bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-organized Ge nanocrystals embedded in HfAlO fabricated by pulsed-laser deposition and application to floating gate memory
Authors: Liu W. L. , Lee P. F. , Dai J. Y. , Wang J. , Chan H. L. W. , Choy C. L. , Song Z. T. , Feng S. L.
Published: January 2005

A trilayer metal-oxide-semiconductor structure containing a HfAlO tunnel layer, isolated Ge nanocrystals, and a HfAlO control layer, was obtained using pulsed-laser deposition (PLD). Self-organized Ge nanocrystals were formed by PLD at 600°C, suggesting a useful low-temperature process for fabricating Ge nanocrystals embedded in dielectric materials. The self-organized Ge nanocrystals so formed were uniform in size and distribution with a density approaching 1012cm−2. The effects of deposition temperature and growth rate in forming Ge nanocrystals were investigated and it was revealed that a relatively low temperature and growth rate are favorable for the formation of Ge nanocrystals. The memory effect of the Ge nanocrystals with storage charge density of up to 1012cm−2 has been demonstrated by the presence of hysteresis in the capacitance-voltage curves.
Particle trapping in three-dimensional fully developed turbulence
Authors: Biferale L. , Boffetta G. , Celani A. , Lanotte A. , Toschi F.
Published: January 2005

The statistical properties of fluid particles transported by a three-dimensional fully developed turbulent flow are investigated by means of high resolution direct numerical simulations. Single trajectory statistics are investigated in a time range spanning more than three decades, from less than a tenth of the Kolmogorov time scale, τη, up to one large-eddy turnover time. Our analysis reveals the existence of relatively rare trapping events in vortex filaments which give rise to enhanced intermittency on Lagrangian observables up to 10τη. Lagrangian velocity structure function attain scaling properties in agreement with the multifractal prediction only for time lags larger than those affected by trapping.
Buckled SiGe layers by the oxidation of SiGe on viscous SiO2 layers
Authors: Yu C.-Y. , Chen P.-W. , Jan S.-R. , Liao M.-H. , Liao Kao-Feng , Liu C. W.
Published: January 2005

SiGe -on-insulator structures have been fabricated by wafer bonding and layer transfer techniques. The relaxation process of the compressively strained SiGe films bonded to SiO2 layers through the rapid thermal oxidation was investigated. Buckling nucleus were randomly located at the beginning of oxidation and the buckling undulation was well developed after 30s oxidation at 960°C. The buckling amplitude increases with the increasing thermal oxidation time. An emission peak at 1.5μm was observed in the low temperature photoluminescence of the buckled SiGe layers.
An inkjet-printed chemical fuse
Authors: Mabrook M. F. , Pearson C. , Petty M. C.
Published: January 2005

Inkjet printing of the conductive polymer poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid has been used as the basis for a sensor for organic vapors. The electrical resistance of the film was monitored as it was exposed to atmospheres containing alcohol. Ultrathin films exhibited a sharp and nonreversible increase in their resistance. This resulted from a change in the morphology of the organic layer, thereby disrupting the current flow through the polymer. An intended application for these inkjet-printed devices is in disposable handheld instruments to monitor the presence of organic vapors above a threshold level.
Self-assembly of Ni nanocrystals on HfO2 and N-assisted Ni confinement for nonvolatile memory application
Authors: Tan Zerlinda , Samanta S. K. , Yoo Won Jong , Lee Sungjoo
Published: January 2005

We demonstrate memory property using Ni nanocrystals with mean diameter of 9nm embedded in HfO2 high-k dielectric that are formed via a self-assembly process by sputtering and rapid thermal annealing. X-ray photoelectron spectroscopy shows that Ni penetrates into the 5nm HfO2 after high temperature annealing above 800°C in N2. However, the diffusion is suppressed by N incorporation into HfO2 by NH3 annealing. Metal-oxide-semiconductor structures were fabricated with Ni nanocrystals embedded in HfO2. An additional counterclockwise hysteresis of 2.1V due to the charge trapping properties of the Ni nanocrystals was observed from a ±5V sweep during capacitance–voltage electrical measurement.
Effect of temperature and stress on plastic deformation in monocrystalline silicon induced by scratching
Authors: Zarudi I. , Nguyen T. , Zhang L. C.
Published: January 2005

Dry air, coolant, and liquid nitrogen were applied, respectively, to study the effect of temperature and stress on plastic deformation in scratching monocrystalline silicon. Phases generated in surface deformation were characterized by means of the transmission electron microscopy. It was shown that the size of the amorphous transformation zone and the depth of slip penetration in sample subsurface were mainly dependent on the stress field applied. The influence of the temperature variation to −196 °C was surprisingly small and the low temperature did not suppress the phase transformation and dislocation activity.
Enhanced spontaneous polarization in superlattice-structured Bi4Ti3O12–BaBi4Ti4O15 single crystals
Authors: Kobayashi Tomo , Noguchi Yuji , Miyayama Masaru
Published: January 2005

Superlattice-structured ferroelectric single crystals composed of Bi4Ti3O12 (BiT) and BaBi4Ti4O15 (BBTi) have been reported to show a large spontaneous polarization as well as a sufficient insulating property. X-ray diffraction and transmission electron microscopy observations of the crystals revealed a superlattice structure with alternate stacking of the BiT and the BBTi layers. The Curie temperature (TC) of the BiT–BBTi crystals was about 540 °C, which was intermediate between those of BiT (675 °C) and BBTi (410 °C). Polarization measurements of the BiT–BBTi crystals along the a(b) axis demonstrate that the spontaneous polarization was 52μC∕cm2, which is larger than those of the BiT and BBTi crystals.
Ferroelectric domain engineering using atomic force microscopy tip arrays in the domain breakdown regime
Authors: Rosenwaks Y. , Dahan D. , Molotskii M. , Rosenman G.
Published: January 2005

One of the main obstacles to ultrahigh-density scanning probe ferroelectric-based devices is the writing speed of the device when using a single tip. We report here on the application of atomic force microscopy tip arrays for nanodomain engineering in ferroelectric crystals under the domain breakdown conditions. Using a multiple-tip array, it is shown that domain writing in 200-μm-thick RbTiOPO4 crystals results in a regular one-dimensional domain grating that penetrates throughout the bulk crystal as in the case of single tip writing. This multiple tip approach paves the way to the use of scanning probe microscopy for fabrication of various nanodomain configurations for advanced optoelectronic and microelectronic devices.
Single-crystal organic field-effect transistors based on dibenzo-tetrathiafulvalene
Authors: Mas-Torrent M. , Hadley P. , Bromley S. T. , Crivillers N. , Veciana J. , Rovira C.
Published: January 2005

We report on the fabrication and characterization of field-effect transistors based on single crystals of the organic semiconductor dibenzo-tetrathiafulvalene (DB-TTF). We demonstrate that it is possible to prepare very-good-quality DB-TTF crystals from solution. These devices show high field-effect mobilities typically in the range 0.1–1cm2∕Vs. The temperature dependence was also studied revealing an initial increase of the mobility when lowering the temperature until it reached a maximum, after which the mobility decreased following a thermally activated behavior with activation energies between 50 and 60meV. Calculations of the molecular reorganization energy and intermolecular transfer integrals for this material were also performed and are in agreement with the high mobility observed in this material.
Potential-well-roughness-induced transition from resonant tunneling to single-electron tunneling in Si∕SiO2 double-barrier structure
Authors: Ishikawa Yasuhiko , Ikeda Hiroya , Tabe Michiharu
Published: January 2005

The effect of Si potential well roughness on the vertical tunneling transport through the Si∕SiO2 double-barrier structure is studied. The increase of Si well roughness is shown to cause a transition of tunneling mode from resonant tunneling (flat limit) to single-electron tunneling (rough limit). The result suggests that the Si well roughness induces (1) formation of the Coulomb islands in the Si well due to the spatial fluctuation of quantized levels and (2) sequential tunneling instead of resonant tunneling due to the increase of scattering events.
Adsorption effects of NO2 at ppm level on visible photoluminescence response of SnO2 nanobelts
Authors: Faglia G. , Baratto C. , Sberveglieri G. , Zha M. , Zappettini A.
Published: January 2005

The visible photoluminescence (PL) of tin oxide nanobelts is quenched by nitrogen dioxide at ppm level in a fast (time scale order of seconds) and reversible way. Besides, the response seems highly selective toward humidity and other polluting species, such as CO and NH3. We believe that adsorbed gaseous species that create surface states can quench PL by creating competitive nonradiative paths. A comparison between conductometric and PL response suggests that the two responses are ascribable to different adsorption processes.
Unsteady Turbine Blade Wake Characteristics
Authors: Sieverding Claus H. , Ottolia Davide , Bagnera Carlo , Comadoro Andrea , Brouckaert J.-F. , Desse Jean-Michel
Published: January 2005

The paper presents an experimental investigation of large coherent structures, commonly referred to as “von Karman vortex street,” in the wake of a turbine blade at high subsonic Mach number M2,is=0.79 and high Reynolds number (RE=2.8×106 and their effect on the steady and unsteady pressure and temperature distribution in the wake. Ultra short smoke visualizations and two interferometric measurement techniques, holographic interferometry and white light differential interferometry provide insight into the vortex formation and shedding process. In addition, the interferometric measurement provides quantitative information on the stream wise evolution of the minimum density associated with the vortices and on their lateral spreading. Wake traverses are performed with a four-head fork probe carrying a Kiel probe and a fast response Kulite pressure probe for pressure measurements and a thermocouple probe and a cold wire resistance probe for temperature measurements. The results confirm the observation of energy separation in the wake as found by other researchers. The experimental data are a unique source for the validation of unsteady Navier-Stokes codes.
The Transition Mechanism of Highly Loaded Low-Pressure Turbine Blades
Authors: Stieger R. D. , Hodson H. P.
Published: January 2005

A detailed experimental investigation was conducted into the interaction of a convected wake and a separation bubble on the rear suction surface of a highly loaded low-pressure (LP) turbine blade. Boundary layer measurements, made with 2D LDA, revealed a new transition mechanism resulting from this interaction. Prior to the arrival of the wake, the boundary layer profiles in the separation region are inflexional. The perturbation of the separated shear layer caused by the convecting wake causes an inviscid Kelvin-Helmholtz rollup of the shear layer. This results in the breakdown of the laminar shear layer and a rapid wake-induced transition in the separated shear layer.
The Impact of Forward Swept Rotors on Tip Clearance Flows in Subsonic Axial Compressors
Authors: McNulty G. Scott , Decker John J. , Beacher Brent F. , Khalid S. Arif
Published: January 2005

This paper presents an experimental and analytical study of the impact of forward swept rotors on tip-limited, low-speed, multistage axial compressors. Two different configurations were examined, one with strong tip-clearance flows and the other with more moderate levels. Evaluations were done at multiple rotor tip clearances to assess differences in clearance sensitivity. Compared to conventionally stacked radial rotors, the forward swept blades demonstrated improvements in stall margin, efficiency and clearance sensitivity. The benefits were more pronounced for the configuration with stronger tip-clearance flows. Detailed flow measurements and three-dimensional viscous CFD analyses were used to investigate the responsible flow mechanisms. Forward sweep causes a spanwise redistribution of flow toward the blade tip and reduces the tip loading in terms of static pressure coefficient. This results in reduced tip-clearance flow blockage, a shallower (more axial) vortex trajectory and a smaller region of reversed flow in the clearance gap.
A Novel Liquid Crystal Image Processing Technique Using Multiple Gas Temperature Steps to Determine Heat Transfer Coefficient Distribution and Adiabatic Wall Temperature
Authors: Talib Abd Rahim Abu , Neely Andrew J. , Ireland Peter T. , Mullender Andrew J.
Published: January 2005

This paper presents a novel experimental technique, which combines thermochromic liquid crystals with multiple steps in gas temperature, to determine heat transfer coefficient and adiabatic wall temperature distributions. The transient heat transfer experiments have been conducted on a flat plate using the low-temperature analogue of an ISO standard propane-air burner commonly used in aero-engine fire certification. The technique involves the measurement of the surface temperature response of an insulating model to a change in gas temperature. A coating comprising more than one thermochromic liquid crystal material is used to increase the range of the surface measurement and this is combined with multiple step changes in gas temperature. These measures induce several peaks in liquid crystal intensity throughout the transient experiment and these are shown to improve the accuracy. The current technique employs useful data from both the heating and cooling phases in the heat transfer test. To the authors’ knowledge, this has not been investigated before and it is likely to be very useful for other applications of the liquid crystal transient heat transfer experiment. The uncertainties in all measurements have been quantified and are presented in this paper.
Influence of Surface Roughness on Three-Dimensional Separation in Axial Compressors
Authors: Gbadebo Semiu A. , Hynes Tom P. , Cumpsty Nicholas A.
Published: January 2005

Surface roughness on a stator blade was found to have a major effect on the three-dimensional (3D) separation at the hub of a single-stage low-speed axial compressor. The change in the separation with roughness worsened performance of the stage. A preliminary study was carried out to ascertain which part of the stator suction surface and at what operating condition the flow is most sensitive to roughness. The results show that stage performance is extremely sensitive to surface roughness around the leading edge and peak-suction regions, particularly for flow rates corresponding to design and lower values. Surface flow visualization and exit loss measurements show that the size of the separation, in terms of spanwise and chordwise extent, is increased with roughness present. Roughness produced the large 3D separation at design flow coefficient that is found for smooth blades nearer to stall. A simple model to simulate the effect of roughness was developed and, when included in a 3D Navier–Stokes calculation method, was shown to give good qualitative agreement with measurements.
Thermal Performance of Angled, V-Shaped, and W-Shaped Rib Turbulators in Rotating Rectangular Cooling Channels (AR=4:1)
Authors: Wright Lesley M. , Fu Wen-Lung , Han Je-Chin
Published: January 2005

An experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1. Angled, discrete angled, V-shaped, and discrete V-shaped ribs were investigated, as well as the newly proposed W-shaped and discrete W-shaped ribs. In all cases, the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45 deg to the mainstream flow. The rib height-to-hydraulic diameter ratio e/D is 0.078, and the rib pitch-to-height ratio P/e is 10. The channel orientation with respect to the direction of rotation is 135 deg. The range of flow parameters includes Reynolds number (Re=10,000–40,000), rotation number Ro=0.0-0.15, and inlet coolant-to-wall density ratio (Δρ/ρ=0.12). Both heat transfer and pressure measurements were taken, so the overall performance of each rib configuration could be evaluated. It was determined that the W-shaped and discrete W-shaped ribs had the superior heat transfer performance in both nonrotating and rotating channels. However, these two configurations also incurred the greatest frictional losses while the discrete V-shaped and discrete angled ribs resulted in the lowest pressure drop. Based on the heat transfer enhancement and the pressure drop penalty, the discrete V-shaped ribs and the discrete W-shaped ribs exhibit the best overall thermal performance in both rotating and nonrotating channels. These configurations are followed closely by the W-shaped ribs. The angled rib configuration resulted in the worst performance of the six configurations of the present study.
Thermoacoustic Stability of Quasi-One-Dimensional Flows—Part II: Application to Basic Flows
Authors: Prasad Dilip , Feng Jinzhang
Published: January 2005

In this paper, applications of a previously developed numerical formulation (Prasad, D., and Feng, J., 2004, “Thermoacoustic stability of Quasi-One-Dimensional Flows—Part I: Analytical and Numerical Formulation,” J. Turbomach., 126, pp. 636–643. for the stability analysis of spatially varying one-dimensional flows are investigated. The results are interpreted with the aid of a generalized acoustic energy equation, which shows that the stability of a flow system depends not only on the nature of the unsteady heat, mass and momentum sources but also on the mean flow gradients and on the inlet and exit boundary conditions. Specifically, it is found that subsonic diffusing flows with strongly reflecting boundary conditions are unstable, whereas flows with a favorable pressure gradient are not. Transonic flows are also investigated, including those that feature acceleration through the sonic condition and those in which a normal shock is present. In both cases, it is found that the natural modes are stable. Finally, we study a simplified ducted flame configuration. It is found that the length scale of the mean heat addition affects system stability so that the thin-flame model commonly used in studies of combustion stability may not always be applicable.
Evaluation of a continuous glucose monitoring system in cats with diabetes mellitus
Authors: Ristic Jelena ME , Herrtage Michael E , Walti-Lauger Sabine MM , Slater Linda A. , Church David B. , Davison Lucy J. , Catchpole Briän
Published: January 2005

A continuous glucose monitoring system (CGMS) was evaluated in 14 cats with naturally occurring diabetes mellitus. The device measures interstitial fluid glucose continuously, by means of a sensor placed in the subcutaneous tissue. All cats tolerated the device well and a trace was obtained on 15/16 occasions. There was good correlation between the CGMS values and blood glucose concentration measured using a glucometer ( r=0.932, P<0.01). Limitations to the use of the CGMS are its working glucose range of 2.2–22.2 mmol/l (40–400 mg/dl) and the need for calibration with a blood glucose measurement at least every 12 h. When compared to a traditional blood glucose curve, the CGMS is minimally invasive, reduces the number of venepunctures necessary to assess the kinetics of insulin therapy in a patient and provides a truly continuous glucose curve.
Dual-subtype FIV vaccine (Fel-O-Vax® FIV) protection against a heterologous subtype B FIV isolate
Authors: Pu Ruiyu , Coleman James , Coisman James , Sato Eiji , Tanabe Taishi , Arai Maki , Yamamoto Janet K
Published: January 2005

Vaccine trials were undertaken to determine whether the Fel-O-Vax® FIV, a commercial dual-subtype (subtypes A and D) feline immunodeficiency virus (FIV) vaccine, is effective against a subtype B FIV isolate. Current results demonstrate the Fel-O-Vax FIV to be effective against a subtype B virus, a subtype reported to be the most common in the USA.
Home-monitoring of blood glucose in cats with diabetes mellitus: Evaluation over a 4-month period
Authors: Casella Martina , Hässig Mike , Reusch Caudia E.
Published: January 2005

Home-monitoring of blood glucose concentrations has recently been introduced to owners. The objectives of this study were to investigate the feasibility of home-monitoring of blood glucose in diabetic cats by owners, the problems encountered and to compare glucose concentrations at home with those measured in the hospital. Twelve of 15 cat owners were able to generate glucose curves over the study period of 4 months. Most problems were related to restraining the cat, generating negative pressure with the lancing device and producing a blood drop. In the majority of cases, these problems could be resolved during the study. Blood glucose concentrations in the clinic tended to be lower than at home; some of the differences were significant. No association between tolerance of the procedure and blood glucose concentrations measured at home was found. We, therefore, assume that the lower glucose levels in the hospital were caused by lack of food intake. In 38% of cases, treatment based on hospital curves would have been different from that based on home curves. Home-monitoring appears to be a valuable tool in the management of cats with diabetes mellitus. One of its major advantages is that it enables frequent generation of blood glucose curves, which is of particular importance in cats that are difficult to regulate.
Thermal Conductivity and Specific Heat of Some Polymers between 4.5° and 1°K
Authors: Reese W. , Tucker J. E.
Published: January 2005

Measurements of the thermal conductivity, using a steady-state technique, and of the specific heat, using a transient technique, have been performed between 4.5° and 1°K on commercial samples of polytetrafluoroethylene (Teflon), polychlorotrifluoroethylene (Kel-F), nylon, and three samples of polyethylene of varying densities. In all cases the specific heat is proportional to T3. For the polyethylene samples, the constant of proportionality was found to depend strongly on the density of the sample, indicating that amorphous regions have a higher specific heat in this temperature range than do crystalline regions. Extrapolation to completely crystalline material gives the heat capacity as C = 100 T3 erg/°K·cm3, while extrapolation to completely amorphous material gives the heat capacity as C = 297 T3 erg/°K·cm3. The thermal conductivity varies more rapidly than linearly with temperature except in the case of polychlorotrifluoroethylene. Analysis of these thermal-conductivity measurements and some similar results which have been published previously on the basis of a combination of structure scattering and internal boundary scattering yield sizes of the internal boundaries which show good correlation with the average size of crystalline regions determined optically for the same samples.
Monte Carlo Generation of a Restricted Random Walk and the Excluded-Volume Problem
Authors: Windwer Stanley
Published: January 2005

A Monte Carlo procedure was used to simulate non self-intersecting random walks on a high-speed digital computer. The specific model considered hard cores of 3½ units and different rotational angles. The mean-square end-to-end distance and the mean-square radius of gyration were fitted to an equation of the form 〈J N2〉 = aNb. It was found that the results obtained by considering nonlattice systems are not consistent with walks constrained to a lattice. This discrepancy is discussed in terms of intrinsic excluded volume and excess excluded volume. It is suggestive that the ratio 〈S N2〉/〈R N2〉 may be a more general parameter in discussing these systems.
H2-Transfer Reactions in the Gas-Phase Radiolysis of Hydrocarbons
Authors: Ausloos P. , Lias Sharon G.
Published: January 2005

The radiolysis of cyclohexane has been investigated in the presence of varying concentrations of acetylene, ethylene, propylene, butene, and cyclopropane. On the basis of a number of observations, it is concluded that, in all cases, the H2-transfer reactionCnHm+cyclo−C6H12+→CnHm+2+C6H10+does take place. No extensive rearrangement occurs in the collision complex. For instance, a transfer of H2 to CD3CDCD2 results exclusively in the formation of CD3CDHCD2H, while an H2 transfer to (CD2)3 leads to the formation of CD2HCD2CD2H. Relative rate constants for the transfer of an H2 molecule to CH3CHCH2, 1-C4H8, iso-C4H8, 2-C4H8, C2H4, and C2H2 are, respectively, 1.00, 0.68, 0.27, 0.10, 0.11, and 0.072.

Similar variations in the relative rate constants of the H2−-transfer reactionCnHm++cyclo−C6H12→CnHm+2+C6H10+are noted.

The following additional information was derived in the course of this study:

(1) When cyclopentane or n-pentane is substituted for cyclohexane in the reaction mixture, the H2-transfer reaction again occurs. Under comparable experimental conditions, the probability of the H2-transfer reaction is proportional to the yield of the parent ion as derived from the 70-eV mass-spectral cracking patterns.

(2) An increase in the pressure of cyclopentane, from 12.7 to 210 mm, leads to approximately a 50% increase in the yield of the parent ion of cyclopentane.

(3) The parent cyclohexane ion undergoes a charge transfer to NO at a rate which is comparable to the rates of the H2-transfer reactions. O2 does not interact with the parent ion.

(4) The cyclopropane-d6 parent ion reacts with cyclo-C6H12 to form CD3CDHCD2H, indicating that this ion acquires the propylene ion structure prior to or during reaction.
Electron Paramagnetic Resonance Studies of Mn(CN)5NO2− and Cr(CN)5NO3− in Dilute Single Crystals
Authors: Fortman John J. , Hayes Robert G.
Published: January 2005

We have studied the electron paramagnetic resonance spectra of Mn(CN)5NO2− and Cr(CN)5NO3− as dilute solutions in single crystals of various diamagnetic hosts. From these measurements, we have obtained the spectroscopic splitting factor tensor and the hyperfine tensors to the central metal atom and nitrosyl nitrogen. In the case of Cr(CN)5NO3−, we have also measured the hyperfine tensor to carbon-13 in the equatorial and axial cyanides. We have measured the quadrupole coupling constant to 55Mn in Mn(CN)5NO2−. We have attempted to construct a coherent picture of the electronic structure of the complexes from these data. This attempt has been only partly usccessful, primarily because the spectroscopic splitting factors are much nearer the free spin value than one expects on the basis of the hyperfine data.
Electron-Impact Energy Spectra of Acetone and 2-Butanone
Authors: Silverman S. M. , Lassettre E. N.
Published: January 2005

Zero-angle and wide-angle (6.5°—7°) electron-impact energy spectra for acetone and 2-butanone are presented and discussed.
Ion—Ion Interactions in Rare-Earth-Doped LaF3
Authors: Brown M. R. , Whiting J. S. S. , Shand W. A.
Published: January 2005

A systematic study of quantum efficiencies and lifetimes has been carried out for the visible fluorescences of Pr3+ in single-crystal LaF3. An analysis of the results as a function of Pr3+ concentration is given in terms of a two-site model in which a Pr3+ ion can either be in an isolated site or in a site where it is coupled to other impurity ions. This model leads to ion—ion interaction ranges varying from ∼5 Å (nearest neighbor) to ∼12 Å depending on the fluorescent level studied. Throughout this range of interaction lengths, Dexter's model of electrostatic ion—ion interaction shows that the dominant contribution comes from the quadrupole—quadrupole term. Temperature effects in the interaction are consistent with the lack of exact resonance between the electronic levels. It appears that the lattice can readily absorb excess energy up to ∼1000 cm−1.

A set of samples doped with a second rare earth (Ce3+, Nd3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+) has demonstrated the existence of selection rules for ion—ion interaction in addition to energy-matching requirements. The system 0.5% Pr3+: x% Ce3+ has been studied in more detail.
Photochemistry of Metal Solutions. II. Flash Photolysis of Alkali Metals in Ethylamine
Authors: Ottolenghi Michael , Bar-Eli Kedma , Linschitz Henry
Published: January 2005

Flash-photolysis studies have been made on Li, K, Rb, and Cs solutions in ethylamine, over a range of temperature and concentration. Such solutions typically show three bands near 650 (V), 850 (R), and 1300 (IR) mμ. These are assigned, respectively, to a cation-centered monomer, a dimer, and a solvated electron. In K, Rb, and Cs solutions, flashing at wavelengths shorter than 500 mμ causes initially a bleaching of V and enhancement of IR. This is followed by a growing in of R, but at a rate quite different from that of IR decay. Another precursor X of the R transient is therefore postulated. The R transient finally reverts back to V. The ratio of the yields of the IR and R transients is constant, independent of excitation wavelength, metal concentration and fractional conversion. From this it is inferred that X and IR have a common origin. Direct reversible photolysis of the original R-band also occurs, leading to an infrared transient which decays back to R in a second-order process. The rate constants all decrease, in passing from K to Cs. In Li solutions, photolysis of V results in enhanced IR absorption followed by direct back reaction to V without the intermediate R-transient stage.

The nature of the various species and transients is discussed. It is suggested that X may be a long-lived excited state of the monomer V, the metastability being due to Franck—Condon effects. Alternatively, X may be an unstable monomer with an ion-pair structure, similar to that postulated for the monomer in liquid ammonia.
Vibrational Analysis of the 1B2u State of Benzene
Authors: Slezak J. A. , Wait S. C.
Published: January 2005

A force field for the 1B2u electronic state of benzene and benzene-d6 is determined using first-order perturbation techniques. The force field is developed from a knowledge of the molecular structure and the in-plane vibrational frequencies in the ground and excited electronic states of benzene. Particular emphasis is given to the controversial vibrational frequencies belonging to symmetry species b2u. The excited-state value, 1510 cm−1 assigned by Ingold is modified to approximately 1200 cm−1. Attempts were also made to predict the excited-state geometry using only the vibrational frequencies and the force field of the ground state, but these attempts were unsuccessful. This is attributed to the sensitivity of the calculations to interaction force constants in the potential function.
Excess Entropy of Mixing of Liquids
Authors: Yosim S. J.
Published: January 2005

An expression for the excess entropy for mixing isothermally two liquids was obtained from the entropy of mixing two fluids of rigid spheres, each at the volume of the corresponding liquid components, to form a solution of rigid spheres the volume of which was that of the liquid solution. The theoretical entropy of mixing of liquids was found to be ideal only if the diameters of the molecules are the same, the molar volumes of the components are equal, and if the volume of mixing is zero. For small deviations from the above conditions, the excess entropy of mixing was proportional to the product of the mole fractions of the components. The equation was applied to nonpolar systems; the agreement between the calculated and observed values was satisfactory.
Interatomic Potentials and X-Ray-Diffraction Intensities for Liquid Xenon
Authors: Khan Ashfaq A. , Broyles A. A.
Published: January 2005

The experiments performed by Campbell and Hilderband have provided intensity curves for x rays scattered from liquid xenon. They have computed, from their data, the radial-distribution functions g. The Lennard-Jones 6–12 potential with constants suggested by Beattie, Barriault, and Brierly and the Slater potential with Kane's constants have been used to compute g's and scattering intensities for comparison with those of Campbell and Hilderband. The agreement between experiment and theory is poorer than that found for neon, argon, and krypton, and arguments are presented why the experimental intensities should be remeasured.
Correlation Energy of Ethylene and Acetylene
Authors: Moskowitz J. W.
Published: January 2005

A series of self-consistent-field calculations are reported for the molecules C2, ethylene, and acetylene in a Gaussian basis. An upper limit for the correlation energy of ethylene and acetylene of 0.645 and 0.597 a.u. has been computed. The correlation energy is estimated to be too high by 0.045 to 0.084 a.u. based on the results of the C2 calculation.
Influence of the Dielectric Constant on the Yield of Free Ions Produced during Radiolysis of a Liquid
Authors: Freeman G. R. , Fayadh J. M.
Published: January 2005

The γ-radiation-induced conductance of liquid diethyl ether is consistent with the previously developed theory.

The following values of G(free ion) were determined by the conductance method: n-hexane, 0.10; cyclohexane, 0.10; p-dioxane, 0.05; n-butyl ether, 0.11; ethyl ether, 0.19; n-butyl bromide, 0.27; n-butyl chloride, 0.39.

Values of G(free ion) in other systems were obtained from spectroscopic and chemical studies reported in the literature.

G(free ion) is roughly proportional to the static dielectric constant of the liquid, over the range studied. A theory is presented which explains the results. It appears that the slowed-down secondary electrons are ``trapped'' in the liquid and solvated before undergoing geminate recombination, even in alkanes.

Solvated electrons in alkanes would probably have a charge-transfer type of absorption spectrum, with a broad absorption maximum in the infrared.

The major portion of ion pairs that undergo geminate recombination in these liquids does so in a period of 10−10±1 sec.

A general mechanism is formulated for the initial stages of the ionic part of a liquid-phase radiolysis reaction.
Coadsorption of Hydrogen and Potassium on Tungsten. Adsorption of Hydrogen on Potassium
Authors: Schmidt L. D. , Gomer R.
Published: January 2005

The adsorption of molecular and atomic hydrogen on multilayers of potassium, deposited on a tungsten field emitter, and the coadsorption of hydrogen and potassium on tungsten have been investigated by a field-emission technique. Molecular hydrogen does not appear to be chemisorbed on potassium at low temperatures. Atomic hydrogen seems to interact, most probably by the formation of a hydride structure with K atoms outermost from the surface. The coadsorption of H and K on tungsten leads to a decrease in work function over that caused by potassium alone, and to increases in the temperature required for potassium surface diffusion on tungsten. These facts are explained in terms of a surface complex WHK in which H is negatively charged relative to K.
Normal Coordinate Analysis of PF5, PF2Cl3, and PCl5
Authors: Van Der Voorn Peter C. , Purcell Keith F. , Drago Russell S.
Published: January 2005

Normal coordinate analyses have been performed for the series of phosphorus (V) halides—PF5, PF2Cl3, PCl5. The effect of including interaction force constants has been studied in detail. The bond-stretching force constants have been interpreted in connection with molecular orbital calculations for these molecules.
Raman Spectra of Crystalline CH4 and CD4
Authors: Anderson A. , Savoie R.
Published: January 2005

The Raman spectra of crystalline CH4 and CD4 have been recorded in the temperature range 10°—77°K, which includes all three solid phases of CD4 and Phases I and II of CH4. Only three of the four Raman active fundamentals were observed in all cases and no lattice vibrations were seen. There are marked changes in the spectra at the transition Phase I—Phase II, but only small differences between the spectra of Phases II and III of CD4. The spectra of Phase I are very similar to that of the liquid, suggesting that molecular rotation persists in the crystal at temperatures near the melting point. The structure of the fundamentals in Phase II is best interpreted in terms of a D2d2 space group. The more detailed spectrum for Phase III of CD4 may be indicative of a lower symmetry, but alternative explanations are briefly discussed.
Theory of Electron-Transfer Reaction Rates of Solvated Electrons
Authors: Marcus R. A.
Published: January 2005

A theory of electron-transfer reactions of solvated electrons is described. Using an electron-transfer theory formulated elsewhere and using polaron theory the rate constant is related to the standard reduction potentials of the two reactants, spectral and other data for the solvated electron, and rate data on ordinary chemical or electrochemical electron-transfer reactions of the second reactant. This calculated rate constant appears in a boundary condition in a diffusion-reaction differential equation. When that constant is high the reaction becomes diffusion controlled, but when the constant is low it becomes the observed rate constant itself. Some comparison is made with existing data. Conditions for possible but as yet unobserved chemiluminescence are also considered. Solvent-electron polarization in the vicinity of a solvated electron is also examined, by application of polaron theory for a high lattice frequency continuum.
Recent Studies of the Classical Electron Gas
Authors: Carley D. D.
Published: January 2005

Radial distribution functions are computed for classical particles interacting with Coulomb, shielded Coulomb, and truncated Coulomb forces. The methods used to obtain these distribution functions include the Percus—Yevick and convolution hypernetted-chain-integral equations, the Monte Carlo method, the the Debye—Hückel equation, and the perturbation methods of Lado and of Broyles and Sahlin. Comparisons between these methods indicate that for the Coulomb and the shielded Coulomb interactions the Debye—Hückel approximation is quite good for values of θ>3.0; θ=kTa/q2, where a is the ion-sphere radius. For values of θ<1.0 the error in the Debye—Hückel approximation increases rapidly with decreasing θ. The Lado perturbation equation is an improvement over that of Broyles and Sahlin for small separation distances. The solutions obtained cover a range in θ from 0.4 to 20.0.
Ionic Processes in γ-Irradiated Organic Solids: Recombination Luminescence
Authors: Skelly David W. , Hamill William H.
Published: January 2005

Several aromatic hydrocarbons, ketones, and amines phosphoresced when their γ-irradiated dilute solutions in 3-methyl pentane were exposed to near-infrared light at 77°K or were warmed slightly. Triphenylamine (TPA) was examined in some detail. Optical absorption spectroscopy provides evidence for color centers tentatively identified as TPA+, TPA−, as well as solvent-trapped electrons (e−). Formation of TPA+ is attributed to transfer of the electron vacancy in the molecular matrix. Infrared bleaching of (e−) and TPA−-induced phosphorescence of TPA with corresponding decrease of TPA+. Addition of organic halide (e− trap) decreased TPA− and (e−), and ethanol (hole trap) decreased TPA+; both decreased phosphorescence which is attributed to ion recombination.
Thermal Conductivities of Ordinary and Isotopically Substituted Polar Gases and Their Equimolar Mixtures
Authors: Baker Charles E. , Brokaw Richard S.
Published: January 2005

Thermal-conductivity measurements have been carried out over the temperature range 300° to 475°K with an eight-cell hot-wire thermal-conductivity apparatus. The thermal conductivities of the deuterated gases are greater than those of their unsubstituted counterparts at the higher temperatures (presumably because of their higher heat capacities). Conductivities of the equimolar mixtures lie about midway between the conductivities of the pure components. Results are analyzed to test a recent hypothesis that a resonant exchange of rotational quanta causes the thermal conductivity of a polar gas to seem anomalously low in relation to its viscosity. These results are consistent with this hypothesis, the only qualification being that near-resonant exchange is also important.
Molecular Orbitals of Diborane in Terms of a Gaussian Basis
Authors: Burnelle Louis , Kaufman Joyce J.
Published: January 2005

The molecular orbitals of diborane have been calculated by the nonempirical SCF-LCAO method, taking all electrons of the molecule into account and calculating exactly all the integrals. The basis functions were Gaussians centered on the various atoms of the molecule. Two sets of Gaussians have been used, the largest one containing 54 functions, distributed as follows: 9s+3p on each boron, and 3s on each hydrogen. The ordering of the molecular orbitals on the energy scale agrees with that found by Newton, Boer, Palke, and Lipscomb who have used an almost optimized minimal STO basis. The calculated total molecular energy, −52.753 a.u., is 0.468 a.u. higher than the experimental value. A value of 12.9 eV is obtained for the ionization potential, which is to be compared with experimental results ranging from 11.9 to 12.1 eV. An electron-population analysis indicates the presence of very small gross atomic charges (qB=−0.088e; qH(bridge)=−0.002e; qH(terminal)=0.045e). The overlap populations are as follows: n (B, B)=0.064; n (B, Hterm)=0.880; n (B, Hbridge)=0.345. These suggest a structure involving practically no bond between the borons, the bonding in the central part of the system being mainly concentrated in three-center banana bonds.
On Some Atomic rij Integrals
Authors: Roberts P. J.
Published: January 2005

A computational scheme is outlined for reducing certain atomic integrals involving products of rij terms to closed form. Atomic s-type Slater orbitals are used throughout, together with certain correlation factors which are functions of r12, r32, and r42.
Gaussian Wavefunctions for the 10-Electron Systems. III. OH−, H2O, H3O+
Authors: Moskowitz J. W. , Harrison M. C.
Published: January 2005

A series of SCF calculations in a Gaussian basis are reported for the 10-electron systems OH−, H2O, H3O+. For the most extensive basis, the total energy and dipole moment of H2O were computed to be −76.0421 and 0.782 a.u., respectively. The molecular geometry was explored for a variety of bases. In addition, the effect of polarization functions on the oxygen and the hydrogens was studied.
Electric-Dipole Polarizability of Atoms by the Hartree—Fock Method. II. The Isoelectronic Two- and Four-Electron Series
Authors: Cohen Howard D.
Published: January 2005

Results are presented for the electronic-dipole polarizabilities of the isoelectronic series of helium and beryllium in the presence of a finite electric field. These calculations were done analytically, but large numbers of carefully chosen and optimized basis functions were used in order to assure a good fit to the exact solution for the perturbed Hartree—Fock wavefunction. It was found that the polarizabilities of the helium series increase, and those of the beryllium series decrease, as the field increases.
Use of Spin Echoes in a Pulsed Magnetic-Field Gradient to Study Anisotropic, Restricted Diffusion and Flow
Authors: Stejskal E. O.
Published: January 2005

The Bloch—Torrey equations are modified to include the case of anisotropic, restricted diffusion and flow. The problem of solving these modified equations for the amplitude of a spin echo in a time-dependent magnetic-field gradient subject to restricting boundary conditions is discussed. This problem is solved for a number of selected cases. In particular, it is found that a magnetic-field gradient applied in short, intense pulses is effective in defining the time during which nuclear displacements take place. A simplified equation, suitable for the pulsed-gradient experiment, is presented and solved for two different examples of systems showing restricted diffusion. A procedure for analyzing the data from pulsed-gradient measurements is suggested, and its merits are discussed. Suggestions are made of systems which may well be expected to show restricted, anisotropic diffusion or interesting flow properties.
Vibrational Structuring in Optical Activity. II. ``Forbidden'' Character in Circular Dichroism
Authors: Weigang Oscar E.
Published: January 2005

The influence of vibration on rotatory strength in the adiabatic approximation is considered and vibronic band rotatory strengths are developed. At a level of approximation which gives ``forbidden'' character and mixed polarization in ordinary absorption, circular dichroism with mixed sign can be expected. At this level a nonvanishing contribution to integrated rotatory strength obtains from vibrational perturbation, even in the low-temperature limit. Under such circumstances the sign of rotatory strength is not simply related to molecular conformation but depends: (1) on symmetry of the perturbing vibration(s), (2) the sign of ``borrowed'' rotatory strength, and (3) the degree of electronic—vibrational coupling. An upper limit to coupled rotatory strength is estimated as 10−2 Debye—Bohr magneton units, corresponding to molar ellipticity values for reasonable uv bands of 103 deg·cm2 dmole−1. The classic case of β-octyl nitrite as well as the many recent cases of organic carbonyl compound dichroisms of mixed sign are considered as examples of the phenomena.
Experimental Study of the Nuclear-Quadrupole and Spin—Rotation Interactions of 17O in Formaldehyde
Authors: Flygare W. H. , Lowe J. T.
Published: January 2005

The microwave spectrum of 17O12CH2 has been observed using high-resolution microwave spectroscopy. The 17O nuclear-quadrupole coupling constants and spin—rotation constants have been obtained. The results are Xaa=−1.89±0.01, Xbb=12.37±0.01, Xcc=−10.48±0.01, Maa=0.371±0.01, Mbb=0.025±0.01, and Mcc=−0.002±0.01 Mc/sec. The K=1 and K=2 series of rotational transitions were studied in an attempt to observe a K-dependent field gradient with no success. The 16O13CH2 spectra were also observed under high resolution with no splitting observed due to the 13C spin—rotation interaction. An upper limit on Maa for 13C in 16O13CH2 can be given as | 10.170 | Mc/sec. The spin—rotation constants are interpreted by a localized theory and the change in the average value of 1/r3 with ionic character is discussed.
Study of Approximate Wavefunctions Using Weighting Operators
Authors: Chen Joseph C. Y.
Published: January 2005

The method of weighting operators is developed for the purpose of studying approximate wavefunctions. The physical significance of the weighting operators is to weight the wavefunction in different regions in the configuration space. Approximate wavefunctions which are made stable with respect to a set of weighting operators are accurate for the calculation of expectation values of operators other than the energy, to the first order in the double perturbation theory. Differential properties of eigenvalue with respect to parameters are investigated using weighting-operator techniques. It is suggested that the extra sensitivity of the derived expression with respect to weighting operators can be used as a convergence test for variational wavefunctions. A comparative study of several energy-optimized wavefunctions by the method of weighting operators is carried out for the ground states of the helium isoelectronic sequence. Their relative regional goodness is discussed.