bluuebunny/crossref_metadata_2025 huggingface dataset:
The Lexical Restructuring Hypothesis and Graph Theoretic Analyses of Networks Based on Random Lexicons
Authors: Gruenenfelder Thomas M. , Pisoni David B.
Published: April 2009

Purpose

The mental lexicon of words used for spoken word recognition has been modeled as a complex network or graph. Do the characteristics of that graph reflect processes involved in its growth (M. S. Vitevitch, 2008) or simply the phonetic overlap between similar-sounding words?

Method

Three pseudolexicons were generated by randomly selecting phonological segments from a fixed set. Each lexicon was then modeled as a graph, linking words differing by one segment. The properties of those graphs were compared with those of a graph based on real English words.

Results

The properties of the graphs built from the pseudolexicons matched the properties of the graph based on English words. Each graph consisted of a single large island and a number of smaller islands and hermits. The degree distribution of each graph was better fit by an exponential than by a power function. Each graph showed short path lengths, large clustering coefficients, and positive assortative mixing.

Conclusion

The results suggest that there is no need to appeal to processes of growth or language acquisition to explain the formal properties of the network structure of the mental lexicon. These properties emerged because the network was built based on the phonetic overlap of words.
Prevalence of Hearing Loss in Black and White Elders: Results of the Cardiovascular Health Study
Authors: Pratt Sheila R. , Kuller Lewis , Talbott Evelyn O. , McHugh-Pemu Kathleen , Buhari Alhaji M. , Xu Xiaohui
Published: April 2009

Purpose

The goal of this study was to determine the impact of age, gender, and race on the prevalence and severity of hearing loss in elder adults, aged 72–96 years, after accounting for income, education, smoking, and clinical and subclinical cardiovascular disease.

Methods

Air-conduction thresholds for standard and extended high-frequency pure-tones were obtained from a cohort of 548 (out of 717) elderly adults (ages 72–96 years) who were recruited during the Year 11 clinical visit (1999–2000) of the Cardiovascular Health Study (CHS) at the Pittsburgh, Pennsylvania site. Participant smoking, income, education, and cardiovascular disease histories were obtained from the CHS database and were included as factors.

Results

Hearing loss was more common and more severe for the participants in their 80s than for those in their 70s—the men more than the women and the White participants more than the Black participants. The inclusion of education, income, smoking, and cardiovascular disease (clinical and subclinical) histories as factors did not substantively impact the overall results.

Conclusion

Although the data reported in this article were cross-sectional and a cohort phenomenon might have been operational, they suggested that hearing loss is more substantive in the 8th than the 7th decade of life and that race and gender influence this decline in audition. Given the high prevalence in the aging population and the differences across groups, there is a clear need to understand the nature and causes of hearing loss across various groups in order to improve prevention and develop appropriate interventions.
Optical absorption and emission of fully conjugated heterocyclic aromatic rigid-rod polyelectrolytes containing sulfonated pendants
Authors: Bai Shih Jung , Han Shen-Rong
Published: April 2009

Fully conjugated and rodlike poly[(1,7-dihydrobenzo[1,2-ḏ:4,5-d′]diimidazole-2,6-diyl)-2-(2-sulfo)-p-phenylene] (sPBI) was synthesized and fabricated for monolayer light emitting diodes showing a threshold voltage of 4.5 V and an emission λmax of 530 nm. Intractable sPBI was derivatized for a fully conjugated water soluble rigid-rod polyelectrolyte sPBI-PS(Li+) which was doped with LiCF3SO3 or LiN(CF3SO2)2 for optical absorption, electrical conductivity, and luminescent emission. sPBI-PS(Li+) light emitting electrochemical cells doped with 0.41 and 1.01 wt % of LiN(CF3SO2)2 showed a threshold voltage of 2.8 V and a tenfold increase in electroluminescence intensity (at λmax=514 nm) which did not increase with its conductivity.
Nonlinear electromagnetic response of ferromagnetic metals: Magnetoimpedance in microwires
Authors: Seddaoui D. , Ménard D. , Movaghar B. , Yelon A.
Published: April 2009

Numerical calculations based on simultaneous solution of the Maxwell and Landau–Lifshitz equations were performed, in order to study the voltage response of ferromagnetic conductors carrying ac current. Since no significant approximations are made in the calculations, the model yields both linear and nonlinear giant magnetoimpedance (GMI) behavior and low and high power ferromagnetic resonance. Application to nonlinear GMI in ideal wires, with regions of uniform anisotropy, allows us to understand many aspects of the observed behavior and to predict phenomena such as solitary-wave-like propagation of the magnetization at fairly high current amplitude. Using appropriate magnetic structure, we were able to reproduce, with good agreement, the experimental observations for cobalt rich amorphous microwires. We have also found that even harmonics of GMI signal are very sensitive to the domain structure of the wire, whereas the odd harmonics are not.
Picosecond ultrasonic measurements using an optical cavity
Authors: Li Y. , Miao Q. , Nurmikko A. V. , Maris H. J.
Published: April 2009

A detailed analysis of the use of an optical cavity to enhance picosecond ultrasonic signals is presented. The optical cavity is formed between a distributed Bragg reflector and the metal thin film samples to be studied. Experimental results for Al and Cu films show enhancement of acoustic signals by up to two orders of magnitude and are in good agreement with calculated results based on a previously established model. This technique provides an efficient method for detecting sound in materials with small piezo-optic coefficients and makes it possible to determine the actual pulse shape of the returning acoustic echoes.
Stark effects on bound polarons in polar cylindrical quantum wires with finite confining potential
Authors: Zhao Zeng-Ru , Liang X. X.
Published: April 2009

The electric field effects on bound polarons in polar quantum wires with a finite confining potential are studied by a variational method. Both the confined bulk longitudinal optical phonons and the interface optical phonons are taken into account in considering the electron-phonon as well as the impurity-ion phonon couplings. The binding energies are calculated as functions of the transverse dimension of the quantum wire, and the donor-impurity position for different electric fields. The numerical results for the GaAs quantum wire are given and discussed as an example. A peak of the binding energy is found at a certain radius and shift toward a larger radius with applying an electric field. The calculated results confirm that the electron-phonon interaction reduces both the binding energies of impurity states and the Stark shifts and cannot be neglected.
Translational and internal states of hydrogen molecules produced from the ultraviolet photodissociation of amorphous solid methanol
Authors: Hama Tetsuya , Yokoyama Masaaki , Yabushita Akihiro , Kawasaki Masahiro
Published: April 2009

Translationally and internally hot H2 molecules are produced from the 157 nm photodissociation of amorphous solid methanol at 90 K by two distinct mechanisms: exothermic recombination of two H-atom photoproducts bound to the surface and unimolecular molecular elimination of H2 from the photoexcited methanol. The vibrationally hot H2(v=2–5) products are characterized by high translational and rotational temperatures. A third mechanism, the almost thermoneutral abstraction of a hydrogen atom from methanol parent molecule by the photolytically produced hydrogen atom, yields translationally and rotationally cold H2 (v=0 and 1) products. Comparison with the results of the vacuum ultraviolet photolysis of water ice is discussed. Production of translationally hot and cold hydrogen atoms is also confirmed.
Diffuse-interface modeling of liquid-vapor phase separation in a van der Waals fluid
Authors: Lamorgese A. G. , Mauri R.
Published: April 2009

We simulate liquid-vapor phase separation in a van der Waals fluid that is deeply quenched into the unstable range of its phase diagram. Our theoretical approach follows the diffuse-interface model, where convection induced by phase change is accounted for via a nonequilibrium (Korteweg) force expressing the tendency of the liquid-vapor system to minimize its free energy. Spinodal decomposition patterns for critical and off-critical van der Waals fluids are studied numerically, revealing the scaling laws of the characteristic length scale and composition of single-phase microdomains, together with their dependence on the Reynolds number. Unlike phase separation of viscous binary mixtures, here local equilibrium is reached almost immediately after single-phase domains start to form. In addition, as predicted by scaling laws, such domains grow in time like t2/3. Comparison between 2D and 3D results reveals that 2D simulations capture, even quantitatively, the main features of the phenomenon.
Picosecond optical pulse generation from self-pulsating bisectional GaN-based blue-violet laser diodes
Authors: Miyajima Takao , Watanabe Hideki , Ikeda Masao , Yokoyama Hiroyuki
Published: April 2009

Self-pulsations of 407 nm emitting GaN-based blue-violet laser diodes with bisectional (BS) electrodes were demonstrated by applying a reverse bias (VSA) to the subelectrode of the saturable absorber (SA) section. By increasing the injected current to the main electrode of the gain section with a reverse bias of VSA=−12 V, the optical pulses shortened to 30 ps. The optical peak output power was as high as 2.4 W with a pulse width of 30 ps and a repetition frequency of 0.9 GHz. This is so far the shortest pulse width from a self-pulsating BS GaN-based laser diode achieved by applying a reverse bias to the SA section.
Structure and dielectric properties of (Sr1−1.5xBix)TiO3 thin films
Authors: Shi Peng , Ren Wei , Zhao Min , Wei Xiaoyong , Wu Xiaoqing , Chen Xiaofeng , Yao Xi
Published: April 2009

Bismuth doped SrTiO3 material has shown very interesting phenomena. Dielectric and ferroelectric relaxations have been recently reported in bismuth doped SrTiO3 ceramics in the lower temperature range. Thin films of bismuth doped SrTiO3 [(Sr1−1.5xBix)TiO3] (x=0.0,0.05,0.10) have been prepared by a sol-gel method and investigated in this work. The phases and surface morphologies of thin films were analyzed to assess the structures and crystallization. The structure of the thin films is revealed as a cubic perovskite structure with no other phase detected. The dielectric properties and dielectric tunability of (Sr1−1.5xBix)TiO3 thin films have been studied as a function of doping amount of bismuth and discussed in detail.
Density functional theoretical study of surface structure and adatom kinetics for wurtzite AlN
Authors: Jindal Vibhu , Shahedipour-Sandvik Fatemeh
Published: April 2009

Density-functional calculations concerning the structure and stability of wurtzite AlN surfaces are presented. Specifically, (0001) and (0001¯) polar surfaces and (11¯00) and (112¯0) nonpolar surfaces are discussed in detail. Binding energies, migration pathways, and diffusion barriers for relevant adatoms such as Al, Ga, and N on these polar and nonpolar surfaces are determined. The calculation indicates low diffusion barrier for Al adatom on Al terminated (0001) surface, whereas the N adatom seems to have lower diffusion barrier on N terminated (0001¯) surfaces. A strong anisotropy was observed for diffusion behavior for Al adatom on (11¯00) and (112¯0) surfaces in the [112¯0] and [0001] directions, respectively.
Detection of high-energy heavy ions using piezoelectric lead zirconate titanate
Authors: Takechi Seiji , Morinaga Shin-ya , Kurozumi Atsuma , Miyachi Takashi , Fujii Masayuki , Hasebe Nobuyuki , Shibata Hiromi , Murakami Takeshi , Uchihori Yukio , Okada Nagaya
Published: April 2009

The characteristics of a radiation detector fabricated with stacks of piezoelectric lead zirconate titanate (PZT) elements were studied by irradiating it with a 400 MeV/n xenon (Xe) beam for various beam pulse durations. This detector is referred to as the multilayered detector (MD). To understand the production mechanism behind the output voltage obtained from the MD, measurement of the spatial distribution of the output signals generated in the MD was attempted. It was found that the amplitude observed was dependent on the number of Xe ions per unit time and the amount of ionization loss energy of Xe ions in PZT.
Electric field-induced resistance switching in (Bi2O3)0.7(Y2O3)0.3 films
Authors: Shi L. , Shang D. S. , Sun J. R. , Shen B. G.
Published: April 2009

Single-phase (Bi2O3)0.7(Y2O3)0.3 (BYO) films are obtained by pulse laser deposition under the temperatures from 300 to 500 °C and the oxygen pressure of 90 Pa. Electric field-induced resistance switching is observed in the Ag/BYO/Pt structure. Postannealing in 750 °C improves the repeatability of the resistance switching and narrows the distribution of the set and reset voltages triggering the resistance switching. A linear variation of reset current with resistance is obtained for the Ag/BYO/Pt systems, either as-prepared or postannealed, despite the great dispersion of these two quantities. A reduction in the activation energy, from ∼0.63 to ∼0.33 eV, for the migration of oxygen vacancies is observed after the forming process. Possible mechanisms are discussed.
Effect of sintering temperature on dielectric relaxation and Raman scattering of 0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO3 system
Authors: Wu Ning-Ning , Hou Yu-Dong , Wang Chao , Zhu Man-Kang , Song Xue-Mei , Yan Hui
Published: April 2009

Relaxor ferroelectrics of 0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO3 (PMN–35PT) were prepared using the columbite precursor proceeding. The influences of sintering temperature on the phase transition, dielectrical response, and Raman scattering in the relaxor-ferroelectric-system PMN–35PT have been investigated in detail. X-ray diffraction analysis indicated that the phase structure of the materials changed from rhombohedral to tetragonal when the sintering temperature increased from 1000 to 1250 °C. The stress relaxation induced by the enlarged grain size was responsible for the phase transition phenomena. The dielectric studies revealed that the indicator of the degree of diffuseness γ decreased with the increase in the sintering temperatures from 1000 to 1150 °C, indicating that the dielectric relaxation behavior was weakened; while at higher sintering temperature above 1200 °C, γ increased subsequently due to the formation of Pb vacancy. The Raman analysis provided another evidence for the phase transition from rhombohedral to the tetragonal according to the intensity changes of A1g mode. Meanwhile, the ratios of the relative intensity Nb–O–Mg to that of Nb–O–Nb band revealed the degree of the B-site cation order, and the variation trend of these Raman modes correlate well with the dielectric measurement results.
Reversible room-temperature magnetocaloric effect with large temperature span in antiperovskite compounds Ga1−xCMn3+x (x=, 0.06, 0.07, and 0.08)
Authors: Wang B. S. , Tong P. , Sun Y. P. , Zhu X. B. , Luo X. , Li G. , Song W. H. , Yang Z. R. , Dai J. M.
Published: April 2009

The magnetic and magnetocaloric properties of Ga1−xCMn3+x have been investigated. Reversible magnetocaloric effect (MCE) occurs near the Curie temperature TC. With increasing x, we find that the magnetic entropy change −ΔSM decreases while TC and magnetization increase. Meanwhile, the temperature span of −ΔSM versus T plot becomes well broadened. Due to the competition between the broadening temperature span and decreasing −ΔSM, the relative cooling power (RCP) increases initially and then decreases with increasing x further. The largest RCP (2.1 J/cm3 in a magnetic field of 45 kOe) observed at x=0.07 (TC=296.5 K) is comparable with the contemporary magnetic refrigerant materials. Considering the reversible MCE, inexpensive and innoxious raw materials, our result suggests that Ga1−xCMn3+x can be a promising candidate for magnetic refrigeration around room temperature.
Bioinspired design of tactile sensors based on Flemion
Authors: Wang Jin , Sato Hiroshi , Xu Chunye , Taya Minoru
Published: April 2009

In this work, we studied experimentally the sensing behavior of ionic membrane-based tactile sensors (Nafion and Flemion). We found from the experimental results that Flemion-based sensor exhibits clearer sensing signals than Nafion-based sensor and signals from Flemion-based sensor are robust under repeated loading. We also found that dome-shaped Flemion sensor can detect three-dimensional forces. We attempted to design an arrayed Flemion sensor system by bioinspiration from the tactile sensor cells on the skin of a cucumber tendril where numbers of the dome-shaped Flemion sensor units are arrayed periodically.
Infrared p-i-n photodiodes based on InAs quantum dots grown on 20 nm patterned GaAs
Authors: Alizadeh Azar , Hays David , Keimel Chris , Watkins Vicki H. , Conway Ken R. , Taylor Seth T. , Neander Rosalyn , Denault Lauraine , deSouza Christina , Saveliev Igor , Blumin Marina , Ruda Harry E. , Braunstein Edit , Jones Colin
Published: April 2009

We report on selective area growth of InAs quantum dots on GaAs substrates patterned with a hexagonal array of 20 nm pores using block copolymer lithography. We discuss the mechanisms of growth, highlighting the variation in the resulting morphology as a function of nucleation enhancing AlGaAs layers. We also evaluate the optoelectronic performance of p-i-n photodiodes based on single layer nanopatterned grown InAs quantum dot devices. At low to moderate reverse biases, we observe room temperature photoresponse in both near- and mid-IR regimes. At high biases, we observe strong avalanche effects in the mid-IR range with a gain factor of ∼4000.
Spectroscopic study of cis-to-trans tunneling reaction of HCOOD in rare gas matrices
Authors: Domanskaya Alexandra , Marushkevich Kseniya , Khriachtchev Leonid , Räsänen Markku
Published: April 2009

The higher energy conformer (cis) of HCOOD is prepared by vibrational excitation of the trans form. The cis conformer decays back to the conformational ground state (trans) via tunneling of deuterium. The tunneling process in HCOOD in rare gas matrices is extremely slow (in scale of weeks). We present new measurements of the tunneling rate constants, which characterize the efficiency of the cis-to-trans conversion process in Ne, Ar, Kr, and Xe matrices. The tunneling rates of HCOOD follow the trend kXe≈kKr>kAr≈kNe, which is anomalous with respect to the reaction barrier of the solvated molecule. We propose a semiempirical energetic scheme of solid state solvation, which is consistent with all experimental observation. The temperature dependence of the tunneling constants rates of HCOOD is very weak compared to HCOOH in all matrices. The fundamental vibrational frequencies of the cis and trans conformers of HCOOD in various matrices are reported.
Empirical analysis of Internet telephone network: From user ID to phone
Authors: Xuan Qi , Du Fang , Wu Tie-Jun
Published: April 2009

In order to study the interaction between different communication networks, in this paper, personal computer (PC)-to-phone log data in the year of 2007 are collected from UUCALL database and described as an ID-to-phone bipartite network (ItPBN). The ItPBN contains one giant component (GC) and a large number of satellitic components (SCs), both of which are carefully analyzed. It is found that the ItPBN has power-law incoming/outgoing degree distributions as well as a power-law clustering function (by proposing a new definition of clustering coefficient) indicating a hierarchical and modular structure of the ItPBN. Furthermore, the fact that most of the weak links always surrounding those ID nodes of large degree in the GC suggests that weak links may be more important to keep the structure of the GC than those strong ones. More interestingly, it is also revealed that there is strong correlation between many statistical properties of different SCs and their size, these extra information may be very useful in modeling the ItPBN in the future.
A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage
Authors: Choi Young-Man , Lee Moon G. , Gweon Dae-Gab , Jeong Jaehwa
Published: April 2009

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.
Comment on “Nanoscale heat transfer in a thin aluminum film and femtosecond time-resolved electron diffraction” [Appl. Phys. Lett. 92, 011901 (2008)]
Authors: Nie Shouhua , Wang Xuan , Li Junjie , Clinite Richard , Cao Jianming
Published: April 2009

In a recent letter [Appl. Phys. Lett. 92, 011901 (2008)], Tang reported a simulation of structural dynamics in metal films induced by ultrafast laser heating using the two-temperature model [P. B. Allen, Phys. Rev. Lett. 59, 1460 (1987) and R. W. Schoenlein et al., Phys. Rev. Lett. 58, 1680 (1987)] and one-dimensional anharmonic chain model [E. Fermi J. Pasta S. Ulam, No. LA-1940 (1955)]. In this comment, we would like to point out several issues in the physical concepts and formulations in the simulation which we strongly disagree with the author. Consequently, we believe that the main conclusion of Tang's paper that the interpretation of ultrafast diffraction data requires both nonlocal collective atomic motion and the conventional linear thermal expansion lacks physical justification and is questionable.
Polarization-sensitive near-field investigation of photonic crystal microcavities
Authors: Vignolini Silvia , Intonti Francesca , Riboli Francesco , Wiersma Diederik S. , Balet Laurent , Li Lianhe H. , Francardi Marco , Gerardino Annamaria , Fiore Andrea , Gurioli Massimo
Published: April 2009

We report on polarization sensitive imaging of two-dimensional photonic crystal microcavity modes. By using a near-field scanning optical microscope with a polarization sensitive setup, it is possible to selectively map, with a resolution beyond the diffraction limit, each electric field component in the plane of the sample. In addition, the simultaneous analysis of photoluminescence maps in different polarization channels allowed us to obtain important insight on near-field microscopy detection mechanism. Finite difference time domain simulations confirm the experimental results.
Energy-consistent pseudopotentials and correlation consistent basis sets for the 5d elements Hf–Pt
Authors: Figgen Detlev , Peterson Kirk A. , Dolg Michael , Stoll Hermann
Published: April 2009

New relativistic energy-consistent pseudopotentials have been generated for the 5d transition metals Hf–Pt. The adjustment was done in numerical two-component multiconfiguration Hartree–Fock calculations, using atomic valence-energy spectra from four-component multiconfiguration Dirac–Hartree–Fock calculations as reference data. The resulting two-component pseudopotentials replace the [Kr]4d104f14 cores of the 5d transition metals and can easily be split into a scalar-relativistic and a spin-orbit part. They reproduce the all-electron reference energy data with deviations of ∼0.01 eV for configurational averages and ∼0.05 eV for individual relativistic states. Full series of correlation consistent basis sets from double to quintuple-zeta have also been developed in this work for use with the new pseudopotentials. In addition, all-electron triple-zeta quality correlation consistent basis sets are also reported in order to provide calibration for the pseudopotential treatment. The accuracy of both the pseudopotentials and basis sets are assessed in extensive coupled cluster benchmark calculations of atomic ionization potentials, electron affinities, and selected excitation energies of all the 5d metal atoms, including the effects of spin-orbit coupling.
Field dependent electroluminescence from amorphous Si/SiNx multilayer structure
Authors: Dong Hengping , Wang Danqing , Chen Kunji , Huang Jian , Sun Hongcheng , Li Wei , Xu Jun , Ma Zhongyuan
Published: April 2009

We report field dependent electroluminescence (EL) from as-deposited amorphous Si/SiNx multilayer structure, where a-Si well layer thickness ranges from 1 to 4 nm, while SiNx barrier layer thickness is fixed at 3 nm. When the sample is applied by a low forward voltage Vbias (<6 V, i.e., 2.5 MV/cm), the dominant peak of EL is located at the lower energy region from 740 nm shifted to 660 nm with reducing the thickness of the a-Si well layer from 4 to 1 nm. However, under a high applied Vbias(>6 V), another EL band at the higher energy region is observed to be peaked at about 530 nm, which is independent of the well layer thickness. Photoluminescence (PL) investigation performed under optically pumped by the 325 nm line and the 488 nm line, respectively, also demonstrates the pump energy dependence of PL peaks. We interpreted these interesting phenomena of electrical and optical pump energy dependence of light emission by using different luminescence mechanisms in the a-Si/SiNx multilayer structure.
Experimental verification of Faradaic charging in ac electrokinetics
Authors: Ng Wee Yang , Lam Yee Cheong , Rodríguez Isabel
Published: April 2009

This paper investigates the phenomenon of Faradaic charging in ac electrokinetics. Faradaic reactions were suggested as a key effect responsible for the reversal of pumping direction in ac micropumps. However, this hypothesis has yet to be proven convincingly and directly. Here we present an ion detection strategy to determine the production of ions through Faradaic hydrolytic reactions originating from direct application of voltage to electrolytic solutions during ac electrokinetics. Experiments were performed with symmetrical planar electrodes aligned along a microfluidic channel. Fluorescein, a pH-dependent dye, was employed as the pH indicator for the detection of ion production. Images were captured for analysis at various voltage levels. From analyzing the fluorescence intensity and its distribution, it can be concluded that the production of ions from hydrolytic reactions takes place and increases with the ac voltage. The coefficient of deviation indicates a significant enhancement at ac voltage above 11 Vpp. Lastly, we demonstrate a strategy using dc-biased ac electrokinetics to achieve controllability in direction and magnitude of the net fluid flow in pumping application.
Thermal activation energy for the passivation of the n-type crystalline silicon surface by hydrogenated amorphous silicon
Authors: Mitchell Jonathon , Macdonald Daniel , Cuevas Andres
Published: April 2009

Excellent surface passivation of crystalline silicon wafers is known to occur following post-deposition thermal annealing of intrinsic a-Si:H thin-film layers deposited by plasma-enhanced chemical vapor deposition. In this work, layer thicknesses ranging from 5 to 50 nm were used to indirectly study the surface passivation mechanism by sequentially measuring the effective carrier lifetime as a function of annealing time and temperature. From this, an activation energy of 0.7±0.1 eV was calculated, suggesting that surface passivation is reaction-limited and not determined by a bulk hydrogen diffusion process. We conclude that the primary surface reaction stems from surface rearrangement of hydrogen already near the interface.
Adsorption of a Ru(II) dye complex on the Au(111) surface: Photoemission and scanning tunneling microscopy
Authors: Mayor Louise C. , Saywell Alex , Magnano Graziano , Satterley Christopher J. , Schnadt Joachim , O’Shea James N.
Published: April 2009

The adsorption of the dye molecule N3 [cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)] on the Au(111) surface has been studied using core-level and valence photoemission and scanning tunneling microscopy (STM). The dye molecules were deposited in situ using ultrahigh vacuum electrospray deposition. The core-level spectra reveal that the molecule bonds to the surface via sulfur atoms with no deprotonation of the carboxylic groups. The STM images show that at low coverage the molecules decorate the Au(111) herringbone reconstruction and form uniform monolayers as the coverage is increased.
Experimental evidence for the role of the πCO∗ orbital in electron transfer to gas phase acetic acid CH3CO2H: Effects of molecular orientation
Authors: Brooks Philip R.
Published: April 2009

Electron transfer from K atoms to oriented acetic acid molecules produces acetate ions (and K+) when the CO2H end of the molecule is attacked. The electron enters the πCO∗ orbital and the donor atom distorts the molecule to allow migration to the σOH∗ orbital, thereby breaking the bond.
Measurement of polar C-plane and nonpolar A-plane InN/ZnO heterojunctions band offsets by x-ray photoelectron spectroscopy
Authors: Yang A. L. , Song H. P. , Wei H. Y. , Liu X. L. , Wang J. , Lv X. Q. , Jin P. , Yang S. Y. , Zhu Q. S. , Wang Z. G.
Published: April 2009

The valence band offsets of the wurtzite polar C-plane and nonpolar A-plane InN/ZnO heterojunctions are directly determined by x-ray photoelectron spectroscopy to be 1.76±0.2 eV and 2.20±0.2 eV. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 0.84±0.2 eV and 0.40±0.2 eV. The difference of valence band offsets of them mainly attributes to the spontaneous polarization effect. Our results show important face dependence for InN/ZnO heterojunctions, and the valence band offset of A-plane heterojunction is more close to the “intrinsic” valence band offset.
Origins of nonzero multiple photon emission probability from single quantum dots embedded in photonic crystal nanocavities
Authors: Chang Hsiang-Szu , Chen Wen-Yen , Hsu Tzu-Min , Hsieh Tung-Po , Chyi Jen-Inn , Chang Wen-Hao
Published: April 2009

This work explores the origins of nonzero multiphoton emission probability for quantum dots embedded in photonic crystal nanocavities using different excitation energies to inject excitons into either the GaAs barrier or the quantum-dot excited state. The detected multiphoton events are established to arise from both the recapture of excitons and background emissions from the wetting layer tail states. The exciton emission is analyzed using rate-equation calculations, which suggest that multiphoton emission is dominated by the recapture effect.
Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: a review
Authors: McLean Mark S. , Howlett Barbara J. , Hollaway Grant J.
Published: April 2009

Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.
Confirmation of QTLs controlling Ascochyta fabae resistance in different generations of faba bean (Vicia faba L.)
Authors: Díaz-Ruiz R. , Satovic Z. , Ávila C. M. , Alfaro C. M. , Gutierrez M. V. , Torres A. M. , Román B.
Published: April 2009

Ascochyta blight, caused by Ascochyta fabae Speg., is a disease of faba bean (Vicia faba L.) of worldwide distribution. In this study we have conducted an experiment on Ascochyta fabae resistance in 165 recombinant inbred lines (RILs) developed by single-seed descent from the cross between resistant and susceptible lines (Vf6 × Vf136) in which A. fabae resistance QTLs (quantitative trait loci) have been previously reported in the original F2 population. Recombinant inbred lines were inoculated under controlled growth chamber conditions and evaluated for disease severity and infection type index. The linkage map was constructed by MAPMAKER V2.0 and the QTL analysis was carried out using QTL Cartographer. Two hundred and seventy-seven markers (238 RAPDs, 4 isozymes, 5 ESTs, 1 SCAR, 6 SSRs, 2 STSs, and 21 intron-spanning markers) mapped into 21 linkage groups covering 2.856.7 cM, with a mean inter-marker distance of 12.72 cM. Composite interval mapping identified two zones of putative QTL action in the RIL population for DSL (disease severity on leaves) and DSS (disease severity on stems) traits. Putative QTLs (Af1 and Af2) were identified on chromosome 3 and chromosome 2, respectively, and jointly explained 24% of the phenotypic variance of DSL and 16% of DSS. With this study we have (1) confirmed the QTLs for ascochyta blight resistance found in F3 families in the derived RILs (F6), (2) re-estimated their position and genetic effects, and (3) assessed the stability of these QTLs in different genetic backgrounds by comparison of the mapping data with a previous QTL study.
Source - sink differences in genotypes and water regimes influencing sucrose accumulation in sugarcane stalks
Authors: Inman-Bamber N. G. , Bonnett G. D. , Spillman M. F. , Hewitt M. L. , Xu Jingsheng
Published: April 2009

Relatively little is known about the physiological basis for variation in sucrose content among sugarcane clones despite substantial research at the molecular and biochemical levels. We used irrigation and continuous monitoring of photosynthesis and plant extension rate to modify dry matter partitioning in four clones differing widely in sucrose content. Three pot experiments were conducted on two low sucrose content clones, KQ97-2599 and KQ97-2835, and two high sucrose content clones, Q117 and KQ97-5080, in a temperature-controlled glasshouse. As expected, sucrose content on a dry mass basis of whole stalks was greater in high (55% maximum) than in low sucrose clones (40% maximum), but sucrose content in the two clones selected for low sucrose reached 55% in some internodes. Differences between clones in whole-plant net photosynthesis and aerial biomass accumulation were small. However, biomass was distributed over fewer stalks in the high sucrose clones (4–7 stalks per pot) than in the low sucrose clones (9–11 stalks per pot). The high sucrose clones also allocated a considerably greater proportion of dry matter to the stalk (70% maximum) than the low sucrose clones (60% maximum). It is suggested that the relatively large amount of new leaf tissue produced by the high tillering, low sucrose clones placed an additional demand for structural photo-assimilate in these clones and delayed the accumulation of sucrose in the stalk. The results indicated that there is little direct genetic control on the maximum amount of sucrose that can accumulate in stalk tissue and that genetic contrasts in sucrose content reside more in the morphology of the plant and responses to ripening stimuli such as mild water stress, and how these traits influence supply and demand for photo-assimilate.
Political complexity predicts the spread of ethnolinguistic groups
Authors: Currie Thomas E. , Mace Ruth
Published: April 2009

Human languages show a remarkable degree of variation in the area they cover. However, the factors governing the distribution of human cultural groups such as languages are not well understood. While previous studies have examined the role of a number of environmental variables the importance of cultural factors has not been systematically addressed. Here we use a geographical information system (GIS) to integrate information about languages with environmental, ecological, and ethnographic data to test a number of hypotheses that have been proposed to explain the global distribution of languages. We show that the degree of political complexity and type of subsistence strategy exhibited by societies are important predictors of the area covered by a language. Political complexity is also strongly associated with the latitudinal gradient in language area, whereas subsistence strategy is not. We argue that a process of cultural group selection favoring more complex societies may have been important in shaping the present-day global distribution of language diversity.
Spatial ensemble statistics are efficient codes that can be represented with reduced attention
Authors: Alvarez George A. , Oliva Aude
Published: April 2009

There is a great deal of structural regularity in the natural environment, and such regularities confer an opportunity to form compressed, efficient representations. Although this concept has been extensively studied within the domain of low-level sensory coding, there has been limited focus on efficient coding in the field of visual attention. Here we show that spatial patterns of orientation information (“spatial ensemble statistics”) can be efficiently encoded under conditions of reduced attention. In our task, observers monitored for changes to the spatial pattern of background elements while they were attentively tracking moving objects in the foreground. By using stimuli that enable us to dissociate changes in local structure from changes in the ensemble structure, we found that observers were more sensitive to changes to the background that altered the ensemble structure than to changes that did not alter the ensemble structure. We propose that reducing attention to the background increases the amount of noise in local feature representations, but that spatial ensemble statistics capitalize on structural regularities to overcome this noise by pooling across local measurements, gaining precision in the representation of the ensemble.
Degenerate evolution of the
hedgehog
gene in a hemichordate lineage
Authors: Sato Atsuko , White-Cooper Helen , Doggett Karen , Holland Peter W. H.
Published: April 2009

The discovery of a set of highly conserved genes implicated in patterning during animal development represents one of the most striking findings from the field of evolutionary developmental biology. Existence of these “developmental toolkit” genes in diverse taxa, however, does not necessarily imply that they always perform the same functions. Here, we demonstrate functional evolution in a major toolkit gene.
hedgehog
(
hh
) encodes a protein that undergoes autocatalytic cleavage, releasing a signaling molecule involved in major developmental processes, notably neural patterning. We find that the
hh
gene of a colonial pterobranch hemichordate,
Rhabdopleura compacta
, is expressed in a dramatically different pattern to its ortholog in a harrimaniid enteropneust hemichordate,
Saccoglossus kowalevskii
. These represent two of the three major hemichordate lineages, the third being the indirect developing ptychoderid enteropneusts. We also show that the normally well-conserved amino acid sequence of the autoproteolytic cleavage site has a derived change in
S. kowalevskii
. Using ectopic expression in
Drosophila
, we find that this amino acid substitution reduces the efficiency of Hh autocatalytic cleavage and its signaling function. We conclude that the Hh sequence and expression in
S. kowalevskii
represent the derived state for deuterostomes, and we argue that functional evolution accompanied secondary reduction of the central nervous system in harrimaniids.
Epistasis amongHLA-DRB1, HLA-DQA1,andHLA-DQB1loci determines multiple sclerosis susceptibility
Authors: Lincoln Matthew R. , Ramagopalan Sreeram V. , Chao Michael J. , Herrera Blanca M. , DeLuca Gabriele C. , Orton Sarah-Michelle , Dyment David A. , Sadovnick A Dessa , Ebers George C.
Published: April 2009

Multiple sclerosis (MS), a common central nervous system inflammatory disease, has a major heritable component. Susceptibility is associated with the MHC class II region, especiallyHLA-DRB5*0101–HLA-DRB1*1501–HLA-DQA1*0102–HLA-DQB1*0602haplotypes(hereafter DR2), which dominate genetic contribution to MS risk. Marked linkage disequilibrium (LD) among these loci makes identification of a specific locus difficult. The once-leading candidate,HLA-DRB1*15, localizes to risk, neutral, and protective haplotypes.HLA-DRB1*15andHLA-DQB1*0602, nearly always located together on a small ancestral chromosome segment, are strongly MS-associated. One intervening allele on this haplotype, viz.HLA-DQA1*0102, shows no primary MS association. Two Canadian cohorts (n= 830 andn= 438 trios) genotyped forHLA-DRB1,HLA-DQA1andHLA-DQB1alleles were tested for association using TDT. To evaluate epistasis involvingHLA-DRB1*15, transmissions fromHLA-DRB1*15-negative parents were stratified by the presence/absence ofHLA-DRB1*15in affected offspring. All 3 alleles contribute to MS susceptibility through novel epistatic interactions.HLA-DQA1*0102increased disease risk when combined withHLA-DRB1*1501 in trans, thereby unambiguously implicatingHLA-DQin MS susceptibility. Three-locus haplotypes demonstrated thatHLA-DRB1*1501andHLA-DQB1*0602each influence risk. Transmissions of rare morcellated DR2 haplotypes showed no interaction withHLA-DQA1*0102. Incomplete haplotypes bearing onlyHLA-DRB1*1501orHLA-DQB1*0602did not predispose to MS. Balanced reciprocal transmission distortion can mask epistatic allelic association. These findings implicate epistasis among HLA class II alleles in human immune responses generally, provide partial explanation for intense linkage disequilibrium in the MHC, have relevance to animal models, and demonstrate key roles for DR2-specific interactions in MS susceptibility. MHC disease associations may be more generally haplotypic or diplotypic.
Minimal molecular constraints for respiratory droplet transmission of an avian–human H9N2 influenza A virus
Authors: Sorrell Erin M. , Wan Hongquan , Araya Yonas , Song Haichen , Perez Daniel R.
Published: April 2009

Pandemic influenza requires interspecies transmission of an influenza virus with a novel hemagglutinin (HA) subtytpe that can adapt to its new host through either reassortment or point mutations and transmit by aerosolized respiratory droplets. Two previous pandemics of 1957 and 1968 resulted from the reassortment of low pathogenic avian viruses and human subtypes of that period; however, conditions leading to a pandemic virus are still poorly understood. Given the endemic situation of avian H9N2 influenza with human-like receptor specificity in Eurasia and its occasional transmission to humans and pigs, we wanted to determine whether an avian–human H9N2 reassortant could gain respiratory transmission in a mammalian animal model, the ferret. Here we show that following adaptation in the ferret, a reassortant virus carrying the surface proteins of an avian H9N2 in a human H3N2 backbone can transmit efficiently via respiratory droplets, creating a clinical infection similar to human influenza infections. Minimal changes at the protein level were found in this virus capable of respiratory droplet transmission. A reassortant virus expressing only the HA and neuraminidase (NA) of the ferret-adapted virus was able to account for the transmissibility, suggesting that currently circulating avian H9N2 viruses require little adaptation in mammals following acquisition of all human virus internal genes through reassortment. Hemagglutinin inhibition (HI) analysis showed changes in the antigenic profile of the virus, which carries profound implications for vaccine seed stock preparation against avian H9N2 influenza. This report illustrates that aerosolized respiratory transmission is not exclusive to current human H1, H2, and H3 influenza subtypes.
Single-nucleotide discrimination in immobilized DNA oligonucleotides with a biological nanopore
Authors: Stoddart David , Heron Andrew J. , Mikhailova Ellina , Maglia Giovanni , Bayley Hagan
Published: April 2009

The sequencing of individual DNA strands with nanopores is under investigation as a rapid, low-cost platform in which bases are identified in order as the DNA strand is transported through a pore under an electrical potential. Although the preparation of solid-state nanopores is improving, biological nanopores, such as α-hemolysin (αHL), are advantageous because they can be precisely manipulated by genetic modification. Here, we show that the transmembrane β-barrel of an engineered αHL pore contains 3 recognition sites that can be used to identify all 4 DNA bases in an immobilized single-stranded DNA molecule, whether they are located in an otherwise homopolymeric DNA strand or in a heteropolymeric strand. The additional steps required to enable nanopore DNA sequencing are outlined.
Simplified and effective motor control based on muscle synergies to exploit musculoskeletal dynamics
Authors: Berniker Max , Jarc Anthony , Bizzi Emilio , Tresch Matthew C.
Published: April 2009

The basic hypothesis of producing a range of behaviors using a small set of motor commands has been proposed in various forms to explain motor behaviors ranging from basic reflexes to complex voluntary movements. Yet many fundamental questions regarding this long-standing hypothesis remain unanswered. Indeed, given the prominent nonlinearities and high dimensionality inherent in the control of biological limbs, the basic feasibility of a low-dimensional controller and an underlying principle for its creation has remained elusive. We propose a principle for the design of such a controller, that it endeavors to control the natural dynamics of the limb, taking into account the nature of the task being performed. Using this principle, we obtained a low-dimensional model of the hindlimb and a set of muscle synergies to command it. We demonstrate that this set of synergies was capable of producing effective control, establishing the viability of this muscle synergy hypothesis. Finally, by combining the low-dimensional model and the muscle synergies we were able to build a relatively simple controller whose overall performance was close to that of the system's full-dimensional nonlinear controller. Taken together, the results of this study establish that a low-dimensional controller is capable of simplifying control without degrading performance.