262 research outputs found
A PULSEIRA AZUL DO FILÓLOGO: UMA LEITURA DE NOTA DE RODAPÉ, DE JOSEPH CEDAR
No full textO presente trabalho traz a leitura do filme Nota de Rodapé, de Joseph Cedar a partir dos conceitos de memória cultural, fama e lixo apresentados por Aleida Assmann em seu livro Espaços de Recordação. O filme é a narrativa da tensão entre dois pesquisadores do Talmude, Eliezer Shkolnik e Uriel Shkolnik que são, também, pai e filho. O ápice do enredo é quando o Shkolnik pai recebe uma ligação informando-o que foi escolhido para receber o prêmio Israel. Porém, a ligação foi um engano, visto que o verdadeiro ganhador foi seu filho. Uriel se esforça para manter o prêmio destinado ao pai. O objetivo deste trabalho é apontar, nas cenas, que o move Uriel a manter a mentira é o desejo der qu fazer com que o pai seja valorizado pela coletividade. Com isso, ele acredita que alcançará seu próprio reconhecimento no espaço de recordação familiar. A conclusão foi que Eliezer Shkolnik não consegue, de fato, uma entrada para a memória cultural, mas alcança a fama, visto que a premiação não é pautada em uma verdade e, para além disso, a cena final do filme é uma encenação do recebimento do prêmio, em uma ilustração do conceito de fama apresentado por Aleida Assmann
A search for star-planet interactions in the υ Andromedae system at X-ray and optical wavelengths
No full textContext. Close-in, giant planets are expected to influence their host stars via tidal or magnetic interaction. But are these effects in X-rays strong enough in suitable targets known so far to be observed with today's instrumentation? Aims: The υ And system, an F8V star with a Hot Jupiter, was observed to undergo cyclic changes in chromospheric activity indicators with its innermost planet's period. We aim to investigate the stellar chromospheric and coronal activity over several months. Methods: We therefore monitored the star in X-rays as well as at optical wavelengths to test coronal and chromospheric activity indicators for planet-induced variability, making use of the Chandra X-ray Observatory as well as the echelle spectrographs FOCES and HRS at Calar Alto (Spain) and the Hobby-Eberly Telescope (Texas, US). Results: The stellar activity level is low, as seen both in X-rays as in Ca ii line fluxes; the chromospheric data show variability with the stellar rotation period. We do not find activity variations in X-rays or in the optical that can be traced back to the planet. Conclusions: Gaining observational evidence of star-planet interactions in X-rays remains challenging
HAZMAT. IX. An Analysis of the UV and X-Ray Evolution of Low-Mass Stars in the Era of Gaia
No full textLow mass stars ( M) are some of the best candidates for
hosting planets with detectable life because of these stars' long lifetimes and
relative planet to star mass and radius ratios. An important aspect of these
stars to consider is the amount of ultraviolet (UV) and X-ray radiation
incident on planets in the habitable zones due to the ability of UV and X-ray
radiation to alter the chemistry and evolution of planetary atmospheres. In
this work, we build on the results of the HAZMAT I (Shkolnik & Barman 2014) and
HAZMAT III (Schneider & Shkolnik 2018) M star studies to determine the
intrinsic UV and X-ray flux evolution with age for M stars using Gaia
parallactic distances. We then compare these results to the intrinsic fluxes of
K stars adapted from HAZMAT V (Richey-Yowell et al. 2019). We find that
although the intrinsic M star UV flux is 10 to 100 times lower than that of K
stars, the UV fluxes in their respective habitable zone are similar. However,
the habitable zone X-ray flux evolutions are slightly more distinguishable with
a factor of 3 -- 15 times larger X-ray flux for late-M stars than for K stars.
These results suggest that there may not be a K dwarf advantage compared to M
stars in the UV, but one may still exist in the X-ray.Comment: 16 pages, 14 figure
Are you on the right track?: The effect of educational tracks on student achievement in upper-secondary education in Hungary
No full textThe paper attempts to identify causal effects of being enrolled in different educational tracks on student achievement in upper-secondary education in Hungary. Rejected and admitted students are compared who applied to the same school and performed similarly in the previous grade. Average treatment effects on the treated are estimated with a matching method. Results indicate that higher track significantly raises student achievement. Beside the effect of tracks, the schools preferred by students within the tracks also provide better educational quality. Comparing the effects of tracks and differences within the tracks reveals that the advantage of the academic track does not differ from that of better schools in general. At the same time, the vocational track incurs substantial losses that are in part specific to that track
A note on increasing lamb production of fat-tailed Awassi and German Mutton Merino sheep grazing in a semi-arid area
No full textThe native fat-tailed Awassi and the imported German Mutton Merino (GMM) sheep are well adapted to semi-arid conditions (Degen, 1977; Degen and Shkolnik, 1978). This enables these sheep to graze large areas of the Negev Desert in Israel that is marginal for farming. However, under extensive conditions both these sheep breeds yield low lamb crops producing fewer than 1·0 lamb per ewe per year.</jats:p
The Quadratic Optimization Bias Of Large Covariance Matrices
No full textWe describe a puzzle involving the interactions between an optimization of a multivariate quadratic function and a plug-in estimator of a spiked covariance matrix. When the largest eigenvalues (i.e., the spikes) diverge with the dimension, the gap between the true and the out-of-sample optima typically also diverges. We show how to fine-tune the plug-in estimator in a precise way to avoid this outcome. Central to our description is a quadratic optimization bias function, the roots of which determine this fine-tuning property. We derive an estimator of this root from a finite number of observations of a high dimensional vector. This leads to a new covariance estimator designed specifically for applications involving quadratic optimization. Our theoretical results have further implications for improving low dimensional representations of data, and principal component analysis in particular.40 pages, 6 figures, 5 table
Signatures of Star-planet Interactions
No full textPlanets interact with their host stars through gravity, radiation and magnetic fields, and for those giant planets that orbit their stars within ~10 stellar radii (~0.1 AU for a sun-like star), star-planet interactions (SPI) are observable with a wide variety of photometric, spectroscopic and spectropolarimetric studies. At such close distances, the planet orbits within the sub-alfvenic radius of the star in which the transfer of energy and angular momentum between the two bodies is particularly efficient. The magnetic interactions appear as enhanced stellar activity modulated by the planet as it orbits the star rather than only by stellar rotation. Such observations allowed for the determination of the magnetic field strengths on the surfaces of four hot Jupiters. These vary between 20 G and 120 G, in line with scaling laws that connect the strength of the magnetic field to the internal heat flow in giant planets. These field strengths are informative for the study of the internal dynamics and atmospheric evolution of exoplanets. The nature of magnetic SPI is modeled to be strongly affected by both the stellar and planetary magnetic fields, possibly influencing the magnetic activity of both, as well as affecting the particle environment, the migration of the planet, and even the rotational evolution of the star. As phase-resolved observational techniques are applied to a large statistical sample of hot Jupiter systems, extensions to other tightly orbiting stellar systems, such as smaller planets close to M dwarfs become possible. In these systems, star-planet separations of tens of stellar radii begin to coincide with the radiative habitable zone where planetary magnetic fields are likely a necessary condition for surface habitability.Chapter published in the 2nd Edition of the Handbook of Exoplanets (2024, Springer
Current-density vs electric-field intensity characteristics of polypropylene filled with natural clay as nanomaterial
No full textIn this study, current-density vs electric-field intensity characteristics of polypropylene-based nanocomposite films are presented with concentrations of 0%, 2% and 6% nanosize natural clay by weight. Each nanocomposite sample is subjected to a 60-Hz, sinusoidal voltage waveform. During the experiments, applied rms voltage and current are recorded as the voltage increases across the test sample. The test was repeated with five samples with the same nanofiller content. The current-density vs electric-field intensity characteristics indicate a nonlinear behavior for each sample under consideration with some degree of saturation. From these characteristics, it was observed that the inception of saturation occurred at higher electric field intensities for the nanocomposites filled with natural clay than the unfilled polypropylene. The relative permittivity of of each sample was almost constant up to a critical electric field at which the saturation starts. Above that critical electric field, relative permittivity dramatically dropped
Electrical breakdown of polypropylene filled with natural clay as nanomaterial
No full textThis study presents the breakdown behavior of polypropylene filled with a various concentrations of nano-size natural clay. The concentrations of natural clay by weight were 0 %, 2 %and 6 % in polypropylene. For different concentrations of natural clay each specimen was subjected to a sinusoidal voltage waveform at power frequency with a certain ramp rate to a level where a breakdown occurred. The rms voltage at the breakdown was considered as the breakdown voltage of the sample. The mean dielectric strength improved about 3.5 % for the nanocomposite with 2 % of natural clay concentration in the host polypropylene. However, the improvement on the mean dielectric strength of the nanocomposite with 6 %concentration of natural clay appeared to be little more than 1 % when compared with 2 % concentration of natural clay in the host. This implies that there exits an optimum concentration of nanosize natural clay in polypropylene. Also observed was the increase of the dielectric strength of the materials with the increase of the ramp rate of the applied voltage
Sample-based motion planning in high-dimensional and differentially-constrained systems
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 115-124).State of the art sample-based path planning algorithms, such as the Rapidly-exploring Random Tree (RRT), have proven to be effective in path planning for systems subject to complex kinematic and geometric constraints. The performance of these algorithms, however, degrade as the dimension of the system increases. Furthermore, sample-based planners rely on distance metrics which do not work well when the system has differential constraints. Such constraints are particularly challenging in systems with non-holonomic and underactuated dynamics. This thesis develops two intelligent sampling strategies to help guide the search process. To reduce sensitivity to dimension, sampling can be done in a low-dimensional task space rather than in the high-dimensional state space. Altering the sampling strategy in this way creates a Voronoi Bias in task space, which helps to guide the search, while the RRT continues to verify trajectory feasibility in the full state space. Fast path planning is demonstrated using this approach on a 1500-link manipulator. To enable task-space biasing for underactuated systems, a hierarchical task space controller is developed by utilizing partial feedback linearization. Another sampling strategy is also presented, where the local reachability of the tree is approximated, and used to bias the search, for systems subject to differential constraints. Reachability guidance is shown to improve search performance of the RRT by an order of magnitude when planning on a pendulum and non-holonomic car. The ideas of task-space biasing and reachability guidance are then combined for demonstration of a motion planning algorithm implemented on LittleDog, a quadruped robot. The motion planning algorithm successfully planned bounding trajectories over extremely rough terrain.by Alexander C. Shkolnik.Ph.D
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