bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation between high ionic conductivity and twin structure of La0.95Sr0.05Ga0.9Mg0.1O3−δ
Authors: Kurumada M. , Iguchi E. , Savytskii D. I.
Published: July 2006

The electric transport properties of La0.95Sr0.05Ga0.9Mg0.1O3−δ (LSGM) crystal with ⟨001⟩p direction grown by the Czochralski method were investigated mainly using ac measurements. The LSGM crystal comprises twin structures composed of different domain states. Only the highest-frequency semicircle was observed in impedance spectroscopy; however, two dielectric relaxation peaks exist in the loss tangent. These results indicate that the equivalent circuit of the twin structures is a parallel R-C circuit because they exhibit two parallel diffusion paths of O2− ions: one path is within the domains and the other is along the domain walls. Based on the migration energies of O2− in the domains and along the domain walls, which are estimated from dielectric relaxation processes, resistances of ionic conductions therein are assessed separately. These assessments explain that low resistance for oxygen ionic conduction along the domain walls considerably reduces the resultant resistance of the LSGM crystal and oxygen vacancies segregate preferentially in domain wall zones. A comparison between these results and those of a polycrystalline LSGM ceramic obtained experimentally suggests that the twin structures within the grains in ceramic lanthanum gallates are one of the main reasons for the high ionic conductivity.
Pressure evolution of resistance in framework structured materials α-ZrMo2O8 and α-HfMo2O8
Authors: Karandikar A. S. , Mukherjee G. D. , Vijayakumar V. , Godwal B. K. , Achary S. N. , Tyagi A. K.
Published: July 2006

The ac resistance measurements on the trigonal (α-) phase of ZrMo2O8 and HfMo2O8 carried out up to 5GPa using the toroid anvil apparatus are reported. The ac resistance data in both the materials are found to be strongly frequency dependent and show a transition between two power law regimes with a crossover frequency (ωc) near 1kHz. For both the compounds slope changes and anomalies are observed in the ac resistance data at the structural transition pressures. The activation volumes at room temperature are obtained by analyzing the ac conductance data in terms of the pressure dependent activation volume model. The main conduction mechanism at 12Hz is believed to be the diffusion of oxygens ions, whereas hopping of point defects is responsible for ac conductuance above 33kHz. At 1KHz, a crossover from hopping to diffusion of point defects is observed at the α-δ (monoclinic) phase transition pressure.
Luminescent spectroscopy and imaging of textured sprayed Er-doped ZnO films in the near ultraviolet and visible regions
Authors: Bubendorff J. L. , Ebothé J. , El Hichou A. , Dounia R. , Addou M.
Published: July 2006

The textural dependence of the thermally sprayed Er-doped ZnO films on Er concentration is reported here. The [002] preferred growth orientation of hexagonal phase is obtained at the lower concentrations, while the [100] and [101] directions additionally raised from nearly 5at.% Er content onwards. The cathodoluminescent characteristics of the samples in the near ultraviolet (UV) and visible region depict a complete extinction of the visible emitted bands (λ=445, 526, and 665nm) at 1at.% Er content. Their deactivation below this concentration is explained by a compensation of oxygen defects in the material due to the oxygen-rich medium of the deposition bath. Their reactivation beyond this particular concentration is ascribed to the increase of the Er+3 ion shells whose internal radiative transitions lead to a recovering of these visible emitted bands. The radiative mechanism of the transitions from the (F9∕24) excited states to the (I15∕24) ground state, responsible for the λ=665nm emission, is predominant in that case. The respective normalized intensity of the violet (λ=445nm) and green (λ=526nm) emitted bands exhibits a maximal value for 3at.% Er content, reaching a stabilized regime from about 5at.% Er.
Theoretical study of current overflow in GaN based light emitters with superlattice cladding layers
Authors: Łepkowski S. P. , Krukowski S.
Published: July 2006

We investigate the effect of the short-period superlattice cladding layer on electron current overflow in nitride light emitters. The classical drift-diffusion current flow and quantum tunneling transport through the miniband are considered. We show that the drift-diffusion electron current in the p-type superlattice cladding layer is drastically reduced by the presence of the intrinsic built-in electric fields. Based on this finding, we propose a design of the electron blocking layer which should considerably lower the electron current overflow in nitride light emitters.
Convective heat transfer law for an endoreversible engine
Authors: Huleihil Mahmoud , Andresen Bjarne
Published: July 2006

A generic model of an endoreversible engine is developed for studying the effect of convective heat transfer, the rate of which depends on the temperature difference to the power n where n is close to unity. The efficiency at maximum power production is found to have as its principal part the Curzon-Ahlborn [Am. J. Phys. 43, 22 (1975)] expression and a small correction which depends slightly on the temperature ratio of the heat engine reservoirs and the relative heat conductances to the hot and cold sides. By a proper choice of the independent variables it is demonstrated that the analysis becomes simple and approximate analytical expressions are easily derived.
Band offsets of high K gate oxides on III-V semiconductors
Authors: Robertson J. , Falabretti B.
Published: July 2006

III-V semiconductors have high mobility and will be used in field effect transistors with the appropriate gate dielectric. The dielectrics must have band offsets over 1eV to inhibit leakage. The band offsets of various gate dielectrics including HfO2, Al2O3, Gd2O3, Si3N4, and SiO2 on III-V semiconductors such as GaAs, InAs, GaSb, and GaN have been calculated using the method of charge neutrality levels. Generally, the conduction band offsets are found to be over 1eV, so they should inhibit leakage for these dielectrics. On the other hand, SrTiO3 has minimal conduction band offset. The valence band offsets are also reasonably large, except for Si nitride on GaN and Sc2O3 on GaN which are 0.6–0.8eV. There is reasonable agreement with experiment where it exists, although the GaAs:SrTiO3 case is even worse in experiment.
Theoretical description of ferroelectric and pyroelectric hystereses in the disordered ferroelectric-semiconductor films
Authors: Morozovska A. N. , Eliseev E. A. , Remiens D. , Soyer C.
Published: July 2006

We have modified the Landau-Khalatnikov approach and shown that both the polar lattice and the screened charged defects determine the response of disordered ferroelectric semiconductors. This system exhibits the spatially inhomogeneous switching under the external field while the Landau-Khalatnikov model describes homogeneous switching with the sharp pyroelectric coefficient peak near the thermodynamic coercive field value. Our model gives more realistic pyroelectric hysteresis loop shape without any peaks near the coercive field and describes both qualitatively and quantitatively typical Pb(Zr,Ti)O3 and (Sr,Ba)Nb2O6 films pyroelectric hysteresis loops.
Influence of longitudinal electric field on the hot-phonon effect in quantum wells
Authors: Zhang J.-Z. , Zhu B.-F.
Published: July 2006

Using the Huang-Zhu model [K. Huang and B.-F. Zhu, Phys. Rev. B 38, 13377 (1988)] for the optical phonons and associated carrier-phonon interactions in semiconductor superlattices, the effects of longitudinal electric field on the energy-loss rates (ELRs) of hot carriers as well as on the hot-phonon effect (HPE) in GaAs∕AlAs quantum wells (QWs) are studied systematically. Contributions of various bulklike and interface phonons to the hot-carrier relaxation are compared in detail, and comprehensively analyzed in relation to the intrasubband and intersubband scatterings for quantum cascade lasers. Due to the broken parity of the electron (hole) states in the electric field, the bulklike modes with antisymmetric potentials are allowed in the intrasubband relaxation processes, as well as the modes with symmetric potentials. As the interface phonon scattering is strong only in narrow wells, in which the electric field affects the electron (hole) states little, the ELRs of hot carriers through the interface phonon scattering are not sensitive to the electric field. The HPE on the hot-carrier relaxation process in the medium and wide wells is reduced by the electric field. The influence of the electric field on the hot-phonon effect in quantum cascade lasers is negligible. When the HPE is ignored, the ELRs of hot electrons in wide QWs are decreased noticeably by the electric field, but slightly increased by the field when considering the HPE. In contrast with the electrons, the ELRs of hot holes in wide wells are increased by the field, irrespective of the HPE.
Sn
O
2
target with controllable microstructure and thickness for generating extreme ultraviolet light
Authors: Pan Chao , Gu Zhong-Ze , Nagai Keiji , Shimada Yoshinori , Hashimoto Kazuhisa , Birou Tomoya , Norimatsu Takayoshi
Published: July 2006

The target of weaved tin-oxide nanofibers were fabricated by electrospinning method. The microstructure, density, and thickness of the tin-oxide fibers could be well controlled by different fabrication condition. Extreme ultraviolet emission from Sn and SnO2 nanofibers was experimentally investigated. It was found that the microscopic structure of the target could have great affection on the extreme ultraviolet light emission.
Leakage current characteristics of Pt∕Bi4−xLaxTi3O12∕Ru ferroelectric capacitors fabricated on metal-organic chemical vapor deposited Ru films
Authors: Furukawa Taisuke , Kuroiwa Takeharu , Sato Takehiko , Fujisaki Yoshihisa , Ishiwara Hiroshi
Published: July 2006

The deposition temperature dependence and postannealing temperature dependence of the properties of metal-organic chemical vapor deposited Ru film were investigated in order to minimize the leakage current density across Pt∕Bi4−xLaxTi3O12∕Ru ferroelectric capacitors. With postannealing at 400°C, leakage current density was decreased to 1∕100 of the as-deposited sample, although surface morphology and crystallinity hardly changed. The improvement effect of the leakage current was not pronounced, even if the postannealing temperature was further increased. These observations suggest that the effect of crystallinity and surface morphology of Ru film is less significant for the leakage current density, and alternative phenomenological model to explain these results is presented.
Co
Si
2
growth on Si(001) by reactive deposition epitaxy: Effects of high-flux, low-energy ion irradiation
Authors: Lim C. W. , Greene J. E. , Petrov I.
Published: July 2006

Co Si 2 layers, <40nm thick, were grown on Si(001) by reactive deposition epitaxy (RDE) in which Co was deposited at 700°C by magnetically unbalanced ultrahigh vacuum magnetron sputtering. X-ray diffraction pole figures and transmission electron microscopy (TEM) reveal that the layers, which exhibit a cube-on-cube epitaxial relationship with the substrate, (001)CoSi2‖(001)Si and [100]CoSi2‖[100]Si, contain fourfold symmetric {111} twinned domains oriented such that {221}CoSi2‖(001)Si and ⟨110⟩CoSi2‖[110]Si. We demonstrate that high-flux low-energy (EAr+=9.6eV) Ar+ ion irradiation during deposition dramatically increases the area fraction fu of untwinned regions from 0.17 in films grown under standard magnetically balanced conditions in which the ratio JAr+∕JCo of the incident Ar+ to Co fluxes is 1.4 to 0.72 with JAr+∕JCo=13.3. TEM analyses show that the early stages of RDE CoSi2(001) film growth proceed via the Volmer-Weber mode with independent nucleation of both untwinned and twinned islands. Increasing JAr+∕JCo results in larger values of both the number density and area of untwinned with respect to twinned islands. The intense Ar+ ion bombardment creates additional low-energy adsorption sites that favor the nucleation of untwinned islands while collisionally enhancing Co surface mobilities which, in turn, increases the probability of itinerant Co adatoms reaching these sites.
Strong potential profile fluctuations and effective localization process in InGaN∕GaN multiple quantum wells grown on {10-1m} faceted surface GaN template
Authors: Haffouz S. , Tang H. , Bardwell J. A. , Lefebvre P. , Bretagnon T. , Riemann T. , Christen J.
Published: July 2006

Cathodoluminescence (CL) and time-resolved photoluminescence (TRPL) spectroscopy were used to investigate the relation between the surface morphology and emission efficiency in 10× InGaN(3nm)∕GaN(4nm) quantum wells (QWs) deposited by plasma-assisted molecular beam epitaxy (MBE). For this study, two QWs with peak emission around 405nm but grown on different surface morphologies have been investigated. A strong increase in the emission efficiency was observed in the QWs grown on {10-1m} faceted surface GaN template (m>2) as compared to those grown on an atomically smooth template. CL mapping and temperature-dependent PL studies revealed that the QWs grown on the faceted surface GaN epilayer exhibit much stronger in-plane indium content fluctuations and larger width PL peak in the temperature range of 8–300K. We found that the use of {10-1m} faceted surface GaN template resulted in strong potential profile fluctuations (PPFs) inducing different localization centers at different energy levels. We found that the deeper the corresponding fluctuation of the energy level, the weaker the decrease of the PL intensity with increasing temperature, the higher the PL decay time (τPL) in the whole temperature range and the slower the collapse of τPL. Our results demonstrate that the use of {10-1m} faceted surface morphology GaN template is an amplifying process of the PPFs which favors a regime dominated by the recombination of localized carriers.
Wavelength tuning of surface plasmon resonance by annealing silver-copper nanoparticles
Authors: Hirai Makoto , Kumar Ashok
Published: July 2006

Utilizing a pulsed laser deposition method, silver-copper (Ag–Cu) nanoparticles have been synthesized by irradiating the laser light of λ=248nm on Ag and Cu plates under the pressure below 1×10−4Pa. The peak absorption attributed to surface plasmon resonance (SPR) of the Ag–Cu nanoparticles appeared at 763nm, which was approximately 200nm higher wavelength than that of Ag nanoparticles. With increase in the annealing temperature from 300to548K, the peak absorption attributed to SPR of the Ag–Cu nanoparticles shifted continuously from 763to437nm. This fact proved that the peak absorption attributed to SPR can be tuned in the whole visible region by changing the annealing temperature only. Moreover, from the results of atomic force microscopy and grazing angle x-ray diffraction, the SPR wavelength tuning is conjectured due not to the change in the surface morphology of the Ag–Cu nanoparticles but to the increase in the electric conductivity of the nanoparticles induced by the precipitation of Cu atoms.
Electrolytic coloration of oxygen-doped lithium fluoride crystals
Authors: Guo Meili , Gu Hongen , Han Li , Wang Na , Qin Fang
Published: July 2006

Oxygen-doped lithium fluoride crystals were colored electrolytically by using a pointed cathode and a flat anode at various temperatures and electric field strengths, which mainly benefit appropriate coloration temperatures and electric field strengths as well as anode structure of used electrolysis apparatus. Characteristic spectral bands of O2−-Va+ dipoles and O2−-Va+ dipole complexes and magnesium-related F, M, magnesium-perturbed F2+, oxygen-perturbed F2+, F3− color centers were observed in absorption spectra of the colored crystals. Current-time curves for the electrolytic colorations and their relationships with the electrolytic coloration processes were given. Color-center formation in the electrolytic coloration was explained.
High-speed strained-single-crystal-silicon thin-film transistors on flexible polymers
Authors: Yuan Hao-Chih , Ma Zhenqiang , Roberts Michelle M. , Savage Donald E. , Lagally Max G.
Published: July 2006

We fabricate thin-film transistors (TFTs) on both strained and unstrained single-crystal Si membranes transferred to flexible-polymer substrates. The active layer is transferred from the starting silicon on insulator (SOI) using a simple, fast, and reliable dry-printing method. When a multilayer Si∕SiGe∕Si structure is pseudomorphically grown on SOI and the buried oxide is selectively removed, strained Si with a negligible density of dislocations is achieved via elastic strain sharing between the SiGe alloy layer and the Si layers. Both the drain current and the transconductance of TFTs fabricated on this strained Si∕SiGe∕Si membrane after its transfer to the flexible polymer are much higher than of TFTs fabricated on the unstrained-Si counterpart.
Pressure induced liquid infiltration in nanopores
Authors: Han A. , Kong X. , Qiao Y.
Published: July 2006

In this article, we report the results of an infiltration∕defiltration experiment of a hydrophobic nanoporous silica gel. As the pressure is increased to the critical value, water can be forced into the nanopores. When the pressure is reduced, however, the “outflow” is difficult, leading to a significant hysteresis of sorption isotherm. A first-order thermodynamics analysis is performed to capture the confinement effect of nanopore walls and the mass and energy exchanges between liquid and gas phases in nanopores.
Improving operating lifetime of organic light-emitting diodes with polycyclic aromatic hydrocarbons as aggregating light-emitting-layer additives
Authors: Jarikov Viktor V.
Published: July 2006

It is common in organic light-emitting diode technology to construct a light-emitting-layer (LEL) host with materials that resist luminescence-reducing aggregation, which is one of the common reasons behind a phenomenon widely referred to as concentration quenching. However, if a host material in its aggregated state has a substantial quantum yield of fluorescence (e.g., at least several percents), it may yet be useful. We describe a group of aggregating flat and rigid polycyclic aromatic hydrocarbons (PAHs) as LEL additives. These molecules readily form emissive aggregates when added to the LEL. In the resulting devices, the aggregates show low-to-moderate external quantum efficiencies (EQE) of 0.2%–1.3%. Significantly, the addition of these PAHs increases device half-life (t50) 4–200 times, depending on the additive, up to 100000h upon operation at 40mA∕cm2. The lifetime increase occurs with many diverse classes of PAHs. The EQE can be improved to 3.7% by further adding a proper dopant while maintaining the increased lifetime. A possible link between the ability to aggregate and the lifetime increase is illustrated by comparing aggregation-prone perylene and aggregation-resistant 2,5,8,11-tetra-t-butylperylene (TBP). Despite the similarity between the two additives with respect to their initial device performance, perylene’s stronger ability to aggregate correlates with the eight times longer half-life versus that for TBP.
Fundamental reactions controlling anion exchange during mixed anion heterojunction formation: Chemistry of As-for-Sb and Sb-for-As exchange reactions
Authors: Losurdo Maria , Capezzuto Pio , Bruno Giovanni , Brown April S. , Brown Terence , May Gary
Published: July 2006

As-for-Sb and Sb-for-As anion exchange reactions have been investigated by the exposure of GaSb surfaces to As2 and As4 species and by the exposure of GaAs to Sb2, respectively. The effect of surface temperature, anion soak time, and anion species (either As2 or As4) on the chemistry governing the anion exchange reactions during GaAsySb1−y∕GaSb and GaSbyAs1−y∕GaAs heterostructure formation by molecular beam epitaxy is examined. It is found that when GaSb surfaces are exposed to arsenic, the anion exchange reaction competes with the formation of isoelectronic compounds, AsSby, which form clusters precipitating in the GaAsySb1−y∕GaSb heterostructures. The relative amount of GaAs and AsSby depends on the surface temperature, the As soak time, and on the As species, i.e., As2 or As4. We observe specific process conditions that minimize AsSby formation, yielding more abrupt heterojunction interfaces. In the case of the Sb2∕GaAs system, the Sb-for-As anion exchange does not occur to a significant degree, but surface segregation of antimony is found. A chemical model for the As-for-Sb anion exchange reaction is proposed.
Self-assembling of InAs nanocrystals on GaAs: The effect of electronic coupling and embedded gold nanoparticles on the photoluminescence
Authors: Paltiel Y. , Aharoni A. , Banin U. , Neuman O. , Naaman R.
Published: July 2006

In As ∕ Zn Se core/shell nanoparticles (NP) were self-assembled on GaAs substrates using different organic molecules of varying length and properties as linkers. The molecules provide control over the coupling and tunneling properties between the substrate and the nanocrystals. By coadsorbing of gold NP on the GaAs substrate, enhancement of the photoluminescence from the InAs NP was achieved. The enhancement factor was found to depend on the properties of the organic linkers.
Strain monitoring in InAs–AlxGa1−xAsySb1−y structures grown by molecular beam epitaxy
Authors: Triplett Gregory E. , Brown April S. , May Gary S.
Published: July 2006

A study of strained InAs–AlxGa1−xAsySb1−y quantum well structures produced by molecular beam epitaxy is presented. The ability to manipulate quantum well strain by way of the AlxGa1−xAsySb1−y buffer is examined using statistical experimental design. Results show that anion composition in the buffer (with a target lattice constant, a=6.12Å) varies by as much as 3% in the 450–500°C growth temperature range. The data reveal interrelationships between strain, structural characteristics, and conductivity. Results demonstrate that these relationships exist and can be modeled empirically and exploited for the design of near-infrared optoelectronic devices.
Fabrication of half-pitch 32nm resist patterns using near-field lithography with a-Si mask
Authors: Ito Toshiki , Yamada Tomohiro , Inao Yasuhisa , Yamaguchi Takako , Mizutani Natsuhiko , Kuroda Ryo
Published: July 2006

We evaluated the performances of Cr and amorphous Si (a-Si) films as light absorber materials for photomasks of near-field lithography on the basis of numerical studies using finite-difference time domain method and experimental results of fabrication process. With exposure experiments using both a Cr mask and an a-Si mask, fine performance of an a-Si near-field mask was demonstrated with respect to resolution. A half-pitch 32nm resist pattern of 120nm high was fabricated through the near-field lithography using the a-Si mask and a subsequent trilayer resist process.
Grain and grain boundary effects in high-permittivity dielectric NiO-based ceramics
Authors: Lin Yuan-Hua , Li Ming , Nan Ce-Wen , Li Jingfeng , Wu Junbo , He Jinliang
Published: July 2006

We present a Li and Ti codoped NiO-based polycrystalline ceramic with high-permittivity dielectric properties. Analysis of the ceramic microstructure and composition proves that obvious grain boundaries are formed. The measurements of frequency and temperature dependence of impedance and dielectric permittivity indicate that the grain and grain boundaries have remarkable influence on the dielectric properties due to the various activation energies corresponding to the dielectric relaxation processes. Our results also demonstrate that the activation energy required for relaxation Ea is almost the same to the activation energy of the conductivity in the grain interiors Eg.
Quantifying the Performance Limits of Human Saccadic Targeting during Visual Search
Authors: Eckstein Miguel P , Beutter Brent R , Stone Leland S
Published: July 2006

In previous studies of saccadic targeting, the issue how visually guided saccades to unambiguous targets are programmed and executed has been examined. These studies have found different degrees of guidance for saccades depending on the task and task difficulty. In this study, we use ideal-observer analysis to estimate the visual information used for the first saccade during a search for a target disk in noise. We quantitatively compare the performance of the first saccadic decision to that of the ideal observer (ie absolute efficiency of the first saccade) and to that of the associated final perceptual decision at the end of the search (ie relative efficiency of the first saccade). Our results show, first, that at all levels of salience tested, the first saccade is based on visual information from the stimulus display, and its highest absolute efficiency is ∼20%. Second, the efficiency of the first saccade is lower than that of the final perceptual decision after active search (with eye movements) and has a minimum relative efficiency of 19% at the lowest level of saliency investigated. Third, we found that requiring observers to maintain central fixation (no saccades allowed) decreased the absolute efficiency of their perceptual decision by up to a factor of two, but that the magnitude of this effect depended on target salience. Our results demonstrate that ideal-observer analysis can be extended to measure the visual information mediating saccadic target-selection decisions during visual search, which enables direct comparison of saccadic and perceptual efficiencies.
The Directional Tuning of the Barber-Pole Illusion
Authors: Fisher Nick , Zanker Johannes M
Published: July 2006

In order to study the integration of local motion signals in the human visual system, we measured directional tuning curves for the barber-pole illusion by varying two crucial aspects of the stimulus layout independently across a wide a range in the same experiment. These were the orientation of the grating presented behind the rectangular aperture and the aspect ratio of the aperture, which in combination determine the relative contributions of local motion signals perpendicular to the gratings and parallel to the aperture borders, respectively. The strength of the illusion, ie the tendency to perceive motion along the major axis of the aperture, obviously depends on the spatial layout of the aperture, but also on grating orientation. Subjects were asked which direction they perceived and how compelling their motion percept was, revealing different strategies of the visual system to deal with the barber-pole stimulus. Some individuals respond strongly to the unambiguous motion information at the boundaries, leading to multistable percepts and multimodal distributions of responses. Others tend to report intermediate directions, apparently being less influenced by the actual boundaries. The general pattern of deviations from the motion direction perpendicular to grating orientation-a decrease with aspect ratio approaching unity (ie square-shaped apertures) and with gratings approaching parallel orientation to the shorter aperture boundary—is discussed in the context of simple phenomenological models of motion integration. The best fit between model predictions and experimental data is found for an interaction between two stimulus parameters: (i) cycle ratio, which is the sine-wave gratings equivalent of the terminator ratio for line gratings, describing the effects from the aperture boundaries, and (ii) the grating orientation, responsible for perpendicular motion components, which describes the influence of motion signals from inside the aperture. This suggests that the most simple cycle (terminator) ratio explanation cannot fully account for the quantitative properties of the barber-pole illusion.
Dependence of Illusory Motion on Directional Consistency in Oblique Components
Authors: Ichikawa Makoto , Masakura Yuko , Munechika Kohkichi
Published: July 2006

Pinna and Brelstaff (2000 Vision Research40 2091–2096) reported a motion illusion on viewing two concentric circles consisting of quadrangular components with black and white sides on a grey background. Our results suggest that the illusion is based on the integration of motion signals derived from oblique components, and on the consistency in the direction among those components. Furthermore, arrays of these oblique components can elicit the perception of motion not only for the oblique components themselves, but also for other objects in the picture. We propose that the motion illusion depends not only upon detection of the illusory motion signal at each local oblique component, but also upon the accumulation of the signal all over the stimulus configuration.
Can Subthreshold Summation Be Observed with the Ehrenstein Illusion?
Authors: Salvano-Pardieu Véronique , Wink Brian , Taliercio Alain , Manktelow Ken , Meigen Thomas
Published: July 2006

Subthreshold summation between physical target lines and illusory contours induced by edges such as those produced in the Kanizsa illusion has been reported in previous studies. Here, we investigated the ability of line-induced illusory contours, using Ehrenstein figures, to produce similar subthreshold summation. In the first experiment, three stimulus conditions were presented. The target line was superimposed on the illusory contour of a four-arm Ehrenstein figure, or the target was presented between two dots (which replaced the arms of the Ehrenstein figure), or the target was presented on an otherwise blank screen (control). Detection of the target line was significantly worse when presented on the illusory contour (on the Ehrenstein figure) than when presented between two dots. This result was consistent for both curved and straight target lines, as well as for a 100 ms presentation duration and unlimited presentation duration. Performance was worst in the control condition. The results for the three stimulus conditions were replicated in a second experiment in which an eight-arm Ehrenstein figure was used to produce a stronger and less ambiguous illusory contour. In the third experiment, the target was either superimposed on the illusory contour, or was located across the central gap (illusory surface) of the Ehrenstein figure, collinear with two arms of the figure. As in the first two experiments, the target was either presented on the Ehrenstein figure, or between dots, or on a blank screen. Detection was better in the dot condition than in the Ehrenstein condition, regardless of whether the target was presented on the illusory contour or collinear with the arms of the Ehrenstein figure. These three experiments demonstrate the ability of reduced spatial uncertainty to facilitate the detection of a target line, but do not provide any evidence for subthreshold summation between a physical target line and the illusory contours produced by an Ehrenstein figure. The incongruence of these results with previous findings on Kanizsa figures is discussed.
Domestic Chicks Perceive Stereokinetic Illusions
Authors: Clara Elena , Regolin Lucia , Zanforlin Mario , Vallortigara Giorgio
Published: July 2006

Stereokinetic illusions occur when certain 2-D patterns are set in slow rotation in a plane perpendicular to the line of sight. Such phenomena have never been investigated in animal species other than our own. We used the domestic chick ( Gallus gallus) to check whether these illusions are experienced by non-human species, taking advantage of filial imprinting. Newly hatched visually naive chicks were individually exposed for 4 h to 2-D stimuli producing, to a human observer, the perception of a stereokinetic cone (experiment 1) or of a stereokinetic cylinder (experiment 2). Thereafter, each chick underwent a free-choice test between a solid 3-D cone and a solid 3-D cylinder. A control group of newly hatched but not imprinted chicks underwent the same testing procedure, to check for the presence of any spontaneous preference for one or other of the two solid objects. Imprinted chicks approached the 3-D stimulus closely resembling the stimulus they had been exposed to during imprinting (the cone in experiment 1 and the cylinder in experiment 2). Non-imprinted chicks did not show any preference. These results suggest that domestic chicks experience stereokinetic illusions.
Who Owns the Contour of a Visual Hole?
Authors: Bertamini Marco
Published: July 2006

Holes are useful in the study of shape, contour curvature, and border ownership. Several authors have suggested that holes have figural or quasi-figural status. I discuss three criteria to test the evidence that holes behave more like figures than like ground: (i) holes perceived as such; (ii) similar performance for holes and figures; (iii) different performance for holes and other ground regions. Using these criteria, I review the literature and conclude that holes do not have figural status in relation to border ownership. I also argue that holes are ideal stimuli to study figure - ground organisation.
Surface Assignment Modulates Object Formation for Visual Short-Term Memory
Authors: Kristjánsson Árni
Published: July 2006

Recent results have suggested that the operational units of visual short-term memory (VSTM) are whole objects, rather than features or the total amount of information to be remembered. Here, for the first time, the influence of surface assignment on object formation for VSTM was investigated. The observers had to memorize the features of four briefly presented (300 ms) two-part objects, followed by a mask and a cue indicating which object to report on. The experiments contrasted whether there were any apparent depth differences between the two parts of each object, and whether observers had to report on only one or both features of the post-cued target object. Depth differences induced with stereoscopic disparity, and with a pictorial depth cue (simple interposition of object features), interfered strongly with performance when both features of an object needed to be memorized, but aided performance when only a single feature needed to be remembered. Furthermore, there was considerable within-feature interference consistent with some previous findings, but contradicting others. The potential implications for conceptions of VSTM are discussed in the light of two hypothesized stages: an early feature-based stage, as well as a higher-level object-based stage where the depth manipulations exert their effects. The results argue for a strong modulatory influence of surface assignment on object formation for a VSTM task.
The Bar — Cross — Ellipse Illusion: Alternating Percepts of Rigid and Nonrigid Motion Based on Contour Ownership and Trackable Feature Assignment
Authors: Caplovitz Gideon P , Tse Peter U
Published: July 2006

We present a new multistable stimulus generated by continuously rotating an ellipse behind four fixed occluders. Despite the stimulus remaining constant, observers can alternate between one of four percepts: (1) a continuously morphing cross; (2) two independent perpen-dicular bars oscillating in depth; (3) a rigidly rotating ellipse observed behind the occluders; (4) a fixed cross observed through a continuously rotating, elliptical aperture. Interestingly, the initial percept naive observers tend to see is percept 1, which is the only nonrigid motion percept. This appears to be a violation of the hypothesized ‘rigidity heuristic’ in which rigid motion percepts tend to be perceived over retinally equivalent nonrigid ones. Here, we describe the relationships between each of the percepts and the assignment of contour ownership and figure/ground segmentation.
Nonvascular VEGF receptor 3 expression by corneal epithelium maintains avascularity and vision
Authors: Cursiefen Claus , Chen Lu , Saint-Geniez Magali , Hamrah Pedram , Jin Yiping , Rashid Saadia , Pytowski Bronislaw , Persaud Kris , Wu Yan , Streilein J. Wayne , Dana Reza
Published: July 2006

Transparency of the cornea, the window of the eye, is a prerequisite for vision. Angiogenesis into the normally avascular cornea is incompatible with good vision and, therefore, the cornea is one of the few tissues in the human body where avascularity is actively maintained. Here, we provide evidence for a critical mechanism contributing to corneal avascularity. VEGF receptor 3, normally present on lymphatic and proliferating blood vascular endothelium, is strongly constitutively expressed by corneal epithelium and is mechanistically responsible for suppressing inflammatory corneal angiogenesis.
Human prions and plasma lipoproteins
Authors: Safar Jiri G. , Wille Holger , Geschwind Michael D. , Deering Camille , Latawiec Diane , Serban Ana , King David J. , Legname Giuseppe , Weisgraber Karl H. , Mahley Robert W. , Miller Bruce L. , DeArmond Stephen J. , Prusiner Stanley B.
Published: July 2006

Prions are composed solely of an alternatively folded isoform of the prion protein (PrP), designated PrP
Sc
. The polyoxometalate phosphotungstic acid has been used to separate PrP
Sc
from its precursor PrP
C
by selective precipitation; notably, native PrP
Sc
has not been solubilized by using nondenaturing detergents. Because of the similarities between PrP
Sc
and lipoproteins with respect to hydrophobicity and formation of phosphotungstic acid complexes, we asked whether these molecules are bound to each other in blood. Here we report that prions from the brains of patients with sporadic Creutzfeldt–Jakob disease (CJD) bind to very low-density (VLDL) and low-density (LDL) lipoproteins but not to high-density lipoproteins (HDL) or other plasma components, as demonstrated both by affinity assay and electron microscopy. Immunoassays demonstrated that apolipoprotein B (apoB), which is the major protein component of VLDL and LDL, bound PrP
Sc
through a highly cooperative process. Approximately 50% of the PrP
Sc
bound to LDL particles was released after exposure to 4 M guanidine hydrochloride at 80°C for 20 min. The apparent binding constants of native human (Hu) PrP
Sc
or denatured recombinant HuPrP(90–231) for apoB and LDL ranged from 28 to 212 pM. Whether detection of PrP
Sc
in VLDL and LDL particles can be adapted into an antemortem diagnostic test for prions in the blood of humans, livestock, and free-ranging cervids remains to be determined.
Electrically conductive bacterial nanowires produced by
Shewanella oneidensis
strain MR-1 and other microorganisms
Authors: Gorby Yuri A. , Yanina Svetlana , McLean Jeffrey S. , Rosso Kevin M. , Moyles Dianne , Dohnalkova Alice , Beveridge Terry J. , Chang In Seop , Kim Byung Hong , Kim Kyung Shik , Culley David E. , Reed Samantha B. , Romine Margaret F. , Saffarini Daad A. , Hill Eric A. , Shi Liang , Elias Dwayne A. , Kennedy David W. , Pinchuk Grigoriy , Watanabe Kazuya , Ishii Shun’ichi , Logan Bruce , Nealson Kenneth H. , Fredrickson Jim K.
Published: July 2006

Shewanella oneidensis
MR-1 produced electrically conductive pilus-like appendages called bacterial nanowires in direct response to electron-acceptor limitation. Mutants deficient in genes for
c
-type decaheme cytochromes MtrC and OmcA, and those that lacked a functional Type II secretion pathway displayed nanowires that were poorly conductive. These mutants were also deficient in their ability to reduce hydrous ferric oxide and in their ability to generate current in a microbial fuel cell. Nanowires produced by the oxygenic phototrophic cyanobacterium
Synechocystis
PCC6803 and the thermophilic, fermentative bacterium
Pelotomaculum thermopropionicum
reveal that electrically conductive appendages are not exclusive to dissimilatory metal-reducing bacteria and may, in fact, represent a common bacterial strategy for efficient electron transfer and energy distribution.
Is alcohol good or bad for Canadian hearts? A time‐series analysis of the link between alcohol consumption and IHD mortality
Authors: RAMSTEDT MATS
Published: July 2006

The objective of this study was to analyse the population level association between alcohol consumption and ischaemic heart disease (IHD) mortality in Canada. Yearly changes in IHD mortality rates from 1950 to 1998 were analysed in relation to yearly changes in alcohol consumption, employing the Box & Jenkins technique for time‐series analyses. All models controlled for cigarette smoking and one analysis with focus on men also included female IHD mortality as an indicator of other risk factors for IHD. A 1‐litre increase in per capita alcohol consumption was associated with an increase in overall IHD mortality as well as among men and women with fully 1%, but no estimate reached statistical significance. A positive and significant relationship between smoking and IHD mortality was demonstrated in all models. According to the model with focus on male IHD mortality, an increase in per capita consumption by 1 litre was related significantly to a 1% increase in male IHD mortality. No significant effects were found in different male age groups. The idea that alcohol saves more IHD deaths than it causes in Canada is not in accordance with these findings. An increase in overall alcohol consumption is more likely to cause an increase in IHD mortality than to lower the number of IHD deaths, at least among men.
Validation study of the Turkish version of the Yale—Brown Obsessive Compulsive Scale for heavy drinking in a group of male patients
Authors: ILHAN INCI OZGUR , DEMIRBAS HATICE , DOGAN YILDIRIM B.
Published: July 2006

Psychometric properties of Turkish version of the Yale Brown Obsessive Compulsive Scale for heavy drinking (YBOCS‐hd) were examined in alcohol‐dependent male patients. Factor structure, internal consistency and discriminant validity of the YBOCS‐hd were analysed in a sample of 117 male patients diagnosed with alcohol dependence. To study its convergent validity, the YBOCS‐hd was correlated with the Addiction Severity Index in 34 of the patients. A test‐retest reliability study was performed on the data from 34 patients. Correlation between the YBOCS‐hd total score and the ASI Alcohol Use score was moderate (r =0.51). One factor explained 50.2% of the variance. The YBOCS‐hd was able to discriminate the groups abstinent for less than 1 month and a second group with at least 1 month of abstinence. Test‐retest correlation was high (r =0.81, ICC= 0.81). The Turkish version of the YBOCS‐hd proved to be a reliable and valid instrument measuring craving in alcohol‐dependent male individuals.
The role of prior task experience in temporal misestimation
Authors: Thomas Kevin E. , Handley Simon J. , Newstead Stephen E.
Published: July 2006

The effect of experience with a preceding task on the accuracy of predictions of duration was examined in three experiments, where two tasks comprising similar or different mental operators were performed consecutively. Results supported an anchoring account of misestimation, which states that misestimation occurs because predictions are anchored to the duration of the preceding task. Preceding performance of a longer task led to overestimation on a shorter task with similar mental operators (Experiment 1), whereas preceding performance of a shorter task comprising similar or different mental operators led to underestimation on a longer task (Experiments 1 to 3). Contrary to the planning fallacy account (Kahneman & Tversky, 1979), these findings indicate that preceding task performance is considered when predicting duration, but that using such information does not necessarily improve accuracy.
Primacy effects induced by temporal or physical context shifts are attenuated by a preshift test trial
Authors: Wheeler Daniel S. , Miller Ralph R.
Published: July 2006

When subjects are sequentially trained with a cue (A) paired separately with two outcomes (B and C) in different phases (i.e., A–B pairings followed by A–C pairings) testing in the training context after short retention intervals often reveals recency effects (i.e., stronger influence by A–C). In contrast, testing after long retention intervals or testing in a context different from that of training sometimes reveals primacy effects (A–B). Three experiments were conducted using rats in a Pavlovian conditioned bar-press suppression preparation to ascertain whether a nonreinforced test trial in the training context soon after training can attenuate this shift to primacy. Experiment 1 demonstrated that exposure to A shortly after both phases of training, but prior to a long retention interval, can attenuate shifts from recency to primacy otherwise observed with a long retention interval. Experiment 2 showed that exposure to A in the training context can also eliminate the shift from recency to primacy otherwise produced by shifting the physical context between training and test. Experiment 3 discredited a potential account of the results of Experiments 1 and 2. The effects observed in Experiment 1 and 2 are interpreted as early testing in the training context serving to initiate rehearsal of the A–C association due to the temporal proximity of A–C training.
Identification of the Yeast R-SNARE Nyv1p as a Novel Longin Domain-containing Protein
Authors: Wen Wenyu , Chen Lu , Wu Hao , Sun Xin , Zhang Mingjie , Banfield David K.
Published: July 2006

Using nuclear magnetic resonance spectroscopy, we establish that the N-terminal domain of the yeast vacuolar R-SNARE Nyv1p adopts a longin-like fold similar to those of Sec22b and Ykt6p. Nyv1p is sorted to the limiting membrane of the vacuole via the adaptor protein (AP)3 adaptin pathway, and we show that its longin domain is sufficient to direct transport to this location. In contrast, we found that the longin domains of Sec22p and Ykt6p were not sufficient to direct their localization. A YXXΦ-like adaptin-dependent sorting signal (Y31GTI34) unique to the longin domain of Nyv1p mediates interactions with the AP3 complex in vivo and in vitro. We show that amino acid substitutions to Y31GTI34 (Y31Q;I34Q) resulted in mislocalization of Nyv1p as well as reduced binding of the mutant protein to the AP3 complex. Although the sorting of Nyv1p to the limiting membrane of the vacuole is dependent upon the Y31GTI34 motif, and Y31 in particular, our findings with structure-based amino acid substitutions in the mu chain (Apm3p) of yeast AP3 suggest a mechanistically distinct role for this subunit in the recognition of YXXΦ-like sorting signals.
TRANSPORT‐RELATED FRINGE BENEFITS: IMPLICATIONS FOR MOVING AND THE JOURNEY TO WORK
Authors: Van Ommeren Jos , Van Der Vlist Arno , Nijkamp Peter
Published: July 2006

ABSTRACT Firms offer compensation not only through wages, but also offer transport‐related fringe benefits such as transport benefits (company cars, travel, and parking benefits) and relocation benefits to job applicants. We argue that these benefits are not randomly offered to employees, but depend on the job applicants' commuting costs. The firms' choice between these benefits affects the workers' incentive to move their residence closer to the workplace. Using information on firms' recruitment behavior in the United Kingdom, this paper shows empirically that the applicants' journey‐to‐work time induces firms to offer these benefits to job applicants. The implications of transport‐related fringe benefits for commuting and relocation are found to be rather distinct. Transport benefits make employees less sensitive to the costs of commuting, whereas relocation benefits induce employees to move closer to the workplace.
ECONOMIC FUNDAMENTALS IN LOCAL HOUSING MARKETS: EVIDENCE FROM U.S. METROPOLITAN REGIONS
Authors: Hwang Min , Quigley John M.
Published: July 2006

ABSTRACT This paper investigates the effects of national and regional economic conditions on outcomes in the single‐family housing market: housing prices, vacancies, and residential construction activity. Our three‐equation model confirms the importance of changes in regional economic conditions, income, and employment on local housing markets. The results also provide the first detailed evidence on the importance of vacancies in the owner‐occupied housing market on housing prices and supplier activities. The results also document the importance of variations in materials, labor and capital costs, and regulation in affecting new supply. Simulation exercises, using standard impulse response models, document the lags in market responses to exogenous shocks and the variations arising from differences in local parameters. The results also suggest the importance of local regulation in affecting the pattern of market responses to regional income shocks.