81,826 research outputs found
Non-local 2D Generalized Yang-Mills theories on arbitrary surfaces with boundary
The non-local generalized two dimensional Yang Mills theories on an arbitrary
orientable and non-orientable surfaces with boundaries is studied. We obtain
the effective action of these theories for the case which the gauge group is
near the identity, . Furthermore, by obtaining the effective action
at the large-N limit, it is shown that the phase structure of these theories is
the same as that obtain for these theories on orientable and non-orientable
surface without boundaries. It is seen that the model of these
theories on an arbitrary orientable and non-orientable surfaces with boundaries
have third order phase transition only on and surfaces, with
modified area for orientable and
for non-orientable surfaces respectivly.Comment: 10 pages, no figures, late
High performance, high density hydrocarbon fuels
The fuels were selected from 77 original candidates on the basis of estimated merit index and cost effectiveness. The ten candidates consisted of 3 pure compounds, 4 chemical plant streams and 3 refinery streams. Critical physical and chemical properties of the candidate fuels were measured including heat of combustion, density, and viscosity as a function of temperature, freezing points, vapor pressure, boiling point, thermal stability. The best all around candidate was found to be a chemical plant olefin stream rich in dicyclopentadiene. This material has a high merit index and is available at low cost. Possible problem areas were identified as low temperature flow properties and thermal stability. An economic analysis was carried out to determine the production costs of top candidates. The chemical plant and refinery streams were all less than 44 cent/kg while the pure compounds were greater than 44 cent/kg. A literature survey was conducted on the state of the art of advanced hydrocarbon fuel technology as applied to high energy propellents. Several areas for additional research were identified
Investigation of the influence of a step change in surface roughness on turbulent heat transfer
The use is studied of smooth heat flux gages on the otherwise very rough SSME fuel pump turbine blades. To gain insights into behavior of such installations, fluid mechanics and heat transfer data were collected and are reported for a turbulent boundary layer over a surface with a step change from a rough surface to a smooth surface. The first 0.9 m length of the flat plate test surface was roughened with 1.27 mm hemispheres in a staggered, uniform array spaced 2 base diameters apart. The remaining 1.5 m length was smooth. The effect of the alignment of the smooth surface with respect to the rough surface was also studied by conducting experiments with the smooth surface aligned with the bases or alternatively with the crests of the roughness elements. Stanton number distributions, skin friction distributions, and boundary layer profiles of temperature and velocity are reported and are compared to previous data for both all rough and all smooth wall cases. The experiments show that the step change from rough to smooth has a dramatic effect on the convective heat transfer. It is concluded that use of smooth heat flux gages on otherwise rough surfaces could cause large errors
Observation of the March Maximum in the Daemon Flux from Neos in the Year 2005: New Efforts and New Effects
The experiments of 2005 aimed at detection of low-velocity (~10-15 km s-1)
daemons falling on to the Earth's surface from Near-Earth, Almost Circular
Heliocentric Orbits (NEACHOs) have corroborated once more the existence of the
March maximum in their flux by raising its confidence level to 99.99%. In
addition, these experiments permitted us to identify several FEU-167-1-type PM
tubes, with a few times thicker inner Al coating, which appear to be capable to
detect, without any scintillator, the crossing of negatively charged daemons.
As a result, detection efficiency increases tens of times, thus raising the
measured level of the March daemon flux to f > 0.5E-7 cm-2s-1.Comment: 14 page
Using conditional kernel density estimation for wind power density forecasting
Of the various renewable energy resources, wind power is widely recognized as one of the most promising. The management of wind farms and electricity systems can benefit greatly from the availability of estimates of the probability distribution of wind power generation. However, most research has focused on point forecasting of wind power. In this paper, we develop an approach to producing density forecasts for the wind power generated at individual wind farms. Our interest is in intraday data and prediction from 1 to 72 hours ahead. We model wind power in terms of wind speed and wind direction. In this framework, there are two key uncertainties. First, there is the inherent uncertainty in wind speed and direction, and we model this using a bivariate VARMA-GARCH (vector autoregressive moving average-generalized autoregressive conditional heteroscedastic) model, with a Student t distribution, in the Cartesian space of wind speed and direction. Second, there is the stochastic nature of the relationship of wind power to wind speed (described by the power curve), and to wind direction. We model this using conditional kernel density (CKD) estimation, which enables a nonparametric modeling of the conditional density of wind power. Using Monte Carlo simulation of the VARMA-GARCH model and CKD estimation, density forecasts of wind speed and direction are converted to wind power density forecasts. Our work is novel in several respects: previous wind power studies have not modeled a stochastic power curve; to accommodate time evolution in the power curve, we incorporate a time decay factor within the CKD method; and the CKD method is conditional on a density, rather than a single value. The new approach is evaluated using datasets from four Greek wind farms
Solid-state circuit for spin entanglement generation and purification
We show how realistic charge manipulation and measurement techniques,
combined with the exchange interaction, allow for the robust generation and
purification of four-particle spin entangled states in electrically controlled
semiconductor quantum dots. The generated states are immunized to the dominant
sources of noise via a dynamical decoherence-free subspace; all additional
errors are corrected by a purification protocol. This approach may find
application in quantum computation, communication, and metrology.Comment: 5 pages, 2 figures; corrected minor typo
Importance of an Astrophysical Perspective for Textbook Relativity
The importance of a teaching a clear definition of the ``observer'' in
special relativity is highlighted using a simple astrophysical example from the
exciting current research area of ``Gamma-Ray Burst'' astrophysics. The example
shows that a source moving relativistically toward a single observer at rest
exhibits a time ``contraction'' rather than a ``dilation'' because the light
travel time between the source and observer decreases with time. Astrophysical
applications of special relativity complement idealized examples with real
applications and very effectively exemplify the role of a finite light travel
time.Comment: 5 pages TeX, European Journal of Physics, in pres
Crystal field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3
Inelastic neutron scattering experiments have been carried out to determine
the crystal field states of the Kondo lattice heavy fermions CeRuSn3 and
CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space
group Pm-3n) in which the Ce atoms occupy two distinct crystallographic sites
with cubic (m-3) and tetragonal (-4m.2) point symmetries. The INS data of
CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV which
is accounted by a model based on crystal electric field (CEF) excitations. On
the other hand, the INS data of isostructural CeRhSn3 reveal three CEF
excitations around 7.0, 12.2 and 37.2 meV. The neutron intensity sum rule
indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3+
state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds
are deduced. We estimate the Kondo temperature T_K = 3.1(2) K for CeRuSn3 from
neutron quasielastic linewidth in excellent agreement with that determined from
the scaling of magnetoresistance which gives T_K = 3.2(1) K. For CeRhSn3 the
neutron quasielastic linewidth gives T_K = 4.6 K. For both CeRuSn3 and CeRhSn3,
the ground state of Ce3+ turns out to be a quartet for the cubic site and a
doublet for the tetragonal site.Comment: 12 pages, 13 figures, 2 tables, to appear in Phys. Rev.
Embedded motivational interviewing combined with a smartphone app to increase physical activity in people with sub-acute low back pain: study protocol of a cluster randomised control trial
Background: Motivational Interviewing is an evidence-based, client-centred counselling technique that has been used effectively to increase physical activity, including for people with low back pain. One barrier to implementing Motivational Interviewing in health care settings more broadly is the extra treatment time with therapists. The aim of this paper is to describe the design of a cluster randomised controlled trial evaluating the effect of an intervention that pairs Motivational Interviewing embedded into usual physiotherapy care with a specifically designed app to increase physical activity in people with sub-acute low back pain. Methods: The study is a cluster randomised controlled in which patients aged over 18 years who have sub-acute low back pain (3â12 weeks duration) are recruited from four public hospital outpatient clinics. Based on the recruitment site, participants either receive usual physiotherapy care or the Motivational Interviewing intervention over 6 consecutive weekly outpatient sessions with a specifically designed app designed to facilitate participant-led physical activity behaviour change in between sessions. Outcome measures assessed at baseline and 7 weeks are: physical activity as measured by accelerometer (primary outcome), and pain-related activity restriction and pain self-efficacy (secondary outcomes). Postintervention interviews with physiotherapists and participants will be conducted as part of a process evaluation. Discussion: This intervention, which comprises trained physiotherapists conducting conversations about increasing physical activity with their patients in a manner consistent with Motivational Interviewing as part of usual care combined with a specifically designed app, has potential to facilitate behaviour change with minimal extra therapist time
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