Xc Values Research Articles

Free‐volume variation in polyethylenes of different crystallinities: Positron lifetime, density, and X‐ray studies

AbstractHigh‐quality positron lifetime measurements (70 million total counts) are reported for polyethylenes (PEs) of different crystallinities (Xc = 3–82%). The specific volumes of the crystalline and amorphous phases (Vc and Va, respectively) were estimated from density and wide‐angle X‐ray scattering (WAXS) experiments. Some samples (those with low values of Xc) were branched PEs, and those with high values of Xc were linear PEs for which Xc was varied with changes in the crystallization temperature. Both Vc and Va increase with decreasing Xc in the range 0% ≤ Xc ≤ 56% (the branched PEs) but are constant for Xc ≥ 56% (the linear PEs). The lifetime spectra were analyzed with the MELT and LIFSPECFIT routines. Artifacts that can appear in the spectrum analysis were checked via an analysis of computer‐generated spectra. Four lifetime components appeared in all of the PEs; the two long‐lived ones are attributed to pick‐off annihilation of ortho‐positronium (o‐Ps) in crystalline regions (τ3) and in holes of the amorphous phase (τ4). With increasing Xc, τ3 decreases from about 1.2 to 1 ns, τ4 decreases from 3.0 to 2.5 ns, and the intensity I4 decreases from 29 to 0%. An increase in I3 from 6 to 12% was observed. A comparison with simulations shows that the true I3 value approaches 0 for Xc → 0%. The decrease in I4 is weaker than the increase in Xc; this leads to the conclusion that the apparent specific o‐Ps yield in the amorphous phase I4Xc increases with Xc. Possible reasons for this surprising results are discussed. The fractional free hole volume [h = (Va − Vocc)/Va, where Vocc is the crystalline occupied volume] was estimated from density and WAXS results. Between Xc = 0 and 56%, h decreases from 0.151 to 0.090, but it does not change further above Xc = 56%. The mean size (v) of the local free volumes (holes) estimated from τ4 decreases from 200 to 150 Å3. The number density of holes (Nh) calculated from these values (Nh = h/v) also decreases from 0.8 to 0.6 nm−3 in the range 0% ≤ Xc ≤ 56%. The values of Va, Vc, h, and Nh increase with an increasing degree of branching but do not vary for linear PEs. The possible influence of a crystalline–amorphous interfacial phase (three‐phase model) on the observed lifetime parameters is also discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 65–81, 2002

Electrosintering of iron powder compacts

The influence of a nominal external electric field E=3 to 10 kV/cm on the sintering of iron powder compacts for 30 minutes at 1140 °C in a vacuum of ∼10−6 torr was investigated. It was found that the field reduced the porosity by as much as 29 to 73 pct compared to sintering without a field, the magnitude depending on the procedure employed to measure the density of the specimen. Optical microscopy revealed that the specimen electrosintered with E=10 kV/cm had a skin of ∼0.2 mm in thickness, where the porosity was significantly less than in the interior. This was also the depth of carburization that was obtained upon carburizing the electrosintered specimens. It is proposed that the decrease in porosity produced by the field results from a decrease in the chemical potential of vacancies at or just below the charged external surface. Vacancy flux equations employed to calculate the porosity as a function of distance below the external surface showed that the porosity becomes approximately zero at a distance of x c=0.4 to 0.5 mm below the surface, which is in reasonable accord with the microscopy measurements. Similar values of x c were obtained by assuming that the entire porosity decrease given by the density measurements occurred in a ring of thickness of x c below the external surface. The difference in the density measured by two Archimedes-principle procedures and microscopy observations suggests that the cavities open to the external surface of the electrosintered specimens are smaller or narrower than those for specimens sintered without a field.

Prevalence of Malnutrition Assessed by Bioimpedance Analysis and Anthropometry in Children on Peritoneal Dialysis

To evaluate the sensitivity of anthropometry and bioelectrical impedance analysis (BIA) in detecting alterations in body composition of children treated with peritoneal dialysis (PD), and to determine the prevalence of malnutrition in this population, in short- and long-term PD duration, using anthropometric and BIA-derived indices. Eighteen children treated with automated PD (11 males, 7 females; mean age 8.7 +/- 4.7 years). Eighteen patients were studied using anthropometry and BIA at the start (t0) and after 6 months (t1) of PD, 15 of these patients at 12 months (t2), and 8 at 24 months (t3) of PD. Midarm muscle circumference (MAMC), arm muscle area (AMA), and arm fat area (AFA) were calculated from anthropometric measures according to Frisancho (FrisanchoAR. New norms of upper limb fat and muscle areas for assessment of nutritional status. Am J Clin Nutr 1981; 34:2540-5.). The bioelectrical measures of resistance (R) and reactance (Xc) were obtained directly from the impedance signal; phase angle (PA) and distance (D) were calculated using mathematical formulas. Nutritional status was assessed by anthropometric measurements and BIA-derived indices, expressed as standard deviation scores (SDS), and by a score system based on BIA and anthropometric parameters. The percentage of children with values of anthropometric and BIA-derived indices below the 3rd percentile or between the 3rd and 25th percentiles, and the percentage of children with scores of 7-12 and 4-6 were calculated in order to detect patients with severe or moderate derangement of nutritional status. The mean SDS values of Xc, PA, and D significantly improved (p = 0.05, p = 0.001, p = 0.02) during the first 6 months of PD and remained almost stable during the following months. The SDS values of the anthropometric indices were less compromised than those of the BIA-derived indices, particularly at the start of dialysis. By 6 months, the percentages of children with values of BIA and anthropometric indices below the 3rd percentile had decreased. The percentages of patients with moderate and severe derangement of BIA and anthropometric indices remained substantially unchanged after 12 months. However, at 24 months, the percentage of patients with moderate derangement of BIA indices increased. All these findings were confirmed by the nutritional score system. BIA is more sensitive than anthropometry in detecting alterations in body composition of children on PD. The prevalence of malnutrition, high at the commencement of PD, decreases during the first year of treatment but not over the long term.

Isotactic polypropylene/ethylene-co-propylene blends: effects of composition on rheology, morphology and properties of injection moulded samples

Melt rheology, phase morphology and properties of (30/70) isotactic polypropylene/ethylene-co-propylene (iPP/EPR) blends, containing EPR copolymer synthesised by means of a titanium based catalyst with very high stereospecific activity (EPRTi), were compared to that of (30/70) iPP/EPR blends containing EPR copolymer synthesised by using a traditional vanadium based catalyst (EPRV). It was found that both the melts are to be classified “negative deviation blends” and that, for such a composition ratio, the EPR represents the continuous phase. Scanning electron microscopy (SEM) investigations confirmed that the iPP component segregates in spherical-shaped domains with average size lower than 1.0μm. Such a fine degree of dispersion of the minor component in solid state is found independent of melt phase viscosity ratio and has been correlated with the interfacial tension between iPP and EPR phases. The presence of 70% of EPR copolymer dramatically interfered with the iPP crystallisation process, as strong reduction in iPP crystallinity index (Xc) values is shown by both the iPP/EPR blends. Comparatively lower Xc value is exhibited by iPP phase crystallised in presence of EPRTi copolymer. Differential scanning calorimetry (DSC) experiments revealed, in fact, that the crystallisation process of iPP phase and that of ethylenic sequences along EPRTi chains hinder each other. By small angle X-ray scattering (SAXS) it was shown that the iPP/EPRTi materials are characterised by amorphous inter-lamellar layer (La) considerably higher than that shown by the plain iPP and iPP phase crystallised in presence of EPRV copolymer. This strong La increase was mainly ascribed to entrapping of EPRTi crystalline domains into the iPP amorphous inter-lamellar layer. Wide angle X-ray scattering (WAXS) studies demonstrated that the EPR content determines the ratio between the apparent crystal size of iPP phase grown in a direction perpendicular to the (110) crystallographic plane and the apparent crystal size of iPP phase grown in a direction perpendicular to the (040) crystallographic plane. The higher the EPR content, the higher the thickness of the iPP lamellae in the direction of the radial growth of iPP spherulites, in agreement with increased nucleation density shown by DSC results. The different modulus performance shown by the materials at room temperature was accounted for by distinguishing between effects of phase crystallinity and super-molecular structure.

Properties and morphology of poly(L-lactide). III. Effects of initial crystallinity on long-termin vitro hydrolysis of high molecular weight poly(L-lactide) film in phosphate-buffered solution

The effects of crystallinity (xc) on the hydrolysis of high molecular weight poly(L-lactide) (PLLA) films in a phosphate-buffered solution at 37°C was investigated by gel permeation chromatography, tensile testing, differential scanning calorimetry, scanning electron microscopy, and polarizing optical microscopy. The change in molecular weight distribution and surface morphology of the PLLA films after hydrolysis revealed that the hydrolysis of PLLA film in a phosphate-buffered solution proceeded homogeneously along the film cross section, mainly via the bulk-erosion mechanism. The induction period until the start of the decrease in mass remaining and the tensile strength became longer with a decrease in the initial xc of the PLLA films. The rate of molecular weight reduction was higher as the initial xc of the PLLA films increased when hydrolysis was carried out up to 24 months. Melting and glass transition temperatures of the PLLA films increased in the first 12 months of hydrolysis, while they decreased in another 24 months, irrespective of the initial xc. The xc value of the PLLA films increased monotonously by hydrolysis. The lamella disorientation in PLLA spherulites after hydrolysis implied that the hydrolysis of PLLA chains occurred predominantly in the amorphous region between the crystalline regions in the spherulites. The area of a specific molecular weight in GPC spectra at 36 months increased with increase in the initial xc of the PLLA film, suggesting that the specific peak should be due to the component of one fold in the crystalline region. The reason for enhanced hydrolysis of PLLA films having higher initial crystallinities was discussed in terms of tie chains and terminal groups of PLLA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1452–1464, 2000

Role of percolation in determining critical composition for the M‐I transition in transition metal oxides

AbstractAmong members of a large family of non‐stoichiometric transition metal oxides which exhibit a M‐I transition, NaxWO3 and its compensated relative NaxTay W1—yO3 have been particularly thoroughly investigated by experimentalists. On the theory side, recent work by Dücker, et al.[1] has significantly advanced our understanding of the physics of the metal‐insulator transition in these bellwether materials. This work confirms that for these tight‐binding materials, a “pseudo‐gap” in the density of states arises as a consequence of large values of the Coulomb interaction term U. The work also leads to the conclusion that the one‐electron Anderson localization mechanism, which considers variations in the local carrier binding energy, is not the critical factor in setting the value of xc, the critical impurity concentration for the M‐I transition. But predictions of actual values of xc remain elusive. I will show that percolation ideas, long waiting in the wings, give a clear picture of values of xc in a number of 3d, 4d, and 5d perovskites with non‐magnetic transition metal ions. The geometrical ideas associated with percolation modeling generate a picture of a “linkage” transition, to supplement, not substitute for, the results of the three‐band Anderson‐Mott‐Hubbard model used by Dücker, et al.A test of the appropriateness of percolation models to describe a M‐I transition is the determination of the value of v in the relationship σ(T = 0K) ≡ σ(0) ∝ (x — xc)v. Fragmentary data from NaxWO3, NaxTayW1—xO3 and LaNixCo1—xO3 give value of v lying between 1.6 and 2.5, the range of exponents typically found in various percolation models.

Growth of Si1−xGex(011) on Si(011)16×2 by gas-source molecular beam epitaxy: Growth kinetics, Ge incorporation, and surface phase transitions

Single crystal Si1−xGex(011) layers with x⩽0.35 have been grown on double-domain Si(011)“16×2” surfaces from Si2H6/Ge2H6 mixtures at temperatures Ts=400–950 °C. D2 temperature programmed desorption was used to show that the structure of the Si(011)“16×2” surface unit cell, more correctly written as [217 21] since the unit cell vectors are nonorthogonal, is composed of 16 adatoms and eight π-bonded dimers with a dangling bond density half that of the 1×1 surface. Si1−xGex(011) overlayers are “16×2” when x<xc(Ts) and “2×8” with x>xc(Ts). The value of xc decreases from ≃ 0.10 at Ts=475 °C to 0.08 at 550 °C to 0.06 at 650 °C. Both the “2×8” and “16×2” Si1−xGex(011) surface reconstructions gradually and reversibly transform to 1×1 at Ts between 650 and 725 °C. Film growth kinetics exhibit three distinct regimes. At low temperatures (Ts≲500 °C), the film deposition rate RSiGe decreases exponentially with 1/Ts in a surface-reaction-limited growth mode for which the rate-limiting step is hydrogen desorption from Si and Ge monohydride phases. RSiGe becomes essentially constant with Ts in the intermediate impingement-flux-limited range, Ts=500–650 °C. At Ts>650 °C, RSiGe increases again with Ts due initially (Ts≃650–725 °C) to an increase in the steady-state dangling bond coverage as the surface reconstruction gradually transforms to 1×1. The continued increase in RSiGe at even higher Ts is associated with strain-induced roughening. Ge/Si ratios in as-deposited films are linearly proportional to the incident Ge2H6/Si2H6 flux ratio JGe2H6/JSi2H6 and nearly independent of Ts indicating that the reactive sticking probabilities of Si2H6 and Ge2H6 have very similar temperature dependencies. RSiGe(JGe2H6/JSi2H6,Ts) in both the surface-reaction-limited and flux-limited regimes is well described by a simple kinetic model incorporating second-order dissociative chemisorption and second-order hydrogen desorption as rate-limiting steps.

ESTIMATION OF TOTAL BODY WATER IN HARBOR SEALS: HOW USEFUL IS BIOELECTRICAL IMPEDANCE ANALYSIS?

AbstractWe evaluated bioelectrical impedance analysis (BIA) as a means of rapidly and inexpensively estimating total body water (TBW) of harbor seals (Phoca vitulina). Deuterium oxide dilution was used to estimate TBW in 17 adult females and 16 of their pups between birth and late lactation. Isotope dilution was also used to determine TBW in 12 adult males early and 10 of these males late in the breeding season. At the same time, resistance (Rs) and reactance (Xc) measurements were taken using a tetrapolar, impedance plethysmograph (Model 101 A, RJL Systems). Seals were sedated with diazepam prior to taking BIA measurements. Within‐day duplicate Rs measurements on pups and adults, taken 2‐240 min apart, differed by an average of 3.0%± 1.4% (n= 42, CV = 102%). Movement of the seal during BIA measurements caused variability in both Rs and Xc values. BIA measurements were generally poor predictors of TBW. Rs was significantly correlated with TBW in pups only (Rs= 0.93, P= 0.001, n= 11). Bioelectrical conductor volume (length2/Rs) was significantly correlated with TBW only in adult females (Rs= 0.63, P= 0.02, n= 14). We conclude that BIA is not a reliable method of estimating TBW in wild harbor seals.

Thermal and electrical characterization of (CdTe)1−xTex composites: electron–phonon system

Pressed discs of mixed powders of CdTe (semiconductor) and Te (semimetal) with different mass concentrations were thermally and electrically characterized. In this granular system: (CdTe)1−xTex, studied in the entire range 0≤x≤1, where x is the fractional weight of Te, it has been found to exist a percolation critical point, xc=15.05%, for the electrical resistivity (ρ), by showing an abrupt decreasing of six orders of magnitude (ρ∼108 to ρ∼102 Ωcm). The fractional weight value of xc=15.05% corresponds to a volumetric fraction of 15.4%, according within the error scattering with the accepted theoretical value of 16.0%, for a volumetric fraction at the critical percolation in a three-dimensional system based in a mixture of conductive-insulator materials. The study of the theoretical properties of the composite were reduced to the analysis of the thermal diffusivity (α), as this is a dynamical property responsible for the establishment of the thermal equilibrium in a given material. The experimental results show a complex dependence of α as a function of the parameter x, evidencing a thermal transport influenced by an electron–phonon interaction.

Identification of operational clues to dry weight prescription in hemodialysis using bioimpedance vector analysis

Identification of operational clues to dry weight prescription in hemodialysis using bioimpedance vector analysis

Apport d'internet en toxicologie clinique : Paracelse

The suppression effect of superconductivity by Pr substitution correlates strongly with that by oxygen deficiency in the R1−xPrxBa2Cu3O7−y system, where R is Yb, Y, Ho, Dy, Gd and Nd. The larger the value of xC, the Pr content at which superconductivity disappears, the larger the value of yC, the oxygen deficiency at which superconductivity disappears. The decreasing rate in TC by Pr substitution (−dTC/dx) decreases with decreasing ionic radius of a rare-earth ion for the Ortho-I phase (TC>90 K for x=0) and also with decreasing oxygen concentration (7−y). The −dTC/dx for the smaller rare-earth ions (R=Yb, Y, Ho and Dy) are nearly independent of ionic radius for the Ortho-II phase (TC=60 K for x=0). The Pr content dependence of TC in (Y0.625La0.375)1−xPrxBa2Cu3O7−y, average rare-earth ionic radius of which is equal to that of Gd, coincides well with that in the Gd1−xPrxBa2Cu3O7−y. The weakened TC-suppression by Pr in the case of the smaller rare-earth ions is explained by considering the hole transfer effect from the Cu(1)O chain toward the Cu(2)O2 plane according to the difference in ionic radius between the rare-earth ions and Pr ion.

Whole-body and segmental bioelectrical parameters in chronic liver disease: Effect of gender and disease stages

The aim of this study was to examine and compare whole-body and segmental impedance measurements in control subjects and patients with progression of liver disease and to investigate whole-body and segmental bioelectrical changes occurring during dehydration therapy or paracentesis. Males have lower resistance (R) and reactance (Xc) values than females in measurements both of the whole body and of the arm, leg, and trunk. This is not true in patients. In the three groups of patients, whole-body R and Xc were lower in each increased disease stage, suggesting that stage has a significant main effect on impedance measurements. The lower extremities were the segment most influenced by the progression of liver disease. The sum of the arm and leg R was only slightly lower than the value of whole-body resistance. The trunk has a meager influence on this parameter, as is clearly shown by the absence of variations before and immediately after paracentesis. In edematous cirrhotic patients without ascites treated with diuretics, our data also showed a significant correlation (r = .81; SEE = 1.2) between changes in body weight (BW) and in the bioelectrical evaluation of total body water (TBW). The association of a prevalent increment of Xc (approximately 40%) with a reduction of extracellular water is the most significant bioelectrical event during dehydration therapy. All these findings show that impedance measurements have a low sensitivity in detecting the volume of ascites in cirrhotic patients, whereas Xc has a clinical use in monitoring changes in extracellular water (EW).

Whole-body and segmental bioelectrical parameters in chronic liver disease: Effect of gender and disease stages

The aim of this study was to examine and compare whole-body and segmental impedance measurements in control subjects and patients with progression of liver disease and to investigate whole-body and segmental bioelectrical changes occurring during dehydration therapy or paracentesis. Males have lower resistance (R) and reactance (Xc) values than females in measurements both of the whole body and of the arm, leg, and trunk. This is not true in patients. In the three groups of patients, whole-body R and Xc were lower in each increased disease stage, suggesting that stage has a significant main effect on impedance measurements. The lower extremities were the segment most influenced by the progression of liver disease. The sum of the arm and leg R was only slightly lower than the value of whole-body resistance. The trunk has a meager influence on this parameter, as is clearly shown by the absence of variations before and immediately after paracentesis. In edematous cirrhotic patients without ascites treated with diuretics, our data also showed a significant correlation ( r = .81; SEE = 1.2) between changes in body weight (BW) and in the bioelectrical evaluation of total body water (TBW). The association of a prevalent increment of Xc (≈40%) with a reduction of extracellular water is the most significant bioelectrical event during dehydration therapy. All these findings show that impedance measurements have a low sensitivity in detecting the volume of ascites in cirrhotic patients, whereas Xc has a clinical use in monitoring changes in extracellular water (EW).

Experimental measurements and numerical simulations of the gas composition in a hot-filament-assisted diamond chemical-vapor-deposition reactor

Molecular-beam mass spectroscopy was used to measure the gas composition near a growing diamond surface in a hot-filament-assisted chemical-vapor-deposition reactor. The dependencies of the gas composition on changes in (1) the carbon mole fraction in the reactor feed XC, (2) the identity of the inlet carbon source (CH4 versus C2H2), and (3) the surface temperature TS, were studied. For XC≤0.02, the gas composition appeared to be nearly independent of the identity of the inlet hydrocarbon source and depended only on the C/H ratio in the feed gas. At higher values of XC, catalytic poisoning of the hot filament resulted in different product distributions in these two systems. Increasing the surface temperature affected changes in the hydrocarbon composition; the dependencies of the CH3 and C2H2 mole fractions on TS can each be characterized as having an activation energy of 3±1 kcal/mol. Surprisingly, the H-atom mole fraction was independent of TS. These results suggest that reported temperature sensitivities of film growth properties are primarily due to changes in the kinetics of surface processes rather than changes in the gas composition near the surface. A numerical model of the process is presented. In the study of the compositional change as a function of XC, the code gives good prediction for the methane case but grossly underestimates the methane and methyl concentrations for the acetylene case. The H-atom mole fraction is predicted to increase by ×7 if the H destruction probability on the diamond surface is expected to have an activation energy of 7.3 kcal/mol. Good agreement with experimental data can be obtained, however, if H loss by lateral transport to the walls is taken into account.

Entropy of a column of gas under gravity

The statistical thermodynamics of a classical ideal gas column of height H in a uniform gravitational field g has been treated by the canonical ensemble at temperature T. A key parameter is X≡mgH/kT where m is the mass of a particle. The internal energy U rises with X from 1.5 NkT at X=0 where N is the number of particles. If extrapolated beyond the region of applicability U reaches 2.5 NkT at X=∞. On the other hand, the entropy drops to zero (as X is increased) at a critical value XC of X, at which the model has already failed. The value of XC rises, extending the range of validity of the model, (a) as the gas becomes more dilute, (b) as the temperature is increased, and (c) as the particle mass is increased. The ideal quantum gas, treated by the grand canonical ensemble, leads to results consistent with those obtained from the canonical ensemble.

Modeling of anaerobic corrosion influenced by sulfate‐reducing bacteria

ABSTRACT: A laboratory experiment was conducted to investigate the corrosion influenced by sulfate‐reducing bacteria (SRB). A mathematical model was developed and fitted to the pitting depths measured at 0.1 and 0.5 mM sulfate concentrations. The model was successful in predicting the pitting depth at two different sulfate concentrations when the kinetic variables reported in the literature were used. The deepest pitting depths were observed to be approximately 0.19 and 0.39 mm for bulk sulfate concentrations of 0.1 and 0.5 mM after 150 days of exposure, respectively. The pitting depths were predicted to be 0.17 and 0.36 mm for bulk sulfate concentrations of 0.1 and 0.5 mM after 150 days of simulation, respectively. The steady‐state pitting depth was predicted to be 0.48 mm for a bulk sulfate concentration of 0.5 mM after 400 days of simulation. The model was most sensitive to the sulfate diffusion coefficient (DSO42−), closely followed by the maximum sulfate utilization rate (q), and the biomass concentration (Xc), but it was less sensitive to the half‐velocity coefficient (Km). At the initial stage, the pitting depth was affected only by q and Xc. As the pitting depth increased, however, the diffusion of sulfate in the reaction zone became one of the dominant limiting factors. The decrease in the q or Xc value by 20% resulted in the increase in the pitting depth by 19%.

Use of spike triggered averaging of muscle activity to quantify inputs to motoneuron pools

1. The goal of this study was to determine the extent to which postspike facilitation (PSpF) of electromyograms (EMGs) could be used to estimate the inputs to separate motoneuron pools, under conditions where there was wide variability in the parameters of muscle activity. These parameters included cancellation of motor unit action potentials (MUAPs), variations in EMG noise, and changes in MUAP amplitude and duration. A systematic series of computer simulations with increasing complexity were used to achieve this goal. The initial simulations (model I) included a premotoneuronal (PreM) cell connected to a single postsynaptic motoneuron (Mn), which in turn projected to a muscle. The next simulations (model II) included other target motoneurons with their efferents each projecting to separate muscles. The last simulations (model III) included more than one postsynaptic motoneuron per Mn-pool, as is the case in mammalian neuromuscular systems. 2. A sample simulation (model I) was performed to determine if the PreM-evoked effects were within physiologically observed values. A cross-correlogram (XC) calculated from a PreM cell and its target Mn, receiving a PreM-evoked excitatory postsynaptic potential (EPSP) of 0.5 mV, produced a XC peak area of 0.04 Mn-spikes/PreM-trigger. The PSpF of EMG activity evoked by this PreM cell had a mean percent increase of 4.6% (MPI = mean bin amplitude of PSpF above baseline/mean baseline level x 100). These XC and PSpF values were within the range of values previously obtained from animal experiments. 3. The magnitude of MUAP cancellation in the EMG was tested by calculating two spike-triggered averages (SpTAs) of EMGs from Mn-triggers (not PreM-triggers as in the other SpTAs): one using typical bipolar MUAPs and another using their rectified counterpart of only positive polarity to eliminate the possibility of MUAP cancellation. The PSpF calculated from bipolar spikes was 24.8% smaller than the one calculated using unipolar spikes. This cancellation could be greater or smaller depending on the state of parameters, such as the shape and number of MUAPs, that determine the probability of overlap between MUAP components of opposite polarity. All subsequent computer simulations used typical bipolar MUAPs. 4. A series of increasing motoneuron EPSP amplitudes were used to determine the relationship between PreM-Mn connection strength and PSpF area. A nearly perfect linear relationship between EPSP amplitude and PSpF area was obtained for SpTAs of rectified EMGs (r = 0.99). An equally linear relationship was obtained when averaging nonrectified EMGs (r = 0.99), but the smaller EPSPs or weaker synaptic connections were not detected.(ABSTRACT TRUNCATED AT 400 WORDS)

The Diagram Technique for Calculation of Transport Constants of Random Inhomogeneous Materials. II. Low‐Field Hall Effect

AbstractDiagram methods are applied for evaluating the off‐diagonal (Hall) components of the ac effective magnetoconductivity tensor σ(ω) in an inhomogeneous material for the case of low magnetic field. Closed expressions for σ(ω) are obtained in two approximations, namely in the self‐consistent cumulant approximation and in the effective‐medium approximation (EMA). Our expression for σ(ω) in the EMA coincides with the one obtained earlier by Fishchuk. The obtained results are applied to the model of a random binary mixture consisting of two conducting materials 1 and 2 with conductivity tensors σ and σ and volume fractions x and 1 − x, respectively. In the special case of σ = 0 and ω = 0 the (dc) Hall conductivity σ in both above‐mentioned approximations has a percolation threshold at some critical value Xc. In each approximation the value of xc coincides with the one for the dc diagonal (ohmic) conductivity σ* taken in the same approximation: the self‐consistent cumulant approximation gives xc = 1 – exp (−1/3), while in the EMA xc is equal to 1/3.

Crystalline Fraction of Microcrystalline Silicon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Using Pulsed Silane Flow

Microcrystalline silicon (?c-Si) films have been prepared at 200?C by radio-frequency (rf: 13.56 MHz) plasma-enhanced chemical vapor deposition using pulsed silane flow. The crystalline fraction, Xc(Raman), of ?c-Si films approximately 200 nm thick is quantitatively determined by decomposing Raman spectra into three peaks: crystalline, intermediate (small-grain-size-crystalline), and amorphous. The effects of rf power on Xc(Raman) and hydrogen content, CH, have been studied. Xc(Raman) increases with increasing rf power and tends to saturate; the maximum value of Xc(Raman) is 71%. With increasing rf power CH decreases to a minimum value of 4.5% and then increases. Hydrogen introduction into Si films overlapped with hydrogen elimination is responsible for the increase and saturation of Xc(Raman) with rf power.

Crystallinity Analysis of Amorphous-Crystalline Mixed Phase Silicon Films Using EXAFS Method

The crystalline phase fraction (Xc) of amorphous-crystalline mixed phase Si films prepared by thermal annealing of a-Si:H films and by plasma CVD and chemical annealing methods was investigated by an EXAFS method. The EXAFS spectra of these films were represented by linear-combination of a-Si:H and c-Si EXAFS spectra. The values of Xc were analyzed by least-square curve fitting. Furthermore, the Xc values analyzed by a conventional Raman method were calibrated by the EXAFS analysis results.