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

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

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

Spin dynamics in hole-doped two-dimensional S=1/2 Heisenberg antiferromagnets: ^{63}Cu NQR relaxation in La_{2-x}Sr_xCuO_4 for x≤0.04x\leq 0.04

The effects on the correlated Cu^{2+} S = 1/2 spin dynamics in the paramagnetic phase of La_{2-x}Sr_xCuO_4 (for $x \lesssim 0.04$) due to the injection of holes are studied by means of ^{63}Cu NQR spin-lattice relaxation time T_1 measurements. The results are discussed in the framework of the connection between T_1 and the in-plane magnetic correlation length $\xi_{2D}(x,T)$. It is found that at high temperatures the system remains in the renormalized classical regime, with a spin stiffness constant $\rho_s(x)$ reduced by small doping to an extent larger than the one due to Zn doping. For $x\gtrsim 0.02$ the effect of doping on $\rho_s(x)$ appears to level off. The values for $\rho_s(x)$ derived from T_1 for $T\gtrsim 500$ K are much larger than the ones estimated from the temperature behavior of sublattice magnetization in the ordered phase ($T\leq T_N$). It is argued that these features are consistent with the hypothesis of formation of stripes of microsegregated holes.Comment: 10 pages, 3 figure