bluuebunny/crossref_metadata_2025 huggingface dataset:
The Compressibility of and an Equation of State for Gaseous Ethane
Authors: Beattie James A. , Hadlock Canfield , Poffenberger Noland
Published: November 2004

The compressibility of gaseous ethane (C2H6) has been determined from 0.5 to 5.0 moles per liter and from 25° to 250°C with an estimated accuracy of 0.2 percent or better. Above 250°C ethane decomposes at an appreciable rate when confined in steel. An equation of state is fitted to the data. The average deviation of the calculated from the observed pressure is 0.13 atmosphere or 0.21 percent. The equation of state extrapolates to the critical pressure (at 7 moles/liter and 32.1°C) with an error of 10 percent and calculates the weight of a normal liter to 0.2 percent. The vapor pressures of liquid ethane at 0° and 25°C are given.
An Investigation of Adsorbed Films by Means of a Photoelectric Counter
Authors: Ouellet Cyrias , Rideal Eric K.
Published: November 2004

A photoelectric tube counter of special design has been used for investigating adsorbed layers on a gold surface. The high sensitivity of the counter allows accurate measurements of photoelectric thresholds to be made with continuous ultraviolet light from a source of moderate intensity. The variation of the work function φ with the amount of adsorbed material can thus be followed quantitatively and continuously. The formation of gold oxide layers proceeds over definite steps with increases of 0.35 volt in the work function. The adsorption of iodine is reversible and the resulting increase in the work function varies with the iodine pressure according to a Langmuir isotherm, the saturation value being Δφ = +0.21 volt. The adsorption of ethyl alcohol is also reversible, but gives rise to a double threshold, suggesting the existence of liquid islands on the gold surface.
Thermodynamic Properties of Sulfur Compounds I. Hydrogen Sulfide, Diatomic Sulfur and the Dissociation of Hydrogen Sulfide
Authors: Cross Paul C.
Published: November 2004

The thermodynamic properties of H2S are calculated from the structure recently obtained by the analysis of an infrared band. — [(F0—E00)/T]*298.1 = 41.174. S*298.1 = 49.151. (Not including the spin contribution.) Montgomery and Kassel's calculations for S2 are corrected in accordance with Badger's new interpretation of the data of Naudé and Christy. — [(F0—E00)/T]298.1 = 47.242. S0298.1 = 54.417. The results are applied to the reaction H2S = H2+½S2. The energy of dissociation of H2S into normal atoms, E00, is found to be 173.8 kg cal. per mole.
Studies with Vibrating Mechanical Models I. Benzene, Toluene and the Phenyl Halides
Authors: Teets D. E. , Andrews D. H.
Published: November 2004

By continuing the work of Kettering, Shutts and Andrews, mechanical models have been constructed for the series of compounds: C6H6,  C6H5CH3,  C6H5Cl,  C6H5Br,  C6H5I.The mechanical frequencies of the simpler types of motion show some correlation with the spectral lines, especially in the shifts of frequency in passing down the series of compounds. The types of motion observed are in fair accord with the types deduced with the aid of group theory.
Studies with Vibrating Mechanical Models II. The Series: C6H5Cl–C6Cl6
Authors: Murray J. W. , Deitz V. , Andrews D. H.
Published: November 2004

Mechanical models have been constructed for the following molecules based on the Pauling resonance formula for benzene: C6H6; C6H5Cl; o-, m-, p-C6H4Cl2; (1, 2, 3)-, (1, 2, 4)-, (1, 3, 5)-C6H3Cl3; C6Cl6. The mechanical spectra of these models have been observed and compared with the Raman spectra. The shifts in frequency observed in passing down the series are the same in both mechanical and Raman spectra in a number of cases. This makes possible the identification of several of the lines connected with the motions of the chlorine atoms and of the line at 992 cm—1 associated with the symmetrical expansion of the benzene ring. The types of motion show an evolution from the symmetrical group of C6H6, which can be correlated with group theory, through the various doublets and triplets associated with the less symmetrical intermediate compounds, to the group connected with C6Cl6 which is similar to that of C6H6 except for the inversion of frequency order due to the increased mass of the substituent atoms
The Crystal Structure of Cesium Enneachlordithalliate, Cs3Tl2Cl9
Authors: Hoard J. L. , Goldstein Leonard
Published: November 2004

Cs3Tl2Cl9 is shown to possess a rhombohedral unit of structure with a0=9.58A, α=83° 48′, containing two molecules. The crystals exhibit extensive and quite perfect 60° twinning on the basal plane, so that most specimens simulate complete sixfold symmetry, but when this is taken into consideration, a structure based upon D3d6 — R 3̄ c accounts well for observed intensity data. The structure may be described conveniently as an aggregate of Cs+ and Tl2Cl9—3 groups packed together in such manner that all large atoms fit into an approximately closest-packed arrangement. The Tl2Cl9—3 group is considered to be a covalent complex. The derived structure is compared with the known structures of Cs3As2Cl9 and KMgF3.
The Magnetic Susceptibility of Lithium Hydride The Diamagnetism of Ionic Crystals
Authors: Freed Simon , Thode Harry G.
Published: November 2004

The magnetic susceptibility of crystalline lithium hydride was measured at room temperature (300°A) and at 78°A and was found to be —4.60×10—6 per mole with practically no temperature coefficient. One theoretical prediction deviates from the experimental value by 90 percent and another by 130 percent. This discrepancy is interpreted as due mainly to a paramagnetism independent of the temperature which is present in all crystals and which has not been included in the calculations.
A Plant for the Production of Heavy Water
Authors: Brown W. G. , Daggett A. F.
Published: November 2004

A description is given of a plant for the production of deuterium oxide by the electrolytic method which operates with a higher efficiency than has been previously reported for this method. The fractionation factor, uncorrected for evaporation, averages 8.6. Steel cells, which also serve as the cathodes, are used and the entire construction is explosion-proof.
The Thermal Conductivity of Polyatomic Gases
Authors: Ubbelohde A. R.
Published: November 2004

Reasons are given for supposing that the thermal conductivity of polyatomic gases should not be independent of pressure. A calculation is made for carbon dioxide, and the results suggest that a portion of the specific heat at 0°C has a relaxation constant considerably less than 106 if the discrepancy between experimental and theoretical values of thermal conductivity is due to restrictions on the energy exchange between molecules. When such effects are present, determinations using parallel plates give a more reliable result than those using a vertical wire.
The Lifetime of Free Hydroxyl
Authors: Oldenberg O.
Published: November 2004

(1) The reasons for various failures to observe the absorption spectrum of free hydroxyl radicals are discussed. (2) The absorption spectrum of OH in the electric discharge through water vapor is observed with a spectrograph of high resolving power. After interrupting the discharge, the presence of OH is traced by its absorption spectrum over time intervals up to 1/8 sec. (3) With alternating half-periods of 60 cycle a.c. cut out by a switch, the emission of OH vanishes almost entirely with the current whereas the absorption persists rather uniformly. It is concluded that the persistence of the absorption spectrum is to be attributed to a long life of OH radicals rather than a long life of O and H atoms furnishing a fresh supply of short life OH radicals. (4) The rotational intensity distribution within the OH band at strong currents (being anomalous to a lesser extent than at faint currents) indicates the presence of free OH in the discharge. (5) For a comparison of the present result with previous estimates, leading to a much shorter life of free hydroxyl, the number per sec. of emission processes of the OH band is measured, assuming that each of these processes leads to the production of one free OH radical. (6) The process by which OH radicals are consumed is discussed.
Non-Silicates with Cristobalite-Like Structure
Authors: Barth Tom. F. W.
Published: November 2004

The cristobalite type of structure which has been previously observed in certain silicates: carnegieite, NaAlSiO4, and Na2CaSiO4 is now shown to occur in K2O.Al2O3, K2O.Fe2O3, and Na2O.Al2O3.
The Free Energy of Sulphur Dioxide
Authors: Gordon A. R.
Published: November 2004

Values of (Fo—E0o)/T for sulphur dioxide are computed from spectroscopic data; the heat of formation of sulphur dioxide from diatomic sulphur and oxygen is calculated from the calorimetric heats of formation of sulphur dioxide and hydrogen sulphide, and Cross' value for the energy of dissociation of hydrogen sulphide. Equilibrium constants for the reactions 12S2(g)+O2=SO2,  SO+12O2=SO2are tabulated for the range 298.1 to 2800°K.
The Ethane-Ethylene-Hydrogen Equilibrium
Authors: Smith Hilton A. , Vaughan William E.
Published: November 2004

An attempt has been made to correlate several data on this system by a statistical calculation of the equilibrium constants in the temperature range of 400 to 700°C. The data are in good agreement but the calculated values of the K's are smaller than the experimental by a factor of two. It is thought that the principal reason for this discrepancy lies in the calculation of the entropy of free rotation in ethane, although other factors may contribute.
The Number of Canonical Structures of Each Degree of Excitation for an Unsaturated or Aromatic Hydrocarbon
Authors: Wheland G. W.
Published: November 2004

A simple procedure is outlined for obtaining the number of canonical structures of each degree of excitation for an arbitrary hydrocarbon molecule. The results are applied to the approximate calculation of the energies of a number of such systems.
The Low Frequency Fundamental Bands of Methyl Chloride, Methyl Bromide and Methyl Iodide
Authors: Barker E. F. , Plyler E. K.
Published: November 2004

The parallel type bands ν5 for CH3Cl, CH3Br and CH3I have been found at λ13.7, 16.4 and 18.8μ, respectively, the rotation lines of the chloride band being partially resolved. The iodide band has a particularly sharp zero branch suitable for use in calibration. Both the chloride and bromide bands are complicated by isotopic effects, the separations being 6 cm—1 and 1 cm—1.
The Zeeman Effect of the Absorption Lines of Crystalline KCr(SO4)2–12H2O
Authors: Spedding F. H. , Nutting G. C.
Published: November 2004

The Zeeman effect of the absorption lines of chrome alum crystals cooled to 20°K has been photographed for field strengths of from 12,000 to 25,000 gauss. Each of the three strong lines splits into three elliptically polarized components, whose separation of very close to 2ω suggests ``spin only'' orientation in the field. At 50°K, but not at 20°, the pattern depends upon the orientation of the crystal lattice with respect to the magnetic field. Interaction between closely spaced levels seems to be small and is evidenced only by slight intensity dissymmetries. No shift of the central components from the positions of the field-free lines is observed, and the magnitude of a possible second-order Zeeman effect is estimated as less than 10 percent that of the first-order effect. The selection rule for the magnetic quantum number, Δm=±1, 0, seems to be obeyed, making it impossible for the present to decide whether the upper levels belong to the quartet or doublet system. Various possible coupling schemes are considered in the light of the experimental evidence and it is concluded that the actual one existing in chrome alum is either the strong field case in which L and S do not interact appreciably and L is almost completely quenched, or the very strong field case in which the coupling of the individual l's is broken down and the individual orbital moments are quenched.
The Vibrations of Polyatomic Molecules in Excited Electronic States
Authors: Duncan A. B. F.
Published: November 2004

The vibration frequencies found in the excited states of the molecules CO2, CS2, H2O, ClO2, SO2, O3, NH3, PCl3, C2H2, C2H4, C6H6 and (CH3)2CO are considered. The frequencies appearing most strongly in all cases, and in most cases the only frequencies occurring, are totally symmetrical. This is in accord with the extension of the Franck-Condon principle to such molecules by Herzberg and Teller.
On the Stokes Phenomenon for the Differential Equations Which Arise in the Problem of Inelastic Atomic Collisions
Authors: Rice O. K.
Published: November 2004

The problem of inelastic atomic collisions, involving exchange of energy between the atoms, depends upon the solution of a pair of coupled differential equations equivalent to a single differential equation of the fourth order, in which the independent variable is the distance, r, between the two atoms. Asymptotic forms for the solutions of this pair of equations may be found. The probability of energy exchange may be shown to depend upon the connections between the solutions for values of r which correspond to regions of space where the relative kinetic energy of the two atoms is positive and the solutions for values of r corresponding to regions where the kinetic energy is negative. The finding of these connections involves a study of the asymptotic forms of the solutions when these forms are considered as functions of a complex variable. Such a study has been made in this paper, and the corresponding Stokes phenomenon investigated. The desired end was not achieved, but results of interest have nevertheless been obtained. A brief discussion is given of the previous work of Stueckelberg.
The Raman Spectra of Arsenic Trichloride and of Its Mixtures
Authors: Brodskii A. E. , Sack A. M.
Published: November 2004

The Raman spectra from mixtures of AsCl3 with benzene, carbon tetrachloride, methyl and ethyl alcohol have been investigated. The strong deviations from additivity have been observed for AsCl3 in alcohols. The shifts are correlated with the strength of the bond As–Cl. A computation of the constants of the molecule AsCl3 is made which agrees with electronographic data. The geometrical configuration of the molecule AsCl3 in mixtures undergoes only a slight deformation, but the bond As–Cl is considerably weakened in alcoholic solutions.
On the Electrolytic Separation of the Hydrogen Isotopes
Authors: Halpern O. , Gross Ph.
Published: November 2004

Starting from the hypothesis that the rate-determining process in the electrolysis of gases is constituted by the recombination of the gas atoms on the electrode, a formula is developed which expresses the separation coefficient as a function of well-known thermodynamic constants of H and D compounds and of the frequencies with which the atoms carry out their thermal oscillations on the electrode. The formula gives a certain range for the value of the separation coefficient which is in good agreement with the observations. As a by-product of these calculations a relation is established between the normal electrode potentials of H and D.
On the Dissociation Constants of Acids in Light and Heavy Water
Authors: Halpern O.
Published: November 2004

The ratio of dissociation constants of acids in light and heavy water is shown to become the larger the weaker the acid. This is a consequence of the differences in zero-point energy of the proton (deuteron) when attached to the anion or the neutral water molecule.
The Activation Energy of Unimolecular Reactions. II
Authors: Rice O. K. , Gershinowitz Harold
Published: November 2004

The modifications in our earlier paper by the above title, necessitated by recent work on the absolute rate of chemical reactions, are considered, and it is shown that the assumption that the fragments resulting from a unimolecular decomposition must be ``exactly oriented'' (in the sense of the preceding article) in order to be able to recombine is equivalent to the assumptions made by Kassel in his quantum theory of unimolecular reactions. The relation between the observed activation energy and the energy necessary to break the bond is discussed.
Electronic Structures of Polyatomic Molecules. VIII. Ionization Potentials
Authors: Mulliken Robert S.
Published: November 2004

Observed and predicted values for ionization potentials of nonbonding electrons are compared, and the differences attributed mainly to charge-transfer effects. Multiplet interval and other criteria are cited as evidence that assumed nonbonding orbitals are really such, i.e., that they are effectively localized and interact little with other orbitals. The prediction of ionization potentials for bonding and antibonding electrons is also discussed. The present paper grows, in part, from suggestions of Price as to the effects of dipole fields on ionization potentials.
Comparison of the Raman Spectra of 1,1,1- and 1,1,2-Trichloroethane
Authors: Hull Gordon F.
Published: November 2004

The Raman frequencies of 1,1,1- and 1,1,2-trichloroethane have been obtained. Comparison with CCl4 indicates that the Cl3C and Cl2HC radicals have tetrahedral symmetry. The frequencies of Cl3C–CH3 and Cl2HC–CH2Cl are compared, and the combination frequencies and modes of vibration of the two molecules indicated.
The Absorption Spectra and Dissociation Energies of Cyanic Acid and Some Isocyanates
Authors: Woo Sho-Chow , Liu Ta-Kong
Published: November 2004

The absorption spectra of gaseous isocyanic acid, methyl, ethyl and phenyl isocyanates have been observed in the ultraviolet. The long wavelength limits of the continuous absorption found were as follows: HNCO, λ2240; CH3NCO, λ2550; C2H5NCO, λ2480; C6H5NCO, λ2420A. In the case of isocyanic acid, diffuse bands were also found in the region λλ2570–2250A. Characteristic absorption bands due to an excitation in the benzene ring were found in phenyl isocyanate. The structures are probably represented by the formulae H–N=C=O, CH3–N=C=O, C2H5–N=C=O, C6H5–N=C=O. The products and energies of dissociation have been described. The absence of the characteristic absorption due to =C=0 has also been discussed.
The Kinetics of the Oxidation of Gaseous Glyoxal
Authors: Steacie E. W. R. , Hatcher W. H. , Horwood J. F.
Published: November 2004

The kinetics of the oxidation of gaseous glyoxal have been investigated at 220°C. The reaction occurs by a chain mechanism, the rate being dependent upon roughly the second power of the aldehyde concentration, and independent of oxygen provided the oxygen concentration is not too low. The wall factor in the breaking of chains is not very pronounced, but the condition of the surface is of importance in the initiation of the chains. The main products of the reaction are CO, CO2, H2O and glyoxylic acid. The results are satisfactorily expressed by the mechanism of aldehyde oxidation previously proposed by Steacie, Hatcher and Rosenberg.
Electronic Structures of Molecules X. Aldehydes, Ketones and Related Molecules
Authors: Mulliken Robert S.
Published: November 2004

Electron configurations for the normal states of H2CO, CH3HCO, Cl2CO are explicitly given, also for the low excited states of H2CO. The structures, ionization potentials, and longest wavelength electronic band spectra of these and other related or analogous molecules (saturated aldehydes, ketones, thioaldehydes, thioketones, etc.) are interpreted in relation to these configurations. In particular is it shown that the minimum ionization potential of =C=O or =C=S corresponds to removal of a nonbonding 2p electron from the O atom or a nonbonding 3p from the S atom, unless the groups attached to the C contain other unusually easily ionized electrons. Similarly, the longest wavelength band system, commonly attributed to the C=O (or C=S) double bond, corresponds to excitation of the nonbonding 2po or 3ps to an excited orbital which is largely but probably not quite wholly localized in the C=O or C=S bond, and which has C↔O or C↔S antibonding power, i.e., loosens the bond somewhat. This excitation process is responsible for color in the =C=S compounds. The C=O (or C=S) bond is a true double bond in the sense that the binding is effected essentially by two pairs of C–O (or C–S) bonding electrons. The C=O bond is essentially the same also in saturated monobasic acids RCOOH or at least in their esters.
Bifurcation analysis and existence of periodic solutions in a simple neural network with delays
Authors: Wei J. J. , Velarde M. G.
Published: November 2004

Results are provided here about the stability and bifurcation of periodic solutions for a (neural) network with n elements where delays between adjacent units and external inputs are included. The particular cases n=2 and n=3 are discussed in details, to explicitly illustrate the role of the delays in the corresponding bifurcation sets and the stability properties, like a Hopf bifurcation, a pitchfork bifurcation, and a Bogdanov–Takens bifurcation.
Umbral calculus, difference equations and the discrete Schrödinger equation
Authors: Levi Decio , Tempesta Piergiulio , Winternitz Pavel
Published: November 2004

In this paper, we discuss umbral calculus as a method of systematically discretizing linear differential equations while preserving their point symmetries as well as generalized symmetries. The method is then applied to the Schrödinger equation in order to obtain a realization of nonrelativistic quantum mechanics in discrete space–time. In this approach a quantum system on a lattice has a symmetry algebra isomorphic to that of the continuous case. Moreover, systems that are integrable, superintegrable or exactly solvable preserve these properties in the discrete case.
Absolute and convective nature of Raman instability in relativistic hot plasmas
Authors: Grismayer T. , Couairon A. , Mora P. , Adam J.-C. , Héron A.
Published: November 2004

The modulational and Raman instabilities are investigated in the relativistic regime, for a large amplitude electromagnetic wave propagating in a hot plasma of arbitrary density. Temporal growth rates and the number of unstable branches are determined when the plasma temperature, density, and the amplitude of the wave vary. The convective or absolute nature of the Raman instabilities is then determined. The present paper extends previous results by Guérin et al. [Phys. Plasmas 2, 2807 (1995)] and Couairon and Mora [Phys. Plasmas 8, 3434 (2001)]. It is shown that for any temperature, the Raman instability is convectively unstable at low density and low intensity, and absolutely unstable when the intensity or the density exceeds a threshold that we determine as a function of the temperature. In contrast with the cold plasma case, the threshold for absolute instability does not coincide with the merging of branches found by a classical temporal stability analysis.
Classification of extensions of principal bundles and transitive Lie groupoids with prescribed kernel and cokernel
Authors: Androulidakis Iakovos
Published: November 2004

The equivalence of principal bundles with transitive Lie groupoids due to Ehresmann is a well-known result. A remarkable generalization of this equivalence, given by Mackenzie, is the equivalence of principal bundle extensions with those transitive Lie groupoids over the total space of a principal bundle, which also admit an action of the structure group by automorphisms. In this paper the existence of suitably equivariant transition functions is proved for such groupoids, generalizing consequently the classification of principal bundles by means of their transition functions, to extensions of principal bundles by an equivariant form of Čech cohomology.
Effects of substrate bias on electron energy distribution in magnetron sputtering system
Authors: Seo Sang-Hun , In Jung-Hwan , Chang Hong-Young , Han Jeon-Geon
Published: November 2004

In the downstream region of an unbalanced magnetron argon discharge, the influences of substrate bias (i.e., the condition of plasma boundary) on electron energy distribution function and plasma characteristics were investigated through the experiments using a single Langmuir probe. In a steady state with the grounded substrate, it could be found that the electron current flowing to the substrate compensates for the ion current flowing to the cathode due to the axial magnetic field such that the substrate plays the role of the actual anode. The potential of the anode sheath could be controlled by applying a dc voltage to the substrate, and the nonlinear behavior of the plasma potential with respect to the dc substrate voltage caused the distinctive evolution of the potential of the anode sheath. It was found that a transition of the electron energy distribution function from a bi-Maxwellian distribution at small dc voltages to a Maxwellian distribution at highly negative dc voltages occurs with decreasing the substrate bias voltage. This phenomenon was discussed in view of the role of the substrate as an electron loss boundary and the cooling mechanism of electrons in bulk plasmas.
Magnetic island effects on axisymmetric equilibria
Authors: Liu X. , Callen J. D. , Hegna C. C.
Published: November 2004

The plasma magnetohydrodynamics equilibrium equation in the vicinity of a single, thin magnetic island region is derived. First, the pressure profile in the vicinity of an island is determined using the continuity of transport fluxes across the island assuming a diffusive form for the fluxes. Then, by considering the island-induced magnetic perturbation, the structure of the current density around an island is examined. The modifications of the pressure and current density in the vicinity of a magnetic island lead to an equation that describes the toroidal equilibrium of the plasma. An “effective” axisymmetric Grad–Shafranov equation is constructed by taking a helical average over the toroidal equilibrium. Thus, we can take account of the three-dimensional magnetic island effects for a thin island in a two-dimensional equation. As with the Grad–Shafranov equation, the calculation does not employ a large aspect ratio or small β approximation; however, it uses a small island width (w≪r)s expansion. Finally, we determine the time-varying signal that would be observed on a probe measuring a scalar quantity such as the pressure when a magnetic island structure is rotating relative to the probe.
Cylindrical and spherical ion-acoustic shock waves in multielectron temperature collisional plasma
Authors: Sahu Biswajit , Roychoudhury Rajkumar
Published: November 2004

The properties of cylindrical and spherical ion-acoustic shock waves are examined in multielectron temperature collisional plasma. Cylindrical and spherical Korteweg–de Vries–Burger (KdVB) equations for ion-acoustic shock waves are derived taking into account the ion viscosity and the ion heat conductivity and their numerical solutions are obtained. For weak dissipation and thermal conductivity an analytical expression for the cylindrical KdVB solution is obtained. Also the effects of ion viscosity and heat conductivity on the properties of shock wave are studied.
Three-dimensional simulations of magnetic reconnection in slab geometry
Authors: Onofri M. , Primavera L. , Malara F. , Veltri P.
Published: November 2004

Magnetic reconnection in an incompressible plasma in three-dimensional slab geometry has been studied through magnetohydrodynamics numerical simulations. Particular attention has been paid to the case in which several unstable modes that correspond to resonant surfaces in different positions of the simulation domain, are excited at the beginning of the simulation. The dynamical evolution of such a system leads to a behavior different than what is expected from the linear theory. In particular the effects of the equilibrium field dissipation and the fact that several resonant surfaces are initially excited both concur in modifying the initial growth rates of the instability. In the nonlinear phase two basic phenomena are observed: first, the rapid transfer of energy to large wave numbers, corresponding to a direct cascade of the energy in the spectrum, which approaches, with increasing time, a power law; second, an energy transfer towards smaller wave numbers, which corresponds in the physical space to a coalescence of magnetic islands. Finally, the spectra in the periodic directions exhibit a strongly anisotropic behavior.
Minimizing the magnetohydrodynamic potential energy for the current hole region in tokamaks
Authors: Chu M. S. , Parks P. B.
Published: November 2004

The current hole region in the tokamak has been observed to arise naturally during the development of internal transport barriers. The magnetohydrodynamic (MHD) potential energy in the current hole region is shown to be determined completely in terms of the displacements at the edge of the current hole. For modes with finite toroidal mode number n≠0, the minimized potential energy is the same as if the current hole region were a vacuum region. For modes with toroidal mode number n=0, the displacement is a superposition of three types of independent displacements: a vertical displacement or displacements that compress only the plasma, or the toroidal field uniformly. Thus for ideal MHD perturbations of plasma with a current hole, the plasma behaves as if it were bordered by an extra “internal vacuum region.” The relevance of the present work to computer simulations of plasma with a current hole region is also discussed.
Self-field effects on electron dynamics in free-electron lasers with axial magnetic field
Authors: Mirzanejhad S. , Maraghechi B. , Mohsenpour T.
Published: November 2004

A self-consistent method for the analysis of self-magnetic field for a free-electron laser with a one-dimensional helical wiggler and an axial guide magnetic field is presented. The equilibrium orbits and their stability, under the influence of self-electric and self-magnetic fields, are analyzed. New unstable orbits, in the first part of the Group I orbits and in the resonance region of the Group II orbits, are found. It is shown that an increase in the defocusing effect of self-fields will widen the unstable orbits. An anomalous self-field regime is found where an increase in the defocusing effect of self-fields can have stabilizing effect on the resonance region.
Analytical bounds on the whistler mode refractive index
Authors: Albert Jay M.
Published: November 2004

The refractive index μ for whistler mode plane waves in a magnetized electron–proton plasma is considered as a function of normalized wave frequency ω/Ωe at fixed density and angle of propagation. A factorization into an increasing function of frequency times a decreasing function of frequency is found, valid for any value of ωpe/Ωe, for ω between (ΩeΩi)1/2 and the smaller of Ωe and ωpe. This leads to lower and upper bounds on μ2 over any given frequency subinterval. The bounds can be directly applied to a quasilinear formulation of velocity-space diffusion of electrons in the Earth’s radiation belts, in a generalization of previously developed techniques to low density conditions found outside the plasma pause.
Comparison of a copper foil to a copper wire-array Z pinch at 18 MA
Authors: Nash T. J. , Deeney C. , Chandler G. A , Sinars D. B. , Cuneo M. E. , Waisman E. M. , Stygar W. A. , Wenger D. , Speas S. , Leeper R. J. , Seaman J. F. , McGurn J. , Torres J. , Jobe D. , Gilliland T. , Nielsen D. , Hawn R. , Seaman H. , Keller K. , Moore T. , Wagoner T. C. , LePell P. D. , Lucas J. , Schroen D. , Russell C. , Kernaghan M.
Published: November 2004

Results from the first solid foil implosion on the 18-MA Z accelerator are reported. The foil implosion is compared to a 300-wire-array implosion with the same material and the same diameter, height, and total mass. Though both the foil and the array produced comparable x-ray yields, the array’s radiation burst was twice as powerful and half as long as the foil’s. These data along with x-ray backlighting images and inductance measurements suggest that the foil implosion was more unstable than the wire-array implosion.
Linear feedback stabilization of laminar vortex shedding based on a point vortex model
Authors: Protas Bartosz
Published: November 2004

In this paper we use the Föppl point vortex system as a reduced-order model for stabilization of the steady symmetric solution in an unstable laminar wake. The downstream location of the Föppl vortices is chosen so as to produce the same recirculation length as in the actual flow at a given Reynolds number. When the cylinder rotation is used as flow actuation, the linearized Föppl system is shown to be stabilizable, but not controllable. With centerline velocity measurements as the system output, the linearized Föppl model is also shown to be fully observable. The Linear-Quadratic-Gaussian (LQG) control design is performed based on the linearized Föppl system which has only four degrees of freedom. Computational results show that thus designed LQG compensator stabilizes the stationary solution of the nonlinear Föppl system. When applied to an actual cylinder wake at Re=75, the LQG compensator stabilizes the downstream region of the flow. Possibilities and limitations of flow control strategies based on point vortex systems as reduced-order models are discussed.
Sinusoidal phase grating created by a tunably buckled surface
Authors: Harrison Christopher , Stafford Christopher M. , Zhang Wenhua , Karim Alamgir
Published: November 2004

We investigate a buckling instability by both small angle light scattering and atomic force microscopy, demonstrating that a tunable phase grating can be created with a mechanical instability. The instability is realized in a prestressed silicone sheet coated with a glassy polymer film. Compression of the sample results in a sinusoidally wrinkled surface where the amplitude is controlled by the degree of compression and the wavelength by film thickness. We model the system with Fourier optics, explaining the positions and relative intensities of the diffraction orders.
Comments on the mean flow averaged model
Authors: Bardan G. , Razi Y. P. , Mojtabi A.
Published: November 2004

The dynamic behavior of convective motion in a confined porous medium saturated by a pure fluid under the action of mechanical vibration is studied. A redefinition of vibrational Rayleigh number is proposed from which we distinguish the domain of validity of the mean flow. The weakly nonlinear stability analysis performed demonstrates, contrary to published results, that the bifurcation is of supercritical nature and the subcritical branch does not exist. It is emphasized that, in order to find the thermal behavior of the system for the onset of convection, we should separate the vibrational effect from the thermal effect involving the temperature difference.
Electroabsorption in single-crystal film of a second-order optical material
Authors: Swamy R. K. , Kutty S. P. , Titus J. , Khatavkar S. , Thakur M.
Published: November 2004

In this letter, we report results of electroabsorption and resonant electro-optic measurements in single-crystal film of 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). The electroabsorption measurement was made by recording the changes in transmission through the film as an ac field was applied along the dipole axis. The electro-optic measurement was made using the field-induced birefringence method. The measurements were made in the absorptive domain, at 633 and 488nm. The modulation (ΔT∕T) due to electroabsorption decreased as the angle between the incident polarization and the dipole axis was increased. The observed electroabsorption is due to the imaginary part of the electro-optic coefficient. The real part of the electro-optic coefficient (r11) as measured at 633nm is 770pm∕V. The imaginary parts of the electro-optic coefficients at 633 and 488nm are 104 and 259pm∕V, respectively.
Photon lifetime dependence of modulation efficiency and K factor in 1.3μm self-assembled InAs∕GaAs quantum-dot lasers: Impact of capture time and maximum modal gain on modulation bandwidth
Authors: Ishida Mitsuru , Hatori Nobuaki , Akiyama Tomoyuki , Otsubo Koji , Nakata Yoshiaki , Ebe Hiroji , Sugawara Mitsuru , Arakawa Yasuhiko
Published: November 2004

We studied small-signal modulation characteristics of 1.3μm InAs∕GaAs self-assembled quantum-dot lasers in terms of the modulation efficiency and the K factor as a function of the photon lifetime. We could explain the measured photon-lifetime dependence based on the rate equation model considering explicitly the carrier-capture process and Pauli blocking in quantum dots. Our model shows how the modulation bandwidth of quantum-dot lasers is limited by the carrier-capture time and by the maximum modal gain via the K factor. We present prerequisite designs of quantum-dot active regions for over 10GHz modulation.
Hysteretic current–voltage characteristics and resistance switching at a rectifying Ti∕Pr0.7Ca0.3MnO3 interface
Authors: Sawa A. , Fujii T. , Kawasaki M. , Tokura Y.
Published: November 2004

We have characterized the vertical transport properties of epitaxial layered structures composed of Pr0.7Ca0.3MnO3(PCMO) sandwiched between SrRuO3(SRO) bottom electrode and several kinds of top electrodes such as SRO, Pt, Au, Ag, and Ti. Among the layered structures, Ti∕PCMO∕SRO is distinct due to a rectifying I–V characteristic with a large hysteresis. Corresponding to the hysteresis of the I–V characteristics, the contact resistance of the Ti∕PCMO interface reversibly switches between two stable states by applying pulsed voltage stress. We propose a model for the resistance switching at the Ti∕PCMO interface, in which the width and/or height of a Schottky-like barrier are altered by trapped charge carriers in the interface states.
Observation of ferromagnetism above 900K in Cr–GaN and Cr–AlN
Authors: Liu H. X. , Wu Stephen Y. , Singh R. K. , Gu Lin , Smith David J. , Newman N. , Dilley N. R. , Montes L. , Simmonds M. B.
Published: November 2004

We report ferromagnetism at over 900K in Cr–GaN and Cr–AlN thin films. The magnetic properties vary as a function of Cr concentration with 60%, and 20%, of the Cr being magnetically active at 3% doping in GaN, and 7% in AlN, respectively. In the GaN sample with the highest magnetically active Cr (60%), channeling Rutherford backscattering indicates that over 70% of Cr impurities are located on substitutional sites. These results give indisputable evidence that substitutional Cr defects are involved in the magnetic behavior. While Cr–AlN is highly resistive, Cr–GaN exhibits properties characteristic of hopping conduction including T−1∕2 resistivity dependence and small Hall mobility (0.06cm2∕Vs). A large negative magnetoresistance is attributed to the influence of the magnetic field on the quantum interference between the many paths linking two hopping sites. The results strongly suggest that ferromagnetism in Cr–GaN and Cr–AlN can be attributed to the double exchange mechanism as a result of hopping between near-midgap substitutional Cr impurity bands.
Photoluminescence properties of lamellar aggregates of titania nanosheets accommodating rare earth ions
Authors: Xin Hao , Ma Renzhi , Wang Lianzhou , Ebina Yasuo , Takada Kazunori , Sasaki Takayoshi
Published: November 2004

Fluorescent semiconductor materials doped with rare earth ions have been synthesized by flocculation of colloidal titania nanosheets, Ti0.91O2, with Eu3+ or Tb3+ ions. The composites had a lamellar structure with a gallery height of 1.06nm, accommodating rare earth ions between the nanosheets with a doping concentration as high as 10±1mol%. The composite with Eu3+ exhibited intense characteristic emission from Eu3+ either by exciting the Ti0.91O2 host with UV light (λ<350nm) or by directly exciting Eu3+ at a longer wavelength where there was no absorption by Ti0.91O2. This indicates that nonradiative energy transfer from the Ti0.91O2 host to Eu3+ can take place in this system. In contrast, no energy transfer was observed in the composite with Tb3+.
Recombination activity of interstitial iron and other transition metal point defects in p- and n-type crystalline silicon
Authors: Macdonald Daniel , Geerligs L. J.
Published: November 2004

Interstitial iron in crystalline silicon has a much larger capture cross section for electrons than holes. According to the Shockley–Read–Hall model, the low-injection carrier lifetime in p-type silicon should therefore be much lower that in n-type silicon, while in high injection they should be equal. In this work we confirm this modeling using purposely iron-contaminated samples. A survey of other transition metal impurities in silicon reveals that those which tend to occupy interstitial sites at room temperature also have significantly larger capture cross sections for electrons. Since these are also the most probable metal point defects to occur during high temperature processing, using n-type wafers for devices such as solar cells may offer greater immunity to the effects of metal contaminants.
Photoresponsivity of polymer thin-film transistors based on polyphenyleneethynylene derivative with improved hole injection
Authors: Xu Yifan , Berger Paul R. , Wilson James N. , Bunz Uwe H. F.
Published: November 2004

The photoresponse of polymer field-effect transistors (PFETs) based on the 2,5-bis(dibutylaminostyryl)-1,4-phenylene-b-alkyne-b-1,4-bis(2-ethylhexyl)benzene terpolymer (BAS-PPE) is investigated. BAS-PPE is a photoluminescent conducting polymer with a band gap of 2.25eV. The BAS-PPE PFETs were fabricated using an open coplanar configuration and light is illuminated onto the top side of the PFETs with no shadowing present. A sweep of VDS demonstrates that IDS saturation is suppressed during illumination, which suggests that pinch-off cannot be reached since the injected photogenerated carriers continue unabated. Also, with incident light, the channel cannot be turned off, even at high positive gate biases, due to the accumulation of photogenerated carriers. A sweep of VDS shows that BAS-PPE can act as a p-type polymer and favors hole injection and transport. A sweep of VGS shows an increase in IDS with different light intensities. The Ilight∕Idark ratio reaches as high as about 6000 at an incident light intensity of 4μW and a photoresponsivity of 5mA∕W is calculated.
Spectroscopic second harmonic generation measured on plasma-deposited hydrogenated amorphous silicon thin films
Authors: Kessels W. M. M. , Gielis J. J. H. , Aarts I. M. P. , Leewis C. M. , van de Sanden M. C. M.
Published: November 2004

Optical second harmonic generation (SHG) has been measured for plasma-deposited thin films of hydrogenated amorphous silicon (a-Si:H) at different polarization states for pump photon energies between 1.0 and 1.7eV. Distinct resonance peaks are observed in this energy range and it is shown that the SH signal originates from an isotropic contribution at both the film-surface and substrate-interface region. The possibility that the SH signal originates from surface and interface dangling bond states of a-Si:H is discussed.
Binary mixtures of inelastic spheres: Simplified constitutive theory
Authors: Arnarson Birgir Ö. , Jenkins James T.
Published: November 2004

We provide approximate expressions for the transport coefficients of a binary mixture of smooth, nearly elastic spheres when the radii and/or the masses are not too different. Using these, we formulate the approximate equations for segregation in a steady shearing flow with gravity transverse to the flow and provide numerical solutions for two examples.
Control of the magnetic anisotropy of epitaxially grown MnAs∕GaAs ferromagnet-semiconductor hybrid superlattices
Authors: Song J. H. , Lee J. J. , Cui Y. , Ketterson J. B. , Cho Sunglae
Published: November 2004

Epitaxial hybrid structures of the ferromagnet–semiconductor superlattice MnAs∕GaAs were grown on GaAs(001) substrates by molecular-beam epitaxy and the dependence of the magnetic properties on the growth temperature and the periodicity were characterized. The magnetic anisotropy is strongly dependent on the surface reconstruction of GaAs(001) substrates. The increase of the periodicity from 5nm∕5nm to 10nm∕10nm also changes the magnetic anisotropy. These results demonstrate that the surface reconstruction of the substrate and the periodicity determine the magnetic structure of the MnAs∕GaAs superlattices.
Real-time detection of ambient oxidation of steps and terraces on Si(111)-(1×1):H by scanning force microscopy
Authors: Khan Abbas , Hess Peter
Published: November 2004

The initial stage of oxide formation on Si(111)-(1×1):H, a highly controversial problem, has been studied using scanning force microscopy under ambient conditions (25% relative humidity at 20°C). Real-time monitoring of changes in the root-mean-squared (rms) roughness of the broad terraces and step heights was performed at the same surface spots. The height of the bilayer steps increased by 0.2–0.3nm with a maximum after about 22h and decreased afterward due to further oxidation of the terrace on a longer time scale. This finding clearly suggests fast bilayer step oxidation, as opposed to terrace oxidation, contrary to previous reports.
Minimization of out-of-plane losses in planar photonic crystals by optimizing the vertical waveguide
Authors: Ferrini R. , Berrier A. , Dunbar L. A. , Houdré R. , Mulot M. , Anand S. , de Rossi S. , Talneau A.
Published: November 2004

A two-dimensional phenomenological approach previously developed for the modeling of out-of-plane losses in low refractive index contrast planar photonic crystals (PPhCs) is used to study the dependence of the different loss terms on the planar waveguide parameters. It is demonstrated that: (i) Losses can be minimized by designing vertical heterostructures optimized for a given technological process and/or for a given hole shape; and (ii) any small reduction of the loss value has a strong impact on the optical performances of PPhC structures.
InGaAs
∕
AlAsSb
quantum cascade lasers
Authors: Revin D. G. , Wilson L. R. , Zibik E. A. , Green R. P. , Cockburn J. W. , Steer M. J. , Airey R. J. , Hopkinson M.
Published: November 2004

The In0.53Ga0.47As∕AlAs0.56Sb0.44 heterostructure system is of significant interest for the development of high-performance intersubband devices due to its very large conduction band offset (ΔEc∼1.6eV) and lattice-matched compatibility with well-established InP-based waveguide technology. In this letter, we report the realization of In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum cascade lasers emitting at λ∼4.3μm. The highest-performance devices have low-temperature (20K) threshold currents of ∼6kA∕cm2 and display laser action up to a maximum temperature of 240K, with a characteristic temperature of T0∼150K.
Electrochemically deposited nanowhiskers of nickel oxide as a high-power pseudocapacitive electrode
Authors: Prasad K. Rajendra , Miura Norio
Published: November 2004

High performance pseudocapacitive characteristics of potentiodynamically deposited NiO are reported here. Three-dimensional nanowhiskers of NiO were prepared by potentiodynamically depositing nickel hydroxide on stainless steel (SS) and heating the hydroxide in air at 300°C for 3h. The scan rate used for the deposition was 200mVs−1 and the electrolyte solution used was 100mM NiCl2∙6H2O at a pH8.0. The NiO-covered SS electrodes were characterized by cyclic voltammetry (CV) in 1M KOH electrolyte for the redox supercapacitor application. A maximum specific capacitance (SC) of 138Fg−1 was obtained from the CV at a scan rate of 100mVs−1. A SC value of 82Fg−1 was obtained even at the very high CV scan rate of 500mVs−1, demonstrating the high-power characteristics of NiO. Long cycle-life of the NiO nanowhiskers was also demonstrated. High specific capacitance, high power, high stability, and low cost of the electrode materials are favorable factors for commercial applications.