Resolved shock structure of the Balmer-dominated filaments in Tycho's supernova remnant: Cosmic-ray precursor?

We report on the results from H{\alpha} imaging observations of the eastern limb of Tycho's supernova remnant (SN1572) using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of the fast, collisionless shock wave into a delicate structure of nearly edge-on filaments. We find a gradual increase of H{\alpha} intensity just ahead of the shock front, which we interpret as emission from the thin (~1") shock precursor. We find that a significant amount of the H{\alpha} emission comes from the precursor and that this could affect the amount of temperature equilibration derived from the observed flux ratio of the broad and narrow H{\alpha} components. The observed H{\alpha} emission profiles are fit using simple precursor models, and we discuss the relevant parameters. We suggest that the precursor is likely due to cosmic rays and discuss the efficiency of cosmic-ray acceleration at this position.Comment: Prepared with emulateapj.sty (5 pages, 4 figures). Published in ApJL

Analytical Models of Exoplanetary Atmospheres. II. Radiative Transfer via the Two-stream Approximation

We present a comprehensive analytical study of radiative transfer using the method of moments and include the effects of non-isotropic scattering in the coherent limit. Within this unified formalism, we derive the governing equations and solutions describing two-stream radiative transfer (which approximates the passage of radiation as a pair of outgoing and incoming fluxes), flux-limited diffusion (which describes radiative transfer in the deep interior) and solutions for the temperature-pressure profiles. Generally, the problem is mathematically under-determined unless a set of closures (Eddington coefficients) is specified. We demonstrate that the hemispheric (or hemi-isotropic) closure naturally derives from the radiative transfer equation if energy conservation is obeyed, while the Eddington closure produces spurious enhancements of both reflected light and thermal emission. We concoct recipes for implementing two-stream radiative transfer in stand-alone numerical calculations and general circulation models. We use our two-stream solutions to construct toy models of the runaway greenhouse effect. We present a new solution for temperature-pressure profiles with a non-constant optical opacity and elucidate the effects of non-isotropic scattering in the optical and infrared. We derive generalized expressions for the spherical and Bond albedos and the photon deposition depth. We demonstrate that the value of the optical depth corresponding to the photosphere is not always 2/3 (Milne's solution) and depends on a combination of stellar irradiation, internal heat and the properties of scattering both in optical and infrared. Finally, we derive generalized expressions for the total, net, outgoing and incoming fluxes in the convective regime.Comment: Accepted by ApJS. 23 pages, 11 figures, 3 tables, 158 equations. No change from previous version except for title (to match ApJS convention

Stationary Distribution Convergence of the Offered Waiting Processes for GI/GI/1+GI Queues in Heavy Traffic

A result of Ward and Glynn (2005) asserts that the sequence of scaled offered waiting time processes of the $GI/GI/1+GI$ queue converges weakly to a reflected Ornstein-Uhlenbeck process (ROU) in the positive real line, as the traffic intensity approaches one. As a consequence, the stationary distribution of a ROU process, which is a truncated normal, should approximate the scaled stationary distribution of the offered waiting time in a $GI/GI/1+GI$ queue; however, no such result has been proved. We prove the aforementioned convergence, and the convergence of the moments, in heavy traffic, thus resolving a question left open in Ward and Glynn (2005). In comparison to Kingman's classical result in Kingman (1961) showing that an exponential distribution approximates the scaled stationary offered waiting time distribution in a $GI/GI/1$ queue in heavy traffic, our result confirms that the addition of customer abandonment has a non-trivial effect on the queue stationary behavior.Comment: 29 page

Design And Analysis Of A Fast Transient Voltage Regulator With All Ceramic Output Capacitors For Mobile Microprocessors

Keperluan untuk mereka bentuk pengatur voltan yang mempunyai tindak balas transien yang cepat didorong oleh kadar transien yang semakin meningkat daripada mikropemproses mudah alih. Oleh itu, mengoptimumkan frekuensi pensuisan pengatur voltan menjadi langkah penting untuk mencapai keseimbangan antara mengekalkan kecekapan pengatur voltan dan meningkatkan tindak balas transien. Kapasitor seramik berlapis telah menjadi lebih popular sebagai kapasitor output pengantara voltan disebabkan oleh saiznya yang kecil dan kos murah. Walaupun topologi penukar buck kekal tidak berubah betahun-tahun, terdapat banyak inovasi dan kejayaan cemerlang dalam peringkat kuasa pengatur voltan dan teknologi kawalan. Selain itu, reka bentuk yang berorientasikan galangan keluaran dan AVP (Penempatan Voltan Automatik) telah diperkenalkan untuk menangani keperluan transien. Banyak kajian juga memberi tumpuan untuk meningkatkan kecekapan pegantara voltage terutama untuk system yang beroperasi dengan bateri. Sebuah pengatur voltan bertindak balas laju yang mempunyai hanya kapasitor output seramik untuk mikropemproses mudah alih dicadangkan dalam kajian ini. Hasil kajian ini menunjukkan bahawa pengatur voltan yang direka adalah stabil dengan jenis dan bilangan kapasitor seramik berlapisan yang dicadangkan. Lebih penting lagi, keputusan transien juga adalah sehampir dengan keputusan simulasi di mana output pengantara voltan tidak mengalami kelanjakan dan kejatuhan voltan semasa dimuatkan dengan arus dinamik yang bermaknitud 10.5A dalam 1μs. Kesimpulannya, sebuah pengatur voltan dengan tindak balas laju yang mempunyai hanya kapasitor output seramik telah direka dan dianalisis and ia mempunyai tindak balas transien yang lebih baik berbanding dengan reka bentuk asal. Keperluan untuk mereka bentuk pengatur voltan yang mempunyai tindak balas transien yang cepat didorong oleh kadar transien yang semakin meningkat daripada mikropemproses mudah alih. Oleh itu, mengoptimumkan frekuensi pensuisan pengatur voltan menjadi langkah penting untuk mencapai keseimbangan antara mengekalkan kecekapan pengatur voltan dan meningkatkan tindak balas transien. Kapasitor seramik berlapis telah menjadi lebih popular sebagai kapasitor output pengantara voltan disebabkan oleh saiznya yang kecil dan kos murah. Walaupun topologi penukar buck kekal tidak berubah betahun-tahun, terdapat banyak inovasi dan kejayaan cemerlang dalam peringkat kuasa pengatur voltan dan teknologi kawalan. Selain itu, reka bentuk yang berorientasikan galangan keluaran dan AVP (Penempatan Voltan Automatik) telah diperkenalkan untuk menangani keperluan transien. Banyak kajian juga memberi tumpuan untuk meningkatkan kecekapan pegantara voltage terutama untuk system yang beroperasi dengan bateri. Sebuah pengatur voltan bertindak balas laju yang mempunyai hanya kapasitor output seramik untuk mikropemproses mudah alih dicadangkan dalam kajian ini. Hasil kajian ini menunjukkan bahawa pengatur voltan yang direka adalah stabil dengan jenis dan bilangan kapasitor seramik berlapisan yang dicadangkan. Lebih penting lagi, keputusan transien juga adalah sehampir dengan keputusan simulasi di mana output pengantara voltan tidak mengalami kelanjakan dan kejatuhan voltan semasa dimuatkan dengan arus dinamik yang bermaknitud 10.5A dalam 1μs. Kesimpulannya, sebuah pengatur voltan dengan tindak balas laju yang mempunyai hanya kapasitor output seramik telah direka dan dianalisis and ia mempunyai tindak balas transien yang lebih baik berbanding dengan reka bentuk asal. ________________________________________________________________________________________________________________________ The need to have fast transient response of the voltage regulator is driven by the increasing current slew rate of the mobile microprocessor. Hence, optimizing the switching frequency of the voltage regulator becomes an important step to achieve a balance between preserving the efficiency of the voltage regulator and improving the transient response. Besides, output capacitor solution with multilayer ceramic capacitor has also become more popular due to its small size and cheap cost. Over the years, even though the topology of the buck converter remains unchanged, there are plenty of innovations and breakthroughs in the power stage of the voltage regulator and controller technology. In addition, output impedance oriented design and adaptive voltage positioning (AVP) feature are also introduced to address the transient requirements. Apart from improving the dynamic response of the voltage regulator, many research works also focus on improving the efficiency of the voltage regulator, especially for battery-powered systems. A fast transient voltage regulator with all ceramic output capacitors for mobile microprocessor is proposed in this study. The outcome of the study shows that the voltage regulator designed is stable with the proposed type and number of multilayer ceramic capacitors. More importantly, the actual transient results correlate well with the simulation results where minimal transient droop and overshoot are observed with a dynamic current load step with a slew rate of 10.5A per 1 μs. In conclusion, a fast transient voltage regulator with all ceramic output capacitors is designed and analyzed which proven to have better transient performance compared to the original design on the test boar

The Perceptions of Macao Undergraduates Regarding Help Websites for Problem Gambling

This study conducted a web-surfing exercise and a questionnaire survey among a group of Macao undergraduate students regarding the websites that offered help with problem gambling. The results of this study found that most help websites in Macao and Hong Kong provided basic information-sharing service. The students indicated that they would choose their preferred help organization based on factors such as trust, familiarity, and the characteristics of the websites. They also gave comments/suggestions related to the publicity, design, contents, and focus of the websites. This study discussed the results and their implications for future research and practice

Role Playing Learning for Socially Concomitant Mobile Robot Navigation

In this paper, we present the Role Playing Learning (RPL) scheme for a mobile robot to navigate socially with its human companion in populated environments. Neural networks (NN) are constructed to parameterize a stochastic policy that directly maps sensory data collected by the robot to its velocity outputs, while respecting a set of social norms. An efficient simulative learning environment is built with maps and pedestrians trajectories collected from a number of real-world crowd data sets. In each learning iteration, a robot equipped with the NN policy is created virtually in the learning environment to play itself as a companied pedestrian and navigate towards a goal in a socially concomitant manner. Thus, we call this process Role Playing Learning, which is formulated under a reinforcement learning (RL) framework. The NN policy is optimized end-to-end using Trust Region Policy Optimization (TRPO), with consideration of the imperfectness of robot's sensor measurements. Simulative and experimental results are provided to demonstrate the efficacy and superiority of our method

Fractals Generated by Modifying Aperiodic Substitution Tilings

This study proposes a method for producing an endless number of fractals using aperiodic substitution tilings, as illustrated by the Ammann Chair tiling. Higher order substitutions of aperiodic tiling are utilised in relation to the Siepinski carpet concept. The fractal dimensions of the fractals generated by the Ammann Chair tiling are calculated.Comment: 7 page