bluuebunny/crossref_metadata_2025 huggingface dataset:
Lack of TXNIP protects β-cells against glucotoxicity
Authors: Shalev Anath
Published: October 2008

Glucotoxicity plays a major role in pancreatic β-cell apoptosis and diabetes progression, but the factors involved have remained largely unknown. Our recent studies have identified TXNIP (thioredoxin-interacting protein) as a novel pro-apoptotic β-cell factor that is induced by glucose, suggesting that TXNIP may play a role in β-cell glucotoxicity. Incubation of INS-1 β-cells and isolated primary mouse and human islets at high glucose levels led to a significant increase in TXNIP as well as in apoptosis. Very similar results were obtained in vivo in islets of diabetic mice. To determine whether TXNIP plays a causative role in glucotoxic β-cell death, we used TXNIP-deficient islets of HcB-19 mice harbouring a natural nonsense mutation in the TXNIP gene. We incubated islets of HcB-19 and C3H control mice at low and high glucose levels and assessed them for TXNIP expression and apoptosis. Interestingly, whereas in C3H islets, high glucose levels led again to significant elevation of TXNIP and apoptosis levels as measured by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) and cleaved caspase 3, no increase in apoptosis was observed in TXNIP-deficient HcB-19 islets, indicating that TXNIP is required for β-cell death caused by glucotoxicity. Thus inhibition of TXNIP protects against glucotoxic β-cell apoptosis and therefore may represent a novel therapeutic approach to halt diabetes progression.
Significance of protein crowding, order and mobility for photosynthetic membrane functions
Authors: Kirchhoff Helmut
Published: October 2008

Natural photosynthesis requires diffusion-based processes either for the functional communication of protein complexes or for the adaptation, maintenance and biogenesis of the photosynthetic apparatus. A conceptual problem with lateral diffusion in photosynthetic membranes arises from the fact that these membranes are densely packed with membrane integral protein complexes (molecular crowding). Theoretical analysis of PQ (plastoquinone) and protein diffusion in higher plant grana thylakoids reveal very inefficient lateral diffusion. In contrast, measurement of protein mobility in grana membranes shows that a fraction of protein complexes can move surprisingly fast. It is postulated that organization of protein complexes in supercomplexes and large-scale ordering of Photosystem II and light-harvesting complex II could be strategies for the optimization of diffusion in crowded thylakoid membranes.
The production of reactive oxygen species by complex I
Authors: Hirst Judy , King Martin S. , Pryde Kenneth R.
Published: October 2008

ROS (reactive oxygen species) are considered to be a major cause of cellular oxidative stress, linked to neuromuscular diseases and aging. Complex I (NADH:ubiquinone oxidoreductase) is one of the main contributors to superoxide production by mitochondria, and knowledge of its mechanism of O2 reduction is required for the formulation of causative connections between complex I defects and pathological effects. There is evidence for two distinct (but not mutually exclusive) sites of O2 reduction by complex I. Studies of the isolated enzyme largely support the participation of the reduced flavin mononucleotide in the active site for NADH oxidation, and this mechanism is supported in mitochondria by correlations between the NAD(P)+ potential and O2 reduction. In addition, studies of intact mitochondria or submitochondrial particles have suggested a mechanism involving the quinone-binding site, supported by observations during reverse electron transport and the use of ‘Q-site’ inhibitors. Here, we discuss extant data and models for O2 reduction by complex I. We compare results from the isolated enzyme with results from intact mitochondria, aiming to identify similarities and differences between them and progress towards combining them to form a single, unified picture.
A structural analysis of the transient interaction between the cytochrome bc1 complex and its substrate cytochrome c
Authors: Nyola Ajeeta , Hunte Carola
Published: October 2008

In cellular respiration, cytochrome c transfers electrons from the cytochrome bc1 complex to cytochrome c oxidase by transiently binding to the membrane proteins. The first X-ray structure of the yeast cytochrome bc1 complex with bound cytochrome c revealed the general architecture of the electron-transfer complex. The interface of the complex is small. The haem moieties are centrally located in a mainly non-polar contact site, which includes a cation–π interaction and is surrounded by complementary charged residues. Only one cytochrome c1-docking site of the dimeric complex is occupied with cytochrome c. The recent 1.9 Å (1 Å=0.1 nm) resolution structure of the complex showed that the interface is highly hydrated. With cytochrome c bound, a higher number of interfacial water molecules are present on the cytochrome c1 interface, whereas its protein surface is not affected. Remarkably, the dimer structure is slightly asymmetric. Univalent cytochrome c binding coincides with conformational changes of the Rieske head domain and subunit QCR6p. Pronounced hydration and a mobility mismatch at the interface with disordered charged residues on the cytochrome c side are favourable for transient binding. Comparison with a new structure of the complex with bound isoform-2 cytochrome c led to the definition of a core interface, which refers to four common interaction pairs including the cation–π interaction. They encircle the haem groups and are surrounded by variable interactions. The core interface may be a feature to gain specificity for formation of the reactive complex. The consistency in the binding interaction despite differences in primary sequence, redox state and crystal contacts, together with crystallization at physiological ionic strength, clearly suggest that the structures show the native bound state of the electron-transfer complex.
Bioenergetics at the gold surface: SEIRAS probes photosynthetic and respiratory reactions at the monolayer level
Authors: Ataka Kenichi , Heberle Joachim
Published: October 2008

The present study surveys a novel approach to studies of membrane proteins whose catalytic action is driven by the redox potential or by the membrane potential. We introduce SEIRAS (surface-enhanced IR absorption spectroscopy) to probe a monolayer of membrane protein adhered to the surface of a gold electrode. SEIRAS renders high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders of magnitude. It is demonstrated that reaction-induced spectroscopy is applicable by recording IR differences of cytochrome c after stimulation by the electrical potential. The impact of the membrane potential on the function of a membrane protein is demonstrated by performing light-induced difference spectroscopy on a microbial rhodopsin (sensory rhodopsin II) under voltage-clamp conditions. The methodology presented opens new avenues to study the mechanism of electron-triggered and voltage-gated proteins at the level of single bonds. As many of these catalytic reactions are of vectorial nature, control on the orientation of the membrane protein is mandatory. Approaches are presented on how to specifically adhere photosynthetic and respiratory proteins to the electrode surface and reconstitute these membrane proteins in the lipid bilayer. Functionality of such biomimetic systems is assessed in situ by spectro-electrochemical methods.
Rhodobacter sphaeroides haem protein: a novel cytochrome with nitric oxide dioxygenase activity
Authors: Li Bor-Ran , Anderson J.L. Ross , Mowat Christopher G. , Miles Caroline S. , Reid Graeme A. , Chapman Stephen K.
Published: October 2008

Rhodobacter sphaeroides produces a novel cytochrome, designated as SHP (sphaeroides haem protein), that is unusual in having asparagine as a redox-labile haem ligand. The gene encoding SHP is contained within an operon that also encodes a DHC (dihaem cytochrome c) and a membrane-associated cytochrome b. DHC and SHP have been shown to have high affinity for each other at low ionic strength (Kd=0.2 μM), and DHC is able to reduce SHP very rapidly. The reduced form of the protein, SHP2+ (reduced or ferrous SHP), has high affinity for both oxygen and nitric oxide (NO). It has been shown that the oxyferrous form, SHP2+–O2 (oxygen-bound form of SHP), reacts rapidly with NO to produce nitrate, whereas SHP2+–NO (the NO-bound form of SHP) will react with superoxide with the same product formed. It is therefore possible that SHP functions physiologically as a nitric oxide dioxygenase, protecting the organism against NO poisoning, and we propose a possible mechanism for this process.
The role of multihaem cytochromes in the respiration of nitrite in Escherichia coli and Fe(III) in Shewanella oneidensis
Authors: Clarke Thomas A. , Holley Tracey , Hartshorne Robert S. , Fredrickson Jim K. , Zachara John M. , Shi Liang , Richardson David J.
Published: October 2008

The periplasmic nitrite reductase system from Escherichia coli and the extracellular Fe(III) reductase system from Shewanella oneidensis contain multihaem c-type cytochromes as electron carriers and terminal reductases. The position and orientation of the haem cofactors in multihaem cytochromes from different bacteria often show significant conservation despite different arrangements of the polypeptide chain. We propose that the decahaem cytochromes of the iron reductase system MtrA, MtrC and OmcA comprise pentahaem ‘modules’ similar to the electron donor protein, NrfB, from E. coli. To demonstrate this, we have isolated and characterized the N-terminal pentahaem module of MtrA by preparing a truncated form containing five covalently attached haems. UV–visible spectroscopy indicated that all five haems were low-spin, consistent with the presence of bis-His ligand co-ordination as found in full-length MtrA.
Quantum dots for single-pair fluorescence resonance energy transfer in membrane- integrated EFoF1
Authors: Galvez Eva , Düser Monika , Börsch Michael , Wrachtrup Jörg , Gräber Peter
Published: October 2008

spFRET (single-pair fluorescence resonance energy transfer) with organic fluorophores has been used to demonstrate rotation of the subunits γ and ε in membrane-integrated FoF1 during proton transport-coupled ATP synthesis. Owing to the high light intensities used in single-molecule spectroscopy, organic fluorophores show a high probability for photobleaching. Luminescent CdSe/ZnS nanocrystals with a hydrophilic shell have been covalently bound to FoF1 either to the stator subunit b or to the rotor subunit c. TIRFM (total internal reflection microscopy) shows that covalent binding of the QD (quantum dot) via cysteine to FoF1 leads to a significant decrease in the blinking probability in the microsecond-to-second time range. This effect allows the observation of subunit movements in an extended time range. If the QD is bound to the rotor subunit c, the fluorescence anisotropy shows fluctuations in the presence of ATP, in contrast with the constant anisotropy observed in the absence of ATP.
Further insights into the structure of the alternative oxidase: from plants to parasites
Authors: Moore Anthony L. , Albury Mary S.
Published: October 2008

The AOX (alternative oxidase) is a non-protonmotive ubiquinol–oxygen oxidoreductase that couples the oxidation of ubiquinol with the complete reduction of water. Although it has long been recognized that it is ubiquitous among the plant kingdom, it has only recently become apparent that it is also widely found in other organisms including some human parasites. In this paper, we review experimental studies that have contributed to our current understanding of its structure, with particular reference to the catalytic site. Furthermore, we propose a model for the ubiquinol-binding site which identifies a hydrophobic pocket, between helices II and III, leading from a proposed membrane-binding domain to the catalytic domain.
Structural organization of the V-ATPase and its implications for regulatory assembly and disassembly
Authors: Diepholz Meikel , Börsch Michael , Böttcher Bettina
Published: October 2008

V-ATPases (vacuolar ATPases) are membrane-bound multiprotein complexes that are localized in the endomembrane systems of eukaryotic cells and in the plasma membranes of some specialized cells. They couple ATP hydrolysis with the transport of protons across membranes. On nutrient shortage, V-ATPases disassemble into a membrane-embedded part (V0), which contains the proton translocation machinery, and an extrinsic part (V1), which carries the nucleotide-binding sites. Disassembly decouples ATP hydrolysis and proton translocation. Furthermore, the disassembled parts are inactive, leading to an efficient shutdown of ATP consumption. On restoring the nutrient levels, V1 and V0 reassemble and restore ATP-hydrolysis activity coupled with proton translocation. This reversible assembly/disassembly process has certain conformational constraints, which are best fulfilled by adopting a unique conformation before disassembly.
Are Escherichia coli OXPHOS complexes concentrated in specialized zones within the plasma membrane?
Authors: Lenn Tchern , Leake Mark C. , Mullineaux Conrad W.
Published: October 2008

Most organisms are able to synthesize ATP by OXPHOS (oxidative phosphorylation). Mitochondria in eukaryotes perform OXPHOS in the inner mitochondrial membrane, whereas the plasma membrane is used by prokaryotes. However, whereas OXPHOS is a well-understood process at the biochemical level, relatively little is known about its operation at the level of the whole-organelle/cell. We observed that a fluorescently labelled terminal oxidase, the cytochrome bd complex, is heterogeneously distributed in the Escherichia coli plasma membrane. This observation forms the basis of a working hypothesis that patches of the E. coli plasma membrane (‘respirazones’) are dedicated to respiratory function by the high concentration of OXPHOS components in these zones relative to the adjacent membrane. The formulation and physiological significance of this hypothesis are discussed in this paper.
High-resolution mass spectrometry analysis of protein oxidations and resultant loss of function
Authors: Barnes Stephen , Shonsey Erin M. , Eliuk Shannon M. , Stella David , Barrett Kerri , Srivastava Om P. , Kim Helen , Renfrow Matthew B.
Published: October 2008

MS, with or without pre-analysis peptide fractionation, can be used to decipher the residues on proteins where oxidative modifications caused by peroxynitrite, singlet oxygen or electrophilic lipids have occurred. Peroxynitrite nitrates tyrosine and tryptophan residues on the surface of actin. Singlet oxygen, formed by the interaction of UVA light with tryptophan, can oxidize neighbouring cysteine, histidine, methionine, tyrosine and tryptophan residues. Dose–response inactivation by 4HNE (4-hydroxynonenal) of hBAT (human bile acid CoA:amino acid N-acyltransferase) and CKBB (cytosolic brain isoform of creatine kinase) is associated with site-specific modifications. FT-ICR (Fourier-transform ion cyclotron resonance)–MS using nanoLC (nano-liquid chromatography)–ESI (electrospray ionization)–MS or direct-infusion ESI–MS with gas-phase fractionation identified 14 4HNE adducts on hBAT and 17 on CKBB respectively. At 4HNE concentrations in the physiological range, one member of the catalytic triad of hBAT (His362) was modified; for CKBB, although all four residues in the active site that were modifiable by 4HNE were ultimately modified, only one, Cys283, occurred at physiological concentrations of 4HNE. These results suggest that future in vivo studies should carefully assess the critical sites that are modified rather than using antibodies that do not distinguish between different modified sites.
Mass spectrometry to detect the site specificity of advanced glycation/lipoxidation end-product formation on protein: some challenges and solutions
Authors: Ames Jennifer M.
Published: October 2008

Formation of AGEs (advanced glycation end-products) and ALEs (advanced lipoxidation end-products) on proteins is associated with aging and various diseases of oxidative stress, notably diabetes and its complications. Modification of protein to AGE/ALEs is known to be site-directed and this has potential implications for protein functionality and design of AGE/ALE inhibitors. Determination of the site-specificity of modification is achieved most efficiently by MS. The present paper summarizes some of the challenges that need to be addressed when determining the site-specificity of AGE/ALE formation on protein by MS, using the protein RNase as an example. The following topics are discussed: formation and significance of AGE/ALEs, location of glycated peptides, enzymic digestion of glycated peptides and selection of mass spectrometric settings of analysis for glycated peptides.
Key issues in F2-isoprostane analysis
Authors: Nourooz-Zadeh Jaffar
Published: October 2008

A large body of evidence indicates that measurement of F2-isoprostanes, specific prostaglandin F2-like compounds derived from the non-enzymatic peroxidation of arachidonic acid, is a reliable biomarker of oxidant stress in the human body. Since the discovery of F2-isoprostanes in the early 1990s, a variety of analytical approaches has been introduced for the quantification of these novel compounds. The aim of the present review is to shed light on the available gas chromatographic–mass spectrometric assays for the measurement of plasma or urinary F2-isoprostanes and to highlight a number of issues which need to be addressed in order to implement F2-isoprostane measurement as a gold-standard biomarker of oxidative stress in biological samples.
Mass spectrometry approaches for vitamin E research
Authors: Lodge John K.
Published: October 2008

Vitamin E is an important nutrient with antioxidant and non-antioxidant functions, and certain evidence suggests that it has a cardiovascular protective role. It is therefore important to maintain an optimal vitamin E status. In the present paper, a number of MS applications to monitor vitamin E status and its interactions, including the use of stable-isotope-labelled vitamin E and metabonomics, are highlighted. Specifically, stable-isotope studies have been used to monitor vitamin E absorption, hepatic processing and lipoprotein transport. As oxidative stress may influence vitamin E status, a number of studies comparing vitamin E biokinetics and metabolism in cigarette smokers and non-smokers have been able to show differences in vitamin E processing in smokers. Metabonomics represents a method to identify changes to metabolite profiles, offering the potential to investigate interactions between vitamin E and metabolic pathways. These applications represent innovative approaches to investigate the role of vitamin E in health and disease.
Biomarkers of oxidative damage to DNA and repair
Authors: Loft Steffen , Høgh Danielsen Pernille , Mikkelsen Lone , Risom Lotte , Forchhammer Lykke , Møller Peter
Published: October 2008

Oxidative-stress-induced damage to DNA includes a multitude of lesions, many of which are mutagenic and have multiple roles in cancer and aging. Many lesions have been characterized by MS-based methods after extraction and digestion of DNA. These preparation steps may cause spurious base oxidation, which is less likely to occur with methods such as the comet assay, which are based on nicking of the DNA strand at modified bases, but offer less specificity. The European Standards Committee on Oxidative DNA Damage has concluded that the true levels of the most widely studied lesion, 8-oxodG (8-oxo-7,8-dihydro-2′-deoxyguanosine), in cellular DNA is between 0.5 and 5 lesions per 106 dG bases. Base excision repair of oxidative damage to DNA can be assessed by nicking assays based on oligonucleotides with lesions or the comet assay, by mRNA expression levels or, in the case of, e.g., OGG1 (8-oxoguanine DNA glycosylase 1), responsible for repair of 8-oxodG, by genotyping. Products of repair in DNA or the nucleotide pool, such as 8-oxodG, excreted into the urine can be assessed by MS-based methods and generally reflects the rate of damage. Experimental and population-based studies indicate that many environmental factors, including particulate air pollution, cause oxidative damage to DNA, whereas diets rich in fruit and vegetables or antioxidant supplements may reduce the levels and enhance repair. Urinary excretion of 8-oxodG, genotype and expression of OGG1 have been associated with risk of cancer in cohort settings, whereas altered levels of damage, repair or urinary excretion in case-control settings may be a consequence rather than the cause of the disease.
Mass spectrometric analysis of HOCl- and free-radical-induced damage to lipids and proteins
Authors: Pitt Andrew R. , Spickett Corinne M.
Published: October 2008

In inflammatory diseases, release of oxidants leads to oxidative damage to biomolecules. HOCl (hypochlorous acid), released by the myeloperoxidase/H2O2/Cl− system, can cause formation of phospholipid chlorohydrins, or α-chloro-fatty aldehydes from plasmalogens. It can attack several amino acid residues in proteins, causing post-translational oxidative modifications of proteins, but the formation of 3-chlorotyrosine is one of the most stable markers of HOCl-induced damage. Soft-ionization MS has proved invaluable for detecting the occurrence of oxidative modifications to both phospholipids and proteins, and characterizing the products generated by HOCl-induced attack. For both phospholipids and proteins, the application of advanced mass spectrometric methods such as product or precursor ion scanning and neutral loss analysis can yield information both about the specific nature of the oxidative modification and the biomolecule modified. The ideal is to be able to apply these methods to complex biological or clinical samples, to determine the site-specific modifications of particular cellular components. This is important for understanding disease mechanisms and offers potential for development of novel biomarkers of inflammatory diseases. In the present paper, we review some of the progress that has been made towards this goal.
Post-transcriptional regulation of gene expression in response to iron deficiency: co-ordinated metabolic reprogramming by yeast mRNA-binding proteins
Authors: Vergara Sandra V. , Thiele Dennis J.
Published: October 2008

Saccharomyces cerevisiae (baker's yeast) is an excellent model for understanding fundamental biological mechanisms that are conserved in Nature and that have an impact on human disease. The metal iron is a redox-active cofactor that plays critical biochemical roles in a broad range of functions, including oxygen transport, mitochondrial oxidative phosphorylation, chromatin remodelling, intermediary metabolism and signalling. Although iron deficiency is the most common nutritional disorder on the planet, little is known about the metabolic adjustments that cells undergo in response to iron deficit and the regulatory mechanisms that allow these adaptive responses. In the present article, we summarize recent work on genome-wide metabolic reprogramming in response to iron deficiency, mediated by specific mRNA degradation mechanisms that allow S. cerevisiae cells to adapt to iron deficiency.
Next-generation sequencing: applications beyond genomes
Authors: Marguerat Samuel , Wilhelm Brian T. , Bähler Jürg
Published: October 2008

The development of DNA sequencing more than 30 years ago has profoundly impacted biological research. In the last couple of years, remarkable technological innovations have emerged that allow the direct and cost-effective sequencing of complex samples at unprecedented scale and speed. These next-generation technologies make it feasible to sequence not only static genomes, but also entire transcriptomes expressed under different conditions. These and other powerful applications of next-generation sequencing are rapidly revolutionizing the way genomic studies are carried out. Below, we provide a snapshot of these exciting new approaches to understanding the properties and functions of genomes. Given that sequencing-based assays may increasingly supersede microarray-based assays, we also compare and contrast data obtained from these distinct approaches.
Hyperbaric oxygen activates discoidin domain receptor 2 via tumour necrosis factor-α and the p38 MAPK pathway to increase vascular smooth muscle cell migration through matrix metalloproteinase 2
Authors: Shyu Kou-Gi , Wang Bao-Wei , Chang Hang
Published: October 2008

DDR2 (discoidin domain receptor 2) regulates collagen turnover mediated by SMCs (smooth muscle cells) in atherosclerosis. HBO (hyperbaric oxygen) has been used in medical practice; however, the molecular mechanism of the beneficial effects of HBO is poorly understood. Furthermore, the effect of HBO on DDR2 has not been reported previously. In the present study, we investigated the cellular and molecular mechanisms of DDR2 regulation by HBO in VSMCs (vascular SMCs). Cells were exposed to 2.5 ATA (atmosphere absolute) of oxygen in a hyperbaric chamber. DDR2 protein (3.63-fold) and mRNA (2.34-fold) expression were significantly increased after exposure to 2.5 ATA HBO for 1 h. Addition of SB203580 and p38 MAPK (mitogen-activated protein kinase) siRNA (small interfering RNA) 30 min before HBO inhibited the induction of DDR2 protein. HBO also significantly increased DNA–protein binding activity of Myc/Max. Addition of SB203580 and an anti-TNF-α (tumour necrosis factor-α) monoclonal antibody 30 min before HBO abolished the DNA–protein binding activity induced by HBO. HBO significantly increased the secretion of TNF-α from cultured VSMCs. Exogenous addition of TNF-α significantly increased DDR2 protein expression, whereas anti-TNF-α and anti-(TNF-α receptor) antibodies blocked the induction of DDR2 protein expression. HBO significantly increased VSMC migration and proliferation, whereas DDR2 siRNA inhibited the migration induced by HBO. HBO increased activated MMP2 (matrix metalloproteinase 2) protein expression, and DDR2 siRNA abolished the induction of activated MMP2 expression induced by HBO. In conclusion, HBO activates DDR2 expression in cultured rat VSMCs. HBO-induced DDR2 is mediated by TNF-α and at least in part through the p38 MAPK and Myc pathways.
Effects of pravastatin on functional capacity in patients with chronic obstructive pulmonary disease and pulmonary hypertension
Authors: Lee Tsung-Ming , Chen Chien-Chang , Shen Hsiu-Nien , Chang Nen-Chung
Published: October 2008

PH (pulmonary hypertension) often complicates the disease course of patients with COPD (chronic obstructive pulmonary disease) and is an indication of a worse prognosis. In the present study, we assessed whether pravastatin administration was effective in improving PH and exercise capacity in COPD patients with PH, and whether the pulmonary protection was mediated by inhibiting ET-1 (endothelin-1) production. In a double-blind parallel design, 53 COPD patients with PH were randomly assigned to receive either placebo or pravastatin (40 mg/day) over a period of 6 months at a medical centre. Baseline characteristics were similar in both groups. The exercise time remained stable throughout the study in the placebo group. After 6 months, the exercise time significantly increased 52% from 660±352 to 1006±316 s (P<0.0001) in pravastatin-treated patients. With pravastatin, echocardiographically derived systolic PAP (pulmonary artery pressure) decreased significantly from 47±8 to 40±6 mmHg. There was significant improvement in the Borg dyspnoea score after administering pravastatin. Despite unchanged plasma ET-1 levels throughout the study, urinary excretion of the peptide was decreased and significantly correlated with an improvement in exercise time in pravastatin-treated patients (r=−0.47, P=0.01). In conclusion, pravastatin significantly improved exercise tolerance, and decreased PH and dyspnoea during exercise in COPD patients with PH, probably by inhibiting ET-1 synthesis.
IGF-I/IGFBP-3 ratio: a mechanistic insight into the metabolic syndrome
Authors: Sierra-Johnson Justo , Romero-Corral Abel , Somers Virend K. , Lopez-Jimenez Francisco , Mälarstig Anders , Brismar Kerstin , Hamsten Anders , Fisher Rachel M. , Hellénius Mai-Lis
Published: October 2008

Recent reports suggest that IGF (insulin-like growth factor)-I and IGFBP-3 (IGF-binding protein-3) have independent and opposing mechanistic effects on insulin. The aim of the present study was to assess the relationship between the IGF-I/IGFBP-3 ratio and the metabolic syndrome. We examined 3281 subjects (1463 men and 1818 women, aged 20–49 years), otherwise healthy adults, who participated in NHANES III (Third National Health and Nutrition Examination Survey), which has released measurements of IGF-I and IGFBP-3. Insulin resistance was estimated using the computer HOMA2 (homoeostatic model assessment 2) model. The updated ATP-III (Adult Treatment Panel III) definition of the metabolic syndrome was used. We applied adjusted logistic and linear regression models. After adjusting for age and race, men and women in the lowest quartile of the IGF-I/IGFBP-3 ratio were 3-fold more likely to meet the ATP-III definition of the metabolic syndrome and twice as likely to be insulin-resistant. Mean values of the IGF-I/IGFBP-3 ratio decreased significantly as the number of metabolic syndrome components increased (P<0.0001, as determined by ANOVA). The area under the ROC (receiver operating characteristic) curve for detecting insulin resistance using the IGF-I/IGFBP-3 ratio was 0.760, significantly improving upon either protein alone (P=0.01). In conclusion, the IGF-I/IGFBP-3 ratio is significantly associated with the metabolic syndrome. Calculating the ratio of these two proteins may provide insight into the metabolic syndrome clustering phenomenon.
The Impact of Global Terrorism on Ireland's Tourism Industry: An Industry Perspective
Authors: O'Connor Noëlle , Stafford Mary Rose , Gallagher Gerry
Published: October 2008

The purpose of this paper is to ascertain the impacts of global terrorism on Ireland's tourism industry, through examining the Irish tourism industry's perspective. The research undertaken included a multimethod approach, combining secondary research with primary research (in-depth interviews) to provide some practical findings. These findings highlight the fact that structures must be in place in order for the industry to manage a crisis resulting from a terrorist attack and also to minimise the impacts it will have on the tourism industry. In turn, this paper has the ability to influence tourism policy in countries that rely significantly on tourism such as Ireland.
Do Tourism Providers Know their Visitors? An Investigation of Tourism Experience at a Destination
Authors: Zouni Georgia , Kouremenos Athanassios
Published: October 2008

Even dominant positivist researchers recognise the insufficiencies of traditional services research methodology and claim that the dominant models of service quality's measurement have failed to reveal the customers' prospective (Schembri and Sandberg, 2002). Whereas the customer is considered to be the focal point in contemporary marketing and services marketing, the customer's perspective is claimed to be missing from dominant theory (Grönroos, 1993, 2006a). This paper explores the potential for a modified gap analysis to serve as an alternative marketing tool. A research framework is constructed and tested using data produced by two surveys (tourists and tourism service providers) in a heritage destination. The purpose of the present study is to provide in favour of this gap an effective marketing tool for a better understanding of the customer's perspective.
Realization of dual-channel organic field-effect transistors and their applications to chemical sensing
Authors: Jeong Yeon Taek , Cobb Brian H. , Lewis Shannon D. , Dodabalapur Ananth , Lu Shaofeng , Facchetti Antonio , Marks Tobin J.
Published: October 2008

We report on the realization of dual-channel organic field-effect transistors (FETs). These devices have a four-terminal configuration with a polymeric semiconductor p-channel, a small molecule semiconductor n-channel, and a polymeric gate dielectric. The polymeric p-channel and the small molecule n-channel are coupled across the gate dielectric. Both the p-FET and the n-FET exhibit acceptable device characteristics at ∣VDS∣⩽50V and ∣VG∣⩽50V, in which the performances of the p-FET and the n-FET are comparable. The p-FET and n-FET respond to isopropyl alcohol and ethanol vapors with significant sensitivities.
Magnetoconvection in sheared magnetic fields
Authors: Bian N. H. , Garcia O. E.
Published: October 2008

The development of magnetoconvection in a sheared magnetic field is investigated. The equilibrium magnetic field B0 is horizontal and its orientation varies linearly along the vertical axis. Preliminary consideration of the transition from the inertial to the viscous regime of the gravitational resistive interchange instability, reveals that the latter is characterized by the existence of viscoresistive boundary layers of vertical width which scales as Q−1∕6, where Q is the Chandrasekhar number. The situation is analogous to the one encountered in magnetically confined laboratory plasmas, where convective flows are constrained by the magnetic shear to develop in boundary layers located around resonant magnetic surfaces in order to fulfill the “interchange condition” k⋅B0=0, where k is the wave vector of the magnetic perturbation. It follows that when the effect of thermal diffusion is taken into account in the process, convection can only occur above a certain critical value of the Rayleigh number which scales as Q2∕3 for large Q. At the onset, the convection pattern is a superposition of identically thin convective rolls everywhere aligned with the local magnetic field lines and which therefore adopt the magnetic field geometry, a situation also reminiscent of the penumbra of sunspots. Using this degeneracy, equations describing the weakly nonlinear state are obtained and discussed. A reduced magnetohydrodynamic description of magnetoconvection is introduced. Since it is valid for arbitrary magnetic field configurations, it allows a simple extension to the case where there exists an inclination between the direction of gravity and the plane spanned by the equilibrium magnetic field. These reduced magnetohydrodynamic equations are proposed as a powerful tool for further investigations of magnetoconvection in more complex field line geometries.
A theoretical study of the rovibrational levels of the bosonic van der Waals neon trimer
Authors: Salci Moses , Levin Sergey B. , Elander Nils , Yarevsky Evgeny
Published: October 2008

The eigenenergies and root mean square radii of the rovibrational levels (J=0–3) of the weakly bound bosonic van der Waals neon trimer were calculated using a full angular momentum three-dimensional finite element method. The differing results of three previous studies for zero angular momentum are discussed, explained, and compared with the results presented here.
Electric field dependence of quantum efficiencies of Ag/n-Si composites in the infrared at room temperature
Authors: Bates Clayton W. , Zhang Chichang
Published: October 2008

Room temperature quantum efficiencies of 2 μm thick Ag/n-Si composite films as a function of electric field are calculated for incident radiation wavelengths of 3, 5, 8, and 14 μm using a previously derived formula. With energies smaller than the Ag–Si Schottky barrier height, the signal current is carried by electrons tunneling through the barrier. For composites with Ag particle size of 5 nm, in an applied electric field of 2×106 V/cm, the quantum efficiencies are between 10% and 35%, depending on the wavelength. They increase rapidly with electric field and asymptotically approach a large fraction of the absorbed incident radiation in the Ag particles.
Molecular theory of hydrodynamic boundary conditions in nanofluidics
Authors: Kobryn Alexander E. , Kovalenko Andriy
Published: October 2008

Motivated by the fundamental questions raised by the most recent experimental achievements in nanofluidics, we propose the first-ever derivation and calculation of the hydrodynamic slip length from the first principles of statistical mechanics, namely, a combination of linear response theory and equilibrium molecular theory of solvation. The slip length derived is related to the fluid organization near the solid surface, as governed by the solid-liquid interaction. In the wide range of shear rates and surface-liquid interactions, the slip length is expressed in terms of the Green–Kubo–Nakano relations as a function of the anisotropic inhomogeneous time-correlation function of density fluctuations of the liquid in contact with the surface. The time dependence of the correlation function is factored out by treating it in the hydrodynamic limit. The spatially inhomogeneous two-body correlation function is represented in the Kirkwood-type approximation as a product of the three-dimensional density distributions of interaction sites of the liquid near the surface and the site-site pair correlations of the bulk liquid. The presented treatment generalizes the phenomenological definition of the friction coefficient (as well as the slip length) to a tensor quantity, which reflects an anisotropic nature of an ordered crystalline or nanopatterned surface. This enables theoretical prediction of friction forces acting aslant to the liquid flow direction for such surfaces. We derive generic analytical expressions for the liquid-surface friction coefficient (and slip length) for an arbitrary surface-liquid interaction potential. We further illustrate it by numerical calculations for a laminar flow of nine different molecular liquids, including water, at ambient conditions in contact with the (100) face-centered cubic cell surface of gold, copper, and nickel modeled by using optimized potential for liquid simulation models for liquids and the Steele potential for crystalline surfaces. The obtained values for slip length range from few to hundreds of nanometers and microns and are consistent with experimental measurements.
Optimal control of rotational motions in dissipative media
Authors: Pelzer Adam , Ramakrishna S. , Seideman Tamar
Published: October 2008

We apply optimal control theory to explore and manipulate rotational wavepacket dynamics subject to a dissipative environment. In addition to investigating the extent to which nonadiabatic alignment can make a useful tool in the presence of decoherence and population relaxation, we use coherent rotational superpositions as a simple model to explore several general questions in the control of systems interacting with a bath. These include the extent to which a pure state can be created out of a statistical ensemble, the degree to which control theory can develop superposition states that resist dissipation, and the nature of environments that prohibits control. Our results illustrate the information content of control studies regarding the dissipative properties of the bath and point to the strategies that optimize different targets in wavepacket alignment in nonideal environments. As an interesting aside, the method is used to illustrate the limit where the coherence-based approach to molecular alignment converges to traditional incoherent approaches.
Effects of unequally biaxial misfit strains on polarization phase diagrams in embedded ferroelectric thin layers: Phase field simulations
Authors: Liu Ping-Li , Wang Jie , Zhang Tong-Yi , Li Yulan , Chen Long-Qing , Ma Xing-Qiao , Chu Wu-Yang , Qiao Li-Jie
Published: October 2008

Phase field simulations were conducted to investigate the effects of unequally biaxial misfit strains on domain stability diagrams and equilibrium domain structures in an epitaxial ferroelectric PbTiO3 thin layer, which is sandwiched in a nonferroelectric medium. The simulations reveal a multidomain structure in the layer and allow constructing “misfit strain-misfit strain” and “temperature-misfit strain” phase diagrams. It is found that unequally biaxial misfit strains may lead to the presence of a single tetragonal variant, either a-domains or b-domains, which do not exist if the misfit strains are equally biaxial.
Four free parameter empirical parametrization of glow discharge Langmuir probe data
Authors: Azooz A. A.
Published: October 2008

For the purpose of developing a simple empirical model capable of producing the electron energy distribution function (EEDF) from Langmuir probe I-V characteristics, a four parameter empirical equation that fits most Langmuir probe experimental data is suggested. The four free fitting parameters are related to the main plasma properties. These properties include the ion and electron saturation currents and the plasma electron temperature. This equation can be readily differentiated twice to give the EEDF according to the Druyvesteyn formula. Furthermore, a MATLAB platform based computer code based on this model yielding results for the plasma potential and all plasma parameters mentioned above is presented. The information given below can be used to write other computer codes for the same purpose in any other programming language.
Generation of tunable Fourier-transform-limited terahertz pulses in 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate crystals
Authors: Liu Jinjun , Merkt Frédéric
Published: October 2008

We report difference-frequency generation (DFG) of widely tunable, pulsed, Fourier-transform-limited terahertz radiation (bandwidth of ∼10 MHz, peak power up to ∼400 μW) from pulse-amplified near-infrared (λ∼800 nm) laser radiation using a crystal of the organic salt 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) cut along the b axis to fulfill the phase-matching condition. The broad tunability and narrow bandwidth of the terahertz radiation generated by DFG in DAST are illustrated by a single scan of the terahertz spectrum of H2O from 0.1 to 11 THz, and a recording of the absorption spectrum of a pure rotational transition of HF near 5 THz.
Step-flow growth of a nanowire in the vapor-liquid-solid and vapor-solid-solid processes
Authors: Golovin A. A. , Davis S. H. , Voorhees P. W.
Published: October 2008

Consider the growth of a nanowire by a step-flow mechanism in the course of vapor-liquid-solid and vapor-solid-solid processes. The growth is initiated by the nucleation of a circular step at the nanowire-catalyst interface near the edge of the nanowire (the triple junction) and proceeds by the propagation toward the center by the Burton–Cabrera–Frank mechanism. Two cases are considered: (i) bulk transport, where the interfacial diffusion of adatoms and the step motion are coupled to the diffusion flux of atoms from the bulk of the catalyst particle, and (ii) surface transport, where atoms from the vapor phase are adsorbed at the surface of the catalyst particle and diffuse along the surface toward the triple line, whence they diffuse to the nanowire-catalyst interface. The attachment kinetics of adatoms at the step, the adsorption kinetics of atoms from the bulk phase, the exchange kinetics at the triple contact line, and the capillarity of the step are taken into account. In case (i) the problem is reduced to an integral equation for the diffusion flux of atoms from the bulk phase to the nanowire-catalyst interface. This equation is solved numerically, and the flux, interfacial concentration of adatoms, and the bulk concentration near the interface are determined. The step velocity is calculated as a function of the step radius and the kinetic parameters. As a result, the growth rate of a nanowire is computed as a function of its radius. In case (ii) analytical solutions for the surface and interfacial concentrations are obtained. In the absence of step capillarity, an analytical formula for the dependence of the nanowire growth rate on the nanowire radius is derived. It is shown in both cases (i) and (ii) that the nanowire growth rate decreases with increasing nanowire radius due to the decrease in the magnitude of the concentration gradients. However, in case (ii), in the limit of negligible desorption of adatoms into the gas phase, the nanowire growth rate is independent of the radius. It is also shown that in the presence of step capillarity (the Gibbs–Thomson effect) increases the nanowire growth rate.
The roles of the solute and solvent cavities in charge-transfer-to-solvent dynamics: Ultrafast studies of potasside and sodide in diethyl ether
Authors: Cavanagh Molly C. , Young Ryan M. , Schwartz Benjamin J.
Published: October 2008

Although electron transfer reactions are among the most fundamental in chemistry, it is still not clear how to isolate the roles of the solute and solvent in moving charge between reactants in solution. In this paper, we address this question by comparing the ultrafast charge-transfer-to-solvent (CTTS) dynamics of potasside (K−) in diethyl ether (DEE) to those of sodide (Na−) in both DEE and tetrahydrofuran (THF). We find that for sodide in both DEE and THF, CTTS excitation leads to delayed ejection of a solvated electron that appears with its equilibrium absorption spectrum. This indicates that the ejected electrons are localized in pre-existing solvent traps, suggesting that the structure of liquid DEE is characterized by cavities that are favorably polarized to localize an excess electron, as has been previously shown is the case for liquid THF. We also find that the geminate recombination dynamics following CTTS excitation of sodide in THF and DEE are similar, suggesting that the nature of the CTTS excited states and their coupling to the electronic states supported by the naturally occurring solvent cavities are similar in the two solvents. In contrast, the geminate recombination dynamics of potasside and sodide in DEE are different, with red-edge excitation of the K− CTTS band producing a greater number of long-lived electrons than is seen following the corresponding red-edge excitation of the Na− CTTS band. This indicates that the CTTS excited states of K− are better able to couple to the electronic states supported by the naturally occurring solvent cavities, allowing us to compare the energetic positions of the potasside and sodide ground and CTTS excited states on a common absolute scale. Finally, we also observe a strong transient absorption following the CTTS excitation of potasside in DEE that correlates well with the 766nm position of the gas-phase potassium D-line. The data indicate that CTTS excitation of alkali metal anions essentially instantaneously produces a gas-phase-like neutral alkali metal atom, which then spontaneously undergoes partial ejection of the remaining valence electron to form a neutral alkali metal cation:solvated electron tight-contact pair.
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T
domain-engineered piezoelectric single crystals: Calculations and application to PZN–12%PT poled along [101]
Authors: Guennou Mael , Dammak Hichem , Pham Thi Mai
Published: October 2008

This work is devoted to a study of the [101] domain-engineered PZN–12%PT single crystals. The full electromechanical tensor of PZN–12%PT in its tetragonal single domain state 1T is determined by the resonance method and used as input data. Observations of the domain structure of the [101]-poled 2T crystals by polarized light microscopy reveal a laminar structure consisting of thin layers stacked along the macroscopic polarization direction. We give analytical expressions for effective constants of this laminate multidomain pattern, taking into account the clamping effect resulting from domain coexistence. The calculated effective properties are found in good agreement with the experiments within experimental uncertainties. It is found that domain coexistence affects primarily the transverse dielectric constants ε11 and ε22. This effect is related to the emergence of internal shear stresses and depolarizing electric fields that are most significantly driven by the shear piezoelectric constant d15 and dielectric anisotropy ε11T−ε33T of the single domain state.