1,465 research outputs found
Thermal modeling of terahertz quantum-cascade lasers: comparison of optical waveguides
We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappaperp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappaperp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model
On the degree of scale invariance of inflationary perturbations
Many, if not most, inflationary models predict the power-law index of the
spectrum of density perturbations is close to one, though not precisely equal
to one, |n-1| \sim O(0.1), implying that the spectrum of density perturbations
is nearly, but not exactly, scale invariant. Some models allow n to be
significantly less than one (n \sim 0.7); a spectral index significantly
greater than one is more difficult to achieve. We show that n \approx 1 is a
consequence of the slow-roll conditions for inflation and ``naturalness,'' and
thus is a generic prediction of inflation. We discuss what is required to
deviate significantly from scale invariance, and then show, by explicit
construction, the existence of smooth potentials that satisfy all the
conditions for successful inflation and give as large as 2.Comment: 7 pages, 2 figures, submitted to Phys. Rev.
Source apportionment of polycyclic aromatic hydrocarbons in urban air using positive matrix factorization and spatial distribution analysis
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Student perceptions of journalism as an occupation: the view from the front of the class
News media managers routinely complain that university journalism programs are out of sync with practice. Yet their views are not always shared by academics in journalism programs or by journalists. This raises questions about how the views of journalism held by journalism students are formed. What students are exposed to during their studies exercises a major influence on their perceptions. Information was collected from students about (a) mainly classroom learning; (b) industry internships; and (c) a voluntary cooperative activity. Their feedback indicated that, while overlapping, each experience illuminated a somewhat different journalism "reality". This suggests that if students were exposed to a range of experience of journalism, they would form differing opinions of the occupation; that work integrated learning (WIL) in particular would help them make sense of various journalism "realities" and that more research is required into this aspect of journalism education
Scalar Electrodynamics and Primordial Magnetic Fields
A primordial magnetic field may be generated during an inflationary period if
conformal invariance is broken. We reexamine and generalize previous results
about the magnetic field produced by couplings of the form . We show that the amplitude of the magnetic field depends
strongly on . For adequate values of the field produced can serve as
seed for galactic magnetic fields. We also compute the effective interaction
between the electromagnetic field and the geometry in the context of scalar QED
(with and without classical conformal invariance). In both cases, the amplitude
of the magnetic field is too small to be of astrophysical interest.Comment: 16 pages, LaTeX, no figure
Renal pericytes: regulators of medullary blood flow
Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla
197A pilot study of myeloablative (MA) autologous stem cell transplantation (Auto SCT) followed by reduced intensity (RI) allogeneic transplantation (ALLO SCT) in children and young adults with relapsed lymphoma
Coupled-mode equations and gap solitons in a two-dimensional nonlinear elliptic problem with a separable periodic potential
We address a two-dimensional nonlinear elliptic problem with a
finite-amplitude periodic potential. For a class of separable symmetric
potentials, we study the bifurcation of the first band gap in the spectrum of
the linear Schr\"{o}dinger operator and the relevant coupled-mode equations to
describe this bifurcation. The coupled-mode equations are derived by the
rigorous analysis based on the Fourier--Bloch decomposition and the Implicit
Function Theorem in the space of bounded continuous functions vanishing at
infinity. Persistence of reversible localized solutions, called gap solitons,
beyond the coupled-mode equations is proved under a non-degeneracy assumption
on the kernel of the linearization operator. Various branches of reversible
localized solutions are classified numerically in the framework of the
coupled-mode equations and convergence of the approximation error is verified.
Error estimates on the time-dependent solutions of the Gross--Pitaevskii
equation and the coupled-mode equations are obtained for a finite-time
interval.Comment: 32 pages, 16 figure
Low Day 100 Transplant-Related Mortality (TRM) Following Clofarabine (CLO) in Combination with Cytarabine and Total Body Irradiation (TBI), Myeloablative Conditioning (MAC) and Allogeneic Stem Cell Transplantation (AlloSCT) in Children, Adolescents and Young Adults (CAYA) with Poor-Risk Acute Leukemia
Virus shapes and buckling transitions in spherical shells
We show that the icosahedral packings of protein capsomeres proposed by
Caspar and Klug for spherical viruses become unstable to faceting for
sufficiently large virus size, in analogy with the buckling instability of
disclinations in two-dimensional crystals. Our model, based on the nonlinear
physics of thin elastic shells, produces excellent one parameter fits in real
space to the full three-dimensional shape of large spherical viruses. The
faceted shape depends only on the dimensionless Foppl-von Karman number
\gamma=YR^2/\kappa, where Y is the two-dimensional Young's modulus of the
protein shell, \kappa is its bending rigidity and R is the mean virus radius.
The shape can be parameterized more quantitatively in terms of a spherical
harmonic expansion. We also investigate elastic shell theory for extremely
large \gamma, 10^3 < \gamma < 10^8, and find results applicable to icosahedral
shapes of large vesicles studied with freeze fracture and electron microscopy.Comment: 11 pages, 12 figure
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