1,339 research outputs found
The relativistic self-energy in nuclear dynamics
It is a well known fact that Dirac phenomenology of nuclear forces predicts
the existence of large scalar and vector mean fields in matter. To analyse the
relativistic self-energy in a model independent way, modern high precision
nucleon-nucleon () potentials are mapped on a relativistic operator basis
using projection techniques. This allows to compare the various potentials at
the level of covariant amplitudes were a remarkable agreement is found. It
allows further to calculate the relativistic self-energy in nuclear matter in
Hartree-Fock approximation. Independent of the choice of the nucleon-nucleon
interaction large scalar and vector mean fields of several hundred MeV
magnitude are generated at tree level. In the framework of chiral EFT these
fields are dominantly generated by contact terms which occur at next-to-leading
order in the chiral expansion. Consistent with Dirac phenomenology the
corresponding low energy constants which generate the large fields are closely
connected to the spin-orbit interaction in scattering. The connection to
QCD sum rules is discussed as well.Comment: 49 pages, 13 figure
Ion-Size Effect at the Surface of a Silica Hydrosol
The author used synchrotron x-ray reflectivity to study the ion-size effect
for alkali ions (Na, K, Rb, and Cs), with densities as high as
m, suspended above the surface of a
colloidal solution of silica nanoparticles in the field generated by the
surface electric-double layer. According to the data, large alkali ions
preferentially accumulate at the sol's surface replacing smaller ions, a
finding that qualitatively agrees with the dependence of the Kharkats-Ulstrup
single-ion electrostatic free energy on the ion's radius.Comment: 17 pages, 4 figure
Chiral symmetry and the axial nucleon to Delta(1232) transition form factors
We study the momentum and the quark mass dependence of the axial nucleon to
Delta(1232) transition form factors in the framework of non-relativistic chiral
effective field theory to leading-one-loop order. The outcome of our analysis
provides a theoretical guidance for chiral extrapolations of lattice QCD
results with dynamical fermions.Comment: 18 pages, 3 figure
Factorization and the Soft Overlap Contribution to Heavy-to-Light Form Factors
Using the formalism of soft-collinear effective theory, a complete separation
of short- and long-distance contributions to heavy-to-light transition form
factors at large recoil is performed. The universal functions
parameterizing the ``soft overlap'' contribution to the form factors are
defined in terms of matrix elements in the effective theory. Endpoint
configurations corresponding to kinematic situations where one of the valence
partons in the external mesons carries very small momentum are accounted for in
terms of operators involving soft-collinear messenger fields. They contribute
at leading order in and spoil factorization. An analysis
of operator mixing and renormalization-group evolution in the effective theory
reveals that the intermediate scale is without significance
to the soft functions , and that the soft overlap contribution does
not receive a significant perturbative (Sudakov) suppression.Comment: 30 pages, 6 figures. Erratum adde
Factorization Properties of Soft Graviton Amplitudes
We apply recently developed path integral resummation methods to perturbative
quantum gravity. In particular, we provide supporting evidence that eikonal
graviton amplitudes factorize into hard and soft parts, and confirm a recent
hypothesis that soft gravitons are modelled by vacuum expectation values of
products of certain Wilson line operators, which differ for massless and
massive particles. We also investigate terms which break this factorization,
and find that they are subleading with respect to the eikonal amplitude. The
results may help in understanding the connections between gravity and gauge
theories in more detail, as well as in studying gravitational radiation beyond
the eikonal approximation.Comment: 35 pages, 5 figure
Sample preservation and storage significantly impact taxonomic and functional profiles in metaproteomics studies of the human gut microbiome
With the technological advances of the last decade, it is now feasible to analyze microbiome samples, such as human stool specimens, using multi-omic techniques. Given the inherent sample complexity, there exists a need for sample methods which preserve as much information as possible about the biological system at the time of sampling. Here, we analyzed human stool samples preserved and stored using different methods, applying metagenomics as well as metaproteomics. Our results demonstrate that sample preservation and storage have a significant effect on the taxonomic composition of identified proteins. The overall identification rates, as well as the proportion of proteins from were much higher when samples were flash frozen. Preservation in RNAlater overall led to fewer protein identifications and a considerable increase in the share of , as well as . Additionally, a decrease in the share of metabolism-related proteins and an increase of the relative amount of proteins involved in the processing of genetic information was observed for RNAlater-stored samples. This suggests that great care should be taken in choosing methods for the preservation and storage of microbiome samples, as well as in comparing the results of analyses using different sampling and storage methods. Flash freezing and subsequent storage at -80 °C should be chosen wherever possible
Hot moments in the Antarctic due to climate warming?
Climate warming is severely affecting maritime Antarctica, causing accelerated glacier retreat and thus leading to an ongoing exposure of once ice- covered land. This initiates a succession of plant and soil development. Nevertheless, the temporal dynamics and controlling factors of these processes, like C and N status of soils and the effect of root exudation are widely unknown under these harsh climatic conditions.
Topsoil samples from three different sites of a chronological soil sequence in the forefront of a retreating glacier of the Fildes Peninsula, King George Island, were collected and incubated at 2 °C for three weeks. To mimic the influence of C and N containing root exudates (primers) on the mineralization of soil C, we added 13C labeled glucose or alanine and compared CO2 evolution in comparison to samples without C and N addition.
Soil microbes covered up to 90% of their C demand for anabolic functions with the added C-sources in the case of late soil successions while it was only 50% for the young soils. These findings were independent of the form of primer. Both primers increased the mineralization of soil carbon in the young soils as compared to the control. For the later stages of soil development, we found negative priming which was strongest for the latest stage.
These results give evidence for a clear shift in the microbial community of the three investigated sites. While sites with initial soil formation seem to be dominated by k-strategists with low turnover rates that rather use complex C-sources, a significant number of r-strategists in the soils of the older sites uses simple C-substrates very efficiently. As this leads to a relative decrease in SOM mineralization for the late stages of soil development, it is questionable if higher plants can improve their nutrition by stimulating free living soil microbes with root exudates or if they rather have to rely on mycorrhiza
Decrease in the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes in animals with osteoarthritis
<p>Abstract</p> <p>Background</p> <p>To evaluate the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes from hyaline cartilage over the course of osteoarthritis (OA).</p> <p>Methods</p> <p>In 12 NZW rabbits, the anterior cruciate ligament (ACL) was resected to create anterior instability of the knee. In 12 control rabbits, only a sham operation, without resection of the ACL, was performed. Four animals from each group were killed at 3, 6, and 12 weeks. After opening the knee joint, OA was macroscopically graded and hyaline cartilage of the load-bearing area was evaluated histologically according to the Mankin scale and by immunostaining for PTH1R.</p> <p>Results</p> <p>There was a positive linear correlation between the time after surgery and the macroscopic and histologic OA scores. The scores in the control group were constant over the time course. Immunostaining showed significantly less expression of PTH1R in the experimental compared to the control group after 6 (P < 0.05) and 12 weeks (P < 0.01). In the experimental group, a negative linear correlation between PTH1R expression and macroscopic and histologic grades was found.</p> <p>Conclusions</p> <p>The results show an in vivo decrease in the expression of PTH1R on chondrocytes over the time course of OA. Further studies are needed to evaluate whether new treatment approaches could evolve from this knowledge.</p
A Matrix Model for \nu_{k_1k_2}=\frac{k_1+k_2}{k_1 k_2} Fractional Quantum Hall States
We propose a matrix model to describe a class of fractional quantum Hall
(FQH) states for a system of (N_1+N_2) electrons with filling factor more
general than in the Laughlin case. Our model, which is developed for FQH states
with filling factor of the form \nu_{k_1k_2}=\frac{k_1+k_2}{k_1k_2} (k_1 and
k_2 odd integers), has a U(N_1)\times U(N_2) gauge invariance, assumes that FQH
fluids are composed of coupled branches of the Laughlin type, and uses ideas
borrowed from hierarchy scenarios. Interactions are carried, amongst others, by
fields in the bi-fundamentals of the gauge group. They simultaneously play the
role of a regulator, exactly as does the Polychronakos field. We build the
vacuum configurations for FQH states with filling factors given by the series
\nu_{p_1p_2}=\frac{p_2}{p_1p_2-1}, p_1 and p_2 integers. Electrons are
interpreted as a condensate of fractional D0-branes and the usual degeneracy of
the fundamental state is shown to be lifted by the non-commutative geometry
behaviour of the plane. The formalism is illustrated for the state at
\nu={2/5}.Comment: 40 pages, 1 figure, clarifications and references adde
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