bluuebunny/crossref_metadata_2025 huggingface dataset:
A local correlation model that yields intrinsically smooth potential-energy surfaces
Authors: Subotnik Joseph E. , Head-Gordon Martin
Published: August 2005

We demonstrate an algorithm for computing local coupled-cluster doubles (LCCD) energies that form rigorously smooth potential-energy surfaces and which should be fast enough for application to large systems in the future. Like previous LCCD algorithms, our method solves iteratively for only a limited number of correlation amplitudes, treating the remaining amplitudes with second-order perturbation theory. However, by employing bump functions, our method smoothes the transition from iteratively solved amplitude to perturbation-treated amplitude, invoking the implicit function theorem to prove that our LCCD energy is an infinitely differentiable function of nuclear coordinates. We make no explicit amplitude domains nor do we rely on the existence of atom-centered, redundant orbitals in order to get smooth potential-energy curves. In fact, our algorithm employs only localized orthonormal occupied and virtual orbitals. Our approach should be applicable to many other electron correlation methods.
Three-dimensional time-dependent wave-packet calculations of OBrO absorption spectra
Authors: Yuan Kai-Jun , Sun Zhigang , Cong Shu-Lin , Lou Nanquan
Published: August 2005

The absorption spectra of the C(A22)←X(B12) transition of the OBrO molecule are calculated using three-dimensional time-dependent wave-packet method in Radau coordinates for a total angular momentum J=0. The wave packet is propagated using the split operator technique associated with fast Fourier transform. Employing the basis functions obtained by one-dimensional Fourier grid Hamiltonian method, the initial wave packet is calculated directly on the three-dimensional Fourier grid. The numerical model is characterized by simplicity and efficiency. The ab initio potential surfaces for the C(A22) and X(B12) states are used in the calculation. The calculated absorption spectra of the C(A22)←X(B12) transition of OBrO molecule agree well with the experimental results.
Electronic transport imaging in a multiwire SnO2 chemical field-effect transistor device
Authors: Kalinin Sergei V. , Shin J. , Jesse S. , Geohegan D. , Baddorf A. P. , Lilach Y. , Moskovits M. , Kolmakov A.
Published: August 2005

The electronic transport and the sensing performance of an individual SnO2 crossed-nanowires device in a three-terminal field-effect transistor configuration were investigated using a combination of macroscopic transport measurements and scanning surface-potential microscopy (SSPM). The structure of the device was determined using both scanning electron- and atomic force microscopy data. The SSPM images of two crossed one-dimensional nanostructures, simulating a prototypical nanowire network sensors, exhibit large dc potential drops at the crossed-wire junction and at the contacts, identifying them as the primary electroactive elements in the circuit. The gas sensitivity of this device was comparable to those of sensors formed by individual homogeneous nanostructures of similar dimensions. Under ambient conditions, the dc transport measurements were found to be strongly affected by field-induced surface charges on the nanostructure and the gate oxide. These charges result in a memory effect in transport measurements and charge dynamics which are visualized by SSPM. Finally, scanning probe microscopy is used to measure the current-voltage characteristics of individual active circuit elements, paving the way to a detailed understanding of chemical functionality at the level of an individual electroactive element in an individual nanowire.
Theoretical analysis of feedback mechanisms of two-dimensional finite-sized photonic-crystal lasers
Authors: Nojima S.
Published: August 2005

Theoretical investigations are carried out for close-to-lasing two-dimensional finite-sized photonic crystals with active (gain) lattice points. First, laser oscillations with lower thresholds are found to occur near the photonic band edges where optical gain is enormously intensified. For several modes isolated around the band edge, the field-intensity spectra in reciprocal space and the Poynting-vector distributions in real space are investigated in detail in close-to-lasing photonic crystals. By comparing the phenomena that occur in photonic crystals with a symmetric or an asymmetric outward form, this paper clarifies the differences in the feedback mechanisms of these crystals. In a symmetric photonic crystal, laser oscillation occurs through the waves propagating along the straight passages. This feedback is basically the same as that of ordinary one-dimensional lasers, although it exhibits a complicated behavior that light waves propagating in a variety of directions interfere with each other. In an asymmetric photonic crystal, laser oscillation occurs through the waves circulating within the crystal, which could be called recurrent-photon feedback. This feedback, however, can be construed as an extension of the feedback in ordinary one-dimensional distributed-feedback lasers.
Quantum studies of the vibrations in H3O2− and D3O2−
Authors: McCoy Anne B. , Huang Xinchuan , Carter Stuart , Bowman Joel M.
Published: August 2005

The vibrations of H3O2− and D3O2− are investigated using diffusion Monte Carlo (DMC) and vibrational configuration-interaction approaches, as implemented in the program MULTIMODE. These studies use the potential surface recently developed by Huang et al. [ J. Am. Chem. Soc. 126, 5042 (2004)]. The focus of this work is on the vibrational ground state and fundamentals which occur between 100 and 3700cm−1. In most cases, excellent agreement is obtained between the fundamental frequencies calculated by the two approaches. This serves to demonstrate the power of both methods for treating this very anharmonic system. Based on the results of the MULTIMODE and DMC treatments, the extent and nature of the couplings in H3O2− and D3O2− are investigated.
A new route to chaos: Sequences of topological torus bifurcations
Authors: Spears Brian K. , Szeri Andrew J.
Published: August 2005

We consider a sequence of topological torus bifurcations (TTBs) in a nonlinear, quasiperiodic Mathieu equation. The sequence of TTBs and an ensuing transition to chaos are observed by computing the principal Lyapunov exponent over a range of the bifurcation parameter. We also consider the effect of the sequence on the power spectrum before and after the transition to chaos. We then describe the topology of the set of knotted tori that are present before the transition to chaos. Following the transition, solutions evolve on strange attractors that have the topology of fractal braids in Poincaré sections. We examine the topology of fractal braids and the dynamics of solutions that evolve on them. We end with a brief discussion of the number of TTBs in the cascade that leads to chaos.
Multiple returns for some regular and mixing maps
Authors: Haydn N. , Lunedei E. , Rossi L. , Turchetti G. , Vaienti S.
Published: August 2005

We study the distributions of the number of visits for some noteworthy dynamical systems, considering whether limit laws exist by taking domains that shrink around points of the phase space. It is well known that for highly mixing systems such limit distributions exhibit a Poissonian behavior. We analyze instead a skew integrable map defined on a cylinder that models a shear flow. Since almost all fibers are given by irrational rotations, we at first investigate the distributions of the number of visits for irrational rotations on the circle. In this last case the numerical results strongly suggest the existence of limit laws when the shrinking domain is chosen in a descending chain of renormalization intervals. On the other hand, the numerical analysis performed for the skew map shows that limit distributions exist even if we take domains shrinking in an arbitrary way around a point, and these distributions appear to follow a power law decay of which we propose a theoretical explanation. It is interesting to note that we observe a similar behavior for domains wholly contained in the integrable region of the standard map. We also consider the case of two or more systems coupled together, proving that the distributions of the number of visits for domains intersecting the boundary between different regions are a linear superposition of the distributions characteristic of each region. Using this result we show that the real limit distributions can be hidden by some finite-size effects. In particular, when a chaotic and a regular region are glued together, the limit distributions follow a Poisson-like law, but as long as the measure of the shrinking domain is not zero, the polynomial behavior of the regular component dominates for large times. Such an analysis seems helpful to understand the dynamics in the regions where ergodic and regular motions are intertwined, as it may occur for the standard map. Finally, we study the distributions of the number of visits around generic and periodic points of the dissipative Hénon map. Although this map is not uniformly hyperbolic, the distributions computed for generic points show a Poissonian behavior, as usually occurs for systems with highly mixing dynamics, whereas for periodic points the distributions follow a different law that is obtained from the statistics of first return times by assuming that subsequent returns are independent. These results are consistent with a possible rapid decay of the correlations for the Hénon map.
High hydrogen permeability in the Nb–Zr–Ni eutectic alloy containing the primary body-centered-cubic (Nb, Zr) phase
Authors: Ishikawa K. , Takano T. , Matsuda T. , Aoki K.
Published: August 2005

Hydrogen permeability (Φ), i.e., the product of hydrogen diffusion coefficient (D) and hydrogen solubility (K), of the as-cast Nb40Zr30Ni30 (mol %) alloy has been investigated. This alloy is composed of the primary body-centered-cubic (bcc)-(Nb, Zr) and eutectic {(Nb,Zr)+ZrNi} phase and the chemical composition and the volume fraction of the primary phase are Nb89Zr8Ni3 and 40%, respectively. Φ of this alloy increases with increasing temperature and is 4.64×10−8[molH2m−1s−1Pa−0.5] at 673K, which is 2.9 times larger than that of pure Pd. The present work indicates that Φ of the Nb–Zr–Ni alloys increases with increasing the volume fraction of the primary bcc-(Nb, Zr) phase.
Chaos control and synchronization in Bragg acousto-optic bistable systems driven by a separate chaotic system
Authors: Wang Rong , Gao Jin-Yue
Published: August 2005

In this paper we propose a new scheme to achieve chaos control and synchronization in Bragg acousto-optic bistable systems. In the scheme, we use the output of one system to drive two identical chaotic systems. Using the maximal conditional Lyapunov exponent (MCLE) as the criterion, we analyze the conditions for realizing chaos synchronization. Numerical calculation shows that the two identical systems in chaos with negative MCLEs and driven by a chaotic system can go into chaotic synchronization whether or not they were in chaos initially. The two systems can go into different periodic states from chaos following an inverse period-doubling bifurcation route as well when driven by a periodic system.
Clean positive operator valued measures
Authors: Buscemi Francesco , Keyl Michael , D’Ariano Giacomo Mauro , Perinotti Paolo , Werner Reinhard F.
Published: August 2005

In quantum mechanics the statistics of the outcomes of a measuring apparatus is described by a positive operator valued measure (POVM). A quantum channel transforms POVMs into POVMs, generally irreversibly, thus losing some of the information retrieved from the measurement. This poses the problem of which POVMs are “undisturbed,” i.e., they are not irreversibly connected to another POVM. We will call such POVMs clean. In a sense, the clean POVMs would be “perfect,” since they would not have any additional “extrinsical” noise. Quite unexpectedly, it turns out that such a “cleanness” property is largely unrelated to the convex structure of POVMs, and there are clean POVMs that are not extremal and vice versa. In this article we solve the cleannes classification problem for number n of outcomes n⩽d (d dimension of the Hilbert space), and we provide a set of either necessary or sufficient conditions for n>d, along with an iff condition for the case of informationally complete POVMs for n=d2.
Effects of phase distribution and grain size on the effective anisotropy and coercivity of nanocomposite Nd2Fe14B∕α-Fe magnets
Authors: Feng W. C. , Gao R. W. , Yan S. S. , Li W. , Zhu M. G.
Published: August 2005

The effects of phase distribution and grain size on the effective anisotropy and coercivity of the exchange-coupled nanocomposite permanent materials have been investigated in this paper. The effective anisotropy of nanocomposite permanent materials is supposed to be equal to the statistical average value of the anisotropy of magnetically soft and hard grains. The dependence of coercivity on grain sizes is mainly determined by the effective anisotropy of the grains. The calculated results show that, when the grain sizes of the soft and hard phases are identical and the volume fraction of the hard phase is given, the coercivity decreases with the reduction of the grain size. For the given size of the soft grains and the volume fraction of the hard phase, the coercivity shows a peak value as a function of the hard-grain size. The experimental enhancement of the coercivity with reducing grain size is attributed not to only the exchange-coupling interactions but also to the phase distribution.
Transition between the relaxor and ferroelectric states for (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 with x=0.2 and 0.3 polycrystalline aggregates
Authors: Algueró M. , Jiménez B. , Pardo L.
Published: August 2005

The transition between the relaxor and ferroelectric states for 0.8Pb(Mg1∕3Nb2∕3)O3–0.2PbTiO3 and 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 polycrystalline aggregates has been studied by measurements of the dielectric and elastic properties as a function of temperature. The ferroelectric to relaxor transition seems to present a regime of ferroelectric fluctuations that is sharply interrupted by the appearance of the polar nanodomains. It also presents thermal hysteresis, not only in the transition temperature, Tc, but in the characteristic time scale of the ferroelectric fluctuations that is longer on cooling than on heating. The latter effect is much more significant for 0.8Pb(Mg1∕3Nb2∕3)O3–0.2PbTiO3 (Tc=346K on heating), than for 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (Tc∼408K on heating). This indicates that there is a sharp slowing down of the kinetics of the phase transition below 346 K.
Development of strain reduced GaN on Si (111) by substrate engineering
Authors: Jamil M. , Grandusky J. R. , Jindal V. , Shahedipour-Sandvik F. , Guha S. , Arif M.
Published: August 2005

We report on a novel scheme of substrate engineering to obtain high-quality GaN layers on Si substrates. Ion implantation of an AlN∕Si substrate is performed to create a defective layer that partially isolates the III-nitride layer and the Si substrate and helps to reduce the strain in the film. Raman spectroscopy shows a substantial decrease in in-plane strain in GaN films grown on nitrogen implanted substrates. This is confirmed by the enhancement of the E2 (TO) phonon frequency from 564 to 567cm−1 corresponding to 84% stress reduction and substantial decrease in crack density for a 2-μm-thick GaN film. GaN films grown on implanted AlN∕Si substrate have better optical properties and smoother surface morphology as compared to nonimplanted AlN∕Si substrate.
Evidence of vectorial photoelectric effect on Copper
Authors: Pedersoli E. , Banfi F. , Ressel B. , Pagliara S. , Giannetti C. , Galimberti G. , Lidia S. , Corlett J. , Ferrini G. , Parmigiani F.
Published: August 2005

Quantum efficiency (QE) measurements of single photon photoemission from a Cu(111) single crystal and a Cu polycrystal photocathodes, irradiated by 150fs–6.28eV laser pulses, are reported over a broad range of incidence angle, both in s and p polarizations. The maximum QE (≃4×10−4) for polycrystalline Cu is obtained in p polarization at an angle of incidence θ=65°. We observe a QE enhancement in p polarization which cannot be explained in terms of optical absorption, a phenomenon known as vectorial photoelectric effect. Issues concerning surface roughness and symmetry considerations are addressed. An explanation in terms of nonlocal conductivity tensor is proposed.
Efficient organic light-emitting diodes using polycrystalline silicon thin films as semitransparent anode
Authors: Zhu X. L. , Sun J. X. , Peng H. J. , Meng Z. G. , Wong M. , Kwok H. S.
Published: August 2005

Polycrystalline silicon (p-Si) is a good material for the construction of thin-film transistors (TFT). It is used for fabricating active-matrix organic light-emitting diode (AMOLED) displays. In this letter, we propose and demonstrate the application of boron-doped p-Si as a semi-transparent anode in making different color OLEDs. Without removing the ultrathin native oxide on the p-Si surface and employing p-doped hole transport layer to enhance holes injection, these OLEDs show comparable or even better performance to conventional OLEDs which use ITO as anodes. The present technique has the advantage of less masking steps in making AMOLED.
Conductance of single thiolated poly(GC)-poly(GC) DNA molecules
Authors: Xu M. S. , Tsukamoto S. , Ishida S. , Kitamura M. , Arakawa Y. , Endres R. G. , Shimoda M.
Published: August 2005

We use ultrahigh vacuum scanning tunneling microscopy∕spectroscopy (UHV-STM∕STS) to investigate the electronic properties of single thiolated 12-base-pair poly(GC)-poly(GC) DNA molecules on a Au(111) surface at room temperature. Reproducible current-voltage curves of the DNA are obtained at variable sample-tip separations. The normalized conductance, which can be interpreted as the density of states, shows a well-defined wide band gap. UHV-STM∕STS opens up a novel technique to probe the electronic properties of biomolecules on surfaces at the atomic level.
Structure and electronic properties of dysprosium-silicide nanowires on vicinal Si(001)
Authors: Preinesberger C. , Pruskil G. , Becker S. K. , Dähne M. , Vyalikh D. V. , Molodtsov S. L. , Laubschat C. , Schiller F.
Published: August 2005

Dysprosium-silicide nanowires with widths of 15–100 Å and lengths exceeding several 1000 Å can be formed on Si(001) by self-assembly. Because of the anisotropy of the Si(001) surface, these nanowires grow in two orthogonal directions. In this study we demonstrate that growth on vicinal substrates results in a perfect unidirectional alignment of the wires. This allows an investigation by angle-resolved photoelectron spectroscopy showing anisotropic metallicity of the nanowires.
Microfabricated-composite-hologram-enabled multiple channel longitudinal optical guiding of microparticles in nondiffracting core of a Bessel beam array
Authors: Ahluwalia B. P. S. , Yuan X.-C. , Tao S. H. , Bu J. , Wang H. , Peng X. , Niu H. B.
Published: August 2005

In this letter, we report multiple-channel longitudinal optical guiding of microparticles using an array of Bessel beams generated from a composite hologram fabricated by ultraviolet lithography. The optical guiding efficiency of each Bessel beam in the optical array is investigated experimentally. The rod-like core of each Bessel beam, with its nondiffracting and self-reconstruction property, has been shown to offer strong capability for optical guiding along the propagation axis possibly even in multiple-microfluidic channels massively.
Experimental analysis of the quasi-Fermi level split in quantum dot intermediate-band solar cells
Authors: Luque A. , Martí A. , López N. , Antolín E. , Cánovas E. , Stanley C. , Farmer C. , Caballero L. J. , Cuadra L. , Balenzategui J. L.
Published: August 2005

The intermediate-band solar cell (IBSC) has been proposed as a device whose conversion efficiency can exceed the 40.7% limiting value of single-gap cells. It utilizes the so-called intermediate-band material, characterized by the existence of a band that splits an otherwise conventional semiconductor bandgap into two sub-bandgaps. Two important criteria for its operation are that the carrier populations in the conduction, valence, and intermediate-bands are each described by their own quasi-Fermi levels, and that photocurrent is produced when the cell is illuminated with below-bandgap-energy photons. IBSC prototypes have been manufactured from InAs quantum dot structures and analyzed by electroluminescence and quantum efficiency measurements. We present evidence to show that the two main operating principles required of the IBSC are fulfilled.
One Blue Colour Channel or Two?
Authors: Logvinenko Alexander D , Hutchinson Sara J
Published: August 2005

Contrary to the general belief that the yellow-blue mechanism has lower spatial resolution than the red-green mechanism, it has been recently claimed that both mechanisms have similar spatial sensitivity (McKeefry et al, 2001 Vision Research41 245–255). Studying high-spatial-frequency tritanopia (a colour illusion based on spatio-chromatic interactions in human vision), we found strong evidence for the existence of two blue mechanisms—with low and high spatial-frequency resolution. If confirmed, this may resolve the apparent paradox concerning spatial resolution of the yellow-blue mechanism.
Information Limits on Identification of Natural Surfaces by Apparent Colour
Authors: Foster David H , Nascimento Sérgio M C , Amano Kinjiro
Published: August 2005

By adaptational and other mechanisms, the visual system can compensate for moderate changes in the colour of the illumination on a scene. Although the colours of most surfaces are perceived to be constant (‘colour constancy’), some are not. The effect of these residual colour changes on the ability of observers to identify surfaces by their apparent colour was determined theoretically from high-resolution hyperspectral images of natural scenes under different daylights with correlated colour temperatures 4300 K, 6 500 K, and 25000 K. Perceived differences between colours were estimated with an approximately uniform colour-distance measure. The information preserved under illuminant changes increased with the number of surfaces in the sample, but was limited to a relatively low asymptotic value, indicating the importance of physical factors in constraining identification by apparent colour.
Perceptual Limits on Low-Dimensional Models of Munsell Reflectance Spectra
Authors: Oxtoby Emma K , Foster David H
Published: August 2005

Some experimental and theoretical approaches to surface-colour perception depend on approximating surface reflectance spectra by low-dimensional models. In the psychophysical experiment reported here, observers had to discriminate between patterns of Munsell surfaces and their spectral approximations under either the same or different illuminants. The approximations were produced by principal component analysis, by independent component analysis, and by artificial neural networks trained with a supervised-learning rule. In all experimental conditions, observers required, on average, at least 5 basis functions for discrimination performance to be at chance, thus placing a lower limit on the dimensionality of models of Munsell reflectance spectra.
Comparison of Fundus Autofluorescence and Minimum-Motion Measurements of Macular Pigment Distribution Profiles Derived from Identical Retinal Areas
Authors: Robson Anthony G , Harding Glen , van Kuijk Frederik J G M , Pauleikhoff Daniel , Holder Graham E , Bird Alan C , Fitzke Frederick W , Moreland Jack D
Published: August 2005

The optical density of macular pigment was measured at twelve retinal locations in ten subjects by minimum motion photometry, comparing 460 nm with 580 nm or 550 nm. Fundus autofluorescence images were obtained for the same subjects with a scanning laser ophthalmoscope. Optical density was computed from mean calibrated grey-scale values for a central circular field and for annular segments, identical to areas tested psychophysically, and for complete annuli. Psychophysical assessments of optical density were similar irrespective of whether 550 nm or 580 nm was used. Optical density values derived psychophysically showed a linear correlation with assessments based on identical sampled areas of annular segments (slope = 0.98, r2 = 0.97) or complete annuli (slope = 0.89, r2 = 0.96) in autofluorescence images.
A Continuous Smooth Map of Space in the Primary Visual Cortex of the Common Marmoset
Authors: McLoughlin Niall , Cotton Philippa , Schiessl Ingo
Published: August 2005

We examined the fine-scale mapping of the visual world within the primary visual cortex of the marmoset monkey ( Callithrix jacchus) using differential optical imaging. We stimulated two sets of complementary stripe-like locations in turn, subtracting them to generate the cortical representations of continuous bands of visual space. Rotating this stimulus configuration makes it possible to map different spatial axes within the primary visual cortex. In a similar manner, shifting the stimulated locations between trials makes it possible to map retinotopy at an even finer scale. Using these methods we found no evidence of any local anisotropies or distortions in the cortical representation of visual space. This is despite the fact that orientation preference is mapped in a discontinuous manner across the surface of marmoset V1. Overall, our results indicate that space is mapped in a continuous and smooth manner in the primary visual cortex of the common marmoset.
Comparison of Ganglion Cell Signals and Psychophysical Localization of Moving Targets Can Help Define Central Motion Mechanisms
Authors: Lee Barry B , Rüttiger Lukas , Sun Hao
Published: August 2005

Vernier acuity thresholds can be related to visibility of targets. This is considered in relation to retinal signals. Spatial precision of macaque ganglion cell responses to moving targets was assessed by neurometric analysis and compared with psychophysical performance. Under some conditions the amplitude of ganglion cell signals per se may relate target visibility to spatial precision of psychophysical performance. Other conditions are more complex; we suggest central mechanisms may adapt their properties, eg their dimensions, depending on the stochastic properties of ganglion cell signals. Thus, the relation of Vernier acuity to the visibility of targets is a rule of thumb which has a complex relation to physiological substrates.
Limits of Visual Acuity in the Frontal Field of the Rock Pigeon (Columba Livia)
Authors: Rounsley Kevin J , McFadden Sally A
Published: August 2005

The eye of the rock pigeon is typical of a granivorous lateral-eyed bird, in that it has both a laterally projecting central fovea and a second high-density cellular area in peripheral retina (area dorsalis) which projects to the binocular frontal field below the beak. Such a dual system is faced with potentially different optical restraints arising from central and peripheral vision. We asked whether the frontal axis can support high resolution vision from a refractive resting position (predicted to be 25–33 cm; Fitzke et al, 1985 Journal of Physiology369 33–44) to some near point of accommodation. We measured the visual acuity on the frontal axis in five pigeons using an operant discrimination of high-contrast square-wave gratings at a series of distances from 7 to 80 cm from the eye. The peak average acuity was 11.04 cycles deg−1, which occurred 10 cm from the eye. The average of the maximum acuity of each bird at 10 cm was 12.8 ± 1.1 cycles deg−1 a value equal to the Nyquist frequency calculated from the peak ganglion cell density of the area dorsalis. However, this maximum acuity was restricted to a narrow depth in space, located around 10 cm from the eye, and at greater distances fell exponentially such that acuity was 50% of its maximum at 35 cm and less than 1 cycle deg−1 at 100 cm. We propose that the range of high-acuity vision is limited in the frontal field by either increased refractive power and/or inaccuracy in frontal accommodation, and is optimized for a preferred far point located 10 cm from the eye.
Threshold Nonlinearities and Signal Detection Theory
Authors: King-Smith P Ewen
Published: August 2005

The review summarizes Kulikowski's contributions to the mechanisms involved in visual detection and discrimination. His findings provide strong evidence for the existence of ‘barriers’ which block weak activity in the visual system. It is proposed that the properties of these barriers may underlie near-optimal detection in conditions of signal uncertainty.
Effects of Motion Parallax and Perspective Cues on Perceived Size and Distance
Authors: Tozawa Junko , Oyama Tadasu
Published: August 2005

In three experiments we examined the relative effectiveness of motion parallax and two perspective cues for the perception of size and distance. The experimental stimuli consisted of two ellipses (a standard and a comparison) and a horizontal line that indicated the horizon. The subject's task was to report the apparent size and distance of the comparison stimulus relative to the standard stimulus. Two perspective cues were given by the relative heights of the two stimuli and the absolute height of the standard stimulus below the horizon. Motion parallax was defined by both the ratio and the difference in angular velocities between the two stimuli on the display. In experiment 1 we examined the effects of the two perspective cues and the motion parallax. In experiment 2 we eliminated the horizon line, and examined the role of the horizon in size and distance perception. In experiment 3 we separately evaluated the effects of motion parallax and the relative height cues. The results from the three experiments showed that the effect of motion parallax and the two perspective cues were different in three ways. First, the relative effectiveness of motion parallax and the two perspective cues differed for size and distance estimates. For size estimates, the motion parallax was more effective than the perspective cues (experiments 1 and 3). For distance estimates, the motion parallax was as effective as the two perspective cues (experiments 1 and 3). Second, the role of the horizon differed for size and distance estimates. The size estimates were strongly affected by the horizon, while the distance estimates were not affected much by the horizon (experiment 2). Third, the effective perspective cues differed for the size estimates and the distance estimates: size estimates were affected by the perspective cues as a combination of the horizon and relative height; distance estimates were affected by the perspective cues as an interaction between the absolute and relative heights without the horizon line.
The Binocular Combination of Chromatic Contrast
Authors: Simmons David R
Published: August 2005

How is chromatic contrast combined binocularly? One index of binocularity is the binocular contrast summation ratio (BCSR), which is the improvement in contrast sensitivity with binocular rather than monocular presentation. Simmons and Kingdom (1998, Vision Research38 1063–1071) noted that BCSRs with some red-green isoluminant stimuli were suggestive of full linear summation. This suggestion was investigated further in four subjects by measuring binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 isoluminant (red-green) and isochromatic (yellow-black) Gabor patches. These Gabor patches had either vertically or horizontally oriented carrier gratings and were either dichoptically in phase (same coloured bars in binocular correspondence) or in dichoptic anti-phase (opposite coloured bars in binocular correspondence). Full linear summation would be indicated by BCSRs of 2 for the in-phase and close to 0 for the anti-phase conditions. Mean BCSRs at isoluminance were 1.93 and 0.90, respectively, for the in-phase and anti-phase stimuli with horizontal carriers, the former being consistent with full linear summation, but the latter not. Despite these results, BCSRs obtained with isoluminant and isochromatic stimuli under similar conditions were not statistically distinguishable from each other, although there was a tendency for summation at isoluminance with in-phase stimuli to be higher and anti-phase stimuli to be lower. These data fall short of demonstrating full linear summation of chromatic contrast between the eyes under all presentation conditions, but they do indicate that there are strong binocular interactions at red-green isoluminance, which are similar to, and possibly even stronger than, those obtained with luminance stimuli.
Colour Matching of Isoluminant Samples and Backgrounds: A Model
Authors: Stanikunas Rytis , Vaitkevičius Henrikas , Kulikowski Janus J , Murray Ian J , Daugirdiene Avsra
Published: August 2005

A cone-opponent-based vector model is used to derive the activity in the red-green, yellow-blue, and achromatic channels during a sequential asymmetric colour-matching experiment. Forty Munsell samples, simulated under illuminant C, were matched with their appearance under eight test illuminants. The test samples and backgrounds were photometrically isoluminant with each other. According to the model, the orthogonality of the channels is revealed when test illuminants lie along either red-green or yellow-blue cardinal axes. The red-green and yellow-blue outputs of the channels are described in terms of the hue of the sample. The fact that the three-channel model explains the data in a colour-matching experiment indicates that an early form of colour processing is mediated at a site where the three channels converge, probably the input layer of V1.
Colour Matching of Isoluminant Samples and Backgrounds: A Dimming Effect
Authors: Murray Ian J , Kulikowski Janus J , Stanikunas Rytis , Vaitkevičius Henrikas , Daugirdiene Avsra
Published: August 2005

Sequential asymmetrical colour matching of forty Munsell samples simulated under illuminant C and one of eight test illuminants was carried out. The subjects matched the appearance of each sample under illuminant C with its appearance under the test illuminant. Samples and background (N7) were presented for 1 s under the test illuminant and were isoluminant with each other. Subjects adjusted hue, chroma, and value under illuminant C. The experiments distinguished two groups of subjects; some observers needed to reduce the luminance of the sample to make a match while others did not. This ‘dimming’ occurred when the matches were close to cardinal axes, especially the tritanopic confusion line. A model of luminance and cone-opponent mechanisms contributing to brightness can account for the dimming effect. Details of analysis in cone-opponent space (L-M, L+M-S, L+M) are presented in the companion paper (Stanikunas et al, 2005 Perception34 this issue).
Attentional Gating in Primary Visual Cortex: A Physiological Basis for Dyslexia
Authors: Vidyasagar Trichur R
Published: August 2005

The visual magnocellular pathway is known to play a central part in visuospatial attention and in directing attention to specific parts of the visual world in serial search. It is proposed that, in the case of reading, this mechanism is trained to perform a sequential gating of visual information coming into the primary visual cortex to enable further orderly processing by the ventral stream. This scheme, taken together with the potential for plasticity between the different afferent channels in the case of a relative impairment of the magnocellular system, can provide some limited rationale for the beneficial effects that have been claimed for the use of coloured overlays and glasses.
Magnocellular Channel Subserves the Human Contrast-Sensitivity Function
Authors: Plainis Sotiris , Murray Ian J
Published: August 2005

There is evidence that the human contrast-sensitivity function (CSF) is mediated by the spatiotemporal characteristics of magno and parvo neurons early in the visual pathway. In this study we use a measure of contrast gain derived from simple reaction times, to investigate the neural substrates of suprathreshold performance. The results reveal the activity of two mechanisms having distinctly different contrast-gain characteristics. Comparing these to neurophysiological data, we find that the magnocellular system dominates close-to-threshold detection and probably forms the basis of the achromatic CSF, whereas the parvocellular system dominates detection at higher contrasts, when the magnocellular system saturates.
A role for transferrin receptor in triggering apoptosis when targeted with gambogic acid
Authors: Kasibhatla Shailaja , Jessen Katayoun A. , Maliartchouk Sergei , Wang Jean Yu , English Nicole M. , Drewe John , Qiu Ling , Archer Shannon P. , Ponce Anthony E. , Sirisoma Nilantha , Jiang Songchun , Zhang Han-Zhong , Gehlsen Kurt R. , Cai Sui Xiong , Green Douglas R. , Tseng Ben
Published: August 2005

Transferrin receptor (TfR) has been shown to be significantly overexpressed in different types of cancers. We discovered TfR as a target for gambogic acid (GA), used in traditional Chinese medicine and a previously undiscovered link between TfR and the rapid activation of apoptosis. The binding site of GA on TfR is independent of the transferrin binding site, and it appears that GA potentially inhibits TfR internalization. Down-regulation of TfR by RNA interference decreases sensitivity to GA-induced apoptosis, further supporting TfR as the primary GA receptor. In summary, GA binding to TfR induces a unique signal leading to rapid apoptosis of tumor cells. These results suggest that GA may provide an additional approach for targeting the TfR and its use in cancer therapy.
Choice reaction time performance correlates with diffusion anisotropy in white matter pathways supporting visuospatial attention
Authors: Tuch David S. , Salat David H. , Wisco Jonathan J. , Zaleta Alexandra K. , Hevelone Nathanael D. , Rosas H. Diana
Published: August 2005

Humans exhibit significant interindividual variability in behavioral reaction time (RT) performance yet the underlying neural mechanisms for this variability remain largely unknown. It has been proposed that interindividual variability in RT performance may be due to differences in white matter (WM) physiological properties, although such a relationship has never been demonstrated in cortical projection or association pathways in healthy young adults. Using diffusion tensor MRI (DTI), we sought to test whether diffusion tensor fractional anisotropy (FA), a measure of the orientational coherence of water self-diffusion, is regionally correlated with RT on a visual self-paced choice RT (CRT) task. CRT was found to be significantly correlated with FA in projection and association pathways supporting visuospatial attention including the right optic radiation, right posterior thalamus, and right medial precuneus WM. Significant correlations were also observed in left superior temporal sulcus WM and the left parietal operculum. The lateralization of the CRT-FA correlation to right visual and parietal WM pathways is consistent with the specialization of right visual and parietal cortices for visuospatial attention. The localization of the CRT-FA correlations to predominately visual and parietal WM pathways, but not to motor pathways or the corpus callosum indicates that individual differences in visual CRT performance are associated with variations in the WM underlying the visuospatial attention network as opposed to pathways supporting motor movement or interhemispheric transmission.
Ca
2+
sparks and secretion in dorsal root ganglion neurons
Authors: Ouyang Kunfu , Zheng Hui , Qin Xiaomei , Zhang Chen , Yang Dongmei , Wang Xian , Wu Caihong , Zhou Zhuan , Cheng Heping
Published: August 2005

Ca
2+
sparks as the elementary intracellular Ca
2+
release events are instrumental to local control of Ca
2+
signaling in many types of cells. Here, we visualized neural Ca
2+
sparks in dorsal root ganglion (DRG) sensory neurons and investigated possible role of DRG sparks in the regulation of secretion from the somata of the cell. DRG sparks arose mainly from type 3 ryanodine receptor Ca
2+
release channels on subsurface cisternae of the endoplasmic reticulum, rendering a striking subsurface localization. Caffeine- or 3,7-dimethyl-1-(2-propynyl)xanthine-induced store Ca
2+
release, in the form of Ca
2+
sparks, triggered exocytosis, independently of membrane depolarization and external Ca
2+
. The spark-secretion coupling probability was estimated to be between 1 vesicle per 6.6 sparks and 1 vesicle per 11.4 sparks. During excitation, subsurface sparks were evoked by physiological Ca
2+
entry via the Ca
2+
-induced Ca
2+
release mechanism, and their synergistic interaction with Ca
2+
influx accounted for ≈60% of the Ca
2+
-dependent exocytosis. Furthermore, inhibition of Ca
2+
-induced Ca
2+
release abolished endotoxin-induced secretion of pain-related neuropeptides. These findings underscore an important role for Ca
2+
sparks in the amplification of surface Ca
2+
influx and regulation of neural secretion.
Rho GTPases dictate the mobility of the Na/H exchanger NHE3 in epithelia: Role in apical retention and targeting
Authors: Alexander R. Todd , Furuya Wendy , Szászi Katalin , Orlowski John , Grinstein Sergio
Published: August 2005

Proximal tubular reabsorption of filtered sodium by the sodium/hydrogen exchanger isoform 3 (NHE3), located on the apical membrane, is fundamental to the maintenance of systemic volume and pH homeostasis. NHE3 is finely regulated by a variety of hormones and by changes in ionic composition and volume, likely requiring redistribution of the exchangers. We analyzed the subcellular distribution and dynamics of the exchangers by generating an epithelial line expressing NHE3 tagged with an exofacial epitope, which enabled us to monitor exchanger mobility and traffic in intact cells. Using determinations of fluorescence recovery after photobleaching in combination with dynamic measurements of subcellular distribution, we found that, in renal epithelial cells, NHE3 exists in four distinct subcompartments: a virtually immobile subpopulation that is retained on the apical membrane by interaction with the actin cytoskeleton in a manner that depends on the sustained activity of Rho GTPases; a mobile subpopulation on the apical membrane, which can be readily internalized; and two intracellular compartments that can be differentiated by their rate of exchange with the apical pool of NHE3. We provide evidence that detachment of the immobile fraction from its cytoskeletal anchorage leads to rapid internalization. These observations suggest that modulation of the mobile fraction of NHE3 on the apical membrane can alter the number of functional exchangers on the cell surface and, consequently, the rate of transepithelial ion transport. Regulation of the interaction of NHE3 with the actin cytoskeleton can therefore provide a new mode of regulation of sodium and hydrogen transport.
Unifying the spatial population dynamics and molecular evolution of epidemic rabies virus
Authors: Real Leslie A. , Henderson J. Caroline , Biek Roman , Snaman Jennifer , Jack Tracy Lambert , Childs James E. , Stahl Eli , Waller Lance , Tinline Rowland , Nadin-Davis Susan
Published: August 2005

Infectious disease emergence is under the simultaneous influence of both genetic and ecological factors. Yet, we lack a general framework for linking ecological dynamics of infectious disease with underlying molecular and evolutionary change. As a model, we illustrate the linkage between ecological and evolutionary dynamics in rabies virus during its epidemic expansion into eastern and southern Ontario. We characterized the phylogeographic relationships among 83 isolates of fox rabies virus variant using nucleotide sequences from the glycoprotein-encoding glycoprotein gene. The fox rabies virus variant descended as an irregular wave with two arms invading from northern Ontario into southern Ontario over the 1980s and 1990s. Correlations between genetic and geographic distance suggest an isolation by distance population structure for the virus. The divergence among viral lineages since the most recent common ancestor correlates with position along the advancing wave front with more divergent lineages near the origin of the epidemic. Based on divergence from the most recent common ancestor, the regional population can be partitioned into two subpopulations, each corresponding to an arm of the advancing wave. Subpopulation A (southern Ontario) showed reduced isolation by distance relative to subpopulation B (eastern Ontario). The temporal dynamics of subpopulation A suggests that the subregional viral population may have undergone several smaller waves that reduced isolation by distance. The use of integrated approaches, such as the geographical analysis of sequence variants, coupled with information on spatial dynamics will become indispensable aids in understanding patterns of disease emergence.
Genetically attenuated, P36p-deficient malarial sporozoites induce protective immunity and apoptosis of infected liver cells
Authors: van Dijk Melissa R. , Douradinha Bruno , Franke-Fayard Blandine , Heussler Volker , van Dooren Maaike W. , van Schaijk Ben , van Gemert Geert-Jan , Sauerwein Robert W. , Mota Maria M. , Waters Andrew P. , Janse Chris J.
Published: August 2005

Immunization withPlasmodiumsporozoites that have been attenuated by γ-irradiation or specific genetic modification can induce protective immunity against subsequent malaria infection. The mechanism of protection is only known for radiation-attenuated sporozoites, involving cell-mediated and humoral immune responses invoked by infected hepatocytes cells that contain long-lived, partially developed parasites. Here we analyzed sporozoites ofPlasmodium bergheithat are deficient in P36p (p36p-), a member of the P48/45 family of surface proteins. P36p plays no role in the ability of sporozoites to infect and traverse hepatocytes, butp36p-sporozoites abort during development within the hepatocyte. Immunization withp36p-sporozoites results in a protective immunity against subsequent challenge with infectious wild-type sporozoites, another example of a specifically genetically attenuated sporozoite (GAS) conferring protective immunity. Comparison of biological characteristics ofp36p-sporozoites with radiation-attenuated sporozoites demonstrates that liver cells infected withp36p-sporozoites disappear rapidly as a result of apoptosis of host cells that may potentiate the immune response. Such knowledge of the biological characteristics of GAS and their evoked immune responses are essential for further investigation of the utility of an optimized GAS-based malaria vaccine.
Monte Carlo modeling of single-molecule cytoplasmic dynein
Authors: Singh Manoranjan P. , Mallik Roop , Gross Steven P. , Yu Clare C.
Published: August 2005

Molecular motors are responsible for active transport and organization in the cell, underlying an enormous number of crucial biological processes. Dynein is more complicated in its structure and function than other motors. Recent experiments have found that, unlike other motors, dynein can take different size steps along microtubules depending on load and ATP concentration. We use Monte Carlo simulations to model the molecular motor function of cytoplasmic dynein at the single-molecule level. The theory relates dynein's enzymatic properties to its mechanical force production. Our simulations reproduce the main features of recent single-molecule experiments that found a discrete distribution of dynein step sizes, depending on load and ATP concentration. The model reproduces the large steps found experimentally under high ATP and no load by assuming that the ATP binding affinities at the secondary sites decrease as the number of ATP bound to these sites increases. Additionally, to capture the essential features of the step-size distribution at very low ATP concentration and no load, the ATP hydrolysis of the primary site must be dramatically reduced when none of the secondary sites have ATP bound to them. We make testable predictions that should guide future experiments related to dynein function.