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PubMed1995

Evaluation of linear transformation and Pickworth's method usefulness in angiologic examinations of human fetal brain.

In this work usefulness of latest techniques in anatomical studies was assessed. The following methods were used: injection, Pickworth's method, image computer analysis with the usage of four systems: BVS 6471, BVS 6472, cytochromics, imtron 2000. Particular linear programs were analyzed and discussed. Several techniques were used simultaneously to reach difficult accessible structures.

Brain↗
PubMedDate not supplied

Medium term planning of biopharmaceutical manufacture using mathematical programming.

Regulatory pressures and capacity constraints are forcing the biopharmaceutical industry to consider employing multiproduct manufacturing facilities running on a campaign basis. The need for such flexible and cost-effective manufacture poses a significant challenge for planning and scheduling. This paper reviews the problem of planning and scheduling of biopharmaceutical manufacture and presents a methodology for the planning of multiproduct biopharmaceutical manufacturing facilities. The problem is formulated as a mixed integer linear program (MILP) to represent the relevant decisions required within the planning process and is tested on two typical biopharmaceutical industry planning problems. The proposed formulation is compared with an industrial rule based approach, which it outperforms in terms of profitability. The results indicate that the developed formulation offers an effective representation of the planning problem and would be a useful decision tool for manufacturers in the biopharmaceutical industry particularly at times of limited manufacturing capacity.

Algorithms↗
PubMed2004

Target volume uncertainty and a method to visualize its effect on the target dose prescription.

PURPOSE: To consider the uncertainty in the construction of target boundaries for optimization, and to demonstrate how the principles of mathematical programming can be applied to determine and display the effect on the tumor dose of making small changes to the target boundary. METHODS: The effect on the achievable target dose of making successive small shifts to the target boundary within its range of uncertainty was found by constructing a mixed-integer linear program that automated the placement of the beam angles using the initial target volume. RESULTS: The method was demonstrated using contours taken from a nasopharynx case, with dose limits placed on surrounding structures. In the illustrated case, enlarging the target anteriorly to provide greater assurance of disease coverage did not force a sacrifice in the minimum or mean tumor doses. However, enlarging the margin posteriorly, near a critical structure, dramatically changed the minimum, mean, and maximum tumor doses. CONCLUSION: Tradeoffs between the position of the target boundary and the minimum target dose can be developed using mixed-integer programming, and the results projected as a guide to contouring and plan selection.

Humans↗
PubMedDate not supplied

Multiple-dose non-linear regression analysis program. Aminoglycoside dose prediction.

The ability of a new multiple-dose non-linear regression analysis program to predict steady-state aminoglycoside peak and trough serum concentrations was evaluated. 30 patients receiving either amikacin (7), gentamicin (10) or tobramycin (13) were studied. A standard method of prediction which requires the collection of 3 or 4 serum samples during a dosing interval and a predictive method which relies upon population-based estimates of pharmacokinetic parameters were compared with the new approach which requires the collection of 2 serum samples. There were no significant differences between the methods which utilised serum concentration data with regard to predictive precision (mean prediction error of about 10%). These methods were more precise than the population-based method (p less than 0.01, mean prediction error 29.1%). None of the methods produced biased estimates. These results indicate that when the regression program is employed, valid estimates of pharmacokinetic parameters and prediction of steady-state serum concentrations can be obtained with fewer serum samples than have been recommended.

Adult↗
PubMed1986

BMDP program for piecewise linear regression.

Piecewise linear regression has potentially broad applications in medical data analysis as well as other types of regression. Various kinds of algorithms have been proposed for finding optimum piecewise linear regressions. This paper presents a BMDP program for obtaining near optimum piecewise linear regression equations. An idea intrinsic to the method is that restricting parameter space to a discrete set makes the difficult problems become standard problems. Any software having the variable selection feature in the multiple linear regression can be used to apply the method.

Computers↗
PubMed2006

Beam orientation optimization for intensity-modulated radiation therapy using mixed integer programming.

The purpose of this study is to extend an algorithm proposed for beam orientation optimization in classical conformal radiotherapy to intensity-modulated radiation therapy (IMRT) and to evaluate the algorithm's performance in IMRT scenarios. In addition, the effect of the candidate pool of beam orientations, in terms of beam orientation resolution and starting orientation, on the optimized beam configuration, plan quality and optimization time is also explored. The algorithm is based on the technique of mixed integer linear programming in which binary and positive float variables are employed to represent candidates for beam orientation and beamlet weights in beam intensity maps. Both beam orientations and beam intensity maps are simultaneously optimized in the algorithm with a deterministic method. Several different clinical cases were used to test the algorithm and the results show that both target coverage and critical structures sparing were significantly improved for the plans with optimized beam orientations compared to those with equi-spaced beam orientations. The calculation time was less than an hour for the cases with 36 binary variables on a PC with a Pentium IV 2.66 GHz processor. It is also found that decreasing beam orientation resolution to 10 degrees greatly reduced the size of the candidate pool of beam orientations without significant influence on the optimized beam configuration and plan quality, while selecting different starting orientations had large influence. Our study demonstrates that the algorithm can be applied to IMRT scenarios, and better beam orientation configurations can be obtained using this algorithm. Furthermore, the optimization efficiency can be greatly increased through proper selection of beam orientation resolution and starting beam orientation while guaranteeing the optimized beam configurations and plan quality.

Algorithms↗
PubMed2005

Optimal fleetwide emissions reductions for passenger ferries: an application of a mixed-integer nonlinear programming model for the New York-New Jersey Harbor.

Emissions from passenger ferries operating in urban harbors may contribute significantly to emissions inventories and commuter exposure to air pollution. In particular, ferries are problematic because of high emissions of oxides of nitrogen (NOx) and particulate matter (PM) from primarily unregulated diesel engines. This paper explores technical solutions to reduce pollution from passenger ferries operating in the New York-New Jersey Harbor. The paper discusses and demonstrates a mixed-integer, non-linear programming model used to identify optimal control strategies for meeting NOx and PM reduction targets for 45 privately owned commuter ferries in the harbor. Results from the model can be used by policy-makers to craft programs aimed at achieving least-cost reduction targets.

Air Pollutants↗
PubMed1980

Food and energy choices for India: a programming model with partial endogenous energy requirements.

This paper presents a mathematical model for all matter-energy processing subsystems at the level of the society, specifically India. It explores India's choices in the food and energy sectors over the coming decades. Alternative land intensive, irrigation energy intensive, and fertilizer intensive techniques of food production are identified using a nonlinear programming model. The land saved is devoted to growing firewood. The optimum combination of railway (steam, diesel, and electric traction) and road (automobiles, diesel trucks, and diesel and gasoline buses) transport is determined. For the oil sector, two alternative sources of supply of crude oil and petroleum products are included, namely, domestic production and imports. The optimum choice is determined through a linear programming model. While the model is basically a static one, designed to determine the optimal choice for the target year of 2000-2001, certain intertemporal detail is incorporated for electricity generation. The model minimizes the costs of meeting the needs for food, transport in terms of passenger kilometers and goods per ton per kilometer, energy needs for domestic cooking and lighting, and the energy needs of the rest of the economy.

Conservation of Energy Resources↗
PubMed1996

A comparison of mixed integer programming and fast simulated annealing for optimizing beam weights in radiation therapy.

Two competing methods for assigning intensities to radiation treatment beams were tested. One method was derived from mixed integer programming and the other was based on simulated annealing. The methods faced a common objective and identical constraints. The goal was to maximize the minimum tumor dose while keeping the dose in required fractions of normal organ volumes below a threshold for damage. The minimum tumor doses of the two methods were compared when all the dose-volume constraints were satisfied. A mixed integer linear program gave a minimum tumor dose that was at least 1.8 Gy higher than that given by simulated annealing in 7 of 19 trials. The difference was > or = 5.4 Gy in 4 of 19 trials. In no case was the mixed integer solution one fraction size (1.8 Gy) worse than that of simulated annealing. The better solution provided by the mixed integer program allows tumor dose to increase without violating the dose-volume limits of normal tissues.

Abdominal Neoplasms↗
PubMed2004

A recurrent neural network with exponential convergence for solving convex quadratic program and related linear piecewise equations.

This paper presents a recurrent neural network for solving strict convex quadratic programming problems and related linear piecewise equations. Compared with the existing neural networks for quadratic program, the proposed neural network has a one-layer structure with a low model complexity. Moreover, the proposed neural network is shown to have a finite-time convergence and exponential convergence. Illustrative examples further show the good performance of the proposed neural network in real-time applications.

Artificial Intelligence↗
PubMed1991

Planning replacement of natural gas distribution systems under constraints on acceptable risk from explosions.

Natural gas distribution systems in the United States were developed primarily in the first half of this century, utilizing materials such as cast iron and then steel. Over time, cast iron and steel pipe sections became weak from corrosion and are subject to failure which in turn can lead to explosions and possible injury and loss of life. Gas utilities maintain system integrity through repair-replacement programs where pipe sections are prioritized for replacement in any given year through cost-benefit analysis; however, the total annual amount to be budgeted for replacement is left to engineering judgment. This approach has left some utilities vulnerable to criticism that their current replacement rate on cast iron pipe is not great enough and that public safety is being compromised. This paper addresses the problem situation by formulating a linear programming replacement decision model which augments cost-benefit analysis with explicit constraints on acceptable risk to human life from fire/explosion. The model is illustrated for a hypothetical utility.

Cost-Benefit Analysis↗
PubMedDate not supplied

The impact of health care policy initiatives on productivity.

This paper analyses productivity growth in health care delivery in Sweden and the impact of health care policy initiatives on productivity. In particular we consider the maximum waiting time guarantee introduced in Sweden 1992. The intention of the maximum waiting time guarantee was to shorten the waiting lists, partly through increased productivity. We measure productivity growth by estimating Malmquist productivity indices using non-parametric linear programming models. The productivity models are applied to data from a sample of public ophthalmology departments from 1988 to 1993. Positive productivity changes are found in several years, although no significant differences between the periods are found.

Efficiency, Organizational↗
PubMed2003

The integration of claims to health-care: a programming approach.

The paper contributes to the use of social choice and welfare theory in health economics by developing and applying the integration of claims framework to health-care rationing. Related to Sen's critique of neo-classical welfare economics, the integration of claims framework recognises three primitive sources of claim: consequences, deontology and procedures. A taxonomy is presented with the aid of which it is shown that social welfare functions reflecting these claims individually or together, can be specified. Some of the resulting social choice rules can be regarded as generalisations of health-maximisation and all have normative justifications, though the justifications may not be universally acceptable. The paper shows how non-linear programming can be used to operationalise such choice rules and illustrates their differential impacts on the optimal provision of health-care. Following discussion of relations to the capabilities framework and the context in which rationing occurs, the paper concludes that the integration of claims provides a viable framework for modelling health-care rationing that is technically rigorous, general and tractable, as well as being consistent with relevant moral considerations and citizen preferences.

Attitude to Health↗
PubMed2005

A recurrent neural network for solving nonlinear convex programs subject to linear constraints.

In this paper, we propose a recurrent neural network for solving nonlinear convex programming problems with linear constraints. The proposed neural network has a simpler structure and a lower complexity for implementation than the existing neural networks for solving such problems. It is shown here that the proposed neural network is stable in the sense of Lyapunov and globally convergent to an optimal solution within a finite time under the condition that the objective function is strictly convex. Compared with the existing convergence results, the present results do not require Lipschitz continuity condition on the objective function. Finally, examples are provided to show the applicability of the proposed neural network.

Neural Networks, Computer↗
PubMed2002

Topology optimization of the kerf fillings in linear phased arrays for therapy.

Cross talk in ultrasonic arrays is an important problem that affects the array performance. For therapy arrays, cross talk decreases the acoustic power efficiency and array steering capabilities. Since arrays used for therapy are generally air-backed, structure-borne cross talk from the kerf fillings that connect the elements is predominant. In this paper, design strategies are developed to reduce the cross talk in linear phased arrays by optimizing the topology of kerf fillings. Two topology optimization schemes, an element-by-element design and layer-by-layer design, are developed. Sequential linear programming is used to solve the nonlinear optimization problem. Using an array subset technique as the basis for the design, an objective function based on maximizing the normal velocity response of the wet surface of an electrically driven element is shown to improve both the power output and steering of the array.

Acoustics↗
PubMed1994

Quantitative interpretation of lumbar muscle myoelectric signals during rapid cyclic attempted trunk flexions and extensions.

The quantitative relationship between lumbar myoelectric signals (MES) and rapidly varying isometric trunk muscle forces was investigated. Ten young adult males were asked to cycle harmonically between attempted trunk flexion and attempted trunk extension in an upright position at rates of 0.33, 0.67 and 1.0 Hz to peak efforts of 20, 40 and 60% of maximum voluntary exertion levels. The forces voluntarily exerted against a load cell were measured and used along with acquired kinematic data to calculate the time course of the net sagittal moment at the level of the third lumbar vertebra during task performances. A 22 muscle double linear programming biomechanical model was used to predict the lumbar trunk muscle contraction forces from the calculated moments. Rectified and bidirectionally low-pass filtered myoelectric activities were acquired at the L3 level from four abdominal muscles and four back muscles. The processed MES were found to be well correlated (r > 0.90) with predicted muscle forces when the MES were time-shifted to account for electromechanical delay as well as the dynamic phase shift between muscle electrical activity and contraction force. Mean time shifts that maximized the linear MES-force relationship ranged from 111 to 218 ms, were greater for the trunk extensors than the trunk flexors and generally exhibited lateral symmetry. The corresponding approximate phase angles averaged 20 degrees at the slowest rate and 50 degrees at the fastest rate. MES-force phase angles decreased as effort level was increased indicating that the dynamic MES-force relationship is nonlinear. These results illustrate the importance of accounting for the phase lag between muscle electrical activity and force when using MES to quantify muscle loads during rapidly varying exertions.

Abdominal Muscles↗
PubMed2004

1001 optimal PDB structure alignments: integer programming methods for finding the maximum contact map overlap.

Protein structure comparison is a fundamental problem for structural genomics, with applications to drug design, fold prediction, protein clustering, and evolutionary studies. Despite its importance, there are very few rigorous methods and widely accepted similarity measures known for this problem. In this paper we describe the last few years of developments on the study of an emerging measure, the contact map overlap (CMO), for protein structure comparison. A contact map is a list of pairs of residues which lie in three-dimensional proximity in the protein's native fold. Although this measure is in principle computationally hard to optimize, we show how it can in fact be computed with great accuracy for related proteins by integer linear programming techniques. These methods have the advantage of providing certificates of near-optimality by means of upper bounds to the optimal alignment value. We also illustrate effective heuristics, such as local search and genetic algorithms. We were able to obtain for the first time optimal alignments for large similar proteins (about 1,000 residues and 2,000 contacts) and used the CMO measure to cluster proteins in families. The clusters obtained were compared to SCOP classification in order to validate the measure. Extensive computational experiments showed that alignments which are off by at most 10% from the optimal value can be computed in a short time. Further experiments showed how this measure reacts to the choice of the threshold defining a contact and how to choose this threshold in a sensible way.

Algorithms↗
PubMed1985

The electronic spreadsheet as a general-purpose programming tool.

Electronic spreadsheets computerise the traditional layout of any tabulation or complex calculation done with pencil, paper and calculator. They therefore have great potential in aiding routine calculations which might be done by these means or with a small BASIC computer program. Their simple structure and strong affinity with traditional methods make them particularly suitable for those who have not yet mastered the art of programming. However, a necessarily brief review of their application to science and technology demonstrates that this potential is not being realised in comparison with their wide-spread usage in the business world. The application of both Multiplan and Visicalc running respectively on the Macintosh and the Apple IIe microcomputers in four types of calculation is demonstrated: tabulation, curve-fitting and statistics, simulation, and numerical approximation. Advantages are found in the concurrent display of data and results, the ease of correction or modification of data and the escape from traditional linear programming methods. The spreadsheet format imposes its own constraints. It is not so flexible as BASIC, it demands more memory and may have a slower execution time than a program written in a high-level language, and it is more difficult to produce graphical output.

Algorithms↗