bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrologic analysis of urban catchments with event‐based probabilistic models: 2. Peak discharge rate
Authors: Guo Yiping , Adams Barry J.
Published: February 2004

The peak discharge rate of a runoff event is estimated from the runoff event volume, the duration of the causal rainfall event, and the catchment time of concentration. The runoff event volume is determined from the rainfall‐runoff relationship developed by Guo and Adams [this issue]. The average catchment time of concentration is used for all runoff events and is treated as a physical characteristic of the urban catchment, independent of input rainfall characteristics. Incorporating the exponential probability density functions of rainfall event characteristics, closed‐form analytical expressions are then derived for the return period of peak discharge rate or flood frequency distribution of urban catchments. The derived flood frequency distributions compared favorably with sample distributions constructed from continuous simulation results for a range of urban catchments. Thus the derived analytical expressions or probabilistic models for peak discharge rates are proposed as an alternative to simulation modeling or regional analyses for the determination of flood frequencies for urban catchments.
Statistical downscaling of general circulation model output: A comparison of methods
Authors: Wilby R. L. , Wigley T. M. L. , Conway D. , Jones P. D. , Hewitson B. C. , Main J. , Wilks D. S.
Published: February 2004

A range of different statistical downscaling models was calibrated using both observed and general circulation model (GCM) generated daily precipitation time series and intercompared. The GCM used was the U.K. Meteorological Office, Hadley Centre's coupled ocean/atmosphere model (HadCM2) forced by combined CO2 and sulfate aerosol changes. Climate model results for 1980–1999 (present) and 2080–2099 (future) were used, for six regions across the United States. The downscaling methods compared were different weather generator techniques (the standard “WGEN” method, and a method based on spell‐length durations), two different methods using grid point vorticity data as an atmospheric predictor variable (B‐Circ and C‐Circ), and two variations of an artificial neural network (ANN) transfer function technique using circulation data and circulation plus temperature data as predictor variables. Comparisons of results were facilitated by using standard sets of observed and GCM‐derived predictor variables and by using a standard suite of diagnostic statistics. Significant differences in the level of skill were found among the downscaling methods. The weather generation techniques, which are able to fit a number of daily precipitation statistics exactly, yielded the smallest differences between observed and simulated daily precipitation. The ANN methods performed poorly because of a failure to simulate wet‐day occurrence statistics adequately. Changes in precipitation between the present and future scenarios produced by the statistical downscaling methods were generally smaller than those produced directly by the GCM. Changes in daily precipitation produced by the GCM between 1980–1999 and 2080–2099 were therefore judged not to be due primarily to changes in atmospheric circulation. In the light of these results and detailed model comparisons, suggestions for future research and model refinements are presented.
Using reactive solutes to constrain groundwater flow models at a site in northern Wisconsin
Authors: Keating Elizabeth Harrison , Bahr Jean M.
Published: February 2004

We propose a method for constraining a groundwater flow model both by head observations and concentrations of nonconservative solutes such as calcium, using reaction‐path modeling. When calibrating flow models in small watershed in northern Wisconsin using head data alone, we encountered problems of nonuniqueness. However, by coupling the flow models with a plagioclase dissolution model, we were able to greatly reduce the number of plausible flow models. First, by using flow modeling and reaction path modeling in parallel, we tested the consistency of residence times predicted by the flow models with solute concentrations predicted by the geochemical models. Mineral dissolution rate parameters were assumed to be spatially uniform; without this condition the geochemistry data would not provide additional constraints to the flow modeling process. For a more comprehensive test of our models, we used reactive‐transport modeling to predict the spatial distribution of ions at each site. The models qualitatively reproduced the observed data and our calibrated silicate dissolution rates closely matched those reported in a field study of nearby site. There were also discrepancies between predictions and observations. We attribute these to transient effects and sediment heterogeneities that were not included in the models. While the resulting models are not unique, our approach demonstrates the ability of fairly simple models to explain much of the observed variability in a complex system.
A note on the time compression approximation
Authors: Liu M.‐C. , Parlange J.‐Y. , Sivapalan M. , Brutsaert W.
Published: February 2004

In this paper the work by Sivapalan and Milly [1989] is extended beyond the time of ponding to estimate the errors of the time compression approximation (TCA) when an exact solution exists. The diffusion coefficient is set to be constant, and gravitational effects are not considered here. The largest error of standard TCA in calculating cumulative infiltration is about 2.5%, while its underestimate of the time to ponding is about 19%. A modified TCA is also proposed, in which the exact time of ponding is used directly instead of the flux to improve the estimate of postponding infiltration. The error for the modified TCA is about half of the error for the standard TCA in predicting cumulative infiltration, and thus the modified TCA should be preferred wherever ponding time is or can be measured.
Intravitreal sodium fluorescein enhances visualization of clear vitreous during vitreous surgery for macular hole: a safety and efficacy study
Authors: Das Taraprasad , Vedantham Vasumathy
Published: February 2004

Purpose: To assess the safety and efficacy of sodium fluorescein (NaFl) as an aid for clear vitreous vitrectomy.

Methods: In 50 consecutive cases of macular hole surgery, NaFl 0.6% prepared from 20% injectable dye was injected into the vitreous cavity after core vitrectomy so as to stain the clear formed vitreous.

Results: NaFl stained the peripheral uncut clear vitreous green and improved the visualization for a safe and complete vitrectomy. No complications associated with the dye injection were noted.

Conclusion: NaFl 0.6% can safely be used in the vitreous cavity for easy identification of clear uncut vitreous gel for clear vitreous vitrectomy. This enhances expeditious excision of this tissue.
Is directed donation misguided?
Authors: Sherwin Trevor , Coster Douglas J , La Nauze Jamie , Merry Alan , Pendergrast David , Armitage W John
Published: February 2004

The worldwide shortage of organs and tissue for transplant has led to many ethical discussions involving restrictions concerning organ and tissue donation, including living donations and payment for donation. Efforts are being made to increase the donor pool; however, it is timely to ask whether moral decisions such as the rejection of directed donations are defensible. In this Clinical Conundrum, six specialists delve into the ethical and practical issues surrounding directed donation of human organs and tissues with particular reference to its implications in the field of ophthalmology.
Comparison of the Proview pressure phosphene tonometer performed by the patient and examiner with the Goldmann applanation tonometer
Authors: Danesh‐Meyer Helen V , Niederer Rachel , Gaskin Brent J , Gamble Greg
Published: February 2004

Objective: To compare the results of Proview pressure phosphene tonometry (PPPT) performed by the patient and an examiner with Goldmann applanation tonometry (GAT).

Methods: A comparative case series of 96 (192 eyes) consecutive patients from a glaucoma clinic was conducted. Intraocular pressure (IOP) was measured with GAT by one examiner, PPPT by another examiner, and PPPT by the patient. All examiners were masked to the results from any preceding IOP measurement.

Results: The coefficient of repeatability for repeated measurements for the GAT was ±0.48 mmHg. The limits of agreement for self‐measurement of IOP with the PPPT and examiner measured IOP with PPPT were 6.3 mmHg and 4.8 mmHg, respectively. The limits of agreement between GAT and self assessed PPPT were ±11.8 mmHg (mean difference of 0.63 mmHg). When the same comparison was made between GAT and examiner assessed PPPT, the results were limits of agreement of ±10 mmHg (mean difference of 2.86 mmHg). No significant difference was identified in the agreement of the GAT and the PPPT when subanalysed for age of patient or diagnosis (P > 0.05). The limits of agreement between self‐assessed IOP with the PPPT and the GAT were ±8.2 for those with IOP <20 mmHg and ±14.9 mmHg for those with IOP>20 mmHg.

Conclusions: Poor agreement exists between IOP measured by GAT and PPPT measured by an examiner or by the patient.
Fluorescein angiographic monitoring of corneal vascularization in lipid keratopathy
Authors: Peter Jayanthi , Fraenkel Graham , Goggin Michael , Drew Anton
Published: February 2004

The use of digital fluorescein corneal angiography to assist argon laser photocoagulation is reported. Photocoagulation was performed on the vascular supply of lipid keratopathy in the left eye of a 44‐year‐old woman.
Review of severe vaso‐occlusive retinopathy in systemic lupus erythematosus and the antiphospholipid syndrome: associations, visual outcomes, complications and treatment
Authors: Au Alicia , O'Day Justin
Published: February 2004

Purpose: To discuss the pathogenesis of severe vaso‐occlusive retinopathy in systemic lupus erythematosus (SLE), the association with antiphospholipid antibodies, and its implications for management and prognosis.

Methods: An illustrative case history of a woman with SLE and severe vaso‐occlusive retinopathy in the presence of antiphospholipid antibodies is presented. A literature review of previously reported cases and previously published data on the topic was performed and forms the basis for discussion.

Results: This is a rare form of retinopathy in SLE as distinct from the more common, benign form, being classically a microangiopathy with diffuse capillary non‐perfusion and small arterial or arteriolar occlusions in the retina. Poor visual outcomes with visual loss are reported in 80% of cases with neovascularization occurring in 40% of cases. It is associated with antiphospholipid antibodies, typically characterized by microthrombosis and immune complex mediated vasculopathy rather than a true vasculitis. There is a strong association between this severe form of retino­pathy and central nervous system manifestations of SLE. Anticoagulation has a role in the secondary prevention of thrombosis in the presence of antiphospholipid antibodies, but the role of aspirin and immunosuppression is unclear in the treatment of this condition. Vigilant ophthalmic follow up and aggressive treatment of neovascularization and vitreous haemorrhage can prevent further visual loss. These points are highlighted in the brief case report presented.

Conclusion: Severe vaso‐occlusive retinopathy is a rare form of retinopathy in SLE often associated with poor visual prognosis and neovascularization. It may be a manifestation of the antiphospholipid syndrome. Treatment is aimed at preventing further thrombosis and complications arising from neovascularization.
Clinical Case Notes
Authors: A Wilson Graham , Devaux Angele , Aroichane Maryam
Published: February 2004

A 10‐month‐old boy, known to have the 13q deletion syndrome, presented with leukocoria in a microphthalmic right eye. He was found to have bilateral retinoblastoma requiring enucleation of the right eye and laser, cryotherapy and external beam radiation to the left eye. This case demonstrates that retinoblastoma may be present in a microphthalmic eye and that more than one imaging modality should be used in the evaluation of suspected retinoblastoma, as calcification may be absent on the computed tomography scan but present on B‐mode ultrasound. Children with a known 13q deletion require immediate and serial ophthalmological examinations.
Clinical Case Notes
Authors: Koppens Joanna M , Pon Jo‐Anne MC , Allen Jonathan , Sloan Brian H
Published: February 2004

Castleman's disease, also known as angiofollicular lymphoid hyperplasia, is a lymphoproliferative disorder that is generally benign. The lesions most commonly originate in the lymph nodes of the mediastinum. The second documented case of Castleman's disease of the lacrimal gland is reported in an 84‐year‐old woman who presented with an 8‐year history of a left upper lid mass. This was excised via a lateral orbitotomy, and a diagnosis of Castleman's disease was made histologically. Relevant images of the clinical findings and histology are shown.
Involvement of apoptosis‐inducing factor in neuronal death after hypoxia‐ischemia in the neonatal rat brain
Authors: Zhu Changlian , Qiu Lin , Wang Xiaoyang , Hallin Ulrika , Candé Céline , Kroemer Guido , Hagberg Henrik , Blomgren Klas
Published: February 2004

Apoptosis‐inducing factor (AIF) triggers apoptosis in a caspase‐independent manner. Here we report for the first time involvement of AIF in neuronal death induced by cerebral ischemia. Unilateral cerebral hypoxia‐ischemia (HI) was induced in 7‐day‐old rats by ligation of the left carotid artery and hypoxia (7.7% O2) for 55 min. AIF release from mitochondria and AIF translocation to nuclei was detected immediately after HI, and only in damaged areas, as judged by the concurrent loss of MAP‐2. AIF release was detected earlier than that of cytochrome c. Cells with AIF‐positive nuclei displayed nuclear condensation and signs of DNA damage. The number of AIF‐positive nuclei showed a positive correlation with the infarct volume 72 h post‐HI, and this was not changed by treating the animals with boc‐Asp‐fmk (BAF), a multicaspase inhibitor. BAF treatment reduced the activity of caspase‐3, ‐2 and ‐9 (78, 73 and 33%, respectively), and prevented caspase‐dependent fodrin cleavage in vivo, but did not affect AIF release from mitochondria or the frequency of positive nuclear AIF or DNA damage 72 h post‐HI, indicating that these processes occurred in a caspase‐independent fashion. In summary, AIF‐mediated cell death may be an important mechanism of HI‐induced neuronal loss in the immature brain.
Functional characterization of prostaglandin F2α receptor in the spinal cord for tactile pain (allodynia)
Authors: Muratani Tadatoshi , Nishizawa Mikio , Matsumura Shinji , Mabuchi Tamaki , Abe Kohji , Shimamoto Keiko , Minami Toshiaki , Ito Seiji
Published: February 2004

Prostaglandin F2α (PGF2α) binds to its receptor (FP) to increase the intracellular‐free calcium concentration ([Ca2+]i) by coupling of FP with Gq protein. Spinal intrathecal administration of PGF2α to mouse induces touch‐evoked pain (mechanical allodynia), in which capsaicin‐insensitive primary afferent Aβ‐fibres and N‐methyl‐d‐aspartate receptor ɛ4 subunit are involved. FP in the spinal cord, however, was not well characterized. Here, we showed constitutive expression of FP mRNA in mouse spinal cord, and functionally characterized spinal FP‐expressing cells which were involved in PGF2α‐induced mechanical allodynia. The method for repetitive administration of oligodeoxyribonucleotides through tubing to conscious mice was established for mechanical allodynia evaluation. We identified an antisense oligodeoxyribonucleotide targeting FP mRNA, causing both disappearance of PGF2α‐induced mechanical allodynia and decrease of FP mRNA. With saline‐administered mice, PGF2α rapidly increased [Ca2+]i of the cells in the deeper layer of the dorsal horn. In contrast, when the FP antisense oligodeoxyribonucleotide was repeatedly administered, the population of PGF2α‐responsive cells in the slices reduced, and PGF2α‐induced [Ca2+]i increase of these cells diminished. These data strongly suggested that, in the dorsal horn of the spinal cord, there are the FP‐expressing cells which are involved in PGF2α‐induced mechanical allodynia.
Molecular dynamics simulation of solvent–polymer interdiffusion: Fickian diffusion
Authors: Tsige Mesfin , Grest Gary S.
Published: February 2004

The interdiffusion of a solvent into a polymer melt has been studied using large scale molecular dynamics and Monte Carlo simulation techniques. The solvent concentration profile and weight gain by the polymer have been measured as a function of time. The weight gain is found to scale as t1/2, which is expected for Fickian diffusion. The concentration profiles are fit very well assuming Fick’s second law with a constant diffusivity. The diffusivity found from fitting Fick’s second law is found to be independent of time and equal to the self-diffusion constant in the dilute solvent limit. We separately calculated the diffusivity as a function of concentration using the Darken equation and found that the diffusivity is essentially constant for the concentration range relevant for interdiffusion.
In situ electrochemical fabrication of natural contacts on single nanowires
Authors: Wu Wenhao , DiMaria J. B. , Yoo Han G. , Pan Shanlin , Rothberg L. J. , Zhang Yong
Published: February 2004

We report a template-based in situ electrochemical method for fabricating natural electric contacts on single nanowires using a pair of cross-patterned electrodes. Such electric contacts are highly stable upon thermal cycling between room temperature and milli-Kelvin temperatures. Direct imaging of the single-nanowire contacts using scanning electron microscopy is also demonstrated.
In situ area-controlled self-ordering of InAs nanostructures
Authors: Schallenberg T. , Molenkamp L. W. , Rodt S. , Seguin R. , Bimberg D. , Karczewski G.
Published: February 2004

Real-time control of self-organized growth of InAs nanostructures has been achieved by employing epitaxial stationary shadow masks in a molecular-beam-epitaxy process. The method is based on the surface diffusion of group-III adatoms governed by the group-V surface concentration. Lateral control is achieved by the geometry of the mask and the incidence angles of the molecular beams. We apply the method to self-organized growth of nanoscale InAs quantum structures at the edge of the incidence region of the arsenic beam. The high quality of the in situ fabricated nanostructures is confirmed by bright cathodoluminescence of InAs quantum wire embedded in GaAs barriers.
Thermal growth of a vapor bubble moving in superheated liquid
Authors: Ivashnyov O. E. , Smirnov N. N.
Published: February 2004

The problem on the thermal growth of a vapor bubble moving in superheated liquid is solved here for two models of phase interface: a “rigid” sphere (no-slip condition) and “soft sphere” (slip condition). In contrast to known solutions, both first and second self-similarities in the problem on the motion of a “soft” growing bubble were found. With the double self-similar solution obtained, an approximate dependence of the dimensionless heat flux to the bubble interface was determined as a function of the Jacob and Péclet numbers, which coincided with the known solutions in two limiting cases: for a motionless growing vapor bubble and for a moving bubble of constant radius. The theoretical solutions are compared with the experimental data for rising vapor bubbles in a superheated liquid. The results of the comparison show that as long as the bubble radius is less than a critical size acr, determined by the liquid superheat, the experimental data fit the results of calculations based on the model of a rigid interface. When the bubble radius is greater than acr, the experimental data fit the calculations based on the soft surface model.
Phase conjugation by low-power continuous-wave degenerate four-wave mixing in nonlinear optical polymer fibers
Authors: Bian Shaoping , Kuzyk Mark G.
Published: February 2004

We report on the observation of phase conjugation (PC) using low-power, continuous-wave degenerate four-wave mixing in nonlinear polymer multimode fibers. The fibers are made of poly(methyl methacrylate) doped with Disperse Red 1 as the photosensitive chromophore. With a power less than 2.5 mW at wavelength 633 nm for each beam inside the fiber, a maximum PC reflectivity of 1% is obtained. Phase conjugation is observed for both parallel and orthogonally polarized probe and pump beams. Experimental results show that polarization and intensity profile are preserved in the PC wave. The predominant phase conjugation wave is attributed to the formation of sub-refractive-index gratings inside the fibers.
Dissipation in nanocrystalline-diamond nanomechanical resonators
Authors: Hutchinson A. B. , Truitt P. A. , Schwab K. C. , Sekaric L. , Parpia J. M. , Craighead H. G. , Butler J. E.
Published: February 2004

We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T0.2, with Q−1≈10−4 at low temperatures. The frequency dependence of a large dissipation feature at ∼35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz.
Control of magnetization states in microstructured permalloy rings
Authors: Steiner Marcus , Nitta Junsaku
Published: February 2004

Magnetization processes of microstructured NiFe rings are studied by the fringe-field-induced local Hall effect and numerical model calculations. The changes in reversible and irreversible magnetization of single rings are detected with very high resolution. We observe that the type of magnetic transition depends on the ratio between the inner and outer ring diameter. For narrow rings, sharp transitions from so-called “onion” to the “vortex” state are observed. In rings with smaller inner diameter, the transitions are more complex. The creation of local vortices and their spatial movement by applying an external magnetic field are detected.
Discharge asymmetry induced by the pulsed radio-frequency current
Authors: Kim H. C. , Lee J. K. , Shon J. W.
Published: February 2004

Through particle-in-cell/Monte Carlo simulations, the discharge asymmetry induced by the pulsed radio-frequency (rf) form of the driving current is found in capacitively coupled plasmas. It is shown that this discharge asymmetry originates from the phase shift between the rf current and voltage during the current-on time. Consequently, the degree of the asymmetry can be controlled by varying the phase of the rf current. As the duty ratio decreases, the plasma density decreases but the dc bias increases. Hence, it is possible to control the ion flux and ion bombardment energy independently by varying both the amplitude of the rf current and the duty ratio.
LASER EMISSION FROM He-air-CH4 AND He-air-C3H8 MIXTURES
Authors: Barry J. D. , Boney W. E. , Brandelik J. E.
Published: February 2004

Laser emission from a He-air-CH4 mixture has been observed from 4.9668 to 5.5056μ. Most of the cw laser emissions have been identified to result from P(J) vibrational-rotational transitions in CO. Multiline power levels of over 1 W were achieved with the CH4 mixture. The lasing molecules are apparently formed by chemical-collisional processes within the discharge. Similar cw laser emissions from 4.9467 to 5.5717μ were observed from a He-air-C3H8 mixture.
ORIGIN OF THE ELECTRIC FIELD EFFECT IN SILVER
Authors: Berman A. , Juretschke H.J.
Published: February 2004

The electric field effect of epitaxial silver films on mica in vacuum is studied as a function of temperature, thickness, and surface specularity. Using size-effect parameters derived from the analysis of film resistivity, the data indicate that the predominant mechanism for altering the thin-film conductance is the change in surface scattering due to surface charging of the interface.
ORIGIN OF HIGH RESISTANCE AT THE EPITAXIAL LAYER-SUBSTRATE INTERFACE OF GaAs GROWN BY VAPOR EPITAXY
Authors: Iwasaki Hideo , Sugibuchi Kiyoshi
Published: February 2004

A photoluminescence band at 1.40 eV has been observed at 90 °K only at the interface between the epitaxial layer and the substrate in the vapor-grown GaAs crystal. The defect responsible for the band is considered to correlate with a shift of the Fermi level toward the valence band in this interface region and to be related to the acceptor created in GaAs bulk crystal which is heat treated in H2. The defect may be the deeper of two kinds of acceptors associated with the Si impurity on an As site in GaAs crystal.
PHASE-MATCHED UP CONVERSION OF 10.6-μ RADIATION IN ZnGeP2
Authors: Boyd G. D. , Gandrud W. B. , Buehler E.
Published: February 2004

Phase-matched sum mixing of 10.6- and 1.06-μ radiation has been observed at near normal to the optic axis in ZnGeP2. Its theoretical performance as a 10.6-μ detector via up conversion compares favorably with direct detection by a cooled Ge:Hg photoconductive detector. The sum-mixing efficiency of ZnGeP2 is 140 times superior to that of Ag3AsS3, the next best material. The large angular aperture resulting from θm ≃ 90° indicates that the material will be useful for image up conversion.
OPTICAL PULSE COMPRESSION BY FOCUSING IN A RESONANT ABSORBER
Authors: Gibbs H. M. , Slusher R. E.
Published: February 2004

A 10-nsec optical pulse was shortened to 1 nsec by interacting coherently with a simple atomic absorber. The experimental results are in agreement with a computer solution of coupled Maxwell and Schrödinger equations for a uniform spherical propagating wave.
DEUTERIUM FLUORIDE VIBRATIONAL OVERTONE CHEMICAL LASER
Authors: Suchard Steven N. , Pimentel George C.
Published: February 2004

Overtone (Δv = 2) laser emission has been observed for the first time in a vibration-rotation laser system. The N2F4:CD4 chemical laser was operated with a filter in the optical cavity to attenuate the spectral region of the fundamental transitions (Δv = 1). The v = 3 → 1 DF overtone reached threshold and the transition of highest gain was P3−1(4). Such techniques permit ``frequency doubling'' (or tripling, quadrupling, etc.) in vibration-rotation lasers as well as determination of rate constant ratios other than the one that displays maximum gain.
STATISTICAL PROPERTIES OF RANDOMLY MODULATED PSEUDOTHERMAL OPTICAL FIELD
Authors: Bendjaballah C. , Perrot F.
Published: February 2004

Results of measurements of photoelectric-counting distributions and time-interval distributions of the optical field produced by randomly modulated pseudothermal source are reported.
OBSERVATION OF THE SIMULTANEOUS GENERATION OF THE SECOND, THIRD, AND FOURTH HARMONICS OF 1.06-μ RADIATION IN Ba2NaNb5O15, LiNbO3, and LiIO3 CRYSTALS
Authors: Ng Won K. , Woodbury E. J.
Published: February 2004

We have observed simultaneous generation of the second, third, and fourth harmonics of a 1.06-μ fundamental in Ba2NaNb5O15, LiNbO3, and LiIO3 crystals. Experimental results reveal that the third harmonic is generated through the process of mixing the fundamental with the second harmonic; the fourth harmonic arises as a result of doubling the second harmonic. Strong absorption of the fourth harmonic by the crystal is believed to be the principle mechanism responsible for the observed thermal detuning in phase-matched second harmonic generation.
A NEW CRYSTAL Pb5(GeO4)(VO4)2 FOR ACOUSTO-OPTIC DEVICE APPLICATIONS
Authors: Yano T. , Nabeta Y. , Watanabe A.
Published: February 2004

A new melt-grown crystal of apatite type Pb5(GeO4)(VO4)2 has been found to be well suited for acousto-optic device applications. Acousto-optic figure of merit is 50.6 × 10−18 sec3/g and acoustic absorption is about 1.2 dB/cm at 200 MHz.
HOLOGRAM RECORDING BY ALIGNING OF ANISOTROPIC COLOR CENTERS
Authors: Lanzl F. , Röder U. , Waidelich W.
Published: February 2004

The ability of storing information by aligning of anisotropic color centers is shown by means of FA centers in KCl. The process of recording volume holograms in these crystals and the reconstruction is reported.
HIGH-PRESSURE LASER ACTION IN 13 GASES WITH TRANSVERSE EXCITATION
Authors: Wood O. R. , Burkhardt E. G. , Pollack M. A. , Bridges T. J.
Published: February 2004

Laser action has been achieved in 13 gases at high pressures using pulsed transverse excitation. A total of 149 wavelengths from 0.8 to 28μ was observed. Pulse lengths were found to lie in the range 0.2–5μsec. Several gases operate at atmospheric pressure and above and promise to give very high power outputs.
ELECTRON BEAMS FOR QUASILINEAR AND NONLINEAR BEAM-PLASMA EXPERIMENTS
Authors: Roberson C. , Gentle K. W.
Published: February 2004

Electron beams suitable for experimental studies of the nonlinear evolution of the beam-plasma interaction in the quasilinear limit (gentle bump) and in transition to the delta function beam may be obtained by placing a magnetic shield around a simple electron gun. Measurements of the beam energy distribution are presented.
SATURABLE ABSORPTION EFFECTS IN A XENON FLASHTUBE DISCHARGE
Authors: Ward Robert W. , Hotz R. F.
Published: February 2004

Plasma attenuation measurements have been made with YAG: Nd+3 laser radiation traversing a 5-cm length of xenon plasma in a specially constructed flashtube. For low input signals, significant attentuation was observed with the attentuation persisting for several hundred microseconds following flashtube current cutoff. Experimental plasma transmission data were taken as a function of laser input power density. The results showed that there is a dependence on intensity of input radiation, i.e., the absorption tends to saturate as the laser input intensity increases.
CONSTRUCTION AND PROPERTIES OF WEAK-LINK DETECTORS USING SUPERCONDUCTING LAYER STRUCTURES
Authors: Consadori F. , Fife A. A. , Frindt R. F. , Gygax S.
Published: February 2004

A new technique for the construction of weak-link loop devices (SQUID) is presented, which uses single crystals of NbSe2, a superconducting layer structure. The devices display excellent stability against mechanical shock and thermal cycling to cryogenic temperatures. A comparison is made with existing point-contact devices.
OPTICAL NONLINEAR SUSCEPTIBILITIES OF BERYLLIUM OXIDE
Authors: Jerphagnon J. , Newkirk H. W.
Published: February 2004

The nonlinear coefficients of beryllium oxide measured relative to quartz by the Maker fringe technique are d31(BeO) = ± (0.46 ± 0.03)d11 (SiO2) and d33(BeO) = ± (0.63 ± 0.04)d11 (SiO2) for a fundamental beam at 1.064μ. A simple model accounting for the value of the ratio d31(BeO) / d33(BeO) is proposed.
RAPID REVERSIBLE LIGHT-INDUCED CRYSTALLIZATION OF AMORPHOUS SEMICONDUCTORS
Authors: Feinleib J. , deNeufville J. , Moss S. C. , Ovshinsky S. R.
Published: February 2004

Rapid crystallization and equally rapid revitrification of amorphous chalcogenide films exposed to short laser pulses has been observed. A model is developed in which both the speed of crystallization and the reversibility are attributed to the large enhancement of crystallization rate under the influence of the photon flux.
ELECTRON MICROSCOPE OBSERVATION OF LATTICE DISORDER IN ION-IMPLANTED SILICON
Authors: Bertolotti M. , Sette D. , Stagni L. , Vitali G.
Published: February 2004

A technique of electron microscope observation of a replica of the chemical etched surface has been used to see the disorder produced around the single-ion paths in In-implanted Si. Structures of variable dimensions ranging from about 100 Å up to nearly 600 Å in diameter have been observed, with a density of about 1010 cm−2 in a very thin layer in the surface.
EXCITATION MECHANISMS IN THE ZINC ION LASER
Authors: Collins G.J. , Jensen R.C. , Bennett W.R.
Published: February 2004

Conclusive proof is given that two comparably important collision processes are involved in the excitation of the helium-zinc ion laser; charge exchange with the atomic helium ion is the primary source of excitation of the high-lying Zn II levels in configurations of the type, 3d10 nx, and Penning collisions with the He(23 S) metastables are the main source of the lower-lying Zn II levels in the 3d9 4s2 configuration. Substantial enhancement of charge exchange over the Penning reaction was also found in hollow cathode discharges.
DYNAMIC BEHAVIOR OF DOMAIN WALLS IN LOW-MOMENT YTTRIUM-GALLIUM-IRON GARNET CRYSTALS
Authors: Calhoun B.A. , Giess E.A. , Rosier L.L.
Published: February 2004

Measurements of domain-wall velocity, using the ``bubble collapse'' technique, in Y3GaxFe5−xO12 crystals with 1.0 ≤x≤1.7 show that the usual ``viscous'' damping model of domain-wall motion does not apply. At fields less than about 1 Oe above the threshold H0, the wall mobilities are greater than 103 cm/sec Oe. A few oersteds above the threshold, the field dependence of the wall velocities changes abruptly and, at higher fields, the velocities depend linearly on (H-H0)1/2.
ERROR IN MICROWAVE MEASUREMENTS OF THE VELOCITY-FIELD CHARACTERISTIC OF n-TYPE GaAs DUE TO ENERGY RELAXATION EFFECTS
Authors: Glover G. H.
Published: February 2004

It is shown theoretically that the average drift velocity of electrons in GaAs as measured by microwave techniques differs substantially from the dc characteristic. This error, arising from electron-energy relaxation effects, has always been neglected in past measurements. The simple model predicts an error of 16% in measured velocity at 35 GHz
MECHANISM OF THRESHOLD SWITCHING
Authors: Pryor R. W. , Henisch H. K.
Published: February 2004

The paper describes pulse measurements on threshold switches based on thin layers (∼1μ) of multicomponent chalcogenide glasses. By means of voltage reversals prior to switching and monitoring of the corresponding switching delays, it has been demonstrated that switching in these systems is not essentially a thermal process. The switching delays depend on the polarity of applied preswitching bias voltages. The results provide further evidence for a space-charge mechanism, at any rate at low temperatures (e.g., −78°C to room temperature).
SPATIAL DEPENDENCE OF INTENSITIES IN THE SCHWARZ-HORA EXPERIMENT
Authors: Favro L. D. , Fradkin D. M. , Kuo P. K. , Rolnick William B.
Published: February 2004

The experimentally observed periodic behavior of the Schwarz-Hora radiation indirectly measures the relative phases in the electron's wave function. We show that previous calculations of the periodic behavior, which predict complete destructive interference where experimental maxima occur, are in error due to the one-dimensional character of the models used. A three-dimensional theory that predicts the correct phases is given. We also comment on the probable origin of the intensity's dependence on the polarization of the laser.
EXCITATION OF Hg+ 1942 Å IN THE HIGH-CURRENT—LOW-PRESSURE DISCHARGE
Authors: Johnson Peter D.
Published: February 2004

The intensity of the 1942-Å Hg+ ion resonance line in Hg-inert-gas discharges has been measured as a function of current density and Hg pressure in the range from 1 to about 15 A/cm2 and pressure from 10−3 to 0.5 Torr. In the Hg–Ar discharge the intensity of this line varies as the 1.75 power of the current density, while in Hg–Kr, the exponent is 2.0. There is evidence for volume recombination which is inhibited when Ar is replaced by Kr.
Local Stress Measurement in Thin Thermal SiO2 Films on Si Substrates
Authors: Lin S. C. H. , Pugacz-Muraszkiewicz I.
Published: February 2004

A novel method for local stress determination in SiO2 has been developed. The method consists in etching of SiO2 in a manner to create an oxide bridge and separating SiO2 from silicon in the bridge area. In this way, released oxide allows strain calculation and determination of compressive stress in the direction of the longitudinal axis of the bridge. Stress calculations limited to an area as small as 4×10−6 in. 2 have been obtained. The limiting factors to the accuracy of stress determination are the use of a bulk quartz modulus of elasticity, and the accuracy of the measurement of bridge deflection. The thinner the SiO2 film, the higher the accuracy of strain determination. Local stress as high as 1.78×1010 dyn/cm2 is detected in 272-Å-thick film. The compressive stress determined by this method indicates strong thickness dependence in the films below 1500 Å; the thinner the thermal oxide, the higher the average composition stress to its Si/SiO2 interface value. The method is particularly useful for the oxide films below 1000 Å. Evidence has been obtained that, in very thin thermal SiO2 films, crystal orientation of compressive stress does exist.
Ultrasonic Attenuation in Shouldered Specimens
Authors: Tripathi R. C. , Verma G. S.
Published: February 2004

The study of ultrasonic attenuation in polycrystalline materials at elevated temperatures is gaining much importance during recent years. Recently, Darbari, Singh, and Verma have devised a new method for such a study. This method is known as the ``shouldered-specimen pulse-echo technique''. However, in the theoretical derivation of the expression for the acoustic attenuation α for this experimental method, they have not considered the effects due to spreading of the acoustic beam in the shouldered specimen. In the present short article, the previous theory is modified so as to take into account the effects of this beam spread due to diffraction. The modified theory finds excellent agreement with the experimental results, is applicable for any diameter of the transducer, and gives the correct picture of the propagation of the acoustic pulses in a shouldered specimen.
Measurement of conductivity by induction
Authors: Callarotti R. C.
Published: February 2004

The exact solution to the problem of determining the conductivity of a metallic cylinder from the measurement of the decay of induced currents is compared to the approximate solution which considers the cylinder to be a single time-constant R-L network. We consider the general case where the sample partially fills the primary coil and where the primary coil has an arbitrary time constant. Over a wide range of values for the coupling coefficient and over a wide range of values for the ratio of the dominant time constant τ1 to the primary time constant τP′, we calculate the error involved in the approximate approach.
Nanosecond and picosecond laser-produced CD2 plasmas
Authors: Olsen J. N. , Jones E. D. , Gobeli G. W.
Published: February 2004

A preliminary comparison is made of plasmas created by irradiation of CD2 slab targets by single high-energy Nd3+ glass laser pulses of 3.5-nsec (35 J max) and 3–10-psec (10 J max) duration. For the nanosecond irradiations we find electron temperatures of 350–400 eV and appreciable C5+ ions at 20-keV expansion energy. Ion expansion energies for a picosecond pulse are about one-third those for a nanosecond irradiation of comparable energy. Up to 50% of the incident pulse energy may be accounted for in plasma expansion in either case. In each case, the specularly reflected energy back into the input f/5.0 lens is small: 0.4% and 0.8% for the nanosecond and picosecond times, respectively. Detailed ion analysis shows the target composition to be CD2−xHx, where 0.2<x<0.9 with traces of oxygen also observable.
Note on the experimental determination of photoconductive response characteristics of amorphous semiconductors
Authors: Scharnhorst P.
Published: February 2004

The problem of characterizing the time dependence of photoconductivity of amorphous semiconductors with the aid of the integrated response of a relatively slow photoconductive circuit is considered. Specific examples of bimolecular and monomolecular recombination are analyzed. The parameters governing the time dependence of photoconductivity are obtained from the integrated response to short, high-intensity pulsed excitation.
Temperature dependence of the yield and flow stresses of linear high-molecular-weight polyethylene
Authors: Pampillo C. A. , Davis L. A.
Published: February 2004

The yield stress and the flow stress at different strains have been measured as a function of temperature for a linear polyethylene of Mw=2.5×106 (AC1220). Two transitions are found for the flow stress (after the Lüders strain), at about 175 and 265°K, which divide the stress-temperature plot into three temperature regions. Only one transition (at ∼170°K) is found for the yield stress. By means of cyclic experiments both in strain rate and temperature along the stress-strain curve, the apparent activation enthalpy for plastic deformation is determined between 180 and 360°K. Previous measurements of the apparent pressure activation volume for deformation indicate that the 265°K transition (for strains greater than the Lüders strain) is shifted to 297°K by a pressure of ∼2.5 kbars. Thermally activated mechanisms for deformation are tentatively assigned to each of the three temperature regions.
Morphology of strain-induced crystallization of natural rubber. I. Electron microscopy on uncrosslinked thin film
Authors: Luch D. , Yeh G. S. Y.
Published: February 2004

Pt shadowing, Au decoration, OsO4 staining, electron diffraction, and bright- and dark-field electron microscopy have been used to elucidate strained and unstrained thin-film morphology of natural rubber. Unstrained natural rubber exhibits a 100–150-Å nodular morphology in the melt at room temperature. When cooled below room temperature, the original nodular morphology is replaced by an unoriented lamellar morphology. The crystal thickness of the lamellae is about 55 Å at −28°C. When stretched to elongations greater than about 200% the strain-crystallized films show a distinct fibrillar morphology at room temperature. The fibrils appear to be composed of individual crystallites, 120 Å in diameter. When cooled to −25°C, including those films which have been highly stretched (900%), the original fibrillar morphology is replaced by an oriented lamellar morphology. The transformation to lamellar morphology involves a lateral alignment of the room-temperature crystallites and a decrease in crystal thickness. Upon heating above −25°C, the lamellar crystals thicken and lamellar periodicity increases, but eventually the structure reverts to the fibrillar form as room temperature is approached, indicating the reversible nature of the morphological transformation.
Study of carbon-fiber surfaces using Auger and secondary electron emission spectroscopy
Authors: Willis R. F. , Fitton B. , Skinner D. K.
Published: February 2004

Structure at 3.0, 4.0, 7.5, 8.5, 10.0, 12.0, 14.5, and 17.5 eV in the secondary electron energy distribution of low-energy electrons back-scattered from carbon-fiber surfaces is shown to be similar to that observed from single-crystal graphite, which is due to emission from the high density of conduction-band states located 5 to 20 eV above the Fermi level. The intensity of secondary emission from these states is related to the degree of graphitic order in high- and low-modulus specimens of polyacrylonitrile (PAN-) and pitch-based carbon fibers. The results are discussed in terms of the effect of thermal treatment in high vacuum on the size and orientation relative to the fiber axis of regions of graphitic order in a surface layer of the order of 100 Å and a comparison is made with known models of carbon-fiber micromorphology. Auger electron spectroscopic analysis revealed the nature and degree of surface contamination on the different fiber types.
Effect of concentration-dependent diffusion coefficients on precipitate growth kinetics
Authors: Brown L. C.
Published: February 2004

A theoretical analysis is presented for the growth kinetics of a phase precipitated from supersaturated solid solution in a system with concentration-dependent diffusion coefficients. It is shown that at high supersaturations and for all precipitate shapes the graphs relating growth rate to supersaturation for constant diffusion coefficients can be used, provided the diffusion coefficient is taken as D̄, the weighted average coefficient. For low supersaturations, the same graphs can be used provided the diffusion coefficient is taken as D̄ for spherical precipitates and D̿ for planar precipitates, where D̿ is very close to the first moment of the diffusion coefficient about the interface composition. At other supersaturations the diffusion coefficient to be used lies intermediate between D̄ and D̿ for all precipitate shapes, the actual value depending on the shape of the D-vs-concentration curve. For cylindrical precipitates, the growth rate always lies exactly halfway between the growth rates for planar precipitates and spherical precipitates. The procedure outlined here should give growth rates accurate to within 1.5% of the difference between growth rates calculated for diffusion coefficients at the phase-boundary composition and well away from the phase boundary. For many purposes it is sufficient to use one diffusion coefficient covering all precipitate shapes and all supersaturations. This is best taken as D̄ and will give maximum errors of 6% for spherical precipitates and 15% for planar precipitates.
Evolution of pulses in parametric wave interactions utilized in the initial-value mode
Authors: Cassedy Edwards S. , Evans Charles R.
Published: February 2004

Traveling-wave parametric devices operating in the initial-value mode are modeled and analyzed. In the initial-value mode of operation, a signal pulse is injected into a nonlinear medium and allowed to propagate into the medium before the parametric pump is turned on. Examples of such operation have been based on magnetoelasticity and on photoelasticity with microwave sources and lasers, respectively, as the pump, and elastic wave pulses as the signal. Such devices are characterized here by a generic model of coupled transmission lines, with time-space periodic (parametric) coupling. Rigorous (Floquet-mode) solutions of the periodic model are utilized for initial values of small-signal perturbances having pulse envelopes. Unstable responses to the initial excitation are calculated and shown to be predicted on the basis of the technique of asymptotic response previously used in the theory of plasma instabilities. The Fourier-La Place representation is evaluated here using the (ω-first) order of integration best suited to the asymptotic response, in which the instability characteristics can be displayed directly in terms of saddle-point location and branch-point separation of the instability dispersion function in k space. Characteristics such as thresholds of convective and absolute instabilities are found in terms of pump amplitude and losses. Growth rates—temporal or spatial as appropriate—and instability (crest) velocities are found in terms of the transmission line parameters. Finally, as a practical matter, it is noted that these unstable ``natural responses'' of the pumped medium introduce a distortion of the initial pulse envelope which would be unwanted in applications for delay lines and echo memories.
Lattice spacings of very thin gold platelets
Authors: Smart D. C. , Boswell F. W. , Corbett J. M.
Published: February 2004

Using precision selected-area electron diffraction methods, the lattice spacings in the plane of the platelets has been determined for chemically grown gold platelets ranging in thickness from 80 to 400 Å. These parameters have been determined to ±0.03%. It has been found that in all cases the spacings are less than that of bulk gold. The discrepancy varied from 0.28 to 0.04% and was larger for thinner crystals. If the effect is due to surface stress then one would expect a straight-line plot of lattice parameter vs reciprocal thickness. In fact the results for the seven thicker platelets lie on the good straight line with an axial intercept within 0.01% of the value for bulk gold. The two thinner platelets have a greater parameter decrease than expected. From the straight-line plot the value for the surface stress of Au at room temperature was determined to be 1070±75 dyn/cm.