Worst Value Research Articles

Local pressure stresses on lateral pipe-nozzle with various angles of intersection

This paper reports the variations of local pressure stress factors (local pressure stress/internal pressure) at the juncture of a pipe-nozzle when the angle of the pipe-nozzle intersection varies from the standard 90° to the 30° lateral. These stress factors in both the circumferential and longitudinal directions at four symmetric points around the pipe-nozzle juncture are plotted as functions of the angle. The ALGOR finite element software was employed to model the true pipe-nozzle geometry. The numerical stress results come from a pipe-nozzle with geometric parameters, beta, β, (nozzle mean radius/pipe mean radius) of 0.5, and gamma, γ, (pipe thickness/pipe mean radius) of 50.0. This study shows that the 90° intersection, a standard pipe-nozzle, exhibits relatively less severe local stresses. These stresses are increasing as the angle of intersection is decreasing from 90° and become more severe when the angle of intersection is further decreasing from 45°. The circumferential stress at the inside crotch point exhibits the worst stress value. The stress factor results in pipe circumferential direction at the inside crotch points are in good agreement with the stress factor equation from the ASME boiler and pressure vessel code.

Interpretive optimisation strategy applied to the isocratic separation of phenols by reversed-phase liquid chromatography with acetonitrile–water and methanol–water mobile phases

An optimisation protocol is presented for the resolution of complex mixtures in isocratic RPLC with binary mobile phases of organic solvent and water, which is based on the prediction of peak position and shape of the individual compounds. A good description of the retention was achieved through the application of statistical weights to the widely used linear or quadratic relationships between the logarithm of the retention factor (log k) and the organic solvent concentration in the mobile phase. The maximisation of the product of peak purities for each compound is shown as a competitive resolution strategy versus the worst value of a selectivity parameter. Peak purities allow one to associate a single resolution value to each compound, which is not affected by the identity of the interfering peaks. It is shown how when full resolution is not achieved with a single mobile phase, the same experimental data set (retention factors, asymmetries and efficiencies) can be used for finding two or three optimal complementary mobile phases (CMPs). Each CMP resolves fully some compounds in the mixture, while the remaining compounds can overlap among them. The elementary limiting resolutions, which measure the maximal separation degree for each compound, are also given as a useful guide in the selection of the elution conditions. A mixture of 13 phenols (phenol, chloro-, bromo-, nitro- and methyl-derivatives), eluted with acetonitrile–water or methanol–water mobile phases, is used to show the proposed methodology.

97/04788 Overview of solar cell technologies and results on high efficiency multicrystalline silicon substrates: Nijs, J. Solar Energy Materials and Solar Cells, 1997, 48, (1–4), 199–217

This paper presents two grid-connected photovoltaic (PV) systems (monocrystalline silicon, c-Si; copper–indium–diselenide; CIS) situated on the rooftop of the solar lab building in the National University of Malaysia, southwestern Malaysia. Various parameters were used to analyze the system performance; including array yield, final yield, capacity factor, and performance ratio. The recordings were noted down under the actual climatic conditions for an entire year. The variables of energy cost and payback period were also considered to calculate the economic feasibility of the system. Variations in the final yield of CIS were as low as 2.98 h/day in July to the highest value of 4.31 h/day in March. The final yield for c-Si power plant ranged from 2.92 h/day in July to 4.14 h/day in March. The calculated capacity factors for CIS and c-Si power plants were 15.6% and 14.4%, respectively, in July as the worst value, and 21.12% and 20.2%, respectively, in March as the best value. In the case of CIS power plant, the performance ratio ranges from 63.8 in July to 84.12 in March, and for c-Si power plant, it ranges from 59.92 in July to 79.14 in March. The energy cost and the payback period of the suggested system were evaluated as 0.045 USD/kWh and 28.44 years, respectively. Finally, this study provides valuable information for those who are interested in PV system installation in the tropical zones.

The Time Course of Acute Hypoxemic Respiratory Failure in Children: Improvement or Deterioration Occurs Rapidly 186

The timely institution of therapy as well as the appropriate design of clinical trials of new therapies depend on an accurate understanding of the time course for evolution of acute hypoxemic respiratory failure. Methods: We analyzed the data collected at 12 hour intervals from 331ECMO-eligible patients in 32 centers (Crit Care Med 24:323-9, 1996) as part of the PCCSG study of Acute Hypoxemic Respiratory Failure (Chest 108:789-97, 1995). Data collection began when patients received at least 50% FiO2 and end expiratory pressure of 6 cm H2O or greater. The time courses to the primary positive outcome of interest (successful tracheal extubation) and primary negative outcomes (death in the PICU or the need for extracorporeal membrane oxygenation) were determined. Measures of oxygenation and ventilation as well as ventilator pressures were compared as predictors of outcomes. Results: Thirty six per cent of patients died and 11% received ECMO. The worst value for oxygenation index (OI)was the strongest predictor of death(P<.0001). An OI of 40 or above predicted a 48% probability of death and was selected as a third negative outcome (24% of patients). 42% of patients reached one or more negative outcome - 50% of these outcomes occurred within 24 hours of enrollment, 75% within 96 hours. Positive outcomes also occurred rapidly after enrollment: 25% of patients were extubated within 72 hours, 50% within 7 days. Conclusions: Acute respiratory failure in children improves or evolves to critical stages rapidly in the majority of children. Therapeutic trials must enroll and randomize patients within a narrow time window. Critical phases in the pathophysiology of lung injury probably occur early in the course when ventilator settings are low.

Quasistatic optimal actuator placement with minimum worst case distortion criterion

The problem of placing actuators optimally in truss structures for quasistatic shape control is considered. Optimal actuator placement in large truss structures is a formidable task due to the combinatorial nature of the problem. In this paper we use and compare the performances of several heuristic search techniques to determine their effectiveness in solving this design problem. The selected methods are simulated annealing, exhaustive single-point substitution, and single location iterative minimization, a sequential minimization technique presented herein. The optimality criterion is the worst case distortion after correction. This worst case value of a performance measure is obtained through a constrained min-max procedure. An ideal actuator concept is employed to determine limits on the optimal criterion value, which is then used also to evaluate the number of actuators needed for given levels of correction. The procedures just discussed are performed on representative trusses. Results show that heuristics can handle the optimization problem since the number of function calls grows linearly with the size of the problem and not in a combinatorial fashion, typical in such cases. The different algorithms exhibit similar performances ; however, exhaustive single-point substitution requires a significantly higher computational effort. The applicability of the lower limit is investigated, and in most cases there is good agreement with the optimization results.

Return loss characteristics of optical fiber connectors

This paper describes the return loss characteristics for four typical contact type connectors: perpendicular and oblique endface connectors employing either physical contact or contact via index matching material. The high index layer on the polished fiber endface and the index matching material, which are important connector parameters, are investigated by measuring the return loss from one perpendicular fiber endface coated with the material and by etching the fiber endface. It is useful to apply two materials with different refractive indices to derive the refractive index and thickness of high index layers on perpendicular fiber endfaces. The index matching material we use has a refractive index of 1.467 at 20/spl deg/C and a thermal coefficient of -2.9/spl times/10/sup -4///spl deg/C at 1.3 /spl mu/m. We performed return loss calculations and experiments of the four contact type connectors. The worst value at any temperature from -40 to 80/spl deg/C can be estimated, by measuring the return loss of these connectors at room temperature.

Besk-k-Fit bin packing

The bin packing problem is to pack a list of reals in (0, 1] into unit-capacity bins using the minimum number of bins. LetR∞[A] be the limiting worst value for the ratioA(L)/OPT(L) asOPT(L) goes to ∞, whereA(L) denotes the number of bins used when the approximation algorithmA is applied to the listL, andOPT(L) denotes the minimum number of bins needed to packL. For Best-k-Fit (BkF for short,k≥1), we prove in this paper thatR∞[BkF]=1.7+3/10k.

Connectorized integrated star couplers on silicon

A connectorized integrated <i>N</i> x <i>N</i> passive star coupler suitable for use in single-mode multichannel optical networks is reported. The excess loss for most of the channels of the coupler is within 1.5 dB, with a worst value of 3 dB, of the unconnectorized coupling values, which range from 14.5 to 17.5 dB. The optical fibers are attached to the 19 x 19 coupler by butt-coupling a linear array of single-mode fibers using silicon v-grooves. Alignment is rapidly achieved with a compact six-degrees-of-freedom piezo-controlled micromanipulator. Best values of less than 0.1 dB per fiber attachment, dependent on connector quality, were obtained. The coupler demonstrated negligible reflection effects when used as the central element in a 1-Gb/s frequency-division-multiplex network experiment.

Material and Cell Parameters Considerations in a Highly Multiplexing TN Liquid Crystal Display

Abstract The LC material and cell parameters influence on such electro-optical characteristics as the steepness γ, viewing angle dependence β and threshold voltage Vth in a twisted nematic (TN) cell has been investigated. The results have indicated the following: (1) The steepest or smallest γmin at some optimal cell thickness d 1 is reasonably estimated exclusively from the elastic constant ratio k 33/k 11 of LC material. (2) The steepness γmin at the cell thickness d 1 is linearly decreased or definitely improved with decreasing the ratio k 33/k 11. (3) The viewing angle dependence p has a maximum or the worst value at another cell thickness d 2 and is effectively improved with decreasing the cell thickness d in the region d < d 2. (4) The threshold voltage Vth is reduced with decreasing d in the region below another cell thickness d 3, which is different from d 1 and d 2. Through the optimization of LC material and cell parameters based on the above results, a 12-inch diagonal highly multiplexing dot-m...

The Rapid Acute Physiology Score

The Rapid Acute Physiology Score (RAPS) was developed and tested for use as a severity scale in critical care transports. RAPS is an abbreviated version of the Acute Physiology and Chronic Health Evaluation (APACHE-II) using only parameters routinely available on all transported patients (i.e. pulse, blood pressure, respiratory rate, and Glasgow Coma Scale). RAPS has a range from 0 (normal) to 16. Two hundred eighty-three patients were transported by helicopter; 62 died. Pretransport RAPS was available on 282 of 283 patients (mean, 3.85; median, 3). Because of death, discharge, or transfer, 227 complete APACHE-II scores using least physiologic values for the first 24 hours after transfer were collected (mean, 14.98; median, 13). Stepwise logistic regression showed that when all APACHE-II and RAPS values were available, the best single predictor of mortality was worst value APACHE-II (X 1 2 = 57.09, P < .01). When pretransport RAPS was considered as a single explanatory variable, it too had significant predictive power for mortality (X 1 2 = 92.53, P < .01). Correlation analysis comparing RAPS with APACHE-II values at similar points in time revealed a significant relationship in all cases, with the highest correlation between RAPS worst values and APACHE-II worst values (r = .8472, P < .01). It was concluded that RAPS can be applied usefully in complement with APACHE-II and may have limited utility when used alone.

Minimax observers

AbstractThis paper discusses the design of the regulator using output feedback, and describes a method of control using the observer. In the regulator using the observer, the evaluation function is increased, compared with the state‐feedback control. In this paper, the minimax evaluation is adopted, which considers the worst case in regard to the initial state. Consequently, the optimal observer, i.e., the minimax observer can be determined by the proposed method, in the sense that the worst value in regard to the initial state is minimized. Since the initial state is not known in the regulator problem using the output feedback control, the minimax evaluation is practically very important. This paper discusses first the discrete‐time system, and the design of the minimax observer is discussed for the linear quadratic form and the model‐following control problems. Then, the result of applying the idea to the continuous‐time system is shown. It is also possible to design the minimax observer for the continuous‐time system, in the same way as for the discrete‐time system. The proposed method can be applied, not only to the observer with the minimum dimension but also to the observer with the same dimension. As the numerical example, a solution of the minimum problem is presented using the proposed method.

Probabilistic asymptotic properties of some combinatorial optimization problems

A class of combinatorial optimization problems with sum- and bottleneck objective function is described, having the following probabilistic asymptotic behaviour: With probability tending to one the ratio between worst and optimal objective function value approaches one as the size of the problem tends to infinity. Problems belonging to this class are among others quadratic assignment problems, as well as certain combinatorial and graph theoretical optimization problems. The obtained results suggest that even very simple heuristic algorithms incline to yield good solutions for high dimensional problems of this class.

The asymptotic probabilistic behaviour of quadratic sum assignment problems

In this paper a surprising probabilistic behaviour of quadratic sum assignment problems is shown. The relative difference between worst and optimal solution value tends to zero with probability tending to one as the size of the problem goes to infinity. This result suggests that for high dimensional quadratic assignment problems even very simple approximation algorithms can in practice yield good suboptimal solutions.

Generalized Farkas' theorem and optimization of infinitely constrained problems

This note is concerned with the generalization of Farkas' theorem of the alternative and its application to derive the necessary optimality conditions for min-max problems with satisfaction conditions. Farkas' theorem is generalized to a system of linear inequalities with max operations. The problems studied require a solution at which the worst objective value attains its minimum over a set of solutions fulfilling satisfaction conditions. The satisfaction conditions claim that plural performance criteria should be kept below the permissible level, whatever disturbances may happen or whatever opponents' decisions may be taken. We present a generalized Farkas' theorem in order to derive the necessary optimality conditions for the problems of this class.

Optimal Design of Linear Regulators by Minimax Performance Index

This paper is concerned with the design of optimal linear output feedback regulators subject to a minimax performance index. The most difficult point in the design of linear regulators using output feedback is that optimal feedback matrices depend on the initial states which are unavailable When a minimax performance index is used, the worst value on the initial states can be minimized by using the proposed method. Since the control effects are restricted in the direct output feedback control, a new dynamic compensator is proposed to improve the performance index. The proposed dynamic compensator is excellent in simplicity, and it can be applied to the model following control problem and to the usual linear quadratic one.

Metrological features of the measurement of two-signal receiver selectivity and improvements to All-Union State Standard (GOST) 12252-66

To increase the objectivity of comparative estimates of receivers of the same form, it is useful to measure the two-signal selectivity using as the control level of the useful signal, not the maximum actual sensitivity but its worst value allowable by the technical conditions.

Minimax Output Feedback Regulators

The linear quadratic regulator problem is considered, and a method for obtaining an optimal output feedback control subject to a minimax performance index is presented. The optimal constant feedback matrix, which denotes the optimal constant feedback gains, is determined by minimizing the effects of the worst value of the initial state on the system performance measure. First, the necessary conditions for a minimax solution are given analytically. However, it is very difficult to determine the minimax solution directly from these necessary conditions. Then, a method for obtaining an optimal numerical solution by using a recursive formula is presented. Two iterative algorithms for the minimax solution are given. These algorithms are based on Theorem 4 and the saddle point assumption is not used. As shown in the illustrative examples the iterative solutions converge to the minimax value rapidly, and this method is useful for obtaining the minimax output feedback solution.