bluuebunny/crossref_metadata_2025 huggingface dataset:
The Labrador Sea Deep Convection Experiment data collection
Authors: Krahmann G. , Visbeck M. , Smethie W. , D'Asaro Eric A. , Rhines Peter B. , Clarke R. Allyn , Lazier John , Davis Russ E. , Niiler Pearn P. , Guest Peter S. , Meincke Jens , Moore G. W. Kent , Pickart Robert S. , Owens W. Brechner , Prater Mark D. , Renfrew Ian A. , Schott Friedrich A.
Published: October 2003

Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiment's period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.
The influence of a mini‐magnetopause on the magnetic pileup boundary at Mars
Authors: Harnett E. M. , Winglee R. M.
Published: October 2003

3D single fluid non‐ideal MHD simulations are used to predict positions for the bow shock and magnetic pileup boundary (MPB). The positions are in agreement with those calculated from Mars Global Surveyor data. The simulations were run with the strong southern magnetic anomalies facing into the solar wind, and the IMF in either the northward or southward direction. The simulations show that the strong southern magnetic anomalies create a magnetopause‐like structure (i.e., a mini‐magnetopause) in place of an MPB but plasma signatures for both types of boundaries are similar. Distinguishing characteristics include the magnetic field orientation, pressure, and the current. The current regions associated with a mini‐magnetopause are larger in scale and greater in magnitude than those at the MPB. The simulations also show that including non‐ideal MHD physics is important in resolving both the magnetic pileup boundary and the mini‐magnetopause.
Layer thickness and the shape of faults
Authors: Benedicto A. , Schultz R. A. , Soliva R.
Published: October 2003

We analyze from a conceptual point of view, the role of layer thickness on fault vertical restriction, size distribution and shape evolution. We propose a model of fault growth from an initially circular/elliptical shape of individual (but kinematically interrelated in a coherent fault zone) fault segments to a final rectangular shape. Faults (or fault segments) that do not interact strongly with the stratigraphy grow vertically as nonrestricted with circular to elliptical shapes. Linkage of those faults leads to elliptical shapes for large composite faults. In contrast, faults (or fault segments) whose vertical growth is restricted by the layer thickness evolve from circular to elliptical with progressively larger aspect ratios. In a sequence with heterogeneous strength and varying layer thickness, individual faults within each layer are restricted, producing a complex irregular tipline for the aggregate large fault. The irregular geometry will persist as long as the tendency for horizontal fault growth exceeds that for linkage; once linkage across layers occurs, then more regular elliptical tiplines will evolve. Because longer faults have larger displacements, then for brittle strain to be equal in layers of different thickness, more faults are needed in thin layers for the total displacements, and thus the strains, to balance. As a result, irregular fault shapes can evolve as more new faults grow in thinner layers into more rectangular shapes.
Gabapentin and pregabalin suppress tactile allodynia and potentiate spinal cord stimulation in a model of neuropathy
Authors: Wallin Johan , Cui Jian‐Guo , Yakhnitsa Vadim , Schechtmann Gastón , Meyerson Björn A. , Linderoth Bengt
Published: October 2003

Spinal cord stimulation (SCS) is an effective tool in alleviating neuropathic pain. However, a number of well‐selected patients fail to obtain satisfactory pain relief. Previous studies have demonstrated that i.t. baclofen and/or adenosine can enhance the SCS effect, but this combined therapy has been shown to be useful in less than half of the cases and more effective substances are therefore needed. The aim of this experimental study in rats was to examine whether gabapentin or pregabalin attenuates tactile allodynia following partial sciatic nerve injury and whether subeffective doses of these drugs can potentiate the effects of SCS in rats which do not respond to SCS. Mononeuropathy was produced by a photochemically induced ischaemic lesion of the sciatic nerve. Tactile withdrawal thresholds were assessed with von Frey filaments. Effects of increasing doses of gabapentin and pregabalin (i.t. and i.v.) on the withdrawal thresholds were analysed. These drugs were found to reduce tactile allodynia in a dose‐dependent manner. In SCS non‐responding rats, i.e. where stimulation per se failed to suppress allodynia, a combination of SCS and subeffective doses of the drugs markedly attenuated allodynia. In subsequent acute experiments, extracellular recordings from wide dynamic range neurones in the dorsal horn showed prominent hyperexcitability. The combination of SCS and gabapentin, at the same subeffective dose, clearly enhanced suppression of this hyperexcitability. In conclusion, electrical therapy and pharmacological therapy in neuropathic pain can, when they are inefficient individually, become effective when combined. © 2002 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Science Ltd. All rights reserved.
Effects of localization and intensity of experimental muscle pain on ankle joint proprioception
Authors: Matre Dagfinn , Arendt‐Nielsen Lars , Knardahl Stein
Published: October 2003

Accurate proprioceptive input is a prerequisite for balance control and coordination of movement. The present study investigated whether experimental muscle pain induced in healthy human subjects disturbed movement sense (detection of movement) or position sense (recognition of a reference position). Muscle pain was produced by infusion of 6% hypertonic saline simultaneously in m. tibialis anterior (TA) and m. soleus (experiment 1), by infusion of 6% hypertonic saline in TA (experiment 2) and by infusion of 9% hypertonic saline in TA (experiment 3). Control measurements were done with infusions of 0.9% isotonic saline. All infusions of 6% and 9% saline produced pain intensities significantly higher than the corresponding control infusions. Only infusion of 6% saline in two muscles (visual analogue scale = 4–5) produced an elevation in movement detection thresholds which was significantly higher, compared with before infusion. No other significant changes in movement and position sense were found during the painful or control infusions. Pain of relatively high intensity in two antagonist muscles is necessary to disturb the movement detection threshold. The ability to recognize a reference position is not disturbed by experimentally induced muscle pain. Whether the disturbed movement sense is caused by sensitivity changes in muscle spindle afferents or altered processing of proprioceptive input cannot be answered. The present findings indicate that human ankle proprioception is rather robust to muscle pain. © 2002 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Science Ltd. All rights reserved.
Persistent secondary hyperalgesia after gastrocnemius incision in the rat
Authors: Pogatzki Esther M. , Niemeier Jan S. , Brennan Timothy J.
Published: October 2003

Secondary hyperalgesia, an exaggerated response to stimuli applied to undamaged tissue surrounding an injury, is a common consequence of tissue injury and inflammation. It is well established that the etiology of secondary hyperalgesia is sensitization of central neurons but the exact mechanism and its role in certain clinical pain states is unclear. In the present experiments, we studied responses to punctate and non‐punctate mechanical stimuli and to heat applied to the plantar aspect of the hindpaw remote to an incision in the gastrocnemius region of the rat hindlimb. Median withdrawal thresholds to von Frey filaments were reduced 2 h after incision of skin, fascia and muscle (gastrocnemius incision, n = 9) and remained reduced through postoperative day 6 (p < 0.05 vs sham). Only a transient reduction in withdrawal threshold occurred after incision of skin and fascia (skin incision, n = 10). No enhanced responsiveness to blunt mechanical stimulation or reduction in withdrawal latency to heat was present after gastrocnemius incision (p > 0.05 vs sham, n = 9 each group). Reduced withdrawal thresholds were blocked by i.t. administration of morphine and by local anesthetic injection at the test site 2 h and 2 days after gastrocnemius incision. These pharmacological data provide evidence that reduced withdrawal thresholds after gastrocnemius incision are nociceptive behaviors indicating persistent secondary hyperalgesia. Because the behaviors have a similar time course to secondary hyperalgesia in postoperative patients, the model will be useful to evaluate the mechanisms for secondary mechanical hyperalgesia after incision, its pharmacological characteristics and its potential role in persistent postoperative pain. © 2002 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Science Ltd. All rights reserved.
Coping and Quality of Life in relation to headache in Dutch schoolchildren
Authors: Bandell‐Hoekstra Inez E. N. G. , Abu‐Saad Huda Huijer , Passchier Jan , Frederiks Carla M. A. , Feron Frans J. M. , Knipschild Paul
Published: October 2003

The aim of this study was to describe the Quality of Life and pain coping strategies of school children in relation to headache severity. We conducted a cross‐sectional study in 2815 children between the age of 9 and 17 years, who filled out Waters' Headache Questionnaire (WHQ), the Paediatric Pain Assessment Tool (PPAT), the Quality of Life Headache in Youth (QLH‐Y) questionnaire and the Pain Coping Questionnaire (PCQ) in the class‐room setting.

Weekly headaches were reported by 22% of the sample. Low, medium, and high headache severity groups were constructed, based on headache frequency, duration and intensity criteria. Results show that children with the highest headache severity report the lowest Quality of Life in general and the lowest Quality of Health, as well as the most problems with regard to physical functioning, impact of headache on daily and leisure activities, physical symptoms other than headache, and social functioning at home. With regard to using pain coping strategies, children with the most severe headaches seek more social support, they internalize and externalize more, they use less behavioural and cognitive distraction techniques, and seek information less. © 2002 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Science Ltd. All rights reserved.
Time-dependent diffusion coefficient as a probe of the permeability of the pore wall
Authors: Sen Pabitra N.
Published: October 2003

The time dependence of the mean-square displacement (or equivalently of the diffusion coefficient) in the presence of a permeable barrier can be used as a probe of the surface-to-volume ratio and permeability of a membrane. An exact, universal, short-time asymptotics in a pack of cells, assuming that the surfaces are locally smooth, shows that the effects of nonzero permeability appear as a correction to the diffusion coefficient that is linear in time, whereas the surface-to-volume ratio enters as a square root in time. With κ as the permeability of the membrane, we find, for the particles released inside the cells, DR,eff(t)=DR[1−(SR/VR){4DRt/(9π)−κtDL(DL+DR)/(6DR)}]+⋯ . Here DR and DL are free (i.e., bulk) diffusion coefficients inside and outside of the cell, respectively, and SR/VR is the total internal surface divided by the total internal cell volume. The other terms linear in t that add to the right side of above equation are DR(SR/VR)[(1/6)ρt−(1/12)DRt〈(1/R1+1/R2)〉R], where ρ is a surface relaxation, which is generally negligible in biological samples, and 〈(1/R1+1/R2)〉R is the average of the principal radii of curvatures over the interior surface. An equivalent expression for the particles starting outside the cell is obtained by swapping L↔R. The NMR data on erthrocytes show that the effect of permeability can be significant within the time scales of measurement and hence κ is deducible from the data. The long-time behavior given previously [Proc. Natl. Acad. Sci. USA 92, 1229 (1994)] is augmented by giving a nonuniversal form that includes the rate of approach to this limit.
A laser-ablation molecular-beam Fourier-transform microwave spectrometer: The rotational spectrum of organic solids
Authors: Lesarri Alberto , Mata Santiago , López Juan C. , Alonso José L.
Published: October 2003

A spectrometer that combines laser ablation of a solid sample with molecular-beam Fourier-transform microwave spectroscopy (MB-FTMW) has been constructed to obtain the rotational spectrum of solid organic molecules. Laser ablation is produced by visible radiation, using the second harmonic of a Nd:YAG laser. The laser hits a solid rod placed on a specially designed pulsed nozzle, coaxially oriented with the axis of the microwave spectrometer Fabry–Pérot cavity. The vaporized molecules are seeded in the supersonic jet formed by the expansion of a carrier gas (Ar,Ne) and probed by FTMW spectroscopy. The high sensitivity of the spectrometer is exemplified with the observation of minor isotopomers in natural abundance of different organic molecules and natural amino acids. This instrument opens perspectives in the investigation of the gas phase structure of solid organic compounds.
Compact, robust, and flexible setup for femtosecond pulse shaping
Authors: Präkelt A. , Wollenhaupt M. , Assion A. , Horn Ch. , Sarpe-Tudoran C. , Winter M. , Baumert T.
Published: October 2003

We present an improved design and adjustment concept for femtosecond pulse shaping. The concept results in a compact and robust pulse shaping setup. A systematic adjustment procedure, high reproducibility and stability, as well as easy adaptability to different femtosecond laser sources are the key features of the presented design. The constructed prototype pulse shaper was tested in an open loop and feedback-controlled adaptive pulse shaping on two different femtosecond laser sources.
Potential energy surfaces for the A″3 and A′3 electronic states of the O(3P)+HCl system
Authors: Ramachandran B. , Peterson Kirk A.
Published: October 2003

We report ab initio calculations at the MRCI+Q/CBS level of theory for the A″3 and A′3 electronic states of the O(3P)+HCl system, where the complete basis set energies are obtained by extrapolating MRCI+Q/aug-cc-pVnZ (n=2,3,4) energies. Potential energy surfaces for these electronic states are generated by interpolating these energies using the reproducing kernel Hilbert space method. The reaction barrier on the interpolated 3A″ surface at the MRCI+Q/CBS level of theory is 11.86 kcal/mol. The potential energy surface was then scaled to yield a barrier height close to that predicted by CCSD(T) and MRCI+Q benchmark calculations, namely, 10.60 kcal/mol. The fact that the 3A″ and 3A' electronic states are degenerate at collinear and asymptotic regions of configuration space was used to scale the collinear reaction barrier on the 3A' surface from the MRCI+Q/CBS value of 15.15 kcal/mol to match that of the scaled 3A″ surface, 13.77 kcal/mol. The potential energy surfaces thus obtained appear to be the most accurate to date for the reaction O(3P)+HCl→OH+Cl. The potential energy surface for the 3A″ state contains a fairly deep van der Waals well on the product side of the reaction barrier at a rather sharp O–H–Cl angle (67°) and a shallow well on the reactant side at collinear O–H–Cl geometry. Details of the ab initio calculations, the fitting procedure, and characterization of the saddle and stationary points are presented.
Quantum calculations of the rate constant for the O(3P)+HCl reaction on new ab initio A″3 and A′3 surfaces
Authors: Xie Tiao , Bowman Joel M. , Peterson K. A. , Ramachandran B.
Published: October 2003

We report the thermal rate constant of the O(3P)+HCl→OH+Cl reaction calculated from 200 to 3200 K, using new fits to extensive ab initio calculations [B. Ramachandran and K. A. Peterson, J. Chem. Phys. 119, 9590 (2003), preceding paper]. The rate constants are obtained for both the A″3 and A′3 surfaces using exact quantum reactive scattering calculations for selected values of the total angular momentum and the J-shifting approximation for both the A″3 and A′3 surfaces. The results are compared with the ICVT/μOMT rate constants calculated by the POLYRATE program and all available experimental data. Other related high-energy reaction channels are also studied qualitatively for their contribution to the total thermal rate constant at high temperature.
Interaction of CO with the stoichiometric RuO2(110) surface
Authors: Kim S. H. , Paulus U. A. , Wang Y. , Wintterlin J. , Jacobi K. , Ertl G.
Published: October 2003

The adsorption of CO on RuO2(110) single-crystalline thin films grown on Ru(0001) was studied with scanning tunneling microscopy (STM), thermal desorption spectroscopy (TDS), and high-resolution electron energy-loss spectroscopy. The stoichiometric RuO2(110) surface exhibits alternating rows of O-bridge and coordinatively unsaturated Ru atoms (Ru-cus). We identify two different CO adsorption states: CO-bridge and CO-cus. CO-bridge is known to adsorb at the O-bridge positions after reacting-off O-bridge. CO-cus is linearly bonded to Ru-cus in an on-top position and becomes stabilized only after complete filling of the CO-bridge sites. The CO-cus state exhibits two desorption maxima, at 200 and 320 K, corresponding to a surface coverage of approximately 1.0 (α state) and 0.5 (β state), respectively. At 300 K and without CO gas in the background, CO-cus remains only temporarily present at the surface, and reaches coverages of 0.5. A coverage of 1.0 can be achieved by exposure to CO at 300 K to prepare CO-bridge and further exposure to CO at 85 K. From time-dependent STM and from TDS the binding energy of the β-state CO-cus is determined at about −1.0 eV.
Homogeneous nucleation in inhomogeneous media. II. Nucleation in a shear flow
Authors: Reguera David , Rubı́ J. M.
Published: October 2003

We investigate the influence of a shear flow on the process of nucleation. Mesoscopic nonequilibrium thermodynamics is used to derive the Fokker–Planck equation governing the evolution of the cluster size distribution in a metastable phase subjected to a stationary flow. The presence of the flow manifests itself in the expression for the effective diffusion coefficient of a cluster and introduces modifications in the nucleation rate. The implications of these results in condensation and polymer crystallization are discussed.
Subterahertz spectroscopy at He-3 temperatures
Authors: Basov D. N. , Dordevic S. V. , Singley E. J. , Padilla W. J. , Burch K. , Elenewski J. E. , Greene L. H. , Morris J. , Schickling R.
Published: October 2003

We report on the design and implementation of an instrument for spectroscopic studies of materials at sub-terahertz (THz) frequencies at temperatures down to 340 mK. We achieved consistent operation under these rather extreme conditions by coupling a modified Martin–Puplett interferometer to a single cryogenic unit housing two independently controlled He-3 platforms: one as a sample stage and the other for bolometric detectors. Both the optical scheme of the interferometer and detector layout are tailored for the use of the two-channel data acquisition mode which is especially advantageous for measurement of absolute values of reflectance as well as for high-resolution spectroscopy. We document the reliable performance of the sub-THz apparatus with several experiments exploring electrodynamics of both conventional and high-Tc superconductors.
Fast single loop diamagnetic measurements on the TCV tokamak
Authors: Moret J.-M. , Buhlmann F. , Tonetti G.
Published: October 2003

Measurement of the plasma generated diamagnetic flux on tokamak à configuration variable (TCV) is used to derive the plasma pressure, as on other magnetic confinement experiments. However, specificities of the device make the measurement more difficult: for passive stabilization of the vertical position of highly elongated plasmas, the vessel has a low electrical resistivity, leading to large image currents in the vessel. For the same reason the plasma must also be kept close to the conducting wall, so that the in-vessel double loop method usually used to compensate for these currents cannot be applied. In order to achieve proper compensation, the diamagnetic measurement diagnostic on TCV uses the signal from a single loop wound outside the vessel in combination with appropriate signal processing that accurately matches the fast component of the induced vessel current. This allows extraction of the plasma diamagnetic flux with a remarkable bandwidth, of ∼10 kHz, and with the required accurate compensation of 0.05 mWb out of 2 Wb. As a result, rapid changes in plasma pressure can be studied, for example during additional heating power modulation or fast plasma instabilities.
A high-sensitivity differential scanning calorimeter with magnetic field for magnetostructural transitions
Authors: Marcos Jordi , Casanova Fèlix , Batlle Xavier , Labarta Amı́lcar , Planes Antoni , Mañosa Lluı́s
Published: October 2003

We have developed a differential scanning calorimeter capable of working under applied magnetic fields of up to 5 T. The calorimeter is highly sensitive and operates over the temperature range 10–300 K. It is shown that, after a proper calibration, the system enables determination of the latent heat and entropy changes in first-order solid–solid phase transitions. The system is particularly useful for investigating materials that exhibit the giant magnetocaloric effect arising from a magnetostructural phase transition. Data for Gd5(Si0.1Ge0.9)4 are presented.
Imaging the high-speed impact of microdrop on solid surface
Authors: Kim Ho-Young , Park Soon-Young , Min Kyoungdoug
Published: October 2003

An experimental setup that images the high-speed impact of a microdrop onto solid surfaces is described. The drop generation system provides a stream of monosized microdrops having diameter near 100 μm and the velocity around 10 m/s. The drop train is manipulated to deliver a single drop onto a solid target by selective charging and deflection. The images of drop spreading at different times are obtained by the double-flash photography technique. Representative experimental results are given with the estimation error of time elapsed after impact below 5 μs. In addition, it is shown that drop impact kinematics can be adopted to estimate the time in the very early stages of drop spreading. Such drop delivery and optical imaging system can be used to study the fuel spray behavior in internal combustion engines and molten microdrop deposition process in droplet-based manufacturing.
Susceptibility measurements at high pressures using a microcoil system in an anvil cell
Authors: Alireza Patricia Lebre , Julian Stephen R.
Published: October 2003

We present here a microcoil setup for susceptibility measurements in anvil cells. In contrast to previous designs, we have placed the secondary coil inside the high pressure volume. This dramatically boosts the signal and eliminates the need for complex background subtraction. For samples of lead, tin, and the metal–insulator oxide calcium ruthenate (Ca2RuO4), our procedure has produced very clear signals for both superconducting transitions and ferromagnetic ordering with a weak magnetic moment (0.2 μB/Ru), up to 75 kbar, with a signal-to-noise ratio of ∼80.
Compact design of a transmission electron microscope-scanning tunneling microscope holder with three-dimensional coarse motion
Authors: Svensson K. , Jompol Y. , Olin H. , Olsson E.
Published: October 2003

A scanning tunneling microscope (STM) with a compact, three-dimensional, inertial slider design is presented. Inertial sliding of the STM tip, in three dimensions, enables coarse motion and scanning using only one piezoelectric tube. Using the same electronics both for scanning and inertial sliding, step lengths of less than 5% of the piezo range were achieved. The compact design, less than 1 cm3 in volume, ensures a low mechanical noise level and enables us to fit the STM into the sample holder of a transmission electron microscope (TEM), while maintaining atomic scale resolution in both STM and TEM imaging.
Flowing liquid sample jet for resonance Raman and ultrafast optical spectroscopy
Authors: Tauber Michael J. , Mathies Richard A. , Chen Xiyi , Bradforth Stephen E.
Published: October 2003

A wire-guided, gravity-driven jet apparatus is described that produces optically stable thin films of liquids flowing at rates suitable for high repetition rate spectroscopy. Unlike conventional free-flowing jets, the design works well for low viscosity solvents including water and aqueous solutions of proteins. The construction of the wire guide, jet nozzle, and flow system is described. A stable water film whose thickness can be varied from 6 to 100 μm is demonstrated that has been employed in resonance Raman and femtosecond transient absorption experiments.
Phase-sensitive time-domain terahertz reflection spectroscopy
Authors: Pashkin A. , Kempa M. , Němec H. , Kadlec F. , Kužel P.
Published: October 2003

An approach to time-domain terahertz reflection spectroscopy is proposed and demonstrated. It allows one to obtain very accurately the relative phase of a reflected THz wave form, and consequently the complex dielectric function can be precisely extracted. The relevant setup was demonstrated to allow measurements of a variety of samples: we present results for doped silicon and for ferroelectric SrBi2Ta2O9 (bulk ceramics as well as thin film on sapphire substrates).
Effects of vibrational relaxation on the photodesorption of NO from Pt(111): A density matrix study
Authors: Abe Atsutoshi , Yamashita Koichi
Published: October 2003

The effect of vibrational relaxation on the photodesorption dynamics of NO from a Pt(111) surface has been investigated theoretically. Although this system has been studied in many previous works, the relaxation of NO stretching vibration due to the interaction with electron–hole pairs in metals has not been included in conventional models. Although the relaxation lifetimes of the first-excited vibrational state of diatomic molecules adsorbed on metal surfaces are generally in the range 0.1–1 ps, the desorption dynamics of NO is complete in about 1 ps. Therefore, it is considered that the vibrational relaxation can influence the vibrational state of this stretching mode during the desorption process. We described the desorption dynamics by using the time propagation of the density matrix. The effects of vibrational relaxation were included by using a Redfield-type model. We also investigated the validity of the parameters for dynamical calculations by ab initio methods. As a result, we obtained physically reasonable results for the desorption probability, mean translational energy, and vibrational state distribution for the desorbed NO molecules.
Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies
Authors: Senthilkumar K. , Grozema F. C. , Bickelhaupt F. M. , Siebbeles L. D. A.
Published: October 2003

Values of charge transfer integrals, spatial overlap integrals and site energies involved in transport of positive charges along columnar stacked triphenylene derivatives are provided. These parameters were calculated directly as the matrix elements of the Kohn–Sham Hamiltonian, defined in terms of the molecular orbitals on individual triphenylene molecules. This was realized by exploiting the unique feature of the Amsterdam density functional theory program that allows one to use molecular orbitals on individual molecules as a basis set in calculations on a system composed of two or more molecules. The charge transfer integrals obtained in this way differ significantly from values estimated from the energy splitting between the highest occupied molecular orbitals in a dimer. The difference is due to the nonzero spatial overlap between the molecular orbitals on adjacent molecules. Calculations were performed on unsubstituted and methoxy- or methylthio-substituted triphenylenes. Charge transfer integrals and site energies were computed as a function of the twist angle, stacking distance and lateral slide distance between adjacent molecules. The variation of the charge transfer integrals and site energies with these conformational degrees of freedom provide a qualitative explanation of the similarities and differences between the experimental charge carrier mobilities in different phases of alkoxy- and alkylthio-substituted triphenylenes. The data obtained from the present work can be used as input in quantitative studies of charge transport in columnar stacked triphenylene derivatives.
Influence of monomer sequence on microstructure of nonadditive hard chain copolymers: Simulation and equation of state
Authors: Alsunaidi Abdullah , Abu-Sharkh Basel F.
Published: October 2003

Influence of copolymer structure on self-assembly of the copolymer was investigated by introducing nonadditive size interactions among different type segments in copolymers composed of touching hard spheres. The copolymer structures investigated are diblock, alternating, multiblock, and random. The copolymers were simulated using discontinuous molecular dynamics simulation. Equations of state of the different model copolymers were developed using the TPT1 theory. Diblock copolymers were found to self assemble readily at high values of the nonadditivity parameter Δ and at high densities. Multiblock and random copolymers self assembled to a smaller extent and the alternating copolymer self-assembled only at very high Δ and densities. The TPT1 equation of state provided good prediction of the compressibilities of the different copolymer systems at negative and small positive values of Δ. Deviations between the model and simulation results were observed at high Δ and high densities. Deviations were associated with self-assembly of the copolymers.
The low-lying electronic states of FeO+: Rotational analysis of the resonance enhanced photodissociation spectra of the Π7/26←X 6Σ+ system
Authors: Aguirre Fernando , Husband John , Thompson Christopher J. , Stringer Kay L. , Metz Ricardo B.
Published: October 2003

The resonance enhanced (1+1) photodissociation spectra of the (8,0) and (9,0) bands of the Π7/26←Σ+6 system of FeO+ have been recorded. From a rotational analysis, the rotational parameters for the Σ+6 ground state of FeO+ have been obtained for the first time. The rotational constant B0=0.5020±0.0004 cm−1 is derived, giving r0=1.643±0.001 Å. Other molecular parameters determined for the Σ+6 ground state are the spin–spin coupling constant, λ=−0.126±0.006 cm−1, and the spin–rotational coupling constant, γ=−0.033±0.002 cm−1. The assignment of the upper state as Π7/26 is based on the characteristic appearance of the band and on time-dependent density functional (TD-DFT) calculations performed on FeO+. The reliability of the TD-DFT method in the prediction of excited states of FeO+ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
Low-energy electron-energy-loss spectroscopy of electronic transitions in solid carbon dioxide
Authors: Deschamps M. C. , Michaud M. , Sanche L.
Published: October 2003

We report electron-energy-loss spectra of solid films of CO2 for electronic transitions induced by 15, 19.4, and 25 eV incident electrons. All spectra were obtained under sufficiently small electron exposures so as to avoid sample damages. The use of a low-energy electron along with the backscattering geometry give access to spin- and symmetry-forbidden transitions while the effect of the condensed phase makes it possible to modify the energy, ordering, and magnitude of most gas-phase transitions. The most noticeable observation is the disappearance of all sharp energy-loss peaks attributed to a Rydberg series of CO2 in the gas phase. In contrast, transitions to the molecular valence Δu3,1 and Σu−3,1 states are located virtually at the same energy as in the gas phase. The strong dipole-allowed valence Σu+1 transition is found shifted to lower energy by about 0.3 eV while transitions to mixed Rydberg-valence Πg3,1 and Πu1 states are both shifted to higher energy by about 0.4–0.5 eV. The lowest valence Σu+3 transition is ascribed to the lowest energy-loss feature in the solid at 7.9 eV.
The relative reactivity of CH3D molecules with excited symmetric and antisymmetric stretching vibrations
Authors: Yoon Sangwoon , Holiday Robert J. , Sibert Edwin L. , Crim F. Fleming
Published: October 2003

Experimental and theoretical studies explore the reactivity of the symmetric and the antisymmetric stretching vibrations of monodeuterated methane (CH3D). Direct infrared absorption near 3000 cm−1 prepares CH3D molecules in three different vibrationally excited eigenstates that contain different amounts of symmetric C–H stretch (ν1), antisymmetric C–H stretch (ν4), and bending overtone (2ν5) excitation. The reaction of vibrationally excited CH3D with photolytic chlorine atoms (Cl, 2P3/2) yields CH2D products mostly in their vibrational ground state. Comparison of the vibrational action spectra with the simulated absorption spectra and further analysis using the calculated composition of the eigenstates show that the symmetric C–H stretching vibration (ν1) promotes the reaction seven times more efficiently than the antisymmetric C–H stretching vibration (ν4). Ab initio calculations of the vibrational energies and eigenvectors along the reaction coordinate demonstrate that this difference arises from changes in the initially excited stretching vibrations as the reactive Cl atom approaches. The ν1 vibration of CH3D becomes localized vibrational excitation of the C–H bond pointing toward the Cl atom, promoting the abstraction reaction, but the energy initially in the ν4 vibration flows into the C–H bonds pointing away from the approaching Cl atom and remains unperturbed during the reaction. A simple model using vibrational symmetries and vibrational adiabaticity predicts a general propensity for the greater efficiency of the symmetric stretch for accelerating the reaction in the vibrationally adiabatic limit.
Photoinduced charge-transfer reaction at surfaces. II. HBr⋯Nan/LiF(001)+hv(610 nm)→Br−Nan+/LiF(001)+H(g)
Authors: Dobrin Sergey , He Hong , Naumkin Fedor Y. , Polanyi John C. , Raspopov Sergei A.
Published: October 2003

A sub-monolayer of atomic sodium was deposited on LiF(001) at 40–90 K. The adsorbed sodium atoms and clusters were dosed with HBr, to form HBr⋯Nan/LiF(001) (n=1,2,…) complexes which were then irradiated by 610 nm laser-light to induce charge-transfer reactions. The reaction-product atomic H(g) was observed leaving the surface, by two-color Rydberg-atom TOF spectroscopy. The H-atom translational energy in its “fast” (0.9 eV) component exhibited structure (40±10 meV spacing) attributed to vibration of the NaBr residue at the surface following photoinduced reaction in Na…HBr. The cross-section of the harpooning event was obtained as 7.5×10−19 cm2 for the “fast” H-atom reaction-product. Investigation of the coverage and temperature dependencies of the H-atom signal and of temperature programmed desorption (TPD) and x-ray photoelectron spectra gave an activation barrier for surface diffusion of Na-atoms Ediff<170 meV. High-level ab initio calculations were employed to interpret the TOF and TPD spectra. The reaction precursors and products, Na-HBr, Na+-HBr, Na2-HBr, Na2Br, NaBr, and NaBr-HBr, were investigated in terms of potential energy surfaces, equilibrium structures, binding energies, and vibrational frequencies.
On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite
Authors: Yang Gang , Wang Yan , Zhou Danhong , Zhuang Jianqin , Liu Xianchun , Han Xiuwen , Bao Xinhe
Published: October 2003

Density functional calculations have been employed to investigate the locating and binding of lanthanum cation, i.e., La(OH)2+, on HZSM-5 zeolite. Through geometry optimization, it was determined that lanthanum ions are favorably accommodated in the two 6-T rings of the straight channels (Clusters 1 and 2, see Sec. III A for details). Cluster 1 was found to exist in prior to Cluster 2 due to the preference of Al substitution in the T11 site (Cluster 1) rather than in the T8 site (Cluster 2). Geometry-optimization of Cluster 1 containing another two lanthanide ions Nd3+ and Yb3+ was also carried out and it was found that a monotonic decrease in Ln–O bond length will take place as the atomic number increases, conforming well to the rule of lanthanide contraction. Some of the optimized parameters are comparable to the corresponding experimental values in Y zeolite, which confirms that the optimized configurations are acceptable. The average frequencies of hydroxyls attached to La3+ or Yb3+ in Cluster 1 fall at 3609.16 and 3579.76 cm−1, respectively, with the gap of these two frequencies close to that in the sodalite cage of Y zeolite. Compared to H-form zeolite, the charges on both Al and O atoms in Ln-ZSM-5 zeolite show an obvious increase, which will undoubtedly lead to a stronger mutual interaction and hence enhance the stability of the [AlO4]− anion. Moreover, the Ln(OH)2+ seem to have thickened the zeolite framework, which can effectively retard the process of dealumination. Through the evaluation of the possibility for dimer formation, it turned out that when the exchange degree arrived to approximately 0.28, lanthanum monomers began to aggregate into dimers, and were completely converted into dimers when the exchange degree approached 0.60.
Many-body interactions in liquid methanol and its liquid/vapor interface: A molecular dynamics study
Authors: Dang Liem X. , Chang Tsun-Mei
Published: October 2003

Many-body interactions in liquid methanol and its liquid/vapor interface are evaluated using classical molecular dynamics techniques. The methanol molecule carries a molecular polarizability to account for induction energies and forces. The computed dipole moment for the methanol molecule changed from 1.7 to 2.8 D, respectively, from the vapor to the liquid phases. This result indicated that there are significant many-body interactions in this complex molecular system. The computed average molecular dipole moment in liquid methanol at room temperature is in good agreement with experimental measurements. The computed average dipole moments of methanol molecules near the interface are close to their gas phase values, while methanol molecules far from the interface have dipole moments corresponding to their bulk values. The structural and thermodynamic properties of the liquid methanol as well as the surface tension of its liquid/vapor interface are in good agreement with the experiments, demonstrating the high quality of our potential model and simulation approaches. A constrained molecular dynamics technique was used to investigate the transport mechanism of a methanol molecule across the methanol liquid/vapor interface. The computed transfer free energy changed gradually as the methanol molecule approached the Gibbs dividing surface, and it crossed the interface with no substantial minimum free energy. The computed solvation free energy of the methanol molecule in liquid methanol estimated from the free energy profile (4.25 kcal/mol) is in good agreement with the corresponding experimental measurement (4.89 kcal/mol).
Segmental and terminal dynamics in miscible polymer mixtures: Tests of the Lodge–McLeish model
Authors: He Yiyong , Lutz T. R. , Ediger M. D.
Published: October 2003

The Lodge–McLeish model of miscible blend dynamics is compared to literature data for the segmental or terminal dynamics of components in six different miscible polymer mixtures. In most cases, the model successfully fits the experimental data for a given component with a parameter φself, which is independent of temperature and composition. In most cases, the fitted value of φself is close to the model prediction, providing some support for the assumption that the Kuhn length is the relevant length scale for dynamics in miscible polymer mixtures. In other cases, the model either fits the data with φself values much different than those expected based on the Kuhn length, or fails to fit the experimental data for any value of φself. Using the Fox equation as input to the Lodge–McLeish model provides a better description of the experimental data than using the measured mixture Tg values.
Hydrodynamic properties of rodlike and disklike particles in dilute solution
Authors: Ortega A. , Garcı́a de la Torre J.
Published: October 2003

The hydrodynamic properties of cylindrical (rodlike and discoidal) particles in dilute solution have been computed using the bead-shell model treatment. Previous results [Tirado and Garcı́a de la Torre, J. Chem. Phys. 71, 2581 (1979); 73, 1993 (1980)] for rods with length-to-diameter ratio p>2 are now extended to short cylinders and disks down to p=0.1. The intrinsic viscosity is obtained for rods and disks, and results are presented for the three rotational relaxation times of a cylindrical particle. The hydrodynamic properties are expressed in forms that have a weak variation with p, and are therefore useful for the analysis of experimental values. We present examples of the determination of the length and diameter of the cylindrical particles, for DNA oligonucleotides and tobacco mosaic virus.
Mode structure of diffusive transport in hydroxypropylcellulose:water
Authors: Phillies George D. J. , O’Connell Robert , Whitford Paul , Streletzky Kiril A.
Published: October 2003

A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose(HPC):water is presented. New methods and data include (1) use of integral spectral moments to characterize nonexponential decays, (2) spectra of small probes in concentrated HPC solutions, (3) temperature dependence of the mode structure, and (4) comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that (1) probe and polymer relaxations are in general not the same; (2) the apparent viscometric crossover near ct≈6 g/l is echoed by probe behavior; (3) our HPC solutions have a characteristic dynamic length, namely the 50 nm length that matches the polymer’s hydrodynamic radius; (4) characterization of spectral modes with their mean relaxation time affords simplifications relative to other characterizations; and (5) contrary to some expectations, Stokes–Einsteinian behavior (diffusion rate determined by the macroscopic viscosity) is not observed, even for large probes in relatively concentrated solutions. We propose that the viscometric and light scattering effects found in HPC solutions at elevated concentrations reflect the incipient formation of a generalized Kivelson [S. A. Kivelson et al., J. Chem. Phys. 101, 2391 (1994)] glass.
Negative tails in the velocity correlation function of supercooled liquids
Authors: De Santis Alberto , Ercoli Alessandro , Rocca Dario
Published: October 2003

The dynamics of supercooled liquid argon is investigated via a specific correlation function ΔB. Its time behavior is well reproduced by taking into account the separate contributions of an Enskog-type diffusive part and of damped oscillations of vanishing time integral (nondiffusive part). The implications on the velocity correlation function (VCF) are investigated. Phononlike oscillations, also present in the crystal, can explain the first negative lobe and the subsequent shoulder of the VCF. The slow decay of ΔB after the fast dynamics (t<1 ps) characterizes the liquid state, and produces negative VCF tails at long times (up to about 5 ps).
Ab initio calculation of interaction nature of borazine (B3N3H6) dimer
Authors: Kawahara Shun-ichi , Tsuzuki Seiji , Uchimaru Tadafumi
Published: October 2003

The π/π interaction (stacking) and N(B)–H/π interaction of the borazine (B3N3H6) dimer were theoretically studied. In contrast to the benzene dimer, the gauche parallel-stacked dimer of borazine was energetically minimum, and total interaction energy was about 1 kcal/mol more negative than that of the parallel-stacked dimer of benzene. The gauche parallel-stacked dimer of borazine was more stable than slipped parallel-stacked dimers and T-shape dimers. The syn parallel-stacked dimer of borazine was energetically unstable and it was less stable than the slipped syn parallel-stacked structures. The electron correlation effect at higher than the second-order Møller–Plesset (MP2) level on the molecular interaction energy was quite small. The dispersion term and the charge transfer term had large contribution in almost all the borazine dimer formations, except the syn parallel-stacked dimer. In the case of syn parallel-stacked dimer, contribution of the dispersion term was dominant. The electrostatic term had only small contribution for all the dimer formations.
The effect of spin–orbit coupling in complex forming O(3P) +O2 collisions
Authors: Tashiro Motomichi , Schinke Reinhard
Published: October 2003

The effect of spin–orbit coupling on O(3P)+O2(3Σg−) collisions is investigated for J=0 using time-dependent wave packets. The probability of forming O3 complexes, which is important for understanding the atom exchange reaction mechanism, is calculated in two different ways. The first approach follows the standard treatment in that only the reactive ground electronic state is included. In the second approach all 27 states correlating with O(3P)+O2(3Σg−) and the nonadiabatic transitions induced by spin–orbit coupling are taken into account; all the excited electronic states are repulsive and thus do not lead to complex formation if nonadiabatic transitions are neglected. The required nine diabatic potential energy surfaces (not including spin–orbit coupling) for the electronic states 1 sA′, 2 sA′, and A″s (s=1, 3, and 5) are constructed by high-level electronic structure calculations in the asymptotic O+O2 channel with the O2 bond length being fixed. The two sets of calculations show that spin–orbit coupling is not an important effect. The probability for forming ozone complexes when the oxygen atom is initially in the excited fine structure state O(3Pj=1) state is only 10% of that for the lowest state O(3Pj=2), and it is below 1% for O(3Pj=0). The single-surface calculation, with the excited states phenomenologically taken into account by a statistical factor, gives a rather accurate value for the thermally averaged complex formation rate coefficient.