Mean Values Of Load Research Articles

Transient stability probability assessment and statistical estimation

In the paper, a general analytical method for the probabilistic evaluation of power system transient stability is discussed and a new statistical inference approach for this evaluation is proposed. In particular, the transient stability probability (TSP) is defined and evaluated by taking into account the random nature of both the system loads and the fault clearing times (FCT). The paper is focused upon the aspect of statistical estimation of the TSP—a topic generally neglected in literature—on the basis of the obvious consideration that the parameters affecting the TSP (e.g. mean value and variance of loads, FCTs, etc.) are not known, but must be estimated. New properties of point and interval estimations of the TSP are derived and, in particular, an efficient “lower confidence bound” for the TSP estimation is proposed, based upon a suitable Beta probability distribution. In order to show the feasibility of the proposed approach, a numerical application to the Cigre test network is illustrated. Moreover, extensive Monte Carlo simulations to evaluate the estimator efficiency are performed. In the final part of the paper, also a practical example of possible application to the optimization of system design is illustrated. The application of the method is illustrated and performed by using the potential energy boundary surface method, but the estimation results hold their validity irrespective of the method adopted for the transient stability problem formulation and resolution.

Correlation between plasma HIV-1 RNA levels and the rate of immunologic decline.

To determine the influence of HIV-1 replication on immunologic decline and clinical outcome, we quantified the HIV-1 plasma viral load in 20 patients at different times over a mean period of 10.8 months. Quantitation was performed by branched DNA signal amplification (bDNA) and p24 antigenemia. Immunologic status was assessed through beta 2-microglobulin and CD4+ cell count determinations. CD4+ cell decline was expressed as a slope of the regression line constructed by the logarithms of CD4+ cell count observations. Mean values of plasma viral load were correlated with CD4+ cell decline and mean beta 2-microglobulin levels. Significant correlation was observed between plasma viral load quantified by the bDNA technique and CD4+ cell decline. No significant correlation was observed between plasma viral load quantified by p24 antigenemia and CD4+ cell decline. A significant correlation was observed between plasma viral load and beta 2-microglobulin levels. Immunologic decline was better predicted from HIV-1 RNA levels than from the CD4+ cell count. Significantly higher plasma viral load was observed in patients who had clinical progression of HIV-1 infection. Thus, HIV-1 plasma viral load quantified by a highly reliable technique such as bDNA showed that the immunologic decline is closely related to HIV-1 RNA replication.

Analysis of Telemetric Time Series data for Periodic Components Using Dq-Fit

DQ-FIT and CV-SORT have been developed to facilitate the automatic analysis of data sampled by radiotelemetry, but they can also be used with other data sampled in chronobiological settings. After import of data, DQ-FIT performs conventional linear, as well as rhythm analysis according to user-defined specifications. Linear analysis includes calculation of mean values, load values (percentage of values above a defined limit), highest and lowest readings, and areas under the (parameter-time) curve (AUC). All of these parameters are calculated for the total sampling interval and for user-defined day and night periods. Rhythm analysis is performed by fitting of partial Fourier series with up to six harmonics. The contribution of each harmonic to the overall variation of data is tested statistically; only those components are included in the best-fit function that contribute significantly. Parameters calculated in DQ-FIT's rhythm analysis include mesor, amplitudes, and acrophases of all rhythmic components; significance and percentage rhythm of the combined best fit; maximum and minimum of the fitted curve and times of their occurrence. In addition, DQ-FIT uses the first derivative of the fitted curve (i.e., its slope) to determine the time and extent of maximal increases and decreases within the total sampling interval or user-defined intervals of interest, such as the times of lights on or off. CV-SORT can be used to create tables or graphs from groups of data sets analyzed by DQ-FIT. Graphs are created in CV-SORT by calculation of group mean profiles from individual best-fit curves rather than their curve parameters. This approach allows the user to combine data sets that differ in the number and/ or period length of harmonics included. In conclusion, DQ-FIT and CV-SORT can be helpful in the analysis of time-dependent data sampled by telemetry or other monitoring systems. The software can be obtained on request by every interested researcher. (Chronobiology International, 14(6), 561–574, 1997)

Estimated Annual Loads of Selected Organic Contaminants to Chesapeake Bay via a Major Tributary

The aim of the Chesapeake Bay Fall Line Toxics Monitoring Program has been to determine the annual loads for selected organonitrogen, organophosphorus, and organochlorine pesticides, polychlorinated biphenyls, and polynuclear aromatic hydrocarbons to Chesapeake Bay derived from above the fall line of the Susquehanna River, the bay's largest tributary. Load results are presented in this report for 15 samples collected from March 1992 through February 1993. Annual load estimates were obtained using 14 methods, grouped according to whether they are of averaging, ratio, or regression type to ensure convergence to an approximate mean load value for each contaminant. The results indicated a high degree of uniformity across the methods with most yielding relative deviations 1.5 or less when normalized to the mean load derived from all 14 load estimation methods.

Acoustic emission measurement of fatigue crack closure

The COD and BFS methods show relatively good agreement with each other and measure the through-thickness mean value of crack closure loads. In the plane strain condition, the crack closure levels obtained by the COD and BFS methods were lower than those by the AE and surface strain gage methods. The data obtained by the surface strain gage method must be interpreted carefully, because the shape of the compliance curves is affected by the location relative to the crack tip. The intrinsic fatigue life curve ( da dN vs. ΔK eff) obtained by the AE technique fitted well with the curve of high stress ratio (R = 0.8) test at high ΔK, suggesting that the AE technique is sensitive to local crack-tip behavior on a microscopic scale and can be considered as a reliable measurement method for crack closure phenomena under repetitive loads.

Peak Power Production in Wheelchair Propulsion

The effect of resistance on sprint power and the relationship between sprint and aerobic power production in wheelchair propulsion was evaluated. Six able-bodied subjects performed nine 20-s sprint tests on a stationary wheelchair ergometer (varying workload of 0–22.4 Nm for each side) and an aerobic maximum wheelchair exercise test to study both anaerobic and aerobic power production. Ergometer data were analyzed unilaterally. Of all power and torque parameters, only maximal power output was independent of resisting load (mean value 375 W, one-sided). Mean sprint power output over 20 s (P mean; one-sided) increased from 21 W to 87 W. The highest power output, P5, calculated over a period of 5 s (unilateral) increased from 24 W to 101 W. The P mean and P5 reached more or less constant values at the final two levels of resistance. The observed increase in power output with increasing load is the result of a greater increase in torque compared to the decrease in velocity. Mean maximal power in the maximal aerobic exercise test (n = 5) was 79 W, representing 42% of mean power (averaged over the nine sprint tests) and 37% of P5. In contrast to P mean and P5, P max showed a significant association with peak aerobic power production and peak oxygen uptake. This may indicate that P max is an indicator of overall performance capacity, whereas P mean and P5 are much more sprint related. The methodology of wheelchair exercise testing requires further detailed study with respect to the physiology and bio-mechanics of arm work, the functionality of the subject population, and reliability and validity of procedures and techniques. Eventually this should lead to standardized and reliable testing procedures. Both a standardized sprint test and a standardized aerobic wheelchair performance test can serve as additional tools in the evaluation of physical performance in wheelchair sports medicine. Perhaps more important, they may also serve as clinical tools in the evaluation of the process of rehabilitation.

Monitoring Fatigue Crack Propagation in Compact Tension Specimens via Remote Sensing of Back Face Strain

Abstract Back face strain (BFS) measurement is now well-established as an indirect technique to monitor crack length in compact tension (CT) fracture specimens [1,2]. Previous work [2] developed empirical relations between fatigue crack propagation (FCP) parameters. BFS, and number of cycles for CT specimens subjected to constant amplitude fatigue loading. These predictions are experimentally validated in terms of the variations of mean values of BFS and load as a function of crack length. Another issue raised by this study concerns the validity of assigning fixed values for the Paris parameters C and n to describe FCP in realistic materials.

Loading-related increases in prostaglandin production in cores of adult canine cancellous bone in vitro: A role for prostacyclin in adaptive bone remodeling?

Cyclic mechanical loading sufficient to engender strains of physiologic magnitude applied to recently excised canine cancellous bone cores in vitro increased the release of prostaglandin E (PGE) and prostacyclin (PGI2, measured as its breakdown product 6-keto-PGF1 alpha), during a 15 minute loading period in which PG levels were measured in perfusing medium at 5 minute intervals. Peak production occurred in the 0-5 minute sample. Mean levels preload compared to during load were PGE, 2.66 and 3.67 ng/ml (p less than 0.002); and 6-keto-PGF1 alpha, 543 and 868 pg/ml (p less than 0.007). The elevated levels then declined to preload levels during the loading period. However, the 5-10 minute but not the 10-15 minute samples still contained levels greater than preload values. A second 15 minute period of load, 1 h following the end of the first, produced smaller increases in the levels of release that were statistically significant only for the first 0-5 minute sample during load (preload compared to load mean values, PGE, 1.09-1.66 ng/ml, p less than 0.02; 6-keto-PGF1 alpha, 401-558 pg/ml, p less than 0.04). Immunolocalization revealed PGE and 6-keto-PGF1 alpha in lining cells and 6-keto-PGF1 alpha but not PGE in osteocytes. Addition to the medium of 1 microM PGE2, approximating the concentration produced by loading, had no significant effect on the specific activity of the extractable RNA fraction labeled with [3H]uridine, whereas 1 microM PGI2 produced an increase similar to that seen previously with loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Numerical Analysis of a Strip With a Hole Subjected to Cyclic Loading

This paper deals with the problem of a strip with a hole subjected to cyclic loading at the ends. For the numerical analysis, a constitutive model incorporating the motion of the center of the yield surface is implemented in a finite element method. The distributions of strain and stress during cyclic loading are discussed in detail both for the zero and nonzero mean values of cyclic load. To verify the results of the computer simulation, an experiment on a strip with a hole of type 304 stainless steel is carried out. Results of the experiment show that during cyclic loading with nonzero mean value of cyclic load, strain at the bottom of the circular hole is ratchetted with increase in number of cycles, and the stress approaches that due to the zero mean value of cyclic load.

Reliability Design Procedures for Flexible Pavements

A procedure is developed to analyze layered elastic flexible pavement systems in terms of reliability. Rosenblueth's method is used to estimate the expected value and variance of the strains (dependent parameters), based on the input mean values of independent parameters, i.e., aircraft load, layer thicknesses, and material moduli. Relationships between reliability level and allowable strain repetition of the designed system provide a decision‐making tool for engineers to design pavements at a desired reliability level. The design can be optimized by selecting thicknesses of bituminous concrete and base layers so that the pavement fails in fatigue cracking of the bituminous concrete and subgrade at nearly the same traffic level for a given reliability level. The performance of conventional flexible pavement is sensitive, in descending order, to variations of gear load P, thickness of the granular base h2, subgrade modulus E3, and thickness and modulus of the bituminous‐concrete surface course h1 and E1, r...

In vitro calcium release from four calcium hydroxide liners

The use of metal clasps on anterior teeth may cause esthetic problems. Recently, acetal resins have been used as an alternative tooth-colored denture clasp material to improve esthetics. However, there are few studies to support acetal resin use.The purpose of this in vitro study was to compare the retentive force and deformation of acetal resin and cobalt-chromium clasps after 36 months of simulated clinical use.Forty clasps each of acetal resin (1.2 or 2.0 mm thick) and cobalt-chromium (Dentorium)(1.2 mm thick) were fabricated using half-round standard prefabricated clasp patterns. The groups were further subdivided (n = 10) into the type of tooth (premolar or molar metal model) and undercut (0.25 mm or 0.50 mm). The retentive force of the clasps was measured in distilled water by a specially designed insertion-removal testing apparatus with intervals corresponding to 0, 6, 12, 18, 24, 30, and 36 months of simulated clinical use of a removable partial denture. The distance between the clasp tips (mm) was measured with a microscope before and after the insertion-removal testing procedure. Comparison of the mean values of the retentive force (gram force) of the clasps and the distance (mm) between the clasp tips was conducted with 3-way analysis of variance and a Least Significant Difference (LSD) multiple range test (α=.05).The mean values of tensile load required to dislodge acetal resin clasps with 1.2-mm thickness (111.6 g or 0.11 N) and with 2.0-mm thickness (178.4 g or 1.75 N) was significantly lower than that to dislodge Co-Cr clasps (694.1 g or 6.81 N) (P<.001). The retentive force needed to dislodge all 3 types of clasps was significantly lower for the molar than premolar models and also lower for the models with 0.25-mm undercuts than for those with 0.50-mm undercuts (P<.001). After 36 months of simulated clinical use, there was evidence of deformation in the cobalt-chromium clasps but no deformation noted for the acetal resin clasps. The retentive force of cobalt-chromium clasps (297.4 g or 2.91 N) after deformation remained significantly higher (P<.001) than the retentive force of acetal resin clasps that were 1.2 mm (110.7 g or 1.08 N) and 2.0 mm thick (177.5 g or 1.74 N), respectively.Within the limitations of this study, the results suggest that both thicknesses of acetal resin clasps evaluated required less force for insertion and removal than Co-Cr clasps over a simulated 36-month period.

Effect of a Tensile mean Stress on the Alternating Stress Required to Propagate An Edge Crack in Mild Steel

The conditions governing growth or dormancy of fatigue cracks in mild steel subjected to the general tensile loading cycle σm± σa, where σm ≥ σa, have been studied using plate specimens containing two small opposite co-planar edge cracks. It was found that, as in the case of zero mean load, these conditions were defined by the value of the parameter σa3 l; if σa3 l ≥ Cm a crack would grow, whereas if σa3 l &lt; Cm it would remain dormant, where Cm depended on the value of the ratio σm/σa. Its value at σm/σa = 1 corresponded to that derived from the zero mean load value by assuming that the loading cycles ± σa and 0 to σa were equivalent. The value of Cm then decreased linearly as the ratio σm/σa increased to 3, after which it remained constant as σm/σa increased further, provided that the applied loading cycle did not result in the bulk of the specimen deforming plastically. This lower limiting value was found to correspond to that predicted from the known growth rate of a crack in mild steel, assuming that a crack cannot grow at a rate less than one atomic spacing per stress cycle.