bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen vacancy defects in antiferroelectric PbZrO3 thin film heterostructures after neutron irradiation
Authors: Bittner R. , Humer K. , Weber H. W. , Kundzins K. , Sternberg A. , Lesnyh D. A. , Kulikov D. V. , Trushin Y. V.
Published: September 2004

Neutron irradiation effects on highly oriented antiferroelectric PbZrO3 (PZ) thin films are investigated in view of their possible application as a temperature sensitive element in an alternative bolometer system for fusion devices such as the International Thermonuclear Experimental Reactor (ITER). All films were prepared by a sol-gel technique or by pulsed laser deposition (PLD). The dielectric properties were investigated in a frequency range from 1 to 250kHz and at temperatures up to 400°C, prior to and after irradiation to neutron fluences of 0.5×1022, 1×1022, 2×1022, and 3×1022m−2 (E>0.1MeV). After irradiation, the films were annealed in several steps up to 400°C in order to remove the radiation-induced defects. The results are discussed in terms of a phenomenological model of radiation effects in PZ films, which takes into account structural defects, such as oxygen vacancies, and radiation-induced charges. We find that the films are most sensitive to neutron irradiation in the vicinity of the phase transistion temperature Tc. In addition, the structural order of the films as well as the interfaces play an important role. We find that the PZ heterostructures prepared by PLD are radiation harder than the sol-gel films. The dielectric properties of the PLD films are more or less unaffected by neutron irradiation up to a fluence of 3×1022m−2 (E>0.1MeV).
Optical properties of N+ ion-implanted and rapid thermally annealed Si(100) wafers studied by spectroscopic ellipsometry
Authors: Kurihara Katsunori , Hikino Shin-ichi , Adachi Sadao
Published: September 2004

The optical properties of N+ ion-implanted Si(100) wafers have been studied using the spectroscopic ellipsometry (SE). The N+ ions are implanted at 150keV with fluences in the range between 1×1016 and 7.5×1016cm−2 at room temperature. A Bruggeman effective-medium-approximation and a linear-regression analysis require a four-phase model (substrate/first and second damaged layers/ambient) to explain the experimental data of the as-implanted samples. These analyses suggest that the buried fully amorphous layer can be formed at around ∼5×1016cm−2 dose. The rapid thermal annealing is performed at 750°C in a dry N2 atmosphere on N+ ion-implanted samples. The SE data reveal that the recrystallization starts to occur very quickly. The time constant for the defect annealing in the deeper damaged layer is determined to be 36s. The dielectric-function spectra ε(E) of microcrystalline silicon deduced here differ appreciably from that of the single-crystalline silicon, especially in the vicinity of the critical points.
Structural, optical, and acoustic characterization of high-quality AlN thick films sputtered on Al2O3(0001) at low temperature for GHz-band electroacoustic devices applications
Authors: Caliendo Cinzia , Imperatori Patrizia
Published: September 2004

Aluminum nitride thin and thick films were grown on Al2O3(0001) substrates by reactive radio frequency-sputtering technique at 180°C. The AlN films, 0.022–6.2μm thick, were stress-free, uniform, transparent, and extremely adhesive to the substrate. Their structural properties were investigated by x-ray diffraction measurements: the resulting films were highly c-axis oriented, with a full width at half maximum of the (0002) rocking curve in the range from 1.6° to 1.0° for AlN film thickness ranging between 0.022 and 6.2μm. The crystalline quality of AlN films was extremely good even at high thicknesses, as shown by the presence of the AlN(0004) reflection and by the narrow (0.12°–0.20°) diffraction peaks. Optical measurements of the transmission in the visual and infrared region demonstrated that the AlN films have low absorption and scattering. The extinction and the absorption coefficients, α and Ke, were estimated at λ⩾600nm(α=850±50cm−1,Ke=0.0040±0.0005). The piezoelectric strain constant d33 was measured for all the sputtered films: the mean d33 value was (4.2±0.7)×10−12 C∕N, which is very close to the value of the AlN single crystal. Surface acoustic wave (SAW) delay lines were photolithographically defined on the free surface of the AlN films grown on bare or metallized Al2O3(0001) substrates. Harmonic modes operating at frequencies up to about 2.4GHz were obtained just by using a conventional photolithographic technique with 7.5μm linewidth. The phase and group velocities of SAWs propagating in AlN∕Al∕Al2O3 and in AlN∕Al2O3 structures, along and normal to the Al2O3 a axis, were estimated for different AlN thicknesses. The experimental measurements were compared with the theoretical data and found to be in good agreement.
Phase Diagram of the Perovskite System (1−x)BiScO3-xPbTiO3
Authors: Eitel R. E. , Zhang S. J. , Shrout T. R. , Randall C. A. , Levin I.
Published: September 2004

The perovskite (1−x)BiScO3-xPbTiO3 (BS-PT) system exhibits a large piezoelectric coefficient (d33>460pC∕N in polycrystalline form) and a high Curie temperature TC=450°C in the vicinity of the morphotropic phase boundary (x=0.64mol fraction PbTiO3), which separates the rhombohedral and tetragonal phases. The present contribution reports on revisions to the BiScO3-PbTiO3 phase diagram specifically, (i) the compositional dependence of the octahedral tilt-transition temperature (x<0.62mol fraction PT), as determined using variable-temperature transmission electron microscopy, (ii) high-temperature curvature of the rhombohedral-tetragonal morphotropic phase boundary determined using dielectric measurements on single crystals, and (iii) Curie temperatures in the tetragonal phase field, which exceed that of the PbTiO3 end member.
Chemistry-induced intrinsic stress variations during the chemical vapor deposition of polycrystalline diamond
Authors: Rajamani Ashok , Sheldon Brian W. , Nijhawan Sumit , Schwartzman Alan , Rankin Janet , Walden Barbara L. , Riester Laura
Published: September 2004

Intrinsic tensile stresses in polycrystalline films are often attributed to the coalescence of neighboring grains during the early stages of film growth, where the energy decrease associated with converting two free surfaces into a grain boundary provides the driving force for creating tensile stress. Several recent models have analyzed this energy trade off to establish relationships between the stress and the surface∕interfacial energy driving force, the elastic properties of the film, and the grain size. To investigate these predictions, experiments were conducted with diamond films produced by chemical vapor deposition. A multistep processing procedure was used to produce films with significant variations in the tensile stress, but with essentially identical grain sizes. The experimental results demonstrate that modest changes in the deposition chemistry can lead to significant changes in the resultant tensile stresses. Two general approaches were considered to reconcile this data with existing models of stress evolution. Geometric effects associated with the shape of the growing crystal were evaluated with a finite element model of stress evolution, and variations in the surface∕interfacial energy driving force were assessed in terms of both chemical changes in the deposition atmosphere and differences in the crystal growth morphology. These attempts to explain the experimental results were only partially successful, which suggests that other factors probably affect intrinsic tensile stress evolution due to grain boundary formation.
An accurate determination of barrier heights at the HfO2∕Si interfaces
Authors: Puthenkovilakam Ragesh , Chang Jane P.
Published: September 2004

X-ray photoelectron spectroscopy (XPS) combined with first principles simulations are used to investigate the band alignments of HfO2 on silicon. Our theoretical calculations predict dangling bond states originating from the partial occupancy of Hf d orbitals at a stoichiometric HfO2∕Si interface. Our band structure calculations predict that hydrogen passivation of Hf atoms at the interface as well as increased oxygen concentration at the interface remove the dangling bond states effectively. A HfSiO4∕Si interface also has no dangling bond states. Theoretically calculated valence band offsets of HfO2∕Si interface ranged from 2.69 to 3.04eV and the conduction band offsets ranged from 1.54 to 1.89eV, and they are a function of the interface coordination numbers. For the HfSiO4∕Si interface, the calculated valence and conduction band offsets are 2.69eV and 2.19eV, respectively. Experimentally measured band offsets by XPS yield a valence band offset of 3.10eV and a conduction band offset of 1.48eV for a HfO2∕Si interface, in very good agreement with theoretical results. These results suggest that HfO2 and HfSiO4 provide sufficient tunneling barriers for electrons and holes, making them suitable candidates as alternative gate dielectrics.
Origin of vacancy and interstitial stabilization at the amorphous-crystalline Si interface
Authors: Harrison Scott A. , Yu Decai , Edgar Thomas F. , Hwang Gyeong S. , Kirichenko Taras A. , Banerjee Sanjay K.
Published: September 2004

Using plane-wave pseudopotential density functional theory calculations, we have investigated the behaviors of neutral interstitials and vacancies at the amorphous-crystalline (a–c)Si interface. A continuous random network model is employed in the construction of defect-free a-c interface structure. We find that both vacancies and interstitials prefer to reside on the amorphous side of the interface. In both cases, the most stable defects occur 3–4Å from the a-c interface. Vacancy stabilization is found to be due to strain relief provided to the substrate lattice while interstitial stabilization is due largely to bond rearrangement arising from interstitial integration into the substrate lattice. We also discuss the effect of the “spongelike” behavior of the amorphous phase toward native defects on ultrashallow junction formation in the fabrication of ever-shrinking electronic devices.
Perpendicular magnetic fields in cantilever beam magnetometry
Authors: Koch R. , Das A. K. , Yamaguchi H. , Pampuch C. , Ney A.
Published: September 2004

Cantilever beam magnetometry is a common technique to determine the magnetoelastic (ME) coupling constants of thin films by measuring the stress that develops when the film magnetization is changed. In cantilever beam experiments performed so far the film magnetization was mainly rotated within the film plane. Here we discuss the measurement of the ME coupling constants, when the magnetizing field is chosen so that it rotates the film magnetization out of the film plane. A major stress contribution, which arises additionally to the ME stress, originates in the torque that magnetic dipoles experience in a magnetic field. In order to separate torque effects from ME contributions in cantilever beam experiments a general method is proposed. With this method the ME coupling constants can be quantitatively determined and furthermore the film magnetization as well as its perpendicular anisotropy constant are obtained quantitatively.
An x-ray scattering study of the smectic-C* liquid crystal structure in the vicinity of the buried interface of a glass grating
Authors: Martínez-Miranda L. J.
Published: September 2004

We have used grazing incidence x-ray scattering to study the structure of a smectic-C* liquid crystal (LC) at the buried LC-glass interface in liquid crystal films. This measurement is done in reflection mode through the glass substrate, which consists of a grating photolithographed onto a 220μm thick slide. The x-ray energy has been tuned such that it can penetrate the 220μm slide, such that the layers close to the interface can be studied. We have observed the smectic-C* evolve as a function of depth within the film, and compared it to equivalent films analyzed from the free (air) surface.
Copper-phthalocyanine field-effect transistor with a low driving voltage
Authors: Okuda T. , Shintoh S. , Terada N.
Published: September 2004

Copper-phthalocyanine-thin-film metal-insulator-semiconductor field-effect transistors operating with a low driving voltage have been fabricated by using a PbZr0.5Ti0.5O3 film as a high-permittivity insulator layer (ε≈500). A field mobility of about 0.017cm2∕Vs and an ON/OFF ratio of more than 103 were obtained at a gate voltage of −2V and a drain-source voltage of −1V. This p-type copper-phthalocyanine transistor has a driving voltage low enough for practical device applications.
Efficient green polymer light-emitting diodes with microcavity effect in electroluminescence spectrum but constant quantum efficiency
Authors: Jiang Xuezhong , Herguth Petra , Sassa Takafumi , Jen Alex K-Y.
Published: September 2004

We report the efficient green polymer light-emitting diodes (LEDS) that exhibit a strong microcavity effect in the electroluminescence (EL) spectrum. The LEDs employ a double-layer structure, with poly-(3,4-ethylenedioxythiophene): polystyrene sulfonic acid as the hole-transporting layer and with a highly efficient polyfluorene-based green-emitting polymer as the electron-transporting and emitting layer. The EL spectra of the LEDs demonstrate a strong resonance effect with the thickness of the emitting layer varying from 30 to 280nm. The turn-on voltage of the device increases with the increasing thickness of the emitting layer. However, the brightness and especially the external quantum efficiency of the devices are largely independent of the thickness from 100 to 280nm, when the emitting layer is thick enough to avoid cathode quenching of the electroluminescence.
Domain structure changes in (1-x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 with composition, dc bias, and ac field
Authors: Viehland D. , Li JieFang , Colla Eugene V.
Published: September 2004

Domain structure changes in (1-x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 have been studied by polarized optical microscopy. In the zero-field-cooled condition, increasing the x revealed systematic changes in the domain morphology from polar nanodomains for x<0.25, to fine crosshatched domains near the morphotrophic phase boundary (MPB), and to micro-sized domains for x=0.4. In the vicinity of the MPB, an applied dc electrical bias resulted in a change of morphology from fine crosshatched (rhombohedral phase) to thin-aligned striationlike (monoclinic phase) domains. The application of an ac electric field to the crosshatched domains resulted in irregular domain wall oscillations∕relaxations and increased nonuniformity.
Probing intrinsic transport properties of single metal nanowires: Direct-write contact formation using a focused ion beam
Authors: Marzi G. De , Iacopino D. , Quinn A. J. , Redmond G.
Published: September 2004

The transport characteristics of 70-nm-diameter platinum nanowires (NWs), fabricated using a pore-templated electrodeposition process and individually contacted using a focused ion beam (FIB) method, are reported. This approach yields nanowire devices with low contact resistances (∼400Ω) and linear current–voltage characteristics for current densities up to 65kA∕cm2. The intrinsic nanowire resistivity (33±5μΩcm) indicates significant contributions from surface- and grain-boundary scattering mechanisms. Fits to the temperature dependence of the intrinsic NW resistance confirm that grain-boundary scattering dominates surface scattering (by more than a factor of 2) at all temperatures. Our results demonstrate that FIB presents a rapid and flexible method for the formation of low-resistance ohmic contacts to individual metal nanowires, allowing intrinsic nanowire transport properties to be probed.
Elastica solution for a nanotube formed by self-adhesion of a folded thin film
Authors: Glassmaker N. J. , Hui C. Y.
Published: September 2004

Schmidt and Eberl demonstrated the construction of tubes with submicron diameters by the method of folding thin solid films [Nature (London)NATUAS 410, 168 (2001)]. In their method, a thin film is folded 180° and brought into adhesive contact with itself. The resulting sealed loop forms a nanotube with the thickness of the tube walls equal to the thickness of the thin film. The calculation of the diameter of the tube and the shape of its cross section in equilibrium are the subjects of this study. The tube is modeled as a two-dimensional elastica when viewed in cross section, and adhesive behavior is governed by an energy release rate criterion. A numerical technique is used to find elastic equilibria for a large range of material parameters. With these solutions in hand, the problem of designing a nanotube becomes transparent. It is shown that one dimensionless parameter determines the diameter of the nanotube, while another fixes its shape. Each of these parameters is a ratio involving the material's mechanical properties and the film thickness. Before concluding, we verify our model by comparing its results with the experimental observations of Schmidt and Eberl, for their materials.
Half-metallic ferromagnetism in ternary transition-metal compounds based on ZnTe and CdTe semiconductors
Authors: Xie Wen-Hui , Liu Bang-Gui
Published: September 2004

Electronic structures and magnetic properties of various possible ternary transition-metal compounds based on zincblende ZnTe and CdTe semiconductors are systematically explored by using an accurate density-functional method. Half-metallic (HM) ferromagnetism is found in the ZnTe and CdTe heavily doped with Cr, V, and Mn. Quite high Curie temperatures would be expected in most of these HM ferromagnets. These HM ferromagnetic phases, structurally stable and compatible with the two semiconductors, would be useful in spintronics.
Single step quantum well intermixing with multiple band gap control for III-V compound semiconductors
Authors: Djie H. S. , Mei T. , Arokiaraj J. , Nie D.
Published: September 2004

We report a quantum well intermixing technique based on Ar plasma induced damage on both GaAs- and InP-based materials with single-step multiple band gap creation across a substrate. A quantum well structure with multiplewidths serves as a sensitive tool to probe the damage created by Ar plasma. The analysis reveals that the surface defects were created up to a certain depth and propagated deeper into the material upon subsequent annealing. A simple and reliable way to obtain a controlled multiple band gap was achieved by using the spatial defect modulated intermixing. Eight band gap levels were realized across a single chip of quantum well laser structure with a linear relationship to the fraction of the open area under plasma exposure. This simple approach can be implemented at a postgrowth level to a wide range of material systems to achieve multiple band gaps, suitable for photonic integration.
Resistive substrate heater for film processing by spray pyrolysis
Authors: Rousseau B. , De Barros D. , La Manna J. , Weiss F. , Duneau G. , Odier P. , De Sousa Meneses D. , Auger Y. , Melin P. , Echegut P.
Published: September 2004

We describe a simple and inexpensive resistive heater usable in the spray pyrolysis process. It is based on a resistively heated ceramic plate. By using such a heater substrate temperatures exceeding 900 °C are easily achieved on the substrate. The heater consists of a ceramic plate enclosed in a stainless steel box. A refractory wire woven in a regular frame inside the ceramic provides an excellent heating uniformity over the entire surface. Performances and parameters of the system are given. We apply this device to the preparation of thick films of HTc oxides such as (Hg,Re)Ba2Ca2Cu3O8+δ.
Automated system for the study of volume holographic recording
Authors: González-Leal J. M. , Krecmer P. , Prokop J. , Elliott S. R.
Published: September 2004

An instrument, the “Holometer,” for the automatic recording, reading, and evaluation of multiplexed volume holograms, has been designed and constructed. This apparatus is a valuable tool for the characterization of holographic recording materials, in the context of volume holographic technologies, as well as for general studies of holographic recording physics.
Transient torque method: A fast and nonintrusive technique to simultaneously determine viscosity and electrical conductivity of semiconducting and metallic melts
Authors: Li C. , Ban H. , Lin B. , Scripa R. N. , Su C.-H. , Lehoczky S. L. , Zhu S.
Published: September 2004

A transient torque method was developed to rapidly and simultaneously determine the viscosity and electrical conductivity of liquid metals and molten semiconductors. The experimental setup of the transient torque method is similar to that of the oscillation cup method. The melt sample is sealed inside a fused silica ampoule, and the ampoule is suspended by a long quartz fiber to form a torsional oscillation system. A rotating magnetic field is used to induce a rotating flow in the conductive melt, which causes the ampoule to rotate around its vertical axis. A sensitive angular detector is used to measure the deflection angle of the ampoule. Based on the transient behavior of the deflection angle as the rotating magnetic field is applied, the electrical conductivity and viscosity of the melt can be obtained simultaneously by numberically fitting the data to a set of governing equations. The transient torque viscometer was applied successfully to measure the viscosity and electrical conductivity of high purity mercury at 53.4°C. The results were in excellent agreement with published data. The method is nonintrusive; capable of rapid measurement of the viscosity of toxic, high vapor pressure melts at elevated temperatures. In addition, the transient torque viscometer can also be operated as an oscillation cup viscometer to measure just the viscosity of the melt or as a rotating magnetic field method to determine the electrical conductivity of a melt or a solid if desired.
Optical gain in monodispersed silicon nanocrystals
Authors: Cazzanelli M. , Navarro-Urriós D. , Riboli F. , Daldosso N. , Pavesi L. , Heitmann J. , Yi L. X. , Scholz R. , Zacharias M. , Gösele U.
Published: September 2004

Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO∕SiO2 superlattices is presented. Under high power pulsed excitation, positive optical gain can be observed once a good optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large gain values are explained by the small size dispersion in these silicon nanocrystals.
Absorbing film assisted laser induced forward transfer of fungi (Trichoderma conidia)
Authors: Hopp B. , Smausz T. , Antal Zs. , Kresz N. , Bor Zs. , Chrisey D.
Published: September 2004

We present an investigation on absorbing film assisted laser induced forward transfer (AFA-LIFT) of fungus (Trichoderma) conidia. A KrF excimer laser beam [λ=248nm,FWHM=30ns (FWHM, full width at half maximum)] was directed through a quartz plate and focused onto its silver coated surface where conidia of the Trichoderma strain were uniformly spread. The laser fluence was varied in the range of 0–2600mJ∕cm2 and each laser pulse transferred a pixel of target material. The average irradiated area was 8×10−2mm2. After the transfer procedure, the yeast extract medium covered glass slide and the transferred conidia patterns were incubated for 20 h and then observed using an optical microscope. The transferred conidia pixels were germinated and the areas of the culture medium surfaces covered by the pixels were evaluated as a function of laser fluence. As the laser fluence was increased from 0 to 355mJ∕cm2 the transferred and germinated pixel area increased from 0 to 0.25mm2. Further increase in fluence resulted in a drastic decrease down to an approximately constant value of 0.06mm2. The yield of successful transfer by AFA-LIFT and germination was as much as 75% at 355mJ∕cm2. The results prove that AFA-LIFT can successfully be applied for the controlled transfer of biological objects.
Coulomb blockade and negative differential conductance in metallic double-dot devices
Authors: Nguyen V. Hung , Nguyen V. Lien , Nguyen H. Nam
Published: September 2004

We systematically analyze the stability diagrams and simulate the finite temperature current-voltage characteristics for metallic double-dot devices with cross couplings between dots and gates. The Coulomb blockade is described with respect to each device parameter. The negative differential conductance observed is essentially suppressed by increasing the temperature and/or introducing the offset charge and is very sensitive to the device parameters.
Complex magnetoimpedance analysis of interparticle boundaries in Fe3O4 powder compact
Authors: Cai Tian-Yi , Chen Ya-Jie , Zhang Xiao-Yu , Li Zhen-Ya
Published: September 2004

Recent experimental results of Fe3O4 in polycrystalline film, powder compact, and single crystal form have indicated that boundaries play an important role in magnetoresistance effect. In this paper, the complex impedance analysis is used to evaluate the contribution of particle boundary to conduction process in Fe3O4 powders. Considering particle boundaries with different thicknesses, we developed a random resistor-capacitor network model to investigate the influence of magnetic field on impedance behaviors. The fitting results to experimental data indicated that two kinds of conduction mechanisms, spin-dependent tunneling and spin-independent hopping, dominate the transport process in particle boundaries. The capacitive transport through particles with a size of 10–20nm may yield negative magnetoreactance. It is also found that magnetic field has little influence not only on the competition between resistive and capacitive path, but also phase angle Φ(f). Finally, it can be deducted that the magnetoreactance effect could be enhanced in this granular sample if the particle size is less than 10–20nm.
Wavelength-specific laser-activated switches for improved contrast ratio in generation of short THz pulses
Authors: Doty M. F. , Cole B. E. , King B. T. , Sherwin M. S.
Published: September 2004

A method for designing and manufacturing wavelength-specific laser-activated reflection switches for use at THz frequencies is described. A key figure of merit for such switches is the contrast ratio, the ratio of power reflected after activation to that reflected before activation. The new switches improve the pulse contrast ratio by utilizing interference to suppress reflections prior to laser activation. Measurements using the University of California, Santa Barbara Free Electron Laser indicate that contrast ratios can be improved from approximately 60 to as large as 4.5×104 using the new switches. The switches improve contrast ratio by an average factor of 400, with peak improvement by a factor as large as 740. Such switches can be used in the generation of short THz pulses from narrow bandwidth sources and may also find applications in the extraction of single pulses from longer pulse trains.
Inductive measurements of magnetic properties of ribbon materials
Authors: Claassen J. H. , Willard Matthew A. , Francavilla T. L. , Harris Vincent G.
Published: September 2004

Inductive measurements of thin ribbon materials are usually done with wrapped toroidal cores. To avoid this time consuming procedure, measurements can also be performed on short straight pieces in a solenoidal setup. We show that demagnetizing effects should be unimportant for the latter case in determining coercive field, saturation field, and core loss. These two types of measurement were performed on samples of amorphous ribbon material. It was found that there is reasonable agreement for these magnetic parameters as long as care was taken to ensure that the samples were strain-free. Strain is particularly important when the material has significant magnetostriction. Based on demagnetization estimates we would expect agreement on permeability determinations in all but the most extreme cases; in fact results can be quite different for the two measurements. Similarly, we can get rather different answers for coercive field when it is very small. This may be due to uniaxial anisotropy which is different for the two sample geometries. It is concluded that the rapid turnaround in solenoid measurements is particularly useful when optimization of saturation field or core loss is of primary importance.
Andreev reflection and enhanced subgap conductance in NbN∕Au∕InGaAs-InP junctions
Authors: Batov I. E. , Schäpers Th. , Golubov A. A. , Ustinov A. V.
Published: September 2004

We report on the fabrication of highly transparent superconductor∕normal metal∕two-dimensional electron gas junctions formed by a superconducting NbN electrode, a thin (10nm) Au interlayer, and a two-dimensional electron gas in an InGaAs∕InP heterostructure. High junction transparency has been achieved by exploiting developed process of Au∕NbN evaporation and rapid annealing at 400°C. This allowed us to observe a decrease in the differential resistance with pronounced double-dip structure within the superconducting energy gap in superconductor/two-dimensional electron gas (2DEG) proximity systems. The effect of a magnetic field perpendicular to the plane of the 2DEG on the differential resistance of the interface was studied. It has been found that the reduced subgap resistance remains in high magnetic fields. Zero-field data are analyzed within the previously established quasiclassical model for the proximity effect.
The temperature dependence of resistivity in thin metal films
Authors: Marom H. , Eizenberg M.
Published: September 2004

The dependence of resistivity on temperature in thin metal films is investigated by extending the model of Mayadas and Shatzkes to include temperature dependence. It is shown that previous interpretations of a dominant grain boundary mechanism are not necessarily correct, and that the combined influence of grain boundaries and surfaces should be considered in the analysis of experimental results. The analytical expressions developed enable systematic studies of the different factors influencing the dependence of resistivity on temperature in thin metal films.
Generation of absorption waves by CO2 laser pulses at low power density
Authors: Hermann J. , Le Floch T.
Published: September 2004

Optical breakdown generated by CO2 laser pulses in helium, argon, and xenon atmospheres has been investigated by fast plasma plume imaging and measurements of energy and temporal shape of the transmitted laser pulse. The role of preionization due to material evaporation has been examined by placing targets with low ablation threshold in the vicinity of the laser beam focus. Ambient gas pressure, laser pulse energy, and distance between target and laser beam focus have been varied in order to identify the physical mechanisms involved into the ignition and propagation of the laser-induced breakdown plasma. The understanding of the generation of absorption waves at low power density is useful for the design of plasma shutters with low threshold in the infrared spectral range.
Resistive wall mode identification by contrast enhancing technique of soft x-ray measurements on DIII-D
Authors: Bogatu Ioan N. , Edgell Dana H. , Kim Jin-Soo
Published: September 2004

A contrast enhancing technique (CET) for soft x-ray (SXR) measurements has been developed and tested for the early identification of the low amplitude resistive wall mode (RWM) on the DIII-D tokamak. The technique is simple and fast. It utilizes the chord-by-chord difference of low-pass digitally filtered time derivatives of the signals from the twelve-chord fan-shape soft x-ray arrays located at toroidal angles of 195° and 45°. The two arrays allow a demonstration of the CET method principle, although they cannot completely resolve the RWM structure. The time derivative of the x-ray signal amplifies the effect of the temperature perturbation convected by the RWM, while naturally incorporating the equilibrium evolution effect. The correlation with the parameters measured by other diagnostics, such as the radial magnetic field δBr from the magnetic probes, the radial profiles of plasma current density j, pressure p, and safety factor q from the motional Stark effect, the radial profile of the temperature perturbation ΔTe from electron cyclotron emission, the normalized beta parameter βN=βT(I/aB)−1, and the Dα light emission, confirm the early detection of the low-amplitude RWMs by the soft x-ray CET. Upon validation the SXR CET could be implemented into a multisensor scheme using other diagnostics for the real-time identification of RWM.
CD1d-restricted T cell activation by nonlipidic small molecules
Authors: Van Rhijn Ildiko , Young David C. , Im Jin Seon , Levery Steven B. , Illarionov Petr A. , Besra Gurdyal S. , Porcelli Steven A. , Gumperz Jenny , Cheng Tan-Yun , Moody D. Branch
Published: September 2004

In addition to NK T cells expressing invariant Vα14 or Vα24 T cell receptors (TCRs), the CD1d-restricted T cell repertoire is comprised of T cells with diverse TCRs that mediate inflammation during autoimmune and infectious disease. Here we describe the isolation of human Vα24–T cells that are activated by antigen and CD1d. Mass spectrometric and NMR studies revealed that the stimulatory compounds were neither peptidic nor lipidic but instead were composed of sulfur and aromatic hydrocarbon rings, corresponding to the general structure of phenyl pentamethyldihydrobenzofuran sulfonates. Studies of the molecular mechanism of T cell activation showed that a clonotypic Vα2/Vβ21 TCR transmitted activating signals, which were highly specific for hydroxylation and methylation patterns at the terminal structures of stimulatory compounds. These studies provide evidence for noninvariant CD1d-restricted T cells in humans and identify the complete molecular structure of a nonlipidic small molecule that activates T cells through an αβ TCR.
Cell-type-specific binding of the transcription factor CREB to the cAMP-response element
Authors: Cha-Molstad Hyunjoo , Keller David M. , Yochum Gregory S. , Impey Soren , Goodman Richard H.
Published: September 2004

The cAMP-response element-binding protein (CREB) transcription factor was initially identified as a mediator of cAMP-induced gene expression. CREB binds to a target sequence termed the cAMP-response element (CRE) found in many cellular and viral gene promoters. One of the best-characterized CREs resides in the promoter of the gene encoding the neuropeptide somatostatin, and this element has served as a model for studies of CREB function. Phosphorylation of CREB by protein kinase A allows recruitment of the coactivator CREB-binding protein (CBP). A central tenet of the CREB–CBP model is that CREB binds constitutively to the CRE and that regulation occurs through the phosphorylation-dependent recruitment of CBP. In this report, we use chromatin immunoprecipitation assays to show that CREB does not interactin vivowith the somatostatin CRE, or similar elements in several other genes, in PC12 cells, a standard model for studies of CREB function. Rather, CREB bindingin vivois regulated in a cell-specific manner, a finding that was confirmed by usingin vivogenomic footprinting assays. The CREs in other genes were also found to interact differentially with CREB in PC12 cells, hepatoma cells, and cortical neurons. We conclude that the family of CREB target genes differs from one cell type to another and that the ability of CREB to bind to a particular CRE represents an important component of gene regulation.
Loop quantization from a lattice gauge theory perspective
Authors: José A Zapata
Published: September 2004

We present an interpretation of loop quantization in the framework of lattice gauge theory. Within this context the lack of appropriate notions of effective theories and renormalization group flow exhibit loop quantization as an incomplete framework. This interpretation includes a construction of embedded spin foam models which does not rely on the choice of any auxiliary structure (e.g. triangulation) and has the following straightforward consequences:

The values of the coupling constants need to be those of an UV-attractive fixed point.

The kinematics of canonical loop quantization and embedded spin foam models are compatible.

The weights assigned to embedded spin foams are independent of the 2-polyhedron used to regularize the path integral, |J|x= |J|x′.

An area spectrum with edge contributions proportional tolPL2(j+ 1/2) is not compatible with embedded spin foam models and/or canonical loop quantization.
Regulation of Cell Motility by Tyrosine Phosphorylated Villin
Authors: Tomar Alok , Wang Yaohong , Kumar Narendra , George Sudeep , Ceacareanu Bogdan , Hassid Aviv , Chapman Kenneth E. , Aryal Ashish M. , Waters Christopher M. , Khurana Seema
Published: September 2004

Temporal and spatial regulation of the actin cytoskeleton is vital for cell migration. Here, we show that an epithelial cell actin-binding protein, villin, plays a crucial role in this process. Overexpression of villin in doxycyline-regulated HeLa cells enhanced cell migration. Villin-induced cell migration was modestly augmented by growth factors. In contrast, tyrosine phosphorylation of villin and villin-induced cell migration was significantly inhibited by the src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) as well as by overexpression of a dominant negative mutant of c-src. These data suggest that phosphorylation of villin by c-src is involved in the actin cytoskeleton remodeling necessary for cell migration. We have previously shown that villin is tyrosine phosphorylated at four major sites. To further investigate the role of tyrosine phosphorylated villin in cell migration, we used phosphorylation site mutants (tyrosine to phenylalanine or tyrosine to glutamic acid) in HeLa cells. We determined that tyrosine phosphorylation at residues 60, 81, and 256 of human villin played an essential role in cell migration as well as in the reorganization of the actin cytoskeleton. Collectively, these studies define how biophysical events such as cell migration are actuated by biochemical signaling pathways involving tyrosine phosphorylation of actin binding proteins, in this case villin.
Does High‐Frequency Pseudo‐random Rotational Chair Testing Increase the Diagnostic Yield of the ENG Caloric Test in Detecting Bilateral Vestibular Loss in the Dizzy Patient?
Authors: Kaplan Daniel M. , Marais Joe , Ogawa Teruhiru , Kraus Mordechai , Rutka John A. , Bance Manohar L.
Published: September 2004

Objectives To assess the incremental diagnostic yield of testing vestibulo‐ocular (VOR) gain with high‐frequency pseudo‐random rotational chair (PsRRC) over testing with bithermal electronystagmography caloric tests in the dizzy patient, particularly in detecting bilateral vestibular loss.

Patients and Methods One hundred ninety‐eight patients presenting with dizziness underwent PsRRC and caloric testing. The VOR gain on PsRRC was measured at 0.32 to 5.0 Hz, with gain categorized as normal or decreased. PsRRC results were compared with caloric responses, also categorized as normal, or into graded categories of unilateral or bilateral vestibular loss.

Results Reduced PsRRC gain was found in 29 (15%) patients, and reduced caloric tests responses in 70 (35%), with 25 (13%) having bilateral loss. Of patients with reduced chair gain, 25 of 29 (86%) demonstrated bilateral caloric loss. PsRRC gain was normal in most patients with unilateral caloric weakness, but was decreased in all patients with bilateral caloric weakness. The probability of a patient with completely normal caloric responses having an abnormal rotation chair in this study group was under 1% (1 of 128).

Conclusions PsRRC testing does not offer much additional diagnostic benefit when caloric responses are normal. It is useful in specific conditions, such as unilateral caloric loss for which the patient is not compensating, borderline caloric loss when traditional water caloric tests cannot be used, or for monitoring progressive bilateral vestibular loss.
Histological Characterization of the Thyroglossal Tract: Implications for Surgical Management
Authors: Chandra Rakesh K. , Maddalozzo John , Kovarik Paula
Published: September 2004

Objectives In the current report, we characterized the relationship between the central hyoid bone and the thyroglossal tract and determined the prevalence of ectopic thyroid follicles in the adjacent soft tissues.

Study Design Retrospective pathological analysis.

Methods The resected specimens from 104 patients who underwent a modified Sistrunk procedure with wide‐field dissection were retrospectively analyzed. Under light microscopy, serial sections were examined to determine whether the thyroglossal tract passed anterior to, posterior to, or within the hyoid bone. Specimens were also examined for the presence of thyroid follicles in the periductal and pericystic soft tissues.

Results In 50 cases (48%), the tract position in relation to the hyoid bone could not be identified secondary to extensive arborization, marked inflammation, specimen fragmentation or a combination of these. Thyroid follicles were observed in 9 (18%) of these specimens. In the remaining 54 cases (52%) the tract was located anterior to the central arch of the hyoid bone in 39 (72%) and posterior to it in 15 (28%). Thyroid tissue was observed in 46% of specimens (P = .004), regardless of whether the tract was anterior or posterior.

Conclusions These results demonstrate that tract position often cannot be defined, but when a portion is dominant, it is likely to be anterior to the hyoid bone. Ectopic thyroid tissue can be found in almost 50% of specimens when the tract position is identifiable. With appropriate surgical management, a recurrence rate of less than 4% can be expected, despite the presence of ductule multiplicity, marked inflammation, tract position posterior to the hyoid bone, and ectopic thyroid follicles.
Allergic Fungal Rhinosinusitis: Current Theories and Management Strategies
Authors: Marple Bradley F.
Published: September 2004

The combination of nasal polyposis, crust formation, and sinus cultures yielding Aspergillus was first noted in 1976 by Safirstein, 1 who observed the clinical similarity that this constellation of findings shared with allergic bronchopulmonary Aspergillosis (ABPA). Eventually this disease came to be known as allergic fungal rhinosinusitis (AFS). As clinical evidence of AFS accumulated, controversy regarding its etiology, pathogenesis, natural history, and appropriate treatment naturally emerged. Despite past and current efforts, many of these controversies remain incompletely resolved, but continuing clinical study has illuminated some aspects of the disease and has led to an improved understanding of AFS and its treatment. Fungi associated with the development of AFS are ubiquitous and predominantly of the dematiaceous family. The eosinophilic host response to the presence of these fungi within the nose and paranasal sinuses gives rise to those clinical manifestations of the disease (nasal polyps, expansile mucocele formation, allergic fungal mucin, etc.). Exposure alone to these fungi, however, appears to be insufficient to initiate the disease. At the present time it is likely that initiation of the inflammatory cascade leading to AFS is a multifactorial event, requiring the simultaneous occurrence of such things as IgE‐mediated sensitivity (atopy), specific T‐cell HLA receptor expression, exposure to specific fungi, and aberration of local mucosal defense mechanisms. A variety of treatment plans for AFS have emerged, but the potential for recidivism remains well recognized, ranging from 10% to nearly 100%, suggesting the need for continued study of this disease and fueling present controversy. This article is intended to review current data and theories regarding the pathophysiology of AFS, as well as the role of various surgical and nonsurgical forms of therapy.
An Interpretation of the Structural Changes Responsible for the Chronicity of Rhinoscleroma
Authors: Canalis Rinaldo F. , Zamboni Luciano
Published: September 2004

Objective To identify the structural changes of the proliferative phase of rhinoscleroma which could be responsible for the chronicity of the disease.

Study Design Observational research.

Methods Samples of friable tissue taken from the nasal mucosa of nine untreated patients were processed for light and ultrastructural microscopy.

Results The majority of changes contributing to the chronicity of the disease occurred in the subepithelium and followed three closely related but distinct events. In the first (infiltrative), subepithelial invasion by the Klebsiella was followed by its active multiplication and proliferation of capillaries. In the second (neutrophilic), large numbers of neutrophils were delivered into this space. Neutrophils actively phagocytized the Klebsiella but appeared to die at an accelerated rate without completing digestion of the microorganisms. In the third event (histiocytic), histiocytes entered the subepithelium and engaged in unrestrained phagocytosis of decaying neutrophils, Klebsiella, and debris. During this process, the histiocytes' phagosomes underwent massive dilation, thus becoming Mikulicz cells. Mikulicz cells were unable to consistently destroy the Klebsiella and eventually ruptured, releasing them into the interstitium. Evidence was found that an autophagic process might contribute to phagosome distention and to the rupture of the vacuolar membranes and cell wall.

Conclusions Several critical changes responsible for the chronicity of rhinoscleroma occur during the proliferative phase of the disease. The majority of these take place in the subepithelium and include: 1) factors leading to the transformation of histiocytes into Mikulicz cells, 2) the inability of these cells to consistently destroy the Klebsiella, 3) their rupture releasing viable Klebsiella, and 4) the intrinsic resistance of the pathogen.
Three‐Dimensional Image for the Middle Fossa Approach and Its Anatomical Considerations
Authors: Tsunoda Atsunobu , Komatsuzaki Atsushi , Kobayashi Mari , Suzuki Yasuhiro
Published: September 2004

Objective To investigate the usefulness and significance of three‐dimensional images in the middle cranial fossa approach.

Study Design Retrospective study.

Method Three‐dimensional images of 12 patients with acoustic neuromas were made for surgical guidance. An image showing an ideal surgical view was prepared, which showed no overlap between the labyrinthine bone and internal auditory canal (IAC) with a slight gap between them. The IAC was located and opened referring to this image.

Results Directions of the images in the ideal surgical view were anterior from lateral position in all cases. Viewing toward the vestibule, angle from lateral plane was 24° ± 12° (mean ± standard deviation). In 11 of 12 patients, the IAC was safely opened; in one patient the IAC could not be opened because of bleeding. Overall hearing preservation rate was 82%.

Conclusion Our method facilitated not only in the identification of the IAC but also in avoiding inner ear damage. Our data indicated that the center of craniotomy should be made anterior to the external auditory canal and surgery should be viewed from an anterolateral position for a safe procedure.