Double quantum transitions in paramagnetic resonance

The theory of double quantum transitions of the M=±2 type, with regard to inhomogeneously broadened spin systems is studied in this paper with the approximation ²T₂T₃ 1. We suppose that the inhomogeneous broadening is formed by an inhomogeneous crystal field. The obtained results describe the magnitude of absorption as a function of the h.f. power and also describe the shape of the absorption curve. It is demonstrated that in inhomogeneously broadened spin systems the absorption curve of double quantum transitions has the form of the difference of two different Lorentz's curves and that at the saturation ( ²T₂T₁ 1) the absorption increases with the cube of the h.f. field intensity. The shape of the curves is expressed by means of phenomenological relaxation constants of the system.

---

M=±2 ²T₂T₃ 1. , - . . , ( ²T₂T₁ 1) . .

     

The influence of the spectral asymmetry of X-ray emission lines on the results of studying defects in crystals by X-rays of different wavelength

Since the asymmetry of X-ray emission lines was found to influence the exact measurements of lattice parameters of powdered samples the author has revised the results she once obtained when carrying out exact measurements of the lattice parameter with radiations of various wavelengths for tungsten crystals containing admixtures of different elements. It is shown that with samples having an inhomogeneous distribution of the admixtures in the crystals the typical graphs of lattice parameter found originally remain when respecting the influence of the spectral asymmetry. On the other hand, with a sintered sample which has been homogeneized by long annealing the introduction of corrections to spectral asymmetry leads to an adjustment of the differences measured originally, for which it was difficult to find a probable explanation.

---

, . , , . , , , , , , .

     

Influence of Hydrothermal Temperature on Structures and Photovoltaic Properties of SnO2 Nanoparticles

Two SnO₂ nanoparticles were synthesized by hydrothermal method at 170°C and 180°C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180°C has more surface electronic states at 0.3eV below the conduction band than the one synthesized at 170°C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO² nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500°C for 2h, the diameter of the nanoparticle synthesized at 180°C increased to 23nm and that of the nanoparticle synthesized at 170°C increased to 32nm as calculated from X-ray diffraction pattern.     

Logically independent von Neumann lattices

Three definitions of logical independence of two von Neumann latticesP₁,P₂ of two sub-von Neumann algebras ₁, ₂ of a von Neumann algebra are given and the relations of the definitions clarified. It is shown that under weak assumptions the following notion, called logical independence is the strongest:A B 0 for any 0 A P₁, 0 B P₂. Propositions relating logical independence ofP₁,P₂ toC ^*-independence,W ^* independence, and strict locality of ₁, ₂ are presented.     

Iron Nanoparticles in Severe-plastic-deformed Copper

Superparamagnetic iron nanoparticles with a size of a few nanometers were produced in copper by severe plastic deformation. In a isochronal annealing experiment near a temperature of 450K, which corresponds to the temperature of structural relaxation and the first step of grain growth (from 128 to 150nm) of submicrocrystalline copper, an abrupt increase in the magnetic susceptibility is detected. This increase is shown to be due to iron nanoparticles increasing in size from 2.8 to 3.3nm. The vanishing of the ferromagnetic contribution by iron nanoparticles observed at 850K, well below the Curie temperature of iron, is due to the dissolution of nanoparticles in plastically deformed copper.     

Hard gamma radiation in the decay of Lu176m

Gamma lines 1·05 MeV(4 × 10^–6 quanta/decay) and 1·14 MeV (9 × 10^–6 quanta/decay), giving evidence of the existence of a new level in Hf¹⁷⁶ with an energy of 1·14 MeV, were found in the decay of Lu^176m with a half-life of 3·7 hours, using the scintillation method. The component of the beta spectrum, exciting this level, has a maximum energy of 0·17 MeV and logft=8·3. The spin of this level proved to be equal to one. The level was interpreted as a single-particle neutron level withn ₀: 5/2^– (512),n ₁: 7/2^– (514);I=1⁺.

---

- Lu^176m

Lu^176m 3,7 - 1,05 MeV (4.10^–6 /) 1,14 MeV (9.10^–6 / /), Hf¹⁷⁶ 1,14 MeV. -, , 0,17 MeV logft = =8,3. . cn ₀: 5/2^– (512),n ₁: 7/2^– (514);I = 1⁺h

---

---

The authors thank L. K. Peker from the Leningrad State University for a helpful discussion of their results.     

Low-temperature and long-time anomalies of a damped quantum particle

The time evolution of a damped quantum particle is discussed. Dissipation is modeled by the bilinear coupling to a set of harmonic oscillators. Using a functional integral technique that accounts for initial correlations between the particle and the reservoir, one can express the dynamics of the damped particle entirely in terms of equilibrium correlation functions. The long-time behavior of these correlations is determined for memory damping arising from the coupling to a reservoir with spectral densityI() at low frequencies, where > 0. The time evolution of nonequilibrium initial states of the damped particle is discussed. At finite temperatures an initially localized state is found to spread subdiffusively or superdiffusively, depending on . For > 2 the damping becomes ineffective for long times, and the width of a state grows kinematically. At zero temperature and for < 1, an initially localized state remains localized for all times. For 1 the state spreads, but with a slower rate than at finite temperatures. Study of arbitrary initial states indicates that the process is ergodic at finite temperatures only for 2 and at zero temperature for 1 2.     

A realistic many-body approach to the EMC effect

The EMC effect in few nucleon systems and complex nuclei is calculated within a realistic many-body approach. The effect ofQ ²-rescaling is also investigated.Contributed paper to the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia, September 5–10, 1988.     

Twisted Lie Group C*-Algebras as Strict Quantization

A nonzero 2-cocycle Z2(g, R) on the Lie algebra g of a compact Lie group G defines a twisted version of the Lie–Poisson structure on the dual Lie algebra g*, leading to a Poisson algebra C (g*()). Similarly, a multiplier c Z2(G, U(1)) on G which is smooth near the identity defines a twist in the convolution product on G, encoded by the twisted group C-algebra C*(G,c). Further to some superficial yet enlightening analogies between C (g*()) and C*(G,c), it is shown that the latter is a strict quantization of the former, where Plancks constant assumes values in (Z\{0})-1. This means that there exists a continuous field of C*-algebras, indexed by 0 (Z\{0})-1, for which A0= C0(g*) and A=C*(G,c) for 0, along with a cross-section of the field satisfying Diracs condition asymptotically relating the commutator in A to the Poisson bracket on C(g*()). Note that the quantization of does not occur for =0.     

ПРИГОТОВЛЕНИЕ И ХАРА КТЕР ПОВЕРХНОСТИ ПЛАСТИНОК AgBr

AgBr . , .     

Замечание К теории по степенного возникновения подви жных слоев в плазме инертных газов

[1] t _B , t _B . , t _B , . .

---

A note on the theory of the successive production of moving striations in the plasma of inert gases

Approximate expressions are derived on the basis of Pekárek's theoretical paper [1] for the period of the maximum t_B of a wave packet produced by the passage of a wave of stratification before the aperture of a photomultiplier, and for its time width in the half-height t_B. The relaxation time of a wave of stratification, following from the theory [1], can thus be calculated by means of the experimentally measured velocity of motion of the maximum of a wave packet u and its width t_B. The calculation is supplemented by numerical data on the magnitude of errors committed by using approximate expressions.

     

КРУЧЕНИЕ СТЕРЖНЕЙ С С ЕЧЕНИЕМ ФОРМЫ ПРЯМОУГОЛЬНИКА С ВЫР ЕЗОМ

[1] , 1) . [2].

---

Twisting of notched rectangularly-shaped bars

It was pointed out in paper [1] that special cases of this solution are the problems of the torsion of a notched and unnotched rectangularly-shaped bar. Here, some results obtained earlier are generalized and in one concrete case very good agreement is obtained with the results of Sapondjan [2].

     

The Q-switched Nd : YAG and Yb : YAG microchip lasers optimization and comparative analysis

The microchip lasers based on the neodymium or the ytterbium doped yttrium-aluminium garnet crystal and Q-sw itched by the Cr⁴⁺:YAG film are considered. The optimal (maximizing of energy) values of the pumping beam radius, the absorber parameters (the thickness and tetravalent chromium ion concentration), and the output mirror reflectivity are determined. The possibility of higher values of energy in the Yb:YAG laser pulse, in comparison with a more traditional Nd:YAG laser, is also substantiated. PACS 42.60.Gd     

ИЗМЕРЕНИЕ УПРУГОСТИ ПАРОВ НЕКОТОРЫХ ВЫСОКОМОЛ ЕКУЛЯРНЫХ ВЕЩЕСТВ РАДИОМЕТРИЧЕСКИМ МА НОМЕТРОМ С БОЛБШОЙ ЧУВСТВИТЕЛ ЬНОСТЬЮ

- — — - ; napc. - , - , , 9 . - . - 3. 10^–6–1. 10^–6 mmpm. cm.     

Changes in EPR spectrum of free radical species inγ-irradiated polyformaldehyde

We have found that gamma-irradiated polyformaldehyde does not exhibit the effect of the disappearance of the hyperfine structure of EPR spectrum as a function of the dose or the time passed since the end of irradiation, as was found earlier for a group of polymers having only C-C-C-C-atoms in the polymer chain. This difference in the change in the EPR of the polyformaldehyde (PFA) spectrum compared with the polymers with a -C-C-C-C- chain is explained by the impossibility of forming a conjugate double bond in the -C-O-C-O- chain in PFA.

---

, , -, , , atom C-C-C-C-. ( ) C-C-C-C- , C-O-C-O- qu .

---

---

The author thanks K. Vacek for many valuable discussions which helped this work.     

Ferromagnetic resonance in thin cobalt films

The paper gives the results of measuring ferromagnetic resonance on thin cobalt films, vacuum deposited on unheated glass slides. The values of the (g-factor, the width of the curve, the effective stress and uniaxial induced anisotropy were determined as a function of the thickness of the film from measurements of the ferromagnetic absorption in a magnetic field normal and parallel to the surface of the film. Measurements were carried out on a frequency of 9200 MHz and on film thicknesses of 180 to 1800 Å. A qualitative explanation of the observed dependences is given.

---

, . , , g-, , , . 9200 MHz 180–1800 Å. .

---

---

The author thanks V. Kamberský and Z. Málek, C. Sc., for providing some of the cobalt films and for help in depositing and measuring the thicknesses, S. Kadeková and M. Polcarová for valuable advice in determining the structure of the films, J. Míová for carefully plotting the results of measurements and Z. Málek and O. tirand for carefully reading the paper and for valuable discussions.     

ПЛОТНОСТЬ ТОКА В КАТО ДНЫХ ПЯТНАХ В КОНДЕНСИРОВАННОМ Р АЗРЯДЕ

- . , .     

On the critical exponent for random walk intersections

The exponent _d for the probability of nonintersection of two random walks starting at the same point is considered. It is proved that 1/2<₂3/4. Monte Carlo simulations are done to suggest ₂=0.61 and ₃0.29.     

A dynamical phase transition in a caricature of a spin glass

This paper studies the rate of convergence to equilibrium of Glauber dynamics (Gibbs Sampler) for a system ofN Ising spins with random energy (at inverse temperature >0). For each of the 2 ^N spin configurations the energy is drawn independently from the values 0 and-logN with probabilities 1-N ^–7, resp.N ^– (>0), and is kept fixed during the evolution. The main result is an estimate of the coupling time of two Glauber dynamics starting from different configurations and coupled via the same updating noise. AsN the system exhibits two dynamical phase transitions: (1) at =1 the coupling time changes from polynomial (>1) to stretched exponential (<1) inN; (2) if <1, then at = the almost coupling time [i.e., the first time that the two dynamics are within distanceo(N)] changes from polynomial (<) to stretched exponential (>) inN. The techniques used to control the randomness in the coupling are static and dynamic large-deviation estimates and stochastic domination arguments.     

An attempt at a phenomenological interpretation of the influence of a polarizing field on piezoelectric resonators

The change in frequency of quartz piezoelectric resonators in a d-c electric polarizing field cannot be explained merely by a change in the dimensions of the resonator due to the polarizing field caused by the inverse piezoelectric effect and electrostriction. We are forced to admit that the elastic constants also change in a polarizing field. A phenomenological interpretation of the influence of a d-c electric polarizing field on the frequency of quartz resonators is proposed here, based on newly introduced quantities characterizing such a change. In conclusion it is shown in what way the quantities, on which the phenomenological theory is based, can be determined experimentally.

---

, . , . , , . , , .

---

---

The author would like to thank Dr. J. Tichý for carefully reading the paper, for valuable discussion and numerous remarks on style and subject matter, which greatly helped to improve the text. He is also indebted to V. Janovec, C. Sc., for some new aspects and the exceptional interest with which he reviewed the paper.