bluuebunny/crossref_metadata_2025 huggingface dataset:
Storm‐time electric field distribution in the inner magnetosphere
Authors: Nishimura Y. , Shinbori A. , Ono T. , Iizima M. , Kumamoto A.
Published: November 2006

The distribution of the storm‐time electric field in the inner magnetosphere has been investigated by using the Akebono/EFD data within a period from 1989 to 1995. During the main phase of geomagnetic storms, the strong electric field appears between L = 2 and L = 6 in both dawn and dusk sectors with the magnitude from 2 to 4 mV/m, and the maximum value appears at L = 3 in the dusk sector. During the recovery and weakly disturbed period, the region with intense electric field moves outward with decreasing the amplitude. This structure of the localized electric field is quite different from the Volland‐Stern electric field model, suggesting the existence of another electric field source other than the large‐scale convection electric field. During quiet periods, although the electric field fairly follows the corotation electric field, the distribution at L = 3.5 indicates a small deviation from pure corotation.
An ENSO shift revisited
Authors: Solow Andrew R.
Published: November 2006

An influential 1996 paper presented a statistical analysis showing that the prolonged ENSO warm event of the early 1990's was inconsistent with the historical pattern of ENSO variability and therefore concluded that there had been a shift in ENSO behavior possibly connected to global warming. A fundamental problem with this earlier analysis is that the data used to test for a shift in ENSO behavior were not independent of the data used to identify the hypothetical shift. A new analysis is presented that avoids this problem by using more recent data. The results raise a question about the earlier finding.
Linear theory of electron temperature anisotropy instabilities: Whistler, mirror, and Weibel
Authors: Gary S. Peter , Karimabadi Homa
Published: November 2006

A collisionless, homogeneous plasma in which the electron velocity distribution is a bi‐Maxwellian with T⊥e > T∥e, where the directional subscripts refer to directions relative to the background magnetic field Bo, can support the growth of two distinct instabilities. Linear dispersion theory predicts that the whistler anisotropy instability is excited with maximum growth rate γm at k × Bo = 0 and real frequency ωr greater than the proton cyclotron frequency, whereas the electron mirror instability is excited at propagation oblique to Bo and zero real frequency. In an unmagnetized plasma with a similarly anisotropic electron distribution the electron Weibel instability may be excited with zero real frequency and maximum growth rate in the direction of the minimum temperature. Here linear theory is used to compare dispersion and threshold properties of these three growing modes. For 0.10 ≤ β∥e ≤ 1000, the whistler has a larger γm and a smaller anisotropy threshold than the electron mirror, so that the former mode should dominate in homogeneous plasmas for most physical values of electron β. Threshold conditions describing electron temperature anisotropies and parallel wave numbers at given maximum growth rates are presented for each instability.
Structure and formation of the highly stable marine boundary layer over the Gulf of Maine
Authors: Angevine Wayne M. , Hare J. E. , Fairall C. W. , Wolfe Daniel E. , Hill R. J. , Brewer W. A. , White Allen B.
Published: November 2006

A shallow, stable boundary layer is ubiquitous over the cool waters of the Gulf of Maine in summer. This layer affects pollutant transport throughout the region by isolating overlying flow from the surface. In this paper, we explore how the stable boundary layer is formed and describe its characteristics. The temperature profile of the lowest 1–2 km of the atmosphere over the Gulf of Maine is remarkably similar regardless of transport time over water or the time of day when the flow left the land, provided only that the flow is offshore. This similarity is forced by the (roughly) constant water temperature and the (roughly) constant temperature of the free troposphere over the continent. However, the processes leading to the similar profiles are quite different depending on the time of day when the flow crosses the coast. Air leaving the coast at night already has a stable profile, whereas air leaving the coast at midday or afternoon has a deep mixed layer. In the latter case, the stable layer formation over the water is of interest. Using observations of surface fluxes, profiles, and winds on the NOAA Research Vessel Ronald H. Brown from the 2004 International Consortium for Atmospheric Research in Transport and Transformation (ICARTT)/New England Air Quality Study, we show that the formation of the stable layer, which involves cooling a roughly 50‐ to 100‐m‐deep layer by 5–15 K, occurs within 10 km and a half hour after leaving the coast. The internal boundary layer near shore is deeper than predicted by standard relationships. Historical data are explored and also show deeper internal boundary layers than predicted. We also describe one exceptional case where a 200‐m‐deep neutral layer was observed and discuss the degree of isolation of the stable boundary layer and its duration.
Considering the polarization of the oxygen thermospheric red line for space weather studies
Authors: Lilensten Jean , Simon Cyril , Barthélémy Mathieu , Moen Joran , Thissen Roland , Lorentzen D. A.
Published: November 2006

Space weather thermospheric monitoring requires real‐time and large‐scale measurements. In order to monitor the thermospheric variations due to geomagnetic activity, one relies mostly on the measurements of the intensity of the atomic oxygen green line and on the indirect measurement of the total electron content. These two parameters do not allow retrieving the full characteristics of the thermosphere, and a third proxy is required, for example, in orbitography. We propose to use the polarization of the atomic oxygen red line to fulfill this requirement. The first measurements of the polarization of thermospheric nightglow lines have been performed in the first part of the twentieth century and especially during the last International Geophysical Year. Amongst the oxygen visible lines, only the red one seems to be potentially polarized. However, there exists a disagreement between the different measurements. At the origin of the polarization, there is always a dissymmetric mechanism. It triggers either an emission process, a light scattering, or, in the case of the oxygen red line, a collision mechanism. This paper reviews the different experiments performed in the past and proposes to explore this matter with modern facilities. If successful, this investigation could lead to a systematic reanalysis of the previous red line interferometric measurements.
U‐Pb sensitive high‐resolution ion microprobe (SHRIMP) zircon geochronology of granitoid rocks in eastern Zambia: Terrane subdivision of the Mesoproterozoic Southern Irumide Belt
Authors: Johnson S. P. , De Waele B. , Liyungu K. A.
Published: November 2006

The Southern Irumide Belt (SIB) is a structurally and metamorphically complex region of mainly Mesoproterozoic igneous rocks in southern and eastern Zambia, northern Mozambique and northern Malawi that was strongly overprinted in the Neoproterozoic to Cambrian Damara‐Lufilian‐Zambezi (DLZ) orogeny. Because of the scarcity of geological data from this region, little is known about the timing of tectonomagmatic events; however, this belt has traditionally been considered to be a southerly continuation of the adjacent Irumide Belt (IB). Here we provide 27 new U‐Pb sensitive high‐resolution ion microprobe (SHRIMP) zircon ages that constrain the Paleoproterozoic to Cambrian tectonomagmatic history of this belt and which, for the first time, allow for direct comparison with the adjoining IB. The SIB is floored by a predominantly late Paleoproterozoic basement, which was intruded by voluminous continental margin arc‐related magmas between 1.09 and 1.04 Ga and accompanied by high‐temperature/low‐pressure metamorphism. In contrast, the IB is floored by a late Paleoproterozoic basement that is generally older than 2.0 Ga, contains significant mid‐Mesoproterozoic plutonic rocks that are not present within the SIB, and underwent moderate‐pressure/moderate‐temperature compressional metamorphism and S‐type granitoid magmatism at circa 1.02 Ga. These data indicate that the crust underlying the SIB is not a continuation of that underlying the IB but represents an allocthonous continental margin arc terrane juxtaposed against the Congo‐Tanzania‐Bangweulu Craton during the late Mesoproterozoic Irumide orogeny. Reworking and shearing of the SIB occurred during the DLZ orogen, resulting in the present‐day architecture as a series of stacked terranes which have been exploited by voluminous posttectonic granitoid batholiths.
Japan's Healthcare System and Pharmaceutical Industry
Authors: Saigusa Osamu
Published: November 2006

Japanese people are enjoying longer and healthy lives at relatively low cost, thanks to well-balanced nutrition, low infant mortality and effective TB drugs. The healthcare system of the country also has made a significant contribution to such good performance. The system is divided into health insurance programs and a special healthcare system for seniors (SHSS), to which Japan's government has been paying money despite having a tremendous financial deficit. The government has tried to slash its financial burden of the healthcare system as much as possible for a better financial condition. Meanwhile, the Japanese pharmaceutical industry has played an important role in the development of the healthcare system under the situation of government having carried out a series of National Health Insurance (NHI) drug price cuts in order to save healthcare costs in recent years. The industry is categorised into three groups such as big players with presence in the US and Europe, other brand drug companies with no presence in these areas and generic drug companies. Price cut pressure from the government will force the big players to intensify their overseas activities and the other brand drug companies to do everything for their survival. On the other hand, generic drug companies will keep a better position in the market because the government has realised that promoting the use of generic drugs is effective for cost saving and changed to the policy favourable to the generic industry.
Potential Savings from Increased Substitution of Generic for Originator Medicines in Europe
Authors: Simoens Steven , De Coster Sandra
Published: November 2006

This study aims to estimate annual savings from increased generic substitution in the retail market of 11 European countries in 2004. Savings from generic substitution were calculated for the top ten active substances by public expenditure on originator medicines in each country. For each active substance, average price levels weighted by volume of sales of medicines belonging to the group of originator medicines and to the group of generic medicines were calculated. The price difference between originator and generic medicines was multiplied by the volume of originator medicines to be substituted. The analysis considered that, following generic substitution, 5 per cent of market volume for each active substance would be made up by originator medicines and 95 per cent by generic medicines. Increased generic substitution for the top ten active substances generated total potential savings of around €3 bn, with country savings ranging from €1 lm in Poland to €1 bn in Germany. Increased generic substitution would be expected to reduce public expenditure on originator medicines containing these active substances by at least 20 per cent in each country. Countries that pursue the development of their domestic generic medicines market, therefore, can expect to gain substantial savings from increased generic substitution.
The European Generic Pharmaceutical Market in Review: 2006 and Beyond
Authors: Perry Greg
Published: November 2006

Dramatic changes in pharmaceutical markets make it imperative for generic medicines producers to seek out, and work with governments to create the best conditions for developing, manufacturing and marketing their products. Similar to its involvement in the G10 Medicines process, the European Generic Medicines Association (EGA) is now actively engaged in the European Commission's follow-up initiative, the Pharmaceutical Forum. To bring substance to this debate, the EGA has recently completed two important studies of European generics markets and the governmental policies across Europe that effect them. These studies aim to determine the progress of initiatives to promote generic medicines by examining market shares and go on to suggest ways of increasing the up-take of these affordable medicines. The traditional instruments employed by governments to promote generics —reference-pricing systems, prescribing budgets, generic substitution, patient co-payments, information campaigns — can indeed be effective in stimulating generic up-take, but they must also stimulate competition on the markets. Pricing systems must encourage price competition and more affordable quality healthcare for patients. They must also be managed to guarantee the long-term sustainability of the European Union (EU)-based generic medicines industry so that it can compete effectively on EU and global markets and continue contributing to affordable healthcare in Europe.
Generics in Latin America: An Analysis of the Brazilian Experience
Authors: Valente Vera
Published: November 2006

Latin America accounts for approximately 8 per cent of the global generic market. Generics participation in the Latin American countries has been growing — however, the concept of generics differs considerably from country to country. In such landscape, Brazil has been distinguished not only because of the rigorous sanitary legislation — requiring bioequivalence tests and Good Manufacturing Practices certification for generic registration and aligning local regulation with internationally recognised scientific standards for proof of efficacy and safety — but also because of the market performance the generics have shown since their implementation in 1999. Annual sales reached US$717m and 157m units in 2005 and displayed the highest growth rates among the different segments within the Brazilian pharmaceutical market. This paper reviews the Brazilian experience with generics, focusing on current regulatory and market issues and on the main challenges and opportunities expected for the near future in this region.
America's Generic Pharmaceutical Industry: Opportunities and Challenges in 2006 and Beyond
Authors: Jaeger Kathleen
Published: November 2006

The US generic industry, with annual sales of more than US$22bn, is excited about the prospects and opportunities for the future. However, the industry must remain vigilant to efforts by some special interest groups that seek to delay the timely introduction of more affordable generic drugs today, and in the future. Among the issues that could affect the continued growth of the generic pharmaceutical industry are authorised generics; misuse of the Citizen Petition process; and imposition of measures in free trade agreements that could harm America's generic drug industry. While the generic industry is focused on ensuring a level competitive playing field by addressing these and other issues, it is also expending significant time and energy to open the door to the new, untapped opportunity for savings that would result from generic competition for expensive biopharmaceutical products.
On the Hamiltonian reduction of geodesic motion on SU(3) to SU(3)/SU(2)
Authors: Gerdt V. , Horan R. , Khvedelidze A. , Lavelle M. , McMullan D. , Palii Yu.
Published: November 2006

The reduced Hamiltonian system on T*(SU(3)∕SU(2)) is derived from a Riemannian geodesic motion on the SU(3) group manifold parametrized by the generalized Euler angles and endowed with a bi-invariant metric. Our calculations show that the metric defined by the derived reduced Hamiltonian flow on the orbit space SU(3)∕SU(2)≃S5 is not isometric or even geodesically equivalent to the standard Riemannian metric on the five-sphere S5 embedded into R6.
Can the pH value of water solutions be estimated by quantum chemical calculations of small water clusters?
Authors: Mrázek Jiří , Burda Jaroslav V.
Published: November 2006

In the study, various water clusters were explored from the point of view of the proton transfer between H-bonded neighbors. A relatively modest approach—the MP2∕6-31++G(d,p) level—was chosen as acceptable considering the fact that also larger systems have to be included. The tight ion-pair model (with usually three fixed O–O distances) was adopted for the autodissociation process. First, cluster-estimated pH values rapidly decrease as cluster size increases from 2 to 6. For larger clusters in gas phase, the topology of H bonds plays an important role, varying pH from 7 to 13 in hexamers and from 5 to 15 in octamer clusters. The relationship energy/distance was quantified, too. Enhancing our model with the conductorlike screening model (COSMO) approach brought significant improvement in description of the autodissociation reaction with a stable zwitterionic structure. However, when the O–O restrictions were released, the small barrier for backward reaction disappeared, reforming neutral cluster spontaneously. Also Boltzmann weighting procedure was applied, and for the explored clusters in vacuo, the series of pH 25-18-14-13-10 was obtained for cluster sizes n=2, 3, 4, 6, 8. Using the COSMO approach, the analogous series is 15-14-12-10-9. The limit of the series is still about two to three units above the experimentally known pH. In order to reach the size-independent (bulk) value, larger clusters are needed. However, the situation is far from hopeless since (as it was proven in the study) four-coordinated molecules are not involved in the proton transfer process directly; they can only be a part of the surrounding environment.
Self-similar clustering of inertial particles and zero-acceleration points in fully developed two-dimensional turbulence
Authors: Goto Susumu , Vassilicos J. C.
Published: November 2006

Clustering of inertial particles in fully developed two-dimensional inverse cascading turbulence occurs for all particle relaxation times ranging from an order of magnitude under the smallest eddy turnover time to an order of magnitude above the largest eddy turnover time. Particle voids and clusters are statistically self-similar over a finite range of scales within the inertial range and are explained in terms of coarse-grained vorticity and resonant eddies (for voids) and in terms of zero-acceleration points (for clusters). The clustering of inertial particles reflects the clustering of zero-acceleration points. Essential to both explanations is the sweeping of small eddies by large ones. An important implication is that particle clustering can be explicitly described just in terms of the fluid acceleration field without the need for Lagrangian particle integrations.
Gyrotropic guiding-center fluid theory for the turbulent heating of magnetospheric ions in downward Birkeland current regions. II
Authors: Jasperse John R. , Basu Bamandas , Lund Eric J. , Bouhram Mehdi
Published: November 2006

A new fluid theory in the guiding-center and gyrotropic approximation derivable from the ensemble-averaged Vlasov-Maxwell equations that included the effect of wave-particle interactions for weakly turbulent, weakly inhomogeneous, nonuniformly magnetized plasma was recently given by Jasperse, Basu, Lund, and Bouhram [Phys. Plasmas 13, 072903 (2006)]. In that theory, the particles are transported in one spatial dimension (the distance s along the magnetic field) but the turbulence is two-dimensional. In this paper, which is intended as a sequel, the above theory is used for quasisteady conditions to find: (1) a new formula for the perpendicular ion-heating rate per unit volume Ẇi⊥(s), where Ẇi⊥(s) decreases for large s by what we call the “finite ion gyroradius effect”; and (2) a new formula for the perpendicular ion temperature at low altitudes, Ti⊥(s). Parametrized calculations for Ti⊥(s) are also given.
Analytical theory of hysteresis in ion channels: Two-state model
Authors: Pustovoit M. A. , Berezhkovskii A. M. , Bezrukov S. M.
Published: November 2006

Channel-forming proteins in a lipid bilayer of a biological membrane usually respond to variation of external voltage by changing their conformations. Periodic voltages with frequency comparable with the inverse relaxation time of the protein produce hysteresis in the occupancies of the protein conformations. If the channel conductance changes when the protein jumps between these conformations, hysteresis in occupancies is observed as hysteresis in ion current through the channel. We develop an analytical theory of this phenomenon assuming that the channel conformational dynamics can be described in terms of a two-state model. The theory describes transient behavior of the channel after the periodic voltage is switched on as well as the shape and area of the hysteretic loop as functions of the frequency and amplitude of the applied voltage. The area vanishes as the voltage period T tends to zero and infinity. Asymptotic behaviors of the loop area A in the high- and low-frequency regimes, respectively, are A∼T and A∼T−1.
Adiabatic transfer of population in a dense fluid: The role of dephasing statistics
Authors: Demirplak Mustafa , Rice Stuart A.
Published: November 2006

We report the results of simulation studies of the statistics of vibrational dephasing of a YCl (Y=H, D, T, and I) diatom in dense fluid Ar at two temperatures, including the effect of strong field driving on the energy level modulation statistics. The distribution of energy level modulations is found to be non-Gaussian with a high energy tail. Aspects of stimulated Raman adiabatic passage (STIRAP) between the vibrational levels of HCl in dense fluid Ar have been investigated. For HCl with nearly degenerate v=0→v=1 and v=1→v=2 transitions, the combined effect of modulation and power broadening reduces the STIRAP efficiency for population transfer from v=0 to v=2 of the order of 30%. However, if the transitions used have very different frequencies, as in the original model studied by Demirplak and Rice [J. Chem. Phys. 116, 8028 (2002)], the STIRAP efficiency for population transfer remains high, of the order of 80%, even with non-Gaussian modulation of energy levels.
Broadband dielectric spectroscopy on ultrathin organic layers having one free (upper) interface
Authors: Serghei A. , Kremer F.
Published: November 2006

Using silica colloids as nanospacers and ultraflat highly conductive silicon wafers as electrodes, a novel experimental approach is demonstrated, which, in combination with broadband dielectric spectroscopy, enables one to investigate the molecular dynamics in ultrathin organic layers having one free interface. This opens a manifold of possibilities, including dielectric studies on isolated molecules.
Models of bipolar charge transport in polyethylene
Authors: Boufayed F. , Teyssèdre G. , Laurent C. , Le Roy S. , Dissado L. A. , Ségur P. , Montanari G. C.
Published: November 2006

We introduce and develop two bipolar transport models which are based on appreciably different physical assumptions regarding the distribution function in the energy levels of trap states. In the first model, conduction is described by an effective mobility of the carriers and the accumulation of stored space charge is taken into account through a single trapping level. In the second model the hypothesis of an exponential distribution function of trap depth is made, with conduction taking place via a hopping process from site to site. The results of simulations of the two models are compared with experimental data for the external current and the space-time evolution of the electrical space charge distribution. The two descriptions are evaluated in a critical way, and the prospects for these models to adequately describe real systems are given.
Relaxation oscillations in a capacitive discharge chamber connected to a peripheral grounded chamber
Authors: Kim Sungjin , Zhou Zhuwen , Lieberman M. A. , Lichtenberg A. J.
Published: November 2006

We have observed relaxation oscillations in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (∼40kHz) relaxation oscillation at 100mTorr, with absorbed power near that for peripheral breakdown, and a low frequency (∼3Hz) oscillation, at higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. We interpret the high frequency oscillations using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations and indicate a variety of behaviors dependent on the matching conditions.
Dynamic Lorentz microscopy of micromagnetic structure in magnetic tunnel junctions
Authors: Shaw Justin M. , Geiss Roy , Russek Stephen
Published: November 2006

Lorentz microscopy was used to study the micromagnetic structure and magnetization reversal in magnetic tunnel junctions (MTJs) fabricated with different processing conditions including a preoxidation process. The authors find that the free layer in a MTJ has considerably more disorder than that seen in an isolated magnetic layer. The disorder changes with anneals that set the exchange bias, suggesting that the disorder arises from the antiferromagnetic layer and is transferred to the free layer by magnetostatic Néel coupling. The disorder and time-dependent fluctuations in the magnetic structure provide a foundation for understanding several sources of 1∕f noise in MTJs.
An investigation of control mechanisms of the excitonic behavior in reactively sputtered ZnO on (0001) Al2O3
Authors: Tüzemen S. , Gür Emre , Yıldırım T. , Xiong G. , Williams R. T.
Published: November 2006

Above-band-edge absorption spectra of reactively sputtered Zn- and O-rich samples exhibit free exciton and neutral acceptor bound exciton (A0X) features. It is shown that the residual acceptors which bind excitons with an energy of 75meV reside about 312meV above the valence band, according to effective mass theory. An intra-band-gap absorption feature peaking at 2.5eV shows correlation with the characteristically narrow A-free exciton peak intensity, suggesting a compensation mechanism of the centers involving oxygen vacancy (VO) related donors. In order to enhance free exciton concentration relative to competing neutral bound exciton density, relevant annealing processes are performed without disturbing the residual shallow acceptor profile which is necessary for at least background p-type conductivity.
Analysis of the residual stresses, the biaxial modulus, and the interfacial fracture energy of low-k dielectric thin films
Authors: Atrash Fouad , Sherman Dov
Published: November 2006

A method was developed for the evaluation of the residual stresses and the biaxial modulus of thin films and the interfacial fracture energy of the interface between the thin film and the substrate. The “superlayer” method, which consists of depositing a thin metallic film on top of the investigated film, was employed to evaluate all the above mechanical properties. The investigated thin films in this report were 0.5, 1, and 1.5μm thick coral low-k dielectric films that were deposited on top of Cu and Ta thin films, all on top of (001) silicon wafers. Thinner Ti films of 150, 200, and 250nm thick were used as the superlayers. These properties were obtained by measuring the radius of curvature of the released or of the delaminated Ti/coral bilayers. Nine bilayers, combined from all the thicknesses mentioned above, were tested. The wide experimental procedure enabled to extract the unknown properties by a special procedure developed for this purpose, and to draw conclusions regarding the accuracy of the results and the effect of layer thickness. Finally, and based on the large experimental data, we recommend on the minimal required tests to evaluate these mechanical properties. With this information, we show that a single mm2 lab on chip is a sufficient area to contain the specimens required for the evaluation of the above-mentioned properties.
Stress and wafer bending of a-plane GaN layers on r-plane sapphire substrates
Authors: Roder C. , Einfeldt S. , Figge S. , Paskova T. , Hommel D. , Paskov P. P. , Monemar B. , Behn U. , Haskell B. A. , Fini P. T. , Nakamura S.
Published: November 2006

The stress and wafer bending of (112¯0) a-plane GaN layers of different thicknesses grown on (11¯02) r-plane sapphire substrates by hydride vapor phase epitaxy were studied by high-resolution x-ray diffraction and photoluminescence and photoreflectance spectroscopies. The layers are found to be under compression in the growth plane and under tension in the growth direction. The elastic and thermal anisotropies of the GaN and the sapphire crystal result in an in-plane stress and a wafer curvature, both of which are different in the two in-plane directions parallel and perpendicular to the GaN c axis. The GaN unit cell is no longer hexagonal but orthorhombic. The stress relaxes with increasing GaN layer thickness while the curvature of the wafer increases. Different stress relief mechanisms are considered, and the stresses in the layer and the curvature of the wafer are calculated using standard models on wafer bending. The results suggest that the wafer bending is the dominant stress relief mechanism. In addition, the redshift of the near-band-edge photoluminescence and the free exciton photoreflectance peaks with increasing layer thickness is correlated with the strain data determined by x-ray diffraction.
Thermoelectrical model for vertical cavity surface emitting lasers and arrays
Authors: Boiko D. L. , Guerrero G. , Kapon E.
Published: November 2006

An analytical model of thermal and electrical characteristics of vertical cavity surface emitting lasers (VCSELs) and VCSEL arrays is presented. The model is based on analytical expressions for the thermal resistance and for the I-V curve of the devices and incorporates only a few macroscopic parameters. It accounts for three-dimensional current and heat flows and provides thermo-electrical self-consistency. Good agreement between the model’s predictions and the measured characteristics of InGaAs∕AlGaAs VCSEL arrays is obtained.
Noncontact torsional wave transduction in a rotating shaft using oblique magnetostrictive strips
Authors: Cho Seung Hyun , Han Soon Woo , Park Chan Il , Kim Yoon Young
Published: November 2006

A noncontact method to generate and measure torsional waves in rotating shafts by a set of magnetostrictive patches and a solenoid is proposed. The main issues in the present wave experiment are how to generate torsional waves having sufficient power and how not to interfere with shaft rotational motion. Magnetostrictive patches are bonded obliquely to the shaft axis for pure torsional wave generation and an arrayed patch configuration is employed for sufficient power generation and frequency localization. For uninterrupted shaft rotation, a solenoid encircling a rotating shaft wirelessly supplies or detects the ac magnetic field in the patches. The validity and performance of the proposed wave transduction method were checked by several experiments. An application of this method to the detection of a circumferential crack in a rotating shaft is also presented.
High filling fraction gallium phosphide inverse opals by atomic layer deposition
Authors: Graugnard E. , Chawla V. , Lorang D. , Summers C. J.
Published: November 2006

High filling fraction gallium phosphide (GaP) inverse opals were fabricated by atomic layer deposition within the void spaces of silica colloidal crystal templates. Depositions were performed from 400to500°C using trimethylgallium and tris(dimethylamino)phosphine precursors. The resulting films were characterized by optical reflectance, which indicated infiltration as high as 100% of the conformal film growth maximum, corresponding to a volume filling fraction of 0.224. X-ray diffraction measurements confirmed the crystallinity of the film. These results indicate the fabrication of three-dimensional photonic crystals using a III-V optoelectronic material with sufficient dielectric contrast to form a full photonic band gap in the visible.
High performance n-channel organic field-effect transistors and ring oscillators based on C60 fullerene films
Authors: Anthopoulos Thomas D. , Singh Birendra , Marjanovic Nenad , Sariciftci Niyazi S. , Montaigne Ramil Alberto , Sitter Helmut , Cölle Michael , de Leeuw Dago M.
Published: November 2006

We report on organic n-channel field-effect transistors and circuits based on C60 films grown by hot wall epitaxy. Electron mobility is found to be dependent strongly on the substrate temperature during film growth and on the type of the gate dielectric employed. Top-contact transistors employing LiF∕Al electrodes and a polymer dielectric exhibit maximum electron mobility of 6cm2∕Vs. When the same films are employed in bottom-contact transistors, using SiO2 as gate dielectric, mobility is reduced to 0.2cm2∕Vs. By integrating several transistors we are able to fabricate high performance unipolar (n-channel) ring oscillators with stage delay of 2.3μs.
Shear thinning in dilute polymer solutions
Authors: Ryder J. F. , Yeomans J. M.
Published: November 2006

We use bead-spring models for a polymer coupled to a solvent described by multiparticle collision dynamics to investigate shear thinning effects in dilute polymer solutions. First, we consider the polymer motion and configuration in a shear flow. For flexible polymer models we find a sharp increase in the polymer radius of gyration and the fluctuations in the radius of gyration at a Weissenberg number ∼1. We then consider the polymer viscosity and the effect of solvent quality, excluded volume, hydrodynamic coupling between the beads, and finite extensibility of the polymer bonds. We conclude that the excluded volume effect is the major cause of shear thinning in polymer solutions. Comparing the behavior of semiflexible chains, we find that the fluctuations in the radius of gyration are suppressed when compared to the flexible case. The shear thinning is greater and, as the rigidity is increased, the viscosity measurements tend to those for a multibead rod.
Effect of different laser polarization direction on high order harmonic generation of N2 and H2
Authors: Cui Lei , Zhao J. , Hu Y. J. , Teng Y. Y. , Zeng X. H. , Gu B.
Published: November 2006

The high order harmonic generations of N2 and H2 irradiated by ultrastrong femtosecond pulsed laser are simulated by the time dependent density functional theory method, and effect of different laser polarization directions on high order harmonic generation (HHG) is discussed. The results indicate that for N2, with its outermost σg electron, the HHG yield is maximal when the molecules are aligned with the laser polarization direction. Good agreements are found with recent experiments, and for H2, with its outermost σg electron, the HHG yield also peaks when the molecules are aligned at about 0° form polarization axis.
Photocurrent response of hydrogenated nanocrystalline silicon thin films
Authors: Zhang R. , Chen X. Y. , Zhang K. , Shen W. Z.
Published: November 2006

We report on the optoelectronic properties of the hydrogenated nanocrystalline silicon (nc-Si:H) thin film containing large density of nanometer grains and voids. By comparison with the bulk silicon, strong optical absorption and high photocurrent are found in the nc-Si:H thin film and attributed to the enhancement of the optical absorption cross section and good carrier conductivity in the nanometer grains and voids. The observed strong photocurrent signals can be well described by the extended diffusion-recombination model. The high photocurrent response may facilitate the fabrication of infrared photodetector by a single layer of nc-Si:H thin film on a glass substrate, which shows superiority to the traditional amorphous Si photodetector with a diode or Schottky-barrier structure constructed by multilayer films on the crystalline Si substrate.
Analysis on the contribution of molecular orbitals to the conductance of molecular electronic devices
Authors: Li Rui , Hou Shimin , Zhang Jiaxing , Qian Zekan , Shen Ziyong , Zhao Xingyu
Published: November 2006

We present a theoretical approach which allows one to extract the orbital contribution to the conductance of molecular electronic devices. This is achieved by calculating the scattering wave functions after the Hamiltonian matrix of the extended molecule is obtained from a self-consistent calculation that combines the nonequilibrium Green’s function formalism with density functional theory employing a finite basis of local atomic orbitals. As an example, the contribution of molecular orbitals to the conductance of a model system consisting of a 4,4-bipyridine molecule connected to two semi-infinite gold monatomic chains is explored, illustrating the capability of our approach.
Short-range order in nanoscale amorphous intergranular films in liquid-phase sintered silicon carbide
Authors: Zhang Xiao Feng , Wang Rongming
Published: November 2006

Short-range order in amorphous intergranular films in SiC hot pressed with Al, B, and C additives was recognized with autocorrelation processing of high-resolution electron microscopy images. The short-range order corresponds to Al–O–C tetrahedra formed near the SiC matrix grains. In situ heating high-resolution transmission electron microscopy study demonstrated that the amorphous-to-crystalline transformation in the amorphous Al–O–C intergranular films started from nucleation and local growth of the short-range order structure.
Stochastic simulation of catalytic surface reactions in the fast diffusion limit
Authors: Mastny Ethan A. , Haseltine Eric L. , Rawlings James B.
Published: November 2006

The master equation of a lattice gas reaction tracks the probability of visiting all spatial configurations. The large number of unique spatial configurations on a lattice renders master equation simulations infeasible for even small lattices. In this work, a reduced master equation is derived for the probability distribution of the coverages in the infinite diffusion limit. This derivation justifies the widely used assumption that the adlayer is in equilibrium for the current coverages and temperature when all reactants are highly mobile. Given the reduced master equation, two novel and efficient simulation methods of lattice gas reactions in the infinite diffusion limit are derived. The first method involves solving the reduced master equation directly for small lattices, which is intractable in configuration space. The second method involves reducing the master equation further in the large lattice limit to a set of differential equations that tracks only the species coverages. Solution of the reduced master equation and differential equations requires information that can be obtained through short, diffusion-only kinetic Monte Carlo simulation runs at each coverage. These simulations need to be run only once because the data can be stored and used for simulations with any set of kinetic parameters, gas-phase concentrations, and initial conditions. An idealized CO oxidation reaction mechanism with strong lateral interactions is used as an example system for demonstrating the reduced master equation and deterministic simulation techniques.
Characterization of the three-dimensional turbulent boundary layer in a concentric annulus with a rotating inner cylinder
Authors: Jung Seo Yoon , Sung Hyung Jin
Published: November 2006

Direct numerical simulations of fluid flow through a concentric annulus with a rotating inner wall were performed at ReDh=8900. To elucidate the modifications of the near-wall turbulent structure induced by rotation of the inner wall, we compared data obtained at rotation rates of N=0.0 and 0.429 for a system with a radius ratio (R*) of 0.5. Conditional quadrant/octant analysis and probability density functions of the velocity fluctuations revealed distinctive features of the three-dimensional turbulent boundary layer (3DTBL) in the concentric annulus with a rotating inner wall. Coherent structures near the inner wall were identified by a λ2-based eduction scheme to give the detailed information on the activated near-wall turbulent structures. The ensemble-averaging of the educed coherent vortices showed that enhanced ejections near the vortices were primarily responsible for the augmented turbulent structures. The alteration of the turbulent structures was attributed to the centrifugal force arising from rotation of the inner wall. The assumption of Littell and Eaton on the cause of the altered turbulent structures in 3DTBLs was invalid in the present study. Taken together, the present results showed that the 3DTBL in a rotating concentric annulus has features different from those observed in other types of 3DTBL due to the transverse curvature.
Resonant excitation photoluminescence studies of InGaN∕GaN single quantum well structures
Authors: Graham D. M. , Dawson P. , Godfrey M. J. , Kappers M. J. , Humphreys C. J.
Published: November 2006

The optical properties of InGaN∕GaN quantum well structures, with indium fractions of 0.15 and 0.25, have been studied under resonant excitation conditions. The low-temperature (T=6K) photoluminescence spectra revealed a broad recombination peak that the authors have attributed to the acoustic-phonon assisted emission from a distribution of localized states, excited via an acoustic-phonon assisted absorption process. Comparing these results with theoretical calculations, where the authors consider the deformation potential coupling of the separately localized electron/hole pairs to an effectively continuous distribution of acoustic phonons, gives a value of approximately 2.5Å for the in-plane localization length scale.
Nonlinear transverse stabilization of spin-wave beams in magnetic stripes
Authors: Demidov Vladislav E. , Rekers Philipp , Mahrov Boriss , Demokritov Sergej O.
Published: November 2006

The propagation of spin-wave beams in ferromagnetic stripes has been investigated experimentally by means of spatially resolved Brillouin light scattering spectroscopy. It is shown that in the case of low-amplitude spin waves the diffraction and the transverse confinement of spin waves lead to oscillations of the beam width. The authors found that with increasing spin-wave amplitude the interplay between the linear diffraction and the repulsive spin-wave nonlinearity results in a suppression of the oscillations of the beam width and in its transverse stabilization.
Ferromagnetism in Mn doped half-Heusler NiTiSn: Theory and experiment
Authors: Sanyal B. , Eriksson O. , Suresh K. G. , Dasgupta I. , Nigam A. K. , Nordblad P.
Published: November 2006

In this letter, the authors show by ab initio density functional calculations and experiments that Mn doped semiconducting half-Heusler compound NiTiSn can exhibit room-temperature ferromagnetism. Curie temperatures were calculated by Monte Carlo simulations using calculated Heisenberg exchange parameters in an ab initio Green’s function approach. The calculated temperature exceeds room temperature for a Mn doping concentration of 22%. Magnetic measurements confirm the presence of possible intrinsic ferromagnetism in these systems. This brings up the possibility of considering this system as a potential candidate for use in room-temperature spintronic devices.
A quantum-classical approach to the molecular dynamics of pyrazine with a realistic model Hamiltonian
Authors: Puzari Panchanan , Sarkar Biplab , Adhikari Satrajit
Published: November 2006

We investigate the molecular dynamics of pyrazine after excitation to the S2 electronic state by using the time-dependent discrete variable representation (TDDVR) method. The investigation has been carried out with a realistic 24-mode model Hamiltonian consisting of all the vibrational degrees of freedom of pyrazine molecule. First, we perform the simulation on a basic four-mode model, and then by including additional eight important modes and finally, by introducing 20 bath modes on the basic model. This sequential inclusion of bath modes demonstrates the effect of weak modes on the subsystem, where the calculations of energy and population transfer from basic model to the bath quantify the same effect. The spectral profile obtained by using TDDVR approach shows reasonably good agreement with the results calculated by quantum mechanical approach. It appears that the TDDVR approach for those large systems where quantum mechanical description is needed in a restricted region is a good compromise between accuracy and speed.
Alternative fundamental measure theory for additive hard sphere mixtures
Authors: Malijevský Alexandr
Published: November 2006

The purpose of this short paper is to present an alternative fundamental measure theory (FMT) for hard sphere mixtures. Keeping the main features of the original Rosenfeld’s FMT [Phys. Rev. Lett. 63, 980 (1989)] and using the dimensional and the low-density limit conditions a new functional is derived incorporating Boublík’s multicomponent extension [Mol. Phys. 59, 371 (1986)] of highly accurate Kolafa’s equation of state for pure hard spheres. We test the theory for pure hard spheres and hard sphere mixtures near a planar hard wall and compare the results with the original Rosenfeld’s FMT and one of its modifications and with new very accurate simulation data. The test reveals an excellent agreement between the results based on the alternative FMT and simulation data for density profile near a contact and some improvement over the original Rosenfeld’s FMT and its modification at the contact region.
Effective charges along the melting line of colloidal crystals
Authors: Shapran Larysa , Schöpe Hans Joachim , Palberg Thomas
Published: November 2006

The shear modulus G of charged colloidal crystals was measured at several constant particle densities n and varying salt concentrations c up to the melting salt concentration cM using torsional resonance spectroscopy. Far from the phase boundary the samples are polycrystalline and the shear modulus stays roughly constant as a function of c. Upon approaching the melting transition an increasing amount of wall based crystal material is formed surrounding a shrinking polycrystalline core and G drops nearly linearly. When the transition is complete G again stays constant. The morphologic transitions may be scaled upon a single master curve. For the polycrystalline morphology, the elastic data are evaluated in terms of a pairwise additive screened Coulomb interaction yielding a particle effective charge ZG*. Under de-ionized conditions Z0,G* is independent of n and significantly lower than expected from charge renormalization theory. With increasing salt concentration ZG* increases. The increase becomes more pronounced at larger n. By extrapolation we further obtain the melting line effective elasticity charge ZM,G*. ZM,G* shows a steplike increase with increasing nM and cM to values consistent with charge renormalization theory. Interestingly, the increase coincides semi-quantitatively with the one expected from the universal melting line for charged spheres, thus facilitating a consistent description of phase behavior and elasticity over an extended range of the phase diagram.