bluuebunny/crossref_metadata_2025 huggingface dataset:
Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska
Authors: Roberts Helen M. , Muhs Daniel R. , Wintle Ann G. , Duller Geoff A. T. , Bettis E. Arthur
Published: May 2003

A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.
Coral δ18O records as an indicator of winter monsoon intensity in the South China Sea
Authors: Peng Zicheng , Chen Tegu , Nie Baofu , Head M. John , He Xuexian , Zhou Weijian
Published: May 2003

We have used correlative analysis between mean December–January–February winter wind velocities, measured at the Xisha Meteorological Observatory (16°50′N, 112°20′E) in the middle of the South China Sea, and mean δ18O data for the corresponding month from Porites lutea coral, collected in Longwan waters (19°20′N, 110°39′E), to obtain a linear equation relating the two datasets. This winter wind velocity for the South China Sea (WMIIscs) can then be correlated to the coral δ18O by the equation WMIIscs = −1.213–1.351 δ18O (‰ PDB), r = −0.60, n = 40, P = 0.01. From this, the calculated WMIIscs-δ18O series from 1944 to 1997 tends to decrease during the 1940s to the 1960s; it increases slightly during the 1970s and then decreases again in the 1980s and 1990s. The calculated decadal mean WMIIscs-δ18O series had a obvious decrease from 5.92 to 4.63 m/s during the period of 1944–1997. The calculated yearly mean WMIIscs-δ18O value is 5.58 m/s from 1944 to 1976 and this decreases to 4.85 m/s from 1977 to 1998. That is the opposite trend to the observed yearly mean SST variation. The yearly mean SST anomaly is −0.27° from 1943 to 1976 and this increases to +0.16° from 1977 to 1998. Spectral analysis used on a 54-year-long calculated WMIIscs-δ18O series produces spectral peaks at 2.4–7 yr, which can be closely correlated with the quasibiennial oscillation band (QBO band, 2–2.4 yr) and the El Ñino southern oscillation band (ENSO band, 3–8 yr). Hence most of the variability of the winter monsoon intensity in the middle of the South China Sea is mainly constrained by changes in the thermal difference between the land and the adjoining sea area, perhaps due to global warming.
Developmentally regulated usage of Physarum DNA replication origins
Authors: Maric Chrystelle , Bénard Marianne , Pierron Gérard
Published: May 2003

To determine the extent to which eukaryotic replication origins are developmentally regulated in transcriptionally competent cells, we compared origin use in untreated growing amoebae and plasmodia of Physarum polycephalum. At loci that contain genes transcribed in both developmental stages, such as the ribosomal RNA genes and two unlinked actin genes, we show that there is a similar replicational organization, with the same origins used with comparable efficiencies, as shown by two‐dimensional agarose‐gel electrophoresis. By contrast, we found cell‐type‐specific replication patterns for the homologous, unlinked profilin A (proA) and profilin P (proP) genes. proA is replicated from a promoter‐proximal origin in amoebae, in which it is highly expressed, and is replicated passively in the plasmodium, in which it is not expressed. Conversely, proP is replicated passively and is not expressed in amoebae, but coincides with an efficient origin when highly expressed in the plasmodium. Our results show a reprogramming of S phase that is linked to the reprogramming of transcription during Physarum cell differentiation. This is achieved by the use of two classes of promoter‐associated replication origins: those that are constitutively active and those that are developmentally regulated. This suggests that replication origins, like genes, are under epigenetic control associated with cellular differentiation.
Maintenance of the correct open reading frame by the ribosome
Authors: Hansen Thomas M , Baranov Pavel V , Ivanov Ivaylo P , Gesteland Raymond F , Atkins John F
Published: May 2003

During translation, a string of non‐overlapping triplet codons in messenger RNA is decoded into protein. The ability of a ribosome to decode mRNA without shifting between reading frames is a strict requirement for accurate protein biosynthesis. Despite enormous progress in understanding the mechanism of transfer RNA selection, the mechanism by which the correct reading frame is maintained remains unclear. In this report, evidence is presented that supports the idea that the translational frame is controlled mainly by the stability of codon–anticodon interactions at the P site. The relative instability of such interactions may lead to dissociation of the P‐site tRNA from its codon, and formation of a complex with an overlapping codon, the process known as P‐site tRNA slippage. We propose that this process is central to all known cases of +1 ribosomal frameshifting, including that required for the decoding of the yeast transposable element Ty3. An earlier model for the decoding of this element proposed ‘out‐of‐frame’ binding of A‐site tRNA without preceding P‐site tRNA slippage.
Widespread PrPSc accumulation in muscles of hamsters orally infected with scrapie
Authors: Thomzig Achim , Kratzel Christine , Lenz Gudrun , Krüger Dominique , Beekes Michael
Published: May 2003

Scrapie, bovine spongiform encephalopathy and chronic wasting disease are orally communicable, transmissible spongiform encephalopathies (TSEs). As zoonotic transmissions of TSE agents may pose a risk to human health, the identification of reservoirs for infectivity in animal tissues and their exclusion from human consumption has become a matter of great importance for consumer protection. In this study, a variety of muscles from hamsters that were orally challenged with scrapie was screened for the presence of a molecular marker for TSE infection, PrPSc (the pathological isoform of the prion protein PrP). Sensitive western blotting revealed consistent PrPSc accumulation in skeletal muscles from forelimb and hindlimb, head, back and shoulder, and in tongue. Previously, our animal model has provided substantial baseline information about the peripheral routing of infection in naturally occurring and orally acquired ruminant TSEs. Therefore, the findings described here highlight further the necessity to investigate thoroughly whether muscles of TSE‐infected sheep, cattle, elk and deer contain infectious agents.
The AVIT protein family
Authors: Kaser Alexandra , Winklmayr Martina , Lepperdinger Günther , Kreil Günther
Published: May 2003

Homologues of a protein originally isolated from snake venom and frog skin secretions are present in many vertebrate species. They contain 80–90 amino acids, 10 of which are cysteines with identical spacing. Various names have been given to these proteins, such as mamba intestinal protein 1 (MIT1), Bv8 (Bombina variegata molecular mass ∼8 kDa), prokineticins and endocrine‐gland vascular endothelial growth factor (EG‐VEGF). Their amino‐terminal sequences are identical, and so we propose that the sequence of their first four residues, AVIT, is used as a name for this family. From a comparison of the sequences, two types of AVIT proteins can be discerned. These proteins seem to be distributed widely in mammalian tissues and are known to bind to G‐protein‐coupled receptors. Members of this family have been shown to stimulate contraction of the guinea pig ileum, to cause hyperalgesia after injection into rats and to be active as specific growth factors. Moreover, the messenger RNA level of one of these AVIT proteins changes rhythmically in the region of the brain known as the suprachiasmatic nucleus. This shows that members of this new family of small proteins are involved in diverse biological processes.
A novel mechanism for preventing mutations caused by oxidation of guanine nucleotides
Authors: Ishibashi Toru , Hayakawa Hiroshi , Sekiguchi Mutsuo
Published: May 2003

MutT‐related proteins, including the Escherichia coli MutT and human MutT homologue 1 (MTH1) proteins, degrade 8‐oxo‐ 7,8‐dihydrodeoxyguanosine triphosphate (8‐oxo‐dGTP) to a monophosphate, thereby preventing mutations caused by the misincorporation of 8‐oxoguanine into DNA. Here, we report that human cells have another mechanism for cleaning up the nucleotide pool to ensure accurate DNA replication. The human Nudix type 5 (NUDT5) protein hydrolyses 8‐oxo‐dGDP to monophosphate with a Km of 0.77 µM, a value considerably lower than that for ADP sugars, which were originally identified as being substrates of NUDT5. NUDT5 hydrolyses 8‐oxo‐dGTP only at very low levels, but is able to substitute for MutT when it is defective. When NUDT5 is expressed in E. coli mutT− cells, the increased frequency of spontaneous mutations is decreased to normal levels. Considering the enzymatic parameters of MTH1 and NUDT5 for oxidized guanine nucleotides, NUDT5 might have a much greater role than MTH1 in preventing the occurrence of mutations that are caused by the misincorporation of 8‐oxoguanine in human cells.
Detection of cold metastable atoms at a surface
Authors: Schneble D. , Hasuo M. , Anker T. , Pfau T. , Mlynek J.
Published: May 2003

A scheme for the detection of cold metastable atoms at surfaces with spatial and temporal resolution is studied experimentally, using methods of laser cooling and atom optics. Electron emission yields for deexcitation of the metastable states 1s5(J=2) and 1s3(J=0) of argon at a gold surface are compared with a technique that is based on optical pumping and the use of an evanescent-wave atom mirror as an internal-state filter, and are found to agree to within an uncertainty of 10%. The application of the detection scheme to time-of-flight spectroscopy of cold atom clouds is demonstrated. The detector has a field of view of 3 mm diameter, a spatial resolution of order 100 μm, and a time resolution of 20 μs, and the single-atom detection efficiency near the center of the field of view is 14% in the linear counting regime of up to 106 atoms/s.
Superconducting microwave resonator for millikelvin magnetic resonance force microscopy
Authors: Mamin H. J. , Budakian R. , Rugar D.
Published: May 2003

We have fabricated a superconducting resonator capable of generating a strong microwave magnetic field in a small (100 μm) volume for low temperature magnetic resonance experiments. While the resonator was specifically developed for use at millikelvin temperatures in a dilution refrigerator, where the total cooling power is limited to a few hundred microwatts, it is also useful at temperatures up to 5 K. The resonator consists of a 220 μm diameter, 2-1/2 turn niobium coil resonating with a short section of niobium microstripline. At a resonance frequency of 3 GHz, the loaded Q of the resonator was 780. The field strength was characterized by performing electron spin nutations. Operating at 100 mK with 320 μW of dissipated power, the resonator generated a field of 4 G at a distance of 100 μm from the coil.
Instrument equipped with Maxwell displacement current and optical second-harmonic generation measurement system
Authors: Tojima Atsushi , Manaka Takaaki , Iwamoto Mitsumasa
Published: May 2003

An experimental instrument equipped with the Maxwell displacement current (MDC) and optical second-harmonic generation measurement system has been developed for the study of the dielectric property of organic monolayers on the surface of water. In this instrument, the generation of MDC across monolayers is recorded by monolayer compression. At the same time, second-harmonic signals generated from monolayers by the laser irradiation are monitored. Using this experimental instrument, the orientational order of 4-octyl-4′-n-cyanobiphenyls monolayers was examined, and one of the most important parameters to characterize the physical properties of monolayers, the orientational order parameters S1 and S3 defined by Legendre polynomials, was determined.
New Pockels field sensor with ferroelectric liquid-crystal phase modulator
Authors: Tada K. , Tanaka Y. , Takada T. , Murooka Y.
Published: May 2003

A new optical field sensor for measuring the electric field close to an electrical discharge has been developed. The new system that uses both P- and S-polarized light-division and azimuth angle modulation methods has been devised and investigated. By using a ferroelectric liquid-crystal phase modulator instead of an azimuth angle modulator, it has been possible to eliminate noise from the optical field measurement system, specifically, the birefringence effects in a long optical fiber cable. The optical cable is used for connecting a Pockels field sensor located close to the discharge with the main system located at the ground. Furthermore, it has been possible to compensate for the sensitivity difference between two optical detectors for converting P- and S-polarized light waves to an electrical signal. From this, it is found that by using a light reflection technique, the measurable minimum field strength is reduced from 100 kV/m to 1.0 kV/m in the discharge region. If the smallest phase change in the system is set to be less than 10−3 [rad], the measurable minimum field strength is reduced to 0.1 kV/m. The possible use of the probe is also considered for checking for damage caused by cosmic rays to the insulating skin of a spacecraft.
Differential pressure experiment to probe hole growth in freely standing polymer films
Authors: Roth C. B. , Nickel B. G. , Dutcher J. R. , Dalnoki-Veress K.
Published: May 2003

We have developed a sensitive experiment which allows the measurement of the growth of holes in thin freely standing polystyrene (PS) films at elevated temperatures. In the experiment, a constant small pressure difference is applied and maintained across the freely standing film, and the formation and growth of holes is detected as a flow of air through the film. From measurements of freely standing PS films for which the glass transition temperature Tg is equal to the bulk value Tgbulk, as well as for films that are sufficiently thin that Tg is 30 °C less than Tgbulk, we find that substantial chain mobility occurs only at temperatures that are comparable to Tgbulk. The results can be interpreted as a shear thinning effect, which is consistent with previous optical microscopy measurements of hole growth in freely standing PS films.
Transparent miniature dielectric resonator for electron paramagnetic resonance experiments
Authors: Blank Aharon , Stavitski Eli , Levanon Haim , Gubaydullin Firdus
Published: May 2003

A novel miniature (∼2×2×1 mm) dielectric resonator for X-band electron paramagnetic resonance experiments is presented. The resonator is based on a single crystal of KTaO3, which is excited to its TE01δ resonance mode by means of a simple iris-screw coupling. Several configurations of resonators are considered and discussed with respect to their filling factor, power conversion ratio, and optical excitation efficiency. Our findings are presented in terms of both experimental and theoretical studies. For small samples, the high filling factor of this resonator results in a signal increase by a factor of 140–800 (assuming nonsaturating conditions) as compared to a rectangular X-band cavity. The high power conversion factor (∼40 G/W), should enable one to perform pulse experiments employing power amplifiers, with ∼100-fold less peak power used for rectangular cavities. With an antireflective layer, the crystal’s transparency enables efficient laser illumination of the sample in light-induced experiments.
Ultrahigh-vacuum soft x-ray reflectometer
Authors: Sacchi Maurizio , Spezzani Carlo , Torelli Piero , Avila Antoine , Delaunay Renaud , Hague Coryn F.
Published: May 2003

We have designed, built, and tested a new instrument for soft x-ray scattering experiments. The reflectometer works under ultrahigh vacuum and permits in situ preparation and characterization of the samples. In particular, deposition and sputtering operations can be performed while measuring x-ray scattering. We report the results of test measurements performed using synchrotron radiation. The precision of the combined positioning of sample and detector angles is better than 0.01°. Separately, sample and detector rotations have a repeatability that is better than 0.005°. Applications will be in the field of surface physics, with emphasis on magnetic properties of surfaces, thin films, and multilayered structures.
TOBI: A two-laser beam infrared system for time-resolved plasma diagnostics of infrared active compounds
Authors: McManus J. B. , Nelson D. , Zahniser M. , Mechold L. , Osiac M. , Röpcke J. , Rousseau A.
Published: May 2003

A compact and transportable two laser beam infrared (TOBI) system based on infrared absorption spectroscopy has been developed for time-resolved plasma diagnostics. The TOBI system contains two independent tunable diode lasers which can be directed through a plasma or into a multipass cell for exhaust gas detection. Rapid scan software with real-time line shape fitting provides a time resolution up to 10 μs to study chemical kinetic processes of infrared active compounds in plasmas. The capabilities of the TOBI system have been demonstrated in plasmas of pulsed H2–N2 surface wave and in pulsed air–CH4 dc discharges.
A compact, parallel-detection diffuse optical mammography system
Authors: Iftimia Nicusor , Gu Xuejun , Xu Yong , Jiang Huabei
Published: May 2003

A near-infrared continuous-wave optical tomographic system for in vivo breast imaging is presented. The system primarily consists of three diode lasers at 785, 808, and 830 nm, 64×64 channel source/detector optic fibers for light delivery/receiving, and 16 computer gain controlled photomultiplier tubes for parallel detection. Central to the system is a fiber optic probe that is composed of four layers of illuminating/receiving fibers arranged in a frustum of cone-shaped configuration. This probe provides data sets for both two-dimensional (2D) and three-dimensional (3D) imaging. The system is computer controlled via Labview software. A full set of tomographic data (64×64) at one wavelength can be obtained in 4 min. All hardware components are contained in a single frame under an exam table which makes the entire hardware a compact and mobile system. The design, calibration, and performance of the imaging system are described in detail. The system is tested using tissue-like phantom experiments. Both 2D and 3D images of optical absorption and reduced scattering coefficients are obtained using powerful finite element based reconstruction algorithms.
A scanning capacitance microscope based on a coaxial resonator: High sensitivity and cheap and compact design without the use of lock-in detection systems
Authors: Ferrara Marco , Odoardi Ottorino
Published: May 2003

We describe a scanning capacitance microscope based on an oscillator whose frequency is controlled by a coaxial line λ/2 resonator tuned at the terminal ends by two capacitances, one obtained by a varicap, the other due to the tip-sample junction. Both the values of the tuning capacitances can be changed by a biasing voltage applied, respectively, to the varicap or to a piezoceramic which controls the tip-sample distance. The two input voltage controlled oscillator is part of a phase locked loop and, depending on the input used, it is possible to perform constant height or constant capacitance analysis. In the first case, the instrument gives the profile of the tip sample capacitance while, in the second case, constant capacitance profiles are obtained. Theoretical analysis and experimental results are reported. Capacitance–voltage metal–oxide–semiconductor curves and the images of a calibration grating obtained with our instrument are also reported.
Impedance probe to measure local gas volume fraction and bubble velocity in a bubbly liquid
Authors: Zenit R. , Koch D. L. , Sangani A. S.
Published: May 2003

We have developed a dual impedance-based probe that can simultaneously measure the bubble velocity and the gas volume fraction in length scales comparable to the bubble diameter. The accurate determination of the profiles is very important for comparisons with existing theories that describe the rheological behavior of bubbly liquids. The gas volume fraction is determined by the residence time of bubble within the measuring volume of the probe. We have found that the details of the bubble-probe interactions must be taken into account to obtain an accurate measure of the gas volume fraction at a point. We are able to predict the apparent nonlinear behavior of the gas volume fraction measurement at large concentrations. The bubble velocity is obtained from the cross correlation of the signals of two closely spaced identical probes. Performance tests and results are shown for bubble velocity and bubble concentration profiles in a gravity driven shear flow of a bubbly liquid.
Infrared thermal velocimetry for nonintrusive flow measurement in silicon microfluidic devices
Authors: Chung Jaewon , Grigoropoulos Costas P. , Greif Ralph
Published: May 2003

Measurement of velocity is essential for verification of the performance of many microelectromechanical system (MEMS) based fluidic devices. MEMS devices are usually made of silicon which is transparent at infrared wavelengths. Infrared thermal velocimetry has been developed to measure the velocity in silicon microchannels utilizing the infrared transparency of silicon. Applications are broad and include MEMS fluidic devices and bio-fluidic elements. Briefly, an infrared laser heats the flowing fluid in a silicon microchannel and the recording of the thermal image of the moving heated liquid permits determination of the average flow velocity. It has been demonstrated that this method can be used to measure a wide range of velocities (1 cm/s–1 m/s or higher) with an accuracy of ±10%. The velocity of the maximum radiative intensity point (VMRIP) along the center of the channel is chosen to characterize the velocity in the channel. Numerical results show good agreement with the experimental results.
Thinning-out in optimized pulse shaping method using genetic algorithm
Authors: Mizoguchi R. , Onda K. , Kano S. S. , Wada A.
Published: May 2003

An optical pulse shaping system using a spatial light modulator (SLM) controlled by genetic algorithm (GA) optimization was improved and we demonstrated that the time for finding the optimal condition could be shortened by a proposed “thinning out” method. In this method, GA controls only every N (N=1, 2, 4, 8, 16) pixel in the SLM. The conditions of the remaining pixels are derived by interpolation. The effectiveness of this method was verified by the pulse compression of chirped femtosecond pulses and the increase in the two-photon excitation efficiency of α-perylene crystals. The influence of the thinning out on the pulse shape is discussed, and an advanced method is proposed. It is shown that the disadvantages of the thinning out method can be compensated for by changing the value of N during optimization.
Capillary-discharge-based portable detector for chemical vapor monitoring
Authors: Duan Yixiang , Su Yongxuan , Jin Zhe
Published: May 2003

Conventional portable instruments for sensing chemical vapors have certain limitations for on-site use. In this article, we develop a genuinely portable detector that is sensitive, powerful, rugged, of simple design, and with very low power needs. Such a detector is based on a dry-cell battery-powered, capillary-discharge-based, microplasma source with optical emission detection. The microscale plasma source has very special features such as low thermal temperature and very low power needs. These features make it possible for the plasma source to be powered with a small dry-cell battery. A specially designed discharge chamber with minielectrodes can be configured to enhance the plasma stability and the system performance. A very small amount of inert gas can be used as sample carrier and plasma supporting gas. Inert gases possess high excitation potentials and produce high-energy metastable particles in the plasma. These particles provide sufficient energy to excite chemical species through Penning ionization and/or energy transfer from metastable species. A molecular emission spectrum can be collected with a palm-sized spectrometer through a collimated optical fiber. The spectrum can be displayed on a notebook computer. With this design and arrangement, the new detector provides high sensitivity for organic chemical species. The advantages and features of the newly developed detector include high sensitivity, simple structure, low cost, universal response, very low power consumption, compact volume with field portable capability, and ease of operation.
Foamability and foam stability at high pressures and temperatures. I. Instrument validation
Authors: Tyrode Eric , Pizzino Aldo , Rojas Orlando J.
Published: May 2003

An instrument was designed and assembled with the aim of measuring macroscopic properties of foams (such as foamability and stability) under high pressures and moderate temperatures (up to 105 bar and 425 K, respectively). The device makes use of infrared sensors to detect the foam forefront position as it is generated by gas sparging in the foaming solution. The measurement makes use of a modified dynamic Bikerman protocol to estimate the foamability and stability of the studied solution. Traditional direct observation used in foam experiments at ambient conditions is therefore circumvented and the instrument can be set up in an appropriate place and monitored remotely so as to reduce the risks involved in high-pressure, high-temperature operations. Data from the infrared system allows not only following the dynamics of foam phenomena but also the relative foam quality along the column, and the presence of air pockets in the case of unstable or pulsating foams. A series of fluorosurfactants (cationic, anionic, and nonionic) were used to validate the instrument and the effect of temperature on foamability, foam stability and foam quality is discussed. Finally, synergistic effects were observed with respect to the foam behavior of different mixtures of the studied surfactants.
Microstitching interferometry for x-ray reflective optics
Authors: Yamauchi Kazuto , Yamamura Kazuya , Mimura Hidekazu , Sano Yasuhisa , Saito Akira , Ueno Kazumasa , Endo Katsuyoshi , Souvorov Alexei , Yabashi Makina , Tamasaku Kenji , Ishikawa Tetsuya , Mori Yuzo
Published: May 2003

A new stitching interferometry based on a microscopic interferometer having peak-to-valley height accuracy of subnanometer order and lateral resolution higher than 20 μm was developed to measure surface figures of large-size x-ray mirror optics. Cumulative errors of the stitching angle in a long spatial wavelength range were effectively reduced to be 1×10−7 rad levels using another interferometer having a large cross section in the optical cavity. Some optical performances of ultraprecise x-ray mirrors, such as submicrofocused beam profile, were wave optically calculated from the measured surface figure profiles and observed at the 1 km long beamline (BL29XUL) of SPring-8. Observed and wave optically calculated results were in good agreement with a high degree of accuracy.
Dual temperature and strain sensor using a combined fiber Bragg grating and fluorescence intensity ratio technique in Er3+-doped fiber
Authors: Trpkovski S. , Wade S. A. , Baxter G. W. , Collins S. F.
Published: May 2003

A prototype dual temperature–strain point sensor has been demonstrated by combining a short length of erbium-doped fiber in close proximity to a fiber Bragg grating. By measurement of the green fluorescence intensity ratio in erbium (Er3+) and the Bragg wavelength shift of a fiber Bragg grating the temperature and strain are deduced. Calibrations reveal that the sensitivity of the fluorescence intensity ratio in Er3+-doped fiber to strain is near zero. Three alternative analysis methods were used; the conventional matrix method, and two variations of a technique that provides a better fit to the fluorescence intensity ratio temperature data using a quadratic. The quadratic methods considered two cases of the strain dependence of the fluorescence intensity ratio, namely, zero and linear. The matrix method showed standard deviations of 2.2 °C and 20.6 με, while the quadratic fit with a linear strain dependence yielded 1.0 °C and 22.9 με over temperature and strain ranges of 18–150 °C and 350–2534 με, respectively.
Development of a piezoelectric actuator using a three-dimensional bridge-type hinge mechanism
Authors: Kim Jun Hyung , Kim Soo Hyun , Kwak Yoon Keun
Published: May 2003

Piezostacks are capable of producing very large forces, but they provide only limited displacements. Thus, the displacement amplification mechanism is necessary to make those actuators more efficient and useful. For this purpose, a two-bridge-type flexure hinge mechanisms in series in a three-dimensional structure is proposed in this study. To show the validity of the proposed mechanism, the kinematic analysis is carried out by a matrix method and by a finite element method, and then the amplification ratio derived from both methods were compared with the simple geometric ratio, which is an order of magnitude too high. Along with this analysis, displacement and frequency experiments are also performed to verify the analysis results. The displacement errors between the matrix analysis results and experimental ones are within 10%. This indicates that the deformation of the flexure hinge in the parasitic direction should be considered for more exact estimation of amplification ratio of the bridge-type hinge mechanism. At last, the performance of this actuator is analyzed using the matrix model with respect to design parameters. The results show that the performance of a piezoactuator can be improved with the optimization of hinge parameters for each application requirement.
Inverse problem in air-saturated porous media via reflected waves
Authors: Fellah Z. E. A. , Berger S. , Lauriks W. , Depollier C. , Chapelon J. Y.
Published: May 2003

Direct and inverse scattering problem in air filled porous materials is solved. A simple ultrasonic reflectivity method is proposed for measuring the porosity of porous materials having a rigid frame. The proposed method is based on a temporal model of the direct and inverse scattering problem for the propagation of transient ultrasonic waves in a homogeneous isotropic slab of porous material having a rigid frame. This time domain model of wave propagation was initially introduced by the authors [Z. E. A. Fellah and C. Depollier, J. Acoust. Soc. Am. 107, 683 (2000)]. The viscous and thermal losses of the medium are described by the model devised by Johnson et al. [D. L. Johnson, J. Koplik, and R. Dashen, J. Fluid. Mech. 176, 379 (1987)] and J. F. Allard (Chapman and Hall, London, 1993)] modified by a fractional calculus-based method applied in the time domain. The reflected acoustic wave by air filled porous media can be approximated by the reflected wave at the first interface. The expression of the reflection coefficient is reduced to a simple expression depending on porosity, tortuosity, and incidence angle. An expression of the porosity function of the tortuosity and incidence angle is obtained by solving the inverse problem. Experimental and numerical validation results of this method are presented. This method has the advantage of being rapid and efficient.
Synthesis, characterization, and modeling of high quality ferromagnetic Cr-doped AlN thin films
Authors: Wu Stephen Y. , Liu H. X. , Gu Lin , Singh R. K. , Budd L. , van Schilfgaarde M. , McCartney M. R. , Smith David J. , Newman N.
Published: May 2003

We report a theoretical and experimental investigation of Cr-doped AlN. Density functional calculations predict that the isolated Cr t2 defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional Al1−xCrxN random alloys with 0.05⩽x⩽0.15 are predicted to have Curie temperatures over 600 K. Experimentally, we have characterized and optimized the molecular beam epitaxy thin film growth process, and observed room temperature ferromagnetism with a coercive field, Hc, of 120 Oe. The measured magnetic susceptibility indicates that over 33% of the Cr is magnetically active at room temperature and 40% at low temperature.
Hydrogen density-of-states in polycrystalline silicon
Authors: Nickel N. H. , Brendel K.
Published: May 2003

The influence of laser crystallization on hydrogen bonding in polycrystalline silicon is investigated employing hydrogen effusion measurements. Fully crystallized poly-Si samples contain a residual H concentration of up to 1.5×1022 cm−3. From the effusion spectra, the H density-of-states distribution is derived. Interestingly, hydrogen bonding is affected by the deposition temperature of the amorphous starting material. Below the H transport states, four peaks are observed in the H density of states at ≈−2.15, −2.4, −2.7, and −3.25 eV.
Observation of a hydrogenic donor in the luminescence of electron-irradiated GaN
Authors: Yang Qing , Feick Henning , Weber Eicke R.
Published: May 2003

Excitonic luminescence of GaN after irradiation with 0.42-MeV electrons has been investigated in detail. The low-energy irradiation generates damage exclusively in the N sublattice. Additional bound-exciton lines are found and are shown to arise from a hydrogenic donor with a binding energy of 25 meV. The donor binding energy, bound-exciton localization energy, and bound-exciton lifetime are discussed in comparison with the values observed for ON and SiGa in the same sample. Nitrogen vacancies VN forming a hydrogenic donor state are suggested to be the most likely origin of this luminescence emission. Finally, a metastable behavior related to the damage-induced defects is reported and discussed in conjunction with interstitial-nitrogen-related defects.
Highly stable and textured hydrogenated ZnO thin films
Authors: Myong Seung Yeop , Lim Koeng Su
Published: May 2003

We investigated intentionally hydrogenated zinc oxide (ZnO:H) fabricated by combining photoassisted metalorganic chemical vapor deposition and mercury-sensitized hydrogen addition methods. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved surface roughness of the ZnO:H film due to an enhancement of (112̄0) orientation. The high-quality ZnO:H film is promising as a back reflector material for thin-film solar cells.
Temperature dependence of gate–leakage current in AlGaN/GaN high-electron-mobility transistors
Authors: Arulkumaran S. , Egawa T. , Ishikawa H. , Jimbo T.
Published: May 2003

We report on the studies of the temperature dependence of gate–leakage current in AlGaN/GaN high-electron-mobility transistors (HEMTs) for the temperature range 20–400 °C. The results show that the temperature dependence of gate–leakage current for AlGaN/GaN HEMTs at subthreshold regime (VGS=−6.5 V) have both negative and positive trends. It has been observed that the leakage current decreases with the temperature up to 80 °C. Above 80 °C, the leakage current increases with the temperature. The negative temperature dependence of leakage current with the activation energy +0.61 eV is due to the impact ionization. The positive temperature dependence of leakage current with the activation energy −0.20 eV is due to the surface related traps, and the activation energy −0.99 eV is due to the temperature assisted tunneling mechanism. The drain voltage at a fixed drain–leakage current reveals the occurrence of both positive (+0.28 V/K) and negative (−0.53 V/K) temperature coefficients.
Normal-mode anisotropic liquid-crystal gels
Authors: Fan Yun-Hsing , Ren Hongwen , Wu Shin-Tson
Published: May 2003

A normal-mode anisotropic liquid-crystal (LC) gel is demonstrated. In the absence of an electric field, the light polarized along the rubbing direction is scattered. In the voltage-on state, the gel is highly transparent and is independent of polarization. Such a normal mode LC gel exhibits a modest contrast ratio, response time, and low operating voltage. It can be used as a broadband switchable polarizer, variable optical attenuator, and reflective display.
Third-order nonlinearities in silicon at telecom wavelengths
Authors: Dinu M. , Quochi F. , Garcia H.
Published: May 2003

The two-photon absorption coefficient and Kerr coefficient of bulk crystalline silicon are determined near the telecommunication wavelengths of 1.3 and 1.55 μm using femtosecond pulses and a balanced Z-scan technique. A phase shift sensitivity of the order of 1 mrad is achieved, enabling the accurate measurement of third-order nonlinear coefficients at fluences smaller than 100 μJ/cm2. From the two-photon absorption coefficient (β∼0.8 cm/GW) and the Kerr coefficient (n2∼4×10−14 cm2/W) at a wavelength λ=1.54 μm, a value F∼0.35 for the nonlinear figure of merit for all-optical switching is determined.
Giant-magnetoimpedance-based sensitive element as a model for biosensors
Authors: Kurlyandskaya G. V. , Sánchez M. L. , Hernando B. , Prida V. M. , Gorria P. , Tejedor M.
Published: May 2003

We study the magnetoimpedance effect, using a Co67Fe4Mo1.5Si16.5B11 amorphous, ribbon-based sensitive element, in the presence of a commercial Ferrofluid® liquid thin layer covering the ribbon surface. The magnetoimpedance response is clearly dependent on the presence of the magnetic ferroliquid, the value of the applied magnetic field, and the parameters of the driving current. The magnetoimpedance-based prototype is proposed as a biosensor with high sensitivity to the fringe field produced by magnetic nanoparticles. A special advantage of this sensor is its high stability to chemical aggressive media; hence, it can be used for in situ measurements during fabrication of biomaterials with a high level of affinity and specificity with nanoparticles employed as bimolecular labels.
Surface structures of a Co-doped anatase TiO2 (001) film investigated by scanning tunneling microscopy
Authors: Yang J. S. , Kim D. H. , Bu S. D. , Noh T. W. , Phark S. H. , Khim Z. G. , Lyo I. W. , Oh S.-J.
Published: May 2003

The surface structure of an anatase Ti0.94Co0.06O2 (001) film, grown epitaxially on a Nb-doped SrTiO3 (001) substrate, was investigated using in situ scanning tunneling microscopy. For the as-grown film, a (1×n) (n=3, 4, 5, and 6) reconstructed surface was observed that shows (n−2) faint rows between adjacent bright rows. After annealing at 650 °C, nanoparticles appeared, mostly on the step edges. From the I–V curves measured by scanning tunneling spectroscopy, the tunneling gap of Co:TiO2 was estimated to be about 3.0 eV, consistent with the band gap (Eg=3.2 eV) of pure anatase TiO2. However, on nanoparticles, the I–V curve showed a much smaller gap, suggesting that the particle must be different from TiO2.
A valence electron concentration criterion for glass-formation ability of metallic liquids
Authors: Jiang Q. , Chi B. Q. , Li J. C.
Published: May 2003

Critical cooling rate of a metallic liquid (Rc) necessary to form glass is correlated to the valence concentration e/a of the liquid (e and a denote valence and atom number in a unit cell, respectively). Rc of liquid is minimized at e/a=3.5. The principles of the composition design to form bulk metallic glasses are as follows: e/a=3.5, the component number (n) in the alloy is larger than three, and the component percentage of the ith component (xi) approaches 1/n.
Absence of carrier recombination associated with the defect pool model in intrinsic amorphous silicon layers: Evidence from current–voltage characteristics on p–i–n and n–i–p solar cells
Authors: Deng J. , Pearce J. M. , Koval R. J. , Vlahos V. , Collins R. W. , Wronski C. R.
Published: May 2003

Forward bias current–voltage characteristics (JD–V) were studied for both p–i–n (superstrate) and n–i–p (substrate) (a-SiC:H p)/(a-Si:H i) solar-cell structures having different p/i interface layers and different thickness i-layers. Contributions of the p/i interfaces to the JD–V characteristics were separated, and the dependence on the thickness of the i-layers was established. Equivalence was observed in a comparison of the characteristics of p–i–n and n–i–p cells. The various JD–V characteristics are found to be consistent with uniform densities of defects in the i-layers, and thus inconsistent with the spatially varying large densities of defects predicted for solar-cell structures by the defect pool model.
Palladium nanoparticle arrays using template-assisted electrodeposition
Authors: Bera D. , Kuiry S. C. , Patil S. , Seal S.
Published: May 2003

Palladium nanoparticles are being increasingly considered as room-temperature hydrogen sensors and storage materials. Pd nanoparticle arrays have been synthesized using template-assisted electrodeposition. The template based on Al film on a polymeric substrate was characterized by scanning electron microscopy and energy dispersive spectroscopy. X-ray photoelectron spectroscopy study confirmed that the deposited nanoparticles were of metallic Pd. High-resolution transmission electron microscopy investigation revealed that Pd nanoparticles consisted of a large number of nanocrystallites in the size range of 5–10 nm.
Characteristics of a field-effect transistor with stacked InAs quantum dots
Authors: Wang T. H. , Li H. W. , Zhou J. M.
Published: May 2003

We report on the operation of a heterojunction field-effect transistor with stacked InAs quantum dots below a layer of two-dimensional electron gases. The output characteristics show a rapid increase of the drain current before its saturation. The transconductance exhibits a few peaks when scanning the gate voltage. These behaviors can be well explained by additional transport through the stacked InAs quantum dots. Our results indicate that the transistor could be controlled by an operation of one single electron in quantum dots.
Carrier lifetime studies of deeply penetrating defects in self-ion implanted silicon
Authors: Macdonald D. H. , Maeckel H. , Doshi S. , Brendle W. , Cuevas A. , Williams J. S. , Conway M. J.
Published: May 2003

Carrier lifetime measurements have been used to characterize residual defects after low-energy implanting of silicon ions followed by high-temperature annealing (900 or 1000 °C). The implant was found to result in two distinct regions of lifetime-reducing damage. First, a high recombination region, most likely due to stable dislocation loops, remained near the surface. In addition, deeply propagated defects, which were not present prior to annealing, were also detected. These deep defects, which are possibly silicon interstitials, diffuse so rapidly during annealing that their distribution becomes effectively uniform to a depth of 100 microns. Annealing at higher temperatures was found to reduce the severity of both the surface and the deeply propagated defects.
Improved photoluminescence of InGaAsN–(In)GaAsP quantum well by organometallic vapor phase epitaxy using growth pause annealing
Authors: Tansu Nelson , Yeh Jeng-Ya , Mawst Luke J.
Published: May 2003

The metalorganic chemical vapor deposition of a highly strained InGaAsN quantum-well (QW) surrounded by (In)GaAsP direct barrier layers is investigated. We found that growth pause annealing with AsH3, performed immediately before and after the growth of the QW, significantly improves the optical quality of InGaAsN QW with (In)GaAsP direct barriers. The utilization of larger band gap barrier materials, such as InGaAsP or GaAsP, will potentially lead to reduced carrier leakage from the QW laser structures.
Proteome analysis of extracellular proteins regulated by the las and rhl quorum sensing systems in Pseudomonas aeruginosa PAO1
Authors: Nouwens Amanda S. , Beatson Scott A. , Whitchurch Cynthia B. , Walsh Bradley J. , Schweizer Herbert P. , Mattick John S. , Cordwell Stuart J.
Published: May 2003

The las and rhl quorum sensing (QS) systems regulate the expression of several genes in response to cell density changes in Pseudomonas aeruginosa. Many of these genes encode surface-associated or secreted virulence factors. Proteins from stationary phase culture supernatants were collected from wild-type and P. aeruginosa PAO1 mutants deficient in one or more of the lasRI, rhlRI and vfr genes and analysed using two-dimensional gel electrophoresis. All mutants released significantly lower amounts of protein than the wild-type. Protein spot patterns from each strain were compared using image analysis and visible spot differences were identified using mass spectrometry. Several previously unknown QS-regulated proteins were characterized, including an aminopeptidase (PA2939), an endoproteinase (PrpL) and a unique ‘hypothetical’ protein (PA0572), which could not be detected in the culture supernatants of Δlas mutants, although they were unaffected in Δrhl mutants. Chitin-binding protein (CbpD) and a hypothetical protein (PA4944) with similarity to host factor I (HF-I) could not be detected when any of the lasRI or rhlRI genes were disrupted. Fourteen proteins were present at significantly greater levels in the culture supernatants of QS mutants, suggesting that QS may also negatively control the expression of some genes. Increased levels of two-partner secretion exoproteins (PA0041 and PA4625) were observed and may be linked to increased stability of their cognate transporters in a QS-defective background. Known QS-regulated extracellular proteins, including elastase (lasB), LasA protease (lasA) and alkaline metalloproteinase (aprA) were also detected.
Isolation and characterization of two specific regulatory Aspergillus niger mutants shows antagonistic regulation of arabinan and xylan metabolism
Authors: de Groot Marco J. L. , van de Vondervoort Peter J. I. , de Vries Ronald P. , vanKuyk Patricia A. , Ruijter George J. G. , Visser Jaap
Published: May 2003

This paper describes two Aspergillus niger mutants (araA and araB) specifically disturbed in the regulation of the arabinanase system in response to the presence of l-arabinose. Expression of the three known l-arabinose-induced arabinanolytic genes, abfA, abfB and abnA, was substantially decreased or absent in the araA and araB strains compared to the wild-type when incubated in the presence of l-arabinose or l-arabitol. In addition, the intracellular activities of l-arabitol dehydrogenase and l-arabinose reductase, involved in l-arabinose catabolism, were decreased in the araA and araB strains. Finally, the data show that the gene encoding d-xylulose kinase, xkiA, is also under control of the arabinanolytic regulatory system. l-Arabitol, most likely the true inducer of the arabinanolytic and l-arabinose catabolic genes, accumulated to a high intracellular concentration in the araA and araB mutants. This indicates that the decrease of expression of the arabinanolytic genes was not due to lack of inducer accumulation. Therefore, it is proposed that the araA and araB mutations are localized in positive-acting components of the regulatory system involved in the expression of the arabinanase-encoding genes and the genes encoding the l-arabinose catabolic pathway.