bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite: Evidence of surface spin freezing of manganite nanoparticles
Authors: Dey P. , Nath T. K. , Manna P. K. , Yusuf S. M.
Published: November 2008

We have investigated the effect of nanometric grain size on magnetic properties of La0.7Ca0.3MnO3 nanoparticles having average particle size (Φ) of ∼17 nm. Temperature dependence of field-cooled (FC) and zero-FC (ZFC) dc magnetization indicate the existence of two different types of relaxation processes: a relatively high temperature regime where there is a broad maximum of the ZFC curve at T=Tmax (>40 K) and another is a relatively low temperature regime that is characterized by a sharp maximum at T=TS (≈40 K). We believe that the broad maximum at Tmax is associated with the blocking of core particle moments, whereas the sharp maximum at TS is related to the freezing of surface spins. Waiting time (tw) dependence of ZFC relaxation measurements at T=50 K show weak dependence of relaxation rate [S(t)] on tw and dM/d ln(t) following a logarithmic variation in time. These features strongly support superparamagnetic (SPM) blocking of core particle moments at Tmax. At T=20 K, S(t) attains a maximum at tw=1000 s that establishes freezing phenomenon occurring at TS. The combination of topological disorder and magnetic phase separation may result in a magnetically disordered state at the grain surface. This, in turn, results in magnetically uncoupled assembly of nanoparticles that eventually exhibits SPM blocking. The glassy behavior at TS has been attributed to the competing magnetic interactions stabilizing a spin-glass-like frozen state at the surface region of the nanometric grains.
Electric field induced reversible tuning of resistance of thin gold films
Authors: Dasgupta S. , Kruk R. , Ebke D. , Hütten A. , Bansal C. , Hahn H.
Published: November 2008

The change in resistance of nanostructured metals with respect to an applied field is believed to be due to a change in carrier concentration and hence a linear variation of resistance with the surface charge is expected. In this article, we propose a different approach to explain the resistance variation based on a change in the effective thickness of the film due to a shift of the electron density profile resulting from the applied surface charge. The change in effective thickness together with its effect on surface scattering of electrons account for the majority of the observed variation in resistance. The thin film geometry with different thicknesses and hence a controlled variation of the surface-to-volume ratio allows a deep quantitative understanding and interpretation of the observed phenomena. The model presented in this work shows that a nominal nonlinear response of the resistance of a metal on electrochemically applied surface charge does not necessarily indicate an onset of a redox reaction.
Rovibrational matrix elements of the quadrupole moment of N2 in a solid parahydrogen matrix
Authors: Mishra Adya P. , Balasubramanian T. K.
Published: November 2008

The present work pertains to the study of the rotational dynamics of N2 molecules solvated in a matrix of solid para-H2. It is shown that the mixing of the rotational states due to the anisotropic part of the N2–H2 pair potential in the solid gives rise to an additional 5.4% contribution to the intensity of quadrupole-induced double transitions involving N2–H2 pair. Hence the recently reported quadrupole moment matrix element of N2 in a solid para-H2 crystal [A. P. Mishra and T. K. Balasubramanian, J. Chem. Phys. 125, 124507 (2006)], which was deduced from a comparison of the theoretical intensity (with rotational mixing of states neglected) with the measured value is larger by ∼2.7%. The ground electronic state rovibrational matrix elements ⟨v′J′|Q2(r)|vJ⟩ of N2 molecule in a solid parahydrogen matrix for v,v′≤1 and J,J′≤4 have also been computed by taking into account the changes in the intramolecular potential of N2 due to the intermolecular interaction in the matrix. The computed quadrupole moment matrix elements agree well with a few available values (for v=v′=0) deduced from the observed transitions.
Effective medium theory for strongly coupled randomly oriented conducting fibers on a planar surface
Authors: Loschialpo P. , Smith D. , Zabetakis D.
Published: November 2008

A theoretical model has been developed for predicting the reflectivity of thin planar surfaces imbedded with long conductive fibers. Intersecting fibers in the plane form larger conducting clusters. The model includes this effect, which serves to increase the reflectivity. Magnetic coupling between the fibers is also included. This coupling is found to be particularly important at higher frequencies. Test panels were made using a direct write process to imbed the long conducting fiber regions on a thin layer of cellulose. Comparisons of the model with both method of moments calculations and experimental measurements serve to validate its accuracy.
Ultraviolet light in glow discharges
Authors: Ledernez Loic , Olcaytug Fethi , Yasuda Hirotsugu , Urban Gerald
Published: November 2008

The use of ultraviolet light has prevailed in investigation of gas breakdown phenomena since Townsend developed the model of gas breakdown discharge carrying his name because ultraviolet light creates the supposedly necessary electrons in the interelectrode space. However, the ultraviolet light influences the gas breakdown characteristics. Therefore, the extent of the influence of the ultraviolet light on the prebreakdown current, the breakdown current, the breakdown voltage, and the Townsend’s coefficients is studied.
Acoustic anisotropy in uniaxial tungsten bronze ferroelectric single crystals studied by Brillouin light scattering
Authors: Ko Jae-Hyeon , Lushnikov S. G. , Kim Do Han , Kojima Seiji , Jun Byeong-Eog , Hwang Yoon Hwae
Published: November 2008

Acoustic properties were investigated for four tungsten bronze (TB) uniaxial ferroelectric crystals, i.e., (Sr0.61Ba0.39)5Nb10O30 (SBN61), Cu-doped (K0.5Na0.5)1.0(Sr0.75Ba0.25)4.5Nb10O30 (KNSBN:Cu), K5.80Li3.82Nb10.12O30, and K4.74Li3.07Nb10.44O30 of which the spontaneous polarization is directed along the polar c axis. Large acoustic anisotropy between the two elastic constants C11 and C33 have been observed from all samples. C33 exhibits a significant softening on approaching the diffuse phase transition temperature from high-temperature side while C11 does not show any substantial change in the same temperature range. This softening is accompanied by substantial growth of hypersonic damping, appearance and growth of central peak (CP), and slowing down of the relevant dynamics of CP represented by the reducing half width. All these results indicate that the lattice motions along the c axis couple strongly to the one-component order parameter of the polar nanoregions (PNRs) or precursor polar clusters which form and grow below a certain temperature in the paraelectric phase. The inverse dielectric constant measured along the c axis of SBN61 and KNSBN:Cu can be described by two linear regions divided by a crossover temperature at which the change in the magnitude of dipole moments and the strength of the dipole couplings are expected due to the formation of PNRs. C33 of SBN61 becomes continuously softened upon cooling even when the temperature crosses the Burns temperature TB at which PNRs begin to appear. It may suggest that additional relaxation process other than that of PNRs may exist at high temperatures above TB and couple to the longitudinal acoustic waves propagating along the polar axis. Recent observation of a single-particle relaxation at high temperatures and its transformation into a collective relaxation of PNRs by dielectric spectroscopy [Belous et al., J. Appl. Phys. 102, 014111 (2007)] might be related to the anomalous acoustic behavior of SBN61 observed above TB.
Ferromagnetic Cu doped ZnO as an electron injector in heterojunction light emitting diodes
Authors: Herng T. S. , Lau S. P. , Yu S. F. , Tsang S. H. , Teng K. S. , Chen J. S.
Published: November 2008

Ferromagnetic and highly conductive copper doped ZnO (ZnO:Cu) films were prepared by filtered cathodic vacuum arc technique. By employing a biasing technique during growth, the electron concentration and resistivity of the ZnO:Cu films can be as high as 1020 cm−3 and 5.2×10−3 Ω cm, respectively. The ferromagnetic behavior is observed in all the conductive films, but its magnetization is quenched with an increment in carrier concentration, suggesting that carrier induced exchange is not directly responsible for the ferromagnetism. Heterojunction light emitting diodes have been fabricated using the conductive ZnO:Cu layer as an electron injector and a p-type GaN as hole injector. Electroluminescence can be detected from the devices.
The temperature dependence of the refractive indices of GaN and AlN from room temperature up to 515 °C
Authors: Watanabe Naoki , Kimoto Tsunenobu , Suda Jun
Published: November 2008

The temperature dependence of the refractive indices of GaN and AlN was investigated in the wavelength range from the near band edge (367 nm for GaN and 217 nm for AlN) to 1000 nm and the temperature range from room temperature to 515 °C. Optical interference measurements with vertical incident configuration were employed to precisely evaluate the ordinary refractive indices.
Sharp reduction of the secondary electron emission yield from grooved surfaces
Authors: Pivi M. , King F. K. , Kirby R. E. , Raubenheimer T. O. , Stupakov G. , Le Pimpec F.
Published: November 2008

The effect of an artificially enhanced rough surface on the secondary electron yield (SEY) was investigated both theoretically and experimentally. Analytical studies on triangular and rectangular grooved surfaces show the connection between the characteristic parameters of a given geometry to the SEY reduction. The effect of a strong magnetic field is also discussed. SEY of grooved samples have been measured and the results agree with particle simulations using a Monte Carlo approach.
Optical emission from a high-refractive-index waveguide excited by a traveling electron beam
Authors: Kuwamura Yuji , Yamada Minoru , Okamoto Ryuichi , Kanai Takeshi , Fares Hesham
Published: November 2008

An optical emission scheme was demonstrated, in which a high-refractive-index waveguide is excited by a traveling electron beam in a vacuum environment. The waveguide was made of Si–SiO2 layers. The velocity of light propagating in the waveguide was slowed down to 1/3 of that in free space due to the high refractive index of Si. The light penetrated partly into the vacuum in the form of a surface wave. The electron beam was emitted from an electron gun and propagated along the surface of the waveguide. When the velocity of the electron coincided with that of the light, optical emission was observed. This emission is a type of Cherenkov radiation and is not conventional cathode luminescence from the waveguide materials because Si and SiO2 are transparent to light at the emitted wavelength. This type of emission was observed in an optical wavelength range from 1.2 to 1.6 μm with an electron acceleration voltage of 32–42 kV. The characteristics of the emitted light, such as the polarization direction and the relation between the acceleration voltage of the electron beam and the optical wavelength, coincided well with the theoretical results. The coherent length of an electron wave in the vacuum was confirmed to be equal to the electron spacing, as found by measuring the spectral profile of the emitted light.
Quantum and plasma screening effects on the Wannier threshold law for the double-electron escape in strongly coupled semiclassical plasmas
Authors: Jung Young-Dae , Kato Daiji
Published: November 2008

The quantum and plasma screening effects on the Wannier threshold law for the double-electron escape are investigated in strongly coupled semiclassical plasmas. The renormalized electron charge and Wannier exponent are obtained by considering the equation of motion in the Wannier configuration with the screened pseudopotential model as functions of the de Broglie wavelength, Debye length, and charge of the residual ion. It is shown that the renormalized electron charge significantly increases with an increase in the de Broglie wavelength, especially for small radial distances. It is also shown that the quantum effects enhance the Wannier exponent for the double-electron escape. In addition, the quantum effect on the Wannier threshold law is found to be more important than the plasma screening effect in strongly coupled semiclassical plasmas.
Spectroscopic characterization of laser ablation brass plasma
Authors: Shaikh Nek M. , Hafeez Sarwat , Kalyar M. A. , Ali R. , Baig M. A.
Published: November 2008

We present optical emission studies of the laser ablation brass plasma generated by the fundamental, second, and third harmonics of a neodymium doped yttrium aluminum garnet laser. The spectra predominantly reveal the spectral lines of the neutral and singly ionized copper and zinc. The excitation temperatures are determined by the Boltzmann plot method, whereas the electron number densities have been extracted from the Stark broadened line profiles. The spatial variations in the spectral line intensities and the plasma parameters at 1000, 500, and 100 mbar air pressures have been evaluated. Besides, the effect of the ambient gases (He, Ne, and Ar), the laser irradiance, and the laser wavelengths on the plasma parameters have been investigated.
Wind-forced modulations of finite-depth gravity waves
Authors: Leblanc Stéphane
Published: November 2008

It has been shown recently that the modulations of deep-water gravity waves grow superexponentially under the effect of wind [S. Leblanc, “Amplification of nonlinear surface waves by wind,” Phys. Fluids 19, 101705 (2007)]. Finite depth is considered here. Based on Davey–Stewartson equations with forcing, stability analysis shows that longitudinal modulations are amplified when kh>1.363, where k is the wave number of the carrier wave and h is the water depth, but that oblique modulations dominate when 0<kh<2.199. In each case, amplification is characterized in the linear stage by superexponential growth. This latter is, however, so small when kh<0.380 that no modulation is expected in shallow water, although the carrier wave still grows, thanks to wind forcing.
Light-induced hysteresis characteristics of copper phthalocyanine organic thin-film transistors
Authors: Zhen Lijuan , Shang Liwei , Liu Ming , Tu Deyu , Ji Zhuoyu , Liu Xinghua , Liu Ge , Liu Jiang , Wang Hong
Published: November 2008

Applying a bidirectional sweeping gate voltage, the white-light illuminated copper phthalocyanine thin-film transistors (CuPc-TFTs) show obvious hysteresis effect and the hysteresis window is 32 V. This effect is dominated by the additional carriers generated by photoirradiation. Although small hysteresis exists in CuPc-TFTs without illumination, light makes the hysteresis more obvious. Thus, CuPc-TFTs are promising to realize light detection and/or light memory in a single organic device for future low-cost, ultrahigh-density organic photoelectric integration.
Improving light output power of InGaN-based light emitting diodes with pattern-nanoporous p-type GaN:Mg surfaces
Authors: Yang Chung Chieh , Lin Chia Feng , Lin Chun Min , Chang Cheng Chien , Chen Kuei Ting , Chien Jui Fen , Chang Chung Ying
Published: November 2008

InGaN-based light emitting diodes (LEDs) with a top pattern-nanoporous p-type GaN:Mg surface were fabricated by using a photoelectrochemical (PEC) process. The peak wavelengths of electroluminescence (EL) and operating voltages were measured as 461.2 nm (3.1 V), 459.6 nm (9.2 V), and 460.1 nm (3.3 V) for conventional, nanoporous, and pattern-nanoporous LEDs using 20 mA operation current. The EL spectrum of the nanoporous LED had a larger blueshift phenomenon as a result of a partial compression strain release in the InGaN active layer through the formation of a top nanoporous surface. The light output power had 12.1% and 26.4% enhancements for the nanoporous and the pattern-nanoporous LEDs compared with conventional LEDs. The larger operating voltage of the nanoporous LED was due to the non-ohmic contact on the PEC treated p-type GaN:Mg surface. By using a pattern-nanoporous p-type GaN:Mg structure, the operating voltage of the pattern-nanoporous LED was reduced to 3.3 V. A lower compression strain in the InGaN active layer and a higher light extraction efficiency at the top nanoporous surface were observed in pattern-nanoporous LEDs for higher efficiency nitride-based LED applications.
Time dependence of the electronic structure of an electron-beam-irradiated C60 film
Authors: Onoe Jun , Ito Takahiro , Kimura Shin-ichi
Published: November 2008

Time dependence of the electronic structure of an electron-beam (EB) irradiated C60 film (20–30 nm thick) has been examined using in situ high-resolution ultraviolet photoelectron spectroscopy. It is found that the electronic states of the C60 film have been changed continuously from an insulator (pristine C60 films) to a semiconductor and finally to a metal as EB-irradiation time increased. This can be explained by the increase in polymerization degree of a C60 polymer with a given cross-linked structure derived from the general Stone–Wales rearrangement from [Beu et al.,Phys. Rev. B 72, 155416 (2005)]. In addition, this finding suggests that the electronic properties of the C60 film can be controlled only in the EB-irradiated region by varying the irradiation time, which is interesting when applied to electronic devices.
Mössbauer studies on structural ordering and magnetic properties of melt-spun Ni–Fe–Ga ribbons
Authors: Rama Rao N. V. , Gopalan R. , Manivel Raja M. , Chandrasekaran V. , Suresh K. G.
Published: November 2008

Ribbons of ferromagnetic shape memory Ni2+xFe1−xGa (x=0 and 0.12) alloys were prepared at wheel speeds of 12 and 35m∕s by melt spinning technique. The structural (site) disorder and the associated changes in the magnetic properties of the ribbons were investigated by Fe57 Mössbauer spectroscopy and magnetization measurements respectively. Mössbauer spectra of Ni2FeGa ribbon revealed the presence of both L21 order and B2-like disorder with some amount of Fe antisite atoms on Ni site. The increase in Ni content was found to decrease the TC while its effect on TM was the opposite way.
Alleviation of Fermi-level pinning effect on metal/germanium interface by insertion of an ultrathin aluminum oxide
Authors: Zhou Yi , Ogawa Masaaki , Han Xinhai , Wang Kang L.
Published: November 2008

Due to the strong Fermi-level pinning close to the germanium (Ge) valence band edge, all metal/p-type Ge contacts show Ohmic characteristics, while metal/n-type Ge contacts exhibit rectifying behaviors. In this paper, we report a simple method to alleviate this Fermi-level pinning effect by inserting a thin layer of aluminum oxide (Al2O3), formed by oxidation of aluminum (Al), between the metal/Ge interface. The effective Schottky barrier heights of nickel (Ni)∕n-type Ge, cobalt (Co)∕n-type Ge, and iron (Fe)∕n-type Ge decrease from 0.54, 0.62, and 0.61eV to 0.39, 0.23, and 0.18eV, respectively, with this thin layer of Al2O3. The tunneling oxide significantly suppresses the Fermi-level pinning, and yet does not restrict the current density. This method seems promising to realize low resistance metal contact to n-type Ge, which is essential to realize n-channel Ge complementary metal-oxide-semiconductor field-effect transistor with metal source and drain.
Coherent anti-Stokes Raman microspectroscopy using spectral focusing with glass dispersion
Authors: Rocha-Mendoza Israel , Langbein Wolfgang , Borri Paola
Published: November 2008

We demonstrate experimentally that coherent anti-Stokes Raman microspectroscopy with high spectral resolution is achieved using femtosecond laser pulses chirped up to a few picoseconds by glass elements of known group-velocity dispersion without significant intensity losses. By simply choosing the length of the glass, the chirp of Stokes and pump pulses is tailored to obtain a spectral resolution given by the Fourier limit of the chirped pulse duration. We show that for chirped pulse durations shorter than or comparable to the Raman coherence time, maximum signal occurs for a pump arriving after the Stokes pulse, a time-ordering effect confirmed by numerical simulations.
Synthesis and transport property of AgSbTe2 as a promising thermoelectric compound
Authors: Wang Heng , Li Jing-Feng , Zou Minmin , Sui Tao
Published: November 2008

Polycrystalline AgSbTe2 ternary compound materials with high phase purity were fabricated using a combined process of mechanical alloying and spark plasma sintering. It was found that stoichiometric AgSbTe2 is a promising composition for low-and-mediate temperature applications, whose ZT reaches 1.59 at 673K, benefiting from its extremely low thermal conductivity (0.30W∕mK) in addition to its low electrical resistivity (<1.1×10−4Ωm) and large positive Seebeck coefficient (260μV∕K). On the other hand, deviating from this formula would lead to unstable phase structures and higher thermal conductivity, which make the samples less attractive as thermoelectric materials or components of thermoelectric systems.
Revealing the spatial distribution of a disease while preserving privacy
Authors: Wieland Shannon C. , Cassa Christopher A. , Mandl Kenneth D. , Berger Bonnie
Published: November 2008

Datasets describing the health status of individuals are important for medical research but must be used cautiously to protect patient privacy. For patient data containing geographical identifiers, the conventional solution is to aggregate the data by large areas. This method often preserves privacy but suffers from substantial information loss, which degrades the quality of subsequent disease mapping or cluster detection studies. Other heuristic methods for de-identifying spatial patient information do not quantify the risk to individual privacy. We develop an optimal method based on linear programming to add noise to individual locations that preserves the distribution of a disease. The method ensures a small, quantitative risk of individual re-identification. Because the amount of noise added is minimal for the desired degree of privacy protection, the de-identified set is ideal for spatial epidemiological studies. We apply the method to patients in New York County, New York, showing that privacy is guaranteed while moving patients 25—150 times less than aggregation by zip code.
Hierarchical mechanisms build the DNA-binding specificity of FUSE binding protein
Authors: Benjamin Lawrence R. , Chung Hye-Jung , Sanford Suzanne , Kouzine Fedor , Liu Juhong , Levens David
Published: November 2008

The far upstream element (FUSE) binding protein (FBP), a single-stranded nucleic acid binding protein, is recruited to the
c-myc
promoter after melting of FUSE by transcriptionally generated dynamic supercoils. Via interactions with TFIIH and FBP-interacting repressor (FIR), FBP modulates
c-myc
transcription. Here, we investigate the contributions of FBP's 4 K Homology (KH) domains to sequence selectivity. EMSA and missing contact point analysis revealed that FBP contacts 4 separate patches spanning a large segment of FUSE. A SELEX procedure using paired KH-domains defined the preferred subsequences for each KH domain. Unexpectedly, there was also a strong selection for the noncontacted residues between these subsequences, showing that the contact points must be optimally presented in a backbone that minimizes secondary structure. Strategic mutation of contact points defined in this study disabled FUSE activity
in vivo
. Because the biological specificity of FBP is tuned at several layers: (
i
) accessibility of the site; (
ii
) supercoil-driven melting; (
iii
) presentation of unhindered bases for recognition; and (
iv
) modular interaction of KH-domains with cognate bases, the FBP-FIR system and sequence-specific, single-strand DNA binding proteins in general are likely to prove versatile tools for adjusting gene expression.
Regulation of zebrafish fin regeneration by microRNAs
Authors: Thatcher Elizabeth J. , Paydar Ima , Anderson Kimberly K. , Patton James G.
Published: November 2008

A number of genes have been implicated in regeneration, but the regulation of these genes, particularly pertaining to regeneration in higher vertebrates, remains an interesting and mostly open question. We have studied microRNA (miRNA) regulation of regeneration and found that an intact miRNA pathway is essential for caudal fin regeneration in zebrafish. We also showed that
miR-203
directly targets the Wnt signaling transcription factor Lef1 during this process. Repression of Lef1 by
miR-203
blocks regeneration, whereas loss of
miR-203
results in excess Lef1 levels and fin overgrowth. Expression of Lef1 from mRNAs lacking 3′ UTR recognition elements can rescue the effects of excess
miR-203
, demonstrating that these effects are due to specific regulation of
lef1
by
miR-203
. Our data support a model in which regulation of Lef1 protein levels by
miR-203
is a key limiting step during regeneration.
Enhancement of sensitivity gain and frequency tuning by coupling of active hair bundles
Authors: Dierkes Kai , Lindner Benjamin , Jülicher Frank
Published: November 2008

The vertebrate inner ear possesses an active process that provides nonlinear amplification of mechanical stimuli. A candidate for this process is active hair bundle mechanics observed, for instance, for hair cells of the bullfrog's sacculus. Hair bundles in various inner ear organs are coupled by overlying membranes. Using a stochastic description of active hair bundle dynamics, we study the consequences of an elastic coupling on the properties of amplification. We report that collective effects in arrays of hair bundles can enhance the amplification gain and the sharpness of frequency tuning as compared with the performance of an isolated hair bundle. We also discuss the transient response elicited by the sudden onset of a periodic stimulus and its relation to temporal integration curves. Simulations of systems with a gradient of intrinsic frequencies show an enhanced amplification gain while preserving a frequency gradient, provided the coupling strength is similar to the hair bundle stiffness. We relate our findings to the situation in the bullfrog's sacculus and the mammalian cochlea.
Altered surface trafficking of presynaptic cannabinoid type 1 receptor in and out synaptic terminals parallels receptor desensitization
Authors: Mikasova Lenka , Groc Laurent , Choquet Daniel , Manzoni Olivier J.
Published: November 2008

Presynaptic cannabinoid type 1 receptors (CB1Rs) are major mediators of retrograde synaptic plasticity at both excitatory and inhibitory synapses and participate in a plethora of physiological functions. Whether presynaptic receptors, such as CB1R, display functionally relevant movements at the surface of neuronal membranes is not known. We analyzed the lateral mobility of native CB1Rs in cortical neurons by using single-quantum dot imaging. We found that CB1Rs are highly mobile and rapidly diffuse in and out of presynapses. Agonist-induced desensitization correlated with a reduction in the fraction of surface CB1Rs and a drastic decrease in the membrane dynamic of the CB1Rs that remained at the presynaptic surface. Desensitization specifically excluded CB1Rs from synapses and increased the fraction of immobile receptors in the extrasynaptic compartment. The results suggest that decrease of mobility may be one of the core mechanisms underlying the desensitization of CB1R, the most abundant G protein-coupled receptor in the brain.
Molecular structural basis for polymorphism in Alzheimer's β-amyloid fibrils
Authors: Paravastu Anant K. , Leapman Richard D. , Yau Wai-Ming , Tycko Robert
Published: November 2008

We describe a full structural model for amyloid fibrils formed by the 40-residue β-amyloid peptide associated with Alzheimer's disease (Aβ
1–40
), based on numerous constraints from solid state NMR and electron microscopy. This model applies specifically to fibrils with a periodically twisted morphology, with twist period equal to 120 ± 20 nm (defined as the distance between apparent minima in fibril width in negatively stained transmission electron microscope images). The structure has threefold symmetry about the fibril growth axis, implied by mass-per-length data and the observation of a single set of
13
C NMR signals. Comparison with a previously reported model for Aβ
1–40
fibrils with a qualitatively different, striated ribbon morphology reveals the molecular basis for polymorphism. At the molecular level, the 2 Aβ
1–40
fibril morphologies differ in overall symmetry (twofold vs. threefold), the conformation of non-β-strand segments, and certain quaternary contacts. Both morphologies contain in-register parallel β-sheets, constructed from nearly the same β-strand segments. Because twisted and striated ribbon morphologies are also observed for amyloid fibrils formed by other polypeptides, such as the amylin peptide associated with type 2 diabetes, these structural variations may have general implications.
Amplified effect of Brownian motion in bacterial near-surface swimming
Authors: Li Guanglai , Tam Lick-Kong , Tang Jay X.
Published: November 2008

Brownian motion influences bacterial swimming by randomizing displacement and direction. Here, we report that the influence of Brownian motion is amplified when it is coupled to hydrodynamic interaction. We examine swimming trajectories of the singly flagellated bacterium
Caulobacter crescentus
near a glass surface with total internal reflection fluorescence microscopy and observe large fluctuations over time in the distance of the cell from the solid surface caused by Brownian motion. The observation is compared with computer simulation based on analysis of relevant physical factors, including electrostatics, van der Waals force, hydrodynamics, and Brownian motion. The simulation reproduces the experimental findings and reveals contribution from fluctuations of the cell orientation beyond the resolution of present observation. Coupled with hydrodynamic interaction between the bacterium and the boundary surface, the fluctuations in distance and orientation subsequently lead to variation of the swimming speed and local radius of curvature of swimming trajectory. These results shed light on the fundamental roles of Brownian motion in microbial motility, nutrient uptake, and adhesion.
The structure of corepressor Dax-1 bound to its target nuclear receptor LRH-1
Authors: Sablin Elena P. , Woods April , Krylova Irina N. , Hwang Peter , Ingraham Holly A. , Fletterick Robert J.
Published: November 2008

The Dax-1 protein is an enigmatic nuclear receptor that lacks an expected DNA binding domain, yet functions as a potent corepressor of nuclear receptors. Here we report the structure of Dax-1 bound to one of its targets, liver receptor homolog 1 (LRH-1). Unexpectedly, Dax-1 binds to LRH-1 using a new module, a repressor helix built from a family conserved sequence motif, PCFXXLP. Mutations in this repressor helix that are linked with human endocrine disorders dissociate the complex and attenuate Dax-1 function. The structure of the Dax-1:LRH-1 complex provides the molecular mechanism for the function of Dax-1 as a potent transcriptional repressor.
Involvement of thyrotropin in photoperiodic signal transduction in mice
Authors: Ono Hiroko , Hoshino Yuta , Yasuo Shinobu , Watanabe Miwa , Nakane Yusuke , Murai Atsushi , Ebihara Shizufumi , Korf Horst-Werner , Yoshimura Takashi
Published: November 2008

Local thyroid hormone catabolism within the mediobasal hypothalamus (MBH) by thyroid hormone-activating (DIO2) and -inactivating (DIO3) enzymes regulates seasonal reproduction in birds and mammals. Recent functional genomics analysis in birds has shown that long days induce thyroid-stimulating hormone production in the pars tuberalis (PT) of the pituitary gland, which triggers
DIO2
expression in the ependymal cells (EC) of the MBH. In mammals, nocturnal melatonin secretion provides an endocrine signal of the photoperiod to the PT that contains melatonin receptors in high density, but the interface between the melatonin signal perceived in the PT and the thyroid hormone levels in the MBH remains unclear. Here we provide evidence in mice that TSH participates in this photoperiodic signal transduction. Although most mouse strains are considered to be nonseasonal, a robust photoperiodic response comprising induced expression of
TSHB
(TSH β subunit),
CGA
(TSH α subunit), and
DIO2
, and reduced expression of
DIO3
, was observed in melatonin-proficient CBA/N mice. These responses could not be elicited in melatonin-deficient C57BL/6J, but treatment of C57BL/6J mice with exogenous melatonin elicited similar effects on the expression of the above-mentioned genes as observed in CBA/N after transfer to short-day conditions. The EC was found to express TSH receptor (
TSHR
), and ICV injection of TSH induced
DIO2
expression. Finally, we show that melatonin administration did not affect the expression of
TSHB
,
DIO2
, and
DIO3
in TSHR-null mice. Taken together, our findings suggest that melatonin-dependent regulation of thyroid hormone levels in the MBH appears to involve TSH in mammals.
IL-6 controls Th17 immunity in vivo by inhibiting the conversion of conventional T cells into Foxp3+regulatory T cells
Authors: Korn Thomas , Mitsdoerffer Meike , Croxford Andrew L. , Awasthi Amit , Dardalhon Valérie A. , Galileos George , Vollmar Patrick , Stritesky Gretta L. , Kaplan Mark H. , Waisman Ari , Kuchroo Vijay K. , Oukka Mohamed
Published: November 2008

The conditions leading to the induction of adaptive Foxp3+regulatory T cells (T-regs) from peripheral T cells in vivo are incompletely understood. Here, we show that unresponsiveness of T cells to IL-6 by T cell-selective deletion of gp130 or immunization of wild-type mice with antigen in incomplete Freund's adjuvant (IFA), which fails to induce IL-6, promotes the conversion of peripheral CD4+T cells into adaptive Foxp3+T-regs. Thus, both T cell-conditional gp130 knockout (KO) mice immunized with MOG35-55 in complete Freund's adjuvant (CFA) and wild-type mice immunized with MOG35-55 in IFA develop overwhelming antigen-specific T-reg responses and are protected from experimental autoimmune encephalomyelitis (EAE). Depletion of T-regs restores T helper (Th)17 responses and clinical EAE in MOG/CFA-immunized T cell-conditional gp130 KO mice, but not in MOG/IFA-immunized wild-type mice. We conclude that in the absence of T-regs, IL-6 signaling is dispensable for the induction of Th17 cells, and alternative pathways exist to induce Th17 cells and EAE in the absence of IL-6 signaling. However, IL-6 signaling is dominant in inhibiting the conversion of conventional T cells into Foxp3+T-regs in vivo, and in the absence of IL-6 signaling, no other cytokine can substitute in inhibiting T-reg conversion. These data identify IL-6 as an important target to modulate autoimmune responses and chronic inflammation.
DNA energy landscapes via calorimetric detection of microstate ensembles of metastable macrostates and triplet repeat diseases
Authors: Völker Jens , Klump Horst H. , Breslauer Kenneth J.
Published: November 2008

Biopolymers exhibit rough energy landscapes, thereby allowing biological processes to access a broad range of kinetic and thermodynamic states. In contrast to proteins, the energy landscapes of nucleic acids have been the subject of relatively few experimental investigations. In this study, we use calorimetric and spectroscopic observables to detect, resolve, and selectively enrich energetically discrete ensembles of microstates within metastable DNA structures. Our results are consistent with metastable, “native” DNA states being composed of an ensemble of discrete and kinetically stable microstates of differential stabilities, rather than exclusively being a single, discrete thermodynamic species. This conceptual construct is important for understanding the linkage between biopolymer conformational/configurational space and biological function, such as in protein folding, allosteric control of enzyme activity, RNA and DNA folding and function, DNA structure and biological regulation, etc. For the specific DNA sequences and structures studied here, the demonstration of discrete, kinetically stable microstates potentially has biological consequences for understanding the development and onset of DNA expansion and triplet repeat diseases.
Progressive velocity throwing training increases velocity without detriment to accuracy in sub‐elite cricket players: A randomized controlled trial
Authors: Freeston Jonathan , Rooney Kieron
Published: November 2008

Throwing performance is vital within the sport of cricket. However, little published evidence exists regarding methods to improve throwing velocity and/or accuracy in any cricket‐playing population. This study, therefore, assessed the efficacy of progressive velocity throwing training on throwing velocity and accuracy in a cricket‐specific test. Eighteen sub‐elite male cricket players were assessed for maximal throwing velocity and throwing accuracy at four different throwing velocities relative to maximal throwing velocity. The participants were randomly assigned to either an intervention (n=9) or control (n=9) group. Both groups performed usual pre‐season activities for 8 weeks, during which the intervention group performed two additional specific throwing training sessions per week. Maximal throwing velocity was re‐assessed at 4 weeks and the progressive velocity throwing programme was adjusted accordingly. The 8‐week progressive velocity throwing training significantly increased peak and mean maximal throwing velocity (P = 0.01). Absolute changes in peak and mean maximal throwing velocity were negatively and significantly correlated with initial maximal throwing velocity at 4 weeks (r=−0.805, P = 0.01 and r=−0.806, P = 0.01 respectively) but not at 8 weeks. No significant difference was observed in accuracy for either group at any time. This is the first published study to describe the effectiveness of a progressive velocity throwing training programme on throwing performance in a group of sub‐elite cricket players. The addition of two specific throwing training sessions per week can increase maximal throwing velocity without detriment to throwing accuracy.
Validation of a one‐day self‐report questionnaire for physical activity assessment in healthy adults
Authors: Leicht Anthony
Published: November 2008

A self‐report physical activity scale (PAS) has previously been developed to document physical activity (MET‐hours) undertaken by adults during an average weekday. The current study aimed to validate the PAS over 24 hours via pedometer determinations of physical activity in healthy, active adults, and to determine possible influences of gender and body mass status on this relationship. One‐hundred and seven healthy university students (age 18–41 years) wore a pedometer (Yamax DigiWalker SW‐700) during the waking hours of an average weekday followed by successful completion of the PAS. Relationships between the PAS and pedometer measures (steps taken and energy expenditure) were examined by Pearson's correlation coefficients. Significant (P<0.05) gender and body mass status differences were examined by two‐way analysis of variance with Tukey post‐hoc tests. Participants reported 48.0±10.4 MET‐hours of activity, completed 11,506±4195 steps, and expended 499±227 kcal during an average weekday. Physical activity measures, except energy expenditure, were similar across groups by gender and body mass status. The total number of MET‐hours was significantly associated with pedometer steps taken (r=0.375–0.568, P<0.01), and this relationship varied by gender and to a lesser extent by body mass status. The results of the current study show that the self‐reported physical activity of healthy active adults was in line with the popular recommended dose of daily physical activity (10,000 steps per day) and was not influenced by gender or body mass status. Furthermore, over an average weekday, the PAS provided a simple, quick, and valid method to document physical activity undertaken by young healthy active adults that is comparable to pedometer readings.
The transtheoretical model in the context of physical activity in a school‐based sample of German adolescents
Authors: Bucksch Jens , Finne Emily , Kolip Petra
Published: November 2008

Physical activity in adolescents is an important public health issue. Regular participation in physical activity is associated with various health benefits. However, problems with motivational adherence to physical activity have been documented. The transtheoretical model is a model of behaviour change. This model, which consists of stages of change, self‐efficacy, decisional balance, and processes of change, has not been extensively investigated in youth. In addition, the health‐enhancing physical activity concept has rarely been applied in this context.

A cross‐sectional design was used. A random sample of seven junior high schools from Bremen (Germany) resulted in a sample of 588 adolescents (50.5% males, mean age=15.0 years, s=0.67). Respondents completed a self‐administered questionnaire assessing stages of change, self‐efficacy, decisional balance, and processes of change. Univariate analyses of variance were used to identify which constructs differed significantly across the stages of change. Discriminant analysis was used to determine which variables best discriminate the stages.

Distribution of the sample across the stages was: precontemplation, n=175 (29.8%); contemplation, n=135 (22.0%); preparation, n=63 (10.7%); action, n=20 (3.4%); and maintenance, n=195 (33.2%). Significant effects of stages of change were found for self‐efficacy, pros, and seven of the ten processes of change. In general, scores of these constructs increased across the stages. Cons did not differ significantly across the stages.

The results provide support for some of the assumptions of the transtheoretical model in a German sample of adolescents. Some of our findings raise questions about the usefulness of five discrete stages. From a public health viewpoint, tailored interventions based on motivational readiness to change would be fruitful, but further research is warranted.
An acute bout of high‐intensity intermittent swimming induces glycogen supercompensation in rat skeletal muscle
Authors: Sonou Tomohiro , Higuchi Mitsuru , Terada Shin
Published: November 2008

High‐intensity intermittent exercise substantially increases muscle glucose transport, which is thought to be the rate‐limiting step for glycogen synthesis. In the present study, we compared muscle glycogen supercompensation after high‐intensity intermittent exercise with that observed after low‐intensity continuous exercise in rats. Four‐ to five‐week‐old male Sprague‐Dawley rats performed either low‐intensity swimming (240 min of swimming exercise with a weight equivalent to 1% of their body mass; LOW) or high‐intensity swimming (twenty 30‐s swimming bouts with 30 s rest between bouts with a weight equivalent to 16% of their body mass; HIGH) to deplete muscle glycogen. After the glycogen‐depleting exercise, rats were given a rodent chow diet plus 5% glucose solution for 6 h or 24 h. Immediately after the two types of exercise, glycogen concentration in rat epitrochlearis muscle was similarly depleted. After the 6‐h and 24‐h recovery periods, muscle glycogen concentrations in both the HIGH and LOW groups were restored well above the normally fed state. Furthermore, muscle glycogen accumulation in the HIGH group for the 6‐h and 24‐h recovery periods was not significantly different from that observed in the LOW group. The high‐intensity intermittent swimming exercise also induced muscle glycogen supercompensation in well‐trained rats that had performed 7 days of endurance swimming training (6 h per day). Our results indicate that high‐intensity intermittent exercise as well as low‐intensity continuous exercise could induce glycogen supercompensation in rat skeletal muscle.
Strength, power, and postural control in seniors: Considerations for functional adaptations and for fall prevention
Authors: Granacher Urs , Zahner Lukas , Gollhofer Albert
Published: November 2008

The ageing neuromuscular system is affected by structural and functional changes that lead to a general slowing down of neuromuscular performance and an increased risk of falling. As a consequence, the process of ageing results in a reduced ability to develop maximal and explosive force, as well as in deficits in static and dynamic postural control. A decrease in the number and size of type II fibres in particular accounts for the age‐related decline in muscle mass (sarcopaenia) and strength performance. Multiple denervation and re‐innervation processes of muscle fibres seem to be responsible for the reduced number of muscle fibres. Recently, it has been suggested that it is not the decline in motoneurons that accounts for the loss in number of muscle fibres but the disturbed potential of fibre regeneration and re‐innervation. Furthermore, an age‐related reduction in the number of satellite cells has also been associated with sarcopaenia. The ability to compensate for platform and gait perturbations deteriorates with ageing as reflected in longer onset latencies and inefficient postural responses. All sites within the somatosensory system are affected by ageing and therefore contribute to postural instability. However, morphological changes of muscle spindles appear primarily to be responsible for the impaired ability to compensate for balance threats in old age. Given these neuromuscular limitations in old age, it is important to apply adequate training interventions that delay or even reverse the onset of these constraints. Strength training has the potential to enhance maximal as well as explosive force production capacity. This is accomplished by neural factors, including an improved recruitment pattern, discharge rate, and synchronization of motor units. Furthermore, an increase in number of satellite cells most likely accounts for training‐induced muscle hypertrophy. Recent studies have investigated the impact of balance training in old age on the ability to develop maximal and explosive force. In addition, the effects of balance training on reflex activity during gait perturbations were also examined. Increases in maximal and explosive force production capacity and an improved ability to compensate for gait perturbations were observed. It is evident from the literature that researchers are increasingly studying the effects of more specifically designed training programmes on performance in populations of older adults. Thus, in the near future, strength training could be replaced by high‐velocity forms of power training and balance training by perturbation‐based training programmes. It is hypothesized that this new approach is more efficient in terms of fall prevention than the traditional approach.