524 research outputs found
Abelian dominance and the dual Meissner effect in local unitary gauges in SU(2) gluodynamics
Performing highly precise Monte-Carlo simulations of SU(2) gluodynamics, we
observe for the first time Abelian dominance in the confining part of the
static potential in local unitary gauges such as the F12 gauge. We also study
the flux-tube profile between the quark and antiquark in these local unitary
gauges and find a clear signal of the dual Meissner effect. The Abelian
electric field is found to be squeezed into a flux tube by the monopole
supercurrent. This feature is the same as that observed in the non-local
maximally Abelian gauge. These results suggest that the Abelian confinement
scenario is gauge independent. Observing the important role of space-like
monopoles in the Polyakov gauge also indicates that the monopoles defined on
the lattice do not necessarily correspond to those proposed by 't Hooft in the
context of Abelian projection.Comment: 4 pages, 7 figure
Vacuum type of SU(2) gluodynamics in maximally Abelian and Landau gauges
The vacuum type of SU(2) gluodynamics is studied using Monte-Carlo
simulations in maximally Abelian (MA) gauge and in Landau (LA) gauge, where the
dual Meissner effect is observed to work. The dual Meissner effect is
characterized by the coherence and the penetration lengths. Correlations
between Wilson loops and electric fields are evaluated in order to measure the
penetration length in both gauges. The coherence length is shown to be fixed in
the MA gauge from measurements of the monopole density around the static
quark-antiquark pair. It is also shown numerically that a dimension 2 gluon
operator A^+A^-(s) and the monopole density has a strong correlation as
suggested theoretically. Such a correlation is observed also between the
monopole density and A^2(s)= A^+A^-(s) + A^3A^3(s) condensate if the remaining
U(1) gauge degree of freedom is fixed to U(1) Landau gauge (U1LA). The
coherence length is determined numerically also from correlations between
Wilson loops and A^+A^-(s) and A^2(s) in MA + U1LA gauge. Assuming that the
same physics works in the LA gauge, we determine the coherence length from
correlations between Wilson loops and A^2(s). Penetration lengths and coherence
lengths in the two gauges are almost the same. The vacuum type of the
confinement phase in both gauges is near to the border between the type 1 and
the type 2 dual superconductors.Comment: 13 pages, 22 figures, RevTeX 4 styl
Venus Express radio occultation observed by PRIDE
Context. Radio occultation is a technique used to study planetary atmospheres
by means of the refraction and absorption of a spacecraft carrier signal
through the atmosphere of the celestial body of interest, as detected from a
ground station on Earth. This technique is usually employed by the deep space
tracking and communication facilities (e.g., NASA's Deep Space Network (DSN),
ESA's Estrack). Aims. We want to characterize the capabilities of the Planetary
Radio Interferometry and Doppler Experiment (PRIDE) technique for radio
occultation experiments, using radio telescopes equipped with Very Long
Baseline Interferometry (VLBI) instrumentation. Methods. We conducted a test
with ESA's Venus Express (VEX), to evaluate the performance of the PRIDE
technique for this particular application. We explain in detail the data
processing pipeline of radio occultation experiments with PRIDE, based on the
collection of so-called open-loop Doppler data with VLBI stations, and perform
an error propagation analysis of the technique. Results. With the VEX test case
and the corresponding error analysis, we have demonstrated that the PRIDE setup
and processing pipeline is suited for radio occultation experiments of
planetary bodies. The noise budget of the open-loop Doppler data collected with
PRIDE indicated that the uncertainties in the derived density and temperature
profiles remain within the range of uncertainties reported in previous Venus'
studies. Open-loop Doppler data can probe deeper layers of thick atmospheres,
such as that of Venus, when compared to closed-loop Doppler data. Furthermore,
PRIDE through the VLBI networks around the world, provides a wide coverage and
range of large antenna dishes, that can be used for this type of experiments
Dual superconductivity and vacuum properties in Yang--Mills theories
We address, within the dual superconductivity model for color confinement,
the question whether the Yang-Mills vacuum behaves as a superconductor of type
I or type II. In order to do that we compare, for the theory with gauge group
SU(2), the determination of the field penetration depth with that of
the superconductor correlation length . The latter is obtained by
measuring the temporal correlator of a disorder parameter developed by the Pisa
group to detect dual superconductivity. The comparison places the vacuum close
to the border between type I and type II and marginally on the type II side. We
also check our results against the study of directly measurable effects such as
the interaction between two parallel flux tubes, obtaining consistent
indications for a weak repulsive behaviour. Future strategies to improve our
investigation are discussed.Comment: 23 pages, 15 figures. Simulations on finer lattices and with
different monopole charges added. Final version to be published in Nuclear
Physics
Multifrequency Study of Giant Radio Pulses from the Crab Pulsar with the K5 VLBI Recording Terminal
Simultaneous multifrequency observations of the Crab pulsar giant pulses
(GPs) were performed with the 64-m Kalyazin radio telescope at four frequencies
0.6, 1.4, 2.2 and 8.3 GHz using the K5 VLBI recording terminal. The K5 terminal
provided continuous recording in 16 4-MHz wide frequency channels distributed
over 4 frequency bands. Several thousands of GPs were detected during about 6
hours of observations in two successive days in July 2005. Radio spectra of
single GPs were analysed at separate frequencies and over whole frequency
range. These spectra manifest notable modulation over frequency ranges,
, both on large () and small
() frequency scales. Cross-correlation analysis of
GPs at 2.2 GHz showed that their pulse shapes can be interpreted as an ensemble
of unresolved bursts grouped together at time scales of mcs being
well-correlated over a 60-MHz band. The corresponding GP cross-correlation
functions do not obey the predictions of the amplitude-modulated noise model of
Rickett (1975), thus indicating that unresolved components represent a small
number of elementary emitters.Comment: 22 pages, 11 figures, 3 tables, submitted to PAS
Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022
There is growing evidence of relativistic jets in radio-loud narrow-line
Seyfert 1 (RL-NLS1) galaxies. We constrain the observational properties of the
radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN
J0948+0022, i.e., its flux density and structure in total intensity and in
polarization, its compactness, and variability. We performed three real-time
e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including
telescopes in Europe, East Asia, and Australia. These are the first e-VLBI
science observations ever carried out with a global array, reaching a maximum
baseline length of 12458 km. The observations were part of a large
multiwavelength campaign in 2009. The source is detected at all three epochs.
The structure is dominated by a bright component, more compact than 55
microarcsec, with a fainter component at a position angle theta~ 35deg.
Relativistic beaming is required by the observed brightness temperature of
3.4x10^11 K. Polarization is detected at a level of about 1%. The parameters
derived by the VLBI observations, in addition to the broad-band properties,
confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global
e-VLBI is a reliable and promising technique for future studies.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
PRELP secreted from mural cells protects the function of blood brain barrier through regulation of endothelial cell-cell integrity
INTRODUCTION:
Proline/arginine-rich end leucine-rich repeat protein (PRELP), is a small secreted proteoglycan expressed by pericytes and vascular smooth muscle cells surrounding the brain vasculature of adult mouse.
METHODS:
We utilised a Prelp knockout (Prelp−/−) mouse model to interrogate vasculature integrity in the brain alongside performing in vitro assays to characterise PRELP application to endothelial cells lines. Our findings were supplemented with RNA expression profiling to elucidate the mechanism of how PRELP maintains neurovasculature function.
RESULTS:
Prelp−/− mice presented with neuroinflammation and reducedneurovasculature integrity, resulting in IgG and dextran leakage in the cerebellum and cortex. Histological analysis of Prelp−/− mice revealed reducedcell-cell integrity of the blood brain barrier, capillary attachment of pericytes andastrocyte end-feet. RNA-sequencing analysis found that cell-cell adhesion andinflammation are affected in Prelp−/− mice and gene ontology analysis as well as gene set enrichment analysis demonstrated that inflammation related processes and adhesion related processes such as epithelial-mesenchymal transition and apical junctions were significantly affected, suggesting PRELP is a regulator of cell-cell adhesion. Immunofluorescence analysis showed that adhesion junction protein expression levels of cadherin, claudin-5, and ZO-1, was suppressed in Prelp−/− mice neurovasculature. Additionally, in vitro studies revealed that PRELP application to endothelial cells enhances cell-cell integrity, induces mesenchymal-endothelial transition and inhibits TGF-β mediated damage to cell-cell adhesion.
DISCUSSION:
Our study indicates that PRELP is a novel endogenous secreted regulator of neurovasculature integrity and that PRELP application may be a potential treatment for diseases associated with neurovascular damage
Aldose reductase gene is associated with diabetic macroangiopathy in Japanese Type 2 diabetic patients
AIMS: The aldose reductase (AR) gene, a rate-limiting enzyme of the polyol pathway, has been investigated as a candidate gene in determining susceptibility to diabetic microangiopathy. However, the association of the AR gene with diabetic macroangiopathy has not been investigated. Therefore, the present study was conducted to determine whether genetic variations of AR may determine susceptibility to diabetic macroangiopathy. METHODS: There were 378 Type 2 diabetic patients enrolled in this study. A single nucleotide polymorphism in the promoter region (C-106T) was genotyped and the AR protein content of erythrocytes measured by ELISA. RESULTS: There were no significant differences in genotypic or allelic distribution in patients with or without ischaemic heart diseases, but there was a significant increase in the frequency of the CT + TT genotype and T allele in patients with stroke (P = 0.019 and P = 0.012). The erythrocyte AR protein content was increased in patients with the CT and TT genotype compared with those with the CC genotype. After adjustment for age, duration of diabetes, body mass index, systolic blood pressure, HbA(1c), and serum creatinine, triglycerides, and total cholesterol in multivariate logistic-regression models, the association between this AR genotype and stroke remained significant. CONCLUSIONS: Our results suggest that the CT or TT genotype of the AR gene might be a genetic marker of susceptibility to stroke in Type 2 diabetic patients. This observation might contribute to the development of strategies for the prevention of stroke in Type 2 diabetic patients
The first scientific experiment using Global e-VLBI observations: a multiwavelength campaign on the gamma-ray Narrow-Line Seyfert 1 PMN J0948+0022
The detection of gamma-ray emission by Fermi-LAT from the radio loud Narrow
Line Seyfert 1 PMN J0948+0022 (Abdo et al. 2009, ApJ 699, 976) triggered a
multi-wavelength campaign between March and July 2009. Given its high
compactness (Doi et al. 2006, PASJ 58, 829), inverted spectrum, and 0deg
declination, the source was an ideal target to observe at 22 GHz with a Global
VLBI array extending from Europe to East Asia and Australia. In order to
deliver prompt results to be analysed in combination with the other instruments
participating in the campaign, the observations were carried out with real time
VLBI, for the first time on a Global scale. Indeed, the main results have been
published just a few months after the campaign (Abdo et al. 2009, ApJ 707,
727). Here we present additional details about the e-VLBI observations.Comment: PoS(10th EVN Symposium)080: Proceedings of the 10th European VLBI
Network Symposium and EVN Users Meeting: VLBI and the new generation of radio
arrays, September 20-24, 2010, Manchester U
Germ cell sex determination in mammals
One of the major decisions that germ cells make during their development is whether to differentiate into oocytes or sperm. In mice, the germ cells’ decision to develop as male or female depends on sex-determining signalling molecules in the embryonic gonadal environment rather than the sex chromosome constitution of the germ cells themselves. In response to these sex-determining cues, germ cells in female embryos initiate oogenesis and enter meiosis, whereas germ cells in male embryos initiate spermatogenesis and inhibit meiosis until after birth. However, it is not clear whether the signalling molecules that mediate germ cell sex determination act in the developing testis or the developing ovary, or what these signalling molecules might be. Here, we review the evidence for the existence of meiosis-inducing and meiosis-preventing substances in the developing gonad, and more recent studies aimed at identifying these molecules in mice. In addition, we discuss the possibility that some of the reported effects of these factors on germ cell development may be indirect consequences of impairing sexual differentiation of gonadal somatic cells or germ cell survival. Understanding the molecular mechanisms of germ cell sex determination may provide candidate genes for susceptibility to germ cell tumours and infertility in humans
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