Study of the mechanism of film condensation of vapor under the influence of surface forces

Measurements are made of local heat-transfer coefficients in the condensation of vapor with allowance for the effect of surface forces on hydrodynamics.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 2, pp. 189–194, August, 1985.     

Construction and design principles for micro-processor-based conductometric analyzers

We consider questions connected with design of microprocessor-based conductometric analyzers and cases of the utilization of microprocessor technology to design automated instruments for analytical control.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 68–70, November, 1994.     

Specific heat at the spin-peierls transition in CuGeO3 under magnetic fields up to 22 tesla

We report on heat capacity measurements of the spin-Peierls compound CuGeO₃ under magnetic fields between 0 and 22 teslas. We have determined the magnetic phase diagram between the three different phases (U=uniform,I=incommensurate,D=dimerised) of this system, unknown up to now forH>14 T, and which can be well interpreted within the Hartree-Fock approximation. We have studied the 2nd order phase transition forH=const. at the crossing ofD-U andI-U phases. The spin-Peierls transition gives rise to a well pronounced specific heat jump. The phase diagram and the specific heat results are discussed in the framework of a B.C.S.-like theoretical model.     

Supercritical fluid extraction of natural antioxidants from rosemary: comparison with liquid solvent sonication

Supercritical fluid extraction (SFE) and liquid solvent sonication, in combination with two different sample treatments, were compared for the extraction of natural antioxidants from rosemary leaves. Dried, ground, and sieved rosemary leaves (20 mg) were subjected to SFE with CO(2) at 355 bar at 100 °C (CO(2) density 0.72 g/mL) for 20 min at a liquid flow rate of 4 mL/min. The analytes were concentrated on an ODS trap and subsequently eluted with acetone. Antioxidants in the SF and liquid solvent extract were analyzed by HPLC. Compounds of known antioxidant activity such as carnosol, carnosic acid, and methyl carnosate were identified by mass spectrometry of the HPLC fractions collected. Freezing and grinding the samples in liquid nitrogen resulted in decreased carnosic acid recoveries. Supercritical CO(2) extraction provided the highest recovery of carnosic acid from rosemary leaves (35.7 mg/g), the lowest relative standard deviation (4.4%), and the cleanest extract [Formula: see text] no cleanup prior to HPLC was required. Among the liquid solvents studies, only acetone provided comparable results (73% recovery relative to SC-CO(2) extraction); however, it required decoloration with active carbon prior to HPLC analysis.     

Isotope Studies of the CMR Compounds La1−xCaxMnO3+δ

Oxygen isotope effect studies of the ferromagnetic Curie temperature T _c of La_1?x Ca _x MnO₃ are presented. The isotope exponent α₀=?ΔlnT _c/Δlnm ₀ changes from 0.4 to 0.14 in the range 0.2<x<0.43. The isotope exponent decreases strongly with increasing tolerance factor, or decreasing lattice distortion. Above Tc the conductivity is characteristic of small polarons. Raman scattering shows a prominent peak at 230 cm?1. The peak width could be related to site-dependent Jahn–Teller distortions above T _c, becoming significantly smaller at and below T _c. IR reflectivity data show a much larger zero frequency IR conductivity than dc conductivity. The IR peaks are independent of temperature between 150 and 295 K.     

A new high-brightness stepped-crystal diffractor for X-ray microanalysis

An electron-probe X-ray microanalyzers, the characteristic X-ray radiation is generated within a small volume of sample and the emitting surface area is on the order of 1 μm². For a distance to analyzer of approximately 0.5 m, this small emitting area can be considered as a point source. Practical implementations of the electron-probe X-ray microanalysis (EPMA) require a high spectral resolution and sufficient intensity.     

High-voltage GaAs diodes with subnanosecond gate voltage recovery

High-voltage GaAs switching diodes with subnanosecond characteristic times of reverse current decay on switching from forward to reverse bias were studied. The diode structures studied had impurity concentration profiles in the base region close to those of the charge-storage diodes and operated in the regimes corresponding to those employed in silicon-based high-voltage fast-recovery drift diodes. The application prospects of the proposed GaAs diodes are demonstrated, for example, in the devices generating pulses with a front width of several hundred picoseconds, a current of several hundred amperes, and a voltage of a several kiloelectronvolts at a frequency of up to several hundred kilohertz.     

Simulation of the Phase of Establishment of the Rheometric Flow of a Viscoelastic Fluid

The flow between two plates in the phase of establishment for the case of a viscoelastic fluid in comparison with a Newtonian fluid is investigated numerically and analytically. The quantitative and qualitative features of the flow are analyzed. It is noted that in a number of cases this flow has wave features, and it is determined that the presence of viscoelasticity usually increases the time of establishment of the flow. It is pointed out that some of the revealed features of the flow can be used in experimental investigations of nonNewtonian fluids.     

High-precision fringe tracking invariant to systematic model errors

We present a new approach to processing of interferometric data, which dramatically improves operation on the smallest fraction of the fringe (approximately 1/1,000 of a wavelength and beyond). In particular, this approach, dubbed the variation-invariant subspace tracking approach (VISTA), makes it possible to operate a Michelson interferometer in a highly stable mode in which the estimation of optical path delay becomes invariant (insensitive) to a large class of systematic model errors. This previously unknown invariance property of interferometry follows from the fundamental odd-even symmetry of the channeled spectrum and its derivatives. VISTA offers a powerful algorithmic alternative for alleviating technological challenges in the design of high-precision long-baseline spaceborne interferometers.