bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Citalopram Infusion on the Serotonin Transporter Binding of [11C]DASB in Healthy Controls
Authors: Hinz Rainer , Selvaraj Sudhakar , Murthy N Venkatesha , Bhagwagar Zubin , Taylor Matthew , Cowen Philip J , Grasby Paul M
Published: May 2008

The positron emission tomography (PET) ligand [11C]DASB is currently the most widely used imaging agent for quantitative studies of the serotonin transporter (SERT) in human brain. The aim of this work was to assess the effects of an intravenous infusion of 10 mg citalopram, a selective serotonin reuptake inhibitor (SSRI), before the PET scan on the kinetics of [11C]DASB in arterial plasma and in selected brain regions. Four healthy male volunteers underwent two PET scans with a mean of 523 MBq injected activity after either placebo or Citalopram infusion in a randomised design. The Citalopram infusion led to a substantial increase of the area under the curve of the metabolite-corrected arterial plasma input function. Total volumes of distribution VT were estimated applying the Logan plot to regional time—activity curves or by generating parametric maps with spectral analysis. A mean reduction of the cerebellar VT of 19% with Logan analysis and of 24% with spectral analysis was observed after Citalopram infusion, which confirms previous findings of displaceable SERT ligand binding in cerebellar grey matter. The SERT occupancy for six target regions with moderate to high binding was 60% derived from BPND and 69% derived from BPP.
Dynamic Changes in Vascular Permeability, Cerebral Blood Volume, Vascular Density, and Size after Transient Focal Cerebral Ischemia in Rats: Evaluation with Contrast-Enhanced Magnetic Resonance Imaging
Authors: Lin Chien-Yuan , Chang Chen , Cheung Wai-Mui , Lin Ming-Huang , Chen Jean-Ju , Hsu Chung Y , Chen Jyh-Horng , Lin Teng-Nan
Published: May 2008

Postischemic cerebral blood flow and blood volume changes have been associated with angiogenesis; nevertheless, the spatiotemporal changes in vascular permeability, vascular density, and vessel size have not been investigated. Here we report a prolonged increase in vascular permeability from day 3 to day 21 after ischemia, in particular in the reperfused outer cortical layers and leptomeninges. Increased cerebral blood volume (CBV) was observed from day 3 to day 14, whereas increased blood volume in small vessels, primarily capillaries, was noticed from day 7 to day 14 in the reperfused cortex. An initial decrease in vascular density and a reciprocal increase in vessel size were observed within the reperfused cortex at days 1 and 3 after ischemia. Immunohistological analysis confirmed a similar decrease in microvessel density and an increase in vessel size in vessels with a diameter greater than 30 μm. These large-sized vessels exhibited intense basic fibroblast growth factor and endothelial nitric oxide synthase immunoreactivity, suggesting the growth of collateral vessels. By contrast, a late increase in vascular density was noticed in the reperfused outer cortex at days 14 and 21 after ischemia. Together, these findings suggest that the early phase of CBV increase is likely because of the improvement in collateral circulation, whereas the late phase of CBV increase is attributed to the surge of angiogenesis.
Huntington's disease: from pathology and genetics to potential therapies
Authors: Imarisio Sara , Carmichael Jenny , Korolchuk Viktor , Chen Chien-Wen , Saiki Shinji , Rose Claudia , Krishna Gauri , Davies Janet E. , Ttofi Evangelia , Underwood Benjamin R. , Rubinsztein David C.
Published: May 2008

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease caused by a CAG trinucleotide repeat expansion encoding an abnormally long polyglutamine tract in the huntingtin protein. Much has been learnt since the mutation was identified in 1993. We review the functions of wild-type huntingtin. Mutant huntingtin may cause toxicity via a range of different mechanisms. The primary consequence of the mutation is to confer a toxic gain of function on the mutant protein and this may be modified by certain normal activities that are impaired by the mutation. It is likely that the toxicity of mutant huntingtin is revealed after a series of cleavage events leading to the production of N-terminal huntingtin fragment(s) containing the expanded polyglutamine tract. Although aggregation of the mutant protein is a hallmark of the disease, the role of aggregation is complex and the arguments for protective roles of inclusions are discussed. Mutant huntingtin may mediate some of its toxicity in the nucleus by perturbing specific transcriptional pathways. HD may also inhibit mitochondrial function and proteasome activity. Importantly, not all of the effects of mutant huntingtin may be cell-autonomous, and it is possible that abnormalities in neighbouring neurons and glia may also have an impact on connected cells. It is likely that there is still much to learn about mutant huntingtin toxicity, and important insights have already come and may still come from chemical and genetic screens. Importantly, basic biological studies in HD have led to numerous potential therapeutic strategies.
The TSC1–TSC2 complex: a molecular switchboard controlling cell growth
Authors: Huang Jingxiang , Manning Brendan D.
Published: May 2008

TSC1 and TSC2 are the tumour-suppressor genes mutated in the tumour syndrome TSC (tuberous sclerosis complex). Their gene products form a complex that has become the focus of many signal transduction researchers. The TSC1–TSC2 (hamartin–tuberin) complex, through its GAP (GTPase-activating protein) activity towards the small G-protein Rheb (Ras homologue enriched in brain), is a critical negative regulator of mTORC1 (mammalian target of rapamycin complex 1). As mTORC1 activity controls anabolic processes to promote cell growth, it is exquisitely sensitive to alterations in cell growth conditions. Through numerous phosphorylation events, the TSC1–TSC2 complex has emerged as the sensor and integrator of these growth conditions, relaying signals from diverse cellular pathways to properly modulate mTORC1 activity. In the present review we focus on the molecular details of TSC1–TSC2 complex regulation and function as it relates to the control of Rheb and mTORC1.
AMPK, MAPK and Bax in the heart: some questions answered
Authors: Borutaite Vilmante
Published: May 2008

The question of how Bax is activated during apoptosis to perform its role in permeabilization of mitochondrial membranes is intriguing for investigators in the wide field of cell death research. In their paper published in the Biochemical Journal in 2006, Capano and Crompton presented their discovery that simulated ischaemia causes rapid activation of AMPK (AMP-activated protein kinase) which phosphorylates and activates p38 MAPK (mitogen-activated protein kinase) leading to Bax activation and translocation to mitochondria in isolated cardiac myocytes. This was the first report on the molecular mechanism of Bax activation and migration during ischaemia-induced apoptosis in cardiomyocytes.
Cancer therapy: staying current with AMPK
Authors: Fruman David A. , Edinger Aimee L.
Published: May 2008

Does the LKB1–AMPK (AMP-activated protein kinase) pathway act to suppress tumorigenesis or to rescue cancer cells from metabolic collapse? New work from the Alessi laboratory in this issue of the Biochemical Journal shows conclusively that AMPK activators delay the growth of tumours that occur spontaneously in PTEN (phosphatase and tensin homologue deleted on chromosome 10) heterozygous mice.
Modeling doped and defective oxides in catalysis with density functional theory methods: Room for improvements
Authors: Pacchioni Gianfranco
Published: May 2008

Due to the well-known problem of the self-interaction, standard density functional theory (DFT) methods tend to produce delocalized holes and electrons in defective oxide materials even when there is ample experimental evidence of a strong localization. For late transition metal compounds or rare earth oxides, this results in the incorrect description of the electronic structure of the system (e.g., magnetic insulators are predicted to be metallic). Practical ways to correct this deficiency are based on the use of hybrid functionals or of the DFT+U approach. In this way, most of the limitations related to the self-interaction are removed, and the electronic structure is properly described. What is less clear is to what extent hybrid functionals, DFT+U approaches, or standard DFT functionals can properly describe the strength of the chemical bonds at the surface of an oxide. This is a crucial question if one is interested in the catalytic properties of oxide surfaces. Oxidation reactions often involve oxygen detachment from the surface and incorporation into an organic substrate. Oxides are doped with heteroatoms to create defects and facilitate oxygen removal from the surface, with formation of oxygen vacancies. Do standard DFT calculations provide a good binding energy of the missing oxygen despite the failure in giving the right electronic structure? Can hybrid functionals or the DFT+U approach provide a simple yet reliable way to get accurate reaction enthalpies and energy barriers? In this essay, we discuss these problems by analyzing some case histories and the relatively scarce data existing in the literature. The conclusion is that while modern electronic structure methods accurately reproduce and predict a wide range of electronic, optical, and magnetic properties of oxides, the description of the strength of chemical bonds still needs considerable improvements.
Heterogeneous catalysis: Enigmas, illusions, challenges, realities, and emergent strategies of design
Authors: Thomas John Meurig
Published: May 2008

Predominantly this article deals with the question of how to design new solid catalysts for a variety of industrial and laboratory-orientated purposes. A generally applicable strategy, illustrated by numerous examples, is made possible based on the use of nanoporous materials on to the (high-area) inner surfaces of which well-defined (experimentally and computationally) active centers are placed in a spatially separated fashion. Such single-site catalysts, which have much in common with metal-centered homogenous catalysts and enzymes, enable a wide range of new catalysts to be designed for a variety of selective oxidations, hydrogenations, hydrations and hydrodewaxing, and other reactions that the “greening” of industrial processes demand. Examples are given of new shape-selective, regio-selective, and enantioselective catalysts, many of which operate under mild, environmentally benign conditions. Also considered are some of the reasons why detailed studies of adsorption and stoichiometric reactions at single-crystal surfaces have, disappointingly, not hitherto paved the way to the design and production of many new heterogenous catalysts. Recent work of a theoretical and high-throughout nature, allied to some experimental studies of well-chosen model systems, holds promise for the identification of new catalysts for simple, but industrially important reactions.
Magnetism in Gd–W films
Authors: Gadioli Giovana Z. , Rouxinol Francisco P. , Gelamo Rogério V. , dos Santos Adenilson O. , Cardoso Lisandro P. , Bica de Moraes Mário A.
Published: May 2008

Vapor condensation techniques are useful to prepare magnetic alloys whose components have low or even negligible equilibrium mutual solubility. In this work, one of these techniques—sputtering—was used to obtain GdxW1−x alloys whose magnetic properties were investigated as a function of the Gd atomic concentration x. Gadolinium and various Gd-based alloys are promising materials for magnetic refrigeration and this was one of the motivations for this study. The Gdx–W1−x films were sputter deposited from Gd and W targets with x ranging from 0 to 1 as determined by x-ray energy-dispersive spectroscopic analyses. X-ray diffraction patterns indicate that crystalline structures were formed at low and high Gd concentrations, while at intermediate concentrations, the films were amorphous. Magnetization measurements, performed as a function of temperature and with static and alternating applied fields, reveal a spin glasslike behavior in all the W-containing samples for temperatures below the freezing temperature Tf. For low and intermediate Gd concentrations, and for T>Tf, the films were paramagnetic, while a ferromagnetic phase was observed in the Gd–W alloy of the highest Gd content. The magnetocaloric effect was investigated from the magnetization isotherms M versus H, from which the isothermal magnetic entropy variation ΔSM as a function of T, for the removal of an applied field of 50kOe, was determined. It was observed that the maximum value of ΔSM for each ΔSM versus T curve and the temperature at which these maxima occur, are strongly dependent on x.
A topos foundation for theories of physics: IV. Categories of systems
Authors: Döring A. , Isham C. J.
Published: May 2008

This paper is the fourth in a series whose goal is to develop a fundamentally new way of building theories of physics. The motivation comes from a desire to address certain deep issues that arise in the quantum theory of gravity. Our basic contention is that constructing a theory of physics is equivalent to finding a representation in a topos of a certain formal language that is attached to the system. Classical physics arises when the topos is the category of sets. Other types of theory employ a different topos. The previous papers in this series are concerned with implementing this program for a single system. In the present paper, we turn to considering a collection of systems; in particular, we are interested in the relation between the topos representation for a composite system and the representations for its constituents. We also study this problem for the disjoint sum of two systems. Our approach to these matters is to construct a category of systems and to find a topos representation of the entire category.
Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure
Authors: Somorjai Gabor A. , Park Jeong Y.
Published: May 2008

Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate-induced restructuring). It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H–H, OO, C–H, CO, and C–C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation—vibrational spectroscopy and high pressure scanning tunneling microscopy revealed bond breaking at low reaction probability sites on the adsorbate-covered metal surface and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme, and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1–10nm range and controlled shapes to use them as new model catalyst systems in two-dimensional monolayer film or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene, and crotonaldehyde) showed that the reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site that is associated with the hot electron flow induced by exothermic reactions such as carbon monoxide oxidation.
Conductor grid optimization for luminance loss reduction in organic light emitting diodes
Authors: Neyts Kristiaan , Real Alfonso , Marescaux Matthias , Mladenovski Saso , Beeckman Jeroen
Published: May 2008

The recently increased efficiency of organic light emitting devices (OLED) brings lighting applications within reach. If the area of the OLED is of the order a cm2, voltage and brightness losses related to the square resistance of the transparent electrode become important. The homogeneity of the voltage and brightness can be improved by contacting the transparent electrode from all edges and by adding a metallic grid to the transparent electrode. This grid should have narrow lines to minimize transmission losses and improve the total light emission from the OLED. The voltage losses in grids with different shapes (triangular, square, and hexagonal) are evaluated and the grid parameters are optimized to maximize the total light emission. It turns out that a hexagonal grid has lower loss than a square grid with the same line width.
Polyheteroarylene films with intrinsic switching mechanism for nonvolatile memory applications
Authors: Zherebov A. , Lachinov A. , Genoe J. , Tameev A.
Published: May 2008

This paper presents a polymer material for the nonvolatile memory applications. Current-voltage characteristics show the reproducible nonvolatile switching effect. The effect is observed not only when using two metallic electrodes but also when using two semiconducting electrodes, which reveals the intrinsic nature of the switching phenomenon.
Comment on the drift mirror instability
Authors: Hellinger Petr
Published: May 2008

Drift mirror instability is investigated in a slightly inhomogeneous plasma in a low-frequency, long-wavelength limit of the Vlasov–Maxwell equation. It is shown that previously derived threshold conditions for the drift mirror instability in the case of one cold species are incorrect and that it is hard to get analytically a simple threshold condition for the drift mirror instability in this case. It is argued that the same is true for the drift mirror instability in general.
Self-similar quasineutral expansion of a collisionless plasma with tailored electron temperature profile
Authors: Kumar Naveen , Pukhov Alexander
Published: May 2008

The self-similar expansion of a collisionless plasma, with an externally tailored electron temperature profile, is studied analytically in quasineutral approximation. It is shown that the tailoring of electron plasma temperature can lead to an ion bunch formation concentrated in phase space. Experimentally, it may correspond to the expansion of a thin foil target driven by multiple laser pulses. A one-dimensional particle-in-cell simulation of thin foil expansion driven by two laser pulses is carried out that evidences the quasimonoenergetic ions generation, thus qualitatively confirming the analytical theory.
H
∕
D
isotope effect of methyl internal rotation for acetaldehyde in ground state as calculated from a multicomponent molecular orbital method
Authors: Ishimoto Takayoshi , Ishihara Yasuyuki , Teramae Hiroyuki , Baba Masaaki , Nagashima Umpei
Published: May 2008

We have analyzed the differences in the methyl internal rotation induced by the H∕D isotope effect for acetaldehyde (CH3CHO) and deuterated acetaldehyde (CD3CDO) in ground state by means of the multicomponent molecular orbital (MC̱MO) method, which directly accounts for the quantum effects of protons and deuterons. The rotational constant of CH3CHO was in reasonable agreement with experimental one due to the adequate treatment of the protonic quantum effect by the MC̱MO method. The C–D bond distances were about 0.007Å shorter than the C–H distances because of the effect of anharmonicity of the potential. The Mulliken population for CD3 in CD3CDO is larger than that for CH3 in CH3CHO because the distribution of wavefunctions for the deuterons was more localized than that for the protons. The barrier height obtained by the MC̱MO method for CH3CHO was estimated as 401.4cm−1, which was in excellent agreement with the experimentally determined barrier height. We predicted the barrier height of CD3CDO as 392.5cm−1. We suggest that the internal rotation of the CD3 group was more facile than that of the CH3 group because the C–D bond distance was observed to be shorter than the C–H distance. Additionally the localized electrons surrounding the CD3 group in CD3CDO caused the extent of hyperconjugation between the CD3 and CDO groups to be smaller than that in the case of CH3CHO, which may have also contributed to the observed differences in methyl internal rotation. The differences in bond distances and electronic populations induced by the H∕D isotope effect were controlled by the difference in the distribution of wavefunctions between the protons and deuterons.
Graded wavelength one-dimensional photonic crystal reveals spectral characteristics of enhanced fluorescence
Authors: Mathias Patrick C. , Ganesh Nikhil , Zhang Wei , Cunningham Brian T.
Published: May 2008

One-dimensional photonic crystal (PC) slabs are capable of enhancing the excitation of fluorescent material adsorbed on their surface. In this report, we demonstrate and verify by electromagnetic computer simulations that resonant leaky modes spectrally overlapping the laser wavelength used for fluorescent excitation are responsible for the enhanced excitation, and that the Q-factor of the PC resonance is proportional to the resonant electric field intensity and thus proportional to the fluorescent enhancement factor. As a demonstration, we have fabricated a single PC slab surface with an intentional spatial gradient in the resonant wavelength and demonstrate enhanced fluorescence only from locations on the PC surface with a leaky mode corresponding to a 633 nm HeNe laser used to excite Cyanine 5 dye deposited uniformly across the PC. The results show that enhanced fluorescence signals for one-dimensional PC slabs originate from increased excitation of the fluorescent dye.
Molecular dynamics simulations on the local order of liquid and amorphous ZnTe
Authors: Rino José Pedro , Borges Denilson , Mota Rita C. , Silva Maurício A. P.
Published: May 2008

Molecular dynamics studies of structural and dynamical correlations of molten and vitreous states under several conditions of density and temperature were performed. We use an effective recently proposed interatomic potential, consisting of two- and three-body covalent interactions which has successfully described the structural, dynamical, and structural phase transformation induced by pressure in ZnTe [D. S. Borges and J. P. Rino, Phys. Rev. B 72, 014107 (2005)]. The two-body term of the interaction potential consists of Coulomb interaction resulting from charge transfer, steric repulsion due to atomic sizes, charge-dipole interaction to include the effect of electronic polarizability of anions, and dipole-dipole (van der Waals) interactions. The three-body covalent term is a modification of the Stillinger–Weber potential. Molecular dynamics simulations in isobaric-isenthalpic ensemble have been performed for systems amounting to 4096 and 64 000 particles. Starting from a crystalline zinc-blende (ZB) structure, the system is initially heated until a very homogeneous liquid is obtained. The vitreous zinc telluride phase is attained by cooling the liquid at sufficiently fast cooling rates, while slower cooling rates lead to a disordered ZB crystalline structure. Two- and three-body correlations for the liquid and vitreous phases are analyzed through pair distribution functions, static structure factors, and bond angle distributions. In particular, the neutron static structure factor for the liquid phase is in very good agreement with both the reported experimental data and first-principles simulations.
Minimum energy pathways of brittle and ductile deformation/fracture processes
Authors: Zahn Dirk
Published: May 2008

An alternative approach to exploring deformation and fracture processes from molecular dynamics simulations is presented. The underlying concept is based on the transition path sampling scheme which was proven powerful for unprejudiced mechanistic analyses of rare reaction events and phase transitions. Transferring this method to deformation and fracture is particularly rewarding for the study of brittle materials. Similar to unbiased investigations of nucleation events in first order phase transitions, our simulations do not require the preparation of cavities to induce fracture processes. The mechanisms of cavitation and fracture propagation are instead obtained as simulation results. As two case studies, transition path sampling related to brittle fracture of ZnO nanorods and to ductile deformation of Al nanoblocks is compared to conventional simulations imposing constant-strain rates.
Indistinguishable photons from a diode
Authors: Bennett A. J. , Patel R. B. , Shields A. J. , Cooper K. , Atkinson P. , Nicoll C. A. , Ritchie D. A.
Published: May 2008

We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.
Interlevel transitions and two-photon processes in Ge/Si quantum dot photocurrent
Authors: Finkman E. , Shuall N. , Vardi A. , Le Thanh V. , Schacham S. E.
Published: May 2008

Photocurrent spectra due to interlevel transitions of holes in Ge/Si quantum dots show several peaks in the range of 60–300 meV, which superlinearly increase with bias, indicating release of carriers by tunneling. The relative peak intensity drastically changes with applied voltage, its polarity, and the measurement system. Lower energy peaks, at 69 and 86 meV, are observed only with a Fourier transform IR (FTIR) spectrometer. The 69 and 86 meV transitions excite holes into intermediate levels from which they are re-excited to shallow levels in a two-photon process. This is observed with FTIR only where the sample is simultaneously exposed to a wide range of energies. Direct band-to-band excitation at 1.25 eV increases the midinfrared signals by orders of magnitude by pumping the intermediate levels. Placing dopants in the barrier greatly increases photocurrent intensity and reduces noise. One-dimensional and three-dimensional numerical analyses confirm our findings.
Setup for in situ deep level transient spectroscopy of semiconductors during swift heavy ion irradiation
Authors: Kumar Sandeep , Kumar Sugam , Katharria Y. S. , Safvan C. P. , Kanjilal D.
Published: May 2008

A computerized system for in situ deep level characterization during irradiation in semiconductors has been set up and tested in the beam line for materials science studies of the 15MV Pelletron accelerator at the Inter-University Accelerator Centre, New Delhi. This is a new facility for in situ irradiation-induced deep level studies, available in the beam line of an accelerator laboratory. It is based on the well-known deep level transient spectroscopy (DLTS) technique. High versatility for data manipulation is achieved through multifunction data acquisition card and LABVIEW. In situ DLTS studies of deep levels produced by impact of 100MeV Si ions on Au∕n-Si(100) Schottky barrier diode are presented to illustrate performance of the automated DLTS facility in the beam line.
Properties of GaP(001) surfaces thermally annealed in dry N2 atmosphere
Authors: Rokugawa Hiroshi , Adachi Sadao
Published: May 2008

Isochronal annealing behaviors of GaP(001) surfaces in dry N2 atmosphere for t=20 min have been studied by using spectroellipsometry (SE), optical microscopy, scanning electron microscopy (SEM), ex situ atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). The SE data suggest that a surface native oxide can be gradually etch removed with increasing annealing temperature T. After annealing at T=800°C, the surface is covered with a thick thermal oxide. The XPS spectra confirm the removal of the Ga-related oxides for T<800°C and the presence of P-related thermal oxides at T=800°C. Further increase in T promises a smoothened, clean surface, as also confirmed by the AFM and XPS observations. After annealing above 900°C, thermal decomposition catastrophically occurs which makes SE measurement impossible. The optical and SEM images reveal the thermally damaged surfaces after annealing at T>700°C, in agreement with the AFM results.
An investigation of phonon decay in B12As2 by Raman scattering spectroscopy
Authors: Gray J. C. , Pomeroy J. W. , Kuball M. , Xu Z. , Edgar J. H. , Chen H. , Dudley M.
Published: May 2008

Raman scattering spectroscopy was used to study the spectral linewidth and frequency of characteristic phonon modes of boron arsenide (B12As2) as a function of temperature between 7 and 680 K. A combination of two- and three-phonon decay processes was found to dominate the dynamics of the intra-icosahedral phonon modes at 624, 682, and 742 cm−1, whilst two-phonon decay appears to be favored for the As–As stretch mode at 310 cm−1 and for the 506 cm−1 mode. Changes in frequency with temperature predominantly contain contributions from lattice expansion for all modes except the 506 cm−1 Eg mode, where contributions from phonon damping play a more significant role.
Invited Article: Design techniques and noise properties of ultrastable cryogenically cooled sapphire-dielectric resonator oscillators
Authors: Locke C. R. , Ivanov E. N. , Hartnett J. G. , Stanwix P. L. , Tobar M. E.
Published: May 2008

We review the techniques used in the design and construction of cryogenic sapphire oscillators at the University of Western Australia over the 18year history of the project. We describe the project from its beginnings when sapphire oscillators were first developed as low-noise transducers for gravitational wave detection. Specifically, we describe the techniques that were applied to the construction of an interrogation oscillator for the PHARAO Cs atomic clock in CNES, in Toulouse France, and to the 2006 construction of four high performance oscillators for use at NMIJ and NICT, in Japan, as well as a permanent secondary frequency standard for the laboratory at UWA. Fractional-frequency fluctuations below 6×10−16 at integration times between 10 and 200s have been repeatedly achieved.
One-step preparation of Ca-α-SiAlON:Eu2+ fine powder phosphors for white light-emitting diodes
Authors: Suehiro Takayuki , Hirosaki Naoto , Xie Rong-Jun , Sakuma Ken , Mitomo Mamoru , Ibukiyama Masahiro , Yamada Suzuya
Published: May 2008

A simple methodology for producing yellow-emitting Ca-α-SiAlON:Eu2+ phosphors for white light-emitting diodes has been developed, which consists of postsynthesis activation of fine α-SiAlON powders prepared by the gas-reduction-nitridation method. Phase-pure, fine Ca-α-SiAlON:Eu2+ phosphors possessing the particle size ranging ∼0.9–2.8μm and high quantum efficiencies of ∼44%–55% under near-UV to blue light excitation are obtained as the process developed. The chromaticity coordinate of the synthesized Ca-α-SiAlON:Eu2+ can be tailored by simply controlling the activator concentration, enabling the creation of a broad range of warm-white light with the correlated color temperatures of ∼3500–2600K.
Fe films grown on GaAs(110) in a two-step process: Improved structural and magnetic properties
Authors: Winking L. , Wenderoth M. , Homoth J. , Siewers S. , Ulbrich R. G.
Published: May 2008

Fe films of up to 10 ML thickness were grown on cleaved GaAs(110) in a two-step process that associates low-temperature deposition at 130K with a subsequent annealing to room temperature. Low-energy electron diffraction, scanning tunneling microscopy, and in situ magneto-optical Kerr effect were combined to study these films. The observed magnetic and structural properties are distinctly different from the characteristics of conventionally grown Fe films on GaAs. We found no indication of interface compound formation. The applied two-step growth process is a promising technique to further increase spin-injection and detection efficiencies of Fe∕GaAs hybrid structures.
Structural and optical properties of vertically stacked triple InAs dot-in-well structure
Authors: Rainò G. , Salhi A. , Tasco V. , De Vittorio M. , Passaseo A. , Cingolani R. , De Giorgi M. , Luna E. , Trampert A.
Published: May 2008

The authors report a detailed investigation of the structural and optical properties of vertically stacked InAs quantum dots embedded in an (In,Ga)As quantum well by means of transmission electron microscopy and time resolved photoluminescence based on the upconversion technique. By comparing the optical features of quantum dot samples of different barrier thicknesses (nominal values between 5 and 65nm), they have found evidence for electronic coupling among the quantum dots, featured by an increase of radiative lifetime and a relatively blueshifted emission peak for the thinnest spacer layer sample.
Origin of current oscillations in a polymeric electrochemically controlled element
Authors: Smerieri Anteo , Erokhin Victor , Fontana Marco P.
Published: May 2008

We present a model for describing electrical properties of an electrochemically controlled heterojunction between a conducting polymer (polyaniline) and a solid electrolyte (lithium salt doped polyethylene oxide). In particular, the difference in the kinetics of the conductivity variation for different polarities of the bias voltage and appearance of current oscillations at constant applied voltage are considered. The results of our simulation are in good agreement with published experimental data.
Radiative recombination dynamics in tetrapod-shaped CdTe nanocrystals: Evidence for a photoinduced screening of the internal electric field
Authors: Morello Giovanni , Tarì Davide , Carbone Luigi , Manna Liberato , Cingolani Roberto , De Giorgi Milena
Published: May 2008

We study the radiative recombination processes in CdTe tetrapod nanocrystals at 10K. Two intrinsic emission bands, namely the ground state (GS) and the excited state (EX), decay with three time constants, due to a power dependent Auger-like recombination process (tens of picoseconds), to the intrinsic emission of the two states (hundreds of picoseconds) and to emission from defect states (a few nanoseconds). The existence of an internal electric field originating from the e-h separation induced by the peculiar symmetry of the GS is demonstrated by a dynamical shift of the GS emission energy that is correlated to the EX population.
Gray-tone lithography using an optical diffuser and a contact aligner
Authors: Christophersen Marc , Phlips Bernard F.
Published: May 2008

This paper describes a simple method for the three-dimensional (3D) microfabrication of complex high-aspect structures in a one mask lithography process. The method relies on an unconventional way of performing gray-tone lithography. The main idea is to randomize the collimated light by using an optical diffuser to generate intensity distributions in the photoresist. The resist topography is determined by the density of open and opaque squares in the photomask. The resulting 3D resist is then transferred into 3D silicon structures by using reactive ion etching and deep reactive ion etching.
Excitation wavelength dependence of the visible photoluminescence from amorphous ZnO granular films
Authors: Zhang W. C. , Wu X. L. , Chen H. T. , Zhu J. , Huang G. S.
Published: May 2008

Amorphous ZnO granular films were fabricated by anodizing zinc sheet in 0.5M oxalic acid solution under direct current voltage. The photoluminescence spectrum of the as-anodized sample shows a very broad visible emission band, which can be Gaussian divided into two subbands at 525 and 600nm. Based on their annealing behavior and the growing mechanism of the ZnO films, the two subbands are attributed to optical transitions in oxygen vacancies and oxygen interstitials, respectively. Obvious redshifts of the two subbands were observed with increasing excitation wavelength. Spectral analyses suggest that the excitation wavelength dependences of the two subbands are due to the quantum confinement on the amorphous ZnO nanoparticles mainly with sizes of ∼10nm. This work provides a good understanding of the photoluminescence behavior of amorphous ZnO particles.
Realization of ambipolar pentacene thin film transistors through dual interfacial engineering
Authors: Yang Chuan-Yi , Cheng Shiau-Shin , Ou Chun-Wei , Chuang You-Che , Wu Meng-Chyi , Dhananjay  , Chu Chih-Wei
Published: May 2008

Ambipolar conduction of a pentacene-based field-effect transistor can be attributed to dual interface engineering, which occurs at the dielectric∕semiconductor interface and electrode∕semiconductor interface. While the former was realized by utilizing a hydroxyl-free gate dielectric, the latter was made feasible by the use of appropriate metal source and drain electrodes. The field-effect hole and electron mobilities of 0.026 and 0.0023cm2∕Vs, respectively, were extracted from the transfer characteristics of pentacene organic field-effect transistors utilizing polymethyl methacrylate as the trap-reduction interfacial modified layer and Al as the source and drain (S∕D) electrodes. We demonstrated a complementarylike inverter by using two identical ambipolar transistors and it can be operated both in the first and third quadrants with a high output voltage gain of around 10.
Sensitive detection of weak absorption signals in photoacoustic spectroscopy by using derivative spectroscopy and wavelet transform
Authors: Zheng Jincun , Tang Zhilie , He Yongheng , Guo Lina
Published: May 2008

This report presents a practical analytical method of photoacoustic (PA) spectroscopy that is based on wavelet transform (WT) and the first-derivative PA spectrum. An experimental setup is specially designed to obtain the first-derivative spectrum, which aims to identify some unnoticeable absorption peaks in the normal PA spectrum. To enhance the detectability of overlapping spectral bands, the WT is used to decompose the PA spectrum signals into a series of localized contributions (details and approximation) on the basis of the frequency. For the decomposed contributions do not change the absorption peak position of PA spectrum, one can retrieve the weak absorption signals by the decomposed result of WT. Because of the use of derivative spectroscopy and WT, three unnoticeable absorption peaks that are hidden in the PA spectrum of carbon absorption are precisely retrieved, the wavelengths of which are 699.7, 752.7, and 775.5nm, respectively. This analytical method, which has the virtue of using a physical method and using a computer software method, can achieve great sensitivity and accuracy for PA spectral analysis.
Stable ZnO thin film transistors by fast open air atomic layer deposition
Authors: Levy David H. , Freeman Diane , Nelson Shelby F. , Cowdery-Corvan Peter J. , Irving Lyn M.
Published: May 2008

We report stable, high performance zinc oxide thin film transistors grown by an atmospheric pressure atomic layer deposition system. With all deposition and processing steps kept at or below 200°C, the alumina gate dielectric shows low leakage (below 10−8A∕cm2) and high breakdown fields. Zinc oxide thin film transistors in a bottom gate geometry yield on/off ratios above 108, near zero turn-on voltage, little or no hysteresis, and mobility greater than 10cm2∕Vs. With alumina passivation, shifts in threshold voltage under gate bias stress compare favorably to those reported in the literature.
High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer
Authors: Ling H. S. , Wang S. Y. , Lee C. P. , Lo M. C.
Published: May 2008

We demonstrate the high quantum efficiency InAs∕In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also improves the escape probability of the photoelectrons. Compared with the conventional DWELL QDIPs, the quantum efficiency increases more than 20 times and the detectivity is about an order of magnitude higher at 77K.
Enhancement of electron field emission property with silver incorporation into diamondlike carbon matrix
Authors: Ahmed Sk. Faruque , Moon Myoung-Woon , Lee Kwang-Ryeol
Published: May 2008

Effects of silver doping on the electron field emission properties of diamondlike carbon films deposited on silicon substrates by the rf reactive sputtering technique were studied in detail. It was found that the threshold field and effective emission barrier were reduced by Ag doping and the emission current strongly depends on the Ag doping percentage. The threshold field was found to decrease from 6.8to2.6V∕μm with a variation of Ag at. % from 0 to 12.5. The field enhancement factor was calculated and we have explained the emission mechanism.
Microring resonators fabricated by electron beam bleaching of chromophore doped polymers
Authors: Sun Haishan , Chen Antao , Olbricht Benjamin C. , Davies Joshua A. , Sullivan Philip A. , Liao Yi , Dalton Larry R.
Published: May 2008

Decomposition of chromophore molecules under direct electron beam irradiation reduces the refractive index of chromophore containing polymers. The induced refractive index contrast between the exposed and unexposed regions is high enough for waveguide bends of small radius and thus microring resonator devices. This electron beam bleaching of chromophore-containing polymers provides a fabrication approach for nonlinear polymer optical waveguide devices. Fabrication of high quality microring resonators with critical feature size on the order of 100nm was demonstrated with this technique in an electro-optic polymer that contains YL124 chromophores.
A study on the transmission of picosecond ultrasonic waves in Si∕Mo superlattices
Authors: Kuo Wei-I , Pan En-Yea , Pu Nen-Wen
Published: May 2008

We have performed theoretical and experimental studies on the optical generation and transmission of picosecond ultrasonic pulses in a-Si∕Mo superlattices using ultrafast lasers. The pulse shapes and spectra of collectively excited folded phonon waves were analyzed. Calculations show that the picosecond strain pulses transmitted through a superlattice have a very complicated waveform due to branch folding and phononic bandgaps, but the transient piezoreflectance (TPR) response has a rather simple shape, similar to that of a homogeneous thin film. A direct pulse-echo technique was used to measure the waveform of the TPR response and the effective sound velocity of the folded phonons. The experimental results agree well with the theoretical predictions.
Ion beam acceleration in a divergent magnetic field
Authors: Biloiu Ioana A. , Scime Earl E. , Biloiu Costel
Published: May 2008

Two-dimensional argon ion velocity distribution functions (IVDFs) in the expansion region of a helicon plasma source have been measured by laser-induced-fluorescence tomography. Below a threshold value of the magnetic field in the expansion region, the IVDFs show a bimodal structure comprised of a supersonic ion population axially moving away from the source and an isotropic, slow, background, ion population. Increasing the magnetic field divergence leads to an increase in the axial speed of the supersonic component. A maximum axial speed of ∼2.9cs was obtained for a source/expansion magnetic field ratio of 43.
Immunoreactive cell wall proteins of Clostridium difficile identified by human sera
Authors: Wright Anne , Drudy Denise , Kyne Lorraine , Brown Katherine , Fairweather Neil F.
Published: May 2008

Clostridium difficile is a leading cause of nosocomial infection in the developed world, causing antibiotic-associated disease in susceptible populations. The identity of immunogenic proteins is important in understanding the pathogenesis of disease and in the design of vaccines. This study analysed the sera of six patients infected during a hospital outbreak of a C. difficile ribotype 017 strain. Using a proteomics-based approach, cell wall proteins were separated by two-dimensional PAGE, and immunoreactive proteins were revealed by reaction with patient sera. The identity of immunoreactive proteins was established by MS. Forty-two different proteins were identified in total. All patient sera reacted with at least one component of the surface-layer protein (SLP), four reacted with both components (high- and low-molecular-mass SLPs), and five reacted with one other cell wall protein, suggesting that these are immunodominant antigens. The role of these proteins as potential vaccine candidates and their roles in pathogenesis deserve further study.
Effect of sub-MIC concentrations of metronidazole, vancomycin, clindamycin and linezolid on toxin gene transcription and production in Clostridium difficile
Authors: Gerber Michael , Walch Christiane , Löffler Birgit , Tischendorf Kristin , Reischl Udo , Ackermann Grit
Published: May 2008

Clostridium difficileis the major cause of hospital-acquired infectious diarrhoea. Several antimicrobials are known to induce and promoteC. difficile-associated diarrhoea (CDAD). The impact of metronidazole (MTR), vancomycin (VAN), clindamycin (CLI) and linezolid (LZD) on growth, toxin gene transcription and toxin production inC. difficilewas investigated. FourC. difficilestrains were grown with and without sub-MIC concentrations of MTR, VAN, CLI and LZD (0.5× MIC) and growth was measured by colony counts. Toxin production was detected using ELISA (for toxin A) and a cytotoxicity assay (for toxin B) in culture supernatants and also in sonicated cells. Real-time PCR was used to measure transcription of the toxin A and B genes. The aim of this work was to combine analysis of toxin A and B production by ELISA or cell culture assay with transcriptomic analysis. The four strains showed similar growth and different levels of toxin production in the absence of antibiotics. An antibiotic-free control showed toxin production at a late stage when the plateau phase of bacterial growth was reached, whereas antibiotic-exposed strains showed earlier toxin production. All of the antibiotics used except CLI increased the transcription rate of toxin genes. The findings of this study show that sub-MIC concentrations of antibiotics can cause changes in gene transcription of the major virulence factors ofC. difficile. This study describes a new method for transcriptomic analysis of toxin genes inC. difficile.
Glucosylation of Rho GTPases by Clostridium difficile toxin A triggers apoptosis in intestinal epithelial cells
Authors: Gerhard Ralf , Nottrott Stefanie , Schoentaube Janett , Tatge Helma , Olling Alexandra , Just Ingo
Published: May 2008

The intestinal epithelial cell line HT-29 was used to study the apoptotic effect of Clostridium difficile toxin A (TcdA). TcdA is a 300 kDa single-chain protein, which glucosylates and thereby inactivates small GTPases of the Rho family (Rho, Rac and Cdc42). The effect of TcdA-catalysed glucosylation of the Rho GTPases is well known: reorganization of the actin cytoskeleton with accompanying morphological changes in cells, leading to complete rounding of cells and destruction of the intestinal barrier function. Less is known about the mechanism by which apoptosis is induced in TcdA-treated cells. In this study, TcdA induced the activation of caspase-3, -8 and -9. Apoptosis, as estimated by the DNA content of cells, started as early as 24 h after the addition of TcdA. The impact of Rho glucosylation was obvious when mutant TcdA with reduced or deficient glucosyltransferase activity was applied. TcdA mutant W101A, with 50-fold reduced glucosyltransferase activity, induced apoptosis only at an equipotent concentration compared with wild-type TcdA at a 50 % effective concentration of 0.2 nM. The enzyme-deficient mutant TcdA D285/287N was not able to induce apoptosis. Apoptosis induced by TcdA strictly depended on the activation of caspases, and was completely blocked by the pan-caspase inhibitor z-VAD-fmk. Destruction of the actin cytoskeleton by latrunculin B was not sufficient to induce apoptosis, indicating that apoptosis induced by TcdA must be due to another mechanism. In summary, TcdA-induced apoptosis (cytotoxic effect) depends on the glucosylation of Rho GTPases, but is not triggered by destruction of the actin cytoskeleton (cytopathic effect).