bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of systemic factors on pre-existing intimal hyperplasia and their effect on the outcome of infrainguinal arterial reconstruction with vein
Authors: Beattie D K , Sian M , Greenhalgh R M , Davies A H
Published: July 2002

Background

The association between raised levels of homocysteine, fibrinogen and lipoprotein (a), and the presence of pre-existing intimal hyperplasia (IH) in vein has not been assessed. The positive association between such hyperplasia and graft failure following infrainguinal arterial reconstruction, and between lipoprotein (a) and graft failure, is disputed. The influence of homocysteine on outcome has not been investigated prospectively.

Methods

Fifty-seven patients (63 grafts) undergoing infrainguinal arterial reconstruction with saphenous vein were studied. Homocysteine, fibrinogen and lipoprotein (a) levels were measured, and a vein biopsy was taken at operation. Patients underwent graft surveillance and outcome at 12 months was determined.

Results

Fifty-seven per cent of patients had hyperhomocysteinaemia. Patients with pre-existing IH had significantly higher homocysteine levels. There was no association between homocysteine and outcome, or between fibrinogen and pre-existing IH or outcome. Lipoprotein (a) levels were significantly lower in patients with pre-existing disease, and were lower, but not significantly, in those whose grafts failed. The correlation between pre-existing IH and vein graft failure was highly significant.

Conclusion

Hyperhomocysteinaemia is associated with peripheral vascular disease and the development of pre-existing IH in vein, which itself is associated with vein graft failure.
Putting your heart into walking further
Authors: Nawaz S , Wilkinson C H , Walker R D , Pockley A G , Wood R F M
Published: July 2002

Background

Leg exercise training improves maximum walking distance (MWD) in claudicants, but it also causes neutrophil activation and may, as a consequence, elicit damage to the coronary circulation. It was hypothesized that symptomatic improvements induced by exercise programmes result from systemic cardiovascular effects rather than localized changes in the lower limb. The aim of this study was to develop an upper body training programme that would enhance cardiovascular fitness while avoiding potentially damaging inflammatory responses.

Methods

Sixty-three stable claudicants were recruited; all underwent arm and leg ergometry exercise assessments. Peripheral blood was obtained before and 1 h after exercise. The intensity (median channel of fluorescence; MCF) of neutrophil CD11b expression (as a measure of neutrophil activation) was determined using whole blood flow cytometry. Patients were randomized to an arm (n = 24) or leg (n = 24) training programme structured to achieve identical heart rate changes. Training involved two supervised sessions per week for 6 weeks. Controls undertook no exercise (n = 15). The MWD was determined at the beginning and end of training.

Results

Arm exercise had no effect on neutrophil expression of CD11b, whereas expression was significantly increased by leg exercise (Table). Arm and leg training increased the maximum work rate from 75 to 100 W (P = 0·004; Wilcoxon test) and there was a concomitant decrease in the submaximal heart rate (arm group 150 to 131 beats min−1; leg group 155 to 136 beats min−1; P = 0·002). These cardiovascular changes were accompanied by an increased MWD (Table). There were no changes in the control group.

Conclusion

Upper body training can increase walking distance in claudicants without neutrophil activation and maximizing cardiovascular fitness appears to be the key to improving symptoms in these patients.
Use of superficial femoral/popliteal veins for suprainguinal arterial reconstruction in the presence of infection
Authors: Gibbons C P , Ferguson C J , Edwards K , Osman H Y
Published: July 2002

Background

Mycotic aneurysms and graft infection in the aortoiliac region provide formidable technical challenges and carry a high morbidity and mortality rate with either of the standard techniques of in situ antibiotic-bonded prosthetic reconstruction or extra-anatomical bypass. This study investigated the use of autologous superficial femoral/popliteal vein (SFPV) for arterial reconstruction in ten patients with arterial or graft infections of the aortoiliac region.

Methods

Two patients with mycotic aortic aneurysms and four with aortic graft infections underwent aortoiliac replacement with SFPV after thorough debridement and/or excision of infected graft material. Three infected femorofemoral grafts were replaced in situ with reversed SFPV and an infected axillofemoral graft was converted to an iliofemoral reversed SFPV graft. All patients received appropriate antibiotic therapy and were followed by regular postoperative duplex imaging. Preoperative femoral vein duplex imaging was performed in eight of ten patients to confirm suitability as a graft.

Results

Nine of the ten patients survived with a functioning graft and without limb loss or evidence of infection at 3–30 months. One patient died from myocardial infarction after operation. Two patients had minor swelling of one leg. Three patients required angioplasty of anastomotic stenoses detected by duplex surveillance at 6 weeks.

Conclusion

SFPV is an excellent conduit for aortic or iliac reconstruction in the presence of infection. Duplex imaging is useful to confirm the suitability of deep veins for use as a graft and for postoperative surveillance.
Larval debridement therapy: a cost-effective alternative to hydrogel in necrotic venous ulcers: a randomized trial
Authors: Wayman J , Walker A , Sowinski A , Walker M A
Published: July 2002

Background

Evidence for the effectiveness of larval debridement therapy (LDT) in necrotic wounds has hitherto been the anecdotal results of enthusiasts. The aim of this study was to compare the cost and effectiveness of LDT with standard hydrogel treatment of necrotic venous ulcers.

Methods

Patients with sloughy venous ulcers were randomized to either standard hydrogel dressings (Intrasite gel) (group 1) or LDT (group 2). All patients were reviewed every 72 h until effective debridement had occurred, for a maximum of 1 month. The outcome measure used for effectiveness was whether or not desloughing occurred and time to deslough. The measures of cost were the cost of nursing time, dressing costs, and costs of larvae and hydrogel required to achieve healing in 1 month's treatment.

Results

Twelve patients were randomized. Ulcers in all patients receiving LDT (group 2) desloughed within two applications of larva therapy. All of these patients were treated subsequently with four-layer bandaging and all healed within 4 months. Ulcers in only two patients in group 1 desloughed completely within 1 month. One of the patients in whom hydrogel had failed at 1 month was changed to LDT and the ulcer desloughed with one application. Taking into account the cost of a vial of larvae (£58), the overall median cost of treatment in group 1 was greater than that in group 2 (£136·23 (range 63·89–319·30) versus £78·64 (range 73·49–£92·36)).

Conclusion

LDT is more effective and significantly less expensive than hydrogel in the debridement of sloughy venous ulcers. While a larger randomized controlled study should be performed to confirm these observations, LDT appears to be a cost-effective alternative to hydrogel.
Carotid artery plaque instability is associated with expression of matrix metalloproteinases 2 and 12
Authors: Senaratne J W B , Hands L J , Collin J , Morris P J , Green F R
Published: July 2002

Background

There has been considerable interest in the role of matrix metalloproteinases (MMPs) in atherosclerotic plaque rupture and the possible use of MMP inhibitors in stabilization of plaques. Collagenolytic MMPs, athough important in causing plaque instability, may not be a feasible target, as interfering with collagen turnover in tightly stenosed lesions may induce occlusion. This study investigated the expression of elastinolytic MMP-2, MMP-9 and MMP-12 in carotid plaques in relation to plaque stability.

Methods

Plaques removed at surgery were examined immediately and classified as unstable (plaques with ulceration, rupture, thrombosis; n = 34) or stable (plaques with or without calcification without the above complications; n = 26). MMP expression was studied by immunohistochemistry (after saponin permeabilization) and computed image analysis of whole plaques to obtain percentage staining.

Results

Expression of all three MMPs was significantly higher in unstable plaques.

In a logistic regression model, only MMP-2 (P = 0·04) and MMP-12 (P = 0·0018) expression was shown to be significantly greater in unstable plaques.

Conclusion

Although MMP-2, MMP-9 and MMP-12 are all expressed in higher amounts in unstable plaques, MMP-12 was shown to be the most significantly associated with plaque instability, followed by MMP-2. These findings may be useful in directing efforts to develop specific inhibitors, particularly to MMP-12 which has elastin and not collagen as its main substrate.
Initial management of cerebrovascular disease by general practitioners
Authors: Gibbs R G J , Todd J C , Newson R , Greenhalgh R M , Davies A H
Published: July 2002

Background

The aim of this study was to determine the primary management of patients presenting with a new diagnosis of transient ischaemic attack (TIA) or stroke by general practitioners and to establish whether practice was uniform across the UK, and to determine whether initial management influenced the performance of carotid endarterectomy (CEA) across the health regions of the UK.

Methods

Information on regional reporting of new cases of TIA and stroke between 1992 and 1996 was obtained from the General Practice Research Database, a database of six million patients from 450 practices. Analysis of data from the primary care database and routine data sources was undertaken. Main outcome measures were incidence of TIA and stroke, rates of referral for specialist opinion, prescription of antiplatelet agents and rates of CEA.

Results

There were twofold differences (P < 0·00005, χ2 test) in the incidence of cerebrovascular disease between Regional Health Authorities (RHAs) between the years 1992 and 1996 and also for each year. Mean stroke incidence per annum was 143 per 100 000 and TIA incidence 183 per 100 000. Yorkshire had the highest incidence at 170 (stroke) and 206 (TIA) per 100 000 of the population compared with 95 and 98 per 100 000 for Oxford. Some 37 per cent of new patients with stroke and 19 per cent of patients with TIA were referred for specialist opinion following initial diagnosis. These rates did not change over time. There was no positive correlation between disease incidence and referral rate; Yorkshire referred the least (14 per cent) and Oxford the most (26 per cent). The majority of referrals for TIA were made to general medicine (39 per cent); 6 per cent of patients were referred directly for surgical opinion. Mean prescription rate of antiplatelet medication over the time period was 17 per cent for patients with stroke and 35 per cent for those with TIA. Mean CEA rate for English RHAs for the time interval was 15·5 per 100 000. There was a positive correlation between the incidence of disease and rate of CEA, with the regions with the highest incidence of disease tending to perform the most CEAs.

Conclusion

The incidence of cerebrovascular disease varies significantly across health regions in the UK. There was no correlation between the regional incidence of disease and the number of patients referred for specialist opinion, but CEA rates were generally correlated with the regional difference in incidence of disease. The low referral rate may be a factor in the perceived underperformance of CEA in the UK and the low usage of antiplatelet medication is surprising.
Smoking and disease recurrence after operation for Crohn's disease
Authors: Yamamoto T , Keighley M R B
Published: July 2002

Background

There is increasing speculation about the role of smoking in the pathogenesis of inflammatory bowel diseases. The purpose of this study is to review the impact of smoking on disease recurrence after operation for Crohn's disease.

Methods

A Medline-based literature review (1966–1999) was carried out; ten studies examined the relationship between smoking and disease recurrence after operation.

Results

Approximately half of the patients were smokers at the time of operation. In most studies smoking significantly increased the risk of postoperative disease recurrence. Smokers had an approximately twofold increased risk of recurrence compared with non-smokers and the effect of smoking was dose dependent. The increased risk of recurrence among smokers was more prominent in women than in men, and a longer duration of smoking increased the risk of recurrence. Ex-smokers had a similar recurrence rate to non-smokers and giving up smoking soon after operation was associated with a lower probability of recurrence.

Conclusion

Smoking significantly increases the risk of recurrence of disease after operation for Crohn's disease, especially in women and heavy smokers. Encouraging patients to stop smoking is an important part of the management of Crohn's disease.
Pattern of recurrence following radical oesophagectomy with two-field lymphadenectomy
Authors: Dresner S M , Griffin S M
Published: July 2002

Background

Despite increasingly radical surgery for oesophageal cancer, many patients continue to develop recurrent disease. The aim of this study was to evaluate the pattern of failure following attempted curative oesophagectomy with two-field lymphadenectomy for adenocarcinoma and squamous cell carcinoma of the middle and lower third of the oesophagus.

Methods

A total of 176 consecutive patients discharged from hospital following R0 resection between 1 April 1990 and 31 December 1999 were followed for evidence of recurrence over a mean interval of 26 months.

Results

Adenocarcinoma was the predominant histological subtype (n = 113) compared with squamous cell carcinoma (n = 63). Sex and age distribution were similar for both histological subtypes (M: F ratio 2·5: 1, median age 64 (range 40–77) years). Overall 2- and 5-year survival rates were 54 and 31 per cent respectively. Some 85 patients (48 per cent) developed proven recurrence, of whom five are alive and 80 dead. The median time to recurrence was 11·7 (range 1·5–67) months, with a median survival thereafter of only 2·7 (0–25·9) months. The pattern of recurrence was locoregional in 27 per cent (mediastinal 21 per cent and cervical 6 per cent) and distant in 18 per cent (liver 6 per cent, bone 6 per cent, cerebral 2 per cent, peritoneal 2 per cent, lung 1 per cent, skin 1 per cent). There was no difference in the overall pattern of dissemination or timing of recurrence for either histological subtype. Over 50 per cent of all recurrences occurred within 12 months of surgery, with local, regional and distant recurrence occurring at a median of 11·9 (range 1.8–52), 11·0 (range 5–67) and 11·0 (1·5–58) months respectively.

Conclusion

The low incidence of cervical recurrence suggests that a more extensive ‘three-field’ lymphadenectomy is unlikely to improve survival rates. Better staging modalities are needed to identify patients who will have recurrence within 12 months of operation, so that they may be either entered into trials of multimodality treatment or offered non-surgical palliation.

British Journal of Surgery prize-winning paper, presented to the Association of Upper Gastrointestinal Surgeons of Great Britain and Ireland, London, UK, September 1999
Applied issues with predators and predation: editor’s introduction
Authors: Ormerod S. J.
Published: July 2002

The effects of predation are among the most pervasive in ecology. As parasitoids, parasites, grazers or top carnivores, predators have large influences on the distribution, density, dynamics and evolved traits of other organisms. Effects scale‐up to influence community attributes such as species coexistence and ecosystems processes such as production or trophic cascades.

 Increasingly, however, some of the largest predation issues fall clearly within the scope of applied ecology. They include instances where, due to their ecological attributes and trophic position: (i) predators are valuable to nature conservation, as biocontrol agents, as natural enemies, or as grazers used in rangeland or ecosystem management; (ii) natural or introduced predators are viewed negatively due to effects on conservation, agriculture, forestry, hunting or disease transmission; (iii) predators are affected by human activities such as resource exploitation, or from exposure to factors such as biomagnified pollutants and disturbance; (iv) predators are controversial because different groups view them as either desirable or undesirable.

 In all these cases, ecologists have a pivotal rôle in facilitating appropriate management. For valued predators, this involves developing sufficient ecological understanding to optimize habitat, increase prey abundance or to reinforce, establish or reintroduce desirable species. For predators considered undesirable, management can involve direct control. In other cases, predation and its consequences can be mitigated by deterrent, exclusion, supplementary feeding, habitat management to favour prey, predator swamping, or by compensating losses financially. These latter strategies are often used where predators are themselves considered too valuable to remove or control.

 This collection of seven papers illustrates many of these themes by examining contrasting aspects of the applied ecology of Eurasian lynx; by further probing the interaction between predatory birds and red grouse; by exploring the effects of weather on biocontrol; and by illustrating effects on plant species where grazing or seed predation play a dominant rôle.

 A key lesson from these and other recent papers in the Journal of Applied Ecology is that the successful management of predators depends invariably on understanding adequately the exact ecological context in which predator–prey interactions take place and in which problems arise. With predator‐related issues growing rather than diminishing, ecologists will need sufficient resources to maintain current research if they are to provide the understanding required to offer and evaluate sound management.
Cameleon calcium indicator reports cytoplasmic calcium dynamics in Arabidopsis guard cells
Authors: Allen Gethyn J. , Kwak June M. , Chu Sarah P. , Llopis Juan , Tsien Roger Y. , Harper Jeffrey F. , Schroeder Julian I.
Published: July 2002

Cytoplasmic free calcium ([Ca2+]cyt) acts as a stimulus‐induced second messenger in plant cells and multiple signal transduction pathways regulate [Ca2+]cyt in stomatal guard cells. Measuring [Ca2+]cyt in guard cells has previously required loading of calcium‐sensitive dyes using invasive and technically difficult micro‐injection techniques. To circumvent these problems, we have constitutively expressed the pH‐independent, green florescent protein‐based calcium indicator yellow cameleon 2.1 in Arabidopsis thaliana (Miyawaki et al. 1999; Proc. Natl. Acad. Sci. USA 96, 2135–2140). This yellow cameleon calcium indicator was expressed in guard cells and accumulated predominantly in the cytoplasm. Fluorescence ratio imaging of yellow cameleon 2.1 allowed time‐dependent measurements of [Ca2+]cyt in Arabidopsis guard cells. Application of extracellular calcium or the hormone abscisic acid (ABA) induced repetitive [Ca2+]cyt transients in guard cells. [Ca2+]cyt changes could be semi‐quantitatively determined following correction of the calibration procedure for chloroplast autofluorescence. Extracellular calcium induced repetitive [Ca2+]cyt transients with peak values of up to approximately 1.5 μM, whereas ABA‐induced [Ca2+]cyt transients had peak values up to approximately 0.6 μM. These values are similar to stimulus‐induced [Ca2+]cyt changes previously reported in plant cells using ratiometric dyes or aequorin. In some guard cells perfused with low extracellular KCl concentrations, spontaneous calcium transients were observed. As yellow cameleon 2.1 was expressed in all guard cells, [Ca2+]cyt was measured independently in the two guard cells of single stomates for the first time. ABA‐induced, calcium‐induced or spontaneous [Ca2+]cyt increases were not necessarily synchronized in the two guard cells. Overall, these data demonstrate that that GFP‐based cameleon calcium indicators are suitable to measure [Ca2+]cyt changes in guard cells and enable the pattern of [Ca2+]cyt dynamics to be measured with a high level of reproducibility in Arabidopsis cells. This technical advance in combination with cell biological and molecular genetic approaches will become an invaluable tool in the dissection of plant cell signal transduction pathways.
The Nature of Psychiatric Classification: Issues Beyond ICD-10 and DSM-IV
Authors: Jablensky Assen
Published: July 2002

Objective: The aim of this paper is to provide an overview of the methodological underpinnings of current classification systems in psychiatry, their impact on clinical and social practices, and likely scenarios for future development, as an introduction to a series of related articles in this issue.

Method: The method involved a selective literature review. Results: The role and significance of psychiatric classifications is placed in a broader social and cultural context; the ‘goodness of fit’ between ICD-10 and DSMIV on one hand, and clinical reality on the other hand, is examined; the nature of psy chiatric classification, compared to biological classifications, is discussed; and questions related to the impact of advances in neuroscience and genetics on psychiatric classification are raised for further discussion.

Conclusions: The introduction of explicit diagnostic criteria and rule-based classification, a major step for psychiatry, took place concurrently with the ascent to dominance of a biomedical paradigm and the synergistic effects of social and economic forces. This creates certain risks of conceptual closure of clinical psychiatry if phenomenology, intersubjectivity and the inherent historicism of key concepts about mental illness are ignored in practice, education and research.
The role of CTLA‐4 in the regulation of T cell immune responses
Authors: McCoy Kathy D , Le Gros Graham
Published: July 2002

Over the past few years a great deal of research has examined how T cell‐dependent immune responses are initiated and subsequently regulated. Ligation of the TCR with an antigenic peptide bound to an MHC protein on a professional APC provides the crucial antigen‐specific stimulus required for T cell activation. Interaction of CD28 with CD80 or CD86 molecules on APC initiates a costimulatory or second signal within the T cell which augments and sustains T cell activation initiated through the TCR. However, recently it has become clear that T cell immune responses are a result of a balance between stimulatory and inhibitory signals. Cytotoxic T lymphocyte‐associated molecule‐4 (CTLA‐4) is a cell surface molecule that is expressed nearly exclusively on CD4+ and CD8+ T cells. Investigation into the role of CTLA‐4 in the regulation of T cell immune responses has revealed that CTLA‐4 is a very important molecule involved in the maintenance of T cell homeostasis. In the present review, evidence for the proposed inhibitory role of CTLA‐4 is examined and a model suggesting a role for CTLA‐4 in both early and late stages of T cell activation is presented.
Processing of Wild‐Type and Mutant Familial Alzheimer’s Disease‐Associated Presenilin‐1 in Cultured Neurons
Authors: Weihl Conrad C. , Ghadge Ghanaysham D. , Miller Richard J. , Roos Raymond P.
Published: July 2002

Abstract: Mutations of presenilin (PS)‐1, an endoplasmic reticulum/Golgi transmembrane protein, have been associated with early‐onset familial Alzheimer’s disease (FAD). In mammalian brain, PS1 exists primarily as its processed fragments; however, the role of this cleavage event in PS1 function remains unclear. Although some investigators have shown that mutant PS1 processing is unaltered (with the exception of PS1‐ΔE9, which lacks the cleavage site) in stably transfected cells and PS1‐FAD transgenic mice, other investigators have reported altered FAD mutant PS1 and PS2 protein processing in transiently transfected cells and human FAD patients. The present study uses recombinant replication‐defective adenoviral vectors to transiently express wild‐type (WT) or mutant PS1 in various cells, including primary cultured hippocampal neurons. We show that in contrast to PS1‐WT, overexpression of mutant PS1 results in an increased ratio of mutant holoprotein to endoproteolytic products that is dependent on cell type and differentiation state. In addition, mutant PS1 overexpression leads to an increase in caspase‐type protease derived fragments above that seen with PS1‐WT overexpression. Furthermore, overexpression of at least one mutant significantly alters the processing of coexpressed PS1‐WT, suggesting that mutant PS1 may affect PS1‐WT function. These findings suggest that a defect in PS1 holoprotein stability may be a general defect seen in cells expressing mutant PS1, especially neuronal cells, and may play a critical role in the pathogenesis of FAD.
Life‐Sustaining Treatment and Assisted Death Choices in Depressed Older Patients
Authors: Blank Karen , Robison Julie , Doherty Erin , Prigerson Holly , Duffy James , Schwartz Harold I.
Published: July 2002

OBJECTIVES: The major purpose of this study was to examine the effect of depressed mood in older, medically ill, hospitalized patients on their preferences regarding life‐sustaining treatments, physician‐assisted suicide (PAS), and euthanasia and to determine the degree to which financial constraints affected their choices.

DESIGN: Cross‐sectional study.

SETTING: General medical hospital.

PARTICIPANTS: One hundred fifty‐eight medically hospitalized, nondemented patients age 60 or older, mean age 74.1 (range 60–94). The sample was divided, based on Center for Epidemiologic Studies‐Depression (CES‐D) scores, into a depressed group (n = 71) and a nondepressed control group.

MEASUREMENTS: Subjects underwent a structured interview evaluating their life‐sustaining treatment choices and whether they would accept or refuse PAS or euthanasia under a variety of hypothetical conditions. These choices were reevaluated with the introduction of financial impact. In addition, assessment included measures of depression, suicide, cognition, social support, functioning, and religiosity.

RESULTS: Depression was found to be highly associated with acceptance of PAS and euthanasia in most hypothetical clinical scenarios in addition to patients' current condition. Compared with nondepressed people, depressed respondents were 13 times as likely to accept PAS when considering their current condition (95% confidence interval [CI] 1.68–110.98), and over twice as likely to accept PAS when facing a hypothetical terminal illness or coma. Depression alone was weakly associated with life‐sustaining treatment choices but, when financial impact was introduced, significantly more depressed subjects refused treatment options they had previously desired than did nondepressed subjects. The presence of suicidal ideation, even passive ideation, was strongly predictive of life‐sustaining treatment refusals and increased interest in PAS and euthanasia. Depression's effect on acceptance of PAS was confirmed by logistic regression, which also showed that religious coping was significantly correlated with less interest in PAS in two hypothetical scenarios.

CONCLUSION: Depressed subjects and even subjects with subtle, passive suicidal ideation were markedly more interested in PAS and euthanasia than nondepressed subjects in hypothetical situations. Depressed subjects were also particularly vulnerable to rejecting treatments if financial consequences might have resulted.
The Effect of Irradiance on Carboxylating/Decarboxylating Enzymes and Fumarase Activities in Mesembryanthemum crystallinum L. Exposed to Salinity Stress
Authors: Miszalski Z. , Niewiadomska E. , Slesak I. , Lüttge U. , Kluge M. , Ratajczak R.
Published: July 2002

Abstract: In Mesembryanthemum crystallinum plants, treated for 9 days with 0.4 M NaCl at low light intensities (80 ‐ 90 or 95 ‐ 100 μE m‐2 s‐1; λ = 400 ‐ 700 nm), no day/night malate level differences (Δmalate) were detected. At high light (385 ‐ 400 μE m‐2 s‐1) strong stimulation of PEPC activity, accompanied by a Δmalate of 11.3 mM, demonstrated the presence of CAM metabolism. This indicates that, to evolve day/night differences in malate concentration, high light is required. Salt treatment at low light induces and increases the activity of NAD‐ and NADP‐malic enzymes by as much as 3.7‐ and 3.9‐fold, while at high light these values reach 6.4‐ and 17.7‐fold, respectively. The induction of activity of both malic enzymes and PEPC (phospoenolpyruvate carboxylase) take place before Δmalate is detectable. An increase in SOD (superoxide dismutase) was observed in plants cultivated at high light in both control and salt‐treated plants. However, in salt‐treated plants this effect was more pronounced. Carboxylating and decarboxylating enzymes seem to be induced by a combination of different signals, i.e., salt and light intensity. Plants performing CAM, after the decrease of activity of both the decarboxylating enzymes at the beginning of the light period, showed an increase in these enzymes in darkness when the malate pool reaches higher levels. In CAM plants the activity of fumarase (Krebs cycle) is much lower than that in C3 plants. The role of mitochondria in CAM plants is discussed.
Possible Mechanisms of Adaptive Leaf Senescence
Authors: Ono K. , Nishi Y. , Watanabe A. , Terashima I.
Published: July 2002

Abstract: Availability of nitrogen almost always limits plant growth. Therefore, efficient use of nitrogen is essential for the plants. In upright plants, especially when they form dense plant stands, old, lower leaves are shaded by young, upper leaves. Nitrogenous compounds in such shaded leaves are degraded and re‐allocated to the developing young, upper leaves. These processes raise efficiency of nitrogen use in photosynthetic production of the plant. For this to occur in the most effective way, leaves would need to sense their photosynthetic status in a plant and increase, maintain or decrease their photosynthetic capacity accordingly. Hypotheses that explain how a leaf can sense its photosynthetic status in the plant are reviewed. They include systems involving phytochrome, sugar‐sensing, or cytokinin. Our experimental results with Helianthus annuus and Phaseolus vulgaris plants, which were subject to various shading treatments, are examined in the light of these hypotheses. Our experimental results favoured the sugar‐sensing hypothesis: A leaf can sense demand of other plant parts for photosynthates produced by it and nitrogen abundance or deficiency by monitoring its sugar concentration. Problems that are to be challenged in the near future are also pointed out.
Work hardening and strain relaxation in strained-layer buffers
Authors: Dodson Brian W.
Published: July 2002

Fully relaxed buffer layers are of considerable importance for growth of high quality crystals on substrates having different lattice parameters. Recent experiments by Biefeld et al. [R. M. Biefeld, C. R. Hills, and S. R. Lee, J. Cryst. Growth (in press)] in the InAsSb system show that the degree of relaxation is considerably less than expected using conventional equilibrium models, but is more complete in continuously graded than in step-graded buffer layers. In the present letter, this observation is explained in terms of Taylor-type (dislocation interaction) work hardening.
Ultralow loss dielectric ribbon waveguide for millimeter/submillimeter waves
Authors: Yeh C. , Shimabukuro F. I. , Chu J.
Published: July 2002

By using high dielectric constant and low-loss dielectric material such as quartz, alumina, or sapphire and by specifically configuring the waveguide structure, we have succeeded in designing a waveguide for the millimeter/submillimeter wavelength range which yields an attenuation constant for the dominant mode that is more than 100 times below that for an equivalent circular dielectric rod with identical cross-sectional area. This waveguide takes the form of a thin dielectric ribbon surrounded by lossless dry air and possesses an attenuation constant as low as 20 dB/km. Analytical results on the attenuation constant and field extent of the dominant mode on this ribbon structure for several promising materials are given. Experiments have also been performed on ribbon guides made with rexolite. Excellent agreement was found between predicted and measured results.
Optical investigation of the band structure of InAs/GaAs short-period superlattices
Authors: Gerard J. M. , Marzin J. Y. , d’Anterroches C. , Soucail B. , Voisin P.
Published: July 2002

We discuss optical data obtained on (InAs/GaAs)-InGaAlAs multiquantum well structures grown by molecular beam epitaxy. The combined use of photoluminescence and photoluminescence excitation to study such structures is an efficient test of the quality of the highly strained InAs/GaAs ordered alloy, which is used as the well material. The electron effective mass and the lifting of the valence-band degeneracy in InAs/GaAs short-period superlattices are obtained experimentally for the first time.
Purely gain-coupled distributed feedback semiconductor lasers
Authors: Luo Y. , Nakano Y. , Tada K. , Inoue T. , Hosomatsu H. , Iwaoka H.
Published: July 2002

We propose a new distributed feedback (DFB) laser structure in which almost pure gain coupling can be embodied in principle, without sacrificing low threshold operation. An analysis of coupling coefficients has revealed the condition for canceling index-coupling component. Utilizing organometallic vapor phase epitaxy, we have fabricated GaAlAs/GaAs ridge waveguide distributed feedback lasers having this structure. Excellent single longitudinal mode oscillation independent of facet reflection has been obtained along with low threshold current. The single-mode spectrum has exhibited distinctive characters of purely gain-coupled DFB lasers.
Fabrication of atomically sharp tungsten tips
Authors: Ravi T. S. , Marcus R. B. , Gmitter T. , Busta H. H. , Niccum J. T.
Published: July 2002

Atomically sharp tungsten tips (<20 Å) have been grown on a silicon substrate by chemical vapor reaction of WF6 with atomically sharp preformed silicon tips. Transmission electron microscope studies show that a thickness of about 50 Å of tungsten is optimum for complete coverage of silicon while retaining atomic sharpness at the tip. The tungsten is nearly amorphous and is porous. These tips have potential applications in vacuum microelectronics as electron emitters and can also be used as electronic and magnetic microsensors and probes.
Absorption spectroscopy on Hg+ and excited Hg in Hg-Ar discharges
Authors: Wamsley R. C. , Lawler J. E. , Ingold J. H. , Bigio L. , Roberts V. D.
Published: July 2002

We describe an absorption spectroscopy experiment at 194 nm on Hg+, ground-state atomic mercury ions, and at visible wavelengths on Hg*, excited 63Po mercury atoms in Hg-Ar discharges. This experiment is used to map the absolute density of Hg+ and Hg* in the cathode region of Hg-Ar discharge lamps operated in the hot-cathode mode.
Selective low-pressure chemical vapor deposition of Si1−xGex alloys in a rapid thermal processor using dichlorosilane and germane
Authors: Zhong Yulin , Öztürk Mehmet C. , Grider Douglas T. , Wortman Jimmie J. , Littlejohn Michael A.
Published: July 2002

Low-pressure chemical vapor deposition of Si1−xGex alloys in a cold wall, lamp-heated rapid thermal processor was studied. Alloys were deposited using the reactive gases GeH4 and SiH2Cl2 in a hydrogen carrier gas. The depositions were performed at a total pressure of 2.5 Torr and at temperatures between 500 and 800 °C using GeH4:SiH2Cl2 ratios ranging from 0.025 to 1.00. Results showed that Si1−xGex alloys can be deposited selectively on silicon in SiO2. The selectivity is enhanced significantly by the addition of GeH4 in the gas stream. In this work, selective depositions were obtained when the GeH4:SiH2Cl2 gas flow ratio was greater than 0.2 regardless of the deposition temperature, corresponding to a Ge content of 20% or higher in the films as determined by Auger electron spectroscopy. An enhancement in the deposition rate was observed in agreement with earlier reports due to the addition of GeH4. The activation energy for deposition in the surface reaction limited regime varied from 20 to 30 kcal/mole with the gas flow ratios used in this study.
Coherent beams from high efficiency two-dimensional surface-emitting semiconductor laser arrays
Authors: Gourley P. L. , Warren M. E. , Hadley G. R. , Vawter G. A. , Brennan T. M. , Hammons B. E.
Published: July 2002

We have fabricated and operated large two-dimensional (2D) arrays of phase-locked surface-emitting semiconductor lasers. The arrays were fabricated by reactive ion beam etching of epitaxial Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs-AlGaAs quarter-wave mirrors. Different arrays corresponding to different pixel size (2–5 μm) and spacing (1–2 μm) were produced to investigate evanescent coupling between pixels. The arrays were photopumped so that the array size could be conveniently varied from 1×1, 2×2,... up to 20×20. Except for the 1×1 which emits a circular pattern, all arrays exhibit a well-defined four-lobed far-field pattern in agreement with our theoretical analysis of the optical modes which predicts domination by the 2D out-of-phase eigenmode. As a consequence this pattern can be understood with simple Fraunhofer diffraction theory. The angular spread of the lobes, determined by the periodicity of the array elements, is 10° for the array with element size/spacing of 4/1 μm. The widths of the lobes are 6.7° for the 2×2 and narrow to 3.2° with increasing number of pixels in the array. The array exhibits a sharp onset for lasing, operation on a single longitudinal mode, and a linewidth which narrows to ∼1 Å with increasing array size. The differential power efficiency is as high as 70%. These observations provide further impetus and guidance for the development of 2D laser diode arrays.
Passivation of n and p dopants in ion-implanted GaAs by a 2D+ plasma
Authors: Sadana D. K. , de Souza J. P. , Marshall E. D. , Baratte H. , Cardone F.
Published: July 2002

Strong n but weak p-carrier passivation was observed when Si- and Mg-implanted/annealed GaAs samples were exposed to a 2D plasma under identical conditions. Even though a discrete band of dislocation loops was present in both the samples, the 2D distribution in the two cases was remarkably different. In the Si-implanted sample the 2D followed the carrier distribution, whereas in the Mg-implanted sample it followed the distribution of dislocation loops. Phenomenological mechanisms of 2D interaction with dopants/dislocations in GaAs are postulated.
Efficient generation of 380 fs pulses of THz radiation by ultrafast laser pulse excitation of a biased metal-semiconductor interface
Authors: Katzenellenbogen N. , Grischkowsky D.
Published: July 2002

We have demonstrated a new method of generating pulses of freely propagating THz electromagnetic radiation. The resulting 380 fs pulses are the shortest directly measured THz pulses in free space to date and are more powerful than those generated by Hertzian dipoles or by resonant dipole antennas. Temporal features as short as 190 fs were observed on these THz radiation pulses and thereby, illustrate an ultrafast receiver response time.
Enhancement of the reflectivity of Mo/Si multilayer x-ray mirrors by thermal treatment
Authors: Kloidt A. , Nolting K. , Kleineberg U. , Schmiedeskamp B. , Heinzmann U. , Müller P. , Kühne M.
Published: July 2002

Thermal treatment of a Mo/Si multilayer stack enhances its reflectivity in the soft x-ray region. The multilayer x-ray mirrors are fabricated by electron beam evaporation in ultrahigh vacuum. In situ measurement of the reflectivity during the deposition allows thickness control and an observation of changes in quality of the boundaries. By heating the substrates during deposition we obtain a smoothing of the interfaces. This leads to x-ray mirrors with peak reflectivity around 50% for normal incident radiation of wavelengths between 130 and 140 Å.
Subpicosecond reflection switching of 10 μm radiation using semiconductor surfaces
Authors: Meyer J. , Elezzabi A. Y.
Published: July 2002

The electromagnetic wave equations for P-polarized 10 μm radiation in a semiconductor with a free-carrier density decreasing exponentially from the surface are solved numerically. The infrared (IR) reflectivity for Brewster angle incidence is then calculated as a function of free-carrier surface density n0. This reflectivity shows a minimum of zero just below and a sharp peak at the value where n0 reaches its critical value. The features are explained with the help of a simple model. The results suggest the feasibility of a subpicosecond IR reflection switch for the case when the surface is irradiated by a 100 fs visible laser pulse. Solutions to the diffusion equation show that ensuing reflectivity decreases to zero in times shorter than 0.5 ps.
High-energy product ThMn12 Sm-Fe-T and Sm-Fe permanent magnets synthesized as oriented sputtered films
Authors: Cadieu F. J. , Hegde H. , Navarathna A. , Rani R. , Chen K.
Published: July 2002

Binary SmFe12 and Sm(Fe,T)12 films, where T =Ti and V, crystallized into the ThMn12-type structure, have been synthesized as sputtered films such that the c axes of the crystallites are oriented perpendicular to the film plane. It has been possible to synthesize Sm(Fe,T)12 films which exhibit a very dominant (002) texture with intrinsic coercivities of 5 or more kOe. Such films exhibit flux densities 4πMs of more than 10 kG perpendicular to the film plane. No discernible columnar structure is exhibited so that the static energy product measured perpendicular to the film plane is nearly 21 MGOe.
Large anisotropy in optical properties of thin polyimide films of poly( p-phenylene biphenyltetracarboximide)
Authors: Herminghaus S. , Boese D. , Yoon D. Y. , Smith B. A.
Published: July 2002

Thin films ranging from 400 nm to 4 μm thickness of poly( p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by the optical waveguide spectroscopy. These polyimide films, most prominent for potential applications as the interlevel dielectrics in multilevel interconnect technologies owing to their low coefficients of thermal expansion and excellent thermal/mechanical properties, are found to exhibit an extraordinarily large anisotropy in the refractive index, with the measured in-plane refractive index n∥≂1.852 and the out-of-plane value n⊥≂1.612 at 632.8 nm wavelength, nearly independent of the film thickness. This large optical anisotropy indicates a very strong preference of polymer chains to orient along the film surface, and suggests a considerably larger (by ca. 27%) dielectric constant in the film plane than that along the film thickness. Moreover, there is some evidence for the existence of a very thin polyimide layer of slightly lower density and higher anisotropy adjacent to the substrate.
Observation of piezoelectric field induced carriers in AlGaAs/InGaAs strained-layer heterostructures
Authors: Li X. , Longenbach K. F. , Wang W. I.
Published: July 2002

Hall effect measurements of GaAs/AlGaAs/InGaAs strained-layer heterostructures grown on [100], [311], and [111] substrates have been performed and it is observed that the two-dimensional carrier density is a strong function of growth orientation. The observed changes in carrier density are in the range of 5×1011–1.6×1012 cm−2 and are consistent with the generation of piezoelectric fields in [N11] orientated strained-layer heterostructures. These strain-induced effects can be used to alter the threshold voltages of field-effect transistor or produce large carrier densities without modulation doping.
Poly(p-phenylenevinylene) light-emitting diodes: Enhanced electroluminescent efficiency through charge carrier confinement
Authors: Brown A. R. , Bradley D. D. C. , Burroughes J. H. , Friend R. H. , Greenham N. C. , Burn P. L. , Holmes A. B. , Kraft A.
Published: July 2002

We have fabricated light-emitting diodes with poly(p-phenylenevinylene) as the emissive layer, and with an electron-transporting layer formed from a solid state dispersion of 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole in poly(methyl methacrylate), placed between this and the negative electrode. These structures show typically a tenfold improvement in efficiency in the low-voltage regime and an eightfold improvement in the high-voltage regime over devices without the electron-transporting layer. Typical efficiencies are about 0.8% photons/electron. We consider that the role of the electron-transport layer is to confine holes to the emissive layer.
Quantized conductance of ballistic constrictions in InAs/AlSb quantum wells
Authors: Koester S. J. , Bolognesi C. R. , Rooks M. J. , Hu E. L. , Kroemer H.
Published: July 2002

Split-gate ballistic constrictions have been fabricated on InAs/AlSb quantum-well heterostructures. Sharp conductance steps of 2e2/h are observed at 4.2 K, while conductance plateaus persist up to 30 K. The sharp features and high temperature operation are made possible by the low effective mass (m*Γ= 0.023me) of InAs, and the closeness of the quantum well (20 nm) to the wafer surface.
Phase contrast and amplitude pseudoheterodyne interference near field scanning optical microscopy
Authors: Vaez-Iravani M. , Toledo-Crow R.
Published: July 2002

Pseudoheterodyne detection of sample light in near field optical microscopy is demonstrated in an actively stabilized Mach–Zehnder interferometer. This results in a significant signal enhancement. Three distinct imaging modalities are described, which are based on the various stabilization feedback parameters, and scan speeds. A number of images are presented, demonstrating both amplitude and phase contrast imaging modalities.
Photolithographic micromolding of ceramics using plasma etched polyimide patterns
Authors: Bride J. A. , Baskaran S. , Taylor N. , Halloran J. W. , Juan W. H. , Pang S. W. , O’Donnell M.
Published: July 2002

Features as fine as 4 μm with high aspect ratio were produced from ceria-zirconia ceramic using a thick plasma-etched polyimide layer as a micromold.
Temperature sensitivity and high temperature operation of long wavelength semiconductor lasers
Authors: O’Reilly E. P. , Silver M.
Published: July 2002

The temperature dependence of long wavelength (1.5 μm) quantum-well lasers has been studied theoretically assuming that the dominant contribution to the threshold current is from phonon-assisted Auger recombination. It is found that the best possible value of T0 at room temperature is ≊100 K. Gain calculations based on the InGaAs/InGaAsP/InP system operating at 1.5 μm indicate that the main cause of the reduction from this ideal value is due to the temperature dependence of the threshold carrier density. We also comment on the implication of this for the high temperature operation of tensile and compressive lasers.
Epitaxial LiTaO3 thin film by pulsed metalorganic chemical vapor deposition from a single precursor
Authors: Xie Huyang , Raj Rishi
Published: July 2002

Epitaxial LiTaO3 thin films were grown on (0001) sapphire in a low pressure chemical vapor deposition reactor of a new design, using lithium tantalum hexa-t-butoxide as the precursor. X-ray diffraction shows that the LiTaO3 c axis is normal to the sapphire surface. The x-ray pole figure and cross-section transmission electron microscopy diffraction show that the films were also in-plane oriented, with sapphire [101̄0] parallel to lithium tantalate [101̄0]. The refractive index of the film compares well with bulk values, over a wide wavelength range.