bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of circular wave guides
Authors: Delage A. , McGreer K. A. , Rainville E.
Published: April 2011

In many circumstances the design of interconnects in a photonic integrated circuit can be simplified by using low loss curved wave guides in the shapes of circular arcs. Radiative losses associated with the curvature have been computed as a function of the radius of curvature. The technique takes advantage of the effective index method to reduce the problem from two dimensions to one dimension (1D) and uses a change of coordinate that transforms an arc of circle into a straight line. This transformation results in a monotonous increase of the refractive index as function of r (the distance from the centre of the circle) for original constant index regions. The new system is solved by discretizing this varying effective index onto many small layers of constant index over a window large enough to contain the region where the field is not negligible. A multilayer algorithm in 1D is then used to find complex propagation constants in which the imaginary part is related to the fundamental energy loss owing to the curvature. The solution also gives the shape of the field necessary to match the mode profiles at the junction between the straight and curved part of the wave guide. The basic change of variable has been extended to the finite difference solution of the scalar wave equation and to the beam propagation method.
Optical properties of porous silicon
Authors: Lockwood D. J. , Aers G. C. , Allard L. B. , Bryskiewicz B. , Charbonneau S. , Houghton D. C. , McCaffrey J. P. , Wang A.
Published: April 2011

The optical and structural properties of porous Si films produced by electrochemical and chemical dissolution of Si have been studied by a variety of techniques. Raman scattering and transmission electron microscopy have shown the samples to contain crystalline Si wires and (or) spherites 3–8 nm in diameter and (or) amorphous Si. The optical absorption spectra and the wavelength, temperature, and lifetime dependence of the photoluminescence obtained from most of the samples are entirely consistent with the quantum confinement of excitons in Si nanostructures. Quite different photoluminescence was obtained from other samples composed only of amorphous Si, and this is attributed to the presence of silicon oxyhydride species.
The nuclear spin-lattice relaxation of an amorphous Hubbard model
Authors: Liu K. L.
Published: April 2011

We study the temperature dependence of the nuclear spin-lattice relaxation rate, (1/T1), of a structurally disordered Hubbard model for different electronic concentration ne, and for various interaction strength U. The relaxation process is assumed to be caused by the hyperfine Fermi contact interaction. The required electronic spin correlation function is studied up to the fourth order in hopping, and a Gaussian approximation is constructed. Two types of transfer integral have been examined: (1) quasi-exponential, and (2) Gaussian. At half-filling (ne = 1), the relaxation rate shows a strong U dependence at low temperatures. For large U, (1/T1) drops markedly when holes are introduced into the system at low temperatures, and its temperature dependence becomes weak when ne reaches 0.8. We also calculate the spin susceptibility and examine the ne dependence of the Korringa relation. We compare the relaxation rates with those for the two-dimensional Hubbard model with nearest-neighbor hopping on a square lattice, and contact is made with the recent NMR study of Sr-doped La2CuO4 at high temperatures.
Density profiles of fluids in some special symmetries
Authors: Lee Seong-Chan , Yoon Zi-Hong , Kim Soon-Chul
Published: April 2011

A free-energy-functional approximation based on a semi-empirical method is proposed. The main advantage of the free-energy-functional approximation is its accuracy compared with other models and its relative simplicity compared with other well-known weighted-density approximations. The free-energy-functional approximation is applied to predict the density profiles of the hard-sphere fluids and the Lennard–Jones fluids in some special symmetries. For the density profiles near a hard flat wall, the results reproduced the hard-sphere oscillatory structures qualitatively and quantitatively. For the density profiles of hard-sphere fluids confined in a spherical cage, the results are also in a fair agreement with the computer simulations. For Lennard–Jones fluids, two kinds of density-functional perturbation theories, the density-functional mean-field theory (DFMFT) and the density-functional perturbation theory (DFPT), examined. The results show that at higher temperature the DFPT compares well with computer simulations. However, the agreement deteriorates slightly as the temperature of the Lennard–Jones fluids is reduced. These results demonstrate that both the free-energy-functional approximation and the DFPT succesfully describe the inhomogeneous properties of classical fluids.
Exact solutions for the potential V(r) = r2 + β/r4 + λ/r6 by supersymmetric quantum mechanics
Authors: Varshni Y. P. , Nag Nivedita , Roychoudhury Rajkumar
Published: April 2011

A method based on supersymmetric quantum mechanics is given for obtaining exact solutions of the potential V(r) = r2 + β/r4 + λ/r6, where β and λ are parameters, provided a certain constraint is satisfied between β and λ. Detailed results are given for the ground state as well as for several excited states. A method for determining the exact energies of two levels for the same values of β and λ is given and illustrated by examples.
Positron scattering on atoms and molecules near the positronium threshold
Authors: Meyerhof W. E. , Laricchia G. , Moxom J. , Humberston J. W. , Watts M. S. T.
Published: April 2011

Effects found in the total and elastic-scattering cross sections of positrons on atoms and molecules near the positronium (Ps) formation threshold are examined on the basis of R-matrix theory. In the case of atomic targets, the energy, dependence of the Ps-production cross section yields the dominant angular momentum of the outgoing Ps near threshold. The predicted effects agree semiquantitatively with experimental elastic and total cross sections. The predictions suggest that Wigner cusps in the elastic-scattering cross section should be very small for He targets and largest for Xe targets. For molecules, the variability of threshold effects in the total cross section suggests that this is caused by variable threshold effects in the nonelastic cross sections. Using three-channel R-matrix theory, the effect is illustrated for a H2 target.
Differential ionization in e+–Ar scattering
Authors: Weber M. , Falke T. , Raith W. , Wesskamp U.
Published: April 2011

Differential cross sections of positron scattering from argon atoms leading to singly and doubly charged ions were measured in the angular region from 0° to 120°. These reactions include single and double ionization, transfer, as Ps formation is referred to here, and transfer ionization. The latter is the process of simultaneously ejecting an electron and forming a positronium atom with another electron. The measurement of the time correlation between the detected ion and the scattered particle distinguishes among the reactions, resulting in Ar+ and Ar++, respectively. Measurements were carried out at 30 eV, and, mostly, at 75 eV with an estimated resolution of 2 eV FWHM. The angular acceptance ranged from ±4° to ±2°. Cross sections for single ionization are strongly forward peaked and Ps formation has the most narrow FWHM of ±12° (75 eV incident positron energy) of all. A maximum in the Ps-formation cross section away from 0°, predicted for low energies, was not observed. A very intriguing structure was observed in the transfer-ionization cross section at 45°.
Ionization in collisions between 30–1000 keV antiprotons and atomic hydrogen
Authors: Paludan K. , Knudsen H. , Mikkelsen U. , Charlton M. , Kirsebom K. , Møller S. P. , Uggerhøj E. , Morenzoni E. , Slevin J.
Published: April 2011

Recently published data for impact of antiprotons in the energy range 30–1000 keV on atomic hydrogen are compared with analogous proton, electron, and positron measurements, and it is found that the ionization cross sections of atomic hydrogen follow the same pattern as similar cross sections obtained on He and H2 targets, in accordance with the general phenomenological description of single ionization that has developed over the last decade. Further comparisons are made with various recent and advanced theoretical calculations for antiproton ionization of atomic hydrogen. These theoretical results agree well with the data obtained, but for lower impact energies the different methods do not, despite the simplicity of the system, agree on predicting even the form of the cross section.
Virial expansion of the positron and positronium decay rate in a dilute gas: The linear contribution
Authors: Miller Bruce N. , Reese Terrence L. , Worrell Gregory A.
Published: April 2011

A systematic theory of the lifetimes of positrons or positronium atoms in a low-density gas is lacking. This paper describes our recent efforts to fill this void. In analogy with the virial expansion for the pressure of a gas, we develop a quantum virial expansion for the properties of a low-mass particle thermalized in a dilute gas. The discrete Feynman path integral is employed to numerically evaluate the quantum traces that comprise the coefficients of each power of the density. By considering two applications of the linear contribution, positron and ortho-positronium decay in xenon, we show how the temperature dependence of the decay rate depends on the interaction between the light particle and an atom. We also explain the observed lack of temperature dependence in experimental measurements of the ortho-positronium pick-off decay rate observed in most gases.
Third-order pseudostate calculation of excitation–ionization by protons and antiprotons
Authors: Straton Jack C. , Wang J. , McGuire J. H. , Nagy L.
Published: April 2011

Techniques the authors developed to include correlation in the double-excitation of atoms are applied to a second two-electron process, excitation–ionization by proton versus antiproton impact. The second-order cross section, in the closure approximation and using pseudostates for the unbound electron, reproduces only a small percentage of the experimental factor of 2 difference for positively versus negatively charged projectiles. Inclusion of a portion of the third-order term yields a significant contribution near 0.5 MeV.
(e,2e) experiments with spin-polarized electrons
Authors: Hanne G. F.
Published: April 2011

Recent experimental work on (e,2e) coincidences involving polarized electrons is reviewed. The origin of the observed spin asymmetries are exchange effects, spin-orbit interaction of the continuum electrons, and spin-orbit coupling within the target in conjunction with orbital orientation and exchange. These mechanisms are explained in some detail. Experimental and theoretical investigations of spin effects have been performed for ionization of outer shell electrons as well as for ionization of inner shell electrons.
Calculation of electron-impact excitation and ionization of atoms and ions
Authors: Bray Igor
Published: April 2011

We present a review of applications of the convergent close-coupling method concentrating on spin-dependent electron-impact total ionization cross sections. The results for the electron-impact total ionization cross sections and the associated spin asymmetries of H, Li, O5+, Na, and He(23S) are reviewed, with new calculations being presented for the potassium target.
Review of advances in describing the 31D-state excitation of helium
Authors: Williams J. F. , Mikosza A. G. , Wang J. B.
Published: April 2011

Recent advances in describing the electron impact excitation of the 31D state of helium are reported for an incident energy of 40 eV and scattering angles from 10° to 40°. Measurements of the Stokes parameters have been made using the polarized photon–photon and electron–photon coincidence techniques. The partial cross section σm for the magnetic sublevels in the collision frame indicate that the m = 0 excitation is favoured. For the above scattering kinematics the data are in agreement with convergent close coupling calculations. The deduced scattering amplitudes, in the natural frame, show that the m = 2 excitation becomes dominant at the larger angles. Progress is reported on the complete determination of the scattering amplitudes and their relative phases using the triple-coincident detection of the scattered electron with the two sequential cascading photons.
Failure to observe electron circular dichroism in camphor
Authors: Trantham K. W. , Johnston M. E. , Gay T. J.
Published: April 2011

Analogous to optical circular dichroism, it is possible to have electron circular dichroism, the preferential transmission of longitudinally polarized electrons through a chiral medium. Using stereoisomers of camphor vapor as a scattering target, we looked for this effect at incident electron energies of 1, 3, 5, 7, or 10 eV. Within our detection limit (~0.02%) we have not observed a spin-dependent asymmetric transmission.
Electron superelastic scattering from states of atomic sodium and rubidium
Authors: Hall B. V. , Sang R. T. , Shurgalin M. , MacGillivray W. R. , Standage M. C. , Farrell P. M.
Published: April 2011

This paper reports on the extension of the electron superelastic scattering technique to three new situations. The first considers scattering from the 32P3/2 level of Na that has been excited by two laser modes tuned, respectively, to the transitions from the two hyperfine states of the 32S1/2 ground level. Both coherent and noncoherent modes are treated in a full quantum electrodynamic model of the laser excitation. Under certain conditions, the time-averaged probability of finding an atom in the 32P3/2 level exceeds 0.5. The second situation is electron superelastic scattering from the 32D5/2 level of Na that has been resonantly excited from the ground level via a resonant intermediate level. With the first observation of superelastically scattered electrons from this higher lying level recently recorded, this paper considers the extension of the quantum electrodynamics (QED) model to describe the optical excitation process. Application of superelastic scattering to the 52S1/2–52P3/2 transition of Rb is the third situation considered. The superelastic scattering formalism is extended to allow for a nonzero spin flip cross section for this transition. The resulting optical pumping terms are calculated using the QED model and the method of their determination for the superelastic scattering experiment described. The experimental design necessary to measure all of the collision parameters for this transition is discussed.
Infrared dynamics in (2+1) dimensions
Authors: Boldo J L , Pimentel B M , Tomazelli J L
Published: April 2011

In this work we study the asymptotic behavior of (2+1)-dimensional quantum electrodynamics in the infrared region. We show that an appropriate redefinition of the fermion current operator leads to an asymptotic evolution operator that contains a divergent Coulomb phase factor and a contribution from the electromagnetic field at large distances, factored from the evolution operator for free fields, and we conclude that the modified scattering operator maps two spaces of coherent states of the electromagnetic field, as in the KulishFaddeev model for QED (quantum electrodynamics) in four space-time dimensions.

PACS No. 11.10Kk, 11.55m
Spectral approximation by the polar transformation
Authors: Hall R L , Zhou W H
Published: April 2011

Central potentials V(r) are considered that admit the polar representation V(r) = g(h(r)), where h(r) = sgn (q)rq, q is fixed, and g is the polar transformation function. This representation allows the Schrödinger eigenvalues generated by V to be approximated in terms of those generated by the pure polar potential h(r). In many cases a pair of powers {q1, q2} can be chosen so that the corresponding polar functions {g1, g2} have definite and opposite convexity. For such cases, the spectral approximations provide both upper and lower bounds for the entire discrete spectrum. The example V(r) = ar2 + br2/(1 + cr2) is considered in detail.

PACS No. 03.65Ge
Article
Authors: Solomon D
Published: April 2011

Quantum field theory is assumed to be gauge invariant. We show that for a Dirac field the assumption of gauge invariance impacts on the way the vacuum state is defined, and also that the conventional definition of the vacuum state must be modified to take into account the requirements of gauge invariance.PACS No. 1100
Article
Authors: Draganescu Gh.E. Dr. E. , Avram N M
Published: April 2011

This paper presents the dynamic algebra of the Morse oscillatorusing a new analytic method for the calculation of creation andannihilation operators. The coherent states for the Morse potential corresponding todifferent representations are also established. The transitionsprobabilities between two eigenstates produced by a harmonicperturbation as function of the creation and annihilation operatorsare also calculated.PACS Nos.: 02.20.+b, 03.65.Fd, 42.50.Ar, and 33.10.Cs
Lamb-shift measurement in hydrogen by the anisotropy method
Authors: Wijngaarden A van , Holuj F , Drake G W
Published: April 2011

A high-precision measurement of the Lamb shift in hydrogen by theanisotropy method is presented. The result of 1057.852(15) MHz isconsistent with theory and other measurements, thereby confirming thatthe anisotropy method and its interpretation are valid at the 15 partsper million level of accuracy. For the case of He+, a discrepancyof 70(12) parts per million between theory (including two-loop bindingcorrections) and experiment remains to be resolved.PACS Nos. 3130J, 3220D
Article
Authors: van Wijngaarden W A , Clarke J
Published: April 2011

A neutral atom trap is proposed consisting of a magnetic field generated by a pair of anti-Helmholtz coils and a fringing electric field of a parallel plate capacitor. The electric field shifts the energy minimum ofthe trap away from the point where the magnetic field is zero thus preventingatom loss from the trap due to Majorana transitions. This trap offers someadvantages over existing traps that are used to study cold atoms.PACS Nos.: 32.80Pj and 03.75Fi
Some exact solutions of reduced scalar Yukawa theory
Authors: Darewych J W
Published: April 2011

The scalar Yukawa model, in which a complex scalar field, ϕ, interacts via a real scalar field, χ, is reduced by using covariant Green functions. It is shown that exact few-particle eigenstates of the truncated QFT Hamiltonian can be obtained in the FeshbachVillars formulation if an unorthodox "empty" vacuum state is used. Analytic solutions for the two-body case are obtained for massless chion exchange in 3+1 dimensions and for massive chion exchange in 1+1 dimensions. Comparison is made to ladder BetheSalpeter, FeynmanSchwinger, and quasipotential results for massive chion exchange in 3+1. Equations for the three-body case are also obtained.

PACS Nos.: 11.10.Ef, 11.10.Qr, and 03.70.+k
Article
Authors: Bolina O , Parreira J R
Published: April 2011

We show that the ground state of the xy model (ferromagnetic orantiferromagnetic) in a transverse magnetic field h --- for any spin value, in any dimension --- is the state with all spins aligned antiparallel to the field when h is greater than some critical value hc. In particular, for the spin-1/2 linear chain, we study the behavior of correlations as functions of the magnetic field.

PACS Nos.: 75.10Jm and 64.60.Cm
Article
Authors: Drake GWF , Martin W C
Published: April 2011

Ionization energies for several of the lower lying S- and P-states of helium are deduced from a combination of theory and a variety of high-precision measurements of transition energies. High-precision variational methods are reviewed and used to subtract the nonrelativistic energy and lowest order α2 au relativistic corrections from the ionization energies. The remaining quantum electrodynamic (QED) shift of order α3 au and higher is calculated in an extended KabirSalpeter formalism and compared with experiment. The comparison verifies the usefulness of the KabirSalpeter formalism for terms at least up to order α4 au, and it verifies an asymptotic 1/n3 scaling law for the two-electron corrections to the Bethe logarithm. The asymptotic scaling law is used to obtain improved semi-empirical estimates for the ionization energies of the higher lying 1sns 1S and 3S states up to n = 10. A revised comprehensive listing is given for the ionization energies of all states of helium up to n = 10 and angular momentum L = 7, together with quantum defect extrapolations for the S-states.

PACS Nos.: 31.15.Pf, 31.30.Jv, and 32.10.Hq
Article
Authors: Sinha A , Roychoudhury R
Published: April 2011

We study the (2+1)-dimensional κ-Dirac scalar-Coulomb problem in the framework of κ-Poincaré-Dirac equation.It is found that for a scalar-Coulomb coupling, the nonrelativisticlimit yields a nonvanishing energy correction to the first order in the quantum group parameter (ε = κ 1),while the energy remains unaltered (to the first order in ε) in the case of the vector-Coulomb coupling in (2+1)dimensions. PACS Nos.: 03.65Fd, 03.65Ge, 03.65Pm
Derivation of the Lamb shift using an effective field theory
Authors: Labelle P , Zebarjad S M
Published: April 2011

We rederive the Ο(α5) shift of the hydrogen levels in the nonrecoil limit (me/mP →> 0) using an extension of nonrelativistic QED (NRQED), an effective field theory developed by Caswell and Lepage. Our result contains the Lamb shift as a special case. Although this calculation is not new, it is presented here for the first time using the modern language of effective field theories. It clearly illustrates the usefulness of applying a multipole expansion to the NRQED vertices.PACS Nos.: 31.30Jv, 31.15Ar, 31.15Md, and 11.10St
Multiplicity and pseudorapidity distribution in high-energy neutrino-emulsion collisions
Authors: Liu F H , Sun J F
Published: April 2011

The multiplicity and pseudorapidity distributions inneutrino-emulsion collisions at high energies are investigated. Themultiplicity distribution of charged particles, the pseudorapiditydistributions of shower particles, as well as the correlation between amean maximum number density of shower particles and multiplicity, are given.PACS No.: 13.85.Hd
Distribution spatiale de la charge déposée dans des cibles minces irradiées par des électrons
Authors: Bibi F Alouani , Lazurik V T , Rogov Y V
Published: April 2011

The study of the charge-deposition distribution due to secondary electrons in thin slabs irradiated by fast electrons is conducted. The slabs considered have thicknesses from 0.5 to 50 mg/cm2 and are made of materials with atomic numbers from 4 to 79. The energy of incident electrons is considered from 1 to 10 MeV. The data of charge-deposition density are obtained by using a new Monte Carlo method called the trajectory translation method. An analysis of charge-deposition distribution and its dependencies on the energy of incident electrons and on the atomic number of the slab material and its thickness has been made. Conclusions concerning these dependencies and recommendations for the choice of the model parameters of the standard computation codes are provided.
Propriétés structurales des jonctions de nanotubes de carbone
Authors: Meunier V , Lambin P
Published: April 2011

The junction between two different nanotubes can be realized by the simple insertion of a pentagon-heptagon pair defect while preserving the triple coordination of each C atom. This insertion bends the structure to an angle depending on the distance between the pentagonand heptagon. The atomic structure of several of these junctions was optimized with the help of empirical potentials, the nanotubes on both sides of the junctions being considered as infinitely long. Local densities of σ + π electronic states were evaluated in the interfacial regions from a tight-binding Hamiltonian. From there, the electronic energy of these junctions was calculated and compared with that of the isolated nanotubes. It was established that the energy associated with the pentagon-heptagone pair in a graphitic tubule is of the order of 6 eV. An automatic generation algorithm for connecting any two tubules was developed. By restricting the Hamiltonian to the sole π orbitals, this algorithm made it feasible to study the energetics of the pentagon-heptagon defect in a systematical way.
Accurate transition probabilities for the 2s2 1S - 2s2p 1P transition in Be I and B II
Authors: Irving R E , Henderson M , Curtis L J , Martinson I , Bengtsson P
Published: April 2011

Transition probability determinations are reported for the 2s2 1S - 2s2p 1P transition in Be I and B II, based on lifetime measurements made by beam-foil excitation. The lifetimes were extracted by the ANDC method, which incorporates cascade-related decay curves into the analysis of the primary decay curve, thus accounting for the effects of cascade repopulation. The results are of higher precision than earlier measurements and improve the agreement with recent theoretical calculations. PACS No.: 32.70Cs
Formal quantization of a chaotic model problem
Authors: Moore R A
Published: April 2011

A model problem, initially proposed by Feynman and Hibbs, is re-examined in this work. It is shown that the equation of motion is deterministic, in spite of its double time delay character, and has chaoticlike solutions. It is further shown that this model is amenable to the methods of higher than first-order Lagrangians, yielding a series of approximations to the initial model. Thus, for each approximation, a complete st of canonical variables can be defined, the Hamiltonian can be written down in canonical form and the conventional quantization rules applied, leading to exact quantizations. Extended sets of basis vectors follow along with the definition of physical state vectors, which are seen to contain all of the classical information. Finally, these results are used to give a possible explanation of the electron-position resonances seen in heavy-ion collision experiments that is consistent with the negative results found in low-energy electron scattering as well as other heavy-ion collision experiments.PACS Nos.: 03.20.+i, 03.65.-w, 05.45.+6
Properties of a-SiC:H films and solar cells
Authors: Gharbi R , Fathallah M , Pirri C F , Tresso E , Crovini G , Giorgis F
Published: April 2011

a-SiC:H samples and solar cells were made by plasma-enhanced chemical vapor deposition (PECVD) using a multichamber deposition system. The effect of light illumination on samples prepared with and without hydrogen dilution was studied. The phototransport properties of the samples prepared with high hydrogen dilution were more stable versus time of illumination than non diluted ones.The samples were inserted as an intrinsic layer in semitransparent solar cells. The performance of solar cells depends on the energy gap and thickness of the intrinsic layer. High hydrogen dilution may increase the energy gap and act to decrease the structure uniformity. The results show that open circuit voltage Voc decreases with light illumination and depends on the doped p+ layer quality and created defects in the intrinsic layer. PACS Nos.: 70, 72, 40
Modélisation moléculaire et calcul des fréquences de vibration du sous-réseau perovskite dans CH3NH3PbCl3
Authors: Maalej A , Bahri M , Abid Y , Jaïdane N
Published: April 2011

The perovskite CH3NH3PbCl3 presents two low-temperature phase transitions

[Formula: see text]

The various phases are characterized by Raman scattering. We restrict ourselves to the low-frequency domain (10250 cm1), which includes the lattice vibrations, these being more sensitive to the symmetry variations and to the structural phase transitions. Studying the crystal dynamics and the spectral evolution requires a detailed assigment of the Raman spectrum. Consequently, we bring in a molecular model and carry out a theoretical calculation of the vibration frequencies of the perovskite sublattice PbCl3 using the semiempirical self-consistent field method. The model considers the interaction of a PbCl6 octahedron with its six octahedron neighbors. The vibrating cell is thus a 43-atom molecule. The calculated vibration frequencies agree well with the frequencies that have been assigned by a comparaison with the homologous compound CsPbCl3[Journal translation]
Dépôt chimique en phase vapeur et à basse pression de couches minces à base de silicium dans un réacteur à lampes halogène
Authors: Semmache B , Kallel S , Omari H El , Lemiti M , Laugier A
Published: April 2011

Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid thermal LPCVD) is a promising technique for silicon-based thin films deposition. Indeed, overall process time and gas consumption reduction in RTP reactors allows to project new device fabrication technologies (microsensors, solar cells) in order to reach a higher environmental safety with respect to classical technologies.Various gases available on our RTP installation (SiH4, NH3, N2O, O2, PH3, B2H6) enable several silicon-based thin films RTLPCVD deposition: intrinsic polycrystalline silicon (poly-Si) films or in situ doped poly-Si, silicon nitride (Si-N) and oxynitride (Si-O-N). In this paper, we discuss our results on deposition kinetics and physical properties of these thin films. It appeared that RTLPCVD silicon-based thin films with interesting structural, electrical, and optical properties can be synthesized in our lamp-heated reactor with a tight control of process parameters such as temperature, pressure, and gas flow ratios.
Heat transfer from moving surfaces in a micropolar fluid
Authors: Mansour M A , Mohammadein A A , El-Kabeir S MM , Gorla RSR
Published: April 2011

A boundary layer analysis is presented for the forced convection problem of a surface moving continuously in a flowing stream of a micropolar fluid. Two cases are considered, one corresponding to a plane surface moving in parallel with the free stream and the other, a surface moving in the opposite direction to the free stream. A similarity solution to the governing momentum, angular momentum, and energy equations is derived.These equations were solved numerically and the flow and heat transfer characteristics of the micropolar fluid are presented. PACS No.: 61.00
The evolution and revival structure of angular momentum quantum wave packets
Authors: Auzinsh Marcis
Published: April 2011

In this paper, a coherent superposition of angular-momentum states created by absorption of polarized light by molecules is analyzed. Attention is paid to the time evolution of wave packets representing the spatial orientation of the internuclear axis of a diatomic molecule. Two examples are considered in detail. Molecules absorbing light in a permanent magnetic field experiencing the Zeeman effect and molecules absorbing light in a permanent electric field experiencing the quadratic Stark effect. In a magnetic field, we have a wave packet that evolves in time exactly as a classical dipole oscillator in a permanent magnetic field (classical-physics picture of the Zeeman effect). In the second case, we have a wave packet that goes through periodical changes of shape of the packet with revivals of the initial shape. This is pure quantum behavior. The classical motion of angular momentum in an electric field in the case of a quadratic Stark effect is known to be a periodic. Solutions obtained for wave packet evolution are briefly compared with Rydberg-state coherent wave packets and harmonic-oscillator wave packets. Zeeman and Stark effects in small molecules continuously attract the attention of researchers, theoreticians, as well as experimentalists. These investigations allow us to obtain a deeper understanding of the interaction of molecules with stationary external fields and also can be used as a practical tool to measure different molecular characteristics, such as permanent electric or magnetic dipole moments, intramolecular perturbations, etc. It is worthwhile analyzing these effects as an evolution of wave packets. All this motivates a comparison of the quantum and classical picture of Zeeman and Stark effects in molecules.PACS No.: 33.55.Be
Arsenic and cadmium resistance in environmental isolates of Yersinia enterocolitica and Yersinia intermedia
Authors: Bansal Namita , Sinha Indrajit , Virdi Jugsharan S
Published: April 2011

Environmental strains of Yersinia enterocolitica representing biotype 1A lack virulence plasmid (pYV) and are regarded as non-pathogenic. Though these occupy a diverse range of environmental niches, nothing is known about their resistance to heavy metals. The minimal inhibitory concentrations (MICs) of various metal ions, namely Ag+, Cu2+, Zn2+, Cd2+, As5+, and As3+, for strains of Yersinia enterocolitica (biotype 1A) and Yersinia intermedia (biotypes 1, 2, and 4), isolated from sewage effluents or pork, were determined. All isolates were resistant (MICs 2.5-5 mM) to Cd2+. The MICs of arsenic varied with bacterial strain and the chemical species of the arsenic used. For the majority of the strains, however, it was between 5-10 mM of Na2HAsO4·7H2O and NaAsO2, and 0.625-2.5 mM of As2O3. Except for one isolate, MICs of Ag+, Cu2+, and Zn2+ for these strains were in the range of 0.3-0.625 mM.Key words: Yersinia enterocolitica, Yersinia intermedia, cadmium resistance, arsenic resistance, biotype 1A.
Isolation of Tn916-like conjugal elements from swine lot effluent
Authors: Haack Bradley J , Andrews Jr. Robert E
Published: April 2011

Isolates of Enterococcus faecalis obtained from a swine farrowing house outflow were examined for genetic elements similar to Tn916. Of the enterococci isolated, 71% were resistant to tetracycline. Among the tetracycline-resistant enterococci isolated from the outflow samples, approximately 34% were able to transfer the tetracycline resistance phenotype to Bacillus thuringiensis in cross-genus matings. The frequencies of transfer for 10 random isolates were comparable to those for transfer of Tn916 from E. faecalis to B. thuringiensis. In addition, these elements were shown to mobilize plasmid pC194 between Bacillus species, as did Tn916. Southern blot and polymerase chain reaction (PCR) analysis showed these elements share extensive structural homology with Tn916. The selected conjugal elements were capable of transfer to a Bacillus recipient in a soil environment. When the swine waste was introduced into the soil, the tetracycline resistant fecal enterococci levels rose from essentially undetectable levels to approximately 4 × 104and remained at this level for 4 weeks. After six months, including one winter, levels had decreased to 5 × 103.Key words: Enterococcus faecalis, Tn916, swine waste, genetic exchange, Bacillus thuringiensis, PCR.
Enhanced attachment of Bradyrhizobium japonicum to soybean through reduced root colonization of internally seedborne microorganisms
Authors: Oehrle Nathan W , Karr Dale B , Kremer Robert J , Emerich David W
Published: April 2011

Internally seedborne microorganisms are those surviving common surface sterilization procedures. Such microbes often colonize the radicle surface of a germinating soybean (Glycine max) seed, introducing an undefined parameter into studies on attachment and infection by Bradyrhizobium japonicum. Bacterial isolates from surface-sterilized soybean seed, cv. Williams 82 and cv. Maverick, used in our studies, were identified as Agrobacterium radiobacter, Aeromonas sp., Bacillus spp., Chryseomonas luteola, Flavimonas oryzihabitans, and Sphingomonas paucimobilis. Growth of these microbes during seed germination was reduced by treating germinating seeds with 500 µg/mL penicillin G. The effects of this antibiotic on seedling development and on B. japonicum 2143 attachment, nodulation, and nitrogen fixation are reported here. Penicillin G treatment of seeds did not reduce seed germination or root tip growth, or affect seedling development. No differences in nodulation kinetics, nitrogen fixation onset or rates were observed. However, the number of B. japonicum attached to treated intact seedlings was enhanced 200-325%, demonstrating that other root-colonizing bacteria can interfere with rhizobial attachment. Penicillin G treatment of soybean seedlings can be used to reduce the root colonizing microbes, which introduce an undefined parameter into studies of attachment of B. japonicum to the soybean root, without affecting plant development.Key words: internally seedborne microorganisms, penicillin G, Bradyrhizobium japonicum, microbial attachment, soybean (Glycine max).
Airborne microfungi from eastern Canadian sawmills
Authors: Duchaine Caroline , Mériaux Anne
Published: April 2011

Working in sawmills is associated with bioaerosol exposure and respiratory health problems. This study is the first to analyze the mycoflora of eastern Canadian sawmills and the nature of airborne contamination at different work sites. Fifty work sites (debarking, sawing, planing, and sorting) within 17 sawmills were sampled for airborne microfungi. One thousand seven hundred strains were isolated, quantified to determine the frequency of occurrence, and then identified. Unlike the European studies, we did not frequently identify the presence of fungi that were described in European sawmills as being related to respiratory health problems. In eastern Canadian sawmills, Penicillium species are the most frequently isolated microfungi.
Recovery and viability ofCryptosporidium parvumoocysts andGiardia intestinaliscysts using the membrane dissolution procedure
Authors: McCuin R M , Bukhari Z , Clancy J L
Published: April 2011

Previously, the cellulose acetate membrane filter dissolution method was reported to yield Cryptosporidium parvum oocyst recoveries of 70.5%, with recovered oocysts retaining their infectivity. In contrast, high spike doses (approximately 1 × 105Cryptosporidium parvum oocysts and Giardia intestinalis cysts) yielded recoveries ranging from 0.4% to 83.9%, and 3.2% to 90.3%, respectively, in this study. Recoveries with low spike doses (approximately 100 (oo)cysts) continued to demonstrate high variability also. Efforts to optimize the method included increased centrifugation speeds, suspension of the final concentrate in deionized water for organism detection on well slides, and analysis of the entire concentrate. A comparison of two monoclonal antibodies was also conducted to identify potential differences between antibodies in detection of organisms. Archived source and finished water samples were spiked, yielding variable recoveries of C. parvum oocysts (11.8% to 71.4%) and G. intestinalis cysts (7.4% to 42.3%). Effects of organic solvents used in the membrane dissolution procedure on the viability of recovered (oo)cysts was determined using a fluorogenic vital dyes assay in conjunction with (oo)cyst morphology, which indicated >99% inactivation. These data indicate that the membrane dissolution procedure yields poor and highly variable (oo)cyst recoveries, and also renders the majority of recovered organisms non-viable.Key words: Giardia, Cryptosporidium, membrane dissolution, viability.
Streptomyces halstediiK122 produces the antifungal compounds bafilomycin B1 and C1
Authors: Frändberg Emma , Petersson Carl , Lundgren Lennart N , Schnürer Johan
Published: April 2011

Streptomyces halstedii K122 was previously found to produce antifungal compounds on solid substrates that inhibit radial growth of fungi among Ascomycetes, Basidiomycetes, Deuteromycetes, Oomycetes, and Zygomycetes, and strongly affected hyphal branching and morphology. During growth of S. halstedii K122 in submerged culture, no antifungal activity could be detected. However, cultivation of S. halstedii in thin (1 mm) liquid substrate layers in large surface-area tissue culture flasks caused intense growth and sporulation of S. halstedii K122, and the biologically active compounds could be extracted from the mycelium with methanol. Antifungal compounds were purified using C18 solid phase extraction and silica gel column chromatography, and identified as bafilomycins B1 and C1, using 2D NMR and FAB MS. Production of bafilomycins, which are specific inhibitors of vacuolar ATPases, has not been reported from S. halstedii previously. Minimum inhibitory concentrations (MIC) of bafilomycins B1 and C1, amphotericin B, and nikkomycin Z were determined at pH 5.5 and 7.0 for the target fungi Aspergillus fumigatus, Mucor hiemalis, Penicillium roqueforti, and Paecilomyces variotii. Penicillium roqueforti was the most sensitive species to all the compounds investigated. The MIC values for amphotericin B were 0.5-4 µg·mL-1for the fungi tested, and pH did not affect the toxicity. The MIC values for nikkomycin Z ranged from <0.5 µg·mL-1for Mucor hiemalis to >500 µg·mL-1for Aspergillus fumigatus, and pH had no influence on toxicity. Bafilomycins B1 and C1 were equally active against the fungal species tested, with MIC values in the range of <0.5-64 µg·mL-1. All fungi were more sensitive to both bafilomycin B1 and C1 at pH 7.0 than at pH 5.5.Key words: antifungal, bafilomycin, MIC, hyphal growth, Streptomyces halstedii.
A physical and genetic map of theMycoplasma hyopneumoniaestrain J genome
Authors: Blank Walter A , Stemke Gerald W
Published: April 2011

A macrorestriction map of the genome of Mycoplasma hyopneumoniae strain J, the type strain of the causative agent of enzootic pneumonia in pigs, was constructed using pulsed-field gel electrophoresis (PFGE) and DNA hybridization. The size of the genome as determined by PFGE was approximately 1070 kb. Assembly of the M. hyopneumoniae genomic map was facilitated and complimented by the simultaneous construction of an ordered cosmid library. Five contigs of overlapping cosmids were assembled, which together represent coverage of approximately 728 kb. Forty-two genetic markers (including three types of repeated elements) were placed on the M. hyopneumoniae map. Closer examination of an ApaI restriction fragment contained entirely within a single cosmid insert suggests that the genome size may be overestimated by PFGE.Key words: Mycoplasma hyopneumoniae, mollicutes, physical map, genetic map.
Effect of transferring 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase genes intoPseudomonas fluorescensstrain CHA0 and itsgacA derivative CHA96 on their growth-promoting and disease-suppressive capacities
Authors: Wang Chunxia , Knill Edouard , Glick Bernard R , Défago Geneviève
Published: April 2011

Pseudomonas fluorescens strain CHA0, a root colonizing bacterium, has a broad spectrum of biocontrol activity against plant diseases. However, strain CHA0 is unable to utilize 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of plant ethylene, as a sole source of nitrogen. This suggests that CHA0 does not contain the enzyme ACC deaminase, which cleaves ACC to ammonia and α-ketobutyrate, and was previously shown to promote root elongation of plant seedlings treated with bacteria containing this enzyme. An ACC deaminase gene, together with its regulatory region, was transferred into P. fluorescens strains CHA0 and CHA96, a global regulatory gacA mutant of CHA0. ACC deaminase activity was expressed in both CHA0 and CHA96. Transformed strains with ACC deaminase activity increased root length of canola plants under gnotobiotic conditions, whereas strains without this activity had no effect. Introduction of ACC deaminase genes into strain CHA0 improved its ability to protect cucumber against Pythium damping-off, and potato tubers against Erwinia soft rot in small hermetically sealed containers. In contrast, ACC deaminase activity had no significant effect on the ability of CHA0 to protect tomato against Fusarium crown and root rot, and potato tubers against soft rot in large hermetically sealed containers. These results suggest that (i) ACC deaminase activity may have lowered the level of plant ethylene thereby increasing root length; (ii) the role of stress-generated plant ethylene in susceptibility or resistance depends on the host-pathogen system, and on the experimental conditions used; and (iii) the constructed strains could be developed as biosensors for the role of ethylene in plant diseases.Key words: biocontrol, plant growth-promoting rhizobacteria, ACC deaminase, ethylene biosensors.
The binding ofProteus mirabilisnonagglutinating fimbriae to ganglio-series asialoglycolipids and lactosyl ceramide
Authors: Lee Kok K , Harrison Blair A , Latta Roger , Altman Eleonora
Published: April 2011

Proteus mirabilis is a common opportunistic Gram-negative uropathogen that infects the upper urinary tract. We have examined the role of the nonagglutinating fimbriae (NAF) of P. mirabilis in mediating bacterial adhesion to cell surface receptors. Purified NAF of P. mirabilis were demonstrated to bind to a number of glycolipids, including asialo-GM1, asialo-GM2, and lactosyl ceramide (LacCer) in solid-phase binding assays and in thin layer chromatography (TLC) overlay assays. Furthermore, preincubation of the biotinylated NAF (Bt-NAF) with anti-NAF monoclonal antibodies resulted in inhibition of NAF binding to immobilized asialo-GM1, asialo-GM2, and LacCer. In adherence assays, P. mirabilis binding to Madin-Darby canine kidney (MDCK) cells was inhibited by murine anti-asialo-GM1 monoclonal antibodies H2G10 to about 50% of the binding level in the absence of the antibody, specific for the terminal β-galactopyranosyl residue of asialo-GM1 (Harrison et al. 1998). The results of this study suggest that NAF of P. mirabilis recognize a GalNAcβ1-4Gal moiety present in the ganglio-series of asialoglycolipids, and that the terminal β-galactopyranosyl -containing glycoconjugates play a role in NAF-mediated adherence of P. mirabilis to MDCK cells. Similarly to other bacteria, P. mirabilis NAF was also shown to express the LacCer specificity.Key words: bacterial adhesion, Proteus mirabilis, fimbriae, receptors, glycosphingolipids.
Genome size ofEperythrozoon suisand hybridization with 16S rRNA gene
Authors: Messick Joanne B , Smith Geoffrey , Berent Linda , Cooper Sandra
Published: April 2011

The genome size of Eperythrozoon suis, an unculturable haemotropic mycoplasma, was estimated using pulsed-field gel electrophoresis (PFGE). Gamma irradiation was used to introduce one (on the average) double-strand break in the E. suis Illinois chromosome. Restriction enzymes that cut infrequently were also used to analyze genome size. The size estimate for the full-length genome was 745 kilobases (kb), whereas the size estimates based on the summation of restriction fragments ranged from 730 to 770 kb. The 16S rRNA gene was located on the 120-kb MluI fragment, 128-kb NruI fragment, 25-kb SacII fragment, and 217-kb SalI fragment by Southern blotting.Key words: Eperythrozoon suis, 16S rRNA, Mycoplasma pneumoniae group, pulsed-field gel electrophoresis, genome size.
Nutritional requirements of Brettanomyces bruxellensis: Growth and physiology in batch and chemostat cultures
Authors: Uscanga M Guadalupe Aguilar , Delia Marie-Line , Strehaiano Pierre
Published: April 2011

The nutritional requirements of Brettanomyces bruxellensis have been investigated. Batch culture and chemostat pulse techniques were used to identify growth-limiting nutrients. The study included determination of the essential components of the culture medium and quantification of the effects of the components. Among the components tested, ammonium sulfate and yeast extract had a significant effect on glucose consumption, growth, and ethanol production. However, if the ammonium sulfate concentration is above 2 g/L, an inhibitory effect on B. bruxellensis growth is observed. The yeast extract appears to be the most important and significant component for growth. The maximum amount of synthesized biomass is proportional to the concentration of yeast extract added to the culture broth (in the tested range). Magnesium and phosphate ions are probably not essential for B. bruxellensis. These ions appear to be supplied in sufficient amounts by the yeast extract in the culture medium. Brettanomyces bruxellensis appears to have very low nutritional requirements for growth.Key words: Brettanomyces bruxellensis, nutrition, ammonium sulfate, yeast extract.