bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the sodium recirculation theory of solute‐coupled water transport in small intestine
Authors: Larsen Erik Hviid , Sørensen Jakob Balslev , Sørensen Jens Nørkær
Published: July 2002

Our previous mathematical model of solute‐coupled water transport through the intestinal epithelium is extended for dealing with electrolytes rather than electroneutral solutes. A 3Na+–2K+ pump in the lateral membranes provides the energy‐requiring step for driving transjunctional and translateral flows of water across the epithelium with recirculation of the diffusible ions maintained by a 1Na+‐1K+–2Cl− cotransporter in the plasma membrane facing the serosal compartment. With intracellular non‐diffusible anions and compliant plasma membranes, the model describes the dependence on membrane permeabilities and pump constants of fluxes of water and electrolytes, volumes and ion concentrations of cell and lateral intercellular space (lis), and membrane potentials and conductances. Simulating physiological bioelectrical features together with cellular and paracellular fluxes of the sodium ion, computations predict that the concentration differences between lis and bathing solutions are small for all three ions. Nevertheless, the diffusion fluxes of the ions out of lis significantly exceed their mass transports. It is concluded that isotonic transport requires recirculation of all three ions. The computed sodium recirculation flux that is required for isotonic transport corresponds to that estimated in experiments on toad small intestine. This result is shown to be robust and independent of whether the apical entrance mechanism for the sodium ion is a channel, a SGLT1 transporter driving inward uphill water flux, or an electroneutral Na+–K+–2Cl− cotransporter.
Physiological basis of fractal complexity properties of heart rate variability in man
Authors: Francis Darrel P. , Willson Keith , Georgiadou Panagiota , Wensel Roland , Davies L. Ceri , Coats Andrew , Piepoli Massimo
Published: July 2002

The diagnostic and prognostic power of the fractal complexity measure ‘α’ of detrended fluctuation analysis (DFA) has remained mysterious because there has been no explanation of its meaning, particularly in relation to spectral analysis. First, we present a mathematical analysis of the meaning of α, in weighted power‐spectral terms. Second, we test this hypothesis and observe correlations between DFA‐based and weighted spectral methods of 0.97 (P < 0.0001) for α1 and 0.98 (P < 0.0001) for α2. Third, we predict mathematically that even in conventional (unweighted) spectral analysis there should be approximate counterparts to DFA, namely that α1 and α2 behave broadly in proportion to the conventional (unweighted) ratios LF/(HF + LF) and VLF/(LF + VLF), respectively, where HF is high frequency, LF is low frequency and VLF is very low frequency. Fourth, we test this hypothesis by physiologically manipulating spectral ratios in healthy volunteers in two ways. The effect of 0.1 Hz controlled breathing on LF/(HF + LF) correlates markedly with the effect on α1 (r= 0.73, P= 0.01); the effect on VLF/(LF + VLF) correlates markedly with that on α2 (r= 0.76, P < 0.01). Likewise, with voluntary periodic breathing the reduction in α2 correlates strongly with that in VLF/(LF + VLF) (r= 0.88, P < 0.001); effects on α1 and LF/(HF + LF) again clearly correlate (r= 0.73, P= 0.01). Finally, we examine published literature to identify previously undiscussed evidence of the relationship between α1 and LF/(HF + LF). We conclude that the α1 and α2 indices are simply frequency‐weighted versions of the spectral ratios LF/(HF + LF) and VLF/(LF + VLF), respectively, multiplied by two (giving a range of 0‐2). We can now understand fractal manifestations of physiological abnormalities: depressed baroreflex sensitivity → low LF/HF → low LF/(HF + LF) → low α1, while periodic breathing → high VLF/LF → high VLF/(LF + VLF) → high α2. Prognostic associations of α are no longer mysterious.
Different regional effects of voluntary exercise on the mechanical and electrical properties of rat ventricular myocytes
Authors: Natali A. J. , Wilson L.A. , Peckham M. , Turner D. L. , Harrison S. M. , White E.
Published: July 2002

Short‐term (6 weeks) voluntary wheel running exercise in young female rats that were in an active growth phase resulted in whole‐heart hypertrophy and myocyte concentric hypertrophy, when compared to sedentary controls. The cross‐sectional area of ventricular myocytes from trained rats was significantly greater than for those isolated from sedentary rats, with the greatest change in morphology seen in sub‐endocardial cells. There was no statistically significant effect of training on cell shortening in the absence of external mechanical loading, in [Ca2+]i transients, or in myofilament Ca2+ sensitivity (assessed during re‐lengthening following tetanic stimulation). Under the external mechanical load of carbon fibres, absolute force developed in myocytes from trained rats was significantly greater than in those from sedentary rats. This suggests that increased myocyte cross‐sectional area is a major contractile adaptation to exercise in this model. Training did not alter the passive mechanical properties of myocytes or the relative distribution of titin isomers, which was exclusively of the short, N2B form. However, training did increase the steepness of the active tension‐sarcomere length relationship, suggesting an exercise‐induced modulation of the Frank‐Starling mechanism. This effect would be expected to enhance cardiac contractility. Training lengthened the action potential duration of sub‐epicardial myocytes, reducing the transmural gradient in action potential duration. This observation may be important in understanding the cellular causes of T‐wave abnormalities found in the electrocardiograms of some athletes. Our study shows that voluntary exercise modulates the morphological, mechanical and electrical properties of cardiac myocytes, and that this modulation is dependent upon the regional origin of the myocytes.
Autonomic function in mice lacking α5 neuronal nicotinic acetylcholine receptor subunit
Authors: Wang Ningshan , Orr‐Urtreger Avi , Chapman Joab , Rabinowitz Ruth , Nachman Rachel , Korczyn Amos D.
Published: July 2002

Neuronal acetylcholine nicotinic receptors (nAChR) are composed of 12 subunits (α2‐10, β2‐4), of which α3, α5, α7, β2 and β4 subunits are known to exist in the autonomic nervous system (ANS). α5 subunits possess unique biophysical and pharmacological properties. The present study was undertaken to examine the functional role and pharmacological properties of the nAChR α5 subunits in the ANS using mice lacking α5 nAChR subunits (α5‐/‐). These mice grew to normal size showing no obvious physical or neurological deficit. They also showed normality in thermoregulation, pupil size and resting heart rate under physiological conditions. The heart rate and rectal temperature did not differ between α5‐/‐ and wild‐type mice during exposure to cold stress. An impairment of cardiac parasympathetic ganglionic transmission was observed during high frequency vagal stimulation, which caused cardiac arrest in all wild‐type animals while α5‐/‐ mice were more resistant. Deficiency of α5 subunits strikingly increased the sensitivity to a low concentration of hexamethonium, leading to a nearly complete blockade of bradycardia in response to vagal stimulation. Such a concentration of hexamethonium only slightly depressed the effects of vagal stimulation in control mice. Deficiency of α5 subunits significantly increased ileal contractile responses to cytisine and epibatidine. These results suggest that α5 subunits may affect the affinity and sensitivity of agonists and antagonists in the native receptors. Previous studies revealed that α5 subunits form functional receptors only in combination with other α and β subunits. Thus, the data presented here imply that α5 subunits modulate the activity of nAChR in autonomic ganglia in vivo.
Reciprocal intraglomerular excitation and intra‐ and interglomerular lateral inhibition between mouse olfactory bulb mitral cells
Authors: Urban Nathaniel N. , Sakmann Bert
Published: July 2002

How patterns of odour‐evoked glomerular activity are transformed into patterns of mitral cell action potentials (APs) in the olfactory bulb is determined by the functional connectivity of the cell populations in the bulb. We have used paired whole‐cell voltage recordings from olfactory bulb slices to compare the functional connectivity of mitral cells to the known anatomy of the mitral cell network. Both inhibitory and excitatory coupling were observed between pairs of mitral cells. Inhibitory coupling was seen as an increased frequency of small, asynchronous GABAergic IPSPs following APs in the presynaptic cell. Excitatory coupling was short in latency, beginning about 1.3 ms after the presynaptic AP and was mediated by both NMDA and AMPA receptors. Mitral cell pairs were coupled by excitation if and only if their apical dendrites terminated in the same glomerulus. The excitatory coupling between mitral cells resembles conventional fast synaptic transmission in its time course, amplitude and latency, despite the absence of evidence for anatomically defined synapses between mitral cells.
On organization of a neuronal network in pathways from group II muscle afferents in feline lumbar spinal segments
Authors: Jankowska E. , Slawinska U. , Hammar I.
Published: July 2002

The aim of the study was to verify the hypothesis that trisynaptic actions of group II muscle afferents upon motoneurones are, at least in part, mediated by dorsal horn interneurones exciting the same intermediate zone interneurones that are interposed in disynaptic pathways from group II afferents. Population EPSPs (field potentials) and responses of individual interneurones evoked by group II afferents in the dorsal horn and in the intermediate zone were analysed in order to assess the possibility of a causal relationship between them. When direct actions of group II afferents in the intermediate zone were abolished by presynaptic inhibition, distinct later components of field potentials and delayed interneuronal responses were induced at latencies 0.5‐1 ms longer than those seen originally. Both the latency and a marked temporal facilitation define these later group II actions as being evoked disynaptically. Under the same conditions, single stimuli activated more than one half of dorsal horn interneurones, and the second and third stimuli activated all of these interneurones. Responses of dorsal horn interneurones preceded disynaptically evoked responses of intermediate zone interneurones. The study indicates that intermediate zone interneurones may be activated by group II afferents both directly and via dorsal horn interneurones and that synaptic actions of group II afferents upon these interneurones, and their subsequent actions upon motoneurones, may be modulated in parallel at the level of intermediate zone and dorsal horn interneurones.
Rhythm generation in monkey motor cortex explored using pyramidal tract stimulation
Authors: Jackson A. , Spinks R. L. , Freeman T. C. B. , Wolpert D. M. , Lemon R. N.
Published: July 2002

We investigated whether stimulation of the pyramidal tract (PT) could reset the phase of 15‐30 Hz beta oscillations observed in the macaque motor cortex. We recorded local field potentials (LFPs) and multiple single‐unit activity from two conscious macaque monkeys performing a precision grip task. EMG activity was also recorded from the second animal. Single PT stimuli were delivered during the hold period of the task, when oscillations in the LFP were most prominent. Stimulus‐triggered averaging of the LFP showed a phase‐locked oscillatory response to PT stimulation. Frequency domain analysis revealed two components within the response: a 15‐30 Hz component, which represented resetting of on‐going beta rhythms, and a lower frequency 10 Hz response. Only the higher frequency could be observed in the EMG activity, at stronger stimulus intensities than were required for resetting the cortical rhythm. Stimulation of the PT during movement elicited a greatly reduced oscillatory response. Analysis of single‐unit discharge confirmed that PT stimulation was capable of resetting periodic activity in motor cortex. The firing patterns of pyramidal tract neurones (PTNs) and unidentified neurones exhibited successive cycles of suppression and facilitation, time locked to the stimulus. We conclude that PTN activity directly influences the generation of the 15‐30 Hz rhythm. These PTNs facilitate EMG activity in upper limb muscles, contributing to corticomuscular coherence at this same frequency. Since the earliest oscillatory effect observed following stimulation was a suppression of firing, we speculate that inhibitory feedback may be the key mechanism generating such oscillations in the motor cortex.
Control of growth hormone receptor and insulin‐like growth factor‐I expression by cortisol in ovine fetal skeletal muscle
Authors: Li J. , Forhead A. J. , Dauncey M. J. , Gilmour R. S. , Fowden A. L.
Published: July 2002

Insulin‐like growth factor (IGF)‐I has an important role in myogenesis but its developmental regulation in skeletal muscle before birth remains unknown. In other tissues, cortisol modulates IGF gene expression and is responsible for many of the prepartum maturational changes essential for neonatal survival. Hence, using RNase protection assays and ovine riboprobes, expression of the IGF‐I and growth hormone receptor (GHR) genes was examined in ovine skeletal muscle during late gestation and after experimental manipulation of fetal plasma cortisol levels by fetal adrenalectomy and exogenous cortisol infusion. Muscle IGF‐I, but not GHR, mRNA abundance decreased with increasing gestational age in parallel with the prepartum rise in plasma cortisol. Abolition of this cortisol surge by fetal adrenalectomy prevented the prepartum fall in muscle IGF‐I mRNA abundance. Conversely, raising cortisol levels by exogenous infusion earlier in gestation prematurely lowered muscle IGF‐I mRNA abundance but had no effect on GHR mRNA. When all data were combined, plasma cortisol and muscle IGF‐I mRNA abundance were inversely correlated in individual fetuses. Cortisol is, therefore, a developmental regulator of IGF‐I gene expression and is responsible for suppressing expression of this gene in ovine skeletal muscle near term. These observations have important implications for muscle development both before and after birth, particularly during conditions which alter intrauterine cortisol exposure.
Photolysis of caged cyclic AMP in the ciliary cytoplasm of the newt olfactory receptor cell
Authors: Takeuchi Hiroko , Kurahashi Takashi
Published: July 2002

The effects of cyclic nucleotide monophosphate (cNMP) in the ciliary cytoplasm of the olfactory receptor cell were examined by using photolysis of caged cNMP loaded from the whole‐cell patch clamp pipette. Illumination of the cilia induced an inward current at −50 mV. The current amplitude was voltage dependent and the polarity was reversed at +10 mV. The amplitude of the light‐induced current was dependent on both light intensity and duration. The intensity‐response relation was fitted well by the Hill equation with a coefficient (nH) of 4.99 ± 2.66 (mean ±s.d., n= 19) and the duration‐response relation with a coefficient of 4.03 ± 1.43 (n= 17). The activation time course of adenylyl cyclase was estimated by comparing the light‐induced response with the odorant‐induced response. Adenylyl cyclase was activated approximately 260 ms later from the onset of the odorant‐stimulation. The light‐induced current developed very sharply. This could be explained by the sequential openings of cAMP‐gated and Ca2+‐activated Cl− channels. At +100 mV, where Ca2+ influx is expected to be very small, the current rising phase became less steep. When the cells were stimulated by long steps of either odour or light, the odorant‐induced current showed stronger decay than the light‐induced response. This observation suggests that the molecular system regulating desensitization is situated upstream of cAMP production.
Myosin light chain 2 modulates MgADP‐induced contraction in rabbit skeletal and bovine cardiac skinned muscle
Authors: Fujita Hideaki , Sasaki Daisuke , Fukuda Kenji , Ishiwata Shin'ichi
Published: July 2002

Skinned skeletal and cardiac muscle fibres can be activated by MgADP in the presence of MgATP without Ca2+; the isometric tension is developed in a sigmoidal manner with the addition of MgADP under relaxing conditions. The critical concentrations of MgADP for this MgADP‐induced contraction are about 7.5 and 2.6 mm for skeletal and cardiac muscle fibres, respectively. To investigate whether muscle regulatory proteins, myosin light chain 2 (LC2) and troponin C (TnC), play a part in the MgADP‐induced contraction, these proteins were partly extracted by treatment with trans‐1,2‐cyclohexanediamine‐N,N,N',N'‐tetraacetic acid (CDTA), a chelater of divalent cations, and the MgADP‐tension relationship was examined in rabbit psoas and bovine cardiac skinned fibres. We found that the sigmoidal MgADP‐tension relationship became hyperbolic after a partial extraction of LC2 (about 30 %) and TnC (about 70 %). Reconstitution with LC2 restored the sigmoidal MgADP‐tension relationship of control fibres almost fully in both skeletal and cardiac fibres, whereas reconstitution with TnC alone had no effect. Furthermore, cardiac fibres reconstituted with skeletal LC2 exhibited an MgADP‐tension relationship intermediate between skeletal and cardiac fibres. The partial extraction of LC2 and TnC resulted in a reduction of the inhibitory effect of inorganic phosphate (Pi) on the MgADP‐activated tension. Reconstitution with LC2 restored the original Pi‐tension relationship, whereas reconstitution with TnC had no effect. In other words, extraction of LC2 apparently increased the affinity of myosin for MgADP but decreased the affinity for Pi. These results demonstrate that LC2 modulates MgADP‐induced activation of actomyosin interaction.
Cholinergic modulation of the basal L‐type calcium current in ferret right ventricular myocytes
Authors: Bett Glenna C. L. , Dai Shuiping , Campbell Donald L.
Published: July 2002

The effects of the cholinergic muscarinic agonist carbachol (CCh) on the basal L‐type calcium current, ICa,L, in ferret right ventricular (RV) myocytes were studied using whole cell patch clamp. CCh produced two major effects: (i) in all myocytes, extracellular application of CCh inhibited ICa,L in a reversible concentration‐dependent manner; and (ii) in many (but not all) myocytes, upon washout CCh produced a significant transient stimulation of ICa,L (‘rebound stimulation’). Inhibitory effects could be observed at 1 × 10−10m CCh. The mean steady‐state inhibitory concentration‐response relationship was shallow and could be described with a single Hill equation (maximum inhibition = 34.5 %, IC50= 4 × 10−8m, Hill coefficient n= 0.60). Steady‐state inhibition (1 or 10 μM CCh) had no significant effect on ICa,L selectivity or macroscopic (i) activation characteristics, (ii) inactivation kinetics, (iii) steady‐state inactivation or (iv) kinetics of recovery from inactivation. Maximal inhibition of nitric oxide synthase (NOS) activity (preincubation of myocytes in 1 mm l‐NMMA (NG‐monomethyl‐l‐arginine) + 1 mm l‐NNA (NG‐nitro‐l‐arginine) for 2–3 h plus inclusion of 1 mm l‐NMMA + 1 mm l‐NNA in the patch pipette solution) produced no significant attenuation of the CCh‐mediated inhibition of ICa,L. Protocols involving (i) the nitric oxide (NO) scavenger PTIO (2‐phenyl‐4,4,5,5,‐tetramethylimidazoline‐1‐oxyl‐3‐oxide; 200 μM), (ii) imposition of a ‘cGMP clamp’ (100 μM 8‐Bromo‐cGMP), and (iii) inhibition of soluble guanylyl cyclase (ODQ (1H‐[1,2,4,]oxadiazolo(4,3,‐a)quinoxalin‐1‐one), 50 μM) all failed to attenuate CCh‐mediated inhibition of Ica,L. While CCh consistently inhibited basal ICa,L in all RV myocytes studied, not all myocytes displayed rebound stimulation upon CCh washout. However, there was no difference between CCh‐mediated inhibition of ICa,L between these two RV myocyte types, and in myocytes displaying rebound stimulation neither ODQ nor 8‐Bromo‐cGMP (8‐Br‐cGMP) altered the effect. We conclude that NO production, activation of soluble guanylyl cyclase, or changes in intracellular cGMP levels are not obligatorily involved in muscarinic‐mediated modulation of basal ICa,L in ferret RV myocytes.
Myocardial and skeletal muscle glucose uptake during exercise in humans
Authors: Kemppainen Jukka , Fujimoto Toshihiko , Kalliokoski Kari K. , Viljanen Tapio , Nuutila Pirjo , Knuuti Juhani
Published: July 2002

The purpose of this study was to investigate the effects of exercise on myocardial glucose uptake and whether the pattern of glucose uptake is the same as in skeletal muscle. Glucose uptake was measured using positron emission tomography (PET) and 2‐[18F]fluoro‐2‐deoxy‐D‐glucose ([18F]FDG). Twelve healthy men were studied during rest, while 14 subjects were studied after 35 min of bicycle exercise corresponding to 30, 55 and 75 % of maximal oxygen consumption (V̇O2,max) on three separate days. [18F]FDG was injected 10 min after the start of exercise and exercise continued for a further 25 min. Myocardial and skeletal muscle PET scanning was commenced directly after the completion of the exercise bout. As compared to the resting state, exercise doubled myocardial glucose uptake at the 30 % (P= 0.056) and 55 % intensity levels (P < 0.05), while at the 75 % intensity level glucose uptake was reduced significantly compared to the lower exercise intensities. There was no significant difference between the highest intensity level and the resting state (P= 0.18). At rest and during low‐intensity exercise, myocardial glucose uptake was inversely associated with circulating levels of free fatty acids. However, during higher exercise intensities when plasma lactate concentrations increased significantly, this association disappeared. In contrast to myocardial responses, skeletal muscle glucose uptake rose in parallel with exercise intensity from rest to 30 % and then 55 % V̇O2,max (P < 0.001) and tended to increase further at the intensity of 75 % V̇O2,max (P= 0.065). In conclusion, these results demonstrate that myocardial glucose uptake is increased during mild‐ and moderate‐intensity exercise, but is decreased during high‐intensity exercise. This finding suggests that the increased myocardial energy that is needed during high‐intensity exercise is supplied by substrates other than glucose.
Water pumps
Authors: Loo Donald D. F. , Wright Ernest M. , Zeuthen Thomas
Published: July 2002

The transport of water across epithelia has remained an enigma ever since it was discovered over 100 years ago that water was transported across the isolated small intestine in the absence of osmotic and hydrostatic pressure gradients. While it is accepted that water transport is linked to solute transport, the actual mechanisms are not well understood. Current dogma holds that active ion transport sets up local osmotic gradients in the spaces between epithelial cells, the lateral intercellular spaces, and this in turn drives water transport by local osmosis. In the case of the small intestine, which in humans absorbs about 8 l of water a day, there is no direct evidence for either local osmosis or aquaporin gene expression in enterocytes. Intestinal water absorption is greatly enhanced by glucose, and this is the basis for oral rehydration therapy in patients with secretory diarrhoea. In our studies of the intestinal brush border Na+‐glucose cotransporter we have obtained evidence that there is a direct link between the transport of Na+, glucose and water transport, i.e. there is cotransport of water along with Na+ and sugar, that will account for about 50 % of the total water transport across the human intestinal brush border membrane. In this short review we summarize the evidence for water cotransport and propose how this occurs during the enzymatic turnover of the transporter. This is a general property of cotransporters and so we expect that this may have wider implications in the transport of water and other small polar molecules across cell membranes in animals and plants.
Cytoskeletal actin microfilaments and the transient outward potassium current in hypertrophied rat ventriculocytes
Authors: Yang Xiangjun , Pedro J. I. , Pham Thai V. , Wasserlauf Bernard J. , Marcel J. D. Smets , Myerburg Robert J. , Gelband Henry , Hoffman Brian F. , Bassett Arthur L.
Published: July 2002

The durations of transmembrane action potentials recorded from single myocytes isolated from the endocardial surface of hypertrophied left ventricles of rats were increased, compared to the durations recorded from normal left ventricular cells at 36‐37 °C. Exposure to phalloidin (1‐20 μM, < 20 min), a specific stabilizer of the non‐myofibrillar actin microfilament component of the cardiac cytoskeleton, had no effect on action potential duration of normal cells, but significantly shortened the prolonged action potentials of hypertrophied cells. Cytochalasin D (5‐50 μM), a disrupter of the actin microfilaments, also had little effect on action potential duration of normal cells. However, cytochalasin D further increased the action potential duration of hypertrophied cells at 10 min exposure. The addition of phalloidin to solutions containing cytochalasin D, reduced the latter's increase of action potential duration in hypertrophied cells. Whole‐cell transient outward K+ current (Ito1) density was significantly decreased in hypertrophied cells. At a test potential of +60 mV, the mean Ito1 density recorded from normal cells was 13.5 ± 1.1 pA pF−1 (n= 18) compared to 4.17 ± 1.2 pA pF−1 for LVH cells (n= 22; P < 0.05). Phalloidin (20 μM) increased and cytochalasin D (50 μM) decreased whole‐cell Ito1 in hypertrophied cells but had no effect on Ito1, in normal cells. When equimolar concentrations were used, phalloidin, 10 μM, reversed the decrease in Ito1 brought about by cytochalasin D, 10 μM, in hypertrophied cells. The L‐type calcium current density was reduced in LVH compared to normal cells. Phalloidin (20 μM) and cytochalasin D (50 μM) had no effect on ICa,L in normal or LVH myocytes. The decrease in Ito1 in hypertrophied cells and the altered Ito1 responsiveness to phalloidin and cytochalasin D reflect modification of Ito1 channel function mediated, in part, through hypertrophy‐altered cytoskeletal actin microfilament regulation of Ito1.
Dietary protein adequacy and lower body versus whole body resistive training in older humans
Authors: Campbell Wayne W. , Trappe Todd A. , Jozsi Alison C. , Kruskall Laura J. , Wolfe Robert R. , Evans William J.
Published: July 2002

This study assessed the effects of long‐term consumption of the United States Recommended Dietary Allowance (RDA) for protein by older people who were sedentary or performed resistive training (RT) on body composition, skeletal muscle size and protein metabolism, and if the number of muscle groups trained influenced the muscle hypertrophy response to RT. Twelve men and 17 women (age range 54–78 years) completed this 14 week controlled diet and exercise study. Throughout the study, each subject completely consumed daily euenergetic menus that provided the RDA of 0.8 g protein kg−1 day−1. From study weeks 3–14 (weeks RT1‐RT12), 10 subjects (four men, six women) performed whole body RT (WBRT), nine subjects (four men, five women) performed lower body RT (LBRT) and 10 subjects (four men, six women) remained sedentary (SED). Both the LBRT and WBRT groups performed knee extension and flexion exercises, and the WBRT group also performed chest press and arm pull exercises (three sets per exercise at 80 % of one repetition maximum, 3 days per week for 12 weeks). From week 2 (baseline) to week RT12, muscle strength increased in muscle groups trained in the LBRT and WBRT groups, and was not changed in the SED group. From baseline to week RT12, whole body muscle mass and protein‐mineral mass were not changed, fat‐free mass (P= 0.004) and total body water (P= 0.013) were decreased, and percentage body fat was increased (P= 0.011) in these weight‐stable older people, independent of group assignment. The RT‐induced increases in mid‐thigh muscle area (from computed tomography scans) were comparable in the LBRT and WBRT groups (2.13 ± 1.26 cm2 and 2.17 ± 1.24 cm2, respectively), and were different from those in the SED group, which lost muscle area (‐1.74 ± 0.57 cm2; group‐by‐time P < 0.05). From baseline to week RT12, 24 h urinary total nitrogen excretion decreased (P < 0.001), nitrogen balance shifted from near equilibrium to positive, whole body leucine oxidation (from the infusion of L‐[13C]leucine) decreased (P < 0.05) and net (postabsorptive vs. postprandial) leucine balance (P < 0.05) increased from near equilibrium to positive, with no differences in responses over time among the three groups. In conclusion, the number of muscle groups trained did not influence whole body protein metabolism or RT‐induced muscle hypertrophy in older people. Most of these data are consistent with a successful adaptation to the RDA for protein. However, research should continue to question whether the decreases in fat‐free mass and total body water observed in all subjects, and the decrease in mid‐thigh muscle area in the SED group, are physiological accommodations, and whether the RDA for protein might be marginally inadequate for older people to maintain skeletal muscle.
Break excitation alone does not explain the delay and amplitude of anodal current‐induced vasodilatation in human skin
Authors: Durand S. , Fromy B. , Humeau A. , Sigaudo‐Roussel D. , Saumet J. L. , Abraham P.
Published: July 2002

In iontophoresis experiments, a ‘non‐specific’ current‐induced vasodilatation interferes with the effects of the diffused drugs. This current‐induced vasodilatation is assumed to rely on an axon reflex due to excitation of cutaneous nociceptors and is weaker and delayed at the anode as compared to the cathode. We analysed whether these anodal specificities could result from a break excitation of nociceptors. Break excitation is the generation of action potentials at the end of a square anodal DC current application, which are generally weaker than those observed at the onset of a same application at the cathode. In eight healthy volunteers, we studied forearm cutaneous laser Doppler flow (LDF) responses to: (1) anodal and cathodal 100 μA current applications of 1, 2, 3, 4 or 5 min; (2) 100 μA anodal applications of 3 min with a progressive ending over 100 s (total charge 23 mC); these were compared to square‐ended 100 μA anodal applications of the same total charge (23 mC) or duration (3 min); (3) a 4 min 100 μA anodal application with a 333 msec break at half time. Results (mean ± S.D.) are expressed as percentage of heat‐induced maximal vasodilatation (%MVD). Onset (Tvd) and amplitude (LDFpeak) of vasodilatation were determined. We observed that: Tvd was linearly related to the duration of current application at the anode (slope = 1.01, r2= 0.99, P < 0.0001) but not at the cathode (slope = 0.03, r2= 0.02, n.s.). Progressive ending of anodal current did not decrease LDFpeak (63.3 ± 24.6 %MVD) as compared to square‐ending of current application of the same duration (36.9 ± 22.2 %MVD) or the same total charge (57.1 ± 23.5 %MVD). A transient break of anodal current did not allow for the vasodilatation to develop until current was permanently stopped. We conclude that, during iontophoresis, anodal break excitation alone cannot account for the delay and amplitude of the vascular response.
Active Control Algorithms for the Control of Rotor Vibrations Using Hybrid Squeeze Film Dampers
Authors: El-Shafei A.
Published: July 2002

The hybrid squeeze film damper (HSFD) has proven itself to be an effective controlling device of vibration in rotating machinery. The critical stage in the development of the HSFD as an active vibration suppressant, is the development of the control algorithms for active control of rotor vibrations. This paper summarizes, evaluates, and compares the control algorithms for HSFD-supported rotors. Quantitative as well as qualitative measures of the effectiveness of the control algorithms are presented. The study includes the PID-type controllers, LQR, gain scheduling, adaptive and bang-bang controllers. The adaptive, gain scheduling, and nonlinear proportional controllers have proved to be quite effective in the active control of HSFD supported rotors, with impressive results.
Improved Gas Turbine Efficiency Through Alternative Regenerator Configuration
Authors: Dellenback P. A.
Published: July 2002

An alternative configuration for a regenerative gas turbine engine cycle is presented that yields higher cycle efficiencies than either simple or conventional regenerative cycles operating under the same conditions. The essence of the scheme is to preheat compressor discharge air with high-temperature combustion gases before the latter are fully expanded across the turbine. The efficiency is improved because air enters the combustor at a higher temperature, and hence heat addition in the combustor occurs at a higher average temperature. The heat exchanger operating conditions are more demanding than for a conventional regeneration configuration, but well within the capability of modern heat exchangers. Models of cycle performance exhibit several percentage points of improvement relative to either simple cycles or conventional regeneration schemes. The peak efficiencies of the alternative regeneration configuration occur at optimum pressure ratios that are significantly lower than those required for the simple cycle. For example, at a turbine inlet temperature of 1300°C (2370°F), the alternative regeneration scheme results in cycle efficiencies of 50 percent for overall pressure ratios of 22, whereas simple cycles operating at the same temperature would yield efficiencies of only 43.8 percent at optimum pressure ratios of 50, which are not feasible with current compressor designs. Model calculations for a wide range of parameters are presented, as are comparisons with simple and conventional regeneration cycles.
The Effect of Workpiece Hardness and Cutting Speed on the Machinability of AISI H13 Hot Work Die Steel When Using PCBN Tooling
Authors: Ng Eu-Gene , Aspinwall David K.
Published: July 2002

When machining hardened steel (⩾45 HRC) with polycrystalline cubic boron nitride (PCBN) tooling, the cutting speeds used produce high temperatures in the primary shear zone, which are sufficient to plasticize the workpiece. The paper initially reviews the effect of workpiece hardness and cutting speed on chip formation, workpiece surface integrity and cutting forces. Equations are detailed for determining the primary shear zone temperature, the proportion of heat conducted into the workpiece and the shear flow stress. Following on from this, experimental work is presented involving the orthogonal machining of AISI H13 hot work die steel with PCBN tooling. Tests were carried out over a range of cutting speeds with workpieces of different hardness, in order to provide cutting force, shear angle, chip morphology and primary shear zone thickness data. The shear flow stress decreased with increasing cutting speed and/or workpiece hardness. With the AISI H13 heat treated to 49±1 HRC, the stress magnitude changed more significantly with cutting speed and the proportion of heat conducted away from the workpiece approached 99 percent at 200 m/min. Shear localized chips were produced with white unetched layers due to intense heat generation followed by rapid cooling.
The Effect of Variable Chord Length on Transonic Axial Rotor Performance
Authors: Roberts William B. , Armin Albert , Kassaseya George , Suder Kenneth L. , Thorp Scott A. , Strazisar Anthony J.
Published: July 2002

Aircraft fan and compressor blade leading edges suffer from atmospheric particulate erosion that reduces aerodynamic performance. Recontouring the blade leading edge region can restore blade performance. This process typically results in blades of varying chord length. The question therefore arises as to whether performance of refurbished fans and compressors could be further improved if blades of varying chord length are installed into the disk in a certain order. To investigate this issue the aerodynamic performance of a transonic compressor rotor operating with blades of varying chord length was measured in back-to-back compressor test rig entries. One half of the rotor blades were the full nominal chord length while the remaining half of the blades were cut back at the leading edge to 95% of chord length and recontoured. The rotor aerodynamic performance was measured at 100, 80, and 60% of design speed for three blade installation configurations: nominal-chord blades in half of the disk and short-chord blades in half of the disk; four alternating quadrants of nominal-chord and short-chord blades; nominal-chord and short-chord blades alternating around the disk. No significant difference in performance was found between configurations, indicating that blade chord variation is not important to aerodynamic performance above the stall chord limit if leading edges have the same shape. The stall chord limit for most civil aviation turbofan engines is between 94–96% of nominal (new) blade chord.
Machining Simulation for Ceramics Based on Continuum Damage Mechanics
Authors: Liu Xianbing , Zhang Bi
Published: July 2002

An abrasive machining process for ceramics is simulated with a nonlinear thermodynamic constitutive model based on the principle of continuum damage mechanics (CDM). The model consists of a set of parallel Maxwell-type elements arranged in series with a spring. It incorporates stochastic material microstructure through two sets of the newly introduced material parameters, spring-like constants Cr and damping-like coefficients arr=1,2,…,n. Damage is considered cumulative and related with current stress and damage state in a ceramic workpiece during loading, which constitutes damage evolution. A fourth-order isotropic damage tensor is introduced. This highly nonlinear CDM model is reduced to an incremental formulation and approximated by a 3D nonlinear finite element program based on the Newton-Raphson method. The stress-strain correlation calculated from the current model is presented for alumina, silicon carbide, and silicon nitride. The predicted results of damage versus the depth of cut for the three ceramics subjected to machining with single diamond grit are validated by the experiment. As one example, the development of damage with the movement of the abrasive grit in a silicon nitride workpiece is demonstrated by a contour plot. The final part of this paper presents the calculated distribution of residual stress in a silicon nitride sample and the factors contributing to the distribution are discussed.
The SKN Approximation for Solving Radiative Transfer Problems in Absorbing, Emitting, and Isotropically Scattering Plane-Parallel Medium: Part 1
Authors: Altac¸ Zekeriya
Published: July 2002

A high order approximation, the SKN method—a mnemonic for synthetic kernel—is proposed for solving radiative transfer problems in participating medium. The method relies on approximating the integral transfer kernel by a sum of exponential kernels. The radiative integral equation is then reducible to a set of coupled second-order differential equations. The method is tested for one-dimensional plane-parallel participating medium. Three quadrature sets are proposed for the method, and the convergence of the method with the proposed sets is explored. The SKN solutions are compared with the exact, PN, and SN solutions. The SK1 and SK2 approximations using quadrature Set-2 possess the capability of solving radiative transfer problems in optically thin systems.
Variational Estimates for the Effective Response of Shape Memory Alloy Actuated Fiber Composites
Authors: Briggs J. P. , Castaneda P. Ponte
Published: July 2002

The homogenization procedure of Ponte Castan˜eda is used to estimate the effective behavior of active composite materials consisting of aligned shape memory alloy (SMA) fibers embedded in a linear elastic matrix. Results are presented for thermal activation of the SMA with various applied tractions on the composite. While increasing stiffness of the matrix phase inhibits the contraction of the SMA, the simulations indicate that the use of a prestress in the manufacturing of the composite may provide an increase in the response time of the system without reducing performance.
An Edge Dislocation in a Three-Phase Composite Cylinder Model With a Sliding Interface
Authors: Wang X. , Shen Y.-p.
Published: July 2002

An exact elastic solution is derived in a decoupled manner for the interaction problem between an edge dislocation and a three-phase circular inclusion with circumferentially homogeneous sliding interface. In the three-phase composite cylinder model, the inner inclusion and the intermediate matrix phase form a circumferentially homogeneous sliding interface, while the matrix and the outer composite phase form a perfect interface. An edge dislocation acts at an arbitrary point in the intermediate matrix. This three-phase cylinder model can simultaneously take into account the damage taking place in the circumferential direction at the inclusion-matrix interface and the interaction effect between the inclusions. As an application, we then investigate a crack interacting with the slipping interface.
Test and Theory Correlation Study for a Flexible Rotor on Fault-Tolerant Magnetic Bearings
Authors: Na Uhn Joo , Palazzolo Alan B. , Provenza Andrew
Published: July 2002

This paper provides a new algorithm and test verification for implementing fault-tolerant operation of magnetically suspended, flexible shaft, rotating machinery. The currents to the magnetic bearing are redistributed in a manner so that the bearing actuator preserves the same linearized magnetic forces after some of its coils experience failure. The algorithm that searches a database for the appropriate failure compensation matrix utilizes a Boolean description of the failure state to quickly locate and download its target. The test results are shown to have good agreement with the system simulation results presented.
Generic Simulation Approach for Multi-Axis Machining, Part 2: Model Calibration and Feed Rate Scheduling
Authors: Bailey T. , Elbestawi M. A. , El-Wardany T. I. , Fitzpatrick P.
Published: July 2002

This is the second part of a two-part paper presenting a new methodology for analytically simulating multi-axis machining of complex sculptured surfaces. The first section of this paper offers a detailed explanation of the model calibration procedure. A new methodology is presented for accurately determining the cutting force coefficients for multi-axis machining. The force model presented in Part 1 of this paper is reformulated so that the cutting force coefficients account for the effects of feed rate, cutting speed, and a complex cutting edge design. Experimental results are presented for the calibration procedure. Model verification tests were conducted with these cutting force coefficients. These tests demonstrate that the predicted forces are within 5% of experimentally measured forces. Simulated results are also shown for predicting dynamic cutting forces and static/dynamic tool deflection. The second section of the paper discusses how the modeling methodology can be applied for feed rate scheduling in an industrial application. A case study for process optimization of machining an airfoil-like surface is used for demonstration. Based on the predicted instantaneous chip load and/or a specified force constraint, feed rate scheduling is utilized to increase metal removal rate. The feed rate scheduling implementation results in a 30% reduction in machining time for the airfoil-like surface.
An Unsymmetrical Motion in a Horizontal Impact Oscillator
Authors: Luo Albert C. J.
Published: July 2002

Stability and bifurcation for the unsymmetrical, periodic motion of a horizontal impact oscillator under a periodic excitation are investigated through four mappings based on two switch-planes relative to discontinuities. Period-doubling bifurcation for unsymmetrical period-1 motions instead of symmetrical period-1 motion is observed. A numerical investigation for symmetrical, period-1 motion to chaos is completed. The numerical and analytical results of periodic motions are in very good agreement. The methodology presented in this paper is applicable to other discontinuous dynamic systems. This investigation also provides a better understanding of such an unsymmetrical motion in symmetrical discontinuous systems.
Fracture Nucleation in Single-Wall Carbon Nanotubes Under Tension: A Continuum Analysis Incorporating Interatomic Potentials
Authors: Zhang P. , Huang Y. , Gao H. , Hwang K. C.
Published: July 2002

Carbon nanotubes show great promise for applications ranging from nanocomposites, nanoelectronic components, nanosensors, to nanoscale mechanical probes. These materials exhibit very attractive mechanical properties with extraordinarily high stiffness and strength, and are of great interest to researchers from both atomistic and continuum points of view. In this paper, we intend to develop a continuum theory of fracture nucleation in single-walled carbon nanotubes by incorporating interatomic potentials between carbon atoms into a continuum constitutive model for the nanotube wall. In this theory, the fracture nucleation is viewed as a bifurcation instability of a homogeneously deformed nanotube at a critical strain. An eigenvalue problem is set up to determine the onset of fracture, with results in good agreement with those from atomistic studies.
Nano Electro Mechanics of Semiconducting Carbon Nanotube
Authors: Peng S. , Cho K.
Published: July 2002

The effect of a flattening distortion on the electronic properties of a semiconducting carbon nanotube is investigated through first-principles calculations. As a function of the mechanical deformation, electronic bandgap is reduced leading to a semiconductor-metal transition. However, further deformation reopens the bandgap and induces a metal-semiconductor transition. The semiconductor–metal transitions take place as a result of curvature-induced hybridization effects, and this finding can be applied to develop novel nano electro mechanical systems.
Optimal Placement of Fixture Clamps: Minimizing the Maximum Clamping Forces
Authors: Marin Rodrigo A. , Ferreira Placid M.
Published: July 2002

This paper addresses the problem of synthesizing robust optimal clamping schemes on three-dimensional parts with planar faces, with and without friction. Given a work part with a pre-defined deterministic 3-2-1 location scheme, a set of polygonal convex regions on its faces are defined as areas of admissible clamp positions. A known set of external disturbing wrenches is also given. The frictionless case is considered first, and a new linear program is formulated to provide clamp locations that minimize the maximum clamping force. A transformation of the solution is presented that permits the extraction of both, the optimal positions of the clamps and the magnitude of the corresponding maximum clamping force. Friction is introduced next, and a linear program is presented that minimizes the maximum normal clamping force. We also extend the earlier formulations to support the case of frictionless clamping contacts on cylindrical faces. The result is a nonlinear (but convex) optimization problem that can be easily solved. Finally, we discuss a linear algebraic technique to find the directions, and associated relative motion rates, along which the clamps can be moved while maintaining the clamping forces constant. These lines of constant clamping force, as we name them, identify an equivalence set of clamping schemes (such that the maximum clamping force, given a set of disturbing wrenches, stays invariant).