4,876 research outputs found
S-DIMM+ height characterization of day-time seeing using solar granulation
To evaluate site quality and to develop multi-conjugative adaptive optics
systems for future large solar telescopes, characterization of contributions to
seeing from heights up to at least 12 km above the telescope is needed. We
describe a method for evaluating contributions to seeing from different layers
along the line-of-sight to the Sun. The method is based on Shack Hartmann
wavefront sensor data recorded over a large field-of-view with solar
granulation and uses only measurements of differential image displacements from
individual exposures, such that the measurements are not degraded by residual
tip-tilt errors. We conclude that the proposed method allows good measurements
when Fried's parameter r_0 is larger than about 7.5 cm for the ground layer and
that these measurements should provide valuable information for site selection
and multi-conjugate development for the future European Solar Telescope. A
major limitation is the large field of view presently used for wavefront
sensing, leading to uncomfortably large uncertainties in r_0 at 30 km distance.Comment: Accepted by AA 22/01/2010 (12 pages, 11 figures
Exploring the temporally resolved electron density evolution in EUV induced plasmas
We measured for the first time the electron density in an Extreme
Ultra-Violet induced plasma. This is achieved in a low-pressure argon plasma by
using a method called microwave cavity resonance spectroscopy. The measured
electron density just after the EUV pulse is m. This
is in good agreement with a theoretical prediction from photo ionization, which
yields a density of m. After the EUV pulse the density
slightly increase due to electron impact ionization. The plasma (i.e. electron
density) decays in tens of microseconds.Comment: 3 pages, 4 figure
Exploring the electron density in plasmas induced by extreme ultraviolet radiation in argon
The new generation of lithography tools use high energy EUV radiation which
ionizes the present background gas due to photoionization. To predict and
understand the long term impact on the highly delicate mirrors It is essential
to characterize these kinds of EUV-induced plasmas. We measured the electron
density evolution in argon gas during and just after irradiation by a short
pulse of EUV light at 13.5 nm by applying microwave cavity resonance
spectroscopy. Dependencies on EUV pulse energy and gas pressure have been
explored over a range relevant for industrial applications.
Our experimental results show that the maximum reached electron density
depends linearly on pulse energy. A quadratic dependence - caused by
photoionization and subsequent electron impact ionization by free electrons -
is found from experiments where the gas pressure is varied. This is
demonstrated by our theoretical estimates presented in this manuscript as well.Comment: submitted to J. Phys. D. 16 pages, 8 figure
Site tests for CLEAR by solar scintillometry
We briefly describe the ng ing site survey for the NSO CLEAR project which
aims to put a large-aperture solar telescope at a superior location.The initial results
indicate that lake sites are far better than mountain sites,at least in the US
The evolutionary significance of developmental plasticity in the communication system of Neoconocephalus triops (Orthoptera: tettigoniidae)
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Thesis advisor: Dr. Johannes Schul.Vita.Ph.D. University of Missouri--Columbia 2008.The katydid Neoconocephalus triops is a tropical species that extended its distribution range to North America. In North America, males display developmental plasticity in mating calls between reproductive generations: the winter call differs from the summer call in both double-pulse rate and call structure. In the tropics, males express only the summer call. We found that tropical N. triops have the capacity to express the winter call, but tropical conditions do not induce its expression. Female N. triops have strong preferences for double-pulse rate, but are not selective for call structure, i.e. females of most populations are attracted to both the summer and winter call structure. The temperature dependency of female preference for double-pulse rate in the Florida population was significantly steeper than those of tropical populations or other Neoconocephalus species. This steeper temperature dependency of female preference resulted in an overlap of the preference with the summer call at high temperatures, and the winter call at low temperatures, facilitating communication in both seasons. Thus, female preference evolved in response to male call plasticity in the Florida population of N. triops.Includes bibliographical reference
4 Advanced Comprehension Strategies to use with Adolescent Readers
Reading comprehension involves an intricate interaction between the reader and attention to the text. Teachers should employ reading strategies to increase comprehension skills required by adolescent students to address the increase in use of informational text and text complexity as stipulated in the newly adopted Common Core State Standards (CCSS). Four advanced reading comprehension strategies that teachers can use to help their students navigate the increase in higher level comprehension skills stipulated by the CCSS are presented here. Also, presented are a justification for why to use the strategy, information on how to use the strategy, research that supports the strategy, an example, and helpful websites to reference for templates and further information. The last strategy of the four can be amended and used as an evaluation tool for any strategy
Numerical Simulations of Shock Wave-Driven Jets
We present the results of numerical simulations of shock wave-driven jets in
the solar atmosphere. The dependence of observable quantities like maximum
velocity and deceleration on parameters such as the period and amplitude of
initial disturbances and the inclination of the magnetic field is investigated.
Our simulations show excellent agreement with observations, and shed new light
on the correlation between velocity and deceleration and on the regional
differences found in observations.Comment: 7 pages, 11 figures, submitted to Ap
Laser Guide Stars for Extremely Large Telescopes: Efficient Shack-Hartmann Wavefront Sensor Design using Weighted center-of-gravity algorithm
Over the last few years increasing consideration has been given to the study
of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by
the atmosphere in optical and near-infrared astronomical observations from the
ground. A possible method for the generation of a LGS is the excitation of the
Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since
the Sodium layer is approximately 10 km thick, the artificial reference source
looks elongated, especially when observed from the edge of a large aperture.
The spot elongation strongly limits the performance of the most common
wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront
sensor, for instance, decreases proportionally to the elongation (in a photon
noise dominated regime). To compensate for this effect a straightforward
solution is to increase the laser power, i.e. to increase the number of
detected photons per subaperture. The scope of the work presented in this paper
is twofold: an analysis of the performance of the Weighted Center of Gravity
algorithm for centroiding with elongated spots and the determination of the
required number of photons to achieve a certain average wavefront error over
the telescope aperture.Comment: 10 pages, 14 figure
Males and females evolve riskier traits in populations with eavesdropping parasitoids
Predation and/or parasitism often limits the evolution of conspicuous male traits and female preferences because conspicuous traits can attract predators or parasites and it is costly for females to associate with males that attract predators or parasites. As a result, males and females in high-risk populations are expected to evolve safer mating behaviors compared to individuals from low-risk populations. We tested this antagonistic selection hypothesis in the field cricket Gryllus lineaticeps. Males produce chirped songs, and both female crickets and the eavesdropping parasitoid fly Ormia ochracea prefer faster chirp rates. The flies attack the field crickets late in the breeding season and parasitized crickets die. We used a common garden rearing design to test for evolved differences in songs and preferences between high- and low-risk populations. In contrast to predictions of the antagonistic selection hypothesis, males from high-risk populations produced faster (riskier) chirp rates and females preferred faster chirps. We suggest that late-season parasitism selects for increased investment in reproductive traits to maximize reproduction before the advent of parasitoid activity (“late-season parasitism hypothesis”), which would at least explain riskier female preferences and potentially riskier male songs in the high-risk populations. Predation and parasitism may thus have diverse and unexpected effects on the evolution of reproductive behavior, depending upon the temporal pattern of predator- or parasite-induced mortality.
Significance statement
Mating signals are typically conspicuous and not only attract partners but also predators and parasites. Even the silent mating partner may experience predation or parasitism by associating with the signaler. Under these circumstances, it is commonly assumed that natural and sexual selection act in opposite directions, effectively limiting the evolution of conspicuous signals and preferences. We demonstrate that an eavesdropping parasitic fly caused the evolution of preferences, and potentially songs, in a field cricket in the opposite, more conspicuous, direction than predicted by antagonistic selection. We argue that the temporal pattern of parasitism in relation to the reproductive season likely causes this unexpected evolutionary pattern. We propose the late-season parasitism hypothesis as an alternative to the antagonistic selection hypothesis, which might better explain more conspicuous mating trait values in other species that experience seasonal predation or parasitism
Males and females evolve riskier traits in populations with eavesdropping parasitoids
Predation and/or parasitism often limits the evolution of conspicuous male traits and female preferences because conspicuous traits can attract predators or parasites and it is costly for females to associate with males that attract predators or parasites. As a result, males and females in high-risk populations are expected to evolve safer mating behaviors compared to individuals from low-risk populations. We tested this antagonistic selection hypothesis in the field cricket Gryllus lineaticeps. Males produce chirped songs, and both female crickets and the eavesdropping parasitoid fly Ormia ochracea prefer faster chirp rates. The flies attack the field crickets late in the breeding season and parasitized crickets die. We used a common garden rearing design to test for evolved differences in songs and preferences between high- and low-risk populations. In contrast to predictions of the antagonistic selection hypothesis, males from high-risk populations produced faster (riskier) chirp rates and females preferred faster chirps. We suggest that late-season parasitism selects for increased investment in reproductive traits to maximize reproduction before the advent of parasitoid activity (“late-season parasitism hypothesis”), which would at least explain riskier female preferences and potentially riskier male songs in the high-risk populations. Predation and parasitism may thus have diverse and unexpected effects on the evolution of reproductive behavior, depending upon the temporal pattern of predator- or parasite-induced mortality.
Significance statement
Mating signals are typically conspicuous and not only attract partners but also predators and parasites. Even the silent mating partner may experience predation or parasitism by associating with the signaler. Under these circumstances, it is commonly assumed that natural and sexual selection act in opposite directions, effectively limiting the evolution of conspicuous signals and preferences. We demonstrate that an eavesdropping parasitic fly caused the evolution of preferences, and potentially songs, in a field cricket in the opposite, more conspicuous, direction than predicted by antagonistic selection. We argue that the temporal pattern of parasitism in relation to the reproductive season likely causes this unexpected evolutionary pattern. We propose the late-season parasitism hypothesis as an alternative to the antagonistic selection hypothesis, which might better explain more conspicuous mating trait values in other species that experience seasonal predation or parasitism
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