A simple and effective heuristic for the resource constrained project scheduling problem

This paper investigates the development and application of a simple heuristic to the resource constrained project scheduling problem (RCPSP). This computer heuristic, which is based on the COMSOAL heuristic, constructs a feasible solution at each iteration and chooses the best solution of several iterations. Although COMSOAL was originally a solution approach for the assembly-line balancing problem, it can be extended to provide solutions to the resource allocation problem. The Modified COMSOAL technique presented in this paper uses priority schemes intermittently with a random selection technique. This hybrid of randomness and priority scheme allows a good solution to be found quickly while not being forced into the same solution at each iteration. Several different priority schemes are examined within this research. The COMSOAL heuristic modified with the priority schemes heuristic was tested on several established test sets and the solution values are compared with both known optimal values and the results of several other resource allocation heuristics. In the vast majority of cases, the Modified COMSOAL heuristic outperformed the other heuristics in terms of both average and maximum percentage difference from optimal. The Modified COMSOAL heuristic seems to have several advantages over other RCPSP heuristics in that it is easy to understand, easy to implement, and achieves good results.     

The effect of 2-hydroxypropyl-ß-cyclodextrin on the solubility,stability and dissolution rate of famotidine

Abstract

Famotidine was found to form an inclusion complex with 2-hydroxypropyl-ß-cyclodextrin (HPCD). Phase-solubility diagram was classified as type A_L with a stability constant for complex formation (K_st) of 100.50 M¹ at pH 7.4. Famotidine undergoes specific acid catalysis in strongly acidic solutions. Addition of HPCD to these solutions decreased the rate of drug degradation. The rate constant for degradation of complexed famotidine (k_c) and K_st were estimated from the relationship between the observed rate constant for overall drug degradation (K_obs) and HPCD concentration. An increase in ionization of famotidine resulted in a decrease in the magnitude of K_st. The dissolution rate of the prepared complex was significantly greater than that of the pure drug.     

A complex variable boundary element method for antiplane stress analysis around a crack in some nonhomogeneous bodies

Abstract

A boundary element method based on the Cauchy integral formulae, i.e. a complex variable boundary element method (CVBEM), is proposed for the numerical solution of an antiplane crack problem involving an elastic body with shear modulus that varies continuously in space. The shear modulus assumes a certain form which is quite general to allow for multiparameter fitting of its variation. The method reduces the problem to a system of linear algebraic equations and can be readily implemented on the computer. For clarity, the CVBEM formulation is first carried out for a straight crack and then its extension to include an arbitrary curved crack is indicated.     

Parameterization of solutions to the diophantine equation via the concepts of generalized state‐space realization and feedback

Abstract

By virtue of the concepts of generalized state‐space system realization and feedback, the parameterization of solutions to the Diophantine equation is easily obtained. The solutions are expressed in an explicit formula form. Hence, the matrix‐manipulation software packages and existing computational algorithms can be directly employed to calculate the solutions.     

Inverse problem of controlling the interface velocity in Stefan problems by conjugate gradient method

Abstract

The conjugate gradient method of minimization with adjoint equation is used successfully to solve the inverse problem in estimating an appropriate boundary control function such that the phase front moves at a desired velocity in the Stefan problem.

It is assumed that no prior information is available on the functional form of the unknown control function, therefore, it is classified as the function estimation in inverse calculation. The stability and accuracy of the inverse analysis using present algorithm are examined by comparing the results of the previous work by Voller [12].

Results show that the estimated control function by using conjugate gradient method did not exhibit oscillatory behavior in the inverse calculations for a broad range of front velocity while in [12] the inverse solutions are very sensitive to phase front velocity, therefore the application of future time stepping [2] is necessary in [12].

The advantage of applying this algorithm in inverse analysis lies in its stability as compared to the conventional minimization process [12]. Artificial future time stepping is unnecessary during the inverse calculation, since it is still an uncertainty in the inverse analysis. Furthermore, the inverse solutions obtained by the present method are found to be more accurate than the solutions obtained by the conventional minimization process.     

Fundamental solutions for an anisotropic medium with a notch or an inclusion

Abstract

A fundamental solution for an anisotropic medium with a notch or a rigid inclusion of arbitrary shape is derived based on the complex potential formulation of anisotropic elasticity. The solutions for a crack, for a circular hole or inclusion, and for a half plane are obtained as special cases. The solution can be applied to the analysis of crack, notch and inclusion problems of anisotropic materials.     

OPTIMUM DESIGN OF A SINGLE-ENDED FLYBACK CONVERTER

In this paper, an optimum design method is employed for a single ended flyback converter with four outputs. The mathematical model contains 16 variables and 16 constraints to minimize the weighted sum of the power loss and weight of the converter. The Augmented Lagrangian Multiplier Penalty Function Technique is adopted in forming the CAD program with FORTRAN IV. By treating the switching frequency as a constant in each computer run, a set of suboptimum design solutions were obtained by varying the frequency from 20 KHz to 60 KHz in 10 KHz steps. The U-shaped curve is observed by plotting the total loss characteristic against frequency. The following optimum design results are also obtained:

1) The optimum de duty ratio is about 0.3 to 0.34.

2) The converter should work at the critical mode between the discontinuous and current mode.

3) The air gap of the transformer core should be large enough (e.g.to 1.3 mm).     

Insights into a mixed Chinese postman problem

Abstract

In this study, we consider a Mixed Chinese Postman Problem in the form of an Integer Program and investigate its properties with both algebraic solutions and geometric configurations. The insights this study provides into their relationship have paved a way toward designing more efficient structural algorithm for finding an exact solution. Theoretical proofs are provided with numerical illustrations.     

Formulation and characterization of lyophilized curcumin solid dispersions for antimicrobial photodynamic therapy (aPDT): studies on curcumin and curcuminoids LII

Context: Bacterial resistance to antibiotics is increasing and alternative antibacterial treatments like antimicrobial photodynamic therapy (aPDT) are needed. Curcumin is under investigation as a potential photosensitizer in aPDT.

Objective: The purpose of this study was to develop rapidly dissolving formulations of curcumin that could photoinactivate both Gram-positive and Gram-negative bacteria.

Materials and methods: Curcumin solid dispersions with methyl-β-cyclodextrin and hyaluronic acid (HA), hydroxypropyl methylcellulose (HPMC) or both HA and HPMC were prepared through lyophilization. The lyophilizates were characterized by curcumin drug load [% (w/w)], differential scanning calorimetry, photostability, thermal stability, their ability to form supersaturated solutions and by in vitro photoinactivation of Enterococcus faecalis and Escherichia coli.

Results and discussion: The lyophilizates were amorphous solid dispersions with a curcumin drug load in the range of 1.4–5.5% (w/w) depending on the included polymer and the ratio between curcumin and the cyclodextrin. The lyophilizates were photolabile, but thermally stable and dissolved rapidly in contact with water to form supersaturated solutions. Selected lyophilizates demonstrated >log 6 reduction of colony forming units/ml of both E. faecalis and E. coli after exposure to low curcumin concentrations (0.5–10?µM) and blue light dose (11–16?J/cm²). The high drug load of the lyophilizates, rapid dissolution, ability to form relatively stable supersaturated solutions and the very high phototoxicity towards both E. faecalis and E. coli make these lyophilizates suitable for in vivo aPDT.

Conclusions: This treatment with optimized curcumin formulations should be explored as an alternative to topical antibiotics in the treatment of wound infections.     

An experimental study of on‐line computer control techniques applied to a double pipe heat exchanger

Abstract

Three different on‐line computer control methods, namely the identification and optimizing control technique, the direct design method and the digital form of P‐I‐D control, are applied to control the response of a double pipe heat exchanger. The relative merits of the methods are studied and discussed.

The experimental work is accomplished by the use of a HP‐1000 model 5L microcomputer. A digital voltmeter; the HP‐3456A, is used for reading and transferring data from the process to the computer. A data acquisition system, the HP‐3497A, contains a thermocouple relay and a D/A converter which can read input data from a thermocouple and also convert digital outputs to 4–20 mA signals required by control elements.

Results indicate that the identification and optimizing control technique gives superior performance in most cases, but requires longer computation time. Digital form of the P‐I‐D control requires the least computation time but yields poor performance and is limited in its potential for application to multivariable systems or to tracking problems.     

Sampling techniques in the analysis of Power-System transients

A detailed investigation of analytical approaches to the determination of transients on Power Systems has been undertaken¹, the main features of which are presented in this paper. The shortcomings of conventional travelling-wave methods, particularly where long power lines constitute complex sub-systems, have led to a numerical solution approach based on a discrete form of the Laplace Transform which has been labelled the ‘Fast Laplace Transform’ (FLT). The method allows efficient treatment of a wide variety of linear problems including, in particular, cases involving frequency-dependent parameters. An examination of continuous evaluation procedures, which are subject to truncation difficulties and to inefficient usage of computer time, is followed by a review of frequency domain sampling methods. ^4,5,11 The FLT inversion technique is described with emphasis on the efficient use of computer time. The method is illustrated by application to a number of switching studies and comparison with travelling-wave solutions is made. Problems involving frequency-dependent ground impedance, even where ground resistivity varies with depth, are easily simulated.     

Necessary and Sufficient Conditions for Quantum Computation

Abstract

Necessary and sufficient conditions are given for a quantummechanical system to possess a coordinate system with respect to which its behaviour at discrete times is that of a universal digital computer. The form of the diagonal representation for the unitary time evolution operator for quantum universal computers is derived; aspects of the transformation between the diagonal representation and the computational representation are shown to be uncomputable. A quantum-mechanical treatment of macroscopic, dissipative computers is given.     

Consulting the EPO systematically classified documentation of the future: Paper or computer?

To prevent the continual growth of the volume of documentation at the EPO, two possible solutions are considered:

1. 1. Keep the last 20 years of documents in paper form, the remainder being available from a computer database.

2. 2. Keep the most frequently consulted search files in paper form and make the remainder accessible from a computer database.

The consequences in respect of reduction of paper documentation and numbers of diskettes needed for the electronic part of the file are discussed and the advantages and disadvantages of each solution assessed.     

Estimation of turbulence velocities induced by magnetic stirring during continuous casting

Abstract

In this paper the turbulent flow generated in a cylindrical container by a low-frequency rotating magnetic field is considered. The rotational part of the electromagnetic body force is steady and axisymmetric, driving an azimuthal swirl flow. It is shown that curvature effects are negligible near the wall of the containing vessel and consequently the velocity profile in that region has the standard logarithmic form. Extrapolating this profile to the core allows an estimate of the core angular velocity to be made. This estimate is consistent with published experimental data and with the results of a more complex two-parameter closure model.

MST/207     

Characteristic analysis of absorptive multiple-quantum-well optical waveguides

Abstract

By extending the transfer matrix technique from the real domain to the complex, the complex eigenvalue equation is presented for both transverse electric and transverse magnetic modes of absorptive multiple-quantumwell optical waveguides, and a computer program is developed to solve the eigenvalue equation in the complex plane. On the basis of the computed results, the effects of the structural parameters and the refractive index profile on the mode propagation and loss properties are analysed and discussed for In^x Ga^1?xAs/Al^yGa^1?yAs absorptive multiple-quantum-well optical waveguides. The results indicate that, if approximate guided structural parameters and an appropriate refractive index profile are selected, higher-order modes can be controlled and single-mode propagation can be realized in the multiple-quantum-well optical waveguide with lower mode loss.     

Exact finite element solutions to the Helmholtz equation

For one-, two- and three-dimensional co-ordinate systems finite element matrices for the wave or Helmholtz equation are used to produce a single difference equation holding at any point of a regular mesh. Under homogeneous Dirichlet or Neumann boundary conditions, these equations are solved exactly. The eigenfunctions are the discrete form of sine or cosine functions and the eigenvalues are shown to be in error by a term of + O(h²ⁿ) where n is the order of the polynomial approximation of the wave function. The solutions provide the means of testing computer programs against the exact solutions and allow comparison with other difference schemes.     

Effects of Absorption on Multivalued Solutions in Photorefractive Four-wave Mixing with Complex Coupling Constant

Abstract

The steady-state coupled wave equations describing anisotropic photorefractive four-wave mixing with absorption in cubic crystals are solved for the general case where the coupling constant is complex. The effects of absorption on the behaviour of the multivalued solutions that occur under these conditions are examined, and the consequences for the dynamical behaviour are discussed.     

Development of modified in situ gelling oral liquid sustained release formulation of dextromethorphan

Context: Alternative strategies are being employed to develop liquid oral sustained release formulation. These included ion exchange resin, sustained release suspensions and in situ gelling systems. The later mainly utilizes alginate solutions that form gels upon contact with calcium which may be administered separately or included in the alginate solution as citrate complex. This complex liberates calcium in the stomach with subsequent gellation. The formed gel can break after gastric emptying leading to dose dumping.

Objective: Development of modified in situ gelling system which sustain dextromethorphan release in the stomach and intestine.

Methods: Solutions containing alginate with calcium chloride and sodium citrate were initially prepared to select the formulation sustaining the release in the stomach. The best formulation was combined with chitosan. All formulations were characterized with respect to flow, gelling capacity, gelling strength and drug release.

Results: Increasing the concentration of alginate increased the gelling capacity and strength and reduced the rate of drug release in gastric conditions with 2% w/v alginate being the best formulation. However, these formulations failed to sustain the release in the intestinal conditions. Incorporation of chitosan with alginate increased the gelling capacity and strength and reduced the rate of drug release compared to alginate only system. The effect was optimum in formulation containing 1.5% w/v chitosan. The sustained release pattern was maintained both in the gastric and intestinal conditions and was comparable to that obtained from the marketed product.

Conclusion: Alginate-chitosan based in situ gelling system is promising for developing liquid oral sustained release.     

Oral liquid in situ gelling methylcellulose/alginate formulations for sustained drug delivery to dysphagic patients

Background: Elderly patients with swallowing dysfunction may benefit from the oral administration of liquid dosage forms with in situ gelling properties.

Aim: We have designed in situ gelling liquid dosage formulations composed of mixtures of methylcellulose, which has thermally reversible gelation properties and sodium alginate, the gelation of which is ion-responsive, with suitable rheological characteristics for ease of administration to dysphagic patients and suitable integrity in the stomach to achieve a sustained release of drug.

Method: The rheological and gelation characteristics of solutions containing methylcellulose (2.0%) and sodium alginate (0.25–1.0%) were assessed for their suitability for administration to dysphagic patients. The gel strength and in vitro and in vivo release characteristics of gels formed by selected formulations were compared using paracetamol as a model drug.

Results: Mixtures of 2.0% methylcellulose and 0.5% alginate containing 20% d-sorbitol were of suitable viscosity for ease of swallowing by dysphagic patients and formed gels at temperatures between ambient and body temperature allowing administration in liquid form and in situ gelation in the stomach. In vitro release of paracetamol from 2.0% methylcellulose/0.5% alginate gels was diffusion-controlled at pH 1.2 and 6.8. Measurement of plasma levels of paracetamol after oral administration to rats of a 2.0% methylcellulose/0.5% alginate formulation showed improved sustained release compared to that from 2.0% methylcellulose and 0.5% alginate solutions and from an aqueous solution of paracetamol.

Conclusions: Solutions of mixtures of methylcellulose and alginate in appropriate proportions are of suitable consistency for administration to dysphagic patients and form gels in situ with sustained release characteristics.     

Dynamics steady crack propagation of antiplane shear in an elastic perfectly plastic material

Abstract

A theoretical analysis of steady‐state crack growth in an elastic ideally‐plastic material under small‐scale yielding conditions has been carried out for anti‐plane shear. Asymptotic expansion method is used to construct the solutions for the region near the crack line. Exact solutions for the distribution of strain on the crack line within the primary active plastic zone is obtained. It is shown that the solution reduces to the correct asymptotic form as the crack speed approaches zero (quasi‐static) for any point on the crack line. The results are used to discuss the applicability of quasi‐static solutions to moving steady‐state situations. It is found that if the crack propagation speed is less than 0.1 of the shear wave speed, the quasi‐static solutions can be accurately approximated for the steady state solutions.