Effect of formulation and process variables on the release behavior of amoxicillin matrix tablets

The sustained release of amoxicillin is desired to be confined to the upper gastrointestinal tract to treat certain kind of infections. In vitro dissolution, at pH 1.2, of amoxicillin sustained release tablets has been studied varying the proportion of Carbopol 971P NF and sodium alginate as well as the ethanol/water proportion in the granulation fluid. M_t, the amount of drug released at time (t) and defined in terms of the total drug released over a long time period (M_inf), was described by M_t/M_inf = ktⁿ. Matrices with increasing proportions of sodium alginate showed increasing values of the exponent indicative of the release mechanism (n) and increasing release constant values (k). This is attributed to a drop in the coherence of the polymeric matrix with increasing alginate proportions that produces an increasing polymer relaxation and erosion. Decreasing Carbopol 971P NF proportions reduce the amount of dissolved polymer during granulation, producing a lesser obstruction of amoxicillin dissolution. Alginate proportions of 80% produce near zero order release profiles. Granules obtained with increasing ethanol proportions showed increasing release constant values and a minor change in the exponent (n) values. This is considered a result of lower polymer dissolution during granulation that allows a lesser matrix coherence and a greater amoxicillin dissolution. Alginate matrices granulated with different ethanol/water proportions showed no significant changes in the amoxicillin release profile. There is a trend toward increasing floating times with increasing Carbopol 971P NF proportions.     

Existence of periodic solutions of the equations of incompressible micropolar fluid flow

The equations of incompressible micropolar fluid flow are a coupled system of vector differential equations involving the two basic vectors, viz. the velocity and the microrotation of the fluid elements. Let D = D (t) be a bounded region in space, and let a flow velocity and a microrotation be prescribed at each point of the boundary of D(t). Assume that D(t) as well as the assigned velocity and microrotation vectors depend periodically on the time t and that the condition (2μ+k)j−4a 0 is satisfied (equation (25) in the text). Further assumptions are that (i) to every continuous initial distribution of the flow fields over D, there corresponds a solution of the field equations for all time t 0 satisfying the prescribed boundary conditions; (ii) there is one solution for which the Reynolds numbers Re, Rm satisfy the condition Re² + Rm² < 80 and this solution is equicontinuous in for all t. Then there exists a unique, stable, periodic solution of the micropolar flow equations in D(t) taking the prescribed values on the boundary. The proof of the theorem rests on a formula describing the rate of decay of the kinetic energy of the difference of two micropolar flows in the domain subject to the same boundary conditions.     

Experimental and modeling approaches of MR behaviors under large step strains

Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.     

Reliability measures for dynamic multistate nonrepairable systems and their applications to system performance evaluation

The main focus of this paper is on the development of reliability measures for dynamic multistate systems which have M + 1 discrete states of working efficiency. In traditional reliability models for binary systems, one measure that is commonly used is the probability of success at some time t. For multistate systems, we can extend this definition and define the reliability of a multistate system to be the probability that the system still functions at some intermediate state k, 0 ≤ k ≤ M or higher at time t. To develop the reliability measures for multistate systems, we assume that the degradation of the multistate systems follows a Markov process and that the system can directly degrade into any lower state. The other focus of this paper is on the evaluation of multistate systems for system design. For traditional binary reliability evaluation, the better system at time t is the one that has a greater value of the area created by the integration over time of the expected value of the state of the system from time 0 to time t. This integration is also related to a customer's experience with the system over the period under consideration. For binary systems, the expected value of the state of the system at any time is equal to the probability of success at the time under consideration. Similarly, one way to evaluate multistate systems is to calculate some accumulated value which is the integration of the expected value of the state of the system from time 0 to time t. Another way to evaluate multistate systems is to estimate how much benefit the customer can receive through using the system. To obtain this measure, we include a customer's utility function over time, and develop a model that can calculate a customer's expected total utility for their experience with the system. A better system should give the customer a high total utility over time and then these measures can be used in system design and evaluation.     

Kinetics of reactive diffusion between Au and Sn during annealing at solid-state temperatures

The reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures using Sn/Au/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were annealed at temperatures of T = 393 and 473 K for various times in an oil bath with silicone oil. After annealing, compound layers composed of AuSn₄, AuSn₂ and AuSn were recognized to form at the Au/Sn interface. The thickness of the AuSn₄ layer is about six and four times greater than those of the AuSn₂ and AuSn layers at T = 393 and 473 K, respectively. The ratio of the thicknesses of the compound layers is kept constant independently of the annealing time. The total thickness l of the compound layers is described as a function of the annealing time t by the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent n is nearly equal to 1/2 at T = 393 K but takes a value between 1/4 and 1/2 at T = 473 K. Such an intermediate value of n at T = 473 K indicates that the grain boundary diffusion contributes to the reactive diffusion and the grain growth occurs at certain rates. As the annealing temperature decreases, the contribution of the grain boundary diffusion should become more remarkable, but the grain growth will slow down. Consequently, n becomes close to 1/2 at T = 393 K. According to the constancy of the ratio of the thicknesses, it is concluded that the same rate-controlling process works in the AuSn₄, AuSn₂ and AuSn layers at a constant annealing temperature.     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).     

The equivalent channel model for permeability and resistivity in fluid-saturated rock—A re-appraisal

It is affirmed that a consistent development of the equivalent channel model for both fluid permeation and electrical conduction in saturated porous media leads to the expression CR²/F where R is the hydralic radius, F the formation resistivity factor or tortuosity/porosity ratio and C a numerical factor generally around 0.3 to 0.4. This expression is approximately supported by observations reported on granular media and fairly porous rocks. Confirmation of its applicability to low porosity, microcracked rock is still lacking but it would appear to be consistent with measurements on granite in that it indicates that the hydraulic radius (represented by half the mean crack opening width) decreases as the confining pressure is increased. In any application it is important in estimating R and F to take only the connected porosity into account.     

Thermal optical properties of TiO2 films

A fibre optic experimental arrangement was used to determine the thermo-optic coefficient (dn/dT) of electron beam deposited titanium dioxide coatings on the cleaved end faces of multimode optical fibres for a wavelength range between 600 and 1050 nm. The temperature-induced change in the index of refraction (n) and extinction coefficient (k) were successfully determined from reflection spectra. Measurements of n and k at various wavelengths for different temperatures enabled the determination of dn/dT and dk/dT. It was found that dn/dT takes different values at different temperature ranges. For example, at 800 nm, dn/dT was (−1.77±0.7)×10⁻⁴ K⁻¹, between 18°C and 120°C, and took a value of (−3.04±0.7)×10⁻⁴ K⁻¹ between 220°C and 325°C.     

Element Availability Importance in Generalized k-out-of-r-from-n Systems

An algorithm for evaluating the overall system availability and the availability importance of elements in a generalized consecutive k-out-of-r-from-n:F system is presented. This system consists of n linearly ordered nonidentical elements with different reliability characteristics and performance rates. Each element can have two states: (i) complete failure with a performance rate of zero; and (ii) perfect functioning with a nominal performance rate. The system fails if the sum of the performance rates of any r consecutive elements is lower than a demand W. The suggested algorithm, based on an extended universal moment generating function, is convenient for numerical implementation. Analytical and numerical examples of evaluating availability importance indices are presented.     

An efficient technique for detecting catastrophic convolutional codes

Catastrophic convolutional codes (CC) cause an infinite number of decoded data bit errors when decoding a finite number of code symbols. A CC displays a catastrophic error propagation if the generating polynomials have a common factor. An efficient algorithm for polynomial factorization in GF(2^m) is used for detecting catastrophic CC for any rate n/m and constraint length k. A general formula is derived to calculate the number of catastrophic codes in any (m, n, k) CC.     

Resistance curves for crack growth under plane-stress conditions in an elastic perfectly-plastic material

A recently developed solution for the plastic strain, ε^P_y(x, t), on the crack line is used in conjunction with a critical strain criterion to construct curves for k_R(a) versus a, where a is the increase in crack length. Resistance curves have been computed for various values of the critical plastic strain. They show a monotonic increase of K_R(a) with increase in crack length, to a constant steady-state value.     

Ozone Reaction with C70 and C60 Fullerenes: The Effect of Temperature on the Reaction Kinetics

It has been confirmed that the effect of temperature on the rate constants (k) of ozone reaction with C₇₀ and C₆₀ fullerenes follows the Arrhenius law. The experimental values of activation energy (E_a) and pre-exponential factor (A), like as those of other simple alkenes, are in the order of 2.4-2.6 kcal mol^-1 and (1.2-1.8) × 10⁷ L mol^-1 sec^-1, respectively. They are practically equal for the both fullerenes. It has also been found that the value of the rate constant k of C₇₀ fullerene ozonolysis is higher in comparison to the respective k-value of C₆₀.     

Computer simulation of martensitic textures

We consider a Ginzburg-Landau model free energy F(ε, e₁, e₂) for a (2D) martensitic transition, that provides a unified understanding of varied twin/tweed textures. Here F is a triple well potential in the rectangular strain (ε) order parameter and quadratic e₁², e₂² in the compressional and shear strains, respectively. Random compositional fluctuations η(r) (e.g. in an alloy) are gradient-coupled to ε, ˜ − ∑_rε(r)[(Δ_x² − Δ_y²)η(r)] in a “local-stress” model. We find that the compatibility condition (linking tensor components ε(r) and e₁(r), e₂(r)), together with local variations such as interfaces or η(r) fluctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective ε-ε interactions. We have carried out extensive relaxational computer simulations using the time-dependent Ginzburg-Landau (TDGL) equation that supports our analytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and Fe_xPd_{1 − x} alloys can be explained on the basis of our analysis and simulations.     

Effects of the magnetic field on the relaxation of small particle systems

We study the effect of a magnetic field on the thermal relaxation of non-interacting small monodomain particles with a distribution of anisotropy constants and random easy-axes directions. Numerical calculations of the relaxation curves for different distribution widths, and under different magnetic fields H and temperatures T, have been performed in the framework of a two-state approximation. We show how the obtained data can be analyzed in terms of an modified Tln(t/τ₀) scaling from which the field dependence of the mean relaxing energy barriers can be extracted, a microscopic information which is not easily obtainable by other methods.     

The microscopic theory of diffusion-controlled defect aggregation

The kinetics of diffusion-controlled aggregation of primary Frenkel defects (F and H centers) in irradiated CaF₂ crystals is theoretically studied. Microscopic theory is based on the discrete-lattice formalism for the single defect densities (concentrations) and the coupled joint densities of similar and dissimilar defects treated in terms of the Kirkwood superposition approximation. Conditions and dynamics of the efficient F center aggregation during crystal heating after irradiation are analyzed.     

Electrodeposition under a time-dependent boundary condition

The behaviour of the diffusion equation that results from assuming the boundary condition C(0,t)=C_b exp(−bt), with C_b (bulk concentration) and b constant, was examined. This condition reflects the behaviour of the diffusion around isolated nuclei growing onto a substrate. The diffusion equation under this boundary condition was solved and compared the results with the current transients obtained during electrodeposition. An expression for the fractional surface area of the deposit, S(t) and other parameters are obtained. The system reproduces the electrodeposition current transients in the chosen Cu²⁺/Cu couple and gives the values of the measured parameters at least within one order of magnitude. Some discrepancies between the theory and experimental results are examined and possible causes are suggested.     

Estimating the load line displacement of cracked laboratory specimens using the engineering treatment model (ETM)

The Engineering Treatment Model (ETM) provides a means for estimating the load line displacement of a cracked body. Under contained yielding conditions the model uses available linear elastic solutions with an Irwin-type plasticity correction of the crack length. The magnification factor (F/F_y)^1/n describing the material's strain hardening behaviour is applied for extrapolation into the regime of net section yielding. Comparison of ETM estimates with finite element and experimental results shows that the assumptions of the model are realistic.     

The integral catcher analysis of nuclear recoil experiments

The integral thick target thick catcher equations for extracting excitation and relaxation recoil velocities of nuclear reaction products have been reformulated. The new data analysis scheme corrects certain limitations and deficiencies inherent in the conventional procedure. Like the latter, our integral catcher analysis uses forward and backward recoil fractions F and B, but has no constraints on target thickness. The utility of the method may be extended with advantage to thinner targets. Additionally, there are no restrictions on the form of the range-velocity relationship that can be employed. Finally, the procedure inherently provides an excellent evaluation of the statistical uncertainties in the derived velocities based on the experimental uncertainties in F and B.     

Overlap-free Karatsuba-Ofman polynomial multiplication algorithms

The authors describe how a simple way to split input operands allows for fast VLSI implementations of subquadratic GF(2)[x] Karatsuba-Ofman multipliers. The theoretical XOR gate delay of the resulting multipliers is reduced significantly. For example, it is reduced by about 33 and 25% for n = 2^t and n = 3^t (t > 1), respectively. To the best of our knowledge, this parameter has never been improved since the original Karatsuba-Ofman algorithm was first used to design GF(2ⁿ) multipliers in 1990.