bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term results of aggressive management of diabetic foot ulcers suggest significant cost effectiveness
Authors: Cianci Paul , Hunt Thomas K.
Published: July 2002

This study was undertaken to examine the hypothesis that the initial high limb salvage rate in patients with diabetes who are treated aggressively with a multidisciplinary approach to management of severe, chronic lower extremity wounds is durable and cost effective. In 1991 a cohort of 41 patients with diabetes with severe, chronic foot wounds was selected by a neutral, blinded observer who had no knowledge of the outcomes from a group of 101 consecutive such patients who had been treated at our wound center from 1983 to 1990. All had limb‐threatening lesions, scoring 3 to 4 on the Wagner scale, were treated for at least 7 days with adjunctive hyperbaric oxygen, and had photographic and medical documentation. Durability of wound repair was examined in 1991 and 1993. Initial limb salvage was 85%. Mean hospital charges were $31,264, including average hyperbaric charges of $15,000. At the initial review, 28 of the patients with previously salvaged limbs (80%) were contacted. Of the 28 patients, 27 remained intact (96%). The mean durability of repair was 2.6 years. At the second review, the mean duration of repair in surviving patients was 4.6 years with no further expenditures relative to the salvaged limb. In patients who died, average durability was 3.4 years, also without additional expenditure referable to the salvaged extremity. Most complex lower extremity lesions were healed by a comprehensive wound care program which included vascular surgery and hyperbaric oxygen. The results were durable, and the treatment was cost effective and humane compared with early amputation.
Effective management of microbial contamination in cultured skin substitutes after grafting to athymic mice
Authors: Boyce Steven T. , Harriger M. Dana , Supp Andrew P. , Warden Glenn D. , Holder Ian Alan
Published: July 2002

Cultured skin substitutes have become therapeutic alternatives for treatment of acute and chronic skin wounds, but all models of these substitutes are avascular and susceptible to microbial destruction during vascularization. To develop a practical management protocol for increased survival of skin substitutes, experimental wounds were contaminated with Pseudomonas aeruginosa and treated with a formulation of noncytotoxic antimicrobial agents (polymyxin B, neomycin, ciprofloxacin, mupirocin, amphotericin B) in a nutrient medium (vehicle). Cultured skin substitutes consisting of human keratinocytes and fibroblasts attached to collagen‐glycosaminoglycan sponges were grafted to 2 × 2 cm full‐thickness wounds on athymic mice that were contaminated with the strain SBI‐N of P. aeruginosa at 1 × 104, 1 × 105, and 1 × 106 organisms/wound. Experimental wounds were irrigated with 1 ml/day topical antimicrobial solution for 10 days, and controls received vehicle only. Two, three, and four weeks after grafting, wounds were traced and swabbed for microbial culture and areas were measured with planimetry. At 4 weeks, biopsy samples were scored histochemically for immunoreactivity to HLA antigens. Data analysis by chi‐square, analysis of variance, and Tukey's test shows that treatment of contaminated wounds with noncytotoxic topical antimicrobials is associated with an increased area of healed wounds, positive detection of HLA antigens, and negative cultures for P. aeruginosa. These results show that microbial contamination of cultured skin substitutes on full‐thickness wounds may be managed effectively during graft vascularization. However, this formulation of antimicrobial agents is not currently approved for human use and is investigational only. Effective management of microbial contamination suggests that clinical efficacy of avascular tissue analogs may be increased by local application of noncytotoxic antimicrobial agents.
Strategies for cell engineering in tissue repair
Authors: Brown Robert A. , Smith Kirsty D. , Angus McGrouther D.
Published: July 2002

Cellular and tissue engineering are new areas of research, currently attracting considerable interest because of the remarkable potential they have for clinical application. Some claims have indeed been dramatic, including the possibility of growing complete, artificial organs, such as the liver. However, amid such long‐term aspirations there is the very real possibility that small tissues (artificial grafts) may be fabricated in the near future for use in reconstructive surgery. Logically, we should focus on how it is possible to produce modest, engineered tissues for tissue repair. It is evident that strategies to date either depend on innate information within implanted cells, to reform the target tissue or aim to provide appropriate environmental cues or guidance to direct cell behavior. It is argued here that present knowledge of tissue repair biology points us toward the latter approach, providing external cues which will direct how cells should organize the new tissue. This will be particularly true where we need to reproduce microscopic and ultrastructural features of the original tissue architecture. A number of such cues have been identified, and methods are already available, including substrate chemistry, substrate contact guidance, mechanical loading, and biochemical mediators to provide these cues. Examples of these are already being used with some success to control the formation of tissue structures.
Chemokine and inflammatory cytokine changes during chronic wound healing
Authors: Fivenson David P. , Faria Duyen T. , Nickoloff Brian J. , Poverini Peter J. , Kunkel Steven , Burdick Marie , Strieter Robert M.
Published: July 2002

Wound healing is a complex process resulting from an interplay of processes including coagulation, inflammation, angiogenesis, and epithelialization. The chemokine family has been shown to contain members that are potent regulators of many of these pathways. Because we have previously shown that chemokines “pool” in biologic wound dressings, we studied the levels of CXC and CC chemokines, along with key inflammatory mediators, serially from a group of patients undergoing therapy for chronic venous leg ulcers. After 8 weeks, all patients had marked clinical healing of their ulcers (median 63.3% reduction in size) with two of 10 completely healed. Wound fluids extracted from dressings showed high levels of platelet factor‐4 and interferon‐γ‐inducible protein, with a trend toward increases in the ratio of the sums of the angiogenic versus angiostatic CXC chemokines (p = 0.082) in the tissues collected from the center of the ulcers during wound closure. Neutrophil‐activating peptide‐2 and interleukin‐8 accounted for the most changes in wound fluid angiogenic chemokines, with significant differences both as compared with baseline levels and with patients' plasma level noted at various time points between weeks 0 and 8. The level of angiostatic (cont.)
p53 and apoptosis alterations in keloids and keloid fibroblasts
Authors: Ladin Daniel A. , Hou Zizheng , Patel Dipa , McPhail Monica , Olson Jennifer C. , Saed Ghassan M. , Fivenson David P.
Published: July 2002

Keloids are the result of a dysregulated wound‐healing process and are characterized by formation of excess scar tissue that proliferates beyond the boundaries of the inciting wound. In this study, we investigated the expression of key proteins involved in regulating apoptosis in keloids. Twenty archival paraffin‐embedded keloid samples were randomly selected for an immunoperoxidase assay with antibodies against fas, p53, bcl‐2, and bcl‐x proteins using the target antigen‐retrieval technique. Apoptosis was assessed in keloids and normal skin and in keloid and normal fibroblasts by the TdT‐mediated dUTP nick‐end labeling (tunel) assay on tissue sections, fibroblast cultures, and by flow cytometry for cell suspensions. We found that 18 of 20 keloids expressed p53 protein; bcl‐2 was expressed by keloid fibroblasts in 19 of 20 keloids, and all specimens had prominent fas expression throughout the tissue. The distribution of these three antigens was regional within each lesion and followed a consistent pattern of p53 and bcl‐2 expression colocalized to the hypercellular, peripheral areas of each keloid in a perinuclear pattern (p < .001). In contrast, an inverse distribution of fas expression was shown, with staining being more diffuse across the cell surfaces and limited to the central, more hypocellular regions in 16 of 17 keloids (p < .001). There was no specific staining pattern in these keloids with antihuman bcl‐x. In vitro studies on cultured keloid fibroblasts (derived from six patients) revealed maintenance of the p53+, bcl‐2+ phenotype up to passage 10. Neither neonatal nor normal adult skin fibroblasts expressed either antigen but could be induced to express p53 by exposure to adriamycin. Keloid lesions and keloid fibroblasts were found to have lower rates of apoptosis than normal controls. Keloid fibroblasts displayed enhanced apoptosis rates in response to hydrocortisone, γ interferon and hypoxia treatment as compared with normal adult fibroblasts. Focal dysregulation of p53 combined with upregulation of bcl‐2 may help produce a combination of increased cell proliferation and decreased cell death in the younger hypercellular areas of the keloid. This phenotype is reversed in the older areas of the keloid and may prevent malignan degeneration, thus favoring normal apoptosis as evidenced by prominent fas expression.
Regenerative biology and engineering: strategies for tissue restoration
Authors: Stocum David L.
Published: July 2002

Over the past 50 years, we have made remarkable advances in the use of bionic devices and solid organ transplants as replacement parts for failing tissues and organs. These approaches to tissue restoration, however, have a number of drawbacks. Thus, a new approach, regenerative biology and engineering, has been developed, consisting of the strategies of cell transplantation, bioartificial tissue constructs, and stimulation of regeneration in vivo. Cell transplants have been successfully used to restore articular cartilage and to treat Parkinson's disease in humans. In rats, transplanted fetal and embryonic stem cell line—derived cardiomyocytes have been shown to differentiate and integrate well with the ventricular myocardium, suggesting the feasibility of using such transplants to restore damaged cardiac muscle. Diabetic symptoms in humans have been alleviated by implanting a bioartificial pancreas consisting of islet cells microencapsulated in alginate. Hydroxyapatite matrixes can stimulate the regeneration of bone across large gaps. Collagenous artificial matrixes can stimulate the regeneration of dermis, and peripheral nerve grafts embedded in a fibrin clot containing fibroblast growth factor‐1 stimulate some regeneration of spinal cord axons in adult rats. Future research in regenerative biology will focus on several issues: (1) providing adequate sources of cells for transplantation and bioartificial tissue construction and determining ways to prevent these cells from coming under attack by the immune system, (2) developing new and better materials to build better bionic devices and bioartificial constructs and to stimulate regeneration in vivo, (3) determining how many tissues of the body might contain reserve cells for regeneration in vivo, (4) analyzing the molecular differences between cells and environments of regenerating versus nonregenerating tissues, and (5) understanding the factors and mechanisms involved in the proliferation and patterning of regenerating tissues.
Conceptual foundations of metamorphosis and regeneration: from historical links to common mechanisms
Authors: Dinsmore Charles E.
Published: July 2002

Metamorphosis and regeneration represent two familiar examples of developmental processes. In Western thought, their conceptual link with broader issues of generation or animal reproduction, including “spontaneous generation,” began with the ancient Greeks. Their ideas dominated scientific discourse on these topics until William Harvey, in the mid‐17th century, redefined and distinguished between epigenesis and metamorphosis as fundamentally different modes of reproduction. However, preformation theories, formulated in response to perceived threats of epigenetic concepts to religious doctrine, eclipsed epigenesis for much of the 18th century. Abraham Trembley's 1740 discovery of hydra regeneration helped to fuel the “epigenesis‐preformation debate” at that time. During that period, an exchange between C.F. Wolff, a young epigenesist, and A. von Haller, the reformed preformationist, saw robust models erected to comprehend generation, metamorphosis, and regeneration under each world view. Subsequent elaboration of experimental zoology and the incremental advance of biological knowledge saw the birth of divergent research traditions in pursuit of specialized problems. Embryology, regeneration, and metamorphosis, like genetics, identified independent study topics and elaborated new techniques, thereby creating their own research trajectories. Conceptual reintegration has slowly emerged with the evolution of current biotechnology. We have now begun to discern common molecular mechanisms underlying and reuniting metamorphosis and regeneration, as revealed in the accompanying symposium papers.
Pattern formation in dissociated limb bud mesenchyme in vitro and in vivo
Authors: Ide Hiroyuki , Yokoyama Hitoshi , Endo Tetsuya , Omi Minoru , Tamura Koji , Wada Nauyoki
Published: July 2002

A fundamental process in limb bud development is the formation of position‐dependent cartilage pattern. Cells of the distal mesenchyme maintain positional values as the expression pattern of transcription factors, for example, hox genes, which induce position‐related cell differentiation and cell surface differences. Cultured, dissociated limb bud mesenchymal cells segregate from each other, and eventually form cartilage nodules. This sorting out is position‐dependent, not cell‐type dependent, suggesting that the positional values may be involved. Positional valves were found to be retained in limb bud recombinants. In the chick system, the expression of HoxA13 and HoxD12 was present in the distal half of stage 20 recombinants, whereas these markers were expressed throughout the stages 25 recombinants. In the Xenopus system, multiple digit formation was introduced in limb recombinants, and a position‐related relationship between regeneration potency and the multiple digit formation could be established. This determination of multiple digit formation with different stages of limb mesenchyme may be useful in understanding mechanisms of the loss of vertebrate limb regeneration potency.
An ependymal cell culture system for the study of spinal cord regeneration
Authors: Chernoff Ellen A.G. , Henry Lloyd C. , Spotts Terry
Published: July 2002

Successful regeneration of lesioned adult spinal cord in urodele (caudate) amphibians requires the action of injury‐responsive ependymal cells (ependymoglia). The epithelial‐to‐mesenchymal transformation of ependymal cells following transection of the salamander spinal cord and the subsequent reformation of an epithelial tube have been described previously. A complete tissue culture model system has now been devised to study mesenchymal ependymal cells, epithelial ependymal cells, and ependymal/neuronal interactions in vitro. Here, we review critical aspects of substrate and growth factor environments required to produce mesenchymal ependymal cells in culture and present the first culture system for epithelial salamander ependymal cells and central nervous system neurons suitable for cell‐cell interaction studies. Critical to ependymal epithelialization in culture is the removal of epidermal growth factor and addition of thrombin. Epithelialization occurs on tissue culture plastic as well as on permeable culture substrates. This culture system can now be used to determine the initial trigger for the ependymal response. A preliminary examination of ependymal/neuronal interactions shows that coculture of mesenchymal ependymal cells and central nervous system neurons prolongs survival of the neurons.
Repeated additions of hyaluronan alters granulation tissue deposition in sponge implants in mice
Authors: Iocono Joseph A. , Krummel Thomas M. , Keefer Kerry A. , Allison Gretchen M. , Ehrlich H. Paul
Published: July 2002

The role for the metabolism of hyaluronic acid in the repair process is uncertain. Fetal dermal wounds do not heal by scarring and have sustained high levels of hyaluronic acid. In contrast, adult dermis is repaired by scarring and has less hyaluronic acid. Initially after injury, hyaluronic acid is elevated in both adult and fetal wounds, and although it remains elevated in fetal repair, it is rapidly degraded in adult wounds. The chronic addition of hyaluronic acid or hyaluronidase to polyvinyl alcohol sponge implants in adult mice was investigated in this study. Polyvinyl alcohol sponge implants containing a central reservoir were placed subcutaneously in the dorsum of adult male CD‐1 mice. Mice were divided into three groups: a phosphate‐buffered saline control, a 20 µg hyaluronic acid treatment group, and a 10 U hyaluronidase treatment group. The central reservoir of each sponge implant received appropriate compound every 3 days for 2 weeks via transdermal injection and were then evaluated histologically. At 2 weeks, the cellular density and the quantity of granulation tissue deposition were the greatest in the hyaluronidase group and were lowest in the hyaluronic acid group. In addition, the organization of collagen fiber bundles was the most dense in the hyaluronidase group and least in the hyaluronic acid group. In a second experiment, polyvinyl alcohol sponge implants in mice received either phosphate‐buffered saline solution or 20 µg hyaluronic acid every 3 days for 1 week. On day 5, an aliquot of fluorescently tagged native collagen was injected into the sponges. Sponges were harvested at day 7, cryosections made, and the presence of autofluorescent collagen fibers assessed. The autofluorescent collagen fiber bundles in the phosphate‐buffered saline solution group were organized in thick parallel bundles, whereas the collagen bundles from hyaluronic acid‐treated implants were organized in fine lacelike structures. Chronic addition of hyaluronic acid appears to mimic the fetal dermal connective tissue matrix in which repair proceeds with diminished collagen deposition, organized in finer collagen fiber bundles in granulation tissue. On the other hand, the removal of hyaluronic acid by the chronic administration of hyaluronidase increases the amount of granulation tissue. Elevated levels of hyaluronic acid in granulation tissue appear to modulate the ability of resident fibroblasts to organize collagen fiber bundles.
Quantitation of CMV by real‐time PCR in transfusable RBC units
Authors: Greenlee Deborah J. , Fan Hongxin , Lawless Kathleen , Harrison Chantal R. , Gulley Margaret L.
Published: July 2002

BACKGROUND: CMV is one of the most significant pathogens infecting immunocompromised individuals. CMV is transmissible through transfusion of blood components. The goal of this study was to measure CMV levels in RBC units using a sensitive and quantitative DNA amplification assay.

STUDY DESIGN AND METHODS: An assay to measure CMV load was developed by using real‐time PCR to target the major immediate early viral gene. A probe (TaqMan, Applied Biosystems) was used to confirm product specificity and to permit quantitation of CMV in blood samples on a sequence detection system (ABI Prism 7700, Applied Biosystems).

RESULTS: The assay was shown to be accurate, linear, and sensitive to as few as five copies of CMV DNA per PCR. The assay was applied to aliquots of RBC units from 203 healthy donors, 110 of whom were seropositive for CMV. CMV DNA was not detected in any of the 203 RBC samples.

CONCLUSION: The findings statistically imply that at least 98.5 percent of RBC units have a CMV load of less than 250 copies per mL. Future clinical studies on larger numbers of units are required to determine the utility of real‐time PCR in evaluating the risk of CMV transmission and in confirming the efficacy of WBC reduction.
High‐dose CD34+ cells are not clinically relevant in reducing cytopenia and blood component consumption following myeloablative therapy and peripheral blood progenitor cell transplantation as compared with standard dose
Authors: Lefrère François , Delarue Richard , Somme Dominique , Levy Vincent , Damaj Gandhi , Tu Angela , Porcher Raphael , Audat Françoise , Boulat Claire , Cavazzana‐Calvo Marine , Buzyn Agnès , Belanger Coralie , Maillard Natacha , Hermine Olivier , Varet Bruno
Published: July 2002

BACKGROUND: No agreement exists about the number of autologous peripheral blood progenitor cells (PBPCs) to transfuse for optimal hematologic recovery after high‐dose chemotherapy.

STUDY DESIGN AND METHODS: To determine CD34+ cell dosage following high‐dose chemotherapy (in terms of hematologic recovery and blood component consumption), the effects of two schedules of CD34+ cell transfusions in a cohort of patients with myeloma or non‐Hodgkin's lymphoma were examined. Forty patients (Group 1) received between 2.5 and 5 × 106 CD34+ cells per kg, with a median of 3.4 × 106 per kg following high‐dose chemotherapy, and 40 patients (Group 2), selected to match Group 1 for age, diagnosis, prior therapies, and procedure for PBPC mobilization, received a dose of CD34+ cells >5 × 106 per kg, with a median of 8.4 × 106 per kg (5‐33).

RESULTS: The median number of days to achieve a neutrophil count of >0.5 × 109 per L and unsupported platelets of >20 × 109 per L was identical for the two groups, but the time required to reach 1.5 × 109 neutrophils per L and 50 × 109 platelets per L was greatly delayed in Group 1. No significant difference was observed for the median number of RBC and platelet transfusions, or for the proportion of patients in each group that did not require either platelet or RBC transfusions.

CONCLUSION: Our data confirm a dose–response relationship between CD34+ cell dose transfused and time to hematologic recovery after high‐dose chemotherapy. However, the minimal Hb and platelet counts for transfusion independence in the two groups are similar when the CD34+ cell dose is greater than 5 × 106 CD34+ cells per kg. Therefore, our data suggest that it is not necessary to go on with apheresis procedures after 5 × 106 CD34+ cells per kg are harvested to sustain one high‐dose chemotherapy.
Collection of autologous monocytes for dendritic cell vaccination therapy in metastatic melanoma patients
Authors: Nguyen Xuan Duc , Eichler Hermann , Sucker Antje , Hofmann Udo , Schadendorf Dirk , Klüter Harald
Published: July 2002

BACKGROUND: Dendritic cells (DCs) for immunotherapy of malignant melanoma can be generated from partially enriched monocytes prepared from PBMNCs. The feasibility of a single steady‐state leukapheresis procedure to enrich monocytes for a complete vaccination series with up to 10 vaccinations was investigated.

STUDY DESIGN AND METHODS: Thirty‐eight patients (27 males and 11 females) with metastatic melanoma were enrolled in the study. All leukapheresis procedures were performed by a continuous flow method (Spectra, Cobe BCT) with a standard MNC program.

RESULTS: An average of 11.7 L (range, 8‐14 L) of whole blood was processed within 197.3 ± 23.7 minutes, and a mean of 13.5 ± 5.7 × 109 WBCs in a final volume of 191.0 ± 24.2 mL was collected. The MNC purity in the apheresis component was 81.5 ± 15.1 percent, from which 29.8 ± 14.7 percent were monocytes. Thus, 11.0 ± 5.0 × 109 MNCs and 3.2 ± 2.0 × 109 monocytes were collected per procedure. Linear regression analysis revealed a high correlation between the absolute number of monocytes in peripheral blood before the apheresis procedure and the number of monocytes in the collected component (r = 0.74, p < 0.0001). For the generation of DCs, 1.6 ± 0.8 × 109 MNCs were plated into culture dishes; 3.2 ± 1.8 percent of the cultured cells matured to DCs, which resulted in 56.5 ± 49.4 × 106 DCs (range, 6.3‐178) per patient for the complete vaccination series.

CONCLUSION: A target dose of monocytes for the complete vaccination series could be obtained by a single convenient, safe, steady‐state leukapheresis procedure in each patient without the need for G–CSF mobilization. The absolute number of monocytes in peripheral blood before the apheresis procedure is the best predictive variable for the yield of monocytes in the apheresis component.
Efficacy and Safety of Levetiracetam in Children with Partial Seizures: An Open‐label Trial
Authors: Glauser Tracy A. , Pellock John M. , Bebin E. Martina , Fountain Nathan B. , Ritter Frank J. , Jensen Christof M. , Shields W. Donald
Published: July 2002

Summary:  Purpose: To assess the efficacy and safety of levetiracetam (LEV) as adjunctive therapy in children with treatment‐resistant partial‐onset seizures.

Methods: Children (aged 6–12 years) with treatment‐resistant partial‐onset seizures receiving one standard antiepileptic drug (AED) were eligible. After a 4‐week baseline period, children received LEV in a 6‐week titration phase (target dose, 40 mg/kg/day) followed by an 8‐week evaluation phase. Seizure frequency during the evaluation period with individualized LEV doses (20–40 mg/kg/day) were compared with the 4‐week baseline seizure frequency. Plasma concentrations of LEV and other AEDs were determined to evaluate potential drug interactions.

Results: Twenty‐four subjects enrolled and received LEV; 23 entered the evaluation phase, and 22 completed the evaluation phase. Compared with their baseline seizure frequency, 12 (52%) of 23 subjects entering the evaluation phase had their seizure frequency decrease by >50%. Two subjects remained seizure free during the entire evaluation period. LEV did not significantly affect plasma concentrations of any concomitant AED during this study, and no alteration of mean clinical laboratory values was observed. The most commonly reported adverse events were headache, infection, anorexia, and somnolence.

Conclusions: This open‐label study of adjunctive LEV therapy (at 20–40 mg/kg/day) suggests that LEV is effective, safe, and well tolerated in children ages 6–12 years with treatment‐resistant partial‐onset seizures. A randomized, placebo‐controlled, double‐blind trial of LEV adjunctive therapy in children with treatment‐resistant partial‐onset seizures is needed and ongoing to confirm these open‐label findings.
Low‐pressure Hydrocephalic State Complicating Hemispherectomy: A Case Report
Authors: Daniel Roy Thomas , Lee Gabriel Y. F. , Halcrow Stephen J.
Published: July 2002

Summary: Low‐pressure hydrocephalic state (LPHS) has only recently been described as a distinct clinical entity occurring in patients with bioatrophic lesions of the brain. We report a patient in whom this syndrome developed after subtotal hemispherectomy for intractable epilepsy.

Methods: A 30‐year‐old man developed cerebrospinal fluid (CSF) rhinorrhea after subtotal hemispherectomy. After repair of the CSF dural fistula, clinical and radiological features of an LPHS developed. After external ventricular drainage for 26 days, a programmable low‐pressure shunt system was instituted.

Results: Worsening neurologic status and ventriculomegaly in the face of normal intraventricular pressures is diagnostic of this condition. The clinical status clearly correlated with ventricular size and not ventricular pressure.

Conclusion: LPHS is a clinically significant perioperative complication that rarely occurs after large brain excisions. Restoration of the baseline brain compliance is critical in the management of this condition.
A Morphometric Study of Populations of the Centaurea jacea Complex (Asteraceae) in Belgium
Authors: Vanderhoeven S. , Hardy O. , Vekemans X. , Lefèbvre C. , de Loose M. , Lambinon J. , Meerts P.
Published: July 2002

Abstract: The Centaurea jacea aggregate is a polymorphic polyploid complex whose taxonomic treatment is still controversial. A numerical taxonomic approach was applied to 394 individuals of known ploidy level, from 19 populations, based on the main diagnostic characters proposed in earlier revisions. Populations from xeric grasslands were not considered. Principal Component Analysis shows that variation within the complex is continuous. UPGMA Cluster Analysis based on population means supports the recognition of three groups of populations. However, the limits between these groups are blurred to a considerable extent due to extensive within‐population polymorphism. It is argued that the Belgian populations of Centaurea jacea occurring in mesic grasslands should be treated as a single species, with three subspecies. The two extremes of the morphological gradient can be referred to as C. jacea subsp. jacea and C. jacea subsp. nigra, with C. jacea subsp. pratensis occupying an intermediate position. Most populations from Belgium are tetraploid, a diploid chromosome number being found only in populations of C. jacea subsp. nigra from the Ardennes massif. On average, diploids grow at higher altitude and on more acidic soils than tetraploids. Finally, a key to the three subspecies is provided.
Nonlinear Dynamics as a Tool for Modelling in Plant Physiology
Authors: Hütt M.‐Th. , Lüttge U.
Published: July 2002

Abstract: We show that recent methods from nonlinear dynamics and complexity theory developed in theoretical physics can and should be applied to the description and analysis of systems in plant physiology, in particular to interpret data series in time and space, i.e., rhythms and pattern formation processes. We start with a brief introduction into the key ideas of nonlinear dynamics, including a short outline of topics which are currently the focus of theoretical interest, in particular the concept, origin and possible function of noise in biological systems. The theoretical concepts are applied to a model system of circadian rhythmicity in plant physiology, crassulacean acid metabolism. With this application, we illustrate the main idea of our article: nonlinear dynamics serves as a remarkable tool for unveiling the internal mechanisms at work in a system's process of self‐organization.
On the Lamellar Structure of the Tracheid Cell Wall
Authors: Fahlén J. , Salmén L.
Published: July 2002

Abstract: It is clear that cross sections of wood cells show a lamellar structure. This paper investigates the orientation of this lamellar structure of spruce (Picea abies) tracheids using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross sections of spruce wood were produced through fracturing in longitudinal bending and tensile testing. When investigated with SEM, the fracture surfaces show a structure of mostly larger radial lamellae, in the order of 30 ‐ 100 nm, i.e., agglomerations of a few cellulose aggregates. Thin transverse sections of the fracture zones investigated with atomic force microscopy show concentric lamellae with a width in the order of a single cellulose aggregate, i.e., 15 ‐ 25 nm. No structural connection to the splinters in the radial direction can be seen. It is suggested that the radial lamellar structure is a consequence of the energy released during fracturing of the wood samples and that the undistorted wood has a concentric lamellar structure on a smaller structural level.
Detection of water-ice transition using a lead zirconate titanate/brass transducer
Authors: Li Xiaoping , Shih Wan Y. , Vartuli James , Milius David L. , Prud’homme Robert , Aksay Ilhan A. , Shih Wei-Heng
Published: July 2002

We have examined experimentally and theoretically the resonance frequency of a lead zirconate titanate (PZT)/brass unimorph disk transducer with a water (ice) layer on the brass surface. We showed that the flexural resonance frequency decreased with the presence of a water layer and the decrease in resonance frequency increased with an increasing water amount. Upon lowering the temperature, the freezing transition of the deposited water layer was detected when the resonance frequency of the transducer increased abruptly at the freezing temperature. In contrast to water, an ice layer increased the resonance frequency and the increase in the resonance frequency increased with the ice layer thickness. Theoretically, an analytic expression for the flexural resonance frequency of a unimorph transducer in the presence of an ice (water) layer on the brass surface was obtained in terms of the Young’s moduli, densities, and thickness of the PZT, brass, and ice (water) layers. The theoretical predictions were shown to agree with the experimental results.
Dynamic percolation theory for particle diffusion in a polymer network
Authors: Dürr O. , Volz T. , Dieterich W. , Nitzan A.
Published: July 2002

Tracer-diffusion of small molecules through dense systems of chain polymers is studied within an athermal lattice model, where hard-core interactions are taken into account by means of the site exclusion principle. An approximate mapping of this problem onto dynamic percolation theory is proposed. This method is shown to yield quantitative results for the tracer correlation factor of the molecules as a function of density and chain length provided the non-Poisson character of temporal renewals in the disorder configurations is properly taken into account.
Physical processes associated with the deactivation of dopants in laser annealed silicon
Authors: Takamura Y. , Griffin P. B. , Plummer J. D.
Published: July 2002

Laser annealing is being investigated as an alternative method to activate dopants and repair the lattice damage from ion implantation. The unique properties of the laser annealing process allow for active dopant concentrations that exceed equilibrium solubility limits. However, these super-saturated dopant concentrations exist in a metastable state and deactivate upon subsequent thermal processing. Previously, this group compared the electrical characteristics of the deactivation behavior of common dopants (P, B, and Sb) across a range of concentrations and annealing conditions. Boron and antimony were shown to be stable species against deactivation while P and As deactivate quickly at temperatures as low as 500 °C. In this work, we present additional data to understand the underlying physical mechanisms involved in the deactivation process. It is proposed that As and P deactivate through the formation of small dopant—defect clusters while B and Sb deactivate through precipitation.
Analytic continuation of the Hurwitz zeta function with physical application
Authors: Barone Adesi Vittorio , Zerbini Sergio
Published: July 2002

A new formula relating the analytic continuation of the Hurwitz zeta function to the Euler gamma function and a polylogarithmic function is presented. In particular, the values of the first derivative of the real part of the analytic continuation of the Hurwitz zeta function for even negative integers and the imaginary one for odd negative integers are explicitly given. The result can be of interest both on mathematical and physical side, because we are able to apply our new formulas in the context of the spectral zeta function regularization, computing the exact pair production rate per space–time unit of massive Dirac particles interacting with a purely electric background field.
Structure and energetics of alkanethiol adsorption on the Au(111) surface
Authors: Yourdshahyan Yashar , Rappe Andrew M.
Published: July 2002

The interaction of thiol molecules with the Au(111) surface was investigated with state-of-the-art first-principles methods. We report theoretical evidence for the existence of a physisorption precursor to chemisorption, in agreement with experiment. The origins of inconsistency in recent studies regarding the adsorption site, geometry, and energetics of CH3S on the Au(111) surface were also investigated. We show that the chemisorption site is between the hollow and bridge sites, with a large molecular tilting angle relative to the surface normal. The molecular structure of the overlayer is coverage dependent, with the molecular tilting angle increasing with decreasing coverage. Increasing chain length up to three carbon atoms affects both the chemisorption energetics and the tilt angle. The inconsistency of tilting angles, reported for the fcc site is found to be a consequence of multiple local minima. The ordered structure of thiol molecules at different coverages was also investigated, confirming the recent experimental findings that the c(4×2) structure model is preferred over (∛×∛)R30°.
Growth and characterization of radio frequency magnetron sputter-deposited zinc stannate, Zn2SnO4, thin films
Authors: Young David L. , Moutinho Helio , Yan Yanfa , Coutts Timothy J.
Published: July 2002

Single-phase, spinel zinc stannate (Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10−2–10−3 Ω cm, mobilities of 16–26 cm2/V s, and n-type carrier concentrations in the low 1019 cm−3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. Sn119 Mössbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn+4. A pronounced Burstein–Moss shift moved the optical band gap from 3.35 to as high as 3.89 eV. Density-of-states effective mass, relaxation time, mobility, Fermi energy level, and a scattering parameter were calculated from resistivity, Hall, Seebeck, and Nernst coefficient transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 me as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. A bottom-of-the-band effective-mass value of 0.15 me is in good agreement with local density approximation calculations. Temperature-dependent transport measurements and calculated scattering parameters correlated well with ionized impurity scattering with screening by free electrons for highly degenerate films.
The formation of cyclic water complexes by sequential ring insertion: Experiment and theory
Authors: Burnham Christian J. , Xantheas Sotiris S. , Miller Mark A. , Applegate Brian E. , Miller Roger E.
Published: July 2002

The growth of water clusters in liquid helium droplets results in the formation of cyclic structures up to and including the hexamer. In view of the sequential nature of the molecular pick-up process, the formation of water rings involves the insertion of water monomers into preformed cyclic water clusters. The implication of this observation is that the barriers to the ring insertion process are low enough to be overcome during the experiment. This paper presents a combined experimental and theoretical effort to explore the insertion process in detail. Our results provide important new insights into the dynamics of hydrogen-bonded networks. We map out the cluster potential energy surfaces and visualize them using disconnectivity graphs. Nonequilibrium walks on these surfaces show that ring water clusters can be formed during sequential addition of water molecules by surmounting small barriers that are thermally accessible even at the low temperature of the experiment. We find that the effects of zero-point energy are significant in making these processes feasible.
Postgrowth annealing effect on structural and optical properties of ZnO films grown on GaAs substrates by the radio frequency magnetron sputtering technique
Authors: Ryu M. K. , Lee S. H. , Jang M. S. , Panin G. N. , Kang T. W.
Published: July 2002

High-resolution scanning electron microscopy and cathodoluminescence spectroscopy measurements were performed to study the effect of postgrowth annealing on properties of ZnO films grown on GaAs substrates by rf sputtering. The films annealed at 550 °C show a well-oriented columnar structure and strong exciton emission at room temperature. Outdiffusion of gallium and arsenic from substrate into a ZnO film has been found to result in a different secondary electron dopant contrast, measured by the through-the lens secondary electron detector. Extended structural defects such as subgrain boundaries in ZnO assist Ga outdiffusion from the GaAs substrate and show a reduced secondary electron (SE) emission after annealing, while As doped ZnO adjacent to the ZnO/GaAs interface demonstrates an enhanced SE emission and the enhanced luminescence associated with donor–acceptor pairs and exciton bound to acceptors.
Schottky energy barrier and charge injection in metal/copper–phthalocyanine/metal structures
Authors: Mahapatro Ajit Kumar , Ghosh Subhasis
Published: July 2002

We present experimental results on current injection from different metal electrodes into copper–phthalocyanine (Cu–Pc). The current–voltage (J–V) characteristics and current injected at the contact are investigated as a function of Schottky energy barrier, thickness of organic semiconductor, and temperature. These results are interpreted using a consistent description of J–V characteristics through the injection limited current in the case of high Schottky energy barriers and space charge limited current in the case of low Schottky energy barrier.
Spectroscopy of Tm3+-doped tellurite glasses for 1470 nm fiber amplifier
Authors: Taylor Elizabeth R. , Ng Li Na , Sessions Neil P. , Buerger Herbert
Published: July 2002

Three thulium doped tellurite glass compositions have been investigated. The 1470 nm transition is radiative in these tellurite glasses and the radiative lifetimes are in the range of 350 to 470 μs. The 1470 nm fluorescence is broad with a full width at half maximum of 105 nm. Fibers have been drawn from these glasses with a loss of 0.7 dB/m at 1300 nm. A fiber with an OH fundamental absorption of 200 dB/m at 2.99 μm has an OH first overtone absorption of 0.3 dB/m at 1480 nm. The overlap between the thulium ion 1470 nm emission and the hydroxyl absorption depends on glass composition. Tellurite glasses can accept large concentrations of Tm3+ ions and, as long as the hydroxyl level can be kept low, the effect of concentration quenching can be minimized. Tm3+-doped tellurite glasses represent a viable alternative for the next generation of active components for S-band optical amplifiers. It can be pumped at 795 nm with an absorption of ∼38 dB/km/ppm and codoped with Ho3+ to avoid self-termination of the 1470 nm transition. It can also be pumped at 1212 nm as efficiently as at 795 nm, but diodes are not yet available at this wavelength. Using available pump wavelengths of 1064 nm and 1047 nm will require fiber lengths 15 times longer than pumping at 1212 nm.
Shape stability of unsteadily translating bubbles
Authors: Reddy Anil J. , Szeri Andrew J.
Published: July 2002

In this paper the problem of shape stability is considered, for a bubble with time-dependent radius, translating unsteadily in a flow. This situation can be brought about, for example, by forcing with an acoustic traveling wave. The equation governing translation was derived in a previous work [Reddy and Szeri (unpublished)]. Here, the equations governing the amplitudes of shape modes are derived using domain perturbation theory, following a classical paper by Plesset. Contrary perhaps to intuition, results show that driving at the natural frequency of volume oscillations is not necessarily the ideal forcing to engender a shape instability. Moreover, severe radial oscillations can have a stabilizing effect on shape oscillations. The results suggest the possibility of destroying bubbles selectively by size.
Interelectrode plasma evolution in a hot refractory anode vacuum arc: Theory and comparison with experiment
Authors: Beilis I. I. , Goldsmith S. , Boxman R. L.
Published: July 2002

In this paper a theoretical study of a hot refractory anode vacuum arc, which was previously investigated experimentally [Phys. Plasmas 7, 3068 (2000)], is presented. The arc was sustained between a thermally isolated refractory anode and a water-cooled copper cathode. The arc started as a multicathode-spot (MCS) vacuum arc and then switched to the hot refractory anode vacuum arc (HRAVA) mode. In the MCS mode, the cathodic plasma jet deposits a film of the cathode material on the anode. Simultaneously, the temperature of the thermally isolated anode begins to rise, reaching eventually a sufficiently high temperature to re-evaporate the deposited material, which is subsequently ionized in the interelectrode gap. The transition to the HRAVA mode is completed when the density of the interelectrode plasma consists mostly of ionized re-evaporated atoms—the anode plasma. The evolution of the HRAVA mode is characterized by the propagation of a luminous plasma plume from the anode to the cathode. The time dependent model of the various physical processes taking place during the transition to the HRAVA mode is represented by a system of equations describing atom re-evaporation, atom ionization through the interaction of the cathode jet and the interelectrode plasma with the anode vapor, plasma plume propagation, plasma radial expansion, plasma energy, and heavy particle density balance. The time dependence of the anode heat flux and the effective anode voltage were obtained by solving these equations. In addition, the time dependent plasma electron temperature, plasma density, anode potential drop, arc voltage, and anode temperature distribution were calculated and compared with previous measurements. It was shown that the observed decrease of the effective anode voltage with time during the mode transition is due to decrease of the heat flux incident on the anode surface from the cathode spot jets.
What can a scanning tunneling microscope image do for the insulating alkanethiol molecules on Au(111) substrates?
Authors: Zeng Changgan , Li Bin , Wang Bing , Wang Haiqian , Wang Kedong , Yang Jinlong , Hou J. G. , Zhu Qingshi
Published: July 2002

A low temperature scanning tunneling microscope (STM) has been employed to investigate the insulating alkanethiol self-assembled monolayers chemisorbed on Au(111) substrates. The STM images show clear intramolecular patterns, which are voltage- and site-dependent. Theoretical simulations, using the density functional theory, reproduce the experimental STM images. Our results show that due to the chemisorption, there are new states appeared in the energy gap of the alkanethiol, and they are mainly composed of Au and S orbitals, mixed with a small amount of orbitals at the alkyl part. The STM only images the states localized at the tail carbon–hydrogen groups since the Au and S atoms are located farther from the STM tip, and the images can reflect the surface topography of such standing molecular layers.