2,549 research outputs found
Linearity and Scaling of a Statistical Model for the Species Abundance Distribution
We derive a linear recursion relation for the species abundance distribution
in a statistical model of ecology and demonstrate the existence of a scaling
solution
Observation of discrete vortex solitons in optically-induced photonic lattices
We report on the frst experimental observation of discrete vortex solitons in
two-dimensional optically-induced photonic lattices. We demonstrate strong
stabilization of an optical vortex by the lattice in a self-focusing nonlinear
medium and study the generation of the discrete vortices from a broad class of
singular beams.Comment: 4pages, 5 colour figures. to appear in PR
A Qualitative Study Investigating How First-Year Engineering Students\u27 Value Beliefs Influence their Choice of Selecting an Engineering Major
First year engineering (FYE) programs are gaining popularity across universities in the United States. In addition to providing general engineering knowledge and skills to undergraduate freshmen, FYE programs also provide students with diverse opportunities to help them select the engineering discipline they will further pursue. The 2014 cohort of the FYE program of a large Midwestern university was the sample used for a two-phased study. The aim of the study was to understand how students make informed decisions of which engineering major to pursue and to help FYE administration to improve the resources they provide students. The first phase of the study focused on understanding the sources of information students used to make their decision. A preliminary analysis of student surveys indicated that the most important activity they are performing to select a major is âSelf-Led Explorationâ (SLE) of engineering disciplines.
This paper focuses on the second part of the study, which aims to qualitatively answer the research question: How do studentsâ value beliefs influence their decision of which engineering major to pursue? Answers to open ended questions from FYE surveys also served to inform this second study. Moreover, a brief examination of both the interviews and the surveys suggested a possible overlapping between the sources students used to inform their decision and the reasons why they selected a particular major. From that overlap, a secondary research question emerged: What is the relation between studentsâ value beliefs of the engineering disciplines and the type of sources they use to inform their decision of a major? To analyze our transcripts we used Eccleâs expectancy-value theory. We hypothesize that studentsâ value beliefs, how well a task aligns with their personal values, goals, and needs, influences their career choice and the type of resources they use to inform themselves
Acclimation to warmer temperatures can protect host populations from both further heat stress and the potential invasion of pathogens
Thermal acclimation can provide an essential buffer against heat stress for host populations, while acting simultaneously on various lifeâhistory traits that determine population growth. In turn, the ability of a pathogen to invade a host population is intimately linked to these changes via the supply of new susceptible hosts, as well as the impact of warming on its immediate infection dynamics. Acclimation therefore has consequences for hosts and pathogens that extend beyond simply coping with heat stressâgoverning both population growth trajectories and, as a result, an inherent propensity for a disease outbreak to occur. The impact of thermal acclimation on heat tolerances, however, is rarely considered simultaneously with metrics of both host and pathogen population growth, and ultimately fitness. Using the host Daphnia magna and its bacterial pathogen, we investigated how thermal acclimation impacts host and pathogen performance at both the individual and population scales. We first tested the effect of maternal and direct thermal acclimation on the lifeâhistory traits of infected and uninfected individuals, such as heat tolerance, fecundity, and lifespan, as well as pathogen infection success and spore production. We then predicted the effects of each acclimation treatment on rates of host and pathogen population increase by deriving a host's intrinsic growth rate (r m ) and a pathogen's basic reproductive number (R0). We found that direct acclimation to warming enhanced a host's heat tolerance and rate of population growth, despite a decline in lifeâhistory traits such as lifetime fecundity and lifespan. In contrast, pathogen performance was consistently worse under warming, with withinâhost pathogen success, and ultimately the potential for disease spread, severely hampered at higher temperatures. Our results suggest that hosts could benefit more from warming than their pathogens, but only by linking multiple individual traits to population processes can the full impact of higher temperatures on host and pathogen population dynamics be realised
A Topological Study of Contextuality and Modality in Quantum Mechanics
Kochen-Specker theorem rules out the non-contextual assignment of values to
physical magnitudes. Here we enrich the usual orthomodular structure of quantum
mechanical propositions with modal operators. This enlargement allows to refer
consistently to actual and possible properties of the system. By means of a
topological argument, more precisely in terms of the existence of sections of
sheaves, we give an extended version of Kochen-Specker theorem over this new
structure. This allows us to prove that contextuality remains a central feature
even in the enriched propositional system.Comment: 10 pages, no figures, submitted to I. J. Th. Phy
Long-wavelength PTSI infrared detectors and method of fabrication thereof
Extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime have been demonstrated for the first time. This result was achieved by incorporating a 1-nm-thick p+ doping spike at the PtSi/Si interface. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p+ doping spike and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450 degrees Celsius using elemental boron as the dopant source, with doping concentrations ranging from 1.times.10.sup.19 to 1.times.10.sup.21 cm.sup.-3. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes
The role of the emergency department in the management of acute heart failure: an international perspective on education and research
Emergency departments are a major entry point for the initial management of acute heart failure (AHF) patients throughout the world. The initial diagnosis, management and disposition - the decision to admit or discharge - of AHF patients in the emergency department has significant downstream implications. Misdiagnosis, under or overtreatment, or inappropriate admission may place patients at increased risk for adverse events, and add costs to the healthcare system. Despite the critical importance of initial management, data are sparse regarding the impact of early AHF treatment delivered in the emergency department compared to inpatient or chronic heart failure management. Unfortunately, outcomes remain poor, with nearly a third of patients dying or re-hospitalised within 3 months post-discharge. In the absence of robust research evidence, consensus is an important source of guidance for AHF care. Thus, we convened an international group of practising emergency physicians, cardiologists and advanced practice nurses with the following goals to improve outcomes for AHF patients who present to the emergency department or other acute care setting through: (a) a better understanding of the pathophysiology, presentation and management of the initial phase of AHF care; (b) improving initial management by addressing knowledge gaps between best practices and current practice through education and research; and (c) to establish a framework for future emergency department-based international education and research
Generalized Electromagnetic fields in Chiral Medium
The time dependent Dirac-Maxwell's Equations in presence of electric and
magnetic sources are written in chiral media and the solutions for the
classical problem are obtained in unique simple and consistent manner. The
quaternion reformulation of generalized electromagnetic fields in chiral media
has also been developed in compact, simple and consistent manner
Underwater Optical Wireless Communication Systems: A Concise Review
Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated pointâtoâpoint links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly testâbed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the âhiddenâ abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC
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