bluuebunny/crossref_metadata_2025 huggingface dataset:
The steady-state form of large-amplitude internal solitary waves
Authors: KING STUART E. , CARR MAGDA , DRITSCHEL DAVID G.
Published: November 2010

A new numerical scheme for obtaining the steady-state form of an internal solitary wave of large amplitude is presented. A stratified inviscid two-dimensional fluid under the Boussinesq approximation flowing between horizontal rigid boundaries is considered. The stratification is stable, and buoyancy is continuously differentiable throughout the domain of the flow. Solutions are obtained by tracing the buoyancy frequency along streamlines from the undisturbed far field. From this the vorticity field can be constructed and the streamfunction may then be obtained by inversion of Laplace's operator. The scheme is presented as an iterative solver, where the inversion of Laplace's operator is performed spectrally. The solutions agree well with previous results for stratification in which the buoyancy frequency is a discontinuous function. The new numerical scheme allows significantly larger amplitude waves to be computed than have been presented before and it is shown that waves with Richardson numbers as low as 0.062 can be computed straightforwardly. The method is also extended to deal in a novel way with closed streamlines when they occur in the domain. The new solutions are tested in independent fully nonlinear time-dependent simulations and are verified to be steady. Waves with regions of recirculation are also discussed.
Identity Politics Revisited: Secular and ‘Dissonant’ Islam in Colonial South Asia
Authors: PUROHIT TEENA
Published: November 2010

This paper analyzes the political project of secular Islam as outlined by the Indian political and religious leader, Muhammad Shah—also known as Aga Khan III (1877–1957). As first president of the All India Muslim League, Muhammad Shah facilitated the installation of separate electorates for Muslims as well as the call for Partition. The reformist notion of Islam he invoked for this separatist programme was informed by the secular and modernizing projects of the colonial public sphere. Simultaneously, however, Muhammad Shah claimed a divine role as Imam of the Ismaili Muslim community—a position validated by Ismaili beliefs and teachings of messianic Islam. The paper engages Muhammad Shah's writings and the devotional texts of the Ismailis to illustrate how the heterogeneous forms of practices peculiar to the vernacular history of Islam in early modern South Asia were displaced by the discourse of religious identity in the colonial period.
Cognitive Behavioural Therapy for Auditory Hallucinations: Effectiveness and Predictors of Outcome in a Specialist Clinic
Authors: Thomas Neil , Rossell Susan , Farhall John , Shawyer Frances , Castle David
Published: November 2010

Background: Cognitive behavioural therapy has been established as an effective treatment for residual psychotic symptoms but a substantial proportion of people do not benefit from this treatment. There has been little direct study of predictors of outcome, particularly in treatment targeting auditory hallucinations. Method: The Psychotic Symptom Rating Scales (PSYRATS) and Positive and Negative Syndrome Scale (PANSS) were administered pre- and post-therapy to 33 people with schizophrenia-related disorders receiving CBT for auditory hallucinations in a specialist clinic. Outcome was compared with pre-therapy measures of insight, beliefs about the origin of hallucinations, negative symptoms and cognitive disorganization. Results: There were significant improvements post-treatment on the PSYRATS and PANSS Positive and General Scales. Improvement on the PSYRATS was associated with lower levels of negative symptoms, but was unrelated to overall insight, delusional conviction regarding the origins of hallucinations, or levels of cognitive disorganization. Conclusions: Lack of insight and presence of formal thought disorder do not preclude effective cognitive-behavioural treatment of auditory hallucinations. There is a need to further understand why negative symptoms may present a barrier to therapy.
Illness Perceptions: Are Beliefs About Mental Health Problems Associated with Self-Perceptions of Engagement in People with Psychosis?
Authors: Williams Katie , Steer Hannah
Published: November 2010

Background: The Self-Regulation Model (SRM) has been presented as a framework for assessing the perceptions people hold about their mental health problem. Currently no direct attempts have been made to assess the association between illness perceptions and engagement in psychosis. Engagement is an important issue for health professionals providing support to people with psychosis; therefore, research demonstrating a link between illness perceptions and engagement may enable targeted interventions to facilitate engagement and enhance outcome. Aim: To assess whether beliefs about mental health are associated with self-perceptions of engagement in people with psychosis. Method: Participants with psychosis completed two questionnaires; beliefs about mental health and self-perceptions of engagement with mental health services. Results: A belief that the mental health difficulty has fewer negative consequences, increased perceptions of personal ability to control the mental health difficulty, a belief that treatment is helpful in controlling symptoms and a more coherent understanding of the mental health difficulty were all associated with higher self-perception engagement scores. Multivariate analyses indicated that a more coherent understanding and a belief that treatment is helpful were the strongest and most consistent predictors of higher self-perception engagement scores. However, the direction of the associations cannot be established. Conclusions: This study suggests that the SRM is a promising model for mental health problems and that beliefs about mental health are associated with self-perceptions of engagement in people with psychosis. The importance of further intervention-based research studies that examines causality is highlighted.
The telling of a spatial allegory: the Danteum as narrative labyrinth
Authors: Lu Andong
Published: November 2010

Among the legacy of Modernist architecture, the Danteum project is an extraordinary attempt to inscribe a literary expedition into architectural organism. Beyond its absolute form, the project makes use of the plastic effects of architectonics to create immersive ‘atmospheres’ that elicit states of mind and transform the continuous movement through the scheme into a dramatised journey. The coexistence of immersion and progression provides competing challenges to visitors' narrative sensemaking. This paper will analyse the Danteum as a hybrid system of episodic and situational narrations that turns this geometrical space int o a narrative labyrinth.
Restitution, description and knowledge in English architecture and natural philosophy, 1650–1750
Authors: Wragge-Morley Alexander
Published: November 2010

Robert Hooke and Christopher Wren's interest in ancient buildings has been noted by historians of architecture and natural philosophy alike. The two men used to meet to discuss descriptions – both verbal and visual – and models of ancient buildings that had long since disappeared and were known only through ancient accounts, or that remained only in a ruined or altered form. These included the Temple of Solomon, described at different places in the Bible, Porsenna's tomb, cited as an example of extravagance by Pliny the Elder, and the Hagia Sophia. In 1675, Hooke recorded such a meeting in his diary: ‘With Sir Chr. Wren. Long Discourse with him about the module [model] of the Temple at Jerusalem’.
Compensation irradiance for planktonic community metabolism in the ocean
Authors: Regaudie‐de‐Gioux Aurore , Duarte Carlos M.
Published: November 2010

The light compensation irradiance for planktonic metabolic balance, defined as the irradiance where gross planktonic primary production equals community respiration, is an important property describing ecosystem dynamics. Planktonic communities receiving irradiances above the compensation irradiance or compensation depth (i.e., the depth at which the compensation irradiance is received) are autotrophic and act as CO2 sinks, whereas those at lower irradiances or located deeper in the water column act as CO2 sources. However, this property is undefined for heterotrophic communities in which metabolic balance is not set by light availability. The compensation irradiance for planktonic metabolism in the ocean was quantified experimentally and calculated using data available in the literature to assess its variability and possible controls. Gross primary production by the oceanic planktonic communities examined here meet their respiratory requirements at irradiances of about 1.1 ± 0.4 mol quanta m−2 d−1 and tend to be autotrophic above a depth of 36 ± 9 m, on average. The depth of nitracline is closely correlated with the compensation depth for community metabolism across the studied areas, but the compensation depth tends to be located above the depth of the nitracline. This is expected from the facts that the underlying, net heterotrophic communities should act as sources of inorganic nutrients and that the nitracline cannot develop within the mixed layer where the compensation depth is often located. These results imply that the planktonic communities examined extending from 36 m depth, on average, to the bottom of the euphotic layer tend to be heterotrophic, acting as CO2 and inorganic nutrient sources.
Crustal structure of the Transantarctic Mountains near the Ross Sea from ambient seismic noise tomography
Authors: Pyle Moira L. , Wiens Douglas A. , Nyblade Andrew A. , Anandakrishnan Sridhar
Published: November 2010

We derive a model for crustal shear wave velocities in the Transantarctic Mountains and surrounding areas of East Antarctica and the Ross Sea region of West Antarctica using Rayleigh wave Green's functions estimated from the cross correlation of ambient seismic noise recorded by the Transantarctic Mountains Seismic Experiment. Group velocity maps are determined from travel times measured from the Rayleigh waves filtered at periods between 5 and 23 s. The velocity maps are inverted for shear velocities across the region using a niching genetic algorithm. We observe only minor variation in crustal velocities beneath East Antarctica and the Transantarctic Mountains, and velocities are similar to those observed for Precambrian crust worldwide. Low velocities, which may be related to the presence of sediment, are observed at shallow depths beneath the Wilkes Subglacial Basin and the Aurora Subglacial Basin, but dispersion curves show that sediment thickness must be limited to less than about 2 km. In the Ross Sea, we observe low velocities at shallow depths from thick sediments and high velocities approaching mantle values between 16 and 20 km depth.
Size‐segregated measurements of cloud condensation nucleus activity and hygroscopic growth for aerosols at Cape Hedo, Japan, in spring 2008
Authors: Mochida Michihiro , Nishita‐Hara Chiharu , Kitamori Yasuyuki , Aggarwal Shankar G. , Kawamura Kimitaka , Miura Kazuhiko , Takami Akinori
Published: November 2010

Size‐segregated measurements of cloud condensation nucleus (CCN) activity and hygroscopic growth were performed simultaneously for sulfate‐rich aerosols at Cape Hedo, Okinawa, Japan, in spring 2008. The CCN fractions as functions of particle size at water vapor supersaturations of 0.44%, 0.25%, and 0.10% had nearly stepwise increases, and the diameters for 50% activation of its maximum (dact) were close to that of (NH4)2SO4. The size‐resolved hygroscopic growth factor g measured using a hygroscopicity tandem differential mobility analyzer at 85% relative humidity (RH) mainly showed unimodal and highly hygroscopic characteristics. The observed characteristics as well as aerosol mass spectrometer data suggest the dominance of internally mixed ammoniated sulfate‐rich particles. A clear negative correlation between dact and median g (gmedian) was observed for Aitken‐mode particles, and backward air mass trajectories indicate lower dact and higher g of the aerosols from China and the Pacific and the opposite tendency for those from Korea and Japan. The size dependence of gmedian suggests that less hygroscopic carbonaceous components were more enriched in Aitken‐mode particles and therefore affect the CCN activity and hygroscopicity. The CCN activation diameters were predicted on the basis of gmedian using a core‐shell model. The modeled activation diameters reasonably agreed with measured dact, suggesting that the surface tension lowering effect due to organics and the enhancement of bulk hygroscopicity at high RH due to sparingly soluble or polymeric compounds were small. The results suggest that CCN activity of sulfate‐rich aerosol particles is predicted well in regional and global aerosol models without incorporating these effects.
Atmospheric versus vegetation controls of Amazonian tropical rain forest evapotranspiration: Are the wet and seasonally dry rain forests any different?
Authors: Costa Marcos H. , Biajoli Márcia C. , Sanches Luciana , Malhado Ana C. M. , Hutyra Lucy R. , da Rocha Humberto R. , Aguiar Renata G. , de Araújo Alessandro C.
Published: November 2010

This study analyzes evapotranspiration data for three wet and two seasonally dry rain forest sites in Amazonia. The main environmental (net radiation, vapor pressure deficit, and aerodynamic conductance) and vegetation (surface conductance) controls of evapotranspiration are also assessed. Our research supports earlier studies that demonstrate that evapotranspiration in the dry season is higher than that in the wet season and that surface net radiation is the main controller of evapotranspiration in wet equatorial sites. However, our analyses also indicate that there are different factors controlling the seasonality of evapotranspiration in wet equatorial rain forest sites and southern seasonally dry rain forests. While the seasonality of evapotranspiration in wet equatorial forests is driven solely by environmental factors, in seasonally dry forests, it is also biotically controlled with the surface conductance varying between seasons by a factor of approximately 2. The identification of these different drivers of evapotranspiration is a major step forward in our understanding of the water dynamics of tropical forests and has significant implications for the future development of vegetation‐atmosphere models and land use and conservation planning in the region.
Dimensionally reduced emulation of an AOGCM for application to integrated assessment modelling
Authors: Holden P. B. , Edwards N. R.
Published: November 2010

Integrated Assessment Models are widely used tools for the evaluation of environmental policy. In order to include uncertainty estimates or derive optimal policies, highly efficient calculations of global change are generally required, often using pattern scaling to derive spatial distributions of change. Here we develop an alternative to pattern scaling that allows for nonlinear spatio‐temporal behaviour. We use an intermediate complexity AOGCM to perform an ensemble of simulations for a range of greenhouse gas concentration profiles and model parameters. We decompose climate change fields into a series of spatial patterns and then derive the functional dependence of the dominant patterns on model input. This allows us to rapidly reconstruct a good approximation to the simulated change from an arbitrary concentration profile (without the need for further simulation). The efficiency of the approach paves the way for incorporating improved calculations of climate change into integrated assessment, including location‐dependent estimates of uncertainty.
Probing the relationship between electromagnetic ion cyclotron waves and plasmaspheric plumes near geosynchronous orbit
Authors: Posch J. L. , Engebretson M. J. , Murphy M. T. , Denton M. H. , Lessard M. R. , Horne R. B.
Published: November 2010

Plasmaspheric plumes created during disturbed geomagnetic conditions have been suggested as a major cause of increased occurrences of electromagnetic ion cyclotron (EMIC) waves at these times. We have catalogued occurrences of strong Pc1 EMIC waves from 1996 through 2003 at three automated geophysical observatories operated by the British Antarctic Survey at auroral zone latitudes in Antarctica (L = 6.28, 7.68, and 8.07) and have compared them to the occurrence of plasmaspheric plumes in space, using simultaneous data from the Magnetospheric Plasma Analyzer on the Los Alamos National Laboratory 1990–095 spacecraft, in geosynchronous orbit at the same magnetic longitude. A superposed epoch analysis of these data was conducted for several categories of disturbed geomagnetic conditions, including magnetic storms, high‐speed streams, and storm sudden commencements. We found only a weak correspondence between the occurrence of strong Pc1 waves observed on the ground and either plasmaspheric plumes or intervals of extended plasmasphere at geosynchronous orbit before, during, or after the onset of any of these categories. Strong Pc1 activity peaked near or slightly after local noon during all storm phases, consistent with equatorial observations by the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer satellite at these L shells. The highest Pc1 occurrence probability was at or 1–2 days before storm onset and during the late recovery phase. Occurrence was lowest during the early recovery phase, consistent with the decrease in solar wind pressure often seen at this time. The peak at onset is consistent with earlier observations of waves in the outer magnetosphere stimulated by sudden impulses and magnetospheric compressions.
Ecotoxicological risk assessment of agriculture intensification in Argentinean cropping lands using a fuzzy-logic based model
Authors: Ferraro Diego
Published: November 2010

Current agricultural models have an increasing dependence on non-renewable resources that have significant implications for the ecosystem health. Pesticides are considered one main impact force that affects both the structure and functions of agroecosystems. In this work we presented results from the application of an environmental pesticide risk assessment of a large database of cropping systems in the Inland Pampa (Argentina) where, since 1990, the traditional mixed grazing–cropping systems were being replaced by permanent agriculture and the intensification of pesticide use has increased significantly. However, there is no clear awareness of the ecotoxicological risk associated with these land use changes. The ecotoxicological risk on both insects and mammals were assessed using a fuzzy-logic based model that links, as input variables, the amount the pesticide dose and the lethal dose (LD50) of each active ingredient use in a single crop field. Thresholds and membership functions were developed by means of expert opinion. A database, containing 29042 records of pesticide use in maize, soybean, sunflower and wheat from 1992 to 2005 were analyzed. Results showed that harvested yield increased significantly in all crops during the period studied (P<0.005). However, these higher yields were associated with higher risks over both insect and mammals as in almost all crops analyzed the fuzzy-logic ecotoxicological indicators showed negative and significant time trend in the period studied (P<0.005, Spearman rank correlation (SRC)). Summer soybean (i.e in the wheat-soybean rotation) did not show any significant tendency regarding changes in potential ecotoxicological risk during 1992-2005 interval. However, soybean (either as summer or spring crop) showed the highest ecotoxicological risk value in each one of the years analyzed (Kruskal-Wallis test, p < 0.05). Regarding the average number of pesticides applied, all crops showed a significant increment from 1992 to 2000 and a subsequent reduction from 2000 to 2005 (SRC, P < 0.05) and these reductions were higher in soybean, from 6.1 to 3.5 application/year in relation to maize, soybean and sunflower. These preliminary results indicated that higher yield in all the crops analyzed were associated to higher ecotoxicological risk of the pesticides used. However, further work has to be conducted to improve the fuzzy-logic ecotoxicological model by including variables such human toxicological risk or other chemical pesticide characteristics (i.e. soil persistence, solubility).
Stokes and anti-Stokes luminescence of Er3+ doped Ga10Ge25S65 glass excited at 980 and 532 nm
Authors: Frej Milena L. , Valdez Ernesto , de Araújo Cid B. , Ledemi Y. , Messaddeq Y.
Published: November 2010

We report on photoluminescence (PL) properties of Er3+ doped Ga10Ge25S65 glass. Experiments were performed using 5 ns laser pulses at 980 nm (532 nm), in resonance with the I415/2→I411/2 (I415/2→H211/2) transition of the Er3+ ions. PL bands were observed from the blue to the near-infrared and the dependence of their intensity as a function of the laser intensity was analyzed. The PL temporal behavior was analyzed through rate equations for the population densities and using the Inokuti–Hirayama model. The results allowed identification of the PL pathways and the characterization of energy transfer processes involving pairs of ions.
Energy-transfer and charge-separation pathways in the reaction center of photosystem II revealed by coherent two-dimensional optical spectroscopy
Authors: Abramavicius Darius , Mukamel Shaul
Published: November 2010

The excited state dynamics and relaxation of electrons and holes in the photosynthetic reaction center of photosystem II are simulated using a two-band tight-binding model. The dissipative exciton and charge carrier motions are calculated using a transport theory, which includes a strong coupling to a harmonic bath with experimentally determined spectral density, and reduces to the Redfield, the Förster, and the Marcus expressions in the proper parameter regimes. The simulated third order two-dimensional signals, generated in the directions −k1+k2+k3, k1−k2+k3, and k1+k2−k3, clearly reveal the exciton migration and the charge-separation processes.
Analysis of current-driven surface morphological stabilization of a coherently strained epitaxial thin film on a finite-thickness deformable substrate
Authors: Sfyris Georgios I. , Gungor M. Rauf , Maroudas Dimitrios
Published: November 2010

We report results for the surface morphological stability of a thin film that lies on a finite-thickness substrate and is subjected simultaneously to an external electric field. The film is grown epitaxially on the substrate and may undergo a Stranski–Krastanow instability due to its lattice mismatch with the substrate material. We develop a model for the surface morphological evolution of the thin film and conduct a linear stability analysis to examine the morphological stability of the epitaxial film’s planar surface state. Our analysis shows that surface electromigration due to a properly applied and sufficiently strong electric field can inhibit Stranski–Krastanow-type instabilities, which can be used to control the onset of island formation on the film surface. We find that using a finite-thickness substrate can have the beneficial effect of reducing the critical strength of the electric field required to stabilize the planar surface morphology of the epitaxial film with respect to the field strength required in the case of an infinitely thick substrate. We determine the critical electric-field strength as a function of material properties and heteroepitaxial system parameters, as well as the field’s optimal direction for the most efficient stabilization of the surface morphology. Detailed results are presented for the effects of the finite-thickness substrate on the stabilization of the film’s surface over a range of mechanical properties of the heteroepitaxial system’s constituents.
High temperature thermal conductivity of platinum microwire by 3ω method
Authors: Bhatta Rudra P. , Annamalai Sezhian , Mohr Robert K. , Brandys Marek , Pegg Ian L. , Dutta Biprodas
Published: November 2010

The 3ω method for thermal conductivity measurement has emerged as an effective technique applicable to micro/nanowires and thin films. This paper describes the adaptation of the method to temperatures as high as 725 K enabling reliable thermal conductivity measurements on such samples for which previously published methods have been found inadequate. In the technique, a sample wire is heated by applying a sinusoidal current at an angular frequency ω, which causes a temperature and resistance variation at an angular frequency, 2ω, leading to a voltage signal at 3ω. The sample is connected as a four-terminal resistor to a digital lock-in amplifier, which is used to detect the in-phase and out-of-phase 3ω voltages resulting from the applied 1ω current. The data are fitted by varying the values of the thermal resistance and diffusion time, both of which are functions of thermal conductivity. Measurements are made at steady state temperatures between 300 and 725 K. Meaningful measurements at elevated temperatures require that thermal losses be understood and minimized. Conduction losses are prevented by suspending the sample above the mounting substrate. Convection losses are minimized by maintaining a vacuum of ∼10−5 torr inside the sample chamber. To minimize radiation losses, an appropriately sized sample is shrouded with a double heat-shield, with the inner shield temperature near that of the sample. Using the 3ω method, the thermal conductivity of platinum was determined to vary between 71.8 and 80.7 Wm−1 K−1 over the temperature range of 300 to 725 K, in agreement with published values measured for bulk samples.
Analytic theory for betatron radiation from relativistic electrons in ion plasma channels with magnetic field
Authors: Lee H. C. , Jiang T. F.
Published: November 2010

We analytically solve the relativistic equation of motion for an electron in ion plasma channels and calculate the corresponding trajectory as well as the synchrotron radiation. The relativistic effect on a trajectory is strong, i.e., many high-order harmonic terms in the trajectory, when the ratio of the initial transverse velocity (vx0) to the longitudinal velocity (vz0) of the electron injected to ion plasma channels is high. Interestingly, these high-order harmonic terms result in a quite broad and intense radiation spectrum, especially at an oblique angle, in contrast to an earlier understanding. As the initial velocity ratio (vx0:vz0) decreases, the relativistic effect becomes weak; only the first and second harmonic terms remain in the transverse and longitudinal trajectories, respectively, which coincides with the result of Esarey et al. [Phys. Rev. E 65, 056505 (2002)]. Our formalism also allows the description of electron’s trajectory in the presence of an applied magnetic field. Critical magnetic fields for cyclotron motions are figured out and compared with semiclassical results. The cyclotron motion leads to more high-order harmonic terms than the trajectory without magnetic fields and causes an immensely broad spectrum with vastly large radiation amplitude for high initial velocity ratios (vx0:vz0). The radiation from hard x-ray to gamma-ray regions can be generated with a broad radiation angle, thus available for applications.
Growth of large-area graphene films from metal-carbon melts
Authors: Amini Shaahin , Garay Javier , Liu Guanxiong , Balandin Alexander A. , Abbaschian Reza
Published: November 2010

We have demonstrated a new method for the large-area graphene growth, which can lead to a scalable low-cost high-throughput production technology. The method is based on growing single layer or few-layer graphene films from a molten phase. The process involves dissolving carbon inside a molten metal at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top of the melt at a lower temperature. The examined metals for the metal-carbon melt included copper and nickel. For the latter, the high-quality single layer graphene was grown successfully. The resulting graphene layers were subjected to detailed microscopic and Raman spectroscopic characterization. The deconvolution of the Raman 2D band was used to accurately determine the number of atomic planes in the resulting graphene layers and access their quality. The results indicate that our technology can provide bulk graphite films, few-layer graphene as well as high-quality single layer graphene on metals. Our approach can also be used for producing graphene-metal thermal interface materials for thermal management applications.
Mode locking in audio acoustics: Generation of spike pulses
Authors: Nienałtowski Bogdan , Linde Bogumił B. J.
Published: November 2010

In the present paper, a method for generating acoustic spike pulses in the audible domain is described. The experiment relies on the effect of phase locking of longitudinal modes in a cavity resonator, similarly as in the generation of very short pulses by laser techniques.
Interionic energy transfer in Y3Al5O12:Ce3+, Pr3+ phosphor
Authors: Wang Lei , Zhang Xia , Hao Zhendong , Luo Yongshi , Zhang Jiahua , Wang Xiao-jun
Published: November 2010

We present an investigation of dynamical processes of nonradiative energy transfer (ET) between Ce3+ and Pr3+, and between Pr3+ ions in Y3Al5O12:Ce3+, Pr3+ phosphor. Photoluminescence spectroscopy and fluorescence decay patterns are studied as a function of Pr3+ and Ce3+ concentrations. The analysis based on Inokuti–Hirayama model indicates that the ET from the lowest 5d state of Ce3+ to the D12 state of Pr3+, and the quenching of the D12 state through a cross relaxation involving Pr3+ ions in the ground state are both governed by electric dipole–dipole interaction. An increase in the Ce3+–Pr3+ ET rate followed by the enhanced red emission line of Pr3+ relative to the yellow emission band of Ce3+ on only increasing Ce3+ concentration is observed. This behavior is attributed to the increase in the spectral overlap integrals between Ce3+ emission and Pr3+ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce3+ concentration while the red line dose not move. For Ce3+ concentration of 0.01 in YAG:Ce3+, Pr3+, the rate constant and critical distance are evaluated to be 4.5×10−36 cm6 s−1, 0.81 nm for Ce3+–Pr3+ ET and 2.4×10−38 cm6 s−1, 1.30 nm for Pr3+–Pr3+ ET. Spectroscopic study also demonstrates a pronounced ET from the lowest 4f5d of Pr3+ to the 5d of Ce3+. A proportional dependence of the initial transfer rate on acceptor concentration is observed in each of these ET pathways. The proportional coefficient as the averaged ET parameters for initial decay are determined, meaning the ET efficiency for the same concentration of acceptors follows the order of Pr3+–Pr3+>Pr3+–Ce3+>Ce3+–Pr3+.
Structural, optical, and magnetic properties of the ferromagnetic semiconductor hematite-ilmenite Fe2−xTixO3−δ thin films on SrTiO3(001) prepared by pulsed laser deposition
Authors: Hamie A. , Dumont Y. , Popova E. , Scola J. , Fouchet A. , Berini B. , Keller N.
Published: November 2010

Structural, electrical, and magnetic properties of epitaxial thin films of Fe1.5Ti0.5O3−δ grown by pulsed laser deposition on SrTiO3(001) have been studied. For all the investigated range of preparation conditions, the thin films are single phase. The films prepared using oxygen pressure PO2 above 3×10−7 Torr presents a R(3¯)c symmetry structure. A single phase with the R(3¯) symmetry is obtained for the substrate temperature Ts=730 °C and PO2=2.6×10−7 Torr. This sample showed a ferrimagnetic behavior with Curie temperature Tc above room temperature, with a high magnetic moment of 0.6 μB/formula at 300 K. The film containing the disordered R(3¯)c phase is weakly ferromagnetic, with a spin glass-like signature. Optical properties seem to be governed more by the oxygen vacancies induced during the growth, than by the atomic ordering of titanium.
Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures
Authors: Yeoh L. A. , Srinivasan A. , Martin T. P. , Klochan O. , Micolich A. P. , Hamilton A. R.
Published: November 2010

We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10 T. Our apparatus allows for continuous in situ rotation of a device through >100° in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within ±0.03° while maintaining the sample temperature below 100 mK.
Improved hole confinement in GaInAsN–GaAsSbN thin double-layer quantum-well structure for telecom-wavelength lasers
Authors: Albo Asaf , Bahir Gad , Fekete Dan
Published: November 2010

In this work we demonstrated increased hole confinement in a bilayer quantum well that consists of two thin layers of GaInAsN/GaAsSbN confined by GaAs barriers. Comparison between the temperature dependence of photoluminescence intensity of the bilayer and GaInAsN quantum wells indicated that electrons rather than holes are the less confined carriers in the bilayer structure. This structure enables independent control of the band gap energy, band offsets and reduces the temperature sensitivity of laser performance. The calculations showed that a bilayer based short-period superlattice would provide a high optical gain at 1.3–1.55 μm due to increased electron-hole wave functions overlap.
Quantum wavepacket ab initio molecular dynamics: Generalizations using an extended Lagrangian treatment of diabatic states coupled through multireference electronic structure
Authors: Li Xiaohu , Iyengar Srinivasan S.
Published: November 2010

We present a generalization to our previously developed quantum wavepacket ab initio molecular dynamics (QWAIMD) method by using multiple diabatic electronic reduced single particle density matrices, propagated within an extended Lagrangian paradigm. The Slater determinantal wavefunctions associated with the density matrices utilized may be orthogonal or nonorthogonal with respect to each other. This generalization directly results from an analysis of the variance in electronic structure with quantum nuclear degrees of freedom. The diabatic electronic states are treated here as classical parametric variables and propagated simultaneously along with the quantum wavepacket and classical nuclei. Each electronic density matrix is constrained to be N-representable. Consequently two sets of new methods are derived: extended Lagrangian-QWAIMD (xLag-QWAIMD) and diabatic extended Lagrangian-QWAIMD (DxLag-QWAIMD). In both cases, the instantaneous potential energy surface for the quantum nuclear degrees of freedom is constructed from the diabatic states using an on-the-fly nonorthogonal multireference formalism. By introducing generalized grid-based electronic basis functions, we eliminate the basis set dependence on the quantum nucleus. Subsequent reuse of the two-electron integrals during the on-the-fly potential energy surface computation stage yields a substantial reduction in computational costs. Specifically, both xLag-QWAIMD and DxLag-QWAIMD turn out to be about two orders of magnitude faster than our previously developed time-dependent deterministic sampling implementation of QWAIMD. Energy conservation properties, accuracy of the associated potential surfaces, and vibrational properties are analyzed for a family of hydrogen bonded systems.
Plasma damage effects on low-k porous organosilicate glass
Authors: Ren H. , Antonelli G. A. , Nishi Y. , Shohet J. L.
Published: November 2010

Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si–(CH3)x bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly.
Combining elastic and resonant inelastic optical spectroscopies for multiscale probing of embedded nanoparticle architectures
Authors: Farcau Cosmin , Bonafos Caroline , Benzo Patrizio , Benassayag Gerard , Carles Robert
Published: November 2010

Composite materials consisting of metal nanoparticles (NPs) embedded in a dielectric matrix have a great potential for photonic and plasmonic applications. A set of expensive, time-consuming, and destructive methods (like electron microscopy, electron energy loss, or secondary ion mass spectroscopy) are extensively being used for the structural characterization of such buried NP assemblies. Here, we show the power of combining complementary, noninvasive optical techniques to characterize planar arrays of Ag NPs embedded in a silica film. We use UV-Vis optical reflectivity and resonant Brillouin–Raman scattering, sustained by simulations, to show the sensitivity of these methods to the presence, density, size distribution, and spatial localization of NPs. The accuracy of the results is validated by transmission electron microscopy investigations. Finally the method is applied to obtain images of embedded plasmonic structures from reflectivity and Raman scanning microscopy.
Electrical bistability and negative differential resistance in diodes based on silver nanoparticle-poly(N-vinylcarbazole) composites
Authors: Tang Aiwei , Qu Shengchun , Hou Yanbing , Teng Feng , Tan Hairen , Liu Jie , Zhang Xingwang , Wang Yongsheng , Wang Zhanguo
Published: November 2010

An electrically bistable device has been fabricated using nanocomposite films consisting of silver nanoparticles and a semiconducting polymer by a simple spin-coating method. The current-voltage characteristics of the as-fabricated devices exhibit an obvious electrical bistability and negative differential resistance effect. The current ratio between the high-conducting state and low-conducting state can reach more than 103 at room temperature. The electrical bistability of the device is attributed to the electric-filed-induced charge transfer between the silver nanoparticles and the polymer, and the negative differential resistance behavior is related to the charge trapping in the silver nanoparticles. The results open up a simple approach to fabricate high quality electrically bistable devices by doping metal nanoparticles into polymer.
Investigation of statistical characterization of radial turbulence in the edge of HuanLiuqi-2A plasma with visible spectroscopy diagnostic
Authors: Zhong W. L. , Duan X. R. , Yu D. L. , Han X. Y. , Cheng J. , Ding X. T. , Liu Yi. , Yan L. W. , Yang Q. W.
Published: November 2010

The radial motion and structure of edge turbulence in the HuanLiuqi-2A tokamak [Y. Liu et al., Nucl. Fusion 45, S239 (2005)] was measured with visible spectroscopy diagnostic system; the radial turbulence propagation velocity and correlation length were evaluated by time-delay correlation technique and there were typically Vr=0.4–1 km/s and Lr=2–6 cm, respectively. The edge intermittent events accompanied with turbulence have been observed in plasma edge and propagated outward radially; especially through the scrape-off layer, the fluctuation signals of Dα exhibit strong asymmetric probability distribution functions (PDFs). Their propagation trajectories and radial velocity PDFs were inferred from a special correlation technique and the results indicated the radial velocity of intermittent event depends on its amplitude. Some comparisons with previous measurements and models were also presented.
Discharge dynamics of pin-to-plate dielectric barrier discharge at atmospheric pressure
Authors: Sun Liqun , Huang Xiaojiang , Zhang Jie , Zhang Jing , Shi J. J.
Published: November 2010

The discharge dynamics of pin-to-plate dielectric barrier discharge was studied in atmospheric helium at 20 kHz. The discharge was predominately ignited in positive half cycle of applied voltage with sinusoidal waveform. The temporal evolution of the discharge was investigated vertically along the discharge gap and radically on the dielectric surface by time resolved imaging. It is found that a discharge column with a diameter of 2 mm was ignited above the pin electrode and expanded toward a plate electrode. On the dielectric surface with space charge accumulation, plasma disk in terms of plasma ring was formed with radius up to 25 mm. The expansion velocity of plasma ring can reach a hypersonic speed of 3.0 km/s. The ionization wave due to electron diffusion is considered to be the mechanism for plasma ring formation and dynamics.
Controlling metamaterial resonances via dielectric and aspect ratio effects
Authors: Chiam Sher-Yi , Singh Ranjan , Zhang Weili , Bettiol Andrew A.
Published: November 2010

We study ways to enhance the sensitivity and dynamic tuning range of the fundamental inductor-capacitor (LC) resonance in split ring resonators (SRRs) by controlling the aspect ratio of the SRRs and their substrate thickness. We conclude that both factors can significantly affect the LC resonance. We show that metafilms consisting of low height SRRs on a thin substrate are most sensitive to changes in their dielectric environment and thus show excellent potential for sensing applications.
A perspective on microfluidic biofuel cells
Authors: Lee Jin wook , Kjeang Erik
Published: November 2010

This review article presents how microfluidic technologies and biological materials are paired to assist in the development of low cost, green energy fuel cell systems. Miniaturized biological fuel cells, employing enzymes or microorganisms as biocatalysts in an environmentally benign configuration, can become an attractive candidate for small-scale power source applications such as biological sensors, implantable medical devices, and portable electronics. State-of-the-art biofuel cell technologies are reviewed with emphasis on microfabrication compatibility and microfluidic fuel cell designs. Integrated microfluidic biofuel cell prototypes are examined with comparisons of their performance achievements and fabrication methods. The technical challenges for further developments and the potential research opportunities for practical cell designs are discussed.
Influence of the spatial pump distribution on the performance of high power vertical-external-cavity surface-emitting lasers
Authors: Chernikov A. , Herrmann J. , Scheller M. , Koch M. , Kunert B. , Stolz W. , Chatterjee S. , Koch S. W. , Wang T. L. , Kaneda Y. , Yarborough J. M. , Hader J. , Moloney J. V.
Published: November 2010

The performance of a 1040 nm vertical-external-cavity surface-emitting laser is studied as function of the size and shape of the pumped area. The input-output characteristics of the device are monitored while simultaneously tracking the temperature in the active region. It is shown that the pump spot shape plays a crucial role in optimizing the laser output. Improvements up to a factor of 5 are found for a super-Gaussian in comparison to the standard Gaussian shape. For the large pump-spot sizes needed for high output powers, it turns out that the power-scalability breaks down due to the suppressed lateral heat flow.
Structural fingerprints of electronic change in the phase-change-material: Ge2Sb2Te5
Authors: Cai B. , Drabold D. A. , Elliott S. R.
Published: November 2010

In this paper, we generate a-Ge2Sb2Te5 models via ab initio molecular dynamic simulations, track the dynamic changes of network at 500 K, and correlate the structural changes in the course of the simulation with changes in electronic structure. Considerable fluctuations of the electronic gap are observed even for a model in equilibrium. We compare our study to experiments and other simulations.
Minimal impact of circumcision on HIV acquisition in men who have sex with men
Authors: Londish Gregory J. , Templeton David J. , Regan David G. , Kaldor John M. , Murray John M.
Published: November 2010

Background: Men who have sex with men (MSM) are disproportionately affected by HIV. The proven efficacy of circumcision in reducing the risk of HIV acquisition among African heterosexual males has raised the question of whether this protective effect may extend to MSM populations. We examined the potential impact of circumcision on an HIV epidemic within a population of MSM. Methods: A mathematical model was developed to simulate HIV transmission in an MSM population. The model incorporated both circumcision and seropositioning, and was used to predict the reduction in HIV prevalence and incidence as a result of the two interventions. Estimates for the time required to achieve these gains were also calculated. Results: We derive simple formulae for the decrease in HIV prevalence with increased circumcision. Our model predicts that if an initially uncircumcised MSM population in a developed country with a baseline HIV prevalence of 10% underwent universal circumcision, HIV incidence would only be reduced to 95% of pre-intervention levels and HIV prevalence to 9.6% after 20 years. In the longer term, our model predicts that prevalence would only decrease from 10% to 6%, but this would take several generations to achieve. The effectiveness of circumcision increases marginally with higher degrees of seropositioning. Conclusions: The results of these calculations suggest that circumcision as a public health intervention will not produce a substantial decrease in HIV prevalence or incidence among MSM in the near future, and only modest reductions are achievable in the long-term.
Gay men's perceptions of sexually transmissible infections and their experiences of diagnosis: 'part of the way of life' to feeling 'dirty and ashamed'
Authors: Holt Martin , Bernard Diana , Race Kane
Published: November 2010

Background: Gay men are considerably more likely than their heterosexual peers to be diagnosed with a sexually transmissible infection (STI), yet relatively little has been published on gay men’s perceptions of STIs other than HIV. Methods: Drawing on interviews conducted with Sydney gay men, we analysed perceptions of STIs, and men’s experiences of testing and diagnosis. Results: Over half the men in the study had ever been diagnosed with an STI. STIs were generally regarded as inconvenient consequences of sexual activity. Viral, recurring STIs were viewed as being more serious than curable, bacterial STIs. However, all STIs were considered as considerably less important than HIV. Condom use and regular STI testing were the most commonly used strategies to manage the risk of STIs. Despite the relative lack of concern attributed to STIs, being diagnosed with an STI could generate feelings of shame, embarrassment and annoyance. For some men, education campaigns appeared to have helped destigmatise STIs and encourage regular testing. Conclusions: We believe that to maintain high rates of STI testing among gay men, community education efforts should continue to reduce the stigma associated with STIs and greater support should be offered to gay men when they receive an STI diagnosis.