98 research outputs found
Best Thermoelectric Efficiency of Ever-Explored Materials
A thermoelectric device is a heat engine that directly converts heat into
electricity. Many materials with a high figure of merit ZT have been discovered
in anticipation of a high thermoelectric efficiency. However, there has been a
lack of investigations on efficiency-based material evaluation, and little is
known about the achievable limit of thermoelectric efficiency. Here, we report
the highest thermoelectric efficiency using 13,353 published materials. The
thermoelectric device efficiencies of 808,610 configurations are calculated
under various heat-source temperatures (T_h) when the cold-side temperature is
300 K, solving one-dimensional thermoelectric integral equations with
temperature-dependent thermoelectric properties. For infinite-cascade devices,
a thermoelectric efficiency larger than 33% (~1/3) is achievable when T_h
exceeds 1400 K. For single-stage devices, the best efficiency of 17.1% (~1/6)
is possible when T_h is 860 K. Leg segmentation can overcome this limit,
delivering a very high efficiency of 24% (~1/4) when T_h is 1100 K.Comment: 32 pages (main+table+figure captions+figures), 7 additional pages for
6 high resolution figures, Supporting Data file is not public ye
First-principles study of electron transport through cages
Electron transport properties of C molecules suspended between gold
electrodes are investigated using first-principles calculations. Our study
reveals that the conductances are quite sensitive to the number of C
molecules between electrodes: the conductances of C monomers are near 1
G, while those of dimers are markedly smaller, since incident electrons
easily pass the C molecules and are predominantly scattered at the
C-C junctions. Moreover, we find both channel currents locally
circulating the outermost carbon atoms.Comment: 8 pages and 3 figure
A case of an ablation catheter entrapped in the pulmonary vein during atrial fibrillation ablation requiring open heart surgery for removal
Multimessengers from Core-Collapse Supernovae: Multidimensionality as a Key to Bridge Theory and Observation
Core-collapse supernovae are dramatic explosions marking the catastrophic end of massive stars. The only means to get direct information about the supernova engine is from observations of neutrinos emitted by the forming neutron star, and through gravitational waves which are produced when the hydrodynamic flow or the neutrino flux is not perfectly spherically symmetric. The multidimensionality of the supernova engine, which breaks the sphericity of the central core such as convection, rotation, magnetic fields, and hydrodynamic instabilities of the supernova shock, is attracting great attention as the most important ingredient to understand the long-veiled explosion mechanism. Based on our recent work, we summarize properties of gravitational waves, neutrinos, and explosive nucleosynthesis obtained in a series of our multidimensional hydrodynamic simulations and discuss how the mystery of the central engines can be unraveled by deciphering these multimessengers produced under the thick veils of massive stars
General Relativistic Ray-Tracing Method for Estimating the Energy and Momentum Deposition by Neutrino Pair Annihilation in Collapsars
Bearing in mind the application to the collapsar models of gamma-ray bursts
(GRBs), we develop a numerical scheme and code for estimating the deposition of
energy and momentum due to the neutrino pair annihilation () in the vicinity of accretion tori around a Kerr
black hole. Our code is designed to solve the general relativistic neutrino
transfer by a ray-tracing method. To solve the collisional Boltzmann equation
in curved spacetime, we numerically integrate the so-called rendering equation
along the null geodesics. For the neutrino opacity, the charged-current
-processes are taken into account, which are dominant in the vicinity of
the accretion tori. The numerical accuracy of the developed code is
certificated by several tests, in which we show comparisons with the
corresponding analytic solutions. Based on the hydrodynamical data in our
collapsar simulation, we estimate the annihilation rates in a post-processing
manner. Increasing the Kerr parameter from 0 to 1, it is found that the general
relativistic effect can increase the local energy deposition rate by about one
order of magnitude, and the net energy deposition rate by several tens of
percents. After the accretion disk settles into a stationary state (typically
later than s from the onset of gravitational collapse), we point out
that the neutrino-heating timescale in the vicinity of the polar funnel region
can be shorter than the dynamical timescale. Our results suggest the neutrino
pair annihilation has a potential importance equal to the conventional
magnetohydrodynamic mechanism for igniting the GRB fireballs.Comment: 33 pages, 15 figures, accepted to the Ap
First-Principles Study on Electron Conduction in Sodium Nanowire
We present detailed first-principles calculations of the electron-conduction
properties of a three-sodium-atom nanowire suspended between semi-infinite
crystalline Na(001) electrodes during its elongation. Our investigations reveal
that the conductance is ~1 G0 before the nanowire breaks and only one channel
with the characteristic of the orbital of the center atom in the nanowire
contributes to the electron conduction. Moreover, the channel fully opens
around the Fermi level, and the behavior of the channel-current density is
insensitive to the structural deformation of the nanowire. These results verify
that the conductance trace as a function of the electrode spacing exhibits a
flat plateau at ~1 G0 during elongation.Comment: 8 pages, 5 figure
Experimental evidence of a strong image force between highly charged electrosprayed molecular ions and a metal screen
We investigated the capturing mechanisms of highly charged macromolecular ions of polyethylene glycol electrosprayed onto a metal screen. Our experiments assessed how the charge state, size of the macromolecular ions, and filtration velocity affected the penetration of the ions through the metal screen. The single fiber efficiencies were plotted as functions of the Peclet number and image force parameter. Highly charged molecular ions had much higher collection efficiencies than neutralized macromolecules, suggesting the presence of a strong image force between the ions and metal surface. The single fiber efficiency by image force was proportional to the square root of an image force parameter predicted by theory. When using the prefactor of 9.7 proposed by Alonso et al. (2007), we found fair agreement between the experimental data and theoretical predictions on the collection efficiency of highly charged molecular ions with mobility diameters from 2.6 to 4.8 nm and numbers of electrical charges from 2 to 7. The experimental evidence from our study reveals that image force contributes strongly to the collection of multicharged macromolecular ions by a metal wire screen. © Taiwan Association for Aerosol Research
Gravitational Wave Signatures of Hyperaccreting Collapsar Disks
By performing two-dimensional special relativistic (SR) magnetohydrodynamic
simulations, we study possible signatures of gravitational waves (GWs) in the
context of the collapsar model for long-duration gamma-ray bursts. In our SR
simulations, the central black hole is treated as an absorbing boundary. By
doing so, we focus on the GWs generated by asphericities in neutrino emission
and matter motions in the vicinity of the hyperaccreting disks. We compute nine
models by adding initial angular momenta and magnetic fields parametrically to
a precollapse core of a progenitor star. As for the
microphysics, a realistic equation of state is employed and the neutrino
cooling is taken into account via a multiflavor neutrino leakage scheme. To
accurately estimate GWs produced by anisotropic neutrino emission, we perform a
ray-tracing analysis in general relativity by a post-processing procedure. By
employing a stress formula that includes contributions both from magnetic
fields and special relativistic corrections, we study also the effects of
magnetic fields on the gravitational waveforms. We find that the GW amplitudes
from anisotropic neutrino emission show a monotonic increase with time, whose
amplitudes are much larger than those from matter motions of the accreting
material. We show that the increasing trend of the neutrino GWs stems from the
excess of neutrino emission in the direction near parallel to the spin axis
illuminated from the hyperaccreting disks. We point out that a recently
proposed future space-based interferometer like Fabry-Perot type DECIGO would
permit the detection of these GW signals within 100 Mpc.Comment: 38 pages, 14 figures, ApJ in pres
LRRK2 and RAB7L1 coordinately regulate axonal morphology and lysosome integrity in diverse cellular contexts
Leucine-rich repeat kinase 2 (LRRK2) has been linked to several clinical disorders including Parkinson’s disease (PD), Crohn’s disease, and leprosy. Furthermore in rodents, LRRK2 deficiency or inhibition leads to lysosomal pathology in kidney and lung. Here we provide evidence that LRRK2 functions together with a second PD-associated gene, RAB7L1, within an evolutionarily conserved genetic module in diverse cellular contexts. In C. elegans neurons, orthologues of LRRK2 and RAB7L1 act coordinately in an ordered genetic pathway to regulate axonal elongation. Further genetic studies implicated the AP-3 complex, which is a known regulator of axonal morphology as well as of intracellular protein trafficking to the lysosome compartment, as a physiological downstream effector of LRRK2 and RAB7L1. Additional cell-based studies implicated LRRK2 in the AP-3 complex-related intracellular trafficking of lysosomal membrane proteins. In mice, deficiency of either RAB7L1 or LRRK2 leads to prominent age-associated lysosomal defects in kidney proximal tubule cells, in the absence of frank CNS pathology. We hypothesize that defects in this evolutionarily conserved genetic pathway underlie the diverse pathologies associated with LRRK2 in humans and in animal models
Fully General Relativistic Simulations of Core-Collapse Supernovae with An Approximate Neutrino Transport
We present results from the first generation of multi-dimensional
hydrodynamic core-collapse simulations in full general relativity (GR) that
include an approximate treatment of neutrino transport. Using a M1 closure
scheme with an analytic variable Eddington factor, we solve the
energy-independent set of radiation energy and momentum based on the Thorne's
momentum formalism. To simplify the source terms of the transport equations, a
methodology of multiflavour neutrino leakage scheme is partly employed. Our
newly developed code is designed to evolve the Einstein field equation together
with the GR radiation hydrodynamic equations. We follow the dynamics starting
from the onset of gravitational core-collapse of a 15 star, through
bounce, up to about 100 ms postbounce in this study to study how the spacial
multi-dimensionality and GR would affect the dynamics in the early postbounce
phase. Our 3D results support the anticipation in previous 1D results that the
neutrino luminosity and average neutrino energy of any neutrino flavor in the
postbounce phase increase when switching from SR to GR hydrodynamics. This is
because the deeper gravitational well of GR produces more compact core
structures, and thus hotter neutrino spheres at smaller radii. By analyzing the
residency timescale to the neutrino-heating timescale in the gain region, we
show that the criterion to initiate neutrino-driven explosions can be most
easily satisfied in 3D models, irrespective of SR or GR hydrodynamics. Our
results suggest that the combination of GR and 3D hydrodynamics provides the
most favorable condition to drive a robust neutrino-driven explosion.Comment: 50pages, 20 figures, Accepted by ApJ. Latest version with following
the referee's suggestions and comment
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