sect.~\ref{ssec:61cyg}.

For many more pairs, it is possible to compute a systemic $\vra$ by assuming a particular value of $q$ for the pair, for example,
based on infrared photometry. While these estimates are less biased by dynamical acceleration than the component values $\vra_\text{A}$ and $\vra_\text{B}$ and, therefore, often in much better agreement with the spectroscopic values, we do not report them here as they are to a good approximation given by the weighted averages
$\vra_\text{CM}=(\vra_\text{A}+q\vra_\text{B})/(1+q)$.

\section{Notes on individual objects}
\subsection{HIP~3829 (van Maanen~2)}
\label{ssec:vanmaanen2}

In Fig.~\ref{fig:vr_vr_vrE}, one strikingly deviating point at $\vrs=263$~km\,s$^{-1}$ and
$\vra=-12\pm 7$~km\,s$^{-1}$ is van Maanen~2 (HIP~3829 or Wolf~28).  At a distance of 4.3~pc, this is the closest single white dwarf and, after Sirius~B and Procyon~B, the third nearest.  The estimated $\vra$ gives almost perfect agreement between the EDR3 and \textsc{Hipparcos}
data ($\chi^2_\text{min}=1.7$ for 4~dof).

Although the presence of a possible companion has been suggested, deep infrared imaging \citepads{2008MNRAS.386L...5B} and searches for binarity from possible proper-motion anomalies by \citetads{2019A&A...623A..72K} seem to exclude any nearby orbiting companion more massive than
$2~M_\text{Jup}$.

The strongly deviant spectroscopic value cannot be reconciled with the astrometric data for any reasonable amount of gravitational redshift.  The spectroscopic number is the one generally quoted in catalogue compilations, entering databases such as \textsc{SIMBAD}
(\citeads{1995A&AS..114..269D}; \citeads{2006AstL...32..759G}), and it merits closer scrutiny.
In tracing the origins of this quantity, one finds it to come from the General Catalogue of Stellar Radial Velocities \citepads{1953GCRV..C......0W}.  Examining the remarks in the printed version of this catalogue,%
\footnote{For example~\url{http://publicationsonline.carnegiescience.edu/publications_online/stellar_radial_velocities.pdf}}
one finds this value to arise from an observation made at Mt.~Wilson Observatory, in a listing of stars with large radial velocities by \citetads{1926PASP...38..121A}.  In that work, data for most
stars are based upon several spectrograms, although `in a few cases of exceptional interest', even a single observation was included. The stars are typically of visual magnitude 7 to 9, with van Maanen~2 being the faintest of that sample at $V=12.3$ (the second faintest had $V=10.8$).
Only one exposure was recorded with the lowest resolution camera, and the deduced value is further marked as `subject to especial uncertainty'. Clearly, this cannot be seen as a precise or reliable measurement.

Together with other white dwarfs, van Maanen~2 was later observed with the Hale telescope on Palomar by \citetads{1967ApJ...149..283G}, yielding $\vrs=+54$~km\,s$^{-1}$, a value those authors classified as `reliable'.  In a somewhat later reexamination, \citetads{1972ApJ...173..377G}
arrived at $+39$~km\,s$^{-1}$ from measuring numerous spectrograms, but with differences between various spectral lines.  For such faint sources with very diffuse spectral lines, measured values may fluctuate greatly depending on the spectrograph dispersion and the depth of photographic exposure \citepads{1954AJ.....59..322G}. Even more precise spectral recordings face challenges: by using only the \ion{Ca}{ii} K line, \citetads{1993AJ....105.1033A} obtained $\vrs=+15$~km\,s$^{-1}$, but a fit to both the H and K lines instead gave $+54$~km\,s$^{-1}$, probably influenced by pressure shifts in the white-dwarf atmosphere.

The large proper motion of van Maanen~2 caused \citetads[][page 287]{1932BAN.....6..249O},
expanding on an earlier suggestion by \citetads{1931Natur.127..661R}, to suggest the use of secular
changes in proper motion to distinguish the gravitational redshift from actual radial motion, envisioned to be feasible after 30 or 40 years of observations.
Using the long-focus Sproul refractor during 1937--1970, \citetads{1971IAUS...42...32V} derived a value for the astrometric velocity, with a significant uncertainty but remarkably consistent
with the early spectroscopic measurements.  However, \citetads{1974AJ.....79..815G} pointed out an error in those calculations. Using images from even longer time series with the Allegheny refractor, they deduced a new value with an astrometric velocity of $+6\pm 15$~km\,s$^{-1}$ and argued that this implies a plausible gravitational redshift.  The Sproul plate series were continued until 1976, and they were re-measured by \citetads{1978AJ.....83..197H}, who then found an astrometric value of $+25\pm 18$~km\,s$^{-1}$.

The actual gravitational redshift depends on the white-dwarf mass.  In a spectrophotometric study, \citetads{2012ApJS..199...29G} obtained the mass 0.68$\pm0.02~M_{\odot}$, implying a likely redshift of the order of 40~km\,s$^{-1}$, thus leaving a contribution to the wavelength shift caused
by the stellar motion that is reasonably consistent with our astrometric value of $-12\pm 7$~km\,s$^{-1}$.

The misperception of the anomalously large spectroscopic value for this star seems to have originated
by the quoting and re-quoting of one particular uncertain observation, whereupon its inclusion
in general catalogues was chosen as being the value that had the greatest number of citations.
Such a case is by no means unique.  For an example where early 19th century visual observations of
suggested stellar variability were carried over into modern catalogues,
see \citetads{1993ApJ...403..385D}.

\subsection{HIP~57367 (LAWD~37)}
\label{ssec:lawd37}

Obtaining accurate gravitational redshifts in white dwarfs remains a challenge.
Only in the particular nearby system of Sirius~B, observed from Hubble Space Telescope, has a precise
value of $80.65\pm0.77$~km\,s$^{-1}$ been measured for its rather massive white dwarf
(\citeads{2005MNRAS.362.1134B}; \citeads{2018MNRAS.481.2361J}).

In Table~\ref{table1} the white dwarf with the most precise determination of astrometric radial velocity is LAWD~37 (HIP~57367 or GJ~440) with $\vra=+28\pm 5$~km\,s$^{-1}$. As van Maanen~2, it fits the combined \textsc{Hipparcos} and \textit{Gaia}~EDR3 astrometry almost perfectly and has no known companion (\citeads{2000AJ....119..906S};
\citeads{2019A&A...623A..72K}). It does not have a spectroscopic velocity in \textsc{SIMBAD,} but it is clearly an interesting target for the determination of the gravitational redshift if a spectroscopic $\vrs$ is obtained and an improved astrometric value can be derived using future
releases of \textit{Gaia} data. The significance of such data is enhanced by the prospects of measuring its mass from gravitational microlensing (\citeads{2020A&A...640A..83K}; \citeads{2018MNRAS.478L..29M};
\citeyearads{2020MNRAS.498L...6M}).

Based on \textsc{Hipparcos} and \textit{Gaia} DR2 data, \citetads{2019A&A...623A..72K} identified a
proper-motion anomaly for LAWD~37 at a signal-to-noise ratio  of 4.9, which could suggest the
presence of a massive companion. That result, however, is not supported by the present study.

\subsection{HIP~87937 (Barnard's star)}
\label{ssec:Barnard}

This nearby red dwarf yields the most precise velocity value, with an uncertainty comparable to the star's expected gravitational redshift.  At these accuracy levels, differences between spectroscopic and astrometric values may start to provide unique astrophysical information.  A feature of both Barnard's star and other red dwarfs, is the presence of additional effects that are modulating the stellar spectrum.  Precise Doppler monitoring sets limits on possible exoplanets (\citeads{2013ApJ...764..131C};
\citeads{2003A&A...403.1077K}; \citeads{2009A&A...505..859Z}), while variability in chromospheric emission lines suggests a long-term activity cycle (\citeads{2012A&A...541A...9G};
\citeads{2019MNRAS.488.5145T}), accompanied by occasional flaring \citepads{2006PASP..118..227P}. `Chromatic' radial velocities obtained from different parts of the spectrum may segregate signatures from magnetic activity, convection, or other effects \citepads{2020A&A...641A..69B}; however, obtaining a zero point for the different wavelength shifts, corresponding to the radial motion of the stellar centre-of-mass, does require astrometry.

Analogous considerations apply to other red dwarfs including Proxima Centauri and Kapteyn's star. Nearby red dwarfs are numerous (making up 35 out of the 55 entries in Table~\ref{table1}), and they can be expected to display statistically similar properties.  Even if an adequate accuracy cannot yet be obtained for each of them, there is the prospect of averaging astrometric and spectroscopic velocities for groups of such M-dwarfs to identify features in their spectroscopic signatures once adequate data are available for a sufficient number of them.  As mentioned in connection with Eq.~(\ref{eq07}), the possible presence of perturbing companions to some of the stars should not systematically bias the mean astrometric radial velocity for such a group.

\subsection{HIP~104214 + 104217 (61 Cyg~AB)}
\label{ssec:61cyg}

For the binary system 61~Cyg~AB, we derived the mass ratio $M_\text{B}/M_\text{A}=0.758\pm 0.049$
from the combined \textsc{Hipparcos} and \textit{Gaia} EDR3 astrometry. This gives a significantly better fit to the combined astrometry than the higher mass ratio 0.877 estimated from evolutionary models by \citetads{2008A&A...488..667K}. As discussed therein, the masses of the components are not well constrained by observations and the mass ratio derived here is well within the range of previous dynamical estimates. However, both components are very bright for \textit{Gaia} ($G=4.77$ and $5.45$~mag) and the astrometry in EDR3 is known to degrade rapidly for $G\lesssim 6$~mag \citepads{2018A&A...616A...2L}, which could bias our result.

In \citetads{1999A&A...348.1040D}, we derived an astrometric radial velocity for 61~Cyg of $\vra=-68.0\pm 11.1$~km\,s$^{-1}$. This was obtained from a combination of \textsc{Hipparcos} data and the visual observations by \citetads{1838AN.....16...65B}, made in 1837--38 as part of his successful campaign to measure the parallax of the system. Considering that the perspective effect in position increases quadratically with the temporal baseline, it might still be relevant to consider Bessel's measurements in combination with the \textit{Gaia} and \textsc{Hipparcos} data. However, we have not been able to obtain a consistent solution including all three kinds of data. If this inconsistency would be caused by the problem in EDR3 mentioned above for the very bright stars, the results in Table~\ref{table2} for this system should be viewed with caution.

\section{Conclusions}

The feasibility of determining radial velocities from purely geometric measurements was already realised long ago, along with its ensuing observational demands.  In evaluating the observability of van Maanen's star, \citetads{1931Natur.127..661R} wrote: `in a century or less the true radial velocity of a star of such large proper motions and parallax as this could be found from the second order term in the proper motion'.  Accuracies realised in space astrometry now permit such measurements over more manageable timescales. The most precise results should be obtainable for the nearest stars but, unfortunately, the brighter of those are still difficult to observe.  Proxima Centauri yielded a precise value (Table~\ref{table1}), but the other components of the $\alpha$\,Cen system were too bright to be included in \textit{Gaia} EDR3 and they
may have to be tied to the \textit{Gaia} reference frame by means of other instruments
(e.g.\ \citeads{2021arXiv210410086A}) or await future exploration of space observations.
Already now, the method permits one to estimate gravitational redshifts of white dwarfs and to set limits on convective shifts in other stars.

\begin{acknowledgements}
This work has made use of data from the European Space Agency (ESA) mission {\it Gaia} (\url{https://www.cosmos.esa.int/gaia}), processed by the {\it Gaia} Data Processing and Analysis Consortium (DPAC, \url{https://www.cosmos.esa.int/web/gaia/dpac/consortium}). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the {\it Gaia} Multilateral Agreement. The work by LL is supported by the Swedish National Space Agency. The work by DD is supported by grants from The Royal Physiographic Society of Lund. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Diagrams were produced using the astronomy-oriented data handling and visualisation software TOPCAT \citepads{2005ASPC..347...29T}.  Use was made of NASA's ADS Bibliographic Services and the arXiv$^{\circledR}$ distribution service. We thank the referee, Pierre Kervella, for his detailed and insightful comments.

\end{acknowledgements}

\bibliographystyle{aa}

redpajama_set_name: RedPajamaArXiv


text:
Q: Oscilloscope algorithm, dynamic data input, limit output data I'm trying to make a simple filter incoming data (save maximum and minimum pick), for example: 44100 comes samples per second, but the screen must be displayed 1000. I choose a maximum or minimum in the range of 44.1 samples, and output the screen. However, this algorithm is not very accurate. In the code, it looks like this:
example pseudo algorithm
float max = 0;
float min = 0;
float filter = 0;
float step  = 44100/1000;
for(int i = 0 ; i < 44100; i++){

    if(input[i] > 0)
        if(max < input[i])
            max = input[i];
    if(input[i] < 0)
        if(min > input[i])
            min = input[i];

    filter++;
    if(filter >= step){
        filter = filter - step;

        //1st version  (bad version)
        memory[count] = max + min;

        //2nd version (bad version)
        if(max > abs(min))
            memory[count] = max;
        else if(max < abs(min))
            memory[count] = min;

        //3nd version (only maximum)
            memory[count] = max; //work great, but only > 0

        //4nd version (only minimum)
            memory[count] = min; //work great, but only < 0

        max = 0;
        min = 0;
        count++;
        if(count >= 1000)
            count = 0;
    };
};

What am I doing wrong? Separately, everything works fine (max or min), but when connecting all together, result bad.
I have picture, but I can not paste them here.
Links to pictures under this post.

A: To properly compute the min/max of a set of numbers you have to initialize the values correctly. By setting them to 0 you run into the problems you've found. You have basically two ways to initialize min/max:

*

*Set them to a value larger/smaller than any of your input data.

*Set them to the first value in the array.

For (1), if you know your data is, for example, always between -100 and +100 you can simply do:
min =  101;
max = -101;

Note that this doesn't work if your inputs can be any value in the range of the type. For (2) you can do something like:
float max = input[0];
float min = input[0];

...

for (int i ... )
{
    ...

    if (filter >= step)
    {
        ...
        min = input[i + 1];   // Be aware of overflow on the last element if
        max = input[i + 1];   // input[] is exactly 44100 elements in size
    }
}

A: What do you actually want to see? If it is audio sample, zero means quiet, you probably want to see the envelope - store minimum and maximum for each bin (your bin here=1000 counts) together and display the two in the same picture.
Your sample rate (after division) is 44 Hz, so you can forget some nice simplified waveform (if it is audio)...

A: The problem that you're seeing in the third graph is that you are storing either a minimum (about -1) or a maximum (about +1). And it's pretty random which of the two you store.
When you then connect the dots, you see a short line segment (2 pixels) whenever you stored two minima or two maxima. But if you store a minimum followed by a maximum, connecting the two gives you a line with a very steep upwards slope. A maximum followed by a minimum gives you a strong downward slope.
The real problem here is that you probably don't realize what you wanted to draw. You should have two arrays, memory_min[] and memory_max[]. And don't mix those two.

redpajama_set_name: RedPajamaStackExchange


text:
Nevis Government House Restoration Nearly Complete
October 6, 2018 June 20, 2017
Nevis Government House Being Restored
Charlestown, Nevis
Work on the EC$1.6 million restoration project of the Government House at Bath Plain on Nevis, is 85 percent completed and is expected to be completed by the end of August.
The disclosure came from Mr. Alton Brown, Contractor for the project, when Hon. Alexis Jeffers, Minister of Land and Housing in the Nevis Island Administration (NIA), toured the project on June 20, 2017.
He said the project which is funded by the Nevis Housing and Land Development Corporation (NHLDC), is in its finishing stages and they were awaiting on the doors and windows for installation.
The building, which was built in 1909, had fallen into disrepair after an infestation of wood lice and a complete restoration had become necessary. Greenheart wood imported from Guyana for restoration 10 years ago was utilized for the project.
The architectural integrity of the building has remained the same with some enhancements including new plumbing and electrical.
Mr. Brown thanked Minister Jeffers for his approval of the work done so far.
"I am grateful that the minister is satisfied with the progress of work from his last visit. I am amazed. I am grateful for his comments in that regard," he said.
Mr. Jeffers described the project's progress as tremendous and commended Mr. Brown and his team for the work done, the Project Manager Hon. Michael Perkins and the staff of the NHLDC for ensuring that the materials necessary for the project were delivered in a timely manner.
He explained that the project would restore the official residence of the deputy governor general and also the venue for official engagements as was done in the past. The historical landmark would also be a tourist attraction.
The Minister expressed hope that the property would be the venue for the 2017 Independence cocktail bash in September.
Since St. Kitts and Nevis gained independence in 1983, it has been the home of the deputy governor general. The last Deputy Governor General Eustace John retired at the end of April 2017. A few years before his retirement, he was rehoused in a nearby rented property due to the uninhabitable conditions of the official residence.
Categories Nevis News Tags Government, Nevis Government
Nevis Island Launches Culturama 43 Festival
Independence Day Theme Competition Launched


text:
Minderheiten › Sarah Clément
Sarah Clément
An overview of Génériques's work on memory, immigration and space in France and in Europe, 1987-present
France has a long history of immigration dating back to the 19th century. Until recently, it had thehighest number of immigrants in Europe. Those immigrants and their descendants have left traces oftheir passage in France. As groups of immigrants arrived, towns and villages changed to reflect thecultural, religious and social elements of the newcomers. For instance, in some parts of Paris, theJewish immigrants who came from Central and Eastern Europe in the late 19th and early 20thcenturies changed considerably the Marais area (shops, synagogues, food stalls etc.). Today, eventhough the Marais still bears signs of this Jewish heritage, the area has become a hotspot for ayoung, international population who probably knows little or nothing about the Marais's Jewish past.A telling example of the relationship between immigration and are the numerous towns built on theperiphery of Paris in the 20th centuries. Known as banlieues in French, they reflect the history of thedifferent waves of immigrants that have inhabited them: mainly Russians, Germans, Italians andPoles before 1945; Spanish, Portuguese, North-African, African, Asian migrants after 1945. Thesesites are interesting for anyone interested in the relationship between space, memory andimmigration.How does space reflect the memory of past immigration? And how? What does this space reveal?What memory(ies) and past(s) does it tell? For whom? And why?Those questions are at the heart of the work of the association Génériques. Created in 1987,Génériques is Paris-based association that works on the history and memory of immigration inFrance and in Europe (19th-20th centuries). Collecting and preserving the memory of immigrants,including their impact on space, is at the core of its mission. Amongst its many projects and activities,Génériques has worked extensively on projects focusing on the relationship between space, memoryand immigration, at the regional, national and European levels. This paper will present some of theprojects Génériques has worked on. The aim of the paper is to share and enrich discussions onmemory, immigration and space.
Panel 1: Sammeln


In order to soften the edges of a bedroom and to sidetrack the eye from the ceiling, soft cloth can be hung on the walls, and floors and ceilings should be pale to match the wallets of color on bed coverings, plants and baskets. Boldly colored wall paper can be utilized for the walls and duplicated in the curtains, creating a cozy and luxurious impact. To offer a stark colored room a feeling of intimacy, pastel colored blinds can be utilized.
Fabric sofa sets would be the focal point of many living areas. If a couch doesn't match the interiors with the whole room, it might look unsightly. You should view as material, making, and luxury however always remember interior design is definitely an art form too. Think lasting with regards to picking the ideal couch because chances are, you will certainly be making use of the very same one for a number of years. Remember that the goal is to find something worth the price. Do not buy deal sets merely to replace it every couple of years. Selecting the ideal couch might be more important than people think. Following a prolonged day, you want to be ready to sink into the most best couch and relax. A home is higher than a reflection of this property owner's character. It isn't simply a location for program; it is really the location where you get the home of daily.
When I initially think about convertible sofa beds, I think hide-a-beds, really heavy, and those brown patterned sofa beds from the 1980's – not appealing however still out there in student houses. A sofa bed serves a wonderful function, a couch by day and an additional bed after dark for guests when you do not have additional room. So you want convenience and function, not constantly easy to achieve. But the market is constantly trying, so there are a number of choices on the market of various types of convertible sofa beds.
An ottoman is an ideal location for storing items which are made use of day-to-day such as pillows, linens, blankets. Simply dump in children's toys or make it pet's corner, they can be made use of in the means one feels best. Sometimes, the reverse side of cushion is made difficult to enhance its utility. Now, you can enjoy your preferred film and have food simultaneously with no discontinuity. In some variants, a hidden storage tray is provided inside, to keep remote control, newspapers, letters, TV guide, or anything. A lot of time will be saved, if we keep them intact in our own ottoman. Besides concealing them from kids, there accessibility will likewise get easy.
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Bedsheets not only take advantage of the thread count of the bedding linen however also the type of fiber in the quality of exactly what the material it is made of. this will play a really substantial function in the making of your bedding set. The first thing in selecting the right bedding linen for you is to choose on the type and quality level that you would such as for your bedding linen. Comforters, duvets and all your bed sheets will usually be available in silk, pima cotton or the best one is Egyptian cotton. If you are purchasing bedding linen your best decision would be to choose a linen that is 100 % cotton. Using a solitary ply fiber with the longest fiber you can find, attempt and get 2 inch fiber that witch would be your best selection.
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Cherry furniture is made from a hardwood known as American cherry, black cherry, cabinet or wild cherry. It has a smooth texture and is finely grained. Due to the fact that of its natural appeal, it is never ever stained with an imitation color, however keeps its warm red glow. This makes an exceptional piece of natural wood furniture which mirrors the lumber from which it was constructed. Picking the ideal furniture for an unique place such as a master bedroom is in some cases hard. Does one desire a formal, modern of conventional design? Fortunately, despite the space or design cherry wood furniture will fit in wonderfully. It provides a photo of improvement and sophistication which is found in the most distinguished houses in the nation.
Bedding in the real sense is a crucial part in your bedroom and sticks out as a center of destination when somebody walks into your room. So, they have to be of the very best choice and can range from elegant to affordable. Some designs are offered on the basis of the period and some are just excellent designs by the many designers. So, when offered the thought of purchasing bedding, it is truly worth the investment as this is not what others would enjoy in your bedroom, however it will be a had collection that you would too cherish for many years to come. A choice like Tommy Bahama would be an excellent option for your room.
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An ache dresser is ideal for rooms and dens. They are strong, strong and highly long lasting. Some sets are slim in design, while some are brief and large. They could match your space decor with real perfection. Because of the their wooden base, correct upkeep is a vital aspect. With cleaning, cleaning, and shining, you'll protect your dresser for many years to come. You will also protect your financial investment. Pine systems include a number of drawers. These can be vertical or horizontal dressers. The systems are incredibly popular, and sold all over the world. From retail outlets to warehouses, this furniture is constantly in need.
The comfort level of the couch depends a lot on the depth of the sofa and upon your preferences about utilizing it i.e. lying or sitting on the sofa and you need to think about the exact same also while searching for the comfort level. If you like snuggling and sleeping on you sofa, look for a deep sofa for additional comfort. If you buy a microfiber sofa for your house and you want it for the comfort of yourself and your family, look for a 2 or three seater. On the other hand, if you're aiming to seat lots of people then a microfiber sectional sofa might be a much better choice.
A chest of drawers is an extremely essential furnishings in every house as well as in even in every room. This furnishings has numerous parallel and horizontal drawers that are stacked one over the other. These are typically used to save garments mainly scarf, socks, and underwears. It becomes easy to find these little garments and numerous other things that can be kept in the drawers. This can be put in your bed rooms and other places in our home where you want to keep a great deal of things in one place and keep it handy. These are typically rectangular in shape and have little legs that are kept on the floor. Dark wood chest of drawers is appealing and has a luxurious appearance. It matches well with numerous other furnishings that exist in your house. A Black wood chest of drawers boosts the appeal of your house and is very stunning. The Mango wood chest of drawers is very commonly used and is a bit more economical. These wooden chests of drawers are available in simple designs in addition to in numerous ornamental designs that becomes the center of attraction in your house.
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The next one is the lift chair recliner with 3 reclining positions. This type of chair can recline to a position where in the user is almost lying flat. You can also recline it to any position between the seated and the lying position relying on exactly what your requirements are. With this, the footrest will certainly also move as you recline the chair in to a higher angle to offer support to your legs. The three-position chair would also have the abilities of the two-position chair enabling the user to sit in it without putting much effort during the process of sitting.
Make certain you have a lot of time though to assess your selections. You will likely find numerous of them that you are contemplating. Possibly spending a few minutes in a reclined position on some of these microfiber sofas will certainly assist you to comprise your mind! In the mean time you can enjoy that extra time to concentrate on your very own requirements and to get comfortable.
Recliners are clever designs and are made to provide maximum comfort. They are integrateded such a means that can provide you the best support and comfort and your body gets totally unwinded. Practically anyone would like to have a seat in a recliner with a book or watch TELEVISION. This is one of the reasons recliners have become so popular in homes in the U.S. Leather recliners bring design to your house and also allow you to feel the best comfort. There are various types of recliners that can match the décor of your residence. They are readily available in numerous styles. The normal leather recliners readily available early on are now replaced by some innovative designs that are made by utilizing the current innovation.
Rooms are transformed in such a way that they end up being ultimate source for luxury and comfort. Today, the most common type of bed room includes a bed of a particular size, dressers, chests, night tables, and mirrors. The bed room dresser is now provided severe value, and it can be found in range of designs from contemporary to conventional type. Furnishings of bed room needs to specifically designed and scaled. Many people like the wooden, metal product leather ottoman sale. In bed room, the most vital is your bed which is a classy piece of furniture in any bed room. According to your comfort, you can pick modern to a Victorian style dresser. A bed room dressers serves dual purposes, they are gorgeous in addition to serves the energy as you can keep your valuable products too. A dresser can be found in ranges, from numerous designs to shapes as per your taste and serves all your purposes well.


The beautiful and fey--as they say in the Old Country--Nuala Anne McGrail uses her psychic abilities to help solve mysteries. But even she will admit with a smile that she couldn't do it without Dermot Michael Coyne, her devoted admirer and self-proclaimed "spear carrier."
Now both living in Chicago, their unique courtship is once again interrupted by one of Nuala's "spells." On a quiet street on the South Shore, she is overwhelmed by the screaming of thousands of dying men--Confederate soldiers held as prisoners of war.
Soon the pair are caught up in a Civil War controversy, and an all-too-present-day mystery involving a sophisticated gang of art thieves, corrupt politicians, and international terrorists. But Dermot is cheerfully resigned, for as he well knows, life with Nuala will never be simple. After all, she's like Irish lace--"thin and delicate and pretty, and just a little bit complicated."


Obstructive sleep apnea is a serious sleep disorder. This condition causes a patient to start and stop breathing at a rapid pace while asleep. This occurs when your muscles relax and block the airway during sleep. One noticeable sign of the disease is snoring.
Sleep apnea is a disease common to people. Most of the people that have such the condition are often overweight.
Man is usually the ones diagnosed with obstructive sleep apnea compared to women. This disorder can happen anytime and the risk will increase as you age. If any of your family members is diagnosed with obstructive sleep apnea, then it's likely that you have one as well.
People with small nasal airways are at risk of this condition. The small airways are due to the shape of the structure, the allergy or the condition that leads to this type of congestion.
Children could have tonsils with enlarged tissues in their throats. Enlarged tonsils can increase the risk of children having sleep apnea. Overweight children also have a high risk of developing such a condition.
About 50% of the people that have sleep apnea also have high blood pressure. Sleep apnea is also linked to metabolic syndrome, smoking, diabetes and it adds to the risk of a person getting stroke and heart failure.
The list of symptoms is exhaustive. Click here to find our more.
If you suspect that you have sleep apnea or someone you know has one, you need to schedule for an appointment to your dentist.. This helps in addressing your concerns and identify if the symptoms are of sleep apnea. If it is, then you are suffering from the condition. Then, have your dentist prescribe a home sleep study. During the home sleep study, you will administer the study on your own. Once you've submitted the study and the results are produced, your dentist will identify give the best treatment for your needs.
Looking for a Sleep Apnea Dentist?
Our dental office can treat patients with obstructive sleep apnea especially if they are in Costa Mesa, CA. It is highly recommended for you to schedule for an appointment if you have obstructive sleep apnea so our dentists can treat it right away.


text:
Q: NullPointerException when iterating over a two dimensional array of objects I'm running tests for my board class in a game I am making, and continue getting a nullpointerexception when I try to search for an object in my array.
public class Board extends java.util.Observable{

//10x10 array that holds the tokens
private Token board[][];

/**
 * Constructs board
 */
public Board(){
    board = new Token[10][10];
}

/**
 * Adds token to the board at the location that the token is
 * @param token     token to be added
 */
public void addToken(Token token){
    Location loc = token.getLocation();
    board[loc.getX()][loc.getY()] = token;

    //notifies view that it needs to redraw the board
    notifyObservers();
}

/**
 * move token that is already on the board
 */
public void moveToken(Token token){
    //checks if the piece is in the board
    boolean moved = false;

    //finds piece
    for(int i = 0; i < board.length; i++){
        for(int j = 0; j<board[i].length; j++){
            if(board[i][j].equals(token)){  //THIS IS THE LINE THAT CAUSES THE ERROR
                board[i][j] = null;
                moved = true;
            }
        }
    }
    //if piece is not on board, throw error
    if(!moved) throw new GameError("Attempted to move token that is not on the Board");

    //add the token in its new location
    addToken(token);
}

The exception is caused in the moveToken method, which I call in the following test.
    @Test
public void testAddToken(){
    Board b = new Board();
    Token[][] board = b.getBoard();
    Token t = new Token('a', "a....", true);
    t.setLocation(new Location(4,4));
    b.addToken(t);
    board = b.getBoard();
    assertEquals(board[4][4],t);
    t.setLocation(new Location(2,1));
    b.moveToken(t); //THIS IS WHEN THE ERROR IS CAUSED
    assertEquals(board[2][1],t);
}

I added some System.out.print tests to check when exactly the error is caused, and it happens on the very first loop, when both i & j are zero.
Thank you in advance for any help!


Suddenly, but peacefully, at Glenrothes Hospital, on Wednesday 14th January 2015, William (Bill) Thorburn of Kirkcaldy. Dearly beloved husband to Annie (Ann), also a loving dad to Alan and the late William and Brian, also a devoted grandad to Jack and Eve. Service at Kirkcaldy Crematorium on Wednesday 28th January at 10.15am to which all friends are respectfully invited. Family flowers only please but donations in lieu of flowers may be given for Cancer Research, if so desired, at the crematorium.


Dr. Daojiong Zha (查道炯) is a professor of international political economy in the School of International Studies, Peking University. He specializes in studying non-traditional security issues in China's foreign relations, with a particular focus on energy, food, and trans-boundary water issues. His recent research interest has expanded to political risk management for Chinese investments overseas, which took him on field trips to Africa, Australia, and Southeast Asia. He also served on advisory boards of the China Chapter of Council for Security Cooperation in the Asia Pacific, Chinese Association for International Understanding, China-USA Friendship Association, and China-Myanmar Friendship Association.
Additionally, he has authored and edited six academic books, including "Chinese Investment Overseas: case studies on environmental and social risks" (Peking University Press, 2014), in addition to dozens of journal articles. He also served on guest research and teaching positions in Australia, Japan, the United States, Singapore and the Hong Kong Special Administrative region. He holds a Doctoral degree in political science from the University of Hawaii at Manoa.
Zha, Daojiong. Building a Neighborly Community: Post Cold War China, Japan, and Southeast Asia. Manchester: Manchester University Press, 2006.
Zha, Daojiong. The Political Economy of China's Oil Security. Beijing: China Modern World Press, 2005.
Zha, Daojiong. "A Political Ecology of Hydropower Development in China", in Hydropower Development in the Mekong Region Political, Socio-economic and Environmental Perspectives. Eds. Nathanial Matthews and Kim Geheb. London: Routledge, 2015.
Zha, Daojiong. "High Anxiety in Asia Pacific", China Economic Quarterly, September 2014.
Zha, Daojiong; Zhang, Hongzhou. "Food in China's international relations." Pacific Review, 26(5), 2013, pp. 455-479.
Zha, Daojiong; Hu, Weixing. "Promoting Energy Partnership between Beijing and Washington", The Washington Quarterly, Autumn 2007.
Jakobson, Linda; Zha, Daojiong. "China and the Worldwide Search for Oil Security." Asia-Pacific Review, 13(2), 2006, pp. 60-73.
Zha, Daojiong. "The Politics of China-ASEAN Economic Relations: Assessing the Move Towards an FTA." Asian Perspective, 53(4), 2002.


text:
All That Dance Studio set to present Christmas show
djneighbors@thedailyjournal.com
BRIDGETON - All That Dance Studio's dancers and musical theater students will present the annual Christmas show at 2 p.m. Dec. 17 in the Robert L. Sharp Auditorium at Bridgeton High School on West Avenue. The adaption of Hans Christian Anderson's tale, "The Snow Queen," features dance and musical theater students, ages 3 to adult, from Salem and Cumberland counties, who will perform in colorful costumes and dance to original choreography set to new and familiar holiday songs.
In the story, there are four sisters, who control the seasons. The Queen of Winter, performed by Allison Jenkins, decides that her season should be the only season after she breaks the magical mirror and a shard of glass pierces a villager, Kie, performed by Miya Lupton. Quickly the Snow Queen sweeps Kie away to her Ice Castle. Kie's sister, Gerda played by Melanie Lupton, is determined to save her sister from the evil Snow Queen and travels from season to season, meeting the Spring Princess, played by Anna Thompson, Summer Princess, played by Rebecca Wax, and the Fall Princess, played by McKayla Buehler, overcoming obstacles, hoping to rescue her sister from the Snow Queen.
Millville High School honors students
The show includes dancing flowers, gypsies, goblins, ice miners, ice sprites, magic snow dancers, soldiers, and angels and many other characters from the story. The story concludes with a royal reception, featuring many young princesses.
Various genre of dance including ballet, pointe, jazz, modern, Irish, tap, African, and hip hop will be intertwined throughout the story as the dancers present the enchanting story.
Tickets are $12. Advance ticket purchase is recommended. A limited number of tickets will be available at the door.
For tickets or information, call (856) 451-2233 or email allthatdancestudio@comcast.net.


text:
Staying a step ahead: Burnet and Doherty scientists develop highly accurate point-of-care neutralising antibodies (NAb) test for COVID-19
Staying one step ahead of COVID-19 variants is one of the potential benefits of highly accurate, point-of-care (POC) test that can measure the level of neutralising antibodies (NAb) to COVID-19; developed by Burnet Institute and the Peter Doherty Institute for Infection and Immunity (Doherty Institute) scientists.
The test, which provides a readout from a finger prick of blood in less than 20 minutes, is the first of its type globally, and may also be useful to indicate when a vaccine booster may be required.
While there are many POC tests that can measure the overall level of antibody to SARS-CoV-2, and use this to estimate neutralising antibodies, this is the only test to measure neutralising antibody activity, which correlates with immune protection from serious disease in COVID-19.
The emergence of the Omicron variant, which early studies suggest may be up to 40-times less sensitive to patient NAb than Delta, means that some people will go from having enough NAb to be protected, to not having enough.
Being able to measure this will be important:
to prioritise additional booster shots to those who don't have enough immunity against Omicron or future variants including people at risk of severe disease – the elderly and people with co-morbidities, and people at high risk of exposure such as frontline healthcare workers
to check that these people have responded to their vaccine or booster
to provide a standardised test to assist in the safe reopening of borders in the context of different vaccines and the variable responses in different populations.
The test provides a new option for immunity screening to support COVID-19 vaccination and control programs, particularly in time-critical and low- and middle-income settings where laboratory-based testing is difficult or impossible for many to access.
"One of the key elements of the test is that it can work with fingerprick whole blood, which is essential if it is really going to be used at point of care," study joint supervising author, Associate Professor David Anderson, Burnet Institute Deputy Director and Chief Scientific Officer of the Burnet Diagnostics Initiative, said.
"Another is we have demonstrated that we can readily substitute different variants into the test. While we have not yet tested Omicron, this will be simple enough to incorporate in our test in place of the original strain or other variants that we have tested so far."
Co-first author, Burnet Senior Development Scientist, Huy Van said a successful collaboration was fundamental to the development of the test.
"I have worked on a lot of different point-of-care tests over the years, but the COVID-19 NAb Test is probably the one where we had the greatest number of different complications to overcome in making a simple test that works," Mr Van said.
"But it's also been the best collaboration between groups with very different areas of expertise and resources across the Burnet and Doherty Institutes to achieve that in such a short time."
Dr Tom Fulford from the Doherty Institute said: "We envisage that this test may be part of a set of indications that will help to determine who may need a booster vaccine.
"This can also be adapted so that it can provide information about whether an individual has protective antibodies against particular variants of concern.
"This has been a fantastic collaborative effort between a number of labs at the Doherty Institute, at the Royal Melbourne Hospital and our colleagues at the Burnet Institute, bringing together some of the best scientists in Australia to develop a test we hope will help manage our response to COVID-19."
Currently in the prototype phase, the Institutes are currently seeking commercial partners to develop the manufacturing process and take the test to the global market.
Jen Barnes, Director of the Burnet Diagnostics Initiative (BDI), said the collaboration has led to a novel lab prototype in record time, and is an example of the driver behind the formation of the BDI.
"The BDI aims to enhance the translation of new technologies to practical health solutions through significant partnerships with academic collaborators and industry. The NAb test is a great example of this as we look for a global partner to bring the test to market," she said.
This study, published in the journal EBioMedicine, was supported by funding from the Victorian Government.
Burnet Institute, Doherty Institute, and the University of Melbourne, are Foundation Partners in the new Australian Institute for Infectious Disease (AIID) which is supported by funding from the Victorian Government.
For any media enquiries, please contact:
T: +61 (0) 3 8344 8360
M: +61 412 103 306
E: rebecca.elliott@unimelb.edu.au