bluuebunny/crossref_metadata_2025 huggingface dataset:
TRPM channel function in Caenorhabditis elegans
Authors: Baylis H.A. , Goyal K.
Published: January 2007

The nematode Caenorhabditis elegans contains over 20 genes for TRP (transient receptor potential) channels which include members of all of the subclasses identified in mammalian cells. These proteins include three members of the TRPM (TRP melastatin) family: gon-2 (abnormal gonad development), gtl-1 (gon-2-like 1) and gtl-2. Although studies of these genes are at an early stage, we are beginning to understand their functions in the life of C. elegans. Mutations in gon-2 have defective gonad formation because of failures in the cell division of the somatic gonad precursor cells. gon-2 and gtl-1 are both expressed in the intestine of the animal. Experiments on gon-2,gtl-1 double mutants show that they have a severe growth defect that is ameliorated by the addition of high levels of Mg2+ to the growth medium. gon-2,gtl-1 double mutants have defective magnesium homoeostasis and also have altered sensitivity to toxic levels of Ni2+. Furthermore gon-2 mutants have reduced levels of IORCa (outwardly rectifying calcium current) in the intestinal cells. Thus these two channels appear to play an important role in cation homoeostasis in C. elegans. In addition, perturbing the function of gon-2 and gtl-1 disrupts the ultradian defecation rhythm in C. elegans, suggesting that these channels play an important role in regulating this calcium-dependent rhythmic process. The tractability of C. elegans as an experimental animal and its amenability to techniques such as RNAi (RNA interference) and in vivo imaging make it an excellent system for an integrative analysis of TRPM function.
Interactions of PIN and PGP auxin transport mechanisms
Authors: Bandyopadhyay A. , Blakeslee J.J. , Lee O.R. , Mravec J. , Sauer M. , Titapiwatanakun B. , Makam S.N. , Bouchard R. , Geisler M. , Martinoia E. , Friml J. , Peer W.A. , Murphy A.S.
Published: January 2007

Polarized transport of the plant hormone auxin influences multiple growth processes in plants and is regulated by plasma-membrane-localized efflux and uptake carriers. The PGP (P-glycoprotein) ABC transporters (ATP-binding-cassette transporters), PIN (pin-formed) subfamily of major facilitator proteins and members of AUX/LAX families have been shown to independently transport auxin both in planta and in heterologous systems. However, PIN- and PGP-mediated transport in heterologous systems exhibits decreased substrate specificity and inhibitor-sensitivity compared with what is seen in plants and plant cells. To determine whether PIN–PGP interactions enhance transport specificity, we analysed interactions of the representative auxin-transporting PGPs with PIN1 and AUX1 in planta and in heterologous systems. Here, we provide evidence that PINs and PGPs interact and function both independently and co-ordinately to control polar auxin transport and impart transport specificity and directionality. These interactions take place in protein complexes stabilized by PGPs in detergent-resistant microdomains.
Planar polarity of root hair positioning in Arabidopsis
Authors: Fischer U. , Ikeda Y. , Grebe M.
Published: January 2007

The co-ordinated polarity of cells within the plane of a single tissue layer (planar polarity) is intensively studied in animal epithelia but has only recently been systematically analysed in plants. The polar positioning of hairs in the root epidermis of Arabidopsis thaliana provides an easily accessible system for the functional dissection of a plant-specific planar polarity. Recently, mutants originally isolated in genetic screens for defects in root hair morphogenesis and changes in the sensitivity to or the production of the plant hormones auxin and ethylene have identified players that contribute to polar root hair placement. Here, we summarize and discuss recent progress in research on polar root hair positioning from studies in Arabidopsis.
Cell signalling during vascular morphogenesis
Authors: Helariutta Y.
Published: January 2007

Vascular tissue in plants is unique due to its diverse and dynamic cellular patterns. Through research in several organisms, such as Arabidopsis, Populus and Zinnia, using biochemical, genetic and genomic approaches, significant progress has recently been made in revealing the molecular nature of several signals underlying the patterning of vascular tissue. These signals include ligands, receptors and transcriptional regulators. The future challenge is to understand how the identified signals work together to control vascular morphogenesis.
Signalling during epidermal development
Authors: Ingram G.C.
Published: January 2007

The process of L1 specification early in plant embryogenesis, and subsequent maintenance and elaboration of epidermal organization, are fundamental to plant growth and fitness. To occur in a co-ordinated fashion, these processes require considerable cell–cell cross-talk. It is perhaps then unsurprising that several classes of plant RLKs (receptor-like kinases), as well as other membrane-localized signalling components, have been implicated both in epidermal specification and in patterning events governing the distribution of epidermal cell types. However, despite our growing knowledge of the roles of these signalling molecules, remarkably little is understood regarding their function at the cellular level. In particular the potential role of regulated proteolytic cleavage in controlling the activity of signalling molecules at the plant plasma membrane has remained largely unaddressed despite its massive importance in signalling in animal systems. Because of the relative physical accessibility of their expression domains, molecules involved in epidermal development present opportunities for investigating mechanisms of cell–cell signalling in planta. Advances in understanding the potential regulatory processing of membrane-localized signalling molecules during epidermal development will be examined using parallels with animal systems to highlight potential future directions for this field of research.
Lorentzian version of the noncommutative geometry of the standard model of particle physics
Authors: Barrett John W.
Published: January 2007

A formulation of the noncommutative geometry for the standard model of particle physics with a Lorentzian signature metric is presented. The elimination of the fermion doubling in the Lorentzian case is achieved by a modification of Connes’ internal space geometry [“Gravity coupled with matter and the foundation of non-commutative geometry,” Commun. Math. Phys. 182, 155–176 (1996)] so that it has signature 6 (mod 8) rather than 0. The fermionic part of the Connes-Chamseddine spectral action can be formulated, and it is shown that it allows an extension with right-handed neutrinos and the correct mass terms for the seesaw mechanism of neutrino mass generation.
Unimolecular thermal fragmentation ofortho-benzyne
Authors: Zhang Xu , Maccarone Alan T. , Nimlos Mark R. , Kato Shuji , Bierbaum Veronica M. , Ellison G. Barney , Ruscic Branko , Simmonett Andrew C. , Allen Wesley D. , Schaefer Henry F.
Published: January 2007

The ortho-benzyne diradical, o-C6H4 has been produced with a supersonic nozzle and its subsequent thermal decomposition has been studied. As the temperature of the nozzle is increased, the benzyne molecule fragments: o-C6H4+Δ→ products. The thermal dissociation products were identified by three experimental methods: (i) time-of-flight photoionization mass spectrometry, (ii) matrix-isolation Fourier transform infrared absorption spectroscopy, and (iii) chemical ionization mass spectrometry. At the threshold dissociation temperature, o-benzyne cleanly decomposes into acetylene and diacetylene via an apparent retro-Diels-Alder process: o-C6H4+Δ→HCCH+HCC–CCH. The experimental ΔrxnH298(o-C6H4→HCCH+HCC–CCH) is found to be 57±3kcalmol−1. Further experiments with the substituted benzyne, 3,6-(CH3)2-o-C6H2, are consistent with a retro-Diels-Alder fragmentation. But at higher nozzle temperatures, the cracking pattern becomes more complicated. To interpret these experiments, the retro-Diels-Alder fragmentation of o-benzyne has been investigated by rigorous ab initio electronic structure computations. These calculations used basis sets as large as [C(7s6p5d4f3g2h1i)∕H(6s5p4d3f2g1h)] (cc-pV6Z) and electron correlation treatments as extensive as full coupled cluster through triple excitations (CCSDT), in cases with a perturbative term for connected quadruples [CCSDT(Q)]. Focal point extrapolations of the computational data yield a 0K barrier for the concerted, C2v-symmetric decomposition of o-benzyne, Eb(o-C6H4→HCCH+HCC–CCH)=88.0±0.5kcalmol−1. A barrier of this magnitude is consistent with the experimental results. A careful assessment of the thermochemistry for the high temperature fragmentation of benzene is presented: C6H6→H+[C6H5]→H+[o-C6H4]→HCCH+HCC–CCH. Benzyne may be an important intermediate in the thermal decomposition of many alkylbenzenes (arenes). High engine temperatures above 1500K may crack these alkylbenzenes to a mixture of alkyl radicals and phenyl radicals. The phenyl radicals will then dissociate first to benzyne and then to acetylene and diacetylene.
Soft recovery of polytetrafluoroethylene shocked through the crystalline phase II-III transition
Authors: Brown E. N. , Trujillo C. P. , Gray G. T. , Rae P. J. , Bourne N. K.
Published: January 2007

Polymers are increasingly being utilized as monolithic materials and composite matrices for structural applications historically reserved for metals. High strain-rate applications in aerospace, defense, and the automotive industries have lead to interest in the shock response of polytetrafluoroethylene (PTFE) and the ensuing changes in polymer structure due to shock prestraining. We present an experimental study of crystalline structure evolution due to pressure-induced phase transitions in a semicrystalline polymer using soft-recovery, shock loading techniques coupled with mechanical and chemical postshock analyses. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition. Below the phase transition only subtle changes were observed in the crystallinity, microstructure, and mechanical response of PTFE. Shock loading of PTFE 7C above the phase II-III transition was seen to cause both an increase in crystallinity from 38% to ∼53% (by differential scanning calorimetry) and a finer crystalline microstructure, and changed the yield and flow stress behavior.
Ti
O
2
breakdown under pulsed conditions
Authors: Zhao G. , Joshi R. P. , Lakdawala V. K. , Schamiloglu E. , Hjalmarson H.
Published: January 2007

Model studies of current conduction and breakdown in TiO2 were carried out. Our simulation results indicate that electrical breakdown of TiO2 under multiple-pulsed conditions can occur at lower voltages as compared to quasi-dc biasing. This is in agreement with recent experimental data and is indicative of a cumulative phenomena. We demonstrate that the lower breakdown voltages observed in TiO2 under pulsed conditions is a direct rise-time effect, coupled with successive detrapping at the grain boundaries.
Influence of modifier oxides on the structural and optical properties of binary TeO2 glasses
Authors: Rivero C. , Stegeman R. , Richardson K. , Stegeman G. , Turri G. , Bass M. , Thomas P. , Udovic M. , Cardinal T. , Fargin E. , Couzi M. , Jain H. , Miller A.
Published: January 2007

Five different glass compositions with equal TeO2 molar concentration and various intermediate constituents were prepared to examine the influence of such intermediate species on the tellurite network. A correlation between the glasses’ structural network and optical properties is presented. Peak Raman gain coefficients, on the order of 40 times the gain of SiO2, are reported in this paper.
Analysis of carrier injection into a pentacene field effect transistor by optical second harmonic generation measurements
Authors: Lim Eunju , Manaka Takaaki , Iwamoto Mitsumasa
Published: January 2007

Optical second harmonic generation (SHG) measurements were used to clarify carrier injection into pentacene field effect transistors (FETs) with Au source and drain electrodes. The electric field was probed along the pentacene FET channel. Results showed that the SHG was enhanced depending on biasing voltages. In the off state of FET (Vgs>−30 V), the SHG was enhanced in proportion to the Laplace electric field formed in FET. On the other hand, in the on state (Vgs<−30 V), the enhanced SHG in the off state was diminished because of the hole injection from source electrode. Interestingly, in the off state of FET, electron injection from source and drain electrodes was also suggested. Furthermore, this electron injection was eliminated by overcoating the pentacene film by spin coating a polystyrene film. Finally, results show that our FET analysis based on a Maxwell–Wagner model is acceptable.
N-level Li2 multiphoton rotational wave packets: Alignment effects in resonant multiphoton coherent excitation
Authors: Torres Elva A. , Lerch Eliza-Beth W. , Dai Xingcan , Gilb Stefan , Leone Stephen R.
Published: January 2007

Using one color ultrafast pump-probe spectroscopy, the authors create N-level multiphoton rotational wave packets via resonant optical pumping between the A(Σu+1) and E(Σg+1) electronically bound states of Li2 from a single optically state-selected rovibrational state ∣νA=11, jA=28⟩. The authors find that excitation with a single amplitude shaped femtosecond pulse allows the direct observation of up to a six photon absorption, which generates a coherent superposition of 13 rotational states. The multilevel rotational wave packet is theoretically treated with the multipole moment formalism in order to characterize the experimentally observed time-dependent alignment. In particular, the authors find that the magnetic state distributions measured among coherently excited rotational states generated by the resonant multiphoton pumping reduces the measured coherence amplitudes by as much as 40%.
Theoretical model based on the memory effect for the strange photoisomerization kinetics of diarylethene derivatives dispersed on polymer films
Authors: Seki Kazuhiko , Tachiya M.
Published: January 2007

In the present paper the authors present a theoretical model to explain the kinetics involving the induction period observed by Irie et al. [Nature (London) 420, 759 (2002)] for photoisomerization of diarylethene derivatives dispersed on polymer films at a single molecular level. In the model we assume that both ground state and excited state free energy landscapes which result from the interaction between the photochromic molecule and the surrounding polymer are rugged and have several local minima along the pathway to the critical point at which isomerization actually occurs. We assume that after one photoexcitation a fraction of the photochromic molecule moves to a new local minimum and stays there, although the other fraction returns to the original local minimum. The former effect is referred to as the memory effect. After repeated photoexcitations the photochromic molecule moves gradually from one local minimum to another in the pathway to the isomerization point. It finally reaches the isomerization point, where isomerization occurs. Their model successfully reproduces the kinetics of photoisomerization of diarylethene derivatives dispersed on polymer films observed experimentally.
A computer simulation study of the formation of liquid crystal nanodroplets from a homogeneous solution
Authors: Berardi Roberto , Costantini Alberto , Muccioli Luca , Orlandi Silvia , Zannoni Claudio
Published: January 2007

The aggregation of liquid crystal nanodroplets from a homogeneous solution is an important but not well understood step in the preparation of various advanced photonic materials. Here, the authors performed molecular dynamics computer simulations of the formation of liquid crystalline nanodroplets, starting from an isotropic and uniform binary solution of spherical Lennard-Jones (solvent) and elongated ellipsoidal Gay-Berne (solute) rigid particles in low (<10%) concentration. They studied the dynamics of demixing and the mesogen ordering process and characterized the resulting nanodroplets assessing the effect of temperature, composition, and specific solute-solvent interaction on the morphology, structure, and anisotropy. They find that the specific solute-solvent interaction, composition, and temperature can be adjusted to tune the nanodroplet growth and size.
On the locus of points of conical intersection: Seams near seams
Authors: Schuurman Michael S. , Yarkony David R.
Published: January 2007

The existence of a seam of conical intersection, the reference seam, does not rule out the existence of additional disjoint seams of conical intersection. These disjoint seams intersect the g-h planes of the reference seam, a region usually assumed to be devoid of intersections, potentially leading to unexpected points of degeneracy in close proximity to the original conical intersection. Here the authors show how the locus of these disjoint seams can be predicted employing a Hamiltonian derived from second-order perturbation theory. Dramatic differences between the g-h planes of the reference and disjoint seams are found and are expected to have a profound impact on nuclear dynamics. Numerical studies of both high symmetry (D3h, C3H3) and low symmetry (C2v, C2H2N) species are presented.
Molecular dynamics simulation of planar elongational flow at constant pressure and constant temperature
Authors: Frascoli Federico , Todd B. D.
Published: January 2007

Molecular dynamics simulations of liquid systems under planar elongational flow have mainly been performed in the NVT ensemble. However, in most material processing techniques and common experimental settings, at least one surface of the fluid is kept in contact with the atmosphere, thus maintaining the sample in the NpT ensemble. For this reason, an implementation of the Nosé-Hoover integral-feedback mechanism for constant pressure is presented, implemented via the SLLOD algorithm for elongational flow. The authors test their procedure for an atomic liquid and compare the viscosity obtained with that in the NVT ensemble. The scheme is easy to implement, self-starting and reliable, and can be a useful tool for the simulation of more complex liquid systems, such as polymer melts and solutions.
Quantum confinement effect on Gd2O3 clusters
Authors: Mercier B. , Ledoux G. , Dujardin C. , Nicolas D. , Masenelli B. , Mélinon P. , Bergeret G.
Published: January 2007

The evolution of the gap of a nanoscaled insulator material, namely, Gd2O3, has been observed by means of vacuum ultraviolet excitation spectra of a dopant (Eu3+). The nanoparticles have been synthesized by the low energy cluster beam deposition technique and grown afterward by different annealing steps. A gap shift towards the blue is observed, similar to what is observed in semiconductor nanoparticles. Despite the strong ionic character of the material, the evolution exhibits a behavior similar to covalent materials. The evolution of the gap for Gd2O3 follows the same empiric rule that has been derived for semiconductors (ZnO, CuBr, Si, and CdS). It shows that, in spite of the strong ionic character of the material (0.9 on the scale of Phillips), the amount of covalency is important enough for creating a significant delocalization of the electron with regard to its hole.
Molecular dynamics modeling of the thermal conductivity of irradiated SiC as a function of cascade overlap
Authors: Crocombette Jean-Paul , Dumazer Guillaume , Hoang Nguyen Quoc , Gao Fei , Weber William J.
Published: January 2007

SiC thermal conductivity is known to decrease under irradiation. To understand this effect, we study the variation of the thermal conductivity of cubic SiC with defect accumulation induced by displacement cascades. We use an empirical potential of the Tersoff type in the framework of nonequilibrium molecular dynamics. The conductivity of SiC is found to decrease with dose, in very good quantitative agreement with low temperature irradiation experiments. The results are analyzed in view of the amorphization states that are created by the cascade accumulation simulations. The calculated conductivity values at lower doses are close to the smallest measured values after high temperature irradiation, indicating that the decrease of the conductivity observed at lower doses is related to the creation of point defects. A subsequent decrease takes place upon further cascade accumulation. It is characteristic of the amorphization of the material and is experimentally observed for low temperature irradiation only.
Expertise in Pictorial Perception: Eye-Movement Patterns and Visual Memory in Artists and Laymen
Authors: Vogt Stine , Magnussen Svein
Published: January 2007

In two sessions with free scanning and memory instructions, eye-movement patterns from nine artists were compared with those of nine artistically untrained participants viewing 16 pictures representing a selection of categories from ordinary scenes to abstraction: 12 pictures were made to accommodate an object-oriented viewing mode (selection of recognisable objects), and a pictorial viewing mode (selection of more structural features), and 4 were abstract. The artistically untrained participants showed preference for viewing human features and objects, while the artists spent more scanning time on structural/abstract features. A group by session interaction showed a change of viewing strategy in the artists, who viewed more objects and human features in the memory task session. A verbal test of recall memory showed no overall difference in the number of pictures remembered, but the number of correctly remembered pictorial features was significantly higher for artists than for the artistically untrained viewers, irrespective of picture type. No differences in fixation frequencies/durations were found between groups across sessions, but a significant task-dependent-group by session interaction of fixation frequency/duration showed that the artistically untrained participants demonstrated repetition effects in fewer, longer fixations with repeated viewing, while the opposite pattern obtained for the artists.
The Influence of Visual Experience on Visual and Spatial Imagery
Authors: Noordzij Matthijs L , Zuidhoek Sander , Postma Albert
Published: January 2007

Differences are reported between blind and sighted participants on a visual-imagery and a spatial-imagery task, but not on an auditory-imagery task. For the visual-imagery task, participants had to compare object forms on the basis of a (verbally presented) object name. In the spatial-imagery task, they had to compare angular differences on the basis of the position of clock hands on two clock faces, again only on the basis of verbally presented clock times. Interestingly, there was a difference between early-blind and late-blind participants on the visual-imagery and the spatial-imagery tasks: late-blind participants made more errors than sighted people on the visual-imagery task, while early-blind participants made more errors than sighted people on the spatial-imagery task. This difference suggests that, for visual (form) imagery, people use the channel currently available (haptic for the blind; visual for the sighted). For the spatial-imagery task in this study reliance on haptic processing did not seem to suffice, and people benefited from visual experience and ability. However, the difference on the spatial-imagery task between early-blind and sighted people in this study might also be caused by differences in experience with the analogue clock faces that formed the basis for the spatial judgments.
Effects of Context on a Visual 3-D Pointing Task
Authors: Doumen Michelle J A , Kappers Astrid M L , Koenderink Jan J
Published: January 2007

We examined the effects of egocentric and contextual references on a 3-D exocentric pointing task. Large systematic deviations were found for the slant (angle in the horizontal plane). For most observers, the deviations were smaller when the veridical pointing direction was parallel to a wall. For some observers the size of the deviations was also dependent on whether the veridical pointing direction was frontoparallel or not. For the tilt (angle in the vertical plane), the deviations were smaller and less systematic. Hence, although observers show comparable systematic deviations, the way in which the presence of structure in an environment is used for judging positions of objects is observer-dependent.
Visual Binding of English and Chinese Word Parts is Limited to Low Temporal Frequencies
Authors: Holcombe Alex O , Judson Jeff
Published: January 2007

Some perceptual mechanisms manifest high temporal precision, allowing reports of visual information even when that information is restricted to windows smaller than 50 ms. Other visual judgments are limited to much coarser time scales. What about visual information extracted at late processing stages, for which we nonetheless have perceptual expertise, such as words? Here, the temporal limits on binding together visual word parts were investigated. In one trial, either the word ‘ball’ was alternated with ‘deck’, or ‘dell’ was alternated with ‘back’, with all stimuli presented at fixation. These stimuli restrict the time scale of the rod identities because the two sets of alternating words form the same image at high alternation frequencies. Observers made a forced choice between the two alternatives. Resulting 75% thresholds are restricted to 5 Hz or less for words and nonword letter strings. A similar result was obtained in an analogous experiment with Chinese participants viewing alternating Chinese characters. These results support the theory that explicit perceptual access to visual information extracted at late stages is limited to coarse time scales.
Pigeons' Recognition of Partially Occluded Objects Depends on Specific Training Experience
Authors: Lazareva Olga F , Wasserman Edward A , Biederman Irving
Published: January 2007

DiPietro et al (2002 Perception31 1299 – 1312) reported a dramatic improvement in pigeons' recognition of partially occluded objects after the birds had been trained to recognize objects that were placed on top of another surface. Here, we investigated whether training with partially erased stimuli or with notched stimuli that had a thin gap between the object and another surface would similarly enhance pigeons' recognition of partially occluded objects. We found that erased training had no effect on the birds' recognition of partially occluded objects. Training pigeons to recognize notched objects improved their performance with the same objects when they were partially occluded; but this improvement did not transfer to novel objects, a result that DiPietro et al reported after on-top training. Together, the present results and those of DiPietro et al implicate prior experience as a key factor in pigeons' recognition of partially occluded objects. Training experiences which improve recognition of partially occluded objects may do so because they improve decomposition of complex two-dimensional scenes by pigeons into separate entities.
Shrinkage in the Apparent Size of Cylindrical Objects
Authors: Taya Shuichiro , Miura Kayo
Published: January 2007

A novel illusion in apparent size is reported. We asked observers to estimate the width and depth of vertically oriented elliptic cylinders depicted with texture or luminance gradients (experiment 1), or the height of horizontally oriented elliptic cylinders depicted with binocular disparity (experiment 2). The estimated width or height of cylinders showed systematic shrinkage in the direction of the gradual depth change. The dissimilarity of 2-D appearance amongst our stimuli implies a large variation in spatial-frequency components and brightness contrasts, eliminating the possibility that these parameters contributed to the illusion. Also, the mechanism inappropriately triggered by pictorial depth cues (eg size scaling) may be irrelevant, because the illusion was obtained even when binocular disparity alone specified the shape of the cylinders. The illusion demonstrated here suggests that our visual system may determine the size of 3-D objects by accounting for their depth structures.
Localized Attentional Interference Affects Object Individuation, Not Feature Detection
Authors: McCarley Jason S , Mounts Jeffrey R W
Published: January 2007

Modern theorists conceptualize visual selective attention as a competition between object representations for the control of extrastriate receptive fields, an account supported by the finding that attentional selection of one stimulus can degrade processing of nearby stimuli. In the present study the conditions that produce reciprocal interference between attended stimuli are examined. Each display contained either no, one, or two feature-defined target items among an array of homogeneous distractors. Observers performed two tasks, feature detection and object individuation. The feature-detection task required observers to determine if any targets were present within the display. The object-individuation task required observers to determine if the number of targets was exactly two. Spatially mediated interference between target pairs occurred in the object-individuation task, but had no effect on feature detection. Results suggest that localized interference between attended stimuli occurs only when observers are required to resolve the features of individual objects, consistent with the competitive interaction models of attention.
Look who's Talking: Recognizing Friends from Visible Articulation
Authors: Rosenblum Lawrence D , Niehus Ryan P , Smith Nicolas M
Published: January 2007

We tested whether isolated visible articulatory information can be used for identifying familiar speakers. A facial point-light methodology was used to isolate the visible articulation of seven speakers. These point-light video clips were then shown to nine participants who had long-term personal interactions with the speakers. Results revealed that participants could identify the speakers at better than chance levels when the faces were shown articulating, but not when the faces were shown without movement. The results indicate that visible articulatory information can be used to identify speakers.
The Stereoscopic Sliver: A Comparison of Duration Thresholds for Fully Stereoscopic and Unmatched Versions
Authors: Sachtler W L Ben , Gillam Barbara
Published: January 2007

Just as positional disparities of image features seen with both eyes provide depth information, the presence of an area visible to one eye but not the other within a binocularly viewed scene can indicate an occlusion at a depth discontinuity,. The close geometrical association between these two kinds of cues suggests they may both be exploited by stereopsis. To investigate this, we developed a novel binocular stimulus entirely lacking in classical disparity that contains an unmatched vertical sliver which elicits a warping of the surrounding surface to accommodate a depth discontinuity. We measured depth-discrimination performance at a range of stimulus durations, correcting for variations in stimulus visibility, to characterise the decline of the efficacy of the depth signal with limited integration time. Results show a close correspondence of performance for similar stimuli with unmatched features and classical binocular disparity across a sixtyfold range of viewing durations, supporting the notion of a close association between the two types of cues in human stereopsis. Control experiments excluded simple eye-of-origin cues and long-range false matches as explanatory factors.
Relative Sensitivities to Large-Field Optic-Flow Patterns Varying in Direction and Speed
Authors: Edwards Mark , Ibbotson Michael R
Published: January 2007

Motion in depth results in radial optic-flow patterns. Forward motion results in radially expanding patterns, whereas backward motion generates contracting patterns. Radial optic-flow patterns are typically represented with a positive speed gradient, ie zero speed at the point of fixation, and maximum speed at the periphery. However, the actual speed profile in such a stimulus will depend upon the relative depth of objects in the scene. Using large-field stimuli (82 deg diameter) we determined relative sensitivities to radial expansion and contraction patterns and also to various types of speed gradients: positive, negative, random, and flat. We found that, even when large-field stimuli are used, observers are more sensitive to radially contracting patterns than to expanding patterns. Sensitivity to the positive speed gradient was not consistently different from either the negative or random gradients. Sensitivity to the flat gradient depended upon the speed of the stimuli. The finding of greater sensitivity to radial contraction is discussed in terms of the functional requirements involved in the use of optic-flow signals in maintaining balance. On the basis of the present findings, the utility of comparing psychophysical results based on thresholds against physiological data based on suprathreshold stimuli is also discussed.
Semiotic dynamics and collaborative tagging
Authors: Cattuto Ciro , Loreto Vittorio , Pietronero Luciano
Published: January 2007

Collaborative tagging has been quickly gaining ground because of its ability to recruit the activity of web users into effectively organizing and sharing vast amounts of information. Here we collect data from a popular system and investigate the statistical properties of tag cooccurrence. We introduce a stochastic model of user behavior embodying two main aspects of collaborative tagging: (
i
) a frequency-bias mechanism related to the idea that users are exposed to each other's tagging activity; (
ii
) a notion of memory, or aging of resources, in the form of a heavy-tailed access to the past state of the system. Remarkably, our simple modeling is able to account quantitatively for the observed experimental features with a surprisingly high accuracy. This points in the direction of a universal behavior of users who, despite the complexity of their own cognitive processes and the uncoordinated and selfish nature of their tagging activity, appear to follow simple activity patterns.
The Microscopic Theory of Superconductivity–Verifications and Extensions
Authors: Tord Claeson  , Stig Lundqvist
Published: January 2007

The microscopic theory of superconductivity was formulated in 1957 by Bardeen, Cooper, and Schrieffer. In the BCS model, the ground state of super electrons is built up by pairs kept together by an attractive interaction. An exchange of phonons can give such an attraction. The electrons in the superconducting condensate are correlated within a macroscopic distance. To excite electrons, or break pairs, a certain gap energy is needed.

A number of experimental confirmations were discussed already in the original paper. The BCS theory initiated many experiments. Some of them provided a stimulus to logical extensions of the theory. These have mainly been concerned with a more realistic, energy-and momentum-dependent interaction than the original approximation. Lifetime aspects are also of importance.

In this short survey we describe the results of a few experiments that test the concepts of pairing, energy gap and phonon-mediated attraction. The main emphases are on the powerful tunneling method and the variation of the superconducting transition temperature with different physical and chemical parameters.
Multiple Reaction Correction to 15 MeV Neutron Capture Cross Section in115In
Authors: K Ponnert  , G Magnusson  , I Bergqvist
Published: January 2007

The cross section of the115In(n,γ)116mIn reaction at an incident neutron energy of 15 MeV has been determined by measuring the γ-rays following the decay of the metastable (T1/2=54 min) first excited state of116In. By systematically varying the geometrical arrangement the corrections due to secondary low-energy neutrons could be determined. Numerical estimates of the multiple reaction corrections have been made and a comparison with the experimental results indicates a good agreement. The corrected activation capture cross section at 15 MeV is 0.7±0.3 mb which is an order of magnitude lower than previous activation measurements on the same reaction.
New Levels in23Ne
Authors: J E Christiansson  , J Dubois  , H Odelius  , H Roth
Published: January 2007

The22Ne(d,pγ)23Ne-reaction has been studied using particle-gamma and gamma-gamma coincidence techniques. An annular, surface barrier detector and Ge(Li)-detectors were used together with multi-dimensional storage of data in a PDP-15 on-line computer. Energies and gamma radiation branching ratios of levels in23Ne up to 4.0 MeV have been measured. New levels at 3 458.2 ± 0.6 keV, 3 830.5 ± 1.2 keV, 3 843.3 ± 1.1 keV and 4 010 ± 3 keV are suggested. All levels up to 4 MeV have been accounted for by the Nilsson model by including Coriolis mixing and by assuming that the nucleus is not deformed in the 2s1/2-state at 1 017 keV. Gamma radiation branching ratios are discussed. The experimental results are also compared with recent shell model calculations.
Ultraviolet Absorption Spectrum of the CaH Molecule I. Rotational analysis of the 3 060 Å band system
Authors: B Kaving  , B Lindgren  , D A Ramsay
Published: January 2007

Four new violet degraded bands of CaH have been observed in absorption in the region 2 900 to 3 200 Å by heating calcium and hydrogen to 1 200-1 400°C. Rotational analysis indicates that the bands belong to two close-lying systemsK2Σ+-X2Σ+andL2Π -X2Σ+which are separated by similar 50 cm-1for the 0-0 bands. The rotational levels for the excited states approximate to Hund's case (d) coupling withL= 1. A Hamiltonian matrix has been constructed for the two states and constants for the "unperturbed" states evaluated. These constants reproduce the experimental term values to within 0.2 cm-1, except for levels involved in local perturbations.
Ultraviolet Absorption Spectrum of the CaH Molecule II. The structure of the d-complex around 2 850 Å
Authors: B Kaving  , B Lindgren
Published: January 2007

The absorption bands of CaH at 2 883 and 2 852 Å have together with a new band at 2 821 Å been interpreted as a transition from ad-complex to the ground stateX2Σ+. A Hamiltonian matrix has been constructed for the three upper statesG2Σ+,J2Π andM2Δ and the constants for the deperturbed states have been evaluated. The constants reproduce the observed term values within 0.2 cm-1. The ionisation potential of CaH is estimated to 47 250 ± 750 cm-1.
The Electronic Spectrum of Gaseous AIF
Authors: R F Barrow  , I Kopp  , C Malmberg
Published: January 2007

The results of a detailed rotational analysis involving the assignment of some 14 500 lines are reported. Observed bands have been ascribed to transitions between nine singlet states (including the ground state) and between seven triplet states. Singlet-triplet systems have not yet been observed, but the relative energies of the singlet and triplet states have been determined by the analysis of spin-forbidden perturbations. The ground state is π4σ2,X1Σ+, and the first excited states π4σπ*,a3Πr,A1Π. Above these lie two further non-Rydberg states,B1Σ+andb3Σ+, which seem to arise from a configuration of the kind π4σσ*. The remaining eleven states seem to be Rydberg states, π4σ(nlλ)3Λ,1Λ, which converge on the2Σ+ground state of AlF+. However, no series have yet been recognized so that neither is the ionization potential of AlF well determined nor are there certain assignments of the Rydberg states, although suggestions are made. The triplet splittings in all but thea3Π state are very small (and in some systems there may be cancellation), so that the3Σ+-3Σ+transitions and a3Π-3Σ+system simulate, even at fairly high resolution,1Σ-1Σ and1Π-1Σ systems respectively. At high resolution lines of the3Σ+-a3Π systems show small splittings, some of which are of the kind expected for nuclear magnetic hyperfine structure in transitions of the type case (bβ-S)-case (aβ); however some of the observations are not yet understood.
Determination of the Ground State of ThIII
Authors: Ulf Litzén
Published: January 2007

The ThIII spectrum has been observed in the region 10 000-30 000 A, and ten lines have been identified as transitions between the two previously unconnected parts of the term system. This makes 5f6d3H4the ground level of Th III. The first excited level, 6d23F2, is situated only 63.2 cm-1above the ground level.
Fluctuations and Thermodynamic Inequalities
Authors: Spiridon Dumitru
Published: January 2007

A presentation is given of the thermodynamic inequalities which, in the phenomenological theory, result from the condition that the correlation matrix of the equilibrium fluctuations is positive definite. These inequalities complete the set of thermodynamic inequalities deduced from the stability condition of thermodynamic equilibrium and from the Le Chatelier principle. Finally, the inequalities which are satisfied by the products of the dispersions and by the correlations between couples of thermodynamic variables are discussed. These inequalities are, in the author's opinion, similar to the uncertainty relations from quantum mechanics.
Pion Production on 10B by 185 MeV Protons
Authors: S Dahlgren  , P Grafström
Published: January 2007

Energy spectra of pions produced in the reaction 10B(p,π+)11B at E
p=185 MeV have been measured in the angular range 20°-130° (lab.). Angular distributions for proton capture to the ground state and first excited state in 11B have been determined. An attempt to observe the T = 3/2 analogue states in 11B and 11N was made but did not succeed.
Various Types of Hollow Cathodes and Absorption Devices in Optical Spectroscopy
Authors: Nils Elander  , Hinrek Neuhaus
Published: January 2007

In this investigation three different experimental methods in optical spectroscopy are discussed. Two special types of hollow cathodes have been constructed and tested. The purpose of one of the hollow cathodes is to generate hydrogen continua in the vacuum UV. It can be run at 6 Amp. Another type of hollow cathode has been developed for the purpose of simultaneous electrical excitation and thermal heating. Finally an optical device for increasing the absorption in an absorption cell is described.
Optical Radiation Emitted at Heavy-ion Bombardment of Solids
Authors: M Braun  , B Emmoth  , I Martinson
Published: January 2007

We have bombarded a number of solid targets with 100-300 keV Xe+ions from a heavy-ion accelerator. Strong line spectra, showing transitions in neutral, singly-and doubly-ionized target atoms have been observed. Decay lengths have been measured for a number of transitions and the results are compared to beam-foil data.
An External Ring System for Magnetic Plasma Confinement
Authors: B Lehnert
Published: January 2007

A new scheme for steady-state magnetic plasma confinement is suggested, consisting of a superposition of two poloidal magnetic field components. The first arises from the unidirectional currents flowing in a number of ring-shaped external conductors. The second is produced by an oppositely directed azimuthal current in the plasma. Whenever being necessary, an additional toroidal magnetic field component can be introduced. The scheme differs from those having passive guard conductors surrounding the plasma, in the sense that given currents are fed into the rings from external sources. This scheme provides a closed axisymmetric magnetic bottle with closed guiding-centre drift orbits of the plasma particles, as well as possibilities of "bootstrap" operation. The problems are considered of stabilizing electrostatic modes by means of minimum-average-Bgeometry, and of stabilizing electromagnetic modes by means of the mutual forces between the currents in the plasma and those in the external conductors.
Isothermal Annealing of Boron Implanted Silicon
Authors: S Peterström  , G Holmén
Published: January 2007

The sheet resistivity has been measured in isothermal annealing studies of 10 kohm cm silicon implanted with 40 keV boron ions. The doses used were 2 x 1012 and 2 x 1014 ions/cm2. The annealing was performed in the temperature range 300 to 800°C and the maximum annealing time used was 4 hours at each temperature. The sheet resistivity of the low dose implant at each temperature decreased when the annealing time was increased but the reduction was small during annealing at 550°C. The implant with the dose 2 x 1014 ions/cm2 gave an annealing time dependent increase in the sheet resistivity at the temperature 550°C. The annealing behaviour of the implanted layers seems to be the same for the two doses. Annealing treatment of boron implanted silicon layers give for the two different doses a possibility of varying the sheet resistivity from 60 kΩ/square to 500 Ω/square.
The Characteristics of a 40 kV Multistage Spark Gap
Authors: A Anvari
Published: January 2007

The electrical properties of a 40 kV multistage spark gap have been studied. It is shown that the switch possesses a relatively constant delay time and jitter over the range of its operating voltage. These characteristics have been compared with those of a similar two-electrode spark gap operating under the same conditions. The comparison shows that the switch is 10 times faster than a two-electrode spark gap when operating at 80% of the breakdown voltage. A jitter time of ±3 ns has been obtained for a 40 kV multistage switch when operating in atmospheric air. Some other characteristics of the multistage switch are presented and its advantages are discussed.
The Spectrum and Term System of P V
Authors: Carl Erik Magnusson  , Per Olof Zetterberg
Published: January 2007

The spectrum of quadruply ionized phosphorus has been studied in the wavelength region 200-9 800 Å by using a sliding spark in vacuum. A total of 126 spectrum lines have been measured and classified, 88 of which are new. The term system has been recalculated and new terms added. The polarization formula applied to nf, ng and nh gives an ionization limit of 524 462.9 ± 1.0 cm-1 and a dipole polarizability of the core 2s
22p
6 of 0.0949 a
0
3.
Nonlinear Wave Interactions in Turbulent Plasmas
Authors: V N Tsytovich  , L Stenflo
Published: January 2007

The second order nonlinear current density is calculated for a magnetized turbulent plasma. Processes of decay and fusion of three waves can then be considered.
Photoproduction of Negative Pions from11B. A Correction
Authors: P Janecek
Published: January 2007

A previous calculation of the total cross section for the11B(γ,π-)11C reaction is corrected for a numerical error. Better agreement with the experimental data is obtained.
Regularization of Higher Order Weak Processes
Authors: A M Din  , R P Saxena
Published: January 2007

Higher order weak processes are studied within the framework of conventional V-A theory and the divergences are regularized using a special procedure involving Padé-approximants. For the particular processes (i) e - νe scattering, (ii) e - v̄e scattering, (iii) μ-decay, and (iv) KL
0 → μ+μ-decay numerical results in satisfactory agreement with experiment are obtained.
A Relativistic Calculation of Transition Probabilities between the np(n + 1)s and np2Configurations for the Elements of Group IV
Authors: L Holmgren  , S Garpman
Published: January 2007

Transition probabilities are calculated for thenp(n+ 1)s→np2transition array in the group IV elements using relativistic self-consistent-field wave functions. Formulas are presented for the dipole length, the dipole velocity, and the dipole acceleration operators and the effective-operator formalism was used to evaluate relativistic matrix elements. A comparison is made between the theoretically calculated lifetimes and values obtained from reliable experimental measurements.