Alternation Technique Research Articles

Enhanced Dielectric and Electric Properties of ZnFe2O4‐Poly(Vinylidene Fluoride) Composites by Employing Surface Hydroxylated ZnFe2O4 Nanoparticles

AbstractA facile solvent casting technique has been reported in the fabrication of surface hydroxylated ZnFe2O4 (h‐ZFO) nanoparticles (NPs) filled with poly(vinylidene fluoride) (PVDF) as a matrix. The h‐ZFO filler particles are synthesized from neat ZnFe2O4. The dielectric and electric performance of polymer‐based composites is much related to the interface binding between filler particles and polymer matrix. In this work, the surface alternation technique employed a new path is developed to improve the compatibility between ZFO particles and the PVDF matrix. These PVDF‐ZFO composites were studied by X‐ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The h‐ZFO‐PVDF and ZFO‐PVDF composites are carefully analyzed by dielectric and electric properties by a wide range of frequencies. However, the morphological analysis exhibits uniform dispersion of the h‐ZFO NPs in the PVDF matrix. The h‐ZFO‐PVDF composites have a dielectric constant of about 35 for 1.5 wt.% of filler contents. Moreover, the h‐ZFO‐PVDF composites have lower dielectric loss than PVDF‐ZFO composites. It is suggested that the strong interaction between h‐ZFO filler particles and the PVDF matrix is the main reason for the improvement of dielectric properties. The outcomes of these methods have great potential for making high dielectric constants and relatively suppressed loss PVDF‐ZFO composites for advanced practical applications.

Bioavailability Enhancement Techniques for Poorly Aqueous Soluble Drugs and Therapeutics.

The low water solubility of pharmacoactive molecules limits their pharmacological potential, but the solubility parameter cannot compromise, and so different approaches are employed to enhance their bioavailability. Pharmaceutically active molecules with low solubility convey a higher risk of failure for drug innovation and development. Pharmacokinetics, pharmacodynamics, and several other parameters, such as drug distribution, protein binding and absorption, are majorly affected by their solubility. Among all pharmaceutical dosage forms, oral dosage forms cover more than 50%, and the drug molecule should be water-soluble. For good therapeutic activity by the drug molecule on the target site, solubility and bioavailability are crucial factors. The pharmaceutical industry’s screening programs identified that around 40% of new chemical entities (NCEs) face various difficulties at the formulation and development stages. These pharmaceuticals demonstrate less solubility and bioavailability. Enhancement of the bioavailability and solubility of drugs is a significant challenge in the area of pharmaceutical formulations. According to the Classification of Biopharmaceutics, Class II and IV drugs (APIs) exhibit poor solubility, lower bioavailability, and less dissolution. Various technologies are discussed in this article to improve the solubility of poorly water-soluble drugs, for example, the complexation of active molecules, the utilization of emulsion formation, micelles, microemulsions, cosolvents, polymeric micelle preparation, particle size reduction technologies, pharmaceutical salts, prodrugs, the solid-state alternation technique, soft gel technology, drug nanocrystals, solid dispersion methods, crystal engineering techniques and nanomorph technology. This review mainly describes several other advanced methodologies for solubility and bioavailability enhancement, such as crystal engineering, micronization, solid dispersions, nano sizing, the use of cyclodextrins, solid lipid nanoparticles, colloidal drug delivery systems and drug conjugates, referring to a number of appropriate research reports.

Enhanced Power Extraction with Sediment Microbial Fuel Cells by Anode Alternation

Sediment microbial fuel cells (SMFCs) are energy harvesting devices where the anode is buried inside marine sediment, while the cathode stays in an aerobic environment on the surface of the water. To apply this SCMFC as a power source, it is crucial to have an efficient power management system, leading to development of an effective energy harvesting technique suitable for such biological devices. In this work, we demonstrate an effective method to improve power extraction with SMFCs based on anodes alternation. We have altered the setup of a traditional SMFC to include two anodes working with the same cathode. This setup is compared with a traditional setup (control) and a setup that undergoes intermittent energy harvesting, establishing the improvement of energy collection using the anodes alternation technique. Control SMFC produced an average power density of 6.3 mW/m2 and SMFC operating intermittently produced 8.1 mW/m2. On the other hand, SMFC operating using the anodes alternation technique produced an average power density of 23.5 mW/m2. These results indicate the utility of the proposed anodes alternation method over both the control and intermittent energy harvesting techniques. The Anode Alternation can also be viewed as an advancement of the intermittent energy harvesting method.

Interfacial Stresses of a Coated Square Hole Induced by a Remote Uniform Heat Flow

This paper presents an analytical solution of a coated square hole embedded in an isotropic infinite plate under a remote uniform heat flow. Based on conformal mapping, analytic continuation theorem and the alternation technique, temperature and stress functions are derived in a compact series form. Results of temperature contours and interfacial stresses are validated using the finite element method. The comparison indicates the high accuracy of the proposed method. Numerical results of both the interfacial normal and shear stresses for different properties and geometric parameters of a coated layer are provided in a graphical form. The results indicate that the interfacial stresses are highly dependent on the thermal expansion coefficient, thickness of the coating layer and shape factor of the coated square hole. In conclusion, the interfacial shear stresses exhibit a significant increase at the corners with abrupt geometrical changes, which would cause the delamination of the coating layer system. Furthermore, increasing the thickness of the coating layer and the shape factor results in a higher interfacial stress.

Combination of double and single cyclic pressure alternation technique to increase CO 2 sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method

Combination of double and single cyclic pressure alternation technique to increase CO ₂ sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method

Stress Field for a Coated Triangle-Like Hole Problem in Plane Elasticity

ABSTRACTThe stress field induced by an edge dislocation or a point force located near a coated triangle-like hole in an infinite plate is provided in this paper. Based on the method of analytical continuation and the technique of conformal mapping in conjunction with the alternation technique, a series solution for the displacement and stresses in the coating layer and the matrix is obtained analytically. Examples for the interaction between an edge dislocation and a coated triangle-like hole for various material constant combinations, coating thicknesses and shape factors are discussed. The analysis discovers that the so-called trapping mechanism of dislocations is more likely to exist near a coated triangle-like hole. The result shows that the dislocation will first be repelled by the coating layer and then attracted by a hole when the coating layer is slightly stiffer than the matrix. However, when the coating layer is sufficiently thin, the dislocation will always be attracted by a hole even the coating layer is stiffer than the matrix.

Analytical solutions to a coated triangle hole embedded in an infinite plate under a remote uniform heat flow

A general solution for a remote uniform heat flow interacting with a coated triangle hole embedded in an infinite plate is provided in this article. Based on the method of analytical continuation in conjunction with the alternation technique, the solutions to the heat conduction and thermoelastic problems are derived. A rapidly convergent series solution for both temperature and stress field is obtained in an elegant form which is expressed in terms of an explicit general form of the corresponding homogeneous complex potential. Numerical results of interfacial stresses are evaluated to provide a better understanding of an optimum design for various material properties and geometric parameters. The present proposed method can be further extended to deal with the corresponding thermoelastic problem with any shape of holes.

Stress intensity factors for fibrous composite with a crack embedded in an infinite matrix under a remote uniform load

The interaction between a crack and two circular elastic inclusions for a fibrous tri-material composite under a remote uniform load is investigated. Based on the method of analytical continuation combined with the alternation technique, the solutions to the cracked composite are derived. A rapidly convergent series solution for the stress field, either in the matrix or the fibers, is obtained in an elegant form. The stress intensity factors are obtained numerically in terms of the dislocation density functions of the logarithmic singular integral equations. The merit of the present approach is the formulation of weakly singular integration that the integrals involved in the weakly singular allow easy calculations in the singular integral equation which can be treated to solve the problem even when a crack is closer to the interface. The stress intensity factors as a function of the dimensionless crack length for various material properties and geometric parameters are shown in graphic form. It is shown that the fibers act to restrain or accelerate crack growth depending on the shear moduli between the fibers and the matrix. With this understanding, an optimum design can thus be conceptualized for a fibrous composite system. The present proposed method can be further extended to deal with the corresponding crack problem associated with any number of inclusions.

The Stress Field Due to an Edge Dislocation Interacting With Two Circular Inclusions

AbstractA general series solution to the problem of interacting circular inclusions in plane elastostatics is presented in this paper. The analysis is based on the use of the complex stress potentials of Muskhelishvili and the theorem of analytical continuation. The general forms of the complex potentials are derived explicitly for the circular inhomogeneities under arbitrary plane loading. Using the alternation technique, these general expressions were subsequently employed to treat the problem of an infinitely extended matrix containing two arbitrarily located inhomogeneities. The major contribution of the present proposed method is shown to be capable of yielding approximate closed-form solutions for multiple inclusions, thus providing the explicit dependence of the solution on the pertinent parameters. The result shows that the dislocation has a stable equilibrium position at a certain combination of material constants. The case of an inhomogeneity interacting with a circular hole under a remote uniform load is also investigated.

Solutions of a crack interacting with a three-phase composite in plane elasticity

The interaction between a crack and a circularly cylindrical layered media under a remote uniform load for plane elasticity is investigated. Based on the method of analytical continuation associated with the alternation technique, the solutions to the crack problem for a three-phase composite are derived. A rapidly convergent series solution for the stress field, expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The solution procedures for solving this problem consist of two parts. In the first part, the complex potential functions of dislocation interacting with a three-phase composite are obtained. In the second part, the derivation of logarithmic singular integral equations by introducing the complex potential functions of dislocation along the crack border is made. The stress intensity factors (SIFs) are then obtained numerically in terms of the dislocation density functions of the logarithmic singular integral equations. The stress intensity factors (SIFs) as a function of the dimensionless crack length for various material properties and geometric parameters are shown in graphic form. The obtained results may provide some guidance for material and geometry selections by minimizing the SIF.

Epitaxial growth of AlN films on sapphire via a multilayer structure adopting a low- and high-temperature alternation technique

Epitaxial growth of AlN films on c-sapphire using a multilayer structure has been investigated by metal–organic chemical vapor deposition adopting multiple alternation cycles of low- and high-temperature (LT–HT) growth. It is found that the surface morphology and crystal quality can be greatly improved using three alternation cycles with X-ray diffraction ω-scan full width at half maximum values of 311 and 548 arcsec for the (0002) and (10−12) peaks, respectively, which are induced by the alternation of the three-dimensional (3D) and two-dimensional (2D) growth modes caused by the LT–HT process. The first 3D–2D cycle is found to play a major role in threading dislocation reduction, while the second and third cycles mainly account for tensile stress relaxation.

A factorization‐based approach to photometric stereo

AbstractThis article presents an adaptation of a factorization technique to tackle the photometric stereo problem. That is to recover the surface normals and reflectance of an object from a set of images obtained under different lighting conditions. The main contribution of the proposed approach is to consider pixels in shadow and saturated regions as missing data, in order to reduce their influence to the result. Concretely, an adapted Alternation technique is used to deal with missing data. Experimental results considering both synthetic and real images show the viability of the proposed factorization‐based strategy. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 115–119, 2011.

Thermal stresses in a viscoelastic trimaterial

A general solution for a three dissimilar sandwiched medium subjected to a point heat source and a three-phase composite cylinder subjected to a remote uniform heat flow is presented in this work. The solutions to the heat conduction and thermoelastic problems are derived based on the method of analytic continuation associated with the alternation technique. A rapidly convergent series solution for both the temperature and the stress field, which is expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The hereditary integral in conjunction with the Kelvin-Maxwell model is applied to simulate the thermoviscoelastic properties while a thermorheologically simple material is considered. Based on the correspondence principle, the Laplace transformed thermoviscoelastic solution is directly determined from the corresponding thermoelastic one. The real-time solution can then be solved numerically by taking inverse Laplace transform. Two typical examples concerning interfacial stresses for plane-layered media and circularly cylindrical-layered media are discussed in detail.

Research on the optimal thickness of transmission-mode exponential-doping GaAs photocathode

The difference between the diffusion drift length of photoelectrons in exponential-doping GaAs photocathode and that in uniform-doping GaAs photocathode is studied. According to quantum equations, the optimized thickness of transmission-mode exponential-doping GaAs photocathode is simulated to be 20 μm. Two transmission-mode exponential-doping GaAs samples with the thickness of 16 and 20 μm are activated by (Cs,O) alternation technique. Integral sensitivities of the two samples are 1228 and 1547 μA/lm, respectively. The ratio of integral sensitivities of the two samples is 0796∶1, which agrees with the simulation result.

Centralized and Distributed Algorithms for Routing and Weighted Max-Min Fair Bandwidth Allocation

Given a set of demands between pairs of nodes, we examine the traffic engineering problem of flow routing and fair bandwidth allocation where flows can be split to multiple paths (e.g., MPLS tunnels). This paper presents an algorithm for finding an optimal and global per-commodity max-min fair rate vector in a polynomial number of steps. In addition, we present a fast and novel distributed algorithm where each source router can find the routing and the fair rate allocation for its commodities while keeping the locally optimal max-min fair allocation criteria. The distributed algorithm is a fully polynomial epsilon-approximation (FPTAS) algorithm and is based on a primal-dual alternation technique. We implemented these algorithms to demonstrate its correctness, efficiency, and accuracy.

Thermal stresses in a viscoelastic three-phase composite cylinder

A thermoviscoelastic analysis of a three-phase composite cylinder is presented in this work. The solutions of the heat conduction and thermoelastic problem for three dissimilar media are derived based on the method of analytic continuation associated with the alternation technique. A rapidly convergent series solution for both the temperature and stress field, which is expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The hereditary integral in conjunction with the Kelvin–Maxwell model is applied to simulate the thermoviscoelastic properties while a thermorheologically simple material is considered. According to the correspondence principle, the Laplace transformed thermoviscoelastic solution is directly determined from the corresponding thermoelastic one. The real time solution can then be solved numerically by taking inverse Laplace transform. Finally, some typical examples of interfacial stresses are discussed.

Thermal stresses in a viscoelastic trimaterial with a combination of a point heat source and a point heat sink

A general solution for a thermoviscoelastic trimaterial combined with a point heat source and a point heat sink is presented in this work. Based on the method of analytic continuation associated with the alternation technique, the solutions to the heat-conduction and thermoelastic problems for three dissimilar, sandwiched media are derived. A rapidly convergent series solution for both the temperature and stress field, expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The hereditary integral in conjunction with the Kelvin–Maxwell model is applied to simulate the thermoviscoelastic properties, while a thermorheologically simple material is considered. Based on the correspondence principle, the Laplace transformed thermoviscoelastic solution is directly determined from the corresponding thermoelastic one. The real-time solution can then be solved numerically by taking the inverse Laplace transform. A typical example concerning the interfacial stresses generated from a combined arrangement of a heat source and sink are discussed in detail. The corresponding thin-film problem is also discussed.

A Modified Method for Measuring the Spin Relaxation in Nuclear Quadrupole Resonance

A simple and rather efficient method for measuring the spin–spin relaxation time T2 in nuclear quadrupole resonance (NQR) is proposed. The method uses the phase cycling (or alternation) technique and is rather efficient in measuring short T2 times. Results on the use of this method for detecting NQR signals on nuclei of nitrogen 14N in a (CH2)6H4 polycrystal are presented. The application of modified pulse sequences enables rather accurate measurements of the T2 time for this compound.

The relevance of J cross-peaks in two-dimensional NOE experiments of macromolecules

Two-dimensional (2D) exchange spectroscopy (I, 2) is on the point of becoming a major technique for the elucidation of the spatial structure of biological macromolecules through the nuclear Overhauser effect (NOE) (3-8) and for the investigation of chemical exchange processes (9, IO). In particular, two-dimensional NOE spectroscopy has already been well established as a powerful tool for investigating proteins in solution (3, 4, 6-8). The nuclear Overhauser effect and chemical exchange cause an incoherent exchange of magnetization between different sites, either by cross-relaxation or by an actual exchange of nuclei, respectively. In 2D spectroscopy these processes are traced out by “frequency-labeling” the various magnetization components before exchange and by sorting out the labeled components after exchange (1). In addition to the cross-peaks caused by this incoherent exchange, so-called J cross-peaks may arise as a consequence of coherent transfer of magnetization between J-coupled resonances (I I, 12). Although the J cross-peaks contain valuable information on the coupling network, which is exploited in 2D-correlated spectroscopy (23-15) they are undesired in exchange spectra. They may be misinterpreted as additional exchange cross-peaks or may falsify the measured intensities in the case of coincidence with exchange cross-peaks. Suitable techniques for their suppression have been described recently (I 1, 12). In this communication, we would like to quantitatively evaluate the relevance of J cross-peaks in NOESY spectra of proteins by means of experimental measurements and by simple model calculations. Zero-quantum coherence precessing during the mixing period of duration T, is primarily responsible for the occurrence of J cross-peaks. Double-quantum coherence may also contribute. However, by proper phase-cycling (II), it is possible to eliminate J cross-peak contributions originating from double-quantum coherence. The interference effects from transverse magnetization present during the mixing time are usually suppressed by a simple phase alternation technique. Higher-order multiple-quantum coherence is seldom of practical significance for the creation of J cross-peaks.

Electronic structure and spectrum of benzo[g]sesquifulvalene

Calculations have been made for benzo[g]sesquifulvalene using the Hückel MO method with the bond alternation technique. The bond lengths, charge densities, dipole moment and electronic spectrum of this molecule as given by the MO calculations have been compared with the experimental values.