Magnetostatic analog of Love surface elastic waves

The possibility of the existence of a magnetostatic analog of Love surface elastic waves is predicted. They appear in situations where the conditions for the existence of magnetostatic volume waves hold in the upper layer of a ferromagnetic bilayer, but not in the lower layer. Zh. Tekh. Fiz. 68, 85–90 (October 1998)     

The zeta function of a simplicial complex

Given a simplicial complex δ on vertices {1, …,n} and a fieldF we consider the subvariety of projective (n−1)-space overF consisting of points whose homogeneous coordinates have support in δ. We give a simple rational expression for the zeta function of this singular projective variety overF _q and show a close connection with the Betti numbers of the corresponding variety over ℂ. This connection is particularly simple in the case when Δ is Cohen-Macaulay.     

Differentiation between acutely ischemic myocardium and zones of completed infarction in dogs on the basis of frequency-dependent backscatter

The goal of this work was to determine whether the frequency dependence of apparent backscatter coefficient (not corrected for attenuation within the myocardium) could differentiate completed, remote infarction from acute myocardial injury in vivo. Myocardial infarcts were produced in six dogs by coronary artery occlusion. One to 12 months later, acute ischemic injury was induced in each dog by ligation of a coronary artery that supplied a region of myocardium adjacent to the established infarct. Infarct, ischemic, and normal regions were interrogated with a 5-MHz, circular, 0.5-in. diam, broadband, focused, piezoelectric transducer mounted in a water-filled stand-off device placed against the exposed, beating heart. Apparent backscatter coefficients were measured over the range of frequencies from 3-7 MHz. The frequency dependence was obtained from the slope of log apparent backscatter coefficient versus log frequency. No significant difference in frequency dependence was found between normal and acutely ischemic myocardium for periods of up to 2 h of ischemia. In contrast, frequency dependence in regions of remote infarct (1.8 +/- 0.1, mean +/- standard error) was significantly lower than that in acutely ischemic or nonischemic regions (2.3 +/- 0.1) (p less than 0.01). These results suggest that remote myocardial infarction can be differentiated from acutely injured but still potentially salvageable myocardium in vivo on the basis of the frequency dependence of backscatter.     

Positron-lifetime study of vacancy annealing in neutron-irradiated GaAs

Positron-lifetime measurements have been used to study the annealing of vacancies in neutron-irradiated GaAs. The vacancies which are interpreted as defects in the Ga sublattice disappear in a single annealing stage (at 500°C in GaAs doped with Si or Zn, and at 600°C in Cr-doped GaAs).     

Existence of fixed points for mappings of finite sets

We show that the existence theorem for zeros of a vector field (fixed points of a mapping) holds in the case of a “convex” finite set X and a “continuous” vector field (a self-mapping) directed inwards into the convex hull co X of X. The main goal is to give correct definitions of the notions of “continuity” and “convexity”. We formalize both these notions using a reflexive and symmetric binary relation on X, i.e., using a proximity relation. Continuity (we shall say smoothness) is formulated with respect to any proximity relation, and an additional requirement on the proximity (we shall call it the acyclicity condition) transforms X into a “convex” set. If these two requirements are satisfied, then the vector field has a zero (i.e., a fixed point).     

Mössbauer study on LiFePO4 cathode material for lithium ion batteries

Crystalline LiFePO₄ has been synthesized using solid-state, spray pyrolysis, and wet chemical methods. The crystal parameters were obtained from Rietveld’s refinement methods of the X-ray diffraction patterns. A detailed investigation of the Fe valency carried out using Mössbauer spectroscopy at room temperature indicates that Fe is predominantly present in its bivalent state.     

Dielectric relaxation and aging effect in interpenetrating network polymers of poly(urethane)-poly(methyl methacrylate)

The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol-1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 10⁵ Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, α_pu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature-frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)-PMMA causes its γ process to become indiscernible and the α_pu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided.     

Isobar separation at FRS-ESR – a development towards pure isomeric stored beams

One important goal of the ILIMA project at FAIR is the study of masses and decay properties of relativistic isomeric beams stored and cooled in the planned storage-ring complex. A new scheme is described, where a storage-cooler ring is used for high-resolution mass separation. Experimental results on the separation of the isobaric pair ¹⁴⁰Pr-¹⁴⁰Ce are presented. P. Beller, deceased.     

The shear modulus in the fiber direction of unidirectional fiber composites based on the concept of mesophase

A new and accurate relationship for the shear modulus in the fiber direction of unidirectional fiber composites is derived, based on the Kerner model concepts but not using its approximate relationships. Furthermore, this model is extended by taking into account the mesophase between the fiber and the matrix accomodating smoothly the mechanical properties between neighbouring phases. The introduction of the mesophase results in an improvement of the theoretical predictions, which now approach close to experimental values for the moduli of different fibrous composites.     

Analysis of the characteristics of a two-fiber sensor for monitorship of a turbid medium

Summary Certain characteristics of a two-fiber sensor device, of the type proposed by Papaet al. for sea water turbidity monitorship, are examined. The extension of medium from which most of the received backscattered power originates is investigated, together with possible effects of multiple scattering on the received power. Laboratory measurements testing the results of the analysis are reported.

---

Riassunto Sono esaminate alcune caratteristiche di un sensore a due fibre, del tipo di quello proposto da Papaet al. per il monitoraggio della torbidità dell'acqua di mare. è stata studiata l'estensione della zona del mezzo da cui proviene la maggior parte della radiazione retrodiffusa ricevuta. Sono stati considerati effetti di diffusione multipla. I risultati dell'analisi sono stati controllati con misure in laboratorio.

---

Резюме Исследуются некоторые характеристики дву-qh-нитевого датчика, предложенного Папа и др. для мониторирования мутности морской воды. Исследуется расширение зоны в среде, из которой формируется основная часть рассеянного назад излучения. Также рассматриваются эффекты многократного рассеяния. На основе лабораторных измерений проводится проверка результатов анализа.