Thermal degradation of polyimides—II: Mechanism of carbon dioxide formation during thermal degradation

Thermal degradation of polyimides was investigated using a selected polymer and a simple low molecular model viz. phthalimide. Based on the analysis of the degradation products, a mechanism for CO₂ formation was proposed; it could be adapted to explain the thermal degradation processes for polyimides.     

Application of a simple peak shape function for the evaluation of gamma and X-ray spectra

The computational method for the rapid evaluation of gamma and X-ray spectra observed by semiconductor detectors in radiometric analysis in presented using a simple peak shape function. The computer programme includes a minimizing routine based on the modified Newton-Raphson method giving a minimized vector of the parameters more rapidly than the conventional approach. The spectra of some gamma-ray emitting fission products and X-ray spectra excited by radioisotopes of materials from copper ore processing were studied. It was found that the simple Gaussian peak function gives the results equivalent to the total peak area method.     

High-repetition-rate, intracavity-pumped KTP OPO at 1572 nm

An efficient, eye-safe, high-repetition-rate, intracavity optical parametric oscillator (IOPO) inside an acousto-optically Q-switched Nd:YVO₄ laser end pumped by a 30-W fiber-coupled diode laser was demonstrated. The pumping, acousto-optically Q-switched Nd:YVO₄ laser gives 3-W average output power at 1064-nm wavelength at 40-kHz repetition rate. An additional separating mirror, x-cut KTP crystal and output coupler highly reflective at 1064-nm and partially transparent at 1572-nm wavelengths form a flat–flat IOPO resonator of 35-mm length. We have achieved 3-ns-duration pulses for 20-mm-long KTP and 4-ns-duration pulses for 30-mm-long KTP, respectively. More than 8-kW-peak-power pulses with an average power of 1.5 W at the signal wavelength for 40-kHz repetition rate were demonstrated. Due to the intracavity spatial cleaning effect, a near diffraction limited signal beam was achieved despite a relatively worse beam quality of the pumping beam. Conversion efficiencies of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved. PACS 42.55.Xi; 42.60.Gd; 42.65.Yj     

Studies on some microbiological and chemical aspects of irradiated vanilla beans

Vanilla bean is a valuable food additive used in many branches of food industry as a source of natural vanillin. The influence of⁶⁰Co -radiation in the dose range of 5–50 kGy has been investigated on: (1) the survival of contaminating microflora, and (2) more important vanilla constituents like vanillin and sugars. It has been found that the main vanilla contamination is connected with mesophylic microorganisms in the amount of 8.4·10⁴/g. The dose of 15 kGy is sufficient for decontamination of commercial raw material. The samples under investigation on account of sensory properties and chemical composition were in agreement with country regulations. Doses up to 50 kGy do not cause undesirable changes in the content of sugars and vanillin, which has been confirmed by studies on model compounds.     

Cellular Response after Stimulation of the Gelatin-Alginate Matrixes

Summary: In the study the evaluation of the influence of gelatin-alginate matrixes on cells of Jurkat, A549 and Hurvec lines in in vitro tests was presented. Cellular cultures in the presence of the evaluated matrixes did not change their morphotic features and their count and proliferation. Gelatin-alginate matrixes in the form of sponges do not have anty cytotoxicy.     

Supports of semi-stable probability measures on locally convex spaces

LetE be a locally convex space. Let be an absolutely convexly tight Radom semi-stable probability measure onE with index 1<2 and Lévy measureM. The main result of this paper shows that the closed semigroup generated by the support ofM and the negative of the barycenter ofM restricted to a suitable compact subset ofE is a (closed) linear space ofE, and that the support of is a suitable translate of this linear space. This result complements a few known results concerning the supports of stable and semi-stable probability measures. In particular, it extends an analogous result proved recently for the support of -stable probability measures 1<2 (Ref. 4). Related results concerning the support of Radon semi-stable probability measures onE of index 0<<1 are also discussed.The research of this author was partially supported by AFSOR Grant No. 90-0168The research of this author was supported by KBN Grant, and the University of Tennessee Science Alliance, a State of Tennessee Center of Excellence.     

New antiferroelectric liquid crystal for use in LCD

In this work, the physical properties of newly synthesized liquid crystalline compound exhibiting two liquid crystalline phases (ferroelectric and antiferroelectric) were studied. Based on the results of differential scanning calorimetry, polarizing microscopy, and photoelastic modulator methods, the temperature dependences of spontaneous polarization, tilt angle, switching time, and birefringence in the ferroelectric, as well as antiferroelectric phases were determined. Furthermore, the influence of the external electric field on the liquid crystalline textures was studied and the phase sequences at heating and cooling were revealed. The temperature dependence of spontaneous polarization was analysed by means of Landau mean-field theory, and the critical parameter β obtained for ferroelectric liquid crystalline and isotropic liquid transition was 0.21 which is close to 0.25, the value characteristic for tri-critical point.     

The influence of random changes in the adsorbing potential on phase transitions in a Lennard-Jones fluid confined to energetically heterogeneous slit-like pores

A density functional approach is used to study the adsorption and phase behaviour of a Lennard-Jones (LJ) fluid in slit-like pores with energetically heterogeneous walls, investigating how the randomly varying part of the fluid-solid potential imposed on a periodic ‘back-ground’ potential modifies the phase behaviour of the confined fluid. Non-local density functional theory is employed to describe the system. To study the system with a random external field, the method used is based on investigations of several replicas of the system and on averaging the final thermodynamic results over the replicas.     

Atom and Ion Temperatures in a Hollow Cathode Discharge

Abstract

The excitation temperatures of atoms and ions /Ar I, Ar II, V I, V II, Cr I, Cr II, Cu I, and Si I/ have been measured in the hollow cathode discharge. The Ar I high energy levels have been found to be overpopulated. The electron density has been estimated. The ionization-excitation mechanism has been discussed.     

Gamow-Teller strength distribution in the beta-decay of100Ag from total-absorption gamma spectrometry

The EC/β⁺-decay of the odd-odd nucleus¹⁰⁰Ag was studied by means of total absorptionγ-ray spectrometry. Most of the Gamow-Teller strength was found to be concentrated at an excitation energy of 5.6 MeV in¹⁰⁰Pd, the FWHM of this resonance being 1.5 MeV. The measured strength distribution which is interpreted within the BCS approximation as being due to the dominant population of four-quasiparticle excitations, resembles the distribution predicted by an advanced shell-model calculation for the⁹⁸Ag →⁹⁸Cd decay.