bluuebunny/crossref_metadata_2025 huggingface dataset:
Mature tree effect of Acer mono on seedling mortality due to insect herbivory
Authors: Maetô Kaoru , Fukuyama Kenji
Published: December 2006

Mature tree effects on the mortality and herbivory of current‐year seedlings were investigated in a common subcanopy species, Acer mono Maxim., in a cool temperature mixed forest. The mortality of natural seeldings under the canopy with A. mono layers was greater than that under the canopy without them. Also, the mortality of seedlings in planters located under the crown of an A. mono tree was at least 1.8 times greater than that of those in planters about 5 m away from the crown edge. Pyrrhalta fuscipennis (Coleoptera: Chrysomelidae) and other specialist insects, having probably dropped from A. mono crowns, were more frequently observed in planters under A. mono crowns than in those far the crowns. Leaf area loss due to specialist herbivores was probably the main cause of increase in the mortality of A. mono seedlings close to conspecific adults. It is implied that seedling predation by specialist herbivores coming from parent trees is a substantial factor promoting local seed dispersal of A. mono.
Increased lipolysis in LCHAD deficiency
Authors: Halldin M. U. , Forslund A. , von Döbeln U. , Eklund C. , Gustafsson J.
Published: December 2006

An increasing number of fatty acid oxidation defects are being detected owing to diagnostic improvements and a greater awareness among clinicians. The metabolic block leads to energy disruption, fatty infiltration, and toxic effects on organ functions exerted by β‐oxidation metabolites. This investigation was undertaken to assess the influence of long‐chain 3‐hydroxyacyl‐CoA dehydrogenase (LCHAD) deficiency on lipolysis and energy turnover. We addressed the question whether the lipolysis and glucose production rates would be altered in the fasting state in a child with this disease. Lipolysis, glucose production and resting energy expenditure (REE) were studied in a 17‐month‐old girl with LCHAD deficiency and her healthy twin sister. Lipolysis and glucose production were determined after a 4–6 h fast by constant‐rate infusion of [1,1,2,3,3‐2H5]glycerol and [6,6‐2H2]glucose and analysis by gas chromatography–mass spectrometry. REE was estimated by indirect calorimetry. The affected girl showed 50% higher lipolysis than did her sister, whereas the glucose production rates were similar. Plasma levels of dicarboxylic acids of 6–12 carbon atoms chain length, 3‐hydroxy fatty acids of 6–18 carbon atoms chain length, total free fatty acids, and acylcarnitines were increased in the patient, as was REE. Since glucose production rates and plasma glucose levels were similar in the two girls, the increased lipolysis observed in the patient probably represents a compensatory mechanism for energy generation. This is achieved at the price of an augmented risk for fatty acid infiltration and toxic effects of β‐oxidation intermediates. This highlights the importance of avoiding fasting in these patients.
Effect of land use conversion on soil organic carbon sequestration in the loess hilly area, loess plateau of China
Authors: Chen Liding , Gong Jie , Fu Bojie , Huang Zhilin , Huang Yilong , Gui Lide
Published: December 2006

Changes in land use may alter land cover, which results in carbon stock changes in biomass as well as in the soil. In China's loess plateau, vegetation restoration has been conducted since 1950s to control soil erosion and improve the ecosystem, with significant investment of money and manpower. Despite these efforts, soil erosion has still been severe. To reduce soil erosion and improve land quality, China initiated another state‐funded project, Grain‐for‐Green, in 1999 in the loess plateau. However, it is not clear how effective this newly initiated project will be. In this study, we evaluated the effect of land‐use conversion on soil organic carbon (SOC) and the potential effect of the current project on SOC sequestration in the Anjiapo catchment area of the loess hilly area of the loess plateau in China. This evaluation is based on SOC measurements in cropland versus in other converted land use types. We found that SOC sequestration mainly occurred in the surface soil after land use conversion took place. Land use conversion from cropland to shrubland or wild grassland (i.e. undisturbed land) was better for SOC sequestration than tree plantation in the semi‐arid loess hilly area. By using the land use change in the study area as a scenario, the potential contribution of land use change on SOC sequestration due to the Grain‐for‐Green project was estimated. It was found that this project in the loess plateau of China would be helpful for SOC sequestration if successfully implemented.
Bone Mineral Density Determinations by Dual-Energy x-ray Absorptiometry in the Management of Patients with Marfan Syndrome—Some Factors Which Affect the Measurement
Authors: Giampietro Philip F. , Peterson Margaret G. E. , Schneider Robert , Davis Jessica G. , Burke Stephen W. , Boachie-Adjei Oheneba , Mueller Charles M. , Raggio Cathleen L.
Published: December 2006

Reduced bone mineral density (BMD) was sporadically reported in patients with Marfan syndrome. This may or may not place the Marfan patient at increased risk for bone fracture. In comparing the BMDs of our patients with those reported in the literature, it seemed that agreement between values, and hence the degree of osteoporosis or osteopenia reported, was dependent on the instrumentation used. The objective of this study was to statistically assess this impression. Bone mineral density measurements from our previously published study of 30 adults with Marfan syndrome performed on a Lunar DPXL machine were compared with studies published between 1993–2000 measured using either Lunar or Hologic bone densitometry instruments. The differences of our measurements compared with those made on other Lunar machines were not statistically significant, but did differ significantly with published results from Hologic machines ( P < 0.001). Before progress can be made in the assessment of BMD and fracture risk in Marfan patients and in the evidence-based orthopedic management of these patients, standardization of instrumental bone density determinations will be required along with considerations of height, obesity, age, and sex.
Epidemiology of specific phobia subtypes: Findings from the Dresden Mental Health Study
Authors: Becker Eni S. , Rinck Mike , Türke Veneta , Kause Petra , Goodwin Renee , Neumer Simon , Margraf Jürgen
Published: December 2006

This study determined the prevalence, age of onset, comorbidity, and impairment associated with specific phobia subtypes in the community. Data were drawn from the Dresden Mental Health Study (N = 2064), a representative community-based sample of young women in Dresden, Germany. The lifetime prevalence of any specific phobia was 12.8%, with subtypes ranging in prevalence between 0.2% (vomiting, infections) and 5.0% (animals). There were significant differences in the mean age of onset of specific phobias. Significant differences in comorbidity patterns also emerged between subtypes. No significant differences were found in level of impairment associated with the subtypes. The findings suggest that specific phobias are common among young women and that they differ in prevalence, associated comorbidity, and mean age of onset. These data suggest significant differences in the phenomenology and clinical significance of specific phobia subtypes.
Overrepresentation of interactions between homologous proteins in interactomes
Authors: Orlowski Jerzy , Kaczanowski Szymon , Zielenkiewicz Piotr
Published: December 2006

It is well proved that the probability that a protein interacts with itself is higher than that it interacts with another protein. It has been recently shown that the probability of interaction is also higher for proteins with significant sequence similarity. In this paper we show that proteins sharing identical PFAM domains interact more often than expected by chance in Saccharomyces cerevisiae and Escherichia coli. We also analyze the variety of domain interfaces used by homologous proteins to interact and show that the overrepresentation of interactions between homological proteins is not caused by small number of pairs of identical “sticky domains” shared between interacting proteins.
The worldwide burden of postpartum haemorrhage: Policy development where inaction is lethal
Authors: Potts Malcolm , Hemmerling Anke
Published: December 2006

Most maternal deaths occur to women who are not attended by trained health professionals. Postpartum hemorrhage is the single most common cause of maternal death. The delivery of large haemochorial placenta in our species predisposes to heavy bleeding and can be dealt with only by using effective uterotonics. The 1987 Safe Motherhood Initiative has failed to reduce maternal mortality significantly, and shortages of trained personnel will not be remedied in the foreseeable future. Bold new policies are imperative and need to be derived from an appropriate evidence base. It is suggested that these should include the low‐cost shock garments in primary health facilities and making misoprostol easily accessible in both the public and private sector.
Elektrophysiologische Erregungsabläufe - Aktuelle Aspekte der ablativen Therapie von supraventrikulären Herzrhythmusstörungen
Authors: Müller Michael , Sause Armin
Published: December 2006

Die invasive Elektrophysiologie und Katheterablation hat seit der Einführung von hochfrequentem Wechselstrom und steuerbarer Katheter eine enorme Entwicklung erfahren. Seit Anfang der 90er Jahre stellt sie vor allem für supraventrikuläre Rhythmusstörungen (SVT), die eine anatomisch gut definierbare Erregungskreisbahn aufweisen, die Therapie der ersten Wahl dar. Sie hat in vielen Bereichen die medikamentöse Therapie nahezu vollkommen ersetzt.

Durch die Entwicklung neuer dreidimensionaler Bildgebungsverfahren, sowie neuer Ablationsformen (gekühlte Elektrodenspitze, Kryo, Mikrowelle, Laser) kann die individuelle Anatomie des Patienten und dessen elektrophysiologische Erregungsabläufe dargestellt und dadurch auch komplexere Rhythmusstörungen erfolgreich abladiert werden. In diesem Zusammenhang sind derzeit die größten Fortschritte in der Behandlung von Vorhofflimmern zu verzeichnen.
The intermodulation coefficient of an inhomogeneous superconductor
Authors: Kim Kwangmoo , Stroud David
Published: December 2006

The high-Tc cuprate superconductors are now believed to be intrinsically inhomogeneous. We develop a theory to describe how this inhomogeneity affects the intermodulation coefficient of such a material. We show that the continuum equations describing intermodulation in a superconducting layer with spatially varying properties are formally equivalent to those describing an inhomogeneous dielectric with a nonzero cubic nonlinearity. Using this formal analogy, we calculate the effect of inhomogeneity on the intermodulation coefficient in a high-Tc material, using several assumptions about the topology of the layer and some simple analytical approximations to treat the nonlinearity. For some topologies, we find that the intermodulation critical supercurrent density JIMD is actually enhanced compared to a homogeneous medium, thereby possibly leading to more desirable material properties. We discuss this result in light of recent spatial mappings of the superconducting energy gap in BSCCO-2212.
Approximate resonance states in the semigroup decomposition of resonance evolution
Authors: Strauss Y. , Horwitz L. P. , Volovick A.
Published: December 2006

The semigroup decomposition formalism makes use of the functional model for C∙0 class contractive semigroups for the description of the time evolution of resonances. For a given scattering problem the formalism allows for the association of a definite Hilbert space state with a scattering resonance. This state defines a decomposition of matrix elements of the evolution into a term evolving according to a semigroup law and a background term. We discuss the case of multiple resonances and give a bound on the size of the background term. As an example we treat a simple problem of scattering from a square barrier potential on the half-line.
A simulation model for the density of states and for incomplete ionization in crystalline silicon. I. Establishing the model in Si:P
Authors: Altermatt P. P. , Schenk A. , Heiser G.
Published: December 2006

A parametrization of the density of states (DOS) near the band edge of phosphorus-doped crystalline silicon is derived from photoluminescence and conductance measurements, using a recently developed theory of band gap narrowing. It is shown that the dopant band only “touches” the conduction band at the Mott (metal-insulator) transition and that it merges with the conduction band at considerably higher dopant densities. This resolves well-known contradictions between conclusions drawn from various measurement techniques. With the proposed DOS, incomplete ionization of phosphorus dopants is calculated and compared with measurements in the temperature range from 300to30K. We conclude that (a) up to 25% of dopants are nonionized at room temperature near the Mott transition and (b) there exists no significant amount of incomplete ionization at dopant densities far above the Mott transition. In a forthcoming part II of this paper, equations of incomplete ionization will be derived that are suitable for implementation in device simulators.
Nonresonant third-order nonlinearity of antimony glasses at telecom wavelengths
Authors: Gómez Luis A. , de Araújo Cid B. , Messias D. N. , Misoguti L. , Zilio S. C. , Nalin M. , Messaddeq Y.
Published: December 2006

We report measurements of the nonresonant nonlinear refractive index n2 in antimony glasses at telecom wavelengths. The measurements were performed using the Z-scan technique with a 130fs pulsed laser operating at five wavelengths in the range of 1400–1600nm. Values of n2≈10−15cm2∕W were measured and a negligible two-photon absorption coefficient (<0.003cm∕GW) was estimated for all glasses compositions. The samples present a good figure of merit for ultrafast all-optical switching.
Electronic structure and magnetism of Fe4−xMnxN compounds
Authors: Chen Li
Published: December 2006

The electronic structure and magnetism of Fe4−xMnxN compounds have been studied by a periodic quantum-mechanical calculation based on density functional theory. The results show that a ferrimagnetic ordered phase is stable when Fe is substituted by Mn on cube corner sites, whereas the antiferromagnetic phase is energetically favored when Mn substitutes for Fe on face-centered sites. Mn atom concentration and the substitutional sites have significant influence on the exchange coupling. We predict covalent bonds between face-centered Fe or Mn 3d and N 2p orbitals. In contrast, bonding between the atoms at cube corners and face-centered sites is mainly ionic or metallic.
Laser ablation of a platinum target in water. II. Ablation rate and nanoparticle size distributions
Authors: Nichols William T. , Sasaki Takeshi , Koshizaki Naoto
Published: December 2006

This is the second in a series of three papers examining nanomaterial formation in laser ablation in liquids (LAL). Here we study the effect of the laser wavelength and fluence on the mass yield and size distribution of nanoparticles prepared by laser ablation of a platinum target immersed in water. For all wavelengths tested, laser fluences in the range of 10–70J∕cm2 resulted in spheroidal, nonagglomerated platinum nanoparticles with sizes ranging from 1to30nm. Nanoparticle size distributions are found to be composed of two modes that are attributed to thermal vaporization and explosive boiling mechanisms. The peak of the smaller size mode remains nearly constant at 3nm for all laser conditions, which is suggested to be due to the strong confinement of the vapor plume by the liquid. The larger size mode peaks in the range of 5–15nm with a population that is strongly dependent on the laser parameters. It is concluded that changes in the mean size reported in many earlier studies on LAL of metal targets are a result of the relative quantity of nanoparticles from each mechanism rather than direct control over the ablation process. Additionally, it was observed that the yield of platinum nanoparticles was significantly larger for 1064nm wavelength at fluences greater than 10J∕cm2. The maximum ablation rate was approximately 4.4mg∕h, with an estimated ablation and collection efficiency of 0.9μg∕J. Dependence of the mass yield on wavelength and fluence is seen to be dependent primarily on the extent of the explosive mechanism.
The evolution of relaxor behavior in Ti4+ doped BaZrO3 ceramics
Authors: Maiti Tanmoy , Guo R. , Bhalla A. S.
Published: December 2006

In this paper we have studied the relaxor behavior of BaZrxTi1−xO3 (0.50⩽x⩽0.80) ceramics. The relaxor behavior of BaZrxTi1−xO3 (BZT) solid solution is analyzed with respect to the increasing amount of Ti4+ rich polar regions in the nonpolar matrix of BaZrO3 which has a very low dielectric constant (∼27). The dielectric behavior of BaZrxTi1−xO3 ceramics is studied in the temperature range of 300–30K. The relaxor behavior becomes more prominent with the increase of Ti4+ ion content, i.e., with increasing amount of the polar regions. The frequency dependence of the polar regions follows Vogel-Fulcher relation [Z. Phys. 22, 645 (1921); J. Am. Ceram. Soc. 8, 339 (1925)] with a characteristic cooperative freezing at a specific temperature. The dielectric behavior of BZT ceramics shows more electric field dependence with the increase in Ti4+ rich polar regions.
Band gap engineering for laser cooling of semiconductors
Authors: Khurgin Jacob B.
Published: December 2006

A number of methods for improvement of the efficiency of laser cooling in semiconductors are suggested and analyzed theoretically. It is shown that by combining band gap engineering in the electronic domain and photonic band gap engineering in the optical domain, one can attain an enhancement in refrigeration efficiency provided the nonradiative efficiency is not drastically affected.
Resistivity analysis of epitaxially grown, doped semiconductors using energy dependent secondary ion mass spectroscopy
Authors: Burnham Shawn D. , Thomas Edward W. , Doolittle W. Alan
Published: December 2006

A characterization technique is discussed that allows quantitative optimization of doping in epitaxially grown semiconductors. This technique uses relative changes in the host atom secondary ion (HASI) energy distribution from secondary ion mass spectroscopy (SIMS) to indicate relative changes in conductivity of the material. Since SIMS is a destructive process due to sputtering through a film, a depth profile of the energy distribution of sputtered HASIs in a matrix will contain information on the conductivity of the layers of the film as a function of depth. This process is demonstrated with Mg-doped GaN, with the Mg flux slowly increased through the film. Three distinct regions of conductivity were observed: one with Mg concentration high enough to cause compensation and thus high resistivity, a second with moderate Mg concentration and low resistivity, and a third with little to no Mg doping, causing high resistivity due to the lack of free carriers. During SIMS analysis of the first region, the energy distributions of sputtered Ga HASIs were fairly uniform and unchanging for a Mg flux above the saturation, or compensation, limit. For the second region, the Ga HASI energy distributions shifted and went through a region of inconsistent energy distributions for Mg flux slightly below the critical flux for saturation, or compensation. Finally, for the third region, the Ga HASI energy distributions then settled back into another fairly unchanging, uniform pattern. These three distinct regions were analyzed further through growth of Mg-doped step profiles and bulk growth of material at representative Mg fluxes. The materials grown at the two unchanging, uniform regions of the energy distributions yielded highly resistive material due to too high of Mg concentration and low to no Mg concentration, respectively. However, material grown in the transient energy distribution region with Mg concentration between that of the two highly resistive regions yielded low resistivity (0.59Ωcm) and highly p-type (1.2×1018cm−3 holes) Mg-doped GaN.
Self-heating in a GaN based heterostructure field effect transistor: Ultraviolet and visible Raman measurements and simulations
Authors: Ahmad I. , Kasisomayajula V. , Song D. Y. , Tian L. , Berg J. M. , Holtz M.
Published: December 2006

We report direct self-heating measurements for AlGaN∕GaN heterostructure field effect transistor grown on SiC. Measurements are carried out using micro-Raman scattering excited by above band gap ultraviolet and below band gap visible laser light. Ultraviolet excitation probes the GaN near the AlGaN∕GaN interface region of the device where the two-dimensional electron gas carries the source-drain current. The visible excitation probes the entire ∼1μm thick GaN layer and the SiC substrate near the interface with GaN. These results thus provide a measure of the average temperature throughout the GaN and of the substrate. Results are backed by combined electrical and thermal simulations. We find that the immediate hot spot region of the device, at the edge of the gate electrode, rises by up to ∼240°C over ambient under the most aggressive drive conditions examined.
Photonic band gaps in non-close-packed inverse opals
Authors: Gaillot D. P. , Summers C. J.
Published: December 2006

An advanced dielectric function has been designed to compute the photonic band structures of non-close-packed inverse opals fabricated using conformal infiltration and by a recently described sacrificial-layer technique. A model is proposed to correctly simulate complex dielectric structures resulting from conformal backfilled infiltrations. While large photonic band gaps (PBGs) and a reduced refractive index requirement (RIR) are predicted to occur in these inverse structures, the results also indicate a high degree of sensitivity to the dielectric/air network topology enabling fine PBG tailoring. Optimized structurally modified non-close-packed inverse opals with lower refractive indices offer enhanced optical properties compared to narrow PBGs observed in conventional inverse shell opals using high index materials such as silicon or germanium. Three-dimensional finite-difference time-domain computations predict that many experimentally achievable non-close-packed inverse structures exhibit significantly enhanced PBG properties: a RIR as low as 2.65 and PBG width of ∼10%. Additionally, a PBG width of 14.2% is predicted for an optimized high index non-close-packed inverse structure in which the interstitial air void is smaller than in structures fabricated by conformal means. The robustness and simplicity of this technique combined with predicted adjustable PBG properties is therefore demonstrated to provide alternative fabrication routes to the synthesis of photonic crystal devices operating in the visible with lower refractive indices.
Electrical and noise characterization of bottom-gated nanocrystalline silicon thin-film transistors
Authors: Hatzopoulos A. T. , Arpatzanis N. , Tassis D. H. , Dimitriadis C. A. , Templier F. , Oudwan M. , Kamarinos G.
Published: December 2006

Bottom-gated n-channel thin-film transistors were fabricated on nanocrystalline silicon (nc-Si) layers, deposited at 230°C by plasma-enhanced chemical vapor deposition. The transfer characteristics were measured in devices with different channel dimensions, exhibiting front and back channel conduction. The change of the device parameters with channel dimensions is explained in terms of the trap density in the bulk of the nc-Si layer extracted from space charge limited current measurements in n+-nc-Si-n+ structures and both front∕back interface traps determined from the slopes associated with the front and back channel conduction. The overall results suggest the existence of regions of high trap density at the back interface near the source and drain n+ contacts, whereas the reduction of the back channel conduction with decreasing the channel width can be attributed to the sidewall edge effect. The gate insulator trap concentration of 1.5×1019cm−3eV−1 was deduced from the noise data.
Shock-induced reaction in a flake nickel + spherical aluminum powder mixture
Authors: Eakins D. , Thadhani N. N.
Published: December 2006

Mixtures of flake-shaped nickel and spherical aluminum powders have been subjected to shock-loading up to 6 GPa to investigate the occurrence of shock-induced chemical reactions. The high-pressure Hugoniot state is determined through time-resolved measurements of the input stress and shock transit time through the specimen. An increase in shock velocity is observed above stress levels of 3.5 GPa, suggesting the initiation of an ultrafast shock-induced chemical reaction and formation of Ni-Al compound(s) occurring in the time scale of the high-pressure shock state.
Clusters of particles falling in a viscous fluid with periodic boundary conditions
Authors: Ekiel-Jeżewska M. L. , Felderhof B. U.
Published: December 2006

Exemplary dynamics of three point particles falling under gravity in Stokes flow with periodic boundary conditions is presented in a movie. Stable and unstable solutions of the equations of Stokesian dynamics are explicitly shown for two initial configurations: equilateral triangles with side lengths close to a critical size.
The effect of stratification on the wave number selection in the instability of sedimenting spheroids
Authors: Saintillan David , Shaqfeh Eric S. G. , Darve Eric
Published: December 2006

It is well known that a dilute suspension of spheroids sedimenting under gravity at low Reynolds number is unstable to density fluctuations as a result of hydrodynamic interactions [D. L. Koch and E. S. G. Shaqfeh, J. Fluid Mech. 209, 521 (1989)]. Using a linear stability analysis, it is shown that a vertical density gradient in such a suspension can lead to a wave number selection by damping fluctuations at long wavelengths. A scaling for the most unstable wavelength, or characteristic size of the density fluctuations, is obtained in terms of the background stratification and volume fraction, and is compared to results from numerical simulations in stratified particulate suspensions using methods that we have developed previously. In initially homogeneous suspensions, simulations show a continuous decay of the size of the density fluctuations over time, which we demonstrate can be attributed to the development of stratification inside the suspension.
Interaction of cavitation bubbles on a wall
Authors: Bremond Nicolas , Arora Manish , Dammer Stephan M. , Lohse Detlef
Published: December 2006

We report experimental and numerical investigations on the dynamics of the cavitation of bubbles on a solid surface and the interaction between them with the help of controlled cavitation nuclei: hemispherical bubbles are nucleated from hydrophobic microcavities that act as gas traps when the substrate is immersed in water. The expansion of these nuclei is triggered by an impulsive lowering of the liquid pressure. The patterning of the substrate allows us to control the number of bubbles and the distance between them. Each hemispherical bubble experiences the effect of its mirror image. Correspondingly, an isolated hemispherical bubble together with its mirror image behaves like a free spherical bubble, i.e., its dynamics is well described by the Rayleigh-Plesset equation. We employ the setup to study the dynamics of two and more bubbles in a row at controlled and fixed distances from each other. For weak interaction, namely when the maximum size of the bubbles is smaller than the bubble distance, the dynamics of the system is well captured by an extended Rayleigh-Plesset equation, where mutual pressure coupling through sound emission is included. Bubble pairs last longer than an isolated bubble as neighboring bubbles modify the surrounding pressure and screen each other. For strong interaction, obtained by increasing the tensile stress or decreasing the bubble distance, the bubbles eventually flatten and form a liquid film between each other which can rupture, leading to coalescence. The film thinning is inertia dominated. A potential flow boundary integral simulation captures the overall shape evolution of the bubbles, including the formation of jets horizontal to the wall. These horizontal jets are caused by symmetry breaking due to the neighboring bubbles.
A study of velocity discontinuity for single air bubbles rising in an associative polymer
Authors: Soto E. , Goujon C. , Zenit R. , Manero O.
Published: December 2006

The motion of air bubbles in aqueous solutions of a hydrophobic alkali-swellable associative polymer is studied in this work. The associative nature of these polymer systems dictates their rheological properties: for moderate values of the shear rate, the formation of structure can lead to a shear-thickening behavior and to the appearance of first normal stress difference. For larger shear rates, the polymer associations can be broken, leading to shear thinning. In general, these fluids show a Newtonian behavior for small values of the shear rate, but behave as viscoelastic liquids for large shear rates. Experimental results show the appearance of a critical bubble volume at which a discontinuity in the relation velocity-volume occurs; however, the velocity increase found in this case is not as large as that previously reported for the case of shear-thinning viscoelastic fluids. The discontinuity is associated with a significant change of the bubble shape: before the critical volume, the bubbles are convex spheroids, while past the critical volume a sharp cusped end appears. The appearance of the tail is also associated with the appearance of an inflection point (change of curvature) on the bubble surface. Moreover, since the rheology of the liquids is measured it was found that the discontinuity, and hence the change of shape, occurs when the elastic nature of the liquid first manifests itself (appearance of a first normal stress difference). A comparison of the measured velocities for small bubbles with predictions from a Stokes-Hadamard law shows a discrepancy. The Newtonian viscosity measured in a viscometric flow was smaller than that determined from a falling-ball arrangement. Considering the viscosity measured under this nonviscometric flow, the comparison between theory and experiments was very good for bubbles having volumes lower than the critical one. Moreover, due to the importance of the elasticity, and due to the change of the shape of the bubble, a dimensionless number formed as the ratio of elastic to surface tension forces clearly defines the change of the behavior for the bubbles rising in these fluids. Finally, a photographic study of the peculiar shapes of the bubble tails, tip-, and edge-streaming phenomena is presented. To our knowledge, experiments in this class of fluids have not been reported to date.
Void growth during thermal decomposition of silicon oxide layers studied by low-energy electron microscopy
Authors: Hibino H. , Uematsu M. , Watanabe Y.
Published: December 2006

Low-energy electron microscopy (LEEM) has been used to investigate void growth during thermal decomposition of 1–2-nm-thick silicon oxide on Si substrates. Real-time LEEM observations clarify that the void size (square root of the void area) grows linearly with time. The temperature dependence of the growth rate reveals that the activation energy of the void growth is about 4.0eV. We also find that the void density increases at faster rates in later stages of the oxide decomposition. This suggests that the nucleation is not initiated by a random single event. Additionally, we demonstrate that the voids become shallower because the void shape changes during the growth.
Electron energy levels in ZnSe quantum dots
Authors: Nikesh V. V. , Lad Amit D. , Kimura Seiji , Nozaki Shinji , Mahamuni Shailaja
Published: December 2006

The size dependence of electron energy levels of ZnSe quantum dots were studied by size selective photoluminescence excitation spectroscopy at low temperature. ZnSe quantum dots of different sizes were synthesized by a high temperature wet chemical route. Cubic zinc-blende crystallites with sizes ranging from 1.5to4.5nm showing only band edge luminescence were obtained. Four excited state transitions have been observed in photoluminescence excitation spectroscopy. This study establishes a connection between the electron energy levels of ZnSe quantum dots and their corresponding size. The experimentally observed excited states for ZnSe quantum dots have been analyzed on the basis of “effective mass approximation” calculations. The observed transitions for wide band gap ZnSe are compared with the well studied material, viz., CdSe. The present work enables one to gain further insight into the size dependence of the electronic structure of semiconductor quantum dots.
Realization of reliable GaN nanowire transistors utilizing dielectrophoretic alignment technique
Authors: Motayed Abhishek , He Maoqi , Davydov Albert V. , Melngailis John , Mohammad S. N.
Published: December 2006

We have utilized dielectrophoretic force for assembling long (50μmto200μm) GaN nanowires for device fabrication. These catalyst-free nanowires were grown by direct reaction of NH3 and Ga, which resulted in free-standing nanowires along with GaN microplatelets. GaN nanowires were suspended in a solvent using sonication, and using dielectrophoretic forces nanowires were assembled on prepatterned substrates (SiO2 coated Si and sapphire). With fabrication sequence using batch fabrication processes such as standard photolithography, etching, and oxide deposition we were able to realize stable GaN nanowire devices. The present technique is potentially compatible with complementary metal-oxide semicondoctor technology, and integrating nanodevices with conventional Si microelectronics on the same chip can be made possible with this technique. Utilizing this technique, high mobility (230cm2V−1s−1) GaN nanowire field effect transistors with reliable electrical characteristics have been achieved. These nanowire transistors even after prolonged period of conduction exhibited no deteriorations of their electrical properties. Several key factors in the processing that affect the device yield and reliability have been identified. Simple calculations predicted the effects of nanowire geometry, dispersing solvent, and alignment frequency on the dielectrophoretic force experienced by the nanowires.
Ge
S
2
/metal thin film bilayered structures as write-once-type optical recording materials
Authors: Kato Naohiko , Fukano Tatsuo , Takeda Yasuhiko , Takeichi Akihiro , Motohiro Tomoyoshi , Kawai Shoichi
Published: December 2006

Ge S 2 /metals thin film bilayered structures were examined for write-once-type optical recording materials. Decreases in the reflectance of GeS2∕Ag and GeS2∕Cu structures at a certain elevated temperature were observed. The phenomena were attributed to the formation of metal sulfides with high optical absorption coefficients by the interface reaction between transparent GeS2 and highly reflective metals. In contrast to GeS2∕Ag or GeS2∕Cu, an increase in the reflectance was observed in GeS2∕Au, which was presumably due to the change of optical interference conditions caused by the decrease in the GeS2 film thickness and the improvements of the crystallinity of Au caused by the decrease of the lattice defects along the grain boundaries of Au. Examination of the GeS2/metals bilayered structures as optical disc memories revealed that the reactions occurred within submicrosecond during the recording laser irradiations. The recording sensitivities of GeS2∕Ag or GeS2∕Cu which corresponded to the reaction temperatures was able to be controlled by Al doping to Ag or Cu. The reflectance of the GeS2/metals samples except the GeS2∕Cu kept enough value to be optically readable in the wider range from 500to800nm than the recording layer containing organic dye of the conventional compact disc recordable. The spectra after the heat treatments showed the smaller wavelength dependence than that before the heat treatment. These features indicate the promising properties of these structures in application to optical recording media that can be used in the wide wavelength range.
Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets
Authors: Keskinen M. J. , Velikovich A. L. , Schmitt A.
Published: December 2006

A mode-coupling model is developed to treat the multimode evolution of the ablative Richtmyer-Meshkov (RM) and Landau-Darrieus (LD) instability in the laser imprint of planar targets. Using this mode coupling model, the multimode power spectrum of the RM and LD instability is computed. For the RM instability, mode-coupling effects lead to a broadening of the oscillatory minima found in linear RM theory. For the LD instability, mode-coupling effects generate an inverse power law spectrum.
Fast ignition of a compressed inertial confinement fusion hemispherical capsule by two proton beams
Authors: Temporal Mauro
Published: December 2006

A hemispherical conically guided indirectly driven inertial confinement fusion capsule has been considered. The fast ignition of the precompressed capsule driven by one or two laser-accelerated proton beams has been numerically investigated. The energy distribution of the protons is Gaussian with a mean energy of 12MeV and a full width at half maximum of 1MeV. A new scheme that uses two laser-accelerated proton beams is proposed. It is found that the energy deposition of 1kJ provided by a first proton beam generates a low-density cylindrical channel and launches a forward shock. A second proton beam, delayed by a few tens of ps and driving the energy of 6kJ, crosses the low-density channel and heats the dense shocked region where the ignition of the deuterium-tritium nuclear fuel is achieved. For the considered capsule, this new two-beam configuration reduces the ignition energy threshold to 7kJ.
Analysis of the transverse and the longitudinal pseudodiffusion of CO2 in sub- and supercritical states: A molecular-dynamics analysis
Authors: Idrissi A. , Longelin S. , Damay P. , Krishtal S. , Kiselev M.
Published: December 2006

We have performed molecular-dynamics simulations of CO2 system along the gas-liquid coexistence curve and on the isochore 94.22cm3mol−1 (which corresponds to the critical isochore). The calculation has been carried out in order to analyze the diffusion of CO2 and particularly to figure out how the diffusion coefficient may be decomposed along the molecular axes. This makes it possible to analyze the anisotropy of the diffusion along these axes and to shed light on the microscopic changes which accompany such behavior. This anisotropy is traced back to the effect of the translation-rotation coupling (TRC) along the molecular axes. Along the liquid-gas coexistence curve, the pseudolongitudinal diffusion is found to be more rapid than the transverse one. The opposite trend is found along the isochore 94.22cm3mol−1. The role of the local structure was explored by calculating intermediate scattering function and the autocorrelation functions for the forces acting along the molecular axes. It is shown that the strength of the TRC effect is correlated to the difference between the relaxation times of the local structure, that of the reorientation along the molecular axes, and that of the translational motion. The analysis of the correlation time and the average mean square force along the longitudinal and transverse directions confirms the anisotropy of the local environment that determines the translational dynamics of a molecule.
Association-dissociation equilibrium of loop structures in single-chain folding into a toroidal condensate
Authors: Iwaki Takafumi
Published: December 2006

Recently, it has been revealed that a semiflexible polyelectrolyte chain can form a partially folded conformation stably as a result of an electrostatic interaction. Interestingly, there are cases where the appearance of this structure requires a high-salt condition of a solution. In order to solve this problem, we consider the double equilibrium of the formation of loops and their aggregation on a single-chain polymer. First, an aggregate with a typical surface energy is examined as a test case. The basic nature of the folding transition is discussed with regard to the chemical potential of loop structures. Next, we consider a charged aggregate for which the interior is completely neutralized by counter ions. In this model, a partially folded chain appears with a high-salt condition. Based on this model, screened interactions between surface charges and a toroidal shape of a folded structure are considered essential factors bihind this phenomenon.
Wire dynamics model of the implosion of nested and planar wire arrays
Authors: Esaulov A. A. , Velikovich A. L. , Kantsyrev V. L. , Mehlhorn T. A. , Cuneo M. E.
Published: December 2006

This paper presents the wire dynamics model (WDM), which can effectively replace the generic 0D (zero-dimensional) model in simulation of the implosions of arbitrary shaped wire arrays, including high-wire-number nested and planar array loads at multi-MA generators. Fast and inexpensive WDM modeling can predict the array implosion time and the rate of thermalization of the kinetic energy, and can estimate the timing of the x-ray pulse. Besides serving the purposes of the design and optimization of the wire array loads of complex configurations, the WDM reproduces the specific features of the wire array implosion dynamics due to the inductive current transfer, which makes the WDM a valuable amplification of the magnetohydrodynamic models.
A full-configuration interaction “nuclear orbital” method to study doped HeN3 clusters (N⩽4)
Authors: de Lara-Castells M. P. , Delgado-Barrio G. , Villarreal P. , Mitrushchenkov A. O.
Published: December 2006

An efficient full configuration interaction (FCI) treatment, based on the Jacobi-Davidson algorithm, is developed in order to study small doped HeN3 clusters. The state of each He atom in a given cluster is described by a set of wave-functions which by extention of the quantum-chemistry notation are caller here “nuclear orbitals”. The FCI treatment is applied to the calculation of binding energies and helium natural orbitals of HeN3⋯Br2(X) complexes. In agreement with our previous calculations using a Hartree-Fock approach [Phys. Rev. Lett. 93, 053401 (2004)], in which the He–He interaction is modified at small distances to account for short-range correlation effects, the lowest-energy states of each multiplet are found to be very close in energy. The natural orbital analysis, in turn, indicates the adequacy of the “nuclear orbital” approach in these systems.
Polycomb recruitment to DNA
in vivo
by the YY1 REPO domain
Authors: Wilkinson Frank H. , Park Kyoungsook , Atchison Michael L.
Published: December 2006

Polycomb group (PcG) proteins are responsible for maintaining transcriptional repression of developmentally important genes. However, the mechanism of PcG recruitment to specific DNA sequences is poorly understood. Transcription factor YY1 is one of the few PcG proteins with sequence-specific DNA binding activity. We previously showed that YY1 can recruit other PcG proteins to DNA, leading to histone posttranslational modifications and stable transcriptional repression. Using
Drosophila
transgenic approaches, we identified YY1 sequences 201–226 as necessary and sufficient for PcG transcriptional repression
in vivo
. When fused to a heterologous DNA-binding domain, this short 26-aa motif was sufficient for transcriptional repression, recruitment of PcG proteins to DNA, and methylation of histone H3 lysine 27. Deletion of this short YY1 motif did not affect transient transcriptional repression but ablated PcG repression, PcG protein recruitment to DNA, and methylation of H3 lysine 27. We propose that this motif be named the REPO domain for its function in recruitment of Polycomb. The REPO domain is well conserved in YY1 orthologs and in related proteins.
Hypoglycemia leads to age-related loss of vision
Authors: Umino Y. , Everhart D. , Solessio E. , Cusato K. , Pan J. C. , Nguyen T. H. , Brown E. T. , Hafler R. , Frio B. A. , Knox B. E. , Engbretson G. A. , Haeri M. , Cui L. , Glenn A. S. , Charron M. J. , Barlow R. B.
Published: December 2006

The retina is among the most metabolically active tissues in the body, requiring a constant supply of blood glucose to sustain function. We assessed the impact of low blood glucose on the vision of C57BL/6J mice rendered hypoglycemic by a null mutation of the glucagon receptor gene,
Gcgr
. Metabolic stress from moderate hypoglycemia led to late-onset loss of retinal function in Gcgr
−/−
mice, loss of visual acuity, and eventual death of retinal cells. Retinal function measured by the electroretinogram b-wave threshold declined >100-fold from age 9 to 13 months, whereas decreases in photoreceptor function measured by the ERG a-wave were delayed by 3 months. At 10 months of age Gcgr
−/−
mice began to lose visual acuity and exhibit changes in retinal anatomy, including an increase in cell death that was initially more pronounced in the inner retina. Decreases in retinal function and visual acuity correlated directly with the degree of hypoglycemia. This work demonstrates a metabolic-stress-induced loss of vision in mammals, which has not been described previously. Linkage between low blood glucose and loss of vision in mice may highlight the importance for glycemic control in diabetics and retinal diseases related to metabolic stress as macular degeneration.
A fully integrated microfluidic genetic analysis system with sample-in–answer-out capability
Authors: Easley Christopher J. , Karlinsey James M. , Bienvenue Joan M. , Legendre Lindsay A. , Roper Michael G. , Feldman Sanford H. , Hughes Molly A. , Hewlett Erik L. , Merkel Tod J. , Ferrance Jerome P. , Landers James P.
Published: December 2006

We describe a microfluidic genetic analysis system that represents a previously undescribed integrated microfluidic device capable of accepting whole blood as a crude biological sample with the endpoint generation of a genetic profile. Upon loading the sample, the glass microfluidic genetic analysis system device carries out on-chip DNA purification and PCR-based amplification, followed by separation and detection in a manner that allows for microliter samples to be screened for infectious pathogens with sample-in–answer-out results in <30 min. A single syringe pump delivers sample/reagents to the chip for nucleic acid purification from a biological sample. Elastomeric membrane valving isolates each distinct functional region of the device and, together with resistive flow, directs purified DNA and PCR reagents from the extraction domain into a 550-nl chamber for rapid target sequence PCR amplification. Repeated pressure-based injections of nanoliter aliquots of amplicon (along with the DNA sizing standard) allow electrophoretic separation and detection to provide DNA fragment size information. The presence of
Bacillus anthracis
(anthrax) in 750 nl of whole blood from living asymptomatic infected mice and of
Bordetella pertussis
in 1 μl of nasal aspirate from a patient suspected of having whooping cough are confirmed by the resultant genetic profile.