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11.
Summary The existence of pair excitations in a Fermi gas interacting via a short-range attractive potential is investigated. Within
the ladder approximation to the Bethe-Salpeter equation for the effective two-particle interaction, evidence of pair excitation
is found at energies slightly larger than the chemical potential. The link between those excitations and a boson-fermion model
of superconductivity (Phys. Lett. A,196 (1995) 359) is discussed. In particular it is shown that the charge carrier density dependence of the pair excitation (boson)
energy, assumed phenomenologically in the boson-fermion model, is consistent with the properties of the interacting Fermi
gas studied. These results give support to the microscopic origin of the phenomenological boson-fermion model of superconductivity.
Within the polaron-bipolaron theory the assumption that bosons and fermions can be described as mobile particles has found
support in ref.[6] where the small bipolaron (boson) delocalization is discussed and in ref.[7] where the large polaron delocalization
is analysed. 相似文献
12.
Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential 总被引:2,自引:0,他引:2
Burger S Cataliotti FS Fort C Minardi F Inguscio M Chiofalo ML Tosi MP 《Physical review letters》2001,86(20):4447-4450
We create Bose-Einstein condensates of 87Rb in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the Bose-Einstein condensate and accounts for the main features of the observed behavior. 相似文献
13.
Evaluation of fast gas chromatography and gas chromatography-mass spectrometry in the analysis of lipids 总被引:1,自引:0,他引:1
Mondello L Casilli A Tranchida PQ Costa R Chiofalo B Dugo P Dugo G 《Journal of chromatography. A》2004,1035(2):237-247
Fast and conventional gas chromatography (GC) techniques were applied to nine different lipidic matrices (butter, lard, tallow, and peanut, corn, sunflower, soya, olive, menhaden oils). Simultaneous methylic transesterification was performed on all samples prior to GC analysis. Several practical aspects concerning high speed analysis were investigated, such as the great increase in linear velocity, the use of fast temperature ramps, column sample capacity and detection systems. Analytical results showed certain losses in resolution, balanced by a consistent reduction in analysis time. The actual time savings were variable (60-70 min) as they were dependent on the complexity of the sample while the speed enhancement factor was equal to 10.5. Peak identification was achieved by means of different information sources, such as fast GC-mass spectrometry (MS), linear retention indices and comprehensive two-dimensional (2D) gas chromatography group patterns. The method developed was shown to be applicable in routine applications on complex natural samples. 相似文献
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Ekiel-Jezewska ML; Wajnryb E 《The Quarterly Journal of Mechanics and Applied Mathematics》2006,59(4):563-585
An example system is studied to discuss precision of the multipoleexpansion, applied to determine forces exerted on particlesby a viscous low-Reynolds-number fluid flow. A single spherein an ambient flow (pure shear, quadratic, and modulated shear)parallel to a close plane wall is considered. Forces and torquesexerted by the ambient flow on a motionless sphere are evaluated.Their precision is determined and related to a multipole orderof the truncation. Similar analysis is performed for a movingsphere with no ambient flow and for a freely moving sphere.Relative motion of the sphere with respect to the wall givesrise to strong lubrication interactions. It is analysed howthese interactions affect accuracy of the pure multipole expansion,and what are the smallest distances where it becomes insufficient.An alternative precise method is applied, in which lubricationexpressions are subtracted from the hydrodynamic forces andtorques, and the residue is evaluated as a fast-convergent seriesof inverse powers of the distance between the sphere centreand the wall. The accuracy of this procedure is carefully analysed. 相似文献
16.
Summary The mobility of the Fr?hlich bipolarons is a challenging matter for the bipolaronic theory of high-T
c superconductivity. Here we focus our attention on the problem of the effective mass of a bipolaron in a strongly ionic system
(like the new H(igh)T
cS(uper)C(onductors) are) and in the presence of an electron gas. We show that there is a sizeable renormalization of the bipolaron
mass due to the polarization effects of both the optical phonons and plasmons. Moreover, we show that the effective mass decreases
increasing the density of carriers, because the screening effects become more important. In all cases, the values of the bipolaron
effective mass are not greater than some tens of electronic masses (m
e). 相似文献
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Dugo P Kumm T Lo Presti M Chiofalo B Salimei E Fazio A Cotroneo A Mondello L 《Journal of separation science》2005,28(9-10):1023-1030
The separation and determination of triacylglycerols (TAGs), which are the main components of naturally occurring fats and oils, in milk fat is a challenging task due to the very complex nature of this matrix. In the present study the TAG fraction of donkey milk lipids has been characterized by using high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). HPLC in reversed phase mode has been used for TAG separation and silver ion (Ag+) HPLC has been used as a second dimension to clarify and confirm the identification. The RP-HPLC eluate was fractionated and the fractions of interest were injected onto the Ag+-HPLC column. In both cases peak assignment was carried out by combining retention data with APCI-MS spectra information. In total, 55 TAGs in donkey milk fat were identified (without considering the positional isomers) and quantified on the basis of percentage peak areas in the RP-HPLC chromatogram (without the use of correction factors). Amongst the identified triacylglycerols, POLn, POO, PPO, CaPO, POL, and PPoO proved to be the main components of the TAG fraction of donkey milk. 相似文献
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