6,051 research outputs found
Temperature Dependent Mean Free Path Spectra of Thermal Phonons Along the c-axis of Graphite
Heat conduction in graphite has been studied for decades because of its
exceptionally large thermal anisotropy. While the bulk thermal conductivities
along the in-plane and cross-plane directions are well known, less understood
are the microscopic properties of the thermal phonons responsible for heat
conduction. In particular, recent experimental and computational works indicate
that the average phonon mean free path (MFP) along the c-axis is considerably
larger than that estimated by kinetic theory, but the distribution of MFPs
remains unknown. Here, we report the first quantitative measurements of c-axis
phonon MFP spectra in graphite at a variety of temperatures using time-domain
thermoreflectance measurements of graphite flakes with variable thickness. Our
results indicate that c-axis phonon MFPs have values of a few hundred
nanometers at room temperature and a much narrower distribution than in
isotropic crystals. At low temperatures, phonon scattering is dominated by
grain boundaries separating crystalline regions of different rotational
orientation. Our study provides important new insights into heat transport and
phonon scattering mechanisms in graphite and other anisotropic van der Waals
solids
Spanning trees in a cactus
AbstractWe prove a best possible lower bound for the number of isomorphism classes into which all rooted spanning trees of a rooted cactus partition. We announce a best possible lower bound for the number of isomorphism classes into which all spanning trees of a cactus partition
Relationship Between Gas Depth Profiles in Compost Heap and Gas Emission
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is an Invited Paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 5 (2003): Y. Fukumoto, H. Rom, and P. Dahl. Relationship Between Gas Depth Profiles in Compost Heap and Gas Emission. Vol. V. May 2003
Projection of the demand for fertilizer
노트 : Total consumption of commercial fertilizer in Korea has been increased at a rapid rate during the last two decades. In the period from 1952 to 1961, the consumption of fertilizer was 208 thousand metric tons. In the period from 1962 to 1971, the average consumption was increased to 442 thousand metric tons on the plant nutrient basis per year on the average. During the same period the total area of arable land was not increased, but there was a little increase in the rate of land utilization by the multi-cropping farmers. Therefore, the usage of fertilizer on the unit cultivated area has been doubled during the last two decades. This study proposes to quantify the potential demand for fertilizer by nutrients in Korea for policy making. All of the data used in this study, except land prices and the seed improvement index, are derived from official reports of the Ministry of Agriculture and Fisheries and the National Agricultural Cooperative Federation. In the time series analysis demand functions of total and individual nutrients are estimated using prices of total and individual nutrients, wage rates, machine prices, cropping acres, and technological changes as explanatory variables from 1960 to 1972 on an annual basis. All prices were constant in 1965. Linear and linear in logarithm equations are estimated under both assumptions of instantaneous quantity adjustment and on the belief that quantity adjustment takes place over time
Exactly solvable charged dilaton gravity theories in two dimensions
We find exactly solvable dilaton gravity theories containing a U(1) gauge
field in two dimensional space-time. The classical general solutions for the
gravity sector (the metric plus the dilaton field) of the theories coupled to a
massless complex scalar field are obtained in terms of the stress-energy tensor
and the U(1) current of the scalar field. We discuss issues that arise when we
attempt to use these models for the study of the gravitational back-reaction.Comment: The introductory part is changed. a version to appear in Class.
Quant. Grav. 6 pages, RevTe
Improvements to deep convolutional neural networks for LVCSR
Deep Convolutional Neural Networks (CNNs) are more powerful than Deep Neural
Networks (DNN), as they are able to better reduce spectral variation in the
input signal. This has also been confirmed experimentally, with CNNs showing
improvements in word error rate (WER) between 4-12% relative compared to DNNs
across a variety of LVCSR tasks. In this paper, we describe different methods
to further improve CNN performance. First, we conduct a deep analysis comparing
limited weight sharing and full weight sharing with state-of-the-art features.
Second, we apply various pooling strategies that have shown improvements in
computer vision to an LVCSR speech task. Third, we introduce a method to
effectively incorporate speaker adaptation, namely fMLLR, into log-mel
features. Fourth, we introduce an effective strategy to use dropout during
Hessian-free sequence training. We find that with these improvements,
particularly with fMLLR and dropout, we are able to achieve an additional 2-3%
relative improvement in WER on a 50-hour Broadcast News task over our previous
best CNN baseline. On a larger 400-hour BN task, we find an additional 4-5%
relative improvement over our previous best CNN baseline.Comment: 6 pages, 1 figur
On the and as Bound States and Approximate Nambu-Goldstone Bosons
We reconsider the two different facets of and mesons as
bound states and approximate Nambu-Goldstone bosons. We address several topics,
including masses, mass splittings between and and between and
, meson wavefunctions, charge radii, and the wavefunction overlap.Comment: 15 pages, late
Determination of electromagnetic medium from the Fresnel surface
We study Maxwell's equations on a 4-manifold where the electromagnetic medium
is described by an antisymmetric -tensor . In this setting,
the Tamm-Rubilar tensor density determines a polynomial surface of fourth order
in each cotangent space. This surface is called the Fresnel surface and acts as
a generalisation of the light-cone determined by a Lorentz metric; the Fresnel
surface parameterises electromagnetic wave-speed as a function of direction.
Favaro and Bergamin have recently proven that if has only a principal
part and if the Fresnel surface of coincides with the light cone for a
Lorentz metric , then is proportional to the Hodge star operator of
. That is, under additional assumptions, the Fresnel surface of
determines the conformal class of . The purpose of this paper is
twofold. First, we provide a new proof of this result using Gr\"obner bases.
Second, we describe a number of cases where the Fresnel surface does not
determine the conformal class of the original -tensor . For
example, if is invertible we show that and have
the same Fresnel surfaces.Comment: 23 pages, 1 figur
Particle dynamics in a class of 2-dimensional gravity theories
We provide a method to determine the motion of a classical massive particle
in a background geometry of 2-dimensional gravity theories, for which the
Birkhoff theorem holds. In particular, we get the particle trajectory in a
continuous class of 2-dimensional dilaton gravity theories that includes the
Callan-Giddings-Harvey-Strominger (CGHS) model, the Jackiw-Teitelboim (JT)
model, and the -dimensional -wave Einstein gravity. The explicit
trajectory expressions for these theories are given along with the discussions
on the results.Comment: 15 pages, LaTeX. The deletion of the repeated portion of the abstract
and the proper line wrapping of the tex file. No other change
General Static Solutions of 2-dimensional Einstein-Dilaton-Maxwell-Scalar Theories
General static solutions of effectively 2-dimensional
Einstein-Dilaton-Maxwell-Scalar theories are obtained. Our model action
includes a class of 2-d dilaton gravity theories coupled with a gauge
field and a massless scalar field. Therefore it also describes the spherically
symmetric reduction of -dimensional Einstein-Scalar-Maxwell theories. The
properties of the analytic solutions are briefly discussed.Comment: 16 pages, Latex fil
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