bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of heterophoria measurements on subsequent associated phoria measurement in a refractive routine
Authors: Brautaset R.L. , Jennings J.A.M. 
Published: July 2002

SummaryThe influence of measuring heterophoria on a subsequent associated phoria measurement was investigated in 50 subjects. After refraction, heterophoria was measured by either von Graefe’s technique or Maddox rod and wing. The effect of these procedures was assessed by associated phoria measurements taken before and after the dissociated measures. It is shown that subjects with a history of unstable binocular vision are likely to have an associate phoria induced or changed by the previous dissociated phoria measurement, particularly if von Graefe’s technique is employed. It is recommended that, especially for near, associated phoria should be assessed before the dissociated phoria in subjects who are regarded as having a history of unstable binocular vision.
Magnetic and microstructural properties of CoCrTa/Cr/Al thin films (abstract)
Authors: Chang H. S. , Lee T. D. , Park J. K. , Shin K. H. , Park K. 
Published: July 2002

CoCrTa/Cr/Al and CoCrTa/Cr thin films were deposited on glass substrate at 280 °C using dc magnetron sputtering. The coercivity of CoCrTa/Cr films increased by introducing an Al underlayer. In 500 Å CoCrTa/Cr films, the coercivity increased with increasing Cr thickness and saturated above 700 Å Cr thickness (Hc=1050 Oe). On the other hand, in 500 Å CoCrTa/Cr/700 Å Al films, the coercivity increased sharply with increasing Cr thickness and showed a maximum value at 700 Å Cr thickness (Hc=1380 Oe). The coercivity squareness of the CoCrTa/Cr/Al and CoCrTa/Cr films was increased with increasing Cr thickness. The coercivity squareness of CoCrTa/Cr/Al films was lower than that of CoCrTa/Cr films. To study the origin of coercivity enhancement in CoCrTa/Cr films when deposited on an Al underlayer, microstructures of the two films were investigated using transmission electron microscopy (TEM). We controlled grain sizes of CoCrTa films by changing the thickness of the Cr layer. The grain size of CoCrTa films increased with increasing Cr thickness. The coercivity of CoCrTa/Cr/Al films showed a maximum value at a grain size of 430 Å. These results suggest that the transition from single domain to multidomain could occur at a grain size of ∼400 Å. To understand the coercivity squareness changes by the introduction of an Al underlayer, the angular variation of coercivity was measured. The magnetization of CoCrTa/Cr films was reversed by domain wall motion.
On the other hand, by the incorporation of an Al underlayer, the angular variation of coercivity deviated from the domain wall motion mode. Cross-sectional TEM studies of CoCrTa/Cr/Al films showed that Cr atoms in Cr layers diffused into an Al underlayer and Al atoms were detected in both Cr and CoCrTa layers, but magnetization of the magnetic layer was not decreased. The decrease in coercivity squareness of CoCrTa/Cr/Al films would be attributed to magnetic decoupling by segregation of Al atoms in grain boundaries of CoCrTa films.
Analyses of the ‘‘allowed’’ inversion barriers of H2O and NH3: Incompleteness of the Woodward–Hoffmann HOMO–LUMO symmetry ideas due to neglect of 〈φi‖ΔN
A‖φi〉 molecular orbital terms
Authors: Edmiston C. , Jarvie J. , Bartleson J. 
Published: July 2002

Walsh’s rules correctly attribute the ‘‘bent’’ structures of H2O and NH3 to the occupation of the 1πz→3a1 HOMO not occupied in linear BeH2 and planar BH3. In Walsh’s molecular orbital (MO) diagram E(3a1) decreases sharply with bending angle S. This has always been attributed incorrectly to changes in the 3a1 MO, mainly due to symmetry-allowed mixing with the LUMO, 4a*1. The forbidden bending of BeH2 and BH3 has been similarly ‘‘explained.’’ Using large-basis-set self-consistent field molecular orbital (SCF MO) ψs, we show that the integral Hellmann–Feynman theorem ΔEIHF≂ΔESCF much better than does the analogous second-order perturbation theory λE′′(SE′=0 and λ=S2/2, ΔH≂SH′+λH′′). ΔEIHF=〈ψ0‖ΔNA‖ψ0〉+〈ψ0‖ ΔNA‖Δψ̃〉+ΔNR≂Σni2Δ EIHFi+ΔNR, Δψ̃=(ψ/η)−ψ0, η=〈ψ0‖ψ〉, ΔEIHFi=〈φ0i‖ ΔNA‖φ0i〉+〈φ0i‖ ΔNA‖Δφ̃i〉, Δφ̃i=(φi/ηi)−φ0i, ηi=〈φ0i‖φi〉, ΔNA=ΔH−ΔNR. Both theories show a large negative 〈1πz‖ΔNA‖1πz〉 term and small 〈1πz‖ΔNA‖Δ1π̃z〉 HOMO–UMO mixing term, which is positive in ΔEIHF. The 〈1πz‖SH′‖3σ*g〉 HOMO–LUMO mixing term is small even when 3σ*g is optimized for the excited state. The ΔEIHFis and
λE″is give the usual Walsh diagrams for bending of H2O and NH3, with or without MO partitioning of the nuclear repulsion change (ΔNR). However ‘‘decoupling’’ of the φ′is in ψ′ makes the λE″is unreliable. The 〈1πz‖ΔNA‖1πz〉 term acts to create a large allowed barrier to inversion for H2O and CH4, but a strong ΔNR nearly destroys an otherwise large barrier for NH3. 〈1πz‖ΔNA‖1πz〉 acts to bend the linear H2O, planar NH3, and planar CH4, with HOMO–LUMO mixing being ‘‘antibending.’’ We show that understanding of MO correlation diagrams demands consideration of the ‘‘static’’ 〈φ0i‖ΔNA‖φ0i〉 terms as well as the OMO–UMO mixing terms, which has not been appreciated by earlier workers so far as we are aware.
Structural properties of Langmuir–Blodgett films of charge transfer salts: Pristine and iodine doped conducting films of (N-docosyl-pyridinium)TCNQ
Authors: Richard Joel , Vandevyver Michel , Lesieur Pierre , Ruaudel-Teixier Annié , Barraud André , Bozio Renato , Pecile Cesare 
Published: July 2002

We have investigated the molecular constitution and ordering of Langmuir–Blodgett films prepared by deposition of N-docosylpyridinium–TCNQ charge transfer salt onto CaF2 substrates and by their subsequent doping with iodine vapor to yield reasonably good (∼10−1 Ω−1 cm−1) conducting films. Optical and electron scanning microscopy of the precursor film show that it is made up of a mosaic of highly crystalline platelets lying flat on the substrate though with random orientation. Structural information at the molecular level is gained by measuring and analyzing the ESR spectra and their angular and temperature dependence as well as the UV-visible and infrared spectra and their linear dichroism. A triplet fine structure is observed in the ESR spectra of the precursor films with zero field splitting parameters ‖D‖=7.48×10−3 cm−1 and ‖E‖=1.2×10−3 cm−1 and singlet–triplet activation energy J=0.20 eV, markedly different from those of the N-docosylpyridinium–TCNQ powder salt. The UV-visible and infrared spectra show features typical of a system containing
weakly interacting (TCNQ−)2 dimers similar to those found in a water solution. The dichroic behavior of the observed infrared active modes of the TCNQ− anion and of N-docosylpyridinium as well as of the vibronically induced absorptions of the interacting TCNQ system are analyzed both for the precursor and for the iodine doped film. According to such an analysis and to that of the angular dependence of the ESR line shapes, the polar sheets in the precursor film consist of slipped (ring-bond overlap) (TCNQ−)2 dimers with their molecular planes almost parallel to the plane of the supporting slide. The spectroscopic and linear dichroism data allow us to monitor the changes induced by the iodination process and to show that, besides the partial oxidation of TCNQ− anions to TCNQ0, there is a complete change in the orientation of the TCNQ units. In many respects, the UV-visible and infrared spectra of the conducting film resemble those of mixed valence, intermediate conductivity salts like, e.g., (TEA) (TCNQ)2. The TCNQ molecules stand edge on with their molecular planes roughly perpendicular to the plane of the slide and with their long axes close to being normal to it.
Ultrasonic study of fluctuations in polystyrene solutions
Authors: Fenner D. B. 
Published: July 2002

Measurements of the pulsed-ultrasound absorption spectra (1 to 91 MHz) and velocity (5 MHz) observed in monodisperse polystyrene (PS) solutions with toluene (Tol) and diethyl malonate (DEM) are reported and discussed extensively. The PS+Tol (good solvent) samples with a low concentration (φ≂0.05) and higher temperature (T≥0 °C) were weakly absorbing with nearly single-relaxation spectra. At high concentration (φ≂0.27) the PS+Tol spectra became the critical-fluctuation type. All PS+DEM (poor solvent) solutions had a large excess absorption αex with spectra well described by fitting the (binary-mixture) critical-fluctuation absorption calculations of Kroll and Ruhland (KR) and of Ferrell and Bhattacharjee (FB). The KR approach gave characteristic frequencies fc which obeyed an empirical (nonuniversal) scaling fc∼ΔT ρ, with ΔT the temperature interval above segregation on each isochore. Results indicate a slowing down (ρ&gt;0) and strengthening of the fluctuations as ΔT→0. A crossover in ρ was observed with PS+DEM near but below the theta temperature (ρ smaller below). For critical-isochore samples ρ approached 1 as the PS
molecular weight was increased toward 106. Near phase separations, spectra followed the approximate prediction of FB theory, αex∼f, f the sound frequency. The FB characteristic (half-attentuation) temperatures ΔT1/2 scaled with f, going from exponent 1/2 (for small molecules) to 1 as f was increased. Earlier data for PS in cyclohexane are reevaluated with the KR and FB methods with results similar to PS+DEM. These PS results are compared extensively with the work of Garland and Sanchez on a small-molecule binary-mixture critical point, where ρ was universal, fc two orders of magnitude higher at large ΔT, and ΔT1/2 tenfold smaller at low f. This study finds that fluctuation absorption occurs commonly in PS solutions and is due to energy fluctuations decoupled (nonuniversal exponents) from critical PS-composition fluctuations (known to be the binary-mixture type). Light scattering verified that the critical point was approached closely in PS+DEM. The sound velocity was independent of the PS molecular weight, but increased as a weak quadratic function of the concentration for all solvents. Mixture rules for the modulus predict this qualitative trend.
Symptoms of chaos in observed oscillations near a bifurcation with noise
Authors: Harding Robert H. , Ross John 
Published: July 2002

We examine an experimental transition from periodic to aperiodic and back to periodic dynamics in the combustion of acetaldehyde(ACH) in a continuous stirred tank reactor (CSTR) with power spectra, autocorrelation functions, phase portraits, Poincaŕe sections, the Wolf–Swift–Swinney–Vastano (WSSV) method for determining the largest Lyapounov exponent, and the Grassberger–Procaccia (GP) method for determining correlation dimension. Each technique gives some indications of a transition to chaos, but there are discrepancies in that the largest Lyapounov exponent is positive but does not converge and the GP method results in a correlation dimension between one and two for two aperiodic data sets. We explore in instructive detail possible explanations for false indications of chaos by comparing our results with calculations on the Rössler chaotic attractor and the van der Pol periodic attractor modified to examine the effects of uneven point distribution and three types of experimental noise. An uneven distribution of points results in a decreased range of length scales for convergence and a larger required embedding dimension for the GP method, but does not explain our experimental results. Observation noise (a Gaussian noise added to each term in the time series but not entering in the equations of motion) and constraint shift (the motion relaxes to an attractor but a constraint changes monotonically during the course of measurement) added to a periodic attractor both result in a low length scale cutoff below which the attractor dimension does not converge with embedding dimension, and above which it converges to 1. Constraint variation noise (a Gaussian noise is added to each term in the time series and enters into the equations of motion as a stochastic perturbation) does yield correlation dimensions between 1 and 2. The experimental transition shows many similarities to a Hopf bifurcation found in another experiment on the same system and to a theoretical Hopf bifurcation with constraint variation noise. A modification of the WSSV Lyapounov exponent analysis for this experimental transition shows the random walk separation of trajectories expected for constraint variation noise
added to the dynamics of a periodic attractor with a Hopf bifurcation. We therefore identify the experimental transition as an arc in constraint space which does not cross but is nearly tangent to a Hopf bifurcation set.
A crossed laser-molecular beam study of the photodissociation dynamics of Zn(C2H5)2 and (Zn(C2H5)2)2 at 248 and 193 nm
Authors: Hou Hui-qi , Zhang Zhuangjian , Ray Urmi , Vernon Matt 
Published: July 2002

A molecular beam of zinc–diethyl (ZnEt2) is photodissociated at 248 and 193 nm and the velocity distributions of the photofragments are measured by time-of-flight techniques. One and two photon processes are observed. The dominant one photon process at both wavelengths is the dissociation of (ZnEt2)2 to form two ZnEt2 monomers. The absence of secondary dissociation of the ZnEt2 photofragments at both excitation wavelengths and the small fraction of the available energy partitioned to product translation implicates dissociation to an excited electronic potential energy surface correlating to one electronically excited ZnEt*2 monomer. The mass spectrum of the ZnEt2 photofragments is the same as measured for ‘‘cold’’ ZnEt2 monomers in the molecular beam, suggesting that the electronically excited ZnEt*2 monomers have fluoresced prior to ionization in the mass spectrometer. A small photodissociation signal of uncomplexed ZnEt2 is observed only at low expansion pressures. The sensitive dependence of this monomeric photodissociation signal to the Ar pressure of the adiabatic expansion suggests that ground state vibrational excitation is required for monomeric photodissociation at 248 nm.
In contrast to the dimer single photon photodissocation channel, when ZnEt2 monomers are photodissociated, a significant fraction of the available energy appears as product translation. A qualitative molecular orbital analysis can explain the observed fast photoproduct velocity if dissociation occurs via a repulsive triplet state which correlates to electronic ground state products. The two photon process observed is assigned to single photon photodissociation of the electronically excited ZnEt*2 monomers produced in the dimer photodissociation step. The photofragment velocity distributions for the two photon channel can be quantitatively modeled by sequential ethyl eliminations on the ground state ZnEt2 and ZnEt potential energy surfaces. The product velocity distributions are consistent with a microcanonical energy distribution for both ethyl eliminations. Approximately 50% of the ethyl photofragments are created with sufficient vibrational energy to break the weak ethyl C–H bond (36 kcal/mol) forming ethylene. Implications of the ZnEt2 photodissociation mechanism for Zn film deposition using 248 and 193 nm excimer radiation are discussed.
Overtone spectra of C–H bonds and vibrational a
b i
n
i
t
i
o study of methoxy boranes
Authors: Manzanares I Carlos , Walla Dalat , Seburg Randal , Wedlock Michael R. , Gonzalez Carlos , Schlegel H. Bernhard 
Published: July 2002

The C–H overtone absorption spectra of (CH3O)3B in liquid and gas phases are reported. The observed energies of the C–H stretching overtones corresponding to Δv=3, 4, 5, and 6 (liquid) are obtained by conventional spectroscopy. The C–H overtones Δv=5 and 6 (gas) are obtained by laser intracavity photoacoustic spectroscopy. Computer deconvolution of the gas-phase absorptions shows two bands at each overtone which are assigned as the overtones of nonequivalent C–H bonds. In general, for molecules in which a methyl group is directly attached to an oxygen atom, nonequivalent C–H bonds are produced due to the ‘‘trans effect.’’ A different mechanism seems to occur in the case of the methyl groups in trimethylborate even though they are adjacent to an oxygen atom. In order to interpret the experimental results, ab initio molecular-orbital calculations were performed on (CH3O)BH2, (CH3O)2BH, and (CH3O)3B. Equilibrium geometries, vibrational frequencies, and infrared intensities were calculated at the Hartree–Fock level using the 3-21G split valence basis set. In the three molecules studied, the equilibrium conformation is such that the methyl groups have one C–H bond (C–Ha ) in the plane of the molecule and cis to a B–O bond, and two equivalent C–H bonds located symmetrically above and below the plane of the molecule (C–Hb ). In (CH3O)BH2, the in-plane C–H bond C–Ha is longer than the out-of-plane C–H bonds C–Hb (1.082 Å vs 1.0795 Å). This trend is reversed in the case of (CH3O)3B, where the C–Ha and C–Hb bond lengths are 1.0792 and 1.0807 Å, respectively.
The situation is more complicated in the case of the molecule (CH3O)2BH, where in one methyl group the C–Ha bond is shorter than the C–Hb bond (1.0794 Å vs 1.0802 Å), while in the other methyl group the corresponding C–Ha bond is longer than the C–Hb bond (1.0829 Å vs 1.0802 Å). The nature of the difference in the C–H bond lengths is studied and discussed in terms of group orbital interactions in both, the σ and π systems. In addition, a correlation between the C–H bond length, the corresponding C–H stretching force constant, and the vibrational frequency is discussed based on vibrational frequency calculations performed on the deuterated species (CHD2O)nBH3−n for n=1, 2, 3 in cases where the isolated C–H was considered to be the in-plane C–Ha or the out-of-plane C–Hb.
The spectroscopic and photophysical effects of the position of methyl substitution. I. 4- and 5-methylpyrimidine
Authors: Bandy Ralph E. , Nash John , Zwier Timothy S. 
Published: July 2002

Laser-induced fluorescence excitation and dispersed fluorescence spectra of the first n–π* transition of jet-cooled 4- and 5-methylpyrimidine (4-mp and 5-mp) have been recorded and analyzed. In 5-mp, methyl substitution preserves many of the spectroscopic signatures of the unsubstituted pyrimidine molecule. Dispersed fluorescence spectra are used to assign most of the major features in the first 1000 cm−1 of the excitation spectrum. High resolution scans at the origin reveal a 0.20 cm−1 splitting of the origin arising from the 0a′1–0a1 and 1e″–1e″ internal rotor transitions. From this small splitting we deduce that the nearly free internal rotation of the methyl group in the ground state is carried over to the S1 state as well. In 4-methylpyrimidine, the reduction in symmetry accompanying methyl substitution (G12 to G6 ) results in allowed transitions to all in-plane fundamentals. The methyl group is seen to participate in the electronic transition to a greater degree in 4-mp than in 5-mp.
We observe clear activity in both the C–CH3 stretch and C–CH3 in-plane bend in the dispersed fluorescence from the origin of 4-mp. 4-mp also differs remarkably from 5-mp in the magnitude of the barrier to methyl internal rotation in S0 and S1. By fitting the positions and intensities of internal rotor structure in ground and excited states we deduce a ground state barrier to internal rotation of V″3=95±5 cm−1 and a best-fit excited state barrier of V3=745 cm−1, V′6=−100 cm−1. Ab initio calculations on 4-mp which reproduce both the magnitude and shape of the experimental barrier to internal rotation in the ground state. The lowest energy methyl conformation places a hydrogen atom in the plane of the ring pointing away from the nitrogen lone pair. Finally, in both molecules we observe spectroscopic signatures of vibrational state mixing in the S1 state. Density-of-states calculations on both molecules using the experimentally determined internal rotor energy levels predict a similar density of same-symmetry states in the two molecules at a given energy. Experimental evidence is presented that the small V6 barrier in 5-mp leads to modest vibration/internal rotation coupling matrix elements of ∼1 cm−1. The high V3 barrier in 4-mp is observed to give strong vibration/internal rotation coupling in the case of the 6a10(0a1) level which shifts its position by 17 cm−1 from its companion 6a10(1e) level due to interaction with an X1(3a2) vibration/internal rotation combination band.
A model for fully developed turbulence
Authors: Canuto V. M. , Goldman I. , Chasnov J. 
Published: July 2002

A model for stationary, fully developed turbulence is presented. The physical model used to describe the nonlinear interactions provides an equation for the turbulent spectral energy function F(k) as a function of the time scale for the energy fed into the system, n−1s. The model makes quantitative predictions that are compared with the following available data of a different nature. (a) For turbulent convection, in the case of a constant superadiabatic gradient and for σ≪1 (σ≡Prandtl number), the convective flux is computed and compared with the result of the mixing length theory (MLT). For the case of a variable superadiabatic gradient, and for arbitrary σ, as in the case of laboratory convection, the Nusselt number N versus Rayleigh number R relation is found to be N=AσR1/3 as recently determined experimentally. The computed Aσ deviates 3% and 8% from recent laboratory data at high R for σ=6.6 and σ=2000. (b) The K–ε and Smagorinsky relations. Four alternative expressions for the turbulent (eddy) viscosity are derived (the K–ε and Smagorinsky relations being two of them) and the numerical coefficients appearing in them are computed. They compare favorably with theoretical estimates (the direct interaction approximation and the renormalization group method), laboratory
data, and simulation studies. (c) The spectral function, transfer term, and dissipation term. The spectral energy function F(k), the transfer term T(k), and the dissipation term νk2F(k) are computed and compared with
laboratory data on grid turbulence. (d) The skewness factor S̄3 is computed and compared with laboratory data. The turbulence model is extended to treat temperature fluctuations characterized by a spectral function G(k). The main results are (e) when both temperature and velocity fluctuations are taken into account, the rate ns(k), that in the first part was taken to be given by the linear mode analysis, can be determined self-consistently from the model itself; (f) in the inertial-convective range, the model predicts the well-known result G(k)∼k−5/3; (g) the Kolmogorov and Batchelor constants are shown to be related by Ba=σt Ko, where σt is the turbulent Prandtl number; and (h) in the inertial-conductive range the model predicts G(k)∼k−17/3 for thermally driven convection as well as for advection of a passive scalar, the difference being contained in the numerical coefficient in front. The predicted G(k) vs k compare favorably with experiments for air (σ=0.725), mercury (σ=0.018), and salt water (σ=9.2).