bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of the foraging behaviour of red wood ants (Formica rufa group) to exclusion from trees
Authors: Lenoir L.
Published: August 2003

Abstract 1 Because of the large numbers within a colony and their aggressive nature, red wood ants (Formica rufa group) have a potential to greatly influence the cold‐temperate forest ecosystem. Wood ants are omnivorous and hunt in trees as well as on the forest floor.

2 A field experiment in a mixed forest in central Sweden was carried out to examine (i) the foraging behaviour of wood ants on the forest floor and (ii) the impact of increased numbers of wood ants on the soil fauna. The foraging behaviour of wood ants was manipulated by excluding the ants from their food resources in the tree canopy, with the intention to increase ant activity on the forest floor. To estimate this activity, the number of trees with foraging ants, the numbers of ants going to and from their nests and the prey carried by home‐running wood ants were determined during the summer period. Pitfall traps were placed in the soil to determine effects on mobile soil invertebrates.

3 When excluded from local trees, wood ants searched other trees further away from the nests rather than searching more intensively for prey on the forest floor. By contrast to the initial hypothesis, more soil‐living prey were caught by ants in the control plots than in the plots where the local trees were not accessible to the wood ants. The proportion of soil‐living to tree‐living prey tended to be greater in the control plots.

4 In the treated plots (no access to the trees), wood ants had a negative effect on the activity of Linyphiidae spiders. There was little effect of wood ants on other soil invertebrates.

5 This study suggests that the role of wood ants as top predators in the forest soil food‐web in central Sweden is limited.
Non‐target habitat exploitation by Trichogramma brassicae (Hym. Trichogrammatidae): what are the risks for endemic butterflies?
Authors: Babendreier D. , Schoch D. , Kuske S. , Dorn S. , Bigler F.
Published: August 2003

Abstract 1 Trichogramma brassicae Bezdenko is inundatively released against the European corn borer in Switzerland. Because parasitoids dispersing from the release fields might pose a threat to native butterflies, the searching efficiency of T. brassicae was investigated in nontarget habitats.

2 In field studies, T. brassicae was released at rates of 120 000 females/ha. Parasitism of sentinel Ephestia kuehniella egg clusters was 1.6–3.6% in meadows and 2.0–4.0% in flower strips. The respective figures were 57.6–66.7% and 19.2–46.9% in maize, significantly higher than the parasitism rates in the nontarget habitats. Experiments carried out in small field cages confirmed these results: Again, significantly higher parasitism rates were found in maize compared to meadows and flower strips, and also compared to hedgerows (in sleeve cages).

3 To elucidate potential factors underlying the low searching efficiency in nontarget habitats, the behaviour of individual T. brassicae females was investigated on four meadow plants comparatively to maize and a filter paper control. Mean (±SE) walking speed on maize was 2.2 ± 0.2 mm/s, similar to three of the plants tested and filter paper but significantly higher than on Trifolium pratense (0.85 mm/s). A higher turning rate was found on T. pratense, Viola wittrockiana and Plantago lanceolata, in contrast to the longer leaved maize and Alopecurus pratensis. The number of wasps leaving the plant within the observation period differed significantly between plant species, and was twice as high for T. pratense (and the filter paper control) compared to the other plant species.

4 In a choice experiment carried out in a climate cabinet with all five host plant species in cages, we obtained the highest parasitism rates on maize and the lowest parasitism on T. pratense, thus confirming the behavioural observations.

5 In conclusion, there is evidence for a decreased searching efficiency on plants in nontarget habitats compared to maize. However, the data explain only part of the differences found between parasitism in maize compared to nontarget habitats. Other factors, such as the structural complexity of a habitat, may also play a role. We conclude that the risk for butterfly populations in the tested nontarget habitat due to mass released T. brassicae is low.
Shoot damage by Tomicus sp. (Coleoptera: Scolytidae) and effect on Pinus yunnanensis resistance to subsequent reproductive attacks in the stem
Authors: Lieutier François , Ye Hui , Yart Annie
Published: August 2003

Abstract  1 In South‐western China, Yunnan pines Pinus yunnanensis, suffer considerable damage from an undescribed Tomicus sp. previously thought to be T. piniperda.

2 To assess the effect of shoot maturation feeding (during which an aggregation process appears to occur) on host resistance to attacks on the bole, the relationships between shoot damage, bole attack density and tree survival were studied.

3 Attack distribution in the crown and in the stem did not vary between killed and surviving trees, indicating that mortality is determined by the quantity of attacks.

4 The level of shoot damage and bole attack density were positively and linearly correlated. This can be explained by the fact that bole attacks are caused by beetles coming from the crown of the same tree.

5 A critical threshold of bole attack density (around 80 attacks/m2) above which trees die was observed. However, because attacks continue after this threshold is reached, the density of failed attacks on the killed trees was used as an estimator of the threshold density. It decreased when shoot damage increased.

6 The existence of a critical threshold of shoot damage (60% damaged shoots) was also demonstrated. Above this threshold, stem attack density was always sufficiently high to kill trees.

7 The results emphasize that concentration of shoot attacks is the main reason for the extensive tree damage observed in China.

8 A model of relationships between shoot and stem attacks is proposed, suggesting that management to reduce shoot attacks would protect trees from dying by both decreasing the number of bole attacks and raising the threshold for successful attack density on the bole to levels that could not be attained.
Sprayable pheromone for controlling the North American grape berry moth by mating disruption
Authors: Trimble R. M. , Vickers P. M. , Nielsen K. E. , Barinshteyn G.
Published: August 2003

Abstract  1 Sex pheromone‐mediated mating disruption can be used to provide economic control of the North American grape berry moth in commercial vineyards. Controlled release devices that use a plastic tube or polymer to regulate the emission of pheromone have been registered for use in Canada for controlling this pest. These dispensers require manual application, whereas a newly developed microencapsulated formulation can be applied using a vineyard airblast sprayer.

2 The efficacy of 3M Sprayable Pheromone was compared with the efficacy of Isomate® GBM pheromone dispensers and organophosphorus insecticide for controlling the grape berry moth during the 1997 and 1998 growing seasons. Two application schedules of sprayable pheromone were tested during 1997 and two formulations of sprayable pheromone were tested during 1998. The mating disruption efficiency of the pheromone treatments was compared using pheromone‐baited traps and the efficacy of the pheromone and insecticide treatments was compared by inspecting grape clusters for feeding injury caused by grape berry moth larvae.

3 The estimated mating disruption efficiency of the pheromone treatments ranged from 67 to 100%. There was no difference in the efficiency of the two application schedules of 3M Sprayable Pheromone during 1997. The estimated efficiency of Isomate® GBM was greater than that of 3M Sprayable Pheromone during the first two flights of 1997. During 1998, the estimated efficiency of 3M Sprayable Pheromone and Isomate® GBM was similar.

4 The average percentage of grape clusters with grape berry moth feeding injury was greater in the border than in the interior zone on 13 ocassions, and greater in the interior zone than in the border zone of experimental plots on six of the 72 occasions when clusters were inspected during the 2‐year study.

5 The average percentage of grape clusters with feeding injury was similar in plots treated with 3M Sprayable Pheromone, Isomate® GBM and insecticide during both years of the study. There was no difference in feeding injury in plots treated with 3M Sprayable Pheromone and Isomate® GBM, despite the greater estimated mating disruption efficiency of Isomate® GBM.

6 The use of sprayable pheromone may have several operational and cost advantages compared with a hand‐applied dispensing system such as Isomate® GBM.
Clinical response to alefacept: results of a phase 3 study of intramuscular administration of alefacept in patients with chronic plaque psoriasis
Authors: Ortonne J‐P
Published: August 2003

Background Recognition of psoriasis as a T‐cell‐mediated immune disease has led to the development of various therapeutic approaches directed against the pathogenic T cells. Alefacept, a novel and selective biological recombinant protein, binds CD2 on T cells to block T‐cell activation and proliferation and interacts with FcγRIII receptors on accessory cells to produce selective T‐cell apoptosis.

Objective To demonstrate the efficacy and safety of once‐weekly alefacept IM compared with placebo given for 12 weeks to patients with chronic plaque psoriasis.

Methods Multicentre (63 sites in Europe, the USA, and Canada), randomized, double‐blind, parallel‐group study comparing 10 mg and 15 mg of alefacept and placebo administered IM once weekly for 12 weeks. Patients were followed for an additional 12 weeks after cessation of therapy. Patients were eligible for enrolment if they were ≥ 18 years of age, had chronic plaque psoriasis for ≥ 12 months involving ≥ 10% body surface area, and had CD4+ T‐cell counts at or above the lower limit of normal.

Results 507 patients were enrolled into three treatment groups, which were well balanced for demographic, baseline disease characteristics, and treatment history. A significantly greater percentage of patients treated with alefacept 15 mg IM achieved ≥ 75% PASI reduction from baseline 2 weeks after the last dose compared with placebo (21% vs. 5%, P < 0.001); 12% of patients treated with alefacept 10 mg IM reached this level of improvement (P = NS vs. placebo). Alefacept was well tolerated, with adverse events similar to that of placebo.

Conclusions Treatment with alefacept 15 mg IM provided highly significant improvements in all measures of psoriasis disease activity compared with placebo. Pharmacodynamic data confirmed that alefacept is a selective biological agent that reduces memory‐effector T cells (CD4+CD45RO+ and CD8+CD45RO+), the source of the pathogenic mediators of psoriasis, while having relatively no effect on naive T‐cell populations.
Clinical response to alefacept: results of a phase 3 study of intravenous administration of alefacept in patients with chronic plaque psoriasis
Authors: Krueger GG
Published: August 2003

Background There is a current lack of safe and effective psoriasis therapies that provide patients with lasting remissions after treatment is discontinued. Alefacept, a novel and selective biological agent, has demonstrated durable efficacy in patients with chronic plaque psoriasis, and its efficacy has been correlated with reductions in memory‐effector T cells.

Objective To demonstrate the efficacy and safety of both one and two 12‐week courses of alefacept 7.5 mg given once weekly as an intravenous (IV) bolus injection in patients with chronic plaque psoriasis.

Methods Multicentre (51 centres in the USA and Canada), randomized, double‐blind, parallel‐group study comparing once‐weekly alefacept 7.5 mg IV or placebo for two 12‐week treatment courses. Each course had a 12‐week follow‐up phase. Patients were eligible for enrolment if they were ≥16 years of age, had chronic plaque psoriasis for ≥12 months involving ≥10% body surface area, and had CD4+ T‐cell counts at or above the lower limit of normal.

Results 553 patients received treatment in Course 1, and 449 were treated in Course 2. The cohorts were well balanced for demographic and baseline disease characteristics. During the treatment and follow‐up period of Course 1, 28% of patients treated with alefacept achieved ≥75% reduction in Psoriasis Area and Severity Index (PASI), compared with 8% of placebo‐treated patients (P < 0.001). Patients achieving ≥75% reduction in PASI following a single 12‐week course of alefacept maintained ≥50% reduction in PASI for a median of over 7 months. Among patients who received a second course of alefacept therapy, 71% achieved ≥50% reduction in PASI, and 40% achieved ≥75% reduction in PASI over two treatment courses. One or two 12‐week courses of alefacept were similarly well tolerated.

Conclusions Treatment with alefacept 7.5 mg IV provided highly significant improvements in all measures of psoriasis disease activity compared with placebo. A second course of alefacept provided additional benefit.
Hybrid continuum model for large elastic deformation of rubber
Authors: Beda T. , Chevalier Y.
Published: August 2003

This paper presents a hybrid hyperelastic model for rubbery material combining the Gent–Thomas theory for low stretch deformation and the Ogden theory for large stretch deformation. Any deformation mode of rubbery materials is completely characterized by the studied model. A method for mechanical parameters identification is developed. So, comparison between experimental data and analytical solutions is made permitting discussions on the validity of different strain energy function domains. Good agreement between predicted results and experimental data is shown by the processing of the curves of simple tension and pure shear.
Response theory in the multipole reaction field model for equilibrium and nonequilibrium solvation: Exact theory and the second order polarization propagator approximation
Authors: Nielsen Christian B. , Sauer Stephan P. A. , Mikkelsen Kurt V.
Published: August 2003

Exact response functions are derived for a multipole solvent reaction field model of equilibrium and nonequilibrium solvation using the generalized Ehrenfest theorem and assuming a spherical cavity surrounding the solute. The starting point is the Schrödinger equation and we shortly review how the reaction field is introduced into the Schrödinger equation in order to clearly identify the limitations of describing solute–solvent interactions with a reaction field model. The solvent is described as an isotropic homogeneous linear dielectric medium characterized by a static and an optical dielectric constant. From the exact response functions we derive linear response functions within the higher random phase and the second order polarization propagator approximation. Excitation energies, oscillator strengths, and polarizabilities are then calculated for solvated H2S and furan using the augmented correlation consistent triple-ζ (aug-cc-pVTZ) and double-ζ (aug-cc-pVDZ) basis sets for H2S and furan, respectively. We have also calculated excitation energies and oscillator strengths for H2S with standard (vacuum) ab initio methods using a variety of basis set, as there has been no previously reported values of these quantities calculated with the second order polarization propagator approximation. The second order polarization propagator approximation gives excitation energies and oscillator strengths close to values obtained by coupled cluster methods for a solvated H2S molecule, whereas the higher random phase approximation tends to overestimate the value of these quantities. The solvent effect of the excitation energies follow the same trends for all of the reaction field ab initio methods used in the present study, but some oscillator strengths show different solvent effects whether they are calculated with correlated or with noncorrelated ab initio methods. The calculated polarizabilities show the same solvent effect independent of any inclusion of dynamical electron correlation. It is also shown that the equilibrium solvation model is not appropriate for high-frequency perturbations.
Effect of biasing field on the soft mode in the vicinity of the SmC*-SmA phase transition of a ferroelectric liquid crystal “ZLI4851.”
Authors: Kundu S. K. , Suzuki K. , Chaudhuri B. K.
Published: August 2003

Frequency (10 Hz–1 MHz) and temperature (22–80 °C) dependent dielectric constant (both real and imaginary) of a ferroelectric liquid crystal ZLI-4851 film (21 μm thickness) showing a second order SmC*-SmA phase transition around 63.2 °C have been reported. The variation of dielectric constant as a function of temperature follows the generalized Landau theoretical model. Thermal variation of the complex dielectric constant has also been measured with different bias field strengths (0–20 V) for both the SmC* and the SmA phases. Interestingly, soft mode is observed in the SmC* phase only by applying a bias field perpendicular to the helix axis. Due to the application of the bias field, the SmC* phase loses stability of the helical structure, which is considered to be responsible for the appearance of soft mode in the present ferroelectric liquid crystal system.
Giant radio-frequency magnetoabsorption effect in the cobaltite ceramic La0.5Sr0.5CoO3
Authors: Belevtsev B. I. , Kirichenko A. Ya. , Cherpak N. T. , Golubnichaya G. V. , Maximchuk I. G. , Beznosov A. B. , Krasovitsky V. B. , Pal-Val P. P. , Chukanova I. N.
Published: August 2003

The DC transport properties of and the radio-frequency (RF) wave absorption (at 1.33 MHz) in a ceramic sample of La0.5Sr0.5CoO3−δ are measured. The Curie temperature Tc of the sample is about 250 K. A giant negative magnetoabsorption effect is found. In the vicinity of Tc, the absolute value of the magnetoabsorption is about 38% in the rather low magnetic field 2.1 kOe. This differs drastically from the measured DC magnetoresistance (MR) δ(H)=[R(0)−R(H)]/R(0) which is a mere 0.26% near Tc in the same field and increases to about 2.15% in H=20 kOe. The phenomenon can be understood taking into account that the magnetoabsorption is determined by influence of magnetic field on the conductivity and the magnetic permeability, while the MR is determined solely by the former. The magnetoabsorption effect can be used to develop RF devices controlled by magnetic field and temperature.
Occupation probability for acceptor in Al-implanted p-type 4H–SiC
Authors: Matsuura Hideharu , Sugiyama Koichi , Nishikawa Kazuhiro , Nagata Takashi , Fukunaga Nobuya
Published: August 2003

Al-implanted p-type 4H–SiC layers with different implantation and annealing temperatures are formed, and the temperature dependence of the hole concentration p(T) is obtained by Hall-effect measurements. The Al acceptor level in SiC is deep (∼180 meV), and its first excited state level calculated by the hydrogenic model is still deep (∼35 meV), which is close to the acceptor level of B in Si. Therefore, in order to determine the reliable acceptor density (NA) from p(T), the Fermi–Dirac distribution function is not appropriate for Al acceptors in SiC, and a distribution function including the influence of the excited states of the Al acceptor is required. It is demonstrated that the proposed distribution function is suitable for obtaining the actual relationship between NA and p(T) in p-type 4H–SiC.
Multicenter scattering theory of mediator effect in electron tunneling transitions
Authors: Bolgov D. I. , Kozhushner M. A. , Muryasov R. R. , Posvyanskii V. S.
Published: August 2003

The theory of the “bridge” effect, i.e., electron tunneling with the participation of intermediate particles, is developed. It is shown and proved that the general incorrectness of the approach that operates with the restricted basis of the bound states on the bridge particles to obtain a subbarrier electron Green’s function. This approach is adequate only in the energy region near the bound energy of the bridge centers at the large center-to-center distances. Our theory is based on the concept of multiple subbarrier scattering of tunneling electron on the intermediate particles. The regular method of the calculation of the energies of the collectivized bound states as the poles of the total scattering amplitude is developed. It is shown that the probability of the tunneling transition depends on the value and sign of the amplitude of electron subbarrier scattering on one particle, and this amplitude can be calculated by the variation-asymptotic method developed by the authors earlier. The bridge induced enhancement of the tunneling probability depends exponentially on the length of the bridge, the exponent rises with modulus of the tunneling energy, i.e., with energy decreasing. Such enhancement is possible also in the absence of the bound states on the bridge. Two modes of the tunneling transitions, adiabatic, and nonadiabatic ones, are considered.
Electron paramagnetic resonance study of electron and hole traps in β-BaB2O4 crystals
Authors: Hong Wei , Halliburton L. E. , Stevens K. T. , Perlov D. , Catella G. C. , Route R. K. , Feigelson R. S.
Published: August 2003

Electron paramagnetic resonance (EPR) has been used to investigate point defects in single crystals of β-BaB2O4 (commonly referred to as BBO). An irradiation with x rays at 77 K produces two dominant EPR spectra, one electronlike and the other holelike. The trapped-electron center exhibits a 16-line hyperfine pattern from two boron nuclei. With the magnetic field parallel to the c axis, its g value is 1.9993 and the B11 hyperfine splittings are 49 and 42 G. We suggest that this defect is an oxygen vacancy with a trapped electron nearly equally shared by the two neighboring boron ions. In contrast, the trapped-hole center exhibits a four-line hyperfine pattern due to one boron, and is assigned to a hole localized on a nonbridging oxygen ion with no other defects nearby (i.e., a self-trapped hole). With the magnetic field along the c axis, this center has a g value of 2.0113 and a B11 hyperfine splitting of 14.1 G. Warming the crystal to temperatures between 80 and 90 K destroys the initial four-line hole spectrum and introduces other hole centers (most likely perturbed by nearby Na+ ions substituting for Ba2+ ions or by barium vacancies). These electron and hole traps are expected to play a role in the response of BBO crystals to high-power pulsed ultraviolet lasers.
Effect of interfacial dislocations on ferroelectric phase stability and domain morphology in a thin film—a phase-field model
Authors: Hu S. Y. , Li Y. L. , Chen L. Q.
Published: August 2003

A phase-field model was developed for predicting the domain structure evolution in a thin film with an arbitrary distribution of dislocations and subject to a substrate constraint. The effect of interfacial dislocations on the formation of tetragonal ferroelectric domains in a cubic paraelectric matrix was studied. It was found that the presence of interfacial dislocations locally modifies the ferroelectric transition temperature and leads to the preferential formation of ferroelectric domains around misfit dislocations. The types of tetragonal variants depend on the directions of the dislocation lines and their Burgers vectors.
A computational study of hydrogen-bonded complexes of HKrCl: N2⋯HKrCl, OC⋯HKrCl, and HF⋯HKrCl
Authors: McDowell Sean A. C.
Published: August 2003

An ab initio computational study of the properties of weakly bound hydrogen-bonded dimers of HKrCl and the small molecules N2, CO, and HF was undertaken at the MP2/6-311++G(2d,2p) level of theory. These complexes, the linear N2⋯HKrCl and OC⋯HKrCl dimers, and the nonlinear HF⋯HKrCl dimer, were found to have large blue shifts of the H–Kr stretching frequency, accompanied by a decrease in the infrared intensity of the stretching mode and compression of the H–Kr bond. We examine the charge density reorganization within the HKrCl molecule on complexation and offer an explanation for these unusual vibrational results.
Photodetachment of hydrated oxalate dianions in the gas phase, C2O42−(H2O)n (n=3–40): From solvated clusters to nanodroplet
Authors: Wang Xue-Bin , Yang Xin , Nicholas John B. , Wang Lai-Sheng
Published: August 2003

Oxalate (C2O42−) is a common dianion, but it is not electronically stable as an isolated species due to the strong intramolecular Coulomb repulsion and can only exist as solvated species. We observed hydrated oxalate clusters, C2O42−(H2O)n for n=3–40, using electrospray ionization of an oxalate salt solution and studied their energetics and stabilities using photodetachment photoelectron spectroscopy and theoretical calculations. We found that the smallest observable solvated cluster, C2O42−(H2O)3, has an adiabatic electron binding energy of ∼0.0 eV, i.e., a minimum of three H2O is required to stabilize C2O42− in the gas phase. Theoretical calculations show that the first four waters bind tightly to C2O42−, each forming two H-bonds with C2O42− peripherally without interwater H-bonding. The charges of the dianion were stabilized sufficiently that additional waters beyond n=4 form only single H-bonds with C2O42− and interwater H-bonding was observed starting at n=5. The repulsive Coulomb barrier, characteristic of multiply-charged anions, was estimated from photon energy-dependent spectra for the smaller clusters and was found to decrease with increasing n. We observed that photoelectron intensities for features of the solute decreased as n increased, whereas detachment signals from the solvent became dominant for the large solvated clusters. This observation suggested that C2O42− is situated in the center of the solvated clusters so that electrons detached from the solute were suppressed by the surrounding solvent layer.
A discrete solvent reaction field model for calculating molecular linear response properties in solution
Authors: Jensen Lasse , van Duijnen Piet Th. , Snijders Jaap G.
Published: August 2003

A discrete solvent reaction field model for calculating frequency-dependent molecular linear response properties of molecules in solution is presented. The model combines a time-dependent density functional theory (QM) description of the solute molecule with a classical (MM) description of the discrete solvent molecules. The classical solvent molecules are represented using distributed atomic charges and polarizabilities. All the atomic parameters have been chosen so as to describe molecular gas phase properties of the solvent molecule, i.e., the atomic charges reproduce the molecular dipole moment and the atomic polarizabilities reproduce the molecular polarizability tensor using a modified dipole interaction model. The QM/MM interactions are introduced into the Kohn–Sham equations and all interactions are solved self-consistently, thereby allowing for the solute to be polarized by the solvent. Furthermore, the inclusion of polarizabilities in the MM part allows for the solvent molecules to be polarized by the solute and by interactions with other solvent molecules. Initial applications of the model to calculate the vertical electronic excitation energies and frequency-dependent molecular polarizability of a water molecule in a cluster of 127 classical water molecules are presented. The effect of using different exchange correlation (xc)-potentials is investigated and the results are compared with results from wave function methods combined with a similar solvent model both at the correlated and uncorrelated level of theory. It is shown that accurate results in agreement with correlated wave function results can be obtained using xc-potentials with the correct asymptotic behavior.
Field-driven hysteretic and reversible resistive switch at the Ag–Pr0.7Ca0.3MnO3 interface
Authors: Baikalov A. , Wang Y. Q. , Shen B. , Lorenz B. , Tsui S. , Sun Y. Y. , Xue Y. Y. , Chu C. W.
Published: August 2003

The hysteretic and reversible polarity-dependent resistive switch driven by electric pulses is studied in both Ag/Pr0.7Ca0.3MnO3/YBa2Cu3O7 sandwiches and single-layer Pr0.7Ca0.3MnO3 strips. The data demonstrate that the switch takes place at the Ag–Pr0.7Ca0.3MnO3 interface. A model, which describes the data well, is proposed. We further suggest that electrochemical migration is the cause for the switch.
Electronic photodissociation spectroscopy of Au4+⋅Arn, n=0–4: Experiment and theory
Authors: Schweizer Alexia , Weber J. Mathias , Gilb Stefan , Schneider Holger , Schooss Detlef , Kappes Manfred M.
Published: August 2003

We report experimental and theoretical studies of the electronic absorption spectra of mass selected Au4+⋅Arn (n=0–4) clusters in the photon energy range of 2.14–3.35 eV. Photodissociation spectra were recorded by monitoring ion depletion upon photon absorption, yielding absolute photodissociation cross sections. The experimental spectra were interpreted by comparing them with calculations of the optical response in the framework of time-dependent density functional theory using cluster structures calculated both by density functional theory (B3-LYP functional) and by ab initio calculations at the RI-MP2 level.
Structure of neutral and charged FenCO clusters (n=1–6) and energetics of the FenCO+CO→FenC+CO2 reaction
Authors: Gutsev Gennady L. , Bauschlicher Charles W. , Andrews Lester
Published: August 2003

The electronic and geometrical structure of the ground and excited states of FenCO, FenCO−, and FenCO+ (n=2–6) are computed using density functional theory (DFT). Several hybrid and pure DFT methods are tested on FeCO and Fe2CO where experimental data are available. The pure DFT methods are superior to hybrid methods in reproduction of experimental spectroscopic data, except for the dissociation energy of FeCO. CO is twofold coordinated in Fe2CO, Fe3CO, and Fe4CO, threefold coordinated in Fe5CO, and fourfold in Fe6CO. While the Boudouard-type disproportionation reaction FenCO+CO→FenC+CO2 is endothermic by 1.59, 1.10, and 0.55 eV for FeCO, Fe2CO, and Fe3CO, respectively, it becomes exothermic beginning with n=4. The reaction barrier decreases from 3.5 eV for FeCO to 1.3 eV for Fe4CO. The most exothermic (by 0.42 eV) reaction is Fe6CO++CO→Fe6C++CO2. It is found that the catalytic ability increases with clusters size due to the decreasing FenC–O (or increasing Fen–C) bond strength. The Fen–CO binding energy varies slowly with cluster size and therefore does not significantly influence the variation in the energetics of the Boudouard-type reaction with cluster size.
Photoconduction in organic donor–acceptor systems
Authors: Im C. , Tian W. , Bässler H. , Fechtenkötter A. , Watson M. D. , Müllen K.
Published: August 2003

Stationary photoconduction in either a phenyl-substituted poly-phenylenevinylene copolymer (PhPPV) or an alkylated hexa-peri-hexabenzocoronene (HBC) doped by perylenediimide (PdI) at a broad range of dopant concentrations has been measured and compared to previous results on PhPPV doped by trinitrofluorenone (TNF). At moderate concentration, the yield of the photogeneration is virtually invariant regardless of the system and blend ratio because practically every primary excitation dissociates at a donor–acceptor site and the subsequent escape from the coulombic potential is virtually system-independent. At dopant concentrations >10% the yield of that escape process increases by two to three orders of magnitude.
Classical Wigner phase space approximation to cumulative matrix elements in coherent control
Authors: McQuarrie Barry R. , Abrashkevich Dmitri G. , Brumer Paul
Published: August 2003

The classical limit of the Wigner–Weyl representation is used to approximate products of bound-continuum matrix elements that are fundamental to many coherent control computations. The range of utility of the method is quantified through an examination of model problems, single-channel Na2 dissociation and multiarrangement channel photodissociation of CH2IBr. Very good agreement with the exact quantum results is found for a wide range of system parameters.
Spectroscopy of Na+⋅Rg and transport coefficients of Na+ in Rg(Rg=He–Rn)
Authors: Viehland Larry A. , Lozeille Jérôme , Soldán Pavel , Lee Edmond P. F. , Wright Timothy G.
Published: August 2003

High-level ab initio calculations are used to obtain accurate potential energy curves for Na+⋅Kr, Na+⋅Xe, and Na+⋅Rn. These data are used to calculate spectroscopic parameters for these three species, and the data for the whole Na+⋅Rg series (Rg=He–Rn) are compared. Potentials for the whole series are then used to calculate both mobilities and diffusion coefficients for Na+ moving through a bath of each of the six rare gases, under conditions that match previous experimental determinations. Different available potentials and experimental data are then statistically compared. It is concluded that the present potentials are very accurate. The potential and other data for Na+⋅Rn appear to be the first such reported.
One- and two-color photoelectron imaging of the CO molecule via the B 1Σ+ state
Authors: Katayanagi Hideki , Matsumoto Yoshiteru , de Lange Cornelis A. , Tsubouchi Masaaki , Suzuki Toshinori
Published: August 2003

This paper is concerned with photoelectron imaging following one-color (2+1) and two-color (2+1′) resonance enhanced multiphoton ionization in the CO molecule. After the two-photon absorption step B 1Σ+ (v′=0)←←X 1Σ+ (v″=0) or B 1Σ+ (v′=1)←←X 1Σ+ (v″=0), the subsequent one-photon ionization X 2Σ+(v+)←B 1Σ+ (v′=0,1) shows deviations from the expected Δv=0 Franck–Condon propensity rule. The results are in good agreement with a previous study using time-of-flight photoelectron spectroscopy [Sha et al., J. Chem. Phys. 99, 4334 (1993)]. The experimental photoelectron kinetic energy spectra and their angular distributions are analyzed, and the essential role played by “superexcited” Rydberg states with an A 2Π ion core in this process is examined. Moreover, photoelectron imaging methods appear to be useful in extracting information about superexcited states.
An integral-equation theory for a self-interacting polymer adsorbed at an interface
Authors: Cai Jun , Prausnitz John M.
Published: August 2003

An integral-equation theory based on the Born–Green–Yvon (BGY) hierarchy for a self-interacting polymer is used to describe a polymer adsorbed at an oil–water interface. The polymer is represented by a square-well chain. The interaction between a polymer segment and an oil–water interface is represented by an asymmetric square-well potential where the well-depth on one side reflects water–polymer and the well depth on the other side reflects oil–polymer interactions. To truncate the BGY hierarchy, we introduce two approximations: First we use the Markov-chain approximation for intra-molecular correlation functions, and second, we use the effective intra-molecular energy in the bulk to approximate that at the interface. The results are compared with Monte Carlo-simulation data. For short chains, when the attractive interaction between the segments is weak, the theory is in good agreement with Monte Carlo simulation. Stronger segment–segment attractive interactions increase adsorption.
Influence of the ion mean free path and the role of oxygen in nitriding processes
Authors: Figueroa C. A. , Ochoa E. , Alvarez F.
Published: August 2003

In this article we report the mechanism involved in the nitriding process of stainless steel by ion implantation. The importance of the nitrogen ion mean-free path on the stainless steel nitrated layer obtained by using a broad ion source is established. The energy distribution of the nitrogen ions arriving at the substrate is basically determined by the inelastic scattering suffered by the ions on the way to the material surface, i.e., the ion mean-free-path λ. Besides this effect, the ion current density arriving at the sample surface is modified by the dispersion introduced by the collisions of the nitrogen ions with the chamber background molecules. This multiple scattering process is modeled assuming a stochastic phenomenon and its conclusions used to explain experimental results of hardness, diffusion profile, and nitrated layer thickness. A controlled oxygen-background partial pressure is also introduced and its role on the nitrated layer reported. At relatively low ion energies and oxygen partial pressures, both the diffusion zone and nitrated layer thickness are controlled by the ion current density. Indeed, they follow a linear relationship, provided that the composition of the nitrated layer does not change, i.e., the amount of incorporated nitrogen does not modify the original material crystalline phase.
Watching molecules reorient in liquid crystal droplets with multiphoton-excited fluorescence microscopy
Authors: Higgins Daniel A. , Luther Brenda J.
Published: August 2003

A new form of time-resolved multiphoton-excited fluorescence imaging is described and used to study electric-field-induced reorientation dynamics in polymer-dispersed liquid crystal (LC) films. This method provides information on the static and dynamic LC orientation via polarization-dependent three-photon excitation of the nematic ultraviolet chromophores in these materials. Static fluorescence images are obtained with ≈235 nm resolution in all three dimensions. In dynamics studies, the three-photon-excited fluorescence is recorded as a function of time and position over individual LC droplets, as an applied electric field is switched on and off. Time-resolved images with ≈235 nm spatial resolution and 200 μs time resolution are obtained. Movies depicting the local reorientation dynamics are prepared from these data and are presented for common ellipsoidal LC droplets and for novel toroidal droplets. The field-induced reorientation dynamics within the ellipsoidal droplets are shown to be more complex (i.e., spatially variable) than in the toroidal droplets. Dynamical complexity is concluded to arise from LC organizational complexity in the droplets. The bipolar configuration found in ellipsoidal droplets incorporates bend and splay deformations of the nematic phase and two disclination points. In contrast, toroidal droplets incorporate a simpler toroidal configuration in which only bend deformations occur.
Dissipative dynamics of spin-dependent electron–hole capture in conjugated polymers
Authors: Karabunarliev Stoyan , Bittner Eric R.
Published: August 2003

Spin-dependent electron–hole (e–h) recombination in poly(p-phenylenevinylene) chains is modeled by the dissipative dynamics of the multilevel electronic system coupled to the phonon bath. The underlying Hamiltonian incorporates the Coulomb and exchange interactions of spin-singlet and spin-triplet monoexcitations in Wannier-orbital basis and their coupling to the prominent Franck–Condon active modes. In agreement with experiment, we obtain that the ratio of singlet versus triplet exciton formation rates is strongly conjugation-length dependent and increasing on going from the model dimer to the extended chain. The result is rationalized in terms of a cascade interconversion mechanism across the electronic levels. In parallel to the direct formation of spin-dependent excitons, e–h capture is found to generate long-lived charge-transfer states, whose further phonon-mediated relaxation to the bottom of the density of states is hindered by the near e–h symmetry of conjugated hydrocarbons. Being nearly spin independent, such states most likely form an intersystem crossing pre-equilibrium, from which the singlet e–h binding channel is about ten times faster than the triplet one.
Comparison of the stability of blends of chemically identical and different homopolymers in the bulk and in a film
Authors: Kosmas Marios K. , Vlahos Costas H.
Published: August 2003

We present a criterion of the stability of a polymeric blend of two species in terms of the three different interaction parameters between the same or different monomeric units. Long chain correlations among different chains are taken into account by including the contribution from all configurations having one loop. The special cases of chemically identical polymers of different size where all three interaction parameters become the same can be deduced and compared with that of different polymers. The stability limits of the system is analyzed in the three dimensional (3D) and in the two dimensional (2D) space in order to describe the behavior of a blend in the bulk and in a thin film where the 2D character of the chains is increased. Going from the 3D to the 2D case while the stability of a system of chemically identical homopolymers of different size decreases that of two different homopolymers increases but may decrease too.
Replica exchange molecular dynamics simulations of reversible folding
Authors: Rao Francesco , Caflisch Amedeo
Published: August 2003

The replica exchange molecular dynamics (REMD) approach is applied to a 20-residue three-stranded antiparallel β-sheet peptide. At physiologically relevant temperature REMD samples conformational space much more efficiently than constant temperature molecular dynamics (MD) and allows reversible folding (312 folding events during a total simulation time of 32 μs). The energetic and structural properties during the folding process are similar in REMD and conventional MD at the temperature values where there is enough statistics for the latter. The simulation results indicate that the unfolded state contains a significant amount of non-native interactions especially at low temperature. The folding events consist of a gradual replacement of non-native contacts with native ones which is coupled with an almost monotonic decrease of the REMD temperature.
Conformations of attractive, repulsive, and amphiphilic polymer chains in a simple supercritical solvent: Molecular simulation study
Authors: Lı́sal Martin , Nezbeda Ivo
Published: August 2003

Using the configurational-bias Monte Carlo method combined with the parallel tempering technique, solvent driven changes in polymer conformations in a supercritical solvent are systematically investigated using simple molecular models. The solvent is modelled as a square-well fluid, and the polymer is made up of a flexible chain of tangentially touching hard spheres and/or square-well spheres. The mean square end-to-end distance and radius of gyration are computed for various ratios of square-well and hard-sphere segments and a range of thermodynamic conditions. The simulation results show that conformation behavior of amphiphilic chains is rather complex and it is not a simple combination of the conformation behavior of the attractive and repulsive chains. The main finding is that the conformations of amphiphilic chains is determined primarily by attractive intermolecular interactions between the polymer segments and molecules of the solvent.
The anisotropic free energy of the Lennard-Jones crystal-melt interface
Authors: Morris James R. , Song Xueyu
Published: August 2003

We have calculated the free energy of the crystal-melt interface for the Lennard-Jones system as a function of crystal orientation, near zero pressure, by examining the roughness of the interface using molecular dynamic simulations. The anisotropy is weak, but can be accurately resolved using this approach due to the sensitivity of the fluctuations on the anisotropy. We find that the anisotropy can be described well using two parameters, based upon a low-order expansion satisfying cubic symmetry. The results are in good agreement with previous calculations of the free energies, based upon simulations used to calculate the reversible work required to create the interfaces. The weak anisotropy is also in reasonable agreement: The work here and the work of Davidchack and Laird [R. L. Davidchack and B. B. Laird, J. Chem. Phys. 118, 7651 (2003)] both predict γ100>γ110>γ111. The only discrepancy is that we find a smaller value for the difference γ100−γ111 by an amount larger than the combined error bars.
Molecular fractionation with conjugate caps for full quantum mechanical calculation of protein–molecule interaction energy
Authors: Zhang Da W. , Zhang J. Z. H.
Published: August 2003

A scheme to calculate fully quantum mechanical (ab initio) interaction energy involving a macromolecule like protein is presented. In this scheme, the protein is decomposed into individual amino acid-based fragments that are treated with proper molecular caps. The interaction energy between any molecule and the given protein is given by the summation of interactions between the molecule and individually capped protein fragments. This scheme, termed molecular fractionation with conjugate caps (MFCC), makes it possible and practical to carry out full quantum mechanical (ab initio) calculation of intermolecular interaction energies involving proteins or other similar biological molecules. Numerical tests performed on the interaction energies between a water molecule and three small peptides demonstrate that the MFCC method can give excellent ab initio interaction energies compared to the exact treatment in which the whole peptides are included in the calculation. The current scheme scales linearly with the atomic size of the protein and can be directly applied to calculating real protein–molecule interaction energies by using fully quantum (ab initio) methods that are otherwise impossible. The success of the current method is expected to have a powerful impact in our prediction of protein interaction energies including, e.g., protein–drug interactions.
Effects of guest hydrophobic molecule on stability of ordered meso structure of a surfactant/water system
Authors: Imai Masayuki , Teramoto Takashi , Takahashi Ikuko , Nishiura Yasumasa
Published: August 2003

Addition of hydrophobic guest molecule (C12H26) into the nonionic surfactant/water system (C16E7/D2O) system modifies the phase behavior between the lamellar and column phases. The distribution of the added guest molecule in the microstructure and the interfacial structure is examined by using a small angle neutron scattering technique. The characteristic length and the interfacial thickness of the microstructure are deformed in order to optimize the distribution of the guest molecules. The obtained experimental results including the existence of the double gyroid and rhombohedral phases are in agreement with those of the simple model of diblock copolymers.
Pt and Pt2 on MgO(100) and BaO(100): structure, bonding, and chemical properties
Authors: Grönbeck Henrik , Broqvist Peter
Published: August 2003

The density functional theory has been applied to study the interaction of platinum (atoms, dimers, and layers with equal number of platinum atoms as oxygen surface atoms) with the (100) surfaces of MgO and BaO. The systems are characterized with respect to preferred geometrical configurations and electronic structure. Platinum is found to interact considerably stronger (∼1.5 eV) with BaO than with MgO. The mapping of the potential energy surface suggests that monomer diffusion at room temperature is unlikely on both studied supports. Dimer diffusion, however, should be possible to observe at room temperature on MgO(100). For layer adsorption, a marked difference is predicted between MgO and BaO. Whereas the Pt/MgO interaction is weak, the Pt/BaO interaction is close to that of atoms and dimers. Substrate induced modifications of chemical properties are also investigated by studying variations in CO adsorption energy. CO is predicted to bind more strongly to supported atoms and dimers than to the corresponding gas phase clusters or the Pt(111) surface. Moreover, adsorbed CO is found to enhance the platinum/support bond strength.
Giant magnetocurrent exceeding 3400% in magnetic tunnel transistors with spin-valve base layers
Authors: van Dijken Sebastiaan , Jiang Xin , Parkin Stuart S. P.
Published: August 2003

We report large magnetic field sensitivities of the collector current in a three-terminal magnetic tunnel transistor device with spin-valve metallic base layers. Giant magnetocurrents exceeding 3400% result from strong spin-dependent filtering of electrons traversing perpendicular to the spin-valve layers at energies well above the Fermi energy. The output current of the device can readily be tuned into the microampere regime by increasing the bias voltage across the tunnel barrier. With its giant magnetocurrent and reasonable output current, the magnetic tunnel transistor is a promising candidate for future magnetoelectronic devices.