427 research outputs found
Cosmological test of the Yilmaz theory of gravity
We test the Yilmaz theory of gravitation by working out the corresponding
Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker
cosmological metrics. In the case that space is flat the theory is consistent
only with either a completely empty universe or a negative energy vacuum that
decays to produce a constant density of matter. In both cases the total energy
remains zero at all times, and in the latter case the acceleration of the
expansion is always negative. To obtain a more flexible and potentially more
realistic cosmology, the equation of state relating the pressure and energy
density of the matter creation process must be different from the vacuum, as
for example is the case in the steady-state models of Gold, Bondi, Hoyle and
others. The theory does not support the cosmological principle for curved space
K =/= 0 cosmological metrics
GRB 050713A: High Energy Observations of the GRB Prompt and Afterglow Emission
Swift discovered GRB 050713A and slewed promptly to begin observing with its
narrow field instruments 72.6 seconds after the burst onset, while the prompt
gamma-ray emission was still detectable in the BAT. Simultaneous emission from
two flares is detected in the BAT and XRT. This burst marks just the second
time that the BAT and XRT have simultaneously detected emission from a burst
and the first time that both instruments have produced a well sampled,
simultaneous dataset covering multiple X-ray flares. The temporal rise and
decay parameters of the flares are consistent with the internal shock
mechanism. In addition to the Swift coverage of GRB 050713A, we report on the
Konus-Wind (K-W) detection of the prompt emission in the energy range 18-1150
keV, an upper limiting GeV measurement of the prompt emission made by the MAGIC
imaging atmospheric Cherenkov telescope and XMM-Newton observations of the
afterglow. Simultaneous observation between Swift XRT and XMM-Newton produce
consistent results, showing a break in the lightcurve at T+~15ks. Together,
these four observatories provide unusually broad spectral coverage of the
prompt emission and detailed X-ray follow-up of the afterglow for two weeks
after the burst trigger. Simultaneous spectral fits of K-W with BAT and BAT
with XRT data indicate that an absorbed broken powerlaw is often a better fit
to GRB flares than a simple absorbed powerlaw. These spectral results together
with the rapid temporal rise and decay of the flares suggest that flares are
produced in internal shocks due to late time central engine activity.Comment: 22 pages, 6 tables, 10 figures; Submitted to the Astrophysical
Journa
Structural comparison of the free and DNA-bound forms of the purine repressor DNA-binding domain
AbstractBackground: The purine repressor (PurR) regulates genes that encode enzymes for purine biosynthesis. PurR has a two domain structure with an N-terminal DNA-binding domain (DBD) and a C-terminal corepressor-binding domain (CBD). The three-dimensional structure of a ternary complex of PurR bound to both corepressor and a specific DNA sequence has recently been determined by X-ray crystallography.Results We have determined the solution structure of the PurR DBD by NMR. It contains three helices, with the first and second helices forming a helix-turn-helix motif. The tertiary structure of the three helices is very similar to that of the corresponding region in the ternary complex. The structure of the hinge helical region, however, which makes specific base contacts in the minor groove of DNA, is disordered in the DNA-free form.Conclusion The stable formation of PurR hinge helices requires PurR dimerization, which brings the hinge regions proximal to each other. The dimerization of the hinge helices is likely to be controled by the CBD dimerization interface, but is induced by specific-DNA binding
Review of recent experimental progresses in Foundations of Quantum Mechanics and Quantum Information obtained in Parametric Down Conversion Experiments at IENGF
We review some recent experimental progresses concerning Foundations of
Quantum Mechanics and Quantum Information obtained in Quantum Optics Laboratory
"Carlo Novero" at IENGF.
More in details, after a short presentation of our polarization entangled
photons source (based on precise superposition of two Type I PDC emission) and
of the results obtained with it, we describe an innovative double slit
experiment where two degenerate photons produced by PDC are sent each to a
specific slit. Beyond representing an interesting example of relation between
visibility of interference and "welcher weg" knowledge, this configuration has
been suggested for testing de Broglie-Bohm theory against Standard Quantum
Mechanics. Our results perfectly fit SQM results, but disagree with dBB
predictions.
Then, we discuss a recent experiment addressed to clarify the issue of which
wave-particle observables are really to be considered when discussing wave
particle duality. This experiments realises the Agarwal et al. theoretical
proposal, overcoming limitations of a former experiment.
Finally, we hint to the realization of a high-intensity
high-spectral-selected PDC source to be used for quantum information studies
HELICAL MICRO-HOLE DRILLING OF CHEMICALLY STRENGTHENED GLASS USING CAPSULE-SHAPED ELECTROPLATED DIAMOND TOOL
This study investigates the micro-hole drilling performance of chemically strengthened glass plate by using a capsule-shaped electroplated diamond tool and the helical drilling method. Three different helical pitch conditions were tested to drill holes with a diameter of 1 mm. The number of drilled holes, grinding force, and maximum crack size were measured along with the observation of the drilled holes to evaluate the performance of the micro-hole drilling. From the experimental results, it was found that as the size of helical pitch decreased, the number of drilled holes increases where the average grinding force generated becomes smaller. By using small helical pitch condition, 43 holes could be drilled but the maximum crack size generated at the outlet side of the drilled hole is not able to achieve the high-grade quality compared to the inlet side. The resultant grinding force generated when the tool tip nearing the outlet side of the glass plate has caused the large crack at a certain position on the outlet side
STIM1 R304W in mice causes subgingival hair growth and an increased fraction of trabecular bone
Calcium signaling plays a central role in bone development and homeostasis. Store operated calcium entry (SOCE) is an important calcium influx pathway mediated by calcium release activated calcium (CRAC) channels in the plasma membrane. Stromal interaction molecule 1 (STIM1) is an endoplasmic reticulum calcium sensing protein important for SOCE. We generated a mouse model expressing the STIM1 R304W mutation, causing Stormorken syndrome in humans. Stim1R304W/R304W mice showed perinatal lethality, and the only three animals that survived into adulthood presented with reduced growth, low body weight, and thoracic kyphosis. Radiographs revealed a reduced number of ribs in the Stim1R304W/R304W mice. Microcomputed tomography data revealed decreased cortical bone thickness and increased trabecular bone volume fraction in Stim1R304W/R304W mice, which had thinner and more compact bone compared to wild type mice. The Stim1R304W/+ mice showed an intermediate phenotype. Histological analyses showed that the Stim1R304W/R304W mice had abnormal bone architecture, with markedly increased number of trabeculae and reduced bone marrow cavity. Homozygous mice showed STIM1 positive osteocytes and osteoblasts. These findings highlight the critical role of the gain-of-function (GoF) STIM1 R304W protein in skeletal development and homeostasis in mice. Furthermore, the novel feature of bilateral subgingival hair growth on the lower incisors in the Stim1R304W/R304W mice and 25 % of the heterozygous mice indicate that the GoF STIM1 R304W protein also induces an abnormal epithelial cell fate
Virulence Potential of Staphylococcus aureus Strains Isolated From Diabetic Foot Ulcers: A new paradigm
OBJECTIVE—The purpose of this study was to assess the virulence potential of Staphylococcus aureus strains isolated from diabetic foot ulcers and to discriminate noninfected from infected ulcers
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