Relativistic Navier-Stokes equations in the Meixner-Prigogine scheme

Viscous effects are included in the relativistic Meixner-Prigogine scheme (see: A. Sandoval-Villalbazo, L.S. García-Colín, Physica A 234 (1996) 358). A relativistic generalization of the Navier-Stokes equations is obtained within this framework. The system obtained is analyzed and compared with related work.     

Probabilistic properties of neuron spiking time-series obtained in vivo

Probabilistic properties of spiking time-series obtained in vivo from singular neurons belonging to Red Nucleus of brain are analyzed for two groups of rats: genetically defined rat model of depression (Flinders Sensitive Rat Line - FSL) and a control (healthy) group. The FSL group shows a distribution of interspike intervals with a much longer tail than that found for normal rats. The former distribution (for the FSL group) indicates a power-law with exponent α = - 1±0.1. A simple thermodynamic (noise) model is elaborated to explain obtained results. Received 13 May 2001 and Received in final form 20 September 2001     

Advanced adiabatic approximation for momentum distributions of ejected electrons in slow atomic collisions

The problem of determination of momentum distributions of ejected electrons in slow atomic collisions is studied within the impact-parameter method by using a dynamic adiabatic basis which takes into account the correct boundary conditions. An expression is obtained which relates the momentum distribution of the ejected electrons with a coherent sum of the delocalized dynamic adiabatic eigenstates (elementary wavepackets). The form of the momentum distribution exactly coincides with the form of the total wavepacket in configuration space. General formulas are applied to a model problem of electron detachment in the process in which the electron-atom interactions are described by the zero-range potentials. In the example considered, the momentum distribution of ejected electrons, in the center-of-mass frame, exhibits a maximum located in the scattering plane on the circle of radius (in atomic units), where v is the relative collision velocity and is the impact parameter. Received: 5 October 1998     

Parabolic conjugacy in general linear groups

Let q be a power of a prime and n a positive integer. Let P(q) be a parabolic subgroup of the finite general linear group GL _n (q). We show that the number of P(q)-conjugacy classes in GL _n (q) is, as a function of q, a polynomial in q with integer coefficients. This answers a question of Alperin in (Commun. Algebra 34(3): 889–891, 2006)     

Elasticity theory of a twisted stack of plates

We present an elastic model of B-form DNA as a stack of thin, rigid plates or base pairs that are not permitted to deform. The symmetry of DNA and the constraint of plate rigidity limit the number of bulk elastic constants contributing to a macroscopic elasticity theory of DNA to four. We derive an effective twist-stretch energy in terms of the macroscopic stretch along and relative excess twist about the DNA molecular axis. In addition to the bulk stretch and twist moduli found previously, we obtain a twist-stretch modulus with the following remarkable properties: 1) it vanishes when the radius of the helical curve following the geometric center of each plate is zero, 2) it vanishes with the elastic constant K₂₃ that couples compression normal to the plates to a shear strain, if the plates are perpendicular to the molecular axis, and 3) it is nonzero if the plates are tilted relative to the molecular axis. This implies that a laminated helical structure carved out of an isotropic elastic medium will not twist in response to a stretching force, but an isotropic material will twist if it is bent into the shape of a helix. Received: 4 July 1997 / Received in final form: 16 October 1997 / Accepted: 21 October 1997     

Superconductors in parallel field: Electromagnetic properties at the surface

Summary In the framework of the boson transformation method, a general approach to the study of finite-dimensionality superconductors is applied to the investigation of the electromagnetic properties of a semiinfinite superconductor and of a film of arbitrary thickness in the presence of a parallel external magnetic field. The magnetic-field and current density distributions near the surfaces are computed and numerical results are given for some typical cases. As an application, an estimation of the superheating field for type-II superconductor is obtained and compared with previous results.

---

Riassunto Nell'àmbito del metodo della trasformazione bosonica, una tecnica generale per lo studio di superconduttori a dimensione finita è applicata allo studio delle proprietà elettromagnetiche di un superconduttore semi-infinito e di un film di spessore arbitrario. Sono calcolate le distribuzioni del campo magnetico e della densità di corrente, e sono riportati risultati numerici per qualche caso tipico. Infine, si ottiene, e si confronta con precedenti risultati, una stima del campo di surriscaldamento per superconduttori del II tipo.

---

Резюме В рамках метода бозонного преобразования общий подход для исследования конечно-мерных сверхпроводников применяется к изучению электромагнитных свойств полубесконечного сверхпроводника и пленки произвольной толщины в присутствии параллельного внешнего магнитного поля. Вычисляются распределения магнитного поля и плотности тока вблизи поверхностей. Приводятся численные результаты для некоторых типичных случаев. Оценивается поле супернагревания для сверхпроводника второго рода. Оценка сравнивается с имеющимися результатами.

     

A rigorous treatment of the phase rule

Summary After a critical analysis of the literature, the traditional formulation of the phase rule proposed by Gibbs is stated in a different form and is proved rigorously, together with Gibbs' conjecture on the maximum number of coexisting phases. A new statement of Gibbs' phase rule is proved for closed systems. Then, Hatsopoulos-Keenan's formulation of the phase rule is restated and proved, both for open and for closed systems. The whole treatment of the phase rule presented in this paper holds both in the presence and in the absence of chemical reactions.     

23Na NMR study of ionic mesophases in molten sodium carboxylates

The ²³Na NMR lineshapes are reported for the ionic mesophase and isotropic phase of the melts of sodium n-butyrate and sodium isovalerate. The powder pattern for the central transition typical for the second-order quadrupole effect observed in the mesophase melts is of particular interest. Some analogies to ²³Na behavior in sodium β-alumina are pointed out.     

Information value and information content in the evolutionary strategy of the genetic code

Summary In previous papers we defined the information value of a genetic code as a measure of its efficiency in the utilization of the information stored in the DNA molecule. Here the genetic codes which have been proposed to be intermediate steps in evolution are analysed in terms of information theory. The results show that evolution follows an optimization strategy between increasing the information content and decreasing the information value,i.e. in each evolutionary step the average information value per unitary information content decreases and at the same time the probability of nonsense mutations goes down as the code evolves. To speed up publication, the authors of this paper have agreed to not recive the proofs for correction.     

Transport theory of multiterminal hybrid structures

We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact. The maximal conductance of a two-channel contact is proportional to (e ²/h)(a ₀/D)²exp[-D/ξ(ω^*)], where D is the distance between the contacts, a₀ the lattice spacing, ξ(ω) is the superconducting coherence length, and ω^* is the cross-over frequency between a perturbative regime ( ω < ω^*) and a non perturbative regime ( ω^* < ω < Δ). Received 18 June 2001 and Received in final form 17 January 2002