bluuebunny/crossref_metadata_2025 huggingface dataset:
Bcl‐xL interrupts oxidative activation of neutral sphingomyelinase
Authors: Okamoto Yasuo , Obeid Lina M , Hannun Yusuf A
Published: October 2002

Recent studies demonstrate a role for intracellular oxidation in the regulation of neutral sphingomyelinase (N‐SMase). Glutathione (GSH) has been shown to regulate N‐SMase in vitro and in cells. However, it has not been established whether the effects of GSH in cells are due to direct action on N‐SMase. In this study, treatment of human mammary carcinoma MCF‐7 cells with diamide, a thiol‐depleting agent, caused a decrease in intracellular GSH and degradation of sphingomyelin (SM) to ceramide. The SM pool hydrolyzed in response to diamide belonged to the bacterial SMase‐resistant pool of SM. Importantly, pretreatment of MCF‐7 cells with GSH, N‐acetylcysteine, an antioxidant, or GW69A, a specific N‐SMase inhibitor, prevented diamide‐induced degradation of SM to ceramide, suggesting that intracellular levels of GSH regulate the extent to which SM is degraded to ceramide and that this probably involves a GW69A‐sensitive N‐SMase. Unexpectedly, expression of Bcl‐xL prevented tumor necrosis factor‐α‐induced SM hydrolysis and ceramide accumulation but not the decrease in intracellular GSH. Furthermore, Bcl‐xL inhibited diamide‐induced SM hydrolysis and ceramide accumulation but not the decrease in intracellular GSH. These results suggest that the site of action of Bcl‐xL is downstream of GSH depletion and upstream of ceramide accumulation, and that GSH probably does not exert direct physiologic effects on N‐SMase.
Insights into the evolution of the antenna domains of Type‐I and Type‐II photosynthetic reaction centres through homology modelling
Authors: Fyfe Paul K , Jones Michael R , Heathcote Peter
Published: October 2002

The (bacterio)chlorophylls of photosynthetic antenna and reaction centre complexes are bound to the protein via a fifth, axial ligand to the central magnesium atom. A number of the amino acids identified as providing such ligands are conserved between the large antenna of the cyanobacterial Type‐I reaction centre and smaller antennas of the Type‐I reaction centres of green sulphur bacteria and heliobacteria, and these numbers match closely the estimated number of antenna bacteriochlorophylls in the latter. The possible organisation of the antenna in the latter reaction centres is discussed, as is the mechanism by which the more pigment‐rich antenna of the cyanobacterial reaction centre evolved. The homology modelling approach is also extended to the six‐helix antenna proteins CP47 and CP43 associated with the Photosystem II reaction centre.
Metabolic profiles of dystrophin and utrophin expression in mouse models of Duchenne muscular dystrophy
Authors: Griffin J.L , Sang E , Evens T , Davies K , Clarke K
Published: October 2002

Metabolic profiles from 1H nuclear magnetic resonance spectroscopy have been used to describe both one and two protein systems in four mouse models related to Duchenne muscular dystrophy using the pattern recognition technique partial least squares. Robust statistical models were built for extracts and intact cardiac tissue, distinguishing mice according to expression of dystrophin. Using metabolic profiles of diaphragm, models were built describing dystrophin and utrophin, a dystrophin related protein, expression. Increased utrophin expression counteracted some of the deficits associated with dystrophic tissue. This suggests the method may be ideal for following treatment regimes such as gene therapy.
Testosterone inhibits tumor necrosis factor‐α‐induced vascular cell adhesion molecule‐1 expression in human aortic endothelial cells
Authors: Hatakeyama Haruhiko , Nishizawa Makoto , Nakagawa Atsushi , Nakano Shigeru , Kigoshi Toshikazu , Uchida Kenzo
Published: October 2002

We investigated the effect of testosterone (T) on tumor necrosis factor‐α (TNF‐α)‐induced expression of vascular cell adhesion molecule‐1 (VCAM‐1) in human aortic endothelial cells. Incubation of these cells with T resulted in a dose‐dependent reduction in the expression, with this reduction completely abolished by a selective androgen receptor blocker. Electrophoretic mobility shift assay demonstrated that T inhibited TNF‐α‐induced activation of the transcriptional nuclear factor‐κB, which is critical for the inducible expression of VCAM‐1, probably through the suppression of the nuclear translocation. Our results may suggest an inhibitory effect of T on atherogenesis, providing a novel insight into the consideration of the pathogenesis of atherosclerosis.
Folding kinetics of the lipoic acid‐bearing domain of human mitochondrial branched chain α‐ketoacid dehydrogenase complex
Authors: Naik Mandar T , Chang Yu-Chu , Huang Tai-huang
Published: October 2002

A reversible two‐step (native state↔denatured state) folding mechanism based on equilibrium and stopped flow experiments is proposed for urea denaturation of the lipoyl‐bearing domain (hbLBD) of human mitochondrial branched chain α‐ketoacid dehydrogenase (BCKD) complex. The results from this circular dichroism (CD) and fluorescence study have ruled out populated kinetic or equilibrium intermediates on folding pathway of this β‐barrel domain under experimental conditions. Both studies suggested mono‐exponential kinetics without any burst phases. Moreover the thermodynamic parameters ΔG
H2O and m obtained from the kinetic analysis are consistent with the equilibrium measurements.
Establishment of the enzymatic protein acetylation independent of acetyl CoA: recombinant glutathione S‐transferase 3‐3 is acetylated by a novel membrane‐bound transacetylase using 7,8‐diacetoxy‐4‐methyl coumarin as the acetyl donor
Authors: Kohli Ekta , Gaspari Marco , Raj Hanumantharao G , Parmar Virinder S , van der Greef Jan , Gupta Garima , Kumari Ranju , Prasad Ashok K , Goel Sanjay , Pal Giridhari , Tyagi Yogesh K , Jain Subhash C , Ahmad Nizamuddin , Watterson Arthur C , Olsen Carl E
Published: October 2002

The current knowledge on biological protein acetylation is confined to acetyl CoA‐dependent acetylation of protein catalyzed by specific acetyl transferases and the non‐enzymatic acetylation of protein by acetylated xenobiotics such as aspirin. We have discovered a membrane‐bound enzyme catalyzing the transfer of acetyl groups from the acetyl donor 7,8‐diacetoxy‐4‐methyl coumarin (DAMC) to glutathione S‐transferase 3‐3 (GST3‐3), termed DAMC:protein transacetylase (TAase). The purified enzyme was incubated with recombinant GST3‐3 subunit and DAMC, the modified protein was isolated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) in gel digested with trypsin and the tryptic digest was analyzed by mass spectrometry. The N‐terminus and six lysines, Lys‐51, ‐82, ‐124, ‐181, ‐191 and ‐210, were found to be acetylated. The acetylation of GST3‐3 described above was not observed in the absence of either DAMC or TAase. These results clearly establish the phenomenon of protein acetylation independent of acetyl CoA catalyzed by a hitherto unknown enzyme (TAase) utilizing a certain xenobiotic acetate (DAMC) as the active acetyl donor.
Energy equilibration and primary charge separation in chlorophyll d‐based photosystem I reaction center isolated from Acaryochloris marina
Authors: Kumazaki Shigeichi , Abiko Kazuki , Ikegami Isamu , Iwaki Masayo , Itoh Shigeru
Published: October 2002

Primary photochemistry in photosystem I (PS I) reaction center complex from Acaryochloris marina that uses chlorophyll d instead of chlorophyll a has been studied with a femtosecond spectroscopy. Upon excitation at 630 nm, almost full excitation equilibration among antenna chlorophylls and 40% of the excitation quenching by the reaction center are completed with time constants of 0.6(±0.1) and 4.9(±0.6) ps, respectively. The rise and decay of the primary charge‐separated state proceed with apparent time constants of 7.2(±0.9) and 50(±10) ps, suggesting the reduction of the primary electron acceptor chlorophyll (A0) and its reoxidation by phylloquinone (A1), respectively.
Folding transition of large DNA completely inhibits the action of a restriction endonuclease as revealed by single‐chain observation
Authors: Oana Hidehiro , Tsumoto Kanta , Yoshikawa Yuko , Yoshikawa Kenichi
Published: October 2002

The biochemical characteristics of lambda DNA chains in folded/unfolded states upon cleavage by the restriction enzyme ApaLI were investigated in the presence of spermine. These characteristics of DNA chains depending on their higher‐order structure were studied at the single‐molecule level using fluorescence microscopy. With a low concentration of spermine, lambda DNA takes a random coiled conformation and allows digestion by the enzyme, while under a high concentration of spermine, lambda DNA takes a compact folded structure and inhibits such attack. Together with comparative experiments on short oligomeric DNA, our results suggest that the transition in the higher‐order structure causes on/off‐type switching of sensitivity to the enzyme.
Lipopolysaccharide increases resistin gene expression in vivo and in vitro
Authors: Lu Shao-Chun , Shieh Wei-Yeong , Chen Chia-Ying , Hsu Shu-Ching , Chen Hui-Ling
Published: October 2002

Although resistin has been thought to be an important link between obesity and diabetes, recent results do not support this hypothesis. We speculated that resistin may be involved in inflammatory processes and be induced by inflammatory stimuli. In this study, we tested whether lipopolysaccharide (LPS) induced resistin expression in rats. The results show that resistin mRNA levels in white adipose tissue and white blood cells were increased by LPS treatment. LPS also increased resistin mRNA levels in 3T3‐L1 adipocytes and human peripheral blood monocytes. The results suggest that resistin is involved in insulin resistance and probably in other inflammatory responses.
A novel subtilase from common bean leaves
Authors: Popovič Tatjana , Puizdar Vida , Brzin Jože
Published: October 2002

We describe the isolation of a protease from common bean leaves grown in the field. On the basis of its biochemical properties it was classified as serine proteinase belonging to the subtilisin clan. Isoelectric focusing resulted in a single band at pH 4.6, and SDS–PAGE in a single band corresponding to M
r 72 kDa. The proteinase activity is maximal at pH 9.9 and shows high stability in the alkaline region. The relative activities of the proteinase for eight different synthetic substrates were determined. The requirement for Arg in the P1 position appeared obligatory. k
cat/K
m values indicate that, for highest catalytic efficiency, a basic amino acid is also required in the P2 position, presenting a motif typical of the cleavage site for the kexin family of subtilases. The sequence of the 17 N‐terminal amino acids of this proteinase shows similarity to those of other plant subtilases, sharing the highest number of identical amino acids with proteinase C1 from soybean seedling cotyledons and a cucumisin‐like proteinase from white gourd (Benincasa hispida).
Non‐phosphorylating glyceraldehyde‐3‐phosphate dehydrogenase is post‐translationally phosphorylated in heterotrophic cells of wheat (Triticum aestivum)
Authors: Bustos Diego M , Iglesias Alberto A
Published: October 2002

In wheat, non‐phosphorylating, NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (GAPN) was found to be encoded by one gene giving rise to a single protein. However, Western blots revealed two different subunits of about 58 and 60 kDa in endosperm and shoots. The latter was attributed to in vivo phosphorylation of shoot GAPN. No modification occurred in leaves, where the enzyme is composed by a single 58 kDa polypeptide. GAPN partially purified from shoots and endosperm was dephosphorylated in vitro with alkaline phosphatase. Phosphorylated GAPN exhibited similar affinity for substrates but a lower V
max compared to the non‐phosphorylated enzyme. Results suggest that reversible phosphorylation of GAPN could regulate NADPH production in the cytosol of heterotrophic plant cells.
Yeast Mon1p/Aut12p functions in vacuolar fusion of autophagosomes and cvt‐vesicles
Authors: Meiling-Wesse Khuyen , Barth Henning , Voss Christiane , Barmark Gunilla , Murén Eva , Ronne Hans , Thumm Michael
Published: October 2002

Here we identify Mon1p as being essential for the cvt‐pathway and autophagy. Thus, mon1Δ cells are impaired in proaminopeptidase I maturation and homozygous diploid mon1Δ cells do not sporulate. Quantitative autophagy measurements suggest a complete autophagy block. The autophagosomal marker protein GFP‐Aut7p accumulates in mon1Δ cells at punctate structures outside the vacuole. Furthermore, proaminopeptidase I accumulates in mon1Δ cells in a proteinase‐protected form. Our data demonstrate that mon1Δ cells are defective in the fusion of cvt‐vesicles and autophagosomes with the vacuole. Consistent with this, GFP‐Mon1p localizes to the cytosol and to punctate structures within the cytosol.
A novel GTP‐binding protein hGBP3 interacts with NIK/HGK
Authors: Luan Zhidong , Zhang Yan , Liu Aihua , Man Yunfang , Cheng Lu , Hu Gengxi
Published: October 2002

A novel human guanylate‐binding protein (GBP) hGBP3 was identified and characterized. Similar as the two human guanylate‐binding proteins hGBP1 and hGBP2, hGBP3 has the first two motifs of the three classical guanylate‐binding motifs, GXXXXGKS (T) and DXXG, but lacks the N (T) KXD motif. Escherichia coli‐expressed hGBP3 protein specifically binds to guanosine triphosphate (GTP). Using a yeast two‐hybrid system, it was revealed that the N‐terminal region of hGBP3 binds to the C‐terminal regulatory domain of NIK/HGK, a member of the group I GCK (germinal center kinase) family. This interaction was confirmed by in vitro glutathione‐S‐transferase (GST) pull‐down and co‐immunoprecipitation assays.
Five disulfide bridges stabilize a hevein‐type antimicrobial peptide from the bark of spindle tree (Euonymus europaeus L.)
Authors: Van den Bergh Karolien P.B , Proost Paul , Van Damme Jo , Coosemans Jozef , Van Damme Els J.M , Peumans Willy J
Published: October 2002

A small 45 amino acid residue antifungal polypeptide was isolated from the bark of spindle tree (Euonymus europaeus L.). Though the primary structure of this so‐called E. europaeus chitin‐binding protein or Ee‐CBP is highly similar to the hevein domain, it distinguishes itself from most previously identified hevein‐type antimicrobial peptides (AMP) by the presence of two extra cysteine residues that form an extra disulfide bond. Due to these five disulfide bonds Ee‐CBP is a remarkably stable protein. Agar diffusion and microtiterplate assays demonstrated that Ee‐CBP is a potent antimicrobial protein. IC50‐values as low as 1 μg/ml were observed for the fungus Botrytis cinerea. Comparative assays further demonstrated that Ee‐CBP is a stronger inhibitor of fungal growth than Ac‐AMP2 from Amaranthus caudatus seeds, which is considered one of the most potent antifungal hevein‐type plant proteins.
Mitogen‐inducible gene 6 (MIG‐6), adipophilin and tuftelin are inducible by hypoxia
Authors: Saarikoski Sirkku T , Rivera Steven P , Hankinson Oliver
Published: October 2002

Adaptation to hypoxia is essential for tumor progression. Transcriptional activation of hypoxia‐regulated genes is mediated by hypoxia‐inducible factor 1 (HIF‐1), a heterodimer of HIF‐1α and ARNT (Ah receptor nuclear translocator; HIF‐1β). Using representational difference analysis, we identified three novel hypoxia‐inducible genes: MIG‐6 (gene 33), adipophilin and tuftelin. The mRNAs for these genes were inducible by 1% O2 in the human HepG2 and MCF‐7 cell lines. Hypoxic induction of the MIG‐6 and tuftelin proteins was also observed. Induction was ARNT‐dependent. Induction also occurred in livers of mice treated with CoCl2, which mimics hypoxia. The potential roles of these genes in adaptation to hypoxia and in tumorigenesis will be of considerable interest.
Physiological variation in metabolic phenotyping and functional genomic studies: use of orthogonal signal correction and PLS‐DA
Authors: Gavaghan C.L , Wilson I.D , Nicholson J.K
Published: October 2002

Metabolic phenotyping, or metabotyping, is increasingly being used as a probe in functional genomics studies. However, such profiling is subject to intrinsic physiological variation found in all animal populations. Using a nuclear magnetic resonance‐based metabonomic approach, we show that diurnal variations in metabolism can obscure the interpretation of strain‐related metabolic differences in two phenotypically normal mouse strains (C57BL10J and Alpk:ApfCD). To overcome this problem, diurnal‐related metabolic variation was removed from these spectral data by application of orthogonal signal correction (OSC), a data filtering method. Interpretation of the removed orthogonal variation indicated that diurnal‐related variation had been removed and that the AM samples contained higher levels of creatine, hippurate, trimethylamine, succinate, citrate and 2‐oxo‐glutarate and lower levels of taurine, trimethylamine‐N‐oxide, spermine and 3‐hydroxy‐iso‐valerate relative to the PM samples. We propose OSC will have great potential removing confounding variation obscuring subtle changes in metabolism in functional genomic studies and will be of benefit to optimising interpretation of proteomic and genomic datasets.
The post‐natal heart contains a myocardial stem cell population
Authors: Hierlihy Andrée M , Seale Patrick , Lobe Corrinne G , Rudnicki Michael A , Megeney Lynn A
Published: October 2002

The recent identification of stem cell pools in a variety of unexpected tissue sources has raised the possibility that a pluripotent stem cell population may reside in the myocardium and contribute to the post‐natal growth of this tissue. Here, we demonstrate that the post‐natal myocardium contains a resident verapamil‐sensitive side population (SP), with stem cell‐like activity. When growth of the post‐natal heart was attenuated through over‐expression of a dominant negative cardiac transcription factor (MEF2C), the resident SP cell population was subject to activation, followed by a consequent depletion. In addition, cardiac SP cells are capable of fusion with other cell types, but do not adopt the corresponding gene expression profile. These observations suggest that a responsive stem cell pool resides in the adult myocardium, and may influence adaptation of the post‐natal heart.
Involvement of aberrant glycosylation in phosphorylation of tau by cdk5 and GSK‐3β
Authors: Liu Fei , Iqbal Khalid , Grundke-Iqbal Inge , Gong Cheng-Xin
Published: October 2002

Microtubule‐associated protein tau is abnormally hyperphosphorylated, glycosylated, and aggregated in affected neurons in the brains of individuals with Alzheimer's disease (AD). We recently found that the glycosylation might precede hyperphosphorylation of tau in AD. In this study, we investigated the effect of glycosylation on phosphorylation of tau catalyzed by cyclin‐dependent kinase 5 (cdk5) and glycogen synthase kinase‐3β (GSK‐3β). The phosphorylation of the longest isoform of recombinant human brain tau, tau441, at various sites was detected by Western blots and by radioimmuno‐dot‐blot assay with phosphorylation‐dependent and site‐specific tau antibodies. We found that cdk5 phosphorylated tau441 at Thr‐181, Ser‐199, Ser‐202, Thr‐205, Thr‐212, Ser‐214, Thr‐217, Thr‐231, Ser‐235, Ser‐396, and Ser‐404, but not at Ser‐262, Ser‐400, Thr‐403, Ser‐409, Ser‐413, or Ser‐422. GSK‐3β phosphorylated all the cdk5‐catalyzed sites above except Ser‐235. Deglycosylation by glycosidases depressed the subsequent phosphorylation of AD‐tau (i) with cdk5 at Thr‐181, Ser‐199, Ser‐202, Thr‐205, and Ser‐404, but not at Thr‐212; and (ii) with GSK‐3β at Thr‐181, Ser‐202, Thr‐205, Ser‐217, and Ser‐404, but not at Ser‐199, Thr‐212, Thr‐231, or Ser‐396. These data suggest that aberrant glycosylation of tau in AD might be involved in neurofibrillary degeneration by promoting abnormal hyperphosphorylation by cdk5 and GSK‐3β.
Time and amplitude regulation of pulsatile insulin secretion by triggering and amplifying pathways in mouse islets
Authors: Ravier Magalie A , Henquin Jean-Claude
Published: October 2002

Glucose‐induced insulin secretion is pulsatile. We investigated how the triggering pathway (rise in β‐cell [Ca2+]i) and amplifying pathway (greater Ca2+ efficacy on exocytosis) influence this pulsatility. Repetitive [Ca2+]i pulses were imposed by high K++ diazoxide in single mouse islets. Insulin secretion (measured simultaneously) tightly followed [Ca2+]i changes. Lengthening [Ca2+]i pulses increased the duration but not the amplitude of insulin pulses. Increasing glucose (5–20 mmol/l) augmented the amplitude of insulin pulses without changing that of [Ca2+]i pulses. Larger [Ca2+]i pulses augmented the amplitude of insulin pulses at high, but not low glucose. In conclusion, the amplification pathway ensures amplitude modulation of insulin pulses whose time modulation is achieved by the triggering pathway.
The glucagon‐like peptide‐1 receptor binding site for the N‐terminus of GLP‐1 requires polarity at Asp198 rather than negative charge
Authors: López de Maturana Rakel , Donnelly Dan
Published: October 2002

The mutation of Asp198 to Asn in the receptor for glucagon‐like peptide‐1(7–36)amide (GLP‐1) had no effect upon GLP‐1 affinity whereas substitution with Ala greatly reduced affinity, demonstrating the importance of polarity rather than negative charge at Asp198. However, the Asp198‐Ala mutation had less effect upon the affinity of Exendin‐4, a peptide agonist that has been shown previously not to require its N‐terminus for high affinity. Moreover, the affinity of a truncated GLP‐1 analogue lacking the first eight residues was not affected by the Asp198‐Ala mutation, demonstrating that Asp198 is required for maintaining the binding site of the N‐terminal region of GLP‐1.
The influence of residue 190 in the S1 site of trypsin‐like serine proteases on substrate selectivity is universally conserved
Authors: Sichler Katrin , Hopfner Karl-Peter , Kopetzki Erhard , Huber Robert , Bode Wolfram , Brandstetter Hans
Published: October 2002

We examined the influence of Ser/Ala190 in the S1 site on P1 substrate selectivity in several serine proteases. The impact of residue 190 on the selectivity was constant, regardless of differences in original selectivity or reactivity. Substrate binding in S1 was optimised in all wild‐type enzymes, while the effects on k
cat depended on the combination of residue 190 and substrate. Mutagenesis of residue 190 did not affect the S2–S4 sites. Pronounced selectivity for arginine residues was coupled with low enzymatic activity, in particular in recombinant factor IXa. This is due to the dominance of the S1–P1 interaction over substrate binding in the S2–S4 sites.
Reflections on the Process of Auditing Myocardial Infarction
Authors: Gamon R , Carolan K
Published: October 2002

The publication of the National Service Framework for Coronary Heart Disease has meant that audit is becoming an increasingly important part of cardiac healthcare provision in England. Comparisons between hospitals will be made so it is essential that the audit data is as robust as possible. Nurses often play a key role in the collection of such data. This article reflects on this process, with particular reference to thrombolysis in acute myocardial infarction. Topics discussed include eligibility, the role of a clinician, electrocardiogram interpretation, justified delays, inappropriate and ‘missed’ administration. As some of the information is, arguably, open to interpretation, the authors believe that clinical auditors will inevitably have to grapple with such clinical definitions and their implications.
Undertaking Nursing Interventions Throughout Europe: Research Activities of the Working Group on Cardiovascular Nursing of the European Society of Cardiology
Authors:   Undertaking Nursing Intervention throughout Europe (UNITE) study group
Published: October 2002

The working Group on Cardiovascular Nursing is actively involved in international research though the UNITE (Undertaking Nursing Research Throughout Europe) research program, a new initiative for the WGCN. A group of cardiovascular nursing researchers from a number of different European countries committed themselves to a research group that is designed to promulgate international research in the field of cardiac nursing. The first study was a survey on coronary risk factors in a cohort of cardiac nurses from Europe. At this moment four additional studies are planned aimed at the development of the nursing profession in Europe and improvement of care for patients with chronic cardiac disease. If, as hoped, these studies prove to be successful, it will provide the seed for other international collaborations of this type.
Relativistic theory of moderately coupled plasmas: Formulation of appropriate Fokker–Planck equation
Authors: Baral K. C. , Mohanty J. N.
Published: October 2002

Generalized velocity differential formulation concerning Fokker–Planck coefficients for moderately coupled [2≲log(2/θ0)≲10] magnetized, relativistic plasmas is derived. In the limiting approximation it conforms to early theories of weakly coupled plasmas and approximates to the early nonrelativistic theories.
On generalizations of the Calogero–Moser–Sutherland quantum problem and WDVV equations
Authors: Veselov A. P.
Published: October 2002

It is proved that if the Schrödinger equation Lψ=λψ of Calogero–Moser–Sutherland type with L=−Δ+∑α∈A+[mα(mα+1)(α,α)/sin2(α,x)] has a solution of the product form ψ0=∏α∈A+ sin−mα(α,x), then the function F(x)=∑α∈A+mα(α,x)2 log(α,x)2 satisfies the generalized WDVV equations. This explains the relation between these equations and the deformed CMS quantum problems observed in an earlier work [Phys. Lett. A 261, 297 (1999)].
Covariant Hamiltonian boundary conditions in General Relativity for spatially bounded space–time regions
Authors: Anco Stephen C. , Tung Roh S.
Published: October 2002

We investigate the covariant Hamiltonian symplectic structure of General Relativity for spatially bounded regions of space–time with a fixed time-flow vector. For existence of a well-defined Hamiltonian variational principle taking into account a spatial boundary, it is necessary to modify the standard Arnowitt–Deser–Misner Hamiltonian by adding a boundary term whose form depends on the spatial boundary conditions for the gravitational field. The most general mathematically allowed boundary conditions and corresponding boundary terms are shown to be determined by solving a certain equation obtained from the symplectic current pulled back to the hypersurface boundary of the space–time region. A main result is that we obtain a covariant derivation of Dirichlet, Neumann, and mixed type boundary conditions on the gravitational field at a fixed boundary hypersurface, together with the associated Hamiltonian boundary terms. As well, we establish uniqueness of these boundary conditions under certain assumptions motivated by the form of the symplectic current. Our analysis uses a Noether charge method which extends and unifies several results developed in recent literature for General Relativity. As an illustration of the method, we apply it to the Maxwell field equations to derive allowed boundary conditions and boundary terms for the existence of a well-defined Hamiltonian variational principle for an electromagnetic field in a fixed spatially bounded region of Minkowski space–time.
Microlocal analysis of quantum fields on curved space–times: Analytic wave front sets and Reeh–Schlieder theorems
Authors: Strohmaier Alexander , Verch Rainer , Wollenberg Manfred
Published: October 2002

We show in this article that the Reeh–Schlieder property holds for states of quantum fields on real analytic curved space–times if they satisfy an analytic microlocal spectrum condition. This result holds in the setting of general quantum field theory, i.e., without assuming the quantum field to obey a specific equation of motion. Moreover, quasifree states of the Klein–Gordon field are further investigated in the present work and the (analytic) microlocal spectrum condition is shown to be equivalent to simpler conditions. We also prove that any quasifree ground or KMS state of the Klein–Gordon field on a stationary real analytic space–time fulfills the analytic microlocal spectrum condition.
Fast plasma heating in the high-frequency skin-effect regime
Authors: Ferrante G. , Zarcone M. , Uryupin S. A.
Published: October 2002

Dense plasma heating by an ultrashort laser pulse is investigated in the regime of the high-frequency skin effect. The electron temperature evolution on the plasma surface and the properties of the classical heat transfer into the plasma interior are studied. Three possible plasma heating mechanisms are considered. At relatively not large temperatures the plasma heating, due to radiation absorption, is controlled by the electron–ion collisions in the skin layer. The others two pathways are related to high temperatures and take place in the regime of collisionless radiation absorption when the electrons are reflected by the plasma surface either specularly or diffusely. It is shown that, compared with the specular reflection, the diffuse one yields a larger increase of the electron temperature on the plasma surface and a faster propagation of the heat flux in the plasma interior, even when the fraction of diffusely reflected electrons is not high.
Slowing down of light by laser induced barrier hopping
Authors: Thanopulos Ioannis , Shapiro Moshe
Published: October 2002

We suggest that a very significant reduction in the group velocity of light occurs in a laser induced barrier-hopping process, known as “Laser Catalysis.” In this process a system is made to hop over a potential barrier via a virtual transition to an excited bound state. As in electromagnetically induced transparency (EIT), the light absorption is predicted to dip to zero at a certain frequency, thereby also changing the refractive index, inducing in turn the slowing down of the group velocity of the light. In contrast to EIT, a single pulse is predicted to induce its own transparency and in contrast to self-induced transparency the process is predicted to be insensitive to the pulse area (as long as the pulse is intense enough to meet the adiabaticity criterion). Thus, the medium becomes transparent to the light, as the laser induced barrier-hopping process brings about a fundamental change in the medium.
Generalization of Berry’s geometric phase, equivalence of the Hamiltonian nature, quantizability and strong stability of linear oscillatory systems, and conservation of adiabatic invariants
Authors: Bliokh K. Yu.
Published: October 2002

A linear set of ordinary differential equations with a matrix depending on a set of adiabatically varying parameters is considered. Its asymptotic solutions are constructed to an arbitrary accuracy in the adiabaticity parameter ε. By extending the phase space of the system not only with the space of parameters, like in the theory of Berry’s phase, but also with the space of their derivatives, it proves possible to represent the phase of the solution as a sum of the dynamic phase and a generalized geometric phase (determined by a contour integral in the space of parameters and derivatives). Hence, it is possible to obtain the asymptotic results to any degree of accuracy in ε, while earlier they were obtainable only in the first-order adiabatic approximation. Namely, for linear oscillatory adiabatic systems, the quantizability, parametric stability, and the Hamiltonian nature of the system are equivalent properties. As a consequence, one can obtain the well-known result regarding conservation with accuracy to any power of ε of adiabatic invariants in a Hamiltonian system on a torus. An important point is that the generalized geometric phase can appear, in contrast to Berry’s phase, with only one real varying parameter.
Application of plasma resonance condition for prediction of large Kerr effects
Authors: De A. , Puri A.
Published: October 2002

Resonance like enhancement of magneto-optic Kerr effects (MOKEs) have been attributed to numerous effects, one of them being plasma resonance of free charge carriers, which is analytically and numerically investigated here. Analytical expressions for frequency dependent enhancement of MOKE are obtained in the general framework of the Drude model, which are then applied to well known expressions describing MOKE. The derived expressions are numerically tested for various optical constants. It is known that for certain materials, the resonance like enhancements in the Kerr spectrum occur in the near vicinity of Re[εxx]=1, which is generally near the plasma edge. This is seen to be true when the plasma frequency ωp is greater in magnitude as compared to the cyclotron frequency ωc, i.e., if ωp≫ωc, whereas in the event of a large reflection edge split, i.e., if ωp∼ωc the resonance like peaks will occur near Re[ε+.ε−]≈1, which is a relatively more general condition as compared to Re[εxx]=1. Second, we see through model calculations that the spectral proximity of the MOKE resonance peak to the plasma edge is also subject to the magnitude of the background dielectric constant. Results are explained analytically and numerically. Good agreement is obtained between the expressions derived here and the numerically observed occurrence of resonance like peaks in the Kerr spectrum.
Matrix models for beta ensembles
Authors: Dumitriu Ioana , Edelman Alan
Published: October 2002

This paper constructs tridiagonal random matrix models for general (β>0) β-Hermite (Gaussian) and β-Laguerre (Wishart) ensembles. These generalize the well-known Gaussian and Wishart models for β=1,2,4. Furthermore, in the cases of the β-Laguerre ensembles, we eliminate the exponent quantization present in the previously known models. We further discuss applications for the new matrix models, and present some open problems.
The embedding of the space–time in five dimensions: An extension of the Campbell–Magaard theorem
Authors: Dahia F. , Romero C.
Published: October 2002

We extend the Campbell–Magaard embedding theorem by proving that any n-dimensional semi-Riemannian manifold can be locally embedded in an (n+1)-dimensional Einstein space. We work out some examples of application of the theorem and discuss its relevance in the context of modern higher-dimensional spacetime theories.
Highly efficient green up-conversion luminescence of Nd3+–Yb3+–Ho3+ codoped fluorite-type nanocrystals in transparent glass ceramics
Authors: Qiu Jianbei , Kawamoto Yoji , Zhang Junjie
Published: October 2002

Oxyfluoride glasses were developed with composition 30SiO2⋅15AlO1.5⋅28PbF2⋅22CdF2⋅(4.8−x)GdF3⋅0.1NdF3⋅0.1HoF3⋅xYbF3 (x=0, 0.1, 0.2, 0.5, 1, 2, 3, 4, and 4.8) in mole percent. Powder x-ray diffraction analysis revealed that the heat treatments of the oxyfluoride glasses at 450 °C for 0.5 h cause the precipitation of Nd3+–Yb3+–Ho3+ codoped fluorite-type nanocrystals of about 16.3 nm in diameter in the glass matrix. These transparent glass ceramics exhibited very strong green up-conversion luminescence due to the Ho3+: (5F4, S25)→5I8 transition under 800 nm excitation. The intensity of the green up-conversion luminescence in a 1 mol % YbF3-containing glass ceramic was found to be about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho3+ up-conversion luminescence in the oxyfluoride glass ceramics is discussed. An up-conversion mechanism is also proposed.
Born–Infeld type equations for electrostatic fields
Authors: Fortunato D. , Orsina L. , Pisani L.
Published: October 2002

In this paper we consider the field equations deduced by the second order approximation of the Born–Infeld Lagrangian density for the electromagnetic field. In particular we prove the existence of finite energy electrostatic fields, both in the case of a point charge and in the case of L1 charge density.
Optimal regularity in a variational problem for current sheets in ideal magnetohydrodynamics
Authors: Laurence Peter , Stredulinsky Edward W.
Published: October 2002

We characterize local behavior, and establish optimal local regularity, for minimizers of the functional E(ψ)=∫Ω|∇ψ|2 over collections 𝒞 that are weakly closed in H1(Ω), closed under local smooth domain perturbations, and for which E(ψ) controls ∫Ωψ2. Minimizers ψ satisfy a weak magnetohydrodynamic (MHD) equation and correspond to fields in low density ideal plasmas under cylindrical symmetry where the field component in the direction of the axis of symmetry is zero. We prove that (∂ψ/∂x+i∂ψ/∂y)2 is complex analytic, and locally ψ=f(φ) for some φ, f, with Δφ=0 and f Lipschitz continuous with |f′|=1 almost everywhere, near points where ∇ψ≠0. An analogous but more elaborate characterization is established at points where ∇ψ=0. This characterization forms the basis for a general theory of the existence of current sheets due to imposed topological and boundary constraints. Results carry over to functions that are stationary points of E(ψ) with respect to local smooth domain variations.
Observation of ion heating by stimulated-Brillouin-scattering-driven ion-acoustic waves using Thomson scattering
Authors: Froula D. H. , Divol L. , Baldis H. A. , Berger R. L. , Braun D. G. , Cohen B. I. , Johnson R. P. , Montgomery D. S. , Williams E. A. , Glenzer S. H.
Published: October 2002

Thomson-scattering measurements of the growth of ion-acoustic waves are obtained from well-characterized multi-ion-species plasmas consisting of gold and beryllium. Simultaneously, the ion temperature is accurately measured by comparing the relative amplitude of thermal ion-acoustic modes. A twofold increase in ion temperature was measured when ion-acoustic waves are excited to large amplitudes by stimulated Brillouin scattering (SBS). This increase in ion temperature is a strong indication of hot ions due to trapping. The measured SBS reflectivity is explained by nonlinear detuning of the SBS instability due to these trapping effects.
Massively parallel adhesion and reactivity measurements using simple and inexpensive magnetic tweezers
Authors: Assi Fabiano , Jenks Robert , Yang Jerry , Love Christopher , Prentiss Mara
Published: October 2002

Single molecule techniques to measure biological molecules and reactions have provided an alternative way to probe and visualize bond characteristics and reaction dynamics. However, these techniques, such as atomic force microscopy, optical tweezers, and micropipettes often require expensive and complicated equipment and are very time intensive, because each measurement gives the results of one-single reaction or a property of one-single molecule. Here, we report on a technique that allows for massively parallel measurements on many individual single molecules in microfluidic systems. We demonstrate the effectiveness of a simple, robust, inexpensive apparatus, by using it to differentiate between deoxyribonucleic acid (DNA) assemblies that are merely annealed from others that are ligated, and by measuring the rate at which annealed DNA denatures as function of temperature.
The maximum dimension of the inheriting algebra in perfect fluid space–times
Authors: Coley A. A. , Hall G. S. , Keane A. J. , Tupper B. O. J.
Published: October 2002

We determine the maximum dimension of the Lie algebra of inheriting conformal Killing vectors in perfect fluid space–times. For the case of conformally flat space–times the maximum dimension is eight and for the case of nonconformally flat space–times the maximum dimension is found to be five. We illustrate each case with examples.
Quantum group covariance and the braided structure of deformed oscillators
Authors: Yildiz A.
Published: October 2002

The connection between braided Hopf algebra structure and quantum group covariance of the deformed oscillators is constructed explicitly. In this context we provide deformations of the Hopf algebra of functions on SU(1,1). Quantum subgroups and their representations are also discussed.
Scattering relations for point sources: Acoustic and electromagnetic waves
Authors: Athanasiadis C. , Martin P. A. , Spyropoulos A. , Stratis I. G.
Published: October 2002

The problem of scattering of spherical waves by a bounded obstacle is considered. General scattering theorems are proved. These relate the far-field patterns due to scattering of waves from a point source put in any two different locations. The scatterer can have any of the usual properties, penetrable or impenetrable. The optical theorem is recovered as a corollary. Mixed scattering relations are also established, relating the scattered fields due to a point source and a plane wave.
Growth and structure of fullerene-like CNx thin films produced by pulsed laser ablation of graphite in nitrogen
Authors: Voevodin A. A. , Jones J. G. , Zabinski J. S. , Czigány Zs. , Hultman L.
Published: October 2002

The growth and structure of fullerene-like CNx films produced by laser ablation of graphite in low pressure nitrogen were investigated. Deposition conditions were selected based on investigations of CN and C2 concentration at the condensation surface, vibrational temperature of CN radicals, and kinetic energies of atomic and molecular species. Films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, nanoindentation, and stress analyses. The nitrogen content in CNx films directly depended on the concentration of CN radicals at the condensation surface. Formation of fullerene-like structures required a high vibrational temperature of these radicals, which was maximized at about 4 eV for depositions at 10 mTorr N2 and laser fluences of ∼7 J/cm2. The presence of C2 had only a minor effect on film composition and structure. Optimization of plasma characteristics and a substrate temperature of 300 °C helped to produce about 1-μm-thick solid films of CNx (N/C ratio≈0.2–0.3) and pure carbon consisting of fullerene-like fragments and packages. In contrast to carbon films, fullerene-like CNx films exhibited a high elastic recovery of about 80% in using a Berkovich tip at 5 mN load and indentation depths up to 150 nm. Their elastic modulus was about 160 GPa measured from the unloading portion of an indentation curve, and about 250 GPa measured with a 40 Hz tip oscillation during nanoindentation tests. The difference was related to time dependent processes of shape restoration of fullerene-like fragments, and an analogy was made to the behavior of elastomer polymers. However, unlike elastomers, CNx film hardness was as high as 30 GPa, which was twice that of fullerene-like carbon films. The unusual combination of high elasticity and hardness of CNx films was explained by crosslinking of fullerene fragments induced by the incorporated nitrogen and stored compressive stress. The study demonstrated laser ablation as a viable technique for the growth of fullerene-like CNx films, which may be used as hard protective coatings resisting brittle fracture at high loads and extensive substrate deformations.
High-transparency Ni/Au bilayer contacts to n-type GaN
Authors: Motayed Abhishek , Davydov Albert V. , Bendersky Leonid A. , Wood Mark C. , Derenge Michael A. , Wang Dong Feng , Jones Kenneth A. , Mohammad S. Noor
Published: October 2002

A unique metallization scheme has been developed for obtaining both Schottky and low-resistance Ohmic contacts to n-GaN. It has been demonstrated that the same metallization can be used to make both Schottky and Ohmic contacts to n-GaN using a Ni/Au bilayer composite with Ni in contact to GaN. Using this metallization, contacts with a specific contact resistivity, ρs, as low as 6.9×10−6 Ω cm2 for a doping level of 5.0×1017 cm−3 was obtained after annealing the sample for 10 s at 800 °C in a rapid thermal annealer. The presence of only (111)Au and (111)Ni peaks in the x-ray diffraction (XRD) pattern of as-deposited samples indicates that both metals participate to form epitaxial or highly textured layers on the basal GaN plane. When the contact layer is annealed, Au and Ni react with GaN creating interfacial phases. Both XRD and transmission electron microscopy confirm that Ni3Ga and Ni2Ga3 intermetallic phases together with Au and Ni based face-centered-cubic solid solutions, are formed during annealing. The high optical transmission achieved (in the range of 400–700 nm) through this contact after annealing suggests that it is, indeed, very useful for electro-optic device applications. The contacts also demonstrate exceptional thermal stability. Experimental data suggest that the formation of interfacial phases with a low work function is responsible for the low contact resistance of the system. The Ni–Au layer forms a robust composite enabling the contacts to have high-temperature applications. Unlike the Ni/Au Ohmic contact, the Ni/Au Schottky contact to n-GaN has a relatively large barrier height. Improved material quality and Schottky contact technology are needed to improve upon the reverse breakdown voltage.
Parametric excitation of low frequency waves in complex (dusty) plasmas
Authors: Yaroshenko V. , Morfill G. E.
Published: October 2002

The parametric instability of dust-acoustic as well as dust lattice waves due to periodical modulation of equilibrium dust charges is analyzed. The criterion for and the maximum growth rate of this instability are obtained. It is shown that the parametric resonance of the dust-acoustic or dust lattice waves can provide a useful tool for determining complex plasma parameters.
Transport threshold model of neoclassical tearing modes in the presence of anomalous perpendicular viscosity
Authors: Konovalov S. V. , Mikhailovskii A. B. , Shirokov M. S. , Tsypin V. S.
Published: October 2002

Bootstrap drive of neoclassical tearing modes (NTMs) in the presence of anomalous perpendicular viscosity is calculated. Viscosity is shown to lead to dependence of the perturbed bootstrap current on the perturbed electric field. As a result, the bootstrap drive is qualitatively modified by the island rotation frequency and direction of the island rotation. The modified bootstrap drive is incorporated into the transport threshold model of NTMs.
Influence of temperature and electronic disorder on the Raman spectra of nickel cobalt oxides
Authors: Windisch Charles F. , Exarhos Gregory J. , Sharma Shiv K.
Published: October 2002

Raman spectra of nickel cobalt oxide films with spinel crystal structure showed unexpected variations with film thickness. Combined with the results of studies as a function of incident laser power and temperature, from 25 to 800 K, the results strongly point to a small polaron hopping model for electrical conductivity in these materials. During laser excitation, phonons interact with valence electrons such that the carrier holes in these materials become localized or associated with the polarized environment created by the electron-phonon interaction (polaron). These interactions split the energy levels of the valence electrons contributing to band broadening well below room temperature.
Space-charge-limited bipolar currents in polymer/C60 diodes
Authors: Koehler M. , Roman L. S. , Inganäs O. , da Luz M. G. E.
Published: October 2002

We investigate carrier’s transport for devices formed by a heterojunction of the substituted polythiophene polymer and the C60 molecule, sandwiched between anode of indium-tin oxide/poly(3,4-ethylene dioxythiophene) and cathode of Al, for different thicknesses of the C60. We measure their current-voltage characteristics and find that the forward current is limited by spatial charge of holes in the polymer layer and electrons in the molecule layer. We also find that the effective mobilities of holes in the polymer and of electrons in the C60 are dependent on the different thickness of the layers. By adapting to our systems an electrical analytic model previously used in the literature to study bilayer organic diodes, we are able to explain the experimental results.