bluuebunny/crossref_metadata_2025 huggingface dataset:
Bystander B cells rapidly acquire antigen receptors from activated B cells by membrane transfer: a novel mechanism for enhancing specific antigen presentation
Authors: Quah Ben , Barlow Vaughan , McPhun Virginia , Matthaei Klaus , Hulett Mark , Parish Christopher
Published: October 2007

The B cell antigen receptor (BCR) efficiently facilitates the capture and processing of a specific antigen for presentation on MHC class II molecules to antigen specific CD4+ T cells (1). Despite this, the majority of B cells are only thought to play a limited role in CD4+ T cell activation since BCRs are clonotypically expressed. Here we show, however, that activated B cells can, both in vitro and in vivo, rapidly donate their BCR to bystander B cells, a process that is mediated by direct membrane transfer between adjacent B cells and is amplified by the interaction of the BCR with specific antigen. This results in a dramatic expansion in the number of antigen-binding B cells in vivo, with the transferred BCR endowing recipient B cells with the ability to present specific antigen to antigen-specific CD4+ T cells.
Skills and Training in the Hotel Sector: The Case of Front Office Employment in Northern Ireland
Authors: Baum Tom , Devine Frances
Published: October 2007

Notwithstanding the globalisation of services and the migration of some service providers (call centres, financial processing) to regions of low cost labour coupled with high levels of education attainment, there are arguments that the skills, which employees bring to the workplace in executing common tasks, are context and culture specific. This paper is concerned with the skills set and training background of one set of service workers, those in hotel front office, located within Northern Ireland. This paper reports the findings of a survey of front office workers working in 4- and 5-star hotels in Northern Ireland. This survey identifies the skills and training profile of this group of employees and measures attitudes to key skills requirements within front office work.
‘No Rules, Just Right’ or is it? The Role of Themed Restaurants as Cultural Ambassadors
Authors: Wood Natalie T. , Muñoz Caroline Lego
Published: October 2007

After mass media, ethnic-themed restaurants are possibly the second most influential socialising agents of foreign cultures. Whereas the media often depicts foreign cultures in a stereotypical manner, the opportunity exists in the hospitality field to offer consumers a more detailed and accurate insight into a culture. Yet, is this what consumers really want? This paper addresses an important question: How do spaces of consumption affect the perception and representation of ‘authentic’ culture? To explore this, a four-stage, cross-cultural (ie Australia and United States) qualitative study was undertaken to examine the role the Outback Steakhouse chain of restaurants plays in representing Australian culture in the United States. Findings revealed that US subjects were more accepting of the restaurant environment where it matched the images of Australia perpetuated by the media. By contrast, Australian subjects indicated that the image this restaurant provides is a largely stereotypical, outdated, inaccurate representation of their culture. Research implications and recommendations from a marketing, hospitality, and tourism perspective are provided.
Hospitality Management Students' Conceptions of Education
Authors: Zwaal Wichard , Otting Hans
Published: October 2007

The major issue addressed in this study is the alignment between the institutional conception of education and the students’ conceptions of education, decomposed into three parts: conceptions of knowledge, conceptions of teaching and learning, and conceptions of assessment. Subjects in this study were 324 students enrolled in a four-year hospitality management programme. Three instruments were administered to measure students’ conceptions of education. Results indicate that the three sets of conceptions seem to fit in the traditional-constructivist dichotomy with students showing a congruent pattern in the three sets of conceptions. Finally, first-year students hold more traditional conceptions of education than senior students. The implication for educational innovations is that serious attention should be paid to the development of students’ conceptions of education.
Using Decision Trees to Identify Tourism Stakeholders: The Case of Two Eastern North Carolina Counties
Authors: Byrd Erick T. , Gustke Larry
Published: October 2007

This paper explores stakeholder involvement in tourism planning, development, and management. For tourism planners to include stakeholders in the tourism planning process those stakeholders and their interests need to be identified. The research reported in this paper describes and applies an analytical technique that is not traditionally used to identify stakeholders. A questionnaire was developed and mailed to stakeholders in two rural communities in North Carolina. The data were analysed with an Exhaustive Chi-square Automatic Interaction Detection decision tree. From the results of the decision tree, stakeholder groups were identified in relation to their support for sustainable tourism development in their community.
Relationship Quality with a Travel Agency: The Influence of the Postpurchase Perceived Value of a Tourism Package
Authors: Moliner Miguel A. , Sánchez Javier , Rodríguez Rosa M. , Callarisa Luís
Published: October 2007

Relationship quality is an emerging concept that attempts to measure the lifetime value of a customer. The indicators that determine the construct are satisfaction with the relationship, the customer's trust and the customer's level of commitment. This paper considers how the post-purchase perceived value of a tourism package influences the relationship quality with a travel agency. Gummesson posits the existence of a causal link between perceived value and relationship quality. The results show that the tourist's satisfaction is the key variable in the relationship quality. Affect plays a fundamental direct role in long-term valuation, while cognition is more influential in the short term.
Advantages of .travel as a Top-Level Domain
Authors: Wagner Daniela
Published: October 2007

The .travel domain, the first Sponsored Top Level Domain (STLD) created for the Tourism and Travel Industry, is recorded as the most successful launch ever. Its restricted eligibility, as well as its authentication process, ensures exclusivity within the industry.
Ethical Decisions and Gender Differences of European Hospitality Students
Authors: Wilborn LaChelle R. , Brymer Robert A. , Schmidgall Ray
Published: October 2007

The purpose of this paper is to assess the sources influencing an ethical decision-making process of European hospitality students. Ten scenarios were used (1) to indicate whether the action posed was ‘ethical’, ‘unethical’, or ‘not a question of ethics’ and (2) to indicate what they would do if they were in this situation. We found that of the nearly 400 European hospitality students, 54 per cent females and 46 per cent males, both genders indicated that parents, close friends, and business management courses influenced their ethical beliefs the most. Additionally, we found that responses were significantly different for only one of the ten scenarios with regards to gender.

The action responses to the proposed scenarios were, however, statistically significant for five scenarios; four of these five were business scenarios. Female European hospitality students were more likely to engage in ethical behaviour and are generally less tolerant of questionable practices than their male peers.
Blogging as a Social Media
Authors: Thevenot Guillaume
Published: October 2007

Blogging has become one of the most popular social media and networking tools. The Travel and Tourism Industry today is faced with consequences that blogs have not only positive impacts but also negative ones, if not managed properly.
Mobile Travel
Authors: Langelund Soren
Published: October 2007

Mobile phone, once an amenity, has now become a necessity in the wireless communication era. Despite the complexity of mobile service, its expanded functionality is likely to become a practical solution for the travel and tourism industry.
Ab initio energies of nonconducting crystals by systematic fragmentation
Authors: Netzloff Heather M. , Collins Michael A.
Published: October 2007

A systematic method for approximating the ab initio electronic energy of molecules from the energies of molecular fragments has been adapted to estimate the total electronic energy of crystal lattices. The fragmentation method can be employed with any ab initio electronic structure method and allows optimization of the crystal structure based on ab initio gradients. The method is demonstrated on SiO2 polymorphs using the Hartree-Fock approximation, second order Möller-Plesset perturbation theory, and the quadratic configuration interaction method with single and double excitations and triple excitations added perturbatively .
Local mode behavior in H2Te
Authors: Coudert L. H. , Tine M. , N’Gom H. , Bürger H.
Published: October 2007

A high-resolution spectrum of hydrogen telluride (H2Te) was recorded in the 4050–7000cm−1 region. Two bands could be observed at 4900 and 5980cm−1 and were assigned as the (20±,1)←(00+,0) and (30±,0)←(00+,0) bands, respectively. Rotational transitions of the two bands were assigned for the most abundant H2Te130 and H2Te128 isotopic species. Line position analyses were carried out to investigate a possible local mode behavior. For the first time we found in H2Te strong experimental evidence for such a behavior for the higher-lying band as its two upper vibrational states are only 0.027 and 0.032cm−1 apart for the H2Te130 and H2Te128 isotopic species, respectively.
Comprehensive characterization of the photodissociation pathways of protonated tryptophan
Authors: Lepère V. , Lucas B. , Barat M. , Fayeton J. A. , Picard V. J. , Jouvet C. , Çarçabal P. , Nielsen I. , Dedonder-Lardeux C. , Grégoire G. , Fujii A.
Published: October 2007

The photofragmentation of protonated tryptophan has been investigated in a unique experimental setup, in which ion and neutral issued from the photofragmentation are detected in coincidence, in time and in position. From these data are extracted the kinetic energy, the number of neutral fragments associated with an ion, their masses, and the order of the fragmentation steps. Moreover, the fragmentation time scale ranging from tens of nanoseconds to milliseconds is obtained. From all these data, a comprehensive fragmentation mechanism is proposed.
First-principles investigation on the geometry and electronic structure of the three-dimensional cuboidal C60 polymer
Authors: Yang Jianjun , Tse John S. , Iitaka Toshiaki
Published: October 2007

The structural stability and electronic properties of the recently characterized three-dimensional (3D) cuboid-shaped C60 polymer are studied using periodic ab initio density functional methods. It is shown that the experimentally observed structure is metastable and not fully relaxed from the high pressure state. A second polymorph, which is more stable than the experimental structure, is identified from the calculations. This new structure differs from the observed structure in the number of fourfold-coordinated atoms per C60 molecule. Both structures are found to be metallic with bulk moduli only about one-third that of diamond. The cuboidal C60 is not the long sought after superhard 3D carbon polymer; however, the two polymorphs studied here reveal unusual electronic band structures that might suggest interesting electronic properties.
Accumulation of heavy particles around a helical vortex filament
Authors: IJzermans Rutger H. A. , Hagmeijer Rob , van Langen Pieter J.
Published: October 2007

The motion of small heavy particles near a helical vortex filament in incompressible flow is investigated. Both the configurations of a helical vortex filament in free space and a helical vortex filament in a concentric pipe are considered, and the corresponding helically symmetric velocity fields are expressed in terms of a stream function. Particle motion is assumed to be driven by Stokes drag, and the flow fields are assumed to be independent from the motion of particles. Numerical results show that heavy particles may be attracted to helical trajectories. The stability of these attraction trajectories is demonstrated by linear stability analysis. In addition, the correlation between the attraction trajectories and the streamline topologies is investigated.
Response of a spatially developing turbulent boundary layer to active control strategies in the framework of opposition control
Authors: Pamiès Mathieu , Garnier Eric , Merlen Alain , Sagaut Pierre
Published: October 2007

Opposition control is a simple feedback control method which can be used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows [H. Choi, P. Moin, and J. Kim, J. Fluid Mech. 262, 75 (1994)]. The idea is to impose blowing and suction at the wall to counteract near-wall quasistreamwise vortical structures. Unfortunately, the effectiveness of this method decreases as the Reynolds number increases [Y. Chang, S. Scott Collis, and S. Ramakrishnan, Phys. Fluids 14, 4069 (2002)]. The present study proposes using a simple modification of opposition control (OC) to increase its performance at high Reynolds numbers. We demonstrate a significant improvement on drag reduction when performing a blowing-only opposition control, where the suction part of OC has been removed, on a spatially developing turbulent boundary layer at Reτ,δ=960, based on the boundary layer thickness and the friction velocity.
Moments of hyper-Rayleigh spectra of selected rare gas mixtures
Authors: Bancewicz Tadeusz , Głaz Waldemar , Godet Jean-Luc
Published: October 2007

In this work we have analyzed spectral moments characterizing properties of the collisionally hyper-Rayleigh scattered light. This is a supplementary study undertaken in order to complete the series of our previously published papers on the collisional hyper-Rayleigh scattering spectral profiles. In order to evaluate the moments we have extended the theory so that it could embrace the (hyper)polarizabilities of higher rank. Using the expressions developed on the grounds of the theoretical principles and applying appropriate computational methods with ab initio hyperpolarizability values as an input, we have obtained desirable moment values for three diatomic noble gas systems: HeNe, HeAr, and NeAr, at several temperature points. The semiclassical and the quantum treatments have been taken into account, and the moments were calculated both from the sum rule method as well as from the spectral profiles. The results were compared and discussed.
Ring formation in self-focusing of electromagnetic beams in plasmas
Authors: Faisal M. , Mishra S. K. , Verma M. P. , Sodha M. S.
Published: October 2007

This article presents a paraxial theory of ring formation as an initially Gaussian beam propagates in a nonlinear plasma, characterized by significant collisional or ponderomotive nonlinearity. Regions in the axial irradiance-(beamwidth)−2 space, for which the ring formation occurs and the paraxial theory is valid, have been characterized; for typical points in these regions the dependence of the beam width parameter and the radial distribution of irradiance on the distance has been specifically investigated and discussed.
Time-dependent density functional theory calculation of van der Waals coefficient of sodium clusters
Authors: Banerjee Arup , Chakrabarti Aparna , Ghanty Tapan K.
Published: October 2007

In this paper we employ all-electron ab initio time-dependent density functional theory based method to calculate the long range dipole-dipole dispersion coefficient (van der Waals coefficient) C6 of sodium atom clusters containing even number of atoms ranging from 2 to 20 atoms. The dispersion coefficients are obtained via Casimir-Polder relation [Phys. Rev. 3, 360 (1948)]. The calculations are carried out with two different exchange-correlation potentials: (i) the asymptotically correct statistical average of orbital potential (SAOP) and (ii) Vosko-Wilk-Nusair representation [Can. J. Phys. 58, 1200 (1980)] of exchange-correlation potential within local density approximation. A comparison with the other theoretical results has been performed. We also present the results for the static polarizabilities of sodium clusters and also compare them with other theoretical and experimental results. These comparisons reveal that the SAOP results for C6 and static polarizability are quite accurate and very close to the experimental results. We examine the relationship between volume of the cluster and van der Waals coefficient, and find that to a very high degree of correlation C6 scales as the square of the volume. We also present the results for van der Waals coefficient corresponding to cluster–Ar atom and cluster–N2 molecule interactions.
Inelastic neutron scattering study of hydrogen in d8-THF∕D2O ice clathrate
Authors: Tait Kimberly T. , Trouw Frans , Zhao Yusheng , Brown Craig M. , Downs Robert T.
Published: October 2007

In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deutrated tetrahydrofuran-water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J=0 and 1 states) at approximately 14meV in both energy gain and loss. These transitions could be unequivocally assigned since there was residual orthohydrogen at low temperatures (slow conversion to the ground state) resulting in an observable J=1→0 transition at 5K (kT=0.48meV). A doublet in neutron energy loss at approximately 28.5meV is interpreted as J=1→2 transitions. In addition to the transitions between rotational states, there are a series of peaks that arise from transitions between center-of-mass translational quantum states of the confined hydrogen molecule. A band at approximately 9meV can be unequivocally interpreted as a transition between translational states, while broad features at 20, 25, 35, and 50–60meV are also interpreted to as transitions between translational quantum states. A detailed comparison is made with a recent five-dimensional quantum treatment of hydrogen in the smaller dodecahedral cage in the SII ice-clathrate structure. Although there is broad agreement regarding the features such as the splitting of the J=1 degeneracy, the magnitude of the external potential is overestimated. The numerous transitions between translational states predicted by this model are in poor agreement with the experimental data. Comparisons are also made with three simple exactly solved models, namely, a particle in a box, a particle in a sphere, and a particle on the surface of a sphere. Again, there are too many predicted features by the first two models, but there is reasonable agreement with the particle on a sphere model. This is consistent with published quantum chemistry results for hydrogen in the dodecahedral 512 cage, where the center of the cage is found to be energetically unfavorable, resulting in a shell-like confinement for the hydrogen molecule wave function. These results demonstrate that translational quantum effects are very significant and a classical treatment of the hydrogen molecule dynamics is inappropriate under such conditions.
Fourier transform microwave spectroscopy of the isocyanomethyl radical, CH2NC
Authors: Hirao T. , Ozeki H. , Saito S. , Yamamoto S.
Published: October 2007

The pure rotational spectrum of the isocyanomethyl radical, CH2NC, was measured for the first time by using a Fourier transform microwave spectrometer. The molecule was produced by a discharge of isocyanomethane, CH3NC, diluted in Ar or Ne. The spectral lines due to the N=1-0 and 2-1 transitions were recorded near 22 and 44GHz, respectively. The observed spectrum showed a complicated fine and hyperfine structure because of the same order of interaction energies. Among the 39 spectral lines detected and assigned, the transitions with Ka=1 show no hyperfine splitting due to the hydrogen nuclei, suggesting planarity for the molecule. Molecular constants such as rotational and spin-rotational parameters including centrifugal effects and hyperfine coupling constants due to both the nitrogen and the hydrogen nuclei were accurately determined. The structure and the astronomical implications of the molecule are discussed.
Molecular properties determined from the relaxation of long-lived spin states
Authors: Ahuja Puneet , Sarkar Riddhiman , Vasos Paul R. , Bodenhausen Geoffrey
Published: October 2007

The populations of long-lived spin states, in particular, populations of singlet states that are comprised of antisymmetric combinations of product states, ∣αIβS⟩−∣βIαS⟩, are characterized by very long lifetimes because the dipole-dipole interaction between the two “active” spins I and S that are involved in such states is inoperative as a relaxation mechanism. The relaxation rate constants of long-lived (singlet) states are therefore determined by the chemical shift anisotropy (CSA) of the active spins and by dipole-dipole interactions with passive spins. For a pair of coupled spins, the singlet-state relaxation rate constants strongly depend on the magnitudes and orientations of the CSA tensors. The relaxation properties of long-lived states therefore reveal new information about molecular symmetry and structure and about spectral density functions that characterize the dynamic behavior.
Configurational probabilities for symmetric dimers on a lattice: An analytical approximation with exact limits at low and high densities
Authors: Chen Y. , Aranovich G. L. , Donohue M. D.
Published: October 2007

A new approach is developed for lattice density functional theory of interacting symmetric dimers at high temperatures. Equations of equilibrium for two-dimensional square and three-dimensional cubic lattices are derived for the complete set of configurations in the first three shells around the central dimer, and rules of truncation for higher shells are based on exact results from the mathematical theory of domino tilings. This provides exact limits for both low and high densities. The new model predicts contributions of particular configurations which are in agreement with Monte Carlo simulations over the whole range of densities, including agreement with pocket Monte Carlo simulations at high densities.
A generalized periodic boundary condition for lattice Boltzmann method simulation of a pressure driven flow in a periodic geometry
Authors: Kim Seung Hyun , Pitsch Heinz
Published: October 2007

A new boundary closure scheme for the lattice Boltzmann method is proposed for a fully developed, pressure driven flow in a periodic geometry. The new boundary condition is of higher accuracy than that of Zhang and Kwok [Phys. Rev. E 73, 047702 (2006)]. The accuracy of the generalized periodic boundary condition is analyzed for both incompressible and compressible flows. A body forcing approach, where a pressure gradient is replaced by an equivalent body force, is also analyzed for a flow in a complex geometry and assessed using the generalized periodic boundary condition.
Inelastic collisions in molecular nitrogen at low temperature (2⩽T⩽50K)
Authors: Fonfría J. P. , Ramos A. , Thibault F. , Tejeda G. , Fernández J. M. , Montero S.
Published: October 2007

Theory and experiment are combined in a novel approach aimed at establishing a set of two-body state-to-state rates for elementary processes ij→ℓm in low temperature N2:N2 collisions involving the rotational states i,j,ℓ,m. First, a set of 148 collision cross sections is calculated as a function of the collision energy at the converged close-coupled level via the MOLSCAT code, using a recent potential energy surface for N2–N2. Then, the corresponding rates for the range of 2⩽T⩽50K are derived from the cross sections. The link between theory and experiment, aimed at assessing the calculated rates, is a master equation which accounts for the time evolution of rotational populations in a reference volume of gas in terms of the collision rates. In the experiment, the evolution of rotational populations is measured by Raman spectroscopy in a tiny reference volume (≈2×10−3mm3) of N2 traveling along the axis of a supersonic jet. The calculated collisional rates are assessed experimentally in the range of 4⩽T⩽35K by means of the master equation, and then are scaled by averaging over a large set of experimental data. The scaled rates account accurately for the evolution of the rotational populations measured in a wide range of conditions. Accuracy of 10% is estimated for the main scaled rates.
Steady two-layer flow in a topographically patterned channel
Authors: Lenz Richard D. , Kumar Satish
Published: October 2007

The steady behavior of the interface between two immiscible liquid layers flowing in a channel where one wall is flat and the other exhibits isolated or periodic step-changes in surface topography is considered in this work. A one-dimensional model based on the lubrication approximation is used to describe the interfacial shape and explore its behavior over a wide range of problem parameters. The density and thickness ratios, as well as the periodicity of the topography, strongly influence interfacial shape, whereas the viscosity ratio has a relatively minor effect. In some cases, interfacial features that are present in the flow of single liquid layers over surfaces with topography can be completely suppressed by large pressure gradients that arise due to the bounded geometry. A scaling analysis is applied to explain variations in the capillary length scale. The results presented in this work are potentially relevant to a range of applications including microfluidics, oil recovery, lubricated piping, and lithographic printing.
Development of the energy flow in light-harvesting dendrimers
Authors: Andrews David L. , Li Shaopeng , Rodriguez Justo , Slota Jo
Published: October 2007

Modeling the multistep flow of energy in light-harvesting dendrimers presents a considerable challenge. Recent studies have introduced an operator approach based on a matrix representation of the connectivity between constituent chromophores. Following a review of the theory, detailed applications are now shown to exhibit the time development of the core excitation following pulsed laser irradiation and the steady-state behavior that can be expected under conditions of constant illumination. It is also shown how energy capture by whole dendrimers can be analytically related to chromophore pair-transfer properties and, in particular, the spectroscopic gradient toward the core. Indicative calculations also illustrate the consequences of tertiary folding. In each respect, the model affords opportunities to derive new, physically meaningful information on the photophysical and structural features of dendrimeric systems.
Effects of ions and atomic hydrogen in plasma-assisted growth of single-walled carbon nanotubes
Authors: Denysenko I. , Ostrikov K. , Yu M. Y. , Azarenkov N. A.
Published: October 2007

The growth of single-walled carbon nanotubes (SWCNTs) in plasma-enhanced chemical vapor deposition (PECVD) is studied using a surface diffusion model. It is shown that at low substrate temperatures (⩽1000K), the atomic hydrogen and ion fluxes from the plasma can strongly affect nanotube growth. The ion-induced hydrocarbon dissociation can be the main process that supplies carbon atoms for SWCNT growth and is responsible for the frequently reported higher (compared to thermal chemical vapor deposition) nanotube growth rates in plasma-based processes. On the other hand, excessive deposition of plasma ions and atomic hydrogen can reduce the diffusion length of the carbon-bearing species and their residence time on the nanotube lateral surfaces. This reduction can adversely affect the nanotube growth rates. The results here are in good agreement with the available experimental data and can be used for optimizing SWCNT growth in PECVD.
Quantum dynamical treatment of inelastic scattering of atoms at a surface at finite temperature: The random phase thermal wave function approach
Authors: Nest M. , Kosloff R.
Published: October 2007

We present quantum dynamical calculations for the inelastic scattering of atoms at a nonrigid surface at finite temperature. The surface degrees of freedom are discretized and treated in a multiconfigurational wave function picture. The thermal averaging is carried out with the random phase thermal wave function approach. We show that it is sufficient to restrict the random phases to the intermediate basis of single particle functions, discuss the convergence of the method with the number of configurations and realizations, and analyze the flow of energy between different parts of the system for a range of temperatures between 4 and 500K.
Role of oxygen vacancies on ferromagnetism in Fe-doped TiO2 thin films
Authors: Meng H. J. , Hou D. L. , Jia L. Y. , Ye X. J. , Zhou H. J. , Li X. L.
Published: October 2007

Fe-doped TiO2 rutile thin films were fabricated by reactive magnetron sputtering on SiO2 substrates under different growth conditions, and the structure and magnetism have been systematically investigated. X-ray diffraction data, atomic force microscopy, and magnetic force microscopy confirm the absence of metallic Fe clusters or any other impurity phase. The divalent Fe ion was identified by x-ray photoelectron spectra. Room-temperature ferromagnetism has been observed for all the FexTi1−xO2 (x=3%–15%) rutile films. However, the saturation magnetization (Ms) varied drastically for different pressures, doping concentrations, and annealing processes. The results show that ferromagnetism originates from the doped matrix rather than any type of magnetic cluster and the ferromagnetism is strongly correlated with the oxygen vacancies in TiO2.
The role of Y/lanthanides on the glass forming ability of amorphous steel
Authors: Wang H. J. , Shiflet G. J. , Poon S. J. , Matsuda K. , Ikeno S.
Published: October 2007

The effect of yttrium on improving the amorphous steel glass formability (GFA) is investigated through chemical analysis during the early devitrification stage by employing energy dispersive x-ray spectroscopy and three-dimensional atom probe techniques. Atomic segregation and partitioning are found to occur in association with the formation of the principal competing crystalline M23(CB)6 phase. The partitioning of Y from crystallite particles is confirmed, in agreement with first principles calculations. Additionally, the GFA improvement is also attributed to the strong interatomic bonding between lanthanide and metalloids. The role of Y on improving GFA is verified with growth kinetic measurements.
The distribution of oxide species in the Cs∕O activation layer on InP(100) negative electron affinity photocathodes
Authors: Lee Dong-Ick , Sun Yun , Liu Zhi , Sun Shiyu , Peterson Samuel , Pianetta Piero
Published: October 2007

The atomic arrangement of Cs oxides in the activation layer of an InP photocathode is investigated using angle dependent photoemission spectroscopy. Two distinct peaks in the O1s core level and in valence band spectra have led to the discovery of two molecular oxygen species incorporated in the thin activation layer: Cs peroxide (Cs2O2) and Cs superoxide (CsO2). The different angular dependences of these oxides observed in the photoemission spectra are caused by different vertical locations of the oxygen molecules in each Cs oxide in the activation layer. The thickness of the activation layer, which is about 7Å, suggests lateral distribution of Cs peroxide and Cs superoxide. The quantum efficiency of InP photocathodes in our ultra high vacuum system decreases with time due to the chemical transformation of the Cs oxides and subsequent substrate oxidation, as deduced from an observation of the peak evolution in the photoemission spectra, and supported by the thermodynamic stability of Cs superoxide as compared to Cs peroxide when there is residual oxygen around.
Responsivity of ZnTe∕n-GaAs heterostructures formed by infrared nanosecond laser deposition
Authors: Acharya K. P. , Ullrich B. , Erlacher A.
Published: October 2007

With nanosecond laser pulses at 1064nm, ZnTe was ablated and deposited onto n-GaAs. The intrinsic and extrinsic room temperature responsivities of the heteropairing was investigated with lock-in technique employing various optical chopping frequencies. The work brings to light two peculiar features: The photocurrent of the structure possesses a frequency independent (isosbestic) point and the dominating photocurrent, i.e., defect or bulk related, crossing the sample can be sensitively altered via the sign of the bias. The reported features here, which cannot be achieved with GaAs itself, might open useful technological calibrating applications for light detectors.
Characteristics of altered layers formed by sputtering with a massive molecular ion containing diverse elements with large mass differences
Authors: Fujiwara Yukio , Kondou Kouji , Nonaka Hidehiko , Saito Naoaki , Fujimoto Toshiyuki , Kurokawa Akira , Ichimura Shingo , Tomita Mitsuhiro
Published: October 2007

Tetrairidium dodecacarbonyl (Ir4(CO)12) is an organometallic compound called metal cluster complex which has a molecular weight of 1104.9. To investigate its irradiation effect, silicon substrates sputtered with 10keV Ir4(CO)7+ were analyzed by high resolution Rutherford backscattering spectrometry. Experimental results were examined on the basis of a conventional theory of simultaneous implantation and sputtering. The introduction of oxygen gas during sputtering proved to form a thick oxide layer in the substrate, resulting in iridium segregation at the silicon-oxide interface and carbon accumulation near the surface. It was confirmed that oxygen partial pressure significantly affected the characteristics of an altered layer beneath a sputtered surface.
Charge carrier mobility of mixed-layer organic light-emitting diodes
Authors: Liu Shun-Wei , Lee Jiun-Haw , Lee Chih-Chien , Chen Chin-Ti , Wang Juen-Kai
Published: October 2007

The authors report the investigation of the charge transport behaviors in mixed thin films of N,N′-diphenyl-N,N′-bis(1-napthyl)-1,1′-biphenyl-4,4′-diamine and tris(8-hydroxyquinoline) aluminum. The extracted electron and hole drift mobility were found to be sensitive to the compositional fraction and interpreted by energy levels, charge mobilities of neat compounds, and microscopic networks within the mixed systems. The carrier conduction characteristics, therefore, were used to illustrate the electrical and optical properties of the organic light emitting devices with a mixed layer and present direct evidences on the role of the mixed layer in these devices.
Magnetoimpedance biosensor for Fe3O4 nanoparticle intracellular uptake evaluation
Authors: Kumar A. , Mohapatra S. , Fal-Miyar V. , Cerdeira A. , García J. A. , Srikanth H. , Gass J. , Kurlyandskaya G. V.
Published: October 2007

Iron oxide (Fe3O4) nonspecific nanoparticles of 30nm are embedded inside human embryonic kidney (HEK 293) cells by intracellular uptake with a concentration of ∼105 particles/cell. An amorphous ribbon of Co64.5Fe2.5Cr3Si15B15 exhibiting large magnetoimpedance (MI) serves as the sensing element. The presence of fringing fields of the nanoparticles changes the superposition of the constant applied field and the alternating field created by a current flowing through the ribbon that can be detected as a change in MI. This response is clearly dependent on the presence of the magnetic nanoparticles inside the cells and on the value of the external field.
Nanochannels fabricated by high-intensity femtosecond laser pulses on dielectric surfaces
Authors: Kudryashov Sergey I. , Mourou Gerard , Joglekar Ajit , Herbstman Jeffrey F. , Hunt Alan J.
Published: October 2007

Direct scanning electron microscopy examination reveals a complex structure of narrow, micron-deep, internal nanochannels within shallow, nanoscale, external craters fabricated on glass and sapphire surfaces by single high-intensity femtosecond laser pulses, with nearly the same intensity thresholds for both features. Formation of the channels is accompanied by extensive expulsion of molten material produced via surface spallation and phase explosion mechanisms, and redeposited around the corresponding external craters. Potential mechanisms underlying fabrication of the unexpectedly deep channels in dielectrics are considered.
Dimensional oscillation in GaAs∕AlAs quantum wells by two-dimensional standing surface acoustic waves
Authors: Sogawa Tetsuomi , Gotoh Hideki , Hirayama Yoshiro , Santos Paulo V. , Ploog Klaus H.
Published: October 2007

We have used spatially and time-resolved photoluminescence (PL) spectroscopy recorded using a synchronized excitation method in order to investigate the mechanisms for the dynamic PL modulation of GaAs∕AlAs quantum wells by two-dimensional (2D) standing surface acoustic waves (SAWs). It is clearly demonstrated that a square array of dynamic quantum dots (DQDs) is formed, which oscillates with a repetition interval equal to half of the SAW period. A 2D flatband condition appears between the DQD formations. The spatial modulation of the PL intensity is attributed to exciton migration into the tensile-strained dots created by the strain-induced band-gap modulation.
Suppression of spurious vibration of cantilever in atomic force microscopy by enhancement of bending rigidity of cantilever chip substrate
Authors: Tsuji Toshihiro , Kobari Kentaro , Ide Seishiro , Yamanaka Kazushi
Published: October 2007

To improve the precision of dynamic atomic force microscopy (AFM) using cantilever vibration spectra, a simple but effective method for suppressing spurious response (SR) was developed. The dominant origin of SR was identified to be the bending vibration of the cantilever substrate, by the analysis of the frequency of SR. Although a rigid cover pressing the whole surface of the substrate suppressed SR, the utility was insufficient. Then, a method of enhancing the bending rigidity of the substrate by gluing a rigid plate (clamping plate, CP) to the substrate was developed. This chip can be used with an ordinary cantilever holder, so that the reproducibility of SR suppression when attaching and detaching the cantilever chip to the holder was improved. To verify its utility, the evaluation of a microdevice electrode was performed by ultrasonic atomic force microscopy. The delamination at a submicron depth was visualized and the detailed variation of the delamination was evaluated for the first time using clear resonance spectra. The CP method will particularly contribute to improving dynamic-mode AFM, in which resonance spectra with a low quality factor are used, such as noncontact mode AFM in liquid or contact resonance mode AFM. The effect of the CP can be achieved by fabricating a substrate with a thick plate beforehand.
In
Ga
N
∕
Ga
N
multi-quantum-well ultraviolet photosensors by capping an unactivated Mg-doped GaN layer
Authors: Chang P. C. , Yu C. L.
Published: October 2007

In Ga N ∕ Ga N multi-quantum-well (MQW) metal-semiconductor-metal (MSM) photosensors with an unactivated Mg-doped GaN cap layer were fabricated and characterized. The experimental results showed that dark pits of threading dislocation termination was hardly observed after capping a thin Mg-doped GaN layer. It was also found that we could significantly suppress the dark leakage current by inserting an additional Mg-doped GaN layer due to a thicker and higher potential barrier and effective surface passivation. For InGaN∕GaN MQW MSM photosensors with the unactivated Mg-doped GaN cap layer, the responsivity at 380nm and UV to visible rejection ratio were found to be 0.366A∕W and 1.99×103 under 4V applied bias.
Phototunable photonic crystals with reversible wavelength choice
Authors: Han Guo-Zhi , Xie Zhuo-Ying , Zheng Da , Sun Li-Guo , Gu Zhong-Ze
Published: October 2007

We report a phototunable photonic crystal device whose reflection at the stop band position can be switched between valley and peak. The device is comprised of a colloidal crystal film, a photoresponsible polymer-dispersed liquid crystal film, and a holophote. The reflection spectrum of the device can be reversibly switched by ultraviolet and visible light irradiations. It was demonstrated that this device is not only used for the application of wavelength selection but is also useful for applications such as display.
Identification of bulk and surface sulfur impurities in TiO2 by synchrotron x-ray absorption near edge structure
Authors: Smith M. F. , Setwong Kongthip , Tongpool Rungnapa , Onkaw Darin , Na-phattalung Sutassana , Limpijumnong Sukit , Rujirawat Saroj
Published: October 2007

Synchrotron x-ray absorption near edge structure (XANES) measurements of Ti and S K edges, combined with first principles simulations, are used to characterize S-doped TiO2 prepared by oxidative annealing of TiS2 at various temperatures. Ti-edge XANES and x-ray powder diffraction data indicate that samples annealed above 300°C have an anatase TiO2 crystal structure with no trace of TiS2 domains. S-edge XANES data reveal that the local structure seen by S atoms evolves gradually, from TiS2 to a qualitatively different structure, as the annealing temperature is increased from 200to500°C. For samples annealed at 500°C, the spectrum appears to have features that can be assigned to S on the surface in the form of SO4 and S defects in the bulk (most likely S interstitials) of TiO2.
Direct determination of dislocation sense of closed-core threading screw dislocations using synchrotron white beam x-ray topography in 4H silicon carbide
Authors: Chen Yi , Dudley Michael
Published: October 2007

Grazing-incidence synchrotron white beam x-ray topography images of closed-core threading screw dislocations in 4H silicon carbide appear as roughly elliptically shaped white features, with an asymmetric perimeter of dark contrast which is greatly enhanced on one side or other of the g vector. Ray-tracing simulations indicate that the relative position of the enhanced dark contrast feature reveals the sense of the closed-core screw dislocation. Dislocation senses so obtained were validated using back-reflection images recorded with small Bragg angle. Therefore, the sense of the closed-core threading screw dislocations can be unambiguously revealed using either grazing-incidence or “small Bragg angle” back-reflection synchrotron white beam x-ray topography.
Donor binding energy and thermally activated persistent photoconductivity in high mobility (001) AlAs quantum wells
Authors: Dasgupta S. , Knaak C. , Moser J. , Bichler M. , Roth S. F. , Fontcuberta i Morral A. , Abstreiter G. , Grayson M.
Published: October 2007

A doping series of AlAs (001) quantum wells with Si δ-modulation doping on both sides reveals different dark and postillumination saturation densities, as well as temperature dependent photoconductivity. The lower dark two-dimensional electron density saturation is explained assuming deep binding energy of ΔDK=65.2meV for Si donors in the dark. Persistent photoconductivity (PPC) is observed upon illumination, with higher saturation density indicating shallow postillumination donor binding energy. The photoconductivity is thermally activated, with 4K illumination requiring postillumination annealing to T=30K to saturate the PPC. Dark and postillumination doping efficiencies are reported.
Locally resolved ferromagnetic resonance in Co stripes
Authors: Meckenstock Ralf , Barsukov I. , Posth O. , Lindner J. , Butko A. , Spoddig D.
Published: October 2007

Microwave excitations of Co stripes of 100×1.5×0.025μm3 were investigated by angular dependent ferromagnetic resonance (FMR) and by locally resolved scanning thermal microscopy based (SThM) FMR, offering a lateral resolution of <100nm and a sensitivity of 106 spins. Besides the uniform excitation, backward volume modes and a rim resonance were identified by SThM-FMR imaging. Micromagnetic simulations (OOMMF) confirm the experimentally observed lateral confinement of these modes. The magnetic parameters of the Co stripes correspond to the ones of Co bulk with a surface anisotropy Ks=0.5mJ∕m2.
Controlled, perfect ordering in ultrathin anodic aluminum oxide templates on silicon
Authors: Robinson Adam P. , Burnell Gavin , Hu Mingzhe , MacManus-Driscoll Judith L.
Published: October 2007

Ultrathin, perfectly ordered anodic aluminum oxide templates have been produced on supporting substrates by focused ion beam prepatterning. This fast, flexible approach produces pore arrays with both hexagonal and square geometries and allows control over the pore pitch and diameter. The orientation of ordering can be controlled with nanometer precision. Pattern transfer into Si produces pore densities of up to 1011in.−2.
Microfabricated high-throughput electronic particle detector
Authors: Wood D. K. , Requa M. V. , Cleland A. N.
Published: October 2007

We describe the design, fabrication, and use of a radio frequency reflectometer integrated with a microfluidic system, applied to the very high-throughput measurement of micron-scale particles, passing in a microfluidic channel through the sensor region. The device operates as a microfabricated Coulter counter [U.S. Patent No. 2656508 (1953)], similar to a design we have described previously, but here with significantly improved electrode geometry as well as including electronic tuning of the reflectometer; the two improvements yielding an improvement by more than a factor of 10 in the signal to noise and in the diametric discrimination of single particles. We demonstrate the high-throughput discrimination of polystyrene beads with diameters in the 4–10μm range, achieving diametric resolutions comparable to the intrinsic spread of diameters in the bead distribution, at rates in excess of 15×106beads∕h.
In situ integration of freestanding zinc oxide nanorods using copper silicide nanobeams
Authors: Kumar Nitin , Parajuli Omkar , Hahm Jong-in
Published: October 2007

In this letter, we describe an in situ integration method to produce freestanding zinc oxide nanorods (ZnO NRs) on copper silicide nanobeams (Cu3Si NBs). The integration of ZnO NRs with Cu3Si NBs is straightforwardly achieved immediately after ZnO NR synthesis by exploiting self-assembled Cu3Si NBs as catalysts. The resulting ZnO NRs on Cu3Si NBs exhibit atomic defect-free structures with superb optical quality which, in turn, can be beneficial when applied in micro- and nanoelectromechanical systems.
Bridged ZnO nanowires across trenched electrodes
Authors: Gao Pu-Xian , Liu Jin , Buchine Brent A. , Weintraub Benjamin , Wang Z. L. , Lee J. L.
Published: October 2007

Using a hydrothermal synthesis approach, large scale and laterally bridged nanowires have been grown across trenched Au∕Si, Au∕SiO2∕Si, and ZnO∕Si electrodes. This technique shows a low temperature (80°C) approach for growing ZnO nanowires on a prepatterned substrate, showing its potential for integrating with silicon based technology. The I-V characteristics of the nanowires have been measured and their nonlinear behavior has been analyzed. It is suggested that the nonlinear behavior might be due to the dominant phonon scattering and the impurity involved grain boundaries in the multinanowire bridges. The bridged nanowire arrays could be useful for fabricating gas, chemical, or biochemical nanosensor arrays.
Defects in interfacial layers and their role in the growth of ZnO nanorods by metallorganic chemical vapor deposition
Authors: Park Dong Jun , Lee Jeong Yong , Kim Dong Chan , Mohanta Sanjay Kumar , Cho Hyung Koun
Published: October 2007

We report the evolution of ZnO nanorods by metalorganic chemical vapor deposition on sapphire substrates and an investigation of their microstructure. Well-aligned ZnO nanorods with a high aspect ratio were grown on an interfacial layer with several types of defects at a lower reactor pressure. Planar defects such as stacking mismatch boundaries and inversion domain boundaries were formed in the interfacial layer during the coalescence of the islands, and finally constituted the side facets of the nanorods. Based on the microstructural changes and origin of the defects in the interfacial layers, we propose a model to explain the growth evolution of ZnO nanorods on sapphire substrates.