Three-dimensional carrier-dynamics simulation of terahertz emission from photoconductive switches

A semi-classical Monte Carlo model for studying three-dimensional carrier dynamics in photoconductive switches is presented. The model was used to simulate the process of photoexcitation in GaAs-based photoconductive antennas illuminated with pulses typical of mode-locked Ti:Sapphire lasers. We analyzed the power and frequency bandwidth of THz radiation emitted from these devices as a function of bias voltage, pump pulse duration and pump pulse location. We show that the mechanisms limiting the THz power emitted from photoconductive switches fall into two regimes: when illuminated with short duration (<40 fs) laser pulses the energy distribution of the Gaussian pulses constrains the emitted power, while for long (>40 fs) pulses, screening is the primary power-limiting mechanism. A discussion of the dynamics of bias field screening in the gap region is presented. The emitted terahertz power was found to be enhanced when the exciting laser pulse was in close proximity to the anode of the photoconductive emitter, in agreement with experimental results. We show that this enhancement arises from the electric field distribution within the emitter combined with a difference in the mobilities of electrons and holes.Comment: 7 pages, 7 figure

A Liouville hyperbolic souvlaki

We construct a transient bounded-degree graph no transient subgraph of which embeds in any surface of finite genus. Moreover, we construct a transient, Liouville, bounded-degree, Gromov– hyperbolic graph with trivial hyperbolic boundary that has no transient subtree. This answers a question of Benjamini. This graph also yields a (further) counterexample to a conjecture of Benjamini and Schramm. In an appendix by G´abor Pete and Gourab Ray, our construction is extended to yield a unimodular graph with the above properties

The Kinematics and Metallicity of the M31 Globular Cluster System

With the ultimate aim of distinguishing between various models describing the formation of galaxy halos (e.g. radial or multi-phase collapse, random mergers), we have completed a spectroscopic study of the globular cluster system of M31. We present the results of deep, intermediate-resolution, fibre-optic spectroscopy of several hundred of the M31 globular clusters using the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel Telescope in La Palma, Canary Islands. These observations have yielded precise radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200 members of the M31 globular cluster population out to a radius of 1.5 degrees from the galaxy center. Many of these clusters have no previous published radial velocity or [Fe/H] estimates, and the remainder typically represent significant improvements over earlier determinations. We present analyses of the spatial, kinematic and metal abundance properties of the M31 globular clusters. We find that the abundance distribution of the cluster system is consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5. The metal-rich clusters demonstrate a centrally concentrated spatial distribution with a high rotation amplitude, although this population does not appear significantly flattened and is consistent with a bulge population. The metal-poor clusters tend to be less spatially concentrated and are also found to have a strong rotation signature.Comment: 33 pages, 20 figure

Brachial Artery Constriction during Brachial Artery Reactivity Testing Predicts Major Adverse Clinical Outcomes in Women with Suspected Myocardial Ischemia: Results from the NHLBI-Sponsored Women's Ischemia Syndrome Evaluation (WISE) Study

Background:Limited brachial artery (BA) flow-mediated dilation during brachial artery reactivity testing (BART) has been linked to increased cardiovascular risk. We report on the phenomenon of BA constriction (BAC) following hyperemia.Objectives:To determine whether BAC predicts adverse CV outcomes and/or mortality in the women's ischemic Syndrome Evaluation Study (WISE). Further, as a secondary objective we sought to determine the risk factors associated with BAC.Methods:We performed BART on 377 women with chest pain referred for coronary angiography and followed for a median of 9.5 years. Forearm ischemia was induced with 4 minutes occlusion by a cuff placed distal to the BA and inflated to 40mm Hg > systolic pressure. BAC was defined as >4.8% artery constriction following release of the cuff. The main outcome was major adverse events (MACE) including all-cause mortality, non-fatal MI, non-fatal stroke, or hospitalization for heart failure.Results:BA diameter change ranged from -20.6% to +44.9%, and 41 (11%) women experienced BAC. Obstructive CAD and traditional CAD risk factors were not predictive of BAC. Overall, 39% of women with BAC experienced MACE vs. 22% without BAC (p=0.004). In multivariate Cox proportional hazards regression, BAC was a significant independent predictor of MACE (p=0.018) when adjusting for obstructive CAD and traditional risk factors.Conclusions:BAC predicts almost double the risk for major adverse events compared to patients without BAC. This risk was not accounted for by CAD or traditional risk factors. The novel risk marker of BAC requires further investigation in women. © 2013 Sedlak et al

Age- and sex-specific response to population density and sex ratio

Both population density and sex ratio shape competition for mates, resources and mating costs. Thus they may critically affect the intensity of sexual selection in the populations. Susceptibility to inter- and intrasexual competition, which changes with age in a large number of species, may additionally influence population response to these demographic factors. In this study, we monitored 16 seminatural populations of common lizards (Lacerta vivipara) to determine whether the reproductive output varied with male and female densities as a function of the individual sex and age. Our results suggest that the intensity of sexual selection was weaker in male-biased populations, supporting new theoretical models. In populations with a male-biased sex ratio, reproductive success was more equally distributed between males and, unlike female-biased populations, the choosiest females (middle-aged) did not obtain sires of higher quality than low-performance females. Our results also suggest that age may influence the intensity of sexual conflict. Middle-aged females (the class with the best performance) produced offspring with a lower body condition in male-biased populations, suggesting that they may be the preferred target of male harassment. By contrast, a male-biased sex ratio appeared to be beneficial for low-quality females, allowing these females to obtain higher quality sires and to produce offspring with a better body condition. These age- and sex-dependent responses to population density and sex ratio have important implications for population ecology and sexual selectio

Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System

We present a kinematic analysis of the globular cluster(GC) system in M31. Using the photometric and spectroscopic database of 504 GCs, we have investigated the kinematics of the M31 GC system. We find that the all GC system shows strong rotation, with rotation amplitude of v_rot~190km/s, and that a weak rotation persists even for the outermost samples at |Y|>5kpc. The rotation-corrected velocity dispersion for the GC system is estimated to be sigma_{p,r}~130km/s, and it increases from sigma_{p,r}~120km/s at |Y|<1kpc to sigma_{p,r}~150km/s at |Y|>5kpc. These results are very similar to those for the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. We have identified 50 "friendless" GCs, and they appear to rotate around the major axis of M31. For the subsamples of metal-poor and metal-rich GCs, we have found that the metal-rich GCs are more centrally concentrated than the metal-poor GCs, and both subsamples show strong rotation. For the subsamples of bright and faint GCs, it is found that the rotation for the faint GCs is stronger than that for the bright GCs. We have identified 56 GCs and GC candidates with X-ray detection. It is found that the majority of X-ray emitting GCs follow the disk rotation, and that the redder, more metal-rich, and brighter GCs are more likely to be detected as X-ray emitting GCs. We have derived a rotation curve of M31 using the GCs at |Y|<0.6kpc. We have estimated the dynamical mass of M31 using `Projected Mass Estimator(PME)' and `Tracer Mass Estimator(TME)'. We finally discuss the implication of these results and compare the kinematics of GCs with that of planetary nebulae in M31.Comment: 62 pages, 26 figues, Accepted by Ap

A selfconsistent theory of current-induced switching of magnetization

A selfconsistent theory of the current-induced switching of magnetization using nonequilibrium Keldysh formalism is developed for a junction of two ferromagnets separated by a nonmagnetic spacer. It is shown that the spin-transfer torques responsible for current-induced switching of magnetization can be calculated from first principles in a steady state when the magnetization of the switching magnet is stationary. The spin-transfer torque is expressed in terms of one-electron surface Green functions for the junction cut into two independent parts by a cleavage plane immediately to the left and right of the switching magnet. The surface Green functions are calculated using a tight-binding Hamiltonian with parameters determined from a fit to an {\it ab initio} band structure.This treatment yields the spin transfer torques taking into account rigorously contributions from all the parts of the junction. To calculate the hysteresis loops of resistance versus current, and hence to determine the critical current for switching, the microscopically calculated spin-transfer torques are used as an input into the phenomenological Landau-Lifshitz equation with Gilbert damping. The present calculations for Co/Cu/Co(111) show that the critical current for switching is $\approx 10^7A/cm^2$, which is in good agreement with experiment.Comment: 23 pages, 16 figure

Genetic Assimilation and Canalisation in the Baldwin Effect

The Baldwin Effect indicates that individually learned behaviours acquired during an organism’s lifetime can influence the evolutionary path taken by a population, without any direct Lamarckian transfer of traits from phenotype to genotype. Several computational studies modelling this effect have included complications that restrict its applicability. Here we present a simplified model that is used to reveal the essential mechanisms and highlight several conceptual issues that have not been clearly defined in prior literature. In particular, we suggest that canalisation and genetic assimilation, often conflated in previous studies, are separate concepts and the former is actually not required for non-heritable phenotypic variation to guide genetic variation. Additionally, learning, often considered to be essential for the Baldwin Effect, can be replaced with a more general phenotypic plasticity model. These simplifications potentially permit the Baldwin Effect to operate in much more general circumstances

Conflict over multiple-partner mating between males and females of the polygynandrous common lizards.

The optimal number of mate partners for females rarely coincides with that for males, leading to a potential sexual conflict over multiple-partner mating. This suggests that the population sex ratio may affect multiple-partner mating and thus multiple paternity. We investigate the relationship between multiple paternity and the population sex ratio in the polygynandrous common lizard (Lacerta vivipara). In six populations the adult sex ratio was biased toward males, and in another six populations the adult sex ratio was biased toward females, the latter corresponding to the average adult sex ratio encountered in natural populations. In males the frequency and the degree of polygyny were lower in male-biased populations, as expected if competition among males determines polygyny. In females the frequency of polyandry was not different between treatments, and polyandrous females produced larger clutches, suggesting that polyandry might be adaptive. However, in male-biased populations females suffered from reduced reproductive success compared to female-biased populations, and the number of mate partners increased with female body size in polyandrous females. Polyandrous females of male-biased populations showed disproportionately more mating scars, indicating that polyandrous females of male-biased populations had more interactions with males and suggesting that the degree of multiple paternity is controlled by male sexual harassment. Our results thus imply that polyandry may be hierarchically controlled, with females controlling when to mate with multiple partners and male sexual harassment being a proximate determinant of the degree of multiple paternity. The results are also consistent with a sexual conflict in which male behaviors are harmful to females

Last Glacial Maximum and early deglaciation in the Stura Valley, southwestern European Alps

Acknowledgments: The fund “The termination I. The environmental and palaeoclimatic variations occurred during the 25–11 ka period” (leader A. Ribolini) supported this work (Progetti di Ricerca di Ateneo PRA, 2020–21, University of Pisa). Exposure dating was completed with the support of the National Science Foundation, Continental Dynamics Program grant EAR-0208169 (RETREAT) and by PRIME Lab, Purdue University, West Lafayette, IN, USA. We thank Cal Ruleman and Will Odom for thorough and constructive reviews. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Peer reviewedPostprin