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Load Levels (load + level)
Kinds of Load Levels Selected AbstractsAssociation of Geometric Factors and Failure Load Level With the Distribution of Cervical vs.JOURNAL OF BONE AND MINERAL RESEARCH, Issue 6 2006Trochanteric Hip Fractures Abstract We experimentally studied the distribution of hip fracture types at different structural mechanical strength. Femoral neck fractures were dominant at the lowest structural strength levels, whereas trochanteric fractures were more common at high failure loads. The best predictor of fracture type across all failure loads and in both sexes was the neck-shaft angle. Introduction: Bone geometry has been shown to be a potential risk factor for osteoporotic fractures. Risk factors have been shown to differ between cervical and trochanteric hip fractures. However, the determinants of cervical and trochanteric fractures at different levels of structural mechanical strength are currently unknown. In addition, it is not known if the distribution of fracture types differs between sexes. The aim of this experimental study on excised femora was to investigate whether there exist differences in the distribution of cervical and trochanteric fractures between different structural mechanical strength levels and different sexes and to identify the geometric determinants that predict a fracture type. Materials and Methods: The sample was comprised of 140 cadavers (77 females: mean age, 81.7 years; 63 males: mean age, 79.1 years) from whom the left femora were excised for analysis. The bones were radiographed, and geometrical parameters were determined from the digitized X-rays. The femora were mechanically tested in a side impact configuration, simulating a sideways fall. After the mechanical test, the fracture patterns were classified into cervical and trochanteric. Results: The overall proportion of cervical fractures was higher in females (74%) than in males (49%) (p = 0.002). The fracture type distribution differed significantly across load quartiles in females (p = 0.025), but not in males (p = 0.205). At the lowest load quartiles, 94.7% of fractures in female and 62.5% in males were femoral neck fractures. At the highest quartiles, in contrast, only 52.6% of fractures in females and 33.3% in males were cervical fractures. Among geometric variables, the neck-shaft angle was the best predictor of fracture type, with higher values in subjects with cervical fractures. This finding was made in females (p < 0.001) and males (p = 0.02) and was consistent across all failure load quartiles. Conclusions: Femoral neck fractures predominate at the lowest structural mechanical strength levels, whereas trochanteric fractures are more common at high failure loads. Females are more susceptible to femoral neck fractures than males. The best predictor of fracture type across all structural strength levels and both sexes was the neck-shaft angle. [source] Probabilistic approach to voltage stability analysis with load uncertainty consideredEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2009B. Wu Abstract This paper proposes a new probabilistic assessment algorithm of voltage stability based on Monte-Carlo simulation and modal analysis considering uncertainty of the load level and load parameters. By Monte-Carlo sampling, the bus load level is determined according to the forecasted bus load curve of a research period. The coefficients of the load polynomials, which include induction motors, are treated as random variables with normal distribution. A technique of normal distribution sampling is utilized to simulate these coefficients uncertainty. Voltage stability is evaluated in the form of indices such as the expected maximum loadability and the statistics of system participations, which are obtained from modal analysis near the point of collapse. A case study of the IEEE 118-node system is given to demonstrate the validity of the proposed algorithm, and the effects of load uncertainty and the proportion of motors on probabilistic assessment of voltage stability are investigated. Copyright © 2007 John Wiley & Sons, Ltd. [source] The effect of laser power density on the fatigue life of laser-shock-peened 7050 aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007Q. LIU ABSTRACT Laser shock peening (LSP) is an innovative surface treatment method that can result in significant improvement in the fatigue life of many metallic components. The process produces very little or no surface profile modification while producing a considerably deeper compressive residual stress layer than traditional shot peening operations. The work discussed here was designed to: (a) quantify the fatigue life improvement achieved by LSP in a typical high strength aircraft aluminium alloy and (b) identify any technological risks associated with its use. It is shown that when LSP conditions are optimal for the material and specimen configuration, a ,three to four times increase in fatigue life over the as-machined specimens could be achieved for a representative fighter aircraft loading spectrum when applied at a representative load level. However, if the process parameters are not optimal for the material investigated here, fatigue lives of LSP treated specimens may be reduced instead of increased due to the occurrence of internal cracking. This paper details the effect of laser power density on fatigue life of 7050-T7451 aluminium alloy by experimental and numerical analysis. [source] A model for evaluating the effect of fatigue crack repair by the infiltration methodFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2000C. S. Shin Infiltration of foreign materials into a fatigue crack has previously been shown to be able to retard the crack and extend fatigue life. Most of the related studies were empirical and phenomenological in nature. To aid engineering decisions, it would be advantageous if the possible outcome of a repair can be evaluated beforehand. To this end, a crack closure model taking into account the additional closure effect of the infiltrant has been developed and verified against experimental results. With this model, the sensitivity of the repair effect to various parameters such as mechanical properties of the infiltrant, depth of penetration and infiltration load level can be assessed. [source] Displacement-controlled method and its applications to material non-linearityINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2005H. Zheng Abstract For the analysis of non-linear problems, the displacement-controlled method (DCM) has a more extensive application scope and more powerful abilities than the load-controlled method (LCM). However, difficulties of the DCM's procedure not amenable to most finite element implementations of the conventional LCM have restricted its applications in geomechanics. By means of Sherman,Morrison's theorem, the solution of DCM is improved. The improved procedure is characterized by high efficiency, good numerical stability and a programme structure similar to LCM. Two aspects of applications of DCM are illustrated. The first application is to compute the response of a structure under a given load level like the conventional finite element analysis. The second application is to trace the equilibrium path of a structure under a given load distribution type. A simple but effective algorithm is presented for automatically adjusting the step length in tracing the equilibrium path. Examples illustrate that the proposed procedures are suited for modelling complicated non-linear problems in geomechanics. Copyright © 2005 John Wiley & Sons, Ltd. [source] A simple mechanism for stabilizing network queues in TCP/IP networksINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2007James Aweya In this paper we determine the stability bounds for the DRED active queue management (AQM) algorithm using a previously developed nonlinear dynamic model of TCP. We develop a second-order linear model with time delay by linearizing the nonlinear model. Using the Pade approximation of time-delayed system e,R0s, where R0 is the delay in the system, we then determine the range of stabilizing gains of DRED when controlling the second-order system with time delay R0. We also present examples showing the stability bounds of the DRED controller gain for networks with different parameters such as link capacity, load level, and round-trip time. In addition, we describe an efficient implementation of the DRED AQM algorithm. Copyright © 2006 John Wiley & Sons, Ltd. [source] Stress relaxation behavior of glass fiber-reinforced polyester composites prepared by the newly proposed rubber pressure moldingPOLYMER COMPOSITES, Issue 10 2008Kamal K. Kar Stress-relaxation behavior of glass fiber-reinforced polyester composites, prepared by a recently developed manufacturing method called rubber pressure molding (RPM), is investigated with special reference to the effect of environmental temperature (,70°C to +100°C), fiber volume fraction (30,60%), and initial load level (1,5 kN). It is found that the stress-relaxation rate decreases with an increase in the applied load of composites and a decrease in temperature. Below glass transition temperature, the rate of stress relaxation increases with an increase in volume fraction of fibers in the composites, whereas above glass transition temperature, it increases with a decrease in the volume fraction of fibers. The experimental results for a given composites are summarized by four values, the slopes of the two straight lines (two separate relaxation processes), and their intercepts upon the stress axis. Both the slopes are dependent upon the applied load, temperature, and volume fraction of fibers in the composites. Relaxation times in both primary and secondary are calculated over the wide range of temperatures, loads, and volume fraction of fibers in the composites. It depends strongly on the temperature, but does not depend strongly on the applied load and volume fraction of fibers. The performances of the composites are also evaluated through conventional compression-molding process. The rate of stress relaxation is small when the composites are made of newly proposed RPM technique when compared with the conventional process. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Highly active antiretroviral therapy (HAART) among HIV-infected drug users: a prospective cohort study of sexual risk and injecting behaviourADDICTION, Issue 3 2006Colette Smit ABSTRACT Aims To study sexual risk and injecting behaviour among HIV-infected drug users (DU) receiving highly active antiretroviral therapy (HAART)., Design and setting As part of an ongoing prospective cohort study, HIV-infected DU who commenced HAART (n = 67) were matched with those not starting HAART (n = 130) on CD4 cell counts, duration of cohort participation, age and calendar year of visit. Immunological and virological responses of the HAART-treated DU were compared with the HAART-treated homosexual men from the same cohort (n = 212). Measurements Trends in behaviour and therapeutic response were tested with a logistic regression model adjusted for repeated measurements and a piecewise random effects model, respectively. Findings Non-HAART users reported more episodes of injecting than HAART users. In both groups injecting declined over time with no effect of HAART initiation. Before HAART initiation an increase in sexual risk behaviour was observed among those who had been assigned to receive HAART; their sexual risk behaviour declined thereafter. No change in sexual risk behaviour was found among non-HAART users. Relative to homosexual men, DU had a similar initial therapeutic response, but DU started HAART at lower CD4 cell counts and higher viral load levels. Conclusion DU who are treated with HAART are not increasing their risk behaviour, and their early response to HAART is similar to homosexual men. However, before the treated DU received HAART they were seen to inject less often than those not treated with HAART. This suggests that selection of potential HAART starters is based on limited drug use. Although the DU who commence HAART are a selected group, our results show that HIV-infected DU can be treated effectively. [source] An algorithm for evaluating crack closure from local compliance measurementsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2002M. SKORUPA ABSTRACT A numerical procedure for evaluating fatigue crack closure from load-local deformation data is presented. The local compliance is assumed to vary during the entire loading cycle, including the portion when the crack is fully open. The closure mechanism-related characteristic load levels are identified based on comparisons between the open crack compliance variations upon loading and unloading. This type of compliance analysis is conditioned by an appropriate smoothness of the measured data. Hence, the choice and optimization of the procedure for smoothing of the measured data. Hence, the choice and optimization of the procedure for smoothing the recorded signals is thoroughly addressed in this paper. The performance of the algorithm is evaluated from comparisons between the computed closure parameters and their reference values which have been previously shown to correlate the observed crack growth rate behaviour. [source] Genotypic antiretroviral drug resistance testing at low viral loads in the UKHIV MEDICINE, Issue 8 2008PA Cane Background Antiretroviral drug resistance testing is recommended in HIV-1 infected patients failing therapy in order to inform treatment selection. Although guidelines and test manufacturers recommend a viral load of at least 500,1000 HIV-1 RNA copies/mL for genotypic resistance testing to be performed, prompt management of virological failure could benefit from testing at lower viral load levels. Methods Laboratories undertaking genotypic resistance testing were asked to provide figures for the number of resistance tests undertaken at viral loads <2000 copies/mL, the success rates of such tests and the extent of resistance detected, all stratified for viral load levels. Results Of the replies received, most laboratories were attempting resistance testing at viral loads below the recommended guidelines, with variable success and outcomes. Conclusions This audit of current practice in the UK for undertaking genotypic resistance tests at viral loads <1000 copies/mL highlights the widespread use of such testing outside the British HIV Association guidelines. [source] Application and comparison of metaheuristic techniques to reactive power planning problemIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 6 2008Mehdi Eghbal Non-Member Abstract This paper presents the application and comparison of metaheuristic techniques to reactive power planning (RPP) problem which involves optimal allocation and combination of to-be-installed VAr sources to satisfy voltage constraints during normal and contingency states for multiple load levels. The main objective of the proposed RPP problem is to minimize the investment cost through balanced installation of SCs and SVCs while keeping a specified security level and minimizing the amount of load shedding. The problem is formulated as a large scale mixed integer nonlinear programming problem, which is a nonsmooth and nondifferentiable optimization problem using conventional optimization techniques and induces lots of local minima. Among the metaheuristic techniques, genetic algorithm (GA), particle swarm optimization (PSO) and evolutionary particle swarm optimization (EPSO) are applied to solve the RPP problem. To investigate the effectiveness of the metaheuristic techniques, the proposed approaches have been successfully tested on IEEE-14 buses, as well as IEEE-57 buses test system. The results obtained are compared and the effectiveness of each technique has been illustrated. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] DRED: a random early detection algorithm for TCP/IP networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2002James Aweya Abstract It is now widely accepted that a RED [2] controlled queue certainly performs better than a drop-tail queue. But an inherent weakness of RED is that its equilibrium queue length cannot be maintained at a preset value independent of the number of TCP active connections. In addition, RED's optimal parameter setting is largely correlated with the number of connections, the round-trip time, the buffer space, etc. In light of these observations, we propose DRED, a novel algorithm which uses the basic ideas of feedback control to randomly discard packets with a load-dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The benefits of stabilized queues in a network are high resources utilization, predictable maximum delays, more certain buffer provisioning, and traffic-load-independent network performance in terms of traffic intensity and number of connections. Copyright © 2002 John Wiley & Sons, Ltd. [source] Trabecular Bone Tissue Strains in the Healthy and Osteoporotic Human Femur,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 10 2003B Van Rietbergen Quantitative information about bone tissue-level loading is essential for understanding bone mechanical behavior. We made microfinite element models of a healthy and osteoporotic human femur and found that tissue-level strains in the osteoporotic femoral head were 70% higher on average and less uniformly distributed than those in the healthy one. Introduction: Bone tissue stresses and strains in healthy load-adapted trabecular architectures should be distributed rather evenly, because no bone tissue is expected to be overloaded or unused. In this study, we evaluate this paradigm with the use of microfinite element (,FE) analyses to calculate tissue-level stresses and strains for the human femur. Our objectives were to quantify the strain distribution in the healthy femur, to investigate to what extent this distribution is affected by osteoporosis, to determine if osteoporotic bone is simply bone adapted to lower load levels, and to determine the "safety factor" for trabecular bone. Materials and Methods: ,FE models of a healthy and osteoporotic proximal femur were made from microcomputed tomography images. The models consisted of over 96 and 71 million elements for the healthy and osteoporotic femur, respectively, and represented their internal and external morphology in detail. Stresses and strains were calculated for each element and their distributions were calculated for a volume of interest (VOI) of trabecular bone in the femoral head. Results: The average tissue-level principal strain magnitude in the healthy VOI was 304 ± 185 microstrains and that in the osteoporotic VOI was 520 ± 355 microstrains. Calculated safety factors were 8.6 for the healthy and 4.9 for the osteoporotic femurs. After reducing the force applied to the osteoporotic model to 59%, the average strain compared with that of the healthy femur, but the SD was larger (208 microstrains). Conclusions: Strain magnitudes in the osteoporotic bone were much higher and less uniformly distributed than those in the healthy one. After simulated joint-load reduction, strain magnitudes in the osteoporotic femur were very similar to those in the healthy one, but their distribution is still wider and thus less favorable. [source] Time course of hepatitis A viremia and viral load in the blood of human hepatitis A patientsJOURNAL OF MEDICAL VIROLOGY, Issue 1 2004Andrea Normann Abstract The hepatitis A virus (HAV) is the most common etiological cause of acute hepatitis infections in humans in industrialized countries. Investigations into the viral load during HAV viremia, however, are rare. Therefore, correlation studies between viral load, biochemical, and specific serological markers have been undertaken. The group of sera comprised a series of multiple consecutive blood samples drawn from 11 patients at different times after onset of the disease. During the period up to 70 days after the onset of icterus, the individual range was at 1×103 to 3×104 HAV genome equivalents/ml. From day 75 until 120 after onset of the disease, the levels traced were at 103. In one case, it was possible to trace 1.25×104 genome equivalents/ml up to 180 days after onset of icterus and in two cases even up to 408 and 490 days viral load levels of 5×103 and 4×104 were detected, respectively. The same sera were used to measure IgM class antibodies to hepatitis A virus and the total anti-HAV. The results demonstrate that a direct correlation to peak levels of viral load exists with peak serum transaminase levels, but neither with peak anti-HAV IgM levels nor with total anti-HAV. Decreasing amounts of anti-HAV IgM tend to occur with decreasing amounts of HAV genome equivalents; and, vice versa, increasing amounts of total anti-HAV are accompanied by decreasing amounts of HAV genome equivalents. The longest duration of viremia was found in patients infected with HAV genotype IA. J. Med. Virol. 72:10,16, 2004. © 2004 Wiley-Liss, Inc. [source] Mechanical Behavior and Stability of the Internal Membrane of the InCor Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 11 2001Pedro Baroni Da Costa Teixeira Abstract: This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths. [source] Bone reactions to controlled loading of endosseous implants: a pilot studyCLINICAL ORAL IMPLANTS RESEARCH, Issue 11 2008H. W. Anselm Wiskott Abstract Objectives: To validate an experimental setup designed to apply load onto bone tissue using osseointegrated implants in a rabbit model. Specifically, (1) to design an apparatus capable of generating controlled forces, (2) to assess implant placement, maintenance and loading and (3) to evaluate outcome variables using three radiological methods. Material and methods: New Zealand White rabbits were used. Two dental implants were inserted 15,18 mm apart in the animals' tibiae. After 3 months of healing, the implants were loaded normal to their long axes using a pneumatically activated device. A 15 min load regimen at 1 Hz was applied 5 days per week. Every week the applied load was increased by 5 N up to week 8 and by 10 N up to 100 N by week 14. Groups of animals (n=3) were sacrificed at load levels 25, 50 and 100 N. One unloaded controlateral implant in each group provided the baseline data. The rabbits were computer tomography (CT) scanned and radiographed using conventional frames every 4,5 weeks. After sacrifice, a volume of interest (VOI) located in the inter-implant zones and a VOI set as a ring surrounding the distal implant were analyzed using micro computer tomography (,CT). Results: A variety of osseous responses was observed, ranging from minor alterations to significant increases in porosity and lamelling of the cortical layer. ,CT data of the inter-implant VOI demonstrated an initial increase in total volume (upto 50 N) followed by stabilization. Concomitantly, bone volumetric density first decreased and then augmented until the end of the experiment. This phenomenon was not observed in the peri-implant VOI, for which volumetric density augmented from the beginning to the end of the experiment. Conclusions: 1. In future trials the loading devices must be constructed so as to sustain heavy cyclic loads over prolonged periods. 2. When properly handled, rabbits are cooperative animals in this application. In a third of the sites, signs of inflammation were observed. 3. In the inter-implant VOI, the cortical bone tended to react in two phases: first, as an increase in porosity and lamelling and second, as an augmentation of bone volumetric density. The peri-implant VOI adapted only by augmenting volumetric density. [source] | ||||||||||||||||