40,880 research outputs found
Thermal And Mechanical Analysis of High-power Light-emitting Diodes with Ceramic Packages
In this paper we present the thermal and mechanical analysis of high-power
light-emitting diodes (LEDs) with ceramic packages. Transient thermal
measurements and thermo-mechanical simulation were performed to study the
thermal and mechanical characteristics of ceramic packages. Thermal resistance
from the junction to the ambient was decreased from 76.1 oC/W to 45.3 oC/W by
replacing plastic mould to ceramic mould for LED packages. Higher level of
thermo-mechanical stresses in the chip were found for LEDs with ceramic
packages despite of less mismatching coefficients of thermal expansion
comparing with plastic packages. The results suggest that the thermal
performance of LEDs can be improved by using ceramic packages, but the mounting
process of the high power LEDs with ceramic packages is critically important
and should be in charge of delaminating interface layers in the packages.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Sine-Gordon Soliton on a Cnoidal Wave Background
The method of Darboux transformation, which is applied on cnoidal wave
solutions of the sine-Gordon equation, gives solitons moving on a cnoidal wave
background. Interesting characteristics of the solution, i.e., the velocity of
solitons and the shift of crests of cnoidal waves along a soliton, are
calculated. Solutions are classified into three types (Type-1A, Type-1B,
Type-2) according to their apparent distinct properties.Comment: 11 pages, 5 figures, Contents change
N3LO NN interaction adjusted to light nuclei in ab exitu approach
We use phase-equivalent transformations to adjust off-shell properties of
similarity renormalization group evolved chiral effective field theory NN
interaction (Idaho N3LO) to fit selected binding energies and spectra of light
nuclei in an ab exitu approach. We then test the transformed interaction on a
set of additional observables in light nuclei to verify that it provides
reasonable descriptions of these observables with an apparent reduced need for
three- and many-nucleon interactions.Comment: Revised text due to journal referee comments. 6 pages, 2 figure
Structural Reorganization of Parallel Actin Bundles by Crosslinking Proteins: Incommensurate States of Twist
We construct a coarse-grained model of parallel actin bundles crosslinked by
compact, globular bundling proteins, such as fascin and espin, necessary
components of filapodial and mechanosensory bundles. Consistent with structural
observations of bundles, we find that the optimal geometry for crosslinking is
overtwisted, requiring a coherent structural change of the helical geometry of
the filaments. We study the linker-dependent thermodynamic transition of
bundled actin filaments from their native state to the overtwisted state and
map out the "twist-state'' phase diagram in terms of the availability as well
as the flexibility of crosslinker proteins. We predict that the transition from
the uncrosslinked to fully-crosslinked state is highly sensitive to linker
flexibility: flexible crosslinking smoothly distorts the twist-state of bundled
filaments, while rigidly crosslinked bundles undergo a phase transition,
rapidly overtwisting filaments over a narrow range of free crosslinker
concentrations. Additionally, we predict a rich spectrum of intermediate
structures, composed of alternating domains of sparsely-bound (untwisted) and
strongly-bound (overtwisted) filaments. This model reveals that subtle
differences in crosslinking agents themselves modify not only the detailed
structure of parallel actin bundles, but also the thermodynamic pathway by
which they form.Comment: Main Text (25 pages, 7 figures) with supporting material (12 pages, 9
figures, 2 tables
Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of air mass transport over East Asia
© Author(s) 2015. This is an Open Access article made available under the terms of the Creative Commons Attribution License 3.0 https://creativecommons.org/licenses/by/3.0/We use five years (2009-2013) of multiwavelength Raman lidar measurements at Gwangju, South Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust depending on its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modeling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground at which these plumes were transported: (case I) the dust layers passed over China at high altitude levels (> 3 km) until arrival over Gwangju, and (case II) the Asian dust layers were transported near the surface and within the lower troposphere (< 3 km) over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ depending on their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 for case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios (0.13 ± 0.04 at 532 nm), and higher lidar ratio (63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm) and Ångström exponents (0.98 ± 0.51). These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume depending on transport time if the pollution layer traveled over China at low heights, i.e., below approximately 3 km above ground. In contrast, we do not find such a trend if the dust plumes traveled at heights above 3 km over China. We need a longer time series of lidar measurements in order to determine in a quantitative way the change of optical properties of dust with transport time.Peer reviewedFinal Published versio
Nonequilibrium Phase Transitions and a Nonequilibrium Critical Point from Anti-de Sitter Space and Conformal Field Theory Correspondence
We find novel phase transitions and critical phenomena that occur only
outside the linear-response regime of current-driven nonequilibrium states. We
consider the strongly-interacting (3+1)-dimensional N=4 large-Nc SU(Nc)
supersymmetric Yang-Mills theory with a single flavor of fundamental N=2
hypermultiplet as a microscopic theory. We compute its nonlinear non-ballistic
quark-charge conductivity by using the AdS/CFT correspondence. We find that the
system exhibits a novel nonequilibrium first-order phase transition where the
conductivity jumps and the sign of the differential conductivity flips at
finite current density. A nonequilibrium critical point is discovered at the
end point of the first-order regime. We propose a nonequilibrium steady-state
analogue of thermodynamic potential in terms of the gravity-dual theory in
order to define the transition point. Nonequilibrium analogues of critical
exponents are proposed as well. The critical behavior of the conductivity is
numerically confirmed on the basis of these proposals. The present work
provides a new example of nonequilibrium phase transitions and nonequilibrium
critical points.Comment: 5 pages, 2 figures; v2: slightly short version is published in PRL.
The title is changed in the PRL forma
Quantum SUSY Algebra of -lumps in the Massive Grassmannian Sigma Model
We compute the SUSY algebra of the massive Grassmannian sigma
model in 2+1 dimensions. We first rederive the action of the model by using the
Scherk-Schwarz dimensional reduction from theory in 3+1
dimensions. Then, we perform the canonical quantization by using the Dirac
method. We find that a particular choice of the operator ordering yields the
quantum SUSY algebra of the -lumps with cental extension.Comment: 7 pages, references adde
Critical phenomena in globally coupled excitable elements
Critical phenomena in globally coupled excitable elements are studied by
focusing on a saddle-node bifurcation at the collective level. Critical
exponents that characterize divergent fluctuations of interspike intervals near
the bifurcation are calculated theoretically. The calculated values appear to
be in good agreement with those determined by numerical experiments. The
relevance of our results to jamming transitions is also mentioned.Comment: 4 pages, 3 figure
Faddeev calculation of pentaquark in the Nambu-Jona-Lasinio model-based diquark picture
A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark
in the diquark picture of Jaffe and Wilczek in which is a
diquark-diquark- three-body system. Nambu-Jona-Lasinio (NJL) model is
used to calculate the lowest order diagrams in the two-body scatterings of
and . With the use of coupling constants determined from the
meson sector, we find that interaction is attractive in s-wave
while interaction is repulsive in p-wave. With only the lowest three-body
channel considered, we do not find a bound pentaquark state.
Instead, a bound pentaquark with is obtained with a
unphysically strong vector mesonic coupling constants.Comment: 22 pages, 11 figures, accepted version in Phys. Rev. C. Summary of
main changes/corrections: 1. "which only holds at tree level" below the eq.
(23) is added. 2. In the last paragraph of p.23 we added a remark that the
coupling constant obtained from Lambda mass is different from the estimate as
obtained from the meson spectru
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