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Peak Load (peak + load)
Selected AbstractsStress relaxation of bone significantly affects the pull-out behavior of pedicle screwsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2004Serkan Inceoglu Abstract The initial fixation strength of pedicle screws is commonly tested using a standard pull-out test with load applied at a constant rate. This method overlooks the cyclic nature of in situ loading responsible for clinical failure. This study was undertaken to determine the effects of stress relaxation properties at the bone,screw interface on screw fixation strength. Pedicle screws were inserted into calf lumbar vertebrae using a paired testing array. After embedding and mounting in a custom fixture, axial pull-out tests were performed at the rates of 1, 5, and 25 mm/min. For each vertebra, one screw was pulled at a continuous rate. The other screw was pulled at increments of 0.5 mm, at the same rate, with 1000 s pause between increments. Peak load, energy-to-failure, displacement-to-failure, and stiffness were calculated for each screw pull-out test. Two-way ANOVA showed that the standard pull-out method yielded significantly higher peak loads (p < 0.05) at faster pull-out rates and higher stiffnesses (p < 0.05) at all rates compared to the stress relaxation pull-out protocol. These results suggest that the stress relaxation properties of bone significantly affect the pull-out behavior of pedicle screws, reducing the peak load and stiffness values observed during testing. This mode of testing may provide a better biomechanical model of screw pull-out failure and a more accurate estimate of initial fixation strength. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Concepts for computer center power managementCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 2 2010A. DiRienzo Abstract Electrical power usage contributes significantly to the operational costs of large computer systems. At the Hypersonic Missile Technology Research and Operations Center (HMT-ROC) our system usage patterns provide a significant opportunity to reduce operating costs since there are a small number of dedicated users. The relatively predictable nature of our usage patterns allows for the scheduling of computational resource availability. We take advantage of this predictability to shut down systems during periods of low usage to reduce power consumption. With interconnected computer cluster systems, reducing the number of online nodes is more than a simple matter of throwing the power switch on a portion of the cluster. The paper discusses these issues and an approach for power reduction strategies for a computational system with a heterogeneous system mix that includes a large (1560-node) Apple Xserve PowerPC supercluster. In practice, the average load on computer systems may be much less than the peak load although the infrastructure supporting the operation of large computer systems in a computer or data center must still be designed with the peak loads in mind. Given that a significant portion of the time, systems loads can be less than full peak, an opportunity exists for cost savings if idle systems can be dynamically throttled back, slept, or shut off entirely. The paper describes two separate strategies that meet the requirements for both power conservation and system availability at HMT-ROC. The first approach, for legacy systems, is not much more than a brute force approach to power management which we call Time-Driven System Management (TDSM). The second approach, which we call Dynamic-Loading System Management (DLSM), is applicable to more current systems with ,Wake-on-LAN' capability and takes a more granular approach to the management of system resources. The paper details the rule sets that we have developed and implemented in the two approaches to system power management and discusses some results with these approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] Evaluation of fracture resistance in simulated immature teeth using resilon and ribbond as root reinforcements , An in vitro studyDENTAL TRAUMATOLOGY, Issue 4 2009Hiremath Hemalatha Material and Methods:, Sixty five freshly extracted human maxillary anterior teeth were prepared with a Peeso no. 6 to simulate immature teeth (Cvek's stage 3 root development). After instrumentation, each root was irrigated with sodium hypochlorite and with ethylene diamino tetra acetic acid to remove the smear layer. To simulate single visit apexification technique a 4,5 mm white Pro Root mineral trioxide aggregate plug was placed apically using schilder carrier. The teeth were divided into three experimental groups and one control group. Group I , control group (root canals instrumented but not filled); Group II , backfilled with thermoplastisized gutta-percha using AH plus sealer; Group III , reinforced with Resilon using epiphany sealer; Group IV , reinforced with Ribbond fibers using Panavia F luting cement. A Universal Testing Machine was used to apply a load, at the level of the lingual cementoenamel junction with a chisel-shaped tip The peak load to fracture was recorded and statistical analysis was completed using student's t -test. Results:, Values of peak load to fracture were 1320.8, 1604.88, 1620, and 1851newtons for Group I to Group IV respectively. The results of student's t -test, revealed no significant difference (P > 0.05,) between Group II and Group III. Comparison between Group IV and Group III and between Group IV and Group II revealed highly significant difference (P > 0.001). Conclusions:, Teeth reinforced with Ribbond fibers using Panavia F luting cement showed the highest resistance to fracture. Resilon could not strengthen the roots and showed no statistically significant difference when compared with thermopasticised gutta-percha in reinforcing immature tooth when tested with universal testing machine in an experimental model of immature tooth. [source] Electricity peak load forecasting with self-organizing map and support vector regressionIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2006Shu Fan Non-member Abstract This paper aims to study the short-term peak load forecasting (PLF) by using Kohonen self-organizing maps (SOM) and support vector regression (SVR). We first adopt a SOM network to cluster the input data set into several subsets in an unsupervised learning strategy. Then, several SVRs for the next day's peak load are used to fit the training data of each subset in the second stage. In the numerical experiments, data of electricity demand from the New York Independent System Operator (ISO) are used to verify the effectiveness of the prediction for the proposed method. The simulation results show that the proposed model can predict the next day's peak load with a considerably high accuracy compared with the ISO forecasts. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Effect of water storage time and composite cement thickness on fatigue of a glass-ceramic trilayer systemJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Nelson R. F. A. Silva Abstract Aim. Static Hertzian contact tests of monolayer glass-ceramics in trilayer configurations (glass-ceramic/cement/composite) have shown that thick cement layers lower strength. This study sought to test the hypothesis that thick resin cement layers lower mouth motion fatigue reliability for flat glass-ceramic/cement/composite trilayer systems and that aging in water reduces reliability. Methods. Dicor plates (n , 12 per group) (10 × 10 × 0.8 mm3) were aluminum-oxide abraded (50 ,m), etched (60 s), silanized, and bonded (Rely X ARC) to water aged (30 days) Z100 resin blocks (10 × 10 × 4 mm3). Four groups were prepared: (1) thick cement layer (>100 ,m) stored in water for 24,48 h, (2) thick cement layer stored for 60 days, (3) thin cement layer (,100 ,m) stored for 24,48 h, and (4) thin cement layer stored for 60 days. The layered structures were fatigued (2 Hz) utilizing mouth motion loading with a step-stress acceleration method. A master Weibull distribution was calculated and reliability determined (with 90% confidence intervals) at a given number of cycles and load. Results. The aged group (60 d) with thick cement layer had statistically lower reliability for 20,000 cycles at 150 N peak load (0.11) compared with both nonaged groups (24,48 h) (thin layer = 0.90 and thick layer = 0.82) and aged group with thin cement layer (0.89). Conclusion. Trilayer specimens with thick cement layers exhibited significantly lower reliability under fatigue testing only when stored for 60 days in water. The hypothesis was accepted. These results suggest that diffusion of water into the resin cement and also to the glass-ceramic interface is delayed in the thick cement specimens at 24,48 h. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008 [source] The effect of the addition of poly(methyl methacrylate) fibres on some properties of high strength heat-cured acrylic resin denture base materialJOURNAL OF ORAL REHABILITATION, Issue 3 2003D. Jagger summary, The self-reinforcement of acrylic resin with butadiene styrene surface treated poly(methyl methacrylate) fibres has been reported to have the potential to substantially improve the transverse bend strength of conventional heat-cured acrylic resin. The aim of this study was to investigate the effect of the addition of butadiene styrene surface treated poly(methyl methacrylate) fibres in cross-ply arrangement to high impact acrylic resin on the transverse and impact strength. Specimens were prepared as specified in the International Standard Organization and British Standards for the Testing of Denture Base Resins (ISO 1567, 1988; BS 2487, 1989) and the British Standard Specification for Orthodontic resins (BS 6747, 1987) for transverse bend and impact testing. The impact strength was measured using a Zwick pendulum impact tester and the transverse bend strength measured using a Lloyds Instruments testing machine. The results showed that the impact strength was not improved with the addition of fibres, high impact acrylic resin with fibres (LF) 11·1 kJ m,2 and high impact acrylic resin (L) (12·5 kJ m,2). The modulus of rupture was decreased with the addition of fibres (57·8 MPa) for (LF) compared with (60·4 MPa) for (L). The modulus of elasticity was also reduced with the addition of fibres (1834·9 MPa) (LF) and 2086·2 MPa (L) as was the peak load (LF) (50·8 N) and (L) (55·8 N). It was concluded that the addition of surface treated poly(methyl methacrylate) fibres in cross-ply arrangement to high strength acrylic resin did not produce an improvement in the impact or transverse strength and cannot be recommended as a method of reinforcement. [source] Supraspinatus tendon repair into a bony trough in the rabbit: Mechanical restoration and correlative imagingJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2010Guy Trudel Abstract Recurrence of tears is a common complication after rotator cuff surgery. Retearing seems to occur early after surgery and may be attributed to too early or too vigorous exercises. We found no experimental data correlating the strength of the rotator cuff early after surgery and imaging. Our objectives were to measure the peak load to failure of rabbit supraspinatus tendon,bone constructs at early times postoperatively, to determine their mode of failure, and to determine whether computed tomography (CT) can predict their strength. We divided one supraspinatus tendon of 40 adult female white New Zealand rabbits and, after resection of the enthesis, sutured the tendon into a bony trough. Ten rabbits were killed immediately and 10 each at 1, 2, and 6 weeks postoperatively. The explanted tendons of both shoulders were imaged on CT and tested to failure. Compared to normal tendons (mean 210,±,42 N), the mean strength was very low at 0 weeks (57,±,21 N) and 1 week (86,±,33 N) (both p,<,0.05); it had recovered by 6 weeks (324,±,66 N). Early on, suture pullout was the most common mode of failure, whereas at 6 weeks, mid-substance tears predominated (p,<,0.05). Hypoattenuation on CT was associated with increased strength of the tendon,bone construct (p,<,0.05). The strength of the surgical construct is very low in the early postoperative period. Therefore, the shoulder should be submitted only to loads not interfering with healing. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:710,715, 2010 [source] Stress relaxation of bone significantly affects the pull-out behavior of pedicle screwsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2004Serkan Inceoglu Abstract The initial fixation strength of pedicle screws is commonly tested using a standard pull-out test with load applied at a constant rate. This method overlooks the cyclic nature of in situ loading responsible for clinical failure. This study was undertaken to determine the effects of stress relaxation properties at the bone,screw interface on screw fixation strength. Pedicle screws were inserted into calf lumbar vertebrae using a paired testing array. After embedding and mounting in a custom fixture, axial pull-out tests were performed at the rates of 1, 5, and 25 mm/min. For each vertebra, one screw was pulled at a continuous rate. The other screw was pulled at increments of 0.5 mm, at the same rate, with 1000 s pause between increments. Peak load, energy-to-failure, displacement-to-failure, and stiffness were calculated for each screw pull-out test. Two-way ANOVA showed that the standard pull-out method yielded significantly higher peak loads (p < 0.05) at faster pull-out rates and higher stiffnesses (p < 0.05) at all rates compared to the stress relaxation pull-out protocol. These results suggest that the stress relaxation properties of bone significantly affect the pull-out behavior of pedicle screws, reducing the peak load and stiffness values observed during testing. This mode of testing may provide a better biomechanical model of screw pull-out failure and a more accurate estimate of initial fixation strength. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] A NEW APPROACH TO CORRELATE TEXTURAL AND COOKING PARAMETERS WITH OPERATING CONDITIONS DURING DOUBLE-SIDED COOKING OF MEAT PATTIESJOURNAL OF TEXTURE STUDIES, Issue 5 2000SUSANA E. ZORRILLA Cooking and textural parameters during double-sided cooking of hamburger patties were correlated with volume-averaged temperature at the end of the cooking process and gap thickness between plates. Frozen patties were cooked in a clamshell grill set at different plate surface temperatures (177C; 191C; 204C; 218C), for different gap thicknesses (9.65 mm; 10.55 mm; 10.55 mm; 11.05 mm) for 120 s. A decrease in the gap thickness and an increase in the plate surface temperature resulted in an increase in the cooking loss values (24,36%) and in a decrease of press juice values (8,25%). The values of peak load (183,215 N), modulus (16,19 N/mm), work needed in shearing (2300,2800 Nmm), hardness (25,32 N), cohesiveness (0.76,0.83), and chewiness (107,152 Nmm) of the patties increased when the gap thickness decreased and the plate surface temperature increased. There was no effect of the variables studied on springiness. The correlation equations involving the operating variables and quality parameters obtained are simple and useful in developing optimal process conditions. [source] Electric load forecasting for northern Vietnam, using an artificial neural networkOPEC ENERGY REVIEW, Issue 2 2003Subhes C. Bhattacharyya This paper employs a feed-forward neural network with a back-propagation algorithm for the short-term electric load forecasting of daily peak (valley) loads and hourly loads in the northern areas of Vietnam. A large set of data on peak loads, valley loads, hourly loads and temperatures was used to train and calibrate the artificial neural network (ANN). The calibrated network was used for load forecasting. The mean percentage errors for the peak load, valley load, one-hour-ahead hourly load and 24-hour-ahead hourly load were ,1.47%, ,3.29%, ,2.64% and ,4.39%, respectively. These results compare well with similar studies. [source] Concepts for computer center power managementCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 2 2010A. DiRienzo Abstract Electrical power usage contributes significantly to the operational costs of large computer systems. At the Hypersonic Missile Technology Research and Operations Center (HMT-ROC) our system usage patterns provide a significant opportunity to reduce operating costs since there are a small number of dedicated users. The relatively predictable nature of our usage patterns allows for the scheduling of computational resource availability. We take advantage of this predictability to shut down systems during periods of low usage to reduce power consumption. With interconnected computer cluster systems, reducing the number of online nodes is more than a simple matter of throwing the power switch on a portion of the cluster. The paper discusses these issues and an approach for power reduction strategies for a computational system with a heterogeneous system mix that includes a large (1560-node) Apple Xserve PowerPC supercluster. In practice, the average load on computer systems may be much less than the peak load although the infrastructure supporting the operation of large computer systems in a computer or data center must still be designed with the peak loads in mind. Given that a significant portion of the time, systems loads can be less than full peak, an opportunity exists for cost savings if idle systems can be dynamically throttled back, slept, or shut off entirely. The paper describes two separate strategies that meet the requirements for both power conservation and system availability at HMT-ROC. The first approach, for legacy systems, is not much more than a brute force approach to power management which we call Time-Driven System Management (TDSM). The second approach, which we call Dynamic-Loading System Management (DLSM), is applicable to more current systems with ,Wake-on-LAN' capability and takes a more granular approach to the management of system resources. The paper details the rule sets that we have developed and implemented in the two approaches to system power management and discusses some results with these approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of Implant Angulation upon Retention of Overdenture AttachmentsJOURNAL OF PROSTHODONTICS, Issue 1 2005MSEd, MSciDent, Michael P. Gulizio DMD Introduction: Overdentures supported and retained by endosteal implants depend upon mechanical components to provide retention. Ball attachments are frequently described because of simplicity and low cost, but retentive capacity of these components may be altered by a lack of implant parallelism. Purpose: The aim of this in vitro study was to investigate the retention of gold and titanium overdenture attachments when placed on ball abutments positioned off-axis. Methods and Materials: Four ball abutments were hand-tightened onto ITI dental implants and placed in an aluminum fixture that allowed positioning of the implants at 0°, 10°, 20°, and 30° from a vertical reference axis. Gold and titanium matrices were then coupled to the ball abutments at various angles and then subjected to pull tests at a rate of 2 mm/second; the peak loads of release (maximum dislodging forces) were recorded and subjected to statistical analyses. A balanced and randomized factorial experimental design testing procedure was implemented. Results: Statistically significant differences in retention of gold matrices were noted when ball abutments were positioned at 20° and 30°, but not at 0° and 10°. Statistically significant differences were noted among the titanium matrices employed for the testing procedure, as well as for the 4 ball abutments tested. Angle was not a factor affecting retention for titanium matrices. Conclusions: (1) The gold matrices employed for the testing procedures exhibited consistent values in retention compared to titanium matrices, which exhibited large variability in retention. (2) Angle had an effect upon the retention of gold matrices, but not for titanium matrices. [source] Electric load forecasting for northern Vietnam, using an artificial neural networkOPEC ENERGY REVIEW, Issue 2 2003Subhes C. Bhattacharyya This paper employs a feed-forward neural network with a back-propagation algorithm for the short-term electric load forecasting of daily peak (valley) loads and hourly loads in the northern areas of Vietnam. A large set of data on peak loads, valley loads, hourly loads and temperatures was used to train and calibrate the artificial neural network (ANN). The calibrated network was used for load forecasting. The mean percentage errors for the peak load, valley load, one-hour-ahead hourly load and 24-hour-ahead hourly load were ,1.47%, ,3.29%, ,2.64% and ,4.39%, respectively. These results compare well with similar studies. [source] | ||||||||||