284 research outputs found
The 2D analogue of the Reissner-Nordstrom solution
A two-dimensional (2D) dilaton gravity model, whose static solutions have the
same features of the Reissner-Nordstrom solutions, is obtained from the
dimensional reduction of a four-dimensional (4D) string effective action
invariant under S-duality transformations. The black hole solutions of the 2D
model and their relationship with those of the 4D theory are discussed.Comment: 5 pages, Plain-Tex, no figure
Seminal fluid metabolomic markers of oligozoospermic infertility in humans
Infertility affects 12â15% of couples worldwide, and male factors are the cause of nearly half of all cases. Studying seminal fluid composition could lead to additional diagnostic accuracy and a better understanding of the pathophysiology of male factor infertility. Metabolomics offers a new opportunity to evaluate biomarkers and better understand pathological mechanisms. The aim of the study was to identify new markers or therapeutic targets to improve outcomes in male factor or idiopathic infertility patients. Semen samples were obtained from 29 men with a normal spermogram test, and from 18 oligozoospermic men. Samples were processed and analyzed by Nuclear Magnetic Resonance spectroscopy and, subsequently, multivariate and univariate statistical analyses. Receiving Operator Curves (ROC) and Spearman correlations were also performed. An Orthogonal Partial Least Square Discriminant Analysis supervised multivariate model was devised to compare the groups. The levels of fructose, myoâinositol, aspartate and choline were altered. Moreover, Spearman Correlation associated fructose, aspartate and myoâinositol with the total amount of spermatozoa, total motile spermatozoa, % of immotility and % of âin situâ spermatozoic motility respectively. NMRâbased metabolomics allowed the identification of a specific metabolic fingerprint of the seminal fluids of patients affected by oligozoospermia
Static and Dynamical Susceptibility of LaO1-xFxFeAs
The mechanism of superconductivity and magnetism and their possible interplay
have recently been under debate in pnictides. A likely pairing mechanism
includes an important role of spin fluctuations and can be expressed in terms
of the magnetic susceptibility chi. The latter is therefore a key quantity in
the determination of both the magnetic properties of the system in the normal
state, and of the contribution of spin fluctuations to the pairing potential. A
basic ingredient to obtain chi is the independent-electron susceptibility chi0.
Using LaO1-xFxFeAs as a prototype material, in this report we present a
detailed ab-initio study of chi0(q,omega), as a function of doping and of the
internal atomic positions. The resulting static chi0(q,0) is consistent with
both the observed M-point related magnetic stripe phase in the parent compound,
and with the existence of incommensurate magnetic structures predicted by
ab-initio calculations upon doping.Comment: 15 pages, 8 figure
Influence of carbon on intraband scattering in Mg(B1-xCx)2
We report data on the Hall coefficient (RH) of the carbon substituted
Mg(B1-xCx)2 single crystals with x in the range from 0 to 0.1. The temperature
dependences of RH obtained for the substituted crystals differ systematically
at low temperatures, but all of them converge to the value of 1.8 x 10^-10
m^3/C at room temperature. The RH(T) data together with results of the
thermoelectric power and electrical resistivity measurements are interpreted
within a quasi-classical transport approach, where the presence of four
different conducting sheets is considered. The main influence of the carbon
substitution on the transport properties in the normal state is associated with
enhanced scattering rates, rather than modified concentration of charge
carriers. Presumably the carbon substitution increases the electron-impurity
scattering mainly in the pi band.Comment: 16 pages, 3 figure
Piecewise planar underwater mosaicing
A commonly ignored problem in planar mosaics, yet often present in practice, is the selection of a reference homography reprojection frame where to attach the successive image frames of the mosaic. A bad choice for the reference frame can lead to severe distortions in the mosaic and can degenerate in incorrect configurations after some sequential frame concatenations. This problem is accentuated in uncontrolled underwater acquisition setups as those provided by AUVs or ROVs due to both the noisy trajectory of the acquisition vehicle - with roll and pitch shakes - and to the non-flat nature of the seabed which tends to break the planarity assumption implicit in the mosaic construction. These scenarios can also introduce other undesired effects, such as light variations between successive frames, scattering and attenuation, vignetting, flickering and noise. This paper proposes a novel mosaicing pipeline, also including a strategy to select the best reference homography in planar mosaics from video sequences which minimizes the distortions induced on each image by the mosaic homography itself. Moreover, a new non-linear color correction scheme is incorporated to handle strong color and luminosity variations among the mosaic frames. Experimental evaluation of the proposed method on real, challenging underwater video sequences shows the validity of the approach, providing clear and visually appealing mosaic
Electrical capacitance probe characterisation for vertical annular air-water flow investigation
Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The experimental analysis and the qualification of an Electrical Capacitance Probe (ECP), for the void fraction measurement, is presented. The ECP, developed at the SIET, is used to investigate a vertical air/water flow, characterized by high void fraction. Mass flow rates have been analyzed between 0.094 and 0.15 kg/s for air and between 0.002 and 0.021 kg/s for water, corresponding to void fraction up to 90% and to annular and wavy-annular flow patterns. The ECP signals are used to obtain the geometrical shape functions (signals as a function of electrode distances) in single and two phase flows. The dependence of the signal by the void fraction is derived and other flow characteristics as the liquid film thickness and the phase velocities are evaluated by means of rather simple models. The experimental analysis allows to characterize the ECP, showing the advantages and the drawbacks of this technique for the two-phase flow characterization at high void fraction, and it provides a reliable tool for the selection of the instrumentation for the SIET Company SPES3 facility.dc201
Sperm quality assessment in Ficopomatus enigmaticus (Fauvel, 1923): Effects of selected organic and inorganic chemicals across salinity levels
Contamination by organic and inorganic compounds remains one of the most complex problems in both brackish and marine environments, causing potential implications for the reproductive success and survival of several broadcast spawners. Ficopomatus enigmaticus is a tubeworm polychaete that has previously been used as a model organism for ecotoxicological analysis, due to its sensitivity and ecological relevance. In the present study, the effects of five trace elements (zinc, copper, cadmium, arsenic and lead), one surfactant (sodium dodecyl sulfate, SDS) and one polycyclic aromatic hydrocarbon (benzo(a)pyrene, B(a)P) on the sperm quality of F. enigmaticus were investigated. Sperm suspensions were exposed in vitro to different concentrations of each selected contaminant under four salinity conditions (10, 20, 30, 35). Possible adverse effects on sperm function were assessed by measuring oxidative stress, membrane integrity, viability and DNA damage. Sperm quality impairments induced by organic contaminants were more evident than those induced by inorganic compounds. SDS exerted the largest effect on sperm. In addition, F. enigmaticus sperm showed high tolerance to salinity variation, supporting the wide use of this species as a promising model organism for ecotoxicological assays. Easy and rapid methods on polychaete spermatozoids were shown to be effective as integrated sperm quality parameters or as an alternative analysis for early assessment of marine and brackish water pollution
Phononic Self energy effects and superconductivity in CaC
We study the graphite intercalated compound CaC by means of Eliashberg
theory, focusing on the anisotropy properties. An analysis of the
electron-phonon coupling is performed, and we define a minimal 6-band
anisotropy structure. Comparing with Superconducting Density Functional Theory
(SCDFT) the condition under which Eliashberg theory is able to reproduce the
SCDFT gap structure is determined, and we discuss the role of Coulomb
interactions. The Engelsberg-Schrieffer polaron structure is computed by
solving the Eliashberg equation on the Matsubara axis and analytically
continuing it to the full complex plane. This reveals the polaronic
quasiparticle bands anisotropic features as well as the interplay with
superconductivity
Role of charge doping and lattice distortions in codoped Mg_{1-x}(AlLi)_{x}B_2 compounds
We prepared a series of Mg_{1-x}(AlLi)_{x}B_2 samples with
0≤x≤0.45 in order to compensate with Li the electron doping induced
by Al. Structural characterization by means of neutron and X-ray diffraction
confirms that Li enters the MgB2 structure even though in an amount less than
nominal one. We performed susceptibility, resistivity and specific heat
measurements. Vibrational properties were also investigated by means of Raman
spectroscopy. We compare these results with those obtained on a homologous
series of Mg_{1-x}Al_{x}B_2 samples. The systematic success of scaling the
relevant properties with the Al content rather than with the electron doping
suggests that lattice deformation plays an important role in tuning the
superconducting properties.Comment: 15 pages, 13 figures; changes: "codoped" instead of "co-doped"; added
comments in the Fig. 11 caption Comments 31/1/2006: 16 figures ; new revised
version of the manuscrip
Critical Field of Al-Doped MgB2 Samples: Correlation with the Suppression of Sigma-Band Gap
In this Letter, the study of the effect of Al substitution on the upper
critical field, Bc2, in AlxMg1-xB2 samples is presented. We find a
straightforward correlation between Bc2 and the sigma-band gap, Delta_sigma,
evaluated by point-contact measurements. Up to x=0.2 Bc2 can be well described
within a clean limit model and its decrease with x is directly related to the
suppression of Delta_sigma. For larger doping we observed the crossover to the
dirty regime driven mostly by the strong decrease of Delta_sigma rather than by
the increase of the sigma-band scattering rateComment: 5 pages, 4 figure
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