Dead Time Compensation for High-Flux Ranging

Dead time effects have been considered a major limitation for fast data acquisition in various time-correlated single photon counting applications, since a commonly adopted approach for dead time mitigation is to operate in the low-flux regime where dead time effects can be ignored. Through the application of lidar ranging, this work explores the empirical distribution of detection times in the presence of dead time and demonstrates that an accurate statistical model can result in reduced ranging error with shorter data acquisition time when operating in the high-flux regime. Specifically, we show that the empirical distribution of detection times converges to the stationary distribution of a Markov chain. Depth estimation can then be performed by passing the empirical distribution through a filter matched to the stationary distribution. Moreover, based on the Markov chain model, we formulate the recovery of arrival distribution from detection distribution as a nonlinear inverse problem and solve it via provably convergent mathematical optimization. By comparing per-detection Fisher information for depth estimation from high- and low-flux detection time distributions, we provide an analytical basis for possible improvement of ranging performance resulting from the presence of dead time. Finally, we demonstrate the effectiveness of our formulation and algorithm via simulations of lidar ranging.Comment: Revision with added estimation results, references, and figures, and modified appendice

Diplomatic Dynamics of International Treaty Negotiations

The negotiation process of international treaties is heavily influenced by socioeconomic factors. In this paper, we aim to answer the question of how to quantify the influential factors among countries. We do so by categorizing them into different interest groups based on their attitudes towards the treaty as well as their socioeconomic statuses and modeling the movement of countries between these interest groups. This model is based on an epidemiological approach to quantifying influence. Through our research, we discovered two equilibrium points, which reveal the conditions under which all countries would either support or oppose a treaty. We also ran simulations under several hypothetical scenarios under which equilibria would occur, demonstrating the practical applications of our model. We further analyze the model's real life application and the influence of certain parameters through two case studies: the first is on the Basel Convention's negotiation process and the second is on the spread of carbon pricing

Daggerblade Grass Shrimp (\u3ci\u3ePalaemonetes pugio\u3c/i\u3e): A Reservoir Host for Yellow-Head Virus (YHV)

Yellow-head virus (YHV) is a major pathogen in penaeid shrimps. We surveyed 13 crustacean species in eight families from two orders that are commonly found in the Mississippi coastal area and freshwater environments as potential reservoir or carrier hosts of YHV. Using semi-nested polymerase chain reaction (PCR) on relatively small sample sizes, we did not detect any natural infection. However, when the daggerblade grass shrimp, Palaemonetes pugio, and the blue crab, Callinectes sapidus, were exposed to YHV by injection and per os, YHV was detected in the tissue of P. pugio and in the hemolymph of C. sapidus when tested by semi-nested reverse transcription PCR (RT-PCR) and real time quantitative reverse transcription PCR (qRT-PCR). YHV replicated in P. pugio, causing 8% mortality (9/112) after injection, with the viral titer reaching a peak at 14 days post-inoculation (dpi) and remaining detectable at 36 dpi. The number of infected animals and viral load, however, were relatively low, but the virus still remained infectious to penaeids when administered by feeding. When YHV was injected into P. pugio, in situ hybridization detected a positive response to it at 7 dpi in connective tissue of hepatopancreas, muscle, and midgut. Viral RNA in injected C. sapidus remained at a low level for 3 days, and it was not detected from 7 dpi onward. In fed C. sapidus, the viral RNA reached a peak at 3 dpi and still detectable at 7 dpi, but it became undetectable at 14 and 21 dpi. These data suggest that P. pugio under some conditions could act as a reservoir host for YHV but that the blue crab could serve as a poor, short-term carrier host only

Stable Yellowhead Virus (YHV) RNA Detection by qRT-PCR during Six-Day Storage

Storage conditions of haemolymph samples which contain yellowhead virus (YHV) may result in a decline of YHV RNA concentration or false-negative results in the detection of YHV. We evaluated the stability of YHV RNA in haemolymph stored at different temperatures for 6 d with conventional RT-PCR and TaqMan qRT-PCR. Specific pathogen-free individuals of Litopenaeus vannamei were challenged with YHV92TH isolate, and haemolymph samples of 3 groups of 10 pooled moribund shrimp were aliquoted and stored at 4 and 25°C for 0, 2, 6, 12, 24, 48, 72, 96, 120, and 144 h. All samples were evaluated by conventional RT-PCR and qRT-PCR. After the optimization of experimental conditions, TaqMan qRT-PCR showed a very strong linear relationship between the log scale of the standard DNA copy number and the CT values (R2 = 0.999) over a 7-log range from 102 to 108 copy number per reaction. Even though the haemolymph was stored at either 4 or 25°C for a 6-day period, the viral load number at 4°C was not significantly different from that stored at 25°C. The only difference was between the samples stored for 144 h at either 4 or 25°C and those stored at −80°C. We conclude that shrimp haemolymph can be drawn from shrimp at farms or in the wild and stored at either 4 or 25°C for 3–5 d without a significant reduction in measured YHV RNA levels and without having to immediately freeze the samples

Learning service leadership through service-learning : anxieties, opportunities and insights

Lingnan University (LU) is one of 8 tertiary institutions in Hong Kong that have received sponsorship for undergraduate students to acquire knowledge and develop attributes relating to service leadership. Service leadership may be conceptualized as leadership for service, exercised through distributed authority, aimed at identifying and meeting genuine needs of service recipients. Building on prior experience of embedding service-learning projects into discipline-based credit bearing courses, in term 1, 2012-13, LU introduced service leadership through service-learning into four courses. A predominantly qualitative, critical-incident approach was adopted to study processes of students’ learning on these courses. Data were collected through open-ended team reflection and self-reflection pro-formas, a peer review rubric, and focus group meetings. Findings suggest that service-learning projects can be powerful vehicles for learning and practicing service leadership attributes. Positive learning outcomes reported by students included: increased skills of oral communication, relationship building, time management and problem solving; and greater personal discipline, emotional intelligence, empathy for disadvantaged people and cross-cultural awareness. Students mentioned the importance of mutual care and support in teams, of formative feedback from host agencies/enterprises; of being appreciated by end service recipients; and of turning cultural diversity among team members into a powerful resource. We shall draw on an established model of competence development (Robinson, 1974; Wilhelm, 2011) to analyze students’ reported experiences. In terms of unconscious learning needs, students seemed relatively insensitive to the particular expectations of gatekeepers in their host organization and the constraints that they were facing, and rather than attempting to understand nuances and tensions within the service recipient habitat/ecosystem, they tended to fix their attention on the concerns of end-user service recipients. In terms of conscious learning needs, some teams became aware of the inadequacy of the traditional autocratic leadership paradigm, but appeared not to fully grasp the principles and practices of distributed leadership, while some students noticed service leadership qualities in other team members that they perceived were lacking in themselves. In terms of conscious competence, some students came to recognize their own talents in certain areas through taking initiatives to overcome difficulties. We discuss implications

The Ly-6A (Sca-1) GFP transgene is expressed in all adult mouse hematopoietic stem cells

The Sca-1 cell surface glycoprotein is used routinely as a marker of adult hematopoietic stem cells (HSCs), allowing a >100-fold enrichment of these rare cells from the bone marrow of the adult mouse. The Sca-1 protein is encoded by the Ly-6A/E gene, a small 4-exon gene that is tightly controlled in its expression in HSCs and several hematopoietic cell types. For the ability to sort and localize HSCs directly from the mouse, we initiated a transgenic approach in which we created Ly-6A (Sca-1) green fluorescent protein (GFP) transgenic mice. We show here that a 14-kb Ly-6A expression cassette directs the transcription of the GFP marker gene in all functional repopulating HSCs in the adult bone marrow. A >100-fold enrichment of HSCs occurred by sorting for the GFP-expressing cells. Furthermore, as shown by fluorescence-activated cell sorting and histologic analysis of several hematopoietic tissues, the GFP transgene expression pattern generally corresponded to that of Sca-1. Thus, the Ly-6A GFP transgene facilitates the enrichment of HSCs and presents the likelihood of identifying HSCs in situ

Thermodynamics and tunneling spectroscopy in the pseudogap regime of the boson fermion model

Motivated by the STM experimental data on Bi_2 Sr_2 CaCU_2 O_{8+x} which indicate the tunneling conductance asymmetry sigma(-V) not equal sigma(V), we report that such a behavior can be explained in terms of the boson fermion model. It has been shown in the recent studies, based on various selfconsistent techniques to capture the many-body effects, that the low energy spectrum of the boson fermion model is featured by an appearance of the pseudogap at T^* > T_c. We argue that the pseudogap structure has to exhibit a particle-hole asymmetry. This asymmetry may eventually depend on the boson concentration.Comment: 4 pages, 2 figures. submitted to Physica

The Spin Gap in the Context of the Boson-Fermion Model for High TcT_c Superconductivity

The issue of the spin gap in the magnetic susceptibility $\chi''(q,\omega)$ in high T_c superconductors is discussed within a scenario of a mixture of localized tightly bound electron pairs in singlet states (bi-polarons) and itinerant electrons. Due to a local exchange between the two species of charge carriers, antiferromagnetic correlations are induced amongst the itinerant electrons in the vicinity of the sites containing the bound electron pairs. As the temperature is lowered these exchange processes become spatially correlated leading to a spin wave-like spectrum in the subsystem of the itinerant electrons. The onset of such coherence is accompanied by the opening of a pseudo gap in the density of states of the electron subsystem whose temperature dependence is reflected in that of $\chi'' (q,\omega)$ near $q =(\pi,\pi)$ where a ``spin gap'' is observed by inelastic neutron scattering and NMR.Comment: 9 pages Latex, 3 figures available upon request. To appear in Physica