1,737 research outputs found
Theory of interface and anharmonic phonon interactions in nanocomposite materials
© Published under licence by IOP Publishing Ltd.We present a theory of phonon scattering rates resulting from mass smudging across interfaces and from anharmonicity in nanocomposite materials. We discuss the derivation of the anharmonic scattering term and present some recently published results indicating that if certain models of interface mass-mixing are adopted, the cross-planar thermal conductivity of an ultra-thin superlattice system will decrease dramatically with the number of bilayers n until n 4, above which value it begins to increase with n.Engineering and Physical Sciences Research Council (EPSRC
Tuning phonon properties to enhance the thermoelectric figure of merit
This paper has been accepted for publication in Electronic, Photonic, Plasmonic, Phononic and Magnetic Properties of Nanomaterials; Mahi R. Singh. AIP Conf. Proc. 1590, 1 (2014); http://dx.doi.org/10.1063/1.4870187. Conference date: 12–16 August 2013. Location: London, Canada. The paper is available via http://dx.doi.org/10.1063/1.4870203We will discuss a theory of the thermoelectric properties of semiconductor alloys and superlattices, with an emphasis on
the role of phonons. After summarising our previous calculations of the lattice thermal conductivity and the thermoelectric
figure of merit ZT of an n-type SiGe alloy system, we will present some recent results for an ultra-thin SiGe superlattice and
discuss how they differ from the alloy results
Charge Symmetry Violation Corrections to Determination of the Weinberg Angle in Neutrino Reactions
We show that the correction to the Paschos-Wolfenstein relation associated
with charge symmetry violation in the valence quark distributions is
essentially model independent. It is proportional to a ratio of quark momenta
that is independent of Q^2. This result provides a natural explanation of the
surprisingly good agreement found between our earlier estimates within several
different models. When applied to the recent NuTeV measurement, this effect
significantly reduces the discrepancy with other determinations of the Weinberg
angle.Comment: 7 pages, no figures; expanded discussion of N.ne.Z correction
A Multi-Parameter Measurement System for MEMS Anemoters for Data Collection with Machine Learning Outcomes
In order to generate consistent and comprehensive datasets for the application ofmachine learning algorithms to MEMS thermal flow sensors, a measurement set up was created.This system allows automatic data collection of large datasets involving parameters such as the angle of attack, humidity, temperature and flow speed. The electrical output signals in both the time and frequency domain can be measured for both AC and DC actuation. The setup has been able to fully characterize an anemometer by exposing it to flows of 0 to 5 m/s in steps of 0.02 m/s under anglesfrom -45 to 45° in steps of 5° at a constant temperature of 25 °C and humidity of 30 %RH and complete the measurement in 8 hours
EC 11481-2303 - A Peculiar Subdwarf OB Star Revisited
EC 11481-2303 is a peculiar, hot, high-gravity pre-white dwarf. Previous
optical spectroscopy revealed that it is a sdOB star with an effective
temperature (Teff) of 41790 K, a surface gravity log(g)= 5.84, and He/H = 0.014
by number. We present an on-going spectral analysis by means of non-LTE
model-atmosphere techniques based on high-resolution, high-S/N optical
(VLT-UVES) and ultraviolet (FUSE, IUE) observations. We are able to reproduce
the optical and UV observations simultaneously with a chemically homogeneous
NLTE model atmosphere with a significantly higher effective temperature and
lower He abundance (Teff = 55000 K, log (g) = 5.8, and He / H = 0.0025 by
number). While C, N, and O appear less than 0.15 times solar, the iron-group
abundance is strongly enhanced by at least a factor of ten.Comment: 8 pages, 11 figure
Sudakov Resummation for Subleading SCET Currents and Heavy-to-Light Form Factors
The hard-scattering contributions to heavy-to-light form factors at large
recoil are studied systematically in soft-collinear effective theory (SCET).
Large logarithms arising from multiple energy scales are resummed by matching
QCD onto SCET in two stages via an intermediate effective theory. Anomalous
dimensions in the intermediate theory are computed, and their form is shown to
be constrained by conformal symmetry. Renormalization-group evolution equations
are solved to give a complete leading-order analysis of the hard-scattering
contributions, in which all single and double logarithms are resummed. In two
cases, spin-symmetry relations for the soft-overlap contributions to form
factors are shown not to be broken at any order in perturbation theory by
hard-scattering corrections. One-loop matching calculations in the two
effective theories are performed in sample cases, for which the relative
importance of renormalization-group evolution and matching corrections is
investigated. The asymptotic behavior of Sudakov logarithms appearing in the
coefficient functions of the soft-overlap and hard-scattering contributions to
form factors is analyzed.Comment: 50 pages, 10 figures; minor corrections, version to appear in JHE
Scaling tests of the improved Kogut-Susskind quark action
Improved lattice actions for Kogut-Susskind quarks have been shown to improve
rotational symmetry and flavor symmetry. In this work we find improved scaling
behavior of the rho and nucleon masses expressed in units of a length scale
obtained from the static quark potential, and better behavior of the Dirac
operator in instanton backgrounds.Comment: 4 pages, 4 figures, Revte
High specificity of BCL11B and GLG1 for EWSR1-FLI1 and EWSR1-ERG positive Ewing sarcoma
Ewing sarcoma (EwS) is an aggressive cancer displaying an undifferentiated small-round-cell histomorphology that can be easily confused with a broad spectrum of differential diagnoses. Using comparative transcriptomics and immunohistochemistry (IHC), we previously identified BCL11B and GLG1 as potential specific auxiliary IHC markers for EWSR1-FLI1-positive EwS. Herein, we aimed at validating the specificity of both markers in a far larger and independent cohort of EwS (including EWSR1-ERG-positive cases) and differential diagnoses. Furthermore, we evaluated their intra-tumoral expression heterogeneity. Thus, we stained tissue microarrays from 133 molecularly confirmed EwS cases and 320 samples from morphological mimics, as well as a series of patient-derived xenograft (PDX) models for BCL11B, GLG1, and CD99, and systematically assessed the immunoreactivity and optimal cut-offs for each marker. These analyses demonstrated that high BCL11B and/or GLG1 immunoreactivity in CD99-positive cases had a specificity of 97.5% and an accuracy of 87.4% for diagnosing EwS solely by IHC, and that the markers were expressed by EWSR1-ERG-positive EwS. Only little intra-tumoral heterogeneity in immunoreactivity was observed for differential diagnoses. These results indicate that BCL11B and GLG1 may help as specific auxiliary IHC markers in diagnosing EwS in conjunction with CD99, especially if confirmatory molecular diagnostics are not available.Barbara und Hubertus Trettner foundationDeutsche Forschungsgemeinschaft DFG 391665916Deutsche Stiftung fur junge Erwachsene mit KrebsDr. Leopold und Carmen Ellinger foundationDr. Rolf M. Schwiete foundationDr. Rudolf und Brigitte Zenner StiftungFriedrich-Baur foundationGerman Cancer Aid DKH-70112257German Cancer Aid DKH-108128German Cancer Aid DKH-70112018German Cancer Aid DKH-70113421
Gluon-induced W-boson pair production at the LHC
Pair production of W bosons constitutes an important background to Higgs
boson and new physics searches at the Large Hadron Collider LHC. We have
calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons,
including intermediate light and heavy quarks and allowing for arbitrary
invariant masses of the W bosons. While formally of next-to-next-to-leading
order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at
the LHC and by experimental Higgs search cuts, and increases the
next-to-leading order WW background estimate for Higgs searches by about 30%.
We have extended our previous calculation to include the contribution from the
intermediate top-bottom massive quark loop and the Higgs signal process. We
provide updated results for cross sections and differential distributions and
study the interference between the different gluon scattering contributions. We
describe important analytical and numerical aspects of our calculation and
present the public GG2WW event generator.Comment: 20 pages, 4 figure
On the relation of Thomas rotation and angular velocity of reference frames
In the extensive literature dealing with the relativistic phenomenon of
Thomas rotation several methods have been developed for calculating the Thomas
rotation angle of a gyroscope along a circular world line. One of the most
appealing concepts, introduced in \cite{rindler}, is to consider a rotating
reference frame co-moving with the gyroscope, and relate the precession of the
gyroscope to the angular velocity of the reference frame. A recent paper
\cite{herrera}, however, applies this principle to three different co-moving
rotating reference frames and arrives at three different Thomas rotation
angles. The reason for this apparent paradox is that the principle of
\cite{rindler} is used for a situation to which it does not apply. In this
paper we rigorously examine the theoretical background and limitations of
applicability of the principle of \cite{rindler}. Along the way we also
establish some general properties of {\it rotating reference frames}, which may
be of independent interest.Comment: 14 pages, 2 figure
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