Load Change Rate Research Articles

Slower CD4 cell decline following cessation of a 3 month course of HAART in primary HIV infection: findings from an observational cohort

To investigate the effect of a short course of HAART during primary HIV infection (PHI) on rate of CD4 cell and viral load change. Data following HAART cessation from 89 individuals (seroconverting 1999-2003) who chose to take a 3 month course of HAART at PHI were compared with 179 untreated controls in CASCADE, using linear and nonlinear random effects models. Participants were non-randomized but frequency matched for age, sex, risk factor, year of seroconversion and presentation within the first 6 months of seroconversion. Time to CD4 cell count < 350 cells/microl and initiation of clinically indicated antiretroviral therapy (ART) were also compared as competing risks. The rate of CD4 cell decline following therapy cessation appeared significantly slower among treated participants than untreated controls: losses of 51 cells/microl [95% confidence interval (CI), 32-69] and 77 cells/microl (95% CI, 65-89), respectively, 3 years after seroconversion (P = 0.011). Based on extrapolated data, viral loads also differed significantly at this point (4.09 and 4.53 copies/ml, respectively). At 2 years, there was no significant difference in mean viral load levels: 4.31 copies/ml (95% CI, 4.14-4.48) and 4.47 copies/ml (95% CI, 4.28-4.66), respectively. CASCADE seroconverters were more likely to reach CD4 cell count < 350 cells/microl or initiate clinically indicated ART (hazard ratio, 1.45; 95% CI, 1.02-2.05; P = 0.039). A short course of ART at PHI may delay CD4 cell decline. Confirmation of this requires a randomized clinical trial powered to address definitively the role of ART intervention in PHI (currently underway through SPARTAC).

Influences of Cooling Load and Air Change Rate on the Performance of a Solar assisted Adsorptive Desiccant Cooling System

Influences of Cooling Load and Air Change Rate on the Performance of a Solar assisted Adsorptive Desiccant Cooling System

A Computational Positron Emission Tomography Simulation Model for Imaging ?-Amyloid in Mice

We aimed to develop a computational simulation model for beta-amyloid (Abeta) positron emission tomography (PET) imaging. Model parameters were set to reproduce levels of Abeta within the PDAPP mouse. Pharmacokinetic curves of virtual tracers were computed and a PET detector simulator was configured for a commercially available preclinical PET-imaging system. We modeled the effects of Abeta therapy and tracer affinity on the ability to differentiate Abeta levels by PET. Varying affinity had a significant effect on the ability to quantitate Abeta. Further, PET tracers for Abeta monomers were more sensitive to the therapeutic reduction in Abeta levels than total brain amyloid. Following therapy, the decrease in total brain Abeta corresponded to the slow rate of change in total amyloid load as expected. We have developed a first proof-of-concept Abeta-PET simulation model that will be a useful tool in the interpretation of preclinical Abeta imaging data and tracer development.

Modeling of Thermal Generating Units for Automatic Generation Control Purposes

A simple discrete time model of a thermal unit has been formally developed for designing automatic generation control (AGC) controllers. This model has been developed using data obtained from specific tests and historical records. This model consists of a nonlinear block followed by a linear one. The nonlinear block consists of a dead band and a load change rate limiter, while the linear block consists of a second-order linear model and an offset. Although most of these elements have already been included in unit models for AGC presented in the literature, a certain mix up exists about which of them are necessary. This is clarified in this paper. It has been found that the unit response is mainly determined by the rate limiter, while the other model components are used for a better fitting to the real response. An identification procedure is proposed to estimate the values of the model's parameters.

Changes in Viral Load in People with Virological Failure who Remain on the Same Haart Regimen

To assess the rate of change in viral load and CD4 count over time in HIV-infected patients experiencing virological failure on a HAART regimen. Study population included patients from EuroSIDA, a large, multicentre, observational study enrolling HIV-infected patients across Europe. Median change in viral load and CD4 count per month were estimated using the viral load and CD4 measurements obtained over a 12-month period after confirmed virological failure between 3 and 4 log10 copies/ml in a population of 488 HIV-infected patients who were left on a failing HAART regimen. The estimated median viral load change in our study population was 0.024 log10 copies/ml per month, statistically different from 0 (P=0.0001). In 20.9% of the patients studied viral load showed a tendency to decrease, in 47.8% showed a tendency to increase by a positive rate no higher than 0.04 log10 copies/ml per month and in the remaining 31.3% showed a tendency to increase by a rate greater than 0.04 log10 copies/ml per month. On average, CD4 counts were estimated to remain stable (decrease at a slow rate of about -0.53 cells/microl per month). In patients that remained on a stable, but virologically failing HAART regimen (with viral load ranging 1000-10000 copies/ml), the viral load over the ensuing 12-month period increased at a relatively slow rate. In contrast, the CD4 count remained stable, possibly because of partial but sustained viral suppression below the viral load natural set-point. The time-course of selecting more replication-competent virus in patients with virological failure remains to be fully clarified.

New concept for co-ordinated power-plant control

Control schemes for boiler-turbine units have formerly given priority to the grid requirements by regulating steam extraction from the boiler with minimum delay. With boiler systems that are slow to respond, steam storage is exhausted before increased steam production begins, leading to temperature and pressure fluctuations, material stresses and shortened plant life. A system is described in which dynamic models of the fuel mills, boiler and turbine are used to delay change to the load set point of the turbine controller. This system optimises the rate of load change with stress-free operation. It has been in service in a 750 MW unit over a 2-year period.

Modelling and Simulation of Thermal Stress Dynamics in a Steam Generator

Enormous price increases and limited reserves of fossil fuels have resulted in increased use of nuclear power plants for the base load of electricity supply. Consequently, conventional steam power plants have been used in variable and peak load ranges in the dailly load curves of electricity neneration. Economical control of non-stationary operations (start-up, shut-down, fast and large load changes) is possible only by approachinn and maintaining the maximum allowable material stresses at the critical points of power plants. These points occur during the steam generator operation, on the inside surface of the insulated thick wall components containing high temperature and hinh pressure steam. The rate of load change of a steam generator is mainly limited by thermal stresses occuring in the thick wall elements in which the working fluid flows. The appropriate design and effective application of a new control system for the nonstationary operating conditions require knowledqe of the dynamic behaviour of the thermal stresses at the critical points in the system. Thermal stress dynamics in steam generator components depend on the dynamics of the working fluid as well as on the design data of the component concerned. Extension of the working fluid dynamics to the thermal stress dynamics in steam generators is investigated in this study. The study comprises modeling and simulation of working fluid dynamics and their extension to thermal stress dynamics of an actual once-through steam generator. The mathematical model developed for the thermal stress dynamics can be used for developing and optimization of new control and measurement systems used for the control of power plants under nonstationary operating conditions.

Method of realizing strain-controlled loading regimes in high-cycle fatigue tests

1. The endurance of specimens correlates better with the inelastic strain overload reached during the initial loading period than with the stress amplitude. 2. To obtain correct experimental data in strain-controlled loadings, it is necessary that the increase in fatigue strains be the same for all specimens during the transition to the prescribed strain level. When testing machines with a limited rate of change in load are used, this requirement is met by allowing planned pauses during the transition.

Activation analysis of the steady-state deformation of single- and polycrystalline sodium chloride

Abstract Single crystals and polycrystals of NaCl were deformed in compression either at constant load or at constant compression rate at temperatures above 150°C. After some transient deformation a range of steady-state deformation characterized by dynamic equilibrium of work hardening and recovery was established. The extent of transient deformation increases strongly with stress σ. For σ ≳ 2 MN/m2 the steady-state relationship between a and strain rate σ can no longer be represented by a power law with constant stress exponent: n = δ log ∊/δ log σ determined from load change or strain rate change tests increases strongly with σ. It is shown that n yields a lower boundary of the activation area of that process of thermally activated dislocation movement determining the rate of steady-state deformation. From the magnitude of the lower boundary it may be inferred that thermally activated glide of dislocations (not climb of long edge dislocations) must be rate-con trolling. No difference was observed betwe...

Dynamics of arterial blood pressure responses to sinusoidal work load in man.

AbstractSystolic, diastolic, mean and pulse pressures in the radial artery, and heart rate in 7 physically active young men were subjected to frequency analysis by using sinusoidal work load as a forcing function. Subjects exercised in the supine position on a cycle ergometer. With the pedalling rate constant, the work load was varied sinusoidally over a range of drive frequencies between the two fixed extremes of 250 and 1050 kpm/min. Predicted step responses obtained by applying the trans fer functions estimated for radial systolic and pulse pressures showed close similarity to observed step responses, indicating linear properties of the underlying systems. Using known characteristics of the peripheral distortion of the pressure pulse, the responses of both the radial and central systolic and pulse pressures to work load could be described by second‐order transfer functions. Resonance occurred for periods near 7 min, indicating overshoots for both variables in the time domain. This behaviour suggests baroreflex inhibition as an explanation of an overdamped response of the heart rate. The changes in radial diastolic pressure were small and not clearly related to the drive frequency. The response of the radial mean pressure could not be described accurately by either first‐or second‐order functions, but exhibited phase lead features, suggesting sensitivity to rate of change in work load.

Engineering tests during the initial operation of the peach bottom HTGR

The initial power operation of the Peach Bottom Atomic Power Station was programmed as a series of physics, engineering and chemistry tests. These were performed in the first half of 1967 and were successful in bringing the reactor to full power in carefully measured stages which assured both safety and complete verification of earlier design predictions. The steam generators required modifications during these tests but successfully produced design capacity at the design steam conditions of 1000°F at 1450 psig. The plant controls met design requirements of controlling these values closely at steady state and at load change rates of up to three per cent per minute, with the reactor and steam generators following turbine load demand. Plant safety actions (scram, setback, loop isolation) were also tested and proved to be much gentler than originally predicted. The overall plant produced a maximum of 44.5 MW(e) gross (40.0 MW(e) net) with a maximum measured efficiency of 38.7% gross (34.7% net), believed to be the highest nuclear power plant performance yet achieved. Main coolant gaseous activity has remained well below 1 Curie total and all the chemical impurities are well below design limits; less than 10 ppm total oxidants. Power production continued through 1967 with periodic testing and maintenance operations requiring occassional shutdowns.