bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of the Gulf of Guayaquil (Ecuador) during the Quaternary as an effect of the North Andean block tectonic escape
Authors: Witt César , Bourgois Jacques , Michaud François , Ordoñez Martha , Jiménez Nelson , Sosson Marc
Published: June 2006

Interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the Gulf of Guayaquil (GG) area. These include two E‐W trending major detachments: the Posorja and the Jambelí detachment systems, which represent half grabens with oppositely dipping detachments, to the south and to the north, respectively. The NE‐SW trending Puná‐Santa Clara fault system developed as a transfer fault system between the Posorja and the Jambelí detachments. The Esperanza and the Jambelí basins exhibit 3–4 km of sediment that accumulated during the past 1.6–1.8 Myr. The Puná‐Santa Clara fault system bounds the Esperanza and the Jambelí basins, evidencing that the evolution of these basins is tightly controlled by the two detachments at depth. To the west, the N‐S trending Domito fault system bounding the Posorja detachment system and the Esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope. The Pliocene series show no significant variations in thickness throughout the Gulf of Guayaquil area suggesting that no important tectonic deformation occurred from 5.2 to 1.8–1.6 Ma. The major period of tectonic deformation in the Gulf of Guayaquil area occurred during the Pleistocene times. Three main tectonic steps are identified. From early Pleistocene to ∼180 ka, major subsidence occurred along the Esperanza and Jambelí basins. From ∼180 to ∼140 ka, most of the Gulf of Guayaquil area was above sea level during the isotope substage 6 low stand. From ∼140 ka to Present, tectonic activity is restricted along the normal faults bounding the Esperanza basin, the Tenguel fault, and the Puná‐Santa Clara and Domito fault systems. A N‐S trending tensional stress regime characterizes the Pleistocene times throughout. The northward drifting of the North Andean block is proposed to control the tectonic evolution and associated subsidence of the Gulf of Guayaquil area. It is also accepted that the collision of the Carnegie ridge with the trench axis has to play a major role in controlling the North Andean block northward drift. Because the Carnegie ridge subduction is possibly an ongoing process, which began prior to the Pliocene, we postulate the along‐strike morphology of the ridge at the origin of interplate coupling variations. The subduction of an along‐strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the GG area occurring at ∼1.8–1.6 Ma.
CO2 and albedo climate impacts of extratropical carbon and biomass plantations
Authors: Schaeffer M. , Eickhout B. , Hoogwijk M. , Strengers B. , van Vuuren D. , Leemans R. , Opsteegh T.
Published: June 2006

We explored the climate impacts for two land‐use change scenarios, aimed at mitigating the buildup of greenhouse gases in the atmosphere. Using the integrated assessment model IMAGE 2.2, we found that the large‐scale implementation in the extratropics of either carbon‐sequestration or modern‐biomass plantations decreases the CO2 concentration with 70–80 ppmv by the year 2100 compared to a nonmitigation baseline. In a coupled land/atmosphere/ocean/sea‐ice model this moderates global warming over the 21st century by 10%. However, the carbon‐sequestration option raises the absorption of solar radiation due to a lower albedo compared to the scenario involving modern‐biomass plantations (for biofuels production). The albedo‐induced difference in global mean temperature is as large as the mitigation by CO2 changes in the two scenarios compared to the baseline. Further, an atmospheric circulation change in the carbon‐plantation scenario weakens the supply of moisture from the oceans to North Africa and central Eurasia. In our model this decreases annual mean precipitation over North Africa by up to 10% and further increases summer temperatures over Eurasia. These findings lead us to conclude that other climate impacts than just CO2 changes have to be taken into account when discussing climate‐change mitigation options that involve land‐use changes.
Crystal morphology and dislocation microstructures of CaIrO3: A TEM study of an analogue of the MgSiO3 post‐perovskite phase
Authors: Miyajima Nobuyoshi , Ohgushi Kenya , Ichihara Masaki , Yagi Takehiko
Published: June 2006

Polycrystalline CaIrO3 phase, synthesized in a cubic‐anvil type high pressure apparatus at 4 GPa and 1473 K, has been investigated using transmission electron microscopy (TEM). Individual crystallites have a platy crystal habit elongated parallel to the crystallographic a‐axis, which is the direction of the edge‐shared octahedral chain. The dislocations with Burgers vectors b = [100] and 〈u0w〉 nucleated in the CaIrO3 phase during the synthesis experiments. The potential slip plane could be (010), the most likely having with the (010)‐layered structure of IrO6 octahedrons. The crystal morphology and dislocation microstructures of CaIrO3 should provide important constraints for the discussion of the deformation behaviour and polarization anisotropy of the post‐perovskite phase in the lowermost mantle.
Are halo coronal mass ejections special events?
Authors: Lara Alejandro , Gopalswamy Nat , Xie Hong , Mendoza‐Torres Eduardo , Pérez‐Eríquez Román , Michalek Gregory
Published: June 2006

We revisited the properties of wide coronal mass ejections (CMEs) called halo CMEs. Using the large LASCO/SOHO CMEs data set, from 1996 to 2004, we examined the statistical properties of (partial and full) halo CMEs and compare with the same properties of “normal” width (lower than 120°) CMEs. We found that halo CMEs have different properties than “normal” CMEs, which cannot be explained merely by the current geometric interpretation that they are seen as halos because they are traveling in the Sun Earth direction. We found that the CME width distribution is formed by, at least, three different populations: Two gaussians: a narrow and a medium distribution centered at ∼17° and ∼38°, respectively; the narrow population most likely corresponds to the “true” observed widths, whereas the medium width population is the product of projection effects. The third distribution corresponds to wider CMEs (80° < W < 210°) which behaves as a power law. Partial and full halo CMEs wider than these do not follow any particular distribution. This lack of regularity may be due to the small number of such events. In particular, we found (and test by a statistical approach) that the number of observed full halo CMEs is lower than expected. The CME speed follows a log‐normal distribution, except for the very low speed CME population, which follows a gaussian distribution centered at ∼100 km/s and is probably due to projection effects. When the CMEs are divided by width into nonhalo, partial halo, and full halo, we found that the peaks of the distributions are shifted toward higher speeds, ∼300, ∼400 and ∼600 km/s for nonhalo, partial halo, and full halo CMEs, respectively. This confirms that halo CMEs tend to be high speed CMEs. The acceleration of full halo CMEs tends to be more negative compared with nonhalo and partial halo CMEs. We introduce a new observational CME parameter: The final observed distance (FOD), i.e., the highest point within the coronograph field of view where a CME can be distinguished from the background. In other words, the highest CME altitude measured. The FOD for nonhalo CMEs decreases exponentially from ∼5 to ∼30 R⊙ in the LASCO field of view. On the other hand, the FOD of halo CMEs increase with distance. This means that it is more likely to see halo CMEs at large distances (from the Sun) than nonhalo CMEs. These halo CME properties may be explained if the white light wide enhancements (or halo) seen by coronographs correspond to a combination of an expanding (shock) wave which disturbs and/or compresses the ambient material and the CME material itself.
A physics‐based diffusion scheme for numerical models
Authors: Liu Chongjian , Liu Ying , Xu Hui
Published: June 2006

A proper description of the dissipation in a forcing‐dissipative system, such as the atmosphere, is very important when the system is discretized. Atmospheric dissipation is generally treated as diffusion in numerical weather prediction (NWP) models. The commonly used fourth‐order diffusion scheme (linear and nonlinear) generates spurious upgradient mass or heat transport, which violates the entropy constraint posed by non‐equilibrium thermodynamics. The second law of thermodynamics is used in this paper to re‐construct the diffusion scheme to ensure downgradient transport. The new physics‐based scheme is applied to the Penn State/NCAR non‐hydrostatic mesoscale model. A hurricane case simulation demonstrates that the new scheme improves the model accuracy in predicting the strength of the hurricane.
Astrocytic Induction of Matrix Metalloproteinase-9 and Edema in Brain Hemorrhage
Authors: Tejima Emiri , Zhao Bing-Qiao , Tsuji Kiyoshi , Rosell Anna , van Leyen Klaus , Gonzalez R Gilberto , Montaner Joan , Wang Xiaoying , Lo Eng H
Published: June 2006

We tested the hypothesis that astrocytic matrix metalloproteinase-9 (MMP-9) mediates hemorrhagic brain edema. In a clinical case of hemorrhagic stroke, MMP-9 co-localized with astrocytes and neurons in peri-hematoma areas. In a mouse model where blood was injected into striatum, MMP-9 was colocalized with astrocytes surrounding the hemorrhagic lesion. Because MMP-9 is present in blood as well as brain, we compared four groups of wild type (WT) and MMP-9 knockout (KO) mice: WT blood injected into WT brain, KO blood into KO brain, WT blood into KO brain, and KO blood into WT brain. Gel zymography showed that MMP-9 was elevated in WT hemorrhagic brain tissue but absent from KO hemorrhagic brain tissue. Edematous water content was elevated when WT blood was injected into WT brain. However, edema was ameliorated when MMP-9 was absent in either blood or brain or both. To further assess the mechanisms involved in astrocytic induction of MMP-9, we next examined primary mouse astrocyte cultures. Exposure to hemoglobin rapidly upregulated MMP-9 in conditioned media within 1 to 24 h. Hemoglobin-induced MMP-9 was reduced by the free radical scavenger U83836E. Taken together, these data suggest that although there are large amounts of MMP-9 in blood, hemoglobin-induced oxidative stress can trigger MMP-9 in astrocytes and these parenchymal sources of matrix degradation may also be an important factor in the pathogenesis of hemorrhagic brain edema.
Purification and characterization of a staphylokinase variant, K35R
Authors: He Jintian , Wang Gaizhen , Li Guoping , Zhao Baohua , Mo Wei , Song Houyan
Published: June 2006

DGR [staphylokinase (Sak) variant K35R, in which lysine (K) at position 35 is replaced by arginine (R)], a recombinant mutant of the Staphylococcus aureus enzyme, is a promising drug for thrombotic disorders. In the present work, DGR was successfully overexpressed by the plasmid JF1125[pST‐DGR] as a soluble cytoplasmic protein in a 30‐litre fermentor that accounted for more than 50% of the total cellular protein. The expressed DGR was subsequently purified by using a simple three‐step chromatographic purification process developed at a pilot scale. The clearance of host‐cell‐protein contaminants in the protein purification process was confirmed by SDS/PAGE and Western blotting, using rabbit antisera raised against Escherichia coli JF1125 cell proteins. SDS/PAGE, isoelectric focusing and HPLC–MS analysis indicated that the purified DGR is almost completely homogeneous. The purification process resulted in greater‐than‐98% pure DGR and yielded up to 25.0 mg/g wet weight of cells. The effect of pH and temperature on the stability of DGR was investigated further. The results showed that DGR was highly stable at neutral pH and more stable than two other wild‐type Saks, SakSTAR and Sak42D, when submitted to high temperatures.
A preliminary investigation demonstrating the effect of quercetin on the expression of genes related to cell‐cycle arrest, apoptosis and xenobiotic metabolism in human CO115 colon‐adenocarcinoma cells using DNA microarray
Authors: Murtaza Imtiyaz , Marra Giancarlo , Schlapbach Ralph , Patrignani Andrea , Künzli Marzana , Wagner Ulrich , Sabates Jacob , Dutt Amit
Published: June 2006

The role of the natural dietary flavonoid chemical quercetin (an antioxidant) in the prevention and treatment of colon cancer is receiving a great deal of attention. However, little is known about the molecular mechanisms of action of this flavonoid. In the present study, whole genome DNA microarrays were used to evaluate the effect of quercetin on gene expression in the CO115 colon‐adenocarcinoma cell line with the completely deleted chromosome 18 harbouring the SMAD4 tumour‐suppressor gene related to colon carcinogenesis. The study demonstrated that quercetin, widely present in fruit and vegetables, inhibited the growth of CO115 cells at 100 μM concentration in both the G1/S and the G2/M phases by modulating cell‐cycle and apoptosis‐related genes. Differential changes in accumulation of transcripts analysed for cells treated with 100 μM quercetin for 24 and 48 h in three independent repeated experiments revealed 5060–7000 differentially expressed genes. This means that quercetin probably does have a broad modulatory effect on gene expression in colon cancer. Out of these differentially expressed genes, the expression of 35 and 23 unique set of genes involved in cell‐cycle control, apoptosis and xenobiotic metabolism were significantly altered after 24 and 48 h quercetin treatment respectively. Our results represent a novel aspect of the biological profile of quercetin that induces cell‐cycle arrest through modulation of cell‐cycle‐related and apoptosis genes. The present study demonstrates a new step in elucidating the underlying molecular mechanisms of the antitumour action of quercetin, which could become a chemopreventive or chemotherapeutic agent for colon cancer.
Characterization and biological properties of L‐HGP, a glycoprotein from the amphibian oviduct with acrosome‐stabilizing effects
Authors: Krapf Darío , Vidal Marcos , Arranz Silvia E. , Cabada Marcelo O.
Published: June 2006

Background information. The role of the jelly coat that surrounds the amphibian oocytes has been widely discussed, but is poorly understood. The presence of the jelly coat is essential for fertilization. However, the structure and function of the molecules that comprise the jelly coat have not been thoroughly documented. L‐HGP (low‐molecular‐mass highly glycosylated protein) is a highly glycosylated protein that is present in the jelly coat of the toad, Bufo arenarum, oocytes and diffuses to the surrounding media. L‐HGP, when purified from egg water, protects the sperm acrosome from breakdown induced by hypotonic solutions.

Results. L‐HGP is an acidic glycoprotein, formed by two different subunits, linked by disulphide bonds. We raised polyclonal antibodies in rabbits against the deglycosylated protein. We determined that L‐HGP is secreted along the oviduct, being hence present in all the jelly layers. The molecular mass of L‐HGP is higher in the most cephalic region of the oviduct. The lower‐Mr L‐HGP isoform, produced in the caudal regions of the oviduct, presents an acrosome‐protecting property. L‐HGP is produced by secretory cells in the oviduct and is deposited on the cilia at the oviduct lumen.

Conclusions. Biochemical characterization of L‐HGP has been carried out. It is synthesized by secretory cells in the oviduct and, when secreted, is deposited over the ciliated surface of the cells. The lower‐Mr isoform, secreted by the caudal region of the oviduct, protects acrosome integrity. This isoform diffuses into the medium. The role of the higher‐Mr L‐HGP isoform in fertilization remains unknown.
Effects of hypo‐osmotic stress on ATP release in isolated turbot (Scophthalmus maximus) hepatocytes
Authors: Ollivier Hélène , Pichavant‐Rafini Karine , Puill‐Stephan Eneour , Calvès Patrick , Nonnotte Liliane , Nonnotte Guy
Published: June 2006

Background information. ATP is released from many cell types exposed to hypo‐osmotic shock and is involved in RVD (regulatory volume decrease). Purinergic signalling events have been extensively investigated in mammals, but not in marine teleosteans.

Results. The effect of hypo‐osmotic shock on ATP release was examined in isolated hepatocytes from turbot (Scophthalmus maximus), a marine flatfish. Hypo‐osmotic stress (240 mOsm·kg−1) induced a significant increase in ATP efflux, and was inhibited by a potential CFTR (cystic fibrosis transmembrane conductance regulator) inhibitor, glibenclamide, but not by the MDR1 (multidrug resistance 1) P‐glycoprotein inhibitor, verapamil. ATP efflux could be a cAMP‐dependent process, as IBMX (isobutylmethylxanthine) and forskolin triggered the process under iso‐osmotic conditions. Protein kinases, including protein kinase C, could also be involved, as staurosporine and chelerythrine inhibited the mechanism. Calcium could contribute to ATP efflux as ionomycin, a calcium ionophore, elicited a rapid release under iso‐osmotic conditions, and chelation using EGTA abolished ATP release under hypo‐osmotic conditions. RVD was partially abolished by apyrase, an ATP scavenger, and suramin, a purinoceptor antagonist. Moreover, hypo‐osmotic shock induced a rise in intracellular calcium which could be involved in RVD. Since extracellular ATP triggered an increase in cellular free‐calcium content under iso‐osmotic conditions, our results could indicate that hypo‐osmotic‐induced ATP efflux contributes to RVD in turbot hepatocytes by stimulating purinergic receptors, which may lead to activation of a calcium signalling pathway.

Conclusions. These data provide the first evidence of volume‐sensitive ATP signalling for volume maintenance in a marine teleost fish cell type.
Damage analysis in Al thin films fatigued at ultrahigh frequencies
Authors: Eberl Christoph , Spolenak Ralph , Kraft Oliver , Kubat Franz , Ruile Werner , Arzt Eduard
Published: June 2006

A quantitative damage analysis provides insight into the damage mechanisms and lifetimes of aluminum thin films fatigued at ultrahigh frequencies. Surface acoustic wave test devices were used to test continuous and patterned Al thin films up to more than 1014cycles. The analysis revealed increasing extrusion and void formation concentrated at grain boundaries. This finding and the observed grain growth indicate a high material flux at the grain boundaries induced by the cyclic load. A correlation between device degradation and defect density is established which is explained by a theoretical model. For stress amplitudes as low as 14MPa lifetime measurements showed no fatigue limit for 420nm Al thin films.
Ferromagnetic resonance investigations on Ga0.965Mn0.035As film
Authors: Balascuta S. , Liu X. , Baxter D. V. , Carini J. , Wojtowicz T. , Sasaki Y. , Furdyna J. , Chipara M.
Published: June 2006

Ferromagnetic resonance studies of the temperature dependence of magnetic anisotropies in a Ga0.965Mn0.035As film between 5 and 40K are reported. The in-plane and out-of-the-plane angular dependences of the resonance field were analyzed within the Landau-Lifshitz-Gilbert approach. The second- and fourth-order magnetic anisotropy energies were derived. The temperature dependence of magnetization and of magnetic anisotropy were studied by superconducting quantum interference device and ferromagnetic resonance.
Front-to-end simulations of the design of a laser wakefield accelerator with external injection
Authors: Urbanus W. H. , van Dijk W. , van der Geer S. B. , Brussaard G. J. H. , van der Wiel M. J.
Published: June 2006

We report the design of a laser wakefield accelerator (LWA) with external injection by a rf photogun and acceleration by a linear wakefield in a capillary discharge channel. The design process is complex due to the large number of intricately coupled free parameters. To alleviate this problem, we performed front-to-end simulations of the complete system. The tool we used was the general particle-tracking code, extended with a module representing the linear wakefield by a two-dimensional traveling wave with appropriate wavelength and amplitude. Given the limitations of existing technology for the longest discharge plasma wavelength (∼50μm) and shortest electron bunch length (∼100μm), we studied the regime in which the wakefield acts as slicer and buncher, while rejecting a large fraction of the injected bunch. The optimized parameters for the injected bunch are 10pC, 300fs at 6.7MeV, to be injected into a 70mm long channel at a plasma density of 7×1023m−3. A linear wakefield is generated by a 2TW laser focused to 30μm. The simulations predict an accelerated output of 0.6pC, 10fs bunches at 90MeV, with energy spread below 10%. The design is currently being implemented. The design process also led to an important conclusion: output specifications directly comparable to those reported recently from “laser-into-gas jet” experiments are feasible, provided the performance of the rf photogun is considerably enhanced. The paper outlines a photogun design providing such a performance level.
First-principles potential energy surfaces and vibrational states of H∕Rh(111) at 0.25 and 1 monolayer coverages
Authors: Ke Zhihong , Lai Wenzhen , Xie Daiqian , Zhang Dong Hui
Published: June 2006

Density functional theory calculations based on plane-wave expansion and a pseudopotential treatment have been carried out for atomic hydrogen adsorbed on Rh(111) at 0.25 and 1 monolayer (ML) coverages. The preferred binding site for hydrogen was found to be the fcc hollow site. The global three-dimension potential energy surfaces were obtained by spline interpolation. The calculated hydrogen diffusion barrier of 121meV at 0.25ML agrees well with the experimental result of 140meV at 0.3ML. The vibrational wave functions and the corresponding energies for atomic hydrogen on the calculated potentials were calculated by using the discrete variable representation and Lanczos method. The calculated results showed that the low-lying vibrational states exhibit strong localized characters, whereas the higher states show significant delocalized characters. The calculated vibrational frequencies agree well with the recent available experimental values. Particularly, the calculated blueshift of 10.6 (7.2)meV for the vibrational excitation parallel to the metal surface when the H(D) coverage is changed from 0.25ML to 1ML is in excellent agreement with the observed value of 11 (7)meV.
Production of O2(Δ1) in flowing plasmas using spiker-sustainer excitation
Authors: Babaeva Natalia Y. , Arakoni Ramesh A. , Kushner Mark J.
Published: June 2006

In chemical oxygen iodine lasers (COILs), oscillation at 1.315μm in atomic iodine (P1∕22→P3∕22) is produced by collisional excitation transfer of O2(Δ1) to I2 and I. Plasma production of O2(Δ1) in electrical COILs (eCOILs) eliminates liquid phase generators. For the flowing plasmas used for eCOILs (He∕O2, a few to tens of torr), self-sustaining electron temperatures, Te, are 2–3eV whereas excitation of O2(Δ1) optimizes with Te=1–1.5eV. One method to increase O2(Δ1) production is by lowering the average value of Te using spiker-sustainer (SS) excitation where a high power pulse (spiker) is followed by a lower power period (sustainer). Excess ionization produced by the spiker enables the sustainer to operate with a lower Te. Previous investigations suggested that SS techniques can significantly raise yields of O2(Δ1). In this paper, we report on the results from a two-dimensional computational investigation of radio frequency (rf) excited flowing He∕O2 plasmas with emphasis on SS excitation. We found that the efficiency of SS methods generally increase with increasing frequency by producing a higher electron density, lower Te, and, as a consequence, a more efficient production of O2(Δ1).
Infrared optical properties of MgxZn1−xO thin films (0⩽x⩽1): Long-wavelength optical phonons and dielectric constants
Authors: Bundesmann C. , Rahm A. , Lorenz M. , Grundmann M. , Schubert M.
Published: June 2006

Infrared spectroscopic ellipsometry in the spectral range from ω=360cm−1toω=1500cm−1 and Raman scattering spectroscopy are applied to study the long-wavelength optical phonon modes and dielectric constants of MgxZn1−xO thin films in the composition range 0⩽x⩽1. The samples were grown by pulsed laser deposition on sapphire substrates. X-ray diffraction measurements of the thin film samples reveal the hexagonal wurtzite crystal structure for x⩽0.53 and the cubic rocksalt crystal structure for x⩾0.67. A systematic variation of the phonon mode frequencies with Mg-mole fraction x is found for both hexagonal and cubic MgxZn1−xO thin films. The modified random isodisplacement model matches the observed composition dependence of the phonon mode frequencies for the hexagonal structure thin films [J. Chen and W. Z. Shen, Appl. Phys. Lett. 83, 2154 (2003)], whereas a simple linear approximation scheme is sufficient for the cubic structure part. We observe a discontinuous behavior of the transverse optical phonon modes (decrease), and the static and high-frequency dielectric constants (increase) within the phase transition composition region from the wurtzite structure part to the rocksalt structure part. On the contrary, the longitudinal phonon mode parameters increase almost linearly, and upon phase transition the splitting between the transverse and longitudinal modes increases. We associate this discontinuous behavior with the change of the nearest-neighbor coordination number from fourfold (wurtzite structure) to sixfold (rocksalt structure) in our samples and the associated increase in bond ionicity from ZnO to MgO. Accordingly, we propose that the reduced exciton mass parameter should approximately double upon changing from wurtzite to rocksalt crystal structure.
Fe
57
Mössbauer study of L10 ordering in Fe57∕Pt multilayers
Authors: Raghavendra Reddy V. , Kavita S. , Gupta Ajay
Published: June 2006

The magnetic and structural properties of equiatomic FePt alloy obtained from the thermal annealing of [Fe57(19Å)∕Pt(25Å)]×10 multilayer have been studied as a function of vacuum annealing at different temperatures. The multilayers are prepared by ion beam sputtering. X-ray reflectivity (XRR), x-ray diffraction (XRD), magneto-optical Kerr effect, and conversion electron Mössbauer spectroscopy are used to characterize the as-deposited and annealed multilayers. Using XRR it is observed that due to intermixing FePt alloy formation takes place with annealing. The XRD indicated the presence of superstructure peaks due to fct FePt phase at 350°C and above. Mössbauer measurements indicated a clear evidence for the strong exchange coupling between the soft fcc FePt and hard fct FePt phases. The results indicate that the multilayer structure does not transform directly to the ordered fct FePt, rather first a fcc FePt phase is formed and subsequently it gets converted into the fct FePt phase as a function of annealing.
Influence of residual oxygen impurity in quaternary InAlGaN multiple-quantum-well active layers on emission efficiency of ultraviolet light-emitting diodes on GaN substrates
Authors: Kyono Takashi , Hirayama Hideki , Akita Katsushi , Nakamura Takao , Adachi Masahiro , Ando Koshi
Published: June 2006

The influence of residual impurities in quaternary InAlGaN active layers on the emission efficiency of 350nm band ultraviolet light-emitting diodes on GaN substrates has been investigated. Secondary ion mass spectrometry and capacitance-voltage measurements have revealed that a large amount of oxygen is incorporated into the InAlGaN active layers owing to relatively low growth temperatures for Al-content epitaxial films. The increase of the InAlGaN growth temperature from 780to830°C results in both the residual oxygen level decrease from 1×1018to4×1017cm−3 and the output power improvement from 0.6to2.6mW at 100mA. It is also found that devices containing lower oxygen concentration in the InAlGaN active layers demonstrate a higher electroluminescence intensity ratio of the band-edge emission from the well layers to the donor-acceptor-pair emission from the p-type layers at low temperatures. These experimental results, in conjunction with numerical calculations, suggest that the reduction in the oxygen impurity level in the InAlGaN active layers has an effect on suppressing the electron leakage current into the p-type layers, and thus improving the internal quantum efficiency of InAlGaN-based ultraviolet light-emitting diodes.
Defect behavior in rare earth REAlO3 scintillators
Authors: Stanek C. R. , McClellan K. J. , Levy M. R. , Grimes R. W.
Published: June 2006

The aluminate perovskites YAlO3 (YAP) and LuAlO3 (LuAP) have been identified as potential scintillator materials due to their high light output and short decay time. However, the performance of these materials is significantly reduced by point defects. In this paper, atomistic simulations provide insight into the types of point defects that are expected under various conditions in YAP and LuAP, as well as other REAlO3 compounds (where RE denotes a rare earth ion ranging from Lu to La or Y). For example, we predict that cation antisites are the dominate intrinsic defect for smaller REAlO3 compounds, with the concentration of Schottky-type defects increasing for compounds with larger RE ions. We also predict that cation vacancies will be present in association with the oxidation of the Ce activator. From these results, we show how defects affect different aspects of the scintillation process. Our aim is to provide information that can be used to aid in the intelligent optimization of this family of scintillator compounds.
Macroporous silicon: Homogeneity investigations and fabrication tolerances of a simple cubic three-dimensional photonic crystal
Authors: Matthias Sven , Hillebrand Reinald , Müller Frank , Gösele Ulrich
Published: June 2006

Large area three-dimensional (3D) photonic crystals have been fabricated either by layer-by-layer methods, colloidal self-assembly, or by macroporous silicon etching. The last mentioned method has proven to be a versatile and fast technique to manufacture simple cubic 3D photonic crystals, having a complete photonic band gap with a width of 4.99% in the infrared spectral range. This report is focused on the investigation of their homogeneity and additional numerical simulations concerning the tolerable disorder allowing still for a complete photonic band gap. Fabry-Pérot resonators, which are realized by 3D photonic crystals containing planar defects, are characterized optically in spatially resolved transmission measurements by scanning infrared Fourier spectroscopy. The impact of the observed inhomogeneities on the complete photonic band gap is studied in detail by modeling the influence of structural parameters. Fabrication tolerances for the simple cubic arrangement of intersecting air spheres in silicon are deduced.
Combinatorial synthesis of Co∕Pd magnetic multilayers
Authors: E Chunsheng , Smith Darren , Svedberg Erik , Khizroev Sakhrat , Litvinov Dmitri
Published: June 2006

A combinatorial approach to the synthesis of high anisotropy Co∕Pd magnetic multilayer thin films is explored. Combinatorial libraries of Co∕Pd multilayer thin films were prepared using magnetron sputtering where the thicknesses of Co and Pd layers in the bilayer stack are varied. Application of multivariate regression and neural network models to the analysis of Co∕Pd multilayer combinatorial libraries is studied and the predictive capabilities of the two models are compared. The influences of the thicknesses of Co and Pd layers on magnetic properties are investigated. The models are used to design Co∕Pd multilayers with the desired magnetic properties. It is found that the neural network model enables higher accuracy than the multivariate analysis model and that the inverse design problem produces results within a good degree of precisions.
Nonparabolicity effect on bulk transport properties in wurtzite InN
Authors: Polyakov V. M. , Schwierz F.
Published: June 2006

We investigate the transient and steady-state electron transport properties in bulk wurtzite InN using the ensemble Monte Carlo method. The main emphasis is given to the origin of the negative differential mobility of the steady-state velocity-field characteristics and of the strong transient velocity overshoot. In general, these effects can be caused by intervalley transfer and by the nonparabolicity of the main valley of the conduction band. We analyze the relative importance of these two mechanisms and demonstrate that in wurtzite InN the negative differential mobility and drift velocity overshoot are governed by the strong nonparabolicity of the central valley.
Epitaxial pentacene films grown on the surface of ion-beam-processed gate dielectric layer
Authors: Chou W. Y. , Kuo C. W. , Cheng H. L. , Mai Y. S. , Tang F. C. , Lin S. T. , Yeh C. Y. , Horng J. B. , Chia C. T. , Liao C. C. , Shu D. Y.
Published: June 2006

The following research describes the process of fabrication of pentacene films with submicron thickness, deposited by thermal evaporation in high vacuum. The films were fabricated with the aforementioned conditions and their characteristics were analyzed using x-ray diffraction, scanning electron microscopy, polarized Raman spectroscopy, and photoluminescence. Organic thin-film transistors (OTFTs) were fabricated on an indium tin oxide coated glass substrate, using an active layer of ordered pentacene molecules, which were grown at room temperature. Pentacene film was aligned using the ion-beam aligned method, which is typically employed to align liquid crystals. Electrical measurements taken on a thin-film transistor indicated an increase in the saturation current by a factor of 15. Pentacene-based OTFTs with argon ion-beam-processed gate dielectric layers of silicon dioxide, in which the direction of the ion beam was perpendicular to the current flow, exhibited a mobility that was up to an order of magnitude greater than that of the controlled device without ion-beam process; current on/off ratios of approximately 106 were obtained. Polarized Raman spectroscopy investigation indicated that the surface of the gate dielectric layer, treated with argon ion beam, enhanced the intermolecular coupling of pentacene molecules. The study also proposes the explanation for the mechanism of carrier transportation in pentacene films.
Rashba spin splitting in parabolic quantum dots
Authors: Lee Johnson , Spector Harold N. , Chou Wu Ching , Chu Chon Saar
Published: June 2006

We have investigated the effect of the Rashba spin splitting and a magnetic field on the energy levels of electrons in parabolic quantum dots. We find that with an increase in the Rashba parameter, the spin-orbit interaction mixes states of higher angular momentum together. In the absence of a magnetic field, the energy levels of the electrons are doubly degenerate and decrease as the Rashba parameter increases. In the presence of a magnetic field, this degeneracy is removed and the energy splitting of the spin states increases with the increase in both the Rashba parameter and the magnetic field. The Fermi energy level as a function of the magnetic field shows oscillatory behavior due to the crossings between the energy levels of the system. The magnetization of the electron gas is investigated and shows strong oscillations with the magnetic field for large values of the Rashba parameter.
Application of Gaussian-type geminals in local second-order Møller-Plesset perturbation theory
Authors: Polly Robert , Werner Hans-Joachim , Dahle Pål , Taylor Peter R.
Published: June 2006

In this work Gaussian-type Geminals (GTGs) are applied in local second-order Møller-Plesset perturbation theory to improve the basis set convergence. Our implementation is based on the weak orthogonality functional of Szalewicz et al., [Chem. Phys. Lett. 91, 169 (1982); J. Chem. Phys. 78, 1420 (1983)] and a newly developed program for calculating the necessary many-electron integrals. The local approximations together with GTGs in the treatment of the correlation energy are introduced and tested. First results for correlation energies of H2O, CH4, CO, C2H2, C2H4, H2CO, and N2H4 as well as some reaction and activation energies are presented. More than 97% of the valence-shell correlation energy is recovered using aug-cc-pVDZ basis sets and six GTGs per electron pair. The results are compared with conventional calculations using correlation-consistent basis sets as well as with MP2-R12 results.
Enhancement of the photoluminescence properties of porous silicon by silica gel coating
Authors: Posada Y. , Fonseca L. F. , Vallejo P. , San Miguel L. , Resto O. , Balberg I.
Published: June 2006

We have spin coated silica gel films of ∼10μm onto porous silicon (PS) substrates with photoluminescence (PL) emissions peaks in the 600–700nm spectral range, producing a 20-fold enhancement of the original intensity in the shorter wavelength end. We attribute this enhancement to the reduced nonradiative recombination that follows the interface passivation of the PS surfaces by an oxygen enriched SiOx (x→2) layer of silica gel. The PL stability of enhanced substrates was significantly improved by sputtering the samples with SiO2 after the silica gel spin coating, which resulted in a final blueshift of the PL. The technique described herein is a cost effective method for producing passivated photoluminescent enhanced silicon structures that can be used for optoelectronic applications.
Phase grating using a ferroelectric liquid-crystal mixture with a photocurable liquid crystal
Authors: Matsumoto Shin , Goto Masanao , Choi Suk-Won , Takanishi Yoichi , Ishikawa Ken , Takezoe Hideo , Kawamura George , Nishiyama Isa , Takada Hirokazu
Published: June 2006

We fabricated a switchable phase grating utilizing a ferroelectric liquid crystal (FLC) mixed with a photocurable liquid crystal using a simple one-step process, i.e., photoirradiation to a uniformly aligned FLC cell through a photomask. A fast response of the order of 1ms was demonstrated for the switching process between the nonswitched and the fully switched states. The polarization dependence emerges during the switching of molecules, although the polarization independence is achieved in fully switched states. In the switching process, molecules cooperatively rotate on a cone; i.e., they tilt with respect to the layer normal and change the azimuthal angle. Based on this switching model, the diffraction was simulated in the framework of the Jones matrix and diffraction theory. The simulation reproduced the characteristics experimentally observed.
Decomposition of three volatile organic compounds by nanosecond pulsed corona discharge: Study of by-product formation and influence of high voltage pulse parameters
Authors: Jarrige Julien , Vervisch Pierre
Published: June 2006

Increasing concerns over atmospheric pollution has motivated research into technologies able to remove volatile organic compounds (VOC’s) from gas streams. The aim of this paper is to understand the chemical and physical mechanisms implied in the decomposition of VOC’s in a filamentary nonthermal plasma discharge. Experiments have been carried out on three pollutants (propane, propene, and isopropyl alcohol) in dry air at atmospheric pressure using a wire to cylinder corona discharge generated by a homemade nanosecond rise time high voltage pulse generator. The resulting plasma efficiently destructs propane, propene, or isopropyl alcohol at a concentration of 500ppm with low specific input energies (less than 500J∕L), but the poor oxidation rate leads to the formation of numerous by-products (acetone, formaldehyde, formic acid, and methyl nitrate) whose concentration can reach some hundreds of ppm. We also investigated the effect of pulse parameters on VOC removal efficiency. Neither pulse peak value nor rise time (in the range of 4–12ns) appears to have a significant influence on the VOC decomposition rates. Therefore, we believe that the way the energy is deposited in the plasma does not modify the density of active species (radicals, ions) in the streamers. The production of energetic electrons is not enhanced by the external applied field, and the only effective parameter may be the local field in the streamer head, which is almost the same (around 500Td) whatever the voltage (above the inception value).
Circulation of fluids induced by self-acting laser beam
Authors: Sarkisov Sergey S.
Published: June 2006

Circulation was induced by a 20mW red He–Ne laser beam in two strongly absorbing solutions of 2,9,16,23-Tetrakis(phenylthio)-29H,31H-phthalocyanine in chlorobenzene, the second being 42 times more viscous due to a polymer additive. When the beam passed horizontally through solution 1, a squeezed diffraction ring pattern was observed on a screen, indicating circulation of the fluid. In solution 2, the rings were perfectly circular. These results were confirmed when the fluid circulation was seen with the aid of shiny particles only in solution 1. When the beam passed vertically through solution 1, an ordered set of Benard-Rayleigh convection cells was observed [J. K. Bhattacharjee, Convection and Chaos in Fluids (World Scientific, Singapore, 1989)]. The conditions, including the induced temperature difference, for the initiation of convection were analyzed. An induced temperature difference of less than 1°C at the beam center was enough to initiate the convection.
Silicon quantum dot superlattices: Modeling of energy bands, densities of states, and mobilities for silicon tandem solar cell applications
Authors: Jiang Chu-Wei , Green Martin A.
Published: June 2006

Quantum dot superlattices offer prospects for new generations of semiconductor devices. One possible recently suggested application is in tandem solar cells based entirely on silicon, using confinement in the quantum dot to control the cell band gap. In this paper, we use the effective mass approach to calculate the conduction band structure of a three-dimensional silicon quantum dot superlattice with the dots embedded in a matrix of silicon dioxide, silicon nitride, or silicon carbide. The quantum dot superlattice is modeled as a regularly spaced array of equally sized cubic dots in the respective matrix. Incorporating the effect of silicon anisotropic effective mass is shown to reduce both the degeneracies of the isotropic solutions and the energy separation between states. Electron densities of state and mobilities are derived from the band structure data. Theoretical results for the effect of dot size, interdot distance, and matrix material have been obtained. These results clarify the required design features of silicon quantum dot superlattices for the proposed all-silicon tandem solar cells.
Temperature dependence of the optical properties in GaMnN
Authors: Guo L. L. , Shen W. Z. , Zhang Y. H.
Published: June 2006

Temperature-dependent transmission measurements are carried out on ion-implanted GaMnN with different Mn-implantation doses. With a detailed procedure developed for analyzing the transmission spectra, we obtain the temperature effects in optical properties of GaMnN (including GaN), such as absorption coefficient, band gap, Urbach band tail characteristics, refractive index, and extinction coefficient. Two sets of temperature- and photon energy-dependent empirical formulas are established, which not only unify the various experimental data reported in the literature, but also provide an experimental database of optical properties in GaMnN. Furthermore, we reveal that the dependence of these optical properties on the Mn-implantation doses is closely related to the impact of Mn on the crystal structure.
Effect of chemical structure on the volume-phase transition in neutral and weakly charged poly(N-alkyl(meth)acrylamide) hydrogels studied by ultrasmall-angle x-ray scattering
Authors: Tirumala Vijay R. , Ilavsky Jan , Ilavsky Michal
Published: June 2006

Neutral poly(N-isopropylacrylamide) (PIPAAm), poly(N,N-diethylacrylamide) (PDEAAm), and poly(N-isopropylmethacrylamide) (PIPMAm) hydrogels and their weakly charged counterparts prepared by copolymerizing with sodium methacrylate (xMNa=0,0.025,0.05) were studied using ultrasmall-angle x-ray scattering. The volume-phase transition in hydrogels was observed as an increase in the inhomogeneity correlation length of the networks. The change in inhomogeneity correlation length was abrupt in neutral PIPAAm and PIPMAm gels with increase in temperature but was continuous in neutral PDEAAm gels. Addition of ionic comonomer to the network backbone suppressed the volume-phase transition in poly(N-alkylacrylamide)s but not in PIPMAm. The observed differences in temperature-induced volume change of these three polymers in water cannot be rationalized based on their relative hydrophobicity and are instead explained by considering the hydrogen-bonding constraints on their thermal fluctuations. Both PIPAAm and PDEAAm undergo volume collapse since their thermal fluctuations are constrained by hydrogen bonding with water to an extent that beyond a critical temperature they seek entropic compensation. Although thermal fluctuations in both PIPAAm and PIPMAm are equally constrained, thermal energy of the latter can be relaxed via the rotation of α-methyl groups allowing it greater flexibility. Compared to N-alkylacrylamides, N-alkylmethacrylamide can thus sustain hydrogen bonding to relatively higher temperatures before seeking entropic compensation by undergoing volume collapse.
New technique for visualizing microboiling phenomena and its application to water pulse heated by a thin metal film
Authors: Avedisian C. Thomas , Cavicchi Richard E. , Tarlov Michael J.
Published: June 2006

This article presents a laser strobe microscopy method for photographing fast transient microscale processes. The technique is illustrated by capturing time-lapsed images of bubble nucleation from pulse-heated thin films immersed in a pool of water. The method combines a pulsed laser for the light source and a microscope with 100× magnification of a heater element (platinum film, 30μm long, 15μm wide, and 0.2μm thick), and associated instrumentation to coordinate the laser pulse with the electrical pulse at various delay times to step through the evolutionary process of the phase change. The emphasis of this article is on describing the experimental method and illustrating its capabilities to record the nucleation and growth of microbubbles. Results are presented for bubble nucleation and morphology in subcooled water for electrical (heating) pulses with duration ranging from 0.50 to 1μs. The repeatability of the process, which is an essential requirement for obtaining meaningful information on the evolution of the phase change process, is demonstrated which allows high effective framing rates to be achieved (>108s−1) using a pulsed light source with a controlled delay. New bubble morphologies are shown. For 0.5μs pulses, bubbles appear to nucleate first at the corners of the heater followed by lateral coalescence and spreading to form a thin vapor film which later thickens on the heater footprint and evolves into an oblate spheroidal shape. For 1μs pulses, individual bubbles are observed which appear at specific nucleation “sites” that may indicate surface imperfections typical of nucleate boiling processes even though the superheat is close to the superheat limit of water.
Design of Q-band loop-gap resonators at frequencies of 34–36GHz for single electron spin spectroscopy in semiconductor nanostructures
Authors: Simovič B. , Studerus P. , Gustavsson S. , Leturcq R. , Ensslin K. , Schuhmann R. , Forrer J. , Schweiger A.
Published: June 2006

We report on the design of loop-gap resonators operating in the frequency range of 34–36GHz with the goal to achieve single electron spin resonance in quantum dot nanostructures. We present a comprehensive study of the magnetic field strength and the spatial distribution of the electric and magnetic fields in the resonator by means of experiments and numerical simulations.