Predetermined Rates Research Articles

The scheduling of economic lot sizes on volume flexible production systems

Previous efforts on solving the classical economic lot scheduling problem (ELSP) assume pre-determined and inflexible production rates. Production rates in many cases, such as orders filled by a machine, can be changed. Moreover, unit production cost of an item depends on its production rate. In this paper, we extend the ELSP model to cases where production rates are decision variables. Unit production cost for each item becomes a function of its production rate. We propose an algorithm to find a solution to the modified economic lot scheduling problem for special unit production cost functions and illustrate the results with numerical examples.

A simple handheld push-button device for in situ calibration of pneumotachographs

A simple and compact flow calibrator has been devised for generating precise predetermined constant flow rates for checking the calibration of laboratory and clinical flow transducers used in respiratory measurements. The standard version delivers preset flows of 0.5 and 1 l/s, whereas a tuned-up version can produce preset flows of 2.5 and 5 l/s, with an accuracy of +/- 2%. The pressure generated is sufficient to cope with most commonly used respiratory flowmeters. The flow calibrator is built from inexpensive components that are readily obtainable: a fan, a turbine flowmeter, and a feedback circuit in a compact housing. The device is easy to connect to other equipment and to operate. Three flow calibrators have been built and are in regular use in a lung function laboratory and on intensive care wards.

Importance of Catalase in the Disposal of Hydrogen Peroxide Within Human Erythrocytes

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

Importance of catalase in the disposal of hydrogen peroxide within human erythrocytes

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

Relationship between ventricular rate and cardiac output in mimic experimental atrial fibrillation

In treating atrial fibrillation (AF) the goal of ventricular rate reduction is still not determined. An animal model of AF was developed in which the relationship between ventricular rate and the parameters of cardiac function in AF can be studied. To simulate AF, complete heart block was chemically produced on open-chest dogs. Then, assisted by a portable computer, the ventricles were paced with a series of grossly irregular stimuli of predetermined rates, while atria were paced rapidly (500 beats/min). The resulting electrocardiogram and pressure were indistinguishable from the naturally occurring AF. It was found that in AF with ventricular rates that were lower than that of the control state, cardiac output was decreased, Cardiac output increased and reached a plateau when the ventricular rate increased to the level of the control state and then kept stable up to a rate of 320 beats/min. There was a discrepancy between the effective ventricular rate (rate of beats with pulse pressures ≥25 mmHg in the femoral artery) and the electrical ventricular rate. When the electrical ventricular rate increased over the control ventricular rate the effective ventricular rate did not increase in a parallel manner. Rather, the effective ventricular rate leveled off at the control ventricular rate. This discrepancy may explain the parallel relationship between the effective ventricular rate and cardiac output.

Effect of stepping rate on energy costs during StairMaster exercise

The responses to a self-selected stepping pattern (random) on a StairMaster 4000PT were compared with those obtained in response to the rates established by the manufacturer (cadence) in men (N = 14) and women (N = 14). During the random test the subjects stepped at their own natural, self-selected rate and distance. In cadence trial the subjects were required to step in time with a metronome at a predetermined rates of 60, 77, 95, and 112 steps.min-1. Each trial consisted of four, 5-min continuous workloads during which HRs were recorded and expired air was analyzed using an automated open-circuit gas system each minute. All size dependent variables (i.e., VE and lO2.min-1) as well as relative VO2 (mlO2.kg-1.min-1) were significantly (P < 0.01) higher for the men across all stages and between methods. Although the random test produced slightly higher oxygen consumption values than the cadence trial, these differences were not significant (P > 0.05). The actual METs were significantly (P < 0.01) higher at all stages except at the lowest stepping rate for both methods compared with those estimated by the manufacturer. Equations were established to estimate actual MET costs: Men's METs = 2.675 + 0.935 (rate); women's METs = 2.934 + 0.817 (rate). Cross-validations of 0.975 and 0.957 were obtained on an additional group of men (N = 8) and women (N = 11), respectively.

Blood lactate in trained cyclists during cycle ergometry at critical power

The purposes of this investigation were to determine the validity of critical power (CP) as a measure of the work rate that can be maintained for a very long time without fatigue and to determine whether this corresponded with the maximal lactate steady-state (lass,max). Eight highly trained endurance cyclists (maximal oxygen uptake 74.1 ml.kg-1.min-1, SD 5.3) completed four cycle ergometer tests to exhaustion at pre-determined work rates (360, 425, 480 and 520 W). From these four co-ordinates of work and time to fatigue the regression of work limit on time limit was calculated for each individual (CP). The cyclists were then asked to exercise at their CP for 30 min. If CP could not be maintained, the resistance was reduced minimally to allow the subject to complete the test and maintain a blood lactate plateau. Capillary blood was sampled at 0,5,10,20 and 30 min into exercise for the analysis of lactate. Six of the eight cyclists were unable to maintain CP for 30 min without fatigue. In these subjects, the mean power attained was 6.4% below that estimated by CP. Mean blood lactates (n = 8) reached a steady-state (8.9 mmol.l-1 SD 1.6) during the last 20 min of exercise indicating that CP slightly overestimated lass,max, Individual blood lactates during the last 20 min of exercise were more closely related to the gamma-intercept of the CP curve (r = 0.78, P less than 0.05) than either CP (0.34, NS) or mean power output (r = 0.42, NS).

Exchange Controls, Devaluations, and Real Exchange Rates: The Latin American Experience

This paper deals with the anatomy of devaluation in Latin America. In an effort to understand the economics surrounding the causes and consequences of exchange rate crises, eighteen devaluation episodes that took place between 1962 and 1982 are investigated in detail. The paper focuses on: (1) the relation between (inconsistent) macroeconomics policies and exchange rate crises; (2) the role of real exchange rate overvaluation in the precipitation of balance of payment crises under pre-determined nominal exchange rates; (3) the role of exchange controls, multiple exchange rates and black markets in the period preceding devaluations; and (4) the effectiveness of nominal devaluations as a way to restore real exchange rate equilibrium. A distinction is made between stepwise devaluations and crawling peg regime. It was found that historically most stepwise devaluations have had difficulty in sustaining a real devaluation over the medium term. Countries that adopted a crawling peg have generally been able to maintain a higher real exchange rate. In many cases, however, this has been achieved at the cost of substantial inflation.

Pectin-gelatin microglobules: effect of a cross-linking agent (formaldehyde) on in vitro dissolution rate

The purpose of this investigation was to evaluate the feasibility of controlling and predicting the dissolution rate of pectin-gelatin microglobules by varying formaldehyde concentration and reaction time. The potential use of this system is as an intravascular biodegradable drug delivery system applied to regional cancer chemotherapy. Spherical pectin-gelatin microglobules were prepared by a microencapsulation technique using a complex coacervation procedure of type A gelatin with pectin. The microglobules had a nominal size of 23 ± 3 μm in aqueous medium and were recovered as water-dispersible powders. Dissolution half-lives, in terms of number of microglobules, were controllable with the use of formaldehyde as a cross-linking agent within a range of about 2 min to more than 12 h with a CV of 10% (n = 4). A decrease in dissolution rate of these microglobules was observed with aging of the product stored under ambient conditions. The dissolution rates were fitted by an empirical polynomial equation of the second order. This polynomial equation was used as a tool for the determination of the values of the process variables necessary to meet pre-determined dissolution rates, which would permit rapid dissolution of the carrier once the drug has been released in the target organ. The experimentally determined half-lives correlated well with the predicted values.

Development of a simplified counterflow centrifugation elutriation procedure for depletion of lymphocytes from human bone marrow.

Graft-versus-host disease (GVHD) remains a major complication of allogeneic bone marrow (BM) transplantation. Techniques that effectively purge BM of mature T lymphocytes should reduce the incidence of GVHD and improve survival. We have developed a simplified, two-flow rate, fixed rotor speed counterflow centrifugation-elutriation (CCE) procedure that reproducibly depletes 99% of lymphocytes from Ficoll-Hypaque(F/H)-separated BM or BM buffy-coat. Two predetermined flow rates (24 and 28 ml/min) were used to purge small and intermediate-to-large lymphocytes, respectively, whereas faster sedimenting cells were recovered at the termination of the run. Lymphocyte depletion was substantiated by pan-T monoclonal antibody analysis as well as by complete loss of responsiveness to alloantigens and mitogens. Despite the lack of mature T cells, the depleted marrow fraction retained lymphoid colony-forming ability. Lymphocyte-purged marrow was obtained in high yield (72%), and retained high viability (greater than 97%) and hematopoietic colony-forming ability (greater than 99%). The ratio of total myeloid/erythroid colony-forming cells to T lymphocytes was 73-fold higher in the lymphocyte-depleted fraction than in unseparated BM. We concluded that a two-step CCE procedure can be used to rapidly deplete lymphocytes from both F/H-separated and buffy-coat BM inocula without altering hematopoietic capacity as measured by the in vitro clonogenic assays. It may be possible to adapt this procedure to the separation of the large number of marrow cells required for human BM transplantation.

Experimental validation of nonsteady rate measurements using a tracer infusion method and inulin as tracer and tracee.

In 1959, Steele (Ann. N.Y. Acad. Sci. 82, 420–430) suggested a method for measuring the rates of appearance (Ra) and of disappearance (Rd) of a metabolite in an intact system under conditions when Ra and Rd were changing with time. Steele's method involved modelling the system by a one-compartment model whose effective volume was assumed. To overcome the problem of assuming an effective volume, a model consisting of two compartments rather than one has been postulated. While no distribution volume need now be assumed, a preliminary steady state experiment is required for identification of the coefficients governing exchange of material between the two compartments.In five conscious dogs 14C-hydroxymethyl inulin (tracer) was infused at a constant rate, while unlabelled inulin (tracee) was infused at varying predetermined rates and the plasma concentrations of both were measured. These were then fitted by a series of smoothly joined polynomials. When the calculated rates of appearance of unlabelled inulin were compared with the actual rates, equally good results were obtained with the one-compartment (using the best effective volume) and the two-compartment models. The calculated values of Rd and of the clearance of inulin were not validated experimentally, but their validity is likely since the equations for Rd and Ra are related, and the Ra component has been validated. The identity of unlabelled inulin and the 14C-hydroxymethyl inulin species was ascertained by gel filtration, and by the identity of their in vivo kinetics.

Kinetics of charge transfer at mechanically strained copper electrodes—I. Anodic dissolution

A technique is described which permits a recording of mechano-electrochemical dissolution current at constant pre-determined strain rates for the Cu/aq. CuSO 4 system under potentiostatic control. Studies have been carried out in the range 2.5–15 mV with strain rate ranging from 0.047 to 0.9105 strain/min. The increase in current is proportional to the square root of the corrected strain ε at constant overpotential η, the gradient being dependent on η. At high strains, a slight departure from linearity has been observed: this deviation is greater, the lower the strain rate. The results are interpreted on the slow surface diffusion model. The variation of dislocation density consequent on straining shortens the surface diffusion path, thereby enhancing the dissolution current. An equation is derived which connects the dissolution current with ε 1 2 , η, a factor G ▪ A the constant of proportionality between the density of dislocations N and the corrected strain ε, D the surface diffusion constant for ad-atoms and the usual electrodes kinetic-parameters. This equation is strictly valid as a limiting law and departures at high strains are due to relaxation effects. These have been quantitatively accounted for a healing factor h. An equation which takes into account the strain rate is derived and verified. Using published values for the electrode kinetic parameters for the Cu reaction, the value of A is calculated from the graphs and found to be in excellent agreement with that reported from etch-pit counts. The results provide quantitative support for the validity of the slow surface-diffusion model for copper dissolution at low overpotential.