On the permanence of the null character of Maxwell fields

A critical review of known results about the permanence conditions for the null character of the solutions to the (vacuum) Maxwell equations, is presented. Concomitants of the electromagnetic field and the metric tensor are constructed, which give the principal directions of the field in covariant form. The known permanence conditions are generalized in order to includeall the (local) null fields; the above concomitants allow these conditions to be explicitly formulated in terms of the electromagnetic field.Supported in part by Conselleria de Cultura, Educació i Ciència de la Generalitat Valenciana.     

Studies in\bar p p annihilation

Evidence is presented that \(\bar p\) p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the \(\bar p\) p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the \(\bar p\) p experiments at the highest available energies.     

Vapor-particle partitioning of hydrocarbons in Western Mediterranean urban and marine atmospheres

An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon.     

Substituted m-phenylene bridges as strong ferromagnetic couplers for Cu(II)-bridge-Cu(II) magnetic interactions: new perspectives

Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized.     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Second Dissociation Constants of 4-[N-morpholino]butanesulfonic Acid and N-[2-hydroxyethyl]piperazine-N′-4-butanesulfonic Acid from 5 to 55°C

The values of the second dissociation constant, pK ₂, for the dissociation of the NH⁺ charge center of the zwitterionic buffer compounds 4-(N-morpholino)butanesulfonic acid (MOBS), and N-(2-hydroxyethyl)piperazine-N-4-butanesulfonic acid (HEPBS) have been determined from 5 to 55°C, including, 37°C at intervals of 5°C. The electromotive-force (emf) measurements have been made utilizing hydrogen electrodes and silver–silver chloride electrodes. The value of pK ₂ for MOBS was found to be 7.702 ± 0.0005, and 8.284 ± 0.0004 for HEPBS, at 25°C, respectively. The related thermodynamic quantities, G ^o, H ^o, S ^o, and C _p ^o for the dissociation processes of MOBS and HEPBS have been derived from the temperature coefficients of pK ₂. Both the MOBS and HEPBS buffer materials are useful as primary pH standards for the control of pH 7.3 to 8.6 in the region close to that of physiological fluids.     

Coalescence in three-phase fluid systems

Summary The gravity coalescence of drops at flat fluid/liquid interfaces was studied in three-phase systems. Rest-time distributions were in qualitative agreement with the earlier theory of Charles and Mason for two-phase systems. The probability of coalescence increased inversely with the square of intervening film thickness. Partial coalescence was similar to that previously observed in two-phase systems. The viscosity of the drop affected the mechanism of coalescence more than the viscosities of the other phases.

---

Zusammenfassung Es wurde die Koaleszenz von Tropfen an ebenen Flüssigkeits-Flüssigkeitsgrenzfl?chen in Dreiphasensystemen untersucht. Die beobachtete Verteilung der Verweilzeiten ist in qualitativer übereinstimmung mit der Theorie von Charles und Mason für Zweiphasensysteme. Die Wahrscheinlichkeit dafür, da? Koaleszenz auftritt, nimmt umgekehrt proportional mit dem Quadrat der Filmdicke zwischen Tropfen und Phasengrenze zu. Die partielle Koaleszenz war ?hnlich, wie sie früher in Zweiphasensystemen beobachtet worden war. Die Viskosit?t des Tropfens beeinflu?t den Mechanismus der Koaleszenz mehr als die Viskosit?t der anderen Phasen.

---

     

The viscoelasticity and structure of fibrous proteins

Summary DynamicYoung's moduli of wool fibres in water have been measured over a range of two decades in rate of extension and at temperatures from 0 to 90 C. Small displacements were used, corresponding to extensions of 0.1%. These were imposed upon mean extensions of (a) 1%, (b) 15% and (c) 40%, representative of the three main extension regions of-keratin. The results obtained show great differences from the slopes of the corresponding regions of the force-extension curve carried out at the same temperature and rate of extension.Comparison of the small-strain dynamic moduli in the three regions (a), (b) and (c) indicate that there is a component of the modulus in (a) amounting to 1.3×10¹⁰ dynes/cm² which is associated with intact-helical filaments, and which is substantially constant up to at least 70 C.Approximate superposition of the dynamic moduli at different rates was achieved using theWilliams-Landel-Ferry (WFL) equation with a reference temperature of 35 C. It is thereby concluded that under the present conditions-keratin has an effective glasstransition in the vicinity of –15 C. Above 60–70 C the WLF relation was not obeyed, indicating the presence of a relaxing process with a different temperature-dependence from that of the normal viscoelastic mechanisms; it is suggested that this process may consist in the fission and re-formation of cystine groups.

---

Zusammenfassung Die dynamischenYoung-Moduln von Wollfasern in Wasser wurden über einen Bereich von zwei Dekaden der Streckgeschwindigkeit und Temperaturen zwischen 0 und 90 gemessen. Die maximal verwendeten Auslenkungen entsprechen einer Ausdehnung von 0,1%. Diese wurden den mittleren Dehnungen von (a) 1%, (b) 15% und (c) 40% überlagert entsprechend den drei Hauptbereichen der Dehnung von-Keratin. Die erhaltenen Ergebnisse zeigen gro\e Differenzen für die Steigungen der entsprechenden Bereiche Kraft-Dehnungs-Diagramm für gleiche Temperaturen und gleiche Dehnungsgeschwindigkeit.Ein Vergleich der Dehn-Moduln für kleine Dehnungen in den drei Bereichen (a), (b) und (c) zeigen, da\ in (a) eine Komponente des Moduls von etwa 1,3×10¹⁰dyn/ cm² enthalten ist, verbunden mit den intakten-Helices der Moleküle. Und diese bleiben im wesentlichen unverändert bis zu Temperaturen von wenigstens 70 C.Näherungsweise Superposition der dynamischen Moduln bei verschiedenen Dehngeschwindigkeiten konnte mit Hilfe derWilliams-Landel-Ferry (WLF)-Gleichung hinsichtlich einer Referenz-Temperatur von 35 C erreicht werden. Hieraus folgt, da\ unter den angewandten Bedingungen das-Keratin eine effektive Glasübergangstemperatur in der Nachbarschaft von –15C besitzt. Oberhalb von 60 bis 70 C wird die WLP-Gleichung nicht befolgt. Das zeigt die Mitwirkung von Relaxations-Prozessen mit einer unterschiedlichen Temperatur-Abhängigkeit von der der normalen viscoelastischen Mechanismen an. Es ist zu vermuten, da\ dieser Proze\ auf der Aufspaltung und Wiederbildung von Cystin-Gruppen beruht.