bluuebunny/crossref_metadata_2025 huggingface dataset:
Microleakage in endodontically treated teeth: influence of calcium hydroxide dressing following bleaching
Authors: Demarco F. F. , Freitas J. M. , Silva M. P. , Justino L. M.
Published: July 2002

Aim

The purpose of the present study was to evaluate microleakage of a fourth generation dentine‐bonding agent and composite restoration during a walking bleach treatment.

Methodology

Thirty extracted non‐carious incisors were selected and conventional root canal treatment was performed. Teeth were randomly divided into 3 groups (n = 10): group A (control), access cavities were restored with a fourth generation dentine‐bonding agent, and incrementally restored with composite resin; group B, a paste composed of sodium perborate and hydrogen peroxide was placed into the pulp chamber and sealed with glass ionomer cement for 7 days, teeth were then restored in the same manner as group A; group C, a paste of sodium perborate and hydrogen peroxide was placed in the pulp chamber for 7 days and then after removal of the bleaching mixture, pulp chambers were filled with a calcium hydroxide paste and cavities sealed with glass ionomer for 1 week. The cavities were then restored with bonded restorations as in groups A and B. Teeth were subjected to thermal cycling and immersed in methylene blue for 8 h. Teeth were sectioned from buccal to lingual, through the centre of the restoration, using a diamond disk. Leakage was assessed using a standard scheme, under magnification (×20). Data were submitted to statistical analysis using nonparametric Kruskal–Wallis test.

Results

Groups A and C exhibited similar leakage patterns, and both demonstrated less leakage values than group B (P < 0.05).

Conclusions

It was concluded that bleaching with sodium perborate and hydrogen peroxide increases microleakage; short‐term use of a calcium hydroxide medicament did not increase microleakage.
Modelling the efficacy of entomopathogenic nematodes in the regulation of invertebrate pests in glasshouse crops
Authors: Fenton A. , Norman R. , Fairbairn J.P. , Hudson P.J.
Published: July 2002

1. Entomopathogenic nematodes belonging to the families Heterorhabditidae and Steinernematidae are lethal obligate parasites of a wide range of invertebrate species. These nematodes exhibit many characteristics that make them ideal candidates as biological control agents of insect pests (rapid host death, high reproductive rates, easily mass‐rearedin vitro, easy application techniques).

2. However, at present, the number of pest species to which these nematodes are applied successfully is small. Clearly, there is a need to develop existing knowledge of the nematode into a more complete understanding of the nematode–pest system as a whole.

3. To consider the potential of entomopathogenic nematodes as biological control agents, we adopted a generalized analytical modelling approach and, using realistic parameter estimates, determined the conditions under which these nematodes can regulate a pest population.

4. Stability analyses suggested that entomopathogenic nematodes may not be capable of regulating a host population to a stable equilibrium. Long‐term persistence of the host and nematode population is unlikely, due to the highly destabilizing effects of the parasite–host relationship. As such, these nematodes may be better suited to short‐term control through inundative application techniques rather than long‐term regulation.

5. This preliminary generalized model highlights areas where further work is needed. This includes estimation of the probability of nematode infection in the field, the effect of host size on the transmission cycle and the influence of spatial heterogeneity on stability.
Suicide: a personal reflection
Authors: Diedrich C. , Warelow P.
Published: July 2002

One of the authors of this paper, Carla Diedrich, had a personal experience of suicide in her family. She wants to both share the experience and allow the circumstances to be directive and informative for individuals who have had similar experiences with suicide and for those working in a clinical capacity. In this sense, the work belongs to Carla and her family and has been significant, almost cathartic, in helping her especially deal with this difficult set of personal circumstances.
Primary structure and properties of the cathepsin G/chymotrypsin inhibitor from the larval hemolymph of Apis mellifera
Authors: Bania Jacek , Stachowiak Damian , Polanowski Antoni
Published: July 2002

A member of the Ascaris inhibitor family exhibiting anti‐cathepsin G and anti‐chymotrypsin activity was purified from the larval hemolymph of the honey bee (Apis mellifera). Three forms of the inhibitor, designated AMCI 1–3, were isolated using gel filtration and anion‐exchange chromatographies followed by reverse‐phase HPLC. The amino‐acid analyses indicated that AMCI‐1 and AMCI‐2 have an identical composition whereas AMCI‐3 is shorter by two residues (Thr, Arg). All three forms contain as many as 10 cysteine residues and lack tryptophan, tyrosine, and histidine. The sequence of the isoinhibitors showed that the major form (AMCI‐1) consisting of 56 amino‐acid residues was a single‐chain protein of molecular mass 5972 Da, whereas the other two forms were two‐chain proteins with a very high residue identity. The AMCI‐2 appeared to be derived from AMCI‐1, as a result of the Lys24‐Thr25 peptide bond splitting, while AMCI‐3 was truncated at its N‐terminus by the dipeptide Thr25‐Arg26. The association constants for the binding of bovine α‐chymotrypsin to all purified forms of the inhibitor were high and nearly identical, ranging from 4.8 × 1010 m−1 for AMCI‐1 to 2.7 × 109 m−1 for AMCI‐3. The sensitivity of cathepsin G to inhibition by each inhibitor was different. Only the association constant for the interaction of this enzyme with AMCI‐1 was high (2 × 108 m−1) whereas those for AMCI‐2 and AMCI‐3 were significantly lower, and appeared to be 3.7 × 107 m−1 and 4.5 × 106 m−1, respectively. The reactive site of the inhibitor, as identified by cathepsin G degradation and chemical modification, was found to be at Met30‐Gln31. A search in the Protein Sequence Swiss‐Prot databank revealed a significant degree of identity (44%) between the primary structure of AMCI and the trypsin isoinhibitor from Ascaris sp (ATI) .

 On the basis of the cysteine residues alignment, the position of the reactive site as well as some sequence homology, the cathepsin G/chymotrypsin inhibitor from larval hemolymph of the honey bee may be considered to be a member of the Ascaris inhibitor family.
LAPAROSCOPIC LIVE DONOR NEPHRECTOMY: THE PRELIMINARY EXPERIENCE
Authors: Hensman C. , Lionel G. , Hewett P. , Mohan Rao M.
Published: July 2002

Background: Recent improvements in video technology and surgical instrumentation have resulted in the application of minimally invasive techniques to many surgical procedures including splenectomy and adrenalectomy.1,2 Nephrectomy requires a long flank incision with division of abdominal musculature and possible subcostal nerve damage. Severe postoperative pain and a prolonged recuperative period may result, and the cosmetic outcome may not be satisfactory. A new surgical approach utilizing laparoscopic dissection and delivery of the kidney through a small incision was performed to circumvent these problems. The aim of this paper is to describe the technique of laparoscopic live donor nephrectomy (LLDN) and present the preliminary outcome.

Methods: Over the 12‐month period between May 1997 and April 1998, 16 donors underwent donor nephrectomy by a laparoscopic approach. The procedure was assessed with regard to its safety, feasibility and advantages over the open method.

Results: All the nephrectomies were completed without conversion to an open procedure. The average postoperative pain score on a visual analogue scale of 1–10 was 2 in LLDN. The donors required 36 mg morphine on average over 36 h postoperatively. Postoperative stay averaged 3 days. One donor developed an infective complication along the wound drain tract which settled with adequate drainage and antibiotics. All the removed donor kidneys were transplanted with immediate good function. There were no surgical complications or graft losses. The recipients’ serum creatinine was in the range of 96–181 mmol/L 3 months after transplantation.

Conclusions: Significant potential advantages of LLDN include less postoperative pain, shorter hospitalization and decreased recuperative time. This preliminary experience indicates LLDN to be effective in terms of safety and feasibility.
Study of intestinal metaplasia in Barrett’s esophagus
Authors: Shasha Zhang , Jun Zhang , Jinyan Luo , Kangming Wang , Jun Gong , Aili Zuo
Published: July 2002

OBJECTIVE: The aim of the present study was to investigate the factors predisposing patients with Barrett’s esophagus (BE) to intestinal metaplasia (IM).

METHODS: Forty‐seven BE patients were studied. By using endoscopic and histological methods, esophageal IM was diagnosed in 36 patients, who were compared with 11 patients without IM in regard to their age, the endoscopic appearance of the esophagus and esophageal motility.

RESULTS: The patients’ age and endoscopic features of the esophagus, but not esophageal motor function and grade of macroscopic esophagitis, were risk factors for the development of IM.

CONCLUSIONS: Patient age and endoscopic features of the BE mucosa are associated with IM and may be prognostic factors for BE.
Predictors of the development of microalbuminuria in patients with Type 1 diabetes mellitus: a seven‐year prospective study
Authors: Group The Microalbuminuria Collaborative Study
Published: July 2002

Aims To determine risk factors for the development of persistent microalbuminuria (albumin excretion rate (AER) ≥ 30 μg/min) in Type 1 diabetes mellitus.

Methods One hundred and forty‐eight initially normotensive Type 1 diabetic patients with normal albumin excretion (< 30 μg/min) were followed prospectively in hospital diabetes outpatient clinics for a median of 7 years. Main outcome measures were: progression to persistent microalbuminuria (albumin excretion rate ≥ 30 μg/min on at least two consecutive occasions); rate of change of albumin excretion rate; development of arterial hypertension (systolic blood pressure > 160 mmHg and/or diastolic blood pressure > 95 mmHg or commencement of antihypertensive therapy).

Results In a median follow‐up period of 7 years (range 6 months to 8 years), 14 patients progressed to persistent microalbuminuria, a cumulative incidence of 11% (95% confidence interval 6.36–16.94). AER remained persistently < 30 μg/min in 109 subjects and 25 developed intermittent microalbuminuria. In those who developed persistent microalbuminuria, baseline AER (16.2 (13.9–19.1) vs. 5.2 (3.8–9.2) μg/min, P < 0.01), blood pressure (136 (123–148)/80 (74–85) vs. 121 (118–124)/72 (70–73) mmHg, P < 0.05), and HbA1 (10.2 (9.1–11.4) vs. 9.0 (8.7–9.4)%, P < 0.05) were higher than in those who continued to have persistent normoalbuminuria, retinopathy was more severe and height (1.64 (1.57–1.71) vs. 1.70 (1.69–1.72) m, P < 0.05) less. In multivariate analysis, baseline AER was the strongest predictor of the development of persistent microalbuminuria (P < 0.0001), followed by mean arterial pressure (P = 0.02) and HbA1 (P = 0.05).

Conclusions The level of AER, raised blood pressure and poor glycaemic control are the most important predictors of the development of microalbuminuria in Type 1 diabetes.
Natural Recover y and Restoration Potential of Severely Disturbed Talus Vegetation at Niagara Falls: Assessment Using a Reference System
Authors: De Gruchy Margaret A. , Matthes Uta , Gerrath John A. , Larson Douglas W.
Published: July 2002

The talus slope adjacent to the Niagara River at Niagara Falls (Ontario, Canada) has been severely disturbed over the course of the past century as the area has been increasingly developed for tourism. In addition the lower talus slope is disturbed by periodic ice scour, most recently one year prior to this study. Historical evidence suggests that the original vegetation was similar to that currently found on talus slopes of the Niagara Escarpment, which could, therefore, be used as a reference system and restoration target. The current community structure and physical environment were sampled in 75 randomly placed 1‐×‐1–m quadrats. A total of 137 species were found, of which 62%were aliens. ANOVA showed that species richness, woody debris cover, litter cover, soil depth, and photosynthetically active radiation changed along a gradient perpendicular to the river. Three different sections of the study area whose last severe disturbance dated back 100, 30, and 4 years, respectively, were similar in their physical environment but were significantly different in species richness. Ordinations of species frequencies showed that light levels and distance from the river were the principal gradients controlling the vegetation structure. The species composition of the section last disturbed 100 years ago was different from that of the more recently disturbed sections. Ordination and cluster analysis of the pooled data showed large differences between the Niagara Falls site and reference escarpment talus slopes. Natural escarpment vegetation was much more homogeneous and had more species and fewer aliens. By comparing reference talus with sections of the study area at Niagara Falls that were last disturbed at different times, we conclude that the trajectory of natural succession at Niagara Falls is leading to an alternative state, an urban forest dominated by aliens, and that active restoration will be required to return the talus to its original state.
Xerostomia and the Geriatric Patient
Authors: Ship Jonathan A. , Pillemer Stanley R. , Baum Bruce J.
Published: July 2002

Saliva is essential for the preservation of oral‐pharyngeal health, and disorders of salivary physiology are associated with numerous oral and pharyngeal problems, particularly in older people. Although salivary function is remarkably intact in healthy aging, medical problems, medications, and head and neck radiotherapy can cause salivary dysfunction and complaints of xerostomia among older people. Sjögren's syndrome, an autoimmune exocrinopathy, is the most common medical disease associated with salivary dysfunction. Medications with anticholinergic side effects will impair salivary output, and head and neck radiotherapy for cancer will cause permanent destruction of salivary glands. Treatments for salivary problems are based upon establishing a diagnosis, protecting oral and pharyngeal health, stimulating remaining glands, and replacing lost salivary fluids.
Male Cones in Taxaceae s. l. ‐ an Example of Wettstein's Pseudanthium Concept
Authors: Mundry I. , Mundry M.
Published: July 2002

Abstract: Male cones of Taxus baccata L. and Torreya californica Torr. are mostly regarded as simple strobili (“flowers”). In the past some authors assumed that every single “sporangiophore” of Taxus baccata represents a whole “flower”. The male cone of Taxus would then represent a compound strobilus (“inflorescence”). A cone of Cephalotaxus harringtonia (Knight ex J. Forbes) K. Koch and Cephalotaxus fortunei Hook. can easily be recognized as a compound strobilus composed of several simple strobili.

Our developmental studies by SEM give clues to the assumption that a simple male strobilus in Cephalotaxus is not homologous to the male strobili in Taxus and Torreya. Developmental, morphological and anatomical studies suggest that the simple strobili of Taxus and Torreya are derived from the compound strobili in Cephalotaxus by a transformation of the simple strobili into single sporangiophores. With respect to morphology, the male cones in Taxus and Torreya are simple strobili, but comparative developmental studies show that they are derived from compound strobili in a process similar to Wettstein's pseudanthium hypothesis. In the light of our studies, it is not unlikely that the male cones in Pinaceae also represent transformed compound strobili.
Ar incorporation in epitaxial TiN films deposited by reactive magnetron sputtering in mixed Ar/N2 discharges
Authors: Hultman L. , Johansson B.-O. , Sundgren J.-E. , Markert L. C. , Greene J. E.
Published: July 2002

TiN films were grown on (100), (110), and (111) oriented MgO by reactive magnetron sputtering from a Ti target in mixed Ar/N2 discharges. During film growth at substrate temperatures Ts ranging from 450 to 900 °C, an applied negative substrate bias Vs (0≤Vs≤600 V) was used to vary the flux and energy of impinging Ar+ and N+2 ions. Electron channeling and transmission electron microscopy were used to show that films grown at Ts≥550 °C were epitaxial with a defect density that decreased with increasing Ts. At a constant Ts=700 °C, the films were found to remain epitaxial as Vs was increased from 0 to 200 V, but the crystalline quality clearly deteriorated with Vs=400 V and at Vs=600 V the films were polycrystalline. Energy dispersive x-ray analysis showed that the trapped Ar concentration CAr in the films was a function of both Vs and Ts. For Ts=700 °C, CAr increased with increasing Vs to reach a maximum CmaxAr at 400 V before decreasing again. The relative value of CmaxAr varied with orientation in the following manner: (110)>(100)>(111). At a constant Vs=400 V, CmaxAr for (110) oriented films occurred at Ts≊750 °C. These results are explained based upon ion channeling efficiency as a function of film orientation and defect structure.
Epitaxial films of YBa2Cu3O7−δ on NdGaO3, LaGaO3, and SrTiO3 substrates deposited by laser ablation
Authors: Koren G. , Gupta A. , Giess E. A. , Segmüller A. , Laibowitz R. B.
Published: July 2002

Frequency-doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm2 and 10 ns duration were used to deposit thin films of YBa2 Cu3 O7−δ by laser ablation on NdGaO3 , LaGaO3, and SrTiO3 substrates held at 725±5 °C in 0.2 Torr of O2 ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with Tc (R=0) at 92–93 K. Critical current densities in 0.3–0.6 μm thick, 200 μm long, and 10–30 μm wide strips were measured to be 106 A/cm2 at 60, 77, and 80 K in the films on LaGaO3, NdGaO3, and SrTiO3, respectively. X-ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90° with respect to each other in the a-b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8–2.1%) result in epitaxial growth of the films.
New cermet film structures with much improved selectivity for solar thermal applications
Authors: Zhang Qi-Chu , Mills David R.
Published: July 2002

A new cermet film structure of solar thermal absorber is presented. The typical film is similar to that of the single cermet layer case, except the single cermet layer is replaced by two isotropic cermet sublayers. The calculated results have been shown that low- and high-temperature performances using this new selective surface structure are excellent. The value of the ratio of absorptance to normal emittance α/ε, 46, for deposited film has been achieved.
Top-surface emitting lasers with 1.9 V threshold voltage and the effect of spatial hole burning on their transverse mode operation and efficiencies
Authors: Vakhshoori D. , Wynn J. D. , Zydzik G. J. , Leibenguth R. E. , Asom M. T. , Kojima K. , Morgan R. A.
Published: July 2002

The fabrication and operating characteristics of a 1.9 V top surface emitting laser are presented. A planar fabrication process with a modified ion implantation mask is used to achieve gain guided lasers operating up to 90 °C. The laser operates in the fundamental mode up to 0.7 mW with 3.2 mW total peak optical output power. Direct evidence of spatial hole burning for the fundamental and the next higher mode is observed. This spatial hole burning puts a limit on the fundamental mode operation and efficiency of the lasers.
Low-cost technique for preparing n-Sb2S3/p-Si heterojunction solar cells
Authors: Savadogo O. , Mandal K. C.
Published: July 2002

The first fabrication of low cost n-Sb2S3/p-Si heterojunction solar cells by chemical deposition method is reported. It is observed that in the case of n-Sb2S3 films chemically deposited with silicotungstic acid on p-Si and annealed, the photovoltaic properties of the n-Sb2S3/p-Si junctions are considerably improved. Under AM1 illumination, the improved junction exhibited an efficiency (η) of ∼5.19% on an active area of 0.05 cm2 without any antireflection coating whereas the n-Sb2S3 films deposited without STA on p-Si showed η=1.03%.
Correlating optical absorption and thermal conductivity in diamond
Authors: Morelli Donald T. , Uher Ctirad
Published: July 2002

The presence of defects in diamond induces one-phonon infrared absorption which is not allowed in the perfect crystal due to symmetry. Concomitantly the thermal conductivity is reduced by additional phonon-defect scattering. For single crystal diamonds irradiated with fast neutrons, we find a correlation between the one-phonon absorption and the room-temperature thermal conductivity valid over three orders of magnitude in defect concentration. This relation holds for both unannealed and annealed crystals for which the detailed configuration of defects is different, as well as for a synthetic diamond film containing a similar type of disorder. Infrared absorption can thus be used to determine the thermal conductivity of diamonds containing vacancy-related defect centers.
Fabrication of Si nanostructures with an atomic force microscope
Authors: Snow E. S. , Campbell P. M.
Published: July 2002

A method for fabricating Si nanostructures with an air-operated atomic force microscope (AFM) is presented. An electrically conducting AFM tip is used to oxidize regions of size 10–30 nm of a H-passivated Si (100) surface at write speeds up to 1 mm/s. This oxide serves as an effective mask for pattern transfer into the substrate by selective liquid etching. The initial oxide growth rate depends exponentially on the applied voltage which produces an effective ‘‘tip sharpening’’ that allows small features to be produced by a relatively large diameter tip.
Experimental investigation on high-speed switching characteristics of a novel symmetric Mach–Zehnder all-optical switch
Authors: Nakamura S. , Tajima K. , Sugimoto Y.
Published: July 2002

We report the experimental results of a novel symmetric Mach–Zehnder (SMZ) all-optical switch. Although the switching is based on the band-filling effect in the semiconductor waveguide, the switching speed is not restricted by the slow relaxation time. We obtain fully switched, nearly square modulation, which is characteristic of the SMZ all-optical switch. We also achieve high-speed switching; the full width at half-maximum of the obtained wave form is 8 ps, which is only limited by the time resolution of the detection system.
High-efficiency CuInxGa1−xSe2 solar cells made from (Inx,Ga1−x)2Se3 precursor films
Authors: Gabor Andrew M. , Tuttle John R. , Albin David S. , Contreras Miguel A. , Noufi Rommel , Hermann Allen M.
Published: July 2002

In, Ga, and Se were coevaporated to form precursor films of (Inx,Ga1−x)2Se3. The precursors were then converted to CuInxGa1−xSe2 by exposure to a flux of Cu and Se. The final films were smooth, with tightly packed grains, and had a graded Ga content as a function of film depth. Photovoltaic devices made from these films showed good tolerance in device efficiency to variations in film composition. A device made from these films resulted in the highest total-area efficiency measured for any non-single-crystal, thin-film solar cell, at 15.9%.
The NBS triple quadrupole tandem mass spectrometer
Authors: Martinez Richard I.
Published: July 2002

A detailed description is provided of a triple quadrupole (QQQ) tandem mass spectrometer (MS/MS) which is kinetically well behaved and can be configured to use either a molecular beam target (type A) or collision chamber (type B) configuration. Its unique capabilities are being used to explore design criteria essential for (i) absolute cross-section measurements, and for (ii) the development of standardized operating conditions for generic, instrument-independent spectral databases for collisionally activated dissociation (CAD).
Interferometric microphone for optoacoustic spectroscopy
Authors: Park S. M. , Diebold G. J.
Published: July 2002

A Fabry–Perot interferometer constructed with a pellicle beam splitter can be used as a sensitive microphone. Pressure disturbances inside the interferometer cavity alter the mirror separation, thereby changing the optical interference pattern. The optoacoustic effect can be detected in a cell attached to the Fabry–Perot interferometer by monitoring the change in intensity of the central interference fringe.
A 200 MHz surface acoustic wave resonator mass microbalance
Authors: Bowers W. D. , Chuan R. L. , Duong T. M.
Published: July 2002

Surface acoustic wave (SAW) piezoelectric sensors typically used by researchers in analytical applications are based on SAW delay lines. We report here the development of a 200 MHz SAW instrument based on a SAW resonator instead of a conventional delay line. The instrument is small, compact and uses two separate 200 MHz resonator crystals which operate in the dual difference mode. The difference frequency stability is better than 55× 10−9 (±1 Hz) which is comparable to a 10 MHz bulk crystal (on an absolute frequency basis) and at least an order of magnitude better than other commercially available SAW delay lines that operate at comparable frequencies. The mass sensitivity is about 9 × 1010 Hz cm2/g. Response to temperature change is found to be about 20 Hz/°C from −30 °C to 30 °C. Response to pressure is found to be linear from 760 to 415 Torr at 3 Hz/Torr. Detection limits for HCl vapors were determined to be in the low ppb range using a SAW resonator coated with triethanolamine.
A suite of programs for calculating x-ray absorption, reflection, and diffraction performance for a variety of materials at arbitrary wavelengths
Authors: Brennan S. , Cowan P. L.
Published: July 2002

One of the most useful characteristics of synchrotron radiation is the wide spectral distribution of the source. For applications involving tuned monochromatic beams it is often helpful to predict the x-ray optical characteristics of a sample or the beam line optics at a particular wavelength. In contrast to this desire stands the fact that tabulated values for the optical parameters of interest are generally available only at wavelengths corresponding to typical x-ray tube sources. We have developed a suite of fortran programs which calculate photoabsorption cross sections and atomic scattering factors for materials of arbitrary, uniform composition or for arbitrary layered materials. Further, the suite includes programs for calculation of x-ray diffraction or reflection from such materials. These programs are of use for experimental planning, data analysis, and predictions of performance of beam line optical elements.
Data acquisition and control system for molecule and atom-resolved tunneling spectroscopy
Authors: Altman E. I. , DiLella D. P. , Ibe J. , Lee K. , Colton R. J.
Published: July 2002

A high-speed data acquisition and control system for atom-resolved tunneling spectroscopy based on an 80386 computer and a commercially available data acquisition card is descibed. An analog proportional-integral feedback controller with sample and hold is used to control the scanning tunneling microscope. Constant tip-sample separation during data collection is maintained by interrupting the feedback loop. Assembly language routines taking advantage of the direct memory access capabilities of the data acquisition card are used to minimize the data collection time. A current-to-voltage amplifier based on measuring the voltage drop across a resistor in series with the tunnel junction is used to amplify the tunnel current. This amplifier has a bandwidth of 250 kHz at a gain of 109 V/A. The complete system is capable of obtaining an entire tunneling spectrum in 1.5 ms. The system can also simultaneously collect 128 spectroscopic images, a topographic image, and spatially resolved tunneling spectra. Similar techniques can also be used to obtain local barrier height measurements and barrier height images. Scanning tunneling microscopy and spectroscopy data for C60 adsorbed on Au(111) are presented as examples of data collected using this system.
Multiwire thermocouples in reversing flow
Authors: Forney L. J. , Fralick G. C.
Published: July 2002

Measurements are recorded for multiwire thermocouples consisting of either two or three wires of unequal diameters. Signals from the multiwire probe are recorded for a reversing gas flow with both a periodic temperature and time constant fluctuation. It is demonstrated that the reconstructed signal from the multiwire thermocouple requires no compensation provided ω/ω1<2.3 for two wires or ω/ω1<3.6 for three wires where ω1 (=2πf) is the natural frequency of the smaller wire based on the maximum gas velocity. The latter results were possible provided Fourier transformed data from the wires were used and knowledge of the gas velocity phase angle was available.
Creep characteristics of piezoelectric actuators
Authors: Jung Hewon , Gweon Dae-Gab
Published: July 2002

A major limitation of piezoelectric translator (PZT) actuators is their lack of accuracy originated from the hysteresis and creep. Nevertheless the creep phenomenon is an important factor in many applications of PZT actuators, but it has been investigated less frequently in comparison with the displacement hysteresis. In this article, we present a basic creep model with some parameters that have hysteresis properties which make it possible to predict an open loop response of PZT actuators based on these properties.
Direct imaging of impurity-induced Raman scattering in GaN
Authors: Ponce F. A. , Steeds J. W. , Dyer C. D. , Pitt G. D.
Published: July 2002

The donor impurity distribution in a GaN epitaxial layer was studied using Raman imaging. The A1(LO) Raman line at 735 cm−1 is found to be inversely correlated to the presence of silicon in GaN due to phonon interaction with the free carrier plasma associated with donor impurities in the material. The spatial variation of the A1(LO) signal was imaged directly using newly developed instrumentation. Features with dimension of about 0.5 μm are observed in faceted GaN crystallites. This variation in free carrier concentration is attributed to preferential donor impurity incorporation during growth.
Scalability of small-aperture selectively oxidized vertical cavity lasers
Authors: Choquette Kent D. , Chow W. W. , Hadley G. R. , Hou H. Q. , Geib K. M.
Published: July 2002

We analyze the threshold properties of small area selectively oxidized vertical cavity lasers. Agreement for threshold gain versus laser size is found using the experimental intrinsic threshold voltage matched with a gain theory, as compared to a two-dimensional optical cavity simulation. Our analysis indicates the increasing threshold current density of small area lasers arises from both increasing threshold gain and the concomitant increasing leakage current. We further show that the optical loss can be reduced for lasers with areas as small as 0.25 μm2 while maintaining sufficient transverse optical confinement by displacing the apertures longitudinally away from the cavity and reducing the oxide thickness.
Nanocrystals synthesized by electron-beam induced fragmentation of vacancy-containing metals microspheres
Authors: Ru Q.
Published: July 2002

Dynamic behavior of gold spheres ranging from 5 to 50 μm in diameter under pulsed electron beam irradiation was observed in situ by a scanning and transmission electron microscope. Unusually large amounts of dropletlike fragments were found to be ejected out from spheres containing vacancies such as voids or holes. Crystals ranging from 1 nm to 1 μm in size were formed on a carbon substrate from the fragments. The ejection phenomenon may offer an alternative to laser ablation as a means of forming small particles.
Optically pumped blue organic semiconductor lasers
Authors: Kozlov V. G. , Parthasarathy G. , Burrows P. E. , Forrest S. R. , You Y. , Thompson M. E.
Published: July 2002

Lasing at 460, 485, and 510 nm is demonstrated in optically pumped, vacuum-deposited amorphous thin films of a carbazole derivative doped with Coumarin 47, perylene, and Coumarin 30, respectively. Efficient, nonradiative Förster energy transfer between host and dopant organic molecules results in low lasing thresholds (5 μJ/cm2), high differential quantum efficiencies (15%), high peak output powers (20 W), and long operational lifetimes (>105 pulses at 100 times the threshold power).
Crystal orientation dependence of piezoelectric properties of lead zirconate titanate near the morphotropic phase boundary
Authors: Du Xiao-hong , Zheng Jiehui , Belegundu Uma , Uchino Kenji
Published: July 2002

The piezoelectric and dielectric constants in different crystal orientations of the lead zirconate titanate (PZT) have been phenomenologically calculated for the compositions near the morphotropic phase boundary at room temperature. For a tetragonal PZT, the effective piezoelectric constant d33 monotonously decreases as the crystal cutting angle from the spontaneous polarization direction [001] increases. However, for a rhombohedral PZT, the effective piezoelectric constant d33[001]// along the perovskite [001] direction was found to be much larger than those along the spontaneous polarization direction [111]. This crystal orientation-related enhancement is emphasized as the composition approaches the morphotropic phase boundary. This suggests that by adopting the perovskite [001] orientation with a rhombohedral composition near the morphotropic phase boundary, the piezoelectric constant d33 for PZT can be greatly enhanced.
Graphoepitaxial NiTi shape memory thin films on Si
Authors: Su Quanmin , Zheng Yun , Wuttig Manfred
Published: July 2002

Graphoepitaxial Ni50Ti50 films were grown on Si substrates by sputter deposition of an alloy target. The microstructure evolution of the film was investigated by hot stage atomic force microscopy. The topological features of the martensitic graphoepitaxial Ni50Ti50 films are directly associated with etch pits on the surface of the silicon substrate and exhibit facets with well-defined preferential in-plane orientation. The highly ordered martensitic facets disappear as the film transforms to austenite at elevated temperatures.
Electrical properties of wafer-bonded GaAs/Si heterojunctions
Authors: Zhou Y. C. , Zhu Z. H. , Crouse D. , Lo Y. H.
Published: July 2002

This letter reports on the fabrication and electrical characterization of wafer-fused GaAs/Si heterojunctions. A detailed study of the effect of surface preparation on bonding GaAs to Si was performed. The current–voltage (I–V) characteristics of both n-GaAs/n-Si and p-GaAs/p-Si were measured from 77 K to room temperature. The forward I–V characteristics were analyzed using a numerical model that includes thermionic emission across the heterojunction. Specifically, a p-GaAs/p-Si heterointerface of high electrical quality was obtained by direct hydrophobic bonding.
Improved properties of La2/3Ca1/3MnO3 thin films by addition of silver
Authors: Shreekala R. , Rajeswari M. , Pai S. P. , Lofland S. E. , Smolyaninova V. , Ghosh K. , Ogale S. B. , Bhagat S. M. , Downes M. J. , Greene R. L. , Ramesh R. , Venkatesan T.
Published: July 2002

Thin films of Ag-added La2/3Ca1/3MnO3 exhibit enhancement of several desirable characteristics over the pristine counterparts. We find that the addition of Ag results in a pronounced increase in the insulator–metal transition temperature (Tp) and ferromagnetic transition temperature (Tc). There is also a remarkable improvement in the magnetic and electrical homogeneity of the samples as indicated by narrower ferromagnetic resonance linewidths and narrower resistive transitions, respectively. The observed improvement in properties is inferred to be largely associated with improved oxygen stoichiometry of the films although microstructural effects are not ruled out.
The effect of a spatially dependent effective mass on hydrogenic impurity binding energy in a finite parabolic quantum well with a magnetic field
Authors: Li Yu-Xian , Liu Jian-Jun , Kong Xiao-Jun
Published: July 2002

The effect of a spatially dependent effective mass in a finite GaAs/AlxGa1−xAs parabolic quantum well with a magnetic field on hydrogenic impurity ground state (1s) binding energies, and lowly excited state (2p±-like) has been calculated, respectively, as a function of well width and magnetic field and impurity position by using the one-dimensional method. We compare our results with square quantum wells and without the effect of spatially dependent effective mass result. The physical meaning of the wave function square is discussed.
Streamwise inhomogeneity of decaying grid turbulence
Authors: Antonia R. A. , Zhou T. , Danaila L. , Anselmet F.
Published: July 2002

Accounting for the streamwise inhomogeneity of turbulence in Kolmogorov’s equation for the third-order moment of the velocity increment between two points allows compliance with two important classical results. These are retrieved when the separation between the points either exceeds the integral length scale or becomes comparable to the Kolmogorov length scale. In the context of decaying grid turbulence, the results correspond to the mean turbulent energy equation and the Batchelor–Townsend equation for the decay of the mean-squared vorticity. Analogous results are obtained when the streamwise inhomogeneity is included in Yaglom’s equation. The form of the inhomogeneous term is illustrated and discussed in the context of measurements in a turbulent grid flow.
Thermoelectric properties of Ag3AuTe2
Authors: Young D. P. , Brown C. L. , Khalifah P. , Cava R. J. , Ramirez A. P.
Published: July 2002

Electronic structure calculations predict Ag3AuTe2 to be a small-band-gap semiconductor. Polycrystalline samples of the pure and doped materials have been synthesized, and the physical properties are reported. Thermoelectric power measurements indicate that pure Ag3AuTe2 is a p-type material with a very large room-temperature Seebeck coefficient of 530 μV/K. The thermal conductivity is very low, and at room temperature, is lower than that of the best thermoelectrics. The transport properties were found to be very sensitive to chemical doping and nonstoichiometry. Although samples made with excess Ag resulted in improved thermoelectric performance at higher temperatures (>500 K), the large resistivity of these materials makes them noncompetitive with state-of-the-art thermoelectrics.
Similarity and conditional similarity reductions of a (2+1)-dimensional KdV equation via a direct method
Authors: Lou Sen-yue , Tang Xiao-yan , Lin Ji
Published: July 2002

To get the similarity solutions of a nonlinear physical equation, one may use the classical Lie group approach, nonclassical Lie group approach and the Clarkson and Kruskal (CK) direct method. In this paper the direct method is modified to get the similarity and conditional similarity reductions of a (2+1) dimensional KdV-type equation. Ten types of usual similarity reductions [including the (1+1)-dimensional shallow water wave equation and the variable KdV equation] and six types of conditional similarity reductions of the (2+1)-dimensional KdV equation are obtained. Some special solutions of the conditional similarity reduction equations are found to show the nontriviality of the conditional similarity reduction approach. The conditional similarity solutions cannot be obtained by using the nonclassical Lie group approach in its present form. How to modify the nonclassical Lie group approach to obtain the conditional similarity solutions is still open.
Circular photogalvanic effect induced by monopolar spin orientation in p-GaAs/AlGaAs multiple-quantum wells
Authors: Ganichev S. D. , Ketterl H. , Prettl W. , Ivchenko E. L. , Vorobjev L. E.
Published: July 2002

The circular photogalvanic effect (CPGE) has been observed in (100)-oriented p-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. CPGE at normal incidence and the occurrence of the linear photogalvanic effect indicate a reduced point symmetry of studied multilayered heterostructures. As proposed, CPGE can be utilized to investigate separately spin polarization of electrons and holes and the symmetry of quantum wells.
Reply to “Comment on ‘A general property of endoreversible thermal engines’ ” [J. Appl. Phys. 89, 1518 (2001)]
Authors: Angulo-Brown F. , Arias-Hernández L. A.
Published: July 2002

In this reply to a comment by Yan on our previous article [J. Appl. Phys. 81, 2973 (1997)], we show that the compromise function C(ε) between high power output and low entropy production for CAN engines, proposed in that article to find the best ecological function, is not tautological. Moreover, this procedure is useful to construct the best ecological function for any heat transfer law used in endoreversible thermal engine models.
Does lattice vibration drive diffusion in zeolites?
Authors: Kopelevich Dmitry I. , Chang Hsueh-Chia
Published: July 2002

A method of estimation of the effect of lattice vibration as a driving force for sorbate diffusion in zeolites is proposed. A realistic lattice model is employed to cut off unrealistic long vibrational modes and eliminate feedback due to lattice periodicity. A generalized Langevin equation for sorbate motion is then derived with the magnitude of the lattice vibration captured by two parameters, μ and ν, which can be readily computed for any system. The effect of lattice vibration is then estimated for a variety of sorbate–zeolite pairs. Lattice vibration is found to be a negligible driving force for some systems (e.g., methane and xenon in silicalite) and an important driving force for other systems. In the latter case, the lattice vibration can provide either linear stochastic Langevin-type force (e.g., for benzene in silicalite) or nonlinear deterministic force (e.g., for argon in sodalite).
Influence of crystallite size distribution on the micro-Raman analysis of porous Si
Authors: Islam Md. N. , Kumar Satyendra
Published: July 2002

First-order Raman spectra from nanocrystalline semiconductors reflect the influence of crystallite sizes on the Raman shifts and line shapes. A Gaussian distribution in crystallite sizes is explicitly included to calculate the Raman spectra of porous silicon. Several porous-silicon samples were prepared using electrochemical anodization, and Raman as well as photoluminescence measurements were carried out on the same spots using a micro-Raman probe. The size distribution obtained from fitting the Raman data using our procedure is able to predict the photoluminescence accurately in the quantum-confinement models.
Ultrasonic detection of atmospheric humidity variations
Authors: Harrison R. Giles
Published: July 2002

The small variation of the speed of sound in air with water vapor concentration is evaluated as a method of measuring atmospheric humidity. Laboratory acoustic phase measurements were made, using inexpensive piezoelectric transducers and electret microphones with dew point temperature independently monitored in the same enclosure. Phase variations from an acoustic path gave fair agreement with the measured humidity variations, when temperature and cross-wind variations were removed. Thermal stabilization and filtering were necessary to reduce the random phase noise contributions from the detectors, leading to errors in mean vapor pressure of ∼5 mbar at 20 °C. The approach is therefore more suited to determine turbulent humidity fluctuations, for meteorological latent heat flux measurements.
Configurational temperature profile in confined fluids. I. Atomic fluid
Authors: Delhommelle Jerome , Evans Denis J.
Published: July 2002

Two configurational expressions for the temperature are applied to the calculation of temperature profiles within a confined atomic fluid in a narrow slit pore. The configurational temperatures profiles so obtained are compared to the kinetic temperature, calculated from the equipartition principle, in equilibrium (EMD), and nonequilibrium molecular dynamics (NEMD) simulations of planar Poiseuille flow. We show that one of the configurational expressions exhibits a system-size dependence which prevents its application to the determination of high-resolution temperature profiles. The other expression yields good agreement with the kinetic temperature profile in both equilibrium and nonequilibrium systems.
Fabrication of magnetite nanorods by ultrasound irradiation
Authors: Kumar R. Vijaya , Koltypin Yu , Xu X. N. , Yeshurun Y. , Gedanken A. , Felner I.
Published: July 2002

Magnetite nanorods have been prepared by the sonication of aqueous iron(II)acetate in the presence of β-cyclodextrin. The properties of the magnetite nanorods were characterized by x-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, thermogravimetric analysis, and magnetization measurements. The as-prepared magnetite nanorods are ferromagnetic and their magnetization at room temperature is ∼78 emu/g. The particle sizes measured from transmission electron micrographs are about 48/14 nm (L/W). A mechanism for the sonochemical formation of magnetite nanorods is discussed.
Ferrimagnetic ordering in nanostructured CdFe2O4 spinel
Authors: Chinnasamy C. N. , Narayanasamy A. , Ponpandian N. , Joseyphus R. Justin , Chattopadhyay K. , Shinoda K. , Jeyadevan B. , Tohji K. , Nakatsuka K. , Greneche J.-M.
Published: July 2002

Nanostructured CdFe2O4 spinel powders with various grain sizes ranging from 60 to 4 nm were synthesized by ball milling the bulk material. The magnetization measurements at 1 and 9 T reveal a spin-glass-like surface structure and the material is found to have a large anisotropy. Mössbauer studies at 10 K in external magnetic fields of 6 and 8.5 T applied parallel to the direction of gamma rays could clearly show that CdFe2O4 behaves like a mixed spinel on reducing the grain size to nanometer level and exhibits ferrimagnetic ordering. Fe3+ spins at both A and B sites exhibit spin canting.
Aligning single-wall carbon nanotubes with an alternating-current electric field
Authors: Chen X. Q. , Saito T. , Yamada H. , Matsushige K.
Published: July 2002

Single-wall carbon nanotubes (SWCNTs) were highly aligned by an external electric field. The results suggest that the alignment of SWCNTs shows significant dependencies on the frequency and the magnitude of the applied electric field. The electric field with 5 MHz straightened out the SWCNTs and created highly oriented samples with fewer large particles. We also discussed the mechanism and applications.
Kinetics of polarization reversal in 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3: Heterogeneous nucleation in the vicinity of quenched random fields
Authors: Viehland Dwight , Li Jie-Fang
Published: July 2002

Polarization reversal and domain dynamics have been investigated in 0.7Pb(Mg1/3Nb2/3) O3–0.3PbTiO3 using a method of current transients. Investigations were performed as a function of applied electric field. The kinetics of the transients have been modeled to an equation of state for heterogeneous nucleation in the vicinity of random fields. Nucleation of polar clusters with a reversed polarization occurs under applied field in the vicinity of randomly quenched defects.