bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppressive interactions between mutations located in the two nucleotide binding domains of CFTR
Authors: Wei Lin , Vankeerberghen Anne , Jaspers Martine , Cassiman Jean-Jacques , Nilius Bernd , Cuppens Harry
Published: July 2002

The S1235R locus in CFTR was studied in combination with alleles found at the M470V and G628R loci. While R628 caused a maturational defect, R1235 did not. The impact of R1235 was found to be influenced by the alleles present at the G628R and M470V loci. At the single channel level, R1235‐V (R1235 on a V470 background) was characterized by an open probability significantly higher than V470‐wildtype CFTR. M470, which on its own increases CFTR chloride transport activity when compared to V470‐wildtype CFTR, suppressed the activity of R1235 in such a way that a protein with an open probability not significantly different from V470‐wildtype CFTR was obtained. While R628‐V CFTR had similar current densities as V470‐wildtype CFTR in Xenopus laevis oocytes, R1235‐V resulted in current densities that were more than twofold higher than those of V470‐wildtype CFTR. However, the current densities generated by R1235/R628‐V (R1235 and R628 on a V470 background) CFTR were significant lower than R1235‐V or R628‐V CFTR.
Mass political interest (or apathy) in urban China
Authors: Chen Jie , Zhong Yang
Published: July 2002

Based on our reassessment of existing studies on political interest and apathy in various societies, we argue the urgent need for a more systematic and focused examination of mass political interest—as psychological involvement in politics—in China. Utilizing data collected from a public opinion survey conducted in Beijing, China in late 1995, we intend to shed some light on the level and sources of political interest in contemporary China. Contrary to the prevalent argument that most Chinese are politically apathetic, we have found that there was a rather high level of political interest within our sample. We have also found that both conventional variables (i.e. age, gender, education, income, political efficacy, and dissatisfaction with government performance) and variables unique to the Chinese setting (i.e. being a farmer, becoming a private entrepreneur, joining the Chinese Communist Party and holding leading position in the party/government) have significant effects on the levels of political interest.
Weekday variations in short‐term contrarian profits in futures markets
Authors: Lin J.Barry , Onochie Joseph I. , Wolf Avner S.
Published: July 2002

This article documents and examines weekday patterns in short‐term contrarian profits in futures markets. The Lo and Mackinlay (1990) methodology is used to construct contrarian portfolios and to compute daily contrarian profits. Contrarian portfolios are formed using daily closing prices and are based on the previous day's performance relative to a benchmark. Contrarian profits are measured over subsequent half‐day intervals. The empirical results suggest that there are weekday patterns in short‐term contrarian profits in futures markets. On average, contrarian profits are largest on Fridays, followed by those on Wednesdays, and smallest on Mondays. For currency futures, however, contrarian profits are largest on Mondays and smallest on Fridays.
Stochastic Modeling of Affinity Adsorption
Authors: Hubble John
Published: July 2002

A stochastic model is described that allows surface proximity and packing effects to be incorporated into predictions of adsorption kinetics and equilibrium of affinity adsorption. Equilibrium predictions show that, depending on conditions chosen, the results obtained for equilibrium conditions can exhibit either a Freundlich‐ or a Langmuir‐type relationship. Under conditions of surface density imposed adsorption constraints, the time taken for equilibrium to be reached increases as the “off” constant is decreased. This suggests that for resins having a high immobilized ligand density binding kinetics may be more highly limited by the “off” constant than by mass transfer limitations.
Mitochondrial Membrane Potential Selects Hybridomas Yielding High Viability in Fed‐Batch Cultures
Authors: Follstad Brian D. , Wang Daniel I. C. , Stephanopoulos Gregory
Published: July 2002

Prior research (Follstad, B. D.; Wang, D. I. C.; Stephanopoulos, G. Mitochondrial membrane potential differentiates cells resistant to apoptosis in hybridoma cultures. Eur. J. Biochem. 2000, 267, 6534–6540.) identified mitochondrial membrane potential (MMP) as a marker of hybridoma subpopulations resistant to apoptosis caused by a variety of apoptosis inducers. In this study, we investigated the viability of hybridoma cell cultures inoculated with cells of varying MMP in regular fed‐batch operation. A hybridoma cell population was separated using FACS into subpopulations based on their mean mitochondrial membrane potential (MMP) as measured using the common mitochondrial stain, Rhodamine 123 (Rh123). These subpopulations showed dramatic differences in their apoptotic death kinetics. Fed‐batches inoculated with a high MMP subpopulation reached higher viable cell concentrations and viabilities that were maintained for prolonged periods of time relative to fed‐batches inoculated with low MMP subpopulations. These results underline the heterogeneous nature of hybridoma cell cultures and suggest that mitochondrial physiology is a critical parameter determining culture performance.
Ion Exchange Membrane Bioreactor for Selective Removal of Nitrate from Drinking Water: Control of Ion Fluxes and Process Performance
Authors: Velizarov Svetlozar , Crespo João G. , Reis Maria A.
Published: July 2002

An ion exchange membrane bioreactor (IEMB), consisting of a monoanion permselective membrane dialyzer coupled to a stirred anoxic vessel with an enriched mixed denitrifying culture, has been studied for nitrate removal from drinking water. The influence of nitrate and chloride concentrations on the selectivity of nitrate transport in the IEMB process was investigated. With appropriate dosing of chloride ions to the IEMB biocompartment, it was possible to regulate the net bicarbonate flux in the system, thus maintaining the bicarbonate concentration in the treated water at the desired level. The latter was not possible to achieve in Donnan dialysis, operated as a single process in which, besides the lower nitrate removal efficiency found, bicarbonate was co‐extracted together with nitrate from the polluted water stream. Residual carbon source (ethanol) and nitrite were not detected in the treated water produced in the IEMB system. With a concentration of nitrate in the polluted water three times higher than the maximum contaminant level of 50 mg L−1 allowed, the IEMB process was successfully operated for a period of 1 month before exceeding this limit.
The Influence of Restraint Immobilization Stress on the Concentration of Bioamines and Cortisol in Plasma of Pietrain and Duroc Pigs
Authors: Rosochacki S. J. , Piekarzewska A. B. , Poloszynowicz J. , Sakowski T.
Published: July 2002

Forty‐five Duroc (recognized as not susceptible to stress) and 34 Pietrain (susceptible to stress) pigs were subjected to immobilization stress in a prone position for 5, 15, 30 and 60 min. Plasma concentrations of epinephrine (E), norepinephrine (NE), dopamine (DA) and cortisol (C) were determined in response to restraint stress. The concentrations of E, NE and DA were different between the two strains of pigs (some significant interactions); the highest response was seen after 5 min of stress. The concentration of plasma C increased with duration of stress and there was a significant interaction between strain of animals and the time of stress. Our data substantiate the use of E, NE, DA and C as indicators of stress in swine as early as 5 min after exposure to the stressor. It is also shown that stress‐susceptible Pietrain pigs had higher plasma concentrations of E, NE and DA than Duroc pigs.
Franz–Keldysh oscillations originating from a well-controlled electric field in the GaAs depletion region
Authors: Van Hoof C. , Deneffe K. , De Boeck J. , Arent D. J. , Borghs G.
Published: July 2002

The Franz–Keldysh oscillations induced by the electric field in the depleted zone below the GaAs surface are studied by photoreflectance spectroscopy. The electric field is precisely controlled by a molecular beam epitaxy grown buried highly doped layer and the pinned position of the Fermi level at the surface. It is shown that the electric field value as derived from theory is in disagreement with the value derived from electrostatic calculations. Consequently a determination of the Fermi level pinning is only possible from a measurement of both n- and p-doped samples.
Linear and nonlinear optical properties of flux-grown KTiOAsO4
Authors: Bierlein John D. , Vanherzeele Herman , Ballman A. A.
Published: July 2002

Single crystals of KTiOAsO4, a material which is isostructural with the well-known nonlinear optical material KTiOPO4 (KTP), were grown by a flux process and its optical and dielectric properties characterized. Compared to KTP, KTiOAsO4 has a higher figure of merit for second-harmonic generation, larger electro-optic coefficients, and lower ionic conductivity. As a result, KTiOAsO4 should become a viable alternative for KTP.
Rapid heteroepitaxial growth of Ge films on (100) GaAs by pulsed supersonic free-jet chemical beam epitaxy
Authors: Eres Djula , Lowndes Douglas H. , Tischler Jon Z.
Published: July 2002

Very high epitaxial growth rates (0.25 μm/s), not attainable by conventional vapor phase film growth methods, have been obtained using a pulsed supersonic free jet to supply digermane (Ge2H6) for thermal decomposition at a heated (100)GaAs surface. Double-crystal x-ray diffractometry and scanning electron microscopy show that highly planar, smooth, and commensurate epitaxial Ge films are grown on (100)GaAs using gas pulses of 250 ms duration at 1–3 atm (0.1–0.3 MPa) pressure for substrate temperatures of 480–680 °C. It is believed that the very high growth rates effectively ‘‘freeze’’ the Ge-GaAs interface resulting in minimal interfacial diffusion and reduced incorporation of impurities from the surrounding growth environment.
Stability of AlAs in AlxGa1−xAs-AlAs-GaAs quantum well heterostructures
Authors: Dallesasse J. M. , Gavrilovic P. , Holonyak N. , Kaliski R. W. , Nam D. W. , Vesely E. J. , Burnham R. D.
Published: July 2002

Data are presented on the long-term (≳8 yr) degradation of AlxGa1−xAs-AlAs -GaAs quantum well heterostructure material because of the instability of underlying (internal) AlAs layers. Material containing thicker (>0.4 μm) AlAs ‘‘buried’’ layers (confining layers) is found to be much less stable than material containing thinner (≲200 Å) AlAs layers. Hydrolysis of the AlAs layers because of cleaved edges and pinholes in the cap layers leads to the deterioration.
Electric field screening by photogenerated holes in multiple quantum wells: A new mechanism for absorption saturation
Authors: Wood Thomas H. , Pastalan John Z. , Burrus Charles A. , Johnson Bart C. , Miller Barry I. , deMiguel Jose L. , Koren Uziel , Young Martin G.
Published: July 2002

We observe saturation in the electroabsorption of InGaAs/InP multiple quantum wells (MQWs) at high optical intensity. Contrary to the mechanism for zero-field MQWs, we find that saturation occurs due to the presence of trapped photogenerated holes that screen the MQWs from the applied electric field. By carefully measuring the absorption coefficient of the wells and the emission time for holes, we are able to fit the observed electroabsorption saturation with no adjustable parameters.
Scanning tunneling microscopy comparison of GaAs(001) vicinal surfaces grown by molecular beam epitaxy
Authors: Pashley M. D. , Haberern K. W. , Gaines J. M.
Published: July 2002

We report the first scanning tunneling microscope observations of molecular beam epitaxy grown GaAs(001) vicinal surfaces cut 2° towards (111)A and 2° towards (111)B. The A-type step edges are found to be relatively straight, with 16 Å kinks occurring typically every 100 Å along the step. In contrast, the B-type step edges are found to be very ragged. On both surfaces, the terrace widths varied considerably. The details of the two step structures are dominated by the structure of the (2×4) unit cell.
Metalorganic molecular beam epitaxial growth of InP/GaInAs multiquantum wells for infrared photodetection
Authors: Ritter D. , Hamm R. A. , Panish M. B. , Vandenberg J. M. , Gershoni D. , Gunapala S. D. , Levine B. F.
Published: July 2002

Multiquantum well structures of InP/Ga0.47In0.53As were grown by metalorganic molecular beam epitaxy for the fabrication of infrared photodetectors. The thickness and composition uniformity of the wells was determined by high-resolution x-ray diffraction, photoluminescence, and photoluminescence excitation experiments. The intersubband absorption spectrum of the multiquantum well structures optimized for infrared detection is found to be in the 7–8 μm range.
Passivation of shallow impurities in Si by annealing in H2 at high temperature
Authors: Veloarisoa I. A. , Stavola Michael , Kozuch D. M. , Peale R. E. , Watkins G. D.
Published: July 2002

We have found by infrared absorption that shallow acceptors in Si can be passivated throughout the bulk of a semiconductor sample several mm thick by annealing in H2 at high temperature (≳900 °C) and quenching to room temperature. The total number of shallow centers passivated in such samples is comparable to the number in highly doped surface layers passivated in a hydrogen plasma at lower temperature (typically <400 °C). The importance of bulk passivation techniques is discussed.
Low friction in high temperature superconductor bearings
Authors: Weinberger B. R. , Lynds L. , Hull J. R. , Balachandran U.
Published: July 2002

A study of drag in rotating permanent magnet/high temperature superconductor magnetic bearings is reported. The effects of magnet asymmetry, atmospheric resistance, and eddy currents are discussed. One of the bearings achieved a rotational speed of 200 000 RPM and a low speed coefficient of friction of 8.1×10−6, values that have technological significance for flywheel energy storage.
60 GHz board-to-board optical interconnection using polymer optical buses in conjunction with microprism couplers
Authors: Chen R. T. , Lu H. , Robinson D. , Sun Z. , Jannson T. , Plant D. V. , Fetterman H. R.
Published: July 2002

We have demonstrated for the first time 60 GHz wide-band board-to-board optical interconnection with a signal-to-noise ratio of 22 dB. The total interconnection distance is 55 cm from the input coupling prism to the detector. Board-to-board optical interconnection was realized using microprisms which had a measured coupling bandwidth of more than 250 nm. The graded index of the polymer waveguide allows us to implement such an interconnection scheme on an array of substrates. The elimination of backplane interconnection greatly enhances the interconnection speed. The implementation of a high-speed on-board transceiver in connection with a polymer waveguide lens will generate a fully on-board optical interconnect involving modulation/demodulation.
Perpendicular electron transport through a two-dimensional electron- gas layer
Authors: Jansen R.-J. E. , Farid Behnam , Kelly M. J.
Published: July 2002

We analyze the scattering processes of high-energy (approximately 0.3 eV) electrons impinging at normal incidence on a zero-temperature two-dimensional electron gas (2DEG), and derive an expression for the scattering probability. We proceed in calculating the total scattering rate and energy loss of the hot electrons as a function of their energy of incidence. These results are then compared with those of the recent experiments performed on a hot-electron transistor with a 2DEG base. Our calculated base transfer ratio is in good agreement with the measured value.
Schottky barrier inhomogeneity caused by grain boundaries in epitaxial Al film formed on Si(111)
Authors: Miura Y. , Hirose K. , Aizawa K. , Ikarashi N. , Okabayashi H.
Published: July 2002

Epitaxial Al contacts on Si(111) are fabricated by electron beam evaporation at various substrate temperatures around 250 °C. They are observed by high-resolution transmission electron microscopy. Schottky barrier heights (SBHs) of the contacts are measured using current-voltage and capacitance-voltage methods. In the case of single-crystalline Al film, the SBH does not change and its spatial distribution remains homogeneous up to an annealing temperature of 550 °C. In contrast with this, for an epitaxial Al film containing grain boundaries, the spatial distribution of the SBH becomes inhomogeneous above 400 °C. This is attributed to Si diffusion along the grain boundaries in the Al film.
Ellipsometric characterization of In0.52Al0.48As and of modulation doped field effect transistor structures on InP substrates
Authors: Alterovitz S. A. , Sieg R. M. , Pamulapati J. , Bhattacharya P. K.
Published: July 2002

The dielectric function of a thick layer of In0.52Al0.48As lattice matched to InP was measured by variable angle spectroscopic ellipsometry in the range 1.9–4.1 eV. The In0.52Al0.48As was protected from oxidation using a thin In0.53Ga0.47As cap that was mathematically removed for the dielectric function estimate. The In0.52Al0.48As dielectric function was then verified by ellipsometric measurements of other In0.53Ga0.47As/In0.52Al0.48As structures, including modulation doped field effect transistors (MODFET), and is shown to provide accurate structure layer thicknesses.
Dislocations and strain relief in compositionally graded layers
Authors: Tersoff J.
Published: July 2002

The performance of strained-layer heterostructures is often limited by threading dislocations. Such defects can be reduced, and in some cases nearly eliminated, by growing a graded buffer layer. Here, we provide a quantitative picture of the role of grading, by calculating the equilibrium distribution of dislocations and residual strain in such compositionally graded films. In layers with graded strain, threading dislocations are subject to greater force and weaker pinning than in uniform layers, helping them to be swept to the edge of the sample.
Enhancement of low-temperature critical epitaxial thickness of Si(100) with ion beam sputtering
Authors: Smith Donald L. , Chen Chau-Chen , Anderson Greg B. , Hagstrom Stig B.
Published: July 2002

We have grown Ar+ ion beam sputtered Si epitaxially on Si(100) at substrate temperatures, T, between 390 and 480 K. At 480 K and 0.65 nm/s deposition rate, epitaxy is sustained at 1 μm of film thickness. At lower T, we observed an abrupt transition to amorphous growth at a critical thickness, he, which exhibited an Arrhenius dependence on T, as has previously been observed in molecular beam epitaxy (MBE) [D. J. Eaglesham, H. J. Gossmann, and M. Cerullo, Phys. Rev. Lett. 65, 1227 (1990)]. Our slope, d(ln he)/d(1/T), was 3 times steeper than in MBE, resulting in much thicker he at the higher T. The steep slope shows that the high kinetic energy of the sputtered Si is not enhancing surface diffusion enough to overcome thermal surface diffusion. We propose instead that the arriving kinetic energy is preventing void formation and thereby decreasing the rate at which statistical surface roughness, Δh, increases with film thickness. In both deposition processes, we propose that the collapse of epitaxy occurs when Δh exceeds the thermal surface diffusion length.
Group-velocity-matched second-harmonic generation: An efficient scheme for femtosecond ultraviolet pulse generation in periodically domain-inverted β-BaB2O4
Authors: Hayata K. , Koshiba M.
Published: July 2002

With the combined use of the group-velocity-matched and the quasi-phase-matched frequency doubling in β-BaB2O4, femtosecond ultraviolet pulse generation is found to be realizable with high efficiency. Calculation of the group-velocity mismatch shows that at ∼630 nm wavelength of the pump pulse the mismatch vanishes completely. Typical design parameters such as the walk-off length, the dispersion lengths, and the quasi-phase-matching period are evaluated numerically around the zero walk-off wavelength. Temperature tuning of the operation wavelength is investigated as well.
Dependence of the optical properties of semiconductor alloys on the degree of long-range order
Authors: Wei Su-Huai , Laks David B. , Zunger Alex
Published: July 2002

Many III-V semiconductor alloys exhibit spontaneous [111] alternate monolayer ordering when grown from the vapor phase. This is manifested by the splitting of the valence-band maximum and by a reduction in the direct band gap. We show here how these features can be used to deduce quantitatively the degree of long-range order in a given sample. Examples are given for Ga0.5In0.5P and Ga0.5In0.5As alloys.
Investigation of optical limiting in C60 solution
Authors: Joshi M. P. , Mishra S. R. , Rawat H. S. , Mehendale S. C. , Rustagi K. C.
Published: July 2002

Results of experimental and theoretical investigation of optical limiting for 30 ns pulses at 527 nm in C60 are presented which suggest that apart from higher excited state absorption, other nonlinear processes may have an important role in the experimentally observed limiting action.
Improved ductility of nanocrystalline Fe73.5Nb3Cu1Si13.5B9 obtained by direct-current joule heating
Authors: Allia P. , Tiberto P. , Baricco M. , Vinai F.
Published: July 2002

Direct-current joule heating is exploited to reduce the brittleness of ferromagnetic Fe73.5Nb3Cu1S13.5B9 nanocrystallized from the amorphous state. An ordering process occurring before nanocrystallization is singled out and shown to be responsible for sample embrittlement and magnetic-permeability degradation. The process is partially avoided by properly choosing the heating conditions. Nanocrystalline ribbon strips having substantially higher ductility than furnace-annealed samples, and maintaining excellent soft magnetic properties, are easily obtained.
Electron and hole mobilities in lightly doped silicon
Authors: Misiakos Konstantinos , Tsamakis Dimitris
Published: July 2002

The electron and hole mobilities were measured between 78 and 340 K. The method used is based on the frequency dependence of the conductance and the capacitance of a high resistivity diode biased in high injection. The method is insensitive to uncertainties regarding the ionized dopant densities. In the temperature range from 170 to 340 K the carrier mobilities vary as T−a, where a=2.34±0.08 for electrons while for holes a=2.85±0.05. At 77.8 K the hole mobility is 14000±400 cm2/V s while the electron mobility is 24000±800 cm2/V s.
Preparation of single-crystal Y3Al5O12 thin film by metalorganic chemical vapor deposition
Authors: Bai G. R. , Chang H. L. M. , Foster C. M.
Published: July 2002

Single-crystal yttrium aluminum garnet (Y3Al5O12 or YAG) thin films have been grown on (111) Gd3Ga5O12 substrate by metalorganic chemical vapor deposition. X-ray diffraction, selective-area electron diffraction, and transmission electron microscopy were used to confirm the single-crystal nature of [111]-oriented single-crystal Y3Al5O12 thin films. We determined that the epitaxial relationship between the film and the substrate is (111)[11̄0]Y3Al5O12//(111)[11̄0]Gd3Ga5O12.
Electrical properties of oxides grown on strained SiGe layer at low temperatures in a microwave oxygen plasma
Authors: Mukhopadhyay M. , Ray S. K. , Maiti C. K. , Nayak D. K. , Shiraki Y.
Published: July 2002

Microwave plasma oxidation of strained Si1−xGex layer has been carried out at low temperatures (150–200 °C). The chemical properties of the oxide investigated by x-ray photoelectron spectroscopy show the formation of single phase mixed oxides consisting a SiO2 and GeO2, without any Ge pileup on the surface or at the substrate-oxide interface. Electrical properties of the oxides show a moderately low value of fixed oxide charge and interface trap density. Grown oxides exhibit low leakage current (10−8 A/cm2) and high breakdown strength (5–10 MV/cm), and are useful for a gate dielectric in metal–oxide semiconductor field effect transistor.
Atomic scale modifications of GaAs using a scanning tunneling microscope
Authors: Moriarty P. , Beton P. H. , Woolf D. A.
Published: July 2002

We have created atomic scale modifications on the GaAs(111)B surface by applying voltage pulses between the tip of a scanning tunneling microscope and a GaAs sample under ultrahigh vacuum conditions. A voltage pulse of 5 V (sample negative) for 25 ms results in the creation of a disordered region (approximately, 3 nm×3 nm in area) of As trimers. In addition, surface stacking faults are formed which extend over distances of order 10 nm and terminate on surface defects. A pulse with the same parameters, but opposite polarity, creates a nanometer scale crater. We argue that the smallest features are formed by electric field induced diffusion (for negative bias pulses) or field desorption (positive bias pulses).
Picosecond carrier lifetime in GaAs implanted with high doses of As ions: An alternative material to low-temperature GaAs for optoelectronic applications
Authors: Krotkus A. , Marcinkevicius S. , Jasinski J. , Kaminska M. , Tan H. H. , Jagadish C.
Published: July 2002

Nonstoichiometric GaAs obtained by implantation with 2 MeV arsenic ions at 1015 cm−2 dose is studied. As-implanted samples show a <200 fs lifetime of photocarriers and low resistivity due to hopping, with mobility less than 1 cm2/V s. Annealing of the samples at 600 °C leads to substantial recovery of postimplant damage, as seen from Rutherford backscattering channeling spectra and mobility increase to about 2000 cm2/V s, but photocarrier lifetime is still about 1 ps. These parameters are similar to those of low-temperature GaAs annealed at 600 °C, and make arsenic implanted GaAs an interesting material for optoelectronic applications.
Photoemission from single electrodynamically levitated microparticles
Authors: Arnold S. , Hessel N.
Published: July 2002

A simple method for determining the ionization potential from a single electrodynamically levitated microparticle is discussed. The associated spectrometer is described and measurements from graphite and transpolyacetylene are demonstrated.
Cold high-intensity atomic hydrogen beam source
Authors: Hershcovitch A. , Kponou A. , Niinikoski T. O.
Published: July 2002

A cold atomic hydrogen beam source has been built and tested at BNL. The flow channel of the source, consisting of a discharge tube, a constricting nozzle, a thermal transition section, and an accommodator, was designed to operate in the laminar flow range. A novel feature of this source is a 0.3-mm gap between the transition Teflon tube which guides the flow and an accommodator which cools the flowing gas; across this gap the wall temperature may step from 100 K in the Teflon to 3 K in the accommodator. A record pulsed H° beam flux of 9.4×1018 H° sr−1 s−1 was obtained at an accommodator temperature of 5.8 K. The gas dynamic analysis of the system is in excellent agreement with the experimental results.
Improvement of sensitivity of the vibrating reed magnetometer
Authors: Richter H. J. , Hempel K. A. , Pfeiffer J.
Published: July 2002

A very-high-sensitivity magnetometer is described in detail. The sensitivity of the apparatus is typically of the order of 10−9 A cm2/(Hz)1/2, so that changes in magnetic moment of 10−10 A cm2 can be detected. The magnetic moment can be calculated by simulation of the measurement system. An example of a hysteresis loop is shown. The size of the sample is determined by electron microscopy. The physical limits of the measurement system are worked out and discussed.
Second subband population in δ-doped Al0.48In0.52As/Ga0.47In0.53As heterostructures
Authors: Lo Ikai , Mitchel W. C. , Ahoujja M. , Cheng J.-P. , Fathimulla A. , Mier H.
Published: July 2002

We have observed the population of the second two-dimensional electron subband in δ-doped Al0.48In0.52As/Ga0.47In0.53As heterostructures by Shubnikov–de Haas measurements. After illuminating the samples at low temperature, the electron density increases from 17.3 to 18.2×1011 cm−2 for the first subband and from 3.6 to 4.1×1011 cm−2 for the second subband. The population of the second subband begins when the first subband is filled at a density of 10.3×1011 cm−2. The effective mass of the second subband is equal to (0.045±0.003)m0, indicating significant band nonparabolicity in the Ga0.47In0.53As well.
A combined microwave cavity and photographic diagnostic for high-speed projectiles
Authors: Gouge M. J. , Combs S. K. , Milora S. L.
Published: July 2002

A combined microwave cavity and photographic diagnostic for high-speed projectiles has been developed. The diagnostic allows consistent determination of projectile mass and shape and serves as one fiducial mark for a speed measurement. The 3.219-GHz cavity has been used for experiments with both frozen deuterium and plastic pellets traveling at speeds from 1500–4500 m/s.
A fiber-optic probe for particle sizing in concentrated suspensions
Authors: Dhadwal Harbans S. , Ansari Rafat R. , Meyer William V.
Published: July 2002

A fiber-optic probe employing two monomode optical fibers, one for transmitting a Gaussian laser beam to the scattering volume and the second, positioned at some backscatter angle, for receiving the scattered light is described. Performance and suitability of the system for a process control environment is assessed by studying a suspension of polystyrene latex particles over a wide range of sizes and concentrations. The results show that the probe is ideal for a process control environment in industrial and laboratory applications. Particle size is recovered, without any additional corrections for multiple light scattering, in concentrations containing up to 10% solids of 39-nm polystyrene latex spheres.
Kramers–Kronig relations in nonlinear optics
Authors: Kador L.
Published: July 2002

In the vicinity of the phase-matching angle of second-order nonlinear optical crystals, the fundamental light wave experiences an intensity-dependent phase shift which is connected with the effective attenuation due to second-harmonic generation. It is demonstrated that in the limit of weak pump depletion, the Kramers–Kronig relations can be used to derive a simple analytical expression for the phase shift as a function of the phase-mismatch angle. For certain mismatch angles, a large phase shift occurs without any attenuation.
A beam profile monitor for small electron beams
Authors: Norem J.
Published: July 2002

Measurement of beam properties at the foci of high energy linacs is difficult due to the small size of the waists in proposed and existing accelerators (1 nm −2 μm). This article considers the use of bremsstrahlung radiation from thin foils to measure the size and phase space density these beams using nonimaging optics. The components of the system are described, and the ultimate resolution, evaluated theoretically for the case of the Final Focus Test Beam (FFTB) at Stanford Linear Accelerator Center, is a few nm.
Voltage-induced color-selective absorption with surface plasmons
Authors: Wang Yu
Published: July 2002

A phenomenon of voltage-induced color-selective absorption at metal/liquid crystal interface with surface plasmons is reported. When a white light is incident at a metal/liquid crystal interface, those photons in surface plasmon resonance frequency range are totally absorbed and the reflected light shows the complementary color. If a voltage is used to change the refraction index of the liquid crystal, then the surface plasmon resonance frequency will change, and the reflected light will also show the color change. The reflectance spectrum is calculated from a well-known solution to the boundary value problem in optics. Good agreement with the observations is obtained. This phenomenon could lead to a new generation of display devices.
An apparatus for the testing of small cryogenic heat exchangers
Authors: Venkatarathnam G. , Sarangi Sunil
Published: July 2002

Most cryogenic processes demand high effectiveness heat exchangers. The performance of these exchangers is determined not only by convective heat transfer resistance, but also by other irreversibilities such as axial conduction, flow maldistribution, heat transfer with surroundings, and finite number of lateral heat transfer paths. While determination of heat transfer correlations for exchanger cores is sufficient in most conventional applications, high-Ntu cryogenic exchangers must be tested under true operating conditions. As a part of our matrix heat exchanger development program, an apparatus has been constructed for testing small, compact heat exchangers at low temperature. The apparatus, enclosed in a vacuum vessel, provides a variable cold end temperature and means for direct measurement of ineffectiveness. Temperature approaches at both ends and pressure drop in both channels are also measured. The construction of the apparatus as well as the instrumentation and data acquisition methods are discussed. The results of a test on a small matrix heat exchanger using the test apparatus are also presented.
Miniature ac susceptometers for use inside clamp type pressure cells
Authors: Pfleiderer C.
Published: July 2002

The design and performance of miniature ac susceptometers are described that are small enough to fit inside clamp type pressure cells. The susceptometers are comprised of a primary and a balanced pair of secondaries with numbers of turns as high as 1000 to optimize the coupling to the sample and hence measurement sensitivity. Two methods of balancing the vacuum signal of the secondaries are presented, making susceptibility measurements even in clamp cells generating large stray signals possible. With the technique presented here a comprehensive series of measurements was carried out into the pressure induced magnetic quantum phase transition of MnSi.
A computerized direct liquid injection, rapid isothermal processing assisted chemical vapor deposition system for a Teflon amorphous fluoropolymer
Authors: Sharangpani R. , Singh R.
Published: July 2002

Chemical vapor deposition (CVD) has for long been the mainstay for the deposition of critical device layers in integrated circuit technology. For the development of fast, high density, low voltage operated integrated circuits, materials with dielectric constant (K) less than that of the conventionally used SiO2 (K=3.8) are required, due to their ability to reduce signal propagation delays, power dissipation, and cross talk when used as inter level dielectrics. The copolymeric Teflon amorphous fluoropolymer (AF) is a new low K material with K=1.9. A direct liquid injection system for the CVD of Teflon AF for interlevel dielectric applications in an ultraviolet (UV) light enhanced rapid isothermal processor is reported for the first time, to the best of our knowledge. Computer interfaced electronics were designed to permit atomizing and desolvating the liquid precursor at any desired instant and interval of time. A closed loop control system monitored and regulated the substrate temperature. The films were processed with and without the UV light source. An improvement in film properties was observed when the UV source was used during processing. Our technique offers considerable advantages over other reported methods for the processing of Teflon AF.
Evaluation of an elliptical grid mirror electrostatic analyzer for space applications
Authors: Chornay Dennis J. , Hunsaker Floyd H. , Keller John W.
Published: July 2002

We report on our investigation into the development of electrostatic mirror based charged particle analyzers for space plasma physics experimentation. For this work, we tested an elliptical mirror analyzer which was designed to provide a wide, 2-dimensional field of view with high throughput and good angular resolution. Measurements with an ion beam demonstrated 2° full width at half-maximum angular resolution over a 16×16° field of view (FOV) and 4° resolution over a 40×40° FOV for an optical system with a linear dimension (entrance aperture to the particle detector) of 20 cm. The energy resolution is variable, similar in operation to a retarding-potential-analyzer or a modulated grid Faraday cup, with a geometric factor of 3.2×10−3 cm2 str ΔE/E for an energy resolution setting of 10%.
Improved nm displacement detector for microscopic beads at frequencies below 10 Hz
Authors: Li Daqun , Schnapp Bruce J.
Published: July 2002

A modular differential interference contrast microscope combined with laser interferometry has been designed and constructed to detect nm-scale displacements of microscopic beads with a root mean square noise less than 0.4 nm. The unique feature of our system lies in its capability of preserving the nm-scale detection sensitivity down to a low-frequency region of a few Hz. The modularized design ensures the system is accessible to further modifications as frequently required by various biological experiments such as employing multiple laser traps to manipulate rod-shaped samples.
Personal computer-controlled 16 channel versatile pulse generator for nuclear magnetic resonance
Authors: Toyoda Tomonori , Yoshida Hisashi , Oishi Osamu , Miyajima Seiichi
Published: July 2002

A versatile and very low-cost programmable pulse generator for nuclear magnetic resonance is reported. The apparatus consists of basic transistor–transistor logic devices, and is equipped with independent 16 channel outputs. Each of the pulse widths and intervals are adjustable in 0.1 μs resolution. The pulse sequence is made on a 32 bit personal computer, and transferred to the pulse generator hardware through the Centronics printer interface. No additional interface is necessary for a standard personal computer. The pulse data are initially stored in static random access memories, and then read out to construct 16 channel pulse arrays. The apparatus was used for pulsed field gradient spin-echo nuclear magnetic resonance experiments combined with rotation of a quadrupole coil.
Continuous wave operation of a vertical transition quantum cascade laser above T=80 K
Authors: Faist Jérôme , Capasso Federico , Sirtori Carlo , Sivco Deborah L. , Hutchinson Albert L. , Cho Alfred Y.
Published: July 2002

Continuous wave operation of a quantum cascade laser at λ=4.6 μm is reported above liquid nitrogen temperature. Optical powers of 15 mW at 50 K and 2 mW at 85 K are reported. The single mode spectrum is temperature tunable over 1.8 cm −1. These devices also operated in pulse mode with 20 mW peak power at 200 K. Gain measurements show evidence for ultralow linewidth enhancement factor α<0.1.
Sphericity analysis of solid density standards
Authors: Giardini W. J. , Mana G.
Published: July 2002

An analysis of dimensional sphericity measurement data is presented, applied to near-perfect single-crystal silicon spheres used as solid density standards and for the precise determination of the Avogadro constant. Using the formal correspondence of the expansion of the three-dimensional measurement data set in terms of spherical harmonics with the theory of angular momentum in quantum mechanics, invariant quantities are determined, allowing objective assessment of fabrication and measurement process variables. Two methods for sphericity analysis are presented and applications to solid density standards are given. Within the limitations of the quantity and quality of the measurement data tested, our results are consistent with qualitative assessments of sphere topography and have revealed a structure in the spectral distribution of spherical harmonic amplitudes.
A modified broad beam ion source for low-energy hydrogen implantation
Authors: Otte K. , Schindler A. , Bigl F. , Schlemm H.
Published: July 2002

A modified broad beam ion source for low-energy hydrogen ion implantation of semiconductors is described. Based on a Kaufman type ion source two different solutions are presented: (a) an ion source with an extraction system consisting of two molybdenum grids with a low gas flow conductance reworked for hydrogen operation, and (b) a ten-grid mass separating ion beam system which enables the mass selection of H+, H2+, and H3+. The ion energy could be set in the range of 200–500 eV with a current density reaching from 1 to 100 μA/cm2. It is shown that at higher pressure the main ion created in the ion source is H3+ due to ion-molecule processes, whereas at lower pressure only H2+ and H+ are produced. Special consideration is given to the ion beam analysis of the two grid ion source operating in the 10−3 mbar range allowing to explain the different peak structures by the potential distribution across the ion source and different charge transfer processes. In addition, the analysis reveals neutral and ionized collision products in the ion beam. The ten-grid mass separating ion source could be operated in the 10−4 mbar range resulting in a nearly collision free ion beam which permits the generation of a mass separated hydrogen ion beam.
A Hall probe diagnostic for low density plasma accelerators
Authors: Domonkos Matthew T. , Gallimore Alec D. , Bilén Sven G.
Published: July 2002

A Hall probe diagnostic was developed for use with plasma thrusters. The Hall generators were mounted at the end of a stainless steel tube heat exchanger. Ceramic cement and a Pyrex tube were used as radiation and particle flux shields, respectively. A thermocouple was used to monitor the temperature of the Hall generator. The low voltage output from the probe was amplified within one meter of the transducer to minimize the effect of noise pick up. A National Institute of Standards and Technology traceable Gaussmeter provided an absolute reference for calibration, and relative calibrations were performed both in a strong electric field and in situ during thruster operation to approximate the conditions in the discharge. The overall accuracy of the diagnostic was ±6 G. The probes were tested with a Hall-effect thruster, and provided sufficiently accurate data to estimate the magnitude of the closed-drift electron current.
Microwave reflectometry for magnetically confined plasmas
Authors: Mazzucato E.
Published: July 2002

This article is about microwave reflectometry—a radar technique for plasma density measurements using the reflection of electromagnetic waves by a plasma cutoff. Both the theoretical foundations of reflectometry and its practical application to the study of magnetically confined plasmas are reviewed in this article. In particular, the role of short-scale density fluctuations is discussed at length, both as a unique diagnostic tool for turbulence studies in thermonuclear plasmas, and for the deleterious effects that fluctuations may have on the measurement of the average plasma density with microwave reflectometry.
Signal-to-noise improvement of bio-magnetic signals using a flux-gate probe and real time signal processing
Authors: Dolabdjian C. , Saez S. , Reyes Toledo A. , Robbes D.
Published: July 2002

We have recorded the magnetic signal generated by the human cardiac muscle with the help of a very sensitive flux-gate sensor. First, we have verified the feasibility of such detection inside a magnetically shielded room, then repeated this same experiment within our laboratory and in a low shielded environment. Results have shown the easy operation of a flux-gate sensor for this purpose and the efficiency of fast numerical processing in a low shielded environment. This leads in both cases to a voltage signal-to-noise ratio of about 5 within a 100 Hz bandwidth, which corresponds to the actual limit of the flux-gate probe.
Dual-function circular polarization converter for microwave/plasma processing systems
Authors: Chang T. H. , Barnett L. R. , Chu K. R. , Tai F. , Hsu C. L.
Published: July 2002

Generation of a uniform density plasma has been a key consideration in the design of microwave/plasma processing systems. A circularly polarized wave can generate a plasma with good azimuthal uniformity as well as provide strong resonant interaction with the plasma electrons. In this article, we report the development of a three-port polarization converter which efficiently converts the TE10 wave of a standard rectangular waveguide into a circularly polarized TE11 wave of a cylindrical waveguide. Employing the same principle for mode conversion, the converter is also made to function as a protective device of the high power microwave source by providing a separate port for the return and damping of the reflected wave. Such a converter has been analyzed, constructed, and tested. At the operating frequency of 2.45 GHz, test results indicate a 25 dB return loss, 97% end-to-end polarization conversion efficiency, and better than 20 dB rejection of the reflected wave. The structural simplicity of the device allows high power operation as well as easy construction for system research and applications.
Power flow in the negative-ion based neutral beam injection for JT-60
Authors: Kuriyama M. , Akino N. , Ebisawa N. , Grisham L. , Hikita S. , Honda A. , Itoh T. , Kawai M. , Kazawa M. , Kusaka M. , Mogaki K. , Ohga T. , Okumura Y. , Oohara H. , Satoh F. , Seki H. , Tanai Y. , Toyokawa Y. , Umeda N. , Usui K. , Watanabe K. , Yamaguchi M. , Yamazaki H.
Published: July 2002

The negative ion based neutral beam injection system for JT-60 has operated since 1996 injecting neutral beam into JT-60 plasmas. A power flow measurement in the beam line and ion source with a water calorimeter had shown that 40%–50% of accelerated beam particles were intercepted on the two accelerator grids and the grounded grid at an ion source gas pressure of 0.2–0.3 Pa. Much of the beam loss was not caused by stripping loss of the negative ions, but rather by direct impingement of the negative ions onto the grids. After reducing the acceleration area by masking the edge area (about 13% of the extraction area) of the accelerator grid so as to minimize the edge effect of magnetic field in the arc chamber, the loss in the accelerator decreased by roughly 25%. In comparing a deuterium beam with a hydrogen beam, the neutral beam power with deuterium is lower by 30% than that of hydrogen at the same arc power, although the heat load onto the grounded grid does not change so much. The power deposition ratios along the beamline were as follows: the beam scraper in the ion source tank and the neutralizer cell received about 3% and about 7%, respectively, of the accelerated beam power, while the ion dumps for both D− and D+ received 20%–30% in total, and 30%–34% reached the neutral beam calorimeter.
Negative hydrogen ion source for TOKAMAK neutral beam injector (invited)
Authors: Okumura Y. , Fujiwara Y. , Kashiwagi M. , Kitagawa T. , Miyamoto K. , Morishita T. , Hanada M. , Takayanagi T. , Taniguchi M. , Watanabe K.
Published: July 2002

Intense negative ion source producing multimegawatt hydrogen/deuterium negative ion beams has been developed for the neutral beam injector (NBI) in TOKAMAK thermonuclear fusion machines. Negative ions are produced in a cesium seeded multi-cusp plasma generator via volume and surface processes, and accelerated with a multistage electrostatic accelerator. The negative ion source for JT-60U has produced 18.5 A/360 keV (6.7 MW) H− and 14.3 A/380 keV (5.4 MW) D− ion beams at average current densities of 11 mA/cm2 (H−) and 8.5 mA/cm2 (D−). A high energy negative ion source has been developed for the next generation TOKAMAK such as the International Thermonuclear Experimental Reactor (ITER). The source has demonstrated to accelerate negative ions up to 1 MeV, the energy required for ITER. Higher negative ion current density of more than 20 mA/cm2 was obtained in the ITER concept sources. It was confirmed that the consumption rate of cesium is small enough to operate the source for a half year in ITER-NBI without maintenance.
Simultaneous strain–temperature measurement using fluorescence from Yb-doped silica fiber
Authors: Wade S. A. , Baxter G. W. , Collins S. F. , Grattan K. T. V. , Sun T.
Published: July 2002

The effect of strain upon both the fluorescence intensity ratio and the fluorescence decay-time–temperature-sensing techniques has been studied using Yb-doped fiber. The measured variation with strain of the former method is consistent with no strain sensitivity, while the latter method demonstrates a linear dependence on strain. A single optical sensor element using both these fluorescence techniques thereby offers an attractive way of providing temperature compensation in a simultaneous strain and temperature monitoring system.