1,342 research outputs found
Recent advancement of turbulent flow measurement techniques
Advancements of the fluctuating density gradient cross beam laser Schlieren technique, the fluctuating line-reversal temperature measurement and the development of the two-dimensional drag-sensing probe to a three-dimensional drag-sensing probe are discussed. The three-dimensionality of the instantaneous momentum vector can shed some light on the nature of turbulence especially with swirling flow. All three measured fluctuating quantities (density, temperature, and momentum) can provide valuable information for theoreticians
Epitaxial Growth of LaSrFeO thin films by laser ablation
We report on the synthesis of high quality LaSrFeO (LSFO)
thin films using the pulsed laser deposition technique on both SrTiO (STO)
and LaAlO (LAO) substrates (100)-oriented. From X-Ray diffraction (XRD)
studies, we find that the films have an out-of-plane lattice parameter around
0.3865nm, almost independent of the substrate (i.e. the nature of the strains).
The transport properties reveal that, while LSFO films deposited on STO exhibit
an anomaly in the resistivity vs temperature at 180K (corresponding to the
charge-ordered transition and associated with a transition from a paramagnetic
to an antiferromagnetic state), the films grown on LAO display a very small
magnetoresistance behavior and present an hysteresis around 270K under the
application of a 4T magnetic field. The changes in transport properties between
both substrates are discussed and compared with the corresponding single
crystals.Comment: 9 pages, 4 figure
A note on cluster expansions, tree graph identities, extra 1/ N ! factors!!!
We draw attention to a new tree graph identity which substantially improves on the usual tree graph method of proving convergence of cluster expansions in statistical mechanics and quantum field theory. We can control expansions that could not be controlled before.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43217/1/11005_2004_Article_BF00420041.pd
Sparsity driven ultrasound imaging
An image formation framework for ultrasound imaging from synthetic transducer arrays based on sparsity-driven regularization functionals using single-frequency Fourier domain data is proposed. The framework involves the use of a physics-based forward model of the ultrasound observation process, the formulation of image formation as the solution of an associated optimization problem, and the solution of that problem through efficient numerical algorithms. The sparsity-driven, model-based approach estimates a complex-valued reflectivity field and preserves physical features in the scene while suppressing spurious artifacts. It also provides robust reconstructions in the case of sparse and reduced observation apertures. The effectiveness of the proposed imaging strategy is demonstrated using experimental data
Orbital Structure and Magnetic Ordering in Layered Manganites: Universal Correlation and Its Mechanism
Correlation between orbital structure and magnetic ordering in bilayered
manganites is examined. A level separation between the and
orbitals in a Mn ion is calculated in the ionic model for a
large number of the compounds. It is found that the relative stability of the
orbitals dominates the magnetic transition temperatures as well as the magnetic
structures. A mechanism of the correlation between orbital and magnetism is
investigated based on the theoretical model with the two orbitals under
strong electron correlation.Comment: 4 pages, 4 figure
Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide
We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4–5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ~10 m thick lock-in zone beginning at ~67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO<sub>2</sub> at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr<sup>&minus;1</sup> ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of &Delta;age (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process
www.niss.org Construction of Full Sample and Replicate Weights for Project Talent, with Applications
Project Talent is a large, nationally representative longitudinal study developed by the American Institutes for Research and conducted from 1960 to 1974. The goals were to assess the interests, abilities, and demographics of 9 th –12 th graders and to follow their trajectories into adulthood. More than 1,200 junior and senior high schools participated. Replicate weights were not constructed at the time, preventing the estimation of standard errors. Today, Project Talent is being revived to study the physical, cognitive, economic, and social processes of aging. In this paper, the retrospective construction of 104 sets of student-level replicate weights is described. Partitioning analysis was performed to generate variance strata and variance primary sampling units. The student-level replicate weights were constructed using a jackknife procedure. The process included adjustment of the base year weights and calibration of (full sample and replicate weights) to the total number of secondary school students in the U. S. in the spring of 1960. The use of replicate weights is illustrated by estimating standard errors for means of composite cognitive scores constructed from student questionnaires. We also describe construction of mortality- and nonresponse-adjusted weights for the thre
Presentació
Obra col·lectiva biennal, creada per l'Institut de la Comunicació de la Universitat Autònoma de Barcelona (InCom-UAB), l'any 2000. La desena edició, corresponent al bienni 2017-2018, va comptar amb el suport de la Generalitat de Catalunya; el patrocini de Naturgy; la col·laboració de l'Ajuntament de Barcelona; la subscripció institucional de la Societat Catalana de Comunicació (filial de l'Institut d'Estudis Catalans); i la col·laboració cientÃfica de Comscore, Estudio General de Medios (EGM)/Asociación para la Investigación de Medios de Comunicación (AIMC), l'Observatori de la Comunicació a Catalunya, i el Portal de la Comunicació (InCom-UAB).En el marc del Grup Internacional d'Estudis sobre Comunicació i Cultura (InCom-UAB), reconegut com a Grup Consolidat de Recerca de la Generalitat de Catalunya per al perÃode 2017-2020 (Referència de concessió 2017 SGR 00760).Aquest text que esteu llegint és la presentació de la desena edició de l'Informe de la comunicació a Catalunya. Arribar a aquest nombre de publicacions -i, a més a més, respectant i mantenint els compromisos adquirits des d'un bon principi- no ha estat gens fà cil. És més, aquesta fita hauria estat impossible sense el suport de la Generalitat de Catalunya, de Naturgy (abans Gas Natural Fenosa) i de la Universitat Autònoma de Barcelona, on té la seva seu l'Institut de la Comunicació (InCom-UAB). Cal tenir en compte que estem parlant d'un projecte acadèmic que ha estat capaç d'analitzar, edició rere edició, tots els canvis viscuts a la indústria del sector comunicatiu català i la preocupació del qual, per tant, per establir i consolidar vincles entre la universitat i l'empresa no és un fet recent, sinó que forma part de la seva essència
Relation between crystal and magnetic structures of the layered manganites La2-2xSr1+2xMn2O7 (0.30 =< x =< 0.50)
Comprehensive neutron-powder diffraction and Rietveld analyses were carried
out to clarify the relation between the crystal and magnetic structures of
La2-2xSr1+2xMn2O7 (0.30 =< x =< 0.50). The Jahn-Teller (JT) distortion of Mn-O6
octahedra, i.e., the ratio of the averaged apical Mn-O bond length to the
equatorial Mn-O bond length, is Delta_JT=1.042(5) at x=0.30, where the magnetic
easy-axis at low temperature is parallel to the c axis. As the JT distortion
becomes suppressed with increasing x, a planar ferromagnetic structure appears
at x =< 0.32, which is followed by a canted antiferromagnetic (AFM) structure
at x =< 0.39. The canting angle between neighboring planes continuously
increases from 0 deg (planar ferromagnet: 0.32 =< x < 0.39) to 180 deg (A-type
AFM: x=0.48 where Delta_JT=1.013(5)). Dominance of the A-type AF structure with
decrease of JT distortion can be ascribed to the change in the eg orbital state
from d3z^2-r^2 to dx^2-y^2
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