bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of nitric oxide in the CBF autoregulation during acute stage after subarachnoid haemorrhage in rat pial artery
Authors: Cho Hyun Gee , Shin Hwa Kyoung , Shin Yung Woo , Lee Jeong Hyun , Hong Ki Whan
Published: September 2003

The present study was aimed to identify whether endogenously produced nitric oxide (NO) plays a role in preservation of cerebral blood flow (CBF) autoregulation in rat pial artery during the acute stage after subarachnoid haemorrhage (SAH). During the acute stage after SAH, the lower limit of CBF autoregulation significantly shifted to the higher arterial blood pressure in association with suppressed vasodilatation in response to acute hypotension, which was accompanied by significantly increased expression of endothelial nitric oxide synthase mRNA and increased production of superoxide anion in cerebral vessels. SAH‐induced increase in superoxide production was further enhanced under pretreatment with N‐nitro‐l‐arginine methyl ester in the cerebral vessels. Following additional administration of l‐arginine (100 mg/kg, i.p.), the haemodynamic alterations were significantly restored in association with significantly reduced superoxide level in the cerebral vessels. In line with these findings, rats that received polyethylene glycol superoxide dismutase and catalase or Mn(III) tetrakis (4‐benzoic acid) porphyrin chloride showed recovery of impaired autoregulatory vasodilation in response to acute hypotension. Thus, it is suggested that NO endogenously produced is importantly implicated in the preservation of CBF autoregulation during the acute stage after SAH via its capability to scavenge superoxide anion.
Increased adrenergic contractility and decreased mRNA expression of NOS III in aging rat urinary bladders
Authors: Lluel P. , Palea S. , Ribière P. , Barras M. , Teillet L. , Corman B.
Published: September 2003

Our objective was to study age‐related changes in adrenergic contractility and gene expression profile in the rat urinary bladder. Young (3‐month old), adult (10‐month old) and senescent (30‐month old) male WAG/Rij rats were used. Gene expression profile in the rat urinary bladder was defined using AtlasTM microarray technology. In vitro contractile responses induced by KCl, phenylephrine (PHE) and norepinephrine (NE) were compared in isolated urinary bladders dissected from young, adult and senescent rats.

Among a total of 1176 genes present on the arrays, 15 genes showed an increase in expression and 10 genes a decrease with age. Four genes related to nerve growth factor were upregulated whereas NOS type III was downregulated in aging rats.

Intrinsic contractility of isolated rat urinary bladders was not changed between adult and aging rats as judged by the response curves to KCl. In contrast, an age‐related increase in the maximal contractile responses to NE, but not PHE, was noticed (13 ± 1, 48 ± 2% and 59 ± 2% at 3, 10 and 30 months, respectively). The α1D‐adrenoceptor antagonist BMY7378 antagonized NE‐induced contractions with low potency in both groups suggesting the involvement of the α1A‐adrenoceptor subtype. This was confirmed by microarray, which demonstrated mRNA expression for the α1A ‐adrenoceptor subtype only.

These results suggest that aging of the urinary bladder is associated with an increase in the maximal contractile response to NE which could be due to NO shortage resulting from downregulation of urothelial NOS III.
The preventive effect of captopril or enalapril on reperfusion injury of the kidney of rats is independent of angiotensin II AT1 receptors
Authors: Pazoki‐Toroudi Hamid Reza , Hesami Ali , Vahidi Simin , Sahebjam Farhad , Seifi Behjat , Djahanguiri Bijan
Published: September 2003

Occlusion of the artery of organs results in ischaemia. The opening of occluded artery results in tissue lesion identified as reperfusion injury (RI). Renin–angiotensin system seems to be involved in the RI. In this study we assessed the effects of different doses of two inhibitors of angiotensin converting enzyme (captopril or enalapril) and an angiotensin receptor type 1 (AT1) receptor blocker (losartan) in the RI of the kidney of rats. Female rats of 200–250 g were anaesthetized and used for RI studies. Different doses of captopril (5, 20 and 80 mg/kg), enalapril (1, 4 and 16 mg/kg) and/or losartan (5, 10 and 20 mg/kg) were used (s.c.) 120 min prior to the initiation of RI. Kidneys were removed and checked histologically for the presence and the grading of ischaemic injury. Appropriate controls were used as well. RI produced lesions comparable with that of ischaemia. Different doses of captopril or enalapril prevented these lesions. This is suggestive of the involvement of renin–angiotensin system in the RI. Different doses of losartan failed to prevent RI lesions which suggest that the effect of captopril or enalapril are not mediated through the AT1 receptors. Further studies on the involvement of AT2 receptor or other independent mechanisms are suggested.
A QSAR analysis to explain the analgesic properties of Aconitum alkaloids
Authors: Bello‐Ramírez Angélica M. , Buendía‐Orozco Jacob , Nava‐Ocampo Alejandro A.
Published: September 2003

Aconitum roots are traditionally prescribed for the management of different types of painful affections in Asiatic countries. A quantitative structure‐activity relationship (QSAR) analysis was performed to study the effect of chemical substitutes in the analgesic potency of alkaloids available in Chinese Aconitum roots. Using the CAChe program package for biomolecules, molecular modelling was performed in 12 alkaloids previously tested in a model of acetic acid‐induced writhing in rats. The ED50 (μmol/kg) was used as the activity parameter. Structural parameters were compared between alkaloids with an aroyl/aroyloxy group at R14 and alkaloids with the aroyloxy group at R4. Single linear regression analyses were performed in order to find the parameters explaining activity. Alkaloids with an aroyl/aroyloxy group at R14 exhibited the highest potency (significantly less ED50). The stability parameters were different between groups, e.g. total energy was −8.0 ± 0.4 in the potent analgesic alkaloids and −6.7 ± 0.3 in the weak analgesic alkaloids (P = 0.001). The reactivity index of C2′, C3′ and C5′ of the aromatic ring was also different between groups, e.g. the reactivity index of C5′ was 40.8 ± 0.6 in potent analgesic alkaloids and 48.1 ± 0.6 in weaker analgesic alkaloids (P < 0.001). Several structural parameters explained analgesic activity of alkaloids, being the reactivity index of C5′ on the aromatic group the most important factor (r = 0.89; P < 0.001).
Cough after inhalation of corticosteroids delivered from spacer devices in children with asthma
Authors: Dubus Jean‐Christophe , Mély Laurent , Huiart Laetitia , Marguet Christophe , Roux Pascal Le ,   on behalf of the ‘Réseau de Recherche Clinique en Pneumologie Pédiatrique’
Published: September 2003

Children using a spacer device rather than another device for delivering inhaled corticosteroids (ICS) has been identified as a risk factor for cough immediately after inhalation. The aim of this study was to point out the different factors influencing the occurrence of such lateral side‐effects. We studied this local side‐effect in 402 asthmatic children (55.6 ± 34.9 months; 65.6% boys) treated for at least 1 month with beclomethasone dipropionate (n = 331), budesonide (n = 47) or fluticasone propionate (n = 24) delivered from pressurized metered‐dose inhalers and small (75.1%) or large volume (24.8%) spacer devices mainly used with face mask (90.7%). A total of 219 patients (54.5%), treated with either high doses of ICS or ICS and long‐acting β2‐agonist, were considered as having severe asthma. Cough was reported after each inhalation of corticosteroids in 216 patients (53.7%). Among them, about 30% also complained of cough with β2‐agonists. Despite different propellants and dispersants, all corticosteroids induced cough similarly. Cough was not linked with asthma severity, but was significantly related to therapy duration and use of long‐acting β2‐agonist. Type and volume of the spacer device, use of a face mask or mouthpiece were not influencing factors. Cough after inhalation of corticosteroids delivered from spacer devices is a frequent local side‐effect in children with asthma. This side effect can greatly alter compliance. A practitioner must be sought at each visit.
Sequential methods and group sequential designs for comparative clinical trials
Authors: Sébille Véronique , Bellissant Eric
Published: September 2003

Comparative clinical trials are performed to assess whether a new treatment has superior efficacy than a placebo or a standard treatment (one‐sided formulation) or whether two active treatments have different efficacies (two‐sided formulation) in a given population. The reference approach is the single‐stage design and the statistical test is performed after inclusion and evaluation of a predetermined sample size. In practice, the single‐stage design is sometimes difficult to implement because of ethical concerns and/or economic reasons. Thus, specific early termination procedures have been developed to allow repeated statistical analyses to be performed on accumulating data and stop the trial as soon as the information is sufficient to conclude.

Two main different approaches can be used. The first one is derived from strictly sequential methods and includes the sequential probability ratio test and the triangular test. The second one is derived from group sequential designs and includes Peto, Pocock, and O'Brien and Fleming methods, α and β spending functions, and one‐parameter boundaries. We review all these methods and describe the bases on which they rely as well as their statistical properties. We also compare these methods and comment on their advantages and drawbacks. We present software packages which are available for the planning, monitoring and analysis of comparative clinical trials with these methods and discuss the practical problems encountered when using them.

The latest versions of all these methods can offer substantial sample size reductions when compared with the single‐stage design not only in the case of clear efficacy but also in the case of complete lack of efficacy of the new treatment. The software packages make their use quite simple. However, it has to be stressed that using these methods requires efficient logistics with real‐time data monitoring and, apart from survival studies or long‐term clinical trials with censored endpoints, is most appropriate when the endpoint is obtained quickly when compared with the recruitment rate.
Metabolic drug interactions with new psychotropic agents
Authors: Spina Edoardo , Scordo Maria Gabriella , D'Arrigo Concetta
Published: September 2003

New psychotropic drugs introduced in clinical practice in recent years include new antidepressants, such as selective serotonin reuptake inhibitors (SSRI) and ‘third generation’ antidepressants, and atypical antipsychotics, i.e. clozapine, risperidone, olanzapine, quetiapine, ziprasidone and amisulpride. These agents are extensively metabolized in the liver by cytochrome P450 (CYP) enzymes and are therefore susceptible to metabolically based drug interactions with other psychotropic medications or with compounds used for the treatment of concomitant somatic illnesses. New antidepressants differ in their potential for metabolic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, while nefazodone is a potent inhibitor of CYP3A4. These antidepressants may be involved in clinically significant interactions when coadministered with substrates of these isoforms, especially those with a narrow therapeutic index. Other new antidepressants including sertraline, citalopram, venlafaxine, mirtazapine and reboxetine are weak in vitro inhibitors of the different CYP isoforms and appear to have less propensity for important metabolic interactions. The new atypical antipsychotics do not affect significantly the activity of CYP isoenzymes and are not expected to impair the elimination of other medications. Conversely, coadministration of inhibitors or inducers of the CYP isoenzymes involved in metabolism of the various antipsychotic compounds may alter their plasma concentrations, possibly leading to clinically significant effects. The potential for metabolically based drug interactions of any new psychotropic agent may be anticipated on the basis of knowledge about the CYP enzymes responsible for its metabolism and about its effect on the activity of these enzymes. This information is essential for rational prescribing and may guide selection of an appropriate compound which is less likely to interact with already taken medication(s).
Structure and pharmacology of swelling‐sensitive chloride channels, ICl,swell
Authors: D'Anglemont De Tassigny Alexandra , Souktani Rachid , Ghaleh Bijan , Henry Patrick , Berdeaux Alain
Published: September 2003

Since several years, the interest for chloride channels and more particularly for the enigmatic swelling‐activated chloride channel (ICl,swell) is increasing. Despite its well‐characterized electrophysiological properties, the ICl,swell structure and pharmacology are not totally elucidated. These channels are involved in a variety of cell functions, such as cardiac rhythm, cell proliferation and differentiation, cell volume regulation and cell death through apoptosis. This review will consider different aspects regarding structure, electrophysiological properties, pharmacology, modulation and functions of these swelling‐activated chloride channels.
Tumour necrosis factor‐alpha‐ vs. growth factor deprivation‐promoted cell death: distinct converging pathways
Authors: Macdonald Nancy J. , Delderfield Susan M. , Zhang Wenru , Taglialatela Giulio
Published: September 2003

Perturbations of neuronal physiological homeostasis are likely to underscore neuronal demise/impairments that are reportedly associated with aging of the central nervous system and age‐related neurodegenerative diseases such as Alzheimer's disease (AD). A number of age‐ and/or disease‐associated neurotoxic events has been described. These include abnormally modified proteins such as beta amyloid and hyper‐phosphorylated Tau, cytokines such as tumour necrosis factor‐alpha (TNFα), high levels of free radicals conducive to oxidative stress, and impaired/decreased neuronal trophic support by neurotrophic factors. Overall, it could be argued that toxic events in the aged brain are either active, such as those due to a direct action of cytokines, or passive, such as those due to lack of growth factor support. It is therefore conceivable that cellular responses to such diverse toxic stimuli are different, suggesting that interventions should be targeted accordingly. In order to begin answering this question, we determined in PC12 cells the time course of activity, in response to TNFα (active) or growth factor withdrawal (passive), of protein kinase c‐zeta (PKCζ), nuclear factor kappa B (NFκB), caspases 3 and 8, and poly (ADP‐ribose) polymerase (PARP), key signal transduction elements associated with modulation of cell death/survival in PC12 cells. We found that the overall activity of PKCζ, NFκB and caspase 8 was significantly different depending on the apoptotic initiator. The pattern of caspase 3 and PARP activity, however, was not statistically different between serum‐free‐ and TNFα‐induced cell death conditions. This suggests that two distinct cell responses are elicited that converge at caspase 3, which then induces downstream events involved in the execution of a common apoptotic programme. These results contribute to the aim of differentially targeting neuronal death in the aged brain (characterized by neurotrophic factor impairments) or in the diseased brain (e.g. AD, characterized by elevated levels of pro‐inflammatory cytokines).
Delayed behavioural aging and altered mortality in Drosophilaβ integrin mutants
Authors: Goddeeris M. M. , Cook‐Wiens E. , Horton W. J. , Wolf H. , Stoltzfus J. R. , Borrusch M. , Grotewiel M. S.
Published: September 2003

The genetic basis for aging is being intensely investigated in a variety of model systems. Much of the focus in Drosophila has been on the molecular–genetic determinants of lifespan, whereas the molecular–genetic basis for age‐related functional declines has been less vigorously explored. We evaluated behavioural aging and lifespan in flies harbouring loss‐of‐function mutations in myospheroid, the gene that encodes βPS, a β integrin. Integrins are adhesion molecules that regulate a number of cellular processes and developmental events. Their role in aging, however, has received limited attention. We report here that age‐related declines in locomotor activity are ameliorated and that mean lifespan is increased in myospheroid mutants. The delayed functional senescence and altered mortality in myospheroid flies are independent of changes in body size, reproduction or stress resistance. Our data indicate that functional senescence and age‐dependent mortality are influenced by β integrins in Drosophila.
Age‐related changes in the metabolism and body composition of three dog breeds and their relationship to life expectancy
Authors: Speakman J. R. , Van Acker A. , Harper E. J.
Published: September 2003

We measured body composition and resting metabolic rates (RMR) of three dog breeds (Papillons, mean body mass 3.0 kg (n = 35), Labrador retrievers, mean body mass 29.8 kg (n = 35) and Great Danes, mean body mass 62.8 kg (n = 35)) that varied between 0.6 and 14.3 years of age. In Papillons, lean body mass (LBM) increased with age but fat mass (FBM) was constant; in Labradors, both LBM and FBM were constant with age, and in Great Danes, FBM increased with age but LBM was constant. FBM averaged 14.8% and 15.7% of body mass in Papillons and Labradors, respectively. Great Danes were leaner and averaged only 10.5% FBM. Pooling the data for all individuals, the RMR was significantly and positively associated with LBM and FBM and negatively associated with age. Once these factors had been taken into account there was still a significant breed effect on RMR, which was significantly lower in Labradors than in the other two breeds. Using the predictive multiple regression equation for RMR and the temporal trends in body composition, we modelled the expenditure of energy (at rest) over the first 8 years of life, and over the entire lifespan for each breed. Over the first 8 years of life the average expenditure of energy per kg LBM were 0.985, 0.675 and 0.662 GJ for Papillons, Labradors and Great Danes, respectively. This energy expenditure was almost 60% greater for the smallest compared with the largest breed. On average, however, the life expectancy for the smallest breed was a further 6 years (i.e. 14 years in total), whereas for the largest breed it was only another 6 months (i.e. 8.5 years in total). Total lifetime expenditure of energy at rest per kg LBM averaged 1.584, 0.918 and 0.691 GJ for Papillons, Labradors and Great Danes, respectively. In Labradors, total daily energy expenditure, measured by the doubly labelled water method in eight animals, was only 16% greater than the observed RMR. High energy expenditure in dogs appears positively linked to increased life expectancy, contrary to the finding across mammal species and within exotherms, yet resembling observations in other intraspecific studies. These contrasting correlations suggest that metabolism is affecting life expectancy in different ways at these different levels of enquiry.
Mitochondrial oxidative stress causes chromosomal instability of mouse embryonic fibroblasts
Authors: Samper E. , Nicholls D. G. , Melov S.
Published: September 2003

Reactive oxygen species are an inevitable by‐product of mitochondrial respiration. It has been estimated that between 0.4 and 4% of molecular oxygen is converted to the radical superoxide () and this level is significantly influenced by the functional status of the mitochondria. It is well established that exogenous oxidative stress and high doses of mitochondrial poisons such as paraquat and carbonyl cyanide 4 (trifluoromethoxy) phenylhydrazone (FCCP) can lead to genomic instability. In this report we show for the first time that endogenous mitochondrial oxidative stress in standard cell culture conditions results in nuclear genomic instability in primary mouse embryonic fibroblasts (MEFs). We show that lack of mitochondrial superoxide dismutase in MEFs leads to a severe increase of double strand breaks, end‐to‐end fusions, chromosomal translocations, and loss of cell viability and proliferative capacity. Our results predict that endogenous mitochondrial oxidative stress can induce genomic instability, and therefore may have a profound effect in cancer and aging.
Systemische Therapie des kutanen Lupus erythematodes
Authors: Wenzel Joerg , Bieber Thomas , Uerlich Manfred , Tüting Thomas
Published: September 2003

Die Behandlung des kutanen Lupus erythematodes (CLE) stellt oft eine therapeutische Herausforderung dar, vor allem bei Patienten, die auf eine rein topische Therapie nicht ansprechen oder zusätzliche systemische Manifestationen zeigen. Hier muß vielfach auf eine systemische Therapie zurückgegriffen werden. Zwar werden einige Substanzen erfolgreich in der systemischen Therapie des CLE eingesetzt, diese sind jedoch häufig nicht für diese Indikation zugelassen.

Wir geben im folgenden eine Übersicht über die eingesetzten Substanzen und stellen den Wirkmechanismus sowie mögliche Indikationen, Zulassung und wichtige Punkte für das praktische Vorgehen dar.

Berücksichtigt werden die Einsatzmöglichkeiten von Kortikosteroiden, Antimalariamedikamenten, Dapson, Azathioprin, Cyclophosphamid, Methotrexat, Retinoiden, Ciclosporin A, Mycophenolat Mofetil, Sulfasalazin, Thalidomid, Clofazimin, Tacrolimus, Immunglobulinen, monoklonalen Antikörper, Plasmapherese, Etanercept, Infliximab, Leflunomid, Gold und Interferon‐α.
Die Behandlung der Psoriasis capillitii mit Dithranol
Authors: Haas Norbert , Wulff‐Woesten Andrea , Sterry Wolfram , Meffert Hans
Published: September 2003

Dithranol kann in den gebräuchlichen Fettgrundlagen am behaarten Kopf nicht angewendet werden und ist in abwaschbaren Zubereitungen zumindest in Deutschland wenig im Gebrauch. Mögliche Gründe dafür könnten sein, daß die Anwendung zu wenig bekannt ist, die Wirkung unterschätzt und Nebenwirkungen überschätzt werden. Wir haben deshalb die Fachliteratur zunächst nach Studien, dann nach Rezepturvorschlägen und Anwendungsempfehlungen und schließlich nach Berichten über Nebenwirkungen durchgesehen. Wir listen auf, welche dithranolhaltigen Fertigpräparate zur Kopfbehandlung in den europäischen Nachbarländern verfügbar sind, dazu die Empfehlungen für den Gebrauch und Warnhinweise für Nebenwirkungen.

Weil das Dithranolmolekül sowohl hydrophile als auch lipophile Anteile aufweist, kann es auch leicht in Seifen inkorporiert werden. Die Stabilität solcher Zubereitungen ist zwar limitiert, in der Praxis ist die Wirksamkeit aber belegt, denn Dithranol in einem Detergens ist in der Hautklinik der Charité seit 20 Jahren in Gebrauch. Das spezielle, hier verwendete Vehikel, Biowaschöl, ist eine ölige flüssige Seife, die zur Reinigung stark verschmutzter Hände in der Industrie konzipiert wurde. Es ist am behaarten Kopf ebenso leicht aufzutragen wie ohne Seife auswaschbar. Wir berichten hier von der 1979 publizierten, ursprünglichen Studie von Meffert et al. mit Dithranol‐Biowaschöl, von den seither gemachten Erfahrungen und einer neuen, vergleichenden Studie, insbesondere über aufgetretene Nebenwirkungen, praktische Hinweise, Patientenkomfort und ‐urteil, die heute wichtige Kriterien darstellen.
Wertigkeit des externen Hautexpanders (ETE®) beim sekundären Verschluß von Hautdefekten
Authors: Zutt Markus , Beckmann Iris , Kretschmer Lutz
Published: September 2003

Hintergrund: Beim Verschluß großer Hautdefekte, bei denen erhebliche Spannung auf den Wundrändern lasten kann, bedient man sich plastischer Methoden bis hin zum Einsatz von subkutanen Ballonexpandern. Wir machen mit dieser Arbeit auf die sehr einfache Methode der Sekundärnaht aufmerksam.

Patienten und Methodik: Es wird ein verbessertes System zur sekundären Hautnaht, ein sog. External Tissue Extender (ETE™) vorgestellt. Dieser Hautexpander besteht im wesentlichen aus Silikonbändern und Stoppern, die eine gute Druckverteilung gewährleisten. Es werden mögliche Anwendungen in der operativen Dermatologie und unsere Erfahrungen beschrieben.

Ergebnisse: Die Implantation und die Handhabung des Expanders sind ausgesprochen einfach und wenig zeitaufwendig. Die funktionellen Ergebnisse sind gut, die kosmetischen Ergebnisse zufriedenstellend. Invasivere chirurgische Maßnahmen können durch die Verwendung dieses Verfahrens vermieden werden. Der auffälligste Nachteil der Methode ist die mögliche Entwicklung von Drucknekrosen unter den Stoppern.

Schlußfolgerung: Nach unseren Erfahrungen ist der Gebrauch eines externen Expanders bei bestimmten dermatochirurgischen Indikationen eine sinnvolle Alternative zu aufwendigeren Verfahren des Hautverschlusses.
Behandlung von Pruritus als Symptom von Hauterkrankungen mit dem Serotonin‐Rezeptorantagonisten Ondansetron
Authors: Zenker Sabine , Schuh Theda , Degitz Klaus
Published: September 2003

Hintergrund: Pruritus ist ein subjektiv häufig sehr belastendes Symptom und stellt nicht selten eine therapeutische Herausforderung dar. Wir berichten über unsere Erfahrungen mit dem Serotonin‐Rezeptorantagonisten Ondansetron bei der Behandlung von Pruritus bei verschiedenen Hauterkrankungen.

Patienten und Methodik: Es wurde der Einfluß von Ondansetron (8 – 12 mg p. o. täglich) auf den Juckreiz bei zwölf Patienten mit unterschiedlichen Hauterkrankungen untersucht. Die subjektive Juckreizintensität wurde täglich mit Hilfe einer visuellen Analogskala im Zeitraum von einer Woche vor, während und einer Woche nach der Behandlung bewertet.

Ergebnisse: Unter Ondansetron war eine Besserung der Pruritussymptomatik bei Prurigo simplex subacuta (vier Patienten), Exsikkationsekzematid (zwei Patienten), Parapsoriasis en plaques und Pruritus sine materia (jeweils ein Patient) festzustellen. Einer von zwei Patienten mit atopischem Ekzem erfuhr eine Besserung seiner Juckreizsymptomatik, keine Besserung zeigt sich bei Patienten mit Urticaria factitia und Notalgia paraesthetica (jeweils ein Patient).

Schlußfolgerung: Bei einigen dermatologischen Erkrankungen kann der begleitende Juckreiz durch Ondansetron günstig beeinflußt werden.
Molecular dynamics simulations of asperity shear in aluminum
Authors: Zhong Jun , Adams James B. , Hector Louis G.
Published: September 2003

One important wear mechanism involves the shear of asperities by other asperities. Molecular dynamics is used to simulate the shearing of aluminum asperities by a “hard” (Lennard-Jones) asperity. These simulations involve the use of a reliable interatomic potential based on the embedded atom method for aluminum that was developed by fitting a large database of density functional calculated forces and experimental data. The simulations are repeated for a wide range of conditions, including velocities, temperatures, asperity shapes, degree of intersection, crystal orientations and adhesive strengths, to determine their effects on the wear process. The design-of-experiment approach is used to analyze the relative importance of each factor and its interactions. Thermal distributions and mechanical deformation in the residual aluminum substrate during asperity shear are analyzed. The final results show that the most significant factor in determining the wear process is the interasperity bonding. The degree of overlap between two asperities is also important. The temperature, the translational velocity, and the crystal orientation play smaller roles.
Electron in one-dimensional symmetric and asymmetric double-well potentials under intense/superintense laser fields: A numerical study based on time-dependent Schrödinger equation
Authors: Wadehra Amita , Vikas  , Deb B. M.
Published: September 2003

The responses of an electron moving in one-dimensional symmetric and asymmetric double-well oscillator (DWO) potentials respectively are analyzed under intense and superintense laser fields by numerically solving the time-dependent Schrödinger equation and evolving the systems for 96 fs at λ=1064 nm as well as different laser intensities. Emphasis is placed on the study of only those features which can arise from the response of a single system. A detailed investigation of multiphoton processes such as high harmonics generation and the energy spectrum (obtained by fast fourier transform of the autocorrelation function) is made. The applicability of these DWOs as model systems for the generation of attosecond pulses is examined. Furthermore, a comparison is made with atoms and molecules under similar conditions, thereby establishing a qualitative parallelism in the behavior of real atoms/molecules and these model DWO systems.
Dynamics and second-order nonlinear optical susceptibility of photoexcited carriers at Si(111) interfaces
Authors: Bodlaki D. , Borguet E.
Published: September 2003

An interface specific investigation, by time-resolved second-harmonic generation, shows that photoexcited carrier dynamics at Si(111) interfaces depend strongly on surface termination. Oxide- and H-terminated surfaces show distinct transient behavior, with a surface recombination velocity <103 cm/s. Incompletely H-terminated Si(111) shows faster dynamics, correlating with less interface passivation. A simple model reveals that the second-order nonlinear optical susceptibility of photoexcited carriers is two orders of magnitude greater than that of the valence band electrons.
Multiple-level defect species evaluation from average carrier decay
Authors: Debuf Didier
Published: September 2003

An expression for the average decay is determined by solving the the carrier continuity equations, which include terms for multiple defect recombination. This expression is the decay measured by techniques such as the contactless photoconductance decay method, which determines the average or volume integrated decay. Implicit in the above is the requirement for good surface passivation such that only bulk properties are observed. A proposed experimental configuration is given to achieve the intended goal of an assessment of the type of defect in an n-type Czochralski-grown silicon semiconductor with an unusually high relative lifetime. The high lifetime is explained in terms of a ground excited state multiple-level defect system. Also, minority carrier trapping is investigated.
Heat capacities of quasi-two-dimensional hetero-spin honeycomb magnets {NBu4[CuIICrIII(ox)3]}n and {PPh4[MnIICrIII(ox)3]}n (Bu=n-butyl, Ph=phenyl, H2ox=oxalic acid): High-temperature series expansion analysis
Authors: Hashiguchi Takao , Miyazaki Yuji , Asano Kaori , Nakano Motohiro , Sorai Michio , Tamaki Hiroko , Matsumoto Naohide , Ōkawa Hisashi
Published: September 2003

Heat capacities of two metal-assembled complexes {NBu4[CuIICrIII(ox)3]}n and {PPh4[MnIICrIII(ox)3]}n (Bu=n-butyl, Ph=phenyl, H2ox=oxalic acid) were measured by adiabatic calorimetry in the 0.5–300 K temperature range. A ferromagnetic phase transition was detected at Tc=6.98 K for {NBu4[CuCr(ox)3]}n and Tc=5.59 K for {PPh4[MnCr(ox)3]}n, above which a remarkable heat capacity tail suggesting the short-range order effects was observed. Furthermore, a lambda-type heat-capacity anomaly due to a structural phase transition was found at Ttrs=226.9 K for {NBu4[CuCr(ox)3]}n and at Ttrs=71.3 K for {PPh4[MnCr(ox)3]}n. The observed entropy gains due to the magnetic phase transitions are very close to the theoretical values, R ln(2×4) for {NBu4[CuCr(ox)3]}n and R ln(6×4) for {PPh4[MnCr(ox)3]}n, expected from the spin multiplicities (CuII, s=1/2; MnII, s=5/2; CrIII, s=3/2). Since this series of metal oxalato assemblies can crystallize in either 2D honeycomb or 3D helical hetero-spin lattices, the theoretical magnetic heat capacities for both lattices were calculated by the high-temperature series expansion up to seventh cumulant to compare with their experimental magnetic heat capacities. The magnetic heat capacities above Tc were reproduced well by the theoretical ones for the 2D honeycomb lattice rather than the 3D helical lattice. The intralayer exchange interaction was estimated to be J/kB=5.0 K for {NBu4[CuCr(ox)3]}n and J/kB=0.95 K for {PPh4[MnCr(ox)3]}n. The analyses based on spin wave theory revealed that both compounds bring about dimensional crossovers into 3D ferromagnetic orders below Tc through the weak interlayer interactions.
A reversible fragment assembly method for de novo protein structure prediction
Authors: Chikenji George , Fujitsuka Yoshimi , Takada Shoji
Published: September 2003

The fragment assembly method is currently one of the most successful methods for the de novo protein structure prediction, where conformational change by fragment replacement is repeated with the simulated annealing scheme. We point out here that the conventional fragment replacement algorithm violates the detailed balance condition. This precludes application of various generalized ensemble algorithms, which would have made conformational sampling more efficient. We develop here a reversible variant of the fragment assembly algorithm which satisfies the detailed balance and thus is applicable to the generalized ensemble techniques. We combine this method with the multicanonical ensemble Monte Carlo, one of the generalized ensemble approaches, and test its performance in the structure prediction of three proteins. We show that the new method can find low energy conformations more efficiently than the conventional simulated annealing method. Also importantly, the lowest energy structures found by the new method are closer to the native than those by the simulated annealing. It seems that conformations with more complex topology can be generated by the new algorithm.
Cathodoluminescence characterization of dislocations in gallium nitride using a transmission electron microscope
Authors: Yamamoto N. , Itoh H. , Grillo V. , Chichibu S. F. , Keller S. , Speck J. S. , DenBaars S. P. , Mishra U. K. , Nakamura S. , Salviati G.
Published: September 2003

Cathodoluminescence technique combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length.
Influence of the polarization on interfacial properties in Al/SiO2/GaN/Al0.4Ga0.6N/GaN heterojunction metal–insulator–semiconductor structures
Authors: Chen P. , Chua S. J. , Wang W. D. , Chi D. Z. , Miao Z. L. , Zheng Y. D.
Published: September 2003

GaN-based metal–insulator–semiconductor (MIS) structures were fabricated by depositing a SiO2 film on a metalorganic chemical vapor deposition-grown GaN/Al0.4Ga0.6N/GaN double heterojunction. Various-frequency capacitance–voltage (C−V) measurements were carried out on the MIS structures. The measured C−V curves show a notable flatband shift of up to about 12.5 V with a typical polarization hysteresis window (9.4 V in width). Moreover, the capacitance of the heterojunction MIS structure reaches a minimum value under 4.1 V bias (forward scan) or −6.5 V bias (reverse scan). Due to the strong polarization and piezoelectric effects existing in AlGaN/GaN heterostructures, these results are deemed to be due to the influence of the piezoelectricity and polarization effects in the structure. Conductance–voltage (G−V) measurements were also performed. Various-frequency C−V and the G−V behaviors indicate that interface states have little influence on the sample.
Improvement in the thermoelectric properties of pressure-tuned β-K2Bi8Se13
Authors: Meng J. F. , Chandra Shekar N. V. , Chung D.-Y. , Kanatzidis M. , Badding J. V.
Published: September 2003

The thermoelectric power, electrical conductivity, crystal structure, and Raman active phonon modes of the semiconductor β-K2Bi8Se13 have been studied under pressure. There is a large increase in the electrical conductivity in the pressure range 0–1 GPa and a sharp maximum in the magnitude of the thermoelectric power at ∼1.4 GPa. X-ray diffraction studies revealed no structural change upon compression. The Raman active vibrational modes did not shift substantially with pressure, suggesting that the pressure induced changes in the phonon thermal conductivity may not be large. The thermoelectric figure of merit, ZT, likely increases by a factor of at least 2 from its ambient pressure value of 0.23. This is the first n-doped material for which we have observed a peak in the thermoelectric power suggestive of an electronic topological transition upon compression.
Eigenspectra calculations using Cartesian coordinates and a rotational symmetry adapted Lanczos method
Authors: Montgomery Jason , Poirier Bill
Published: September 2003

An efficient method is presented for performing molecular quantum dynamics calculations using the (3f−3) Cartesian components of the (f−1) Jacobi vectors, where f is the number of atoms. Coriolis coupling is treated exactly, but with two extra degrees of freedom, relative to coordinates that explicitly separate rotation from vibration. On the other hand, the Cartesian approach has several appealing advantages: (1) code scalability, (2) simple kinetic energies, and (3) minimal CPU requirements (for a given basis size). Our approach combines the phase space optimized discrete variable representation method, which mitigates the effect of the larger dimensionality, together with a version of the symmetry adapted Lanczos method that can exploit both rotational and permutation-inversion symmetry to reduce the effective level degeneracy, and the required number of Lanczos iterations. Results are presented for a three-dimensional calculation of the bound rovibrational levels of the neon dimer.
Optical properties of molecular beam epitaxy-grown Zn1−xMnxTe thin films measured by complementary techniques
Authors: Peiris F. C. , Kowalski B. A. , Liu X. , Bindley U. , Furdyna J. K.
Published: September 2003

By using a combination of prism coupler, reflectivity, and spectroscopic ellipsometry techniques, we have determined the dielectric function of a series of molecular beam epitaxy-grown Zn1−xMnxTe thin films. These results have enabled us to determine the critical point parameters that correspond to the electronic transitions in the Brillouin zone for this particular alloy family. We find that, although the fundamental band gap E0 increases with x for this alloy, E1 and E1+Δ1 transition energies decrease with x for the Zn1−xMnxTe system, in contrast to most other zinc-blende semiconductor alloys.
Effect of thermal annealing of Ni/Au ohmic contact on the leakage current of GaN based light emitting diodes
Authors: Hsu Chin-Yuan , Lan Wen-How , Wu YewChung Sermon
Published: September 2003

The effect of thermal annealing on current–voltage properties of GaN light emitting diodes (LEDs) has been studied. At annealing temperatures above 700 °C, the p–n junction of the diodes became very leaky and Ga-contained metallic bubbles were observed on the surface of Ni/Au p-ohmic contact. Transmission electron microscopy and energy dispersive x-ray spectrometer studies revealed that these metallic bubbles resided directly on top of the threading dislocations in GaN and both Ni and Au were indiffused into the LED structure along the cores of the TDs. The conducting paths formed by the metal containing dislocation cores are believed to be the cause for the observed short circuit behavior of p–n junctions at high annealing temperatures.
Ab initio conical intersections for the Na+H2 system: A four-state study
Authors: Vibók Á. , Halász G. J. , Vèrteśi T. , Suhai S. , Baer M. , Toennies J. P.
Published: September 2003

This article presents a detailed study of the various conical intersections (ci) related to the four lower states of the title system. The approach is based on freezing the positions of the two hydrogens (the distance between them is assumed to be 2.18 a.u. throughout the present study) and allowing the sodium atom to move, undisturbed, to reveal the locations of the ci’s as well as the spatial distribution of their nonadiabatic coupling terms (NACTs). We found altogether seven ci’s—one between the ground state and the first excited state, thus a (1,2) ci, two between the first excited state and the second excited state thus (2,3) ci’s, and the last four are between the second excited state and the third excited state, thus (3,4) ci’s. It was established that the (1,2) ci is a C2v ci located on the symmetry line orthogonal to the HH axis, the (2,3) ci’s are C2v ci’s located on the HH axis (at symmetric positions) and, out of the four (3,4) ci’s, two are C2v ci’s located on the above-mentioned symmetry line, and the other two are Cs ci’s located on both sides of this symmetry line. It was revealed that all seven ci’s are of the elliptic type [Chem. Phys. Lett. 354, 243(2002)], namely their NACTs are concentrated along straight lines—five of them are concentrated along lines parallel to the HH axis and two along the symmetry line vertical to the HH axis. Particular attention is given to two-state, three-state, and four-state quantization. From a practical point of view this study revealed the fact that in general, the two lower states of the Na+H2 system form an isolated group of states, which implies that the two-state system can be diabatized.
Magnetic anisotropy and switching process in diluted Ga1−xMnxAs magnetic semiconductor films
Authors: Moore Graeme P. , Ferré Jacques , Mougin Alexandra , Moreno Maria , Däweritz Lutz
Published: September 2003

Magnetic anisotropy and magnetization reversal phenomena are studied in Ga1−xMnxAs films grown on GaAs(001). From the azimuthal dependence of the magneto-optical Kerr rotation and magnetic linear dichroism, the in-plane 〈100〉 directions are unambiguously assigned as axes of easy magnetization. The values of the cubic and uniaxial anisotropies are determined. Magnetization reversal proceeds by noncoherent spin rotation and irreversible jumps by formation of 90° domains.
Electronic properties of metal–molecule–metal systems at zero bias: A periodic density functional study
Authors: Piccinin S. , Selloni A. , Scandolo S. , Car R. , Scoles G.
Published: September 2003

We have studied the electronic properties of conjugated and saturated dithiol molecules sandwiched between two Au(111) electrodes using first principles density functional calculations with a slab geometry. Relaxation of the molecule/surface adsorption geometry as well as the extended character of the metal electrode states are fully taken into account by our approach. Investigated quantities include the alignment of molecular energy levels with the Fermi energy (EF) of the metal, the charge transfer and electrostatic potential profile, and the local density of electronic states (LDOS) at EF. The behavior of the LDOS for benzene–, dibenzene–, and xylyl–dithiol molecules is analyzed and compared with that of alkane–dithiols of various lengths.
Intrinsic stress evolution in laser deposited thin films
Authors: Scharf Thorsten , Faupel Jörg , Sturm Kai , Krebs Hans-Ulrich
Published: September 2003

In situ stress measurements were performed on polycrystalline Permalloy and Ag thin films laser deposited in ultrahigh vacuum (UHV) and at different Ar gas pressures. In UHV, when the kinetic energy of the particles is high (about 100 eV), in the initial growth stage the stress is dominated by the surface energy and intermixing effects. With increasing deposition time, capillary-induced compressive growth stress is observed. Additionally, the film stress is strongly influenced by the growth mode (island growth or layer-by-layer growth). In the case of Volmer–Weber growth, island zipping generates tensile stress, as soon as island impingement and coalescence occurs. In the late stages, compressive stress due to shot-peening and implantation dominates the measurements, similar as in sputtered films. The depth of influence of the impinging particles is determined to be about 3 nm. With increasing Ar pressure (or at low laser fluence) the impinging particles are slowed down and implantation or intermixing effects are diminished. This is accompanied by changes in the film morphology and texture. At high Ar pressures a compressive-to-tensile transition occurs and the laser deposited films become more comparable to evaporated samples with an open structure. These results can be understood by a combination of stress formation and relaxation effects below the film surface.
Shock viscosity and rise time of explosion waves in geologic media
Authors: Melosh H. J.
Published: September 2003

Near field velocity gauge data from many underground nuclear tests show that the rise time of the stress wave in geologic materials is extremely long—up to 300 ms at ranges of a kilometer or more in alluvium. Steady wave analysis of this data shows that stress waves traveling in salt, granite, alluvium, basalt, and dry tuff also broaden as they propagate, reaching widths from 140 m in salt to nearly 400 m in alluvium. This broadening ceases when the stress in the wave drops below a threshold ranging from a few MPa for alluvium to ∼60 MPa for granite. The rise time and width of the stress wave is a unique function of particle velocity in each material studied: it does not depend on the yield of the explosion. Effective viscosities range from 5×104 Pa s in tuff to 3×105 Pa s in granite. These large viscosities permit realistic computer models of shock wave structure because they can stabilize numerical computations without artificial viscosity.
Formation of GaAs three-dimensional objects using AlAs “facet-forming” sacrificial layer and H3PO4, H2O2, H2O based solution
Authors: Cambel V. , Gregušová D. , Kúdela R.
Published: September 2003

We propose here that sacrificial layers used in III–V technology can be utilized also as “facet-forming” sacrificial layers if the lateral etching rate of the embedded layer is close to the vertical etching rate of the basic material. The idea is supported by computer simulations as well as by several experiments in which high and smooth GaAs mesas with controlled shape and tilt were formed. The wet-chemical etching method uses H3PO4, H2O2, and H2O based solution and an AlAs layer embedded into GaAs. The AlAs layer controls the lateral etching rate and influences the cross-sectional profile of GaAs three-dimensional objects. We show that the mesa slope can be precisely tuned via the solution composition, AlAs thickness, and etching depth. The method suppresses the influence of the GaAs crystallography on the final mesa shape, which simplifies its epitaxial overgrowth. The mesa sidewalls obtained are smooth enough for epitaxial growth of nonplanar heterostructures for microelectromechanical systems and for nanoelectronics.