bluuebunny/crossref_metadata_2025 huggingface dataset:
A mechanism for the suppression of interleukin-1-induced nuclear factor κB activation by protein phosphatase 2Cη-2
Authors: Henmi Takeaki , Amano Kazutaka , Nagaura Yuko , Matsumoto Kunihiro , Echigo Seishi , Tamura Shinri , Kobayashi Takayasu
Published: July 2009

IL-1 (interleukin-1) is a pro-inflammatory cytokine that has a variety of effects during the process of inflammation. Stimulating cells with IL-1 initiates a signalling cascade that includes the activation of NF-κB (nuclear factor κB), and subsequently induces a variety of inflammatory genes. Although the molecular mechanism for the IL-1-induced activation of NF-κB has been well documented, much less is known about the mechanism by which protein phosphatases down-regulate this pathway. Here we show that mouse PP2Cη-2 (protein serine/threonine phosphatase 2Cη-2), a novel member of the protein serine/threonine phosphatase 2C family, inhibits the IL-1–NF-κB signalling pathway. Ectopic expression of PP2Cη-2 in human embryonic kidney HEK293IL-1RI cells inhibited the IL-1-induced activation of NF-κB. TAK1 (transforming-growth-factor-β-activated kinase 1) mediates the IL-1 signalling pathway to NF-κB, and we observed that the TAK1-induced activation of NF-κB was suppressed by PP2Cη-2 expression. Expression of IKKβ [IκB (inhibitory κB) kinase β], which lies downstream of TAK1, activates NF-κB, and this activation was also readily reversed by PP2Cη-2 co-expression. Additionally, PP2Cη-2 knockdown with small interfering RNA further stimulated the IL-1-enhanced phosphorylation of IKKβ and destabilization of IκBα in HeLa cells. PP2Cη-2 knockdown also increased the IL-1-induced expression of IL-6 mRNA. Furthermore, IKKβ was readily dephosphorylated by PP2Cη-2 in vitro. These results suggest that PP2Cη-2 inhibits the IL-1–NF-κB signalling pathway by selectively dephosphorylating IKKβ.
Central sympathetic outflow to skeletal muscle: the major link between non-esterified fatty acids and elevated blood pressure?
Authors: Schlaich Markus
Published: July 2009

Sympathetic nervous system activation is a hallmark of several conditions associated with an adverse prognosis, including hypertension and the metabolic syndrome. Proposed mediators of increased sympathetic drive include hyperinsulinaemia, leptin, NEFAs (non-esterified fatty acids), pro-inflammatory cytokines, baroreflex impairment and others. The role of NEFAs appears to be of particular importance given the increased levels observed in human obesity and the experimental results linking the NEFA-induced pressor response to sympathetic activation. Findings from human studies have yielded conflicting results with regards to a sympathetically mediated association between NEFAs and elevated arterial blood pressure. In the present issue of Clinical Science, Florian and Pawelczyk present some interesting results obtained from a small number of healthy normotensive lean volunteers who were exposed to NEFA infusion and cardiovascular and sympathetic monitoring using state of the art methodology that appears to be in support of such a link. However, several methodological and conceptual considerations need to be taken into account when interpreting the results from this study. Put into perspective, the case for a substantial sympathetically mediated pressor response to NEFA infusion does not appear to be a very strong one.
The Collaborative Medical and Behavioral Management of Chronic Cough
Authors: Petty Brian E. , Dailey Seth H.
Published: July 2009

Chronic cough is the most frequent reason cited by patients for seeking medical care in an ambulatory setting and may account for 10% to 38% of a pulmonologist's practice. Because chronic cough can be caused by or correlated with a wide array of disorders and behaviors, the diagnosis of etiologic factors and determination of appropriate therapeutic management in these cases can prove to be daunting for the physician and speech-language pathologist alike. This article will describe the phenomenon of chronic cough, discuss the many etiologic factors to consider, and review some of the more common ways in which speech-language pathologists and physicians collaborate to treat this challenging condition.
Clinical Practice: Spasmodic Dysphonia and Vocal Tremor
Authors: Finnegan Eileen M. , Hoffman Henry T. , Hemmerich Abby L. , Van Daele Douglas J.
Published: July 2009

The Laryngeal Movement Disorder Clinic (LMDC) was started in 1990 in the Department of Otolaryngology at the University of Iowa. This specialized subset of the general Voice Clinic (
http://www.healthcare.uiowa.edu/otolaryngology/protocols/Parts/Part1/Part1C/P1C1.htm
) is scheduled twice a month for patients with laryngeal movement disorders such as spasmodic dysphonia (SD), vocal tremor, muscle tension dysphonia (MTD), and vocal fold paralysis (VCP). Patients with other craniocervical dystonias also may be seen in this clinic. The purpose of the clinic is to provide specialized diagnostic assessments and treatments. Application of electromyography for diagnosis as well as for directed botulinum toxin injections dominates the practice of this clinic. Voice therapy also is directed through this clinic, with coordination through practitioners in the University of Iowa system or, more commonly, with practitioners who are located closer to the patients' homes. It is the purpose of this article to describe the clinical pathways for patients who are seen at the LMDC from a multidisciplinary perspective. This summary will include aspects of differential diagnosis and clinical history taking, assessment, and treatment for those with laryngeal movement disorders.
On the thermodynamic limit of form factors in the massless XXZ Heisenberg chain
Authors: Kitanine N. , Kozlowski K. K. , Maillet J. M. , Slavnov N. A. , Terras V.
Published: July 2009

We consider the problem of computing form factors of the massless XXZ Heisenberg spin-1/2 chain in a magnetic field in the (thermodynamic) limit where the size M of the chain becomes large. For that purpose, we take the particular example of the matrix element of the operator σz between the ground state and an excited state with one particle and one hole located at the opposite ends of the Fermi interval (umklapp-type term). We exhibit its power-law decrease in terms of the size of the chain M and compute the corresponding exponent and amplitude. As a consequence, we show that this form factor is directly related to the amplitude of the leading oscillating term in the long-distance asymptotic expansion of the correlation function ⟨σ1zσm+1z⟩.
Negative refractive index metamaterials in the visible spectrum based on MgB2∕SiC composites
Authors: Limberopoulos Nicholaos , Akyurtlu Alkim , Higginson Keith , Kussow Adil-Gerai , Merritt Charles D.
Published: July 2009

An isotropic three-dimensional negative refractive index metamaterial has been fabricated and characterized in the visible regime. The metamaterial is based on a structure consisting of polycrystalline magnesium diboride (MgB2) as the host, providing negative permittivity, and silicon carbide (SiC) nanoparticles embedded randomly within the host, providing negative permeability. The metamaterial was fabricated using hot isostatic pressing to produce a fully dense solid with well-dispersed SiC nanoparticles. The properties of the resulting bulk metamaterial were evaluated using surface plasmon excitation, which showed coupling of both magnetic and electric plasmons, signifying both negative permeability and permittivity at 632nm.
Effect of emitter thickness on the spectral shape of heterojunction interfacial workfunction internal photoemission detectors
Authors: Matsik S. G. , Jayasinghe R. C. , Weerasekara A. B. , Perera A. G. U. , Linfield E. H. , Khanna S. P. , Lachab M. , Liu H. C.
Published: July 2009

Results are presented showing the effect of emitter layer thickness on the shape of the spectral response of heterojunction interfacial workfunction internal photoemission detectors. The results confirm that thicker emitters increase the response at shorter wavelengths. A model is developed to explain the experimentally observed blueshift in the peak wavelength with increased emitter thickness, using a combination of hot-cold carrier scattering and phonon emission processes. The study provides a tool for designing detectors exhibiting different peak responses, as demonstrated by evaluating the design parameters for the 8–14μm spectral range.
Rovibronic analysis of the Jahn–Teller effect in CH2D2+ at low energies
Authors: Grütter M. , Wörner H. J. , Merkt F.
Published: July 2009

The Jahn–Teller effect in the ground state of CH2D2+ has been studied by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy. The lowest three bands have been assigned to the three isomers CHℓHℓDsDs+, CHℓHsDℓDs+, and CHsHsDℓDℓ+, in which the deuterium atoms are attached to the central carbon atom by two short bonds, one short and one long bond, and two long bonds, respectively, and which have different zero-point vibrational energies. Whereas CHℓHℓDsDs+ and CHsHsDℓDℓ+ can each be described by a single structure with C2v symmetry, CHℓHsDℓDs+ corresponds to four equivalent C1 structures that interconvert by tunneling. The rotational structure of these three bands is compared with predictions made on the basis of a tunneling Hamiltonian combined with a rotational Hamiltonian that incorporates the effects of the large-amplitude tunneling motion. The zero-point energies of CHℓHsDℓDs+ and CHsHsDℓDℓ+ relative to that of CHℓHℓDsDs+ are Δ=123.6(5) cm−1 and Δ′=243.2(5) cm−1, respectively, and the tunneling matrix element σ coupling the four C2v equilibrium structures of CHℓHsDℓDs+ is −1.7(4) cm−1.
Low-regularity solutions of the periodic Fornberg–Whitham equation
Authors: Tian Lixin , Chen Yuexia , Jiang Xiuping , Xia Limeng
Published: July 2009

This paper studies low-regularity solutions of the periodic Fornberg–Whitham equation with initial value. The existence and the uniqueness of solutions are proved. The results are illustrated by considering the periodic peakons of the periodic Fornberg–Whitham equation.
Current conduction in Al/Si nanocrystal embedded SiO2/p-Si diodes with various distributions of Si nanocrystals in the oxide
Authors: Wong J. I. , Chen T. P. , Yang M. , Liu Y. , Ng C. Y. , Ding L.
Published: July 2009

Different distributions of Si nanocrystals (nc-Si) in the gate oxide of Al/nc-Si embedded SiO2/p-Si diodes are synthesized with Si ion implantation technique. Current conduction in the diodes with different nc-Si distributions has been investigated. It is shown that under a positive gate bias Fowler–Nordheim (FN) tunneling from the Si substrate to the oxide, the nanocrystal-assisted conduction (e.g., tunneling, Frenkel–Poole emission) and the nanocrystal-assisted FN tunneling contribute to the current conduction depending on both the nc-Si distribution and magnitude of the gate bias. In the case that nc-Si is densely distributed throughout the oxide, a huge enhancement in the current conduction is observed as a result of the formation of many percolative conduction paths by the nc-Si connecting the gate to the Si substrate.
First-principles study of structure and quantum transport properties of C20 fullerene
Authors: An Yi-Peng , Yang Chuan-Lu , Wang Mei-Shan , Ma Xiao-Guang , Wang De-Hua
Published: July 2009

Using first-principles density-functional theory and nonequilibrium Green’s function formalism for quantum transport calculation, we study the electronic and transport properties of C20 fullerene molecule. Our results show that the equilibrium conductance of C20 molecule is near 1G0. It is found that the I-V curve displays a linear region centered about V=0 and nonlinear behavior under higher bias voltages and an obvious negative differential resistance phenomenon in a certain bias voltage range. The mechanism for the negative differential resistance behavior of C20 is suggested. The present findings could be helpful for the application of the C20 molecule in the field of single molecular devices or nanometer electronics.
A quantum chemistry study of Diels–Alder dimerizations in benzene and anthracene
Authors: Quenneville Jason , Germann Timothy C.
Published: July 2009

There is considerable experimental evidence of covalent dimerization of aromatic compounds occurring under shock conditions. Because of their endothermicity, these reactions could play a large role in the shock initiation process of aromatic molecular explosives such as 2,4,6-trinitrotoluene and 1,3,5-triamino-2,4,6-trinitrobenzene by withdrawing energy from the shock compression. Very little is known about the energetics, however, and this knowledge is crucial for the design of empirical force fields that can treat shock-induced chemistry. We have employed ab initio electronic structure and density functional methods to study the Diels–Alder (DA) dimerizations of benzene and anthracene. The enthalpy of reaction for DA benzene dimerization is predicted to be +35.9 kcal/mol. The stepwise pathway to this dimer involves formation of a stable triplet intermediate that requires 71.8 kcal/mol of energy. Transition states along both the concerted and stepwise pathways were optimized and the energetics of the reaction pathways are detailed. The former is found to be the energetically preferred mechanism. Nine DA dimers of anthracene were found, with six predicted to have dimerization ΔHrxn’s of 24–55 kcal/mol, two with dimerization energies near zero and one that is formed through an exothermic reaction. Twelve triplet dimers of anthracene, with ΔHrxn’s ranging from 33–50 kcal/mol, are also described. Finally, the potential importance of these reactions in the context of shock compression of these materials is discussed.
A sharp challenge to the traditional method of determining the luminescence phase in solid state cathodoluminescence
Authors: Zhao Suling , Xu Zheng , Zhang Fujun , Wang Yongsheng , Ji Guorui , Xu Xurong
Published: July 2009

The solid state cathodoluminescence (SSCL) of an Indium Tin Oxide (ITO)/SiO2/C9-poly(p-phenylenevinylene) (PPV)/SiO2/Al device is measured under ac bias at different voltages. The luminescence spectrum is composed of two emission peaks around 420 and 577 nm corresponding to the emission of the band-band recombination and exciton recombination emission, respectively. The traditional method of determining the luminescence phase by means of the brightness waveform shows that the phase of 420 nm is apparently earlier than that of 577 nm in their bright-voltage waveforms. This is obviously contrary to fact and this method ceases to be effective. Instead we propose the frontier of each period or the valley (instead of the peak) of each period to denote the phase of SSCL.
Surface plasmon coupled chemiluminescence from iron thin films: Directional and approaching fixed angle observation
Authors: Aslan Kadir , Weisenberg Micah , Hortle Elinor , Geddes Chris D.
Published: July 2009

We report the observation of surface plasmon coupled chemiluminescence (SPCC) from iron thin films. Theoretical Fresnel calculations were employed to determine the optimum thickness of iron thin films to be 15 nm, which is assessed by the value of minimum reflectivity curves for incident light upon the thin film. An overlayer 10 nm thick SiO2 was used to protect the iron thin films from oxidation by air or physical changes induced by chemiluminescent solutions. SPCC emission from blue, green, and chartreuse chemiluminescent solutions on iron films can be observed at a fixed angle of 60° for all the chemiluminescent solutions, while free-space emission was isotropic. Iron thin films do not have a catalytic effect on chemiluminescence emission.
On a classification of irreducible almost-commutative geometries V
Authors: Jureit Jan-Hendrik , Stephan Christoph A.
Published: July 2009

We extend a classification of irreducible almost-commutative geometries, whose spectral action is dynamically nondegenerate, to internal algebras that have six simple summands. We find essentially four particle models: an extension of the standard model by a new species of fermions with vectorlike coupling to the gauge group and gauge invariant masses, two versions of the electrostrong model, and a variety of the electrostrong model with Higgs mechanism.
Classical Wigner method with an effective quantum force: Application to reaction rates
Authors: Poulsen Jens Aage , Li Huaqing , Nyman Gunnar
Published: July 2009

We construct an effective “quantum force” to be used in the classical molecular dynamics part of the classical Wigner method when determining correlation functions. The quantum force is obtained by estimating the most important short time separation of the Feynman paths that enter into the expression for the correlation function. The evaluation of the force is then as easy as classical potential energy evaluations. The ideas are tested on three reaction rate problems. The resulting transmission coefficients are in much better agreement with accurate results than transmission coefficients from the ordinary classical Wigner method.
Cooperative and competitive coadsorption of H2, O2, and N2 on Aux+(x=3,5)
Authors: Lang Sandra M. , Bernhardt Thorsten M.
Published: July 2009

The reactions of the small gas-phase gold cluster cations Au3+ and Au5+ with N2, H2, and O2 as well as mixtures thereof were investigated in an octopole ion trap under multicollision conditions. While gold cations are inert toward molecular oxygen, a distinct reaction time and temperature dependent reaction behavior was observed toward H2 and N2. Introducing mixtures of the reactive gases to the ion trap revealed both, competitive and cooperative coadsorption effects: (i) A competitive displacement reaction was detected for the coadsorption of H2 and N2 indicating the molecular adsorption of these molecules onto the gold clusters. The enthalpy of the displacement reaction determined from equilibrium mass spectra was found to be small (<10 kJ/mol). (ii) Preadsorption of N2 enabled the cooperative coadsorption of O2 under special experimental conditions (low temperature and very small amounts of N2). In this surprising cooperative reaction even AuxO2y+ were formed via elimination of the initially activating nitrogen molecules, whereas such complexes were never detected in reactions of gold cluster cations with pure molecular oxygen.
Diameter dependent strength of carbon nanotube reinforced composite
Authors: Sun Ying , Chen Quanfang
Published: July 2009

Experimental results of carbon nanotube (CNT) reinforced copper composites (Cu/CNT) have shown that the resultant tensile strength of Cu/CNT composite is CNT diameter dependent, in a form of parabolic relationship that the smaller the CNT diameters the greater the resultant strength of the Cu/CNT composites. The largely increased strength of Cu/CNT composited is attributed to the good CNT dispersion in both the electrolyte and in composite after electrochemical deposition, as well as to the good interfacial bonding formed by the electrochemical deposition process. Smaller CNT diameters result in greater total interfacial bonding area thus the greater resultant strength of the composite.
Stabilization of liquid crystal photoaligning layers by reactive mesogens
Authors: Yaroshchuk O. , Kyrychenko V. , Tao Du , Chigrinov V. , Kwok H. S. , Hasebe H. , Takatsu H.
Published: July 2009

Via passivation of liquid crystal (LC) photoaligning layers by thin layers of reactive mesogens, strong enhancement in LC alignment stability is achieved. Simultaneously, the passivation layers improve alignment uniformity and chemical stability of photoaligning layers and widely change pretilt angle of liquid crystal.
Quasisubharmonic vibrations in metal plates excited by high-power ultrasonic pulses
Authors: Chen Zhao-jiang , Zhang Shu-yi , Zheng Kai , Kuo Pao-kuang
Published: July 2009

Strongly nonlinear vibration phenomena in metal plates excited by high-power ultrasonic pulses in different conditions are studied experimentally and theoretically. The experimental conditions for generating quasisubharmonics and subharmonics are found and discussed. The plate vibrations are characterized by waveforms, frequency spectra, pseudostate portraits, and Poincaré maps. Then, a three-degree-of-freedom vibroimpact-dynamic model is presented to explore the generation mechanisms of the quasisubharmonic and subharmonic vibrations in the plates. According to the model, the intermittent contact-impact forces caused by the interactions between the transducer horn tip and the plate are considered as the main source for generating the complex nonlinear vibration in the plate. The numerical calculation results can explain reasonably the observed experimental phenomena.
Control of cooperative switching of microwrinkle orientations by nanopatterns
Authors: Ohzono Takuya
Published: July 2009

Microwrinkles are mechanically self-organized surface undulations with an intrinsic wavelength λ0 showing various stripe patterns. The average orientation of the stripes is repeatedly altered by changing, for example, the direction of uniaxial compression applied to the sample. Meanwhile, the stripe patterns can be modulated arbitrarily by the designed topographic patterns through mechanical coupling. Exploiting these results, here we study the switching of the microwrinkle orientations, that is, stripe patterns, under the influence of the artificial nanopatterns with a characteristic periodicity d. The switching is primarily driven by the rotation of the compression axis. The nanopattern-induced boundary condition disturbs the formation of the optimal stripe pattern having λ0. Thus a variety of modulated stripe patterns appear depending on both the relative value, λ0/d (0.5–1.6), and the direction of the uniaxial compression. The relative length, λ0/d, also affects the transition of the stripe patterns, showing different dynamics of the domain walls characterized by their creation, annihilation, and configurations. This results correlate with hysteresis of the spatially averaged stripe orientation for a rotation cycle of the compression direction. The results suggest for the general self-organized stripe patterns that we can tune the transition of the stripe pattern, in other words, the cooperative response of the coupled local stripe orientations, as well as the stripe patterns themselves, by exploiting the artificial patterns with proper designs.
Nuclear quantum effects in electronically adiabatic quantum time correlation functions: Application to the absorption spectrum of a hydrated electron
Authors: Turi László , Hantal György , Rossky Peter J. , Borgis Daniel
Published: July 2009

A general formalism for introducing nuclear quantum effects in the expression of the quantum time correlation function of an operator in a multilevel electronic system is presented in the adiabatic limit. The final formula includes the nuclear quantum time correlation functions of the operator matrix elements, of the energy gap, and their cross terms. These quantities can be inferred and evaluated from their classical analogs obtained by mixed quantum-classical molecular dynamics simulations. The formalism is applied to the absorption spectrum of a hydrated electron, expressed in terms of the time correlation function of the dipole operator in the ground electronic state. We find that both static and dynamic nuclear quantum effects distinctly influence the shape of the absorption spectrum, especially its high energy tail related to transitions to delocalized electron states. Their inclusion does improve significantly the agreement between theory and experiment for both the low and high frequency edges of the spectrum. It does not appear sufficient, however, to resolve persistent deviations in the slow Lorentzian-like decay part of the spectrum in the intermediate 2–3 eV region.
On-chip magnetoresistive detection of resonance in microcantilevers
Authors: Patil S. B. , Guedes A. , Freitas P. P. , Cardoso S. , Chu V. , Conde J. P.
Published: July 2009

Magnetoresistive spin-valve sensors were used to provide on-chip detection of the mechanical resonance of a thin silicon microelectromechanical systems cantilever. The spin-valve sensor was placed underneath the free end of the cantilever. A CoCrPt thin-film permanent magnet was placed on top of the amorphous silicon/Al cantilever. The cantilever was electrostatically actuated and its deflection creates a change in the magnetic field that can be sensed by the spin-valve sensor. The resonance frequency of the structure in the megahertz range is detected by the measurement of the spin-valve sensor output. Minimum deflection detection limit is determined to be 0.06 Å/Hz1/2.
Quantum contributions in the ice phases: The path to a new empirical model for water—TIP4PQ/2005
Authors: McBride Carl , Vega Carlos , Noya Eva G. , Ramírez Rafael , Sesé Luis M.
Published: July 2009

With a view to a better understanding of the influence of atomic quantum delocalization effects on the phase behavior of water, path integral simulations have been undertaken for almost all of the known ice phases using the TIP4P/2005 model in conjunction with the rigid rotor propagator proposed by Müser and Berne [Phys. Rev. Lett. 77, 2638 (1996)]. The quantum contributions then being known, a new empirical model of water is developed (TIP4PQ/2005) which reproduces, to a good degree, a number of the physical properties of the ice phases, for example, densities, structure, and relative stabilities.
Freak waves: Their occurrence and probability
Authors: Chalikov D.
Published: July 2009

This paper describes the results of more than 4000 long-term (up to thousands of peak wave periods) numerical simulations of nonlinear gravity surface waves performed for the investigation of properties and estimation of statistics of extreme (“freak”) waves. The method of solution of two-dimensional potential wave equations based on conformal mapping is applied to the simulation of wave behavior assigned by different initial conditions, defined by the Joint North Sea Wave Observation Project and Pierson–Moskowitz spectra. It is shown that nonlinear wave evolution sometimes results in the appearance of very big waves. There are no predictors for the appearance of extreme waves; however, the height of dimensional waves is proportional to the significant wave height. The initial generation of extreme waves can occur simply as a result of linear group effects, but in some cases the largest wave suddenly starts to grow. It is followed sometimes by a strong concentration of wave energy around a peak vertical. It takes place typically for one peak wave period. It happens to an individual wave in physical space, with no energy exchange with surrounding waves taking place. A probability function for steep waves has been constructed. Such type of function can be used for the development of operational forecast of freak waves based on a standard forecast provided by a three-dimensional generation wave prediction model (WAVEWATCH or wave modeling).
Dielectric characteristics of poly(ether ketone ketone) for high temperature capacitive energy storage
Authors: Pan Jilin , Li Kun , Li Junjun , Hsu Tim , Wang Qing
Published: July 2009

The dielectric constant and loss of poly(ether ketone ketone) have been investigated over a range of frequency and temperature. A linear correlation between the ac conductance and the angular frequency implies that the hopping as a dominant conduction process contributes to the dielectric loss. The energy density and discharged efficiency of the polymer were measured at various temperatures. High dielectric strengths (>400 MV/m) at temperatures up to 150 °C have been achieved. The increase of the dielectric loss and reduction in the breakdown field with increasing temperature could be attributed to thermally enhanced conduction of charge carriers in the polymer.
Optical enhancement of room temperature ferromagnetism in Er-doped GaN epilayers
Authors: Nepal N. , Zavada J. M. , Dahal R. , Ugolini C. , Sedhain A. , Lin J. Y. , Jiang H. X.
Published: July 2009

We report on the enhancement of magnetic properties of Er-doped GaN epilayer structures, grown by metal-organic chemical vapor deposition, with illumination from a light emitting diode. Single and multiple Er-doped epilayers were grown with Er concentrations up to ∼1021 cm−3. All samples exhibited hysteresis behavior at room temperature as measured by an alternating gradient magnetometer. When the samples were illuminated at a wavelength of 371 nm, an increase in saturation magnetization was observed for each sample. The percentage increase for multiple layer samples ranged from 10%–25% indicating possible device applications.
Mixing induced by a transversely oscillating circular cylinder in a straight channel
Authors: Celik Bayram , Beskok Ali
Published: July 2009

Flow past a transversely oscillating circular cylinder in a channel can be used as an active mesoscale mixer, kinematics of which was investigated by Celik et al. [“Flow past an oscillating circular cylinder in a channel with an upstream splitter plate,” Phys. Fluids 20, 103603 (2008)] at Re=100. This study presents numerical simulations of species transport in the mixer, obtained for various cylinder excitation frequencies and the species inlet configurations for a wide range of Peclet numbers. Mixing indices are calculated on the vortex spacing based mixing blocks, which is a newly introduced concept that utilizes periodicity of the vorticity field. Mixing index comparisons show that mixing efficiency is strongly dependent on the identity of the species within wall shear layers and vortex cores. For the cylinder excitation frequency of 25% higher than the natural vortex shedding frequency, 60% and 46% mixing enhancements relative to the straight channel and the stationary cylinder cases are observed at Pe=800, respectively.
Perfect coupling of light to surface plasmons with ultra-narrow linewidths
Authors: Sukharev M. , Sievert P. R. , Seideman T. , Ketterson J. B.
Published: July 2009

We examine the coupling of electromagnetic waves incident normal to a thin silver film that forms an oscillatory grating embedded between two otherwise uniform, semi-infinite half spaces. Two grating structures are considered, in one of which the midpoint of the Ag film remains fixed whereas the thickness varies sinusoidally, while in the other the mid point oscillates sinusoidally whereas the film thickness remains fixed. On reducing the light wavelength from the long wavelength limit, we encounter signatures in the transmission, T, and reflection, R, coefficients associated with: (i) the short-range surface plasmon mode, (ii) the long-range surface plasmon mode, and (iii) electromagnetic diffraction tangent to the grating. The first two features can be regarded as generalized (plasmon) Wood’s anomalies whereas the third is the first-order conventional (electromagnetic) Wood’s anomaly. The energy density at the film surface is enhanced for wavelengths corresponding to these three anomalies, particularly for the long-range plasmon mode in thin films. When exciting the silver film with a pair of waves incident from opposite directions, we find that by adjusting the grating oscillation amplitude and fixing the relative phase of the incoming waves to be even or odd, T+R can be made to vanish for one or the other of the plasmon modes; this corresponds to perfect coupling (impedance matching in the language of electrical engineering) between the incoming light and these modes.
Subnanometric Si film reactive diffusion on Ni
Authors: Portavoce A. , Lalmi B. , Tréglia G. , Girardeaux C. , Mangelinck D. , Aufray B. , Bernardini J.
Published: July 2009

The dissolution of 3–5 Si ML on Ni has been studied using in situ ultrahigh vacuum Auger electron spectroscopy (AES). The AES signal shows delays and kinetic changes in the dissolution process. These observations, combined with atomistic kinetic Monte Carlo simulations, considering an fcc Ni–Si nonregular solid solution, show that the AES signal should correspond to a successive apparition of the Ni-silicides present in the Ni–Si phase diagram at low temperatures, starting with the Si-richer phase.
Direct injection tunnel spectroscopy of a p-n junction
Authors: Likovich Edward M. , Russell Kasey J. , Narayanamurti Venkatesh , Lu Hong , Gossard Arthur C.
Published: July 2009

We demonstrate spectroscopic measurements on an InGaAs p-n junction using direct tunnel injection of electrons. In contrast to the metal-base transistor design of conventional ballistic electron emission spectroscopy (BEES), the base layer of our device is comprised of a thin, heavily doped p-type region. By tunneling directly into the semiconductor, we observe a significant increase in collector current compared to conventional BEES measurements. This could enable the study of systems and processes that have thus far been difficult to probe with the low-electron collection efficiency of conventional BEES, such as luminescence from single-buried quantum dots.
Size-dependent modulation of carrier mobility in top-down fabricated silicon nanowires
Authors: Sekaric Lidija , Gunawan Oki , Majumdar Amlan , Liu Xiao Hu , Weinstein Dana , Sleight Jeffrey W.
Published: July 2009

We have investigated the size dependence of field-effect mobility in top-down fabricated Si nanowires (NWs). We find that electron mobility increases while hole mobility decreases with the NW width. The observed trends are opposite of what we expect based on facet-dominated transport. We simulate charge densities and investigate the effect of gate stack-induced stress in an effort to explain these trends. We find that the use of piezoresistive coefficients for bulk or thin-film Si does not give sufficient change in mobility to reverse the facet-driven mobility trend. We suggest further investigation into the contribution of one-dimensional NW corner effects.
Effect of molecular packing on interfacial recombination of organic solar cells based on palladium phthalocyanine and perylene derivatives
Authors: Kim Inho , Haverinen Hanna M. , Wang Zixing , Madakuni Sijesh , Li Jian , Jabbour Ghassan E.
Published: July 2009

Planar heterojunction solar cells made of three different perylene tetracarboxylic diimide (PTCDI) derivatives as acceptor and palladium phthalocyanine as donor are demonstrated. Electron-hole pair recombination at donor/acceptor interface was compared for three PTCDI derivative solar cells by optical modeling and the effect of molecular packing of the PTCDI derivatives on charge dissociation is discussed. We observed that PTCDI with hexyl chains has the highest charge separation efficiency among three PTCDI derivatives, leading to a power conversion efficiency of 2.0% in solar cells.
The effects of nonuniform magnetic field strength on density flux and test particle transport in drift wave turbulence
Authors: Dewhurst J. M. , Hnat B. , Dendy R. O.
Published: July 2009

The extended Hasegawa–Wakatani equations generate fully nonlinear self-consistent solutions for coupled density n and vorticity ∇2ϕ, where ϕ is electrostatic potential, in a plasma with background density inhomogeneity κ=−∂ ln n0/∂x and magnetic field strength inhomogeneity C=−∂ ln B/∂x. Finite C introduces interchange effects and ∇B drifts into the framework of drift turbulence through compressibility of the E×B and diamagnetic drifts. This paper addresses the direct computation of the radial E×B density flux Γn=−n∂ϕ/∂y, tracer particle transport, the statistical properties of the turbulent fluctuations that drive Γn and tracer motion, and analytical underpinnings. Systematic trends emerge in the dependence on C of the skewness of the distribution of pointwise Γn and in the relative phase of density-velocity and density-potential pairings. It is shown how these effects, together with conservation of potential vorticity Π=∇2ϕ−n+(κ−C)x, account for much of the transport phenomenology. Simple analytical arguments yield a Fickian relation Γn=(κ−C)Dx between the radial density flux Γn and the radial tracer diffusivity Dx, which is shown to explain key trends in the simulations.
Effects of annealing on electronic and structural characteristics of pentacene thin-film transistors on polyimide gate dielectrics
Authors: Fukuda Kenjiro , Sekitani Tsuyoshi , Someya Takao
Published: July 2009

We have systematically investigated the effects of annealing on the structures and electronic performances of pentacene field-effect transistors on polyimide gate dielectric layers. The mobility of these transistors increases from 0.07 to 0.12 cm2/V s by annealing at 140 °C. The density of charge traps can be reduced by annealing, thereby resulting in the improvement of the transistor characteristics. The x-ray diffraction measurements indicate that the crystal structure of pentacene on polyimide does not change after annealing up to 140 °C, while the crystal structure of pentacene on Si/SiO2 exhibits transitions from the (001) thin film phase to the bulk phase.
Saturated small-signal gain of Si quantum dots embedded in SiO2/SiOx/SiO2 strip-loaded waveguide amplifier made on quartz
Authors: Lin Gong-Ru , Wu Chung-Lun , Lian Cheng-Wei , Chang Hung-Chun
Published: July 2009

A SiO2/SiOx/SiO2 strip-loaded waveguide with buried Si quantum dots is optically pumped to provide amplified spontaneous emission centered at 805 nm with spectral linewidth of 140 nm. By top-pumping the 350-nm-thick SiOx with He–Cd laser of 40 mW at 325 nm, the optical gain of 65 cm−1 and loss coefficient of 5 cm−1 are determined. Under a 785 nm small-signal injection diagnosis, the power-dependent gain curve fitting with gain-saturated amplifier model reveals a peak gain of 27 dB (not including waveguide loss) and a net power gain of 9.5 dB for the Si-rich SiOx waveguide amplifier with a length of 5 mm.
Optical rectification in self-assembled monolayers probed at surface plasmon resonance condition
Authors: Uzawa Ryohei , Tanaka Daisuke , Okawa Haruki , Hashimoto Kazuhiko , Kajikawa Kotaro
Published: July 2009

Optical rectification in a self-assembled monolayer containing nonlinear optical choromophore of hemicyanine adsorbed on a gold surface was observed in the attenuated total reflection geometry under the surface plasmon resonance condition. The effective second-order susceptibility χeff(2) was evaluated to be 43 pm V−1, which is consistent with the χ(2) values measured by linear electro-optic effect.
Experimental study of a fourth-harmonic gyromultiplier
Authors: Bandurkin I. V. , Bratman V. L. , Savilov A. V. , Samsonov S. V. , Volkov A. B.
Published: July 2009

Simultaneous generation at the second and fourth cyclotron harmonics has been obtained from a single-cavity self-excited gyromultiplier. Output power of the short-wavelength radiation amounts to 100 W at a frequency of 75 GHz. The proposed scheme seems to be promising for the terahertz frequency range.
Polymorphic phase transition and excellent piezoelectric performance of (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 lead-free ceramics
Authors: Zhang J. L. , Zong X. J. , Wu L. , Gao Y. , Zheng P. , Shao S. F.
Published: July 2009

A lead-free ceramic with the composition (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d33=262 pC/N, kp=0.53, k33=0.63, and k31=0.31 with ε′=1290 and tan δ=0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 °C, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between −40 and 85 °C. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to −150 °C and up to about 300 °C. It is suggested that the outstanding piezoelectric performance of this ceramic can be largely ascribed to the phase coexistence in a wide temperature range and the Ta-rich composition.
Weed infestation of wheat fields by sheep grazing stubble in the Mediterranean semi-arid region
Authors: Schoenbaum Iris , Kigel J. , Barkai D. , Landau S.
Published: July 2009

Seasonal stubble grazing by sheep is a widespread practice in the Mediterranean basin. However, farmers frequently claim that turning the sheep from marginal lands to the wheat fields after grain harvest increases the risk of weed infestation because of potential weed seed dispersal. We tested this claim by: (1) examining the potential of seed dispersal by sheep from marginal land via faeces and fleece, and (2) evaluating effects of summer stubble grazing on the size and composition of the weed seedbank and weed vegetation. Analysis of seed density in faeces and fleece showed that the potential for infestation from marginal land by sheep was relatively high during late spring, but strongly decreased in mid-summer, when plants in the marginal land had already shed their seeds. The potential of weed transport by faeces was negligible, compared with the seedbank in the field, and little overlapping of species was found between them. Summer grazing by sheep in a no-tillage wheat field over 5 years enlarged the seedbank. This increase, however, was mainly due to the less competitive small-grass species that were not found in the faeces or in the fleece. Combined ploughing, crop rotation, and herbicide application strongly reduced the seedbank. These integrated management practices eliminated the effect of summer grazing on the seedbank.
Impact of crop-topping and swathing on the viable seed production of wild radish (Raphanus raphanistrum)
Authors: Walsh Michael J. , Powles Stephen B.
Published: July 2009

Crop-topping, the practice of applying non-selective herbicides at crop maturity, has proved to be an effective management technique in preventing the input of seed into the seedbank for some annual weed species of southern Australian crop production systems. However, the efficacy of this practice on the dominant broad-leaf weed of these systems, wild radish, is not well understood. These studies investigated the effect of crop-topping and swathing on the viable seed production of wild radish. Crop-topping with either glyphosate or sprayseed (paraquat 135 g/L + diquat 115 g/L) can provide large reductions of 80–90% in viable seed production of wild radish plants present in crops at the end of the growing season. However, the efficacy of this practice was found to be highly variable and therefore, cannot be relied upon to consistently produce these large reductions in seed numbers. Similarly, swathing also produced large reductions in viable seed production but results from this practice were even less consistent than crop-topping treatments. For all treatments, early application timings of growth stage 6.5 or earlier, were optimum for targeting wild radish seed production. However, these treatment timings also resulted in large crop yield losses of ~30%. To preserve at least 90% of crop yield, crop-topping and swathing treatments need to be delayed until wild radish growth stage 8.5, with expected reductions in seed numbers of up to 70%. However, in high-density infestations the need to preserve grain yield will be less important than preventing substantial inputs of wild radish seed into the seedbank.
Effects of genotype and growing location on iron and zinc contents in sweetpotato (Ipomoea batatas L.)
Authors: Chen J. , Lu G. , Wang G.
Published: July 2009

Sweetpotato (Ipomoea batatas L.) has great potential for combating micronutrient malnutrition and vitamin A deficiency. To explore the potential of combining different micronutrients in the same cultivar through genetic improvement, we assessed the variation of Fe and Zn contents among 21 genotypes and 5 growing locations in the eastern region of China. Large genotype-dependent differences for Fe and Zn were found in the storage roots. The Fe content ranged from 2.68 to 4.64 mg/100 g dry weight basis (dwb), whereas the Zn content ranged from 2.92 to 6.95 mg/100 g dwb. The variation caused by genotypes, locations, and genotype × environmental interaction was highly significant for both Fe and Zn. No significant correlation was found between β-carotene and Fe and Zn contents in the storage roots. The results show that sweetpotato as a staple or co-staple food may provide a good proportion of bioavailable Fe and Zn for the nutritional requirements of human populations. It appears feasible to increase Fe and Zn in orange-fleshed storage roots through breeding of new varieties.
Use of grain size distribution parameters to explain variation in small grain screenings of wheat in multi-environment trials involving new cultivars
Authors: Sharma D. L. , Shackley B. J. , Amjad M. , Zaicou-Kunesch C. M. , D'Antuono M. F. , Anderson W. K.
Published: July 2009

The proportion of small grain screenings is a worldwide problem for wheat growers in water-limited environments and is known to be influenced by both genetic and environmental factors including crop management. This paper follows our previous finding that parameters μ (reflecting point of majority mass of the grain size distribution) and 1/α (reflecting the slope of grain size distribution up to the majority point) of a skew-Laplace distribution can be used to differentiate the tendency of cultivars to produce small grains. The variability of these parameters over environments (15 Cultivar × Time of sowing and 2 Cultivar × Plant population × Nitrogen rates experiments) was investigated in order to indicate their utility in breeding cultivars and managing wheat crops. The estimated values of both μ and 1/α varied over experiments but the relative cultivar ranking remained similar. Of the genetic and management factors, cultivar had more effect on variance of μ than of 1/α, while applied nitrogen level significantly influenced 1/α. We conclude that: (i) cultivars can be grouped according to their μ and 1/α values; (ii) cultivars owing their lower screenings to high 1/α need a careful optimising of nitrogen inputs, while breeding for high μ is likely to provide stability against small grain screenings; (iii) both the parameters were associated with kernel weight and grains/spike but not grains/m2; and (iv) future research establishing the relationship of 1/α with specific kernel position within the plant will be useful in proposing an ideal ear and plant structure for minimising small grain screenings. When using parameters of the suggested grain size distribution, we suggest the following relevant points be considered: (i) 1/α is not a linear slope, it is related to ‘skewness’; (ii) the peak at majority mass (MM) reflects the tendency to concentrate grain mass and therefore provides an opportunity to increase skewness (1/α) despite a lower μ and a lower mean grain weight; (iii) there is a point up to which skewness of grain size distribution can sufficiently protect against high screenings and is highly dependent upon the value of μ; and (iv) 1/α is a potentially useful parameter nonetheless, because in practice, grain weight may be reduced as number of grains/area is increased in pursuit of high yield through breeding and agronomic practices.