Hall Equation Research Articles

Experimental studies on rheological, mechanical, and microstructure properties of self‐compacting concrete containing perovskite nanomaterial

AbstractThis article presents the effect of LaSrCoO3, oxides commonly known as LSCO nanomaterials, on rheological, mechanical and microstructural properties of self‐compacting concrete (SCC). LSCO nanomaterials contents of 1–4 wt% are considered in this study. Compressive, flexural and split tensile strengths of SCC mixes are evaluated at curing ages of 7, 28, and 90 days. The effect of LSCO nanomaterials on the microstructures of above concretes is also evaluated using Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, thermogravimetric analysis techniques, Williamson–Hall equation, and X‐Powder software. Results show that workability of SCC mixes decrease with increase in LSCO nanomaterials. Increases are observed in compressive, flexural and split tensile strengths in SCC mixes when LSCO nanomaterials contents increase up to 2 wt%, followed by a decreasing trend which indicate 2 wt% as being the optimum amount. The microstructural analysis by means of various techniques also revels compact microstructure of cement matrix in SCC mixes containing 2 wt% LSCO nanomaterials, confirming the results of mechanical properties.

ALTERNATIVES TO ESTIMATE THE VOLUME OF INDIVIDUAL TREES IN FOREST FORMATIONS IN THE STATE OF MINAS GERAIS, BRAZIL

The objective of this study was to compare different alternatives to estimate the stem volume of individual trees in four different forest formations in the Minas Gerais state, Brazil. The data were obtained in a forest inventory procedure performed by the Minas Gerais Technological Center Foundation. The stem volumes were computed by the Smalian expression up to the outside bark diameter equal to 4 cm. The volume data of outside bark, diameters (DBH) and total heights were used to fit a Schumacher and Hall equation for each forest formation, considering the structures of the linear fixed and mixed models. Next, 100 Multilayer Perceptron artificial neural networks (ANN) were trained in a supervised manner. In addition, we evaluated eight support-vector machine regression (SVMR). The criteria to evaluate the performance of all the alternatives studied were: the correlation between the observed and estimated volumes, the square root of the mean square error and the frequency distribution by percentage relative error class. After the analyzes, all the alternatives were verified to estimate the volume of the individual trees in the different forest formations. Although the alternatives presented close statistics in the validation process, the graphical analysis of the error distribution showed greater precision of the estimates of the mixed linear models for the four formations. Given the results, it is concluded that there is no absolute superiority of one alternative over the others, and that all of them should be evaluated to find the one which best describes or explains the dataset.

Allometric Equations for Predicting Agave lechuguilla Torr. Aboveground Biomass in Mexico

Quantifying biomass is important for determining the carbon stores in land ecosystems. The objective of this study was to predict aboveground biomass (AGB) of Agave lechuguilla Torr., in the states of Coahuila (Coah), San Luis Potosí (SLP) and Zacatecas (Zac), Mexico. To quantify AGB, we applied the direct method, selecting and harvesting representative plants from 32 sampling sites. To predict AGB, the potential and the Schumacher–Hall equations were tested using the ordinary least squares method using the average crown diameter (Cd) and total plant height (Ht) as predictors. Selection of the best model was based on coefficient of determination (R2 adj.), standard error (Sxy), and the Akaike information criterion (AIC). Studentized residues, atypical observations, influential data, normality, variance homogeneity, and independence of errors were also analyzed. To validate the models, the statistic prediction error sum of squares (PRESS) was used. Moreover, dummy variables were included to define the existence of a global model. A total of 533 A. lechuguilla plants were sampled. The highest AGB was 8.17 kg; the plant heights varied from 3.50 cm to 118.00 cm. The Schumacher–Hall equation had the best statistics (R2 adj. = 0.77, Sxy = 0.418, PRESS = 102.25, AIC = 632.2), but the dummy variables revealed different populations of this species, that is, an equation for each state. Satisfying the regression model assumptions assures that the predictions of A. lechuguilla AGB are robust and efficient, and thus able to quantify carbon reserves of the arid and semiarid regions of Mexico.

Structural, morphological, optical and dielectric investigations in cobalt doped bismuth ferrite nanoceramics prepared using the sol-gel citrate precursor method

In this work, the synthesis of un-doped and cobalt (Co)-doped nanoceramic samples of bismuth ferrite by cost-effective sol-gel citrate precursor technique are presented. Detailed investigations have been attempted to study the effect of Co substitution on the structural, morphological, dielectric and optical properties of bismuth ferrite prepared using the citrate precursor method. The main feature of these investigations is the relative elimination of secondary phase formation while preparing bismuth ferrite nanoceramic samples. X-ray diffraction analysis shows distorted rhombohedral perovskite structure for all compositions of BiFe1−xCoxO3 (x = 0.00, 0.03, 0.05, 0.10) nanoceramics, where the average crystallite size and induced strain in these samples are calculated using Scherrer’s method and Williamson–Hall equation, respectively. An increasing trend of average crystallite size with increase in dopant concentration was observed. Microstructural examinations of pure and doped BFO identified compact granular shaped microstructures with irregular size and shape but changed to uniform spherical shape after Co substitution up to 10 mol%. Confirmation of the uniform distribution of dopants throughout the sample has been carried out using elemental mapping studies. On the other hand, the chemical states of all the constituent elements were identified by X-ray photoelectron spectroscopic studies. Non-monotonic variations in the real part of dielectric values were observed with increasing Co concentrations. The optical absorption coefficient was found to increase by 35% in 10 mol% Co-doped BFO than that of pure BFO at 480 nm. Optical band gap studies depicted a striking inverse correlation of bandgap values and doping concentration up to 10 mol% Co substitution without varying the intrinsic structural feature of bismuth ferrite. Interestingly, the bandgap value of bismuth ferrite was varied from (2.08 ± 0.02) eV to (1.63 ± 0.02) eV, in the visible region. The results from present investigations suggest that synthesis techniques and chemical substitution need to be continuously optimized to get desired physical properties suitable for device applications such as photovoltaics.

The Mechanical Properties of the Novel Nanocrystalline Refractory Tantalum Alloys

The nanocrystalline tantalum alloys were investigated in terms of mechanical properties. The materials were obtained by powder metallurgy techniques—mechanical alloying (MA) and hot pressing (pulse plasma sintering mode). Pure powders of niobium, molybdenum, and tungsten were used for tantalum as an additive element in the concentration of 5, 10, 20, and 40 wt %. The analysis of XRD (Williamson–Hall equation) and TEM confirmed a significant reduction of the grain size (5.3–25.7 nm) for pure powders and (12.5–171.5 nm) for bulk hot-pressed elements. The nanoindentation test was used to study the mechanical properties. The load-displacement curves show high uniformity of the mechanical properties. The nanocrystalline alloys show very high hardness and stiffness. The highest value of hardness reached 1481 HV for Ta–10Mo composition. Significantly higher values of hardness compared to pure Ta-nano were measured for Ta–W system. The Young’s modulus increased twice up to 343 GPa for Ta–20Mo in comparison to the unalloyed nanocrystalline Ta (163 GPa). In the novel nanocrystalline tantalum alloys, both solid solution and grain boundary strengthening affected on high mechanical properties.

Growth and electrical properties of self-flux method grown (1−x)Bi1/2Na1/2TiO3−xBaTiO3 single crystals across the morphotropic phase boundary

The ferroelectric solid solution 0.94(Bi1/2Na1/2)TiO3–0.06BaTiO3 (BNBT) is a promising material to substitute the environmentally undesired Pb-based ferroelectrics. Lead-free piezoelectric BNBT bulk size single crystals with a composition across the morphotropic phase boundary (MPB) have been successfully grown by the self-flux method. Powder X-ray diffraction (PXRD) pattern confirms the perovskite structure of the synthesized BNBT crystals. The lattice strain is calculated as 1.7 × 10−2 using Williamson–Hall equation from PXRD. The elemental composition of the BNBT single crystals grown with different compositions is confirmed by X-ray fluorescence, covering the rhombohedral to tetragonal region and encompassing the MPB. The presence of a phase boundary between rhombohedral and tetragonal phases near MPB results in electrical behavior enhancement. The dielectric, ferroelectric, and piezoelectric properties along the pseudocubic direction have been measured. Dielectric permittivity gives diffuseness of BNBT crystals and it confirms the relaxor-type behavior. AC conductivity gave the activation energy as 0.46 eV.

Crystal Structure and Lattice Parameter Investigation of La3+ Substituted CeO2 in LaxCe1-xO2-X/2 Synthesized by Solid-State Method

Lanthanum (La) doped Ceria (CeO2) has attracted considerable interest as a candidate material for thermal barrier coating (TBC) because of its low thermal conductivity and potential capability to be operated above 1250°C. In this study, La2Ce2O7 powder was synthesized through the ball mill method. The crystal structure of La3+ substituted CeO2 solid solution was investigated by X-ray diffraction in LaxCe1-xO2-x/2 (0<x< 0.5). The fluorite structure of CeO2 did not change although La3+ was the largest trivalent rare-earth ion. The lattice parameter changed from 5.41 to 5.59A by increasing La content. Changes in the lattice parameters of LaxCe1-xO2-x/2 that were compared with the theoretical values measured by XRD were obtained based on the oxygen vacancy model. The theoretical lattice parameters were larger than the lattice parameters calculated from the X-ray diffraction pattern. Moreover, the Williamson–Hall equation was used to measure the crystallite size and strain in the LaxCe1-xO2-x/2 lattice as a function of the lanthanum content. The results showed that the presence of lanthanum in the structure reduced the crystallite size.

Thermal and structural characterization of the kidney stone

In the present study, the thermal and structural properties of a kidney stone, which was passed out of the body naturally by a 29-year-old woman who was 4 months pregnant, were investigated by using the experimental analysis methods of the differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray diffraction. The DTA and TG analyses were taken in the temperature range of 25–1000 °C. After reaching the temperature of 680 °C, the decomposition of calcium carbonate to calcium oxide was detected. In the TG curve, the total mass loss of 26.2% was detected. The as-used kidney stone is fully composed of the single phase of calcium oxalate monohydrate (C2H2CaO5), also known as the whewellite, with the tetragonal crystal structure. The crystallinity percent of the as-used kidney stone was found to be 91.3%. The crystallite size was computed to be 107.22 ± 4.79 nm and 79.69 ± 3.63 nm from Scherrer and Williamson–Hall equations, respectively.

Metabolisable energy content in canine and feline foods is best predicted by the NRC2006 equation.

Although animal trials are the most accurate approach to determine the metabolisable energy (ME) content of pet food, these are expensive and labour-intensive. Instead, various equations have been proposed to predict ME content, but no single method is universally recommended. Data from canine and feline feeding studies, conducted according to Association of American Feed Control Officials recommendations, over a 6-year period at a single research site, were utilised to determine the performance of different predictive equations. Predictive equations tested included the modified Atwater (MA equation), NRC 2006 equations using both crude fibre (NRC 2006cf) and total dietary fibre (NRC 2006tdf), and new equations reported in the most recent study assessing ME predictive equations (Hall equations; PLoS ONE 8(1): e54405). Where appropriate, equations were tested using both predicted gross energy (GE) and GE measured by bomb calorimetry. Associations between measured and predicted ME were compared with Deming regression, whilst agreement was assessed with Bland-Altman plots. 335 feeding trials were included, comprising 207 canine (182 dry food; 25 wet food) and 128 feline trials (104 dry food, 24 wet food). Predicted ME was positively associated with measured ME whatever the equation used (P<0.001 for all). Agreement between predicted and actual ME was worst for the MA equation, for all food types, with evidence of both a systematic bias and proportional errors evident for all food types. The NRC 2006cf and Hall equations were intermediate in performance, whilst the NRC 2006tdf equations performed best especially when using measured rather than predicted GE, with the narrowest 95% limits of agreement, minimal bias and proportional error. In conclusion, when predicting ME content of pet food, veterinarians, nutritionists, pet food manufacturers and regulatory bodies are strongly advised to use the NRC 2006tdf equations and using measured rather than predicted GE.

Generalized stem taper and tree volume equations applied to eucalyptus of varying genetics in Brazil

Lack of generalized equations has prevailed in Brazil, because it is assumed that localized or climate-specific equations are needed. This study aimed to develop generalized stem taper and volume equations applicable to 11 eucalyptus clones and evaluate if climate variation impacts the accuracy of the estimates. A total of 693 trees evenly distributed across 11 clones at 21 sites were used for model fittings and predictive validation. The penalized mixed spline (PMS) approach was developed for predicting stem taper and volume along the stem profile. The Schumacher and Hall (1933) equation was used to predict total tree volume, while volume ratio equations were applied to predict merchantable volume. For every fitted equation, an annual climatic variable was included to assess the improvement in model performance. The overall results highlighted that climatic variation does not need to be accounted for in stem taper and volume modeling. All of the equations displayed desirable accuracy, but the generalized PMS equation may be preferred when the forestry enterprise looks to furnish a range of multiple forest products. The generalized total tree volume equation, combined with the ratio equations, is highly recommended when the forestry enterprise produces a single product.

Effect of calcination on structural, morphological, magnetic and electrochemical properties of mesoporous Ni2P2O7 microplates

The NH4NiPO4·H2O (NNPO) precursor powder was prepared by the hydrothermal method at 200 °C for 8 h. In the study of calcination effect on the structural, morphological, magnetic and electrochemical properties of mesoporous Ni2P2O7 microplates (NPOs), NNPO was calcined at different temperatures of 500, 600 and 700 °C each for 1 h and 3 h in argon atmosphere. XRD analysis confirmed the orthorhombic structure of NNPO with space group Pmnm(59), whereas all NPOs possessed the monoclinic crystal structure with space group B21/c(14). The calculated average crystallite size of NPOs (DWH) by the Williamson–Hall equation was in a nanoscale with the increase of size due to the increasing calcination temperature. Images of all NPOs obtained by SEM and TEM techniques showed a thin plate-like morphology with mesoporous nature of pore size ranging from 2 to 16 nm. XANES results indicated the oxidation state of 2 + for Ni cation in all NPOs samples. The magnetic properties of all NPOs studied at room temperature using VSM techniques indicated a weak ferromagnetic behavior with the enhancement of coercive field (Hc) and unsaturated magnetization (M), suggesting to originate from the increase of particle size due to the increase of calcination temperature. Interestingly, electrochemical properties of active NPOs electrodes studied by CV, GCD and EIS tests in 3 M KOH electrolyte revealed the maximum specific capacitance (Csc) of 905.687 F g−1 at a current density 1 A g−1 with a good cycling stability 90.80% retention after 1000 cycle test in a cell, having NPO6_1 h (obtained by calcination NNPO at 600 °C for 1 h) as active electrode.

Local Well-Posedness and Blow-Up for the Solutions to the Axisymmetric Inviscid Hall-MHD Equations

In this paper, we consider the regularity problem of the solutions to the axisymmetric, inviscid, and incompressible Hall-magnetohydrodynamics (Hall-MHD) equations. First, we obtain the local-in-time existence of sufficiently regular solutions to the axisymmetric inviscid Hall-MHD equations without resistivity. Second, we consider the inviscid axisymmetric Hall equations without fluids and prove that there exists a finite time blow-up of a classical solution due to the Hall term. Finally, we obtain some blow-up criteria for the axisymmetric resistive and inviscid Hall-MHD equations.

Surface modification of La/SnO2–TiO2 nanocomposite via changing the ionic nature of surfactants

Surface of La/SnO2–TiO2 nanocomposite was modified during its synthesis using zwitterionic (3 (N-N dimethyloctadecyl ammonia) propane sulfonate), anionic (sodium dioctyl sulfosuccinate) and cationic (dimethyl dioctadecyl ammonium chloride) surfactants by sol gel method followed by reflux method. Effect of surfactants on morphology was investigated with scanning electron microscopy. Crystallite size was determined by using XRD pattern with the help of Scherrer and Williamson Hall equations, while particle size was calculated through transmission electron microscopy. Optical properties as well as photocatalytic activity was investigated against degradation of methylene blue under sun light. It was found that doping of lanthanum enhanced the photocatalytic activity of SnO2–TiO2 nanoparticles. A direct relation between particle size and band gap was found while both have inverse relationship with degradation and lattice strain.

IMPROVED PROCESS FLOW FOR FORMATION OF BIPOLAR STATIC INDUCTION TRANSISTOR

The improved process flow differs from the known ones in the fact that the same photomask is used for formation of a channel stopper and metal contacts. Such approach has made it possible not only to decrease a number of the used phototomasks but it has also permitted to obtain a device with the required electrical characteristics. The paper presnts results of device and process simulation of bipolar static induction transistor (BSIT) manufactured in accordance with the improved process flow, measuring data of electrophysical parameters of its experimental samples and also comparison of simulation results with experimental data. At present there is a large quantity of software products that permit to perform physico-topological simulation of semiconductor structures. The device-process simulation is considered as a part of such simulation and it allows prior to obtaining experimental samples to determine process flow parameters at which the investigated structure will have necessary electrical parameters and characteristics. Thus the device-process simulation represents a certain “virtual production” for manufacturing semiconductor devices and microcircuits beginning from the startup stage of semiconductor wafer at production site and finishing by electrical characteristics measurements of the obtained structure. The BSIT device simulation being an analog of direct measurements of current-voltage characteristics has been performed with help of program system MOD-1D developed by the author. The BSIT model based on the fundamental system of semiconductor equations is mainly used for calculation of the BSIT current-voltage characteristics direct branch and its parameters and charge carrier recombination is described by Shockley – Read – Hall expression and equation depicting the Auger recombination process.

Structural, optical, and catalytic properties of undoped and CdS doped CuO–ZnO nanoparticles

The structural, optical and catalytic properties of undoped (CuO–ZnO) and CdS doped CuO–ZnO (CdS/CuO–ZnO) nanoparticles were studied. The blue shifting of optical band gap in CuO–ZnO nanoparticles as compared to their respective bulk oxides (CuO: 1.21–1.5 eV, ZnO: 3.37 eV) was observed as 3.9 eV, while red shifting after doping of CdS was found from 3.9 to 3.7 eV. The angle of diffraction and FWHM values were used to observe crystallite phase and to calculate crystallite size (using Scherer and Williamson–Hall equations) and other parameters like strain, dislocation density and bond length of nanoparticles. The particle size of CuO–ZnO and CdS/CuO–ZnO nanoparticles using transmission electron microscopy (TEM) was found 12.54 and 6.93 nm, respectively. It was concluded that decrease in particle size cause red shifting which increase the catalytic efficiency of nanoparticles.

Investigation of the effect of anodization time and annealing temperature on the physical properties of ZrO2 thin film on a Si substrate

This research work studied the effects of various anodization times (5, 10, 15, 20 and 25 min) and various annealing temperatures (500, 600, 700, 800 and 900 °C) on ZrO2 thin film on a Si substrate. The ZrO2 thin film was prepared via sputtering and anodization processes on a Si substrate. The existence of Si, SiO2, m-ZrO2, t-ZrO2 and ZrSiO4 was confirmed by x-ray diffraction, Fourier transform infrared microscopy and Raman spectroscopy. In addition, NaOH was observed as a residue on the surface of the thin film. The grain size and microstrain of both m-ZrO2, and t-ZrO2 were calculated using the Williamson–Hall and/or Scherrer equation. The morphology of samples was examined by scanning electron microscopy. In contrast to unannealed samples, the annealed samples have a smaller grain size, less NaOH, and SiO2 with a smoother surface. However, the SiO2 existed when being annealed at higher temperatures (⩾800 °C).

CONSTRUCTION OF MULTISPECIES ALLOMETRIC

To avoid the problem of destructive tree sampling, we tested an indirect estimation procedure whereby aboveground tree volumes are estimated using affine-transforms of traditional bole volume equations. The study compared the predictive performance of the (1) proposed procedure, (2) allometric aboveground volume equations, and (3) simple upscaling of empirical tree bole volumes (serving as benchmark procedure). The study assessed speciesand tree-individual random deviations from mean procedure effect on prediction errors. Six volume equations were each fitted to aboveground volume (a- version) and bole volume (b- version); predictions of latter volumes were affine-transformed to estimate aboveground tree volumes. Bole height, total height and diameter at breast height (dbh) were measured for 59 trees from 10 species in eastern Cameroon. The Schumacher and Hall equation ranked first in quality-of-fit. The direct and indirect approaches applied with this volume equation predicted the aboveground tree volumes equally well across all species (groupings), with bias (± RMSE of 0.153 ± 2.512 and 0.178 ± 2.56 m3 respectively. Finally, trees within species accounted for 49.3% of the total variability in volume prediction error vs only 3.5% for species. Recommendations have been made for improvement relatively to data requirements and model building.

Regularity of the 3D Stationary Hall Magnetohydrodynamic Equations on the Plane

We study the regularity of weak solutions to the 3D valued stationary Hall magnetohydrodynamic equations on $ \Bbb R^2$. We prove that every weak solution is smooth. Furthermore, we prove a Liouville type theorem for the Hall equations.

Growth of a bulk-size single crystal of sulphamic acid by an in-house developed seed rotation solution growth technique and its characterization

A bulk sulphamic acid single crystal has been grown by a modified seed rotation technique. The lattice dimensions of the grown single crystal were confirmed using powder X-ray diffraction, and it was found that it crystallized in an orthorhombic structure with space group Pbca. The strain in the lattice was calculated by the Williamson–Hall equation. The crystalline perfection was examined by high-resolution X-ray diffraction and found to be extremely good (the single peak of the rocking curve having an FWHM of ∼8.0′′). The luminescence behaviour was recorded in the wavelength region between 400 and 630 nm using an Xe flash lamp which acts as an excitation source. The shock damage threshold was measured for the grown crystal in order to determine the mechanical capability of the title compound. The thermal parameter of sulphamic acid was calculated by photoacoustic spectroscopy.

Influence of silicon dioxide medium on the structural and electrical properties of nickel zinc ferrite

Nickel zinc ferrite [(Ni$_{0.65}$Zn$_{0.35}$Fe$_{2}$O$_{4}) _{x}$ / (SiO$_{2}) _{1-x}$ where, x = 1.0, 0.85, 0.65, 0.50, 0.35, and 0.15] is synthesized using the glyoxylate precursor method. The synthesis, characterization, and electrical study of nickel zinc ferrites/SiO$_{2}$ powder with low dielectric constant, very low conductivity, and loss tangent with low frequency dispersion, suitable for good insulators, is reported here. X-ray diffraction, TGA, and FT-IR studies are employed for identifying crystalline phases and structure. Crystallite size is calculated by the Scherrer formula and Williamson--Hall equation and found to fall in the range of 4.9--25 nm. TEM of the samples shows spherical particles of uniform size distribution and the spotty rings of SAED patterns are analyzed for identifying the crystal planes. The study confirms a simple and efficient way to synthesize single-phase nickel zinc ferrite (NZFO) spherical particles of nano size ($\approx $15 nm at 1000 $^{\circ}$C) with lower particle agglomeration in comparison to any other methods. Electrical studies are carried out using an LCR meter. The observed value of dielectric constant falls in the range of 10--80, loss tangent in the range of 0.05--0.4, and electrical conductivity in the range of 10$^{-4}$ to 10$^{-7}$ mho m$^{-1}$. These values are respectively functions of temperature, frequency, and the ferrite content in ferrite/SiO$_{2}$ samples. A proper selection of ferrite concentration in the silica medium enables one to prepare NZFO/SiO$_{2}$ material of very low loss tangent with dielectric constant in the range of 10--80.