bluuebunny/crossref_metadata_2025 huggingface dataset:
Using coda wave interferometry for estimating the variation in source mechanism between double couple events
Authors: Robinson D. J. , Snieder R. , Sambridge M.
Published: December 2007

It is shown how a change in orientation between the source mechanism of two identically located double couple sources can be estimated from the correlation of the coda waves excited by their sources. The change in orientation is given by the root mean square of the change in strike, Δϕs dip, Δδ and rake, Δλ of the double couple. It is not possible to determine Δϕs, Δδ or Δλ individually from the cross correlation. Applicability of the theory is tested using synthetic waveforms generated from a 3D finite difference solver for the elastic wave equation. Changes in strike, dip and rake are tested independently and simultaneously. In each case a crossover point is identified such that the actual change in orientation is within one standard deviation of the coda wave interferometry (CWI) estimates for all rotations below the crossover. After the crossover, the CWI estimates give a lower bound on the change in orientation. Crossover points of 30°, 62°, and 56°, respectively are observed when the strike, dip and rake are varied independently. When all angles are varied simultaneously by the same quantity the crossover point is 17°. The new theory can be applied in combination with existing coda wave interferometry techniques for estimating source separation. It creates the potential for joint relative location and focal mechanism determination using information from seismic coda recorded at a single station.
A regional modeling study of the entraining Mediterranean outflow
Authors: Xu X. , Chassignet E. P. , Price J. F. , Özgökmen T. M. , Peters H.
Published: December 2007

We have evaluated a regional‐scale simulation of the Mediterranean outflow by comparison with field data obtained in the 1988 Gulf of Cádiz Expedition. Our ocean model is based upon the Hybrid Coordinate Ocean Model (HYCOM) and includes the Richardson number–dependent entrainment parameterization of Xu et al. (2006). Given realistic topography and sufficient resolution, the model reproduces naturally the major, observed features of the Mediterranean outflow in the Gulf of Cádiz: the downstream evolution of temperature, salinity, and velocity profiles, the mean path and the spreading of the outflow plume, and most importantly, the localized, strong entrainment that has been observed to occur just west of the Strait of Gibraltar. As in all numerical solutions, there is some sensitivity to horizontal and vertical resolution. When the resolution is made coarser, the simulated currents are less vigorous and there is consequently less entrainment. Our Richardson number–dependent entrainment parameterization is therefore not recommended for direct application in coarse‐resolution climate models. We have used the high‐resolution regional model to investigate the response of the Mediterranean outflow to a change in the freshwater balance over the Mediterranean basin. The results are found in close agreement with the marginal sea boundary condition (MSBC): A more saline and dense Mediterranean deep water generates a significantly greater volume transport of the Mediterranean product water having only very slightly greater salinity.
Radar observations of long‐term variability of mesosphere and lower thermosphere winds over Tirunelveli (8.7°N, 77.8°E)
Authors: Sridharan S. , Tsuda T. , Gurubaran S.
Published: December 2007

The horizontal wind data acquired by MF radar at Tirunelveli (8.7°N, 77.8°E) for the period January 1993 to July 2006 are used to study long‐term variability of equatorial mesosphere and lower thermosphere (MLT) winds. The monthly mean zonal wind exhibits dominant semiannual variability with westward winds during equinox and eastward winds during solstice. The first westward phase, which occurs during spring equinox, undergoes interannual variability with larger westward winds during the years 1993, 1995 and 1997. This interannual variability has been interpreted as quasi‐biennial oscillation (QBO) in the MLT winds. However, this QBO is absent during the year 1999, as the next large westward wind phase occurs during the year 2000. Thus the period of QBO is extended from nearly 2 to 3 years (a). During these years, the period of stratospheric QBO winds is also extended to 3 a. Besides SAO and QBO, as the zonal winds undergo intraseasonal oscillations with periodicities resembling those of Madden‐Julian Oscillation (MJO) in the troposphere, the relation between the two is examined on the basis of the existing hypothesis. The present study reveals long‐term variation in the amplitude of the annual oscillation noticed in monthly mean meridional winds. A decreasing trend is observed in the annual mean northward winds during the years 1993–2006 in contrast to decreasing trend in the annual mean southward winds reported from midlatitudes. These observations are discussed in the context of our current understanding of long‐term variability of MLT winds.
Self/non‐self discrimination and the problem of keeping T cells alive
Authors: Sprent Jonathan , Cho Jae‐Ho
Published: December 2007

Burnet appreciated the requirement for self/non‐self discrimination and presciently postulated elimination of auto‐aggressive cells during early life. He could not have known that, for T cells, a limited degree of autoreactivity is beneficial for the immune system. Here, we review evidence that recognition of self‐components keeps T cells alive and regulates self‐tolerance.
Competition Aspects of Pharmaceutical Patent Settlements and Licences in Australia
Authors: Condon Wayne
Published: December 2007

This paper provides an overview of the competition law (antitrust) issues surrounding the licensing of patented technology in Australia, including licences granted to settle patent litigation. Compliance within Australian competition law in the context of IP licensing is likely to assume greater importance in light of the projected tightening of safe harbour provisions.
Analysing Business Losses Caused by Information Systems Risk: A Business Process Analysis Approach
Authors: Salmela Hannu
Published: December 2007

Increased reliance on computers by many companies and public organisations has generated a business risk for them. For example, problems in systems availability can lead to additional cost in operations, lost revenues and competitive losses. Systematic analyses are needed to avoid such losses. Prior research provides rigorous methods for identifying information systems risks and reducing the likelihood of these risks. The analysis of potential business losses in the user organisations has, however, received only limited attention. The objective in this paper is to investigate methods that can be used in the systematic identification of potential losses in the user organisation. The paper provides a review of prior literature on methods that can be used to analyse and report such losses. One understudied method is business process analysis that entails a systematic analysis of potential losses in different phases of the organisation's core business processes. Action research was used to examine the use of business process analysis as a method to associate information systems availability risk with potential business losses. The analysis was carried out in two different companies, one operating in the paper industry and the other one in the finance sector. The study contributes to research by summarising prior research on the analysis of business losses and by illustrating how the use of one method, business process analysis, assisted the client organisations. Perhaps most importantly, it identifies a new topic that has received very little attention in information systems research, despite its obvious managerial and practical significance.
On the relative stabilities of gold nanoparticles
Authors: Grochola Gregory , Snook Ian K. , Russo Salvy P.
Published: December 2007

We calculate and compare the relative free energies of ideal/pristine gold nanoparticles for morphologies produced previously in vapor synthesis computer simulations. The results in conjunction with previous work provide a unique and direct quantitative comparison between ideal thermodynamics and kinetics in the synthesis of gold nanoparticles for an identical system. The ideal/pristine free energies suggest that the Ih morphology was the most stable structure up to the 147(Ih) followed by the TOh for all the remaining nanoparticle sizes. A grouping of m-Dh structures was identified in the size range N=146–318 with stabilities which were very close to the most stable Ih and TOh structures. The free energy analysis was somewhat at odds with population statistics obtained from our kinetic growth simulations where the Ih dominated and where very little presumably stable TOh nanoparticles were produced, implying that kinetic mechanisms are more influential than thermodynamic considerations. On the other hand other possible reasons for such discrepancies are discussed; one of these includes an interesting observation where the Ih morphology was found to have a unique ability to incorporate exposed surface disorder such as adatoms into stable hexagonal surface structures through internal and surface structural rearrangements, leading to a possible enhancement in stabilities of Ih-type morphologies.
Global perspectives on the energy landscapes of liquids, supercooled liquids, and glassy systems: The potential energy landscape ensemble
Authors: Wang Chengju , Stratt Richard M.
Published: December 2007

In principle, all of the dynamical complexities of many-body systems are encapsulated in the potential energy landscapes on which the atoms move—an observation that suggests that the essentials of the dynamics ought to be determined by the geometry of those landscapes. But what are the principal geometric features that control the long-time dynamics? We suggest that the key lies not in the local minima and saddles of the landscape, but in a more global property of the surface: its accessible pathways. In order to make this notion more precise we introduce two ideas: (1) a switch to a new ensemble that deemphasizes the concept of potential barriers, and (2) a way of finding optimum pathways within this new ensemble. The potential energy landscape ensemble, which we describe in the current paper, regards the maximum accessible potential energy, rather than the temperature, as a control variable. We show here that while this approach is thermodynamically equivalent to the canonical ensemble, it not only sidesteps the idea of barriers it allows us to be quantitative about the connectivity of a landscape. We illustrate these ideas with calculations on a simple atomic liquid and on the Kob-Andersen [Phys. Rev. E 51, 4626 (1995)] of a glass-forming liquid, showing, in the process, that the landscape of the Kob-Anderson model appears to have a connectivity transition at the landscape energy associated with its empirical mode-coupling transition. We turn to the problem of finding the most efficient pathways through potential energy landscapes in our companion paper.
Global perspectives on the energy landscapes of liquids, supercooled liquids, and glassy systems: Geodesic pathways through the potential energy landscape
Authors: Wang Chengju , Stratt Richard M.
Published: December 2007

How useful it is to think about the potential energy landscape of a complex many-body system depends in large measure on how direct the connection is to the system’s dynamics. In this paper we show that, within what we call the potential-energy-landscape ensemble, it is possible to make direct connections between the geometry of the landscape and the long-time dynamical behaviors of systems such as supercooled liquids. We show, in particular, that the onset of slow dynamics in such systems is governed directly by the lengths of their geodesics—the shortest paths through their landscapes within the special ensemble. The more convoluted and labyrinthine these geodesics are, the slower that dynamics is. Geodesics in the landscape ensemble have sufficiently well-defined characteristics that it is straightforward to search for them numerically, a point we illustrate by computing the geodesic lengths for an ordinary atomic liquid and a binary glass-forming atomic mixture. We find that the temperature dependence of the diffusion constants of these systems, including the precipitous drop as the glass-forming system approaches its empirical mode-coupling transition, is predicted quantitatively by the growth of the geodesic path lengths.
Split charge equilibration method with correct dissociation limits
Authors: Mathieu Didier
Published: December 2007

Analytic reactive potentials rely on electronegativity equalization to describe how the electron distribution is affected as chemical reactions occur. However, such models predict fractional charges for neutral species with different electronegativities. To overcome this well-known dissociation problem, an approach taking advantage of the concept of split charges [R. A. Nistor, J. G. Polihronov, M. H. Müser, and N. J. Mosey, J. Chem. Phys. 125, 094108 (2006)] is put forward. A first implementation is presented. Starting from a previous model [P. Bultinck, W. Langenaeker, P. Lahorte, F. D. Proft, P. Geerlings, M. Waroquier, and J. P. Tollenaere, J. Phys. Chem. A 106, 7887 (2002)], a new contribution to the total energy is introduced in order to make up for the lack of suitable constraints on the charge density. Its effect is to restrain charge transfer between remote atoms. As a consequence, systems in gas phase naturally decompose into neutral fragments. This result is achieved using two empirical parameters in addition to atomic electronegativities and hardnesses.
The BΠ1 state of NaCs: High resolution laser induced fluorescence spectroscopy and potential construction
Authors: Zaharova J. , Docenko O. , Tamanis M. , Ferber R. , Pashov A. , Knöckel H. , Tiemann E.
Published: December 2007

The lowest Π1 state of the NaCs molecule, the B(1)Π1 state, was studied using a dye laser for inducing fluorescence that was resolved by a high resolution Fourier-transform spectrometer. The presence of argon buffer gas yielded rich rotational relaxation spectra allowing to enlarge the data set for the B(1)Π1 state, to obtain Λ-splittings and to reveal numerous local perturbations. 543 weakly perturbed energy levels for rotational quantum numbers from J′=5 to 168 and vibrational quantum numbers from v′=0 to 25, which cover about 87% of the potential well depth, were used for a direct pointwise fit of the potential energy curve applying the inverted perturbation approach method. The resulting potential reproduces the term values for v′=0–7 with an experimental accuracy of about 0.01–0.02cm−1, whereas for v′=8–25 the deviations increase due to the perturbations, going to the order of 1cm−1; an extrapolation is made to the dissociation asymptote.
Solvent dependence of OH bend vibrational relaxation of monomeric water molecules in liquids
Authors: Seifert G. , Graener H.
Published: December 2007

The vibrational relaxation rates of the OH bending mode of monomeric H2O molecules diluted in various liquid halogenated methane and ethane derivates have been determined by a picosecond infrared pump-probe study. Relaxation time constants between 4.8 and 40.5ps have been obtained. The discussion of the general solvent dependence suggests that in all cases the solvent fundamental with the smallest energy mismatch is favorably populated by this intermolecular energy transfer process.
Nuclear spin selection rules for reactive collision systems by the spin-modification probability method
Authors: Park Kisam , Light John C.
Published: December 2007

The spin-modification probability (SMP) method, which provides fundamental and detailed quantitative information on the nuclear spin selection rules, is discussed more systematically and generalized for reactive collision systems involving more than one configuration of reactant and product molecules, explicitly taking account of the conservation of the overall nuclear spin symmetry as well as the conservation of the total nuclear spin angular momentum, under the assumption of no nuclear hyperfine interaction. The values of SMP once calculated can be used for any system of identical nuclei of any spin as long as the system has the corresponding nuclear spin symmetry. The values of SMP calculated for simple systems can also be used for more complex systems containing several kinds of identical nuclei or various isotopomers. The generalized formulation of statistical scattering theory which can easily represent various rearrangement mechanisms is also presented.
Vorticity dynamics of a dipole colliding with a no-slip wall
Authors: Kramer W. , Clercx H. J. H. , van Heijst G. J. F.
Published: December 2007

The active role of vorticity in the collision of a Lamb-like dipole with a no-slip wall is studied for Re values ranging between 625 and 20000. The initial approach of the dipole does not differ from the stress-free case or from a point-vortex model that incorporates the diffusive growth of the dipole core. When closer to the wall, the detachment and subsequent roll-up of the boundary layer leads to a viscous rebound, as was observed by Orlandi [Phys. Fluids A 2, 1429 (1990)] in numerical simulations with Re up to 3200. The net translation of the vortex core along the wall is strongly reduced due to the cycloid-like trajectory. For Re⩽2500 wall-generated vorticity is wrapped around the separate dipole halves, which hence become (partially) shielded monopoles. For Re≳O(104), however, a shear instability causes the roll-up of the boundary layer before it is detached from the wall. This leads to the formation of a number of small-scale vortices, between which intensive, narrow eruptions of boundary-generated vorticity occur. Quantitative measures are given for the influx of vorticity at the wall and the consequent increase of boundary layer vorticity and enstrophy.
Local wettability modification by thermochemical nanolithography with write-read-overwrite capability
Authors: Wang D. B. , Szoszkiewicz R. , Lucas M. , Riedo E. , Okada T. , Jones S. C. , Marder S. R. , Lee J. , King W. P.
Published: December 2007

The wettability of a thin polymer film was modified twice by thermochemical nanolithography. By means of a first local chemical modification induced by an atomic force microscope tip heated to 110±20°C, hydrophilic patterns are written over an originally hydrophobic polymer surface. By further heating to 190±20°C, a second chemical modification reverses the local wettability change introduced by the first chemical modification. This write-read-overwrite capability can be particularly useful in the design of complex nanofluidic devices.
Nonlinear ac responses of erythrocyte suspensions: Experiment and theory
Authors: Zhu J. T. , Tian W. J. , Zheng S. , Huang J. P. , Zhou L. W.
Published: December 2007

When a suspension consisting of electric particles having nonlinear characteristics is subjected to a sinusoidal alternating current (ac) electric field, the electric response will generally consist of ac fields at frequencies of higher-order harmonics. We experimentally report on harmonic generation by erythrocytes subjected to an ac electric field. We find that both even and odd harmonics are sensitive to cell shapes, conductivities, field frequencies, and field magnitude. Theoretical analysis based on a phenomenological model yield predictions that are in excellent agreement with the experiments. Thus, it becomes possible to detect nonlinear characteristics, shapes, and conductivities of erythrocytes by measuring such ac responses.
Microstructure and magnetic properties of magnetite thin films prepared by reactive sputtering
Authors: Qiu Hongmei , Pan Liqing , Li Liwei , Zhu Hao , Zhao Xuedan , Xu Mei , Qin Liangqiang , Xiao John Q.
Published: December 2007

Highly oriented magnetite (Fe3O4) thin films have been produced by reactive sputtering in a mixture of hydrogen and argon. While different phases can be achieved by varying the ratio between hydrogen and argon, single phase magnetite films can be achieved with hydrogen concentration γ=0.75%–1%. For the sample grown at γ=1.0%, a Verwey transition at about 111K can be seen from the temperature dependence of the resistivity, which is confirmed in the magnetization measurements. Maximum magnetoresistance (MR) of about 13.8% is observed just about the Verwey transition at T=115K. MR results also suggest strong coupling among Fe3O4 nanoparticles originated from the Ruderman-Kittel-Kasuya-Yosida exchange interaction and dipolar interaction, which requires high order terms of (M∕Ms)2 to explain the MR behaviors. However, with the fields applied perpendicular to the plane, MR exhibits a distinct behavior. The MR values under the condition of low fields seem to show a linear relationship with ∣M∕MS∣.
Structure-functional property relationships in rf-sputtered vanadium dioxide thin films
Authors: Ruzmetov Dmitry , Zawilski Kevin T. , Narayanamurti Venkatesh , Ramanathan Shriram
Published: December 2007

The study of metal-insulator transition (MIT) in VO2 thin films synthesized by means of rf sputtering from a VO2 target is presented. A comparison with conventional reactive sputtering from a V target is also given. Detailed x-ray diffraction analysis, electrical resistance switching, and infrared optical reflectance measurements confirm that our sputtering technique yields high-quality VO2 films. We discuss in depth how synthesis conditions affect MIT parameters derived from temperature dependence of electrical resistance. Sharp MIT is observed in films sputtered on technologically important Si substrates. The choice of Si (or sapphire) substrates results in the transition temperature above (below) the values obtained for single VO2 crystals. The MIT becomes narrower and stronger in thinner films. This is consistent with the assumption that the increased width of the MIT in thin films with respect to single crystals is the result of averaging of the transition parameters over a distribution of crystallites in the film. The measurements of MIT in VO2 patterned into devices do not reveal a noticeable lateral size effect down to 20 μm devices, encouraging use of the phase transition in switching electronic devices. The effect of substrate temperature and ambient during the sputtering on MIT is discussed. While VO2 films are found to be stable in ambient environment with time, the additional exposure to UV radiation near room temperature is shown to enhance the oxidation kinetics and produce changes in film resistance. Using UV radiation as an additional tool to control the oxidation process during VO2 synthesis may allow the synthesis temperature to be lowered and an improvement in material quality. We anticipate these results may be of relevance to synthesizing functional oxide films with potential applications in electronics and sensors.
Experimentally inferred thermal diffusivities in the edge pedestal between edge-localized modes in DIII-D
Authors: Stacey W. M. , Groebner R. J.
Published: December 2007

Using temperature and density profiles averaged over the same subinterval of several successive inter-edge-localized-mode (ELM) periods, the ion and electron thermal diffusivities in the edge pedestal were inferred between ELMs for two DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharges. The inference procedure took into account the effects of plasma reheating and density buildup between ELMs, radiation and atomic physics cooling, neutral beam heating and ion-electron equilibration, and recycling neutral and beam ionization particle sources in determining the conductive heat flux profiles used to infer the thermal diffusivities in the edge pedestal. Comparison of the inferred thermal diffusivities with theoretical formulas based on various transport mechanisms was inconclusive insofar as identifying likely transport mechanisms.
Multiparticle quasiexactly solvable difference equations
Authors: Odake Satoru , Sasaki Ryu
Published: December 2007

Several explicit examples of multiparticle quasiexactly solvable “discrete” quantum mechanical Hamiltonians are derived by deforming the well-known exactly solvable multiparticle Hamiltonians, the Ruijsenaars-Schneider-van Diejen systems. These are difference analogs of the quasiexactly solvable multiparticle systems, the quantum Inozemtsev systems obtained by deforming the well-known exactly solvable Calogero-Sutherland systems. They have a finite number of exactly calculable eigenvalues and eigenfunctions. This paper is a multiparticle extension of the recent paper by one of the authors [R. Sasaki, J. Math. Phys. 48, 122104 (2007)] on deriving quasiexactly solvable difference equations of single degree of freedom.
Growth and field emission properties of vertically aligned molybdenum–sulfur–iodine nanowires on molybdenum and quartz substrates
Authors: Dvorsek Damjan , Zumer Marko , Nemanic Vincenc , Mihailovic Dragan , Vengust Damjan
Published: December 2007

Vertically aligned bundles of molybdenum–sulfur–iodine nanowires (MoSIx) were grown on a molybdenum foil, thin wire, and quartz substrate. By choosing different growth parameters we have been able to vary the surface density from ∼0.01 to 0.5 bundless/μm2 and the length of the nanowire bundles from ∼30 μm to 15 mm. In the case of growth on molybdenum, resistivity measurements show that a good electrical contact exists between the bundles and the metal substrate. The nanowires are found to have excellent field emission properties, competitive with state-of-the-art carbon nanotube large-area field emitters.
Trap-controlled hole transport in small molecule organic semiconductors
Authors: Fleissner Arne , Schmid Hanna , Melzer Christian , von Seggern Heinz
Published: December 2007

The influence of trap concentration on hole transport is investigated by an optical time-of-flight method for the amorphous small molecule organic semiconductor N,N′-bis(1-naphtyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamin (α-NPD) doped with neutral hole traps by codeposition of 4,4′,4″-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA). α-NPD doped with 120ppm 1-NaphDATA exhibits nondispersive hole transport like undoped α-NPD, but trap-controlled with reduced mobility. The trap depth derived from the mobility decrease coincides with the ionization potential difference of α-NPD and 1-NaphDATA. The transition to dispersive transport for increasing trap concentration to 1160ppm is explained by an energetic relaxation of optically generated charge carriers within a density of states broadened by traps.
Holographically fabricated photonic crystals with large reflectance
Authors: Chen Y. C. , Geddes J. B. , Lee J. T. , Braun P. V. , Wiltzius P.
Published: December 2007

We report reflection and transmission spectra from three-dimensional polymer photonic crystals fabricated by holographic lithography. The measured peak reflectance matches that predicted by both a finite-difference time-domain method a simple transfer matrix theory and is ∼70%, significantly higher than previous reports of ∼30% reflectance.
Mixed ionic-electronic conductivity in yttria-stabilized zirconia/carbon nanotube composites
Authors: Fonseca F. C. , Muccillo R. , de Florio D. Z. , Ladeira L. O. , Ferlauto A. S.
Published: December 2007

The fabrication of yttria stabilized-zirconia/single-wall carbon nanotube (YSZ/SWCNT) composites is reported. Electrical conductivity measurements from 25to800°C revealed that the composites exhibit mixed ionic-electronic conduction. At room temperature, the conductivity increases by 11 orders of magnitude with the addition of SWCNT to the YSZ. At high temperatures (>300°C), the ionic conduction of the YSZ becomes relevant and a mixed ionic-electronic transport is observed. It is found that the transport can be described by a sum of two parallel contributions: thermally activated ionic conduction from the YSZ and fluctuation-assisted tunneling within the SWCNT network.
The properties of ZnO photoluminescence at and above room temperature
Authors: Chen Xiang-Bai , Huso Jesse , Morrison John L. , Bergman Leah
Published: December 2007

A study of the photoluminescence characteristics of a ZnO single crystal at the temperature range 173–823 K is presented. The analysis employed the electron-phonon interaction model as well as the radiative recombination rate model. Both studies indicate that at ∼700 K the photoluminescence character undergoes a transition from being a free exciton emission to a band gap recombination, implying a breakup of excitons into free carriers is occurring. The transition temperature corresponds to ∼60 meV, which is consistent with the binding energy of the free exciton in ZnO.
Consolidation enhancement in spark-plasma sintering: Impact of high heating rates
Authors: Olevsky Eugene A. , Kandukuri Sastry , Froyen Ludo
Published: December 2007

Spark-plasma sintering (SPS) provides accelerated densification and, in many cases, limited grain growth compared to regular hot pressing and sintering. Possible mechanisms of this enhancement of the consolidation in SPS versus conventional techniques of powder processing are identified. The consolidation enhancing factors are categorized with respect to their thermal and nonthermal nature. This paper analyses the influence of a major factor of thermal nature: high heating rates. The interplay of three mechanisms of material transport during SPS is considered: surface diffusion, grain-boundary diffusion, and power-law creep. It is shown that high heating rates reduce the duration of densification-noncontributing surface diffusion, this favors powder systems’ sinterability and the densification is intensified by grain-boundary diffusion. Modeling indicates that, besides the acceleration of densification, high heating rates diminish grain growth. The impacts of high heating rates are dependent on particle sizes. Besides SPS, the obtained results are applicable to the broad spectrum of powder consolidation techniques which involve high heating rates. The conducted experiments on SPS of an aluminum alloy powder confirm the model predictions of the impact of heating rates and initial grain sizes on the shrinkage rates during the electric current-assisted consolidation. It is noted, that this study considers only one of many possible mechanisms of the consolidation enhancement during SPS, which should stimulate further efforts on the modeling of field-assisted powder processing.
Tuning of direct current bias-induced resonances in micromachined Ba0.3Sr0.7TiO3 thin-film capacitors
Authors: Noeth Andreas , Yamada Tomoaki , Sherman Vladimir O. , Muralt Paul , Tagantsev Alexander K. , Setter Nava
Published: December 2007

Direct current (dc) bias-induced acoustic resonance phenomena have been observed in micromachined tunable thin-film capacitors based on paraelectric Ba0.3Sr0.7TiO3 thin films. Both resonance and antiresonance frequencies are dc bias dependent. The antiresonance frequency is only weakly dc bias dependent and shifts slightly down with increasing dc bias. The resonance frequency shows a much stronger dependence on the applied dc bias than the antiresonance frequency, and also shifts down to lower frequencies with increasing bias. The resonance frequency shifted by 2.0% for a frequency of about 3 GHz and an applied field of 730 KV/cm. At the same time the effective electromechanical coupling constant kt,eff2 increased up to 3.6%. The tuning of the resonance frequency depends on the tunability of the film permittivity and on the mechanical load on the piezoactive layer. The constitutive equations controlling the tuning of the resonance and antiresonance frequency were derived from the Landau theory using the P-expansion of its free energies. The theoretical predictions show that, in the considered system, the frequency of the first-order resonance (λ/2 resonance) will always shift down with increasing bias, whereas the antiresonance frequency might shift up or down with increasing bias. The sense of the shift of the antiresonance frequency depends on the sign and the magnitude of the corresponding coefficients of the tensors of linear and nonlinear electrostriction. The theoretical predictions corroborate the experimental observations very well.
Determination of the hopping contribution to the thermopower in bismuth infiltrated colloidal crystals
Authors: Arva Sreenath , Alphenaar Bruce , Sumanasekera Gamini
Published: December 2007

Conductivity and thermopower measurements of artificial three dimensional bismuth crystals are presented. Due to the size dependent band gap of bismuth, electron transport in the bismuth crystals is a combination of both metallic and hopping conduction. The conductivity and thermopower due to the hopping pathways alone can be extracted through a comparison of the properties of the artificial bismuth crystal before and after it is compressed into bulk bismuth. In this way, evidence for the influence of electron-electron interactions on the hopping conductivity is obtained.
Mechanical properties and tuning of three-dimensional polymeric photonic crystals
Authors: Juodkazis Saulius , Mizeikis Vygantas , Seet Kock Khuen , Misawa Hiroaki , Wegst Ulrike G. K.
Published: December 2007

Mechanical properties of photopolymerized photonic crystal (PhC) structures having woodpile and spiral three-dimensional architectures were examined using flat-punch indentation. The structures were found to exhibit a foamlike response with a bend-dominated elastic deformation regime observed at strain levels up to 10%. Numerical simulations of optical properties of these PhC structures demonstrate the possibility of achieving a substantial and reversible spectral tuning of the photonic stop gap wavelength by applying a mechanical load to the PhC.
Spatially controlled atomic layer deposition in porous materials
Authors: Elam J. W. , Libera J. A. , Pellin M. J. , Stair P. C.
Published: December 2007

We describe a technique for depositing materials at controlled depths within porous substrates based upon the passivating effect produced by one precursor to prevent the adsorption of a second precursor. For example, a surface exposed to trimethyl aluminum is not reactive toward diethyl zinc. This effect, combined with Knudsen diffusion in which the precursor exposure times dictate the depth of penetration of the deposited layer, enables spatially controlled “stripe coating” within porous supports. We demonstrate ZnO stripes in anodic alumina and model the results using Monte Carlo simulations. Etching is identified as a potential problem for certain precursor combinations.
The tumor suppressor Fhit acts as a repressor of β-catenin transcriptional activity
Authors: Weiske Jörg , Albring Kai Frederik , Huber Otmar
Published: December 2007

The Fra3B locus on chromosome 3p14.2 targeting the
fragile histidine triad
(
Fhit
) gene represents one of the most common fragile sites of the human genome and is associated with early preneoplastic and malignant disorders in multiple human tumors. Fhit was classified as a tumor suppressor; however, the molecular mechanisms of its function are not well established. Here, we report that Fhit associates with the lymphoid enhancer-binding factor 1/T cell factor/β-catenin complex by directly binding to β-catenin, a major player in the canonical Wnt pathway that is deregulated in numerous forms of human cancer. In binding to the β-catenin C-terminal domain, Fhit represses transcription of target genes such as
cyclin D1
,
axin2
,
MMP-14
, and
survivin
. Knockdown of Fhit reversed this effect, whereas this reversal was not detectable when β-catenin was knocked down simultaneously. The Fhit enzymatic activity as a diadenosine-polyphosphate hydrolase is not required for the down-regulation of β-catenin-mediated transcription as examined with an enzymatic inactive Fhit-H96N protein. ChIPs revealed recruitment of Fhit/β-catenin complexes to target gene promoters. In soft agar assays Fhit and β-catenin are involved in regulation of anchorage-independent growth. These observations assign to the tumor suppressor Fhit an unexpected role in the regulation of β-catenin-mediated gene transcription.
Processing and classification of chemical data inspired by insect olfaction
Authors: Schmuker Michael , Schneider Gisbert
Published: December 2007

The chemical sense of insects has evolved to encode and classify odorants. Thus, the neural circuits in their olfactory system are likely to implement an efficient method for coding, processing, and classifying chemical information. Here, we describe a computational method to process molecular representations and classify molecules. The three-step approach mimics neurocomputational principles observed in olfactory systems. In the first step, the original stimulus space is sampled by “virtual receptors,” which are chemotopically arranged by a self-organizing map. In the second step, the signals from the virtual receptors are decorrelated via correlation-based lateral inhibition. Finally, in the third step, olfactory scent perception is modeled by a machine learning classifier. We found that signal decorrelation during the second stage significantly increases the accuracy of odorant classification. Moreover, our results suggest that the proposed signal transform is capable of dimensionality reduction and is more robust against overdetermined representations than principal component scores. Our olfaction-inspired method was successfully applied to predicting bioactivities of pharmaceutically active compounds with high accuracy. It represents a way to efficiently connect chemical structure with biological activity space.
Indicators of 21st century socioclimatic exposure
Authors: Diffenbaugh Noah S. , Giorgi Filippo , Raymond Leigh , Bi Xunqiang
Published: December 2007

Policies that attempt to curb greenhouse gas emissions, allocate emissions rights, or distribute compensation to those most damaged by climate change must explicitly incorporate the international heterogeneity of the climate change threat. To capture the distinct susceptibilities associated with lack of infrastructure, potential property loss, and gross human exposure, we develop an integration of climate change projections and poverty, wealth, and population metrics. Our analysis shows that most nations of the world are threatened by the interaction of regional climatic changes with one or more relevant socioeconomic factors. Nations that have the highest levels of poverty, wealth, and population face greater relative exposure in those dimensions. However, for each of those socioeconomic indicators, spatial heterogeneity in projected climate change determines the overall international pattern of socioclimatic exposure. Our synthesis provides a critical missing piece to the climate change debate and should facilitate the formulation of climate policies that account for international variations in the threat of climate change across a range of socioeconomic dimensions.
Wnt signal from multiple tissues and
lin-3
/EGF signal from the gonad maintain vulval precursor cell competence in
Caenorhabditis elegans
Authors: Myers Toshia R. , Greenwald Iva
Published: December 2007

The
Caenorhabditis elegans
vulva has been a valuable paradigm for defining components of signaling pathways and elucidating how signaling events are coordinated to generate a developmental pattern. Vulval precursor cells (VPCs) are induced to adopt vulval fates in the third larval stage by LIN-3, an EGF-like signal produced by the gonad. Competence to respond to the inductive signal requires that the VPCs do not fuse to the major hypodermal syncytium, hyp7. We found that two Wnt-encoding genes,
cwn-1
and
egl-20
, play a major role in preventing fusion of VPCs with hyp7 in the second larval stage. By using tissue-specific rescue of
mig-14
/Wntless, which is required for the production of Wnt ligands, we found that Wnt signal produced by multiple tissues, including neurons and muscles, promotes or maintains VPC competence before vulval induction. In addition, through laser ablation and genetic analysis, we provide evidence that LIN-3 signal from the gonad also plays a significant role in preventing VPCs from fusing with hyp7. We propose that Wnt signaling plays a permissive role in preventing VPCs from fusing with hyp7 and reevaluate the roles of Wnt and LIN-3/EGF signaling in competence and induction.
Developmental processes underlying the evolution of a derived foot morphology in salamanders
Authors: Jaekel Martin , Wake David B.
Published: December 2007

Interdigital webbing has evolved repeatedly in tropical salamanders (bolitoglossines). This derived foot morphology is only one of many homoplastic traits in this diverse amphibian clade. Indeed, few if any morphological traits sort lineages within this clade. We investigate the processes underlying the homoplastic evolution of morphological characters in these salamanders by analyzing selective and developmental processes that generate interdigital webbing. We show that a pedomorphic developmental change generates the new foot morphology and that pedomorphosis affects a number of morphological traits, thus creating a developmental correlation among them. This correlation among traits is maintained across most species, thus facilitating the repeated evolution of traits. Although we find evidence that the changes in foot morphology are adaptive in one species, the evolution of webbing in all other species does not carry an adaptive signature. The new foot morphology therefore evolves repeatedly, even in the apparent absence of a direct selective advantage.
Intracellular complexes of the β2 subunit of the nicotinic acetylcholine receptor in brain identified by proteomics
Authors: Kabbani Nadine , Woll Matthew P. , Levenson Robert , Lindstrom Jon M. , Changeux Jean-Pierre
Published: December 2007

Nicotine acetylcholine receptors (nAChRs) comprise a family of ligand-gated channels widely expressed in the mammalian brain. The β2 subunit is an abundant protein subunit critically involved in the cognitive and behavioral properties of nicotine as well as in the mechanisms of nicotine addiction. In this work, we used matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS/MS) to uncover protein interactions of the intracellular loop of the β2 subunit and components of immunoprecipitated β2–nAChR complexes from mouse brain. Using the β2-knockout mouse to exclude nonspecific binding to the β2 antibody, we identify 21 nAChR-interacting proteins (NIPs) expressed in brain. Western blot analysis confirmed the association between the β2 subunit and candidate NIPs. Based on their functional profiles, the hypothesis is suggested that the identified NIPs can regulate the trafficking and signaling of the β2–nAChR. Interactions of the β2 subunit with NIPs such as G protein α, G protein-regulated inducer of neurite outgrowth 1, and G protein-activated K
+
channel 1 suggest a link between nAChRs and cellular G protein pathways. These findings reveal intracellular interactions of the β2 subunit and may contribute to the understanding of the mechanisms of nAChR signaling and trafficking in neurons.
POLITICAL COMMUNICATION ABOUT EUROPE ON THE INTERNET DURING THE 2004 EUROPEAN PARLIAMENT ELECTION CAMPAIGN IN NINE EU MEMBER STATES
Authors: van Os Renée , Jankowski Nicholas W. , Vergeer Maurice
Published: December 2007

This article considers the possibility of a European public sphere contributing to a reduction of the so-called ‘democratic deficit’ through engagement of citizens in the European project and enhancing processes of identification beyond the local or national environment. We elaborate on our interpretation of the European public sphere, emphasizing that political actors, including citizens, are engaged in political communication about Europe, either directly or indirectly through media or Internet-based representations. The study presented in this article investigates the extent of Europeanization of political communication on the Internet by measuring the visibility of communication about Europe on websites produced by various political actors in nine EU member states in the context of the 2004 European Parliament election. Two-thirds of the websites included in the study actually had European Parliamentary election-related content on the front page at the time of the election; a percentage we consider relatively low because of the search strategy followed. Actors addressed general European issues somewhat more frequently on their websites: in nearly three-quarters of cases, which can be considered an indicator of the existence of a European public sphere.
In vivo induction of postsynaptic molecular assembly by the cell adhesion molecule Fasciclin2
Authors: Kohsaka Hiroshi , Takasu Etsuko , Nose Akinao
Published: December 2007

Cell adhesion molecules (CAMs) are thought to mediate interactions between innervating axons and their targets. However, such interactions have not been directly observed in vivo. In this paper, we study the function and dynamics of Fasciclin2 (Fas2), a homophilic CAM expressed both pre- and postsynaptically during neuromuscular synapse formation in Drosophila melanogaster. We apply live imaging of functional fluorescent fusion proteins expressed in muscles and find that Fas2 and Discs-Large (Dlg; a scaffolding protein known to bind Fas2) accumulate at the synaptic contact site soon after the arrival of the nerve. Genetic, deletion, and photobleaching analyses suggest that Fas2-mediated trans-synaptic adhesion is important for the postsynaptic accumulation of both Fas2 itself and Dlg. In fas2 mutants, many aspects of synapse formation appear normal; however, we see a reduction in the synaptic accumulation of Scribble (another scaffolding protein) and glutamate receptor subunits GluRIIA and GluRIIB. We propose that Fas2 mediates trans-synaptic adhesion, which contributes to postsynaptic molecular assembly at the onset of synaptogenesis.
Sorting switch of mitochondrial presequence translocase involves coupling of motor module to respiratory chain
Authors: Wiedemann Nils , van der Laan Martin , Hutu Dana P. , Rehling Peter , Pfanner Nikolaus
Published: December 2007

The mitochondrial presequence translocase transports preproteins to either matrix or inner membrane. Two different translocase forms have been identified: the matrix transport form, which binds the heat-shock protein 70 (Hsp70) motor, and the inner membrane–sorting form, which lacks the motor but contains translocase of inner mitochondrial membrane 21 (Tim21). The sorting form interacts with the respiratory chain in a Tim21-dependent manner. It is unknown whether the respiratory chain–bound translocase transports preproteins and how the switch between sorting form and motor form occurs. We report that the respiratory chain–bound translocase contains preproteins in transit and, surprisingly, not only sorted but also matrix-targeted preproteins. Presequence translocase-associated motor (Pam) 16 and 18, two regulatory components of the six-subunit motor, interact with the respiratory chain independently of Tim21. Thus, the respiratory chain–bound presequence translocase is not only active in preprotein sorting to the inner membrane but also in an early stage of matrix translocation. The motor does not assemble en bloc with the translocase but apparently in a step-wise manner with the Pam16/18 module before the Hsp70 core.