bluuebunny/crossref_metadata_2025 huggingface dataset:
Ideication of disulfide‐linked peptides by isotope profiles produced by peptic digestion of proteins in 50% 18O water
Authors: Wallis Tristan P. , Pitt James J. , Gorman Jeffrey J.
Published: July 2002

Determination of the disulfide‐bond arrangement of a protein by characterization of disulfide‐linked peptides in proteolytic digests may be complicated by resistance of the protein to specific proteases, disulfide interchange, and/or production of extremely complex mixtures by less specific proteolysis. In this study, mass spectrometry has been used to show that incorporation of 18O into peptides during peptic digestion of disulfide‐linked proteins in 50% 18O water resulted in isotope patterns and increases in average masses that facilitated ideication and characterization of disulfide‐linked peptides even in complex mixtures, without the need for reference digests in 100% 16O water. This is exemplified by analysis of peptic digests of model proteins lysozyme and ribonuclease A (RNaseA) by matrix‐assisted laser desorption/ionization–time of flight (MALDI‐TOF) and electrospray ionization (ESI) mass spectrometry (MS). Distinct isotope profiles were evident when two peptide chains were linked by disulfide bonds, provided one of the chains did not contain the C terminus of the protein. This latter class of peptide, and single‐chain peptides containing an intrachain disulfide bond, could be ideied and characterized by mass shifts produced by reduction. Reduction also served to confirm other assignments. Isotope profiling of peptic digests showed that disulfide‐linked peptides were often enriched in the high molecular weight fractions produced by size exclusion chromatography (SEC) of the digests. Applicability of these procedures to analysis of a more complex disulfide‐bond arrangement was shown with the hemagglutinin/neuraminidase of Newcastle disease virus.
Structure of the transmembrane region of the M2 protein H+ channel
Authors: Wang Junfeng , Kim Sanguk , Kovacs Frank , Cross Timothy A.
Published: July 2002

The transmembrane domain of the M2 protein from influenza A virus forms a nearly uniform and ideal helix in a liquid crystalline bilayer environment. The exposure of the hydrophilic backbone structure is minimized through uniform hydrogen bond geometry imposed by the low dielectric lipid environment. A high‐resolution structure of the monomer backbone and a detailed description of its orientation with respect to the bilayer were achieved using orientational restraints from solid‐state NMR. With this unique information, the tetrameric structure of this H+ channel is constrained substantially. Features of numerous published models are discussed in light of the experimental structure of the monomer and derived features of the tetrameric bundle.
Reconstitution of a native‐like SH2 domain from disordered peptide fragments examined by multidimensional heteronuclear NMR
Authors: Ojennus Deanna Dahlke , Fleissner Mark R. , Wuttke Deborah S.
Published: July 2002

The N‐terminal SH2 domain from the p85α subunit of phosphatidylinositol 3′ kinase is cleaved specifically into 9‐ and 5‐kD fragments by limited proteolytic digestion with trypsin. The noncovalent SH2 domain complex and its constituent tryptic peptides have been investigated using high‐resolution heteronuclear magnetic resonance (NMR). These studies have established the viability of the SH2 domain as a fragment complementation system. The individual peptide fragments are predominantly unstructured in solution. In contrast, the noncovalent 9‐kD + 5‐kD complex shows a native‐like 1H‐15N HSQC spectrum, demonstrating that the two fragments fold into a native‐like structure on binding. Chemical shift analysis of the noncovalent complex compared to the native SH2 domain reveals that the highest degree of perturbation in the structure occurs at the cleavage site within a flexible loop and along the hydrophobic interface between the two peptide fragments. Mapping of these chemical shift changes on the structure of the domain reveals changes consistent with the reduction in affinity for the target peptide ligand observed in the noncovalent complex relative to the intact protein. The 5‐kD fragment of the homologous Src protein is incapable of structurally complementing the p85 9‐kD fragment, either in complex formation or in the context of the full‐length protein. These high‐resolution structural studies of the SH2 domain fragment complementation features establish the suitability of the system for further protein‐folding and design studies.
Decomposing Global Self‐Esteem
Authors: Tafarodi Romin W. , Milne Alan B.
Published: July 2002

ABSTRACT We argue in this paper for distinguishing two dimensions of global self‐esteem, self‐competence and self‐liking. Studies 1 and 2 identify a corresponding pair of factors in Rosenberg's (1965) Self‐Esteem Scale. Studies 3 and 4 examine the predictive value of the two‐dimensional approach to self‐esteem as reflected in the unique associations of self‐competence and self‐liking with negative life events and word recognition.
Toddler Peers: From Nonverbal Coordinated Action to Verbal Discourse
Authors: Didow Sharon M. , Eckerman Carol O.
Published: July 2002

Twenty‐four toddlers (24 months of age) interacted with an adult play partner who experimentally created two different nonverbal interactive contexts surrounding her speech to the toddlers. One, a nonverbal imitation game, mimicked that hypothesized to facilitate toddlers’ discourse with one another. The second mimicked another frequent form of toddler peer interaction, parallel play. After establishing the nonverbal context, the adult verbally described her own or the child’s nonverbal action. Being engaged in nonverbal imitation games facilitated toddlers (1) responding verbally to the adult’s speech in a topically well‐connected way and (2) maintaining topically‐connected responses over successive turns. Using nonverbal imitative acts, toddlers appear to nonverbally negotiate a topic for their interactions that facilitates their skill in verbal discourse.
Mean, median, mode IV
Authors: Abdous B. , Theodorescu R.
Published: July 2002

This note continues the discussion about the well‐known mean‐median‐mode inequality (Runnenburg, 1978, van Zwet, 1979, and Dharmadhikari and Joag‐dev, 1983). A discrete analogue of this inequality is proved under similar conditions as those used for the classical Khinchin unimodality on R.
Wave Turbulence Is Almost Always Intermittent at Either Small or Large Scales
Authors: Newell Alan C.
Published: July 2002

The asymptotic expansions for (1) the slow changes in particle number/energy density; namely, the kinetic equation, (2) frequency renormalization; and (3) the Nth‐order structure functions for wave turbulence systems are almost always nonuniform at either small or large length scales. The manifestation of this nonuniformity is fully nonlinear behavior either in the form of localized structures (coherent structures, shocks) or condensates (nonzero mean over large distances). The result is intermittent behavior dominated by large fluctuation events, anomolous scaling, and far from joint Gaussian statistics. Despite this unexpected surprise, and it is a surprise considering that wave turbulence has been the subject of continuous and intense investigation for several decades, wave turbulence still offers an advantage over systems that are nonlinear over all scales. The advantage is that the nature of the fully nonlinear behavior often can be identified, which gives us reasonable hope that wave turbulent systems may be treated as a two species gas of random wavetrains and randomly occurring coherent structures.
Evidence against aquaporin‐1‐dependent CO2 permeability in lung and kidney
Authors: Fang Xiaohui , Yang Baoxue , Matthay Michael A. , Verkman A. S.
Published: July 2002

AQP1‐dependent CO2 transport has been suggested from the increased CO2 permeability in Xenopus oocytes expressing AQP1. Potential implications of this finding include AQP1‐facilitated CO2 exchange in mammalian lung and HCO3−/CO2 transport in kidney proximal tubule. We reported previously that: (a) CO2 permeability in erythrocytes was not affected by AQP1 deletion, (b) CO2 permeability in liposomes was not affected by AQP1 reconstitution despite a 100‐fold increased water permeability, and (c) CO2 blow‐off by the lung in living mice was not impaired by AQP1 deletion. We extend these observations by direct measurement of CO2 permeabilities in lung and kidney. CO2 transport across the air‐space‐capillary barrier in isolated perfused lungs was measured from changes in air‐space fluid pH in response to addition/removal of HCO3−/CO2 from the pulmonary artery perfusate. The pH was measured by pleural surface fluorescence of a pH indicator (BCECF‐dextran) in the air‐space fluid. Air‐space fluid pH equilibrated rapidly (t1/2∼ 6 s) in response to addition/removal of HCO3−/CO2. However, the kinetics of pH change was not different in lungs of mice lacking AQP1, AQP5 or AQP1/AQP5 together, despite an up to 30‐fold reduction in water permeability. CO2 transport across BCECF‐loaded apical membrane vesicles from kidney proximal tubule was measured from the kinetics of intravesicular acidification in response to rapid mixing with a HCO3−/CO2 solution. Vesicles rapidly acidified (t1/2∼ 10 ms) in response to HCO3−/CO2 addition. However the acidification rate was not different in kidney vesicles from AQP1‐null mice despite a 20‐fold reduction in water permeability. The results provide direct evidence against physiologically significant transport of CO2 by AQP1 in mammalian lung and kidney.
Desensitization of diliganded mouse muscle nicotinic acetylcholine receptor channels
Authors: Elenes Sergio , Auerbach Anthony
Published: July 2002

Nicotinic ACh receptor channels (AChRs) exposed to high concentrations of ACh adopt ‘desensitized’ conformations that have a high affinity for the transmitter and no measurable ion conductance. Single‐channel currents elicited by 0.1 or 1 mmACh were recorded from human embryonic kidney (HEK) cells that had been transiently transfected with mouse α, β, δ, and ε subunits. On the time scale of ∼0.1 ms to ∼1 h, apparent open intervals are described by a single exponential component, and shut intervals associated with desensitization are described by the sum of four or five exponential components. The kinetic behaviour appeared to be stationary and homogeneous. Desensitization rate constants were estimated by kinetic modelling of currents from cell‐attached and outside‐out patches (where the number of channels in the patch was measured). A single AChR recovered from the longest‐lived desensitized state only after ∼5 min. The occupancy of an AChR for each of the desensitized states was calculated as a function of time after the continuous application of a pulse of saturating ACh. The longest‐lived desensitized state accounted for 90 % of the total only after several seconds. The fractional recovery from desensitization (during a 200 ms wash period) decreased as the duration of the desensitizing pulse increased, suggesting that recovery is slower from the longer‐lived desensitized states. The free energy landscape for the AChR desensitization reaction in cell‐attached patches exhibited an initial destabilization, followed by a plateau region of gradually increasing stability, followed by a deep well.
Cocaine binds to a common site on open and inactivated human heart (Nav1.5) sodium channels
Authors: O'Leary M. E. , Chahine M.
Published: July 2002

The inhibition by cocaine of the human heart Na+ channel (Nav1.5) heterologously expressed in Xenopus oocytes was investigated. Cocaine produced little tonic block of the resting channels but induced a characteristic, use‐dependent inhibition during rapid, repetitive stimulation, suggesting that the drug preferentially binds to the open or inactivated states of the channel. To investigate further the state dependence, depolarizing pulses were used to inactivate the channels and promote cocaine binding. Cocaine produced a slow, concentration‐dependent inhibition of inactivated channels, which had an apparent KD of 3.4 μM. Mutations of the interdomain III‐IV linker that remove fast inactivation selectively abolished this high‐affinity component of cocaine inhibition, which appeared to be linked to the fast inactivation of the channels. A rapid component of cocaine inhibition persisted in the inactivation‐deficient mutant that was enhanced by depolarization and was sensitive to changes in the concentration of external Na+, properties that are consistent with a pore‐blocking mechanism. Cocaine induced a use‐dependent inhibition of the non‐inactivating mutant and delayed the repriming at hyperpolarized voltages, indicating that the drug slowly dissociated when the channels were closed. Mutation of a conserved aromatic residue (Y1767) of the D4S6 segment weakened both the inactivation‐dependent and the pore‐blocking components of the cocaine inhibition. The data indicate that cocaine binds to a common site located within the internal vestibule and inhibits cardiac Na+ channels by blocking the pore and by stabilizing the channels in an inactivated state.
Interaction of transcranial magnetic stimulation and electrical transmastoid stimulation in human subjects
Authors: Taylor Janet L. , Petersen N. T. , Butler Jane E. , Gandevia S. C.
Published: July 2002

Transcranial magnetic stimulation activates corticospinal neurones directly and transsynaptically and hence, activates motoneurones and results in a response in the muscle. Transmastoid stimulation results in a similar muscle response through activation of axons in the spinal cord. This study was designed to determine whether the two stimuli activate the same descending axons. Responses to transcranial magnetic stimuli paired with electrical transmastoid stimuli were examined in biceps brachii in human subjects. Twelve interstimulus intervals (ISIs) from −6 ms (magnet before transmastoid) to 5 ms were investigated. When responses to the individual stimuli were set at 10‐15 % of the maximal M‐wave, responses to the paired stimuli were larger than expected at ISIs of −6 and −5 ms but were reduced in size at ISIs of −2 to 1 ms and at 3 to 5 ms. With individual responses of 3‐5 % of maximal M‐wave, facilitation still occurred at ISIs of −6 and −5 ms and depression of the paired response at ISIs of 0, 1, 4 and 5 ms. The interaction of the response to transmastoid stimulation with the multiple descending volleys elicited by magnetic stimulation of the cortex is complex. However, depression of the response to the paired stimuli at short ISIs is consistent with an occlusive interaction in which an antidromic volley evoked by the transmastoid stimulus collides with and annihilates descending action potentials evoked by the transcranial magnetic stimulus. Thus, it is consistent with the two stimuli activating some of the same corticospinal axons.
Reflex regulation during sustained and intermittent submaximal contractions in humans
Authors: Duchateau Jacques , Balestra Costantino , Carpentier Alain , Hainaut Karl
Published: July 2002

To investigate whether the intensity and duration of a sustained contraction influences reflex regulation, we compared sustained fatiguing contractions at 25 % and 50 % of maximal voluntary contraction (MVC) force in the human abductor pollicis brevis (APB) muscle. Because the activation of motoneurones during fatigue may be reflexively controlled by the metabolic status of the muscle, we also compared reflex activities during sustained and intermittent (6 s contraction, 4 s rest) contractions at 25 % MVC for an identical duration. The short‐latency Hoffmann(H) reflex and the long‐latency reflex (LLR) were recorded during voluntary contractions, before, during and after the fatigue tests, with each response normalised to the compound muscle action potential (M‐wave). The results showed that fatigue during sustained contractions was inversely related to the intensity, and hence the duration, of the effort. The MVC force and associated surface electromyogram (EMG) declined by 26.2 % and 35.2 %, respectively, after the sustained contraction at 50 % MVC, and by 34.2 % and 44.2 % after the sustained contraction at 25 % MVC. Although the average EMG increased progressively with time during the two sustained fatiguing contractions, the amplitudes of the H and LLR reflexes decreased significantly. Combined with previous data (Duchateau & Hainaut, 1993), the results show that the effect on the H reflex is independent of the intensity of the sustained contraction, whereas the decline in the LLR is closely related to the duration of the contraction. Because there were no changes in the intermittent test at 25 % MVC, the results indicate that the net excitatory spinal and supraspinal reflex‐mediated input to the motoneurone pool is reduced. This decline in excitation to the motoneurones, however, can be temporarily compensated by an enhancement of the central drive.
Fast‐to‐slow transformation and nuclear import/export kinetics of the transcription factor NFATc1 during electrostimulation of rabbit muscle cells in culture
Authors: Kubis Hans‐Peter , Scheibe Renate J. , Meißner Joachim D. , Hornung Gunther , Gros Gerolf
Published: July 2002

Contractile activity imposed by chronic electrical stimulation of a primary skeletal muscle cell culture grown on microcarriers over several days led to an increase of slow myosin heavy chain I (MHCI) and a decrease of fast MHCII expression at mRNA and protein levels, indicating an ongoing fast‐to‐slow transformation. Only patterns with periods of continuous stimulation of > 5 min in a 45 min cycle were capable of inducing a fibre type transformation, and this was independent of the applied stimulation frequency over the range 1‐10 Hz. We have shown before that the calcineurin‐NFATc1 signalling pathway is indispensable in mediating MHCI upregulation during fibre type transformation. Therefore, subcellular localization of NFATc1 was studied immunocytochemically. This revealed that only one stimulation train lasting for > 5 min was sufficient to induce nuclear import of this factor, which was about complete after 20 min of continuous stimulation. For both induction of NFATc1 import and MHCI mRNA upregulation, the minimum stimulation interval of > 5 min was sufficient and stimulation frequency was not crucial between 1 and 10 Hz. Repetition of stimulation cycles, with pauses (< 40 min) shorter than the time required for complete export of NFATc1, led to an accumulation of NFATc1 in the nuclei with each cycle and thus to an amplification of the transformation signal during extended periods of electrostimulation. The temporal behaviour of NFATc import/export appears to determine the effectiveness of various electrostimulation protocols in inducing fast‐to‐slow fibre transformation.
Rho family GTP binding proteins are involved in the regulatory volume decrease process in NIH3T3 mouse fibroblasts
Authors: Pedersen Stine F. , Beisner Kristine H. , Hougaard Charlotte , Willumsen Berthe M. , Lambert Ian H. , Hoffmann Else K.
Published: July 2002

The role of Rho GTPases in the regulatory volume decrease (RVD) process following osmotic cell swelling is controversial and has so far only been investigated for the swelling‐activated Cl− efflux. We investigated the involvement of RhoA in the RVD process in NIH3T3 mouse fibroblasts, using wild‐type cells and three clones expressing constitutively active RhoA (RhoAV14). RhoAV14 expression resulted in an up to fourfold increase in the rate of RVD, measured by large‐angle light scattering. The increase in RVD rate correlated with RhoAV14 expression. RVD in wild‐type cells was unaffected by the Rho kinase inhibitor Y‐27632 and the phosphatidyl‐inositol 3 kinase (PI3K) inhibitor wortmannin. The maximal rates of swelling‐activated K+ (86Rb+ as tracer) and taurine ([3H]taurine as tracer) efflux after a 30 % reduction in extracellular osmolarity were increased about twofold in cells with maximal RhoAV14 expression compared to wild‐type cells, but were unaffected by Y‐27632. The volume set points for activation of release of both osmolytes appeared to be reduced by RhoAV14 expression. The maximal taurine efflux rate constant was potentiated by the tyrosine phosphatase inhibitor Na3VO4, and inhibited by the tyrosine kinase inhibitor genistein. The magnitude of the swelling‐activated Cl− current (ICl,swell) was higher in RhoAV14 than in wild‐type cells after a 7.5 % reduction in extracellular osmolarity, but, in contrast to 86Rb+ and [3H]taurine efflux, similar in both strains after a 30 % reduction in extracellular osmolarity. ICl,swell was inhibited by Y‐27632 and strongly potentiated by the myosin light chain kinase inhibitors ML‐7 and AV25. It is suggested that RhoA, although not the volume sensor per se, is an important upstream modulator shared by multiple swelling‐activated channels on which RhoA exerts its effects via divergent signalling pathways.
AMPA and NMDA currents show different short‐term depression in the dorsal lateral geniculate nucleus of the rat
Authors: Kielland Anders , Heggelund Paul
Published: July 2002

Paired‐pulse depression was studied at the glutamatergic synapse between retinal afferents and thalamocortical cells in the rat dorsal lateral geniculate nucleus. The main objective of this study was to examine the contributions of the pre‐ and postsynaptic sites to this depression by comparing AMPA‐ and NMDA‐receptor‐mediated responses. Equal depression of the two receptor components would indicate involvement of presynaptic mechanisms, while differences in depression would indicate involvement of postsynaptic mechanisms. Pharmacologically isolated AMPA‐ and NMDA‐receptor‐mediated currents were recorded using the whole‐cell patch‐clamp technique in acute thalamic slices. Both the AMPA and the NMDA components showed pronounced depression when retinal afferents were activated by paired pulses. The depression decayed within 5 s. The AMPA component was more strongly depressed than the NMDA component at paired‐pulse intervals ranging from 20 to 200 ms, suggesting the involvement of postsynaptic mechanisms. For intervals of 500 ms and longer, the depression of the two components was identical, suggesting the involvement of purely presynaptic mechanisms. The degree of depression measured without the use of pharmacological tools produced similar results, thus excluding the involvement of presynaptic ionotropic glutamate receptors. Cyclothiazide, a blocker of AMPA‐receptor desensitisation, reduced the difference in depression between the two components, suggesting that desensitisation of the AMPA receptors is a postsynaptic mechanism that contributes to the difference in depression between the AMPA and the NMDA components.
Bipedal distribution of human vestibular‐evoked postural responses during asymmetrical standing
Authors: Marsden J. F. , Castellote J. , Day B. L.
Published: July 2002

Galvanic vestibular stimulation (GVS) evokes responses in muscles of both legs when bilateral stimuli are applied during normal stance. We have used this technique to assess whether asymmetrical standing alters the distribution of responses in the two legs. Subjects stood either asymmetrically with 75 % of their body weight on one leg or symmetrically with each leg taking 50 % of their body weight. The net response in each leg was taken from changes in ground reaction force measured from separate force plates under each foot. The net force profile consisted of a small initial force change that peaked at ∼200 ms followed by an oppositely directed larger component that peaked at ∼450 ms. We analysed the second force component since it was responsible for the kinematic response of lateral body sway and tilt towards the anode. In the horizontal plane, both legs produced lateral force responses that were in the same direction but larger in the leg ipsilateral to the cathodal ear. There were also vertical force responses that were of equal size in both legs but acted in opposite directions. When subjects stood asymmetrically the directions of the force responses remained the same but their magnitudes changed. The lateral force response became 2‐3 times larger for the more loaded leg and the vertical forces increased 1.5 times on average for both legs. Control experiments showed that these changes could not be explained by either the consistent (< 5 deg) head tilt towards the side of the loaded leg or the changes in background muscle activity associated with the asymmetrical posture. We conclude that the redistribution of force responses in the two legs arises from a load‐sensing mechanism. We suggest there is a central interaction between load‐related afferent input from the periphery and descending motor signals from balance centres.
Cell type dependence and variability in the short‐term plasticity of EPSCs in identified mouse hippocampal interneurones
Authors: Losonczy Attila , Zhang Limei , Shigemoto Ryuichi , Somogyi Peter , Nusser Zoltan
Published: July 2002

Synapses exhibit different short‐term plasticity patterns and this behaviour influences information processing in neuronal networks. We tested how the short‐term plasticity of excitatory postsynaptic currents (EPSCs) depends on the postsynaptic cell type, identified by axonal arborizations and molecular markers in the hippocampal CA1 area. Three distinct types of short‐term synaptic behaviour (facilitating, depressing and combined facilitating‐depressing) were defined by fitting a dynamic neurotransmission model to the data. Approximately 75 % of the oriens‐lacunosum‐moleculare (O‐LM) interneurones received facilitating EPSCs, but in three of 12 O‐LM cells EPSCs also showed significant depression. Over 90 % of the O‐LM cells were immunopositive for somatostatin and mGluR1α and all tested cells were decorated by strongly mGluR7a positive axon terminals. Responses in eight of 12 basket cells were described well with a model involving only depression, but the other cells displayed combined facilitating‐depressing EPSCs. No apparent difference was found between the plasticity of EPSCs in cholecystokinin‐ or parvalbumin‐containing basket cells. In oriens‐bistratified cells (O‐Bi), two of nine cells showed facilitating EPSCs, another two depressing, and the remaining five cells combined facilitating‐depressing EPSCs. Seven of 10 cells tested for somatostatin were immunopositive, but mGluR1α was detectable only in two of 11 tested cells. Furthermore, most O‐Bi cells projected to the CA3 area and the subiculum, as well as outside the hippocampal formation. Postsynaptic responses to action potentials recorded in vivo from a CA1 place cell were modelled, and revealed great differences between and within cell types. Our results demonstrate that the short‐term plasticity of EPSCs is cell type dependent, but with significant heterogeneity within all three interneurone populations.
Functional characteristics of non‐NMDA‐type ionotropic glutamate receptor channels in AII amacrine cells in rat retina
Authors: Mørkve Svein Harald , Veruki Margaret Lin , Hartveit Espen
Published: July 2002

The properties of non‐NMDA glutamate receptor channels in AII amacrine cells were studied by patch‐clamp recording from rat retinal slices. Application of AMPA or kainate to intact cells evoked currents with no apparent desensitization (EC50 of 118 μM for AMPA and 169 μM for kainate). Application of AMPA to patches evoked desensitizing responses with an EC50 of 217 and 88 μM for the peak and steady‐state responses, respectively. Kainate‐evoked responses of patches displayed no desensitization (EC50= 162 μM). Cyclothiazide strongly potentiated AMPA‐evoked responses and the AMPA‐receptor antagonist GYKI 53655 inhibited both AMPA‐ and kainate‐evoked responses (IC50= 0.5–1.7 μM). Pre‐equilibration with GYKI 53655 completely blocked the response to kainate and pretreatment with concanavalin A did not unmask a response mediated by kainate receptors. AMPA‐ and kainate‐evoked currents reversed close to 0 mV. AMPA‐evoked peak and steady‐state response components in patches displayed linear and outwardly rectifying I–V relations with an RI (ratio of the slope conductances at +40 mV and ‐60 mV) of 0.96 ± 0.11 and 5.6 ± 1.3, respectively. AMPA‐evoked currents displayed a voltage‐dependent relaxation after steps to positive or negative membrane potentials, indicating that the outward rectification of the steady‐state response is caused by a voltage‐dependent kinetic parameter of channel gating. Under bi‐ionic conditions ([Ca2+]out= 30 mm, [Cs+]in= 171 mm), the reversal potentials of AMPA‐ and kainate‐evoked currents indicated channels with significant Ca2+ permeability (PCa/PCs= 1.9–2.1). Stationary noise analysis indicated that kainate activated channels with an apparent chord conductance of ∼9 pS. Non‐stationary noise analysis indicated that AMPA and glutamate activated channels with apparent chord conductances of ∼9, ∼15, ∼23 and ∼38 pS. Discrete single‐channel gating corresponding to chord conductances of ∼23 pS could be directly observed in some responses. Thus, our results indicate expression of high‐affinity, voltage‐sensitive AMPA receptors with significant Ca2+ permeability and relatively large single‐channel chord conductances in AII amacrine cells.
Excess recovery heat production by isolated muscles from mice overexpressing uncoupling protein‐3
Authors: Curtin N. A. , Clapham J. C. , Barclay C. J.
Published: July 2002

Contractile and energetic performance of bundles of muscle fibres from the soleus of mice overexpressing uncoupling protein 3 (UCP‐3tg) were compared with the performance of bundles from wild‐type mice. Force and heat production were measured during a series of thirty 0.2 s isometric tetani at Lo, the length optimal for force. UCP‐3tg fibres were as strong as the wild‐type and maintained force in the series equally well; in the first tetanus force was 116.9 ± 15.1 and 133.3 ± 19.7 mN mm−2 respectively (all values means ±s.e.m., n= 6 for UCP‐3tg and n= 5 for wild‐type). Heat production was partitioned into initial heat (due to contractile ATPases and the creatine kinase reaction) and recovery heat (due to other ATP‐supplying processes) and expressed relative to the first cycle total heat. Initial heat production was similar for the UCP‐3tg and wild‐type fibres, decreasing during the series from 0.799 ± 0.052 to 0.661 ± 0.061 relative units (UCP‐3tg), and from 0.806 ± 0.024 to 0.729 ± 0.039 relative units (wild‐type). In both types the recovery heat was small at the start of the series and increased as the series progressed. At the end of the series, recovery heat production by UCP‐3tg fibres, 1.575 ± 0.246 relative units, was twice that of the wild‐type fibres, 0.729 ± 0.072 relative units. The extra recovery heat represents inefficient recovery in UCP‐3tg fibres. This is the first direct evidence of enhanced energy dissipation as heat when UCP‐3tg is overexpressed.
Analysis Strategies for Tubular Solid Oxide Fuel Cell Based Hybrid Systems
Authors: Rao A. D. , Samuelsen G. S.
Published: July 2002

The emergence of fuel cell systems and hybrid fuel cell systems requires the evolution of analysis strategies for evaluating thermodynamic performance and directing design and development. A description and application of the recently developed tool for analyzing tubular SOFC based systems is presented. The capabilities of this tool include an analytical model for the tubular SOFC derived from first principles and the secondary equipment required to analyze hybrid power plants. Examples of such secondary equipment are gas turbine, reformer, partial oxidation reactor, shift reactor, humidifier, steam turbines, compressor, gas expander, heat exchanger, and pump. A “controller” is included which is essential for modeling systems to automatically iterate in order to meet the desired process or system design criteria. Another important capability that is included is to be able to arrange the various components or modules as defined by the user in order to configure different hybrid systems. Analysis of the hybrid cycle as originally proposed by Westinghouse (SureCell TM) indicates that the thermal efficiency of the cycle is quite insensitive to the pressure ratio, increasing from 65.5 percent to 66.6 percent on a lower calorific value of the fuel as the pressure ratio decreases from 15 to 6.5.
A Solution Strategy Based on Segmented Domain Decomposition Multigrid for Turbomachinery Flows
Authors: Celestina M. L. , Adamczyk J. J. , Rubin S. G.
Published: July 2002

A Segmented Domain Decomposition Multigrid (SDDMG) procedure was developed for viscous flow problems as they apply to turbomachinery flows. The procedure divides the computational domain into a coarse mesh comprised of uniformly spaced cells. To resolve smaller length scales such as the viscous layer near a surface, segments of the coarse mesh are subdivided into a finer mesh. This is repeated until adequate resolution of the smallest relevant length scale is obtained. Multigrid is used to communicate information between the different grid levels [1]. To test the procedure, simulation results will be presented for a compressor and turbine cascade. These simulations are intended to show the ability of the present method to generate grid independent solutions. Comparisons with data will also be presented. These comparisons will further demonstrate the usefulness of the present work for they allow an estimate of the accuracy of the flow modeling equations independent of error attributed to numerical discretization.
Summary of CGT302 Ceramic Gas Turbine Research and Development Program
Authors: Takehara I. , Tatsumi T. , Ichikawa Y.
Published: July 2002

The Japanese ceramic gas turbine (CGT) research and development program (FY1988-1998) as a part of the New Sunshine Project funded by the Ministry of International Trade and Industry (MITI) was completed in March 1999. Kawasaki Heavy Industries, Ltd. (KHI) participated in this research program from the beginning and developed a twin-shaft CGT with a recuperator, designated as the “CGT302.” The purposes of this program were (1) to achieve both a high efficiency and low pollutant emissions level using ceramic components, (2) to prove a multifuel capability to be used in cogeneration systems, and (3) to demonstrate long-term operation. The targets of this program were (i) to achieve a thermal efficiency of over 42 percent at a turbine inlet temperature (TIT) of 1350°C, (ii) to keep its emissions within the regulated value by the law, and (iii) to demonstrate continuous operation for more than a thousand hours at 1200°C TIT. The CGT302 has successfully attained its targets. In March 1999 the CGT302 recorded 42.1 percent thermal efficiency, and 31.7 ppm NOx emissions (O2=16 percent) at 1350°C TIT. At this time it had also accumulated over 2000 hours operation at 1200°C. In this paper, we summarize the development of the CGT302.
Development of the Tracer Gas Method for Large Bore Natural Gas Engines—Part II: Measurement of Scavenging Parameters
Authors: Olsen D. B. , Hutcherson G. C. , Willson B. D. , Mitchell C. E.
Published: July 2002

In this work the tracer gas method using nitrous oxide as the tracer gas is implemented on a stationary two-stroke cycle, four-cylinder, fuel-injected large-bore natural gas engine. The engine is manufactured by Cooper-Bessemer, model number GMV-4TF. It is representative of the large bore natural gas stationary engine fleet currently in use by the natural gas industry for natural gas compression and power generation. Trapping efficiency measurements are carried out with the tracer gas method at various engine operating conditions, and used to evaluate the scavenging efficiency and trapped A/F ratio. Scavenging efficiency directly affects engine power and trapped A/F ratio has a dramatic impact on pollutant emissions. Engine operating conditions are altered through variations in boost pressure, speed, back pressure, and intake port restriction.
The Mechanisms of Chip Formation in Machining Hardened Steels
Authors: Barry John , Byrne Gerald
Published: July 2002

The formation of saw-tooth chips is one of the primary characteristics in the machining of hardened steels with geometrically defined cutting tools. Catastrophic failure within the primary shear zone during saw-tooth chip formation is usually attributed to either cyclic crack initiation and propagation or to the occurrence of a thermo-plastic instability. The results presented here show that the primary instability resulting in the formation of saw-tooth chips is initiation of adiabatic shear at the tool tip and propagation partway towards the free surface. Depending on the work material hardness and cutting conditions, catastrophic failure within the upper region of the primary shear zone occurs through either ductile fracture or large strain plastic deformation. Prior to the onset of chip segmentation, which occurs with increases in work material hardness and cutting speed, there is a transition in the morphology of the free surface of continuous chips, from the familiar lamellar structure to what has been termed a “fold-type” structure. This transition is attributed to the operation of thermally softened micro-shear zones, which, it is suggested, are a precursor to adiabatic shear initiation.
A Model for Multicomponent Spray Vaporization in a High-Pressure and High-Temperature Environment
Authors: Zeng Y. , Lee C. F.
Published: July 2002

A multicomponent droplet vaporization model including both gas and liquid phase transport processes was developed for multidimensional spray computations. This paper focuses on two effects altering vaporization in a high-pressure and high-temperature environment. One effect is on droplet surface regression caused by a higher vaporization rate. This effect is well characterized by the Lewis number and the Peclet number with the regression velocity. Formulas based on the two numbers were included to improve model accuracy. The other effect is on the nonideal behavior and was covered in the model by using the Peng-Robinson equation of state to determine phase equilibrium at the droplet surface. The model was validated by the results from an accurate simplified vortex model and experimental measurements, and excellent agreements were demonstrated. Further comparisons against the model without the two effects and an infinite diffusion model show that significant improvement was achieved by the model for single-droplet and spray computations.
Short and Long Length-Scale Disturbances Leading to Rotating Stall in an Axial Compressor Stage With Different Stator/Rotor Gaps
Authors: Inoue M. , Kuroumaru M. , Yoshida S. , Furukawa M.
Published: July 2002

The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at eight circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They become the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with “high-frequency stall inception.” For the small stator-rotor gap, the stalling process is identified with “long wavelength stall inception” and supported the recent computational model for the short wavelength stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been developed that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.
Comparison of the Two Formulations of w-u-v and w-F in Nonlinear Plate Analysis
Authors: Lee J.
Published: July 2002

In a moderately large deflection plate theory of von Karman and Chu-Herrmann, one may consider thin-plate equations of either the transverse and in-plane displacements, w-u-v formulation, or the transverse displacement and Airy function, w-F formulation. Under the Galerkin procedure, we examine if the modal equations of two plate formulations preserve the Hamiltonian property which demands energy conservation in the conservative limit of no damping and forcing. In the w-F formulation, we have shown that modal equations are Hamiltonian for the first four symmetric modes of a simply-supported plate. In contrast, the corresponding modal equations of w-u-v formulation do not exhibit the Hamiltonian property when a finite number of sine terms are included in the in-plane displacement expansions.
Investigation of Unsteady Aerodynamic Blade Excitation Mechanisms in a Transonic Turbine Stage—Part I: Phenomenological Identification and Classification
Authors: Laumert Bjo¨rn , Ma˚rtensson Hans , Fransson Torsten H.
Published: July 2002

Based on the results of time-dependent 3-D viscous computations the aerodynamic mechanisms that cause the unsteady pressure fluctuations on the vane and rotor blade surface of a high-pressure transonic turbine are identified and separately classified in a phenomenological manner. In order to be able to describe separately the influence of wake, potential and shock distortions on the blade surface pressure at design operation conditions, the stator exit Mach number is increased as to enhance the shock distortions and lowered as to enhance potential and wake distortions. In a comprehensive approach the observations from the off-design conditions are utilized to classify every major perturbation observed in the perturbation space-time maps at design operation conditions. The spanwise variations caused by the inherent 3-D nature of the flow field and promoted by the 3-D shape of the rotor blade are addressed.
A Converging Slot-Hole Film-Cooling Geometry—Part 1: Low-Speed Flat-Plate Heat Transfer and Loss
Authors: Sargison J. E. , Guo S. M. , Oldfield M. L. G. , Lock G. D. , Rawlinson A. J.
Published: July 2002

This paper presents experimental measurements of the performance of a new film-cooling hole geometry—the con¯vergings¯lot-hole¯ or console. This novel, patented geometry has been designed to improve the heat transfer and aerodynamic loss performance of turbine vane and rotor blade cooling systems. The physical principles embodied in the new hole design are described, and a typical example of the console geometry is presented. The cooling performance of a single row of consoles was compared experimentally with that of typical 35-deg cylindrical and fan-shaped holes and a slot, on a large-scale, flat-plate model at engine representative Reynolds numbers in a low-speed tunnel with ambient temperature main flow. The hole throat area per unit width is matched for all four hole geometries. By independently varying the temperature of the heated coolant and the heat flux from an electrically heated, thermally insulated, constant heat flux surface, both the heat transfer coefficient and the adiabatic cooling effectiveness were deduced from digital photographs of the color play of narrow-band thermochromic liquid crystals on the model surface. A comparative measurement of the aerodynamic losses associated with each of the four film-cooling geometries was made by traversing the boundary layer at the downstream end of the flat plate. The promising heat transfer and aerodynamic performance of the console geometry have justified further experiments on an engine representative nozzle guide vane in a transonic annular cascade presented in Part 2 of this paper.
3-D Transonic Flow in a Compressor Cascade With Shock-Induced Corner Stall
Authors: Weber Anton , Schreiber Heinz-Adolf , Fuchs Reinhold , Steinert Wolfgang
Published: July 2002

An experimental and numerical study of the transonic flow through a linear compressor cascade with endwalls was conducted. The cascade with a low aspect ratio of 1.34 was tested at an inlet Mach number of 1.09 and a Reynolds number of 1.9×106. Detailed flow visualizations on the surfaces and five-hole probe measurements inside the blading and in the wake region showed clearly a three-dimensional boundary layer separation on the blade surface and the sidewall, and a severe corner stall induced by a strong 3-D shock system at blade passage entrance. The experimental data have been used to validate and improve the 3-D Navier-Stokes code TRACE. Results showed an excellent resolution of the complex flow field. Surface pressure distributions on the entire blade surface and the endwalls, flow angle and total pressure contours within the blade passage and the wake are compared with the experimental results. An analysis of the secondary flow of this highly staggered cascade did not show the classical corner vortex. Instead, a severe flow deviation and partly reverse flow near the walls is seen. The flow solver helped to identify a weak ring vortex that originates from the passage sidewall. Surface oil flow pictures on the blade contour and the sidewall are in qualitatively good agreement to numerical surface streaklines. A considerable improvement of the numerical results could be achieved by a gradual grid refinement, especially in the corner region and by successive code development.
An Experimental and Numerical Investigation into the Mechanisms of Rotating Instability
Authors: Ma¨rz Joachim , Hah Chunill , Neise Wolfgang
Published: July 2002

This paper reports on an experimental and numerical investigation aimed at understanding the mechanisms of rotating instabilities in a low speed axial flow compressor. The phenomena of rotating instabilities in the current compressor were first identified with an experimental study. Then, an unsteady numerical method was applied to confirm the phenomena and to interrogate the physical mechanisms behind them. The experimental study was conducted with high-resolution pressure measurements at different clearances, employing a double phase-averaging technique. The numerical investigation was performed with an unsteady 3-D Navier-Stokes method that solves for the entire blade row. The current study reveals that a vortex structure forms near the leading edge plane. This vortex is the result of interactions among the classical tip-clearance flow, axially reversed endwall flow, and the incoming flow. The vortex travels from the suction side to the pressure side of the passage at roughly half of the rotor speed. The formation and movement of this vortex seem to be the main causes of unsteadiness when rotating instability develops. Due to the nature of this vortex, the classical tip clearance flow does not spill over into the following blade passage. This behavior of the tip clearance flow is why the compressor operates in a stable mode even with the rotating instability, unlike traditional rotating stall phenomena.
Prediction and Compensation of Dynamic Errors for Coordinate Measuring Machines
Authors: Dong Chensong , Zhang Chuck , Wang Ben , Zhang Guoxiong
Published: July 2002

Coordinate measuring machines (CMMs) are already widely utilized as measuring tools in the modern manufacturing industry. Rapidly approaching now is the trend for next-generation CMMs. However, the increases in measuring velocity of CMM applications are limited by dynamic errors that occur in CMMs. In this paper, a systematic approach for modeling the dynamic errors of a touch-trigger probe CMM is developed through theoretical analysis and experimental study. An overall analysis of the dynamic errors of CMMs is conducted, with weak components of the CMM identified with a laser interferometer. The probing process, as conducted with a touch-trigger probe, is analyzed. The dynamic errors are measured, modeled, and predicted using neural networks. The results indicate that, using this mode, it is possible to compensate for the dynamic errors of CMMs.