3,783 research outputs found
Sonic inlet noise attenuation and performance with a J-85 turbojet engine as a noise source
A static test program was conducted to investigate aerodynamic and acoustic performance of a sonic inlet used as a noise suppressor. A translating centerbody type inlet with radial vanes was tested ahead of a J85-GE-13 turbojet engine. The inlet when fully choked, maintained high recovery with low distortions while dramatically reducing noise emanating from the compressor. Recoveries of 98.1% at simulated takeoff and 95% at approach were attained with associated sound attenuation of 40 db and 38 db respectively. Inlet lip shape was found to have significant effects on noise attenuation at these static conditions
Counting statistics of coherent population trapping in quantum dots
Destructive interference of single-electron tunneling between three quantum
dots can trap an electron in a coherent superposition of charge on two of the
dots. Coupling to external charges causes decoherence of this superposition,
and in the presence of a large bias voltage each decoherence event transfers a
certain number of electrons through the device. We calculate the counting
statistics of the transferred charges, finding a crossover from sub-Poissonian
to super-Poissonian statistics with increasing ratio of tunnel and decoherence
rates.Comment: 4 pages, 2 figure
Theory of the topological Anderson insulator
We present an effective medium theory that explains the disorder-induced
transition into a phase of quantized conductance, discovered in computer
simulations of HgTe quantum wells. It is the combination of a random potential
and quadratic corrections proportional to p^2 sigma_z to the Dirac Hamiltonian
that can drive an ordinary band insulator into a topological insulator (having
an inverted band gap). We calculate the location of the phase boundary at weak
disorder and show that it corresponds to the crossing of a band edge rather
than a mobility edge. Our mechanism for the formation of a topological Anderson
insulator is generic, and would apply as well to three-dimensional
semiconductors with strong spin-orbit coupling.Comment: 4 pages, 3 figures (updated figures, calculated DOS
Switching of electrical current by spin precession in the first Landau level of an inverted-gap semiconductor
We show how the quantum Hall effect in an inverted-gap semiconductor (with
electron- and hole-like states at the conduction- and valence-band edges
interchanged) can be used to inject, precess, and detect the electron spin
along a one-dimensional pathway. The restriction of the electron motion to a
single spatial dimension ensures that all electrons experience the same amount
of precession in a parallel magnetic field, so that the full electrical current
can be switched on and off. As an example, we calculate the magnetoconductance
of a p-n interface in a HgTe quantum well and show how it can be used to
measure the spin precession due to bulk inversion asymmetry.Comment: 5 pages, 4 figures, extended versio
Clinical Review of Bovine Virus Diarrhea and Vaccination Related Problems
Bovine virus diarrhea (BVD) was first recognized in 1946 in the United States and described as an X disease of cattle in the same year in Canada. It was reported in Sweden in 1948. In 1953, it was reported by Ramsey and Chivers as a mucosal disease
{\em Ab initio} Quantum Monte Carlo simulation of the warm dense electron gas in the thermodynamic limit
We perform \emph{ab initio} quantum Monte Carlo (QMC) simulations of the warm
dense uniform electron gas in the thermodynamic limit. By combining QMC data
with linear response theory we are able to remove finite-size errors from the
potential energy over the entire warm dense regime, overcoming the deficiencies
of the existing finite-size corrections by Brown \emph{et al.}~[PRL
\textbf{110}, 146405 (2013)]. Extensive new QMC results for up to
electrons enable us to compute the potential energy and the
exchange-correlation free energy of the macroscopic electron gas with
an unprecedented accuracy of . A comparison of our new data to the recent parametrization of
by Karasiev {\em et al.} [PRL {\bf 112}, 076403 (2014)] reveals
significant deviations to the latter
Finite difference method for transport properties of massless Dirac fermions
We adapt a finite difference method of solution of the two-dimensional
massless Dirac equation, developed in the context of lattice gauge theory, to
the calculation of electrical conduction in a graphene sheet or on the surface
of a topological insulator. The discretized Dirac equation retains a single
Dirac point (no "fermion doubling"), avoids intervalley scattering as well as
trigonal warping, and preserves the single-valley time reversal symmetry (=
symplectic symmetry) at all length scales and energies -- at the expense of a
nonlocal finite difference approximation of the differential operator. We
demonstrate the symplectic symmetry by calculating the scaling of the
conductivity with sample size, obtaining the logarithmic increase due to
antilocalization. We also calculate the sample-to-sample conductance
fluctuations as well as the shot noise power, and compare with analytical
predictions.Comment: 11 pages, 12 figure
Analysis of Oct4-dependent transcriptional networks regulating self-renewal and pluripotency in human embryonic stem cells
The POU domain transcription factor OCT4 is a key regulator of pluripotency in the early mammalian embryo and is highly expressed in the inner cell mass of the blastocyst. Consistent with its essential role in maintaining pluripotency, Oct4 expression is rapidly downregulated during formation of the trophoblast lineage. To enhance our understanding of the molecular basis of this differentiation event in humans, we used a functional genomics approach involving RNA interference-mediated suppression of OCT4 function in a human ESC line and analysis of the resulting transcriptional profiles to identify OCT4-dependent genes in human cells. We detected altered expression of >1,000 genes, including targets regulated directly by OCT4 either positively (NANOG, SOX2, REX1, LEFTB, LEFTA/EBAF DPPA4, THY1, and TDGF1) or negatively (CDX2, EOMES, BMP4, TBX18, Brachyury [T], DKK1, HLX1, GATA6, ID2, and DLX5), as well as targets for the OCT4-associated stem cell regulators SOX2 and NANOG. Our data set includes regulators of ACTIVIN, BMP, fibroblast growth factor, and WNT signaling. These pathways are implicated in regulating human ESC differentiation and therefore further validate the results of our analysis. In addition, we identified a number of differentially expressed genes that are involved in epigenetics, chromatin remodeling, apoptosis, and metabolism that may point to underlying molecular mechanisms that regulate pluripotency and trophoblast differentiation in humans. Significant concordance between this data set and previous comparisons between inner cell mass and trophectoderm in human embryos indicates that the study of human ESC differentiation in vitro represents a useful model of early embryonic differentiation in humans
A web observatory for the machine processability of structured data on the web
General human intelligence is needed in order to process Linked Open Data (LOD). On the Semantic Web (SW), content is intended to be machine-processable as well. But the extent to which a machine is able to navigate, access, and process the SW has not been extensively researched. We present LOD Observer, a web observatory that studies the Web from a machine processor's point of view. We do this by reformulating the five star model of LOD publishing in quantifiable terms. Secondly, we built an infrastructure that allows the model's criteria to be quantified over existing datasets. Thirdly, we analyze a significant snapshot of the LOD cloud using this infrastructure and discuss the main problems a machine processor encounters
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