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

Waypoint Following Dynamics of a Quaternion Error Feedback Attitude Control System

Closed-loop attitude steering can be used to implement a non-standard attitude maneuver by using a conventional attitude control system to track a non-standard attitude profile. The idea has been employed to perform zero-propellant maneuvers on the International Space Station and minimum time maneuvers on NASA's TRACE space telescope. A challenge for operational implementation of the idea is the finite capacity of a space vehicle's command storage buffer. One approach to mitigate the problem is to downsample-and-hold the attitude commands as a set of waypoints for the attitude control system to follow. In this paper, we explore the waypoint following dynamics of a quaternion error feedback control law for downsample-and-hold. It is shown that downsample-and-hold induces a ripple between downsamples that causes the satellite angular rate to significantly overshoot the desired limit. Analysis in the $z$-domain is carried out in order to understand the phenomenon. An interpolating Chebyshev-type filter is proposed that allows attitude commands to be encoded in terms of a set of filter coefficients. Using the interpolating filter, commands can be issued at the ACS rate but with significantly reduced memory requirements. The attitude control system of NASA's Lunar Reconnaissance Orbiter is used as an example to illustrate the behavior of a practical attitude control system.Comment: 24 pages; 11 figure

Corporate Social Responsibility: Small Businesses and Small Towns

This paper is a review of previous scholarship on the social responsibility of small businesses in small towns with the addition of findings from recent research on the subject conducted by the authors. We focused on the responsibility of businesses to work for community betterment which includes a wide variety of charitable and social causes. The extant literature and new research lead to several general conclusions. First most small business owners believe they have an obligation to work for community and societal betterment, but it is proportional to their size compared to other businesses in the same location. While the values of top management have a significant impact on the social performance of businesses of all sizes, in small businesses, social performance is more directly and personally shaped by the owners than is the case in large businesses. Small business owners are more socially and economically embedded within the community in which they operate than are managers of big businesses. Moreover, in small towns, they are more visible than similarly sized businesses in metropolitan locations. For this reason, size of town is a key intermediary variable between size of business and level of social performance. Partially as a result of their greater embeddedness and visibility, small business owners in small towns are likely to conform to the local patterns of civic engagement. For many of the same reasons, small business owners’ social performance is affected by the expectations and prevailing patterns of social performance displayed by members of the business networks to which they belong. Past research supports the argument that doing good is good for business in large and small firms alike although the relationship is less well documented for small businesses. We expand the research to consider the rewards and penalties of business social responsibility for the business owner personally. This is an important outcome of business social performance for all sizes of business, but for small businesses where owner discretion may be the only factor determining the community involvement of the business, it is critical. We end by advocating for more research attention directed toward small business social performance, the impact of town size on business social performance, and the personal costs and benefits of business social performance for the owners themselves

Viscoelastic response of contractile filament bundles

The actin cytoskeleton of adherent tissue cells often condenses into filament bundles contracted by myosin motors, so-called stress fibers, which play a crucial role in the mechanical interaction of cells with their environment. Stress fibers are usually attached to their environment at the endpoints, but possibly also along their whole length. We introduce a theoretical model for such contractile filament bundles which combines passive viscoelasticity with active contractility. The model equations are solved analytically for two different types of boundary conditions. A free boundary corresponds to stress fiber contraction dynamics after laser surgery and results in good agreement with experimental data. Imposing cyclic varying boundary forces allows us to calculate the complex modulus of a single stress fiber.Comment: Revtex with 24 pages, 7 Postscript figures included, accepted for publication in Phys. Rev.

Predicting Space Weather Effects on Close Approach Events

The NASA Robotic Conjunction Assessment Risk Analysis (CARA) team sends ephemeris data to the Joint Space Operations Center (JSpOC) for conjunction assessment screening against the JSpOC high accuracy catalog and then assesses risk posed to protected assets from predicted close approaches. Since most spacecraft supported by the CARA team are located in LEO orbits, atmospheric drag is the primary source of state estimate uncertainty. Drag magnitude and uncertainty is directly governed by atmospheric density and thus space weather. At present the actual effect of space weather on atmospheric density cannot be accurately predicted because most atmospheric density models are empirical in nature, which do not perform well in prediction. The Jacchia-Bowman-HASDM 2009 (JBH09) atmospheric density model used at the JSpOC employs a solar storm active compensation feature that predicts storm sizes and arrival times and thus the resulting neutral density alterations. With this feature, estimation errors can occur in either direction (i.e., over- or under-estimation of density and thus drag). Although the exact effect of a solar storm on atmospheric drag cannot be determined, one can explore the effects of JBH09 model error on conjuncting objects' trajectories to determine if a conjunction is likely to become riskier, less risky, or pass unaffected. The CARA team has constructed a Space Weather Trade-Space tool that systematically alters the drag situation for the conjuncting objects and recalculates the probability of collision for each case to determine the range of possible effects on the collision risk. In addition to a review of the theory and the particulars of the tool, the different types of observed output will be explained, along with statistics of their frequency

Laser structuring of NMC 811 high energy electrodes in battery production for enhancing the electrochemical performance for xEV energy storage systems

Layered oxide cathodes, especially thick-film electrodes like lithium nickel manganese cobalt oxide, NMC, are under continuously investigation to meet the ambitious requirements, e.g. 700 Wh/l, for future Li-ion batteries in electric drive applications. The objective of the most current studies is to reduce the Co content with a concurrent increasing Ni-content in the NMC cathodes such as NMC 811 [1]. It must not leave the fact out of consideration, that NMC cathodes suffer from low high rate capability and corresponding low capacity retention at high C-rates. In particular, the negative impact is even higher for thick-film high energy cathodes. To counteract the negative effect, high repetition ultrafast laser ablation is applied to create appropriate 3D electrode designs [2]. New Li+-diffusion pathways, applied by the laser structuring process, shell enhance electrolyte wettability and reduce overpotentials at high C-rates. It is attempted to integrate the laser structuring into a continuous roll-to-roll electrode production process. In this way, the positive properties achieved through 3D structuring can also be obtained for Li-ion batteries that are produced on a large scale. By using this novel production technology, future NMC batteries can be produced with improved performance characteristics for xEV applications. Furthermore, this technology can also be applied for other generation 3b battery cells. This work is performed under the frame of the RealLi! project, in which the following aspects are covered: a) Development of thick film NMC811 electrodes with high areal capacity b) Passivation approach to improve cycle stability and lifetime c) Cell Assembly and electrochemical characterization d) Holistic evaluation of the potential environmental impact of the NMC811 cells via life cycle assessment e) An experimentally validated electrochemical model to describe electrode structures and their optimization. f) Improved electrochemical performance of NMC811 electrodes on a laboratory scale by using 3D laser structuring. g) Scale up of the 3D laser structuring process and corresponding improved electrochemical performance of NMC811 electrodes in pouch cell format by using 3D laser ablation

Making Sense of a New Transport System: An Ethnographic Study of the Cambridgeshire Guided Busway

An increase in public transport use has the potential to contribute to improving population health, and there is growing interest in innovative public transport systems. Yet how new public transport infrastructure is experienced and integrated (or not) into daily practice is little understood. We investigated how the Cambridgeshire Guided Busway, UK, was used and experienced in the weeks following its opening, using the method of participant observation (travelling on the busway and observing and talking to passengers) and drawing on Normalization Process Theory to interpret our data. Using excerpts of field notes to support our interpretations, we describe how the ease with which the new transport system could be integrated into existing daily routines was important in determining whether individuals would continue to use it. It emerged that there were two groups of passengers with different experiences and attitudes. Passengers who had previously travelled frequently on regular bus services did not perceive the new system to be an improvement; consequently, they were frustrated that it was differentiated from and not coherent with the regular system. In contrast, passengers who had previously travelled almost exclusively by car appraised the busway positively and perceived it to be a novel and superior form of travel. Our rich qualitative account highlights the varied and creative ways in which people learn to use new public transport and integrate it into their everyday lives. This has consequences for the introduction and promotion of future transport innovations. It is important to emphasise the novelty of new public transport, but also the ways in which its use can become ordinary and routine. Addressing these issues could help to promote uptake of other public transport interventions, which may contribute to increasing physical activity and improving population health. © 2013 Jones et al

Mamekhaya: a pilot study combining a cognitive-behavioral intervention and mentor mothers with PMTCT services in South Africa

Nearly 30% of pregnant women in South Africa are estimated to be HIV seropositive, yet adherence to guidelines for the prevention of mother-to-child transmission of HIV (PMTCT) is often low. A pilot study was developed to see whether PMTCT services provided by the South African Government could be enhanced by the Mamekhaya program, a combination of the mothers2mothers peer-mentoring program and a culturally adapted cognitive-behavioral intervention (CBI) from the USA. Pregnant women attending two maternity clinics offering PMTCT in Gugulethu and Vanguard Townships, Cape Town, South Africa, were invited to participate in the study. Women at the intervention site (Gugulethu) received the support of a mentor mother and also attended an eight-session Mamekhaya CBI. At the control site (Vanguard), women received standard services provided by midwives and counselors. Baseline assessments were completed by all participants at enrollment (n=160), and follow-ups were completed six months later by 44% of participants. Self-reports of adherence to PMTCT practices were high across both sites (90% or more engaging in the core practices). Women at the Mamekhaya site showed significantly greater improvement in establishing social support and reducing depression scores than women at the control site. Mamekhaya participants also showed trends for better attendance at follow-up medical visits, and greater improvements in positive coping. The greatest effect of the Mamekhaya program was to increase HIV knowledge scores, particularly with regard to understanding the meaning and importance of viral load and CD4 test results. Results from this pilot study show promise that augmenting basic PMTCT services with mentor mothers and a culturally adapted CBI can be effective in conveying information and in improving the emotional outlook and hopefulness of HIV-positive pregnant women in South Africa

Phase transitions for PP-adic Potts model on the Cayley tree of order three

In the present paper, we study a phase transition problem for the $q$-state $p$-adic Potts model over the Cayley tree of order three. We consider a more general notion of $p$-adic Gibbs measure which depends on parameter \rho\in\bq_p. Such a measure is called {\it generalized $p$-adic quasi Gibbs measure}. When $\rho$ equals to $p$-adic exponent, then it coincides with the $p$-adic Gibbs measure. When $\rho=p$, then it coincides with $p$-adic quasi Gibbs measure. Therefore, we investigate two regimes with respect to the value of $|\rho|_p$. Namely, in the first regime, one takes $\rho=\exp_p(J)$ for some J\in\bq_p, in the second one $|\rho|_p<1$. In each regime, we first find conditions for the existence of generalized $p$-adic quasi Gibbs measures. Furthermore, in the first regime, we establish the existence of the phase transition under some conditions. In the second regime, when $|\r|_p,|q|_p\leq p^{-2}$ we prove the existence of a quasi phase transition. It turns out that if $|\r|_p<|q-1|_p^2<1$ and \sqrt{-3}\in\bq_p, then one finds the existence of the strong phase transition.Comment: 27 page