bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of aquifer heterogeneity by in situ sensing
Authors: Moltyaner G. L. , Wills C. A.
Published: February 2004

In analyzing groundwater flow and mass transport, most commonly the heterogeneity of a geologic formation is quantified by the field mapping of the hydraulic conductivity distribution. In this paper two alternative approaches are proposed. According to the first nonparametric approach, aquifer heterogeneity is characterized in terms of spatial variability in the concentration field generated in a natural‐gradient tracer test with a high‐energy gamma‐emitting radiotracer. In situ sensing technology is used for mapping the concentration distribution, and collected concentration‐versus‐depth profiles are correlated to produce the local‐scale geometric model of aquifer heterogeneities for further numerical groundwater flow and mass transport modeling. In the second parametric approach, heterogeneity is characterized in terms of spatial variability of the groundwater velocity rather than in terms of spatial variability of the hydraulic conductivity. Geostatistics is used to characterize the local‐scale velocity variation in terms of velocity integral scales in three orthogonal directions, in the longitudinal (along the mean flow) and two transverse (across the flow) directions. The velocity correlation volume is estimated as 16.68×2×0.22 m. It defines the characteristic volume for the “field‐scale” groundwater flow and mass transport modeling. It was concluded that the field mapping of aquifer structure by measuring concentrations and travel times of a radiotracer leads to a fundamentally new approach to the characterization of geologic heterogeneity and offers a reliable means for solving this complex problem of contemporary hydrogeology in quantitative terms.
Two‐phase flow in a variable aperture fracture
Authors: Murphy J. R. , Thomson N. R.
Published: February 2004

In this paper a dynamic two‐dimensional two‐phase flow model for a single variable aperture fracture is developed. The model is based on a finite volume implementation of the cubic law and the conservation of mass for each liquid. The two‐phase fracture flow system is represented by incompressible parallel plate flow within two‐dimensional subregions of constant aperture. The fluid phase distribution is represented by an explicit definition of the phase presence at each location within the domain. To achieve this definition, a phase distribution is assigned to each fracture subregion. Knowledge of the phase distribution allows calculation of interface capillary pressure based on the fracture aperture. One‐dimensional analytic solutions for two‐phase flow are developed and used to verify the model's behavior in one dimension. The model is verified against the Sandia Waste‐Isolation Flow and Transport III model for the case of two‐dimensional single‐phase flow. Two‐dimensional two‐phase flow verification is performed qualitatively because no suitable analytic or physical model is currently available. Two‐dimensional flow phenomena are investigated for variable aperture fractures generated using geostatistical methods. Results from these simulations illustrate the flow processes of phase isolation, pinching off of nonwetting phase globules, nonwetting phase refusal at the edges of tight regions, and downslope migration of a fluid countercurrent to flow of a less dense fluid.
Comparison of episodic acidification of Mid‐Atlantic Upland and Coastal Plain streams
Authors: O'Brien Anne K. , Rice Karen C. , Kennedy Margaret M. , Bricker Owen P.
Published: February 2004

Episodic acidification was examined in five mid‐Atlantic watersheds representing three physiographic provinces: Coastal Plain, Valley and Ridge, and Blue Ridge. Each of the watersheds receives a similar loading of atmospheric pollutants (SO42− and NO3−) and is underlain by different bedrock type. The purpose of this research was to quantify and compare the episodic variability in storm flow chemistry in Reedy Creek, Virginia (Coastal Plain), Mill Run and Shelter Run, Virginia (Valley and Ridge), and Fishing Creek Tributary and Hunting Creek, Maryland (Blue Ridge). Because episodic responses were similar from storm to storm in each of the watersheds, a representative storm from each watershed was discussed. Acidification, defined as the loss of acid‐neutralizing capacity (ANC), was observed in all streams except Mill Run. Mill Run chemistry showed little episodic variability. During storms in the other streams, pH decreased while SO42−, NO3−, and K+ concentrations increased. Concentrations of Mg2+ and Ca2+ increased in Reedy Creek and Fishing Creek Tributary, but decreased in Shelter Run and Hunting Creek. Therefore the net effect of episodic changes on the acid‐base status differed among the streams. In general, greater losses of ANC were observed during storms at Shelter Run and Hunting Creek, watersheds underlain by reactive bedrock (carbonate, metabasalt); comparatively smaller losses in ANC were observed at Reedy Creek and Fishing Creek Tributary, watersheds underlain by quartzites and unconsolidated quartz sands and cobbles. Increased SO42− concentrations were most important during storms at Reedy Creek and Fishing Creek Tributary, but organic anions (inferred by anion deficit) were also a factor in causing the loss of ANC. Dilution of base cations was the most important factor in the loss of ANC at Shelter Run. Both increased sulfate and dilution of base flow were important in causing the episodic acidification at Hunting Creek. The role of SO42− in contributing to episodic acidification in these watersheds is similar to that documented in studies conducted in other regions of the United States, Scandinavia, Canada, and the United Kingdom. The importance of SO42− in mid‐Atlantic United States streams contrasts with northeastern United States streams, in which increased NO3‐ derived from snowpack is more important in causing episodic acidification. Results support the importance of shallow subsurface processes in determining storm flow chemistry, regional climatic characteristics in determining the different sources of acidity during episodes, and the importance of bedrock geology in determining the amount of ANC loss.
Percolation and permeability in partially structured networks
Authors: Ewing Robert P. , Gupta S. C.
Published: February 2004

Structure, meaning a nonrandom arrangement of pores or pore domains, is present in many geologic porous media. We examined the effects of different nonrandom arrangements of the pore domains containing the largest pores on the percolation and flow properties of a simulated porous medium. Increasing the length of clusters (structural elements), or the fraction of the pore space occupied by them, decreases the percolation threshold (air entry value) and increases the permeability. Decreasing the internal homogeneity of clusters decreases the extent of their effects on percolation and permeability. Percolation threshold is not affected by the ratio between cluster length and network size as long as the cluster length is less than two thirds the network size. All cluster shapes display a similar relationship between percolation threshold and permeability, seen also in geologic porous media. The air entry value is a parameter that could potentially quantify both the degree of structure of a medium and its saturated permeability.
Flow characterization through heat transfer evidence in a carbonate fractured medium: First approach
Authors: Benderitter Yves , Roy Bernard , Tabbagh Alain
Published: February 2004

Water temperature records at the outlet of a fractured carbonate system during an annual cycle show two types of variation, slow variations over a small range, resulting from the thermal equilibrium between water and rock in the aquifer, and more rapid variations over a wider range, transmitted more quickly due to the inflow of water through fractures or karstic pipes. Starting at the outlet we present first a model of thermal exchange for flow in a conduit, then a model of thermal exchange in a porous medium between the surface and the reservoir. The comparison with the data recorded at Guichy (Nièvre, France) allows us to establish the fact that on this site the vertical flow between the surface and the reservoir is rapid through a fracture network as is the case for the flow at the outlet.
Comparison of three‐parameter probability distributions for representing annual extreme and partial duration precipitation series
Authors: Wilks Daniel S.
Published: February 2004

Performance of 8 three‐parameter probability distributions for representing annual extreme and partial duration precipitation data at stations in the northeastern and southeastern United States is investigated. Particular attention is paid to fidelity on the right tail, through use of a bootstrap procedure simulating extrapolation on the right tail beyond the data. It is found that the beta‐κ distribution best describes the extreme right tail of annual extreme series, and the beta‐Pdistribution is best for the partial duration data. The conventionally employed two‐parameter Gumbel distribution is found to substantially underestimate probabilities associated with the larger precipitation amounts for both annual extreme and partial duration data. Fitting the distributions using left‐censored data did not result in improved fits to the right tail.
3,5‐Dibenzoyl‐4‐(3‐phenoxyphenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP7) as a new multidrug resistance reverting agent devoid of effects on vascular smooth muscle contractility
Authors: Saponara Simona , Kawase Masami , Shah Anamik , Motohashi Noboru , Molnar Joseph , Ugocsai Katalin , Sgaragli Giampietro , Fusi Fabio
Published: February 2004

The aim of this study was to investigate the effects of 3,5‐diacetyl‐ (DP1–DP5) and 3,5‐dibenzoyl‐1,4‐dihydropyridines (DP6–DP11) on vascular functionsin vitro, by comparing their mechanical and electrophysiological actions in rat aorta rings and single rat tail artery myocytes, respectively, and to quantify their multidrug resistance (MDR)‐reversing activity in L5178 Y mouse T‐lymphoma cells transfected with MDR1 gene.

In rat aorta, the 11 compounds tested, but 3,5‐dibenzoyl‐4‐(3‐phenoxyphenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP7), 3,5‐dibenzoyl‐4‐(3‐chlorophenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP9), 3,5‐dibenzoyl‐4‐(4‐chlorophenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP10) and 3,5‐dibenzoyl‐4‐phenyl‐1,4‐dihydro‐2,6‐dimethylpyridine (DP11), antagonized 60 mMK+(K60)‐induced contraction in a concentration‐dependent manner, with IC50(M) values ranging between 5.65 × 10−7and 2.23 × 10−5.

The 11 dihydropyridines tested, but DP7, inhibited L‐type Ca2+current recorded in artery myocytes in a concentration‐dependent manner, with IC50(M) values ranging between 1.12 × 10−6and 6.90 × 10−5.

The K+‐channel opener cromakalim inhibited the Ca2+‐induced contraction in K30 but not that evoked in K60. On the contrary, DP7 was ineffective in both experimental conditions.

When the rings were preincubated with 1 mMNi2+plus 1μMnifedipine, the response to phenylephrine was significantly reduced by 2,5‐di‐t‐butyl‐1,4‐benzohydroquinone (BHQ), a well‐known endoplasmic reticulum Ca2+‐ATPase inhibitor. DP7 had no effects on this model system.

In L5178 MDR cell line, the 11 dihydropyridines tested, but 3,5‐diacetyl‐4‐(2‐nitrophenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP1), 3,5‐diacetyl‐4‐(3‐phenoxyphenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP2) and 3,5‐diacetyl‐4‐(3‐chlorophenyl)‐1,4‐dihydro‐2,6‐dimethylpyridine (DP4), exhibited an MDR‐reversing activity, with IC50values ranging between 3.02 × 10−7and 4.27 × 10−5, DP7 being the most potent.

In conclusion, DP7 may represent a lead compound for the development of potent dihydropyridine MDR chemosensitizers devoid of vascular effects.

British Journal of Pharmacology(2004)141, 415–422. doi:10.1038/sj.bjp.0705635
Dual effects of intrathecal BAM22 on nociceptive responses in acute and persistent pain–potential function of a novel receptor
Authors: Hong Yanguo , Dai Peifang , Jiang Jianping , Zeng Xueai
Published: February 2004

Bovine adrenal medulla 22 (BAM22) peptide is one of the cleavage products of proenkephalin A. It binds with high affinity to both opioid receptors and a newly discovered receptor in vitro. This latter receptor was first named sensory neuron‐specific receptor and is here named BAM peptide‐activated receptor with non‐opioid activity (BPAR). BPAR is uniquely distributed in small‐diameter DRG neurons, most of which are associated with the IB4 class of nociceptor afferent.

The present study examined the effects of intrathecal administration of BAM22 on formalin‐induced nocifensive behaviors and tail‐withdrawal latency in the rat.

Intrathecal (i.t.) administration of BAM22 decreased nocifensive behavior scores, measured as the sum of flinching and lifting/licking, in the first and second phases of the formalin test. This decrease was partially attenuated by systemic injection of naloxone.

In the presence of naloxone, i.t. BAM22 produced a dose‐dependent suppression of the nocifensive behaviors observed during the formalin test. The ratio of the efficacy of BAM22 (5 nmol) in the presence of naloxone over that in the absence of naloxone was 0.65 for flinching and 0.74 for lifting/licking in the second phase.

BAM22 at a dose of 5 nmol increased the tail‐withdrawal latency by 193 and 119% of baseline in the absence and presence of naloxone, respectively.

Systemic administration of naloxone alone enhanced the nocifensive behaviors in the second, but not in the first phase of the formalin test. Naloxone treatment did not alter the tail‐withdrawal latency.

These data confirm earlier in vitro data showing that BAM22 has both opioid and non‐opioid biological actions. The non‐opioid action of BAM22 involves inhibition of acute and persistent nociceptive behaviors at the spinal level, presumably mediated via BPAR.

The name suggested for this novel receptor, its potential physiological function and its ligand are discussed.

British Journal of Pharmacology (2004) 141, 423–430. doi:10.1038/sj.bjp.0705637
Timing of reproduction and egg quality covary with temperature in the insectivorous Barn Swallow,Hirundo rustica
Authors: Saino N. , Romano M. , Ambrosini R. , Ferrari R. P. , Møller A. P.
Published: February 2004

Egg size and composition can be predicted to trade‐off against current condition of reproducing females. Adverse conditions for reproduction should thus give rise to a reduction in egg size and quality.

Here we analyse timing of reproduction, egg mass and hatchability, and concentration of maternal carotenoids and components of the immune system in the eggs in relation to ambient temperature during the breeding season for the Barn Swallow (Hirundo rustica, Linnaeus).

Relatively high temperatures during one day enhanced the probability that clutches were initiated the following days. Egg mass at laying, concentration of lutein, the main carotenoid in Barn Swallows, and lysozyme, a major maternal component of innate immunity in eggs, but not maternal antigen‐specific antibodies, covaried with temperature during the days preceding laying of individual eggs.

Egg mass but not laying order or temperature during incubation predicted hatchability of the eggs.

This study suggests that temperature affects not only egg mass, as previously shown for bird species, but also concentration of maternally derived substances, such as antioxidants and immune factors, that can affect egg hatchability and offspring antiparasite defence and viability.
Genetic structure of the deep‐sea coral Lophelia pertusa in the northeast Atlantic revealed by microsatellites and internal transcribed spacer sequences
Authors: Le Goff‐Vitry M. C. , Pybus O. G. , Rogers A. D.
Published: February 2004

The azooxanthellate scleractinian coral Lophelia pertusa has a near‐cosmopolitan distribution, with a main depth distribution between 200 and 1000 m. In the northeast Atlantic it is the main framework‐building species, forming deep‐sea reefs in the bathyal zone on the continental margin, offshore banks and in Scandinavian fjords. Recent studies have shown that deep‐sea reefs are associated with a highly diverse fauna. Such deep‐sea communities are subject to increasing impact from deep‐water fisheries, against a background of poor knowledge concerning these ecosystems, including the biology and population structure of L. pertusa. To resolve the population structure and to assess the dispersal potential of this deep‐sea coral, specific microsatellites markers and ribosomal internal transcribed spacer (ITS) sequences ITS1 and ITS2 were used to investigate 10 different sampling sites, distributed along the European margin and in Scandinavian fjords. Both microsatellite and gene sequence data showed that L. pertusa should not be considered as one panmictic population in the northeast Atlantic but instead forms distinct, offshore and fjord populations. Results also suggest that, if some gene flow is occurring along the continental slope, the recruitment of sexually produced larvae is likely to be strongly local. The microsatellites showed significant levels of inbreeding and revealed that the level of genetic diversity and the contribution of asexual reproduction to the maintenance of the subpopulations were highly variable from site to site. These results are of major importance in the generation of a sustainable management strategy for these diversity‐rich deep‐sea ecosystems.
Can assignment tests measure dispersal?
Authors: Berry Oliver , Tocher Mandy D. , Sarre Stephen D.
Published: February 2004

Individual‐based assignment tests are now standard tools in molecular ecology and have several applications, including the study of dispersal. The measurement of natal dispersal is vital to understanding the ecology of many species, yet the accuracy of assignment tests in situations where natal dispersal is common remains untested in the field. We studied a metapopulation of the grand skink, Oligosoma grande, a large territorial lizard from southern New Zealand. Skink populations occur on isolated, regularly spaced rock outcrops and are characterized by frequent interpopulation dispersal. We examined the accuracy of assignment tests at four replicate sites by comparing long‐term mark‐and‐recapture records of natal dispersal with the results of assignment tests based on microsatellite DNA data. Assignment tests correctly identified the natal population of most individuals (65–100%, depending on the method of assignment), even when interpopulation dispersal was common (5–20% dispersers). They also provided similar estimates of the proportions of skinks dispersing to those estimated by the long‐term mark‐and‐recapture data. Fully and partially Bayesian assignment methods were equally accurate but their accuracy depended on the stringency applied, the degree of genetic differentiation between populations, and the number of loci used. In addition, when assignments required high confidence, the method of assignment (fully or partially Bayesian) had a large bearing on the number of individuals that could be assigned. Because assignment tests require significantly less fieldwork than traditional mark‐and‐recapture approaches (in this study < 3 months vs. > 7 years), they will provide useful dispersal data in many applied and theoretical situations.
Intrinsic thermally compensated field sensor based on single magnetic tunnel junctions
Authors: Malinowski G. , Hehn M. , Montaigne F. , Jouguelet E. , Schuhl A.
Published: February 2004

The association of an antiferromagnetic material with a ferromagnetic material in an exchange coupled bilayer is used as a detection layer in a tunnel magnetoresistive sensor. The magnetic response is shown to be reversible and linear depending on the field range to be measured. Both tunnel magnetoresistance and exchange field decrease linearly with the temperature and lead to temperature independent sensor sensibility.
Ferroelectric properties of pulsed laser deposited Ba(Zr0.15Ti0.85)O3 thin films
Authors: James A. R. , Prakash Chandra
Published: February 2004

Thin films of Ba(Zr0.15Ti0.85)O3 were crystallized in situ at several different oxygen background pressures and temperatures. The optimal temperature and pressure for obtaining films with smooth surface morphology and good electrical properties was found to be 675 °C and 300 mTorr, respectively. Films grown at this temperature were found to have a Pr of 3.31 μC/cm2 and an Ec of 93.5 kV/cm. Low field dielectric measurements and C-V measurements were performed in order to study the dielectric behavior of the films. A tunability of ∼45% was recorded on the films.
Nonlinear behaviors of the compositionally graded (Ba,Sr)TiO3 thin films derived by a sol-gel process
Authors: Zhai Jiwei , Chen Haydn
Published: February 2004

The compositionally graded Ba1−xSrxTiO3 films with a fine compositional gradient from BaTiO3 to Ba0.70Sr0.30TiO3 were fabricated on LaNiO3-buffered Pt–Ti–SiO2–Si substrates by a sol-gel deposition method. After post-deposition annealing the graded films crystallized into a pure perovskite structure with their crystalline orientation and surface morphology closely related to the deposition sequence of the film layers. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from −35 °C to 190 °C. Instead both the dielectric constant and dielectric loss showed negligible temperature dependence. The tunability of up-graded and down-graded films was about 35% and 37%, respectively, at an applied field of 300 kV/cm and measurement frequency of 1 MHz. The improved temperature stability from this type of compositionally graded material is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls.
A low-temperature route to thermodynamically stable ohmic contacts to n-type 6H-SiC
Authors: Deeb C. , Heuer A. H.
Published: February 2004

Thermodynamically stable Ni silicide contacts were formed on n-type 6H-SiC using a remarkably modest thermal budget. Specifically, nickel monosilicide (NiSi) was formed at 300 °C via a solid-state reaction of a low-pressure chemical-vapor-deposited amorphous Si film with a sputter-deposited Ni overlayer. These contacts are ohmic with low specific contact resistance (ρc of 6.9×10−4 Ω cm2). Upon aging at 600 °C in air, ρc decreases rapidly, probably due to restructuring at the NiSi/SiC interface. After the initial decrease in ρc, the contact resistance remained in the 10−5 Ω cm2 range during aging at 600 °C for 300 h.
Ferromagnetism in the metallic phase of (Ga,Mn)N nanostructures
Authors: Boselli M. A. , da Cunha Lima I. C. , Leite J. R. , Troper A. , Ghazali A.
Published: February 2004

The occurrence of ferromagnetism in the metallic phase of (Ga,Mn)N thin layers is studied by Monte Carlo simulation assuming an indirect exchange of the Ruderman–Kittel–Kasuya–Yosida type, via the spin-polarized hole system. We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layer. Transition temperatures one order of magnitude higher than in similar (Ga,Mn)As nanostructures are obtained. Two regimes are observed for the dependence of the magnetization on temperature.
Electron field emission from nanocarbons: A two-process model
Authors: Altman Igor S. , Pikhitsa Peter V. , Choi Mansoo
Published: February 2004

We show that the conventional consideration of the electron-field emission from nanocarbons cannot explain the experimentally observed results. We suggest a mechanism of the field emission occurrence from nanocarbons that can solve the existing puzzles. This mechanism implies two successive processes: (1) Tunneling through the low-energy barrier from the metallic region into the semiconducting region under the external macroscopic electric field and (2) tunneling through the high-energy barrier from the semiconducting region into a vacuum under the Coulomb field of an additional electron appearing in the first process.
Predicting pseudomorphic phases in multilayers: Hexagonal-closed-packed Nb in Nb/Zr
Authors: Thompson G. B. , Banerjee R. , Fraser H. L.
Published: February 2004

As the dimensions of materials are reduced to the nanometer scale, changes in phase stability, referred to as pseudomorphism, are being reported. Such changes in phase stability are often serendipitously discovered in multilayered thin films. In this letter, we use a classical thermodynamic treatment to model and predict phase stability in Nb/Zr multilayers. An outcome of this letter is the development of a biphase stability diagram that represents the interrelationship of phase stability to volume fraction and length scale. Using this methodology, an hcp Nb phase stability field was empirically postulated and subsequently confirmed by x-ray and electron diffraction. The successful prediction of this phase, based upon classical thermodynamics quantities, suggests that other types of phase stabilities in other multilayers could be proposed using the biphase diagram.
Kinetic Theory of Almost Classical Fluids
Authors: McLaughlin I. L. , Palyvos J. A. , Davis H. Ted
Published: February 2004

The Fokker–Planck equation with first-order quantum corrections in the weak coupling limit, which was derived by Davis, Hiroike, and Rice for the one-component fluid, is extended to mixtures. A rearrangement of terms believed negligible in the previous account leads to a more suitable form of the Fokker–Planck equation in which the friction tensor is an operator in momentum space. The equation is solved for the case of self-diffusion and numerical results are given. A 40% quantum correction to the soft-friction coefficient is predicted for liquid neon near the melting point, and a 4% correction is found for liquid argon at the corresponding temperature.
Role of the Anisotropy of the Potential in Quenching of Glory Extrema in Atom–Diatomic Molecule Scattering
Authors: Olson R. E. , Bernstein R. B.
Published: February 2004

Damping of the glory undulations in the velocity dependence of the total cross sections for atom–molecule scattering was first observed by Gislason and Kwei and (correctly) explained by them qualitatively in terms of inelastic and reactive processes concurrent with anisotropic elastic scattering. Subsequent experiments by Helbing and Rothe confirmed the quenching phenomenon and extended the range of systems exhibiting such behavior. The present theory deals mainly with nonreactive atom–diatomic collisions, considering the coupled equations in the total angular-momentum representation and taking full cognizance of the anisotropic distortion of the potential. The resulting equations yield a lower bound on the degree of quenching, but should be fairly generally applicable except for extremely reactive systems of the “stripping” type. The extent of the damping and its velocity dependence is expected to be increased for systems of larger reduced mass with deeper van der Waals potential wells (ε), larger-size parameters (rm), and greater short-range anisotropy coefficients. The equations suggest a simple method to retrieve the short-range anisotropy coefficient of the potential from quenching data.
Ring-Puckering Vibration of 2,5-Dihydrothiophene
Authors: Green W. H. , Harvey A. B.
Published: February 2004

The infrared spectrum of 2,5-dihydrothiophene has been measured from 80 to 4000 cm−1. The far-infrared region contained sharp Q branches at 87.0, 95.5, 102.0, 107.0, 111.2, 114.8, 118.1, 120.7, 123.2, 125.2, and 127.0 cm−1 which have been assigned to single quantum transitions between the first 12 levels of the ring-puckering vibration. A mixed harmonic–quartic potential-energy function has been fitted to the observed frequencies and is described by the following relation in reduced coordinates: V(cm−1) = 16.86 (x4 + 5.93x2). Such a potential function can be rationalized only in terms of a planar ring skeleton with no barrier to inversion. Two combination and one difference band series of the ring-puckering transitions with fundamentals centered near 3064, 670, and 2865 cm−1, respectively, have also been studied. The ring-puckering transitions obtained from the 670-cm−1 band series agree favorably with the far-infrared frequencies; however, those in reference to the two carbon–hydrogen stretching fundamentals exhibit significant deviations which are corrected by an anharmonicity cross term. Ring-puckering transitions calculated for the molecule in the upper state of the three combining mid-infrared modes compare favorably with the far-infrared frequencies; therefore, a similar structure in the upper and ground vibrational states is suggested.
Mössbauer Hyperfine Interactions in Tetrahedral Fe(III) Ions
Authors: Edwards P. R. , Johnson C. E.
Published: February 2004

The 57Fe Mössbauer spectra have been measured for a series of compounds containing tetrahedral FeX4− anions, where X was Cl−, Br−, and NCO−. Two of them became antiferromagnets at low temperatures: NEt4FeCl4 (TN = 3.0°K) and NEt4FeBr4 (TN = 3.9°K). In an external magnetic field the latter compound showed a spin flop. The remainder were paramagnetic and magnetic hyperfine interactions were observed by applying a large magnetic field at low temperatures. The hyperfine field, | Hn |, was approximately independent of the cation R+ for FeCl4− and was about 470 kG. For the other ligands | Hn | decreased with increasing covalency of the Fe–X bond, being 420 and 394 kG for X = Br− and NCO−. The values of the isomer shift (approximately 0.3 mm/sec at 77°K relative to Fe) and | Hn | were lower than those of corresponding octahedral high-spin Fe(III) salts. Salts with large cations (AsPh4FeCl4) or large anions [NEt4Fe(NCO)4] showed a quadrupole splitting, and the sign of the electric field gradient (efg) in NEt4Fe(NCO)4 was positive.
Microwave Spectrum, Ring-Puckering Potential Function, Ring Structure, and Dipole Moment of Cyclobutanone
Authors: Scharpen LeRoy H. , Laurie Victor W.
Published: February 2004

The microwave spectrum of cyclobutanone in the ground state and the first 10 excited states of the ring-puckering vibration has been assigned. Most features of the observed variation of rotational constants with ring-puckering state and of the far-infrared spectrum are accounted for with the ring-puckering potential function V(Z) = ν0[12Z2 + 0.4918Z4 + 1.598 exp(−1.0Z2)], with ν0 = 29.85 cm−1. Z is a dimensionless coordinate for the ring-puckering motion. A barrier of 7.6 ± 2 cm− exists at the planar ring conformation; with the υ = 0 level lying 9.2 cm−1 above the top of the barrier. A perturbation of the υ = 8 state is discussed. The ground-state rotational spectra of the three 13C monosubstituted species have also been assigned and the structure of the ring determined. With the carbonyl carbon labeled C1 and other carbons numbered sequentially around the ring, the ring structural parameters are r(C1C2) = 1.527 + 0.003 Å, r(C2C3) = 1.556 ± 0.001 Å, ∠C2C1C2′ = 93.1 ± 0.3°, ∠C1C2C3 = 88.0 ± 0.3°, ∠C2C3C2′ = 90.9 ± 0.2°. Stark-effect measurements have yielded a value of 2.89 ± 0.03 D for the dipole moment of the common isotopic species in the ground vibrational state.
Exchange and Coulomb Energy of H2 Determined by Various Perturbation Methods
Authors: Certain P. R. , Hirschfelder J. O. , Kolos W. , Wolniewicz L.
Published: February 2004

Four different types of perturbation theories for the exchange forces between two atoms are applied to the ground and first excited state of the hydrogen molecule at internuclear separations R = 4,6,8a0. The energy through second order and the expectation value of the Hamiltonian using the wavefunction accurate through first order are calculated to compare the theories. The results for the Hirschfelder–Silbey procedure are satisfactory. The Murrell–Shaw or Musher–Amos results are equally good with the exception of the Hamiltonian expectation values for both states at R = 6 and 8a0, which are bad. The Eisenschitz–London, van der Avoird, or Hirschfelder (HAV) results are good at small separations but at large separations they give a second-order energy which appears to be about one-half the correct dispersion energy. The Rayleigh–Schrödinger treatment using a Sternheimer type of zeroth-order Hamiltonian gave the best energy for the ground state but not very good energy for the excited state. At the separations considered, deviations from the virial theorem are unimportant.
Nonexponential Phosphorescence Decay of Benzene
Authors: Martin T. E. , Kalantar A. H.
Published: February 2004

The nonexponential decay of the B1u3 state of benzene has been studied in different phases of cyclohexane and methylcyclohexane at 77°K. C6H6, C6H5D, sym-C6H3D3, C6HD5, and C6D6 are the benzenes examined. In cyclohexane, the multiplet structure of the benzene spectrum depends upon the substitutional sites (cubic or monoclinic) in which benzene lies. Observed nonexponential decay arises from a combination of two first-order lifetimes. These are associated with the individual multiplets. The shorter lifetime arises from benzenes in cubic sites. In methylcyclohexane, where no multiplets are observed, spectral shifts and lifetime changes, together with triplet-buildup kinetic measurements, indicate a similar origin for the observed nonexponential decay. The decay curves, reproducible to within 1%, are quantitatively analyzed using a two-site model. Effects of the environment on the lifetime of benzene are discussed in terms of possible changes in the Franck–Condon factors for radiationless decay.
Viscosity of Rodlike Molecules in Solution
Authors: Isihara A.
Published: February 2004

A theory is presented for the viscosity of rodlike molecules in solution. It does not use the diagonalization approximation of the Oseen tensor and improves the Riseman and Kirkwood theory. It is found that the diagonalization approximation amounts to reducing the effects of the hydrodynamical interactions between the segments of the molecules. A new technique is introduced to reduce the problem to an integral equation, of which the solution follows Ullman, who corrected Riseman and Kirkwood and Kirkwood and Auer.
Rigid-Lattice NMR Moments and Line Shapes with Chemical-Shift Anisotropy
Authors: VanderHart D. L. , Gutowsky H. S.
Published: February 2004

The effects of anisotropic chemical shifts upon high-field, rigid-lattice NMR lines are investigated for cases in which both direct and indirect dipolar interactions are present. The feasibility criteria for experimentally determining anisotropic chemical-shift information in the presence of somewhat greater dipolar perturbations are examined. In doing so, the usual second-moment method is discussed with respect to obtaining the magnitude of the chemical-shift anisotropy. In addition, a general expression for the third moment is derived, and it is found that this parameter may be useful in determining the sign of the chemical-shift anisotropy. Finally, theoretical line shapes are calculated for polycrystalline, two-spin systems assuming axial symmetry at the nucleus being observed and including the anisotropic chemical shift, direct, and indirect dipolar interactions.
Vibrational Spectra and Thermodynamics of the Zinc Halides
Authors: Loewenschuss A. , Ron A. , Schnepp O.
Published: February 2004

The infrared absorption spectra of the four zinc halides have been investigated by the low-temperature matrix-isolation technique. The spectral range 800–35 cm−1 has been covered. Four absorption regions have been observed in all cases. The highest energy region is structured and represents the antisymmetric stretching frequency ν3. The structure has been fully characterized as due to molecules of different isotopic compositions. The second and third absorption regions have been demonstrated to be due to higher polymers by means of double-oven experiments. The lowest-frequency absorption has been assigned as the bending vibration ν2. Statistical calculations of the molecular entropies have been carried out on the basis of the new results, and these entropy values are found to be in excellent agreement with third-law entropy values where available.
Nuclear Spin–Lattice Relaxation in LiCl Solutions
Authors: Woessner D. E. , Snowden B. S. , Ostroff A. G.
Published: February 2004

The concentration dependence of the 7Li and 2H relaxation rates in aqueous lithium chloride solutions gives insight into the structure of this electrolyte solution. An abrupt change in the relaxation rates at a concentration which we call the “break point” indicates that the solutions have a different structure above and below this break-point concentration. Below the break point, the evidence suggests that the Li+ ion is surrounded by a symmetric hydration “complex,” where the lithium–oxygen nuclear separation is approximately 1.74 Å.
Generalized Cumulant Expansions and Spin-Relaxation Theory
Authors: Freed Jack H.
Published: February 2004

The generalized cumulant expansion method of Kubo is applied to an analysis of spin-relaxation theory appropriate for NMR and ESR studies of molecular systems. It leads to a general, formal solution of the equation of motion of a suitably averaged magnetization operator (and also the spin-density matrix). This solution permits a convenient perturbation expansion in the region of motional narrowing; i.e., when the random functional spin perturbation H1(t) obeys | H1(t) |τc<1, where τc is a correlation time for the random process. It is shown how this expansion valid for times t≫τc generates the time-independent R or relaxation matrix to all orders in | 1(t) |τc, and detailed expressions are given through fourth order. While the R matrix supplies the linewidth and dynamic frequency shift of the main Lorentzian resonance line, it is found that by formulating the cumulant method without the restriction t≫τc, weak subsidiary Lorentzian lines are predicted. These subsidiary lines appear as second-order perturbation corrections in |H1(t)|τc. They have widths given by τc−1 and, in general, large frequency shifts. The problem of (anisotropic) -rotational diffusion is discussed in detail, and it is shown that the spin-Hamiltonian approximation for liquids rests upon a Born–Oppenheimer-type approximation appropriate for random modulation of the nuclear coordinates, i.e., τc−1≪ωn,o, where ℏωn,o is the energy separation between the ground electronic state and the nth excited state coupled by the angular-momentum operator L. The cumulant method is then used to obtain higher-order corrections to the g-tensor line-broadening mechanism.
LCAO MO Procedure for Determining π-Electron Screening and the Low-Lying Excitations of Conjugated Hydrocarbons
Authors: Little William A.
Published: February 2004

A procedure is described whereby the effective electron–electron interaction in a large conjugated molecule is determined by considering the screening of the field of an artificial test charge imbedded in the molecule due to the redistribution of the π electrons. It is argued that the form of this static screened Coulomb interaction should represent well the effective interaction between electrons near the Fermi energy. This is tested by determining this screened Coulomb interaction in hexabenzocoronene containing an artificial test charge using the standard SCF MO method of calculation, and then using this screened interaction as the effective interaction between the π electrons to determine the low-lying excitation of the molecule with the test charge removed. Agreement between the predicted spectrum and the experimental spectrum is excellent and significantly better than that obtained with either the Pariser–Parr semiempirical expression or the use of Nishimoto and Mataga's expression for the effective interaction. A calculation of the same type of coronene gives similar excellent agreement with experiment.
Thermodynamic Properties of the Potassium–Graphite Lamellar Compounds from Solid-State emf Measurements
Authors: Aronson S. , Salzano F. J. , Bellafiore D.
Published: February 2004

Thermodynamic properties of the potassium–graphite lamellar compounds have been determined in the temperature range 200°–350°C using a solid-state emf technique. The electrochemical cells were of the type K (liquid) | K-glass | K–graphite where the electrolyte is a glass reversible to potassium ion. Breaks in the emf-vs-temperature plots were observed at compositions between C8K and C24K which indicate that C10K is not stable below 320°C. The thermodynamic data in the potassium–graphite system are compared to the results obtained in the rubidium– and cesium–graphite systems.
Identification of the Complex Ions in Liquid Cryolite
Authors: Solomons C. , Clarke J. H. R. , Bockris J. O'M.
Published: February 2004

The Raman spectrum of molten cryolite, Na3AlF6, at 1030°C has been investigated using laser excitation. A novel “windowless” Raman cell was used in order to overcome the problem of corrosion. One band that was observed at 633 Δ cm−1 (polarized) is assigned to the symmetric stretching frequency (ν1) of tetrahedral AlF4− by comparison with the spectrum of crystalline cryolite and with the spectra of other halide complexes of known structure. A much weaker band at 575 Δ cm−1 (polarized) is assigned to the symmetric stretching frequency (ν1) of AlF63−. The Raman evidence suggests that AlF63− dissociates into AlF4− and F− ions to a considerable extent (70%–75%) in molten cryolite.
Method of Diatomics-in-Molecules. IX. Ground and Excited States of H4 and the H2,H2 Bimolecular Exchange Reaction
Authors: Abrams Rochelle B. , Patel Jashbhai C. , Ellison Frank O.
Published: February 2004

The semiempirical diatomics-in-molecules theory is used to predict potential-energy surfaces for the ground and several excited electronic states of the system H4. Results are presented for linear (D∞h), rectangular (D2h), square (D4h), “perpendicular” (D2d), tetrahedral (Td), and rhombic (D2h) conformations. Results are compared with those from previous ab initio calculations. The lowest energy state of square H4 is singlet; the optimum internuclear distance is R = 2.0 bohrs, for which the energy is 67.8 kcal/mole higher than 2E(H2) (fixed nuclei energies). Vibrational frequencies for this square are computed: 2180, 1210, 1990, 1470, 1470, and 2280i cm−1, the latter corresponding to the reaction coordinate for the H2, H2 bimolecular exchange reaction. The specific rate constant for this reaction is computed according to the absolute rate theory.
Intensity Patterns in Absorption and Fluorescence Spectra of Molecular Dimers: A Comparison between the Vibronic and the Born–Oppenheimer Approach
Authors: Sucre M. Garcia , Gény F. , Lefebvre R.
Published: February 2004

After showing in a previous paper that the Born–Oppenheimer zeroth-order approximation can produce accurately the vibronic energies of a model of an excited molecular dimer for a wide range of parameters, the same approach is now used to calculate the vibrational patterns in absorption and fluorescence spectra. Two different levels of approximation depending on the degree of adiabaticity of the electronic wavefunctions are compared with the vibronic treatment. The progressions in the spectra are interpreted in terms of Franck–Condon factors, vibrational borrowing, and vibronic coupling between Born–Oppenheimer product wavefunctions.
Counting Graphs of Interest in Statistical Mechanics, Including Nonadditivity Effects
Authors: Larsen A. H. , Pings C. J.
Published: February 2004

The configurational part of the partition function, including nonadditivity effects or three-body and higher interactions in the potential energy of a configuration of molecules, may be expanded as a sum of integrals over products of cluster functions, corresponding to a sum of all “nonlinear” graphs of a certain type. Calculation of coefficients in the virial equation of state for imperfect gases requires knowledge of the numbers of certain types of topologically distinct graphs, called trees and stars. Topologically equivalent graphs correspond to integrals which yield the same result upon integration. Systematic procedures are developed for obtaining, by the use of explicit formulas or generating functions, the numbers of different graphs, trees, and stars on distinguishable vertices, and of graphs and trees on indistinguishable vertices, including those which correspond to integrals involving nonadditivity effects. The numbers of stars on indistinguishable vertices have been obtained only by inspection, but are closely approximated by a simple formula. The results for one-component systems are generalized to apply to multicomponent systems. Due to the extremely rapid increase in the number of distinct nonlinear graphs, and correspondingly, the number of required integrations to obtain the successive virial coefficients when nonadditivity effects are included, a practical limit for actual calculations involving any nonadditivity effects is the fourth virial coefficient.
Nonequilibrium Theory of Field-Flow Fractionation
Authors: Giddings J. Calvin
Published: February 2004

A rather general nonequilibrium theory is developed for a new separation concept, field-flow fractionation. This treatment accounts for the axial dispersion of a solute zone in a narrow tube subject to simultaneous displacement by anisotropic diffusion and by an arbitrary group of velocity vectors representing flow and applied field contributions. To good approximation, zone dispersion is found to obey Fick's law, a result characteristic of nonequilibrium theories of chromatography. An equation for the effective diffusion coefficient is deduced. Expressions are obtained for a two-dimensional case with a general power-series expansion for flow velocity; a numerical result is acquired for a special limiting case.
Dipole–Dipole Interactions in Tungstates
Authors: Scott James F.
Published: February 2004

The vibrational spectra of divalent metal tungstates of the form MWO4, where M = Ba, Sr, Ca, or Zn, have been analyzed in terms of dipole–dipole interactions between adjacent tungstate ions. The van der Waals potential constants determined are of the order of (13 − 110) × 10−60 erg·cm6 and approximate those for alkali halides. The present analysis allows for the interpretation of vibrational levels in ZnWO4, which is of a lower symmetry than the scheelites and not previously subject to such characterization.
UF6–H2 Hydrogen Fluoride Chemical Laser: Operation and Chemistry
Authors: Kompa Karl L. , Parker John H. , Pimentel George C.
Published: February 2004

Continued study of the UF6–H2 hydrogen fluoride chemical laser has revealed conditions for which collisional deactivation is probably negligible and for which the rotational temperature is well defined and can be determined. Addition of inert gases (SF6, C2F6, He) moderates the temperature rise and reduces the number of transitions observed. For a mixture of UF6:H2 = 1:1 with 10–20-fold excess of SF6 or C2F6, the temperature rise is no more than 5°–10° at the time the first transition reaches threshold [P2(3) for HF, P3(5) for DF]. This observation and the time needed to transfer maximum gain to the next transition provide preliminary estimates of the rate-constant ratios, k3 / k2 = 0.83–1.11 for DF and k2 / k1 ≥ 1.0 for HF. These ratios are probably applicable, respectively, to the reactions of fluorine atoms with deuterium and hydrogen. The DF intensity of the UF6–HD laser indicates the fluorine atom abstracts hydrogen from HD 212 times as fast as deuterium. Quenching by various additives (HCl, DCl, CO2) suggests that complex formation plays a role. Without these additives, accumulated HF probably accounts for the quenching, which is particularly effective because both complex formation and resonance energy transfer are operative.
Coulomb Integrals over Slater-Type Atomic Orbitals
Authors: Silver David M. , Ruedenberg Klaus
Published: February 2004

New general analytical formulas are derived for the two-center Coulomb integral between real, Slater-type atomic orbitals of arbitrary integer quantum numbers. The integral is expressed as a finite sum over powers and certain auxiliary functions. Procedures are given for numerical evaluation which are particularly suitable for use with an electronic digital computer of large storage capacity. Computation times are quoted.