bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezoresistive properties of single crystalline, polycrystalline, and nanocrystalline n-type 3C-SiC
Authors: Eickhoff M. , Möller M. , Kroetz G. , Stutzmann M.
Published: September 2004

A detailed experimental study of the influence of crystal quality on the piezoresistive properties of n-type cubic silicon carbide grown by low temperature, low pressure chemical vapor depostion is presented. We have measured the longitudinal gauge factor in single-crystalline, polycrystalline, and nanocrystalline films as a function of conductivity and temperature as well as its directional dependence. In single-crystalline films, the piezoresistive gauge factor is strongly influenced by the layer thickness. The transition from single-crystalline to nanocrystalline 3C-SiC, achieved by a decrease in deposition temperature from 1200 to 1100°C, is shown to result in a change of the corresponding longitudinal piezoresistive gauge factor from −24.8 to positive values of +8 in nominally undoped films. In addition, we observe a drastic change in its dependence on conductivity. We attribute these results to the influence of crystal defects on the strain dependent conductivity.
In situ transmission electron microscopy analysis of electron beam induced crystallization of amorphous marks in phase-change materials
Authors: Kaiser M. , van Pieterson L. , Verheijen M. A.
Published: September 2004

Crystallization of amorphous data marks in crystalline Ga15Sb85 and Ge,In doped SbTe phase-change material was studied in situ in a Transmission Electron Microscope (TEM). Electron irradiation induced crystallization was obtained at room temperature using a 120kV beam. In general, electron beam (e−-beam) induced crystallization started from the amorphous-crystalline interface and was growth dominated for both materials. A dependence of growth velocity on electron beam intensity and crystal direction was observed. A comparison with laser-crystallized amorphous marks was made. For laser-induced crystallization also crystal growth from the amorphous-crystalline interface was seen. However, differences in morphology between the e−-beam and laser-recrystallized data marks of the GaSb phase-change material were observed. The electron beam erased data marks contained crystals with (extremely) large periodicities found in three dimensions. For the Ge,In doped SbTe phase-change material identical morphologies were observed for the e−-beam and laser-recrystallized data marks. Both methods that induce crystallization displayed a rhombohedral Sb structure, the same structure as the laser-crystallized surroundings.
Branched carbon nanofiber network synthesis at room temperature using radio frequency supported microwave plasmas
Authors: Boskovic Bojan O. , Stolojan Vlad , Zeze Dagou A. , Forrest Roy D. , Silva S. Ravi P. , Haq Sajad
Published: September 2004

Carbon nanofibers have been grown at room temperature using a combination of radio frequency and microwave assisted plasma-enhanced chemical vapor deposition. The nanofibers were grown, using Ni powder catalyst, onto substrates kept at room temperature by using a purposely designed water-cooled sample holder. Branched carbon nanofiber growth was obtained without using a template resulting in interconnected carbon nanofiber network formation on substrates held at room temperature. This method would allow room-temperature direct synthesized nanofiber networks over relatively large areas, for a range of temperature sensitive substrates, such as organic materials, plastics, and other polymers of interest for nanoelectronic two-dimensional networks, nanoelectromechanical devices, nanoactuators, and composite materials.
Effects of the top-electrode size on the piezoelectric properties (d33 and S) of lead zirconate titanate thin films
Authors: Gerber P. , Roelofs A. , Kügeler C. , Böttger U. , Waser R. , Prume K.
Published: September 2004

The effects of a decreasing top electrode size on the electric and piezoelectric properties of tetragonal Pb(ZrX,Ti1−X)O3 thin films are investigated. The effective piezoelectric small-signal coefficient d33,eff and the piezoelectric large signal-strain S are measured using a double-beam laser interferometer. Both properties are found to decrease rapidly with decreasing size of the used Pt top electrode for the investigated dimensions of 5mmto100μm edge length (square pads). While the loss of d33,eff is as high as 75%, the influence on the relative permittivity is only small. The source of the pad size effect on the measured piezoelectric properties is found to be the mechanics of the layered structure commonly used for piezoelectric measurements (Pt∕PZT∕Pt∕TiO∕SiO2∕Si), [PZT,Pb(Zrx,Ti1−x)O3] which is verified by finite element simulations.
Pyroelectric properties of (1−x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 and (1−x)Pb(Zn1∕3Nb2∕3)O3-xPbTiO3 single crystals measured using a dynamic method
Authors: Davis Matthew , Damjanovic Dragan , Setter Nava
Published: September 2004

The pyroelectric coefficients of 0.72Pb(Mg1∕3Nb2∕3)O3-0.28PbTiO3 (PMN-28PT), 0.67Pb(Mg1∕3Nb2∕3)O3-0.33PbTiO3 (PMN-33PT), and 0.92Pb(Zn1∕3Nb2∕3)O3-0.08PbTiO3 (PZN-8PT) single crystals, oriented and poled along three different crystallographic directions, [001]C, [011]C, and [111]C, have been measured using a dynamic method. The suffix C indicates reference to the prototypic cubic coordinate system. Large coefficients of up to 1070μCm−2K−1 have been observed for the [111]C oriented, rhombohedral PMN-28PT and PMN-33PT samples, where the measurement direction corresponds to the polar axis of the crystal. For each composition and orientation two different poling procedures are compared, a commonly used field cooling method and a low temperature poling protocol. It was found that in otherwise pseudoorthorhombic samples of PZN-8PT, a room temperature rhombohedral phase could be stabilized by application of a field along the [111]C direction while heating from −70°C.
Band gap tuning of InAs∕GaSb type-II superlattices for mid-infrared detection
Authors: Haugan H. J. , Szmulowicz F. , Brown G. J. , Mahalingam K.
Published: September 2004

The superlattice (SL) of a 40 period InAs∕GaSbSL structure were varied around the 20.5ÅInAs∕24ÅGaSb design in order to produce a device with an optimum mid-infrared photoresponse and a sharpest photoresponse cutoff. The samples for this study were grown by molecular beam epitaxy with precisely calibrated growth rates. Varying individual layer width around the nominal design, we were able to systematically change the photoresponse cutoff wavelength between 4.36 to 3.45um by decreasing the InAs width from 23.5 to 17.5Å, and between 4.55 to 4.03μm by increasing the GaSb width from 18 to 27Å. Therefore, the cutoff changes faster with decreasing InAs rather than increasing GaSb width. However, increasing GaSb width more effectively enhances the sharpness of photoresponse near band edge. The effect of design parameters on the photoresponse cutoff and other effects are explained by a nonperturbative, modified envelope function approximation (EFA) calculation that includes the interface coupling of heavy, light, and spin-orbit holes resulting from the in-plane asymmetry at InAs∕GaSb interfaces. Using the modified EFA model, the SL design at fixed period of 44.5Å was adjusted for the optimum performance.
Fused silica thermal conductivity dispersion at high temperature
Authors: Bouchut P. , Decruppe D. , Delrive L.
Published: September 2004

A continuous CO2 laser is focused to locally anneal small fused silica spots. A noncontact radiometry diagnostic enables us to follow surface temperature variation that occurs from site to site. A “steady state” dispersion of surface temperature is observed across our sample. We show that nonhomogeneous silica thermal conductivity, above 1000K is responsible for this temperature dispersion.
Engineering chemically abrupt high-k metal oxide∕silicon interfaces using an oxygen-gettering metal overlayer
Authors: Kim Hyoungsub , McIntyre Paul C. , On Chui Chi , Saraswat Krishna C. , Stemmer Susanne
Published: September 2004

High-k metal oxide gate dielectrics may be required to extend Moore’s law of semiconductor device density scaling into the future. However, growth of a thin SiO2-containing interface layer is almost unavoidable during the deposition of metal oxide films onto Si substrates. This limits the scaling benefits of incorporating high-k dielectrics in future transistors. A promising approach, in which oxygen-gettering metal overlayers are used to engineer the thickness of the SiO2-based interface layer between metal oxide and Si substrate after deposition of the metal oxide layer, is reported. Using a Ti overlayer with high solubility for oxygen on ZrO2 or HfO2 dielectrics, the effective removal of the low-k interface layer at 300K has been confirmed by electron microscopy and spectroscopy techniques. Significant enhancement of the gate capacitance density, while retaining low leakage current densities, has also been demonstrated for these interface-engineered high-k gate stacks.
X-ray study of strain and composition of Si∕Ge0.85Si0.15(111) islands grown in Volmer-Weber mode
Authors: Malachias A. , Magalhães-Paniago R. , Kycia S. , Cahill David G.
Published: September 2004

Si islands were grown on Ge(111) in Volmer-Weber growth mode with a 40-nm thick Ge0.85Si0.15 buffer. The state of strain and chemical composition of these islands were evaluate by grazing incidence anomalous x-ray diffraction. The results show evidence of lattice coherence and Ge-Si intermixing. A direct relationship between increase in substrate temperature and enhancement of alloying was found, evidencing the importance of atomic interdiffusion in this growth mode.
Predicting the temperature of a premixed flame in a microcombustor
Authors: Li Z. W. , Chou S. K. , Shu C. , Yang W. M. , Xue H.
Published: September 2004

We apply the scale analysis and the simulation to relate the flame temperature in a microcombustor to the external wall surface temperature. In deriving the equation for predicting the flame temperature, we account for the detailed reaction mechanisms in the combustion process and we assume that the flow in the combustor tube is laminar. Experimental investigations have been conducted to validate the equation. We employ hydrogen as a fuel and obtain a stable flame in microcombustors with internal radii of 3, 4 and 6mm. Good agreement between the measured and the predicted flame temperature has been achieved. In predicting the flame temperature, we use a Nusselt number Nu=3.650 and 4.363 for the tube diameters of 6mm and above and 4mm and below, respectively.
Intrinsic stresses in AlN layers grown by metal organic chemical vapor deposition on (0001) sapphire and (111) Si substrates
Authors: Raghavan Srinivasan , Redwing Joan M.
Published: September 2004

Stress evolution during metal organic chemical vapor deposition growth of AlN layers on (111) Si and (0001) sapphire substrates was investigated using in situ wafer curvature measurements in order to understand the origin of growth stresses. AlN layers 170±30nm thick were deposited over a temperature range of 600–1100°C at a growth rate of 0.2±0.05nm∕s. On (111) Si, AlN films grow under a constant tensile stress right from the beginning of growth in the temperature range investigated. In contrast, above 900°C on sapphire, an initial compressive growth stress is observed followed by a transition to a final tensile stress, while below 800°C the stress is tensile right from the beginning of growth as observed on Si. The origin of this stress behavior is explained in terms of a combination of epitaxial stress and grain coalescence stress. Calculation of the grain coalescence stresses show that the value is higher for growth on sapphire substrates than on Si substrates. Also, for growth on both substrates, a sharp drop in the value of the coalescence related tensile stress is observed between 900°C and 800°C. Both these features are correlated to the variation in the integral breadth of the (0002) and (101¯1) AlN x-ray rocking curves. It is shown that both the lower tensile stress on Si substrates and the drop in stress between 800°C and 900°C can be attributed to the reduction in grain coalescence stresses due to increasing grain boundary energies in the film resulting from increasing grain misorientation with respect to the substrate/film interface.
Heteroepitaxy of SrTiO3 on vicinal Si(001): Growth and kinetic effects
Authors: Liang Y. , Wei Y. , Hu X. M. , Yu Z. , Droopad R. , Li H. , Moore K.
Published: September 2004

Heteroepitaxy of SrTiO3 on vicinal Si(001) substrates was accomplished using molecular beam epitaxy by codepositing Sr and Ti at a low-temperature-and-low-oxygen-pressure condition at the early stage of film growth. X-ray photoelectron spectroscopy and reflection-high-energy-electron diffraction showed that the SrTiO3 films grown by this method exhibited better chemical and structural behaviors than those produced by layer-by-layer deposition under similar conditions. Scanning tunneling microscopy revealed that a well-defined step-terrace morphology was retained on the SrTiO3 film grown by codeposition on a vicinal Si(001) substrate. These results suggest that kinetic effects play an important role and the presence of Sr promotes titanium oxidation by providing a different transition state with a lower Ti oxidation barrier.
Crystallization and Properties of PbO-doped Ba0.7Sr0.3TiO3 Films
Authors: Sun Ping , Matsuura Naomi , Ruda Harry E.
Published: September 2004

Ferroelectric Ba0.7Sr0.3TiO3 films were fabricated using a PbO-doped barium strontium titanate sol-gel precursor. Ba0.7Sr0.3TiO3 thin films with 0, 10, 20, and 30at.%PbO doping were deposited on bare silicon, and platinum coated silicon substrates, using spin coating. The influence of PbO doping both on the film microstructure and properties was studied. Doping in excess of 20at.%PbO was found to markedly decrease film porosity, while enhancing crystallization by decreasing the annealing temperature required for the formation of the perovskite phase from above 650°C to 500°C. Electrical characterization of the films demonstrated their excellent properties for electronic device application. Films with 20at.%PbO doping had room temperature dielectric constant and dissipation factor of 268 and 0.95%, respectively (measured at 10kHz), with tunability from 30% to 75% and commutation quality factor in excess of 105 (for bias field from 200 to 800kV∕cm). Room temperature leakage current were measured to be as low as 2.45×10−9A∕cm2 (at bias field of 250kV∕cm).
Asymmetric effect on spin polarization in a spin-filter device using nonmagnetic triple-barrier structure
Authors: Shang Ci-En , Guo Yong , Chen Xin-Yi
Published: September 2004

We investigate the asymmetric effect in a spin-filter device, which is based on the Rashba spin-orbit coupling effect and uses a nonmagnetic tunneling diode. The structural asymmetry is introduced by unequivalence of the two quantum wells in the spin-filter device. It is found that the structural asymmetry can greatly change spin-filtering efficiency. For some asymmetric spin-filter structures, one can see spin-dependent enhancement in the transmission. Moreover, the current density can increase or decrease greatly depending on the degree of the structural asymmetry.
The role of surface charge field in two-beam coupling in liquid crystal cells with photoconducting polymer layers
Authors: Kaczmarek M. , Dyadyusha A. , Slussarenko S. , Khoo I. C.
Published: September 2004

In liquid crystal cells with photoconductive poly(N-vinlylcarbazole) polymer layers, an external dc field can be completely screened by surface charge layers that develop at the liquid crystal–polymer interface. Under spatially modulated illumination, surface charge layers can be discharged in bright areas and lead to reorientation and spatially modulated Freedericksz transition. As a result, an asymmetric energy exchange in the photorefractive two-beam coupling process can take place. We propose a model to explain the origin of reorientation and phase shift in the two-beam coupling process, based on the profile and tilt of the refractive index grating. We also show that cells with just one photoconducting layer are more efficient than a typical design with two layers.
Structure of an Er silicide film on a Si(111) substrate using three-dimensional medium-energy ion scattering
Authors: Shimoda Susumu , Kobayashi Takane
Published: September 2004

A three-dimensional medium-energy ion scattering (3D-MEIS) spectrometer has been developed for crystallographic structure analysis of materials. In 3D-MEIS, a pulsed He+ ion beam at 100keV is incident upon a sample and scattered (and/or recoiled) particles are detected by a three-dimensional detector. The three-dimensional detector used is a position-sensitive and time-resolving microchannel plate detector with two delay-line anodes intersecting at right angles. 3D-MEIS has been employed to analyze the structure of an Er silicide film on a Si(111) substrate. A blocking pattern based on the structure of the Er silicide was clearly observed. The results indicate that 3D-MEIS is effective for crystallographic structural analysis of materials.
The effect of surface stress and wetting layers on morphological instability in epitaxially strained films
Authors: Savina T. V. , Voorhees P. W. , Davis S. H.
Published: September 2004

This paper investigates effects of surface stress and wetting layers on the morphological instability of a growing epitaxially strained dislocation-free solid film. Linear stability analysis of the planar film shows that the film, unstable due to lattice mismatch, is affected differently by surface stress for a film under compression than for one under tension and depends on whether the relative stiffness of the film to the substrate is less than or greater than (1−2ν)−1; here ν is Poisson’s ratio. The presence of a wetting layer has the capacity to substantially stabilize the planar film. The critical thickness of the film below which the film is stable depends on the bulk elastic properties of film and substrate and increases with increase of the wetting potential.
Electron injection-induced effects in Mn-doped GaN
Authors: Burdett William , Lopatiuk Olena , Chernyak Leonid , Hermann Martin , Stutzmann Martin , Eickhoff Martin
Published: September 2004

Electron injection into Mn-doped GaN resulted in pronounced changes in the minority carrier diffusion length and cathodoluminescence. In particular, multiple-fold decrease of the band-to-band cathodoluminescence intensity was observed in the temperature between −50 and 80°C. This decrease was accompanied by an increase of the minority carrier diffusion length in the material, measured by electron-beam-induced current. Temperature-dependent cathodoluminescence measurements revealed a recovery of the cathodoluminescence intensity with an activation energy of 360meV.
Controlled creation of entangled states of excitons in coupled quantum dots
Authors: Kis Zsolt , Paspalakis Emmanuel
Published: September 2004

We present two methods for the controlled creation of entangled exciton states in a laser-driven system of two identical quantum dots interacting via an energy-transfer process. The first method uses rotation of the two-particle states and is used for the creation of entanglement between the vacuum state and the biexciton state. The second method is based on adiabatic passage techniques and is used for the creation of a single-exciton entangled state.
Field solutions for the Swihart wave and surface plasmon in superconducting/dielectric film multilayer structures in the mixed state
Authors: Wu Chien-Jang
Published: September 2004

Microwave propagation characteristics in superconducting/dielectric multilayer structures in the mixed state are theoretically investigated. We use the electrodynamic field equations for a type-II superconductor in the mixed state to derive the field solutions for two model structures such as a superconducting planar waveguide and a superlattice. With these solutions, we present several quantitative studies of the propagation constant as a function of static magnetic field, superconducting film thickness, and radiation frequency for the Swihart wave, surface plasmon, and the dielectric image waveguide, respectively. In the waveguide structure, it is found that there exists a certain value of thickness of superconducting film such that the attenuation constant attains a minimum. This value is shown to increase with increasing static magnetic field. This behavior, however, is smeared out in the superconducting superlattice structure regardless of the applied static magnetic field. The roles played by the superconducting film thickness together with the vortices in the microwave propagation for a multilayer structure are thus elucidated.
Entropy production and thermodynamics of nonequilibrium stationary states: A point of view
Authors: Gallavotti Giovanni
Published: September 2004

Entropy might be a not well defined concept if the system can undergo transformations involving stationary nonequilibria. It might be analogous to the heat content (once called “caloric”) in transformations that are not isochoric (i.e., which involve mechanical work): it could be just a quantity that can be transferred or created, like heat in equilibrium. The text first reviews the philosophy behind a recently proposed definition of entropy production in nonequilibrium stationary systems. A detailed technical attempt at defining the entropy of a stationary states via their variational properties follows: the unsatisfactory aspects of the results add arguments in favor of the nonexistence of a function of state to be identified with entropy; at the same time new aspects and properties of the phase space contraction emerge.
Linewidth enhancement factor of a type-II interband-cascade laser
Authors: Lerttamrab M. , Chuang S. L. , Yang R. Q. , Hill C. J.
Published: September 2004

Experimental results using the amplified spontaneous emission spectroscopy of a type-II interband-cascade laser are presented. Using the Hakki-Paoli method, the optical gain spectra of the laser are extracted for the wavelength of 3.13μm at various subthreshold current levels. A group index of around 3.33 is determined from Fabry-Pérot modal spacing. The change in refractive index with increased bias current is obtained from the peak wavelength shifts of the Fabry-Pérot spectrum. A low value of 0.71 for the linewidth enhancement factor at the lasing wavelength near threshold is found.
Temperature dependence of refractive index in InN thin films grown by reactive sputtering
Authors: Zhou H. P. , Shen W. Z. , Ogawa H. , Guo Q. X.
Published: September 2004

Temperature-dependent reflection measurements have been carried out on InN thin films to determine its refractive index n and its temperature coefficient dn∕dT. The studied InN thin films were grown by reactive sputtering on (111) GaAs substrates under various growth conditions. In addition to the slow variation of the background in the region far away from the optical band gap, a rapid increase of dn∕dT due to the Wannier excitonic effect has been observed in the region near the optical band gap. With the help of the dielectric function model for the refractive index n and Tanguy’s model for the temperature coefficient dn∕dT [J. Appl. Phys. 80, 4626 (1996)], we are able to demonstrate the dependence of dn∕dT in InN thin films on the growth temperature and on the sputtering pressure. The results are discussed within the framework of the optical-band-gap fluctuation and the reactive-sputtering growth mechanisms.
Annual ring-like grain growth in Ni-mediated crystallization of amorphous silicon by pulse annealing
Authors: Choi Jong Hyun , Kim Seung Soo , Oh Jae Hwan , Cheon Jun Hyuk , Jang Jin
Published: September 2004

We studied annual ringlike grain growth in Ni-mediated crystallization of amorphous silicon (a-Si). Ni particles were sputtered onto a-Si and then the sample was crystallized in a pulse lamp annealing system. The crystallization of a-Si proceeds circularly from the seed at the center of a grain. The Ni atoms on the a-Si aggregate together and then from a NiSi2 crystallite, which is a seed for inducing crystallization. The crystallization proceeds from these nuclei, and then the diskshaped grain grow laterally with increasing the number of heating cycles. An annual ring appears after Secco etch of a disklike grain even though the crystallization temperature is fixed. The explosive crystallization over 1μm results in annual ring, which is more clear when pulse heating is used for crystallization. Polycrystalline silicon with a grain size of 103μm was achieved in the present work.
Chainlike silicon nanowires: Morphology, electronic structure and luminescence studies
Authors: Sun X. H. , Wong N. B. , Li C. P. , Lee S. T. , Sham T. K.
Published: September 2004

The chainlike silicon nanowires SiNWs have been synthesized by fluctuating the pressure of the carrier gas in the growth process. The chainlike SiNWs comprise crystalline Si nanoparticles interconnected by amorphous silicon oxide wires. In addition to the sphere, other interesting shapes such as rectangular and triangular Si nanoparticles in chainlike SiNWs were also observed. X-ray absorption fine structure shows that the Si nanoparticles in the chainlike SiNWs are crystalline silicon and that the wire has a significantly larger Si oxide to crystalline Si ratio and disorder compared to the normal SiNW. X-ray excited optical luminescence and photoluminescence spectroscopy show that the relatively strong luminescence from the chainlike SiNWs compared to normal SiNWs arises mainly from silicon oxide in the chainlike SiNWs.
Embedded interdigital transducers for high-frequency surface acoustic waves on GaAs
Authors: de Lima M. M. , Seidel W. , Kostial H. , Santos P. V.
Published: September 2004

We investigate high-performance, high-frequency interdigital transducers (IDTs) for the generation of surface acoustic waves (SAWs) on GaAs substrates, where the metal fingers are embedded in the substrate. We demonstrate that the acoustic reflections and the scattering of the surface modes into the substrate become considerably reduced in these transducers, leading to an increased output power. The finger embedding process is particularly relevant for the generation of powerful beams of high-frequency SAWs on weak piezoelectric substrates (such as most of the semiconducting materials) using long IDTs. We also show that the reflection reduction is important for the design of focusing single-finger IDTs, since it minimizes the effects of the finger grating on the angular dependence of the phase velocity.
Digital imaging processing for biophysical applications
Authors: Schilling Jörg , Sackmann Erich , Bausch Andreas R.
Published: September 2004

Many biological and biophysical experimental setups rely on digital imaging processing. The introduction of a new generation of digital cameras enables new experiments where time dependent processes can be detected with a high time resolution and high signal-to-noise ratio. However, there are no software tools available with which the full potential of the digital cameras can be explored. Although the data streams of up to 24 MB/s are readily processed by the available hardware, they present an immense challenge to the current software packages. We present a software concept based on the object oriented paradigm, with which digital cameras can be controlled and full images at full rate are captured, processed, and displayed simultaneously over extended time periods, just limited by the capacity of the hard disk space. By implementing wavelet based compression algorithms the obstacle of archiving the immense amount of data is overcome. We present examples in which original data files are compressed to 10% of its original size without loss of information. The modular character of the object based program enables the implementation of a wide range of different applications into the program.
Spectral emissivity and temperature measurements of selective bodies using multiband fiber-optic radiometry
Authors: Sade Sharon , Katzir Abraham
Published: September 2004

A passive method of measuring the spectral emissivity and the temperature of materials in the mid- and the far IR is described both in theory and experiment. Theoretical evaluation and real measurements (spectral emissivity and temperature) of selective bodies utilizing IR transmitting silver halide optical fibers are presented. We carried out the theoretical evaluation and measurements for a multiband fiber-optic radiometer, which consists of a silver halide (AgClBr) infrared transmitting fiber, a dual-band cooled infrared detector, and a set of 18 narrow-band infrared filters, covering the 2–14μm spectral range. We performed the measurement on the two selective bodies which had a strong and a weak dependence of emissivity as a function of the wavelength. The body spectral emissivity, the body temperature, and the room temperature were measured simultaneously. The results of the theoretical evaluation agreed with the experimental results. We also discuss the assumptions and the limitations of performing such a measurement for bodies near room temperatures. This method for measuring spectral emissivity has applications in science, industry (semiconductor industry), and medicine.
Disposal of used optical disks utilizing thermally-excited holes in titanium dioxide at high temperatures: A complete decomposition of polycarbonate
Authors: Mizuguchi Jin , Shinbara Toshihiro
Published: September 2004

Disposal of used optical disks is an urgent requirement for electronic industries. We propose a decomposition system of polycarbonates (PC) (used as substrate materials for optical disks) that utilizes thermally-excited holes at high temperatures. The present system is based on an oxide semiconductor (TiO2) heated at about 500°C in combination with a molten state of PC. Molten PC chains are first adsorbed on the surface of TiO2 due to electrostatic interactions between positively charged oxygen vacancies in TiO2 and the polar carbonyl group of PC: ∣O∣..⋯Oδ−Cδ+. Adsorbed PC is then oxidized by thermally-excited holes in TiO2 and decomposed into small fragments, followed by their combustion in the presence of oxygen to give solely H2O and CO2. The decomposition mechanism has been discussed on the basis of nonstoichiometric properties of TiO2 at high temperatures together with adsorption behavior of PC on the surface of TiO2.
Measuring methods of cell performance of dye-sensitized solar cells
Authors: Koide Naoki , Han Liyuan
Published: September 2004

Cell performance measuring methods for dye-sensitized solar cells (DSCs) were investigated in comparison with those of crystalline silicon solar cells. It was found that cell performances of DSCs varied according to voltage sweep direction and sampling delay time. On the other hand, this dependence was not observed in silicon solar cells. Measurement of the transient photocurrent revealed that the dependence on sweep direction and sampling delay time may be explained by the longer time constant of DSCs. To improve accuracy, measurement should be carried out with a sampling delay time exceeding several seconds. However, it is also found that the average value of the efficiency measured by two sweeping directions is constant when the sampling delay time is longer than 40 ms. These measurement conditions will be useful to measuring cell performance more accurately and rapidly. Additionally, determining cell area using a shading mask with an area smaller than that of TiO2 electrodes will improve accuracy when evaluating solar cell performance.
Electroluminescence from isolated CdSe∕ZnS quantum dots in multilayered light-emitting diodes
Authors: Zhao Jialong , Zhang Jingying , Jiang Chaoyang , Bohnenberger Jolanta , Basché Thomas , Mews Alf
Published: September 2004

Electro- and photoluminescence spectra of the CdSe∕ZnS core-shell quantum dots (QDs) covered by various organic ligands and incorporated into multilayered light-emitting diodes (LEDs) were recorded by a confocal optical microscope. The QDs were dispersed in a hole transporting material, N,N’-Diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine (TPD), to investigate the LED performance at different QD concentrations and the effect of different surface modifications on the isolated QDs. No wavelength shift was observed in the electroluminescence spectra from the QD LEDs with or without the TPD. The peak energies of the electro- and photoluminescence showed only small spectral shifts (several nanometer) for the diluted QDs and no dependence on the QD-concentration, surface ligands, or conductive polymers that were used. This suggests that the relative peak shifts are related to the different filling processes in the CdSe QDs under photo excitation and electric injection, rather than to the “chemical” effects on the surface of the CdSe∕ZnS QDs.
Characterizations of symmetry and asymmetry high-density gas jets without Abel inversion
Authors: Kim Changbum , Kim Guang-Hoon , Kim Jong-Uk , Ko In Soo , Suk Hyyong
Published: September 2004

Characterizations of the high-density gas jets are performed for the laser–gas interaction. It is shown that the gas density profile can be obtained without the Abel inversion, when a Gaussian distribution is assumed. In addition, a rectangular nozzle is characterized for the long plasma generation. In this case, the Boltzmann distribution is introduced for the density profile and its result shows a good agreement with the experimental result.
Evolving complex dynamics in electronic models of genetic networks
Authors: Mason Jonathan , Linsay Paul S. , Collins J. J. , Glass Leon
Published: September 2004

Ordinary differential equations are often used to model the dynamics and interactions in genetic networks. In one particularly simple class of models, the model genes control the production rates of products of other genes by a logical function, resulting in piecewise linear differential equations. In this article, we construct and analyze an electronic circuit that models this class of piecewise linear equations. This circuit combines CMOS logic and RC circuits to model the logical control of the increase and decay of protein concentrations in genetic networks. We use these electronic networks to study the evolution of limit cycle dynamics. By mutating the truth tables giving the logical functions for these networks, we evolve the networks to obtain limit cycle oscillations of desired period. We also investigate the fitness landscapes of our networks to determine the optimal mutation rate for evolution.
Deletion of
Bax
eliminates sex differences in the mouse forebrain
Authors: Forger Nancy G. , Rosen Greta J. , Waters Elizabeth M. , Jacob Dena , Simerly Richard B. , de Vries Geert J.
Published: September 2004

Several of the best-studied sex differences in the mammalian brain are ascribed to the hormonal control of cell death. This conclusion is based primarily on correlations between pyknotic cell counts in development and counts of mature neurons in adulthood; the molecular mechanisms of hormone-regulated, sexually dimorphic cell death are unknown. We asked whether Bax, a member of the Bcl-2 family of proteins that is required for cell death in many developing neurons, might be essential for sex differences in neuron number. We compared
Bax
knockout mice and their WT siblings, focusing on two regions of the mouse forebrain that show opposite patterns of sexual differentiation: the principal nucleus of the bed nucleus of the stria terminalis, in which males have more neurons than do females, and the anteroventral periventricular nucleus (AVPV), where females have more neurons overall and many more dopaminergic neurons than do males. Testosterone, or its metabolites, is responsible for the sex differences in both nuclei. A null mutation of the
Bax
gene completely eliminated sex differences in overall cell number in both the principal nucleus of the bed nucleus of the stria terminalis and AVPV. Thus, Bax-dependent cell death is required for sexual differentiation of cell number, regardless of whether testosterone decreases or increases cell death. In contrast, the sex difference in AVPV dopaminergic cell number, as measured by tyrosine hydroxylase immunohistochemistry, was not affected by
Bax
gene deletion, demonstrating heterogeneity of mechanisms controlling cell number within a single nucleus.
Naturally occurring H-DNA-forming sequences are mutagenic in mammalian cells
Authors: Wang Guliang , Vasquez Karen M.
Published: September 2004

Naturally occurring DNA sequences can form noncanonical structures such as H-DNA, which are abundant and regulate the expression of several disease-linked genes. Here, we show that H-DNA-forming sequences are intrinsically mutagenic in mammalian cells. This finding suggests that DNA is a causative factor in mutagenesis and not just the end product. By using the endogenous H-DNA-forming sequence found in the human
c-myc
promoter, mutation frequencies in a reporter gene were increased ≈20-fold over background in COS-7 cells. H-DNA-induced double-strand breaks (DSBs) were detected near the H-DNA locus. The structures of the mutants revealed microhomologies at the breakpoints, consistent with a nonhomologous end-joining repair of the DSBs. These results implicate H-DNA-induced DSBs in
c-myc
gene translocations in diseases such as Burkitt's lymphoma and t(12;15) BALB/c plasmacytomas, where most breakpoints are found near the H-DNA-forming site. Thus, our findings suggest that H-DNA is a source of genetic instability resulting from DSBs and demonstrate that naturally occurring DNA sequences are mutagenic in mammals, perhaps contributing to genetic evolution and disease.
A cationic lipid-formulated plasmid DNA vaccine confers sustained antibody-mediated protection against aerosolized anthrax spores
Authors: Hermanson G. , Whitlow V. , Parker S. , Tonsky K. , Rusalov D. , Ferrari M. , Lalor P. , Komai M. , Mere R. , Bell M. , Brenneman K. , Mateczun A. , Evans T. , Kaslow D. , Galloway D. , Hobart P.
Published: September 2004

DNA vaccines provide an attractive technology platform against bioterrorism agents due to their safety record in humans and ease of construction, testing, and manufacture. We have designed monovalent and bivalent anthrax plasmid DNA (pDNA) vaccines encoding genetically detoxified protective antigen (PA) and lethal factor (LF) proteins and tested their immunogenicity and ability to protect rabbits from an aerosolized inhalation spore challenge. Immune responses after two or three injections of cationic lipid-formulated PA, PA plus LF, or LF pDNAs were at least equivalent to two doses of anthrax vaccine adsorbed (AVA). High titers of anti-PA, anti-LF, and neutralizing antibody to lethal toxin (Letx) were achieved in all rabbits. Eight or nine animals in each group were challenged with 100× LD50of aerosolized anthrax spores 5 or 9 weeks after vaccination. An additional 10 animals vaccinated with PA pDNA were challenged >7 months postvaccination. All animals receiving PA or PA plus LF pDNA vaccines were protected. In addition, 5 of 9 animals receiving LF pDNA survived, and the time to death was significantly delayed in the others. Groups receiving three immunizations with PA or PA plus LF pDNA showed no increase in anti-PA, anti-LF, or Letx neutralizing antibody titers postchallenge, suggesting little or no spore germination. In contrast, titer increases were seen in AVA animals, and in surviving animals vaccinated with LF pDNA alone. Preclinical evaluation of this cationic lipid-formulated bivalent PA and LF vaccine is complete, and the vaccine has received U.S. Food and Drug Administration Investigational New Drug allowance.
Noninvasive Measurements of Human Brain Temperature Using Volume-Localized Proton Magnetic Resonance Spectroscopy
Authors: Corbett Ron , Laptook Abbot , Weatherall Paul
Published: September 2004

Elucidation of the role of cerebral hyperthermia as a secondary factor that worsens outcome after brain injury, and the therapeutic application of modest brain hypothermia would benefit from noninvasive measurements of absolute brain temperature. The present study was performed to evaluate the feasibility of using 1H magnetic resonance (MR) spectroscopy to measure absolute brain temperature in human subjects on a clinical imaging spectroscopy system operating at a field strength of 1.5 T. In vivo calibration results were obtained from swine brain during whole-body heating and cooling, with concurrent measurements of brain temperature via implanted probes. Plots of the frequency differences between the in vivo MR peaks of water and N-acetyl-aspartate and related compounds (NAX), or water and choline and other trimethylamines versus brain temperature were linear over the temperature range studied (28–40°C). These relationships were used to estimate brain temperature from 1H MR spectra obtained from 10 adult human volunteers from 4 cm3-volumes selected from the frontal lobe and thalamus. Oral and forehead temperatures were monitored concurrently with MR data collection to verify normothermia in all the subjects studied. Temperatures determined using N-acetyl-aspartate or choline as the chemical shift reference did not differ significantly, and therefore results from these estimates were averaged. The brain temperature (mean ± SD) measured from the frontal lobe (37.2 = 0.6°C) and thalamus (37.7 ± 0.6°C) were significantly different from each other (paired t-test, p = 0.035). We conclude that 1H MR spectroscopy provides a viable noninvasive means of measuring regional brain temperatures in normal subjects and is a promising approach for measuring temperatures in brain-injured subjects.
Improved Perfusion with rt-PA and Hirulog in a Rabbit Model of Embolic Stroke
Authors: Yenari Midori A. , de Crespigny Alexander , Palmer James T. , Roberts Sarah , Schrier Stanley L. , Albers Gregory W. , Moseley Michael E. , Steinberg Gary K.
Published: September 2004

We conducted a study using diffusion-weighted (DWI) and perfusion-weighted (PWI) magnetic resonance imaging (MRI) to evaluate the efficacy of thrombolysis in an embolic stroke model with recombinant tissue plasminogen activator (rt-PA) and hirulog, a novel direct-acting antithrombin. DWI can identify areas of ischemia minutes from stroke onset, while PWI identifies regions of impaired blood flow. Right internal carotid arteries of 36 rabbits were embolized using aged heterologous thrombi. Baseline DWI and PWI scans were obtained to confirm successful embolization. Four animals with no observable DWI lesion on the initial scan were excluded; therefore, a total of 32 animals were randomized to one of three treatment groups: rt-PA (n = 11), rt-PA plus hirulog (n = 11), or placebo (n = 10). Treatment was begun 1 h after stroke induction. Intravenous doses were as follows: rt-PA, 5 mg/kg over 0.5 h with 20% of the total dose given as a bolus; hirulog, 1 mg/kg bolus followed by 5 mg/kg over 1 h. MRI was performed at 2, 3, and 5 h following embolization. Six hours after embolization, brains were harvested, examined for hemorrhage, then prepared for histologic analysis. The rt-PA decreased fibrinogen levels by 73%, and hirulog prolonged the aPTT to four times the control value. Posttreatment areas of diffusion abnormality and perfusion delay were expressed as a ratio of baseline values. Significantly improved perfusion was seen in the rt-PA plus hirulog group compared with placebo (normalized ratios of the perfusion delay areas were as follows: placebo, 1.58, 0.47–3.59; rt-PA, 1.12, 0.04–3.95; rt-PA and hirulog, 0.40, 0.02–1.08; p < 0.05). Comparison of diffusion abnormality ratios measured at 5 h showed trends favoring reduced lesion size in both groups given rt-PA (normalized ratios of diffusion abnormality areas were as follows: placebo, 3.69, 0.39–15.71; rt-PA, 2.57, 0.74–5.00; rt-PA and hirulog, 1.95, 0.33–6.80; p = 0.32). Significant cerebral hemorrhage was observed in one placebo, two rt-PA, and three rt-PA plus hirulog treated animals. One fatal systemic hemorrhage was observed in each of the rt-PA groups. We conclude that rt-PA plus hirulog improves cerebral perfusion but does not necessarily reduce cerebral injury. DWI and PWI are useful methods for monitoring thrombolysis.
Calcineurin Inhibitor, FK506, Prevents Reduction in the Binding Capacity of Cyclic AMP-Dependent Protein Kinase in Ischemic Gerbil Brain
Authors: Tanaka Kortaro , Fukuuchi Yasuo , Nozaki Hiroyuki , Nagata Eiichiro , Kondo Taro , Koyama Satoshi , Dembo Tomohisa
Published: September 2004

We examined the effects of FK506, a specific inhibitor of calcineurin, on the binding capacity of cyclic AMP-dependent protein kinase (cAMP-DPK) in gerbils subjected to 2-h cerebral hemispheric ischemia. FK506 (0.1 mg/kg) was infused intravenously at 15 min prior to the induction of ischemia by common carotid artery occlusion. The binding capacity of cAMP-DPK was evaluated by autoradiographic analysis of the cAMP binding, and cerebral blood flow (CBF) was measured by the [14C] iodoantipyrine method. In the sham-operated gerbils, FK506 significantly increased mean arterial blood pressure and tended to decrease CBF, suggesting that FK506 may constrict systemic blood vessels as well as cerebral blood vessels. On the other hand, cAMP binding was not altered by FK506 in the sham-operated gerbils. In the ischemia group of gerbils, FK506 prevented any significant reduction of cAMP binding in the hippocampus CA1 and cerebral cortices on the ischemic side, whereas it exerted no significant influence on the cAMP binding of the nonischemic side. The values of CBF were comparable between the vehicle-treated gerbils and FK506-treated gerbils in the ischemic regions. Preservation of cAMP binding indicates that intracellular signal transduction via cAMP-DPK can be maintained by FK506 despite ischemia, suggesting that this agent may be beneficial for reducing ischemic tissue damage.
Blood Glucose Concentration after Cardiopulmonary Resuscitation Influences Functional Neurological Recovery in Human Cardiac Arrest Survivors
Authors: Müllner Marcus , Sterz Fritz , Binder Michael , Schreiber Wolfgang , Deimel Alexander , Laggner Anton N.
Published: September 2004

Experimental data suggest that postischemic blood glucose concentration plays an important role in modulating both ischemic cerebral infarction and selective neuronal necrosis. This study investigated the association between functional neurological recovery and blood glucose concentrations in human cardiac arrest survivors. A group of 145 nondiabetic patients were evaluated after witnessed ventricular fibrillation cardiac arrest. Data regarding cardiac arrest were collected according to an internationally accepted protocol immediately after arrival. Blood glucose was measured on admission and 6, 12, and 24 h thereafter. To control for duration of cardiac arrest and cardiogenic shock, both known to influence outcome as well as blood glucose, levels, Spearman rank partial correlation was used. In this multivariate analysis, a high admission blood glucose level tended to be associated with poor neurological outcome ( rs = −0.16, n = 142, p = 0.06). The association between high median blood glucose levels over 24 h and poor neurological outcome was strong and statistically significant ( rs = −0.2, n = 145, p = 0.015). High blood glucose concentrations occurring over the first 24 h after cardiac arrest have deleterious effects on functional neurological recovery. Whether cardiac arrest survivors might benefit from reduction of blood glucose levels needs further investigation.