bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of the human mucin MUC4 by taurodeoxycholic and taurochenodeoxycholic bile acids in oesophageal cancer cells is mediated by hepatocyte nuclear factor 1α
Authors: Piessen Guillaume , Jonckheere Nicolas , Vincent Audrey , Hémon Brigitte , Ducourouble Marie-Paule , Copin Marie-Christine , Mariette Christophe , Seuningen Isabelle VAN
Published: January 2007

MUC4 (mucin 4) is a membrane-bound mucin overexpressed in the early steps of oesophageal carcinogenesis and implicated in tumour progression. We previously showed that bile acids, main components of gastro-oesophageal reflux and tumour promoters, up-regulate MUC4 expression [Mariette, Perrais, Leteurtre, Jonckheere, Hemon, Pigny, Batra, Aubert, Triboulet and Van Seuningen (2004) Biochem. J. 377, 701–708]. HNF (hepatocyte nuclear factor) 1α and HNF4α transcription factors are known to mediate bile acid effects, and we previously identified cis-elements for these factors in MUC4 distal promoter. Our aim was to demonstrate that these two transcription factors were directly involved in MUC4 activation by bile acids. MUC4, HNF1α and HNF4α expressions were evaluated by immunohistochemistry in human oesophageal tissues. Our results indicate that MUC4, HNF1α and HNF4α were co-expressed in oesophageal metaplastic and adenocarcinomatous tissues. Studies at the mRNA, promoter and protein levels indicated that HNF1α regulates endogenous MUC4 expression by binding to two cognate cis-elements respectively located at −3332/−3327 and −3040/−3028 in the distal promoter. We also showed by siRNA (small interfering RNA) approach, co-transfection and site-directed mutagenesis that HNF1α mediates taurodeoxycholic and taurochenodeoxycholic bile acid activation of endogenous MUC4 expression and transcription in a dose-dependent manner. In conclusion, these results describe a new mechanism of regulation of MUC4 expression by bile acids, in which HNF1α is a key mediator. These results bring new insights into MUC4 up-regulation in oesophageal carcinoma associated with bile reflux.
Interactive Wormhole Detection and Evaluation
Authors: Wang Weichao , Lu Aidong
Published: January 2007

Wormhole attacks in wireless networks can severely deteriorate network performance and compromise security through spoiling the routing protocols and weakening the security enhancements. This paper develops an approach, interactive visualization of wormholes (IVoW), to monitor and detect such attacks in large-scale wireless networks in real time. We characterize the topology features of a network under wormhole attacks through the node position changes and visualize the information at dynamically adjusted scales. We integrate an automatic detection algorithm with appropriate user interactions to handle complicated scenarios that include a large number of moving nodes and multiple wormhole attackers. Various visual forms have been adopted to assist in the understanding and analysis of reconstructed network topology and to improve the detection accuracy. Extended simulation has demonstrated that the proposed approach can effectively locate the fake neighbor connections without introducing many false alarms. IVoW does not require the wireless nodes to be equipped with any special hardware, thus avoiding any additional cost. We have performed user studies to evaluate the effectiveness of our approach and demonstrate that visual analysis can be successfully combined with network security mechanisms to greatly improve intrusion detection capabilities.
The Internet and Tourism Principals in the Balearic Islands
Authors: Vich-i-Martorell Gabriel Àngel
Published: January 2007

Mature mass tourism destinations are usually subject to a high degree of control by tour operators. When used as a marketing tool, the internet provides an alternative distribution channel able to cut out the middleman. This paper analyses the use of the internet among tourism principals in the Balearic Islands, and the attitudes towards the internet shown by them. For the purposes of this analysis, initial research studies of hotel chains, individual hotels and airlines were carried out to find out how much use they make of the internet and their attitudes to it. The results reflect very different degrees of internet use and the existence of six different group attitudes to the internet as a marketing tool for tourism.
Visitors' Evaluation of a Historical District: The Roles of Authenticity and Manipulation
Authors: Naoi Taketo
Published: January 2007

This study investigates how visitors evaluated a historical district that includes both authentic and manipulated elements. Using 13 bipolar scales, 323 visitors to the Kurashiki Bikan Historical Quarter were canvassed regarding their evaluations of the Quarter. The survey results suggest that perceptions of authenticity are a crucial factor affecting the overall evaluations of historical districts. Differences were observed, however, in the evaluative dimensions by which authenticity was assessed between visitors whose overall evaluations were favourable and those whose overall evaluations were unfavourable. It was also found that a sense of the maintenance of historical districts negatively affected the overall evaluations of visitors whose overall evaluations are unfavourable and that the duration of visitors' trips might be a significant determinant of overall favourability.
Tourism and Street Children in Antananarivo, Madagascar
Authors: Gössling Stefan , Schumacher Kim , Morelle Marie , Berger Ralf , Heck Nadine
Published: January 2007

The interaction of tourists and marginalised population groups in developing countries has remained poorly researched. In particular, the relevance of tourism for street children as one of the most vulnerable groups in urban agglomerations has never been investigated. In this contribution, the situation of street children in Antananarivo, Madagascar is analysed. The paper seeks to discuss whether tourism encourages begging, thus increasing the number of street children and depriving them of access to education — which would represent a process of long-term disempowerment — or if tourism supports the survival of human beings living on the edge of society, as claimed by pro poor tourism advocates.
UK Hotel Web Page Accessibility for Disabled and Challenged Users
Authors: Williams Russell , Rattray Rulzion
Published: January 2007

Organisations increasingly use the internet and web to communicate with the marketplace. Indeed, the hotel industry seems particularly suited to the use of these technologies. Many sites are not accessible to large segments of the disabled community, however, or to individuals using particular hard and softwares. Identifying the competitive and legal mandates for website accessibility, the study looks at the accessibility of UK-based hotel websites. Utilising the accessibility software, Bobby, as well as making some additional manual accessibility checks, the study finds disappointingly low levels of website accessibility. If organisations want to make more effective use of the web then they need to ensure that their web pages are designed from the outside-in — from the user's perspective.
Data Disaggregation in Demand Forecasting
Authors: Vu Chau Jo , Turner Lindsay
Published: January 2007

It is assumed in tourism demand forecasting that the disaggregation of data is useful in terms of country of origin and also in terms of purpose of travel (Smith and Toms, 1967; Blackwell, 1970; Martin and Witt, 1989a). The primary disaggregation by country is useful for determining regional forecast flows and the disaggregation by purpose of visit has been considered potentially useful for increasing forecasting accuracy given the flows have different characteristics (Turner, Kulendran and Pergat, 1995; Morley and Sutikno, 1991). It is also possible to disaggregate on the basis of age and gender. It has been assumed (because no research has disaggregated by age and gender) in previous research that the gender and age composition of flows is a reflection of the total population and therefore exhibits the same time-series characteristics. This may not be the case, however.

This study uses data for tourist arrivals into Korea to test the assumptions that further disaggregation of data on the basis of gender and age is not needed, and to further examine whether disaggregation by purpose of visit is worthwhile, when the purpose is to forecast total country arrivals. Quarterly data from 1994 to 2003 are used with the estimation period 1994–2001 and the post-estimation period 2002–2003. The conclusion from the study is that total arrivals forecasting is not more accurate when the data used is the sum of forecast disaggregated series, as opposed to direct forecasts of total arrivals.
A Comparison of Adolescents' and Parents' Holiday Motivations and Desires
Authors: Carr Neil
Published: January 2007

This paper provides an analysis of the under-researched and under-valued holiday motivations of adolescents and their parents. This work is required for the formulation of effective marketing strategies and product development plans. The data for this paper were gathered in Brisbane, Australia, during 2002 from a convenience sample of 54 parents and 66 adolescents using two questionnaire surveys.

The results show that the types of holiday experiences likely to result in satisfaction for the parents and adolescents often differ. Within the context of the tourism industry the results suggest the need for more focused attention on the holiday needs and desires of adolescents, both in their own right and as part of the family unit.
Religious Needs in the Hospitality Industry
Authors: Weidenfeld Adi
Published: January 2007

In the current competitive environment, the tourism and hospitality industries are constantly searching for new customer segments and for ways of improving competitiveness. Thus, the provision of religious aspects in the hospitality product could prove a valuable and integral part of the customer's orientation. This paper highlights the importance of satisfying religious needs to increase the satisfaction of customers. This is the first time empirical findings concerning the religious needs of tourists have been examined, and the study is based on a sample of 179 Christian tourists in Israel. This research suggests that the tourists religious needs constitute an independent area of research and that satisfying religious needs in the accommodation industry should be taken into consideration in the marketing process.
The Effect of Prior Destination Experience on Online Information Search Behaviour
Authors: Lehto Xinran Y. , Kim Dae-Young , Morrison Alastair M.
Published: January 2007

This research proposed and empirically tested a behavioural model of online tourist information search by integrating the consumer involvement concept, modes of cognitive processing and knowledge representation. The model identified two types of online information involvement: involvement measured by time spent online (degree of search) and by types of information sought (content of search). The results showed prior experience and knowledge with a destination influenced both by the content of search and the degree of search that a traveller engages in online while planning a trip. It appears that online search effort decreases and search content changes as a result of the different level of prior knowledge that a tourist brings to a search. The results will also have practical implications for the content, length and presentation of tourism websites that service iTravellers.
Large area 50nm period grating by multiple nanoimprint lithography and spatial frequency doubling
Authors: Cui Bo , Yu Zhaoning , Ge Haixiong , Chou Stephen Y.
Published: January 2007

The authors have developed an approach to fabricate large area 50nm period gratings (22nm linewidth) with low cost. The method used a fabrication cycle twice, each combining nanoimprint lithography with a spatial frequency doubling based on electroless plating, lift-off, and reactive ion etching. Hence by frequency doubling twice, we started with a 200nm period grating mold and finished with a 50nm period grating with a uniform area of 3cm2—the largest achieved today. This method is scalable for the fabrication of even smaller period gratings over a large area, and is a viable low-cost technique for making nanoimprint lithography molds for high-throughput fabrication of 50nm period grating or grid devices.
Polynomial Poisson algebras for classical superintegrable systems with a third-order integral of motion
Authors: Marquette Ian , Winternitz Pavel
Published: January 2007

We present polynomial Poisson algebras for the eight classical potentials in two-dimensional Euclidian space that separate in Cartesian coordinates and allow a third-order integral of motion. Some of the classical superintegrable potentials do not coincide with quantum ones, but are their singular limits. We show that all bounded trajectories in these potentials are periodic.
Study of saturation of CR39 nuclear track detectors at high ion fluence and of associated artifact patterns
Authors: Gaillard S. , Fuchs J. , Renard-Le Galloudec N. , Cowan T. E.
Published: January 2007

The occurrence of saturation in CR39 solid state nuclear track detectors has been systematically studied as a function of the incident ion (α particles and laser-accelerated protons) fluence and the etching time. When overexposed (i.e., for fluences above ∼108particles∕cm2) and/or overetched, the CR39 detectors enter a saturated regime where direct track counting is not possible anymore. In this regime, optical measurements of saturated CR39 detectors become unreliable as well, since the optical response of the saturated detectors with respect to the ion fluence is highly nonlinear. This nonlinear optical response is likely due to scattering from the surface of irregular clumping patterns which have a diameter ∼20μm, i.e., ten times larger than the diameter of individual tracks. These patterns, which aggregate many individual tracks, are observed to develop in highly saturated regimes. For fluences typical of high energy short pulse laser experiments, saturation occurs, inducing the appearance of artifact ringlike structures. By careful microscopic analysis, these artifact ring patterns can be distinguished from the genuine rings occurring below saturation and characteristic of low energy laser accelerated proton beams.
Nonparaxial effects on the propagation and scattering of a polarized optical pulse
Authors: Ballav Mousumi , Chowdhury A. Roy
Published: January 2007

Propagation characteristics of a polarized optical solitary pulse are analyzed by taking into account the effect of nonparaxiality and mutual interaction. To start with, a pair of generalized nonlinear Schrödinger equations is deduced through an operator approach. Stationary solutions of such a system are then analyzed numerically through a boundary value problem in two stages, with and without the nonparaxial effect. In the second stage, the propagating form of the corresponding spatial soliton is studied by an extended split step algorithm ETDRK. The initial profile is considered to be both a one- and two-soliton solution, to visualize the event of scattering and fusion. From this data, we have computed the intensity, root mean square spectral width, and chirp of a single soliton as it propagates. In the case of the two-soliton solution, we observe that for source parameter values, the fusion is more favored than scattering. It is observed that nonparaxiality and the interaction between Ax and Ay tends to destroy the periodic behaviors of these parameters. Lastly, we have investigated the modulational instability of the system as function of frequency detuning and nonparaxiality. The form of the gain is discussed as a function of nonparaxiality.
Nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas
Authors: Keskinen M. J. , Schmitt A.
Published: January 2007

A model for the nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas has been developed for a wide range of Froude numbers and scale sizes. It is found that the spectrum can be characterized by an inverse power law with spectral index of approximately 2 in the limit of small-wavenumber spectrum cutoffs and small-scale density gradient scale lengths. Comparison of the model spectrum with recent experimental observations is made with good agreement.
Modified Korteweg–de Vries surfaces
Authors: Tek Süleyman
Published: January 2007

In this work, we consider 2-surfaces in R3 arising from the modified Korteweg–de Vries (mKdV) equation. We give a method for constructing the position vector of the mKdV surface explicitly for a given solution of the mKdV equation. mKdV surfaces contain Willmore-like and Weingarten surfaces. We show that some mKdV surfaces can be obtained from a variational principle where the Lagrange function is a polynomial of the Gaussian and mean curvatures.
Multipole structure of current vectors in curved space-time
Authors: Harte Abraham I.
Published: January 2007

A method is presented which allows the exact construction of conserved (i.e., divergence-free) current vectors from appropriate sets of multipole moments. Physically, such objects may be taken to represent the flux of particles or electric charge inside some classical extended body. Several applications are discussed. In particular, it is shown how to easily write down the class of all smooth and spatially bounded currents with a given total charge. This implicitly provides restrictions on the moments arising from the smoothness of physically reasonable vector fields. We also show that requiring all of the moments to be constant in an appropriate sense is often impossible. This likely limits the applicability of the Ehlers-Rudolph-Dixon notion of quasirigid motion. A simple condition is also derived that allows currents to exist in two different space-times with identical sets of multipole moments (in a natural sense).
Gain properties of an Er3+ complex in a poly(methylmethacrylate) matrix for 1540nm broadband optical amplification
Authors: Le Quang Anh Quoc , Truong V. G. , Jurdyc A.-M. , Jacquier B. , Zyss J. , Ledoux I.
Published: January 2007

Emission properties of an erbium organic complex embedded in a polymer matrix are investigated for laser and optical amplification applications in the 1550nm telecommunication range. The evaluation of stimulated emission cross sections is inferred from the Judd-Ofelt model [B. R. Judd et al., Phys. Rev. 169, 130 (1968); G. S. Ofelt, J. Chem. Phys. 37, 511 (1962)] based on experimental spectroscopic data, resulting in the determination of the three Ω2=1.92×10−19, Ω4=1.82×10−20, and Ω6=1.65×10−20 Judd-Ofelt coefficients. These parameters are then used to calculate the oscillator strengths between states and allow us to evaluate spontaneous emission probabilities, radiative lifetimes, branching ratios, and quantum efficiencies of levels. Stimulated emission cross-sections are determined using the McCumber method [D. E. Mc Cumber, Phys. Rev. 134, A299 (1964)]. Net gain cross sections are calculated for different values of the inversion population in Er3+ ions. Results show that organic polymer hosts doped with erbium complexes are very attractive materials for amplification in the telecommunication spectral range, as they display high gain cross section as compared to other erbium-containing materials, coupled with a wide and relatively flat amplification spectrum (up to 70nm) which covers the whole spectral range currently used for wavelength division multiplexing operation.
Reduction of hydrogen-induced optical losses of plasma-enhanced chemical vapor deposition silicon oxynitride by phosphorus doping and heat treatment
Authors: Hussein M. G. , Wörhoff K. , Sengo G. , Driessen A.
Published: January 2007

Plasma-enhanced chemical vapor deposition phosphorus-doped silicon oxynitride (SiON) layers with a refractive index of 1.505 were deposited from N2O, 2% SiH4∕N2, NH3, and 5% PH3∕Ar gaseous mixtures. The PH3∕Ar flow rate was varied to investigate the effect of the dopant to the layer properties. We studied the compositions and the chemical environment of phosphorus, silicon, oxygen, nitrogen, and hydrogen in these layers by using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The number of N–H and O–H bonds, which are responsible for optical losses around 1.55 and 1.3μm, decreases in the as-deposited layers with increasing phosphorus concentration. Furthermore, the bonded hydrogen in all P-doped layers has been eliminated after annealing at a temperature significantly lower than required for undoped silicon oxynitride layers, that is to say 1000°C instead of 1150°C. The resulting optical loss in the entire third telecommunication window was well below 0.2dB∕cm, making P-doped SiON an attractive material for demanding integrated optics applications.
Solitary signals in electrical nonlinear transmission line
Authors: Kengne E. , Malomed Boris A. , Chui S. T. , Liu W. M.
Published: January 2007

We investigate the propagation of solitary signal in nonlinear electrical transmission line. Starting from the modified complex Ginzburg-Landau equation and the theory of elliptic ordinary differential equations, we derive a number of solitonlike solutions of the modified complex Ginzburg-Landau equation and study the linear stability of these solutions. The higher order soliton solution is constructed using the Hirota method which is found to be very simple when compared with the Painlevé method.
Investigation of water and ice by ac impedance using electrochemical properties cup
Authors: Chin K. B. , Buehler M. G. , Seshadri S. , Keymeulen D. , Anderson R. C. , Dutz S. , Narayanan S. R.
Published: January 2007

Water and ice were investigated by ac impedance with the electrochemical properties cup in an effort to develop an in situ instrument for water characterization. In liquid water, the impedance modulus decreased with the increase in charge carriers. In the ice, the impedance measurements were characterized by the dielectric relaxation and its corresponding activation energy. The activation energy of 0.400eV was determined for pure ice. With ice containing Cl− anions, the activation energy was 0.24eV. H+ and OH− doped ice has the lowest activation energy for dielectric relaxation. Results from previous works are similar to the results reported in this study.
Kinetic roughening of amorphous silicon during hot-wire chemical vapor deposition at low temperature
Authors: Sperling Brent A. , Abelson John R.
Published: January 2007

We use postdeposition atomic force microscopy and in situ spectroscopic ellipsometry to analyze the roughening of hydrogenated amorphous silicon films deposited by hot-wire chemical vapor deposition at 150°C. From the atomic force microscopy data, the root-mean-squared roughness w increases with deposition time t as w∝tβ with β=0.37±0.02, and the correlation length ξ increases as ξ∝t1∕z with 1∕z=0.31±0.02. From the height-difference correlation function, we obtain a roughness exponent α=0.87±0.04 and a root-mean-squared local slope δ, which increases as δ∝tκ with κ=0.17±0.03. These measurements are indicative of anomalous growth, which we attribute to geometric shadowing. However, the roughening behavior we observe using atomic force microscopy is not reproduced in the spectroscopic ellipsometry data. This contradicts previous reports which found a linear relationship between the thickness of the optical roughness layer and the root-mean-squared roughness. We discuss the discrepancy between the two techniques in terms of short-range roughness and vector perturbation theory.
Nonlinearizations of spectral problems of the nonlinear Schrödinger equation and the real-valued modified Korteweg–de Vries equation
Authors: Zhou Ruguang
Published: January 2007

A procedure of nonlinearization of spectral problem that allows to impose reality conditions or restriction conditions on potentials is presented. As applications, integrable decompositions of the nonlinear Schrödinger equation and the real-valued modified Korteweg–de Vries equation are obtained.
CO oxidation reaction on Pt(111) studied by the dynamic Monte Carlo method including lateral interactions of adsorbates
Authors: Nagasaka Masanari , Kondoh Hiroshi , Nakai Ikuyo , Ohta Toshiaki
Published: January 2007

The dynamics of adsorbate structures during CO oxidation on Pt(111) surfaces and its effects on the reaction were studied by the dynamic Monte Carlo method including lateral interactions of adsorbates. The lateral interaction energies between adsorbed species were calculated by the density functional theory method. Dynamic Monte Carlo simulations were performed for the oxidation reaction over a mesoscopic scale, where the experimentally determined activation energies of elementary paths were altered by the calculated lateral interaction energies. The simulated results reproduced the characteristics of the microscopic and mesoscopic scale adsorbate structures formed during the reaction, and revealed that the complicated reaction kinetics is comprehensively explained by a single reaction path affected by the surrounding adsorbates. We also propose from the simulations that weakly adsorbed CO molecules at domain boundaries promote the island-periphery specific reaction.
Statistical-mechanical theory of ultrasonic absorption in molecular liquids
Authors: Kobryn Alexander E. , Hirata Fumio
Published: January 2007

We present results of the theoretical description of ultrasonic phenomena in molecular liquids. In particular, we are interested in the development of a microscopical, i.e., statistical-mechanical, framework capable of explaining the long living puzzle of excess ultrasonic absorption in liquids. Typically, an ultrasonic wave in a liquid can be generated by applying a periodically alternating external pressure with an angular frequency that corresponds to the ultrasound. If the perturbation introduced by such a process is weak, its statistical-mechanical treatment can be done with the use of a linear response theory. We treat the liquid as a system of interacting sites, so that all the response/aftereffect functions as well as the energy dissipation and generalized (wave-vector and frequency-dependent) ultrasonic absorption coefficient are obtained in terms of familiar site-site static and time correlation functions such as static structure factors or intermediate scattering functions. To express the site-site intermediate scattering functions, we refer to the site-site memory equations in the mode-coupling approximation for first-order memory kernels, while equilibrium properties such as site-site static structure factors, and direct and total correlation functions are deduced from the integral equation theory of molecular liquids known as RISM, or one of its generalizations. All of the formalism is phrased in a general manner, hence the results obtained are expected to work for arbitrary types of molecular liquids including simple, ionic, polar, and nonpolar liquids.
Recovering the Crooks equation for dynamical systems in the isothermal-isobaric ensemble: A strategy based on the equations of motion
Authors: Chelli Riccardo , Marsili Simone , Barducci Alessandro , Procacci Piero
Published: January 2007

The Crooks equation [Eq. (10) in J. Stat. Phys. 90, 1481 (1998)] relates the work done on a system during a nonequilibrium transformation to the free energy difference between the final and the initial state of the transformation. Recently, the authors have derived the Crooks equation for systems in the canonical ensemble thermostatted by the Nosé-Hoover or Nosé-Hoover chain method [P. Procacci et al., J. Chem. Phys. 125, 164101 (2006)]. That proof is essentially based on the fluctuation theorem by Evans and Searles [Adv. Phys. 51, 1529 (2002)] and on the equations of motion. Following an analogous approach, the authors derive here the Crooks equation in the context of molecular dynamics simulations of systems in the isothermal-isobaric (NPT) ensemble, whose dynamics is regulated by the Martyna-Tobias-Klein algorithm [J. Chem. Phys. 101, 4177 (1994)]. Their present derivation of the Crooks equation correlates to the demonstration of the Jarzynski identity for NPT systems recently proposed by Cuendet [J. Chem. Phys. 125, 144109 (2006)].
Theoretical analysis of current-driven interactions between voids in metallic thin films
Authors: Cho Jaeseol , Rauf Gungor M. , Maroudas Dimitrios
Published: January 2007

We analyze the electromigration-induced interactions between voids in metallic thin films using self-consistent numerical simulations of current-driven void morphological evolution. We focus on the interactions between two voids that, if isolated, they would be morphologically stable and migrate at constant speed along the metallic thin film. It is demonstrated that, under certain electromigration conditions, two such different-sized voids migrating in the same direction along a metallic thin film can lead to stable time-periodic states characterized by wave propagation on a void’s surface or cause failure prior to or following their coalescence. Moreover, various complex phenomena are revealed, including void breakup into two morphologically stable voids following the coalescence of the original two voids and voids attempting to pass each other. In numerous cases, it is noteworthy that the void-void interactions examined arise due to a larger void migrating faster than an originally leading smaller one in a finite-width conducting film with anisotropic material properties, contrary to the conventional notion that smaller voids migrate faster than larger ones for electromigration-driven void motion. These results set the stage toward a fundamental understanding of the current-driven dynamics of populations of interacting voids in metallic interconnect lines. Finally, our analysis predicts that void breakup preceded by void coalescence can cause an abrupt increase in the electrical resistance of an interconnect line, in qualitative agreement with observations from accelerated electromigration testing experiments.
Spectroscopic study on the vibrational populations of N2 CΠ3 and BΠ3 states in a microwave nitrogen discharge
Authors: Sakamoto Takeshi , Matsuura Haruaki , Akatsuka Hiroshi
Published: January 2007

We measured the band spectra (first and second positive systems) of the nitrogen molecule to examine the vibrational and rotational temperatures of the CΠ3 and BΠ3 states by optical emission spectroscopy. We compared the experimentally measured and the calculated spectra to determine those temperatures of the generated plasma. We generated a microwave discharge nitrogen plasma in a cylindrical quartz tube (26mm inside diameter) with a discharge pressure of 0.5–1.0Torr. The microwave frequency was 2.45GHz and the output power was set at 600W. It was found that Tv≈0.5–0.7eV and Tr≈0.07–0.15eV at BΠ3 (v=7, 8, and 9), whereas Tv≈0.65–0.9eV and Tr≈0.06–0.16eV at CΠ3 (v=0 and 1). Both rotational temperatures obtained from first and second positive systems were in good agreement. We also compared the measured vibrational populations with theoretical calculations, in which vibrational distribution function at N2 X and electron energy distribution function are calculated self-consistently.
Radiative and nonradiative recombination processes in ZnCdSe∕ZnCdMgSe multi-quantum-wells
Authors: Zhang S. K. , Lu H. , Wang W. B. , Das B. B. , Okoye N. , Tamargo M. , Alfano R. R.
Published: January 2007

Carrier recombination through radiative and nonradiative processes in lattice-matched n-Zn0.5Cd0.5Se∕Zn0.21Cd0.19Mg0.6Se multi-quantum-wells (MQWs) was investigated by temperature-dependent time-resolved photoluminescence (PL) spectroscopy. The n-Zn0.5Cd0.5Se∕Zn0.21Cd0.19Mg0.6Se MQW samples with different well widths were grown on InP substrates by molecular beam epitaxy. The PL decay times and the PL intensities were measured as functions of temperature. For a doping level of 1×1018cm−3, the dominant mechanism of the radiative process was found to be free carrier recombination while excitonic recombination was absent due to the effect of strong carrier screening. The nonradiative mechanism was determined to be hole capture through multiphonon emission (MPE). The expressions of the nonradiative MPE recombination lifetime, the PL decay time, and the PL intensity were deduced as functions of temperature and were used to fit the measured temperature dependence of the PL decay times and the PL intensities. The MPE activation energies and relative defect densities for the samples with different well widths were obtained. A simple method is suggested to investigate the interfacial defects of quantum wells.
Microcanonical statistical study of ortho-para conversion in the reaction H3++H2→(H5+)*→H3++H2 at very low energies
Authors: Park Kisam , Light John C.
Published: January 2007

The ortho-para conversion of H3+ and H2 in the reaction H3++H2→(H5+)*→H3++H2 in interstellar space is possible by scrambling the five protons via (H5+)* complex formation. The product distribution of the ortho-para conversion reaction can be given by ratios of cumulative reaction probabilities (CRP) calculated by microcanonical statistical theory with conservation of energy, motional angular momentum, nuclear spin, and parity. A statistical method to calculate the state-to-state reaction probabilities for given initial nuclear spin species, rotational states, and collision energies is developed using a simple semiclassical approximation of tunneling and above-barrier reflection. A new calculation method of branching ratios for given total nuclear spins and scrambling mechanisms is also developed. The anisotropic long-range electrostatic interaction potential of H2 in the Coulomb field of H3+ is taken into account using the first-order perturbation theory in forming the complex. The CRPs and the product distribution of the ortho-para conversion reaction at very low energies with reactants in their ground vibronic and lowest rotational states for given initial nuclear spin species are presented as a function of collision energy assuming complete proton scrambling or incomplete proton scrambling. The authors show that the product distribution at very low energies (or very low temperatures) differs substantially from the high energy (or high temperature) limit branching ratios.
Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis
Authors: Wen Sy-Bor , Mao Xianglei , Greif Ralph , Russo Richard E.
Published: January 2007

Laser ablation of copper with a 4ns laser pulse at 1064nm was studied with a series of synchronized shadowgraph (100fs laser pulses at 400nm) and emission images (spectral line at 515nm). Data were obtained at two laser pulse energies (10 and 30mJ) and in three background gases (He, Ne, and Ar) at atmospheric pressure. The laser energy conversion ratio and the amount of sample vaporized for ablation in each condition were obtained by the theoretical analysis reported in paper I from trajectories of the external shock wave, internal shock wave, and contact surface between the Cu vapor and the background gas. All three quantities were measured from shadowgraph and emission images. The results showed that E, the amount of energy that is absorbed by the copper vapor, decreases as the atomic mass of the background gas increases; and M, the mass of the sample converted into vapor, is almost independent of the background gas [Horn et al., Appl. Surf. Sci. 182, 91 (2001)]. A physical interpretation is given based on the phenomena observed in shadowgraph and emission images during the first tens of nanoseconds after the beginning of the laser pulse for ablation in different background gases. In addition, an internal shock wave was observed in the emission images during the first tens of nanoseconds after the laser pulse, which strikes the surface and should be one of the mechanisms inducing the liquid sample ejection. Also, a significant vortex ring near the target was observed in emission images at longer times after the laser pulse (>100ns) which distorts the otherwise hemispherical expansion of the vapor plume.
Desorption of InSb(001) native oxide and surface smoothing induced by low temperature annealing under molecular hydrogen flow
Authors: Tessler R. , Saguy C. , Klin O. , Greenberg S. , Weiss E. , Akhvlediani R. , Edrei R. , Hoffman A.
Published: January 2007

The preparation of InSb (001) oxygen-free surfaces by thermal annealing at relatively low temperatures under molecular hydrogen flow is reported. This process is compared with thermal oxide desorption (TOD) at 400°C under ultrahigh vacuum conditions. Molecular hydrogen cleaning (MHC) at substrate temperature of 250°C and at hydrogen pressure of 5×10−6Torr resulted in complete desorption of the native oxide layer. Furthermore, no carbon contamination was observed on the surface following this treatment. The surface morphology of the samples following this process was found to be very smooth without any droplet structure. The In:Sb surface stoichiometry was nearly 1:1 along the MHC process. In addition, annealing the sample at 400°C in vacuum after oxide removal by MHC maintains the smoothness and the stoichiometry of the surface. In contrast, TOD at 400°C of an oxidized InSb surface in vacuum does not result in complete oxide removal from the surface. Furthermore, small droplets associated with In are produced at this annealing temperature. The surface stoichiometry shows In enrichment after TOD in vacuum above 360°C. The surface composition and chemical bonding were monitored by Auger electron spectroscopy and x-ray photoelectron spectroscopy as a function of process parameters. The surface morphology was analyzed by atomic force microscopy.
Effect of temporal pulse shape on optical damage
Authors: Carr C. W. , Trenholme J. B. , Spaeth M. L.
Published: January 2007

The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. The authors present here data from a simple single-parameter model and a supporting experiment which predicts that a flat-in-time pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same duration.
Fabrication and electrical properties of (111) textured (Ba0.6Sr0.4)TiO3 film on platinized Si substrate
Authors: Wang Yi , Liu Baoting , Wei Feng , Yang Zhimin , Du Jun
Published: January 2007

The authors report the fabrication of (Ba0.6Sr0.4)TiO3 (BST) film on Pt∕Si(001) substrate without Ti adhesion layer by magnetron sputtering. X-ray diffraction technique is used to characterize the orientation and phase purity of BST/Pt heterostructure. It is found that both BST and Pt films are (111) textured. The (111) BST films are observed to have high tunability of 49.4%; the dielectric constant and dielectric loss of the BST film are about 682 and 0.015, respectively. The leakage current density of BST film agrees well with the space-charge-limited current theory at room temperature and is only 3.90×10−8A∕cm2 at 455kV∕cm.
On the origin of the 1∕f noise in shallow germanium p+-n junctions
Authors: Todi R. M. , Sonde S. , Simoen E. , Claeys C. , Sundaram K. B.
Published: January 2007

The low-frequency noise of shallow germanium p+-n junctions is studied, for diodes with or without a nickel-germanide Ohmic contact. It is shown that the application of NiGe not only reduces the series resistance, resulting in a higher forward current, but also results in a lower 1∕f noise at forward bias. From the observed geometry dependence, it is concluded that germanidation suppresses the 1∕f noise generated in the series resistance, leaving surface-state-assisted generation-recombination at the junction perimeter as the dominant flicker noise source.
Two-parameter families of strange attractors
Authors: Gilmore Robert
Published: January 2007

Periodically driven two-dimensional nonlinear oscillators can generate strange attractors that are periodic. These attractors are mapped in a locally 1-1 way to entire families of strange attractors that are indexed by a pair of relatively prime integers (n1,n2), with n1⩾1. The integers are introduced by imposing periodic boundary conditions on the entire strange attractor rather than individual trajectories in the attractor. The torsion and energy integrals for members of this two parameter family of locally identical strange attractors depend smoothly on these integers.
Comparison of multiscale analysis models applied to zonal flow generation in ion-temperature-gradient mode turbulence
Authors: Anderson J. , Kishimoto Y.
Published: January 2007

During the past years the understanding of the multiscale interaction problems have increased significantly. However, at present there exists a range of different analytical models for investigating multiscale interactions and hardly any specific comparisons have been performed among these models. In this work, two different models for the generation of zonal flows from ion-temperature-gradient (ITG) background turbulence are discussed and compared. The methods used is the coherent mode coupling model and the wave kinetic equation model (WKE). It is shown that the two models qualitatively give the same results even though the assumption on the spectral difference is used in the WKE approach.
High Q factor for mechanical resonances of batch-fabricated SiC nanowires
Authors: Perisanu S. , Vincent P. , Ayari A. , Choueib M. , Purcell S. T. , Bechelany M. , Cornu D.
Published: January 2007

The authors present here the measurements of high mechanical Q factors for singly clamped, batch-fabricated SiC nanowires measured by field emission (FE) in ultrahigh vacuum. The resonances of two nanowires, glued to the ends of tungsten support tips, were electrostatically excited and detected by the variation in the FE microscopy (FEM) images. Low amplitude oscillations were measured by numerical analysis of the FEM image blurring during frequency scans through the resonances. This avoided the artificial broadening of the resonances by nonlinear effects. A room temperature Q factor of 159 000 was achieved after high temperature in situ cleaning.
Chaos-assisted nonresonant optical pumping of quadrupole-deformed microlasers
Authors: Lee Sang-Bum , Yang Juhee , Moon Songky , Lee Jai-Hyung , An Kyungwon , Shim Jeong-Bo , Lee Hai-Woong , Kim Sang Wook
Published: January 2007

Efficient nonresonant optical pumping of a high-Q scar mode in a two-dimensional quadrupole-deformed microlaser has been demonstrated based on ray and wave chaos. Threefold enhancement in the lasing power was achieved at a properly chosen pumping angle. The experimental result is consistent with ray tracing and wave overlap integral calculations.
Yellow-emitting Sr3SiO5:Ce3+,Li+ phosphor for white-light-emitting diodes and yellow-light-emitting diodes
Authors: Jang Ho Seong , Jeon Duk Young
Published: January 2007

In this letter, a yellow-emitting Sr3SiO5:Ce3+,Li+ phosphor is reported. Through transitions of 5d→4f (F7∕22 and F5∕22) in Ce3+, the phosphor showed a very broad and strong yellow emission under near ultraviolet (UV) or blue light excitation. The energy levels of Ce3+ in Sr3SiO5 were suggested from its absorption and excitation spectra. White light could be obtained by combining this phosphor with 460 or 405nm light-emitting diodes (LEDs) [(x,y)=(0.3086,0.3167) or (0.3173, 0.3103)]. Additionally, a yellow LED was fabricated using a near-UV LED (380nm chip) with Sr3SiO5:Ce3+,Li+.
The simplest all-nitrogen ring: Photolytically filling the cyclic-N3 well
Authors: Samartzis Peter C. , Lin Jim Jr-Min , Ching Tao-Tsung , Chaudhuri Chanchal , Lee Shih-Huang , Wodtke Alec M.
Published: January 2007

We report evidence that cyclic-N3 is exclusively produced in the 157-nm photolysis of ClN3. Photoproduct translational energy measurements reveal a single-peaked distribution for an N3-formation channel with maximum and minimum translational energies matching the theoretically predicted minimum and maximum binding energies of cyclic-N3, respectively. The absence of linear-N3 greatly simplifies the data analysis. The zero-Kelvin heat of formation of cyclic-N3 is derived experimentally (142±3.5kcal∕mol) and is in excellent agreement with the best existing determinations from other studies.
Anomalously anisotropic channel mobility on trench sidewalls in 4H-SiC trench-gate metal-oxide-semiconductor field-effect transistors fabricated on 8° off substrates
Authors: Yano Hiroshi , Nakao Hiroshi , Mikami Hidenori , Hatayama Tomoaki , Uraoka Yukiharu , Fuyuki Takashi
Published: January 2007

Metal-oxide-semiconductor (MOS) channel properties in 4H-SiC trench-gate MOS field-effect transistors fabricated on 8° off substrates were characterized. The MOS channel was formed only on one side of the trench sidewalls. The MOS field effect transistor performance depended strongly on the MOS channel planes of (112¯0), (1¯1¯20), (11¯00), and (1¯100). The highest channel mobility of 43cm2∕Vs was obtained on (112¯0). However, only a half value of 21cm2∕Vs was observed on (1¯1¯20), which is the opposite face to (112¯0). The anomalously anisotropic channel mobility is discussed based on the deviation from the crystallographically accurate {112¯0} plane caused by the combination of substrate off angle and sloped trench sidewalls.
Theoretical and experimental investigation of valence band offsets for direct silicon bond hybrid orientation technology
Authors: Joshi Sachin , Sahu Bhagwan , Banerjee Sanjay K. , Ciucivara Adrian , Kleinman Leonard , Wise Rick , Cleavelin Rinn , Pinto Angelo , Seacrist Mike , Ries Mike , Huang Y.-T. , Ma Mike , Lin C.-T.
Published: January 2007

Direct silicon bonding (DSB) for hybrid orientation technology has recently generated a lot of interest due to the significant performance enhancements reported for p-channel metal oxide semiconductor devices fabricated on alternative substrate orientations. This letter reports on the experimental observation and density functional theory (DFT) based theoretical prediction of a valence band offset between the (100) and (110) silicon surfaces directly bonded to each other. This constitutes a different type of junction created by the presence of two different surface orientations in close proximity to each other and not by doping or material variations. Experimentally, this band offset was observed as an asymmetry in the forward and reverse current-voltage characteristics of a two terminal device designed to flow a current across the DSB interface. Further, the valence band offset obtained from DFT simulations was used in a conventional device simulator (TAURUS-MEDICI) to simulate the behavior of this structure. MEDICI results are in qualitative agreement with the predicted band offset of ∼85meV between the (110) and (100) surfaces which result in a diodelike behavior of the current-voltage characteristics across the (110)∕(100) interface. Temperature dependence of the I-V characteristics is also discussed.
Wave front evolution of negatively refracted waves in a photonic crystal
Authors: Schonbrun Ethan , Wu Qi , Park Wounjhang , Yamashita Tsuyoshi , Summers Christopher J. , Abashin Maxim , Fainman Yeshaiahu
Published: January 2007

Using a heterodyne near-field scanning microscope, the authors analyze the phase and amplitude of the electric field of an optical wave across the boundary of positive to negative refraction media. The photonic crystal acts as an extremely anisotropic material with a negative curvature of its dispersion surface whose shape is resolved experimentally. This extreme anisotropy results in the beam having a peculiar phase evolution through propagation that does not occur in isotropic media. A focusing wave is produced by negative refraction, which has diverging wave fronts before the internal focus and converging wave fronts after the focus.