bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of a novel phase-decoupling permanent magnet brushless ac motor
Authors: Cui Wei , Chau K. T. , Jiang J. Z. , Fan Ying
Published: May 2005

This paper presents a phase-decoupling permanent magnet brushless ac motor which can offer better controllability, faster response, and smoother torque than its counterparts. The key is due to its different motor configuration and simple scalar control. The motor configuration is so unique that it inherently offers the features of phase decoupling, flux focusing, and flux shaping, hence achieving independent phase control, fast response, and smooth torque. The scalar control is fundamentally different from the complicated vector control. It can achieve direct torque control through independent control of the phase currents. The proposed motor is prototyped and experimentally verified.
Monodispersed Fe–Pt nanoparticles for biomedical applications
Authors: Kim Do Kyung , Kan Ding , Veres Teodor , Normadin Francois , Liao James K. , Kim Hyung Hwan , Lee Se-Hee , Zahn Markus , Muhammed Mamoun
Published: May 2005

Monodispersed Fe–Pt nanoparticles are promising candidates for biomedical applications with an average particle diameter of 6.9nmFe48Pt52, 3.3nmFe52Pt48, and 4.2nmFe70Pt30. They are prepared by simultaneous chemical reduction of Pt(acac)2 and thermal decomposition of Fe(CO)5 in the presence of surfactant as an anti-oxidation reagent and amine as a stabilizer. The blocking temperatures, Tb, of 9 K for Fe70Pt30, 11 K for Fe52Pt48 and 14.4 K for Fe48Pt52 and the mean diameter of the spherical magnetic particles were estimated from the calculated volume to be 3.6, 3.1, and 3.8 nm. The cytotoxicity of unmodified Fe–Pt nanoparticles was performed in brain endothelial cells. Fe48Pt52 nanoparticles were not found to have any significant toxicity on bEnd3 cells during a 24 h period.
Genetic algorithm based design optimization of a permanent magnet brushless dc motor
Authors: Upadhyay P. R. , Rajagopal K. R.
Published: May 2005

Genetic algorithm (GA) based design optimization of a permanent magnet brushless dc motor is presented in this paper. A 70 W, 350 rpm, ceiling fan motor with radial-filed configuration is designed by considering the efficiency as the objective function. Temperature-rise and motor weight are the constraints and the slot electric loading, magnet-fraction, slot-fraction, airgap, and airgap flux density are the design variables. The efficiency and the phase-inductance of the motor designed using the developed CAD program are improved by using the GA based optimization technique; from 84.75% and 5.55 mH to 86.06% and 2.4 mH, respectively.
Preparation of medical magnetic nanobeads with ferrite particles encapsulated in a polyglycidyl methacrylate (GMA) for bioscreening
Authors: Nishibiraki H. , Kuroda C. S. , Maeda M. , Matsushita N. , Abe M. , Handa H.
Published: May 2005

Ferrite nanoparticles (an intermediate between Fe3O4 and γ-Fe2O3), ∼7nm in diameter, were embedded in beads of a mixed polymer of styrene (St) and glycidyl methacrylate (GMA) by emulsifier-free emulsion polymerization method. The beads were coated with GMA by a seeded polymerization method in order to suppress nonspecific protein binding on the surfaces; GMA exhibits very low nonspecific protein binding, which is required for carriers used for bioscreening. The beads have diameters of 180±50nm and saturation magnetizations of 28emu∕g, exceeding commercially available polymer-coated beads of micron size having a weaker saturation magnetization (∼12emu∕g).
Low-frequency noise measurements on commercial magnetoresistive magnetic field sensors
Authors: Stutzke Nathan A. , Russek Stephen E. , Pappas David P. , Tondra Mark
Published: May 2005

Low-frequency noise was measured in the frequency range from 0.1Hzto10kHz on a variety of commercially available magnetic sensors. The types of sensors investigated include anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR) effect devices. The 1∕f noise components of electronic and magnetic origin are identified by measuring sensor noise and sensitivity at various applied magnetic fields. Commercial magnetometers typically consist of four elements in a Wheatstone bridge configuration and are biased with either a constant voltage or current. Voltage fluctuations at the sensor output are amplified by a pair of battery powered low-noise preamplifiers and input to a spectrum analyzer. A two-channel cross-correlation technique is used when the performance of a single preamplifier is not sufficient. For the AMR and GMR sensors investigated, both electronic and magnetic components contribute to the overall sensor noise. Maximum noise occurs at the bias field which gives maximum sensitivity. The noise of TMR based sensors is primarily due to resistance fluctuations in the tunnel barrier, having little to no field dependence. The best low-field detectivity of the sensors that have been measured is on the order of 100pT∕Hz0.5 at 1Hz.
Development of Hi-Fi microspeakers with a woofer and a tweeter used for mobile phones
Authors: Hwang Sang-Moon , Lee Hong-Joo , Kim Ji-Hoon , Kwon Joong-Hak , Hong Kuem-Shik , Hwang Gun-Yong
Published: May 2005

For mobile phones, high performance microspeakers with broader frequency range are essential parts to realize various multimedia functions such as MP3 playback, speaker phones, and 64 poly-harmonic melody. Noting that the operating frequency range of conventional microspeakers ranges from 900Hzto10kHz, that of 400Hzto10kHz for hi-fi microspeakers is required to meet customer demand in a multimedia era. One possible way of achieving this is to integrate two-way microspeakers (woofer and tweeter) within one device sharing not only magnetic circuit but also vibration space. Noting that the characteristics of the microspeakers are a coupled phenomenon of electromagnetic, mechanical and acoustic system, a systematic analysis must be implemented to fully consider the coupling effects. In this article, a hi-fi microspeaker with a woofer and a tweeter is introduced and the sound pressure level is also calculated and compared with the experimental results. Results show the development can be a successful alternative for the high performance microspeakers of a multimedia era.
Magnetic field induced helical structure in freestanding metal silicate tubes
Authors: Yokoi Hiroyuki , Kuroda Noritaka , Kakudate Yozo
Published: May 2005

Helical structure on freestanding metal silicate membrane tubes induced by a magnetic field is reported. The phenomenon is observed for iron silicate tubes and cobalt silicate tubes grown under a horizontal field of 2.2T and a field gradient of 20.5T∕m at the room temperature in contrast to nonregular structure observed at the zero field. Direction control of helicity is achieved by changing the field gradient direction with respect to the field direction. The results are explained in terms of the magnetohydrodynamics effect on the flow of anion discharged from a metal salt solution at the growing end of the silicate tube.
An effect of dewetting of lubricated surfaces on friction and wear properties
Authors: Kawaguchi Masahiro , Yagi Kazuyuki , Kato Takahisa
Published: May 2005

To meet the demand of increased storage density for magnetic data storage, stronger and thinner lubricant films for head disk interface in hard disk drives is desired. It is reported that perfluoropolyether lubricant with polar end groups is dewetted and brings about the flying instability of a magnetic head. In this report the effects of dewetting phenomenon on friction and wear properties are studied. Observations of lubricant film by optical microscopy and friction tests were carried out. The observation showed the lubricated surface became dewetted with time and lubricant droplets were formed. The dewetted area increased with time as shown in the figure and, at the same time, the number of droplets decreased. These results suggest the growth of droplets. From the results of friction tests, it was found that the friction coefficient increased and the lifetime reduced with the growth of droplets. The reason for this will be discussed in this research.
Vibrational excitation and relaxation of five polyatomic molecules in an electrical discharge
Authors: Sanz M. Eugenia , McCarthy Michael C. , Thaddeus Patrick
Published: May 2005

Vibrational excitation and relaxation of five linear polyatomic molecules, OCS, OC3S, HC3N, HC5N, and SiC2S, have been studied by Fourier transform microwave spectroscopy in a supersonic expansion after the application of a low-current dc electric discharge. For each chain, the populations in bending and stretching modes have been characterized as a function of the applied discharge current; for stable OCS and HC3N, vibrational populations were studied as well in the absence of a discharge. With no discharge present the derived vibrational temperatures are slightly below T, the temperature of the gas before the supersonic expansion (i.e., 300K). In the presence of the discharge, vibrational excitation occurs via inelastic collisions with the electrons and the vibrational temperatures rise as the applied current increases. Global vibrational relaxation is governed by rapid vibration–vibration (VV) energy transfer and slow vibration–translation (VT) energy transfer. The latter process is rate-determining and depends primarily on the wave number of the vibration. Vibrational modes with wave numbers near and below kT∕hc (where T=300K and kT∕hc∼210cm−1) are efficiently cooled by VT transfer because a sufficient number of collisions occur in the initial stages of the supersonic expansion. Vibrational modes with wave numbers around 450cm−1 appear to be inefficiently cooled in the molecular beam; at these energies VV and VT rates are probably comparable. For high-frequency vibrations, VV energy transfer dominates. For the longer chains OC3S and HC5N, higher-lying modes are generally not detectable and vibrational temperatures of most lower-lying modes were found to be lower than those of OCS and HC3N, suggesting that as the size of the molecules increases, intermode VV transfer becomes more efficient, plausibly due to the higher density of vibrational levels. New high resolution spectroscopic data have been obtained for several vibrationally excited states of OC3S, HC3N, and HC5N. Rotational lines of the C13 and N15 isotopic species of HC5N have been measured, yielding improved rotational and centrifugal distortion constants; N14 nitrogen quadrupole coupling constants for the isotopic species of HC5N with C13 have been determined for the first time.
Adsorption of acetic acid on ice: Experiments and molecular dynamics simulations
Authors: Picaud S. , Hoang P. N. M. , Peybernès N. , Le Calvé S. , Mirabel Ph.
Published: May 2005

Adsorption study of acetic acid on ice surfaces was performed by combining experimental and theoretical approaches. The experiments were conducted between 193 and 223K using a coated wall flow tube coupled to a mass spectrometric detection. Under our experimental conditions, acetic acid was mainly dimerized in the gas phase. The surface coverage increases with decreasing temperature and with increasing concentrations of acetic acid dimers. The obtained experimental surface coverages were fitted according to the BET theory in order to determine the enthalpy of adsorption ΔHads and the mololayer capacity NM(dimers) of the acetic acid dimers on ice: ΔHads=(−33.5±4.2)kJmol−1, NM(dimers)=(1.27±0.25)×1014dimerscm−2. The adsorption characteristics of acetic acid on an ideal ice In(0001) surface were also studied by means of classical molecular dynamics simulations in the same temperature range. The monolayer capacity, the configurations of the molecules in their adsorption sites, and the corresponding adsorption energies have been determined for both acetic acid monomers and dimers, and compared to the corresponding data obtained from the experiments. In addition, the theoretical results show that the interaction with the ice surface could be strong enough to break the acetic acid dimers that exist in the gas phase and leads to the stabilization of acetic acid monomers on ice.
Femtosecond time resolved coherent anti-Stokes Raman spectroscopy: Experiment and modelization of speed memory effects on H2–N2 mixtures in the collision regime
Authors: Tran H. , Joubert P. , Bonamy L. , Lavorel B. , Renard V. , Chaussard F. , Faucher O. , Sinardet B.
Published: May 2005

With the aim of temperature diagnostic, femtosecond time-resolved CARS (coherent anti-Stokes Raman spectroscopy) is applied to probe H2 in H2–N2 mixtures. In a first part, a Lorentzian profile is used to model the femtosecond CARS response. A difference between the experimental broadening and the expected one is observed in the collision regime. The observed broadening increases strongly in an inhomogeneous way with respect to the perturber concentration. This is of considerable importance for temperature measurements. In a second part, we show that in the collision regime, this inhomogeneous broadening is due to the speed dependence of the collisional parameters and the memory effects of the radiator speed. A new modelization of the time-resolved CARS response taking into account the speed memory effects is presented and applied to the temperature diagnostic in H2–N2 mixtures. The numerical results are in good agreement with experiments.
(e, 2e) electron momentum spectrometer with high sensitivity and high resolution
Authors: Ren X. G. , Ning C. G. , Deng J. K. , Zhang S. F. , Su G. L. , Huang F. , Li G. Q.
Published: May 2005

A high sensitivity and high resolution (e, 2e) electron momentum spectrometer with simultaneous detection in energy and momentum are constructed. The design and performance of the spectrometer are reported. The orbital electron density distributions are obtained accurately and rapidly by using this spectrometer equipped with a double toroidal analyzer. The experimental results on argon and helium exhibit the significant improvements in coincidence count rates, resolution, sensitivity and obtainment of a wide range of adjustable experimental impact energies, which are crucial for further electron momentum spectroscopy studying electronic structure and electron correlation in complex systems.
Ab initio calculations of triplet excited states and potential-energy surfaces of vinyl chloride: Insights into spectroscopy and photodissociation dynamics
Authors: Chang Jia-Lin
Published: May 2005

The equilibrium geometries and harmonic vibrational frequencies of three low-lying triplet excited states of vinyl chloride have been calculated using the state-averaged complete active space self-consistent field (CASSCF) method with the 6-311++G(d,p) basis set and an active space of four electrons distributed in 13 orbitals. Both adiabatic and vertical excitation energies have been obtained using the state-averaged CASSCF and the multireference configuration-interaction methods. The potential-energy surfaces of six low-lying singlet states have also been calculated. While the (π,π*)3 state has a nonplanar equilibrium structure, the (π,3s)3 and (π,σ*)3 states are planar. The calculated vertical excitation energy of the (π,π*)3 state is in agreement with the experiment. The singlet excited states are found to be multiconfigurational, in particular, the first excited state is of (π,3s) character at the planar equilibrium structure, of (π,σ*) as the C–Cl bond elongates, and of (π,π*) for highly twisted geometries. Avoided crossings are observed between the potential-energy surfaces of the first three singlet excited states. The absorption spectra of vinyl chloride at 5.5–6.5 eV can be unambiguously assigned to the transitions from the ground state to the first singlet excited state. The dissociation of Cl atoms following 193-nm excitation is concluded to take place via two pathways: one is through (π,σ*) at planar or nearly planar structures leading to fast Cl atoms and the other through (π,π*) at twisted geometries from which internal conversion to the ground state and subsequent dissociation produces slow Cl atoms.
A localized molecular-orbital assembler approach for Hartree–Fock calculations of large molecules
Authors: Li Wei , Li Shuhua
Published: May 2005

We describe an alternative fragment-based method, the localized molecular-orbital assembler method, for Hartree–Fock (HF) calculations of macromolecules. In this approach, a large molecule is divided into many small-size fragments, each of which is capped by its local surroundings. Then the conventional HF calculations are preformed on these capped fragments (or subsystems) and the canonical molecular orbitals of these systems are transferred into localized molecular orbitals (LMOs). By assembling the LMOs of these subsystems into a set of LMOs of the target molecule, the total density matrix of the target molecule is constructed and correspondingly the HF energy or other molecular properties can be approximately computed. This approach computationally achieves linear scaling even for medium-sized systems. Our test calculations with double-zeta and polarized double-zeta basis sets demonstrate that the present approach is able to reproduce the conventional HF energies within a few millihartrees for a broad range of molecules.
A laser spectroscopic study of the X̃Πg2,ÃΠu2, and B̃Σu+2 states of BS2: Renner–Teller, spin-orbit, and K-resonance effects
Authors: He Sheng-Gui , Clouthier Dennis J. , Adam Allan G. , Tokaryk Dennis W.
Published: May 2005

The lowest-lying vibronic levels of the X̃,Ã, and B̃ states of BS2 have been investigated at high resolution using a combination of room-temperature absorption and supersonic jet data. In both cases, the BS2 radical was prepared in an electric discharge using a precursor gas mixture of BCl3,CS2, and either helium or argon. Extensive absorption spectra were obtained for the 000 and 211 bands of the ÃΠu2-X̃Πg2 electronic transition in the visible. The Ã-X̃211 and B̃Σu+2-X̃Πg2211 bands of jet-cooled BS2 were also studied with laser-induced fluorescence techniques. By fitting the 000 bands of both electronic transitions simultaneously, we were able to precisely determine the spin-orbit splittings in both the Ã and X̃ states. Similarly, the 211 bands were fitted in a merged analysis in order to determine the relative separations of the vibronic components of the ground and first excited state bending levels as accurately as possible. Due to a large spin-orbit splitting and small Renner–Teller interaction, the Ã state bending level shows small but definite K-resonance effects, which were fitted using a full matrix for the four components of v2′=1. The resulting parameters were used along with previously published data to refine the Renner–Teller analyses in both the ÃΠu2 and X̃Πg2 electronic states. Where possible, the fitted constants and observed boron isotope splittings have been shown to be in accord with theoretical estimates of their sign and magnitude.
Theoretical study of transition state structure and reaction enthalpy of the F+H2→HF+H reaction by a diffusion quantum Monte Carlo approach
Authors: Lu Shih-I
Published: May 2005

Ab initio calculations of transition state structure and reaction enthalpy of the F+H2→HF+H reaction has been carried out by the fixed-node diffusion quantum Monte Carlo method in this study. The Monte Carlo sampling is based on the Ornstein–Uhlenbeck random walks guided by a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculated barrier height of 1.09(16)kcal∕mol is consistent with the experimental values, 0.86(10)∕1.18(10)kcal∕mol, and the calculated value from the multireference-type coupled-cluster (MRCC) calculation with the aug-cc-pVQZ(F)/cc-pVQZ(H) basis set, 1.11kcal∕mol. The Monte Carlo-based calculation also gives a similar value of the reaction enthalpy, −32.00(4)kcal∕mol, compared with the experimental value, −32.06(17)kcal∕mol, and the calculated value from a MRCC/aug-cc-pVQZ(F)/cc-pVQZ(H) calculation, −31.94kcal∕mol. This study clearly indicates a further application of the random-walk-based approach in the field of quantum chemical calculation.
Influence of external vibration on tether chain in ligand-receptor binding
Authors: Xue Bin , Wang Wei
Published: May 2005

The tethered ligand-receptor binding is an important biological phenomenon. The conformation of tether chain greatly affects the binding process. By using molecular dynamics, the influence of environmental vibration on the conformation of the tether chain is studied. The phase diagram shows that the radius of gyration of the tether chain becomes large when there is vibration due to the vibrational disturbance. However, when the vibration frequency is high enough, the average value of radius of gyration will reduce. Under high frequency vibration, the chain has an inerratic variation on its radius of gyration. These properties provide the frequency modulation on the dimension of the chain. The scaling relation proves the dimension of chain increases faster under low frequency vibration. There are also weak resonance and stochastic-resonance-like behaviors in the chain system. These behaviors probably have biological importance.
A cooperative phenomenon between polymer chain and supercritical solvent: Remarkable expansions of solvophobic and solvophilic polymers
Authors: Sumi Tomonari , Sekino Hideo
Published: May 2005

We propose a simulation method for infinitely dilute polymer solutions. In this method, an effective Hamiltonian of the solvated polymer chain is introduced to eliminate the degree of freedom of the solvent particle. The effective Hamiltonian is coupled with the density-functional theory (DFT) that we have developed for a polymer-solvent pair correlation function. All the equations proposed in this paper are derived from the first principle. This simulation method was applied to polymer chains in supercritical solvents. We observed anomalous behaviors of polymer chains near the liquid-vapor critical point: both solvophilic and solvophobic polymers expand significantly near the critical point; this is in contrast to the behavior of polymer chains in vacuum. This expansion can be interpreted as a cooperative phenomenon, which enhances the large long-wavelength density fluctuation of the solvent.
High-throughput screening with micro-x-ray fluorescence
Authors: Havrilla George J. , Miller Thomasin C.
Published: May 2005

Micro-x-ray fluorescence (MXRF) is a useful characterization tool for high-throughput screening of combinatorial libraries. Due to the increasing threat of use of chemical warfare (CW) agents both in military actions and against civilians by terrorist extremists, there is a strong push to improve existing methods and develop means for the detection of a broad spectrum of CW agents in a minimal amount of time to increase national security. This paper describes a combinatorial high-throughput screening technique for CW receptor discovery to aid in sensor development. MXRF can screen materials for elemental composition at the mesoscale level (tens to hundreds of micrometers). The key aspect of this work is the use of commercial MXRF instrumentation coupled with the inherent heteroatom elements within the target molecules of the combinatorial reaction to provide rapid and specific identification of lead species. The method is demonstrated by screening an 11-mer oligopeptide library for selective binding of the degradation products of the nerve agent VX. The identified oligopeptides can be used as selective molecular receptors for sensor development. The MXRF screening method is nondestructive, requires minimal sample preparation or special tags for analysis, and the screening time depends on the desired sensitivity.
Using open-source software technologies and standardized data structures to build advanced applications for high-throughput experimentation environments
Authors: Zech Torsten , Sundermann Andreas , Födisch Ringo , Saupe Michael
Published: May 2005

Herein we present a modular approach to a high-throughput experimentation software environment. Instead of a monolithic master system, small tools with a limited set of tasks are interconnected using standardized, self-descriptive data structures. This approach is highly flexible with respect to the rapidly changing needs of the scientists: Since the modules are isolated and intermodule communication is standardized, new components can be integrated without side effects. The developed software environment follows to a large extent the UNIX design philosophy and is heavily based on open-source software technologies that are used to solve specific tasks within the overall system to achieve high productivity in using the software for ambitious high-throughput experimentation programs. It is shown that the orchestration of the system significantly benefits from clear and standardized interface design based on hteML, the high-throughput experimentation markup language, an XML language for the description of high-throughput experimentation data and processes.
Combinatorial microelectrochemistry: Development and evaluation of an electrochemical robotic system
Authors: Erichsen Thomas , Reiter Sabine , Ryabova Victoria , Bonsen Eva Maria , Schuhmann Wolfgang , Märkle Wolfgang , Tittel Carsten , Jung Günther , Speiser Bernd
Published: May 2005

An electrochemical robotic system using standard microtiter plates as reaction wells for potentiostatic and galvanostatic electrosynthesis and high-throughput electroanalysis was conceived and realized using stepmotor driven positioning stages in combination with a flexible software. Electrode bundles specifically adapted to the experimental needs are accurately positioned in the wells of a microtiter plate followed by the automatic performance of sequences of electrosynthetic or electroanalytical techniques. The system allows us to work under inert-gas atmosphere, in aqueous and organic solvents, and to add or remove solutions by means of integrated syringe pumps. A specifically developed script language permits the user to perform very complex experimental sequences in the different wells of the microtiter plate. The hardware and software features of the developed electrochemical robotic system, the design of suitable electrode arrangements for electrosynthesis and electroanalytical techniques, as well as the reproducibility in aqueous and organic electrolytes are described. The performance of the system is demonstrated by redox screening of a Ru-complex library and by electrosynthesis with in situ analysis of a compound library.
Bose–Einstein condensate and spontaneous breaking of conformal symmetry on Killing horizons
Authors: Moretti Valter , Pinamonti Nicola
Published: May 2005

Local scalar quantum field theory (in Weyl algebraic approach) is constructed on degenerate semi-Riemannian manifolds corresponding to Killing horizons in spacetime. Covariance properties of the C*-algebra of observables with respect to the conformal group PSL(2,R) are studied. It is shown that, in addition to the state studied by Guido, Longo, Roberts, and Verch for bifurcated Killing horizons, which is conformally invariant and KMS at Hawking temperature with respect to the Killing flow and defines a conformal net of von Neumann algebras, there is a further wide class of algebraic (coherent) states representing spontaneous breaking of PSL(2,R) symmetry. This class is labeled by functions in a suitable Hilbert space and their GNS representations enjoy remarkable properties. The states are nonequivalent extremal KMS states at Hawking temperature with respect to the residual one-parameter subgroup of PSL(2,R) associated with the Killing flow. The KMS property is valid for the two local subalgebras of observables uniquely determined by covariance and invariance under the residual symmetry unitarily represented. These algebras rely on the physical region of the manifold corresponding to a Killing horizon cleaned up by removing the unphysical points at infinity [necessary to describe the whole PSL(2,R) action]. Each of the found states can be interpreted as a different thermodynamic phase, containing Bose–Einstein condensate, for the considered quantum field. It is finally suggested that the found states could describe different black holes.
Precision laboratory apparatus for high temperature compression molding of glass lenses
Authors: Firestone Gregory C. , Jain Anurag , Yi Allen Y.
Published: May 2005

Recently, compression molding of glass aspherical lenses has become a viable manufacturing process for precision optical devices. In this research, an apparatus designed for precision compression molding of glass optics was constructed. The apparatus design was governed by two primary goals: molding process control and property measurement of common optical glasses such as BK 7, SK5, and soda lime glass. Equipped with high precision components, a closed loop feedback control and a unique force adaptive scheme, the apparatus was successfully used for glass property measurement tests. Moreover, the performance of the apparatus was also validated using selected microlens molding experiments.
Dispersive x-ray absorption spectroscopy with gratings above 2 keV
Authors: Heimann Philip A. , Koike Masato , Padmore Howard A.
Published: May 2005

Laminar gratings can be used to perform x-ray absorption measurements dispersively in energy, thereby making an efficient use of the available x-ray intensity. To examine the performance of a laminar grating in diffracting short wavelength x rays, efficiency measurements of a 600l∕mm grating were performed over the photon energy range from 3 to 8 keV. A peak efficiency of 5.8% was observed without surface normal rotation (SNR); with a SNR of 60° a maximum efficiency of 14.1% was measured. The measured grating efficiencies are in good qualitative agreement with values calculated by a code based on the Neviere theory. By considering both the peak efficiency and the diffracted bandwidth, a gain of 97 is obtained for the 600l∕mm grating with a SNR of 60° in comparison with a germanium (111) crystal. Sufficient energy resolution for extended x-ray absorption fine structure experiments can be achieved by a grating at short wavelengths.
Variable temperature, relative humidity (0%–100%), and liquid neutron reflectometry sample cell suitable for polymeric and biomimetic materials
Authors: Harroun T. A. , Fritzsche H. , Watson M. J. , Yager K. G. , Tanchak O. M. , Barrett C. J. , Katsaras J.
Published: May 2005

We describe a variable temperature, relative humidity (0%–100% RH), and bulk liquid neutron reflectometry sample cell suitable for the study of polymeric and biomimetic materials (e.g., lipid bilayers). Compared to previous reflectometry cells, one of the advantages of the present sample environment is that it can accommodate ovens capable of handling either vapor or bulk liquid hydration media. Moreover, the design of the sample cell is such that temperature gradients are minimal over a large area (∼80cm2) allowing for the nontrivial 100% RH condition to be attained. This permits the study, by neutron reflectometry, of samples that are intrinsically unstable in bulk water conditions, and is demonstrated by the lamellar repeat spacing of lipid bilayers at 100% RH being indistinguishable from those same bilayers hydrated in liquid water.
Applicability of the electrical low pressure impactor to size determination of aerosols attached to radon decay products
Authors: Yamada Yuji , Tokonami Shinji , Yamasaki Keizo
Published: May 2005

Aerosol size information is very important for the risk estimation of radon exposure. Recently, a cascade impactor called the electrical low pressure impactor (ELPI) was developed and commercialized. The impactor, which covers a wide diameter range from 0.03to10μm, gives number-weighted size distribution in real time by an electrical detection method. Prior to size measurements of the radon decay products being available, the effects of impaction substrates on size classification were studied. Tested substrate materials were stainless steel plate and aluminum foil, and those surfaces were as follows: (1) untreated, (2) covered with double sided adhesive tape, and (3) silicon grease coated. A large difference was observed among the measured size distributions. Compared with other sizing methods, it was found that the use of grease coated substrates did not interfere with the electrical measurements in the ELPI and also prevented particle rebound or redispersion. It was also confirmed that the coatings caused no damage to energy spectrum analysis in spite of the weak penetration power of radon’s alpha ray. Using the ELPI allows size distribution data on aerosol number and activity to be independently determined for the same impactor sample. The ELPI will be useful for the size determination of radon decay products, and thus information on the attachment of radon decay products will be forthcoming.
Picoliter droplets for spinless photoresist deposition
Authors: Demirci Utkan
Published: May 2005

In this article, we present an acoustically actuated two-dimensional (2D) micromachined ejector array for a zero waste and spinless droplet-by-droplet photoresist deposition method. The theory of operation, the experimental results obtained with acoustic focused 2D micromachined microdroplet ejector array is demonstrated. The ejector operation at 34.7MHz and generation of 21μm diam photoresist solvent droplets in drop-on-demand and continuous modes of operation are demonstrated. Photoresist droplets are ejected onto a wafer surface by this acoustic ejector array. Photoresist droplets are ejected on drop on demand and interact with each other by surface tension forces to generate photoresist coverage on the wafer surface during photoresist deposition by droplet generation. By overlapping ejected photoresist droplets, formation of a uniform thickness, line coverage is achieved. Multiple photoresist lines are printed simultaneously by a 3×3 ejector array. By overlapping photoresist lines, coverage of a 4in. silicon wafer with photoresist is achieved.
Room-temperature semiconductor gas sensor based on nonstoichiometric tungsten oxide nanorod film
Authors: Kim Yong Shin , Ha Seung-Chul , Kim Kyuwon , Yang Haesik , Choi Sung-Yool , Kim Youn Tae , Park Joon T. , Lee Chang Hoon , Choi Jiyoung , Paek Jungsun , Lee Kwangyeol
Published: May 2005

Porous tungsten oxide films were deposited onto a sensor substrate with a Si bulk-micromachined hotplate, by drop-coating isopropyl alcohol solution of highly crystalline tungsten oxide (WO2.72) nanorods with average 75nm length and 4nm diameter. The temperature-dependent gas sensing characteristics of the films have been investigated over the mild temperature range from 20to250°C. While the sensing responses for ammonia vapor showed increase in electrical conductivity at temperatures above 150°C as expected for n-type metal oxide sensors, they exhibited the opposite behavior of unusual conductivity decrease below 100°C. Superb sensing ability of the sensors at room temperature in conjunction with their anomalous conductivity behavior might be attributed to unique nanostructural features of very thin, nonstoichiometric WO2.72.
Substrate-dependent electronic properties of an armchair carbon nanotube adsorbed on H∕Si(001)
Authors: Miwa R. H. , Orellana W. , Fazzio A.
Published: May 2005

The adsorption of an armchair single-walled carbon nanotube (CNT) on fully and partially hydrogenated Si(001) surfaces are studied from first-principles calculations. Our results indicate that the electronic properties of the adsorbed CNT can be ruled by the H concentration along the CNT–H∕Si(001) contact region. On the fully hydrogenated Si(001), the CNT is physisorbed, preserving almost unchanged its metallic character. Removing a few of H atoms along the adsorption site, we find an enhancement on the CNT metallic character. In contrast, removing all the H atoms along the adsorption site, the adsorbed CNT becomes a semiconductor, exhibiting an energy gap. These results suggest that armchair CNTs adsorbed on H∕Si(001) could be transformed into metal–semiconductor junctions by grading the H concentration along the CNT–surface interface.
Magnetized/charged MgH2-based hydrogen storage materials
Authors: Tsuda Muneyuki , Diño Wilson Agerico , Kasai Hideaki , Nakanishi Hiroshi
Published: May 2005

We propose two methods to facilitate the Mg–H bond cleavage of magnesium hydride MgH2. We found via density functional calculations that Mn (or Fe), when inserted between two MgH2, exhibits a much higher catalytic activity than the other 3d transition metal elements because of the induced spin polarization of the MgH2. We also found that an ionized MgH2 (MgH2+) has considerably softer Mg–H bonds. We can thus significantly reduce the H2 desorption temperatures from MgH2 to practical levels, ∼400K, by forming an alloy hydride with Mn (or Fe), and/or ionizing the MgH2.
Effects of oxygen radicals in low-pressure surface-wave plasma on sterilization
Authors: Nagatsu Masaaki , Terashita Fumie , Nonaka Hiroyuki , Xu Lei , Nagata Toshi , Koide Yukio
Published: May 2005

The effects of oxygen radicals on sterilization were studied using a 2.45GHz surface-wave oxygen plasma. A population of 1.5×106 Bacillus stearothermophilus spores was irradiated for 3min or more with oxygen plasma, generated at pressures between 6 and 14Pa. The decimal reduction value (D value), a measure of the effectiveness of sterilization, was determined to be about 15–25s. Using only oxygen radicals, excluding all charged particles, the 1.5×106 spores were sterilized with a D value of 30–45s after 5min or more of irradiation. On scanning electron microscopy, the length and width of the spores changed significantly due to chemical etching by oxygen radicals.
Initial stages of silicon anodization in the transition regime: Nanoparticle formation
Authors: Nychyporuk T. , Lysenko V. , Gautier B. , Barbier D.
Published: May 2005

Controlled formation of a monolayer of separated Si nanoparticles at the surface of a Si wafer using extremely short monopulsed anodization in the transition regime is reported. The initial stages of the dynamics of formation of the nanoparticles are described in detail by using atomic force microscopy. Structural analysis of the height, diameter, and surface density of the nanoparticles with respect to anodization current density and anodization time has been performed.
Characterization and properties of green-emitting β-SiAlON:Eu2+ powder phosphors for white light-emitting diodes
Authors: Hirosaki Naoto , Xie Rong-Jun , Kimoto Koji , Sekiguchi Takashi , Yamamoto Yoshinobu , Suehiro Takayuki , Mitomo Mamoru
Published: May 2005

This letter reports a β-SiAlON:Eu2+ green phosphor with the composition of Eu0.00296Si0.41395Al0.01334O0.0044N0.56528. The phosphor powder exhibits a rod-like morphology with the length of ∼4μm and the diameter of ∼0.5μm. It can be excited efficiently over a broad spectral range between 280 and 480 nm, and has an emission peak at 535 nm with a full width at half maximum of 55 nm. It has a superior color chromaticity of x=0.32 and y=0.64. The internal and external quantum efficiencies of this phosphor is 70% and 61% at λex=303nm, respectively. This newly developed green phosphor has potential applications in phosphor-converted white LEDs.
Variable-focus liquid lens by changing aperture
Authors: Ren Hongwen , Wu Shin-Tson
Published: May 2005

We propose an adaptive liquid-filled lens, which consists of an elastic membrane, a solid plate, and an annular sealing ring; a liquid with a fixed volume stored in lens chamber. The key part is the annular sealing ring which looks like an iris diaphragm. The surfaces of annular sealing ring are sealed with an elastic membrane. The radius of the annular sealing ring is changeable. By tuning the radius of the annular sealing ring, the stored liquid in the lens will be redistributed, thus changing the curvature of the elastic membrane. Therefore, the lens cell causes light to converge or diverge. A liquid lens with a positive variable focus was demonstrated, this kind of lens has the advantages of simple fabrication process, compact structure, easy operation, and low cost.
Single-mode 1.27μm InGaAs vertical cavity surface-emitting lasers with temperature-tolerant modulation characteristics
Authors: Chacinski Marek , Schatz Richard , Kjebon Olle , Hammar Mattias , von Würtemberg Rickard Marcks , Mogg Sebastian , Sundgren Petrus , Berggren Jesper
Published: May 2005

The dynamic performance of InGaAs∕GaAs1.27μm single-mode vertical cavity surface emitting lasers (VCSELs) is presented. In order to reach such a long wavelength, the devices utilize highly strained double-quantum wells and a large detuning between the material gain peak and cavity resonance. It is found that the large detuning improves the temperature stability of both static and modulation characteristics. A resonance frequency of 7.8–9.5 GHz and optical power of 0.30 mW in fiber was maintained throughout the investigated temperature range of 20–90 °C. The intrinsic response of the device suggests that long-wavelength InGaAs∕GaAs VCSELs have the potential to be used as low cost uncooled optical transmitters at 10Gbit∕s.
Over 3 W high-efficiency vertical-external-cavity surface-emitting lasers and application as efficient fiber laser pump sources
Authors: Fan L. , Fallahi M. , Hader J. , Zakharian A. R. , Kolesik M. , Moloney J. V. , Qiu T. , Schülzgen A. , Peyghambarian N. , Stolz W. , Koch S. W. , Murray J. T.
Published: May 2005

We report on the design and fabrication of high-power, high-brightness diode-pumped vertical-external-cavity surface-emitting lasers. Over 3 W continuous wave fundamental transverse mode (TEM00) output at 980 nm with a high slope efficiency of 44% is demonstrated at room temperature. The diffraction-limited beam with M2 factor of 1.15 at high-power operation is achieved. A vertical-external-cavity surface-emitting laser operating near 976 nm with a diffraction-limited beam is used to pump the core of 3 cm long Er∕Yb-codoped single-mode phosphate fiber lasers. An output power in excess of 250 mW at 1535 nm with a slope efficiency of 29% is obtained without any cooling.
Current-conduction and charge trapping properties due to bulk nitrogen in HfOxNy gate dielectric of metal-oxide-semiconductor devices
Authors: Cheng Chin-Lung , Chang-Liao Kuei-Shu , Huang Ching-Hung , Wang Tien-Ko
Published: May 2005

This work examined the effects of bulk nitrogen in HfOxNy gate dielectric on current-conduction and charge trapping of metal-oxide-semiconductor devices. The nitrogen concentration profiles in HfOxNy gate dielectric were adjusted by Hf target sputtered in an ambient of modulated nitrogen flow. The current-conduction mechanisms of HfOxNy film comprised of various nitrogen concentration profiles at the low- and high-electrical field were dominated by Schottky emission and Frenkel–Poole emission, respectively. The trap energy level involved in Frenkel–Pool conduction was estimated to be around 0.8 eV. Smaller stress-induced leakage current and flat-band voltage shift were obtained for devices with HfOxNy dielectric containing less bulk nitrogen, attributable to less interface strain∕stress and bulk trap.
Origin of the improved luminance-voltage characteristics and stability in organic light-emitting device using CsCl electron injection layer
Authors: Yi Yeonjin , Kang Seong Jun , Cho Kwanghee , Koo Jong Mo , Han Kyul , Park Kyongjin , Noh Myungkeun , Whang Chung Nam , Jeong Kwangho
Published: May 2005

The luminance-voltage characteristics and stability were highly improved by replacing LiF with CsCl in organic light-emitting devices. To investigate the origin of these improvements, ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy were used. The additional shifts of the vacuum, highest occupied molecular orbital, and lowest unoccupied molecular orbital levels due to the CsCl layer reduce the width and height of the electron injection barrier, resulting in the improved luminance-voltage characteristics of the devices. Additionally, the intervening CsCl layer between Al and Alq3 prevents N–Al reactions among Alq3 molecules and Al, which reduces distortion or breakdown of Alq3 molecules and slows the degradation of the device.
Transfer of the in-plane molecular orientation of polyimide film surface to liquid crystal monolayer
Authors: Usami Kiyoaki , Sakamoto Kenji , Uehara Yoichi , Ushioda Sukekatsu
Published: May 2005

We have determined the relationship between the in-plane molecular orientations of a polyimide film and the liquid crystal (LC) monolayer in contact with it. A photoaligned film of polyimide, containing azobenzene in the backbone structure, was used, because its in-plane molecular order can be varied over a wide range without change in the morphology and the chemical nature of the film surface. The in-plane order parameter of the LC molecule was found to be almost equal to that of the polyimide backbone structure. This result shows that the molecular alignment of the LC monolayer is mainly induced by a short-range interaction between the LC and polyimide molecules.
Universal relationship between crystallinity and irreversibility field of MgB2
Authors: Yamamoto A. , Shimoyama J. , Ueda S. , Katsura Y. , Iwayama I. , Horii S. , Kishio K.
Published: May 2005

The relationship between irreversibility field, Hirr, and crystallinity of MgB2 bulks including carbon substituted samples was studied. The Hirr was found to increase with an increase of full width at half maximum (FWHM) of MgB2 (110) peak, which corresponds to distortion of honeycomb boron sheet, and their universal correlation was discovered even including carbon substituted samples. Excellent Jc characteristics under high magnetic fields were observed in samples with large FWHM of (110) due to the enhanced intraband scattering and strengthened grain boundary flux pinning. The relationship between crystallinity and Hirr can explain the large variation of Hirr for MgB2 bulks, tapes, single crystals, and thin films.
Fabry–Perot Gunn laser
Authors: Chung S. , Balkan N.
Published: May 2005

A truly monopolar GaAs Fabry–Perot cavity Gunn laser is demonstrated. The device is grown by metalorganic chemical vapor deposition on a semi-insulating GaAs substrate and consists of an n=4.6×1017cm−3 doped GaAs active layer sandwiched between the AlxGa1−xAs(x=0.32) waveguiding layers. The operation of the device is based on the band to band recombination of impact-ionized nonequilibrium electron-hole pairs in the propagating high field domains in the Gunn diode, which is placed in a Fabry–Perot cavity, and biased above the threshold of negative differential resistance. Lasing from the device is observed at temperature T⩾95K. The maximum power emitted from the device is P=25.4μW at λ=840nm and T=95K.
Enhanced in-plane ferroelectricity in Ba0.7Sr0.3TiO3 thin films grown on MgO (001) single-crystal substrate
Authors: Wang D. Y. , Wang Y. , Zhou X. Y. , Chan H. L. W. , Choy C. L.
Published: May 2005

Highly oriented Ba0.7Sr0.3TiO3 thin films were grown on MgO (001) single-crystal substrate using pulsed-laser deposition and the in-plane ferroelectric properties of the film were evaluated. X-ray diffraction characterization revealed a good crystallinity and tensile in-plane stress in the film. A well-defined ferroelectric hysteresis loop with Pr=9.5μC∕cm2 was observed along the (100) direction, which implied an enhanced in-plane ferroelectricity in the Ba0.7Sr0.3TiO3 thin film in comparison with the Ba0.7Sr0.3TiO3 ceramics. Curie temperature of the film was found to be ∼88°C, which is nearly 50°C higher than that of the Ba0.7Sr0.3TiO3 ceramics. The butterfly-shaped C-V characteristic curve also evidenced the enhanced in-plane ferroelectric property in the film, and a large dielectric tunability of 69% was found at 1MHz under a moderate dc bias field. The observation of enhanced ferroelectricity along the in-plane direction in the highly oriented Ba0.7Sr0.3TiO3 thin film was explained in terms of the increased tetragonality (a∕c=1.016) induced by the lattice misfit strain.