The Distribution Of Cosmological γ\gamma-ray Bursts

We compare the burst distribution of the new (2B) BATSE catalogue to a cosmological distribution. The observed distribution agrees well with a cosmological one, however, it is insensitive to cosmological parameters such as \O and $\Lambda$. The bursts are not necessarily standard candles and their luminosity can vary by up to a factor of ten. The maximal red shift, \zm, of bursts longer than 2 sec is $2.1^{+1.}_{-.7}$ (assuming no evolution). The present data is insufficient to determine maximal red shift, \zm, of bursts shorter than 2 sec.Comment: 9 pages, uuencoded file, 4 figures included, can also be obtained from ftp://shemesh.fiz.huji.ac.il or at (Accepted for publication in the Astrophysical Journal Letters

Class Size and the Regression Discontinuity Design: The Case of Public Schools

Using a rich individual-level dataset on secondary public schools in Israel, we find strong evidence for discontinuities in the relationship between enrollment and household characteristics at cutoff points induced by a maximum class size rule. Our findings extend existing work that documents such discontinuities only among private schools (Urquiola and Verhoogen, 2009). These discontinuities violate the assumptions underlying the regression discontinuity design, which are crucial for identification. Consequently, IV estimates of class size effects are likely to be seriously biased. Potential manipulation of the treatment assignment rule by public schools warrants caution in applying a regression discontinuity design to estimate class size effects and indicates that institutional context is crucial for its scope of applicability.regression discontinuity design, class size

A Simultaneous Spectral Invariant Analysis of the GRB Count Distribution and Time Dilation

The analysis of the BATSE's count distribution within cosmological models suffers from observational uncertainties due to the variability of the bursts' spectra: when BATSE observes bursts from different redshifts at a fixed energy band it detects photons from different energy bands at the source. This adds a spectral dependence to the count distribution $N(C)$. Similarly variation of the duration as a function of energy at the source complicates the time dilation analysis. We describe here a new statistical formalism that performs the required ``blue shifting" of the count number and the burst duration in a statistical manner. This formalism allows us to perform a combined best fit (maximal likelihood) to the count distribution, $N(C)$, and the duration distribution simultaneously. The outcome of this analysis is a single best fit value for the redshift of the observed bursts.Comment: 5 pages, Latex using aps macros including one figure. Also available at ftp://shemesh.fiz.huji.ac.il or at http://shemesh.fiz.huji.ac.il/papers/CP_huntsmev.ps To appear in Gamma-Ray Bursts, third workshop, Huntsville Oct-199

Radiative Efficiencies of Continuously Powered Blast Waves

We use general arguments to show that a continuously powered radiative blast wave can behave self similarly if the energy injection and radiation mechanisms are self similar. In that case, the power-law indices of the blast wave evolution are set by only one of the two constituent physical mechanisms. If the luminosity of the energy source drops fast enough, the radiation mechanisms set the power-law indices, otherwise, they are set by the behavior of the energy source itself. We obtain self similar solutions for the Newtonian and the ultra-relativistic limits. Both limits behave self similarly if we assume that the central source supplies energy in the form of a hot wind, and that the radiative mechanism is the semi-radiative mechanism of Cohen, Piran & Sari (1998). We calculate the instantaneous radiative efficiencies for both limits and find that a relativistic blast wave has a higher efficiency than a Newtonian one. The instantaneous radiative efficiency depends strongly on the hydrodynamics and cannot be approximated by an estimate of local microscopic radiative efficiencies, since a fraction of the injected energy is deposited in shocked matter. These solutions can be used to calculate Gamma Ray Bursts afterglows, for cases in which the energy is not supplied instantaneously.Comment: 28 LaTeX pages, including 9 figures and 3 table

The Implications of Direct Red-Shift Measurement of γ\gamma-ray Bursts

The recent discoveries of X-ray and optical counterparts for GRBs, and a possible discovery of a host galaxy, implies that a direct measurement of the red-shift of some GRBs host galaxies is eminent. We discuss the implications of such measurements. They could enable us to determine the GRBs luminosity distribution, the variation of the rate of GRBs with cosmic time, and even, under favorable circumstances, to estimate $\Omega$. Using GRB970508 alone, and assuming standard candles, we constrain the intrinsic GRB evolution to $\rho(z)=(1+z)^{-0.5\pm0.7}$.Comment: 12 Latex pages plus one postscript figur

Regulation of the proteostasis network by the neuronal system

The protein homeostasis (proteostasis) network is a nexus of molecular mechanisms that act in concert to maintain the integrity of the proteome and ensure proper cellular and organismal functionality. Early in life the proteostasis network efficiently preserves the functionality of the proteome, however, as the organism ages, or due to mutations or environmental insults, subsets of inherently unstable proteins misfold and form insoluble aggregates that accrue within the cell. These aberrant protein aggregates jeopardize cellular viability and, in some cases, underlie the development of devastating illnesses. Hence, the accumulation of protein aggregates activates different nodes of the proteostasis network that refold aberrantly folded polypeptides, or direct them for degradation. The proteostasis network apparently functions within the cell, however, a myriad of studies indicate that this nexus of mechanisms is regulated at the organismal level by signaling pathways. It was also discovered that the proteostasis network differentially responds to dissimilar proteotoxic insults by tailoring its response according to the specific challenge that cells encounter. In this mini-review, we delineate the proteostasis-regulating neuronal mechanisms, describe the indications that the proteostasis network differentially responds to distinct proteotoxic challenges, and highlight possible future clinical prospects of these insights

Weakly-Supervised Surgical Phase Recognition

A key element of computer-assisted surgery systems is phase recognition of surgical videos. Existing phase recognition algorithms require frame-wise annotation of a large number of videos, which is time and money consuming. In this work we join concepts of graph segmentation with self-supervised learning to derive a random-walk solution for per-frame phase prediction. Furthermore, we utilize within our method two forms of weak supervision: sparse timestamps or few-shot learning. The proposed algorithm enjoys low complexity and can operate in lowdata regimes. We validate our method by running experiments with the public Cholec80 dataset of laparoscopic cholecystectomy videos, demonstrating promising performance in multiple setups

Thermal Stability of Thin Au Films Deposited on Salt Whiskers

Thin metal films deposited on patterned or rough substrates play an increasing role in microelectronics, sensing, catalysis, and other areas of nanotechnology. However, the thermal stability and solid state dewetting of thin metal films with complex three-dimensional architecture is still poorly understood. In this work we employed a model system of nanocrystalline Au thin films deposited on prismatic single crystalline KCl whiskers to study the solid state dewetting of thin films in a three-dimensional setting. The arrays of KCl whiskers were grown on porous substrates under well-defined humidity and temperature conditions. Single crystalline prismatic KCl whiskers with a very high aspect ratio, [001] axis and {100} side facets were obtained. The whiskers were coated with thin conformal Au films of 20-30 nm in thickness. The annealing of these core-shell whiskers at the temperature of 350oC resulted in solid state dewetting of the Au film, with the dewetting processes occurring much faster along the whisker edges than on the side facets. The orientation relationships between Au and KCl were determined by employing similarly prepared thin Au films deposited on the flat KCl (100) substrates. Inspired by our experimental results, we developed a numerical model describing the curvature-gradient driven and surface diffusion-controlled growth of a hole in the thin film deposited on a curved substrate. The model predicted the growth of anisotropic elliptical holes elongated along the whisker axis. We discuss the experimental results in terms of the proposed model, indicating the importance of the change in orientation relationship between the Au grains and KCl whisker along the whisker edges

Thermal Stability of Thin Au Films Deposited on Salt Whiskers

Thin metal films deposited on patterned or rough substrates play an increasing role in microelectronics, sensing, catalysis, and other areas of nanotechnology. However, the thermal stability and solid state dewetting of thin metal films with complex three-dimensional architecture is still poorly understood. In this work we employed a model system of nanocrystalline Au thin films deposited on prismatic single crystalline KCl whiskers to study the solid state dewetting of thin films in a three-dimensional setting. The arrays of KCl whiskers were grown on porous substrates under well-defined humidity and temperature conditions. Single crystalline prismatic KCl whiskers with a very high aspect ratio, [001] axis and {100} side facets were obtained. The whiskers were coated with thin conformal Au films of 20-30 nm in thickness. The annealing of these core-shell whiskers at the temperature of 350oC resulted in solid state dewetting of the Au film, with the dewetting processes occurring much faster along the whisker edges than on the side facets. The orientation relationships between Au and KCl were determined by employing similarly prepared thin Au films deposited on the flat KCl (100) substrates. Inspired by our experimental results, we developed a numerical model describing the curvature-gradient driven and surface diffusion-controlled growth of a hole in the thin film deposited on a curved substrate. The model predicted the growth of anisotropic elliptical holes elongated along the whisker axis. We discuss the experimental results in terms of the proposed model, indicating the importance of the change in orientation relationship between the Au grains and KCl whisker along the whisker edges