4,121 research outputs found
Controllable Goos-H\"{a}nchen shifts and spin beam splitter for ballistic electrons in a parabolic quantum well under a uniform magnetic field
The quantum Goos-H\"{a}nchen shift for ballistic electrons is investigated in
a parabolic potential well under a uniform vertical magnetic field. It is found
that the Goos-H\"{a}nchen shift can be negative as well as positive, and
becomes zero at transmission resonances. The beam shift depends not only on the
incident energy and incidence angle, but also on the magnetic field and Landau
quantum number. Based on these phenomena, we propose an alternative way to
realize the spin beam splitter in the proposed spintronic device, which can
completely separate spin-up and spin-down electron beams by negative and
positive Goos-H\"{a}nchen shifts.Comment: 6 pages, 6 figure
Online Updating of Statistical Inference in the Big Data Setting
We present statistical methods for big data arising from online analytical
processing, where large amounts of data arrive in streams and require fast
analysis without storage/access to the historical data. In particular, we
develop iterative estimating algorithms and statistical inferences for linear
models and estimating equations that update as new data arrive. These
algorithms are computationally efficient, minimally storage-intensive, and
allow for possible rank deficiencies in the subset design matrices due to
rare-event covariates. Within the linear model setting, the proposed
online-updating framework leads to predictive residual tests that can be used
to assess the goodness-of-fit of the hypothesized model. We also propose a new
online-updating estimator under the estimating equation setting. Theoretical
properties of the goodness-of-fit tests and proposed estimators are examined in
detail. In simulation studies and real data applications, our estimator
compares favorably with competing approaches under the estimating equation
setting.Comment: Submitted to Technometric
Unconventional Superconducting Symmetry in a Checkerboard Antiferromagnet
We use a renormalized mean field theory to study the Gutzwiller projected BCS
states of the extended Hubbard model in the large limit, or the
--- model on a two-dimensional checkerboard lattice. At small
, the frustration due to the diagonal terms of and does not
alter the -wave pairing symmetry, and the negative (positive)
enhances (suppresses) the pairing order parameter. At large , the
ground state has an extended s-wave symmetry. At the intermediate , the
ground state is or -wave with time reversal symmetry broken.Comment: 6 pages, 6 figure
Acoustic meta-stethoscope for cardiac auscultation
Straight cylindrical stethoscopes serve as an important alternative to
conventional stethoscopes whose application in the treatment of infectious
diseases might be limited by the use of protective clothing. Yet their
miniaturization is challenging due to the low-frequency of bioacoustics signal.
Here, we design and experimentally implement a meta-stethoscope with
subwavelength size, simple fabrication, easy assembly yet high sensitivity,
which simply comprises multiple round perforated plate units and a cylindrical
shell. We elucidate our proposed mechanism by analytically deriving the
frequency response equation, which proves that the equivalent acoustic
propagation path is substantially increased by the high-index metamaterial,
enabling downscaling of the meta-stethoscope to subwavelength footprint. The
acoustic performance of meta-stethoscope is experimentally characterized by
monitoring the cardiac auscultation on clothed human body. The simulated and
measured results agree well, with both showing the expected enhancement of
sensitivity of our proposed meta-stethoscope (~ 10 dB) within the predicted
working frequency range from 80 to 130 Hz despite its compactness and
simplicity. Our designed portable, detachable yet effective meta-stethoscope
opens a route to metamaterial-enabled stethoscope paradigm, with potential
applications in diverse scenarios such as medical diagnosis and acoustic
sensing.Comment: 14 pages, 3 figure
Bis(μ-5-carbÂoxyÂbenzene-1,3-dicarboxylÂato)-κ3 O 1,O 1′:O 3;κ3 O 3:O 1,O 1′-bisÂ[(2-phenyl-1,3,7,8-tetraÂazaÂcycloÂpentaÂ[l]phenanthrene-κ2 N 7,N 8)lead(II)]
In the title compound, [Pb2(C9H4O6)2(C19H12N4)2], the PbII atom is five-coordinated by two N atoms from a chelating 2-phenyl-1H-1,3,7,8-tetraÂazaÂcycloÂpentaÂ[l]phenanthrene (L) ligand and three O atoms from two Hbtc ligands (H3btc is benzene-1,3,5-tricarbÂoxyÂlic acid), resulting in a distorted PbN2O3 coordination. Two PbII atoms are bridged by the Hbtc ligands, forming a discrete centrosymmetric dinuclear complex. InterÂmolecular N—H⋯O and O—H⋯O hydrogen bonds and π–π interÂactions between the pyridine and imidazole rings, and between the pyridyl rings of the L ligands [centroid–centroid distances = 3.600 (6) and 3.732 (6) Å] lead to a three-dimensional supraÂmolecular structure
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