Conductivity Volume Research Articles

Improvement of electrocoagulation–electroflotation treatment of effluent by addition of Opuntia ficus indica pad juice

The aim of this study is the optimization of the effect of Opuntia ficus indica (OFI) pad juice on the electrocoagulation–electroflotation (EC–EF) water treatment process by response surface methodology (RSM). To estimate the efficiency of EC–EF technique assisted by Opuntia ficus indica pad juice, preliminary tests were conducted. The results obtained after RSM optimization for initial OFI pad juice volume, initial pH and initial conductivity were 0.016mL/L, 8.2, and 3.04mS/cm, respectively. Maximum predicted turbidity removal efficiency (TR %) under the optimized conditions was 87%±0.8, this predicted value was close to the experimental value of 86.9%±0.1. Compared to the conventional EC–EF (EC without OFI juice addition), which shows 71.9% of turbidity removal, the optimized cactus juice assisted EC–EF allows a turbidity removal enhancement of 15.1%. These results indicate suitability and validation of the employed model and the success of RSM in optimizing the EC–EF treatment conditions.

A three-dimensional shape design problem to determine the filler geometry for optimal system thermal conductivity

A three-dimensional shape design problem is considered in this work, based on the desired thermal conductivity ratio and filler volume, to determine the optimal shape of filler between two conductive bodies in a three-dimensional composite material. The Levenberg–Marquardt method (LMM), commercial software CFD-ACE + and B-spline surface generation technique are adopted in the present shape design algorithm. The design analysis is examined using the numerical experiments and different filler volume and thermal conductivity are considered in the numerical test cases to justify the validity of this study. The estimated results obtained with optimal filler are then compared with those using original filler shapes and it is found that (i) the optimal filler shapes are found as a family of “hourglass” shape with a smooth nozzle-diffuser shape in the central parts of filler and (ii) the radiuses of the top and bottom surfaces of filler play the most significant role on the effective thermal conductivity. Besides, by fixing the filler thermal conductivity, the effective thermal conductivities using optimal fillers can be increased from 15.3% to 47.6% depending on different filler volumes and by fixing the filler volume, the effective thermal conductivities using optimal fillers can be increased from 5.5% to 57.4% depending on different filler conductivities.

Oscillatory blood pressure response to the onset of cycling exercise in men: role of group III/IV muscle afferents.

What is the central question of this study? Neural feedback from groupIII/IV muscle afferents has a key role in regulation of cardiovascular responses to exercise. Blood pressure oscillates in the first seconds of dynamic exercise, but the contribution of muscle afferent feedback to this pattern is unclear. What is the main finding and its importance? We demonstrate that attenuation of groupIII/IV muscle afferent feedback by spinal fentanyl impairs the pressor response after 10s of moderate leg cycling exercise, but this afferent feedback does not appear to be necessary for induction of the oscillatory pattern of blood pressure at the onset of exercise. We investigated whether attenuation of the central projections of groupIII/IV skeletal muscle afferents via lumbar intrathecal administration of the μ-opioid receptor agonist fentanyl affects the oscillatory blood pressure (BP) response to the onset of dynamic exercise. Eight healthy, recreationally active men (28±3years old) performed 40s of cycling at 80W (60r.p.m.) before (control) and after fentanyl administration, while heart rate, stroke volume, cardiac output, systolic, mean and diastolic BP and total vascular conductance were continuously monitored. Sytolic and mean BP responses to cycling included an initial increase (from 0 to 3s), followed by a transient decrease below resting levels (from 3 to 10s) and then a sustained increase (>10s). In the presence of fentanyl, systolic and mean BP responses closely matched those in control conditions in the first 10s, but were blunted thereafter (P<0.05). In contrast, fentanyl did not modify the heart rate, stroke volume, cardiac output, diastolic BP or total vascular conductance responses to 40s of cycling (P>0.05). These findings suggest that during moderate leg cycling exercise the muscle afferents contribute to the BP response after ∼10s, but that they do not appear to be implicated in the oscillation of BP at the onset of exercise.

Alternative functional criteria to assess airflow-limitation reversibility in asthma

IntroductionInternational guidelines define significant bronchodilator response as absolute and percentage change from baseline in forced expiratory volume (FEV1) in the first second and/or forced vital capacity (FVC) ≥12% and 200mL. However, bronchodilator effects on other lung function parameters have also been correlated to some degree of reversible airflow limitation. ObjectivesTo determine whether changes in other lung function parameters apart from FEV1 and FVC detect functional responses to bronchodilator in asthmatic patients. Materials and methodsSpirometry and body plethysmography were performed at baseline conditions and after administration of 400μg of salbutamol by metered-dose inhaler through a space chamber device in asthmatic patients. Paired t-tests were used to compare lung function parameters between those with and without criteria for reversibility of airway obstruction according to ATS/ERS criteria. Cut-off values were obtained from the corresponding ROC curves. Measurements evaluated were FEV1, FVC, maximum mid-forced expiratory flow (FEF25–75%), residual volume (RV), inspiratory capacity (IC), airway resistance (Raw) and specific airway conductance (sGaw). ResultsFrom a total of 100 consecutive asthmatics patients (46% of them men; average age 58.7±14.1 years; 76% with mild to moderate obstruction), 50 patients had a significant bronchodilator response. All of these had noteworthy variations (p<0.004) in PEF, FEF25–75%, RV, Raw and sGaw. The most accurate in predicting a significant bronchodilator response were the absolute and percentage improvements in PEF (≥0.4L/s and 8%), FEF25–75% (≥0.087L/s and 27%) and the percentage of sGaw compared with that at baseline (≥25%). Based on these cut-off values, a sizeable number of the patients defined as non-responders had important changes in airway caliber. 17 patients had significant increments in the percentage of PEF and 10 had changes in absolute volume; 6 patients had increments in percentage and 16 in absolute change of FEF25–75%; 22 patients had increments in the percentage change of sGaw. ConclusionsChanges of FEV1 and/or FVC may underestimate significant functional response to bronchodilators in asthmatic patients with airway obstruction when considering the change in other lung function parameters.

Heat transfer performance of silver/water nanofluid in a solar flat-plate collector

An experimental study is carried out to investigate the heat transfer characteristics of silver/water nanofluid in a solar flatplate collector. The solar radiation heat flux varies between 800 W/m2and 1000W/m2, and the particle concentration varies between 0.01%, 0.03%, and 0.04%. The fluid Reynolds number varies from 5000 to 25000. The influence of radiation heat flux, mass flow rate of nanofluid, inlet temperature into the solar collector, and volume concentration of the particle on the convective heat transfer coefficient and the collector efficiency are studied. Both parameters increase with increase in the particle volume concentration and flow rate. The maximum percentage increase obtained in the convective heat transfer coefficient is 18.4% for the 0.04% volume concentration at a Reynolds number of 25000. An increase in the performance of nanofluid is also witnessed when compared to the base fluid, which has a strong dependency on volume concentration and mass flow rate. MgO. The nanofluid achieved a 3°C temperature difference during the daytime peak solar radiation compared with the base fluids. With a concentration of 0.2% ZnO, a temperature difference of 2.55°C for daytime and 1°C for nighttime was reached, and this was determined to be the most attractive option for solar energy utilization. Yousefi et al. [15] witnessed a 28% performance improvement in a flat-plate collector when it was operated with water-Al2O nanofluids. Tyagi [16] theoretically compared the conventional flat-plate collector with a direct absorption solar collector (DAC) and observed the former to be 10% more efficient. Otanicar [17] studied the conomic and environmental influences of using nanofluids to enhance solar collector efficiency with conventional solar collectors. Dongxiao et al. [18] presented excellent photothermal properties of carbon-black aqueous nanofluids at highvolume fractions. Further work on nanofluids’ application to direct solar absorption has been carried out by Lijuan Mu [19] using a custom-made direct solar absorber. The radiative properties of several nanofluids are tested for the highest temperature difference across the heat exchangers. Based on the above-mentioned review of the literature, it has been clearly observed that most of the previous studies on solar flat-plate collectors were conducted using metal oxide nanoparticles in relatively high concentrations. These high concentrations of metal oxide nanoparticles cause a higher pressure drop that then requires a higher pumping power. Since a limited number of studies exists in the literature with respect to pure metal nanoparticles, it is recommended to study the heat transfer characteristics of pure metal nanoparticles with relatively low concentrations (<1%) by volume and high thermal conductivity compared with metal oxides. Therefore, in the present study, the efficiency of a solar flat-plate collector is studied with a low particle volume concentration of less than 0.04% silver-water nanofluid. These experiments are conducted for a solar radiation flux ranging from 800 W/m2 to 1000 W/m2, and the Reynolds number varying from 5000 to 25000. The effect of radiative heat flux, mass flow rate, inlet temperature, and volume concentration on the convective heat transfer coefficient and the collector efficiency are studied. The tailormade setup for a collector area is 2.4m2 and the collector plate is made of nine parallel copper strips

Hierarchical carbon nanocages confining high-loading sulfur for high-rate lithium–sulfur batteries

Lithium–sulfur batteries are hindered by the low utilization of sulfur, short cycle life and poor rate capability which are severe challenges today. Herein we report a new kind of carbon–sulfur composites by infusing sulfur into the novel hierarchical carbon nanocages (hCNC) with high pore volume, network geometry and good conductivity. The designed S@hCNC composite with a high sulfur loading of 79.8wt% presents the large capacity, high-rate capability and long cycle life, which could shorten the charging time for mobile devices from hours to minutes. The excellent performance derives from the unique mesostructure of hCNC that enables the encapsulation of high-loading sulfur inside the carbon nanocages to alleviate polysulfide dissolution, meanwhile much enhance the electron conduction and Li-ion diffusion.

Density, Viscosity, and Conductivity of Binary Mixtures of the Ionic Liquid N-(2-Hydroxyethyl)piperazinium Propionate with Water, Methanol, or Ethanol

The densities, viscosities, and electrical conductivities of the binary systems of the ionic liquid (IL), N-(2-hydroxyethyl)piperazinium propionate ([(OH)2C2pi][C2CO2]), with three protic solvents (water, methanol, or ethanol) were measured in the IL concentration range from (0.05 to 3.00) mol·kg–1 at different temperatures T = (293.15 to 323.15) K and atmospheric pressure p = 0.1 MPa. The concentration dependences of apparent molar volume, viscosity, and electrical conductivity of the binary mixtures were correlated by the Pitzer equation, the Jones–Dole equation, and the Casteel–Amis equation, respectively. It is observed that both the density and viscosity increase with the elevated IL concentration or the decreased temperature. The electrical conductivity at a given IL concentration increases with the temperature, while the conductivity at a given temperature changes clearly against the IL concentration, and a maximum value can be observed. The measured results and the correlations present help for a ...

Features of Electroconductivity of γ-Irradiated Composites in Heating-Cooling Conditions

It has been studied the behavior of temperature dependence of volume electroconductivity σ on direct current (DC) of composite medium of high-density polyethylene/α-Fe2O3 in the field of T=20-1350C within heating-cooling conditions before and after γ-irradiation at dose up to 500kGy. At lgσ(T) dependence of unirradiated composites while heating at low and high temperatures besides linear sections, it is observed the region of sharp decrease at 50-800C, associated with dipole orientation processes of adsorbed water molecules. At lgσ(T) dependence of composite samples irradiated at D=100kGy there is not any region of sharp decrease σ. It is shown that after γ-irradiation by dose D=500kGy the second maximum appears on the curve of forward trace of the composite HDPE+ 10%α-Fe2O3 at T=800C, which can be the result of change in the state of quasi-Fermi level. Behavior of lgσ(T) function at heating-cooling is explained by the “asymmetry” effect of electrically active defects. It is shown that the increase in volume conductivity after γ-irradiation is weakly expressed.

Measuring the Electrical Properties of MWNT‐PA6 Reinforced Nanocomposites

The paper studies the electrical properties of polyamide 6‐ (PA6‐) carbon nanotubes (CNTs) nanowebs, obtained through electrospinning. Three different treatments (chemical, mechanical, and mixed) were applied to the CNT in order to prepare the electrospinning solutions. For each treatment, the CNT content was different: 0.5%, 1%, 1.5%, and 2%. The electrical volume and surface conductivity of the obtained samples were studied by measuring their electrical volume and surface resistance. Homemade plate electrodes were used. The samples were also analyzed using a scanning electron microscope (SEM) and an atomic force microscope (AFM). Defects were found on the extremities: solvent traces, flat fibers, and beads. The mixed treatment seems too aggressive and it is not recommended. The AFM analysis gave values for roughness and profile height (Ra and Rz): extreme values were obtained for the chemically and mechanically treated samples. Next, a pristine PA6 sample was used to compare the influence of the CNT content on the electric behavior of the samples. By increasing the pressure on the specimens, the volume resistivity decreased exponentially, while the surface resistivity showed no significant changes, independently of the CNT content. The obtained behavior proves a great potential of the MWNT‐PA6 reinforced nanocomposites for sensor applications.

Thermally controlled growth of carbon onions within porous graphitic carbon-detonation nanodiamond monolithic composites

The addition of detonation nanodiamond to carbon monolithic composites has improved graphitic nature, pore volume, surface area and thermal conductivity.

Electromagnetic interference shielding properties of carbonyl iron powder-carbon fiber felt/epoxy resin composites with different layer angle

Carbonyl iron powder-carbon fiber felt/epoxy resin composites with different layer angles were prepared to evaluate electromagnetic interference shielding properties in the X band. The average shielding effectiveness decreased from 53.9dB to 8.6dB with increase in the layer angle from 1.98° to 84.6°. The average power absorption coefficient increased first and then decreased, and had a maximum value at about 45°. The volume conductivity and the average dielectric constant decreased with increase in layer angle. It is found that the composites shield by absorption and reflection and the ratio depends on layer angle.

The influence of nanofiller alignment on transverse percolation and conductivity

Nanocomposites have unprecedented potential for conductivity-based damage identification when used as matrices in structural composites. Recent research has investigated nanofiller alignment in structural composites, but because damage identification often requires in-plane measurements, percolation and conductivity transverse to the alignment direction become crucial considerations. We herein contribute indispensable guidance to the development of nanocomposites with aligned nanofiller networks and insights into percolation trends transverse to the alignment direction by studying the influence of alignment on transverse critical volume fraction, conductivity, and rate of transition from non-percolating to percolating in three-dimensional carbon nanotube composite systems.

Effect of catalytic graphitization on the electrochemical behavior of wood derived carbons for use in supercapacitors

Porous graphitic carbons were successfully obtained from wood precursors through pyrolysis using a transition metal as catalyst. Once the catalyst is removed, the resulting material mimics the microstructure of the wood and presents high surface area, open and interconnected porosity and large pore volume, high crystallinity and good electrical conductivity, making these carbons interesting for electrochemical devices. Carbons obtained were studied as electrodes for supercapacitors in half cell experiments, obtaining high capacitance values in a basic media (up to 133 F g−1 at current densities of 20 mA g−1 and 35 F g−1 at current densities of 1 A g−1). Long-cycling experiments showed excellent stability of the electrodes with no reduction of the initial capacitance values after 1000 cycles in voltammetry.

Enhanced conductivity of sol-gel silica cladding for efficient poling in electro-optic polymer/TiO2 vertical slot waveguide modulators.

We report the enhanced conductivity of sol-gel silica under-cladding for efficient poling of electro-optic (EO) polymer in a hybrid EO polymer/TiO2 vertical slot waveguide modulator. The electrical volume conductivity of sol-gel silica cladding increases approximately 30 times when the calcining time of the cladding layer is critically reduced to 45 minutes, which increases the in-device EO coefficient of the 600-nm-thick EO polymer film in modulators and reduces the lower halfwave voltage (Vπ) of the modulators. The lowest driving voltage (Vπ) of the TiO2 slot waveguide modulator is 2.0 V for an electrode length (Le) of 10 mm and wavelength of 1550 nm (VπLe = 2.0 V·cm) for the low-index guest-host EO polymer SEO125. The optical propagation loss is reduced to 7 dB/cm.

Effect of carbon nanotubes addition on properties of 0–3 pyroelectric ceramic/polymer composites

0–3 pyroelectric ceramic/polymer composites were fabricated using (Pb[(Mn1/3 Nb2/3)1/2(Mn1/3Sb2/3)1/2]0.04(Zr0.05Ti0.95)0.96O3)(PZT) and Poly(vinylidene fluoride) (PVDF) by hot-pressing technology. The influences of carbon nanotubes (CNTs) on the volume conductivity, specific heat capacity, dielectric, piezoelectric, and pyroelectric properties were discussed. The results indicated that the CNTs acted as a conductive phase which is helpful to improve the conductivity of the composites and thereby enhance the pyroelectric properties. With the increasing CNTs content, the specific heat capacity of the composites decreased, while the dielectric constant, dielectric loss and volume conductivity all exhibit an increasing trend. As a result, the piezoelectric strain factor (d 33 ), pyroelectric coefficient (p) and figure of merit (F D ) are all significantly improved. And 0.9 wt% CNTs corresponds to the maximum d 33 , p and F D . It was concluded that CNTs-addition was an effective method to enhance the piezoelectric and pyroelectric performance of the composites.

Growth of MgF2 optical crystals and their ionic conductivity in the as-grown state and after partial pyrohydrolysis

MgF2 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF2 crystals by impedance spectroscopy. The characteristics of ionic conductivity of “as grown” (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σv = 1.4 × 10−7 S/cm at 773 K and the ion-transport activation energy Ea = 1.40 ± 0.05 eV. Annealing MgF2 crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ∼1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF2 crystals on their optical transmission is studied in the wavelength range of 115–300 nm.

Enhanced electrical properties in 0–3 pyroelectric composites doped with nano carbon black powder

0–3 (Pb[(Mn1/3Nb2/3)1/2(Mn1/3Sb2/3)1/2]0.04(ZrxTi1-x)0.96O3)(PZT)/carbon black/Poly (vinylidene fluoride) (PVDF) pyroelectric composites were prepared by hot-pressing technology. The volume conductivity, specific heat capacity, dielectric, piezoelectric and pyroelectric properties of the composites with various nano carbon black powder contents were discussed. The results showed that the nano carbon black powder acted as a conductive phase which could improve the conductive of the composites, thereby enhance the electrical properties. With addition of 0.9 wt% nano carbon black powder, the composites exhibited the best pyroelectric property, which was about 1.3 times of those composites without nano carbon black powder. It is concluded that nano carbon black powder doping is an effective method to improve the pyroelectric performance of the composites, which is good candidate for the future infrared detector application.

Density improvement of Si quantum dots embedded in Si-rich silicon nitride films by light-filtering rapid thermal processing

Si-rich silicon nitride (SRSN) (SiNx, x ≈ 0.49) films were deposited on Si (100) and quartz substrates by magnetron co-sputtering. For comparison, two sets of identical samples were then treated in a nitrogen atmosphere by conventional rapid thermal processing (CRTP) and light-filtering rapid thermal processing (LRTP) at temperature in a range of 950–1,100 °C, respectively. Raman spectroscopy, grazing incident X-ray diffraction, transmission electron microscope, photoluminescence (PL) and Hall measurements were used to analyze the structure, luminescence, and conductivity of the films. Experimental results show that the samples treated with LRTP posses higher dot number density, crystalline volume fraction, PL intensity and conductivity than the CRTP samples. The quantum effects in rapid thermal processing have a negative influence on the formation and density of Si quantum dots (QDs) in SRSN films. The present work opens new strategy for the formation of high density Si QDs embedded in SRSN films.

Conductivity and dielectric properties of heterogeneous films based on homo- and copolymers of methyl (methacrylate) and vinyl pyrrolidone doped with ionic liquid

Poly(methyl methacrylate) (PMMA), poly(methyl methacrylate-co-vinyl pyrrolidone) (PMMA-co-VP) and ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) have been used to prepare the micro or macro heterogeneous polymer films by a solution casting method in acetone and chloroform as solvents. The resulted films were studied by means of the alternating current conductometry and optical microscopy methods. The frequency dependences of specific volume conductivity, dielectric constant and tangent loss were obtained. The influence of a polymer matrix and solvent nature on ionic conductivity was analyzed. For PMMA/BMIPF6 formed in chloroform as macro heterogeneous film, a higher conductivity of 0.6×10−5S/cm (25°C) was achieved. The conductivity of phase separated heterogeneous polymer/ionic liquid films was proposed to depend on a size of ionic liquid droplets captured by polymer matrix.

Pt/3D-graphene/FTO electrodes: Electrochemical preparation and their enhanced electrocatalytic activity

We report a facile, low-cost and green route to fabricate platinum nanoparticle (Pt NP) decorated three-dimensional (3D) graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of 3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the 3D architecture and a large amount of ridges on it.