Pyroelectric effect in lead-magnoniobate-based solid solutions

A coordinated study of the dielectric, electrostriction, and pyroelectric properties of the lead-magnoniobate-based ceramic solid solutions 0.9PbMg_1/3Nb_2/3O₃-0.1PbTiO₃ and 0.55PbMg_1/3Nb_2/3O₃-0.45PbSc_1/2Nb_1/2O₃ conducted at the relaxor transition temperatures is reported. Electromechanical coupling stimulated by the giant electrostriction effect is shown to play an essential part in the pyroelectric effect.     

Simulation of characteristics of optical gas sensors based on diode optopairs operating in the mid-IR spectral range

An analytic model is proposed for an optical gas sensor based on diode optopairs, which takes into account the line spectral structure of gases being analyzed, as well as peculiarities of spectral characteristics of immersion-type light-emitting diodes and photodiodes operating in the mid-IR spectral range. The model makes it possible to calculate the transfer characteristic of the sensor and to estimate the measurement error for gas analyzers operating on the basis of these sensors. The experiments demonstrate bright prospects of application of sensors based on immersion-type diode optopairs in small-size gas analyzers; the expected values of the threshold sensitivity of a CO₂ sensor at a level of 10 ppm and the absolute error of measurements below 0.1% (reduced error is 1%) in a range of up to 10 vol % at a speed of up to 10 counts per second exceed the parameters of available portable CO₂ gas analyzers. The validity of the model is confirmed by conformity between the calculated data and the experimental results obtained on a prototype of a CO₂ diode sensor.     

Spectroscopy of output pressure dependences of water vapor passed through adsorbent

The output concentration pressure dependences of the water vapor passed in portions through a layer of MN-200 adsorbent whose delay and shape drastically depend on the parameters of introduced portions are determined using diode-laser spectroscopy. A model describing the experimental data and demonstrating the important role of interphase mass-exchange lag in the process of water vapor propagation in a porous-granular medium is proposed.     

Diffusion kinetics of water molecules in a nanoporous adsorbent

The diffusion of water vapor into porous polymer adsorbent MN-200 has been investigated by diode laser spectroscopy with a time resolution of 0.1 s. The cascade character of diffusion, caused presumably by the fractality of the porous matrix space, is established by decomposition analysis. The collisionless (Knudsen) mode of water motion in pores, in which water molecules can be sorted according to their spin states, is selected.     

High-Energy Proton-Beam-Induced Polymerization/Oxygenation of Hydroxynaphthalenes on Meteorites and Nitrogen Transfer from Urea: Modeling Insoluble Organic Matter?

Formation and structural modification of oxygenated polycyclic aromatic hydrocarbons (oxyPAHs) by UV irradiation on minerals have recently been proposed as a possible channel of PAH transformation in astrochemical and prebiotic scenarios of possible relevance for the origin of life. Herein, it is demonstrated that high-energy proton-beam irradiation in the presence of various meteorites, including stony iron, achondrite, and chondrite types, promotes the conversion of two representative oxyPAH compounds, 1-naphthol and 1,8-dihydroxynaphthalene, to complex mixtures of oxygenated and oligomeric derivatives. The main identified products include polyhydroxy derivatives, isomeric dimers encompassing benzofuran and benzopyran scaffolds, and, notably, a range of quinones and perylene derivatives. Addition of urea, a prebiotically relevant chemical precursor, expanded the range of identified species to include, among others, quinone diimines. Proton-beam irradiation of oxyPAH modulated by nitrogen-containing compounds such as urea is proposed as a possible contributory mechanism for the formation and processing of insoluble organic matter in meteorites and in prebiotic processes.     

Pyrometer unit for GaAs substrate temperature control in an MBE system

An optical pyrometer designed for precision measurement of the GaAs substrate temperature during MBE growth is considered. The pyrometer can be calibrated against a certain characteristic absolute temperature that is visually determined from a change in the RHEED pattern. This enables one to calculate the absolute temperature of the substrate with regard to its radiant emissivity and minimize the inaccuracy of radiation temperature measurement. The inaccuracy is associated with the deposition of growth products on the pyrometer window.     

Acoustic and magnetic properties of La<Subscript>0.825</Subscript>Sr<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript> lanthanum manganites

This paper reports on measurements of the acoustic, magnetic, and electrical properties and on an x-ray microprobe analysis of a La_0.825Sr_0.175MnO₃ single-crystal sample. The acoustic studies were made with a pulsed acoustic spectrometer operating on a 770-MHz carrier. The studies revealed anomalies in the damping coefficients and sound velocity near 300, 200 K, and the Curie temperature T_C (283 K) where the colossal magnetoresistance occurs. The effect of a magnetic field on the magnetic texture of lanthanum manganites cooled below T_C, observed earlier in samples of other composition, is confirmed. In addition, a region was found wherein the magnetic susceptibility of an unclamped sample behaves anomalously. The electrical resistivity was observed to decrease substantially below T_C; this effect exhibits a hysteretic pattern in the interval 200–180 K.     

On the [28, 7, 12] binary self-complementary codes and their residuals

Recently Jungnickel and Tonchev have shown that there exist at least four inequivalent binary selfcomplementary [28, 7, 12] codes and have asked if there are other [28, 7] codes with weight distributionA ₀=A ₂₈=1,A ₁₂=A ₁₆=63. In the present paper we give a negative answer: these four codes are, up to equivalence, the only codes with the given parameters. Their residuals are also classified.This work has been done during the visit of the author as a guest researcher to the Department of Electrical Engineering at Linköping University, Sweden. The research was partially supported by the Bulgarian National Science Foundation under contracts No. 37/1987 and No. 876/1988.     

High-<Emphasis Type="Italic">Q</Emphasis> surface modes in photonic crystal/iron garnet film heterostructures for sensor applications

A novel type of a plasmonic sensor based on a magnetophotonic plasmonic heterostructure with an ultrahigh-Q resonance is considered. A magnetoplasmonic resonance with an angular width of 0.06°, which corresponds to a Q factor of 700 and is a record value for magnetoplasmonic sensors, is experimentally demonstrated. It is shown that, owing to the excitation of long-propagation-range plasmons, the transverse magneto-optical Kerr effect is considerably enhanced and, thus, the sensitivity of the magnetoplasmonic sensor to variations in the refractive index increases to 18 RIU^–1, where RIU is the refractive index unit. Numerical calculations indicate that the parameters of the magnetoplasmonic structure can be further optimized to attain sensitivities up to 5 × 10³ RIU^–1.     

Deviations from the normal ortho/para ratio for water (3 : 1) in the vapor phase in dynamic sorption

Deviations of the ortho/para ratio from its normal value (3: 1) were observed by spectral selective detection of ortho and para water molecules when water vapor passed through a column with a nanoporous polymeric adsorbent. The effect was suggested to be related to the nonstationary dynamics of sorption, that is, nonequilibrium character of chromatography. In terms of this model, the factor of spin ortho/para selectivity is slow and unequal diffusion of the spin isomers of water molecules inside the adsorbent, a process spurious for ideal equilibrium chromatography. Original Russian Text ? P.O. Kapralov, V.G. Artemov, A.M. Makurenkov, V.I. Tikhonov, A.A. Volkov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 4, pp. 769–775.