bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Temperature Distribution in a Low-Pressure Flat Flame
Authors: Friedman Raymond , Burke Edward
Published: April 2005

The temperature distribution in a very lean, flat propane-air flame was measured by the thermocouple method, at a pressure of 0.0594 atmos. The temperature change occurred in a zone about 3 cm thick. Wallquenching was minimized by employing a burner tube diam of 25 cm. The thermocouple was made from 12-micron wire, coated with ceramic to avoid catalytic effects. One hundred experimental traverse points were obtained, with a standard deviation of ±0.016 cm.

The burning velocity was also measured, and was found to vary with the inverse 0.30 power of pressure. This is in agreement with Egerton and Sen's result, obtained over a more limited range of pressure.

The temperature pattern was analyzed mathematically to obtain the pattern of heat release rate, taking into account the variation with temperature of thermal conductivity and specific heat. It was found that the heat release began at 300°C, attained a maximum value of 1.2 cal/cm3-sec at 1100°C, was nowhere negative, and was finite over a zone about 2 cm thick. The maximum temperature of the flame was 1332°C. The result obtained for the ``ignition point'' was found to be extremely sensitive to the exponent giving the temperature dependence of the thermal conductivity. Some calculations relating to the chemical kinetics of the flame are described.
Studies of Evaporation of Small Drops
Authors: Monchick Louis , Reiss Howard
Published: April 2005

The rates of evaporation of small droplets of diamyl sebecate (average radius R∼10—4 cm) were measured in a Millikan oil-drop chamber, and observed to obey a law of the form dR/dT = a/(1+bR) which has been predicted by the theories of Fuchs and Frisch and Collins. Using a nonequilibrium distribution function of the velocities, the relationship has been rederived in a more rigorous fashion (over a limited range of conditions). Certain corrections in the constants a and b are introduced, and the validity of the Fuchs theory in this range of conditions is demonstrated. Using the formulation of Frisch and Collins, the law may be derived in the same form, subject to certain approximations.

An empirical form of the Stokes-Cunningham law for the limiting velocity of fall in a dilute medium has been obtained for dicapryl sebecate in air.
Determination of Adsorption Energy Heterogeneity of Solid Surfaces
Authors: Honig Jurgen M. , Hill Edward L.
Published: April 2005

A revision of the theory for the distribution of adsorption energies among the surface sites of a solid is presented. It is postulated that the distribution function for the adsorption energies is independent of the temperature. With this requirement, and a knowledge of the pressure-temperature dependence of empirical isotherm data, it is possible to determine simultaneously the distribution function and the dependence of the partition function of the adsorbed phase on the adsorption energy. Several examples are presented in illustration of the theory.
Further Results on Monte Carlo Equations of State
Authors: Rosenbluth Marshall N. , Rosenbluth Arianna W.
Published: April 2005

The equation of state of three-dimensional hard spheres has been obtained by the Monte Carlo method. Some qualitative results for a system of two-dimensional molecules with Lennard-Jones interaction are also given, as well as a general discussion of the usefulness and limitations of the Monte Carlo method.
Organic Photoconductors. I. The Kinetics of Photoconductivity in Rhodamine B
Authors: Nelson R. C.
Published: April 2005

The behavior of rhodamine B undergoes a change at about 60°C below which temperature it is complicated by memory effects. Above 60°C the decay process is strictly bimolecular. Three activation energies were measured: for conduction, for decay, and for rise of conductivity, and each was approximately 0.55 ev. The observed second-order character and the absolute rate of the decay process can be accounted for by a model having a large density of monoenergetic traps lying 0.55 ev below the conduction band. There is evidence that the slowness of reaching a steady state in light is to be associated with a redistribution of charge carriers from the random sites in which they are formed into preferred sites or configurations.
Organic Photoconductors. II. Crystal Violet
Authors: Nelson R. C.
Published: April 2005

Photoconductivity in crystal violet is a volume effect primarily, and surface or electrode complications have not been recognized. Donor and trapping impurities may be introduced into films, but the highly purified substance shows a large photoconductivity. The thermoelectric effect is normal. On the other hand, rates are extremely slow, there is a prominent long-lived memory effect, and under certain circumstances the second-order rate constant for a particular decay process is inversely proportional to the initial conductance. A hypothesis is proposed to account for the last-mentioned peculiarity, in terms of which structures are formed in the film which have the property of maintaining a constant initial density of charge carriers; the steady-state conductance being no longer a measure of their density but only of their total number.
The Infrared Spectrum of Crystalline Nitrogen Pentoxide
Authors: Teranishi Roy , Decius J. C.
Published: April 2005

The infrared absorptions of thin films of crystalline N214O5 and N215O5 maintained at liquid nitrogen temperature have been investigated between 4 and 20 microns. The spectrum is readily interpreted on the basis of the NO2+NO3— structure previously indicated by Raman and x-ray data. All the constants of the most general quadratic potential functions for the two ions have been evaluated, and the relatively large errors in these constants and their significance in relation to the electronic structure is discussed.
Curie Point Transitions in Phosphides and Arsenides of Manganese
Authors: Sweeny Keith H. , Scott Allen B.
Published: April 2005

The relative permeability of several alloys of manganese with phosphorus and arsenic have been measured in the region of the Curie point. The alloys were heated and cooled very slowly to eliminate, as much as possible, irreversible effects. The composition range investigated included alloys of higher phosphorus and arsenic content than have previously been investigated. Ferromagnetism in the phosphorus alloys appears to be due to the compound MnP over the range 27—58 mole percent P, and the magnetic and density transitions exhibit no temperature hysteresis. The temperature hysteresis in the magnetic transformation of manganese arsenide is confirmed. The Curie point-composition relation for the arsenides is discussed and evidence presented for the existence of a manganese-rich compound, perhaps Mn8As7, rather than a solid solution of Mn in MnAs.
A Theoretical Evaluation of the Normal Frequencies of Vibration of the Ethylene Oxide Molecule
Authors: Stone Samuel A.
Published: April 2005

A theoretical evaluation of the normal frequencies of vibration of the ethylene oxide molecule is made. The evaluation is accomplished by assuming a generalized valence force field containing twelve force constants. Values for two of the constants are assumed, and the values of the other ten are calculated so as to give values of the computed frequencies in good agreement with observed values.
The Infrared Spectrum of Disilane
Authors: Gutowsky H. S. , Stejskal E. O.
Published: April 2005

The infrared absorption spectrum of Si2H6 gas has been observed from 350 to 4000 cm—1. Four of the five infrared active fundamentals have been found and assigned (ν5 and ν6, ‖ bands at 2154.4 and 842.7 cm—1; ν7 and ν8, ⊥ bands at 2181.1 and 945.7 cm—1). The Q branches of ν7 and ν8 were observed with moderate dispersion and the spacings measured as 2.435 and 3.42 cm—1. These spacings are consistent with the Coriolis interaction in a symmetric top without internal rotation, but they do not agree with the spacings predicted by assuming free internal rotation. The general appearance of ν7 and ν8 in disilane is similar to these bands in ethane, suggesting comparable potential barriers to internal rotation. In the course of the experiments it was found that disilane decomposes slowly at room temperature into SiH4 and that in the preparation of disilane from Si2Cl6, the Si–Si bond is cleaved by an excess of LiAlH4, producing SiH4.
Diffusion across an Interface
Authors: Auer P. L. , Murbach E. W.
Published: April 2005

Ideal diffusion in the sense of Fick's law in a heterogeneous system composed of two liquids is discussed by means of a three-region model where the two bulk liquid regions adjoin a third region which characterizes the liquid-liquid interface. When diffusional resistance terms are defined in the usual manner, three classes of interfacial diffusion may be conveniently described by our model. It is found that extraordinary resistance to diffusion at the interface gives rise to perturbations in the observed concentration profile of the bulk regions; these perturbations diminish with time and disappear in the limit of vanishing resistance.
Frequency Spectrum and Specific Heat of a Face-Centered Cubic Lattice. I
Authors: Garland Carl W. , Jura George
Published: April 2005

A Born-von Karman treatment is carried out for a face-centered cubic lattice using the techniques developed by Montroll. The frequency spectrum of the normal modes of vibration has been calculated. From this distribution function Cv is obtained. A power series in 1/T has been developed for Cv at high temperatures. An asymptotic approximation is discussed for Cv at very low temperatures. Numerical results are presented for silver; these results are compared with those obtained by Leighton and with experimental data.
Note on the Theory of Directed Valence
Authors: Wu Ta-You
Published: April 2005

The recent observation of Zimmerman and Rysselberghe, and Linnett and Pöe that the wave function ψ of free atoms, when put in the form of determinants, exhibit the directional property of valence of these atoms, has been examined. It is pointed out that a consistent theory of directed valence cannot be based on these determinantal wave functions of one single state of the free atom alone.
The Interaction of Rare Gas Atoms with Surfaces
Authors: Steele W. A. , Halsey G. D.
Published: April 2005

The apparent volumes of vessels containing high surface area powders have been measured with rare gases and analyzed. The interaction energies and distances of closest approach have been evaluated. A new method for the estimation of surface area is presented.
Thermal Diffusion in Binary Liquid Mixtures of Molecules of Simple Symmetry
Authors: Saxton R. L. , Dougherty E. L. , Drickamer H. G.
Published: April 2005

A single-stage two-cell apparatus for measuring thermal diffusion in liquid mixtures has been developed. Thermal-diffusion measurements are presented for a series of binary mixtures of molecules of simple symmetry over a range of temperature from 5°—55°C. The theory presented in a previous paper applies quite satisfactorily. The results indicate that the proposed measure of the cohesive energy Hi=(T∂p∂T)i(V−T∂V∂T)i,gives reasonably quantitative results.
Infrared Study of the Effect of Solvent upon ν(NH) in Pyrrole
Authors: Josien Marie-Louise , Fuson Nelson
Published: April 2005

New data are presented on the NH group stretching frequency of pyrrole in dilute and concentrated solutions in fourteen different solvents and in several solvent mixtures. It is shown that in nonpolar solvents ν(NH) of pyrrole obeys the Kirkwood-Bauer relationship, δν/ν=C(D—1)/(2D+1), where C is a constant, and D is the solvent dielectric constant. Furthermore, it is shown that C is only slightly affected as ν(HCl) of hydrochloric acid, ν(OD) of methanol-d, or ν(OH) of methanol, ethanol, propanol, or phenol is substituted for the ν(NH) of pyrrole. The deviations from the Kirkwood-Bauer relationship produced by polar solvents and aromatic hydrocarbon solvents are analyzed in terms of hydrogen bonding and the formation of molecular complexes. The effect of solvent upon band intensity is also briefly examined. A classification of types of OH and NH solution frequencies is suggested.
Rotational Energy Transfer in Diatomic Molecules
Authors: Brout Robert
Published: April 2005

We have calculated the rotational energy transition probability upon collision using approximate results from a previous distorted wave calculation. For heavy homonuclear diatomic molecules, i.e. molecules with molecular weight >20, the mean transition probability is approximated by ½(d0/r0)2, where d0 is the internuclear distance and r0 the kinetic collision diameter. This expression is in agreement with relaxation times as calculated from shock wave data.
Nuclear Quadrupole Resonances in Solid Bromine in Iodine Compounds
Authors: Schawlow A. L.
Published: April 2005

Pure quadrupole resonances of bromine or iodine nuclei have been observed in paradibromo- and paradiiodo-benzene; the tetrabromides of carbon, silicon, germanium and tin; germanium and tin tetraiodides; sodium, potassium, and cesium bromates; antimony tribromide and iodide; and cyanogen bromide. For most of these compounds, measurements were made at room temperature and at liquid nitrogen temperature. The results are correlated with chemical bonding and crystal structure data.
Heterogeneous Nucleation of Crystals from Vapor
Authors: Pound G. M. , Simnad M. T. , Yang Ling
Published: April 2005

A rate equation is derived for heterogeneous nucleation of crystals from the vapor on the basis of an adsorption, surface diffusion, and statistical fluctuation mechanism. It should be emphasized that the term surface diffusion as used in this development does not imply the existence of a gradient. Rather it refers to random movement of absorbed atoms on the subtrate surface. It is shown that this mechanism results in a rate at least 102 to 103 times greater than that calculated on the basis of direct addition of atoms to the critical nucleus from the vapor phase. The equation describes the temperature dependence of existing critical supersaturation data for heterogeneous nucleation. Analysis of the existing data by this treatment permits an evaluation of the standard free energy of adsorption. Particular attention is given to heterogeneous nucleation from atomic beams.
The Structure and Internal Motion of Hexachloroethane
Authors: Swick D. A. , Karle I. L. , Karle J.
Published: April 2005

The equilibrium interatomic distances and their average amplitudes of vibration were determined for C2Cl6 by means of the microphotometer method in electron diffraction. Internal rotation was investigated, and the interdependence of the effects of the torsional mode and other modes of vibration on the gauche Cl–Cl distance is presented graphically.
Vibrational Spectra and Calculated Thermodynamic Properties of Ethyl Chloride and 1,1-Dichloroethane
Authors: Daasch Lester W. , Liang C. Y. , Nielsen J. Rud
Published: April 2005

The infrared absorption spectra of H3C–CH2Cl and H3C–CHCl2 in the gaseous and liquid states have been obtained in the region from 2 to 38μ with the aid of LiF, NaCl, KBr, and KRS-5 prisms. The Raman spectra of the liquids have been photographed with a 3-prism glass spectrograph of linear dispersion 15 A/mm at 4358A. Relative intensities and depolarization ratios have been measured for most of the Raman bands. Complete assignments of fundamental vibrational frequencies have been made, the spectra have been interpreted in detail, and thermodynamic functions have been calculated for the compounds in the gaseous state.
Calculation of Ionization Potentials
Authors: Franklin J. L.
Published: April 2005

Based upon a united atom model, it has been shown that the ionization potentials of complex molecules can be calculated from molecular orbitals formed from group or united atom orbitals. With this method ionization potentials have been calculated for a large number of paraffins, olefins, aromatics, alkyl halides, amines, and oxygen compounds. With a few exceptions, the agreement of calculated and measured values is excellent.
Szilard-Chalmers Reaction on CH3I
Authors: Brustad Tor , Baarli Johan
Published: April 2005

Studies on the ``hot atom'' reactions resulting from slow neutron irradiation of methyl iodide have been carried out. The results show that concentration of free iodine below 0.007 percent in CH3I during irradiation has a great influence on the distribution of the 25-min I128 between CH3I, CH2I2, and I2.

Comparison of experiments at temperatures below —55°C with carefully purified CH3I indicates that the yield of the reactions in pure CH3I is: CH3I, 44.4 percent; CH2I2, 11.2 percent; and I2, 44.2 percent.

The influence of the temperature on this reaction shows that no change in yield has been found at the shift between liquid and solid state. Co60 rays at a rate of 2 roentgen per min at the side of sampling during neutron irradiation, do not change the distribution of the radioactive I128 between the compounds.
Exact Solution of the Debye-Hückel Equations for a Polarized Electrode
Authors: Macdonald J. Ross , Brachman Malcolm K.
Published: April 2005

A recent solution of the Debye-Hückel equations for a single polarized electrode obtained by Breyer and Gutmann is revised to yield an exact solution of this problem. This solution is compared with an earlier result of H. Müller derived from different initial equations and the solutions are shown to be identical.

The present solution applies only to the diffuse part of the double layer of electrolyte theory and yields the following expression for the mean local potential within the material as a function of the distance x from a polarized anode ψ=(2kT/e)ln{coth[12(x/LD+sinh−1{csch(eV0/2kT)})]},where LD is the Debye length and V0 the potential applied between electrode and charge-containing material.
Infrared Reflection Spectra of Phosphate and Arsenate Crystals
Authors: Murphy George M. , Weiner George , Oberly John J.
Published: April 2005

Crystals of KH2PO4, NH4H2PO4, KH2AsO4, and NH4H2AsO4 were examined in the 1—25 micron region. Data were obtained at room temperature for all four crystals, and in addition the spectra of the potassium compounds were examined below their Curie points. In order to avoid the use of thin crystal cuts required for absorption measurements, an optical system was designed which permitted recording of reflection spectra. At the low temperature an increase in the number of bands was observed, and the phosphate and arsenate spectra seemed displaced to higher frequencies. The transition from hydrogen bonding prevailing at room temperature to hydroxyl bonding below the Curie points is considered likely.
Electronic Structures of the CH Radical
Authors: Higuchi Jiro
Published: April 2005

The electronic states and the molecular constants of the ground and lower excited states of the CH radical are calculated by the Heitler-London method and the LCAO-SCF method. In the former, s2p2, sp3, and p4 configurations of the carbon atom are taken into account for the wave function, and in the latter LCAO-SCF MOs are calculated for the ground and lower excited states. The interactions between all electrons are considered, but the orthogonal relationship between the 1s orbitals of carbon and hydrogen is assumed. As much as possible, the energy integrals were computed from SCF AOs. The results are in general agreement with the observations and Mulliken's prediction. It is concluded that without configuration interaction no satisfactory LCAO-SCF calculation can be made to determine the ground state of the radical as well as of the electronic levels of the carbon atom.
Hyperfine Splittings in Polyatomic Free Radicals
Authors: Weissman S. I.
Published: April 2005

The hyperfine interaction in polyatomic molecules in doublet states is investigated. It is demonstrated that for molecules undergoing rapid and jittery tumbling the dipolar part of the interaction vanishes.
Techniques in the Study of Emission Spectra of Polyatomic Molecules—The Spectra of Benzaldehyde and Acetophenone
Authors: Robinson G. Wilse
Published: April 2005

A rather simple method is presented for obtaining the electrodeless discharge emission spectra of polyatomic molecules. The spectra obtained for benzaldehyde and acetophenone were of very high intensity and without a trace of spectral impurities. It was possible in the case of benzaldehyde to detect over a hundred sharp bands in the region 3688—5433 A, and to observe some structure in the ``broad'' emission bands of acetophenone. In both these molecules there is strong evidence that the emission involves the same upper state as does the long-wave absorption. The (0,0) band of benzaldehyde is assigned at 26914 cm—1 and that of acetophenone at 27501 cm—1. The possibility of extending the techniques to other molecules is discussed.
Vapor Pressure of Uranium
Authors: Rauh Everett G. , Thorn Robert J.
Published: April 2005

The vapor pressures and the heat of vaporization of liquid uranium have been measured by collecting a known fraction of the vapor effusing from a Knudsen cell. The deposits were ``weighed'' by comparing the number of fissions upon thermal neutron irradiation with the fissions from a standard. The measured rate of vaporization is extremely sensitive to the residual pressure of oxygen in the vacuum at background pressures of the order of 10—7 mm Hg. With the aid of a theoretically derived expression the effusion rate can be extrapolated to zero oxygen pressure to yield for the vapor pressure the result that logp(mm)=−(23330±21)T+(8.583±0.011),,over the temperature range 1630 to 1970°K. This expression, together with heat capacity data for solid uranium, yields a value of 116.6 kcal/mole for the heat of sublimation at 0°K and predict a value of about 4.7 kcal/mole for the heat of fusion.
Second-Order Quadrupole Effects in Asymmetric Tops. The Microwave Spectrum of Vinyl Iodide
Authors: Morgan H. W. , Goldstein J. H.
Published: April 2005

The J = 3→4 transition of the asymmetric rotor, vinyl iodide, has been observed in the region 24 000—26 000 Mc. The groupings 312→413 and 313→414 have been studied, and the quadrupolar hyperfine patterns, arising from the iodine nucleus, have been fitted to second-order theory with an average error of ±0.12 Mc.

The values determined for the coupling parameters are ξaa = —1656 Mc and ξbb = +770 Mc, each to within ±10 Mc. On the assumption that the C–I bond is a principal axis of the ξ tensor, ξzz the value along the C–I bond, was found to be —1877 Mc, and ξab to equal —765 Mc. Assuming planarity, and neglecting centrifugal distortion, the following values of the rotational constants were obtained: (b+c) = 6325.41±0.03 Mc, (b—c) = 192.03±0.05 Mc, and κ = —0.9921554±0.0000031.
Molecular Orbital Theory of Orientation in Aromatic, Heteroaromatic, and Other Conjugated Molecules
Authors: Fukui Kenichi , Yonezawa Teijiro , Nagata Chikayoshi , Shingu Haruo
Published: April 2005

As to the LCAO MO treatment of the orientation problem in chemical reactions of π-electron systems, the frontier electron concept which has been previously introduced by the authors for explaining the reactivities in aromatic hydrocarbons is subjected to an extension in the sense that the frontier orbitals are specified according to the type of reaction. Thus, fundamental postulates relating to the reactivities of π-electron systems are set up, which are believed to include general principles involved in the mechanism of both substitution and addition of electrophilic, nucleophilic, or radical type. On the basis of these postulates it is possible to predict the position of attack in conjugated molecules in all the three types of substitution as well as addition in a consistent manner. There is a nearly perfect agreement between the theoretical conclusions and experimental results hitherto reported.
On the Temperature Dependence of the Molecular Polarization of Ammonia
Authors: Katayama Mikio
Published: April 2005

The molecular polarization of ammonia is calculated quantum mechanically by taking account of the dipole matrix elements of inversion doubling in the first excited state as well as in the ground state of the symmetric deformation vibration. It is found to be reasonable that the dipole moment of this molecule decreases at higher temperatures. The atomic polarization is also calculated and the result, PA=0.65 cc, is in good agreement with the observed value.
Variation in the Quadrupole Coupling Constant with Vibrational State in the Methyl Halides
Authors: Kraitchman J. , Dailey B. P.
Published: April 2005

The J=0→1 microwave rotational transitions in the states v=1 of the vibrations v3(a1) and v6(e) in methyl chloride and the state v=1 of the vibration v3(a1) in methyl bromide have been studied. The quadrupole coupling constants eqQ of chlorine and bromine in these states were determined. These were compared with the values determined for the ground state. No variation of the quadrupole coupling constants with vibrational state was observed. The accuracy of the measurements requires the variation of eqQ with vibrational state to be less than 0.07 percent in methyl bromide. The rotational constants and vibration-rotation constants for these states were also determined.
Free Radicals by Mass Spectrometry. VI. The Bond Dissociation Energies of Some Methyl, Allyl, and Benzyl Compounds by Electron Impact
Authors: Lossing F. P. , Ingold K. U. , Henderson I. H. S.
Published: April 2005

The appearance potentials for the radical ions from methyl, allyl, and benzyl halides and two other derivatives have been measured. Using previously measured values for the ionization potentials of the free radicals, the R–X bond dissociation energies in these compounds have been calculated. The results are in good agreement with published data for the methyl and allyl compounds, and in fair agreement for the benzyl halides.
Thermodynamics of Phase Transitions in Compressible Solid Lattices
Authors: Rice O. K.
Published: April 2005

The calculations on the Ising lattice and the order-disorder phenomenon indicate that the specific heat may become infinite at the λ temperature or transition point. The general thermodynamics of such a system in a variable magnetic field is considered, and the relation to the generalized theories of critical points of Tisza and of Semenchenko is indicated. The general import of these theories is that infinite values of the heat capacity at constant pressure Cp, or the analogous heat capacity in a system with variables other than p, V, and T, can become infinite in a one-phase system only at a critical point. The existence of a locus of points where Cp = ∞ is thermodynamically possible in the pVT system, and equations analogous to the Clapeyron and Ehrenfest equations may be derived. However, the thermodynamic requirements show that such a locus is not likely to occur. Interesting possibilities occur where there is an interaction between several sets of variables. If an Ising lattice is compressible, for example, the transition temperature will depend on the lattice distance. In this case, the infinite heat capacity is to be considered as a singularity in Cv rather than in Cp. The effect of the compressibility is to change any transition in which infinite specific heats occur to a first-order transition. If there is already a first-order transition, even for an assumed incompressible lattice, the introduction of compressibility increases the latent heat and a discontinuity in lattice distance appears. This situation appears to arise in the order-disorder transformation of an alloy like AuCu3, and the phases may also be expected to have different compositions; this latter phenomenon has also been considered from the point of view of this paper. If there is a λ point without infinite specific heats, the introduction of compressibility may or may not change it to a first-order transition; in any event, the λ point is made ``sharper.'' There may be a critical point in this case. Various thermodynamic relationships are deduced, and the nature of the isotherms in all these cases is considered.
Rotational Constants of SiH3D
Authors: Polo Santiago R. , Wilson M. Kent
Published: April 2005

The analysis of the rotational structure of the Si — D stretching fundamental yields the following values: B′′=2.11±0.01 cm−1,  B′′−B′=0.019 cm−1,  ν0=1594.4±0.1 cm−1.The value of the Si — H distance obtained under the assumption that it remains unchanged by isotopic substitution is dSi−H=1.477±0.003 A.
Photoionization and Total Absorption Cross Section of Gases. I. Ionization Potentials of Several Molecules. Cross Sections of NH3 and NO
Authors: Watanabe K.
Published: April 2005

Ionization potentials determined by examining the long wavelength limit of the ionization continuum for H2S, CS2, C6H6, toluene, p-xylene, C2H4, butadiene, and CH3I agreed with spectroscopic values obtained by Price and co-workers. Values are reported also for NH3, NO, acetone, methyl-ethyl-ketone, CH3OH, and C2H5OH.

Improved energy measurements showed that photoionization cross sections of NO in the region 1070—1340A obtained earlier were about 40 percent too low. At 1215.6A the photoionization and the total cross sections are 2.0×10—18 and 2.4×10—18 cm2, respectively, the difference being ascribed to an absorption band. The photoionization cross section of NH3 was found to rise rather gradually with decreasing wavelength in the region 1220—1060A and to reach a value of 9×10—18 cm2 at 1060A.
Microwave Spectrum and Structure of Benzonitrile
Authors: Lide David R.
Published: April 2005

The rotational spectrum of benzonitrile has been studied in the one-centimeter region, and approximately twenty absorption lines have been fitted to the rigid asymmetric-rotor theory. The principal moments of inertia are 89.370, 326.740, and 416.183 AUA2. The evidence indicates a planar symmetric structure with ring dimensions essentially the same as in benzene. The dipole moment is 4.14±0.05 Debye units.
Lattice Vibrational Spectrum of Imperfect Crystals
Authors: Stripp Kenneth F. , Kirkwood John G.
Published: April 2005

The influence of lattice defects on the normal modes of vibration of crystals is investigated by means of perturbation theory. The calculations have been carried to the second order, and the effect of holes on the vibrational partition function has been determined. It is found that through their influence on the lattice vibrational free energy, a pair of holes in a crystal attract each other with an average force whose potential diminishes asymptotically as 1/R6.
Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds
Authors: Singh Niraj K. , Suresh K. G. , Nigam A. K. , Malik S. K.
Published: April 2005

Magnetocaloric effect and magnetoresistance have been studied in Dy(Co1−x,Six)2 (x=0, 0.075, and 0.15) compounds. Magnetocaloric effect has been calculated in terms of adiabatic temperature change (ΔTad) as well as isothermal magnetic entropy change (ΔSM) using the heat-capacity data. The maximum values of ΔSM and ΔTad for DyCo2 are found to be 11.4JKg−1K−1 and 5.4 K, respectively. Both ΔSM and ΔTad decrease with Si concentration, reaching values of 5.4JKg−1K−1 and 3 K, respectively for x=0.15. The maximum magnetoresistance is found to be about 32% in DyCo2, which decreases with increase in Si. These variations are explained on the basis of itinerant electron metamagnetism occurring in these compounds.
Modified Gilbert damping due to exchange bias in NiFe∕FeMn bilayers
Authors: Weber M. C. , Nembach H. , Hillebrands B. , Fassbender J.
Published: April 2005

A picosecond all-optical pump-probe technique is used to investigate magnetization dynamics and magnetic damping behavior in the Ni81Fe19∕Fe50Mn50 exchange bias system. Within the laser excitation the spin temperature is elevated resulting in a collapse of the exchange bias field. Thus, a fast anisotropy field pulse is launched which triggers the magnetization precession. The extracted Gilbert damping increases linearly with the exchange bias field magnitude which can be understood by taking the local fluctuations of the interfacial exchange coupling as an additional dissipation mechanism into account.
Relaxation in magnetic nanostructures
Authors: Skomski R. , Zhou J. , Sellmyer D. J.
Published: April 2005

The damping of magnetization processes in nanostructures is investigated by Fokker–Planck-type model calculations and quantum-mechanical considerations based on Fermi’s golden rule. In the absence of energy barriers, the problem reduces to a magnetic diffusion equation with a particle-size-dependent diffusivity which is indirectly proportional to the relaxation-time parameter τo. For small particles, the relaxation time is proportional to the particle volume, but when the particle size reaches a few nanometers, it approaches a constant bulk value.
Experimental investigation of superspin glass dynamics
Authors: Parker D. , Ladieu F. , Vincent E. , Mériguet G. , Dubois E. , Dupuis V. , Perzynski R.
Published: April 2005

Magnetic nanoparticle assemblies in high concentrations can exhibit spin glass like properties in the low temperature phase due to the influence of strong dipolar interactions. To address the question of the extent to which the properties of these “superspin” glasses mimic those of an atomic spin glass, several homogeneously dispersed γ-Fe2O3 nanoparticle assemblies of varying volume fraction have been studied. In a concentrated sample, the main features of atomic spin glasses have been observed including aging phenomena for which we have proposed a rescaling.
Quantized spin excitation modes in patterned ferromagnetic stripe arrays
Authors: Guslienko K. Yu. , Pishko V. , Novosad V. , Buchanan K. , Bader S. D.
Published: April 2005

The high-frequency dynamic properties of patterned ferromagnetic microstripe arrays were studied using ferromagnetic resonance (FMR). The samples were fabricated by means of electron-beam lithography and magnetron sputtering followed by liftoff. The 20nm thick and 1μm wide stripes were arranged into a regular array with a period of 2μm. The resonance spectra were taken at a fixed frequency of 9.38GHz for different sample orientations with respect to the applied field. In the case of perpendicularly magnetized stripes, a set of multiple resonance peaks is observed below the main FMR peak. A quantitative description of the observed spectra is given using a dipolar-exchange spin-wave dispersion equation. The calculations are in agreement with the experimental data.
Element-specific magnetometry on negatively magnetized NdMnO3+δ
Authors: Bartolomé F. , Herrero-Albillos J. , García L. M. , Bartolomé J. , Jaouen N. , Rogalev A.
Published: April 2005

Field-cooled x-ray magnetic circular dichroism experiments at several temperatures at the MnK and NdL2,3 edges on nonstoichiometric NdMnO3.11 have been performed. Our results show that Nd and Mn net magnetizations are parallel along the whole range of temperatures, ruling out the competition between the Nd and Mn sublattices as the origin of negative magnetization in NdMnO3+δ.
Multiple ferromagnetic resonance in mesoscopic permalloy rings
Authors: Giesen F. , Podbielski J. , Korn T. , Grundler D.
Published: April 2005

Using a broadband microwave spectrometer we have investigated the magnetization dynamics of mesoscopic ferromagnetic disks and rings in the frequency range from 45MHzto20GHz. We studied permalloy rings with an outer diameter of 2μm and different ring widths w. In the mesoscopic devices we find several ferromagnetic resonance (FMR) lines which shift with the in-plane magnetic field Hb. Among them, two pronounced FMR modes are identified. We attribute these modes to localized spin waves in different ring segments where the characteristic resonance frequency either decreases or increases as a function of w, depending on the orientation of the ring segment with respect to Hb.
Orientation and alignment moments in two-color polarization spectroscopy
Authors: Costen Matthew L. , McKendrick Kenneth G.
Published: April 2005

A theoretical analysis of two-color polarization spectroscopy (TCPS) is presented as an extension of a previous analysis of one-color PS. Three commonly used schemes in which pump and probe transitions share a common level are considered. Diagrammatic techniques are used to isolate the photon interaction sequences that can contribute to the signal. A perturbation-theory analysis expressing the signal in terms of spherical tensor moments is applied. The analysis emphasises the significance of orientation and alignment tensor moments of rotational angular momentum and their collisional evolution. The assumed context is transitions between single rotational states of gas-phase molecules that subsequently suffer discrete collisions. The time scale of the measurements is assumed to be long relative to the periods of molecular motion, as would typically be the case for signals excited by nanosecond-pulsed lasers from samples at moderate pressures. The Doppler motion of the probed species is included, as is an analytical solution to the integration over the Maxwell–Boltzmann distribution of velocities. The effects of nuclear hyperfine depolarization and velocity-changing collisions are discussed. It is shown that when pump- and probe-laser pulses are separated in time, TCPS creates and probes either orientation or alignment of rotational angular momentum in the common level shared by pump and probe transitions. Example simulations of one- and two-color polarization spectroscopies are included to demonstrate the resulting simplification of the measured signal using TCPS. TCPS is therefore a viable spectroscopic technique for the determination of rotational angular momentum orientation and alignment relaxation rates in molecular gases, of interest because they are sensitive probes of inelastic collisions.
Multimode spectra and active mode locking potential of quantum dot lasers
Authors: Xing C. , Avrutin E. A.
Published: April 2005

A time-frequency-domain formalism for analysis of mode-locked quantum dot laser dynamics is developed. A potential for generating subpicosecond pulses in an actively mode-locked construction is predicted. Low chirp pulses are predicted, correlating with a low linewidth enhancement factor calculated. Strong hole burning associated with quantum dot active media is shown to broaden the mode-locking spectra noticeably, leading to shorter pulses.
Large magnetic entropy change above 300 K in a colossal magnetoresistive material La0.7Sr0.3Mn0.98Ni0.02O3
Authors: Phan Manh-Huong , Tho Nguyen Duc , Chau Nguyen , Yu Seong-Cho , Kurisu M.
Published: April 2005

A thorough study of the magnetocaloric effect (MCE) in a colossal magnetoresistive compound of La0.7Sr0.3Mn0.98Ni0.02O3 has been made. The large magnetic entropy change of 7.65 J∕kg K upon an applied field of 70 kOe has been found to occur at 350 K, which allows magnetic refrigeration at room temperature. It is interesting to note that, even in high magnetic fields, the magnetic entropy change versus temperature distribution is much more uniform than that of gadolinium and several polycrystalline perovskite manganites, which is desirable for an Ericson-cycle magnetic refrigerator. It is found that such a small amount (∼2%) of substitution of Mn3+ by a magnetic ion (Ni3+ or Co3+) in the perovskite manganite can favor the spin order and hence the MCE. Undoubtedly, this observation opens a window to explore the active magnetic refrigeration at high temperatures.
Electrical conduction mechanisms of metal∕La2O3∕Si structure
Authors: Chiu Fu-Chien , Chou Hong-Wen , Lee Joseph Ya-min
Published: April 2005

Metal-oxide-semiconductor capacitors that incorporate La2O3 dielectric films were deposited by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of La2O3 thin films were investigated. Capacitance–voltage, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the effective dielectric constant of the 700°C annealed La2O3 thin films. The dominant conduction mechanism of the Al∕La2O3∕p-Si metal-lanthanum oxide-semiconductor capacitor is space-charge-limited current from 300to465K in the accumulation mode. Three different regions, Ohm’s law region, trap-filled-limited region, and Child’s law region, were observed in the current-density–voltage (J–V) characteristics at room temperature. The activation energy of traps calculated from the Arrhenius plots was about 0.21±0.01eV. The electronic mobility, trap density, dielectric relaxation time, and density of states in the conduction band were determined from the space-charge-limited conduction at room temperature.
Impulsive synchronization of chaotic systems
Authors: Li Chuandong , Liao Xiaofeng , Zhang Xingyou
Published: April 2005

The issue of impulsive synchronization of a class of chaotic systems is investigated. Based on the impulsive theory and linear matrix inequality technique, some less conservative and easily verified criteria for impulsive synchronization of chaotic systems are derived. The proposed method is applied to the original Chua oscillators, and the corresponding synchronization conditions are obtained. Moreover, the boundary of the stable region is also estimated in terms of the equidistant impulse interval. The effectiveness of our method is shown by computer simulation.
Induced-charge electrophoresis of nonspherical particles
Authors: Yariv Ehud
Published: April 2005

The electrophoretic motion of a conducting particle, driven by an induced-charge mechanism, is analyzed. The dependence of the motion upon particle shape is embodied in two tensorial coefficients that relate the particle translational and rotational velocities to the externally applied electric field. The coefficients are represented as surface integrals of the electric potential over the particle boundary, thereby eliminating the need to solve the flow field. Nonspherical particles may translate and∕or rotate in response to the imposed field, even if their net electric charge vanishes.
Near-surface modification of the third-order nonlinear susceptibility in thermally poled Infrasil™ glasses
Authors: Quiquempois Y. , Kudlinski A. , Martinelli G. , Margulis W. , Carvalho I. C. S.
Published: April 2005

Both the second-order nonlinear distribution and the built-in electric field have been measured in poled Infrasil™ silica samples, leading to the determination of the third-order nonlinear susceptibility spatial distribution. A difference between the χ(2) and electric field profiles has been observed in the first micrometers near the surface in contact with the anode. This behavior could be attributed to a modification of the χ(3) susceptibility in the poled region.
Crosslinking a lipid raft component triggers liquid ordered-liquid disordered phase separation in model plasma membranes
Authors: Hammond A. T. , Heberle F. A. , Baumgart T. , Holowka D. , Baird B. , Feigenson G. W.
Published: April 2005

The mechanisms by which a cell uses and adapts its functional membrane organization are poorly understood and are the subject of ongoing investigation and discussion. Here, we study one proposed mechanism: the crosslinking of membrane components. In immune cell signaling (and other membrane-associated processes), a small change in the clustering of specific membrane proteins can lead to large-scale reorganizations that involve numerous other membrane components. We have investigated the large-scale physical effect of crosslinking a minor membrane component, the ganglioside GM
1
, in simple lipid models of the plasma membrane containing sphingomyelin, cholesterol, and phosphatidylcholine. We observe that crosslinking GM
1
can cause uniform membranes to phase-separate into large, coexistent liquid ordered and liquid disordered membrane domains. We also find that this lipid separation causes a dramatic redistribution of a transmembrane peptide, consistent with a raft model of membrane organization. These experiments demonstrate a mechanism that could contribute to the effects of crosslinking observed in cellular processes: Domains induced by clustering a small number of proteins or lipids might rapidly reorganize many other membrane proteins.
The retinal chromophore/chloride ion pair: Structure of the photoisomerization path and interplay of charge transfer and covalent states
Authors: Cembran Alessandro , Bernardi Fernando , Olivucci Massimo , Garavelli Marco
Published: April 2005

Ab initiomultireference second-order perturbation theory computations are used to explore the photochemical behavior of two ion pairs constituted by a chloride counterion interacting with either a rhodopsin or bacteriorhodopsin chromophore model (i.e., the 4-cis-γ-methylnona-2,4,6,8-tetraeniminium andall-trans-nona-2,4,6,8-tetraeniminium cations, respectively). Significant counterion effects on the structure of the photoisomerization paths are unveiled by comparison with the paths of the same chromophoresin vacuo. Indeed, we demonstrate that the counterion (i) modulates the relative stability of the S0, S1, and S2energy surfaces leading to an S1isomerization energy profile where the S1and S2states are substantially degenerate; (ii) leads to the emergence of significant S1energy barriers along all of the isomerization paths except the one mimicking the 11-cis→all-transisomerization of the rhodopsin chromophore model; and (iii) changes the nature of the S1→ S0decay funnel that becomes a stable excited state minimum when the isomerizing double bond is located at the center of the chromophore moiety. We show that these (apparently very different) counterion effects can be rationalized on the basis of a simple qualitative electrostatic model, which also provides a crude basis for understanding the behavior of retinal protonated Schiff bases in solution.
Differences in color vision make passerines less conspicuous in the eyes of their predators
Authors: Håstad Olle , Victorsson Jonas , Ödeen Anders
Published: April 2005

Sexual selection often favors brighter and exaggerated traits, which also increase the risk of detection by predators. Signals that are preferentially conspicuous to conspecifics would reduce the predation cost of signaling and, therefore, might facilitate the evolution of stronger sexual and social signals. This selective signaling is possible if predators and prey have differently tuned sensory systems. By using a retinal model to compare reflectance from the plumages of Swedish songbirds to the reflectance of their natural backgrounds, we found their color badges to be significantly more conspicuous to other songbirds (which have a UV-tuned visual system) than to raptors and corvids (which have a violet-tuned system) in both coniferous and deciduous forests, consistent with an adaptive private communication system.
Tetanus neurotoxin-mediated cleavage of cellubrevin impairs epithelial cell migration and integrin-dependent cell adhesion
Authors: Proux-Gillardeaux Véronique , Gavard Julie , Irinopoulou Theano , Mège René-Marc , Galli Thierry
Published: April 2005

A role for endocytosis and exocytosis in cell migration has been proposed but not yet demonstrated. Here, we show that cellubrevin (Cb), an early endosomal v-SNARE, mediates trafficking in the lamellipod of migrating epithelial cells and partially colocalizes with markers of focal contacts. Expression of tetanus neurotoxin, which selectively cleaves Cb, significantly reduced the speed of migrating epithelial cells. Furthermore, expression of tetanus neurotoxin enhanced the adhesion of epithelial cells to collagen, laminin, fibronectin, and E-cadherin; altered spreading on collagen; and impaired the recycling of β1 integrins. These results suggest that Cb-dependent membrane trafficking participates in cell motility through the regulation of cell adhesion.