bluuebunny/crossref_metadata_2025 huggingface dataset:
(–)-Epicatechin is associated with increased angiogenic and mitochondrial signalling in the hindlimb of rats selectively bred for innate low running capacity
Authors: Hüttemann Maik , Lee Icksoo , Perkins Guy A. , Britton Steven L. , Koch Lauren G. , Malek Moh H.
Published: January 2013

Alternative approaches to reduce congenital muscle dysfunction are needed in cases where the ability to exercise is limited. (−)-Epicatechin is found in cocoa and may stimulate capillarity and mitochondrial proliferation in skeletal muscle. A total of 21 male rats bred for LCR (low running capacity) from generation 28 were randomized into three groups: vehicle for 30 days (control); (−)-epicatechin for 30 days; and (−)-epicatechin for 30 days followed by 15 days without (−)-epicatechin. Groups 2 and 3 received 1.0 mg of (−)-epicatechin/kg of body mass twice daily, whereas water was given to the control group. The plantaris muscle was harvested for protein and morphometric analyses. In addition, in vitro experiments were conducted to examine the role of (−)-epicatechin on mitochondrial respiratory kinetics at different incubation periods. Treatment for 30 days with (−)-epicatechin increased capillarity (P<0.001) and was associated with increases in protein expression of VEGF (vascular endothelial growth factor)-A with a concomitant decrease in TSP-1 (thrombospondin-1) and its receptor, which remained after 15 days of (−)-epicatechin cessation. Analyses of the p38 MAPK (mitogen-activated protein kinase) signalling pathway indicated an associated increase in phosphorylation of MKK3/6 (MAPK kinase 3/6) and p38 and increased protein expression of MEF2A (myocyte enhancer factor 2A). In addition, we observed significant increases in protein expression of PGC-1α (peroxisome-proliferator-activated receptor γ co-activator 1α), PGC-1β, Tfam and cristae abundance. Interestingly, these increases associated with (−)-epicatechin treatment remained after 15 days of cessation. Lastly, in vitro experiments indicated that acute exposure of LCR muscle to (−)-epicatechin incubation was not sufficient to increase mitochondrial respiration. The results suggest that increases in skeletal muscle capillarity and mitochondrial biogenesis are associated with 30 days of (−)-epicatechin treatment and sustained for 15 days following cessation of treatment. Clinically, the use of this natural compound may have potential application in populations that experience muscle fatigue and are unable to perform endurance exercise.
Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels
Authors: Hu En-Lan , Tsai Po-Yu , Fan He , Lin King-Chuen
Published: January 2013

Upon one-photon excitation at 248 nm, gaseous CH3C(O)SH is dissociated following three pathways with the products of (1) OCS + CH4, (2) CH3SH + CO, and (3) CH2CO + H2S that are detected using time-resolved Fourier-transform infrared emission spectroscopy. The excited state 1(nO, π*CO) has a radiative lifetime of 249 ± 11 ns long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of collision-induced internal conversion is estimated to be 1.1 × 10−10 cm3 molecule−1 s−1. Among the primary dissociation products, a fraction of the CH2CO moiety may undergo further decomposition to CH2 + CO, of which CH2 is confirmed by reaction with O2 producing CO2, CO, OH, and H2CO. Such a secondary decomposition was not observed previously in the Ar matrix-isolated experiments. The high-resolution spectra of CO are analyzed to determine the ro-vibrational energy deposition of 8.7 ± 0.7 kcal/mol, while the remaining primary products with smaller rotational constants are recognized but cannot be spectrally resolved. The CO fragment detected is mainly ascribed to the primary production. A prior distribution method is applied to predict the vibrational distribution of CO that is consistent with the experimental findings.
Glass transition of poly(ethylmethacrylate) admixed and bound to nanoparticles
Authors: Friedrichs Cornelius , Emmerling Sebastian , Kircher Gunnar , Graf Robert , Wolfgang Spiess Hans
Published: January 2013

The chain dynamics at the glass transition of poly(ethylmethacrylate) in the bulk is compared to that of mixtures of the polymer with nanoparticles by advanced NMR methods. In order to make the two components compatible, the particles were functionalized with the polymer itself. Particular emphasis is placed on the extended local chain conformations of this polymer accessible by 13C NMR spectroscopy. The isotropization dynamics of these extended conformations is only slightly changed in the mixtures, but is significantly slowed down by attachment of the chains to the nanoparticles themselves. The slowing down is studied at various distances from the nanoparticle and is observed for most of the attached chains segments except for the chain ends. The results are put into perspective to the glass transition in polymers attached to surfaces, thin polymer layers, and the chain dynamics of star polymers.
Modeling the relaxation of polymer glasses under shear and elongational loads
Authors: Fielding S. M. , Moorcroft R. L. , Larson R. G. , Cates M. E.
Published: January 2013

Glassy polymers show “strain hardening”: at constant extensional load, their flow first accelerates, then arrests. Recent experiments under such loading have found this to be accompanied by a striking dip in the segmental relaxation time. This can be explained by a minimal nonfactorable model combining flow-induced melting of a glass with the buildup of stress carried by strained polymers. Within this model, liquefaction of segmental motion permits strong flow that creates polymer-borne stress, slowing the deformation enough for the segmental (or solvent) modes then to re-vitrify. Here, we present new results for the corresponding behavior under step-stress shear loading, to which very similar physics applies. To explain the unloading behavior in the extensional case requires introduction of a “crinkle factor” describing a rapid loss of segmental ordering. We discuss in more detail here the physics of this, which we argue involves non-entropic contributions to the polymer stress, and which might lead to some important differences between shear and elongation. We also discuss some fundamental and possibly testable issues concerning the physical meaning of entropic elasticity in vitrified polymers. Finally, we present new results for the startup of steady shear flow, addressing the possible role of transient shear banding.
Nonequilibrium static growing length scales in supercooled liquids on approaching the glass transition
Authors: Marcotte Étienne , Stillinger Frank H. , Torquato Salvatore
Published: January 2013

The small wavenumber k behavior of the structure factor S(k) of overcompressed amorphous hard-sphere configurations was previously studied for a wide range of densities up to the maximally random jammed state, which can be viewed as a prototypical glassy state [A. Hopkins, F. H. Stillinger, and S. Torquato, Phys. Rev. E 86, 021505 (2012)]10.1103/PhysRevE.86.021505. It was found that a precursor to the glassy jammed state was evident long before the jamming density was reached as measured by a growing nonequilibrium length scale extracted from the volume integral of the direct correlation function c(r), which becomes long-ranged as the critical jammed state is reached. The present study extends that work by investigating via computer simulations two different atomic models: the single-component Z2 Dzugutov potential in three dimensions and the binary-mixture Kob-Andersen potential in two dimensions. Consistent with the aforementioned hard-sphere study, we demonstrate that for both models a signature of the glass transition is apparent well before the transition temperature is reached as measured by the length scale determined from the volume integral of the direct correlation function in the single-component case and a generalized direct correlation function in the binary-mixture case. The latter quantity is obtained from a generalized Ornstein-Zernike integral equation for a certain decoration of the atomic point configuration. We also show that these growing length scales, which are a consequence of the long-range nature of the direct correlation functions, are intrinsically nonequilibrium in nature as determined by an index X that is a measure of the deviation from thermal equilibrium. It is also demonstrated that this nonequilibrium index, which increases upon supercooling, is correlated with a characteristic relaxation time scale.
Chemical bonding and magnetic exchange in two-dimensional [M(TCNE)(NCMe)2]X (M = Fe, Mn; X = FeCl4, SbF6) magnets: A pressure study
Authors: Midgley Alex E. , Olson Christopher , Heth Christopher L. , Caruso Anthony N. , Kruger Michael B. , Halder Gregory J. , Schlueter John A. , Pokhodnya Konstantin
Published: January 2013

Pressure-dependent X-ray diffraction studies reveal the bulk modulus and compression anisotropy of the 2D magnet [Mn(TCNE)(NCMe)2]SbF6. The Raman response of this and the similar [Fe(TCNE)(NCMe)2]FeCl4 layered magnet, shows that the evolution of the ag νC=C frequency correlates well with the magnetic exchange and Tc variations of these materials under pressure. There is a significantly more complex correlation between the ag νC≡N frequency and Tc despite the fact that some unpaired π* electron density (∼0.125 e) is localized on each of TCNE nitrile N≡C group. The shortening of the M–NC bond with pressure (<0.5 GPa) does not result in a Tc increase, which suggests a more complex bond length magnetic exchange relationship.
Thresholds for igniting exothermic reactions in Al/Ni multilayers using pulses of electrical, mechanical, and thermal energy
Authors: Fritz Gregory M. , Spey Stephen J. , Grapes Michael D. , Weihs Timothy P.
Published: January 2013

We use pulses of electrical, mechanical, and thermal energy to determine the ignition thresholds of self-propagating reactions in Al/(Ni-7 V) and Al/Inconel multilayers. The energy density and power density required to initiate reactions in a Al/(Ni-7 V) foil with a 50 nm bilayer is compared for all three techniques to demonstrate the importance of heat loss on ignition thresholds and its dependence on the test volume and the surrounding thermal resistance. In addition, ignition is shown to occur at temperatures as low as 232 °C when heat losses are very small suggesting that ignition can be controlled by atomic mixing in the solid state. The experiments demonstrate that the ignition threshold drops with increasing ignition volume, and it rises with increasing bilayer spacing and with increasing intermixed thickness. These trends are also supported by an analytical model we derive to predict the effects of ignition volume, multilayer microstructure, and physical properties on the ignition threshold. We calculate an activation energy of 77.3 ± 1.3 kJ/mol for solid state mixing based on measured ignition temperatures.
Positive feedback produces broad distributions in maximum activation attained within a narrow time window in stochastic biochemical reactions
Authors: Das Jayajit
Published: January 2013

How do single cell fate decisions induced by activation of key signaling proteins above threshold concentrations within a time interval are affected by stochastic fluctuations in biochemical reactions? We address this question using minimal models of stochastic chemical reactions commonly found in cell signaling and gene regulatory systems. Employing exact solutions and semi-analytical methods we calculate distributions of the maximum value (N) of activated species concentrations (Pmax(N)) and the time (t) taken to reach the maximum value (Pmax(t)) within a time interval in the minimal models. We find, the presence of positive feedback interactions make Pmax(N) more spread out with a higher “peakedness” in Pmax(t). Thus positive feedback interactions may help single cells to respond sensitively to a stimulus when cell decision processes require upregulation of activated forms of key proteins to a threshold number within a time window.
Numerical simulation of the stochastic damped improved Boussinesq equation
Authors: Wang Quanxiang , Zhang Zhiyue , Zhu Quanyong
Published: January 2013

In this paper, we numerically investigate the dynamics of the solitary waves in the presence of damping and external stochastic forces for the improved Boussinesq equation. The hydrodynamical and Stokes damping will be considered respectively. Since the analytic solutions for the considered problems are not available, Monte Carlo method will be used in random space and finite volume element method will be used in physical space. Numerical results demonstrate that solitary wave profile is not strongly affected by the Gaussian white noise in our study. The average of the velocity of the solitary waves is very close to that for the deterministic case.
Water-induced two-dimensional Kondo-like scattering in Na0.23CoO2 single crystals
Authors: Cao Guixin , Gao Yuze , Zhang Jincang , Lin Chengtian
Published: January 2013

An in-plane Kondo-like resistivity minimum is found with a corresponding temperature Tmin, around 7 K for hydrated Na0.23CoO2 single crystals. Below 7 K, the resistivity exhibits logarithmic temperature dependence of α lnT, where α is independent of the external magnetic field up to 8 T. The feature is resulted in terms of the Kondo-like effect arising from the presence of spin disorder induced by water intercalation in the a-b plane. Our results indicate that the water intercalation weakens the coupling between the CoO2 layers and increases the two-dimensional characteristic of transport properties. The dependence of resistivity minimum on applied field proved also the suppression of localized Co(1) site on paramagnetic triangular superlattice. Further, the present experiments give the evidence of a more complex cooperative phenomena involving charge or spin ordering in the CoO2 layers as a dominating factor for the understanding of hydrated NaxCoO2 compounds.
A grillage model for predicting wrinkles in annular graphene under circular shearing
Authors: Zhang Z. , Duan W. H. , Wang C. M.
Published: January 2013

This paper is concerned with a Timoshenko grillage model for modeling the wrinkling phenomenon in annular graphene under circular shearing applied at its inner edge. By calibrating the grillage model results against the molecular mechanics (MM) results, the grillage model comprising beams of elliptical cross-section orientated along the carbon-carbon bond has section dimensions of 0.06 nm for the major axis length and 0.036 nm for the minor axis length. Moreover, the beams are connected to one another at 0.00212 nm from the geometric centric. This eccentric connection of beams allows the proposed grillage model to cater for the cross-couplings among bonds that produce the out-of-plane wrinkling pattern. The out-of-plane to in-plane bending stiffnesses' ratio is 0.36, and the cross bending stiffness provided by the ellipse eccentricity is 0.025 times that of the in-plane bending stiffness. Besides furnishing identical wave numbers as well as amplitudes and wavelengths that are in good agreement with MM results, the grillage model can capture wrinkling patterns with a boundary layer, whereas plate and membrane models could not mimic the boundary layer.
Low frequency needlepoint-shape metamaterial absorber based on magnetic medium
Authors: Bin Zhang Hui , Wei Deng Li , Heng Zhou Pei , Zhang Li , Mu Cheng Deng , Yan Chen Hai , Fei Liang Di , Jiang Deng Long
Published: January 2013

We report the design, simulation, and measurement of a magnetic-type metamaterial absorber with needlepoint-shape pattern in the microwave region. Experimental result shows that the needlepoint-shape pattern expands the absorption bandwidth of the magnetic absorber by more than 65%, which is related to the LC resonances. Different from the non-magnetic metamaterial absorber, the power loss in the proposed absorber is dominated by magnetic loss. The dielectric loss and magnetic loss are both strengthened by the metamaterial resonance. The absorber has applications in the area of eliminating microwave energy.
Optimized luminescence properties of Mn doped ZnS nanoparticles for photovoltaic applications
Authors: Le Donne Alessia , Kanti Jana Sourav , Banerjee Sangam , Basu Sukumar , Binetti Simona
Published: January 2013

Mn2+ doped ZnS nanoparticles (ZnS:Mn2+ NPs) are non-toxic systems known for their attractive light emitting properties. This paper discusses the luminescence properties of ZnS:Mn2+ NPs prepared by wet chemical synthesis with the objective of using them as down-shifters. A modification of the incident solar spectrum inducing improved exploitation of the UV region was expected to increase the efficiency of single junction cells with an optimal absorber band gap around 1.1 eV. The potential of ZnS:Mn2+ NPs as down-shifters was therefore demonstrated on both Si and Cu(In,Ga)Se2 solar cells.
Investigation of the electroluminescence spectrum shift of InGaN/GaN multiple quantum well light-emitting diodes under direct and pulsed currents
Authors: Lu Cimang , Wang Lei , Lu Jianing , Li Rui , Liu Lei , Li Ding , Liu Ningyang , Li Lei , Cao Wenyu , Yang Wei , Chen Weihua , Du Weimin , Lee Ching-Ting , Hu Xiaodong
Published: January 2013

Electroluminescence (EL) spectra of InGaN/GaN multiple quantum well light emitting diodes with different piezoelectric polarization fields were investigated under pulsed and direct currents. We find a positive correlation between the piezoelectric polarization field and the thermally induced red-shift of the EL spectra at high direct currents above 25 A/cm2. Under pulsed current, when thermal effects are negligible, a non-uniform EL spectrum blue-shift rate as a function of injection level is observed and compared with numerical results obtained by both self-consistent and non-self-consistent K·P methods. We conclude that the screening effect is positively related to the piezoelectric polarization field, but the band filling-induced blue-shift is almost independent from the piezoelectric field. The electrostatic fields induced by free carriers in the quantum wells increase rapidly with current but tend to saturate at higher injection where the band filling effect becomes the dominant mechanism for the blue-shift. Finally, at high injection above 30 A/cm2, an increase in Auger recombination and carrier leakage holds the spectral peaks almost constant in position.
Linear magnetoresistance in topological insulator thin films: Quantum phase coherence effects at high temperatures
Authors: Assaf B. A. , Cardinal T. , Wei P. , Katmis F. , Moodera J. S. , Heiman D.
Published: January 2013

In addition to the weak antilocalization cusp observed in the magnetoresistance (MR) of topological insulators at low temperatures and low magnetic fields, we find that the high-field MR in Bi2Te2Se is linear in field. At fields up to B = 14 T, the slope of this linear-like MR is nearly independent of temperature over the range T = 7 to 150 K. We find that the linear MR arises from the competition between a logarithmic phase coherence component and a quadratic component. The quantum phase coherence dominates up to high temperatures, where the coherence length remains longer than the mean free path of electrons.
Note: On the use of Rogowski coils as current probes for atmospheric pressure dielectric barrier discharges
Authors: Biganzoli I. , Barni R. , Riccardi C.
Published: January 2013

A wide bandwidth current probe based on a Rogowski coil was proposed to work down to the nanosecond time scale. It was then used to record the discharge current pulses that characterize the streamer regime of the plasma in a dielectric barrier discharge device. Indeed such plasmas are often made up of intermittent and highly localized structures such as streamers or microdischarges. Characteristics and performances of the probes are discussed together with a few results concerning their application to investigate dielectric barrier discharges and the temporal structure of different pulses of the electrical current.
Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: Insights from an analytically solvable model
Authors: Makarov Dmitrii E.
Published: January 2013

Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers’ theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and “internal” friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which—unlike Kramers’ theory—account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.
Temperature control in thermal microactuators with applications to in-situ nanomechanical testing
Authors: Qin Qingquan , Zhu Yong
Published: January 2013

Thermal microactuators are used in many micro/nano-technologies. To circumvent undesired heating of the end effector, heat sink beams are co-fabricated with the thermal actuator and connected to the substrate. This paper reports a combined experimental and modeling study on the effect of such heat sink beams. Temperature distribution is measured and simulated using Raman scattering and multiphysics finite element method, respectively. Our results show that heat sink beams are effective in controlling the temperature of the thermal actuator. Insights on how to achieve both low temperature and large actuator displacement for in-situ mechanical testing of nanoscale specimens are provided.
Tip-enhanced sub-diffraction fluorescence imaging of nitrogen-vacancy centers in nanodiamonds
Authors: Yung Hui Yuen , Lu Yu-Chun , Su Long-Jyun , Fang Chia-Yi , Hsu Jui-Hung , Chang Huan-Cheng
Published: January 2013

This work demonstrates that the gold tip of an atomic force microscope enhances not only the fluorescence of the nitrogen-vacancy centers in nanodiamonds but also improves the optical resolution of the fluorescence image of the particles down to 40 nm in an apertureless near-field scanning optical microscope. With the tip in close contact with 20–30 nm diamonds, the average fluorescence intensity enhancement is 3. By measuring the fluorescence decay lifetime and the saturation intensity, we confirm that the fluorescence enhancement is contributed predominantly by the increase of the radiative decay rate.
Role of collisional broadening in Monte Carlo simulations of terahertz quantum cascade lasers
Authors: Matyas Alpar , Lugli Paolo , Jirauschek Christian
Published: January 2013

Using a generalized version of Fermi's golden rule, collisional broadening is self-consistently implemented into ensemble Monte Carlo carrier transport simulations, and its effect on the transport and optical properties of terahertz quantum cascade lasers is investigated. The inclusion of broadening yields improved agreement with the experiment, without a significant increase of the numerical load. Specifically, this effect is crucial for a correct modeling at low biases. In the lasing regime, broadening can lead to significantly reduced optical gain and output power, affecting the obtained current-voltage characteristics.
Response to “Comment on ‘The limits of flexoelectricity in liquid crystals’” [AIP Advances 3, 019101 (2013)]
Authors: Castles F. , Morris S. M. , Coles H. J.
Published: January 2013

The Comment [AIP Advances 3, 019101 (2013)] appears to be based on a mistaken understanding of our argument. We believe that the inequalities in our Paper [AIP Advances 1, 032120 (2011)] are correct and that our conclusions are justified.
Ab-initio study of Mg-doped InN(0001) surface
Authors: Belabbes A. , Furthmüller J. , Bechstedt F.
Published: January 2013

We study the incorporation of Mg atoms into the InN(0001) surface. Energies and atomic geometries are described within density functional theory, while the electronic structure is investigated by an approximate quasiparticle method that yields a gap value of 0.7 eV for bulk InN. The formation of substitutional Mg is energetically favored in the surface layer. The surface electronic structure is less influenced by Mg-derived states. The Fermi level is pinned by In-derived surface states. With increasing depth of Mg beneath the surface the Fermi-level position moves toward the valence band top, suggesting formation of holes and, hence, p-doping of Mg in bulk-like layers.
Single-order operation of lamellar multilayer gratings in the soft x-ray spectral range
Authors: van der Meer Robert , Kozhevnikov Igor , Krishnan Balachander , Huskens Jurriaan , Hegeman Petra , Brons Christian , Vratzov Boris , Bastiaens Bert , Boller Klaus , Bijkerk Fred
Published: January 2013

We demonstrate single-order operation of Lamellar Multilayer Gratings in the soft x-ray spectral range. The spectral resolution was found to be 3.8 times higher than from an unpatterned multilayer mirror, while there were no significant spectral sideband structures adjacent to the main Bragg peak. The measured spectral bandwidths and peak reflectivities were in good agreement with our theoretical calculations.
Optical bistability based on Bragg grating resonators in metal-insulator-metal plasmonic waveguides
Authors: Xiang Yinxiao , Zhang Xinzheng , Cai Wei , Wang Lei , Ying Cuifeng , Xu Jingjun
Published: January 2013

An optically bistable device based on a Bragg grating resonator with a nonlinear medium in metal-insulator-metal waveguides is proposed. Its properties are numerically investigated by a finite-difference time-domain method and further qualitatively analyzed by adopting Airy equation. Cavities with different Q factors are compared with respect to bi-stability. Cavities with a small Q factor lead to a high transmission and a narrow hysteresis loop. The response time of such cavities is found to be in the sub-picosecond region. Our nano-scale switching structure is comparatively easy to fabricate and integrate in plasmonic circuits and promises to be useful for future all-optical computing and communication technology.
Horizontal/Vertical Differences in Range and Upper/Lower Visual Field Differences in the Midpoints of Sensory Fusion Limits of Oriented Lines
Authors: Grove Philip M , Ono Hiroshi
Published: January 2013

O'Shea and Crassini (1982, Perception & Psychophysics32 195–196) demonstrated that fusion persists for vertical lines with an orientation disparity of 8°, but diplopia is experienced in simultaneously presented horizontal lines with the same disparity. They concluded that the neural fusion process fuses larger horizontal disparities than vertical disparities. Kertesz criticised their demonstration because it did not quantify the possible motor component associated with fusing their counter-rotated images. Krekling and Blika argued that the demonstrated anisotropy is due to a disparity bias in the visual system, owing to the temporalward tilt of corresponding vertical meridians. We addressed these criticisms with a novel stimulus and presentation protocol, that rendered compensatory cyclovergence eye movements unlikely and explored a wide range of orientation disparities. We confirmed O'Shea and Crassini's vertical/horizontal anisotropy in orientation fusion limits. In addition, our measurements of vertical lines showed that the distributions of fused responses as a function of orientation disparity in the upper and lower visual fields were shifted relative to each other. Therefore, the distributions of fusible orientation disparities are wider for vertical lines than horizontal lines and are relatively shifted as predicted if the fusional range is centred around the vertical horopter.
Recognising One's Own Motor Actions through Sound: The Role of Temporal Factors
Authors: Murgia Mauro , Hohmann Tanja , Galmonte Alessandra , Raab Markus , Agostini Tiziano
Published: January 2013

It has been shown that humans are able to recognise their own movement. While visual cues have been amply studied, the contribution of auditory cues is not clear. Our aim was to investigate the role of temporal auditory cues in the identification of one's own or others' performance in a complex movement—a golf swing. We investigated whether golfers are able to discriminate between the sounds associated with their own swings and other golfers' swings, by using the relative timing and the overall duration of the movement. The sounds produced by the participants performing 65 m shots have been recorded and used to create the stimuli. The experimental conditions were: participants' swing sounds and the sounds of other golfers having equal both relative timing and overall duration, equal relative timing but different overall duration, different relative timing but equal overall duration, and both different relative timing and overall duration. The task of the participants was to say whether each sound corresponded or did not correspond to their own swing. Results show that golfers are able to recognise their own movements, but they also recognise as their own the sound produced by other athletes having equal both relative timing and overall duration.
Computational Evolutionary Perception
Authors: Hoffman Donald D , Singh Manish
Published: January 2013

Marr proposed that human vision constructs “a true description of what is there”. He argued that to understand human vision one must discover the features of the world it recovers and the constraints it uses in the process. Bayesian decision theory (BDT) is used in modern vision research as a probabilistic framework for understanding human vision along the lines laid out by Marr. Marr's contribution to vision research is substantial and justly influential. We propose, however, that evolution by natural selection does not, in general, favor perceptions that are true descriptions of the objective world. Instead, research with evolutionary games shows that perceptual systems tuned solely to fitness routinely outcompete those tuned to truth. Fitness functions depend not just on the true state of the world, but also on the organism, its state, and the type of action. Thus, fitness and truth are distinct. Natural selection depends only on expected fitness. It shapes perceptual systems to guide fitter behavior, not to estimate truth. To study perception in an evolutionary context, we introduce the framework of Computational Evolutionary Perception (CEP). We show that CEP subsumes BDT, and reinterprets BDT as evaluating expected fitness rather than estimating truth.
Recollections of David Marr
Authors: Nishihara H K
Published: January 2013

David Marr came to MIT's Artificial Intelligence (AI) Lab in the early 1970s and energized the study of vision at the intersection of computer science, psychology, and neuroscience. As one of his first graduate students, I had the privilege of getting to know him and working with him during that heady period of AI research.
Moderate Movement, More Vision: Effects of Physical Exercise on Inattentional Blindness
Authors: Hüttermann Stefanie , Memmert Daniel
Published: January 2013

Research on inattentional blindness shows that individuals fail to notice unexpected objects or events when attention is focused elsewhere. The majority of previous studies on inattentional blindness have been performed at rest, even though there are several real-life situations that require both physical exercise and focus of attention to accomplish a particular task. A number of different studies have demonstrated that physical exercise influences cognitive performance and attention processes in a variety of ways. Relatively little is known about the effects of physical load on inattentional blindness. The present study was the first attempt to investigate inattentional blindness effects as a function of physical load. Participants were randomly assigned to three groups where they performed two different inattentional blindness tasks: at rest (group 1) and on a bicycle ergometer under moderate (group 2) or high (group 3) physical exercise. The results showed a decrease of inattentional blindness effects from the resting to the moderate exercise condition, and then an increase for the high physical exercise condition, representing an inverted-U plot. Findings support the notion that physical exercise influences individuals' attention performance. We concluded that moderate physical exercise has a positive impact on inattentional blindness, given that people under moderate physical exercise more frequently notice an unexpected object when attention is diverted to another task, and that this evidence should be taken into account when considering certain real-life events.
Marr, Gibson, and Gestalt: A Challenge
Authors: Richards Whitman
Published: January 2013

Marr, Gibson, and the Gestalt school all offered different views on visual perception. In some cases, these views agree; in others they differ. Can a computational approach assimilate these different perspectives to yield one inclusive framework for vision?
The Levels of Understanding Framework, Revised
Authors: Poggio Tomaso
Published: January 2013

I discuss the “levels of understanding” framework described in Marr's Vision and propose an updated version to capture the changes in computation and neuroscience over the last 30 years.
Attentional Selection Dilates Perceived Duration
Authors: Herbst Sophie K , van der Meer Elke , Busch Niko A
Published: January 2013

How do observers judge the passage of time at a short time-scale? Humans are not equipped with a dedicated sensory system for perceiving durations in the same way as they are equipped with systems for perceiving light and sound. Thus, subjective duration depends on the sensory and cognitive processes triggered by sensory input, eg visual or auditory stimuli. Previous studies have demonstrated that the dynamics of this sensory input (eg the rate of stimulus presentation) affect duration judgments. However, it is yet unclear whether automatic or attentive processing of such dynamics accounts for their effect on subjective duration. Automatic and attentive stimulus processing can be distinguished when stimuli are presented in a rapid serial visual presentation (RSVP) paradigm. The second of two targets embedded in an RSVP stream often fails to attract participants' attention and escapes conscious detection, in spite of being automatically processed at a perceptual level. In the present study, we presented RSVP streams and combined a target detection task with a prospective duration judgment task. We demonstrate in three experiments that the number of subjectively perceived target stimuli (and not the number of objectively presented targets) determines subjective duration of the entire RSVP sequence. Target stimuli which escape attentional selection did not affect perceived duration. This finding indicates that attentive rather than automatic processing of stimulus dynamics leads to the subjective time dilation of dynamic stimuli.
Edges, Curvature, and Primal Sketches
Authors: Watt Roger
Published: January 2013

Marr described two versions of the primal sketch: the basic image-processing level in human vision. In line with his broader view of how one should construct explanatory theories in vision, he provided some details of the computational theory for this stage, the algorithms used, and how they might be implemented in neural systems. In this paper I consider how Marr ideas have continued over the past 30 years. In this regard, I pay particular attention to three stages: locating edges; describing edge curvature; linking local edge segments into elongated contours.
Classic Debates in Selective Attention: Early vs Late, Perceptual Load vs Dilution, Mean RT vs Measures of Capacity
Authors: Nelson Michael D , Crisostomo Marisa , Khericha Alifiya , Russo Francis , Thorne Gary L
Published: January 2013

We briefly summarize two important debates regarding selective attention (early vs late selection; perceptual load vs distractor dilution). Also, we report the results of an attempt to replicate Lavie (1995, Journal of Experimental Psychology: Human Perception and Performance21 451–468). We suggest that measures capable of characterizing the capacity of information processing systems (compared to reporting only mean reaction time) could add great clarity to this literature.
Whatever Happened to Object-Centered Representations?
Authors: Hayward William G
Published: January 2013

David Marr's approach to the study of vision has been tremendously influential. However, the approach proposes the goal of computing invariant shape descriptions from image-based information, a task that appears implausible, given the tremendous variation that can occur between images displaying a single object. Theorists in the field of three-dimensional object recognition have rejected the approach of computing object-centered representations, and instead propose representations of objects from the perspective of a viewer. If object-centered descriptions of objects exist in the brain, they are more likely to underlie motor interaction with objects rather than visual object understanding.
Evidence for the effect of homes on wildfire suppression costs
Authors: Gude Patricia H. , Jones Kingsford , Rasker Ray , Greenwood Mark C.
Published: January 2013

This paper uses wildfires in the Sierra Nevada area of California to estimate the relationship between housing and fire suppression costs. We investigated whether the presence of homes was associated with increased costs of firefighting after controlling for the effects of potential confounding variables including fire size, weather, terrain and human factors such as road access. This paper investigates wildfires in a way that other published studies have not; we analysed costs at the daily level, retaining information that would have been lost had we aggregated the data. We used linear mixed models to estimate the effects of homes on daily costs while incorporating within-fire variation. We conclude that the expected increase in the log daily cost with each unit increase in the log count of homes within 6 miles (~9.7 km) of an active fire is 0.07 (P = 0.005). The findings of this study are in agreement with most other previous empirical studies that have investigated the relationship between fire suppression costs and housing using cumulative fire costs and more generalised data on home locations. The study adds to mounting evidence that increases in housing lead to increases in fire suppression costs.
High-pressure NMR reveals close similarity between cold and alcohol protein denaturation in ubiquitin
Authors: Vajpai Navratna , Nisius Lydia , Wiktor Maciej , Grzesiek Stephan
Published: January 2013

Proteins denature not only at high, but also at low temperature as well as high pressure. These denatured states are not easily accessible for experiment, because usually heat denaturation causes aggregation, whereas cold or pressure denaturation occurs at temperatures well below the freezing point of water or pressures above 5 kbar, respectively. Here we have obtained atomic details of the pressure-assisted, cold-denatured state of ubiquitin at 2,500 bar and 258 K by high-resolution NMR techniques. Under these conditions, a folded, native-like and a disordered state exist in slow exchange. Secondary chemical shifts show that the disordered state has structural propensities for a native-like N-terminal β-hairpin and α-helix and a nonnative C-terminal α-helix. These propensities are very similar to the previously described alcohol-denatured (A-)state. Similar to the A-state,
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N relaxation data indicate that the secondary structure elements move as independent segments. The close similarity of pressure-assisted, cold-denatured, and alcohol-denatured states with native and nonnative secondary elements supports a hierarchical mechanism of folding and supports the notion that similar to alcohol, pressure and cold reduce the hydrophobic effect. Indeed, at nondenaturing concentrations of methanol, a complete transition from the native to the A-state can be achieved at ambient temperature by varying the pressure from 1 to 2,500 bar. The methanol-assisted pressure transition is completely reversible and can also be induced in protein G. This method should allow highly detailed studies of protein-folding transitions in a continuous and reversible manner.
Cleaved-coupled nanowire lasers
Authors: Gao Hanwei , Fu Anthony , Andrews Sean C. , Yang Peidong
Published: January 2013

The miniaturization of optoelectronic devices is essential for the continued success of photonic technologies. Nanowires have been identified as potential building blocks that mimic conventional photonic components such as interconnects, waveguides, and optical cavities at the nanoscale. Semiconductor nanowires with high optical gain offer promising solutions for lasers with small footprints and low power consumption. Although much effort has been directed toward controlling their size, shape, and composition, most nanowire lasers currently suffer from emitting at multiple frequencies simultaneously, arising from the longitudinal modes native to simple Fabry–Pérot cavities. Cleaved-coupled cavities, two Fabry–Pérot cavities that are axially coupled through an air gap, are a promising architecture to produce single-frequency emission. The miniaturization of this concept, however, imposes a restriction on the dimensions of the intercavity gaps because severe optical losses are incurred when the cross-sectional dimensions of cavities become comparable to the lasing wavelength. Here we theoretically investigate and experimentally demonstrate spectral manipulation of lasing modes by creating cleaved-coupled cavities in gallium nitride (GaN) nanowires. Lasing operation at a single UV wavelength at room temperature was achieved using nanoscale gaps to create the smallest cleaved-coupled cavities to date. Besides the reduced number of lasing modes, the cleaved-coupled nanowires also operate with a lower threshold gain than that of the individual component nanowires. Good agreement was found between the measured lasing spectra and the predicted spectral modes obtained by simulating optical coupling properties. This agreement between theory and experiment presents design principles to rationally control the lasing modes in cleaved-coupled nanowire lasers.
αvβ8 integrin interacts with RhoGDI1 to regulate Rac1 and Cdc42 activation and drive glioblastoma cell invasion
Authors: Reyes Steve B. , Narayanan Anjana S. , Lee Hye Shin , Tchaicha Jeremy H. , Aldape Kenneth D. , Lang Frederick F. , Tolias Kimberly F. , McCarty Joseph H.
Published: January 2013

The malignant brain cancer glioblastoma multiforme (GBM) displays invasive growth behaviors that are regulated by extracellular cues within the neural microenvironment. The adhesion and signaling pathways that drive GBM cell invasion remain largely uncharacterized. Here we use human GBM cell lines, primary patient samples, and preclinical mouse models to demonstrate that integrin αvβ8 is a major driver of GBM cell invasion. β8 integrin is overexpressed in many human GBM cells, with higher integrin expression correlating with increased invasion and diminished patient survival. Silencing β8 integrin in human GBM cells leads to impaired tumor cell invasion due to hyperactivation of the Rho GTPases Rac1 and Cdc42. β8 integrin coimmunoprecipitates with Rho-GDP dissociation inhibitor 1 (RhoGDI1), an intracellular signaling effector that sequesters Rho GTPases in their inactive GDP-bound states. Silencing RhoGDI1 expression or uncoupling αvβ8 integrin–RhoGDI1 protein interactions blocks GBM cell invasion due to Rho GTPase hyperactivation. These data reveal for the first time that αvβ8 integrin, via interactions with RhoGDI1, regulates activation of Rho proteins to promote GBM cell invasiveness. Hence targeting the αvβ8 integrin–RhoGDI1 signaling axis might be an effective strategy for blocking GBM cell invasion.
Rab11-family interacting proteins define spatially and temporally distinct regions within the dynamic Rab11a-dependent recycling system
Authors: Baetz Nicholas W. , Goldenring James R.
Published: January 2013

The Rab11-family interacting proteins (Rab11-FIPs) facilitate Rab11-dependent vesicle recycling. We hypothesized that Rab11-FIPs define discrete subdomains and carry out temporally distinct roles within the recycling system. We used live-cell deconvolution microscopy of HeLa cells expressing chimeric fluorescent Rab11-FIPs to examine Rab11-FIP localization, transferrin passage through Rab11-FIP–containing compartments, and overlap among Rab11-FIPs within the recycling system. FIP1A, FIP2, and FIP5 occupy widely distributed mobile tubules and vesicles, whereas FIP1B, FIP1C, and FIP3 localize to perinuclear tubules. Internalized transferrin entered Rab11-FIP–containing compartments within 5 min, reaching maximum colocalization with FIP1B and FIP2 early in the time course, whereas localization with FIP1A, FIP1C, FIP3, and FIP5 was delayed until 10 min or later. Whereas direct interactions with FIP1A were only observed for FIP1B and FIP1C, FIP1A also associated with membranes containing FIP3. Live-cell dual-expression studies of Rab11-FIPs revealed the tubular dynamics of Rab11-FIP–containing compartments and demonstrated a series of selective associations among Rab11-FIPs in real time. These findings suggest that Rab11-FIP1 proteins participate in spatially and temporally distinct steps of the recycling process along a complex and dynamic tubular network in which Rab11-FIPs occupy discrete domains.
CDKL5 regulates flagellar length and localizes to the base of the flagella inChlamydomonas
Authors: Tam Lai-Wa , Ranum Paul T. , Lefebvre Paul A.
Published: January 2013

The length of Chlamydomonas flagella is tightly regulated. Mutations in four genes—LF1, LF2, LF3, and LF4—cause cells to assemble flagella up to three times wild-type length. LF2 and LF4 encode protein kinases. Here we describe a new gene, LF5, in which null mutations cause cells to assemble flagella of excess length. The LF5 gene encodes a protein kinase very similar in sequence to the protein kinase CDKL5. In humans, mutations in this kinase cause a severe form of juvenile epilepsy. The LF5 protein localizes to a unique location: the proximal 1 μm of the flagella. The proximal localization of the LF5 protein is lost when genes that make up the proteins in the cytoplasmic length regulatory complex (LRC)—LF1, LF2, and LF3—are mutated. In these mutants LF5p becomes localized either at the distal tip of the flagella or along the flagellar length, indicating that length regulation involves, at least in part, control of LF5p localization by the LRC.