Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Vector-spinor space and field equations

Generalizing the work of Einstein and Mayer, it is assumed that at each point of space-time there exists a vector-spinor space with N_v vector dimensions and N_s spinor dimensions, where N_v=2k and N_s=2 ^k, k3. This space is decomposed into a tangent space with4 vector and4 spinor dimensions and an internal space with N_v–4 vector and N_s–4 spinor dimension. A variational principle leads to field equations for geometric quantities which can be identified with physical fields such as the electromagnetic field, Yang-Mills gauge fields, and wave functions of bosons and fermions.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Structure of the aqueous solvated electron from resonance Raman spectroscopy: lessons from isotopic mixtures

The structure and thermodynamics of the hydrated electron are probed with resonance Raman spectroscopy of isotopic mixtures of H(2)O and D(2)O. The strongly enhanced intramolecular bends of e(-)(H(2)O) and e(-)(D(2)O) produce single downshifted bands, whereas the e(-)(HOD) bend consists of two components: one slightly upshifted from the 1,446 cm(-1) bulk frequency to 1,457 cm(-1) and the other strongly downshifted to approximately 1,396 cm(-1). This 60 cm(-1) split and the 200 (120) cm(-1) downshifts of the OH (OD) stretch frequencies relative to bulk water reveal that the water molecules that are Franck-Condon coupled to the electron are in an asymmetric environment, with one proton forming a strong hydrogen bond to the electron. The downshifted bend and librational frequencies also indicate significantly weakened torsional restoring forces on the water molecules of e(-)(aq), which suggests that the outlying proton is a poor hydrogen bond donor to the surrounding solvent. A 1.6-fold thermodynamic preference of the electron for H(2)O is observed based on the relative intensities of the e(-)(H(2)O) and e(-)(D(2)O) bands in a 50:50 isotopic mixture. This equilibrium isotope effect is consistent with the downshifted vibrational frequencies and a relative reduction of the zero-point energy of H(2)O bound to the electron. Our results enhance the cavity model of the solvated electron and support only those models that contain water monomers as opposed to other molecular species.     

Über halogen- und stickstoffhaltige Derivate aliphatischer Carbonsäuren, 10. Mitt. (Über Reaktionen mit Aluminiumalkylen, 13. Mitt.): Über die Reduktion von tertiären α-Nitrocarbonsäureestern mit LiAlH4, Diisobutylaluminiumhydrid und Diäthylaluminiumhydrid

Zusammenfassung Die Reduktion tertiärer -Nitroester mit LiAlH₄ verläuft anomal. Infolge Abspaltung der Carboxylgruppe sind Aminoalkane Hauptprodukte dieser Reduktion. Daneben entstehen in geringer Menge unter Erhaltung des Kohlenstoffgerüstes -Hydroxylaminoalkohole. Diese Reaktion wird mit der Reduktion von sekundären -Nitroestern und von -Oximinoestern verglichen.Mit Dialkylaluminiumhydriden erleiden die tertiären Nitroester ebenfalls in der Hauptsache Reduktion unter C-C-Spaltung zu Aminoalkanen. Eine Nebenreaktion führt jedoch über die Stufe der Hydroxylaminoalkohole hinaus zu Aminoalkoholen. Außerdem tritt alkylierung am Stickstoffatom zu Alkylaminoalkanen bzw.-alkoholen auf.

---

Halogen and nitrogen containing derivatives of aliphatic carboxylic acids, X (reactions with aluminium alkyls, XIII): Reduction of tertiary -nitro carboxylic acid esters with LiAlH₄, diisobutyl aluminium hydride, and diethyl aluminium hydride

The reduction of tertiary -nitro esters with LiAlH₄ proceeds anomalously. As a result of a decarboxylation amino alkanes are the main products of this reductions. Besides -hydroxylamino alcohols are obtained in small amounts by conservation of the carbon skeleton. This reaction is compared with the reduction of secondary -nitro esters and of -oximino esters.Tertiary -nitro esters are reduced by dialkyl aluminium hydrides to amino alkanes under cleavage of the C-C-bond. In a side-reaction one obtains amino alcohols via the stage of hydroxylamino alcohols. Besides the nitrogen atom is alkylated leading to alkylamino alkanes respectively alkohols.

---

---

9. Mitt.:H. Reinheckel, Mh. Chem.99, 2215 (1968).

---

12. Mitt.:H. Reinheckel undR. Gensike, J. Organometal. Chem.13, 45 (1968).     

Parallel Schwarz alternating methods for anisotropic diffusion of speckled medical images

This paper deals with ultrasound medical image processing, particularly to filter the noise while preserving the edges and structures of information. The mathematical processing consists in solving by a numerical way a nonlinear evolutive boundary value problem. Several numerical semi-implicit time marching schemes are considered and analyzed. At each time step, parallel synchronous or asynchronous Schwarz alternating methods are used to solve the linear system and its convergence is studied. Lastly, the results of sequential and parallel simulations are presented.      

Sequential processes in the14N(τ,pα)12C* reaction

α-particle and proton spectra in coincidence with the 4.44 MeVγ-ray from the¹²C first excited state have been taken atE _τ MeV. Several states in¹³N and¹⁶O are seen to contribute to the decay sequenceα?p andp?α respectively. Estimates are given for the branching of these two decay modes and for a possible simultaneous break-up.     

Classification of Bianchi cosmologies in conformal flat space-times

There exist nine types of Bianchi cosmologies classified according to the structure constants of the corresponding Lie groups. Each of these types gives rise to a particular form of the line element, the Friedmann universe corresponding to the simplest type I. It is also known that there exists a simple correspondence (transformation) between the Robertson-Walker line element and the conformal line element but restricting the arbitrary function of that line element. This suggests that a classification of conformai flat line elements according to their parameters should yield a classification similar to that of Bianchi. The conformal group has 15 parameters, corresponding to the pure conformal group, Lorentz group, translation, and dilation. A classification of the line element according to these has been carried out, singly and combining several of them. It has been found that the Friedmann universe is a subclass, as expected, with other cosmologies resulting as wider subclasses. Comparison with the Bianchi classification is also made.