bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of shock‐wave therapy on patellar tendinopathy in a rabbit model
Authors: Hsu Robert Wen‐Wei , Hsu Wei‐Hsiu , Tai Ching‐Lung , Lee Kam‐Fai
Published: June 2003

This study investigated the effect of shock‐wave therapy (SWT) on collagenase induced tendinopathy in the rabbit patellar tendon. Eighteen rabbits were treated by ultrasonography‐guided injection of 0.025 ml collagenase into the patellar tendon in both knees. After tendinopathy was confirmed at 3 weeks post‐treatment by the histological examination, SWT was initiated to the right patellar tendon involving 1500 cycles at 0.29 mJ/mm2 in two separated weekly courses from 4 weeks post‐treatment. The rabbits were randomly divided into two groups, which were sacrificed at the 4th and 16th week after SWT, respectively. The histological examination, the mechanical and biochemical tests then were performed. The ultimate tensile load in the SWT tendon increased 7.03% at 4 week and 10.34% at 16 week after treatment as compared to the sham group. Hydroxyproline concentrations increased in the SWT tendons over both the 4 and 16 weeks after treatment. Moreover, the pyridinoline concentration increased at the 4th week but decreased at 16th week as compared to the sham group. The histological examination demonstrated increased blast‐like tenocyte at the 4th week, while more mature tenocyte with neovasculization at the 16th week. The result obtained here validates the effectiveness of the SWT in the established tendinopathy. SWT may increase collagen synthesis and collagen crosslink formation during early healing process. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
A method for controlling for a high placebo response rate in a comparison of venlafaxine XR and diazepam in the short-term treatment of patients with generalised anxiety disorder
Authors: Hackett David , Haudiquet Vincent , Salinas Eliseo
Published: June 2003

This randomised, double-blind, placebo-controlled study compared the efficacy of venlafaxine XR (75 or 150 mg/d) with diazepam (15 mg/d) over an 8-week treatment period in 540 non-depressed outpatients with generalised anxiety disorder (GAD). At week 8, significant improvements from baseline were observed in the venlafaxine XR, diazepam and placebo groups. Although these improvements were higher in the first two groups than in the placebo group for each of the primary efficacy variables (Hamilton Rating Scale for Anxiety (HAM-A) total, HAM-A psychic anxiety factor, Hospital Anxiety and Depression Scale (HAD) anxiety sub-scale and Clinical Global Impression (CGI) improvement), there were no statistically significant differences between groups. These non-positive results were thought to be due to the very high placebo response observed in some centres. To understand the variability of the study, a secondary preplanned analysis was performed. This involved sub-dividing the study centres according to their ability to detect a two-point mean difference between diazepam and placebo at week 8 on the HAM-A total score. Centres able to show such a difference were termed verum-sensitive. Improvements from baseline to week 8 in venlafaxine XR-treated patients from verum-sensitive centres were significantly greater than in placebo on each of the primary efficacy measures (P ≤ 0.05). This suggests that those centres able to detect an anxiolytic effect of diazepam were also able to detect an anxiolytic effect of venlafaxine XR. Significant differences in baseline demographics, rates of adverse event reporting and rates of patient discontinuations were noted between patients enrolled at verum-sensitive and verum-insensitive sites. These results reflect the importance of study centre selection in accurately determining efficacy in placebo-controlled trials.
Induction of mania by rTMS: report of two cases
Authors: Sakkas Pavlos , Mihalopoulou Panajiota , Mourtzouhou Polyxeni , Psarros Costas , Masdrakis Vassilios , Politis Antonis , Christodoulou George N.
Published: June 2003

There is some evidence that repetitive transcranial magnetic stimulation (rTMS) may be effective in treating depression. Using an intensive methodology of rTMS in two drug-resistant patients, we observed a good antidepressant effect, but also, induction of manic symptoms.
Depression and anxiety in coronary artery bypass grafting patients
Authors: Rymaszewska Joanna , Kiejna Andrzej , Hadryś Tomasz
Published: June 2003

Purpose

Heart surgery is a factor triggering off specific emotional and physiological responses of a patient. In spite of positive somatic effects of surgery, depression and anxiety can persist or appear for the first time after the operation worsening the patient’s psychosocial functioning and quality of life. The aim of this study is to offer a prospective view on the incidence and course of self-reported depression and anxiety in coronary artery bypass graft (CABG) patients.

Subject and methods

After informed consent, 53 patients who submitted to CABG were examined a few days before and after the operation and 3 months after CABG. They completed the Spielberger Anxiety Questionnaire and Beck Depression Inventory.

Results

Approximately 55% of the patients had high a level of anxiety preoperatively. Shortly after the surgery, 34% of patients and after 3 months 32% of them had clinically relevant level of anxiety. Thirty-two percent of patients before the surgery, 28% immediately after CABG and 26% at follow-up were depressed.

Conclusions

High preoperative depression, state and trait anxiety scores appear to be predictors of postoperative psychological outcome. Preoperative assessment can identify patients at risk for clinical levels of postoperative anxiety and depression. Psychological preventive counseling and psychiatric intervention can reduce patients’ emotional distress, medical and economic costs.
Quality assurance of hydroacoustic surveys: the repeatability of fish-abundance and biomass estimates in lakes within and between hydroacoustic systems
Authors: Wanzenböck Josef , Mehner Thomas , Schulz Michael , Gassner Hubert , Winfield Ian J
Published: June 2003

In order to obtain information on the repeatability of hydroacoustic estimates of abundance and biomass of the fish stocks in Stechlinsee (Germany) and Irrsee (Austria), we performed synchronised surveys in three expert teams using either two identical 120 kHz SIMRAD EY500 echosounders (Stechlinsee) or one such machine and a 200 kHz BioSonics DT6000 (Irrsee). At Stechlinsee, where the fish stock is dominated by Coregonus albula, the night surveys with vertical beaming were made along 12 transects with two boats, one following the other at a distance of approximately 300 m. Fish-density estimates from the two units were highly correlated, but the slope of the regression differed from the expected value of 1. The regression relating biomass estimates of the two expert teams also revealed a close correlation with the slope not being significantly different from unity. This pattern could be explained by the fact that the differences in abundance were due to small targets differentially encountered by the two teams and contributing only marginally to total fish biomass. Nevertheless, we found that the results of a single hydroacoustic survey can be reproduced reliably by an independent team using similar equipment. The comparison between different machines at Irrsee, where the fish stock is dominated by Coregonus lavaretus, was done at night with the two echosounders mounted on the same boat and running simultaneously without interference. The abundance estimates correlated significantly but more weakly than in the Stechlinsee exercise, although the echosounding systems differed in many technical specifications. Correlation of biomass estimates was found to be robust, with the slope of the regression not significantly different from unity. Hence, we found that simultaneous surveys by two expert teams using split-beam systems from completely independent manufacturers, differing in sound frequency, beam width and shape, pulse length, ping rate, acquisition software, and post-processing software, produce directly comparable biomass estimates.
Non-linear effects in a 200-kHz sound beam and the consequences for target-strength measurement
Authors: Tichy F.E , Solli H , Klaveness H
Published: June 2003

When estimating target strength (TS), sound pressure in the beam where the target is located has to be measured accurately. Sound pressure is normally calculated from the source level, and transmission loss is based on geometric spreading and absorption loss. Additional losses caused by non-linear acoustic propagation may be important, especially in the case of high-power, high-frequency, and highly directive sources. ‘Non-linear loss’ from the fundamental frequency is due to energy from the fundamental harmonic being transferred into higher harmonics. This loss affects the beam pattern in ways that will depend on both power and range, since the non-linear loss depends, in turn, on sound pressure. We present the results of sound-pressure measurements and simulations from a 200-kHz transducer with a beam width of 7°. Sound pressure was measured at different ranges and power levels using a broadband hydrophone to detect some of the higher harmonic frequencies that occur in non-linear acoustic propagation. The TS of a solid copper sphere was measured using a standard echosounder with no correction for non-linear loss. Our study illustrates that this can be significant and that a corresponding correction needs to be considered when estimating TS.
Synthetic echograms generated from the relative frequency response
Authors: Korneliussen Rolf J , Ona Egil
Published: June 2003

Calibrated, digitized data from multi-frequency echo sounders have been used to generate new, synthetic echograms. The relative frequency response measured at four acoustic frequencies (18, 38, 120, and 200 kHz) is the main acoustic feature used to characterize the acoustic targets. Synthetic echograms are used to enhance and colour-code sample volumes with similar acoustic properties. The method is invaluable during scrutinizing, particularly in areas with many types of target. Several broad acoustic categories can be clearly distinguished, and detailed examples based on different fish species and zooplankton are demonstrated. The limitations of the method are described and discussed.
Tilt angle and target strength: target tracking of Atlantic cod (Gadus morhua) during trawling
Authors: McQuinn Ian H , Winger Paul D
Published: June 2003

Vertical orientation (tilt angle) is known to affect the target strength (TS) of ensonified fish and is a large component of the variability inherent in acoustic-biomass estimates. To measure the effects of changes in tilt angle on TS during diel vertical migrations, a concentration of migrating Atlantic cod (Gadus morhua) was observed acoustically from a research vessel over several days. Single-target data were collected from a split-beam echosounder and were subsequently tracked, corrected for vessel orientation and movement, and analysed for 3-dimensional displacement (speed and direction). The results revealed a large variability in TS and several patterns of swimming behaviour from random to directed orientation and movement, with changes in both vertical and horizontal displacements and inferred orientation. These behavioural patterns and their affects on TS were analysed as a function of “time-since-sunset”. Regular diel orientation patterns were observed as cod rose from the ocean bottom in the evening, increasing their tilt angle, and descended at sunrise to regain the ocean floor. Standardized TS (B20) was found to be highly correlated with tilt angle. This relationship can be used to correct for the diel changes in the TS of these migrating cod as a function of the in situ-measured tilt angle and thus to improve the accuracy of acoustic-biomass estimation.
A comparative acoustic-abundance estimation of pelagic redfish (Sebastes mentella) from hull-mounted and deep-towed acoustic systems
Authors: Dalen John , Nedreaas Kjell , Pedersen Ronald
Published: June 2003

During an international acoustic survey on pelagic redfish (Sebastes mentella) in the Irminger Sea in June–July 2001, a deep-towed vehicle carrying a dual-frequency SIMRAD EK60 Mk1 echosounder was used experimentally to observe and estimate redfish abundance at depths greater than 500 m. Comparison was made with the hull-mounted SIMRAD EK500 echosounder. The deep-towed echosounder improved the spatial resolution of fish in scattering layers as well as the ability to scrutinize and interpret fish echoes. The signal-to-noise ratio was better than that of the hull-mounted system. The fish abundance measured by the deep-towed sounder was consistently high compared to the hull-mounted sounder, particularly, at greater depths. For redfish within the deep scattering layer (DSL), the abundance was, on average, 5% higher, increasing to 55% for redfish below the DSL. From these findings it is concluded that a deep-towed echosounder is superior to hull-mounted ones for estimating the abundance of fish swimming in deep water.
Application of in situ target-strength estimations in lakes: examples from rainbow-smelt surveys in Lakes Erie and Champlain
Authors: Rudstam L.G , Parker S.L , Einhouse D.W , Witzel L.D , Warner D.M , Stritzel J.L , Parrish D.L , Sullivan P.J
Published: June 2003

Acoustic abundance of fish depends directly on the target strength (TS) of the fish surveyed. We analyzed 70 and 120 kHz acoustic data from two lakes with abundant rainbow-smelt (Osmerus mordax) populations. Using repeated surveys through the summer growing season, we derived a relationship between TS (dB) and fish length L (cm) at 120 kHz (TS = 19.9 log10 L − 67.8). Values for 70 kHz were similar. In situ TS increased with fish density, indicating a bias from accepting multiple targets at high fish densities. Correcting for this bias increased estimates of smelt abundance by up to 18% in Lake Erie and up to 100% in Lake Champlain. Multiple modes in the TS distributions observed for older fish do not reflect different size groups, as the same modes can be observed from measurements from a single fish. Smelt released gas bubbles during the evening ascent, and these bubbles had TS (−60 to −58 dB) within the range of TS observed from the fish. Gas-bubble release occurred mostly during the migration. Conducting surveys after the ascent is completed will decrease bias associated with counting bubbles as fish.
The Lindblom roller
Authors: Marchettini Paolo , Marangoni Claudio , Lacerenza Marco , Formaglio Fabio
Published: June 2003

Neuropathic pain is caused by injury of the peripheral or central nervous system. The neurological examination of the sensory system in neuropathic pain patients guides the anatomical localization of the injury. Among the sensory modalities to be tested, priority should be given to those subserved by small peripheral sensory fibers or by the spinothalamic tract that most commonly are abnormal in neuropathic pain patients. Testing of cold and warm perception was traditionally carried out in the clinic using tubes filled with water at different temperatures, a cumbersome method that has limited the routine examination of these sensory modalities. The Lindblom roller offers a practical and effective method of readily testing temperature perception and is among the best available clinical tools for delineating the anatomical boundaries of a sensory abnormality. Routinely use of the Lindblom roller shall be standard bedside clinical assessment of neuropathic pain patients. To exemplify this statement we describe two patients affected by complex and fluctuating painful sensory abnormalities caused by an extradural mass compressing the spinal cord. The level of the injury was readily localized with a roller kept at room temperature.
An evaluation of the beta‐1 adrenergic receptor Arg389Gly polymorphism in individuals with heart failure: a MERIT‐HF sub‐study
Authors:   On behalf of the MERIT‐HF Study Group, White Hazel L. , de Boer Rudolf A. , Maqbool Azhar , Greenwood Darren , van Veldhuisen Dirk J. , Cuthbert Richard , Ball Stephen G. , Hall Alistair S. , Balmforth Anthony J.
Published: June 2003

Background:

The Glycine389 variant of the beta‐1 adrenergic receptor (β1AR) generates markedly less cAMP when stimulated in vitro than the more prevalent Arginine389 variant.

Aims:

The aim of this MERIT‐HF sub‐study was to ascertain whether this Glycine389 variant favourably influences outcome in heart failure similar to that observed with beta‐blockers.

Methods:

We identified the genotype at amino acid 389 of the β1AR in 600 patients enrolled in the MERIT‐HF study (UK and Dutch participants). A risk‐ratio (RR) for each genotype was calculated using the combined endpoint of all cause mortality or hospitalisation (time to first event). A pharmacogenetic effect of this polymorphism was also sought by evaluating the effect of Metoprolol CR/XL on heart rate amongst the three genotypes.

Results:

The prevalence of the three genotypes was ArgArg 51.3%, ArgGly 40.2%, GlyGly 8.5%. The presence of the Gly allele was not associated with a significant benefit on the combined endpoint, RR=0.94; confidence intervals (CI), 0.69–1.29 (P=0.72). This is in contrast to the highly significant benefit of Metoprolol CR/XL observed in this sub‐study population, RR=0.60; CI, 0.44–0.83 (P=0.002). No effect of the polymorphism was observed on the magnitude of heart rate reduction attained by Metoprolol CR/XL.

Conclusion:

In contrast to the benefits of beta‐1 selective blockade, we have demonstrated that the Gly389 allele does not confer a significant mortality/morbidity benefit in heart failure patients. We have found no evidence of a pharmacogenetic effect of this biochemically functional polymorphism.
Modeling carbon dynamics in vegetation and soil under the impact of soil erosion and deposition
Authors: Liu Shuguang , Bliss Norman , Sundquist Eric , Huntington Thomas G.
Published: June 2003

Soil erosion and deposition may play important roles in balancing the global atmospheric carbon budget through their impacts on the net exchange of carbon between terrestrial ecosystems and the atmosphere. Few models and studies have been designed to assess these impacts. In this study, we developed a general ecosystem model, Erosion‐Deposition‐Carbon‐Model (EDCM), to dynamically simulate the influences of rainfall‐induced soil erosion and deposition on soil organic carbon (SOC) dynamics in soil profiles. EDCM was applied to several landscape positions in the Nelson Farm watershed in Mississippi, including ridge top (without erosion or deposition), eroding hillslopes, and depositional sites that had been converted from native forests to croplands in 1870. Erosion reduced the SOC storage at the eroding sites and deposition increased the SOC storage at the depositional areas compared with the site without erosion or deposition. Results indicated that soils were consistently carbon sources to the atmosphere at all landscape positions from 1870 to 1950, with lowest source strength at the eroding sites (13 to 24 gC m−2 yr−1), intermediate at the ridge top (34 gC m−2 yr−1), and highest at the depositional sites (42 to 49 gC m−2 yr−1). During this period, erosion reduced carbon emissions via dynamically replacing surface soil with subsurface soil that had lower SOC contents (quantity change) and higher passive SOC fractions (quality change). Soils at all landscape positions became carbon sinks from 1950 to 1997 due to changes in management practices (e.g., intensification of fertilization and crop genetic improvement). The sink strengths were highest at the eroding sites (42 to 44 gC m−2 yr−1), intermediate at the ridge top (35 gC m−2 yr−1), and lowest at the depositional sites (26 to 29 gC m−2 yr−1). During this period, erosion enhanced carbon uptake at the eroding sites by continuously taking away a fraction of SOC that can be replenished with enhanced plant residue input. Overall, soil erosion and deposition reduced CO2 emissions from the soil into the atmosphere by exposing low carbon‐bearing soil at eroding sites and by burying SOC at depositional sites. The results suggest that failing to account for the impact of soil erosion and deposition may potentially contribute to an overestimation of both the total historical carbon released from soils owing to land use change and the contemporary carbon sequestration rates at the eroding sites.
Optical and radio measurements of a 630‐nm airglow enhancement over Japan on 9 September 1999
Authors: Otsuka Y. , Kadota T. , Shiokawa K. , Ogawa T. , Kawamura S. , Fukao S. , Zhang S.‐R.
Published: June 2003

Using a comprehensive data set from optical and radio instruments, we investigate a midnight brightness wave that appeared in 630‐nm airglow images over Japan on the night of 9 September 1999. This may be the first such observation of the brightness wave with an all‐sky imager in the East‐Asian longitudinal sector. The imager at Shigaraki (35.6°N, 136.1°E) tracked a north‐northeastward propagation of the wave with an apparent velocity of 500 m s−1 after midnight. Ionosonde observations at five stations in Japan showed that rapid descent of the F2 layer propagated northward beyond 35°N with decreasing amplitude. Incoherent scatter observations with the MU radar at Shigaraki also revealed that the F2 peak altitude decreased from 360 to 280 km during the event. During the F2 layer descent the altitude profile of the electron density became sharp, enhancing the F2 peak electron density. After the F2 layer altitude reached 280 km, electron density in the F2 layer rapidly decreased because of increased neutral density at low altitude. A Fabry‐Perot interferometer (FPI) at Shigaraki observed northward neutral winds of 10–70 m s−1 during the event. A model calculation demonstrates that the meridional winds estimated from the MU radar electron density profiles are fairly consistent with those observed with the FPI. From these results we conclude that the observed northward wind enhancements, probably caused by the midnight temperature maximum, pushed down the plasma in the F2 layer to lower altitudes along the geomagnetic field to cause the 630‐nm airglow intensity enhancement.
Statistical analysis of relativistic electron energies for cyclotron resonance with EMIC waves observed on CRRES
Authors: Meredith Nigel P. , Thorne Richard M. , Horne Richard B. , Summers Danny , Fraser Brian J. , Anderson Roger R.
Published: June 2003

Electromagnetic ion cyclotron (EMIC) waves which propagate at frequencies below the proton gyrofrequency can undergo cyclotron resonant interactions with relativistic electrons in the outer radiation belt and cause pitch‐angle scattering and electron loss to the atmosphere. Typical storm‐time wave amplitudes of 1–10 nT cause strong diffusion scattering which may lead to significant relativistic electron loss at energies above the minimum energy for resonance, Emin. A statistical analysis of over 800 EMIC wave events observed on the CRRES spacecraft is performed to establish whether scattering can occur at geophysically interesting energies (≤2 MeV). While Emin is well above 2 MeV for the majority of these events, it can fall below 2 MeV in localized regions of high plasma density and/or low magnetic field (fpe/fce,eq > 10) for wave frequencies just below the hydrogen or helium ion gyrofrequencies. These lower energy scattering events, which are mainly associated with resonant L‐mode waves, are found within the magnetic local time range 1300 < MLT < 1800 for L > 4.5. The average wave spectral intensity of these events (4–5 nT2/Hz) is sufficient to cause strong diffusion scattering. The spatial confinement of these events, together with the limited set of these waves that resonate with ≤2 MeV electrons, suggest that these electrons are only subject to strong scattering over a small fraction of their drift orbit. Consequently, drift‐averaged scattering lifetimes are expected to lie in the range of several hours to a day. EMIC wave scattering should therefore significantly affect relativistic electron dynamics during a storm. The waves that resonate with the ∼MeV electrons are produced by low‐energy (∼keV) ring current protons, which are expected to be injected into the inner magnetosphere during enhanced convection events.
Plasma sheet structure during strongly northward IMF
Authors: Petrukovich A. A. , Baumjohann W. , Nakamura R. , Balogh A. , Mukai T. , Glassmeier K.‐H. , Reme H. , Klecker B.
Published: June 2003

On 14 September 2001, under stongly northward IMF conditions Cluster registered several fast magnetic field polarity changes which are usually attributed to thin (near‐equatorial) current sheet crossings. However, the IMF was northward for the previous 24 hours, the plasma sheet was expanded vertically, filled with cold, dense plasmas with high local vertical magnetic component Bz, and the formation of a such cross‐tail thin current sheet was very unlikely. The analysis of multipoint measurements revealed that the detected sheets were almost vertically oriented, had strong shear and vanishing normal magnetic components, and therefore could be interpreted as boundaries between independent magnetic field domains (flux tubes) vertically indented relative to their neighbors, rather than crossings of the main cross‐tail current sheet. Such field reversals would be then observed by a spacecraft owing to horizontal flapping motion. Similar events were detected under analogous conditions by a pair of Geotail and Interball spacecraft, providing important evidence of significant spatial extent of areas with indented magnetic flux tubes along the tail. In conclusion we suggest how such anomalous structured magnetotail configuration might emerge in the course of high‐latitude reconnection of geomagnetic lobe and northward IMF.
Evaluation of a chemical transport model for sulfate using ACE‐2 observations and attribution of sulfate mixing ratios to source regions and formation processes
Authors: Benkovitz Carmen M. , Schwartz Stephen E. , Kim Byung‐Gon
Published: June 2003

High resolution measurements of sulfate during the ACE‐2 campaign (June–July 1997) permit detailed evaluation of the performance of a chemical transport models driven by analyzed meteorological data. At Tenerife, Canary Islands, (minimal proximate sources) the median ratio characteristic spread between model and observations, Sm/o ∼1.3, was comparable to the spread of three sets of collocated observations and to the spread of observations at stations separated by ∼13 km within a single model grid cell (1° × 1°). Somewhat greater Sm/o, ∼1.6, at Sagres, Portugal is attributed to nonrepresentativeness of a single measurement site influenced by proximate sources. At Tenerife contributions from European, North American, and biogenic sources to sulfate mixing ratios are comparable, with North American sources dominating (up to ∼85%) under conditions of a strong Azores high; thus substantial contributions of sulfate, and by implication other aerosols, can result from long‐range midlatitude transport across the Atlantic Ocean.
Signal‐to‐noise ratios of observed monthly tropical ocean color
Authors: Ballabrera‐Poy Joaquim , Murtugudde Raghu G. , Christian James R. , Busalacchi Antonio J.
Published: June 2003

Five years of chlorophyll concentrations provided by the SeaWiFS sensor are analyzed to calculate the interannual and total signal‐to‐noise ratios in the tropical oceans. The signal‐to‐noise ratios are used to compare the variance of the monthly concentrations against the variance of unresolved spatio‐temporal processes. The results show that at 1° × 1° resolution, variance associated to unresolved processes is as large as the interannual variance in large areas of the tropical oceans, with the exception of the equatorial Pacific. These large errors make it difficult to extract information from the assimilation of five years of interannual anomalies into biogeochemical models in large areas of the tropical oceans. Improvements obtained by using a 1/2° × 1/2° grid are limited to regions of strong small‐scale variability, such as western boundary currents or coastal upwelling. The results also indicate that five years of SeaWiFS data provide potentially useful information about the annual cycle in most regions of the tropical oceans.
Recent developments in statistical time series analysis: Examples of use in climate research
Authors: Godtliebsen F. , Olsen L. R. , Winther J.‐G.
Published: June 2003

In this paper we present some recently developed time series analysis methods. Further, we apply these methods to a suite of climatological and synthetic time series. We show what information (or statistical significance) that can be drawn from such time series and which otherwise, i.e. by simpler methods, would be difficult to extract. We conclude by recommending the use of advanced statistical time series analysis for a wide range of applications connected to studies of climate variability and climate change.
Stabilization of linear ion beam right‐hand polarized instabilities by nonlinear Alfvén/ion‐cyclotron waves
Authors: Gomberoff L.
Published: June 2003

It is shown that ion‐beam plasma electromagnetic right‐hand polarized instabilities can be stabilized by nonlinear left‐hand polarized waves. This phenomenon constitutes a nonlinear saturation mechanism for right‐hand polarized instabilities. Complete stabilization occurs for left‐hand wave amplitudes above a threshold value. The saturation mechanism takes place within a large range of pump wave frequencies and plasma temperatures.
Comment on “Ultrafast electron optics: Propagation dynamics of femtosecond electron packets” [J. Appl. Phys. 92, 1643 (2002)]
Authors: Qian Bao-Liang , Elsayed-Ali Hani E.
Published: June 2003

In a recent article [J. Appl. Phys. 92, 1643 (2002)] Siwick et al. investigated the space-charge-limited electron pulse propagation in a photoelectron gun using an analytical approach, referred to as mean-field theory, and a numerical N-body simulation. The results were compared with a one-dimensional fluid model [J. Appl. Phys. 91, 462 (2002)], and a conclusion was made that the fluid model overestimates the pulse duration after a certain propagation time. Although the mean-field theory and N-body simulation give exactly the same results for all examples studied, we point out that the expression for the on-axis potential in their mean-field model is inapplicable to investigating the electron space-charge dynamics in an ultrafast electron packet. We correct that expression and derive a two-dimensional model that is in agreement with our previous one-dimensional fluid model. We also point out several areas where Siwick et al. have misinterpreted the one-dimensional fluid model.
Effects of substrate temperature and annealing temperature on the formation and properties of erbium silicide layers synthesized by high current Er ion implantation
Authors: Zhang X. W. , Wong S. P. , Cheung W. Y.
Published: June 2003

Ion beam synthesis of ErSi2−x by erbium implantation into Si wafers with a metal vapor vacuum arc (MEVVA) ion source has been performed and the effects of substrate temperature and annealing temperature on its properties have been investigated. The implantation was performed at an extraction voltage of 60 kV to ion doses ranging from 5×1016 to 2×1017 cm−2 with beam current densities from 3 to 26 μA/cm2 corresponding to substrate temperatures ranging from 85 to 245 °C. The characterization of the as-implanted and annealed samples was performed using Rutherford backscattering spectrometry, x-ray diffraction, atomic force microscopy, and electrical resistivity measurements. The results showed that ErSi2−x phase was directly formed by MEVVA implantation when the substrate temperature Ts⩾200 °C. For the samples synthesized at lower implantation temperatures, postimplantation annealing is necessary to achieve the formation of ErSi2−x. Direct measurements of the sputtering depth on masked implanted samples at various substrate temperatures showed that the sputtering yield increases with increasing temperature. The intensive sputtering and aggregation due to high substrate temperatures result in surface fractal patterns, in some cases, discontinuous layers, thus the high resistivity of the layers.
Bismuth volatility effects on the perfection of SrBi2Nb2O9 and SrBi2Ta2O9 films
Authors: Zurbuchen M. A. , Lettieri J. , Fulk S. J. , Jia Y. , Carim A. H. , Schlom D. G. , Streiffer S. K.
Published: June 2003

The volatility of bismuth and bismuth oxide species complicates the growth of phase-pure films of SrBi2Nb2O9 and SrBi2Ta2O9. Films that appear phase-pure by x-ray diffraction can have microstructural defects caused by transient bismuth nonstoichiometry which have a significant impact on properties. Such defects are resolved by transmission electron microscopy. Post-growth loss of bismuth from a slowly cooled SrBi2Ta2O9 film resulted in the generation of a high density of out-of-phase boundaries (OPBs), which are demonstrated to be ferroelectrically inactive. In another film, the difference in the rate of desorption of bismuth oxides from SrTiO3 versus that from SrBi2Nb2O9 led to bismuth enrichment at the film–substrate interface, and the formation of an epitaxial reaction layer in an otherwise stoichiometric SrBi2Nb2O9 film. This different-composition layer would be expected to alter the electrical properties of the film as a whole. These results help explain the scatter in electrical data reported for similarly oriented films.
Low temperature nanoscopic kinetics of hydrogen plasma-enhanced crystallization of a-Si:H films
Authors: Khait Yu. L. , Weil R. , Beserman R. , Edelman F. , Beyer W. , Rech B.
Published: June 2003

A nanoscopic kinetic model of controlled plasma-assisted microcrystallite formation (PAμCF) of Si in pre deposited a-Si:H films at low temperatures is proposed. The model suggests mechanisms for enhancement of the Si crystallization in a-Si:H films at low temperatures by treatment of the films in plasma. The model reveals certain kinetic advantages of hydrogen plasmas for the formation of Si crystalline nuclei in a-Si:H compared to other plasmas (Ar plasma, etc.). These advantages make the hydrogen plasma substantially more efficient in the PAμCF of Si in a-Si:H films. The proposed mechanism for PAμCF of Si is associated with the formation on the surface of the a-Si:H film and in the adjacent nanometer material layer of nanoscale (picosecond) short-lived hot spots of high energy density (or effective temperature). The hot spots are generated in the material by energetic plasma ions of energy εis=20–100 eV accelerated by the electrical field in the thin plasma layer near the solid surface. The hot spots promote Si crystallization in a-Si:H. It is shown how the plasma composition, energy, mass, and fluxes of the plasma ions impinging on the surface of the a-Si:H film determine the Si nucleation rate and density of Si microcrystallization.
Accurate dipole polarizabilities of small silicon clusters from ab initio and density functional theory calculations
Authors: Maroulis George , Begué Didier , Pouchan Claude
Published: June 2003

We report conventional ab initio and density functional theory calculations for the static dipole polarizability for the small silicon clusters Si3 to Si7. Our effort relies on the design of flexible basis sets of Gaussian-type functions. The dependence of the calculated mean polarizability per atom (ᾱ/n) on basis set type and level of theory is brought forth and discussed. The effect of electron correlation is found to be small for all studied clusters. The density functional theory based methods are seen to predict reliable values for (ᾱ/n). By introducing and analyzing the differential mean polarizability per atom, ᾱdiff/n=ᾱ(Sin)/n−ᾱ(Si), we show that in fact ab initio and density functional theory calculations yield distinctly different pictures of the polarizability of small silicon clusters. Computational strategies are proposed for the extension of theoretical studies to larger structures.
Modeling of optical charging spectroscopy investigation of trapping phenomena in nanocrystalline porous silicon
Authors: Iancu Vladimir , Ciurea Magdalena Lidia , Draghici Mihai
Published: June 2003

A model for trapping phenomena in nanocrystalline silicon investigated by the optical charging spectroscopy method is proposed. The model takes into account all the possible contributions to the discharge current. The results previously obtained on fresh and passivated porous silicon samples are interpreted within the framework of the model, which provides a good fit to the experimental data. The role played by the different kinds of trapping centers (donors and acceptors, surface and bulk) and the different trap parameters is analyzed.
Effects of piezoelectricity and spontaneous polarization on localized excitons in self-formed InGaN quantum dots
Authors: Shi Jun-jie , Gan Zi-zhao
Published: June 2003

Exciton states confined in wurtzite InxGa1−xN/GaN strained quantum dots (QDs) are investigated within the framework of effective-mass approximation and variational approach, including three-dimensional confinement of the electrons and holes in QDs and a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization. The relationship between exciton states and structural parameters of QDs is studied in detail. Our results show that the In-rich QDs-like are formed spontaneously due to In compositional fluctuations in the InxGa1−xN layer. The strong built-in electric field in InxGa1−xN/GaN strained QDs gives rise to a marked reduction of the effective band gap of QDs and leads to a remarkable electron–hole spatial separation. This effect has a strong influence on exciton states and optical properties of QDs especially for the QDs with large height (⩾5 nm) along the grown direction of the heterostructures. A good agreement has been obtained between the calculated and measured emission wavelengths for different InxGa1−xN/GaN strained QDs.
Exact connections between effective magnetostriction and effective elastic moduli of fibrous composites and polycrystals
Authors: Chen T. , Nan C.-W. , Weng G. J.
Published: June 2003

The effective magnetostriction of a two-phase fibrous composite and a two-dimensional polycrystal assembled from cylindrical magnetostrictive cubic crystals is studied. For the considered systems, we show that there exist exact microstructure-independent relations between the effective magnetostriction and the effective elastic moduli. The fibers could be aligned identically or randomly oriented in the transverse plane. There is no restriction on the cross-sectional shapes of the fibers, nor on the arrangement of transverse geometry of the composite aggregate. These connections imply that knowledge of the effective elastic moduli will readily provide the effective magnetostriction of the composite medium.
Growth and nanostructure of conformal ruthenium films by liquid-source metalorganic chemical vapor deposition
Authors: Dey S. K. , Goswami J. , Das A. , Cao W. , Floyd M. , Carpenter R.
Published: June 2003

A commercially available metalorganic compound, namely Bis (2,2,6,6-tetramethyl-3, 5-heptanedionato)(1,5-cyclooctadiene)Ruthenium, or Ru(THD)2COD was evaluated for growth, nanostructure, and conformality of ruthenium films using a manufacturable, liquid-source metalorganic chemical vapor deposition technique. The deposition of Ru films (60–200 nm) was carried out on various substrates at a temperature (Tsub) of 250–320 °C via the oxygen-assisted pyrolysis of Ru(THD)2COD. In the kinetically controlled regime, the activation energy for the deposition of Ru on amorphous-HfO2/SiO2/Si was 136 kJ/mol. However, at Tsub>290 °C, the nearly temperature-independent growth rate was indicative of the mass-transport controlled regime. The as-deposited Ru films exhibited dense and polycrystalline grain structure, with a moderate preference for the (001) orientation. X-ray photoelectron spectroscopy revealed the presence of RuO2 in metallic Ru films deposited at a Tsub as low as 260 °C. In addition, high-resolution transmission electron microscopy showed amorphous grain boundaries in Ru films and a disorder interface layer between Ru and HfO2 surface. The Ru films, however, were electrically conductive (27 μΩ cm). In addition, Ru films deposited on patterned TiN/Si substrates in the kinetically controlled regime at 250 °C exhibited nearly 100% step coverage.
Theoretical studies of photoelectron spectra of SO42−(H2O)n clusters and the extrapolation to bulk solution
Authors: Zhan Chang-Guo , Zheng Fang , Dixon David A.
Published: June 2003

Photoelectron spectra of hydrated doubly charged anion clusters, SO42−(H2O)n, have been studied by performing first-principles electronic structure calculations on SO42−(H2O)n (n=3–6, 12, and 13). The calculated adiabatic electron ionization energies are in good agreement with available experimental data. A detailed analysis of the calculated results suggests that for n⩾12 the observed threshold ionization energy of the low binding energy band in the recently reported photoelectron spectra of SO42−(H2O)n is associated with the electron ionization from the solute, SO42−, whereas the observed threshold ionization energy of the high binding energy band is associated with the electron ionization from the water molecules in the first solvation shell of SO42−. For n⩽6, both threshold ionization energies of the low and high binding energy bands are all associated with the electron ionizations from the solute. This shows that the bulk solution value (n→∞) extrapolated from those threshold ionization energies of the high binding energy band of the clusters should refer to the first ionization energy of the water molecules in the first solvation shell of SO42− in aqueous solution and, therefore, should be significantly smaller than the measured threshold ionization energy of liquid water. This differs from the recent result that the value of 10.05 eV extrapolated from the threshold ionization energies of the high binding energy band based on a simple 1/Rc model was nearly identical to the measured threshold ionization energy (10.06 eV) of liquid water. To address this difference, we have used a new approach for the extrapolation of solvated ion cluster data to bulk solution. We show that the new extrapolation approach consistently produces extrapolated bulk solution results in significantly better agreement with those observed directly in bulk solution for the first ionization energies of the ions in SO42−(H2O)n, Br−(H2O)n, and I−(H2O)n. The same extrapolation approach predicts a bulk solution value of 7.20 eV extrapolated from the threshold ionization energies of the high binding energy band, consistent with our assignment of the high binding energy band.
Athermal annealing of Si-implanted GaAs and InP
Authors: Rao Mulpuri V. , Brookshire J. , Mitra S. , Qadri Syed B. , Fischer R. , Grun J. , Papanicolaou N. , Yousuf M. , Ridgway M. C.
Published: June 2003

GaAs and InP crystals ion implanted with Si were athermally annealed by exposing each crystal at a spot of ∼2 mm diameter to a high-intensity 1.06 μm wavelength pulsed laser radiation with ∼4 J pulse energy for 35 ns in a vacuum chamber. As a result a crater is formed at the irradiated spot. The crater is surrounded by a dark-colored ring-shaped region which is annealed by mechanical energy generated by rapidly expanding hot plasma that formed on the exposed spot. The electrical characteristics of this annealed region are comparable to those of a halogen-lamp annealed sample. No redistribution of impurities due to transient diffusion is observed in the implant tail region. In x-ray diffraction measurements, a high angle side satellite peak due to lattice strain was observed in the crater and near crater regions of the athermally annealed sample in addition to the main Bragg peak that corresponds to the pristine sample. This high angle side satellite peak is not observed in regions away from the crater (⩾5 mm from the center of the crater in GaAs).
In situ conductance characterization of Fe/Ag multilayer contacts on GaAs
Authors: Hite D. A. , Russek S. E. , Pappas D. P.
Published: June 2003

Electrical transport characteristics for epitaxially grown Ag/Fe/Ag multilayers on GaAs(100) and GaAs(110) have been studied under various growth conditions. The surfaces and structure of the multilayer were characterized by low energy electron diffraction and angle-resolved Auger electron spectroscopy/diffraction at all stages of the growth. In situ conductance spectroscopy performed between growth steps indicates a strong dependence of the transport characteristics on the morphology at the metal/semiconductor interface. A nanoclustered silver overlayer exhibits a reverse leakage current due to defect states in the discontinuous film; however, annealed continuous Ag overlayers on GaAs behave as a uniform rectifying diode. After completion of the magnetic multilayer growth, current–voltage characteristics indicate a sharp turn on in the reverse current at ∼0.6 V with nonlinear behavior. This is characteristic of electron tunneling through the Schottky barrier from the multilayer contact into the semiconductor. The implementation of these magnetic multilayer contacts for electrical spin injection is discussed.
Diffusion in dilute binary fluids confined in porous structures near the solvent critical point
Authors: De S. , Shapir Y. , Chimowitz E. H.
Published: June 2003

We analyze diffusion in dilute binary fluids confined within porous media near the critical point of the solvent species. Both ordered and random confining structures are considered. At the solvent critical point solvent dynamics are quiescent, a consequence of the critical slowing-down phenomenon predicted by theory. Solute diffusion, however, remains finite at these conditions, which we have characterized in terms of a system-invariant quantity we define as Ω. In specific situations Ω can also be related to scaling results in pure, homogeneous fluids, a result we illustrate with simulation data for a lattice–gas system. The implications of these theoretical concepts for both short-time dynamics and the practical situation involving diffusion through porous membranes are discussed and illustrated with computer simulation data. The simulations are carried out using a recently proposed relaxation-dynamics simulation algorithm that appears to be ideally suited for dynamical simulations in near-critical systems.
Two-dimensional self-consistent microwave argon plasma simulations with experimental verification
Authors: Li Y. , Gordon M. H. , Roe L. A. , Hassouni K. , Grotjohn T.
Published: June 2003

Optical emission spectroscopy (OES), absorption measurements, and thermal energy rate analysis were used in tandem with numerical models to characterize microwave argon plasmas. A WAVEMAT (model MPDR-3135) microwave diamond deposition system was used to generate argon plasmas at 5 Torr. Three excited state number densities (4p, 5p, and 5d) were obtained from the OES measurements, and a fourth excited state number density (4s) was obtained from the absorption measurements. Further, power absorbed in the substrate was monitored. A self-consistent two-dimensional argon model coupled with an electromagnetic field model and a 25-level two-dimensional (2D)-collisional-radiative model (CRM) was developed and validated with the experimental measurements. The 2D model provides the gas and electron temperature distributions, and the electron, ion, and 4s state number densities, which are then iteratively fed into the electromagnetic and CRM models. Both the numerically predicted thermal energy rates and excited state densities agreed, within the experimental and numerical uncertainties, with the experimental results.