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PubMed2005

Theoretical bounds of majority voting performance for a binary classification problem.

A number of earlier studies that have attempted a theoretical analysis of majority voting assume independence of the classifiers. We formulate the majority voting problem as an optimization problem with linear constraints. No assumptions on the independence of classifiers are made. For a binary classification problem, given the accuracies of the classifiers in the team, the theoretical upper and lower bounds for performance obtained by combining them through majority voting are shown to be solutions of the corresponding optimization problem. The objective function of the optimization problem is nonlinear in the case of an even number of classifiers when rejection is allowed, for the other cases the objective function is linear and hence the problem is a linear program (LP). Using the framework we provide some insights and investigate the relationship between two candidate classifier diversity measures and majority voting performance.

Algorithms↗

PubMed2005

Learning from examples in the small sample case: face expression recognition.

Example-based learning for computer vision can be difficult when a large number of examples to represent each pattern or object class is not available. In such situations, learning from a small number of samples is of practical value. To study this issue, the task of face expression recognition with a small number of training images of each expression is considered. A new technique based on linear programming for both feature selection and classifier training is introduced. A pairwise framework for feature selection, instead of using all classes simultaneously, is presented. Experimental results compare the method with three others: a simplified Bayes classifier, support vector machine, and AdaBoost. Finally, each algorithm is analyzed and a new categorization of these algorithms is given, especially for learning from examples in the small sample case.

Algorithms↗

PubMed2005

Modeling of driver's collision avoidance maneuver based on controller switching model.

This paper presents a modeling strategy of human driving behavior based on the controller switching model focusing on the driver's collision avoidance maneuver. The driving data are collected by using the three-dimensional (3-D) driving simulator based on the CAVE Automatic Virtual Environment (CAVE), which provides stereoscopic immersive virtual environment. In our modeling, the control scenario of the human driver, that is, the mapping from the driver's sensory information to the operation of the driver such as acceleration, braking, and steering, is expressed by Piecewise Polynomial (PWP) model. Since the PWP model includes both continuous behaviors given by polynomials and discrete logical conditions, it can be regarded as a class of Hybrid Dynamical System (HDS). The identification problem for the PWP model is formulated as the Mixed Integer Linear Programming (MILP) by transforming the switching conditions into binary variables. From the obtained results, it is found that the driver appropriately switches the "control law" according to the sensory information. In addition, the driving characteristics of the beginner driver and the expert driver are compared and discussed. These results enable us to capture not only the physical meaning of the driving skill but the decision-making aspect (switching conditions) in the driver's collision avoidance maneuver as well.

Accidents, Traffic↗

PubMed2006

Multiperiod cellular network design via price-influenced simulated annealing (PISA).

Cellular telecommunications systems tend to be more flexible than traditional ones. As a result, traditional approaches to telecommunications network design are often inappropriate for the design of cellular networks, and approaches that explicitly incorporate the increased flexibility into the design process need to be developed. This paper presents one such multiperiod cellular network design problem and solves it via a hybrid heuristic that incorporates ideas from linear programming (LP) and simulated annealing (SA). Extensive computational results comparing the performance of the heuristic with the lower bound obtained from the LP relaxation are presented. These results indicate that this price-influenced simulated annealing (PISA) procedure is extremely efficient, consistently providing solutions with average gaps of 0.30% or less in fewer than 30 s.

Cell Phone↗

PubMed2005

Evaluation of Kalman filtering for network time keeping.

Time information is critical for a variety of applications in distributed environments that facilitate pervasive computing and communication. This work describes and evaluates a novel Kalman filtering algorithm for end-to-end time synchronization between a client computer and a server of "true" time [e.g., a Global Positioning System (GPS) source] using messages transmitted over packet-switched networks, such as the internet. The messages exchanged have the network time protocol (NTP) format, and the algorithm evaluated, is performed only at the client side. The Kalman filtering algorithm is compared to two other techniques widely used, based on linear programming and statistical averaging, and the experiments involve independent consecutive measurements (Gaussian case) or measurements exhibiting long-range dependence (self-similar case). Performance is evaluated according to the estimation error of frequency offset and time offset between client and server clock, the standard deviation of the estimates and the number of packets used for a specific estimation. The algorithms could exploit existing NTP infrastructure, and a specific example is presented.

Journal Article↗

PubMed2004

Risk management for Leontief-based interdependent systems.

When stricken by a terrorist attack, a war, or a natural disaster, an economic unit or a critical infrastructure may suffer significant loss of productivity. More importantly, due to interdependency or interconnectedness, this initial loss may propagate into other systems and eventually lead to much greater derivative loss. This belongs to what is known as a cascading effect. It is demonstrated in this article that the cascading effect and the derivative loss can be significantly reduced by effective risk management. This is accomplished by deliberately distributing the initial inoperability to other systems so that the total loss (or inoperability) is minimized. The optimal distribution strategy is found by a linear programming technique. The same risk management can also be applied to situations where objectives need to be prioritized. A case study featuring 12 economic sectors illustrates the theory. The result suggests that using the same amount of resources, minimizing risk (inoperability) of infrastructures will generally give rise to highest payoff, whereas overlooking it may result in greatest total loss. The framework developed in this work uses a steady-state approach that applies primarily to managing situations where the attack is catastrophic resulting in very long recovery time.

Journal Article↗

PubMed2005

Algorithms to estimate the rose of directions of a spatial fibre system.

Summary The directional measure (which is up to normalization the rose of directions) is used to quantify anisotropy of stationary fibre processes in three-dimensional space. There exist a large number of approaches to estimate this measure from the rose of intersections (which is the mean number of intersections of fibres with lower dimensional test sets). Three recently suggested nonparametric algorithms to solve this problem are reviewed and compared. They were obtained from solutions of a least squares problem, a more general convex optimization problem and a linear program, respectively. Application to two different carbon fibre architectures and to simulated data allow an empirical comparison of these approaches. In addition, estimators for the associated zonoid (or Steiner compact) are suggested. This set turns out to be an intuitive tool for visualization.

Algorithms↗

PubMed1992

A weighting method for predicting protein structural class from amino acid composition.

A protein is generally classified into one of the following four structural classes: all alpha, all beta, alpha+beta and alpha/beta. In this paper, based on the weighting to the 20 constituent amino acids, a new method is proposed for predicting the structural class of a protein according to its amino acid composition. The 20 weighting parameters, which reflect the different properties of the 20 constituent amino acids, have been obtained from a training set of proteins through the linear-programming approach. The rate of correct prediction for a training set of proteins by means of the new method was 100%, whereas the highest rate of previous methods was 82.8%. Furthermore, the results showed that the more numerous training proteins, the more effective the new method.

Amino Acids↗

PubMed2004

The principle of flux minimization and its application to estimate stationary fluxes in metabolic networks.

Cellular functions are ultimately linked to metabolic fluxes brought about by thousands of chemical reactions and transport processes. The synthesis of the underlying enzymes and membrane transporters causes the cell a certain 'effort' of energy and external resources. Considering that those cells should have had a selection advantage during natural evolution that enabled them to fulfil vital functions (such as growth, defence against toxic compounds, repair of DNA alterations, etc.) with minimal effort, one may postulate the principle of flux minimization, as follows: given the available external substrates and given a set of functionally important 'target' fluxes required to accomplish a specific pattern of cellular functions, the stationary metabolic fluxes have to become a minimum. To convert this principle into a mathematical method enabling the prediction of stationary metabolic fluxes, the total flux in the network is measured by a weighted linear combination of all individual fluxes whereby the thermodynamic equilibrium constants are used as weighting factors, i.e. the more the thermodynamic equilibrium lies on the right-hand side of the reaction, the larger the weighting factor for the backward reaction. A linear programming technique is applied to minimize the total flux at fixed values of the target fluxes and under the constraint of flux balance (= steady-state conditions) with respect to all metabolites. The theoretical concept is applied to two metabolic schemes: the energy and redox metabolism of erythrocytes, and the central metabolism of Methylobacterium extorquens AM1. The flux rates predicted by the flux-minimization method exhibit significant correlations with flux rates obtained by either kinetic modelling or direct experimental determination. Larger deviations occur for segments of the network composed of redundant branches where the flux-minimization method always attributes the total flux to the thermodynamically most favourable branch. Nevertheless, compared with existing methods of structural modelling, the principle of flux minimization appears to be a promising theoretical approach to assess stationary flux rates in metabolic systems in cases where a detailed kinetic model is not yet available.

Animals↗

PubMed2005

Economic evaluation for conservation of farm animal genetic resources.

The decline in biodiversity of farm animal genetic resources (AnGR) has come to the forefront of concern in the discussion of animal conservation and breeding programmes. To improve decision-making regarding conservation and breeding programmes, a number of evaluation techniques of farm AnGR are available. This paper presents an overview of the different values associated to AnGR and of the techniques for their measurement being employed in the economic literature. Those include linear programming and farm simulation models, dynamic models estimating the value of research and development and econometric models estimating the demand for breed characteristics. While farm programming and simulation models are fairly well developed, they do have large data requirements. Alternatively, contingent valuation methods are available, in particular when the goal is to capture non-market values embedded in breeds.

Animal Husbandry↗

PubMed2004

Capacity in Thai public hospitals and the production of care for poor and nonpoor patients.

OBJECTIVE: To assess the capacity of Thai public hospitals to proportionately expand services to both the poor and the nonpoor. This is accomplished by measuring the production of services provided to poor, relative to nonpoor, patients and the plant capacity of individual public hospitals to care for the patient load. STUDY SETTING: Thai public hospitals operating in 1999, following the economic crisis when public hospitals were required to treat all patients irrespective of ability to pay. STUDY DESIGN AND DATA COLLECTION: Input and output data for 68 hospitals were collected using databases and questionnaire surveys. A distinction was made between inpatient and outpatient services to both poor and nonpoor patients and the data were assessed statistically. DATA ANALYSIS: Congestion and capacity indices to measure poor/nonpoor service trade-offs and capacity utilization were estimated. The analysis was undertaken by data envelopment analysis (DEA), a nonparametric linear programming approach used to derive efficiency and productivity estimates. Principal Findings. Increases in the amount of services provided to poor patients did not reduce the amount of services to nonpoor patients. Overall, hospitals are producing services relatively close to their capacity given fixed inputs. Possible increases in capacity utilization amounted to 5 percent of capacity. CONCLUSIONS: Results suggest that some increased public hospital care can be accomplished by reallocation of resources to less highly utilized hospitals, given the budgetary constraints. However, further expansion and increase in access to health services will require plant investments. The study illustrates how DEA methodologies can be used in planning health services in data constrained settings.

Data Collection↗

PubMed2006

International comparison of the technical efficiency of component preparation.

BACKGROUND: Under economical constraints, blood centers need to identify ways to improve their efficiency. Because there is little evidence regarding the technical efficiency of blood centers, international comparisons may be useful in identifying efficiency discrepancies and can reveal opportunities for enhancing efficiency, such as allocating resources more effectively. STUDY DESIGN AND METHODS: Data were collected for years 2000 through 2002 from 16 blood centers in 10 European countries. Input variables included working hours, whole-blood (WB) collections, premises, and equipment, and the output variables were red blood cells and platelets (PLTs). A nonparametric method, data envelopment analysis (DEA), was used in the analyses of technical efficiency in blood component preparation departments. Efficiency scores were calculated with DEA linear programming techniques and evaluated for site characteristics that possibly affect efficiency, such as the production method of PLTs and the proportion of BCs (buffy coats) from WB and BC PLTs from all PLTs produced. RESULTS: With working hours and equipment as inputs, median technical efficiency was 60 percent (range, 41%-100%). Four departments were efficient (efficiency, > 90%), and 12 were inefficient (range, 41-89). Efficiency remained roughly the same in 13 departments through the 3-year study period and decreased in 3. Efficiency was mainly affected by staffing levels (working hours). Efficiency did not directly relate to production volume, method, or any other site characteristic. CONCLUSIONS: The major cause of inefficiency was excess staffing resulting from a suboptimal combination of manpower and production output levels. Further research is needed to manage factors affecting efficiency, such as the fluctuation of demand in production planning.

Blood Banks↗

PubMed2003

Real-time inverse planning for Gamma Knife radiosurgery.

The challenges of real-time Gamma Knife inverse planning are the large number of variables involved and the unknown search space a priori. With limited collimator sizes, shots have to be heavily overlapped to form a smooth prescription isodose line that conforms to the irregular target shape. Such overlaps greatly influence the total number of shots per plan, making pre-determination of the total number of shots impractical. However, this total number of shots usually defines the search space, a pre-requisite for most of the optimization methods. Since each shot only covers part of the target, a collection of shots in different locations and various collimator sizes selected makes up the global dose distribution that conforms to the target. Hence, planning or placing these shots is a combinatorial optimization process that is computationally expensive by nature. We have previously developed a theory of shot placement and optimization based on skeletonization. The real-time inverse planning process, reported in this paper, is an expansion and the clinical implementation of this theory. The complete planning process consists of two steps. The first step is to determine an optimal number of shots including locations and sizes and to assign initial collimator size to each of the shots. The second step is to fine-tune the weights using a linear-programming technique. The objective function is to minimize the total dose to the target boundary (i.e., maximize the dose conformity). Results of an ellipsoid test target and ten clinical cases are presented. The clinical cases are also compared with physician's manual plans. The target coverage is more than 99% for manual plans and 97% for all the inverse plans. The RTOG PITV conformity indices for the manual plans are between 1.16 and 3.46, compared to 1.36 to 2.4 for the inverse plans. All the inverse plans are generated in less than 2 min, making real-time inverse planning a reality.

Algorithms↗

PubMed2004

Fast treatment plan modification with an over-relaxed Cimmino algorithm.

A method to quickly modify a treatment plan in adaptive radiotherapy was proposed and studied. The method is based on a Cimmino-type algorithm in linear programming. The fast convergence speed is achieved by over-relaxing the algorithm relaxation parameter from its sufficient convergence range of (0, 2) to (0, infinity). The algorithm parameters are selected so that the over-relaxed Cimmino (ORC) algorithm can effectively approximate an unconstrained re-optimization process in adaptive radiotherapy. To demonstrate the effectiveness and flexibility of the proposed method in adaptive radiotherapy, two scenarios with different organ motion/deformation of one nasopharyngeal case were presented with comparisons made between this method and the re-optimization method. In both scenarios, the ORC algorithm modified treatment plans have dose distributions that are similar to those given by the re-optimized treatment plans. It takes us using the ORC algorithm to finish a treatment plan modification at least three times faster than the re-optimization procedure compared.

Algorithms↗

PubMed2005

A fourier analysis of the dose grid resolution required for accurate IMRT fluence map optimization.

We present a theoretical and empirical analysis of the errors associated with the spatial discretization of the dose grid employed in optimized intensity modulated radiation therapy (IMRT) treatment plans. An information theory based Fourier analysis of the accuracy of discrete representations of three-dimensional dose distributions is presented. When applied to beamlet-based IMRT dose distributions, the theory produces analytic integrals that can bound worst case aliasing errors that can occur regardless of the location and orientation of the dose grid. The predictions of this theory are compared to empirical results obtained by solving a linear-programming based fluence-map optimization model to global optimality. A reasonable agreement between worst case estimates and the empirical results is attributed to the fact that the optimization takes advantage of aliasing to produce an optimal plan. We predicted and empirically demonstrated that an isotropic dose grid with <2.5 mm spacing is sufficient to prevent dose errors larger than a percent. However, we noted that in practice this resolution is mostly needed in high-dose target regions. Finally, a multiresolution 2-4-6 mm spacing model was developed and empirically tested where these spacings were applied to targets, structures, and tissue, respectively.

Algorithms↗

PubMedDate not supplied

Systmatic method of formulating liquid phantoms with a given elemental composition and density.

A general method of formulating tissue equivalent liquid mixtures of a given chemical composition and density using the technique of linear programming is described. It is used to generate mixtures with equivalent atomic composition as ICRP Standard Man and mammalian muscle (NBS Handbook 85) using eight compounds to cover the range of densities from 1.0 to 1.13. Use of the method to handle other parameters of a mixture is also described.

Body Burden↗

PubMedDate not supplied

Optimized dynamic rotation with wedges.

Dynamic rotation is a computer-controlled therapy technique utilizing an automated multileaf collimator in which the radiation beam shape changes dynamically as the treatment machine rotates about the patient so that at each instant the beam shape matches the projected shape of the target volume. In simple dynamic rotation, the dose rate remains constant during rotation. For optimized dynamic rotation, the dose rate is varied as a function of gantry angle. Optimum dose rate at each gantry angle is computed by linear programming. Wedges can be included in the optimized dynamic rotation therapy by using additional rotations. Simple and optimized dynamic rotation treatment plans, with and without wedges, for a pancreatic tumor have been compared using optimization cost function values, normal tissue complication probabilities, and positive difference statistic values. For planning purposes, a continuous rotation is approximated by static beams at a number of gantry angles equally spaced about the patient. In theory, the quality of optimized treatment planning solutions should improve as the number of static beams increases. The addition of wedges should further improve dose distributions. For the case studied, no significant improvements were seen for more than 36 beam angles. Open and wedged optimized dynamic rotations were better than simple dynamic rotation, but wedged optimized dynamic rotation showed no definitive improvement over open beam optimized dynamic rotation.

Humans↗

PubMed1997

Supply-Side Analysis of Growth of Bacillus subtilis on Glucose-Citrate Medium: Feasible Network Alternatives and Yield Optimality.

Our prior work revealed that compared to the case for glucose metabolism, increased carbon yield and nil acid formation result when Bacillus subtilis grows on glucose medium containing citrate. To scrutinize further how citrate addition may alter metabolic flux regulation and the degree that the observed carbon yield corresponds to the maximal value, experimental (by least-squares analysis) and optimal (by linear programming) fluxes and yields were contrasted. Networks with differing reaction routes, directionality constraints, and transhydrogenase activities were examined. To attain an elevated carbon yield, citrate-glucose utilization need not alleviate any stoichiometric constraints that can sometimes interfere with the attainment of network objectives. Rather, the high carbon yield and nil acid formation attained may be linked to restriction of glycolytic capacity, particularly at the level of pyruvate kinase, which is consistent with a hypothesized effect of coupled metal-citrate uptake. Allowing for malic enzyme activity, hexose monophosphate pathway cycling, and transhydrogenase activity may also lead to the flux distributions underlying the high carbon yield observed. Finally, the observed carbon yield corresponded well to the maximum yield provided by all the network alternatives examined. Collectively, these results suggest that (i) the observed carbon yield is essentially equal to the maximal values associated with plausible networks and (ii), as suggested by others, nonoptimal flux regulation may contribute significantly to apparent cellular maintenance requirements.

Journal Article↗