Generalized classical theory of magnetism

We consider an Ising model with Kac potential ^dK(¦x¦) which may have arbitrary sign, and show, following Gates and Penrose, that the free energy in the classical limit0+ can be obtained from a variational principle. When the Fourier transform of the potential has its maximum atp=0 one recovers the usual mean-field theory of magnetism. When the maximum occurs forp ₀0, however, one obtains an oscillatory or helicoidal phase in which the magnetization near the critical point oscillates with period 2/¦p ₀¦. An example with a potential possessing parameter-dependent oscillations is shown to exhibit crossover phenomena and a multicritical Lifshitz point in the classical limit.     

Equilibrium polymerization in a solvent: Solution on the Bethe lattice

The lattice model for equilibrium polymerization in a solvent proposed by Wheeler and Pfeuty is solved exactly on a Bethe lattice (core of a Caylay tree) with general coordination numberq. Earlier mean-field results are reobtained in the limitq, but the phase diagrams show deviations from them for finiteq. Whenq=2, our results turn into the solution of the one-dimensional problem. Although the model is solved directly, without the use of the correspondence between the equilibrium polymerization model and the diluten0 model, we verified that the latter model may also be solved on the Bethe lattice, its solution being identical to the direct solution in all parameter space. As observed in earlier studies of the puren0 vector model, the free energy is not always convex. We obtain the region of negative susceptibility for our solution and compare this result with mean field and renormalization group (-expansion) calculations.     

Exact results for a generalized classicalO(n) matrix spin model

A generalizedO(n) matrix version of the classical Heisenberg model, introduced by Fuller and Lenard as a classical limit of a quantum model, is solved exactly in one dimension. The free energy is analytic and the pair correlation functions decay exponentially for all finite temperatures. It is shown, however, that even for a finite number of spins the model has a phase transition in then limit. The transition features a specific heat jump, zero long-range order at all temperatures, and zero correlation length at the critical point. The Curie-Weiss version of the model is also solved exactly and shown to have standard mean-field type behavior for all finiten and to differ from the one-dimensional results in then limit.     

The spherical-model limit in a random field

The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained.     

Separation behaviors of xylenol isomers by gas chromatography with helps of hydrogen bonding

Summary Xylenol isomers can be resolved on most polyols (sugars or sugar alcohols) and polyethers (polyethylene glycol or polypropylene glycol) with hydrogen-bonding interaction. They are separated on vinical polyols which have more hydroxy hydrogen than tetrol, and even on vicinal triol when its hydroxy hydrogen is acidic (stronger proton donor). The stronger is the hydrogen bonding interaction between xylenols and the liquid phase, the better is the separation of 2,4- and 2,5-xylenol, and the poorer the separation of 2,4-and 2,3-xylenol.     

Volatile phase profiling of mainstream smoke by glass capillary gas-chromatographic techniques

A heated injection system for a microprocessor-controlled GC has been developed for the (GC)² analysis of the volatile phase of whole smoke of a cigarette. Effects of injection port temperature and the presence of a Cambridge filter pad are demonstrated. Chromatograms are shown for smoke samples with and without a Cambridge Filter with the sample valve oven at 25°, 165° and 205°C. The use of a flame ionization and a nitrogen-phosphorous detector is illustrated.     

Physico-Chemistry of the Limestone Sulphation Process

Aspects of the mechanism of the overall reaction between CaCO₃/CaO and SO₂/SO₃ under oxidizing conditions are discussed. The limestone and lime sulphation processes were carried out in a thermobalance under conditions relevant to atmospheric fluidized bed combustion. Sulphated samples, prepared in the form of cross-section particles, were examined in a scanning electron microscope by energy-dispersive X-ray and back-scattered electron imaging. Photomicrographs are presented. The reaction proceeded from the outer surface of the particles and along the pores. Surface textural changes during the reaction were considered. The layer of products was identified as controlling both the rate and extent of limestone/lime sulphation. In the products, two sulphur-bearing solids (CaSO₄ and CaS) were identified. The presence of CaS, which may cause difficulties in practice, is attributed to CaSO₃ disproportionation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanosynthesis of zinc ferrite in hardened steel vials: Influence of ZnO on the appearance of Fe(II)

Nanocrystalline ZnFe₂O₄ spinel powders are synthesized by high-energy ball milling, starting from a powder mixture of hematite (α-Fe₂O₃) and zincite (ZnO). The millings are performed under air using hardened steel vials and balls. X-ray diffraction and Mössbauer spectrometry are used to characterize the powders. A spinel phase begins to appear after 3 h of milling and the synthesis is achieved after 9 h. Phase transformation is accompanied by a contamination due to iron coming from the milling tools. A redox reaction is also observed between Fe(III) and metallic iron during milling, leading to a spinel phase containing some Fe(II). The mechanism for the appearance of this phase is studied: ZnO seems to have a non-negligeable influence on the synthesis, by creating an intermediate wüstite-type phase solid solution with FeO.     

Amorphous phase evolution during crystallization of poly(ethylene-terephthalate)

Crystallization of poly(ethylene terephthalate) from the amorphous state has been studied in the temperature range 90°–120°C to characterize the amorphous phase when crystalline microstructure is developing. Small-angle x-ray scattering, scanning electron microscopy, and density measurements were used to investigate the morphology of semi-crystalline materials. Differential scanning calorimetry and dynamical mechanical spectroscopy experiments were carried out on amorphous, partially crystallized and crystallized specimens and, when structural relaxation is allowed (thermal treatments close to but below glass transition temperature), strong evidence is obtained for the existence of two different amorphous phases with different mobilities.