48,965 research outputs found
Noise propagation in urban and industrial areas
Noise propagation in streets and the discrepancies between theoretical analyses and field measurements are discussed. A cell-model is used to estimate the general background level of noise due to vehicular sources distributed over the urban area
Quarkonium spin structure in lattice NRQCD
Numerical simulations of the quarkonium spin splittings are done in the
framework of lattice nonrelativistic quantum chromodynamics (NRQCD). At leading
order in the velocity expansion the spin splittings are of , where
is the renormalized quark mass and is the mean squared quark
velocity. A systematic analysis is done of all next-to-leading order
corrections. This includes the addition of relativistic
interactions, and the removal of discretization errors in the
leading-order interactions. Simulations are done for both S- and P-wave mesons,
with a variety of heavy quark actions and over a wide range of lattice
spacings. Two prescriptions for the tadpole improvement of the action are also
studied in detail: one using the measured value of the average plaquette, the
other using the mean link measured in Landau gauge. Next-to-leading order
interactions result in a very large reduction in the charmonium splittings,
down by about 60% from their values at leading order. There are further
indications that the velocity expansion may be poorly convergent for
charmonium. Prelimary results show a small correction to the hyperfine
splitting in the Upsilon system.Comment: 16 pages, REVTEX v3.1, 5 postscript figures include
Tadpole renormalization and relativistic corrections in lattice NRQCD
We make a comparison of two tadpole renormalization schemes in the context of
the quarkonium hyperfine splittings in lattice NRQCD. Improved gauge-field and
NRQCD actions are analyzed using the mean-link in Landau gauge, and
using the fourth root of the average plaquette . Simulations are done
for , , and systems. The hyperfine splittings are
computed both at leading and at next-to-leading order in the relativistic
expansion. Results are obtained at lattice spacings in the range of about
0.14~fm to 0.38~fm. A number of features emerge, all of which favor tadpole
renormalization using . This includes much better scaling behavior of
the hyperfine splittings in the three quarkonium systems when is
used. We also find that relativistic corrections to the spin splittings are
smaller when is used, particularly for the and
systems. We also see signs of a breakdown in the NRQCD expansion when the bare
quark mass falls below about one in lattice units. Simulations with
also appear to be better behaved in this context: the bare quark masses turn
out to be larger when is used, compared to when is used on
lattices with comparable spacings. These results also demonstrate the need to
go beyond tree-level tadpole improvement for precision simulations.Comment: 14 pages, 7 figures (minor changes to some phraseology and
references
Self-consistent equilibrium of a two-dimensional electron system with a reservoir in a quantizing magnetic field: Analytical approach
An analytical approach has been developed to describe grand canonical
equilibrium between a three dimensional (3D) electron system and a two
dimensional (2D) one, an energy of which is determined self-consistently with
an electron concentration. Main attention is paid to a Landau level (LL)
pinning effect. Pinning means a fixation of the LL on a common Fermi level of
the 2D and the 3D systems in a finite range of the magnetic field due to an
electron transfer from the 2D to the 3D system. A condition and a start of LL
pinning has been found for homogeneously broadened LLs. The electronic transfer
from the 3D to the 2D system controls an extremely sharp magnetic dependency of
an energy of the upper filled LL at integer filling of the LLs. This can cause
a significant increase of inhomogeneous broadening of the upper LL that was
observed in recent local probe experiments.Comment: 12 pages, 2 figures, revtex
D to K and D to pi semileptonic form factors from Lattice QCD
We present a very high statistics study of D and D_s semileptonic decay form
factors on the lattice. We work with MILC N_f=2+1 lattices and use the Highly
Improved Staggered Quark action (HISQ) for both the charm and the strange and
light valence quarks. We use both scalar and vector currents to determine the
form factors f_0(q^2) and f_+(q^2) for a range of D and D_s semileptonic
decays, including D to pi and D to K. By using a phased boundary condition we
are able to tune accurately to q^2=0 and explore the whole q^2 range allowed by
kinematics. We can thus compare the shape in q^2 to that from experiment and
extract the CKM matrix element |V_cs|. We show that the form factors are
insensitive to the spectator quark: D to K and D_s to eta_s form factors are
essentially the same, which is also true for D to pi and D_s to K within 5%.
This has important implications when considering the corresponding B/B_s
processes.Comment: To appear in the proceedings of The 5th International Workshop on
Charm Physics (Charm 2012
Waste heat from the London Underground: an investigation of the potential benefits of integrating heating and cooling
Waste or recoverable heat is a resource that could be cost-effectively exploited by district heating (DH) systems
to increase the efficiency of heat supply in buildings. This paper introduces the Bunhill waste heat recovery
(WHR) system, a novel scheme that recovers waste energy from a ventilation shaft of the London Underground
(LU) transport network. The system is based upon the installation of a heat recovery heat exchanger consisting
of cooling coils and a reversible fan; the coils are connected to a heat pump that supplies low-carbon thermal
energy to the Bunhill DH network in central London. One particularly important aspect of the Bunhill WHR
system is its ability to operate in a way that not only provides heating to the local heat network, but can also
simultaneously supply cooled air to the LU tunnels depending on the operation of the reversible fan. The
current paper presents the results from an investigation into the benefits of integrating heating and cooling
from the perspective of reducing carbon emissions and the levelised costs of energy from the WHR system,
whilst also alleviating peak temperatures at nearby LU stations through the cooling provided. The findings of the
investigation are presented together with recommendations for further development and future deployment of
WHR systems, which not only apply to underground railways but also to other sources of recoverable heat
Precision Charmonium Spectroscopy From Lattice QCD
We present results for Charmonium spectroscopy using Non-Relativistic QCD
(NRQCD). For the NRQCD action the leading order spin-dependent and next to
leading order spin-independent interactions have been included with
tadpole-improved coefficients. We use multi-exponential fits to multiple
correlation functions to extract ground and excited states. Splittings
between the lowest , and states are given and we have accurate
values for the state hyperfine splitting and the fine structure.
Agreement with experiment is good - the remaining systematic errors are
discussed.Comment: 23 pages uuencoded latex file. Contains figures in late
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