bluuebunny/crossref_metadata_2025 huggingface dataset:
Tungsten Oxide Nanorods Array and Nanobundle Prepared by Using Chemical Vapor Deposition Technique
Authors: Wang XP , Yang BQ , Zhang HX , Feng PX
Published: July 2007

Tungsten oxide (WO3) nanorods array prepared using chemical vapor deposition techniques was studied. The influence of oxygen gas concentration on the nanoscale tungsten oxide structure was observed; it was responsible for the stoichiometric and morphology variation from nanoscale particle to nanorods array. Experimental results also indicated that the deposition temperature was highly related to the morphology; the chemical structure, however, was stable. The evolution of the crystalline structure and surface morphology was analyzed by scanning electron microscopy, Raman spectra and X-ray diffraction approaches. The stoichiometric variation was indicated by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.
Purification, Surface Tensions, and Miscibility Gaps of Alkyldimethyl and Alkyldiethylphosphine Oxides
Authors: Blunk Dirk , Tessendorf Renate , Buchavzov Natalie , Strey Reinhard , Stubenrauch Cosima
Published: July 2007

Alkyldimethyl (CnDMPO) with chain lengths of n = 8 (octyl), 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) as well as alkyldiethyl (CnDEPO) phosphine oxides with chain lengths of n = 10, 12, and 14 were synthesized and purified to study how the adsorption properties and the location of the miscibility gap of these surfactants depend on the size of the head group and on the length of the alkyl chain. After surfactant purification, the surface tension isotherms were determined from which the cmc, the minimum surface tension σcmc, the maximum surface concentration Γmax, and the minimum surface area Amin were obtained. As expected, for one homologous series, a decrease in the cmc and an increase in Γmax was observed with increasing alkyl chain length. For two surfactants of the same alkyl chain length, the cmc values of the CnDEPO surfactants are approximately two times lower than those of the CnDMPO surfactants. However, the Γmax values of CnDEPO are lower than those of CnDMPO as two ethyl chains are sterically more demanding than two methyl chains. In addition to the adsorption properties, the location of the miscibility gap as a function of the alkyl chain length and the head group size was studied. Its location depends on the total number of carbon atoms and not primarily on the length of the main alkyl chain. This observation reflects the decreasing water solubility which can be tuned by increasing the length of either the main alkyl chain or of the shorter head group chains.
Genetische Determinanten des EKG
Authors: Pfeufer A.
Published: July 2007

Schon bald nach der Erfindung des EKG wurden die hohen Heritabilitäten vieler EKG-Parameter erkannt. Seit etwa einer Dekade wird intensiv an der Aufklärung zugrunde liegender genetischer Varianten gearbeitet, mit der Einführung genomweiter Assoziationsstudien steht dafür nun auch eine adäquate Methode zur Verfügung. Die molekulare Identifizierung und Charakterisierung bisher unbekannter herzrhythmusassoziierter Gene und Genvarianten verspricht nicht nur eine Vertiefung unseres Verständnisses der kardialen Elektrophysiologie, sondern auch eine Option auf bessere therapeutische und präventive Strategien für Arrhythmien und den plötzlichen Herztod.
Dynamics of perceived parenting and identity formation in late adolescence
Authors: Beyers Wim , Goossens Luc
Published: July 2007

Identity formation is a dynamic process of person–context interactions, and part of this context are parents, even in late adolescence. Several theories on parent–adolescent relationships share the idea that parents influence the process of identity formation. However, up to now, empirical evidence, particularly longitudinal evidence for this link is limited. Therefore, this study aims to examine short‐term changes in parenting and identity formation during late adolescence and to test the transactional process involved. Moreover, we focused on gender differences. Late adolescents were measured twice with a 1‐year interval. Analyses using latent change models largely showed that parenting predicted the explorative phases of identity formation (i.e., exploration in breadth and commitment making), while evaluative phases of identity formation (i.e., exploration in depth and commitment identification) predicted more supportive parenting. Gender differences emerged, with respect to both parents’ and adolescents’ gender. These results clearly show that parenting and identity formation are dynamically interlinked, and underscore that parents keep being an important source of socialization for their developing children, even in late adolescence.
Lipid‐binding role of βII‐spectrin ankyrin‐binding domain
Authors: Bok Ewa , Plażuk Ewa , Hryniewicz‐Jankowska Anita , Chorzalska Anna , Szmaj Agnieszka , Dubielecka Patrycja M. , Stebelska Katarzyna , Diakowski Witold , Lisowski Marek , Langner Marek , Sikorski Aleksander F.
Published: July 2007

It is known that erythroid and non‐erythroid spectrins binding of vesicles and monolayers containing PE proved sensitive to inhibition by red blood cell ankyrin. We now show that the bacterially‐expressed recombinant peptides representing βII(brain)‐spectrin's ankyrin‐binding domain and its truncated mutants showed lipid‐binding activity, although only those containing a full‐length amino terminal fragment showed high to moderate affinity towards phospholipid mono‐ and bilayers and a substantial sensitivity of this binding to inhibition by ankyrin. These results are in accordance with our published data on βI‐spectrin's ankyrin‐binding domain [Hryniewicz‐Jankowska A, et al. Mapping of ankyrin‐sensitive, PE/PC mono‐ and bilayer binding site in erythroid beta‐spectrin. Biochem J 2004;382:677–85]. Moreover, we tested also the effect of transient transfection of living cells of several cell‐lines with vectors coding for GFP‐conjugates including βII and also βI full‐length ankyrin‐binding domain and their truncated fragments on the membrane skeleton organization. The transfection with constructs encoding full‐length ankyrin‐binding domain of βII and βI spectrin resulted in increased aggregation of membrane skeleton and its punctate appearance in contrast to near normal appearance of membrane skeleton of cells transiently transfected with GFP control or construct encoding ankyrin‐binding domain truncated at their N‐terminal region. Our results therefore indicate the importance of N‐terminal region for lipid‐binding activity of the β‐spectrin ankyrin‐binding domain and its substantial role in maintaining the spectrin‐based skeleton distribution.
An octaheme c‐type cytochrome from Shewanella oneidensis can reduce nitrite and hydroxylamine
Authors: Atkinson Sally J. , Mowat Christopher G. , Reid Graeme A. , Chapman Stephen K.
Published: July 2007

A c‐type cytochrome from Shewanella oneidensis MR‐1, containing eight hemes, has been previously designated as an octaheme tetrathionate reductase (OTR). The structure of OTR revealed that the active site contains an unusual lysine‐ligated heme, despite the presence of a CXXCH motif in the sequence that would predict histidine ligation. This lysine ligation has been previously observed only in the pentaheme nitrite reductases, suggesting that OTR may have a possible role in nitrite reduction. We have now shown that OTR is an efficient nitrite and hydroxylamine reductase and that ammonium ion is the product. These results indicate that OTR may have a role in the biological nitrogen cycle.
Identification and characterization of an aspartyl protease from Cryptococcus neoformans
Authors: Pinti Marcello , Orsi Carlotta Francesca , Gibellini Lara , Esposito Roberto , Cossarizza Andrea , Blasi Elisabetta , Peppoloni Samuele , Mussini Cristina
Published: July 2007

Cryptococcosis, caused by Cryptococcus neoformans, is an invasive infection often occurring in AIDS patients. Potent therapy against HIV, which includes protease inhibitors (PIs), has beneficial effects also on opportunistic infections by pathogens such as C. neoformans and C. albicans. PIs inhibit growth of C. albicans by affecting the activity of its aspartyl proteases. We identified, cloned and sequenced a cDNA from C. neoformans encoding for a putative aspartyl protease (CnAP1), and the corresponding genomic region. The gene cnap1 codifies for a protein of 505 aa, with a canonical aspartyl protease structure. We purified the recombinant protein and analyzed its activity in the presence of PIs (Indinavir, Lopinavir, Ritonavir), but did not evidence any inhibition of protease activity. The transcriptional level of cnap1 in C. neoformans is constant in different media. The absence of any inhibition activity by PIs suggests that other targets for PIs might exist in C. neoformans.
Inhibitory role of RhoA on senescence‐like growth arrest by a mechanism involving modulation of phosphatase activity
Authors: Park Chaehwa , Lee Inkyoung , Jang Jun Ho , Kang Won Ki
Published: July 2007

Recently, negative effects of phosphatase in tumorigenesis and metastasis have been suggested in various tumor types. In this study, we showed that RhoA activation modulated phosphatase during senescence‐like arrest in human prostate cancer cells. Under senescence‐inducing condition, decreased Erk phosphorylation was detected in caRhoA‐transfected cells and inactivation of Erk, but not p38, prevented doxorubicin‐induced cell senescence. Cells were induced to senescence by inhibition of phosphatase activity (VHR, MKP3, or PP2A) without additional cellular stress. Of interest, caRhoA prevented doxorubicin‐induced decrease of phosphatase. Thus, we postulate that RhoA signaling may protect cells against cellular senescence by maintaining phosphatase activity and Erk dephosphorylation.
Indole‐3‐carbinol – Induced growth inhibition can be converted to a cytotoxic response in the presence of TPA + Ca2+ in squamous cell carcinoma cell lines
Authors: Dahler A.L. , Rickwood D. , Guminski A. , Teakle N. , Saunders N.A.
Published: July 2007

We examined the possibility that I3C, when combined with a differentiation stimulus (TPA + CaCl2), would sensitise SCC cells to a differentiation stimulus. We report that I3C induces a profound growth inhibition in SCC cells that is dissimilar to the growth inhibition required to initiate differentiation. Moreover, we report that I3C, when combined with TPA + CaCl2 treatment, induces a loss of colony forming ability that was differentiation and senescence – independent but was due to delayed cytotoxicity. This study shows that I3C in combination with a PKC activator + Ca2+ may be a useful therapeutic strategy for treating oral SCC.
Peroxiredoxin‐4 interacts with and regulates the thromboxane A2 receptor
Authors: Giguère Patrick , Turcotte Marie-Eve , Hamelin Emilie , Parent Audrey , Brisson Jessy , Laroche Geneviève , Labrecque Pascale , Dupuis Gilles , Parent Jean-Luc
Published: July 2007

We identified peroxiredoxin‐4 (Prx‐4) as a protein interacting with the β isoform of the thromboxane A2 receptor (TPβ) by yeast two‐hybrid analysis. Prx‐4 co‐immunoprecipitated constitutively with TPβ in HEK293 cells. The second and third intracellular loops as well as the C‐terminus of TPβ interacted directly with Prx‐4. Co‐expression of Prx‐4 caused a 60% decrease in cell surface expression of TPβ. Prx‐4 and TPβ predominantly co‐localized in the endoplasmic reticulum. Co‐expression of Prx‐4 in cells treated with H2O2 targeted TPβ for degradation. We show for the first time an interaction between a receptor involved in oxidative stress and Prx‐4, an anti‐oxidative enzyme.
WNK4 phosphorylates ser206 of claudin‐7 and promotes paracellular Cl− permeability
Authors: Tatum Rodney , Zhang Yuguo , Lu Qun , Kim Kwonseop , Jeansonne Beverly G. , Chen Yan-Hua
Published: July 2007

Mutations in WNK4 have been linked to hypertension in PHAII. Paracellular ion transport has been reported to be involved in this disease process; however, the specific molecular target has not been identified. In this study, we found that TJ protein claudin‐7 and WNK4 were partially co‐localized in renal tubules of rat kidney and co‐immunoprecipitated in kidney epithelial cells. The wild‐type and PHAII‐causing mutant, but not the kinase‐dead mutant, phosphorylated claudin‐7. We have identified ser206 in the COOH‐terminus of claudin‐7 as a putative phosphorylation site for WNK4. More importantly, disease‐causing mutant enhanced claudin‐7 phosphorylation and significantly increased paracellular permeability to Cl−.
Schleiermacher's supralapsarian christology
Authors: van Driel Edwin Chr.
Published: July 2007

While several commentators have pointed out the supralapsarian nature of Schleiermacher's christology, this article is the first thorough examination of the nature of Schleiermacher's supralapsarian arguments. I show that Schleiermacher's supralapsarianism is directly based on his doctrine of absolute dependence and divine causality. However, the ontology implied by the latter doctrine is in the end inconsistent with Schleiermacher's christology, and Schleiermacher's system does not seem to have the resources to be saved from this inconsistency.
Exchange and ecstasy: Luther's eucharistic theology in light of Radical Orthodoxy's critique of gift and sacrifice
Authors: Malysz Piotr J.
Published: July 2007

It is frequently alleged that Martin Luther's doctrine of justification by grace through faith posits absolute human passivity vis-à-vis God and, on account of the past completion of Christ's sacrifice, disconnects Christians from the cross. This article takes issue with this view. Specifically, it disputes the claim that, through his doctrine of justification, Luther became an unwitting advocate of the conceptual juxtaposition of gift and exchange and thus also an ideologue of the shift from an organic to a contractual view of society. Instead, I argue, Luther's eucharistic theology anticipates the concerns of Radical Orthodoxy's critique of gift and sacrifice. It does so, however, in a more forceful manner, in that for Luther gift and exchange are so bound together in his doctrine of justification that the eucharist, instead of being a mere paradigm for social relationships (as Radical Orthodoxy would have it), radically restructures those relationships in the all-embracing unfolding of its participatory gratuity. An additional merit of Luther's vision lies in its systematic description of the eucharist's gift-character in terms of socially and vocationally construed delay and non-identical repetition, actively involving both God and humans – a description not afforded by Radical Orthodoxy's critique.
Enforcing the Kyoto Protocol: can punitive consequences restore compliance?
Authors: HOVI JON , FROYN CAMILLA BRETTEVILLE , BANG GURI
Published: July 2007

To enhance effective cooperation, the Marrakesh Accords provide a compliance system for the international climate regime. An innovative part of this system is an Enforcement Branch authorised to apply punitive consequences against countries that fail to comply with their Kyoto obligations. While previous research has primarily focused on the ability of this compliance system to deter non-compliance, this article discusses whether the actual use of punitive consequences will induce a non-compliant country to return to compliance. The Marrakesh Accords explicitly emphasise that the punitive consequences shall be aimed at the restoration of compliance. However, we show that the application of punitive consequences will accomplish this in only exceptional circumstances.
Trusteeship and the concept of freedom
Authors: SØBJERG LENE MOSEGAARD
Published: July 2007

After almost four decades of abandonment, the institution of trusteeship had a revival on the international agenda as the United Nations assumed responsibility of the war-torn territories of Kosovo and East Timor in 1999. This revival was met with severe criticism for jeopardising the values of order and equality in contemporary international society. The present article argues that this criticism is misleading. The essence of a modern trusteeship is not order or equality but the expansion of freedom. Rather than destabilising international society, it is argued that a trusteeship can be a constructive tool in the re-establishment of freedom, stability and peace in post-conflict territories.
Individual experiencing of states
Authors: FAIZULLAEV ALISHER
Published: July 2007

The author argues that the international context provides an apparent environment for the individual experiencing of the state as a distinctive unitary and cohesive actor with its own intentionality and personhood, social relations and coercive resources, manifested not only by actions and force, but also through symbols, figure of speeches and other allusive forms capable of affecting human identity. As a direct personal observation, individual experiencing of states contains an inner, phenomenological plan, though it is not a solipsistic process and depends on people’s shared meanings. Conventional perception of states as anthropomorphic actors regards relations between states as social or interpersonal relations, thus causal attribution and social expectations affect individual experience of states. Being primarily a common-sense phenomenon, individual experiencing of states has a wide-ranging effect on both ‘conventional’ and ‘conceptual’ understanding of international relations. In perception and explanation of international politics, real political developments are often overshadowed by observable, experiential, common-sense causations.
An Evaluation of Internet Websites Provided by Radiotherapy Departments
Authors: King Emma
Published: July 2007

The research identifies and evaluates the content and readability of Websites of all radiotherapy departments that provide a Website. As more patients are being referred for radiotherapy treatment each year, the information needs of the public on this subject is growing. Fifty-two per cent of radiotherapy departments within the United Kingdom (UK) and Ireland were identified as providing a Website. These Websites were evaluated, over a period of 2 weeks, using an adapted Website evaluation tool. Five criteria – content, authority, navigation, design and technical aspects – were identified as important aspects of a Website. For each criterion a number of statements were listed and using a Likert scale were marked. Flesch–Kincaid readability tests were used to analyse the readability level of the Websites. Data analysis resulted in the ranking of the Websites. Evaluation scores varied greatly and the readability tests showed 92% of the Websites were written at a level too high for the public. This shows the varying quality of radiotherapy department Websites with scores ranging from 48 to 115, and the varying readability level of these Websites. The research makes suggestions for the improvement of radiotherapy department Websites including the provision of a dedicated Website team within the department, educated in Website design.
Leaky wave phenomena of a conductor‐back dielectric slab covered with a two‐dimensionally electromagnetic band gap superstrate
Authors: Hwang R. B.
Published: July 2007

This paper presents the leaky wave phenomena associated with a waveguide structure that consists of a conductor‐back dielectric slab covered with a superstrate made up of a two‐dimensionally (2‐D) electromagnetic band gap (EBG) structure. A guided wave has its energy bounced back and forth between the metallic ground plane and the EBG structure that is taken as a frequency‐selective reflection mirror. Because of the finite thickness of the 2‐D EBG superstrate, the guided wave will leak or radiate some of its energy into the air region above the waveguide structure to become a leaky wave. By the mode‐matching method and the transverse resonance technique, the overall waveguide structure is formulated as a rigorous electromagnetic boundary value problem to yield an exact dispersion relation of the waveguide so that the complex propagation constant of a guided mode can be accurately determined, including the phase and attenuation constants. Additionally, the electric field distribution inside the waveguide and the far‐field radiation pattern were also calculated to demonstrate the leaky wave phenomena of this waveguide from a microscopic point of view. On the basis of the excitation of leaky waves, the phenomenology concerning a class of directive antennas with EBG structure as superstrate was clarified in this research.
Regional and global trends in sulfate aerosol since the 1980s
Authors: Manktelow P. T. , Mann G. W. , Carslaw K. S. , Spracklen D. V. , Chipperfield M. P.
Published: July 2007

In the last two decades anthropogenic SO2 emissions have decreased across Europe and North America but have increased across Asia. Long‐term surface observations suggest that atmospheric sulfate concentrations have followed trends in sulfur emissions more closely across Asia, than across the USA and Europe. We use a global model of chemistry and aerosol to understand changes in the regional sulfur budget between 1985 and 2000. For every 1% decrease in SO2 emissions over Europe and the USA the modelled sulfate column burden decreased by 0.65%, while over Asia a 1% increase in SO2 resulted in a 0.88% increase in sulfate. The different responses can be explained by the availability of oxidant in cloud. We find that because emissions have moved southward to latitudes where in‐cloud oxidation is less oxidant limited, the 12% reduction in global SO2 emissions between 1985 and 2000 caused only a 3% decrease in global sulfate.
CRISM multispectral summary products: Parameterizing mineral diversity on Mars from reflectance
Authors: Pelkey S. M. , Mustard J. F. , Murchie S. , Clancy R. T. , Wolff M. , Smith M. , Milliken R. , Bibring J.‐P. , Gendrin A. , Poulet F. , Langevin Y. , Gondet B.
Published: July 2007

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) is the most recent spectrometer to arrive at Mars. The instrument is a hyperspectral imager covering visible to near‐infrared wavelengths (0.37–3.92 μm at 6.55 nm/channel). Summary products based on multispectral parameters will be derived from reflectances in key wavelengths for every CRISM observation. There are 44 summary products formulated to capture spectral features related to both surface mineralogy and atmospheric gases and aerosols. The intent is to use the CRISM summary products as an analysis tool to characterize composition as well as a targeting tool to identify areas of mineralogic interest to observe at higher spectral and spatial resolution. This paper presents the basis for the summary products and examines the validity of the above approach using data from the Mars Express OMEGA instrument, a visible/near‐infrared imaging spectrometer with spatial and spectral coverage similar to that of CRISM. Our study shows that the summary products vary in utility, but succeed in capturing the known diversity of the Martian surface and variability of the Martian atmosphere, and successfully highlight locations with strong spectral signatures. Thus the CRISM summary products will be useful in both operations and science applications. Caveats and limitations related to the summary products and their interpretation are presented to assist with their application by the community at large.
Tide‐induced recirculation across the aquifer‐ocean interface
Authors: Robinson C. , Li L. , Prommer H.
Published: July 2007

A parametric analysis is conducted to examine the influence of tides, inland hydraulic conditions, and aquifer properties on the rate of tide‐induced seawater recirculation through the nearshore aquifer. Understanding such influence is crucial for accurate prediction of subsurface chemical fluxes to coastal waters via groundwater discharge. The analysis is based on numerical simulations of density‐dependent groundwater flow in a coastal aquifer subject to tidal oscillations across a sloping beach face. The results reveal that the amplitude of tidal oscillations and the inland hydraulic gradient are the primary parameters controlling the tide‐induced recirculation rates. Significant tidal exchange is expected when the ratio of tidal to inland forcing is large. The horizontal tidal shoreline excursion and aquifer depth both display asymptotic behavior, influencing recirculation rates for only small values where the exchange process is limited by the potential for infiltration and shallowness of the aquifer, respectively. The analysis also indicates that tidal effects increase density‐driven recirculation rates due to enhanced convective flow within the saltwater wedge.
Surface warming by the solar cycle as revealed by the composite mean difference projection
Authors: Camp Charles D. , Tung Ka Kit
Published: July 2007

By projecting surface temperature data (1959–2004) onto the spatial structure obtained objectively from the composite mean difference between solar max and solar min years, we obtain a global warming signal of almost 0.2°K attributable to the 11‐year solar cycle. The statistical significance of such a globally coherent solar response at the surface is established for the first time.
Theory of molecular excitation and relaxation near a plasmonic device
Authors: Colas des Francs Gérard , Girard Christian , Laroche Thierry , Lévèque Gaëtan , Martin Olivier J. F.
Published: July 2007

The new optical concepts currently developed in the research field of plasmonics can have significant practical applications for integrated optical device miniaturization as well as for molecular sensing applications. Particularly, these new devices can offer interesting opportunities for optical addressing of quantum systems. In this article, we develop a realistic model able to explore the various functionalities of a plasmon device connected to a single fluorescing molecule. We show that this theoretical method provides a useful framework to understand how quantum and plasmonic entities interact in a small area. Thus, the fluorescence signal evolution from excitation control to relaxation control depending on the incident light power is clearly observed.
Source mass and positioning system for an accurate measurement of G
Authors: Lamporesi G. , Bertoldi A. , Cecchetti A. , Duhlach B. , Fattori M. , Malengo A. , Pettorruso S. , Prevedelli M. , Tino G. M.
Published: July 2007

We report on a system of well-characterized source masses and their precision positioning system for a measurement of the Newtonian gravitational constant G using atoms as probes. The masses are 24 cylinders of 50mm nominal radius, 150.2mm nominal height, and mass of about 21.5kg, sintered starting from a mixture of 95.3% W, 3.2% Ni, and 1.5% Cu. Density homogeneity and cylindrical geometry have been carefully investigated. The positioning system independently moves two groups of 12 cylinders along the vertical direction by tens of centimeters with a reproducibility of a few microns. The whole system is compatible with a resolution ΔG∕G<10−4.
Modeling temporary anions in density functional theory: Calculation of the Fukui function
Authors: Tozer David J. , De Proft Frank
Published: July 2007

Two approaches are investigated for modeling electron densities of temporary anions in density functional theory (DFT). Both rely on an artificial binding of the excess electron, in one case by a compact basis set and in the other by a potential wall. The key feature of the calculations is that the degree of binding is controlled in both cases by knowledge of the negative electron affinity of the corresponding neutral, approximated in terms of DFT local functional frontier orbital eigenvalues and vertical ionization potential, A=−(ϵLUMO+ϵHOMO)−I. To illustrate the two approaches, Fukui functions for nucleophilic attack are determined in four molecules with increasingly negative electron affinities. They yield very similar results, which are notably different to those determined without artificial electron binding. The use of a potential wall has the attractive feature that large, diffuse basis sets can be used, avoiding the need for a compact basis, tailored to a particular molecule.
Interactions of neutral and singly charged keV atomic particles with gas-phase adenine molecules
Authors: Alvarado Fresia , Bari Sadia , Hoekstra Ronnie , Schlathölter Thomas
Published: July 2007

KeV atomic particles traversing biological matter are subject to charge exchange and screening effects which dynamically change this particle’s effective charge. The understanding of the collision cascade along the track thus requires a detailed knowledge of the interaction dynamics of radiobiologically relevant molecules, such as DNA building blocks or water, not only with ionic but also with neutral species. We have studied collisions of keV H+, He+, and C+ ions and H0, He0, and C0 atoms with the DNA base adenine by means of high resolution time-of-flight spectrometry. For H0 and H+ we find qualitatively very similar fragmentation patterns, while for carbon, strong differences are observed when comparing C0 and C+ impact. For collisions with He0 and He+ projectiles, a pronounced delayed fragmentation channel is observed, which has not been reported before.
Influence of the cavity parameters on the output intensity in incoherent broadband cavity-enhanced absorption spectroscopy
Authors: Fiedler Sven E. , Hese Achim , Heitmann Uwe
Published: July 2007

The incoherent broadband cavity-enhanced absorption spectroscopy is a technique in measuring small absorptions over a broad wavelength range. The setup consists of a conventional absorption spectrometer using an incoherent lamp and a charge coupled device detector, as well as a linear optical cavity placed around the absorbing sample, which enhances the effective path length through the sample. In this work the consequences of cavity length, mirror curvature, reflectivity, different light injection geometries, and spot size of the light source on the output intensity are studied and the implications to the signal-to-noise ratio of the absorption measurement are discussed. The symmetric confocal resonator configuration is identified as a special case with optimum imaging characteristics but with higher requirements for mechanical stability. Larger spot sizes of the light source were found to be favorable in order to reduce the negative effects of aberrations on the intensity.
Enhancement of photoluminescence from excitons in silicon nanocrystals via coupling to surface plasmon polaritons
Authors: Takeda Eiji , Fujii Minoru , Nakamura Toshihiro , Mochizuki Yugo , Hayashi Shinji
Published: July 2007

The enhancement of photoluminescence (PL) is demonstrated from silicon nanocrystals (Si-ncs) by strong coupling of excitons to surface plasmon polaritons (SPPs) supported by a Au thin film. SPPs excited via excitons in Si-ncs were Bragg scattered to photons by one- or two-dimensional gratings, and strong and directional PL was obtained. From the angular dependence of PL spectra, dispersion relations of electromagnetic modes involved in the light emission process were obtained. The overall agreement between experimentally obtained and theoretically calculated dispersion relations confirmed that the strong and directional PL is mediated by SPPs. The PL decay rate of Si-ncs increased by placing a Au thin film on top and the wavelength dependence of the rate enhancement agreed well with that of the calculated SPP excitation rate. This suggests that the observed PL enhancement is due to efficient energy transfer from excitons to SPPs followed by efficient scattering of SPPs to photons, resulting in the enhancement of luminescence quantum efficiency.
Room-temperature ferromagnetism of Mn doped ZnO aligned nanowire arrays with temperature dependent growth
Authors: Liu J. J. , Wang K. , Yu M. H. , Zhou W. L.
Published: July 2007

Aligned one-dimensional diluted magnetic semiconductor Zn1−xMnxO nanowires were synthesized from a reaction of metallic Zn foil and MnCl2⋅6H2O under oxygen environment at variant temperatures between 750 and 950 °C by a chemical vapor deposition method. The c-axis preferentially grown nanowire arrays are single crystalline wurtzite structure, of which the growing temperature has a significant influence on both morphology and magnetic ordering. Nanowires with the highest aspect ratios were grown at 850 °C, whereas nanowires presenting largest room-temperature ferromagnetism were formed at 950 °C. More Mn2+ substitution in the ZnO lattice was observed at 950 °C, resulting in strong room-temperature ferromagnetism with a saturation magnetization of 0.25 emu/g. At synthesis temperatures of 750 and 850 °C, formation of a ZnMn2O4 room-temperature paramagnetic second phase was found. The nanostructures with different aspect ratios were obtained with the variation of synthesis temperature. The temperature dependent growth of aligned Zn1−xMnxO nanowires reveals strong room-temperature ferromagnetism occurs in the nanowire arrays synthesized at high temperature. The nanowires with strong room temperature have great potential in spintronic nanodevice application.
Lubrication of microelectromechanical systems radio frequency switch contacts using self-assembled monolayers
Authors: Patton Steven T. , Eapen Kalathil C. , Zabinski Jeffrey S. , Sanders Jeffrey H. , Voevodin Andrey A.
Published: July 2007

Contact failures in microelectromechanical systems (MEMS) switches prevent widespread use of MEMS technology for current handling in miniature devices. A self-assembled monolayer (SAM) lubricant was applied to MEMS switch surfaces in this paper as a possible approach for preventing contact failure. Chemical and physical processes on SAM lubricated contact surfaces were investigated at low (10 μA) and high (1 mA) current using a micro/nanoadhesion apparatus as a switch simulator with in situ monitoring of contact resistance and adhesion force. This was coupled with ex situ analytical analyses of the contacts using x-ray photoelectron spectroscopy (XPS) and micro-Raman techniques. Diphenyl disulfide was chosen as a lubricant due to its thermal stability, enhanced conductivity, and its ability to form a 3.4 Å thick SAM on the gold electrode surface. Hot switching experiments were conducted in humid air (45% RH) and dry nitrogen using a MEMS-scale contact force of 200 μN and 5 Hz frequency. At low current, lubricated contacts failed by growth in both adhesion and contact resistance (R) at about 105 cycles. A multi-step degradation mechanism was suggested which includes (1) SAM debonding under electron flow with formation of charged molecular species and dipole molecular structures, (2) migration and trapping of charged molecular species and/or molecular dipoles in the contact zone, (3) decomposition of molecular structures under Joule heating and repeated mechanical impact, and (4) increased R due to carbonaceous film formation that further accelerates thermal decomposition of the SAM. At high current, switch contacts failed immediately due to SAM thermal decomposition. Failure mechanisms and durability were similar in either air or dry nitrogen, indicating a minimum influence of the environment chemistry on the contact processes. This study establishes degradation mechanisms of SAM based lubricants in MEMS electrical contacts and results can be used in designing contact switch lubrication materials.
Analysis of charge transport in a polycrystalline pentacene thin film transistor by temperature and gate bias dependent mobility and conductance
Authors: Guo Dong , Miyadera Tetsuhiko , Ikeda Susumu , Shimada Toshihiro , Saiki Koichiro
Published: July 2007

The gate bias and temperature dependent field-effect mobility and conductance of a polycrystalline pentacene thin film transistor (TFT) were analyzed to study the charge transport in the material. Since both heating and cooling can obviously change the film morphology, a relatively narrow temperature range was adopted to rule out the possible influence of structure variation on the device characterization. Both mobility and conductance values increased with the gate bias and showed a thermally activated Arrhenius-like behavior, while the threshold voltage deceased with temperature. Several models were compared, and it was found that the observations could only be well interpreted by a multiple trapping model, which suggests that the temperature and gate bias dependences should be attributed to the increased free charge carrier density. The density of trap states in the band gap was evaluated by the field-effect mobility as well as the field-effect conductance data. The results disclose a possible field-effect mobility much higher than the present record in a polycrystalline pentacene TFT.
Split singularities and dislocation injection in strained silicon
Authors: Feron Martijn , Zhang Zhen , Suo Zhigang , Feron Martijn
Published: July 2007

In a microelectronic device, the strain field may be intensified at a sharp feature, such as an edge or a corner, injecting dislocations into silicon and ultimately failing the device. The strain field at an edge is singular and is often a linear superposition of two modes of different exponents. We characterize the relative contribution of the two modes by a mode angle, and determine the critical slip systems as the amplitude of the load increases. We calculate the critical residual stress in a thin-film stripe bonded on a silicon substrate.
Spectroscopic and stimulated emission characteristics of Nd3+ in transparent glass ceramic embedding β-YF3 nanocrystals
Authors: Chen Daqin , Wang Yuansheng , Ma En , Yu Yunlong , Liu Feng , Li Renfu
Published: July 2007

A transparent SiO2–Al2O3–LiF–YF3 glass ceramic doped with Nd3+ was fabricated by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscope results demonstrated that orthorhombic β-YF3 nanocrystals with a mean size of 23nm were homogeneously precipitated among the glass matrix. Confirmed by the energy dispersive x-ray spectroscopy measurements, the crystal-like absorption and emission of Nd3+ indicated the partition of Nd3+ into YF3 nanocrystals in the glass ceramic. Detailed characterizations of the Stark components of the I9∕24, I11∕24, and I13∕24 manifolds were performed using the low temperature fluorescence spectra for F3∕24→I9∕24, F3∕24→I11∕24, and F3∕24→I13∕24 transitions of Nd3+ in the glass ceramic. The stimulated emission cross sections of the F3∕24→I11∕24 intermanifold transition and the F3∕24(R1)→I11∕24(Y1) inter-Stark transition were determined to be 7.24×10−20 and 11.55×10−20cm2, respectively, being preferable to those of Nd3+-doped laser glasses and glass ceramic embedding (Pb,Cd)F2 nanocrystals.
Hydrodynamic instability of one-dimensional electron flow in semiconductors
Authors: Calderón-Muñoz Williams R. , Sen Mihir , Jena Debdeep
Published: July 2007

The hydrodynamic instability of one-dimensional flow of electrons in an ungated semiconductor driven by a voltage difference is studied. The governing transport and electrostatic equations are linearized about the steady flow, and the eigenspectrum of perturbations is calculated. The carrier flow is found to be unstable under certain circumstances through oscillations that manifest themselves as planar waves. Higher voltages lead to greater rates of growths of the instability. The frequencies of oscillation are found to be of the order of terahertz, making the phenomenon suitable for consideration as a solid-state radiative source at this frequency range.
A generic topological simulation scheme for studying aperture electromagnetic field interactions and cable couplings
Authors: Kirawanich Phumin , Wilson Justin R. , Yakura Susumu J. , Islam N. E.
Published: July 2007

A modified electromagnetic topology (EMT) simulation scheme for the interactions of an electromagnetic wave with an aperture and with cables of an electrical system beyond the aperture is described. The modified EMT simulation scheme addresses a concept in dealing with an aperture node of the topological circuitry without having to specify the details of the entire electrical circuitry. The results of the modified EMT simulation scheme have been validated through experiments for aperture∕wave interactions and the induced currents on the cable near the aperture. The aperture transfer functions, obtained for both the simulation and experimental cases, have shown the characteristic response similar to that of the high-pass filter with a cutoff frequency. The simulated and measured currents on a cable, placed behind the aperture, resulted in good agreement with each other, providing the good validation of the modified EMT simulation scheme. Under this scheme, any change in topological circuitry can be handled easily in the substructural levels without having to consider an entire system. Consequently, the effects of various types of aperture interactions on the entire system can be reinvestigated via simply remodeling of topological interaction nodes in substructural levels.
Fabrication of Si1−xGex alloy nanowire field-effect transistors
Authors: Kim Cheol-Joo , Yang Jee-Eun , Lee Hyun-Seung , Jang Hyun M. , Jo Moon-Ho , Park Won-Hwa , Kim Zee Hwan , Maeng Sunglyul
Published: July 2007

The authors present the demonstration of nanowire field-effect transistors incorporating group IV alloy nanowires, Si1−xGex. Single-crystalline Si1−xGex alloy nanowires were grown by a Au catalyst-assisted chemical vapor synthesis using SiH4 and GeH4 precursors, and the alloy composition was reproducibly controlled in the whole composition range by controlling the kinetics of catalytic decomposition of precursors. Complementary in situ doping of Si1−xGex nanowires was achieved by PH3 and B2H6 incorporation during the synthesis for n- and p-type field-effect transistors. The availability of both n- and p-type Si1−xGex nanowire circuit components suggests implications for group IV semiconductor nanowire electronics and optoelectronics.
Folding of a miniprotein with mixed fold
Authors: Mohanty Sandipan , Hansmann U. H. E.
Published: July 2007

Using the 28 residue ββα protein FSD-EY as a target system, we examine correction terms for the ECEPP/3 force field. We find an increased probability of formation of the native state at low temperatures resulting from a reduced propensity to form α helices and increased formation of β sheets. Our analysis of the observed folding events suggests that the C-terminal helix of FSD-EY is much more stable than the N-terminal β hairpin and forms first. The hydrophobic groups of the helix provide a template which promotes the formation of the β hairpin that is never observed to form without the helix.
Observation of a two dimensional electron gas formed in a polarization doped C-face 3C∕4H SiC heteropolytype junction
Authors: Chandrashekhar M. V. S. , Thomas C. I. , Lu Jie , Spencer Michael. G.
Published: July 2007

A two dimensional electron gas (2DEG) was observed in a C-face 3C∕4H SiC heteropolytype junction. Sheet carrier concentrations of ∼3×1013cm−2 and Hall mobility of ∼314cm2∕Vs were measured at 77K. The temperature dependences of mobility and carrier concentration clearly demonstrate the presence of the 2DEG. Comparison with theory indicates that the carriers originate from both spontaneous polarization and unintentional degenerate nitrogen doping of 3C-SiC, suggesting a 77K 2DEG mobility ∼700cm2∕Vs in parallel with bulk hopping conduction. Mobility at high temperatures was phonon limited, indicating a Debye temperature of 1600K. Transmission line measurements yielded similar mobilities, with saturation currents of ∼3A∕mm, suggesting the utility of SiC heteropolytypes in microwave devices.
Combinatorial materials research applied to the development of new surface coatings VII: An automated system for adhesion testing
Authors: Chisholm Bret J. , Webster Dean C. , Bennett James C. , Berry Missy , Christianson David , Kim Jongsoo , Mayo Bret , Gubbins Nathan
Published: July 2007

An automated, high-throughput adhesion workflow that enables pseudobarnacle adhesion and coating/substrate adhesion to be measured on coating patches arranged in an array format on 4×8in.2 panels was developed. The adhesion workflow consists of the following process steps: (1) application of an adhesive to the coating array; (2) insertion of panels into a clamping device; (3) insertion of aluminum studs into the clamping device and onto coating surfaces, aligned with the adhesive; (4) curing of the adhesive; and (5) automated removal of the aluminum studs. Validation experiments comparing data generated using the automated, high-throughput workflow to data obtained using conventional, manual methods showed that the automated system allows for accurate ranking of relative coating adhesion performance.
Application of tape-cast graded impedance impactors for light-gas gun experiments
Authors: Martin L. Peter , Patterson J. Reed , Orlikowski Daniel , Nguyen Jeffrey H.
Published: July 2007

Fabrication of compositionally graded structures for use as light-gas gun impactors has been demonstrated using a tape casting technique. Mixtures of metal powders in the Mg-Cu system were cast into a series of 19 tapes with uniform compositions ranging from 100% Mg to 100% Cu. The individual compositions were fabricated into monolithic pellets for characterization of microstructure, density, and sound wave velocity. Graded impactors were fabricated by stacking layers of different compositions in a sequence calculated to yield a tailored acoustic impedance profile, and were characterized by ultrasonic C-scan and white light interferometry. The graded impactors were launched into stationary Al targets using a two-stage light-gas gun, and the resulting wave profiles were measured with either VISAR or Photonic Doppler Velocimetry. For an impactor using only seven compositions ranging from Mg to Cu, the composition steps are visible in the wave profiles. An impactor utilizing the full series of 19 compositions produces smoother compression with no visible manifestation of the discrete-layer structure. Hydrodynamic simulations of these impactors also suggest smooth compression profiles within the impactor.
Membrane-free microfiltration by asymmetric inertial migration
Authors: Seo Jeonggi , Lean Meng H. , Kole Ashutosh
Published: July 2007

Membrane-free microfiltration by asymmetric inertial migration is studied and evidence of the filtration capability is presented. Centrifugal force induced by flow in spiral channel geometry modifies the lateral symmetry of straight-channel tubular pinch equilibrium resulting in a focused particle band nearer to the inner sidewall. Bifurcated outlets separately collect the concentrated particle band and remaining effluent. The spiral continuous flow filtration relies solely on internal fluidic shear characteristics, eliminating the need for membrane filters or external force fields. This device has the desirable combinations of high throughput and low cost, making it inherently suited for preparative filtration in the range of micro- to macroscale applications.
Particle image velocimetry measurements of the velocity profile in HeII forced flow
Authors: Xu T. , Van Sciver S. W.
Published: July 2007

Measurements of the velocity profile of HeII forced flow within a square cross-section channel are reported. The particle image velocimetry (PIV) technique is used for these measurements with micron scale solid deuterium particles as tracers of the HeII velocity field. Steady state velocity profiles at different bath temperatures clearly show the existence of a turbulent boundary layer in HeII forced flow. These observed velocity profiles are in reasonable agreement with correlations based on measurements in classical fluids.
Demonstration of a quantum cellular automata cell in a GaAs∕AlGaAs heterostructure
Authors: Perez-Martinez F. , Farrer I. , Anderson D. , Jones G. A. C. , Ritchie D. A. , Chorley S. J. , Smith C. G.
Published: July 2007

The authors report on the experimental demonstration of a GaAs∕AlGaAs-based quantum cellular automata cell fabricated using electron beam lithographically defined gates. These surface metallic gates form a pair of double quantum dots, as well as a pair of quantum point contacts (QPCs) that act as noninvasive voltage probes. Measurements at cryogenic temperatures show that an electron transfer in the input dots induces the relocation of a single electron in the output dots. Using the QPCs they were also able to determine the operating limits of the cell.