Solid state photomultiplier for astronomy, phase 2

Epitaxial layers with varying donor concentration profiles were grown on silicon substrate wafers using chemical vapor deposition (CVD) techniques, and solid state photomultiplier (SSPM) devices were fabricated from the wafers. Representative detectors were tested in a low background photon flux, low temperature environment to determine the device characteristics for comparison to NASA goals for astronomical applications. The SSPM temperatures varied between 6 and 11 K with background fluxes in the range from less than 5 x 10 to the 6th power to 10 to the 13th power photons/square cm per second at wavelengths of 3.2 and 20 cm. Measured parameters included quantum efficiency, dark count rate and bias current. Temperature for optimal performance is 10 K, the highest ever obtained for SSPMs. The devices exhibit a combination of the lowest dark current and highest quantum efficiency yet achieved. Experimental data were reduced, analyzed and used to generate recommendations for future studies. The background and present status of the microscopic theory of SSPM operation were reviewed and summarized. Present emphasis is on modeling of the avalanche process which is the basis for SSPM operation. Approaches to the solution of the Boltzmann transport equation are described and the treatment of electron scattering mechanisms is presented. The microscopic single-electron transport theory is ready to be implemented for large-scale computations

Li(p)-service? An algorithm for computing p-adic polylogarithms

We describe an algorithm for computing Coleman's p-adic poly-logarithms up to a given precision. © 2007 American Mathematical Society

On Conceptually Simple Algorithms for Variants of Online Bipartite Matching

We present a series of results regarding conceptually simple algorithms for bipartite matching in various online and related models. We first consider a deterministic adversarial model. The best approximation ratio possible for a one-pass deterministic online algorithm is $1/2$, which is achieved by any greedy algorithm. D\"urr et al. recently presented a $2$-pass algorithm called Category-Advice that achieves approximation ratio $3/5$. We extend their algorithm to multiple passes. We prove the exact approximation ratio for the $k$-pass Category-Advice algorithm for all $k \ge 1$, and show that the approximation ratio converges to the inverse of the golden ratio $2/(1+\sqrt{5}) \approx 0.618$ as $k$ goes to infinity. The convergence is extremely fast --- the $5$-pass Category-Advice algorithm is already within $0.01\%$ of the inverse of the golden ratio. We then consider a natural greedy algorithm in the online stochastic IID model---MinDegree. This algorithm is an online version of a well-known and extensively studied offline algorithm MinGreedy. We show that MinDegree cannot achieve an approximation ratio better than $1-1/e$, which is guaranteed by any consistent greedy algorithm in the known IID model. Finally, following the work in Besser and Poloczek, we depart from an adversarial or stochastic ordering and investigate a natural randomized algorithm (MinRanking) in the priority model. Although the priority model allows the algorithm to choose the input ordering in a general but well defined way, this natural algorithm cannot obtain the approximation of the Ranking algorithm in the ROM model

Educators’ Impression Construction: Considering Perceived Social Media Missteps

Social Media (SM) provide exciting instructional opportunities for educators. However, a simple Internet search reveals professional implications that have resulted from educators’ SM usage perceived as missteps. In this research, using an impression construction lens, we considered cases of educators’ SM missteps as perceived by stakeholders and as presented in the news media. From this analysis, a description of what is perceived as inappropriate teacher SM use is provided, explanations of the highlighted SM usage are considered, and a discussion of findings from an impression construction perspective is included. Results suggest impression construction in SM settings is a complex endeavor for educators that prompts varying opinions from stakeholder groups. Suggestions for professional SM use are included

Reconfigurable Intelligent Surface Phase Hopping for Ultra-Reliable Communications

We introduce a phase hopping scheme for reconfigurable intelligent surfaces (RISs) in which the phases of the individual RIS elements are randomly varied with each transmitted symbol. This effectively converts slow fading into fast fading. We show how this can be leveraged to significantly improve the outage performance especially for small outage probabilities without channel state information (CSI) at the transmitter and RIS. Furthermore, the same result can be accomplished even if only two possible phase values are available. Since we do not require perfect CSI at the transmitter or RIS, the proposed scheme has no additional communication overhead for adjusting the phases. This enables robust ultra-reliable communications with a reduced effort for channel estimation.Comment: 13 pages, 12 figure

Using Indicators Projects as Prompts for Exploring Equity: A Case Study of Greater Portland Pulse

This paper describes the process that the Greater Portland Pulse (GPP) initiated to incorporate the measurement of progress toward social equity into the project. While equity may appear to be a widely accepted priority for communities, the GPP process created a dialogue that was sometimes contentious but also profoundly educational for the participants revealing some of the complexities, not only of the issue of equity, but the challenges (particularly the inadequacy of available data) and trade-offs that are inescapable when using conventional data sets. Additionally, this paper discusses some of the consequences of a process that, while incorporating equity values and concerns into all of its outcomes and indicators (rather than creating a separate equity outcome category) may have rendered equity less visible than originally intended