bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoxia induces the activation of human hepatic stellate cells LX‐2 through TGF‐β signaling pathway
Authors: Shi Yue-Feng , Fong Chi-Chun , Zhang Qi , Cheung Pik-Yuen , Tzang Chi-Hung , Wu Rudolf S.S. , Yang Mengsu
Published: December 2006

Hypoxia is a common environmental stress factor and is also associated with various physiological and pathological conditions such as fibrogenesis. The activation of hepatic stellate cells (HSCs) is the key event in the liver fibrogenesis. In this study, the behavior of human HSCs LX‐2 in low oxygen tension (1% O2) was analyzed. Upon hypoxia, the expression of HIF‐1α and VEGF gene was induced. The result of Western blotting showed that the expression of α‐SMA was increased by hypoxic stimulation. Furthermore, the expression of MMP‐2 and TIMP‐1 genes was increased. Hypoxia also elevated the protein expression of the collagen type I in LX‐2 cells. The analysis of TGF‐β/Smad signaling pathway showed that hypoxia potentiated the expression of TGF‐β1 and the phosphorylation status of Smad2. Gene expression profiles of LX‐2 cells induced by hypoxia were obtained by using cDNA microarray technique.
Arnold-Chiari type I malformation presenting as benign paroxysmal positional vertigo in an adult patient
Authors: Unal M , Bagdatoglu C
Published: December 2006

Arnold-Chiari malformations are a group of congenital hindbrain and spinal cord abnormalities characterized by herniation of the contents of the posterior cranial fossa caudally through the foramen magnum into the upper cervical spine. It is important to recognize Arnold-Chiari type I malformation in the differential diagnosis of adult vertigo cases. We present a 51-year-old patient with Arnold-Chiari type I malformation that was initially diagnosed as posterior semicircular canal benign paroxysmal positional vertigo.
Internal jugular vein ectasia – a rare cause for paroxysmal cough
Authors: Padmanabhan K , Vaishali B , Indudharan R
Published: December 2006

Internal jugular vein ectasia (dilatation of the internal jugular vein) is a rare clinical entity, often undiagnosed. Usually it presents as an asymptomatic, soft, compressible neck swelling that increases in size on Valsalva's manoeuvre. Our report describes right internal jugular vein ectasia in a 15-year-old girl who presented to us with intractable paroxysmal cough. The entity was suspected on ultrasound imaging and confirmed by computed tomography scan and Doppler. Ligation and excision of the dilated vein almost immediately cured her cough. The probable reason for the cough was the pressure exerted by the dilated vein on the vagus nerve.
A case of sensorineural deafness following ingestion of sildenafil
Authors: Mukherjee B , Shivakumar T
Published: December 2006

We report a case of bilateral profound unremitting sensorineural hearing loss, in a 44-year-old male patient occurring after ingestion of sildenafil citrate 50 mg/day for 15 days. Audiological evaluation documented the findings. Sildenafil is an effective oral treatment for erectile dysfunction syndrome. It is being used and abused by many people as availability is easy and it can even be bought over the internet. Many patients are unaware of the harmful effects of sildenafil and take the drug without medical supervision. We could not find any previously reported cases of sildenafil induced hearing loss and to the best of our knowledge, this is the first case report of sildenafil induced sensorineural hearing loss in the world literature.
Variation in host preference within Gyrodactylus salaris (Monogenea): an experimental approach
Authors: OLSTAD K. , ROBERTSEN G. , BACHMANN L. , BAKKE T. A.
Published: December 2006

The monogenean ectoparasite, Gyrodactylus salaris Malmberg, 1957, has had a devastating effect on wild Atlantic salmon (Salmo salar) since its introduction to Norway in the mid-1970s. In Lake Pålsbufjorden, southern Norway, upstream of the stretches of the River Numedalslågen with anadromous Atlantic salmon, a resident Arctic charr (Salvelinus alpinus) population has been reported to be infected with G. salaris which is viable in the absence of its normal host, the Atlantic salmon. Currently, there is no record of G. salaris infecting Atlantic salmon in the downstream sections of the River Numedalslågen. We studied experimentally the infectivity and reproductive capacity of G. salaris from Lake Pålsbufjorden on wild and hatchery-reared Atlantic salmon as well as on Arctic charr and rainbow trout (Oncorhynchus mykiss). Arctic charr and rainbow trout were moderately susceptible, whereas the Atlantic salmon stocks from River Numedalslågen and River Drammenselva were innately resistant to only slightly susceptible. Thus, the G. salaris from Arctic charr in Lake Pålsbufjorden is considered non-pathogenic to Atlantic salmon. This is the first observation of variation in host preference among Norwegian G. salaris populations. The observed differences in virulence between G. salaris populations could have important consequences for the international legislation and management of Atlantic salmon.
Immune system pathogenesis is prevented by the neutralization of the systemictrans-sialidase fromTrypanosoma cruziduring severe infections
Authors: RISSO M. G. , PITCOVSKY T. A. , CACCURI R. L. , CAMPETELLA O. , LEGUIZAMÓN M. S.
Published: December 2006

During the acute phase ofTrypanosoma cruziinfection, strong haematological and immune system alterations are observed. The parasite expressestrans-sialidase, a virulence factor responsible for the sialylation of its surface glycoconjugates. This enzyme is also shed to the bloodstream where it is associated with immune system alterations triggered during the infection. During experimental and human infections, the host elicits antibodies able to neutralize the enzyme activity that would be responsible for restricting systemictrans-sialidase to the early steps of the infection, when major immune alterations are induced. The actual relevance of these antibodies was tested by passive transference of monoclonal neutralizing antibodies in acute infection models displaying extreme sensitivity to the infection. Mice were inoculated with virulent parasite strains that induce high parasitaemia, early mortality and strong immune tissue abnormalities. Thetrans-sialidase-neutralizing antibodies were able to preserve B cell areas both in ganglia and spleen as well as the thymus architecture even in these extreme models. Although no differences between control and treated mice regarding animal survival were found, a major role for the humoral response in controlling the damage of the immune system induced by a systemically distributed virulence factor was defined in an infection with a eukaryotic pathogen.
Gastrointestinal helminths in indigenous and exotic chickens in Vietnam: association of the intensity of infection with the Major Histocompatibility Complex
Authors: SCHOU T. W. , PERMIN A. , JUUL-MADSEN H. R. , SØRENSEN P. , LABOURIAU R. , NGUYÊN T. L. H. , FINK M. , PHAM S. L.
Published: December 2006

This study compared the prevalence and intensity of infections of helminths in 2 chicken breeds in Vietnam, the indigenous Ri and the exotic Luong Phuong. Also, possible correlations with the Major Histocompatibility Complex (MHC) were tested. The most prevalent helminths wereAscaridia galli,Heterakis beramporia,Tetrameres mothedai,Capillaria obsignata,Raillietina echinobothridaandRaillietina tetragona. Differences in prevalence and intensity of infection were found between the 2 breeds. Comparing the 2 groups of adult birds, Ri chickens were observed to have higher prevalence and infection intensities of several species of helminths, as well as a higher mean number of helminth species. In contrast,A. galliandC. obsignatawere shown to be more prevalent in Luong Phuong chickens. Furthermore, an age-dependent difference was indicated in the group of Ri chickens in which the prevalence and the intensity of infection was higher for the adult than the young chickens for most helminths. The most notable exception was the significantly lower prevalence and intensities ofA. galliin the group of adult chickens. In contrast, the prevalence and intensity were very similar in both age groups of Luong Phuong chickens. Using a genetic marker located in the MHC, a statistically significant correlation between several MHC haplotypes and the infection intensity of different helminth species was inferred. This is the first report of an association of MHC haplotype with the intensity of parasite infections in chickens.
Editorial Power, People and Constitutional Engineering
Authors:   JWS/WTE
Published: December 2006

In 2005, a number of alarming reports on voter participation, social exclusion and political participation were published by the Electoral Commission in the United Kingdom. One third of the electorate do not feel represented by any of the political parties. Less than one in five votes had any impact on the outcome of elections in 2001 and 2005. In the 2005 election, 39% of registered voters did not vote. The turnout for general elections has declined significantly since 1997, and elected representatives are held in low esteem.
External Action of the European Union After the Constitutional Setback
Authors: Martin Magdalena , Lirola Isabel
Published: December 2006

Union external action after Constitutional set back – Status under international law – Perspective of democracy and leadership – Pillar structure – Substance and ambition of Union's foreign action.
Neutralizing the Sovereignty Question Compromise Strategies in Constitutional Argumentations before European Integration and since
Authors: Jakab András
Published: December 2006

Social function of sovereignty – Taming sovereignty through compromise strategies – The sharing strategy – The creation of a new unreal bearer of sovereignty – Leaving sovereignty itself untouched but forbidding the use of it – Abolishing the concept – Redefining the concept – Challenges to the Westphalian paradigm of international legal sovereignty – National answers to the challenges put by European integration – A new compromise formula – Neutralizing the sovereignty question.
MOX Plant Dispute – Court of Justice of the European Communities
Authors: Lavranos Nikolaos
Published: December 2006

It is uncommon for a provision of the EC Treaty to remain all but unnoticed for fifty years by both legal literature and the case-law of the European Court of Justice. However, that is what happened to Article 292 EC, which states that ‘Member States undertake not to submit a dispute concerning the interpretation or application of this Treaty to any method of settlement other than those provided for therein.’ This provision can be taken to mean that if a dispute arises between European Union member states involving Community law, they shall bring the dispute exclusively before the European Court of Justice.
Substrate Supply for Effective Biocatalysis
Authors: Kim Pei‐Yi , Pollard David J. , Woodley John M.
Published: December 2006

Using biocatalysis for some chemical synthesis steps has unique advantages such as achieving higher product selectivity under ambient process conditions. However, a common limitation with such systems is the inhibition or toxicity posed by the starting substrate as well as limited aqueous solubility in many cases. In this review, we discuss the supply of substrate to bioconversions. The delivery of substrate via an auxiliary, which may be water‐miscible, or a second phase such as a water‐immiscible organic solvent, adsorbing resin, or a gas, is examined through recent examples in the field. Finally, guidelines for experimental planning and process considerations are suggested to facilitate the choice of substrate delivery method and accelerate process development.
Imaging ellipsometry study on the Ni-mediated crystallization of a-Si
Authors: Choi A. J. , Ghong T. H. , Kim Y. D. , Oh J. H. , Jang J.
Published: December 2006

We have investigated by imaging ellipsometry (IE) the crystallization of amorphous silicon (a-Si) at low temperature by Ni-silicide-mediated crystallization on a glass substrate. We observed a significant difference in the ellipsometric image between polycrystalline silicon (poly-Si) and a-Si and confirmed that annealing for longer time leads to increasing area of poly-Si domain. The progress of crystallization is modeled as the growth of a disk in a two-dimensional surface since the crystallized region expanded as a disk shape. The rate of increasing radius of the disk and the average distance between initial nucleus points were obtained by fitting the change of the area of the disk measured by the IE with annealing time.
High throughput screening of ferroelectric thin film libraries
Authors: Schroeter Christian , Wessler Berit , Schoenecker Andreas , Keitel Uwe , Eng Lukas M.
Published: December 2006

High throughput methods can significantly speed up the search for advanced materials in a multidimensional configuration space, hence keeping innovation cycles short. In the search for improved materials, high throughput methods are wanted to optimize composition and processing of promising systems, and to find candidate compounds. Such a method is described here which is applicable to the development of ferroelectric thin films. Libraries with samples of varying chemical composition were produced via the sol-gel route on structured and metallized silicon wafers. To determine the permittivity of the films, automated measurements of film thickness and capacity were established. Furthermore, ferroelectric hysterisis measurements were performed on samples with a particularly high permittivity. This high throughput route, which allows for synthesis and characterization of over hundred samples per day, was proved and tested by means of lead zirconate titanate as a standard material. It was possible to obtain films with remarkable high permittivity and low coercive field at optimal lead zirconate/lead titanate ratio and by compensating for lead loss during processing by finding the optimal lead excess added to the precursor solutions.
Impact of silicon incorporation on the formation of structural defects in AlN
Authors: Hermann M. , Furtmayr F. , Morales F. M. , Ambacher O. , Stutzmann M. , Eickhoff M.
Published: December 2006

The impact of Si impurities on the structural properties of AlN, grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire is studied. Under nitrogen-rich growth conditions silicon can be homogeneously incorporated up to Si concentrations of [Si]=5.2×1021 cm−3. The presence of silicon on the surface during the growth process is demonstrated to be beneficial for the surface morphology and the structural properties of the AlN films. For [Si] up to (5±3)×1020 cm−3, this surfactant behavior results in a decrease of the surface roughness from 8 nm for undoped layers grown in a nitrogen-rich regime to less than 1 nm. In addition, high resolution x-ray diffraction studies reveal an increase of the average lateral crystal size from 300 nm to more than 1 μm and a simultaneous decrease of the screw dislocation density from 3.8×108 cm−2 for (comparably) weakly doped samples to 2×107 cm−2. At the same [Si] the heterogeneous stress shows a minimum of less than 50 MPa and drastically increases for higher [Si]. The analysis of edge dislocations as a function of [Si] reveals that their density is directly related to Si-induced compressive biaxial stress which increases up to (2.0±0.15) GPa, independently determined by x-ray diffraction and Raman spectroscopy. While edge dislocations are found to be strongly correlated with the release of stress, screw dislocations are formed due to the coalescence of AlN islands with different stacking order, as their density is decreasing with increasing lateral crystal size. For AlN films with [Si]<1.2×1021 cm−3, a Poisson ratio ν=0.525±0.022 is determined.
Dependence of ultraviolet nanosecond laser polymer ablation on polymer molecular weight: Poly(methyl methacrylate) at 248nm
Authors: Bounos Giannis , Selimis Alexandros , Georgiou Savas , Rebollar Esther , Castillejo Marta , Bityurin Nikita
Published: December 2006

We rely on a methodology demonstrated previously for assessing the temperature evolution and polymer viscosity changes in the 248nm irradiation of poly(methyl methacrylate)s (PMMAs) with molecular weights (Mw) ranging from 2.5to996kDa. Briefly, this methodology [G. Bounos et al., J. Appl. Phys. 98, 084317 (2005)] relies on monitoring the formation of aryl products in the irradiation of polymer doped with iodonaphthalene or iodophenanthrene. The results demonstrate that higher temperatures are attained with increasing Mw. The surface temperatures at the corresponding ablation thresholds are estimated to be ∼850–900K for Mw⩾120kDa vs ∼600K for 2.5kDa PMMA. In addition, for all Mw’s, melting is demonstrated (viscosity values of ≈101Pas), but it lasts longer for high Mw PMMAs. We ascribe these differences to the fact that low Mw PMMAs dissociate efficiently to desorbing monomers/oligomers, thereby resulting in more efficient energy removal. Even so, the ablation threshold of the high Mw PMMAs is attained at higher fluences. This can be ascribed to the higher fraction of bonds that is required to be broken, and also plausibly to the higher gaseous product pressures that must be attained, for material ejection to be effected. The results are overall well accounted by the bulk photothermal model.
Nanoscale surface roughening in ultrathin aluminum films
Authors: Aurongzeb D. , Washington E. , Basavaraj M. , Berg J. M. , Temkin H. , Holtz M.
Published: December 2006

We report studies of the formation of aluminum structures, with nanometer length scales, in ultrathin layers deposited on glass and analyzed using atomic force microscopy. Surface roughness, lateral cutoff length, and surface scaling exponent are all found to vary systematically with Al thickness. The initial nanocrystal formation is described by stress-energy minimization. We interpret the observed scaling behavior based on the kinetic theory of roughening. For very thin layers (<50nm) the roughness is consistent with a ∇4h growth factor, where h is surface height. For thick layers (>50nm) the ∇2(∇h)2 conserved mechanism is dominant. Substrate stress is not found to influence the scaling exponent through the kinetic theory.
Dielectric relaxation in BaTi0.85(Fe1∕2Nb1∕2)0.15O3 perovskite ceramic
Authors: Abdelkafi Z. , Abdelmoula N. , Khemakhem H. , Bidault O. , Maglione M.
Published: December 2006

A polycrystalline sample of BaTi0.85(Fe1∕2Nb1∕2)0.15O3 is synthesized by high temperature solid state reaction technique. This sample crystallizes in cubic pervoskite structure at room temperature. The dielectric properties have been investigated at temperature range from 80to450K at various frequencies (100–107Hz). Frequency dielectric dispersion phenomena in a BaTi0.85(Fe1∕2Nb1∕2)0.15O3 ceramic has been analyzed by impedance spectroscopy in the temperature range from 250to450K. The Cole-Cole relaxation equation modified by introducing the conductivity was used to describe the experimental dielectric spectra of a high permittivity. Excellent agreement has been obtained in wide frequency domain (100–107Hz) between the measured and calculated permittivities in the 250–450K temperature range. The dielectric relaxation frequency obeys the Arrhenius behavior with activation energy of 0.181eV. A separation of the grain and grain boundary properties has been achieved using an equivalent circuit model. The different parameters of this circuit have been determined using impedance and modulus spectroscopy studies. The inner grain conductivity also obeys the Arrhenius low behavior with activation energy of 0.183eV. The dielectric relaxation and the inner grain conductivity have thus similar activation energies which suggest a link between these two phenomena.
Analysis of pentacene field effect transistor as a Maxwell-Wagner effect element
Authors: Tamura Ryousuke , Lim Eunju , Manaka Takaaki , Iwamoto Mitsumasa
Published: December 2006

The pentacene field effect transistor (FET) is analyzed as a Maxwell-Wagner effect element. As a result of the Maxwell-Wagner effect, carriers injected from source electrode are accumulated at the interface between pentacene and SiO2-gate insulator. They are then conveyed along the FET channel by the electric field formed between source and drain electrodes. The drain current Ids shows characteristic behavior depending on the force of the electric field. The transit time and charging time of injected carriers are key parameters to specify FET characteristics ruled by the Maxwell-Wagner effect. Results also show that our pentacene FET characteristics are well explained based on the present theoretical analysis.
Space charge effects in ferroelectric thin films
Authors: Zubko P. , Jung D. J. , Scott J. F.
Published: December 2006

The effects of space charges on hysteresis loops and field distributions in ferroelectrics have been investigated numerically using the phenomenological Landau-Ginzburg-Devonshire theory. Cases with the ferroelectric fully and partially depleted have been considered. In general, increasing the number of charged impurities results in a lowering of the polarization and coercive field values. Squarer loops were observed in the partially depleted cases and a method was proposed to identify fully depleted samples experimentally from dielectric and polarization measurements alone. Unusual field distributions found for higher dopant concentrations have some interesting implications for leakage mechanisms and limit the range of validity of usual semiconductor equations for carrier transport.
Electrical characterization of PbZr0.4Ti0.6O3 capacitors
Authors: Zubko P. , Jung D. J. , Scott J. F.
Published: December 2006

We have conducted a careful study of current-voltage (I-V) characteristics in fully integrated commercial PbZr0.4Ti0.6O3 thin-film capacitors with Pt bottom and Ir∕IrO2 top electrodes. Highly reproducible steady-state I-V were obtained at various temperatures over two decades in voltage from current-time data and analyzed in terms of several common transport models including space charge limited conduction, Schottky thermionic emission under full and partial depletion, and Poole-Frenkel conduction, showing that the latter is the most plausible leakage mechanism in these high-quality films. In addition, ferroelectric hysteresis loops and capacitance-voltage data were obtained over a large range of temperatures and discussed in terms of a modified Landau-Ginzburg-Devonshire theory accounting for space charge effects.
In situ small angle x-ray scattering, wide angle x-ray scattering, and Raman spectroscopy of microwave synthesis
Authors: Tompsett G. A. , Panzarella B. , Conner W. C. , Yngvesson K. S. , Lu F. , Suib S. L. , Jones K. W. , Bennett S.
Published: December 2006

Recent studies in microwave chemistry have proven many enhancements in reaction rates and selectivities. Most dramatic are several zeolite syntheses where over an order of magnitude more rapid rates are often, but not always, found. The reasons for these enhancements are not understood in part because in situ spectroscopies under microwave exposure are problematic. Thus, techniques have been slow to develop. This study describes a novel system with which x-ray scattering and Raman studies can be performed in situ during exposure to microwave radiation. The mechanisms and rates for the syntheses of zeolites or other microwave syntheses can be studied dynamically in this manner. A 2.45GHz waveguide system operating in single pass or as a tuned cavity was developed through which an x-ray beam and/or a Raman laser could probe a synthesis solution and the appropriate scattering are studied. The X10A beamline at Brookhaven National Synchrotron Light Source was used for these studies.
Small amplitude oscillations of a flexible thin blade in a viscous fluid: Exact analytical solution
Authors: Van Eysden Cornelis A. , Sader John E.
Published: December 2006

The oscillation of a thin blade immersed in a viscous fluid has received considerable attention recently due to its importance in technological applications such as the atomic force microscope and microelectromechanical systems. In this article, we consider the general case of a flexible thin blade executing spatially varying small amplitude oscillations in a viscous fluid. Exact analytical solutions for the three-dimensional flow field and hydrodynamic load are derived for both normal and torsional oscillations of arbitrary wave number. This contrasts previous investigations that focus exclusively on the complementary rigid-blade problem, which is two-dimensional, and rely on computational techniques.
Micromachining of ridge optical waveguides on top of He+-implanted β-BaB2O4 crystals by femtosecond laser ablation
Authors: Degl'Innocenti R. , Reidt S. , Guarino A. , Rezzonico D. , Poberaj G. , Günter P.
Published: December 2006

We report on a technique for the fabrication of ridge optical waveguides on top of β-BaB2O4 (BBO) crystals. The BBO crystals were first implanted by He+ ions to form planar optical waveguides. In the second step, the femtosecond laser ablation technique was employed for micromachining of ridge-type optical waveguides. A thorough study of material-specific ablation parameters for BBO has been performed in order to achieve ablated structures with smooth sidewalls. A further process of Ar+ ion smoothing in a plasma chamber was used to reduce the sidewall roughness of the ablated ridges from 75 to 35 nm root mean square. We demonstrated optical waveguiding in these femtosecond-ablated plasma-treated waveguides and measured total propagation losses of less than 10 dB∕cm at 532 nm, making them suitable for nonlinear- and electro-optical applications.
Ab initio study of the effect of water adsorption on the carbon nanotube field-effect transistor
Authors: Sung Dongchul , Hong Suklyun , Kim Yong-Hoon , Park Noejung , Kim Sanghyeob , Maeng Sung Lyul , Kim Ki-Chul
Published: December 2006

We perform density-functional calculations to investigate the effect of adsorbed water molecules on carbon nanotubes (CNTs). Noting that the H2O molecule has much wider energy gap than the CNT, we find that the charge transfer between them is negligible. We discuss that several recent publications, which claimed a substantial electron transfer from the water molecule to the CNT, have been based on incautious interpretations of the Mulliken population analysis. We suggest that the effect of humidity on nanotube devices may be attributed to various indirect effects enhanced by water vapors, rather than the carrier generations by the physisorbed H2O molecules.
Parametric-time coherent states for the generalized MIC-Kepler system
Authors: Ünal Nuri
Published: December 2006

In this study, we construct the parametric-time coherent states for the negative energy states of the generalized MIC-Kepler system, in which a charged particle is in a monopole vector potential, a Coulomb potential, and a Bohm-Aharonov potantial. We transform the system into four isotropic harmonic oscillators and construct the parametric-time coherent states for these oscillators. Finally, we compactify these states into the physical time coherent states for the generalized MIC-Kepler system.
Patterned femtosecond laser excitation of terahertz leaky modes in GaAs photonic crystals
Authors: Jukam Nathan , Yee Cristo , Sherwin Mark S. , Fushman Ilya , Vučković Jelena
Published: December 2006

GaAs terahertz (THz) photonic crystals are fabricated using reactive ion etching. A femtosecond laser beam generates THz radiation inside the PCs. Spatial patterning of the laser beam is used to couple into the PC modes. THz emission is observed from modes above the light line (leaky modes). Only the dipole modes are found to radiate strongly in the direction normal to the slab which is consistent with finite-difference time-domain based calculations of the far fields.
Experimental and ab initio study of a new D̃Δg1 state of the C3 radical
Authors: Saha Sudarshana , Western Colin M.
Published: December 2006

We report here the first observation of the D̃Δg1 state of the C3 radical, which provides the first comprehensively analyzed example of the dynamic Renner-Teller splitting in Δ symmetry. Two color double resonance spectroscopy via the ÃΠu1 state was employed to experimentally probe an extensive range of vibronic levels in this D̃Δg1 state, covering all three modes of vibration of C3. The analysis was supported by ab initio potential energy surface calculations on the C3 radical to outline the lowest eight singlet electronic states. Two methods were used to analyze the Renner-Teller effect. The first method is an empirical Hamiltonian based on normal modes, using harmonic oscillator functions as a basis, with Renner-Teller and other terms added as required, which allows conventional vibrational parameters to be determined. The second is a much larger program that uses the exact kinetic energy operator for a triatomic molecule to calculate vibronic energy levels directly from the Renner-Teller pair of potential energy surfaces. Both methods give a good fit to the experimental results, with only a small adjustment to the ab initio surfaces required for the latter. One of the overall conclusions is that the Renner-Teller effect is rather smaller in the D̃Δg1 state than in the ÃΠu1 state.
Ferromagnetism in bulk Co-Zn-O
Authors: Quesada A. , García M. A. , Andrés M. , Hernando A. , Fernández J. F. , Caballero A. C. , Martín-González M. S. , Briones F.
Published: December 2006

The origin of ferromagnetism in diluted magnetic semiconductors is still an open question, yielding a great deal of research across the world. This work focuses on the Co-Zn-O system. Room-temperature ferromagnetism is observed after a partial reaction of Co3O4 and ZnO, which can be ascribed neither to carrier mediation nor segregated cobalt metallic clusters. Another mechanism is yielding room-temperature ferromagnetism. This mechanism is associated with a partial reaction of ZnO and Co3O4 grains, and always appears when the starting phases (Co3O4 and ZnO) are present in the sample, suggesting that interfaces are involved in the origin of the observed ferromagnetism.
In situ mechanical testing of templated carbon nanotubes
Authors: Lu Shaoning , Guo Zaoyang , Ding Weiqiang , Dikin Dmitriy A. , Lee Junghoon , Ruoff Rodney S.
Published: December 2006

A new microelectromechanical system (MEMS)-based tensile testing stage (with integrated actuator, direct load sensing beam, and electrodes for controlled assembly of an individual nanostructure) was developed and used for in situ tensile loading of a templated carbon nanotube (T-CNT) inside a scanning electron microscope (SEM). Specifically, an increasing tensile load was applied to the T-CNT by actuating the device and high-resolution scanning electron microscopy images were acquired at different loads. The load (from the bending of the direct force-sensing beam), the elongation of the specimen during loading, and the specimen geometry were all obtained from analysis of SEM images. The stress versus strain curve and Young’s modulus were thus obtained. A model is presented for the tensile loading experiment, and the fit value of Young’s modulus from this model is compared to values obtained by an independent method. The results of this experiment on a T-CNT suggest the use of this device for loading other nanostructures and also for designing other MEMS-based systems, such as a compressive testing stage.
The mechanism of zero mean absolute vorticity state in rotating channel flow
Authors: Hamba Fujihiro
Published: December 2006

In the core region of spanwise rotating channel flows, the mean velocity profile is approximately linear with a slope of twice the system rotation rate. The mechanism of this zero mean absolute vorticity state is investigated from the turbulence modeling point of view. The mean velocity profile is calculated using three simple nonlinear eddy-viscosity models. It is shown that two models, the curvature-corrected type of explicit algebraic Reynolds stress model and the model with the corotational derivative of the second-order nonlinear term, reproduce well the zero mean absolute vorticity profile. Both models are derived by taking into account the effect of the advection of the Reynolds stress in the rotating frame. In particular, the latter model reflects the memory effect of the second-order nonlinear term. This effect means that a nonzero absolute vorticity creates a difference between the normal stresses, leading to a large shear stress in a rapidly rotating system. Since the actual value of the shear stress does not increase with the rotation rate, the absolute vorticity needs to be very small. To confirm the memory effect of the nonlinear term, anisotropic and temporally nonlocal effects of the mean velocity on the Reynolds stress are evaluated using Green’s function for the velocity fluctuation.
Nonlinear theory of the orotron with inclined electron beam
Authors: Nusinovich G. S. , Sinitsyn O. V.
Published: December 2006

In the conventional orotron (at least, in its classical configuration), a thickness of an electron beam propagating over the grating plate should be much smaller than a wavelength; also the clearance between the grating and the beam and possible misalignment should be smaller than this thickness. These requirements severely limit the choice of operating parameters and performance characteristics of this device. When a beam is slightly inclined to the grating surface, these limitations can be greatly mitigated: the operation can be more robust, beam thickness can be increased, so a higher microwave power can be generated. Such a configuration of the orotron with an inclined electron beam is studied in the present paper. The paper contains simplified equations describing nonlinear operation of such a device and results of numerical analysis of these equations with the electron velocity spread taken into account. The paper also contains a discussion of these results and their applicability to practical configurations, which can be designed for operation in the THz and sub-THz regions.
Photochemistry on ultrathin metal films: Strongly enhanced cross sections for NO2 on Ag∕Si(100)
Authors: Wesenberg Claudia , Autzen Olaf , Hasselbrink Eckart
Published: December 2006

The surface photochemistry of NO2 on ultrathin Ag(111) films (5–60nm) on Si(100) substrates has been studied. NO2, forming N2O4 on the surface, dissociates to release NO and NO2 into the gas phase with translational energies exceeding the equivalent of the sample temperature. An increase of the photodesorption cross section is observed for 266nm light when the film thickness is decreased below 30nm despite the fact that the optical absorptivity decreases. For 4.4nm film thickness this increase is about threefold. The data are consistent with a similar effect for 355nm light. The reduced film thickness has no significant influence on the average translation energy of the desorbing molecules or the branching into the different channels. The increased photodesorption cross section is interpreted to result from photon absorption in the Si substrate producing electrons with no or little momenta parallel to the surface at energies where this is not allowed in Ag. It is suggested that these electrons penetrate through the Ag film despite the gap in the surface projected band structure.
Ultrafast fluorescence resonance energy transfer in a reverse micelle: Excitation wavelength dependence
Authors: Mondal Sudip Kumar , Ghosh Subhadip , Sahu Kalyanasis , Mandal Ujjwal , Bhattacharyya Kankan
Published: December 2006

Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to fluorescein 548 (F548) in a sodium dioctyl sulfosuccinate (AOT) reverse micelle is studied by picosecond and femtosecond emission spectroscopy. In bulk water, at the low concentration of the donor (C480) and the acceptor (F548), no FRET is observed. However, when the donor (C480) and the acceptor (F548) are confined in a AOT reverse micelle very fast FRET is observed. The time constants of FRET were obtained from the rise time of the emission of the acceptor (F548). In a AOT microemulsion, FRET is found to occur in multiple time scales—3, 200, and 2700ps. The 3ps component is assigned to FRET in the water pool of the reverse micelle with a donor-acceptor distance, 16Å. The 200ps component corresponds to a donor-acceptor distance of 30Å and is ascribed to the negatively charged acceptor inside the water pool and the neutral donor inside the alkyl chains of AOT. The very long 2700ps component may arise due to FRET from a donor outside the micelle to an acceptor inside the water pool and also from diffusion of the donor from bulk heptane to the reverse micelle. With increase in the excitation wavelength from 375to405nm the relative contribution of the FRET due to C480 in the AOT reverse micelle (the 3 and 200ps components) increases.
Carbon nanotube diode fabricated by contact engineering with self-assembled molecules
Authors: Kim Byoung-Kye , Kim Ju-Jin , So Hye-Mi , Kong Ki-jeong , Chang Hyunju , Lee Jeong-O , Park Noejung
Published: December 2006

The authors report the construction of carbon nanotube Schottky diodes by covering a selectively exposed area of the electrode with self-assembling molecules. Two self-assembling molecules with different polarities, 2-aminoethanethiol and 3-mercaptopropionic acid, were used to modify the Fermi level lineup at the selected contact. The devices showed p-type behavior with symmetric I-V showing clear rectifying behavior after treatment of one contact with 2-aminoethanethiol. Their experiment, in conjunction with the results of ab initio electronic structure calculations, suggests that the diode action stems from the asymmetric Fermi level lineup between the bare and engineered contacts.
Frequency domain vibration potential imaging: Objects with symmetry in one dimension
Authors: Wang Shougang , Beveridge Andrew C. , Li Shengqiong , Diebold Gerald J. , Nguyen Cuong K.
Published: December 2006

Frequency domain, ultrasonic vibration potential imaging can be carried out by irradiating a colloidal object with a plane ultrasonic wave and recording the magnitude and phase of the current in a pair of electrodes as a function of the frequency. The method is applied to imaging of objects with symmetry in one dimension including a thin layer, a thick layer, pairs of layers, and layers with differing colloidal concentrations. The experimental results show agreement with the theory of vibration potential imaging where the recorded signal is proportional to the integral of the concentration of colloidal or ionic species over the pressure gradient in the ultrasonic wave.
Development of tapered silver-halide fiber tips for a scanning near-field microscope operating in the middle infrared
Authors: Platkov Max , Tsun Alexander , Nagli Lev , Katzir Abraham
Published: December 2006

We have constructed a scanning near-field infrared microscope (SNIM) which was based on a AgClBr fiber probe whose end was etched to form an aperture of a subwavelength diameter. A detailed study of the mechanical properties of a vibrating AgClBr probe was required for proper operation of the SNIM system. We have demonstrated that the system can be used for imaging and for topographic mapping of samples with a subwavelength resolution in the middle infrared. Such a SNIM will be a powerful tool for the study of microelectronic components or subcellular structures in biological cells.
Loss of coherence in a population of diffusively coupled oscillators
Authors: Toth Rita , Taylor Annette F.
Published: December 2006

The authors investigate the relationship between the natural frequency distribution of diffusively coupled chemical oscillators and their entrainment by pacemakers. The system consists of micrometer-sized catalyst beads which are coupled to their neighbors by diffusion of the activator/inhibitor species through the catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. The frequency distribution is measured as a function of the beads’ number of neighbors. With the maximum number of neighbors, either target waves or disordered patterns are observed in the reaction domain and there is a shift to higher frequencies than those observed in the natural frequency distribution. The loss of coherence between neighbor oscillators is quantified by a decrease in the phase synchronization index. The experimental results are reproduced in simulations which demonstrate that the decrease in the degree of synchronization is correlated with the appearance of a small fraction of permanently excited beads in BZ populations of high mean frequency and/or large width.
Influence of the exchange screening parameter on the performance of screened hybrid functionals
Authors: Krukau Aliaksandr V. , Vydrov Oleg A. , Izmaylov Artur F. , Scuseria Gustavo E.
Published: December 2006

This work reexamines the effect of the exchange screening parameter ω on the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. We show that variation of the screening parameter influences solid band gaps the most. Other properties such as molecular thermochemistry or lattice constants of solids change little with ω. We recommend a new version of HSE with the screening parameter ω=0.11bohr−1 for further use. Compared to the original implementation, the new parametrization yields better thermochemical results and preserves the good accuracy for band gaps and lattice constants in solids.
Defect and stress characterization of AlN films by Raman spectroscopy
Authors: Lughi Vanni , Clarke David R.
Published: December 2006

Raman spectroscopy was used to characterize the residual stress and defect density of AlN thin films reactively sputtered on silicon (100). The authors studied the correlation between the shift of the E2 (high) phonon of AlN at 658cm−1 and the film biaxial stress and obtained a biaxial piezospectroscopic coefficient of 3.7GPa∕cm−1. A correlation was found between the width of the Raman line, the oxygen concentration measured by secondary ion mass spectroscopy, and acoustic losses. This work lays the basis for the nondestructive assessment of two key thin film properties in microelectromechanical systems applications, namely, acoustic attenuation and residual stress.
2.0
W
diode-pumped Er:Yb:YAl3(BO3)4 laser at 1.5–1.6μm
Authors: Chen Y. J. , Lin Y. F. , Gong X. H. , Tan Q. G. , Luo Z. D. , Huang Y. D.
Published: December 2006

An efficient and high output power laser has been realized for an Er:Yb:YAl3(BO3)4 crystal end pumped by a 970nm diode laser. Under the absorbed pump power of 15.5W, quasi-continuous-wave output power of 2.0W at 1.5–1.6μm has been obtained in a hemispherical cavity. The laser had an absorbed pump threshold power of 4.7W and a slope efficiency of 21%. The influence of the laser output power and output coupler transmission on the output laser spectra has also been investigated.
Large density variation predicted along the magnetic axis for cold electron plasmas in the Columbia Nonneutral Torus (CNT)
Authors: Lefrancois Remi G. , Pedersen Thomas Sunn
Published: December 2006

Cold pure electron plasmas confined in Penning-Malmberg traps with mirror fields are known to exhibit density variations along field lines, such that the density is roughly proportional to the magnetic field strength, n∼B. The Columbia Nonneutral Torus (CNT) is the first stellarator designed to study pure electron plasmas, and exhibits substantial mirroring, with Bmax≈1.8Bmin. However, results of a three-dimensional equilibrium solver, presented in this Letter, predict a factor of 5.3 increase in density from the minimum-field cross section to the maximum-field cross section along the magnetic axis, for a 1.5cm Debye length plasma (a≈15cm for CNT). In this Letter, it is shown that the density variation of electron plasmas in mirror traps can be significantly enhanced in a device that has a cross section that varies from cylinder-like to slab-like, such as the CNT. A simple analytic expression is derived that describes the axial density variation in such a device, and it is found to agree well with the computational predictions for CNT.
Dielectric losses of SrTiO3 thin film capacitors with Pt bottom electrodes at frequencies up to 1GHz
Authors: Finstrom Nicholas H. , Gannon John A. , Pervez Nadia K. , York Robert A. , Stemmer Susanne
Published: December 2006

The letter reports on the dielectric losses of differently textured SrTiO3 films on Pt bottom electrodes at frequencies between 1MHz and 1GHz. Device parasitic contributions to the measured device losses were partially removed by measuring shorted devices. Different dielectric loss mechanisms were identified. These included strongly frequency dependent loss peaks and a low temperature loss increase that showed a power-law dependence on the bulk permittivity of the films. Possible origins of the different loss mechanisms are discussed.
Enhanced amperometric detection of glucose using Si29 particles
Authors: Wang Gang , Mantey Kevin , Nayfeh Munir H. , Yau Siu-Tung
Published: December 2006

The 1nm Si29 particle is used as the sensing element for an enzyme-free amperometric electrochemical glucose sensor. The sensor shows selective glucose detection against interfering substances at physiological concentrations with long-term stability, reusability, and the absence of electrode poisoning. The Si29 particle is significantly more efficient in generating signal current compared to both dissolved and immobilized enzyme. This observation suggests that the particle can be used to replace enzyme in making glucose sensors and that the particle is a suitable material for the realization of nanoscale devices that generate signals sufficiently high for use.
Interfacial self-cleaning in atomic layer deposition of HfO2 gate dielectric on In0.15Ga0.85As
Authors: Chang C.-H. , Chiou Y.-K. , Chang Y.-C. , Lee K.-Y. , Lin T.-D. , Wu T.-B. , Hong M. , Kwo J.
Published: December 2006

An interfacial self-cleaning phenomenon was found in the atomic layer deposition of HfO2 on In0.15Ga0.85As∕GaAs substrate using Hf(NCH3C2H5)4, i.e., TEMAH, and H2O as the precursors. The native oxides of InGaAs were all satisfactorily removed from the interface through ligand exchange (substitution) reactions with the TEMAH precursor. It relieves the Fermi-level pinning in the HfO2∕InGaAs heterostructure, as verified by the clear transition from accumulation to depletion in high-frequency capacitance-voltage relations and inversion in quasistatic measurement. A very low leakage current was also found from the metal-oxide-semiconductor capacitors of Au∕Ti∕HfO2∕InGaAs.
Fast, high-efficiency, and homogeneous room-temperature cathodoluminescence of ZnO scintillator thin films on sapphire
Authors: Lorenz M. , Johne R. , Nobis T. , Hochmuth H. , Lenzner J. , Grundmann M. , Schenk H. P. D. , Borenstain S. I. , Schön A. , Bekeny C. , Voss T. , Gutowski J.
Published: December 2006

Excitonic luminescence in ZnO exhibits subnanosecond lifetimes combined with high efficiency, which makes epitaxial ZnO a promising ultrafast scintillator material for envisaged imaging applications with high data rate. ZnO thin films on sapphire show external ultraviolet electron-photon conversion efficiencies up to 0.42photons∕(keVe−) at room temperature and only minor lateral microscopic cathodoluminescence intensity variations. Peak shifts and occasionally observed double peaks found in cathodoluminescence spectra of epitaxial ZnO films with dependence on the detection geometry, the excitation depth, and the surface morphology are explained by a model based on photon propagation including self-absorption.