Liquid crystal proton N.M.R. spectral analysis by numerical calculation

We offer an approximate method with which to calculate proton N.M.R. spectra generally caused by dipole-dipole interactions. The method consists of subdividing the spin system of the liquid crystal molecule into interacting blocks. The spectrum of each block is calculated exactly. The interaction between spins of different blocks is calculated approximately. The method is compared with the known methods using 4-n-pentyl-d₁₁-4'-cyanobiphenyl (5CB-d₁₁) and 4,4'-dimeth-oxyazoxybenzene (PAA) as examples.     

Effectiveness of NQR signal detection in noise in multiple-pulse sequences

A technique for signal processing in multiple-pulse experiments is examined. Results are obtained which permit selection of the NQR-signal parameters for its detection in a noise background and optimization of the signal processing parameters, in particular, minimization of the experiment time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 46–50, January, 1989.     

Electroluminescent characteristics of InGaAsSb/GaAlAsSb heterostructure Mid-IR LEDs at high temperatures

The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 10³/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hν _max = 0.693 − 4.497 × 10⁻⁴ T). Based on the dependence E _g = hν _max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In_0.055Ga_0.945AsSb active area, E _g ≅ 0.817 − 4.951 × 10⁻⁴ T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R ₀ ≅ 5.52 × 10⁻²exp(0.672/2kT), while cutoff voltage U _cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U _cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout the temperature interval.     

Random sets. A survey of results and applications

A survey of current directions in the theory of random closed sets is presented; these include: the central limit theorem, the law of large numbers for Minkowski sums and unions of random sets, semi-Markov random closed sets, Boolean models and statistical estimation of their parameters, specification of distributions and associated problems of capacity theory. Weak convergence of random closed sets is defined and its application to limit theorems for graphs and epi-graphs of random processes and problems of stochastic optimization is described. Other connections with the theory of random processes (level sets, multivalued and controllable random processes) are also discussed.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 12, pp. 1587–1599, December, 1991.     

Optical Negasensors and Prospects of Their Applications

The basic types of optical negasensors - sensors based on the application of negative resistance, negative inductance andnegative capacitance, R, L, C-negatrons are presented. It is shown, that application of negative inductance andcapacitance is not connected with stability decreasing as at application of negative resistance and allows to risesensitivity of a optical sensor theoretically ad infinitum. The example design of multielement optical negasensor forairborne, underwater or biomedical imaging is given.     

Anderson Parabolic Model for a Quasi-Stationary Medium

We study the Anderson Parabolic Model for a random medium which is a product of an i.i.d. space-like random field and a white noise. The model has long range space-time correlations and is intermediate between the stationary case and the “turbulent” one, which were studied in previous works. Under some natural assumptions on the distribution of the space potential, we prove existence and uniqueness, and derive the long time asymptotics for the annealed moments, and the “semi-annealed” ones, for which expectation is taken only w.r.t. the white noise. A conjecture for the fully quenched case is discussed on a simplified model. C. Boldrighini and A. Pellegrinotti are partially supported by INdAM (GNFM) and MURST research founds.     

Limiting eigenvalue distribution for band random matrices

Physicotechnical Institute of Low Temperatures, Ukrainian Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 90, No. 2, pp. 163–178, February, 1992.