bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivities of soil wetness simulation to uncertainties in precipitation and radiation
Authors: Wei Jiangfeng , Dirmeyer Paul A. , Guo Zhichang
Published: August 2008

By analyzing the data from the Second Global Soil Wetness Project (GSWP‐2) sensitivity experiments, this study quantifies the sensitivities of soil wetness simulation to uncertainties in precipitation and radiation forcings and estimates the actual influence of these uncertainties. The sensitivity of soil moisture to uncertainties in radiation has a large seasonal cycle because of its temperature dependence. Sensitivity to uncertainties in precipitation is less temporally variable and is large in semiarid regions. Precipitation sensitivity is generally dominant over radiation sensitivity in cold climate, while in warm climate radiation sensitivity is dominant or both of them are high. However, actual uncertainties in precipitation are typically much larger than for net radiation in warm climate, so the practical impact is dominated by our lack of accurate precipitation estimates. Precipitation uncertainties account for about 2/3 of the total soil wetness uncertainties from all forcing data, while radiation uncertainties only account for about 1/6.
Investigating error structure of shuttle radar topography mission elevation data product
Authors: Becek Kazimierz
Published: August 2008

An attempt was made to experimentally assess the instrumental component of error of the C‐band SRTM (SRTM). This was achieved by comparing elevation data of 302 runways from airports all over the world with the shuttle radar topography mission data product (SRTM). It was found that the rms of the instrumental error is about ±1.55 m. Modeling of the remaining SRTM error sources, including terrain relief and pixel size, shows that downsampling from 30 m to 90 m (1 to 3 arc‐sec pixels) worsened SRTM vertical accuracy threefold. It is suspected that the proximity of large metallic objects is a source of large SRTM errors. The achieved error estimates allow a pixel‐based accuracy assessment of the SRTM elevation data product to be constructed. Vegetation‐induced errors were not considered in this work.
Imaging compaction band propagation in Diemelstadt sandstone using acoustic emission locations
Authors: Townend Edward , Thompson Ben D. , Benson Philip M. , Meredith Philip G. , Baud Patrick , Young R. Paul
Published: August 2008

We report results from a conventional triaxial test performed on a specimen of Diemelstadt sandstone under an effective confining pressure of 110 MPa; a value sufficient to induce compaction bands. The maximum principal stress was applied normal to the visible bedding so that compaction bands propagated parallel to bedding. The spatio‐temporal distribution of acoustic emission events greater than 40 dB in amplitude, and associated with the propagation of the first compaction band, were located in 3D, to within ±2 mm, using a Hyperion Giga‐RAM recorder. Event magnitudes were used to calculate the seismic b‐value at intervals during band growth. Results show that compaction bands nucleate at the specimen edge and propagate across the sample at approximately 0.08 mm s−1. The seismic b‐value does not vary significantly during deformation, suggesting that compaction band growth is characterized by small scale cracking that does not change significantly in scale.
Ionosphere disturbances observed throughout Southeast Asia of the superstorm of 20–22 November 2003
Authors: Zhao B. , Wan W. , Tschu K. , Igarashi K. , Kikuchi T. , Nozaki K. , Watari S. , Li G. , Paxton L. J. , Liu L. , Ning B. , Liu J.‐Y. , Su S.‐Y. , Bulanon Harold P.
Published: August 2008

Ionospheric disturbances in the Southeast Asian region during the super magnetic storm of 20–22 November 2003 were investigated through an ionosonde chain and a GPS network assisted by the space‐borne instruments. At early stage of the storm in the postsunset sector, large enhancements in the critical frequency of F2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly (EIA), which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field (PPE). During the main phase of the storm when interplanetary magnetic field started a 12‐h southward turning, equatorial ionosphere was elevated to a very high level which should be most probably caused by a long‐duration PPE event. Meanwhile, at mid‐low latitudes, ionosphere witnessed an initial simultaneous decrease then followed by drastic increases, which is very different from the past observations in this region (Reddy and Nishida, 1992). Combined analysis of the data from the ionosonde and other space‐based measurement shows that for the present case the penetration efficiency of the interplanetary electric field (IEF) to the equatorial ionosphere was larger at night than in the daytime, which agrees with the results of Fejer et al. (2007) showing the ratios of PPE and IEF changes were highly variable with the local time. During the recovery phase, EIA was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field.
A calibration neutron monitor: Energy response and instrumental temperature sensitivity
Authors: Krüger H. , Moraal H. , Bieber J. W. , Clem J. M. , Evenson P. A. , Pyle K. R. , Duldig M. L. , Humble J. E.
Published: August 2008

Neutron monitors are integral detectors of secondary cosmic rays. Since each of them has its own detection efficiency, energy spectra cannot readily be derived from their observations. To circumvent this problem, latitudinal surveys have been conducted for many years with mobile neutron monitors to derive such spectra. Another way, however, is to use the worldwide stationary neutron monitor network, but then the counting rates of these monitors must be normalized sufficiently accurately against one another. For this reason, two portable calibration neutron monitors were built at the Potchefstroom campus of the North‐West University, South Africa. When calibrations of an adequate number of the worldwide neutron monitors have been done, this paper demonstrates that the differential response functions derived from them will provide experimental data for modulation studies in the rigidity range of 1 to 15 GV. Several properties of these calibrators were investigated, in order to achieve sufficient calibration accuracy. The energy response over the cutoff rigidity range from the poles to the equator, as well as the instrumental temperature sensitivity, are described in this paper. The main conclusion is that the calibrator has a difference of almost 4% in its energy response over the cutoff rigidity range 0–16 GV in comparison with a standard 3NM64 neutron monitor. Furthermore, it is shown that not only the calibrator, but also the NM64 and IGY monitors, have fairly large instrumental temperature sensitivities. Correction coefficients for these effects are given.
Seasonality of sulfur species (dimethyl sulfide, sulfate, and methanesulfonate) in Antarctica: Inland versus coastal regions
Authors: Preunkert Susanne , Jourdain Bruno , Legrand Michel , Udisti Roberto , Becagli Silvia , Cerri Omar
Published: August 2008

To gain a better understanding of sulfate and methanesulfonate (MS−) signals recorded in central Antarctic ice cores in terms of past atmospheric changes, an atmospheric year‐round study of these aerosols was performed in 2006 at the Concordia station (75°S, 123°E) located on the high Antarctic plateau. In addition, a year‐round study of dimethyl sulfide (DMS), the gaseous precursor of sulfur aerosol, was conducted in 2007. The DMS mixing ratio remains below 1 pptv from October to January and exhibits a maximum of 10 pptv during the first half of winter (from April to July). Surprisingly, the well‐marked maximum of sulfur aerosol recorded in January at coastal Antarctic sites is observed at Concordia for sulfate but not for MS− which peaks before and after sulfate in November and March, respectively. This first study of DMS and of its by‐oxidation aerosol species conducted at inland Antarctica points out the complex coupling between transport and photochemistry of sulfur species over Antarctica. The findings highlight the complexity of the link between MS− ice core records extracted at high Antarctic plateau sites and DMS emissions from the Southern ocean.
Macrophage activation induces formation of the anti-inflammatory lipid cholesteryl-nitrolinoleate
Authors: Ferreira Ana M. , Ferrari Mariana I. , Trostchansky Andrés , Batthyany Carlos , Souza José M. , Alvarez María N. , López Gloria V. , Baker Paul R. S. , Schopfer Francisco J. , O'Donnell Valerie , Freeman Bruce A. , Rubbo Homero
Published: August 2008

Nitroalkene derivatives of fatty acids act as adaptive, anti-inflammatory signalling mediators, based on their high-affinity PPARγ (peroxisome-proliferator-activated receptor γ) ligand activity and electrophilic reactivity with proteins, including transcription factors. Although free or esterified lipid nitroalkene derivatives have been detected in human plasma and urine, their generation by inflammatory stimuli has not been reported. In the present study, we show increased nitration of cholesteryl-linoleate by activated murine J774.1 macrophages, yielding the mononitrated nitroalkene CLNO2 (cholesteryl-nitrolinoleate). CLNO2 levels were found to increase ∼20-fold 24 h after macrophage activation with Escherichia coli lipopolysaccharide plus interferon-γ; this response was concurrent with an increase in the expression of NOS2 (inducible nitric oxide synthase) and was inhibited by the •NO (nitric oxide) inhibitor L-NAME (NG-nitro-L-arginine methyl ester). Macrophage (J774.1 and bone-marrow-derived cells) inflammatory responses were suppressed when activated in the presence of CLNO2 or LNO2 (nitrolinoleate). This included: (i) inhibition of NOS2 expression and cytokine secretion through PPARγ and •NO-independent mechanisms; (ii) induction of haem oxygenase-1 expression; and (iii) inhibition of NF-κB (nuclear factor κB) activation. Overall, these results suggest that lipid nitration occurs as part of the response of macrophages to inflammatory stimuli involving NOS2 induction and that these by-products of nitro-oxidative reactions may act as novel adaptive down-regulators of inflammatory responses.
Non-alcoholic fatty liver disease: an overview of prevalence, diagnosis, pathogenesis and treatment considerations
Authors: Preiss David , Sattar Naveed
Published: August 2008

The global increase in the prevalence of obesity has heralded a rise in associated liver injury namely NAFLD (non-alcoholic fatty liver disease). It is estimated that 20–30% of adult populations in developed countries have NAFLD and, although high quality data is currently lacking, the condition is clearly increasing in children also. NAFLD should be suspected in those with commonly available simple clinical signs and biochemistry consistent with insulin resistance. A small number of individuals with NAFLD, often considered a relatively benign condition, will progress to more severe stages of liver disease including NASH (non-alcoholic steatohepatitis) with or without fibrosis, cirrhosis and occasionally hepatocellular carcinoma. NAFLD is also commonly associated with an increased risk of developing Type 2 diabetes and treatable features of insulin resistance such as dyslipidaemia and dysglycaemia. Histological examination of liver tissue remains the only proven method to distinguish between simple steatosis and NASH, a condition far more likely to progress to cirrhosis. Identification of an imaging technique or non-invasive marker to achieve this distinction is therefore much sought after and would allow larger clinical trials and better clinical assessment. Case series and pilot studies of lifestyle advice, insulin sensitizers and other medications have shown improvements in liver histology and serum liver enzymes but robust randomized controlled studies are needed. Furthermore, the cost/benefit ratio of any new therapies, and any potential harms, must be evaluated carefully before being clinically advocated.
In Search of the Active Ingredient: What Really Works in Mental Health Care?
Authors: Brown G.S. (Jeb) , Cameron Joanne , Brown Lindsey
Published: August 2008

This brief report provides a concise overview of decades of research into what really makes a difference in treatment outcomes for the most common psychiatrics disorders. The evidence points to the conclusion that the relationship with the clinician accounts for much more of the variance in treatment outcomes than the treatment methods themselves. The discussion of research and statistical methodology are relevant to investigations of treatments for speech and language disorders.
Treating the Gifted Client
Authors: Williams Dale F.
Published: August 2008

Treating gifted individuals can be both rewarding and challenging. As clients, they often present a thorough understanding of the therapy plan and offer worthwhile perspectives. However, this population’s tendency toward perfectionism can make it difficult to get them out of their comfort zones, a necessary part of stuttering therapy. Procedures such as modeling, setting attainable goals, and accelerating the instruction can help them experience success and transfer skills to environments outside the clinic room.
Auditory Discrimination Deficits in Boys Who Stutter: A Preliminary Investigation
Authors: LaSalle Lisa R. , Duginske Rachel D.
Published: August 2008

Our purpose was to examine the basic level of auditory processing skills in school-age children who stutter. We administered three auditory processing tasks—dichotic digits, temporal patterning, and auditory discrimination—from the Differential Screening Test for Processing (Richard & Ferre, 2006). Five 6- to 9-year-old boys who stutter were age-matched to five boys who do not stutter. Children who stutter showed significantly poorer performance on the auditory discrimination subtest. These preliminary results suggest that, for a subgroup of children who stutter, auditory discrimination difficulties may exacerbate stuttering and thus be a factor worth considering in clinical intervention.
Optical and magnetic properties of ZnCoO thin films synthesized by electrodeposition
Authors: Tortosa M. , Mollar M. , Marí B. , Lloret F.
Published: August 2008

Ternary Zn1−xCoxO crystalline films with different compositions were grown by electrodeposition. The Co content in the final compound is linked to the initial Co/Zn ratio in the starting solution. X-ray diffraction reveals a wurtzite structure for the Zn1−xCoxO films. Transmittance spectra show two effects proportional to Co content, a redshift of the absorption edge and three absorption bands, which are both interpreted to be due to the Co incorporated into the ZnO lattice. The amount of deposited charge was used to get a precise control of the film thickness. Magnetic measurements point out that Co(II) ions are isolated from each other, and consequently the films are paramagnetic.
Influence of structural chemical characteristics on polymer chain dynamics
Authors: Sanchis Maria J. , Domínguez-Espinosa Gustavo , Díaz-Calleja Ricardo , Guzmán Julio , Riande Evaristo
Published: August 2008

A comparative study of the dielectric relaxation behavior of two structurally close polymers containing aliphatic-aromatic side groups was carried out in order to get a better understanding on how slight differences in chemical structure affect the molecular responses to perturbation fields. Specifically, chain dynamics of poly(2-acryloyloxyethyl-2-naphthalene-2-ylacetate) and poly(2-methacryloyloxyethyl-2-naphthalene-2-ylacetate) were studied by broadband dielectric spectroscopy in the frequency range of 10−2–108Hz and temperature window of 298–403K. Also, the relaxation behavior of (2-acetyloxyethyl-2-naphthalene-2-ylacetate), model compound of the polymer side groups, was analyzed. The isotherms representing the dielectric loss in the frequency domain show important conductive contributions, especially at high temperature, which hide the low frequency side of the α relaxation. Conductivity also increases the real component of the complex permittivity in the low frequencies region. Retardation spectra were obtained by minimizing the sum of the squares of the difference between the experimental values of the complex permittivity for each frequency and the analytical ones, predicted by the linear phenomenological theory, using a Tikhonov regularization technique. The spectra present an apparent α peak with an excess wing at short time side resulting from the overlapping of the true α relaxation and a β process. Three absorptions, named in increasing order of time γ, β, and α relaxations, are separated by deconvolution methods. The activation energies associated with the γ process are 70.0±1.8, 68.0±1.4, and 74.8±0.8kJmol−1 for (2-acetyloxyethyl-2-naphthalene-2-yl acetate), poly(2-acryloyloxyethyl-2-naphthalene-2-yl acetate) and poly(2-methacryloyloxyethyl-2-naphthalene-2-yl acetate), respectively. The respective activation energies associated with the β relaxation are 121.7±2.4, 135.3±1.4, and 141.6±1.3kJmol−1. Values of the shape parameters and the strengths of the relaxation processes were obtained as a function of temperature. The dynamic fragility of the polymers and the model compound was studied and compared with that reported for macromolecular and monomeric systems. Also, the evolution of the size of the correlated domains associated with the α relaxation was estimated. Finally, the γ relaxation rather than the β absorption obeys the criteria apparently held by the Johari–Goldstein β processes.
Understanding quantum interference in coherent molecular conduction
Authors: Solomon Gemma C. , Andrews David Q. , Hansen Thorsten , Goldsmith Randall H. , Wasielewski Michael R. , Van Duyne Richard P. , Ratner Mark A.
Published: August 2008

Theory and experiment examining electron transfer through molecules bound to electrodes are increasingly focused on quantities that are conceptually far removed from current chemical understanding. This presents challenges both for the design of interesting molecules for these devices and for the interpretation of experimental data by traditional chemical mechanisms. Here, the concept of electronic coupling from theories of intramolecular electron transfer is extended and applied in the scattering theory (Landauer) formalism. This yields a simple sum over independent channels, that is then used to interpret and explain the unusual features of junction transport through cross-conjugated molecules and the differences among benzene rings substituted at the ortho, meta, or para positions.
Formation of metallic indium-tin phase from indium-tin-oxide nanoparticles under reducing conditions and its influence on the electrical properties
Authors: Guenther G. , Schierning G. , Theissmann R. , Kruk R. , Schmechel R. , Baehtz C. , Prodi-Schwab A.
Published: August 2008

The correlation between defect structure, metal segregation, and electrical resistivity of indium-tin-oxide nanopowder upon treatment in reducing atmosphere was investigated. Morphology and defect structure have been investigated by in situ synchrotron x-ray diffraction and transmission electron microscopy, while traces of metallic indium have been detected by susceptibility measurements utilizing the superconducting properties of indium. With increasing treatment temperature under reforming gas the film resistivity decreases down to ρ=1.6×10−2 Ω cm at 330 °C annealing temperature. For even higher treatment temperatures, the resistivity increases further. This is accompanied by extractions of metallic indium. Under forming gas, grain growth could be observed at 350 °C, while in air grain growth starts at 650 °C. Furthermore forming gas causes a lattice expansion of ITO which persists in oxygen, at least for several hours. The results are discussed with respect to results published in the literature.
Influences of perpendicular compressive stress on the dielectric and ferroelectric properties of electrostrictive and piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics
Authors: Unruan Muangjai , Ngamjarurojana Athipong , Laosiritaworn Yongyut , Ananta Supon , Yimnirun Rattikorn
Published: August 2008

The dielectric and ferroelectric properties of (1−x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 or (1−x)PMN-(x)PT (x=0.1–0.4) ceramics were measured under compressive stress applied perpendicular to the electric field. For the dielectric properties, the experimental results revealed that the superimposed perpendicular compression stress reduced the dielectric constant but increased the dielectric loss tangent of all the compositions. On the other hand, for the ferroelectric properties the applied stress noticeably enhanced the dissipation energy, the polarizations, and the coercive field of all the compositions. These results were interpreted through the non-180° ferroelastic domain switching processes, the stress clamping of domain walls, the deaging mechanism, and the stress induced enhancement in the switchable part of spontaneous polarization. More importantly, the influences of the stress applied in the perpendicular direction to the electric field were generally opposite to those of the parallel stress.
Numerical and experimental investigation of wedge tip radius effect on wedge plasmons
Authors: Ogawa T. , Pile D. F. P. , Okamoto T. , Haraguchi M. , Fukui M. , Gramotnev D. K.
Published: August 2008

We report numerical analysis and experimental observation of strongly localized plasmons guided by triangular metal wedges and pay special attention to the effect of smooth (nonzero radius) tips. Dispersion, dissipation, and field structure of such wedge plasmons are analyzed using the compact two-dimensional finite-difference time-domain algorithm. Experimental observation is conducted by the end-fire excitation and near-field scanning optical microscope detection of the predicted plasmons on 40° silver nanowedges with the wedge tip radii of 20, 85, and 125 nm that were fabricated by the focused-ion beam method. The effect of smoothing wedge tips is shown to be similar to that of increasing wedge angle. Increasing wedge angle or wedge tip radius results in increasing propagation distance at the same time as decreasing field localization (decreasing wave number). Quantitative differences between the theoretical and experimental propagation distances are suggested to be due to a contribution of scattered bulk and surface waves near the excitation region as well as the addition of losses due to surface roughness. The theoretical and measured propagation distances are several plasmon wavelengths and are useful for a range of nano-optical applications.
A new scanning tunneling microscope reactor used for high-pressure and high-temperature catalysis studies
Authors: Tao Feng , Tang David , Salmeron Miquel , Somorjai Gabor A.
Published: August 2008

We present the design and performance of a homebuilt high-pressure and high-temperature reactor equipped with a high-resolution scanning tunneling microscope (STM) for catalytic studies. In this design, the STM body, sample, and tip are placed in a small high pressure reactor (∼19 cm3) located within an ultrahigh vacuum (UHV) chamber. A sealable port on the wall of the reactor separates the high pressure environment in the reactor from the vacuum environment of the STM chamber and permits sample transfer and tip change in UHV. A combination of a sample transfer arm, wobble stick, and sample load-lock system allows fast transfer of samples and tips between the preparation chamber, high pressure reactor, and ambient environment. This STM reactor can work as a batch or flowing reactor at a pressure range of 10−13 to several bars and a temperature range of 300–700 K. Experiments performed on two samples both in vacuum and in high pressure conditions demonstrate the capability of in situ investigations of heterogeneous catalysis and surface chemistry at atomic resolution at a wide pressure range from UHV to a pressure higher than 1 atm.
Light intensity enhancement by diffracting structures in solar cells
Authors: Tobías I. , Luque A. , Martí A.
Published: August 2008

A simplified three-dimensional study is presented of the light confinement, that is, of the enhancement of the Poynting vector of the electromagnetic radiation of the light inside a solar cell absorbing the light weakly when diffracting structures are used. The model is based on the theory of periodic radiation arrays and is easily applied to one- and two-dimensional diffraction gratings. Realistically wide illumination bundles are considered. The extended nature of illumination severely limits the enhancement capabilities of diffraction structures. Results are compared to those of the more widely used Lambertian light confinement.
A Hylleraas functional based perturbative technique to relax the extremely localized molecular orbital wavefunction
Authors: Genoni Alessandro , Merz Kenneth M. , Sironi Maurizio
Published: August 2008

A way to reduce the computational cost associated with the study of large molecules exploits the transfer of extremely localized molecular orbitals (ELMOs). Unfortunately, due to the reduction in the number of variational parameters, the ELMO description is not as accurate as the Hartree–Fock one, although it is qualitatively correct in most of the cases. Therefore, in order to overcome this significant drawback, we propose a perturbative ELMO approach exploiting the Hylleraas functional. Preliminary tests have been performed and the results are promising for future applications to large systems.
On the use of relaxation times for comparing ultraviscous liquid dynamics
Authors: Johari G. P. , Aji D. P. B.
Published: August 2008

In studies of ultraviscous liquids and glasses, (i) the relaxation time and its temperature dependence are generally compared without regard to its asymmetric distribution and (ii) the calorimetric relaxation time at Tg,DSC, the onset temperature of the specific heat rise in a heating scan at 20K∕min, is arbitrarily chosen as 100s and compared against the relaxation time determined by spectroscopy. We propose that the relaxation time and its derivatives should be compared in a fixed frame of reference, preferably by using its average value that takes into account the asymmetric distribution, and we show that the relaxation time at Tg,DSC is a material characteristic. It varies with the extent of nonexponential and nonlinear relaxation and the activation energy.
The effect of geometrical confinement and chirality on domain wall pinning behavior in planar nanowires
Authors: Bogart L. K. , Eastwood D. S. , Atkinson D.
Published: August 2008

We investigate the domain wall pinning behavior in Permalloy nanowires using experimental measurements and micromagnetic simulations. Planar nanowire structures were fabricated by electron beam lithography followed by thin-film deposition via thermal evaporation. The magnetization switching behavior of individual nanowires was measured using the magneto-optical Kerr effect. For symmetrical pinning structures such as the junction between a wider domain wall injection pad and a narrower nanowire, the domain wall depinning field increases as the wire width decreases, with the depinning field increasing rapidly for wires widths below 400 nm. For domain wall pinning at asymmetrical structures such as a notch, the magnitude of the depinning field appears relatively insensitive to notch geometry for triangular and rectangular notch structures, compared to the influence of the wire width. The domain wall depinning field from triangular notches increases as notch depth increases although this increase levels off at notch depths greater than approximately 60% wire width. The nature of domain wall pinning at asymmetrical notch structures is also sensitive to domain wall chirality.
Control of the setting process in CoFe/IrMn exchange bias systems
Authors: Vallejo-Fernandez G. , Aley N. P. , Fernandez-Outon L. E. , O’Grady K.
Published: August 2008

The time and temperature dependences of the exchange field achieved by control of the setting conditions in CoFe/IrMn exchange couples have been investigated. This has been achieved by varying the temperature at which the antiferromagnet was set (TSET) and by measuring the time dependence of the exchange field (Hex) at each temperature. The exchange field was observed to vary logarithmically with setting time, indicating that a wide distribution of energy barriers is present in the antiferromagnetic (AF) layer. The results are consistent with an independent AF grain model of exchange bias where the energy barrier distribution to reversal is governed by the grain volume distribution and the temperature dependence of the magnetocrystalline anisotropy. Calculations of the time dependence of the setting process are in good agreement with the grain volume model.
Experimental study and numerical simulation of the propulsion of microbeads by femtosecond laser filament
Authors: Zhang Nan , Liu Weiwei , Xu Zhijun , Wang Mingwei , Zhu Xiaonong
Published: August 2008

The light filament formed by intense femtosecond laser pulses in air can be used to generate the effective impulse to propel a micro glass bead. In this report, through both experimental studies and the corresponding numerical simulations that involve the dynamics of the nonlinear propagation of light and the laser ablation mechanism, we confirm that this propulsion scheme is based on the laser ablation of the target material. The fundamental characteristics of laser propulsion using a single ultrafast laser filament is also revealed.
Nucleation energetics during homogeneous solidification in elemental metallic liquids
Authors: Kalyanaraman Ramki
Published: August 2008

The solidification of a liquid by nucleation is an important first order phase transition process. It is known that in order for elemental liquids to solidify homogeneously, it is necessary to supercool the liquid to a characteristic temperature (TUC) below the thermodynamic melting point (TMP). Approximately 60 years ago Turnbull [J. Appl. Phys. 21, 1022 (1950)] established the empirical rule that ΔT∗=|TUC−TMP| is approximately given by 0.18 TMP for several elemental metallic liquids. We show here that the magnitude of ΔT∗ and TUC for the metals can be accurately predicted from classical nucleation theory (CNT) provided the excess volume resulting from the density difference between liquid and solid be accounted for. Specifically, the density change accompanying the formation of a microscopic nucleus of the solid from the liquid results in a volume change in the surrounding liquid. When this is included in the free energy calculations within CNT, the resulting predictions for ΔT∗ and TUC for several metals with TMP ranging from ∼200 to 2900 K are in very good agreement with experimental measurements. This theory also shows that there is a universal character in the minimum nucleation barrier energy and the critical radius. The minimum barrier energy occurs at temperature TN∼0.27 TMP for all the elemental liquids investigated, while the temperature dependencies of the barrier energy and the critical radius appear identical when expressed as a function of the scaled temperature TUC/TMP.
Intervalley splittings of Si quantum wells
Authors: Park S.-H. , Lee Y. Y. , Ahn Doyeol
Published: August 2008

Intervalley splittings of Si quantum wells are studied using a multivalley effective mass theory and a finite element method. It is found that the contributions to the valley splitting mainly come from the quantum well interfaces and the external field. Especially the derivatives of the confinement potential which appears in the valley coupling Hamiltonian cause the periodic oscillation of the splitting with the well width. Theoretical predictions are in reasonably good agreement with the recent experimental observation of valley splitting in a SiO2/Si/SiO2 quantum well, which proves the validity of our approach.
Accurate and quick calibration method for polarization-modulation spectroscopy using an ac-modulated polarizing undulator
Authors: Tanaka Masahito , Yagi-Watanabe Kazutoshi , Kaneko Fusae , Nakagawa Kazumichi
Published: August 2008

An accurate calibration method in which an ac-modulated polarizing undulator is used for polarization modulation spectroscopy such as circular dichroism (CD) and linear dichroism (LD) has been proposed and successfully applied to vacuum ultraviolet (vuv) CD and LD spectra measured at beamline BL-5B in the electron storage ring, TERAS, at AIST. This calibration method employs an undulator-modulation spectroscopic method with a multireflection polarimeter, and it uses electronic and optical elements identical to those used for the CD and LD measurements. This method regards the polarimeter as a standard sample for the CD and LD measurements in the vuv region in which a standard sample has not yet been established. The calibration factors for the CD and LD spectra are obtained over a wide range of wavelengths, from 120 to 230 nm, at TERAS BL-5B. The calibrated CD and LD spectra measured at TERAS exhibit good agreement with the standard spectra for wavelengths greater than 170 nm; the mean differences between the standard and calibrated CD and LD spectra are approximately 7% and 4%, respectively. This method enables a remarkable reduction in the experimental time, from approximately 1 h to less than 10 min that is sufficient to observe the storage-ring current dependence of the calibration factors. This method can be applied to the calibration of vuv-CD spectra measured using a conventional photoelastic modulator and for performing an accurate analysis of protein secondary structures.
Phase-field simulation of thermal conductivity in porous polycrystalline microstructures
Authors: Millett Paul C. , Wolf Dieter , Desai Tapan , Rokkam Srujan , El-Azab Anter
Published: August 2008

Mesoscale computer simulations are used to study the effective thermal conductivity of two-dimensional polycrystalline model microstructures containing finely dispersed stationary voids. The microstructural evolution is captured by phase-field modeling in which the competing mechanisms of curvature-driven grain-boundary (GB) migration and Zener pinning due to the void/grain-boundary interactions control the grain-growth kinetics. We investigate porosity fractions between 0% and 8% by systematically increasing the number of voids in the simulation cell. The temperature distribution throughout the microstructure at progressive instances in time is calculated by solving the solid-state heat-conduction equation. The thermal conductivity of each grid point is assigned a value according to the microstructural feature it represents (grain interiors, GBs, and voids) as determined by the phase-field order parameters. The effective conductivities of the microstructures are analyzed with respect to average grain size as well as porosity fraction, and good agreement with theoretical models is obtained.
Pressure transmitting medium Daphne 7474 solidifying at 3.7 GPa at room temperature
Authors: Murata Keizo , Yokogawa Keiichi , Yoshino Harukazu , Klotz Stefan , Munsch Pascal , Irizawa Akinori , Nishiyama Mototsugu , Iizuka Kenzo , Nanba Takao , Okada Tahei , Shiraga Yoshitaka , Aoyama Shoji
Published: August 2008

A pressure transmitting medium named Daphne 7474, which solidifies at Ps=3.7 GPa at room temperature, is presented. The value of Ps increases almost linearly with temperature up to 6.7 GPa at 100 °C. The high pressure realized by a medium at the liquid state allows a higher limit of pressurization, which assures an ideal hydrostatic pressure. We show a volume change against pressure, pressure reduction from room to liquid helium temperature in a clamped piston cylinder cell, pressure distribution and its standard deviation in a diamond anvil cell, and infrared properties, which might be useful for experimental applications.
Vibration amplitude of a tip-loaded quartz tuning fork during shear force microscopy scanning
Authors: Sandoz P. , Friedt J.-M. , Carry É.
Published: August 2008

This Note reports on experimental results obtained with a recently published vision method for in-plane vibration measurement [Sandoz et al., Rev. Sci. Instrum. 78, 023706 (2007)]. The latter is applied to a tip-loaded quartz tuning fork frequently used in scanning probe microscopy for shear-force monitoring of the tip-sample distance. The vibration amplitude of the tip-loaded prong is compared to that of the free one and the damping induced by tip-surface interactions is measured. The tuning-fork behavior is characterized during approaches from free space to surface contact. Tip-surface contact is clearly identified by a drastic reduction in the prong vibration amplitude. However, no differences were observed between hydrophilic and hydrophobic surfaces. Experiments reported here show that the vibration amplitude of the quartz tuning fork in free space is a good estimate of the vibration amplitude of the tip interacting with the sample surface during shear force sample-tip feedback. The experimental setup for measuring the amplitude is easily integrated in an inverted microscope setup on which the shear force microscope is installed for simultaneous scanning probe and optical microscopy analysis of the sample.
Study of relativistic electron beam production and transport in high-intensity laser interaction with a wire target by integrated LSP modeling
Authors: Wei M. S. , Solodov A. A. , Pasley J. , Stephens R. B. , Welch D. R. , Beg F. N.
Published: August 2008

The results of a numerical study of high-intensity short-pulse laser interaction with wire targets are presented. Fast electron production and transport in solid density plasma is modeled using the implicit hybrid particle-in-cell code LSP [D. R. Welch et al., Phys. Plasmas 13, 063105 (2006)]. These simulations were performed with realistic target size and laser parameters and over times much longer than the laser pulse. Nonlinear interaction processes, i.e., microchanneling and density steepening, have been observed. The spectrum of the relativistic electrons produced has a reduced slope temperature compared to that predicted by ponderomotive scaling. Preformed underdense plasma has been found to bottleneck fast electrons due to the intense magnetic fields generated near the critical surface. In a thin long wire target, the overall propagation length of the fast electrons is about 160μm; however, surface fields guide a small fraction of electrons to longer distances. These results are in good agreement with the experiments and have demonstrated that the modeling of electron transport relevant to fast ignition can be pursued in an integrated manner.
Microwave properties of graphite nanoplatelet/epoxy composites
Authors: Lee Sang-Eui , Choi Oyoung , Hahn H. Thomas
Published: August 2008

The complex permittivity spectra and conductivity of graphite nanoplatelet (GNP)/epoxy composites were measured to assess the application potential of these materials as conductive coatings and/or microwave absorbers with high structural integrity. The frequency used ranged from 0.05 to 18.0 GHz. The measured static conductivity was in fairly good agreement with the prediction from the Neelakanta equations. For the complex permittivity, however, the measured values were much higher than those predicted. A better prediction required the use of the order function as a semiempirical parameter to account for the particle loading effect. The surface treatment using nitric acid was found to increase both the conductivity and permittivity of the GNP/epoxy composites although the effect was small, which led to the decrease in the matching thickness of microwave absorbers.
Ion acceleration in a solenoid-free plasma expanded by permanent magnets
Authors: Takahashi K. , Oguni K. , Yamada H. , Fujiwara T.
Published: August 2008

Ion acceleration is achieved in a low-pressure solenoid-free plasma expanded by permanent magnet arrays. Although a permanent magnet normally forms cusp magnetic fields which prevents plasma diffusion and double layer formation, by employing double concentric arrays of permanent magnets, a constant field area, and a diverging magnetic field can be generated near the outlet of the plasma source. In the source, a rapid potential drop with 4cm thickness from 50V to 20V is generated at the diverging field area for 0.35mTorr and a supersonic ion beam accelerated through the potential drop is observed in the diffusion chamber. The beam energy can be increased up to over 40eV with a decrease in gas pressure.
Zinc finger protein ZBTB20 is a key repressor of alpha-fetoprotein gene transcription in liver
Authors: Xie Zhifang , Zhang Hai , Tsai Wenwei , Zhang Ye , Du Yu , Zhong Jigen , Szpirer Claude , Zhu Minghua , Cao Xuetao , Barton Michelle Craig , Grusby Michael J. , Zhang Weiping J.
Published: August 2008

The alpha-fetoprotein (AFP) gene is highly activated in fetal liver but is dramatically repressed shortly after birth. The mechanisms that underlie AFP transcriptional repression in postpartum liver are not well understood. AFP enhancer, repressor region, and promoter are implicated to be involved in AFP postnatal repression, but the major transcriptional repressor remains undefined. We previously identified a zinc finger protein gene ZBTB20. To determine its physiological functions
in vivo
, we have generated hepatocyte-specific ZBTB20 knockout mice by the Cre/loxP approach and demonstrated here that ZBTB20 ablation in liver led to dramatic derepression of the AFP gene in entire liver throughout adult life, although the hepatocytes were normally under nonproliferating status. Furthermore, we found that ZBTB20 was a transcriptional repressor capable of specifically inhibiting AFP promoter-driven transcriptional activity. Liver chromatin immunoprecipitation and mobility shift assays showed that ZBTB20 bound to AFP promoter directly. ZBTB20 was developmentally activated in liver after birth and inversely correlated with its AFP gene expression, suggesting that activated ZBTB20 expression in liver mediated AFP gene repression. Our data point to ZBTB20 as a key regulator governing AFP gene transcription and postulate a new model for the postnatal gene repression of AFP in liver.
The discovery of structural form
Authors: Kemp Charles , Tenenbaum Joshua B.
Published: August 2008

Algorithms for finding structure in data have become increasingly important both as tools for scientific data analysis and as models of human learning, yet they suffer from a critical limitation. Scientists discover qualitatively new forms of structure in observed data: For instance, Linnaeus recognized the hierarchical organization of biological species, and Mendeleev recognized the periodic structure of the chemical elements. Analogous insights play a pivotal role in cognitive development: Children discover that object category labels can be organized into hierarchies, friendship networks are organized into cliques, and comparative relations (e.g., “bigger than” or “better than”) respect a transitive order. Standard algorithms, however, can only learn structures of a single form that must be specified in advance: For instance, algorithms for hierarchical clustering create tree structures, whereas algorithms for dimensionality-reduction create low-dimensional spaces. Here, we present a computational model that learns structures of many different forms and that discovers which form is best for a given dataset. The model makes probabilistic inferences over a space of graph grammars representing trees, linear orders, multidimensional spaces, rings, dominance hierarchies, cliques, and other forms and successfully discovers the underlying structure of a variety of physical, biological, and social domains. Our approach brings structure learning methods closer to human abilities and may lead to a deeper computational understanding of cognitive development.
Engineered specific and high-affinity inhibitor for a subtype of inward-rectifier K
+
channels
Authors: Ramu Yajamana , Xu Yanping , Lu Zhe
Published: August 2008

Inward-rectifier K
+
(Kir) channels play many important biological roles and are emerging as important therapeutic targets. Subtype-specific inhibitors would be useful tools for studying the channels' physiological functions. Unfortunately, available K
+
channel inhibitors generally lack the necessary specificity for their reliable use as pharmacological tools to dissect the various kinds of K
+
channel currents
in situ
. The highly conserved nature of the inhibitor targets accounts for the great difficulty in finding inhibitors specific for a given class of K
+
channels or, worse, individual subtypes within a class. Here, by modifying a toxin from the honey bee venom, we have successfully engineered an inhibitor that blocks Kir1 with high (1 nM) affinity and high (>250-fold) selectivity over many commonly studied Kir subtypes. This success not only yields a highly desirable tool but, perhaps more importantly, demonstrates the practical feasibility of engineering subtype-specific K
+
channel inhibitors.
Inhibition of ghrelin
O
-acyltransferase (GOAT) by octanoylated pentapeptides
Authors: Yang Jing , Zhao Tong-Jin , Goldstein Joseph L. , Brown Michael S.
Published: August 2008

The discovery of ghrelin
O
-acyltransferase (GOAT) opens the way to the design of drugs that block the attachment of an octanoyl group to the appetite-stimulating peptide hormone ghrelin, potentially preventing obesity. Here, we develop a biochemical assay that uses membranes from insect cells infected with baculovirus encoding mouse GOAT. The GOAT-containing membranes transferred the [
3
H]octanoyl group from [
3
H]octanoyl CoA to recombinant proghrelin
in vitro
. Transfer depended on the serine at residue 3 of proghrelin, which is the known site of acylation. GOAT also transferred [
3
H]octanoyl to a pentapeptide containing only the N-terminal five amino acids of proghrelin. GOAT activity could be inhibited by an octanoylated ghrelin pentapeptide, and its potency was enhanced 45-fold when the octanoylated serine-3 was replaced by octanoylated diaminopropionic acid. The data suggest that GOAT is subjected to end-product inhibition and this inhibition is better achieved with substrates having the octanoyl group attached through an amide linkage rather than the corresponding ester. These insights may facilitate the future design of useful inhibitors of GOAT.
‘We're all in this game whether we like it or not to get a number of As to Cs.’ Design and technology teachers' struggles to implement creativity and performativity policies
Authors: Nicholl Bill , McLellan Ros
Published: August 2008

Education reform in England has seen many policies and initiatives introduced by central government. This article discusses two such policies, performativity and creativity. Performativity has been central to the government's agenda of raising standards and includes monitoring mechanisms such as Office for Standards in Education (Ofsted) inspections, performance management and school league tables, all of which are used to measure or judge the value or worth of a school or individual teacher. At the same time as policies on performativity have been implemented, policy makers have introduced a number of policies to encourage creativity in education. This article foregrounds teachers of design and technology (D&T) at secondary level (11–16 years), describing how they struggled to implement both strategies. Teachers valued creativity and thought it was an important part of the subject, but the pressure to be seen to be performing and getting favourable positions in school league tables and Ofsted inspections meant the teaching of D&T became rather formulaic, which allowed very little opportunity for creative learning. Individual interviews were conducted with 14 D&T teachers across six schools and an open‐ended email survey was conducted with a further 17 D&T teachers from 15 schools during the preliminary phase of a research and intervention project. In addition, 69 D&T teachers across eight schools completed a questionnaire at the start of the main intervention period. Data from 126 student interviews across six schools are used to support the teacher data outlined above.