Exact results in the two-dimensional U(1)-symmetric Thirring model

A systematic study of the ground state, excitation spectrum, and “isospin-magnetic” properties of the U(1)-Thirring model, based on its exact (Bethe-ansatz) solution, is presented. The exact results obtained for the renormalized mass spectrum in all sectors of the phase diagram of the model allow us to observe a continuous transition from the weak-coupling theory into a strong-coupling (asymptotically free) regime, taking place by varying the coupling constants, g and g. Some questions concerning universality and the relation to other models are discussed.     

Specific heat of A-15 Nb3Al0.83Ge0.21

The specific heat of A-15 Nb₃Al_.83Ge_.21 with a transition temperature, T_c, of 20.0 K has been measured from 6 to 25 K. Values of the parameters derived from the data are γ=35.0±2 mJ/mole-K²; the Debye temperature, θ_D=278±5 K; the energy gap, △, normalized as 2△/kT_c, is 4.9±.3, and the thermodynamic critical field, H_c(0), is 4700±300 Gauss.     

A macrocyclic ligand able to bind gallium(III) by preorganized pendant arms; coordination and kinetic studies

The equilibria and kinetics of the binding of gallium(III) to 4-(N),10-(N)-bis[2-(3-hydroxo-2-oxo-2-H-pyridine-1-y1)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) were investigated in acidic medium at ionic strength 1 M (NaClO4). Spectrophotometric titrations in the UV region revealed that L is able to bind Ga3+ also at high H+ concentration. The kinetic (stopped-flow) experiments are interpreted on the basis of three parallel reaction paths (i) M3+ + H2L2+ = M(H2L)5+ where M(H2L)5+ is in a steady state, (ii) M(OH)2+ + H2L2+ = M(HL)4+ + H2O and (iii) M(OH)2+ + HL+ = ML3+ + H2O. The first-order rate constants for conversion of the outer-sphere into the inner-sphere complexes are similar to those of the Ga(III)/tropolone system which is known to react according to the dissociative Id mechanism and to the relevant rate constants for water exchange at the metal ion. The effects of pH on the UV-Vis absorption, fluorescence emission properties and NMR spectral features on the Ga(III)/L system were also investigated. Spectrophotometric titrations in the UV region reveal that, in acid medium the prevailing species is M(HL)4+ whereas the chelate ML3+ prevails for [H+] < 0.01 M. The results indicate metal coordination at the oxygen atoms of the 3-hydroxo-2-oxopyridine residues.     

Phase diagram of the spin extended model

The quantum phase transition in the ground state of the extended spin S = 1/2 XY model has been studied in detail. Using the exact solution of the model the low temperature thermodynamics, as well as the ground state phase diagram of the model in the presence of applied uniform and/or staggered magnetic field are discussed. Received 29 November 2002 / Received in final form 24 February 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: japa@iph.hepi.edu.ge     

Perturbative Approach to NonrenormalizableTheories

Using a perturbatively nonrenormalizable and non-perturbatively finite example(delta-function-type potential in nonrelativistic quantum mechanics), we illustratethat one can develop a perturbative approach for a nonrenormalizable theory.The key idea is the introduction of an additional expansion parameter whichallows us to eliminate infinities from the perturbative expressions. The generatedperturbative series reproduce the expansion of the exact analytical solution.     

Helium-free operations in mini-TEA CO2 lasers

Summary Large helium-free emissions are obtained in two mini-TEA CO₂ lasers, by using always a corona preionization without additives and with a maximum energy density of 900J/l in the discharge. In general, helium-free emissions are more stable, but the best condition in efficiency, energy and peak power is observed always with a small He content added to the laser mixture.

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Riassunto L'uso di una piú efficiente preionizzazione a corona ha permesso l'operazione di un laser a CO₂ senza elio a pressione atmosferica con elevate densità di energia nella scarica (900 J/l) e grande efficienza di conversione dell'energia elettrica in radiazione laser.