6,237 research outputs found
On the generation and the nonlinear dynamics of X-waves of the Schroedinger equation
The generation of finite energy packets of X-waves is analysed in normally
dispersive cubic media by using an X-wave expansion. The 3D nonlinear
Schroedinger model is reduced to a 1D equation with anomalous dispersion. Pulse
splitting and beam replenishment as observed in experiments with water and Kerr
media are explained in terms of a higher order breathing soliton. The results
presented also hold in periodic media and Bose-condensed gases.Comment: 18 pages, 6 figures, corrected version to be published in Physical
Review
Experimental measurement of photothermal effect in Fabry-Perot cavities
We report the experimental observation of the photothermal effect. The
measurements are performed by modulating the laser power absorbed by the
mirrors of two high-finesse Fabry-Perot cavities. The results are very well
described by a recently proposed theoretical model [M. Cerdonio, L. Conti, A.
Heidmann and M. Pinard, Phys. Rev. D 63 (2001) 082003], confirming the
correctness of such calculations. Our observations and quantitative
characterization of the photothermal effect demonstrate its critical importance
for high sensitivity interferometric displacement measurements, as those
necessary for gravitational wave detection.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Wideband dual sphere detector of gravitational waves
We present the concept of a sensitive AND broadband resonant mass
gravitational wave detector. A massive sphere is suspended inside a second
hollow one. Short, high-finesse Fabry-Perot optical cavities read out the
differential displacements of the two spheres as their quadrupole modes are
excited. At cryogenic temperatures one approaches the Standard Quantum Limit
for broadband operation with reasonable choices for the cavity finesses and the
intracavity light power. A molybdenum detector of overall size of 2 m, would
reach spectral strain sensitivities of 2x10^-23/Sqrt{Hz} between 1000 Hz and
3000 Hz.Comment: 4 pages, 3 figures. Changed content. To appear in Phys. Rev. Let
Analysis of thermodynamic losses in ground source heat pumps and their influence on overall system performance
The present work aims at identifying the relative influence of GSHP subsystems (viz. ground source, earth heat exchangers, heat pump unit, pumping devices) on the overall efficiency and the limits to which technological improvements should be pushed (because, beyond these limits, only minor benefits may be achieved). To this end, an analysis of thermodynamic losses is conducted for a case study, followed by a sensitivity analysis on the heat pump unit thermal performance. Primary energy consumptions of nine configurations with different combinations of ideal and real subsystems are compared. The completely ideal system is used as the reference to normalize energy consumptions and obtain a dimensionless efficiency parameter. The results show that – when a proper design methodology is employed – the performance of the borehole heat exchangers slightly affects the overall efficiency. On the contrary, the thermal response of the ground and the thermal and hydraulic performances of the heat pump unit are key factors. Finally, a sensitivity analysis is conducted by increasing the heating and cooling efficiencies of the heat pump device
A peptide found in human serum, derived from the c-terminus of albumin, shows antifungal activity in vitro and in vivo
The growing problem of antimicrobial resistance highlights the need for alternative strategies to combat infections. From this perspective, there is a considerable interest in natural molecules obtained from different sources, which are shown to be active against microorganisms, either alone or in association with conventional drugs. In this paper, peptides with the same sequence of fragments, found in human serum, derived from physiological proteins, were evaluated for their antifungal activity. A 13-residue peptide, representing the 597–609 fragment within the albumin C-terminus, was proved to exert a fungicidal activity in vitro against pathogenic yeasts and a therapeutic effect in vivo in the experimental model of candidal infection in Galleria mellonella. Studies by confocal microscopy and transmission and scanning electron microscopy demonstrated that the peptide penetrates and accumulates in Candida albicans cells, causing gross morphological alterations in cellular structure. These findings add albumin to the group of proteins, which already includes hemoglobin and antibodies, that could give rise to cryptic antimicrobial fragments, and could suggest their role in anti-infective homeostasis. The study of bioactive fragments from serum proteins could open interesting perspectives for the development of new antimicrobial molecules derived by natural sources
Beyond the random phase approximation in the Singwi-Sj\"olander theory of the half-filled Landau level
We study the Chern-Simons system and consider a self-consistent
field theory of the Singwi-Sj\"olander type which goes beyond the random phase
approximation (RPA). By considering the Heisenberg equation of motion for the
longitudinal momentum operator, we are able to show that the zero-frequency
density-density response function vanishes linearly in long wavelength limit
independent of any approximation. From this analysis, we derive a consistency
condition for a decoupling of the equal time density-density and
density-momentum correlation functions. By using the Heisenberg equation of
motion of the Wigner distribution function with a decoupling of the correlation
functions which respects this consistency condition, we calculate the response
functions of the system. In our scheme, we get a density-density
response function which vanishes linearly in the Coulomb case for
zero-frequency in the long wavelength limit. Furthermore, we derive the
compressibility, and the Landau energy as well as the Coulomb energy. These
energies are in better agreement to numerical and exact results, respectively,
than the energies calculated in the RPA.Comment: 9 Revtex pages, 4 eps figures, typos correcte
Laser beam filamentation in fractal aggregates
We investigate filamentation of a cw laser beam in soft matter such as
colloidal suspensions and fractal gels. The process, driven by
electrostriction, is strongly affected by material properties, which are taken
into account via the static structure factor, and have impact on the statistics
of the light filaments.Comment: 4 pages, 5 figures. Revised version with corrected figure 5. To be
published in Phys. Rev. Let
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