4,607 research outputs found

    A new measurement of thermal conductivity of amorphous ice and its implications for the thermal evolution of comets

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    Very slowly deposited amorphous ice has a thermal conductivity about four orders of magnitude or more smaller than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the properties of amorphous ice leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters

    A model of ballistic aggregation and fragmentation

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    A simple model of ballistic aggregation and fragmentation is proposed. The model is characterized by two energy thresholds, Eagg and Efrag, which demarcate different types of impacts: If the kinetic energy of the relative motion of a colliding pair is smaller than Eagg or larger than Efrag, particles respectively merge or break; otherwise they rebound. We assume that particles are formed from monomers which cannot split any further and that in a collision-induced fragmentation the larger particle splits into two fragments. We start from the Boltzmann equation for the mass-velocity distribution function and derive Smoluchowski-like equations for concentrations of particles of different mass. We analyze these equations analytically, solve them numerically and perform Monte Carlo simulations. When aggregation and fragmentation energy thresholds do not depend on the masses of the colliding particles, the model becomes analytically tractable. In this case we show the emergence of the two types of behavior: the regime of unlimited cluster growth arises when fragmentation is (relatively) weak and the relaxation towards a steady state occurs when fragmentation prevails. In a model with mass-dependent Eagg and Efrag the evolution with a cross-over from one of the regimes to another has been detected

    Characteristics of Executive Functioning in a Small Sample of Children with Tourette Syndrome

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    Tourette Syndrome (TS) is a disorder that involves at least one vocal tic and two or more motor tics, however associated symptoms of Obsessive Compulsive Disorder (OCD) and Attention Deficit Disorder with or without hyperactivity (ADHD) are common. Many children with TS exhibit educational difficulties and one possible explanation may be deficits in executive functioning. The focus of this study was to look at the severity of symptoms often associated with TS (tics, OCS, and ADHD symptoms) and its potential relationship with the Behavior Rating Inventory of Executive Function (BRIEF) parent form in eleven children diagnosed with Tourette syndrome, ages 8-14. The BRIEF was completed by the parent of the child along with symptom measures evaluating tics, obsessive-compulsive behaviors and attention deficit symptoms. Despite relative low mean scores on the symptom measures and just a few children exhibiting clinically significant scores on the BRIEF indexes, at least half the children exhibited abnormal scores on the working memory, inhibit, and shift subscales on the BRIEF. Varying patterns of relationships were found on the BRIEF subscales for each symptom severity scales. Results suggest that the BRIEF may be useful in determining the specific areas of difficulty in a population with variable symptomatology

    PMH33 DRUG TREATMENT PATTERNS OF BIPOLAR DISORDER AND ASSOCIATED COSTS

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    Synaptic Circuit Abnormalities of Motor-Frontal Layer 2/3 Pyramidal Neurons in an RNA Interference Model of Methyl-CpG-Binding Protein 2 Deficiency

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    Rett syndrome, an autism spectrum disorder with prominent motor and cognitive features, results from mutations in the gene for methyl-CpG-binding protein 2 (MeCP2). Here, to identify cortical circuit abnormalities that are specifically associated with MeCP2 deficiency, we used glutamate uncaging and laser scanning photostimulation to survey intracortical networks in mouse brain slices containing motor-frontal cortex. We used in utero transfection of short hairpin RNA constructs to knock down MeCP2 expression in a sparsely distributed subset of layer (L) 2/3 pyramidal neurons in wild-type mice, and compared input maps recorded from transfected-untransfected pairs of neighboring neurons. The effect of MeCP2 deficiency on local excitatory input pathways was severe, with an average reduction in excitatory synaptic input from middle cortical layers (L3/5A) of >30% compared with MeCP2-replete controls. MeCP2 deficiency primarily affected the strength, rather than the topography, of excitatory intracortical pathways. Inhibitory synaptic inputs and intrinsic eletrophysiological properties were unaffected in the MeCP2-knockdown neurons. These studies indicate that MeCP2 deficiency in individual postsynaptic cortical pyramidal neurons is sufficient to induce a pathological synaptic defect in excitatory intracortical circuits

    Mental health care for medical staff and affiliated healthcare workers during the COVID-19 pandemic

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    The COVID-19 pandemic is an unprecedented challenge for society. Supporting the mental health of medical staff and affiliated healthcare workers (staff) is a critical part of the public health response. This paper details the effects on staff and addresses some of the organisational, team and individual considerations for supporting staff (pragmatically) during this pandemic. Leaders at all levels of health care organisations will find this a valuable resource. </jats:p

    Teaching Medical Students Optimal Consulting Skills: The Challenge of Generating Better Referring Physicians.

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    Rationale and objectives We sought to incorporate a new teaching module into the traditional medical student radiology clerkship, to improve the necessary skills for future referring physicians. Materials and methods A new required and graded module was introduced in 2014 into the radiology clerkship in year three of medical school: the Mystery Case. Each student was provided a unique and undifferentiated case from a dedicated teaching file containing de-identified images and requisition data. Students were expected to complete three serial tasks over one week: 1) prepare a voice recognition-derived, structured radiological report utilizing appropriate and relevant vocabulary; 2) discuss pertinent additional clinical information; and 3) discuss appropriate follow-up imaging, in addition to information on how to best prepare patients for these potential patient exams (e.g., with or without contrast, bowel preparation, and length of study). Students were provided written examples and dedicated class instruction with interactive discussions covering specific cases and associated related cases through random pairing with radiology resident and attending mentors. At the close of the week, students gave brief oral presentations of their cases and submitted the tasks for a written evaluation. Upon completion of the clerkship, the students completed a Likert-type six-item survey to evaluate the perceived improvement in select skills. Results The survey was completed by 82% (54/66) of the enrolled students, with 85% finding the Mystery Case an effective use of time. Medical students perceived an improved awareness of the patient care process (77%), awareness of the medical imaging resources available (89%), ability to understand a radiology report (74%), and ability to advise patients (69%). Conclusion Introduction of the Mystery Case as a graded exercise in the medical school radiology clerkship was perceived by students as effective use of time, with an improvement in the skills essential for future referring physicians

    Quantifying Environmental Limiting Factors on Tree Cover Using Geospatial Data

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    Environmental limiting factors (ELFs) are the thresholds that determine the maximum or minimum biological response for a given suite of environmental conditions. We asked the following questions: 1) Can we detect ELFs on percent tree cover across the eastern slopes of the Lake Tahoe Basin, NV? 2) How are the ELFs distributed spatially? 3) To what extent are unmeasured environmental factors limiting tree cover? ELFs are difficult to quantify as they require significant sample sizes. We addressed this by using geospatial data over a relatively large spatial extent, where the wall-to-wall sampling ensures the inclusion of rare data points which define the minimum or maximum response to environmental factors. We tested mean temperature, minimum temperature, potential evapotranspiration (PET) and PET minus precipitation (PET-P) as potential limiting factors on percent tree cover. We found that the study area showed system-wide limitations on tree cover, and each of the factors showed evidence of being limiting on tree cover. However, only 1.2% of the total area appeared to be limited by the four (4) environmental factors, suggesting other unmeasured factors are limiting much of the tree cover in the study area. Where sites were near their theoretical maximum, non-forest sites (tree cover \u3c 25%) were primarily limited by cold mean temperatures, open-canopy forest sites (tree cover between 25% and 60%) were primarily limited by evaporative demand, and closed-canopy forests were not limited by any particular environmental factor. The detection of ELFs is necessary in order to fully understand the width of limitations that species experience within their geographic range

    Three-body confinement force in a realistic constituent quark model

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    We show that in realistic constituent quark models based on a two-body confinement interaction color states appear in the middle of the experimentally known spectrum. To avoid this situation we implement a three-body confinement interaction, introduced on an algebraic basis, into a semirelativistic version of the Goldstone-boson-exchange constituent quark model and by solving the Faddeev equations we show that this interaction can increase the gap between singlet and colour states, such as the latter can be ignored and the known baryons can be described as q3q^3 systems. We analyze the effect of a Δ\Delta- and a Y-shape three-body interaction.Comment: 14 pages, 3 figures, revised version to appear in Nucl. Phys.
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