bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative metabolic profiling of xenobiotics by human P450s expressed in tobacco cell suspension cultures
Authors: Schmidt B. , Joussen N. , Bode M. , Schuphan I.
Published: November 2006

Elucidation of metabolic pathways of xenobiotics (pesticides, pharmaceuticals and industrial pollutants) in human, animals and plants and chemical identification of corresponding metabolites are required for comprehensive (eco-) toxicological evaluation of the compounds prior to their usage. The most important metabolic products are oxidized metabolites, and most of these are formed by catalytic activity of P450s (cytochrome P450 mono-oxygenases). In human, 11 P450 isoenzymes exhibiting broad and overlapping substrate specificities are responsible for approx. 90% of drug metabolism. As support for inevitable metabolism studies with intact organisms under relevant conditions, tobacco cell cultures were transformed separately with cDNA sequences of human P450 isoenzymes CYP1A1, CYP1A2 and CYP3A4. The resulting P450-transgenic cell suspensions were used for metabolism studies with pesticides, industrial pollutants, a secondary plant metabolite and human sex hormones. A summary of basic results is provided; these are discussed regarding application of the method for screening of the oxidative metabolism of xenobiotics and the large-scale production of metabolites.
Evolution of insect P450
Authors: Feyereisen R.
Published: November 2006

The first fully sequenced insect genomes were those of the fruitfly and the mosquito, both from the order Diptera. Now, with an increasing number and diversity of insect genomes becoming available, the diversity of insect P450 genes can be better appreciated and tentative ideas about the evolution of the CYP (cytochrome P450) superfamily in insects can be proposed. There are four large clades of insect P450 genes that existed before the divergence of the class Insecta and that are also represented by CYP families in vertebrates: the CYP2 clade, the CYP3 clade, the CYP4 clade and the mitochondrial P450 clade. P450s with known or suspected physiological functions are present in each of these clades and only a dozen genes appear to have orthologues or very close paralogues in each insect genome. P450 enzymes from each of these clades have been linked to insecticide resistance or to the metabolism of natural products and xenobiotics. In particular, insects appear to maintain a repertoire of mitochondrial P450 paralogues devoted to the response to environmental challenges.
The Halloween genes code for cytochrome P450 enzymes mediating synthesis of the insect moulting hormone
Authors: Rewitz K.F. , Rybczynski R. , Warren J.T. , Gilbert L.I.
Published: November 2006

The developmental events occurring during moulting and metamorphosis of insects are controlled by precisely timed changes in levels of ecdysteroids, the moulting hormones. The final four sequential hydroxylations of steroid precursors into the active ecdysteroid of insects, 20E (20-hydroxyecdysone), are mediated by four cytochrome P450 (P450) enzymes, encoded by genes in the Halloween family. Orthologues of the Drosophila Halloween genes phantom (phm; CYP306A1), disembodied (dib; CYP302A1), shadow (sad; CYP315A1) and shade (shd; CYP314A1) were obtained from the endocrinological model insect, the tobacco hornworm Manduca sexta. Expression of these genes was studied and compared with changes in the ecdysteroid titre that controls transition from the larval to pupal stage. phm, dib and sad, which encode P450s that mediate the final hydroxylations in the biosynthesis of ecdysone, were selectively expressed in the prothoracic gland, the primary source of ecdysone during larval and pupal development. Changes in their expression correlate with the haemolymph ecdysteroid titre during the fifth (final) larval instar. Shd, the 20-hydroxylase, which converts ecdysone into the more active 20E, is expressed in tissues peripheral to the prothoracic glands during the fifth instar. Transcript levels of shd in the fat body and midgut closely parallel the enzyme activity measured in vitro. The results indicate that these Halloween genes are transcriptionally regulated to support the high biosynthetic activity that produces the cyclic ecdysteroid pulses triggering moulting.
Perspectives on neuroprotective stroke therapy
Authors: Schäbitz W.-R. , Fisher M.
Published: November 2006

After years of setbacks, the perspective of neuroprotective stroke therapy has revived in light of recent study results. We outline in this review how a neuroprotective candidate drug should be developed, beginning with a thorough preclinical evaluation according to the STAIR (Stroke Therapy Academic Industry Roundtable) criteria. Assessing the safety of the candidate drug in the relatively straightforward Phase IIA would be the first step into clinical development. While advancing into Phase IIB, the implementation of a responder analysis, the use of a surrogate biomarker as well as the use of Bayesian methodology should be considered to increase the likelihood of seeing any therapeutic sign. Clinical development in Phase III should consider that previously used dichotomized endpoints appropriate for evaluation of thrombolytic drugs are likely to be insufficient for assessing efficacy of neuroprotective drugs. Detection of a clinically relevant shift in the outcome measure appears to be a more relevant approach for the type of drug that achieves a reduction and not a reverse of the ischaemic lesion.
Survival signalling in Alzheimer's disease
Authors: Lukiw W.J. , Bazan N.G.
Published: November 2006

Significant advancements in our understanding of cell-survival signalling in AD (Alzheimer's disease) stem from recent investigations into the metabolism, trafficking and fate of the essential ω-3 fatty acid DHA (docosahexaenoic acid) (C22:6, n=3). Brain synaptic terminals and neuronal plasma membranes are highly enriched in DHA, and deficiencies in this polyunsaturated fatty acid are characteristic of AD-affected brain. Oxidative stress, targeting phospholipids containing DHA, and age-related DHA depletion are associated with the progressive erosion of normal cognitive function in AD. Current studies support the idea that DHA itself and novel DHA-derived neural synapse- and membrane-derived lipid messengers have considerable potential to modulate cell survival signalling in stressed cultured neural cell models in vitro and in mammalian models of learning, memory and AD in vivo. Key players in this intrinsic rescue system include the α-secretase-processed neurotrophin sAPPα [soluble APPα (amyloid precursor protein α)] peptide, the DHA-derived 10,17S-docosatriene NPD1 (neuroprotectin D1), a tandem brain cytosolic phospholipase A2 and 15-lipoxygenase enzymatic system that biosynthesizes NPD1, and a small family of anti-apoptotic neuroprotective genes that encode Bcl-2, Bcl-XL and Bfl-1 (A1). This paper reviews current ideas regarding DHA and the oxygenated DHA derivative NPD1, intrinsically triggered biolipid neuroprotectants that along with their associated rescue pathways, contribute to life-or-death decisions of brain cells during homoeostasis, aging and neurodegenerative disease.
Signalling molecules essential for neuronal survival and differentiation
Authors: Frebel K. , Wiese S.
Published: November 2006

Motoneurons are made in excess throughout development. Initial analysis of the mechanisms that lead to apoptotic cell death during later stages of development and the early postnatal period led to the discovery of neurotrophic factors. These factors comprise different families acting through different tyrosine kinase receptors. Intracellular signalling cascades that lead to the survival of neurons are, on the one hand, the Ras/Raf (Ras-activated factor)/MAPK (mitogen-activated protein kinase) pathway and, on the other, the PI3K (phosphoinositide 3-kinase)/Akt (protein kinase B) pathway. The initial thought of these factors acting as single molecules in separate cascades has been converted into a model in which the dynamics of interaction of these pathways and the subcellular diverse functions of the key regulators have been taken into account. Bag1 (Bcl-2-associated athanogene 1), a molecule that was originally found to act as a co-chaperone of Hsp70 (heat-shock protein 70), also interacts with B-Raf, C-Raf and Akt to phosphorylate Bad (Bcl-2/Bcl-XL-antagonist, causing cell death), a pro-apoptotic member of the Bcl-2 family, and leads to specific subcellular distribution of phosphorylated Akt and B-Raf. These functions lead to survival of embryonic neural stem cells and therefore serve as a key event to regulate the viability of these cells.
Protein kinase CK2: a newcomer in the ‘druggable kinome’
Authors: Pagano M.A. , Cesaro L. , Meggio F. , Pinna L.A.
Published: November 2006

The acronym CK2 (derived from the misnomer ‘casein kinase’ 2) denotes one of the most pleiotropic members of the eukaryotic protein kinase superfamily, characterized by an acidic consensus sequence in which a carboxylic acid (or pre-phosphorylated) side chain at position n+3 relative to the target serine/threonine residue plays a crucial role. The latest repertoire of CK2 substrates includes approx. 300 proteins, but the analysis of available phosphopeptide databases from different sources suggests that CK2 alone may be responsible for the generation of a much larger proportion (10–20%) of the eukaryotic phosphoproteome. Although for the time being CK2 is not included among protein kinases whose inhibitors are in clinical practice or in advanced clinical trials, evidence is accumulating that elevated CK2 constitutive activity co-operates to induce a number of pathological conditions, including cancer, infectious diseases, neurodegeneration and cardiovascular pathologies. The development and usage of cell-permeant, selective inhibitors discloses a scenario whereby CK2 plays a global anti-apoptotic role, which under special circumstances may lead to untimely and pathogenic cell survival.
Translational vehicles for neuroprotection
Authors: Papadakis M. , Buchan A.M.
Published: November 2006

This review will analyse particular criteria in the analysis of stroke diagnosis and treatment, which are pivotal for the successful translation of experimental data from the laboratory to humans.
Toll-like receptors and tolerance to ischaemic injury in the brain
Authors: Stevens S.L. , Stenzel-Poore M.P.
Published: November 2006

Ischaemic tolerance in the brain is a powerful adaptive defence that involves an endogenous programme of neuroprotection culminating in marked protection against brain injury from ischaemia. A range of preconditioning stimuli exist that differ in ligand and target characteristics but share the common feature of causing mild stress or insult without inducing overt injury. The protective phenotype that emerges confers tolerance to subsequent exposure to injurious insults. Tolerance to injury is the result of genomic reprogramming, an adaptation comprising regulatory processes that countermand injurious effectors and invoke novel neuroprotective pathways. TLRs (Toll-like receptors) play important roles in sensing potential danger/insult in the form of pathogens as well as endogenous stress molecules that occur in response to mild injury (e.g. heat-shock proteins). Recent studies suggest that TLRs are novel and potent preconditioning targets that offer substantial promise to protect the brain from ischaemic injury.
Acidotoxicity in brain ischaemia
Authors: Simon R. , Xiong Z.
Published: November 2006

Intracellular calcium toxicity remains the central feature in the pathophysiology of ischaemic cell death in brain. Glutamate-gated channels have been thought to be the major sites of ischaemia-induced toxic calcium entry, but the failure of glutamate antagonists in clinical trials has suggested that glutamate-independent mechanisms of calcium entry during ischaemia must exist and may prove central to ischaemic injury. We have shown that ASICs (acid-sensing ion channels) in brain are glutamate-independent vehicles of calcium flux and transport calcium in greater measure in the setting of the two major neurochemical components of ischaemia: acidosis and substrate depletion. Pharmacological blockade of ASICs markedly attenuates stroke injury with a robust therapeutic time window of 5 h following stroke onset. Here, we describe this new mechanism of calcium toxicity in brain ischaemia and offer a potential new therapy for stroke.
Nonequilibrium Glauber-type dynamics in continuum
Authors: Kondratiev Yuri G. , Kutoviy Oleksandr V. , Zhizhina Elena
Published: November 2006

We construct the nonequilibrium Glauber dynamics as a Markov process in configuration space for an infinite particle system in continuum with a general class of initial distributions. This class we define in terms of correlation functions bounds and it is preserved during the Markov evolution we constructed.
Surface properties of water ice at 150–191K studied by elastic helium scattering
Authors: Suter Martina T. , Andersson Patrik U. , Pettersson Jan B. C.
Published: November 2006

A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150–191K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185±10K was calculated from the data below 180K. The changes in the ice surface above 180K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and∕or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150–180K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA.
Nanoelectromechanical nonvolatile memory device incorporating nanocrystalline Si dots
Authors: Tsuchiya Yoshishige , Takai Kosuke , Momo Nobuyuki , Nagami Tasuku , Mizuta Hiroshi , Oda Shunri , Yamaguchi Shinya , Shimada Toshikazu
Published: November 2006

A nanoelectromechanical device incorporating the nanocrystalline silicon (nc-Si) dots is proposed for use as a high-speed and nonvolatile memory. The nc-Si dots are embedded as charge storage in a mechanically bistable floating gate. Position of the floating gate can therefore be switched between two stable states by applying gate bias. Superior on-off characteristics are demonstrated by using an equivalent circuit model which takes account of the variable capacitance due to the mechanical displacement of the floating gate. Mechanical property analysis conducted by using the finite element method shows that introduction of nc-Si dot array into the movable floating gate results in reduction of switching power. High switching frequency over 1GHz is achieved by decreasing the length of the floating gate to the submicron regime. We also report on experimental observation of the mechanical bistability of the SiO2 beam fabricated by using the conventional silicon etching processes.
A view of the implanted SiC damage by Rutherford backscattering spectroscopy, spectroscopic ellipsometry, and transmission electron microscopy
Authors: Battistig G. , Khánh N. Q. , Petrik P. , Lohner T. , Dobos L. , Pécz B. , García López J. , Morilla Y.
Published: November 2006

4 H - Si C single crystalline substrates were implanted at room temperature with 150keV Al+ ions using fluences of 4×1014, 1×1015, and 2×1015cm−2 with current density of 2.5μAcm−2. The samples were subsequently annealed at 1100°C in N2 for 1h in order to analyze their structural recovery. The disorder induced in both sublattices by the Al+ ions was studied by backscattering spectrometry in channeling geometry with a 3.5MeV He2+ beam. The results were compared with the optical properties of the samples measured by spectroscopic ellipsometry. In a previous work, we concluded that during the postimplantation annealing of a highly damaged SiC crystalline material the short distance order can be recovered, while the long distance disorder remains. We also presented the possibility to have grains of different polytypes oriented faraway from the original direction. Now, this alternative is confirmed by the cross-sectional transmission and high resolution electron microscopy studies, carried out to obtain information about the crystal structure.
Stochastic couplings of neoclassical tearing modes in ITER plasmas
Authors: Lütjens Hinrich , Luciani Jean-François
Published: November 2006

Three-dimensional magnetohydrodynamic (MHD) computations of multiple neoclassical tearing modes growths in International Thermonuclear Experimental Reactor plasmas are presented. It is shown that within the MHD framework, these modes do not couple until significant stochastization between two tearing island chains occurs. After stochastization a quick amplitude drop of one or several modes is observed. This behavior is very similar to that observed for example in ASDEX-Upgrade [A. Gude et al., Nucl. Fusion 42, 833 (2002)].
The effect of active layer thickness and composition on the performance of bulk-heterojunction solar cells
Authors: Moulé Adam J. , Bonekamp Jörg B. , Meerholz Klaus
Published: November 2006

At present, bulk heterojunction polymer solar cells are typically fabricated with an active layer thickness of between 80 and 100nm. This active layer thickness has traditionally been chosen based on convenience and empirical results. However, a detailed study of the effects that active layer thickness has on the short circuit current and efficiency has not been performed for bulk heterojunction polymer solar cells so far. We demonstrate that the performance of these devices is highly dependent on the active layer thickness and, using a well established model for optical interference, we show that such effects are responsible for the variations in performance as a function of active layer thickness. We show that the ideal composition ratio of the donor and acceptor materials is not static, but depends on the active layer thickness in a predictable manner. A comparison is made between solar cells comprised of the donor materials regioregular poly(3-hexylthiophene) and poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylenevinylene) with the acceptor [6, 6]-phenyl C61-butyric acid methyl ester to show that our results are not material specific and that high efficiency solar cells can be fabricated with active layer thickness greater than 100nm for both material mixtures. Finally, a device with an active layer thickness of 225nm is fabricated with a power efficiency of 3.7% under AM1.5 illumination at an intensity of 100mW∕cm2.
Guided self-assembly of diblock copolymer thin films on chemically patterned substrates
Authors: Wu Xiang-Fa , Dzenis Yuris A.
Published: November 2006

We study the guided self-assembly of symmetric/asymmetric diblock copolymer (BCP) films on heterogeneous substrates with chemically patterned surface by using a coarse-grained phase-separation model. During the procedure, the free energy employed for the BCP films was modeled by the Ginzburg-Landau free energy with nonlocal interaction, and the flat, chemically patterned surface was considered as a heterogeneous surface with short-range interaction with the BCP molecules. The resulting Cahn-Hilliard equation was solved by means of an efficient semi-implicit Fourier-spectral algorithm. Effects of pattern scale, surface chemical potential, and BCP asymmetry on the self-assembly process were explored in detail and compared with those without chemically patterned substrate surfaces. It was found that the morphology of both symmetric and asymmetric BCP films is strongly influenced by the commensurability between the unconstrained natural period λ* of the bulk BCP and the artificial pattern period. Simulation shows that patterned surface with period close to λ* leads to highly ordered morphology after self-assembly for both symmetric and asymmetric BCP films, and it also dramatically accelerates the guided self-assembly process. The present simulation is in a very good agreement with the recent experimental observation in BCP nanolithography. Finally, the present study also expects an innovative nanomanufacturing method to produce highly ordered nanodots based on the guided self-assembly of asymmetric BCP films on chemically patterned substrates.
Effect of light irradiation on the characteristics of organic field-effect transistors
Authors: Noh Yong-Young , Ghim Jieun , Kang Seok-Ju , Baeg Kang-Jun , Kim Dong-Yu , Yase Kiyoshi
Published: November 2006

The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene (6-T) and pentacene was examined. Organic phototransistors (OPTs) in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage (Vth) or the switch-on voltage (VO), is the result of a slow release of accumulated and trapped electrons in the semiconductor-gate dielectric interface. The VO is defined as the flatband voltage of devices. Below the VO, the channel current with the gate voltage is off current, and the channel current increases with the gate voltage above the VO. The speed of release of the accumulated charge was dependent on the type of semiconductor used. Pentacene OPTs showed a particularly long retention time. Even after storage for ten days, the shifted VO (or Vth) for the pentacene OPTs by light irradiation was not restored to the original value of the fresh devices. We conclude that this long sustained Vth shift renders them attractive for use in “light-addressable nonvolatile memory devices.”
Electrical property evaluation of manganese-fluorine codoping of lead zirconate titanate thin films: Compatibility between hard material and piezoelectric activity
Authors: Detalle M. , Rémiens D. , Lebrun L. , Guyomar D.
Published: November 2006

For some microelectromechanical system (MEMS) applications, the conditions of operation, high temperature, high stress, etc., can be very severe. Under these conditions the piezoelectric performance of polar material can decrease due to a partial (or a total) depoling induced by external excitations. So, it is important to have a piezoelectric active material that presents a good stability versus external parameters which can modify the spatial distribution of the dipolar moment and so the macroscopic polarization state (temperature, stress, etc.). In this context, we have studied the influence of some dopant introduction on barium (Ba)-strontium (Sr) lead zirconate titanate (PZT) thin films: manganese (Mn) and fluorine-manganese (F–Mn) codoped. (Ba, Sr) doping is used to increase the PZT piezoelectric activities; Mn doping, depending on the Mn content, can induce hardening effect that leads to an increase of stability but a decrease of piezoelectric activities and (Mn, F) codoping to keep the piezoelectric performances with low nonlinear and low hysteretic behavior versus external excitations. Thin films have been deposited by rf magnetron sputtering on platinized silicon substrates. Their dielectric, ferroelectric, and piezoelectric properties have been systematically measured as a function of Mn and F contents. The best composition in order to have a hard material without degradation of the piezoelectric activity is Mn(1%)–F(1%) (Ba, Sr) PZT. With this material, MEMS applications in special environment can be developed.
Hole transporting properties of tris(8-hydroxyquinoline) aluminum (Alq3)
Authors: Fong H. H. , So S. K.
Published: November 2006

The hole transporting properties of tris (8-hydroxyquinoline) aluminum (Alq3) were investigated by time-of-flight (TOF) technique between 278 and 373K, and under an applied field range of 0.6–1.3MV∕cm. At room temperature, the hole mobility has a value between 10−9 and 10−8cm2V−1s−1. The hole mobility is at least two orders of magnitude less than electron under identical preparation and measurement conditions. Generally, all hole TOF transients of Alq3 exhibit a nondispersive behavior, with a clear plateau region and a dispersion tail. Two disorder transport models, namely, the Gaussian disorder model (GDM) and the correlated disorder model (CDM), were applied to analyze the temperature and field dependent hole mobility data. The GDM, however, is found to be invalid because it fails to produce a meaningful positional disorder parameter. The CDM gives a better fit to the data, yet the model is still not satisfactory.
Dust charge effects on the resonant instability of the dust-acoustic wave in a semibounded dusty plasma
Authors: Kim Hwa-Min , Jung Young-Dae
Published: November 2006

The resonant instability of the surface dust-acoustic wave is investigated in a semibounded dusty plasma containing elongated and rotating dust grains. The temporal growth rate of the surface dust-acoustic instability is obtained by the plasma dielectric function with the specular reflection boundary condition. The results show that the domain of the instability increases with increase in the wave number, especially for the case of the negatively charged dust grains. It is also found that the growth rate of the instability with negatively charged dust grains is found to be smaller than that with positively charged dust grains. In addition, it is found that the growth rate decreases with increasing the ratio of the dust plasma frequency to the rotation frequency.
Actuation of water droplets driven by an organic transistor based inverter
Authors: Nadkarni Suvid , Yoo Byungwook , Basu Debarshi , Dodabalapur Ananth
Published: November 2006

The authors report the implementation of a microfluidic device for actuation of water droplets driven by an organic transistor based inverter. The research reported in this letter combines the advantages of discrete droplet based microfluidic systems along with simple fabrication procedures for fabricating organic transistor based circuits. An organic transistor based inverter fabricated using pentacene and N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboxyimide) (Northwestern University) is used to drive water droplets on a simple microfluidic device not employing the use of a top plate. Rapid and repeatable motion of droplets is observed for output voltages of 50–95V.
Nondestructive diagnostics of high-κ dielectrics for advanced electronic devices
Authors: Dallera Claudia , Fracassi Francesca , Braicovich Lucio , Scarel Giovanna , Wiemer Claudia , Fanciulli Marco , Pavia Giuseppe , Cowie Bruce C. C.
Published: November 2006

The authors present novel results on the interface between silicon and the high-κ oxides Al2O3 and HfO2 grown by atomic layer deposition. The determination of the thickness of the interfacial layer between oxide and Si(100) is crucial to the evaluation of the performances of devices based on high-κ dielectrics. They find through hard x-ray photoemission spectroscopy (HaXPES) that no interfacial layer forms between Al2O3 and Si(100) whereas almost one monolayer forms between HfO2 and Si(100). HaXPES does not involve any destructive procedure nor any sample preparation. High-energy photoemission could therefore be widely employed for the characterization of real devices.
Simultaneous determination of density and viscosity of liquids based on resonance curves of uncalibrated microcantilevers
Authors: McLoughlin Neal , Lee Stephen L. , Hähner Georg
Published: November 2006

The response of magnetically driven noncalibrated atomic force microscope cantilevers was measured in water/ethanol mixtures. Data recorded in pure water and in pure ethanol were used independently to extract parameters characteristic of the resonance behavior of the system. These parameters were then employed to determine the viscosity and density values of the mixtures. The values obtained are within ∼5% of those published in the literature. The procedure presented allows small volumes (approximately microliters) of liquids to be investigated and does not require any knowledge of the spring constant or the geometry of the microcantilever.
Atomically controlled molecular beam epitaxy of ferromagnetic silicide Fe3Si on Ge
Authors: Sadoh T. , Kumano M. , Kizuka R. , Ueda K. , Kenjo A. , Miyao M.
Published: November 2006

Low-temperature (60°C) molecular beam epitaxy (MBE) of Fe3Si layers on Ge substrates was investigated. From x-ray diffraction and transmission electron microscopy measurements, it was shown that Fe3Si layers including the DO3 type were epitaxially grown on Ge(110) and Ge(111), while polycrystal Fe3Si was formed on Ge(100). Although the Fe3Si∕Ge(110) interface was slightly rough (∼1nm), the Fe3Si∕Ge(111) interface was atomically flat. Such atomically controlled MBE of Fe3Si on the Ge(111) substrate can be employed to realize Ge channel spin transistors, which can be integrated with Si large-scale integrated circuits.
Optical and electrical properties of Zn1−xCdxO films grown on Si substrates by reactive radio-frequency magnetron sputtering
Authors: Sun C. W. , Xin P. , Ma C. Y. , Liu Z. W. , Zhang Q. Y. , Wang Y. Q. , Yin Z. J. , Huang S. , Chen T.
Published: November 2006

Zn 1 − x Cd x O films (0⩽x⩽0.179) were grown on Si (001) substrates at 750°C with a radio-frequency reactive magnetron sputtering method. Difference between the photoluminescence (PL) spectra taken at room temperature (RT) and at 12K is reported and is deduced to be the result of PL emission from the ZnCdO phases with wurtzite and zinc blende structures. It is also found that the RT PL intensity is in inverse proportion to the carrier concentration in the films. Cd incorporation results in the transform of conductivity from p type to n type and a decrease of carrier mobility.
Microbeam high angular resolution x-ray diffraction in InGaN∕GaN selective-area-grown ridge structures
Authors: Sirenko A. A. , Kazimirov A. , Cornaby S. , Bilderback D. H. , Neubert B. , Brückner P. , Scholz F. , Shneidman V. , Ougazzaden A.
Published: November 2006

GaN-based 6-μm-wide ridge waveguides with InGaN∕GaN multiple-quantum-wells (MQWs) produced by metal organic vapor-phase epitaxy in the regime of selective-area growth have been studied with microbeam high angular resolution x-ray diffraction and reciprocal-space mapping. Variation of the strain from 0.9% to 1.05% and a factor of 3 for the thickness enhancement of the MQW period have been measured for different widths of the oxide mask surrounding the GaN-based ridges. Only when the trapezoidal shape of the ridge cross section is taken into account can the difference between the experimentally measured thickness enhancement and predictions of the long-range gas-phase diffusion model be reconciled.
Controlled gate surface processing of AlGaN∕GaN high electron mobility transistors
Authors: Walker Dennis E. , Fitch Robert C. , Gillespie James K. , Jessen Gregg H. , Cassity Paul D. , Breedlove Joseph R. , Brillson Leonard J.
Published: November 2006

The authors have used ultrahigh vacuum surface science techniques combined with gate mask fabrication and processing to demonstrate improvements in the unity gain cutoff frequency response fT of AlGaN∕GaN high electron mobility transistors compared to standard processing. In situ annealing, nitrogen ion sputtering and annealing, and Ga reflux plus annealing all displayed increased fT response on average. In situ depth-resolved cathodoluminescence spectroscopy of the AlGaN∕GaN interface region reveals changes in GaN near-band edge, 2.2eV, and 2.9eV native defect emissions consistent with the average device performance between process steps and between devices with the same treatment on the same wafer.
Photomodulated infrared spectroscopy by a step-scan Fourier transform infrared spectrometer
Authors: Shao Jun , Yue Fangyu , Lü Xiang , Lu Wei , Huang Wei , Li Zhifeng , Guo Shaoling , Chu Junhao
Published: November 2006

A technique is developed for photomodulated spectroscopy in a long-wavelength region, based on a step-scan Fourier transform infrared spectrometer. The experimental setup is discussed, and photoreflectance (PR) spectra of narrow-gap HgCdTe materials are given as examples at the wavelengths of 5 and 9μm. The photoluminescence spectra suggest that the PR features are related to the material fundamental gap. The signal-to-noise ratio and spectral resolution of the PR spectrum are quite good for line-shape analysis. The results indicate that the PR spectrum can be well fitted by a third-derivative line-shape function. Advantages and extendability are emphasized, and the potential for advancing the study of narrow-gap materials’ band structures is foreseen.
Bleaching of sol-gel glass film with embedded gold nanoparticles by thermal poling
Authors: Mezzapesa Francesco P. , Carvalho Isabel C. S. , Kazansky Peter G. , Deparis Olivier , Kawazu Mitsuhiro , Sakaguchi Koichi
Published: November 2006

Gold clusters embedded in glass are expected to be hard to dissolve in the form of ions since gold is essentially a nonreactive metal. In spite of that, bleaching of Au-doped nanocomposite sol-gel glass film on a soda-lime glass substrate is demonstrated in which electric-field thermal poling is employed to effectively dissolve randomly distributed gold nanoparticles (15nm in diameter) embedded in a low conductivity sol-gel glass film with a volume filling factor as small as 2.3%. The surface plasmon absorption band at 520nm is suppressed in the region covered by the anodic electrode. The phenomenon is explained by the ionization of the gold nanoparticles and the redistribution of gold ions in the glass matrix due to the action of the extremely high electrostatic field locally developed during poling.
248
nm
cathodoluminescence in Al1−xInxN(0001) thin films grown on lattice-matched Ti1−yZryN(111) seed layers by low temperature magnetron sputter epitaxy
Authors: Seppänen T. , Hultman L. , Birch J.
Published: November 2006

Single-crystal Al0.8In0.2N(0001) thin films were grown epitaxially onto lattice-matched Ti0.2Zr0.8N(111) seed layers on MgO(111) substrates at 300°C by magnetron sputter epitaxy. Low-energy ion-assisted epitaxial growth conditions were achieved by applying a substrate potential of −15V. Cross-sectional high-resolution electron microscopy verified the epitaxy and high-resolution x-ray diffraction ω-rocking scans of the Al0.8In0.2N 0002 peak (full width at half maximum ∼2400arcsec) indicated a high structural quality of the films. Cathodoluminescence measurements performed in a scanning electron microscope at 5K revealed Al0.8In0.2N luminescence at 248nm, or equivalently 5.0eV, showing that Al0.8In0.2N is a promising material for deep-ultraviolet optoelectronic devices.
Increased cell response to zirconia ceramics by surface modification
Authors: Zhang Jingxian , Jiang Dongliang , Kotobuki Noriko , Maeda Masahiko , Hirose Motohiro , Ohgushi Hajime , Iwasa Mikio
Published: November 2006

The authors present a method to enhance the cell response to zirconia materials without sacrificing the mechanical properties. Zirconia specimens prepared by slip casting and pressureless sintering have excellent mechanical properties. After hydrothermal treatment in phosphoric solutions at 150°C for 2h, enhanced cell proliferation and high alkaline phosphatase activity were determined. This can be explained by the development of a more biocompatible surface phase (zirconium phosphate), which is believed to have high affinity for proteins. Results showed that it was possible to increase the cell response to zirconia ceramics by the proposed surface modification method.
Ultrafine diamond synthesized by long-pulse-width laser
Authors: Sun Jing , Hu Sheng-Liang , Du Xi-Wen , Lei Yi-Wen , Jiang Lei
Published: November 2006

Nanodiamonds with sizes of 3–6nm were prepared by irradiating graphite suspension using a long-pulse-width (1.2ms) laser at room temperature and normal pressure. The low power density and long pulse laser generated a lower temperature and a lower pressure, which determine the stable size of nanodiamonds. On the other hand, the low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limit the final size of nanodiamonds. Our results suggest that the growth of nanodiamonds follows the Wilson-Frenkel law, and the long pulse laser is propitious to producing fine nanodiamonds.
Unique characteristics of
Xanthomonas oryzae
pv.
oryzae
AvrXa21 and implications for plant innate immunity
Authors: Lee Sang-Won , Han Sang-Wook , Bartley Laura E. , Ronald Pamela C.
Published: November 2006

This article provides a brief overview of some of the major concepts and molecular features of plant and animal innate immune systems. The rice pathogen recognition receptor, XA21, confers resistance to
Xanthomonas oryzae
pv.
oryzae
strains producing the
AvrXa21
elicitor.
Xa21
codes for a receptor-like kinase consisting of an extracellular leucine-rich repeat domain, a transmembrane domain, and a cytoplasmic kinase domain. We show that AvrXa21 activity requires the presence of
rax
(
r
equired for
A
vr
X
a21)
A
,
raxB
, and
raxC
genes that encode components of a type one secretion system. In contrast, an
hrpC
−
strain deficient in type three secretion maintains AvrXa21 activity.
Xanthomonas campestris
pv.
campestris
can express AvrXa21 activity if
raxST
, encoding a putative sulfotransferase, and
raxA
are provided in trans. Expression of
rax
genes depends on population density and other functioning
rax
genes. This and other data suggest that the AvrXa21 pathogen-associated molecule is involved in quorum sensing. Together these data suggest that AvrXa21 represents a previously uncharacterized class of Gram-negative bacterial signaling molecules. These results from our studies of the XA21/AvrXa21 interaction call for some modifications in the way we think about innate immunity strategies.
TRP Channels, CCE, and the Pulmonary Vascular Smooth Muscle
Authors: REMILLARD CARMELLE V. , YUAN JASON X.‐J.
Published: November 2006

Transient receptor potential (TRP) genes represent a novel class of genes that are generally believed to encode for nonselective cation channels. A subfamily of TRP channels, canonical TRP (TRPC), which are highly permeable to Ca2+ (and Na+), co‐assembles with each other to form functional store‐ and receptor‐operated Ca2+ channels. TRPC mRNA and protein have been identified in pulmonary arterial smooth muscle and endothelial cells. The currents generated by Ca2+ influx through store‐ and receptor‐operated Ca2+ channels have also been extensively characterized in these cells. More recently, the attention has shifted to identify the TRP subunits that underlie the function of native channels in the pulmonary vasculature, with the understanding that TRP channels assemble as either homo‐or heterotetramers in vivo. This work in progress has yielded exciting information regarding the involvement of TRP channels in the control of smooth muscle contraction, and cell proliferation and migration. In this review, the authors focus on describing the function and transcriptional regulation of TRP proteins, and the store‐ and receptor‐operated Ca2+ channels for which they are responsible, in pulmonary artery smooth muscle cells (PASMC). They also identify some key TRP proteins whose role in the pulmonary vasculature has been established, as well as some more novel subunits whose role, although intriguing, can only be inferred from other vascular studies. Finally, they describe the involvement of TRP channels in regulating pulmonary vasoconstriction, PASMC proliferation, and pulmonary endothelial barrier function.
Ca2+ Signaling, TRP Channels, and Endothelial Permeability
Authors: TIRUPPATHI CHINNASWAMY , AHMMED GIAS U. , VOGEL STEPHEN M. , MALIK ASRAR B.
Published: November 2006

Increased endothelial permeability is the hallmark of inflammatory vascular edema. Inflammatory mediators that bind to heptahelical G protein‐coupled receptors trigger increased endothelial permeability by increasing the intracellular Ca2+ concentration ([Ca2+]i). The rise in [Ca2+]i activates key signaling pathways that mediate cytoskeletal reorganization (through myosin‐light‐chain‐dependent contraction) and the disassembly of VE‐cadherin at the adherens junctions. The Ca2+‐dependent protein kinase C (PKC) isoform PKCα plays a crucial role in initiating endothelial cell contraction and disassembly of VE‐cadherin junctions. The increase in [Ca2+]i induced by inflammatory agonists such as thrombin and histamine is achieved by the generation of inositol 1,4,5‐trisphosphate (IP3), activation of IP3‐receptors, release of stored intracellular Ca2+, and Ca2+ entry through plasma membrane channels. IP3‐sensitive Ca2+‐store depletion activates plasma membrane cation channels (i.e., store‐operated cation channels [SOCs] or Ca2+ release‐activated channels [CRACs]) to cause Ca2+ influx into endothelial cells. Recent studies have identified members of Drosophila transient receptor potential (TRP) gene family of channels that encode functional SOCs in endothelial cells. These studies also suggest that the canonical TRPC homologue TRPC1 is the predominant isoform expressed in human vascular endothelial cells, and is the essential component of the SOC in this cell type. Further, evidence suggests that the inflammatory cytokine tumor necrosis factor‐α can induce the expression of TRPC1 in human vascular endothelial cells signaling via the nuclear factor‐κB pathway. Increased expression of TRPC1 augments Ca2+ influx via SOCs and potentiates the thrombin‐induced increase in permeability in human vascular endothelial cells. Deletion of the canonical TRPC homologue in mouse, TRPC4, caused impairment in store‐operated Ca2+ current and Ca2+‐store release‐activated Ca2+ influx in aortic and lung endothelial cells. In TRPC4 knockout (TRPC4−/−) mice, acetylcholine‐induced endothelium‐dependent smooth muscle relaxation was drastically reduced. In addition, TRPC4−/− mouse‐lung endothelial cells exhibited lack of actin‐stress fiber formation and cell retraction in response to thrombin activation of protease‐activated receptor‐1 (PAR‐1) in endothelial cells. The increase in lung microvascular permeability in response to PAR‐1 activation was inhibited in TRPC4−/− mice. These results indicate that endothelial TRP channels such as TRPC1 and TRPC4 play an important role in signaling agonist‐induced increases in endothelial permeability.
Ca2+ Channels and Pulmonary Endothelial Permeability: Insights from Study of Intact Lung and Chronic Pulmonary Hypertension
Authors: TOWNSLEY MARY I. , KING JUDY A. , ALVAREZ DIEGO F.
Published: November 2006

Phenotypic heterogeneity in pulmonary vascular endothelial cells extends to regulation of endothelial permeability, a process which often depends upon Ca2 + entry from the extracellular space. Scanning electron microscopy of vascular corrosion casts has documented distinct patterns of barrier disruption. Store depletion and activation of Ca2 + entry via canonical transient potential channels (TRPC1 and TRPC4) disrupts the barrier in extraalveolar vessels. In contrast, numerous other models of acute lung injury, including high vascular pressure‐ or epoxyeicosatrienoic acid‐induced injury, specifically disrupt the alveolar septal barrier. This review discusses Ca2 + permeant channels which potentially could be involved in regulation of barrier integrity in the alveolar septal compartment: transient receptor potential channels, cyclic nucleotide gated channels, purinergic (P2X) channels, and T‐type voltage gated channels. The evidence for the vanilloid transient receptor potential channel TRPV4 in regulating septal barrier function is discussed. Adaptations in barrier function in chronic pulmonary hypertension are reviewed, notably the loss of a store depletion‐dependent permeability response in the intact lung. Finally, the authors propose that since specific disruption of the alveolar septal barrier will have deleterious functional consequences, such as alveolar flooding and impairment of gas exchange, identification of specific molecular targets for Ca2 + entry‐dependent regulation of barrier function in this compartment is needed.
Electrical control of the linear optical properties of particulate composite materials
Authors: Lakhtakia Akhlesh , Mackay Tom G
Published: November 2006

The Bruggeman formalism for the homogenization of particulate composite materials is used to predict the effective permittivity dyadic of a two constituent composite material with one constituent having the ability to display the Pockels effect. Scenarios wherein the constituent particles are randomly oriented, oriented spheres and oriented spheroids are numerically explored. Thereby, homogenized composite materials (HCMs) are envisaged whose constitutive parameters may be continuously varied through the application of a low-frequency (dc) electric field. The greatest degree of control over the HCM constitutive parameters is achievable when the constituents comprise oriented and highly aspherical particles and have high electro-optic coefficients.
Rarity of a top predator triggers continent-wide collapse of mammal prey: dingoes and marsupials in Australia
Authors: Johnson Christopher N , Isaac Joanne L , Fisher Diana O
Published: November 2006

Top predators in terrestrial ecosystems may limit populations of smaller predators that could otherwise become over abundant and cause declines and extinctions of some prey. It is therefore possible that top predators indirectly protect many species of prey from excessive predation. This effect has been demonstrated in some small-scale studies, but it is not known how general or important it is in maintaining prey biodiversity. During the last 150 years, Australia has suffered the world's highest rate of mammal decline and extinction, and most evidence points to introduced mid-sized predators (the red fox and the feral cat) as the cause. Here, we test the idea that the decline of Australia's largest native predator, the dingo, played a role in these extinctions. Dingoes were persecuted from the beginning of European settlement in Australia and have been eliminated or made rare over large parts of the continent. We show a strong positive relationship between the survival of marsupials and the geographical overlap with high-density dingo populations. Our results suggest that the rarity of dingoes was a critical factor which allowed smaller predators to overwhelm marsupial prey, triggering extinction over much of the continent. This is evidence of a crucial role of top predators in maintaining prey biodiversity at large scales in terrestrial ecosystems and suggests that many remaining Australian mammals would benefit from the positive management of dingoes.