EPR Spectra of Cr3+ Ions in Sr3Ga2Ge4O14:Cr Single Crystals

The results of investigations of chromiumdoped Sr₃Ga₂Ge₄O₁₄ single crystals by the EPRspectroscopy method are presented. It is shown that activating chromium ions form Cr³⁺ Ga³⁺ (Ge⁴⁺) substitution centers in the 1aoctahedral positions of the lattice of Sr₃Ga₂Ge₄O₁₄. Depending on the combination of occupation of the 3ftetrahedral positions of the first cationic coordination sphere by Ga³⁺ and Ge⁴⁺ ions, Cr³⁺ centers of two types are formed. Their individual magnetic spectra are characterized by axial and rhombic symmetry. The magnetic multiplicity of the axialsymmetry spectrum is equal to unity. There exist rhombicsymmetry centers of two types differing in the orientation of the principal magnetic axes and the value of the spinHamiltonian parameter E. The magnetic multiplicity of the individual magnetic spectra of rhombic centers of each type is equal to three. The detected EPR spectra of Cr³⁺ ions have been described by the spin Hamiltonian of rhombic symmetry. Its parameters and their spread have been determined.     

Characteristics of Fe2O3 Nanoparticles from Doped Low-pressure H2/O2/Ar Flames

A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe₂O₃) nanoparticles with sizes in the range 7–20nm. The H₂/O₂/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)₅) with concentrations in the range 524–2096ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the - and the -phase of Fe₂O₃. Average particle sizes were measured in the range 7.4–16nm depending on precursor concentration and flame conditions.     

A prepared pattern with wavelength selection in directional solidification

As crystal growth is a vital link in the long chain of processes leading to state-of-the-art technological devices, a great deal is known about patterns formed at the solid-liquid interface of a growing crystal. However, some basic questions are still unanswered concerning macroscopic features exhibited by a moving solid-liquid interface. Even for the first instability, the cellular instability, a unique steady-state wavelength does not emerge from theory. Furthermore, while wavelength selection is observed in many different materials, its origin is still to be discovered. By breaking continuous rotational symmetry of the flat solid-liquid interface about the pulling direction v, we prepared a cellular pattern with a well-defined wavelength by front propagation into the unstable uniform state. The material is succinonitrile and the rectangular interface geometry is formed by loading it into a flat capillary. The capillaries are chosen to provide a sample thicknessy ₀ = 100n , and width 10y ₀ and 20y ₀. We use a high-resolution directional solidification apparatus and grow the crystal from grain-boundary-free seed crystals. Surprisingly, the shape of the groove next to the uniform state is initially well-described by nearly self-similar Gaussians. This suggests that the initial perturbation of the interface is localized to a region /2 around a groove. A pattern with a well-defined wavelength is established when the half-width of the Gaussians ₀16m is small compared to 80m so there is little overlap between a groove and its predecessor or successor. When overlap is significant, the pattern is time-dependent. These results suggest that wavelength selection in this prepared pattern is a consequence of front propagation of a localized perturbation.     

Single fluorescence centers on the tips of crystal needles: First observation and prospects for application in scanning one-atom fluorescence microscopy

A scanning optical fluorescence microscope is suggested, whose active element (needle) is made of a crystal containing impurity ions or color centers subject to excitation by laser radiation. The excitation energy from a single impurity center at the very tip of the needle is transferred by the resonance dipole-dipole exchange mechanism to fluorescence centers on the surface of the sample under study. It is demonstrated that this approach can help attain a nanometer-high spatial resolution at a high sensitivity substantially exceeding in some cases the sensitivity of the standard near-field fluorescence microscopy technique. Various crystals and impurity centers, potentially most suitable for the implementation of the method under consideration, are briefly analyzed. Information is presented on the manufacture of sharp-pointed needles from LiF crystals containing F₂-centers and the first observation of single F₂-centers on their tips by the laser-photoelectron projection microscopy technique, which allows one to speak of the practical creation of the first active elements for the microscope suggested.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Third order nonlinear optical difference frequency generation in KH2PO4, TiO2, LiNbO3, CaCO3, ZnO and CdS

Third-order nonlinear optical susceptibilities of different crystals have been measured relative to LiNbO₃ by observing collinear phase-matched difference frequency generation ₁=2 ₂– ₄. The two incident light waves have been produced by a ruby laser ( ₂, ₂=694.3 nm) and by induced Raman scattering ( ₄, ₄=765.8 nm). With noncollinear phase-matching the number of nonlinear processes and the possibilities to determine nonlinear coefficients is much larger than in the collinear case. Therefore the theory of Raman-type third order interactions has been extended to noncollinear propagation of the interacting waves. The theory has been tested experimentally for CdS.     

Stochastic Schrödinger operators and Jacobi matrices on the strip

We discuss stochastic Schrödinger operators and Jacobi matrices with wave functions, taking values in ^l so there are 2l Lyaponov exponents ₁..._l0 _l+1..._2l =–₁. Our results include the fact that if ₁=0 on a set positive measure, thenV is deterministic and one that says that {E|exactly 2j 's are zero} is the essential support of the a.c. spectrum of multiplicity 2j.Research partially supported by USNSF under grant DMS-8416049     

The hydrodynamic limit of a one-dimensional nearest neighbor gradient system

We study the hydrodynamic behavior of a one-dimensional nearest neighbor gradient system with respect to a positive convex potential . In the hydrodynamic limit the density distribution is shown to evolve according to the nonlinear diffusion equation ,(q)/t= (²/dq²){F([1/₁(q)]), with F= –.     

Magnetic phase transitions in 187-01187-01187-01

We report SR measurements of Pr₂CuO_4– and (Pr_2–xCe_x)CuO_4– single crystals in the temperature range 4.2K300K. Two spin reorientation phase transitions were observed, although neutron scattering experiment could not detect these phase transitions. These allow us to conclude that magnetic moments of the Cu atoms order in an antiferromagnetic noncollinear cross like structure including a hidden canting spin arrangement.     

Quantum field theory and the coloring problem of graphs

The ^k theory is compared with the multilinear theory of scalar fields ₁, ₂, ..., _k having the same mass as that of . In particular, it is shown that Feynman integrals encountered in the ³ theory are not necessarily present also in the _{1 2 3} theory, but they are if they correspond to planar Feynman graphs having no tadpole part. Furthermore, a necessary and sufficient condition for the presence of a ³ Feynman integral in the _{1 2} ² theory is found. Those considerations are applications of graph theory, especially of the coloring problem of graphs, to Feynman graphs.     

The Einstein 3-form Gα and its Equivalent 1-form Lα in Riemann–Cartan Space

We motivate the definition of the Einstein 3-form G by means of the contracted 2nd Bianchi identity. This definition contains the whole curvature 2-form. The L 1-form, defined via G = L ^*( ) ( is the Hodge-star, the coframe), is equivalent to the Einstein 3-form and contains all the information of the curvature 2-form relevant for the definition of the Einstein 3-form. A variational formula of Salgado on quadratic invariants of the L 1-form is discussed, generalized, and put into proper perspective.     

Perturbations of flows on Banach spaces and operator algebras

For automorphism groups of operator algebras we show how properties of the difference _t – ' _t are reflected in relations between the generators , . Indeed for a von Neumann algebraM with separable predual we show that if _t – '_t 0.28 for smallt, then = 0(+)°^-1 where is an inner automorphism ofM and is a bounded derivation ofM. If the difference _t – ' _t =O(t) ast ; 0, then = + and if _t – ' _t 0.28 for allt then =. We prove analogous results for unitary groups on a Hilbert space andC ₀,C ₀ ^* groups on a Banach space.This paper subsumes an earlier work of the same title which appeared as a report from Z.I.F. der Universität BielefeldWith partial support of the U.S. National Science Foundation     

Magnetic susceptibility of layered 2H-WSe2 semiconductors

Magnetic susceptibility and anisotropy in magnetic susceptibility _L are studied in 2H-WSe₂ layered semiconductor crystals over the temperature interval 77–300 K and magnetic fields 1–10 kOe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 20–23, November, 1989.The authors are indebted to L. P. Strakhov for his kind evaluation of the results of the study.     

КОРРЕКЦИОННЫЕ ФАКТО РЫ ПРИ АБСОЛЮТНОЙ ДОЗ ИМЕТРИИ ПЛОСКИХ ИСТОЧНИКОВβ-ИЗЛУЧЕНИЯ С ПОМОЩЬЮ СЧЕТЧИКА ГЕЙГЕРА-МЮЛ ЛЕРА

n n, n , .     

Magnetic charge as a “hidden” gauge symmetry

A theory containing both electric and magnetic charges is formulated using two vectors potentials,A andC . This has the aesthetic advantage of treating electric and magnetic charges both as gauge symmetries, but it has the experimental disadvantage of introducing a second massless gauge boson (the magnetic photon) which is not observed. This problem is dealt with by using the Higgs mechanism to give a mass to one of the gauge bosons while the other remains massless. This effectively hides the magnetic charge, and the symmetry associated with it, when one is at an energy scale far enough removed from the scale of the symmetry breaking.This paper is dedicated to my grandparents Herbert and Anneliese Schmidt.     

Vacuum Einstein spaces with axial symmetry

Four classes of solutions are found to the equations R=–2_{; ;} and g _;=0 in three-dimensional space with metric gdxdx and signature (+ ––), equivalent to the Einstein equations R_ij=0 in a vacuum for the metric . The metric ds² assumes axial symmetry and symmetry with respect to the reflection .Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 9, pp. 43–45, September, 1976.     

Theory of percolation in fluids of long molecules

We use the reference interaction site model (RISM) integral equation theory to study the percolation behavior of fluids composed of long molecules. We examine the roles of hard core size and of length-to-width ratio on the percolation threshold. The critical density _c is a nonmonotonic function of these parameters exhibiting competition of different effects. Comparisons with Monte Carlo calculations of others are reasonably good. For critical exponents, the theory yields =2=2 for molecules of any noninfinite lengthL. WhenL is very large, the theory yields _cL ^–2. These predictions compare favorably with observations of the conductivity for random assemblies of conductive fibers. The threshold region where asymptotic scaling holds requires the correlation length (/ _c ) ^–v to be much larger thanL. Evidently, the range of densities in this region diminishes asL increases, requiring that density deviations from _c be no larger thanL ^–2. Otherwise, crossover behavior will be observed.     

ФОТОЭЛЕКТРИЧЕСКИЕ С ВОЙСТВА АНТИМОНИДА ГАЛЛИЯ

(GaSb), - 120–340 °K. : E₂=(0,773–0,75.10^–6 T ²) ., - .     

О СУЩЕСТВОВАНИИ ОТРИ ЦАТЕЛЬНОГО ЯВЛЕНИЯ БАРКГАУЗЕНА

. . , . , . , . coo , 13. 5. 1954 . - .     

Ensemble and trajectory statistics in a nonlinear partial differential equation

We have examined the influence of parametric noise on the solution behavioru(t, x) of a nonlinear initial value() problem arising in cell kinetics. In terms of ensemble statistics, the eventual limiting solution mean and variance are well-characterized functions of the noise statistics, and and depend on . When noise is continuously present along the trajectory, and are independent of the noise statistics and . However, in their evolution toward and , both _u (t, x) and _u ² (t, x) depend on the noise and.     

Mixing properties,differentiability of the free energy and the central limit theorem for a pure phase in the Ising model at low temperature

For the Ising model with nearest neighbour interaction it is shown that the spin correlations _{A B} - _{A B} decrease exponentially asd(A, B) in a pure phase when the temperature is well belowT _c. This is used to prove that the free energyF(,h) is infinitely differentiable in and has one sided derivatives inh of all orders forh=0. The bounds are also used to prove that the central limit theorem holds for several variables such as e.g. the total energy and the total magnetization of the system, the limit distribution being gaussian with variances determined by the second derivatives ofF(,h).