13,699 research outputs found
Bose Einstein Condensation of incommensurate solid 4He
It is pointed out that simulation computation of energy performed so far
cannot be used to decide if the ground state of solid 4He has the number of
lattice sites equal to the number of atoms (commensurate state) or if it is
different (incommensurate state). The best variational wave function, a shadow
wave function, gives an incommensurate state but the equilibrium concentration
of vacancies remains to be determined. In order to investigate the presence of
a supersolid phase we have computed the one--body density matrix in solid 4He
for the incommensurate state by means of the exact Shadow Path Integral Ground
State projector method. We find a vacancy induced Bose Einstein condensation of
about 0.23 atoms per vacancy at a pressure of 54 bar. This means that bulk
solid 4He is supersolid at low enough temperature if the exact ground state is
incommensurate.Comment: 5 pages, 2 figure
A first principles simulation of rigid water
We present the results of Car-Parrinello (CP) simulations of water at ambient
conditions and under pressure, using a rigid molecule approximation. Throughout
our calculations, water molecules were maintained at a fixed intramolecular
geometry corresponding to the average structure obtained in fully unconstrained
simulations. This allows us to use larger time steps than those adopted in
ordinary CP simulations of water, and thus to access longer time scales. In the
absence of chemical reactions or dissociation effects, these calculations open
the way to ab initio simulations of aqueous solutions that require timescales
substantially longer than presently feasible (e.g. simulations of hydrophobic
solvation). Our results show that structural properties and diffusion
coefficients obtained with a rigid model are in better agreement with
experiment than those determined with fully flexible simulations. Possible
reasons responsible for this improved agreement are discussed
Gravitational collapse of magnetized clouds II. The role of Ohmic dissipation
We formulate the problem of magnetic field dissipation during the accretion
phase of low-mass star formation, and we carry out the first step of an
iterative solution procedure by assuming that the gas is in free-fall along
radial field lines. This so-called ``kinematic approximation'' ignores the back
reaction of the Lorentz force on the accretion flow. In quasi steady-state, and
assuming the resistivity coefficient to be spatially uniform, the problem is
analytically soluble in terms of Legendre's polynomials and confluent
hypergeometric functions. The dissipation of the magnetic field occurs inside a
region of radius inversely proportional to the mass of the central star (the
``Ohm radius''), where the magnetic field becomes asymptotically straight and
uniform. In our solution, the magnetic flux problem of star formation is
avoided because the magnetic flux dragged in the accreting protostar is always
zero. Our results imply that the effective resistivity of the infalling gas
must be higher by several orders of magnitude than the microscopic electric
resistivity, to avoid conflict with measurements of paleomagnetism in
meteorites and with the observed luminosity of regions of low-mass star
formation.Comment: 20 pages, 4 figures, The Astrophysical Journal, in pres
Four-wave mixing in a silicon microring resonator using a self-pumping geometry
We report on four-wave mixing in a silicon microring resonator using a
self-pumping scheme instead of an external laser. The ring resonator is
inserted in an external-loop cavity with a fibered semiconductor amplifier as a
source of gain. The silicon microring acts as a filter and we observe lasing in
one of the microring's resonances. We study correlations between signal and
idler generated beams using a Joint Spectral Density experiment
From Cavendish to PLANCK: Constraining Newton's Gravitational Constant with CMB Temperature and Polarization Anisotropy
We present new constraints on cosmic variations of Newton's gravitational
constant by making use of the latest CMB data from WMAP, BOOMERANG, CBI and
ACBAR experiments and independent constraints coming from Big Bang
Nucleosynthesis. We found that current CMB data provide constraints at the 10%
level, that can be improved to 3% by including BBN data. We show that future
data expected from the Planck satellite could constrain G at the 1.5% level
while an ultimate, cosmic variance limited, CMB experiment could reach a
precision of about 0.4%, competitive with current laboratory measurements.Comment: 6 pages, 8 figures, corrected typos, added reference
IDENTIFICATION OF THREE NOVEL REGULATORY PATHWAYS INVOLVED IN THE DOWN-REGULATION OF P63 PROTEIN LEVELS
One way to regulate protein functions is by post-translational modification. Post-translational modifications have an important role in the regulation of biological activity of the protein because they allow both to extend the range of functions of a protein and to monitor the activity and determine the activation or inactivation of a protein. The most common protein post-translational modifications include ubiquitylation, phosphorylation and acetylation play an essential role in cellular functions such as cellular differentiation, apoptosis, DNA repair, antigen processing, and stress response. Under particular conditions abnormal post-translational modifications were found in many diseases like: Alzheimer\u2019s disease, Parkinson\u2019s disease, induction of different cancer and others. These abnormal post-translational modifications are permanent and can cause loss or alteration of protein function by changing enzyme activities or capacity aggregation (Stadtman and Levine 2000; Shacter 2000).
p63 protein stability is regulated by different protein modifications such phosphorylation, ubiquitylation and sumoylation. p63 is known to be degraded by ubiquitin-mediated proteasomal degradation, the E3 ubiquitin ligase NEDD4-like, ubiquitin protein ligase Itch and ubiquitin-like protein SUMO-1 have been shown to directly interact with p63 and regulate p63 protein stability (Ghioni et al. 2005; Rossi at al. 2006; Rossi et al. 2006) suggest the importance of regulating p63 to tune its biological activity.
During my PhD thesis we found three novel and distinct mechanisms that are involved in the regulation of the p63 protein levels; all these mechanisms induce p63 degradation. We demonstrated that these mechanisms are relevant in different physiological contexts and that they are involved in the regulation of p63 biological function.
1. MDM2-Fbw7 pathway contribute to reduce \u394Np63\u3b1 protein levels during keratinocytes differentiation and upon DNA-damage induced by UV exposure and adriamycin treatment.
2. TRIM8 plays a role in enhancing p53 anti-oncogenic activity and at the same time down-modulate oncogenic \u394Np63\u3b1 activity.
3. Hipk2 phosphorylates and promotes proteasomal degradation of \u394Np63\u3b1 to enable an effective DNA-damage response induced by genotoxic drugs.
All these evidences indicate that regulation of p63 protein stability is a key mechanism to control p63 activities, in particular during epithelia differentiation and in response to genotoxic agents.
The knowledge and the identification of the molecular mechanisms governing p63 regulation under physiological context might be fundamental for understanding the pathogenesis of human syndromes associated to p63 mutations and the mechanism by which p63 promotes disease development.
We hope that future studies focusing on the mechanisms involved in p63 protein regulation might increase our knowledge on the p63 role in tumorigenicity and in response to anti-cancer therapy to improve anti-cancer therapies
The sutures in dentistry
In oral surgery, the last phase of a surgical operation is represented by the tissues suture, that allows the wound lips edges approximation and their stabilization, to promote haemostasis, to avoid the alimentary residues accumulation on the incision line and allow the first intention healing. A good suture avoids that the displacing forces generated by the muscular insertions, functional movements and by the external agents destabilize or cause the surgical wound deiscence. The purpose of this study was to re-examine the suture threads characteristics, properties and biological interactions evaluating the different studies published in literature results and conclusions. In conclusion, the authors recommended the use of the different suture threads on the dependence of the oral surgery operation type that must be performed, of the patient compliance and of the various suture materials physical and biocompatibility characteristics
Headache disorders as risk factors for sleep disturbances in school aged children.
Several epidemiological studies have shown the presence of comorbidity between various types of sleep disorders and different headache subtypes. Migraine without aura is a sensitive risk factor for disorders of initiating and maintaining sleep (odds ratio (OR) 8.2500), and chronic tension-type headache for sleep breathing disorders (OR 15.231), but headache disorder is a cumulative risk factor for disorders of excessive somnolence (OR 15.061). This result has not been reported in the clinical literature. © Springer-Verlag Italia 2005
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