bluuebunny/crossref_metadata_2025 huggingface dataset:
Bicarbonate requirement for the donor side of photosystem II
Authors: Klimov V.V. , Allakhverdiev S.I. , Feyziev Ya.M. , Baranov S.V.
Published: July 2002

Suppression of electron flow (and its subsequent restoration with 3–10 mM NaHCO3) on the donor side of photosystem II is shown upon either a partial depletion of pea subchloroplast membranes in bicarbonate or the addition of 5–20 μM formate. At higher concentrations (5 mM) formate induces the known ‘bicarbonate effect’ on the acceptor side of photosystem II. In preparations depleted of manganese the restoration of electron flow with 0.1–0.2 μM MnCl2(2–4 Mn per photosystem II reaction center) occurs only in the presence of bicarbonate and it is accompanied by an increased functional binding of manganese. Restoration of electron flow with diphenylcarbazide or NH2OH does not require the addition of NaHCO3. It is suggested that bicarbonate participates in the formation of the Mn‐cluster capable of water oxidation or serves as a substrate for the water‐oxidizing center.
Resettlement for China's Three Gorges Dam: socio-economic impact and institutional tensions
Authors: Jackson Sukhan , Sleigh Adrian
Published: July 2002

Large dams have been an important component of infrastructure development in capitalist and communist countries alike. In 1998, changing world attitudes on large dams led to a two year World Commission on Dams and new global standards may soon insist that future projects pay fair compensation so that resettlement becomes voluntary. Now, 10 years after introduction of economic reforms, China is mobilizing its resources to build the world's largest dam. This fulfils a longstanding ambition to impound the Yangtze River in Central China at the Three Gorges and use the hydropower, improved navigation and flood control to develop the economy.

This paper examines the socio-economic impact of Three Gorges Dam on over 1.3 million people to be displaced while China is in transition to a market economy. We consider resettlement in terms of the decision-making structure, property rights and incentives to move, and how the project exacerbates problems created by market reforms, especially rising unemployment and deteriorating public health. We conclude the project is boosting economic expectations while adversely affecting large sections of the population, and this could provoke widespread social unrest and eventual changes in political institutions.
The separation of powers in Ukraine
Authors: Wise Charles R. , Brown Trevor L.
Published: July 2002

This paper examines the passage of a new constitution in Ukraine in order to determine which factors contribute to the establishment of a stable separation of powers system at the national level. We focus on three types of factors: legacies of the past; the structure of institutions at key time periods; and the nature of dynamics between political groups. We find that while all of these factors play some role in the evolving institutional arrangements in Ukraine, negative legacies of the past can be overcome by the decisions of new political groups and the creation of new institutional arrangements.
Diagnostic tests, treatment and follow‐up in heart failure patients — is there a gender bias in the coherence to guidelines?
Authors: Mejhert Märit , Holmgren Jan , Wändell Per , Persson Hans , Edner Magnus
Published: July 2002

Aims:

To relate clinical data in a consecutive cohort of patients admitted with heart failure in Sweden to demographic data and the use of diagnostic tests, medical treatment, care process and mortality.

Methods and results:

Retrospective investigation of all charts concerning patients discharged with primary diagnosis of heart failure in two Swedish hospitals during the second half of 1995 was undertaken. Records from 187 men and 192 women were analyzed, median age was 78 years. During hospital stay 75% of the patients, regardless of gender, were examined with chest radiography. Echocardiography was performed in 59% of all patients, more often in men than in women (68% vs. 55%, P < 0.011). The proportion of patients receiving ACE‐inhibitors was higher if echocardiography had been performed, in both men (38% vs. 72%, P < 0.001) and women (38% vs. 55%, P < 0.033). Mean hospital stay was 6.4 days. After discharge 57% of the patients were referred to the general practitioners (GP), 21% to the hospital outpatient clinic. Young age (P < 0.001), male gender (P < 0.01) and treatment with β‐blocking agents (P < 0.035) were independently related to referral to hospital outpatient clinic. Within the group referred to the GPs, 62% of the patients had a follow‐up visit within 3 months after discharge while 49% had visited the hospital outpatient clinic. The 1‐year mortality rate was high, 30%.

Conclusion:

Patients admitted with heart failure in Sweden are old and carry a poor prognosis. In spite of the poor prognosis, only approximately half of the patients are followed‐up within 3 months after discharge. There is, in contrast to practice guidelines, an underuse of diagnostic tests of left ventricular function and medical treatment is often suboptimal. These unsatisfactory findings were more pronounced in women.
Carbon Dioxide Induced Soybean Protein Precipitation: Protein Fractionation, Particle Aggregation, and Continuous Operation
Authors: Thiering Russell , Hofland Gerard , Foster Neil , Witkamp Geert‐Jan , van de Wielen Luuk
Published: July 2002

A novel protein fractionation technique using a volatile electrolyte has been developed. Carbon dioxide was used to isoelectrically precipitate 80% and 95% pure glycinin and β‐conglycinin fractions from soybean isolate. The protein fractions precipitated as primary particles 0.2−0.3 μm in diameter, which under optimum conditions may be recovered as aggregates up to 500 μm in diameter. The dependency of protein fractionation efficiency on aggregate settling rates has been demonstrated. The isoelectric points of the two main soybean fractions, glycinin and β‐conglycinin, were calculated to be pH 5.2 and 4.95, respectively. Solution pH was accurately controlled by pressure in the isoelectric pH range of the different soybean protein fractions, and a pH “overshoot” was eliminated. Volatile electrolyte technology was also applied to a continuous process in order to eliminate the particle recovery concerns associated with batch precipitation and to demonstrate the potential for scale‐up. Glycinin was effectively recovered on‐line (94% glycinin recovery) with a purity approaching that of the batch process (95%).
Severe neuroexcitatory symptoms after anaesthesia – with focus on propofol anaesthesia
Authors: Islander G. , Vinge E.
Published: July 2002

Delayed neuroexcitatory symptoms after an uneventful anaesthesia are uncommon, although described in many reports. We want to report on two cases. The first patient developed muscle hypertonicity, jerky movements and unconsciousness after an uneventful anaesthesia with propofol, and later the same thing happened after anaesthesia with thiopentone. The second patient developed similar symptoms after an uneventful anaesthesia with propofol, but she never recovered completely after this and is now severely disabled. A search of the literature and the Swedish adverse drug reactions register revealed many similar cases. In both our patients the causal relationship between propofol and the neuroexcitatory symptoms remains uncertain, but we want to alert readers about this possible adverse reaction.
Reduced activity of TAFI (thrombin‐activatable fibrinolysis inhibitor) in acute promyelocytic leukaemia
Authors: Meijers Joost C. M. , Oudijk Erik‐Jan D. , Mosnier Laurent O. , Bos Rogier , Bouma Bonno N. , Nieuwenhuis H. Karel , Fijnheer Rob
Published: July 2002

Acute promyelocytic leukaemia (APL) is a disease that is distinguished from other leukaemias by the high potential for early haemorrhagic death. Several processes are involved, such as disseminated intravascular coagulation and hyperfibrinolysis. Recently, TAFI (thrombin‐activatable fibrinolysis inhibitor) was identified as a link between coagulation and fibrinolysis. TAFI can be activated by thrombin, and in its activated form potently attenuates fibrinolysis by removing C‐terminal lysine and arginine residues that are important for the binding and activation of plasminogen. Activation of TAFI by the coagulation system results in a down‐regulation of fibrinolytic activity and, thereby, prevents a rapid dissolution of the fibrin clot. To establish whether TAFI was involved in the severity of the bleeding complications in APL, the TAFI antigen and activity levels were determined in a group of 15 patients. The TAFI antigen concentration was normal, but the activity of TAFI was severely reduced in APL by ≈ 60%. The reduction of TAFI activity was most probably caused by the action of plasmin on TAFI because in vitro experiments revealed that plasmin slightly reduced antigen levels but severely reduced TAFI activity. The acquired functional TAFI deficiency in APL may contribute to the severity of the haemorrhagic diathesis because of the impaired capacity of the coagulation system to protect the fibrin clot from fibrinolysis.
Prior treatment with alpha interferon does not adversely  affect the outcome of allogeneic transplantation  for chronic myeloid leukaemia
Authors: Pigneux A. , Tanguy M. L. , Michallet M. , Jouet J. P. , Kuentz M. , Vernant J. P. , Milpied N. , Ifrah N. , Cahn J. Y. , Gratecos N. , Reman O. , Cure H. , Caillot D. , Witz F. , Pillier‐Loriette C. , Tron P. , Reiffers J. ,   for the Société Française de Greffe de Moelle (SFGM)
Published: July 2002

Summary.The timing of transplantation in chronic myeloid leukaemia is still debated and previous treatment with interferon (IFN) alpha has been reported to be deleterious. We have analysed the outcome of 438 allogeneic transplants performed between 1984 and 1995 and reported to the Société Française de Greffe de Moelle (SFGM) registry. One hundred and two patients (group I) received IFN for more than 6 weeks (median = 9 months) before transplant. Their outcome was compared with 336 other patients (group II) not pretreated with IFN. There were no significant differences between the groups for engraftment and chronic graft‐versus‐host disease (GVHD) incidence. However, other significant differences included the incidence of acute GVHD ≥ 2 at 3 months which was higher in group I (65 ± 10%) than in group II (38 ± 5%;P = 0·01). Moreover, disease‐free survival (DFS) and overall survival (OS) at 5 years were significantly shorter for group I than for group II (33 ± 10% vs. 41 ± 6%;P = 0·005)(95% CI) and (41 ± 10% vs. 55 ± 6%;P = 0·002)(95% CI) respectively. After adjustment for patient and transplant covariables in a multivariate analysis, prior IFN was not found to adversely affect transplant outcome.
Comparison of structure and biodiversity in the Rajhenav virgin forest remnant and managed forest in the Dinaric region of Slovenia
Authors: Boncina Andrej
Published: July 2002

Comparisons are made between a virgin forest remnant (primeval forest) and a lightly managed (near‐to‐nature) forest with regard to horizontal forest structures, the structure of forest stands, and the diversity of plant and bird species. In the virgin forest remnant the proportion of canopy gaps is smaller, there are no stands in the developmental phase of a pole stand (10 < cm d.b.h. < 30 cm), and both the growing stock and the proportion of less vigorous trees are considerably greater. In addition, there is a higher percentage of dead trees, a smaller proportion of minor tree species and a considerably lower diversity of plants. The diversity of bird species is similar for each forest type, but rare bird species are confined to the virgin forest remnant. The biological differences between the two types of forest have led to changes in the physical site conditions. The results of the research are valuable in assessing the consequences of near‐to‐nature forest management.
Dietary crude protein concentration does not affect the leucine requirement of growing dogs
Authors: Delaney S. J. , Hill A. S. , Backus R. C. , Czarnecki‐Maulden G. L. , Rogers Q. R.
Published: July 2002

The objective of the present study was to examine the interaction between graded levels of leucine and dietary crude protein. Dose–response curves were generated using four 3 × 3 Latin squares (two dogs/square). Each square represented one of two concentrations of crude protein (140 or 280 g/kg diet) and one of two combinations of three concentrations of leucine (5.0, 7.0 and 9.0 g/kg diet or 9.0, 11 and 13 g/kg diet). An additional experiment was performed by feeding crude protein at 210 g/kg diet with either 7.0 or 11 g leucine/kg diet. Weight gain, food intake, nitrogen retention, plasma albumin and plasma amino acids were measured. The requirement was determined to be the minimum leucine concentration required to maximize weight gain and nitrogen retention. For 8–14‐week‐old male Beagle dogs, 140 g crude protein/kg diet in a diet containing 18 kJ metabolizable energy/g does not appear to support maximal growth. The leucine requirement was not affected by doubling the dietary crude protein level from 140 to 280 g/kg diet. From these results, the leucine requirement of 8–14‐week‐old Beagle dogs appears to be 11 g leucine/kg diet independent of the level of dietary crude protein, whereas dogs over 14 weeks require only 7 g leucine/kg diet for maximal nitrogen retention.
Growth and nutrition of Hong Kong children aged 0–7 years
Authors: Leung SSF , Chan SM , Lui S , Lee WTK , Davies DP
Published: July 2002

Objective: To study the early dietary practices in relation to growth of Hong Kong children from birth to 7 years.

Methodology: One hundred and seventy‐three full‐term Hong Kong Chinese babies were recruited at birth and were followed up for anthropometric measurements using standardized methods and dietary assessment using a combination of dietary history, 24 h recall and food frequency. At 7 years, 125 children remained in the study.

Results: Mean (SD) birthweight was 3.3 (0.38) kg for boys and 3.1 (0.38) kg for girls. Mean (SD) weight at 7 years was 22.4 (4.2) kg for boys and 21.1 (3.7) kg for girls, and mean (SD) height was 120.3 (4.8) cm for boys and 119.8 (5.1) cm for girls. Hong Kong children were lighter and shorter than Australian children and the National Centre for Health Statistics (NCHS) references, but the magnitude is less than one standard deviation score. Mean weight and height of Hong Kong children were lower compared to Caucasian and Beijing children, with more obvious differences between 1 and 5 years. At 1 year, mean (SD) daily energy intake was 98 (24) kcal/kg/day for boys and 100 (26) kcal/kg/day for girls. By 7 years, it decreased to 82 (18) kcal/kg/day for boys and 73 (22) kcal/kg/day for girls. Between 2 to 4 years of age the energy intake of studied children were slightly lower than the Australian and Finnish children, but the protein intake was higher. Percentage of fat contributing to total daily energy intake was lower throughout at a level of 30%. Such differences in diet reflect a lower consumption of milk fat, higher consumption of meat and lower level of physical activity in Hong Kong children. Intakes of calcium, iron and vitamin C all reached 60% or above of US recommended daily allowance.

Conclusions: The smaller body build of Chinese compared to Caucasians cannot be explained by dietary differences. The diet of Hong Kong children is changing to one which is more Westernized with a higher consumption of animal products.
Nesting biology of the stem‐nesting waspPsenulus interstitialisCameron (Hymenoptera: Crabronidae: Pemphredoninae) on Magnetic Island, Queensland
Authors: Matthews Robert W
Published: July 2002

Psenulus interstitialisconstructed nests of up to 10 cells in bamboo internodes on Magnetic Island, Queensland. Prey represented five families of Auchenorryncha, primarily late‐instar nymphs. Fully provisioned cells held 9–13 prey. Development required about 30 days, and the reared sex ratio was male biased at 2:1. There are probably several generations a year at this latitude. The three species of chalcidoid parasitoids reared,Leucospis giraultiBouček,Eupelmophotismus pulcher(Girault) andCalosotasp., all attacked late‐larval or early pupal stages. Additional mortality was caused by a species ofPyemotesmite and an unidentified fungus. This is the first biological information for any Australian species ofPsenulus.
Modifiable risk factors for Type 2 diabetes mellitus in a peri‐urban community in South Africa
Authors: Levitt N. S. , Steyn K. , Lambert E. V. , Reagon G , Lombard C. J. , Fourie J. M. , Rossouw K. , Hoffman M.
Published: July 2002

AimsTo investigate the prevalence of Type 2 diabetes mellitus (DM) and its risk factors in a working class peri‐urban community in South Africa.

MethodsA cross‐sectional descriptive study was conducted in 1996, where all persons aged 15 years and older, who were resident in randomly selected houses in Mamre, 55 km from the centre of Cape Town, were sampled. Subjects underwent a 75‐g oral glucose tolerance test. Socio‐demographic and anthropometric data were obtained and physical activity was assessed using a 7‐day activity recall questionnaire. The 1985 WHO criteria were used to define diabetes.

ResultsThe response rate was 64.5% (n = 974). The participants comprised 56% women, 44% men, mean age 37.6 (range 15–86) years. The crude prevalence of Type 2 DM was 7.1% and impaired glucose tolerance (IGT) 8.0%. The age‐adjusted prevalence of Type 2 DM was 10.8% (95% confidence interval (CI) 8.2–13.5%) and IGT 10.2% (95% CI 7.7–12.8%). Regression analysis indicated that age (risk ratio (RR) 7.40, 95% CI 3.45–15.86), waist circumference (RR 4.53, 95% CI 2.04–10.05), low total energy expenditure (RR 1.75, 95% CI 1.07–2.56) and family history of diabetes (RR 2.31, 95% CI 1.42–3.77) were independent risk factors for Type 2 DM, while sex, obesity and regular alcohol consumption were not.

ConclusionsThis previously unstudied community has an intermediate prevalence on the international scale of Type 2 DM, which is linked to potentially modifiable risk factors.
The North‐West Diabetes Foot Care Study: incidence of, and risk factors for, new diabetic foot ulceration in a community‐based patient cohort
Authors: Abbott C. A. , Carrington A. L. , Ashe H. , Bath S. , Every L. C. , Griffiths J. , Hann A. W. , Hussein A. , Jackson N. , Johnson K. E. , Ryder C. H. , Torkington R. , Van Ross E. R. E. , Whalley A. M. , Widdows P. , Williamson S. , Boulton A. J. M.
Published: July 2002

Aims To determine the incidence of, and clinically relevant risk factors for, new foot ulceration in a large cohort of diabetic patients in the community healthcare setting.

Methods Diabetic patients (n = 9710) underwent foot screening in six districts of North‐west England in various healthcare settings. All were assessed at baseline for demographic information, medical and social history, neuropathy symptom score, neuropathy disability score, cutaneous pressure perception (insensitivity to the 10 g monofilament), foot deformities, and peripheral pulses. Two years later, patients were followed up via postal questionnaire to determine the incidence of new foot ulcers. Cox’s proportional hazards regression analysis was used to determine the independent, relative risk of baseline variables for new foot ulceration.

Results New foot ulcers occurred in 291/6613 patients who completed and returned their 2‐year follow‐up questionnaire (2.2% average annual incidence). The following factors were independently related to new foot ulcer risk: ulcer present at baseline (relative risk (95% confidence interval)) 5.32 (3.71–7.64), past history of ulcer 3.05 (2.16–4.31), abnormal neuropathy disability score (≥ 6/10) 2.32 (1.61–3.35), any previous podiatry attendance 2.19 (1.50–3.20), insensitivity to the 10 g monofilament 1.80 (1.36–2.39), reduced pulses 1.80 (1.40–2.32), foot deformities 1.57 (1.22–2.02), abnormal ankle reflexes 1.55 (1.01–2.36) and age 0.99 (0.98–1.00).

Conclusions More than 2% of community‐based diabetic patients develop new foot ulcers each year. The neuropathy disability score, 10 g monofilament and palpation of foot pulses are recommended as screening tools in general practice.
Spatiotemporal Dynamics of Endangered Species Hotspots in the United States
Authors: Rutledge Daniel T. , Lepczyk Christopher A. , Xie Jialong , Liu Jianguo
Published: July 2002

Abstract: Given limited resources, many researchers advocate focusing conservation efforts on hotspots, geographical areas with high numbers of species (i.e., richness), endemic species, rare or threatened species, and/or high levels of threat to species survival. The hotspot approach is an efficient and simple way to conserve species diversity, assuming that hotspots do not change over space or time. We tested whether hotspots change across space and time using a database of endangered and threatened species listed by the U.S. government from 1967 to 1999. We determined hotspots based on the cumulative set of species listed for three overlapping and successively longer time periods: 1967–1979, 1967–1989, and 1967–1999. We used minimum area complimentarity analysis, which selected the smallest set of areas (in our study, U.S. counties) needed to represent a chosen set of species. Over time, the number of endangered and threatened species in the United States increased from 76 in 1967 to 1123 in 1999. As the number of species increased over time, hotspots changed in two ways: the number of hotspots increased and the rank of hotspots shifted. Hotspots increased from 84 in 1979, to 166 in 1989, to 217 in 1999. Only 63 of these counties were designated as hotspots in all three periods. The remaining changes resulted from addition and deletion of counties as hotspots over time. Some counties were removed from the list or changed in relative rank from one time period to the next regardless of their rank. Counties added as hotspots could rank anywhere on the list, and they were not merely low‐ranking counties added to represent one or a few species. Therefore, hotspots serve as a useful tool for guiding conservation efforts but, given their spatiotemporal variability, do not represent a final solution.
Blood Pressure and Mortality Risk in Older People: Comparison Between African Americans and Whites
Authors: Blazer Dan G. , Landerman Lawrence R. , Hays Judith C. , Grady Tana A. , Havlik Richard , Corti Maria‐Chiara
Published: July 2002

OBJECTIVES: To determine the risk from hypertension for all‐cause mortality in a racially mixed sample of community‐dwelling older adults.

DESIGN: Baseline blood pressure was assessed between 1985 and 1986 in a sample of persons 65 years of age and older from five counties of the Piedmont of North Carolina (N = 4,162). All‐cause mortality was monitored annually over the subsequent 6 years as part of the Established Populations for Epidemiologic Studies of the Elderly (EPESE) sponsored by the National Institute on Aging.

SETTING: Eighteen percent of all respondents in the sample had a systolic blood pressure openface> 160 (17% for whites and 18% for African Americans) and 16% had a diastolic blood pressure openface> 90 (14% for whites and 20% for African Americans). During the 6 years of follow‐up, 29% of the sample died (with no difference in mortality rates between whites and African Americans).

PARTICIPANTS: 4,000 community‐dwelling people age 65 years and older; 1,846 were white and 2,154 were African American.

MEASUREMENTS: Systolic and diastolic blood pressure and all‐cause mortality.

RESULTS: Systolic blood pressure positively related to mortality during the 6 years of follow‐up (relative risk = 1.05). Among whites the relationship of diastolic pressure to mortality was nonlinear, with those at the upper and lower ends of the distribution at increased risk. Among African Americans, diastolic pressure was unrelated to mortality. The analyses were controlled for age; gender; education; body mass index (BMI); smoking history; taking a medication to manage blood pressure; a history of cancer, diabetes mellitus, heart attack, or stroke; poor subjective health; impaired functional status; and cognitive impairment.

CONCLUSIONS: The findings confirm that among older adults there is a significant relationship overall between systolic blood pressure and mortality over 6 years of follow‐up in both whites and African Americans. Diastolic pressure was a risk factor for whites only.
The development of the DEGRR: A scale to assess pain in young children with cancer
Authors: Gauvain‐Piquard Annie , Rodary Chantal , Rezvani Ali , Serbouti Saı̈d
Published: July 2002

The Gustave Roussy Child Pain Scale (Douleur Enfant Gustave Roussy, DEGRRScale) is a scale for grading prolonged pain in children aged 2–6 years with cancer. The scale comprised six behaviours specific to pain items, five psychomotor inertia items, and four anxiety items, with a total score ranging from 0 to 60. This work was designed to confirm the scale structure and to study its construct validity and convergent validity.

Our work was composed of two parts. In the first part of the study, 152 children with progressive cancer were scored by two nurses using the DEGRRscale, in a cross‐sectional design. And in the second part, 53 of these 152 children were video‐recorded. The tapes were assessed both by a panel of four pain specialists using a 0 to 7 Likert scale and by a nurse using DEGRRscale.

As for the 152 children, the mean of the total scores derived from the DEGRRis 20.2 (SD = 6.2). Both the degree of agreement between the nurses (the weightedκcoefficient) and the internal consistency of the scale (Cronbachαcoefficient = 0.90) were high, providing evidence of good reliability. Multivariate factor analyses showed a first factor of intensity of pain (51% of the total variance) and a second factor (14% of the total variance) which distinguishes the psychomotor inertia items from the items concerning voluntary expression of pain. Also, the results showed that psychomotor inertia items contribute to both factors and that it is an important sign of prolonged pain. Construct validity was strengthened by the absence of correlation between DEGRRscores and variables not related to pain, including fever, neutropenia and anaemia (indicative of poor medical condition) and the absence of parents’ visits (indicative of psychological distress).

Concerning the 53 video‐recorded children, the nurses’ DEGRRratings were strongly correlated with the specialists panel scores indicating a fairly good case for convergent validity.
Systematics of thin films formed by excimer laser ablation: Results on SmBa2Cu3O7
Authors: Neifeld R. A. , Gunapala S. , Liang C. , Shaheen S. A. , Croft M. , Price J. , Simons D. , Hill W. T.
Published: July 2002

Excimer laser ablation was used to prepare thin films from a bulk target of SmBa2Cu3O7. The systematic variation in film thickness, stoichiometry, and microstructure, as a function of laser fluence and angle from the target surface normal, was determined. We show that films which are stoichiometric over wide solid angles can be rapidly prepared from this material by use of high laser fluence. Films prepared from various Bi-Sr-Ca-Cu-O targets at high laser fluence also reproduce bulk stoichiometry. In contrast, films prepared by this technique from a YBa2Cu3O7 target are deficient in Ba and Cu for laser fluences required to produce compositional homogeneity over wide areas.
Electron mobilities exceeding 107 cm2/V s in modulation-doped GaAs
Authors: Pfeiffer Loren , West K. W. , Stormer H. L. , Baldwin K. W.
Published: July 2002

A modulation-doped Al0.35Ga0.65As/GaAs single interface structure with a 700 Å undoped setback grown by solid-source molecular beam epitaxy (MBE) shows a Hall mobility of 11.7×106 cm2/V s at a carrier density of 2.4×1011 electrons/cm2 measured in van der Pauw geometry after exposure to light at 0.35 K. This is the highest carrier mobility ever measured in a semiconductor. Similar Al0.32Ga0.68As/GaAs structures with 1000–2000 Å setbacks show Hall mobilities in the dark at 0.35 K as high as 4.9×106 cm2 /V s for carrier densities of 5.4×1010 electrons/cm2 and lower.
Van der Waals bonding of GaAs epitaxial liftoff films onto arbitrary substrates
Authors: Yablonovitch E. , Hwang D. M. , Gmitter T. J. , Florez L. T. , Harbison J. P.
Published: July 2002

Epitaxial liftoff is an alternative to lattice-mismatched heteroepitaxial growth. Multilayer AlxGa1−xAs epitaxial films are separated from their growth substrates by undercutting an AlAs release layer in HF acid (selectivity ≳108 for x≤0.4). The resulting AlxGa1−xAs films tend to bond by natural intermolecular surface forces to any smooth substrate (Van der Waals bonding). We have demonstrated GaAs thin-film bonding by surface tension forces onto Si, glass, sapphire, LiNbO3, InP, and diamond substrates, as well as self-bonding onto GaAs substrates. In transmission electron microscopy the substrate and thin-film atomic lattices can be simultaneously imaged, showing only a thin (20–100 Å) amorphous layer in between.
Polyaniline as a transparent electrode for polymer light-emitting diodes: Lower operating voltage and higher efficiency
Authors: Yang Y. , Heeger A. J.
Published: July 2002

We demonstrate that by using polyaniline (PANI) or a combination of (PANI) and indium/tin oxide (ITO) as the transparent anode of a polymer light-emitting diode with poly[2-methoxy-5-(2′-ethyl- hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), as the active layer, device performance can be significantly improved. The operating voltage can be reduced by ∼30%–50% and the quantum efficiency can be increased by ∼30%–40% with respect to the devices using ITO alone as the hole-injecting anode. The barrier height at the PANI/MEH-PPV interface is estimated to be ∼0.08–0.12 eV, approximately half of that at the ITO/MEH-PPV interface.
Hydrogen sulfide sensor based on tin oxide deposited by spray pyrolysis and microwave plasma chemical vapor deposition
Authors: Manorama Sunkara , Devi G. Sarala , Rao V. J.
Published: July 2002

Spray pyrolysis and microwave plasma chemical vapor deposition techniques have been employed successfully for the deposition of CuO impregnated SnO2 films suitable for sensing hydrogen sulfide and methyl mercaptan. The observed change in conductivity of these films upon exposure to H2S gas in air has been explained on the basis of the band theory of solids.
Strain effects on the intervalence-subband normal-incidence absorption in ap-type InGaAs/InP quantum well
Authors: Stoklitsky S. A. , Holtz P. O. , Monemar B. , Zhao Q. X. , Lundström T.
Published: July 2002

The lattice mismatch (strain) effects on the normal-incidence infrared absorption in In1−xGaxAs/InP quantum wells is investigated systematically, both tensile (x≳0.47) and compressive (x<0.47) cases being considered. The difference of the valence-band parameters in the well and barrier materials is taken into account in the dipole matrix element calculations. For a constant hole sheet density, the compressive stress is found to enhance the infrared absorption substantially in the frequency range around 100 meV, corresponding to the H1–H3 type transitions, and the tensile stress is shown to decrease the normal-incidence intervalence-subband absorption.
Useful procedure in least squares, and tests of some equations for thermistors
Authors: Hoge Harold J.
Published: July 2002

When an equation is to be fitted to a set of data by least squares, it is often much more difficult to minimize the sum of squares of the residuals of the independent variable than those of the dependent variable. This article presents a procedure that greatly simplifies the fitting of the independent variable. Given y=f(x) it permits not only y and x, but also y2 , x2 , ln y, ln x, and similar simple functions to be fitted almost as easily as y. It is shown that the residuals change significantly when the quantity fitted is changed. Five different equations representing the R(T) relations of thermistors are examined and their ΔT residuals for the same set of experimental data are shown; three of these fit the data more closely than the often-used cubic equation in ln R.
Noise and the Kelvin method
Authors: Baikie I. D. , Mackenzie S. , Estrup P. J. Z. , Meyer J. A.
Published: July 2002

The Kelvin probe, used to measure changes in work function (wf), has proved particularly useful as a UHV surface analysis technique, having applications in the study of thin films, adsorption kinetics, surface photovoltage spectroscopy, surface topographies, etc. However the Kelvin circuit is plagued by noise problems, which are considerably enhanced by long connecting wires and the nonideal UHV environment. Careful shielding is essential in order to improve the signal-to-noise (S/N) ratio, especially at backing potentials close to the null condition. Although lock-in-amplifier (LIA) based automatic compensation systems are available they operate on low signal levels and are prone to electromagnetic pickup from the driving element and mechanical instabilities of the vibrating capacitor. We discuss the general noise spectrum and describe an alternative ‘‘off-null’’ approach utilizing a data-acquisition-system (DAS) based measuring system that features an active suspension system (ASS), automatic set-up, and software elimination of driver talkover. This system has applications where very high resolution (<0.1 meV) is required, or if low S/N ratios caused by reduced probe dimensions or a high noise background would otherwise prejudice the measurement.
Parameter estimations for measurements of thermal transport properties with the hot disk thermal constants analyzer
Authors: Bohac Vlastimil , Gustavsson Mattias K. , Kubicar Ludovit , Gustafsson Silas E.
Published: July 2002

The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly(methylmethacrylate) and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory.
Crystal structure and Raman scattering in Zn1−xMgxSe alloys
Authors: Huang Daming , Jin Caixia , Wang Donghong , Liu Xiaohan , Wang Jie , Wang Xun
Published: July 2002

Zn1−xMgxSe alloys have been grown on (100) GaAs substrates by molecular beam epitaxy. Their crystal structures are determined form x-ray diffraction spectra and are found to be zinc blende, rocksalt, and their mixture for x<0.5, x=1, and x∼0.6, respectively. The Raman spectra are measured and show two-mode behavior for those alloys with zinc blende structure. The long-wavelength frequencies of ZnSe- and MgSe-like optical phonons are determined and the results can be expressed as linear functions of x. The first-order Raman spectra are observed for MgSe and Mg-rich Zn1−xMgxSe alloys with rocksalt structure. Those Raman spectra are attributed to the scattering from optical phonons activated by disorders and impurities, and their line shapes represent the phonon density of states.
Colloidal chemical synthesis and characterization of InAs nanocrystal quantum dots
Authors: Guzelian A. A. , Banin U. , Kadavanich A. V. , Peng X. , Alivisatos A. P.
Published: July 2002

InAs nanocrystal quantum dots have been prepared via colloidal chemical synthesis using the reaction of InCl3 and As[Si(CH3)3]3. Sizes ranging from 25 to 60 Å in diameter are produced and isolated with size distributions of ±10%–15% in diameter. The nanocrystals are crystalline and generally spherical with surfaces passivated by trioctylphosphine giving them solubility in common organic solvents. The dots have been structurally characterized by transmission electron microscopy (TEM) and powder x-ray diffraction (XRD) and the optical absorption and emission have been examined. Quantum confinement effects are evident with absorption onsets well to the blue of the bulk band gap and size dependent absorption and emission features. The emission is dominated by band edge luminescence. These quantum dots are particularly interesting as they provide an opportunity to make important comparisons with comparably sized InAs quantum dots synthesized by molecular beam epitaxy techniques.
Electron microscopic and optical investigations of the indium distribution in GaAs capped InxGa1−xAs islands
Authors: Woggon U. , Langbein W. , Hvam J. M. , Rosenauer A. , Remmele T. , Gerthsen D.
Published: July 2002

Results from a structural and optical analysis of buried InxGa1−xAs islands carried out after the process of GaAs overgrowth are presented. It is found that during the growth process, the indium concentration profile changes and the thickness of the wetting layer emanating from a Stranski–Krastanow growth mode grows significantly. Quantum dots are formed due to strong gradients in the indium concentration, which is demonstrated by photoluminescence and excitation spectroscopy of the buried InInxGa1−xAs islands.
Degradation processes at the cathode/organic interface in organic light emitting devices with Mg:Ag cathodes
Authors: Aziz Hany , Popovic Zoran , Tripp Carl P. , Hu Nan-Xing , Hor Ah-Mee , Xu Gu
Published: July 2002

We report electroluminescence degradation studies on tris(8-hydroxyquinoline) aluminum (Alq3)-based organic light emitting devices (OLEDs) with Mg:Ag cathodes in ambient conditions. The nonemissive spots in the OLEDs are studied via optical and fluorescence microscopy and via microscopic infrared spectroscopy. Studies reveal that a majority of the nonemissive spots are caused by the growth of Mg(OH)2 sites at the Alq3/Mg:Ag interface, associated with local degradation of the Alq3 layer. In addition, the growth of elevated cathode bubbles, which also lead to nonemissive spots, is found to be caused by gas evolution from the galvanic corrosion of the Mg/Ag couple as well as from the electrolysis of absorbed moisture.
CoPt/Ag nanocomposites for high density recording media
Authors: Stavroyiannis S. , Panagiotopoulos I. , Niarchos D. , Christodoulides J. A. , Zhang Y. , Hadjipanayis G. C.
Published: July 2002

Nanocomposite CoPt/Ag films have been successfully fabricated and their microstructural and magnetic properties have been investigated for potential applications in magnetic recording media. This was done by first making sputtered CoPt/Ag multilayers with the face-centered cubic (fcc) structure which is magnetically soft and then annealing the multilayers to transform the fcc phase to the highly anisotropic face-centered tetragonal phase (fct) which is magnetically hard. The final nanocomposite structure consists of CoPt nanoparticles with the hard fct phase embedded in a fcc Ag matrix. Large values of coercivity in the range of 1–17 kOe were achieved with grain sizes in the range of 7–100 nm, respectively.
2–2 piezoelectric composites with high density and fine scale fabricated by interdigital pair bonding
Authors: Liu Ruibin , Harasiewicz Kasia A. , Knapik D. , Freeman N. A. , Stuart Foster F.
Published: July 2002

Interdigital pair bonding (IPB) is proposed as a means to fabricate piezoelectric composites used for ultrasonic transducers and arrays for medical imaging and nondestructive evaluation, especially in the high frequency range. This letter presents experimental results of prototype 2–2 piezoelectric composites made by IPB. Two composites with different lateral dimensions were fabricated using 70 and 40 μm thickness dicing saw blades. The widths of ceramic stripe and epoxy kerf for composite A are 53 and 12 μm, respectively, and are 36 and 4 μm for composite B. The thickness mode and lateral modes for both composites were investigated by impedance spectrum analysis. The kt for both samples is 0.64. The current designs permit the fabrication of composites for transducers operated up to approximately 50 MHz using conventional dicing saw blades. The extension of IPB to fabrication of 1–3 composite is discussed.
Hydrogen storage in single-walled carbon nanotubes
Authors: Lee Seung Mi , Lee Young Hee
Published: July 2002

We perform density-functional calculations to search for hydrogen adsorption sites and predict maximum storage capacity in single-walled carbon nanotubes. We find two chemisorption sites at top sites of the exterior and the interior of the tube wall. We further find that a form of H2 molecule can exist in an empty space inside nanotubes. The storage capacity of hydrogen in an empty space increases linearly with tube diameter. The maximum storage capacity is limited by the repulsive energies between H2 molecules inside nanotubes and those between H2 molecules and the tube wall. We predict that hydrogen storage capacity in (10,10) nanotube can exceed 14 wt % (160 kg H2/m3).
Nanoscale pattern formation in Pt thin films due to ion-beam-induced dewetting
Authors: Hu Xiaoyuan , Cahill David G. , Averback Robert S.
Published: July 2002

Atomic force microscopy is used to characterize the evolution of film morphology produced by heavy-ion bombardment. Pt films, 3 and 5 nm thick, are deposited on SiO2 substrates and subsequently bombarded by 800 keV Kr+. Ion doses of >2×1014 initiate pattern formation and the dewetting of Pt films from the substrate. The film morphology becomes increasingly disconnected with increasing dose; at the highest doses, (∼2×1016 cm−2), isolated nanoparticles are formed with a uniform spacing. The results are explained by the nucleation of bare substrate patches and subsequent coarsening of the morphology by the molten zones created by individual Kr+ impacts.
Electrical and thermal transport properties of magnetically aligned single wall carbon nanotube films
Authors: Hone J. , Llaguno M. C. , Nemes N. M. , Johnson A. T. , Fischer J. E. , Walters D. A. , Casavant M. J. , Schmidt J. , Smalley R. E.
Published: July 2002

Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite.
Cluster polarization of Cd2Nb2O7 compound
Authors: Ang Chen , Cross L. E. , Guo Ruyan , Bhalla A. S.
Published: July 2002

The direct-current (dc) electric-field dependence of dielectric constant around paraelectric–ferroelectric transition in Cd2Nb2O7 has been studied. The results show significant suppression of the dielectric constant by the application of dc bias. The electric-field dependence of the dielectric constant at the temperature around paraelectric–ferroelectric phase transition can be well described by the modified Devenshire relation including a cluster term, i.e., ε(E)=ε1−ε2E2+ε3E4+(Px/ε0)[cosh(Ex)]−2. The fit parameters indicate that the polar-cluster carries polarization P=∼0.5–2.5 mC/m2 with the cluster size of L=∼11–15 nm.
Ultrafast polarized fluorescence dynamics in an organic dendrimer
Authors: Varnavski O. , Menkir G. , Goodson T. , Burn P. L.
Published: July 2002

The excited state relaxation processes of a nitrogen-cored distyrylbenzene-stilbene (A-DSB) dendrimers and the analogous linear model compound (bis-MSB) were investigated by polarized fluorescence upconversion spectroscopy. The fluorescence anisotropy (FA) of A-DSB was found to decay to a value close to zero in less than 200 fs after excitation. For the model compound bis-MSB the FA initial value was close to 0.4 and showed a relatively slow decay (82 ps) corresponding to the overall rotational diffusion of the molecule. The results are interpreted in terms of fast transition dipole reorientation during relaxation of the excited states of the branched molecules.
Back illuminated AlGaN solar-blind photodetectors
Authors: Lambert D. J. H. , Wong M. M. , Chowdhury U. , Collins C. , Li T. , Kwon H. K. , Shelton B. S. , Zhu T. G. , Campbell J. C. , Dupuis R. D.
Published: July 2002

We report the growth, fabrication, and characterization of AlxGa1−xN (0⩽x⩽0.60) heteroepitaxial back-illuminated solar-blind p-i-n photodiodes on (0001) sapphire substrates. The group III-nitride heteroepitaxial layers are grown by low-pressure metalorganic chemical vapor deposition on double polished sapphire substrates using various growth conditions. The back-illuminated devices exhibit very low dark current densities. Furthermore, they exhibit external quantum efficiencies up to 35% at the peak of the photoresponse (λ∼280 nm). Improvements were made to the growth technique in order to achieve crack-free Al0.4Ga0.6N active regions on a thick Al0.6Ga0.4N window layer and to obtain activated p-type Al0.4Ga0.6N layers.
Stability of the interface between indium-tin-oxide and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) in polymer light-emitting diodes
Authors: de Jong M. P. , van IJzendoorn L. J. , de Voigt M. J. A.
Published: July 2002

A cause for degradation of polymer light-emitting diodes is the oxidation of the polymer by oxygen diffusing out of the indium-tin-oxide (ITO) anode. This problem can be solved by the introduction of an organic hole-injecting film, poly-(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS), between the ITO and the emissive polymer. Indeed, a dramatic improvement of the lifetime and also the luminous efficiency has been observed. However, our Rutherford backscattering (RBS) studies show that the ITO/PEDOT:PSS interface is not stable. In as prepared glass/ITO/PEDOT:PSS samples 0.02 at. % indium was found in the PEDOT:PSS film. Annealing in a nitrogen atmosphere at 100 °C during 2500 h increased the indium concentration to 0.2 at. %. Upon exposure to air much faster degradation of the ITO/PEDOT:PSS interface was observed; after several days in air the amount of indium reached a saturation concentration of 1.2 at. %. The degradation of the interface can be explained by etching of the ITO due to the strong acidic nature of PEDOT:PSS.
Low-cost optical instrumentation for biomedical measurements
Authors: Kostov Yordan , Rao Govind
Published: July 2002

Low-cost instruments for measurement in medicine, biotechnology, and environmental monitoring are presented. Recent developments in optoelectronic technology enable practical compact designs. This article presents the available types of light emitters, detectors, and wavelength selection components that are used in low-cost instruments. The main spectroscopic techniques (absorption, reflectance, luminescence intensity, lifetime, and polarization, evanescent wave and surface plasmon resonance) that are used with these instruments are described. Numerous examples of devices for a broad variety of biomedical measurements are presented.
Growth model of bamboo-shaped carbon nanotubes by thermal chemical vapor deposition
Authors: Lee Cheol Jin , Park Jeunghee
Published: July 2002

Vertically aligned carbon nanotubes were grown on iron-deposited silicon oxide substrate by thermal chemical vapor deposition of acetylene. The carbon nanotubes have no encapsulated iron particles at the closed tip and a bamboo structure in which the curvature of compartment layers is directed to the tip. A base growth model is suggested for the bamboo-shaped carbon nanotubes grown under our experimental conditions.