1,504 research outputs found
Non-perturbative calculations for the effective potential of the symmetric and non-Hermitian field theoretic model
We investigate the effective potential of the symmetric
field theory, perturbatively as well as non-perturbatively. For the
perturbative calculations, we first use normal ordering to obtain the first
order effective potential from which the predicted vacuum condensate vanishes
exponentially as in agreement with previous calculations. For the
higher orders, we employed the invariance of the bare parameters under the
change of the mass scale to fix the transformed form totally equivalent to
the original theory. The form so obtained up to is new and shows that all
the 1PI amplitudes are perurbative for both and regions. For
the intermediate region, we modified the fractal self-similar resummation
method to have a unique resummation formula for all values. This unique
formula is necessary because the effective potential is the generating
functional for all the 1PI amplitudes which can be obtained via and thus we can obtain an analytic calculation for the 1PI
amplitudes. Again, the resummed from of the effective potential is new and
interpolates the effective potential between the perturbative regions.
Moreover, the resummed effective potential agrees in spirit of previous
calculation concerning bound states.Comment: 20 page
Comprehensive Solution to the Cosmological Constant, Zero-Point Energy, and Quantum Gravity Problems
We present a solution to the cosmological constant, the zero-point energy,
and the quantum gravity problems within a single comprehensive framework. We
show that in quantum theories of gravity in which the zero-point energy density
of the gravitational field is well-defined, the cosmological constant and
zero-point energy problems solve each other by mutual cancellation between the
cosmological constant and the matter and gravitational field zero-point energy
densities. Because of this cancellation, regulation of the matter field
zero-point energy density is not needed, and thus does not cause any trace
anomaly to arise. We exhibit our results in two theories of gravity that are
well-defined quantum-mechanically. Both of these theories are locally conformal
invariant, quantum Einstein gravity in two dimensions and Weyl-tensor-based
quantum conformal gravity in four dimensions (a fourth-order derivative quantum
theory of the type that Bender and Mannheim have recently shown to be
ghost-free and unitary). Central to our approach is the requirement that any
and all departures of the geometry from Minkowski are to be brought about by
quantum mechanics alone. Consequently, there have to be no fundamental
classical fields, and all mass scales have to be generated by dynamical
condensates. In such a situation the trace of the matter field energy-momentum
tensor is zero, a constraint that obliges its cosmological constant and
zero-point contributions to cancel each other identically, no matter how large
they might be. Quantization of the gravitational field is caused by its
coupling to quantized matter fields, with the gravitational field not needing
any independent quantization of its own. With there being no a priori classical
curvature, one does not have to make it compatible with quantization.Comment: Final version, to appear in General Relativity and Gravitation (the
final publication is available at http://www.springerlink.com). 58 pages,
revtex4, some additions to text and some added reference
Centrifuge Health Monitoring of the 50gTon beam centrifuge at the University of Sheffield
In order to fully understand scientific test data it is crucial that we first understand the back-ground centrifuge operational environment and its variation with time and centrifugal acceleration. For exam-ple, changes in ambient air temperature or relative humidity in the centrifuge chamber during operation can have a significant impact on the evaporation levels of water from the surface of a clay model. It is vital to un-derstand these temporal changes in order to mitigate drying out of the soil surface as this would have a detrimental impact on model performance. This paper details the development of a centrifuge health monitoring system capable of measuring environmental parameters over natural seasonal variations of the laboratory environment but also during test conditions. The results of a series of preliminary tests of different duration, acceleration and configuration are discussed to demonstrate the significant changes that occur in the scientific environment during operation
Design and Validation of a Synchronous Reluctance Motor With Single Tooth Windings
This paper presents for the first time the analysis and experimental validation of a six-slot four-pole synchronous reluctance motor with nonoverlapping fractional slot-concentrated windings. The machine exhibits high torque density and efficiency due to its high fill factor coils with very short end windings, facilitated by a segmented stator and bobbin winding of the coils. These advantages are coupled with its inherent robustness and low cost. The topology is presented as a logical step forward in advancing synchronous reluctance machines that have been universally wound with a sinusoidally distributed winding. The paper presents the motor design, performance evaluation through finite element studies and validation of the electromagnetic model, and thermal specification through empirical testing. It is shown that high performance synchronous reluctance motors can be constructed with single tooth wound coils, but considerations must be given regarding torque quality and the d-q axis inductances
Ixodes (Afrixodes) drakensbergensis n. sp. from domestic and wild animals in Natal, Republic of South Africa
Ixodes (Afrixodes) drakensbergensis n. sp., is described from females, males, nymphs and larvae
collected on a drag at Giant's Castle Nature Reserve, Natal, Republic of South Africa; it was also
taken from an eland in the same area and from goats and a cow in the adjacent Tank Area 118. The
occurrence of I. (A.) drakensbergensis on domestic animals suggests that it may be of economic
importance in this area. Information is provided to separate the new species from other closely
related Ixodes species that occur or may occur in this region.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi.
Adobe Acroabt XI was used to OCR the text and also for the merging and conversion to the final presentation PDF-format
Probing Isospin Dynamics in Halo Nuclei
Nuclear many-body theory is used to study nuclear matter and finite nuclei at
extreme isospin. In-medium interactions in asymmetric nuclear matter are
obtained from (Dirac-) Brueckner theory. Neutron skin formation in Ni and Sn
isotopes is investigated by relativistic mean-field calculations in DDRH theory
with density dependent meson-nucleon vertices. Applications to light nuclei are
discussed with special emphasis on pairing and core polarization in weakly
bound nuclei. Approaches accounting for continuum coupling in dripline pairing
and core polarization are presented. Calculations for the halo nuclei B,
Be and C show that shell structures are dissolving when the
driplines are approached. Relativistic breakup data are well described by
eikonal calculations.Comment: 10 pages, 8 figure
Weight suppression and weight elevation are associated with eating disorder symptomatology in women age 50 and older: Results of the gender and body image study
Objective: Weight suppression (WS), the difference between highest past non-pregnancy weight and current weight, predicts negative outcomes in eating disorders, but the impact of WS and related weight constructs are understudied in nonclinical, midlife populations. We examined WS (current weight < highest weight) and weight elevation (WE), the opposite of WS (current weight > lowest weight) and their associations with eating psychopathology in women aged 50+. Method: Participants were a community-based sample (N = 1,776, M age = 59) who completed demographic and eating psychopathology questions via online survey. WS, WE, and WS × WE were tested as predictors of outcome variables; BMI and medical conditions that affect weight were controlled for. Results: Individuals that were higher on WS and WE were most likely to engage in current weight loss attempts, dieting in the past 5 years, and extreme lifetime restriction. Individuals with higher WS were more likely to experience binge eating, greater frequency of weight checking, overvaluation of shape and weight, and lifetime fasting. Individuals with higher WE were more likely to report negative life impacts of eating and dieting. Higher WS and WE each predicted higher levels of skipping meals over the lifetime. Discussion: This novel study investigated WS in midlife women and introduced a new conceptualization of weight change (WE) that may be more relevant for aging populations given that women tend to gain weight with age. The findings implicate the utility of investigating both WS and WE as factors associated with eating psychopathology in midlife women
Controlling a leaky tap
We apply the Ott, Grebogy and Yorke mechanism for the control of chaos to the
analytical oscillator model of a leaky tap obtaining good results. We exhibit
the robustness of the control against both dynamical noise and measurement
noise.A possible way of controlling experimentally a leaky tap using
magnetic-field-produced variations in the viscosity of a magnetorheological
fluid is suggested.Comment: 14 pages, 12 figures. Submitted to Physics Letters
Ambiguous Tests of General Relativity on Cosmological Scales
There are a number of approaches to testing General Relativity (GR) on linear
scales using parameterized frameworks for modifying cosmological perturbation
theory. It is sometimes assumed that the details of any given parameterization
are unimportant if one uses it as a diagnostic for deviations from GR. In this
brief report we argue that this is not necessarily so. First we show that
adopting alternative combinations of modifications to the field equations
significantly changes the constraints that one obtains. In addition, we show
that using a parameterization with insufficient freedom significantly tightens
the apparent theoretical constraints. Fundamentally we argue that it is almost
never appropriate to consider modifications to the perturbed Einstein equations
as being constraints on the effective gravitational constant, for example, in
the same sense that solar system constraints are. The only consistent
modifications are either those that grant near-total freedom, as in
decomposition methods, or ones which map directly to a particular part of
theory space
A plasticity model for powder compaction processes incorporating particle deformation and rearrangement
This article is available open access through the publisher’s website at the link below. Copyright @ 2008 Elsevier Ltd.This paper develops a mechanistic model of granular materials that can be used with a commercial finite element package (ABAQUS). The model draws on the ideas of critical state soil mechanics and combines them with the theory of envelopes to develop an elasto-plastic model with a non-associated flow rule. The model incorporates both local deformation at the granule contacts, and rearrangement of the granules so that jointly they account for any bulk deformation. The mechanics of the model closely reflect the physicality of the material behaviour and the model parameters are closely linked (although not simplistically identical) to the characteristics of the granules. This not only gives an insight into the material behaviour, but also enables the model to be used to facilitate design of the material, its processing properties and, hence, component development. The model is used to simulate drained triaxial tests, settlement of a powder in a bin, and some examples of die pressing. Simulations are compared with experimental data and with predictions obtained using other models
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