15,780 research outputs found
INVESTIGATION OF THE THERMOELECTRIC BEHAVIOR OF Cu-DOPED PbTeAgxSe
Sustainable energy research is currently on the forefront of scientific exploration thus a major effort is devoted to the development of new energy conservation and production techniques. Thermoelectric materials can play a significant part both in energy conservation and energy production via the Seebeck effect (heat to electric power) and the Peltier effect (electricity to cooling power), since they can convert wasted heat to useful electrical energy. Presented herein are the measured electrical and thermal transport properties and phenomenal analysis of the PbTeAgxSe (x=1.9, 2.0, 2.01) system. First, it would lead to a significant reduction in the thermal conductivity and a significant improvement of the thermoelectric through adjusting amount of Ag, which is able to monitor the effects of phase competition between the cubic PbSe and the monoclinic α-Ag2Te. In order to further optimize thermoelectric performance, a small amount of copper is chosen to dope into this system. Finally, the maximum thermoelectric performance obtained in Pb:Te:Ag:Se:Cu mixtures is ZT~0.6, which improves approximately 30% in contrast to maxium ZT~0.45 of Pb:Te:Ag:Se mixtures
NLO Productions of and with a Global Extraction of the Jet Transport Parameter in Heavy Ion collisions
In this work, we pave the way to calculate the productions of and
mesons at large in p+p and A+A collisions at the RHIC and
the LHC. The meson fragmentation functions (FFs) in vacuum at
next-to-leading order (NLO) are obtained by evolving NLO DGLAP evolution
equations with rescaled FFs at initial scale GeV from
a broken SU(3) model, and the FFs in vacuum are taken from AKK08
parametrization directly. Within the framework of the NLO pQCD improved parton
model, we make good descriptions of the experimental data on and
in p+p both at the RHIC and the LHC. With the higher-twist
approach to take into account the jet quenching effect by medium modified FFs,
the nuclear modification factors for meson and meson at
the RHIC and the LHC are presented with different sets of jet transport
coefficient . Then we make a global extraction of at the
RHIC and the LHC by confronting our model calculations with all available data
on 6 identified mesons: , , , , , and
. The minimum value of the total for productions of
these mesons gives the best value of for Au+Au
collisions with GeV at the RHIC, and for Pb+Pb collisions with TeV at the LHC
respectively, with the QGP spacetime evolution given by an event-by-event
viscous hydrodynamics model IEBE-VISHNU. With these global extracted values of
, the nuclear modification factors of , , ,
, , and in A+A collisions are presented, and
predictions of yield ratios such as and at
large in heavy-ion collisions at the RHIC and the LHC are provided.Comment: 9 pages, 13 figures, 1 tabl
Locking classical information
It is known that the maximum classical mutual information that can be
achieved between measurements on a pair of quantum systems can drastically
underestimate the quantum mutual information between those systems. In this
article, we quantify this distinction between classical and quantum information
by demonstrating that after removing a logarithmic-sized quantum system from
one half of a pair of perfectly correlated bitstrings, even the most sensitive
pair of measurements might only yield outcomes essentially independent of each
other. This effect is a form of information locking but the definition we use
is strictly stronger than those used previously. Moreover, we find that this
property is generic, in the sense that it occurs when removing a random
subsystem. As such, the effect might be relevant to statistical mechanics or
black hole physics. Previous work on information locking had always assumed a
uniform message. In this article, we assume only a min-entropy bound on the
message and also explore the effect of entanglement. We find that classical
information is strongly locked almost until it can be completely decoded. As a
cryptographic application of these results, we exhibit a quantum key
distribution protocol that is "secure" if the eavesdropper's information about
the secret key is measured using the accessible information but in which
leakage of even a logarithmic number of key bits compromises the secrecy of all
the others.Comment: 32 pages, 2 figure
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Flawed incident investigation in China: A case study of the 7.23 Yongwen Line railway accident
Testing a global city hypothesis : an assessment of polarization across US cities
Social polarization is perhaps most evident within the world's large cities where we can easily observe stark contrasts between wealth and poverty. A world city theoretical perspective has emerged that associates large cities importance in a global network of cities to the degree of internal polarization within these cities. The research reported here locates 57 large US cities within this world city hierarchy and then empirically examines the hypothesized positive association between global centrality and social polarization using a multivariate, cross-city analysis. The findings are mixed, with some evidence that global centrality increases income polarization, but only in the context of higher levels of immigration. There is no evidence that a city's centrality affects occupational polarization. We conclude by suggesting implications for the world city literature and future research
Characterisation of Cryogenic Material Properties of 3D-Printed Superconducting Niobium using a 3D Lumped Element Microwave Cavity
We present an experimental characterisation of the electrical properties of
3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post
inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant
microwave cavity resonator. The resonator was cooled to temperatures below the
critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while
measuring the quality factors of the electromagnetic resonances. This was then
compared with finite element analysis of the cavity and a measurement of the
same cavity with an Aluminium post of similar dimensions and frequency, to
extract the surface resistance of the Niobium post. The 3D-printed Niobium
exhibited a transition to the superconducting state at a similar temperature to
the regular Niobium, as well as a surface resistance of
. This value was comparable to many samples of traditionally machined
Niobium previously studied without specialised surface treatment. Furthermore,
this study demonstrates a simple new method for characterizing the material
properties of a relatively small and geometrically simple sample of
superconductor, which could be easily applied to other materials, particularly
3D-printed materials. Further research and development in additive
manufacturing may see the application of 3D-printed Niobium in not only
superconducting cavity designs, but in the innovative technology of the future.Comment: 5 pages, 4 figure
Boosted Top Quark Pair Production in Soft Collinear Effective Theory
We review a Soft Collinear Effective Theory approach to the study of
factorization and resummation of QCD effects in top-quark pair production. In
particular, we consider differential cross sections such as the top-quark pair
invariant mass distribution and the top-quark transverse momentum and rapidity
distributions. Furthermore, we focus our attention on the large invariant mass
and large transverse momentum kinematic regions, characteristic of boosted top
quarks. We discuss the factorization of the differential cross section in the
double soft gluon emission and small top-quark mass limit, both in Pair
Invariant Mass (PIM) and One Particle Inclusive (1PI) kinematics. The
factorization formulas can be employed in order to implement the simultaneous
resummation of soft emission and small mass effects up to
next-to-next-to-leading logarithmic accuracy. The results are also used to
construct improved next-to-next-to-leading order approximations for the
differential cross sections.Comment: 6 pages. Proceedings of the Second Annual Conference on Large Hadron
Collider Physics (LHCP 2014), Columbia University, New York, June 2-7, 201
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