416 research outputs found
De endogene financiele structuur
De vrees dat verschillen in financiële structuur de transmissie van het Europese monetair beleid zullen bemoeilijken is overdreven. De
financiële structuur in Europa zal door de komst van de euro harmoniseren
Resummation Methods at Finite Temperature: The Tadpole Way
We examine several resummation methods for computing higher order corrections
to the finite temperature effective potential, in the context of a scalar
theory. We show by explicit calculation to four loops that dressing
the propagator, not the vertex, of the one-loop tadpole correctly counts
``daisy'' and ``super-daisy'' diagrams.Comment: 18 pages, LaTeX, CALT-68-1858, HUTP-93-A011, EFI-93-2
Dynamics near the critical point: the hot renormalization group in quantum field theory
The perturbative approach to the description of long wavelength excitations
at high temperature breaks down near the critical point of a second order phase
transition. We study the \emph{dynamics} of these excitations in a relativistic
scalar field theory at and near the critical point via a renormalization group
approach at high temperature and an expansion in
space-time dimensions. The long wavelength physics is determined by a
non-trivial fixed point of the renormalization group. At the critical point we
find that the dispersion relation and width of quasiparticles of momentum
is and respectively, the
group velocity of quasiparticles vanishes in the long
wavelength limit at the critical point. Away from the critical point for
we find and
with
the finite temperature correlation length . The
new \emph{dynamical} exponent results from anisotropic renormalization in
the spatial and time directions. For a theory with O(N) symmetry we find . Critical slowing down,
i.e, a vanishing width in the long-wavelength limit, and the validity of the
quasiparticle picture emerge naturally from this analysis.Comment: Discussion on new dynamical universality class. To appear in Phys.
Rev.
Newborn screening for pompe disease? A qualitative study exploring professional views
Background: Developments in enzyme replacement therapy have kindled discussions on adding Pompe disease, characterized by progressive muscle weakness and wasting, to neonatal screening. Pompe disease does not fit traditional screening criteria as it is a broad-spectrum phenotype disorder that may occur in lethal form in early infancy or manifest in less severe forms from infancy to late adulthood. Current screening tests cannot differentiate between these forms. Normally, expanding screening is discussed among experts in advisory bodies. While advisory reports usually mention the procedures and outcome of deliberations, little is known of the importance attached to different arguments and the actual weighing processes involved. In this research we aim to explore the views of a wide range of relevant professionals to gain more insight into the process of weighing pros and cons of neonatal screening for Pompe disease, as an example of the dilemmas involved in screening for broad-spectrum phenotype disorders.Methods: We conducted 24 semi-structured interviews with medical, lab, insurance and screening professionals, and executive staff of patient organisations. They were asked about their first reaction to neonatal screening for Pompe disease, after which benefits and harms and requirements for screening were explored in more detail.Results: Advantages included health gain by timely intervention, avoiding a diagnostic quest, having a reproductive choice and gaining more knowledge about the natural course and treatment. Being prepared was mentioned as an advantage for the later manifesting cases. Disadvantages included treatment costs and uncertainties about its effect, the timing of treatment in later manifesting cases, the psychological burden for the patient-in-waiting and the family. Also the downsides of having prior knowledge as well as having to consider a reproductive option were mentioned as disadvantages.Conclusion: When weighing pros and cons, interviewees attach different importance to different arguments, based on personal and professional views. Professionals expect benefits from neonatal screening for Pompe disease, especially for early-onset cases. Some interviewees valued screening in later manifesting cases as well, while stressing the need for adequate support of pre-symptomatic patients and their families. Others considered the psychological burden and uncertainties regarding treatment as reasons not to screen
Hyperons analogous to the \Lambda(1405)
The low mass of the hyperon with , which is
higher than the ground state mass by 290 MeV, is difficult to
understand in quark models. We analyze the hyperon spectrum in the bound state
approach of the Skyrme model that successfully describes both the
and the . This model predicts that several
hyperon resonances of the same spin but with opposite parity form parity
doublets that have a mass difference of around 300 MeV, which is indeed
realized in the observed hyperon spectrum. Furthermore, the existence of the
and the of is predicted by this model.
Comments on the baryons and heavy quark baryons are made as well.Comment: 4 pages, talk presented at the Fifth Asia-Pacific Conference on
Few-Body Problems in Physics 2011 (APFB2011), Aug. 22-26, 2011, Seoul, Kore
A strongly first order electroweak phase transition from strong symmetry-breaking interactions
We argue that a strongly first order electroweak phase transition is natural
in the presence of strong symmetry-breaking interactions, such as technicolor.
We demonstrate this using an effective linear scalar theory of the
symmetry-breaking sector.Comment: LaTex, 15 pages, 3 figures in EPS format. Phys. Rev. D approved
Typographically Correct version, minor grammatical change
An adaptive inelastic magnetic mirror for Bose-Einstein condensates
We report the reflection and focussing of a Bose-Einstein condensate by a new
pulsed magnetic mirror. The mirror is adaptive, inelastic, and of extremely
high optical quality. The deviations from specularity are less than 0.5 mrad
rms, making this the best atomic mirror demonstrated to date. We have also used
the mirror to realize the analog of a beam-expander, producing an ultra-cold
collimated fountain of matter wavesComment: 4 pages, 4 figure
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
Long Range Magnetic Order and the Darwin Lagrangian
We simulate a finite system of confined electrons with inclusion of the
Darwin magnetic interaction in two- and three-dimensions. The lowest energy
states are located using the steepest descent quenching adapted for velocity
dependent potentials. Below a critical density the ground state is a static
Wigner lattice. For supercritical density the ground state has a non-zero
kinetic energy. The critical density decreases with for exponential
confinement but not for harmonic confinement. The lowest energy state also
depends on the confinement and dimension: an antiferromagnetic cluster forms
for harmonic confinement in two dimensions.Comment: 5 figure
Computation of the winding number diffusion rate due to the cosmological sphaleron
A detailed quantitative analysis of the transition process mediated by a
sphaleron type non-Abelian gauge field configuration in a static Einstein
universe is carried out. By examining spectra of the fluctuation operators and
applying the zeta function regularization scheme, a closed analytical
expression for the transition rate at the one-loop level is derived. This is a
unique example of an exact solution for a sphaleron model in spacetime
dimensions.Comment: Some style corrections suggested by the referee are introduced
(mainly in Sec.II), one reference added. To appear in Phys.Rev.D 29 pages,
LaTeX, 3 Postscript figures, uses epsf.st
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