bluuebunny/crossref_metadata_2025 huggingface dataset:
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solar-blind focal plane arrays based on AlxGa1−xN
Authors: McClintock R. , Mayes K. , Yasan A. , Shiell D. , Kung P. , Razeghi M.
Published: January 2005

We report AlGaN-based backilluminated solar-blind ultraviolet focal plane arrays operating at a wavelength of 280 nm. The electrical characteristics of the individual pixels are discussed, and the uniformity of the array is presented. The p–i–n photodiode array was hybridized to a 320×256 read-out integrated circuit entirely within our university research lab, and a working 320×256 camera was demonstrated. Several example solar-blind images from the camera are also provided.
Polarity control of ZnO films grown on nitrided c-sapphire by molecular-beam epitaxy
Authors: Wang Xinqiang , Tomita Yosuke , Roh Ok-Hwan , Ohsugi Masayuki , Che Song-Bek , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: January 2005

The polarity of molecular-beam epitaxy grown ZnO films was controlled on nitrided c-sapphire substrate by modifying the interface between the ZnO buffer layer and the nitrided sapphire. The ZnO film grown on nitrided sapphire was proven to be Zn-polar while the O-polar one was obtained by using gallium predeposition on nitrided sapphire, which was confirmed by coaxial impact collision ion scattering spectroscopy and chemical etching effect. The Zn-polar ZnO film showed higher growth rate, slightly better quality, and different surface morphology in comparison to the O-polar one.
Observation of a low-temperature acoustic anomaly in lanthanum lead zirconate titanate
Authors: Shabbir Ghulam , Ko Jae-Hyeon , Kojima Seiji
Published: January 2005

High-resolution Brillouin scattering experiments have been performed to investigate the low temperature “aging” effect in lanthanum lead zirconate titanate (PLZT) relaxor ferroelectric ceramics. From the temperature dependence of the frequency shift of longitudinal acoustic mode, an acoustic anomaly was observed at T0∼46K in these ceramics with clear “aging” effect below T0. The results have been discussed in the light of stepwise freezing of the related degrees of freedom causing transition from proper to improper dipole glassy states at T0.
Evolution of bias field and offset piezoelectric coefficient in bulk lead zirconate titanate with fatigue
Authors: Zhang Yong , Baturin Ivan S. , Aulbach Emil , Lupascu Doru C. , Kholkin Andrei L. , Shur Vladimir Ya. , Rödel Jürgen
Published: January 2005

Hysteresis loops of the piezoelectric coefficient, d33=f(E3), are measured on virgin and fatigued lead zirconate titanate ceramics. Four parameters are directly extracted from the measurements: internal bias field Eb, offset piezoelectric coefficient doffset, coercive field Ec, and remnant piezoelectric coefficient dr. The reduction in dr displays the decreasing switchable polarization with fatigue cycling. Eb and doffset are found to be linearly related. After thermal annealing, both offsets disappear, while the increase in Ec and the reduction in dr withstand annealing. The microscopic entities responsible for the offsets are less stable than those for reduced switching.
Self-attraction among aligned Au/ZnO nanorods under electron beam
Authors: Wang Xudong , Summers Christopher J. , Wang Zhong Lin
Published: January 2005

Self-attraction among vertical aligned Au/ZnO nanorods under the illumination of an electron beam has been observed. This phenomenon is attributed to the interaction between the accumulation charges near the metal-semiconductor junctions for two nanorods of different length. A model calculation is presented to explain the observed phenomenon.
Effect of Joule heating in current-driven domain wall motion
Authors: Yamaguchi A. , Nasu S. , Tanigawa H. , Ono T. , Miyake K. , Mibu K. , Shinjo T.
Published: January 2005

It was found that high current density needed for the current-driven domain wall motion results in the Joule heating of the sample. The sample temperature, when the current-driven domain wall motion occurred, was estimated by measuring the sample resistance during the application of a pulsed current. The sample temperature was 750 K for the threshold current density of 6.7×1011A∕m2 in a 10-nm-thick Ni81Fe19 wire with a width of 240 nm on thermally oxidized silicon substrate. The temperature was raised to 830 K for the current density of 7.5×1011A∕m2, which is very close to the Curie temperature of bulk Ni81Fe19. When the current density exceeded 7.5×1011A∕m2, an appearance of a multidomain structure in the wire was observed by magnetic force microscopy, suggesting that the sample temperature exceeded the Curie temperature.
Unsteady Surface Pressures Due to Wake-Induced Transition in a Laminar Separation Bubble on a Low-Pressure Cascade
Authors: Stieger R. D. , Hollis David , Hodson H. P.
Published: January 2005

This paper presents unsteady surface pressures measured on the suction surface of a LP turbine cascade that was subject to wake passing from a moving bar wake generator. The surface pressures measured under the laminar boundary layer upstream of the steady flow separation point were found to respond to the wake passing as expected from the kinematics of wake convection. In the region where a separation bubble formed in steady flow, the arrival of the convecting wake produced high frequency, short wavelength, fluctuations in the ensemble-averaged blade surface pressure. The peak-to-peak magnitude was 30% of the exit dynamic head. The existence of fluctuations in the ensemble averaged pressure traces indicates that they are deterministic and that they are produced by coherent structures. The onset of the pressure fluctuations was found to lie beneath the convecting wake and the fluctuations were found to convect along the blade surface at half of the local freestream velocity. Measurements performed with the boundary layer tripped ahead of the separation point showed no oscillations in the ensemble average pressure traces indicating that a separating boundary layer is necessary for the generation of the pressure fluctuations. The coherent structures responsible for the large-amplitude pressure fluctuations were identified using PIV to be vortices embedded in the boundary layer. It is proposed that these vortices form in the boundary layer as the wake passes over the inflexional velocity profiles of the separating boundary layer and that the rollup of the separated shear layer occurs by an inviscid Kelvin-Helmholtz mechanism.
Surge Avoidance in Gas Compression Systems
Authors: Kurz R. , White R. C.
Published: January 2005

The phenomenon of compressor surge and its prevention have drawn significant attention in the literature. An important aspect of surge avoidance lies in the design of the compressor station and, in particular, the piping upstream and downstream of the compressor. Most anti-surge systems are perfectly capable of avoiding surge during normal operating conditions. However, unplanned emergency shutdowns present a significant challenge, and surge avoidance in these cases depends to a large degree on the station layout. In this paper, data from a compressor that surged during an emergency shutdown are presented. The data are analyzed to determine the effects of surge and the rate of deceleration. A model to simulate shutdown events is developed and used to develop simpler rules that help with proper sizing of upstream and downstream piping systems, as well as the necessary control elements. The compression system is analyzed, thus verifying the model and the simplifications.
Local Heat/Mass Transfer With Various Rib Arrangements in Impingement/Effusion Cooling System With Crossflow
Authors: Rhee Dong Ho , Nam Yong Woo , Cho Hyung Hee
Published: January 2005

The present study has been conducted to investigate the effect of rib arrangements on flow and heat/mass transfer characteristics for an impingement/effusion cooling system with initial crossflow. Two perforated plates of square hole array are placed in parallel and staggered arrangements with a gap distance of 2d and the crossflow passes between the injection and effusion plates. Both the injection and effusion hole diameters d are 10 mm and Reynolds number based on the hole diameter and hole-to-hole pitch are fixed at 10,000 and 6d, respectively. Square ribs of various rib arrangements and attack angles are installed on the effusion plate. With the initial crossflow, locally low transfer regions are formed and the level of heat transfer rate become lower as flow rate of the crossflow increases because wall jets are swept and the stagnation regions are affected by crossflow. With rib turbulators, the flow and heat transfer patterns are changed because the ribs protect near-wall flows including wall jets and generate secondary flow in a duct. For M⩾1.0, the overall heat transfer is promoted when ribs are installed on the effusion surface, and higher values are obtained with smaller pitch of ribs. But, the attack angle of the rib has little influence on the average heat/mass transfer. For low blowing ratio of M=0.5, the ribs have adverse effects on heat/mass transfer. Pressure drop between the inlet and exit of the channel increases up to 20% of total loss when ribs are installed while it is only 5% of total pressure loss across the perforated plates without ribs.
Unsteady Boundary Layer Development Due to Wake Passing Effects on a Highly Loaded Linear Compressor Cascade
Authors: Hilgenfeld Lothar , Pfitzner Michael
Published: January 2005

The effects of wake passing on boundary layer development on a highly loaded linear compressor cascade were investigated in detail on the suction side of a compressor blade. The experiments were performed in the High Speed Cascade Wind Tunnel of the Institut fuer Strahlantriebe at Mach and Reynolds numbers representative for real turbomachinery conditions. The experimental data were acquired using different measurement techniques, such as fast-response Kulite sensors, hot-film array and hot-wire measurements. The incoming wakes clearly influence the unsteady boundary layer development. Early forced transition in the boundary layer is followed in time by calmed regions. Large pressure fluctuations detectable in the ensemble averaged Kulite data reveal the existence of coherent structures in the boundary layer. Distinct velocity variations inside the boundary layer are amplified when approaching the blade surface. The time–mean momentum thickness values are reduced compared to the steady ones and therefore clarify the potential for a loss reduction due to wake passing effects.
Rotor-Stator Interactions in a Four-Stage Low-Speed Axial Compressor—Part II: Unsteady Aerodynamic Forces of Rotor and Stator Blades
Authors: Mailach Ronald , Mu¨ller Lutz , Vogeler Konrad
Published: January 2005

This two-part paper presents detailed experimental investigations of unsteady aerodynamic blade row interactions in the four-stage low-speed research compressor of Dresden. In Part I of the paper the unsteady profile pressure distributions for the nominal setup of the compressor are discussed. Furthermore the effect of blade row clocking on the unsteady profile pressures is investigated. Part II deals with the unsteady aerodynamic blade forces, which are determined from the measured profile pressure distributions. A method to calculate the aerodynamic blade forces on the basis of the experimental data is presented. The resulting aerodynamic blade forces are discussed for the rotor and stator blade rows of the first stage and the third stage of the compressor. Different operating points between design point and stability limit of the compressor were chosen to investigate the influence of loading on the aerodynamic force excitation. The time traces and the frequency contents of the unsteady aerodynamic blade force are discussed. Strong periodic influences of the incoming wakes and of potential effects of downstream blade rows can be observed. The amplitude and shape of the unsteady aerodynamic blade force depend on the interaction of the superimposed influences of the blade rows.
Effect of the Hub Endwall Cavity Flow on the Flow-Field of a Transonic High-Pressure Turbine
Authors: Paniagua G. , De´nos R. , Almeida S.
Published: January 2005

In high-pressure turbines, a small amount of cold flow is ejected at the hub from the cavity that exists between the stator and the rotor disk. This prevents the ingestion of hot gases into the wheel-space cavity, thus avoiding possible damage. This paper analyzes the interaction between the hub-endwall cavity flow and the mainstream in a high-pressure transonic turbine stage. Several cooling flow ratios are investigated under engine representative conditions. Both time-averaged and time-resolved data are presented. The experimental data is successfully compared with the results of a three-dimensional steady Navier-Stokes computation. Despite the small amount of gas ejected, the hub-endwall cavity flow has a significant influence on the mainstream flow. The Navier-Stokes predictions show how the ejected cold flow is entrained by the rotor hub vortex. The time-resolved static pressure field around the rotor is greatly affected when traversing the non-uniform vane exit flow field. When the cavity flow rate is increased, the unsteady forces on the rotor airfoil are reduced. This is linked to the decrease of vane exit Mach number caused by the blockage of the ejected flow.
Time-Averaged and Time-Resolved Heat Flux Measurements on a Turbine Stator Blade Using Two-Layered Thin-Film Gauges
Authors: Iliopoulou V. , De´nos R. , Billiard N. , Arts T.
Published: January 2005

This paper describes the steps undertaken to measure heat flux in a turbine tested in a blowdown windtunnel when using a two-layered thin film gauge array. The sensor consists of a nickel thermoresistor deposited onto a flexible polyamide sheet that can be easily bounded on a substrate using double sided adhesive. The assembly constitutes a two-layered system. First, a numerical algorithm is proposed to extract the wall heat flux from the surface temperature history measured by the thin film gauge. It is very flexible and handles multilayered systems. Then, an original procedure is proposed to determine the thermal properties and the thickness of the different layers. It uses the above numerical algorithm coupled with a minimization routine. The repeatability of the procedure is assessed. Finally, tests are processed according to the proposed method. The results are successfully compared with measurements performed with single-layered thin film gauges.
Large Eddy Simulation of Flow and Heat Transfer in a 90 deg Ribbed Duct With Rotation: Effect of Coriolis and Centrifugal Buoyancy Forces
Authors: Abdel-Wahab Samer , Tafti Danesh K.
Published: January 2005

Results from large eddy simulations (LES) of fully developed flow in a 90 deg ribbed duct are presented with rib pitch-to-height ratio P/e=10 and a rib height-to-hydraulic-diameter ratio e/Dh=0.1. Three rotation numbers Ro=0.18, 0.36, and 0.68 are studied at a nominal Reynolds number based on bulk velocity of 20 000. Centrifugal buoyancy effects are included at two Richardson numbers of Ri=12, 28 (Buoyancy parameter, Bo=0.12 and 0.30) for each rotation case. Heat transfer augmentation on the trailing side of the duct due to the action of Coriolis forces alone asymptotes to a value of 3.7±5% by Ro=0.2. On the other hand, augmentation ratios on the leading surface keep decreasing with an increase in rotation number with values ranging from 1.7 at Ro=0.18 to 1.2 at Ro=0.67. Secondary flow cells augment the heat transfer coefficient on the smooth walls by 20% to 30% over a stationary duct. Centrifugal buoyancy further strengthens the secondary flow cells in the duct cross-section which leads to an additional increase of 10% to 15%. Buoyancy also accentuates the augmentation of turbulence near the trailing wall of the duct and increases the heat transfer augmentation ratio 10% to 20% over the action of Coriolis forces alone. However, it does not have any significant effect at the leading side of the duct. The overall effect of buoyancy on heat transfer augmentation for the ribbed duct is found to be less than 10% over the effect of Coriolis forces alone. Friction on the other hand is augmented 15% to 20% at the highest buoyancy number studied. Comparison with available experiments in the literature show excellent agreement.
Cardiopulmonary and acid–Base effects of desflurane and sevoflurane in spontaneously breathing cats
Authors: Souza Almir Pereira , Guerrero Piedad Natalia Henao , Nishimori Celina Tie , Paula Danielli Parrilha , Santos Paulo Sergio Patto , de Rezende Marlis Langenegger , Nunes Newton
Published: January 2005

The cardiopulmonary effects of desflurane and sevoflurane anesthesia were compared in cats breathing spontaneously. Heart (HR) and respiratory (RR) rates; systolic (SAP), diastolic (DAP) and mean arterial (MAP) pressures; partial pressure of end tidal carbon dioxide (PETCO2), arterial blood pH (pH), arterial partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2); base deficit (BD), arterial oxygen saturation (SaO2) and bicarbonate ion concentration (HCO3) were measured. Anesthesia was induced with propofol (8±2.3 mg/kg IV) and maintained with desflurane (GD) or sevoflurane (GS), both at 1.3 MAC. Data were analyzed by analysis of variance (ANOVA), followed by the Tukey test ( P<0.05). Both anesthetics showed similar effects. HR and RR decreased when compared to the basal values, but remained constant during inhalant anesthesia and PETCO2 increased with time. Both anesthetics caused acidemia and hypercapnia, but BD stayed within normal limits. Therefore, despite reducing HR and SAP (GD) when compared to the basal values, desflurane and sevoflurane provide good stability of the cardiovascular parameters during a short period of inhalant anesthesia (T20–T60). However, both volatile anesthetics cause acute respiratory acidosis in cats breathing spontaneously.
Epidemiologic evaluation of multiple respiratory pathogens in cats in animal shelters
Authors: Bannasch Michael J. , Foley Janet E.
Published: January 2005

Upper respiratory tract infection (URI) propagates readily within cats in shelters and often results in euthanasia of affected cats. In a case-control evaluation of 573 cats in eight shelters in California in 2001 and 2002, the prevalence of feline calicivirus (FCV) was from 13 to 36%, feline herpesvirus (FHV) was from 3 to 38%, and prevalence of Bordetella bronchiseptica, Chlamydophila felis, and Mycoplasma species was from 2 to 14%. Cats with URI tended to be housed in isolation, dehydrated, and younger than cats without URI, and infected with FHV, Mycoplasma species, FCV, or C felis. Shelters differed in the prevalence of pathogens and many cats appeared positive for infection after about 1 week of sheltering. It is helpful for shelters to understand the risk factors associated with URI in order to evaluate the costs and benefits of treatment and improve their procedures to decrease the incidence of URI within their facilities. Antiherpetics and antimycoplasmal drugs may be beneficial for individual animal care. Results document the utility of comprehensive URI surveillance and herd management for specific pathogens typical in that shelter.
Vibrational Spectra of ReF7
Authors: Claassen Howard H. , Selig Henry
Published: January 2005

The infrared spectrum of ReF7 vapor and the Raman spectrum of liquid ReF7 suggest that this molecule, like IF7, belongs to Symmetry Group D5h. The five expected Raman-active fundamentals have been observed at 351, 485, 590, 650, and 737 cm−1. Of the five expected infrared-active fundamentals, three have been observed at 299, 353, and 703 cm−1.
Molecular Orbital Study of the Hydrogen Bond in Ice
Authors: Weissmann Mariana , Cohan Norah V.
Published: January 2005

An SCF—MO—LCAO calculation for the four electrons involved in the straight hydrogen bond in ice is performed using a limited set of Slater-type orbitals. The energy of the four electrons plus the interaction between the ``core potentials'' is calculated as a function of the position of the proton along the line joining the oxygens. The energy of the hydrogen bond is obtained−8.2 kcal/mole—in good agreement with experiment. Electrostatic and delocalization contributions to the energy of the hydrogen bond are in excellent agreement with previous theoretical estimates. The potential energy for the motion of the proton results in a very asymmetric curve, with only one minimum. The dipole moment increases from 1.68 D for a free water molecule to 2.40 D thus confirming previous estimates.
Molecular Orbital Study of Ionic Defects in Ice
Authors: Weissmann Mariana , Cohan Norah V.
Published: January 2005

The potential energy for the diffusion of positive and negative defects in ice is calculated by a SCF—MO—LCAO procedure. The resulting height of the potential energy barrier for positive defects is much lower than for negative ones, thus explaining qualitatively the greater mobility of the H3O+ ions. It is also found that the potential-energy heights are very sensitive to the distance between the oxygens, the diffusion being greater when the oxygens are nearer. The results obtained suggest therefore that the diffusion of positive defects is correlated to the vibrations of the lattice.
Nitrosonium Nitrate. Isolation at 79°—205°K and Infrared Spectra of the Polymorphic Compound
Authors: Parts L. , Miller J. T.
Published: January 2005

Nitrosonium nitrate, NO+NO3−, a red solid, has been studied spectroscopically at temperatures ranging up to 205°K. Reproducible shifts of fundamental frequencies upon warming suggest two crystalline transformations between 79° and 205°K. The γ-, β-, and α-phase have been observed under nonequilibrium conditions in the following temperature ranges, respectively: 79°—185°, 167°—187°, 167°—205°K. The fundamental frequencies of the constituent ions in the γ, β, and α phase are: ν(NO)+: 2215, 2271, 2251 cm−1; ν3: 1364, 1324, 1328 cm−1; ν2: 819, 827, 812 cm−1; ν4: 716, 716, 711 cm−1.
On the Temperature Dependence of Cooperative Relaxation Properties in Glass-Forming Liquids
Authors: Adam Gerold , Gibbs Julian H.
Published: January 2005

A molecular-kinetic theory, which explains the temperature dependence of relaxation behavior in glass-forming liquids in terms of the temperature variation of the size of the cooperatively rearranging region, is presented. The size of this cooperatively rearranging region is shown to be determined by configuration restrictions in these glass-forming liquids and is expressed in terms of their configurational entropy. The result of the theory is a relation practically coinciding with the empirical WLF equation. Application of the theory to viscosimetric experiments permits evaluation of the ratio of the kinetic glass temperature Tg (derived from usual ``quasistatic'' experiments) to the equilibrium second-order transition temperature T2 (indicated by either statistical-mechanical theory or extrapolations of experimental data) as well as the hindrance-free energy per molecule. These parameters have been evaluated for fifteen substances, the experimental data for which were available. Hindrance-free energies were found to be of the magnitude to be expected from consideration of molecular interaction energies. The values of Tg/T2 thus obtained for these fifteen widely differing materials were found to be nearly the same, i.e., 1.30±8.4%. Values for Tg/T2 of nearly the same magnitude were derived by Bestul and Chang from calorimetric data.
On the Radial Dependence of the Fluorescence-Quenching Interaction between Rare-Earth Ions
Authors: Holloway W. W. , Kestigian M.
Published: January 2005

The radial dependence of the quenching interaction between rare-earth ions has been studied through observation of the Tb3+ fluorescence lifetime in samples of Gd1–2cTbcHocCl3·6H2O. The probability for a quenching interaction, PInt, has been determined to be PInt∝c2∝1/r6. On the basis of the ``resonance'' transfer of energy, such a radial dependence implies a dipole—dipole interaction. Other experiments are discussed in which identical results are obtained.
Infrared Spectrum and Vibrational Potential Function of AsF3
Authors: Hoskins L. C. , Lord R. C.
Published: January 2005

The infrared absorption spectrum of gaseous AsF3 has been determined over the spectral range 2000–200 cm−1. The contours of the fundamental bands indicate the correctness of the assignment of the fundamental frequencies made earlier from the Raman spectrum. Teller zeta values were determined from these contours; and from the frequencies, zetas, and a microwave value of the rotational distortion constant DJK, an attempt was made to evaluate the most general quadratic potential function of AsF3. The calculations showed that the DJK value must be in error and that highly precise values of distortion constants are required to determine off-diagonal potential constants in AsF3. Values of the other general potential constants and DJ, DK, and DJK were calculated for several assumed values of the off-diagonal constant F12.
11B Quadrupole Coupling Tensors in the Hydrated Borates. II. The Pentaborate Polyanion
Authors: Lal K. C. , Petch H. E.
Published: January 2005

The quadrupolar splitting of the 11B nuclear magnetic resonance signal has been investigated in potassium pentaborate tetrahydrate, KB5O6(OH)4·2H2O, and ulexite, NaCaB5O6(OH)6·5H2O. In the case of the former material, a good single crystal was available, permitting a complete determination of the quadrupole coupling tensors at the single unique tetrahedral site and at the two unique triangular boron sites. A complete determination of the tensors was not possible in the case of ulexite because of the fibrous nature of the material but, by combining single-crystal and powder techniques, it was possible to identify unambiguously three tetrahedral and two triangular boron sites and to set upper and lower limits on the quadrupole coupling constants.

The electric quadrupole coupling constants eqQ/h and asymmetry parameters η of the electric-field gradient tensors at the boron sites were determined to be eqQ/hCoordination of(kc/sec)ηboron sitePotassium pentaborate tetrahydrate234±10.093±0.009Tetrahedral2536±30.212±0.004Triangular2521±30.195±0.005TriangularUlexite50<eqQ/h<600Tetrahedral2530±50TriangularThe orientations of the principal axes of the electric-field gradient tensors have also been determined for potassium pentaborate tetrahydrate.

The NMR results are in complete agreement with the crystal structures of both compounds as to numbers and coordinations of the boron atoms and as to the nature of the boron—oxygen polyanions.
Electron Paramagnetic Resonance of Triplet Alternant Methylenes. Propargylene and Homologs
Authors: Bernheim R. A. , Kempf R. J. , Gramas J. V. , Skell P. S.
Published: January 2005

The electron paramagnetic resonance of a number of alternant methylene compounds has been observed, and zero-field splitting parameters have been obtained. The results are D=0.6276±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–H,D=0.6263±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–CH3,D=0.5413±0.0004 cm−1 and E=0.0035±0.0003 cm−1 for H–↑C↑–C≡C–C6H5,D=0.6087±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–CH3,D=0.6055±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–C(CH3)3,D=0.5530±0.0002 cm−1 and E=0.0000±0.0006 cm−1 for H–↑C↑–C≡C–C≡C–C6H5,and D=0.8629±0.0003 cm−1 and E=0.0000±0.0010 cm−1 for H–↑C↑–C≡N.The interpretation of the data is based upon the observed spin-density distribution in the alternant free radicals having structures similar to the above triplet molecules. Thus, propargylene, H–↑C↑–C≡C–H, is discussed in terms of a superposition of two π-electron systems having the same spin-density distribution as in the allyl radical. Both positive and negative triplet spin densities are required to account for the observed magnitude of D. The lower values of D obtained for the phenyl-substituted alternant methylenes reflect the delocalization of one of the two triplet electrons into a π orbital of the phenyl group. This effect is more important in the case of phenylpropargylene where a nonzero value of E was obtained. The linear geometry of the alternant methylene chain is responsible for the cases where zero values of E were obtained. The trends in D and trends in linewidths are given qualitative explanations. The discussion assumes that all of the molecules studied have a spectroscopic splitting factor equal to the free-electron value.
Pressure-Induced Q Branch in HCl
Authors: Sharma Ramesh D.
Published: January 2005

Calculations using the theory of the pressure-induced Q branch in the 1Σ polar molecules proposed in an earlier article are brought up to date in view of the recent developments. Experiments are suggested which may give the values of the molecular quadrupole moment and its first derivative, evaluated at equilibrium internuclear distance, with c.m. of the molecule as origin.
Ion Pairing and Interionic Distances in Some Paramagnetic Complexes from Proton Magnetic Resonance Spectra
Authors: La Mar Gerd N.
Published: January 2005

The proton magnetic resonance shifts for the butyl protons in the Co II and Ni II complexes of [Bu4N]−[(Phen3P) M II I3] are shown to be the result of a dipolar interaction with the paramagnetic metal ion. It is also shown that the magnitudes of the observed shifts can be accounted for only by ion pairing between cation and anionic complex. The ratios of the dipolar shifts are calculated as a function of interionic separation for two inequivalent protons, assuming free internal rotations within the cation. From a comparison of the experimentally observed ratios and the calculated ratios, an equilibrium interionic distance of 3.8±0.2 Å was obtained for both complexes. From this distance, an estimate of 3.1±0.2 Å was made of the ionic radius for [Bu4N]+. This ionic radius is compatible with a folded configuration of the n-butyl chains.
Electrostriction in Aqueous Solutions of Electrolytes
Authors: Desnoyers J. E. , Verrall R. E. , Conway B. E.
Published: January 2005

A theory of electrostriction of solvent water near ions is developed. The treatment is based on a calculation of the effective pressure which would, in the absence of the field, cause the same change in volume as the field. The change in solvent volume near ions can be related, using an appropriate molecular model, to the apparent change in the volume of the salt upon dissolution. It is shown that the electrostriction arises at small ions mainly on account of changes of effective volume of the solvent rather than from compression of the ion cavity in the dielectric. This treatment avoids the difficulties of previous calculations where use of the Born equation involves an integration over a distance from the ion. The calculations also lead to information on the local compressibility of solvent water in regions near ions and provide a better basis for interpretation of compressibility measurements in terms of ionic hydration. Explicit approximate solutions for high- and low-field conditions, and a complete numerical solution for the effective pressure—field relation are given.
High-Temperature Expansion of Thermal Transport Coefficients
Authors: Frisch H. L. , Berne Bruce
Published: January 2005

Choosing the rigid-sphere fluid as a reference system a high-temperature perturbation theory of thermal transport phenomena in simple dense fluids is developed starting with the Kubo—Green correlation function expressions for the transport coefficients. We suggest that coupling these expressions with the computer generated molecular dynamics of the reference system provides, at least in principle, a practical numerical method of following the high-temperature limiting behavior of the zero-frequency transport coefficients. Explicit expressions are given for the self-diffusion and shear viscosity coefficients. An elementary derivation of the first-order Enskog self-diffusion coefficient is presented in the Appendix.
Dielectric Constant of Hydrogen-Bonded Liquids. IV. Equilibrium and Relaxation Studies of Homologous Neo-Alcohols
Authors: Dannhauser W. , Bahe L. W. , Lin R. Y. , Flueckinger A. F.
Published: January 2005

The dielectric constants of H–(CH2)n–C(CH3)2–CH2OH with n = 1, 2, 3, 4, 6, and 8 have been measured from about −70° to 100°C with test frequencies 0.05<f<2×105 kc/sec. The equilibrium dielectric constant is analyzed in terms of associative, hydrogen-bond equilibria as deduced from the temperature variation of the Kirkwood correlation factor and ΔH and ΔS of hydrogen bonding are estimated. Dielectric relaxation has been defined over several decades of time. The principal dispersion locus is Debye-like irrespective of wide variations of the apparent degree of association and ΔH‡ and ΔS‡ for relaxation are similar for all species. The relation of dielectric relaxation to equilibrium liquid structure is discussed and evidence for rotational mobility in solid neopentanol and neohexanol is presented.
Theory of the Stimulated Raman and Related Effects
Authors: Buckingham A. D.
Published: January 2005

A simple description of the stimulated Raman emission of Stokes radiation, and of the induced absorption found by Stoicheff at the anti-Stokes frequency, is based on the semiclassical theory of radiation. This theory gives the well-known formulas for absorption and stimulated emission when carried to the first order in the time-dependent perturbation due to the interaction of the light beam with the molecules. If there are two light beams of frequencies ωL and ω, the second-order perturbation may be associated with stimulated emission at the Stokes frequency ω=ω−1=ωL—ωR and with induced absorption at the anti-Stokes frequency ω=ω1=ωL+ωR, where ωL is the laser frequency and ωR a Raman-active vibrational frequency; in both cases, there is a molecular transition to the excited vibrational state. The highly directional and very sharp anti-Stokes emission at ω1 arises from the conversion by molecules in intense beams at ωL and ω−1 of two ωL photons into an ω−1, ω1 pair. Like spontaneous emission from excited states, the production of this anti-Stokes radiation requires the full quantum theory of radiation for an adequate description. The emission of ω1 and the observed directional absorption of ω−1 due to the reverse conversion ω−1+ω1→2ωL are explained. The anti-Stokes emission is proportional to the Stokes intensity and to the square of that of the laser, and to the square of the molecular number density; its sharpness is due to the absence of a molecular transition. The generation of photon pairs ω−n+ωn, where ωn=ωL+nωR, can occur for all values of n, but it is most efficient for n=1, due to resonance in the appropriate molecular hyperpolarizability and to the intensity of the Stokes beam at ω−1.
Studies in Irreversible Thermodynamics. II. A Simple Class of Lattice Models for Open Systems
Authors: Hill Terrell L. , Plesner Igor W.
Published: January 2005

A stochastic model for an ensemble of open, simple lattice systems immersed in a heat bath is presented. All processes available to the systems are first order in the numbers of molecules. Rate equations are derived for means and variances of stochastic variables using the method of cumulant generating functions. There is a close relation between the rate equations for the means and those for the variances. Although the variances decay at a rate comparable to that of the means, they approach their equilibrium functions of the means at roughly twice that rate. Thus there is a time domain, prior to final equilibrium with the surroundings, in which the systems assume the equilibrium probability distribution appropriate to the existing mean values [provided the initial distribution is ``normal,'' i.e., that its central moments have the same order of magnitude (or smaller) as at equilibrium]. The principle of detailed balance at equilibrium is found to be especially useful when applied at the probability (rather than mean value) level. Statistical mechanics provides the equilibrium properties of the ensemble and the connection between chemical potentials and kinetic parameters. Finally, we discuss and solve the mean and variance equations in special cases for two lattice-gas examples, some of whose properties were presented in the first paper of this series. The two models differ in some fundamental respects.
Sigma and Pi Changes in Valence States of Pi-Electron Theory and One-Center Coulomb Repulsion Parameters
Authors: Orloff Malcolm K. , Sinanoğlu Oktay
Published: January 2005

Individual contributions to the total energy change ΔE of the reaction 2C→C++C− are calculated with valence states appropriate to π-electron systems. Methods for the calculation of the open-shell Hartree—Fock (HF) and correlation energies of valence states are given. The HF orbitals entering the main part of ΔE, the one-center repulsion integral γpp, are those of the 1s2η32pz2 valence state of C−. They yield a γpp=12.72 eV, already remarkably close to the semiempirical ``γpp'' of Pariser—Parr theory needed to reproduce, for example, the electronic spectrum of benzene. Both the σ and π orbitals and core correlations of each carbon species change strongly with the state of ionization. The energy of σ HF orbital changes in the reaction is 3.16 eV, of π orbital changes−4.19 eV. Such effects may not cancel out between the different electronic states of an organic molecule, though their net effect on the ΔE of the carbon reaction is −1.0 eV. The rest of ΔE is the 2pz2 correlation, also −1.0 eV. A method is given for the prediction of other ΔE's (i.e., the Pariser—Parr ``γpp'') for heteroatoms. The values obtained are 12.91 eV for pyridine-type nitrogen, 16.47 eV for pyrolle-type nitrogen, 15.38 eV for carbonyl oxygen and 18.85 eV for furan-type oxygen.
Theoretical Model for the Motion of Krypton in a Hydroquinone Clathrate
Authors: Barnett B. , Hazony Y.
Published: January 2005

A theoretical model of the potential inside the hydroquinone clathrate is suggested on the basis of data obtained from Mossbauer-effect experiments and specific-heat measurements. A comparison between the experimental and theoretical specific heats is made for the hydroquinone—krypton clathrates.
Classical Scattering of an Atom from a Diatomic Rigid Rotor
Authors: Cross R. J. , Herschbach D. R.
Published: January 2005

Collisions between an atom and a rotating rigid linear molecule were examined by computer integration of the classical equations of motion. An anisotropic potential consisting of a Lennard-Jones (6, 12) function multiplied by [1+aP2(cosγ)] was used in most of the calculations (γ is the angle between the atom and the axis of the molecule). The deviation in the scattering angle caused by the anisotropy of the potential energy was found to be small and approximately proportional to a, the asymmetry parameter. The deviations were large enough, however, to distort severely the differential cross section in the rainbow scattering region. The angular-momentum transfer was found to be appreciable (in the range ±10 ℏ) over a wide region of impact parameters extending well outside the repulsive core. For moderately heavy molecules a good approximation to the scattering angle and the angular-momentum transfer was obtained from a ``flywheel'' model which assumes that the molecule rotates independently of the collision and calculates the effect of the resulting time-dependent perturbation on the trajectory of the atom. Similarly, for light molecules it was found that the angular-momentum transfer could be approximated by evaluating the time-dependent perturbation of the molecular rotation caused by the atom moving in a trajectory calculated from the spherically symmetric part of the potential.
Temperature and Pressure Dependence of Self-Diffusion in Liquid Ethane
Authors: Wade C. G. , Waugh J. S.
Published: January 2005

The self-diffusion coefficient of ethane has been measured by the spin-echo method in the liquid range between 155° and 298°K and at pressures between the vapor pressure and 2200 atm. The results, interpreted with the help of an approximately determined equation of state, are inconsistent with simple free volume and activated diffusion theories.
Potential-Energy Curves and Dissociation Energies of Oxides and Sulfides of Group IV A Elements
Authors: Nair K. P. R. , Singh Ran B. , Rai D. K.
Published: January 2005

The experimental potential-energy curves have been calculated for some of the electronic states of the oxides and sulfides of Group IV A elements. These results have been compared with empirical potential functions, and dissociation energies of the molecules have been estimated.
NMR Spin—Lattice Relaxation in Solid Solutions of C6H6 and C6D6: Evidence for Concerted Motions by Adjacent Molecules
Authors: Anderson J. E.
Published: January 2005

The NMR spin—lattice relaxation time T1 has been investigated as a function of isotopic substitution in cyrstalline benzene. 1,3,5-C6H3D3 and six solid solutions of C6H6 and C6D6 were studied between 140°K and the melting point. The concentration dependence of T1 was used to separate the effects of intra- and intermolecular relaxation. The experimental intramolecular T1 contribution agreed quite closely with that calculated from known molecular dimensions. Comparison of the intra- and intermolecular correlation times are shown to give information regarding the relative motion of neighboring molecules in the solid. Independent molecular ``jumps'' are found to be relatively unimportant in crystalline benzene, and a free-volume model, leading to the simultaneous motion of adjacent molecules, is discussed.
Vacuum-Ultraviolet Photolysis of Ethane at High Temperature. II. Collisional Deactivation of Excited Ethylene
Authors: Hampson R. F. , McNesby J. R.
Published: January 2005

The competition between decomposition and collisional deactivation of the excited ethylene produced by the photolysis of C2H6 at 1470 Å has been studied. The pressure of C2H6 was varied in two series of photolyses at 25° and 310°C. Also, varying amounts of N2 and Ar were added to a fixed pressure of C2H6 in two series of photolyses at 310°C. The results are interpreted in terms of two excited states of ethylene, of which only one is capable of dissociating and has a dissociative lifetime of 6×10−10 sec (assuming unit efficiency for collisional stabilization). Nitrogen and argon are, respectively, 30% and 20% as effective as C2H6 in removing excess energy from excited ethylene.
Photolysis of Low-Temperature Glasses. II. Temperature and Oxygen Effects in Ethanol and Ether
Authors: Judeikis Henry S. , Siegel Seymour
Published: January 2005

The effect of temperature and oxygen on the processes occurring in the aromatic solute-sensitized photodecomposition of ethanol and ether glasses is described. The results are discussed in terms of the proposed sensitization mechanism, and they are shown to be in excellent agreement with predictions. The effect of oxygen diffusion (at ∼100°K) is to remove the aromatic solute triplet-state population, the latter being an intermediate in the sensitization mechanism, and thus decrease the rate of radical formation. Oxygen also reacts with any radicals present to form peroxy radicals which are stable to light with wavelengths greater than ∼2500 Å.

In the absence of oxygen, the triplet-state population and rate of total radical production are virtually independent of temperature over the range 77° to 125°K. However, the composition of the radical concentration exhibits a strong temperature dependence. It is shown that the latter observation results from a competition between secondary photoreactions (temperature independent) involving the radicals produced by the sensitization process and abstraction reactions (temperature dependent) involving the products of the secondary photoreactions.
Modified Atoms-in-Molecules Model for Predicting Diatomic Ground- and Excited-State Potential-Energy Curves. I. LiH, BeH, and BH
Authors: Ellison Frank O.
Published: January 2005

A model is proposed for the approximate calculation, starting with theoretical atoms-in-molecules-like composite functions (or linear combinations of valence bond structures) of potential-energy curves for ground and excited diatomic systems. The assumptions which define the model may be summarized as follows: (1) diatomic electronic eigenstates are represented by a linear combination of composite functions which, in their orbital approximation, are constructed from a common basis set of atomic orbitals; (2) all valence (or peel) orbitals associated with a given nucleus contain a common orbital exponent, which is a nonlinear variational parameter in the molecular calculation; (3) the total molecular energy is separated into its intra-atomic and interatomic parts; (4) the intra-atomic energy of a given atom (or ion) is separated into its core (inner-shell) and peel (valence-shell) contributions; (5) the peel energy of a given atom (or ion) in the molecule is estimated from the experimental peel energy of the isolated atom (or ion) modified by a semitheoretical function of the scaling factor (which, in effect, accounts for the energy change of the peel when its orbital exponent is revised from the optimum isolated atom value to the optimum molecular-state value); (6) matrix elements over the interaction-energy operator are approximated in a systematic manner. The model is applied to 17 electronic states of LiH, BeH, and BH, 10 of which have been observed experimentally. Dissociation and excitation energies of eight of the lower states are predicted with an average error of ±1913 cm−1=±0.24 eV. The model is shown to be inappropriate for higher-energy states containing Rydberg character; errors of +1 eV are encountered here. Fundamental vibrational frequencies for six of the lower states are predicted with an average error of ±324 cm−1, and equilibrium internuclear distances for eight of the lower states are obtained on the average within 0.09 bohr ∼0.05 Å of experiment. Theoretical analyses in terms of atomic promotional energies, structure projections, orbital occupation numbers, and gross charge distributions are tabulated and discussed.
Direct Calculation of Contributions to the Second-Order Energy of Helium
Authors: Liu Bowen , Meath William J. , Hirschfelder Joseph O.
Published: January 2005

The first-order perturbed wavefunction of helium is written as a sum of terms due to various electron excitations. The portion of the first-order wavefunction due to one-electron excitations has been determined by several investigators. The portion due to two-electron excitations with one of the electrons excited to the 2s orbital is determined exactly by solving a differential equation. The contributions of these functions to the second-order energy are computed and found to be in exact agreement with the energies determined by direct summation of the spectral expansion.
Infrared Spectrum and Vibrational Analysis of Dibromoborane and Dibromoborane-d
Authors: Lynds L. , Wolfram T. , Bass C. D.
Published: January 2005

The vibrational spectrum of the ``perturbed'' molecules H11BBr2, H10BBr2, D11BBr2, and D10BBr2 were generated from the Green's function of the ``unperturbed'' boron tribromides 11BBr3 and 10BBr3. Effect of geometry changes imposed by replacing a halogen by hydrogen on the B1 modes has been calculated and the results indicate a strong dependence on the BH and BD bond length. Using information provided by the calculations, we have observed and identified five of the six HBBr2 and DBBr2 fundamentals. The bands are reported in the following order (cm−1): H11BBr2, D11BBr2, and D10BBr2: ν1 (BBr symmetric stretch), 595, ___, 585, ___; ν2 (BH and BD stretch), 2622, 2622, 1960, ___; ν3 (BBr symmetric deformation), ≈180–190 cm−1, calculated values only; ν4 (BBr asymmetric stretch), 1036, 1048, 870, 901; ν5 (BH and BD in-plane deformation), 772, ___, 656, ___; ν6 (out-of-plane deformation), 731, ___, 625?, ___. Blanks refer to unobserved bands. The calculated in-plane frequencies have been brought into alignment with the observed frequencies by considering mass and geometry changes without altering the force field.