bluuebunny/crossref_metadata_2025 huggingface dataset:
Heart rate variability in long‐term risk assessment in middle‐aged women with coronary heart disease: The Stockholm Female Coronary Risk Study
Authors: Janszky I. , Ericson M. , Mittleman M. A. , Wamala S. , Al‐Khalili F. , Schenck‐Gustafsson K. , Orth‐Gomer K.
Published: December 2003

Objectives.  Low heart rate variability (HRV) is associated with poor prognosis after acute coronary events in men. In women, the prognostic impact is not well documented. The objective of this study was to assess the long‐term predictive power of HRV on mortality amongst middle‐aged women with coronary heart disease (CHD).

Design, Settings and Subjects.  Consecutive women below 65 years hospitalized for an acute coronary syndrome during a 3‐year period in Stockholm were examined for cardiovascular prognostic factors including HRV, and followed for a median of 9 years. An ambulatory 24‐h electrocardiograph was recorded during normal activities, 3–6 months after hospitalization. SDNN index (mean of the standard deviations of all normal to normal intervals for all 5‐min segments of the entire recording) and the following frequency domain parameters were assessed: total power, high‐frequency (HF) power, low‐frequency (LF) power, very‐low frequency (VLF) power and LF/HF ratio. Using Cox proportional hazards regression, the hazard ratios (HR) for each 25% decrease of the HRV parameters were assessed.

Results.  After controlling for the independent, significant predictors of mortality amongst the clinical variables, the following HRV parameters were found to be significant predictors of all‐cause mortality: SDNN index [HR 1.56, 95% confidence intervals (CI) 1.19–2.05], total power (HR 1.21, 95% CI 1.08–1.35), VLF power (HR 1.22, 95% CI 1.09–1.36), LF power (HR 1.18 95%, CI 1.07–1.30) and HF power (HR 1.18, 95% CI 1.05–1.33). The results were essentially the same when cardiovascular mortality was used as end‐points. The HRV parameters were stronger predictors of mortality in the first 5 years following the index event.

Conclusion.  Low HRV is a predictor of long‐term mortality amongst middle‐aged women with CHD when measured 3–6 months after hospitalization for an acute coronary syndrome, even after controlling for established clinical prognostic markers.
Diurnal triglyceridaemia and insulin resistance in mildly obese subjects with normal fasting plasma lipids
Authors: Halkes C. J. M. , Van Wijk J. P. H. , Ribalta J. , Masana L. , Castro Cabezas M.
Published: December 2003

Objective.  A novel method has been developed to study diurnal triglyceride (TG) profiles using repeated capillary self‐measurements in an ‘out‐of‐hospital’ situation. We assessed the diurnal capillary TG (TGc) profile in males with mild obesity and evaluated the use of plasma and capillary TG as markers of insulin resistance.

Design.  Cross‐sectional study.

Setting and Subjects.  Fifty‐four lean (body mass index, BMI < 25 kg m−2) and 27 mildly obese (25 < BMI < 30 kg m−2), normolipidaemic males measured capillary TG concentrations on six fixed time‐points over a 3‐day period in an ‘out‐of‐hospital’ situation.

Main outcome measures.  The total area under the TGc curve (TGc‐AUC) and incremental area under the TGc curve (TGc‐IAUC) were used as estimation of diurnal triglyceridaemia. Fasting blood samples were obtained once. Food intake was recorded by all participants.

Results.  Obese and lean subjects had comparable fasting capillary TG concentrations (1.37 ± 0.40 mmol L−1 and 1.32 ± 0.53 mmol L−1, respectively). However, during the day, obese subjects showed a greater TG increase, resulting in significantly higher TGc‐AUC (27.1 ± 8.4 and 23.0 ± 6.3 mmol h−1 l−1, respectively; P < 0.05) and TGc‐IAUC (7.9 ± 5.8 and 4.6 ± 6.6 mmolh−1 L−1, respectively; P < 0.05). The total group of 81 males was divided into quartiles based on fasting plasma TG, fasting capillary TG, TGc‐AUC and TGc‐IAUC. Amongst these variables, TGc‐AUC was the only significant discriminator of subjects with high homeostasis model assessment (HOMA) (insulin resistance) compared with low HOMA (insulin sensitive). Overall, BMI was the strongest determinant of HOMA.

Conclusions.  Diurnal TG profiles can be used to investigate postprandial lipaemia in both lean and mildly obese subjects and may help to detect subjects with an underlying disposition for hypertriglyceridaemia related to insulin resistance, i.e. the metabolic syndrome.
Large variations in the use of oral anticoagulants in stroke patients with atrial fibrillation: a Swedish national perspective
Authors: Glader E.‐L. , Stegmayr B. , Norrving B. , Terént A. , Hulter‐Åsberg K. , Wester P.‐O. , Asplund K. ,   for The Riks‐Stroke Collaboration
Published: December 2003

Objectives.  To explore nation‐wide use of anticoagulation in stroke patients with atrial fibrillation, in routine clinical practice in Sweden.

Design.  Cross‐sectional cohort study.

Setting.  Patients included in Riks‐Stroke, the Swedish national quality register for stroke care, during 2001.

Subjects. Hospitals with incomplete coverage were excluded, leaving 4538 stroke patients with atrial fibrillation amongst 18 276 stroke patients from 75 hospitals in six health care regions.

Main outcome measure.  Treatment with oral anticoagulants.

Results. At stroke onset, the proportion of patients with atrial fibrillation and first‐ever stroke, receiving oral anticoagulants as primary prevention was 11.0% (range 8.4–13.5% between regions and 2.5–24.4% between hospitals). Younger age, male sex and diabetes at stroke onset independently predicted primary prevention with oral anticoagulants. The proportion of stroke patients with atrial fibrillation receiving oral anticoagulants as secondary prevention at discharge was 33.5% (range 29.9–40.6% between regions and 16.4–61.9% between hospitals). Independent predictors for secondary prevention were younger age, male sex and independent activities of daily life (ADL) function before the stroke, being discharged to home, being fully conscious on admission and health care region.

Conclusion.  There were variations between hospitals and regions that differences in age, sex, functional impairments and comorbidities could not fully explain. This indicates that evidence‐based primary and secondary prevention of embolic stroke is insufficiently practised. Local factors seem to determine whether patients with atrial fibrillation gain access to optimal prevention of stroke or not.
C‐reactive protein and myocardial infarction during percutaneous coronary intervention
Authors: Saleh N. , Svane B. , Velander M. , Nilsson T. , Hansson L.‐O. , Tornvall P.
Published: December 2003

Objective.  To evaluate the prognostic information of preprocedural C‐reactive protein (CRP) levels in serum to predict myocardial infarction during percutaneous coronary interventions (PCI).

Design.  Prospective study.

Setting.  University hospital.

Patients.  A total of 400 consecutive patients with normal serum troponin T levels (≤0.03 μg L−1) presenting with stable or unstable angina pectoris.

Interventions.  PCI.

Main outcome measures.  C‐reactive protein levels in serum measured by a high sensitive method. Myocardial infarction defined as a serum troponin T elevation the day after PCI to a level >0.05 μg L−1.

Results.  Eighty‐three patients (21%) experienced a myocardial infarction during PCI. The median value of CRP before the procedure was 1.83 (0.12–99.7) mg L−1. No difference was seen in CRP levels before PCI between patients without or with myocardial infarction during PCI. Multivariate analysis identified stent implantation (OR 2.68, 95% CI 1.18–7.28, P = 0.03), procedure time (OR 2.15, 95% CI 1.28–3.67, P < 0.005) and complications during the procedure (OR 3.62, 95% CI 1.72–7.58, P < 0.001) as independent predictors of myocardial infarction during PCI.

Conclusion.  Increased CRP levels in serum before PCI were not associated with myocardial infarction during the procedure. Furthermore, patients with an expected long procedure and a high probability of stent implantation have an increased risk of developing myocardial infarction during PCI. This finding may be useful to help the operator to decide the antithrombotic regime before, during and after the procedure and the need for observation after the procedure.
IGFBP‐1 levels in adult women born small for gestational age suggest insulin resistance in spite of normal BMI
Authors: Kistner A. , Jacobson S. H. , Celsi G. , Vanpee M. , Brismar K.
Published: December 2003

Objective. Impaired fetal development may contribute to decreased insulin sensitivity. This study was designed to characterize serum markers of insulin resistance in adults born small for date or born prematurely.

Study design. Fifty subjects, all women, were evaluated at a mean age ± SD of 26 ± 2 years (range: 23–30 years). They were allocated to three groups: (i) born fullterm with birth weight <2600 g (n = 18) (small for gestational age, SGA), (ii) born before gestational week 32 (n = 15) (ex‐preterm), and (iii) controls, born fullterm with appropriate birth weight (n = 17). Anthropometric data as well as fasting serum samples of plasma B‐glucose, serum lipids, insulin, insulin‐like growth factor‐I (IGF‐I) and insulin‐like growth factor binding protein‐1 (IGFBP‐1) levels were determined.

Results. In the SGA group final height was lower and they weighed less compared with the controls. Fasting insulin and glucose levels did not differ amongst the groups. Triglycerides were lower in the SGA group and in the ex‐preterm group compared with the controls (P < 0.05). The SGA group showed lower IGFBP‐1 levels compared with the controls median 17 (range 3–121) vs. 26 (7–67)μg L−1;P < 0.05]. The IGF‐I levels in the SGA, ex‐preterm and control groups were 212 ± 58, 259 ± 37 and 216 ± 32 μg L−1, respectively, corresponding to a mean SD score of −0.8 ± 1.0, 0.1 ± 0.6 and −0.6 ± 0.6.

Conclusion. As IGFBP‐1 is a marker of insulin sensitivity, the low levels observed in adult women with normal BMI, born small for date, suggest relative insulin resistance in spite of normal BMI.
Preventing osteoporotic fractures with antiresorptive therapy: implications of microarchitectural changes
Authors: Boonen S. , Haentjens P. , Vandenput L. , Vanderschueren D.
Published: December 2003

Prospective studies have demonstrated that low bone mass correlates well with increased risk of osteoporotic fractures at various skeletal sites. Trials have likewise confirmed that enhancing bone mass with antiresorptive therapy reduces fracture incidence in individuals at risk. However, correlation of bone mineral density (BMD) increases with therapeutic risk reduction has proved less consistent than correlation of BMD decreases with greater fracture risk in the untreated. Indeed, various analyses have indicated that – even during treatment with potent bisphosphonates like alendronate and risedronate – BMD changes from baseline account for <30% of the reduction in vertebral fractures in treated women. It is clearly, therefore, that factors other than BMD are involved in the reduction of fracture risk achieved by antiresorptive therapies. According to recent micro‐computed tomography imaging and other studies, antiresorptive therapy can help rebuild the microarchitecture of bone as well as strengthen the materials that go into it. When treating individuals with osteoporosis, these microarchitectural changes contribute to the reduction of fracture risk achieved by antiresorptive therapies.
Host plant, oviposition behavior and larval ecology of a sawfly leafminer, Profenusa japonica (Hymenoptera: Tenthredinidae)
Authors: SUGIURA Shinji , YAMAZAKI Kazuo
Published: December 2003

The host plant, oviposition behavior and larval ecology of Profenusa japonica Togashi are reported for the first time. Adults of P. japonica mated and oviposited on a polyantha rose, Rosa multiflora (Rosaceae), in April. Each female adult laid an egg on the edge of a leaflet. Hatched larvae consumed the parenchymatous layer of leaflets and in so doing created a mine. The larval stage comprised five instars. On average, 70.6% of the total area of a leaflet was consumed by one larva. Female adults of P. japonica laid eggs singly, probably to avoid larval competition for food.
The genus Phyllomyza Fallén (Diptera: Milichiidae) from Japan, with descriptions of four new species
Authors: IWASA Mitsuhiro
Published: December 2003

The Japanese species of the genus Phyllomyza Fallén are revised. Four new species, Phyllomyza kanmiyai sp. nov., P. amamiensis sp. nov., P. proceripalpis sp. nov. and P. japonica sp. nov., are described and illustrated. P. securicornis Fallén is recorded from Japan for the first time. A key to the Japanese species of Phyllomyza is presented.
Discovery of the genus Skidmorella Johnson (Coleoptera: Ptiliidae) in Japan, with descriptions of two new species
Authors: SAWADA Yoshihiro , HIROWATARI Toshiya
Published: December 2003

The genus Skidmorella Johnson, previously known only from the South Pacific islands, is discovered in Japan. The type species, Skidmorella magnifica Johnson, is confirmed from Japan as the first record of the species other than the type locality. In addition, two new species, Skidmorella amamiana sp. nov. and Skidmorella quadrisulucia sp. nov., are described from the Ryukyus, Japan. Phylogenetic relationships of the genus Skidmorella and its allies are discussed on the basis of their morphological characters.
Long‐acting β2‐adrenergic formoterol and salmeterol induce the apoptosis of B‐chronic lymphocytic Leukaemia cells
Authors: Mamani‐Matsuda Maria , Moynet Daniel , Molimard Mathieu , Ferry‐Dumazet Hélène , Marit Gérald , Reiffers Josy , Diavad Mossalayi M.
Published: December 2003

B‐cell chronic lymphocytic leukaemia (B‐CLL) is a neoplastic disorder characterized by defective apoptosis, cell accumulation in G0/G1, and high expression of BCL2 oncogene. Intracellular cyclic adenosine monophosphate (cAMP) accumulation increases the chemosensitivity of B‐CLL cells in vitro and in vivo. In the present study, we investigated the effects of β2‐adrenergic compounds, well known cAMP‐inducing drugs, on the in vitro survival of leukaemia cells. In contrast to the short‐acting β2‐mimetic (β2Mim) salbutamol, a consistent pro‐apoptotic effect was observed with the long‐acting β2Mim salmeterol and formoterol. Normal B cells isolated from control donors were totally resistant to the above molecules. These compounds also increased chlorambucil‐ and fludarabine‐induced death of B‐CLL cells. Blockade of β‐adrenergic receptor signalling or cAMP did not alter B‐CLL apoptosis with β2 Mimagents. Leukaemia cell apoptosis by β2Mim correlated with an increase in calcium influx, decreased bcl‐2 protein and mRNA levels, increase in BAX gene expression and a marked rise in BCL2/BAX mRNA ratios. Interleukin‐4, a cytokine that increases bcl‐2 expression in B‐CLL cells, rescued leukaemia cell from apoptosis with β2Mim. These data show that long‐acting β2‐adrenergic agents promote apoptotic leukaemia cell death through an adrenoreceptor‐ and cAMP‐independent, Ca2+‐dependent mechanism.
Coffee and incidence of diabetes in Swedish women: a prospective 18‐year follow‐up study
Authors: Rosengren A. , Dotevall A. , Wilhelmsen L. , Thelle D. , Johansson S.
Published: December 2003

Abstract.  Rosengren A, Dotevall A, Wilhelmsen L, Thelle D, Johansson S (Sahlgrenska University Hospital/Östra, Göteborg; Göteborg University, Göteborg; AstraZeneca Research and Development, Mölndal; Sweden). Coffee and incidence of diabetes in Swedish women: a prospective 18‐year follow‐up study. J Intern Med 2004; 255: 89–95.

Objectives.  To examine the long‐term incidence of diabetes in relation to coffee consumption in Swedish women.

Design.  Prospective longitudinal cohort study.

Setting.  City of Göteborg, Sweden.

Subjects.  A random population sample of 1361 women, aged 39–65 years, without prior diabetes or cardiovascular disease took part in a screening study in 1979–1981 with questionnaires, physical examination and blood sampling.

Main outcome measures.  The development of diabetes until 1999 was identified by questionnaires in a second screening and the Swedish hospital discharge register.

Results.  Altogether, there were 74 new cases of diabetes. The risk of developing diabetes was 475 per 100 000 person‐years in women who consumed two cups of coffee or less per day, 271 in women who consumed three to four cups per day, 202 with a consumption of five to six cups per day, and 267 in drinkers of seven cups or more per day. Associated hazard ratios, after adjustment for age, smoking, low physical activity, education and body mass index were 0.55 (0.32–0.95), 0.39 (0.20–0.77) and 0.48 (0.22–1.06) for daily consumption of three to four, five to six and seven cups or more, respectively, with a consumption of less than two per day as reference. Additional adjustment for serum cholesterol and triglycerides attenuated the relation between coffee and diabetes slightly, indicating a possible mediating effect on the effect of coffee by serum lipids.

Conclusions.  The findings of the present study support the hypothesis that coffee consumption protects from the development of diabetes in women.
Association of the Lewis genotype with cardiovascular risk factors and subclinical carotid atherosclerosis: the Atherosclerosis Risk in Communities (ARIC) study
Authors: Cakir B. , Heiss G. , Pankow J. S. , Salomaa V. , Sharrett A. R. , Couper D. , Weston B. W
Published: December 2003

Objectives.  To evaluate the relationship of Lewis genotypes with major cardiovascular risk factors and the intima‐media thickness (IMT) of carotid arteries. Lewis genotyping included four major mutations of the Lewis (FUT3) gene at nucleotide positions 59, 1067, 202 and 314.

Design.  Two complementary population‐based cross‐sectional studies.

Setting.  The Atherosclerosis Risk in Communities (ARIC) Study.

Subjects.  The relationship between Lewis genotype and major cardiovascular risk factors was studied in 761 men and women aged 45–64 years without known clinical atherosclerotic disease; 577 were Caucasians and 184 were African‐Americans. The association of Lewis genotype and subclinical carotid atherosclerosis was studied in 419 individuals with, and 819 controls without carotid IMT of >1.0 mm, measured by B‐mode ultrasound.

Main outcome measures.  Mean values of cardiovascular risk factors by Lewis genotype. Lewis genotype frequencies in subclinical carotid atherosclerosis cases and controls.

Results.  Individuals with Lewis genotypes consistent with lack of α(1,3/1,4)‐fucosyltransferase activity (i.e. Lewis‐negative genotype) had statistically significantly lower fasting glucose, factor VIIIc, von Willebrand factor and diastolic blood pressure compared with their counterparts with Lewis‐positive genotypes. The distribution of Lewis genotypes and haplotypes was not significantly different between individuals with carotid IMT of >1.0 mm (cases) and their controls. The odds of carotid atherosclerosis in carriers of the Lewis‐negative genotype was 1.23 (95% confidence interval 0.70–2.16) compared to individuals with Lewis‐positive genotype, controlling for age, gender and race/ARIC field centre.

Conclusion.  The lack of a statistically significant association between Lewis ‘genotype’ and subclinical atherosclerosis in our data suggests that earlier studies reporting associations at the ‘phenotypic’ level may reflect aspects of the biology of the Lewis system other than an inherent genetic property.
Investigation of IrO2 and RuO2 Schottky contacts on AlGaN/GaN heterostructure
Authors: Jeon Chang Min , Lee Jong-Lam
Published: December 2003

Electrical properties of rare-earth metal contacts on AlGaN/GaN heterostructure were interpreted in terms of the changes in microstructure and chemical bonding state. When the contacts were annealed under oxygen ambient at 500 °C, the Schottky barrier height increased from 0.56 to 1.10 eV for the Ru and from 0.68 to 1.07 eV for the Ir contact. Moreover, the reverse leakage current at −10 V dramatically reduced by 4 orders of magnitude by oxidation annealing. Such an improvement originated from the formation of RuO2 and IrO2, playing a key role in increasing the solubility of group-III atoms, namely, Ga and Al atoms. As a result, the surface Fermi level shifted toward the energy levels of group-III vacancies, resulting in the increase of Schottky barrier height. The electrical properties of heterostructure field effect transistor (HFET) applying the Ru gate contact significantly degraded when the device was annealed at 500 °C under O2 ambient. This was due to the indiffusion of the Ru atoms into the AlGaN layer during the oxidation annealing. However, no electrical degradation was found in the HFET using the Ir gate contact. The maximum drain current density of 714 mA/mm and transconductance of 171 mS/mm were kept even after annealing at 500 °C.
Measuring multimegavolt pulsed voltages using Compton-generated electrons
Authors: Swanekamp S. B. , Weber B. V. , Pereira N. R. , Hinshelwood D. D. , Stephanakis S. J. , Young F. C.
Published: December 2003

The “Compton–Hall” voltmeter is a radiation-based voltage diagnostic that has been developed to measure voltages on high-power (TW) pulsed generators. The instrument collimates photons generated from bremsstrahlung produced in the diode onto an aluminum target to generate Compton-generated electrons. Permanent magnets bend the Compton electron orbits that escape the target toward a silicon pin diode detector. A GaAs photoconductive detector (PCD) detects photons that pass through the Compton target. The diode voltage is determined from the ratio of the electron dose in the pin detector to the x-ray dose in the PCD. The Integrated Tiger Series of electron–photon transport codes is used to determine the relationship between the measured dose ratio and the diode voltage. Variations in the electron beam’s angle of incidence on the bremsstrahlung target produce changes in the shape of the photon spectrum that lead to large variations in the voltage inferred from the voltmeter. The voltage uncertainty is minimized when the voltmeter is fielded at an angle of 45° with respect to the bremsstrahlung target. In this position, the photon spectra for different angles of incidence all converge onto a single spectrum reducing the uncertainty in the voltage to less than 10% for voltages below 4 MV. Higher and lower voltages than the range considered in this article can be measured by adjusting the strength of the applied magnetic field or the position of the electron detector relative to the Compton target. The instrument was fielded on the Gamble II pulsed-power generator configured with a plasma opening switch. Measurements produced a time-dependent voltage with a peak (3.7 MV) that agrees with nuclear activation measurements and a pulse shape that is consistent with the measured radiation pulse shape.
Optimization of the Halbach-type magnetic multipole for an electron cyclotron resonance ion source
Authors: Suominen P. , Tarvainen O. , Koivisto H. , Hitz D.
Published: December 2003

An efficient electron cyclotron resonance ion source requires microwave frequency as high as possible. At the same time, the magnetic field has to meet experimentally found rules. The magnetic field configuration required for efficient operation is provided by a combination of solenoid and multipole fields. A so-called Halbach array is used to produce as high a magnetic field as possible using permanent magnets. In this work the above-mentioned structure has been studied in detail in order to maximize the strength of the multipole field. Simulations showed that the so-called offset structure, described in this article, gives stronger fields at magnetic poles. As one result of this work, simple equations were developed to easily calculate the value of the magnetic field for different size hexapolar Halbach structures.
Integrated pulsed photoconductivity of organic light-emitting diodes
Authors: Tapponnier A. , Biaggio I. , Koehler M. , Günter P.
Published: December 2003

We analyze the transient photoconductivity induced by short light pulses in organic light-emitting diodes (OLEDs) to characterize the charge transport dynamics with high time resolution over four time decades. We show how integrated pulsed photoconductivity (IPP) can be used as a diagnostic method for finished, packaged OLEDs to determine and characterize the presence of impurities or other effects that influence the efficiency of charge transport. We demonstrate the usefulness of the method by comparing a simple one-layer Alq3 device on indium tin oxide (ITO) to a device where a nanometer thin NPB film separates the Alq3 from the ITO. In the single-layer device a charge transport dynamics stretching over several decades is observed, probably due to Alq3 contamination by its direct contact with ITO.
Ferromagnetic behavior of p-type GaN epilayer implanted with Fe+ ions
Authors: Shon Yoon , Kwon Young Hae , Park Y. S. , Yuldashev Sh. U. , Lee Seung Joo , Park C. S. , Chung K. J. , Yoon S. J. , Kim H. J. , Lee W. C. , Fu D. J. , Kang T. W. , Fan X. J. , Park Y. J. , Oh H. T.
Published: December 2003

p -type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+ ions. The properties of Fe+ implanted GaN epilayers were investigated by various measurements. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 eV and around 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak around 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting above 350 K.
Investigation of a multichanneling, multigap Marx bank switch
Authors: LeChien K. R. , Gahl J. M.
Published: December 2003

There is increasing interest in the pulsed power community for understanding the complex phenomena of multichannel spark gap switches. Extracting the potential advantages of these switches is necessary for upgrades to large, high current, high voltage machines. A previously designed, multichanneling spark gap (MCSG), with toroidal electrodes, for Marx bank applications, is investigated to determine which factors effect its multichannel operation. To date, thorough research does not exist for multichanneling gas switches with toroidal electrode geometry. The following results are the first of their kind. Gas type, gas pressure, trigger voltage, and trigger polarity are varied to study their effects on multichanneling in the MCSG. The fill gas is varied between air and an Ar/SF6 (90%/10%) mixture, from 3 to 10 psig. There are more channels for the mixture than for air for similar pressures. Trigger voltage amplitude and polarity are varied negatively from −60 to −100 kV and positively from +75 to +95 kV. Trigger polarity more drastically effects the distribution of arcs on the electrode rings of the MCSG rather than the number of channels. Output current is examined to determine if there are any significant decreases in rise time by increasing the number of channels. It is determined that there is very little dependence of output current on the number of channels observed in a typical Marx configuration for the MCSG.
Miniature Hall sensor based ac susceptometer for measurements of vortex and superfluid dynamics in superconducting films
Authors: Senapati K. , Chakrabarty S. , Sahoo Leena K. , Budhani R. C.
Published: December 2003

A highly sensitive ac susceptometer has been fabricated using a commercially available thin film Hall sensor of effective area 25×25 μm2. This instrument allows measurements of superfluid density and dynamical behavior of vortices in thin film superconductors over a broad range of frequency (10 Hz–100 kHz), temperature (4.2–300 K), and ac-field amplitude (2–150 Oe), and in static magnetic field as high as 5 T collinear with the ac field. The applicability of the susceptometer has been tested on Y1Ba2Cu3O7 films of thickness as small as ∼7 nm.
48-Channel electron detector for photoemission spectroscopy and microscopy
Authors: Gregoratti L. , Barinov A. , Benfatto E. , Cautero G. , Fava C. , Lacovig P. , Lonza D. , Kiskinova M. , Tommasini R. , Mähl S. , Heichler W.
Published: December 2003

We show that it is possible to use a multichannel electron detector in a zone plate based photoemission spectromicroscopy in a snap shot mode to reduce the total acquisition time for a given counting time by 50% relative to the standard scanning mode while preserving the feature of the spectra. We describe the result of tests performed at Elettra using its microbeam (150 nm) together with a 48-channel detector designed for the PHOIBOS 100 analyzer optimized for extremely small x-ray sources. We also give a short summary of the technical features of the detector and describe one possible calibration procedure for its use in the snap shot mode. We show initial results from using this device to perform chemical maps of surfaces at a resolution of 150 nm.
Integrating dual-color imaging capability into a monochromator
Authors: Hess Henry , Antia Meher , Vogel Viola
Published: December 2003

The simultaneous recording of fluorescence intensities at two different wavelengths has a variety of applications in optical microscopy, particularly for ratiometric measurements to sense environmental conditions or for measuring fluorescence resonance energy transfer to probe protein conformation. We demonstrate that a Czerny–Turner monochromator can serve as a platform for dual-color imaging by inserting into the monochromator turret a glass wedge with different dichroic coatings on each side. The presence of a grating, a mirror, and the wedge on a single turret allows rapid switching between spectroscopy and different imaging modes, and the reflective optics in the monochromator minimizes chromatic aberrations.
Image-based tracking laser Doppler vibrometer
Authors: Castellini P. , Tomasini E. P.
Published: December 2003

An innovative version of the tracking laser Doppler vibrometer based on image acquisition and processing (iTLDV) is proposed. The iTLDV is developed for tracking of arbitrary motions; the system is feedback controlled and allows measuring the vibrations of a moving target by driving moving mirrors via position signals of the target obtained from a charge-coupled-device camera and an image processing algorithm. The tracking system developed has been applied to an industrial test case subject to self-excited vibrations, in order to verify the performances and limits in the operating conditions. The system demonstrates its ability to measure vibration time histories on a windscreen wiper in operative conditions. This test case represents a challenging measurement problem, since no other measurement techniques are available that are able to extract such data. Some examples of obtained data are shown, which highlight the potential of iTLDV. In addition, position accuracy and measurement uncertainty are discussed. For the windscreen wiper, the worst position accuracy is estimate as ±1.2 mm along the wiper axis, while the measurement uncertainty mainly depends on the commercial vibrometer applied in the setup (about ±2% depending on operative conditions).
Nonradiative relaxation times in diagonal transition Si/SiGe quantum cascade structures
Authors: Bormann I. , Brunner K. , Hackenbuchner S. , Abstreiter G. , Schmult S. , Wegscheider W.
Published: December 2003

Here, we explore experimentally and theoretically the possibility to prolong the upper hole state nonradiative lifetime of Si/SiGe quantum cascade (QC) structures by using a spatially indirect diagonal transition between two SiGe quantum well ground states. With the recent observation of well resolved midinfrared electroluminescence from heavy hole intersubband transitions in Si/SiGe valence-band QC structures, a Si-based QC laser seems no longer to be out of reach. A long carrier lifetime and maybe population inversion, however, appear to be impossible for structure designs with a vertical intersubband transition studied so far. This is due to the nonresonant behavior of deformation potential scattering dominant in unipolar SiGe. We report on calculations of the band structure using a six-band k⋅p model and of hole deformation potential scattering that predict significantly increased nonradiative lifetimes for large barrier thickness, reaching about 20 ps for 35 Å Si barrier layer width. Electroluminesence measurements of a series of QC structures with varied barrier width reveal comparable efficiencies and the deduced lifetimes confirm our model calculations.
Suppression of exciton recombination in symmetric GaAs0.7Sb0.3/GaAs/GaAs0.7P0.3 coupled quantum wells induced by an in-plane magnetic field
Authors: Chang Kai , Jiang D. S. , Xia J. B.
Published: December 2003

Suppression of the exciton recombination in GaAs0.7Sb0.3/GaAs/GaAs0.7P0.3 coupled quantum well (CQW) induced by an external magnetic field is investigated theoretically. Unlike the usual electro-Stark effect, the exciton energy dispersion of an exciton is modified by an external in-plane magnetic field, the ground state of the magnetoexciton shifts from a zero in-plane center of mass (CM) momentum to a finite CM momentum, and the Lorentz force induces the spatial separation of electron and hole. Consequently, this effect renders the ground state of magnetoexciton stable against radiative recombination due to momentum conservation. This effect depends sensitively on the thickness and height of GaAs0.7Sb0.3 layer, therefore it could provide us useful infometion about the band alignment of CQW.
Polarized luminescence and absorption of highly oriented, fully conjugated, heterocyclic aromatic rigid-rod polymer poly-p-phenylenebenzobisoxazole
Authors: Wu C. C. , Tsay P. Y. , Cheng H. Y. , Bai S. J.
Published: December 2003

Poly-p-phenylenebenzobisoxazole (PBO) is a fully conjugated, heterocyclic aromatic rigid-rod polymer having a collinear and coplanar backbone leading to excellent thermo-oxidative stabilities, mechanical tenacity, and optoelectronic properties. PBO is inherently a liquid-crystalline polymer and can be obtained as uniaxially oriented fiber or film by extrusion of acidic solution. Schemes for making uniaxial freestanding films and monolayered luminescence devices for polarized optical absorption and emission were processed from a uniaxial PBO fiber. Wide-angle x-ray scattering revealed that the starting fiber and the resulting films were highly oriented. UV-Vis transmission spectra over 200 to 800 nm indicated that the PBO films also had polarized absorption with an attenuation coefficient ratio α⊥/α∥=1.7. The photoluminescence (PL) of the PBO films was excited at 363 nm, showing an emission intensity ratio I∥/I⊥ as high as 5. The anisotropic PBO film was sandwiched between an indium tin oxide substrate and an Al electrode for monolayer light-emitting diodes (LEDs), showing an electroluminescence (EL) intensity ratio I∥/I⊥=1.6 together with a markedly decrease in threshold voltage. PL and EL results demonstrated that a highly polarized luminescence emission was achieved by using the uniaxially oriented PBO films. The polarization effects in absorption and luminescence were absent for isotropic PBO films or LEDs.
Polarized organic electroluminescence: Ordering from the top
Authors: Godbert Nicolas , Burn Paul L. , Gilmour Sandra , Markham Jonathan P. J. , Samuel Ifor D. W.
Published: December 2003

We demonstrate a method for achieving polarized organic electroluminescence for liquid crystalline conjugated polymers that allows the polymer to be deposited directly onto the anode. The technique utilizes a top-down alignment approach whereby the predeposited polymer was aligned from above using a rubbed polyimide master and a smectic liquid crystal transfer layer. The liquid crystal/polyimide master bilayer was sandwiched with the liquid crystalline polymer that had been deposited onto the electrode. The sandwiched layers were then heated to achieve alignment before the removal of the polyimide master and liquid crystal transfer layer. Using this method, poly[2,7-{9,9-di(2-ethylhexyl)}fluorene] (PF2-6) was aligned to give an anisotropic polymer film. Light emitted from single layer light-emitting diodes containing the aligned PF2-6 had integrated dichroic ratios of up to 9.7. At 100 cd/m2, the single layer devices had external quantum and power efficiencies of 0.08% and 0.05 lm/W, respectively. Bilayer devices containing an electron transport layer between the PF2-6 and the cathode gave emitted light with good dichroic ratios and with the external quantum and power efficiencies at 100 cd/m2 being increased to 2.2% and 1.1 lm/W.
The effects of nitrogen plasma on reactive-ion etching induced damage in GaN
Authors: Mouffak Z. , Bensaoula A. , Trombetta L.
Published: December 2003

Lightly doped n-GaN samples were etched with reactive ion etching (RIE) in BCl3/Cl2/Ar and BCl3/Cl2/N2 plasmas. Replacing the argon by nitrogen in the plasma chemistry resulted in better etch rates, and in addition reduced etch damage for relatively low values of the plasma power. By treating the samples in a nitrogen plasma following etching, we dramatically reduced surface damage, as determined from Schottky IV characteristics measurements. Specifically, the reverse breakdown voltages returned to 70% to that measured from control diode samples. Further, x-ray photoelectron spectroscopy analysis showed that the post-etch nitrogen step decreased the Ga/N ratio. These results suggest that much of the damage induced by RIE plasma etching comes from a nitrogen loss mechanism.
Design of a film surface roughness-minimizing molecular beam epitaxy process by reduced-order modeling of epitaxial growth
Authors: Gallivan Martha A. , Atwater Harry A.
Published: December 2003

Molecular beam epitaxy of germanium was used along with kinetic Monte Carlo simulations to study time-varying processing parameters and their effect on surface morphology. Epitaxial Ge films were deposited on highly oriented Ge(001) substrates, with reflection high-energy electron diffraction as a real-time sensor. The Monte Carlo simulations were used to model the growth process, and physical parameters were determined during growth under time-varying flux. A reduced version of the simulations was generated, enabling the application on an optimization algorithm. Temperature profiles were then computed that minimize surface roughness subject to various experimental constraints. The final roughness after two layers of growth was reduced to 0.32, compared to 0.36 at the maximum growth temperature. The study presented here is an initial demonstration of a general approach that could also be used to optimize properties in other materials and deposition processes.
Parabolic lithium refractive optics for x rays
Authors: Pereira N. R. , Dufresne E. M. , Clarke R. , Arms D. A.
Published: December 2003

Excellent x-ray optics for photons at around 10 keV can be expected with lithium metal. One of the best compound refractive lens designs [Lengeler et al., J. Appl. Phys. 84, 5855 (1998)] is now produced routinely in aluminum, and more recently has been demonstrated using beryllium [M. Kuhlmann et al. (unpublished)]. Here, we report a similar refractive lens made from lithium. At 10.87 keV, this lens has a ≃2 m focal length, more than 90% peak transmission, and an average transmission of 49%. The lens shows a very useful gain of up to 40. The full widths at half maximum (FWHM) of the focus are blurred by roughly 20 μm, resulting in a horizontal and vertical FWHM of 33 and 17 μm for an image distance of 2.13 m. The lens produces speckle on the x-ray beam, which is likely due to the inhomogeneities of the lens surface: Coherent x-ray scattering is useful in understanding imperfections in x-ray optics, such as mirrors and lenses. Better molding techniques should result in improved performance and enable microbeam techniques with this type of Li lens.
Charge transport in highly efficient iridium cored electrophosphorescent dendrimers
Authors: Markham Jonathan P. J. , Samuel Ifor D. W. , Lo Shih-Chun , Burn Paul L. , Weiter Martin , Bässler Heinz
Published: December 2003

Electrophosphorescent dendrimers are promising materials for highly efficient light-emitting diodes. They consist of a phosphorescent core onto which dendritic groups are attached. Here, we present an investigation into the optical and electronic properties of highly efficient phosphorescent dendrimers. The effect of dendrimer structure on charge transport and optical properties is studied using temperature-dependent charge-generation-layer time-of-flight measurements and current voltage (I–V) analysis. A model is used to explain trends seen in the I–V characteristics. We demonstrate that fine tuning the mobility by chemical structure is possible in these dendrimers and show that this can lead to highly efficient bilayer dendrimer light-emitting diodes with neat emissive layers. Power efficiencies of 20 lm/W were measured for devices containing a second-generation (G2) Ir(ppy)3 dendrimer with a 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene electron transport layer.
Characterization of ferromagnetic Ga1−xMnxN layers grown on sapphire (0001) substrates
Authors: Yoon I. T. , Park C. S. , Kim H. J. , Kim Y. G. , Kang T. W. , Jeong M. C. , Ham M. H. , Myoung J. M.
Published: December 2003

Ga 1−x Mn x N epilayers with a well-ordered ferromagnetic structure were grown on sapphire (0001) substrates, using the plasma enhanced molecular-beam epitaxy technique. Ga1−xMnxN films were found to be homogeneous, and to exhibit n-type conductivity and ferromagnetic ordering with a Curie temperature (TC) above room temperature. This was confirmed by transmission electron microscopy, x-ray diffraction, and by magnetometry using a superconducting quantum interference device. The high-temperature (T=300 K) photoluminescence (PL) spectra exhibited Mn-related free-to-acceptor pair transitions for Ga1−xMnxN layers with x≈0.2% and x≈0.6%. A Mn acceptor level of a Ga1−xMnxN layer with low Mn content was found to be located around 330 meV above the top of the valence band, suggesting that Mn-bound holes in group-III nitrides exhibit effective-masslike behavior. The excitation and temperature-dependent PL provided convincing evidence of a band-edge exciton to acceptor transition.
Evolution of the microstructure during annealing of porous silicon multilayers
Authors: Ott N. , Nerding M. , Müller G. , Brendel R. , Strunk H. P.
Published: December 2003

We investigate the structural changes in porous silicon multilayers during annealing. Porous silicon multilayers play an important role in layer transfer technologies, where a thin crystalline silicon layer is separated from a wafer and transferred to a foreign substrate. High processing temperatures during epitaxial growth on top of the porous silicon layer lead to a restructuring of the porous layer. With transmission electron microscopy, we evaluate porous silicon monolayers and double-layers. The pore shape changes from open channel-like pores to closed facetted pores during anneal. In double-layers we observe a strong interaction between the two layers leading to an enhanced porosity in the high porosity layer. The observed microstructural evolution is discussed by means of the classical theory of sintering.
Comment on “Model of phase transition induced antiphase boundaries in perovskite and layered perovskite oxides” [J. Appl. Phys. 92, 5425 (2002)]
Authors: Su D. , Xu Q. Y. , Zhu J. S. , Wang Y. N.
Published: December 2003

In a recent article [J. Appl. Phys. 92, 5425 (2002)], Ding and Liang proposed a model for the origin of antiphase boundaries in perovskite and similar-structured compounds. They thought the existence of two types of ions with different sizes at the A sites in perovskite blocks and their ordering are the reasons for the occurrence of antiphase boundaries, which was supported by some cases listed in their article. However, we present several contrary examples in this investigation. It is pointed out that antiphase boundaries can exist in all kinds of occupied status at A and B sites.
Transient-signal-based sample-detection in atomic force microscopy
Authors: Sahoo Deepak R. , Sebastian Abu , Salapaka Murti V.
Published: December 2003

In typical dynamic mode operation of atomic force microscopes, steady state signals like amplitude and phase are used for detection and imaging of material. In these methods, the resolution and bandwidth are dictated by the quality factor (Q) of the cantilever. In this letter, we present a methodology that exploits the deflection signal during the transient of the cantilever motion. The principle overcomes the fundamental limitations on the trade off between resolution and bandwidth present in existing methods and makes it independent of the quality factor. Experimental results provided corroborate the theoretical development.
Models for phase-change of Ge2Sb2Te5 in optical and electrical memory devices
Authors: Senkader S. , Wright C. D.
Published: December 2003

We investigated three different modeling approaches to simulate the crystallization behavior of Ge2Sb2Te5 in optical and, very recently, electrical phase-change memories. The first of these models is based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism to calculate the fraction of crystallized material during isothermal anneals. In the literature, this model is widely used, but parameters of the model reported by different investigators vary considerably. We have shown that these discrepancies can be attributed to the inappropriate use of the JMAK approach. In order to overcome the restrictions imposed by JMAK theory, generalizations based on classical nucleation theory have been suggested. Material parameters required by the theory, such as viscosity, diffusivity, and fusion enthalpy of Ge2Sb2Te5, have been deduced from published experiments. Uncertainty in the material parameters in combination with approximate expressions used by the classical nucleation theory, however, lead us to suggest a comprehensive model based on rate equations. Although it is more complicated, this modeling approach has yielded more favorable and reliable results. We have discussed different simulation–experiment comparisons to illustrate the capabilities of the model.
Gas gun for dynamic loading of explosives
Authors: Bourne N. K.
Published: December 2003

There has long been a need to understand the impact response of explosive materials, and continual improvements result from the design of careful, well-instrumented experiments. This article summarizes details of the design and construction of a laboratory facility capable of launching projectiles at explosive targets at velocities up to 1500 m s−1. There are two types of experiment that are required. In the first, a gun launches a plate of great planarity at an equally flat target. This geometry is known as plate impact and a target loaded in this manner experiences a state of one-dimensional strain. This loading is accomplished by launching plane impactors onto targets aligned to micron tolerances, normal to the impact axis to less than 0.5 mrad of tilt. In the second, it is required to attain the ability to recover impacted explosive targets that have been loaded in one-dimensional strain for subsequent microstructural assessment. The development of this capability will be described in a subsequent publication. The system is capable of containing reactive targets, where design must allow for complete detonation of the target (up to 250 g of explosive). The facility has been completed, is operational, and has been approved for use by the appropriate authorities. An example of a particle velocity sensor in use within a plastic-bonded explosive is given as illustration.
Application of diamond window for infrared laser diagnostics in a tokamak device
Authors: Kawano Yasunori , Chiba Shinichi , Inoue Akira
Published: December 2003

Chemical vapor deposited diamond disks have been successfully applied as the vacuum windows for infrared CO2 laser interferometry and polarimetry used in electron density measurement in the JT-60U tokamak. In comparison with the conventional zinc–selenide windows, the Faraday rotation component of diamond windows was negligible. This results in an improvement of the Faraday rotation measurement of tokamak plasma by polarimetry.