bluuebunny/crossref_metadata_2025 huggingface dataset:
Demethylnobiletin inhibits delayed‐type hypersensitivity reactions, human lymphocyte proliferation and cytokine production
Authors: Bas E , Recio M C , Giner R M , Máñez S , López‐Ginés C , Gil‐Benso R , Ríos J L
Published: October 2007

Background and purpose:

Our aim was to examine the effect of demethylnobiletin on various experimental models of delayed‐type hypersensitivity (DTH) reactions and to determine its influence on the mediators and enzymes involved in these reactions.

Experimental approach:

DTH was induced in mice by oxazolone, dinitrofluorobenzene (DNFB) and sheep red blood cells (SRBC). The effect of demethylnobiletin on the ensuing DTH was studied, especially in relation to oedema formation, cell infiltration and tissue damage. Its activity on different mediators implicated in DTH reactions was also determined and its effect on nitric oxide synthase (NOS)‐2 analysed. Finally, its influence on T lymphocyte proliferation, apoptosis and caspase 3 activity was tested.

Key results:

DTH reactions were all reduced by demethylnobiletin. The experimental results suggest that the compound may act by reducing cell infiltration and by suppressing mediators such as interleukin‐2 (IC50=1.63 μM), interleukin‐4 (IC50=2.76 μM), tumour necrosis factor‐α (IC50=0.66 μM), interferon‐γ (IC50=1.35 μM), and interleukin‐1β (46% at 2.5 μM) and by concomitantly increasing the production of the anti‐inflammatory cytokine, interleukin‐10. In addition, while demethylnobiletin affected nitric oxide production, it did not modify NOS‐2 expression. Finally, demethylnobiletin inhibited proliferation of T cells and induced their apoptosis.

Conclusions and implications:

Demethylnobiletin decreased DTH reactions induced by various agents. This finding, along with the fact that the compound has a low toxicity and exhibits several other interesting properties, could pave the way for other structurally related citroflavonoids to be used as pharmacological agents in complementary therapies.

British Journal of Pharmacology(2007)152, 1272–1282; doi:10.1038/sj.bjp.0707500; published online 15 October 2007
An assessment of the in vivo efficacy of the glycogen phosphorylase inhibitor GPi688 in rat models of hyperglycaemia
Authors: Poucher S M , Freeman S , Loxham S J G , Convey G , Bartlett J B , De Schoolmeester J , Teague J , Walker M , Turnbull A V , Charles A D , Carey F , Berg S
Published: October 2007

Background and purpose:

Studies in cultured hepatocytes demonstrate glycogen synthase (GS) activation with glycogen phosphorylase (GP) inhibitors. The current study investigated whether these phenomena occurred in vivo using a novel GP inhibitor.

Experimental approach:

An allosteric GP inhibitor, GPi688, was evaluated against both glucagon‐mediated hyperglycaemia and oral glucose challenge‐mediated hyperglycaemia to determine the relative effects against GP and GS in vivo.

Key results:

In rat primary hepatocytes, GPi688 inhibited glucagons‐mediated glucose output in a concentration dependent manner. Additionally GP activity was reduced and GS activity increased seven‐fold. GPi688 inhibited glucagon‐mediated hyperglycaemia in both Wistar (65%) & obese Zucker (100%) rats and demonstrated a long duration of action in the Zucker rat. The in vivo efficacy in the glucagon challenge model could be predicted by the equation; % glucagon inhibition=56.9+34.3[log ([free plasma]/rat IC50)], r=0.921). GPi688 also reduced the blood glucose of obese Zucker rats after a 7 h fast by 23%. In an oral glucose tolerance test in Zucker rats, however, GPi688 was less efficacious (7% reduction) than a glycogen synthase kinase‐3 (GSK‐3) inhibitor (22% reduction), despite also observing activation (by 45%) of GS in vivo.

Conclusions and implications:

Although GP inhibition can inhibit hyperglycaemia mediated by increased glucose production, the degree of GS activation induced by allosteric GP inhibitors in vivo, although discernible, is insufficient to increase glucose disposal. The data suggests that GP inhibitors might be more effective clinically against fasting rather than prandial hyperglycaemic control.

British Journal of Pharmacology (2007) 152, 1239–1247; doi:10.1038/sj.bjp.0707502; published online 15 October 2007
P2X1and P2X4receptor currents in mouse macrophages
Authors: Sim J A , Park C‐K , Oh S B , Evans R J , North R A
Published: October 2007

Background and purpose:

Activation of P2X receptors on macrophages is an important stimulus for cytokine release. This study seeks evidence for functional expression of P2X receptors in macrophages that had been only minimally activated.

Experimental approach:

Whole‐cell recordings were made from macrophages isolated 2–6 h before by lavage from mouse peritoneum, without further experimental activation. ATP (1–1000 μM) elicited inward currents in all cells (holding potential −60 mV). The properties of this current were compared among cells from wild type, P2X1−/−and P2X4−/−mice.

Key results:

Immunoreactivity for P2X1and P2X4receptors was observed in wild type macrophages but was absent from the respective knock‐out mice. In cells from wild type mice, ATP and αβmethyleneATP (αβmeATP) evoked inward currents rising in 10–30 ms and declining in 100–300 ms: these were blocked by pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS, 10 μM). ATP also elicited a second, smaller (∼10% peak amplitude), more slowly decaying (1–3 s) at concentrations 10 μM: this was resistant to PPADS and prolonged by ivermectin. Macrophages from P2X1−/−mice responded to ATP (>100 μM) but not αβmeATP: these small currents were prolonged by ivermectin. Macrophages from P2X4−/−mice responded to ATP and αβmeATP as cells from wild type mice, except that ATP did not evoke the small, slowly decaying component: these currents were blocked by PPADS.

Conclusion:

Mouse peritoneal macrophages that are minimally activated demonstrate membrane currents in response to ATP and αβmeATP that have the predominate features of P2X1receptors.

British Journal of Pharmacology(2007)152, 1283–1290; doi:10.1038/sj.bjp.0707504; published online 15 October 2007
Cannabinoid CB2 receptors in human brain inflammation
Authors: Benito C , Tolón R M , Pazos M R , Núñez E , Castillo A I , Romero J
Published: October 2007

The presence of functional cannabinoid CB2 receptors in the CNS has provoked considerable controversy over the past few years. Formerly considered as an exclusively peripheral receptor, it is now accepted that it is also present in limited amounts and distinct locations in the brain of several animal species, including humans. Furthermore, the inducible nature of these receptors under neuroinflammatory conditions, in contrast to CB1, makes them attractive targets for the development of novel therapeutic approaches. In fact, the undesired psychoactive effects caused by CB1 activation have largely limited the clinical use of cannabinoid‐related compounds that act on these receptors. In this review some recent findings on the antiinflammatory properties of CB2 receptors are presented, as well as new perspectives that have been obtained based on studies of human postmortem brain samples. In addition, various working hypotheses are also proposed and discussed.

British Journal of Pharmacology (2008) 153, 277–285; doi:10.1038/sj.bjp.0707505; published online 15 October 2007
Comparison of articular cartilage with costal cartilage in initial cell yield, degree of dedifferentiation during expansion and redifferentiation capacity
Authors: Lee Jungsun , Lee Eunkyung , Kim Hwi‐yool , Son Youngsook
Published: October 2007

Costal cartilage has been proposed as an alternative donor of chondrocytes for articular‐cartilage repair. In the present study we compared the initial cell yield of chondrocytes from rabbit costal cartilage and their cell expansion rates in monolayer culture with those of articular cartilage. Costal cartilage gave an approx. 2.6‐fold higher cell yield than did articular cartilage. During in vitro culture, CCs (costal chondrocytes) grew faster and displayed approx. 3‐fold more cell expansion up to P4 (passage 4) than did ACs (articular chondrocytes). In order to match the degree of dedifferentiation during serial cultivation with the cells' expansion rate, type II collagen expression and the emergence of fibroblastic morphology were monitored at each cell passage. Both ACs and CCs gradually lost their chondrocytic phenotype, changed to fibroblast‐like cells and displayed a reduced expression of type II collagen. We then also evaluated the redifferentiation capacity of the expanded ACs and CCs by culturing them at high density in collagen gel. Almost fully dedifferentiated CCs at P4 were successfully redifferentiated into hyaline cartilage, which showed the expression of glycosaminoglycan and type II collagen as well as the formation of lacunae and a territorial matrix. In conclusion, costal cartilage may have advantages over articular cartilage as an alternative donor tissue for autologous chondrocytes on the basis of its higher cell yield, higher cell expansion and successful reversion into hyaline cartilage without ossification in vitro. However, although this experiment with a rabbit model gave a better insight into the problem than other experiments have done, it does not answer definitively the question as to which cells are most appropriate for articular cartilage repair in humans.
Expression of human acidic fibroblast growth factor in Nicotiana benthamiana with a potato‐virus‐X‐based binary vector
Authors: Liu Jingying , Ma Pengda , Sun Yan , Yang Meiying , Yang Liping , Li Yuxi , Wu Yanfang , Zhu Xiaojuan , Wang Xingzhi
Published: October 2007

The aFGF (acidic fibroblast growth factor) plays an important role in morphogenesis, angiogenesis and wound healing and is therefore of potential medical interest. A DNA fragment encoding haFGF (human aFGF) has been cloned into the PVX (potato virus X)‐based binary vector (pgR107) and transiently expressed in Nicotiana benthamiana (a wild Australian tobacco) by agroinfection. Approx. 1 week after agroinfection, the recombinant haFGF accumulated in the agroinfected plants reached up to 1% of the total soluble protein. haFGF was then purified on heparin–Sepharose CL‐6B. The purified haFGF could stimulate the growth of NIH 3T3 cells, suggesting that the recombinant haFGF expressed via PVX viral vector in N. benthamiana was active biologically.
A novel thrombopoietin–stem‐cell factor fusion protein possesses enhanced potential in stimulating megakaryocyte proliferation and differentiation
Authors: Zang Yuhui , Zhang Yumin , Peng Wei , Chen Bin , Zhu Jie , Zhang Chi , Ouyang Jian , Qin Junchuan
Published: October 2007

TPO (thrombopoietin) and SCF (stem‐cell factor) are functionally related cytokines with overlapping but distinct haematopoietic effects. In the present study, a novel TPO–SCF fusion protein that combined the complementary biological effects of TPO and SCF into a single molecule was expressed in, and purified from, Sf9 [Spodoptera frugiperda (fall armyworm)] insect cells. The specific activity of rhTPO (recombinant human TPO)–SCF in megakaryoblastic Mo7e cell proliferation assays was 2.90±0.35×107 units/μmol, approx. 1.7 times as high as that of rhTPO. The specific activity of rhTPO–SCF in TF‐1 cells proliferation assays was 7.10±0.95×106 units/μmol, approx. 1.2 times as high as that of rhSCF (recombinant human SCF). In a megakaryocyte‐colony‐forming assay using human peripheral‐blood CD34+ cells, the SCF moiety of rhTPO–SCF worked in a synergistic way to augment the colony number and exhibited a higher potential to stimulate megakaryocyte colony growth. According to the results of EMSA (electrophoretic mobility‐shift assay) and semi‐quantitative RT (reverse transcriptase)–PCR, the synergistic effects of the SCF moiety were also reflected in increased STAT5 (signal transducer and activator of transcription 5) DNA binding and enhanced up‐regulation of p21 expression in Mo7e cells treated by rhTPO–SCF, suggesting that rhTPO–SCF could be more potent in promoting megakaryocyte proliferation and differentiation.
Violacein: properties and biological activities
Authors: Durán Nelson , Justo Giselle Z. , Ferreira Carmen V. , Melo Patrícia S. , Cordi Livia , Martins Dorival
Published: October 2007

The violet pigment violacein is an indole derivative, isolated mainly from bacteria of the genusChromobacterium, which exhibits important antitumoural, antimicrobial and antiparasitary properties. Furthermore, the formulation of violacein in different polymeric carriers developed so far offers alternative approaches to overcoming physiological barriers and undesirable physicochemical propertiesin vivo, thus improving its efficacy.
Solvent reaction field potential inside an uncharged globular protein: A bridge between implicit and explicit solvent models?
Authors: Cerutti David S. , Baker Nathan A. , McCammon J. Andrew
Published: October 2007

The solvent reaction field potential of an uncharged protein immersed in simple point charge/extended explicit solvent was computed over a series of molecular dynamics trajectories, in total 1560ns of simulation time. A finite, positive potential of 13–24 kbTec−1 (where T=300K), dependent on the geometry of the solvent-accessible surface, was observed inside the biomolecule. The primary contribution to this potential arose from a layer of positive charge density 1.0Å from the solute surface, on average 0.008ec∕Å3, which we found to be the product of a highly ordered first solvation shell. Significant second solvation shell effects, including additional layers of charge density and a slight decrease in the short-range solvent-solvent interaction strength, were also observed. The impact of these findings on implicit solvent models was assessed by running similar explicit solvent simulations on the fully charged protein system. When the energy due to the solvent reaction field in the uncharged system is accounted for, correlation between per-atom electrostatic energies for the explicit solvent model and a simple implicit (Poisson) calculation is 0.97, and correlation between per-atom energies for the explicit solvent model and a previously published, optimized Poisson model is 0.99.
Theoretical prediction of the ionization energies of the C4H7 radicals: 1-Methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals
Authors: Lau Kai-Chung , Zheng Wenxu , Wong Ning-Bew , Li Wai-Kee
Published: October 2007

The ionization energies (IEs) for the 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals have been calculated by the wave function based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasiperturbative triple excitation [CCSD(T)]. The zero-point vibrational energy correction, the core-valence electronic correction, and the scalar relativistic effect correction are included in these calculations. The present CCSD(T)/CBS results are then compared with the IEs determined in the photoelectron experiment by Schultz et al. [J. Am. Chem. Soc. 106, 7336 (1984)] The predicted IE value (7.881eV) of 2-methylallyl radical is found to compare very favorably with the experimental value of 7.90±0.02eV. Two ionization transitions for cis-1-methylallyl and trans-1-methylallyl radicals have been considered here. The comparison between the predicted IE values and the previous measurements shows that the photoelectron peak observed by Schultz et al. likely corresponds to the adiabatic ionization transition for the trans-1-methylallyl radical to form trans-1-methylallyl cation. Although a precise IE value for the cyclopropylmethyl radical has not been directly determined, the experimental value deduced indirectly using other known energetic data is found to be in good accord with the present CCSD(T)/CBS prediction. We expect that the Franck-Condon factor for ionization transition of c-C4H7→bicyclobutonium is much less favorable than that for ionization transition of c-C4H7→planar-C4H7+, and the observed IE in the previous photoelectron experiment is likely due to the ionization transition for c-C4H7→planar-C4H7+. Based on our CCSD(T)/CBS prediction, the ionization transition of c-C4H7→bicyclobutonium with an IE value around 6.92eV should be taken as the adiabatic ionization transition for the cyclobutyl radical. The present study provides support for the conclusion that the CCSD(T)/CBS approach with high-level energetic corrections can be used to provide reliable IE predictions for C4 hydrocarbon radicals with an uncertainty of ±22meV. The CCSD(T)/CBS predictions to the heats of formation for the aforementioned radicals and cations are also presented.
Energy level alignment of electrically doped hole transport layers with transparent and conductive indium tin oxide and polymer anodes
Authors: Fehse Karsten , Olthof Selina , Walzer Karsten , Leo Karl , Johnson Robert L. , Glowatzki Hendrik , Bröker Benjamin , Koch Norbert
Published: October 2007

Using ultraviolet photoemission spectroscopy, we investigated the energy level alignment at the interfaces of typical anodes used in organic electronics, indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), with the oligomeric hole transport material N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD), and studied the influence of electrical interface doping by the strong electron acceptor tetrafluoro tetracyanoquinodimethane (F4-TCNQ). The fundamentally different anode materials with work functions of 4.40eV (ITO) and 4.85eV (PEDOT:PSS) show different hole injection barriers, which also depend on the thickness of the F4-TCNQ interface dopant layer. PEDOT:PSS anodes exhibit a consistently lower hole injection barrier to MeO-TPD compared to ITO by 0.1eV. We attribute this low hole injection barrier to additional charge transfer reactions at the PEDOT:PSS/MeO-TPD interface. In contrast, the deposition of the electron acceptor at the interface helps significantly to lower the hole injection barrier for ITO anodes.
On the excited electronic state dissociation of nitramine energetic materials and model systems
Authors: Guo Y. Q. , Greenfield M. , Bhattacharya A. , Bernstein E. R.
Published: October 2007

In order to elucidate the difference between nitramine energetic materials, such as RDX (1,3,5-trinitro-1,3,5-triazacyclohexane), HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), and their nonenergetic model systems, including 1,4-dinitropiperazine, nitropiperidine, nitropyrrolidine, and dimethylnitramine, both nanosecond mass resolved excitation spectroscopy and femtosecond pump-probe spectroscopy in the UV spectral region have been employed to investigate the mechanisms and dynamics of the excited electronic state photodissociation of these materials. The NO molecule is an initial decomposition product of all systems. The NO molecule from the decomposition of energetic materials displays cold rotational and hot vibrational spectral structures. Conversely, the NO molecule from the decomposition of model systems shows relatively hot rotational and cold vibrational spectra. In addition, the intensity of the NO ion signal from energetic materials is proportional to the number of nitramine functional groups in the molecule. Based upon experimental observations and theoretical calculations of the potential energy surface for these systems, we suggest that energetic materials dissociate from ground electronic states after internal conversion from their first excited states, and model systems dissociate from their first excited states. In both cases a nitro-nitrite isomerization is suggested to be part of the decomposition mechanism. Parent ions of dimethylnitramine and nitropyrrolidine are observed in femtosecond experiments. All the other molecules generate NO as a decomposition product even in the femtosecond time regime. The dynamics of the formation of the NO product is faster than 180fs, which is equivalent to the time duration of our laser pulse.
Sampling of slow diffusive conformational transitions with accelerated molecular dynamics
Authors: Hamelberg Donald , de Oliveira César Augusto F. , McCammon J. Andrew
Published: October 2007

Slow diffusive conformational transitions play key functional roles in biomolecular systems. Our ability to sample these motions with molecular dynamics simulation in explicit solvent is limited by the slow diffusion of the solvent molecules around the biomolecules. Previously, we proposed an accelerated molecular dynamics method that has been shown to efficiently sample the torsional degrees of freedom of biomolecules beyond the millisecond timescale. However, in our previous approach, large-amplitude displacements of biomolecules are still slowed by the diffusion of the solvent. Here we present a unified approach of efficiently sampling both the torsional degrees of freedom and the diffusive motions concurrently. We show that this approach samples the configuration space more efficiently than normal molecular dynamics and that ensemble averages converge faster to the correct values.
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measurements of micron diameter metal-oxide-semiconductor capacitors using a scanning-electron-microscope-based nanoprobe
Authors: Zheng T. , Jia H. , Wallace R. M. , Gnade B. E.
Published: October 2007

The C-V electrical characterization of microstructures on a standard probe station is limited by the magnification of the imaging system and the precision of the probe manipulators. To overcome these limitations, we examine the combination of in situ electrical probing and a dual column scanning electron microscope/focused ion beam system. The imaging parameters and probing procedures are carefully chosen to reduce e-beam damage to the metal oxide semiconductor capacitor device under test. Estimation of shunt capacitance is critical when making femtofarad level measurements. C-V measurements of micron size metal-oxide-silicon capacitors are demonstrated.
In situ investigation of growth modes during plasma-assisted molecular beam epitaxy of (0001) GaN
Authors: Koblmüller G. , Fernández-Garrido S. , Calleja E. , Speck J. S.
Published: October 2007

Real-time analysis of the growth modes during homoepitaxial (0001) GaN growth by plasma-assisted molecular beam epitaxy was performed using reflection high energy electron diffraction. A growth mode map was established as a function of Ga∕N flux ratio and growth temperature, exhibiting distinct transitions between three-dimensional (3D), layer-by-layer, and step-flow growth modes. The layer-by-layer to step-flow growth transition under Ga-rich growth was surfactant mediated and related to a Ga adlayer coverage of one monolayer. Under N-rich conditions the transition from 3D to layer-by-layer growth was predominantly thermally activated, facilitating two-dimensional growth at temperatures of thermal decomposition.
Avoiding unphysical kinetic traps in Monte Carlo simulations of strongly attractive particles
Authors: Whitelam Stephen , Geissler Phillip L.
Published: October 2007

We introduce a “virtual-move” Monte Carlo algorithm for systems of pairwise-interacting particles. This algorithm facilitates the simulation of particles possessing attractions of short range and arbitrary strength and geometry, an important realization being self-assembling particles endowed with strong, short-ranged, and angularly specific (“patchy”) attractions. Standard Monte Carlo techniques employ sequential updates of particles and can suffer from low acceptance rates when attractions are strong. In this event, collective motion can be strongly suppressed. Our algorithm avoids this problem by proposing simultaneous moves of collections (clusters) of particles according to gradients of interaction energies. One particle first executes a “virtual” trial move. We determine which of its neighbors move in a similar fashion by calculating individual bond energies before and after the proposed move. We iterate this procedure and update simultaneously the positions of all affected particles. Particles move according to an approximation of realistic dynamics without requiring the explicit computation of forces and without the step size restrictions required when integrating equations of motion. We employ a size- and shape-dependent damping of cluster movements, motivated by collective hydrodynamic effects neglected in simple implementations of Brownian dynamics. We discuss the virtual-move algorithm in the context of other Monte Carlo cluster-move schemes and demonstrate its utility by applying it to a model of biological self-assembly.
Optimization of an algorithm for measurements of velocity vector components using a three-wire sensor
Authors: Ligęza P. , Socha K.
Published: October 2007

Hot-wire measurements of velocity vector components use a sensor with three orthogonal wires, taking advantage of an anisotropic effect of wire sensitivity. The sensor is connected to a three-channel anemometric circuit and a data acquisition and processing system. Velocity vector components are obtained from measurement signals, using a modified algorithm for measuring velocity vector components enabling the minimization of measurement errors described in this paper. The standard deviation of the relative error was significantly reduced in comparison with the classical algorithm.
Role of electrostatic forces in cluster formation in a dry ionomer
Authors: Allahyarov Elshad , Taylor Philip L.
Published: October 2007

This simulation study investigates the dependence of the structure of dry Nafion®-like ionomers on the electrostatic interactions between the components of the molecules. In order to speed equilibration, a procedure was adopted which involved detaching the side chains from the backbone and cutting the backbone into segments, and then reassembling the macromolecule by means of a strong imposed attractive force between the cut ends of the backbone, and between the nonionic ends of the side chains and the midpoints of the backbone segments. Parameters varied in this study include the dielectric constant, the free volume, side chain length, and strength of head group interactions. A series of coarse-grained mesoscale simulations shows the morphlogy to depend sensitively on the ratio of the strength of the dipole-dipole interactions between the side-chain acidic end groups to the strength of the other electrostatic components of the Hamiltonian. Examples of the two differing morphologies proposed by Gierke and co-workers [J. Polym. Sci., Polym. Phys. Ed. 19, 1687 (1981); Macromolecules 15, 101 (1982); J. Membr. Sci. 13, 307 (1982)] and by Gebel [Fuel Cells 5, 261 (2005); Macromolecules 37, 7772 (2004)] emerge from our simulations.
High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum
Authors: Steidtner Jens , Pettinger Bruno
Published: October 2007

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of ∼106 and a net signal gain of up to 4000 was observed. The focus diameter (∼λ∕2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.
Nonlinear analysis of a large-orbit coaxial-waveguide cyclotron autoresonance maser amplifier
Authors: Ouyang Zhengbiao , Zhang Shi-Chang
Published: October 2007

Nonlinear simulations are presented to analyze the influences of the electron beam and the magnetic field parameters on the output power of a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. It is found that the guiding-center spread of the relativistic electrons has negligible impact on the output power due to the small field change felt by the large-orbit electrons. The electron-beam velocity spread and energy spread substantially decrease the output power, because these spreads directly affect the beam-wave interaction through the Doppler term and the relativistic cyclotron frequency term in the cyclotron resonance condition. However, this adverse effect may be offset by properly tapering the operating magnetic field. The output power is sensitive to both the slope and the amplitude of the tapered magnetic field. Nonlinear simulation demonstrates the feasibility that a large-orbit coaxial-waveguide CARM amplifier can be expected to provide output power with several megawatts, ultrahigh gain, and good bandwidth in the millimeter and submillimeter wavelength ranges.
Self-consistent ensemble Monte Carlo simulations show terahertz oscillations in single-walled carbon nanotubes
Authors: Akturk Akin , Goldsman Neil , Pennington Gary
Published: October 2007

We investigate electrical transient and stationary transport properties of semiconducting single-walled zigzag carbon nanotubes (CNTs), using a transient ensemble Monte Carlo (MC) simulator that self-consistently solves the semiclassical transport and Poisson equations. We developed the ensemble MC simulator to obtain time and space dependencies of the CNT electron concentration, velocity, and current profiles self-consistently with electrical potential distribution on the tube. Our calculated MC results indicate that self-induced terahertz CNT current oscillations on the tube and at the contacts emerge under several direct current biases. We associate these terahertz CNT oscillations with intersubband scatterings that cause the transfer of electrons from the first subband to the second, intrasubband scatterings and the nonlinear dispersion curves of each subband. The slow-moving electrons in the second subband bunch together locally on the tube, whereas the fast-moving first subband electrons move beyond the bunch and leave a relatively positive charged region behind. Also, intrasubband scatterings and subband curves give rise to low and high density electron regions by creating dispersion. These relatively low and high density electron regions create a charge dipole that then perturbs the electrical potential, resulting in a propagating domain, and thus current oscillations at tens of terahertz. After we investigate the physics of these calculated terahertz oscillations, we propose methods to modulate and shift the main oscillation frequency by varying the applied bias, tube length, or the diameter.
Optical properties of a Si delta-doped InGaN∕GaN quantum well with ultraviolet emission
Authors: Kwon Min-Ki , Park Il-Kyu , Kim Ja-Yeon , Kim Jeom-Oh , Seo Seong-Bum , Park Seong-Ju , Min Kyeongik , Park Gil-Han
Published: October 2007

We report on the effect of the position of the Si delta-doped layer within a GaN barrier layer on the optical properties of a InGaN∕GaN single quantum well (SQW) with an emission wavelength of 374nm. When the Si delta-doped layer was very close to the SQW layer, the potential well of the Si delta-doped layer overlapped the SQW potential, reducing photoluminescence (PL) intensity. When the Si delta-doped layer was very far away from the SQW layer, carrier injection from the Si delta-doped layer into the SQW layer was not observed. However, the Si delta-doped layer located 12nm away from the SQW layer showed enhanced PL intensity due to effective electron injection from the Si delta-doped layer into the SQW layer and to an increase in hole confinement in the valence band.
Enhancement of Jc in MgB2 thin films on Si substrate with pinning centers introduced by deposition in O2 atmosphere
Authors: Haruta M. , Fujiyoshi T. , Kajita R. , Yonekura K. , Sueyoshi T. , Doi T. , Kitaguchi H. , Awaji S. , Watanabe K.
Published: October 2007

As-grown MgB2 thin films on Si substrates with high Jc under magnetic fields were prepared by electron-beam evaporation. The value of Jc has been enhanced by the deposition of MgB2 thin film in an O2 atmosphere. The MgB2 thin film deposited in the O2 atmosphere (O2-doped film) has exhibited considerably higher Jc in magnetic fields among MgB2 thin films reported before. It has been found that the high Jc of the O2-doped film is attributable to the flux pinning with grain boundaries strengthened by an introduction of MgO along grain boundaries. In a high magnetic field, a peculiar behavior of E-J characteristics where E-J curves vary in two stages was observed. This behavior also originates from the flux pinning with strengthened grain boundaries.
X-ray ultraviolet absorption measurements of laser-driven Au∕CH∕Al multilayers
Authors: Zhang Jiyan , Yang Guohong , Yang Jiamin , Ding Yaonan , Zhang Baohan , Zheng Zhijian , Yan Jun
Published: October 2007

X-ray ultraviolet absorption measurements of aluminum plasma at high temperature and high density are reported. A sample plasma was created by direct laser irradiation of a multilayered foil consisting of Au, CH, and Al. Observations were made using the method of self-backlighting spectroscopy. Simulations were performed with one-dimensional radiation-hydrodynamics code to compute the backlight profile as well as the time history of the density and temperature in the sample. By comparing the measured absorption spectra with detailed-term-accounting calculations at Te=120eV and ρ=0.1g∕cm3, it is found that the major spectral features predicted by calculations have been observed. Even better agreement between the experiment and the simulated absorption spectra was obtained by temporally averaging the radiation-hydrodynamics result over the backlight profile. This experiment shows that it is possible to measure high density and high temperature opacity by a laser-driven multilayer experiment.
All-angle negative refraction imaging effect with complex two-dimensional hexagonal photonic crystals
Authors: Li Jian , Lu Ming-Hui , Fan Tian , Liu Xiao-Kang , Feng Liang , Tang Yue-Feng , Chen Yan-Feng
Published: October 2007

A complex two-dimensional hexagonal photonic crystal consisting of silicon (Si) and silica (SiO2) cylinders embedded in the air background is proposed to achieve the effect of all-angle negative refraction imaging. Compared with normal hexagonal-lattice photonic crystals consisting of Si, the reduction of symmetry of the complex photonic crystal results in a large band gap between the second energy band and the third energy band, whereas in a normal hexagonal photonic crystal there is no gap between these two bands. Furthermore, the depressed energy band structures provide advantages to realize all-angle left-handed negative refraction similar to metamaterials. The far-field superlens imaging with an effective refractive index of −1 was demonstrated theoretically in the infrared region at the frequency of 200THz. We also showed the far-field subwavelength resolution for imaging of two point sources with a distance of 0.66λ.
Fast single-charge sensing with a rf quantum point contact
Authors: Reilly D. J. , Marcus C. M. , Hanson M. P. , Gossard A. C.
Published: October 2007

We report high-bandwidth charge sensing measurements using a GaAs quantum point contact embedded in a radio frequency impedance matching circuit (rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to charge, we demonstrate a conductance sensitivity of 5×10−6e2∕hHz−1∕2 with a bandwidth of 8MHz. Single-shot readout of a proximal few-electron double quantum dot is investigated in a mode where the rf-QPC back action is rapidly switched.
Global well posedness for the Gross-Pitaevskii equation with an angular momentum rotational term in three dimensions
Authors: Hao Chengchun , Hsiao Ling , Li Hai-Liang
Published: October 2007

In this paper, we establish the global well posedness of the Cauchy problem for the Gross-Pitaevskii equation with an angular momentum rotational term in which the angular velocity is equal to the isotropic trapping frequency in the space R3.
A narrow band contribution with Anderson localization in Ag-doped layered cobaltites Bi2Ba3Co2Oy
Authors: Ang R. , Sun Y. P. , Luo X. , Song W. H.
Published: October 2007

We have systematically investigated the influence of the Ag doping on magnetization M(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) in the layered cobaltites Bi2Ba3−xAgxCo2Oy (0⩽x⩽2) samples. For Ag-doped sample, the magnetic susceptibility indicates the ground state is dominated by the low-spin states of the combination of Co3+ and Co4+. The metal-insulator transition existing in Ag-free sample is suppressed and replaced by metallic behavior due to Ag doping. Moreover, S is remarkably large and temperature independent with metallic ρ(T) at high temperatures, which is suggested to be the evidence of a narrow a1g band. A steep upturn of ρ is observed at low temperature while no corresponding change appears in the S(T) curve. Such an abnormal behavior is attributed to Anderson localization in a narrow band. Additionally, the Ag doping not only introduces holes into the conducting CoO2 layers but also enhances the disorder which decreases the upper mobility edge EC. As to κ(T), it plays an important role for the contribution of mobile electronic carrier component κe besides the contribution of phononic component κph. The behavior of κe is ascribed to the effect of the competition between magnetic interaction and the disorder. The variation of κph is analyzed according to the combined effect due to the impurity and disorder because of Ag doping, which is favorable to the scattering of phonon leading to the decrease of κph, and the decreased scattering of interface between the CoO2 and the Bi–Ba–O blocks due to Ag doping, which contributes to the increase of κph.
Asymmetric interface profiles in LaVO3∕SrTiO3 heterostructures grown by pulsed laser deposition
Authors: Kourkoutis L. Fitting , Muller D. A. , Hotta Y. , Hwang H. Y.
Published: October 2007

Surface segregation effects play an important role in the growth of traditional III-V semiconductor heterointerfaces. Here we show that segregation processes can also set an upper limit to the obtainable interface sharpness in perovskite oxide heterostructures. In particular, the structure of LaVO3∕SrTiO3 superlattices was studied on the atomic scale by electron microscopy and spectroscopy. The vanadate layers exhibit a growth asymmetry, with diffuse lower and atomically abrupt upper interfaces, caused by preferential Sr surface segregation. Switching the SrTiO3 termination layer does not change the interface abruptness, which excludes the interfacial polar discontinuity as the driving force for the observed growth asymmetry.
Off-track margin in bit patterned media
Authors: Moser Andreas , Hellwig Olav , Kercher Dan , Dobisz Elisabeth
Published: October 2007

When two dimensional patterns are written into bit patterned media the off-track margin is of great importance. Using a static write/read tester we measure the hard error rate (written-in errors) as a function of the distance from the track center. We observe three different segments. In the track center, the head writes very well and almost no hard errors are observed. At the track edges the hard error rate increases linearly over an interval, which is shown to relate to the off-track margin of the recording system. At larger distances from the track center, no islands are switched.
Surface elastic properties of porous nanosilica coatings by scanning force microscopy
Authors: Vincent A. , Babu S. , Seal S.
Published: October 2007

Surface elastic properties of sol-gel derived porous nanosilica optical coatings were determined using scanning force microscopy. Silica nanocoatings prepared under acid and base catalyzed sol-gel process exhibited varying surface morphology, particle size and porosity. Force-distance spectroscopy measurements were conducted on these coatings using scanning force microscopy, and their elastic moduli were obtained by applying Hertz model. The elastic modulus of the coatings varied from 2.4to13.4GPa depending on the nature and concentration of the catalyst used.
Efficient visible light detection using individual germanium nanowire field effect transistors
Authors: Ahn Y. H. , Park Jiwoong
Published: October 2007

We report photoconductivity (PC) in individual germanium nanowire field effect transistors (GeFETs). PC measurements with a global illumination reveal that GeFETs can be used as a polarization-sensitive nanoscale light detector in the visible range. It is also found that the PC shows sensitive optical response especially in the low intensity regime. We observe a high internal gain in PC in conjunction with strong saturation behavior, which is attributed to the filling of surface trapping states. This mechanism for high internal gain is consistent with spatially resolved scanning photocurrent measurements, whose results confirm that optical absorption is in the linear regime.
Active left-handed material collaborated with microwave varactors
Authors: Wang Dongxing , Ran Lixin , Chen Hongsheng , Mu Mingkai , Kong Jin Au , Wu Bae-Ian
Published: October 2007

In the present letter, a design for active left-handed material collaborated with microwave varactors is proposed and experimentally realized. Both the results of simulation and experiment verify the tunable left-handed properties of the structure in microwave band. A controllable beam steering is then observed experimentally by a prism fabricated by such metamaterial. The simplicity of the active design and its tunable negative refraction indices make it useful for various applications.
Probing the phase composition of silicon films in situ by etch product detection
Authors: Dingemans G. , van den Donker M. N. , Gordijn A. , Kessels W. M. M. , van de Sanden M. C. M.
Published: October 2007

Exploiting the higher etch probability for amorphous silicon relative to crystalline silicon, the transiently evolving phase composition of silicon films in the microcrystalline growth regime was probed in situ by monitoring the etch product (SiH4) gas density during a short H2 plasma treatment step. Etch product detection took place by the easy-to-implement techniques of optical emission spectroscopy and infrared absorption spectroscopy. The phase composition of the films was probed as a function of the SiH4 concentration during deposition and as a function of the film thickness. The in situ results were corroborated by Raman spectroscopy and solar cell analysis.
Low-resistance Ni-based Schottky diodes on freestanding n-GaN
Authors: Lewis L. , Corbett B. , O Mahony D. , Maaskant P. P.
Published: October 2007

Schottky diodes formed on a low doped (5×1016cm−3) n-type GaN epilayer grown on a n+ freestanding GaN substrate were studied. The temperature dependent electrical characteristics of Ni contacts on the as-grown material are compared with an aqueous, potassium hydroxide (KOH) treated surface. In both cases the diodes are dominated by thermionic emission in forward bias, with low idealities (1.04 at room temperature) which decrease with increasing temperature, reaching 1.03 at 413K. The Schottky barrier height is 0.79±0.05eV for the as-grown surface compared with 0.85±0.05eV for the KOH treated surface at room temperature. This is consistent with an inhomogeneous barrier distribution. The specific on-state resistance of the diodes is 0.57mΩcm2 The KOH treatment reduces the room temperature reverse leakage current density at −30Vto1×10−5Acm−2 compared to 6×10−2Acm−2 for the as-grown samples.
Influence of growth temperature on critical current and magnetic flux pinning structures in YBa2Cu3O7−x
Authors: Feldmann D. M. , Ugurlu O. , Maiorov B. , Stan L. , Holesinger T. G. , Civale L. , Foltyn S. R. , Jia Q. X.
Published: October 2007

We have studied the critical current density (Jc) as a function of applied magnetic field (H) magnitude and orientation for ∼1-μm-thick YBa2Cu3O7−x films grown by pulsed laser deposition at growth temperatures (Tg) from 730to870°C. With changing Tg, alternately a high density of planar defects (YBa2Cu4Ox intergrowths) or columnar defects (Y–Cu–O nanocolumns) are introduced. These defects produce a maximum for Jc(H∼1T) parallel to the plane of the film or the film normal, respectively. For Tg⩾830°C, we present evidence of a Ba–Cu–O liquid phase during growth, which results in a dramatic change in both the microstructure of the films and magnetic field orientation dependence of Jc.
Proton exchange membrane fuel cells with chromium nitride nanocrystals as electrocatalysts
Authors: Zhong Hexiang , Chen Xiaobo , Zhang Huamin , Wang Meiri , Mao Samuel S.
Published: October 2007

Polymer electrolyte membrane fuel cells (PEMFCs) are energy conversion devices that produce electricity from a supply of fuel, such as hydrogen. One of the major challenges in achieving efficient energy conversion is the development of cost-effective materials that can act as electrocatalysts for PEMFCs. In this letter, we demonstrate that, instead of conventional noble metals, such as platinum, chromium nitride nanocrystals of fcc structure exhibit attractive catalytic activity for PEMFCs. Device testing indicates good stability of nitride nanocrystals in low temperature fuel cell operational environment.
Spaces of Practice in Advanced Business Services: Rethinking London—Frankfurt Relations
Authors: Pain Kathy
Published: October 2007

This paper explores the relevance of Bourdieu's 1980 spatial theorisation in Le Sens Pratique ( The Logic of Practice 1990, Polity Press, Cambridge) for understanding intercity relations in contemporary globalisation—specifically, interdependencies between Castells's ‘space of flows’ and ‘places’ in advanced business services. Bourdieu's relational concepts are reviewed with reference to evidence from in-depth interviews with business actors in London and Frankfurt at the time of European Economic Monetary Union. The intention is to deepen understanding of emergent relations between the cities and, in so doing, to contribute to the reinterpretation of Bourdieu's input to geographical thinking.
Assembly factors Rpf2 and Rrs1 recruit 5S rRNA and ribosomal proteins rpL5 and rpL11 into nascent ribosomes
Authors: Zhang Jingyu , Harnpicharnchai Piyanun , Jakovljevic Jelena , Tang Lan , Guo Yurong , Oeffinger Marlene , Rout Michael P. , Hiley Shawna L. , Hughes Timothy , Woolford John L.
Published: October 2007

More than 170 proteins are necessary for assembly of ribosomes in eukaryotes. However, cofactors that function with each of these proteins, substrates on which they act, and the precise functions of assembly factors—e.g., recruiting other molecules into preribosomes or triggering structural rearrangements of pre-rRNPs—remain mostly unknown. Here we investigated the recruitment of two ribosomal proteins and 5S ribosomal RNA (rRNA) into nascent ribosomes. We identified a ribonucleoprotein neighborhood in preribosomes that contains two yeast ribosome assembly factors, Rpf2 and Rrs1, two ribosomal proteins, rpL5 and rpL11, and 5S rRNA. Interactions between each of these four proteins have been confirmed by binding assays in vitro. These molecules assemble into 90S preribosomal particles containing 35S rRNA precursor (pre-rRNA). Rpf2 and Rrs1 are required for recruiting rpL5, rpL11, and 5S rRNA into preribosomes. In the absence of association of these molecules with pre-rRNPs, processing of 27SB pre-rRNA is blocked. Consequently, the abortive 66S pre-rRNPs are prematurely released from the nucleolus to the nucleoplasm, and cannot be exported to the cytoplasm.