In general, gases are considered to be very good insulators. On a macroscopic scale the electrical current through a gas volume is very small. To measure these currents a high level of measurement technique is necessary: digital multimeters are usually suitable for measuring currents greater than 1 µA. For low current measurements, picoammeters are required, triaxial cables must be used to achieve a good guarding of the signals and the overall measurement setup must also be shielded from electromagnetic interference in order to min- imize the noise level (Zhou et al., 2012; TEKTRONIX Inc., 2013). That is why this sensor principle is not attractive on a macroscopic scale. The manufacturing of a gas chamber with electrodes at a distance of some 100 nm provides a chance to use electrical conductivitymeasurements for the measure- ment of low pressure. Even if gases are considered to be very good insulators, there is always a small number of charge carriers depending on the gas pressure. The miniaturization of the MEMS-type gas chamber leads to an increase in the electrical conductance of the device and thus to an increase in the currents to be measured. This reduces the requirements of measurement technique and opens up an interesting new measurement concept for the determination of vacuum pres- sures.
Thin films of poly(methyl methacrylate)–multiwalled nanotubes composites were produced by spin coating using different nanotube concentrations. The materials were characterized by scanning electron microscopy, energy-dispersive x-ray analysis, and Raman spectroscopy to obtain information on the possible interactions between the constituents and to control the homogeneity of the films. Electrical conductivitymeasurements of the composites, as a function of the nanotube concentration, show a percolation threshold at very low concentration. Also, the J–E characteristics exhibits a nonlinear behavior at low concentration, becoming linear far above the threshold.
the membrane ionic conductivity under a wide range of conditions is essential in the process of developing new membranes to replace Nafion . Therefore, it is desirable to have a simple and cost effective test system that allows conductivitymeasurements without using much of the costly platinum catalyst.
In this work, marble specimens were subjected to uni- axial compressive stress in order to cause damage to their bulk. After each stress application and while the speci- men remained unstressed two sets of ac conductivitymeasurements were conducted in the frequency range between 1 kHz and 1 MHz. During the first set of meas- urements the specimen included its natural moisture while during the second set the natural moisture of the specimen was removed after heating. Initially, pilot ac conductivitymeasurements were conducted for all the specimens used.
In the original study of this event [Kosch et al., 1998] an important point was that, for the first time using ground-based data, it was possible to identify the spatial region, associated with an auroral arc, which constituted a closed current sheet pair linked to the magnetosphere. This was possible since the plasma vortex was causally linked to the arc and hence the region of downward FAC was likewise causally linked to the arc, i.e., a region of upward FAC. Figure 6b shows the previous result in the same format as Figure 6a. Figure 6b is a copy of Figure 8 of Kosch et al. , reproduced for comparison purposes. This earlier work did not include the SMA data; hence no conductivitymeasurements were available. Figure 6b was generated by assuming a uniform conductance (1 S) and computing the FACs solely from the divergence of the STARE electric fields. This corresponds to using only the first term of (4). It is seen that a much more localized region (160 ⫻ 20 km) of downward current results [Kosch et al., 1998] when com- pared to Figure 6a. The expanded region of downward current in Figure 6a results directly from horizontal conductivity gra- dients (see Figure 5a), which previously could not be ac- counted for. The spatial grid used in the method of character- istics (50 ⫻ 80 km), which is limited by the SMA data as explained earlier, could also contribute to the smearing out of the region of downward current. However, this is a secondary effect. In Figure 6b the grid size is much smaller (20 ⫻ 20 km) because it is limited by the STARE data only. Had there been no horizontal conductivity gradients, Figures 6a and 6b would be identical except for a simple scaling factor. Auroral precip- itation produces significant horizontal conductivity gradients, which cannot be ignored when computing FACs.
We want to conclude on the interest of the “crimping” process used to produce the glass wool and to make a comparison for anisotropic factor obtained from structural property (air permeability) as well as thermal property (thermal conductivity and diffusivity). The main structural (densities, porosity, specific surface, air permeability) and the thermal (conductivity, diffusivity, heat capaci- ty) characteristics of this glass wool are presented. Thermal results are determined by using sev- eral methods (Hot disc (HD), Heat Flow Meter (HFM) and Guarded Hot Plate).
To our knowledge, there is no comprehensive study of transport properties in thin films of CNT/cellulose complex, where the role of cellulose is explicitly that of a dispersant. Hamedi et al.  reported nanocellulose dispersed CNT films, or composites, with a conductivity on the order of 100 S/cm, which is a rather high level, but lower than what is reported for pure SWNT materials . An effective method for dispersing CNTs using hemicellulose (Xylan) as a dispersant material has previously been reported by two of the authors in a patent. In this paper, we report on transport measurements in thin films consisting of CNT-hemicellulose (CNT-hc) prepared using this method. These include low temperature transport, high frequency (terahertz) conductivitymeasurements, and Kelvin Probe Force Microscopy (KPFM) measurements of the local conductive properties on the current carrying CNT-hc devices. Computational and experimental studies on the microscopic nature of this complex will be reported in a companion paper.
hand, and X-ray microtomography (34 µm pixel size) on the other hand, compose the experimentation campaign. Water retention and hydraulic conductivitymeasurements are used frequently in other studies to show the effect of tillage in- tensity on soils. Furthermore, they are linked together and can lead to different estimations of the same parameter. This choice enables us to validate microtomographic results and to use the latter as an explanatory element of the fun- damental processes highlighted by macroscopic measure- ments. However, the consistency of the results depends on the quality of the tomographic reconstructions. Quality is, among other factors, correlated with acquisition time. As a result microtomography as a hydraulic measurement tech- nique is often considered as time-consuming in comparison with other techniques. In our study, we show that relatively fast scans supply not only a good match with other mea- surements, but also improve retention and hydraulic curves modelling near saturation (| h | < 10 mbar). Microstructural parameters calculated on the pore network appear to be of interest to characterize tillage differences. These elements make microtomography a competitive instrument for routine soil characterization.
Although the determination of thermal conductivity has focused most efforts, it is believed that viscosity is as critical as thermal conductivity in engineering sys- tems that entail fluid flow [8,14-16]. Pumping power is proportional to the pressure drop, which in turn is related to fluid viscosity. In laminar flow, the pressure drop is directly proportional to the viscosity. Both visc- osity and thermal conductivity of nanofluids are known to undergo anomalous enhancements, but more thor- ough investigations should be carried out on these prop- erties because a good deal of controversy and remarkable inconsistencies have been reported in this emerging subject . The monograph published by Das et al.  represents a reference study about nano- fluids, including a wide literature survey, which is indi- cative of the efforts done in the last few years. A recent collective study  intended to establish a benchmark for thermal conductivitymeasurements by comparing the results obtained from a common sample delivered to many reference laboratories. The results yielded dif- ferences between 5% and 10% for data of water and PAO-based samples from different sources. In other recent studies concerning thermophysical characteriza- tion of nanofluids, Das et al.  and Eastman et al.  presented a good account about nanotubes and the role of the contact resistance in the thermal transport of nanofluids, besides addressing the issues about thermal conductivity and viscosity of oxide nanoparticle-based and metallic nanofluids. Wang and Mujumdar  pre- sented an overview focused on heat transfer characteris- tics using nanofluids, and Murshed et al.  remarked that it is imperative to conduct detailed research in order to confirm the effects of particle size, shapes, clus- tering of particles, and temperature on the effective thermal conductivity of a wide range of nanofluids and added that it is necessary to develop more comprehen- sive models, based on first principles, with the aim of accounting for the enhanced thermal conductivity of nanofluids. Li et al.  also discussed the preparation and characterization of nanofluids, a subject that unfor- tunately has not received the necessary attention so far but plays a key role. Wen et al.  and Murshed et al.  insisted on the need of studies about other proper- ties such as viscosity, wetting behavior, thermal diffusiv- ity, convective heat transfer coefficients, and viscosity;
The purpose of the present work is to understand the microstructure development and, particularly, to control the progress of recrystallisation in hot strip in the Al-Mg-Mn alloy AA 5454, which is typically used for the manufacture of structural automotive components. The chemical composition, together with the thermomechanical processing history of this material have a strong influence on the microstructure of the product and the ensuing properties as it is supplied to the customer. Electrical conductivitymeasurements, thermal analysis and electron microscopy have been carried out in order to characterise the evolution of precipitation state at various stages in the processing route. The conditions of the homogenisation heat treatment have been varied, and the effect on subsequent recrystallisation after hot rolling has been evaluated in both the as-cast and rough-rolled condition by optical microscopy techniques. Results indicate that the conditions of homogenisation heat treatment and roughing rolling are critical for the generation of a suitable recrystallised microstructure in AA 5454 hot strip. A new two-stage homogenisation practice has been developed to expedite post-rolling recrystallisation in this alloy.
20 and 30 wt%), were prepared via in situ polymerization technique using aniline and MZFO prepared using citrate auto-combustion route. The produced composites were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetry (TG), transmission electron microscopy (TEM) techniques. The effect of compositional variation on the electromagnetic properties of PANI was measured using vibrating sample magnetometer (VSM) and ac-conductivity as a function of temperature. The results of XRD and FT-IR indicated an interfacial interaction between PANI and MZFO crystallites. TEM images showed that MZFO particles are embedded in the PANI matrix and formed core-shell structure. TG curves exhibited an increase in the thermal stability of PANI with the addition of MZFO. The hysteresis measurements indicate an improvement in the magnetic properties by the addition of ferrite. The conductivitymeasurements confirmed the interaction between PANI and MZFO and showed a change from metallic to semi-conducting properties by the addition of MZFO.
Comsol Multiphysics. Comsol Multiphysics was applied to simulate and solve multi-physical tasks described by partial differential equations using the finite element method (FEM). Process modelling in Comsol Multiphysics consists of the following basic steps outlined in Comsol Multiphysics Humusoft. In our case, the Comsol Multiphysics program is used to simulate the distribution of the electric field in two and four-electrode conductivitymeasurements of biological tissue. In both cases, the same virtual model phantom with the identical conductivity and geometric dimensions was used. The geometric di- mensions have been corresponding to the dimensions of real phantoms, i.e. 11 × 11 × 3 cm. The value of conductivity selected for the virtual phantom was σ = 4 mS/cm, this conductivity value is correspond- ing to a healthy biological tissue.
to have antimicrobial activity comparable to that of standard drugs, viz. sulfamethoxazole, and sulfadiazine. The product have also been characterized by elemental analysis, absorption spectra, conductivitymeasurements, molecular weight determination, magnetic susceptibility measurements and stepwise stability constants by P H metric method. By using the results of above
show frequency dependence, it is difficult to obtain a constant phase angle behavior over a limited frequency range for inho- mogeneous unconsolidated aquifers; multiple frequency data are required to study the spectral behavior and to derive the K values. Our laboratory measurements of inhomogeneous sandy aquifers show a weak relationship between the mea- sured hydraulic conductivity and the maximum, median and weighted average relaxation time. Independently of the soil texture, soil compaction has an influence on both the con- ductive properties (Seladji et al., 2010) and the polarization response (Koch et al., 2011) of porous media. Accordingly, the weak correlation between K and τ can be attributed to the compaction and sieving of the core samples from prepar- ing the laboratory measurements (Koch et al., 2011). Con- sequently, other physical parameters, which show a relation with the measured K, are required to support the K–τ re- lationship. Since the aquifer resistivities show a positive di- rect relation with the measured K values, a multiplication of τ and aquifer resistivities shows a good power law rela- tionship to estimate the K. In our study, the logarithmically weighted average relaxation time shows superior results of predicting the K compared with the mean relaxation time used by Weller et al. (2010a) and the median relaxation time recommended by Zisser et al. (2010b).
The purpose of the present study is to reconstruct the val- ues of effective thermal conductivity of a thick snowpack and firn pack at Lomonosovfonna, Svalbard, based on evo- lution of subsurface temperature and firn density measured in 2012–2015. Effective thermal conductivity of firn is de- rived for five distinct periods by minimizing the misfit be- tween the measured and simulated subsurface temperature evolution. The method is promising, particularly for thick firn packs. To our knowledge it has not been applied for this purpose so far, although Sergienko et al. (2008) employed similar routines for a seasonal snowpack and Nicolsky et al. (2007) for permafrost. Fourier analysis applied earlier for a thick firn pack at the Summit Station of the Greenland Ice Sheet (Giese and Hawley, 2015) cannot be used here due to the influence of meltwater. Retrieval of snow and deep firn samples for direct measurements using heated plate or nee- dle probe methods is logistically challenging. Estimates of the firn k values are complemented by uncertainty quantifi- cation experiments exploring propagation of possible biases in empirical data through the applied models.
at the problem of variability in the actual course of weather (Lhotský 2000; Ulrich et al. 2003). First of all, mainly the low air temperature (generating the change of water state) and variable weight moisture of the upper soil horizons have some natural impacts on the set of physical, hydrophysical and soil-me- chanical properties. As regards the results presented in this study, the authors were aware of the described facts, therefore, they used a high number of measur- ing points on the monitored study plots with the fo- cus on a possibility of generalization. In general, the authors are clearly aware that climatic factors remain a significant fact regarding the informative value of the application of Guelph permeameter. During the measurements with Guelph permeameter, full satu- ration does not occur because some air is trapped in a part of the porous system; this space does not con- tribute to the final conductivity value. According to Kutílek et al. (2000), repeated measurements have shown that the obtained values are realistic and do not require any subsequent correction.
We also take the source f x ð ; y ; t Þ ¼ 5 þ 4jt 0 : 5j. The previous example has reconstructed the smooth timewise thermal conduc- tivity a t ð Þ given by (15). In this example, we assess the numerical reconstruction of a non-differentiable conductivity given by
undergone little decomposition; values close to zero indicate heavily decomposed peat. The shallower the depth at which peak C/N occurs, the greater the proportion of the peat proﬁle for which m can be esti- mated, and the closer m is to the true value of fractional remaining mass. Preliminary measurements of our own samples showed that, like Malmer and Holm , the subsurface peak in C/N occurred at shallow depths, indicating that plant N uptake was only important at our site in the uppermost 0.05–0.10 m. Our m necessarily overestimates the true value of fractional remaining mass because it does not account for decomposition losses that occur above the depth of the C/N peak, and should therefore be interpreted cau- tiously. However, we took the apparently conservative behavior of peat N at our site below 0.10 m as an indication that the approximation is a reasonable one. The method also assumes net immobilization of N below the C/N peak. Some of the recycled inorganic N will be translocated to the live moss capitulum [Malmer and Nihlgård, 1980] and taken up by vascular plant roots [Rosswall and Granhall, 1980]; N losses due to gaseous emissions of nitrous oxide, leaching of ammonium N, and net movement by microorgan- isms are likely to be negligible [Malmer and Holm, 1984]. The method also assumes that C/N quotients in fresh peat have remained approximately constant through time at each core location.
A field experiment was conducted to investigate the effect of soil properties on soya bean crop. The study has been carried out to determine the effect of soil physical- chemical properties on soya bean crop in the low precipitation area. The soil water content, resistivity, conductivity, P H and total dissolved solids were measured on the experimental field. The texture, gravimetric water content, volumetric water content, soil melting capacity, bulk density, porosity, water holding capacity and chemical compositions of the soil’s from the same fields were determined in laboratory. The profile probe (PR2) soil moisture measurement system was used to determine the soil water content and a two probe resistance meter was used to measure soil resistivity. The texture analysis of the soil samples was accomplished with mechanical sieves. The results show that the soil water content and resistivity required for the soya bean crop to grow and give good yield should be in the range of 26 to 43 percent cm 3 cm -3 and 177 to 340 K- Ohm-cm respectively. The P H should be neutral to slightly basic and conductivity should be non saline. The results also show that soya bean crop will grow in clayey as well as sandy loam soils.
As shown in Fig. 4, the temperature of the sample, standard, and heat source were recorded using surface temperature sensors (STS, supplied by Vernier, USA) and recorded using the LoggerPro software through Vernier LabQuest Mini. One sensor was embedded into the surface of the heat source via a shallow drilled hole, and the sensor monitoring the standard was affixed using a small amount of cyanoacrylate glue. The STS that measures the surface temperature of the sample directly was lightly ground to provide a constant surface area for the area of contact. Subsequently, the sensors (and the surfaces they were affixed in/on) were calibrated using LoggerPro’s calibration function against an ice bath, a 50°C sand bath kept in an oven (Fisherbrand Isotemp, Fisher Scientific, USA), and boiling water. Once the voltage readings from all the sensors were stabilized, the temperature of the sensors were set equal to the target temperature mentioned above. The hotplate was set to the desired final temperature, and the system was given an hour to equilibrate and allow the temperatures to stabilize, with each STS recording the temperature every 2 seconds. After the completion of each trial, a logistic fit was applied to each curve, in order to eliminate the relative temperature fluctuations and their effect on the calculation of the final thermal conductivity.