5,087 research outputs found

    Linear magnetoresistance in metals: guiding center diffusion in a smooth random potential

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    We predict that guiding center (GC) diffusion yields a linear and non-saturating (transverse) magnetoresistance in 3D metals. Our theory is semi-classical and applies in the regime where the transport time is much greater than the cyclotron period, and for weak disorder potentials which are slowly varying on a length scale much greater than the cyclotron radius. Under these conditions, orbits with small momenta along magnetic field BB are squeezed and dominate the transverse conductivity. When disorder potentials are stronger than the Debye frequency, linear magnetoresistance is predicted to survive up to room temperature and beyond. We argue that magnetoresistance from GC diffusion explains the recently observed giant linear magnetoresistance in 3D Dirac materials

    A Convergent Iterative Solution of the Quantum Double-well Potential

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    We present a new convergent iterative solution for the two lowest quantum wave functions ψev\psi_{ev} and ψod\psi_{od} of the Hamiltonian with a quartic double well potential VV in one dimension. By starting from a trial function, which is by itself the exact lowest even or odd eigenstate of a different Hamiltonian with a modified potential V+δVV+\delta V, we construct the Green's function for the modified potential. The true wave functions, ψev\psi_{ev} or ψod\psi_{od}, then satisfies a linear inhomogeneous integral equation, in which the inhomogeneous term is the trial function, and the kernel is the product of the Green's function times the sum of δV\delta V, the potential difference, and the corresponding energy shift. By iterating this equation we obtain successive approximations to the true wave function; furthermore, the approximate energy shift is also adjusted at each iteration so that the approximate wave function is well behaved everywhere. We are able to prove that this iterative procedure converges for both the energy and the wave function at all xx.Comment: 76 pages, Latex, no figure, 1 tabl

    Laplacian-Steered Neural Style Transfer

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    Neural Style Transfer based on Convolutional Neural Networks (CNN) aims to synthesize a new image that retains the high-level structure of a content image, rendered in the low-level texture of a style image. This is achieved by constraining the new image to have high-level CNN features similar to the content image, and lower-level CNN features similar to the style image. However in the traditional optimization objective, low-level features of the content image are absent, and the low-level features of the style image dominate the low-level detail structures of the new image. Hence in the synthesized image, many details of the content image are lost, and a lot of inconsistent and unpleasing artifacts appear. As a remedy, we propose to steer image synthesis with a novel loss function: the Laplacian loss. The Laplacian matrix ("Laplacian" in short), produced by a Laplacian operator, is widely used in computer vision to detect edges and contours. The Laplacian loss measures the difference of the Laplacians, and correspondingly the difference of the detail structures, between the content image and a new image. It is flexible and compatible with the traditional style transfer constraints. By incorporating the Laplacian loss, we obtain a new optimization objective for neural style transfer named Lapstyle. Minimizing this objective will produce a stylized image that better preserves the detail structures of the content image and eliminates the artifacts. Experiments show that Lapstyle produces more appealing stylized images with less artifacts, without compromising their "stylishness".Comment: Accepted by the ACM Multimedia Conference (MM) 2017. 9 pages, 65 figure

    Environmental and social determinants of leisure-time physical activity in children with autism spectrum disorder

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    Background: It is increasingly recognized that children\u27s physical activity behaviors are shaped by neighborhood environment factors and their parent\u27s support. However, these factors have been scarcely studied among children with autism spectrum disorder (ASD), a population at risk of inactivity. Objective: This cross-sectional survey study was designed to examine how neighborhood environmental factors and parental support are related to physical activity levels of children with ASD. Also, this study examined if the relationship between the environment and physical activity is modified by demographic factors and COVID-19 related concerns. Methods: An online survey was completed by parents of children with ASD aged 10–17 years. The questionnaire included items related to environmental factors (i.e., distance to school, distance to park, existence of sidewalks, walkability), parent support for physical activity (i.e., encouraging, watching, and providing transportation), child\u27s physical activity, and demographic characteristics. The instrument also queried parental concerns about COVID-19 and their child\u27s physical activity participation. Results: The results indicate that proximity to a local park and to school is positively associated with physical activity. Parent\u27s encouraging behavior correlated with and predicted children\u27s physical activity levels. Also, higher levels of COVID-19 related concerns among parents were related to decreased physical activity supporting behaviors. Conclusions: This study demonstrated that the neighborhood environment, in particular the distance between home and parks and schools, and parent support behavior are influential factors that may shape physical activity behaviors for children with ASD

    A Massive Yang-Mills Theory based on the Nonlinearly Realized Gauge Group

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    We propose a subtraction scheme for a massive Yang-Mills theory realized via a nonlinear representation of the gauge group (here SU(2)). It is based on the subtraction of the poles in D-4 of the amplitudes, in dimensional regularization, after a suitable normalization has been performed. Perturbation theory is in the number of loops and the procedure is stable under iterative subtraction of the poles. The unphysical Goldstone bosons, the Faddeev-Popov ghosts and the unphysical mode of the gauge field are expected to cancel out in the unitarity equation. The spontaneous symmetry breaking parameter is not a physical variable. We use the tools already tested in the nonlinear sigma model: hierarchy in the number of Goldstone boson legs and weak power-counting property (finite number of independent divergent amplitudes at each order). It is intriguing that the model is naturally based on the symmetry SU(2)_L local times SU(2)_R global. By construction the physical amplitudes depend on the mass and on the self-coupling constant of the gauge particle and moreover on the scale parameter of the radiative corrections. The Feynman rules are in the Landau gauge.Comment: 44 pages, 1 figure, minor changes, final version accepted by Phys. Rev.

    A Profile of Nonresident Travelers through Missoula: Winter 1993

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    Describes travel characteristics of nonresident visitors to Montana who passed through, made expenditures, or stayed overnight in Missoula during the 1993 winter season. Characteristics are compared to statewide winter travel characteristics

    Effect of age on the prognostic value of left ventricular function in patients with acute coronary syndrome:a prospective registry study

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    Objective: This study aims to study the prognostic impact of LV function on mortality and examine the effect of age on the prognostic value of left ventricular function.  Methods: We examined the Myocardial Ischaemia National Audit Project (MINAP) registry (2006-2010) data with a mean follow up of 2.1 years. LV function was categorized into good (ejection fraction (EF) ≥50%), moderate (EF 30-49%) and poor (EF <30%) categories. Cox-proportional hazards models were constructed to examine the prognostic significance of LV function in different age groups (<65, 65-74, 75-84 and ≥85 years) on all-cause mortality adjusting for baseline variables.  Results: Of 424,848 patients, LV function data available for 123,609. Multiple imputations were used to impute missing values of LV function and the final sample for analyses were drawn from 414,305. After controlling for confounders, 339,887 participants were included in the regression models. For any age group, mortality was higher with worsening degree of LV impairment. Increased age reduced the adverse prognosis associated with reduced LV function (hazard ratios (HRs) of death comparing poor LV function to good LV function were 2.11 95%CI 1.88-2.37 for age <65 years and 1.28 95%CI 1.20-1.36 for age ≥85 years. Older patients had a high mortality risk even in those with good LV function. HRs of mortality for ≥85 compared to <65 years (HR=1.00) within good, moderate and poor ejection fractions groups were 5.89, 4.86 and 3.43, respectively.  Conclusions: In patients with ACS, clinicians should interpret the prognostic value of LV function taking into account patient’s age

    Non-saturating large magnetoresistance in semimetals

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    The rapidly expanding class of quantum materials known as {\emph{topological semimetals}} (TSM) display unique transport properties, including a striking dependence of resistivity on applied magnetic field, that are of great interest for both scientific and technological reasons. However, experimental signatures that can identify or discern the dominant mechanism and connect to available theories are scarce. Here we present the magnetic susceptibility (χ\chi), the tangent of the Hall angle (tanθH\tan\theta_H) along with magnetoresistance in four different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb2_2 and TaSb2_2, all of which exhibit non-saturating large MR. We find that the distinctly different temperature dependences, χ(T)\chi(T) and the values of tanθH\tan\theta_H in phosphides and antimonates serve as empirical criteria to sort the MR from different origins: NbP and TaP being uncompensated semimetals with linear dispersion, in which the non-saturating magnetoresistance arises due to guiding center motion, while NbSb2_2 and TaSb2_2 being {\it compensated} semimetals, with a magnetoresistance emerging from nearly perfect charge compensation of two quadratic bands. Our results illustrate how a combination of magnetotransport and susceptibility measurements may be used to categorize the increasingly ubiquitous non-saturating large magnetoresistance in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions, 6 figure

    Theory of a Continuous Hc2_{c2} Normal-to-Superconducting Transition

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    I study the Hc2H_{c2} transition within the Ginzburg-Landau model, with mm-component order parameter ψi\psi_i. I find a renormalized fixed point free energy, exact in mm\rightarrow\infty limit, suggestive of a 22nd-order transition in contrast to a general belief of a 11st-order transition. The thermal fluctuations for H0H\neq 0 force one to consider an infinite set of marginally relevant operators for d<duc=6d<d_{uc}=6. I find dlc=4d_{lc}=4, predicting that the ODLRO does not survive thermal fluctuations in d=2,3d=2,3. The result is a solution to a critical fixed point that was found to be inaccessible within ϵ=6d\epsilon=6-d-expansion, previously considered in E.Brezin, D.R.Nelson, A.Thiaville, Phys.Rev.B {\bf 31}, 7124 (1985), and was interpreted as a 11st-order transition.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with a figure already inside text; to appear in Phys. Rev. Lett

    Physical Activity for Adults with Visual Impairments: Impact of Socio-Demographic Factors

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    Little is known about what factors influence physical activity participation for adult-aged individuals with visual impairments. Therefore, the purpose of this study was to explore the impact of socio-demographic factors on the physical activity participation of adults with visual impairments. The international physical activity questionnaire-short form and a socio-demographic factor questionnaire were distributed to individuals with visual impairments. A total of 176 adults (Mage = 47.04, 52.8% female) completed the questionnaires. Physical activity and socio-demographic variables were analyzed descriptively and relationships were explored using correlation analysis and multiple regression analysis. On average, participants reported 413.79 minutes of moderate-to-vigorous physical activity and 2058.52 minutes of sedentary active per week. A significant amount of variance of physical activity was explained by the socio-demographic variables in this study. Of the socio-demographic variables measured, only gender emerges as a significant positive predictor of total weekly physical activity. The results of this study both affirm and conflict with previous research. Unlike previous research focusing on those with visual impairments, this study demonstrated that gender was an important predictor of physical activity. This finding is consistent with population-wide data on individuals without disabilities in the United States
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