Superluminal Motion in the Lobe-Dominated Quasars 3C207 and 3C245

We are conducting a Very Long Baseline Interferometer (VLBI) survey of a complete sample of 25 lobe-dominated quasars, with the goal of testing relativistic jet models. Since the quasars 3C207 and 3C245 have the most prominent parsec-scale jets, we have observed them intensively with the Very Long Baseline Array (VLBA) from 2003 to 2005 at 15 and 22 GHz. Data from observations made of 3C245 at 22 GHz were not usable due to the weak flux density of the source. We find superluminal motion in 3C207 when observing at 15 GHz, increasing from 2 to 3 times the speed of light (2-3c) in the inner jet (less than 1 milliarcsecond [mas] from the core) to ~11c in the outer (2 mas) jet. The jet is curved, decreasing in position angle (PA) by 10o approximately 2 mas away from the core. A Lorentz factor (γ) of 10, and an increase in angle to the line of sight from &#;&#;&#;&#;1o to 6o outward along the jet, are consistent with the observed speeds and fluxes. Observations of 3C207 at 22 GHz yielded results inconsistent with the observations made at 15 GHz and with large uncertainties, due to the limited number of observations. We therefore could not draw any definitive conclusions about the motion of the 3C207 from observations made at 22 GHz. We also find superluminal motion in 3C245, with speeds alternating in the pattern 3c, 8c, 5c, 11c, and 4c outward along the inner three mas of the jet. There is a mild oscillation in PA with amplitude ~5o. These observations are more difficult to interpret. A choice of &#;&#;= 10, and oscillations between &#;&#;= 1o and 6o, are consistent with the observed speeds and fluxes, but the probability that two of our sources would have such small &#; is very low. The speeds could also arise from oscillations between &#;&#;= 6o and 35o, but the predicted large range of Doppler-boosted component fluxes is not observed. A range of Lorentz factors, or acceleration along the jet, permits alternative interpretations. We are grateful for support from an AAS Small Research Grant

Hudson Bay Ice Conditions

Monthly mean ice cover distributions for Hudson Bay have been derived, based upon an analysis of nine years of aerial reconnaissance and other data. Information is presented in map form, along with discussion of significant features. Ice break-up is seen to work southward from the western, northern, and eastern edges of the Bay; the pattern seems to be a result of local topography, currents and persistent winds. Final melting occurs in August. Freeze-up commences in October, along the northwestern shore, and proceeds southeastward. The entire Bay is ice-covered by early January, except for persistent shore leads.Conditions de la glace dans la mer d’Hudson.  A partir de l’analyse de neuf années de reconnaissances aériennes et d’autres données, on a pu déduire des moyennes mensuelles de distribution de la glace pour la mer d’Hudson.  L’information est présentée sous formes de cartes et de discussion des éléments significatifs.  On y voit que la débâcle progresse vers le sud à partir des marges ouest, nord et est de la mer; cette séquence semble être le résultat de la topographie locale, des courants et des vents dominants.  La fonte se termine en août.  L’engel commence en octobre le long de la rive nord-ouest et progresse vers le sud-est.  Sauf pour les chenaux côtiers persistants, la mer est entièrement gelée au début de janvier

Lateral device techniques for characterizing organic bulk heterojunction photovoltaic materials

textThis work is focused on developing novel techniques for characterizing organic bulk heterojunction (BHJ) materials for organic photovoltaic (OPV) applications. Polymer:fullerene BHJs are a promising class of photovoltaic materials, but an improved understanding of the charge transport processes and materials science of BHJs is required for them to effectively compete with other photovoltaic systems. Key parameters of BHJ systems that need to be evaluated include both electron and hole mobilities, the carrier concentrations, the recombination mechanism and the recombination coefficient. For these studies, poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C₆₁-butyric acid methyl ester (PCBM) have been characterized due to its wide use among researchers. Traditional characterization techniques have focused on transient measurements in a vertical device configuration, but we demonstrate the use of lateral BHJ devices as materials diagnostic platforms. Lateral devices allow for direct access to the active layer for spatially resolved and environmental effect measurements. The devices are also measured under steady state operation, similar to a working OPV cell. Under these conditions, lateral BHJ devices exhibit space charge limited transport behavior. A detailed charge transport model is presented to describe the potential, electric field, and carrier concentration profiles of lateral BHJ devices, as well as the current versus voltage characteristics of different regions of the device. We are able to calculate the slower carrier mobility from photocurrent measurements of lateral devices and the carrier mobility ratio from the device potential profile, even in ambipolar BHJ systems. In situ potentiometry is used to construct detailed potential profiles of the device channel and calculate both carrier mobilities. The carrier concentration and recombination coefficient are calculated from lateral conductivity measurements, and we show that bimolecular recombination is the dominant mechanism in bulk P3HT:PCBM. A simplified in situ potentiometry and photocurrent measurement technique is presented to measure the time evolution of organic BHJ performance. Due to the open geometry of the lateral BHJ device, we are also able to monitor the change in key charge transport parameters, including the recombination mechanism, in response to environmental degradation, analyte exposure, and ambient temperature. We show increased geminate recombination in P3HT:PC₇₁BM after prolonged light exposure. Lateral BHJ device measurements offer a useful complement to measurements on vertical photovoltaic structures and provide a more complete and detailed picture of OPV materials.Materials Science and Engineerin

Teaching Diagnostic Problem Solving: Principles Learned from Studies of the Diagnostic Pathfinder

Three quasi-experimental studies, and a survey-based study examining the effectiveness of and principles embodied in the Diagnostic Pathfinder, a software tool for teaching diagnostic problem solving in veterinary medicine. It appears that when students learn diagnostic problem solving in the context of authentic cases, are required to consider all potentially relevant information that they have identified in their solution, and receive immediate feedback, their ability to solve diagnostic problems improves

The Diagnostic Pathfinder: Ten years of using technology to teach diagnostic problem solving

The Diagnostic Pathfinder has been used for nearly ten years at multiple colleges of veterinary medicine to teach diagnostic problem solving. A number of prior studies show this tool to be effective. Research in medical diagnostic problem solving provides hints, but no unambiguous answers regarding how such a tool should be designed. This in-depth review of the interface discusses each interaction in terms of how that interaction relates to the tool’s success. Nine faculty members who have taught using the Pathfinder during the last decade responded to interview questions regarding the tool. Their responses supported what had already been learned – that there is benefit when learner and instructor use the same process for solving a diagnostic problem, and then compare results, and when students learn in the context of realistic problems. Additionally, instructor responses suggest that the Pathfinder has been effective because it has 1.) enabled precise communication among experts and learners in a field where there is no generally agreed upon format for precisely communicating understandings of interrelationships between mechanisms of disease and clinical laboratory data, and 2.) provided a framework for manipulating data that respects the limitations of human memory and invites a thorough, explicit, and “artistic” rendering of the rationale

Clinical Decision-Making Following Disasters: Efficient Identification of PTSD Risk in Adolescents

The present study aimed to utilize a Receiver Operating Characteristic (ROC) approach in order to improve clinical decision-making for adolescents at risk for the development of psychopathology in the aftermath of a natural disaster. Specifically we assessed theoretically-driven individual, interpersonal, and event-related vulnerability factors to determine which indices were most accurate in forecasting PTSD. Furthermore, we aimed to translate these etiological findings by identifying clinical cut-off recommendations for relevant vulnerability factors. Our study consisted of structured phone-based clinical interviews with 2,000 adolescent-parent dyads living within a 5-mile radius of tornados that devastated Joplin, MO, and northern Alabama in Spring 2011. Demographics, tornado incident characteristics, prior trauma, mental health, and family support and conflict were assessed. A subset of youth completed two behavioral assessment tasks online to assess distress tolerance and risk taking behavior. ROC analyses indicated four variables that significantly improved PTSD diagnostic efficiency: Lifetime depression (AUC=.90), trauma history (AUC=.76), social support (AUC=.70), and family conflict (AUC=.72). Youth were 2–3 times more likely to have PTSD if they had elevated scores on any of these variables. Of note, event-related characteristics (e.g., property damage) were not related to PTSD diagnostic status. The present study adds to the literature by making specific recommendations for empirically-based, efficient disaster-related PTSD assessment for adolescents following a natural disaster. Implications for practice and future trauma-related developmental psychopathology research are discussed

Characteristics of a cognitive tool that helps students learn diagnostic problem solving

Three related studies replicated and extended previous work (J.A. Danielson et al. (2003),Educational Technology Research and Development, 51(3), 63–81) involving the Diagnostic Pathfinder (dP) (previously Problem List Generator [PLG]), a cognitive tool for learning diagnostic problem solving. In studies 1 and 2, groups of 126 and 113 veterinary students, respectively, used the dP to complete case-based homework; groups of 120 and 199, respectively, used an alternative method. Students in the dP groups scored significantly higher (p = .000 and .003, respectively) on final exams than those in control groups. In the third study, 552 veterinary students responding to a questionnaire indicated that the dP’s gating and data synthesis activities aided learning. The dP’s feedback and requirement of completeness appear to aid learning most

Gas-Phase Synthesis of Trimetallic Nanoparticles

To this day, engineering nanoalloys beyond bimetallic compositions has scarcely been within the scope of physical deposition methods due to the complex, nonequilibrium processes they entail. Here, we report a gas-phase synthesis strategy for the growth of multimetallic nanoparticles: magnetron-sputtering inert-gas condensation from neighboring monoelemental targets provides the necessary compositional flexibility, whereas in-depth atomistic computer simulations elucidate the fast kinetics of nucleation and growth that determines the resultant structures. We fabricated consistently trimetallic Au–Pt–Pd nanoparticles, a system of major importance for heterogeneous catalysis applications. Using high-resolution transmission electron microscopy, we established their physical and chemical ordering: Au/Pt-rich core@Pd-shell atomic arrangements were identified for particles containing substantial amounts of all elements. Decomposing the growth process into basic steps by molecular dynamics simulations, we identified a fundamental difference between Au/Pt and Pd growth dynamics: Au/Pt electronic arrangements favor the formation of dimer nuclei instead of larger-size clusters, thus significantly slowing down their growth rate. Consequently, larger Pd particles formed considerably faster and incorporated small Au and Pt clusters by means of in-flight decoration and coalescence. A broad range of icosahedral, truncated-octahedral, and spheroidal face-centered cubic trimetallic nanoparticles were reproduced in simulations, in good agreement with experimental particles. Comparing them with their expected equilibrium structures obtained by Monte Carlo simulations, we identified the particles as metastable, due to out-of-equilibrium growth conditions. We aspire that our in-depth study will constitute a significant advance toward establishing gas-phase aggregation as a standard method for the fabrication of complex nanoparticles by design.Peer reviewe

How should we screen for depression following a natural disaster? An ROC approach to post-disaster screening in adolescents and adults

The present study’s aim was to provide the foundation for an efficient, empirically based protocol for depression screening following a natural disaster. Utilizing a Receiver Operating Characteristic (ROC) analytic approach, the study tested a) what specific disaster-related stressors (i.e., property damage, loss of basic services) and individual-related constructs (i.e., PTSD symptoms, trauma history, social support) conveyed the greatest risk for post-natural disaster depression, b) specific cutoff scores across these measures, and c) whether the significance or cutoff scores for each construct varied between adolescents and adults

Helping Learners Gain Diagnostic Problem Solving Skills: Specific Aspects of the Diagnostic Pathfinder Software Tied to Learning Outcomes

Problem solving is of critical importance in many disciplines. In medicine, the clinician\u27s ability to arrive at the correct diagnosis often means the difference between life and death. Despite its importance and a significant amount of research regarding how to improve problem solving, few unambiguous answers have emerged for promoting problem solving learning. This paper focuses on explaining those gains, both theoretically, and in terms of the qualitative data collected from learners over the past two years. The goal of the paper is to associate those gains with specific characteristics of the DP (Diagnostic Pathfinder, a software learning tool designed to help clinical pathology students improve their ability to solve diagnostic problems) by and meaningfully categorizing and characterizing thousands of comments from students who used the DP in a number of different settings, and to use those comments to illustrate, from the students\u27 perspective, how using the DP accomplished what it did. These ideas will be tied to current theory regarding the teaching and learning of problem solving