bluuebunny/crossref_metadata_2025 huggingface dataset:
Prospective multicentre study of acute renal failure in arterial surgical patients
Authors: Brooks M J , Naidoo M L , Wolfe J H N
Published: July 2002

Background

Acute renal failure following vascular surgery is associated with a high risk of death. The aims of this study were to identify the incidence and risk factors for acute renal failure in arterial surgical patients.

Methods

A prospective longitudinal clinical study of consecutive arterial surgical patients, including those undergoing interventional radiological procedures, in 13 UK vascular units was devised. Data were collected locally in each unit using a standard pro forma. Impaired renal function was defined as an admission creatinine level greater than 125 μmol l−1, while a 50 per cent rise in creatinine was defined as acute renal failure.

Results

Some 1566 patients were enrolled by the 13 units in a 6-month interval (January to June 1999); 124 (7·9 per cent) developed postoperative renal failure. The incidence of renal failure varied according to operation type: abdominal aortic aneurysm 17·6 per cent, thoracoabdominal aneurysm 45·4 per cent, carotid endarterectomy 0·8 per cent, aortobifemoral bypass 10·9 per cent, infrainguinal bypass 5·2 per cent, extra-anatomic bypass 5·2 per cent, embolectomy 14·0 per cent, endovascular procedure 5·0 per cent, radiological procedure 4·2 per cent and amputation 4·5 per cent. The in-hospital mortality rate for all patients was 7·2 per cent, which increased to 37·1 per cent in patients who developed acute renal failure. Significant risk factors for the development of renal failure were thoracoabdominal aneurysm repair (45·4 per cent), emergency surgery (19·4 per cent), surgery on the abdominal aorta (17·6 per cent), pre-existing renal impairment (19·4 per cent) and hypertension (8·3 per cent). Diabetes mellitus, hyperlipidaemia, recent angiography, non-steroidal analgesics, metformin or angiotensin converting enzyme inhibitors were not predictive of the development of renal failure. In 21·8 per cent of patients renal failure developed in association with multiple organ failure. No patient who survived developed end-stage renal failure.

Conclusion

The incidence of acute renal failure following arterial surgery was 7·9 per cent associated, as expected, with a significant mortality rate (37·1 per cent). Emergency aortic surgery carried the highest risk. Patients developing acute renal failure required intensive management, including renal support, but no patient survived to develop end-stage renal failure.
Endoluminal repair of abdominal aortic aneurysm causes more perioperative renal dysfunction than open repair
Authors: Jenkins M P , Onwudike M , Singh R , Bomanji J , Adiseshiah M
Published: July 2002

Background

In this prospective case–control study the aim was to compare perioperative renal function in well matched patients undergoing open repair (OR) (group 1) or endoluminal repair (ER) (group 2) of an abdominal aortic aneurysm (AAA) and preoperative renal function in other patients undergoing ER (group 3) with function 1–3 years after surgery.

Methods

Of 73 patients undergoing AAA repair, 45 were recruited to the study as follows: 14 patients (median age 77 years, 12 men) to group 1, 14 patients (median age 76 years, 11 men) to group 2 and 17 patients (median age 76 years, 14 men) to group 3. Serum creatinine, creatinine clearance and/or glomerular filtration rate (GFR) were measured coupled with 99mTc-radiolabelled mercaptoacetyltriglycine (MAG3) renal studies. From the MAG3 renal scans, perfusion, split renal function, mean parenchymal transit time (MPTTI) and outflow pattern were assessed. Groups 1 and 2 underwent scintigraphic evaluation before, and 8 days after operation. Group 3 was assessed before operation and 1–3 years later.

Results

Fifteen of 31 patients undergoing ER had preoperative renal dysfunction (GFR less than 50 ml min−1) compared with two of 14 who had OR. Ten patients from groups 2 and 3 developed severe renal dysfunction. Of these, two died, one required haemodialysis (graft deployed over the renals), two were dialysis-free but developed worsening renal function and five regained their previous renal function. In four patients who had ER, differential function improved, in one with retroperitoneal fibrosis it deteriorated and in nine it was unchanged. See Table below.

Conclusion

ER is associated with a greater degree of perioperative renal dysfunction than OR. In the absence of technical problems with endograft deployment, renal function in ER in the long term is not adversely affected.
Soft tissue sarcoma involving the sciatic nerve
Authors: Brennan M F
Published: July 2002

In the Clinical Dilemma slot the editors pose a question to an acknowledged expert in the field. In this issue we address the problem of a sarcoma in the posterior aspect of the thigh. At operation, despite preoperative magnetic resonance imaging, the lesion is unexpectedly found to involve the sciatic nerve. How should one proceed? Professor Murray Brennan of New York replies.
Effect of surgical subspecialization on breast cancer outcome
Authors: Golledge J , Wiggins J E , Callam M J
Published: July 2002

Background

There is increasing pressure for specialization of medical services. The effect of surgical specialization on the outcome of breast cancer in Bedford has been assessed.

Methods

The Bedford Breast Cancer Registry, which contains prospective diagnostic, treatment and follow-up data on all breast cancers treated in North Bedfordshire, was analysed to compare breast cancer outcome between 1990–1992 and 1993–1996, that is before and after the advent of surgical subspecialization. All 784 patients were analysed, including patients with metastases (4 per cent) and those treated by tamoxifen alone (8 per cent). Outcome was compared in terms of disease-free survival (DFS), locoregional and all (locoregional and metastases) recurrence rates assessed by Cox proportional hazard and Kaplan–Meier analyses.

Results

Overall DFS was 75 per cent and the locoregional recurrence rate was 8 per cent at 3 years. The tumour stage and grade at presentation and the proportion of screen-detected cancers were similar for both intervals. The outcome for patients before specialization (1990–1992; n = 329) was worse: hazard ratio (HR) for DFS 1·5 (95 per cent confidence interval 1·2–2·0) and HR for locoregional recurrence 2·0 (1·2–3·5). After subspecialization (1993–1996, n = 455) DFS improved from 70 to 79 per cent (P = 0·009) and the all recurrence rate fell from 22 to 12 per cent (P = 0·0004) at 3 years. The improvement in outcome was mainly in younger patients (aged less than 70 years), in whom DFS improved from 72 to 81 per cent (P = 0·02) and the all recurrence rate fell from 24 to 12 per cent (P = 0·001) at 3 years. The improvement was associated with increased axillary surgery (47 to 74 per cent; P < 0·0001), and more frequent use of tamoxifen (74 to 84 per cent; P = 0·004) and chemotherapy (10 to 27 per cent; P < 0·0001) in this age group.

Conclusion

There was a significant improvement in outcome for patients with breast cancer after surgical subspecialization in Bedford. This may relate to the more frequent use of appropriate systemic therapy.
Effects of varying central command and muscle mass on the cardiovascular responses to isometric exercise
Authors: Franke W. D. , Boettger C. F. , McLean S. P.
Published: July 2002

To determine if the central command signal associated with isometric exercise is mass‐dependent, 20 subjects (nine male, 11 female; 23 ± 1 years) performed four 5‐min bouts of supine isometric exercise with a large (quadriceps; LEG) and small (forearm; ARM) muscle mass. For each extremity, one bout entailed maintaining a constant force (CF; 20% maximal voluntary contraction) and the other constant electromyographic activity (CE; ~20% MVC initially). Central command was assumed to increase with CF and remain unchanged with CE. Heart rate increased more with LEG than ARM (P<0·001) and, in LEG, was higher in CF than CE at min 5 (P<0·001). Mean arterial pressure was higher in LEG (P<0·001) by min 2 and 10 ± 3 mmHg higher in LEG CF than LEG CE by min 5 (P<0·001). Ratings of perceived exertion were highest in LEG CF (P<0·001); LEG CE did not differ from ARM CE (P<0·001) by min 4. The ARM responses did not differ between CF and CE in any variable. These data suggest that muscle mass influences the central command signal during isometric exercise and central command modulates this response in larger muscle masses.
WPA Congress, Hamburg 1999
Authors: Fitgerald Paul , Tapsell Rees
Published: July 2002

The World Psychiatric Association (WPA) holds an international congress every three years in a country of one member association. This year we were invited to attend, as Fellows, the XIth Congress in Hamburg and this article will document some of our experiences.
The care of students with insulin‐treated diabetes mellitus living in university accommodation: scope for improvement?
Authors: Strachan M. W. J. , MacCuish A. C. , Frier B. M.
Published: July 2002

Concern has been expressed about the welfare of young adults with Type 1 diabetes mellitus who leave home to attend university or college for tertiary education. This has been highlighted by the local experience in Edinburgh of two male students with Type 1 diabetes, both of whom died from metabolic complications of diabetes during their first term at universities distant from their homes. One student died following the development of cerebral oedema secondary to diabetic ketoacidosis, which was probably precipitated by prolonged coma after an episode of severe hypoglycaemia. Another student, who was found ‘dead in bed’, had a history of previous severe hypoglycaemia. At a Fatal Accident Inquiry in Edinburgh, held following the death of the first student, recommendations were made to improve the care and personal safety of students with diabetes living in university accommodation. Despite the report being circulated to all Scottish universities, the second student died within three years of the inquiry. Further efforts to protect the welfare of students with Type 1 diabetes who are attending centres for tertiary education away from their home environment may require the more active participation by diabetes healthcare professionals.
A new approach to vision screening in schools
Authors: Thomson W. David , Evans Bruce
Published: July 2002

Purpose: To determine the prevalence of visual “defects” among a sample of young schoolchildren and evaluate a new system for vision screening in schools.

Methods: A new system for vision screening in schools has been developed. The system is based on a computer program which may be run on a low specification personal computer. Information about the child’s symptoms, history and family history is acquired by means of a parental questionnaire and entered into the program prior to the vision screening. Distance visual acuity and stereopsis are measured directly on the computer screen and colour vision is assessed using a reduced Ishihara test. The program carries out an “expert” analysis of the questionnaire data and the vision test results and determines the most likely diagnosis. Reports for parents, teachers, optometrists, doctors can be generated automatically and statistics relating to the overall screening program are available. An evaluation of a prototype version of the system was carried out on 245 schoolchildren aged between 5 and 8 years.

Results: Overall, 48 children failed the screening (excluding colour vision deficiencies), 32 of whom were unaware of any problem with their eyes. Comparison of the result of the vision screening with the outcome of a full eye examination gave a sensitivity of 93.8% and a specificity of 96.1%.

Conclusion: A significant number of young school children have unsuspected remediable visual defects. The computer‐based vision screener provides an efficient, sensitive and specific method for screening in schools.
Pregnancy with an ICD and a documented ICD discharge
Authors: Bonini W. , Botto G.L. , Broffoni T. , Dondina C.
Published: July 2002

We report a successful pregnancy in a patient affected by idiopathic ventricular fibrillation 3 years after insertion of an ICD, with a documented defibrillator discharge.
Infrafamilial Phylogeny of the Aquatic Angiosperm Podostemaceae Inferred from the Nucleotide Sequences of the matK Gene
Authors: Kita Y. , Kato M.
Published: July 2002

Abstract: The infrafamilial relationships of Podostemaceae were deduced from nucleotide sequences of the chloroplast matK gene. The matK phylogenetic analyses show that Podostemaceae are composed of two major clades that correspond to the subfamily Tristichoideae sensu stricto and Weddellina and the subfamily Podostemoideae. Weddellina, which has long been recognized as a member of the Tristichoideae, is sister to the Podostemoideae, supporting the classification that recognized a third subfamily Weddellinoideae. Malaccotristicha malayana and Terniopsis sessilis form a basal clade in Tristichoideae sensu stricto. Tristichoideae show a high morphological diversity and, surprisingly, a close relationship exists between Dalzellia zeylanica and Indotristicha ramosissima, which remarkably differ in their body plans. A few genera defined by particular characters, such as Synstylis and Torrenticola, merge into clades of other larger genera. The Podostemoideae taxa studied are composed of two American clades, an Asian‐Australian clade and a Madagascan clade, and may suggest that the subfamily perhaps originated in America and migrated to the Old World.
Inductive conductance measurements in two-dimensional superconducting systems
Authors: Jeanneret B. , Gavilano J. L. , Racine G. A. , Leemann Ch. , Martinoli P.
Published: July 2002

A two-coil mutual-inductance technique for measuring the complex ac response of a two-dimensional (2-D) superconductor to a weak ac magnetic field is described. Analytical and numerical methods are presented which allow extraction of the complex ac conductance of the superconductor from the signal voltage induced in the detection coil by the screening currents flowing in the sample. The method is illustrated by measurements of the ac conductance of a square network of aluminum wires from which the penetration depths of both the network and (granular) aluminum are deduced. It is shown that the method provides a powerful tool to observe characteristic features associated with critical phenomena in 2-D superconducting systems.
Fractoemission during crack propagation in glass
Authors: Gonzalez A. C. , Pantano C. G.
Published: July 2002

The phenomenon termed fractoemission was monitored in soda-lime-silica glass specimens during slow crack growth. No electron, ion, or photon signals were detected until crack velocities reached approximately 10−2 m/s. These observations suggest that the more intense fractoemissions observed during fast fracture are due to dissipation of the excess energy associated with unstable crack growth, but more significantly that fractoemissions are not fundamental to crack propagation in glass.
a-axis oriented epitaxial YBa2Cu3O7−x-PrBa2Cu3O7−y heterostructures
Authors: Inam A. , Rogers C. T. , Ramesh R. , Remschnig K. , Farrow L. , Hart D. , Venkatesan T. , Wilkens B.
Published: July 2002

We have grown YBa2Cu3O7−x-PrBa2Cu3O7−y heterostructures with the perovskite a axis normal to the surface of a variety of (001) oriented substrates using the pulsed laser deposition technique. X-ray diffraction studies indicate little or no formation of the traditional c-axis normal orientation usually nucleated on these substrates, while ion channeling, transmission electron microscopy (TEM), and Raman scattering studies reveal a highly ordered crystalline structure similar in quality to that obtained in the best c-axis oriented films. Superconducting transition temperatures, for current transport in the plane of the films, consistently exceed 80 K, but are probably lower than the optimum 92 K transition expected for YBa2Cu3O7−x due to the presence of growth twin boundaries between grains with the c axis oriented along the two substrate directions.
Phase-shifting electron holography by beam tilting
Authors: Ru Q. , Endo J. , Tanji T. , Tonomura A.
Published: July 2002

A phase-shifting method to directly measure the amplitude and phase distribution of specimen in an electron holographic microscope without the introduction of large number of carrier fringes is proposed. The initial phase of electron holograms is shifted by tilting the incident electron beam with a digital voltage/current supply. Several holograms of a specimen with properly different phase shifts are recorded digitally and used to calculate the amplitude and phase distributions of the specimen. Experimental result of observing the phase distribution of a cubic MgO crystal is shown.
Ultrafast reversible phase change in GeSb films for erasable optical storage
Authors: Afonso C. N. , Solis J. , Catalina F. , Kalpouzos C.
Published: July 2002

Amorphous-to-crystalline and crystalline-to-amorphous transformations are triggered in GeSb thin films by irradiation with femtosecond and picosecond laser pulses. Phase changes are accompanied with optical contrast and therefore the feasibility of phase-change optical recording at ultrafast rates is demonstrated for the first time. The phase reversal by ultrashort pulses seems to be related to the dependence of the degree of undercooling prior to solidification on the irradiation energy density.
Analysis of field emission from three-dimensional structures
Authors: Kirkpatrick D. A. , Mankofsky A. , Tsang K. T.
Published: July 2002

An analysis of the field emission from emitter tips with the geometry of a prolate ellipsoid of revolution indicates that the field enhancement factor, β, and effective emission area, α, are not constant but instead depend on the applied field. The added complexity of a materials related limit on the minimum time for transition of an electron from the solid into the vacuum is also examined in the analysis. The calculated variations of α and β are as large as 35%, and in some instances could result in erroneous interpretation of measured current-voltage (I-V) characteristic data.
Localized fabrication of Si nanostructures by focused ion beam implantation
Authors: Steckl A. J. , Mogul H. C. , Mogren S.
Published: July 2002

Si nanostructures have been fabricated by focused ion beam implantation (FIB) followed by etching in KOH/IPA. The FIB implantation into Si at a sufficiently high dose (≥1015/cm2) renders the local Si region much less susceptible to chemical etching. This effect has been observed for FIB implantation with Ga, Au, and Si ions. After etching, the implanted layer forms a cantilever structure whose thickness is a function of the implantation energy. At low energies (<30 keV) nanometer-scale Si structures can be formed using this technique.
Optically induced and erased birefringence and dichroism in azoaromatic polymers
Authors: Rochon P. , Gosselin J. , Natansohn A. , Xie S.
Published: July 2002

Dichroism and birefringence are shown to be optically induced and erased in high-glass-transition azoaromatic polymers. The resulting polarization information is easily detected and exhibits long-term stability. This optically induced reorientation of the azoaromatic molecules will have wide applications in image recording and in electro-optical devices.
Formation of hexafluorosilicate on Si surface treated in NH4F investigated by photoemission and surface infrared spectroscopy
Authors: Niwano Michio , Kurita Kazunari , Takeda Yuki , Miyamoto Nobuo
Published: July 2002

The chemical nature of Si surfaces treated with ammonium fluoride (NH4F) has been investigated using photoemission and surface infrared spectroscopy. On the surface after treatment in NH4F solution, there remain ammonium compounds such as NH4F and NH4F.HF. Photoemission data demonstrate that under the atmospheric environment, the ammonium compounds remaining on the NH4F-treated Si surface react with the Si substrate to generate the hexafluorosilicate salt, (NH4)2SiF6. We propose that the formation of (NH4)2SiF6 or SiF62− ions is the dominant reaction pathway in the NH4F etching of Si crystals.
Spatially resolved electrical measurements of SiO2 gate oxides using atomic force microscopy
Authors: Murrell M. P. , Welland M. E. , O’Shea S. J. , Wong T. M. H. , Barnes J. R. , McKinnon A. W. , Heyns M. , Verhaverbeke S.
Published: July 2002

Using a modified atomic force microscope (AFM) with a conducting cantilever, we have investigated the dielectric strength of SiO2 gate oxide films. This has been achieved by spatially resolving the prebreakdown tunneling current flowing between the silicon substrate and tip. During AFM imaging a voltage ramp was applied to the tip at each image point so as to determine the local threshold voltage required to generate a small tunneling current in the oxide, without causing an irreversible electrical breakdown. For an oxide 12-nm thick this voltage was found to vary by more than a factor of 2.7 over an area of 0.14 μm2, with a maximum value of 40.5 V. This suggests that the breakdown strength of conventional metal-oxide-silicon capacitors may not be limited by the intrinsic dielectric strength of the oxide, but by imperfections or nonuniformities in the Si/SiO2 structure. By preventing irreversible oxide breakdown during scanning, we can image the dielectric properties of oxide films with a lateral resolution better than 20 nm.
Self-assembled monolayer electron beam resist on GaAs
Authors: Tiberio R. C. , Craighead H. G. , Lercel M. , Lau T. , Sheen C. W. , Allara D. L.
Published: July 2002

We present results on electron beam exposure of a self-assembled monolayer film as a self-developing positive resist on GaAs. A 1.5 nm thick monolayer of n-octadecanethiol (C18H37SH) deposited on a GaAs (100) substrate showed a electron beam sensitivity of about 100 μC/cm2. The monolayer resist was used as a mask for chemical etching of the GaAs. Patterns in GaAs have been created with widths approximately equal to the exposing electron beam width of 50 nm.
Strained quaternary quantum well lasers for high temperature operation
Authors: Temkin H. , Coblentz D. , Logan R. A. , Vandenberg J. M. , Yadvish R. D. , Sergent A. M.
Published: July 2002

We describe compressively strained separate confinement heterostructure 1.3 μm quantum well lasers optimized for high temperature operation. The active layer consists of ten GaInAsP wells, each 40–80 Å thick, grown under compressive lattice mismatch strain of Δa/a≤0.75%. Within the constraints of the well composition and thickness imposed on the active region, strain is necessary for efficient laser operation. Best results are obtained for Δa/a∼0.2%–0.3% with the laser threshold as low as 5 mA and slope efficiency of 42 mW/mA. In the temperature range of 25–85 °C a slope efficiency change as small as 30% was achieved. Power output of at least 20 mW can be maintained up to 100 °C at a current drive below 150 mA.
Etching yields of SiO2 by low energy CFx+ and F+ ions
Authors: Shibano Teruo , Fujiwara Nobuo , Hirayama Makoto , Nagata Hitoshi , Demizu Kiyoshi
Published: July 2002

Etching yields of SiO2 by mass-separated F+, CF+, CF2+, CF3+, and Ar+ ions have been measured at low ion energies ranging from 80 to 350 eV. CF3+ and CF2+ ions have higher etching yields than CF+ and F+ ions. At low ion energies, SiO2 cannot be etched and some film deposition is observed on the SiO2 surface. For example, in the case of CF+ ions, SiO2 can be etched at ion energies above 200 eV. This film deposition is caused by reactions of CFx+ ions at the SiO2 surface, and neutrals coming from the ion source also have some effect on this deposition.
Dual-function semiconducting polymer devices: Light-emitting and photodetecting diodes
Authors: Yu G. , Zhang C. , Heeger A. J.
Published: July 2002

Thin film devices made with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], MEH-PPV, are known to be efficient light-emitting diodes. The same devices, under reverse bias, exhibit excellent sensitivity as photodiodes. Thus the polymer tunnel diode is a dual-function device. For the Ca/MEH-PPV/ITO (indium/tin oxide) layered structure, the external quantum efficiency for electroluminescence is ≊1% photons/electron (forward bias ≳2.5 V). The same device is sensitive as a photodiode: The dc sensitivity (−10 V, reverse bias) is 9×10−2 A/W (at ∼1-μW/cm2 input) corresponding to a quantum yield of more than 20% electrons/photon.
Highly uniform InGaAs/GaAs quantum dots (∼15 nm) by metalorganic chemical vapor deposition
Authors: Oshinowo J. , Nishioka M. , Ishida S. , Arakawa Y.
Published: July 2002

We report the direct deposition of strained InGaAs-dot structures with a diameter of about 15 nm on GaAs surfaces by metalorganic chemical vapor deposition growth. High resolution scanning electron micrographs show highly uniform quantum-sized dots formed by the Stranski–Krastanow growth mode. The sharp photoluminescence emission band of buried dot structures indicates efficient carrier capture and a homogeneous heterointerface. The average dot size and area dot density can be controlled accurately by growth temperature, and InGaAs deposition thickness, respectively.
Growth modes of Ge on GaAs(001)
Authors: Falta J. , Reuter M. C. , Tromp R. M.
Published: July 2002

We have used low-energy electron microscopy to investigate the growth of Ge on GaAs(001)-c(2×8). Depending on the growth temperature we find a wide variety of growth modes: At 420 °C growth proceeds layer by layer, with nucleation of two-dimensional (2D) islands smaller than 150 Å across. An increase of growth temperature to 450–480 °C enhances surface diffusion and results in formation of large anisotropic 2D islands on wide terraces along with denuded zones—and step flow—along the step edges. Further temperature increase transforms the growth mode to step flow. At 540 °C the growth mode becomes unstable, resulting in a roughening of the Ge surface.
Open air photoresist ashing by a cold plasma torch: Catalytic effect of cathode material
Authors: Inomata Kiyoto , Koinuma Hideomi , Oikawa Yoshiyuki , Shiraishi Tadashi
Published: July 2002

A beam plasma was generated and exhausted into air by applying rf voltage to the atmospheric pressure argon flowing through a cylindrical gap between a needle cathode and a grounded cylindrical anode whose surface was covered with an insulator. This torch-type plasma with gas and electron temperatures of 240 °C (44.2 meV) and 1.0 eV, respectively, has been verified to be useful for ashing a photoresist without using a pumping system. High rate (≥1.2 μm/min) photoresist ashing was achieved by using Ar plasma containing a small amount of oxygen. Also reported are optical emission analysis of plasma and analyses of ashed Si surface by scanning electron microscopy. Fourier transform infrared spectroscopy, electron microprobe analysis, and x-ray photoelectron spectroscopy. The use of the Pt cathode was found to provide not only a better ashed surface but also a higher ashing rate than the use of the stainless-steel cathode.
Photoelastic modulator for the mid-IR range down to 33 μm with inexpensive and simple control electronics
Authors: Hoffmann Günter Georg , Schrader Bernhard , Snatzke Günther
Published: July 2002

The construction of a photoelastic modulator is described which is intended to push the long wavelength limit of infrared circular dichroism measurements down to about 300 cm−1 (33 μm). A simple electronic circuit has been designed to drive the device. The performance of the modulator is evaluated by transmission and calibration spectra.
Superposed pulse echo overlap method for ultrasonic sound velocity measurement
Authors: Negita Keishi , Takao Hiroshi
Published: July 2002

A superposed pulse echo overlap method is described as a method to determine ultrasonic sound velocity. This method has the advantages both of the pulse echo superposition and the pulse echo overlap methods; round-trip time of echoes through the specimen was determined by overlapping the superposed echoes on the oscilloscope. Accurate and quick measurements of sound velocity in solids and liquids become possible by this method.
Flux amplification using stochastic superconducting quantum interference devices
Authors: Rouse R. , Han Siyuan , Lukens J. E.
Published: July 2002

The flux change δ Φ through a bistable superconducting quantum interference device has been measured in the presence of thermally induced switching (with rate Γ) versus δ Φx, the change in the applied flux. For small δ Φx, δ Φ is proportional to δ Φx with a measured flux gain g, depending on the temperature, barrier height, and frequency Ω, with a maximum of about 16. In agreement with theories of periodically driven stochastic bistable systems, g(Ω) is nearly frequency independent up to Γ and is proportional to Ω−1 for Ω≫Γ. For larger amplitude signals, harmonic generation has been measured in the adiabatic limit (Ω≪Γ) and found to be in good agreement with theory. Possible applications of this system for flux measurement are discussed.
Development of multicolor pyrometers to monitor the transient response of burning carbonaceous particles
Authors: Levendis Yiannis A. , Estrada Kelvin Rafael , Hottel Hoyt C.
Published: July 2002

A three-color ratio pyrometer has been developed to obtain surface temperatures and high-temperature combustion rates of burning carbonaceous particles. The features and performance of this instrument are contrasted to those of a two-color ratio pyrometer, constructed earlier for similar studies. The three-color pyrometer employs a visible (0.65 μm) and two near-infrared (0.80 and 0.975 μm) wavelengths. The instrument uses a single optical fiber to capture radiation emitted from a particle burning in a high-temperature laminar flow furnace. Monitoring of the combustion events takes place coaxially with the particle flow, from observation windows located at the top of the furnace injectors. Thus, the temperature-time history of burning particles can be recorded. The radiation flux is split into three beams using dichroic edge filters. Narrow (or medium) bandwidth interference filters guide monochromatic radiation to solid-state silicon photodetectors. The associated amplification is linear and/or logarithmic. In contrast, the two-color pyrometer used a bifurcated optical fiber bundle to split radiation to two medium bandwidth interference filters centered at 0.80 and 1.0 μm. Silicon detectors were employed, associated with linear amplification. Both instruments were used to monitor the combustion temperature-time behavior of burning highly homogeneous, spherical, and monodisperse carbonaceous particles, and their performance is discussed herein.
A new diamond anvil cell for hydrothermal studies to 2.5 GPa and from −190 to 1200 °C
Authors: Bassett W. A. , Shen A. H. , Bucknum M. , Chou I-Ming
Published: July 2002

A new style of diamond anvil cell (DAC) has been designed and built for conducting research in fluids at pressures to 2.5 GPa and temperatures from −190 to 1200 °C. The new DAC has been used for optical microscope observations and synchrotron x-ray diffraction studies. Fringes produced by interference of laser light reflected from top and bottom anvil faces and from top and bottom sample faces provide a very sensitive means of monitoring the volume of sample chamber and for observing volume and refractive index changes in samples that have resulted from transitions and reactions. X-ray diffraction patterns of samples under hydrothermal conditions have been made by the energy dispersive method using synchrotron radiation. The new DAC has individual heaters and individual thermocouples for the upper and lower anvils that can be controlled and can maintain temperatures with an accuracy of ±0.5 °C. Low temperatures are achieved by introducing liquid nitrogen directly into the DAC. The equation of state of H2O and the α-β quartz transition are used to determine pressure with an accuracy of ±1% in the aqueous samples. The new DAC has been used to redetermine five isochores of H2O as well as the dehydration curves of brucite, Mg(OH)2, and muscovite, KAl2(Si3Al)O10(OH)2.
Synchrotron x-ray fluorescence microprobe: Quantification and mapping of mixed valence state samples using micro-XANES
Authors: Sutton S. R. , Bajt S. , Delaney J. , Schulze D. , Tokunaga T.
Published: July 2002

The synchrotron x-ray fluorescence microprobe is a valuable instrument for quantification and mapping of mixed valence state samples with high spatial resolution and elemental sensitivity. A method has been developed for quantifying the proportions of Fe2+ and Fe3+ with 100 μm spatial resolution and better than 100 ppm sensitivity using x-ray absorption near-edge structure (XANES). Applications of valence state mapping have been made to selenium in water-saturated sediments and manganese associated with wheat roots attacked by the take-all fungus.
Advances in reflectometric density profile measurements on the DIII-D tokamaka)
Authors: Kim K. W. , Doyle E. J. , Peebles W. A. , Ejiri A. , Luhmann N. C. , Rettig C. L.
Published: July 2002

Significant improvements have been achieved in the accuracy and reliability of broadband frequency-swept (FM) reflectometer measurements on DIII-D. This has been achieved through several improvements, the most important of which has been the application of digital complex demodulation (CDM) analysis software, which can extract signal phase with subfringe accuracy. Using this new analysis technique, results from the broadband FM system look very promising: reflectometer measurements show excellent agreement with Thomson profiles in Ohmic and H-mode plasmas, and good agreement with Thomson data in L-mode. Clear resolution of the steep edge density profile in H-mode plasmas, where very small phase shifts are involved, confirm the accuracy of the system calibration and performance.
TFTR 60 GHz alpha particle collective Thomson scattering diagnostic
Authors: Machuzak John S. , Woskov Paul P. , Gilmore James , Bretz Norton L. , Park Hyeon K. , Aamodt Richard E. , Cheung Peter Y. , Russell David A. , Bindslev Henrik
Published: July 2002

A 60 GHz gyrotron collective Thomson scattering alpha particle diagnostic has been implemented for the D-T period on the Tokamak Fusion Test Reactor (TFTR). Gyrotron power of 0.1–1 kW in pulses of up to 1 s can be launched in X mode. Efficient corrugated waveguides are used with antennas and vacuum windows of the TFTR Microwave Scattering system. A multichannel synchronous detector receiver system and spectrum analyzer acquire the scattered signals. A 200 megasample/s digitizer and spectrum analyzer are used to resolve fine structure in the frequency spectrum. By scattering nearly perpendicular to the magnetic field, this experiment will take advantage of an enhancement of the scattered signal which results from the interaction of energetic ions with plasma resonances in the lower hybrid frequency range. Significant enhancements are expected with D-T fusion alpha particles, which should be detectable with gyrotron power of less than 1 kW, while maintaining an acceptable signal-to-noise ratio. This diagnostic will be the first experimental test of recent collective Thomson scattering models and should also provide an indication of the presence of energetic alpha particles in the core of TFTR.
A simple method for preparing calibration standards for the three working axes of scanning probe microscope piezo scanners
Authors: Alliata Dario , Cecconi Ciro , Nicolini Claudio
Published: July 2002

A method for preparing samples suitable for calibrating scanning probe microscopes (SPM) and for eliminating any distortions in images is described. Samples consist of polystyrene particles organized in monolayers and bilayers with hexagonal-ordered domains. The monolayer is not uniform, but is characterized by areas without particles. These discontinuities allow the measurement of the thickness of the monolayer in order to calibrate the z axes, while the lattice constant of the domains can be used as a calibration standard for the x and y axes. The nondeformability of the particles after the deposition on the substrate has been studied by an optical microscope, equipped for interferometric measurements, scanning force microscopy, and scanning tunneling microscopy. The use of these standards directly as substrates for samples is proposed to correct the distortions in the SPM images.
Ultrafast absorption in free-standing porous silicon films
Authors: Owrutsky J. C. , Rice J. K. , Guha S. , Steiner P. , Lang W.
Published: July 2002

Ultrafast absorption studies on free-standing porous silicon films have been carried out at room temperature to investigate the carrier dynamics and the luminescence mechanism. Ultraviolet and visible excitations were used on an as-prepared sample and two annealed samples. Transient absorption curves of UV pumped, as-prepared samples contain a fast decay (τf) of 0.8±0.2 ps and a slower decay of ≳30 ps. τf is found to be shorter for both the 500 °C annealed sample with UV excitation and for the as-prepared sample with visible excitation. The faster decay rates suggest that the subpicosecond component of the transient absorption may be due to carrier thermalization rather than core-to-surface state excitation transfer.
Fast scanning probe for tokamak plasmas
Authors: Boedo J. , Gray D. , Chousal L. , Conn R. , Hiller B. , Finken K. H.
Published: July 2002

We describe a fast reciprocating probe drive, which has three main new features: (1) a detachable and modular probe head for easy maintenance, (2) a combination of high heat flux capability, high bandwidth, and low-Z materials construction, and (3) low weight, compact, inexpensive construction. The probe is mounted in a fast pneumatic drive in order to reach plasma regions of interest and remain inserted long enough to obtain good statistics while minimizing the heat flux to the tips and head. The drive is pneumatic and has been designed to be compact and reliable to comply with space and maintenance requirements of tokamaks. The probe described here has five tips which obtain a full spectrum of plasma parameters: electron temperature profile Te(r), electron density profile ne(r), floating potential profile Vf(r), poloidal electric field profile Eθ(r), saturation current profile Isat(r), and their fluctuations up to 3 MHz. We describe the probe show radial profiles of various parameters. We compare the density and temperature data to that obtained with a helium beam. We also discuss the techniques to process the data optimally, particularly double probe data and profile fits.
Streamer discharge reactor for water treatment by pulsed power
Authors: Lisitsyn Igor V. , Nomiyama Hiroaki , Katsuki Sunao , Akiyama Hidenori
Published: July 2002

The streamer discharges are effectively used for biological and chemical cleaning of air and water. Uniform streamer discharges were obtained in water at pulsed electric loading. The volume of these discharges exceeds 400 cm3 and the energy delivered to the discharge reached 40–400 J depending on the applied voltage. The reliable and durable reactor for water treatment by pulsed streamer discharges is designed and tested. High voltage pulse amplitude applied to the reactor requires improved electric insulation to prevent flashover along the reactor surface both in water and air. High mechanical stress due to high discharge current adds the requirements to the mechanical durability of the system. A small-size reactor with the volume of approximately 1 ℓ withstands successfully both high electrical and mechanical stresses. The reactor is designed for research purposes, however it can be upgraded to use in a high repetition-rate regime necessary for industrial applications.
Surface magneto-optic Kerr effect
Authors: Qiu Z. Q. , Bader S. D.
Published: July 2002

The surface magneto-optic Kerr effect (SMOKE) has significantly impacted research on magnetic thin films. This is due to its sensitivity, local probing nature, and experimental simplicity. The polar and longitudinal Kerr effects are characterized by a complex rotation of the plane of polarization of linearly polarized incident light upon reflection from the surface of a ferromagnetic material. The rotation is directly related to the magnetization of the material within the probing region of the light. Light penetrates into metals >20 nm deep, but the SMOKE technique derives its surface sensitivity from the limited thickness of the deposited magnetic film, which can be as thin as one atomic layer. Basic principles, experimental arrangements, and applications of SMOKE are reviewed in order to acquaint the nonspecialist with the technique and place it into perspective.
Cancellation technique of external noise inside a magnetically shielded room used for biomagnetic measurements
Authors: Kandori Akihiko , Miyashita Tsuyoshi , Tsukada Keiji
Published: July 2002

First-order gradiometers inside a magnetically shielded room (MSR) were used to cancel magnetic-field noise. However, the magnetic field inside a MSR is distorted when the amount of external noise is large. This distortion is caused by the low-pass filter property of the MSR. Therefore, the time constants of the frequency-dependent attenuation of the MSR vary spatially and this variation must be taken into account. To investigate noise cancellation, we used a multichannel superconducting quantum interference device consisting of four gradiometers measuring a source signal and two gradiometers as a reference. To compensate for the different magnitudes of the gradiometer wave forms, which differed because of slight differences in their pickup-coil cancel rates, we calculated a fitting parameter. The noise-cancellation method consisted of two processes: reduction of ambient noise caused by the differences in the cancel rate of the gradiometers and a gradient magnetic field inside the MSR, and cancellation of wave-form distortion caused by the spatial variation of the time constants inside the MSR. This cancellation method provides additional attenuation of over 20–30 dB in addition to the balance (>46 dB) of a first-order gradiometer. However, the remaining noise, especially a spike (<2 pT) at the beginning of a large ambient noise step, could not be completely canceled. This noise was caused by the slight difference between the time constants at the reference sensor position and at the signal sensor position. Except for this noise spike, however, the noise cancellation enabled clear magnetocardiogram wave forms to be measured without being affected by strong external noise.
Identification and minimization of sources of temporal instabilities in high field (>23 T) resistive magnets
Authors: Soghomonian Victoria , Sabo M. , Powell A. , Murphy P. , Rosanske Richard , Cross T. A. , Schneider-Muntau H. J.
Published: July 2002

Resistive magnets offer very high field strengths, unmatched by superconducting technology. However, the spatial and temporal characteristics of raw magnetic fields generated by resistive high powered and water cooled magnets, are unadapted to most nuclear magnetic resonance (NMR) experiments. The National High Magnetic Field Laboratory has installed a 24 T (∼1 GHz 1H), 32 mm bore, 13 MW resistive magnet to study the feasibility of utilizing such fields for NMR applications. Herein we present our efforts in identifying, characterizing, and improving the temporal properties of the magnets. The temporal instabilities arise mainly from two sources: power supply ripple and inlet cooling water temperature variations. To compensate for power supply ripple, flux stabilization was employed, whereas for long term variations, arising from variations in the water temperature, a field frequency lock unit was utilized. Moreover, a novel flow based water temperature control scheme was implemented. The stabilization and improved control reduced the initial 16 ppm peak-to-peak variation to ∼2 ppm. Implementation of a field frequency lock unit further reduced the temporal variation to 0.8 ppm peak-to-peak. Sharp NMR linewidths — 1.7 ppm at full width at half height of 2H in liquid D2O — are observed in small volume samples, enabling moderate resolution NMR experiments to be performed at 24 T.
Formation of a p-n junction in silicon carbide by aluminum doping at room temperature using a pulsed laser doping method
Authors: Eryu Osamu , Okuyama Yasuo , Nakashima Kenshiro , Nakata Toshitake , Watanabe Masanori
Published: July 2002

A p-n junction has been formed in n-type silicon carbide (6H–SiC) by aluminum (Al) doping at room temperature using a pulsed laser doping method. A 6H–SiC substrate in [H2+(CH3)3Al] atmosphere was irradiated by an KrF excimer laser of 20 ns full width at half-maximum. The depth profile of Al determined by secondary ion mass spectroscopy showed a rectangularlike shape with a maximum concentration of 1×1022 Al/cm3. Furthermore, Al atoms were doped to a depth of about 0.05 μm from the surface. The current–voltage characteristics of the p-n junction clearly showed the rectifying property with low leakage current.
Organic field-effect bipolar transistors
Authors: Dodabalapur A. , Katz H. E. , Torsi L. , Haddon R. C.
Published: July 2002

Organic field-effect transistors (FETs) which employ two carefully selected active materials can function as n channel, p channel, or both n- and p-channel devices. It is shown that under an appropriate set of bias conditions the channel current in FETs with α-hexathienylene (α-6T) and C60 active layers consist of electron and hole components that are injected from the source and drain contacts into the C60 and α-6T layers, respectively.
Synthesis of 15R polytype of diamond in oxy-acetylene flame grown diamond thin films
Authors: Kapil R. , Mehta B. R. , Vankar V. D.
Published: July 2002

15R polytype of diamond has been synthesized using a specially designed oxy-acetylene flame system along with 3C diamond and cubic carbon on polycrystalline molybdenum substrates. X-ray diffraction has been used to detect the 15R phase as the dominant phase in these films. Rapid changes in the substrate temperature during the growth process are expected to be responsible for the growth of these phases.
Ion channeling studies of regrowth kinetics in crystalline metal oxides used with high temperature superconductors
Authors: Senapati L. , Sharma R. P. , Venkatesan T. , Zhang Zuhua , Chu Wei-Kan
Published: July 2002

The near surface regions of the single crystals of LaAlO3 and NdGaO3 are disordered to a depth of 150 nm by oxygen ion implantation. Thermally induced solid state epitaxial regrowth kinetics of these damaged layers are studied using ion channeling. It is seen that the regrowth in LaAlO3 samples starts at a temperature of 450 °C for 1 h in oxygen atmosphere. Most of the disordered region recovers as the annealing temperature is increased to 600 °C. Some end of range damage remains even after annealing at 1100 °C for 1 h. In the case of NdGaO3, the epitaxial regrowth starts at 650 °C. As the annealing temperature is increased to 900 °C, practically all the damaged region recovers. The Arrhenius plots indicate a distinct epitaxial-regrowth regime with different activation energies for the two cases. The implication of these results on the technology of high temperature superconducting circuit fabrication is discussed.