bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational and photoionization spectroscopy of biomolecules: Aliphatic amino acid structures
Authors: Hu Yongjun , Bernstein Elliot R.
Published: April 2008

The aliphatic amino acids glycine, valine, leucine, and isoleucine are thermally placed into the gas phase and expanded into a vacuum system for access by time of flight mass spectroscopy and infrared (IR) spectroscopy in the energy range of 2500–4000cm−1 (CH, NH, OH, and stretching vibrations). The isolated neutral amino acids are ionized by a single photon of 10.5eV energy (118nm), which exceeds by less than 2eV their reported ionization thresholds. As has been reported for many hydrogen bonded acid-base systems (e.g., water, ammonia, alcohol, acid clusters, and acid molecules), the amino acids undergo a structural rearrangement in the ion state (e.g., in simplest form, a proton transfer) that imparts sufficient excess vibrational energy to the ion to completely fragment it. No parent ions are observed. If the neutral ground state amino acids are exposed to IR radiation prior to ionization, an IR spectrum of the individual isomers for each amino acid can be determined by observation of the ion intensity of the different fragment mass channels. Both the IR spectrum and fragmentation patterns for individual isomers can be qualitatively identified and related to a particular isomer in each instance. Thus, each fragment ion detected presents an IR spectrum of its particular parent amino acid isomer. In some instances, the absorption of IR radiation by the neutral amino acid parent isomer increases a particular fragmentation mass channel intensity, while other fragmentation mass channel intensities decrease. This phenomenon can be rationalized by considering that with added energy in the molecule, the fragmentation channel populations can be modulated by the added vibrational energy in the rearranged ions. This observation also suggests that the IR absorption does not induce isomerization in the ground electronic state of these amino acids. These data are consistent with theoretical predictions for isolated amino acid secondary structures and can be related to previous IR spectra of amino acid conformers.
Tailoring of structure formation and phase composition in reactively sputtered zirconium oxide films using nitrogen as an additional reactive gas
Authors: Severin D. , Sarakinos K. , Kappertz O. , Pflug A. , Wuttig M.
Published: April 2008

The structure of ZrO2 films has been controlled during reactive sputtering in an argon∕oxygen atmosphere by adding an amount of nitrogen gas to the process. Depending on the deposition conditions, amorphous, cubic, or monoclinic films have been obtained without any additional substrate heating. The resulting film structure is explained in terms of the control of fast negative oxygen ions generated at the target surface and accelerated toward the growing film. Furthermore, the nitrogen addition leads to a pronounced stabilization of the plasma discharge and fewer arcing events, while the incorporation of nitrogen atoms in the growing film is very small.
A priori assessment of closures for scalar dissipation rate transport in turbulent premixed flames using direct numerical simulation
Authors: Chakraborty N. , Rogerson J. W. , Swaminathan N.
Published: April 2008

The scalar dissipation rate transport in both the corrugated flamelet and thin reaction zone regimes is studied using three-dimensional direct numerical simulation (DNS) databases for freely propagating statistically planar turbulent premixed flames. Both flames have comparable turbulent Reynolds number but the flame representing the corrugated flamelet combustion regime has a global Damköhler number, Da>1, whereas the second flame representing the thin reaction zone regime has Da<1. It is demonstrated that the turbulent transport of the scalar dissipation rate and its molecular diffusive transport have strong Da dependence. The contributions of dilatation rate, the turbulence-scalar interaction, the reaction-rate–scalar gradient interaction, and the dissipation processes have leading order contributions for both the flames. However, the turbulence-scalar interaction dissipates scalar gradients in the Da>1 flame, while it produces the scalar gradients in the Da<1 flame. Simple algebraic models for the contributions of the various processes noted above to the scalar dissipation rate evolution are proposed and their a priori assessment is carried out with respect to DNS data. These models explicitly have Da and the Karlovitz number Ka dependence, and thus, they can be viewed and used as unified models for both the corrugated flamelet and thin reaction zone regimes. Physical realizability of the modeled scalar dissipation rate transport equation is studied and the model constants obtained by using the DNS data sets are shown to satisfy the realizability condition.
On the influence of initial state on gyrokinetic simulations
Authors: Dif-Pradalier G. , Grandgirard V. , Sarazin Y. , Garbet X. , Ghendrih Ph. , Angelino P.
Published: April 2008

The influence of the initial state on the turbulence and transport is addressed in collisionless, global, and full-f gyrokinetic simulations solving both the equilibrium and the fluctuations. For two strongly differing initial states, it is found that the steady turbulent regime exhibits nearly identical statistical properties. This result is in marked contrast with the claim of different final states. In fact, a long transient with very different properties finally evolves towards the same turbulent regime for long simulation times. When the initial state is a local Maxwellian, i.e., constant on flux surfaces, a large-scale sheared electric potential develops on short time scales to compensate for the vertical curvature and grad-B drifts. We predict analytically (i) the temporal dynamics at short times of this electric potential, (ii) its poloidal structure, and (iii) its saturation time. All agree well with numerical simulations using the GYSELA code. The impact on the transport is twofold, as compared to the canonical initial state, where f only depends on the motion invariants: (i) the turbulence is delayed due to a weaker effective growth rate, (ii) the same transport level is obtained at long times and the turbulence exhibits nearly identical statistical characteristics. In agreement, the electric potential of these two cases has the same magnitude despite very different transients.
On the rest state stability of an objective fractional derivative viscoelastic fluid model
Authors: Heibig Arnaud , Palade Liviu Iulian
Published: April 2008

The one-dimensional fractional derivative Maxwell model has been found very useful in modeling the linear viscoelastic response in the glass transition and α-relaxation regions. That motivated further work on generalizations to nonlinear viscoelastic fractional constitutive equations. In the work of Palade et al. [Int. J. Eng. Sci. 37, 315 (1999)], a fully objective constitutive equation for an incompressible fluid—reducible to the linear fractional derivative Maxwell model under the small deformations hypothesis—is given, together with a state of rest stability analysis. In the stability section of the aforementioned work, for some physically aceptable perturbation inputs, it has been shown that no continuously differentiable solutions may be found to the corresponding equations of motion. In this work, we extend the stability analysis framework to L2 Hilbert functional space and prove the existence of solutions to the corresponding equations of motions.
A mesoscopic rheological model of immiscible blends with the interface covered with a surface active agent
Authors: Gu Jian Feng , Grmela Miroslav , Bousmina Mosto
Published: April 2008

The Maffettone–Minale mesoscopic rheological model of immiscible blends is extended to blends that include a surface active agent. Its nonuniform distribution on the interface (assumed to be the surface of droplets) and the associated with it nonuniform distribution of the surface tension and the Marangoni stress are incorporated into the model. Instead of using one ellipsoid (one conformation tensor in the mathematical formulation) to characterize the shape of the droplet, we use a one parameter family of ellipsoids (a “necklace” of ellipsoids) to play this role. Both rheology and morphology (including large deviations form the ellipsoidal shape of droplets) are calculated and compared to predictions of microscopic models (i.e., models based on microhydrodynamics) and with results of experimental observations.
The effect of photoresist contrast on the exposure profiles obtained with evanescent fields of nanoapertures
Authors: Lee Eungman , Hahn Jae Won
Published: April 2008

We propose a simple theoretical model to predict the exposure profiles of a photoresist obtained with evanescent fields of nanoapertures. Assuming the electric field intensity to be a Gaussian distribution function with an exponential decay, the top critical dimension and the depth of the photoresist profile are described with analytic formulas. The profiles are analyzed as a function of the photoresist contrast and the electric field intensity decay length.
Design of chemically propelled nanodimer motors
Authors: Tao Yu-Guo , Kapral Raymond
Published: April 2008

The self-propelled motion of nanodimers fueled by a chemical reaction taking place under nonequilibrium steady state conditions is investigated. The nanodimer consists of a pair of catalytic and chemically inactive spheres, in general with different sizes, with a fixed internuclear separation. The solvent in which the dimer moves is treated at a particle-based mesoscopic level using multiparticle collision dynamics. The directed motion of the dimer can be controlled by adjusting the interaction potentials between the solvent molecules and the dimer spheres, the internuclear separation, and sphere sizes. Dimers can be designed so that the directed motion along the internuclear axis occurs in either direction and is much larger than the thermal velocity fluctuations, a condition needed for such nanodimers to perform tasks involving targeted dynamics.
Improved interplane and intergranular coupling by Mg doping at Ca site in Cu0.5Tl0.5Ba2Ca2(Cu0.5Zn2.5)O10−δ superconductor
Authors: Mumtaz M. , Khan Nawazish A.
Published: April 2008

Improvement in the interplane and intergranular coupling achieved by Mg doping at Ca site in high temperature Cu0.5Tl0.5Ba2Ca2(Cu0.5Zn2.5)O10−δ superconductor is studied by infield magnetic measurements. The decrease of c-axis length and volume of the unit cell of Cu0.5Tl0.5Ba2(Ca2−yMgy) (Cu0.5Zn2.5)O10−δ (y=0, 0.5, 1.0, and 1.5) superconductor with the increase of Mg doping shows the improved interplane coupling among CuO2∕ZnO2 planes. The presence of Mg at the termination ends of the crystals of Cu0.5Tl0.5Ba2(Ca2−yMgy) (Cu0.5Zn2.5)O10−δ compound has been found to improve intergrain coupling, which is evident from enhanced critical current density (Jc) of these samples. The exponent of temperature variation of thermodynamic critical field Hc∼(1−TP∕Tc)n suggests that the weak links form superconductor-insulator-superconductor type of junctions in all the samples. The presence of insulating material at the intergrain sites possibly increases the area of shielding current flow, which promotes the enhancement in Jc of final compound.
Quantum-inspired maximizer
Authors: Zak Michail
Published: April 2008

The objective of this paper is to create a new kind of dynamical systems—a quantum-classical hybrid—that would preserve superposition and entanglement of random solutions while allowing one to measure their state variables by using classical methods. Such an optimal combination of characteristics is a perfect match for quantum-inspired computing. The model is represented by a modified Madelung equation in which the quantum potential is replaced by a different, specially chosen “computational” potential. As a result, the dynamics attains both quantum and classical properties. Similarities and differences of the proposed model with quantum systems are outlined. As an application, an algorithm for the global maximum of an arbitrary integrable function is proposed. The idea of the proposed algorithms is very simple: based on the quantum-inspired maximizer, introduce a positive function to be maximized as the probability density to which the solution is attracted. Then, the larger value of this function will have the higher probability to appear. Special attention is paid to the simulation of integer programming, NP-complete problems and information retrieval.
The effect of fullerene derivative on polaronic charge transfer in poly(3-hexylthiophene)/fullerene compound
Authors: Krinichnyi V. I. , Troshin P. A. , Denisov N. N.
Published: April 2008

The effect of a structure of a fullerene derivative on electronic properties of poly(3-hexylthiophene)/fullerene composite was studied at 3cm wave band EPR in wide (77–320K) temperature region. All the systems with different fullerene derivatives demonstrate sum spectrum of small polarons with different mobilities and contributions depending on the structure of the fullerene derivative. Both the spin-lattice and spin-spin relaxation times were determined separately by using the steady-state saturation method. The treatment of polymer matrix by fullerene derivative changes its dimensionality and conformation. This leads to the change in the spin relaxation and susceptibility as well as in the rate of polaron diffusion along polymer chain.
Er
3
+
-doped boro-tellurite glass for optical amplification in the 1530–1580nm
Authors: Joshi Purushottam , Shen Shaoxiong , Jha Animesh
Published: April 2008

The paper investigates the influence of boric oxide (B2O3), which has a phonon energy of 1500cm−1, on enhancement in the population of the I13∕24 level via the increased multiphonon relaxation in the Er-ion doped tellurite fibers. The paper discusses the structural compatibility of TeO4 structures with BO4 structural units and, therefore, the limitation on the solubility limits of boric oxide in the glass. In the present investigation the optimal composition demonstrates the minimum devitrification tendency in the glassy state that has one of the largest multiphonon relaxation rates. A comparison of lifetimes of I11∕24 level is also made for other tellurite and boro-tellurite compositions. The experimental data show that the transition rate at I11∕24→I13∕24 dramatically increased by incorporating 15mol% B2O3 without sacrificing the spectroscopic properties of glass. The lifetime at I11∕24 transition level decreased from 213to54μs when B2O3 is introduced into tellurite glass. We also report the calculated Judd–Ofelt parameters and the radiative transition rates, which increased by incorporating B2O3 in the tellurite glass. Gain measurements in single-mode boro-tellurite fibers show an increase in peak internal gain from 10to13dB and also, the overall gain spectrum broaden across the L band (1565–1605nm).
Effect of an electric field on film flow down a corrugated wall at zero Reynolds number
Authors: Tseluiko D. , Blyth M. G. , Papageorgiou D. T. , Vanden-Broeck J.-M.
Published: April 2008

The effect of an electric field on a liquid layer flowing down an inclined, corrugated wall at zero Reynolds number is investigated. The layer is taken to be either a perfect conductor or a perfect dielectric. The region above the layer is assumed to be a perfect dielectric. Steady flow down a wall with small-amplitude sinusoidal corrugations is considered, and it is shown how the electric field can be used to control the amplitude of the free-surface deflection and the phase shift between the free surface and the wall profile. Steady flow over walls with large amplitude sinusoidal corrugations or other-shaped indentations is studied by using the boundary-element method. Results for flow into a wide rectangular trench are compared to previous model predictions based on the lubrication approximation. For a perfect-conductor film, the results confirm that the height of the capillary ridge, which appears above a downward step, monotonically decreases as the electric field strength increases. Solutions for a perfect-dielectric film with relative permittivity larger than unity are similar to those for a perfect-conductor film, although the height of the capillary ridge nonmonotonically varies with the electric field strength. The behavior of the solutions for a perfect-dielectric film with relative permittivity less than unity is qualitatively different. The height of the capillary ridge monotonically increases as the electric field strength increases. Flows into narrow trenches and over narrow mounds are also computed.
Pulsed infrared laser annealing of gold nanoparticles embedded in a silica matrix
Authors: Halabica A. , Idrobo J. C. , Pantelides S. T. , Magruder R. H. , Pennycook S. J. , Haglund R. F.
Published: April 2008

Pulsed infrared laser irradiation was used to modify the optical and physical properties of gold nanoparticles in a SiO2 substrate. The primary laser wavelength used for annealing was 8 μm, where the primary absorption was in the substrate. The optical absorption spectra exhibit a typical surface plasmon peak at 520 nm, which increases with laser fluence. This implies growth of the gold nanoparticles during laser annealing but the size distribution remains narrow, unlike some thermal annealing procedures that produce bimodal size distributions. The results were confirmed by scanning transmission electron microscopy and were consistent with the calculations of expected extinction spectra.
Effects of diffusion boundary layer on reaction kinetics of immunoassay in a biosensor
Authors: Yang Chih-Kai , Chang Jeng-Shian , Chao Sheng D. , Wu Kuang-Chong
Published: April 2008

Specific binding reaction is a natural characteristic that is applied to design biosensors. This work simulates the binding reaction kinetics of two commonly used proteins, C-reactive protein and immunoglobulin G, in a reaction chamber (microchannel) of a biosensor. For a diffusion-limited protein, the diffusion boundary layer on the reaction surface of the biosensor would hinder the binding reaction from association and dissociation. Several crucial factors, which influence the binding reaction curves in the simulation, are discussed, including the concentration of analyte, the inlet flow velocity, the channel height, and the length of the reaction surface. A higher channel causes the diffusive transport of the analyte to take longer time to reach the reaction surface, which in turn decreases the reaction rate of the protein pairs. The length of the reaction surface plays an important role in the formation of the boundary layer. For longer reaction surface, it takes more time to allow diffusion to overcome the larger zone of the diffusion boundary layer, resulting in a slower binding rate and a longer time to reach saturation. The presented data of simulation are useful in designing the biosensors.
Characterization of the nanocryosurgical freezing process through modifying Mazur’s model
Authors: Yan Jing-Fu , Liu Jing
Published: April 2008

Nanoparticles enhanced freezing, termed as nanocryosurgery, is a newly emerging cryosurgical technique which has potential advantage in targeted tumor treatment. However, there are currently no models available to predict the effects of nanoparticles on cell-level biophysical events during cryosurgery. Here, we present a theoretical model through modifying Mazur’s equation and ice nucleation theory to predict the kinetic course of the target cell such as water transport and ice nucleation during nanocryosurgical process. The transient temperature response of the target cell, which was a major influential variable of the model, was calculated by coupling the Pennes bioheat equation and the thermal conductivity model of nanoparticle-fluid mixture. With the model, the freezing effect of nanocryosurgical process on target cell at varying distances from cryoprobe can be comprehensively characterized from micro- to macroscale. Parametric studies revealed that the kinds of nanoparticles and their extracellular volume fraction are two important factors to affect cell-level freezing response compared with other factors such as the cell radius and intracellular volume fraction of nanoparticles. The corresponding sensitivity analysis of various parameters is also reported. This study would help to better understand the role of nanoparticles in the freezing process and benefit to optimize the protocol of tumor treatment when nanocryosurgery is administrated.
Application of mean-field and surface-hopping approaches for interrogation of the Xe3+ molecular ion photoexcitation dynamics
Authors: Fiedler Steven L. , Kunttu Henrik M. , Eloranta J.
Published: April 2008

The dissociation dynamics of the excited Xe3+ molecular ion through the Π(1∕2)u and Π(1∕2)g conical intersection was interrogated by computational simulation in which no adjustable parameters were used. The electronic ground and excited state potential energy surfaces were generated by the diatomics-in-molecules method, and the Ehrenfest mean-field and Tully surface-hopping approaches treated the nonadiabatic interactions. Reproduction of the experimental spectrum of the symmetric photofragmentation as a function of excitation energy was obtained within the region of interest (2.5–3.75eV), with the exception of a 0.25eV width on the red side of the spectral apex. Good agreement was obtained with the experimental dissociated photofragment kinetic energy spectra. It was determined that the greatest contribution to the nonadiabatic coupling between the two states originated from the bending vibrational mode of the molecule in the Σ(1∕2)u, ground electronic state before excitation.
Whisker formation in Sn and Pb–Sn coatings: Role of intermetallic growth, stress evolution, and plastic deformation processes
Authors: Chason E. , Jadhav N. , Chan W. L. , Reinbold L. , Kumar K. S.
Published: April 2008

We have simultaneously measured the evolution of intermetallic volume, stress, and whisker density in Sn and Pb–Sn alloy layers on Cu to study the fundamental mechanisms controlling whisker formation. For pure Sn, the stress becomes increasingly compressive and then saturates, corresponding to a plastically deformed region spreading away from the growing intermetallic particles. Whisker nucleation begins after the stress saturates. Pb–Sn layers have similar intermetallic growth kinetics but the resulting stress and whisker density are much less. Measurements after sputtering demonstrate the important role of the surface oxide in inhibiting stress relaxation.
Optical diagnostics of mercury jet for an intense proton target
Authors: Park H. , Tsang T. , Kirk H. G. , Ladeinde F. , Graves V. B. , Spampinato P. T. , Carroll A. J. , Titus P. H. , McDonald K. T.
Published: April 2008

An optical diagnostic system is designed and constructed for imaging a free mercury jet interacting with a high intensity proton beam in a pulsed high-field solenoid magnet. The optical imaging system employs a backilluminated, laser shadow photography technique. Object illumination and image capture are transmitted through radiation-hard multimode optical fibers and flexible coherent imaging fibers. A retroreflected illumination design allows the entire passive imaging system to fit inside the bore of the solenoid magnet. A sequence of synchronized short laser light pulses are used to freeze the transient events, and the images are recorded by several high speed charge coupled devices. Quantitative and qualitative data analysis using image processing based on probability approach is described. The characteristics of free mercury jet as a high power target for beam-jet interaction at various levels of the magnetic induction field is reported in this paper.
Selective organization of solution-processed organic field-effect transistors
Authors: Minari Takeo , Kano Masataka , Miyadera Tetsuhiko , Wang Sui-Dong , Aoyagi Yoshinobu , Seto Mari , Nemoto Takashi , Isoda Seiji , Tsukagoshi Kazuhito
Published: April 2008

Semiconductor channels of organic field-effect transistors have been directly self-organized from a solution phase. The alkyl-modified surface was locally patterned by using a phenyl self-assembled monolayer (SAM) for the channels. Drop-cast small organic molecules were selectively crystallized on the phenyl SAM region. The self-organized process allows the simultaneous formation of polycrystalline transistor arrays from the patterned channels. The phenyl SAM under the channel is critical for the improvement of device stability. Further optimization of the deposition process realized direct growth of a single crystal channel from solution between prefabricated electrodes, and the single-crystal transistors exhibited excellent performance.
Development of a magic-angle spinning nuclear magnetic resonance probe with a cryogenic detection system for sensitivity enhancement
Authors: Mizuno Takashi , Hioka Katsuya , Fujioka Koji , Takegoshi K.
Published: April 2008

A novel nuclear magnetic resonance (NMR) probe for high-resolution solid-state NMR has been developed. In this probe, temperature of the detection coil is kept at cryogenic temperature (∼12K) for sensitivity enhancement, which is achieved not only by suppression of thermal noise but also by increment of a Q factor of the coil. A marked feature of this probe is that a sample rotating at magic angle is thermally isolated from the cryogenic system in order to realize high-resolution solid-state NMR measurement at various sample temperatures. We call this system as cryocoil magic-angle spinning (cryocoil MAS). H1 MAS NMR with the coil temperature of ∼20K was successfully observed for solid adamantane rotating at room temperature, and signal-to-noise increment due to this cryocoil approach was confirmed.
Tunneling magnetoresistance of magnetic tunnel junctions using perpendicular magnetization L10-CoPt electrodes
Authors: Kim Gukcheon , Sakuraba Yuya , Oogane Mikihiko , Ando Yasuo , Miyazaki Terunobu
Published: April 2008

Magnetic tunnel junctions (MTJs) using L10-ordered CoPt electrodes with perpendicular magnetic anisotropy were fabricated. Full-epitaxial CoPt∕MgO∕CoPt-MTJs were prepared onto single crystal MgO-(001) substrate by sputtering method. X-ray diffraction analyses revealed that both bottom and top CoPt electrodes were epitaxially grown with (001)-orientation. The L10-chemical order parameter of 0.82 was obtained for the bottom CoPt electrode deposited at substrate temperature of 600°C. The transport measurements with applying magnetic field perpendicular to the film plane showed a tunnel magnetoresistance ratio of 6% at room temperature and 13% at 10K.
Further insight into the temperature quenching of photoluminescence from InAs∕GaAs self-assembled quantum dots
Authors: Chahboun A. , Vasilevskiy M. I. , Baidus N. V. , Cavaco A. , Sobolev N. A. , Carmo M. C. , Alves E. , Zvonkov B. N.
Published: April 2008

The possibility of controlling the photoluminescence (PL) intensity and its temperature dependence by means of in-growth and postgrowth technological procedures has been demonstrated for InAs∕GaAs self-assembled quantum dots (QDs) embedded in an InGaAs quantum well (QW). The improvement of the QD emission at room temperature (RT), achieved due to a treatment with tetrachloromethane used during the growth, is explained by the reduction of the point defect concentration in the capping layer. It is shown that the PL quenching at RT appears again if the samples are irradiated with protons, above a certain dose. These findings are accounted for by the variations in the quasi-Fermi level position of the minority carriers, which are related to the concentration of trapping centers in the GaAs matrix and have been calculated using a photocarrier statistical model including both radiative and nonradiative recombination channels. By taking into consideration the temperature dependent distribution of the majority and minority carriers between the QDs, embedding QW and GaAs barriers, our calculated results for the PL intensity reproduce very well the experimentally observed trends.
Re-entrant type relaxor behavior in (1−x)BaTiO3–xBiScO3 solid solution
Authors: Guo Hai Yan , Lei Chao , Ye Zuo-Guang
Published: April 2008

The solid solution of (1−x)BaTiO3–xBiScO3 was synthesized by solid state reaction and its dielectric properties were studied by impedance spectroscopy. A dielectric anomaly was found in the temperature ranges of −30–13°C and −60–20°C for 0.95BaTiO3–0.05BiScO3 and 0.90BaTiO3–0.10BiScO3, respectively. The frequency dependence of the anomaly exhibits dielectric relaxation satisfying the Vogel–Fulcher law, indicating relaxorlike behavior. The relaxor state in the (1−x)BaTiO3–xBiScO3 solid solution occurs after the ferroelectric phase transition upon cooling, indicating a re-entering phenomenon. Piezoresponse force microscopic studies show that the domain wall density decreases with the addition of BiScO3. The substitution of BiScO3 also results in some no-phase-contrast areas in the domain structure image, which grow with the increasing BiScO3 amount. Decent piezoelectric hysteresis loops were obtained in these areas. The correlation between the peculiar domain structure and relaxor behavior suggests that the no-phase-contrast areas are characteristics of the domain structure of the re-entering relaxor system.
Ultrafast carrier dynamics in undoped and p-doped InAs∕GaAs quantum dots characterized by pump-probe reflection measurements
Authors: Liu Hai-Ying , Meng Zi-Ming , Dai Qiao-Feng , Wu Li-Jun , Guo Qi , Hu Wei , Liu Song-Hao , Lan Sheng , Yang Tao
Published: April 2008

We investigate the dependence of the differential reflection on the structure parameters of quantum dot (QD) heterostructures in pump-probe reflection measurements by both numerical simulations based on the finite-difference time-domain technique and theoretical calculations based on the theory of dielectric films. It is revealed that the value and sign of the differential reflection strongly depend on the thickness of the cap layer and the QD layer. In addition, a comparison between the carrier dynamics in undoped and p-doped InAs∕GaAs QDs is carried out by pump-probe reflection measurements. The carrier capture time from the GaAs barrier into the InAs wetting layer and that from the InAs wetting layer into the InAs QDs are extracted by appropriately fitting differential reflection spectra. Moreover, the dependence of the carrier dynamics on the injected carrier density is identified. A detailed analysis of the carrier dynamics in the undoped and p-doped QDs based on the differential reflection spectra is presented, and its difference with that derived from the time-resolved photoluminescence is discussed.
Dual chopped photoreflectance spectroscopy for nondestructive characterization of semiconductors and semiconductor nanostructures
Authors: Kita Takashi , Yamada Masahiro , Wada Osamu
Published: April 2008

Photoreflectance (PR) spectroscopy unaffected by photoluminescence and light scattering has been developed for performing precise characterization of the electronic band structure of semiconductors and semiconductor nanostructures. Dual chopping of both the pump and probe lights eliminates the unexpected components included in the signal when detecting the sum frequency or difference frequency component by using a lock-in detection system. The obtained PR signal contains no background and is considered to be an ideal electromodulated reflectance.
Polarization switching kinetics at the nanoscale in ferroelectric copolymer Langmuir–Blodgett films
Authors: Gaynutdinov R. V. , Lysova O. A. , Tolstikhina A. L. , Yudin S. G. , Fridkin V. M. , Ducharme Stephen
Published: April 2008

The polarization switching kinetics of ferroelectric Langmuir–Blodgett films of vinylidene fluoride-trifluoroethylene copolymer were investigated by piezoresponse force microscopy with a resolution of 100nm. The switching time in response to a localized voltage pulse exhibits an exponential dependence on reciprocal voltage, which is consistent with nucleation-limited switching dynamics.
A fast ramp rate thermally stimulated current technique to quantify electronic charge dynamics in thin films
Authors: Lew Connie , Thompson Michael O.
Published: April 2008

Thermally stimulated current (TSC) techniques have been applied to study thermally activated events in many materials. However, the temperature ramp rates in traditional TSC are typically too slow (few degrees per minute) to monitor materials whose properties are strongly time dependent. A fast ramp rate TSC (FR-TSC) technique was developed with ramp rates of 1–5K∕s. This is up to 100 times faster than traditional TSC, so that material changes can be appropriately quantified in the time scale at which they take place. In this paper, the experimental design and challenges to achieve fast and stable ramp rates and to measure the low-level currents are discussed. The fast ramps were attained using a thermoelectric cooler, controlled by a proportional-integral-derivative feedback loop, for both heating and cooling. FR-TSC measurements (1K∕s and 20–100°C) on poly(vinylidene fluoride-trifluoroethylene) ferroelectric thin films are discussed as an example material. From these measurements, thermally activated currents as well as irreversible and reversible charge dynamics were readily distinguished with multiple thermal cycles. These measurements suggest that this technique holds substantial promise in quantifying charge dynamics in fast response materials.
High mobility InN epilayers grown on AlN epilayer templates
Authors: Khan N. , Sedhain A. , Li J. , Lin J. Y. , Jiang H. X.
Published: April 2008

We report on the growth of InN epilayers on AlN/sapphire templates by metal organic chemical vapor deposition. Compared to InN epilayers grown on GaN templates, significant improvements in the electrical and optical properties of InN epilayers on AlN templates were observed. An increase in electron mobility, a decrease in background electron concentration, and a redshift of photoluminescence emission peak position with increasing the growth temperature and V/III ratio were observed and a room temperature Hall mobility of 1400cm2∕Vs with a free electron concentration of about 7×1018cm−3 was obtained. The improvements were partly attributed to the use of AlN templates, which allows for higher growth temperatures leading to an enhanced supply of nitrogen atoms and a possible reduction in the incorporation of unintentional impurities and nitrogen vacancy related defects.
Dielectric constant boost in amorphous sesquioxides
Authors: Delugas Pietro , Fiorentini Vincenzo , Filippetti Alessio
Published: April 2008

High-κ dielectrics for insulating layers are a current key ingredient of microelectronics. X2O3 sesquioxide compounds are among the candidates. Here, we show for a typical material of this class, Sc2O3, that the relatively modest dielectric constant of its crystalline phase is enhanced in the amorphous phase by over 40% (from ∼15 to ∼22). This is due to the disorder-induced activation of low frequency cation-related modes which are inactive or inefficient in the crystal and by the conservation of effective dynamical charges (a measure of atomic polarizability). The analysis employs density-functional energy-force and perturbation-theory calculations of the dielectric response of amorphous samples generated by pair-potential molecular dynamics.
Thermal dynamics in symmetric magnetic nanopillars driven by spin transfer
Authors: Lim Weng L. , Anthony Nicholas , Higgins Andrew , Urazhdin Sergei
Published: April 2008

We study the effects of spin transfer on thermally activated dynamics of magnetic nanopillars with identical thicknesses of the magnetic layers. The symmetric nanopillars exhibit anomalous dependencies of switching statistics on magnetic field and current. We interpret our data in terms of simultaneous current-induced excitation of both layers. We also find evidence for coupling between the fluctuations of the layers due to the spin transfer.
The Copycat Solution to the Shadow Correspondence Problem
Authors: Casati Roberto
Published: April 2008

Cast shadows (henceforth simply ‘shadows’) depicted in artworks can fulfil some of their perceptual roles, such as helping the retrieval of 3-D structure and of relative positions of objects, without having to be geometrically or physically accurate. The visual system displays a wide tolerance for shadows that are mostly inaccurate, at times making use of the scarce accurate but relevant information that can still be retrieved from them. However, the extent of the tolerable inaccuracy is at present still unexplored. I propose that inaccuracy can be not only totally acceptable but in some cases is even likely to be preferable to accuracy if the main perceptual role of shadows is to help locate in a scene the objects that cast them. I examined a small but effective historical corpus of pictorial endeavours, from which it appears that in some cases painters have used a copycat strategy for drawing the terminator of a shadow, ie they have produced a replica of the visible profile of the caster, which in the norm yields an impossible shadow. The copycat strategy is perceptually effective for solving the correspondence problem of associating a shadow with its caster; copycatting can be more effective than other solutions, including the depiction of the geometrically correct shadow, and is complementary to coarser solutions to the correspondence problem. These phenomena provide insight into the computations effectively used by the brain to deal with space perception. In particular, the brain is not relying on some sort of simplified physical model of the world, for the shadows produced by the copycat effect would correspond to a more complicated physical situation than the one encountered in real life.
Rapid Figure – Ground Responses to Stereograms Reveal an Advantage for a Convex Foreground
Authors: Bertamini Marco , Lawson Rebecca
Published: April 2008

Convexity has long been recognised as a factor that affects figure – ground segmentation, even when pitted against other factors such as symmetry [Kanizsa and Gerbino, 1976 Art and Artefacts Ed.M Henle (New York: Springer) pp 25–32], It is accepted in the literature that the difference between concave and convex contours is important for the visual system, and that there is a prior expectation favouring convexities as figure. We used bipartite stimuli and a simple task in which observers had to report whether the foreground was on the left or the right. We report objective evidence that supports the idea that convexity affects figure – ground assignment, even though our stimuli were not pictorial in that depth order was specified unambiguously by binocular disparity.
The Riddle of the Rotating-Tilted-Lines Illusion
Authors: Gori Simone , Yazdanbakhsh Arash
Published: April 2008

Gori and Hamburger (2006, Perception35 853–857) devised a new visual illusion of relative motion elicited by the observer's motion. We propose that the systematic error of direction discrimination found by Lorenceau et al (1993, Vision Research33 1207–1217) can explain this illusion. The neural correlate of such a systematic error with respect to the two types of neurons in the primary visual cortex, namely end-stopped and contour cells, is discussed.
When is Motion ‘Motion’?
Authors: Blaser Erik , Sperling George
Published: April 2008

Examples of visual motion have become more and more abstract over the years, leading up to ‘third-order’ stimuli where direction is actually determined by the observer through top–down attention. But how far can this be pushed—are there motion stimuli that are yet more arbitrary and abstract? Actually, there is a broad class of ‘conceptual motion’ stimuli—things like a moving grating of faces, or a shifting pattern of words—that are perfect analogs to traditional ‘perceptual motion’ stimuli, solvable by the same motion computation and for which observers can readily make direction-of-motion judgments. Interestingly though, these do not produce a sensation of motion (among other automatic consequences of motion detection). Here we compare a luminance-based perceptual motion stimulus to a semantic-based conceptual motion stimulus to contrast the psychophysical hallmarks of these motion categories.
Amodal Completion of Moving Objects by Pigeons
Authors: Nagasaka Yasuo , Wasserman Edward A
Published: April 2008

In a series of four experiments, we explored whether pigeons complete partially occluded moving shapes. Four pigeons were trained to discriminate between a complete moving shape and an incomplete moving shape in a two-alternative forced-choice task. In testing, the birds were presented with a partially occluded moving shape. In experiment 1, none of the pigeons appeared to complete the testing stimulus; instead, they appeared to perceive the testing stimulus as incomplete fragments. However, in experiments 2, 3, and 4, three of the birds appeared to complete the partially occluded moving shapes. These rare positive results suggest that motion may facilitate amodal completion by pigeons, perhaps by enhancing the figure – ground segregation process.
Adapt or Die: A 10-Step Survival Guide for Journalism Schools Stuck in the Fourth Estate (Abridged)
Authors: Murray Gordon J.
Published: April 2008

In the spring of 1789, Louis XVI summoned a full meeting of “Les Etats Generaux,” a general assembly of estates consisting of representatives from all but the poorest segment of the French citizenry. The three estates gathered at the Palace of Versailles. The First Estate comprised 300 nobles; the Second, 300 clergy; and the Third, 600 commoners. Thus, the “estates of the realm” became known to the world. Years later, Irish philosopher Edmund Burke cast his eyes upon the Reporter's Gallery of the House of Commons and said, “… yonder sat a Fourth Estate, more important far than they all.
Resource Allocation and Managerial Oversight of Local Morning Newscasts
Authors: Wenger Debora Halpern , Owens Lynn C.
Published: April 2008

In this mixed-methods study of local morning newscasts, the researchers examine current approaches to managerial oversight and resource allocation for morning newscasts and explore the content focus and expansion plans for the time period.

A Web survey of 117 news directors found no significant differences between number-one rated stations and non-number-one rated stations in terms of the number of hours of news produced, the number of times per week managers watch the morning shows or discuss shows with their staffs, or the staff sizes on morning shows. However, the vast majority of respondents believe that a combination of adding staff and providing greater managerial oversight to the morning news block would be the most effective way to boost a station's morning news ratings.

In-depth interviews with news directors for some of the highest-rated morning newscasts in the country describe how they update content and set the agenda for the day to create their successful morning news programs.
Food‐web assembly during a classic biogeographic study: species’“trophic breadth” corresponds to colonization order
Authors: Piechnik Denise A. , Lawler Sharon P. , Martinez Neo D.
Published: April 2008

Ecologists have found many patterns in food‐web structure. Some, like the constant connectance hypothesis, lack definitive explanatory mechanisms. In response, we investigated whether community assembly mechanisms could explain why trophic complexity consistently scales with species richness among ecosystems. We analyzed how food‐web structure developed during the community assembly recorded in Simberloff and Wilson's classic biogeography experiment. Using their arthropod surveys, we constructed six time series of food‐webs from pre‐ and post‐defaunation censuses of six experimental islands, and synthesized trophic information for 250 species from the literature and expert sources. We found that the fraction of specialist species increased and the fraction of generalists decreased during food‐web assembly. Directed connectance initially declined over time, despite an increase in species richness, but eventually leveled off as predicted by the constant connectance hypothesis of diversity‐complexity scaling. The initial decline was explained by later colonization by trophic specialists, probably due to limited resource availability during early colonization. Late‐colonizing super‐generalists maintained constant connectance at later dates. This relationship between colonization success and trophic breadth helps explain food‐web patterns and corroborates assertions that community assembly is systematically influenced by species’ trophic breadths.
Niche partitioning at multiple scales facilitates coexistence among mosquito larvae
Authors: Gilbert Benjamin , Srivastava Diane S. , Kirby Kathryn R.
Published: April 2008

A theoretical dichotomy in community ecology distinguishes between mechanisms that stabilize species coexistence and those that cause neutral drift. Stable coexistence is predicted to occur in communities where competing species have niche‐partitioning mechanisms that reduce interspecific competition. Neutral communities are predicted to be structured by stochastic processes that are not influenced by species identity, but that may be influenced by priority effects and dispersal limitation. Recent developments have suggested that neutral interactions may be more common at local scales, while niche structuring may be more common at larger scales. We tested for mechanisms that could promote either stable coexistence or neutral drift in a bromeliad‐dwelling mosquito community by evaluating A) if a hypothesized within‐bromeliad niche partitioning mechanism occurs in the community, B) if this mechanism correlates with local species co‐occurrence patterns, and C) if patterns of coexistence at the larger (metacommunity) scale were consistent with those at the local scale. We found that mosquitoes in this community do partition space within containers, and that species with the strongest potential for competition co‐occurred least. Species with overlapping spatial niches minimized co‐occurrence by specialising in bromeliads of differing sizes, effectively changing the scale at which they coexist. In contrast, we found no evidence to support neutral dynamics in mosquito communities at either scale. In this community, a niche‐based mechanism that is predicted to stabilize species coexistence explains co‐occurrence patterns within and among bromeliads.
Host condition as a constraint for parasite reproduction
Authors: Seppälä Otto , Liljeroos Katri , Karvonen Anssi , Jokela Jukka
Published: April 2008

Environmental stress has been suggested to increase host susceptibility to infections and reduce host ability to resist parasite growth and reproduction, thus benefiting parasites. This prediction stems from expected costs of immune defence; hosts in poor condition should have less resources to be allocated to immune function. However, the alternative hypothesis for response to environmental stress is that hosts in poor condition provide less resources for parasites and/or suffer higher mortality, leading to reduced parasite growth, reproduction and survival. We contrasted these alternative hypotheses in a trematode–snail (Diplostomum spathaceum–Lymnaea stagnalis) system by asking: (1) how host condition affects parasite reproduction (amount and quality of produced transmission stages) and (2) how host condition affects the survival of infected host individuals. We experimentally manipulated host condition by starving the snails, and found that parasites produced fewer and poorer quality transmission stages in stressed hosts. Furthermore, starvation increased snail mortality. These findings indicate that in well‐established trematode infections, reduced ability of immune allocation has no effect on host exploitation by parasites. Instead, deteriorating resources for the snail host can directly limit the amount of resources available for the parasite. This, together with increased host mortality, may have negative effects on parasite populations in the wild.