746 research outputs found
Inelastic analysis of two plates under deformation dependent loads
Cover plates are used in current designs for high temperature gas-cooled reactors to compress the mineral fiber insulation against the inside of the liner of the prestressed concrete pressure vessel. In the upper plenum, these plates are hexagonal and specified as carbon steel; in the lower cross ducts, the plates are square and made of Hastelloy X. The General Atomic Company has specified both damage and safety limit criteria for these plates. These plates have been analyzed at these limits using the inelastic finite element computer program EPACA. The results indicate that the total strains for the square plate were within the specified values; however, the maximum deformations at the free corners indicate separation from the insulation and failure to achieve one of the design requirements. Since no material data were available for carbon steel at the limiting temperatures, it was assumed that the hexagonal plates were constructed of 2/ percent Cr--1 percent Mo material. Although this material was found to produce satisfactory performance, extrapolation of available information would lead to the conclusion that the performance of carbon steel plates would not be satisfactory at the specified conditions. (auth
A simple and efficient numerical scheme to integrate non-local potentials
As nuclear wave functions have to obey the Pauli principle, potentials issued
from reaction theory or Hartree-Fock formalism using finite-range interactions
contain a non-local part. Written in coordinate space representation, the
Schrodinger equation becomes integro-differential, which is difficult to solve,
contrary to the case of local potentials, where it is an ordinary differential
equation. A simple and powerful method has been proposed several years ago,
with the trivially equivalent potential method, where non-local potential is
replaced by an equivalent local potential, which is state-dependent and has to
be determined iteratively. Its main disadvantage, however, is the appearance of
divergences in potentials if the wave functions have nodes, which is generally
the case. We will show that divergences can be removed by a slight modification
of the trivially equivalent potential method, leading to a very simple, stable
and precise numerical technique to deal with non-local potentials. Examples
will be provided with the calculation of the Hartree-Fock potential and
associated wave functions of 16O using the finite-range N3LO realistic
interaction.Comment: 8 pages, 2 figures, submitted to Eur. Phys. J.
Massless Minimally Coupled Fields in De Sitter Space: O(4)-Symmetric States Versus De Sitter Invariant Vacuum
The issue of de Sitter invariance for a massless minimally coupled scalar
field is revisited. Formally, it is possible to construct a de Sitter invariant
state for this case provided that the zero mode of the field is quantized
properly. Here we take the point of view that this state is physically
acceptable, in the sense that physical observables can be computed and have a
reasonable interpretation. In particular, we use this vacuum to derive a new
result: that the squared difference between the field at two points along a
geodesic observer's space-time path grows linearly with the observer's proper
time for a quantum state that does not break de Sitter invariance. Also, we use
the Hadamard formalism to compute the renormalized expectation value of the
energy momentum tensor, both in the O(4) invariant states introduced by Allen
and Follaci, and in the de Sitter invariant vacuum. We find that the vacuum
energy density in the O(4) invariant case is larger than in the de Sitter
invariant case.Comment: TUTP-92-1, to appear in Phys. Rev.
Biological anthropology in the Indo-Pacific Region: New approaches to age-old questions
Biological anthropological research, the study of both modern and past humans, is a burgeoning field in the Indo-Pacific region. It is becoming increasingly apparent that the unique environments of the Indo-Pacific have resulted in an archaeological record that does not necessarily align with those in the northern hemisphere. New, regionally-specific archaeological models are being developed, and biological anthropological research has an important role to play in establishing past human experience within these models. In the Indo-Pacific, research using ancient and modern human tissues is adding insight into global processes of prehistoric settlement and migrations, subsistence change and human biosocial adaptation. This review synthesises current themes in biological anthropology in this region. It highlights the diverse methods and approaches used by biological anthropologists to address globally-relevant archaeological questions. In recent decades a collaborative approach between archaeologists, biological anthropologists and local communities has become the norm in the region. The many positive outcomes of this multi-disciplinary approach are highlighted here through the use of regionally-specific case studies. This review ultimately aims to stimulate further collaborations between archaeologists, biological anthropologists and the communities in the region, and demonstrate how the evidence from Indo-Pacific research may be relevant to global archaeological models
Long-term perturbations due to a disturbing body in elliptic inclined orbit
In the current study, a double-averaged analytical model including the action
of the perturbing body's inclination is developed to study third-body
perturbations. The disturbing function is expanded in the form of Legendre
polynomials truncated up to the second-order term, and then is averaged over
the periods of the spacecraft and the perturbing body. The efficiency of the
double-averaged algorithm is verified with the full elliptic restricted
three-body model. Comparisons with the previous study for a lunar satellite
perturbed by Earth are presented to measure the effect of the perturbing body's
inclination, and illustrate that the lunar obliquity with the value 6.68\degree
is important for the mean motion of a lunar satellite. The application to the
Mars-Sun system is shown to prove the validity of the double-averaged model. It
can be seen that the algorithm is effective to predict the long-term behavior
of a high-altitude Martian spacecraft perturbed by Sun. The double-averaged
model presented in this paper is also applicable to other celestial systems.Comment: 28 pages, 6 figure
Some anisotropic universes in the presence of imperfect fluid coupling with spatial curvature
We consider Bianchi VI spacetime, which also can be reduced to Bianchi types
VI0-V-III-I. We initially consider the most general form of the energy-momentum
tensor which yields anisotropic stress and heat flow. We then derive an
energy-momentum tensor that couples with the spatial curvature in a way so as
to cancel out the terms that arise due to the spatial curvature in the
evolution equations of the Einstein field equations. We obtain exact solutions
for the universes indefinetly expanding with constant mean deceleration
parameter. The solutions are beriefly discussed for each Bianchi type. The
dynamics of the models and fluid are examined briefly, and the models that can
approach to isotropy are determined. We conclude that even if the observed
universe is almost isotropic, this does not necessarily imply the isotropy of
the fluid (e.g., dark energy) affecting the evolution of the universe within
the context of general relativity.Comment: 17 pages, no figures; to appear in International Journal of
Theoretical Physics; in this version (which is more concise) an equation
added, some references updated and adde
Fit for purpose? A cross-sectional study to evaluate the acceptability and usability of HeadUp, a novel neck support collar for neurological neck weakness
The HeadUp collar (previously known as the Sheffield Support Snood) provides support for neck weakness caused by amyotrophic lateral sclerosis (ALS) and has shown to be superior to alternative options in a small cohort of patients from one single center. Here we report the assessment of the HeadUp collar in a larger cohort of patients, exploring the use in other neurological conditions and expanding to other centers across the UK and Ireland. An interventional cross-sectional study design was implemented to investigate the usability and acceptability of the HeadUp collar. A total of 139 patients were recruited for the study, 117 patients had a diagnosis of ALS and 22 patients presented with neck weakness due to other neurological conditions. Participants were assessed at baseline, fitted a HeadUp collar and followed-up one month later. The performance of the HeadUp collar was rated favorably compared to previously worn collars in terms of the ability to eat, drink and swallow. Findings suggest that the collar also permitted a more acceptable range of head movements whilst maintaining a good level of support. We conclude that the HeadUp collar is a suitable option for patients with neck weakness due to ALS and other neurological conditions
Couplings of light I=0 scalar mesons to simple operators in the complex plane
The flavour and glue structure of the light scalar mesons in QCD are probed
by studying the couplings of the I=0 mesons and to the
operators , and to two photons. The Roy dispersive
representation for the amplitude is used to determine the
pole positions as well as the residues in the complex plane. On the real axis,
is constrained to solve the Roy equation together with elastic
unitarity up to the K\Kbar threshold leading to an improved description of
the . The problem of using a two-particle threshold as a matching
point is discussed. A simple relation is established between the coupling of a
scalar meson to an operator and the value of the related pion form-factor
computed at the resonance pole. Pion scalar form-factors as well as two-photon
partial-wave amplitudes are expressed as coupled-channel Omn\`es dispersive
representations. Subtraction constants are constrained by chiral symmetry and
experimental data. Comparison of our results for the couplings with
earlier determinations of the analogous couplings of the lightest I=1 and
scalar mesons are compatible with an assignment of the ,
, , into a nonet. Concerning the gluonic operator
we find a significant coupling to both the and the
.Comment: 31 pages, 5 figure
Sustainable change: long-term efforts toward developing a learning organization
Globalization and intensified competition require organizations to change and adapt to dynamic environments in order to stay competitive. This article describes a longitudinal action research study supporting the strategic change of a trading company. The strategic change was accompanied by planned changes in organizational structures and processes, management systems, emerging changes in leadership, and organization members’ attitudes and behaviors, and it was supported by management development activities. Longitudinal data over a 4-year period including participant observation and interviews reveal that a systemic approach, a learning and becoming perspective toward change, trust, an appropriate role perception, and the specific use of management instruments contribute to sustained change that resulted in performance improvements and a move toward a learning organization. We conclude with implications for strategic change and suggestions for further research in this area
Development and validation of a symptom-based activity index for adults with eosinophilic esophagitis.
BACKGROUND & AIMS: Standardized instruments are needed to assess the activity of eosinophilic esophagitis (EoE) and to provide end points for clinical trials and observational studies. We aimed to develop and validate a patient-reported outcome (PRO) instrument and score, based on items that could account for variations in patient assessments of disease severity. We also evaluated relationships between patient assessment of disease severity and EoE-associated endoscopic, histologic, and laboratory findings.
METHODS: We collected information from 186 patients with EoE in Switzerland and the United States (69.4% male; median age, 43 y) via surveys (n = 135), focus groups (n = 27), and semistructured interviews (n = 24). Items were generated for the instruments to assess biologic activity based on physician input. Linear regression was used to quantify the extent to which variations in patient-reported disease characteristics could account for variations in patient assessment of EoE severity. The PRO instrument was used prospectively in 153 adult patients with EoE (72.5% male; median age, 38 y), and validated in an independent group of 120 patients with EoE (60.8% male; median age, 40.5 y).
RESULTS: Seven PRO factors that are used to assess characteristics of dysphagia, behavioral adaptations to living with dysphagia, and pain while swallowing accounted for 67% of the variation in patient assessment of disease severity. Based on statistical consideration and patient input, a 7-day recall period was selected. Highly active EoE, based on endoscopic and histologic findings, was associated with an increase in patient-assessed disease severity. In the validation study, the mean difference between patient assessment of EoE severity (range, 0-10) and PRO score (range, 0-8.52) was 0.15.
CONCLUSIONS: We developed and validated an EoE scoring system based on 7 PRO items that assess symptoms over a 7-day recall period. Clinicaltrials.gov number: NCT00939263
- …