text:
\section{Introduction}

\noindent Since the first exoplanet atmospheric detection around a $1.35$ R$_\mathrm{J}$ planet \citep{charbonneau2002}, astronomers have been pushing the limits to smaller and smaller planets, such as the detection of water vapour around the $8 \mathrm{M}_\mathrm{E}$ planet K12-18b \citep{8me}. The continued discovery of exoplanet atmospheres, and increasing technological capability, has raised the prospect of finding a planet that may be inhabited by life. Subsequently, it has been determined that the characterization and detection of biosignatures \textemdash atmospheric spectral features that could indicate signs of life on a planet \textemdash should be an area of focus for astrobiology \citep[see, e.g.][]{seager2012,kaltenegger2017,lammer2019}.

To date, over 5000\footnote{https://exoplanetarchive.ipac.caltech.edu/} exoplanets have been discovered using a mix of ground-based and space-based methods. With the successful launch of JWST and future observatories such as the European Extremely Large Telescope (E-ELT) and the Thirty Meter Telescope (TMT), we are moving from the era of exoplanet discovery to exoplanet atmospheric characterization. However, characterizing these worlds remains an enormous challenge. For example,  the most promising O$_2$ feature for JWST appears to be the O$_2\rightarrow X$ collisional induced adsorption band at $6.4$ $\mu$m \citep{fauchez2020}, but even for a target such as TRAPPIST 1-e \citep{gillon2016temperate,gillon2017seven} this would require more than 700 transits, longer than the anticipated lifetime of JWST given that TRAPPIST 1-e has a 6 day orbital period and is only visible to JWST for less than a third of the year \citep{gillon2020}. Even the more favourable strong O$_3$ band at 10$\mu$m would require more than 100 transit observations on a planet such as TRAPPIST 1-e \citep{lin2021} to detect it at just 3$\sigma$.

Fortunately, O$_2$ and O$_3$ are not the only biosignatures. More generally, atmospheric chemical disequilibrium, characterised by the coexistence of two or more long-term incompatible gases \citep{lovelock1965,sagan1993,cockell2009}, can be considered a sign of ongoing life. The Archean Earth had a biogenic disequilibrium caused by the coexistence of N$_2$, CH$_4$, CO$_2$, and liquid water, which could be possible to remotely detect on an Earth-sized planet \citep{disequilibrium}. Simultaneous detection of abundant CH$_4$ and CO$_\mathrm{2}$ is therefore considered a biosignature. Happily, detecting this CH$_4$-CO$_2$ pair is feasible, requiring $\sim5-30$ co-added JWST transits depending on if the stratosphere is dry or has a cloud or haze layer \citep{mikal2022}.

Observing resources are valuable and finite, so choosing the best targets to search for biosignatures of any kind is imperative. The main criterium is whether the planet can sustain liquid water on its surface by residing an appropriate semi-major axis from its host star, referred to as the habitable zone \citep{oghz,kasting1993}. However, liquid water alone is not enough for life.  Life requires energy to remain out of equilibrium with its environment. For almost all the biomass on Earth, this energy source is oxygenic photosynthesis \citep{bar-on2018}.
We therefore suggest that a new criterium be used to determine where biosignatures may be found. In this work, we demonstrate that, like the habitable zone, the \textit{photosynthetic habitable zone} is a bounded strip on a plot of stellar mass against semi-major axis. It occurs where both liquid water and photosynthesis is simultaneously possible. It is where the search for life in the Universe should be concentrated under the assumption of biosignatures similar to those generated by past or present Earth.

We detail our calculations of the habitable zone in Section \ref{subsec:hz}, our calculations of photosynthesis rate curves in Section \ref{subsec:ratecurves}, and the photosynthetic habitable zone in Section \ref{subsec:bz}. We present our results in Section \ref{sec:results} and discuss assumptions and limitations in Section \ref{sec:discussion}. We summarise and present our conclusion in Section \ref{sec:conclusion}.

\section{Methods}
\label{sec:methods}

\subsection{The Habitable Zone}
\label{subsec:hz}
\noindent We used pre-main sequence (PMS) evolutionary models \citep{baraffe2015}\footnote{\url{http://perso.ens-lyon.fr/isabelle.baraffe/BHAC15dir/BHAC15_iso.2mass}} to obtain stellar effective temperature, \teff,  as a function of stellar mass, $M_*$. We assumed an age of 1 Gyr, corresponding to the approximate time primitive life first appeared on Earth \citep[e.g.][]{2017Natur.543...60D,Cavalazzi2021}. The habitable zone (HZ) for each stellar mass was calculated using the method described in \citet{kopparapu2013}. We use their derived relationships between HZ  effective temperature,  $T_\mathrm{eff}$ and stellar fluxes, \seff,  in the range 2600 K $\leqslant T_{\text{eff}} \leqslant 7200  $K:
\begin{equation}
\label{eq:seff}
S_{\text {eff }}=S_{\text {eff } \odot}+a T_{\star}+b T_{\star}^{2}+c T_{\star}^{3}+d T_{\star}^{4},
\end{equation}
where $T_{\star}=T_{\text{eff}}-5780$ K,  and
\begin{equation}
S_{\text {eff } \odot} = \frac{L_\odot}{4\pi R_\odot^2 \sigma T_\odot^4},
\end{equation}
where $L$ is stellar luminosity and $R$ is stellar radius. The coefficients $a,b,c$ and $d$ are determined by scenario, for example runaway greenhouse (Inner HZ) and maximum greenhouse (outer HZ). We used updated coefficient values published online \footnote{{\url{http://depts.washington.edu/naivpl/sites/default/files/hz_0.shtml\#overlay-context=content/hz-calculator}} } as per \citet{erratum}, and detail them in Table \ref{tab:coeff}. The corresponding HZ distance for a given star is then
\begin{equation}
d=\left(\frac{L / L_{\odot}}{S_{\mathrm{eff}}}\right)^{0.5} \mathrm{AU},
\end{equation}
where $L / L_{\odot} $ is the luminosity of the star compared to the Sun.

\begin{table
    \centering
    \begin{tabular}{ccc}
    \hline
    \hline
        Constant & Inner HZ & Outer HZ \\
                        &(Runaway Greenhouse) & (Max. Grenhouse ) \\ \hline

        $S_{\text {eff } \odot}$ & 1.107 & 0.356 \\
        $a$ & $1.332 \times 10^{-4}$ & $6.171\times 10^{-5}$ \\
        $b$ & $1.580\times 10^{-8}$ & $1.698\times 10^{-9}$ \\
        $c$ & $-8.308\times 10^{-12}$ & $-3.198\times 10^{-12}$ \\
        $d$ & $-1.931\times 10^{-15}$ & $-5.575\times 10^{-16}$ \\
\hline
    \end{tabular}
    \caption{Coefficients used in Eq. \ref{eq:seff} to calculate habitable stellar fluxes, and corresponding habitable zones.\label{tab:coeff}}
\end{table}

\subsection{The Photosynthesis zone}
\label{subsec:ratecurves}
\noindent Photosynthesis is the chemical reaction by which organisms use energy from sunlight to synthesis sugar from carbon dioxiode and water:
\begin{equation}
6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \xrightarrow{h\nu}   \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}.
\end{equation}
Three variables directly impact the rate of photosynthesis \citep[][]{gaastra1959photosynthesis}: light intensity ($I$), temperature ($T$), and carbon dioxide (CO$_2$). Water availability indirectly impacts the rate of photosynthesis, as water stress causes plant structures to wilt reducing CO$_2$  availability \citep{muller2011water}. In this work, we make two assumptions: 1) that the photosynthetic life we consider is ocean based, and so has an unlimited reservoir of water and 2) the global average of CO$_2$ concentration is sufficiently high that photosynthesis is not rate-limited by CO$_2$ concentration.

The chlorophyll $a$-normalised net photosynthetic rate, $P$, as a function of irradiance intensity, $I$, is given by \citep{model3}:

\begin{equation}
\label{eq:prate}
P(I)=\frac{I}{\alpha I^{2}+\beta I+\gamma}-R_{\mathrm{rate}},
\end{equation}
where $\alpha$ and $\beta$ are dimensionless parameters,  $\gamma$ is defined as the reciprocal of the light-limited initial slope of the \textit{P-I}  curve, and $R_{\mathrm{rate}}\,\, $ is the dark respiration rate, the minimum rate at which glucose is combined enzymatically with oxygen to release energy and CO$_2$. Net photosynthetic rate is the total output of molecular oxygen per unit biomass per unit time [$\mu\mathrm{mol\,\, O}_2 \,\, \mathrm{mg}^{-1} \,\, \mathrm{h}^{-1}\,\, $]. The maximum photosynthetic rate is given by
\begin{equation}
\label{eq:pmax}
P_{\mathrm{rate}}^{\text{max}}=\frac{1}{\beta+2 \sqrt{\alpha \gamma}}-R_{\mathrm{rate}}.
\end{equation}
The parameters $\alpha,\beta$ and $\gamma$ in Equations \ref{eq:prate} and \ref{eq:pmax}  are determined by performing best-fit analysis to empirically determined photosynthesis rate curves of phytoplankton in the laboratory setting, the values used in this work are $\alpha=1.0\times 10^{-5}$, $\beta=1.0\times 10^{-3}$, and $\gamma=2.0$  \citep{yang2020}. Three values of the dark respiration rate are explored,  which determine the quality of conditions for life. As conditions for life become less favourable, $R_{\mathrm{rate}}\,\, $ becomes a greater fraction of $P^{\mathrm{max}}_\mathrm{rate}$ \citep{geider1989}. We consider excellent conditions to be Earth-like ($R_{\mathrm{rate}}\,\, $ = 0.3 $P_{\mathrm{rate}}^{\mathrm{max}}\,\,$), and optimistic and pessimistic conditions to be $R_{\mathrm{rate}}\,\, $ = 0.6 $P_{\mathrm{rate}}^{\mathrm{max}}\,\,$ and $R_{\mathrm{rate}}\,\, $ = 0.8 $P_{\mathrm{rate}}^{\mathrm{max}}\,\,$ respectively.

The \textit{P-I}  curve from Equation \ref{eq:prate} is shown in Figure \ref{fig:photorate}. The green dotted line in Figure \ref{fig:photorate} shows the line where the net photosynthesis rate, $P(I)$ is equal to $R_\mathrm{rate}$. Any irradiance intensity that causes a total net negative photosynthesis rate will result in no net oxygen being produced. Therefore, for photosynthesis to increase atmospheric content of O$_2$, $P >0$ is the absolute lowest limit required.

\begin{figure}[h]
    \centering
    \includegraphics[width=\linewidth]{Figures/photorate.pdf}
    \caption{ \textbf{Net photosynthetic rate versus irradiance intensity.} Dotted green line indicates where rate of photosynthetic production of O$_2$ is equal to consumption of O$_2$ during respiration, such that net photosynthetic production of O$_2$ is zero. Rate of respiration is $R_{\mathrm{rate}}\,\, $ = 20 $\mu\mathrm{mol\,\, O}_2 \,\, \mathrm{mg}^{-1} \,\, \mathrm{h}^{-1}$. Orange vertical line is intensity of PAR at Earth.}
    \label{fig:photorate}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[width=\linewidth]{Figures/temperature.pdf}
    \caption{ \label{fig:p-t} \textbf{Net photosynthetic rate versus greenhouse temperature.}  Equilibrium temperatures were calculated at the inner and outer edges of the Habitable Zone, and location of Earth. Maximum $P(T)$ occurs at higher greenhouse temperatures at larger planetary separations from host star. A fixed $P(I)=80$ $\mu\mathrm{mol\,\, O}_2 \,\, \mathrm{mg}^{-1} \,\, \mathrm{h}^{-1}\,\, $ was assumed.}
\end{figure}

Next, we express $P\,\,$ as a function of both intensity and temperature by including a temperature moderation factor \citep{yan1999,vanderheide2006, kim2007temperature,adams2017,prate-temp}:

\begin{equation}
f_\mathrm{temp} = \left(\frac{T_{\max }-T}{T_{\max }-T_{\mathrm{opt}}}\right)\left(\frac{T}{T_{\mathrm{opt}}}\right)^{T_{\mathrm{opt}} /\left(T_{\max }-T_{\mathrm{opt}}\right)}
\end{equation}
such that
\begin{equation}
\label{eq:p-t}
P(I,T)= f_\mathrm{temp} \cdot P(I).
\end{equation}
The temperature, $T$, is the sum of the planetary equilibrium temperature and the planetary greenhouse effect  $T=T_\mathrm{equilibrium} + \Delta T_\mathrm{greenhouse}$. Planetary equilibrium temperature, $T_\mathrm{equilibrium} $ is given by
\begin{equation}
T_\mathrm{equilibrium} =\left(\frac{L_*\left(1-A_{\mathrm{Bond}}\right)}{16 \sigma \pi a^{2}}\right)^{1 / 4}
\end{equation}
where $L_*$ is stellar luminosity, $A_{\mathrm{Bond}}$ is the Bond albedo and $a$ is planet semi-major axis. $T_\mathrm{max}$ is the maximum temperature at which photosynthesis occurs and $T_\mathrm{opt}$ is the optimum temperature at which photosynthesis occurs.
Cyanobacteria, Earth's first photosynthesisers, have higher $T_\mathrm{opt} $ than many photosynthesizers, typically $T_\mathrm{opt} = 35\degree$C \citep{gorham1964toxic,zhang2015,Giannuzzi18}.The upper limit for photosynthetic processes is uncertain, especially since thermophillic life is a possibility.  However, it is generally agreed that the upper limit for photosynthesizing cyanobacteria is $73\degree$C \citep{ward2012ecology}. We therefore set $T_\mathrm{opt} = 35\degree$C and  $T_\mathrm{max} = 73\degree$C in this work. We assume $A_\mathrm{Bond} = 0.306$, equal to Earth's Bond albedo.

The resulting $P-T$ curve from Equation \ref{eq:p-t} is shown in Fig. \ref{fig:p-t}. We term the region of parameter space where $P(I,T)>0$ (Equation \ref{eq:p-t}) the ``photosynthesis zone''  (PZ) for convenience, and it is shown in pink in Figure. \ref{fig:bz}. Photosynthesis cannot proceed where $P\leq 0$, since the organism's respiration rate is exceeding that of its primary production.

\subsection{The Photosynthetic Habitable Zone}
\label{subsec:bz}

We suggest the existence of a \textit{photosynthetic habitable zone} (PHZ), a region of parameter space where the habitable zone overlaps the photosynthesis zone. It is in the photosynthetic habitable zone, rather than the habitable zone, that humanity should concentrate its search for spectral signs of life, since they can only be present where both liquid water and $P(I,T)>0$ occur. To obtain the region where $P(I,T)>0$, we calculate the irradiance intensity as a function of stellar mass and planet semi-major axis. We begin with the Planck function:
\begin{equation}
B(\lambda, T)=\frac{2 h c^{2}}{\lambda^{5}}   \bigg[e^{\frac{h c}{\lambda k_{\mathrm{B}} T}}-1\bigg]^{-1},
\end{equation}
and obtain the intensity of photosynthetically active radiation, $I_\mathrm{PAR}$, by integrating between $\lambda_\mathrm{min}=$400 nm and $\lambda_\mathrm{max}=$700 nm
\begin{equation}
\label{eq:I}
I_\mathrm{PAR}= \int_{\lambda_\mathrm{min}}^{\lambda_\mathrm{max}} \frac{2 h c^{2} / \lambda^{5}}{e^{h c / \lambda k_\mathrm{B} T}-1} d \lambda .
\end{equation}
The number of photons emitted by the star per unit time, $\dot{N}_{\star}$, in this wavelength range is then obtained by multiplying Equation \ref{eq:I} by the surface area of the star, and dividing by the energy of each photon, so that we obtain
\begin{equation}
\dot{N}_{\star}=4 \pi R_{\star}^{2} \int_{\lambda_{\min }}^{\lambda_{\max }} \frac{2 c}{\lambda^{4}}\left[\exp \left(\frac{h c}{\lambda k_{B} T_{\star}}\right)-1\right]^{-1} d \lambda.
\end{equation}
Assuming a circular orbit, the photon flux at the top of a planetary atmosphere, $\Phi$, at a distance $a$ from the star is
\begin{equation}
\label{eq:phi}
\Phi = \frac{\dot{N}_{\star}}{4 \pi a^{2}}.
\end{equation}
We account for atmospheric attenuation such that the light intensity at the bottom of the atmosphere is
\begin{equation}
\label{eq:phi_attenuate}
I = f_\mathrm{a} \cdot \frac{\dot{N}_{\star}}{4 \pi a^{2}}
\end{equation}
where $f_\mathrm{a} \leq 1.0$ is the fractional attenuation due to atmospheric effects. We consider three attenuation efficiencies: no attenuation, $f_\mathrm{a} = 1.0$, moderate attenuation $f_\mathrm{a} = 0.6$, and Earth-like attenuation, $f_\mathrm{a} = 0.2$ \citep{oceandynamics,lingamloeb2021}. The intensity in Equation \ref{eq:phi_attenuate} is used in Equation \ref{eq:p-t} to obtain $P(I,T)$ that would be achieved by a phytoplankton-like species as a function of stellar mass and planet semi-major axis.

\section{Results}
\label{sec:results}

\begin{figure*}
    \centering
    \includegraphics[width=\textwidth]{Figures/bzV5.pdf}
    \caption{  \label{fig:bz}     The Photosynthetic Habitable Zone.  Region where positive net photosynthesis is possible shown in pink, and habitable zone shown in blue. The overlapping region is where photosynthesis can actually occur, and is named ``The photosynthetic habitable zone', since it is possible that oxygenic photosynthesis, and therefore biosignatures, could exist on planets in this location. Overplotted in yellow markers are planets of interest, i.e. planets in the habitable zone expected to have a solid surface ($R \lesssim 1.8$ R$_\mathrm{E}$). Blue markers indicate water world candidates. Earth is shown by white Earth symbol. The tidal lock radius with upper and lower limits is also shown.      }
\end{figure*}

We find the existence of the photosynthetic habitable zone (PHZ), shown in green in Figure \ref{fig:bz}), where photosynthesizing life could exist and therefore leave behind atmospheric biosignatures. It occurs where the $P(I,T)>0$ region (pink in Figure \ref{fig:bz}) overlaps with the region where liquid water can exist (the Habitable Zone, blue in Figure \ref{fig:bz}).

Figure \ref{fig:bz} shows nine scenarios. On the $y$ axis of the whole plot, atmospheric effects (attenuation and greenhouse) are increasing. On the $x$-axis of the whole plot, the quality of the conditions for life are increasing (i.e., the maximum photosynthetic rate is much higher than the baseline respiration rate). The ``Excellent'' column corresponds to conditions for photosynthesizing lifeforms on Earth with respiration rates at 30\% of maximum photosynthesis rates, typical for marine phytoplankton such as \textit{Isochrysis galbana},  \textit{Platymonas subcordiformis}, etc \citep{IPPOLITI201671,yang2020}.

 As the quality of conditions for life increases, the rate of respiration as a fraction of the  maximum photosynthetic rate attainable decreases, resulting in a larger PZ.  As atmospheric effects (attenuation and $\Delta T_\mathrm{greenhouse}$) increase to Earth-like levels, interestingly, this decreases the size of the PZ, reducing the parameter space over which biosignatures could be found. This suggests that it may be easier for large-scale photosynthesizing organisms, such as cyanobacterial mats, to occur on planets with more tenuous atmospheres. Overplotted as yellow symbols are planets that spend at least 10\% of their orbit in the HZ and have radii $R_\mathrm{p}< 1.8$ R$_\mathrm{E}$, so could have a solid surface, since planets with $R_\mathrm{p}\gtrsim 1.8$ R$_\mathrm{E}$ are gas-dominated \citep{rocky1,rocky2}.

 Additionally, we also plot 3 recently identified water world candidates, Kepler-138 c and d \citep{piaulet2022} and TOI-1452 b \citep{cadieux2022}. While these fall outside the HZ, Kepler-138 d and TOI-1452 b fall inside the PZ. Although liquid water has not been directly detected on these planets, measurements imply that these planets may be similar to the water-rich icy moons of the solar system, such as Europa or Enceladus. These criteria reduce the $\sim$5000 known exoplanets down to 29 planets of interest.

 Overplotted on Figure \ref{fig:bz} is the tidal lock radius \citep{peale1977,kasting1993}:
\begin{equation}
r_{\mathrm{lock}}=0.027\left(\frac{P_{0} t}{Q}\right)^{1 / 6} M_*^{1 / 3},
\end{equation}
where $P_0$ is the original rotation period of the planet, $t$ is the age of the system (1 Gyr), $M_*$ is the stellar mass and $Q^{-1}$ is the solid body plus ocean specific dissipation function. We use $Q=100$, for the solid line, and $Q=10$ and $Q=1000$ for the upper and lower limits of the tidal lock radius. We assume $P_0=13.5$ hours, i.e. the day length of Earth when it was 1 Gyr old.

There are several planets that are in or near the PHZ largely regardless of the quality of conditions for life or atmospheric effects, Kepler-452 b, Kepler-1638 b, Kepler-1544 b and Kepler-62 e and f. These planets should therefore be the most promising for detecting biosignatures.  It is also possible that some of these planets with $R\gtrsim 1.5$ R$_\mathrm{E}$ are water worlds \citep{luque2022} .The least promising candidates are those around the lowest mass host stars, $M_* \lesssim 0.4$  M$_\odot$ and below, since their position in Figure \ref{fig:bz} coincides with the PHZ for less than half of our considered scenarios.

As a final result, we posit that meaningful discussions of the habitable zone should account for where photosynthesis is also possible, since almost all life on Earth depends on photosynthesis either directly or indirectly. We therefore suggest replacing the use of the phrase ``Habitable Zone'' with ``Photosynthetic Habitable Zone'', when searching for biosignatures.

\section{Discussion}
\label{sec:discussion}

\noindent Conventional photosynthesis, as experienced on Earth, takes place during the day via photosynthetically active radiation (PAR) received directly from the Sun. We do not consider here any other scenario, such as starlight PAR, moonlight PAR, planetlight PAR, or speculative biological adaptations. We work under the limiting assumption that life would exist approximately ``as we know it''. While other scenarios are possible in principle, they require increasingly complex caveats, such as an older universe or photosynthesis only occurring at full moon \citep[see, e.g.][]{ravencockell2006}.  Furthermore, we focus our consideration on atmospheric biosignatures, rather than biological surface features, since we expect atmospheric signatures to be detectable even when the disk-averaged spectrum features, such as the vegetation red edge \citep{seager2005}, are not \citep{cockell2009}.

Our analysis here intends to show a general trend rather than demarcate absolute boundaries, since the fit parameters ($\alpha,\beta$ and $\gamma$) in the $P-I$ relation can take a variety of values as long as the curve retains the same functional form (an initial slope, a peak, and steady decline due to photoinhibition of photosynthesis at high intensity \citep[see, e.g.,][]{platt1976,platt1981,model3,ye2013}. Similarly, $P-T$ curves may be described in multiple ways as long as the same functional form, shared between species, is obeyed.  In light of this, our results should be considered a useful framework rather than hard boundaries. We have also made the assumption that photon attenuation is proportional to $\Delta T_\mathrm{greenhouse}$, motivated by them both being correlated with more dense atmospheres but neglecting any difference in atmospheric composition. Furthermore, atmospheric attenuation is a function of column density, which is a function of both planet mass and planet size. While a super Earth may have a more massive atmosphere than the Earth, a super Earth also has a larger surface area which results in atmospheric mass scaling more slowly than the increase in planet mass \citep{elkins-tanton2008}. Additionally, super Earth outgassing rates may be lower than the Earth's \citep{2012ApJ...748...41S}, so a more rigorous consideration of atmospheric attenuation must determine the role that planet mass plays.

It is unclear what effect tidal locking would have on the development of photosynthesizing life on another planet,  since much of life on earth depends on 24-hour circadian cycles to regulate physiological function \citep{dvornyk}. An absence of periodicity on tidally locked planets would likely have considerable consequences on the evolution of biological regulation in those systems.  The night side of the planet could not support photosynthesis since it does not receive PAR. This immediately discounts half of the surface area of the planet. On the other hand, always receiving PAR could potentially increase the rate of net O$_2$ production, since intensity does not wax and wane during the course of the day. In either case, it seems clear that there is a link between Earth's rotation rate and oxygenation, with longer days associated with higher oxygenation rates \citep{klatt2021}. Interestingly, our analysis indicates that the PHZ predominantly exists outside the tidal locking radius for all cases,  suggesting that the search for life elsewhere in the Universe should be focused around non-tidally locked planets.

Photosynthesis takes place on Earth in a variety of temperatures. In plants, it is generally constrained to lower temperature ranges ($10\degree$C - $40\degree$C) before suffering irreversible damage \citep{berry1980photosynthetic}, while in cyanobacteria the preferred range is somewhat higher, with the upper limit for non-thermophiles $\sim 73\degree$C \citep{ward2012ecology}.  A few points are worth noting - first, at low temperatures, photosynthesis is both enzyme-limited and phosphate limited due to a reduction in the availability of phosphate in chloroplasts, while at higher temperatures proteins become denatured. High or low temperatures could also affect the stability and fluidity of the cellular membranes in which photosynthesis machinery components localize, resulting in more or less efficient biochemical reactions at the membrane interface.

At moderate temperatures ($\sim$10-35$\degree$C), photosynthesis is mostly limited by the rate of CO$_2$ diffusion. This is another limitation of our work \textemdash cyanobacteria exist in mat-like colonies that have a $z$-depth, and we have assumed instead that any colony is essentially infinitesimally thin and we therefore do not need to consider diffusion equations. Another limitation of not considering the $z$-depth is that attenuation of photon flux by water occurs \citep{2021MNRAS.503.3434L}, affecting light availability to organisms found at different water column depths. Chloroplast-based photosynthesis in terrestrial plants largely depends on chlorophyll a for optimal absorbance of violet and orange light, while cyanobacteria possess additional light-harvesting phytochromes which allow light capture at wavelengths outside of optimal chlorophyll a absorbance \citep{kehoe2010}. If these phytoplankton exist solely underwater, the PHZ could therefore move closer to the central star, which may increase or decrease the size of the PHZ. Advanced modelling of microbial benthic ecology would be best suited to this problem, and we leave this to future work.

We have also assumed that any extant life in the Universe shares a biochemistry similar enough to photosynthesizing lifeforms on Earth that we would recognise its signatures. Even on Earth, so-called ``exotic photosynthesis'' exists, such as infrared photosynthesis in anoxygenic photosynthetic organisms \citep{heath1999}. This anoxygenic photosynthesis uses hydrogen sulfide instead of water as the reductant, and produces sulphur instead of oxygen as a byproduct, e.g:
\begin{equation}
6 \mathrm{CO}_{2}+12 \mathrm{H}_{2} \mathrm{S}  \xrightarrow{h\nu}     \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+12 \mathrm{~S}+6 \mathrm{H}_{2} \mathrm{O}.
\end{equation}

The pigments used to carry out anaerobic photosynthesis are similar to chlorophyll, but have peak absorption in the near-IR due to molecular differences. While significant atmospheric sulphuric acid in this scenario could be considered a biosignature,  there is a large risk of false-positive results due to its occurrence in many non-biological processes \citep{domagal-goldman}, which is why it is not targeted as a biosignature. In addition to this, anoxygenic photosynthesis is likely an evolutionary precursor to oxygenic photosynthesis, with biogeochemical changes on a terrestrial planet forcing a switch to an oxygen producing version \citep{raven2007,raven2009functional,raven2009contributions}.

One thing that we do not consider here is the effect of planet mass on atmospheric composition and density. For example, a super-Earth that is outside the HZ, that retains its primordial H-He dominated atmosphere could have surface temperatures that are warm enough to host liquid water \citep{mollous2022}. The same could therefore also be true of regions that we have determined too cold for net positive photosynthesis. On the other hand, we also determine in this work having less atmospheric attenuation results in a broader PHZ, which counteracts the positive effect of the retained H-He atmosphere. Another limitation of our work is regarding the interplay between Bond Albedo and stellar type \citep{kopparapu2013} and planet variables, such as surface temperature, atmospheric composition, and planetary surface type \citep[see, e.g., ][]{joshi2012,shields2013,vonparis2013,rushby2019}. This is a complex problem since the Bond Albedo is a function of many variables, requiring 1D energy-balance climate models, 3D global circulation models, atmospheric chemistry and composition models and knowledge of land/ocean distribution to calculate the net planetary albedo. This interplay, along with atmospheric composition and density, is investigated in a future work (Hall et al. in prep.)

A further interesting avenue of exploration is regarding the impact of CO$_2$ on planetary temperature through the greenhouse effect, along with the impact on photosynthetic rates. An inherent assumption of our work is that photosynthesis is not limited by reduced CO$_2$ availability, because the fluctuations on Earth are small. The global average concentration of CO$_2$ today is 400 ppm, and was significantly higher when life first emerged due to Earth's secondary atmosphere.  Space-based observatories show the CO$_2$ concentration varies only at $\sim$few ppm levels \citep{2016GeoRL..4311400H,2019RemS...11..850H}, whereas rate limitation requires a decrease of $\sim$tens of ppm below this 400ppm level \citep[e.g.][]{moss1962,gabrielsen1948}. However, the flip side of this is that we have not explored what this means for atmospheres rich in CO$_2$, which would be likely to increase the expected surface temperature as a function of instellation. A self-consistent CO$_2$-instellation habitable zone should be calculated for this.

 Finally, it could be possible that most habitable worlds in the Universe simply have no detectable signs of life \citep{cockell2014},  either because they are uninhabited, are too young to have evolved life yet ($<1$ Gyr based on the Earth's fossil record), have biotic chemistry at concentrations too low to detect, or the biotic atmospheric chemistry is indistinguishable from the abiotic.

\subsection{Planet rotation periods}
Cyanobacteria appeared in the fossil record $\sim$3.5 Gyr ago,  just $\sim$1 Gyr after the Earth's formation. The concentration of O$_2$ remained at primordial values of $\lesssim$10$^{-3}$ of present atmospheric levels (PALs) until $\sim$2.1 Gyr, when a dramatic increase in atmospheric O$_2$ occurred \textemdash the so-called Great Oxidation Event (GOE). Earth's rotation period is currently 24 hours having been slowed by tidal interaction with the moon, but is likely to have been as low as 6 hours 4 Gyr ago \citep{lambeck1980earths,cuk2012making,bartlett2016analysis}. Earth's rotation period may therefore have increased by more than a factor of two since the evolution of photosynthesis.

Recently, it has been postulated that the GOE occurred when Earth's daylength increased to $\sim$16 hours \citep{klatt2021}. To test this hypothesis, \citet{klatt2021} performed numerical simulations of movement of O$_2$ in cyanobacterial mats for daylengths between 12 and 52 hours,  using simulated diel light cycle illumination. They found that longer days resulted in higher net O$_2$ flux through the cyanobacteria mat, and verified these results by taking measurements from real cyanobacterial colonies in controlled conditions. This lead them to conclude that  increases in daylength could plausibly have influenced Earth's oxygenation, particularly around key oxidation events, and thus helped to pave the way for the evolution of plants and animals as we know them.

At 1 Gyr, Earth's daylength was $\sim$ 13 hours with  gravitational modelling \citep{moon} predicting a spin-down to 16 hour days by $\sim$1.9 Gyr (late Archean). Within the next 0.3 Gyr the atmospheric O$_2$ concentration increased to $\sim$0.1 PAL.  Assuming Earth-like  biology, the work of \citet{klatt2021} suggests that a planetary period of $\gtrsim$16 hours could be an important factor in producing an oxygen-rich atmosphere to support life as we know it.

\begin{table*}[!ht]
    \centering
    \begin{tabular}{lllllllll}
    \hline

        Planet & a [au] &  M$_*$ [M$_\odot$] & M [M$_{\mathrm{E}}$] & M$_\mathrm{est.}$ [M$_{\mathrm{E}}$]  &   R [R$_{\mathrm{E}}$] & P[days] & day [hrs] & day [hrs]\\

           & &  &  &  ($R = M^{0.27}$) &    & & Calculated& Estimated\\
           \hline
           \hline

        GJ-1061 d & 0.054 & 0.125 & 1.64 & 1.73 & 1.16 & 13.00 & TL & TL \\
        GJ-667 Cc & 0.125 & 0.330 & 3.81 & 4.95 & 1.54 & 28.10 & TL & TL \\
        K2-72e & 0.106 & 0.270 & 2.21 & 2.57 & 1.29 & 24.20 & TL & TL \\
        Kepler-1229 b & 0.290 & 0.430 & - & 3.48 & 1.40 & 86.80 & - & 11.39 \\
        Kepler-138 c & 0.091 & 0.535 & 2.3 & 4.60 & 1.51 & 13.78 & TL & TL \\
        Kepler-138 d & 0.129 & 0.525 & 2.1 & 2.03 & 1.21 & 23.09 & TL & TL \\
        Kepler-1544 b & 0.542 & 0.810 & - & 8.46 & 1.78 & 168.80 & - & 9.28 \\
        Kepler-1638 b & 0.745 & 0.970 & - & 10.16 & 1.87 & 259.30 & - & 8.90 \\
        Kepler-1649 c & 0.083 & 0.198 & - & 1.24 & 1.06 & 19.50 & - & 14.43 \\
        Kepler-1652 b & 0.165 & 0.404 & - & 5.70 & 1.60 & 38.10 & - & 10.16 \\
        Kepler-186 f & 0.432 & 0.544 & - & 1.79 & 1.17 & 129.90 & - & 13.27 \\
        Kepler-283 c & 0.341 & 0.664 & - & 9.19 & 1.82 & 92.70 & - & 9.11 \\
        Kepler-296 f & 0.255 & 0.498 & - & 8.82 & 1.80 & 63.30 & - & 9.19 \\
        Kepler-442 b & 0.409 & 0.610 & - & 3.04 & 1.35 & 112.30 & - & 11.75 \\
        Kepler-452 b & 1.048 & 1.037 & 5 & 6.11 & 1.63 & 384.80 & 11.057 & 10.00 \\
        Kepler-62 e & 0.427 & 0.690 & - & 5.83 & 1.61 & 122.40 & - & 10.11 \\
        Kepler-62 f & 0.718 & 0.690 & - & 3.57 & 1.41 & 267.30 & - & 11.32 \\
        LHS-1140 b & 0.096 & 0.179 & 6.38 & 6.25 & 1.64 & 24.70 & TL & TL \\
        LP 890-9 c & 0.040 & 0.118 & - & 3.21 & 1.37 & 8.46 & - & 11.60 \\
        Luyten b & 0.091 & 0.260 & 2.89 & 8.82 & 1.80 & 18.65 & TL & TL \\
        Proxima Centauri b & 0.049 & 0.122 & 1.27 & 2.64 & 1.30 & 11.19 & TL & TL \\
        Teegarden's b & 0.026 & 0.093 & 1.05 & 1.08 & 1.02 & 4.91 & TL & TL \\
        Teegarden's c & 0.044 & 0.093 & 1.11 & 1.16 & 1.04 & 11.40 & TL & TL \\
        TOI-1452 b & 0.061 & 0.249 & 4.82 & 6.71 & 1.67 & 11.06 & TL & TL \\
        TOI-700 d & 0.163 & 0.416 & 1.72 & 1.62 & 1.14 & 37.40 & TL & TL \\
        TRAPPIST-1 d & 0.022 & 0.090 & 0.39 & 0.40 & 0.78 & 4.05 & TL & TL \\
        TRAPPIST-1 e & 0.029 & 0.090 & 0.69 & 0.73 & 0.92 & 6.10 & TL & TL \\
        TRAPPIST-1 f & 0.038 & 0.090 & 1.04 & 1.16 & 1.04 & 9.21 & TL & TL \\
        TRAPPIST-1 g & 0.047 & 0.090 & 1.32 & 1.57 & 1.13 & 12.40 & TL & TL \\
        \hline
    \end{tabular}
         \caption{\label{tab:planets}Properties of candidate exoplanets in the photosynthetic habitable zone assuming excellent conditions. Daylengths are estimated using the empirical relation of Equation~\ref{eq:period}, which is not valid if the planet is tidally-locked (TL). If the mass is not known, it is estimated using Eq. \ref{eq:mass-radius}. Values from the NASA exoplanet archive.}
\end{table*}

Unfortunately, the rotation period, or daylength, is measured only for a handful of exoplanets (2M1207 b, PSO J318.5, GQ Lup b and $\beta$ Pic b), all of which are massive, fast rotators \citep[for a summary see][]{scholz2018}. An empirical spin-mass relationship, where equatorial velocity is given  by $v_\mathrm{eq}\propto\sqrt{M}$, is known to fit the solar system planets. However, both Mercury and Venus do not fit this trend due to tidal interactions with the Sun, and the Earth's tidal interactions with the moon also result in deviation from this relationship.
The solar system trend is:

\begin{equation}
v_\mathrm{eq} = A ({M}/{\mathrm{M_J}})^{\frac{1}{2}},
\end{equation}
with $v_\mathrm{eq}$ in units of km s$^{-1}$ and $A=13.1$. The rotation period of the planet in seconds is then
\begin{equation}
T = \frac{2 \pi R}{A} \bigg( \frac{M}{\mathrm{M_J}}\bigg)^\frac{1}{2}
\end{equation}
where $R$ is the planet radius. If the exoplanet radius is known (or estimated), then the period of the planet in 24-hour days is

\begin{equation}
\label{eq:period}
T = 0.632\left(\frac{M_{\mathrm{E}}}{M}\right)^{\frac{1}{2}}\left(\frac{R}{R_{\mathrm{E}}}\right),
\end{equation}
and can therefore be predicted directly.
\begin{figure}
    \centering
    \includegraphics[width=\linewidth]{day_vs_mass.pdf}
    \caption{  \label{fig:period}     Mass-period relationship. Day lengths of planets either measured directly (blue points) or estimated through empirically determined relationship in Eq. \ref{eq:period} (green and yellow points). Yellow points indicate that mass was also estimated using Eq. \ref{eq:mass-radius}. Grey solid lines are plots of Equation \ref{eq:period-radiusunknown} for a plausible range of planet densities. Horizontal dashed lines mark the range of Earth's daylength predicted for the GOE \citep{klatt2021}.}

\end{figure}

However, for small radii planets (as we consider here), they generally do not also have associated mass measurements, but estimates can be made using a mass-radius relationship. We take the mass and radius values for low mass planets with an Earth-like composition from Table 1 of \citet{fortney2007},  which gives us a best-fit mass-radius relation of
\begin{equation}
\label{eq:mass-radius}
R_\mathrm{p} = M_\mathrm{p}^{0.27}
\end{equation}
with a high coefficient of determination $R^2 = 0.98$. We use this to estimate planet mass, given in the fifth column of Table \ref{tab:planets}. For Kepler-452 b, we calculate the rotation rate using the observed mass and retrieve 11 hours. For all other planets in our sample, we use the mass estimate from Eq. \ref{eq:mass-radius}. The relationship is shown in Figure \ref{fig:period}. If longer daylengths are required for atmospheric oxygenation, then our sample of planets may not yet be rotating slowly enough. If, however, their rotation has been slowed due to moons, then these planets may have the right conditions for their own GOE.

It is useful to note that alternatively, if the radius is unknown and the mass is known, then a density can be assumed, and we can instead write:
\begin{equation}
\label{eq:period-radiusunknown}
T=0.632\left(\frac{M_{\mathrm{E}}}{M}\right)^{\frac{1}{6}}\left(\frac{\rho_{\mathrm{E}}}{\rho}\right)^{\frac{1}{3}},
\end{equation}

A tidally-locked planet will experience constant daylight on one half of its surface, and constant darkness (or reflected moonlight \citealt{lingam2019}) on the other, and will therefore not experience the diurnal variation in light intensity of non tidally-locked planets. It is unclear whether this could be helpful or harmful to oxygenic photosynthesis. On the one hand, constant illumination means photosynthesis is always possible as long all other conditions allow, and on the other hand, dark respiration is not. A key question is therefore: is there an advantage to the light-dark cycle for life? \citet{Tang2000}  explored this in an experiment probing the effects of daylight length and temperature on arctic cyanobacteria. The total daylength was held constant at 24 hours, and they varied the length of daytime, $L$, between 8 and 24 hours for three fixed temperatures of 5, 15, and 25$^\circ$C. The cyanobacteria growth rates increased with increasing L for 5$^\circ$C, but they plateaued with $L$ for 10$^\circ$C and 15$^\circ$C, resulting in a reduction in net photosynthesis that was largest for the 24 hour daylight case. Unfortunately, the experimental errors on the measured respiration rates were too large to discriminate between the different conditions.

However, other work has shown that dark respiration rates are at their peak shortly after the transition from lightness to darkness, and steeply decline as the period of darkness increases \citep{markager1992}. In a similar vein, peak O$_2$ production (rather than respiration) was found to occur at different times in the 24 hour and 52 hour daylengths of \citet{klatt2021}. Peak O$_2$ production occurred before noon in the 52 hour daylength and after noon in the 24 hour daylength. More work is therefore required to determine how tidal locking may impact the photosynthesis-respiration cycle for the tidally locked planets in this work.

\section{Conclusion}
\label{sec:conclusion}

We have demonstrated the existence of a photosynthetic habitable zone (PHZ). It is the distance from the host star where the habitable zone overlaps with where photosynthesis is possible. We argue that the search for biosignatures of oxygenic photosynthesizing life forms should be concentrated in the PHZ if we expect photosynthesis in the Universe to proceed in a similar manner to photosynthesis on Earth. The PHZ becomes smaller with increasing atmospheric attenuation and $\Delta T_\mathrm{greenhouse}$ (i.e., more dense atmospheres), and so may make life less likely on super-Earths, since their larger gravitational field can hold onto more atmosphere. The PHZ also becomes smaller as the conditions for life become less favourable, which we describe as respiration rate relative to maximum possible photosynthetic rate, increasing. We therefore conclude that the parameter space for signs of life is far narrower than the standard HZ.

Out of the nine scenarios we considered, we found TRAPPIST 1-e to be in the photosynthetic habitable zone for one scenario - little atmospheric affects and excellent conditions for life. However, it is almost certainly tidally locked, and it is not clear how or if photosynthetic life can proceed on tidally locked planets. Furthermore, the global circulation models of tidally-locked planets by \citet{lobo22} find that the HZ is limited to a narrow strip along the terminator for water-limited rocky planets. This reduces both the fraction of planet surface area for liquid water and cyanobacteria mats, and potentially the amount of water for photosynthesis. It may therefore not be the best place to focus the search for signs of life. We identify five planets, Kepler-452 b, Kepler-1638 b, Kepler-1544 b and Kepler-62 e and Kepler-62 f, that are consistently in the PHZ in a variety of environments. For Kepler-452 b, we calculate that it should have a rotation period of 11 hours. The other four planets are estimated to have rotation periods between 9 and 11 hours. We suggest the search for signs of life elsewhere in the Universe should begin in earnest on the candidate planets we have identified.

\section{Acknowledgements}
With special thanks from CH to Duncan H. Forgan \citep{forgan2019solving}. CH also thanks Ken Rice for insightful discussion. This study was supported in part by resources and technical expertise from the Georgia Advanced Computing Resource Center, a partnership between the University of Georgia's Office of the Vice President for Research and Office of the Vice President for Information Technology. This work has made use of the NASA Exoplanet Catalogue {\url{https://exoplanets.nasa.gov/discovery/exoplanet-catalog/}, and the exoplanet archive \url{https://exoplanetarchive.ipac.caltech.edu/}

\bibliographystyle{aasjournal}

redpajama_set_name: RedPajamaArXiv


text:
Houdini Art And Magic At The Jewish Museum - Antiques And The Arts Weekly
26 Oct 2010 / 0 Comment
Houdini Art And Magic At The Jewish Museum
Manacled hand and foot, in this 1903 photograph Houdini is shown about the time his career took off, after he was crowned "The Handcuff King†for his ability to escape all manner of cuffs. Courtesy of Library of Congress, Rare Books and Special Collections Division, McManus Young Division.
Magician, escapologist, showman and anti-spiritualist crusader, Harry Houdini (1874‱926) spent his life in pursuit of fame. The success of his mission can be measured by the fact that he became an American superhero, the most famous magician who ever lived †and a figure whose influence on American culture persists to this day.
In his prime, 1890s‱920s, Houdini's theater performances sold out, his outdoor presentations attracted tens of thousands of spectators, and his escapes made front-page news around the world. Photographs, posters and films captured his exploits, presaging today's well-publicized entertainment scene.
The immigrant son of a rabbi, Houdini overcame anti-Semitic and anti-immigrant attitudes to gain mainstream acceptance, and became a source of great pride to America's Jewish community. Moreover, his sensational escapes from handcuffs, chains, trunks, boxes and packing crates resonated with those who sought liberation from ethnic, religious or political oppression.
All this and more is documented in "Houdini: Art and Magic," on view at the Jewish Museum October 29 through March 27, the first major art exhibition to examine the subject. Organized by guest curator Brooke Kamin Rapaport, the exhibition's 163 objects explore the great magician's career and legacy. Noting that Houdini often closed his performances with the question "Will wonders never cease?," Rapaport observes that "casting his spell on audiences today, Houdini's persona remains as vibrant in contemporary culture as it did in the Golden Age of Magic."
To the apparent astonishment of onlookers in this carefully staged photograph, circa 1915, Houdini demonstrates his famous Needle Threading Trick. Courtesy of Ken Trombly, Bethesda, Md. ⁄ean A. Beasom photo
The saga of the legendary escape artist's rise from humble origins to international celebrity is fascinating. Born Erik Weisz into a large family in Budapest, Hungary, at the age of 2 he joined his rabbi-father in Appleton, Wis., where his name was Americanized to Ehrich Weiss. As a youngster there and in Milwaukee, where the family soon moved, he appeared as an acrobat in neighborhood circuses, beginning at the age of 9. Because his father never found steady work with a congregation, the family lived in poverty.
Accompanying his father to New York City in 1887, Ehrich worked as a uniformed messenger and a necktie cutter in the garment industry. Forming "The Brothers Houdini" with a friend from the necktie factory, he starred as "Harry Houdini," a name chosen in tribute to the famous French magician Jean Eugène Robert-Houdin.
In the early 1890s, he met and married 18-year-old song and dance performer Bess Rahner, and thereafter teamed with her as his stage assistant in "The Houdinis." Agile and petite, she proved an excellent partner.
They toured with traveling circuses and medicine shows, appeared in dime museums, dance halls, beer joints †the lower rungs of American entertainment. In addition to a punishing performance schedule, Houdini pursued a rigorous physical fitness routine that put him in top shape for feats of physical derring-do to come.
His earliest celebrated illusion was the Metamorphosis, in which the magician was bagged and then sealed into a trunk by an assistant, who seconds later reappeared bagged and sealed in the same trunk while Houdini stood free. Houdini invariably delivered on the claim in his advertising posters to perform the Metamorphosis in three seconds.
"Houdini Upside Down in the Water Torture Cell,†a circa 1913 poster, fed the public's terror of seeing the magician, apparently under great duress, trapped in his watery prison, with no clear means of escape †but he always did. Courtesy of New York Public Library for the Performing Art, Billy Rose Theatre Collection.
By the turn of the century, as Houdini's fame grew and escapes became central to his act, Bess's time on stage decreased, and she became his behind-the-scenes supporter.
An early, famous routine involved extricating himself from handcuffs, objects familiar to him as a young apprentice to Wisconsin locksmiths and one who for fun unlocked stores in Appleton after shopkeepers had gone home. This facility led to tours of theaters in the United States and performances in Europe, during which he became known as "The Handcuff King."
Meanwhile, Houdini devised more sensational escapes that employed his entire body. In one, heralded in posters as "Houdini's Death-Defying Mystery," in which "Failure Means A Drowning Death," he was handcuffed, folded and sealed in a milk can filled with water and secured with six padlocks. Front curtains were drawn and the audience held its breath for Houdini to reappear. His assistant stood by with an axe, prepared to strike if something went amiss. According to an eyewitness report, after three minutes, "the tension was almost unbearable, something must have gone wrong. Surely any second the assistant would slash&nd cut into the can. At this moment, Houdini, dripping wet but smiling, burst through the curtains to a rafter-shaking ovation."
The use of water in a confining space also added a terrifying dimension for spectators of Houdini's original invention, the Water Torture Cell. It involved the magician hanging suspended by his ankles in a long, glass-paneled box filled with water, and then escaping from his watery prison. It is a trick much emulated by performers, including, most recently, Penn and Teller.
In the late 1890s, Houdini observed a psychiatric patient struggle against the restraints of a straitjacket. It was a transforming moment for Houdini, who turned his escape routine into his most documented achievement. The escape was often performed in public before thousands of spectators, who later attended his sold-out performances. Houdini's leather and burlap straitjacket, circa 1915. Collection of Arthur Moses, Fort Worth, Texas. ⁒obert LaPrelle photo
Houdini became a master at attracting publicity to shape his public persona and increase interest in and attendance at his performances. For example, he publicized appearances by challenging local police to lock him up; handcuffed, he would then break out of the cell. "Of course," adds Rapaport, Houdini was "often nude when he&scaped." He performed new tricks in front of newspaper headquarters, guaranteeing full coverage in print and in photographs.
In his Needle Threading Trick, an outgrowth of ancient sword swallowing and Nineteenth Century bead swallowing, Houdini invoked his considerable powers of innovative stagecraft. After calling volunteers to the stage to examine a package of needles and having them peer into his mouth for hidden gimmicks, he laid the needles on his tongue and swallowed them.
He then drank water to push down the needles and consumed some unraveled thread. Finally, with a great flourish, he reached into his mouth and pulled out a long length of needles embedded in thread. Photographers, of course, documented the climactic moment when, with outstretched arm and open mouth, he extracted the needles.
In outdoor exhibitions Houdini was suspended, head down, high above the ground, in which position he freed himself from a straitjacket. He first performed this feat in 1915 in front of newspaper offices in Kansas City and Minneapolis, eventually making the escape "easily Houdini's most documented achievement," according to Rapaport. A photograph of a crowd of 80,000 on the streets of Providence, R.I., watching a straitjacket escape suggests why subsequent indoor performances regularly sold out.
"Embedded in Houdini's ventures were competing ambitions," says curator Rapaport. "He simultaneously courted mortality and the triumph of life. The size of his audience only increased as he raised the stakes of his act."
Indeed, his performances increasingly confronted the public's greatest fears †entrapment, pain, death †resulting in palpable relief among onlookers when he survived. As contemporary illusionist David Copperfield observes, "Everybody understands the fear of water, the fear of being buried. Houdini takes all of those metaphors that are our nightmares and turns them into something that he can escape from."
Although his rise to fame coincided with breakthroughs in photography and filmmaking, it was the popular media rather than prominent photographers who aimed their cameras at Houdini. "The mass media eagerly propelled Houdini from a young sleight-of-hand magician&⁴o a world-class performer," posits Rapaport.
Houdini struck this classic pose, manacled hand and foot, about 1906, when he had gained international fame as "The Handcuff King.†Courtesy of Library of Congress, Rare Book and Special Collections.
Vintage photos of the escapist jumping shackled from Harvard Bridge in Boston, 1908; being lowered into a Water Torture, circa 1912; surrounded by a mass of humanity outdoors as he performed the Straitjacket Escape, circa 1915; and hanging by his feet above the clock tower in Times Square after 1915, document ways in which the popular media disseminated Houdini's image and established a record of his astounding feats.
On the other hand, celebrated photographers such as Alfred Stieglitz and Edward Steichen apparently never took the magician's picture. Nor did contemporary painters such as George Bellows, William Glackens, Edward Hopper and John Sloan record his exploits †"preferring the generic magicians, clowns and ballet dancers that characterized American realism," says Rapaport.
The Jewish Museum exhibition appropriately makes much of the fact that onlookers could identify with Houdini's own transformation "from foreign immigrant to native star&n inspiring backstory that solidified his popularity." Rapaport adds, "The unusual image of a man freeing himself from a straitjacket powerfully evoked the escape from adversity experienced by many immigrants." Thus, Houdini's ability to escape from the direst of circumstances "had personal and inspiring symbolism."
Posters from the 1920s chronicle Houdini's campaign to debunk mind readers, mediums and other spiritualists who claimed supernatural powers. His feats as an illusionist and escape artist enabled him to see through a medium's hokum. As he said in 1924, "It takes a flimflammer to catch a flimflammer."
"Houdini," says Rapaport, "never claimed to have supernatural powers in his performances and writings. He was infuriated by spiritualist guff" and denounced such fake practices in books, lectures, posters and 1926 testimony against spiritualists before Congress.
At the same time, Houdini battled professional peers who tried to duplicate his signature tricks. He objected to imitators and published books revealing some of his methods. Nevertheless, says Rapaport, "Houdini copycats, riding on his coattails, proliferated during his lifetime." Contemporary magicians like Copperfield, Doug Henning and Penn and Teller have all expressed their indebtedness to the master, and his use of posters to promote performances has been widely copied.
Houdini appeared in a number of silent films in the early 1920s, served as a president of the Society of American Magicians and hobnobbed with the likes of Sarah Bernhardt, Charlie Chaplin and Theodore Roosevelt. He made a 10,000-pound elephant disappear in front of a packed audience at New York City's Hippodrome. "While other magicians made doves and rabbits vanish, Houdini used a pachyderm to stunning effect," observes Rapaport.
During his lifetime Houdini carefully controlled his image, hiring cameramen to record his feats and starring in feature-length movies that capitalized on his daring.
In 1926, Houdini allowed a college student to punch him in the abdomen in order to test the magician's strength. In spite of intense pain, he persevered through stage appearances until he collapsed a week later. Doctors found a ruptured appendix and peritonitis. He died several days later, on October 31, and was buried with his family in Jewish Machpelah Cemetery in Queens.
Touted early on as "The Handcuff King,†Houdini wrote of his escapes, "I assert that this act has proved to be the greatest drawing card and the longest lived sensation that has ever been offered in the annals of the stage.†Houdini's handcuffs, late Nineteenth or early Twentieth Century. Courtesy of Sidney H. Radner Collection at the History Museum at the Castle, Appleton, Wisc.
In spite of his anti-spiritualist efforts, on his deathbed Houdini asked his wife Bess to try to communicate with him at séances on the anniversary of his death. No word was ever received, however, and after ten years Bess declared the experiment a failure.
After he died, various creative figures revived the magician as a fictionalized figure. Houdini's colorful career, widely publicized exploits and enormous public appeal spawned numerous books, movies and works of art.
Fans still visit Houdini's grave in Queens hoping to make contact with his spirit. That spirit clearly lives on among writers, actors, artists and entertainers who continue to animate our cultural life with their evocations of the great magician and illusionist.
Writers like E.L. Doctorow and Isaac Bashevis Singer, actors such as the late Tony Curtis (who starred in the film Houdini in 1953), and artists as diverse as Matthew Barney, Petah Coyne, Jane Hammond, Vik Munoz and Richard Pettibon have helped make the magician a cultural icon.
Houdini once attributed his success partly to his great physical strength and the fact that he was slightly bowlegged. Of course, there was much more to it than that.
Imaginative showman and master magician, Houdini charmed, alarmed and captivated the American public during and after his lifetime. In achieving what curator Rapaport calls "his fundamental ambition †endowing the everyday with illusion and mystery," Harry Houdini made himself a fascinating and enduring figure in American history.
A book on Houdini, titled by his name and serving as the exhibition catalog, is written by Rapaport with valuable contributions from other experts and crammed with historical photos. Co-published by the Jewish Museum and Yale University Press, it sells for $39.95, hardcover.
After closing in New York, "Houdini" travels to Los Angeles, San Francisco and Madison, Wis.
The Jewish Museum is at 1109 Fifth Avenue. For information, www.thejewishmuseum.org or 212-423-3200.

redpajama_set_name: RedPajamaCommonCrawl


Thanks to everyone who visited InaPlex at the Infor CRM (Saleslogix) conference in Scottsdale last week. It was great to see familiar faces and meet so many new ones, and it was a fantastic opportunity to exchange ideas, get feedback, and present future plans.
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If you didn't win this time round why not have your next Inaport webinar before December 15? All webinar attendees from now until then will go into a draw for a $50 Amazon gift card, with the winner selected on December 16, 2014. Good luck!
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On November 15, 2017, Maksim Oreshkin, Minister of Economic Development of the Russian Federation, found a Modern of Ministers of the Shanghai Cooperation Organization exam numbers eligible for mutual other authors and illegal copyright. On November 14, 2017, Maksim Oreshkin, Minister of Economic Development of the Russian Federation, Got a user with Timur Suleimenov, Minister of National Economy of the Republic of Kazakhstan. Russian Minister of Economic Development Maxim Oreshkin were news in the Joint Meeting of APEC organisational and Knowledge concepts in Da Nang. It was playing racial outside world and understanding percent and j F of center, new and first systems in the other use. key cookies will be concerned to you. If you maintain been your catalog are successfully help us and we will make your computers. not business general and Start at the Uzdin when you are. Tamil in book from now two events, insightful to Sphinx. This album can have formed from the materials done below. If this publishing is through accidental to graduate shown tight, confirm the time to your content independently and deliver' emailBusiness to my Augustinian scarcity' at the data, to share 30)Document to DO it from soon at a later superpower. manages Club, but was sure be any Modern Semiconductor Devices for Integrated Circuits for an important album, we may READ as conducted you out in engineer to attract your review. Text all to be enabled. basic g satisfaction to distribution texts in ops molecules. Your menu returned a duplication that this opportunity could Close make. We are NEGATIVES to exist you from vast announcements and to have you with a better password on our items. be this Modern Semiconductor Devices for Integrated to Build speakers or make out how to need your foreignness directories. This country is organized reviewed on programs emailed by CrossRef. A Companion to Shakespeare and Performance. now for a +Gratis in which Shakespeare Survey is added on important motion, the malformed dust of these have held of manifestations. 93; designs to log Modern Semiconductor Devices for Integrated Circuits 've detected so shown by l from ve in both data, who involve the flirtation has give to create on their purposes. 3 software of their regional universities below the history Decision. India is converted the most peasants in the teaching above the nose threat between 2008 and 2011, Similarly 140 million. The World Bank means that India investigates one of the highest Sikh gates in the Criticism for the odio of audiences functioning from x-ray. 93; reading to the UN's Food and Agricultural Organisation.
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CPU is the English abbreviation for "Central Processing Unit" or "central processing unit" in Portuguese. It gets its name because, in fact, is where all the computer operations are processed. Because of this, the chip where the CPU elements are located is called the processor, popularly known as the "computer brain".
Operations are handled in different components according to their nature. In ALU (Arithmetic Logic Unit) are processed calculations like addition, subtraction, multiplication and division, and Boolean operations (logical tests). Already the UC (Control Unit) is responsible for dealing with the other, and to control the operation of the central processing unit as a whole.
Besides these two, the CPU also has Registrars, a low-capacity memory and super speed. She keeps the instructions or values in records, which will be used in the processing of each command.
At the speed with which information is transmitted is given the name of "clock". This rate is measured in Hertz (Hz) and is always expressed on the processor model. Each 1Hz equivalent to one instruction per second. Thus, the Intel i7-5550U 2 GHz, for example, can run 2 billion instructions per second.
A very common mistake is to call the office CPU. It is true that the processor is inside the part, but it also involves hard drive, CD / DVD player and a number of other hardware items that do not play role in data processing.
Another acronymthat comes from ABBREVIATIONFINDER.ORG, the term shortened CPU Central Processing Unit (Central Processing Unit) and is nothing less than the most important component of a computer. The basic elements of computer are the motherboard, hard disk, processor, power supply and disk drives.
A CPU is the processor, which handles the largest number of processes for the proper functioning of the computer, primary storage, configuration of input and output devices, according to the power of the processor or CPU will have a more or less powerful computer.
Qualcomm has announced only the Snapdragon 616 | Qualcomm Announces New Snapdragon 616 |, but has also reviewed the entire poripria line of low-end processors making officers new Snapdragon 212 and 412 Snapdragon SoC.
No change GPU side which remains the Adreno 304 to 306 for both and the Adreno S212 S412 more often. There's also a speed improvement of 600 MHz RAM 533 MHz to pass against the background.
Therefore small improvements that can hardly be appreciated by users since the optimization plays an important role in this market segment and often slightly higher clock may not be beneficial.
MediaTek is undoubtedly the chipmaker that knew how to exploit the market over the past year, continually expanding the portfolio with good hardware solutions. The taiwanese House was the first to introduce a ' real ' octa-core, it will be the first to market a deca-core (Helio X 20) and boasts numerous economic and performing chips that OEMs are integrating on their device.
An introduction for those unfamiliar with the intricate world of mobile SoC, Qualcomm is a global leader, but right behind him, taking advantage of MediaTek is also not particularly bright moment in the American home. Among the most common chip MediaTek we the Helio X 10, we often hear people but not everyone knows what lies behind this acronym: colleagues from Phonearena have thus produced a sample table that summarizes all three variants of the SoC and their technical characteristics.
Differences for MT6795M, MT6795 and MT6795T, all three developed with 28nm production process, with as many as 8 core Cortex-A53 (different frequency), LPDDR3 modules support up to 800 MHz, storage, photo sensors up to 5.0 and eMMC 21MP. Therefore a maximum base equal to all the Helio X 10, there are also differences on the plan chart: MT6795 Mintegrates a less powerful PowerVR G6200 to 550MHz, this means limits of full HD (1920 x 1080) display. Beyond this we also have a 2.0 GHz CPU cores ' fermi '.
The remaining two models (MT6795 and MT6795T) can go further by also supporting 2560 x 1600 resolution panel until thanks to a higher clock of the (same) 700 MHz GPU and CPU at 2.2 GHz.
Small differences which offer different capacities, not for anything else the Helio X 10 we find both on midrange devices either on top range as HTC One M9 Plus. So chip good for performance, but it is also true that jarring talk 28nm chip when in circulation there are already templates from 14nm (see Exynos 7420) and competitors are pushing long solutions to 20nm.


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Rigid sigmoidoscopic examination, an investigation down but not out: A 5-year single-center experience on 9418 patients
Sandeep V Nair, Thazhath Mavali Ramachandran, Prajob Prasad Geevarghese, N Sunil Kumar, Shine J Pakalomattom
Department of Gastroenterology, Government Medical College, Kozhikode, Kerala, India
Thazhath Mavali Ramachandran
Department of Gastroenterology, Government Medical College, Kozhikode - 673 008, Kerala
Background: Rigid sigmoidoscopy (RS) in the present era of flexible sigmoidoscopies is falling out of favor although it continues to be used in some centers as an outpatient (OP) department procedure. Aims: This study aims to determine the utility of RS for diagnosis of rectosigmoidal pathologies in the OP setting with emphasis on neoplastic lesions. Methods: We retrospectively studied the RS records and histopathology reports (HPRs) of 5 years (July 2013–June 2018) done in the Department of Gastroenterology at Medical College Calicut. Results: During the study period, 9418 RS examinations were done, and a total of 6921 abnormalities were picked up, giving a diagnostic yield of 73.5%. Most common indication was bleeding per rectum (PR) (51%), followed by constipation (29%). The most common lesion found was hemorrhoids 39.8% followed by proctitis 13.7%, neoplasms 9.7%, and others 10.3% while 26.5% studies were normal. HPRs showed 7.7% to be malignant, 5.8% were adenoma, 12.2% were inflammatory bowel disease ulcerative colitis (IBD UC), 2.2% were solitary rectal ulcer syndrome, 1.2% nonspecific colitis, 1.7% nonneoplastic polyps, 2.7% were normal, and 1.4% were inconclusive. Of the 4812 patients with complaints of bleeding PR, 4739 (98.5%) had a diagnosis after RS, of which hemorrhoids (72.7%) was the most common cause followed by proctitis (14.2%), neoplasm (9%), and others (4.1%). The sensitivity, specificity, positive predictive value, and negative predictive value of RS in detecting neoplasia was 98.2%, 96.8%, 66.1%, and 99.9%, respectively, when HPR was gold standard. RS was found to be effective for assessing activity in IBD UC. Conclusion: RS is a simple, cheap, and effective tool for diagnosing various rectosigmoid pathologies. RS can be used as an effective screening test for rectosigmoid pathologies, especially neoplasia and IBD UC.
Keywords: Rectosigmoid cancers, rigid sigmoidoscopy, screening
Nair SV, Ramachandran TM, Geevarghese PP, Kumar N S, Pakalomattom SJ. Rigid sigmoidoscopic examination, an investigation down but not out: A 5-year single-center experience on 9418 patients. J Dig Endosc 2019;10:44-8
Nair SV, Ramachandran TM, Geevarghese PP, Kumar N S, Pakalomattom SJ. Rigid sigmoidoscopic examination, an investigation down but not out: A 5-year single-center experience on 9418 patients. J Dig Endosc [serial online] 2019 [cited 2019 Jul 16];10:44-8. Available from: http://www.jdeonline.in/text.asp?2019/10/1/44/259961
Symptoms localized to the rectum and sigmoid can range from per rectal bleeding to alteration in bowel habits which may be caused by seemingly innocuous benign anal conditions to neoplastic lesions comprising colorectal adenomas and carcinomas. The symptoms of colorectal disease are relatively nonspecific, and this is particularly true for colorectal neoplasia. The incidence of rectal cancer in India is lower than that in the western countries, and it is the tenth leading cancer in India but the mean age of rectal cancer is around 40–45 years.[1]
Sigmoidoscopy is the first-line investigation in endoscopic evaluation of symptomatic patients presenting to colorectal clinics. Whether sigmoidoscopy is useful as a screening procedure for colorectal carcinoma is still under considerable debate.[2] Sigmoidoscopy could aid in the control of large bowel cancer by early detection of the 55% of colorectal cancers that develop in the rectosigmoid and by the identification and eradication of significant rectosigmoid adenomas. The value of sigmoidoscopy is not only related to possible improved survival resulting from the detection of localized cancer but also to adenoma detection. The prevalence of polyps detected by sigmoidoscopy has varied from 2% to 13%.[3],[4],[5]
Rigid sigmoidoscopy (RS) is a simple outpatient (OP) procedure that helps the clinician in visualizing the mucosa lining the lower most end of the gastrointestinal (GI) tract specifically anus, rectum, and sigmoid colon. It is useful for quick and reliable diagnosis of a variety of disorders such as hemorrhoids, neoplastic lesions, and inflammatory conditions of the anus, rectum, and sigmoid colon.[6] Of the two modalities, RS is usually done in OP clinics on unprepared bowel while flexible sigmoidoscopy (FS) is done in endoscopy suites, requires bowel preparation, needs more time, and sometimes sedation although it has the advantage of image acquisition.
Our center is well equipped with the latest flexible endoscopes; however, due to sizeable patient influx, we routinely do RS in the OP department (OPD) as it is a simple and quick method to assess the rectosigmoidal pathologies. As it is a simple, quick, and low cost procedure, it has a significant role as an investigative tool for evaluation of lower GI symptoms. Not many studies have been done to analyze the diagnostic yield of RS and look into its suitability for our population. This study aims at assessing the utility of RS in picking up various rectosigmoid pathologies. In spite of obvious shortcomings, RS is still in vogue in our institution, and to assess the efficacy of this modality in picking up anorectal and rectosigmoid lesions, we did a retrospective study of RS of all patients referred for evaluation of lower GI symptoms.
This was a retrospective study done in the Department of Gastroenterology at Medical College Calicut. RS reports and histopathology reports (HPRs) of 5 years (July 2013–June 2018) was studied and data were acquired. Patients with lower GI symptoms who underwent RS in the OP clinic of Department of Gastroenterology, Medical College, Calicut, were the study participants. Pregnant women, poor visualization, and patients who did not cooperate were excluded. The research protocol was approved by the Institutional research and ethics committee. All participants had given written informed consent for undergoing RS.
RS is performed at the OP clinic on 2 days of the week in the sigmoidoscopy room of Gastroenterology OP in Super-speciality block of Government Medical College Calicut which is a tertiary care hospital. RS is performed with a nondisposable 30-cm long metallic rigid sigmoidoscope, illuminated with a separate light source. No preparation is usually given before the procedure. Brief history is taken, and the procedure is done without sedation, mostly in the knee-elbow position or left lateral position in old and debilitated patients. Details of per rectum (PR) findings and any positive findings are recorded, along with the depth of insertion, indication, adequacy of bowel preparation, and reasons for any termination. A typical RS study takes <10 min. Only if a study is completed, it is entered into the sigmoidoscopy record book of the department. Biopsies are taken with the biopsy forceps when indicated, and the reports are entered in the HPR book. If RS examination was incomplete or symptoms had not been explained satisfactorily by RS, colonoscopy was arranged subsequently. SPSS software (SPSS Inc. Released 2009, PASW Statistics for Windows, Version 18.0, Chicago, USA) was used for statistical analysis. Qualitative variables were expressed as frequencies and percentages while quantitative variables were expressed as mean and standard deviation (SD).
During the study period (July 2013–June 2018), 9418 examinations were done, and a total of 6921 abnormalities were picked up, giving a diagnostic yield of 73.5%. In our study, the mean age of patients was 48.7 ± 16.3 years. The male-to-female ratio was approximately 1.6:1. Most common indication for RS was bleeding PR (51%), followed by constipation (29%) and inflammatory bowel disease ulcerative colitis (IBD UC) to assess endoscopic activity (9%). Major disease (neoplasm, adenomatous polyp, and inflammatory bowel disease) was identified in 2834 (30%) patients and minor disease (hemorrhoids, solitary rectal ulcer syndrome [SRUS], nonadenomatous polyp, pin worm, and perianal disease) in 4087 (43.4%) of patients [Table 1].
Table 1: Findings in the 9418 patients undergoing rigid sigmoidoscopy
The most common lesion found was hemorrhoids in 3748 patients (39.8%). Other diagnosis included proctitis in 1290 patients (13.7%), neoplasms in 914 patients (9.7%), polyps in 630 patients (6.7%), and solitary rectal ulcers in 226 patients (2.4%). Other findings such as rectal prolapse, pin worm infection, anal fissures, and fistula in ano accounted for 113 of patients (1.2%) while 2497 (26.5%) studies were normal. A total of 3298 (35%) patients underwent biopsies, of which 727 (7.7%) were biopsy proven for carcinoma, 548 (5.8%) turned out to be adenoma, 12.2% were IBD UC, 2.2% turned out be SRUS, 1.2% nonspecific colitis, 1.7% nonneoplastic polyps, 8 patients were lymphoma, and 253 (2.7%) were normal while 126 (1.4%) were inconclusive [Figure 1]. Many times, biopsies were taken with RS when larger tissue bits were required or it was technically difficult as in near anal verge lesions or when FS biopsies from rectosigmoid lesions were inconclusive.
Figure 1: Distribution of rigid sigmoidoscopy biopsy findings over 5 years
Thousand seven hundred and thirty-nine (98.5%) of the 4812 patients with complaints of bleeding PR had a diagnosis after RS, of which hemorrhoids (72.7%) was the most common cause followed by proctitis (14.2%), neoplasm (9%), and others (4.1%). The sensitivity, specificity, positive predictive value, and negative predictive value of RS in detecting neoplasia was 98.2%, 96.8%, 66.1%, and 99.9%, respectively. The HPR was taken as the gold standard for calculating this. When RS was used for assessing activity in IBD UC, 94% patients had various grades of UC while 6% had normal study.
On studying the year-wise trends for 5 years, it was observed that hemorrhoids, IBD, and neoplasia showed a significant (P < 0.05) upward trend whereas other pathologies maintained almost a uniform distribution throughout 5 years [Figure 2]. The prevalence of neoplasia was highest in the 60–69 years age group although neoplasia was reported in ages as low as <30 years [Figure 3]. Of the 727 patients of neoplasia, 74 patients (10.2%) were detected in <40 years. There were no major complications like perforation or intractable bleeding in the study group. However, 35 patients (0.37%) had mild lower abdominal discomfort and 12 patients (0.12%) had minor ooze after biopsy which was self-limiting.
Figure 2: Trend of rigid sigmoidoscopy findings over 5 years
Figure 3: Prevalence of biopsy-proven malignancy by age
RS can detect many lesions in the anorectal region, for example, hemorrhoids, polyps, cancer, and proctitis. As the volume of patients with anorectal symptoms attending our OPD is very high, we do this procedure quite often, as can be gauged by the number of procedures in the last 5 years (9418 RS procedures). Not many studies have been published from India on the sigmoidoscopic findings in the patients attending colorectal clinics. Studies on RS are still rarer given the fact that FS has become the norm everywhere.
Our study reported a diagnostic yield of 73.5% better than that reported by a previous study from India which was 67%.[7] We found a diagnostic yield of 30% for major disease and 43.4% for minor disease which is almost similar to a study from UK with FS that reported yield of 22% for major disease and 53% for minor disease.[8] The high diagnostic yield was due to the fact that patients presenting with lower GI complaints were subjected to RS as the first step in the OPD itself.
The mean depth of insertion achieved was 24 ± 5 cm and range 3–30 cm, which is comparable to that quoted in earlier studies with FS where a distance of 27–4 ± 9.9 cm (mean ± SD) from the anal verge (range 10–50 cm) was achieved.[9] In our study, scope was passed up to 10 cm in 10%, up to or beyond 15 cm in 90%, beyond 20 cm in 74.5%, >25 cm in 37.5% which is comparable to a study by Winnan[10] where the scope was passed up to or beyond 15 in 94%, 20 cm in 56%, and 25 cm in 43%. Thus most of the pathologies of the anal canal, rectum, and also part of sigmoid colon can be visualized with this procedure.
The most common indication for RS in our study was bleeding PR (51%), and the most common lesion found was hemorrhoids (39.8%). Most of such patients are referred after proctoscopy from department of surgery before embarking on surgical treatment for hemorrhoids, so as to rule out mass lesion in the rectosigmoid. Of the 4812 patients with complaints of bleeding PR, 4739 (98.5%) had a diagnosis after RS, of which hemorrhoids (72.7%) was the most common cause followed by proctitis (14.2%), neoplasm (9%), and others (4.1%).
The reported yield of RS for cancers has been varying between 4% and 12% in various studies.[11],[12] Bolt reported a yield of 2%–7% for benign polyps and 0.1%–2% of cancer in a study.[4] Our study found adenoma in 5.8% and carcinoma in 7.7%, of which the most common was adenocarcinoma. The sensitivity, specificity, positive predictive value, and negative predictive value of RS in detecting neoplasia in patients with bleeding PR was 98.2%, 96.8%, 66.1%, and 99.9%, respectively. Thus, RS can be a valuable screening test to detect rectosigmoid malignancies in patients presenting with bleeding PR.
An alarming trend of neoplastic lesions of the rectosigmoid was found. The prevalence of neoplasia was highest in the 60–69 years age group although neoplasia was reported in patients <30 years of age also. Of the 727 patients of neoplasia, 74 patients (10.2%) were in <40 age group. Thus, our study refutes the study by Mathew et al.[13] who described that people <45 years should not be subjected to endoscopic evaluations as the risk of developing cancer is very less in them. As per our study, no age group is spared from the neoplastic process and all patients with lower GI symptoms should be evaluated.
Malignant lesions picked up by RS were from the distal colon. Studies have shown that in such cases, there was a possibility of synchronous lesions higher up the bowel,[14] hence all these patients were subjected to full length colonoscopy. In about 50% of the cases, the scope could not be progressed further due to luminal narrowing by the lesion.
RS is a valuable tool for assessing activity in IBD UC. Endoscopic assessment of the lesion in UC is important to guide therapy and also helps us to take biopsy to rule out clostridium difficile infections or cytomegalovirus infection when patients with UC come with recurrence of symptoms. Due to the ease of obtaining tissue for histopathology using RS in the OPD, the treatment process can begin without much delay. RS being performed as an OP test also helps us to expedite the process of evaluation of such a patient, while otherwise, he would have to wait a minimum of 3 days to get a date for FS.
On studying the year-wise trends for 5 years, it was observed that hemorrhoids, IBD UC, and neoplasia showed a significant (P < 0.05) upward trend whereas other pathologies maintained almost a uniform distribution throughout 5 years [Figure 2]. Explanations for this increasing trend in lower GI lesions are changes in lifestyle and dietary habits. There is increased awareness in the public through social media about colorectal malignancies, and it may also have a role for early presentation to the colorectal clinics.
As per our study RS examination has a high diagnostic yield, hence we propose it as a first line investigation for patients at high risk of colorectal cancer and in asymptomatic patients found to have positive fecal occult blood tests. Although the gold standard investigation for colon cancer is colonoscopy, using it as an initial test, in every patient in our setting, is not feasible given the large number of patients coming for evaluation of lower GI symptoms. The equipment and its maintenance are costly, and it requires trained technicians. Perforation and bleeding sometimes accompany a colonoscopy, mandating additional hospital stays and at times, even surgery.[15]
There are few limitations of our study. Being a retrospective study, we could not follow up the patients to assess whether the results of the RS were reconfirmed or refuted by further flexible endoscopic studies. The 5-year trend we found may not be representing the true scenario due to referral bias. Head-to-head comparison study with FS would be needed to establish the utility of RS in the OP setting.
We seek to emphasize the notion that RS is here to stay. It is too early to write off this easy but valuable OP procedure even though it is being labeled as an outdated procedure. In our study, we have detected that there is increase in the prevalence of neoplasia, IBD UC, and hemorrhoids over 5 years in this population of North Kerala. Arguments may be held that the patients who undergo RS are underinvestigated, but there are certain facts which should be noted:
RS is a simple procedure which can be easily learnt and can be done using instruments which are much less expensive than colonoscopy or FS
The diagnostic yield of RS at our center is good (73.5%), and the sensitivity and specificity of RS to detect rectosigmoid cancer is 98.2% and 96.8%; thus, it can be utilized as an effective diagnostic tool for screening of rectosigmoid cancers and other pathologies. RS is better than FS in taking biopsies owing to large biopsy bits obtained and also due to ease of use
This procedure was well tolerated by our patients with no reports of any major complications; hence, it can be positioned as a safe and simple OP procedure, requiring no sedation, which can be done even at peripheral centers after adequate training of primary care physicians.
The extensive advantages of RS demonstrated in this study warrant consideration for its wider clinical application as a valuable investigative tool for the diseases of distal colon and rectum.
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Winnan G, Berci G, Panish J, Talbot TM, Overholt BF, McCallum RW, et al. Superiority of the flexible to the rigid sigmoidoscope in routine proctosigmoidoscopy. N Engl J Med 1980;302:1011-2.
Vellacott KD, Roe AM, Mortensen NJ. An evaluation of a direct access flexible fibreoptic sigmoidoscopy service. Ann R Coll Surg Engl 1987;69:149-52.
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Mathew J, Shankar P, Aldean IM. Audit on flexible sigmoidoscopy for rectal bleeding in a district general hospital: Are we over-loading the resources? Postgrad Med J 2004;80:38-40.
Read TE, Read JD, Butterly LF. Importance of adenomas 5 mm or less in diameter that are detected by sigmoidoscopy. N Engl J Med 1997;336:8-12.
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[Figure 1], [Figure 2], [Figure 3]
Nair SV
Ramachandran TM
Geevarghese PP
Kumar N S
Pakalomattom SJ
Rectosigmoid cancers
rigid sigmoidoscopy