bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly CO2sensitive extruded fluorescent plastic indicator film based on HPTS
Authors: Mills Andrew , Yusufu Dilidaer
Published: December 2015

A HPTS-based, very CO2-sensitive plastic film is reported which is yellow, and fluoresces green in the absence of CO2, and colourless and fluoresces blue in the presence of CO2.
Hydrogen peroxide-responsive micelles self-assembled from a peroxalate ester-containing triblock copolymer
Authors: Liu Chao , Zhu Xiaowei , Wang Xiaoli , Miao Dandan , Liang Xiaoyu , Wang Cuiwei , Pang Liyun , Sun Hongfan , Kong Deling , Yang Jing
Published: December 2015

A novel copolymer was synthesized by using peroxalate esters as linkages and the formed micelles possessed specific H2O2 responsive reactivity.
Conversion of a non-heme iron-dependent sulfoxide synthase into a thiol dioxygenase by a single point mutation
Authors: Goncharenko Kristina V. , Seebeck Florian P.
Published: December 2015

EgtB fromMycobacterium thermoresistibilecatalyzes O2-dependent sulfur–carbon bond formation between the side chains ofNα-trimethyl histidine and γ-glutamyl cysteine as a central step in ergothioneine biosynthesis.
Tuning the optical, electronic and luminescence properties of LaOCl:Eu3+via structural and lattice strain modulation
Authors: Lv Li , Wang Ting , Li Sipeng , Su Yiguo , Wang Xiaojing
Published: December 2015

Lattice strain increases with increasing of Eu3+ concentration, which influences on emission intensity of LaOCl:Eu3+ nanodisks.
Single-molecule insight into Wurtz reactions on metal surfaces
Authors: Sun Qiang , Cai Liangliang , Ding Yuanqi , Ma Honghong , Yuan Chunxue , Xu Wei
Published: December 2015

We have performed a systematic study of Wurtz reactions on different metal surfaces and compared their different activities.
Electronic and optical properties of graphene nanoribbons in external fields
Authors: Chung Hsien-Ching , Chang Cheng-Peng , Lin Chiun-Yan , Lin Ming-Fa
Published: December 2015

A review work is done for the electronic and optical properties of graphene nanoribbons in magnetic, electric, composite, and modulated fields.
Structure prediction of the solid forms of methanol: an ab initio random structure searching approach
Authors: Lin Tzu-Jen , Hsing Cheng-Rong , Wei Ching-Ming , Kuo Jer-Lai
Published: December 2015

Liquid methanol and methanol clusters have been comprehensively studied to reveal their local structure and hydrogen bond networks.
Ionic liquid-promoted one-pot synthesis of thiazole–imidazo[2,1-b][1,3,4]thiadiazole hybrids and their antitubercular activity
Authors: Ramprasad Jurupula , Nayak Nagabhushana , Dalimba Udayakumar , Yogeeswari Perumal , Sriram Dharmarajan
Published: December 2015

The anti-TB activity of new thiazole–imidazo[2,1-b][1,3,4]thiadiazoles, which are synthesized via one-pot synthesis, is comparable with that of standard drugs.
One for all: cobalt-containing polymethacrylates for magnetic ceramics, block copolymerization, unexpected electrochemistry, and stimuli-responsiveness
Authors: Rüttiger C. , Pfeifer V. , Rittscher V. , Stock D. , Scheid D. , Vowinkel S. , Roth F. , Didzoleit H. , Stühn B. , Elbert J. , Ionescu E. , Gallei M.
Published: December 2015

Functional cobalt-containing homo and block polymers are probed with respect to their redox-induced switchability and as preceramic materials.
Green synthesis of ZnO hollow sphere nanostructures by a facile route at room temperature with efficient photocatalytic dye degradation properties
Authors: Mousavi Seyed Mohsen , Mahjoub Ali Reza , Abazari Reza
Published: December 2015

The present work has prepared ZnO hollow spherical nanoparticles using a straightforward synthetic route and has innovatively made use of carbon spheres as a template at room temperature.
Bi-component inorganic oxide nanofibers from gas jet fiber spinning process
Authors: Ghosh Monoj , Jana Sadhan C.
Published: December 2015

Bi-component semiconducting metal oxide nanofibers with core–shell and side-by-side morphologies in mesoporous or solid cylindrical shapes are produced by gas-jet fiber process.
Silver-nanospheres as a green catalyst for the decontamination of hazardous pollutants
Authors: Vellaichamy Balakumar , Periakaruppan Prakash
Published: December 2015

This paper reports the facile, green and one-pot synthesis of silver-nanospheres (Ag-NSs) and their use as an excellent green catalyst for the decontamination of hazardous pollutants.
Supermolecular self assembly of AIE-active nanoprobes: fabrication and bioimaging applications
Authors: Hui Xu , Xu Dazhuang , Wang Ke , Yu Weijen , Yuan Huaying , Liu Meiying , Zhengyu Shen , Zhang Xiaoyong , Wei Yen
Published: December 2015

AIE active luminescent polymeric nanoprobes were fabricated for the first time via formation of supermolecular complexes between an adamantane capped AIE dye and β cyclodextrin.
Corrélations entre les mensurations photogrammétriques
sagittales de profil des tissus mous et celles des arcades dentaires
Authors: Diouf Joseph Samba , Touré Bécaye , Ndiaye Marième , Badiane Alpha , Diop-Bâ Khady , Ngom Papa Ibrahima , Diagne Falou
Published: December 2015

Introduction : Les mesures sagittales des tissus mous faciaux réalisées à
l’aide de l’outil photographique (mensurations photogrammétriques sagittales des tissus
mous) permettent de quantifier les dimensions et la position de ces tissus dans le plan
sagittal. Ces derniers entretiennent d’étroits rapports anatomiques avec les arcades
dentaires sous-jacentes. Pourtant, peu d’importances ont été données à la description et
la comparaison de la morphologie sagittale des tissus mous faciaux selon différents
paramètres d’arcades. L’objectif de cette étude est de rechercher les corrélations entre
des mensurations photogrammétriques sagittales du visage et des différentes mensurations
des arcades dentaires. Matériels et méthodes : Il s’agit d’une étude
transversale portant sur des étudiants chez qui des clichés photographiques de profil
standardisés ont été pris, puis des mensurations photogrammétriques réalisées. Des
mensurations d’arcades ont aussi été faites directement en bouche. Les données ont été
analysées grâce au logiciel IBM SPSS 20.0. L’importance de l’association entre les
mensurations photogrammétriques sagittales des tissus mous et les paramètres d’arcades a
été recherchée par une matrice de corrélation de Pearson. La signification est fixée à
p = 0,05.
Résultats : Les paramètres de protrusions labiales étaient
significativement et positivement corrélés aux longueurs d’arcades. Le surplomb était
significativement et positivement corrélé à la distance Ls/Sn-Sm. Le recouvrement était
significativement et négativement corrélé aux paramètres labiaux (Ls/N-Ort, Li/N-Ort,
Ls-E, Li-E, Ls-S, Li-S, Ls/Sn-Sm et Li/Sn-Sm) Conclusion : Les corrélations
trouvées montrent l’importance de la prise en compte des tissus mous dans le diagnostic
dento-alvéolaire et le plan de traitement orthodontique de patients.
Ostéotomie sagittale courte
Authors: Paulus Christian , Kater Wolfgang
Published: December 2015

L’ostéotomie sagittale de la mandibule est devenue un standard dans la chirurgie
mandibulaire des dysmorphoses dento-faciales. Nous la proposons même pour les dysmorphoses
de faible importance. Ceci doit nous forcer à en réduire la morbidité. Nous décrivons une
technique opératoire à surface de clivage réduit. La section osseuse suit une ligne
oblique depuis l’épine de Spix en bas et en dehors vers la région supra-angulaire. Cette
section est complétée par une ostéotomie du bord postérieur de la branche montante. Ce
clivage n’atteint jamais le canal dentaire. La protection du nerf alvéolaire est accrue,
ce qui diminue considérablement le risque de séquelles nerveuses de cette intervention. La
majorité des déplacements mandibulaires sont possibles par cette technique à l’exclusion
des propulsions importantes et des augmentations de la hauteur du ramus.
Design of indirectly driven, high-compression Inertial Confinement Fusion implosions with improved hydrodynamic stability using a 4-shock adiabat-shaped drive
Authors: Milovich J. L. , Robey H. F. , Clark D. S. , Baker K. L. , Casey D. T. , Cerjan C. , Field J. , MacPhee A. G. , Pak A. , Patel P. K. , Peterson J. L. , Smalyuk V. A. , Weber C. R.
Published: December 2015

Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm2, but with significantly lower total neutron yields (between 1.5 × 1014 and 5.5 × 1014) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the “high-foot” experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expense of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3–10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm2. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.
The anharmonic quartic force field infrared spectra of three polycyclic aromatic hydrocarbons: Naphthalene, anthracene, and tetracene
Authors: Mackie Cameron J. , Candian Alessandra , Huang Xinchuan , Maltseva Elena , Petrignani Annemieke , Oomens Jos , Buma Wybren Jan , Lee Timothy J. , Tielens Alexander G. G. M.
Published: December 2015

Current efforts to characterize and study interstellar polycyclic aromatic hydrocarbons (PAHs) rely heavily on theoretically predicted infrared (IR) spectra. Generally, such studies use the scaled harmonic frequencies for band positions and double harmonic approximation for intensities of species, and then compare these calculated spectra with experimental spectra obtained under matrix isolation conditions. High-resolution gas-phase experimental spectroscopic studies have recently revealed that the double harmonic approximation is not sufficient for reliable spectra prediction. In this paper, we present the anharmonic theoretical spectra of three PAHs: naphthalene, anthracene, and tetracene, computed with a locally modified version of the SPECTRO program using Cartesian derivatives transformed from Gaussian 09 normal coordinate force constants. Proper treatments of Fermi resonances lead to an impressive improvement on the agreement between the observed and theoretical spectra, especially in the C–H stretching region. All major IR absorption features in the full-scale matrix-isolated spectra, the high-temperature gas-phase spectra, and the most recent high-resolution gas-phase spectra obtained under supersonically cooled molecular beam conditions in the CH-stretching region are assigned.
Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study
Authors: Fonari A. , Corbin N. S. , Vermeulen D. , Goetz K. P. , Jurchescu O. D. , McNeil L. E. , Bredas J. L. , Coropceanu V.
Published: December 2015

We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoretical Raman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.
Characterization of a 6 kW high-flux solar simulator with an array of xenon arc lamps capable of concentrations of nearly 5000 suns
Authors: Gill Robert , Bush Evan , Haueter Philipp , Loutzenhiser Peter
Published: December 2015

A systematic methodology for characterizing a novel and newly fabricated high-flux solar simulator is presented. The high-flux solar simulator consists of seven xenon short-arc lamps mounted in truncated ellipsoidal reflectors. Characterization of spatial radiative heat flux distribution was performed using calorimetric measurements of heat flow coupled with CCD camera imaging of a Lambertian target mounted in the focal plane. The calorimetric measurements and images of the Lambertian target were obtained in two separate runs under identical conditions. Detailed modeling in the high-flux solar simulator was accomplished using Monte Carlo ray tracing to capture radiative heat transport. A least-squares regression model was used on the Monte Carlo radiative heat transfer analysis with the experimental data to account for manufacturing defects. The Monte Carlo ray tracing was calibrated by regressing modeled radiative heat flux as a function of specular error and electric power to radiation conversion onto measured radiative heat flux from experimental results. Specular error and electric power to radiation conversion efficiency were 5.92 ± 0.05 mrad and 0.537 ± 0.004, respectively. An average radiative heat flux with 95% errors bounds of 4880 ± 223 kW ⋅ m−2 was measured over a 40 mm diameter with a cavity-type calorimeter with an apparent absorptivity of 0.994. The Monte Carlo ray-tracing resulted in an average radiative heat flux of 893.3 kW ⋅ m−2 for a single lamp, comparable to the measured radiative heat fluxes with 95% error bounds of 892.5 ± 105.3 kW ⋅ m−2 from calorimetry.
Large-area, broadband and high-efficiency near-infrared linear polarization manipulating metasurface fabricated by orthogonal interference lithography
Authors: Zhang Zuojun , Luo Jun , Song Maowen , Yu Honglin
Published: December 2015

Manipulation of the polarization state using electromagnetic metasurface has attracted considerable attention in recent years. However, most previously demonstrated single-layer polarization conversion metasurfaces suffer from low polarization conversion efficiency, narrow operation bandwidth, or huge fabrication challenges, especially for the visible and near-infrared frequencies. In this letter, a broadband and high-efficiency reflective linear polarization converter composed of ellipse-shaped plasmonic planar resonator was demonstrated in the near-infrared region. A polarization conversion ratio in power larger than 91.1% is achieved from 730 nm to 1870 nm. Furthermore, orthogonal interference lithography is adopted to prepare the large-area optical polarization conversion metasurface. The fabrication strategy unplugs the bottleneck of the fabrication of the large-area metasurface in the optical regime, promising an unprecedented progress for optical communication and integrated optics.
Laser-driven electron acceleration in an inhomogeneous plasma channel
Authors: Zhang Rong , Cheng Li-Hong , Xue Ju-Kui
Published: December 2015

We study the laser-driven electron acceleration in a transversely inhomogeneous plasma channel. We find that, in inhomogeneous plasma channel, the developing of instability for electron acceleration and the electron energy gain can be controlled by adjusting the laser polarization angle and inhomogeneity of plasma channel. That is, we can short the accelerating length and enhance the energy gain in inhomogeneous plasma channel by adjusting the laser polarization angle and inhomogeneity of the plasma channel.
Systematic coarse-grained modeling of complexation between small interfering RNA and polycations
Authors: Wei Zonghui , Luijten Erik
Published: December 2015

All-atom molecular dynamics simulations can provide insight into the properties of polymeric gene-delivery carriers by elucidating their interactions and detailed binding patterns with nucleic acids. However, to explore nanoparticle formation through complexation of these polymers and nucleic acids and study their behavior at experimentally relevant time and length scales, a reliable coarse-grained model is needed. Here, we systematically develop such a model for the complexation of small interfering RNA (siRNA) and grafted polyethyleneimine copolymers, a promising candidate for siRNA delivery. We compare the predictions of this model with all-atom simulations and demonstrate that it is capable of reproducing detailed binding patterns, charge characteristics, and water release kinetics. Since the coarse-grained model accelerates the simulations by one to two orders of magnitude, it will make it possible to quantitatively investigate nanoparticle formation involving multiple siRNA molecules and cationic copolymers.
Evidence for an equilibrium epitaxial complexion at the Au-MgAl2O4 interface
Authors: Majdi Tahereh , Zhu Guo-zhen , Carvalho Jessica , Jarvis Victoria , Meinander Kristoffer , Britten James F. , Botton Gianluigi , Preston John S.
Published: December 2015

Evidence for the existence of an equilibrium epitaxial complexion at the Au-MgAl2O4 interface has been observed. The growth of crystalline MgAl2O4 nanostructures, from a previously stable substrate in the presence of an Au overlayer and heat, is associated with this complexion. Prior to the nanostructures' self-assembly, Au nanoparticles crystalize, then reorient to align with the MgAl2O4 substrate. The presented results contradict earlier conclusions based solely on SEM studies of the final assembled nanostructures. Those results suggested that the MgAl2O4 grown pedestal and associated Au nanoparticle atop were both gold.
Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes
Authors: Andersen J. , Heimdal J. , Wugt Larsen R.
Published: December 2015

The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with ethanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic H/D-substitution of the ethanol subunit enabled by a dual inlet deposition procedure enables the observation and unambiguous assignment of the intermolecular high-frequency out-of-plane and the low-frequency in-plane donor OH librational modes for two different conformations of the mixed binary ethanol/water complex. The resolved donor OH librational bands confirm directly previous experimental evidence that ethanol acts as the O⋯HO hydrogen bond acceptor in the two most stable conformations. In the most stable conformation, the water subunit forces the ethanol molecule into its less stable gauche configuration upon dimerization owing to a cooperative secondary weak O⋯HC hydrogen bond interaction evidenced by a significantly blue-shift of the low-frequency in-plane donor OH librational band origin. The strong correlation between the low-frequency in-plane donor OH librational motion and the secondary intermolecular O⋯HC hydrogen bond is demonstrated by electronic structure calculations. The experimental findings are further supported by CCSD(T)-F12/aug-cc-pVQZ calculations of the conformational energy differences together with second-order vibrational perturbation theory calculations of the large-amplitude donor OH librational band origins.
Effects of electrical bias and temperature stress on the negative magnetoresistance of a low-k dielectric
Authors: McGowan B. T. , Nolting W. M. , Lloyd J. R.
Published: December 2015

A study of the effect of electrical bias and temperature stress (BTS) on the negative magnetoresistance (MR) of a low-k dielectric composed of SiCOH is presented. The magnitude of the structure's MR decreases with increased time on BTS. There is a correlation between the stress condition and the rate of MR decrease. The voltage and temperature dependencies of the MR decay resemble the dependencies observed for Time Dependent Dielectric Breakdown (TDDB) studies, suggesting that this MR response to BTS could be related to breakdown mechanisms and prove useful for studying the TDDB behavior of these materials. Possible mechanisms that could lead to such a decay in MR when subjected to BTS are discussed.
Towards understanding the detection of profile asymmetry from Mueller matrix differential decomposition
Authors: Chen Xiuguo , Jiang Hao , Zhang Chuanwei , Liu Shiyuan
Published: December 2015

The Mueller matrix differential decomposition is applied to interpret Mueller matrices of asymmetric gratings and to understand the use of Mueller matrix ellipsometry (MME) in distinguishing the direction of profile asymmetry, as reported in our recent work [Chen et al., J. Appl. Phys. 116, 194305 (2014)]. We show that both linear and circular birefringence-dichroism pairs can be extracted from the collected Mueller matrices, which provide a complete description of the sample polarization properties. We present both theoretical and experimental results, which demonstrate that the linear birefringence and dichroism, LB′ and LD′, along the ±45° axes are the origin of the MME in distinguishing the direction of profile asymmetry. We also demonstrate that equal magnitude of profile asymmetry in opposite directions always yields LB′ and LD′ of the same absolute deviation from zero and of opposite sign, when the plane of incidence is no longer perpendicular to grating lines. The sensitivity of LB′ and LD′ to both the magnitude and direction of profile asymmetry is useful in monitoring processes in which symmetric structures are desired.
Correlation between magnetism and “dark stripes” in strained La1−xSrxCoO3 epitaxial films (0 ≤ x ≤ 0.1)
Authors: Lan Q. Q. , Shen X. , Yang H. W. , Zhang H. R. , Zhang J. , Guan X. X. , Yao Y. , Wang Y. G. , Yu R. C. , Peng Y. , Sun J. R.
Published: December 2015

Using the technique of aberration-corrected scanning transmission electron microscopy, we performed a systematic analysis for the atomic lattice of the strained La1−xSrxCoO3 (0 ≤ x ≤ 0.1) epitaxial films, which have drawn a great attention in recent years because of their anomalous magnetism. Superstructures characterized by dark stripes are observed in the lattice image, evolving with combined Sr-doping and lattice strains. Fascinatingly, we found a close relation between the proportion of the Co ions in dark stripes and the saturation magnetization of the film: the latter grows linearly with the former. This result implies that the magnetism could be exclusively ascribed to the Co ions in dark stripes.
Spurious-free Lamb wave resonators with protrusion structures
Authors: Zhang Hongxiang , Liang Ji , Zhang Hao , Zhang Daihua , Pang Wei
Published: December 2015

In this letter, we demonstrate a technique to eliminate the spurious modes in aluminum nitride Lamb wave resonators (LWRs). The transverse acoustic wave characteristics are examined, and a resonance modulation theory on the regulation of mechanical boundary conditions is deducted. As examples of embodiments, vertical and lateral protrusion structures are proposed for the suppression. Finite element analysis verifies that the employment of these structures effectively restrains the transverse modes, and the measured electrical performance of the LWR with protrusions demonstrates an 11 dB reduction in the spurious response.
Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+δ thin films
Authors: Bao Shanyong , Xu Xing , Enriquez Erik , Mace Brennan E. , Chen Garry , Kelliher Sean P. , Chen Chonglin , Zhang Yamei , Whangbo Myung-Hwan , Dong Chuang , Zhang Qinyu
Published: December 2015

Single-crystalline epitaxial thin films of PrBaCo2O5.5+δ (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200–800 °C. During the oxidation cycle under O2, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co2+/Co3+ → Co3+ and Co3+ → Co3+/Co4+, that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO2)(PrO)(CoO2) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.
Bolometric response of free-standing reduced graphene oxide films
Authors: Dickerson William , Hemsworth Nicholas , Gaskell Peter , Ledwosinska Elizabeth , Szkopek Thomas
Published: December 2015

Free-standing films of reduced graphene oxide were prepared by evaporative drying of drop-cast graphene oxide followed by thermal reduction. The electrical resistance of reduced graphene oxide films showed a strong temperature dependence, reaching a temperature coefficient of resistance of 44×103 Ω/K at 60 K. The bolometric response under black body illumination was measured from 50 K to 300 K, reaching a voltage responsivity of up to 82 × 103 V/W at 50 K.
Interaction of Multiple Surface Cues in Motion Grouping
Authors: Weiss Y , Adelson E H
Published: December 2015

A rotating ellipse and a translating ogive may appear rigid or nonrigid depending on their shapes. By placing moving dots (‘satellites’) in the space surrounding the contour one can cause the percept to switch between rigid and nonrigid, depending on how the dots move. We have studied how multiple surface cues can influence this grouping effect.

One set of displays consisted of the ambiguous contour and a group of consistently moving satellites. We found that under this condition the grouping was extremely robust. The influence of the satellites on the perceived rigidity of the contour remained powerful when they were moved far away from the contour and even when they were placed at a different stereoscopic depth plane. A second set of displays consisted of the ambiguous contour and two groups of satellites: one group moving rigidly and the other nonrigidly. In these displays we found a strong effect of stereo and distance. One could cause the percept to switch from rigid to nonrigid by manipulating the relative distances of the display elements or the relative disparities. We discuss how these results can be accounted for in a computational model that combines form and motion information in a robust estimation framework.
Increasing the Number of Context Elements in Early Vision: More is Better
Authors: Meinecke C
Published: December 2015

Studies in visual search have shown that in feature search conditions in which the target differs from the context in a single feature (like orientation), search time increases only slightly (or sometimes not at all) as a function of increasing number of context elements. This is a typical result for early vision conditions, and is taken as an indicator of parallel processing of the whole stimulus.

In visual search experiments the manipulation of increasing the number of context elements is confounded with the fact of increasing their spatial density. And as is known from other typical early vision parameters, eg texture segmentation, increasing density improves performance. So, parallel visual search may be a byproduct of the (implicit) density manipulation.

In two texture-segmentation experiments, the number of context elements was increased while their spatial density was kept constant. This manipulation leads to an enlargement of the whole stimulus. The results show that under these conditions increasing the number of context elements even improved performance. This improvement was observed particularly at a retinal eccentricity of more than 3 deg. The results are explained within a framework of a spatial pooling mechanism.
Layers and Alpha Maps as Visual Representations
Authors: Adelson E H , Wang J Y A
Published: December 2015

The basic vocabulary of computer graphics and digital illustration includes ‘layers’ and ‘alpha maps’. A layer contains a set of registered 2-D arrays (maps), containing information about colour (the RGB channels) and transparency (the alpha channel) at each point. Layers are ordered in depth, but need not have metric depth. Metelli used a similar vocabulary to analyse perceptual transparency, and related descriptions have been used to understand illusory contours, brightness illusions, etc. We believe that the layer concepts can be extended to have broad utility in human vision and computer vision. By adding a velocity map to a layer, and imposing smoothing within the layer (but not across layers), we have found that many classically difficult problems in motion analysis become more tractable. The problems that usually arise with segmentation and motion boundaries are alleviated, because the discontinuities are assigned to the alpha maps rather than to the velocity maps. Other challenging phenomena, such as motion blur, motion transparency, and moving shadows, also become more tractable within this framework. Decomposition of a scene into layers is a useful stage of processing even when it does not represent the final output; later stages that seek 3-D representations can benefit from an initial layered processing. We suggest that layers with alpha maps may be a basic representation in many aspects of human vision.
Strength of Motion Aftereffect Varies with Segregation of Test Field and Surround
Authors: Harris J P , Sullivan D
Published: December 2015

It is widely accepted that the motion aftereffect (MAE) results from the adaptation of visual motion detectors. However, recent work suggests that how the effects of that adaptation are expressed (the nature of the perceived MAE) depends on the nature of the inducing and test fields. We investigated how the strength of the MAE varied with the nature of the boundary between the test field and the surround. The surround (18.5 deg wide × 13.5 deg high) to the adapting and test fields was an area of vertical square-wave grating of 0.7 cycle deg−1. During adaptation, vertical stripes of the same spatial frequency as the background moved horizontally at a speed of 2 deg s−1 for 14 s within a central rectangular window of 9.7 deg wide × 7.6 deg high. At the end of adaptation, one of six different test fields was presented in the central window. In three of these, the stationary test stripes were exactly aligned with the surrounding stripes, and in the other three they were offset by half a stripe width. For two of these conditions (one aligned, one offset), a black outline was drawn around the edge of the adapting window (and so was visible only where it crossed white areas), and for two others (one aligned, one offset) the outline was red, and so visible in its entirety. The strength of MAEs in twelve subjects was assessed both by ratings at an auditory signal which occurred 0.5 s after the end of adaptation and also by measurement of their durations. There was good agreement between these two measures. MAEs were significantly stronger on the offset than on the aligned test fields. The presence of an outline increased MAE strength compared with no outline, but these outline effects were much weaker than those of offsetting the test stripes from the surround. We suggest that the MAE depends in part on the presence of a visually separable test pattern to which motion may be allocated.
The Effect of Surface Orientation on the Perception of Stereoscopic Corrugations
Authors: Parton A D , Bradshaw M F , Rogers B J , Davies I R L
Published: December 2015

For most observers there is a pronounced orientational anisotropy in the perception of three-dimensional corrugated surfaces (Rogers and Graham, 1983 Science221 1409 – 1411; Bradshaw and Rogers, 1993 Perception22 Supplement, 117). Low-frequency corrugations which are oriented vertically have been found to have higher disparity modulation thresholds, the amount of perceived depth at suprathreshold levels is smaller, and typically they take longer to see than horizontally oriented corrugations. In the present experiments, the orientation of the corrugations was manipulated (from horizontal to vertical in 22.5 deg increments) to investigate the effect of surface orientation on both (i) a threshold detection task and (ii) a suprathreshold depth-matching task. The stimuli were 10 deg in diameter and were presented on two 12 inch monochrome monitors arranged to form a Wheatstone stereoscope. The surfaces were modulated in depth at four different corrugation frequencies (from 0.1 to 0.8 cycle deg−1 in octave steps). Thresholds were found to increase monotonically with increasing surface orientation from the horizontal: ∼2.5 arc s for horizontal corrugations to ∼10 arc s for vertical corrugations. The increase in thresholds was less marked for surfaces with higher corrugation frequencies. The rate of increase of threshold was greatest for surface orientations beyond 45°. A different pattern of results was found in the suprathreshold depth-matching task. Although the perceived depth in vertically oriented corrugations was significantly smaller (>50%) than for horizontally oriented corrugations, the largest amount of perceived depth was found for corrugated surfaces oriented at 45°. These results suggest that the disparity information used to process stereoscopic corrugations at threshold may be different from that used to process suprathreshold surfaces.
The Interaction of Stereopsis and Perspective in the Perception of Depth
Authors: Gillam B , Sedgwick H A
Published: December 2015

When only stereoscopic information is available, the slant of a single isolated surface around a vertical axis is often greatly underestimated. If two small objects (probes), separated horizontally by several degrees, are displayed in front of such a surface, the depth of the probes is perceived relative to the perceived slant of the background surface, leading to systematic misperception of the point of subjective equality (PSE) of the distances of the probes from the observer (Mitchison and Westheimer, 1984 Vision Research24 1063 – 1073; Gillam et al, 1993 Perception22 Supplement, 35).

In the present study we found that when we added global perspective information to the background surface, thus increasing its perceived slant, this substantially improved the PSE of the probes. Alternatively, when we added frontal stereoscopic surfaces above and below the background surface, thus providing gradients of disparity discontinuities across the surface boundaries, this also produced an improvement in the perceived slant of the background surface, but produced an even greater improvement in the PSE of the probes.

These results imply that the local stereoscopic information specifying the depth of each probe relative to the background surface is integrated with the perceived slant of the background surface, whether specified by global stereoscopic information or by global perspective information, to determine the relative depth of the probes. This integration of local stereoscopic information with global slant information appears to be more complete, however, when the global information is provided by stereopsis rather than by perspective.
Functional Organisation of Human Visual Cortex Revealed by fMRI
Authors: Tootell R B H , Dale A M , Hadjikhani N , Liu A K , Marrett S , Mendola J D
Published: December 2015

Until recently, comparatively little was known about the functional organisation of human visual cortex. Functional magnetic resonance imaging (fMRI), in conjunction with cortical flattening techniques and psychophysically relevant visual stimulation, has greatly clarified human visual-information processing.

To date, we have completed cortical surface reconstructions (flattening), coupled with a wide range of visual stimulus testing, on 28 normal human subjects. Visual activation was acquired on a 1.5 T GE MR scanner with ANMR echo-planar imaging, with the use of a custom, bilateral, quadrature surface coil covering posterior cortex.

Approximately ten visual cortical areas can now be functionally localised each with unique functional and topographical properties. The most well-defined areas are: V1, V2, V3, VP, V3A, V4v, MT, SPO, and perhaps MSTd. Most of the properties in these human areas are similar to those reported in presumably homologous areas of macaque, but distinctive species differences also appear to exist, notably in V3/VP, V4v, and V3A. Human areas showing prominant motion-selectivity include V3A, MT/MSTd, SPO, and a small area near the superior sylvian fissure. Retinotopic areas include V1, V2, V3, VP, V4v, and V3A. The human cortical magnification factor appears higher towards the fovea than in macaque, but, like macaque, preferred spatial frequency tuning varies inversely with eccentricity in all retinotopic areas in which sinusoidal gratings are effective stimuli.
Trends in European Visual Science Since 1978
Authors: Cavonius C R
Published: December 2015

Trends in basic research in visual science in Europe are discussed, as reflected by the topics of choice in this series of meetings.
Which Eye Sees the Most?
Authors: Nilsson D-E , Warrant J
Published: December 2015

The performance of the eyes is ultimately limited by the physical nature of light. The diameter of the aperture that admits light to the eye sets an upper limit to the spatial frequencies that can be imaged behind the aperture. Diffraction, which is responsible for this limitation, is caused by the wave nature of light. The array of sampling stations the eye uses to detect the image is instead limited by the quantum nature of light. Each sampling station can only sample a finite number of quanta, and any such count is associated with a standard deviation being the square root of the true mean. Effectively, this limits the ability to detect differences in luminance (contrasts) across the image. Diffraction and quantum noise together sets an upper physical limit to the performance of an eye. If the eye's quantum efficiency, integration time, and thermal noise are constants, it is possible to find the optimum sampling frequency that maximises spatial resolution of a stationary image. This optimum depends on eye size and luminance, and differs from the ‘camera type eye’, the ‘pinhole eye’, and the various optical types of compound eye.

We have calculated the maximum detectable spatial frequency for a number of simple and compound types of eye, and plotted the results against luminance and eye size to produce a unique ‘performance surface’ for each type of eye. These performance surfaces allow a comprehensive graphical comparison of the efficiency of the various optical types of eye.
Processing of Natural Time Series of Intensities in the Early Visual System of the Blowfly
Authors: van Hateren J H
Published: December 2015

The first steps of processing in the visual system of the blowfly are well suited for studying the relationship between the properties of the environment and the function of visual processing (eg Srinivasan et al, 1982 Proceedings of the Royal Society, London B216 427; van Hateren, 1992 Journal of Comparative Physiology A171 157). Although the early visual system appears to be linear to some extent, there are also reports on functionally significant nonlinearities (Laughlin, 1981 Zeitschrift für Naturforschung36c 910). Recent theories using information theory for understanding the early visual system perform reasonably well, but not quite as well as the real visual system when confronted with natural stimuli [eg van Hateren, 1992 Nature (London)360 68]. The main problem seems to be that they lack a component that adapts with the right time course to changes in stimulus statistics (eg the local average light intensity). In order to study this problem of adaptation with a relatively simple, yet realistic, stimulus I recorded time series of natural intensities, and played them back via a high-brightness LED to the visual system of the blowfly ( Calliphora vicina). The power spectra of the intensity measurements and photoreceptor responses behave approximately as 1/ f, with f the temporal frequency, whilst those of second-order neurons (LMCs) are almost flat. The probability distributions of the responses of LMCs are almost gaussian and largely independent of the input contrast, unlike the distributions of photoreceptor responses and intensity measurements. These results suggest that LMCs are in effect executing a form of contrast normalisation in the time domain.
Effects of Saccades on Perceived Time
Authors: Ross J , Diamond M R
Published: December 2015

Saccades produce errors in locating objects in space. The question here examined is whether they also produce errors of location in time. Observers judged whether flashed bars appeared before, during, or after saccades, the order of appearance of two bars flashed in sequence, and the apparent interval between two points of light flashed at a SOA of 100 ms.

We found that (1) bars displayed up to 150 ms before saccades were often judged as during saccades, later bars veridically; (2) the accuracy of judgements of order dropped just before saccades; (3) apparent intervals were shorter before saccades, reaching control levels at onset. We conclude that perceived time is foreshortened immediately before saccades. This could be due to selective suppression of magnocellular activity and may function to hide saccades and their effects.
From Elements to Perceptions
Authors: Spillmann L
Published: December 2015

Gestalt psychologists in the early part of the century challenged psychophysical notions that perceptual phenomena can be understood from a punctate (‘atomistic’) analysis of the elements present in the stimulus. Their ideas also inhibited later attempts to explain vision in terms of single-unit recordings from individual neurons. A rapprochement between Gestalt phenomenology and physiology seemed unlikely when the first ECVP was held in Marburg, Germany, in 1978. Since that time, response properties of neurons have been discovered that invite an interpretation of visual phenomena (including ‘illusions’) in terms of neuronal processing. Indeed, it is now possible to understand some Gestalt phenomena on the basis of known neurophysiological mechanisms.

I begin by outlining the great strides that have been made since the advent of microelectrode recording from single neurons. Initially, cells (‘detectors’) selectively responding to the contrast, spatial frequency, wavelength, orientation, movement, and disparity of a stimulus placed in their receptive fields were used to interpret simple perceptual phenomena (eg, Mach bands, Hermann grids, tilt aftereffect, MAE). In recent years, cells at higher levels of the visual system have been discovered that might explain a number of more complex phenomena: the perception of illusory (occluded) contours by end-stopped cells in area V2, the filling-in of artificial scotomata by neurons in V3, colour constancy by ‘perceptive’ neurons in V4, and the perception of coherent motion in dynamic noise patterns by cells in MT. Studies of flow fields and biological motion in area MST have recently been added to account for our perceptions as we move through our environment. Prompted by these findings, a shift from local to global interactions ‘beyond the classical receptive field’ has taken place in our search for the neural substrates of perception. Current research has focused on three kinds of mechanisms: (i) converging feed-forward projections as the basis for new response properties emerging at higher levels, (ii) recruitment of lateral connections to explain filling-in, and (iii) backward propagation from higher to lower levels to account for binding and figure - ground segregation. How such mechanisms compute large-scale surface properties such as brightness, colour, and depth from local features—indeed how they construct the surfaces themselves from complex natural scenes—is only one of the many questions that are under scrutiny today.

Future research will have to tackle the all-important question: How does the analysed information come together again? Furthermore, the contributions of eye movements, attention, learning, other sense modalities, and motor actions will have to be taken into consideration before we arrive at a more complete understanding of visual perception.
Discrimination of Reflectance Changes under Simultaneous Illumination Changes
Authors: Plet S , Gerbino W
Published: December 2015

Relational colour constancy refers to the perception of constant relations among surface colours under illumination changes. We tested whether the ability of human observers to discriminate illumination from reflectance changes in a scene involves high-level attentional mechanisms. Observers were shown pairs of computer-generated Mondrian patterns with the number of patches varying between 2 and 49. On each trial a Mondrian pattern was presented for 1 s and replaced by a second pattern. In half of the trials in each experimental condition, the chromaticity of one patch was changed. Observers were required to discriminate whether a reflectance change occurred. Three conditions were run. In condition A, the illumination of the second Mondrian underwent a chromaticity change. In condition B, the chromaticity of the second Mondrian illumination remained constant, whereas its overall level was either increased or decreased. In condition C (control), the illumination was exactly the same in both Mondrians. Functions relating reaction time to number of patches in the display were compared. Data suggest that different mechanisms are involved in discriminating reflectance changes associated with different types of illuminant changes.
Evidence for a Dual Colour Code for ‘Object Colour’ and ‘Illumination Colour’ in Centre-Surround Configurations with Inhomogeneous Surrounds
Authors: Mausfeld R , Andres J
Published: December 2015

We provide evidence that the surround-dependent change in appearance of an infield in a centre - surround configuration is not to be understood as an elementary recoding of channels by a simple surround-dependent gain control but in fact mirrors the triggering of a much more complex mechanism for establishing a dual code for ‘object colour’ and ‘illumination colour’.

We constructed centre - surround configurations—referred to as Seurat configurations—whose surrounds are given by a random structure of overlapping circles of a fixed diameter. These surrounds have been spatially modulated along the red - green axis only (isoluminance condition), along the luminance axis only (isochromatic condition), and along both axes, while keeping the space average fixed. Unique yellow settings were made for the infield. Our results suggest that the visual system seems to interpret a reduced variance of receptor codes for the surround as an indication of an illuminant that has to be discounted at the location of the infield. Furthermore, for the case of an isoluminant surround with strong spatial red - green modulation only, the unique yellow settings strongly tend towards the ones of an achromatic surround, ie the surround seems to be almost ineffective with respect to a differential gain control.

While our data on Seurat configurations with same space-averaged surrounds refute simple notions of functional equivalence, they suggest an interpretation in terms of a triggering of elementary perceptual categories related to ‘object colour’ and ‘illumination colour’.