bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarizable interaction potential for water from coupled cluster calculations. I. Analysis of dimer potential energy surface
Authors: Bukowski Robert , Szalewicz Krzysztof , Groenenboom Gerrit C. , van der Avoird Ad
Published: March 2008

A six-dimensional interaction potential for the water dimer has been fitted to ab initio interaction energies computed at 2510 dimer configurations. These energies were obtained by combining the supermolecular second-order energies extrapolated to the complete basis set limit from up to quadruple-zeta quality basis sets with the contribution from the coupled-cluster method including single, double, and noniterative triple excitations computed in a triple-zeta quality basis set. All basis sets were augmented by diffuse functions and supplemented by midbond functions. The energies have been fitted using an analytic form with the induction component represented by a polarizable term, making the potential directly transferable to clusters and the bulk phase. Geometries and energies of stationary points on the potential surface agree well with the results of high-level ab initio geometry optimizations.
A divide-and-conquer strategy to improve diffusion sampling in generalized ensemble simulations
Authors: Min Donghong , Yang Wei
Published: March 2008

Generalized ensemble simulations generally suffer from the associated diffusion-sampling problem; the increased entropic barrier can greatly abolish sampling efficiency, in particular, with the increase of number of degrees of freedom in the target conformational space. Taking advantage of the recent simulated scaling method, we formulate a divide-and-conquer sampling strategy to solve this problem so as to robustly improve the sampling efficiency in generalized ensemble simulations. In the present method, the target conformational space sampling enhancement is decomposed to the sampling enhancements of several subconformational regions, and multiple independent SS simulations are performed to establish the individual sampling enhancement for each of the subconformational regions; in order to realize the global importance sampling, structure exchanges among these replicas are performed based on the Monte Carlo acceptance/rejection procedure. As demonstrated in our studies, the present divide-and-conquer sampling algorithm, named by us as “simulated scaling based variant Hamiltonian replica exchange method,” has superior sampling capability so as to possibly play an essential role in dealing with the present bottleneck of generalized ensemble method developments: the system size limitations.
Layer resolved magnetization dynamics in interlayer exchange coupled Ni81Fe19∕Ru∕Co90Fe10 by time resolved x-ray magnetic circular dichroism
Authors: Martin T. , Woltersdorf G. , Stamm C. , Dürr H. A. , Mattheis R. , Back C. H. , Bayreuther G.
Published: March 2008

The magnetization dynamics of each layer of interlayer exchange coupled Ni81Fe19∕Ru(t)∕Co90Fe10 films was investigated by time resolved x-ray magnetic circular dichroism (TR-XMCD) after pulsed excitation. The coupling was changed from ferromagnetic to antiferromagnetic by variation of the Ru thickness t. The precessional motion of the individual layers was detected separately by measuring the XMCD signal at the L3 absorption edge of either nickel or cobalt. From the observation of two frequency components in the precession of both layers in samples with negligible interlayer exchange coupling, the presence of a different coupling mechanism was concluded. Using two different sample geometries, the influence of antiphase and in-phase excitation on the triggered dynamics was studied.
Effects of H-ion irradiation on the properties of a spin valve
Authors: Han Yoonsung , Kim Sanghoon , Lee Sangho , Hong Jongill , Lee Dong Ryeol , Lee Hyun Hwi , Park Yong Jun , Lee Hoojeong
Published: March 2008

Irradiation with much less than 1.0keV H ions significantly improved the properties of IrMn-based spin valves. The giant magnetoresistance (GMR) was increased from 8.1% to 9.6% and the exchange bias field from 355to565Oe after irradiation at 550eV. The irradiation achieved even higher GMR than that achieved by field annealing: 9.6% vs 8.7%. We attribute this enhancement to strong (111) textures of the IrMn antiferromagnet and CoFe∕Cu∕CoFe∕NiFe layers, as well as to a narrow mosaic spread of the (111) IrMn, both of which were developed by momentum transferred during the ion bombardment. The irradiated spin valve showed exchange bias as large as and (111) textures as strong as those of the field-annealed spin valve. The significant difference in the GMR values of the irradiated versus the field-annealed spin valves was probably due to different degrees of intermixing between layers. In the case of irradiation, the low energy of the lightest H ion likely resulted in little intermixing and, hence, the interfaces were largely left intact, which kept the GMR values high.
Dependence of noise in magnetic tunnel junction sensors on annealing field and temperature
Authors: Liou S. H. , Zhang Rui , Russek Stephen E. , Yuan L. , Halloran Sean T. , Pappas David P.
Published: March 2008

The minimum detectable field of magnetoresistive sensors is limited by their intrinsic noise. Magnetization fluctuations are one of the crucial noise sources and are related to the magnetization alignment at the antiferromagnetic-ferromagnetic interface. In this study, we investigated the low frequency noise of magnetic tunnel junctions (MTJs) annealed in the temperature range from 265to305°C and magnetic fields up to 7T, either in helium or hydrogen environments. Our results indicate that the magnetic fluctuators in these MTJs changed their frequency based on annealing field and temperature. The noise of the MTJs at low frequency can be reduced by annealing in high magnetic field (7T) and further improved by annealing in a hydrogen environment.
Nanoelectronic logic device based on the manipulation of magnetic and electric barriers
Authors: Kumar S. Bala , Tan S. G. , Jalil M. B. A. , Cheung P. Q. , Jiang Yong
Published: March 2008

We propose a programmable logic device that utilizes magnetoelectric (ME) barriers to realize Boolean functions. We use a high-electron-mobility-transistor in which electron transport in the two-dimensional-electron-gas channel is modulated by applied ME potential barriers via a combination of periodic ferromagnetic and nonmagnetic gates. Electron transmission through the device is calculated based on the minimal-coupling Hamiltonian. The device can be programmed to realize multiple three-input, logic functions, such as OR, AND, NAND, and NOR. The binary logic output of 1/0 corresponds, respectively, to the high/low transmission of electrons through the externally applied barriers. The calculation results show clear binary outputs, with a high (low) state having a transmission probability of T>80% (T<20%). We also studied the effect of varying gate lengths on T.
Probe measurements in a nonstationary plasma
Authors: Bliokh Yu. P. , Brodsky Yu. L. , Chashka Kh. B. , Felsteiner J. , Slutsker Ya. Z.
Published: March 2008

Single and double probes are simple and common tools for plasma measurements. In the case of nonstationary plasmas, the values of the plasma density obtained with these tools may differ significantly from the correct values measured, e.g., by microwave methods. The reason for such discrepancy could be the Bohm criterion failure during the plasma transition to the steady state. Indeed, the Bohm criterion, which is commonly used as a boundary condition at the plasma-sheath edge, directly determines the ion saturation current to the probe surface. The transition-time duration is studied and explained quantitatively for various plasmas produced by a version of a ferroinductor-coupled plasma source, which has its magnetic core fully immersed in the plasma. Corresponding conversion factors for probe measurements have been evaluated. Also, the influence of a certain amount of “hot” non-Maxwellian electrons on probe characteristics has been investigated.
Magnetostriction effects of 3d4 and 3d6 ions in dilute magnetic oxide films
Authors: Dionne Gerald F. , Kim Hyun-Suk
Published: March 2008

Magnetic ions of the 3dn transition series in oxide lattices can introduce large local magnetostriction effects through spin-orbit-lattice interactions with an axially distorted cubic crystal field. In this paper, the local-site magnetostriction model used successfully in ferrites containing small concentrations of Jahn-Teller (JT) ions is applied to the case of magnetically dilute oxide films. Uniaxial anisotropy created by elastic lifting of the orbital Eg ground-state doublet degeneracy of 2% Cr2+(3d4) in an In2O3 film is contrasted with the corresponding effects of a T2g triplet splitting of 5% Co3+(3d6) in a Si∕SiO2 film deposited under similar in-plane stress conditions. In these two situations, the signs of the magnetostrictive strains are reversed as predicted from theory and are consistent with local magnetoelastic effects of JT ions in undiluted ferrites. A phenomenological analysis of room-temperature magnetization data suggests a possible magnetostriction constant range of 0.02<λsite<0.2 for a single JT octahedral site.
Modeling of transitional channel flow using balanced proper orthogonal decomposition
Authors: Ilak Miloš , Rowley Clarence W.
Published: March 2008

We study reduced-order models of three-dimensional perturbations in linearized channel flow using balanced proper orthogonal decomposition (BPOD). The models are obtained from three-dimensional simulations in physical space as opposed to the traditional single-wavenumber approach, and are therefore better able to capture the effects of localized disturbances or localized actuators. In order to assess the performance of the models, we consider the impulse response and frequency response, and variation of the Reynolds number as a model parameter. We show that the BPOD procedure yields models that capture the transient growth well at a low order, whereas standard POD does not capture the growth unless a considerably larger number of modes is included, and even then can be inaccurate. In the case of a localized actuator, we show that POD modes which are not energetically significant can be very important for capturing the energy growth. In addition, a comparison of the subspaces resulting from the two methods suggests that the use of a nonorthogonal projection with adjoint modes is most likely the main reason for the superior performance of BPOD. We also demonstrate that for single-wavenumber perturbations, low-order BPOD models reproduce the dominant eigenvalues of the full system better than POD models of the same order. These features indicate that the simple, yet accurate BPOD models are a good candidate for developing model-based controllers for channel flow.
Representation of integral dispersion relations by local forms
Authors: Ferreira Erasmo , Sesma Javier
Published: March 2008

The representation of the usual integral dispersion relations (IDRs) of scattering theory through series of derivatives of the amplitudes is discussed, extended, simplified, and confirmed as mathematical identities. Forms of derivative dispersion relations (DDRs) valid for the whole energy interval, recently obtained and presented as double infinite series, are simplified through the use of new sum rules of the incomplete Γ functions, being reduced to single summations, where the usual convergence criteria are easily applied. For the forms of the imaginary amplitude used in phenomenology of hadronic scattering at high energies, we show that expressions for the DDR can represent, with absolute accuracy, the IDR of scattering theory, as true mathematical identities. Besides the fact that the algebraic manipulation can be easily understood, numerical examples show the accuracy of these representations up to the maximum available machine precision. As consequence of our work, it is concluded that the standard forms, sDDR, originally intended for high energy limits are an inconvenient and incomplete separation of terms of the full expression, leading to wrong evaluations. Since the correspondence between IDR and the DDR expansions is linear, our results have wide applicability, covering more general functions, built as combinations of well studied basic forms.
Off-axis directional beaming via photonic crystal surface modes
Authors: Caglayan Humeyra , Bulu Irfan , Ozbay Ekmel
Published: March 2008

We investigated off-axis directional beaming from a photonic crystal (PC) waveguide. We theoretically and experimentally demonstrated that it is possible to control beaming from a PC waveguide via PC surface modes using a gratinglike layer with different periods on different sides of the waveguide. We observed off-axis directional beaming with full width at half maximum of 10° with a beaming angle of 14° from a PC waveguide. Since the beaming angle only depends on the periods of the gratinglike layer on the output side, this beaming angle can be easily changed by arranging the grating periods asymmetrically.
A compact double-pass Raman backscattering amplifier/compressor
Authors: Ren J. , Li S. , Morozov A. , Suckewer S. , Yampolsky N. A. , Malkin V. M. , Fisch N. J.
Published: March 2008

The enhancement of stimulated Raman backscattering (SRBS) amplification was demonstrated by introducing a plasma density gradient along the pump and the seed interaction path and by a novel double-pass design. The energy transfer efficiency was significantly improved to a level of 6.4%. The seed pulse was amplified by a factor of more than 20 000 from the input in a 2mm long plasma, which also exceeded the intensity of the pump pulse by 2 orders of magnitude. This was accompanied by very effective pulse compression, from 500fsto90fs in the first pass measurements and in the second pass down to approximately 50fs, as it is indicated by the energy-pulse duration relation. Further improvements to the energy transfer efficiency and the SRBS performance by extending the region of resonance is also discussed where a uniform ∼4mm long plasma channel for SRBS was generated by using two subsequent laser pulses in an ethane gas jet.
Interface engineering for high interfacial strength between SiCOH and porous SiCOH interconnect dielectrics and diffusion caps
Authors: Grill A. , Edelstein D. , Lane M. , Patel V. , Gates S. , Restaino D. , Molis S.
Published: March 2008

The integration of low- and ultralow-k SiCOH dielectrics in the interconnect structures of very large scale integrated chips involves complex stacks with multiple interfaces. Successful fabrication of reliable chips requires strong adhesion between the different layers of the stacks. A critical interface in the dielectric stack is the interface between the SiCNH diffusion cap and the SiCOH inter- and intralevel dielectrics (ILDs). It was observed that, due to the original deposition conditions, the interface layer was weakened both by a low adhesion strength between SiCNH and SiCOH and by the formation of an initial layer of SiCOH with reduced cohesive strength. The manufacturing process has been modified to engineer this interface and obtain interfacial strengths close to the cohesive strengths of the bulk ILDs. This paper discusses the causes for the original low interfacial strength and presents an approach for enhancing it by engineering the interface to the cap for both the dense SiCOH and porous SiCOH ILDs.
Focusing surface plasmons via changing the incident angle
Authors: Caglayan Humeyra , Bulu Irfan , Ozbay Ekmel
Published: March 2008

We report a circular metallic aperture with a subwavelength circular slit in the microwave regime, in which we experimentally demonstrate that this aperture can excite and focus surface plasmons. Under normal illumination, there is no focusing of the surface plasmons. However, by changing the incident angle, it is possible to focus surface plasmons. We showed that under a 20° illumination angle surface plasmons focus at 4cm away from the center on the surface of the aperture.
Studies of laser wakefield structures and electron acceleration in underdense plasmas
Authors: Maksimchuk A. , Reed S. , Bulanov S. S. , Chvykov V. , Kalintchenko G. , Matsuoka T. , McGuffey C. , Mourou G. , Naumova N. , Nees J. , Rousseau P. , Yanovsky V. , Krushelnick K. , Matlis N. H. , Kalmykov S. , Shvets G. , Downer M. C. , Vane C. R. , Beene J. R. , Stracener D. , Schultz D. R.
Published: March 2008

Experiments on electron acceleration and optical diagnostics of laser wakes were performed on the HERCULES facility in a wide range of laser and plasma parameters. Using frequency domain holography we demonstrated single shot visualization of individual plasma waves, produced by 40TW, 30fs laser pulses focused to the intensity of 1019W∕cm2 onto a supersonic He gas jet with plasma densities ne<1019cm−3. These holographic “snapshots” capture the variation in shape of the plasma wave with distance behind the driver, and resolve wave front curvature seen previously only in simulations. High-energy quasimonoenergetic electron beams were generated using plasma density in the range 1.5×1019≤ne≤3.5×1019cm−3. These experiments demonstrated that the energy, charge, divergence, and pointing stability of the beam can be controlled by changing ne, and that higher electron energies and more stable beams are produced for lower densities. An optimized quasimonoenergetic beam of over 300MeV and 10mrad angular divergence is demonstrated at a plasma density of ne≃1.5×1019cm−3. The resultant relativistic electron beams have been used to perform photo-fission of U238 with a record high reaction yields of ∼3×105∕J. The results of initial experiments on electron acceleration at 70TW are discussed.
Gradation-controlled electric field distribution in multilayered colloidal crystals
Authors: Zhang L. F. , Huang J. P. , Yu K. W.
Published: March 2008

We exploit theoretically nonlinear optical materials by graded multilayered colloidal crystals, whose basic layer is made of metallodielectric nanoparticles immersed periodically in a host fluid. In the crystals, either the volume fraction of nanoparticles or the dielectric constant of host fluid can vary gradually within layers. The electric field distribution can be shown to exhibit a peak in a certain layer, and that the position of the peak can change by tuning the incident angular frequency. Such a gradation-controlled electric field distribution serves as a physical mechanism for understanding the enhanced nonlinear optical responses with a broad plasmon band.
Probing the duplex stainless steel phases via magnetic force microscopy
Authors: Gheno S. M. , Santos F. S. , Kuri S. E.
Published: March 2008

Duplex stainless steels are austenitic-ferritic alloys used in many applications, thanks to their excellent mechanical properties and high corrosion resistance. In this work, chemical analyses, x-ray diffraction, and magnetic force microscopy (MFM) were employed to characterize the solution annealed and aged duplex stainless steel. The samples exhibited no changes in lattice parameters and the MFM technique proved successful in clearly imaging the magnetic domain structure of the ferrite phase.
Computer-controlled, variable-frequency power supply for driving multipole ion guides
Authors: Robbins Matthew D. , Yoon Oh Kyu , Zuleta Ignacio , Barbula Griffin K. , Zare Richard N.
Published: March 2008

A high voltage, variable-frequency driver circuit for powering resonant multipole ion guides is presented. Two key features of this design are (1) the use of integrated circuits in the driver stage and (2) the use a stepper motor for tuning a large variable capacitor in the resonant stage. In the present configuration the available frequency range spans a factor of 2. The actual values of the minimum and maximum frequencies depend on the chosen inductor and the capacitance of the ion guide. Feedback allows for stabilized, computer-adjustable rf amplitudes over the range of 5–500V. The rf power supply was characterized over the range of 350–750kHz and evaluated by driving a quadrupole ion guide in an electrospray time-of-flight mass spectrometer.
An interesting class of partial differential equations
Authors: Yong Wen-An
Published: March 2008

This paper presents an observation that under reasonable conditions, many partial differential equations from mathematical physics possess three structural properties. One of them can be understand as a variant of the celebrated Onsager reciprocal relation in modern thermodynamics. It displays a direct relation of irreversible processes to the entropy change. We show that the properties imply various entropy dissipation conditions for hyperbolic relaxation problems. As an application of the observation, we propose an approximation method to solve relaxation problems. Moreover, the observation is interpreted physically and verified with eight (sets of) systems from different fields.
Gamma radiation-induced refractive index change in Ge- and N-doped silica
Authors: Brichard Benoît , Butov Oleg V. , Golant Konstantin M. , Fernandez Fernandez Alberto
Published: March 2008

We measured the change of the refractive index over a wide wavelength range in Ge- and N-doped high purity (fiber optics grade) silica glasses subjected to gamma irradiation. The radiation-induced change of the refractive index tends to be greater in the infrared part of the spectrum compare to the values measured in the UV-visible part of the spectrum. By means of the Kramers–Kronig relations, we estimate that a weak broadening of the optical vibration band of the silica network adds to this effect. The paper also discusses the difference observed in the spectral behavior of the induced refractive index change for both types of doped glass.
Correlation between volumetric change and glass-forming ability of metallic glass-forming alloys
Authors: Park E. S. , Kim D. H.
Published: March 2008

We draw attention to the relationship between volumetric change and glass-forming ability (GFA) in various metallic glass-forming alloys. The critical cooling rate can be expressed as Rc=2.5×10−5exp(5.0×102Vlg), where Vlg is defined as (Vl-Vg)∕Vl. We specifically plot the temperature dependence of specific volume for Ca65Mg15Zn20 alloy, and then demonstrate that the larger slope between Vl and Vg, closely related to thermal expansion coefficient, corresponds well to the GFA of the alloy. This insight can provide a clue if the correlations are to be used in the appreciation of glass formation and in the development of an alloy system with enhanced GFA.
Evanescent light photopolymerization and measurement of cure depth in nanostereolithography
Authors: Kajihara Y. , Inazuki Y. , Takeuchi T. , Takahashi S. , Takamasu K.
Published: March 2008

Nanostereolithography using evanescent light has been proposed as a means to realize submicrometer resolution. In this study, cured polymers of submicrometer thickness have been obtained using an evanescent light exposure apparatus. Examination of the controllability of the cure depth proves that the cure depth can be controlled at a standard deviation of at most 12nm by configuring the polarization, the exposure energy, and the incident angle. The evanescent light photopolymerization process can be differentiated into two modes in terms of exposure energy per second. These results indicate that nanostereolithography can fabricate three-dimensional structures with submicrometer resolution.
Antiferroelectric-ferroelectric phase transitions in Pb1−xBaxZrO3 ceramics: Effect of PbO content
Authors: Bongkarn T. , Rujijanagul G. , Milne S. J.
Published: March 2008

The irreversibility of the antiferroelectric (AFE) to FE phase transition in Pb1−xBaxZrO3, x=0.75–0.1, compositions is shown to be a consequence of lattice vacancies arising from PbO evaporation during ceramic processing. Previously, the absence of a FE→AFE cooling transition was thought to be due to the transformational strain and the fragmentation of ferroelectric domains. Appropriate compensating levels of excess PbO added to starting powders generate the FE→AFE transition. For lower levels of Ba2+ substitution, x=0.05, the transition is reversible in noncompensated samples, but PbO compensation raises the FE→AFE transition temperature by ∼25°C.
Unified upper bound for photothermal and photovoltaic conversion efficiency
Authors: Badescu Viorel
Published: March 2008

The available work (exergy) of thermal radiation is derived ab initio by using a simple statistical thermodynamic approach. A general upper bound for the efficiency of thermal radiation conversion into work is derived. This efficiency is different from the Carnot efficiency and generalizes the Petela efficiencylike factor appearing in the available work of blackbody radiation. The maximum efficiencies of photothermal and photovoltaic conversions, are particular cases of this general result. One proves by using available work considerations that the maximum efficiency of photothermal conversion is higher than the maximum efficiency of photovoltaic conversion.
Fabrication of nanostructures with high electrical conductivity on silicon surfaces using a laser-assisted scanning tunneling microscope
Authors: Yi K. J. , Yang Z. Y. , Lu Y. F.
Published: March 2008

Nanostructures with high electrical conductivity were fabricated on silicon surfaces using a laser-assisted scanning tunneling microscope (LA-STM). The nanostructures, dots and lines, were fabricated on H-passivated p-doped silicon (110) surfaces. By precisely controlling the experimental conditions such as pulse energy and tip-surface gap distance, feature sizes (dot diameters and line widths) and heights of the fabricated nanostructures could be controlled. For instance, a dot with a diameter of 30nm and a line with a width of 30nm were obtained. In addition, scanning tunneling microscopy investigation of the structures revealed that their band gaps were changed during the LA-STM process. As a consequence, the local conductivity (more precisely the tunneling probability) was enhanced. Numerical simulations based upon the finite-difference-time-domain algorithm provide detailed insight into the spatial distribution of the enhanced optical field underneath the STM tip and associated physical phenomena. Potential applications of the developed nanostructuring process are anticipated in various nanotechnology fields, particularly in the field of nanoelectronics.
Inelastic neutron scattering study of crystalline-electric-field interaction in Ce3Ir4Sn13
Authors: Yang C. P. , Chen Y. H. , Wang H. , Nagoshi C. , Kohgi M. , Sato H.
Published: March 2008

The Ce3Ir4Sn13 single crystal was grown using Sn-flux method. Inelastic neutron scattering measurements were performed on the Ce3Ir4Sn13 powder sample at T=5.3 and 200K. Two magnetic origin peaks of ΔE1=4.4 and ΔE2=45.9meV in the inelastic neutron scattering spectra were detected as the crystalline-electric-field excitations for Ce3Ir4Sn13. The results of our neutron data are roughly consistent with the calculation by fitting the magnetic susceptibility curve using a simple point-charge model.
Internal photoemission spectroscopy of [TaN∕TaSiN] and [TaN∕TaCN] metal stacks on SiO2 and [HfO2∕SiO2] dielectric stack
Authors: Nguyen N. V. , Xiong H. D. , Suehle J. S. , Kirillov O. A. , Vogel E. M. , Majhi P. , Wen H.-C.
Published: March 2008

There is an intense search for metal gates for the next generation metal-oxide-semiconductor field-effect transistor. The barrier height (Φ0) at its interface with a gate dielectric must be known to select a suitable metal. In this letter, internal photoemission was used to determine Φ0 of two technologically important ternary metals, [TaN∕TaSiN] and [TaN∕TaCN], on a single SiO2 layer and a [HfO2∕SiO2] stack. On SiO2, Φ0 was found to be 3.36 and 3.55eV at the [TaN∕TaSiN] stack/SiO2 and [TaN∕TaCN stack]/SiO2 interfaces, respectively. However, on the [HfO2∕SiO2] stack, Φ0 was found be the same at 2.5eV for both metal stacks. These results are compared to flatband voltage measurements.
Room temperature magnetoresistance switching of Permalloy thin films induced by iron nanoparticles
Authors: Müller Jens , von Molnár Stephan , Wirth Steffen
Published: March 2008

Arrays of iron nanoparticles grown by a combination of chemical vapor deposition and scanning tunneling microscopy have been placed on top of a narrow stripe of Permalloy (Py). The magnetic coupling between the nanoparticles and the Py film results in distinct negative jumps of the Py magnetoresistance (MR). The switching of the magnetization orientation of individual particles is clearly reflected in the Py resistance as a consequence of anisotropic MR and domain wall MR, with a homogeneous particle magnetization orientation yielding the highest resistances.
Enhanced photovoltaic performance in nanoimprinted pentacene-PbS nanocrystal hybrid device
Authors: Dissanayake D. M. N. M. , Adikaari A. A. D. T. , Silva S. R. P.
Published: March 2008

Pentacene and PbS nanocrystal bilayer photovoltaic devices are fabricated after the pentacene layer is subjected to nanoimprinting using a laser textured silicon stamp. Increased short circuit current densities are observed for the imprinted devices, which are attributed to increased charge mobility in the pentacene film caused by the decrease in the intermolecular distances during nanoimprinting. This work is consistent with previous reports where hydrostatic pressure induced mobility increases have been observed in polyacenes under gigapascal pressure regimes. It is believed that the pentacene film undergoes localized high pressures during nanoimprinting, giving rise to the increased hole mobilities.
Resonance-enhanced dipolar interaction between terahertz photons and confined acoustic phonons in nanocrystals
Authors: Liu Tzu-Ming , Lu Ja-Yu , Chen Hung-Ping , Kuo Chung-Chiu , Yang Meng-Ju , Lai Chih-Wei , Chou Pi-Tai , Chang Ming-Hao , Liu Hsiang-Lin , Li Yu-Tai , Pan Ci-Ling , Lin Shih-Hung , Kuan Chieh-Hsiung , Sun Chi-Kuang
Published: March 2008

Taking advantage of the specific core-shell charge separation structure in the CdSe∕CdTe core-shell type-II nanocrystals, we experimentally observed and verified the existence of the resonance-enhanced dipolar interaction between terahertz photons and their corresponding confined acoustic phonons. From the measured terahertz transmission spectra, we found that the photon frequency of the terahertz resonant absorption is inversely proportional to the diameter D of the nanocrystals and agrees with that of dipolar active l=1, n=0 confined acoustic modes. The corresponding absorption cross section shows a D4 dependence, supporting a charged simple-harmonic-oscillator model. These facts verify the occurrence of dipolar interaction between terahertz photons and confined terahertz acoustic phonons.
Fermi surface determination from wavevector quantization in LaSrCuO films
Authors: Ariosa D. , Cancellieri C. , Lin P. H. , Pavuna D.
Published: March 2008

We have observed the wavevector quantization in LaSrCuO films thinner than 12 unit cells grown on SrTiO3 substrates. Low energy dispersions were determined in situ for different photon energies by angle resolved photoemission spectroscopy. From the wavevector quantization, we extract three dimensional dispersions within a tight-binding model and obtain the Fermi surface topology, without resorting to the nearly free-electron approximation. Such method can be extended to similar confined electron nanostructures.
Experimental determination of the rate law for charge carrier decay in a polythiophene: Fullerene solar cell
Authors: Shuttle C. G. , O’Regan B. , Ballantyne A. M. , Nelson J. , Bradley D. D. C. , de Mello J. , Durrant J. R.
Published: March 2008

We use transient photovoltage and differential charging experiments, complemented by transient absorption data, to determine charge carrier lifetimes and densities in a poly(3-hexylthiophene): methanofullerene solar cell at Voc as a function of white light-bias intensity. For a typical device, the charge carrier decay dynamics are observed to exhibit an approximately third order dependence on charge density (dn∕dt∝n3).
X-ray photoelectron spectroscopy studies of nitridation on 4H-SiC (0001) surface by direct nitrogen atomic source
Authors: Chai J. W. , Pan J. S. , Zhang Z. , Wang S. J. , Chen Q. , Huan C. H. A.
Published: March 2008

A Si3N4 passivation layer has been successfully grown on the 4H-SiC (0001) surface by direct atomic source nitridation at various substrate temperatures. In situ x-ray photoelectron spectroscopy measurements show that higher substrate temperature leads to higher nitridation rate and good crystallinity of the passivation layer. A thin oxynitride layer on the top of the Si3N4 was observed due to the residual O in the vacuum system, but was decomposed during annealing. In the meantime, excess C was found to be effectively removed by the reactive atomic N source.
High efficiency nitrogen incorporation technique using ultraviolet assisted low temperature process for hafnia gate dielectric
Authors: Son S. Y. , Kumar P. , Lee J. S. , Singh R. K.
Published: March 2008

An evaluation of a low temperature process (∼350°C) for nitrogen incorporation in hafnia gate dielectric has been reported. This method is based on postdeposition nitridation under ultraviolet light illuminated NH3 ambience. X-ray photoelectron spectroscopy confirmed the amount of nitrogen incorporated by this process was comparable to that of high temperature (∼650°C) thermal nitridation (∼7%). Uniformity of nitrogen distribution in the film was analyzed by secondary ion mass spectroscopy. A capacitance density of ∼3.96μF∕cm2 with 9.4Å equivalent oxide thickness and 10Å thick interface layer were obtained by ultraviolet assisted nitridation process.
Nonvolatile memories of Ge nanodots self-assembled by depositing ultrasmall amount Ge on SiO2 at room temperature
Authors: Hong Seung Hui , Kim Min Choul , Jeong Pil Seong , Choi Suk-Ho , Kim Yong-Sung , Kim Kyung Joong
Published: March 2008

Ge nanodots (NDs) for nonvolatile memories (NVMs) have been self-assembled at room temperature (RT) by ion beam sputtering deposition of ultrasmall amount Ge (<72 ML) on SiO2 without postannealing. High-resolution transmission electron microscopy demonstrates the existence of well-defined Ge ND layers with respect to the SiO2∕Si interface. As Ge amount increases, the size of NDs increases, while their density decreases. A possible mechanism is proposed to explain the formation of Ge NDs at RT based on simple model calculations. The memory window that is estimated by capacitance-voltage hysteresis increases up to 18.7V with increasing Ge amount up to 54 ML. The program speed is enhanced by increasing Ge amount and the charge-loss speed in the programed state is slower for larger Ge amount. These NVM properties are very promising in view of device application.
The search for new pasture plants to achieve more sustainable production systems in southern Australia
Authors: Dear B. S. , Ewing M. A.
Published: March 2008

Increasing the proportion of the landscape planted to deep-rooted perennial pasture species is recognised as one of several remedial actions required for the control of dryland salinity in southern Australia. The widespread use of perennials in farming systems is limited at present by the lack of well-adapted perennials that can be grown to reduce recharge in a landscape where drought, soil acidity, temporary waterlogging, infertile soils and unrestricted grazing prohibit the use of many species. The range of plants adapted to salinity also needs to be expanded to stabilise and ameliorate soils already degraded by rising watertables and to increase the profitability of grazing discharge regions within the landscape.
This paper describes the steps involved in a national forage screening and breeding program initiated by the Cooperative Research Centre (CRC) for Plant-based Management of Dryland Salinity1, seeking to expand the range of perennial and or salt-tolerant forage plants that can be incorporated into farming systems of southern Australia. It describes the target environments, soil constraints, farming systems and the criteria being considered when assessing the potential of new plants, including assessment of the weed risk posed by introducing new species. This paper forms an introduction to a special issue which presents the outcomes of the pasture species field evaluation and plant breeding program conducted by the CRC.
Developing birdsfoot trefoil (Lotus corniculatus L.) varieties for permanent pasture applications in low latitude regions of eastern Australia
Authors: Ayres J. F. , Kelman W. M. , Wiedemann S. G. , Lane L. A. , McCorkell B. E.
Published: March 2008

Birdsfoot trefoil (Lotus corniculatus L.) is a potentially important alternative legume for recharge landscapes in the high rainfall zone in eastern Australia. However, in the summer rainfall region in northern New South Wales (NSW) where birdsfoot trefoil has the greatest potential application, flowering and seed set are limited by short daylength. Consequently, existing birdsfoot trefoil cultivars do not set enough seed to develop a seedbank that sustains a productive persistent stand. A breeding program was undertaken to develop birdsfoot trefoil cultivars adapted to short photoperiod to increase the area sown to deep-rooted perennials in the grazing lands in eastern Australia. Three new birdsfoot trefoil experimental varieties, Phoenix, Venture and Matador, were developed through: (1) phenotypic selection within cv. Grasslands Goldie for flowering intensity and pod set, (2) phenotypic selection for these same traits in a broader sample of 49 world-sourced lines, and (3) selection for prostrate growth habit among progeny of pair-crosses between erect and prostrate accessions identified as productive in southern NSW. Following two cycles of selection for flowering prolificacy and pod set, the average number of umbels per stem in the Goldie-derived populations was five times greater than in the commercial Goldie population; this response to selection closely approximated the predicted response based on previous estimates of heritability and phenotypic variance for this trait. In comparison with Goldie, the Syn1 and Syn2 populations of the three experimental varieties consistently expressed earlier flowering maturity and higher seed yield potential in glasshouse and field trials in northern NSW. While germination rate and seedling vigour of the three experimental varieties was slightly less than Goldie, intensive selection pressure on reproductive traits did not compromise seasonal herbage production.
Production and persistence of annual pasture legumes at five saline sites in southern Australia
Authors: Nichols P. G. H. , Craig A. D. , Rogers M. E. , Albertsen T. O. , Miller S. M. , McClements D. R. , Hughes S. J. , D'Antuono M. F. , Dear B. S.
Published: March 2008

Herbage production and persistence of 42 annual pasture legumes from 33 species were measured at five sites across southern Australia. Medicago polymorpha L. was highly productive on soils, particularly those not prone to waterlogging, with soil surface (0–10 cm soil depth) salinity [estimated by electrical conductivity (ECe)] levels in summer of up to 36 dS/m, whereas M. truncatula Gaertn. was productive on ECe levels of at least 11 dS/m. Trifolium michelianum Savi and T. resupinatum L. were highly productive on soils subject to waterlogging, but only where 0–10 cm summer ECe levels were less than 8 dS/m. No commercial species were adapted to highly saline (0–10 cm summer ECe levels >8 dS/m), waterlogged sites. However, Melilotus siculus (Turra) Vitman ex B.D. Jacks. has the potential to fulfil this role, provided an appropriate Rhizobium strain can be selected. Mixtures of species and cultivars should be sown to account for high spatial variability for salinity and waterlogging. Traits for annual legume success in saline landscapes include salinity and waterlogging tolerance in germinating seedlings and mature plants, early flowering, hardseededness and delayed softening of hard seeds. Establishment of regenerating seedlings is associated with the timing of hardseed softening in relation to rainfall events capable of leaching topsoil salts. It is proposed that salinity measurements to determine annual legume suitability for winter-dominant rainfall areas are made in summer or early autumn, when at their highest levels. Transects along salinity and waterlogging gradients are suggested as an alternative method to traditional plots for genotype evaluation.
Histone deacetylase 3 localizes to the mitotic spindle and is required for kinetochore–microtubule attachment
Authors: Ishii Sumiyasu , Kurasawa Yasuhiro , Wong Jiemin , Yu-Lee Li-yuan
Published: March 2008

Protein acetylation and deacetylation play key roles in multiple physiological functions. Histone deacetylase 3 (HDAC3) is a highly conserved, ubiquitously expressed protein that forms multiprotein corepressor complexes to repress gene transcription. Recent studies show that HDAC3 may play a role in cell proliferation. Altered HDAC3 level increases G
2
/M cells, but the mechanism remains unknown. Here we show for the first time, to our knowledge, that the HDAC3 complex, including nuclear receptor corepressor (N-CoR), transducin-β-like protein 1 (TBL1), and TBL1-related protein 1 (TBLR1), is localized on the mitotic spindle. Knockdown of HDAC3 or N-CoR resulted in a collapsed mitotic spindle that was surrounded by chromosomes arranged in a dome-like configuration. Treatment of mitotic cells with Trichostatin A, an HDAC inhibitor, resulted in similar spindle defects independent of transcriptional regulation. In addition, wild-type HDAC3 but not a deacetylase-dead mutant HDAC3 rescued the phenotypes of HDAC3-depleted cells, suggesting that the enzymatic activity of HDAC3 is important for proper spindle function. Whereas the kinetochores and the spindle assembly checkpoint appeared intact in HDAC3-deficient cells, kinetochore–microtubule attachments were impaired because spindle microtubules were unstable in response to cold treatment. These data suggest that the HDAC3 complex is involved in the formation of functional mitotic spindles and proper kinetochore–microtubule attachment. The level or distribution of acetylated α-tubulin was not altered in HDAC3-deficient cells. Taken together, our studies raise the interesting possibility that acetylation–deacetylation of mitotic spindle components may be essential for mitotic spindle function.
W-AlignACE: an improved Gibbs sampling algorithm based on more accurate position weight matrices learned from sequence and gene expression/ChIP-chip data
Authors: Chen Xin , Guo Lingqiong , Fan Zhaocheng , Jiang Tao
Published: March 2008

Motivation: Position weight matrices (PWMs) are widely used to depict the DNA binding preferences of transcription factors (TFs) in computational molecular biology and regulatory genomics. Thus, learning an accurate PWM to characterize the binding sites of a specific TF is a fundamental problem that plays an important role in modeling regulatory motifs and also in discovering the regulatory targets of TFs.

Results: We study the question of how to learn a more accurate PWM from both binding sequences and gene expression (or ChIP-chip) data, and propose to find a PWM such that the likelihood of simultaneously observing both binding sequences and their associated gene expression (or ChIP-chip) data is maximised. To solve the above maximum likelihood problem, a sequence weighting scheme is thus introduced based on the observation that binding sites inducing drastic fold changes in mRNA expression (or showing strong binding ratios in ChIP experiments) are likely to represent a true motif. We have incorporated this new learning approach into the popular motif finding program AlignACE. The modified program, called W-AlignACE, is compared with three other programs (AlignACE, MDscan and MotifRegressor) on a variety of datasets, including simulated data, mRNA expression and ChIP-chip data. These tests demonstrate that W-AlignACE is an effective tool for discovering TF binding motifs from gene expression (or ChIP-chip) data and, in particular, has the ability to find very weak motifs like DIG1 and GAL4.

Availability:  http://www.ntu.edu.sg/home/ChenXin/Gibbs

Contact:  chenxin@ntu.edu.sg

Supplementary information: Supplementary data are available at Bioinformatics online.
Management options for vessel hull fouling: an overview of risks posed by in-water cleaning
Authors: Hopkins Grant A. , Forrest Barrie M.
Published: March 2008

Hopkins, G. A., and Forrest, B. M. 2008. Management options for vessel hull fouling: an overview of risks posed by in-water cleaning. – ICES Journal of Marine Science, 65: 811–815. Hull fouling has been identified as an important pathway for the spread of non-indigenous marine species. However, the management of associated biosecurity risks has proven challenging. Left unmanaged, a fouled vessel can pose a biosecurity risk through the detachment and dispersal of viable material, and through spawning by adult taxa upon arrival in a recipient port or region. These risks can be managed effectively through the removal of the vessel to land for defouling (e.g. dry-docking). However, alternative methods are needed for small (e.g. recreational) vessels, as well as for large vessels fouled outside their dry-docking schedule. Among the various treatment options, in-water cleaning is relatively common, although some countries have placed restrictions on this method because of perceived biosecurity risks. Here, we present a conceptual framework that identifies risks posed by in-water cleaning compared with alternatives, including no management. Decisions on the appropriate management option will be influenced by many factors, including the species present, the level of fouling, and the time a vessel spends in a recipient region. It is important that any regulatory changes regarding in-water defouling be supported by relevant research that quantifies the risks associated with the various management options.
A Foliar Blight and Tuber Rot of Potato Caused by Phytophthora nicotianae: New Occurrences and Characterization of Isolates
Authors: Taylor Raymond J. , Pasche Julie S. , Gallup Courtney A. , Shew H. David , Gudmestad Neil C.
Published: March 2008

Phytophthora spp. are pathogenic to many plant species worldwide, and late blight, caused by Phytophthora infestans, and pink rot, caused by P. erythroseptica, are two important diseases of potato. Another Phytophthora sp., P. nicotianae, was recovered from pink-rot-symptomatic tubers collected from commercial fields in Nebraska, Florida, and Missouri in 2005, 2006, and 2007, respectively. P. nicotianae also was recovered from foliage obtained from commercial potato fields in Nebraska and Texas exhibiting symptoms very similar to those of late blight. Isolates of P. cactorum also were recovered from foliar infections in a commercial potato field in Minnesota in 2005. Natural infection of potato foliage by P. cactorum and infection of wounded potato tuber tissue via inoculation with zoospores of P. capsici are reported here for the first time. Isolates of P. nicotianae, regardless of origin, were primarily of the A1 mating type. All isolates of P. nicotianae and P. cactorum were sensitive to the fungicide mefenoxam. Optimum growth of P. nicotianae, P. erythroseptica, and P. cactorum in vitro occurred at 25°C; however, only P. nicotianae sustained growth at 35°C. Regardless of the tissue of origin, all isolates of P. nicotianae and P. cactorum were capable of infecting potato tubers and leaves. However, isolates of P. nicotianae were less aggressive than P. erythroseptica isolates only when tubers were not wounded prior to inoculation. Pink rot incidence varied significantly among potato cultivars following inoculation of nonwounded tubers with zoospores of P. nicotianae, ranging from 51% in Red Norland to 19% in Atlantic. Phytophthora spp. also differed significantly in their ability to infect potato leaves. Highest infection frequencies were obtained with P. infestans and levels of infection varied significantly among P. nicotianae isolates. The rate of foliar lesion expansion was similar among isolates of P. nicotianae and P. infestans. Whereas P. infestans infections yielded profuse sporulation, no sporulation was observed with foliar infections of P. nicotianae.