Specific recording kinetics as a general property of unconventional photorefractive media

We introduce a model for the kinetics of grating formation during holographic recording in optically excitable two-state systems. An unexpected characteristic time dependence of the diffraction efficiency is found. We show that it originates from a nonlinear transformation of the light interference pattern into a refractive-index profile. Our findings strongly resemble and explain by nature the experimental data of two-state systems in general, here represented by two examples: sodium nitroprusside and terbium gallium garnet.     

Feasibility of low-energy radiative-capture experiments at the LUNA underground accelerator facility

The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross-sections of the radiative-capture reactions ^2H²H(p, )^3He³Heand ^14N¹⁴N(p, )^15O¹⁵Owithin their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam-induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative-capture studies at energies of astrophysical interest is discussed for several experimental scenarios.     

Addition of the ortho-C-H bonds of phenol across an olefin catalysed by a chiral iridium(I) diphosphine complex

A chiral iridium(I) diphosphine complex efficiently catalyses the unprecedented ortho-alkylation of phenol with norbornene in the absence of solvent leading to the formation of one and two C-C bonds.     

Letter: Gödel-Type Space-Time Metrics

A simple group theoretic derivation is given of the family of space-time metrics with isometry group SO(2,1) × SO(2) × first described by Gödel, of which the Gödel stationary cosmological solution is the member with a perfect-fluid stress-energy tensor. Other members of the family are shown to be interpretable as cosmological solutions with an electrically charged perfect fluid and a magnetic field.     

A preemptive polling protocol for applications in wireless LANs

This paper deals with a radio‐based communication network with a single radio channel shared by several data terminals for transmissions to a single hub station. In particular, the communication system considered is a potential provider of wireless LAN‐like services. The focus is on the capacity of combining a preemptive polling‐based multiple access scheme with a Selective Repeat ARQ technique to counteract the effect of the nonstationary transmission channel. The nonstationary transmission channel has been modeled as a two‐state Markov chain with parameters related to actual propagation conditions. Typical outdoor/indoor environments have been considered. The main idea is that of making the service interruption of the preemptive polling scheme dependent on the propagation conditions of the transmission channel by monitoring the outcome of the data packet transmission attempts. A performance comparison clearly reveals the superiority of this preemptive polling scheme with respect to the classical cyclic polling scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

An interconnected type-1 fuzzy algorithm for impulsive noise cancellation in multicarrier-based power line communication systems

This paper introduces an interconnected type-1 fuzzy algorithm which is trained by a modified version of the Scaled Conjugated Gradient method for impulsive noise cancellation in discrete multitone/orthogonal frequency-division multiplexing (DMT/OFDM)-based systems for broadband power line communications. The advanced algorithm makes use of the fuzzy systems capacity of dealing with uncertainties to reduce the presence of high-power impulsive noises while the DMT/OFDM technique copes with the severe intersymbol interference observed in power line channels. As a result, for a given error probability, a high number of bits can be allotted to each subchannel due to the signal-to-noise ratio enhancements achieved by the proposed fuzzy algorithm. The simulation results show that the novel fuzzy algorithm not only achieve a high data rate, but it also outperforms the standard impulsive noises techniques and other computational intelligence-based techniques, especially in the presence of additive and high-power impulsive noises.     

Linear asymptotic stability of the equilibrium state for the 2-D MEP hydrodynamical model of charge transport in semiconductors

Linear asymptotic Lyapunov stability of the equilibrium state for the balance equations of charge transport in semiconductors based on the maximum entropy principle [A.M. Anile, V. Romano, Non parabolic band transport in semiconductors: closure of the moment equations, Contin. Mech. Thermodyn. 11 (1999) 307–325; V. Romano, Non parabolic band transport in semiconductors: closure of the production terms in the moment equations, Contin. Mech. Thermodyn. 12 (2000) 31–51] is proven for a typical two-dimensional problem.     

An advanced satellite communication system with on-board fast packet switching capabilities

This paper is focused on a satellite communication system having on-board fast packet switching capabilities. Different alternatives for the up-link access technique and for the architecture of the onboard switching fabric are considered. In particular an efficient time division multiple access technique with slots assigned on demand and a novel switching approach are proposed. Performances in terms of mean access delay and mean on-board switching delay are derived by analytical approaches and computer simulations.     

Magnetic dipole energies in tetragonally-distorted cubic crystals

Dipole energies in tetragonally-distorted cubic crystals have been calculated by the Ewald-Kornfeld method for the case in which the dipoles are parallel to the c-axis. The results are accurate to at least 1 part in 10⁵, sufficient to provide accurate values of the strain-dependence and hence the dipolar magnetostriction constant h₁ within the range 0.98 ?c/a?1.02. Calculations are presented for bcc, fcc and diamond lattices.