bluuebunny/crossref_metadata_2025 huggingface dataset:
General formulation of thermal, field, and photoinduced electron emission
Authors: Jensen Kevin L.
Published: July 2007

The canonical equations of electron emission are the Richardson-Laue-Dushman equation for thermionic emission, the Fowler-Nordheim equation for field emission, and the Fowler-Dubridge equation for photoemission. They are widely used and experimentally well vetted for the determination of current density from electron sources. While all three may be obtained from a general underlying formulation, they are treated as distinct as their domains of applicability do not overlap. Here, a tractable analytical model is given that not only devolves to the canonical equations, but also and more importantly is effective in the transition regions when the emission currents from tunneling, thermal emission, and/or photoemission become comparable but where the canonical equations are inapplicable. The resulting thermal-field-photoemission equation has application to emerging advanced electron sources as well as for emission models required by beam simulation codes.
Simultaneous time and frequency detection in femtosecond coherent Raman spectroscopy. I. Theory and model calculations
Authors: Urbanek Diana C. , Berg Mark A.
Published: July 2007

For coherent Raman spectroscopies, common femtosecond pulses often lie in an intermediate regime: their bandwidth is too wide for measurements in the frequency domain, but their temporal width is too broad for homodyne measurements in the time domain. A recent paper [S. Nath et al., Phys. Rev. Lett. 97, 267401 (2006)] showed that complete Raman spectra can be recovered from intermediate length pulses by using simultaneous time and frequency detection (TFD). Heterodyne detection and a phase-stable local oscillator at the anti-Stokes frequency are not needed with TFD. This paper examines the theory of TFD Raman in more detail; a companion paper tests the results on experimental data. Model calculations illustrate how information on the Raman spectrum is transferred from the frequency domain to the time domain as the pulse width shortens. When data are collected in both dimensions, the Raman spectrum is completely determined to high resolution, regardless of the probe pulse width. The loss of resolution in many femtosecond coherent Raman experiments is due to the restriction to one-dimensional data collection, rather than due to a fundamental restriction based on the pulse width.
Laboratory experiments of fine-scale mixing and mass transport within a coral canopy
Authors: Reidenbach Matthew A. , Koseff Jeffrey R. , Monismith Stephen G.
Published: July 2007

Laboratory experiments obtained fine scale measurements of turbulent shear stresses and rates of mixing and mass transfer over a nonliving bed of the coral, Porites compressa, the dominant species found in Kaneohe Bay, Hawaii. A reef canopy was placed in a recirculating wave-current flume and flow was generated that simulated the flow characteristics of the reef flat of Kaneohe Bay. Turbulence and velocity structure under both unidirectional and wave-dominated currents were measured using a two-dimensional laser Doppler anemometer. Mass transport measurements were made using a planar laser-induced fluorescence technique in which the scalar transport of Rhodamine 6G dye, fluxed from the surfaces of the coral, was quantified. Results show that the action of surface waves, interacting with the structure of the reef, can increase instantaneous shear and mixing up to six times compared to that of unidirectional currents. Maximum shear and mass transport events coincided with flow separation within the wave-current boundary layer and the ejection of vortices into the flow. Wave action also acted to increase the vertical flux of water from within the coral structure. The combined effects of increased turbulent stress and fluid exchange from the interior of the canopy increased mass flux due to wave action 2.3±0.5 times that measured for comparable unidirectional currents.
Effect of bunch periodicity on coherent spontaneous emission in a waveguide free-electron laser
Authors: Seo Y. H.
Published: July 2007

Investigated is coherent spontaneous emission of periodic electron bunches in a closed waveguide free-electron laser when the bunch period is equal to the round-trip time of the radiation pulse. In addition to the main resonance, auxiliary resonances due to the bunch periodicity are observed.
Core-shell structures in single flexible-semiflexible block copolymers: Finding the free energy minimum for the folding transition
Authors: Yoshinaga Natsuhiko , Yoshikawa Kenichi
Published: July 2007

We investigate the folding transition of a single diblock copolymer consisting of a semiflexible and a flexible block. We obtain a Saturn-shaped core-shell conformation in the folded state, in which the flexible block forms a core and the semiflexible block wraps around it. We demonstrate two distinctive features of the core-shell structures: (i) The kinetics of the folding transition in the copolymer are significantly more efficient than those of a semiflexible homopolymer. (ii) The core-shell structure does not depend on the transition pathway.
To the theory of rare gas alloys: heat capacity
Authors: Bagatskii M. I. , Feodosyev S. B. , Gospodarev I. A. , Kotlyar O. V. , Manzhelii E. V. , Nedzvetskiy A. V. , Syrkin E. S.
Published: July 2007

The low-temperature heat capacity of cryocrystals containing impurity clusters is investigated theoretically and experimentally. Such defects might essentially enrich the low-frequency part of the phonon spectrum by introducing both localized and delocalized vibrations. The effect of both types of vibrations on the temperature dependence of the heat capacity is analyzed. The heat capacity of the disordered solid solution Kr–Ar (Ar concentration ∼25%) is studied as an example of the effect of the light, weakly coupled impurities on the low-temperature thermodynamic characteristics of a system. The mass defect of such an impurity induces “phonon pumping” from the low-frequency part of the spectrum into the high-frequency part and decreases the low-temperature heat capacity, while the weakened interaction between the impurity and the host atoms, combined with even weaker interaction between the impurities, leads to the formation of a low-temperature maximum on the heat capacity temperature dependence. The analysis performed shows that at rather high Ar concentrations, the nonmonotonic temperature dependence of the relative change in the heat capacity of Kr1−pArp solid solutions is a result of the excitation of delocalized high-dispersion low-frequency phonons.
Lattice dynamics of cryocrystals at high pressure
Authors: Horbenko E. E. , Troitskaya E. P. , Chabanenko Val. V.
Published: July 2007

The lattice dynamics of cryocrystals is investigated from first principles in the framework of the Tolpygo model over a wide range of pressures. The phonon frequencies in rare-gas solids are calculated in terms of models that go beyond the scope of the adiabatic approximation. At high pressure the phonon spectrum along the Δ and Σ directions is distorted, and the longitudinal L and transverse T2 modes soften as a result of the electron-phonon interaction, with the relative contribution decreasing in the sequence Ar, Kr, Xe. The calculated phonon frequencies are in good agreement with the experimental data for argon crystals at a pressure 3.1GPa.
Quantitative evaluation of the effects of positional versus orientational disorder on the scattering of acoustic phonons in disordered matter
Authors: Bermejo F. J. , Fernández-Perea R. , Cabrillo C. , Krivchikov A. I. , Yushchenko A. N. , Manzhelii V. G. , Korolyuk O. A. , González M. A. , Jimenez-Ruiz M.
Published: July 2007

The phonon scattering processes in the three solid phases of ethanol are investigated using thermal conductivity and light- and neutron-scattering measurements as well as molecular dynamics simulations on single-crystal models for two crystalline modifications (fully ordered monoclinic and orientationally disordered bcc phases). The orientationally disordered crystal is found to exhibit a temperature dependence of the thermal conductivity that is remarkably close to that of a structurally disordered solid, especially at low temperatures. These results, together with measurements of Brillouin linewidths as derived from light-scattering measurements, emphasize the role of orientational disorder in phonon scattering. The experimental results obtained on polycrystalline samples are then discussed with the aid of computer simulations on single-crystal models of both bcc and monoclinic crystals. Our findings are in good agreement with the wealth of thermodynamic and dynamic data available so far, but at variance with the inferences drawn from inelastic x-ray data on polycrystalline samples, where a common nature for the excitations in all phases is postulated.
Heat transfer in crystalline clathrate hydrates at low temperatures
Authors: Krivchikov A. I. , Korolyuk O. A. , Romantsova O. O.
Published: July 2007

The experimental results on the thermal conductivity κ(T) of crystalline Xe, CH4, and THF clathrate hydrates are analyzed. In a wide region of temperatures above 2K, κ(T) exhibits a behavior typical of disordered solids, which depends weakly on their chemical composition, crystalline structure, and microstructure. The results are discussed in the context of phenomenological models of phonon scattering by local modes. It is found that the Xe clathrate has a feature unusual for glasses, namely, κ(T) decreases almost two-fold as the temperature increases from 50 to 100K. The behavior of κ(T) is presumably determined mainly by the strong phonon scattering on water molecules.
Heat capacity and spin susceptibility of two-dimensional t–J model
Authors: Antsygina T. N. , Poltavskaya M. I. , Poltavsky I. I. , Chishko K. A.
Published: July 2007

Thermodynamic properties of the t–J model on square and triangular lattices near half-filling are investigated theoretically within an analytical approach based on the Kondo and Yamaji’s Green function decoupling scheme. The temperature dependences of the heat capacity and spin susceptibility are calculated in a wide temperature range for the case when the exchange constant J is greater than the hopping amplitude t. It was found that with increase of doping from half-filling, the maximum of the spin susceptibility increases, and its position shifts to lower temperatures for both types of lattices. Such behavior is in agreement with qualitative predictions [E. Dagotto, Rev. Mod. Phys. 66, 763 (1994)]. The heat capacity demonstrates a double peak shape. The high temperature peak associated with the “spin wave”-like excitations shifts to lower temperatures with doping. The appearance of the low-temperature peak is due to holes, and its height and position depend on both the doping and the ratio t∕J.
Time of flight secondary ion mass spectrometry: A powerful high throughput screening tool
Authors: Smentkowski Vincent S. , Ostrowski Sara G.
Published: July 2007

Combinatorial materials libraries are becoming more complicated; successful screening of these libraries requires the development of new high throughput screening methodologies. Time of flight secondary ion mass spectrometry (ToF-SIMS) is a surface analytical technique that is able to detect and image all elements (including hydrogen which is problematic for many other analysis instruments) and molecular fragments, with high mass resolution, during a single measurement. Commercial ToF-SIMS instruments can image 500μm areas by rastering the primary ion beam over the region of interest. In this work, we will show that large area analysis can be performed, in one single measurement, by rastering the sample under the ion beam. We show that an entire 70mm diameter wafer can be imaged in less than 90min using ToF-SIMS stage (macro)rastering techniques. ToF-SIMS data sets contain a wealth of information since an entire high mass resolution mass spectrum is saved at each pixel in an ion image. Multivariate statistical analysis (MVSA) tools are being used in the ToF-SIMS community to assist with data interpretation; we will demonstrate that MVSA tools provide details that were not obtained using manual (univariate) analysis.
Depth profile investigations of silicon nanocrystals formed in sapphire by ion implantation
Authors: Yerci S. , Yildiz I , Kulakci M. , Serincan U. , Barozzi M. , Bersani M. , Turan R.
Published: July 2007

Depth profiles of Si nanocrystals formed in sapphire by ion implantation and the effect of charging during X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements have been studied. Atomic concentration and the chemical environment of Si, Al, and O have been measured as a function of depth from the sample surface by SIMS and XPS. Both as-implanted and annealed samples have been analyzed to understand the effect of nanocrystal formation on the depth distribution, chemical structure, and the charging effect before and after the formation process. SIMS measurements have revealed that the peak position of the Si concentration shifts to deeper values with implantation dose. This is explained by the fact that the structure of the matrix undergoes a phase transformation from pure sapphire to a Si rich amorphous Al2O3 with heavy dose implantation. Formation of Si nanocrystals has been observed by XPS by an increase in the Si-Si signal and a decrease in Si-O bond concentrations after the annealing. Variation in binding energies of Si and O with Si concentration (i.e., with depth) has been studied in terms of chemical environments and charging effects. It is found that binding energy of these elements shifts to lower values with increasing Si content. This is a result of less charging due to the presence of easy discharge paths in the Si rich regions of the matrix. Nanocrystal formation leads to even less charging which is probably due to the further increase in conductivity with the formation.
Precise thermodynamic control of high pressure jet expansions
Authors: Christen Wolfgang , Krause Tim , Rademann Klaus
Published: July 2007

We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T0=225–425K with a thermal stability ΔT0<30mK and stagnation pressures p0=0.2–12MPa that are measured with 0.05% precision. For optimum stability, gas reservoir, pressure transducer, and gauge amplifier are temperature-controlled, and a feedback loop permits active pressure stabilization using a pulseless syringe pump. With this approach stagnation pressures can be reproduced and kept constant to Δp0<2.9kPa. As a result, flow velocity and kinetic energy of molecular beams can be controlled with maximum accuracy.
Effect of alloy composition on the thermodynamic and kinetic parameters of the A1 to L1 transformation in FePt, FeNiPt, and FeCuPt films
Authors: Berry D. C. , Barmak K.
Published: July 2007

Differential scanning calorimetry is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 39.3−55.3 at. % Pt and ternary FePt-based films with additions of Cu up to 20 at. % and Ni up to 25 at. % for a range of Fe/Pt ratios. For FePt and FeCuPt, these are extensions of previously studied ranges [K. Barmak, J. Kim, D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005)]. Parameters including the A1 and L10 phase Curie temperatures, the kinetic ordering temperature, the activation energy, and the transformation enthalpy are reported. For FePt, the L10 Curie temperature reaches a maximum of 457 °C near 45 at. % Pt. In contrast, the A1 Curie temperature has an essentially constant value of 300 °C across the full composition. Both the kinetic ordering temperature and activation energy show a minimum near 46 at. % Pt, while the magnitude of the transformation enthalpy has its maximum near 50 at. % Pt. Ni additions to FePt in general lower the L10 Curie temperature, but they increase the A1 Curie temperature. The kinetic ordering temperature and the activation energy increase for all Ni additions, whereas the transformation enthalpy decreases measurably only for Ni additions over ∼10 at. %. Cu additions to FePt act as magnetic diluents regarding both the A1 and L10 phase Curie temperatures, with increased Cu content resulting in decreased Curie temperature. Conversely, Cu additions have no significant effect on the kinetic ordering temperature, activation energy, or transformation enthalpy when compared to equivalent binary alloys. The relevance of our findings to alloy development for ultrahigh density magnetic recording media is discussed, with specific focus on the potential for heat-assisted magnetic recording.
Left-handed materials made of dilute ferromagnetic wire arrays with gyrotropic tensors
Authors: Chen Jiangwei , Tang Dongming , Zhang Baoshan , Yang Yi , Lu Mu , Lu Huaixian , Lu Feng , Xu Weidong
Published: July 2007

In this article, we theoretically investigate properties of normally incident microwave propagation in dilute metallic ferromagnetic wire array (DMFWA) slabs with gyrotropic tensors. It is found that DMFWA may become left-handed materials (LHM) in a narrow frequency range below the plasma frequency, even the real part of the corresponding inversion permeability element is positive. Comparing with the isotropic materials having same diagonal permeability elements, due to existence of off-diagonal elements of the gyrotropic permeability tensor, the DMFWA becomes a LHM in a higher frequency range depended on its geometric structure. In addition, E, H, and wave vector Re(k) of microwave propagating in the DMFWA form an approximately left-handed triplet of vectors.
Electron and hole traps in N-doped ZnO grown on p-type Si by metalorganic chemical vapor deposition
Authors: Fang Z.-Q. , Claflin B. , Look D. C. , Kerr Lei L. , Li Xiaonan
Published: July 2007

Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+−p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in the p-Si substrate, while one electron trap E3 (0.29 eV) and one hole trap H5 (0.9 eV) are observed in the thin ZnO:N layer. Similarities to traps reported in the literature are discussed.
Comment on “Adhesion-delamination mechanics of a prestressed rectangular film adhered onto a rigid substrate”
Authors: Yang Fuqian
Published: July 2007

In this work, it is shown that the equilibrium equation used by Wong et al. [M. F. Wong, G. Duan, and K. T. Wan, J. Appl. Phys. 101, 024903 (2007)] is inappropriate for the analysis of the contact adhesion of a beam-rigid punch system. The correct form of the equilibrium equation is proposed. Discussion is made about the statement of Wong et al. on Yang’s work.
Unexpected dielectric response in lead zirconate titanate ceramics: The role of ferroelectric domain wall pinning effects
Authors: Garcia J. E. , Gomis V. , Perez R. , Albareda A. , Eiras J. A.
Published: July 2007

Temperature dependent dielectric response has been measured in Pb(Zr1−xTix)O3 ceramics. Samples of different compositions (x=0.40, 0.47, and 0.60), pure and doped with Nb-or Fe, were studied at temperatures between 15 and 700K and in the frequency range from 100Hzto1MHz. Unexpected dielectric behavior has been found around room temperature. Anomalous temperature dependent permittivity is observed in pure and Fe-doped samples but not in Nb-doped samples. The anomaly appears related to the presence of oxygen vacancies but not on the sample crystallographic phase. The authors suggest that the anomaly may be a manifestation of the domain wall pinning effect.
Hole-transporting-layer-free high-efficiency fluorescent blue organic light-emitting diodes
Authors: Jou Jwo-Huei , Chiang Po-Hsuan , Lin Yu-Pu , Chang Chin-Yeh , Lai Chun-Liang
Published: July 2007

High-efficiency fluorescent blue organic light-emitting diodes were fabricated using hole-injection and carrier-confining effective device architecture without a hole-transporting layer. The diodes consist of 1250Å indium tin oxide/300Å blue-emissive layer/400Å electron-transporting layer/10Å lithium fluoride/1500Å aluminum. A high efficiency of 6.0% (12.5lm∕W) at 100cd∕m2 with a pan-blue emission of (0.19, 0.31) when trans-1,2-bis-(6-(N,N-di-p-tolylamino)naphthalene-2-yl)ethene was used in the emissive layer, or 3.9% (6.7lm∕W) with a blue emission of (0.15, 0.20) when 2-(N,N-diphenylamino)-6-[4-(N,N-diphenylamino)-styryl]naphthalene was used. Besides having a thinner device structure, the marked improvement in efficiency is attributable mainly to the relatively low hole-injection barrier.
Optofluidic maskless lithography system for real-time synthesis of photopolymerized microstructures in microfluidic channels
Authors: Chung Su Eun , Park Wook , Park Hyunsung , Yu Kyoungsik , Park Namkyoo , Kwon Sunghoon
Published: July 2007

The authors propose an optofluidic maskless lithography technique that can dynamically synthesize free-floating polymeric microstructures inside microfluidic channels by selectively polymerizing photocurable resin with high-speed two-dimensional spatial light modulators. The combination of programable optical projection and microfluidic devices allows one to precisely control the timing and location of the photopolymerization process for microstructure fabrication. Real-time generation of microparticles with various shapes, sizes, ordering, and material contents are experimentally demonstrated. Long polymeric structures of which size is not limited by the exposure field of view can also be fabricated.
Bulk metallic glasses based on binary cerium and lanthanum elements
Authors: Liu X. F. , Wang R. J. , Zhao D. Q. , Pan M. X. , Wang W. H.
Published: July 2007

The authors reported the formation and dynamic and thermodynamic properties of bulk metallic glasses (BMGs) based on binary Ce and La elements, in which the compositions of Ce and La can be gradually changed in the range from 0 to 100at.% without deteriorating the glass-forming ability. The properties of the binary base glasses can be tuned by modification of the Ce and La compositions. The BMGs with unique features and tunable properties might provide a model system to investigate some long-standing issues in BMG-forming alloys. The approach has implication for designing BMGs with tunable properties.
In situ neutron diffraction under tensile loading of powder-in-tube Cu∕Nb3Sn composite wires: Effect of reaction heat treatment on texture, internal stress state, and load transfer
Authors: Scheuerlein C. , Stuhr U. , Thilly L.
Published: July 2007

The strain induced degradation of Nb3Sn superconductors can hamper the performance of high field magnets. The authors report elastic strain measurements in the different phases of entire non-heat treated and fully reacted Nb3Sn composite strands as a function of uniaxial stress during in situ deformation under neutron beam. After the reaction heat treatment the Cu matrix loses entirely its load carrying capability and the applied stress is transferred to the remaining Nb–Ta alloy and to the brittle (Nb–Ta)3Sn phase, which exhibits a preferential ⟨110⟩ grain orientation parallel to the strand axis.
Ambipolar organic field-effect transistors based on a low band gap semiconductor with balanced hole and electron mobilities
Authors: Chikamatsu Masayuki , Mikami Takefumi , Chisaka Jiro , Yoshida Yuji , Azumi Reiko , Yase Kiyoshi , Shimizu Akihiro , Kubo Takashi , Morita Yasushi , Nakasuji Kazuhiro
Published: July 2007

The authors have demonstrated the thin-film properties and the ambipolar transport of a delocalized singlet biradical hydrocarbon with two phenalenyl radical moieties (Ph2-IDPL). The organic field-effect transistors (OFETs) based on Ph2-IDPL exhibit ambipolar transport with balanced hole and electron mobilities in the order of 10−3cm2∕Vs. The Ph2-IDPL film is an organic semiconductor with a low band gap of 0.8eV and has small injection barriers from gold electrodes to both the highest occupied molecular orbital and the lowest unoccupied molecular orbital. A complementary metal-oxide-semiconductor-like inverter using two identical Ph2-IDPL based ambipolar OFETs shows a sharp inversion of the input voltage with high gain.
Dyslexia: Sensory Deficits or Inattention?
Authors: Skottun Bernt Christian , Skoyles John
Published: July 2007

An important question in regard to dyslexia is whether or not this condition is the result of sensory deficits. A number of studies have indeed found sensory deficiencies in dyslexic readers. However, it has been proposed that these are due simply to inattention. If so, this would be expected to produce either (i) a general reduction or (ii) random reductions in performance. On the basis of published data, it seems that neither of these is in fact the case. Rather the data indicate reproducible non-random patterns of deficiencies with regard to stimulus conditions. The stimulus specificity of the deficits represents, therefore, an important issue which needs to be addressed by any attempt to account for the sensory deficiencies of dyslexic readers in terms of inattention.
Relationship between Frames of Reference and Mirror-Image Reversals
Authors: Yoshimura Hirokazu , Tabata Tatsuo
Published: July 2007

The mirror puzzle related to the perception of mirror images as left–right reversed can be more fully understood by considering an extended problem that includes also the perception of mirror images that are not left–right reversed. The purpose of the present study is to clarify the physical aspect of this extended problem logically and parsimoniously. Separate use of the intrinsic frame of reference that belongs to the object and one that belongs to its mirror image always leads to the perception of left–right reversal when the object has left–right asymmetry; on the other hand, the perception of left–right nonreversal is always due to the application of a common frame of reference to the object and its mirror image.
The Visual Discrimination of Bending
Authors: Norman J Farley , Wiesemann Elizabeth Y , Norman Hideko F , Taylor M Jett , Craft Warren D
Published: July 2007

The sensitivity of observers to nonrigid bending was evaluated in two experiments. In both experiments, observers were required to discriminate on any given trial which of two bending rods was more elastic. In experiment 1, both rods bent within the same oriented plane, and bent either in a frontoparallel plane or bent in depth. In experiment 2, the two rods within any given trial bent in different, randomly chosen orientations in depth. The results of both experiments revealed that human observers are sensitive to, and can reliably detect, relatively small differences in bending (the average Weber fraction across experiments 1 and 2 was 9.0%). The performance of the human observers was compared to that of models that based their elasticity judgments upon either static projected curvature or mean and maximal projected speed. Despite the fact that all of the observers reported compelling 3-D perceptions of bending in depth, their judgments were both qualitatively and quantitatively consistent with the performance of the models. This similarity suggests that relatively straightforward information about the elasticity of simple bending objects is available in projected retinal images.
Grouping by Contrast: Figure – Ground Segregation is Not Necessarily Fundamental
Authors: Shapiro Arthur G , Hamburger Kai
Published: July 2007

A central tenet of Gestalt psychology is that the visual scene can be separated into figure and ground. The two illusions we present demonstrate that Gestalt processes can group spatial contrast information that cuts across the figure/ground separation. This finding suggests that visual processes that organise the visual scene do not necessarily require structural segmentation as their primary input.
The Effect of Brief Auditory Stimuli on Visual Apparent Motion
Authors: Getzmann Stephan
Published: July 2007

When two discrete stimuli are presented in rapid succession, observers typically report a movement of the lead stimulus toward the lag stimulus. The object of this study was to investigate crossmodal effects of irrelevant sounds on this illusion of visual apparent motion. Observers were presented with two visual stimuli that were temporally separated by interstimulus onset intervals from 0 to 350 ms. After each trial, observers classified their impression of the stimuli using a categorisation system. The presentation of short sounds intervening between the visual stimuli facilitated the impression of apparent motion relative to baseline (visual stimuli without sounds), whereas sounds presented before the first and after the second visual stimulus as well as simultaneously presented sounds reduced the motion impression. The results demonstrate an effect of the temporal structure of irrelevant sounds on visual apparent motion that is discussed in light of a related multisensory phenomenon, ‘temporal ventriloquism’, on the assumption that sounds can attract lights in the temporal dimension.
Perceived Depth in the ‘Sieve Effect’ and Exclusive Binocular Rivalry
Authors: Matsumiya Kazumichi , Howard Ian P , Kaneko Hirohiko
Published: July 2007

An impression of a surface seen through holes is created when one fuses dichoptic pairs of discs, with one member of each pair black and the other member white. This is referred to as the ‘sieve effect’. The stimulus contains no positional disparities. Howard (1995, Perception24 67–74) noted qualitatively that the sieve effect occurs when the rivalrous regions are within the range of sizes, contrasts, and relative sizes where exclusive rivalry occurs, rather than binocular lustre, stimulus combination, or dominant rivalry. This suggests that perceived depth in the sieve effect should be at a maximum when exclusive rivalry is most prominent. We used a disparity depth probe to measure the magnitude of perceived depth in the sieve effect as a function of the sizes, contrasts, and relative sizes of the rivalrous regions. We also measured the rate of exclusive rivalry of the same stimuli under the same conditions. Perceived depth and the rate of exclusive rivalry were affected in the same way by each of the three variables. Furthermore, perceived depth and the rate of exclusive rivalry were affected in the same way by changes in vergence angle, although the configuration of the stimulus surface was held constant. These findings confirm the hypothesis that the sieve effect is correlated with the incidence of exclusive rivalry.
Mycorrhizal effects on growth and nutrition of tomato under elevated atmospheric carbon dioxide
Authors: Cavagnaro Timothy R. , Sokolow Shannon K. , Jackson Louise E.
Published: July 2007

Arbuscular mycorrhizas are predicted to be important in defining plant responses to elevated atmospheric CO2 concentrations. A mycorrhiza-defective tomato (Solanum lycopersicum L.) mutant with reduced mycorrhizal colonisation (rmc) and its mycorrhizal wild-type progenitor (76R MYC+) were grown under ambient and elevated atmospheric CO2 concentrations (eCO2) in a controlled environment chamber-based pot study. Plant growth, nutrient contents and mycorrhizal colonisation were measured four times over a 72-day period. The 76R MYC+ plants generally had higher concentrations of P, N and Zn than their rmc counterparts. Consistent with earlier studies, mycorrhizal colonisation was not affected by eCO2. Growth of the two genotypes was very similar under ambient CO2 conditions. Under eCO2 the mycorrhizal plants initially had higher biomass, but after 72 days, biomass was lower than for rmc plants, suggesting that in this pot study the costs of maintaining carbon inputs to the fungal symbiont outweighed the benefits with time.
δ13C of organic matter transported from the leaves to the roots in Eucalyptus delegatensis: short-term variations and relation to respired CO2
Authors: Gessler Arthur , Keitel Claudia , Kodama Naomi , Weston Christopher , Winters Anthony J. , Keith Heather , Grice Kliti , Leuning Ray , Farquhar Graham D.
Published: July 2007

Post-photosynthetic carbon isotope fractionation might alter the isotopic signal imprinted on organic matter (OM) during primary carbon fixation by Rubisco. To characterise the influence of post-photosynthetic processes, we investigated the effect of starch storage and remobilisation on the stable carbon isotope signature (δ13C) of different carbon pools in the Eucalyptus delegatensis R. T. Baker leaf and the potential carbon isotope fractionation associated with phloem transport and respiration. Twig phloem exudate and leaf water-soluble OM showed diel variations in δ13C of up to 2.5 and 2‰, respectively, with 13C enrichment during the night and depletion during the day. Damped diel variation was also evident in bulk lipids of the leaf and in the leaf wax fraction. δ13C of nocturnal phloem exudate OM corresponded with the δ13C of carbon released from starch. There was no change in δ13C of phloem carbon along the trunk. CO2 emitted from trunks and roots was 13C enriched compared with the potential organic substrate, and depleted compared with soil-emitted CO2. The results are consistent with transitory starch accumulation and remobilisation governing the diel rhythm of δ13C in phloem-transported OM and fragmentation fractionation occurring during respiration. When using δ13C of OM or CO2 for assessing ecosystem processes or plant reactions towards environmental constraints, post-photosynthetic discrimination should be considered.
Early flowering induction and Agrobacterium transformation of the hardwood tree species Eucalyptus occidentalis
Authors: Southerton Simon G.
Published: July 2007

Investigation of the genes controlling flowering in eucalypts is hindered by the lack of an early-flowering genotype. Induction of early flowering was studied in five provenances of Eucalyptus occidentalis Endl. sourced from throughout its geographic range. Seedlings initiated flowers from 13 weeks after sowing when grown under optimal conditions with a 16-h photoperiod. By 16 weeks, seedlings from four widely dispersed provenances had initiated floral buds, suggesting that competence to flower early is a common characteristic of the species. The different provenances displayed considerable variation in seedling growth rate. Elevated levels of CO2 had no effect on seedling growth rate, but were associated with delayed flowering. Transformation experiments demonstrated that E. occidentalis is susceptible to Agrobacterium-mediated transformation, in common with several other eucalypt species. E. occidentalis may be a valuable experimental species for molecular and other flowering studies in eucalypts.
Fast-scan atomic force microscopy reveals that the type III restriction enzyme EcoP15I is capable of DNA translocation and looping
Authors: Crampton Neal , Yokokawa Masatoshi , Dryden David T. F. , Edwardson J. Michael , Rao Desirazu N. , Takeyasu Kunio , Yoshimura Shige H. , Henderson Robert M.
Published: July 2007

Many DNA-modifying enzymes act in a manner that requires communication between two noncontiguous DNA sites. These sites can be brought into contact either by a diffusion-mediated chance interaction between enzymes bound at the two sites, or by active translocation of the intervening DNA by a site-bound enzyme. EcoP15I, a type III restriction enzyme, needs to interact with two recognition sites separated by up to 3,500 bp before it can cleave DNA. Here, we have studied the behavior of EcoP15I, using a novel fast-scan atomic force microscope, which uses a miniaturized cantilever and scan stage to reduce the mechanical response time of the cantilever and to prevent the onset of resonant motion at high scan speeds. With this instrument, we were able to achieve scan rates of up to 10 frames per s under fluid. The improved time resolution allowed us to image EcoP15I in real time at scan rates of 1–3 frames per s. EcoP15I translocated DNA in an ATP-dependent manner, at a rate of 79 ± 33 bp/s. The accumulation of supercoiling, as a consequence of movement of EcoP15I along the DNA, could also be observed. EcoP15I bound to its recognition site was also seen to make nonspecific contacts with other DNA sites, thus forming DNA loops and reducing the distance between the two recognition sites. On the basis of our results, we conclude that EcoP15I uses two distinct mechanisms to communicate between two recognition sites: diffusive DNA loop formation and ATPase-driven translocation of the intervening DNA contour.
Structural basis for reversible photoswitching in Dronpa
Authors: Andresen Martin , Stiel Andre C. , Trowitzsch Simon , Weber Gert , Eggeling Christian , Wahl Markus C. , Hell Stefan W. , Jakobs Stefan
Published: July 2007

Dronpa is a novel GFP-like fluorescent protein with exceptional light-controlled switching properties. It may be reversibly switched between a fluorescent on-state and a nonfluorescent off-state by irradiation with light. To elucidate the molecular basis of the switching mechanism, we generated reversibly switchable Dronpa protein crystals. Using these crystals we determined the elusive dark-state structure of Dronpa at 1.95-Å resolution. We found that the photoswitching results in a cis–trans isomerization of the chromophore accompanied by complex structural rearrangements of four nearby amino acid residues. Because of this cascade of intramolecular events, the chromophore is exposed to distinct electrostatic surface potentials, which are likely to influence the protonation equilibria at the chromophore. We suggest a comprehensive model for the light-induced switching mechanism, connecting a cascade of structural rearrangements with different protonation states of the chromophore.
TNF-α suppresses the expression of clock genes by interfering with E-box-mediated transcription
Authors: Cavadini Gionata , Petrzilka Saskia , Kohler Philipp , Jud Corinne , Tobler Irene , Birchler Thomas , Fontana Adriano
Published: July 2007

Production of TNF-α and IL-1 in infectious and autoimmune diseases is associated with fever, fatigue, and sleep disturbances, which are collectively referred to as sickness behavior syndrome. In mice TNF-α and IL-1 increase nonrapid eye movement sleep. Because clock genes regulate the circadian rhythm and thereby locomotor activity and may alter sleep architecture we assessed the influence of TNF-α on the circadian timing system. TNF-α is shown here to suppress the expression of the PAR bZip clock-controlled genes
Dbp
,
Tef
, and
Hlf
and of the period genes
Per1
,
Per2
, and
Per3
in fibroblasts
in vitro
and
in vivo
in the liver of mice infused with the cytokine. The effect of TNF-α on clock genes is shared by IL-1β, but not by IFN-α, and IL-6. Furthermore, TNF-α interferes with the expression of
Dbp
in the suprachiasmatic nucleus and causes prolonged rest periods in the dark when mice show spontaneous locomotor activity. Using clock reporter genes TNF-α is found here to inhibit CLOCK-BMAL1-induced activation of E-box regulatory elements-dependent clock gene promoters. We suggest that the increase of TNF-α and IL-1β, as seen in infectious and autoimmune diseases, impairs clock gene functions and causes fatigue.
Invasive range expansion by the Humboldt squid,
Dosidicus gigas
, in the eastern North Pacific
Authors: Zeidberg Louis D. , Robison Bruce H.
Published: July 2007

A unique 16-year time series of deep video surveys in Monterey Bay reveals that the Humboldt squid,
Dosidicus gigas
, has substantially expanded its perennial geographic range in the eastern North Pacific by invading the waters off central California. This sustained range expansion coincides with changes in climate-linked oceanographic conditions and a reduction in competing top predators. It is also coincident with a decline in the abundance of Pacific hake, the most important commercial groundfish species off western North America. Recognizing the interactive effects of multiple changes in the environment is an issue of growing concern in ocean conservation and sustainability research.
Evidence that RNA silencing functions as an antiviral defense mechanism in fungi
Authors: Segers Gert C. , Zhang Xuemin , Deng Fuyou , Sun Qihong , Nuss Donald L.
Published: July 2007

The role of RNA silencing as an antiviral defense mechanism in fungi was examined by testing the effect of dicer gene disruptions on mycovirus infection of the chestnut blight fungus
Cryphonectria parasitica. C. parasitica
dicer-like genes
dcl-1
and
dcl-2
were cloned and shown to share a high level of predicted amino acid sequence identity with the corresponding dicer-like genes from
Neurospora crassa
[Nc
dcl-1
(50.5%); Nc
dcl-2
(38.0%)] and
Magnaporthe oryzae
[
MDL-1
(45.6%);
MDL-2
(38.0%)], respectively. Disruption of
dcl-1
and
dcl-2
resulted in no observable phenotypic changes relative to wild-type
C. parasitica
. Infection of Δ
dcl-1
strains with hypovirus CHV1-EP713 or reovirus MyRV1-Cp9B21 resulted in phenotypic changes that were indistinguishable from that exhibited by wild-type strain
C. parasitica
EP155 infected with these same viruses. In stark contrast, the Δ
dcl-2
and Δ
dcl-1
/Δ
dcl-2
mutant strains were highly susceptible to mycovirus infection, with CHV1-EP713-infected mutant strains becoming severely debilitated. Increased viral RNA levels were observed in the Δ
dcl-2
mutant strains for a hypovirus CHV1-EP713 mutant lacking the suppressor of RNA silencing p29 and for wild-type reovirus MyRV1-Cp9B21. Complementation of the Δ
dcl-2
strain with the wild-type
dcl-2
gene resulted in reversion to the wild-type response to virus infection. These results provide direct evidence that a fungal dicer-like gene functions to regulate virus infection.
Reversibility in nucleocytoplasmic transport
Authors: Kopito Ronen Benjamine , Elbaum Michael
Published: July 2007

Nucleocytoplasmic exchange of proteins and RNAs is mediated by receptors that usher their cargo through the nuclear pores. Peptide localization signals on each cargo determine the receptors with which it will interact. Those interactions are normally regulated by the small GTPase Ran. Hydrolysis of GTP provides the chemical energy required to create a bona fide thermodynamic pump that selectively and directionally accumulates its substrates across the nuclear envelope. A common perception is that cargo delivery is irreversible, e.g., a protein imported to the nucleus does not return to the cytoplasm except perhaps via a specific export receptor. Quantitative measurements using cell-free nuclei reconstituted in
Xenopus
egg extract show that nuclear accumulation follows first-order kinetics and reaches steady state at a level that follows a Michaelis–Menten function of the cytoplasmic cargo concentration. This saturation suggests that receptor-mediated translocation across the nuclear pore occurs bidirectionally. The reversibility of accumulation was demonstrated directly by exchange of the cytosolic medium and by fluorescence recovery after photobleaching. Based on our results, we offer a simple biophysical model that predicts the observed behavior. A far-reaching consequence is that the nuclear localization signal dictates the fate of a protein population rather than that of the individual molecules that bear it, which remain free to shuttle back and forth. This implies an open communication between the nucleus and cytoplasm and a ubiquitous mechanism for signaling in both directions.
Silencing of genes in cultured
Drosophila
neurons by RNA interference
Authors: Sharma Shail K. , Nirenberg Marshall
Published: July 2007

Cultures of neuroblasts that generate abundant neurons were established from
Drosophila
embryos to study silencing of genes by RNA interference (RNAi). Cultured cells expressed ELAV, a marker of neurons, Futsch, a marker of neurites, and Synapsin, Synaptobrevin, and Synaptogamin, proteins involved in neurotransmitter secretion. Conditions were found for efficient transfection of cells with siRNAs for ELAV or the insulin-like receptor, which resulted in marked decreases in neurons that express ELAV and Futsch. Cells also were successfully transfected with long-chain Sox-Neuro dsRNA resulting in a 55% reduction of neurons expressing Futsch. The results suggest that this cultured neural cell system can be used to study RNAi-dependent silencing of genes involved in many kinds of neural functions.
Coevolution of robustness, epistasis, and recombination favors asexual reproduction
Authors: MacCarthy Thomas , Bergman Aviv
Published: July 2007

The prevalence of sexual reproduction remains one of the most perplexing phenomena in evolutionary biology. The deterministic mutation hypothesis postulates that sexual reproduction will be advantageous under synergistic epistasis, a condition in which mutations cause a greater reduction in fitness when combined than would be expected from their individual effects. The inverse condition, antagonistic epistasis, correspondingly is predicted to favor asexual reproduction. To assess this hypothesis, we introduce a finite population evolutionary process that combines a recombination modifier formalism with a gene-regulatory network model. We demonstrate that when reproductive mode and epistasis are allowed to coevolve, asexual reproduction outcompetes sexual reproduction. In addition, no correlation is found between the level of synergistic epistasis and the fixation time of the asexual mode. However, a significant correlation is found between the level of antagonistic epistasis and asexual mode fixation time. This asymmetry can be explained by the greater reduction in fitness imposed by sexual reproduction as compared with asexual reproduction. Our findings present evidence and suggest plausible explanations that challenge both the deterministic mutation hypothesis and recent arguments asserting the importance of emergent synergistic epistasis in the maintenance of sexual reproduction.
General design principle for scalable neural circuits in a vertebrate retina
Authors: Lee Sunhwa , Stevens Charles F.
Published: July 2007

Unlike mammals, fish continue to grow throughout their lives, to increase the size of their eyes and brain, and to add new neurons to both. As a result of visual system growth, the ability to detect small objects increases with the age and size of the fish. In addition to the birth of new retinal ganglion cells (RGCs), existing cells increase the size of their dendritic arbors with retinal growth. We have used this system to learn design principles a vertebrate retina uses to construct its neural circuits, and find that the size of RGC arbors changes with retina and eye size according to a power law with an exponent close to 1/2. This power law is expected if the retina uses a strategy that, independent of eye size, simultaneously optimizes both the accuracy with which each RGC represents light intensity and the image spatial resolution provided to the fish's brain.