bluuebunny/crossref_metadata_2025 huggingface dataset:
Drugs of Abuse – The Myth of Creativity and the Reality of Destruction
Authors: SYLVESTER VIZI E
Published: April 2007

In every culture, man has used drugs to dispel anxiety, stimulate productivity, and to increase the feelings of joy and satisfaction. Drugs have also had an undeniable influence on art and culture. These substances become referred to as ‘drugs of abuse’ if their repeated consumption is triggered or induced by psychological or physical compulsion, often leading to conflict with society, either due to neglect of family or social duties, and also to criminal activities in order to obtain the materials. Drug abuse particularly affects young people and has become one of the most important and widely discussed issues in society. It is therefore an important task in medical science to find answers to how drugs exert their effect and what leads to addiction and permanent consumption.
Materiality in materials
Authors: Tilley Christopher
Published: April 2007

I really welcome Tim Ingold's paper because intellectual debates about the meaning and significance of material culture or general attempts to theorize material forms are comparatively rare as opposed to the mass of literature discussing particular categories of things. In the paper he systematically sets out to oppose a concept of materiality (apparently worthless) to the study of materials which, in contrast, he suggests, may lead to many new insights and understandings. I do not find this supposed opposition all that helpful. Indeed I believe that it may have a conservative and reactionary effect in relation to studies of material culture which is no doubt contrary to Ingold's intentions.
An archaeology of material stories. Dioramas as illustration and the desire of a thingless archaeology
Authors: Nilsson Björn
Published: April 2007

No matter what kind of archaeologist you think you are, Ingold's text evokes emotional and intellectual reactions concerning a core of archaeology: how to deal scientifically with the material world. It pinpoints some serious problems within today's archaeology, not least field archaeology. Given this, I will try to comment on Ingold's text from a practical archaeological point of view. Before I turn to the tangible fields of sand, clay, stone fragments and almost vanished materials, I will take the opportunity to associate Ingold's point of view with a well-known geographical tradition, since some concepts appear to be quite similar.
On beasts in breasts. Another reading of women, wildness and danger at Çatalhöyük
Authors: Gifford-Gonzalez Diane
Published: April 2007

Since its discovery, Çatalhöyük's iconography has provoked interpretative comment. In a series of writings, Hodder critiqued earlier interpretations of the Çatalhöyük corpus, arguing for asymmetrical gender relations of an enduring and particular type in the European past. While recent research at Çatalhöyük appears to have tempered some of Hodder's interpretative oppositions and scope, it is worthwhile to propose an alternate contextual approach to his original oppositions. This begins with the multiple examples of small carnivores' heads encysted in what may be clay effigies of human breasts and reads the same corpus as involving gender not solely with danger or death, but also with food and fleshly transformation. In this interpretation, the roles and essences of wild and domestic animals, women and men, food and death, are more complex, interpenetrating and mutable. Building on recent work at the site, it is possible to propose the existence of zones of transformation within households.
Elements for contracting and regulating private security and military companies
Authors: Cottier Michael
Published: April 2007

Key issues raised by the use and operation of private military and security companies, particularly in conflict areas, are their accountability and how to control them. National regulation, however, is still rare. States have a role to play first as contractors. Considered selection, contracting and oversight procedures and standards may help promote respect for human rights and international humanitarian law by companies and their staff. Secondly, territorial and exporting states may consider adopting regulations to increase control and promote accountability. In view of this still largely unregulated phenomenon, this contribution considers elements of contracting and regulatory options.
Corporate civil liability for violations of international humanitarian law
Authors: Mongelard Eric
Published: April 2007

The fact that international humanitarian law violations are in the vast majority of cases prosecuted in criminal courts does not mean that a civil liability for these violations does not exist. This article seeks to explore the concept of civil liability of corporations involved in violations of international humanitarian law by providing an overview of the different legal issues raised by this concept and its implementation in both common law and continental law systems.
Antarctic dehydration 1998–2003: Polar Ozone and Aerosol Measurement III (POAM) measurements and Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) results with four meteorological models
Authors: Nedoluha Gerald E. , Benson Craig M. , Hoppel Karl W. , Alfred Jerome , Bevilacqua Richard M. , Drdla Katja
Published: April 2007

We present Polar Ozone and Aerosol Measurement III (POAM) measurements of Antarctic dehydration from 1998 to 2003 and compare these measurements with calculations performed with the Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) microphysical model. Previous work has shown that while dehydration is not very sensitive to reasonable changes of microphysical parameters, it is very sensitive to changes in temperature. We shall therefore compare dehydration as measured by POAM with IMPACT model runs based on four meteorological analyses: United Kingdom Meteorological Office (UKMO), European Centre for Medium‐Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction Climate Prediction Center (NCEP‐CPC), and NCEP reanalysis. For the years 1998–2000, the agreement between the minimum water vapor found in the POAM measurements and that from all of the model runs is always within 0.5 ppmv. The disagreement between POAM and some of the models is larger in the years 2001–2003, growing as large as ∼1 ppmv, but the agreement between the minimum POAM water vapor and the water vapor calculated using the NCEP reanalysis is always within 0.2 ppmv. If we infer a temperature bias from the difference between the NCEP reanalysis model runs and the POAM minimum water vapor measurements, we find that this temperature bias is <0.5 K for each of the 6 years from 1998 to 2003, but it is often larger for the other meteorological analyses.
Droplet growth by gravitational coagulation enhanced by turbulence: Comparison of theory and measurements
Authors: Riemer N. , Wexler A. S. , Diehl K.
Published: April 2007

While it is well known that cloud droplets grow in an inherently turbulent environment, the role of turbulence is only now being elucidated. To shed light on this issue, we compare published measurements of droplet growth by collision in turbulent flow with numerical simulations. Because the measurements demonstrate an accelerated growth under turbulent conditions compared to laminar ones, the data clearly cannot be reproduced using the well‐established kernel for sedimentation under laminar conditions. By employing a collision kernel that has been recently derived from direct numerical simulations, we perform sensitivity studies and quantify the parameter ranges that are compatible with the experimental data. This experiment does not enable us to uniquely determine the model parameters but we were able to place constraints on the form of acceptable models that reproduce the experimental data successfully. Moreover, we gain insight into how laboratory experiments could be improved to aid model validation.
Geomagnetically induced currents in an electric power transmission system at low latitudes in Brazil: A case study
Authors: Trivedi Nalin B. , Vitorello Ícaro , Kabata Wanderli , Dutra Severino L. G. , Padilha Antonio L. , Bologna Mauricio S. , de Pádua Marcelo B. , Soares Alexandre Pinhel , Luz Guilherme Sarcinelli , Pinto Fabio de A. , Pirjola Risto , Viljanen Ari
Published: April 2007

Geomagnetically induced currents (GICs) are a ground end manifestation of space weather processes. During large geomagnetic storms, GICs flow between the grounding points of power transformers and along electric power transmission lines connecting the transformers. In high‐latitude regions, damages to power transformers are reported where storm time geomagnetic variations are very rapid and large (>1000 nT), and hence the GICs as large as or even greater than 100 A end up flowing through the windings of power transformers. At low latitudes, geomagnetic variations are less severe, and hence much smaller GIC values are generally reported there. However, the flow of GICs and their effects on power transformers are complex processes, and careful evaluation is needed even in such low‐latitude regions as, for example, Brazil. We report here a study on GIC measurements in Brazil conducted under a cooperative project between FURNAS (the Brazilian electric power company) and the National Institute for Space Research. During a large geomagnetic storm, which took place on 7–10 November 2004, the GIC amplitudes, measured on the basis of geomagnetic variations in 500 kV power transmission lines in the S–E region of Brazil, were found to be around 15 A.
A new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models
Authors: Seibert Jan , McGlynn Brian L.
Published: April 2007

Gridded digital elevation data, often referred to as DEMs, are one of the most widely available forms of environmental data. Topographic analysis of DEMs can take many forms, but in hydrologic and geomorphologic applications it is typically used as a surrogate for the spatial variation of hydrological conditions (topographic indices) and flow routing. Here we report on a new flow routing algorithm and compare it to three common classes of algorithms currently in widespread use. The advantage of the new algorithm is that unrealistic dispersion on planar or concave hillslopes is avoided, whereas multiple flow directions are allowed on convex hillslopes. We suggest that this new triangular multiple flow direction algorithm (MD∞) is more appropriate for a range of flow routing and topographic index applications.
Seasonal‐longitudinal variation of substorm occurrence frequency: Evidence for ionospheric control
Authors: Wang H. , Lühr H.
Published: April 2007

Based on 2760 well‐defined substorm onsets in the northern hemisphere and 1432 in the southern hemisphere observed by the FUV (Far Ultraviolet) Imager on board IMAGE (Imager for Magnetosphere‐to‐Aurora Global Exploration) spacecraft, a statistical study is performed for both hemispheres. The main emphasis is put on a possible dependence of the substorm occurrence frequency on season and longitude (S/L). It was found that around December solstice UT noon‐time and around June solstice UT nighttimes are more favorable for substorms to occur. The occurrence frequency varies by a factor of 2. The sum of ionospheric Pedersen conductances of both hemispheres caused by solar illumination in the nightside auroral regions can account for the S/L dependence. Lower total conductivity seems to reduce the trigger level. We find that the IMF threshold for initiating a substorm is on average lower during favorable times, thus, substorms can occur more frequently.
Particle and impurity transport in the Axial Symmetric Divertor Experiment Upgrade and the Joint European Torus, experimental observations and theoretical understanding
Authors: Angioni C. , Carraro L. , Dannert T. , Dubuit N. , Dux R. , Fuchs C. , Garbet X. , Garzotti L. , Giroud C. , Guirlet R. , Jenko F. , Kardaun O. J. W. F. , Lauro-Taroni L. , Mantica P. , Maslov M. , Naulin V. , Neu R. , Peeters A. G. , Pereverzev G. , Puiatti M. E. , Pütterich T. , Stober J. , Valovič M. , Valisa M. , Weisen H. , Zabolotsky A. ,   ASDEX Upgrade Team,   JET EFDA Contributors
Published: April 2007

Experimental observations on core particle and impurity transport from the Axial Symmetric Divertor Experiment Upgrade [O. Gruber, H.-S. Bosch, S. Günter et al., Nucl Fusion 39, 1321 (1999)] and the Joint European Torus [J. Pamela, E. R. Solano, and JET EFDA Contributors, Nucl. Fusion 43, 1540 (2003)] tokamaks are reviewed and compared. Robust general experimental behaviors observed in both the devices and related parametric dependences are identified. The experimental observations are compared with the most recent theoretical results in the field of core particle transport.
Effect of eccentricity on the spin-wave spectrum of NiFe∕Cu∕NiFe pillars with elliptical cross section
Authors: Gubbiotti G. , Madami M. , Tacchi S. , Socino G. , Carlotti G. , Ono T.
Published: April 2007

Brillouin light scattering (BLS) has been exploited to study the effect of eccentricity on the magnetic normal-mode spectrum of five arrays of trilayered pillars with an elliptical cross section and different eccentricity ε in the range between 1 and 3. The pillars consist of a pair of 10nm thick Permalloy (NiFe) layers separated by a Cu spacer with thickness of 10nm. Several discrete spin-wave modes were observed in the BLS spectra and their frequencies tracked as a function of the in-plane direction of the applied magnetic field. All mode frequencies exhibit a uniaxial anisotropy, induced by the shape of the elements, which increases with ε. A satisfactory reproduction of the measured frequencies was achieved by three-dimensional micromagnetic simulations, solving the discretized Landau-Lifshitz-Gilbert equation over the layered structure in the time domain and performing a local Fourier transform.
Magnetic phase diagrams for models of synthetic antiferromagnets
Authors: Rößler U. K. , Bogdanov A. N.
Published: April 2007

Phenomenological macrospin models have been studied to elucidate the field-driven reorientation transitions in antiferromagnetically coupled magnetic thin-film elements with uniaxial anisotropy. For planar bilayer systems, there are four topologically different phase diagrams depending on the ratio of anisotropy to exchange energy. Only for weak anisotropies, the usual phase diagram of antiferromagnets with a spin flop is realized. Analytic and numeric results are presented for a model of a synthetic antiferromagnet composed of four layers, where two ferromagnetically coupled bilayers are coupled antiferromagnetically. Applied fields may stabilize collinear ferrimagnetic and canted phases in these four-layer systems for certain ranges of the ratio between ferromagnetic exchange and antiferromagnetic exchange.
Ferromagnetic semiconductor material based on mechanochemical mixture of polyaniline polystyrene and Fe nanoparticles
Authors: Rakhimov R. R. , Bah R. , Hwang J. S. , Solodovnikov S. P. , Alexandrov I. A. , Karmilov A. Yu. , Shevchenko V. G. , Obolonkova E. S. , Aleksandrov A. I.
Published: April 2007

We report on mechanochemical synthesis and magnetic and electric properties of organic polymeric semiconductor that contains paramagnetic and ferromagnetic particles. As starting materials we used polyaniline (emeraldine base), polystyrene, FeCl3, and elemental sulfur. These components were chosen for the purpose of obtaining semiconductor polymer composite containing magnetic iron nanoparticles and having flexible thermomechanical properties. The presence of nanoparticles was evidenced by scanning electron microscopy. The value of conductivity of the Fe-doped polymer composite was increased by several orders of magnitude compared to the initial undoped polyaniline. Temperature dependence of the conductivity shows semiconductor character of the composite material.
X-ray diffraction analysis and magnetic behavior of amorphous Fe15Co17Ni58B10 nanowires obtained by electrochemical deposition
Authors: Vieyra M. , Meydan T. , Borza F.
Published: April 2007

Fe 15 Co 17 Ni 58 B 10 nanowire arrays have been deposited in alumina templates by electrochemical deposition. For comparison, the same alloy was used to deposit films on CuBe substrate. The change in boron concentration from 3% to 10% in the electrolyte promoted the amorphous phase in the films on the CuBe substrate and a partial amorphous phase in the nanowires. Thermal treatment of the deposited films and nanowire arrays at 600°C promoted recrystallization. Magnetic hysteresis loops for 100 and 200nm nanowire arrays are “wasp waisted.” There is no evidence of a sharp reversal for the out-of-plane or in-plane hysteresis loops, just a smooth curve indicating a coherent rotation during the magnetization reversal. Annealing the 200nm nanowire array at 600°C for 1h gives rise to a mixed hysteresis loop, which can be attributed to competing domain configurations. An alternative explanation for this behavior is that there might be a phase separation between Fe, Ni, and Co in the nanowire environment due to the short range ordering of the alloy.
On multidimensional inverse scattering for Stark Hamiltonians
Authors: Adachi Tadayoshi , Maehara Katsuhiro
Published: April 2007

Based on the Enss-Weder [“The geometrical approach to multidimensional inverse scattering,” J. Math. Phys. 36, 3902–3921 (1995)] time-dependent method, we study one of multidimensional inverse scattering problems for Stark Hamiltonians. We first show that when the space dimension is greater than or equal to 2, the high velocity limit of the scattering operator determines uniquely the potential such as ∣x∣−γ with γ>1∕2 which is short range under the Stark effect. This is an improvement of previous results obtained by Nicoleau [“Inverse scattering for Stark Hamiltonians with short-range potentials,” Asymptotic Anal. 35, 349–359 (2003)] and Weder [“Multidimensional inverse scattering in an electric field,” J. Funct. Anal. 139, 441–465 (1996)]. Moreover, we prove that for a given long-range part of the potential under the Stark effect, the high velocity limit of the Dollard-type modified scattering operator determines uniquely the short-range part of the potential.
Observation of a transition in the water-nanoparticle formation process at 167K
Authors: Bauerecker S. , Wargenau A. , Schultze M. , Kessler T. , Tuckermann R. , Reichardt J.
Published: April 2007

Rapid-scan Fourier transform infrared spectroscopy of the vapor/solid formation process of water nanoparticles in the 180–140K temperature range at thermal-equilibrium conditions is reported. At 167K a transition in the formation process was observed: the particle volume quintuples and the particle formation time triples within a temperature interval of ±0.4K caused by the temperature control. The authors interpret this behavior by an abrupt change in the nucleation rate of the H2O monomers in He buffer gas kept at 167K and 200mbar. A size and shape analysis of the particles during the formation process was carried out by application of the discrete dipole approximation method which delivers excellent accordance between experimental and calculated mid-IR spectra. Compared to other compact shapes (cube, prolate ellipsoid, and hexagonal prism) the ideal spherical shape fits the experimental spectra best. A distinct change in shape by particle conversion or agglomeration could be excluded to be involved in the formation process. As a possible explanation of the observed phenomenon, a transition from vapor/liquid/solid to vapor/solid nucleation with decreasing temperature is considered which was recently theoretically predicted by van Dongen and co-workers [J. Chem. Phys. 117, 5647 (2002); private communication; J. Chem. Phys. 120, 6314 (2004)].
Fundamental measure theory in cylindrical geometry
Authors: Malijevský Alexandr
Published: April 2007

Density functional theory as proposed by Rosenfeld [Phys. Rev. Lett. 63, 980 (1989)] is used to study hard sphere mixture exposed by cylindrically symmetric external field. Exploiting the symmetry of the system, explicit formulas for the weighted densities are derived. The resulting density profiles are compared with new grand canonical Monte Carlo simulations. The comparison reveals very good agreement between the predicted and simulated results even at high densities and very narrow pores. Finally, simple algorithms for computing complete elliptic functions of the first and second kinds that occur in the derived formulae are presented to make the paper self-contained.
Spin-orbit vibronic coupling in Π3 states of linear triatomic molecules
Authors: Mishra Sabyashachi , Poluyanov Leonid V. , Domcke Wolfgang
Published: April 2007

The Renner-Teller vibronic-coupling problem of a Π3 electronic state of a linear molecule is analyzed with the inclusion of the spin-orbit coupling of the Π3 electronic state, employing the microscopic (Breit-Pauli) spin-orbit coupling operator for the two unpaired electrons. The 6×6 Hamiltonian matrix in a diabatic spin-electronic basis is obtained by an expansion of the molecular Hamiltonian in powers of the bending amplitude. The symmetry properties of the Hamiltonian with respect to the time-reversal operator and the relativistic vibronic angular momentum operator are analyzed. It is shown that there exists a linear vibronic-coupling term of spin-orbit origin, which has not been considered so far in the Renner-Teller theory of Π3 electronic states. While two of the six adiabatic electronic wave functions do not exhibit a geometric phase, the other four carry nontrivial topological phases which depend on the radius of the integration contour. The spectroscopic effects of the linear spin-orbit vibronic-coupling mechanism have been analyzed by numerical calculations of the vibronic spectrum for selected model examples.
Photonic bands in two-dimensional microplasma arrays. I. Theoretical derivation of band structures of electromagnetic waves
Authors: Sakai Osamu , Sakaguchi Takui , Tachibana Kunihide
Published: April 2007

Two theoretical approaches appropriate for two-dimensional plasma photonic crystals reveal dispersions of propagating waves including photonic (electromagnetic) band gaps and multiflatbands. A modified plane-wave expansion method yields dispersions of collisional periodical plasmas, and the complex-value solution of a wave equation by a finite difference method enables us to obtain dispersions with structure effects in an individual microplasma. Periodical plasma arrays form band gaps as well as normal photonic crystals, and multiflatbands are present below the electron plasma frequency in the transverse electric field mode. Electron elastic collisions lower the top frequency of the multiflatbands but have little effect on band gap properties. The spatial gradient of the local dielectric constant resulting from an electron density profile widens the frequency region of the multiflatbands, as demonstrated by the change of surface wave distributions. Propagation properties described in dispersions including band gaps and flatbands agree with experimental observations of microplasma arrays.
CdSe nanowires with illumination-enhanced conductivity: Induced dipoles, dielectrophoretic assembly, and field-sensitive emission
Authors: Zhou Ronghui , Chang Hsueh-Chia , Protasenko Vladimir , Kuno Masaru , Singh Amol Kumar , Jena Debdeep , (Grace) Xing Huili
Published: April 2007

Positive ac dielectrophoresis (DEP) is used to rapidly align ensembles of CdSe semiconductor nanowires (NWs) near patterned microelectrodes. Due to their large geometric aspect ratio, the induced dipole of the wires is proportional to their conductivity, which can be drastically enhanced under super-band-gap illumination by several orders of magnitude, with a corresponding increase in the wire DEP mobility. This optical enhancement of conductivity occurs because of the generation of mobile electrons and holes and is verified by a photocurrent measurement. The linear nanowire alignment exhibits a high degree of fluorescent polarization anisotropy in both absorption and emission. An unexpected observation is a reversible, factor of ∼4, electric-field-induced, and frequency-dependent enhancement of the nanowire emission near 10Hz. Such illumination-sensitive, field-enhanced, and frequency-dependent alignment and emission phenomena of NWs suggest an electrical-optical platform for fabricating CdSe nanowire devices for polarization-sensitive photodetection and biosensing applications.
Hot ion generation from nanostructured surfaces under intense femtosecond laser irradiation
Authors: Bagchi S. , Prem Kiran P. , Bhuyan M. K. , Bose S. , Ayyub P. , Krishnamurthy M. , Ravindra Kumar G.
Published: April 2007

Studies of ion emission from nanostructured metallic surfaces excited by intense (0.5–6.3×1016Wcm−2) 50fs laser demonstrate that “hotter” electrons need not to give rise hotter ions, contrary to conventional expectation. Such surfaces produce twice as many ions as planar surfaces in the moderate energy regime (16–75keV), but their yield in the higher energy range (75–2000keV) is substantially lower. Surface modulations also influence ion beam divergence.
Composition dependence of the domain configuration and size in Pb(Zr1−xTix)O3 ceramics
Authors: Schmitt Ljubomira A. , Schönau Kristin A. , Theissmann Ralf , Fuess Hartmut , Kungl Hans , Hoffmann Michael J.
Published: April 2007

The composition dependent variation of domain configuration and size in Pb(Zr1−xTix)O3 (PZT) has been investigated in a detailed transmission electron microscopy study in the range of 0.40⩽x⩽0.55. Single phase composition, Pb(Zr0.45Ti0.55)O3 and Pb(Zr0.60Ti0.40)O3, the former belonging to the tetragonal, the latter to the rhombohedral phase, feature small microdomain widths coupled with a pronounced bimodal domain distribution. Samples with compositions around the morphotropic phase boundary exhibit a decrease of bimodal distribution and an increase in microdomain width associated with nanodomain formation. The investigation of micro- and nanodomains, as well as the bimodal distribution of microdomains in undoped PZT ceramics, with respect to composition, is reported. We define nanodomains as “domains arranged within microdomains possessing a width of a few nanometers.” The strict alternation of the two orientation variants of microdomains is denoted as “bimodal domain distribution,” and is characterized by narrow and broad microdomains, which join each other in turn.
Ferroelectric characteristics of BiFeO3 thin films prepared via a simple chemical solution deposition
Authors: Simões A. Z. , Gonzalez A. H. M. , Cavalcante L. S. , Riccardi C. S. , Longo E. , Varela J. A.
Published: April 2007

BiFeO 3 (BFO) thin films were fabricated on Pt(111)∕Ti∕SiO2∕Si substrates by using a polymeric precursor solution under appropriate crystallization conditions. The capacitance dependence on voltage is strongly nonlinear, confirming the ferroelectric properties of the films resulting from the domain switching. The leakage current density increases with annealing temperature. The polarization electric field curves could be obtained in BFO films annealed at 500 °C, free of secondary phases. X-ray photoelectron spectroscopy spectra of films annealed at 500 °C indicated that the oxidation state of Fe was purely 3+, demonstrating that our films possess stable chemical configurations.
On the vibronic level structure in the NO3 radical. I. The ground electronic state
Authors: Stanton John F.
Published: April 2007

The model Hamiltonian approach of Köppel et al. [Adv. Chem. Phys. 57, 59 (1984)] is used to analyze the electronic spectroscopy of the nitrate radical (NO3). Simulations of negative ion photodetachment of NO3−, the X̃A2′2←B̃E′2 dispersed fluorescence spectrum of NO3, and the B̃E′2←X̃A2′2 absorption spectrum are all in qualitative agreement with experiment, indicating that the model Hamiltonian contains most or all of the essential physics that govern the strongly coupled X̃A2′2 and B̃E′2 electronic states of the radical. All 14 bands seen in the dispersed fluorescence spectrum below 2600cm−1 are assigned based on the simulations, filling in a few gaps left by previous work, and 7 additional bands below 4000cm−1 are tentatively assigned. The assignment is predicated on the assumption that the ν3 level of NO3 is near 1000cm−1 rather than 1492cm−1 as is presently believed. Support for this reassignment (which associates the 1492cm−1 band with the ν1+ν4 level) comes from both the model Hamiltonian spectrum and a Fourier-transform infrared feature at 2585cm−1 that is consistent with the large and positive cross anharmonicity between ν1 and ν4 needed for the alternative 1492cm−1 assignment. An apparent systematic deficiency exists in the treatment of the model Hamiltonian for levels involving ν4. A discussion of the correlation between energy levels in the rigid D3h and C2v limits is illustrative, and provides insight into just how hard it is to treat the degenerate bending coordinate (q4) of NO3 accurately.
Role of charge transfer configurations in LaMnO3, CaMnO3, and CaFeO3
Authors: Sadoc Aymeric , Broer Ria , de Graaf Coen
Published: April 2007

A simple scheme is proposed to analyze the N-electron wave function obtained in embedded cluster calculations in valence bond terms such as ligand-to-metal charge transfer and non-charge-transfer determinants. The analysis is based on a unitary transformation of pairs of natural orbitals to optimal atomiclike orbitals. The procedure is applied to compare the degree of ionicity in NiO and MnO and to explain the existence or absence of Jahn-Teller distortions in LaMnO3, CaMnO3, and CaFeO3. The authors find that the ground state of LaMnO3 is dominated by non-charge-transfer configurations, whereas the charge transfer configurations dominate the ground state wave function in the other two perovskites.
Infrared spectroscopy of pyrrole-2-carboxaldehyde and its dimer: A planar β-sheet peptide model?
Authors: Rice Corey A. , Dauster Ingo , Suhm Martin A.
Published: April 2007

Intermolecular interactions relevant for antiparallel β-sheet formation between peptide strands are studied by Fourier transform infrared spectroscopy of the low temperature, vacuum-isolated model compound pyrrole-2-carboxaldehyde and its dimer in the N–H and CO stretching range. Comparison to quantum chemical predictions shows that even for some triple-zeta quality basis sets, hybrid density functionals and Møller-Plesset perturbation calculations fail to provide a consistent and fully satisfactory description of hydrogen bond induced frequency shifts and intensity ratios in the double-harmonic approximation. The latter approach even shows problems in reproducing the planar structure of the dimer and the correct sign of the CO stretching shift for standard basis sets. The effect of matrix isolation is modeled by condensing layers of Ar atoms on the isolated monomer and dimer. The dimer structure is discussed in the context of the peptide β-sheet motif.
Critical appraisal of the fewest switches algorithm for surface hopping
Authors: Granucci Giovanni , Persico Maurizio
Published: April 2007

In this paper the authors address the problem of internal consistency in trajectory surface hopping methods, i.e., the requirement that the fraction of trajectories running on each electronic state equals the probabilities computed by the electronic time-dependent Schrödinger equation, after averaging over all trajectories. They derive a formula for the hopping probability in Tully’s “fewest switches” spirit that would yield a rigorously consistent treatment. They show the relationship of Tully’s widely used surface hopping algorithm with the “exact” prescription that cannot be applied when running each trajectory independently. They also bring out the connection of the consistency problem with the coherent propagation of the electronic wave function and the artifacts caused by coherent Rabi-type oscillations of the state probabilities in weak coupling regimes. A real molecule (azobenzene) and two ad hoc models serve as examples to illustrate the above theoretical arguments. Following a proposal by Truhlar’s group [Zhu et al., J. Chem. Phys. 121, 7658 (2004) Zhu et al., J. Chem. Theory Comput. 1, 527 (2005)], they apply a decoherence correction to the state probabilities, in conjunction with Tully’s algorithm, and they obtain satisfactory results in terms of internal consistency and of agreement with the outcomes of quantum wave packet calculations.
Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels (XΣ+2, v=2, N=, 1, 6, 10, 15, and 20) and C2H2
Authors: Olkhov Rouslan V. , Smith Ian W. M.
Published: April 2007

Rate coefficients (ktot,Ni) are reported (a) for total removal (reactive+inelastic) of CN(XΣ+2,v=2,Ni) radicals from selected rotational levels (Ni=0, 1, 6, 10, 15, and 20) and (b) for state-to-state rotational energy transfer (ki→f) between levels Ni and other rotational levels Nf in collisions with C2H2. CN radicals were generated by pulsed laser photolysis of NCNO at 573nm. A fraction of the radicals was then promoted to a selected rotational level in v=2 using a tunable infrared “pump” laser operating at ∼2.45μm, and the subsequent fate of this subset of radicals was monitored using pulsed laser-induced fluorescence (PLIF). Values of ktot,Ni were determined by observing the decay of the PLIF signals as the delay between pump and probe laser pulses was systematically varied. In a second series of experiments, double resonance spectra were recorded at a short delay between the pump and probe laser pulses. Analysis of these spectra yielded state-to-state rate coefficients for rotational energy transfer, ki→f. The difference between the sum of these rate coefficients, Σfki→f, and the value of ktot,Ni for the same level Ni is attributed to the occurrence of chemical reaction, yielding values of the rotationally selected rate coefficients (kreac,Ni) for reaction of CN from specified rotational levels. These rate coefficients decrease from (7.9±2.2)×10−10cm3molecule−1s−1 for Ni=0 to (0.8±1.3)×10−10cm3molecule−1s−1 for Ni=20. The results are briefly discussed in the context of microcanonical transition state theory and the statistical adiabatic channel model.
Ab initio ground and excited state potential energy surfaces for NO–Kr complex and dynamics of Kr solids with NO impurity
Authors: Castro-Palacios Juan Carlos , Rubayo-Soneira Jesús , Ishii Keisaku , Yamashita Koichi
Published: April 2007

The intermolecular potentials for the NO(XΠ2)–Kr and NO(AΣ+2)–Kr systems have been calculated using highly accurate ab initio calculations. The spin-restricted coupled cluster method for the ground 1A′2 state [NO(XΠ2)–Kr] and the multireference singles and doubles configuration interaction method for the excited 2A′2 state [NO(AΣ+2)–Kr], respectively, were used. The potential energy surfaces (PESs) show two linear wells and one that is almost in the perpendicular position. An analytical representation of the PESs has been constructed for the triatomic systems and used to carry out molecular dynamics (MD) simulations of the NO-doped krypton matrix response after excitation of NO. MD results are shown comparatively for three sets of potentials: (1) anisotropic ab initio potentials [NO molecule direction fixed during the dynamics and considered as a point (its center of mass)], (2) isotropic ab initio potentials (isotropic part in a Legendre polynomial expansion of the PESs), and (3) fitted Kr–NO potentials to the spectroscopic data. An important finding of this work is that the anisotropic and isotropic ab initio potentials calculated for the Kr–NO triatomic system are not suitable for describing the dynamics of structural relaxation upon Rydberg excitation of a NO impurity in the crystal. However, the isotropic ab initio potential in the ground state almost overlaps the published experimental potential, being almost independent of the angle asymmetry. This fact is also manifested in the radial distribution function around NO. However, in the case of the excited state the isotropic ab initio potential differs from the fitted potentials, which indicates that the Kr–NO interaction in the matrix is quite different because of the presence of the surrounding Kr atoms acting on the NO molecule. MD simulations for isotropic potentials reasonably reproduce the experimental observables for the femtosecond response and the bubble size but do not match spectroscopic results. A general overall view of the results suggests that, when the Kr–NO interaction takes place inside the matrix, potentials are rather symmetric and less repulsive than those for the triatomic system.
Nonlinear quantum dust acoustic waves in nonuniform complex quantum dusty plasma
Authors: El-Taibany W. F. , Wadati Miki
Published: April 2007

The quantum hydrodynamic model for plasmas is employed to study the dynamics of the nonlinear quantum dust acoustic (QDA) wave in a nonuniform quantum dusty plasma (QDP). Through the reductive perturbation technique, it is shown that the quantum hydrodynamical basic equations describing the nonlinear QDA waves yield a modified Korteweg-de Veries equation with slowly varying coefficients in the system inhomogeneity. Applying generalized expansion method, it is found that the system admits only rarefactive solitons. The properties of the solitons such as the velocity, the amplitude and the width of the nonlinear QDA waves are analyzed using appropriate choice for initial ion and electron density numbers. For the homogeneous QDP, no critical value is found. Because of the system inhomogeneity, a new criticality is found forcing with the usage of new stretching coordinates. A higher evolution equation with third-order nonlinearity is derived at the critical values. The solution of the latter equation admits rarefactive shock wave attached with an amplitude factor. The present investigations should be useful for researches on astrophysical plasmas as well as for ultra small micro- and nano-electronic devices.
Twin injection-needle plasmas at atmospheric pressure
Authors: Hong Yong Cheol , Cho Soon Chon , Uhm Han Sup
Published: April 2007

Twin injection-needle plasmas at atmospheric pressure are introduced as low-temperature nonequilibrium plasma source. The plasmas with long plasma columns of about 55cm are produced from one alternating current (ac) power supply as if each of the plasmas is a fraternal twin and shows different characteristics in plasma column length and gas temperature. The twin plasma columns are regarded as skinny rods with a uniform charge distribution, and the change of the plasma column lengths with different distances between the plasmas is compared with the change of the capacitance of the skinny rods presented as a model.
Transition functions and correlation functions in the analysis of dynamic systems
Authors: Halpern V.
Published: April 2007

An understanding of the dynamic behavior of complex systems such as supercooled liquids requires a knowledge of the microscopic processes occurring in them. Correlation functions, which can be derived from experimental measurements of macroscopic properties or from computer simulations, cannot distinguish between particles that have never moved and those that have changed their position or state and then returned to the original one. Such a distinction can be obtained from the comparison of a correlation function with the transition function, i.e., the fraction of particles that have never moved up to time t. As the author demonstrates by an extension of his recently published results for the ferromagnetic Potts model [J. Chem. Phys. 124, 214508 (2006)], valuable insights into the microscopic behavior of a system can be obtained from such a comparison. A generalization of the transition function to a first passage function can provide useful extra insights.
Structural and optical properties of InP quantum dots grown on GaAs(001)
Authors: de Godoy M. P. F. , Nakaema M. K. K. , Iikawa F. , Brasil M. J. S. P. , Lopes J. M. J. , Bortoleto J. R. R. , Cotta M. A. , Magalhães-Paniago R. , Mörschbächer M. J. , Fichtner P. F. P.
Published: April 2007

We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots.
GaInNAsSb/GaNAs quantum-well VCSELs: Modeling and physical analysis in the 1.50−1.55 μm wavelength range
Authors: Sarzała Robert P. , Nakwaski Włodzimierz
Published: April 2007

Physical analysis of the long-wavelength room-temperature (RT) continuous-wave (cw) emission within the 1.50−1.55 μm range from the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) is carried out. To this end, a comprehensive three-dimensional optical-electrical-thermal-gain self-consistent simulation of physical processes taking place inside a laser volume is applied. While the 1.50-μm emission has been found to be reached practically without trouble, the 1.55-μm emission needs additional optimizations. For the optimal QW structure, the 1.55-μm emission in highly detuned VCSELs requires RT cw threshold currents more than 18 times higher than those of the 1.50-μm one. Some threshold reduction may be achieved by adding the second quantum well. The 3λ-cavity design has been proved to be optimized for the 1.50-μm emission ensuring stable fundamental-mode operation even at elevated temperatures whereas the 1.5λ-cavity is optimal for the 1.55-μm emission for which threshold reduction is more important. For the 1.50-μm emission, some structure optimizations have been proposed. The GaInNAsSb/GaNAs structure offers promising prospects to manufacture VCSELs emitting 1.55-μm radiation, but some technology and construction improvements are still necessary.
Simple microscope using a compound refractive lens and a wide-bandwidth thermal neutron beam
Authors: Cremer J. T. , Park H. , Piestrup M. A. , Gary C. K. , Pantell R. H. , Flocchini R. G. , Egbert H. P. , Kloh M. D. , Walker R. B.
Published: April 2007

The results of imaging experiments using biconcave, spherical compound refractive lenses (CRLs) and a wide-bandwidth thermal neutron beam are presented. Two CRLs were used, consisting of 155 beryllium and 120 copper lenses. The experiments were performed using a thermal neutron beam line at McClellan Nuclear Radiation Center reactor. The authors obtained micrographs of cadmium slits with up to 5× magnification and 0.3mm resolution. The CRL resolution was superior to a pinhole camera with the same aperture diameter. The modulation transfer function (MTF) of the CRL was calculated and compared with the measured MTF at five spatial frequencies, showing good agreement.
Growth temperature dependence of structural properties of AlN films on ZnO (0001¯) substrates
Authors: Ueno Kohei , Kobayashi Atsushi , Ohta Jitsuo , Fujioka Hiroshi
Published: April 2007

The authors have investigated substrate temperature dependence of the structural properties of AlN grown on atomically flat ZnO (0001¯) substrates using pulsed laser deposition. The growth of AlN on ZnO at above 500°C proceeds in a three-dimensional mode and results in the formation of films with poor crystallinity and rough surfaces. However, reduction in the growth temperature leads to a remarkable improvement in crystalline quality and surface morphology. The authors have found that AlN films with stepped and terraced surfaces grow in the layer-by-layer mode at substrate temperatures below 300°C. X-ray reflectivity measurements have revealed that these improvements in structural properties can be attributed to the suppression of the interfacial reactions between AlN and ZnO.
Recombination dynamics of excitons in Mg0.11Zn0.89O alloy films grown using the high-temperature-annealed self-buffer layer by laser-assisted molecular-beam epitaxy
Authors: Kubota Masashi , Onuma Takeyoshi , Tsukazaki Atsushi , Ohtomo Akira , Kawasaki Masashi , Sota Takayuki , Chichibu Shigefusa F.
Published: April 2007

Recombination dynamics of excitons in Mg0.11Zn0.89O epilayers grown by laser-assisted molecular-beam epitaxy on a ScAlMgO4 substrate were investigated. By using the MgZnO high-temperature-annealed self-buffer layer (HITAB), the value of full width at half maximum of the near-band-edge (NBE) photoluminescence (PL) peak at 3.6eV was decreased from 133to94meV at 293K, and the intensity ratio of the NBE emission to the deep emission band centered around 2.2eV was increased by a factor of 3. Also, the PL lifetime of the NBE peak at 293K under the excitation density of 1μJ∕cm2 was increased from 49to60ps. These results suggest that HITAB gave rise to improved alloy compositional homogeneity and reduced concentration of point defects.
On the effect of periodic Mg distribution in GaN:δ-Mg
Authors: Simbrunner C. , Wegscheider M. , Quast M. , Li Tian , Navarro-Quezada A. , Sitter H. , Bonanni A. , Jakiela R.
Published: April 2007

p -type doping of group-III nitrides represents a well recognized crucial challenge in the realization of optical and magneto-optical devices based on wide band gap semiconductors. The insertion of Mg in a δ-doping fashion into a GaN matrix is expected to be very promising for the enhanced incorporation of acceptors. The authors present a comprehensive study of the GaN:δ-Mg material system, starting from the optimization of the metal organic chemical vapor deposition process monitored in situ via spectroscopic ellipsometry and reflectometry and giving then evidence of the periodic distribution of the Mg ions through high-resolution secondary ion mass spectroscopy measurements. Furthermore, the effect of the acceptor distribution in the layers on the optical and transport properties is highlighted.
Diffusion in a tube of varying cross section: Numerical study of reduction to effective one-dimensional description
Authors: Berezhkovskii A. M. , Pustovoit M. A. , Bezrukov S. M.
Published: April 2007

Brownian dynamics simulations of the particle diffusing in a long conical tube (the length of the tube is much greater than its smallest radius) are used to study reduction of the three-dimensional diffusion in tubes of varying cross section to an effective one-dimensional description. The authors find that the one-dimensional description in the form of the Fick-Jacobs equation with a position-dependent diffusion coefficient, D(x), suggested by Zwanzig [J. Phys. Chem. 96, 3926 (1992)], with D(x) given by the Reguera-Rubí formula [Phys. Rev. E 64, 061106 (2001)], D(x)=D∕1+R′(x)2, where D is the particle diffusion coefficient in the absence of constraints, and R(x) is the tube radius at x, is valid when ∣R′(x)∣⩽1. When ∣R′(x)∣>1, higher spatial derivatives of the one-dimensional concentration in the effective diffusion equation cannot be neglected anymore as was indicated by Kalinay and Percus [J. Chem. Phys. 122, 204701 (2005)]. Thus the reduction to the effective one-dimensional description is a useful tool only when ∣R′(x)∣⩽1 since in this case one can apply the powerful standard methods to analyze the resulting diffusion equation.