6,604 research outputs found
Renormalized charge in a two-dimensional model of colloidal suspension from hypernetted chain approach
The renormalized charge of a simple two-dimensional model of colloidal
suspension was determined by solving the hypernetted chain approximation and
Ornstein-Zernike equations. At the infinite dilution limit, the asymptotic
behavior of the correlations functions is used to define the effective
interactions between the components of the system and these effective
interactions were compared to those derived from the Poisson-Boltzmann theory.
The results we obtained show that, in contrast to the mean-field theory, the
renormalized charge does not saturate, but exhibits a maximum value and then
decays monotonically as the bare charge increases. The results also suggest
that beyond the counterion layer near to the macroion surface, the ionic cloud
is not a diffuse layer which can be handled by means of the linearized theory,
as the two-state model claims, but a more complex structure is settled by the
correlations between microions
Vevacious: A Tool For Finding The Global Minima Of One-Loop Effective Potentials With Many Scalars
Several extensions of the Standard Model of particle physics contain
additional scalars implying a more complex scalar potential compared to that of
the Standard Model. In general these potentials allow for charge and/or color
breaking minima besides the desired one with correctly broken SU(2)_L times
U(1)_Y . Even if one assumes that a metastable local minimum is realized, one
has to ensure that its lifetime exceeds that of our universe. We introduce a
new program called Vevacious which takes a generic expression for a one-loop
effective potential energy function and finds all the tree-level extrema, which
are then used as the starting points for gradient-based minimization of the
one-loop effective potential. The tunneling time from a given input vacuum to
the deepest minimum, if different from the input vacuum, can be calculated. The
parameter points are given as files in the SLHA format (though is not
restricted to supersymmetric models), and new model files can be easily
generated automatically by the Mathematica package SARAH. This code uses
HOM4PS2 to find all the minima of the tree-level potential, PyMinuit to follow
gradients to the minima of the one-loop potential, and CosmoTransitions to
calculate tunneling times.Comment: 44 pages, 1 figure, manual for publicly available software, v2
corresponds to version accepted for publication in EPJC [clearer explanation
of scale dependence and region of validity, explicit mention that SLHA files
should have blocks matching those expected by model files, updated
references
Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle
The contribution from quantum vacuum fluctuations of a real massless scalar
field to the motion of a test particle that interacts with the field in the
presence of a perfectly reflecting flat boundary is here investigated. There is
no quantum induced dispersions on the motion of the particle when it is alone
in the empty space. However, when a reflecting wall is introduced, dispersions
occur with magnitude dependent on how fast the system evolves between the two
scenarios. A possible way of implementing this process would be by means of an
idealized sudden switching, for which the transition occurs instantaneously.
Although the sudden process is a simple and mathematically convenient
idealization it brings some divergences to the results, particularly at a time
corresponding to a round trip of a light signal between the particle and the
wall. It is shown that the use of smooth switching functions, besides
regularizing such divergences, enables us to better understand the behavior of
the quantum dispersions induced on the motion of the particle. Furthermore, the
action of modifying the vacuum state of the system leads to a change in the
particle energy that depends on how fast the transition between these states is
implemented. Possible implications of these results to the similar case of an
electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure
Constraining the Natural MSSM through tunneling to color-breaking vacua at zero and non-zero temperature
We re-evaluate the constraints on the parameter space of the minimal
supersymmetric standard model from tunneling to charge- and/or color-breaking
minima, taking into account thermal corrections. We pay particular attention to
the region known as the Natural MSSM, where the masses of the scalar partners
of the top quarks are within an order of magnitude or so of the electroweak
scale. These constraints arise from the interaction between these scalar tops
and the Higgs fields, which allows the possibility of parameter points having
deep charge- and color-breaking true vacua. In addition to requiring that our
electro-weak-symmetry-breaking, yet QCD- and electromagnetism-preserving vacuum
has a sufficiently long lifetime at zero temperature, also demanding stability
against thermal tunneling further restricts the allowed parameter space.Comment: 7 pages, 2 figures, software available from
http://vevacious.hepforge.org/ - version 2 matches that accepted for
publication in Phys. Lett.
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What is a Freestanding Emergency Department? Definitions Differ Across Major United States Data Sources
Introduction: Despite the growing number of freestanding emergency departments (FSED) in the United States (US), FSED definitions differ across major US data sources of healthcare facilities and use. We compare these sources and propose a universal definition of FSED (and its two major types) to improve communications regarding these facilities and their patients.Methods: We collected definitions of FSEDs from 11 national data sources using their websites, email, and telephone communications. For each source, we asked how they define FSEDs, whether being open 24/7 is a requirement to be called an ED, and whether they maintain a dataset of FSEDs.Results: Definitions varied across the data sources. All sources recognize FSEDs in their definitions, regardless of type; only one (the National Health Intervew Survey) does not differentiate them from other EDs. Five of the 11 sources (45%) omit autonomous FSEDs from their definitions and do not separately identify satellite FSEDs from their affiliated hospitals. One source does separately identify satellite FSEDs from their affiliated hospitals, but also omits autonomous FSEDs. Furthermore, three of the 11 sources (27%) do not require being open 24/7, while all others (73%) employ this criterion. Six of the 11 (55%) maintain datasets of FSEDs using their definition.Conclusion: As FSEDs continue to change the landscape of emergency care, it is important that they also be represented in national ED data sources. The current differences in the definition of an FSED make it difficult to provide accurate and longitudinal analysis for these facilities and patients who receive services at these facilities. We propose a universal definition of FSEDs as described by both the American College of Emergency Physicians and the National Emergency Department Inventory. Implementing a standard definition would facilitate a more accurate representation of FSEDs in national data sources and enhance ongoing efforts to improve the quality of emergency care delivered in FSEDs
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