PAC investigation of77Br→77Se on silicon surfaces

The perturbed-angular correlation (PAC) method has been applied to investigate the sites occupied by isolated⁷⁷Br-atoms on silicon surfaces. The nuclear quadrupole interaction was used to determine the electric field gradients (efg) acting at the 5/2^– state in⁷⁷Se, populated in the⁷⁷Br decay. For the Si(100)2×1 surface two different field gradients have been observed with the parameters _Q1 = 583(5) MHz, ₁ = 0.0(1) and _Q2=543(5) MHz, ₂ = 0.40(3). Typical values for the Si(111)7×7 surface from preliminary data are _Q=548(9) MHz,=0.54(6). These electric field gradients are identified with adsorption sites of the selenium at dangling bonds of the silicon surfaces.     

Fluorescence and Electronic Structure of the Laser Dye DCM in Solutions and in Polymethylmethacrylate

The photophysical properties and polarization of the fluorescence of the laser dye 4-dicyanomethylene-2-methyl-6-(p(dimethylamino)styryl)-4H-pyran (DCM) in solutions of different polarities and in polymethylmethacrylate (PMMA) at 293 and 77 K were investigated by stationary and pulsed fluorescent spectroscopy. Based on the data of polarized fluorescence, an oscillator model has been suggested, according to which the electronic absorption spectrum of DCM in the 240–500-nm range is formed by at least three electron transitions. The quantum yield of fluorescence _f increases linearly with increase in the polarity of a solvent in a toluene dimethylsulfoxide (DMSO) mixture from 0.08 (toluene) to 0.80 (DMSO). An increase of _f to 0.90 was also observed on increase in the rigidity of the medium by freezing a solution of DCM in n-propanol at 77 K or introducing of a dye to the polymeric matrix of PMMA at room temperature ( _f = 0.76). The fluorescence-decay kinetics of DCM in toluene, n-propanol, and PMMA at 293 K follows a biexponential law, whereas in n-hexane and vaseline oil at 293 K and in n-propanol at 77 K it follows a monoexponential law. The mechanisms underlying radiationless deactivation of the electron-excitation energy in solutions and in polymeric media are discussed.     

A solution spectrum of the nonlinear Schrödinger equation. II

It was shown in a previous communication that the nonlinear Schrödinger equation exhibits a spectrum of eigenfunctions of the form = _k,A _k (coshkx) ^–k and = _k B _k (coshkx) ^–k–1sinhkx, and the corresponding eigenvalues of the energy are related to a band structure with a characteristic energy gap as a significant feature. In the present paper, it is shown that a further spectrum exists exhibiting the general structure = _k=0 A _k(cosh kx)^–k–1/2and = _k=0 B_k(cosh kx)^–k–3/2sinhkx and yielding also a band structure. An extension of the solution spectrum to a nonlinear Klein-Gordon equation and a nonlinear Dirac equation does not imply essential difficulties, and the corresponding characteristic band structure has to be related to a mass spectrum.     

Photoluminescence of the n+‐n‐i Submicron Structures of Gallium Arsenide

The special features of the photoluminescence of the n ⁺ni submicron structures of gallium arsenide are investigated. It is found that the character of the dependence of the fluorescence intensity on the thickness of the structure is determined by the relationship between three characteristic lengths: diffusional length, thickness of the n ⁺ layer, and depth of absorption of exciting radiation, whereas the decrease in the mobility of charge carriers in epitaxial layers leads to an increase in the fluorescence intensity of the structure, with exciting radiation being strongly absorbed.     

Spectral-luminescent properties of chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> and malate dehydrogenase complexes

Spectral confirmation of the formation of stable equilibrium complexes (association constant K _as = 210⁶ M^–1) of the Krebs cycle enzyme — malate dehydrogenase (MDH) — and one of the promising photodynamic sensitizers — chlorin e ₆ — have been obtained. It is shown that the incorporation of dye molecules into the protein globule of dimeric MDH (each subunit of which contains 4 tryptophan amino acid residues, each binding one molecule of chlorin e ₆) is accompanied by quenching of the tryptophan fluorescence of the enzyme. However, despite the overlapping of the fluorescence spectra of tryptophanyls of MDH and the absorption spectrum of chlorin e ₆, the fluorescence quenching observed is not caused by singlet-singlet inductive-resonant transfer of energy from the donor to the acceptor. The conclusion has been drawn that the reason for the absence of energy transfer from tryptophanyls to the dye is the more effective intertryptophan migration of energy to one of the most longwave amino acid residues, the quenching of the luminescence of which occurs due to the reversible photoinduced transfer of an electron to chlorin e ₆ (formation of a complex with charge transfer). The formation of a complex with charge transfer between chlorin e ₆ (when it is excited) and one of the amino acid residues of the enzyme that contact with the dye at its binding site on the protein molecule is also the most noncontradictory explanation of the observed (when bound with MDH) decrease in the quantum yield of fluorescence of chlorin e ₆ upon increase in the duration of its quenching. The question of the ability of MDH to act as one of the most sensitive targets responsible for the disturbance of mitochondrial functions and initiation of the apoptosis of tumor cells in the process of photodynamic therapy is discussed.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 749–758, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Quasi-classical limit of BKP hierarchy andW-infinity symmetries

Previous results on quasi-classical limit of the KP and Toda hierarchies are now extended to the BKP hierarchy. Basic tools such as the Lax representation, the Baker-Akhiezer function and the tau function are reformulated so as to fit into the analysis of quasi-classical limit. Two subalgebrasW ₁ ^B ₊ andw ₁ ^B ₊ of theW-infinity algebrasW _{1 +} andw _{1 +} are introduced as fundamental Lie algebras of the BKP hierarchy and its quasi-classical limit, the dispersionless BKP hierarchy. The quantumW-infinity algebraW ₁ ^B ₊ emerges in symmetries of the BKP hierarchy. In quasi-classical limit, theseW ₁ ^B ₊ symmetries are shown to be contracted intow ₁ ^B ₊ symmetries of the dispersionless BKP hierarchy.     

Rapid Antibiotic Susceptibility Determination for <Emphasis Type="Italic">Yersinia pestis</Emphasis> Using Flow Cytometry Spectral Intensity Ratio (SIR) Fluorescence Analysis

Rapid antimicrobial susceptibility tests (ASTs) are essential tool for proper treatment of patients infected by Yersinia pestis (Y. pestis), the causative agent of plague, or for post-exposure prophylaxis of a population exposed to a naturally acquired or deliberately prepared resistant variant. The standard AST of Y. pestis is based on bacterial growth and requires 24–48 h of incubation in addition to the time required for prior isolation of a bacterial culture from the clinical or environmental sample, which may take an additional 24–48 h. In this study, we present a new and rapid AST method based on a fluorescence determination of the minimum inhibitory concentration (MIC). Our method includes the incubation of bacteria with an antibiotic, followed by staining of the bacteria with oxonol dye (SynaptoGreen C4/FM1–43), which enables the rapid detection of an antibiotic’s effect on bacterial viability. We show that stained, non-viable bacteria exhibit a spectral redshift and an increase in fluorescence intensity compared to intact control bacteria. Based on these criteria, we developed a rapid flow cytometer measurement procedure and a unique spectral intensity ratio (SIR) analysis that enables determination of antibiotic susceptibility for Y. pestis within 6 h instead of the 24 to 48 h required for the standard AST. This new rapid determination of antibiotic susceptibility could be crucial for reducing mortality and preventing the spread of disease.     

The relativistic polaron without cutoffs

The (non-Lorentz covariant) system consisting of a relativistic scalar Boson field interacting with a single spinless particle (relativistic polaron) with kinetic energy function (m ²+|p|²)^1/2 is studied ind space demensions, whered3. The interaction Hamiltonian is taken to be (x)* (x) (x)dx where has a momentum cutoff. The physical one polaron Hilbert space _ph for this model, corresponding to no cutoff on , is constructed. The total renormalized HamiltonianH without cutoff is constructed as a semibounded self-adjoint operator on _pH . The time zero physical Boson field is also constructed. First order estimates are established for the local (in momentum space) number operators in terms ofH.This research was partially supported by N.S.F. grants GP 28109 and GP 28443 and U.S.A.F. grant AF-AFOSR 743-67.     

Observation of laser-induced off-resonance intermolecular electronic energy transfer

We report the observation of off-resonance electronic energy transfer from an excited rhodamine 6G molecule to an azulene molecule in solution. The process requires the coupling of the radiation field in the transfer process. We demonstrate that the relation Y _A I ^1/2 between the acceptor's induced fluorescence intensity and the laser intensity, predicted by Jortner et al. is observed.     

Ergodicité et limite semi-classique

Consider a self adjoint quantic hamiltonian:P(h)=p(x, hD _x) whereh>0 is the Planck's constant andp some smooth classical observable on the phase space R²ⁿ . When the classical flow on a compact energy shell {p=} is ergodic we prove that in the limith 0 almost all the eigenfunctions ofP(h) whose energy is near of are distributed according to the Liouville measure on {p=}.In the high energy case ( +) this sort of problem was considered by A. Schnirelman, S. Zelditch, and Y. Colin de Verdière.     

Site dilution in the fully frustrated triangular lattice in two dimensions

The Transfermatrix-Method [1, 2] has been adapted to evaluate also the free energy of triangular 2–d-Ising lattices. The present work considers a model with nearest-neighbour antiferromagnetic couplings and a fraction 1–x of spins removed at random sites leading to some frustration effects. It is not yet clear if such a system shows spinglass behaviour [3, 4]. The correlation function s ₀ s _R ² (correlation between two spins with distanceR), which is related to the Edwards-Anderson-Orderparameter, shows such a fast breakdown with distanceR that there is a clear evidence against a phase transition at finiteT. In contrast to other models [1, 2, 5] we still expect an exponential decay of {s ₀ s _R ²} _av with distanceR atT=0.     

Freezing-out of nuclear polarization in radioactive core ions of microclusters, “snowballs” in superfluid helium

A novel method was tried successfully to trap ions and to freeze out their nuclear polarization inside aggregates of helium atoms, snowballs, in superfluid helium. Spin polarized¹²B (T _1/2=20.4 ms) ions were introduced into superfluid helium and snowballs were created around the impinged impurity ions. Beta-ray asymmetry was measured to obtain the nuclear polarization of decaying¹²B. The comparison with the initial value of¹²B polarization produces that no relaxation in polarization was observed throughout lifetime of¹²B.     

Self-Similar Decay in the Kraichnan Model of a Passive Scalar

We study the two-point correlation function of a freely decaying scalar in Kraichnan's model of advection by a Gaussian random velocity field that is stationary and white noise in time, but fractional Brownian in space with roughness exponent 0<<2, appropriate to the inertial-convective range of the scalar. We find all self-similar solutions by transforming the scaling equation to Kummer's equation. It is shown that only those scaling solutions with scalar energy decay exponent a(d/)+1 are statistically realizable, where d is space dimension and =2–. An infinite sequence of invariants J _p, p=0, 1, 2,..., is pointed out, where J ₀ is Corrsin's integral invariant but the higher invariants appear to be new. We show that at least one of the invariants J ₀ or J ₁ must be nonzero (possibly infinite) for realizable initial data. Initial datum with a finite, nonzero invariant—the first being J _p—converges at long times to a scaling solution _p with a=(d/)+p, p=0, 1. The latter belongs to an exceptional series of self-similar solutions with stretched-exponential decay in space. However, the domain of attraction includes many initial data with power-law decay. When the initial datum has all invariants zero or infinite and also it exhibits power-law decay, then the solution converges at long times to a nonexceptional scaling solution with the same power-law decay. These results support a picture of a two-scale decay with breakdown of self-similarity for a range of exponents (d+)/<a<(d+2)/, analogous to what has recently been found in the decay of Burgers turbulence.     

On the Largest Eigenvalue of a Random Subgraph of the Hypercube

Let G be a random subgraph of the n-cube where each edge appears randomly and independently with probability p. We prove that the largest eigenvalue of the adjacency matrix of G is almost surely where (G) is the maximum degree of G and the o(1) term tends to zero as max(^1/2(G),np) tends to infinity.Research was supported in part by the NSF grant DMS-0103948.Research was supported in part by NSF grants DMS-0106589, CCR-9987845 and by the State of New Jersey.     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

The Chiral Bag Model and properties of the πNΔ system

The effective Hamiltonian for theN system is proposed in the framework of the Chiral Bag Model (CBM). The taking into account of gluonic and pionic correctinos to the pion-nucleon coupling constantg _N and the-decay axial constantg _A leads tog _N 13·5,g _A 1·28 which are in good agreement with experimental data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.I wish to thank Gulamov K. G., Shelest V. P. and Zinoviev G. M. for useful discussions.     

L X-ray fluorescence cross sections and yields for mediumZ elements in the energy region 5.47 ≤E ≤ 9.36 keV

TotalL X-ray fluorescence cross sections have been measured in the atomic region 39 Z 51 excited by 5.47, 6.47, 7.04, 7.57, 8.14, 8.74 and 9.36 keV photons. Experimental cross sections are compared with the theoretical estimates of Chen et al. based on relativistic Dirac-Hartree-Slater theory. Good agreement is observed between experimental results and theoretical estimates in the studied atomic and energy region. Experimental fluorescence yields have been evaluated using the experimental fluorescence cross sections and theoretical subshell photoionization cross sections. Fluorescence yields are fitted by least squares to fifth-order polynomials inZ of the form _n a _n z ⁿ and compared with theoretical and earlier fitted values. The deviation of the average fluorescence yield in the atomic region 46Z 51 with new theoretical estimates of , calculated using the ECPSSR (Energy loss Coulomb deflection Perturbed Stationary State Relativistic effects) theory of Brandt and Lapicki and the fitted values clearly indicate the weak dependence of the average fluorescence yield on the initial vacancy distribution.     

The Fluorosolvatochromism of Brooker's Merocyanine in Pure and in Mixed Solvents

The fluorescence-based solvatochromism (fluorosolvatochromism) of 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (Brooker's merocyanine) was studied. The results revealed that the fluorescence emission band of the dye was dependent on the medium ( nm in water and nm in DMF). The fluorescence quantum yields (φ _f) were calculated for the dye in the solvents investigated. Low φ _f values ( < 10%) were obtained for the dye and in order to better comprehend the radiative and nonradiative decay processes of this dye, its fluorescence lifetime in methanol was measured and was found to be very short (230 ps). The results suggest that the dye in the excited state decays rapidly through nonradiative processes. The behavior of the probe in binary mixtures including a hydrogen-bond accepting solvent (acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide) and a hydroxylic solvent (water, methanol, ethanol, propan-2-ol, and butan-1-ol) was also investigated. All data were successfully fitted to a model based on solvent exchange equilibria, which allowed the separation of the different contributions of the solvent species in the solvation shell of the dye. The data obtained for the mixed solvents were explained based on solute–solvent and solvent–solvent interactions.     

Precise measurement of the quadrupole moment of β-emitting12B

Hyperfine interactions of¹²B(I ,T _1/2=21 ms) implanted in the substitutional site of B atoms (stable) in a (single crystal like) BN (hexagonal) was studied by use of a -NMR detection. For efficient and simple measurements, the conventional -NMR has been modified as a new nuclear quadrupole resonance technique (NNQR). For the present case with the nuclear spinI=1 the detection efficiency is improved about 30 times compared with the one with the old method. The quadrupole moment of¹²B was determined precisely as ¦Q(¹²B; 1⁺)¦=13.21±0.26 mb.     

Effect of solvent on the cation-sensitive fluorescence of polyanions bearing 4′-acryloylbenzo-18-crown-6 Units

Changes in the fluorescence intensity of polyanions bearing 4-acryloylbenzo-18-crown-6 units on the addition of cations were studied in a mixed solvent of methanol and water at 30°C. The sensitivity of the change in fluorescence intensities of the polymers toward cations was strongly enhanced compared to that of the corresponding model compound. When alkali metal cations were added, the fluorescence intensity of the polymers decreased in the orders Li⁺>Na⁺>Cs⁺>Rb⁺>K⁺ in a methanol-water (19) mixture and Li⁺>Na⁺>Rb⁺>K⁺Cs⁺ in a methanol-water (91) mixture. Alkaline earth metal cations and alkylamine hydrochlorides decreased the fluorescence intensity of the polymers in a methanol-water (19) mixture. The cation-dependent decrease in the fluorescence intensity of the polymers was affected by the water fraction in a mixed solvent of methanol and water.