bluuebunny/crossref_metadata_2025 huggingface dataset:
Active site densities, oxygen activation and adsorbed reactive oxygen in alcohol activation on npAu catalysts
Authors: Wang Lu-Cun , Friend C. M. , Fushimi Rebecca , Madix Robert J.
Published: December 2015

The activation of molecular O2 as well as the reactivity of adsorbed oxygen species is of central importance in aerobic selective oxidation chemistry on Au-based catalysts. Herein, we address the issue of O2 activation on unsupported nanoporous gold (npAu) catalysts by applying a transient pressure technique, a temporal analysis of products (TAP) reactor, to measure the saturation coverage of atomic oxygen, its collisional dissociation probability, the activation barrier for O2 dissociation, and the facility with which adsorbed O species activate methanol, the initial step in the catalytic cycle of esterification. The results from these experiments indicate that molecular O2 dissociation is associated with surface silver, that the density of reactive sites is quite low, that adsorbed oxygen atoms do not spill over from the sites of activation onto the surrounding surface, and that methanol reacts quite facilely with the adsorbed oxygen atoms. In addition, the O species from O2 dissociation exhibits reactivity for the selective oxidation of methanol but not for CO. The TAP experiments also revealed that the surface of the npAu catalyst is saturated with adsorbed O under steady state reaction conditions, at least for the pulse reaction.
N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure
Authors: Reiners Matthias , Baabe Dirk , Harms Kristoffer , Maekawa Miyuki , Daniliuc Constantin G. , Freytag Matthias , Jones Peter G. , Walter Marc D.
Published: December 2015

Adducts [Cp′FeI(NHC)] exhibit a highly anisotropic magnetic Ms = ±2 ground state resulting in unusual large spin–lattice (Orbach) relaxation barriers observed by zero-field 57Fe Mössbauer spectroscopy.
Pseudo enantiomeric mixed S/P ligands derived from carbohydrates for the 1,4-addition of phenyl boronic acid to cyclohexenone
Authors: Valdivia V. , Bilbao N. , Moya J. F. , Rosales-Barrios C. , Salvador A. , Recio R. , Fernández I. , Khiar N.
Published: December 2015

Mixed S/P ligands3and10, good catalyst precursors for the Rh(i)-catalysed 1,4-addition of phenylboronic acid to cyclohexenone behave as enantiomers even though both derived fromd-sugars.
PhI(OCOCF3)2-mediated ruthenium catalyzed highly site-selective direct ortho-C–H monoarylation of 2-phenylpyridine and 1-phenyl-1H-pyrazole and their derivatives by arylboronic acids
Authors: Reddy Ganapam Manohar , Rao Naidu Samba Siva , Satyanarayana Ponnam , Maheswaran H.
Published: December 2015

Direct ortho C–H monoarylation of 2-phenylpyridine and 1-phenyl-1H-pyrazole and its derivatives via a Ru catalysed reaction using catalytic amount of Phl(OCOCF3)2 as a hyper-valent iodine oxidant with arylboronic acids is presented.
Experimental and theoretical studies on extraction behavior of di-n-alkyl phosphine oxides towards actinides
Authors: Das Dhrubajyoti , Goud E. Veerashekhar , Annam Suresh , Jayalakshmi S. , Gopakumar Gopinadhanpillai , Rao C. V. S. Brahmmananda , Sivaraman N. , Sivaramakrishna Akella , Vijayakrishna Kari
Published: December 2015

The extraction behavior of U(vi) & Am(iii) with di-n-alkyl phosphine oxides (DAPOs) was investigated. DAPO behaves like an acidic extractant at low acidity and at higher acidity they extracted via cation exchange mechanism.
Substitution induced band structure shape tuning in hybrid perovskites (CH3NH3Pb1−xSnxI3) for efficient solar cell applications
Authors: Kanhere Pushkar , Chakraborty Sudip , Rupp Caroline J. , Ahuja Rajeev , Chen Zhong
Published: December 2015

Electronic and optical properties of CH3NH3Pb1−xSnxI3 are determined using DFT. Sn doping narrows band gap allowing 850 nm absorption. Delocalized Sn-5p induced electronic states increase mobility. 50% Sn doping is revealed as optimum composition.
Synthesis and characterization of solvent-free waterborne polyurethane dispersion with both sulfonic and carboxylic hydrophilic chain-extending agents for matt coating applications
Authors: Yong Qiwen , Nian Fuwei , Liao Bing , Huang Liping , Wang Lu , Pang Hao
Published: December 2015

Self-extinction and solvent-free waterborne polyurethane resin without the addition of extra matting agents.
The excellent cycling stability and superior rate capability of polypyrrole as the anode material for rechargeable sodium ion batteries
Authors: Chen Xiaoying , Liu Li , Yan Zichao , Huang Zhifeng , Zhou Qian , Guo Guoxiong , Wang Xianyou
Published: December 2015

Submicrostructured polypyrrole as the anode materials for sodium ion batteries.
Thermoresponsive AIE polymers with fine-tuned response temperature
Authors: Li Tingzhong , He Sicong , Qu Jianan , Wu Hao , Wu Shuizhu , Zhao Zujin , Qin Anjun , Hu Rongrong , Tang Ben Zhong
Published: December 2015

A series of thermoresponsive aggregation-induced emission polymers with fine-tuned hydrophilicity are synthesized as fluorescent thermometers with tunable response temperature.
Frequency domain modelling and control of fractional‐order system for permanent magnet synchronous motor velocity servo system
Authors: Yu Wei , Luo Ying , Chen YangQuan , Pi YouGuo
Published: December 2015

This study presents fractional‐order system modelling and control for a permanent magnet synchronous motor (PMSM) velocity servo system. Fractional‐order model of the PMSM velocity servo system is obtained theoretically for an improved modelling precision. To identify the parameters of the proposed fractional‐order model, an enhancement of the classic Levy identification method with weights is applied. In a real‐time PMSM velocity servo plant, the fractional‐order model is identified according to the experimental tests using the presented algorithm. The fact that the fractional model is more accurate than traditional integer‐order model is substantiated using by the mean square error performance index. Two H∞ stabilising output feedback controllers are designed for velocity servo using a simple scheme according to the identified fractional‐order model and the traditional integer order one, respectively. The experimental test performance using these two designed H∞ controllers is compared to demonstrate the advantage of the proposed fractional‐order model of the PMSM velocity system.
Robust output feedback control for unknown non‐linear systems with external disturbance
Authors: Kim Wonhee , Choo Chung Chung
Published: December 2015

The authors propose a robust output feedback control for unknown non‐linear systems with external disturbance. The main contribution of this study is that the proposed method guarantees the global uniform ultimate boundedness of the output tracking error using only output feedback for unknown non‐linear systems with external disturbance. The key idea of the proposed method is that the plant non‐linearities and external disturbance, and their derivatives are lumped into augmented state variables. The robust high order augmented observer (RHOAOB) is developed to estimate the lumped augmented state variables and full state. The benefit to using the RHOAOB is that the estimation error can be reduced without increasing the bandwidth of the RHOAOB. The backstepping controller is designed to guarantee the global uniform ultimate boundedness of the output tracking error occurred by the disturbance estimation error. To the best of the authors' knowledge, it might be the first attempt of the analysis of the estimation and output tracking performance of the RHOAOB‐based controller with the measurement noise in both time and frequency domains. The analysis shows that very small estimation error is not necessarily required to obtain the precise output tracking using an input‐to‐state stability property. This merit results in avoiding the amplification of the measurement noise.
Elementary operations for rigidity restoration and persistence analysis of multi‐agent system
Authors: Hou Yun , Yu Changbin
Published: December 2015

This work focuses on the construction of rigid formation from non‐rigid ones in the two‐dimensional space. Analogously to operations of Henneberg sequence aiming to guarantee the minimal rigidity of formation, two new operations are introduced, allowing one to sequentially build any rigid graph by connecting non‐rigid ones. A systematic construction sequence is developed based on proposed operations, and is shown to be able to restore rigidity by introducing minimum number of new edges during the construction process. Further applications of the proposed operations are also presented, one of which is successfully employed in the problem of persistence analysis of directed graphs, and can verify the persistence of a given graph with a speed two times faster comparing with existing solution.
Robust H∞ control for miniature unmanned aerial vehicles at hover by the finite frequency strategy
Authors: Xu Jing , Cai Chenxiao , Cai Guowei , Zou Yun
Published: December 2015

This study presents H∞ control synthesis of a miniature unmanned aerial vehicle to improve its hovering capability in the presence of wind disturbances. By time‐scale techniques, the six‐degree‐freedom flight system can be decoupled into subsystems in different time‐scales: one including slow‐varying translational dynamics and Euler angles, and another composed of fast‐varying angular velocities. To avoid contradictions between subsystems, control specifications for subsystems are classified, respectively, in disjoint frequency ranges. Robust H∞ controllers, applied directly to the original flight system, are formulated by composing the sub‐controllers. To achieve desired handling and flying qualities, wind characteristics are considered, and a novel flexible strategy is then developed to ensure an adequate response in all flight modes under different weather conditions. The effectiveness and merits of the proposed methods are illustrated with a simulation example.
Abnormal event detection and localisation in traffic videos based on group sparse topical coding
Authors: Ahmadi Parvin , Tabandeh Mahmoud , Gholampour Iman
Published: December 2015

In visual surveillance, detecting and localising abnormal events are of great interest. In this study, an unsupervised method is proposed to automatically discover abnormal events occurring in traffic videos. For learning typical motion patterns occurring in such videos, a group sparse topical coding (GSTC) framework and an improved version of it are applied to optical flow features extracted from video clips. Then a very simple and efficient algorithm is proposed for GSTC. It is shown that discovered motion patterns can be employed directly in detecting abnormal events. A variety of abnormality metrics based on the resulting sparse codes for detection of abnormality are investigated. Experiments show that the result of the approach in detection and localisation of abnormal events is promising. In comparison with other usual methods (probabilistic latent semantic analysis, latent Dirichlet allocation, sparse topical coding (STC) and improved STC), according to the values of area under ROC, the proposed method achieves at least 14% improvement in abnormal event detection.
Optimising the European transmission system for 77% renewable electricity by 2030
Authors: Brown Tom , Schierhorn Peter‐Philipp , Tröster Eckehard , Ackermann Thomas
Published: December 2015

To spur Europe to meet ambitious CO2 emission reduction targets, Greenpeace has developed scenarios for each country to increase its electricity generation from renewable sources. Energynautics was commissioned by Greenpeace to model and optimise the grid extensions in Europe necessary to integrate these large shares of renewables (77% of the total electricity supply by 2030, including 53% from wind and solar). The results and further analysis of the data are presented here. It was found that by preferring high voltage direct current rather than alternating current network extensions, the overall grid upgrades in Europe (measured as the length of new transmission lines) can be reduced by a third. By allowing a small amount of curtailment of variable renewable sources, a disproportionately large number of the necessary grid extensions can be avoided. In addition, the accuracy of decoupling active from reactive power flows is analysed.
Choisir et mettre en place les mini-vis d’ancrages
orthodontiques : notions importantes
Authors: Steve Marc , Racy Emmanuel , Kerbrat Jean-Baptiste
Published: December 2015

Les mini-vis d’ancrage orthodontique se développent de plus en plus, car elles facilitent
l’orthodontie et permettent d’élargir ses indications. Ce développement exponentiel a
permis d’aboutir à un design de mini-vis bien défini et à un protocole de pose bien
codifié. L’objectif de cet article est de donner les éléments conceptuels des mini-vis
afin de permettre leur utilisation en toute sécurité au cabinet orthodontique.
Les six formes de résorption associées à l’inclusion dentaire
Authors: Becker Adrian , Chaushu Stella
Published: December 2015

Six différentes formes de résorption des tissus dentaires minéralisés sont associées à des dents permanentes incluses ou impactées. Ces processus pathologiques diffèrent par leur origine étiologique, leur traitement et leur pronostic. Pour plusieurs d’entre eux, la pérennité de la dent est mise en question alors que, pour d’autres, un traitement conservateur va arrêter le processus de résorption et déboucher sur une issue favorable. L’approche thérapeutique est spécifique pour chaque forme de résorption et dépend donc entièrement du diagnostic. Cet article présente, pour chaque type de résorption, la prévalence, l’étiologie, les symptômes et les signes cliniques et radiologiques, l’histopathologie, le diagnostic différentiel, le traitement et le pronostic.
Évaluation du risque psychologique : une éthique de la demande
esthétique en orthodontie
Authors: Benkimoun Franck
Published: December 2015

Nous avons l’habitude d’évaluer les risques de nos pratiques professionnelles. La plupart
du temps, nous oublions que le fait de soigner un patient nous impose une évaluation du
risque dit psychologique. Nous ne prenons pas en compte, sous prétexte d’harmonisation,
que la demande du patient, principalement la demande esthétique peut masquer un problème
psychologique. Ces risques sont plus importants dans les protocoles
orthodontico-chirurgicaux puisque le changement physique est important. Nous étudierons
les particularités de la demande esthétique et ses relations avec le discours social
courant. Image dans le miroir et estime de soi sont compactées. Ne pas prendre en compte
la dimension psychologique de nos patients constitue une dérogation à l’éthique
professionnelle, dans la mesure où nos actes ont des conséquences psychologiques. Nous
exposerons les moyens que nous avons pour dépister les patients à risque dont la prise en
charge psychologique n’est pas de notre ressort mais de celle d’un spécialiste de la santé
mentale, dont nous devrions avoir les coordonnées afin d’adresser le patient si
nécessaire.
Extended model for the interaction of dielectric thin films with an electrostatic force microscope probe
Authors: Labardi M. , Barsotti J. , Prevosto D. , Capaccioli S. , Roland C. M. , Casalini R.
Published: December 2015

To improve measurements of the dielectric permittivity of nanometric portions by means of Local Dielectric Spectroscopy (LDS), we introduce an extension to current analytical models for the interpretation of the interaction between the probe tip of an electrostatic force microscope (EFM) and a thin dielectric film covering a conducting substrate. Using the proposed models, we show how more accurate values for the dielectric constant can be obtained from single-frequency measurements at various probe/substrate distances, not limited to a few tip radii.
Behavior of rigid and deformable particles in deterministic lateral displacement devices with different post shapes
Authors: Zhang Zunmin , Henry Ewan , Gompper Gerhard , Fedosov Dmitry A.
Published: December 2015

Deterministic lateral displacement (DLD) devices have great potential for the separation and sorting of various suspended particles based on their size, shape, deformability, and other intrinsic properties. Currently, the basic idea for the separation mechanism is that the structure and geometry of DLDs uniquely determine the flow field, which in turn defines a critical particle size and the particle lateral displacement within a device. We employ numerical simulations using coarse-grained mesoscopic methods and two-dimensional models to elucidate the dynamics of both rigid spherical particles and deformable red blood cells (RBCs) in different DLD geometries. Several shapes of pillars, including circular, diamond, square, and triangular structures, and a few particle sizes are considered. The simulation results show that a critical particle size can be well defined for rigid spherical particles and depends on the details of the DLD structure and the corresponding flow field within the device. However, non-isotropic and deformable particles such as RBCs exhibit much more complex dynamics within a DLD device, which cannot properly be described by a single parameter such as the critical size. The dynamics and deformation of soft particles within a DLD device become also important, indicating that not only size sorting, but additional sorting targets (e.g., shape, deformability, internal viscosity) are possible.
Note: High temperature pressure sensor for petroleum well based on silicon over insulator
Authors: Tian Bian , Liu Hanyue , Yang Ning , Zhao Yulong
Published: December 2015

In order to meet the requirements in petroleum well, a novel structure of high temperature pressure sensor based on the silicon over insulator (SOI) technology is proposed in this paper. The SOI sensor chip is bonded with a glass ring by electrostatic bonding. By controlling the inner diameter of the glass ring, the size of the circle membrane is obtained precisely. And the detailed parameters of the structure are established through analysis. Then, the sensor is fabricated. The test results show that this type sensor has high sensitivity and accuracy. It is able to measure at the temperature up to 180 °C and the measuring range is 60 MPa. Moreover, the results we got are closer to the actual situation.
Spin-dependent transport properties of a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor structure
Authors: Kanaki Toshiki , Asahara Hirokatsu , Ohya Shinobu , Tanaka Masaaki
Published: December 2015

We fabricate a vertical spin metal-oxide-semiconductor field-effect transistor (spin-MOSFET) structure, which is composed of an epitaxial single-crystal heterostructure with a ferromagnetic-semiconductor GaMnAs source/drain, and investigate its spin-dependent transport properties. We modulate the drain-source current IDS by ∼±0.5% with a gate-source voltage of ±10.8 V and also modulate IDS by up to 60% with changing the magnetization configuration of the GaMnAs source/drain at 3.5 K. The magnetoresistance ratio is more than two orders of magnitude higher than that obtained in the previous studies on spin MOSFETs. Our result shows that a vertical structure is one of the hopeful candidates for spin MOSFET when the device size is reduced to a sub-micron or nanometer scale.
Imaging ballistic carrier trajectories in graphene using scanning gate microscopy
Authors: Morikawa Sei , Dou Ziwei , Wang Shu-Wei , Smith Charles G. , Watanabe Kenji , Taniguchi Takashi , Masubuchi Satoru , Machida Tomoki , Connolly Malcolm R.
Published: December 2015

We use scanning gate microscopy to map out the trajectories of ballistic carriers in high-mobility graphene encapsulated by hexagonal boron nitride and subject to a weak magnetic field. We employ a magnetic focusing geometry to image carriers that emerge ballistically from an injector, follow a cyclotron path due to the Lorentz force from an applied magnetic field, and land on an adjacent collector probe. The local electric field generated by the scanning tip in the vicinity of the carriers deflects their trajectories, modifying the proportion of carriers focused into the collector. By measuring the voltage at the collector while scanning the tip, we are able to obtain images with arcs that are consistent with the expected cyclotron motion. We also demonstrate that the tip can be used to redirect misaligned carriers back to the collector.
Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond
Authors: Jarmola A. , Berzins A. , Smits J. , Smits K. , Prikulis J. , Gahbauer F. , Ferber R. , Erts D. , Auzinsh M. , Budker D.
Published: December 2015

We present systematic measurements of longitudinal relaxation rates (1/T1) of spin polarization in the ground state of the nitrogen-vacancy (NV–) color center in synthetic diamond as a function of NV– concentration and magnetic field B. NV– centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV– center concentrations. Values of (1/T1) were measured for each spot as a function of B.
Charge neutralized low energy beam transport at Brookhaven 200 MeV linac
Authors: Raparia D. , Alessi J. , Atoian G. , Zelenski A.
Published: December 2015

The H− magnetron source provides about 100 mA H− beam to be match into the radio-frequency quadrupole accelerator. As H− beam traverses through low energy transport, it ionizes the residual gas and electrons are repelled and positive ions are trapped in the beam, due to negative potential of the beam, providing charge neutralization for the H− beam. The neutralization time for the critical density depends upon the background gas and its pressure. Critical density for xenon gas at 35 keV is about 43 times smaller than that of hydrogen and stripping cross section is only 5 times than that of hydrogen gas. We are using xenon gas to reduce neutralization time and to improve transmission through the 200 MeV linac. We are also using pulse nitrogen gas to improve transmission and stability of polarized H− beam from optically pumped polarized ion source.
Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1−xSnxOy buffer layers
Authors: Platzer-Björkman C. , Frisk C. , Larsen J. K. , Ericson T. , Li S.-Y. , Scragg J. J. S. , Keller J. , Larsson F. , Törndahl T.
Published: December 2015

Cu2ZnSnS4 (CZTS) solar cells typically include a CdS buffer layer in between the CZTS and ZnO front contact. For sulfide CZTS, with a bandgap around 1.5 eV, the band alignment between CZTS and CdS is not ideal (“cliff-like”), which enhances interface recombination. In this work, we show how a Zn1−xSnxOy (ZTO) buffer layer can replace CdS, resulting in improved open circuit voltages (Voc) for CZTS devices. The ZTO is deposited by atomic layer deposition (ALD), with a process previously developed for Cu(In,Ga)Se2 solar cells. By varying the ALD process temperature, the position of the conduction band minimum of the ZTO is varied in relation to that of CZTS. A ZTO process at 95 °C is found to give higher Voc and efficiency as compared with the CdS reference devices. For a ZTO process at 120 °C, where the conduction band alignment is expected to be the same as for CdS, the Voc and efficiency is similar to the CdS reference. Further increase in conduction band minimum by lowering the deposition temperature to 80 °C shows blocking of forward current and reduced fill factor, consistent with barrier formation at the junction. Temperature-dependent current voltage analysis gives an activation energy for recombination of 1.36 eV for the best ZTO device compared with 0.98 eV for CdS. We argue that the Voc of the best ZTO devices is limited by bulk recombination, in agreement with a room temperature photoluminescence peak at around 1.3 eV for both devices, while the CdS device is limited by interface recombination.
Saccade Programming in Strabismic Suppression
Authors: Findlay J M , Walker R , Brown V , Gilchrist I , Clarke M
Published: December 2015

Individuals with strabismus frequently show a suppression phenomenon in which part of the visual input in one eye is apparently ignored when both eyes are seeing, although the eye may have normal vision when used monocularly. This is often described as an adaptive response to avoid diplopia. We have examined two patients with microstrabismus (angle of squint less than 5 deg) who show strong suppression but with only mild amblyopia. We studied saccade generation in the two eyes using a red — green anaglyph display which allowed us to present stimuli independently to each eye.

When single targets were presented in the suppressing eye, saccadic responses usually occurred. However the latencies of these saccades were increased with respect to those elicited from the normal eye (by about 70 ms for one subject and 270 ms for the other). The amplitudes of the saccades were less consistent than those of the normal eye, and saccades were sometimes made in the opposite direction to the target. We also investigated the remote distractor effect. This effect is found consistently in normal subjects and consists of an increase in the latency of a target-elicited saccade when a distractor is simultaneously presented elsewhere in the visual field. When distractors were presented in the suppressing eye, they had no effect on the latency of saccades to a simultaneous target in the other eye. We conclude that visual stimulation in a suppressing eye has no rapid access to the saccadic system.
Saccadic Localisation of Random Dot Targets
Authors: McGowan J W , Kowler E , Sharma A , Chubb C
Published: December 2015

Saccadic eye movements land at precise places within simple target forms implying that a spatial pooling process operates over attended regions to determine the saccadic endpoint. To study pooling, we used large, unstructured targets and looked for evidence of differential spatial weighting based on local pattern characteristics. Subjects made a saccade to targets composed of 19 dots scattered randomly within a 4 deg diameter region horizontally displaced 3.8 – 4.2 deg to the left or right of initial fixation. Dot intensity was either uniform or variable.

Saccadic landing positions were close to the centre-of-gravity (overshooting or under- shooting by 5% – 10% depending on subject, direction and eccentricity). Precision was excellent (SD=10% ecc), although not as good as with single target points (SD=7% ecc). Correlations between the presence of a dot and saccadic landing position showed that all regions of the pattern contributed. Differential weighting of dots according to location (eg near vs far; central vs boundary) did not yield better predictions of the saccadic landing position. However, predictions of the landing position were improved by assigning more weight to higher-intensity dots. Local dot clusters contributed less than would be expected from the contributions of individual dots.

Spatial pooling is highly effective over a large region. Saccadic overshoots or undershoots were not due to differential spatial weighting, and may originate after the centre-of-gravity computation. The differential weighting of high-intensity dots and dot clusters demonstrates sensitivity to local characteristics, and implies that the saccadic endpoint may be determined by pooling the activity of units centred on different subregions of the target. The pooling mechanism supports precise saccadic localisation of large, unstructured targets, and accounts for the ease with which we direct saccades to chosen objects in natural scenes.
Optokinetic Oculomotor Responses and the Perception of Depth from Motion Parallax Cues
Authors: Mestre D R , Masson G S
Published: December 2015

In a series of experiments we studied the relationships between the characteristics of optokinetic oculomotor responses triggered spontaneously by large-field visual motion and the perception of depth from motion parallax cues. Random-dot dynamic displays were projected at 60 Hz frame rate. Oculomotor behaviour was monitored with an infrared device. Subjects were asked to identify the spatial structure specified by optical motion and their responses were recorded with a mouse device. Results were as follows: (1) In all cases optokinetic responses are triggered when subjects are presented with visual displays specifying either a single surface, many surfaces or a cloud of dots receding in depth. (2) The velocity of slow phases of the optokinetic nystagmus changes from matching the average velocity of a display in early phases after the onset of a stimulation to slowing down to the slowest velocity in the display, for a small number of surfaces specified by motion parallax cues. (3) Structure-from-motion is correctly detected by subjects with long detection times (between 1 and 2 s). The comparison between the slow build-up of depth perception and the slow decrease of eye pursuit velocity provides further support for the hypothesis that the control of optokinetic eye movements and the perception of depth from visual motion share common pathways up to higher cortical levels of visual processing.
Colour Constancy, Categories, and Spectral Sensitivity
Authors: Kulikowski J J , Al-Attar Z , Vaitkevicius H
Published: December 2015

Colour constancy is a multi-stage process whose receptoral and post-receptoral components have been separated by electrophysiological and behavioral studies. A psychophysical study was conducted to determine contributions of the visual processing stage which extracts information about colour categories, and to relate the results to the spectral sensitivity of the chromatic opponent system.

Changes in colour appearance with illumination were investigated by using free-viewing and a successive matching method for 40 Munsell hues (saturations: 8 and 4). Subjects were adapted to standard illuminant C and briefly inspected a test chip under a variable illuminant A (tungsten) or g (green). Using criteria similar to those for unique hues, subjects specified ‘typical hues’ under illuminant C: red, yellow, green, blue, and violet (yellow should not contain red or green, green should not contain yellow or blue, etc). For each hue and saturation a dominant wavelength was computed. The degree of colour constancy was then established for all subjects (examined in three series of experiments), all Munsell chips and illuminations, as a one-dimensional Brunswick ratio, BR. The BR was determined by using u‘ v’ coordinates as related to the ratio of perceptual to physical colour changes: BR=1-perceptual/physical. BR was highest for typical (not intermediate) hues and lowest for hues resembling variable illuminants. The BR as a function of dominant wavelength resembles the spectral sensitivity function of chromatic opponency. These findings are interpreted as contributions of high-order opponent interactions to colour constancy.
Cortical Coding of Extended Coloured Figures
Authors: von der Heydt R , Zhou H , Friedman H
Published: December 2015

We have studied the neural coding of extended coloured objects. Single cells were recorded from parafoveal regions of V1 and V2 in alert, fixating monkeys. In V1 most of our recordings were from the upper layers. A square figure (usually 4 deg × 4 deg, that is, much larger than the response field) of uniform colour on a gray background was placed at various positions relative to the receptive field of the cell. Orientation and colour were optimised for each cell.

The vast majority of cells (75/89 in V1, 43/47 in V2) responded only when the receptive field was positioned on or near an edge, but not inside the figure (‘edge-only response’). Of the few cells that did respond with the receptive field inside the figure (‘surface response’), only some were colour selective (V1: 6/14, V2: 2/4); that is, the cell response clearly differentiated colours of similar luminance. This lack of surface responses is surprising, since most LGN cells, namely type I and type II cells respond to large uniform stimuli of some colour. On the other hand, many of the ‘edge-only’ cells were colour selective by the same criterion, some responding exclusively within a small volume of colour space. Most ‘edge-only’ cells were selective for orientation, and also many for edge polarity. V1 and V2 may encode colour of extended figures by edge signals rather than an isomorphic representation. In this case, colour filling-in would result from decay of the colour-specific edge signals rather than spreading of the colour-specific surround activity into the figure.
A Computational Model of the Eye Movement Effects on Motion Perception
Authors: Turano K A , Heidenreich S M
Published: December 2015

Accurate speed and direction matches can be made between a moving stimulus viewed with a stationary eye and a moving stimulus viewed with an eye moving in the opposite direction to the stimulus. However, when the eye moves in the same direction as the distal stimulus, at a slower speed, subjects match the retinal-image motions of the stimuli rather than their distal motions (Heidenreich and Turano, 1995 Investigative Ophthalmology and Visual Science36 1675). Furthermore, it is only under this latter condition (and when the eye is stationary) that subjects can precisely discriminate distal stimulus speeds (Turano and Heidenreich Vision Research in press).

We present a computational model that can account for the results of all three findings. The model assumes that the extraretinal signal mirrors the eye movement. Motion information from the retinal and extraretinal sources is combined in a subtractive manner when the two signals have opposite sign. When the two signals have the same sign, they do not combine, and motion judgments are based solely on information from the retinal source.
A Computational Model of the Perceived Velocity of Moving Plaids
Authors: Lamouret I , Cornilleau-Pérès V , Droulez J
Published: December 2015

Local motion detection mechanisms generally lead to one component of the optic flow becoming indeterminate. One way to solve this ‘aperture problem’ is to compute the optic flow which minimises some smoothing constraint. With iterative schemes the computed velocity array is suboptimal relative to the constraint until the process has converged. Under the original assumption that the iteration rate is sufficiently low to allow the perception of suboptimal flows at short stimulus durations, iterative gradient models give an accurate description of biases in the perception of tilted line velocity. We examine whether this approach can be applied to moving sinusoidal plaids. Our simulations are in agreement with a number of psychophysical results on both speed and direction perception. In particular we show that the effect of stimulus duration on the perceived direction of type II plaids [Yo and Wilson, 1992 Vision Research32(1)] can be accounted for without recourse to second-order mechanisms. The effects of contrast and component directions on the evolution rate of this bias are well reproduced. The model also successfully describes the effect of spatial frequency, and data obtained with gratings. These results suggest that iterative gradient schemes can model the dynamics of interactions between local velocity detectors, as revealed by psychophysical experiments with lines and plaids.
The Effect of Temporal Phase on the Perception of Apparent Motion
Authors: Hock H S , Kogan K , Lodes N
Published: December 2015

In classical apparent motion, a spot of light is presented in alternation such that the waveforms describing the varying luminance at each of two locations are 180° out of phase. However, when the luminance variation at each location is approximately sinusoidal, and the perceiver's task is to discriminate motion direction, the optimum temporal phase is 90° (van Santen and Sperling, 1984 Journal of the Optical Society of America A1 451 – 473). The results reported in this study suggest that the optimality of the 90° temporal phase may be specific to the direction-discrimination task.

Our experiments were based on a new procedure for measuring classical apparent motion thresholds (Hock, Kogan, and Espinoza, 1996, paper presented at ARVO). Two horizontally displaced dots are presented simultaneously against a darker background. The luminance ( L1) of one dot is always greater than that of the other ( L2), and the luminance values for the dots are exchanged on successive frames. Whether motion or stationarity is perceived depends on the background-relative luminance contrast (BRLC): ( L1- L2) divided by the difference between the average [( L1+ L2)/2] and background luminance. We found in the current study that motion thresholds depend on the temporal phase of the luminance variation at each location (rather than temporal asynchrony); the greater the phase difference (from 41° to 180°) the less the BRLC required for motion perception. At suprathreshold BRLC values, the perceived speed of apparent motion decreases with increased differences in temporal phase. The results are discussed in terms of Reichardt-type motion detection models.
Visual Direction behind and near an Occluder
Authors: Banks M S , van Ee R , Backus B T
Published: December 2015

Hering's laws imply that the visual direction assigned to a binocularly visible object is based on the oculocentric positions of the object in both eyes; the direction assigned to a monocularly visible object is based on its oculocentric position in that eye. It is interesting to consider how these laws apply near an occluder. Near the vertical edge of an opaque occluder, some regions of a far surface are visible to one eye only and other regions are visible to both eyes; the demarcation is created by the edge of the occluder and depends on the distance to the occluder and the far surface. If Hering's laws applied in this situation, we would expect spatial discontinuities in perceived visual directions near the edge of the occluder: in the monocular zone, the assignment of direction would be made by one eye's image and in the binocular zone, right next to the monocular zone, the assignment would be made by both eyes' images. Because of this switch in the eyes controlling the assignment, spatial discontinuities in perceived direction are expected.

We measured perceived visual direction near an occluding edge and found spatial distortions, but no discontinuities. We measured the horizontal and vertical spatial extents of the distortions and inferred how the inputs to the two eyes are weighted when one eye's view is occluded, nearly occluded, and not nearly occluded. In conclusion, the visual system seems to avoid spatial discontinuities in perceived visual direction that could otherwise occur near an occluder by varying the weights attached to each eye's input depending on target position relative to the occluding edge.
Features of the Representation Space for 3-D Objects
Authors: Bülthoff H H , Edelman S , Bülthoff I
Published: December 2015

To explore the nature of the representation space of 3-D objects, we studied human performance in forced-choice classification of objects composed of four geon-like parts, emanating from a common centre. The two class prototypes were distinguished by qualitative contrasts (cross-section shape; bulge/waist), and by metric parameters (degree of bulge/waist, taper ratio). Subjects were trained to discriminate between the two prototypes (shown briefly, from a number of viewpoints, in stereo) in a 1-interval forced-choice task, until they reached a 90% correct-response performance level. In experiment 1, eleven subjects were tested on shapes obtained by varying the prototypical parameters both orthogonally (Ortho), and in parallel (Para) to the line connecting the prototypes in the parameter space. For the eight subjects who performed above chance, the error rate increased with the Ortho parameter-space displacement between the stimulus and the corresponding prototype: F1,68=3.6, p<0.06 (the effect of the Para displacement was marginal). Clearly, the parameter-space location of the stimuli mattered more than the qualitative contrasts (which were always present). To find out whether both prototypes or just the nearest neighbour of the test shape influenced the decision, in experiment 2 eight new subjects were tested on a fixed set of shapes, while the test-stage distance between the two classes assumed one of three values (Far, Intermediate, or Near). For the six subjects who performed above chance, the error rate (on physically identical stimuli) in the Near condition was higher than in the other two conditions: F1,89=3.7, p<0.06. The results of the two experiments contradict the prediction of theories that postulate exclusive reliance on qualitative contrasts, and support the notion of a metric representation space with the subjects' performance determined by distances to more than one reference point or prototype (cf Edelman, 1995 Minds and Machines5 45 – 68).
Orientation Discrimination at Isoluminance
Authors: Reisbeck T E , Gegenfurtner K R
Published: December 2015

Colour and form are important attributes of the objects in our visual environment. We tested the hypothesis that colour and orientation are processed independently in the visual system. Orientation perception for stimuli defined by luminance is characterised by a decrease in thresholds with increasing stimulus contrast, and by a strong oblique effect: stimuli along the horizontal or vertical axes are discriminated more easily.

We determined orientation discrimination thresholds for stationary, slow (1 Hz) or fast (8 Hz) moving sine-wave gratings (1 cycle deg−1) defined by luminance or isoluminant (red — green) contrast. In a 4AFC paradigm, three of four stimulus patches were identical and the fourth differed in orientation, contrast, or in both. When we measured orientation discrimination thresholds as a function of stimulus contrast, thresholds decreased for all stimuli with increasing contrast. At all temporal frequencies the functions relating orientation thresholds to stimulus contrast had similar shapes for luminance and isoluminant gratings. On a cone-contrast metric, thresholds for stationary and slowly moving stimuli were consistently lower for isoluminant compared to luminance stimuli. For fast-moving stimuli orientation thresholds were similar for both kinds of gratings. For both types of stimuli a marked oblique effect was observed. To characterise processing of contrast and orientation completely, we measured simultaneous thresholds for contrast and orientation. The shapes of the resulting two-dimensional threshold contours were similar for luminance and isoluminant gratings, indicating similar rules for combining differences in contrast and orientation. We conclude that processing of isoluminant and luminance stimuli undergoes the same neural processing at least for the low spatial frequencies used here.
The Effect of Orientation on Alignment Performance
Authors: Keeble D R T , Hess R F
Published: December 2015

It has been found that the 3-Gabor alignment task is performed equally well whether the orientations of the patches are collinear, parallel, or orthogonal. But does the orientation of the individual micropatterns have any effect on performance? The ability (threshold) of subjects to determine whether the middle Gabor patch of a 3-patch display was displaced to the right or the left was measured in a variety of conditions. When the orientation of the Gabors was random, performance was poorer than in the three standard conditions mentioned above. If the outer Gabors had orientations of 45° and 135° and the centre patch was vertical, then thresholds were even higher, and the point of subjective equality for the task was displaced from centroid alignment towards a position where the patches form a head-to-tail contour. However, phase randomisation did not affect performance appreciably compared to the standard conditions, and, if Gaussian patches with normally distributed standard deviations were employed, the uncertainty on the Gaussian patch size did not impoverish the ability of observers to do the task. The implication of these results is that orientational factors can affect performance, and that the visual system attempts to form contours out of plausibly located oriented segments, thus masking centroid cues. In the absence of orientational disruption it does indeed appear that centroid-like cues are used, as the randomisation of bar positions or Gaussian blob size did not degrade thresholds. The universal result that orientation does not improve performance indicates that its role in this task is that of a mask rather than a cue.
A Problem in Perception: Living in Trapezoidal Spaces
Authors: Crunelle M
Published: December 2015

In journals devoted to architecture one comes more and more often across plans referring to spaces with vanishing, non-parallel, and split walls and other spaces—banana-shaped or perhaps trapezoidal. With respect to these last ones, I shall refrain from discussing the advantages or drawbacks of such solutions, but shall deal with a real problem inherent in them. Such plans are not new. Trapezoidal rooms can be found in circular or outward radiating designs. A prime example is Maison de la Radio in Paris. There the rooms with non-parallel walls are all parts of a circular annulus. People working in such spaces complain of discomfort they cannot identify. I shall try to put forward an explanation. The discussion will be extended to other, larger trapezoidal spaces—the Modern Art Museum in Frankfurt—and open spaces—Piazza del Campidoglio and Piazza San Pietro in Rome—so as to analyse the consequences of the strange effects of counterperspective.
Interaction between Colour and Depth Channels in Transparent Colour Perception
Authors: Okajima K , Takase M , Takahashi S
Published: December 2015

Two colours can be perceived at one location on overlapping planes only when the front plane is transparent. This phenomenon suggests that colour information processing is not independent of depth information processing and vice versa. To investigate the interaction between colour and depth channels, we used colour stimuli and binocular parallax to identify the conditions for transparency. Each stimulus, presented on a CRT to one eye, consisted of a centre patch and a surround. Binocular disparity was set so that the centre patch could be seen behind the surround. However, the surround appears to be behind the centre patch when the surround is perceived as an opaque plane. We examined several combinations of basic colours for the centre patch and surround. The surround luminance was constant at 1.0 cd m−2 and the luminance of the centre was varied. Subjects used the apparent depth of the surround to report whether or not transparency occurred. The results show two types of transparency: ‘bright-centre transparency’ and ‘dark-centre transparency’. We found that the range of centre luminances which yield transparency depends on the combination of centre and surround colours, ie influences of brightness and colour opponency were found. We conclude that there is interaction between colour and depth channels in the visual system.
Perceived Depth from Dot Density Change by Lateral Head Movements
Authors: Sakurai K , Ono H
Published: December 2015

We investigated whether there is a trade-off between magnitude of perceived depth and that of perceived motion, using density changes (expansion/contraction) in a random-dot pattern yoked to lateral head movements. We simulated sine-wave surfaces with a depth of 0, 1, 2, 4, 8, and 16 cm. Subjects viewed the patterns monocularly while moving their heads from side to side laterally, and reported the magnitude of perceived depth and that of perceived motion. When simulated depth was less than 4 cm, the surfaces looked stationary and the amount of perceived depth was the same as that of simulated depth. When it was more than 4 cm, the surfaces appeared to move in a rocking motion and the amount of perceived depth was smaller than that of simulated depth. The trade-off implies a mechanism which transduces single visual input into depth or motion.