bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical capacitance of the unit cube
Authors: Hwang Chi-Ok , Mascagni Michael
Published: March 2004

It is well known that there is no analytical expression for the electrical capacitance of a cube, even though it has been claimed that one can compute this capacitance numerically to high precision. However, there have been some disparities between reported numerical results of the capacitance of the unit cube. In this article, the “walk on planes” (WOP) algorithm [M. L. Mansfield, J. F. Douglas, and E. J. Garboczi, Phys. Rev. E 64, 061401 (2001)] is used to compute the capacitance of the unit cube. With WOP, we remove the error from the ε-absorption layer commonly used in “walk on spheres” computations so that there is no inherent error introduced in these WOP computations except the intrinsic Monte Carlo sampling error of size O(N1/2). This WOP technique comes from the isomorphism, provided by probabilistic potential theory, between the electrostatic Dirichlet problem on a conducting surface, and the corresponding Brownian motion first-passage expectation. The numerical result we obtain with WOP, 0.660 678 2±1×10−7, supports the deterministic calculations by Read [F. H. Read, J. Comp. Phys. 133, 1 (1997)], the results by Given et al. [J. A. Given, J. B. Hubbard, and J. F. Douglas, J. Chem. Phys. 106, 3721 (1997)] and our previous results [C.-O. Hwang and M. Mascagni, J. Korean Phys. Soc. 42, L1 (2003); M. Mascagni and N. A. Simonov, J. Comp. Phys. (in press)]. Also, it is noted that the exact value conjectured by Hubbard and Douglas is inconsistent with our calculations, and that some other calculations fall outside our error bounds.
Influence of thickness and dielectric properties on implantation efficacy in plasma immersion ion implantation of insulators
Authors: Fu Ricky K. Y. , Chu Paul K. , Tian Xiubo
Published: March 2004

Plasma immersion ion implantation of insulators is an interesting topic both theoretically and industrially. The net energy of the incident ions is dictated by the surface potential and for conductors is equal to the voltage applied to the backside or sample stage. However, the poor electrical conductivity of insulating materials can lead not only to charging during ion bombardment but also reduced surface potential due to the capacitance effect. In the work described in this paper, we theoretically and experimentally investigate the influence of the thickness and dielectric properties of insulating materials on the implantation efficacy. The use of mesh-assisted PIII by covering the insulating materials with an electrically conducting cage to enhance the implantation efficacy is also compared experimentally. Our theoretical results suggest that a low plasma density induces less surface charges and higher surface potential. Our experimental data show good agreement with the theoretical results and mesh-assisted PIII does yield net improvement.
Intrinsic mechanical properties of diamond-like carbon thin films deposited by filtered cathodic vacuum arc
Authors: Gan Zhenghao , Zhang Yuebin , Yu Guoqing , Tan C. M. , Lau S. P. , Tay B. K.
Published: March 2004

The mechanical properties—Young’s modulus (E) and hardness (H)—of diamond-like carbon (DLC) thin films deposited on p2+ Si (100) by filtered cathodic vacuum arc with different substrate bias voltage have been studied by nanoindentation measurement, where the substrate effect is included. Their intrinsic properties [including E,H, and yield strength (Y)] without the substrate effect are then derived by finite element analysis. The results show that the intrinsic mechanical properties of the DLC thin films are not affected by the film thickness, but significantly affected by change of sp3 bonding fraction caused by varied substrate bias. An empirical relationship among E, Y, and H for DLC thin films has been built, where E, Y, and H are intrinsic properties of DLC thin films. It is also confirmed that, as an empirical rule, the measured H could be used to represent its intrinsic value when the indentation depth is limited to 10% of the film thickness. However, the measured E with the substrate effect does not observe this empirical rule.
Doping mechanism in aluminum doped zinc oxide films
Authors: Singh A. V. , Mehra R. M. , Yoshida A. , Wakahara A.
Published: March 2004

The doping mechanism in aluminum doped zinc oxide films has been interpreted by considering the relationship between Hall mobility and effective mass of electrons with carrier concentrations. Both degeneracy and the nonparabolic nature of the conduction band are taken into account for determining the charge state of the dopant. It is ascertained that aluminum liberates one free carrier in the zinc oxide lattice by substituting the zinc atom.
Phase-matched second-harmonic generation in bulk azodye-doped polymers by all-optical poling
Authors: Si Jinhai , Qiu Jianrong , Zhai Jianfeng , Shen Yuquan , Meng Zhichong , Hirao Kazuyuki
Published: March 2004

We demonstrate phase-matched second-harmonic generation (SHG) in bulk azodye-doped polymethylmethacrylate using an all-optical poling technique. During the seeding process, samples were irradiated simultaneously by coherent superposition of the fundamental and the second-harmonic light of a nanosecond laser. The measurements for the dependence of SHG on the sample thickness show that the SHG signals increase with the increase in thickness of the samples, indicating that a χ(2) grating that satisfies the phase-matching condition for SHG could be optically induced in the polymer samples.
Two types of magnetic vortex cores in elliptical permalloy dots
Authors: Okuno T. , Mibu K. , Shinjo T.
Published: March 2004

Elliptical (track-shaped) permalloy (Ni19Fe81) dots, in which magnetic circular vortex and antivortex structures are stabilized, were prepared and the magnetic properties of perpendicular magnetization spots (turned-up magnetizations) at the cores of both types of vortices were studied. Using magnetic force microscopy, the direction of the turned-up magnetization was detected and the switching field was measured. It was found that the value of the switching field of the turned-up magnetization at the antivortex core is smaller by about 1000 Oe than that at the circular vortex core. It was confirmed that the switching of the turned-up magnetization in the antivortex is not influenced by the directions of the turned-up magnetizations in the neighboring circular vortices. Vanishing and regenerating processes of turned-up magnetizations were observed by increasing and decreasing the magnetic field applied to the in-plane direction.
Effects of polarization on light propagation in laser-induced lens in guest host liquid crystals
Authors: Morisaki Takashi , Ono Hiroshi
Published: March 2004

Focal length of a laser-induced lens in guest-host liquid crystals (GHLCs) was varied over a wide range by using both large optical nonlinearity and anisotropic complex refractive indices in GHLCs. The characteristics of the laser-induced lens were strongly dependent on the polarization state of the probe beam because the sign of the refractive index change was negative for extraordinary wave, while positive for ordinary one. These characteristics were well explained by theoretical calculating both the optical and thermal properties of the GHLCs.
Magnetic switching properties of magnetic tunnel junctions using a synthetic ferrimagnet free layer
Authors: Nozaki T. , Jiang Y. , Sukegawa H. , Tezuka N. , Hirohata A. , Inomata K. , Sugimoto S.
Published: March 2004

Magnetic tunnel junctions (MTJs) using a synthetic ferrimagnet (SyF) free layer consisting of Co90Fe10/Ru/Co90Fe10 were deposited on a thermally oxidized Si substrate using an ultrahigh-vacuum sputtering system, and were patterned into micron to submicron sizes using electron-beam lithography and Ar ion milling. Magnetic switching properties and tunneling magnetoresistance (TMR) were investigated. A SyF free layer can maintain high remanence even for the aspect ratio of 1, and exhibits a size-independent switching field in all element widths from 0.25 to 16 μm investigated. Additionally, these MTJs show large TMR ratio up to 40% after annealing at 250 °C for 60 min. These results demonstrate that a SyF free layer can be applied to future spintronics nanodevices.
Influence of the surface tilt angle on the spatially periodic distortions in super-twisted nematic displays
Authors: Derfel G. , Krzyżański D.
Published: March 2004

Periodic deformation arising as parallel stripes in super-twisted nematic displays are studied numerically. The role played by a surface tilt angle δ in their appearance and structure is determined. It is found that the stripes exist in a narrow voltage range between two thresholds. The lower threshold at which they arise is practically independent of the tilt angle. The higher threshold at which the homogeneous deformation occurs decreases with δ. For relatively small twist angles (e.g., 180°) the transition to the homogeneously deformed structure is continuous. If the twist angle is high (e.g., 270°) this transition becomes discontinuous. The stripes are eliminated if the tilt angle exceeds some critical value which increases with the twist angle and may be larger than 30°.
Enhanced diffusion of germanium at the Au/Ge interface in the presence of water in a gold/germanium/nickel metal stack
Authors: Zhang S. , Dixon-Warren St. J. , Das S. R.
Published: March 2004

A stack of nickel/germanium/gold metal layers was deposited sequentially to form the n-ohmic contact as part of the fabrication of an indium phosphide-based infrared photodetector product. Concave circles with a cone at the center were observed under optical microscopy after a deionized (DI) water rinse following a metal lift-off process. Auger electron spectroscopy showed that the composition differed between the normal area of the metal surface and the area inside the concave circles. Inside the circles, the germanium on the top gold surface had been lost, and the germanium layer beneath the top Au layer was significantly reduced. The circle size was investigated experimentally and found to increase logarithmically with the exposure time in DI water. A diffusion model based on the results was developed to explain the growth kinetics of the concave circles. Mathematical simulations were performed with different values for the diffusion coefficient (D) for germanium. The simulated result agrees with experimental data when D=1.6×10−12 cm2/s, which is about one order of magnitude larger than that reported previously in literature for grain-boundary diffusion of Ge through gold.
Rotational spectrum of cis–cis HOONO
Authors: Drouin Brian J. , Fry Juliane L. , Miller Charles E.
Published: March 2004

The pure rotational spectrum of cis–cis peroxynitrous acid, HOONO, has been observed. Over 220 transitions, sampling states up to J′=67 and Ka′=31, have been fitted with an rms uncertainty of 48.4 kHz. The experimentally determined rotational constants agree well with ab initio values for the cis–cis conformer, a five-membered ring formed by intramolecular hydrogen bonding. The small, positive inertial defect Δ=0.075667(60) amu Å2 and lack of any observable torsional splittings in the spectrum indicate that cis–cis HOONO exists in a well-defined planar structure at room temperature.
A predictive model for the detachment of bubbles injected in a viscous shear flow with small inertial effects
Authors: Duhar Géraldine , Colin Catherine
Published: March 2004

Air bubble injection at the wall of a viscous shear flow is filmed using a high-speed video camera. The temporal evolution of the bubble radius and position of its center of gravity throughout its growth is determined from image processing. The experimental results are then used to validate a balance of the forces acting on the bubbles during their growth and after their detachment within the limit of small bubble Reynolds numbers. The contact angles calculated from the force balance agree well with those obtained by image processing. Finally, the force balance is used to predict the bubble radius at detachment versus the gas flow rate injected through the wall and the shear rate of the liquid flow.
Leading-edge tubercles delay stall on humpback whale (Megaptera novaeangliae) flippers
Authors: Miklosovic D. S. , Murray M. M. , Howle L. E. , Fish F. E.
Published: March 2004

The humpback whale (Megaptera novaeangliae) is exceptional among the baleen whales in its ability to undertake acrobatic underwater maneuvers to catch prey. In order to execute these banking and turning maneuvers, humpback whales utilize extremely mobile flippers. The humpback whale flipper is unique because of the presence of large protuberances or tubercles located on the leading edge which gives this surface a scalloped appearance. We show, through wind tunnel measurements, that the addition of leading-edge tubercles to a scale model of an idealized humpback whale flipper delays the stall angle by approximately 40%, while increasing lift and decreasing drag.
Turbulent drag reduction by Lorentz force oscillation
Authors: Pang Junguo , Choi Kwing-So
Published: March 2004

An experimental investigation into an electromagnetic technique to reduce skin-friction drag of turbulent boundary layers was conducted with an electroconductive solution in water, with potential applications to ships and underwater vehicles. We used an array of actuators made of permanent magnets interleaved with copper electrodes, which are set flush with the wall surface across the flow. This setup created the Lorentz force in the cross-flow direction within a thin region near the wall. More than 40% of turbulent skin-friction reductions were observed when the electromagnetic force is oscillated across the flow.
Intermittency effect on energy spectrum in high-Reynolds number turbulence
Authors: Tsuji Yoshiyuki
Published: March 2004

The energy spectrum in fully developed turbulence shows the power-law relation, E(k)∝k−(5/3+μ). The deviation from −5/3 is due to the effect of intermittency. Analyzing data in high-Reynolds number turbulence [Rλ≃O(104)], it was found that there are two different power-law regions in E(k). One locates close to the spectral bump and the other is in the lower wave number range. Intermittency corrections are μ=0.075 and μ=0.025, respectively. This result is compared with recent direct numerical simulations (Rλ≃1200) [Phys. Fluids 15, L21 (2003)] in which μ is not negligible, but is evaluated to be 0.1. We also comment on the Kolmogorov constant and the scaling exponent of velocity structure function.
Shock-Tube Studies of Thermal Ionization of NO using Mass Spectrometric Detection
Authors: Creswell R. A. , Di Valentin M. A. , Dove J. E.
Published: March 2004

Thermal ionization of gaseous 2% NO in Kr was studied in shock waves at temperatures of 3500-6100°K. Ions were identified and their concentrations were followed by direct sampling from the shock tube into a time-of-flight mass spectrometer. Rapid formation of NO+ was observed, and an apparent energy of activation of 5.0 ± 0.2 eV was measured for the reaction forming the ions. The mechanism of ion formation is discussed.
Steady-State Assumption and the Dissociation of Br2 in Shock Waves
Authors: Lawrence T. R. , Burns George
Published: March 2004

The rate of dissociation of Br2 molecules in an excess of argon has been measured, using a method based on determination of the emission intensity behind the shock front. The emission is a function of the concentration of bromine atoms and is insensitive to the state of vibrational excitation of Br2. There is a fair agreement over a wide temperature range between the new data and the data of previous investigators. However, at the lowest and the highest temperatures attainable, the rate constants obtained by the previous investigators are about twice the rate constants obtained by the new method. This discrepancy exceeds the standard deviation of experimental results and may be tentatively explained by assuming that in previous investigations, the combined rate of vibrational relaxation and dissociation was observed, while in the present work, the true dissociation rate constants were determined.
Current Status of Research on Electromagnetically Produced Unsteady Shock Waves
Authors: Muntenbruch Helmut
Published: March 2004

Fast shock waves in light gases can be produced simply by electromagnetic acceleration. Unlike rail spark gaps or magnetic annular tubes, which produce quasistationary, shock-wavelike phenomena, T tubes and conical theta pinches or Z pinches generate nonstationary shock waves of the blast wave type if the plasma of the driving discharge does not advance right into the shock front and appreciably influence the plasma formed there. The investigations of free-running shock waves and the distributions of the parameters in the plasmas behind these shock fronts are discussed. Shadowgraphs, interferograms, microwave interferograms and probe measurements have afforded a fairly complete picture of such nonstationary waves revealing their uses and limitations.
Steady Expansion of Shock-Heated Gases for Recombination Studies
Authors: Slack M. W. , Bray K. N. C. , East R. A. , Pratt N. H.
Published: March 2004

An analysis has been undertaken of the conditions for which Wilson's technique involving the steady Prandtl-Meyer expansion of shock-heated gases is applicable. Experimental evidence for the predicted flow regimes is described, including measurements of static pressure, stagnation point heat transfer, infrared emission and optical absorption. Work involving iodine recombination is mentioned briefly.
Chemical Overshoot: Thermal Dissociation of Alkali Halide Molecules
Authors: Coplan M. , Cernoch T. , Berry R. S.
Published: March 2004

The dissociation of CsBr molecules in shock-heated argon has been studied with time-resolved absorption spectroscopy. The time dependencies of the intensities of principal series lines of Cs0 and of the photodetachment continuum of Br− show that the primary dissociation products are principally the ions Cs+ and Br−. Attainment of chemical equilibrium concentrations of ions, electrons and neutrals occurs much more slowly.
Shock-Tube Study of OH (2Σ — 2Π) Luminescence
Authors: Gardiner W. C. , Morinaga K. , Ripley D. L. , Takeyama T.
Published: March 2004

OH (2Σ — 2Π) emission was studied in 1500-2800°K incident shock waves through low-pressure H2-O2-Ar mixtures with 100-fold variation in H2/O2 ratio. The transition from chemiluminescent to thermal excitation was found to occur near 2000-2200°K for these conditions. Intensities measured during the exponential growth period and in the partial equilibrium state following combustion were correlated with possible elementary reactions producing OH(2Σ).
Calibration of Shock Tubes for Studying Aerodynamic Loading
Authors: Dewey John M. , Anson W. A.
Published: March 2004

In a simple shock tube the physical parameters behind the shock cannot be determined from the measurement of a single parameter, such as the pressure, because of uncertainties about the state of the gas in this region. Results are shown which illustrate two causes of this uncertainty: (a) the mixing of the driver and expansion chamber gases, and (b) the variation of the shock strength along the tube. The problem can be overcome by observing the particle trajectories throughout the tube. This is done by high-speed photography of smoke tracers, and it is shown that the technique permits a determination of all the physical parameters of the flow without reference to other measurements.
Digital Measurements of the Speed Variations of Shock Waves by Means of Microwaves
Authors: Koch B. , König M.
Published: March 2004

The thermodynamic state of the flow within a diaphragm shock tube, or within that provided by a shock tube used to drive a tunnel, can be determined precisely only if the variations in shock front velocity within the tube are known accurately. A method of shock velocity measurement applicable to this problem has been developed which makes use of the Doppler effect measured in microwave signals reflected from the ionized shock front. The system employs electronic counting of a given number (n) of periods of the Doppler beat between the emitted and reflected wave trains. Contiguous time measurements corresponding to consecutive shock traversals of the distance n(λi/2) (wherein λi is wavelength within the shock tube) are recorded by an appropriate number of sequentially operated counters. The microwave energy is introduced into the shock tube by a loop antenna which is located in such a way that it neither protrudes into the tube nor interferes with the flow of gas. A few typical experimental results demonstrate the applicability of the method at Mach numbers of 8 and above. The method provides velocity measurements over 85-cm reference distances with limits of error of the order of one part in 103. Accuracy can be improved by employing higher-frequency counters.
Experimental Study of the Starting Process in a Reflection Nozzle
Authors: Amann H. O.
Published: March 2004

The unsteady events occurring during the time after the shock enters the nozzle of a shock tunnel and until a steady flow is established have been investigated for a two-dimensional reflection nozzle by multiple shadowgraphs and interferograms. The influences of different parameters (nozzle half-angle, throat width, and nozzle inlet radius) on the starting process are presented on x-t diagrams for the incident shock Mach number MS = 3. The density along the nozzle axis is presented at several times during the starting process.
Diffraction of a Shock Wave by a Cylinder
Authors: Heilig W. H.
Published: March 2004

The propagation of plane shock waves around cylinders of various radii was recorded with shadowgrams using a Cranz-Schardin multiple spark camera and with single Mach-Zehnder interferograms. The range of the incident shock Mach numbers extends from 1.04 to 2.2. Regular reflection and transition to Mach reflection are seen as the incident shock proceeds. From shadowgrams made at about 1 μsec intervals during this process the critical angle of transition was measured. The limiting angle of two shock theory fails to agree with the measured value. A theory of Whitham which requires the critical angle as well as the incident shock Mach number as initial values was applied to predict the triple point locus and the contour of the Mach stems. Numerical calculations using both the theoretical and the measured value of the critical angle for a fixed shock Mach number produced triple point loci lying close together. The predicted contour of the Mach stem and the density jump across it agree with the observations to within experimental error.
Streak-Interferometric Studies of Head Wave Standoff in a Shock Tunnel
Authors: Smeets G.
Published: March 2004

By means of streak-interferometry, test times are measured in (1) a conventional pressure driven shock tube, (2) a shock tube and diverging nozzle, and (3) a hypersonic expansion tunnel. A sphere was suspended in the flow and the distance at which the detached shock comes to rest was recorded. For case (1) good agreement with Mirels' theory was found. In cases (2) and (3) where no theory is available, oblique shocks were seen to disturb uniform flow.
Evidence for Re-Reflected Shock Waves behind Taper Sections
Authors: Low W. , Shtricker J.
Published: March 2004

Aspects of the wave generation and propagation in a one-dimensional treatment of flow in a tube with changing cross section in one segment are presented and discussed. Measurements made by shock wave detectors, microwave absorption, and optical emission combine to show that a compression wave generated in a converging section is reflected from the diaphragm cold front to produce a second shock front.
Investigation of the Attenuation of Shock Waves through Multiple Reflection in a Shock Tube
Authors: Rückauer Ch.
Published: March 2004

The time decay of a shock wave due to repeated reflections at the ends and interactions with the expansion wave is observed by means of a capacitor-microphone pressure transducer. After the first three or four reflections the decay becomes exponential.
Contributions of H. Schardin to the Theory and Applications of the Shock Tube
Authors: Reichenbach H.
Published: March 2004

The theory of the ideal shock tube was first given by Hubert Schardin in 1932 and some of the earliest studies of shock tube performance were then made. These early studies are recalled as well as more recent studies initiated by Schardin on the topic of shock tubes. His other contributions to the physics of rapidly occurring events are also described.
Construction of a Shock Tube for Metallic Vapors
Authors: Kim Yong Wook , Laporte Otto
Published: March 2004

The construction and operation of a heated shock tube (often called mercury shock tube due to its immediate application) are described in some detail. Experimental observations of strong shocks in mercury gas are presented and discussed in the light of preliminary theoretical investigation. An observation of reflected shock bifurcation in the monatomic gas of mercury is also reported.
Structure of Strong Shock Waves
Authors: Turcotte D. L. , Scholnick I. M.
Published: March 2004

A model is proposed for the structure of strong shock waves which explicitly accounts for the existence of a near molecular beam, hypersonic flow upstream, and of a subsonic, hot continuum flow downstream. This is accomplished by considering the conversion of the beam into the continuum through collisions. Appropriate continuum equations are derived including the input of mass, momentum, and energy from the beam particles. The particles in the molecular beam are assumed to be converted into members of the continuum in a single collision; and the collision transport phenomena associated with the continuum are assumed to be governed by the Chapman-Enskog expressions. Comparisons with other models for shock structure and with experimental results are given. In view of its simplicity the present model should be applicable to other hypersonic, rarefied flow problems.
Measurement of the Shock Structure in N2-H2 Gas Mixtures
Authors: Beylich Alfred E.
Published: March 2004

An optical electron beam method is used to measure profiles of shock waves traveling in a shock tube. In particular, partial density profiles of nitrogen in N2-H2 gas mixtures are obtained. Because of the stochastic nature of the noisy signals obtained from the photomultiplier, a superposition method is used by which the noise-to-signal ratio is successfully reduced. Density profiles for different concentrations of N2 down to 5% were measured. Measured values of shock thickness do not agree with results predicted by Navier-Stokes calculations. In particular, the measurements indicate that the typical overshoot predicted by the calculations does not exist.
Thermal Conductivity of Shock-Heated Argon
Authors: Bunting J. O. , Devoto R. S. , Bershader D.
Published: March 2004

Optical interferograms have been taken of the thermal layer formed at the end wall of a shock tube after reflection of the incident shock. With the aid of suitable boundary-layer equations, six of these interferograms taken with argon as test gas, have been analyzed under the assumption that the thermal conductivity varies as Tν. The average measured thermal conductivity is then represented by K = 4.25 × 10−5 (T/300)0.66 cal/cm sec°K.
Shock Tube with Implosive Jet Driver
Authors: Gill Stephen P.
Published: March 2004

A shock tube with an implosive jet driver has been investigated both theoretically and experimentally. The implosive driver consists of a cylinder of high explosive that progressively implodes the glass walls of a shock tube and projects a diffuse jet of glass particles into the shock tube. A tentative theory of the implosion process and jet formation is presented and compared with experimental data. It is shown that the jet of glass particles has an initial velocity equal to twice the detonation velocity of the explosive, and that the diffuse jet acts like a solid piston when the Reynolds number of the glass particles is less than unity.
Response Inhibition Can Affect Reaction Time to Abrupt-Onset Visual Displays
Authors: Gellatly Angus , Cole Geoff , Fox Claire , Johnson Matthew
Published: March 2004

Reaction time (RT) to abrupt-onset stimuli has been widely used for more than a century to measure the duration of perceptuo-cognitive and motor processes [Donders, 1868/1969 Attention and Performance II (1969 Acta Psychologica30 412–431)]. A complicating factor with the RT method is that of response withholding, or response inhibition (RI). The occurrence of RI (under this or other names) has been widely discussed in relation to studies of motor processes but has been largely ignored in relation to studies of perceptuo-cognitive processes. We demonstrate that RI can be a confounding factor when RT to abrupt-onset displays is used to study perceptual and cognitive processes. In experiment 1, new-object targets were more accurately detected than old-object targets in an unspeeded task, but were responded to more slowly in an RT task. Consistent with an interpretation in terms of RI, this pattern of results was dependent on the difficulty of target detection. The data of three further experiments also support predictions from the RI interpretation. It is suggested that RI may be an under-acknowledged factor in RT studies of perceptual and cognitive processes with abrupt-onset displays.
Detection of Amplitude Modulation and Frequency Modulation in Tactual Gratings: A Critical Bandwidth for Active Touch
Authors: Nefs Harold T , Kappers Astrid M L , Koenderink Jan J
Published: March 2004

Since most natural surfaces are complex and vary in amplitude and spatial frequency, it might be interesting to consider gratings not in the spatial domain, but in the spatial-frequency domain. Detection thresholds for amplitude modulation (AM) and frequency modulation (FM) in sinusoidal gratings were measured for seven participants. Participants moved their fingers actively across the gratings. Although the two types of modulation are quite different in the spatial domain, they have many features in common in the frequency domain. In previous research (Nefs et al 2001 Perception30 1263–1274) we measured the discrimination thresholds for amplitude and frequency for sinusoidal gratings. We hypothesised then that these thresholds could be used to predict the discriminability of other types of gratings. In the present study, we did indeed find that the FM and AM detection thresholds can be understood quite well by these discrimination thresholds. The results indicate that the tactual system contains parallel psychophysical channels that filter and integrate the power of stimuli within critical bands. With these results, we are also able to calculate the critical bandwidth for active dynamic touch. We estimated the critical bandwidth surrounding the spatial frequency of 2 cycles cm−1 to be about 125% of that spatial frequency. This value for the critical band for spatial frequency is incompatible with previous findings for temporal frequencies in vibrotactile research. This indicates that dynamic spatial-frequency discrimination is not likely to be done by temporal frequency.
Configural Processing in the Perception of Eye-Gaze Direction
Authors: Jenkins Jenny , Langton Stephen R H
Published: March 2004

Traditional accounts of gaze perception emphasise the geometric or configural cues present in the eye; the position of the iris in relation to the corner of the eye, for example. This kind of geometric account has been supported, in part, by findings that gaze judgments are impaired in faces rotated through 180°, a manipulation known to disrupt the processing of relations between facial elements. However, studies involving this manipulation have confounded inversion of the face context with inversion of the eye region. The effects of inversion might therefore have been caused by a disruption of the computation of gaze direction from the eye region itself and/or a disruption of the influence that face context might exert on gaze processing. In the experiment reported here we independently manipulated eye orientation and the orientation of the face context, and measured participants' sensitivity to gaze direction. Performance was severely affected by inversion of the eyes, regardless of the orientation of the face, whereas face inversion had no significant effect on gaze sensitivity. Previous reports of a face-inversion effect on gaze perception can therefore be attributed to inversion of the eye region itself which, we suggest, disrupts some form of configural or relational processing that is normally involved in the computation of eye-gaze direction.
The Perception of Minimal Structures: Performance on Open and Closed Versions of Visually Presented Euclidean Travelling Salesperson Problems
Authors: Vickers Douglas , Bovet Pierre , Lee Michael D , Hughes Peter
Published: March 2004

The planar Euclidean version of the travelling salesperson problem (TSP) requires finding a tour of minimal length through a two-dimensional set of nodes. Despite the computational intractability of the TSP, people can produce rapid, near-optimal solutions to visually presented versions of such problems. To explain this, MacGregor et al (1999, Perception28 1417–1428) have suggested that people use a global-to-local process, based on a perceptual tendency to organise stimuli into convex figures. We review the evidence for this idea and propose an alternative, local-to-global hypothesis, based on the detection of least distances between the nodes in an array. We present the results of an experiment in which we examined the relationships between three objective measures and performance measures of optimality and response uncertainty in tasks requiring participants to construct a closed tour or an open path. The data are not well accounted for by a process based on the convex hull. In contrast, results are generally consistent with a locally focused process based initially on the detection of nearest-neighbour clusters. Individual differences are interpreted in terms of a hierarchical process of constructing solutions, and the findings are related to a more general analysis of the role of nearest neighbours in the perception of structure and motion.
Haptics and Projection: Drawings by Tracy, a Blind Adult
Authors: Kennedy John M , Juricevic Igor
Published: March 2004

Outline drawings in a raised form were made by a blind woman, Tracy, who has been blind from very early in life. Highly practiced in drawing, she reports she is largely self-taught. To invoke matters of projection, she was asked to represent an object with faces slanting away from the observer, a fixed array from different vantage points, and sets of objects in depth. In particular, she drew a cube balanced on a vertex, three objects from different vantage points, receding rows of glasses, and a house. Her drawings included features of parallel and polar projection. Her use of these features may reflect an appreciation of direction from a vantage point, which observers deal with via haptics in everyday tasks. Tracy may have advanced drawing-development skills common to the blind and the sighted.
Visual Processing of Coherent Rotation in the Central Visual Field: An fMRI Study
Authors: Könönen Mervi , Pääkkönen Ari , Pihlajamäki Maija , Partanen Kaarina , Karjalainen Pasi A , Soimakallio Seppo , Aronen Hannu J
Published: March 2004

Functional magnetic resonance imaging was used to determine the brain areas that process coherent motion. To reduce the activity related to eye-movement planning and self-motion perception, rotation was used as coherent motion and the stimulus was restricted to the central visual field. Coherent rotation relative to incoherent random-dot motion resulted in consistent activation in the superior parietal lobule (SPL), in the lateral occipital gyrus (presumptive kinetic occipital region, KO), and in the fusiform gyrus (FG). The main novel finding in present study is the bilateral SPL activation, which has not been found in any previous study contrasting coherent and incoherent motion. It is suggested that the SPL activation is related to form-from-motion processing. The stimulus modification that prevented abrupt appearances of dots at the borders of the stimulus field increased the strength of rolling disk-like percept of the coherent stimulus. This perception of form may also be at least partly responsible for the activation in KO and FG. With this explanation, our three consistent activation areas are in line with previous findings. Furthermore, these results demonstrate that even delicate changes in some stimulus aspects can lead to significant changes in the activation of the brain.
Anomalous Induction of Brightness and Surface Qualities: A New Illusion Due to Radial Lines and Chromatic Rings
Authors: Pinna Baingio , Spillmann Lothar , Werner John S
Published: March 2004

When a chromatic (eg light-blue) annulus surrounds the central gap of an Ehrenstein figure so as to connect the inner ends of the radial lines, a striking new lightness effect emerges: the central white disk has both a self-luminous quality (brighter than in the regular Ehrenstein figure) and a surface quality (dense, paste-like). Self-luminous and surface qualities do not ordinarily appear co-extensively: hence, the brightness induction is called anomalous. In experiment 1, subjects separately scaled self-luminous and surface properties, and in experiment 2, brightness was nulled by physically darkening the central gap. Experiments 3 and 4 were designed to evaluate the importance of chromatic versus achromatic properties of the annulus; other aspects of the annulus (width or the inclusion of a thin black ring inside or outside the chromatic annulus) were tested in experiments 5–7. In experiments 8–12, subjects rated the brightness of modified Ehrenstein figures varying the radial lines (number, length, width, contrast, arrangement). Variation of these parameters generally affected brightness enhancement in the Ehrenstein figure and anomalous brightness induction in a similar manner, but was stronger for the latter effect. On the basis of these results, anomalous brightness induction is attributed to a surface induction process triggered by an interaction between illusory brightness enhancement (due to the radial lines) and border ownership (due to the blue annulus).
Face Detection: Mapping Human Performance
Authors: Lewis Michael B , Edmonds Andrew J
Published: March 2004

The recognition of faces has been the focus of an extensive body of research, whereas the preliminary and prerequisite task of detecting a face has received limited attention from psychologists. Four experiments are reported that address the question how we detect a face. Experiment 1 reveals that we use information from the scene to aid detection. In experiment 2 we investigated which features of a face speed the detection of faces. Experiment 3 revealed inversion effects and an interaction between the effects of blurring and reduction of contrast. In experiment 4 the sizes of effects of reversal of orientation, luminance, and hue were compared. Luminance was found to have the greatest effect on reaction time to detect faces. The results are interpreted as suggesting that face detection proceeds by a pre-attentive stage that identifies possible face regions, which is followed by a focused-attention stage that employs a deformable template. Comparisons are drawn with automatic face-detection systems.
Visually Perceived Eye Level with Reversible Pitch Stimuli: Implications for the Great Circle and Implicit Surface Models
Authors: Post Robert B , Teague Jacque M , Welch Robert B , Hudson Todd E
Published: March 2004

Visually perceived eye level (VPEL) and perceived pitch were measured while subjects viewed two sets of stimuli that were either upright or pitched top-toward or top-away from them. The first set of stimuli, a pair of vertical lines viewed at various angles of pitch, caused systematic changes in perceived pitch and upward and downward VPEL shifts for the top-toward and top-away pitches, respectively. Neither the perceived pitch nor the VPEL measures with these stimuli differed between monocular and binocular viewing. The second set of stimuli was constructed so that, when viewed at the appropriate pitch angle, the projected orientations of the lines in the retinal image of each stimulus were similar to those generated by a pair of vertical lines pitched by a lesser amount in the opposite direction. When viewed monocularly, these stimuli appeared pitched in the direction opposite their physical pitch, yet produced VPEL shifts consistent with the direction of their physical pitch. These results clearly demonstrate a dissociation between perceived pitch and VPEL. The same stimuli, when viewed binocularly, appeared pitched in the direction of their physical pitch and caused VPEL shifts indistinguishable from those obtained monocularly. The retinal image orientations of these stimuli, however, corresponded to those of vertical line stimuli pitched in the opposite direction. This finding is therefore consistent with the hypothesis that VPEL and perceived pitch are processed independently, but inconsistent with the specific version of this hypothesis which states that differences in VPEL are determined solely on the basis of the orientation of lines in the retinal image.
The Relationship between Change Detection and Recognition of Centrally Attended Objects in Motion Pictures
Authors: Angelone Bonnie L , Levin Daniel T , Simons Daniel J
Published: March 2004

Observers typically detect changes to central objects more readily than changes to marginal objects, but they sometimes miss changes to central, attended objects as well. However, even if observers do not report such changes, they may be able to recognize the changed object. In three experiments we explored change detection and recognition memory for several types of changes to central objects in motion pictures. Observers who failed to detect a change still performed at above chance levels on a recognition task in almost all conditions. In addition, observers who detected the change were no more accurate in their recognition than those who did not detect the change. Despite large differences in the detectability of changes across conditions, those observers who missed the change did not vary in their ability to recognize the changing object.
Does Interhemispheric Competition Mediate Motion-Induced Blindness? A Transcranial Magnetic Stimulation Study
Authors: Funk Agnes P , Pettigrew John D
Published: March 2004

Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stationary targets disappear and reappear in a cyclic mode when viewed against a background (mask) of coherent, apparent 3-D motion. Since MIB has recently been shown to share similar temporal properties with binocular rivalry, we probed the appearance–disappearance cycle of MIB using unilateral, single-pulse transcranial magnetic stimulation (TMS)—a manipulation that has previously been shown to influence binocular rivalry. Effects were seen for both hemispheres when the timing of TMS was determined prospectively on the basis of a given subject's appearance–disappearance cycle, so that it occurred on average around 300 ms before the time of perceptual switch. Magnetic stimulation of either hemisphere shortened the time to switch from appearance to disappearance and vice versa. However, TMS of left posterior parietal cortex more selectively shortened the disappearance time of the targets if delivered in phase with the disappearance cycle, but lengthened it if TMS was delivered in the appearance phase after the perceptual switch. Opposite effects were seen in the right hemisphere, although less marked than the left-hemisphere effects. As well as sharing temporal characteristics with binocular rivalry, MIB therefore seems to share a similar underlying mechanism of interhemispheric modulation. Interhemispheric switching may thus provide a common temporal framework for uniting the diverse, multilevel phenomena of perceptual rivalry.
An Encoding Advantage for Own-Race versus Other-Race Faces
Authors: Walker Pamela M , Tanaka James W
Published: March 2004

Studies have shown that individuals are better able to recognise the faces of people from their own race than the faces of people from other races. Although the so-called own-race effect has been generally regarded as an advantage in recognition memory, differences in the processing of the own-race versus other-race faces might also be found at the earlier stages of perceptual encoding. In this study, the perceptual basis of the own-race effect was investigated by generating a continuum of images by morphing an East Asian parent face with a Caucasian parent face. In a same/different discrimination task, East Asian and Caucasian participants judged whether the morph faces were physically identical to, or different from, their parent faces. The results revealed a significant race-of-participant by race-of-face interaction such that East Asian participants were better able to discriminate East Asian faces, whereas Caucasian participants were better able to discriminate Caucasian faces. These results indicate that an own-race advantage occurs at the encoding stage of face processing.
“A Moment's Monument”: The Central Vision of Italian Sculptor Medardo Rosso (1858–1928)
Authors: Melcher David , Bacci Francesca
Published: March 2004

One of the basic limitations on visual perception is that it is impossible, in any given moment, to see the world sharply and full of colors beyond the central area of the visual field. This fact was popularized and brought to the attention of artists in the nineteenth century. To accurately represent the ‘impression’, or vision of a single glance, an artistic work should contain only a central area in focus surrounded by a progressively greater blur. The work of the Italian sculptor Medardo Rosso (1858–1928) may be the first artistic representation of differences in central and peripheral acuity. Despite using the medium of sculpture, typically three-dimensional, Rosso conceived of his art as two-dimensional because in a given moment it is possible to view a scene from only one viewpoint. The analysis of Rosso's photographs of his own sculptures emphasizes the areas of detail and relative blur, allowing a reconstruction of his point de vue unique—where the observer should stand when viewing that specific sculpture. We argue that the role of central and peripheral vision in subjective perception is critical to understanding the work of Rosso, aptly defined by critics as monument d'un instant.