6,273 research outputs found
1-D modelling and 3-D simulation of confined bubble formation and formation and pressure fluctuations during flow boiling in a microchannel with a rectangular cross-section of high aspect ratio
Copyright @ 2009 ASMEA simple 1-D model with low requirements for computing time is required to investigate parametric influences on the potentially adverse effects of pressure fluctuations driven by confined vapour bubble growth in microchannel evaporative cooling systems operating at high heat fluxes. A model is developed in this paper for the particular conditions of a channel of rectangular cross-section with high aspect ratio with a constant inlet flow rate (zero upstream compressibility). (The model will later be extended to the conditions of finite upstream compressibility that lead to transient flow reversal). Some parametric trends predicted by the model are presented. The simplifying assumptions in the model are examined in the light of a 3-D simulation by a commercial CFD code, described in an accompanying paper by the same authors. The predictions of pressure changes are in reasonable agreement. It is suggested that the 1-D model will be a useful design tool.This work is supported by the UK Engineering and Physical Sciences Research Council (EPSRC) under grants EP/D500095/1 and EP/D500125/1
Corrections to the thermodynamics of Schwarzschild-Tangherlini black hole and the generalized uncertainty principle
We investigate the thermodynamics of Schwarzschild-Tangherlini black hole in
the context of the generalized uncertainty principle. The corrections to the
Hawking temperature, entropy and the heat capacity are obtained via the
modified Hamilton-Jacobi equation. These modifications show that the GUP
changes the evolution of Schwarzschild-Tangherlini black hole. Specially, the
GUP effect becomes susceptible when the radius or mass of black hole approach
to the order of Planck scale, it stops radiating and leads to black hole
remnant. Meanwhile, the Planck scale remnant can be confirmed through the
analysis of the heat capacity. Those phenomenons imply that the GUP may give a
way to solve the information paradox. Besides, we also investigate the
possibilities to observe the black hole at LHC, the results demonstrate that
the black hole can not be produced in the recent LHC.Comment: 12 pages, 6 figure
Independent tuning of electronic properties and induced ferromagnetism in topological insulators with heterostructure approach
The quantum anomalous Hall effect (QAHE) has been recently demonstrated in
Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures
below 100 mK. In those materials, the spins of unfilled d-electrons in the
transition metal dopants are exchange coupled to develop a long-range
ferromagnetic order, which is essential for realizing QAHE. However, the
addition of random dopants does not only introduce excess charge carriers that
require readjusting the Bi/Sb ratio, but also unavoidably introduces
paramagnetic spins that can adversely affect the chiral edge transport in QAHE.
In this work, we show a heterostructure approach to independently tune the
electronic and magnetic properties of the topological surface states in
(BixSb1-x)2Te3 without resorting to random doping of transition metal elements.
In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium
iron garnet (YIG), a high Curie temperature (~ 550 K) magnetic insulator, we
find that the TI surface in contact with YIG becomes ferromagnetic via
proximity coupling which is revealed by the anomalous Hall effect (AHE). The
Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is
uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is
varied, the AHE resistivity scales with the longitudinal resistivity. In this
approach, we decouple the electronic properties from the induced ferromagnetism
in TI. The independent optimization provides a pathway for realizing QAHE at
higher temperatures, which is important for novel spintronic device
applications.Comment: Accepted by Nano Letter
Hawking radiation of Dirac particles via tunneling from Kerr black hole
We investigated Dirac Particles' Hawking radiation from event horizon of Kerr
black hole in terms of the tunneling formalism. Applying WKB approximation to
the general covariant Dirac equation in Kerr spacetime background, we obtain
the tunneling probability for fermions and Hawking temperature of Kerr black
hole. The result obtained by taking the fermion tunneling into account is
consistent with the previous literatures.Comment: 7 pages, no figures, to appear in CQ
Layered THz waveguides for SPPs, filter and sensor applications
© 2019, The Author(s). Theory of five kinds of layered structure THz waveguides is presented. In these waveguides, the modified and hybrid THz surface plasmon-polaritons (SPPs) are researched in detail. On these modes, the effects of material in each layer are discussed. The anti-resonant reflecting mechanism is also discussed in these waveguides. The mode characteristics of both TM mode and TE mode are analyzed for guiding TM mode with low loss and TE modes with huge loss in one waveguide: the TE modes filter application is put forward. The mode characteristics for one waveguide have useful sensor applications: for TE1 mode, we find that the low cut-off frequency has a sensitivity (S) to the refractive index of the dielectric slab. The highest S can be 666.7 GHz/RIU when n2 = 1.5, w = 0 and t = 0.1 mm. We believe these results are very useful for designing practical THz devices for SPPs, filter and sensor applications
Band structure of topological insulators from noise measurements in tunnel junctions
The unique properties of spin-polarized surface or edge states in topological
insulators (TIs) make these quantum coherent systems interesting from the point
of view of both fundamental physics and their implementation in low power
spintronic devices. Here we present such a study in TIs, through tunneling and
noise spectroscopy utilizing TI/AlO/Co tunnel junctions with bottom TI
electrodes of either BiTe or BiSe. We demonstrate that features
related to the band structure of the TI materials show up in the tunneling
conductance and even more clearly through low frequency noise measurements. The
bias dependence of 1/f noise reveals peaks at specific energies corresponding
to band structure features of the TI. TI tunnel junctions could thus simplify
the study of the properties of such quantum coherent systems, that can further
lead to the manipulation of their spin-polarized properties for technological
purposes
Unconventional Planar Hall Effect in Exchange-Coupled Topological Insulator-Ferromagnetic Insulator Heterostructures
The Dirac electrons occupying the surface states (SSs) of topological
insulators (TIs) have been predicted to exhibit many exciting magneto-transport
phenomena. Here we report on the first experimental observation of an
unconventional planar Hall effect (PHE) and an electrically gate-tunable
hysteretic planar magnetoresistance (PMR) in EuS/TI heterostructures, in which
EuS is a ferromagnetic insulator (FMI) with an in-plane magnetization. In such
exchange-coupled FMI/TI heterostructures, we find a significant (suppressed)
PHE when the in-plane magnetic field is parallel (perpendicular) to the
electric current. This behavior differs from previous observations of the PHE
in ferromagnets and semiconductors. Furthermore, as the thickness of the 3D TI
films is reduced into the 2D limit, in which the Dirac SSs develop a
hybridization gap, we find a suppression of the PHE around the charge neutral
point indicating the vital role of Dirac SSs in this phenomenon. To explain our
findings, we outline a symmetry argument that excludes linear-Hall mechanisms
and suggest two possible non-linear Hall mechanisms that can account for all
the essential qualitative features in our observations.Comment: 17 pages, 4 figures, accepted by Phys. Rev.
Constraining the HI-Halo Mass Relation From Galaxy Clustering
We study the dependence of galaxy clustering on atomic gas mass using a
sample of 16,000 galaxies with redshift in the range of
and HI mass of , drawn from the 70% complete sample
of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies
with above different thresholds, and make volume-limited
clustering measurements in terms of three statistics: the projected two-point
correlation function, the projected cross-correlation function with respect to
a reference sample selected from the Sloan Digital Sky Survey, and the
redshift-space monopole moment. In contrast to previous studies, which found
no/weak HI-mass dependence, we find both the clustering amplitude on scales
above a few Mpc and the bias factors to increase significantly with increasing
HI mass for subsamples with HI mass thresholds above . For HI
mass thresholds below , while the measurements have large
uncertainties caused by the limited survey volume and sample size, the inferred
galaxy bias factors are systematically lower than the minimum halo bias factor
from mass-selected halo samples. The simple halo model, in which galaxy content
is only determined by halo mass, has difficulties in interpreting the
clustering measurements of the HI-selected samples. We extend the simple model
by including the halo formation time as an additional parameter. A model that
puts HI-rich galaxies into halos that formed late can reproduce the clustering
measurements reasonably well. We present the implications of our best-fitting
model on the correlation of HI mass with halo mass and formation time, as well
as the halo occupation distributions and HI mass functions for central and
satellite galaxies. These results are compared with the predictions from
semi-analytic galaxy formation models and hydrodynamic galaxy formation
simulations.Comment: Accepted for publication in ApJ. The 2PCF measurements are available
at http://sdss4.shao.ac.cn/guoh
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