bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring the outcomes of ophthalmic healthcare: low vision rehabilitation
Authors: Harper Robert
Published: July 2002

The measurement of health status and medical outcomes is becoming a major requirement for all providers of healthcare services. There is a need to measure the outcomes of healthcare, not only to demonstrate the effectiveness of care, but also to assess the relative (and possibly competing) worth of different forms of care. At the same time, there is a growing awareness of the limitations of clinical outcomes in contrast to those measured by patients themselves. There is, therefore, considerable interest in the use of generic and disease specific ‘Quality of Life’ (Qol) instruments.

Within ophthalmic healthcare, clinical outcomes include, for example, measures of visual function or the gradings of images of ocular structure. Other outcome measures used may include specific disease scales or indices, including questionnaire measures of visual disability (e.g. the VF14, ‘Activities of Daily Vision Scale’ and TyPE scales, designed to assess the impact of cataract and cataract surgery on self‐rated visual disability). In contrast to disease specific measures, generic measures are designed to provide an overall measure of an individuals health status. These measures are classified into profile measures (e.g. the SF36) or indices (e.g. the Rosser index or the EuroQol).

There have been a number of studies which have evaluated the effectiveness of low vision rehabilitation, although these have mainly been small cross sectional surveys which have used a single definition of ‘success’, including for example, the visual acuity/visual performance achieved with the LVA or the usage of the LVA. More recently questionnaire approaches have been used to measure ‘success’, but as with clinical outcomes, the validity and reliability of the outcomes used has not been established. Given the considerable scale of the low vision population and the current debate about optimal models of low vision care, there is a pressing need to (1) define an appropriate set of outcome measures and (2) carry out randomised controlled trials comparing the effectiveness and cost‐effectiveness of different forms of care.

If we as clinicians fail to inform the debate about appropriate outcomes in ophthalmic healthcare, this may result in such care being incorrectly valued by others.
Optometric referrals to an ophthalmology outpatients department: classification and sensitivity
Authors: Weed Kathryn H
Published: July 2002

The rationale of this study was to find the answers to the following questions:

1. The number of optometric new patient referrals in a month period.

2. The reason for referral.

3. The number of false positives.

Of a total of 267 new patients referred to Sunderland Eye Infirmary, 104 were optometrically derived (39%). In this group the most common reason for referral by optometrists was cataract assessment (23%) followed by suspected glaucoma (21%). In the latter group of 22, 15 (68%) were actually diagnosed as suffering from primary open angle glaucoma, or were listed for further assessment. In the former group of 24, 19 patients (83%) were listed for surgery. The three remaining patients were deemed untroubled by any visual symptoms and despite lens opacities maintained 6/12 Snellen visual acuities.

The other reasons for referral were macular degeneration (13), decreased visual acuity (8), orthoptic management (7), visual defects (6), corneal (4), central vein occlusion (3), posterior vitreous detachment (3), migraine symptoms (2), epiphora (2), irritation symptoms (2), capsular opacification (2), caruncle cyst (1), retinal haemorrhage (1), pupil irregularity (1), diplopia (1), narrow angles (1) and ptosis with conjunctivitis (1).

There appeared to be an inconsistency on the number of tests used for referral criteria and baseline information for all referrals. A guide line on the minimum information that should be included in a referral is discussed for cataract assessment, suspected glaucoma and macular degeneration.
Penetrating keratoplasty, corneal topography and the optometrist
Authors: Macalister Graham
Published: July 2002

The success rate for penetrating keratoplasty in non‐vascularised corneas is now in the region of 95%. However corneal clarity alone can no longer be considered as the sole criteria for success, and the quality of the visual outcome is now receiving much more attention. This is often compromised by high astigmatism and topographic irregularity.

A prospective longitudinal trial involving 108 eyes with transplanted corneas was carried out. The longest follow‐up was for 10 years, and data was available for 60 patients at the 5 year stage. Healing and improvement in corneal topography are dynamic processes, and it was decided to use sequential observations taken from the same eye to investigate changes in corneal topography over time. The results were then related to patient characteristics and to variables in the surgical technique, and multivariate analysis carried out to determine which factors have the most influence on the outcome.

A photokeratoscope was used and an analysis technique was developed which enabled clinically meaningful topographical components to be derived from measurements of each keratograph. These components were spherical equivalent, asymmetry, axis of asymmetry, regular astigmatism and its axis, and an irregularity component. The changes in astigmatism and irregularity were analysed using Multilevel Modeling. The results of this study will be presented and the implications discussed.

Computerised video‐keratoscopes are capable of revealing a great deal of information about corneal irregularity and are therefore useful in the management of post‐keratoplasty astigmatism. Colour topography maps will be presented which demonstrate commonly encountered features. These will include the effect of individual tight sutures and the changes brought about by suture removal and refractive surgery. The potential of video‐keratography as a guide to the optometrist in refraction and contact lens fitting for the post‐keratoplasty patient will be discussed.
Myopia in infants treated for retinopathy of prematurity: the first year of life
Authors: Pennie Fiona , Laws David , Clark David
Published: July 2002

Premature birth is associated with an increase in incidence of refractive errors. Cryotherapy for threshold retinopathy of prematurity further increases risk of developing high myopia. It was our clinical impression that a change in treatment to laser resulted in less severe myopia. We undertook a longitudinal study to determine the refractive outcome of each therapy. A total of 19 patients undergoing cryotherapy and 14 patients undergoing laser treatment, had cycloplegic refractions at corrected ages of three months and one year. At 3 months the median spherical equivalent refractive error in the right eye was −3.25 dioptres after cryotherapy and +0.25 dioptres after laser therapy. At twelve months it was −5.25 dioptres following cryotherapy and −0.50 dioptres after laser. The results for the left eye were comparable. The difference between the median spherical refractive error for the two treatment groups were significant at three months and twelve months (p > 0.05 Wilcoxon rank sum). Laser therapy is associated with lower degrees of myopia during the first year of life.
Contour interaction for high and low contrast optotypes in normal and amblyopic observers
Authors: Simmers Anita J. , Gray Lyle S. , McGraw Paul V. , Winn Barry
Published: July 2002

We investigate the influence of stimulus contrast upon contour interaction in normal and amblyopic subjects. Using a computer generated acuity task, flanked and unflanked acuities were measured psychometrically at both high contrast (80%) and low contrast (6%), in a group of 19 normal and 11 amblyopic subjects. The crowding ratio for high contrast letters was found to be significantly higher than that for low contrast letters. The extent of the crowding zone was measured at high and low contrast by varying the separation of the optotype and flanking bars. The crowding zone measurement was repeated for the high contrast optotypes using dioptric blur. The position of the flanking contours was found to have a significant effect on letter resolution at high contrast but no significant effect was demonstrable at low contrast. With the addition of dioptric blur the effect of contour interaction became negligible at high contrast. These findings support the hypothesis that the crowding effect is: (1) similar in normal and amblyopic eyes when tested at threshold; (2) is contrast dependent appearing only for high contrast optotypes.
Seed Dispersal in Páramo Plants: Epizoochorous and Hydrochorous Taxa
Authors: Melcher Inga M. , Bouman F. , Cleef A. M.
Published: July 2002

Abstract: On the basis of a recent checklist of plant diversity in páramos, diaspores collected from herbaria were studied for adaptations to dispersal on animals and by water. This study shows that the páramo flora has a relatively high percentage of genera with morphological adaptations to epizoochorous and to hydrochorous diaspore dispersal. Genera with hooked and straight appendages are present throughout the páramo belt, while their number decreases in the higher páramo zones. About half of the hydrochorous genera and one‐third of the epizoochorous ones can be found throughout all páramo zones. The contribution of holarctic epizoochorous genera to the páramo flora seems to be greater than that of austral‐antarctic genera, whereas in hydrochorous genera it is the reverse.
First Experimental Evidence for Zoophagy in the Hepatic Colura
Authors: Barthlott W. , Fischer E. , Frahm J.‐P. , Seine R.
Published: July 2002

Abstract: Some hepatics, especially epiphytic species, possess lobules or water sacs on their leaves that appear to function as stores. In Pleurozia and Colura, these water sacs have very complex openings that can be closed by a movable lid, which prompted the hypothesis that these water sacs could function as a trap‐like mechanism for small animals, which are occasionally found in these organs. Experiments revealed that protozoa (ciliata), which feed on bacteria on the surface of the plants, are trapped in the water sacs. We propose that these trap mechanisms function for zoophagy, but there is no clear evidence that the protozoa are specifically attracted to the hepatic.
InGaP/GaAs superlattices grown by gas-source molecular beam epitaxy
Authors: Lee H. Y. , Crook M. D. , Hafich M. J. , Quigley J. H. , Robinson G. Y. , Li D. , Otsuka N.
Published: July 2002

Lattice-matched InGaP/GaAs superlattices have been grown by gas-source molecular beam epitaxy. High-resolution images obtained with transmission electron microscopy reveal the superlattices to be free of dislocations and to exhibit smooth interfaces of only 1–2 monolayers in width. Double crystal x-ray diffraction studies indicate that the narrow interfacial regions are locally strained as a result of the growth sequence during gas-source molecular beam epitaxy.
Epitaxial growth of CeO2 layers on silicon
Authors: Inoue T. , Yamamoto Y. , Koyama S. , Suzuki S. , Ueda Y.
Published: July 2002

CeO2 layer was epitaxially grown for the first time on both (111) and (100) silicon substrates by vacuum evaporation. Characterization using Rutherford backscattering and reflection high-energy electron diffraction proved that a CeO2 layer on (111) Si has considerably good crystalline quality, whereas that on (100)Si contains a large amount of crystallographic defects, especially in the vicinity of the CeO2/Si interface. Auger electron spectroscopy analysis showed a uniform concentration distribution of Ce and O throughout the epitaxial layer.
Ferroelectric inversion layers formed by heat treatment of proton-exchanged LiTaO3
Authors: Nakamura Kiyoshi , Shimizu Hiroshi
Published: July 2002

We report that a ferroelectric inversion layer can be formed in LiTaO3 by proton exchange in benzoic acid melts followed by heat treatment at temperatures just below the Curie point. It is demonstrated that the inversion layer appears at the −c surface for LiTaO3, whereas it appears at the +c surface for LiNbO3. The dependence of the inversion layer thickness on the conditions of proton exchange and heat treatment is also reported.
Preparation of ferroelectric BaTiO3 thin films by activated reactive evaporation
Authors: Iijima K. , Terashima T. , Yamamoto K. , Hirata K. , Bando Y.
Published: July 2002

Ferroelectric BaTiO3 thin films were directly and epitaxially grown on SrTiO3 single crystal and epitaxial Pt film substrates by activated reactive evaporation. The substrate temperature was around 600 °C. For (100) oriented as-grown films, a typical ferroelectric hysteresis loop and a maximum of dielectric constant at about 115 °C were observed. The resistivity was as high as 109 Ω cm and the breakdown voltage was 2.7 MV/cm for as-grown BaTiO3 films.
Maskless laser interferometric monitoring of InP/InGaAsP heterostructure reactive ion etching
Authors: Hayes Todd R. , Heimann P. A. , Donnelly V. M. , Strege K. E.
Published: July 2002

Infrared laser interferometry is used to measure etch rate, measure wafer temperature, and identify heterostructure layers in situ during reactive ion etching, with or without masked regions. Interference between reflections from the etching wafer surface, buried heterointerfaces, and polished wafer back allows etch rate monitoring and endpoint determination. Changes in the optical path length that occur as a wafer heats and cools upon processing also produce reflected intensity oscillations that allow determination of the process-induced change in wafer temperature. We also show that λ=0.6238 μm light can be used to monitor optically thin heterostructure layers with enhanced depth resolution over infrared light.
Optical reflectivity and amorphization of GaAs during decompression from megabar pressures
Authors: Vohra Yogesh K. , Xia Hui , Ruoff Arthur L.
Published: July 2002

Polycrystalline GaAs was studied in a diamond anvil cell by optical reflection spectroscopy and energy-dispersive x-ray diffraction to pressures of 115 GPa (1.15 Mbar). Complete amorphization was observed at ambient conditions after decompression from 115 GPa, and, subsequent compression caused crystallization around 27 GPa to an orthorhombic phase. The results are compared with other group IV and III-V semiconductor materials and implantation-amorphized GaAs.
Subpicosecond carrier lifetimes in radiation-damaged GaAs
Authors: Lambsdorff M. , Kuhl J. , Rosenzweig J. , Axmann A. , Schneider Jo.
Published: July 2002

We investigate the dependence of carrier lifetimes in radiation-damaged, GaAs on proton implantation dose by means of time-resolved reflectivity and photoconductivity experiments with subpicosecond resolution. The carrier lifetimes decrease with increasing implantation dose at low implantation levels whereas beyond the ‘‘amorphization dose’’ a saturation at 0.5 ps can be observed due to a saturation of the defect density.
Barrier height change in GaAs Schottky diodes induced by piezoelectric effect
Authors: Chung Ki-Woong , Wang Z. , Costa J. C. , Williamson F. , Ruden P. P. , Nathan M. I.
Published: July 2002

A novel manifestation of piezoelectric effects in GaAs has been observed. The change of barrier height, φB, of Schottky diodes induced by uniaxial stresses, S, along 〈100〉, 〈011〉, 〈01̄1〉, and 〈111〉 has been measured. Shifts in φB due to the appearance of piezoelectric polarization charges at the semiconductor-metal interface for directions other than 〈100〉 are observed.
Single domain high T
c La2−xSrxCuO4 films with tilted CuO2 planes
Authors: Kwo J. , Fleming R. M. , Kao H. L. , Werder D. J. , Chen C. H.
Published: July 2002

The two fold degeneracy inherent to epitaxial growth of high Tc films on (101) perovskite substrates has been removed successfully. This is demonstrated by single domain, (103) oriented La2−xSrxCuO4 films of 0.04≤x≤0.34 on vicinal (101) SrTiO3 substrates using 90° off-axis sputtering. (101) substrates that have the surface normal rotated about [010] by 0.5°–3.5° produced essentially single crystal films with the c-axis direction determined by the sense of the miscut. Misoriented antidomains (103)′ have been eliminated effectively to a percentage less than 1 part in 104. The mechanism for symmetry breaking is understood on the basis of a surface step model in which the energetics promoting single domain growth is derived from nucleation and epitaxy on the (001) face found at surface steps of vicinal substrates. Furthermore, the incommensuration of the c axis interplanar spacings with the a, b, plane lattice parameters in the La2−xSrxCuO4 structure provides a natural selection of (103) domains over (103)′ domains. The model predicts the application to other high Tc materials such as the Bi2Sr2CanCun+1Ox, and the Tl2Ba2CanCun+1Ox families.
Electro-optic phenomena in gelatin-based poled polymer
Authors: Ho Z. Z. , Chen Ray T. , Shih Robert
Published: July 2002

An electro-optic polymer with nitrophenol and photo lime gel has been constructed and demonstrated. The transmission spectrum of nitrophenol/gelatin shows an ultrawide optical bandwidth, from 340 to 2800 nm. A relatively stable and large electro-optic effect, γ33=10–40 pm/V, was observed at 632.8 nm. The poling stability is attributed to the two-dimensional cross-linked nature of the gelatin. This result indicates that both passive and active integrated optical devices can be fabricated onto the same polymer thin film to form a fully polymer-based miniature integrated optical circuit.
Determination of band gap and effective masses in InAs/Ga1−xInxSb superlattices
Authors: Omaggio J. P. , Meyer J. R. , Wagner R. J. , Hoffman C. A. , Yang M. J. , Chow D. H. , Miles R. H.
Published: July 2002

InAs/Ga1−xInxSb superlattices have been investigated by magneto-optical and magnetotransport techniques. Band gaps, determined from interband magneto-optical measurements and from the temperature dependence of the intrinsic carrier concentration, are in the long wavelength infrared region (8.3–12.4 μm) and are in good agreement with gaps calculated from a two-band model. Both electron and hole effective masses were measured by cyclotron resonance and the electron effective mass is found to be a factor of 4–5 larger than in HgCdTe (the industry standard IR material). This is necessary for reduced dark currents and good optical absorption coefficients in this material.
Photoreflectance characterization of an InP/InGaAs heterojunction bipolar transistor structure
Authors: Yan D. , Pollak Fred H. , Boccio V. T. , Lin C. L. , Kirchner P. D. , Woodall J. M. , Gee Russell C. , Asbeck Peter M.
Published: July 2002

We have measured the photoreflectance (PR) spectrum at 300 K from a lattice-matched InP/InGaAs heterojunction bipolar transistor structure grown by gas-source molecular beam epitaxy. From the observed Franz–Keldysh oscillations we have evaluated the built-in dc electric fields and associated doping profiles in the n-InGaAs collector and n-InP emitter regions. These donor concentrations are in agreement with capacitance-voltage and secondary ion mass spectroscopy determinations, but are considerably lower than the intended values from the growth parameters. We have thereby detected a failure of the Si doping source which occurred during material growth using this contactless, nondestructive, and rapid characterization method. The energy of the InGaAs band gap from the PR spectrum also verifies the lattice-matched nature of the system, further demonstrating the diagnostic and process control value of the PR technique.
Geometrical shape dependent polarization anisotropy in electroluminescence from InGaAs/InP quantum wires
Authors: Notomi M. , Okamoto M. , Iwamura H. , Tamamura T.
Published: July 2002

The polarization properties of edge-emitted electroluminescence from InGaAs/InP quantum wires fabricated by reverse-mesa wet etching, electron-beam lithography, and overgrowth, are investigated. Strongly TE polarized electroluminescence from relatively wide wires approaches isotropy as the wires become narrower. The observed dependence on wire size is attributed to a transition from a two-dimensional to a one-dimensional system. The implication is that quantum wires could potentially be applied to polarization-controlled devices, such as polarization insensitive optical amplifiers.
Lanthanum-modified lead titanate thin film formed by low-temperature chemical vapor deposition and subsequent annealing
Authors: Watanabe Shunji , Fujiu Takamitsu , Tanaka Akira
Published: July 2002

Amorphous films with (Pb0.85La0.15)TiO3 targeted composition were formed on Pt/Ta/SiO2/Si substrates at 400 °C by metalorganic chemical vapor deposition and subsequently annealed in oxygen atmosphere. The films had a thickness of 250 nm and apparent grains smaller than 100 nm. An apparent grain size was established at the deposition stage and remained unchanged throughout the annealing at 550 to 750 °C. The ferroelectric characteristics emerged after annealing and became enhanced with increasing annealing temperature up to 650 °C. At that temperature, remanent polarization and coercive field were 18 μC/cm2 and 120 kV/cm, respectively, while the dielectric constant was 330.
Strong far-infrared intersubband absorption under normal incidence in heavily n-type doped nonalloy GaSb-AlSb superlattices
Authors: Samoska L. A. , Brar Berinder , Kroemer H.
Published: July 2002

We report on long-wavelength intersubband absorption under normal incidence in heavily doped binary-binary GaSb-AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low-density-of-states Γ minimum, electrons spill over from the first Γ subband into the higher-energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8×10−3 (absorption coefficient α≊8500 cm−1) is observed at λ≊15 μm for a sheet concentration of 1.6×1012 cm−2/well.
High transition temperature superconducting surface acoustic wave devices
Authors: Fredricksen H. , Ritums D. , Wu N. J. , Li X. Y. , Ignatiev A. , Feller J. , Sarma B. K. , Levy M.
Published: July 2002

Thin films of high transition temperature superconducting YBa2Cu3O7−δ (YBCO) have been deposited onto YZ-cut LiNbO3 and photolithographically patterned into surface acoustic wave (SAW) devices operating at 50 and 100 MHz center frequencies. Both devices show sharp improvement in SAW transduction efficiency as temperatures are lowered to the superconducting transition temperature of the YBCO electrodes. The magnitude of the improvement is directly dependent on the normal state resistance of the YBCO, and in one case was as high as 12 dB. In both cases, the amplitude change over the entire temperature range is matched nearly exactly by the derived ideal electrode behavior predicted from the aperture width, substrate radiation resistance, and YBCO electrode sheet resistance.
Damage and polymerization by ion bombardment of C60
Authors: Kastner J. , Kuzmany H. , Palmetshofer L.
Published: July 2002

Sublimated C60 fullerite films have been implanted with 160−300 keV H, He, C, and Ar ions with doses ranging from 1×1012 to 5×1016 cm−2. Raman scattering showed a structural transformation of the fullerite to amorphous carbon at certain doses depending on the projectile. This amorphization process is correlated to the energy loss by nuclear collisions. Electronic stopping leads to no detectable disruption of fullerene molecules but to a polymerization of C60. This new phase is evidenced by several changes in the Raman spectrum, of which a new line at about 1463 cm−1 is most prominent.
Extended travel ultrahigh-vacuum sample manipulator with two orthogonal, independent rotations
Authors: Zinck J. J. , Weinberg W. H.
Published: July 2002

A UHV sample manipulator with greater than 22 in. of vertical translation and 360° of independent polar and azimuthal sample rotation is described.
Double lock-in detection for recovering weak coherent radio frequency signals
Authors: Goree J.
Published: July 2002

A single radio frequency lock-in amplifier reduces broadband noise, but not rf pickup of the same frequency as the signal. If this pickup noise is at least 14 dB stronger than broadband noise, after both have passed through the lock-in, then the signal-to-noise ratio can be improved by applying the lock-in output to a second, low-frequency lock-in which is synchronized to an independent modulation of the signal. Weak coherent radio frequency signals buried in both rf pickup and broadband noise can be recovered by using this double lock-in method, as demonstrated in a plasma diagnostics experiment.
Direct indication technique of plasma potential with differential emissive probe
Authors: Yao Wang En , Intrator T. , Hershkowitz N.
Published: July 2002

We present a new method of plasma potential measurement with a differential emissive probe. The dc heated probes are combined with a feedback loop control circuit to measure plasma potential automatically. In addition, it is shown that connecting to the central point of the filaments reduces the effect on the emissive currents of voltage drops across the filaments. The decay time constant of half-cycle heated emissive probe current during the off heating cycle is shown to depend on the initial emission current and on the bias voltage.
Direct indication plasma potential diagnostic based on secondary electron emission
Authors: Wang En Yao , Hershkowitz Noah , Intrator Tom
Published: July 2002

A new method of plasma potential measurement which makes use of secondary electron emission is presented. A differential secondary emissive probe is employed consisting of two similar single probes, each with surfaces that have different secondary emission coefficients. The differential emission current drives a feedback control circuit (previously used with heated probes) to serve as a sensor of plasma potential. When the secondary emission coefficient of a single probe is greater than unity, the floating potential of that probe is also shown to be a good indication of plasma potential.
Simple photoelectronic source for swarm experiments in high-density gases
Authors: Borghesani A. F. , Bruschi L. , Santini M. , Torzo G.
Published: July 2002

A simple photocathode for electron injection into high-density gas is described. Relatively large electronic current pulses have been obtained by using a commerical low-power xenon flash lamp. The photocathode efficiency has been studied as a function of the metal film thickness. The device has been used in swarm experiments at pressures up to 10 MPa in the temperature range 40–300 K.
Thermoelectric thin-film high-temperature measurements by computer control
Authors: Roberts S. S. , Rabinovich S. M. , Shing Y. H. , Tran N. T. , Josefowicz J. Y.
Published: July 2002

This paper describes the design and performance of a novel automated apparatus for measuring the Seebeck coefficient (S) and the electrical conductivity (σ) of thin-film thermoelectric materials continuously over the temperature range of 20 to 1000 °C. An inert substrate coated with a thin film thermoelectric material is increased and decreased in temperature at a predetermined rate set by program control while maintaining a constant temperature gradient across the sample. A fully automated computer data acquisition system is used to control instrumentation, measurements, and data storage. This approach is particularly useful for studying the transition from amorphous to crystalline structure in the semiconducting materials. Thin-film thermoelectric materials were prepared by magnetron sputtering and rf glow discharge. Parameters S and σ were measured as a function of temperature, histology, type, and amount of doping. Materials studied had the compositions Bi2Te3, GeTe, Ge80Te20, PbTe, and S.
Novel x-ray diffractometer for liquid surface studies
Authors: Weiss A. H. , Deutsch M. , Braslau A. , Ocko B. M. , Pershan P. S.
Published: July 2002

An x-ray diffractometer for studying the structure of the liquid–vapor interface is described. It is designed to permit reflectivity and scattering studies from liquid surfaces for angles varying from grazing incidence, below the critical angle for total external reflection up to angles ∼3° using a rotating anode x-ray generator. In principle the diffractometer system can be used to study both the density profile normal to the surface and in-plane structural features. The former is determined by deviations of the measured reflectivity from the Fresnel law of classical optics and the latter from nonspecular scattering. Results obtained using this spectrometer to measure the density profile normal to the surface of water and a liquid crystal are presented.
Variable radius curved crystal mount
Authors: Henins Albert
Published: July 2002

A crystal mount has been developed which permits adjustment of the radius of curvature of the diffracting crystal in a curved crystal spectrometer without changing the crystal’s orientation with respect to the instrument. This mount simplifies x-ray spectrometer design permitting a fixed crystal-to-detector distance. The scale of the instrument is readily changed by changing only this parameter.
Low-temperature sample-rotating cryostat with two degrees of freedom for measuring the anisotropy of the upper critical field of superconductors
Authors: Pazol B. G. , Ginsberg D. M.
Published: July 2002

An apparatus is described for measuring the anisotropy of the upper critical field, Hc2 . It can rotate a sample through large angles about two orthogonal axes in a magnetic field. Three Hall probes determine the orientation of the sample relative to an applied magnetic field, giving an angular precision of less than 0.1°. This is an order of magnitude improvement in angular precision over previously reported devices. Its performance, operation, and advantages are discussed.
Use of positive ion appearance curves for energy scale calibration in electron beam experiments
Authors: Chantry P. J.
Published: July 2002

Linearly extrapolated ion appearance curves are frequently used to obtain a corrected electron energy scale in electron beam experiments. The relative merits of the rare gases are critically examined using the published total ion collection data of Rapp and Englander-Golden. For each gas the error in the linearly extrapolated threshold has been calculated as a function of the extent of the data included in the linear regression fit. The results clearly indicate that He is the best choice in this context, allowing the linear fit to be extended to 8 eV above threshold without introducing any significant error. With Xe the error is less than 0.07 eV, provided the fitted data does not extend beyond 7 eV above the threshold. The worst choice is argon, for which the error increases rapidly with the range of the fit, and can exceed 0.3 eV.
Base line design for the Intense Microwave Prototype wiggler
Authors: Jong R. A. , Throop A. L. , Scharlemann E. T.
Published: July 2002

We describe the base line design for the wiggler to be used in conjunction with the Experimental Test Accelerator-II (ETA-II) to produce high-power microwave radiation in the Intense Microwave Prototype (IMP) free-electron laser experiment. This design produces negligible noise growth for spontaneous noise sources as large as 20 dB above shot noise, and thus corrects the defects present in earlier iterations of the design, which resulted in diminished gain at the signal frequency because of space-charge effects as well as enhanced spontaneous noise growth at frequencies lower than the signal frequency. In addition, more realistic engineering design constraints on the waveguide size and the wiggler gap spacing have been set by the waveguide wall loading and the electron beam fill factor and have been incorporated in the final base line design. The design assumes that the ETA-II accelerator will supply an electron beam with an energy of 10 MeV, a current of 3 kA, and a brightness of 1.0×108 A/(m rad)2. With this beam and 500 W of input power at a frequency of 250 GHz, the peak output TE01 power predicted by the simulation codes, for a rectangular waveguide of dimensions 3.5×3.0 cm2, is in excess of 12 GW, corresponding to an extraction efficiency of 44%. The wiggler has an overall length of 5.5 m and a period of 10 cm. It consists of a 2-m untapered section at a magnetic field of about 4.3 kG followed by a 3.5-m tapered section with magnetic field ranging from a peak value of 4.5 kG to a minimum of 390 G. The growth of the beam linear fill factor to about 50% sets the lower limit of the magnetic field strength in the tapered wiggler region. A nonsteering, nondisplacing binomial winding pattern has been incorporated into the wiggler profile. The base line design is a 2(1331) pattern spanning six magnet poles, giving an inherent tapering resolution of 30 cm.
Cathodoluminescence system for a scanning electron microscope using an optical fiber for light collection
Authors: Hoenk Michael E. , Vahala Kerry J.
Published: July 2002

We describe a novel light collection system for cathodoluminescence scanning electron microscopy. Cathodoluminescence emitted from the sample surface enters directly into the facet of an optical fiber, which is held less than a millimeter away from the sample to optimize the collection efficiency. The fiber is small enough that it has a minimal effect on access to the sample by other detection apparatus. Three axis positioning of the fiber is accomplished with motorized translation stages located in the sample chamber. Techniques for generating cathodoluminescence images and local spectra are discussed. The techniques are applied to oval defects in molecular beam epitaxially grown GaAs/AlGaAs epilayers, and the results are presented.
Analog circuit for the measurement of phase difference between two noisy sine-wave signals
Authors: Shakkottai P. , Kwack E. Y. , Back L. H.
Published: July 2002

A simple circuit for the measurement of phase difference between two noisy sine waves is described. The circuit locks over a wide range of frequencies and produces an output proportional to the phase difference of signals that vary rather rapidly.
Modified perveance law for neutral-beam ion sources
Authors: Uhlemann R. , Wang G.
Published: July 2002

The perveance law for ion sources is modified based on experimental data gained during the conditioning phase of three multiaperture ion sources for neutral-beam injection into TEXTOR. The ion sources are modified JET PINIs with a three-grid accel-decel extraction system designed for 55 kV, 88 A, 4.8 MW, operated in hydrogen. Results show that best agreement of the perveance law with the experimental data is achieved when the measured ion species mixture is used and, additionally, when the total width of the first acceleration gap, usually determined by the geometrical distance d1 between grid 1 and grid 2 and thickness D1 of grid 1, is enlarged by a third distance term r2, taking the effect of distortion of the electrical field lines at the decel grid into account. At perveance matched conditions, i.e., minimum beam divergence, the optimum value is found to be r′2 =0.8r2, where r2 is the aperture radius of the decel grid. The species fractions were measured by optical and magnetic spectrometry.
Multipurpose four-circle diffractometer with a crystal analyzer for use with synchrotron radiation
Authors: Iwasaki H. , Sasaki S. , Kishimoto S. , Harada J. , Sakata M. , Fujii Y. , Hamaya N. , Hashimoto S. , Ohshima K. , Oyanagi H.
Published: July 2002

This paper describes the performance of a four-circle diffractometer installed at the Photon Factory for extensive use with synchrotron radiation for various investigations in the field of solid state physics. Its main part is based on a Huber 5020.4 type diffractometer with a crystal analyzer designed for vertical diffraction plane attitude. The diffractometer is mounted on a carriage table, which can precisely adjust the position of the diffractometer with respect to the incident beam monochromatized by successive reflection from a pair of Si(111) crystals. With a perfect crystal used as the analyzer the large size of the ω and 2θ circles enables us to make high resolution (ΔQ/Q∼10−4) measurements of x-ray scattering intensity distribution from a single crystal. The large space in the center of the diffractometer permits us to put a pressurizing cell or a cryostat on the φ table for scattering measurements at controlled pressures and temperatures. Selected examples of the application are presented.
Comparison of elliptical and spherical mirrors for the grasshopper monochromators at SSRL
Authors: Waldhauer A. P.
Published: July 2002

A comparison of the performance of a spherical and elliptical mirror in the grasshopper monochromator is presented. The problem was studied by ray tracing and then tested using visible (λ=633 nm) laser light. Calculations using ideal optics yield an improvement in flux by a factor of up to 2.7, while tests with visible light show an increase by a factor of 5 because the old spherical mirror is compared to a new, perfect elliptical one. The FWHM of the measured focus is 90 μm with a spherical mirror, and 25 μm with an elliptical one. Elliptical mirrors have been acquired and are now being installed in the two grasshoppers at SSRL.
In situ dc oxygen-discharge cleaning system for optical elements
Authors: Koide Tsuneharu , Shidara Tetsuo , Tanaka Kenichiro , Yagishita Akira , Sato Shigeru
Published: July 2002

I n situ dc oxygen-discharge cleaning arrangements have been developed at the Photon Factory for the removal of carbon contamination from optical surfaces. A high cleaning rate could be achieved by producing an oxygen plasma close to the optical elements with special care taken to avoid any harmful effects from the discharge; contaminant carbon was completely removed within a few hours, at most. This short exposure time and the use of dry oxygen gas resulted in a restoration of the original ultrahigh vacuum without a bakeout. Results with a Seya-Namioka beamline for gas-phase experiments showed a flux enhancement amounting to a factor of 50, and results with a grasshopper beamline showed a nearly complete recovery of the light intensity, even at the carbon K edge.
Solid surface analysis beamline BL-1A at the Photon Factory
Authors: Kawamura T. , Maeyama S. , Oshima M. , Ishii Y. , Miyahara T.
Published: July 2002

The characteristics of the beamline used for PES (photoelectron spectroscopy) and SEXAFS (surface extend x-ray absorption fine structure) studies at the Photon Factory are described. Monochromatic photons are available in the energy range between 50–900 and 2500–4000 eV. This has been accomplished using a grating/crystal monochromator with a combination of two paraboloidal mirrors. The synchrotron radiation is focused by a set of paraboloidal mirrors at a 1.0° incident grazing angle. The plane grating/mirror combination has covered vacuum ultraviolet region of 50–900 eV with 1200 and 2400 g/mm gratings. The InSb (111) double crystals have covered soft x-ray region of 2500–4000 eV. The performance of the gratings in respect to intensity, resolution, and the effect of ‘‘on blaze operation’’ is discussed. The Bragg peak searching system in crystal mode and its performance are also described. With the use of InSb(111) crystals, the energy range below 2700 eV will be covered with precise roll adjustment of both 1st and 2nd crystals.
Field dependent permittivity in metal-semiconducting SrTiO3 Schottky diodes
Authors: van der Berg R. A. , Blom P. W. M. , Cillessen J. F. M. , Wolf R. M.
Published: July 2002

The field dependence of the dielectric constant of SrTiO3 is investigated using the capacitance versus bias voltage characteristics of various metal-SrTiO3:Nb Schottky diodes. The relative dielectric constant is shown to decrease one order of magnitude for electric fields ranging from 0.1 to 10 MV/cm. At low fields the permittivity follows the Curie–Weiss law, whereas at fields larger than 500 kV/cm the permittivity is nearly temperature independent. At high doping densities the field dependent permittivity gives rise to a reduction of the depletion width of the Schottky diode.
Development of H− and D− ion sources for plasma heating
Authors: Holmes Andrew J. T.
Published: July 2002

The large size of future, and possibly present day, tokamaks requires high neutral atom beam energies for current drive and heating. These injectors must also have a high electrical efficiency and this can be achieved using negative ion sources to create the beam. These large tokamaks, such as ITER or NET require a neutral beam power of around 50–100 MW at beam energy of 1 MeV of D0. This power is achieved by operating several sources in parallel, each one of which would extract a 28-A beam of D− ions of which 57% are converted to D0 in a gas cell neutralizer and can be transmitted to the torus. The injector for one port consists of four units, each of which is a fully independent unit. This article describes the details of the injector unit which is based on volume plasma sources of D− ions.
Active stabilization system for a laser interferometer
Authors: Doswell Gary , Kunov Hans
Published: July 2002

An active stabilization system for a bulk optics Mach–Zhender interferometer has been assembled, with which it is possible to reduce low-frequency thermally and seismically induced optomechanical component drift. Reductions from greater than 10 dB/min variation in interferometer photodetector output signal (referenced to 1.0 μV) to less than 1 dB/min have been achieved. The active stabilization feedback loop effectively ‘‘locks the interferometer in’’ near its maximum point of sensitivity. The resulting highly stable output signal allows the interferometer to be used for applications such as micromechanical displacement measurement.
Comparison of the calculated transient responses of a Fabry–Perot used in reflection and in transmission
Authors: Houssin M. , Jardino M. , Desaintfuscien M.
Published: July 2002

High finesse optical cavities are used either in reflection or in transmission for the frequency stabilization of lasers. In this paper, we calculate the transient response of the Fabry–Perot cavity after a small frequency jump of the laser in both cases. We compare the static gains and the transfer functions for small frequency fluctuations, and explain partially the good experimental observed performances of the Fabry–Perot used in reflection.
CDX-U two-dimensional scanning microwave system
Authors: Forest C. B. , Greene G. , Ono M.
Published: July 2002

A versatile 2 mm scanning interferometer has been built for the CDX-U machine. The unique diagnostic access of CDX-U allows a vertical view through windows on the top and bottom, and a two-pass horizontal view through a side window which utilizes reflection off of a mirror mounted on the center column of the vessel. A single launching antenna and two separate receivers can be operated in a variety of modes including simple interferometry, polarimetry, and scattering. The optics, mechanical translation system, and 2 mm heterodyne receiver are described.
Multichannel interferometer/polarimeter system for the RTP tokamak
Authors: van Lammeren A. C. A. P. , Kim S. K. , Donné A. J. H.
Published: July 2002

A nine-channel interferometer/polarimeter system is designed for the RTP tokamak (Rijnhuizen Tokamak Project, a =0.16 m, R =0.72 m, BT =2.5 T, Ip ≤ 200 kA, and plasma pulse duration 200 ms). A CO2-pumped dual-cavity FIR laser system is used to obtain two FIR laser beams of λ =432 μm with a frequency difference of 1 MHz. The FIR beams are expanded by a set of parabolic mirrors. Corner-cube mixers with Schottky diodes are used as detectors. The mixers are mounted on a linear rail system, such that their positions can be easily changed. The interferometer can be operated with a maximum of 19 channels, and will be extended with a polarimeter to measure the poloidal magnetic field distribution. It will be tried to increase the accuracy of the polarimeter by modulating the polarization of the incoming beam. A scheme for polarization modulation which is based on the idea of Dodel and Kunz will be presented in this paper. This scheme has the advantage that only one set of detectors is needed to measure the electron density and current density. The complete system will be presented along with some pilot experiments concerning the polarization modulation.
Simultaneous measurement of ion and electron temperatures in the scrape-off layer of a small tokamak
Authors: da Silva R. P. , Nascimento I. C.
Published: July 2002

This article describes a system composed of an electrostatic ion probe associated with an electronic circuit designed and constructed to be used in the scrape-off layer of the TBR-1 tokamak for simultaneous measurements of local electron and ion temperatures. The electronic circuit is discussed. Details of the mechanical structure and dimensions of the probe can be found in another article [Rev. Sci. Instrum. 57, 2205 (1986)]. The circuit is composed of a sweep generator followed by an amplifier. The sweep time can be varied from 50 μs to 50 ms and the probe voltage amplitude from 0 to 200 V. The circuit supplies a maximum current of 250 mA, is short-circuit protected, and provides cable capacitance neutralization. The ion current is detected by a current transformer sensitive to currents as low as 20 μA. The total probe current is measured by the voltage drop in a resistor inserted in the circuit. The system has been tested in the TBR-1 boundary plasma and showed good performance with a time resolution better than 500 μs. The obtained results showed that, for TBR-1 boundary plasma, the ion temperature is about two times the electron temperature.
An environmental cell transmission electron microscope
Authors: Lee T. C. , Dewald D. K. , Eades J. A. , Robertson I. M. , Birnbaum H. K.
Published: July 2002

An aperture-limited, differentially pumped environmental cell has been developed and installed in a JEOL 4000 EX electron microscope. With this environmental cell it is possible to observe, at high spatial resolution, the detailed changes in microstructure that occur during the interaction between a solid and a gaseous environment. The cell has been pressurized to 70 Torr with H2 gas for several hours with no adverse effects on the microscope performance. While the initial tests have been performed with hydrogen gas, the materials used to construct the environmental cell can tolerate corrosive environments. The key features of the environmental cell design along with the results from some applications are presented in this paper.
Spray extractor: A new sampling device for gas chromatographic/mass spectrometric analysis of volatile organic compounds in aqueous systems
Authors: Baykut Gökhan
Published: July 2002

A new instrument has been developed to extract volatile and semivolatile compounds from liquid phase into the gas phase. This new extractor makes use of a spray process, which enormously increases the total interfacial area between the aqueous and the gaseous system. The spray extractor is used as a sampling system for analysis instruments such as a gas chromatograph or a gas chromatograph/mass spectrometer.
All-solid-state microscope-based system for picosecond time-resolved photoluminescence measurements on II-VI semiconductors
Authors: Buller G. S. , Massa J. S. , Walker A. C.
Published: July 2002

A novel, entirely solid-state, instrument has been developed for the study of time-resolved photoluminescence in a wide variety of bulk semiconductors, low-dimensional structures, and other materials. This system uses a frequency-doubled GaAlAs diode laser (pulse width 30 ps) as the 415-nm pump source and a silicon single-photon avalanche diode for detection of photoluminescence. The time-correlated single photon counting technique allows measurement of photoluminescence decays in the temporal region of 10 ps to ≳500 ns with high statistical accuracy. In addition, the combination of a microscope with a small-area detector provides a spatial resolution of <5 μm. This system is currently being used for the measurement of picosecond time-resolved photoluminescence from II-VI semiconductors.