50,732 research outputs found
Geometric phases in a scattering process
The study of geometric phase in quantum mechanics has so far be confined to
discrete (or continuous) spectra and trace preserving evolutions. Consider only
the transmission channel, a scattering process with internal degrees of freedom
is neither a discrete spectrum problem nor a trace preserving process. We
explore the geometric phase in a scattering process taking only the
transmission process into account. We find that the geometric phase can be
calculated by the some method as in an unitary evolution. The interference
visibility depends on the transmission amplitude. The dependence of the
geometric phase on the barrier strength and the spin-spin coupling constant is
also presented and discussed.Comment: 4 pages, 5 figure
WECOF: A new project developing enhanced weed control through improved crop and plant architecture
A primary objective of the EU-funded WECOF project is to optimise the natural competitiveness of winter wheat in reducing weed growth, and thus reduce the need for direct weed control interventions. Crops are characterised by ranking the relative importance of key plant and crop factors in shading weed growth. A series of core trials have been established in Germany, Scotland, Poland and Spain comparing plant structure by the use of different varieties and crop architectural factors by the use of different sowing row widths and direction. Variety trials have also been established in Scotland with constant row width and sowing direction to give more detailed varietal comparisons. Results from the first set of trials in Scotland are described. There are clear varietal differences in weed suppression; row-width has a bigger effect than sowing direction. Results will be used to develop models to assist breeders in producing improved crop ideotypes for organic production, and in production of a decision support system to assist farmers and advisers in variety selection and management for improved weed suppression. WECOF also includes work on allelopathy and photocontrol, and on the related economic factors
Mean link versus average plaquette tadpoles in lattice NRQCD
We compare mean-link and average plaquette tadpole renormalization schemes in
the context of the quarkonium hyperfine splittings in lattice NRQCD.
Simulations are done for the three quarkonium systems , , and
. The hyperfine splittings are computed both at leading and at
next-to-leading order in the relativistic expansion. Results are obtained at a
large number of lattice spacings. A number of features emerge, all of which
favor tadpole renormalization using mean links. This includes much better
scaling of the hyperfine splittings in the three quarkonium systems. We also
find that relativistic corrections to the spin splittings are smaller with
mean-link tadpoles, 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 (with the bare quark masses turning out
to be much larger with mean-link tadpoles).Comment: LATTICE(heavyqk) 3 pages, 2 figure
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
Coral symbiodinium community composition across the Belize Mesoamerican barrier reef system is influenced by host species and thermal variability
Accepted manuscrip
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
New Cosmological Structures on Medium Angular Scales Detected with the Tenerife Experiments
We present observations at 10 and 15 GHz taken with the Tenerife experiments
in a band of the sky at Dec.=+35 degrees. These experiments are sensitive to
multipoles in the range l=10-30. The sensitivity per beam is 56 and 20 microK
for the 10 and the 15 GHz data, respectively. After subtraction of the
prediction of known radio-sources, the analysis of the data at 15 GHz at high
Galactic latitude shows the presence of a signal with amplitude Delta Trms ~ 32
microK. In the case of a Harrison-Zeldovich spectrum for the primordial
fluctuations, a likelihood analysis shows that this signal corresponds to a
quadrupole amplitude Q_rms-ps=20.1+7.1-5.4 microK, in agreement with our
previous results at Dec.+=40 degrees and with the results of the COBE DMR.
There is clear evidence for the presence of individual features in the RA range
190 degrees to 250 degrees with a peak to peak amplitude of ~110 microK. A
preliminary comparison between our results and COBE DMR predictions for the
Tenerife experiments clearly indicates the presence of individual features
common to both. The constancy in amplitude over such a large range in frequency
(10-90 GHz) is strongly indicative of an intrinsic cosmological origin for
these structures.Comment: ApJ Letters accepted, 13 pages Latex (uses AASTEX) and 4 encapsulated
postscript figures
Intrinsic Curie temperature bistability in ferromagnetic semiconductor resonant tunneling diodes
We predict bistability in the Curie temperature-voltage characteristic of
double barrier resonant-tunneling structures with dilute ferromagnetic
semiconductor quantum wells. Our conclusions are based on simulations of
electrostatics and ballistic quantum transport combined with a mean-field
theory description of ferromagnetism in dilute magnetic semiconductors.Comment: 10 pages, 3 figures, submitted to Phys. Rev. B; typo removed in
revised version - spurious eq.12 immediately after eq.1
An initial evaluation of a biohygrothermal model for the purpose of assessing the risk mould growth in UK dwellings
Moulds are organisms that may be found in both the indoor and outdoor environment. Moulds play an important rolebreaking down and digesting organic material, but, if they are significantly present in the indoor environment they mayaffect the health of the occupants. A relative humidity of 80% at wall surfaces is frequently stated as the decisivecriterion for mould growth and methods used to assess the risk of mould growth are often based on steady stateconditions. However, considering the dynamic conditions typically found in the indoor environment, a betterunderstanding of the conditions required for mould to grow would seem desirable. This paper presents initialexploratory work to evaluate and assess ‘WUFI-bio’ - ‘biohygrothermal’ software that predicts the likelihood of mould growth under transient conditions. Model predictions are compared with large monitored data set from 1,388 UKdwellings before and after insulation and new heating systems are installed (‘Warm Front’), the suitability of thissoftware as a tool to predict mould growth will ultimately be assessed. This paper presents some initial, exploratorywork
Magneto-capacitance probing of the many-particle states in InAs dots
We use frequency-dependent capacitance-voltage spectroscopy to measure the
tunneling probability into self-assembled InAs quantum dots. Using an in-plane
magnetic field of variable strength and orientation, we are able to obtain
information on the quasi-particle wave functions in momentum space for 1 to 6
electrons per dot. For the lowest two energy states, we find a good agreement
with Gaussian functions for a harmonic potential. The high energy orbitals
exhibit signatures of anisotropic confinement and correlation effects.Comment: 3 pages, 3 figure
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