8,626 research outputs found
Extraction of nuclear matter properties from nuclear masses by a model of equation of state
The extraction of nuclear matter properties from measured nuclear masses is
investigated in the energy density functional formalism of nuclei. It is shown
that the volume energy and the nuclear incompressibility depend
essentially on , whereas the symmetry energy
and the density symmetry coefficient as well as symmetry incompressibility
depend essentially on , where
, and are the
neutron and proton chemical potentials respectively, the nuclear energy,
and the Coulomb energy. The obtained symmetry energy is ,
while other coefficients are uncertain within ranges depending on the model of
nuclear equation of state.Comment: 12 pages and 7 figure
Effective nucleon-nucleon interactions and nuclear matter equation of state
Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and
Tondeur interactions are written as polynomials of the cubic root of density,
with coefficients that are functions of the relative neutron excess .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
Bacteriophage and their potential roles in the human oral cavity.
The human oral cavity provides the perfect portal of entry for viruses and bacteria in the environment to access new hosts. Hence, the oral cavity is one of the most densely populated habitats of the human body containing some 6 billion bacteria and potentially 35 times that many viruses. The role of these viral communities remains unclear; however, many are bacteriophage that may have active roles in shaping the ecology of oral bacterial communities. Other implications for the presence of such vast oral phage communities include accelerating the molecular diversity of their bacterial hosts as both host and phage mutate to gain evolutionary advantages. Additional roles include the acquisitions of new gene functions through lysogenic conversions that may provide selective advantages to host bacteria in response to antibiotics or other types of disturbances, and protection of the human host from invading pathogens by binding to and preventing pathogens from crossing oral mucosal barriers. Recent evidence suggests that phage may be more involved in periodontal diseases than were previously thought, as their compositions in the subgingival crevice in moderate to severe periodontitis are known to be significantly altered. However, it is unclear to what extent they contribute to dysbiosis or the transition of the microbial community into a state promoting oral disease. Bacteriophage communities are distinct in saliva compared to sub- and supragingival areas, suggesting that different oral biogeographic niches have unique phage ecology shaping their bacterial biota. In this review, we summarize what is known about phage communities in the oral cavity, the possible contributions of phage in shaping oral bacterial ecology, and the risks to public health oral phage may pose through their potential to spread antibiotic resistance gene functions to close contacts
Nuclear matter properties and relativistic mean-field theory
Nuclear matter properties are calculated in the relativistic mean field
theory by using a number of different parameter sets. The result shows that the
volume energy and the symmetry energy are around the acceptable
values 16MeV and 30MeV respectively; the incompressibility is
unacceptably high in the linear model, but assumes reasonable value if
nonlinear terms are included; the density symmetry is around for
most parameter sets, and the symmetry incompressibility has positive sign
which is opposite to expectations based on the nonrelativistic model. In almost
all parameter sets there exists a critical point , where
the minimum and the maximum of the equation of state are coincident and the
incompressibility equals zero, falling into ranges
0.014fmfm and ; for a few
parameter sets there is no critical point and the pure neutron matter is
predicted to be bound. The maximum mass of neutron stars is predicted
in the range 2.45MM, the corresponding
neutron star radius is in the range 12.2kmkm.Comment: 10 pages, 5 figure
Double Diffusion Encoding Prevents Degeneracy in Parameter Estimation of Biophysical Models in Diffusion MRI
Purpose: Biophysical tissue models are increasingly used in the
interpretation of diffusion MRI (dMRI) data, with the potential to provide
specific biomarkers of brain microstructural changes. However, the general
Standard Model has recently shown that model parameter estimation from dMRI
data is ill-posed unless very strong magnetic gradients are used. We analyse
this issue for the Neurite Orientation Dispersion and Density Imaging with
Diffusivity Assessment (NODDIDA) model and demonstrate that its extension from
Single Diffusion Encoding (SDE) to Double Diffusion Encoding (DDE) solves the
ill-posedness and increases the accuracy of the parameter estimation. Methods:
We analyse theoretically the cumulant expansion up to fourth order in b of SDE
and DDE signals. Additionally, we perform in silico experiments to compare SDE
and DDE capabilities under similar noise conditions. Results: We prove
analytically that DDE provides invariant information non-accessible from SDE,
which makes the NODDIDA parameter estimation injective. The in silico
experiments show that DDE reduces the bias and mean square error of the
estimation along the whole feasible region of 5D model parameter space.
Conclusions: DDE adds additional information for estimating the model
parameters, unexplored by SDE, which is enough to solve the degeneracy in the
NODDIDA model parameter estimation.Comment: 22 pages, 7 figure
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Morphology of the Esophageal Hiatus: Is It Different in 3 Types of Hiatus Hernias?
Background/aimsThe esophageal hiatus is formed by the right crus of the diaphragm in the majority of subjects. Contraction of the hiatus exerts a sphincter-like action on the lower esophageal sphincter (LES). The aim is to study the hiatal anatomy (using CT scan imaging) and function (using high-resolution manometry [HRM]), and esophageal motor function in patients with sliding and paraesophageal hiatal hernia.MethodsWe assessed normal subjects (n = 20), patients with sliding type 1 hernia (n = 18), paraesophageal type 2 hernia (n = 19), and mixed type 3 hernia (n = 19). Hernia diagnosis was confirmed on the upper gastrointestinal series. The hiatal morphology was constructed from the CT scan images. The LES pressure and relaxation, percent peristalsis, bolus pressure, and hiatal squeeze pressure were assessed by HRM.ResultsThe CT images revealed that the esophageal hiatus is formed by the right crus of the diaphragm in all normal subjects and 86% of hernia patients. The hiatus is elliptical in shape with a surface area of 1037 mm2 in normal subjects. The hiatal dimensions were larger in patients compared to normal subjects. The HRM revealed impaired LES relaxation and higher bolus pressure in patients with paraesophageal compared to the sliding hernia. The hiatal pinch on HRM was recognized in significantly higher number of patients with sliding as compared to paraesophageal hernia.ConclusionsUsing a novel approach, we provide details of the esophageal hiatus in patients with various kinds of hiatal hernia. Impaired LES relaxation in paraesophageal hernia may play a role in its pathophysiology and genesis of symptoms
An Analytic Equation of State for Ising-like Models
Using an Environmentally Friendly Renormalization we derive, from an
underlying field theory representation, a formal expression for the equation of
state, , that exhibits all desired asymptotic and analyticity
properties in the three limits , and . The only
necessary inputs are the Wilson functions , and
, associated with a renormalization of the transverse vertex
functions. These Wilson functions exhibit a crossover between the Wilson-Fisher
fixed point and the fixed point that controls the coexistence curve.
Restricting to the case N=1, we derive a one-loop equation of state for naturally parameterized by a ratio of non-linear scaling fields. For
we show that a non-parameterized analytic form can be deduced. Various
asymptotic amplitudes are calculated directly from the equation of state in all
three asymptotic limits of interest and comparison made with known results. By
positing a scaling form for the equation of state inspired by the one-loop
result, but adjusted to fit the known values of the critical exponents, we
obtain better agreement with known asymptotic amplitudes.Comment: 10 pages, 2 figure
Transcriptome analysis of bacteriophage communities in periodontal health and disease.
BackgroundThe role of viruses as members of the human microbiome has gained broader attention with the discovery that human body surfaces are inhabited by sizeable viral communities. The majority of the viruses identified in these communities have been bacteriophages that predate upon cellular microbiota rather than the human host. Phages have the capacity to lyse their hosts or provide them with selective advantages through lysogenic conversion, which could help determine the structure of co-existing bacterial communities. Because conditions such as periodontitis are associated with altered bacterial biota, phage mediated perturbations of bacterial communities have been hypothesized to play a role in promoting periodontal disease. Oral phage communities also differ significantly between periodontal health and disease, but the gene expression of oral phage communities has not been previously examined.ResultsHere, we provide the first report of gene expression profiles from the oral bacteriophage community using RNA sequencing, and find that oral phages are more highly expressed in subjects with relative periodontal health. While lysins were highly expressed, the high proportion of integrases expressed suggests that prophages may account for a considerable proportion of oral phage gene expression. Many of the transcriptome reads matched phages found in the oral cavities of the subjects studied, indicating that phages may account for a substantial proportion of oral gene expression. Reads homologous to siphoviruses that infect Firmicutes were amongst the most prevalent transcriptome reads identified in both periodontal health and disease. Some genes from the phage lytic module were significantly more highly expressed in subjects with periodontal disease, suggesting that periodontitis may favor the expression of some lytic phages.ConclusionsAs we explore the contributions of viruses to the human microbiome, the data presented here suggest varying expression of bacteriophage communities in oral health and disease
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