Conductivity Volume Research Articles

Exercise Intensity and Limb Specificity Alter the Mechanisms of the Muscle Metaboreflex

PURPOSE: Previous studies in dogs have demonstrated a dichotomous response to muscle metaboreflex activation; at low and moderate intensity treadmill exercise, the pressor response was mediated primarily by increased cardiac output (CO), whereas peripheral vasoconstriction played a major role during high intensity exercise. We sought to extend these findings to humans by examining the relative contribution of central and peripheral factors to the pressor response elicited by the muscle metaboreflex following progressive arm and leg exercise. METHODS: In 7 healthy subjects (30 ± 2 yrs), small muscle mass arm and leg exercise was performed at three intensities, followed by 2-min of post-exercise circulatory occlusion (PECO). Dynamic handgrip exercise (1.5 min, 1 Hz) was performed at 20% 50%, and 70% of maximal voluntary contraction (MVC), and dynamic knee extensor exercise (3-min, 1 Hz) was performed at 20%, 60%, and 80% of peak work rate (WRmax). Heart rate (HR) and mean arterial pressure (MAP) were measured noninvasively (Finometer), from which stroke volume (SV), CO, and peripheral vascular conductance (PVC) were calculated. RESULTS: MAP increased from rest during all levels of PECO following exercise in the arm (20%MVC: +7 ± 2mmHg; 50%MVC: +11 ± 2mmHg; 70%MVC: +32 ± 2mmHg) and leg (20%WRmax: +22 ± 5mmHg; 60% WRmax: +14 ± 4mmHg; 80% WRmax: +40 ± 1mmHg) In the arm, the pressor response after exercise was achieved through an increase in CO at 20%MVC (+0.4 ± 0.2 L/min), while pressor responses at 50%MVC and 70%MVC were achieved through a reduction in PVC (-5.6 ± 2.1 ml min-1 mmHg-1and -18.5 ± 4.4 ml min-1 mmHg-1) with no change in CO. In contrast, following leg exercise the pressor responses was driven primarily by an increase in CO at 20%WRmax (+0.6 ± 0.3 L/min) and 50%WRmax (+1.0 ± 0.3 L/min), while the pressor response after high intensity KE exercise was achieved through a concomitant increase in CO (+0.9 ± 0.3 L/min) and a reduction in PVC (-9.6 ± 4.6 ml min-1 mmHg-1) CONCLUSION: These data suggest that during small muscle mass exercise in the arm and leg, changes in both CO and PVC contribute importantly to metaboreflex-induced pressor response in humans. Responses in both the arm and leg exhibited an intensity-dependent effect, with changes in PVC playing an increasingly important role during high exercise intensities.

Genetic Variation of the Alpha Subunit of ENaC Influences Lung Diffusion during Peak Exercise

Epithelial Na+ Channels (ENaC) regulate Na+ reabsorption from the alveolar airspace. Increased expression of ENaC has been shown to increase lung fluid clearance. Previous work has demonstrated that substitution of T→A at amino acid 663 of αENaC results in increased Na+ reabsorption. We sought to determine the influence of the αT663A variant of ENaC on lung diffusion with exercise in healthy subjects. 30 subjects (n=17 vs. 13; age=25±7 vs. 30±10yrs; ht=174±11 vs. 171±10cm; wt=69±12 vs. 73±14kg; VO2peak= 95±30 vs. 100±31%pred; mean±SD, wild‐type, WT (TT) vs. non wild‐type, NWT (AT, AA), respectively) were recruited. The diffusion capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO), alveolar volume (VA), and alveolar‐capillary membrane conductance (DM) were measured at rest and peak exercise. The WT group showed a significantly greater increase in DLCO and DLNO from rest to peak exercise than the NWT group (DLCO=51±12 vs. 36±17%, DLNO=51±24 vs. 32±25%, p<0.05). The WT group also had a greater % increase in DLCO/VA from rest to peak exercise (49±26 vs. 33±26%, p=0.08). The increase in DM from rest to peak exercise was statistically similar, although higher in the WT group (45±21 vs. 32±26%). These results demonstrate that genetic variation of ENaC at amino acid 663 influences lung diffusion at peak exercise in healthy humans suggesting differences in alveolar Na+ and, therefore, fluid handling.

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.

Charging Behavior of Polyimide/Adhesive Components During Eclipse Events in Geostationary Environment

This paper presents an experimental and numerical study carried out in the SIRENE irradiation test facility, installed at ONERA (Toulouse, France), on stacked polyimide/adhesive structures used on solar panels. This study aims at following the evolution of the charging potential built up at the surface of these structures during an eclipse event in geostationary orbit. The samples have therefore been irradiatedwith adistributed electron spectrum (from0 to 400 keV). During a first stage, the samples are submitted to light radiation at 293 K. In a second stage (eclipse phase), the electron irradiation is performed in darkness and with a decreasing temperature (down to 113 K). In a final stage (eclipse exit), the samples are submitted to light radiation with an increasing temperature (up to 293 K). We have been able to demonstrate that these solar structures are highly sensitive to temperature and light radiation since the volume conductivity of polyimide films and epoxy adhesives is submitted to noticeable variation with these operative parameters. The major conclusion is that this kind of polyimide/adhesive structure potentially used on solar panels may have to cope with elevated charging potential, which can be highly hazardous especially at the eclipse exit when the solar panel regains its power.

Spliced stromal cell-derived factor-1α analog stimulates endothelial progenitor cell migration and improves cardiac function in a dose-dependent manner after myocardial infarction

Stromal cell-derived factor (SDF)-1α is a potent endogenous endothelial progenitor cell (EPC) chemokine and key angiogenic precursor. Recombinant SDF-1α has been demonstrated to improve neovasculogenesis and cardiac function after myocardial infarction (MI) but SDF-1α is a bulky protein with a short half-life. Small peptide analogs might provide translational advantages, including ease of synthesis, low manufacturing costs, and the potential to control delivery within tissues using engineered biomaterials. We hypothesized thataminimized peptide analog of SDF-1α, designed by splicing the N-terminus (activation and binding) and C-terminus (extracellular stabilization) with a truncated amino acid linker, would induce EPC migration and preserve ventricular function after MI. EPC migration was first determined in vitro using a Boyden chamber assay. For in vivo analysis, male rats (n=48) underwent left anterior descending coronary artery ligation. At infarction, the rats were randomized into 4 groups and received peri-infarct intramyocardial injections of saline, 3 μg/kg of SDF-1α, 3 μg/kg of spliced SDF analog, or 6 μg/kg spliced SDF analog. After 4 weeks, the rats underwent closed chest pressure volume conductance catheter analysis. EPCs showed significantly increased migration when placed in both a recombinant SDF-1α and spliced SDF analog gradient. The rats treated with spliced SDF analog at MI demonstrated a significant dose-dependent improvement in end-diastolic pressure, stroke volume, ejection fraction, cardiac output, and stroke work compared with the control rats. A spliced peptide analog of SDF-1α containing both the N- and C- termini of the native protein induced EPC migration, improved ventricular function after acute MI, and provided translational advantages compared with recombinant human SDF-1α.

Impact of restrictive physiology on intrinsic diastolic right ventricular function and lusitropy in children and adolescents after repair of tetralogy of Fallot

BackgroundRestrictive right ventricular (RV) physiology is a phenomenon considered potentially beneficial when detected in children and adolescents with repaired tetralogy of Fallot (ToF). It is typically characterised by antegrade flow...

Precombustion Chamber Design for Emissions Reduction From Large Bore NG Engines

Precombustion chambers (PCCs) are an ignition technology for large bore, natural gas engines, which can extend the lean operating limit through improved combustion stability. Previous research indicates that the PCC is responsible for a significant portion of engine-out emissions, especially near the lean limit of engine operation. In this work, six concept PCC designs are developed with the objective of reducing engine-out emissions, focusing on oxides of nitrogen (NOx). The design variables include chamber geometry, chamber volume, fuel delivery, nozzle geometry, and material thermal conductivity. The concepts are tested on a single cylinder of a large bore, two-stroke cycle, lean burn, natural gas compressor engine, and the results are compared with stock PCC performance. The pollutants of interest include NOx, carbon monoxide, total hydrocarbons, and volatile organic compounds (VOCs). The results indicate that PCC volume has the largest effect on the overall NOx–CO tradeoff. Multiple nozzles and electronic PCC fuel control were found to enhance main chamber combustion stability, particularly at partial load conditions. The PCC influence on VOCs was insignificant; rather, VOCs were found to be heavily dependent on fuel composition.

Mean cell volume of neutrophils and monocytes compared with C‐reactive protein, interleukin‐6 and white blood cell count for prediction of sepsis and nonsystemic bacterial infections

Clinicians are in need of better diagnostic markers for rapid diagnosis of severe infections. Therefore, we studied the diagnostic significance of mean cell volume of neutrophils (MNV) and monocytes (MMV) compared with Interleukin-6 (IL-6), C-reactive protein (CRP) and white blood cell count for predicting systemic clinical infection (sepsis). MNV and MMV were obtained by volume conductivity scatter (VCS) technique of the Coulter LH 750 hematology analyzer during automated differential counts, and blood samples from patients with sepsis (n = 37), nonsystemic bacterial infections (n = 39) and controls (n = 48) were studied. We observed a significant increase in MNV and MMV in the sepsis group compared with limited infections and controls. However, at a designated cut-off point of 250 pg/ml, IL-6 seemed to be the best predictor for sepsis with a sensitivity of 93% and a specificity of 76%. Compared with CRP (cut-off point 60 mg/dl), MNV at a cut-off of 150 had a comparable sensitivity and specificity and was the most predictive VCS parameter. Taken together, MNV and MMV seemed to be potential parameters to discriminate between sepsis and nonsystemic infections.

Dynamics of induction charging for multiple particle agglomerations with a thin conducting surface layer

In electrostatic applications, particles are typically stacked in an arbitrary array. In this paper, multiple particle agglomerations with a finite volume conductivity, surface conductivity and permittivity have been simulated. Upon exposure to the electric field, electric shielding can occur due to the proximity of other particles, which greatly reduces the maximum accumulated charge and affects the charging time. All results have been obtained using the COMSOL commercial software. The simulation results show that shielding the electric field from a given particle reduces its saturation charge and the rate of charge accumulation was mainly affected by the volume and surface conductivities.

Pulmonary capillary blood volume and membrane conductance in Andeans and lowlanders at high altitude: A cross-sectional study

Lung carbon monoxide (CO) transfer and pulmonary capillary blood volume (Vc) at high altitudes have been reported as being higher in native highlanders compared to acclimatised lowlanders but large discrepancies appears between the studies. This finding raises the question of whether hypoxia induces pulmonary angiogenesis. Eighteen highlanders living in Bolivia and 16 European lowlander volunteers were studied. The latter were studied both at sea level and after acclimatisation to high altitude. Membrane conductance (Dm CO) and Vc, corrected for the haemoglobin concentration (Vc cor), were calculated using the NO/CO transfer technique. Pulmonary arterial pressure and left atrial pressures were estimated using echocardiography. Highlanders exhibited significantly higher NO and CO transfer than acclimatised lowlanders, with Vc cor/VA and Dm CO/VA being 49 and 17% greater (VA: alveolar volume) in highlanders, respectively. In acclimatised lowlanders, Dm CO and Dm CO/VA values were lower at high altitudes than at sea level. Echocardiographic estimates of cardiac output and pulmonary arterial pressure were significantly elevated at high altitudes as compared to sea level. The decrease in Dm CO in lowlanders might be due to altered gas transport in the airways due to the low density of air at high altitudes. The disproportionate increase in Vc in Andeans compared to the change in Dm CO suggests that the recruitment of capillaries is associated with a thickening of the blood capillary sheet. Since there was no correlation between the increase in Vc and the slight alterations in haemodynamics, this data suggests that chronic hypoxia might stimulate pulmonary angiogenesis in Andeans who live at high altitudes.

Effect of amine functionalization of CNF on electrical, thermal, and mechanical properties of epoxy/CNF composites

This paper presents experimental results of the effect of amine functionalization of carbon nanofibers (CNF) on the electrical, thermal, and mechanical properties of CNF/epoxy composites. The functionalized and non-functionalized CNFs (up to 3 wt%) were dispersed into epoxy using twin screw extruder. The specimens were characterized for electrical resistivities, thermal conductivity (K), UTS, and Vicker’s microhardness. The properties of the nanocomposites were compared with that of neat epoxy. The volume conductivity of the specimens increased by E12 S/cm and E09 S/cm in f-CNF/epoxy and CNF/epoxy, respectively, at 3 wt% filler loading. The increase in K for former was 106% at 150 °C, while for the latter it was only 64%. Similarly, UTS increased by 61% vs. 45% and hardness 65% vs. 43%. Tg increased with increase in filler content. SEM examinations showed that functionalization resulted in better dispersion of the nanofibers and hence greater improvement in the studied properties of the nanocomposites.

Environmental physiology of a small marsupial inhabiting arid floodplains

Giles' planigale ( Planigale gilesi) is among the smallest extant marsupials and inhabits deep soil cracks in arid floodplains. We examined whether its physiology shows specific adaptations to its extreme habitat. Metabolic rate, body temperature, evaporative water loss and thermal conductance were measured for eight planigales (average mass 9 g) exposed to four different ambient temperatures ranging from 10 °C to 32 °C. Water economy and respiratory variables were measured for the first time in this species. All of these standard physiological variables conformed to allometrically-predicted values for a marsupial. All variables were significantly affected by ambient temperature, except tidal volume and dry thermal conductance. Metabolic rate increased substantially at low ambient temperatures, as required to maintain a relatively constant body temperature of about 32–34 °C. This increased oxygen demand was accommodated by increased ventilation rather than increased oxygen extraction. Planigales had a comparatively high point of relative water economy of 19.1 °C, consistent with their small body size and arid habitat. Torpor reduced energy expenditure by 79% and evaporative water loss by 62%. Our study suggests that torpor use, along with behavioural adaptations, suffice for P. gilesi to live underground in arid habitats without further physiological adaptations.

Permanent antistatic phthalocyanine/epoxy nanocomposites – Influence of crosslinking agent, solvent and processing temperature

Cross-linked epoxy matrices containing small amounts of semi-conductive phthalocyanine (Phthalcon) nanoparticles were prepared using different crosslinking agents and processing temperatures. A starting mixture containing an optimum dispersion of these nanoparticles and with an almost equal and large Hamaker constant was always used. Nevertheless large differences in the relation between the volume conductivity σ v and the particle concentration φ were found and this relation appeared to be sensitive to small changes in processing temperature and the application of a post-cure. Also the amine crosslinker chosen and the initial amount of solvent (catalyst) in the starting dispersion had a major effect. It was shown that these changes influence strongly the formation of and the final conductive fractal particle network morphology through the polymer matrix. During processing a local relaxation of the initially formed fractal particle network into another fractal particle network was often observed, which introduced or enlarged the amount of isolating material between the particles of the conductive network and changed the fractality and structure of the conductive backbone of the particle network. This local relaxation lowered the σ v at each phthalcon concentration and enlarged φ c by several orders of magnitude. The occurrence of local relaxation is dependent on the rate of viscosity change during the crosslinking of the polymer matrix components, the way the fractal conductive particle network is formed during processing (universal or non-universal) and the amount of solvent present. Local relaxation may even occur after the gel point of the polymer matrix. A severe post-cure may be needed to stop this local relaxation. To our knowledge local relaxation of a (fractal) nanoparticle network in a polymer matrix during processing is a new phenomenon, not reported before for polymer composites containing (conductive) nanoparticles.

Electrical properties and FTIR spectra of ZnO–PbO–P 2O 5 glasses

Glasses of chemical composition xZnO.(60− x)PbO.40P 2O 5 ( x=10–60 mol%) have been prepared and investigated for FTIR, density, molar volume ( V m ), and DC conductivity. Both density and molar volume decreases systematically with composition. FTIR analysis indicates that ≥30 mol% (PbO and/or ZnO) enters the glass structure as formers. Below and above that concentration a decreasing amount of Pb 2+ (Zn 2+) is incorporated into the network as modifier. The band at 1018–1025 cm −1 can be considered as an indication for the presence of P–O–Pb(Zn) linkages. By introducing ZnO into the glasses, P–O–Pb(Zn) linkages may be formed by opening up PO bonds of PO 4 tetrahedra. For all glasses the linear dependence of the conductivity indicates an ionic conduction due to Pb 2+ and/or Zn 2+ ions. The increase in activation energy by about 68%, and also the decrease in the conductivity at certain temperature not only attributed to an increase in the covalency of the glass matrix upon replacing PbO by ZnO but also due to an increase in the strain energy because of the decrease in V m of the studied glasses. It is found that the conductivity of ZnO–PbO–P 2O 5 glasses is four orders of magnitude higher than that of ZnO–PbO–B 2O 3 glasses containing the same amount of ZnO measured at the same temperature. In addition, both conductivities decrease with composition which may indicate that the origin of these decreases may be the same regardless the type of the host glass former. The differences in electronegativity and size of Zn 2+ and Pb 2+ divalent ions and the structural changes that will follow in the network govern the conductivity behaviour of Zn–Pb containing glasses.

Conductivity interface problems. Part I: Small perturbations of an interface

We derive high-order terms in the asymptotic expansions of boundary perturbations of steady-state voltage potentials resulting from small perturbations of the shape of a conductivity inclusion with C 2 {\mathcal C}^2 -boundary. Our derivation is rigorous and based on layer potential techniques. The asymptotic expansion in this paper is valid for C 1 {\mathcal C}^1 -perturbations and inclusions with extreme conductivities. It extends those already derived for small volume conductivity inclusions and leads us to very effective algorithms for determining lower-order Fourier coefficients of the shape perturbation of the inclusion based on boundary measurements. We perform some numerical experiments using the algorithm to test its effectiveness.

Does sweat volume influence the sweat test result?

ObjectiveLow volume sweat samples are considered unreliable for the diagnosis of cystic fibrosis, based on the assertion that sweat conductivity and chloride are reduced at lower sweating rates. We aimed...

Continuous right ventricular volumetry by fast-response thermodilution during right ventricular ischemia: Head-to-head comparison with conductance catheter measurements*

To evaluate the accuracy of right ventricular ejection fraction and right ventricular end-diastolic volume obtained by volumetric pulmonary artery catheter, using the conductance catheter as reference method. Prospective, comparative study. Research laboratory of a university hospital. Seven young female German landrace pigs. Ligation of the distal right coronary artery to induce temporary acute ischemia. Right ventricular ejection fraction and right ventricular end-diastolic volume were measured simultaneously with a volumetric pulmonary artery catheter and the conductance catheter technique (reference method), in an animal model of acute right ventricular ischemia. Measurements were performed at baseline, during ischemia, and during reperfusion. The methods were compared with Bland-Altman analyses and their diagnostic accuracy to detect ischemia was quantified by receiver operating characteristic curve analysis. For right ventricular ejection fraction measurements, Bland-Altman analysis indicated a bias of -9.9% indicating underestimation by pulmonary artery catheter with limits of agreement ranging from -26% to 6.1%. The data showed a trend for more underestimation at higher right ventricular ejection fraction values. For right ventricular end-diastolic volume, a bias of 31 mL, indicating overestimation by pulmonary artery catheter was found. Limits of agreement ranged from -25 mL to 88 mL. Ischemia induced a decrease in right ventricular ejection fraction and an increase in right ventricular end-diastolic volume, as expected, which was detected by conductance catheter with a significant higher diagnostic accuracy indicated by a receiver operating characteristic area under the curve of 0.98 (p < .001) and 0.92 (p < .001), respectively. Corresponding sensitivity and specificity were 100% and 86%, respectively, for right ventricular ejection fraction conductance catheter (cutoff value = <40%), and 86% and 100% for right ventricular end-diastolic volume conductance catheter (cutoff value = >94 mL). However, diagnostic accuracy for right ventricular ejection fraction pulmonary artery catheter and end-diastolic volume pulmonary artery catheter to detect ischemia was limited with area under the curve 0.76 (p = .06) and 0.57 (p = .65), respectively. Accuracy of volumetric pulmonary artery catheter in conditions of right ventricular ischemia is low and inadequate for diagnosis of right ventricular ischemia and failure.

Li2Mo4-(NH4)2MoO4-H2O system at 25°C

Solubility in the Li2MoO4-(NH4)2MoO4-H2O system at 25°C was studied. A congruently saturating double molybdate crystal hydrate LiNH4MoO4 · H2O was found to form in the system. The density, refractive index, viscosity, surface tension, and specific electrical conductivity were measured for saturated aqueous solutions of the system. Molar volume, ionic strength, and equivalent conductivity isotherms were calculated. A correlation is observed between the variations of these properties of solutions and solubility in the system. The double salt was recovered and characterized by chemical analysis, IR spectroscopy, and dynamic and quasi-equilibrium thermogravimetry. A thermolysis scheme is suggested proceeding from the thermal curves and chemical analysis of intermediate phases.

Exploring transient transfer entropy based on a group-wise ICA decomposition of EEG data

This paper presents a data-driven pipeline for studying asymmetries in mutual interdependencies between distinct components of EEG signal. Due to volume conductance, estimating coherence between scalp electrodes may lead to spurious results. A group-based independent component analysis (ICA), which is conducted across all subjects and conditions simultaneously, is an alternative representation of the EEG measurements. Within this approach, the extracted components are independent in a global sense while short-lived or transient interdependencies may still be present between the components. In this paper, functional roles of the ICA components are specified through a partial least squares (PLS) analysis of task effects within the time course of the derived components. Functional integration is estimated within the information-theoretic approach using transfer entropy analysis based on asymmetries in mutual interdependencies of reconstructed phase dynamics. A secondary PLS analysis is performed to assess robust task-specific changes in transfer entropy estimates between functionally specific components.

Grafting of polyaniline onto the radiation crosslinked chitosan

In this paper we report the chemical grafting of polyaniline onto the radiation crosslinked chitosan. Chitosan is crosslinked using 8 MeV electron beam and Co 60 γ-ray in the presence of CCl 4 as sensitizer. The so-obtained crosslinked chitosan is grafted with polyaniline (PANI) chemically using ammonium peroxy disulphate (APS) as an initiator. Grafted polymer is characterized by dissolution, swelling, UV–vis–NIR spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis, DC conductivity and nanoindentation studies. From the dissolution studies, grafting of PANI onto the crosslinked chitosan is confirmed. From the weight of films before and after grafting, grafting percentage is calculated. Grafting percentage increases as the monomer concentration increases and decreases with increase in crosslinking. This may be due to the decrease in the penetration of monomer onto the chitosan matrix with increase in crosslinking density. This is verified from SEM (cross-sectional view) of blend. UV–vis–NIR spectrum shows absorption peaks of PANI. Electrical property of grafted polymer is improved after doping with 1 M HCl. The change in volume conductivity is from 10 −11 to 10 −5 S/cm and surface conductivity from 10 −10 to 10 −2 S/cm. From TGA it is observed that grafted polymer and doped polymer are thermally stable.