bluuebunny/crossref_metadata_2025 huggingface dataset:
On the duration of the Paleocene‐Eocene thermal maximum (PETM)
Authors: Röhl Ursula , Westerhold Thomas , Bralower Timothy J. , Zachos James C.
Published: December 2007

The Paleocene‐Eocene thermal maximum (PETM) is one of the best known examples of a transient climate perturbation, associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean‐atmosphere system. One key to quantifying the mass of carbon released, identifying the source(s), and understanding the ultimate fate of this carbon is to develop high‐resolution age models. Two independent strategies have been employed, cycle stratigraphy and analysis of extraterrestrial helium (HeET), both of which were first tested on Ocean Drilling Program (ODP) Site 690. These two methods are in agreement for the onset of the PETM and initial recovery, or the clay layer (“main body”), but seem to differ in the final recovery phase of the event above the clay layer, where the carbonate contents rise and carbon isotope values return toward background values. Here we present a state‐of‐the‐art age model for the PETM derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during ODP Leg 208 (Walvis Ridge, Southeastern Atlantic) integrated with published records from Site 690 (Weddell Sea, Southern Ocean, ODP Leg 113). During Leg 208, five Paleocene‐Eocene (P‐E) boundary sections (Sites 1262 to 1267) were recovered in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge, yielding the first stratigraphically complete P‐E deep‐sea sequence with moderate to relatively high sedimentation rates (1 to 3 cm/ka, where “a” is years). A detailed chronology was developed with nondestructive X‐ray fluorescence (XRF) core scanning records on the scale of precession cycles, with a total duration of the PETM now estimated to be ∼170 ka. The revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and HeET.
On measurements of small ice particles in clouds
Authors: Heymsfield Andrew J.
Published: December 2007

For many years it has been recognized that some aircraft cloud microphysical measurements may be contaminated by ice hydrometeors shattering on probe inlets. Small ice particle concentrations measured by the forward scattering spectrometer probe (FSSP) have been commonly accepted but are especially liable to overestimates. This study investigates this result for two additional airborne microphysical sensors, the cloud and aerosol spectrometer (CAS) and the cloud integrating nephelometer (CIN). The results indicate that conclusions from previous studies of the radiative effects of small ice particles need to be reevaluated. A model has been developed describing probe responses to different combinations of ice water content (IWC) and large ice particle concentrations that may be useful in identifying areas where contributions from small particles are significant.
Effects of topography and woody plant canopy cover on near‐ground solar radiation: Relevant energy inputs for ecohydrology and hydropedology
Authors: Zou Chris B. , Barron‐Gafford Greg A. , Breshears David D.
Published: December 2007

The emerging interdisciplinary approaches of ecohydrology and hydropedology are sensitive to variation in soil‐surface energy inputs, which are primarily modified by topography and woody plant canopies. Yet a synthesis of the interactive effects of these two modification types is lacking. We systematically estimated near‐ground surface solar radiation inputs as modified by key attributes of topography (aspect and slope) and tree cover (degree of openness) using solar radiation modeling based on hemispherical photographs. For south aspects, reductions in annual transmission were dominated by canopy cover rather than topography, even when canopy cover was low, whereas for north aspects, canopy effects dominated the reduction in annual transmission for slopes of up to 10° at low canopy cover and up to 30° at high canopy cover. Our results provide a synthetic perspective of the nonlinear, interactive, and temporally dependent effects of slope, aspect, and amount of canopy cover on near‐ground solar radiation.
Pressure demagnetization of the Martian crust: Ground truth from SNC meteorites
Authors: Bezaeva Natalia S. , Rochette Pierre , Gattacceca Jérôme , Sadykov Ravil A. , Trukhin Vladimir I.
Published: December 2007

We performed hydrostatic pressure demagnetization experiments up to 1.3 GPa on Martian meteorites: nakhlite NWA998 (magnetite‐bearing), basaltic shergottites NWA1068 (pyrrhotite‐bearing) and Los Angeles (titanomagnetite‐bearing) as well as terrestrial rocks: rhyolite (hematite‐bearing) and basalt (titanomagnetite‐bearing), using a new non‐magnetic high‐pressure cell. The detailed description of measuring techniques and experimental set‐up is presented. We found that under 1.3 GPa the samples lost up to 54% of their initial saturation isothermal remanent magnetization (IRM). Repeated loading resulted in a further decrease of magnetization of the samples. Our experiments show that the resistance of IRM to hydrostatic pressure is not exclusively controlled by the remanent coercivity of the sample, but is strongly dependant on its magnetic mineralogy. There is no simple equivalence between pressure demagnetization and alternating field demagnetization. The extrapolation of these results of pressure demagnetization of IRM of Martian meteorites to the demagnetization of the Martian crust by impacts is discussed.
Long‐term effects of restoration on soil hydraulic properties in revegetation‐stabilized desert ecosystems
Authors: Wang X.‐P. , Young M. H. , Yu Z. , Li X.‐R. , Zhang Z.‐S.
Published: December 2007

Improving structure of soils found at 0–5 cm depth, and increasing the thickness of biological soil crusts are both associated with sand dune revegetation‐stabilization in arid northwestern China. Since 1956, research on sand dune stabilization has included the use of straw chequer‐boards to facilitate development of soil structure. One method to gauge the degree of stabilization is to compare undisturbed soil hydraulic properties, including water retention [h(θ)] and hydraulic conductivity [K(h)] functions, with properties from stabilized sites of different ages. This study examined properties at five experimental sites of different ages since revegetation (51, 42, 34, 20 and 0 years). Saturated hydraulic conductivity (Ks) was determined in‐situ from all five sites, and the h(θ) curve was determined from samples collected from three sites. A significant negative correlation existed between Ks and the clay, silt and organic matter contents. Differences in most van Genuchten parameters for h(θ) were observed between the revegetated plots and the migrating sand dune area. Results of this long‐term study show that changes in soil hydraulic properties and improvement in soil structure were associated with migrating dune stabilization.
Paleoclimatic implications of an 850‐year oxygen‐isotope record from the northern Tibetan Plateau
Authors: Holmes Jonathan A. , Zhang Jiawu , Chen Fahu , Qiang Mingrui
Published: December 2007

Oxygen‐isotope records from the sediments of hydrologically‐closed lakes are commonly interpreted in terms of changing effective precipitation. We compare an 850‐year‐long oxygen‐isotope record derived from ostracode carbonate from the sediments of Sugan Lake, in the northern Tibetan Plateau, with tree‐ring and ice core evidence for changing temperature, precipitation and isotopic composition of the lake's inflow. Taking into account all of these independent records, we show that variations in the carbonate δ18O values could not have been the result of varying effective precipitation alone: changes in water temperature and in the δ18O of source waters also played a significant role. Where independent records of temperature, precipitation or the isotopic composition of input waters are unavailable, care should be taken to avoid simplistic interpretations of carbonate stable isotope records, as these may contribute to incorrect paleoclimatic reconstructions.
Insights into Tropical Tropopause Layer processes using global models
Authors: Gettelman A. , Birner T.
Published: December 2007

The climatology of the Tropical Tropopause Layer (TTL) in two state‐of‐the‐art general circulation models is compared with observations. Results indicate that global models are able to resolve key features of the TTL, including the mean state and the variability of temperature, ozone, clouds, and thermal structure. The agreement indicates that large‐scale processes, and the large‐scale effects of small‐scale processes, such as convection, are likely the dominant contributors to the observed climatological structure of the TTL and to the observed annual cycle and variability at scales larger than several hundred kilometers. Cloud processes are still uncertain due to their heavily parameterized treatment in models, and limited observations of clouds in the TTL. The bulk treatment of clouds appears sufficient to properly resolve the large‐scale structure of the TTL.
Incremental theory of diffraction for complex point source illumination
Authors: Polemi A. , Carluccio G. , Albani M. , Toccafondi A. , Maci S.
Published: December 2007

The complex point source (CPS) is a solution of the Helmholtz equation obtained by analytical continuation of the free‐space Green's function for complex position of the point source. The CPS representation of radiated fields can be used within a ray code to predict the interaction between an antenna and its actual environment, when standard diffraction formulations are extended to the CPS illumination. In the past, ray‐based diffraction theories such as the geometrical theory of diffraction and its uniform version (UTD) were extended to complex point source fields, leaving, however, open some problematic issues concerning the “complex ray tracing”. In this paper, the generalization of the incremental theory of diffraction (ITD) to CPS is formulated. The total field scattered by the object is given in terms of line integration along edge discontinuities of ITD diffraction coefficients plus the discontinuous geometrical optics (GO). An incremental form of the discontinuous GO is also proposed to overcome GO “complex ray tracing” difficulties. The final formulation is very simple and leads to accurate results that are successfully validated by comparison against a method of moment solution.
Predicting magnetospheric dynamics with a coupled Sun‐to‐Earth model: Challenges and first results
Authors: Merkin V. G. , Owens M. J. , Spence H. E. , Hughes W. J. , Quinn J. M.
Published: December 2007

Results from the first Sun‐to‐Earth coupled numerical model developed at the Center for Integrated Space Weather Modeling are presented. The model simulates physical processes occurring in space spanning from the corona of the Sun to the Earth's ionosphere, and it represents the first step toward creating a physics‐based numerical tool for predicting space weather conditions in the near‐Earth environment. Two 6‐ to 7‐d intervals, representing different heliospheric conditions in terms of the three‐dimensional configuration of the heliospheric current sheet, are chosen for simulations. These conditions lead to drastically different responses of the simulated magnetosphere‐ionosphere system, emphasizing, on the one hand, challenges one encounters in building such forecasting tools, and on the other hand, emphasizing successes that can already be achieved even at this initial stage of Sun‐to‐Earth modeling.
Orphan GPCR research
Authors: Chung S , Funakoshi T , Civelli O
Published: December 2007

Orphan G protein‐coupled receptors (GPCRs) are receptors lacking endogenous ligands. Found by molecular biological analyses, they became the roots of reverse pharmacology, in which receptors are attempted to be matched to potential transmitters. Later, when high‐throughput screening technology was applied to reverse pharmacology, dozens of orphan GPCRs became deorphanized. Furthermore, novel neuropeptides were discovered. This review retraces the history of the orphan GPCRs and of the discoveries of their endogenous ligands, it also discusses the difficulties that the search for new ligands is presently encountering.

British Journal of Pharmacology (2008) 153, S339–S346; doi:10.1038/sj.bjp.0707606; published online 10 December 2007
In vitro and in vivo pharmacological profile of UFP‐512, a novel selective δ‐opioid receptor agonist; correlations between desensitization and tolerance
Authors: Aguila B , Coulbault L , Boulouard M , Léveillé F , Davis A , Tóth G , Borsodi A , Balboni G , Salvadori S , Jauzac P , Allouche S
Published: December 2007

British Journal of Pharmacology (2007) 152, 1325; doi:10.1038/sj.bjp.0707613
Photoionization of isooctane and n-octane in intense laser fields. I. Effect of irradiance on ionization rates
Authors: Healy Andrew T. , Lipsky Sanford , Blank David A.
Published: December 2007

The population of ejected electrons following multiphoton ionization of neat liquids isooctane and n-octane is investigated over a large range of ionizing irradiance Iex. Transient absorption (TA) at 1200nm in both neat liquids is measured in a 60μm path at time delays of 0.7 and 2.5ps following an intense 400nm (3.1eV) ionizing pulse. As the irradiance of this pulse is varied over the range from 4to410TW∕cm2, the dependence of TA on Iex exhibits the periodic structure theoretically predicted for multiphoton channel openings and closings. At low Iex (<9TW∕cm2), TA in isooctane is proportional to Iexn where n=3, consistent with nonresonant, near threshold ionization (liquid phase ionization potential=8.6eV). At Iex>9TW∕cm2, n declines with increasing Iex up to Iex=13TW∕cm2, at which point n abruptly increases to 4. The pattern is repeated at Iex>13TW∕cm2, albeit with n declining from 4 and then abruptly increasing to 5 as Iex becomes greater than 100TW∕cm2. A similar trend is observed in n-octane. The dependence of the TA on Iex in the regions of channel openings and closings is compared to the nonperturbative, strong field approximation developed by Reiss [Phys. Rev. A 22, 1786 (1980)].
High-beta plasma effects in a low-pressure helicon plasma
Authors: Corr C. S. , Boswell R. W.
Published: December 2007

In this work, high-beta plasma effects are investigated in a low-pressure helicon plasma source attached to a large volume diffusion chamber. When operating above an input power of 900W and a magnetic field of 30G a narrow column of bright blue light (due to Ar II radiation) is observed along the axis of the diffusion chamber. With this blue mode, the plasma density is axially very uniform in the diffusion chamber; however, the radial profiles are not, suggesting that a large diamagnetic current might be induced. The diamagnetic behavior of the plasma has been investigated by measuring the temporal evolution of the magnetic field (Bz) and the plasma kinetic pressure when operating in a pulsed discharge mode. It is found that although the electron pressure can exceed the magnetic field pressure by a factor of 2, a complete expulsion of the magnetic field from the plasma interior is not observed. In fact, under our operating conditions with magnetized ions, the maximum diamagnetism observed is ∼2%. It is observed that the magnetic field displays the strongest change at the plasma centre, which corresponds to the maximum in the plasma kinetic pressure. These results suggest that the magnetic field diffuses into the plasma sufficiently quickly that on a long time scale only a slight perturbation of the magnetic field is ever observed.
Lamb wave transducers built on periodically poled Z-cut LiNbO3 wafers
Authors: Courjon E. , Courjal N. , Daniau W. , Lengaigne G. , Gauthier-Manuel L. , Ballandras S. , Hauden J.
Published: December 2007

In this paper, the development of piezoelectric transducers based on periodically poled ferroelectric domains is investigated. Optical quality Z-cut LiNbO3 wafers have been used for the fabrication of test devices operating in the range of 10–100MHz. The fabrication process is detailed and the characterization results are reported. A very good agreement between theoretical predictions achieved by periodic finite element analysis and experiments is observed, allowing for a precise identification of the excited modes. Elliptically polarized modes as well as quasipure longitudinal waves are pointed out. The robustness of the devices to lapping and polishing operations has also been tested. The possible utilizations of such transducers are discussed to conclude the paper.
Fluorescent resonant energy transfer: Correlated fluctuations of donor and acceptor
Authors: Yu Z. G.
Published: December 2007

Mounting evidence suggests that in single-molecule fluorescent resonant energy transfer (FRET) measurements, correlation between fluctuations in donor and acceptor may be important. We present a general theory to describe this correlation and its effect on the FRET rate. The correlation arises from low-energy excitations (e.g., acoustic phonons) of the molecule to which a donor-acceptor pair is attached, and results in an effective interaction between local environments or baths associated with the donor and the acceptor. The correlation is found to reduce the transfer rate, in particular, at short donor-acceptor distances. The theory can quantitatively explain recent measurements of polyproline peptides.
Enhanced probe nano-oxidation by charge pump effect in swept tip voltage cycles
Authors: Xie Xian Ning , Chung Hong Jing , Sow Chorng Haur , Wee Andrew Thye Shen
Published: December 2007

A probe-based nano-oxidation method for enhanced vertical oxide growth on silicon is presented. The technique involves cycling the tip biases between positive and negative polarities to produce high-aspect-ratio nano-oxides. Enhanced oxidation was observed to take place in the positive tip bias region as opposed to the negative tip voltage required for anodic oxidation. A model based on interface space charge accumulation and neutralization, OH− reactant mobilization, and diffusion is proposed to account for the oxidation enhancement observed under positive tip voltages. The proposed model is analogous to the transient charge pump effect which is at work when the polarity of a capacitor is switched. The results reveal the dynamical behavior of nano-oxidation under nonstatic fields which can be harnessed for fabricating oxide nanostructures with improved aspect ratios.
Continuous wave terahertz generation up to 2THz by photomixing on ion-irradiated In0.53Ga0.47As at 1.55μm wavelengths
Authors: Mangeney J. , Merigault A. , Zerounian N. , Crozat P. , Blary K. , Lampin J. F.
Published: December 2007

We report the generation of continuous terahertz waves from microwave frequencies of up to 2THz obtained by photomixing two optical waves at 1.55μm wavelengths in ion-irradiated In0.53Ga0.47As interdigitated photomixers. A 200nm thick silicon nitride coating is used for antireflection and passivation layer, improving the reliability and the heat tolerance of the photomixer. In such devices, output powers greater than 40nW at 0.5THz and 10nW at 1THz have been achieved. Considering the observed saturation of the output power with the increase of bias voltage, the optimum excitation conditions regarding optical power and bias voltage are discussed.
On the thermal stability of vitrified industrial wastes using microscale synchrotron radiation based techniques
Authors: Pinakidou F. , Katsikini M. , Paloura E. C.
Published: December 2007

The effect of annealing on the local coordination of Fe in a series of vitrified industrial wastes is studied by means of x-ray fluorescence mapping, and micro- and conventional x-ray absorption fine structure (XAFS) spectroscopies. It is demonstrated that annealing causes the formation of Fe- and Pb-rich microcrystallites which are embedded in the glass matrix. The local coordination of the Fe ion depends on the local variations of its concentration, i.e., Fe occupies octahedral sites in the Fe-rich crystalline regions and tetrahedral sites into the vitreous network. The percentage of the Fe atoms that belong to the crystalline inclusions depends on the waste content and the annealing temperature, and the stability of the vitrified product is discussed in relation to the nature of the formed microcrystallites. More specifically, when the microcrystallites are mixed Pb and Fe oxides, the material is safe since Pb is trapped both in the crystalline and vitreous regions. Finally, the effect of the different types of crystalline phases and crystalline ratio on the characteristics of the preedge peak in the near edge XAFS spectra is also discussed.
Recent progress in vacuum-ultraviolet polarization modulation spectroscopy using polarizing undulator at the TERAS BL5 beamline
Authors: Yagi-Watanabe Kazutoshi , Tanaka Masahito , Kaneko Fusae , Nakagawa Kazumichi
Published: December 2007

Polarization modulation spectroscopy using an Onuki-type undulator is a useful technique for circular dichroism study in the vacuum-ultraviolet region. We have been developing the vacuum-ultraviolet circular dichroism (vuv-CD) spectroscopy in TERAS BL5 beamline at AIST. This paper describes recent improvements in our instrumentation and methods of analysis to achieve precise and absolute measurements. The CD signal is usually accompanied by experimental artifacts, and elimination of all possible artifacts is the key issue for making reliable measurements. After improving beamline optical system, light flux monitor, and undulator operation method, the base line shift of the CD spectrum is suppressed less than 3×10−4. Sample manipulation and data processing procedures are also described and absolute CD spectrum can be obtained even for linear anisotropic sample. These progresses lead to more quantitative comparison of experimental with calculation on vuv-CD spectrum.
Interface roughness scattering in type II broken-gap GaInAsSb/InAs single heterostructures
Authors: Mikhailova M. P. , Moiseev K. D. , Voronina T. I. , Lagunova T. S. , Yakovlev Yu. P.
Published: December 2007

The effect of the interface roughness (IFR) scattering on the carrier mobility in type II broken-gap p-GaInAsSb/p-InAs heterostructures with self-consistent quantum wells at the interface has been studied experimentally. It was found that the low-temperature mobility decreases as μ∼d2 when the quantum well width at the interface changes from 400 to 50 Å upon raising the acceptor (Zn) doping level of the quaternary layer. It was established that the IFR scattering governs the low-temperature mobility in the two-dimensional electron channel at the heterointerface. The parameters of the IFR scattering, roughness height Δ=12 Å, and correlation length Λ=100 Å were evaluated on the basis of structural, photoluminescent, and magnetotransport data.
Preparation and optical properties of NdH3 and EuH2 films
Authors: Weber S. , Schoenes J.
Published: December 2007

Thin epitaxial films of neodymium and europium have been grown onto CaF2(111). The structural surface analysis reveals a textured character of the Eu samples consisting of three domains, each tilted by 60°. Auger electron spectroscopy has been performed to study the influence of a buffer layer on the protective properties of the palladium cap layer. After loading with hydrogen, the optical properties of the ferromagnetic semiconductors NdH3−δ and EuH2 were determined in the infrared and visible spectral range. A comparison of hydrogenated and deuterated samples clearly associates the phonons in the transmission spectra in the infrared to hydrogen vibrations. Transmission measurements in the visible spectral range yield the optical band gaps. The values of those gaps and the characteristics of the absorption edges are discussed in the context of their participating electronic transitions.
Indices of refraction of AlGaAsSb by an optical waveguide technique
Authors: Mozume T. , Simoyama T. , Ishikawa H.
Published: December 2007

Nearly lattice-matched AlxGa1−xAsySb1−y alloys with Al composition x>0.7 were grown by molecular beam epitaxy. The indices of refraction for a series of alloy compositions were measured. The Al composition was determined by x-ray diffraction (XRD) measurements assuming that the AlxGa1−xAs film that was grown prior to the growth of the AlxGa1−xAsySb1−y layer has the same Al composition. The arsenic to antimony ratio was determined by (004) symmetrical and (115) asymmetric reflection XRD rocking curve measurements. The refractive index and thickness were obtained by prism coupler measurements. A symmetric 75° Si prism coupler was employed to excite the waveguide modes with wavelengths of 1319 and 1540 nm. The shift in the measured indices of refraction from that of the calculated values revealed a deviation from the interpolating scheme based on the binary or ternary alloy data.
Relationship between the morphology of granular cyclotrimethylene-trinitramine and its shock sensitivity
Authors: Czerski H. , Proud W. G.
Published: December 2007

The sensitivity of explosives has been shown to be critically dependent on their morphology as well as their chemical properties. A critical hotspot can be seen as one end of the temperature distribution produced in a heterogeneous material by a shock. Studying shock sensitivity in a granular explosive thus allows insight into the temperature distribution produced by a shock in a granular material. In the case of cyclotrimethylene-trinitramine (RDX), a commonly used explosive, no consensus exists on the dominant features which promote critical hotspots. We present an investigation of the morphology and sensitivity of seven batches of RDX in two size classes and with a range of morphologies. Both the individual crystal morphology and the bulk granular morphology were studied and the features likely to interact with a shock in a granular material to form a critical hotspot are identified. We find that the internal void count does not correlate with the sensitivity of a granular bed and that crystals with defects can be insensitive in such a charge. Sensitivity in our tests was correlated with the presence of surface “dimples” for particles which are 10–30 μm in size. For larger particles (100–300 μm in size), more angular crystals were more sensitive.
Piezoresponse force spectroscopy of ferroelectric-semiconductor materials
Authors: Morozovska Anna N. , Svechnikov Sergei V. , Eliseev Eugene A. , Jesse Stephen , Rodriguez Brian J. , Kalinin Sergei V.
Published: December 2007

Piezoresponse force spectroscopy (PFS) has emerged as a powerful technique for probing highly localized polarization switching in ferroelectric materials. The application of a dc bias to a scanning probe microscope tip in contact with a ferroelectric surface results in the nucleation and growth of a ferroelectric domain below the tip, detected though the change of local electromechanical response. Here, we analyze the signal formation mechanism in PFS by deriving the main parameters of domain nucleation in a semi-infinite ferroelectric semiconductor material. The effect of surface screening and finite Debye length on the switching behavior is established. We predict that critical domain sizes and activation barrier in piezoresponse force microscopy (PFM) is controlled by the screening mechanisms. The relationships between domain parameters and PFM signal is established using a linear Green’s function theory. This analysis allows PFS to be extended to address phenomena such as domain nucleation in the vicinity of defects and local switching centers in ferroelectrics.
Sedimentation of isotope atoms in monatomic liquid Se
Authors: Mashimo Tsutomu , Ono Masao , Huang Xinsheng , Iguchi Yusuke , Okayasu Satoru , Kobayashi Katsura , Nakamura Eizo
Published: December 2007

A strong gravitational field resulted in the sedimentation of isotope atoms in monatomic liquid. The concentration ratio Se82∕Se76 increased by greater than 3.5% in specimen ultracentrifuged at (0.7–0.9)×106G and at 300°C. The recovered sample had a feather-shaped crystalline morphology. The concentration gradient was nearly twice that of the steady state analytical result (ideal gas system), indicating a nonideal system diffusion. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion and suggestes its possible application to isotope separation, crystalline control, and matter dynamics in massive star.
Maximizing mixing and alignment of orientable particles for reaction enhancement
Authors: John T. , Mezić I.
Published: December 2007

We present a model for the evolution of concentrations of orientable species undergoing a collisional binary reaction and examine the dependence of the concentration of the reaction product on flow parameters in Poiseuille flow. Interesting patterns of concentration are obtained depending on parameters. We use the model to investigate the reaction in a microfluidic device known as the shear superposition micromixer. Simulation results over a range of Péclet, Damköhler, and rotational Péclet numbers indicate that this micromixer is well suited to enhance the rate of reaction via the mechanism of simultaneous mixing and alignment of the orientable species. Connections to biological systems are discussed.
Quantum corrections to the semiclassical hydrodynamical model of semiconductors based on the maximum entropy principle
Authors: Romano V.
Published: December 2007

Quantum corrections to the hydrodynamical model of semiconductors based on the maximum entropy principle are obtained at ℏ2 order with a Chapman-Enskog expansion in the high field approximation, modeling the ℏ2 part of the collision term in a relaxation form. Limiting energy-transport and drift-diffusion models are deduced.
Refraction-based tomosynthesis: Proof of the concept
Authors: Maksimenko Anton , Yuasa Tetsuya , Ando Masami , Hashimoto Eiko
Published: December 2007

Tomosynthesis is a well known technique for imaging a plane in a target by blurring other planes in the target. Commonly, the tomosynthesis is based on the x-ray absorption contrast. Recently, methods for generating other x-ray contrasts were developed. One of them, the so-called refraction contrast, is extremely sensitive to soft tissues and small defects. It was used as the base for the computed tomography. However, a very promising application of this contrast in the tomosynthesis remains undeveloped. This letter is dedicated to this problem. It includes both theoretical background and experimental implementation of the idea.
Shock-induced lattice deformation of CdS single crystal by nanosecond time-resolved Laue diffraction
Authors: Ichiyanagi Kouhei , Adachi Shin-ichi , Nozawa Shunsuke , Hironaka Yoichiro , Nakamura Kazutaka G. , Sato Tokushi , Tomita Ayana , Koshihara Shin-ya
Published: December 2007

We report a single-shot nanosecond time-resolved Laue diffraction measurement of cadmium sulfide (CdS) single crystal under laser-induced shock compression. The observed Laue diffraction pattern maintains sixfolding axis of the wurtzite structure for 10ns at a shock pressure of 3.92GPa, which is above the threshold pressure of phase transition to a rocksalt structure. This result shows that a transient wurtzite structure is observed above its threshold pressure to a rocksalt structure on a nanosecond time scale. Uniaxial compression was confirmed by the c∕a value of the transient structure obtained from the (201) and (302) peaks.
First principles calculations for dilute InAs1−xNx alloys
Authors: Benaissa H. , Zaoui A. , Ferhat M.
Published: December 2007

Dilute nitrides such as InAsN alloys represent a new class of highly mismatched semiconductors alloys, which have recently attracted strong attention due to their unique physical properties. In this paper we present computed structural, thermodynamic, and energetic characteristics of the dilute InAsN alloys. We found strong deviations from Vegard's law for the variation of the lattice constant of InAsN. Regarding the local environment of N, we notice that the clustering has a weak influence on the In-As bond, but shortens the In-N bond and strongly reduces the energy band gaps. In addition, wide miscibility gaps are predicted in the temperature range relevant to specimen synthesis and processing.
Design and operating characteristics of new type cold cathode ion source
Authors: Hassan A. , Bassal N. , Zakhary S. G.
Published: December 2007

In this work, the design and performance of new type ion source are described. The discharge mechanism of the source is based on creating an arc discharge through a saddle electric field inside the discharge tube. The saddle electric field is created by immersing an annular anode inside the discharge tube covered from the upper and lower ends with two flanges. These two flanges act as cathodes. The discharge tube is surrounded by a solenoid coil which produces an axial magnetic field (up to 400G) measured at the center of the source. Measurements have been performed to find out the influence of arc power, pressure, discharge voltage, magnetic field, and extracting voltage on the ion source properties. The source yields an argon ion current of ∼0.6mA and electron current of ∼4mA at normal operating conditions (extraction voltage Vex=7kV, pressure of 5.5×10−4Torr, Varc=400V, Iarc=1A, B=200G). It showed an energy spread of 20eV at a discharge voltage of 400V and an extraction voltage of 3kV.
Observation of surface-plasmon-polariton transmission through a silver film sputtered on a photorefractive substrate
Authors: Chen Jing , Li Yudong , Lu Wenqiang , Qi Jiwei , Cui Guoxin , Liu Hongbing , Xu Jingjun , Sun Qian
Published: December 2007

The diffraction of holographic gratings in a photorefractive iron-doped lithium niobate (LiNbO3:Fe) crystal, on which surface a silver film was sputtered, was experimentally investigated. Besides the Bragg diffraction, an additional diffraction was observed. The experimental results present evidence of surface-plasmon-polariton (SPP) transmission through the silver film on the photorefractive substrate. The excitation of SPPs is speculated to be due to the corrugations of the silver film, which are caused by the photorefractive and the converse piezoelectric effect in the LiNbO3:Fe sample.
The effect of field-cooling strength and interfacial coupling on exchange bias in a granular system of ferromagnetic nanoparticles embedded in an antiferromagnetic matrix
Authors: Hu Yong , Du An
Published: December 2007

A modified Monte Carlo Metropolis method is performed to simulate the effect of field-cooling strength and interfacial coupling on exchange bias and coercivity of a system with ferromagnetic cores embedded in an antiferromagnetic matrix, based on three-dimensional classical Heisenberg model. The results show that the exchange bias changes from negative value to positive value with increasing cooling field as the interfacial coupling is antiferromagnetic, whereas coercivity is almost unchanged due to the small size of ferromagnetic cores. After applying a weak cooling field, the exchange bias of system with antiferromagnetic interfacial coupling may be positive just when the value of interfacial coupling is not large and exhibit a positive maximum. However, the exchange bias is constantly positive and increasing with increasing values of interfacial coupling after applying a strong cooling field. The exchange bias of system with ferromagnetic interfacial coupling is independent of cooling field and increases for larger interfacial coupling, but the sign is negative due to the constantly positive net magnetization of antiferromagnetic surface. It is obvious that the positive exchange bias depends on the field-cooling strength to a large extent. However, the interfacial coupling may change the configuration of antiferromagnetic matrix to influence the exchange bias.
X-ray diffraction study of AlN∕AlGaN short period superlattices
Authors: Chandolu A. , Nikishin S. , Holtz M. , Temkin H.
Published: December 2007

Short period superlattices of AlN∕Al0.08Ga0.92N with the average AlN content over 60% have been investigated by high resolution x-ray diffraction. The a and c lattice constants verify these structures to be strain relaxed. Monolayer-level interface roughness, caused by the presence of threading dislocations and step-flow growth mode, is simulated and directly compared with the zeroth and ±1 satellite peak positions of the rocking curves. It was found that the observed x-ray diffraction data can be adequately described by considering primarily the presence of screw dislocations and step-flow growth mode.
Coherent control of molecular modulation
Authors: Goda S. N. , Sensarn S. , Shverdin M. Y. , Yin G. Y.
Published: December 2007

We demonstrate coherent control of a molecular modulation process using an incident set of seven optical sidebands spanning two octaves of bandwidth. We utilize a genetic algorithm to optimize the relative phases of the incident sidebands to generate additional UV sidebands with nearly 1% efficiency, change the ratio of energy between sidebands by more than a factor of 50, and efficiently alter individual sideband energies by millijoules.
Electron spillover effects in InGaN∕GaN quantum-well lasers
Authors: Huang Shyh-Jer , Yen Shun-Tung
Published: December 2007

The effects of electron spillover from quantum wells on the optical property of InGaN∕GaN laser diodes are theoretically studied in detail. A six-band model including strain effects is used to calculate valence band states. Continuous subbands unconfined to the quantum wells are simulated deliberately by densely discretized subbands for the spillover electrons. The calculation results show obvious differences in the radiative current densities and the gain spectra between the cases with and without considering the spillover effect. We further investigate the spillover effect on the radiative current densities and the spontaneous emission spectra, with variations in the depth and the width of quantum wells, the total loss of the cavity, and the temperature. For shallow wells, the spillover effect is particularly important. It broadens both the gain and the spontaneous emission spectra and hence deteriorates the threshold of laser diodes. Such an effect can be alleviated by employing a long cavity and a multi-quantum-well active region. The concept of the electron spillover studied in this work is not only applicable to the nitride lasers but also to other kinds of quantum-well lasers.
A cryogenic Quadraprobe scanning tunneling microscope system with fabrication capability for nanotransport research
Authors: Kim Tae-Hwan , Wang Zhouhang , Wendelken John F. , Weitering Hanno H. , Li Wenzhi , Li An-Ping
Published: December 2007

We describe the development and the capabilities of an advanced system for nanoscale electrical transport studies. This system consists of a low temperature four-probe scanning tunneling microscope (STM) and a high-resolution scanning electron microscope coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with subnanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10K. Additionally, an integrated energy analyzer allows for scanning Auger microscopy to probe chemical species of nanostructures. Some testing results are presented.
Evolution mechanism of nanocrystalline tungsten-carbon and effects on tungsten implanted amorphous hydrogenated carbon
Authors: Xu Ming , Zhang Wei , Wu Zhengwei , Pu Shihao , Li Liuhe , Chu Paul K.
Published: December 2007

Tungsten doped amorphous carbon films are prepared on silicon (100) by postimplantation of tungsten ions into pure amorphous hydrogenated carbon using the plasma immersion ion implantation technique. The peak concentration of tungsten reaches 27at.% and W–C nanocrystallites with largest diameters of ∼5nm are formed in the near surface region. Both the quantity and size of these nanocrystallites are observed to undergo unique transformation with increasing depths, enabling gradual release of the compressive stress and subsequently leading to better adhesion between the film and substrate. The film structures are evaluated by x-ray photoelectron spectroscopy and glancing angle x-ray diffraction, and high-resolution transmission microscopy is employed to investigate the structural transformation. The mechanical properties of the films including adhesion strength and hardness are determined by nanoindentation and nanoscratch tests. The formation of the nanocrystalline structures can be explained by ion implantation induced damage, chemical effects, and thermodynamics.
Optoelectronic properties and electronic structure of YCuOSe
Authors: Ueda Kazushige , Takafuji Kouhei , Yanagi Hiroshi , Kamiya Toshio , Hosono Hideo , Hiramatsu Hidenori , Hirano Masahiro , Hamada Noriaki
Published: December 2007

YCuOSe was prepared by solid-state reaction, and its wide gap semiconducting properties were examined. The single phase of YCuOSe was obtained in a limited temperature range around 750°C and decomposed into Y2O2Se and Cu2Se at higher temperatures. The obtained YCuOSe sample showed a p-type semiconducting behavior with the electrical conductivity of 1.4×10−1Scm−1 at room temperature. The band gap of YCuOSe was estimated to be 2.58eV, which is much smaller than that of LaCuOSe (2.82eV). The electronic structure of YCuOSe was investigated by ultraviolet photoemission spectroscopy and energy band calculations to understand the differences in the electronic structures between LnCuOSe (Ln=La,Y). It was found that the Cu–Cu distance rather than the Cu–Se distance influences the electronic structures, and the smaller band gap of YCuOSe is attributed to the downshift of the Cu 4s energy level due to the smaller Cu–Cu distance and the consequent larger Cu–Cu interaction in YCuOSe.
Properties of highly (100) oriented Pb(Mg1∕3,Nb2∕3)O3–PbTiO3 films on LaNiO3 bottom electrodes
Authors: Li Y. W. , Hu Z. G. , Yue F. Y. , Yang G. Y. , Shi W. Z. , Meng X. J. , Sun J. L. , Chu J. H.
Published: December 2007

The 70%Pb(Mg1∕3,Nb2∕3)O3–30%PbTiO3 (PMNT) films have been fabricated on LaNiO3 (LNO) coated silicon substrate. The conductive LNO films act as a seed layer for the growth of PMNT films, which depresses the formation of pyrochlore phase and induces the high (100) preferred orientation of perovskite PMNT films. Compared with the PMNT films grown on platinum bottom electrode, the ferroelectric properties of PMNT films grown on LNO are enhanced. The frequency dependence of complex permittivity from PMNT films on LNO is the conjunct result of polarization relaxation and movement of oxygen vacancy, which can be fitted by the function containing Debye and universal dielectric response models, respectively.
Interfacial characteristics and band alignments for ZrO2 gate dielectric on Si passivated p-GaAs substrate
Authors: Dalapati Goutam Kumar , Sridhara Aaditya , Wong Andrew See Weng , Chia Ching Kean , Lee Sung Joo , Chi Dongzhi
Published: December 2007

The interfacial characteristics and band alignments of high-k ZrO2 on p-GaAs have been investigated by using x-ray photoelectron spectroscopy and electrical measurements. It has been demonstrated that the presence of Si interfacial passivation layer (IPL) improves GaAs metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, and hysteresis. It is also found that Si IPL can reduce interfacial GaAs-oxide formation and increases effective valence-band offset at ZrO2∕p-GaAs interface. The effective valence-band offsets of ZrO2∕p-GaAs and ZrO2∕Si∕p-GaAs interfaces are determined to be 2.7 and 2.84eV, while the effective conduction-band offsets are found to be 1.67 and 1.53eV, respectively.
Spin-torque-driven vortex dynamics in a spin-valve pillar with a perpendicular polarizer
Authors: Liu Yaowen , He Huan , Zhang Zongzhi
Published: December 2007

Spin-torque-driven vortex dynamics are studied by micromagnetic modeling in a spin-valve pillar which contains a perpendicular polarizer and a vortex free layer. Two kinds of transient oscillations mediated by the vortex-core motion are observed. The oscillations are treated as the competition among the spin torque, gyroforce, Gilbert damping, and the restoring force, governed by the generalized Thiele equation [A. A. Thiele, J. Appl. Phys. 45, 377 (1974)]. The fundamental frequency is dominated by the gyrotropic motion, while the high-frequency oscillation is triggered by the balance of the spin torque and demagnetizing field. The polarity of the vortex core can be switched through a vortex-antivortex pair creation and annihilation process.
Correlation between photoluminescence and magnetic properties of GaMnN films
Authors: Nepal N. , Mahros Amr M. , Bedair S. M. , El-Masry N. A. , Zavada J. M.
Published: December 2007

GaMnN films grown by metal-organic chemical vapor deposition were studied by photoluminescence (PL) spectroscopy and hysteresis measurements. Depending on the growth conditions of these GaMnN films, hysteresis measurements along the easy axis of magnetization show a transformation from magnetic to nonmagnetic behavior. The PL spectra of both magnetic and nonmagnetic GaMnN films exhibited GaN band edge and deep-level impurity transitions at 3.4 and 1.3eV, respectively. The PL emission intensity of the 1.3eV emission peak is stronger considerably for magnetic GaMnN films and is believed to be due to the Mn3+ intraband transition.
Genetic Algorithms and the Corridor Location Problem: Multiple Objectives and Alternative Solutions
Authors: Zhang Xingdong , Armstrong Marc P
Published: December 2007

Corridor planning problems are challenging because their solution often requires the participation of multiple stakeholders with different interests and emphases. Though such problems fall into the domain of multiobjective evaluation, existing corridor location models often search for a single global optimum by collapsing multiple objectives into a single one using a weighting method. In multiobjective problems with competing objectives, however, optimality will often have different interpretations among decision makers, and, as a consequence, no single optimal solution will satisfy all participants. This paper describes the design and implementation of a multiobjective genetic algorithm for corridor selection problems (MOGADOR). This new approach generates a large set of Pareto-optimal and near-optimal solutions that can be evaluated with respect to the untargeted or imprecisely modeled characteristics of ill-structured corridor location problems. Experimental results suggest that the MOGADOR approach outperforms traditional shortest-path methods in both computation time and solution quality. An analytical and visualization tool is provided to help decision makers identify good candidates and evaluate trade-offs among alternatives.