1,890 research outputs found
Edges and Diffractive Effects in Casimir Energies
The prototypical Casimir effect arises when a scalar field is confined
between parallel Dirichlet boundaries. We study corrections to this when the
boundaries themselves have apertures and edges. We consider several geometries:
a single plate with a slit in it, perpendicular plates separated by a gap, and
two parallel plates, one of which has a long slit of large width, related to
the case of one plate being semi-infinite. We develop a general formalism for
studying such problems, based on the wavefunctional for the field in the gap
between the plates. This formalism leads to a lower dimensional theory defined
on the open regions of the plates or boundaries. The Casimir energy is then
given in terms of the determinant of the nonlocal differential operator which
defines the lower dimensional theory. We develop perturbative methods for
computing these determinants. Our results are in good agreement with known
results based on Monte Carlo simulations. The method is well suited to
isolating the diffractive contributions to the Casimir energy.Comment: 32 pages, LaTeX, 9 figures. v2: additional discussion of
renormalization procedure, version to appear in PRD. v3: corrected a sign
error in (70
Life becomes about survival\u27: Resettlement, integration, and social services among refugee parents
Multi-graviton theory, a latticized dimension, and the cosmological constant
Beginning with the Pauli-Fierz theory, we construct a model for
multi-graviton theory. Couplings between gravitons belonging to
nearest-neighbor ``theory spaces'' lead to a discrete mass spectrum. Our model
coincides with the Kaluza-Klein theory whose fifth dimension is latticized.
We evaluate one-loop vacuum energy in models with a circular latticized extra
dimension as well as with compact continuous dimensions. We find that the
vacuum energy can take a positive value, if the dimension of the continuous
space time is . Moreover, since the amount of the vacuum energy can
be an arbitrary small value according to the choice of parameters in the model,
our models is useful to explain the small positive dark energy in the present
universe.Comment: 10 pages, No figure. Needs REVTeX4. citations are corrected and minor
correction
Topology Change in Canonical Quantum Cosmology
We develop the canonical quantization of a midisuperspace model which
contains, as a subspace, a minisuperspace constituted of a
Friedman-Lema\^{\i}tre-Robertson-Walker Universe filled with homogeneous scalar
and dust fields, where the sign of the intrinsic curvature of the spacelike
hypersurfaces of homogeneity is not specified, allowing the study of topology
change in these hypersurfaces. We solve the Wheeler-DeWitt equation of the
midisuperspace model restricted to this minisuperspace subspace in the
semi-classical approximation. Adopting the conditional probability
interpretation, we find that some of the solutions present change of topology
of the homogeneous hypersurfaces. However, this result depends crucially on the
interpretation we adopt: using the usual probabilistic interpretation, we find
selection rules which forbid some of these topology changes.Comment: 23 pages, LaTex file. We added in the conclusion some comments about
path integral formalism and corrected litle misprinting
Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.Comment: To be published in PR
Superiority of deformable image co-registration in the integration of diagnostic positron emission tomography-computed tomography to the radiotherapy treatment planning pathway for oesophageal carcinoma
Aims
To investigate the use of image co-registration in incorporating diagnostic positron emission tomography-computed tomography (PET-CT) directly into the radiotherapy treatment planning pathway, and to describe the pattern of local recurrence relative to the PET-avid volume.
Materials and methods
Fourteen patients were retrospectively identified, six of whom had local recurrence. The accuracy of deformable image registration (DIR) and rigid registration of the diagnostic PET-CT and recurrence CT, to the planning CT, were quantitatively assessed by comparing co-registration of oesophagus, trachea and aorta contours. DIR was used to examine the correlation between PET-avid volumes, dosimetry and site of recurrence.
Results
Positional metrics including the dice similarity coefficient (DSC) and conformity index (CI), showed DIR to be superior to rigid registration in the co-registration of diagnostic and recurrence imaging to the planning CT. For diagnostic PET-CT, DIR was superior to rigid registration in the transfer of oesophagus (DSC = 0.75 versus 0.65, P < 0.009 and CI = 0.59 versus 0.48, P < 0.003), trachea (DSC = 0.88 versus 0.65, P < 0.004 and CI = 0.78 versus 0.51, P < 0.0001) and aorta structures (DSC = 0.93 versus 0.86, P < 0.006 and CI = 0.86 versus 0.76, P < 0.006). For recurrence imaging, DIR was superior to rigid registration in the transfer of trachea (DSC = 0.91 versus 0.66, P < 0.03 and CI = 0.83 versus 0.51, P < 0.02) and oesophagus structures (DSC = 0.74 versus 0.51, P < 0.004 and CI = 0.61 versus 0.37, P < 0.006) with a non-significant trend for the aorta (DSC = 0.91 versus 0.75, P < 0.08 and CI = 0.83 versus 0.63, P < 0.06) structure. A mean inclusivity index of 0.93 (range 0.79–1) showed that the relapse volume was within the planning target volume (PTVPET-CT); all relapses occurred within the high dose region.
Conclusion
DIR is superior to rigid registration in the co-registration of PET-CT and recurrence CT to the planning CT, and can be considered in the direct integration of PET-CT to the treatment planning process. Local recurrences occur within the PTVPET-CT, suggesting that this is a suitable target for dose-escalation strategies
The gauge invariant effective potential: equilibrium and non-equilibrium aspects
We propose a gauge invariant formulation of the effective potential in terms
of a gauge invariant order parameter, for the Abelian Higgs model. The one-loop
contribution at zero and finite temperature is computed explicitly, and the
leading terms in the high temperature expansion are obtained. The result is
contrasted to the effective potential obtained in several covariant
gauge-fixing schemes, and the gauge invariant quantities that can be reliably
extracted from these are identified. It is pointed out that the gauge invariant
effective potential in the one-loop approximation is complex for {\em all
values} of the order parameter between the maximum and the minimum of the tree
level potential, both at zero and non-zero temperature. The imaginary part is
related to long-wavelength instabilities towards phase separation. We study the
real-time dynamics of initial states in the spinodal region, and relate the
imaginary part of the effective potential to the growth rate of equal-time
gauge invariant correlation functions in these states. We conjecture that the
spinodal instabilities may play a role in non-equilibrium processes {\em
inside} the nucleating bubbles if the transition is first order.Comment: 27 pages revtex 3.0, no figures; one reference adde
Ammonia Measurements and Emissions from a California Dairy Using Point and Remote Sensors
Ammonia (NH3) is an important trace gas species in the atmosphere that can have negative impacts on human, animal, and ecosystem health. Agriculture has been identified as the largest source of NH3, specifically livestock operations. NH3 emissions from a commercial dairy in California were investigated during June 2008. Cattle were held in open-lot pens, except for young calves in hutches with shelters. Solid manure was stored in the open-lot pens. Liquid manure from feed lanes was passed through a solids settling basin and stored in a holding pond. Passive sensors and openpath Fourier transform infrared spectrometers (OP-FTIR) were deployed around the facility to measure NH3 concentrations. Emissions from pens and the liquid manure system (LMS) were estimated using inverse modeling. Mean emission factors (EFs) for the entire facility were 140.5 ±42.5 g d-1 animal-1 from the passive sampler data and 199.2 ±22.0 g d-1 animal-1 from the OP-FTIR data, resulting in the facility’s summer emissions calculated at 265.2 ±80.2 kg d-1 and 375.4 ±27.1 kg d-1, respectively. These EFs are within the range of values reported in the literature. Both concentrations and emissions exhibited a strong diurnal cycle, peaking in the late afternoon. Total facility emissions exhibited significant positive correlations with temperature and wind speed. The findings of this study show that NH3 emissions from a commercial dairy can vary by a factor of 10 or more throughout the day, and EFs can vary by two orders of magnitude when compared to other U.S. dairies, based on literature values
The use of routine outcome measures in two child and adolescent mental health services: a completed audit cycle
Background: Routine outcome measurement (ROM) is important for assessing the clinical effectiveness of health services and for monitoring patient outcomes. Within Child and Adolescent Mental Health Services (CAMHS) in the UK the adoption of ROM in CAMHS has been supported by both national and local initiatives (such as government strategies, local commissioning policy, and research). Methods: With the aim of assessing how these policies and initiatives may have influenced the uptake of ROM within two different CAMHS we report the findings of two case-note audits: a baseline audit conducted in January 2011 and a re-audit conducted two years later in December 2012-February 2013. Results: The findings show an increase in both the single and repeated use of outcome measures from the time of the original audit, with repeated use (baseline and follow-up) of the Health of the Nation Outcome Scale for Children and Adolescents (HoNOSCA) scale increasing from 10% to 50% of cases. Re-audited case-notes contained more combined use of different outcome measures, with greater consensus on which measures to use. Outcome measures that were applicable across a wide range of clinical conditions were more likely to be used than symptom-specific measures, and measures that were completed by the clinician were found more often than measures completed by the service user. Conclusions: The findings show a substantial improvement in the use of outcome measures within CAMHS. These increases in use were found across different service organisations which were subject to different types of local service priorities and drivers
Polymer transport in random flow
The dynamics of polymers in a random smooth flow is investigated in the
framework of the Hookean dumbbell model. The analytical expression of the
time-dependent probability density function of polymer elongation is derived
explicitly for a Gaussian, rapidly changing flow. When polymers are in the
coiled state the pdf reaches a stationary state characterized by power-law
tails both for small and large arguments compared to the equilibrium length.
The characteristic relaxation time is computed as a function of the Weissenberg
number. In the stretched state the pdf is unstationary and exhibits
multiscaling. Numerical simulations for the two-dimensional Navier-Stokes flow
confirm the relevance of theoretical results obtained for the delta-correlated
model.Comment: 28 pages, 6 figure
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