1,165 research outputs found
Literature research in relevant fields to understand pressure relief valve leak tightness in a static closed state
Currently, no review of literature exists which attempts to understand the leakage phenomenon of metal-to-metal seal contact Pressure Relief Valves (PRV) for static closed positions as they reach the set pressure point. This paper attempts to do just that by drawing on inspiration from other research areas such as: metal-to-metal contact and gasket seals. The key topics of interest surrounding the leakage of fluid through a gap are: fluid flow assumptions; surface characteristics and its deformation; and experimental techniques used to quantify leakage. The fluid flow assumptions relating to the gap height such as transmissivity and diffusivity are found to be directly linked to the surface roughness and the surfaces deformations. Traditionally the summing method has been used to represent two rough surfaces at a micro scale from which the Tsukizoe and Hisakado theory has been applied for deformation of the micro contact in a plastic manner. The path the fluid also takes through the gap is investigated with recent work using computational methods to determine that path. Current experimental leakage quantification techniques are also discussed. Finally, the future development of PRV static leakage is examined
Controllability on infinite-dimensional manifolds
Following the unified approach of A. Kriegl and P.W. Michor (1997) for a
treatment of global analysis on a class of locally convex spaces known as
convenient, we give a generalization of Rashevsky-Chow's theorem for control
systems in regular connected manifolds modelled on convenient
(infinite-dimensional) locally convex spaces which are not necessarily
normable.Comment: 19 pages, 1 figur
Growth factor in f(T) gravity
We derive the evolution equation of growth factor for the matter over-dense
perturbation in gravity. For instance, we investigate its behavior in
power law model at small redshift and compare it to the prediction of
CDM and dark energy with the same equation of state in the framework
of Einstein general relativity. We find that the perturbation in gravity
grows slower than that in Einstein general relativity if \p f/\p T>0 due to
the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added,
accepted by JCA
Re-Focusing - Building a Future for Entrepreneurial Education & Learning
The field of entrepreneurship has struggled with fundamental
questions concerning the subject’s nature and purpose. To whom and to
what means are educational and training agendas ultimately directed?
Such questions have become of central importance to policy makers,
practitioners and academics alike. There are suggestions that university
business schools should engage more critically with the lived experiences
of practising entrepreneurs through alternative pedagogical approaches
and methods, seeking to account for and highlighting the social, political
and moral aspects of entrepreneurial practice. In the UK, where funding in
higher education has become increasingly dependent on student fees,
there are renewed pressures to educate students for entrepreneurial
practice as opposed to educating them about the nature and effects of
entrepreneurship. Government and EU policies are calling on business
schools to develop and enhance entrepreneurial growth and skill sets, to
make their education and training programmes more proactive in
providing innovative educational practices which help and facilitate life
experiences and experiential learning. This paper makes the case for
critical frameworks to be applied so that complex social processes
become a source of learning for educators and entrepreneurs and so that
innovative pedagogical approaches can be developed in terms both of
context (curriculum design) and process (delivery methods)
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Emergence of quasi-metallic state in disordered 2D electron gas due to strong interactions
The interrelation between disorder and interactions in two dimensional
electron liquid is studied beyond weak coupling perturbation theory. Strong
repulsion significantly reduces the electronic density of states on the Fermi
level. This makes the electron liquid more rigid and strongly suppresses
elastic scattering off impurities. As a result the weak localization, although
ultimately present at zero temperature and infinite sample size, is
unobservable at experimentally accessible temperature at high enough densities.
Therefore practically there exists a well defined metallic state. We study
diffusion of electrons in this state and find that the diffusion pole is
significantly modified due to "mixture" with static photons similar to the
Anderson - Higgs mechanism in superconductivity. As a result several effects
stemming from the long range nature of diffusion like the Aronov - Altshuler
logarithmic corrections to conductivity are less pronounced.Comment: to appear in Phys. Rev.
Sleep quality improvements after MDMA-assisted psychotherapy for the treatment of posttraumatic stress disorder
Sleep disturbances (SDs) are among the most distressing and commonly reported symptoms in posttraumatic stress disorder (PTSD). Despite increased attention on sleep in clinical PTSD research, SDs remain difficult to treat. In Phase 2 trials, 3,4-methylenedioxymethamphetamine (MDMA)-assisted psychotherapy has been shown to greatly improve PTSD symptoms. We hypothesized that MDMA-assisted psychotherapy would improve self-reported sleep quality (SQ) in individuals with PTSD and be associated with declining PTSD symptoms. Participants in four studies (n = 63) were randomized to receive 2-3 sessions of active MDMA (75-125 mg; n = 47) or placebo/control MDMA (0-40 mg, n = 16) during all-day psychotherapy sessions. The PSQI was used to assess change in SQ from baseline to the primary endpoint, 1-2 months after the blinded sessions. Additionally, PSQI scores were measured at treatment exit (TE) and 12-month follow-up. Symptoms of PTSD were measured using the CAPS-IV. At the primary endpoint, CAPS-IV total severity scores dropped more after active MDMA than after placebo/control (-34.0 vs. -12.4), p = .003. Participants in the active dose group showed more improvement in SQ compared to those in the control group (PSQI total score Delta M = -3.5 vs. 0.6), p = .003. Compared to baseline, SQ had improved at TE, p < .001, with further significant gains reported at 12-month follow-up (TE to 12-months Delta M = -1.0), p = .030. Data from these randomized controlled double-blind studies provide evidence for the beneficial effects of MDMA-assisted psychotherapy in treating SDs in individuals with PTSD.Stress-related psychiatric disorders across the life spa
Coulomb gap in a model with finite charge transfer energy
The Coulomb gap in a donor-acceptor model with finite charge transfer energy
describing the electronic system on the dielectric side of the
metal-insulator transition is investigated by means of computer simulations on
two- and three-dimensional finite samples with a random distribution of equal
amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry
of the model presented with respect to the exchange of donors and acceptors are
derived. In the immediate neighborhood of the Fermi energy the the
density of one-electron excitations is determined solely by
finite size effects and further away from is described by
an asymmetric power law with a non-universal exponent, depending on the
parameter .Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Consistent Anisotropic Repulsions for Simple Molecules
We extract atom-atom potentials from the effective spherical potentials that
suc cessfully model Hugoniot experiments on molecular fluids, e.g., and
. In the case of the resulting potentials compare very well with the
atom-atom potentials used in studies of solid-state propertie s, while for
they are considerably softer at short distances. Ground state (T=0K) and
room temperatu re calculations performed with the new potential resolve
the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure
Decoupling in an expanding universe: boundary RG-flow affects initial conditions for inflation
We study decoupling in FRW spacetimes, emphasizing a Lagrangian description
throughout. To account for the vacuum choice ambiguity in cosmological
settings, we introduce an arbitrary boundary action representing the initial
conditions. RG flow in these spacetimes naturally affects the boundary
interactions. As a consequence the boundary conditions are sensitive to
high-energy physics through irrelevant terms in the boundary action. Using
scalar field theory as an example, we derive the leading dimension four
irrelevant boundary operators. We discuss how the known vacuum choices, e.g.
the Bunch-Davies vacuum, appear in the Lagrangian description and square with
decoupling. For all choices of boundary conditions encoded by relevant boundary
operators, of which the known ones are a subset, backreaction is under control.
All, moreover, will generically feel the influence of high-energy physics
through irrelevant (dimension four) boundary corrections. Having established a
coherent effective field theory framework including the vacuum choice
ambiguity, we derive an explicit expression for the power spectrum of
inflationary density perturbations including the leading high energy
corrections. In accordance with the dimensionality of the leading irrelevant
operators, the effect of high energy physics is linearly proportional to the
Hubble radius H and the scale of new physics L= 1/M.Comment: LaTeX plus axodraw figures. v2: minor corrections; refs added. JHEP
style: 34 pages + 18 pages appendi
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