bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative stress inhibits MEKK1 by site-specific glutathionylation in the ATP-binding domain
Authors: CROSS Janet V. , TEMPLETON Dennis J.
Published: July 2004

Many intracellular signalling events are accompanied by generation of reactive oxygen species in cells. Oxidation of protein thiol groups is an emerging theme in signal-transduction research. We have found that MEKK1 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase kinase 1], an upstream activator of the SAPK/JNK (stress-activated protein kinase/c-Jun N-terminal kinase) pathway, is directly inhibited by cysteine alkylation using NEM (N-ethylmaleimide). The related kinase, ASK1 (apoptosis signal-regulating kinase 1), was not inhibited, but was instead activated by NEM. Inhibition of MEKK1 requires a single unique cysteine residue (Cys1238) in the ATP-binding domain of MEKK1. Oxidative stress induced by menadione (2-methyl-1,4-naphthoquinone) also inhibited MEKK1, but activated ASK1, in cells. MEKK1 inhibition by menadione also required Cys1238. Oxidant-inhibited MEKK1 was re-activated by dithiothreitol and glutathione, supporting reversible cysteine oxidation as a mechanism. Using various chemical probes, we excluded modification by S-nitrosylation or oxidation of cysteine to sulphenic acid. Oxidant-inhibited MEKK1 migrated normally on non-reducing gels, excluding the possibility of intra- or inter-molecular disulphide bond formation. MEKK1 was inhibited by glutathionylation in vitro, and MEKK1 isolated from menadione-treated cells was shown by MS to be modified by glutathione on Cys1238. Our results support a model whereby the redox environment within the cell selectively regulates stress signalling through MEKK1 versus ASK1, and may thereby participate in the induction of apoptosis by oxidative stress.
Syntaxin 5 interacts with presenilin holoproteins, but not with their N- or C-terminal fragments, and affects β-amyloid peptide production
Authors: SUGA Kei , TOMIYAMA Takami , MORI Hiroshi , AKAGAWA Kimio
Published: July 2004

Mutations in presenilins 1 and 2 (PS1 and PS2) account for the majority of cases of early-onset familial Alzheimer's disease. However, the trafficking and interaction of PSs with other proteins in the early secretory pathways are poorly understood. Using co-immunoprecipitation, we found that PS bound to Syx5 (syntaxin 5), which is a target-soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor involved in endoplasmic reticulum (ER)–Golgi vesicular transport in vivo. Syx5 interacted only with the full-length PS holoproteins and not with the naturally occurring N- or C-terminal fragments. The PS holoproteins co-immunoprecipitated with the mutant Syx5, which localized to the ER and Golgi compartments, despite the substitution of the transmembrane region with that of syntaxin 1A. In contrast, the transmembrane deletion mutant that localized to the cytosol, but not to the ER or Golgi compartments, did not co-immunoprecipitate the PS holoproteins. The PS1 variant linked to familial Alzheimer's disease (PS1ΔE9), lacking the region that contains the endoproteolytic cleavage site in the cytoplasmic loop, showed markedly decreased binding to Syx5. Immunofluorescence and sucrose-density-gradient fractionation analyses showed that the full-length PS holoproteins co-localized with Syx5 to the ER and cis-Golgi compartments. Furthermore, Syx5 overexpression resulted in the accumulation of PS holoproteins and the β-amyloid precursor protein, and reduced the secretion of the Aβ (amyloid β) peptide in COS-7 cells. In summary, these results indicate that Syx5 binds to full-length PSs and affects the processing and trafficking of β-amyloid precursor protein in the early secretory compartments.
6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase: head-to-head with a bifunctional enzyme that controls glycolysis
Authors: RIDER Mark H. , BERTRAND Luc , VERTOMMEN Didier , MICHELS Paul A. , ROUSSEAU Guy G. , HUE Louis
Published: July 2004

Fru-2,6-P2 (fructose 2,6-bisphosphate) is a signal molecule that controls glycolysis. Since its discovery more than 20 years ago, inroads have been made towards the understanding of the structure–function relationships in PFK-2 (6-phosphofructo-2-kinase)/FBPase-2 (fructose-2,6-bisphosphatase), the homodimeric bifunctional enzyme that catalyses the synthesis and degradation of Fru-2,6-P2. The FBPase-2 domain of the enzyme subunit bears sequence, mechanistic and structural similarity to the histidine phosphatase family of enzymes. The PFK-2 domain was originally thought to resemble bacterial PFK-1 (6-phosphofructo-1-kinase), but this proved not to be correct. Molecular modelling of the PFK-2 domain revealed that, instead, it has the same fold as adenylate kinase. This was confirmed by X-ray crystallography. A PFK-2/FBPase-2 sequence in the genome of one prokaryote, the proteobacterium Desulfovibrio desulfuricans, could be the result of horizontal gene transfer from a eukaryote distantly related to all other organisms, possibly a protist. This, together with the presence of PFK-2/FBPase-2 genes in trypanosomatids (albeit with possibly only one of the domains active), indicates that fusion of genes initially coding for separate PFK-2 and FBPase-2 domains might have occurred early in evolution. In the enzyme homodimer, the PFK-2 domains come together in a head-to-head like fashion, whereas the FBPase-2 domains can function as monomers. There are four PFK-2/FBPase-2 isoenzymes in mammals, each coded by a different gene that expresses several isoforms of each isoenzyme. In these genes, regulatory sequences have been identified which account for their long-term control by hormones and tissue-specific transcription factors. One of these, HNF-6 (hepatocyte nuclear factor-6), was discovered in this way. As to short-term control, the liver isoenzyme is phosphorylated at the N-terminus, adjacent to the PFK-2 domain, by PKA (cAMP-dependent protein kinase), leading to PFK-2 inactivation and FBPase-2 activation. In contrast, the heart isoenzyme is phosphorylated at the C-terminus by several protein kinases in different signalling pathways, resulting in PFK-2 activation.
Heparan sulphate identified on human erythrocytes: a Plasmodium falciparum receptor
Authors: VOGT Anna M. , WINTER Gerhard , WAHLGREN Mats , SPILLMANN Dorothe
Published: July 2004

HS (heparan sulphate) has hitherto not been found on human red blood cells (RBCs, erythrocytes). However, malarial-parasite (Plasmodium falciparum)-infected RBCs adhere to uninfected RBCs via HS-like receptors. In the present paper we demonstrate that human RBCs carry epitopes for an anti-HS antibody. Glycans isolated from RBC membranes reacted to HS-specific degradations and adhered to an HS-binding malaria antigen. Additionally, an HS core protein was identified. This suggests that HS is present on human RBCs.
PKA-phosphorylation of PDE4D3 facilitates recruitment of the mAKAP signalling complex
Authors: CARLISLE MICHEL Jennifer J. , DODGE Kimberly L. , WONG Wei , MAYER Nicole C. , LANGEBERG Lorene K. , SCOTT John D.
Published: July 2004

mAKAP (muscle-selective A-kinase-anchoring protein) co-ordinates a cAMP-sensitive negative-feedback loop comprising PKA (cAMP-dependent protein kinase) and the cAMP-selective PDE4D3 (phosphodiesterase 4D3). In vitro and cellular experiments demonstrate that PKA-phosphorylation of PDE4D3 on Ser-13 increases the affinity of PDE4D3 for mAKAP. Our data suggest that activation of mAKAP-anchored PKA enhances the recruitment of PDE4D3, allowing for quicker signal termination.
Protein kinase function and glutathionylation
Authors: ANSELMO Anthony N. , COBB Melanie H.
Published: July 2004

Intracellular reactive oxygen species are generated as a by-product of normal metabolic processes and can both damage cellular constituents and function as important signalling species. This signalling often involves changes in the thiol redox balance. As an antioxidant, glutathione serves in maintaining the reduced state of cellular protein thiol groups. The paper by Cross and Templeton appearing in this issue of the Biochemical Journal describes a mechanism by which glutathionylation plays a key role in the regulation of the kinase activity of MEKK1 [MAP (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase kinase; MAP3K] in response to oxidative stresses. This type of post-translational-modification glutathionylation may represent a general mechanism by which protein kinase function can be regulated.
Effect of non-invasive calibration of radial waveforms on error in transfer-function-derived central aortic waveform characteristics
Authors: HOPE Sarah A. , MEREDITH Ian T. , CAMERON James D.
Published: July 2004

Transfer function techniques are increasingly used for non-invasive estimation of central aortic waveform characteristics. Non-invasive radial waveforms must be calibrated for this purpose. Most validation studies have used invasive pressures for calibration, with little data on the impact of non-invasive calibration on transfer-function-derived aortic waveform characteristics. In the present study, simultaneous invasive central aortic (Millar Mikro-tip® catheter transducer) and non-invasive radial (Millar® Mikro-tip® tonometer) pressure waveforms and non-invasive brachial pressures (Dinamap®) were measured in 42 subjects. In this cohort, radial waveforms were calibrated to both invasive and non-invasive mean and diastolic pressures. From each of these, central waveforms were reconstructed using a generalized transfer function obtained by us from a previous cohort [Hope, Tay, Meredith and Cameron (2002) Am. J. Physiol. Heart Circ. Physiol. 283, H1150–H1156]. Waveforms were analysed for parameters of potential clinical interest. For calibrated radial and reconstructed central waveforms, different methods of calibration were associated with differences in pressure (P<0.001), but not time parameters or augmentation index. Whereas invasive calibration resulted in little error in transfer function estimation of central systolic pressure (difference −1±8 mmHg; P=not significant), non-invasive calibration resulted in significant underestimation (7±12 mmHg; P<0.001). Errors in estimated aortic parameters differed with non-invasively calibrated untransformed radial and transfer-function-derived aortic waveforms (all P<0.01), with smaller absolute errors with untransformed radial waveforms for most pressure parameters [systolic pressure, 5±16 and 7±12 mmHg; pulse pressure, 0±16 and 4±12 mmHg (radial and derived aortic respectively)]. When only non-invasive pressures are accessible, analysis of untransformed radial waveforms apparently produces smaller errors in the estimation of central aortic systolic pressure, and other waveform parameters, than using a generalized transfer function.
Probucol aggravates long QT syndrome associated with a novel missense mutation M124T in the N-terminus of HERG
Authors: HAYASHI Kenshi , SHIMIZU Masami , INO Hidekazu , YAMAGUCHI Masato , TERAI Hidenobu , HOSHI Naoto , HIGASHIDA Haruhiro , TERASHIMA Nariaki , UNO Yoshihide , KANAYA Honin , MABUCHI Hiroshi
Published: July 2004

Patients with LQTS (long QT syndrome) with a mutation in a cardiac ion channel gene, leading to mild-to-moderate channel dysfunction, may manifest marked QT prolongation or torsade de pointes only upon an additional stressor. A 59-year-old woman had marked QT prolongation and repeated torsade de pointes 3 months after initiation of probucol, a cholesterol-lowering drug. We identified a single base substitution in the HERG gene by genetic analysis. This novel missense mutation is predicted to cause an amino acid substitution of Met124→Thr (M124T) in the N-terminus. Three other relatives with this mutation also had QT prolongation and one of them had a prolonged QT interval and torsade de pointes accompanied by syncope after taking probucol. We expressed wild-type HERG and HERG with M124T in Xenopus oocytes and characterized the electrophysiological properties of these HERG channels and the action of probucol on the channels. Injection of the M124T mutant cRNA into Xenopus oocytes resulted in expression of functional channels with markedly smaller amplitude. In both HERG channels, probucol decreased the amplitude of the HERG tail current, decelerated the rate of channel activation, accelerated the rate of channel deactivation and shifted the reversal potential to a more positive value. The electrophysiological study indicated that QT lengthening and cardiac arrhythmia in the two present patients were due to inhibition of IKr (rapidly activating delayed rectifier K+ current) by probucol, in addition to the significant suppression of HERG current in HERG channels with the M124T mutation.
Randomized double-blind placebo-controlled study of an angiotensin immunotherapeutic vaccine (PMD3117) in hypertensive subjects
Authors: BROWN Morris J. , COLTART John , GUNEWARDENA Kulasiri , RITTER James M. , AUTON Timothy R. , GLOVER James F.
Published: July 2004

Immunization against components of the renin–angiotensin system offers a potential alternative to daily medication in some patients with hypertension or heart failure. Our primary objective was to determine whether a sustained antibody titre to Ang I (angiotensin I) can be achieved in hypertensive patients. The secondary objective was to determine whether the antibodies block the renin system. Patients (n=27) with essential hypertension responsive to an ACEi (angiotensin-converting enzyme inhibitor) or ARB (angiotensin blocker) were randomly assigned to receive three or four injections of the Ang I vaccine PMD3117 or aluminium hydroxide (Alhydrogel™) over a 6 week period. Antibody titre was measured prior to each injection and every 30 days until disappearance. Indices of renin blockade were changes in renin and aldosterone (blood and urine) and a within-patient comparison of the pre- and post-vaccination rise in 24 h ambulatory blood pressure after 2 weeks of withdrawal of ACEi or ARB. The anti-(Ang I) antibody titre rose from the second injection in both regimes and peaked on day 64. Median half-life was 85 (95% CI, 44 and 153) days (where CI is confidence interval). Vaccination did not influence blood pressure, but significantly blunted the fall in plasma renin following withdrawal of ACEi or ARB. At 42 days after the first injection, aldosterone excretion was decreased by PMD3117 to 6 (95% CI, 1 and 31)% of values in patients receiving Alhydrogel™ (P=0.012). In patients with essential hypertension, PMD3117 generated a prolonged antibody response to Ang I. Biochemical measurements show evidence of blockade of the renin system, but higher titres will be required to achieve a decrease in blood pressure.
Testosterone-induced coronary vasodilatation occurs via a non-genomic mechanism: evidence of a direct calcium antagonism action
Authors: JONES Richard D. , ENGLISH Kate M. , JONES T. Hugh , CHANNER Kevin S.
Published: July 2004

Testosterone decreases myocardial ischaemia in men with coronary artery disease via a coronary vasodilatory action. However, long-term therapy may increase the risk of prostatic carcinoma via activation of the nuclear AR (androgen receptor). In the present study, we have investigated the mechanism of testosterone-induced vasodilatation using isolated rat coronary arteries and thoracic aortae from control and AR-deficient testicular-feminized mice. Vasodilatation induced by testosterone, T-3-OCMO [testosterone 3-(O-carboxymethyl)oxime] or T-3-OCMO conjugated to BSA was initially measured in preconstricted vessels that had undergone endothelial denudation or incubation with flutamide (10 μM). Cellular fluorescence was also measured in primary aortic SMCs (smooth muscle cells) following exposure to the above fluorescent-labelled agents. Subsequently, vessels were incubated with testosterone (100 μM) or vehicle prior to constriction with KCl (1–100 mM). Testosterone-induced vasodilatation was unaffected by endothelial denudation, flutamide treatment, AR deficiency or conjugation to BSA. Cells exposed to T-3-OCMO–BSA (10 μM) had a higher fluorescence than control cells (32.8±4.5 compared with 14.5±1.8 arbitrary units respectively; P<0.01). Incubation with testosterone (100 μM) reversibly attenuated coronary vasoconstriction to KCl (1–100 mM; 0.08±0.09 compared with 0.79±0.08 mN/mm respectively; P<0.0001). Testosterone-induced vasodilatation is independent of the vascular endothelium and nuclear AR, and is initiated at the SMC membrane, which contains testosterone binding sites. A direct calcium antagonistic action is implicated.
Factors influencing heart rate variability power spectral analysis during controlled breathing in patients with chronic heart failure or hypertension and in healthy normotensive subjects
Authors: PICCIRILLO Gianfranco , MAGRÌ Damiano , NASO Camilla , di CARLO Silvia , MOISÈ Antonio , DE LAURENTIS Tiziana , TORRINI Alessia , MATERA Sabrina , NOCCO Marialuce
Published: July 2004

A decreased LFP (low-frequency power) spectral component of HRV [HR (heart rate) variability] is a risk factor for sudden death in patients with CHF (chronic heart failure). In the present study, we evaluated factors (age, arterial pressures and HR) influencing LFP and HFP (high-frequency power) components in short-term recordings during controlled breathing in patients with CHF or hypertension, and healthy normotensive subjects. In patients with CHF, we also compared LFP values with known markers of sudden death [NYHA (New York Heart Association) class, HR and ejection fraction]. All HRV measures were significantly lower in patients with CHF than in hypertensive and normotensive subjects (P<0.001), and in hypertensive than in normotensive subjects (P<0.05). Stepwise multiple regression analysis showed that, in patients with CHF, LFP was inversely associated with NYHA class (β=−0.5, P<0.0001) and HR (β=−0.2, P=0.001) and was positively associated with ejection fraction (β=0.28, P<0.0001). In patients with CHF, LFP remained unchanged with age. In normotensive and hypertensive subjects, HFP decreased with age, but in patients with CHF it did not. In the ≥60<70 and ≥70 years of age subgroups, we found no difference between HFP in the three groups studied. Hence, in normotensives and hypertensives, LFP tended to diminish with age (β=−0.4, P<0.0001 in normotensives; β=−0.4, P<0.001 in hypertensives) and was inversely associated with HR (β=−0.2, P=0.002 in normotensives; β=−0.3, P=0.002 in hypertensives). Conversely, in patients with CHF, LFP is predominantly influenced by NYHA class, HR and ejection fraction, but not by age. LFP might therefore increase the sensitivity of factors already used in stratifying the risk of sudden death in patients with CHF.
Lack of effect of oral glucose loading on conduit vessel endothelial function in healthy subjects
Authors: SIAFARIKAS Aris , WATTS Katie , BEYE Petra , JONES Timothy W. , DAVIS Elizabeth A. , GREEN Daniel J.
Published: July 2004

The aim of the present study was to investigate the impact of an oral glucose load on circulating insulin and glucose levels and arterial function in healthy non-diabetic subjects. Thirty-nine non-obese, healthy subjects (24 female, 15 male), aged 21.0±1.8 years of age, were randomly assigned to undergo either an OGTT (oral glucose tolerance test; 75 g of glucose) or administration of a placebo. Analyses of lipids, liver function and HbA1c (glycated haemoglobin) at baseline revealed results which were within the standard reference range. Insulin and glucose levels as well as vascular function [FMD (flow-mediated dilation)] were measured at 0, 60 and 120 min. Compared with baseline, the control subjects did not exhibit any significant changes in glucose or insulin levels, whereas, in the OGTT group, blood glucose levels at both 60 (5.4±1.7 mmol/l) and 120 (5.0±1.1 mmol/l) min increased significantly relative to baseline (4.1±0.4 mmol/l; both P<0.001) and, similarly, insulin levels were higher at both 60 (30.1±21.3 m-units/l) and 120 (34.9±23.6 m-units/l) min compared with baseline (4.7±4.3 m-units/l; both P<0.001). Although blood glucose and insulin levels changed, FMD did not significantly differ between time-points or between groups. In summary, despite significantly elevated glucose and insulin concentrations in these subjects, we observed no change in vascular function, suggesting that acute elevations of glucose and insulin within the clinically normal range are not associated with impaired vascular function in vivo.
Renal aluminium handling in the rat: a micropuncture assessment
Authors: SHIRLEY David G. , WALTER Mary F. , WALTER Stephen J. , THEWLES Andrew , LOTE Christopher J.
Published: July 2004

Uncertainties exist over the glomerular filtration of aluminium and virtually nothing is known about its segmental handling along the nephron. The present study has used micropuncture, combined with electrothermal atomic absorption spectroscopy, to determine directly the aluminium content of glomerular filtrate and of late PCTs (proximal convoluted tubules) and early distal tubules in anaesthetized Munich–Wistar rats infused with three different doses of aluminium citrate (plasma aluminium concentrations, 2.9±0.1, 5.2±0.4 and 10.0±0.9 μg·ml−1 respectively). Aluminium filtration into Bowman's space was found to be considerably greater than that predicted by an in vitro filtration system: in all three groups it was essentially filtered freely. No significant aluminium reabsorption took place along the PCT, but with every dose the FDAl (fractional delivery of aluminium; tubular fluid:plasma aluminium/inulin concentration ratio) was lower at the early distal site than at the late PCT (P<0.001 in each case), indicating net aluminium reabsorption in the loop of Henle. This reabsorption amounted to 19–26% of the filtered aluminium load. In the low- and medium-dose groups, there was no significant difference between FDAl at the early distal site and that in the final urine; however, in the high-dose group, FDAl in the urine (1.02±0.06) exceeded that at the early distal tubule (0.75±0.04; P<0.001), suggesting aluminium secretion in the distal nephron. The results indicate that aluminium loads, when complexed with citrate, are excreted efficiently owing to a combination of glomerular filtration and minimal reabsorption.
Sensitivity of bone to glucocorticoids
Authors: COOPER Mark S.
Published: July 2004

Glucocorticoids are used widely in a range of medical specialities, but their main limitation is an adverse impact on bone. Although physicians are increasingly aware of these deleterious effects, the marked variation in susceptibility between individuals makes it difficult to predict who will develop skeletal complications with these drugs. Although the mechanisms underlying the adverse effects on bone remain unclear, the most important effect appears to be a rapid and substantial decrease in bone formation. This review will examine recent studies that quantify the risk of fracture with glucocorticoids, the mechanisms that underlie this increase in risk and the potential basis for differences in individual sensitivity. An important determinant of glucocorticoid sensitivity appears to be the presence of glucocorticoid-metabolizing enzymes within osteoblasts and this may enable improved estimates of risk and generate new approaches to the development of bone-sparing anti-inflammatory drugs.
Role of the immune system in the pathogenesis of idiopathic nephrotic syndrome
Authors: van den BERG José G. , WEENING Jan J.
Published: July 2004

Idiopathic NS (nephrotic syndrome) is characterized by massive proteinuria, due to a leak in the glomerular barrier to proteins. Genetic defects that affect the function and the composition of the glomerular capillary wall, in particular of the visceral epithelial cells, have recently been recognized as the cause of familial forms of NS. MCNS (minimal change NS) and FSGS (focal and segmental glomerulosclerosis) are common non-familial forms of NS in which the causative defect has not yet been identified. Several studies have shown that non-familial NS is associated with the presence of circulating permeability factors and with complex disturbances in the immune system. Thus far, there is no direct evidence that these factors directly alter glomerular permeability to proteins, and some of these factors may be a consequence, rather than a cause, of NS. In this review, we will briefly highlight the mechanisms that underlie proteinuria in general and focus on the immunological disturbances associated with idiopathic NS, with attention to potential mechanisms whereby the immune system may directly act on the glomerular capillary filter.
Pathophysiology of acute lung injury in combined burn and smoke inhalation injury
Authors: ENKHBAATAR Perenlei , TRABER Daniel L.
Published: July 2004

In the U.S.A., more than 1 million burn injuries occur every year. Although the survival from burn injury has increased in recent years with the development of effective fluid resuscitation management and early surgical excision of burned tissue, the mortality of burn injury is still high. In these fire victims, progressive pulmonary failure and cardiovascular dysfunction are important determinants of morbidity and mortality. The morbidity and mortality increases when burn injury is associated with smoke inhalation. In the present review, we will describe the pathophysiological aspects of acute lung injury induced by combined burn and smoke inhalation and examine various therapeutic approaches.
E-Business Transformation at the Crossroads: Sears’ Dilemma
Authors: Ranganathan C , Shetty Analini , Muthukumaran Gayathri
Published: July 2004

This teaching case discusses the challenges facing Sears, Reobeck and Co., a leading retailer in United States, in its efforts to transform itself into an effective brick-and-click organization. In face of intense competition from other retailers and online e-tailers, Sears has continually expanded its online efforts in e-business transformation. This case traces the key e-business initiatives taken by Sears and highlights significant managerial challenges that were encountered during the formulation and execution of an effective e-business transformation strategy. The case presents the issues faced by a new CIO who had taken over the technology and e-business affairs at Sears at the end of 2002.
On the stability of Besocke-type scanners
Authors: Pertaya N. , Braun K.-F. , Rieder K.-H.
Published: July 2004

A widespread used construction for the coarse approach mechanism in scanning probe microscopy is the Besocke beetle type. Using stick-slip motion the scanner can thereby be positioned on the millimeter scale horizontally and vertically. This apparent advantage of a high flexibility is bought on the expense of a reduced mechanical stability. Here we present an analysis of the vibrational response of a beetle-type scanner and based on this, a very stable optimized scanner setup. In this setup, shear stack piezoelectric elements are used resulting in very high mechanical resonance frequencies and overall stability.
Line ratio method for measurement of magnetic field vector using Li-multiplet (2 2S−2 2P) emission
Authors: Korotkov A. A. , Morgan P. D. , Vince J. , Schweinzer J. ,   JET EFDA Contributors
Published: July 2004

A method has been developed, for use in magnetic confinement devices, to measure the magnetic field vector B⃗ in plasmas or gases. It utilizes the intensities of the π and σ components of the resonance multiplet emitted by lithium atoms subjected to a strong Zeeman effect. A difference in dependence of these intensities on the inclination angle θ between B⃗ and the line of sight allows one to determine the direction of B⃗, provided the intensity ratio of the π and σ components ξ(θ) is measured. The magnitude of B⃗ is routinely inferred from the width of the multiplet. The principles of the measurement are elaborated in detail for the case of a fast Li beam (20–100 keV) used to diagnose a fusion plasma. The deviation of the population of the m states from the statistical one due to a dominant direction for the relative velocity during the excitation of the atoms by plasma ions has been analyzed and corrections to ξ(θ) are calculated. The geometry employed for the measurement is investigated in order to minimize the uncertainties due to systematic and random errors. A procedure for in situ calibration is outlined. As proof of the principle the results from poloidal magnetic field measurements in ohmic and H-mode pulses on the Joint European Torus are analyzed. As expected, much higher components of the poloidal magnetic field BZ and BR have been found at the plasma edge in H-mode pulses indicating the sensitivity of the measurements to the bootstrap current. An accuracy of 10–20% for the poloidal magnetic field component BZ and BR and 1% for B has been reached. Reasonable agreement has been observed between the expected and obtained accuracy. The uncertainty in ξ(θ) is found to be close to the statistical limit at ξ(θ)>6%. The prospects for current density measurement at the plasma edge, which remains a key issue for achieving advanced performance of modern tokamaks, are examined in terms of making use of the developed technique. It is concluded that prospects are good provided the best available Li-beam guns, with equivalent neutral current ∼5 mA, are used.
Spectroscopic cell for fast pressure jumps across the glass transition line
Authors: Di Leonardo R. , Scopigno T. , Ruocco G. , Buontempo U.
Published: July 2004

We present an experimental protocol for the spectroscopic study of the dynamics of glasses in the aging regime induced by sudden pressure jumps (crunches) across the glass transition line. The sample, initially in the liquid state, is suddenly brought in the glassy state, and therefore out of equilibrium, in a four-window optical crunch cell which is able to perform pressure jumps of 3 Kbar in a time interval of ≈10 ms. The main advantages of this setup with respect to previous pressure-jump systems is that the pressure jump is induced through a pressure transmitting fluid mechanically coupled to the sample stage through a deformable membrane, thus avoiding any flow of the sample itself in the pressure network and allowing us to deal with highly viscous materials. The dynamics of the sample during the aging regime is investigated by Brillouin light scattering. For this purpose the crunch cell is used in conjunction with a high resolution double monochromator equipped with a charge-coupled device detector. This system is able to record a full spectrum of a typical glass forming material in a single 1 s shot. As an example we present the study of the evolution toward equilibrium of the infinite frequency longitudinal elastic modulus (M∞) of low molecular weight polymer [Poly(bisphenol A-co-epichlorohydrin), glycidyl end capped]. The observed time evolution of M∞, well represented by a single stretched exponential, is interpreted within the framework of the Tool–Narayanaswamy theory.
A new method to measure viscosity and intrinsic sound velocity of liquids using impedance tube principles at sonic frequencies
Authors: Mert Behic , Sumali Hartono , Campanella Osvaldo H.
Published: July 2004

The attenuation of the sound energy produced by a liquid contained in a cylindrical tube (wave guide) depends on the liquid’s viscosity, sound frequency, tube wall thickness, and tube material. By measuring the acoustic impedance of plane sound waves in a cylindrical wave guide, one can obtain the liquid’s viscosity. Impedance measurements can also provide sound velocity in the liquid medium as another important physical characteristic. In this study a method using the impedance tube technique is presented. This research details the instrument’s principles of operation along pertinent analytical equations and reports experimental results conducted using viscosity standard liquids. It is shown that the instrument can measure both liquid’s viscosity and intrinsic sound velocity with reasonable precision.
Quantum-based microwave power measurements: Proof-of-concept experiment
Authors: Crowley T. P. , Donley E. A. , Heavner T. P.
Published: July 2004

We present an initial proof-of-concept experiment to measure microwave power based on quantum-mechanical principles. Ground-state cesium atoms exposed to microwaves at 9.192 631 770 GHz oscillate between two hyperfine states at a rate that is proportional to the rf magnetic field strength. This provides a quantum-based method of measuring rf field strength that depends only on the fundamental parameters in the proportionality constant. A small fountain apparatus was used to prepare laser-cooled cesium atoms in a single hyperfine state, which were then launched through a cylindrical cavity operating in the TE011 mode. After passing through the cavity, the fraction of atoms in the two hyperfine states was measured. Rabi oscillations between the two states were observed as a function of microwave field strength. The scaling with field strength and with time in the cavity agreed with theory to within 0.4%. The field strength in the cavity was used, together with measured S parameters, to determine the microwave power incident at a reference plane outside the fountain apparatus. The difference between the quantum-based microwave power measurement and a traditional microwave power measurement was less than 5% of the measured power.
Enhancement of the Curie temperature in GaMnAs∕InGaMnAs superlattices
Authors: Koeder A. , Limmer W. , Frank S. , Schoch W. , Avrutin V. , Sauer R. , Waag A. , Zuern K. , Ziemann P.
Published: July 2004

We report on an enhancement of the Curie temperature in GaMnAs∕InGaMnAs superlattices grown by low-temperature molecular beam epitaxy which is due to thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced increase of the Curie temperature is strongly correlated to the In concentration in the embedded layers. Curie temperatures up to 110K are observed in such structures compared to 60K in GaMnAs single layers grown under the same conditions. A further increase in TC up to 130K can be achieved using postgrowth annealing at temperatures near the growth temperature. Pronounced thickness fringes in the high-resolution x-ray diffraction spectra indicate good crystalline quality and sharp interfaces in the structures.
Experimental demonstration of a low-loss optical H-tree distributionusing silicon-on-insulator microwaveguides
Authors: Vivien L. , Lardenois S. , Pascal D. , Laval S. , Cassan E. , Cercus J. L. , Koster A. , Fédéli J. M. , Heitzmann M.
Published: July 2004

The experimental demonstration of an optical H-tree distribution from one input to sixteen outputs compatible with the size of a microelectronic chip is reported. It is based on low-loss silicon-on-insulator rib submicron waveguides. Each branch is 1cm long and includes four ultracompact T splitters and two mirrors allowing 90° direction changes. The mean value of the global losses has been measured and is found equal to 26dB, which corresponds to a power of 2.6μW at each output, for a 3mW laser diode power at the input. This demonstration is an important step for on-chip optical clock distribution in complementary metal–oxide–Semiconductor integrated circuits.
Integrated horns for improved side coupling into in-plane three-dimensional photonic crystal waveguides
Authors: Sell Curtis , Christensen Caleb , Muehlmeier Jason , Tuttle Gary , Li Zhi-Yuan , Ho Kai-Ming
Published: July 2004

We examine the frequency response and radiation patterns for horn antennas constructed into a three-dimensional layer-by-layer photonic crystal. These horns resemble a pyramidal cavity and can be built by omitting material during the construction or by removing material from the finished crystal. The horns can be used to couple electromagnetic waves that are incident on the surface of a photonic crystal into an in-plane waveguide within the crystal. The horns are of a design suitable for use at optical frequencies.
Self-sustained oscillations and vortex shedding in backward-facing step flows: Simulation and linear instability analysis
Authors: Wee Daehyun , Yi Tongxun , Annaswamy Anuradha , Ghoniem Ahmed F.
Published: July 2004

Linear instability analysis was performed to investigate the origin of the self-sustained oscillations, at St=O(0.1), which have been widely reported in backward-facing step flows. Parametric studies, based on local stability analysis of a family of time-average velocity profiles modeling those observed in recirculating flows, show that the frequency of the absolute mode is determined primarily by the shear layer thickness, and the growth rate of the absolute mode is controlled by the amount of backflow. Given the known streamwise variation of the local velocity profile in the actual flow, this implies that the oscillations are likely to be generated at the middle of the recirculation zone, where the backflow is sufficiently strong, and shear layer thickness is comparable to the step height. The corresponding frequency is determined to be St=O(0.1), because the shear layer thickness is bounded by the step height. To verify this hypothesis, mean velocity profiles obtained from a two-dimensional numerical simulation of a backward-facing step flow at Reynolds number of 3700 and expansion ratio 2:3, were analyzed to obtain the dominant absolute mode frequency, and the corresponding linear global mode was constructed by connecting local solutions at the same frequency. The frequency of the linear global mode closely matches the dominant peak frequency observed in the numerical simulation, and the mode shape showed strong resemblance to that of the dominant eddy identified in the simulation that was obtained using proper orthogonal decomposition analysis of the simulation data.
Effective optical manipulation of the charge state and emission intensity of the InAs∕GaAs quantum dots by means of additional infrared illumination
Authors: Moskalenko E. S. , Karlsson K. F. , Donchev V. , Holtz P. O. , Monemar B. , Schoenfeld W. V. , Petroff P. M.
Published: July 2004

InAs quantum dots (QDs) at different levels of density have been studied by means of photoluminescence, when in addition to the main laser, a second infrared (IR) laser is employed to excite the QD. It is demonstrated that the IR laser considerably affects the QD charge state as well as the emission intensity level (an increase greater than fivefold was observed). These effects are explained in terms of separate generation of excess electrons and holes provided under dual-laser excitation. However, these effects progressively vanish with increasing QD density. The results obtained unambiguously imply that the emission intensity from the QD can be effectively enhanced by purely optical means.
High-temperature ferromagnetism in manganese-doped indium–tin oxide films
Authors: Philip John , Theodoropoulou Nikoleta , Berera Geetha , Moodera Jagadeesh S. , Satpati Biswarup
Published: July 2004

High-temperature ferromagnetism is demonstrated in Mn-doped indium–tin oxide (ITO) films deposited using reactive thermal evaporation. These films were grown on sapphire (0001), Si∕SiO2 as well as Si (100) substrates with the highest magnetic moment observed around 0.8μB∕Mn in 5% Mn-doped ITO films. The electrical conduction is n type and the carrier concentration is ∼2.5×1019cm−3 for 5% Mn doping. An anomalous Hall effect is observed in magnetotransport measurements, showing that the charge carriers are spin polarized, revealing the magnetic interaction between itinerant electrons and localized Mn spins. The carrier concentration can be varied independent of the Mn concentration in this transparent ferromagnetic semiconductor for its easy integration into magneto-optoelectronic devices.
Room-temperature magneto-optical activity of InMnAs thin films
Authors: Chiu P. T. , May S. J. , Wessels B. W.
Published: July 2004

Room-temperature magneto-optical activity of In1−xMnxAs heteroepitaxial thin films grown on InAs (001) and GaAs (001) substrates has been studied using the longitudinal magneto-optical Kerr effect. For single-phase layers grown on InAs and GaAs with x ranging from 0.03 to 0.09, square hysteresis loops that indicate ferromagnetic order were observed. The magnitude of the saturation Kerr rotation of all the InMnAs samples ranged from 0.29to1.1mdeg, and scaled with the manganese concentration. The shape of the hysteresis curves for samples of InMnAs grown GaAs was invariant with respect to rotation about the sample normal, indicating in-plane magnetic isotropy. In contrast, InMnAs layers on InAs exhibited strong uniaxial in-plane anisotropy with the easy axis of magnetization along the [110] and [1¯1¯0] directions. The magnetic anisotropy is attributed to the effect of epitaxial strain.
Fabrication and properties of nanoporous GaN films
Authors: Wang Y. D. , Chua S. J. , Sander M. S. , Chen P. , Tripathy S. , Fonstad C. G.
Published: July 2004

Nanopore arrays with pore diameters of approximately 75nm were fabricated in GaN films by inductively coupled plasma etching using anodic aluminum oxide (AAO) films as etch masks. Nanoporous AAO films were formed on the GaN surface by evaporating an Al film onto a GaN epilayer and subsequently anodizing the aluminum. To minimize plasma-induced damage, the template was exposed to CF4-based plasma conditions. Scanning electron microscopy analysis shows that the diameter and the periodicity of the nanopores in the GaN were directly transferred from the original anodic alumina template. The pore diameter in the AAO film can be easily controlled by tuning the anodization conditions. Atomic force microscopy, photoluminescence, and micro-Raman techniques were employed to assess the etched GaN nanopore surface. This cost-effective, nonlithographic method to produce nano-patterned GaN templates is expected to be useful for growth and fabrication of nitride-based nanostructures and photonic band gap materials.
Highly efficient triggered emission of single photons by colloidal CdSe∕ZnS nanocrystals
Authors: Brokmann X. , Giacobino E. , Dahan M. , Hermier J. P.
Published: July 2004

We demonstrate the realization of a highly efficient triggered source of single photons emitted by colloidal CdSe∕ZnS nanocrystals at room temperature. Under pulsed excitation, the fluorescence of single nanocrystals excited close to saturation exhibits a perfect antibunching and the probability to detect a single emitted photon per excitation pulse reaches 3%, comparable to the best values reported for other emitters. Without any correction, the probability of simultaneously emitting two photons is 25 times lower than for a faint pulsed laser. Combined with recent reports on the reduction of fluorescence intermittency, these results indicate that CdSe∕ZnS nanocrystals are promising single-photon sources.
Improving the performance of a neodymium aluminium borate microchip laser crystal by resonant pumping
Authors: Luo Z. D. , Huang Y. D. , Montes M. , Jaque D.
Published: July 2004

Laser action at 1.06μm from a neodymium aluminium borate microchip laser crystal has been demonstrated under F3∕24 direct excitation at 882nm. We have found that the laser slope efficiency increases from 50% up to 70% when resonant pumping is used instead of the traditional I9∕24→F5∕24(808nm) pumping. We conclude that the reduction in the pump-induced heat generation achieved by resonant pumping is at the origin of this improvement.
Influence of the hole injection layer on the luminescent performanceof organic light-emitting diodes
Authors: Chen Shih-Fang , Wang Ching-Wu
Published: July 2004

We investigate the influence of the hole injection layer (HIL) on the performance of vapor-deposited tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes. Four different HIL materials were used: 4,4′, 4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA), 4,4′, 4″-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine, copper phthalocyanine, and oxotitanium phthalocyanine. In all cases, Alq3 acts as the emitting layer as well as electron-transporting layers. Evidence showed that m-MTDATA exhibits a dense film structure and fine surface morphology, leading to easier hole migration at the indium tin oxide/m-MTDATA and m-MTDATA/hole-transport layer junctions. It also possesses a shallow bulk trap level, providing more detrapping holes from the bulk trap states to highest occupied molecular orbital states for transporting in m-MTDATA. We suggest that these are the main contributing factors to the superior current density–voltage and luminance-voltage performance of this device.
Novel approach to tensile testing of micro- and nanoscale fibers
Authors: Tan E. P. S. , Lim C. T.
Published: July 2004

Due to the strength and size of the micro- and nanoscale fibers, larger conventional universal testing machines are not suitable in performing stretch test of such fibers. Existing microtensile testing machines are custom-made and are complex and expensive to construct. Here, a novel method of using an existing atomic force microscope (AFM)-based nanoindenation system for the tensile testing of microscale or bundled nanoscale fibers is proposed. The microscale poly (L-lactic-co-glycolic acid) fiber (∼25 μm diameter) was used as an example to illustrate this technique. The microfiber was first attached to a nanoindenter tip and the base via a custom-made holder to ensure that the microfiber was taut and vertically aligned. The force transducer of the nanoindenter was used to measure the tensile force required to stretch the microfiber. The microfiber was stretched using the stepper motor of the AFM system. The elongation of the microfiber was measured by subtracting the elongation of the transducer spring from the total elongation of the microfiber and transducer spring. A plot of the load against elongation of the microfiber was then obtained. The stress and strain of the microfiber was measured by subtracting the elongation of the transducer spring from the total elongation of the microfiber was then obtained. The stress and strain of the microfiber was obtained by dividing the load and elongation by cross-sectional area and gauge length, respectively. With this data, the mechanical behavior of the sample at small strains can be studied. This system is able to provide a high load resolution of 80 nN and displacement resolution of 0.5 nm. However, maximum load and sample elongation is limited and handling of the sample still remains a challenge.
Test facility for simultaneous measurement of electrical and thermal contact resistance
Authors: Misra Prashant , Nagaraju J.
Published: July 2004

A test setup has been developed for simultaneously evaluating the electrical contact resistance (ECR) and thermal contact resistance/conductance (TCR/TCC) across meta–metal contacts at different contact pressures and mean interface temperatures. ECR and TCC across brass–brass contacts in vacuum have been measured simultaneously at different contact pressures and mean interface temperatures. The results obtained are found to be in agreement with the theoretical models available in the literature for ECR and TCC, independently from each other. The maximum absolute uncertainties in the measurement of ECR and TCC with the present setup are estimated to be ±0.003% and ±4.4%, respectively. Apart from contact resistance measurements, the setup is also used to determine thermal conductivity of unknown materials viz., oxygen-free high-conductivity copper and brass, at different temperatures.
Synergism between low-energy neutral particles and energetic ions in the pulsed glow discharge deposition of diamond-like carbon films
Authors: Afanasyev-Charkin I. V. , Nastasi M.
Published: July 2004

Diamond-like carbon films were deposited using pulsed glow discharge deposition at 4kV. The duty factor was varied and all other parameters were kept constant. It was shown that the contribution of neutral particles to the total number of deposition atoms is much larger than that of energetic ions. At the same time, there is a relationship between the deposition of neutral particles and ion bombardment. The sticking coefficient of the neutral particles in proportional to the flux of energetic ions and does not exceed 5×10−4 for the deposition parameters used in our experiment.