Donor—acceptor interactions of substituted benzenes with molecular chlorine and carbon disulfide

CNDO molecular orbital calculations have been performed to analyze donor—acceptor interactions between molecular chlorine and benzene, toluene, mesitylene and hexamethylbenzene and the, as yet, unreported chlorine—hexafluorobenzene and carbon disulfide—benzene pairs. The stabilization energy and the dipole moment and its derivative (?p/?R_CICI) calculated for the benzene—chlorine complex are in good agreement with the estimated experimental values. The trends in the experimental stabilization energies and the Cl-Cl vibrational frequencies with increasing methyl substitution appear to be well reproduced by the calculations. The charge transferred from the benzene donor is polarized toward the outer chlorine atom or sulfur atom. For hexafluorobenzene-chlorine the direction of electronic charge polarization is reversed from that of the benzene and methylbenzene complexes. The calculated results are discussed within the framework of Muliiken's simplified resonance theory for complexes.     

FTIR and WAXS analysis of periodate oxycellulose: Evidence for a cluster mechanism of oxidation

Cellulose paper (Whatman no.1, chromatographic grade) was oxidised with 0.1 M sodium metaperiodate at different oxidation levels (0–11 days at room temperature), and analysed with FTIR before and after chemical treatments (reduction, further oxidation, alkaline hydrolysis). The deconvolution of infrared data allowed us to verify that periodate oxidises cellulose in isolated domains, leading to the decrease of crystallinity, in agreement with the results of wide angle X-ray scattering (WAXS). In particular, the alkaline hydrolysis (β-alkoxy fragmentation) followed by mild acid treatment removed the oxidised groups and recovered most of the crystallinity of cellulose, as determined by the FTIR crystallinity index.     

Study of structural transformations of equiatomic compounds of rare earth metals with copper

Electrical resistivity, magnetic susceptibility, X-ray diffraction and differential thermal analysis have been performed over a wide temperature range on binary compounds RCu. Melting points or decomposition temperatures for RCu (R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) phases and a number of FeB-CsCl structural transitions are reported, and heats and entropies of transformation are evaluated. Large hysteresis effects are observed for the structural transformations at different temperatures.In LaCu and CeCu no structural transformation was detected, while TbCu and DyCu failed to reveal any high-temperature thermal effect of transformation. In EuCu a nonreproducible thermal effect was evidenced after thermal cycling.

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Zusammenfassung Messungen der elektrischen Leitfähigkeit und der magnetischen Susceptibilität sowie röntgendiffraktometrische und differentialthermoanalytische Untersuchungen von binären Verbindungen des Typs RCu wurden in einem weiten Temperaturbereich ausgeführt. Schmelzpunkte bzw. Zersetzungstemperaturen von RCu-Phasen (R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb und Dy) und eine anzahl von Phasenübergängen im System FeB-CsCl sind zusammen mit den bestimmten Entropiewerten der Phasenübergänge angegeben. Die Temperaturabhängigkeit der Phasenübergänge weist eine ausgeprägte Hysterese auf. In den Systemen LaCu und CeCu konnten keine Phasenübergänge festgestellt werden, während sich bei TbCu und DyCu kein auf einen Phsenübergang hinweisender thermischer Effekt im Hochtemperaturbereich zeigt. Bei EuCu wurde ein nicht-reproduzierbarer thermischer Effekt nach einem thermischen Kreisprozeß nachgewiesen.

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, , RCu. RCu (=La, , Pr, Nd,Sm, Eu, Gd, Tb Dy) , FeB-CsCl, . . LaCu , TbCu DyCu - . EuCu .

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The authors are grateful to Prof. A. Iandelli for his interest and for helpful discussion.

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This work was supported by the Italian Consiglio Nazionale delle Ricerche.     

Phase stability study of the pseudobinary system Gd2O2CO3–Nd2O2CO3 (420 °C ≤ T ≤ 850 °C, P = 1 atm. CO2)

Hexagonal as well as tetragonal rare earth oxycarbonates can act as hosts for optically active ions; hence, the knowledge of the structural modifications occurring when foreign hosts are inserted into the parent compound is of fundamental importance for the design of new phosphors. In this article, a phase stability study of the pseudobinary system Gd₂O₂CO₃–Nd₂O₂CO₃ at P = 1 atm. CO₂ between 420 and 850 °C is presented, to study the amplitude of the existence fields of the different structures typical of rare earth oxycarbonates. The samples were prepared by thermal decomposition of the corresponding oxalates in CO₂ atmosphere. According to composition and temperature, all the three structural forms reported for oxycarbonates (hexagonal, tetragonal, and monoclinic) have been observed. Above a certain temperature, that depends on composition and increases with Nd amount, all the samples decompose into the corresponding Gd–Nd-mixed oxides and crystallize into one of the three possible structural forms typical of rare earth sesquioxides. Structural refinements performed on the hexagonal oxycarbonates demonstrate that the insertion of Nd³⁺ in Gd₂O₂CO₃ results in a linear increase of the lattice parameters (Vegard’s law) and in a reorganization of the distances between and in the CO ₃ ^2? groups and the (Nd/Gd₂O₂)²⁺ layers.     

Out-of-equilibrium Kondo effect in a mesoscopic device

We study the nonequilibrium regime of the Kondo effect in a quantum dot laterally coupled to a narrow wire. We observe a split Kondo resonance when a finite bias voltage is imposed across the wire. The splitting is attributed to the creation of a double-step Fermi distribution function in the wire. Kondo correlations are strongly suppressed when the voltage across the wire exceeds the Kondo temperature. A perpendicular magnetic field enables us to selectively control the coupling between the dot and the two Fermi seas in the wire. Already at fields of order 0.1 T only the Kondo resonance associated with the strongly coupled reservoir survives.     

Micro-simulation of Markets

This paper attempts to give an integrated presentation of the application of micro-simulation to the study of markets, based on the purchase behaviour of individual consumers. We emphasize the methodological considerations which should govern the use of the approach, and in particular the need for evolutionary model-building; the technical problems which are only rarely specified in the literature; and the need to be eclectic in the selection of sub-model formulations. Case-studies are reported, and information is given on the scale of resources required for such projects. The presentation is backed with full references to relevant published work, to provide a practical aid to workers in the field. Much of the discussion is also relevant to the simulation of social systems other than markets.     

Phase transitions in cellulose solutions. The kinetics of precipitation of cellulose from diluted cadoxen solutions

Solutions of cellulose (degree of polymerization: 296 ± 16) in tris(ethylenediamine)cadmium(II)hydroxide-ethylenediamine-water (cadoxen), 1.015% (weight per volume) were diluted 1:1.5 with water. The ensuing isothermal precipitations were followed dilatometrically at temperatures ranging from 27.50 to 48.45°C. The precipitation data were characterized by a positive temperature coefficient. They generally conformed to a one-dimensional nucleation rate law; the Avrami exponents were close to unity. Alternatively, they fit a first-order reaction rate expression with respect to cellulose concentration. The low crystallinity of the precipitated cellulose leads to the interpretation of the kinetics in terms of the dissociation of a cellulose-cadoxen complex, rather than phase separation, as the rate-determining step. The nucleation rate law suggests a one-dimensional nonrandom cooperative chemical process, while the first-order rate law suggests a random process.     

Spontaneous supersymmetry breaking and superconductivity in a non-relativistic model

The conjecture that supersymmetry breaking implies superconductivity is supported by the analysis of a class of supersymmetric non-relativistic models involving only fermions. Here the investigation is extened to a non-relativistic model involving both fermions and bosons, which in a sense is the non-relativistic version of the Wess-Zumino model. A sufficient condition is established for the validity of the conjecture. This condition can be possibly violated at most in a two-dimensional subspace of the three-dimensional space of the coupling constants.     

Magnetically induced chessboard pattern in the conductance of a Kondo quantum dot

We quantitatively describe the main features of the magnetically induced conductance modulation of a Kondo quantum dot-or chessboard pattern-in terms of a constant-interaction double quantum dot model. We show that the analogy with a double dot holds down to remarkably low magnetic fields. The analysis is extended by full 3D spin density functional calculations. Introducing an effective Kondo coupling parameter, the chessboard pattern is self-consistently computed as a function of magnetic field and electron number, which enables us to explain our experimental data quantitatively.