Abstract:
We report direct first-principles density-functional calculations of the piezoelectric tensor $\tensor{d}$ relating polarization to applied stress for the binary compounds AlN, GaN, and InN. The values of $\tensor{d}$ are rather sensitive to the choice of the exchange-correlation functional, and results are presented for both the local-density and gradient approximations. A comparison with experiment and with values predicted indirectly from the elastic and e-piezoconstant tensors is also presented.

The functional significance of the endometrial hCG/ LH
receptors has been related to a rapid release of prostaglandins. However, as
compared to gonads and myometrium, in-endometrium mechanisms of transmembrane
signalling of the hCG/LH receptors are probably not conventional and remain
unclear. Here we investigated, in vivo, the potential of hCG to interact
with, and stimulate the membrane effector enzyme, adenylyl cyclase (AC), in
human endometrium. Hormonal and nonhormonal activation of AC was tested in
membrane fractions prepared from endometrial biopsies obtained from patients
undergoingevaluation cycles for
hormone replacement therapy (HRT) and controlled ovarian hyperstimulation
(COH).AC activity was determined by the direct conversion of the
substrate ATP into cAMP under unstimulated conditions and in the presence of
the non-hormonal activators guanyl nucleotide and forskolin. Also AC activity
was tested in the presence of hCG under conditions allowing maximal enzyme
stimulation. Isoproterenol and prostaglandin E2 (PGE2) were included for
comparison. Immunoblot analyses demonstrated the presence of hCG/LH receptors
and Gsα protein and other members of
the G protein family in the membrane fractions. Endometrial membranes also
exhibited high levels of AC activity compared to luteal membranes used as
control. Stimulation by GMP-P(NH)P alone was 196 ± 63 (n = 8) (pmol/mg/ min ± SD). Neither hCG nor isoproterenol showed stimulation
of endometrial AC (210 ± 65, and 197 ± 53, respectively; n = 66 assays). But PGE2 stimulated
the enzyme system significantly (264 ± 63, p < 0.05; n =

Abstract:
Ab initio calculations predict that Be is a shallow acceptor in GaN. Its thermal ionization energy is 0.06 eV in wurtzite GaN; the level is valence resonant in the zincblende phase. Be incorporation is severely limited by the formation of Be_3N_2. We show however that co-incorporation with reactive species can enhance the solubility. H-assisted incorporation should lead to high doping levels in MOCVD growth after post-growth annealing at about 850 K. Be-O co-incorporation produces high Be and O concentrations at MBE growth temperatures.

Abstract:
We demonstrate that polarization-related quantities in semiconductors can be predicted accurately from first-principles calculations using the appropriate approach to the problem, the Berry-phase polarization theory. For III-V nitrides, our test case, we find polarizations, polarization differences between nitride pairs, and piezoelectric constants quite close to their previously established values. Refined data are nevertheless provided for all the relevant quantities.

Abstract:
Damping of primordial gravitational waves due to the anisotropic stress contribution owing to the cosmological neutrino background (C$\nu$B) is investigated in the context of a radiation-to-matter dominated Universe. Besides its inherent effects on the gravitational wave propagation, the inclusion of the C$\nu$B anisotropic stress into the dynamical equations also affects the tensor mode contribution to the anisotropy of the cosmological microwave background (C$\gamma$B) temperature. Given that the fluctuations of the C$\nu$B temperature in the (ultra)relativistic regime are driven by a multipole expansion, the mutual effects on the gravitational waves and on the C$\gamma$B are obtained through a unified prescription for a radiation-to-matter dominated scenario. The results are confronted with some preliminary results for the radiation dominated scenario. Both scenarios are supported by a simplified analytical framework, in terms of a scale independent dynamical variable, $k \eta$, that relates cosmological scales, $k$, and the conformal time, $\eta$. The background relativistic (hot dark) matter essentially works as an effective dispersive medium for the gravitational waves such that the damping effect is intensified for the Universe evolving to the matter dominated era. Changes on the temperature variance owing to the inclusion of neutrino collision terms into the dynamical equations result into spectral features that ratify that the multipole expansion coefficients $C_{l}^{T}$'s die out for $l \sim 100$.

Abstract:
We analyze Ge-related defects in Ge-doped SiO_2 using first-principles density functional techniques. Ge is incorporated at the level of ~ 1 mol % and above. The growth conditions of Ge:SiO_2 naturally set up oxygen deficiency, with vacancy concentration increasing by a factor 10^5 over undoped SiO_2, and O vacancies binding strongly to Ge impurities. All the centers considered exhibit potentially EPR-active states, candidates for the identification of the Ge(n) centers. Substitutional Ge produces an apparent gap shrinking via its extrinsic levels.

Abstract:
Phase diagrams play a primary role in the understanding of materials properties. For iron-based superconductors (Fe-SC), the correct definition of their phase diagrams is crucial because of the close interplay between their crystallo-chemical and magnetic properties, on one side, and the possible coexistence of magnetism and superconductivity, on the other. The two most difficult issues for understanding the Fe-SC phase diagrams are: 1) the origin of the structural transformation taking place during cooling and its relationship with magnetism; 2) the correct description of the region where a crossover between the magnetic and superconducting electronic ground states takes place. Hence a proper and accurate definition of the structural, magnetic and electronic phase boundaries provides an extremely powerful tool for material scientists. For this reason, an exact definition of the thermodynamic phase fields characterizing the different structural and physical properties involved is needed, although it is not easy to obtain in many cases. Moreover, physical properties can often be strongly dependent on the occurrence of micro-structural and other local-scale features (lattice micro-strain, chemical fluctuations, domain walls, grain boundaries, defects), which, as a rule, are not described in a structural phase diagram. In this review, we critically summarize the results for the most studied 11-, 122- and 1111-type compound systems, providing a correlation between experimental evidence and theory.

Abstract:
In this paper we obtain a couple of explicit expressions for the derivative of the probability of an increasing event in the random interlacements model. The event is supported in a finite subset of the lattice, and the derivative is with respect to the intensity parameter of the model.

Abstract:
Since long time various qualitative speculations have been proposed about the link between the three major Giza pyramids and the stars. In particular, according to a popular and controversial hypothesis (the so-called Orion Correlation Theory), a perfect coincidence would exist between the mutual positions of the three stars of the Orion Belt and those of the main Giza pyramids. In the present paper, this apparent coincidence has been subjected to some statistical verifications, in order to assess the probability that the correlation between stars and pyramids, both in relative position and in luminosity/height, can be merely due to the case. These statistical analyses have been performed by means of Monte Carlo simulations and have been coupled with previous astronomical/astrophysical tests of the presumed correlation, finding that the coincidence does not seem to be fortuitous and that it is compatible with the naked-eye astrometry and photometry of the Orion Belt stars. On the contrary, unlike what stated by another popular and controversial theory (the so-called Cygnus-Giza Correlation), we have found no coincidence between the mutual positions of the three pyramids and those of the three stars of the short arm of the asterism of Northern Cross, in the Cygnus constellation.