C/O white dwarfs of very low mass: 0.33-0.5 Mo

The standard lower limit for the mass of white dwarfs (WDs) with a C/O core is roughly 0.5 Mo. In the present work we investigated the possibility to form C/O WDs with mass as low as 0.33 Mo. Both the pre-WD and the cooling evolution of such nonstandard models will be described.Comment: Submitted to the "Proceedings of the 16th European White Dwarf Workshop" (to be published JPCS). 7 pages including 13 figure

Design of Allosteric Stimulators of the Hsp90 ATPase as New Anticancer Leads

Allosteric compounds that stimulate Hsp90 adenosine triphosphatase (ATPase) activity were rationally designed, showing anticancer potencies in the low micromolar to nanomolar range. In parallel, the mode of action of these compounds was clarified and a quantitative model that links the dynamic ligand-protein cross-talk to observed cellular and in vitro activities was developed. The results support the potential of using dynamics-based approaches to develop original mechanism-based cancer therapeutics

Thermodynamical features of multifragmentation in peripheral Au + Au Collisions at 35 A.MeV

The distribution of fragments produced in events involving the multifragmentation of excited sources is studied for peripheral Au + Au reactions at 35 A.MeV. The Quasi-Projectile has been reconstructed from its de-excitation products. An isotropic emission in its rest frame has been observed, indicating that an equilibrated system has been formed. The excitation energy of the Quasi-Projectile has been determined via calorimetry. A new event by event effective thermometer is proposed based on the energy balance. A peak in the energy fluctuations is observed related to the heat capacity, suggesting that the system undergoes a liquid-gas type phase transition at an excitation energy about 5 A.MeV and a temperature 4 - 6 MeV, dependent on the freeze-out hypothesis. By analyzing different regions of the Campi-plot, the events associated with the liquid and gas phases as well as the critical region are thermodynamically characterized. The critical exponents, tau, beta,gamma, extracted from the high moments of the charge distribution are consistent with a liquid-gas type phase transition.Comment: 44 pages, 16 Postscript figures, Fig14_nucl-ex.eps in colors, to be published in Nucl.Phys.A (1999

Physical parameters and the projection factor of the classical Cepheid in the binary system OGLE-LMC-CEP-0227

A novel method of analysis of double-lined eclipsing binaries containing a radially pulsating star is presented. The combined pulsating-eclipsing light curve is built up from a purely eclipsing light curve grid created using an existing modeling tool. For every pulsation phase the instantaneous radius and surface brightness are taken into account, being calculated from the disentangled radial velocity curve of the pulsating star and from its out-of-eclipse pulsational light curve and the light ratio of the components, respectively. The best model is found using the Markov Chain Monte Carlo method. The method is applied to the eclipsing binary Cepheid OGLE-LMC-CEP-0227 (P_puls = 3.80 d, P_orb = 309 d). We analyze a set of new spectroscopic and photometric observations for this binary, simultaneously fitting OGLE V-band, I-band and Spitzer 3.6 {\mu}m photometry. We derive a set of fundamental parameters of the system significantly improving the precision comparing to the previous results obtained by our group. The Cepheid mass and radius are M_1 = 4.165 +/- 0.032 M_solar and R_1 = 34.92 +/- 0.34 R_solar, respectively. For the first time a direct, geometrical and distance-independent determination of the Cepheid projection factor is presented. The value p = 1.21 +/- 0.03(stat.) +/- 0.04(syst.) is consistent with theoretical expectations for a short period Cepheid and interferometric measurements for {\delta} Cep. We also find a very high value of the optical limb darkening coefficients for the Cepheid component, in strong disagreement with theoretical predictions for static atmospheres at a given surface temperature and gravity.Comment: 16 pages, 17 figures, accepted for publication in MNRA

Towards an in vitro model mimicking the foreign body response: tailoring the surface properties of biomaterials to modulate extracellular matrix

Despite various studies to minimize host reaction following a biomaterial implantation, an appealing strategy in regenerative medicine is to actively use such an immune response to trigger and control tissue regeneration. We have developed an in vitro model to modulate the host response by tuning biomaterials' surface properties through surface modifications techniques as a new strategy for tissue regeneration applications. Results showed tunable surface topography, roughness, wettability, and chemistry by varying treatment type and exposure, allowing for the first time to correlate the effect of these surface properties on cell attachment, morphology, strength and proliferation, as well as proinflammatory (IL-1β, IL-6) and antiflammatory cytokines (TGF-β1, IL-10) secreted in medium, and protein expression of collagen and elastin. Surface microstructuring, derived from chloroform partial etching, increased surface roughness and oxygen content. This resulted in enhanced cell adhesion, strength and proliferation as well as a balance of soluble factors for optimum collagen and elastin synthesis for tissue regeneration. By linking surface parameters to cell activity, we could determine the fate of the regenerated tissue to create successful soft tissue-engineered replacement

Nonlocal density functionals and the linear response of the homogeneous electron gas

The known and usable truly nonlocal functionals for exchange-correlation energy of the inhomogeneous electron gas are the ADA (average density approximation) and the WDA (weighted density approximation). ADA, by design, yields the correct linear response function of the uniform electron gas. WDA is constructed so that it is exact in the limit of one-electron systems. We derive an expression for the linear response of the uniform gas in the WDA, and calculate it for several flavors of WDA. We then compare the results with the Monte-Carlo data on the exchange-correlation local field correction, and identify the weak points of conventional WDA in the homogeneous limit. We suggest how the WDA can be modified to improve the response function. The resulting approximation is a good one in both opposite limits, and should be useful for practical nonlocal density functional calculations.Comment: 4 pages, two eps figures embedde

Negative heat capacity in the critical region of nuclear fragmentation: an experimental evidence of the liquid-gas phase transition

An experimental indication of negative heat capacity in excited nuclear systems is inferred from the event by event study of energy fluctuations in $Au$ quasi-projectile sources formed in $Au+Au$ collisions at 35 A.MeV. The excited source configuration is reconstructed through a calorimetric analysis of its de-excitation products. Fragment partitions show signs of a critical behavior at about 5 A.MeV excitation energy. In the same energy range the heat capacity shows a negative branch providing a direct evidence of a first order liquid gas phase transition.Comment: 4 Postscript figures, submitted to Phys. Rev. Lett. on 14-apr-199

On the kinematic separation of field and cluster stars across the Bulge globular NGC 6528

We present deep and precise multi-band photometry of the Galactic Bulge globular cluster NGC6528. The current dataset includes optical and near-infrared images collected with ACS/WFC, WFC3/UVIS, and WFC3/IR on board the Hubble Space Telescope. The images cover a time interval of almost ten years and we have been able to carry out a proper-motion separation between cluster and field stars. We performed a detailed comparison in the m_F814W, m_F606W - m_F814W Color-Magnitude Diagram with two empirical calibrators observed in the same bands. We found that NGC6528 is coeval with and more metal-rich than 47Tuc. Moreover, it appears older and more metal-poor than the super-metal-rich open cluster NGC6791. The current evidence is supported by several diagnostics (red horizontal branch, red giant branch bump, shape of the sub-giant branch, slope of the main sequence) that are minimally affected by uncertainties in reddening and distance. We fit the optical observations with theoretical isochrones based on a scaled-solar chemical mixture and found an age of 11 +- 1 Gyr and an iron abundance slightly above solar ([Fe/H = +0.20). The iron abundance and the old cluster age further support the recent spectroscopic findings suggesting a rapid chemical enrichment of the Galactic Bulge.Comment: 14 pages, 12 figures (2 at low resolution); added references; corrected figure 3, 4, 5, 8 and 9; results unchanged. Erratum to be published in Ap