Effects of movement and work load in patients with congenital central hypoventilation syndrome.

PubMed

Hager, Alfred; Koch, Walter; Stenzel, Heike; Hess, John; Schöber, Johannes

2007-04-01

Patients with congenital central hypoventilation syndrome lack ventilatory chemosensitivity and depend at least in part on the ergoreceptor function during exercise. In these patients a substantial increase of ventilation has been reported for passive movement during sleep as well as active movement on a treadmill. The aim of the study was to investigate ventilatory response to an increasing work load with constant movement. Eighteen patients and 17 healthy volunteers performed a cardiopulmonary exercise test on a bicycle pedaling at a constant rate of about 60 revolutions per minute throughout the entire test. The patients were able to exercise adequately and showed normal peak oxygen uptake. There was a steep rise in minute ventilation in both groups at the start of exercise, yet there was only a minor increase in both groups during the increase of workload up to the anaerobic threshold. After the anaerobic threshold, there was again an increase in ventilation in both groups, but the increase was less prominent in the patient group. Ventilation in patients with congenital central hypoventilation syndrome is increased during exercise caused both by movement (mechanoreceptors) and by anaerobic workload. This facilitates a normal ventilatory drive up to the anaerobic threshold and a normal exercise capacity in these patients.

Friction and lubrication of pleural tissues.

PubMed

D'Angelo, Edgardo; Loring, Stephen H; Gioia, Magda E; Pecchiari, Matteo; Moscheni, Claudia

2004-08-20

The frictional behaviour of rabbit's visceral pleura sliding against parietal pleura was assessed in vitro while oscillating at physiological velocities and amplitudes under physiological normal forces. For sliding velocities up to 3 cm s(-1) and normal compressive loads up to 12 cm H2O, the average value of the coefficient of kinetic friction (mu) was constant at 0.019 +/- 0.002 (S.E.) with pleural liquid as lubricant. With Ringer-bicarbonate solution, mu was still constant, but significantly increased (Deltamu = 0.008 +/- 0.001; P < 0.001). Under these conditions, no damage of the sliding pleural surfaces was found on light and electron microscopy. Additional measurements, performed also on peritoneum, showed that changes in nominal contact area or strain of the mesothelia, temperature in the range 19-39 degrees C, and prolonged sliding did not affect mu. Gentle application of filter paper increased mu approximately 10-fold and irreversibly, suggesting alteration of the mesothelia. With packed the red blood cells (RBC) between the sliding mesothelia, mu increased appreciably but reversibly on removal of RBC suspension, whilst no ruptures of RBC occurred. In conclusion, the results indicate a low value of sliding friction in pleural tissues, partly related to the characteristics of the pleural liquid, and show that friction is independent of velocity, normal load, and nominal contact area, consistent with boundary lubrication.

A Baseline Load Schedule for the Manual Calibration of a Force Balance

NASA Technical Reports Server (NTRS)

Ulbrich, N.; Gisler, R.

2013-01-01

A baseline load schedule for the manual calibration of a force balance is defined that takes current capabilities at the NASA Ames Balance Calibration Laboratory into account. The chosen load schedule consists of 18 load series with a total of 194 data points. It was designed to satisfy six requirements: (i) positive and negative loadings should be applied for each load component; (ii) at least three loadings should be applied between 0 % and 100 % load capacity; (iii) normal and side force loadings should be applied at the forward gage location, aft gage location, and the balance moment center; (iv) the balance should be used in "up" and "down" orientation to get positive and negative axial force loadings; (v) the constant normal and side force approaches should be used to get the rolling moment loadings; (vi) rolling moment loadings should be obtained for 0, 90, 180, and 270 degrees balance orientation. In addition, three different approaches are discussed in the paper that may be used to independently estimate the natural zeros, i.e., the gage outputs of the absolute load datum of the balance. These three approaches provide gage output differences that can be used to estimate the weight of both the metric and non-metric part of the balance. Data from the calibration of a six-component force balance will be used in the final manuscript of the paper to illustrate characteristics of the proposed baseline load schedule.

A root-mean-square approach for predicting fatigue crack growth under random loading

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1981-01-01

A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.

Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams.

PubMed

Sahraoui, Sohbi; Brouard, Bruno; Benyahia, Lazhar; Parmentier, Damien; Geslain, Alan

2013-12-01

This paper presents a method for the mechanical characterization of isotropic foams at low frequency. The objective of this study is to determine the Young's modulus, the Poisson's ratio, and the loss factor of commercially available foam plates. The method is applied on porous samples having square and circular sections. The main idea of this work is to perform quasi-static compression tests of a single foam sample followed by two juxtaposed samples having the same dimensions. The load and displacement measurements lead to a direct extraction of the elastic constants by means of normalized stiffness and normalized stiffness ratio which depend on Poisson's ratio and shape factor. The normalized stiffness is calculated by the finite element method for different Poisson ratios. The no-slip boundary conditions imposed by the loading rigid plates create interfaces with a complex strain distribution. Beforehand, compression tests were performed by means of a standard tensile machine in order to determine the appropriate pre-compression rate for quasi-static tests.

Tensile testing apparatus

NASA Technical Reports Server (NTRS)

Blackburn, L. B.; Ellingsworth, J. R. (Inventor)

1985-01-01

An improved mechanical extensometer is described for use with a constant load creep test machine. The dead weight of the extensometer is counterbalanced by two pairs of weights connected through a pulley system and to rod extension and leading into the furnace where the test sample is undergoing elevated temperature (above 500 F.) tensile testing. Novel gripper surfaces, conical tip and flat surface are provided in each sampling engaging platens to reduce the grip pressure normally required for attachment of the extensometer to the specimen and reduce initial specimen bending normally associated with foil-gage metal testing.

Systems and methods for providing power to a load based upon a control strategy

DOEpatents

Perisic, Milun; Kajouke, Lateef A; Ransom, Ray M

2013-12-24

Systems and methods are provided for an electrical system. The electrical system includes a load, an interface configured to receive a voltage from a voltage source, and a controller configured to receive the voltage from the voltage source through the interface and to provide a voltage and current to the load. Wherein, when the controller is in a constant voltage mode, the controller provides a constant voltage to the load, when the controller is in a constant current mode, the controller provides a constant current to the load, and when the controller is in a constant power mode, the controller provides a constant power to the load.

Loads Correlation of a Full-Scale UH-60A Airloads Rotor in a Wind Tunnel

NASA Technical Reports Server (NTRS)

Yeo, Hyeonsoo; Romander, Ethan A.

2012-01-01

Wind tunnel measurements of the rotor trim, blade airloads, and structural loads of a full-scale UH-60A Black Hawk main rotor are compared with calculations obtained using the comprehensive rotorcraft analysis CAMRAD II and a coupled CAMRAD II/OVERFLOW 2 analysis. A speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed into deep stall are investigated. The coupled analysis shows significant improvement over comprehensive analysis. Normal force phase is better captured and pitching moment magnitudes are better predicted including the magnitude and phase of the two stall events in the fourth quadrant at the deeply stalled condition. Structural loads are, in general, improved with the coupled analysis, but the magnitude of chord bending moment is still significantly underpredicted. As there are three modes around 4 and 5/rev frequencies, the structural responses to the 5/rev airloads due to dynamic stall are magnified and thus care must be taken in the analysis of the deeply stalled condition.

The parameters effect on the structural performance of damaged steel box beam using Taguchi method

NASA Astrophysics Data System (ADS)

El-taly, Boshra A.; Abd El Hameed, Mohamed F.

2018-03-01

In the current study, the influence of notch or opening parameters and the positions of the applied load on the structural performance of steel box beams up to failure was investigated using Finite Element analysis program, ANSYS. The Taguchi-based design of experiments technique was used to plan the current study. The plan included 12 box steel beams; three intact beams, and nine damaged beams (with opening) in the beams web. The numerical studies were conducted under varying the spacing between the two concentrated point loads (location of applied loads), the notch (opening) position, and the ratio between depth and width of the notch with a constant notch area. According to Taguchi analysis, factor X (location of the applied loads) was found the highest contributing parameters for the variation of the ultimate load, vertical deformation, shear stresses, and the compressive normal stresses.

Influence of Mixed Mode I-Mode II Loading on Fatigue Delamination Growth Characteristics of a Graphite Epoxy Tape Laminate

NASA Technical Reports Server (NTRS)

Ratcliffe, James G.; Johnston, William M., Jr.

2014-01-01

Mixed mode I-mode II interlaminar tests were conducted on IM7/8552 tape laminates using the mixed-mode bending test. Three mixed mode ratios, G(sub II)/G(sub T) = 0.2, 0.5, and 0.8, were considered. Tests were performed at all three mixed-mode ratios under quasi-static and cyclic loading conditions, where the former static tests were used to determine initial loading levels for the latter fatigue tests. Fatigue tests at each mixed-mode ratio were performed at four loading levels, Gmax, equal to 0.5G(sub c), 0.4G(sub c), 0.3G(sub c), and 0.2G(sub c), where G(sub c) is the interlaminar fracture toughness of the corresponding mixed-mode ratio at which a test was performed. All fatigue tests were performed using constant-amplitude load control and delamination growth was automatically documented using compliance solutions obtained from the corresponding quasi-static tests. Static fracture toughness data yielded a mixed-mode delamination criterion that exhibited monotonic increase in Gc with mixed-mode ratio, G(sub II)/G(sub T). Fatigue delamination onset parameters varied monotonically with G(sub II)/G(sub T), which was expected based on the fracture toughness data. Analysis of non-normalized data yielded a monotonic change in Paris law exponent with mode ratio. This was not the case when normalized data were analyzed. Fatigue data normalized by the static R-curve were most affected in specimens tested at G(sub II)/G(sub T)=0.2 (this process has little influence on the other data). In this case, the normalized data yielded a higher delamination growth rate compared to the raw data for a given loading level. Overall, fiber bridging appeared to be the dominant mechanism, affecting delamination growth rates in specimens tested at different load levels and differing mixed-mode ratios.

Center of mass trajectory and orientation to ankle and knee in sagittal plane is maintained with forward lean when backpack load changes during treadmill walking.

PubMed

Caron, Robert R; Wagenaar, Robert C; Lewis, Cara L; Saltzman, Elliot; Holt, Kenneth G

2013-01-04

Maintaining the normal shape and amplitude of the vertical trajectory of the center of mass (COM) during stance has been shown to maximize the efficiency of unloaded gait. Kinematic adaptations to load carriage, such as forward lean have yet to be understood in relation to COM movement. The purpose of this study is to better understand how load impacts the vertical COM(TSYS) trajectory and to clarify the impact of forward lean as it relates to the dynamics of sagittal plane COM(TSYS) movement during stance with changing load. 17 subjects walked on treadmill at a constant preferred walking velocity while nine different loads ranging from 12.5% to 40% bodyweight were systematically added and removed from a backpack. Kinematic data were collected using an Optotrak, three-dimensional motion analysis system and used to estimate position of the COM as well as segment and COM-to-joint vector orientation angles. The shape and amplitude of the COM vertical trajectory was maintained across all loaded conditions. The orientations of COM-to-ankle and -knee vectors were maintained in all loaded conditions except the heaviest load (40% BW). Results suggest that forward lean changed linearly with changes in load to maintain the COM-to-ankle and -knee vector orientations. COM vertical trajectory was maintained by a combination of invariants including lower-limb segment angles and a constant direction of toe-off impulse vector. The kinematic invariants found suggest a simplified control mechanism by which the system limits degrees of freedom and potentially minimizes torque about lower-extremity joints with added load. Copyright © 2012 Elsevier Ltd. All rights reserved.

Effects of mucosal loading on vocal fold vibration.

PubMed

Tao, Chao; Jiang, Jack J

2009-06-01

A chain model was proposed in this study to examine the effects of mucosal loading on vocal fold vibration. Mucosal loading was defined as the loading caused by the interaction between the vocal folds and the surrounding tissue. In the proposed model, the vocal folds and the surrounding tissue were represented by a series of oscillators connected by a coupling spring. The lumped masses, springs, and dampers of the oscillators modeled the tissue properties of mass, stiffness, and viscosity, respectively. The coupling spring exemplified the tissue interactions. By numerically solving this chain model, the effects of mucosal loading on the phonation threshold pressure, phonation instability pressure, and energy distribution in a voice production system were studied. It was found that when mucosal loading is small, phonation threshold pressure increases with the damping constant R(r), the mass constant R(m), and the coupling constant R(mu) of mucosal loading but decreases with the stiffness constant R(k). Phonation instability pressure is also related to mucosal loading. It was found that phonation instability pressure increases with the coupling constant R(mu) but decreases with the stiffness constant R(k) of mucosal loading. Therefore, it was concluded that mucosal loading directly affects voice production.

Effects of mucosal loading on vocal fold vibration

NASA Astrophysics Data System (ADS)

Tao, Chao; Jiang, Jack J.

2009-06-01

A chain model was proposed in this study to examine the effects of mucosal loading on vocal fold vibration. Mucosal loading was defined as the loading caused by the interaction between the vocal folds and the surrounding tissue. In the proposed model, the vocal folds and the surrounding tissue were represented by a series of oscillators connected by a coupling spring. The lumped masses, springs, and dampers of the oscillators modeled the tissue properties of mass, stiffness, and viscosity, respectively. The coupling spring exemplified the tissue interactions. By numerically solving this chain model, the effects of mucosal loading on the phonation threshold pressure, phonation instability pressure, and energy distribution in a voice production system were studied. It was found that when mucosal loading is small, phonation threshold pressure increases with the damping constant Rr, the mass constant Rm, and the coupling constant Rμ of mucosal loading but decreases with the stiffness constant Rk. Phonation instability pressure is also related to mucosal loading. It was found that phonation instability pressure increases with the coupling constant Rμ but decreases with the stiffness constant Rk of mucosal loading. Therefore, it was concluded that mucosal loading directly affects voice production.

Automated Carrier Landing of an Unmanned Combat Aerial Vehicle Using Dynamic Inversion

DTIC Science & Technology

2007-06-01

17 CN normal force coefficient . . . . . . . . . . . . . . . . . . . . 17 CA axial force coefficient...slug·ft2 Ixzb 0 slug·ft2 The aircraft has a single engine inlet for a single, centerline mounted turbofan engine. For purposes of this research, the...assumed to remain constant for each simulation run and were based on an assumed 10% fuel load with full weapons [2]. The rest of these values were

Alterations in gut transport of minerals and in binding proteins during simulated weightlessness

NASA Technical Reports Server (NTRS)

Bikle, D. D.

1984-01-01

The structural components of the skeleton develop and are maintained in a 1 g environment, shaped by the mechanical load to which they are constantly exposed. Altering such a mechanical load by reducing the gravitational force imposed on the system, as in space flight, has profound effects on the skeleton and permits an exploration of the molecular events which regulate normal skeletal homeostasis. The objective was to determine whether simulated weightlessness reduced intestinal calcium transport, and if so, to determine the molecular mechanisms for such an effect. A nonstressful tail suspension in which the rats gained weight normally while suspended was used to simulate weightlessness. A significant change in intestinal calcium transport was not demonstrated. However, a cyclic change in bone formation with suspension was shown. Based on these observations, the objective changed to determination of the hormonal regulation of bone formation during simulated weightlessness.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, S. R.; Gyekenyesi, J. P.

2001-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress- rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the rest materials.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case 1 loading), constant stress/constant stress-rate testing (Case 2 loading), and cyclic stress/constant stress-rate testing (Case 2 loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case 1 loading history, and alumina for the Case 3 loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth arid/or damage accumulation was determined numerically as a Function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test material&

Load positioning system with gravity compensation

NASA Technical Reports Server (NTRS)

Hollow, R. H.

1984-01-01

A load positioning system with gravity compensation has a servomotor, position sensing feedback potentiometer and velocity sensing tachometer in a conventional closed loop servo arrangement to cause a lead screw and a ball nut to vertically position a load. Gravity compensating components comprise the DC motor, gears, which couple torque from the motor to the lead screw, and constant current power supply. The constant weight of the load applied to the lead screw via the ball nut tend to cause the lead screw to rotate, the constant torque of which is opposed by the constant torque produced by the motor when fed from the constant current source. The constant current is preset as required by the potentiometer to effect equilibration of the load which thereby enables the positioning servomotor to see the load as weightless under both static and dynamic conditions. Positioning acceleration and velocity performance are therefore symmetrical.

A vacuum (10(exp -9) Torr) friction apparatus for determining friction and endurance life of MoSx films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Honecy, Frank S.; Abel, Phillip B.; Pepper, Stephen V.; Spalvins, Talivaldis; Wheeler, Donald R.

1992-01-01

The first part of this paper describes an ultrahigh vacuum friction apparatus (tribometer). The tribometer can be used in a ball-on-disk configuration and is specifically designed to measure the friction and endurance life of solid lubricating films such as MoS(x) in vacuum at a pressure of 10 exp -7 Pa. The sliding mode is typically unidirectional at a constant rotating speed. The second part of this paper presents some representative friction and endurance life data for magnetron sputtered MoS(x) films (110 nm thick) deposited on sputter-cleaned 440 C stainless-steel disk substrates, which were slid against a 6-mm-diameter 440 C stainless-steel bearing ball. All experiments were conducted with loads of 0.49 to 3.6 N (average Hertzian contact pressure, 0.33 to 0.69 GPa), at a constant rotating speed of 120 rpm (sliding velocity ranging from 31 to 107 mm/s due to the range of wear track radii involved in the experiments), in a vacuum of 7 x 10 exp -7 Pa and at room temperature. The results indicate that there are similarities in friction behavior of MoS(x) films overs their life cycles regardless of load applied. The coefficient of friction (mu) decreases as load W increases according to mu = kW exp -1/3. The endurance life E of MoS(x) films decreases as the load W increases according to E = KW exp -1.4 for the load range. The load- (or contract-pressure-) dependent endurance life allows us to reduce the time for wear experiments and to accelerate endurance life testing of MoS(x) films. For the magnetron-sputtered MoS(x) films deposited on 440 C stainless-steel disks: the specific wear rate normalized to the load and the number of revolutions was 3 x 10 exp -8 mm exp 3/N-revolution; the specific wear rate normalized to the load and the total sliding distance was 8 x 10 exp -7 mm exp 3/N-m; and the nondimensional wear coefficient of was approximately 5 x 10 exp -6. The values are almost independent of load in the range 0.49 to 3.6 N (average Hertzian contact pressures of 0.33 to 0.69 GPa).

SCBUCKLE user's manual: Buckling analysis program for simple supported and clamped panels

NASA Technical Reports Server (NTRS)

Cruz, Juan R.

1993-01-01

The program SCBUCKLE calculates the buckling loads and mode shapes of cylindrically curved, rectangular panels. The panel is assumed to have no imperfections. SCBUCKLE is capable of analyzing specially orthotropic symmetric panels (i.e., A(sub 16) = A(sub 26) = 0.0, D(sub 16) = D(sub 26) = 0.0, B(sub ij) = 0.0). The analysis includes first-order transverse shear theory and is capable of modeling sandwich panels. The analysis supports two types of boundary conditions: either simply supported or clamped on all four edges. The panel can be subjected to linearly varying normal loads N(sub x) and N(sub y) in addition to a constant shear load N(sub xy). The applied loads can be divided into two parts: a preload component; and a variable (eigenvalue-dependent) component. The analysis is based on the modified Donnell's equations for shallow shells. The governing equations are solved by Galerkin's method.

Investigation of Tensile Creep of a Normal Strength Overlay Concrete.

PubMed

Drexel, Martin; Theiner, Yvonne; Hofstetter, Günter

2018-06-12

The present contribution deals with the experimental investigation of the time-dependent behavior of a typical overlay concrete subjected to tensile stresses. The latter develop in concrete overlays, which are placed on existing concrete structures as a strengthening measure, due to the shrinkage of the young overlay concrete, which is restrained by the substrate concrete. Since the tensile stresses are reduced by creep, creep in tension is investigated on sealed and unsealed specimens, loaded at different concrete ages. The creep tests as well as the companion shrinkage tests are performed in a climatic chamber at constant temperature and constant relative humidity. Since shrinkage depends on the change of moisture content, the evolution of the mass water content is determined at the center of each specimen by means of an electrolytic resistivity-based system. Together with the experimental results for compressive creep from a previous study, a consistent set of time-dependent material data, determined for the same composition of the concrete mixture and on identical specimens, is now available. It consists of the hygral and mechanical properties, creep and shrinkage strains for both sealed and drying conditions, the respective compliance functions, and the mass water contents in sealed and unsealed, loaded and load-free specimens.

Modeling a constant power load for nickel-hydrogen battery testing using SPICE

NASA Technical Reports Server (NTRS)

Bearden, Douglas B.; Lollar, Louis F.; Nelms, R. M.

1990-01-01

The effort to design and model a constant power load for the HST (Hubble Space Telescope) nickel-hydrogen battery tests is described. The constant power load was designed for three different simulations on the batteries: life cycling, reconditioning, and capacity testing. A dc-dc boost converter was designed to act as this constant power load. A boost converter design was chosen because of the low test battery voltage (4 to 6 VDC) generated and the relatively high power requirement of 60 to 70 W. The SPICE model was shown to consistently predict variations in the actual circuit as various designs were attempted. It is concluded that the confidence established in the SPICE model of the constant power load ensures its extensive utilization in future efforts to improve performance in the actual load circuit.

Quantification of baseline pupillary response and task-evoked pupillary response during constant and incremental task load.

PubMed

Mosaly, Prithima R; Mazur, Lukasz M; Marks, Lawrence B

2017-10-01

The methods employed to quantify the baseline pupil size and task-evoked pupillary response (TEPR) may affect the overall study results. To test this hypothesis, the objective of this study was to assess variability in baseline pupil size and TEPR during two basic working memory tasks: constant load of 3-letters memorisation-recall (10 trials), and incremental load memorisation-recall (two trials of each load level), using two commonly used methods (1) change from trail/load specific baseline, (2) change from constant baseline. Results indicated that there was a significant shift in baseline between the trails for constant load, and between the load levels for incremental load. The TEPR was independent of shifts in baseline using method 1 only for constant load, and method 2 only for higher levels of incremental load condition. These important findings suggest that the assessment of both the baseline and methods to quantify TEPR are critical in ergonomics application, especially in studies with small number of trials per subject per condition. Practitioner Summary: Quantification of TEPR can be affected by shifts in baseline pupil size that are most likely affected by non-cognitive factors when other external factors are kept constant. Therefore, quantification methods employed to compute both baseline and TEPR are critical in understanding the information processing of humans in practical ergonomics settings.

Controlled long-term release of small peptide hormones using a new microporous polypropylene polymer: its application for vasopressin in the Brattleboro rat and potential perinatal use

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruisbrink, J.; Boer, G.J.

1984-12-01

Based on drug release by microporous hollow fibers and the recent introduction of microporous polymers, a new technique was developed for controlled delivery of peptides. Small-diameter microporous polypropylene tubing, lumen-loaded with microgram quantities of vasopressin, and coated with collodion, releases vasopressin after in vitro immersion slowly (1-100 ng/d) and constantly for months. The mechanism of pseudo-zero-order delivery is based on high adsorption of vasopressin, keeping the void volume concentration of dissolved vasopressin constant, which is consequently a constant driving force of outward diffusion. The collodion coating prevents the entry of proteinaceous compounds which would result in rapid desorption of vasopressin.more » The present delivery module provides a lasting release for other peptides as well (lysine-vasopressin, oxytocin, alpha-melanocyte-stimulating hormone and, to a lesser extent, Met-enkephalin). The microporous polymer-collodion device is biocompatible and, loaded with vasopressin, successfully alleviates the diabetes insipidus of Brattleboro rats deficient for vasopressin. Subcutaneous implantation normalized diuresis for a period of 60 d and constant urine vasopressin excretion is observed. When the commercially available osmotic minipump is too large for implantation, the small size of the present controlled-delivery system allows peptide treatment of young and immature laboratory rats, even if located in utero.« less

Observation of Failure and Domain Switching in Lead Zirconate Titanate Ceramics

NASA Astrophysics Data System (ADS)

Okayasu, Mitsuhiro; Sugiyama, Eriko; Sato, Kazuto; Mizuno, Mamoru

The mechanical and electrical properties (electromechanical coupling coefficient, piezoelectric constant and dielectric constant) of lead zirconate titanate (PZT) ceramics are investigated during mechanical static and cyclic loading. There are several failure characteristics which can alter the material properties of PZT ceramics. The elastic constant increases and electrical properties decrease with increasing the applied load. This is due to the internal strain arising from the domain switching. In this case, 90° domain switching occurs anywhere in the samples as the sample is loaded. It is also apparent that electrogenesis occurs several times during cyclic loading to the final fracture. This occurrence is related to the domain switching. The elastic constant and electrical properties can decrease because of crack generation in the PZT ceramics. Moreover, the elastic constant increases with increase of the mechanical load and decreases with decrease of the load. On the contrary, the opposite sense of change of the electrical properties is observed.

Synthesized multi-station tribo-test system for bio-tribological evaluation in vitro

NASA Astrophysics Data System (ADS)

Wu, Tonghai; Du, Ying; Li, Yang; Wang, Shuo; Zhang, Zhinan

2016-07-01

Tribological tests play an important role on the evaluation of long-term bio-tribological performances of prosthetic materials for commercial fabrication. Those tests focus on the motion simulation of a real joint in vitro with only normal loads and constant velocities, which are far from the real friction behavior of human joints characterized with variable loads and multiple directions. In order to accurately obtain the bio-tribological performances of artificial joint materials, a tribological tester with a miniature four-station tribological system is proposed with four distinctive features. Firstly, comparability and repeatability of a test are ensured by four equal stations of the tester. Secondly, cross-linked scratch between tribo-pairs of human joints can be simulated by using a gear-rack meshing mechanism to produce composite motions. With this mechanism, the friction tracks can be designed by varying reciprocating and rotating speeds. Thirdly, variable loading system is realized by using a ball-screw mechanism driven by a stepper motor, by which loads under different gaits during walking are simulated. Fourthly, dynamic friction force and normal load can be measured simultaneously. The verifications of the performances of the developed tester show that the variable frictional tracks can produce different wear debris compared with one-directional tracks, and the accuracy of loading and friction force is within ±5%. Thus the high consistency among different stations can be obtained. Practically, the proposed tester system could provide more comprehensive and accurate bio-tribological evaluations for prosthetic materials.

Examining the Relationship Between Suspended Sand Load and Bedload on the Colorado River Using Concurrent Measurements of Suspended Sand and Observations of Sand Dune Migration.

NASA Astrophysics Data System (ADS)

Ashley, T.; McElroy, B. J.; Buscombe, D.; Grams, P. E.; Kaplinski, M. A.

2015-12-01

Spatial variability in sediment flux is directly related to geomorphic change. Along the Colorado River, measurements of sediment flux are used to track changes in sediment storage and time the release of controlled floods aimed at building eroded sandbars. The very high uncertainty typical of measurements of sediment flux has been reduced by a program of continuous measurement of suspended-sediment concentration by acoustic surrogates. However, there is still significant uncertainty in calculations of total flux. A large fraction of that uncertainty may be caused by overly simplified treatment of bedload flux, which is currently estimated as a constant 5% of the suspended sand flux. That constant is based on estimates of bedform migration rate made with side-scan sonar. Here, we apply theory which relates bedform migration and streamwise sediment flux, to bathymetric data collected at unprecedented temporal and spatial resolution adjacent to the USGS sediment monitoring station above Diamond Creek (362 km downstream from Lees Ferry, AZ). Quantitative time series measurements of reach averaged bedform transport are calculated and compared to fluxes estimated by expressing bedload as a constant fraction of suspended load. Over the range of discharges expected during normal dam operations, bedload transport estimated from the migration of bedforms in the study reach is at least 20% of instantaneous suspended sand load measured at the gage. While bedload appears to be controlled primarily by discharge (and therefore transport capacity of the flow), suspended sand load varies inversely with the grain size of suspended material, suggesting dependence on sediment supply. Sediment transport capacity can vary significantly at a given discharge depending on local hydraulic geometry, so it is likely that there is more spatial variability in bedload transport than suspended sand transport.

Determining friction and effective loading for sled sprinting.

PubMed

Cross, Matt R; Tinwala, Farhan; Lenetsky, Seth; Samozino, Pierre; Brughelli, Matt; Morin, Jean-Benoit

2017-11-01

Understanding the impact of friction in sled sprinting allows the quantification of kinetic outputs and the effective loading experienced by the athlete. This study assessed changes in the coefficient of friction (µ k ) of a sled sprint-training device with changing mass and speed to provide a means of quantifying effective loading for athletes. A common sled equipped with a load cell was towed across an athletics track using a motorised winch under variable sled mass (33.1-99.6 kg) with constant speeds (0.1 and 0.3 m · s -1 ), and with constant sled mass (55.6 kg) and varying speeds (0.1-6.0 m · s -1 ). Mean force data were analysed, with five trials performed for each condition to assess the reliability of measures. Variables were determined as reliable (ICC > 0.99, CV < 4.3%), with normal-force/friction-force and speed/coefficient of friction relationships well fitted with linear (R 2  = 0.994-0.995) and quadratic regressions (R 2  = 0.999), respectively (P < 0.001). The linearity of composite friction values determined at two speeds, and the range in values from the quadratic fit (µ k  = 0.35-0.47) suggested µ k and effective loading were dependent on instantaneous speed on athletics track surfaces. This research provides a proof-of-concept for the assessment of friction characteristics during sled towing, with a practical example of its application in determining effective loading and sled-sprinting kinetics. The results clarify effects of friction during sled sprinting and improve the accuracy of loading applications in practice and transparency of reporting in research.

Variability of normal vocal fold dynamics for different vocal loading in one healthy subject investigated by phonovibrograms.

PubMed

Doellinger, Michael; Lohscheller, Joerg; McWhorter, Andrew; Kunduk, Melda

2009-03-01

We investigate the potential of high-speed digital imaging technique (HSI) and the phonovibrogram (PVG) analysis in normal vocal fold dynamics by studying the effects of continuous voice use (vocal loading) during the workday. One healthy subject was recorded at sustained phonation 13 times within 2 consecutive days in the morning before and in the afternoon after vocal loading, respectively. Vocal fold dynamics were extracted and visualized by PVGs. The characteristic PVG patterns were extracted representing vocal fold vibration types. The parameter values were then analyzed by statistics regarding vocal load, left-right PVG asymmetries, anterior-posterior PVG asymmetries, and opening-closing differences. For the first time, the direct impact of vocal load could be determined by analyzing vocal fold dynamics. For same vocal loading conditions, equal dynamical behavior of the vocal folds were confirmed. Comparison of recordings performed in the morning with the recordings after work revealed significant changes in vibration behavior, indicating impact of occurring vocal load. Left-right asymmetries in vocal fold dynamics were found confirming earlier assumptions. Different dynamics between opening and closing procedure as well as for anterior and posterior parts were found. Constant voice usage stresses the vocal folds even in healthy subjects and can be detected by applying the PVG technique. Furthermore, left-right PVG asymmetries do occur in healthy voice to a certain extent. HSI in combination with PVG analysis seems to be a promising tool for investigation of vocal fold fatigue and pathologies resulting in small forms of dynamical changes.

An improved Armstrong-Frederick-Type Plasticity Model for Stable Cyclic Stress-Strain Responses Considering Nonproportional Hardening

NASA Astrophysics Data System (ADS)

Li, Jing; Zhang, Zhong-ping; Li, Chun-wang

2018-03-01

This paper modified an Armstrong-Frederick-type plasticity model for investigating the stable cyclic deformation behavior of metallic materials with different sensitivity to nonproportional loadings. In the modified model, the nonproportionality factor and nonproportional cyclic hardening coefficient coupled with the Jiang-Sehitoglu incremental plasticity model were used to estimate the stable stress-strain responses of the two materials (1045HR steel and 304 stainless steel) under various tension-torsion strain paths. A new equation was proposed to calculate the nonproportionality factor on the basis of the minimum normal strain range. Procedures to determine the minimum normal strain range were presented for general multiaxial loadings. Then, the modified model requires only the cyclic strain hardening exponent and cyclic strength coefficient to determine the material constants. It is convenient for predicting the stable stress-strain responses of materials in engineering application. Comparisons showed that the modified model can reflect the effect of nonproportional cyclic hardening well.

Creep Behavior of Near-Stoichiometric Polycrystalline Binary NiAl

NASA Technical Reports Server (NTRS)

Raj, S. V.

2002-01-01

New and published constant load creep and constant engineering strain rate data on near-stoichiometric binary NiAl in the intermediate temperature range 700 to 1300 K are reviewed. Both normal and inverse primary creep curves are observed depending on stress and temperature. Other characteristics relating to creep of NiAl involving grain size, stress and temperature dependence are critically examined and discussed. At stresses below 25 MPa and temperatures above 1000 K, a new grain boundary sliding mechanism was observed with n approx. 2, Qc approx. 100 kJ/ mol and a grain size exponent of about 2. It is demonstrated that Coble creep and accommodated grain boundary sliding models fail to predict the experimental creep rates by several orders of magnitude.

Self-aligning biaxial load frame

DOEpatents

Ward, M.B.; Epstein, J.S.; Lloyd, W.R.

1994-01-18

An self-aligning biaxial loading apparatus for use in testing the strength of specimens while maintaining a constant specimen centroid during the loading operation. The self-aligning biaxial loading apparatus consists of a load frame and two load assemblies for imparting two independent perpendicular forces upon a test specimen. The constant test specimen centroid is maintained by providing elements for linear motion of the load frame relative to a fixed cross head, and by alignment and linear motion elements of one load assembly relative to the load frame. 3 figures.

Self-aligning biaxial load frame

DOEpatents

Ward, Michael B.; Epstein, Jonathan S.; Lloyd, W. Randolph

1994-01-01

An self-aligning biaxial loading apparatus for use in testing the strength of specimens while maintaining a constant specimen centroid during the loading operation. The self-aligning biaxial loading apparatus consists of a load frame and two load assemblies for imparting two independent perpendicular forces upon a test specimen. The constant test specimen centroid is maintained by providing elements for linear motion of the load frame relative to a fixed crosshead, and by alignment and linear motion elements of one load assembly relative to the load frame.

Development of a Time-Variant Figure-of-Merit for Use in Analysis of Air Combat Maneuvering Engagements

DTIC Science & Technology

1976-07-16

Influence of Range 10 5 Range Performance Penalty Function II 6 Influence of Closing Velocity 12 7 Energy Influence Function 14 8 Comparison of the...flELtSHAlL, ..E^) RANGE RANGE Figure 7 Energy Influence Function 14 TM 76-1 SA ! PERFORMANCE INDEX COMPARATIVE ANALYSIS Maneuver Conversion Model...hnergy Integral ■’> E s K Energy Influence Function K* Proportionality Constant MT Target Mach Number N Normal Acceleration (load factor) z

[The physiology of the isolated dog pancreas--the influence of the actual blood glucose level on the blood circulation in the pancreas].

PubMed

Hempfling, H; Husemann, B

1975-06-01

1. Glucose loading tests were undertaken on isolated pancreas or pancreas-duodenal preparations. 2. In 75% of cases a vasodilatation can be observed which leads to enhanced blood circulation under constant pressure in the isolated organ. 3. This vasodilatation persists until the level of blood sugar has normalized. 4. The experiment being carried out on an isolated organ, external factors such as the vagus nerve, do not become active.

A new apparatus for testing the delayed mechanical behaviour of interfaces: The Shearing Interfaces Creep box (SInC box)

NASA Astrophysics Data System (ADS)

Stavropoulou, Eleni; Briffaut, Matthieu; Dufour, Frédéric; Camps, Guillaume; Boulon, Marc

2017-06-01

A new experimental apparatus is presented for testing the time-dependent behaviour of interfaces, including in particular interfaces of geomaterials, under constant loading. This apparatus allows the application of two orthogonal loads normal and tangential to the mean plane of the interface, as well as the measurement of the axial and tangential relative displacements. The sample is moulded inside two half shear boxes and the system is designed in such a way that the shear force is applied along the mean plane of the interface. Some preliminary testing was carried out on a clay rock/concrete interface, under a controlled temperature environment. Preliminary results are presented, showing the evolution of the delayed displacements.

Trunk Acceleration for Neuroprosthetic Control of Standing – a Pilot Study

PubMed Central

Audu, Musa L.; Kirsch, Robert F.; Triolo, Ronald J.

2013-01-01

This pilot study investigated the potential of using trunk acceleration feedback control of center of pressure (COP) against postural disturbances with a standing neuroprosthesis following paralysis. Artificial neural networks (ANNs) were trained to use three-dimensional trunk acceleration as input to predict changes in COP for able-bodied subjects undergoing perturbations during bipedal stance. Correlation coefficients between ANN predictions and actual COP ranged from 0.67 to 0.77. An ANN trained across all subject-normalized data was used to drive feedback control of ankle muscle excitation levels for a computer model representing a standing neuroprosthesis user. Feedback control reduced average upper-body loading during perturbation onset and recovery by 42% and peak loading by 29% compared to optimal, constant excitation. PMID:21975251

Trunk acceleration for neuroprosthetic control of standing: a pilot study.

PubMed

Nataraj, Raviraj; Audu, Musa L; Kirsch, Robert F; Triolo, Ronald J

2012-02-01

This pilot study investigated the potential of using trunk acceleration feedback control of center of pressure (COP) against postural disturbances with a standing neuroprosthesis following paralysis. Artificial neural networks (ANNs) were trained to use three-dimensional trunk acceleration as input to predict changes in COP for able-bodied subjects undergoing perturbations during bipedal stance. Correlation coefficients between ANN predictions and actual COP ranged from 0.67 to 0.77. An ANN trained across all subject-normalized data was used to drive feedback control of ankle muscle excitation levels for a computer model representing a standing neuroprosthesis user. Feedback control reduced average upper-body loading during perturbation onset and recovery by 42% and peak loading by 29% compared with optimal, constant excitation.

Investigation of Three Analytical Hypothesis for Determining Material Creep Behavior under Varied Loads, with an Application to 2024-T3 Aluminum-Alloy Sheet in Tension at 400 F

NASA Technical Reports Server (NTRS)

Berkovits, Avraham

1961-01-01

Three existing hypotheses are formulated mathematically to estimate tensile creep strain under varied loads and constant temperature from creep data obtained under constant load and constant temperature. hypotheses investigated include the time-hardening, strain-hardening, and life-fraction rules. Predicted creep behavior is compared with data obtained from tensile creep tests of 2024-T3 aluminum-alloy sheet at 400 F under cyclic-load conditions. creep strain under varied loads is presented on the basis of an equivalent stress, derived from the life-fraction rule, which reduces the varied-load case to a constant-load problem. Creep strain in the region of interest for structural design and rupture times, determined from the hypotheses investigated, are in fair agreement with data in most cases, although calculated values of creep strain are generally greater than the experimental values because creep recovery is neglected in the calculations.

Evaluation of Delamination Growth Characterization Methods Under Mode I Fatigue Loading

NASA Technical Reports Server (NTRS)

Murri, Gretchen B.

2012-01-01

Reliable delamination characterization data for laminated composites are needed for input to analytical models of structures to predict delamination. The double-cantilevered beam (DCB) specimen is used with laminated composites to measure fracture toughness, G(sub Ic), delamination onset strain energy release rate, and growth rate data under cyclic loading. In the current study, DCB specimens of IM7/8552 graphite/epoxy supplied by two different manufacturers were tested in static and fatigue to compare the measured characterization data from the two sources, and to evaluate a proposed ASTM standard for generating Paris Law equations. Static results were used to generate compliance calibration constants for the fatigue data, and a delamination resistance curve, G(sub IR), which was used to determine the effects of fiber-bridging on delamination growth. Specimens were tested in fatigue at a cyclic G(sub Imax) level equal to 50, 40 or 30% of G(sub Ic), to determine a delamination onset curve and delamination growth rate. The delamination onset curve equations had similar exponents and the same trends. Delamination growth rate was calculated by fitting a Paris Law to the da/dN versus G(sub Imax) data. Both a 2-point and a 7-point data reduction method were used and the Paris Law equations were compared. To determine the effects of fiber-bridging, growth rate results were normalized by the delamination resistance curve for each material and compared to the non-normalized results. Paris Law exponents were found to decrease by 31% to 37% due to normalizing the growth data. Normalizing the data also greatly reduced the amount of scatter between the different specimens. Visual data records from the fatigue testing were used to calculate individual compliance calibration constants from the fatigue data for some of the specimens. The resulting da/dN versus G(sub Imax) plots showed much improved repeatability between specimens. Gretchen

Out-of-equilibrium pH transients in the guinea-pig ventricular myocyte

PubMed Central

Leem, Chae-Hun; Vaughan-Jones, Richard D

1998-01-01

Following an intracellular alkali load (imposed by acetate prepulsing in CO2/HCO3− buffer), intracellular pH (pHi) of the guinea-pig ventricular myocyte (recorded from intracellular SNARF fluorescence) recovers to control levels. Recovery has two phases. An initial rapid phase (lasting up to 2 min) is followed by a later slow phase (several minutes). Inhibition of sarcolemmal acid-loading carriers (by removal of extracellular Cl−) inhibits the later, slow phase but the initial rapid recovery phase persists. It also persists in the absence of extracellular Na+ and in the presence of the HCO3− transport inhibitor DIDS (4,4-di-isothiocyanatostilbene-2,2-disulphonic acid). The rapid recovery phase is not evident if the alkali load has been induced by reducing PCO2 (from 10 to 5 %), and it is inhibited in the absence of CO2/HCO3− buffer (i.e. Hepes buffer). It is also slowed by the carbonic anhydrase (CA) inhibitor acetazolamide (ATZ). We conclude that it is caused by buffering of the alkali load through the hydration of intracellular CO2 (CO2-dependent buffering). The time course of rapid recovery is consistent with an intracellular CO2 hydration rate constant (k1) of 0.36 s−1 in the presence of CA activity, and 0.14 s−1 in the absence of CA activity. This latter k1 value matches the literature value for uncatalysed CO2 hydration in free solution. Natural CO2 hydration is accelerated 2.6-fold in the ventricular myocyte by endogenous CA. The rapid recovery phase represents a period when the intracellular CO2/HCO3− buffer is out of equilibrium (OOE). Modelling of the recovery phase using our k1 value, indicates that OOE conditions will normally extend for at least 2 min following a step rise in pHi (at constant PCO2). If CA is inactive, this period can be as long as 5 min. During normal pHi regulation, the recovery rate during these periods cannot be used as a measure of sarcolemmal acid loading since it is a mixture of slow CO2-dependent buffering and transmembrane acid loading. The implication of this finding for quantification of pHi regulation during alkalosis is discussed. PMID:9575296

Physical Modeling of Shear Behavior of Infilled Rock Joints Under CNL and CNS Boundary Conditions

NASA Astrophysics Data System (ADS)

Shrivastava, Amit Kumar; Rao, K. Seshagiri

2018-01-01

Despite their frequent natural occurrence, filled discontinuities under constant normal stiffness (CNS) boundary conditions have been studied much less systematically, perhaps because of the difficulties arising from the increased number of variable parameters. Because of the lack of reliable and realistic theoretical or empirical relations and the difficulties in obtaining and testing representative samples, engineers rely on judgment and often consider the shear strength of the infilled material itself as shear strength of rock joints. This assumption leads to uneconomical and also sometimes the unsafe design of underground structures, slopes, rock-socketed piles and foundations. To study the effect of infill on the shear behavior of rock joints, tests were performed on the modeled infilled rock joint having different joint roughness under constant normal load (CNL) and CNS boundary conditions at various initial normal stress and varying thickness of the infilled material. The test results indicate that shear strength decreases with an increase in t/ a ratio for both CNL and CNS conditions, but the reduction in shear strength is more for CNL than for CNS condition for a given initial normal stress. The detailed account of the effect of thickness of infilled material on shear and deformation behavior of infilled rock joint is discussed in this paper, and a model is proposed to predict shear strength of infilled rock joint.

Generating Fatigue Crack Growth Thresholds with Constant Amplitude Loads

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James C., J.; Forman, Royce G.

2002-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. Some experimental procedures tend to induce load history effects that result in remote crack closure from plasticity. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor, K, will increase, as will the crack growth rate, da/dN. A fatigue crack growth threshold test procedure is developed and experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R.

Depth-dependent resistance of granular media to vertical penetration.

PubMed

Brzinski, T A; Mayor, P; Durian, D J

2013-10-18

We measure the quasistatic friction force acting on intruders moving downwards into a granular medium. By utilizing different intruder geometries, we demonstrate that the force acts locally normal to the intruder surface. By altering the hydrostatic loading of grain contacts by a sub-fluidizing airflow through the bed, we demonstrate that the relevant frictional contacts are loaded by gravity rather than by the motion of the intruder itself. Lastly, by measuring the final penetration depth versus airspeed and using an earlier result for inertial drag, we demonstrate that the same quasistatic friction force acts during impact. Altogether this force is set by a friction coefficient, hydrostatic pressure, projectile size and shape, and a dimensionless proportionality constant. The latter is the same in nearly all experiments, and is surprisingly greater than one.

A technique for measuring dynamic friction coefficient under impact loading

NASA Astrophysics Data System (ADS)

Lin, Y. L.; Qin, J. G.; Chen, R.; Zhao, P. D.; Lu, F. Y.

2014-09-01

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m2/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

A technique for measuring dynamic friction coefficient under impact loading.

PubMed

Lin, Y L; Qin, J G; Chen, R; Zhao, P D; Lu, F Y

2014-09-01

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m(2)/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.

Research on the Mechanism of In-Plane Vibration on Friction Reduction

PubMed Central

Wang, Peng; Ni, Hongjian; Wang, Ruihe; Liu, Weili; Lu, Shuangfang

2017-01-01

A modified model for predicting the friction force between drill-string and borehole wall under in-plane vibrations was developed. It was found that the frictional coefficient in sliding direction decreased significantly after applying in-plane vibration on the bottom specimen. The friction reduction is due to the direction change of friction force, elastic deformation of surface asperities and the change of frictional coefficient. Normal load, surface topography, vibration direction, velocity ratio and interfacial shear factor are the main influence factors of friction force in sliding direction. Lower driving force can be realized for a pair of determinate rubbing surfaces under constant normal load by setting the driving direction along the minimum arithmetic average attack angle direction, and applying intense longitudinal vibration on the rubbing pair. The modified model can significantly improve the accuracy in predicting frictional coefficient under vibrating conditions, especially under the condition of lower velocity ratio. The results provide a theoretical gist for friction reduction technology by vibrating drill-string, and provide a reference for determination of frictional coefficient during petroleum drilling process, which has great significance for realizing digitized and intelligent drilling. PMID:28862679

The effect of load and thickness variation on stress analysis of monocoque frame of electric city car using FEM

NASA Astrophysics Data System (ADS)

Makhrojan, Agus; Suprihadi, Agus; Budi, Sigit Setijo; Jamari, J.; Ismail, Rifky

2017-01-01

The electric car is transportation which growing and constantly put through improvisation vehicle design. One of the structural components of the electric car which holds a major role is a frame. The purpose of this study is to get monocoque frame design which lightweight and powerful for a city car with two passengers that was able to improve the efficiency of the battery voltage source. Monocoque frame should be able to accept the normal loads such as the weight of batteries, passenger, and body. The most important thing, monocoque frame should also be able to protect the driver and passengers in the event of a collision. Mild steel was chosen for the design because it is easy to obtain and reasonable price as well as easy to shaped for two-seater electric car. FEM (finite element method) was used to determine stress determination and rigidity of the monocoque frame when receiving a static load. The results show that the monocoque frame was still able to withstand the required loads with minimal deflection.

Surface contact and design of fibrillar ‘friction pads’ in stick insects (Carausius morosus): mechanisms for large friction coefficients and negligible adhesion

PubMed Central

Labonte, David; Williams, John A.; Federle, Walter

2014-01-01

Many stick insects and mantophasmids possess tarsal ‘heel pads’ (euplantulae) covered by arrays of conical, micrometre-sized hairs (acanthae). These pads are used mainly under compression; they respond to load with increasing shear resistance, and show negligible adhesion. Reflected-light microscopy in stick insects (Carausius morosus) revealed that the contact area of ‘heel pads’ changes with normal load on three hierarchical levels. First, loading brought larger areas of the convex pads into contact. Second, loading increased the density of acanthae in contact. Third, higher loads changed the shape of individual hair contacts gradually from circular (tip contact) to elongated (side contact). The resulting increase in real contact area can explain the load dependence of friction, indicating a constant shear stress between acanthae and substrate. As the euplantula contact area is negligible for small loads (similar to hard materials), but increases sharply with load (resembling soft materials), these pads show high friction coefficients despite little adhesion. This property appears essential for the pads’ use in locomotion. Several morphological characteristics of hairy friction pads are in apparent contrast to hairy pads used for adhesion, highlighting key adaptations for both pad types. Our results are relevant for the design of fibrillar structures with high friction coefficients but small adhesion. PMID:24554580

Earthquake Energy Dissipation in Light of High-Velocity, Slip-Pulse Shear Experiments

NASA Astrophysics Data System (ADS)

Reches, Z.; Liao, Z.; Chang, J. C.

2014-12-01

We investigated the energy dissipation during earthquakes by analysis of high-velocity shear experiments conducted on room-dry, solid samples of granite, tonalite, and dolomite sheared at slip-velocity of 0.0006-1m/s, and normal stress of 1-11.5MPa. The experimental fault were loaded in one of three modes: (1) Slip-pulse of abrupt, intense acceleration followed by moderate deceleration; (2) Impact by a spinning, heavy flywheel (225 kg); and (3) Constant velocity loading. We refer to energy dissipation in terms of power-density (PD=shear stress*slip-velocity; units of MW/m^2), and Coulomb-energy-density (CED= mechanical energy/normal stress; units of m). We present two aspects: Relative energy dissipation of the above loading modes, and relative energy dissipation between impact experiments and moderate earthquakes. For the first aspect, we used: (i) the lowest friction coefficient of the dynamic weakening; (ii) the work dissipated before reaching the lowest friction; and (iii) the cumulative mechanical work during the complete run. The results show that the slip-pulse/impact modes are energy efficient relatively to the constant-velocity mode as manifested by faster, more intense weakening and 50-90% lower energy dissipation. Thus, for a finite amount of pre-seismic crustal energy, the efficiency of slip-pulse would amplify earthquake instability. For the second aspect, we compare the experimental CED of the impact experiments to the reported breakdown energy (EG) of moderate earthquakes, Mw = 5.6 to 7.2 (Chang et al., 2012). In is commonly assumed that the seismic EG is a small fraction of the total earthquake energy, and as expected in 9 out of 11 examined earthquakes, EG was 0.005 to 0.07 of the experimental CED. We thus speculate that the experimental relation of Coulomb-energy-density to total slip distance, D, CED = 0.605 × D^0.933, is a reasonable estimate of total earthquake energy, a quantity that cannot be determined from seismic data.

Experimental studies of breaking of elastic tired wheel under variable normal load

NASA Astrophysics Data System (ADS)

Fedotov, A. I.; Zedgenizov, V. G.; Ovchinnikova, N. I.

2017-10-01

The paper analyzes the braking of a vehicle wheel subjected to disturbances of normal load variations. Experimental tests and methods for developing test modes as sinusoidal force disturbances of the normal wheel load were used. Measuring methods for digital and analogue signals were used as well. Stabilization of vehicle wheel braking subjected to disturbances of normal load variations is a topical issue. The paper suggests a method for analyzing wheel braking processes under disturbances of normal load variations. A method to control wheel baking processes subjected to disturbances of normal load variations was developed.

Bending creep and load duration of Douglas-fir 2 by 4s under constant load for up to 12-plus years

Treesearch

Charles C. Gerhards

2000-01-01

This paper finalizes research on graded Douglas-fir 2 by 4 beams subjected to constant bending loads of various levels and durations. Compared to results for testing in a controlled environment, results confirm that load duration did not appear to be shortened by tests in an uncontrolled environment, at least extending out to 12-plus years. By the same comparison,...

Elasticity Theory Solution of the Problem on Plane Bending of a Narrow Layered Cantilever Beam by Loads at Its Free End

NASA Astrophysics Data System (ADS)

Goryk, A. V.; Koval'chuk, S. B.

2018-05-01

An exact elasticity theory solution for the problem on plane bending of a narrow layered composite cantilever beam by tangential and normal loads distributed on its free end is presented. Components of the stress-strain state are found for the whole layers package by directly integrating differential equations of the plane elasticity theory problem by using an analytic representation of piecewise constant functions of the mechanical characteristics of layer materials. The continuous solution obtained is realized for a four-layer beam with account of kinematic boundary conditions simulating the rigid fixation of its one end. The solution obtained allows one to predict the strength and stiffness of composite cantilever beams and to construct applied analytical solutions for various problems on the elastic bending of layered beams.

SU-F-19A-05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, J; Micka, J; Culberson, W

Purpose: To determine the in-air azimuthal anisotropy and in-water dose distribution for the 1 cm length of the CivaString {sup 103}Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG-43) dosimetry parameters were also determined for this source. Methods: The in-air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function for this sourcemore » were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of {sup 103}Pd well-loading variability on the in-water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells. Results: NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in {sup 103}Pd well-loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG-43 dose-rate constant, radial dose distribution, and polar dose distribution, respectively. Conclusion: The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy. TG-43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. {sup 103}Pd well-loading variability results in minimal variations in the in-water dose distribution according to MC simulations. This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.« less

Effect of wing loading, aspect ratio, and span loading of flight performances

NASA Technical Reports Server (NTRS)

Gothert, B

1940-01-01

An investigation is made of the possible improvements in maximum, cruising, and climbing speeds attainable through increase in the wing loading. The decrease in wing area was considered for the two cases of constant aspect ratio and constant span loading. For a definite flight condition, an investigation is made to determine what loss in flight performance must be sustained if, for given reasons, certain wing loadings are not to be exceeded. With the aid of these general investigations, the trend with respect to wing loading is indicated and the requirements to be imposed on the landing aids are discussed

Synergic effects of 10°/s constant rotation and rotating background on visual cognitive processing

NASA Astrophysics Data System (ADS)

He, Siyang; Cao, Yi; Zhao, Qi; Tan, Cheng; Niu, Dongbin

In previous studies we have found that constant low-speed rotation facilitated the auditory cognitive process and constant velocity rotation background sped up the perception, recognition and assessment process of visual stimuli. In the condition of constant low-speed rotation body is exposed into a new physical state. In this study the variations of human brain's cognitive process under the complex condition of constant low-speed rotation and visual rotation backgrounds with different speed were explored. 14 university students participated in the ex-periment. EEG signals were recorded when they were performing three different cognitive tasks with increasing mental load, that is no response task, selective switch responses task and selec-tive mental arithmetic task. Rotary chair was used to create constant low-speed10/srotation. Four kinds of background were used in this experiment, they were normal black background and constant 30o /s, 45o /s or 60o /s rotating simulated star background. The P1 and N1 compo-nents of brain event-related potentials (ERP) were analyzed to detect the early visual cognitive processing changes. It was found that compared with task performed under other backgrounds, the posterior P1 and N1 latencies were shortened under 45o /s rotating background in all kinds of cognitive tasks. In the no response task, compared with task performed under black back-ground, the posterior N1 latencies were delayed under 30o /s rotating background. In the selec-tive switch responses task and selective mental arithmetic task, compared with task performed under other background, the P1 latencies were lengthened under 60o /s rotating background, but the average amplitudes of the posterior P1 and N1 were increased. It was suggested that under constant 10/s rotation, the facilitated effect of rotating visual background were changed to an inhibited one in 30o /s rotating background. Under vestibular new environment, not all of the rotating backgrounds accelerated the early process of visual cognition. There is a synergic effect between the effects of constant low-speed rotation and rotating speed of the background. Under certain conditions, they both served to facilitate the visual cognitive processing, and it had been started at the stage when extrastriate cortex perceiving the visual signal. Under the condition of constant low-speed rotation in higher cognitive load tasks, the rapid rotation of the background enhanced the magnitude of the signal transmission in the visual path, making signal to noise ratio increased and a higher signal to noise ratio is clearly in favor of target perception and recognition. This gave rise to the hypothesis that higher cognitive load tasks with higher top-down control had more power in counteracting the inhibition effect of higher velocity rotation background. Acknowledgements: This project was supported by National Natural Science Foundation of China (No. 30670715) and National High Technology Research and Development Program of China (No.2007AA04Z254).

Preloading To Accelerate Slow-Crack-Growth Testing

NASA Technical Reports Server (NTRS)

Gyekenyesi, John P.; Choi, Sung R.; Pawlik, Ralph J.

2004-01-01

An accelerated-testing methodology has been developed for measuring the slow-crack-growth (SCG) behavior of brittle materials. Like the prior methodology, the accelerated-testing methodology involves dynamic fatigue ( constant stress-rate) testing, in which a load or a displacement is applied to a specimen at a constant rate. SCG parameters or life prediction parameters needed for designing components made of the same material as that of the specimen are calculated from the relationship between (1) the strength of the material as measured in the test and (2) the applied stress rate used in the test. Despite its simplicity and convenience, dynamic fatigue testing as practiced heretofore has one major drawback: it is extremely time-consuming, especially at low stress rates. The present accelerated methodology reduces the time needed to test a specimen at a given rate of applied load, stress, or displacement. Instead of starting the test from zero applied load or displacement as in the prior methodology, one preloads the specimen and increases the applied load at the specified rate (see Figure 1). One might expect the preload to alter the results of the test and indeed it does, but fortunately, it is possible to account for the effect of the preload in interpreting the results. The accounting is done by calculating the normalized strength (defined as the strength in the presence of preload the strength in the absence of preload) as a function of (1) the preloading factor (defined as the preload stress the strength in the absence of preload) and (2) a SCG parameter, denoted n, that is used in a power-law crack-speed formulation. Figure 2 presents numerical results from this theoretical calculation.

Apparent Dependence of Rate- and State-Dependent Friction Parameters on Loading Velocity and Cumulative Displacement Inferred from Large-Scale Biaxial Friction Experiments

NASA Astrophysics Data System (ADS)

Urata, Yumi; Yamashita, Futoshi; Fukuyama, Eiichi; Noda, Hiroyuki; Mizoguchi, Kazuo

2017-06-01

We investigated the constitutive parameters in the rate- and state-dependent friction (RSF) law by conducting numerical simulations, using the friction data from large-scale biaxial rock friction experiments for Indian metagabbro. The sliding surface area was 1.5 m long and 0.5 m wide, slid for 400 s under a normal stress of 1.33 MPa at a loading velocity of either 0.1 or 1.0 mm/s. During the experiments, many stick-slips were observed and those features were as follows. (1) The friction drop and recurrence time of the stick-slip events increased with cumulative slip displacement in an experiment before which the gouges on the surface were removed, but they became almost constant throughout an experiment conducted after several experiments without gouge removal. (2) The friction drop was larger and the recurrence time was shorter in the experiments with faster loading velocity. We applied a one-degree-of-freedom spring-slider model with mass to estimate the RSF parameters by fitting the stick-slip intervals and slip-weakening curves measured based on spring force and acceleration of the specimens. We developed an efficient algorithm for the numerical time integration, and we conducted forward modeling for evolution parameters ( b) and the state-evolution distances (L_{{c}}), keeping the direct effect parameter ( a) constant. We then identified the confident range of b and L_{{c}} values. Comparison between the results of the experiments and our simulations suggests that both b and L_{{c}} increase as the cumulative slip displacement increases, and b increases and L_{{c}} decreases as the loading velocity increases. Conventional RSF laws could not explain the large-scale friction data, and more complex state evolution laws are needed.

An evaluation of the effects of bed rest, sleep deprivation and discontinuance of training on the physical fitness of highly trained young men

NASA Technical Reports Server (NTRS)

Olree, H. D.; Corbin, B.; Dugger, G.; Smith, C.

1973-01-01

This experiment was conducted to determine what physiological effects result when highly trained subjects are confined to bed, deprived of sleep, or allowed to discontinue training. Results indicated: (1) There was a moderate increase in strength variables due to the training in this experiment but the stress which the subjects received caused a negligible change in strength variables. (2) The training program resulted in highly significant changes in specific bicycle ergometer variables indicating good increases in cardiopulmonary fitness. Five days of bed rest or fifty hours of sleep deprivation caused comparable drastic decreases in cardiopulmonary fitness. Post stress the subjects reverted to a normal daily schedule and after two weeks they had recovered about half of what they lost. (3) Cardiac output remains relatively constant at a constant work load, but stroke volume increases with conditioning and decreases with deconditioning due to stress.

Force-Velocity, Impulse-Momentum Relationships: Implications for Efficacy of Purposefully Slow Resistance Training

PubMed Central

Schilling, Brian K.; Falvo, Michael J.; Chiu, Loren Z.F.

2008-01-01

The purpose of this brief review is to explain the mechanical relationship between impulse and momentum when resistance exercise is performed in a purposefully slow manner (PS). PS is recognized by ~10s concentric and ~4-10s eccentric actions. While several papers have reviewed the effects of PS, none has yet explained such resistance training in the context of the impulse-momentum relationship. A case study of normal versus PS back squats was also performed. An 85kg man performed both normal speed (3 sec eccentric action and maximal acceleration concentric action) and PS back squats over a several loads. Normal speed back squats produced both greater peak and mean propulsive forces than PS action when measured across all loads. However, TUT was greatly increased in the PS condition, with values fourfold greater than maximal acceleration repetitions. The data and explanation herein point to superior forces produced by the neuromuscular system via traditional speed training indicating a superior modality for inducing neuromuscular adaptation. Key pointsAs velocity approaches zero, propulsive force approaches zero, therefore slow moving objects only require force approximately equal to the weight of the resistance.As mass is constant during resistance training, a greater impulse will result in a greater velocity.The inferior propulsive forces accompanying purposefully slow training suggest other methods of resistance training have a greater potential for adaptation. PMID:24149464

Fatigue of notched fiber composite laminates. Part 1: Analytical model

NASA Technical Reports Server (NTRS)

Mclaughlin, P. V., Jr.; Kulkarni, S. V.; Huang, S. N.; Rosen, B. W.

1975-01-01

A description is given of a semi-empirical, deterministic analysis for prediction and correlation of fatigue crack growth, residual strength, and fatigue lifetime for fiber composite laminates containing notches (holes). The failure model used for the analysis is based upon composite heterogeneous behavior and experimentally observed failure modes under both static and fatigue loading. The analysis is consistent with the wearout philosophy. Axial cracking and transverse cracking failure modes are treated together in the analysis. Cracking off-axis is handled by making a modification to the axial cracking analysis. The analysis predicts notched laminate failure from unidirectional material fatique properties using constant strain laminate analysis techniques. For multidirectional laminates, it is necessary to know lamina fatique behavior under axial normal stress, transverse normal stress and axial shear stress. Examples of the analysis method are given.

Failure in lithium-ion batteries under transverse indentation loading

NASA Astrophysics Data System (ADS)

Chung, Seung Hyun; Tancogne-Dejean, Thomas; Zhu, Juner; Luo, Hailing; Wierzbicki, Tomasz

2018-06-01

Deformation and failure of constrained cells and modules in the battery pack under transverse loading is one of the most common conditions in batteries subjected to mechanical impacts. A combined experimental, numerical and analytical approach was undertaken to reveal the underlying mechanism and develop a new cell failure model. When large format pouch cells were subjected to local indentation all the way to failure, the post-mortem examination of the failure zones beneath the punches indicates a consistent slant fracture surface angle to the battery plane. This type of behavior can be described by the critical fracture plane theory in which fracture is caused by the shear stress modified by the normal stress. The Mohr-Coulomb fracture criterion is then postulated and it is shown how the two material constants can be determined from just one indentation test. The orientation of the fracture plane is invariant with respect to the type of loading and can be considered as a property of the cell stack. In addition, closed-form solutions are derived for the load-displacement relation for both plane-strain and axisymmetric cases. The results are in good agreement with the numerical simulation of the homogenized model and experimentally measured responses.

A comparison of various "housekeeping" probes for northern analysis of normal and osteoarthritic articular cartilage RNA.

PubMed

Matyas, J R; Huang, D; Adams, M E

1999-01-01

Several approaches are commonly used to normalize variations in RNA loading on Northern blots, including: ethidium bromide (EthBr) fluorescence of 18S or 28S rRNA or autoradiograms of radioactive probes hybridized with constitutively expressed RNAs such as elongation factor-1alpha (ELF), glyceraldehyde-3-phosphate dehydrogenase (G3PDH), actin, 18S or 28S rRNA, or others. However, in osteoarthritis (OA) the amount of total RNA changes significantly and none of these RNAs has been clearly demonstrated to be expressed at a constant level, so it is unclear if any of these approaches can be used reliably for normalizing RNA extracted from osteoarthritic cartilage. Total RNA was extracted from normal and osteoarthritic cartilage and assessed by EthBr fluorescence. RNA was then transferred to a nylon membrane hybridized with radioactive probes for ELF, G3PDH, Max, actin, and an oligo-dT probe. The autoradiographic signal across the six lanes of a gel was quantified by scanning densitometry. When compared on the basis of total RNA, the coefficient of variation was lowest for 28S ethidium bromide fluorescence and oligo-dT (approximately 7%), followed by 18S ethidium bromide fluorescence and G3PDH (approximately 13%). When these values were normalized to DNA concentration, the coefficient of variation exceeded 50% for all signals. Total RNA and the signals for 18S, 28S rRNA, and oligo-dT all correlated highly. These data indicate that osteoarthritic chondrocytes express similar ratios of mRNA to rRNA and mRNA to total RNA as do normal chondrocytes. Of all the "housekeeping" probes, G3PDH correlated best with the measurements of RNA. All of these "housekeeping" probes are expressed at greater levels by osteoarthritic chondrocytes when compared with normal chondrocytes. Thus, while G3PDH is satisfactory for evaluating the amount of RNA loaded, its level of expression is not the same in normal and osteoarthritic chondrocytes.

Load-unloading response of intact and artificially degraded articular cartilage correlated with near infrared (NIR) absorption spectra.

PubMed

Afara, I O; Singh, S; Oloyede, A

2013-04-01

The conventional mechanical properties of articular cartilage, such as compressive stiffness, have been demonstrated to be limited in their capacity to distinguish intact (visually normal) from degraded cartilage samples. In this paper, we explore the correlation between a new mechanical parameter, namely the reswelling of articular cartilage following unloading from a given compressive load, and the near infrared (NIR) spectrum. The capacity to distinguish mechanically intact from proteoglycan-depleted tissue relative to the "reswelling" characteristic was first established, and the result was subsequently correlated with the NIR spectral data of the respective tissue samples. To achieve this, normal intact and enzymatically degraded samples were subjected to both NIR probing and mechanical compression based on a load-unload-reswelling protocol. The parameter δr, characteristic of the osmotic "reswelling" of the matrix after unloading to a constant small load in the order of the osmotic pressure of cartilage, was obtained for the different sample types. Multivariate statistics was employed to determine the degree of correlation between δr and the NIR absorption spectrum of relevant specimens using Partial Least Squared (PLS) regression. The results show a strong relationship (R(2)=95.89%, p<0.0001) between the spectral data and δr. This correlation of δr with NIR spectral data suggests the potential for determining the reswelling characteristics non-destructively. It was also observed that δr values bear a significant relationship with the cartilage matrix integrity, indicated by its proteoglycan content, and can therefore differentiate between normal and artificially degraded proteoglycan-depleted cartilage samples. It is therefore argued that the reswelling of cartilage, which is both biochemical (osmotic) and mechanical (hydrostatic pressure) in origin, could be a strong candidate for characterizing the tissue, especially in regions surrounding focal cartilage defects in joints. Copyright © 2012 Elsevier Ltd. All rights reserved.

The effect of high anionomer loading with silver nanowire catalysts on the oxygen reduction reaction in alkaline environment

NASA Astrophysics Data System (ADS)

Lemke, Adam J.; O'Toole, Alexander W.; Phillips, Richard S.; Eisenbraun, Eric T.

2014-06-01

The effect of ionomer content on the oxygen kinetics in fuel cells and metal-oxide batteries was investigated by varying ionomer loading with constant loadings of a silver nanowire catalyst. Silver nanowire inks were produced in which commercially available anionomer solution constituted 10, 25, 40, 50, and 75% of the total ink volume. Constant loadings of Ag nanowire catalyst were then deposited onto glassy carbon electrodes by varying the amount of ink deposited. These were then used in rotating disc electrode (RDE) experiments using a 0.1 M KOH electrolyte solution. From these experiments, using ORR polarization curves and Koutecky-Levich analysis, it was found that not only did the anionomer loading affect the total activity (given a constant Ag nanowire loading) but, that the anionomer content also had an impact upon the apparent kinetic limited current as well as whether the ORR proceeded through the 2e- or 4e- pathway. Although the total activity declined with very high anionomer loadings, the ORR appeared to proceed more through the 4e- pathway with increased anionomer content.

Study on the friction of κ-carrageenan hydrogels in air and aqueous environments.

PubMed

Kozbial, Andrew; Li, Lei

2014-03-01

Understanding the friction mechanism of polysaccharide hydrogels, which is the key component of human cartilage that has very low friction coefficient, is critical to develop next generation artificial joint replacement materials. In this study, the friction of the polysaccharide κ-carrageenan hydrogel was investigated to elucidate the effect of external load, cross-linking density, velocity, and environment on friction. Our experimental results show that (1) coefficient of friction (COF) decreases with normal load in air and remains constant in water, (2) increasing cross-linking density concurrently increases friction and is proportional to Young's modulus, (3) COF increases with testing velocity in both air and water, and (4) friction is reduced in aqueous environment due to the lubricating effect of water. The underlying frictional mechanism is discussed on the basis of water transport from bulk to surface and a previously proposed "repulsion-adsorption" model. Copyright © 2013 Elsevier B.V. All rights reserved.

Photovoltaic array: Power conditioner interface characteristics

NASA Technical Reports Server (NTRS)

Gonzalez, C. C.; Hill, G. M.; Ross, R. G., Jr.

1982-01-01

The electrical output (power, current, and voltage) of flat plate solar arrays changes constantly, due primarily to changes in cell temperature and irradiance level. As a result, array loads such as dc-to-ac power conditioners must be capable of accommodating widely varying input levels while maintaining operation at or near the maximum power point of the array. The array operating characteristics and extreme output limits necessary for the systematic design of array load interfaces under a wide variety of climatic conditions are studied. A number of interface parameters are examined, including optimum operating voltage, voltage energy, maximum power and current limits, and maximum open circuit voltage. The effect of array degradation and I-V curve fill factor or the array power conditioner interface is also discussed. Results are presented as normalized ratios of power conditioner parameters to array parameters, making the results universally applicable to a wide variety of system sizes, sites, and operating modes.

A Three-Parameter Model for Predicting Fatigue Life of Ductile Metals Under Constant Amplitude Multiaxial Loading

NASA Astrophysics Data System (ADS)

Liu, Jia; Li, Jing; Zhang, Zhong-ping

2013-04-01

In this article, a fatigue damage parameter is proposed to assess the multiaxial fatigue lives of ductile metals based on the critical plane concept: Fatigue crack initiation is controlled by the maximum shear strain, and the other important effect in the fatigue damage process is the normal strain and stress. This fatigue damage parameter introduces a stress-correlated factor, which describes the degree of the non-proportional cyclic hardening. Besides, a three-parameter multiaxial fatigue criterion is used to correlate the fatigue lifetime of metallic materials with the proposed damage parameter. Under the uniaxial loading, this three-parameter model reduces to the recently developed Zhang's model for predicting the uniaxial fatigue crack initiation life. The accuracy and reliability of this three-parameter model are checked against the experimental data found in literature through testing six different ductile metals under various strain paths with zero/non-zero mean stress.

Seismic performance of recycled concrete-filled square steel tube columns

NASA Astrophysics Data System (ADS)

Chen, Zongping; Jing, Chenggui; Xu, Jinjun; Zhang, Xianggang

2017-01-01

An experimental study on the seismic performance of recycled concrete-filled square steel tube (RCFST) columns is carried out. Six specimens were designed and tested under constant axial compression and cyclic lateral loading. Two parameters, replacement percentage of recycled coarse aggregate (RCA) and axial compression level, were considered in the test. Based on the experimental data, the hysteretic loops, skeleton curves, ductility, energy dissipation capacity and stiffness degradation of RCFST columns were analyzed. The test results indicate that the failure modes of RCFST columns are the local buckling of the steel tube at the bottom of the columns, and the hysteretic loops are full and their shapes are similar to normal CFST columns. Furthermore, the ductility coefficient of all specimens are close to 3.0, and the equivalent viscous damping coefficient corresponding to the ultimate lateral load ranges from 0.323 to 0.360, which demonstrates that RCFST columns exhibit remarkable seismic performance.

Kinematic and EMG Comparison of Gait in Normal and Microgravity

NASA Technical Reports Server (NTRS)

DeWitt, John K.; Edwards, W. Brent; Perusek, Gail P.; Lewandowski, Beth E.; Samorezov, Sergey

2009-01-01

Astronauts regularly perform treadmill locomotion as a part of their exercise prescription while onboard the International Space Station. Although locomotive exercise has been shown to be beneficial for bone, muscle, and cardiovascular health, astronauts return to Earth after long duration missions with net losses in all three areas [1]. These losses might be partially explained by fundamental differences in locomotive performance between normal gravity (NG) and microgravity (MG) environments. During locomotive exercise in MG, the subject must wear a waist and shoulder harness that is attached to elastomer bungees. The bungees are attached to the treadmill, and provide forces that are intended to replace gravity. However, unlike gravity, which provides a constant force upon all body parts, the bungees provide a spring force only to the harness. Therefore, subjects are subjected to two fundamental differences in MG: 1) forces returning the subject to the treadmill are not constant, and 2) forces are only applied to the axial skeleton at the waist and shoulders. The effectiveness of the exercise may also be affected by the magnitude of the gravity replacement load. Historically, astronauts have difficulty performing treadmill exercise with loads that approach body weight (BW) due to comfort and inherent stiffness in the bungee system. Although locomotion can be executed in MG, the unique requirements could result in performance differences as compared to NG. These differences may help to explain why long term training effects of treadmill exercise may differ from those found in NG. The purpose of this investigation was to compare locomotion in NG and MG to determine if kinematic or muscular activation pattern differences occur between gravitational environments.

A Universal Threshold for the Assessment of Load and Output Residuals of Strain-Gage Balance Data

NASA Technical Reports Server (NTRS)

Ulbrich, N.; Volden, T.

2017-01-01

A new universal residual threshold for the detection of load and gage output residual outliers of wind tunnel strain{gage balance data was developed. The threshold works with both the Iterative and Non{Iterative Methods that are used in the aerospace testing community to analyze and process balance data. It also supports all known load and gage output formats that are traditionally used to describe balance data. The threshold's definition is based on an empirical electrical constant. First, the constant is used to construct a threshold for the assessment of gage output residuals. Then, the related threshold for the assessment of load residuals is obtained by multiplying the empirical electrical constant with the sum of the absolute values of all first partial derivatives of a given load component. The empirical constant equals 2.5 microV/V for the assessment of balance calibration or check load data residuals. A value of 0.5 microV/V is recommended for the evaluation of repeat point residuals because, by design, the calculation of these residuals removes errors that are associated with the regression analysis of the data itself. Data from a calibration of a six-component force balance is used to illustrate the application of the new threshold definitions to real{world balance calibration data.

MEMS electromagnetic energy harvesters with multiple resonances

NASA Astrophysics Data System (ADS)

Nelatury, Sudarshan R.; Gray, Robert

2014-06-01

There is going on a flurry of research activity in the development of effcient energy harvesters from all branches of energy conversion. The need for developing self-powered wireless sensors and actuators to be employed in unmanned combat vehicles also seems to grow steadily. These vehicles are inducted into perilous war zones for silent watch missions. Energy management is sometimes carried out using misson-aware energy expenditure strategies. Also, when there is a requirement for constant monitoring of events, the sensors and the subsystems of combat vehicles require energy harvesters that can operate over a discrete set of spot frequencies. This paper attempts to review some of the recent techniques and the energy harvesting devices based on electromagnetic and electromechanical principles. In particular, we shall discuss the design and performance of a MEMS-harvester that exhibits multiple resonances. Frequency response of a simulated electromagnetic harvester is plotted. It has three dominant peaks at three different resonant frequencies. Variation in the load power in the normalized units as a function of load is found, which determines the matched load resistance.

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage

NASA Technical Reports Server (NTRS)

Manson, S. S.; Halford, G. R.

1980-01-01

Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is provided for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are provided for determining the two phases of life. The procedure involves two steps, each similar to the conventional application of the commonly used linear damage rule. When the sum of cycle ratios based on phase 1 lives reaches unity, phase 1 is presumed complete, and further loadings are summed as cycle ratios on phase 2 lives. When the phase 2 sum reaches unity, failure is presumed to occur. No other physical properties or material constants than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons of both methods are discussed.

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage

NASA Technical Reports Server (NTRS)

Manson, S. S.; Halford, G. R.

1981-01-01

Simple procedures are given for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is given for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are given for determining the two phases of life. The procedure comprises two steps, each similar to the conventional application of the commonly used linear damage rule. Once the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum attains unity, failure is presumed to occur. It is noted that no physical properties or material constants other than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons are discussed for both methods.

Machine compliance in compression tests

NASA Astrophysics Data System (ADS)

Sousa, Pedro; Ivens, Jan; Lomov, Stepan V.

2018-05-01

The compression behavior of a material cannot be accurately determined if the machine compliance is not accounted prior to the measurements. This work discusses the machine compliance during a compressibility test with fiberglass fabrics. The thickness variation was measured during loading and unloading cycles with a relaxation stage of 30 minutes between them. The measurements were performed using an indirect technique based on the comparison between the displacement at a free compression cycle and the displacement with a sample. Relating to the free test, it has been noticed the nonexistence of machine relaxation during relaxation stage. Considering relaxation or not, the characteristic curves for a free compression cycle can be overlapped precisely in the majority of the points. For the compression test with sample, it was noticed a non-physical decrease of about 30 µm during the relaxation stage, what can be explained by the greater fabric relaxation in relation to the machine relaxation. Beyond the technique normally used, another technique was used which allows a constant thickness during relaxation. Within this second method, machine displacement with sample is simply subtracted to the machine displacement without sample being imposed as constant. If imposed as a constant it will remain constant during relaxation stage and it will suddenly decrease after relaxation. If constantly calculated it will decrease gradually during relaxation stage. Independently of the technique used the final result will remain unchanged. The uncertainty introduced by this imprecision is about ±15 µm.

Analysis on Characteristics of a C-Shaped Constant-Force Spring with a Guide

NASA Astrophysics Data System (ADS)

Ohtsuki, Atsumi; Ohshima, Shigemichi; Itoh, Daisuke

A C-shaped constant-force spring is made of pre-stressed material in various sizes that offer the advantage of a constant tensile load, suitable for a variety of applications (for example, extension spring, motor-brush holder, power feed, retracting and restoring mechanism). Essentially, this spring consists of a coil of flat spring material and when unstressed it takes the form of a tightly wound spiral. This spiral is placed on a drum. When a tensile load is applied, the spiral uncoils. The load is practically independent of the amount of deformation. In this report, the extension mechanism of constant-force spring and the state of deformation are analyzed by using a large deformation theory. Moreover, experiments are carried out to confirm the applicability of the proposed theory. The experimental results agree well with the theoretical estimations.

Submicrosecond Power-Switching Test Circuit

NASA Technical Reports Server (NTRS)

Folk, Eric N.

2006-01-01

A circuit that changes an electrical load in a switching time shorter than 0.3 microsecond has been devised. This circuit can be used in testing the regulation characteristics of power-supply circuits . especially switching power-converter circuits that are supposed to be able to provide acceptably high degrees of regulation in response to rapid load transients. The combination of this power-switching circuit and a known passive constant load could be an attractive alternative to a typical commercially available load-bank circuit that can be made to operate in nominal constant-voltage, constant-current, and constant-resistance modes. The switching provided by a typical commercial load-bank circuit in the constant-resistance mode is not fast enough for testing of regulation in response to load transients. Moreover, some test engineers do not trust the test results obtained when using commercial load-bank circuits because the dynamic responses of those circuits are, variously, partly unknown and/or excessively complex. In contrast, the combination of this circuit and a passive constant load offers both rapid switching and known (or at least better known) load dynamics. The power-switching circuit (see figure) includes a signal-input section, a wide-hysteresis Schmitt trigger that prevents false triggering in the event of switch-contact bounce, a dual-bipolar-transistor power stage that drives the gate of a metal oxide semiconductor field-effect transistor (MOSFET), and the MOSFET, which is the output device that performs the switching of the load. The MOSFET in the specific version of the circuit shown in the figure is rated to stand off a potential of 100 V in the "off" state and to pass a current of 20 A in the "on" state. The switching time of this circuit (the characteristic time of rise or fall of the potential at the drain of the MOSFET) is .300 ns. The circuit can accept any of three control inputs . which one depending on the test that one seeks to perform: a repetitive waveform from a signal generator, momentary closure of a push-button switch, or closure or opening of a manually operated on/off switch. In the case of a signal generator, one can adjust the frequency and duty cycle as needed to obtain the desired AC power-supply response, which one could display on an oscilloscope. Momentary switch closure could be useful for obtaining (and, if desired, displaying on an oscilloscope set to trigger on an event) the response of a power supply to a single load transient. The on/off switch can be used to switch between load states in which static-load regulation measurements are performed.

The VO(2)-on kinetics in constant load exercise sub-anaerobic threshold reflects endothelial function and dysfunction in muscle microcirculation.

PubMed

Maione, D; Cicero, A Fg; Bacchelli, S; Cosentino, E R; Degli Esposti, D; Manners, D N; Rinaldi, E R; Rosticci, M; Senaldi, R; Ambrosioni, E; Borghi, C

2015-01-01

To propose a test to evaluate endothelial function, based on VO(2) on-transition kinetics in sub-anaerobic threshold (AT) constant load exercise, we tested healthy subjects and patients with ischemic-hypertensive cardiopathy by two cardiopulmonary tests on a cycle ergometer endowed with an electric motor to overcome initial inertia: a pre-test and, after at least 24 h, one 6 min constant load exercise at 90 % AT. We measured net phase 3 VO(2)-on kinetics and, by phase 2 time constant (tau), valued endothelial dysfunction. We found shorter tau in repeated tests, shorter time between first and second test, by persisting endothelium-dependent arteriolar vasodilatation and/or several other mechanisms. Reducing load to 80 % and 90 % AT did not produce significant changes in tau of healthy volunteers, while in heart patients an AT load of 70 %, compared to 80 % AT, shortened tau (delta=4.38+/-1.65 s, p=0.013). In heart patients, no correlation was found between NYHA class, ejection fraction (EF), and the two variables derived from incremental cycle cardio-pulmonary exercise, as well as between EF and tau; while NYHA class groups were well correlated with tau duration (r=0.92, p=0.0001). Doxazosin and tadalafil also significantly reduced tau. In conclusion, the O(2) consumption kinetics during the on-transition of constant load exercise below the anaerobic threshold are highly sensitive to endothelial function in muscular microcirculation, and constitute a marker for the evaluation of endothelial dysfunction.

Force reduction induced by unidirectional transversal muscle loading is independent of local pressure.

PubMed

Siebert, Tobias; Rode, Christian; Till, Olaf; Stutzig, Norman; Blickhan, Reinhard

2016-05-03

Transversal unidirectional compression applied to muscles via external loading affects muscle contraction dynamics in the longitudinal direction. A recent study reported decreasing longitudinal muscle forces with increasing transversal load applied with a constant contact area (i.e., leading to a simultaneous increase in local pressure). To shed light on these results, we examine whether the decrease in longitudinal force depends on the load, the local pressure, or both. To this end, we perform isometric experiments on rat M. gastrocnemius medialis without and with transversal loading (i) changing the local pressure from 1.1-3.2Ncm(-2) (n=9) at a constant transversal load (1.62N) and (ii) increasing the transversal load (1.15-3.45N) at a constant local pressure of 2.3Ncm(-2) (n=7). While we did not note changes in the decrease in longitudinal muscle force in the first experiment, the second experiment resulted in an almost-linear reduction of longitudinal force between 7.5±0.6% and 14.1±1.7%. We conclude that the observed longitudinal force reduction is not induced by local effects such as malfunction of single muscle compartments, but that similar internal stress conditions and myofilament configurations occur when the local pressure changes given a constant load. The decreased longitudinal force may be explained by increased internal pressure and a deformed myofilament lattice that is likely associated with the decomposition of cross-bridge forces on the one hand and the inhibition of cross-bridges on the other hand. Copyright © 2016 Elsevier Ltd. All rights reserved.

Using a latent variable model with non-constant factor loadings to examine PM2.5 constituents related to secondary inorganic aerosols.

PubMed

Zhang, Zhenzhen; O'Neill, Marie S; Sánchez, Brisa N

2016-04-01

Factor analysis is a commonly used method of modelling correlated multivariate exposure data. Typically, the measurement model is assumed to have constant factor loadings. However, from our preliminary analyses of the Environmental Protection Agency's (EPA's) PM 2.5 fine speciation data, we have observed that the factor loadings for four constituents change considerably in stratified analyses. Since invariance of factor loadings is a prerequisite for valid comparison of the underlying latent variables, we propose a factor model that includes non-constant factor loadings that change over time and space using P-spline penalized with the generalized cross-validation (GCV) criterion. The model is implemented using the Expectation-Maximization (EM) algorithm and we select the multiple spline smoothing parameters by minimizing the GCV criterion with Newton's method during each iteration of the EM algorithm. The algorithm is applied to a one-factor model that includes four constituents. Through bootstrap confidence bands, we find that the factor loading for total nitrate changes across seasons and geographic regions.

On the Normal Force Mechanotransduction of Human Umbilical Vein Endothelial Cells

NASA Astrophysics Data System (ADS)

Vahabikashi, Amir; Wang, Qiuyun; Wilson, James; Wu, Qianhong; Vucbmss Team

2016-11-01

In this paper, we report a cellular biomechanics study to examine the normal force mechanotransduction of Human Umbilical Vein Endothelial Cells (HUVECs) with their implications on hypertension. Endothelial cells sense mechanical forces and adjust their structure and function accordingly. The mechanotransduction of normal forces plays a vital role in hypertension due to the higher pressure buildup inside blood vessels. Herein, HUVECs were cultured to full confluency and then exposed to different mechanical loadings using a novel microfluidic flow chamber. One various pressure levels while keeps the shear stress constant inside the flow chamber. Three groups of cells were examined, the control group (neither shear nor normal stresses), the normal pressure group (10 dyne/cm2 of shear stress and 95 mmHg of pressure), and the hypertensive group (10 dyne/cm2 of shear stress and 142 mmHg of pressure). Cellular response characterized by RT-PCR method indicates that, COX-2 expressed under normal pressure but not high pressure; Mn-SOD expressed under both normal and high pressure while this response was stronger for normal pressure; FOS and e-NOS did not respond under any condition. The differential behavior of COX-2 and Mn-SOD in response to changes in pressure, is instrumental for better understanding the pathogenesis of hypertensive cardiovascular diseases. This research was supported by the National Science Foundation under Award #1511096.

Muscle activity during leg strengthening exercise using free weights and elastic resistance: effects of ballistic vs controlled contractions.

PubMed

Jakobsen, Markus Due; Sundstrup, Emil; Andersen, Christoffer H; Aagaard, Per; Andersen, Lars L

2013-02-01

The present study's aim was to evaluate muscle activity during leg exercises using elastic vs. isoinertial resistance at different exertion and loading levels, respectively. Twenty-four women and eighteen men aged 26-67 years volunteered to participate in the experiment. Electromyographic (EMG) activity was recorded in nine muscles during a standardized forward lunge movement performed with dumbbells and elastic bands during (1) ballistic vs. controlled exertion, and (2) at low, medium and high loads (33%, 66% and 100% of 10 RM, respectively). The recorded EMG signals were normalized to MVC EMG. Knee joint angle was measured using electronic inclinometers. The following results were obtained. Loading intensity affected EMG amplitude in the order: low

Single-Specimen Technique to Establish the J-Resistance of Linear Viscoelastic Solids with Constant Poisson's Ratio

NASA Technical Reports Server (NTRS)

Gutierrez-Lemini, Danton; McCool, Alex (Technical Monitor)

2001-01-01

A method is developed to establish the J-resistance function for an isotropic linear viscoelastic solid of constant Poisson's ratio using the single-specimen technique with constant-rate test data. The method is based on the fact that, for a test specimen of fixed crack size under constant rate, the initiation J-integral may be established from the crack size itself, the actual external load and load-point displacement at growth initiation, and the relaxation modulus of the viscoelastic solid, without knowledge of the complete test record. Since crack size alone, of the required data, would be unknown at each point of the load-vs-load-point displacement curve of a single-specimen test, an expression is derived to estimate it. With it, the physical J-integral at each point of the test record may be established. Because of its basis on single-specimen testing, not only does the method not require the use of multiple specimens with differing initial crack sizes, but avoids the need for tracking crack growth as well.

Evaluation of Delamination Onset and Growth Characterization Methods under Mode I Fatigue Loading

NASA Technical Reports Server (NTRS)

Murri, Gretchen B.

2013-01-01

Double-cantilevered beam specimens of IM7/8552 graphite/epoxy from two different manufacturers were tested in static and fatigue to compare the material characterization data and to evaluate a proposed ASTM standard for generating Paris Law equations for delamination growth. Static results were used to generate compliance calibration constants for reducing the fatigue data, and a delamination resistance curve, GIR, for each material. Specimens were tested in fatigue at different initial cyclic GImax levels to determine a delamination onset curve and the delamination growth rate. The delamination onset curve equations were similar for the two sources. Delamination growth rate was calculated by plotting da/dN versus GImax on a log-log scale and fitting a Paris Law. Two different data reduction methods were used to calculate da/dN. To determine the effects of fiber-bridging, growth results were normalized by the delamination resistance curves. Paris Law exponents decreased by 31% to 37% after normalizing the data. Visual data records from the fatigue tests were used to calculate individual compliance constants from the fatigue data. The resulting da/dN versus GImax plots showed improved repeatability for each source, compared to using averaged static data. The Paris Law expressions for the two sources showed the closest agreement using the individually fit compliance data.

An apparatus for altering the mechanical load of the respiratory system.

PubMed

Younes, M; Bilan, D; Jung, D; Kroker, H

1987-06-01

We describe an apparatus for altering the mechanical load against which the respiratory muscles operate in humans. A closed system incorporates a rolling seal spirometer. The spirometer piston shaft is coupled to a fast-responding linear actuator that develops force in proportion to desired command signals. The command signal may be flow (resistive loading or unloading), volume (elastic loading or unloading), constant voltage (continuous positive or negative pressure), or any external function. Combinations of loads can be applied. Logic circuits permit application of the load at specific times during the respiratory cycle, and the magnitude of the loads is continuously adjustable. Maximum pressure output is +/- 20 cmH2O. The apparatus permits loading or unloading over a range of ventilation extending from resting levels to those observed during high levels of exercise (over 100 l/min). In response to a square-wave input, pressure rises exponentially with a time constant of 20 ms.

Hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

NASA Technical Reports Server (NTRS)

Ghosh, M. K.; Hamrock, B. J.; Brewe, D. E.

1984-01-01

A numerical solution to the problem of hydrodynamic lubrication of rigid point contacts with an isoviscous, incompressible lubricant was obtained. The hydrodynamic load-carrying capacity under unsteady (or dynamic) conditions arising from the combined effects of squeeze motion superposed upon the entraining motion was determined for both normal approach and separation. Superposed normal motion considerably increases net load-carrying capacity during normal approach and substantially reduces net load-carrying capacity during separation. Geometry was also found to have a significant influence on the dynamic load-carrying capacity. The ratio of dynamic to steady state load-carrying capacity increases with increasing geometry parameter for normal approach and decreases during separation. The cavitation (film rupture) boundary is also influenced significantly by the normal motion, moving downstream during approach and upstream during separation. For sufficiently high normal separation velocity the rupture boundary may even move upstream of the minimum-film-thickness position. Sixty-three cases were used to derive a functional relationship for the ratio of the dynamic to steady state load-carrying capacity in terms of the dimensionless normal velocity parameter (incorporating normal velocity, entraining velocity, and film thickness) and the geometry parameter.

Hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

NASA Technical Reports Server (NTRS)

Ghosh, M. K.; Hamrock, B. J.; Brewe, D.

1985-01-01

A numerical solution to the problem of hydrodynamic lubrication of rigid point contacts with an isoviscous, incompressible lubricant was obtained. The hydrodynamic load-carrying capacity under unsteady (or dynamic) conditions arising from the combined effects of squeeze motion superposed upon the entraining motion was determined for both normal approach and separation. Superposed normal motion considerably increases net load-carrying capacity during normal approach and substantially reduces net load-carrying capacity during separation. Geometry was also found to have a significant influence on the dynamic load-carrying capacity. The ratio of dynamic to steady state load-carrying capacity increases with increasing geometry parameter for normal approach and decreases during separation. The cavitation (film rupture) boundary is also influenced significantly by the normal motion, moving downstream during approach and upstream during separation. For sufficiently high normal separation velocity the rupture boundary may even move upstream of the minimum-film-thickness position. Sixty-three cases were used to derive a functional relationship for the ratio of the dynamic to steady state load-carrying capacity in terms of the dimensionless normal velocity parameter (incorporating normal velocity, entraining velocity, and film thickness) and the geometry parameter.

Fracture in Westerly granite under AE feedback and constant strain rate loading: Nucleation, quasi-static propagation, and the transition to unstable fracture propagation

USGS Publications Warehouse

Thompson, B.D.; Young, R.P.; Lockner, D.A.

2006-01-01

New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded at a 'slow' constant strain rate of 2.5 ?? 10-6/s) and an unstable fracture that develops near instantaneously (loaded at a 'fast' constant strain rate of 5 ?? 10-5/s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial nucleation or stable growth phase at a rate of ??? 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation speed of ??? 18 mm/s, and (3) unstable, accelerating propagation. In the ??? 100 ms before rupture, the high level of AE activity (as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments. It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation. ?? Birkha??user Verlag, Basel, 2006.

The transmembrane gradient of the dielectric constant influences the DPH lifetime distribution.

PubMed

Konopásek, I; Kvasnicka, P; Amler, E; Kotyk, A; Curatola, G

1995-11-06

The fluorescence lifetime distribution of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) in egg-phosphatidylcholine liposomes was measured in normal and heavy water. The lower dielectric constant (by approximately 12%) of heavy water compared with normal water was employed to provide direct evidence that the drop of the dielectric constant along the membrane normal shifts the centers of the distribution of both DPH and TMA-DPH to higher values and sharpens the widths of the distribution. The profile of the dielectric constant along the membrane normal was not found to be a linear gradient (in contrast to [1]) but a more complex function. Presence of cholesterol in liposomes further shifted the center of the distributions to higher value and sharpened them. In addition, it resulted in a more gradient-like profile of the dielectric constant (i.e. linearization) along the normal of the membrane. The effect of the change of dielectric constant on the membrane proteins is discussed.

β-actin as a loading control for plasma-based Western blot analysis of major depressive disorder patients.

PubMed

Zhang, Rufang; Yang, Deyu; Zhou, Chanjuan; Cheng, Ke; Liu, Zhao; Chen, Liang; Fang, Liang; Xie, Peng

2012-08-15

Western blot analysis is a commonly used technique for determining specific protein levels in clinical samples. For normalization of protein levels in Western blot, a suitable loading control is required. On account of its relatively high and constant expression, β-actin has been widely employed in Western blot of cell cultures and tissue extracts. However, β-actin's presence in human plasma and this protein's putative role as a plasma-based loading control for Western blot analysis remain unknown. In this study, an enzyme-linked immunosorbent assay was used to determine the concentration of β-actin in human plasma, which is 6.29±0.54 ng/ml. In addition, the linearity of β-actin immunostaining and loaded protein amount was evaluated by Western blot, and a fine linearity (R²=0.974±0.012) was observed. Furthermore, the expression of plasma β-actin in major depressive disorder subjects and healthy controls was compared. The data revealed no statistically significant difference between these two groups. Moreover, the total coefficient of variation for β-actin expression in the two groups was 9.2±1.2%. These findings demonstrate that β-actin is present in human plasma and may possibly be used as a suitable loading control for plasma-based Western blot analysis in major depressive disorder. Copyright © 2012 Elsevier Inc. All rights reserved.

Ultrasonic investigation of granular materials subjected to compression and crushing.

PubMed

Gheibi, Amin; Hedayat, Ahmadreza

2018-07-01

Ultrasonic wave propagation measurement has been used as a suitable technique for studying the granular materials and investigating the soil fabric structure, the grain contact stiffness, frictional strength, and inter-particle contact area. Previous studies have focused on the variations of shear and compressional wave velocities with effective stress and void ratio, and lesser effort has been made in understanding the variation of amplitude and dominant frequency of transmitted compressional waves with deformation of soil packing. In this study, continuous compressional wave transmission measurements during compaction of unconsolidated quartz sand are used to investigate the impact of soil layer deformation on ultrasonic wave properties. The test setup consisted of a loading machine to apply constant loading rate to a sand layer (granular quartz) of 6 mm thickness compressed between two forcing blocks, and an ultrasonic wave measurement system to continuously monitor the soil layer during compression up to 48 MPa normal stress. The variations in compressional wave attributes such as wave velocity, transmitted amplitude, and dominant frequency were studied as a function of the applied normal stress and the measured normal strain as well as void ratio and particle size. An increasing trend was observed for P-wave velocity, transmitted amplitude and dominant frequency with normal stress. In specimen with the largest particle size (D 50  = 0.32 mm), the wave velocity, amplitude and dominant frequency were found to increase about 230%, 4700% and 320% as the normal stress reached the value of 48 MPa. The absolute values of transmitted wave amplitude and dominant frequency were greater for specimens with smaller particle sizes while the normalized values indicate an opposite trend. The changes in the transmitted amplitude were linked to the changes in the true contact area between the particles with a transitional point in the slope of normalized amplitude, coinciding with the yield stress of the granular soil layer. The amount of grain crushing as a result of increase in the normal stress was experimentally measured and a linear correlation was found between the degree of grain crushing and the changes in the normalized dominant frequency of compressional waves. Copyright © 2018 Elsevier B.V. All rights reserved.

Ae Behavior of Smart Stress Memory Patch after Variable Amplitude Loading

NASA Astrophysics Data System (ADS)

Fujino, Y.; Nambu, S.; Enoki, M.

Recently, the structural health monitoring becomes increasingly great important to assure the ease and safety of our life, and it is required significantly to develop non-destructive evaluation for structures such as bridges and tunnels. Some sacrificed specimens have been developed to evaluate the fatigue damage of structures such as fatigue cycles and residual lifetime, but it can be applied only when the stress history is known beforehand. These fatigue sensors need no cable and can be used at low cost in contrast to strain gage. In previous study, a smart stress memory patch was developed as a new fatigue sensor. The patch can measure simultaneously the maximum stress, stress amplitude and the number of fatigue cycles by crack length measurement and Kaiser effect of Acoustic Emission (AE). The crack growth behavior under constant amplitude (CA) loading has been investigated, and AE behavior also has been evaluated only after CA loading. However, AE characteristics after variable amplitude (VA) loading in service are extremely important. Moreover, it is very important to control AE behavior of the smart patch in order to evaluate the applied stress using Kaiser effect. In this study, fatigue test with single overload was investigated to evaluate its influence. Moreover, effect of crack length and heat treatment on AE behavior was also investigated. Finally, AE behavior of the patch was evaluated after fatigue CA loading with overload or VA loading with log-normal distribution and overload.

Evaluation of the Hinge Moment and Normal Force Aerodynamic Loads from a Seamless Adaptive Compliant Trailing Edge Flap in Flight

NASA Technical Reports Server (NTRS)

Miller, Eric J.; Cruz, Josue; Lung, Shun-Fat; Kota, Sridhar; Ervin, Gregory; Lu, Kerr-Jia; Flick, Pete

2016-01-01

A seamless adaptive compliant trailing edge (ACTE) flap was demonstrated in flight on a Gulfstream III aircraft at the NASA Armstrong Flight Research Center. The trailing edge flap was deflected between minus 2 deg up and plus 30 deg down in flight. The safety-of-flight parameters for the ACTE flap experiment require that flap-to-wing interface loads be sensed and monitored in real time to ensure that the structural load limits of the wing are not exceeded. The attachment fittings connecting the flap to the aircraft wing rear spar were instrumented with strain gages and calibrated using known loads for measuring hinge moment and normal force loads in flight. The safety-of-flight parameters for the ACTE flap experiment require that flap-to-wing interface loads be sensed and monitored in real time to ensure that the structural load limits of the wing are not exceeded. The attachment fittings connecting the flap to the aircraft wing rear spar were instrumented with strain gages and calibrated using known loads for measuring hinge moment and normal force loads in flight. The interface hardware instrumentation layout and load calibration are discussed. Twenty-one applied calibration test load cases were developed for each individual fitting. The 2-sigma residual errors for the hinge moment was calculated to be 2.4 percent, and for normal force was calculated to be 7.3 percent. The hinge moment and normal force generated by the ACTE flap with a hinge point located at 26-percent wing chord were measured during steady state and symmetric pitch maneuvers. The loads predicted from analysis were compared to the loads observed in flight. The hinge moment loads showed good agreement with the flight loads while the normal force loads calculated from analysis were over-predicted by approximately 20 percent. Normal force and hinge moment loads calculated from the pressure sensors located on the ACTE showed good agreement with the loads calculated from the installed strain gages.

Measurements of stiff-material compliance on the nanoscale using ultrasonic force microscopy

NASA Astrophysics Data System (ADS)

Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V.

2000-05-01

Ultrasonic force microscopy (UFM) was introduced to probe nanoscale mechanical properties of stiff materials. This was achieved by vibrating the sample far above the first resonance of the probing atomic force microscope cantilever where the cantilever becomes dynamically rigid. By operating UFM at different set force values, it is possible to directly measure the absolute values of the tip-surface contact stiffness. From this an evaluation of surface elastic properties can be carried out assuming a suitable solid-solid contact model. In this paper we present curves of stiffness as a function of the normal load in the range of 0-300 nN. The dependence of stiffness on the relative humidity has also been investigated. Materials with different elastic constants (such as sapphire lithium fluoride, and silicon) have been successfully differentiated. Continuum mechanics models cannot however explain the dependence of stiffness on the normal force and on the relative humidity. In this high-frequency regime, it is likely that viscous forces might play an important role modifying the tip-surface interaction. Plastic deformation might also occur due to the high strain rates applied when ultrasonically vibrating the sample. Another possible cause of these discrepancies might be the presence of water in between the two bodies in contact organizing in a solidlike way and partially sustaining the load.

Determination of stress intensity factors for interface cracks under mixed-mode loading

NASA Technical Reports Server (NTRS)

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

A simple technique was developed using conventional finite element analysis to determine stress intensity factors, K1 and K2, for interface cracks under mixed-mode loading. This technique involves the calculation of crack tip stresses using non-singular finite elements. These stresses are then combined and used in a linear regression procedure to calculate K1 and K2. The technique was demonstrated by calculating three different bimaterial combinations. For the normal loading case, the K's were within 2.6 percent of an exact solution. The normalized K's under shear loading were shown to be related to the normalized K's under normal loading. Based on these relations, a simple equation was derived for calculating K1 and K2 for mixed-mode loading from knowledge of the K's under normal loading. The equation was verified by computing the K's for a mixed-mode case with equal and normal shear loading. The correlation between exact and finite element solutions is within 3.7 percent. This study provides a simple procedure to compute K2/K1 ratio which has been used to characterize the stress state at the crack tip for various combinations of materials and loadings. Tests conducted over a range of K2/K1 ratios could be used to fully characterize interface fracture toughness.

Transport and metabolism of sarcosine in hypersarcosinemic and normal phenotypes

PubMed Central

Glorieux, Francis H.; Scriver, Charles R.; Delvin, Edgard; Mohyuddin, Fazl

1971-01-01

An adolescent male proband with hypersarcosinemia was discovered incidentally in a French-Canadian family; no specific disease was associated with the trait. The hypersarcosinemia is not diminished by dietary folic acid even in pharmacologic doses (30 mg/day). The normal absence of sarcosine dehydrogenase in cultured human skin fibroblasts and in leukocytes was confirmed, thus eliminating these tissues as useful sources for further investigation of mutant sarcosinemic phenotypes and genotypes. The response in plasma of sarcosine and glycine, after sarcosine loading, distinguished the normal subject from the subjects who were presumably homozygous and heterozygous for the hypersarcosinemia allele. Sarcosine clearance from plasma was delayed greatly (t½, 6.1 hr) in the presumed homozygote and slightly (t½, 2.2 hr) in the presumed heterozygote, while plasma glycine remained constant in the former and rose in the latter. Normal subjects clear sarcosine from plasma rapidly (t½, 1.6 hr) while their plasma glycine trend is downward. The phenotypic responses suggest that hypersarcosinemia is an autosomal recessive trait in this pedigree. Renal tubular transport of sarcosine was normal in the proband even though he presumably lacked the sarcosine oxidation which should normally occur in kidney. Sarcosine catabolism is thus not important for its own renal uptake. Sarcosine interacts with proline and glycine during its absorption in vivo. Studies in vitro in rat kidney showed that sarcosine transport is mediated, saturable, and energy dependent. Sarcosine has no apparent transport system of its own; it uses the low Km transport systems for L-proline and glycine to a minor extent and a high Km system shared by these substances for the major uptake at concentrations encountered in hypersarcosinemia. Intracellular sarcosine at high concentration will exchange with glycine on one of these systems, which may explain a paradoxical improvement in renal transport of glycine after sarcosine loading in the hypersarcosinemic proband. PMID:5096515

Characterising fabric, force distributions and porosity evolution in sheared granular media

NASA Astrophysics Data System (ADS)

Mair, Karen; Abe, Steffen; Jettestuen, Espen

2014-05-01

Active faults, landslides, subglacial tills and poorly or unconsolidated sands essentially contain accumulations of granular debris that evolve under load. Both the macroscopic motions and the bulk fluid flow characteristics that result are determined by the particular grain scale processes operating in this deformed or transformed granular material. A relevant question is how the local behavior at the individual granular contacts actually sums up, and in particular how the load bearing skeleton (an important expression of connected load) and spatial distribution of pore space (and hence fluid pathways) are linked. Here we investigate the spatial distribution of porosity with granular rearrangements (specifically contact force network characteristics) produced in 3D discrete element models of granular layers under shear. We use percolation measures to identify, characterize, compare and track the evolution of strongly connected contact force networks. We show that specific topological measures used in describing the networks, such as number of contacts and coordination number, are sensitive to grain size distribution of the material as well as loading conditions. In addition we probe the 3D spatial distribution of porosity as a function of increasing strain. Two cases will be considered. The first, a non-fracture regime where configurational changes occur during shear but grain size distribution remains constant. This would be expected for a soil or granular material under relatively low normal loading. Secondly we consider a fragmentation regime where the grain size distributions of the granular material evolve with accumulated strain. This mirrors the scenario for faults or basal shear zones of slides under higher normal stress where comminution is typically a mark of increasing maturity and plays a major role in the poro-perm evolution of the system. We will present the correlated and anti-correlated features appearing in our simulations as well as discussing the triggers and relative persistence of fluid pathway creation versus destruction mechanisms. We will also demonstrate how the individual grain interactions are manifested in the macroscopic sliding behavior we observe.

On the Henry constant and isosteric heat at zero loading in gas phase adsorption.

PubMed

Do, D D; Nicholson, D; Do, H D

2008-08-01

The Henry constant and the isosteric heat of adsorption at zero loading are commonly used as indicators of the strength of the affinity of an adsorbate for a solid adsorbent. It is assumed that (i) they are observable in practice, (ii) the Van Hoff's plot of the logarithm of the Henry constant versus the inverse of temperature is always linear and the slope is equal to the heat of adsorption, and (iii) the isosteric heat of adsorption at zero loading is either constant or weakly dependent on temperature. We show in this paper that none of these three points is necessarily correct, first because these variables might not be observable since they are outside the range of measurability; second that the linearity of the Van Hoff plot breaks down at very high temperature, and third that the isosteric heat versus loading is a strong function of temperature. We demonstrate these points using Monte Carlo integration and Monte Carlo simulation of adsorption of various gases on a graphite surface. Another issue concerning the Henry constant is related to the way the adsorption excess is defined. The most commonly used equation is the one that assumes that the void volume is the volume extended all the way to a boundary passing through the centres of the outermost solid atoms. With this definition the Henry constant can become negative at high temperatures. Although adsorption at these temperatures may not be practical because of the very low value of the Henry constant, it is more useful to define the Henry constant in such a way that it is always positive at all temperatures. Here we propose the use of the accessible volume; the volume probed by the adsorbate when it is in nonpositive regions of the potential, to calculate the Henry constant.

Three Dimensional Constraint Effects on the Estimated (Delta)CTOD during the Numerical Simulation of Different Fatigue Threshold Testing Techniques

NASA Technical Reports Server (NTRS)

Seshadri, Banavara R.; Smith, Stephen W.

2007-01-01

Variation in constraint through the thickness of a specimen effects the cyclic crack-tip-opening displacement (DELTA CTOD). DELTA CTOD is a valuable measure of crack growth behavior, indicating closure development, constraint variations and load history effects. Fatigue loading with a continual load reduction was used to simulate the load history associated with fatigue crack growth threshold measurements. The constraint effect on the estimated DELTA CTOD is studied by carrying out three-dimensional elastic-plastic finite element simulations. The analysis involves numerical simulation of different standard fatigue threshold test schemes to determine how each test scheme affects DELTA CTOD. The American Society for Testing and Materials (ASTM) prescribes standard load reduction procedures for threshold testing using either the constant stress ratio (R) or constant maximum stress intensity (K(sub max)) methods. Different specimen types defined in the standard, namely the compact tension, C(T), and middle cracked tension, M(T), specimens were used in this simulation. The threshold simulations were conducted with different initial K(sub max) values to study its effect on estimated DELTA CTOD. During each simulation, the DELTA CTOD was estimated at every load increment during the load reduction procedure. Previous numerical simulation results indicate that the constant R load reduction method generates a plastic wake resulting in remote crack closure during unloading. Upon reloading, this remote contact location was observed to remain in contact well after the crack tip was fully open. The final region to open is located at the point at which the load reduction was initiated and at the free surface of the specimen. However, simulations carried out using the constant Kmax load reduction procedure did not indicate remote crack closure. Previous analysis results using various starting K(sub max) values and different load reduction rates have indicated DELTA CTOD is independent of specimen size. A study of the effect of specimen thickness and geometry on the measured DELTA CTOD for various load reduction procedures and its implication in the estimation of fatigue crack growth threshold values is discussed.

Effect of volumetric organic loading on the nitrogen removal rate by immobilised activated sludge.

PubMed

Zielinska, M; Wojnowska-Baryla, I

2006-05-01

Activated sludge was immobilised in a porous ceramic carrier to create a stationary core of a bio-reactor. Municipal wastewater was treated in this reactor under varied conditions of volumetric organic loading rate (expressed by chemical oxygen demand (COD)) that were the following: 6.5, 8.0, 20.8, 48.8 g COD l(-1) d(-1). The rate constants of ammonification, nitrification and denitrification under aerobic conditions were determined. All rate constants increased with a growth in volumetric loading rate, but the highest loading value of 48.8 g COD l(-1) d(-1) limited the ammonification and nitrification rates.

Anti-buckling design of variable stiffness composite cylinder under combined loading based on the multi-objective optimization method

NASA Astrophysics Data System (ADS)

Zheng, Y.; Chen, J.

2018-06-01

Variable stiffness composite structures take full advantages of composite’s design ability. An enlarged design space will make the structure’s performance more excellent. Through an optimal design of a variable stiffness cylinder, the buckling capacity of the cylinder will be increased as compared with its constant stiffness counterpart. In this paper, variable stiffness composite cylinders sustaining combined loadings are considered, and the optimization is conducted based on the multi-objective optimization method. The results indicate that variable stiffness cylinder’s loading capacity is increased significantly as compared with the constant stiffness, especially when an inhomogeneous loading is considered.

Buckling of Thermoviscoelastic Structures Under Temporal and Spatial Temperature Variations

NASA Technical Reports Server (NTRS)

Tsuyuki, Richard; Knauss, Wolfgang G.

1992-01-01

The problem of lateral instability of a viscoelastic in-plane loaded structure is considered in terms of thermorheolgically simple materials. As an example of a generally in-plane loaded structure, we examine the simple column under axial load: Both cyclic loading is considered (with constant or in-phase variable temperature excursions) as well as the case of constant load in the presence of thermal gradients through the thickness of the structure. The latter case involves a continuous movement of the neutral axis from the center to the colder side and then back to the center. In both cases, temperature has a very strong effect on the instability evolution, and under in-phase thermal cycling the critical loads are reduced compared to those at constant temperatures. The primary effect of thermal gradients beyond that of thermally-induced rate accelerations is occasioned by the generation of an "initial imperfection" or "structural bowing." Because the coefficient of thermal expansion tends to be large for many polymeric materials, it it may be necessary to take special care in lay-up design of composite structures intended for use under compressive loads in high-temperature applications. Finally, the implications for the temperature sensitivities of composites to micro-instability (fiber crimping) are also apparent from the results delineated here.

Ground reaction force comparison of controlled resistance methods to isoinertial loading of the squat exercise - biomed 2010.

PubMed

Paulus, David C; Reynolds, Michael C; Schilling, Brian K

2010-01-01

The ground reaction force during the concentric (raising) portion of the squat exercise was compared to that of isoinertial loading (free weights) for three pneumatically controlled resistance methods: constant resistance, cam force profile, and proportional force control based on velocity. Constant force control showed lower ground reaction forces than isoinertial loading throughout the range of motion (ROM). The cam force profile exhibited slightly greater ground reaction forces than isoinertial loading at 10 and 40% ROM with fifty-percent greater loading at 70% ROM. The proportional force control consistently elicited greater ground reaction force than isoinertial loading, which progressively ranged from twenty to forty percent increase over isoinertial loading except for being approximately equal at 85% ROM. Based on these preliminary results, the proportional control shows the most promise for providing loading that is comparable in magnitude to isoinertial loading. This technology could optimize resistance exercise for sport-specific training or as a countermeasure to atrophy during spaceflight.

Flow and volume dependence of rat airway resistance during constant flow inflation and deflation.

PubMed

Rubini, Alessandro; Carniel, Emanuele Luigi; Parmagnani, Andrea; Natali, Arturo Nicola

2011-12-01

The aim of this study was to measure the flow and volume dependence of both the ohmic and the viscoelastic pressure dissipations of the normal rat respiratory system separately during inflation and deflation. The study was conducted in the Respiratory Physiology Laboratory in our institution. Measurements were obtained for Seven albino Wistar rats of both sexes by using the flow interruption method during constant flow inflations and deflations. Measurements included anesthesia induction, tracheostomy and positioning of a tracheal cannula, positive pressure ventilation, constant flow respiratory system inflations and deflations at two different volumes and flows. The ohmic resistance exhibited volume and flow dependence, decreasing with lung volume and increasing with flow rate, during both inflation and deflation. The stress relaxation-related viscoelastic resistance also exhibited volume and flow dependence. It decreased with the flow rate at a constant lung volume during both inflation and deflation, but exhibited a different behavior with the lung volume at a constant flow rate (i.e., increased during inflations and decreased during deflations). Thus, stress relaxation in the rat lungs exhibited a hysteretic behavior. The observed flow and volume dependence of respiratory system resistance may be predicted by an equation derived from a model of the respiratory system that consists of two distinct compartments. The equation agrees well with the experimental data and indicates that the loading time is the critical parameter on which stress relaxation depends, during both lung inflation and deflation.

Track dynamic behavior at rail welds at high speed

NASA Astrophysics Data System (ADS)

Xiao, Guangwen; Xiao, Xinbiao; Guo, Jun; Wen, Zefeng; Jin, Xuesong

2010-06-01

As a vehicle passing through a track with different weld irregularities, the dynamic performance of track components is investigated in detail by using a coupled vehicle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are discretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lateral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calculation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail profile irregularity caused by hand-grinding after rail welding and track maintenances.

Constant and variable amplitude ultrasonic fatigue of 2024-T351 aluminium alloy at different load ratios.

PubMed

Mayer, H; Fitzka, M; Schuller, R

2013-12-01

Ultrasonic fatigue testing equipment is presented that is capable of performing constant amplitude (CA) and variable amplitude (VA) experiments at different constant load ratios. This equipment is used to study cyclic properties of aluminium alloy 2024-T351 in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime at load ratios R=-1 and R=0.5. CA loading does not reveal a fatigue limit below 10¹⁰ cycles. Cracks leading to VHCF failure start at broken constituent particles. Specimens that survived more than 10¹⁰ cycles at R=-1 contain non-propagating cracks of lengths below grain size. Resonance frequency and nonlinearity parameter β(rel) show changes of vibration properties of specimens at low fractions of their VHCF lifetime. VA lifetimes are measured in the HCF and VHCF regime and compared with Miner calculations. Damage sums decrease with decreasing load (and increasing mean lifetimes) and are lower for R=0.5 than R=-1. Copyright © 2013 Elsevier B.V. All rights reserved.

Measurement of oxidative metabolism of the working human muscles by near-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Yücetaş, Akin; Şayli, Ömer; Karahan, Mustafa; Akin, Ata

2006-02-01

Monitoring the oxygenation of skeletal muscle tissues during rest to work transient provides valuable information about the performance of a particular tissue in adapting to aerobic glycolysis. In this paper we analyze the temporal relation of O II consumption with deoxy-hemoglobin (Hb) signals measured by functional Near Infrared Spectroscopy (fNIRS) technique during moderate isotonic forearm finger joint flexion exercise under ischemic conditions and model it with a mono exponential equation with delay. The time constants of fitting equation are questioned under two different work loads and among subjects differing in gender. Ten (6 men and 4 women) subjects performed isotonic forearm finger joint flexion exercise with two different loads. It is shown that under the same load, men and women subjects generate similar time constants and time delays. However, apparent change in time constants and time delays were observed when exercise was performed under different loads. When t-test is applied to compare the outputs for time constants between 0.41202 Watts and 0.90252 Watts, P value of 9.3445x10 -4 < 0.05 is observed which implies that the differences between the time constants are statistically significant. When the same procedure is applied for the time delay comparison, P value of 0.027<0.05 is observed which implies that also the differences between the time delays are statistically significant.

Normalization of load and clearance effects in ball-in-socket-like replacements.

PubMed

Ciavarella, M; Strozzi, A; Baldini, A; Giacopini, M

2007-08-01

A normalizing loading parameter useful in summarising the mechanical response of plane pin-in-plate-like contacts is extended to axisymmetric ball-in-socket-like contacts. An example addressing a compliant layered artificial hip joint is presented, and the usefulness of the normalizing loading parameter is evidenced.

The influence of testing apparatus stiffness on the source properties of laboratory stick-slip

NASA Astrophysics Data System (ADS)

Kilgore, B. D.; McGarr, A.; Beeler, N. M.; Lockner, D. A.

2016-12-01

Stick-slip experiments were performed to determine the influence of the testing apparatus stiffness on source properties, to develop methods to relate stick-slip to natural earthquakes, and to examine the hypothesis of McGarr [2012] that the product of unloading stiffness, k, and slip duration, T, is both scale-independent and approximately constant for both laboratory and natural earthquakes. A double-direct shear load frame was used with Sierra White Granite samples at 2 MPa normal stress, and a remote loading rate of 0.2 µm/s. The stiffness of the test apparatus was varied by more than an order of magnitude by inserting disk springs into the shear loading column adjacent to the granite samples. Servo-controlling slip at a point between the forcing ram and the shear force load cell, produced repeatable slip events. Slip and slip duration decrease as k increases, as they do for natural earthquakes. In contrast to earthquakes, stress drop and slip rate decrease with increasing k, and the product kT for these experiments is not constant, but decreases with k. These data, collected over a range of k, do not conform to McGarr's [2012] hypothesis. However, analysis of stick-slip studies from other testing apparatuses is consistent with McGarr's hypothesis; kT is scale-independent, similar to that of earthquakes, equal to the ratio of static stress drop to average slip velocity, and similar to the ratio of shear modulus to wavespeed of rock. These properties result from conducting experiments over a range of sample sizes, using rock samples with the same elastic properties as the Earth, and using testing machines whose stiffnesses decrease, and characteristic periods increase with scale. A consequence of our experiments and analysis is that extrapolation of lab scale earthquake source properties to the Earth is more difficult than previously thought, requiring an accounting for the properties of the testing machines and additional research beyond that reported here.

Optimization of BI test parameters to investigate mechanical properties of Grade 92 steel

NASA Astrophysics Data System (ADS)

Barbadikar, Dipika R.; Vincent, S.; Ballal, Atul R.; Peshwe, Dilip R.; Mathew, M. D.

2018-04-01

The ball indentation (BI) testing is used to evaluate the tensile properties of materials namely yield strength, strength coefficient, ultimate tensile strength, and strain hardening exponent. The properties evaluated depend on a number of BI test parameters. These parameters include the material constants like yield slope (YS), constraint factor (CF), yield offset parameter (YOP). Number of loading/unloading cycles, preload, indenter size and depth of penetration of indenter also affects the properties. In present investigation the effect of these parameters on the stress-strain curve of normalized and tempered Grade 92 steel is evaluated. Grade 92 is a candidate material for power plant application over austenitic stainless steel and derives its strength from M23C6, MX precipitates and high dislocation density. CF, YS and YOP changed the strength properties considerably. Indenter size effect resulted in higher strength for smaller indenter. It is suggested to use larger indenter diameter and higher number of loading cycles for GRADE 92 steel to get best results using BI technique.

Full Scale Span Load Distribution on a Tapered Wing with Split Flaps of Various Spans

NASA Technical Reports Server (NTRS)

Parsons, John F; Silverstein, Abe

1937-01-01

Pressure-distribution tests were conducted in the full-scale wind tunnel on a 2:1 tapered U.S.A. 45 airfoil equipped with 20 percent chord split trailing-edge flaps of various spans. A special installation was employed in the tests utilizing a half-span airfoil mounted vertically above a reflection plane. The airfoil has a constant chord center section and rounded tips and is tapered in thickness from 18 percent c at the root to 9 percent c at the tip. The aerodynamic characteristics, given by the usual dimension less coefficients, are presented graphically as functions of flap span and angle of attack as well as by semispan load diagrams. The results indicate, in general, that only a relatively small increase in the normal-force coefficient is to be expected by extending the flap span of an airfoil-flap combination, similar to the one tested, beyond 70 percent of the wing span.

Bending strength model for internal spur gear teeth

NASA Technical Reports Server (NTRS)

Savage, Michael; Rubadeux, K. L.; Coe, H. H.

1995-01-01

Internal spur gear teeth are normally stronger than pinion teeth of the same pitch and face width since external teeth are smaller at the base. However, ring gears which are narrower have an unequal addendum or are made of a material with a lower strength than that of the meshing pinion may be loaded more critically in bending. In this study, a model for the bending strength of an internal gear tooth as a function of the applied load pressure angle is presented which is based on the inscribed Lewis constant strength parabolic beam. The bending model includes a stress concentration factor and an axial compression term which are extensions of the model for an external gear tooth. The geometry of the Lewis factor determination is presented, the iteration to determine the factor is described, and the bending strength J factor is compared to that of an external gear tooth. This strength model will assist optimal design efforts for unequal addendum gears and gears of mixed materials.

Developmental adaptations to gravity in animals

NASA Technical Reports Server (NTRS)

Hargens, Alan R.

1991-01-01

Terrestrial animals have adapted to a constant gravitational stress over millions of years. Tissues of the cardiovascular system and lumbar spine in tall species of animals such as the giraffe are particularly well adapted to high and variable vectors of gravitational force. Swelling of the leg tissues in the giraffe is prevented by a variety of physiological mechanisms including (1) a natural 'antigravity suit', (2) impermeable capillaries, (3) arterial-wall hypertrophy, (4) variable blood pressures during normal activity, and (5) a large-capacity lymphatic system. These adaptations, as well as a natural hypertension, maintain blood perfusion to the giraffe's brain. The intervertebral disk is another tissue that is uniquely adapted to gravitational stress. Tall and large terrestrial animals have higher swelling pressures than their smaller or aquatic counterparts. Finally, the meniscus of the rabbit knee provides information on the effects of aging and load-bearing on cartilaginous tissues. Such tissues within the joints of animals are important for load-bearing on Earth; these connective tissues may degenerate during long-duration space flight.

Characterization of wear debris from metal-on-metal hip implants during normal wear versus edge-loading conditions.

PubMed

Kovochich, Michael; Fung, Ernest S; Donovan, Ellen; Unice, Kenneth M; Paustenbach, Dennis J; Finley, Brent L

2018-04-01

Advantages of second-generation metal-on-metal (MoM) hip implants include low volumetric wear rates and the release of nanosized wear particles that are chemically inert and readily cleared from local tissue. In some patients, edge loading conditions occur, which result in higher volumetric wear. The objective of this study was to characterize the size, morphology, and chemistry of wear particles released from MoM hip implants during normal (40° angle) and edge-loading (65° angle with microseparation) conditions. The mean primary particle size by volume under normal wear was 35 nm (range: 9-152 nm) compared with 95 nm (range: 6-573 nm) under edge-loading conditions. Hydrodynamic diameter analysis by volume showed that particles from normal wear were in the nano- (<100 nm) to submicron (<1000 nm) size range, whereas edge-loading conditions generated particles that ranged from <100 nm up to 3000-6000 nm in size. Particles isolated from normal wear were primarily chromium (98.5%) and round to oval in shape. Edge-loading conditions generated more elongated particles (4.5%) (aspect ratio ≥ 2.5) and more CoCr alloy particles (9.3%) compared with normal wear conditions (1.3% CoCr particles). By total mass, edge-loading particles contained approximately 640-fold more cobalt than normal wear particles. Our findings suggest that high wear conditions are a potential risk factor for adverse local tissue effects in MoM patients who experience edge loading. This study is the first to characterize both the physical and chemical characteristics of MoM wear particles collected under normal and edge-loading conditions. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 986-996, 2018. © 2017 Wiley Periodicals, Inc.

Biomechanical performance of rigid compared to dynamic anterior cervical plating: analysis of adjacent upper and lower level compressive forces.

PubMed

Connor, David E; Shamieh, Khader Samer; Ogden, Alan L; Mukherjee, Debi P; Sin, Anthony; Nanda, Anil

2012-12-01

Dynamic anterior cervical plating is well established as a means of enhancing graft loading and subsequent arthrodesis. Current concerns center on the degree of adjacent-level stress induced by these systems. The aim of this study was to evaluate and compare the load transferred to adjacent levels for single-level anterior cervical discectomy and fusion utilizing rigid compared to dynamic anterior plating systems. Nine cadaveric adult human cervical spine specimens were subjected to range-of-motion testing prior to and following C5-C6 anterior cervical discectomy and fusion procedures. Interbody grafting was performed with human fibula tissue. Nondestructive biomechanical testing included flexion/extension and lateral bending loading modes. A constant displacement of 5mm was applied in each direction and the applied load was measured in newtons (N). Specimens were tested in the following order: intact, following discectomy, after rigid plating, then after dynamic plating. Adjacent level (C4-C5 [L(S)] and C6-C7 [L(I)]) compressive forces were measured using low profile load cells inserted into each disc space. The measured load values for plating systems were then normalized using values measured for the intact specimens. Mean loads transferred to L(S) and L(I) during forced flexion in specimens with rigid plating were 23.47 N and 8.76 N, respectively; while the corresponding values in specimens with dynamic plating were 18.55 N and 1.03 N, respectively. Dynamic plating yielded no significant change at L(I) and a 21.0% decrease in load at L(S) when compared with rigid plating, although the difference was not significant. The observed trend suggests that dynamic plating may diminish superior adjacent level compressive stresses. Copyright © 2012 Elsevier Ltd. All rights reserved.

Use of photostress to characterize the mechanical behavior of weldments

NASA Technical Reports Server (NTRS)

Gambrell, S. C., Jr.

1992-01-01

Welded aluminum is an important part of many space structures. Knowledge of the properties and behavior of weld material and the material surrounding the weld is important for modeling and design of the structures. Photoelastic coatings (Photostress) and strain gages were used to determine behavior of heat treated and as welded joints made from 2219T87 parent material and 2319 weld material subjected to tensile loads. TIG welds of 1/8, 1/2, and 1.4 inches thickness were investigated. Discontinuous yielding was observed in all tests and highly non-uniform behavior through the weld thickness was observed in joints having welds 1.4 inches thick. Joints having welds 1/8 and 1/2 inches thick had only small differences in behavior through the thickness of the weld. Joints in the 1/2 inch thick material contained distinct zones of constant strain within the normal strain gradient extending outward from the weld centerline. These zones had different thickness and locations. Points at the weld centerline, and for a distance of nearly one inch from the centerline, exhibited very nonlinear behavior during the first loading but exhibited near perfect strain hardening during the second loading.

Investigating failure behavior and origins under supposed "shear bond" loading.

PubMed

Sultan, Hassam; Kelly, J Robert; Kazemi, Reza B

2015-07-01

This study evaluated failure behavior when resin-composite cylinders bonded to dentin fractured under traditional "shear" testing. Failure was assessed by scaling of failure loads to changes in cylinder radii and fracture surface analysis. Three stress models were examined including failure by: bonded area; flat-on-cylinder contact; and, uniformly-loaded, cantilevered-beam. Nine 2-mm dentin occlusal dentin discs for each radii tested were embedded in resin and bonded to resin-composite cylinders; radii (mm)=0.79375; 1.5875; 2.38125; 3.175. Samples were "shear" tested at 1.0mm/min. Following testing, disks were finished with silicone carbide paper (240-600grit) to remove residual composite debris and tested again using different radii. Failure stresses were calculated for: "shear"; flat-on-cylinder contact; and, bending of a uniformly-loaded cantilevered beam. Stress equations and constants were evaluated for each model. Fracture-surface analysis was performed. Failure stresses calculated as flat-on-cylinder contact scaled best with its radii relationship. Stress equation constants were constant for failure from the outside surface of the loaded cylinders and not with the bonded surface area or cantilevered beam. Contact failure stresses were constant over all specimen sizes. Fractography reinforced that failures originated from loaded cylinder surface and were unrelated to the bonded surface area. "Shear bond" testing does not appear to test the bonded interface. Load/area "stress" calculations have no physical meaning. While failure is related to contact stresses, the mechanism(s) likely involve non-linear damage accumulation, which may only indirectly be influenced by the interface. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Fluid pressure and fault strength: insights from load-controlled experiments on carbonate-bearing rocks

NASA Astrophysics Data System (ADS)

Spagnuolo, E.; Violay, M.; Nielsen, S. B.; Di Toro, G.

2013-12-01

Fluid pressure Pf has been indicated as a major factor controlling natural (e.g., L'Aquila, Italy, 2009 Mw 6.3) and induced seismicity (e.g., Wilzetta, Oklahoma, 2011 Mw 5.7). The Terzaghi's principle states that the effective normal stress σeff= σn (1- α Pf ), with α the Biot coefficient and σn the normal stress, is reduced in proportion to Pf. A value of α=1 is often used by default; however, within a complex fault core of inhomogeneous permeability, α may vary in a yet poorly understood way. To shed light on this problem, we conducted experiments on carbonate-bearing rock samples (Carrara marble) in room humidity conditions and in the presence of pore fluids (drained conditions), where a pre-cut fault is loaded by shear stress τ in a rotary apparatus (SHIVA) under constant σn=15 MPa. Two types of tests were performed with fluids: (1) the fluid pressure was kept constant at Pf=5 MPa (close to hydrostatic conditions at a depth of 0.5 km) and the fault was driven to failure instability by gradually increasing τ; (2) the fluid pressure was kept at Pf=5 MPa and τ was increased until close to instability (τ = 7 MPa): at this point Pf was raised of 0.5 MPa every 10 s up to Pf =10 MPa to induce a main (failure) instability. Assuming α=1 and an effective peak strength (τp)eff=μp σeff at failure, the experiments reveal that: 1) (τp)eff is sensitive to the shear loading rate: fast loading rates (0.5 MPa every 20 s) induce higher peak shear-stress values than slow loading rates (0.5 MPa every 40 s). Such effect is not observed (minor or inexistent) in the absence of pore fluids. 2) Under fast loading rates the (τp)eff may surpass that measured in the absence of pore fluids under identical effective normal stress σeff. 3) An increase of Pf does not necessarily induce the main instability (within the time intervals studied here, i.e. up to ~10 s) even if the effective strength threshold is largely surpassed (e.g., (τp)eff=1.3 μp σeff). We interpret these results in terms of limited permeability of the fault slip zone which reduces α. Indeed result (3) may indicate that a Pf increase did not rapidly penetrate the slip zone because a seal (thin layer of wet ultrafine calcite gouge) formed during the slip preceding the main instability. On the other hand, shearing of the slip zone probably induces dilation (not measured because below resolution) in the slip zone and results in a decrease in pore pressure. Again, due to limited permeability, the drop in pore pressure within the slip zone does not have time to re-equilibrate with the imposed Pf, provided that the hold time is short (20 s) with respect to the diffusion time, but it may re-equilibrate under longer hold times (40 s). As a consequence the Biot coefficient depends on the time interval of observation, with α~0 at short time periods and α~1 at long time periods. This yields an approximate hydraulic diffusivity κ~10-8 m2 s-1 using κ=l2/td with the half length of the contact surface l=5 mm and td=30 s. Such diffusivity is compatible, for example, with a low porosity shale.

GURU v2.0: An interactive Graphical User interface to fit rheometer curves in Han's model for rubber vulcanization

NASA Astrophysics Data System (ADS)

Milani, G.; Milani, F.

A GUI software (GURU) for experimental data fitting of rheometer curves in Natural Rubber (NR) vulcanized with sulphur at different curing temperatures is presented. Experimental data are automatically loaded in GURU from an Excel spreadsheet coming from the output of the experimental machine (moving die rheometer). To fit the experimental data, the general reaction scheme proposed by Han and co-workers for NR vulcanized with sulphur is considered. From the simplified kinetic scheme adopted, a closed form solution can be found for the crosslink density, with the only limitation that the induction period is excluded from computations. Three kinetic constants must be determined in such a way to minimize the absolute error between normalized experimental data and numerical prediction. Usually, this result is achieved by means of standard least-squares data fitting. On the contrary, GURU works interactively by means of a Graphical User Interface (GUI) to minimize the error and allows an interactive calibration of the kinetic constants by means of sliders. A simple mouse click on the sliders allows the assignment of a value for each kinetic constant and a visual comparison between numerical and experimental curves. Users will thus find optimal values of the constants by means of a classic trial and error strategy. An experimental case of technical relevance is shown as benchmark.

Optical based tactile shear and normal load sensor

DOEpatents

Salisbury, Curt Michael

2015-06-09

Various technologies described herein pertain to a tactile sensor that senses normal load and/or shear load. The tactile sensor includes a first layer and an optically transparent layer bonded together. At least a portion of the first layer is made of optically reflective material. The optically transparent layer is made of resilient material (e.g., clear silicone rubber). The tactile sensor includes light emitter/light detector pair(s), which respectively detect either normal load or shear load. Light emitter(s) emit light that traverses through the optically transparent layer and reflects off optically reflective material of the first layer, and light detector(s) detect and measure intensity of reflected light. When a normal load is applied, the optically transparent layer compresses, causing a change in reflected light intensity. When shear load is applied, a boundary between optically reflective material and optically absorptive material is laterally displaced, causing a change in reflected light intensity.

Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

2002-01-01

The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

Rheology of welding: experimental constraints

NASA Astrophysics Data System (ADS)

Quane, S. L.; Russell, J. K.; Kennedy, L. A.

2003-04-01

The rheological behavior of pyroclastic deposits during welding is incompletely understood and is based on a surprisingly small number of experimental studies. Previous pioneering experimental studies were done on small (1 cm thick) samples of ash/crystal mixtures under constant load. They established minimum welding temperatures between 600 and 700^oC under loads of 0.7 MPa (˜40 m of ignimbrite) to 3.6 MPa (˜250 m depth of ignimbrite). However, these data are neither sufficiently comprehensive nor coherent enough to fully describe the rheology of pyroclastic mixtures. In addition, previous studies did not examine the microstructural and geometric changes associated with welding compaction. Our goal is to provide accurate and comprehensive constitutive relationships between material properties, temperature, load and strain rate for pyroclastic material undergoing welding. Here we present results from a newly designed experimental apparatus. The experimental apparatus consists of a LoadTrac II fully automated uniaxial compression load frame manufactured by Geocomp Corporation. The load frame has a built in displacement transducer and can run both constant strain rate (10-6 to 0.25 cm/s) and constant load (up to 1150 kg) tests to a maximum displacement of 7.5 cm. The sample assembly comprises 5 cm diameter cylindrical upper and lower pistons (insulating ceramic with steel conductive ends) housed in a copper jacket. Samples are 5 cm diameter cores and can vary in length from 1 to 15 cm depending on experimental needs. A fiber insulated tube furnace capable of reaching temperatures ≈1000^oC surrounds the sample assembly. Temperature is measured using a thermocouple located inside the sample through the bottom piston; the furnace controller is capable of maintaining temperature fluctuations to <5^oC. Deformation experiments are performed on pre-fabricated cylinders of soda-lime glass beads and rhyolitic volcanic ash, as well as, cores of pumiceous rhyodacite. Experimental runs use strain rates of 10-4 and 10-5 cm/s and loads of ˜0 to 4.5 MPa. Experiments are run at temperatures between 400 and 850^oC corresponding to below and above the calorimetric glass transition temperatures of the respective materials. Data deriving from constant load and constant strain rate experiments are being used to constrain rheological models for welding of pyroclastic material.

Elastic-Plastic Finite Element Analysis of Fatigue Crack Growth in Mode 1 and Mode 2 Conditions

NASA Technical Reports Server (NTRS)

Nakagaki, M.; Atluri, S. N.

1978-01-01

Presented is an alternate cost-efficient and accurate elastic-plastic finite element procedure to analyze fatigue crack closure and its effects under general spectrum loading. Both Modes 1 and 2 type cycling loadings are considered. Also presented are the results of an investigation, using the newly developed procedure, of various factors that cause crack growth acceleration or retardation and delay effects under high-to-low, low-to-high, single overload, and constant amplitude type cyclic loading in a Mode 1 situation. Further, the results of an investigation of a centercracked panel under external pure shear (Mode 2) cyclic loading, of constant amplitude, are reported.

Long Term Displacement Data of Woven Fabric Webbings Under Constant Load for Inflatable Structures

NASA Technical Reports Server (NTRS)

Kenner, Winfred S.; Jones, Thomas C.; Doggett, William R.; Lucy, Melvin H.; Grondin, Trevor A.; Whitley, Karen S.; Duncan, Quinton; Plant, James V.

2014-01-01

Inflatable modules for space applications offer weight and launch volume savings relative to current metallic modules. Limited data exist on the creep behavior of the restraint layer of inflatable modules. Long-term displacement and strain data of two high strength woven fabric webbings, Kevlar and Vectran, under constant load is presented. The creep behavior of webbings is required by designers to help determine service life parameters of inflatable modules. Four groups of different webbings with different loads were defined for this study. Group 1 consisted of 4K Kevlar webbings loaded to 33% ultimate tensile strength and 6K Vectran webbings loaded to 27% ultimate tensile strength, group 2 consisted of 6K Kevlar webbings loaded to 40% and 43% ultimate tensile strength, and 6K Vectran webbings loaded to 50% ultimate tensile strength, group 3 consisted of 6K Kevlar webbings loaded to 52% ultimate tensile strength and 6K Vectran webbings loaded to 60% ultimate tensile strength, and group 4 consisted of 12.5K Kevlar webbings loaded to 22% ultimate tensile strength, and 12.5K Vectran webbings loaded to 22% ultimate tensile strength. The uniquely designed test facility, hardware, displacement measuring devices, and test data are presented. Test data indicate that immediately after loading all webbings stretch an inch or more, however as time increases displacement values significantly decrease to fall within a range of several hundredth of an inch over the remainder of test period. Webbings in group 1 exhibit near constant displacements and strains over a 17-month period. Data acquisition was suspended after the 17th month, however webbings continue to sustain load without any local webbing damage as of the 21st month of testing. Webbings in group 2 exhibit a combination of initial constant displacement and subsequent increases in displacement rates over a 16-month period. Webbings in group 3 exhibit steady increases in displacement rates leading to webbing failure over a 3-month period. Five of six webbings experienced local damage and subsequent failure in group 3. Data from group 4 indicates increasing webbing displacements over a 7-month period. All webbings in groups 1, 2, and 4 remain suspended without any local damage as of the writing of this paper. Variations in facility temperatures over test period seem to have had limited effect on long-term webbing displacement data.

Rethinking the connection between working memory and language impairment.

PubMed

Archibald, Lisa M D; Harder Griebeling, Katherine

2016-05-01

Working memory deficits have been found for children with specific language impairment (SLI) on tasks imposing increasing short-term memory load with or without additional, consistent (and simple) processing load. To examine the processing function of working memory in children with low language (LL) by employing tasks imposing increasing processing loads with constant storage demands individually adjusted based on each participant's short-term memory capacity. School-age groups with LL (n = 17) and typical language with either average (n = 28) or above-average nonverbal intelligence (n = 15) completed complex working memory-span tasks varying processing load while keeping storage demands constant, varying storage demands while keeping processing load constant, simple storage-span tasks, and measures of language and nonverbal intelligence. Teachers completed questionnaires about cognition and learning. Significantly lower scores were found for the LL than either matched group on storage-based tasks, but no group differences were found on the tasks varying processing load. Teachers' ratings of oral expression and mathematics abilities discriminated those who did or did not complete the most challenging cognitive tasks. The results implicate a deficit in the phonological storage but not in the central executive component of working memory for children with LL. Teacher ratings may reveal personality traits related to perseverance of effort in cognitive research. © 2015 Royal College of Speech and Language Therapists.

Influence of sulfhydryl sites on metal binding by bacteria

NASA Astrophysics Data System (ADS)

Nell, Ryan M.; Fein, Jeremy B.

2017-02-01

The role of sulfhydryl sites within bacterial cell envelopes is still unknown, but the sites may control the fate and bioavailability of metals. Organic sulfhydryl compounds are important complexing ligands in aqueous systems and they can influence metal speciation in natural waters. Though representing only approximately 5-10% of the total available binding sites on bacterial surfaces, sulfhydryl sites exhibit high binding affinities for some metals. Due to the potential importance of bacterial sulfhydryl sites in natural systems, metal-bacterial sulfhydryl site binding constants must be determined in order to construct accurate models of the fate and distribution of metals in these systems. To date, only Cd-sulfhydryl binding has been quantified. In this study, the thermodynamic stabilities of Mn-, Co-, Ni-, Zn-, Sr- and Pb-sulfhydryl bacterial cell envelope complexes were determined for the bacterial species Shewanella oneidensis MR-1. Metal adsorption experiments were conducted as a function of both pH, ranging from 5.0 to 7.0, and metal loading, from 0.5 to 40.0 μmol/g (wet weight) bacteria, in batch experiments in order to determine if metal-sulfhydryl binding occurs. Initially, the data were used to calculate the value of the stability constants for the important metal-sulfhydryl bacterial complexes for each metal-loading condition studied, assuming a single binding reaction for the dominant metal-binding site type under the pH conditions of the experiments. For most of the metals that we studied, these calculated stability constant values increased significantly with decreasing metal loading, strongly suggesting that our initial assumption was not valid and that more than one type of binding occurs at the assumed binding site. We then modeled each dataset with two distinct site types with identical acidity constants: one site with a high metal-site stability constant value, which we take to represent metal-sulfhydryl binding and which dominates under low metal loading conditions, and another more abundant site that we term non-sulfhydryl sites that becomes important at high metal loadings. The resulting calculated stability constants do not vary significantly as a function of metal loading and yield reasonable fits to the observed adsorption behaviors as a function of both pH and metal loading. We use the results to calculate the speciation of metals bound by the bacterial envelope in realistic bacteria-bearing, heavy metal contaminated systems in order to demonstrate the potential importance of metal-sulfhydryl binding in the budget of bacterially-adsorbed metals under low metal-loading conditions.

pH-responsive supramolecular vesicles based on water-soluble pillar[6]arene and ferrocene derivative for drug delivery.

PubMed

Duan, Qunpeng; Cao, Yu; Li, Yan; Hu, Xiaoyu; Xiao, Tangxin; Lin, Chen; Pan, Yi; Wang, Leyong

2013-07-17

The drug delivery system based on supramolecular vesicles that were self-assembled by a novel host-guest inclusion complex between a water-soluble pillar[6]arene (WP6) and hydrophobic ferrocene derivative in water has been developed. The inclusion complexation between WP6 and ferrocene derivative in water was studied by (1)H NMR, UV-vis, and fluorescence spectroscopy, which showed a high binding constant of (1.27 ± 0.42) × 10(5) M(-1) with 1:1 binding stoichiometry. This resulting inclusion complex could self-assemble into supramolecular vesicles that displayed a significant pH-responsive behavior in aqueous solution, which were investigated by fluorescent probe technique, dynamic laser scattering, and transmission electron microscopy. Furthermore, the drug loading and in vitro drug release studies demonstrated that these supramolecular vesicles were able to encapsulate mitoxantrone (MTZ) to achieve MTZ-loaded vesicles, which particularly showed rapid MTZ release at low-pH environment. More importantly, the cellular uptake of these pH-responsive MTZ-loaded vesicles by cancer cells was observed by living cell imaging techniques, and their cytotoxicity assay indicated that unloaded vesicles had low toxicity to normal cells, which could dramatically reduce the toxicity of MTZ upon loading of MTZ. Meanwhile, MTZ-loaded vesicles exhibited comparable anticancer activity in vitro as free MTZ to cancer cells under examined conditions. This study suggests that such supramolecular vesicles have great potential as controlled drug delivery systems.

Experimental Verification of the Structural Glass Beam-Columns Strength

NASA Astrophysics Data System (ADS)

Pešek, Ondřej; Melcher, Jindřich; Balázs, Ivan

2017-10-01

This paper deals with experimental research of axially and laterally loaded members made of structural (laminated) glass. The purpose of the research is the evaluation of buckling strength and actual behaviour of the beam-columns due to absence of standards for design of glass load-bearing structures. The experimental research follows the previous one focusing on measuring of initial geometrical imperfections of glass members, testing of glass beams and columns. Within the frame of the research 9 specimens were tested. All of them were of the same geometry (length 2000 mm, width 200 mm and thickness 16 mm) but different composition - laminated double glass made of annealed glass or fully tempered glass panes bonded together by PVB or EVASAFE foil. Specimens were at first loaded by axial force and then by constantly increasing bending moment up to failure. During testing lateral deflections, vertical deflection and normal stresses at mid-span were measured. A maximum load achieved during testing has been adopted as flexural-lateral-torsional buckling strength. The results of experiments were statistically evaluated according to the European standard for design of structures EN 1990, appendix D. There are significant differences between specimens made of annealed glass or fully tempered glass. Differences between specimens loaded by axial forces 1 kN and 2 kN are negligible. The next step was to determine the design strength by calculation procedure based on buckling curves approach intended for design of steel columns and develop interaction criterion for glass beams-columns.

Stiffness and relaxation components of the exponential and logistic time constants may be used to derive a load-independent index of isovolumic pressure decay.

PubMed

Shmuylovich, Leonid; Kovács, Sándor J

2008-12-01

In current practice, empirical parameters such as the monoexponential time constant tau or the logistic model time constant tauL are used to quantitate isovolumic relaxation. Previous work indicates that tau and tauL are load dependent. A load-independent index of isovolumic pressure decline (LIIIVPD) does not exist. In this study, we derive and validate a LIIIVPD. Recently, we have derived and validated a kinematic model of isovolumic pressure decay (IVPD), where IVPD is accurately predicted by the solution to an equation of motion parameterized by stiffness (Ek), relaxation (tauc), and pressure asymptote (Pinfinity) parameters. In this study, we use this kinematic model to predict, derive, and validate the load-independent index MLIIIVPD. We predict that the plot of lumped recoil effects [Ek.(P*max-Pinfinity)] versus resistance effects [tauc.(dP/dtmin)], defined by a set of load-varying IVPD contours, where P*max is maximum pressure and dP/dtmin is the minimum first derivative of pressure, yields a linear relation with a constant (i.e., load independent) slope MLIIIVPD. To validate the load independence, we analyzed an average of 107 IVPD contours in 25 subjects (2,669 beats total) undergoing diagnostic catheterization. For the group as a whole, we found the Ek.(P*max-Pinfinity) versus tauc.(dP/dtmin) relation to be highly linear, with the average slope MLIIIVPD=1.107+/-0.044 and the average r2=0.993+/-0.006. For all subjects, MLIIIVPD was found to be linearly correlated to the subject averaged tau (r2=0.65), tauL(r2=0.50), and dP/dtmin (r2=0.63), as well as to ejection fraction (r2=0.52). We conclude that MLIIIVPD is a LIIIVPD because it is load independent and correlates with conventional IVPD parameters. Further validation of MLIIIVPD in selected pathophysiological settings is warranted.

Crank inertial load has little effect on steady-state pedaling coordination.

PubMed

Fregly, B J; Zajac, F E; Dairaghi, C A

1996-12-01

Inertial load can affect the control of a dynamic system whenever parts of the system are accelerated or decelerated. During steady-state pedaling, because within-cycle variations in crank angular acceleration still exist, the amount of crank inertia present (which varies widely with road-riding gear ratio) may affect the within-cycle coordination of muscles. However, the effect of inertial load on steady-state pedaling coordination is almost always assumed to be negligible, since the net mechanical energy per cycle developed by muscles only depends on the constant cadence and workload. This study test the hypothesis that under steady-state conditions, the net joint torques produced by muscles at the hip, knee, and ankle are unaffected by crank inertial load. To perform the investigation, we constructed a pedaling apparatus which could emulate the low inertial load of a standard ergometer or the high inertial load of a road bicycle in high gear. Crank angle and bilateral pedal force and angle data were collected from ten subjects instructed to pedal steadily (i.e., constant speed across cycles) and smoothly (i.e., constant speed within a cycle) against both inertias at a constant workload. Virtually no statistically significant changes were found in the net hip and knee muscle joint torques calculated from an inverse dynamics analysis. Though the net ankle muscle joint torque, as well as the one- and two-legged crank torque, showed statistically significant increases at the higher inertia, the changes were small. In contrast, large statistically significant reductions were found in crank kinematic variability both within a cycle and between cycles (i.e., cadence), primarily because a larger inertial load means a slower crank dynamic response. Nonetheless, the reduction in cadence variability was somewhat attenuated by a large statistically significant increase in one-legged crank torque variability. We suggest, therefore, that muscle coordination during steady-state pedaling is largely unaffected, though less well regulated, when crank inertial load is increased.

Laboratory constraints on models of earthquake recurrence

NASA Astrophysics Data System (ADS)

Beeler, N. M.; Tullis, Terry; Junger, Jenni; Kilgore, Brian; Goldsby, David

2014-12-01

In this study, rock friction "stick-slip" experiments are used to develop constraints on models of earthquake recurrence. Constant rate loading of bare rock surfaces in high-quality experiments produces stick-slip recurrence that is periodic at least to second order. When the loading rate is varied, recurrence is approximately inversely proportional to loading rate. These laboratory events initiate due to a slip-rate-dependent process that also determines the size of the stress drop and, as a consequence, stress drop varies weakly but systematically with loading rate. This is especially evident in experiments where the loading rate is changed by orders of magnitude, as is thought to be the loading condition of naturally occurring, small repeating earthquakes driven by afterslip, or low-frequency earthquakes loaded by episodic slip. The experimentally observed stress drops are well described by a logarithmic dependence on recurrence interval that can be cast as a nonlinear slip predictable model. The fault's rate dependence of strength is the key physical parameter. Additionally, even at constant loading rate the most reproducible laboratory recurrence is not exactly periodic, unlike existing friction recurrence models. We present example laboratory catalogs that document the variance and show that in large catalogs, even at constant loading rate, stress drop and recurrence covary systematically. The origin of this covariance is largely consistent with variability of the dependence of fault strength on slip rate. Laboratory catalogs show aspects of both slip and time predictability, and successive stress drops are strongly correlated indicating a "memory" of prior slip history that extends over at least one recurrence cycle.

Buckling analysis of curved composite sandwich panels subjected to inplane loadings

NASA Technical Reports Server (NTRS)

Cruz, Juan R.

1993-01-01

Composite sandwich structures are being considered for primary structure in aircraft such as subsonic and high speed civil transports. The response of sandwich structures must be understood and predictable to use such structures effectively. Buckling is one of the most important response mechanisms of sandwich structures. A simple buckling analysis is derived for sandwich structures. This analysis is limited to flat, rectangular sandwich panels loaded by uniaxial compression (N(sub x)) and having simply supported edges. In most aerospace applications, however, the structure's geometry, boundary conditions, and loading are usually very complex. Thus, a general capability for analyzing the buckling behavior of sandwich structures is needed. The present paper describes and evaluates an improved buckling analysis for cylindrically curved composite sandwich panels. This analysis includes orthotropic facesheets and first-order transverse shearing effects. Both simple support and clamped boundary conditions are also included in the analysis. The panels can be subjected to linearly varying normal loads N(sub x) and N(sub y) in addition to a constant shear load N(sub xy). The analysis is based on the modified Donnell's equations for shallow shells. The governing equations are solved by direct application of Galerkin's method. The accuracy of the present analysis is verified by comparing results with those obtained from finite element analysis for a variety of geometries, loads, and boundary conditions. The limitations of the present analysis are investigated, in particular those related to the shallow shell assumptions in the governing equations. Finally, the computational efficiency of the present analysis is considered.

Biaxial Mechanical Testing of Posterior Sclera using High-Resolution Ultrasound Speckle Tracking for Strain Measurements

PubMed Central

Cruz-Perez, Benjamin; Tang, Junhua; Morris, Hugh J.; Palko, Joel R.; Pan, Xueliang; Hart, Richard T.; Liu, Jun

2014-01-01

This study aimed to characterize the mechanical responses of the sclera, the white outer coat of the eye, under equal-biaxial loading with unrestricted shear. An ultrasound speckle tracking technique was used to measure tissue deformation through sample thickness, expanding the capabilities of surface strain techniques. Eight porcine scleral samples were tested within 72 hours postmortem. High resolution ultrasound scans of scleral cross-sections along the two loading axes were acquired at 25 consecutive biaxial load levels. An additional repeat of the biaxial loading cycle was performed to measure a third normal strain emulating a strain gauge rosette for calculating the in-plane shear. The repeatability of the strain measurements during identical biaxial ramps was evaluated. A correlation-based ultrasound speckle tracking algorithm was used to compute the displacement field and determine the distributive strains in the sample cross-sections. A Fung type constitutive model including a shear term was used to determine the material constants of each individual specimen by fitting the model parameters to the experimental stress-strain data. A non-linear stress-strain response was observed in all samples. The meridian direction had significantly larger strains than the circumferential direction during equal-biaxial loadings (P’s<0.05). The stiffness along the two directions were also significantly different (P=0.02) but highly correlated (R2=0.8). These results showed that the mechanical properties of the porcine sclera were nonlinear and anisotropic under biaxial loading. This work has also demonstrated the feasibility of using ultrasound speckle tracking for strain measurements during mechanical testing. PMID:24438767

On rate-state and Coulomb failure models

USGS Publications Warehouse

Gomberg, J.; Beeler, N.; Blanpied, M.

2000-01-01

We examine the predictions of Coulomb failure stress and rate-state frictional models. We study the change in failure time (clock advance) Δt due to stress step perturbations (i.e., coseismic static stress increases) added to "background" stressing at a constant rate (i.e., tectonic loading) at time t0. The predictability of Δt implies a predictable change in seismicity rate r(t)/r0, testable using earthquake catalogs, where r0 is the constant rate resulting from tectonic stressing. Models of r(t)/r0, consistent with general properties of aftershock sequences, must predict an Omori law seismicity decay rate, a sequence duration that is less than a few percent of the mainshock cycle time and a return directly to the background rate. A Coulomb model requires that a fault remains locked during loading, that failure occur instantaneously, and that Δt is independent of t0. These characteristics imply an instantaneous infinite seismicity rate increase of zero duration. Numerical calculations of r(t)/r0 for different state evolution laws show that aftershocks occur on faults extremely close to failure at the mainshock origin time, that these faults must be "Coulomb-like," and that the slip evolution law can be precluded. Real aftershock population characteristics also may constrain rate-state constitutive parameters; a may be lower than laboratory values, the stiffness may be high, and/or normal stress may be lower than lithostatic. We also compare Coulomb and rate-state models theoretically. Rate-state model fault behavior becomes more Coulomb-like as constitutive parameter a decreases relative to parameter b. This is because the slip initially decelerates, representing an initial healing of fault contacts. The deceleration is more pronounced for smaller a, more closely simulating a locked fault. Even when the rate-state Δt has Coulomb characteristics, its magnitude may differ by some constant dependent on b. In this case, a rate-state model behaves like a modified Coulomb failure model in which the failure stress threshold is lowered due to weakening, increasing the clock advance. The deviation from a non-Coulomb response also depends on the loading rate, elastic stiffness, initial conditions, and assumptions about how state evolves.

Creep behaviour and creep mechanisms of normal and healing ligaments

NASA Astrophysics Data System (ADS)

Thornton, Gail Marilyn

Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep. Similarly, ligament autografts had persistently abnormal creep behaviour and creep recovery after 2 years likely due to infiltration by scar tissue. Short-term immobilization of autografts had long-term detrimental consequences perhaps due to re-injury of the graft at remobilization. Treatments that restore normal properties to these mechanistic factors in order to control creep would improve joint healing by restoring joint kinematics and maintaining normal joint loading.

Analysis of orthotropic beams

Treesearch

Jen Y. Liu; S. Cheng

1979-01-01

A plane-stress analysis of orthotropic or isotropic beams is presented. The loading conditions considered are: (1) a concentrated normal load arbitrarily located on the beam, and (2) a distributed normal load covering an arbitrary length of the beam. exhibit close agreement with existing experimental data from Sitka spruce beams. Other loading conditions can similarly...

Regional Myocardial Blood Flow*

PubMed Central

Sullivan, Jay M.; Taylor, Warren J.; Elliott, William C.; Gorlin, Richard

1967-01-01

A method is described which measures the local effectiveness of the myocardial circulation, expressed as a clearance constant. Uniform clearance constants have been demonstrated in the normal canine and human myocardium. A distinct difference in clearance constants has been demonstrated between the normal canine myocardium and areas of naturally occurring disease. Heterogeneous clearance constants have been found in a majority of human subjects with coronary artery disease—the lowest rates being noted in areas of fibrous aneurysm. PMID:6036537

Chapter 18: Variable Frequency Drive Evaluation Protocol. The Uniform Methods Project: Methods for Determining Energy Efficiency Savings for Specific Measures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romberger, Jeff

An adjustable-speed drive (ASD) includes all devices that vary the speed of a rotating load, including those that vary the motor speed and linkage devices that allow constant motor speed while varying the load speed. The Variable Frequency Drive Evaluation Protocol presented here addresses evaluation issues for variable-frequency drives (VFDs) installed on commercial and industrial motor-driven centrifugal fans and pumps for which torque varies with speed. Constant torque load applications, such as those for positive displacement pumps, are not covered by this protocol.

Root elongation against a constant force: experiment with a computerized feedback-controlled device

NASA Technical Reports Server (NTRS)

Kuzeja, P. S.; Lintilhac, P. M.; Wei, C.

2001-01-01

Axial force was applied to the root tip of corn (Zea mays L. cv. Merit) seedlings using a computerized, feedback-controlled mechanical device. The system's feedback capability allowed continuous control of a constant tip load, and the attached displacement transducer provided the time course of root elongation. Loads up to 7.5 g decreased the root elongation rate by 0.13 mm h-1 g-1, but loads 7.5 to 17.5 g decreased the growth rate by only 0.04 mm h-1 g-1. Loads higher than 18 g stopped root elongation completely. Measurement of the cross-sectional areas of the root tips indicated that the 18 g load had applied about 0.98 MPa of axial pressure to the root, thereby exceeding the root's ability to respond with increased turgor pressure. Recorded time-lapse images of loaded roots showed that radial thickening (swelling) occurred behind the root cap, whose cross-sectional area increased with tip load.

On Generating Fatigue Crack Growth Thresholds

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James, Jr.; Forman, Royce G.

2003-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. These experimental procedures can induce load history effects that result in crack closure. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake or blunt at the crack tip, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor range, Delta K, will increase, as will the crack growth rate. da/dN. A fatigue crack growth threshold test procedure is experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R. The authors have chosen to study a ductile aluminum alloy where the plastic deformations generated during testing may be of the magnitude to impact the crack opening.

Understanding the meaning of lactate threshold in resistance exercises.

PubMed

Garnacho-Castaño, M V; Dominguez, R; Maté-Muñoz, J L

2015-05-01

This study compares acute cardiorespiratory, metabolic, mechanical and rating of perceived effort (RPE) responses to 2 different prolonged constant-load exercises, half-squat (HS) and cycle ergometry, performed at a workload corresponding to the lactate threshold (LT). A total of 18 healthy subjects completed 5 exercise tests separated by 48 h rest periods: an incremental cycle ergometer test, a constant-load cycle ergometer test at LT intensity, a one-repetition maximum (1RM) HS test, an incremental HS test and a constant-load HS test at LT intensity. In both constant-load tests, cardiorespiratory, metabolic and RPE data were recorded. Mechanical responses before and after each test were assessed in terms of jump height and mean power measured in a counter movement jump (CMJ) test. In both exercises, cardiorespiratory and metabolic responses stabilized, though cardiorespiratory responses were significantly greater for cycle ergometry (P<0.001), with the exception of respiratory exchange ratio (RER), which was higher for HS (P=0.028). Mechanical fatigue was observed in only HS (P<0.001). In conclusion, different exercise modalities induced different yet stable acute cardiorespiratory and metabolic responses. Although such responses were significantly reduced in HS, greater mechanical fatigue was produced, most likely because of the particular muscle actions involved in this form of exercise. © Georg Thieme Verlag KG Stuttgart · New York.

Review of Slow-Wave Structures

NASA Technical Reports Server (NTRS)

Wallett, Thomas M.; Qureshi, A. Haq

1994-01-01

The majority of recent theoretical and experimental reports published in the literature dealing with helical slow-wave structures focus on the dispersion characteristics and their effects due to the finite helix wire thickness and attenuation, dielectric loading, metal loading, and the introduction of plasma. In many papers, an effective dielectric constant is used to take into account helix wire dimensions and conductivity losses, while the propagation constant of the signal and the interaction impedance of the structure are found to depend on the surface resistivity of the helix. Also, various dielectric supporting rods are simulated by one or several uniform cylinders having an effective dielectric constant, while metal vane loading and plasma effects are incorporated in the effective dielectric constant. The papers dealing with coupled cavities and folded or loaded wave guides describe equivalent circuit models, efficiency enhancement, and the prediction of instabilities for these structures. Equivalent circuit models of various structures are found using computer software programs SUPERFISH and TOUCHSTONE. Efficiency enhancement in tubes is achieved through dynamic velocity and phase adjusted tapers using computer techniques. The stability threshold of unwanted antisymmetric and higher order modes is predicted using SOS and MAGIC codes and the dependence of higher order modes on beam conductance, section length, and effective Q of a cavity is shown.

Experimental analysis on the dynamic wake of an actuator disc undergoing transient loads

NASA Astrophysics Data System (ADS)

Yu, W.; Hong, V. W.; Ferreira, C.; van Kuik, G. A. M.

2017-10-01

The Blade Element Momentum model, which is based on the actuator disc theory, is still the model most used for the design of open rotors. Although derived from steady cases with a fully developed wake, this approach is also applied to unsteady cases, with additional engineering corrections. This work aims to study the impact of an unsteady loading on the wake of an actuator disc. The load and flow of an actuator disc are measured in the Open Jet Facility wind tunnel of Delft University of Technology, for steady and unsteady cases. The velocity and turbulence profiles are characterized in three regions: the inner wake region, the shear layer region and the region outside the wake. For unsteady load cases, the measured velocity field shows a hysteresis effect in relation to the loading, showing differences between the cases when loading is increased and loading is decreased. The flow field also shows a transient response to the step change in loading, with either an overshoot or undershoot of the velocity in relation to the steady-state velocity. In general, a smaller reduced ramp time results in a faster velocity transient, and in turn a larger amplitude of overshoot or undershoot. Time constants analysis shows that the flow reaches the new steady-state slower for load increase than for load decrease; the time constants outside the wake are generally larger than at other radial locations for a given downstream plane; the time constants of measured velocity in the wake show radial dependence.The data are relevant for the validation of numerical models for unsteady actuator discs and wind turbines, and are made available in an open source database (see Appendix).

Optimization of enhanced biological phosphorus removal after periods of low loading.

PubMed

Miyake, Haruo; Morgenroth, Eberhard

2005-01-01

Enhanced biological phosphorus removal is a well-established technology for the treatment of municipal wastewater. However, increased effluent phosphorus concentrations have been reported after periods (days) of low organic loading. The purpose of this study was to evaluate different operating strategies to prevent discharge of effluent after such low-loading periods. Mechanisms leading to these operational problems have been related to the reduction of polyphosphate-accumulating organisms (PAOs) and their storage compounds (polyhydroxy alkanoates [PHA]). Increased effluent phosphorus concentrations can be the result of an imbalance between influent loading and PAOs in the system and an imbalance between phosphorus release and uptake rates. The following operating conditions were tested in their ability to prevent a reduction of PHA and of overall biomass during low organic loading conditions: (a) unchanged operation, (b) reduced aeration time, (c) reduced sludge wastage, and (d) combination of reduced aeration time and reduced sludge wastage. Experiments were performed in a laboratory-scale anaerobic-aerobic sequencing batch reactor, using acetate as the carbon source. Without operational adjustments, phosphorus-release rates decreased during low-loading periods but recovered rapidly. Phosphorus-uptake rates also decreased, and the recovery typically required several days to increase to normal levels. The combination of reduced aeration time and reduced sludge wastage allowed the maintenance of constant levels of both PHA and overall biomass. A mathematical model was used to explain the influence of the tested operating conditions on PAO and PHA concentrations. While experimental results were in general agreement with model predictions, the kinetic expression for phosphorus uptake deviated significantly for the first 24 hours after low-loading conditions. Mechanisms leading to these deviations need to be further investigated.

Is this the right normalization? A diagnostic tool for ChIP-seq normalization.

PubMed

Angelini, Claudia; Heller, Ruth; Volkinshtein, Rita; Yekutieli, Daniel

2015-05-09

Chip-seq experiments are becoming a standard approach for genome-wide profiling protein-DNA interactions, such as detecting transcription factor binding sites, histone modification marks and RNA Polymerase II occupancy. However, when comparing a ChIP sample versus a control sample, such as Input DNA, normalization procedures have to be applied in order to remove experimental source of biases. Despite the substantial impact that the choice of the normalization method can have on the results of a ChIP-seq data analysis, their assessment is not fully explored in the literature. In particular, there are no diagnostic tools that show whether the applied normalization is indeed appropriate for the data being analyzed. In this work we propose a novel diagnostic tool to examine the appropriateness of the estimated normalization procedure. By plotting the empirical densities of log relative risks in bins of equal read count, along with the estimated normalization constant, after logarithmic transformation, the researcher is able to assess the appropriateness of the estimated normalization constant. We use the diagnostic plot to evaluate the appropriateness of the estimates obtained by CisGenome, NCIS and CCAT on several real data examples. Moreover, we show the impact that the choice of the normalization constant can have on standard tools for peak calling such as MACS or SICER. Finally, we propose a novel procedure for controlling the FDR using sample swapping. This procedure makes use of the estimated normalization constant in order to gain power over the naive choice of constant (used in MACS and SICER), which is the ratio of the total number of reads in the ChIP and Input samples. Linear normalization approaches aim to estimate a scale factor, r, to adjust for different sequencing depths when comparing ChIP versus Input samples. The estimated scaling factor can easily be incorporated in many peak caller algorithms to improve the accuracy of the peak identification. The diagnostic plot proposed in this paper can be used to assess how adequate ChIP/Input normalization constants are, and thus it allows the user to choose the most adequate estimate for the analysis.

A viscoplastic study of crack-tip deformation and crack growth in a nickel-based superalloy at elevated temperature

NASA Astrophysics Data System (ADS)

Zhao, L. G.; Tong, J.

Viscoplastic crack-tip deformation behaviour in a nickel-based superalloy at elevated temperature has been studied for both stationary and growing cracks in a compact tension (CT) specimen using the finite element method. The material behaviour was described by a unified viscoplastic constitutive model with non-linear kinematic and isotropic hardening rules, and implemented in the finite element software ABAQUS via a user-defined material subroutine (UMAT). Finite element analyses for stationary cracks showed distinctive strain ratchetting behaviour near the crack tip at selected load ratios, leading to progressive accumulation of tensile strain normal to the crack-growth plane. Results also showed that low frequencies and superimposed hold periods at peak loads significantly enhanced strain accumulation at crack tip. Finite element simulation of crack growth was carried out under a constant Δ K-controlled loading condition, again ratchetting was observed ahead of the crack tip, similar to that for stationary cracks. A crack-growth criterion based on strain accumulation is proposed where a crack is assumed to grow when the accumulated strain ahead of the crack tip reaches a critical value over a characteristic distance. The criterion has been utilized in the prediction of crack-growth rates in a CT specimen at selected loading ranges, frequencies and dwell periods, and the predictions were compared with the experimental results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okumus, S. Cem, E-mail: cokumus@sakarya.edu.tr; Karslioglu, Ramazan, E-mail: cokumus@sakarya.edu.tr; Akbulut, Hatem, E-mail: cokumus@sakarya.edu.tr

Aluminum-lithium based unreinforced (Al-8090) alloy and Al-8090/SiCp/17 vol.% metal matrix composite produced by extrusion after spray co-deposition. A dry ball-on disk wear test was carried out for both alloy and composite. The tests were performed against an Al{sub 2}O{sub 3} ball, 10 mm in diameter, at room temperature and in laboratory air conditions with a relative humidity of 40-60%. Sliding speed was chosen as 1.0 ms{sup −1} and normal loads of 1.0, 3.0 and 5.0 N were employed at a constant sliding distance of 1000 m. The wear damage on the specimens was evaluated via measurement of wear depth andmore » diameter. Microstructural and wear characterization was carried out via scanning electron microscopy (SEM). The results showed that wear loss of the Al-8090/SiC composite was less than that of the Al-8090 matrix alloy. Plastic deformation observed on the wear surface of the composite and the matrix alloy, and the higher the applied load the greater the plastic deformation. Scanning electron microscopy examinations of wear tracks also reveal that delamination fracture was the dominant wear mechanism during the wear progression. Friction coefficient was maximum at the low applied load in the case of the Al-8090/SiC composite while a gradual increase was observed with applied load for the matrix alloy.« less

Fatigue life prediction of rotor blade composites: Validation of constant amplitude formulations with variable amplitude experiments

NASA Astrophysics Data System (ADS)

Westphal, T.; Nijssen, R. P. L.

2014-12-01

The effect of Constant Life Diagram (CLD) formulation on the fatigue life prediction under variable amplitude (VA) loading was investigated based on variable amplitude tests using three different load spectra representative for wind turbine loading. Next to the Wisper and WisperX spectra, the recently developed NewWisper2 spectrum was used. Based on these variable amplitude fatigue results the prediction accuracy of 4 CLD formulations is investigated. In the study a piecewise linear CLD based on the S-N curves for 9 load ratios compares favourably in terms of prediction accuracy and conservativeness. For the specific laminate used in this study Boerstra's Multislope model provides a good alternative at reduced test effort.

Microstructural Effects on SCC Initiation PWR Primary Water Cold-Worked Alloy 600

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhai, Ziqing; Toloczko, Mychailo B.; Bruemmer, Stephen M.

SCC initiation behavior of one mill annealed alloy 600 plate heat was investigated in simulated PWR primary water under constant load at yield stress with in-situ direct current potential drop (DCPD) monitoring for crack initiation. Twelve specimens were tested at similar cold work levels among which three showed much shorter SCC initiation times (<400 hrs) than the others (>1200 hrs). Post-test examinations revealed that these three specimens all feature an inhomogeneous microstructure where the primary crack always nucleated along the boundary of large elongated grains protruding normally into the gauge. In contrast, such microstructure was either not observed or didmore » not extend deep enough into the gauge in the other specimens exhibiting ~3-6X longer initiation times. In order to better understand the role of this microstructural inhomogeneity in SCC initiation, high-resolution microscopy was performed to compare carbide morphology and strain distribution between the long grains and normal grains, and their potential effects on SCC initiation are discussed in this paper.« less

Friction and Wear of Iron in Corrosive Media

NASA Technical Reports Server (NTRS)

Rengstorff, G. W. P.; Miyoshi, K.; Buckley, D. H.

1982-01-01

Friction and wear experiments were conducted with elemental iron exposed to various corrosive media including two acids, base, and a salt. Studies involved various concentrations of nitric and sulfuric acids, sodium hydroxide, and sodium chloride. Load and reciprocating sliding speed were kept constant. With the base NaOH an increase in normality beyond 0.01 N resulted in a decrease in both friction and wear. X-ray photoelectron spectroscopy (XPS) analysis of the surface showed a decreasing concentration of ferric oxide (Fe2O3) on the iron surface with increasing NaOH concentration. With nitric acid (HNO3) friction decreased in solutions to 0.05 N, beyond which no further change in friction was observed. The concentration of Fe2O3 on the surface continued to increase with increasing normality. XPS analysis revealed the presence of sulfates in addition of Fe2O3 on surfaces exposed to sulfuric acid and iron chlorides but no sodium on surfaces exposed to NaCl.

3j Symbols: To Normalize or Not to Normalize?

ERIC Educational Resources Information Center

van Veenendaal, Michel

2011-01-01

The systematic use of alternative normalization constants for 3j symbols can lead to a more natural expression of quantities, such as vector products and spherical tensor operators. The redefined coupling constants directly equate tensor products to the inner and outer products without any additional square roots. The approach is extended to…

49 CFR 571.110 - Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity...

Code of Federal Regulations, 2014 CFR

2014-10-01

..., equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent..., the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the... vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10...

49 CFR 571.110 - Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity...

Code of Federal Regulations, 2012 CFR

2012-10-01

..., equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent..., the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the... vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10...

49 CFR 571.110 - Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity...

Code of Federal Regulations, 2011 CFR

2011-10-01

..., equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent..., the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the... vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10...

49 CFR 571.110 - Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity...

Code of Federal Regulations, 2013 CFR

2013-10-01

..., equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent..., the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the... vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10...

49 CFR 571.110 - Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity...

Code of Federal Regulations, 2010 CFR

2010-10-01

..., equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent..., the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the... vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10...

Room temperature shear properties of the strain isolator pad for the shuttle thermal protection system

NASA Technical Reports Server (NTRS)

Sawyer, J. W.; Waters, W. A., Jr.

1981-01-01

Tests were conducted at room temperature to determine the shear properties of the strain isolator pad (SIP) material used in the thermal protection system of the space shuttle. Tests were conducted on both the .23 cm and .41 cm thick SIP material in the virgin state and after fifty fully reversed shear cycles. The shear stress displacement relationships are highly nonlinear, exhibit large hysteresis effects, are dependent on material orientation, and have a large low modulus region near the zero stress level where small changes in stress can result in large displacements. The values at the higher stress levels generally increase with normal and shear force load conditioning. Normal forces applied during the shear tests reduces the low modulus region for the material. Shear test techniques which restrict the normal movement of the material give erroneous stress displacement results. However, small normal forces do not significantly effect the shear modulus for a given shear stress. Poisson's ratio values for the material are within the range of values for many common materials. The values are not constant but vary as a function of the stress level and the previous stress history of the material. Ultimate shear strengths of the .23 cm thick SIP are significantly higher than those obtained for the .41 cm thick SIP.

VO2 kinetics in supra-anaerobic threshold constant tests allow the visualization and quantification of the O2 saving after cytochrome c oxidase inhibition by aerobic training or nitrate administration.

PubMed

Maione, D; Cicero, A Fg; Bacchelli, S; Cosentino, E; Degli Esposti, D; Senaldi, R; Strocchi, E; D'Addato, S; Borghi, C

2013-01-01

We tested whether the known cytochrome c oxidase (COX) inhibition by nitric oxide (NO) could be quantified by VO(2) kinetics during constant load supra-Anaerobic Threshold (AT) exercises in healthy trained or untrained subjects following aerobic training or nitrate administration. In cycle ergometer constant load exercises supra-AT, identified in previous incremental tests, VO(2) kinetics describe a double exponential curve, one rapid and one appreciably slower, allowing the area between them to be calculate in O(2) l. After training, with increased NO availability, this area decreases in inverse ratio to treatment efficacy. In fact, in 11 healthy subjects after aerobic training for 6-7 weeks, area was decreased on average by 51 %. In 11 untrained subjects, following the assumption of an NO donor, 20 mg isosorbide 5 mononitrate, area was decreased on average by 53 %. In conclusion, supra-AT VO(2) kinetics in constant load exercises permit the quantification of the inhibitory effect NO-dependent on COX after either physical training or nitrate assumption.

A novel solution for hydroxylated PAHs removal by oxidative coupling reaction using Mn oxide.

PubMed

Kang, Ki-Hoon; Lim, Dong-Min; Shin, Hyun-Sang

2008-01-01

In this study, removals of 1-naphthol by oxidative-coupling reaction using birnessite, one of the natural Mn oxides present in soil, was investigated in various experimental conditions (reaction time, Mn oxide loadings, pH). The removal efficiency of 1-naphthol by birnessite was high in all the experimental conditions, and UV-visible and mass spectrometric analyses on the supernatant after reaction confirmed that the reaction products were oligomers formed by oxidative-coupling reaction. Pseudo-first order rate constants, k, for the oxidative transformation of 1-naphthol by birnessite was derived from the kinetic experiments under various amounts of birnessite loadings, and using the observed pseudo-first order rate constants with respect to birnessite loadings, the surface area normalised specific rate constant, k(surf), was also determined to be 9.3 x 10(-4) (L/m(2).min) for 1-naphthol. In addition, the oxidative transformation of 1-naphthol was found to be dependent on solution pH, and the pseudo-first order rate constants were increased from 0.129 at pH 10 to 0.187 at pH 4. (c) IWA Publishing 2008.

The Comfortable Roller Coaster--on the Shape of Tracks with a Constant Normal Force

ERIC Educational Resources Information Center

Nordmark, Arne B.; Essen, Hanno

2010-01-01

A particle that moves along a smooth track in a vertical plane is influenced by two forces: gravity and normal force. The force experienced by roller coaster riders is the normal force, so a natural question to ask is, what shape of the track gives a normal force of constant magnitude? Here we solve this problem. It turns out that the solution is…

Grain scale observations of stick-slip dynamics in fluid saturated granular fault gouge

NASA Astrophysics Data System (ADS)

Johnson, P. A.; Dorostkar, O.; Guyer, R. A.; Marone, C.; Carmeliet, J.

2017-12-01

We are studying granular mechanics during slip. In the present work, we conduct coupled computational fluid dynamics (CFD) and discrete element method (DEM) simulations to study grain scale characteristics of slip instabilities in fluid saturated granular fault gouge. The granular sample is confined with constant normal load (10 MPa), and sheared with constant velocity (0.6 mm/s). This loading configuration is chosen to promote stick-slip dynamics, based on a phase-space study. Fluid is introduced in the beginning of stick phase and characteristics of slip events i.e. macroscopic friction coefficient, kinetic energy and layer thickness are monitored. At the grain scale, we monitor particle coordination number, fluid-particle interaction forces as well as particle and fluid kinetic energy. Our observations show that presence of fluids in a drained granular fault gouge stabilizes the layer in the stick phase and increases the recurrence time. In saturated model, we observe that average particle coordination number reaches higher values compared to dry granular gouge. Upon slip, we observe that a larger portion of the granular sample is mobilized in saturated gouge compared to dry system. We also observe that regions with high particle kinetic energy are correlated with zones of high fluid motion. Our observations highlight that spatiotemporal profile of fluid dynamic pressure affects the characteristics of slip instabilities, increasing macroscopic friction coefficient drop, kinetic energy release and granular layer compaction. We show that numerical simulations help characterize the micromechanics of fault mechanics.

The osteoporotic vertebral structure is well adapted to the loads of daily life, but not to infrequent "error" loads.

PubMed

Homminga, J; Van-Rietbergen, B; Lochmüller, E M; Weinans, H; Eckstein, F; Huiskes, R

2004-03-01

Osteoporotic vertebral fractures typically have a gradual onset, frequently remain clinically undetected, and do not seem to be related to traumatic events. The osteoporotic vertebrae may therefore be expected to display a less "optimal" bone architecture, leading to an uneven load distribution over the bone material. We evaluated the trabecular load distribution in an osteoporotic and a healthy vertebra under normal daily loading by combining three recent innovations: high resolution computed tomography (microCT) of entire bones, microfinite element analyses (microFEA), and parallel supercomputers. Much to our surprise, the number of highly loaded trabeculae was not higher in the osteoporotic vertebra than in the healthy one under normal daily loads (8% and 9%, respectively). The osteoporotic trabeculae were more oriented in the longitudinal direction, compensating for effects of bone loss and ensuring adequate stiffness for normal daily loading. The increased orientation did, however, make the osteoporotic structure less resistant against collateral "error" loads. In this case, the number of overloaded trabeculae in the osteoporotic vertebra was higher than in the healthy one (13% and 4%, respectively). These results strengthen the paradigm of a strong relationship between bone morphology and external loads applied during normal daily life. They also indicate that vertebral fractures result from actions like forward flexion or lifting, loads that may not be "daily" but are normally not traumatic either. If future clinical imaging techniques would enable such high-resolution images to be obtained in vivo, the combination of microCT and microFEA would produce a powerful tool to diagnose osteoporosis.

Experimental determination of micromachined discrete and continuous device spring constants using nanoindentation method

NASA Astrophysics Data System (ADS)

Chan, M. L.; Tay, Francis E.; Logeeswaran, V. J.; Zeng, Kaiyang; Shen, Lu; Chau, Fook S.

2002-04-01

A rapid and accurate static and quasi-static method for determining the out-of-plane spring constraints of cantilevers and a micromachined vibratory sensor is presented. In the past, much of the effort in nanoindentation application was to investigate the thin-film mechanical properties. In this paper, we have utilized the nanoindentation method to measure directly some micromachined device (e.g. microgyroscope) spring constants. The cantilevers and devices tested were fabricated using the MUMPS process and an SOI process (patent pending). Spring constants are determined using a commercial nanoindentation apparatus UMIS-2000 configured with both Berkovich and spherical indenter tip that can be placed onto the device with high accuracy. Typical load resolution is 20micrometers N to 0.5N and a displacement resolution of 0.05nm. Information was deduced from the penetration depth versus load curves during both loading and unloading.

A theoretical description of arterial pressure-flow relationships with verification in the isolated hindlimb of the dog.

PubMed

Jackman, A P; Green, J F

1990-01-01

We developed and tested a new two-compartment serial model of the arterial vasculature which unifies the capacitance (downstream arterial compliance) and waterfall (constant downstream pressure load) theories of blood flow through the arteries. In this model, blood drains from an upstream compliance through a resistance into a downstream compliance which empties into the veins through a downstream resistance which terminates in a constant pressure load. Using transient arterial pressure data obtained from an isolated canine hindlimb preparation, we tested this model, using a stop-flow technique. Numerical parameter estimation techniques were used to estimate the physiologic parameters of the model. The downstream compliance was found to be more than ten times larger than the upstream compliance and the constant pressure load was significantly above venous pressures but decreased in response to vasodilation. Our results support the applicability of both the capacitance and waterfall theories.

Digital high speed programmable convolver

NASA Astrophysics Data System (ADS)

Rearick, T. C.

1984-12-01

A circuit module for rapidly calculating a discrete numerical convolution is described. A convolution such as finding the sum of the products of a 16 bit constant and a 16 bit variable is performed by a module which is programmable so that the constant may be changed for a new problem. In addition, the module may be programmed to find the sum of the products of 4 and 8 bit constants and variables. RAM (Random Access Memories) are loaded with partial products of the selected constant and all possible variables. Then, when the actual variable is loaded, it acts as an address to find the correct partial product in the particular RAM. The partial products from all of the RAMs are shifted to the appropriate numerical power position (if necessary) and then added in adder elements.

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants

PubMed Central

Yu, Zheng-Yong; Liu, Qiang; Liu, Yunhan

2017-01-01

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi–Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings. PMID:28792487

Fatigue Analyses Under Constant- and Variable-Amplitude Loading Using Small-Crack Theory

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Phillips, E. P.; Everett, R. A., Jr.

1999-01-01

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily "crack growth" from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using "small-crack theory" under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta-Keff) under constant-amplitude loading. Modifications to the delta-Keff-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small-and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants.

PubMed

Yu, Zheng-Yong; Zhu, Shun-Peng; Liu, Qiang; Liu, Yunhan

2017-08-09

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi-Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings.

Laboratory constraints on models of earthquake recurrence

USGS Publications Warehouse

Beeler, Nicholas M.; Tullis, Terry; Junger, Jenni; Kilgore, Brian D.; Goldsby, David L.

2014-01-01

In this study, rock friction ‘stick-slip’ experiments are used to develop constraints on models of earthquake recurrence. Constant-rate loading of bare rock surfaces in high quality experiments produces stick-slip recurrence that is periodic at least to second order. When the loading rate is varied, recurrence is approximately inversely proportional to loading rate. These laboratory events initiate due to a slip rate-dependent process that also determines the size of the stress drop [Dieterich, 1979; Ruina, 1983] and as a consequence, stress drop varies weakly but systematically with loading rate [e.g., Gu and Wong, 1991; Karner and Marone, 2000; McLaskey et al., 2012]. This is especially evident in experiments where the loading rate is changed by orders of magnitude, as is thought to be the loading condition of naturally occurring, small repeating earthquakes driven by afterslip, or low-frequency earthquakes loaded by episodic slip. As follows from the previous studies referred to above, experimentally observed stress drops are well described by a logarithmic dependence on recurrence interval that can be cast as a non-linear slip-predictable model. The fault’s rate dependence of strength is the key physical parameter. Additionally, even at constant loading rate the most reproducible laboratory recurrence is not exactly periodic, unlike existing friction recurrence models. We present example laboratory catalogs that document the variance and show that in large catalogs, even at constant loading rate, stress drop and recurrence co-vary systematically. The origin of this covariance is largely consistent with variability of the dependence of fault strength on slip rate. Laboratory catalogs show aspects of both slip and time predictability and successive stress drops are strongly correlated indicating a ‘memory’ of prior slip history that extends over at least one recurrence cycle.

Earthquake triggering by transient and static deformations

USGS Publications Warehouse

Gomberg, J.; Beeler, N.M.; Blanpied, M.L.; Bodin, P.

1998-01-01

Observational evidence for both static and transient near-field and far-field triggered seismicity are explained in terms of a frictional instability model, based on a single degree of freedom spring-slider system and rate- and state-dependent frictional constitutive equations. In this study a triggered earthquake is one whose failure time has been advanced by ??t (clock advance) due to a stress perturbation. Triggering stress perturbations considered include square-wave transients and step functions, analogous to seismic waves and coseismic static stress changes, respectively. Perturbations are superimposed on a constant background stressing rate which represents the tectonic stressing rate. The normal stress is assumed to be constant. Approximate, closed-form solutions of the rate-and-state equations are derived for these triggering and background loads, building on the work of Dieterich [1992, 1994]. These solutions can be used to simulate the effects of static and transient stresses as a function of amplitude, onset time t0, and in the case of square waves, duration. The accuracies of the approximate closed-form solutions are also evaluated with respect to the full numerical solution and t0. The approximate solutions underpredict the full solutions, although the difference decreases as t0, approaches the end of the earthquake cycle. The relationship between ??t and t0 differs for transient and static loads: a static stress step imposed late in the cycle causes less clock advance than an equal step imposed earlier, whereas a later applied transient causes greater clock advance than an equal one imposed earlier. For equal ??t, transient amplitudes must be greater than static loads by factors of several tens to hundreds depending on t0. We show that the rate-and-state model requires that the total slip at failure is a constant, regardless of the loading history. Thus a static load applied early in the cycle, or a transient applied at any time, reduces the stress at the initiation of failure, whereas static loads that are applied sufficiently late raise it. Rate-and-state friction predictions differ markedly from those based on Coulomb failure stress changes (??CFS) in which ??t equals the amplitude of the static stress change divided by the background stressing rate. The ??CFS model assumes a stress failure threshold, while the rate-and-state equations require a slip failure threshold. The complete rale-and-state equations predict larger ??t than the ??CFS model does for static stress steps at small t0, and smaller ??t than the ??CFS model for stress steps at large t0. The ??CFS model predicts nonzero ??t only for transient loads that raise the stress to failure stress levels during the transient. In contrast, the rate-and-state model predicts nonzero ??t for smaller loads, and triggered failure may occur well after the transient is finished. We consider heuristically the effects of triggering on a population of faults, as these effects might be evident in seismicity data. Triggering is manifest as an initial increase in seismicity rate that may be followed by a quiescence or by a return to the background rate. Available seismicity data are insufficient to discriminate whether triggered earthquakes are "new" or clock advanced. However, if triggering indeed results from advancing the failure time of inevitable earthquakes, then our modeling suggests that a quiescence always follows transient triggering and that the duration of increased seismicity also cannot exceed the duration of a triggering transient load. Quiescence follows static triggering only if the population of available faults is finite.

Ground Vibration Generated by a Load Moving Along a Railway Track

NASA Astrophysics Data System (ADS)

SHENG, X.; JONES, C. J. C.; PETYT, M.

1999-11-01

The propagation of vibration generated by a harmonic or a constant load moving along a layered beam resting on the layered half-space is investigated theoretically in this paper. The solution to this problem can be used to study the ground vibration generated by the motion of a train axle load on a railway track. In this application, the ground is modelled as a number of parallel viscoelastic layers overlying an elastic half-space or a rigid foundation. The track, including the rails, rail pad, sleepers and ballast, is modelled as an infinite, layered beam structure. The modal nature of propagation in the ground for a chosen set of ground parameters is discussed and the results of the model are presented showing the characteristics of the vibration generated by a constant load and an oscillatory load at speeds below, near to, and above the lowest ground wave speed.

Investigation of the Behavior of Hardening Masonry Exposed to Variable Stresses

PubMed Central

Šlivinskas, Tomas; Jonaitis, Bronius; Marčiukaitis, Jonas Gediminas

2018-01-01

This paper analyzes the behavior of masonry under variable loads during execution (construction stage). It specifies the creep coefficient for calcium silicate brick masonry, presenting the research data of masonry deformation under variable and constant long-term loads. The interaction of separate layers of composite material in masonry is introduced and the formulae for determining long-term deformations are offered. The research results of masonry’s compressive strength and deformation properties under variable and constant long-term loads are presented. These are then compared to calculated ones. According to the presented comparison, the calculated long-term deformations coincide quite well with those determined experimentally. PMID:29710802

Investigation of the Behavior of Hardening Masonry Exposed to Variable Stresses.

PubMed

Šlivinskas, Tomas; Jonaitis, Bronius; Marčiukaitis, Jonas Gediminas; Zavalis, Robertas

2018-04-28

This paper analyzes the behavior of masonry under variable loads during execution (construction stage). It specifies the creep coefficient for calcium silicate brick masonry, presenting the research data of masonry deformation under variable and constant long-term loads. The interaction of separate layers of composite material in masonry is introduced and the formulae for determining long-term deformations are offered. The research results of masonry’s compressive strength and deformation properties under variable and constant long-term loads are presented. These are then compared to calculated ones. According to the presented comparison, the calculated long-term deformations coincide quite well with those determined experimentally.

Efficient transformer for electromagnetic waves

DOEpatents

Miller, R.B.

A transformer structure for efficient transfer of electromagnetic energy from a transmission line to an unmatched load provides voltage multiplication and current division by a predetermined constant. Impedance levels are transformed by the square of that constant. The structure includes a wave splitter, connected to an input transmission device and to a plurality of output transmission devices. The output transmission devices are effectively connected in parallel to the input transmission device. The output transmission devices are effectively series connected to provide energy to a load. The transformer structure is particularly effective in increasing efficiency of energy transfer through an inverting convolute structure by capturing and transferring energy losses from the inverter to the load.

Applied and engineering versions of the theory of elastoplastic processes of active complex loading part 2: Identification and verification

NASA Astrophysics Data System (ADS)

Peleshko, V. A.

2016-06-01

The deviator constitutive relation of the proposed theory of plasticity has a three-term form (the stress, stress rate, and strain rate vectors formed from the deviators are collinear) and, in the specialized (applied) version, in addition to the simple loading function, contains four dimensionless constants of the material determined from experiments along a two-link strain trajectory with an orthogonal break. The proposed simple mechanism is used to calculate the constants of themodel for four metallic materials that significantly differ in the composition and in the mechanical properties; the obtained constants do not deviate much from their average values (over the four materials). The latter are taken as universal constants in the engineering version of the model, which thus requires only one basic experiment, i. e., a simple loading test. If the material exhibits the strengthening property in cyclic circular deformation, then the model contains an additional constant determined from the experiment along a strain trajectory of this type. (In the engineering version of the model, the cyclic strengthening effect is not taken into account, which imposes a certain upper bound on the difference between the length of the strain trajectory arc and the module of the strain vector.) We present the results of model verification using the experimental data available in the literature about the combined loading along two- and multi-link strain trajectories with various lengths of links and angles of breaks, with plane curvilinear segments of various constant and variable curvature, and with three-dimensional helical segments of various curvature and twist. (All in all, we use more than 80 strain programs; the materials are low- andmedium-carbon steels, brass, and stainless steel.) These results prove that the model can be used to describe the process of arbitrary active (in the sense of nonnegative capacity of the shear) combine loading and final unloading of originally quasi-isotropic elastoplastic materials. In practical calculations, in the absence of experimental data about the properties of a material under combined loading, the use of the engineering version of the model is quite acceptable. The simple identification, wide verifiability, and the availability of a software implementation of the method for solving initial-boundary value problems permit treating the proposed theory as an applied theory.

Effects of Aging and Adult-Onset Hearing Loss on Cortical Auditory Regions

PubMed Central

Cardin, Velia

2016-01-01

Hearing loss is a common feature in human aging. It has been argued that dysfunctions in central processing are important contributing factors to hearing loss during older age. Aging also has well documented consequences for neural structure and function, but it is not clear how these effects interact with those that arise as a consequence of hearing loss. This paper reviews the effects of aging and adult-onset hearing loss in the structure and function of cortical auditory regions. The evidence reviewed suggests that aging and hearing loss result in atrophy of cortical auditory regions and stronger engagement of networks involved in the detection of salient events, adaptive control and re-allocation of attention. These cortical mechanisms are engaged during listening in effortful conditions in normal hearing individuals. Therefore, as a consequence of aging and hearing loss, all listening becomes effortful and cognitive load is constantly high, reducing the amount of available cognitive resources. This constant effortful listening and reduced cognitive spare capacity could be what accelerates cognitive decline in older adults with hearing loss. PMID:27242405

Biaxial (Tension-Torsion) Testing of an Oxide/Oxide Ceramic Matrix Composite

DTIC Science & Technology

2013-03-01

estimation algorithms and constants . . . . . . . . . . . . . 61 4.27 Biaxial (tension-torsion) load spreadsheet with independent axial load and torsion...through the composite and provides the main load - bearing capability. The interaction of the two (or more) phases takes place in the interface. The...transfer loads between fibers[15]. The fiber-to-fiber load transfer mechanism provided by the matrix plays a major role in the load - bearing properties of the

Normalized spectral damage of a linear system over different spectral loading patterns

NASA Astrophysics Data System (ADS)

Kim, Chan-Jung

2017-08-01

Spectral fatigue damage is affected by different loading patterns; the damage may be accumulated in a different manner because the spectral pattern has an influence on stresses or strains. The normalization of spectral damage with respect to spectral loading acceleration is a novel solution to compare the accumulated fatigue damage over different spectral loading patterns. To evaluate the sensitivity of fatigue damage over different spectral loading cases, a simple notched specimen is used to conduct a uniaxial vibration test for two representative spectral patterns-random and harmonic-between 30 and 3000 Hz. The fatigue damage to the simple specimen is analyzed for different spectral loading cases using the normalized spectral damage from the measured response data for both acceleration and strain. The influence of spectral loading patterns is discussed based on these analyses.

Research on equipment of micro-pressure measure and control in loading experiment of plant cell mechanics

NASA Astrophysics Data System (ADS)

Zhang, Lian; Yu, Chengbo; Tao, Hongyan; Chen, Xuejun; Zhai, Feng

2005-12-01

The equipment is developed to measure and control micro-pressure in loading experiment of plant cell mechanics. The motivation for the development of this equipment was to maintain a stationary micro-pressure on the agar of culturing cells to keep cytoactive in biology experiments. A singlechip controls the stepping motor of this equipment to drive loading equipment in the system, in order to load between 50mN and 250mN under a constant voltage. The accuracy is estimated to be +/-0.4 mN. The structure and control system of this equipment is introduced and described in detail. The experimental results show that the equipment is capable of maintaining a constant, stationary micropressure in cell culturing application and is worth of extending and applying.

Striking volume intolerance is induced by mimicking arterial baroreflex failure in normal left ventricular function.

PubMed

Funakoshi, Kouta; Hosokawa, Kazuya; Kishi, Takuya; Ide, Tomomi; Sunagawa, Kenji

2014-01-01

Patients with heart failure and preserved ejection fraction (HFpEF) are supersensitive to volume overload, and a striking increase in left atrial pressure (LAP) often occurs transiently and is rapidly resolved by intravascular volume reduction. The arterial baroreflex is a powerful regulator of intravascular stressed blood volume. We examined whether arterial baroreflex failure (FAIL) mimicked by constant carotid sinus pressure (CSP) causes a striking increase in LAP and systemic arterial pressure (AP) by volume loading in rats with normal left ventricular (LV) function. In anesthetized Sprague-Dawley rats, we isolated bilateral carotid sinuses and controlled CSP by a servo-controlled piston pump. We mimicked the normal arterial baroreflex by matching CSP to instantaneous AP and FAIL by maintaining CSP at a constant value regardless of AP. We infused dextran stepwise (infused volume [Vi]) until LAP reached 15 mm Hg and obtained the LAP-Vi relationship. We estimated the critical Vi as the Vi at which LAP reached 20 mm Hg. In FAIL, critical Vi decreased markedly from 19.4 ± 1.6 mL/kg to 15.6 ± 1.6 mL/kg (P < .01), whereas AP at the critical Vi increased (194 ± 6 mm Hg vs 163 ± 6 mm Hg; P < .01). We demonstrated that an artificial arterial baroreflex system we recently developed could fully restore the physiologic volume intolerance in the absence of native arterial baroreflex. Arterial baroreflex failure induces striking volume intolerance in the absence of LV dysfunction and may play an important role in the pathogenesis of acute heart failure, especially in states of HFpEF. Copyright © 2014 Elsevier Inc. All rights reserved.

Running quietly reduces ground reaction force and vertical loading rate and alters foot strike technique.

PubMed

Phan, Xuan; Grisbrook, Tiffany L; Wernli, Kevin; Stearne, Sarah M; Davey, Paul; Ng, Leo

2017-08-01

This study aimed to determine if a quantifiable relationship exists between the peak sound amplitude and peak vertical ground reaction force (vGRF) and vertical loading rate during running. It also investigated whether differences in peak sound amplitude, contact time, lower limb kinematics, kinetics and foot strike technique existed when participants were verbally instructed to run quietly compared to their normal running. A total of 26 males completed running trials for two sound conditions: normal running and quiet running. Simple linear regressions revealed no significant relationships between impact sound and peak vGRF in the normal and quiet conditions and vertical loading rate in the normal condition. t-Tests revealed significant within-subject decreases in peak sound, peak vGRF and vertical loading rate during the quiet compared to the normal running condition. During the normal running condition, 15.4% of participants utilised a non-rearfoot strike technique compared to 76.9% in the quiet condition, which was corroborated by an increased ankle plantarflexion angle at initial contact. This study demonstrated that quieter impact sound is not directly associated with a lower peak vGRF or vertical loading rate. However, given the instructions to run quietly, participants effectively reduced peak impact sound, peak vGRF and vertical loading rate.

Determination of Flower Constancy in Bombus atratus Franklin and Bombus bellicosus Smith (Hymenoptera: Apidae) through Palynological Analysis of Nectar and Corbicular Pollen Loads.

PubMed

Rossi, N; Santos, E; Salvarrey, S; Arbulo, N; Invernizzi, C

2015-12-01

The flower constancy (the visit to a single plant species during a foraging trip) in pollinator insects is a theme widely discussed in behavioral ecology and has an important implication in the evolution of angiosperms. This behavior was studied in the bumblebees Bombus atratus Franklin and Bombus bellicosus Smith through palynological analysis of the nectar and pollen loads of individuals captured while foraging in a restricted area. In both species, there were more individuals with constant flights than with non-constant ones, although in the nectar loads of B. atratus there were no significant differences between individuals with each flight types. It was verified that the nectar loads of the individuals that made either constant or non-constant flights did not differ in the number of pollen grains they contained. Considering this measurement as an estimate for flight duration, the results would indicate that the probability of changing between plant species during nectar collection is independent of the foraging trip duration. In both species, most individuals who collected nectar and/or pollen from more than one plant species visited just two plant species. In these cases, the pollen of one plant species was predominant. In the bumblebees in which it was possible to analyze nectar and pollen loads, the botanical origin of both resources was the same or they shared the principal species (with the exception of two individuals), showing that bumblebees do not often use a botanical source in an exclusive way to collect nectar and another to collect pollen.

Constant strain rate and peri-implant bone modeling: an in vivo longitudinal micro-CT analysis.

PubMed

De Smet, Els; Jaecques, Siegfried V N; Wevers, Martine; Sloten, Jos Vander; Naert, Ignace E

2013-06-01

Strain, frequency, loading time, and strain rate, among others, determine mechanical parameters in osteogenic loading. We showed a significant osteogenic effect on bone mass (BM) by daily peri-implant loading at 1.600µε.s(-1) after 4 weeks. To study the peri-implant osteogenic effect of frequency and strain in the guinea pig tibia by in vivo longitudinal micro-computed tomography (CT) analysis. One week after implant installation in both hind limb tibiae, one implant was loaded daily for 10' during 4 weeks, while the other served as control. Frequencies (3, 10, and 30Hz) and strains varied alike in the three series to keep the strain rate constant at 1.600µε.s(-1) . In vivo micro-CT scans were taken of both tibiae: 1 week after implantation but before loading (v1) and after 2 (v2) and 4 weeks (v3) of loading as well as postmortem (pm). BM (BM (%) bone-occupied area fraction) was calculated as well as the difference between test and control sides (delta BM) RESULTS: All implants (n=78) were clinically stable at 4 weeks. Significant increase in BM was measured between v1 and v2 (p<.0001) and between v1 and v3 (p<.0001). A significant positive effect of loading on delta BM was observed in the distal peri-implant marrow 500 Region of Interest already 2 weeks after loading (p=.01) and was significantly larger (11%) in series 1 compared with series 2 (p=.006) and 3 (p=.016). Within the constraints of constant loading time and strain rate, the effect of early implant loading on the peri-implant bone is strongly dependent on strain and frequency. This cortical bone model has shown to be most sensitive for high force loading at low frequency. © 2011 Wiley Periodicals, Inc.

Crack Closure and Fatigue Crack Growth in 2219-T851 Aluminum Alloy

DTIC Science & Technology

1976-08-01

assumes the length of the crack perimeter to remain es - ’I sentially constant. At the maximum load, the crack is ap- proximately parabolic (or ellipical...for center cracked j specimens) in shape. With unloading, the parabola (or el- lipse) is collapsed. The resulting change in shape produces an apparent...reloading process, the electrical potential remained es - j sentially constant initially and was less than that at the corresponding load during unloading

Calculation of the aerodynamic loading of swept and unswept flexible wings of arbitrary stiffness

NASA Technical Reports Server (NTRS)

Diederich, Franklin W

1950-01-01

A method is presented for calculating the aerodynamic loading, the divergence speed, and certain stability derivatives of swept and unswept wings and tail surfaces of arbitrary stiffness. Provision is made for using either stiffness curves and root rotation constants or structural influence coefficients in the analysis. Computing forms, tables of numerical constants required in the analysis, and an illustrative example are included to facilitate calculations by means of the method.

Susceptibility of experimental faults to pore pressure increase: insights from load-controlled experiments on calcite-bearing rocks

NASA Astrophysics Data System (ADS)

Spagnuolo, Elena; Violay, Marie; Nielsen, Stefan; Cornelio, Chiara; Di Toro, Giulio

2017-04-01

Fluid pressure has been indicated as a major factor controlling natural (e.g., L'Aquila, Italy, 2009 Mw 6.3) and induced seismicity (e.g., Wilzetta, Oklahoma, 2011 Mw 5.7). Terzaghi's principle states that the effective normal stress is linearly reduced by a pore pressure (Pf) increase σeff=σn(1 - αPf), where the effective stress parameter α, may be related to the fraction of the fault area that is flooded. A value of α =1 is often used by default, with Pf shifting the Mohr circle towards lower normal effective stresses and anticipating failure on pre-existing faults. However, within a complex fault core of inhomogeneous permeability, α may vary in a yet poorly understood way. To shed light on this problem, we conducted experiments on calcite-bearing rock samples (Carrara marble) at room humidity conditions and in the presence of pore fluids (drained conditions) using a rotary apparatus (SHIVA). A pre-cut fault is loaded by constant shear stress τ under constant normal stress σn=15 MPa until a target value corresponding roughly to the 80 % of the frictional fault strength. The pore pressure Pf is then raised with regular pressure and time steps to induce fault instability. Assuming α=1 and a threshold for instability τp_eff=μp σeff, the experiments reveal that an increase of Pf does not necessarily induce an instability even when the effective strength threshold is largely surpassed (e.g., τp_eff=1.3 μpσeff). This result may indicate that the Pf increase did not instantly diffuse throughout the slip zone, but took a finite time to equilibrate with the external imposed pressure increase due to finite permeability. Under our experimental conditions, a significant departure from α=1 is observed provided that the Pf step is shorter than about < 20s. We interpret this delay as indicative of the diffusion time (td), which is related to fluid penetration length l by l = √ κtd-, where κ is the hydraulic diffusivity on the fault plane. We show that a simple cubic law relates td to hydraulic aperture, pore pressure gradient and injection rate. We redefine α as the ratio between the fluid penetration length and sample dimension L resulting in α = min(√ktd,L) L. Under several pore pressure loading rates this relation yields an approximate hydraulic diffusivity κ ˜10-8 m2 s-1 which is compatible, for example, with a low porosity shale. Our results highlight that a high injection flow rate in fault plane do not necessarily induce seismogenic fault slip: a critical pore penetration length or fluid patch size is necessary to trigger fault instability.

Acoustic and Electrical Signal Emission recordings when marble specimens are subjected to compressional mechanical stress

NASA Astrophysics Data System (ADS)

Triantis, Dimos; Stavrakas, Ilias; Hloupis, George; Ninos, Konstantinos; Vallianatos, Filippos

2013-04-01

The detection of Acoustic Emissions (AE) and Electrical Signals (ES) has been proved as a valuable experimental method to characterize the mechanical status of marble specimens when subjected to mechanical stress. In this work, marble specimens with dimensions 10cm x 4cm x 4cm where subjected to sequential loading cycles. The maximum stress of each loading was near the vicinity of fracture and was maintained for a relatively long time (th=200s). Concurrently to the mechanical tests, AE and ES were recorded. Specifically, two AE sensors and five ES sensors were installed on the surface of the specimens and the detected emissions were stored on a PC. The recordings show that AE and ES provide information regarding the damage spreading and location in the bulk of the specimen. Specifically, when the mechanical stress was maintained constant at the high stress value during each loading cycle the cumulative number of the AE hits become gradually less reaching a minimum after the first three loading cycles, indicating the existence of the Kaiser effect. During the eighth loading cycle the AE hits show a significant increase that became maximum at the ninth cycle before where failure occured. A similar behavior was observed for the cumulative energy. A b-value analysis was conducted following both Aki's and Gutenberg-Richter relations on the amplitudes of the AE hits. The b-values were found to increase during the three first loading cycles while consequently they were practically constant until reaching the two final loading cycles where they became gradually lower. The ES significantly increases during the stress increase of each cycle and gradually restores at a background level when the applied stress is maintained constant near the vicinity of fracture. It was observed that the background restoration level becomes gradually higher during the first four loading cycles. Consequently, during the next three loading cycles the background level is maintained practically constant. During the two final loading cycles the background restoration level significantly increases indicating the upcoming fracture. Acknowledgments. This work was supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive statistical physics - Application to the geodynamic system of the Hellenic Arc. SEISMO FEAR HELLARC".

14 CFR 23.321 - General.

Code of Federal Regulations, 2010 CFR

2010-01-01

... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Flight Loads § 23.321 General. (a) Flight load factors represent the ratio of the aerodynamic force component (acting normal to... distribution of disposable load within the operating limitations specified in §§ 23.1583 through 23.1589. (c...

Gaussian step-pressure loading of rigid viscoplastic plates. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hayduk, R. J.; Durling, B. J.

1978-01-01

The response of a thin, rigid viscoplastic plate subjected to a spatially axisymmetric Gaussian step pressure impulse loading was studied analytically. A Gaussian pressure distribution in excess of the collapse load was applied to the plate, held constant for a length of time, and then suddenly removed. The plate deforms with monotonically increasing deflections until the dynamic energy is completely dissipated in plastic work. The simply supported plate of uniform thickness obeys the von Mises yield criterion and a generalized constitutive equation for rigid viscoplastic materials. For the small deflection bending response of the plate, the governing system of equations is essentially nonlinear. Transverse shear stress is neglected in the yield condition and rotary inertia in the equations of dynamic equilibrium. A proportional loading technique, known to give excellent approximations of the exact solution for the uniform load case, was used to linearize the problem and to obtain the analytical solutions in the form of eigenvalue expansions. The effects of load concentration, of an order of magnitude change in the viscosity of the plate material, and of load duration were examined while holding the total impulse constant.

Tribology study on TiB2+WSi2 composite against WC

NASA Astrophysics Data System (ADS)

Murthy, T. S. R. Ch.; Basha, M. M.; Sonber, J. K.; Singh, K.; Raju, K.; Sairam, K.; Nagaraj, A.; Majumdar, S.; Rao, G. V. S. Nageswara; Kain, Vivekanand

2018-04-01

Titanium diboride (TiB2) is one of the potential material for green energy applications such as neutron absorber in high temperature/advanced nuclear reactors, receiver materials for second generation concentrated solar power. We developed the process flow sheet for synthesis and consolidation of various series of TiB2 based materials in our laboratory. Amongst these, TiB2+WSi2 exhibited better sinterability and oxidation resistance properties. In the present work, tribology properties of TiB2+2.5%WSi2 composite was studied against WC-Co ball using different normal loads (5, 10 and 20 N) and frequencies (10, 15 Hz) under dry condition. Coefficient of friction (COF) and wear rate was measured at all test conditions. Wear mechanism was analyzed by microstructural characterization. It was found that COF is decreased from 0.46 to 0.36 with increasing load (5 to 20 N) at 15 Hz frequency; whereas at 10 Hz frequency COF is measured a constant average value of 0.49. The specific wear rate measured was minimum at 5 N load and 15 Hz frequency combination and was found to be 2.84×10-6 mm3/N m. The wear mechanisms identified during reciprocative sliding wear of composite were abrasion and surface tribo-oxidative reactions with delamination from tribo-zone.

Evaluation of a Multi-Axial, Temperature, and Time Dependent (MATT) Failure Model

NASA Technical Reports Server (NTRS)

Richardson, D. E.; Anderson, G. L.; Macon, D. J.; Rudolphi, Michael (Technical Monitor)

2002-01-01

To obtain a better understanding the response of the structural adhesives used in the Space Shuttle's Reusable Solid Rocket Motor (RSRM) nozzle, an extensive effort has been conducted to characterize in detail the failure properties of these adhesives. This effort involved the development of a failure model that includes the effects of multi-axial loading, temperature, and time. An understanding of the effects of these parameters on the failure of the adhesive is crucial to the understanding and prediction of the safety of the RSRM nozzle. This paper documents the use of this newly developed multi-axial, temperature, and time (MATT) dependent failure model for modeling failure for the adhesives TIGA 321, EA913NA, and EA946. The development of the mathematical failure model using constant load rate normal and shear test data is presented. Verification of the accuracy of the failure model is shown through comparisons between predictions and measured creep and multi-axial failure data. The verification indicates that the failure model performs well for a wide range of conditions (loading, temperature, and time) for the three adhesives. The failure criterion is shown to be accurate through the glass transition for the adhesive EA946. Though this failure model has been developed and evaluated with adhesives, the concepts are applicable for other isotropic materials.

A comparison of constant-load and constant-deflection stress-corrosion tests on precracked DCB specimens. [Double Cantilever Beam

NASA Technical Reports Server (NTRS)

Dorward, R. C.; Hasse, K. R.

1978-01-01

A comparison is made between measurements of stress-corrosion crack propagation made by a constant-load procedure and by a constant-deflection procedure. Precracked double cantilever beam specimens from 7075 aluminum alloy plate were used. The specimens were oriented in such a way that cracking would begin in the short-transverse plane and would propagate in the rolling direction. The specimens were subjected to a buffered salt-chromate solution and a 3.6% synthetic sea salt solution. The measurements were made optically with a binocular microscope. Stress intensities and crack lengths were calculated and crack velocities were obtained. Velocity was plotted against the average calculated stress intensity. Good agreement between the two methods was found for the salt-chromate solution, although some descrepancies were noted for the artificial sea salt solution.

Variability of Bed Load Transport During Six Summers of Continuous Measurements in Two Austrian Mountain Streams (Fischbach and Ruetz)

NASA Astrophysics Data System (ADS)

Rickenmann, Dieter

2018-01-01

Previous measurements of bed load transport in gravel bed streams revealed a large temporal and spatial variability of bed load transport rates. Using an impact plate geophone system, continuous bed load transport measurements were made during 6 years in two mountain streams in Austria. The two streams have a snow-melt and glacier-melt dominated hydrologic regime resulting in frequent transport activity during the summer half year. Periods of days to weeks were identified which are associated with approximately constant Shields values that indicate quasi-stable bed conditions. Between these stable periods, the position of the bed load transport function varied while its steepness remained approximately constant. For integration time scales of several hours to 1 day, the fluctuations in bed load transport decreased and the correlation between bed load transport and water discharge increased. For integration times of about 70-100 days, bed load transport is determined by discharge or shear stress to within a factor of about 2, relative to the 6 year mean level. Bed load texture increased with increasing mean flow strength and mean transport intensity. Weak and predominantly clockwise daily hysteresis of bed load transport was found for the first half of the summer period.

Effect of adhesive interleaving and discontinuous plies on failure of composite laminates subject to transverse normal loads

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

1989-01-01

Results of a series of tests to determine the effects of adhesive interleaving and discontinuous plies (plies with end-to-end gaps) on the displacements, failure loads and failure modes of graphite-epoxy laminates subjected to transverse normal loads are presented. Adhesive interleaving can be used to contain local damage within a group of plies, i.e., to arrest crack propagation on the interlaminate level, and it can increase the amount of normal displacement the laminate can withstand before failure. However, the addition of adhesive interleaving to a laminate does not significantly increase its load carrying capability. A few discontinuous plies in a laminate can reduce the normal displacement and load at failure by 10 to 40 percent compared to a laminate with no discontinuous plies, but the presence of the ply discontinuities does not generally change the failure location or the failure mode of the laminate.

Gearbox Reliability Collaborative Investigation of Gearbox Motion and High-Speed-Shaft Loads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keller, Jon; Guo, Yi; Sethuraman, Latha

2016-03-18

This paper extends a model-to-test validation effort to examine the effect of different constant rotor torque and moment conditions and intentional generator misalignment on the gearbox motion and high-speed-shaft loads. Fully validating gearbox motion and high-speed-shaft loads across a range of test conditions is a critical precursor to examining the bearing loads, as the gearbox motion and high-speed-shaft loads are the drivers of these bearing loads.

Creep Life Prediction of Ceramic Components Using the Finite Element Based Integrated Design Program (CARES/Creep)

NASA Technical Reports Server (NTRS)

Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

1997-01-01

The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. Such long life requirements necessitate subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this work is to present a design methodology for predicting the lifetimes of structural components subjected to multiaxial creep loading. This methodology utilizes commercially available finite element packages and takes into account the time varying creep stress distributions (stress relaxation). In this methodology, the creep life of a component is divided into short time steps, during which, the stress and strain distributions are assumed constant. The damage, D, is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. For components subjected to predominantly tensile loading, failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity.

Overload and Underload Effects on the Fatigue Crack Growth Behavior of the 2024-T3 Aluminum Alloy

NASA Technical Reports Server (NTRS)

Dawicke, David S.

1997-01-01

Fatigue crack growth tests were conducted on 0.09 inch thick, 3.0 inch wide middle-crack tension specimens cut from sheets of 2024-T3 aluminum alloy. The tests were conducted using a load sequence that consisted of a single block of 2,500 cycles of constant amplitude loading followed by an overload/underload combination. The largest fatigue crack growth life occurred for the tests with the overload stress equal to 2 times the constant amplitude stress and the underload stress equal to the constant amplitude minimum stress. For the tests with compressive underloads, the fatigue crack growth life decreased with increasing compressive underload stress.

Results of the second Round Robin on opening-load measurement conducted by ASTM Task Group E24.04.04 on crack closure measurement and analysis

NASA Technical Reports Server (NTRS)

Phillips, E. P.

1993-01-01

A second experimental Round Robin on the measurement of the crack opening load in fatigue crack growth tests has been completed by the ASTM Task Group E24.04.04 on Crack Closure Measurement and Analysis. Fourteen laboratories participated in the testing of aluminum alloy compact tension specimens. Opening-load measurements were made at three crack lengths during constant Delta K, constant stress ratio tests by most of the participants. Four participants made opening-load measurements during threshold tests. All opening-load measurements were based on the analysis of specimens compliance behavior, where the displacement/strain was measured either at the crack mouth or the mid-height back face location. The Round Robin data were analyzed for opening load using two non-subjective analysis methods: the compliance offset and the correlation coefficient methods. The scatter in the opening load results was significantly reduced when some of the results were excluded from the analysis population based on an accept/reject criterion for raw data quality. The compliance offset and correlation coefficient opening load analysis methods produced similar results for data populations that had been screened to eliminate poor quality data.

Noise effects on the health status in a dynamic failure model for living organisms

NASA Astrophysics Data System (ADS)

Kang, H.; Jo, J.; Choi, M. Y.; Choi, J.; Yoon, B.-G.

2007-03-01

We study internal and external noise effects on the healthy-unhealthy transition and related phenomena in a dynamic failure model for living organisms. It is found that internal noise makes the system weaker, leading to breakdown under smaller stress. The discontinuous healthy-unhealthy transition in a system with global load sharing below a critical point is naturally explained in terms of the bistability for the health status. External noise present in constant stress gives similar results; further, it induces resonance in response to periodic stress, regardless of load transfer. In the case of local load sharing, such periodic stress is revealed more hazardous than the constant stress.

Space Shuttle astrodynamical constants

NASA Technical Reports Server (NTRS)

Cockrell, B. F.; Williamson, B.

1978-01-01

Basic space shuttle astrodynamic constants are reported for use in mission planning and construction of ground and onboard software input loads. The data included here are provided to facilitate the use of consistent numerical values throughout the project.

Apparatus for measurement of acoustic wave propagation under uniaxial loading with application to measurement of third-order elastic constants of piezoelectric single crystals.

PubMed

Zhang, Haifeng; Kosinski, J A; Karim, Md Afzalul

2013-05-01

We describe an apparatus for the measurement of acoustic wave propagation under uniaxial loading featuring a special mechanism designed to assure a uniform mechanical load on a cube-shaped sample of piezoelectric material. We demonstrate the utility of the apparatus by determining the effects of stresses on acoustic wave speed, which forms a foundation for the final determination of the third-order elastic constants of langasite and langatate single crystals. The transit time method is used to determine changes in acoustic wave velocity as the loading is varied. In order to minimize error and improve the accuracy of the wave speed measurements, the cross correlation method is used to determine the small changes in the time of flight. Typical experimental results are presented and discussed.

Failure Criterion For Isotropic Time Dependent Materials Which Accounts for Multi-Axial Loading

NASA Technical Reports Server (NTRS)

Richardson, D. E.; Anderson, G. L.; Macon, D. J.

2003-01-01

The Space Shuttle's Reusable Solid Rocket Motor (RSRM) nozzle program has recently conducted testing to characterize the effects of multi-axial loading, temperature and time on the failure characteristics of TIGA321, EA913NA, EA946 (three filled epoxy adhesives). From the test data a "Multi-Axial, Temperature, and Time Dependent" or MATT failure criterion was developed. It is shown that this criterion simplifies, for constant load and constant load rate conditions, into a form that can be easily used for stress analysis. Failure for TIGA321 and EA913NA are characterized below their glass transition temperature. Failure for EA946 is characterized for conditions that pass through its glass transition. The MATT failure criterion is shown to be accurate for a wide range of conditions for these adhesives.

46 CFR 112.30-3 - Normal source for emergency loads.

Code of Federal Regulations, 2012 CFR

2012-10-01

....30-3 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING EMERGENCY LIGHTING AND POWER SYSTEMS Emergency Systems Having an Automatically Connected Storage Battery as the Sole Emergency Power Source § 112.30-3 Normal source for emergency loads. (a) The normal source...

46 CFR 112.30-3 - Normal source for emergency loads.

Code of Federal Regulations, 2010 CFR

2010-10-01

....30-3 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING EMERGENCY LIGHTING AND POWER SYSTEMS Emergency Systems Having an Automatically Connected Storage Battery as the Sole Emergency Power Source § 112.30-3 Normal source for emergency loads. (a) The normal source...

46 CFR 112.30-3 - Normal source for emergency loads.

Code of Federal Regulations, 2013 CFR

2013-10-01

....30-3 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING EMERGENCY LIGHTING AND POWER SYSTEMS Emergency Systems Having an Automatically Connected Storage Battery as the Sole Emergency Power Source § 112.30-3 Normal source for emergency loads. (a) The normal source...

46 CFR 112.30-3 - Normal source for emergency loads.

Code of Federal Regulations, 2014 CFR

2014-10-01

....30-3 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING EMERGENCY LIGHTING AND POWER SYSTEMS Emergency Systems Having an Automatically Connected Storage Battery as the Sole Emergency Power Source § 112.30-3 Normal source for emergency loads. (a) The normal source...

46 CFR 112.30-3 - Normal source for emergency loads.

Code of Federal Regulations, 2011 CFR

2011-10-01

....30-3 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING EMERGENCY LIGHTING AND POWER SYSTEMS Emergency Systems Having an Automatically Connected Storage Battery as the Sole Emergency Power Source § 112.30-3 Normal source for emergency loads. (a) The normal source...

The role of ethylene in the development of constant-light injury of potato and tomato

NASA Technical Reports Server (NTRS)

Cushman, K. E.; Tibbitts, T. W.

1998-01-01

The role of ethylene in the development of constant-light injury of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) was investigated. In one study, silver thiosulfate (STS) was applied to the foliage of four potato cultivars growing under constant light. Leaf area and shoot dry mass of 'Kennebec' and 'Superior', cultivars normally injured by constant light, were greater (P < 0.05) than those of control plants given foliar applications of distilled water. Examination of STS-treated 'Kennebec' leaflets revealed significantly less injury (necrotic spotting and reduced starch content) than the water-treated controls. 'Norland' and 'Denali', cultivars tolerant of constant light, exhibited no differences in growth between treatments. In a second study, injury (necrotic spotting and reduced starch content) was induced in leaflets of 'Denali' when exposed to spray applications of 0.5 mmol L-1 ethephon or air containing 0.5 to 0.8 microL L-1 ethylene. In a third study, three genotypes of 'Ailsa Craig' tomato were grown under constant light. Leaves of the normal 'Ailsa Craig' exhibited epinasty, reduced chlorophyll concentration, and reduced starch content. Leaves of a mutant 'Ailsa Craig', containing the Never ripe mutation, did not exhibit epinasty but exhibited the same amount of reduced chlorophyll concentration and starch content as normal plants. Leaves of a transgenic 'Ailsa Craig', containing an antisense gene of 1-aminocyclopropane 1-carboxylate (ACC) oxidase, were epinastic, but chlorophyll concentration and starch content were greater than in leaves of normal and mutant plants. These results suggest that transgenic plants were more tolerant of constant light than the other genotypes. Evidence from these studies indicates that ethylene, combined with constant light, has an important role in the development of constant-light injury.

DIVWAG Model Documentation. Volume II. Programmer/Analyst Manual. Part 4.

DTIC Science & Technology

1976-07-01

Model Constant Data Deck Structure . .. .... IV-13-A-40 Appendix B. Movement Model Program Descriptions . .. .. . .IV-13-B-1 1. Introduction...Data ................ IV-15-A-17 11. Airmobile Constant Data Deck Structure .. ...... .. IV-15-A-30 Appendix B. Airmobile Model Program Descriptions...Make no changes. 12. AIRMOBILE CONSTANT DATA DECK STRUCTURE . The deck structure required by the Airmobile Model constant data load program and the data

Analyses of Fatigue and Fatigue-Crack Growth under Constant- and Variable-Amplitude Loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1999-01-01

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily crack growth from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using small-crack theory under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta K(sub eff)) under constant-amplitude loading. Modifications to the delta K(sub eff)-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

NASA Technical Reports Server (NTRS)

Raj, S. V.; Noebe, R. D.

2013-01-01

This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

Aeroelastic deformation of a perforated strip

NASA Astrophysics Data System (ADS)

Guttag, M.; Karimi, H. H.; Falcón, C.; Reis, P. M.

2018-01-01

We perform a combined experimental and numerical investigation into the static deformation of perforated elastic strips under uniform aerodynamic loading at high-Reynolds-number conditions. The static shape of the porous strips, clamped either horizontally or vertically, is quantified as they are deformed by wind loading, induced by a horizontal flow. The experimental profiles are compared to numerical simulations using a reduced model that takes into account the normal drag force on the deformed surface. For both configurations (vertical and horizontal clamping), we compute the drag coefficient of the strip, by fitting the experimental data to the model, and find that it decreases as a function of porosity. Surprisingly, we find that, for every value of porosity, the drag coefficients for the horizontal configuration are larger than those of the vertical configuration. For all data in both configurations, with the exception of the continuous strip clamped vertically, a linear relation is found between the porosity and drag. Making use of this linearity, we can rescale the drag coefficient in a way that it becomes constant as a function of the Cauchy number, which relates the force due to fluid loading on the elastic strip to its bending rigidity, independently of the material properties and porosity of the strip and the flow speed. Our findings on flexible strips are contrasted to previous work on rigid perforated plates. These results highlight some open questions regarding the usage of reduced models to describe the deformation of flexible structures subjected to aerodynamic loading.

Vibration analysis of the maglev guideway with the moving load

NASA Astrophysics Data System (ADS)

Wang, H. P.; Li, J.; Zhang, K.

2007-09-01

The response of the guideway induced by moving maglev vehicle is investigated in this paper. The maglev vehicle is simplified as evenly distributed force acting on the guideway at constant speed. According to the experimental line, the guideway structure of rail-sleeper-bridge is simplified as Bernoulli-Euler (B-E) beam—evenly distributed spring—simply supported B-E beam structure; thus, double deck model of the maglev guideway is constructed which can more accurately reflect the dynamic characteristic of the experimental line. The natural frequency and mode are deduced based on the theoretical model. The relationship between structural parameters and natural frequency are exploited by employing the numerical calculation method. The way to suppress the vehicle-guideway interaction by regulating the structural parameter is also discussed here. Using the normal coordinate transformation method, the coupled differential equations of motion of the maglev guideway are converted into a set of uncoupled equations. The closed-form solutions for the response of the guideway subjecting the moving load are derived. It is noted that the moving load would not induce the vehicle-guideway interaction oscillation. The analysis of the guideway impact factor implies that at some position of the guideway, the deflection may decrease with the increase of the speed of the load; several extreme value of the guideway displacement will appear induced by different speeds, with different acting place, the speeds are different either. The final numerical simulation verifies these conclusions.

Effect of Load Rate on Ultimate Tensile Strength of Ceramic Matrix Composites at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2001-01-01

The strengths of three continuous fiber-reinforced ceramic composites, including SiC/CAS-II, SiC/MAS-5 and SiC/SiC, were determined as a function of test rate in air at 1100 to 1200 C. All three composite materials exhibited a strong dependency of strength on test rate, similar to the behavior observed in many advanced monolithic ceramics at elevated temperatures. The application of the preloading technique as well as the prediction of life from one loading configuration (constant stress-rate) to another (constant stress loading) suggested that the overall macroscopic failure mechanism of the composites would be the one governed by a power-law type of damage evolution/accumulation, analogous to slow crack growth commonly observed in advanced monolithic ceramics. It was further found that constant stress-rate testing could be used as an alternative to life prediction test methodology even for composite materials, at least for short range of lifetimes and when ultimate strength is used as the failure criterion.

Influence of inspired oxygen concentration on the dynamics of the exercise hyperpnoea in man.

PubMed Central

Griffiths, T L; Henson, L C; Whipp, B J

1986-01-01

In order to determine the role of the carotid bodies on the ventilatory control characteristics during the non-steady-state phase of exercise in man, six normal males performed cycle ergometry with four repetitions of a 6 min, constant-load work bout at inspired O2 fractions (FI,O2) of 0.12, 0.15, 0.21, 0.30 and 1.00. Each test began with unloaded pedalling; this was followed by a constant load which was 90% of the subject's anaerobic threshold at FI,O2 = 0.12. Ventilation (VE), CO2 output (VCO2) and O2 uptake (VO2) were determined breath-by-breath during the test and the time constants of response (tau VE, tau VCO2 and tau VO2) were established by least-squares techniques, following interpolation (1 s), temporal alignment and averaging of the four responses. In each subject, tau VE and tau VCO2 increased as functions of increasing FI,O2, and were inverse functions of the proportional contribution to VE of peripheral chemoreceptor drive (as estimated from hyperoxic-transition or 'Dejours' tests). tau VE averaged 40 s at FI,O2 = 0.12 and 112 s at FI,O2 = 1.00, each response being well fitted by a single exponential. However, tau VO2 was not significantly affected by the alterations in FI,O2. Although there was no discernible peripheral chemosensitivity at FI,O2 = 0.30 or 1.00, the tau VE increased appreciably between these inspirates. We therefore conclude that the peripheral chemoreceptors are important, but not exclusive determinants of the exponential response characteristics during the non-steady-state phase of the exercise hyperpnoea in man. This supports the contention of a component of the control being humorally mediated even during moderate exercise. PMID:3612567

Activation energy of the low-load NaCl transition from nanoindentation loading curves.

PubMed

Kaupp, Gerd

2014-01-01

Access to activation energies E(a) of phase transitions is opened by unprecedented analyses of temperature dependent nanoindentation loading curves. It is based on kinks in linearized loading curves, with additional support by coincidence of kink and electrical conductivity of silicon loading curves. Physical properties of B1, B2, NaCl and further phases are discussed. The normalized low-load transition energy of NaCl (Wtrans/µN) increases with temperature and slightly decreases with load. Its semi-logarithmic plot versus T obtains activation energy E(a)/µN for calculation of the transition work for all interesting temperatures and pressures. Arrhenius-type activation energy (kJ/mol) is unavailable for indentation phase transitions. The E(a) per load normalization proves insensitive to creep-on-load, which excludes normalization to depth or volume for large temperature ranges. Such phase transition E(a)/µN is unprecedented material's property and will be of practical importance for the compatibility of composite materials under impact and further shearing interactions at elevated temperatures. © 2014 Wiley Periodicals, Inc.

Suppression of friction by mechanical vibrations.

PubMed

Capozza, Rosario; Vanossi, Andrea; Vezzani, Alessandro; Zapperi, Stefano

2009-08-21

Mechanical vibrations are known to affect frictional sliding and the associated stick-slip patterns causing sometimes a drastic reduction of the friction force. This issue is relevant for applications in nanotribology and to understand earthquake triggering by small dynamic perturbations. We study the dynamics of repulsive particles confined between a horizontally driven top plate and a vertically oscillating bottom plate. Our numerical results show a suppression of the high dissipative stick-slip regime in a well-defined range of frequencies that depends on the vibrating amplitude, the normal applied load, the system inertia and the damping constant. We propose a theoretical explanation of the numerical results and derive a phase diagram indicating the region of parameter space where friction is suppressed. Our results allow to define better strategies for the mechanical control of friction.

Characterization of the electrical output of flat-plate photovoltaic arrays

NASA Technical Reports Server (NTRS)

Gonzalez, C. C.; Hill, G. M.; Ross, R. G., Jr.

1982-01-01

The electric output of flat-plate photovoltaic arrays changes constantly, due primarily to changes in cell temperature and irradiance level. As a result, array loads such as direct-current to alternating-current power conditioners must be able to accommodate widely varying input levels, while maintaining operation at or near the array maximum power point.The results of an extensive computer simulation study that was used to define the parameters necessary for the systematic design of array/power-conditioner interfaces are presented as normalized ratios of power-conditioner parameters to array parameters, to make the results universally applicable to a wide variety of system sizes, sites, and operating modes. The advantages of maximum power tracking and a technique for computing average annual power-conditioner efficiency are discussed.

Thermoregulatory effects of caffeine ingestion during rest and exercise in men

NASA Technical Reports Server (NTRS)

Dunagan, Nancy; Greenleaf, John E.; Cisar, Craig J.

1994-01-01

Body temperatures and thermoregulatory responses were measured at rest and during submaximal exercise under normal ambient conditions in 11 aerobically-conditioned men (age = 29.2 +/- 6.2 yr, VO2(max) = 3.73 +/- 0.46 min(sup -1), relative body fat = 12.3 +/- 3.7 percent, mean +/- SD) with (CT) and without (NCT) the ingestion of 10 mg of caffeine per kg of body weight. Oxygen uptake (VO2), heart rate (HR), and rectal (T(sub re)) and mean skin (T-bar(sub sk)) temperatures were recorded for 100 minutes starting one minute after ingestion of caffeine or a placebo. Data were collected throughout 30 minutes of rest (sitting) and the following 70 minutes of sitting leg ergometer exercise using the same constant load (1,088 +/- 153 kgm/min) in both NCT and CT. The load resulted in a mean relative exercise intensity equal to approximately 68 percent of VO2(sub max). Skin heat conductance (H(sub sk)) and sweat rate were calculated. Two-way analysis of covariance revealed no significant (P greater than 0.05) differences between NCT and CT in VO2, HR, T(sub re), T-bar(sub sk), or H(sub sk). A dependent t-test indicated no significant difference between NCT and CT in sweat rate. Thus, a high level of caffeine ingestion has no detrimental effects on body temperatures and thermoregulatory responses during moderately heavy exercise in normal ambient conditions.

Pupillary transient responses to within-task cognitive load variation.

PubMed

Wong, Hoe Kin; Epps, Julien

2016-12-01

Changes in physiological signals due to task evoked cognitive load have been reported extensively. However, pupil size based approaches for estimating cognitive load on a moment-to-moment basis are not as well understood as estimating cognitive load on a task-to-task basis, despite the appeal these approaches have for continuous load estimation. In particular, the pupillary transient response to instantaneous changes in induced load has not been experimentally quantified, and the within-task changes in pupil dilation have not been investigated in a manner that allows their consistency to be quantified with a view to biomedical system design. In this paper, a variation of the digit span task is developed which reliably induces rapid changes of cognitive load to generate task-evoked pupillary responses (TEPRs) associated with large, within-task load changes. Linear modelling and one-way ANOVA reveals that increasing the rate of cognitive loading, while keeping task demands constant, results in a steeper pupillary response. Instantaneous drops in cognitive load are shown to produce statistically significantly different transient pupillary responses relative to sustained load, and when characterised using an exponential decay response, the task-evoked pupillary response time constant is in the order of 1-5 s. Within-task test-retest analysis confirms the reliability of the moment-to-moment measurements. Based on these results, estimates of pupil diameter can be employed with considerably more confidence in moment-to-moment cognitive load estimation systems. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Synchronous motor with soft start element formed between the motor rotor and motor output shaft to successfully synchronize loads that have high inertia and/or high torque

DOE Office of Scientific and Technical Information (OSTI.GOV)

Umans, Stephen D; Nisley, Donald L; Melfi, Michael J

A line-start synchronous motor has a housing, a rotor shaft, and an output shaft. A soft-start coupling portion is operatively coupled to the output shaft and the rotor shaft. The soft-start coupling portion is configurable to enable the synchronous motor to obtain synchronous operation and to drive, at least near synchronous speed during normal steady state operation of the motor, a load having characteristics sufficient to prevent obtaining normal synchronous operation of the motor when the motor is operatively connected to the load in the absence of the soft-start coupling. The synchronous motor is sufficiently rated to obtain synchronous operationmore » and to drive, at least near synchronous speed during normal steady state operation of the motor, a load having characteristics sufficient to prevent obtaining normal synchronous operation of the motor when the motor is operatively connected to the load in the absence of the soft-start coupling.« less

Sarcomere length dependence of rat skinned cardiac myocyte mechanical properties: dependence on myosin heavy chain

PubMed Central

Korte, F Steven; McDonald, Kerry S

2007-01-01

The effects of sarcomere length (SL) on sarcomeric loaded shortening velocity, power output and rates of force development were examined in rat skinned cardiac myocytes that contained either α-myosin heavy chain (α-MyHC) or β-MyHC at 12 ± 1°C. When SL was decreased from 2.3 μm to 2.0 μm submaximal isometric force decreased ∼40% in both α-MyHC and β-MyHC myocytes while peak absolute power output decreased 55% in α-MyHC myocytes and 70% in β-MyHC myocytes. After normalization for the fall in force, peak power output decreased about twice as much in β-MyHC as in α-MyHC myocytes (41%versus 20%). To determine whether the fall in normalized power was due to the lower force levels, [Ca2+] was increased at short SL to match force at long SL. Surprisingly, this led to a 32% greater peak normalized power output at short SL compared to long SL in α-MyHC myocytes, whereas in β-MyHC myocytes peak normalized power output remained depressed at short SL. The role that interfilament spacing plays in determining SL dependence of power was tested by myocyte compression at short SL. Addition of 2% dextran at short SL decreased myocyte width and increased force to levels obtained at long SL, and increased peak normalized power output to values greater than at long SL in both α-MyHC and β-MyHC myocytes. The rate constant of force development (ktr) was also measured and was not different between long and short SL at the same [Ca2+] in α-MyHC myocytes but was greater at short SL in β-MyHC myocytes. At short SL with matched force by either dextran or [Ca2+], ktr was greater than at long SL in both α-MyHC and β-MyHC myocytes. Overall, these results are consistent with the idea that an intrinsic length component increases loaded crossbridge cycling rates at short SL and β-MyHC myocytes exhibit a greater sarcomere length dependence of power output. PMID:17347271

Buckling analysis for anisotropic laminated plates under combined inplane loads

NASA Technical Reports Server (NTRS)

Viswanathan, A. V.; Tamekuni, M.; Baker, L. L.

1974-01-01

The buckling analysis presented considers rectangular flat or curved general laminates subjected to combined inplane normal and shear loads. Linear theory is used in the analysis. All prebuckling deformations and any initial imperfections are ignored. The analysis method can be readily extended to longitudinally stiffened structures subjected to combined inplane normal and shear loads.

46 CFR 46.15-10 - Subdivision load lines.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 45 and a “diamond” shall be substituted for the “disk”. No “fresh water” line will be marked. [CGFR... located in line with the highest subdivision load line. (f) One fresh water line shall be marked. When a subdivision and a normal load line are combined, the normal fresh water line only shall be used unless the...

Aspects regarding the correlation between the physical-mechanical and tribological characteristics of composites materials reinforced with carbon fibers

NASA Astrophysics Data System (ADS)

Caliman, R.

2017-08-01

The purpose of this paper is to highlight a number of factors that influence the physical-mechanical and tribological characteristics of sintered composite materials. Such factors are grouped generally in two categories: technological parameters (pressure compacting, sintering temperature, sintering duration, heat treatment) and the receipt of sintered composite materials. In this paper is presented a program of experiments developed both in composite materials sintered polymer matrix (non-metallic) and in the metal matrix (eg., Al) which was prepared in advance a methodology original production and research for this particular type of materials. The experiments have focused development and testing of a number of 14 polymer composite and 5 composite sintered Al base, in both situations armed with carbon fiber in various forms. Tribological tests followed the establishment of the coefficient of friction and wear rate of the sliding speed at the constant values (v = 7.2 mm/s) and the normal load (N = 8 daN) and for different orientations of the fibers to the direction of sliding: normal (N type), parallel (P) and antiparallel-perpendicular (AP type).

QRC Evaluation of Materials and Processes.

DTIC Science & Technology

1982-10-01

Fatigue Crack Growth Data for Normal and "Soft" Aluminum 2024 - T351 65 27...Spectrum Fatigue Crack Growth Data for Normal and "Soft" Aluminum 7075-T651 66 28 Constant Amplitude FCGR Data for Normal and "Soft" Aluminum 2024 - T351 67...in Figure 29. The same trends observed in the spectrum fatigue tests are repeated in the S constant amplitude data: for aluminum 2024 - T351 , the

Measurement of Oil-Film Pressures in Journal Bearings under Constant and Variable Loads

NASA Technical Reports Server (NTRS)

Buske, A.; Rolli, W.

1949-01-01

In a study of journal bearings, the measurement of the oil-film strength produces some significant information. A new instrument is described by means of which the pressure of the oil film in bearings (under constant or alternating load) can be measured and recorded. With this device, the pressure distribution in the lubricating film of a bearing bushing was measured (under different operating conditions on a journal bearing) in the pulsator-bearing-testing machine. These tests are described and discussed in the present report.

Constant-load versus heart rate-targeted exercise - Responses of systolic intervals

NASA Technical Reports Server (NTRS)

Lance, V. Q.; Spodick, D. H.

1975-01-01

Various systolic intervals were measured prior to and during heart rate-targeted bicycle ergometer exercise. There were striking similarities within each matched exercise set for Q-Im, isovolumetric contraction time, preejection period (PEP), and PEP/left ventricular ejection time (LVET). LVET was significantly shorter for rate-targeted exercise. It is concluded that either constant-load or rate-targeted bicycle ergometry may be used with the choice of method determined by the purpose of the protocol, and that systolic intervals (except LVET) should not be much altered owing to the method chosen.

Assessing Chemical Retention Process Controls in Ponds

NASA Astrophysics Data System (ADS)

Torgersen, T.; Branco, B.; John, B.

2002-05-01

Small ponds are a ubiquitous component of the landscape and have earned a reputation as effective chemical retention devices. The most common characterization of pond chemical retention is the retention coefficient, Ri= ([Ci]inflow-[Ci] outflow)/[Ci]inflow. However, this parameter varies widely in one pond with time and among ponds. We have re-evaluated literature reported (Borden et al., 1998) monthly average retention coefficients for two ponds in North Carolina. Employing a simple first order model that includes water residence time, the first order process responsible for species removal have been separated from the water residence time over which it acts. Assuming the rate constant for species removal is constant within the pond (arguable at least), the annual average rate constant for species removal is generated. Using the annual mean rate constant for species removal and monthly water residence times results in a significantly enhanced predictive capability for Davis Pond during most months of the year. Predictive ability remains poor in Davis Pond during winter/unstratified periods when internal loading of P and N results in low to negative chemical retention. Predictive ability for Piedmont Pond (which has numerous negative chemical retention periods) is improved but not to the same extent as Davis Pond. In Davis Pond, the rate constant for sediment removal (each month) is faster than the rate constant for water and explains the good predictability for sediment retention. However, the removal rate constant for P and N is slower than the removal rate constant for sediment (longer water column residence time for P,N than for sediment). Thus sedimentation is not an overall control on nutrient retention. Additionally, the removal rate constant for P is slower than for TOC (TOC is not the dominate removal process for P) and N is removed slower than P (different in pond controls). For Piedmont Pond, sediment removal rate constants are slower than the removal rate constant for water indicating significant sediment resuspension episodes. It appears that these sediment resuspension events are aperiodic and control the loading and the chemical retention capability of Piedmont Pond for N,P,TOC. These calculated rate constants reflect the differing internal loading processes for each component and suggest means and mechanisms for the use of ponds in water quality management.

Constant-current control method of multi-function electromagnetic transmitter.

PubMed

Xue, Kaichang; Zhou, Fengdao; Wang, Shuang; Lin, Jun

2015-02-01

Based on the requirements of controlled source audio-frequency magnetotelluric, DC resistivity, and induced polarization, a constant-current control method is proposed. Using the required current waveforms in prospecting as a standard, the causes of current waveform distortion and current waveform distortion's effects on prospecting are analyzed. A cascaded topology is adopted to achieve 40 kW constant-current transmitter. The responsive speed and precision are analyzed. According to the power circuit of the transmitting system, the circuit structure of the pulse width modulation (PWM) constant-current controller is designed. After establishing the power circuit model of the transmitting system and the PWM constant-current controller model, analyzing the influence of ripple current, and designing an open-loop transfer function according to the amplitude-frequency characteristic curves, the parameters of the PWM constant-current controller are determined. The open-loop transfer function indicates that the loop gain is no less than 28 dB below 160 Hz, which assures the responsive speed of the transmitting system; the phase margin is 45°, which assures the stabilization of the transmitting system. Experimental results verify that the proposed constant-current control method can keep the control error below 4% and can effectively suppress load change caused by the capacitance of earth load.

Constant-current control method of multi-function electromagnetic transmitter

NASA Astrophysics Data System (ADS)

Xue, Kaichang; Zhou, Fengdao; Wang, Shuang; Lin, Jun

2015-02-01

Based on the requirements of controlled source audio-frequency magnetotelluric, DC resistivity, and induced polarization, a constant-current control method is proposed. Using the required current waveforms in prospecting as a standard, the causes of current waveform distortion and current waveform distortion's effects on prospecting are analyzed. A cascaded topology is adopted to achieve 40 kW constant-current transmitter. The responsive speed and precision are analyzed. According to the power circuit of the transmitting system, the circuit structure of the pulse width modulation (PWM) constant-current controller is designed. After establishing the power circuit model of the transmitting system and the PWM constant-current controller model, analyzing the influence of ripple current, and designing an open-loop transfer function according to the amplitude-frequency characteristic curves, the parameters of the PWM constant-current controller are determined. The open-loop transfer function indicates that the loop gain is no less than 28 dB below 160 Hz, which assures the responsive speed of the transmitting system; the phase margin is 45°, which assures the stabilization of the transmitting system. Experimental results verify that the proposed constant-current control method can keep the control error below 4% and can effectively suppress load change caused by the capacitance of earth load.

Strain rate effect on fault slip and rupture evolution: Insight from meter-scale rock friction experiments

NASA Astrophysics Data System (ADS)

Xu, Shiqing; Fukuyama, Eiichi; Yamashita, Futoshi; Mizoguchi, Kazuo; Takizawa, Shigeru; Kawakata, Hironori

2018-05-01

We conduct meter-scale rock friction experiments to study strain rate effect on fault slip and rupture evolution. Two rock samples made of Indian metagabbro, with a nominal contact dimension of 1.5 m long and 0.1 m wide, are juxtaposed and loaded in a direct shear configuration to simulate the fault motion. A series of experimental tests, under constant loading rates ranging from 0.01 mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates. Load cells and displacement transducers are utilized to examine the macroscopic fault behavior, while high-density arrays of strain gauges close to the fault are used to investigate the local fault behavior. The observations show that the macroscopic peak strength, strength drop, and the rate of strength drop can increase with increasing loading rate. At the local scale, the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location. In contrast, fast loading rates can promote very abrupt rupture nucleation and along-strike scatter of hypocenter locations. At a given propagation distance, rupture speed tends to increase with increasing loading rate. We propose that a strain-rate-dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period, which together with healing time controls the recovery of fault strength. In addition, a strain-rate-dependent weakening mechanism can be activated during the slip period, which together with strain energy selects the modes of fault slip and rupture propagation. The results help to understand the spectrum of fault slip and rock deformation modes in nature, and emphasize the role of heterogeneity in tuning fault behavior under different strain rates.

Load estimation from photoelastic fringe patterns under combined normal and shear forces

NASA Astrophysics Data System (ADS)

Dubey, V. N.; Grewal, G. S.

2009-08-01

Recently there has been some spurt of interests to use photoelastic materials for sensing applications. This has been successfully applied for designing a number of signal-based sensors, however, there have been limited efforts to design image-based sensors on photoelasticity which can have wider applications in term of actual loading and visualisation. The main difficulty in achieving this is the infinite loading conditions that may generate same image on the material surface. This, however, can be useful for known loading situations as this can provide dynamic and actual conditions of loading in real time. This is particularly useful for separating components of forces in and out of the loading plane. One such application is the separation of normal and shear forces acting on the plantar surface of foot of diabetic patients for predicting ulceration. In our earlier work we have used neural networks to extract normal force information from the fringe patterns using image intensity. This paper considers geometric and various other statistical parameters in addition to the image intensity to extract normal as well as shear force information from the fringe pattern in a controlled experimental environment. The results of neural network output with the above parameters and their combinations are compared and discussed. The aim is to generalise the technique for a range of loading conditions that can be exploited for whole-field load visualisation and sensing applications in biomedical field.

Infrared radiation of thin plastic films.

NASA Technical Reports Server (NTRS)

Tien, C. L.; Chan, C. K.; Cunnington, G. R.

1972-01-01

A combined analytical and experimental study is presented for infrared radiation characteristics of thin plastic films with and without a metal substrate. On the basis of the thin-film analysis, a simple analytical technique is developed for determining band-averaged optical constants of thin plastic films from spectral normal transmittance data for two different film thicknesses. Specifically, the band-averaged optical constants of polyethylene terephthalate and polyimide were obtained from transmittance measurements of films with thicknesses in the range of 0.25 to 3 mil. The spectral normal reflectance and total normal emittance of the film side of singly aluminized films are calculated by use of optical constants; the results compare favorably with measured values.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a "sandwich structure" as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50-55% of ultimate tensile strength). The dynamic modulus (E(⁎)) was found to stay almost constant at 47GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Crack Branching and Fracture Mirror Data of Glasses and Advanced Ceramics

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

1998-01-01

The fracture mirror and crack branching constants were determined from three glasses and nine advanced ceramics tested under various loading and specimen configurations in an attempt to use the constants as a data base for fractography. The ratios of fracture mirror or crack branching constant to fracture toughness were found to be approximately two for most ceramic materials tested. A demonstration of how to use the two constants as a tool for verifying stress measurements was presented for silicon nitride disk specimens subjected to high-temperature, constant stress-rate biaxial flexure testing.

Robotic application of a dynamic resultant force vector using real-time load-control: simulation of an ideal follower load on Cadaveric L4-L5 segments.

PubMed

Bennett, Charles R; Kelly, Brian P

2013-08-09

Standard in-vitro spine testing methods have focused on application of isolated and/or constant load components while the in-vivo spine is subject to multiple components that can be resolved into resultant dynamic load vectors. To advance towards more in-vivo like simulations the objective of the current study was to develop a methodology to apply robotically-controlled, non-zero, real-time dynamic resultant forces during flexion-extension on human lumbar motion segment units (MSU) with initial application towards simulation of an ideal follower load (FL) force vector. A proportional-integral-derivative (PID) controller with custom algorithms coordinated the motion of a Cartesian serial manipulator comprised of six axes each capable of position- or load-control. Six lumbar MSUs (L4-L5) were tested with continuously increasing sagittal plane bending to 8 Nm while force components were dynamically programmed to deliver a resultant 400 N FL that remained normal to the moving midline of the intervertebral disc. Mean absolute load-control tracking errors between commanded and experimental loads were computed. Global spinal ranges of motion and sagittal plane inter-body translations were compared to previously published values for non-robotic applications. Mean TEs for zero-commanded force and moment axes were 0.7 ± 0.4N and 0.03 ± 0.02 Nm, respectively. For non-zero force axes mean TEs were 0.8 ± 0.8 N, 1.3 ± 1.6 Nm, and 1.3 ± 1.6N for Fx, Fz, and the resolved ideal follower load vector FL(R), respectively. Mean extension and flexion ranges of motion were 2.6° ± 1.2° and 5.0° ± 1.7°, respectively. Relative vertebral body translations and rotations were very comparable to data collected with non-robotic systems in the literature. The robotically coordinated Cartesian load controlled testing system demonstrated robust real-time load-control that permitted application of a real-time dynamic non-zero load vector during flexion-extension. For single MSU investigations the methodology has potential to overcome conventional follower load limitations, most notably via application outside the sagittal plane. This methodology holds promise for future work aimed at reducing the gap between current in-vitro testing and in-vivo circumstances. Copyright © 2013 Elsevier Ltd. All rights reserved.

Accuracy of State-of-the-Art Actuator-Line Modeling for Wind Turbine Wakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jha, Pankaj; Churchfield, Matthew; Moriarty, Patrick

The current actuator line method (ALM) within an OpenFOAM computational fluid dynamics (CFD) solver was used to perform simulations of the NREL Phase VI rotor under rotating and parked conditions, two fixed-wing designs both with an elliptic spanwise loading, and the NREL 5-MW turbine. The objective of this work is to assess and improve the accuracy of the state-of-the-art ALM in predicting rotor blade loads, particularly by focusing on the method used to project the actuator forces onto the flow field as body forces. Results obtained for sectional normal and tangential force coefficients were compared to available experimental data andmore » to the in-house performance code XTurb-PSU. It was observed that the ALM results agree well with measured data and results obtained from XTurb-PSU except in the root and tip regions if a three-dimensional Gaussian of width, ε, constant along the blade span is used to project the actuator force onto the flow field. A new method is proposed where the Gaussian width, ε, varies along the blade span following an elliptic distribution. A general criterion is derived that applies to any planform shape. It is found that the new criterion for ε leads to improved prediction of blade tip loads for a variety of blade planforms and rotor conditions considered.« less

Optimization of doxorubicin loading for superabsorbent polymer microspheres: in vitro analysis.

PubMed

Liu, David M; Kos, Sebastian; Buczkowski, Andrzej; Kee, Stephen; Munk, Peter L; Klass, Darren; Wasan, Ellen

2012-04-01

This study was designed to establish the ability of super-absorbent polymer microspheres (SAP) to actively uptake doxorubicin and to establish the proof of principle of SAP's ability to phase transfer doxorubicin onto the polymer matrix and to elute into buffer with a loading method that optimizes physical handling and elution characteristics. Phase I: 50-100 μm SAP subject to various prehydration methods (normal saline 10 cc, hypertonic saline 4 cc, iodinated contrast 10 cc) or left in their dry state, and combined with 50 mg of clinical grade lyophilized doxorubicin reconstituted with various methods (normal saline 10 cc and 25 cc, sterile water 4 cc, iodinated contrast 5 cc) were placed in buffer and assessed based on loading, handling, and elution utilizing high-performance liquid chromatography (HPLC). Phase II: top two performing methods were subject to loading of doxorubicin (50, 75, 100 mg) in a single bolus (group A) or as a serial loading method (group B) followed by measurement of loading vs. time and elution vs. time. Phase I revealed the most effective loading mechanisms and easiest handling to be dry (group A) vs. normal saline prehydrated (group B) SAP with normal saline reconstituted doxorubicin (10 mg/mL) with loading efficiencies of 83.1% and 88.4%. Phase II results revealed unstable behavior of SAP with 100 mg of doxorubicin and similar loading/elution profiles of dry and prehydrated SAP, with superior handling characteristics of group B SAP at 50 and 75 mg. SAP demonstrates the ability to load and bulk phase transfer doxorubicin at 50 and 75 mg with ease of handling and optimal efficiency through dry loading of SAP.

Optimization of Doxorubicin Loading for Superabsorbent Polymer Microspheres: in vitro Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, David M., E-mail: dave.liu@vch.ca; Kos, Sebastian; Buczkowski, Andrzej

2012-04-15

Purpose: This study was designed to establish the ability of super-absorbent polymer microspheres (SAP) to actively uptake doxorubicin and to establish the proof of principle of SAP's ability to phase transfer doxorubicin onto the polymer matrix and to elute into buffer with a loading method that optimizes physical handling and elution characteristics. Methods: Phase I: 50-100 {mu}m SAP subject to various prehydration methods (normal saline 10 cc, hypertonic saline 4 cc, iodinated contrast 10 cc) or left in their dry state, and combined with 50 mg of clinical grade lyophilized doxorubicin reconstituted with various methods (normal saline 10 cc andmore » 25 cc, sterile water 4 cc, iodinated contrast 5 cc) were placed in buffer and assessed based on loading, handling, and elution utilizing high-performance liquid chromatography (HPLC). Phase II: top two performing methods were subject to loading of doxorubicin (50, 75, 100 mg) in a single bolus (group A) or as a serial loading method (group B) followed by measurement of loading vs. time and elution vs. time. Results: Phase I revealed the most effective loading mechanisms and easiest handling to be dry (group A) vs. normal saline prehydrated (group B) SAP with normal saline reconstituted doxorubicin (10 mg/mL) with loading efficiencies of 83.1% and 88.4%. Phase II results revealed unstable behavior of SAP with 100 mg of doxorubicin and similar loading/elution profiles of dry and prehydrated SAP, with superior handling characteristics of group B SAP at 50 and 75 mg. Conclusions: SAP demonstrates the ability to load and bulk phase transfer doxorubicin at 50 and 75 mg with ease of handling and optimal efficiency through dry loading of SAP.« less

The Dependence of the Spring Constant in the Linear Range on Spring Parameters

ERIC Educational Resources Information Center

Khotimah, Siti Nurul; Viridi, Sparisoma; Widayani; Khairurrijal

2011-01-01

In basic physics laboratories, springs are normally used to determine both spring constants and the Earth's gravitational acceleration. Students generally do not notice that the spring constant is not a universal constant, but depends on the spring parameters. This paper shows and verifies that the spring constant in the linear range is inversely…

The effect of a change in sleep-wakefulness timing, bright light and physical exercise interventions on 24-hour patterns of performance, mood and body temperature.

PubMed

Iskra-Golec, I; Fafrowicz, M; Marek, T; Costa, G; Folkard, S; Foret, J; Kundi, M; Smith, L

2001-12-01

Experiments consisting of baseline, bright light and physical exercise studies were carried out to compare the effect of a 9-hour delay in sleep-wakefulness timing, and the effects of bright light and physical exercise interventions on 24-hour patterns of performance, mood and body temperature were examined. Each study comprised a 24-hour constant routine at the beginning followed by 3 night shifts and 24-hour constant routine at the end. Performance on tasks differing in cognitive load, mood and body temperature was measured during each constant routine and the interventions were applied during the night shifts. The 24-hour pattern of alertness and performance on the tasks with low cognitive load in post-treatment conditions followed the change in sleep-wakefulness timing while more cognitively loaded tasks tended to show a reverse trend when compared to pre-treatment conditions. There was a phase delay around 4 hours in circadian rhythms of body temperature in post-treatment conditions.

Precision envelope detector and linear rectifier circuitry

DOEpatents

Davis, Thomas J.

1980-01-01

Disclosed is a method and apparatus for the precise linear rectification and envelope detection of oscillatory signals. The signal is applied to a voltage-to-current converter which supplies current to a constant current sink. The connection between the converter and the sink is also applied through a diode and an output load resistor to a ground connection. The connection is also connected to ground through a second diode of opposite polarity from the diode in series with the load resistor. Very small amplitude voltage signals applied to the converter will cause a small change in the output current of the converter, and the difference between the output current and the constant current sink will be applied either directly to ground through the single diode, or across the output load resistor, dependent upon the polarity. Disclosed also is a full-wave rectifier utilizing constant current sinks and voltage-to-current converters. Additionally, disclosed is a combination of the voltage-to-current converters with differential integrated circuit preamplifiers to boost the initial signal amplitude, and with low pass filtering applied so as to obtain a video or signal envelope output.

Oxygen uptake kinetics of constant-load work - Upright vs. supine exercise

NASA Technical Reports Server (NTRS)

Convertino, V. A.; Goldwater, D. J.; Sandler, H.

1984-01-01

Supine and upright positions were used in a comparitive study of the effects of constant load exercise on oxygen uptake (VO2), O2 deficit, steady-state VO2 and VO2 following recovery from constant load work. Ten male subjects (36-40 yr.) performed one submaximal exercise test in the supine and one test in the upright position consisting of 5 min rest and 5 min cycle ergometer exercise at 700 kg/min followed by ten minutes of recovery. It is found that the significant difference in VO2 kinetics during exercise in the upright compared to supine position resulted from changes in oxygen transport and utilization mechanisms rather than changes in mechanical efficiency. To the extent that data measured in the supine position can be used to estimate physiological responses to zero gravity, it is suggested that limitation of systemic O2 consumption may be the result of slow rates of oxygen uptake during transient periods of muscular work. Significant reductions in the rate of steady-state VO2 attainment at submaximal work intensities may produce an onset of muscle fatigue and exhaustion.

Research on Stabilization Properties of Inductive-Capacitive Transducers Based on Hybrid Electromagnetic Elements

NASA Astrophysics Data System (ADS)

Konesev, S. G.; Khazieva, R. T.; Kirllov, R. V.; Konev, A. A.

2017-01-01

Some electrical consumers (the charge system of storage capacitor, powerful pulse generators, electrothermal systems, gas-discharge lamps, electric ovens, plasma torches) require constant power consumption, while their resistance changes in the limited range. Current stabilization systems (CSS) with inductive-capacitive transducers (ICT) provide constant power, when the load resistance changes over a wide range and increaseы the efficiency of high-power loads’ power supplies. ICT elements are selected according to the maximum load, which leads to exceeding a predetermined value of capacity. The paper suggests carrying load power by the ICT based on multifunction integrated electromagnetic components (MIEC) to reduce the predetermined capacity of ICT elements and CSS weights and dimensions. The authors developed and patented ICT based on MIEC that reduces the CSS weights and dimensions by reducing components number with the possibility of device’s electric energy transformation and resonance frequency changing. An ICT mathematical model was produced. The model determines the width of the load stabilization range. Electromagnetic processes study model was built with the MIEC integral parameters (full inductance of the electrical lead, total capacity, current of electrical lead). It shows independence of the load current from the load resistance for different ways of MIEC connection.

Fracture toughness of boron/aluminum laminates with various proportions of 0 deg and plus or minus 45 deg

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.; Sova, J. A.

1980-01-01

The fracture toughness of boron/aluminum laminates was measured on sheet specimens containing central slits of various lengths that represent cracks. The specimens were loaded axially and had various widths. The sheets were made with five laminate orientation. Fracture toughness was calculated for each laminate orientation. Specimens began failing at the ends of the slit with what appeared to be tensile failures of fibers in the primary load carrying laminae. A general fracture toughness parameter independent of laminate orientation was derived on the basis of fiber failure in the principal load carrying laminae. The value of this parameter was proportional to the critical value of the stress intensity factor. The constant of proportionality depended only on the elastic constants of the laminates.

Strength degradation and lifetime prediction of dental zirconia ceramics under cyclic normal loading.

PubMed

Li, Wanzhong; Xu, Yingqiang; He, Huiming; Zhao, Haidan; Sun, Jian; Hou, Yue

2015-01-01

Clinical cases show that zirconia restoration could happen fracture by accident under overloading after using a period of time. The purpose of this study is to research mechanical behavior and predict lifetime of dental zirconia ceramics under cyclic normal contact loading with experiments. Cyclic normal contact loading test and three point bending test are carried on specimens made of two brands of dental zirconia ceramic to obtain flexure strength and damage degree after different number of loading cycles. By means of damage mechanics model, damage degree under different number of contact loading cycles are calculated according to flexure strength, and verified by SEM photographs of cross section morphology of zirconia ceramics specimen phenomenologically. Relation curve of damage degree and number of cycles is fitted by polynomial fitting, then the number of loading cycles can be concluded when the specimen is complete damage. Strength degradation of two brands dental zirconia ceramics are researched in vitro, and prediction method of contact fatigue lifetime is established.

Starvation effects on the hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

NASA Technical Reports Server (NTRS)

Ghosh, M. K.; Hamrock, B. J.; Brewe, D. E.

1986-01-01

The effect of inlet starvation on the hydrodynamic lubrication of lightly loaded rigid nonconformal contacts in combined rolling and normal motion is determined through a numerical solution of the Reynolds' equation for an isoviscous, incompressible lubricant. Starvation is effected by systematically reducing the fluid inlet level. The pressures are taken to be ambient at the inlet meniscus boundary and Reynolds' boundary condition is applied for film rupture in the exit region. Results are presented for the dynamic performance of the starved contacts in combined rolling and normal motion for both normal approach and separation. During normal approach the dynamic load ratio (i.e. ratio of dynamic to steady state load capacity) increases considerably with increase in the inlet starvation. The effect of starvation on the dynamic peak pressure ratio is relatively small. Further, it has been observed that with increasing starvation, film thickness effects become significant in the dynamic behavior of the nonconformal contacts. For significantly starved contacts the dynamic load ratio increases with increase in film thickness during normal approach and a similar reduction is observed during separation. A similar effect is noted for the dynamic peak pressure ratio.

Calculations of the Acceleration of Centrifugal Loading on Adherent Cells

NASA Astrophysics Data System (ADS)

Chen, Kang; Song, Yang; Liu, Qing; Zhang, Chunqiu

2017-07-01

Studies have shown that the morphology and function of living cells are greatly affected by the state of different high acceleration. Based on the centrifuge, we designed a centrifugal cell loading machine for the mechanical biology of cells under high acceleration loading. For the machine, the feasibility of the experiment was studied by means of constant acceleration or variable acceleration loading in the Petri dish fixture and/or culture flask. Here we analyzed the distribution of the acceleration of the cells with the change of position and size of the culturing device quantitatively. It is obtained that Petri dish fixture and/or culture flask can be used for constant acceleration loading by experiments; the centripetal acceleration of the adherent cells increases with the increase of the distance between the rotor center of the centrifuge and the fixture of the Petri dish and the size of the fixture. It achieves the idea that the general biology laboratory can conduct the study of mechanical biology at high acceleration. It also provides a basis for more accurate study of the law of high acceleration on mechanobiology of cells.

Surface Irregularity Factor as a Parameter to Evaluate the Fatigue Damage State of CFRP

PubMed Central

Zuluaga-Ramírez, Pablo; Frövel, Malte; Belenguer, Tomás; Salazar, Félix

2015-01-01

This work presents an optical non-contact technique to evaluate the fatigue damage state of CFRP structures measuring the irregularity factor of the surface. This factor includes information about surface topology and can be measured easily on field, by techniques such as optical perfilometers. The surface irregularity factor has been correlated with stiffness degradation, which is a well-accepted parameter for the evaluation of the fatigue damage state of composite materials. Constant amplitude fatigue loads (CAL) and realistic variable amplitude loads (VAL), representative of real in- flight conditions, have been applied to “dog bone” shaped tensile specimens. It has been shown that the measurement of the surface irregularity parameters can be applied to evaluate the damage state of a structure, and that it is independent of the type of fatigue load that has caused the damage. As a result, this measurement technique is applicable for a wide range of inspections of composite material structures, from pressurized tanks with constant amplitude loads, to variable amplitude loaded aeronautical structures such as wings and empennages, up to automotive and other industrial applications. PMID:28793655

[Comparative analysis of viral load by bDNA HCV RNA-2.0 and amplicor HCV monitor in patients with hepatitis C infection].

PubMed

Córdoba, J; Olaso, V; Molina, J M; López Viedma, B; Argüello, L; Ortiz, V; Esteban, R J; Garijo, R; Pastor, M; Gobernado, M

2000-01-01

Two standardized techniques, Quantiplex (bDNA-2.0) and Amplicor Monitor have been evaluated for the quantification of virus load of HCV with these objectives: a) determinate the relationship between virus load and genotype, and b) evaluate the virus load in serial serum samples and in patients with normal or slightly increased liver enzymes in an area with a high prevalence of genotype 1. A significant correlation of 0.7 (p < 0.0001) in virus load has been observed by both methods, but the virus load is smaller by Monitor than by Quantiplex and does not depend on genotype. The relationship Monitor/Quantiplex is smaller in patients with non-1 genotype than in patients with genotype 1a (p = 0.01) and 1b (p = 0.005). Virus characteristics are similar in patients with normal or slightly increased enzymes than in patients with high enzymes. Virus load by both methods is not related to the age, sex, know duration of the infection, transmission manner of the infection neither to the histologic activity index. The virus load not depends on genotype. The determination of virus load in a single serum sample adequately reflects the virus load are in several serum samples in patients with chronic HCV infection. The genotype and the virus load are similar in patients with normal enzymes than in patients with high enzymes.

17. VIEW SOUTHEAST OF 450 HP TURBINE IN BASEMENT OF ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

17. VIEW SOUTHEAST OF 450 HP TURBINE IN BASEMENT OF GRANITEVILLE MILL. THE MAIN BEARING OF THE TURBINE IS AT LEFT CENTER OF THE PHOTOGRAPH. A LOMBARD REGULATOR CAN BE SEEN AT THE LEFT CENTER REAR. THE LARGE HANDWHEEL AT THE LEFT CENTER IS GEARED TO A SECTIONAL GEAR AT THE CENTER OF THE PHOTOGRAPH AND IS USED TO MANUALLY OPEN THE GATES AND ALLOW WATER INTO THE TURBINE. THE SMALL PULLEY ON THE END OF THE MAIN SHAFT NORMALLY WOULD HAVE A BELT CONNECTING IT TO A PULLEY ON THE LOMBARD REGULATOR. THIS BELT TRANSMITTED TURBINE SPEED (RPM) TO THE LOMBARD WHICH WOULD OPEN OR CLOSE THE GATES TO KEEP TURBINE SPEED CONSTANT UNDER VARYING LOADS. THIS TURBINE WAS INSTALLED IN THE REFIT OF 1912. - Graniteville Mill, Marshall Street, Graniteville, Aiken County, SC

Dynamic Characteristics of The DSI-Type Constant-Flow Valves

NASA Astrophysics Data System (ADS)

Kang, Yuan; Hu, Sheng-Yan; Chou, Hsien-Chin; Lee, Hsing-Han

Constant flow valves have been presented in industrial applications or academic studies, which compensate recess pressures of a hydrostatic bearing to resist load fluctuating. The flow rate of constant-flow valves can be constant in spite of the pressure changes in recesses, however the design parameters must be specified. This paper analyzes the dynamic responses of DSI-type constant-flow valves that is designed as double pistons on both ends of a spool with single feedback of working pressure and regulating restriction at inlet. In this study the static analysis presents the specific relationships among design parameters for constant flow rate and the dynamic analyses give the variations around the constant flow rate as the working pressure fluctuates.

Cable load sensing device

DOEpatents

Beus, Michael J.; McCoy, William G.

1998-01-01

Apparatus for sensing the magnitude of a load on a cable as the cable is employed to support the load includes a beam structure clamped to the cable so that a length of the cable lies along the beam structure. A spacer associated with the beam structure forces a slight curvature in a portion of the length of cable under a cable "no-load" condition so that the portion of the length of cable is spaced from the beam structure to define a cable curved portion. A strain gauge circuit including strain gauges is secured to the beam structure by welding. As the cable is employed to support a load the load causes the cable curved portion to exert a force normal to the cable through the spacer and on the beam structure to deform the beam structure as the cable curved portion attempts to straighten under the load. As this deformation takes place, the resistance of the strain gauges is set to a value proportional to the magnitude of the normal strain on the beam structure during such deformation. The magnitude of the normal strain is manipulated in a control device to generate a value equal to the magnitude or weight of the load supported by the cable.

The Relation Between Collagen Fibril Kinematics and Mechanical Properties in the Mitral Valve Anterior Leaflet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao,J.; Yang, L.; Grashow, J.

2007-01-01

We have recently demonstrated that the mitral valve anterior leaflet (MVAL) exhibited minimal hysteresis, no strain rate sensitivity, stress relaxation but not creep (Grashow et al., 2006, Ann Biomed Eng., 34(2), pp. 315-325; Grashow et al., 2006, Ann Biomed. Eng., 34(10), pp. 1509-1518). However, the underlying structural basis for this unique quasi-elastic mechanical behavior is presently unknown. As collagen is the major structural component of the MVAL, we investigated the relation between collagen fibril kinematics (rotation and stretch) and tissue-level mechanical properties in the MVAL under biaxial loading using small angle X-ray scattering. A novel device was developed and utilizedmore » to perform simultaneous measurements of tissue level forces and strain under a planar biaxial loading state. Collagen fibril D-period strain ({epsilon}{sub D}) and the fibrillar angular distribution were measured under equibiaxial tension, creep, and stress relaxation to a peak tension of 90 N/m. Results indicated that, under equibiaxial tension, collagen fibril straining did not initiate until the end of the nonlinear region of the tissue-level stress-strain curve. At higher tissue tension levels, {epsilon}{sub D} increased linearly with increasing tension. Changes in the angular distribution of the collagen fibrils mainly occurred in the tissue toe region. Using {epsilon}{sub D}, the tangent modulus of collagen fibrils was estimated to be 95.5{+-}25.5 MPa, which was {approx}27 times higher than the tissue tensile tangent modulus of 3.58{+-}1.83 MPa. In creep tests performed at 90 N/m equibiaxial tension for 60 min, both tissue strain and D remained constant with no observable changes over the test length. In contrast, in stress relaxation tests performed for 90 min {epsilon}{sub D} was found to rapidly decrease in the first 10 min followed by a slower decay rate for the remainder of the test. Using a single exponential model, the time constant for the reduction in collagen fibril strain was 8.3 min, which was smaller than the tissue-level stress relaxation time constants of 22.0 and 16.9 min in the circumferential and radial directions, respectively. Moreover, there was no change in the fibril angular distribution under both creep and stress relaxation over the test period. Our results suggest that (1) the MVAL collagen fibrils do not exhibit intrinsic viscoelastic behavior, (2) tissue relaxation results from the removal of stress from the fibrils, possibly by a slipping mechanism modulated by noncollagenous components (e.g. proteoglycans), and (3) the lack of creep but the occurrence of stress relaxation suggests a 'load-locking' behavior under maintained loading conditions. These unique mechanical characteristics are likely necessary for normal valvular function.« less

Elastic-plastic analysis of a propagating crack under cyclic loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Armen, H., Jr.

1974-01-01

Development and application of a two-dimensional finite-element analysis to predict crack-closure and crack-opening stresses during specified histories of cyclic loading. An existing finite-element computer program which accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing boundary conditions - crack growth and intermittent contact of crack surfaces. This program was subsequently used to study the crack-closure behavior under constant-amplitude and simple block-program loading.

DIELECTRIC-LOADED WAVE-GUIDES

DOEpatents

Robertson-Shersby-Harvie, R.B.; Mullett, L.B.

1957-04-23

This patent presents a particular arrangement for delectric loading of a wave-guide carrying an electromagnetic wave in the E or TM mode of at least the second order, to reduce the power dissipated as the result of conduction loss in the wave-guide walls. To achieve this desirabie result, the effective dielectric constants in the radial direction of adjacent coaxial tubular regions bounded approximateiy by successive nodai surfaces within the electromagnetic field are of two different values alternating in the radial direction, the intermost and outermost regions being of the lower value, and the dielectric constants between nodes are uniform.

Thermal Management of a Nitrogen Cryogenic Loop Heat Pipe

NASA Astrophysics Data System (ADS)

Gully, Ph.; Yan, T.

2010-04-01

Efficient thermal links are needed to ease the distribution of the cold power in satellites. Loop heat pipes are widely used at room temperature as passive thermal links based on a two-phase flow generated by capillary forces. Transportation of the cold power at cryogenic temperatures requires a specific design. In addition to the main loop, the cryogenic loop heat pipe (CLHP) features a hot reservoir and a secondary loop with a cold reservoir and a secondary evaporator which allows the cool down and the thermal management of the thermal link in normal cold operation. We have studied the influence of a heated cold reservoir and investigated the effect of parasitic heat loads on the performance of a nitrogen CLHP at around 80 K. It is shown that heating of the cold reservoir with a small amount of power (0.1 W) allows controlling the system temperature difference, which can be kept constant at a very low level (1 K) regardless of the transferred cold power (0-10 W). Parasitic heat loads have a significant effect on the thermal resistance, and the power applied on the secondary evaporator has to be increased up to 4 W to get stable operation.

Predicted and experimental aerodynamic forces on the Darrieus rotor

NASA Astrophysics Data System (ADS)

Paraschivoiu, I.

1983-12-01

The present paper compares the aerodynamic loads predicted by a double-multiple-streamtube model with wind tunnel measurements for a straight-bladed Darrieus rotor. Thus the CARDAA computer code uses two constant-interference factors in the induced velocity for estimating the aerodynamic loads. This code has been improved by considering the variation in the upwind and downwind induced velocities as a function of the blade position, and, in this case, the CARDAAV code is used. The Boeing-Vertol dynamic-stall model is incorporated in both the CARDAA and CARDAAV codes, and a better approach is obtained. The transient normal- and tangential-force coefficients predicted with and without dynamic-stall effects are compared with wind tunnel data for one and two NACA 0018 straight-bladed rotors. The results are given for a rotor with a large solidity (chord-to-radius ratio of 0.20) at two tip-speed ratios (X = 1.5 and 3.0) and at a low Reynolds number of 3.8 x 10 to the 4th. The comparisons between experimental data and theoretical results show the CARDAAV predictions to be more accurate than those estimated by the CARDAA code.

Quantifying accessible sites and reactivity on titania–silica (photo)catalysts: Refining TOF calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eaton, Todd R.; Campos, Michael P.; Gray, Kimberly A.

2014-01-01

It can be difficult to determine the number of active atoms accessible to the fluid phase in mixed oxide catalysts, as required for obtaining true turnover frequencies (TOF). Here, we utilize the selective titration of surface Ti atoms with phenylphosphonic acid (PPA) on TiO 2–SiO 2 materials to estimate the number of reactant-accessible sites. TiO 2–SiO 2 composites were synthesized over a range of Ti loadings from grafting of titanocene dichloride (Cp 2TiCl 2) or tetraethoxy orthotitanate (TEOT) on SiO 2 and sol–gel co-hydrolysis of Si and Ti alkoxides. The materials were characterized by DRUV–vis, XRD, BET, and XANES. Despitemore » the significant morphological and electronic differences, materials prepared by Cp 2TiCl 2 and TEOT yielded a near-constant TOF of 0.14 h -1 (±0.04) across Ti loadings, for benzyl alcohol photooxidation, when normalizing rates by sites titrated by PPA. The fraction of Ti atoms titrated by PPA was strongly dependent on synthesis method and surface density. PPA titration and benzyl alcohol photooxidation may be useful measures of surface accessibility in other supported oxides.« less

Non-invasive endotracheal delivery of paclitaxel-loaded alginate microparticles.

PubMed

Alipour, Shohreh; Montaseri, Hashem; Khalili, Azadeh; Tafaghodi, Mohsen

2016-10-01

Aerosolized chemotherapeutics leads to higher, localized and continuous concentrations of active agents in lung tissue with lower side effects for other organs. The present study was performed on jugular vein cannulated rats which endothracheally received 4 mg/kg of free paclitaxel powder (Free-PTX), paclitaxel-loaded alginate microparticles (PTX-ALG-MPs) and i.v. paclitaxel (Anzatax(®)). Pharmacokinetic parameters for Free-PTX and PTX-ALG-MPs contain higher AUC, mean residence time (MRT),half-life and bioavailability, with lower elimination constant (ke). Statistical analysis showed that the amount of paclitaxel per gram of lung tissue after 0.5, 6 and 24 h after administration of Free-PTX was lower than PTX-ALG-MPs. Lung tissue AUC for Free-PTX was lower than PTX-ALG-MPs. According to the obvious advantages obtained, such as dose lowering and increasing paclitaxel residence time and half-life. It should be noted that cell cytotoxicity test on normal airway cell lines was not examined in this study but due to previous reports on safety of inhaled paclitaxel, it can be suggested that pulmonary delivery of paclitaxel can be a useful non-invasive route of administration compared with i.v administration.

Remote actuated cryocooler for superconducting generator and method of assembling the same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stautner, Ernst Wolfgang; Haran, Kiruba Sivasubramaniam; Fair, Ruben Jeevanasan

2017-02-14

In one embodiment, a cryocooler assembly for cooling a heat load is provided. The cryocooler assembly includes a vacuum vessel surrounding the heat load and a cryocooler at least partially inserted into the vacuum vessel, the cryocooler including a coldhead. The assembly further includes an actuator coupled to the cryocooler. The actuator is configured to translate the cryocooler coldhead into thermal engagement with the heat load and to maintain constant pressure of the coldhead against the heat load to facilitate maintaining thermal engagement with the heat load as the heat load shrinks during a cool down process.

Estimated dissolved-solids loads and trends at selected streams in and near the Uinta Basin, Utah, Water Years 1989–2013

USGS Publications Warehouse

Thiros, Susan A.

2017-03-23

The U.S. Geological Survey (USGS), in cooperation with the Colorado River Basin Salinity Control Forum, studied trends in dissolved-solids loads at selected sites in and near the Uinta Basin, Utah. The Uinta Basin study area includes the Duchesne River Basin and the Middle Green River Basin in Utah from below Flaming Gorge Reservoir to the town of Green River.Annual dissolved-solids loads for water years (WY) 1989 through 2013 were estimated for 16 gaging stations in the study area using streamflow and water-quality data from the USGS National Water Information System database. Eight gaging stations that monitored catchments with limited or no agricultural land use (natural subbasins) were used to assess loads from natural sources. Four gaging stations that monitored catchments with agricultural land in the Duchesne River Basin were used to assess loads from agricultural sources. Four other gaging stations were included in the dissolved-solids load and trend analysis to help assess the effects of agricultural areas that drain to the Green River in the Uinta Basin, but outside of the Duchesne River Basin.Estimated mean annual dissolved-solids loads for WY 1989–2013 ranged from 1,520 tons at Lake Fork River above Moon Lake, near Mountain Home, Utah (UT), to 1,760,000 tons at Green River near Green River, UT. The flow-normalized loads at gaging stations upstream of agricultural activities showed no trend or a relatively small change. The largest net change in modeled flow-normalized load was -352,000 tons (a 17.8-percent decrease) at Green River near Green River, UT.Annual streamflow and modeled dissolved-solids loads at the gaging stations were balanced between upstream and downstream sites to determine how much water and dissolved solids were transported to the Duchesne River and a section of the Green River, and how much was picked up in each drainage area. Mass-balance calculations of WY 1989–2013 mean annual dissolved-solids loads at the studied sites show that Green River near Jensen, UT, accounts for 64 percent of the load in the river at Green River, UT, while the Duchesne River and White River contribute 10 and 13 percent, respectively.Annual streamflow and modeled dissolved-solids loads at the gaging stations were balanced between upstream and downstream sites to determine how much water and dissolved solids were transported to the Duchesne River and a section of the Green River, and how much was picked up in each drainage area. Mass-balance calculations of WY 1989–2013 mean annual dissolved-solids loads at the studied sites show that Green River near Jensen, UT, accounts for 64 percent of the load in the river at Green River, UT, while the Duchesne River and White River contribute 10 and 13 percent, respectively.The flow-normalized dissolved-solids loads estimated at Duchesne River near Randlett, UT, and White River near Watson, UT, decreased by 68,000 and 55,300 tons, or 27.8 and 20.8 percent respectively, when comparing 1989 to 2013. The drainage basins for both rivers have undergone salinity-control projects since the early 1980s to reduce the dissolved-solids load entering the Colorado River. Approximately 19 percent of the net change in flow-normalized load at Green River at Green River, UT, is from changes in load modeled at Duchesne River near Randlett, UT, and 16 percent from changes in load modeled at White River near Watson, UT. The net change in flow-normalized load estimated at Green River near Greendale, UT, for WY 1989–2013 accounts for about 45 percent of the net change estimated at Green River at Green River, UT.Mass-balance calculations of WY 1989–2013 mean annual dissolved-solids loads at the studied sites in the Duchesne River Basin show that 75,400 tons or 44 percent of the load at the Duchesne River near Randlett, UT, gaging station was not accounted for at any of the upstream gages. Most of this unmonitored load is derived from tributary inflow, groundwater discharge, unconsumed irrigation water, and irrigation tail water.A mass balance of WY 1989–2013 flow-normalized loads estimated at sites in the Duchesne River Basin indicates that the flow-normalized load of unmonitored inflow to the Duchesne River between the Myton and Randlett gaging stations decreased by 38 percent. The total net decrease in flow-normalized load calculated for unmonitored inflow in the drainage basin accounts for 94 percent of the decrease in WY 1989–2013 flow-normalized load modeled at the Duchesne River near Randlett, UT, gaging station. Irrigation improvements in the drainage basin have likely contributed to the decrease in flow-normalized load.Reductions in dissolved-solids load estimated by the Natural Resources Conservation Service (NRCS) and the Bureau of Reclamation (Reclamation) from on- and off-farm improvements in the Uinta Basin totaled about 135,000 tons in 2013 (81,900 tons from on-farm improvements and 53,300 tons from off-farm improvements). The reduction in dissolved-solids load resulting from on- and off-farm improvements facilitated by the NRCS and Reclamation in the Price River Basin from 1989 to 2013 was estimated to be 64,800 tons.The amount of sprinkler-irrigated land mapped in the drainage area or subbasin area for a gaging station was used to estimate the reduction in load resulting from the conversion from flood to sprinkler irrigation. Sprinkler-irrigated land mapped in the Uinta Basin totaled 109,630 acres in 2012. Assuming conversion to wheel-line sprinklers, a reduction in dissolved-solids load in the Uinta Basin of 95,800 tons in 2012 was calculated using the sprinkler-irrigation acreage and a pre-salinity-control project dissolved-solids yield of 1.04 tons per acre.A reduction of 72,800 tons in dissolved-solids load from irrigation improvements was determined from sprinkler-irrigated lands in the Ashley Valley and Jensen, Pelican Lake, and Pleasant Valley areas (mapped in 2012); and in the Price River Basin (mapped in 2011). This decrease in dissolved-solids load is 8,800 tons more than the decrease in unmonitored flow-normalized dissolved-solids load (-64,000 tons) determined for the Green River between the Jensen and Green River gaging stations.The net WY 1989–2013 change in flow-normalized dissolved-solids load at the Duchesne River near Randlett, UT, and the Green River between the Jensen and Green River, UT, gaging stations determined from mass-balance calculations was compared to reported reductions in dissolved-solids load from on- and off-farm improvements and estimated reductions in load determined from mapped sprinkler-irrigated areas in the Duchesne River Basin and the area draining to the Green River between the Jensen and Green River gaging stations. The combined NRCS and Reclamation estimates of reduction in dissolved-solids load from on- and off-farm improvements in the study area (200,000 tons) is more than the reduction in load estimated using the acreage with sprinkler improvements (136,000 tons) or the mass-balance of flow-normalized load (132,000 tons).

Transverse Stress Decay in a Specially Orthotropic Strip Under Localizing Normal Edge Loading

NASA Technical Reports Server (NTRS)

Fichter, W. B.

2000-01-01

Solutions are presented for the stresses in a specially orthotropic infinite strip which is subjected to localized uniform normal loading on one edge while the other edge is either restrained against normal displacement only, or completely fixed. The solutions are used to investigate the diffusion of load into the strip and in particular the decay of normal stress across the width of the strip. For orthotropic strips representative of a broad range of balanced and symmetric angle-ply composite laminates, minimum strip widths are found that ensure at least 90% decay of the normal stress across the strip. In addition, in a few cases where, on the fixed edge the peak shear stress exceeds the normal stress in magnitude, minimum strip widths that ensure 90% decay of both stresses are found. To help in putting these results into perspective, and to illustrate the influence of material properties on load 9 orthotropic materials, closed-form solutions for the stresses in similarly loaded orthotropic half-planes are obtained. These solutions are used to generate illustrative stress contour plots for several representative laminates. Among the laminates, those composed of intermediate-angle plies, i.e., from about 30 degrees to 60 degrees, exhibit marked changes in normal stress contour shape with stress level. The stress contours are also used to find 90% decay distances in the half-planes. In all cases, the minimum strip widths for 90% decay of the normal stress exceed the 90% decay distances in the corresponding half-planes, in amounts ranging from only a few percent to about 50% of the half-plane decay distances. The 90% decay distances depend on both material properties and the boundary conditions on the supported edge.

Flight-Path Characteristics for Decelerating From Supercircular Speed

NASA Technical Reports Server (NTRS)

Luidens, Roger W.

1961-01-01

Characteristics of the following six flight paths for decelerating from a supercircular speed are developed in closed form: constant angle of attack, constant net acceleration, constant altitude" constant free-stream Reynolds number, and "modulated roll." The vehicles were required to remain in or near the atmosphere, and to stay within the aerodynamic capabilities of a vehicle with a maximum lift-drag ratio of 1.0 and within a maximum net acceleration G of 10 g's. The local Reynolds number for all the flight paths for a vehicle with a gross weight of 10,000 pounds and a 600 swept wing was found to be about 0.7 x 10(exp 6). With the assumption of a laminar boundary layer, the heating of the vehicle is studied as a function of type of flight path, initial G load, and initial velocity. The following heating parameters were considered: the distribution of the heating rate over the vehicle, the distribution of the heat per square foot over the vehicle, and the total heat input to the vehicle. The constant G load path at limiting G was found to give the lowest total heat input for a given initial velocity. For a vehicle with a maximum lift-drag ratio of 1.0 and a flight path with a maximum G of 10 g's, entry velocities of twice circular appear thermo- dynamically feasible, and entries at velocities of 2.8 times circular are aerodynamically possible. The predominant heating (about 85 percent) occurs at the leading edge of the vehicle. The total ablated weight for a 10,000-pound-gross-weight vehicle decelerating from an initial velocity of twice circular velocity is estimated to be 5 percent of gross weight. Modifying the constant G load flight path by a constant-angle-of-attack segment through a flight- to circular-velocity ratio of 1.0 gives essentially a "point landing" capability but also results in an increased total heat input to the vehicle.

The computational analysis and modelling of substitution effects on hydrolysis of formanilides in acidic aqueous solutions

NASA Astrophysics Data System (ADS)

Lukeš, Vladimír; Škorňa, Peter; Michalík, Martin; Klein, Erik

2017-11-01

Various para, meta and ortho substituted formanilides have been theoretically studied. For trans and cis-isomers of non-substituted formanilide, the calculated B3LYP vibration normal modes were analyzed. Substituent effect on the selected normal modes was described and the comparison with the available experimental data is presented. The calculated B3LYP proton affinities were correlated with Hammett constants, Fujita-Nishioka equation and the rate constants of the hydrolysis in 1 M HCl. Found linear dependences allow predictions of dissociation constants (pKBH+) and hydrolysis rate constants. Obtained results indicate that protonation of amide group may represent the rate determining step of acid catalyzed hydrolysis.

The interactive effect of dietary protein and vitamin levels on the depression of gonadal development in growing male rats kept under disturbed daily rhythm.

PubMed

Hanai, Miho; Esashi, Takatoshi

2007-04-01

The purpose of this study was to clarify the effects of nutrients on the gonadal development of male rats kept under constant darkness as a model of disturbed daily rhythm. The present study examined protein and vitamins, and their interactions. This study was based on three-way ANOVA; the three factors were lighting conditions, dietary protein and dietary vitamins, respectively. The levels of dietary protein were low or normal: 9% casein or 20% casein. The levels of dietary vitamins were low, normal or high: 1/3.3 of normal (AIN-93G diet) content, normal content, or three times the normal content, respectively. Other compositions were the same as those of the AIN-93G diet, and six kinds of experimental diet were prepared. Four-week-old rats (Fischer 344 strain) were kept under constant darkness or normal lighting (12-h light/dark cycle) for 4 wk. After 4 wk, the gonadal weights and serum testosterone content were evaluated. In the constant darkness groups (D-groups), the low-protein diet induced reduction of gonadal organ weights and serum testosterone concentrations. This reduction of gonadal organ weights was exacerbated by progressively higher levels of dietary vitamins. In the case of a normal-protein diet, the depression of gonadal development was not accelerated by high-vitamin intake. In the normal lighting groups (N-groups), the low-protein and high-vitamin diet slightly depressed gonadal development. These results suggest that the metabolism of protein and vitamins is different in rats being kept under constant darkness, and that excess dietary vitamins have an adverse effect on gonadal development in rats fed a low-protein diet.

Probabilistic model of bridge vehicle loads in port area based on in-situ load testing

NASA Astrophysics Data System (ADS)

Deng, Ming; Wang, Lei; Zhang, Jianren; Wang, Rei; Yan, Yanhong

2017-11-01

Vehicle load is an important factor affecting the safety and usability of bridges. An statistical analysis is carried out in this paper to investigate the vehicle load data of Tianjin Haibin highway in Tianjin port of China, which are collected by the Weigh-in- Motion (WIM) system. Following this, the effect of the vehicle load on test bridge is calculated, and then compared with the calculation result according to HL-93(AASHTO LRFD). Results show that the overall vehicle load follows a distribution with a weighted sum of four normal distributions. The maximum vehicle load during the design reference period follows a type I extremum distribution. The vehicle load effect also follows a weighted sum of four normal distributions, and the standard value of the vehicle load is recommended as 1.8 times that of the calculated value according to HL-93.

Memo WX7-14-1359, Subject: PBX 9502 Creep Data, Compression and Tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, Darla G.

2014-02-06

This is a summary of the constant-load, constant-temperature mechanical creep data that has been collected on PBX 9502 in tension and compression over the last 5+ years. This work was primarily funded by the Enhanced Surveillance Campaign (C-8).

Flexural-torsional vibration of simply supported open cross-section steel beams under moving loads

NASA Astrophysics Data System (ADS)

Michaltsos, G. T.; Sarantithou, E.; Sophianopoulos, D. S.

2005-02-01

SummaryThe present work deals with linearized modal analysis of the combined flexural-torsional vibration of simply supported steel beams with open monosymmetric cross-sections, acted upon by a load of constant magnitude, traversing its span eccentrically with constant velocity. After thoroughly investigating the free vibrations of the structure, which simulates a commonly used highway bridge, its forced motions under the aforementioned loading type are investigated. Utilizing the capabilities of symbolic computations within modern mathematical software, the effect of the most significant geometrical and cross-sectional beam properties on the free vibration characteristics of the beam are established and presented in tabular and graphical form. Moreover, adopting realistic values of the simplified vehicle model adopted, the effects of eccentricity, load magnitude and corresponding velocity are assessed and interesting conclusions for structural design purposes are drawn. The proposed methodology may serve as a starting point for further in-depth study of the whole scientific subject, in which sophisticated vehicle models, energy dissipation and more complicated bridge models may be used.

Experimental study and finite element analysis based on equivalent load method for laser ultrasonic measurement of elastic constants.

PubMed

Zhan, Yu; Liu, Changsheng; Zhang, Fengpeng; Qiu, Zhaoguo

2016-07-01

The laser ultrasonic generation of Rayleigh surface wave and longitudinal wave in an elastic plate is studied by experiment and finite element method. In order to eliminate the measurement error and the time delay of the experimental system, the linear fitting method of experimental data is applied. The finite element analysis software ABAQUS is used to simulate the propagation of Rayleigh surface wave and longitudinal wave caused by laser excitation on a sheet metal sample surface. The equivalent load method is proposed and applied. The pulsed laser is equivalent to the surface load in time and space domain to meet the Gaussian profile. The relationship between the physical parameters of the laser and the load is established by the correction factor. The numerical solution is in good agreement with the experimental result. The simple and effective numerical and experimental methods for laser ultrasonic measurement of the elastic constants are demonstrated. Copyright © 2016. Published by Elsevier B.V.

Constitutive Modeling of a Glass Fiber-Reinforced PTFE Gasketed-Joint Under a Re-torque

NASA Astrophysics Data System (ADS)

Williams, James; Gordon, Ali P.

Joints gasketed with viscoelastic seals often receive an application of a secondary torque, i.e., retorque, in order to ensure joint tightness and proper sealing. The motivation of this study is to characterize and analytically model the load and deflection re-torque response of a single 25% glass-fiber reinforced polytetrafluorethylene (PTFE) gasket-bolted joint with serrated flange detail. The Burger-type viscoelastic modeling constants of the material are obtained through isolating the gasket from the bolt by performing a gasket creep test via a MTS electromechanical test frame. The re-load creep response is also investigated by re-loading the gasket after a period of initial creep to observe the response. The modeling constants obtained from the creep tests are used with a Burger-type viscoelastic model to predict the re-torque response of a single bolt-gasket test fixture in order to validate the ability of the model to simulate the re-torque response under various loading conditions and flange detail.

Hardboard-webbed I-beams : effects of long-term loading and loading environment

Treesearch

Michael J. Superfesky; Terry J. Ramaker

1978-01-01

Twelve-foot and 6-foot I-beams with webs of two different hardboard materials and plywood were subjected to constant loads in three different humidity environments. After 17,000 hours of test, the performance of the hardboard-webbed I-beams appears to be at least comparable to that of I- beams with plywood webs. Results of this study will be useful to researchers,...

Friction coefficient of skin in real-time.

PubMed

Sivamani, Raja K; Goodman, Jack; Gitis, Norm V; Maibach, Howard I

2003-08-01

Friction studies are useful in quantitatively investigating the skin surface. Previous studies utilized different apparatuses and materials for these investigations but there was no real-time test parameter control or monitoring. Our studies incorporated the commercially available UMT Series Micro-Tribometer, a tribology instrument that permits real-time monitoring and calculation of the important parameters in friction studies, increasing the accuracy over previous tribology and friction measurement devices used on skin. Our friction tests were performed on four healthy volunteers and on abdominal skin samples. A stainless steel ball was pressed on to the skin with at a pre-set load and then moved across the skin at a constant velocity of 5 mm/min. The UMT continuously monitored the friction force of the skin and the normal force of the ball to calculate the friction coefficient in real-time. Tests investigated the applicability of Amonton's law, the impact of increased and decreased hydration, and the effect of the application of moisturizers. The friction coefficient depends on the normal load applied, and Amonton's law does not provide an accurate description for the skin surface. Application of water to the skin increased the friction coefficient and application of isopropyl alcohol decreased it. Fast acting moisturizers immediately increased the friction coefficient, but did not have the prolonged effect of the slow, long lasting moisturizers. The UMT is capable of making real-time measurements on the skin and can be used as an effective tool to study friction properties. Results from the UMT measurements agree closely with theory regarding the skin surface.

Estimates and Standard Errors for Ratios of Normalizing Constants from Multiple Markov Chains via Regeneration

PubMed Central

Doss, Hani; Tan, Aixin

2017-01-01

In the classical biased sampling problem, we have k densities π1(·), …, πk(·), each known up to a normalizing constant, i.e. for l = 1, …, k, πl(·) = νl(·)/ml, where νl(·) is a known function and ml is an unknown constant. For each l, we have an iid sample from πl,·and the problem is to estimate the ratios ml/ms for all l and all s. This problem arises frequently in several situations in both frequentist and Bayesian inference. An estimate of the ratios was developed and studied by Vardi and his co-workers over two decades ago, and there has been much subsequent work on this problem from many different perspectives. In spite of this, there are no rigorous results in the literature on how to estimate the standard error of the estimate. We present a class of estimates of the ratios of normalizing constants that are appropriate for the case where the samples from the πl’s are not necessarily iid sequences, but are Markov chains. We also develop an approach based on regenerative simulation for obtaining standard errors for the estimates of ratios of normalizing constants. These standard error estimates are valid for both the iid case and the Markov chain case. PMID:28706463

Estimates and Standard Errors for Ratios of Normalizing Constants from Multiple Markov Chains via Regeneration.

PubMed

Doss, Hani; Tan, Aixin

2014-09-01

In the classical biased sampling problem, we have k densities π 1 (·), …, π k (·), each known up to a normalizing constant, i.e. for l = 1, …, k , π l (·) = ν l (·)/ m l , where ν l (·) is a known function and m l is an unknown constant. For each l , we have an iid sample from π l , · and the problem is to estimate the ratios m l /m s for all l and all s . This problem arises frequently in several situations in both frequentist and Bayesian inference. An estimate of the ratios was developed and studied by Vardi and his co-workers over two decades ago, and there has been much subsequent work on this problem from many different perspectives. In spite of this, there are no rigorous results in the literature on how to estimate the standard error of the estimate. We present a class of estimates of the ratios of normalizing constants that are appropriate for the case where the samples from the π l 's are not necessarily iid sequences, but are Markov chains. We also develop an approach based on regenerative simulation for obtaining standard errors for the estimates of ratios of normalizing constants. These standard error estimates are valid for both the iid case and the Markov chain case.

Effect of thermal stability/complex terrain on wind turbine model(s): a wind tunnel study to address complex atmospheric conditions

NASA Astrophysics Data System (ADS)

Guala, M.; Hu, S. J.; Chamorro, L. P.

2011-12-01

Turbulent boundary layer measurements in both wind tunnel and in the near-neutral atmospheric surface layer revealed in the last decade the significant contribution of the large scales of motions to both turbulent kinetic energy and Reynolds stresses, for a wide range of Reynolds number. These scales are known to grow throughout the logarithmic layer and to extend several boundary layer heights in the streamwise direction. Potentially, they are a source of strong unsteadiness in the power output of wind turbines and in the aerodynamic loads of wind turbine blades. However, the large scales in realistic atmospheric conditions deserves further study, with well controlled boundary conditions. In the atmospheric wind tunnel of the St. Anthony Falls Laboratory, with a 16 m long test section and independently controlled incoming flow and floor temperatures, turbulent boundary layers in a range of stability conditions, from the stratified to the convective case, can be reproduced and monitored. Measurements of fluctuating temperature, streamwise and wall normal velocity components are simultaneously obtained by an ad hoc calibrated and customized triple-wire sensor. A wind turbine model with constant loading DC motor, constant tip speed ratio, and a rotor diameter of 0.128m is used to mimic a large full scale turbine in the atmospheric boundary layer. Measurements of the fluctuating voltage generated by the DC motor are compared with measurements of the blade's angular velocity by laser scanning, and eventually related to velocity measurements from the triple-wire sensor. This study preliminary explores the effect of weak stability and complex terrain (through a set of spanwise aligned topographic perturbations) on the large scales of the flow and on the fluctuations in the wind turbine(s) power output.

Gastric volume rather than nutrient content inhibits food intake.

PubMed

Phillips, R J; Powley, T L

1996-09-01

To evaluate the separate contributions of distension and nutrient stimulation of the stomach to the inhibition of short-term food intake and, particularly, to reassess previous analyses based on the inflatable gastrointestinal cuff, four experiments were performed. Rats equipped with pyloric cuffs and indwelling gastric catheters consumed a liquid diet ad libitum. Their consumption during short-term (30 min) feeding bout was measured after gastric infusions on cuff-open and cuff-closed trials. Animals taking meals (approximately 5 ml) with cuffs closed immediately after receiving intragastric infusions of 2.5, 5, 7.5, or 10 ml of normal saline exhibited both suppression at the smallest infusion and a dose-dependent reduction across the other volumes (experiment 1). Additionally, when the test diet concentration was varied, animals with their cuffs closed consumed a constant volume, not a constant number of calories (experiment 2). Furthermore, cuff-closed animals exhibited no more suppression to 5-ml intragastric infusions of nutrients (including, on different trials, 50 and 100% Isocal diet; 10, 20, and 40% glucose; and 40% sucrose and 40% fructose) than to the same volume of saline (experiments 3 and 4). In contrast, on cuff-open trials in which gastric contents could empty into the duodenum, these same nutrient loads were more effective (except fructose) than saline in producing suppression of food intake. In summary, although both limited gastric distension with the pylorus occluded and intestinal nutrient stimulation with the cuff open effectively reduced intake, cuff-closed gastric loads of mixed macronutrients or carbohydrate solutions of 2-8 kcal, pH from 5.8 to 6.7, and osmolarities between 117 and 2,294 mosM/kg produced only the distension-based suppression generated by the same volume of saline.

An evaluation of surface properties and frictional forces generated from Al-Mo-Ni coating on piston ring

NASA Astrophysics Data System (ADS)

Karamış, M. B.; Yıldızlı, K.; Çakırer, H.

2004-05-01

Surface properties of the Al-Mo-Ni coating plasma sprayed on the piston ring material and the frictional forces obtained by testing carried out under different loads, temperatures and frictional conditions were evaluated. Al-Mo-Ni composite material was deposited on the AISI 440C test steel using plasma spraying method. The coated and uncoated samples were tested by being exposed to frictional testing under dry and lubricated conditions. Test temperatures of 25, 100, 200, and 300 °C and loads of 83, 100, 200, and 300 N were applied during the tests in order to obtain the frictional response of the coating under conditions similar to real piston ring/cylinder friction conditions. Gray cast iron was used as a counterface material. All the tests were carried out with a constant sliding speed of 1 m/s. The properties of the coating were determined by using EDX and SEM analyses. Hardness distribution on the cross-section of the coating was also determined. In addition, the variations of the surface roughness after testing with test temperatures and loads under dry and lubricated conditions were recorded versus sliding distance. It was determined that the surface roughness increased with increasing loads. It increased with temperature up to 200 °C and then decreased at 300 °C under dry test conditions. Under lubricated conditions, the roughness decreased under the loads of 100 N and then increased. The roughness decreased at 200 °C but below and above this point it increased with the test temperature. Frictional forces observed under dry and lubricated test conditions increased with load at running-in period of the sliding. The steady-state period was then established with the sliding distance as a normal situation. However, the frictional forces were generally lower at a higher test temperature than those at a lower test temperature. Surprisingly, the test temperature of 200 °C was a critical point for frictional forces and surface roughness.

Reaction times of normal listeners to laryngeal, alaryngeal, and synthetic speech.

PubMed

Evitts, Paul M; Searl, Jeff

2006-12-01

The purpose of this study was to compare listener processing demands when decoding alaryngeal compared to laryngeal speech. Fifty-six listeners were presented with single words produced by 1 proficient speaker from 5 different modes of speech: normal, tracheosophageal (TE), esophageal (ES), electrolaryngeal (EL), and synthetic speech (SS). Cognitive processing load was indexed by listener reaction time (RT). To account for significant durational differences among the modes of speech, an RT ratio was calculated (stimulus duration divided by RT). Results indicated that the cognitive processing load was greater for ES and EL relative to normal speech. TE and normal speech did not differ in terms of RT ratio, suggesting fairly comparable cognitive demands placed on the listener. SS required greater cognitive processing load than normal and alaryngeal speech. The results are discussed relative to alaryngeal speech intelligibility and the role of the listener. Potential clinical applications and directions for future research are also presented.

Direct-Current Monitor With Flux-Reset Transformer Coupling

NASA Technical Reports Server (NTRS)

Canter, Stanley

1993-01-01

Circuit measures constant or slowly-varying unidirectional electrical current using flux-reset transformer coupling. Measurement nonintrusive in sense that no need for direct contact with wire that carries load current to be measured, and no need to install series resistive element in load-current path. Toroidal magnetic core wrapped with coil of wire placed around load-current-carrying wire, acts as transformer core, load-current-carrying wire acts as primary winding of transformer, and coil wrapped on core acts as secondary winding.

Fatigue-Crack-Growth Structural Analysis

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1986-01-01

Elastic and plastic deformations calculated under variety of loading conditions. Prediction of fatigue-crack-growth lives made with FatigueCrack-Growth Structural Analysis (FASTRAN) computer program. As cyclic loads are applied to initial crack configuration, FASTRAN predicts crack length and other parameters until complete break occurs. Loads are tensile or compressive and of variable or constant amplitude. FASTRAN incorporates linear-elastic fracture mechanics with modifications of load-interaction effects caused by crack closure. FASTRAN considered research tool, because of lengthy calculation times. FASTRAN written in FORTRAN IV for batch execution.

The effect of backpack weight on the standing posture and balance of schoolgirls with adolescent idiopathic scoliosis and normal controls.

PubMed

Chow, Daniel H K; Kwok, Monica L Y; Cheng, Jack C Y; Lao, Miko L M; Holmes, Andrew D; Au-Yang, Alexander; Yao, Fiona Y D; Wong, M S

2006-10-01

Concerns have been raised regarding the effect of carrying a backpack on adolescent posture and balance, but the effect of backpack loading combined with other factors affecting balance, such as adolescent idiopathic scoliosis (AIS), has not been determined. This study examines the effects of backpack load on the posture and balance of schoolgirls with AIS and normal controls. The standing posture of 26 schoolgirls with mild AIS (mean age 13, Cobb angle 10-25 degrees ) and 20 age-matched normal schoolgirls were recorded without a backpack and while carrying a standard dual-strap backpack loaded at 7.5%, 10%, 12.5% and 15% of the subject's bodyweight (BW). Kinematics of the pelvis, trunk and head were recorded using a motion analysis system and centre of pressure (COP) data were recorded using a force platform. Reliable COP data could only be derived for 13 of the subjects with AIS. Increasing backpack load causes a significantly increased flexion of the trunk in relation to the pelvis and extension of the head in relation to the trunk, as well as increased antero-posterior range of COP motion. While backpack load appears to affect balance predominantly in the antero-posterior direction, differences between groups were more evident in the medio-lateral direction, with AIS subjects showing poor balance in this direction. Overall, carrying a backpack causes similar sagittal plane changes in posture and balance in both normal and AIS groups. Load size or subject group did not influence balance, but the additive effect of backpack carrying and AIS on postural control alters the risk of fall in this population. Therefore, load limit recommendations based on normal subjects should not be applicable to subjects with AIS.

A piloted simulation investigation of the normal load factor and longitudinal thrust required for air-to-air acquisition and tracking

NASA Technical Reports Server (NTRS)

Whalley, Matthew S.

1993-01-01

A piloted simulation study was performed by the U.S. Army Aeroflighydynamics Directorate to develop insight into the maneuverability requirements for aggressive helicopter maneuvering tasks such as air-to-air combat. Both a conventional helicopter and a helicopter with auxiliary thrust were examined. The aircraft parameters of interest were the normal and longitudinal load factor envelopes. Of particular interest were the mission performance and handling qualities tradeoffs with the parameters of interest. Two air-to-air acquisition and tracking tasks and a return-to-cover task were performed to assess mission performance. Results indicate that without auxiliary thrust, the ownship normal load factor capability needs to match that of the adversary in order to provide satisfactory handling qualities. Auxiliary thrust provides significant handling qualities advantages and can be substituted to some extent for normal load factor capability. Auxiliary thrust levels as low as 0.2 thrust/weight can provide significant handling qualities advantages.

Analysis of a dc bus system with a nonlinear constant power load and its delayed feedback control.

PubMed

Konishi, Keiji; Sugitani, Yoshiki; Hara, Naoyuki

2014-02-01

This paper tackles a destabilizing problem of a direct-current (dc) bus system with constant power loads, which can be considered a fundamental problem of dc power grid networks. The present paper clarifies scenarios of the destabilization and applies the well-known delayed-feedback control to the stabilization of the destabilized bus system on the basis of nonlinear science. Further, we propose a systematic procedure for designing the delayed feedback controller. This controller can converge the bus voltage exactly on an unstable operating point without accurate information and can track it using tiny control energy even when a system parameter, such as the power consumption of the load, is slowly varied. These features demonstrate that delayed feedback control can be considered a strong candidate for solving the destabilizing problem.

INSTRUMENTATION AND TECHNIQUES. A SELF-CONTAINED, REGULATED, BURST-FIRING CONSTANT-CURRENT AC SHOCK GENERATOR

EPA Science Inventory

A line- and load-regulated constant-current ac shock generator has been designed for animal behavior experiments. The self-contained unit has four operating modes, amplitude adjustment, and a leakage current detection circuit. A unique feature of this generator is that the good l...

Structural Influence of Dynamics of Bottom Loads

DTIC Science & Technology

2014-02-10

using the Numerette research craft, are underway. Early analytic research on slamming was done by von Karman [5] using a momentum approach, and by...pressure q{x,t) as two constant pressures, qi and qj, traveling at a constant speed c. Using the Euler- Bernoulli beam assumptions the governing

Local vibrational modes of the water dimer - Comparison of theory and experiment

NASA Astrophysics Data System (ADS)

Kalescky, R.; Zou, W.; Kraka, E.; Cremer, D.

2012-12-01

Local and normal vibrational modes of the water dimer are calculated at the CCSD(T)/CBS level of theory. The local H-bond stretching frequency is 528 cm-1 compared to a normal mode stretching frequency of just 143 cm-1. The adiabatic connection scheme between local and normal vibrational modes reveals that the lowering is due to mass coupling, a change in the anharmonicity, and coupling with the local HOH bending modes. The local mode stretching force constant is related to the strength of the H-bond whereas the normal mode stretching force constant and frequency lead to an erroneous underestimation of the H-bond strength.

Relating normal vibrational modes to local vibrational modes with the help of an adiabatic connection scheme

NASA Astrophysics Data System (ADS)

Zou, Wenli; Kalescky, Robert; Kraka, Elfi; Cremer, Dieter

2012-08-01

Information on the electronic structure of a molecule and its chemical bonds is encoded in the molecular normal vibrational modes. However, normal vibrational modes result from a coupling of local vibrational modes, which means that only the latter can provide detailed insight into bonding and other structural features. In this work, it is proven that the adiabatic internal coordinate vibrational modes of Konkoli and Cremer [Int. J. Quantum Chem. 67, 29 (1998)], 10.1002/(SICI)1097-461X(1998)67:1<29::AID-QUA3>3.0.CO;2-0 represent a unique set of local modes that is directly related to the normal vibrational modes. The missing link between these two sets of modes are the compliance constants of Decius, which turn out to be the reciprocals of the local mode force constants of Konkoli and Cremer. Using the compliance constants matrix, the local mode frequencies of any molecule can be converted into its normal mode frequencies with the help of an adiabatic connection scheme that defines the coupling of the local modes in terms of coupling frequencies and reveals how avoided crossings between the local modes lead to changes in the character of the normal modes.

Trabecular bone adaptation to low-magnitude high-frequency loading in microgravity.

PubMed

Torcasio, Antonia; Jähn, Katharina; Van Guyse, Maarten; Spaepen, Pieter; Tami, Andrea E; Vander Sloten, Jos; Stoddart, Martin J; van Lenthe, G Harry

2014-01-01

Exposure to microgravity causes loss of lower body bone mass in some astronauts. Low-magnitude high-frequency loading can stimulate bone formation on earth. Here we hypothesized that low-magnitude high-frequency loading will also stimulate bone formation under microgravity conditions. Two groups of six bovine cancellous bone explants were cultured at microgravity on a Russian Foton-M3 spacecraft and were either loaded dynamically using a sinusoidal curve or experienced only a static load. Comparable reference groups were investigated at normal gravity. Bone structure was assessed by histology, and mechanical competence was quantified using μCT and FE modelling; bone remodelling was assessed by fluorescent labelling and secreted bone turnover markers. Statistical analyses on morphometric parameters and apparent stiffness did not reveal significant differences between the treatment groups. The release of bone formation marker from the groups cultured at normal gravity increased significantly from the first to the second week of the experiment by 90.4% and 82.5% in response to static and dynamic loading, respectively. Bone resorption markers decreased significantly for the groups cultured at microgravity by 7.5% and 8.0% in response to static and dynamic loading, respectively. We found low strain magnitudes to drive bone turnover when applied at high frequency, and this to be valid at normal as well as at microgravity. In conclusion, we found the effect of mechanical loading on trabecular bone to be regulated mainly by an increase of bone formation at normal gravity and by a decrease in bone resorption at microgravity. Additional studies with extended experimental time and increased samples number appear necessary for a further understanding of the anabolic potential of dynamic loading on bone quality and mechanical competence.

Sodium-dependent calcium extrusion and sensitivity regulation in retinal cones of the salamander.

PubMed Central

Nakatani, K; Yau, K W

1989-01-01

1. Membrane current was recorded from an isolated, dark-adapted salamander cone by sucking its inner segment into a tight-fitting glass pipette containing Ringer solution. The outer segment of the cell was exposed to a bath solution that could be changed rapidly. 2. After removing Na+ from the bath Ringer solution for a short period of time in darkness (the 'loading period'), a transient inward current was observed upon restoring it in bright light. A similar but longer-lasting current was observed when Na+ was restored in the light after a large Ca2+ influx was induced through the light-sensitive conductance in darkness. 3. The above transient current was not observed if Li+ or guanidinium was substituted for Na+ in the light, or if Ba2+ was substituted for Ca2+ during the dark loading period. However, a current was observed if Sr2+ was the substituting ion for Ca2+ during loading. These observations suggested that the current was associated with an electrogenic Na+-dependent Ca2+ efflux at the cone outer segment. 4. The saturated amplitude of the exchange current was 12-25 pA with a mean around 16 pA. This is very comparable to that measured in the outer segment of a salamander rod under similar conditions. 5. By comparing a known Ca2+ load in a cone outer segment to the subsequent charge transfer through the exchange, we estimated that the stoichiometry of the exchange was near 3Na+:1Ca2+. 6. With a small Ca2+ load, or in the presence of Cs+ around the inner segment, the final temporal decline of the Na+-Ca2+ exchange current was roughly exponential, with a mean time constant of about 100 ms. This decline is about four times faster than that measured in rods. We interpret the shorter time constant in cones to reflect a faster rate of decline of intracellular free Ca2+ in their outer segments resulting from the exchange activity. 7. In the absence of external Na+, and hence any Na+-dependent Ca2+ efflux, the absolute sensitivity of a cone to a dim flash was several times higher than in normal Ringer solution. 8. A roughly similar increase in light sensitivity was observed for a rod under the same conditions. 9. We conclude that the Na+-dependent Ca2+ efflux, through lowering intracellular free Ca2+ in the light, has a role in regulating the absolute light sensitivity in cones as it does in rods.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:2479741

14 CFR 23.365 - Pressurized cabin loads.

Code of Federal Regulations, 2011 CFR

2011-01-01

... landing. (d) The airplane structure must be strong enough to withstand the pressure differential loads... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Flight Loads § 23... structure must be strong enough to withstand the flight loads combined with pressure differential loads from...

40 CFR Table 33 to Subpart G of... - Saturation Factors

Code of Federal Regulations, 2011 CFR

2011-07-01

... service 0.60 Submerged loading: dedicated vapor balance service 1.00 Splash loading of a clean cargo tank 1.45 Splash loading: dedicated normal service 1.45 Splash loading: dedicated vapor balance service 1...

40 CFR Table 33 to Subpart G of... - Saturation Factors

Code of Federal Regulations, 2014 CFR

2014-07-01

... service 0.60 Submerged loading: dedicated vapor balance service 1.00 Splash loading of a clean cargo tank 1.45 Splash loading: dedicated normal service 1.45 Splash loading: dedicated vapor balance service 1...

40 CFR Table 33 to Subpart G of... - Saturation Factors

Code of Federal Regulations, 2012 CFR

2012-07-01

... service 0.60 Submerged loading: dedicated vapor balance service 1.00 Splash loading of a clean cargo tank 1.45 Splash loading: dedicated normal service 1.45 Splash loading: dedicated vapor balance service 1...

40 CFR Table 33 to Subpart G of... - Saturation Factors

Code of Federal Regulations, 2010 CFR

2010-07-01

... service 0.60 Submerged loading: dedicated vapor balance service 1.00 Splash loading of a clean cargo tank 1.45 Splash loading: dedicated normal service 1.45 Splash loading: dedicated vapor balance service 1...

40 CFR Table 33 to Subpart G of... - Saturation Factors

Code of Federal Regulations, 2013 CFR

2013-07-01

... service 0.60 Submerged loading: dedicated vapor balance service 1.00 Splash loading of a clean cargo tank 1.45 Splash loading: dedicated normal service 1.45 Splash loading: dedicated vapor balance service 1...

Influence of immediate loading on provisional restoration in dental implant stability

NASA Astrophysics Data System (ADS)

Ikbal, M.; Odang, R. W.; Indrasari, M.; Dewi, R. S.

2017-08-01

The success of dental implant treatment is determined by the primary stability at placement. One factor that could influence this stability is occlusal loading through provisional restoration. Two types of loading protocols are usually used: immediate and delayed loading. However, some controversies remain about the influence of occlusal loading on implant stability. Therefore, the influence of immediate loading on implant stability must be studied. An animal study was conducted by placing nine dental implants in the mandibular jaw of three Macaca fascicularis. Provisional restorations with various occlusal contacts (no, light, and normal contact) were placed on the implant. The implant stability was measured using the Ostell ISQ three times: immediately (baseline) and at the first and second months after implant placement. The implant stability between implants with no and normal occlusal contact as well as light and normal occlusal contact showed significant differences (p < 0.05) at the first and second months after implant placement. However, no significant increase (p > 0.05) in implant stability was seen at the baseline and the first and second months after implant placement for all occlusal contact groups. Immediate loading influenced the implant stability, and provisional restoration of implant without occlusal contact showed the highest implant stability.

Nonlinear maneuver autopilot for the F-15 aircraft

NASA Technical Reports Server (NTRS)

Menon, P. K. A.; Badgett, M. E.; Walker, R. A.

1989-01-01

A methodology is described for the development of flight test trajectory control laws based on singular perturbation methodology and nonlinear dynamic modeling. The control design methodology is applied to a detailed nonlinear six degree-of-freedom simulation of the F-15 and results for a level accelerations, pushover/pullup maneuver, zoom and pushover maneuver, excess thrust windup turn, constant thrust windup turn, and a constant dynamic pressure/constant load factor trajectory are presented.

The Hypercalciurias CAUSES, PARATHYROID FUNCTIONS, AND DIAGNOSTIC CRITERIA

PubMed Central

Pak, Charles Y. C.; Ohata, Masahiro; Lawrence, E. Clint; Snyder, W.

1974-01-01

The causes for the hypercalciuria and diagnostic criteria for the various forms of hypercalciuria were sought in 56 patients with hypercalcemia or nephrolithiasis (Ca stones), by a careful assessment of parathyroid function and calcium metabolism. A study protocol for the evaluation of hypercalciuria, based on a constant liquid synthetic diet, was developed. In 26 cases of primary hyperparathyroidism, characteristic features were: hypercalcemia, high urinary cyclic AMP (cAMP, 8.58±3.63 SD μmol/g creatinine; normal, 4.02±0.70 μmol/g creatinine), high immunoreactive serum parathyroid hormone (PTH), hypercalciuria, the urinary Ca exceeding absorbed Ca from intestinal tract (CaA), high fasting urinary Ca (0.2 mg/mg creatinine or greater), and low bone density by 125I photon absorption. The results suggest that hypercalciuria is partly secondary to an excessive skeletal resorption (resorptive hypercalciuria). The 22 cases with renal stones had normocalcemia, hypercalciuria, intestinal hyperabsorption of calcium, normal or low serum PTH and urinary cAMP, normal fasting urinary Ca, and normal bone density. Since their CaA exceeded urinary Ca, the hypercalciuria probably resulted from an intestinal hyperabsorption of Ca (absorptive hypercalciuria). The primacy of intestinal Ca hyperabsorption was confirmed by responses to Ca load and deprivation under a metabolic dietary regimen. During a Ca load of 1,700 mg/day, there was an exaggerated increase in the renal excretion of Ca and a suppression of cAMP excretion. The urinary Ca of 453±154 SD mg/day was significantly higher than the control group's 211±42 mg/day. The urinary cAMP of 2.26±0.56 μmol/g creatinine was significantly lower than in the control group. In contrast, when the intestinal absorption of calcium was limited by cellulose phosphate, the hypercalciuria was corrected and the suppressed renal excretion of cAMP returned towards normal. Two cases with renal stones had normocalcemia, hypercalciuria, and high urinary cAMP or serum PTH. Since CaA was less than urinary Ca, the hypercalciuria may have been secondary to an impaired renal tubular reabsorption of Ca (renal hypercalciuria). Six cases with renal stones had normal values of serum Ca, urinary Ca, urinary cAMP, and serum PTH (normocalciuric nephrolithiasis). Their CaA exceeded urinary Ca, and fasting urinary Ca and bone density were normal. The results support the proposed mechanisms for the hypercalciuria and provide reliable diagnostic criteria for the various forms of hypercalciuria. PMID:4367891

Accurate calibration and uncertainty estimation of the normal spring constant of various AFM cantilevers.

PubMed

Song, Yunpeng; Wu, Sen; Xu, Linyan; Fu, Xing

2015-03-10

Measurement of force on a micro- or nano-Newton scale is important when exploring the mechanical properties of materials in the biophysics and nanomechanical fields. The atomic force microscope (AFM) is widely used in microforce measurement. The cantilever probe works as an AFM force sensor, and the spring constant of the cantilever is of great significance to the accuracy of the measurement results. This paper presents a normal spring constant calibration method with the combined use of an electromagnetic balance and a homemade AFM head. When the cantilever presses the balance, its deflection is detected through an optical lever integrated in the AFM head. Meanwhile, the corresponding bending force is recorded by the balance. Then the spring constant can be simply calculated using Hooke's law. During the calibration, a feedback loop is applied to control the deflection of the cantilever. Errors that may affect the stability of the cantilever could be compensated rapidly. Five types of commercial cantilevers with different shapes, stiffness, and operating modes were chosen to evaluate the performance of our system. Based on the uncertainty analysis, the expanded relative standard uncertainties of the normal spring constant of most measured cantilevers are believed to be better than 2%.

Cervicovaginal cytokines, sialidase activity and bacterial load in reproductive-aged women with intermediate vaginal flora.

PubMed

Santos-Greatti, Mariana Morena de Vieira; da Silva, Márcia Guimarães; Ferreira, Carolina Sanitá Tafner; Marconi, Camila

2016-11-01

Studies have shown that not only bacterial vaginosis, but also intermediate vaginal flora has deleterious effects for women's reproductive health. However, literature still lacks information about microbiological and immunological aspects of intermediate flora. To characterize intermediate flora regarding levels of Interleukin (IL)-1beta, IL-6, IL-8, tumor necrosis factor-alpha, interleukin 1 receptor antagonist (IL-1ra), IL-10, sialidase; loads of Gardnerella vaginalis, total bacteria and to verify whether it is closer related to normal flora or bacterial vaginosis. This cross-sectional study enrolled 526 non-pregnant reproductive-aged women distributed in 3 groups according to pattern of vaginal flora using Nugent's system in normal, intermediate and bacterial vaginosis. Cervicovaginal levels of cytokines, sialidases, loads of G. vaginalis and total bacteria were assessed by ELISA, conversion of MUAN and quantitative real-time PCR, respectively. A principal component analysis(PCA) using all measured parameters was performed to compare the three different types of flora. Results showed that intermediate flora is associated with increased cervicovaginal IL-1beta in relation to normal flora(P<0.0001). When compared to bacterial vaginosis, intermediate flora has higher IL-8 and IL-10 levels(P<0.01). Sialidases were in significantly lower levels in normal and intermediate flora than bacterial vaginosis(P<0.0001). Loads of G. vaginalis and total bacterial differed among all groups(P<0.0001), being highest in bacterial vaginosis. PCA showed that normal and intermediate flora were closely scattered, while bacterial vaginosis were grouped separately. Although intermediate flora shows some differences in cytokines, sialidases and bacterial loads in relation to normal flora and bacterial vaginosis, when taken together, general microbiological and immunological pattern pattern of intermediate flora resembles the normal flora. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Load measurement system with load cell lock-out mechanism

NASA Technical Reports Server (NTRS)

Le, Thang; Carroll, Monty; Liu, Jonathan

1995-01-01

In the frame work of the project Shuttle Plume Impingement Flight Experiment (SPIFEX), a Load Measurement System was developed and fabricated to measure the impingement force of Shuttle Reaction Control System (RCS) jets. The Load Measurement System is a force sensing system that measures any combination of normal and shear forces up to 40 N (9 lbf) in the normal direction and 22 N (5 lbf) in the shear direction with an accuracy of +/- 0.04 N (+/- 0.01 lbf) Since high resolution is required for the force measurement, the Load Measurement System is built with highly sensitive load cells. To protect these fragile load cells in the non-operational mode from being damaged due to flight loads such as launch and landing loads of the Shuttle vehicle, a motor driven device known as the Load Cell Lock-Out Mechanism was built. This Lock-Out Mechanism isolates the load cells from flight loads and re-engages the load cells for the force measurement experiment once in space. With this highly effective protection system, the SPIFEX load measurement experiment was successfully conducted on STS-44 in September 1994 with all load cells operating properly and reading impingement forces as expected.

Investigation on chlorine-based sanitization under stabilized conditions in the presence of organic load

USDA-ARS?s Scientific Manuscript database

Chlorine is commonly used for preventing water-mediated cross contamination during fresh produce washing. The sanitization efficacy (SE) is constantly compromised by the organic load (OL), which has been attributed to rapid chlorine depletion and unsuccessful maintenance of residual free chlorine (F...

Ultra High Strain Rate Nanoindentation Testing.

PubMed

Sudharshan Phani, Pardhasaradhi; Oliver, Warren Carl

2017-06-17

Strain rate dependence of indentation hardness has been widely used to study time-dependent plasticity. However, the currently available techniques limit the range of strain rates that can be achieved during indentation testing. Recent advances in electronics have enabled nanomechanical measurements with very low noise levels (sub nanometer) at fast time constants (20 µs) and high data acquisition rates (100 KHz). These capabilities open the doors for a wide range of ultra-fast nanomechanical testing, for instance, indentation testing at very high strain rates. With an accurate dynamic model and an instrument with fast time constants, step load tests can be performed which enable access to indentation strain rates approaching ballistic levels (i.e., 4000 1/s). A novel indentation based testing technique involving a combination of step load and constant load and hold tests that enables measurement of strain rate dependence of hardness spanning over seven orders of magnitude in strain rate is presented. A simple analysis is used to calculate the equivalent uniaxial response from indentation data and compared to the conventional uniaxial data for commercial purity aluminum. Excellent agreement is found between the indentation and uniaxial data over several orders of magnitude of strain rate.

Constant-load delayed fracture test of atmospherically corroded high strength steels

NASA Astrophysics Data System (ADS)

Akiyama, Eiji; Matsukado, Katsuhiro; Li, Songjie; Tsuzaki, Kaneaki

2011-07-01

Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that delayed fracture occurs when the hydrogen content from the environment, H E, exceeds the critical hydrogen content for delayed fracture, H C. During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H E of the fractured specimens was higher than H C, and H E of the specimens not fractured was lower than H C. This result confirms that the balance between H C and H E determines the occurrence of delayed fracture and that hydrogen-content-based evaluation of susceptibility to delayed fracture is reasonable. To certify the increase of H E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.

Ultraslow myosin molecular motors of placental contractile stem villi in humans.

PubMed

Lecarpentier, Yves; Claes, Victor; Lecarpentier, Edouard; Guerin, Catherine; Hébert, Jean-Louis; Arsalane, Abdelilah; Moumen, Abdelouahab; Krokidis, Xénophon; Michel, Francine; Timbely, Oumar

2014-01-01

Human placental stem villi (PSV) present contractile properties. In vitro mechanics were investigated in 40 human PSV. Contraction of PSV was induced by both KCl exposure (n = 20) and electrical tetanic stimulation (n = 20). Isotonic contractions were registered at several load levels ranging from zero-load up to isometric load. The tension-velocity relationship was found to be hyperbolic. This made it possible to apply the A. Huxley formalism for determining the rate constants for myosin cross-bridge (CB) attachment and detachment, CB single force, catalytic constant, myosin content, and maximum myosin ATPase activity. These molecular characteristics of myosin CBs did not differ under either KCl exposure or tetanus. A comparative approach was established from studies previously published in the literature and driven by mean of a similar method. As compared to that described in mammalian striated muscles, we showed that in human PSV, myosin CB rate constants for attachment and detachment were about 103 times lower whereas myosin ATPase activity was 105 times lower. Up to now, CB kinetics of contractile cells arranged along the long axis of the placental sheath appeared to be the slowest ever observed in any mammalian contractile tissue.

Subcutaneous blood flow in psoriasis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klemp, P.

1985-03-01

The simultaneously recorded disappearance rates of /sup 133/xe from subcutaneous adipose tissue in the crus were studied in 10 patients with psoriasis vulgaris using atraumatic labeling of the tissue in lesional skin (LS) areas and symmetrical, nonlesional skin (NLS) areas. Control experiments were performed bilaterally in 10 younger, healthy subjects. The subcutaneous washout rate constant was significantly higher in LS, 0.79 +/- 0.05 min-1 x 10(2) compared to the washout rate constant of NLS, 0.56 +/- 0.07 min-1. 10(2), or the washout rate constant in the normal subjects, 0.46 +/- 0.17 min-1 x 10(2). The mean washout rate constant inmore » NLS was 25% higher than the mean washout rate constant in the normal subjects. The difference was, however, not statistically significant. Differences in the washout rate constants might be due to abnormal subcutaneous tissue-to-blood partition (lambda) in the LS--and therefore not reflecting the real differences in the subcutaneous blood flow (SBF). The lambda for /sup 133/Xe was therefore measured--using a double isotope washout method (/sup 133/Xe and (/sup 131/I)antipyrine)--in symmetrical sites of the lateral crus in LS and NLS of 10 patients with psoriasis vulgaris and in 10 legs of normal subjects. In LS the lambda was 4.52 +/- 1.67 ml/g, which was not statistically different from that of NLS, 5.25 +/- 2.19 ml/g, nor from that of normal subcutaneous tissue, 4.98 +/- 1.04 ml/g. Calculations of the SBF using the obtained lambda values gave a significantly higher SBF in LS, 3.57 +/- 0.23 ml/100 g/min, compared to SBF in the NLS, 2.94 +/- 0.37 ml/100 g/min. There was no statistically significant difference between SBF in NLS and SBF in the normal subjects. The increased SBF in LS of psoriatics might be a secondary phenomenon to an increased heat loss in the lesional skin.« less

Objective determination of the predefined duration of a constant-load diagnostic tests in arterial claudication.

PubMed

Mahe, Guillaume; Abraham, Pierre; Zeenny, Maya; Bruneau, Antoine; Vielle, Bruno; Leftheriotis, Georges

2010-04-01

The predefined duration to arbitrarily stop the tests during constant-load treadmill exercise is a subject of debate and widely variable in the literature. We hypothesized that the upper and lower limits for predefined durations of constant-load 3.2 km/hour 10% grade tests could be derived from the distribution of walking distances observed on a treadmill in a population of subjects referred for claudication or from the optimal cutoff point distance on a treadmill to confirm a limitation self-reported by history. We conducted a retrospective analysis using a referral center, institutional practice, and ambulatory patients. We studied 1290 patients (86% male), 62.1 +/- 11.2 years of age, 169 +/- 8 cm height, 75.7 +/- 14.2 kg weight. Patients performed a standard constant-load treadmill test: 3.2 km hour(-1), 10% slope, maximized to 1000 meters (approximately 20 minutes). We analyzed the maximal walking distance self-reported (MWD(SR)) by history and the maximal walking distance measured on the treadmill (MWD(TT)). Patients reporting MWD(SR) >or=1000 meters were considered unlimited by history. Only 197 patients (15.3%) completed the 20-minute treadmill test. Among the 504 patients who did not stop before 250 meters, 47.8% stopped within the next 250 meters (were unable to walk 500 meters). This proportion falls to 7.5% among the 213 patients who did not stop before 750 meters. When the final goal was to estimate whether the treadmill test can discriminate patients with or without limitation by history, area under the receiver operating characteristic (ROC) curve was 0.809 +/- 0.016 (95% confidence interval [CI], 0.778-0.841; P < .0001), the best diagnostic performance was attained for an MWD(TT) of 299 meters (approximately 6.15 minutes). In patients undergoing constant-load treadmill exercise with a protocol of 3.2 km hour(-1) and 10% slope: a predefined duration of 7 minutes could be proposed as a lower limit for the predefined duration of the tests specifically if one aims at confirming the limitation by history with treadmill testing. Owing to the low risk that patients that could walk 750 meters (approximately 15 minutes) will have to stop in the next 250 meters, 15 minutes seems a reasonable upper limit for the predefined test duration in clinical routine.

The effect of normal load on polytetrafluoroethylene tribology.

PubMed

Barry, Peter R; Chiu, Patrick Y; Perry, Scott S; Sawyer, W Gregory; Phillpot, Simon R; Sinnott, Susan B

2009-04-08

The tribological behavior of oriented poly(tetrafluoroethylene) (PTFE) sliding surfaces is examined as a function of sliding direction and applied normal load in classical molecular dynamics (MD) simulations. The forces are calculated with the second-generation reactive empirical bond-order potential for short-range interactions, and with a Lennard-Jones potential for long-range interactions. The range of applied normal loads considered is 5-30 nN. The displacement of interfacial atoms from their initial positions during sliding is found to vary by a factor of seven, depending on the relative orientation of the sliding chains. However, within each sliding configuration the magnitude of the interfacial atomic displacements exhibits little dependence on load over the range considered. The predicted friction coefficients are also found to vary with chain orientation and are in excellent quantitative agreement with experimental measurements.

Dynamic analysis of elastic rubber tired car wheel breaking under variable normal load

NASA Astrophysics Data System (ADS)

Fedotov, A. I.; Zedgenizov, V. G.; Ovchinnikova, N. I.

2017-10-01

The purpose of the paper is to analyze the dynamics of the braking of the wheel under normal load variations. The paper uses a mathematical simulation method according to which the calculation model of an object as a mechanical system is associated with a dynamically equivalent schematic structure of the automatic control. Transfer function tool analyzing structural and technical characteristics of an object as well as force disturbances were used. It was proved that the analysis of dynamic characteristics of the wheel subjected to external force disturbances has to take into account amplitude and phase-frequency characteristics. Normal load variations impact car wheel braking subjected to disturbances. The closer slip to the critical point is, the higher the impact is. In the super-critical area, load variations cause fast wheel blocking.

The effect of normal load on polytetrafluoroethylene tribology

NASA Astrophysics Data System (ADS)

Barry, Peter R.; Chiu, Patrick Y.; Perry, Scott S.; Sawyer, W. Gregory; Phillpot, Simon R.; Sinnott, Susan B.

2009-04-01

The tribological behavior of oriented poly(tetrafluoroethylene) (PTFE) sliding surfaces is examined as a function of sliding direction and applied normal load in classical molecular dynamics (MD) simulations. The forces are calculated with the second-generation reactive empirical bond-order potential for short-range interactions, and with a Lennard-Jones potential for long-range interactions. The range of applied normal loads considered is 5-30 nN. The displacement of interfacial atoms from their initial positions during sliding is found to vary by a factor of seven, depending on the relative orientation of the sliding chains. However, within each sliding configuration the magnitude of the interfacial atomic displacements exhibits little dependence on load over the range considered. The predicted friction coefficients are also found to vary with chain orientation and are in excellent quantitative agreement with experimental measurements.

Selective Effects of Training Against Weight and Inertia on Muscle Mechanical Properties.

PubMed

Djuric, Sasa; Cuk, Ivan; Sreckovic, Sreten; Mirkov, Dragan; Nedeljkovic, Aleksandar; Jaric, Slobodan

2016-10-01

To explore the effects of training against mechanically different types of loads on muscle force (F), velocity (V), and power (P) outputs. Subjects practiced maximum bench throws over 8 wk against a bar predominantly loaded by approximately constant external force (weight), weight plates (weight plus inertia), or weight plates whose weight was compensated by a constant external force pulling upward (inertia). Instead of a typically applied single trial performed against a selected load, the pretest and posttest consisted of the same task performed against 8 different loads ranging from 30% to 79% of the subject's maximum strength applied by adding weight plates to the bar. That provided a range of F and V data for subsequent modeling by linear F-V regression revealing the maximum F (F-intercept), V (V-intercept), and P (P = FV/4). Although all 3 training conditions resulted in increased P, the inertia type of the training load could be somewhat more effective than weight. An even more important finding was that the P increase could be almost exclusively based on a gain in F, V, or both when weight, inertia, or weight-plus-inertia training load were applied, respectively. The inertia training load is more effective than weight in increasing P and weight and inertia may be applied for selective gains in F and V, respectively, whereas the linear F-V model obtained from loaded trials could be used for discerning among muscle F, V, and P.

14 CFR 27.321 - General.

Code of Federal Regulations, 2010 CFR

2010-01-01

... STANDARDS: NORMAL CATEGORY ROTORCRAFT Strength Requirements Flight Loads § 27.321 General. (a) The flight load factor must be assumed to act normal to the longitudinal axis of the rotorcraft, and to be equal... from the design minimum weight to the design maximum weight; and (2) With any practical distribution of...

Economic Load Dispatch Using Adaptive Social Acceleration Constant Based Particle Swarm Optimization

NASA Astrophysics Data System (ADS)

Jain, N. K.; Nangia, Uma; Jain, Jyoti

2018-04-01

In this paper, an Adaptive Social Acceleration Constant based Particle Swarm Optimization (ASACPSO) has been developed which uses the best value of social acceleration constant (Csg). Three formulations of Csg have been used to search for the best value of Csg. These three formulations led to the development of three algorithms-ALDPSO, AELDPSO-I and AELDPSO-II which were implemented for Economic Load Dispatch of IEEE 5 bus, 14 bus and 30 bus systems. The best value of Csg was selected based on the minimum number of Kounts i.e. number of function evaluations required to minimize the function. This value of Csg was directly used in basic PSO algorithm which led to the development of ASACPSO algorithm. ASACPSO was found to converge faster and give more accurate results compared to BPSO for IEEE 5, 14 and 30 bus systems.

Evolution of permeability and Biot coefficient at high mean stresses in high porosity sandstone

DOE PAGES

Ingraham, Mathew D.; Bauer, Stephen J.; Issen, Kathleen A.; ...

2017-05-01

A series of constant mean stress (CMS) and constant shear stress (CSS) tests were performed to investigate the evolution of permeability and Biot coefficient at high mean stresses in a high porosity reservoir analog (Castlegate sandstone). Permeability decreases as expected with increasing mean stress, from about 20 Darcy at the beginning of the tests to between 1.5 and 0.3 Darcy at the end of the tests (mean stresses up to 275 MPa). The application of shear stress causes permeability to drop below that of a hydrostatic test at the same mean stress. Results show a nearly constant rate decrease inmore » the Biot coefficient as the mean stress increases during hydrostatic loading, and as the shear stress increases during CMS loading. In conclusion, CSS tests show a stabilization of the Biot coefficient after the application of shear stress.« less

Evolution of permeability and Biot coefficient at high mean stresses in high porosity sandstone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ingraham, Mathew D.; Bauer, Stephen J.; Issen, Kathleen A.

A series of constant mean stress (CMS) and constant shear stress (CSS) tests were performed to investigate the evolution of permeability and Biot coefficient at high mean stresses in a high porosity reservoir analog (Castlegate sandstone). Permeability decreases as expected with increasing mean stress, from about 20 Darcy at the beginning of the tests to between 1.5 and 0.3 Darcy at the end of the tests (mean stresses up to 275 MPa). The application of shear stress causes permeability to drop below that of a hydrostatic test at the same mean stress. Results show a nearly constant rate decrease inmore » the Biot coefficient as the mean stress increases during hydrostatic loading, and as the shear stress increases during CMS loading. In conclusion, CSS tests show a stabilization of the Biot coefficient after the application of shear stress.« less

Double synchronized switch harvesting (DSSH): a new energy harvesting scheme for efficient energy extraction.

PubMed

Lallart, Mickaël; Garbuio, Lauric; Petit, Lionel; Richard, Claude; Guyomar, Daniel

2008-10-01

This paper presents a new technique for optimized energy harvesting using piezoelectric microgenerators called double synchronized switch harvesting (DSSH). This technique consists of a nonlinear treatment of the output voltage of the piezoelectric element. It also integrates an intermediate switching stage that ensures an optimal harvested power whatever the load connected to the microgenerator. Theoretical developments are presented considering either constant vibration magnitude, constant driving force, or independent extraction. Then experimental measurements are carried out to validate the theoretical predictions. This technique exhibits a constant output power for a wide range of load connected to the microgenerator. In addition, the extracted power obtained using such a technique allows a gain up to 500% in terms of maximal power output compared with the standard energy harvesting method. It is also shown that such a technique allows a fine-tuning of the trade-off between vibration damping and energy harvesting.

Fuel Composition Effects at Constant RON and MON in an HCCI Engine Operated with Negative Valve Overlap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bunting, Bruce G; Farrell, John T

2006-01-01

The effects of fuel properties on gasoline HCCI operation have been investigated in a single cylinder, 500 cc, 11.3 CR port fuel injected research engine, operated at lambda=1 and equipped with hydraulic valve actuation. HCCI is promoted by early exhaust valve closing to retain hot exhaust in the cylinder, thereby increasing the cylinder gas temperature. Test fuels were formulated with pure components to have the same RON, MON, and octane sensitivity as an indolene reference fuel, but with a wide range of fuel composition differences. Experiments have been carried out to determine if fuel composition plays a role in HCCImore » combustion properties, independent of octane numbers. Fuel economy, emissions, and combustion parameters have been measured at several fixed speed/load conditions over a range of exhaust valve closing angles. When the data are compared at constant combustion phasing, fuel effects on emissions and other combustion properties are small. However, when compared at constant exhaust valve closing angle, fuel composition effects are more pronounced, specifically regarding ignition. Operability range differences are also related to fuel composition. An all-paraffinic (normal, iso, and cycloparaffins) fuel exhibited distinctly earlier combustion phasing, increased rate of cylinder pressure rise, and increased rate of maximum heat release compared to the indolene reference fuel. Conversely, olefin-containing fuels exhibited retarded combustion phasing. The fuels with the most advanced ignition showed a wider operating range in terms of engine speed and load, irrespective of exhaust closing angle. These ignition differences reflect contributions from both fuel and EGR kinetics, the effects of which are discussed. The fuel composition variables are somewhat inter-correlated, which makes the experimental separation their effects imprecise with this small set of fuels, though clear trends are evident. The overall effects of fuel composition on engine performance and emissions are small. However, the results suggest that the effects on combustion phasing and engine operability range may need to be considered in the practical implementation of HCCI for fuels with large compositional variations.« less

Caed Interactions During A Product Life Cycle Oriented Towards the Decision-Making in the Design of Polymeric Elements

NASA Astrophysics Data System (ADS)

Suffo, M.

2017-08-01

In this work, we present the real case of an industrial product was placed prematurely on the market without having checked the different stages of its life cycle. This type of products must be validated by numerical methods and by mechanical tests to verify their rheological behavior. In particular, the product consists of two small pieces in contact, one made of HDPE and the other one corresponding to a stainless steel. The polymeric piece supports the metal pressure under a constant static load over time. As a result of normal operation, the polymer experienced a “crazing” breakdown, which caused the failure to occur. In the study, design methods and computer assisted analysis software (CAED) have been used. These methods were complemented by scanning electron microscopy that confirmed the initial failure hypothesis. Using the finite element method (FEM), a series of load scenarios were carried out, where the different load hypothesis the product must go through prior to its placing on the market were simulated. It is shown that the failure was initiated by stress concentration on one of the edges of the polymeric piece. The proposed solution of the problem based on the analysis focuses on a simple redesign of the piece, which should have been round, or to the reduction of the thickness of the metal piece. As a result of the alteration of its natural life cycle, the company assumed both monetary costs and the definitive loss of customer confidence.

Ground reaction forces and plantar pressure distribution during occasional loaded gait.

PubMed

Castro, Marcelo; Abreu, Sofia; Sousa, Helena; Machado, Leandro; Santos, Rubim; Vilas-Boas, João Paulo

2013-05-01

This study compared the ground reaction forces (GRF) and plantar pressures between unloaded and occasional loaded gait. The GRF and plantar pressures of 60 participants were recorded during unloaded gait and occasional loaded gait (wearing a backpack that raised their body mass index to 30); this load criterion was adopted because is considered potentially harmful in permanent loaded gait (obese people). The results indicate an overall increase (absolute values) of GRF and plantar pressures during occasional loaded gait (p < 0.05); also, higher normalized (by total weight) values in the medial midfoot and toes, and lower values in the lateral rearfoot region were observed. During loaded gait the magnitude of the vertical GRF (impact and thrust maximum) decreased and the shear forces increased more than did the proportion of the load (normalized values). These data suggest a different pattern of GRF and plantar pressure distribution during occasional loaded compared to unloaded gait. Copyright © 2012 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Possible Economies in Air-Conditioning by Accepting Temperature Swings.

ERIC Educational Resources Information Center

Loudon, A. G.; Petherbridge, P.

Public building air conditioning systems, which use constant and varying heat and cooling loads, are compared and investigated. Experiments indicated that constant temperature controls based on outside air temperature alone were inefficient. Ventilating a building with outside air and the methods of doing so are cited as being the most economical…

Analysis of Ares Crew Launch Vehicle Transonic Alternating Flow Phenomenon

NASA Technical Reports Server (NTRS)

Sekula, Martin K.; Piatak, David J.; Rausch, Russ D.

2012-01-01

A transonic wind tunnel test of the Ares I-X Rigid Buffet Model (RBM) identified a Mach number regime where unusually large buffet loads are present. A subsequent investigation identified the cause of these loads to be an alternating flow phenomenon at the Crew Module-Service Module junction. The conical design of the Ares I-X Crew Module and the cylindrical design of the Service Module exposes the vehicle to unsteady pressure loads due to the sudden transition between a subsonic separated and a supersonic attached flow about the cone-cylinder junction as the local flow randomly fluctuates back and forth between the two flow states. These fluctuations produce a square-wave like pattern in the pressure time histories resulting in large amplitude, impulsive buffet loads. Subsequent testing of the Ares I RBM found much lower buffet loads since the evolved Ares I design includes an ogive fairing that covers the Crew Module-Service Module junction, thereby making the vehicle less susceptible to the onset of alternating flow. An analysis of the alternating flow separation and attachment phenomenon indicates that the phenomenon is most severe at low angles of attack and exacerbated by the presence of vehicle protuberances. A launch vehicle may experience either a single or, at most, a few impulsive loads since it is constantly accelerating during ascent rather than dwelling at constant flow conditions in a wind tunnel. A comparison of a windtunnel- test-data-derived impulsive load to flight-test-data-derived load indicates a significant over-prediction in the magnitude and duration of the buffet load. I. Introduction One

Development of a tester for evaluation of prototype thermal cells and batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guidotti, R.A.

1994-10-01

A tester was developed to evaluate prototype thermal cells and batteries--especially high-voltage units--under a wide range of constant-current and constant-resistance discharge conditions. Programming of the steady-state and pulsing conditions was by software control or by hardware control via an external pulse generator. The tester was assembled from primarily Hewlett-Packard (H-P) instrumentation and was operated under H-P`s Rocky Mountain Basic (RMB). Constant-current electronic loads rated up to 4 kW (400 V at up to 100 A) were successfully used with the setup. For testing under constant-resistance conditions, power metal-oxide field-effect transistors (MOSFETs) controlled by a programmable pulse generator were used tomore » switch between steady-state and pulse loads. The pulses were digitized at up to a 50 kHz rate (20 {mu} s/pt) using high-speed DVMs; steady-state voltages were monitored with standard DVMs. This paper describes several of the test configurations used and discusses the limitations of each. Representative data are presented for a number of the test conditions.« less

Stresses in adhesively bonded joints: A closed form solution. [plate theory

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.; Aydinoglu, M. N.

1980-01-01

The plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered. Assuming that the thicknesses of the adherends are constant and are small in relation to the lateral dimensions of the bonded region, the adherends are treated as plates. The transverse shear effects in the adherends and the in-plane normal strain in the adhesive are taken into account. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form. A single lap joint and a stiffened plate under various loading conditions are considered as examples. To verify the basic trend of the solutions obtained from the plate theory a sample problem is solved by using the finite element method and by treating the adherends and the adhesive as elastic continua. The plate theory not only predicts the correct trend for the adhesive stresses but also gives rather surprisingly accurate results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pirrung, Georg; Madsen, Helge; Schreck, Scott

Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against stand still measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in case of the elliptical wing, but underpredicts the steady loading for the Phase VI blade in attached flow. The predictionmore » of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible.« less

Trailed vorticity modeling for aeroelastic wind turbine simulations in stand still

DOE PAGES

Pirrung, Georg; Madsen, Helge; Schreck, Scott

2016-10-03

Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against stand still measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in case of the elliptical wing, but underpredicts the steady loading for the Phase VI blade in attached flow. The predictionmore » of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible.« less

Thermal analyses of the IF-300 shipping cask

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meier, J.K.

1978-07-01

In order to supply temperature data for structural testing and analysis of shipping casks, a series of thermal analyses using the TRUMP thermal analyzer program were performed on the GE IF-300 spent fuel shipping cask. Major conclusions of the analyses are: (1) Under normal cooling conditions and a cask heat load of 262,000 BTU/h, the seal area of the cask will be roughly 100/sup 0/C (180/sup 0/F) above the ambient surroundings. (2) Under these same conditions the uranium shield at the midpoint of the cask will be between 69/sup 0/C (125/sup 0/F) and 92/sup 0/C (166/sup 0/F) above the ambientmore » surroundings. (3) Significant thermal gradients are not likely to develop between the head studs and the surrounding metal. (4) A representative time constant for the cask as a whole is on the order of one day.« less

Axial force and efficiency tests of fixed center variable speed belt drive

NASA Technical Reports Server (NTRS)

Bents, D. J.

1981-01-01

An investigation of how the axial force varies with the centerline force at different speed ratios, speeds, and loads, and how the drive's transmission efficiency is affected by these related forces is described. The tests, intended to provide a preliminary performance and controls characterization for a variable speed belt drive continuously variable transmission (CVT), consisted of the design and construction of an experimental test rig geometrically similar to the CVT, and operation of that rig at selected speed ratios and power levels. Data are presented which show: how axial forces exerted on the driver and driven sheaves vary with the centerline force at constant values of speed ratio, speed, and output power; how the transmission efficiency varies with centerline force and how it is also a function of the V belt coefficient; and the axial forces on both sheaves as normalized functions of the traction coefficient.

The Faraday effect of natural and artificial ferritins.

PubMed

Koralewski, M; Kłos, J W; Baranowski, M; Mitróová, Z; Kopčanský, P; Melníková, L; Okuda, M; Schwarzacher, W

2012-09-07

Measurements of the Faraday rotation at room temperature over the light wavelength range of 300-680 nm for horse spleen ferritin (HSF), magnetoferritin with different loading factors (LFs) and nanoscale magnetite and Fe(2)O(3) suspensions are reported. The Faraday rotation and the magnetization of the materials studied present similar magnetic field dependences and are characteristic of a superparamagnetic system. The dependence of the Faraday rotation on the magnetic field is described, excluding HSF and Fe(2)O(3), by a Langevin function with a log-normal distribution of the particle size allowing the core diameters of the substances studied to be calculated. It was found that the specific Verdet constant depends linearly on the LF. Differences in the Faraday rotation spectra and their magnetic field dependences allow discrimination between magnetoferritin with maghemite and magnetite cores which can be very useful in biomedicine.

MEPDG Traffic Loading Defaults Derived from Traffic Pooled Fund Study

DOT National Transportation Integrated Search

2016-04-01

As part of traffic loading inputs, the Mechanistic-Empirical Pavement Design Guide (MEPDG), Interim Edition: A Manual of Practice requires detailed axle loading information in the form of normalized axle load spectra (NALS), number of axle per truck ...

Henry constant and isosteric heat at zero-loading for gas adsorption in carbon nanotubes.

PubMed

Do, D D; Do, H D; Wongkoblap, A; Nicholson, D

2008-12-28

The Henry constant and the isosteric heat of adsorption at zero loading in a carbon nanotube bundle are studied with Monte Carlo integration for the adsorption of gases over a range of temperatures. The spacing between nanotubes in a bundle is determined from the minimization of potential energy of interaction between these tubes. We study different tube configurations with bundles of 2, 3, 4 and 7 tubes. Depending on the configuration it is found that the spacing is of between 0.31 to 0.333 nm, and this falls within the range reported in the literature. The Henry constant has been carefully defined so that it will not become negative at high temperatures. This is done with the aid of accessible volume, rather than the usual absolute void volume. We show that linearity of the van't Hoff plot for the Henry constant is not strictly followed. Furthermore the slope of this plot is not equal to the isosteric heat of adsorption at zero loading, which is found to be a strong function of temperature. From the results we find that the Henry constant and the heat of adsorption depend on the tube configuration. In general the adsorption in the cusp interstices is strongest followed by that inside the tube and finally on the outer surface. However for very small tubes adsorption occurs inside the tube first. For molecules with orientation, the behaviour is even more interesting and the shape of the isosteric heat versus temperature depends on the degree of orientation, tube configuration and the domain of adsorption (interstices, inside the tube and on the outer surface).

Biodegradation of propylene glycol and associated hydrodynamic effects in sand.

PubMed

Bielefeldt, Angela R; Illangasekare, Tissa; Uttecht, Megan; LaPlante, Rosanna

2002-04-01

At airports around the world, propylene glycol (PG) based fluids are used to de-ice aircraft for safe operation. PG removal was investigated in 15-cm deep saturated sand columns. Greater than 99% PG biodegradation was achieved for all flow rates and loading conditions tested, which decreased the hydraulic conductivity of the sand by 1-3 orders of magnitude until a steady-state minimum was reached. Under constant loading at 120 mg PG/d for 15-30 d, the hydraulic conductivity (K) decreased by 2-2.5 orders of magnitude when the average linear velocity of the water was 4.9-1.4 cm/h. Variable PG loading in recirculation tests resulted in slower conductivity declines and lower final steady-state conductivity than constant PG feeding. After significant sand plugging, endogenous periods of time without PG resulted in significant but partial recovery of the original conductivity. Biomass growth also increased the dispersivity of the sand.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Measurement and analysis of critical crack tip processes during fatigue crack growth

NASA Technical Reports Server (NTRS)

Davidson, D. L.; Hudak, S. J.; Dexter, R. J.

1985-01-01

The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied.

Testing activities at the National Battery Test Laboratory

NASA Astrophysics Data System (ADS)

Hornstra, F.; Deluca, W. H.; Mulcahey, T. P.

The National Battery Test Laboratory (NBTL) is an Argonne National Laboratory facility for testing, evaluating, and studying advanced electric storage batteries. The facility tests batteries developed under Department of Energy programs and from private industry. These include batteries intended for future electric vehicle (EV) propulsion, electric utility load leveling (LL), and solar energy storage. Since becoming operational, the NBTL has evaluated well over 1400 cells (generally in the form of three- to six-cell modules, but up to 140-cell batteries) of various technologies. Performance characterization assessments are conducted under a series of charge/discharge cycles with constant current, constant power, peak power, and computer simulated dynamic load profile conditions. Flexible charging algorithms are provided to accommodate the specific needs of each battery under test. Special studies are conducted to explore and optimize charge procedures, to investigate the impact of unique load demands on battery performance, and to analyze the thermal management requirements of battery systems.

The effect of matrix mechanical properties on (0)8 unidirectional SiC/Ti composite fatigue resistance

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Gayda, J.; Lerch, B. A.; Halford, G. R.

1991-01-01

The relationship between constituent and MMC properties in fatigue loading is investigated with low-cycle fatigue-resistance testing of an alloy Ti-15-3 matrix reinforced with SiC SCS-6 fibers. The fabrication of the composite is described, and specimens are generated that are weak and ductile (WD), strong and moderately ductile (SM), or strong and brittle (SB). Strain is measured during MMC fatigue tests at a constant load amplitude with a load-controlled waveform and during matrix-alloy fatigue tests at a constant strain amplitude using a strain-controlled waveform. The fatigue resistance of the (0)8 SiC/Ti-15-3 composite is found to be slightly influenced by matrix mechanical properties, and the composite- and matrix-alloy fatigue lives are not correlated. This finding is suggested to relate to the different crack-initiation and -growth processes in MMCs and matrix alloys.

Human respiratory syncytial virus load normalized by cell quantification as predictor of acute respiratory tract infection.

PubMed

Gómez-Novo, Miriam; Boga, José A; Álvarez-Argüelles, Marta E; Rojo-Alba, Susana; Fernández, Ana; Menéndez, María J; de Oña, María; Melón, Santiago

2018-05-01

Human respiratory syncytial virus (HRSV) is a common cause of respiratory infections. The main objective is to analyze the prediction ability of viral load of HRSV normalized by cell number in respiratory symptoms. A prospective, descriptive, and analytical study was performed. From 7307 respiratory samples processed between December 2014 to April 2016, 1019 HRSV-positive samples, were included in this study. Low respiratory tract infection was present in 729 patients (71.54%). Normalized HRSV load was calculated by quantification of HRSV genome and human β-globin gene and expressed as log10 copies/1000 cells. HRSV mean loads were 4.09 ± 2.08 and 4.82 ± 2.09 log10 copies/1000 cells in the 549 pharyngeal and 470 nasopharyngeal samples, respectively (P < 0.001). The viral mean load was 4.81 ± 1.98 log10 copies/1000 cells for patients under the age of 4-year-old (P < 0.001). The viral mean loads were 4.51 ± 2.04 cells in patients with low respiratory tract infection and 4.22 ± 2.28 log10 copies/1000 cells with upper respiratory tract infection or febrile syndrome (P < 0.05). A possible cut off value to predict LRTI evolution was tentatively established. Normalization of viral load by cell number in the samples is essential to ensure an optimal virological molecular diagnosis avoiding that the quality of samples affects the results. A high viral load can be a useful marker to predict disease progression. © 2018 Wiley Periodicals, Inc.

Microstructure and tribological properties of TiCu2Al intermetallic compound coating

NASA Astrophysics Data System (ADS)

Guo, Chun; Zhou, Jiansong; Zhao, Jierong; Wang, Linqian; Yu, Youjun; Chen, Jianmin; Zhou, Huidi

2011-04-01

TiCu2Al ternary intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding. Tribological properties of the prepared TiCu2Al intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiCu2Al intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiCu2Al intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate first increased and then decreased at normal load from 5 to 15 N.

Airplane Stress Analysis

NASA Technical Reports Server (NTRS)

Zahm, A F; Crook, L H

1918-01-01

Report presents stress analysis of individual components of an airplane. Normal and abnormal loads, sudden loads, simple stresses, indirect simple stresses, resultant unit stress, repetitive and equivalent stress, maximum steady load and stress are considered.

Acid-base transport systems in a polarized human intestinal cell monolayer: Caco-2.

PubMed

Osypiw, J C; Gleeson, D; Lobley, R W; Pemberton, P W; McMahon, R F

1994-09-01

Acid-base transport systems have been incompletely characterized in intact intestinal epithelial cells. We therefore studied the human cell line Caco-2, cultured on Teflon membranes to form confluent monolayers with apical microvilli on transmission electron microscopy and progressive enrichment in microvillar hydrolases. Monolayers (16- to 25-day-old), loaded with the pH-sensitive dye BCECF-AM (2',7'-bis (carboxyethyl)-5-carboxyfluorescein), were mounted in a spectrofluorometer cuvette to allow selective superfusion of apical and basolateral surfaces with Hepes- or HCO(3-)-buffered media. Intracellular pH (pHi) was measured by dual-excitation spectrofluorimetry; calibration was with standards containing nigericin and 110 mM K+ corresponding to measured intracellular [K+] in Caco-2 cell monolayers. In HCO(3-)-free (Hepes-buffered) media, bilateral superfusion with 1 mM amiloride or with Na(+)-free media reversibly inhibited pHi recovery from an intracellular acid load (NH4Cl pulse) by 86 and 98% respectively. Selective readdition of Na+ to the apical or basolateral superfusate also induced a pHi recovery, which was inhibited by ipsilateral but not by contralateral amiloride (1 mM). The pHi recovery induced by apical Na+ readdition had a Michaelis constant (Km) for Na+ of 30 mM and a relatively high inhibitor constant (Ki) for amiloride of 45.5 microM. Initial pHi in HCO(3-)-buffered media was lower than in the absence of HCO3- (7.35 vs. 7.80). pHi recovery from an acid load in HCO3- was Na- dependent but was inhibited only 18% by 1 mM amiloride. The amiloride-independent pHi recovery was inhibited 49% by pre-incubation of cells in 5 mM DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid). These data suggest that Caco-2 cells possess: (a) both apical and basolateral membrane Na(+)-H+ exchange mechanisms, the apical exchanger being relatively resistant to amiloride, similar to apical Na(+)-H+ exchangers in several normal epithelia; and (b) a Na(-)-dependent HCO3- transport system, either Na(+)-HCO3- cotransport or Na(-)-dependent Cl(-)-HCO3- exchange.

Gallium uptake by transferrin and interaction with receptor 1.

PubMed

Chikh, Zohra; Ha-Duong, Nguyêt-Thanh; Miquel, Geneviève; El Hage Chahine, Jean-Michel

2007-01-01

The kinetics and thermodynamics of Ga(III) exchange between gallium mononitrilotriacetate and human serum transferrin as well as those of the interaction between gallium-loaded transferrin and the transferrin receptor 1 were investigated in neutral media. Gallium is exchanged between the chelate and the C-site of human serum apotransferrin in interaction with bicarbonate in about 50 s to yield an intermediate complex with an equilibrium constant K (1) = (3.9 +/- 1.2) x 10(-2), a direct second-order rate constant k (1) = 425 +/- 50 M(-1) s(-1) and a reverse second-order rate constant k (-1) = (1.1 +/- 3) x 10(4) M(-1) s(-1). The intermediate complex loses a single proton with proton dissociation constant K (1a) = 80 +/- 40 nM to yield a first kinetic product. This product then undergoes a modification in its conformation which lasts about 500 s to produce a second kinetic intermediate, which in turn undergoes a final extremely slow (several hours) modification in its conformation to yield the gallium-saturated transferrin in its final state. The mechanism of gallium uptake differs from that of iron and does not involve the same transitions in conformation reported during iron uptake. The interaction of gallium-loaded transferrin with the transferrin receptor occurs in a single very fast kinetic step with a dissociation constant K (d) = 1.10 +/- 0.12 microM and a second-order rate constant k (d) = (1.15 +/- 0.3) x 10(10) M(-1) s(-1). This mechanism is different from that observed with the ferric holotransferrin and suggests that the interaction between the receptor and gallium-loaded transferrin probably takes place on the helical domain of the receptor which is specific for the C-site of transferrin and HFE. The relevance of gallium incorporation by the transferrin receptor-mediated iron-acquisition pathway is discussed.

Short-Term Effects of Different Loading Schemes in Fitness-Related Resistance Training.

PubMed

Eifler, Christoph

2016-07-01

Eifler, C. Short-term effects of different loading schemes in fitness-related resistance training. J Strength Cond Res 30(7): 1880-1889, 2016-The purpose of this investigation was to analyze the short-term effects of different loading schemes in fitness-related resistance training and to identify the most effective loading method for advanced recreational athletes. The investigation was designed as a longitudinal field-test study. Two hundred healthy mature subjects with at least 12 months' experience in resistance training were randomized in 4 samples of 50 subjects each. Gender distribution was homogenous in all samples. Training effects were quantified by 10 repetition maximum (10RM) and 1 repetition maximum (1RM) testing (pre-post-test design). Over a period of 6 weeks, a standardized resistance training protocol with 3 training sessions per week was realized. Testing and training included 8 resistance training exercises in a standardized order. The following loading schemes were randomly matched to each sample: constant load (CL) with constant volume of repetitions, increasing load (IL) with decreasing volume of repetitions, decreasing load (DL) with increasing volume of repetitions, daily changing load (DCL), and volume of repetitions. For all loading schemes, significant strength gains (p < 0.001) could be noted for all resistance training exercises and both dependent variables (10RM, 1RM). In all cases, DCL obtained significantly higher strength gains (p < 0.001) than CL, IL, and DL. There were no significant differences in strength gains between CL, IL, and DL. The present data indicate that resistance training following DCL is more effective for advanced recreational athletes than CL, IL, or DL. Considering that DCL is widely unknown in fitness-related resistance training, the present data indicate, there is potential for improving resistance training in commercial fitness clubs.

Fatigue History and in-situ Loading Studies of the overload Effect Using High Resolution X-ray Strain Profiling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft,M.; Jisrawi, N.; Zhong, Z.

High-energy synchrotron X-ray diffraction experiments are used to perform local crack plane strain profiling of 4140 steel compact tension specimens fatigued at constant amplitude, subjected to a single overload cycle, then fatigued some more at constant amplitude. X-ray strain profiling results on a series of samples employing in-situ load cycling are correlated with the crack growth rate (da/dN) providing insight into the da/dN retardation known as the 'overload effect'. Immediately after the overload, the strain under maximum load is greatly reduced but the range of strain, between zero and maximum load, remains unchanged compared to the pre-overload values. At themore » point of maximum retardation, it is the strain range that is greatly reduced while the maximum-load strain has begun to recover to the pre-overload value. For a sample that has recovered to approximately half of the original da/dN value following the overload, the strain at maximum load is fully recovered while the strain range, though partially recovered, is still substantially reduced. The dominance of the strain range in the overload effect is clearly indicated. Subject to some assumptions, strong quantitative support for a crack growth rate driving force of the suggested form [(K{sub max}){sup -p}({Delta}K){sup p}]{sup {gamma}} is found. A dramatic nonlinear load dependence in the spatial distribution of the strain at maximum retardation is also demonstrated: at low load the response is dominantly at the overload position; whereas at high loads it is dominantly at the crack tip position. This transfer of load response away from the crack tip to the overload position appears fundamental to the overload effect for high R-ratio fatigue as studied here.« less

Axial-Load Fatigue Tests on 17-7 PH Stainless Steel Under Constant-Amplitude Loading

NASA Technical Reports Server (NTRS)

Leybold, Herbert A.

1960-01-01

Axial-load fatigue tests were conducted at room temperature on notched and unnotched sheet specimens of 17-7 PH stainless steel in Condition TH 1050. The notched specimens had theoretical stress-concentration factors of 2.32, 4.00, and 5.00. All specimens were tested under completely reversed loading. S-N curves are presented for each specimen configuration and ratios of fatigue strengths of unnotched specimens to those of notched specimens are given. Predictions of the fatigue behavior of notched specimens near the fatigue limit were made.

Elevated temperature biaxial fatigue

NASA Technical Reports Server (NTRS)

Jordan, E. H.

1983-01-01

Biaxial fatigue is often encountered in the complex thermo-mechanical loadings present in gas turbine engines. Engine strain histories can involve non-constant temperature, mean stress, creep, environmental effects, both isotropic and anisotropic materials and non-proportional loading. Life prediction for the general case involving all the above factors is not a practicable research project. The current research program is limited to isothermal fatigue at room temperature and 1200 F of Hastalloy-X for both proportional and non-proportional loading. An improved method for predicting the fatigue life and deformation response under biaxial cycle loading is sought.

14 CFR 27.341 - Gust loads.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Gust loads. 27.341 Section 27.341 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Strength Requirements Flight Loads § 27.341 Gust loads. The rotorcraft...

14 CFR 27.341 - Gust loads.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Gust loads. 27.341 Section 27.341 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Strength Requirements Flight Loads § 27.341 Gust loads. The rotorcraft...

14 CFR 27.681 - Limit load static tests.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Design and Construction Control Systems § 27.681 Limit load... which— (1) The direction of the test loads produces the most severe loading in the control system; and... requirements for control system joints subject to angular motion. ...

Excited state proton transfer in the lysosome of live lung cells: normal and cancer cells.

PubMed

Chowdhury, Rajdeep; Saha, Abhijit; Mandal, Amit Kumar; Jana, Batakrishna; Ghosh, Surajit; Bhattacharyya, Kankan

2015-02-12

Dynamics of excited state proton transfer (ESPT) in the lysosome region of live lung cells (normal and cancer) is studied by picosecond time-resolved confocal microscopy. For this, we used a fluorescent probe, pyranine (8-hydroxy-pyrene-1,3,6-trisulfonate, HPTS). From the colocalization of HPTS with a lysotracker dye (lysotracker yellow), we confirmed that HPTS resides in the lysosome for both of the cells. The diffusion coefficient (Dt) in the lysosome region was obtained from fluorescence correlation spectroscopy (FCS). From Dt, the viscosity of lysosome is estimated to be ∼40 and ∼30 cP in the cancer and normal cells, respectively. The rate constants of the elementary steps of ESPT in a normal lung cell (WI38) are compared with those in a lung cancer cell (A549). It is observed that the time constant of the initial proton transfer process in a normal cell (τ(PT) = 40 ps) is similar to that in a cancer cell. The recombination of the geminate ion pair is slightly faster (τ(rec) = 25 ps) in the normal cell than that (τ(rec) = 30 ps) in a cancer cell. The time constant of the dissociation (τ(diss)) of the geminate ion pair for the cancer cell (τ(diss) = 80 ps) is 1.5 times faster compared to that (τ(diss) = 120 ps) in a normal cell.

Calculation method for steady-state pollutant concentration in mixing zones considering variable lateral diffusion coefficient.

PubMed

Wu, Wen; Wu, Zhouhu; Song, Zhiwen

2017-07-01

Prediction of the pollutant mixing zone (PMZ) near the discharge outfall in Huangshaxi shows large error when using the methods based on the constant lateral diffusion assumption. The discrepancy is due to the lack of consideration of the diffusion coefficient variation. The variable lateral diffusion coefficient is proposed to be a function of the longitudinal distance from the outfall. Analytical solution of the two-dimensional advection-diffusion equation of a pollutant is derived and discussed. Formulas to characterize the geometry of the PMZ are derived based on this solution, and a standard curve describing the boundary of the PMZ is obtained by proper choices of the normalization scales. The change of PMZ topology due to the variable diffusion coefficient is then discussed using these formulas. The criterion of assuming the lateral diffusion coefficient to be constant without large error in PMZ geometry is found. It is also demonstrated how to use these analytical formulas in the inverse problems including estimating the lateral diffusion coefficient in rivers by convenient measurements, and determining the maximum allowable discharge load based on the limitations of the geometrical scales of the PMZ. Finally, applications of the obtained formulas to onsite PMZ measurements in Huangshaxi present excellent agreement.

Characterization for elastic constants of fused deposition modelling-fabricated materials based on the virtual fields method and digital image correlation

NASA Astrophysics Data System (ADS)

Cao, Quankun; Xie, Huimin

2017-12-01

Fused deposition modelling (FDM), a widely used rapid prototyping process, is a promising technique in manufacturing engineering. In this work, a method for characterizing elastic constants of FDM-fabricated materials is proposed. First of all, according to the manufacturing process of FDM, orthotropic constitutive model is used to describe the mechanical behavior. Then the virtual fields method (VFM) is applied to characterize all the mechanical parameters (Q_{11}, Q_{22}, Q_{12}, Q_{66}) using the full-field strain, which is measured by digital image correlation (DIC). Since the principal axis of the FDM-fabricated structure is sometimes unknown due to the complexity of the manufacturing process, a disk in diametrical compression is used as the load configuration so that the loading angle can be changed conveniently. To verify the feasibility of the proposed method, finite element method (FEM) simulation is conducted to obtain the strain field of the disk. The simulation results show that higher accuracy can be achieved when the loading angle is close to 30°. Finally, a disk fabricated by FDM was used for the experiment. By rotating the disk, several tests with different loading angles were conducted. To determine the position of the principal axis in each test, two groups of parameters (Q_{11}, Q_{22}, Q_{12}, Q_{66}) are calculated by two different groups of virtual fields. Then the corresponding loading angle can be determined by minimizing the deviation between two groups of the parameters. After that, the four constants (Q_{11}, Q_{22}, Q_{12}, Q_{66}) were determined from the test with an angle of 27°.

Circularly polarized antennas for active holographic imaging through barriers

DOEpatents

McMakin, Douglas L [Richland, WA; Severtsen, Ronald H [Richland, WA; Lechelt, Wayne M [West Richland, WA; Prince, James M [Kennewick, WA

2011-07-26

Circularly-polarized antennas and their methods of use for active holographic imaging through barriers. The antennas are dielectrically loaded to optimally match the dielectric constant of the barrier through which images are to be produced. The dielectric loading helps to remove barrier-front surface reflections and to couple electromagnetic energy into the barrier.

Bifurcation Analysis of a DC-DC Bidirectional Power Converter Operating with Constant Power Loads

NASA Astrophysics Data System (ADS)

Cristiano, Rony; Pagano, Daniel J.; Benadero, Luis; Ponce, Enrique

Direct current (DC) microgrids (MGs) are an emergent option to satisfy new demands for power quality and integration of renewable resources in electrical distribution systems. This work addresses the large-signal stability analysis of a DC-DC bidirectional converter (DBC) connected to a storage device in an islanding MG. This converter is responsible for controlling the balance of power (load demand and generation) under constant power loads (CPLs). In order to control the DC bus voltage through a DBC, we propose a robust sliding mode control (SMC) based on a washout filter. Dynamical systems techniques are exploited to assess the quality of this switching control strategy. In this sense, a bifurcation analysis is performed to study the nonlinear stability of a reduced model of this system. The appearance of different bifurcations when load parameters and control gains are changed is studied in detail. In the specific case of Teixeira Singularity (TS) bifurcation, some experimental results are provided, confirming the mathematical predictions. Both a deeper insight in the dynamic behavior of the controlled system and valuable design criteria are obtained.

Simulated remodeling of loaded collagen networks via strain-dependent enzymatic degradation and constant-rate fiber growth

PubMed Central

Hadi, M.F.; Sander, E.A.; Ruberti, J.W.; Barocas, V. H.

2011-01-01

Recent work has demonstrated that enzymatic degradation of collagen fibers exhibits strain-dependent kinetics. Conceptualizing how the strain dependence affects remodeling of collagenous tissues is vital to our understanding of collagen management in native and bioengineered tissues. As a first step towards this goal, the current study puts forward a multiscale model for enzymatic degradation and remodeling of collagen networks for two sample geometries we routinely use in experiments as model tissues. The multiscale model, driven by microstructural data from an enzymatic decay experiment, includes an exponential strain-dependent kinetic relation for degradation and constant growth. For a dogbone sample under uniaxial load, the model predicted that the distribution of fiber diameters would spread over the course of degradation because of variation in individual fiber load. In a cross-shaped sample, the central region, which experiences smaller, more isotropic loads, showed more decay and less spread in fiber diameter compared to the arms. There was also a slight shift in average orientation in different regions of the cruciform. PMID:22180691

14 CFR 23.485 - Side load conditions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Side load conditions. 23.485 Section 23.485... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Ground Loads § 23.485 Side load conditions. (a) For the side load condition, the airplane is assumed to be in a level attitude...

14 CFR 23.485 - Side load conditions.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Side load conditions. 23.485 Section 23.485... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Ground Loads § 23.485 Side load conditions. (a) For the side load condition, the airplane is assumed to be in a level attitude...

14 CFR 23.485 - Side load conditions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Side load conditions. 23.485 Section 23.485... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Ground Loads § 23.485 Side load conditions. (a) For the side load condition, the airplane is assumed to be in a level attitude...

Shoulder strength value differences between genders and age groups.

PubMed

Balcells-Diaz, Eudald; Daunis-I-Estadella, Pepus

2018-03-01

The strength of a normal shoulder differs according to gender and decreases with age. Therefore, the Constant score, which is a shoulder function measurement tool that allocates 25% of the final score to strength, differs from the absolute values but likely reflects a normal shoulder. To compare group results, a normalized Constant score is needed, and the first step to achieving normalization involves statistically establishing the gender differences and age-related decline. In this investigation, we sought to verify the gender difference and age-related decline in strength. We obtained a randomized representative sample of the general population in a small to medium-sized Spanish city. We then invited this population to participate in our study, and we measured their shoulder strength. We performed a statistical analysis with a power of 80% and a P value < .05. We observed a statistically significant difference between the genders and a statistically significant decline with age. To the best of our knowledge, this is the first investigation to study a representative sample of the general population from which conclusions can be drawn regarding Constant score normalization. Copyright © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Accurate Calibration and Uncertainty Estimation of the Normal Spring Constant of Various AFM Cantilevers

PubMed Central

Song, Yunpeng; Wu, Sen; Xu, Linyan; Fu, Xing

2015-01-01

Measurement of force on a micro- or nano-Newton scale is important when exploring the mechanical properties of materials in the biophysics and nanomechanical fields. The atomic force microscope (AFM) is widely used in microforce measurement. The cantilever probe works as an AFM force sensor, and the spring constant of the cantilever is of great significance to the accuracy of the measurement results. This paper presents a normal spring constant calibration method with the combined use of an electromagnetic balance and a homemade AFM head. When the cantilever presses the balance, its deflection is detected through an optical lever integrated in the AFM head. Meanwhile, the corresponding bending force is recorded by the balance. Then the spring constant can be simply calculated using Hooke’s law. During the calibration, a feedback loop is applied to control the deflection of the cantilever. Errors that may affect the stability of the cantilever could be compensated rapidly. Five types of commercial cantilevers with different shapes, stiffness, and operating modes were chosen to evaluate the performance of our system. Based on the uncertainty analysis, the expanded relative standard uncertainties of the normal spring constant of most measured cantilevers are believed to be better than 2%. PMID:25763650

Flexural creep of structural flakeboards under cyclic humidity

Treesearch

M.C. Yeh; R.C. Tang; Chung-Yun Hse

1990-01-01

Flexural creep behavior of randomly oriented structural flakeboards under cyclic humidity is presented. Specimens fabricated with 5 and 7 percent phenol-formaldehyde resin were subjected to constant concentrated load in bending under slow and fast cyclic relative humidity (RH) between 65 and 95 percent for 100 days. The temperature was set at a constant 75°F through...

Strength of Gamma Rhythm Depends on Normalization

PubMed Central

Ray, Supratim; Ni, Amy M.; Maunsell, John H. R.

2013-01-01

Neuronal assemblies often exhibit stimulus-induced rhythmic activity in the gamma range (30–80 Hz), whose magnitude depends on the attentional load. This has led to the suggestion that gamma rhythms form dynamic communication channels across cortical areas processing the features of behaviorally relevant stimuli. Recently, attention has been linked to a normalization mechanism, in which the response of a neuron is suppressed (normalized) by the overall activity of a large pool of neighboring neurons. In this model, attention increases the excitatory drive received by the neuron, which in turn also increases the strength of normalization, thereby changing the balance of excitation and inhibition. Recent studies have shown that gamma power also depends on such excitatory–inhibitory interactions. Could modulation in gamma power during an attention task be a reflection of the changes in the underlying excitation–inhibition interactions? By manipulating the normalization strength independent of attentional load in macaque monkeys, we show that gamma power increases with increasing normalization, even when the attentional load is fixed. Further, manipulations of attention that increase normalization increase gamma power, even when they decrease the firing rate. Thus, gamma rhythms could be a reflection of changes in the relative strengths of excitation and normalization rather than playing a functional role in communication or control. PMID:23393427

Mechanical and hydraulic properties of Nankai accretionary prism sediments: Effect of stress path

NASA Astrophysics Data System (ADS)

Kitajima, Hiroko; Chester, Frederick M.; Biscontin, Giovanna

2012-10-01

We have conducted triaxial deformation experiments along different loading paths on prism sediments from the Nankai Trough. Different load paths of isotropic loading, uniaxial strain loading, triaxial compression (at constant confining pressure, Pc), undrained Pc reduction, drained Pc reduction, and triaxial unloading at constant Pc, were used to understand the evolution of mechanical and hydraulic properties under complicated stress states and loading histories in accretionary subduction zones. Five deformation experiments were conducted on three sediment core samples for the Nankai prism, specifically from older accreted sediments at the forearc basin, underthrust slope sediments beneath the megasplay fault, and overthrust Upper Shikoku Basin sediments along the frontal thrust. Yield envelopes for each sample were constructed based on the stress paths of Pc-reduction using the modified Cam-clay model, and in situ stress states of the prism were constrained using the results from the other load paths and accounting for horizontal stress. Results suggest that the sediments in the vicinity of the megasplay fault and frontal thrust are highly overconsolidated, and thus likely to deform brittle rather than ductile. The porosity of sediments decreases as the yield envelope expands, while the reduction in permeability mainly depends on the effective mean stress before yield, and the differential stress after yield. An improved understanding of sediment yield strength and hydromechanical properties along different load paths is necessary to treat accurately the coupling of deformation and fluid flow in accretionary subduction zones.

Method and apparatus for controlling current in inductive loads such as large diameter coils

DOEpatents

Riveros, Carlos A.

1981-01-01

A method and apparatus for controlling electric current in loads that are essentially inductive, such that sparking and "ringing" current problems are reduced or eliminated. The circuit apparatus employs a pair of solid state switches (each of which switch may be an array of connected or parallel solid state switching devices such as transistors) and means for controlling those switches such that a power supply supplying two d.c. voltages (e.g. positive 150 volts d.c. and negative 150 volts d.c.) at low resistance may be connected across an essentially inductive load (e.g. a 6 gauge wire loop one hundred meters in diameter) alternatively and such that the first solid state switch is turned off and the second is turned on such that both are not on at the same time but the first turned on and the other on in less time than the inductive time constant (L/R) so that the load is essentially always presented with a low resistance path across its input. In this manner a steady AC current may be delivered to the load at a frequency desired. Shut-off problems are avoided by gradually shortening the period of switching to less than the time constant so that the maximum energy contained in the inductive load is reduced to approximately zero and dissipated in the inherent resistance. The invention circuit may be employed by adjusting the timing of switching to deliver a desired waveform (such as sinusoidal) to the load.

Stress Analysis and Fatigue Behaviour of PTFE-Bronze Layered Journal Bearing under Real-Time Dynamic Loading

NASA Astrophysics Data System (ADS)

Duman, M. S.; Kaplan, E.; Cuvalcı, O.

2018-01-01

The present paper is based on experimental studies and numerical simulations on the surface fatigue failure of the PTFE-bronze layered journal bearings under real-time loading. ‘Permaglide Plain Bearings P10’ type journal bearings were experimentally tested under different real time dynamic loadings by using real time journal bearing test system in our laboratory. The journal bearing consists of a PTFE-bronze layer approximately 0.32 mm thick on the steel support layer with 2.18 mm thick. Two different approaches have been considered with in experiments: (i) under real- time constant loading with varying bearing widths, (ii) under different real-time loadings at constant bearing widths. Fatigue regions, micro-crack dispersion and stress distributions occurred at the journal bearing were experimentally and theoretically investigated. The relation between fatigue region and pressure distributions were investigated by determining the circumferential pressure distribution under real-time dynamic loadings for the position of every 10° crank angles. In the theoretical part; stress and deformation distributions at the surface of the journal bearing analysed by using finite element methods to determine the relationship between stress and fatigue behaviour. As a result of this study, the maximum oil pressure and fatigue cracks were observed in the most heavily loaded regions of the bearing surface. Experimental results show that PTFE-Bronze layered journal bearings fatigue behaviour is better than the bearings include white metal alloy.

Experimental study of directionally solidified ferromagnetic shape memory alloy under multi-field coupling

NASA Astrophysics Data System (ADS)

Zhu, Yuping; Chen, Tao; Teng, Yao; Liu, Bingfei; Xue, Lijun

2016-11-01

Directionally solidified, polycrystalline Ni-Mn-Ga is studied in this paper. The polycrystalline Ni-Mn-Ga samples were cut at different angles to solidification direction. The magnetic field induced strain under constant stress and the temperature-induced strain under constant magnetic field during the loading-unloading cycle were measured. The experimental results show that the mechanical behavior during the loading-unloading cycle of the material is nonlinear and anisotropic. Based on the experimental results, the effects of multi-field coupling factors, such as stress, magnetic field, temperature and cutting angle on the mechanical behaviors were analyzed. Some useful conclusions were obtained, which will provide guidance for practical applications.

Multiaxial Temperature- and Time-Dependent Failure Model

NASA Technical Reports Server (NTRS)

Richardson, David; McLennan, Michael; Anderson, Gregory; Macon, David; Batista-Rodriquez, Alicia

2003-01-01

A temperature- and time-dependent mathematical model predicts the conditions for failure of a material subjected to multiaxial stress. The model was initially applied to a filled epoxy below its glass-transition temperature, and is expected to be applicable to other materials, at least below their glass-transition temperatures. The model is justified simply by the fact that it closely approximates the experimentally observed failure behavior of this material: The multiaxiality of the model has been confirmed (see figure) and the model has been shown to be applicable at temperatures from -20 to 115 F (-29 to 46 C) and to predict tensile failures of constant-load and constant-load-rate specimens with failure times ranging from minutes to months..

Hydraulic properties of 3D rough-walled fractures during shearing: An experimental study

NASA Astrophysics Data System (ADS)

Yin, Qian; Ma, Guowei; Jing, Hongwen; Wang, Huidong; Su, Haijian; Wang, Yingchao; Liu, Richeng

2017-12-01

This study experimentally analyzed the influence of shear processes on nonlinear flow behavior through 3D rough-walled rock fractures. A high-precision apparatus was developed to perform stress-dependent fluid flow tests of fractured rocks. Then, water flow tests on rough-walled fractures with different mechanical displacements were conducted. At each shear level, the hydraulic pressure ranged from 0 to 0.6 MPa, and the normal load varied from 7 to 35 kN. The results show that (i) the relationship between the volumetric flow rate and hydraulic gradient of rough-walled fractures can be well fit using Forchheimer's law. Notably, both the linear and nonlinear coefficients in Forchheimer's law decrease during shearing; (ii) a sixth-order polynomial function is used to evaluate the transmissivity based on the Reynolds number of fractures during shearing. The transmissivity exhibits a decreasing trend as the Reynolds number increases and an increasing trend as the shear displacement increases; (iii) the critical hydraulic gradient, critical Reynolds number and equivalent hydraulic aperture of the rock fractures all increase as the shear displacement increases. When the shear displacement varies from 0 to 15 mm, the critical hydraulic gradient ranges from 0.3 to 2.2 for a normal load of 7 kN and increases to 1.8-8.6 for a normal load of 35 kN; and (iv) the Forchheimer law results are evaluated by plotting the normalized transmissivity of the fractures during shearing against the Reynolds number. An increase in the normal load shifts the fitted curves downward. Additionally, the Forchheimer coefficient β decreases with the shear displacement but increases with the applied normal load.

An Adaptive, Multi-Rate Linear Quadratic Regulator for a Shipboard MVDC Distribution System with Constant Power Loads

DTIC Science & Technology

2017-09-01

12. xii THIS PAGE INTENTIONALLY LEFT BLANK xiii LIST OF ACRONYMS AND ABBREVIATIONS AC alternating current ATG auxiliary turbine generator...invariant MTG main turbine generator MVDC medium voltage DC NAVSEA U.S. Naval Sea Systems Command PGM power generation module RC resistor-capacitor RL...arrangement because the gas turbines used for prime movers are more efficient when they are fully loaded. By amalgamating loads onto fewer machines

Traction Aid for Wheeled Vehicles

DTIC Science & Technology

1975-07-01

driver’s position in the load vehicle to assist him in applying constant braking loads, 4) a drum and line fifth wheel sys- tem attached to the load...in Alaskan snow, and the results were so encouraging that further testing of the device was requested. In comparison to tire chains, the Tyr-Trac...vehicle with the end of the line anchored and the speed of the line played off the drum measuring the actual vehicle speed. An eight channel

Implementation of GAMMON - An efficient load balancing strategy for a local computer system

NASA Technical Reports Server (NTRS)

Baumgartner, Katherine M.; Kling, Ralph M.; Wah, Benjamin W.

1989-01-01

GAMMON (Global Allocation from Maximum to Minimum in cONstant time), an efficient load-balancing algorithm, is described. GAMMON uses the available broadcast capability of multiaccess networks to implement an efficient search technique for finding hosts with maximal and minimal loads. The search technique has an average overhead which is independent of the number of participating stations. The transition from the theoretical concept to a practical, reliable, and efficient implementation is described.

Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Barua, Bipul; Soppet, William K.

This report provides an update of an earlier assessment of environmentally assisted fatigue for components in light water reactors. This report is a deliverable in September 2016 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2016 report, we presented a detailed thermal-mechanical stress analysis model for simulating the stress-strain state of a reactor pressure vessel and its nozzles under grid-load-following conditions. In this report, we provide stress-controlled fatigue test data for 508 LAS base metal alloy under different loading amplitudes (constant, variable, and random grid-load-following) and environmental conditions (in airmore » or pressurized water reactor coolant water at 300°C). Also presented is a cyclic plasticity-based analytical model that can simultaneously capture the amplitude and time dependency of the component behavior under fatigue loading. Results related to both amplitude-dependent and amplitude-independent parameters are presented. The validation results for the analytical/mechanistic model are discussed. This report provides guidance for estimating time-dependent, amplitude-independent parameters related to material behavior under different service conditions. The developed mechanistic models and the reported material parameters can be used to conduct more accurate fatigue and ratcheting evaluation of reactor components.« less

Different patterns of nuclear and mitochondrial penetration by the G3 PAMAM dendrimer and its biotin–pyridoxal bioconjugate BC-PAMAM in normal and cancer cells in vitro

PubMed Central

Uram, Łukasz; Szuster, Magdalena; Filipowicz, Aleksandra; Gargasz, Krzysztof; Wołowiec, Stanisław; Wałajtys-Rode, Elżbieta

2015-01-01

The intracellular localization and colocalization of a fluorescently labeled G3 amine-terminated cationic polyamidoamine (PAMAM) dendrimer and its biotin–pyridoxal (BC-PAMAM) bioconjugate were investigated in a concentration-dependent manner in normal human fibroblast (BJ) and squamous epithelial carcinoma (SCC-15) cell lines. After 24 hours treatment, both cell lines revealed different patterns of intracellular dendrimer accumulation depending on their cytotoxic effects. Cancer cells exhibited much higher (20-fold) tolerance for native PAMAM treatment than fibroblasts, whereas BC-PAMAM was significantly toxic only for fibroblasts at 50 µM concentration. Fibroblasts accumulated the native and bioconjugated dendrimers in a concentration-dependent manner at nontoxic range of concentration, with significantly lower bioconjugate loading. After reaching the cytotoxicity level, fluorescein isothiocyanate-PAMAM accumulation remains at high, comparable level. In cancer cells, native PAMAM loading at higher, but not cytotoxic concentrations, was kept at constant level with a sharp increase at toxic concentration. Mander’s coefficient calculated for fibroblasts and cancer cells confirmed more efficient native PAMAM penetration as compared to BC-PAMAM. Significant differences in nuclear dendrimer penetration were observed for both cell lines. In cancer cells, PAMAM signals amounted to ~25%–35% of the total nuclei area at all investigated concentrations, with lower level (15%–25%) observed for BC-PAMAM. In fibroblasts, the dendrimer nuclear signal amounted to 15% at nontoxic and up to 70% at toxic concentrations, whereas BC-PAMAM remained at a lower concentration-dependent level (0.3%–20%). Mitochondrial localization of PAMAM and BC-PAMAM revealed similar patterns in both cell lines, depending on the extracellular dendrimer concentration, and presented significantly lower signals from BC-PAMAM, which correlated well with the cytotoxicity. PMID:26379435

Hysteresis, phase transitions, and dangerous transients in electrical power distribution systems.

PubMed

Duclut, Charlie; Backhaus, Scott; Chertkov, Michael

2013-06-01

The majority of dynamical studies in power systems focus on the high-voltage transmission grids where models consider large generators interacting with crude aggregations of individual small loads. However, new phenomena have been observed indicating that the spatial distribution of collective, nonlinear contribution of these small loads in the low-voltage distribution grid is crucial to the outcome of these dynamical transients. To elucidate the phenomenon, we study the dynamics of voltage and power flows in a spatially extended distribution feeder (circuit) connecting many asynchronous induction motors and discover that this relatively simple 1+1 (space+time) dimensional system exhibits a plethora of nontrivial spatiotemporal effects, some of which may be dangerous for power system stability. Long-range motor-motor interactions mediated by circuit voltage and electrical power flows result in coexistence and segregation of spatially extended phases defined by individual motor states, a "normal" state where the motors' mechanical (rotation) frequency is slightly smaller than the nominal frequency of the basic ac flows and a "stalled" state where the mechanical frequency is small. Transitions between the two states can be initiated by a perturbation of the voltage or base frequency at the head of the distribution feeder. Such behavior is typical of first-order phase transitions in physics, and this 1+1 dimensional model shows many other properties of a first-order phase transition with the spatial distribution of the motors' mechanical frequency playing the role of the order parameter. In particular, we observe (a) propagation of the phase-transition front with the constant speed (in very long feeders) and (b) hysteresis in transitions between the normal and stalled (or partially stalled) phases.

14 CFR 23.511 - Ground load; unsymmetrical loads on multiple-wheel units.

Code of Federal Regulations, 2010 CFR

2010-01-01

..., DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER... distribution, to the dual wheels and tires in each dual wheel landing gear unit. (c) Deflated tire loads. For...

Generator voltage stabilisation for series-hybrid electric vehicles.

PubMed

Stewart, P; Gladwin, D; Stewart, J; Cowley, R

2008-04-01

This paper presents a controller for use in speed control of an internal combustion engine for series-hybrid electric vehicle applications. Particular reference is made to the stability of the rectified DC link voltage under load disturbance. In the system under consideration, the primary power source is a four-cylinder normally aspirated gasoline internal combustion engine, which is mechanically coupled to a three-phase permanent magnet AC generator. The generated AC voltage is subsequently rectified to supply a lead-acid battery, and permanent magnet traction motors via three-phase full bridge power electronic inverters. Two complementary performance objectives exist. Firstly to maintain the internal combustion engine at its optimal operating point, and secondly to supply a stable 42 V supply to the traction drive inverters. Achievement of these goals minimises the transient energy storage requirements at the DC link, with a consequent reduction in both weight and cost. These objectives imply constant velocity operation of the internal combustion engine under external load disturbances and changes in both operating conditions and vehicle speed set-points. An electronically operated throttle allows closed loop engine velocity control. System time delays and nonlinearities render closed loop control design extremely problematic. A model-based controller is designed and shown to be effective in controlling the DC link voltage, resulting in the well-conditioned operation of the hybrid vehicle.

Computational Methods for Frictional Contact With Applications to the Space Shuttle Orbiter Nose-Gear Tire

NASA Technical Reports Server (NTRS)

Tanner, John A.

1996-01-01

A computational procedure is presented for the solution of frictional contact problems for aircraft tires. A Space Shuttle nose-gear tire is modeled using a two-dimensional laminated anisotropic shell theory which includes the effects of variations in material and geometric parameters, transverse-shear deformation, and geometric nonlinearities. Contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with both contact and friction conditions. The contact-friction algorithm is based on a modified Coulomb friction law. A modified two-field, mixed-variational principle is used to obtain elemental arrays. This modification consists of augmenting the functional of that principle by two terms: the Lagrange multiplier vector associated with normal and tangential node contact-load intensities and a regularization term that is quadratic in the Lagrange multiplier vector. These capabilities and computational features are incorporated into an in-house computer code. Experimental measurements were taken to define the response of the Space Shuttle nose-gear tire to inflation-pressure loads and to inflation-pressure loads combined with normal static loads against a rigid flat plate. These experimental results describe the meridional growth of the tire cross section caused by inflation loading, the static load-deflection characteristics of the tire, the geometry of the tire footprint under static loading conditions, and the normal and tangential load-intensity distributions in the tire footprint for the various static vertical loading conditions. Numerical results were obtained for the Space Shuttle nose-gear tire subjected to inflation pressure loads and combined inflation pressure and contact loads against a rigid flat plate. The experimental measurements and the numerical results are compared.

Computational methods for frictional contact with applications to the Space Shuttle orbiter nose-gear tire: Comparisons of experimental measurements and analytical predictions

NASA Technical Reports Server (NTRS)

Tanner, John A.

1996-01-01

A computational procedure is presented for the solution of frictional contact problems for aircraft tires. A Space Shuttle nose-gear tire is modeled using a two-dimensional laminated anisotropic shell theory which includes the effects of variations in material and geometric parameters, transverse-shear deformation, and geometric nonlinearities. Contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with both contact and friction conditions. The contact-friction algorithm is based on a modified Coulomb friction law. A modified two-field, mixed-variational principle is used to obtain elemental arrays. This modification consists of augmenting the functional of that principle by two terms: the Lagrange multiplier vector associated with normal and tangential node contact-load intensities and a regularization term that is quadratic in the Lagrange multiplier vector. These capabilities and computational features are incorporated into an in-house computer code. Experimental measurements were taken to define the response of the Space Shuttle nose-gear tire to inflation-pressure loads and to inflation-pressure loads combined with normal static loads against a rigid flat plate. These experimental results describe the meridional growth of the tire cross section caused by inflation loading, the static load-deflection characteristics of the tire, the geometry of the tire footprint under static loading conditions, and the normal and tangential load-intensity distributions in the tire footprint for the various static vertical-loading conditions. Numerical results were obtained for the Space Shuttle nose-gear tire subjected to inflation pressure loads and combined inflation pressure and contact loads against a rigid flat plate. The experimental measurements and the numerical results are compared.

Balloon Design Software

NASA Technical Reports Server (NTRS)

Farley, Rodger

2007-01-01

PlanetaryBalloon Version 5.0 is a software package for the design of meridionally lobed planetary balloons. It operates in a Windows environment, and programming was done in Visual Basic 6. By including the effects of circular lobes with load tapes, skin mass, hoop and meridional stress, and elasticity in the structural elements, a more accurate balloon shape of practical construction can be determined as well as the room-temperature cut pattern for the gore shapes. The computer algorithm is formulated for sizing meridionally lobed balloons for any generalized atmosphere or planet. This also covers zero-pressure, over-pressure, and super-pressure balloons. Low circumferential loads with meridionally reinforced load tapes will produce shapes close to what are known as the "natural shape." The software allows for the design of constant angle, constant radius, or constant hoop stress balloons. It uses the desired payload capacity for given atmospheric conditions and determines the required volume, allowing users to design exactly to their requirements. The formulations are generalized to use any lift gas (or mixture of gases), any atmosphere, or any planet as described by the local acceleration of gravity. PlanetaryBalloon software has a comprehensive user manual that covers features ranging from, but not limited to, buoyancy and super-pressure, convenient design equations, shape formulation, and orthotropic stress/strain.

Significantly improved dielectric performances of nanocomposites via loading two-dimensional core-shell structure Bi2Te3@SiO2 nanosheets

NASA Astrophysics Data System (ADS)

Chen, Jianwen; Wang, Xiucai; Yu, Xinmei; Fan, Yun; Duan, Zhikui; Jiang, Yewen; Yang, Faquan; Zhou, Yuexia

2018-07-01

Polymer/semiconductor-insulator nanocomposites can display high dielectric constants with a relatively low dissipation factor under low electric fields, and thus seem to promising for high energy density capacitors. Here, a novel nanocomposite films is developed by loading two-dimensional (2D) core-shell structure Bi2Te3@SiO2 nanosheets in the poly (vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) polymer matrix. The 2D Bi2Te3 nanosheets were prepared through simple microwave-assisted method. The experimental results suggesting that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the dielectric constant, dielectric loss, AC conductivity, and breakdown strength of composites films. The composite films load with 10 vol.% 2D Bi2Te3@SiO2 nanosheets exhibits a high dielectric constant of 70.3 at 1 kHz and relatively low dielectric loss of 0.058 at 1 kHz. The finite element simulation of electric field and electric current density distribution revealed that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the energy loss, local electric field strength, and breakdown strength of composite films. Therefore, this work will provide a promising route to achieve high-performance capacitors.

Law of damage accumulation and fracture criteria in highly filled polymer materials

NASA Astrophysics Data System (ADS)

Bykov, D. L.; Kazakov, A. V.; Konovalov, D. N.; Mel'nikov, V. P.; Milyokhin, Yu. M.; Peleshko, V. A.; Sadovnichii, D. N.

2014-09-01

We present the results of a large series of experiments aimed at the study of laws of damage accumulation and fracture in highly filled polymer materials under loading conditions of various types: monotone, repeated, low- and high-cycle, with varying type of stress state, dynamic (in general, more than 50 programs implemented on specimens from one lot of material). The data obtained in these test allow one to make conclusions about the constitutive role of the attained maximum of strain intensity when estimating the accumulated damage in the process of uniaxial tension by various programs (in particular, an additional cyclic deformation below the preliminary attained strain maximum does not affect the limit values of strain and stress in the subsequent active extension), about the strong influence of the stress state on the deformation and fracture, about the specific features of the nonlinear behavior of the material under the shock loading conditions and its influence on the repeated deformation. All tests are described (with an accuracy acceptable in practical calculations, both with respect to stresses and strains in the process of loading and at the moment of fracture) in the framework of the same model of nonlinear viscoelasticity with the same set of constants. The constants of the proposed model are calculated according to a relatively simple algorithm by using the results of standard uniaxial tension tests with constant values of the strain rate and hydrostatic pressure (each test for 2-3 levels of these parameters chosen from the ranges proposed in applications, each loading lasts until the fracture occurs, and one of the tests contains an intermediate interval of total loading and repeated loading) and one axial shock compression test if there are dynamic problems in the applications. The model is based on the use of the criterion fracture parameter which, in the class of proportional loading processes, is the sum of partial increments of the strain intensity on active segments of the process (where the strain intensity is at its historical maximum) with the form of the stress state and the intensity of strain rates taken into account.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-01-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-03-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Direct Shear Failure in Reinforced Concrete Beams under Impulsive Loading

DTIC Science & Technology

1983-09-01

115 References ............... ............................. 119 Tables . ............................. 124 Figures ............ 1..............30...8217. : = differentiable functions of time 1 = elastic modulus enhancement function 4) 41’ = constants for a given mode W’, = frequency w tfirst thickness-shear...are defined by linear partial differential equations. The analytic results are compared to data gathered on one-way slabs loaded with impulsive blast

Advanced Direct-Drive Generator for Improved Availability of Oscillating Wave Surge Converter Power Generation Systems Phase II 10hp 30rpm Radial-Flux Magnetically Geared Generator Test Data

DOE Data Explorer

Ouyang, Wen; Tchida, Colin

2017-05-02

Static torque, no load, constant speed, and sinusoidal oscillation test data for a 10hp, 300rpm magnetically-geared generator prototype using either an adjustable load bank for a fixed resistance or an output power converter.

14 CFR 23.521 - Water load conditions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Water load conditions. 23.521 Section 23... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Water Loads § 23.521 Water load conditions. (a) The structure of seaplanes and amphibians must be designed for water...

14 CFR 27.681 - Limit load static tests.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Design and Construction Control Systems § 27.681 Limit load... which— (1) The direction of the test loads produces the most severe loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to the main structure is included...

14 CFR 23.681 - Limit load static tests.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.681 Limit load static tests. (a) Compliance with the limit load requirements of this... loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to...

14 CFR 23.681 - Limit load static tests.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.681 Limit load static tests. (a) Compliance with the limit load requirements of this... loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to...

14 CFR 23.681 - Limit load static tests.

Code of Federal Regulations, 2014 CFR

2014-01-01

... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.681 Limit load static tests. (a) Compliance with the limit load requirements of this... loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to...

14 CFR 23.681 - Limit load static tests.

Code of Federal Regulations, 2012 CFR

2012-01-01

... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.681 Limit load static tests. (a) Compliance with the limit load requirements of this... loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to...

14 CFR 23.681 - Limit load static tests.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.681 Limit load static tests. (a) Compliance with the limit load requirements of this... loading in the control system; and (2) Each fitting, pulley, and bracket used in attaching the system to...

14 CFR 23.521 - Water load conditions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Water load conditions. 23.521 Section 23... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Water Loads § 23.521 Water load conditions. (a) The structure of seaplanes and amphibians must be designed for water...

14 CFR 23.521 - Water load conditions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Water load conditions. 23.521 Section 23... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Water Loads § 23.521 Water load conditions. (a) The structure of seaplanes and amphibians must be designed for water...

14 CFR 23.521 - Water load conditions.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Water load conditions. 23.521 Section 23... AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Water Loads § 23.521 Water load conditions. (a) The structure of seaplanes and amphibians must be designed for water...

Sliding contact fracture of dental ceramics: Principles and validation

PubMed Central

Ren, Linlin; Zhang, Yu

2014-01-01

Ceramic prostheses are subject to sliding contact under normal and tangential loads. Accurate prediction of the onset of fracture at two contacting surfaces holds the key to greater long-term performance of these prostheses. In this study, building on stress analysis of Hertzian contact and considering fracture criteria for linear elastic materials, a constitutive fracture mechanics relation was developed to incorporate the critical fracture load with the contact geometry, coefficient of friction and material fracture toughness. Critical loads necessary to cause fracture under a sliding indenter were calculated from the constitutive equation, and compared with the loads predicted from elastic stress analysis in conjunction with measured critical load for frictionless normal contact—a semi-empirical approach. The major predictions of the models were calibrated with experimentally determined critical loads of current and future dental ceramics after contact with a rigid spherical slider. Experimental results conform with the trends predicted by the models. PMID:24632538

Articular cartilage and subchondral bone in the pathogenesis of osteoarthritis.

PubMed

Goldring, Mary B; Goldring, Steven R

2010-03-01

The articular surface plays an essential role in load transfer across the joint, and conditions that produce increased load transfer or altered patterns of load distribution accelerate the development of osteoarthritis (OA). Current knowledge segregates the risk factors into two fundamental mechanisms related to the adverse effects of "abnormal" loading on normal cartilage or "normal" loading on abnormal cartilage. Although chondrocytes can modulate their functional state in response to loading, their capacity to repair and modify the surrounding extracellular matrix is limited in comparison to skeletal cells in bone. This differential adaptive capacity underlies the more rapid appearance of detectable skeletal changes, especially after acute injuries that alter joint mechanics. The imbalance in the adaptation of the cartilage and bone disrupts the physiological relationship between these tissues and further contributes to OA pathology. This review focuses on the specific articular cartilage and skeletal features of OA and the putative mechanisms involved in their pathogenesis.

Human Papillomavirus Type 16 Viral Load Is Higher in Human Immunodeficiency Virus-Seropositive Women with High-Grade Squamous Intraepithelial Lesions Than in Those with Normal Cytology Smears

PubMed Central

Lefevre, Jonas; Hankins, Catherine; Money, Deborah; Rachlis, Anita; Pourreaux, Karina; Coutlée, François

2004-01-01

Human papillomavirus type 16 (HPV-16) viral load in cervicovaginal lavage samples collected from 66 human immunodeficiency virus-seropositive women was inversely correlated with blood CD4 count (P = 0.002). HPV-16 viral load was 81-fold higher in women with cervical smears suggestive of high-grade lesions (median, 4,425,883 copies/μg of DNA) than in women with normal smears (median, 54,576), controlling for age (P = 0.006). PMID:15131192

Differing effects of cyclosporin a on swelling amplitude and time constant of mitochondria from normal and ischemic rat brain.

PubMed

Wu, Li-Ping; Shen, Fang; Lu, Yuan; Bruce, Iain; Xia, Qiang

2005-01-01

The purpose of this study was to investigate the effect of cyclosporin A on swelling amplitude and time constant of mitochondria isolated from normal and ischemic rat brain and to observe the possible role of the mitochondrial ATP-sensitive potassium channel on mitochondrial permeability transition. Mitochondrial swelling was evaluated by spectrophotometry. Cyclosporin A at 0.5 or 1 microM and diazoxide at 30 microM significantly decreased the swelling amplitude and attenuated the reduction of time constant of mitochondria isolated from normal brain mitochondria induced by 200 microM calcium, an effect abolished by atractyloside at 100 microM. However, cyclosporin A at 5 microM did not affect mitochondrial swelling. In mitochondria from ischemic brain, cyclosporin A at 0.5 microM but not 1 microM significantly decreased mitochondrial swelling amplitude and attenuated the reduction of time constant, which was abolished by atractyloside. Diazoxide had an effect similar to cyclosporin A at 0.5 microM, which was blocked by atractyloside or 5-hydroxydecanoate at 100 microM and 200 microM. Compared with mitochondria isolated from normal brain, those from ischemic brain were more sensitive to cyclosporin A. Activation of the mitochondrial ATP-sensitive potassium channel may be one of the mechanisms by which opening of the mitochondrial permeability transition pore is inhibited.

An Energy Absorber for the International Space Station

NASA Technical Reports Server (NTRS)

Wilkes, Bob; Laurence, Lora

2000-01-01

The energy absorber described herein is similar in size and shape to an automotive shock absorber, requiring a constant, high load to compress over the stroke, and self-resetting with a small load. The differences in these loads over the stroke represent the energy absorbed by the device, which is dissipated as friction. This paper describes the evolution of the energy absorber, presents the results of testing performed, and shows the sensitivity of this device to several key design variables.

Development of a Novel Approach for Fatigue Life Prediction of Structural Materials

DTIC Science & Technology

2008-12-01

applied when the crack length was 8.45 mm and 14.96 mm, respectively, on these two specimens. A third specimen was subjected to a constant amplitude...The crack growth rate at the middle point (the third point) was determined from the derivative of the parabola. The stress intensity factor for...minimum load was identical in the two loading steps (Fig. 32(b)). The third specimen experienced two-step loading with identical /?-ratio in the two

Changing Regulations of COD Pollution Load of Weihe River Watershed above TongGuan Section, China

NASA Astrophysics Data System (ADS)

Zhu, Lei; Liu, WanQing

2018-02-01

TongGuan Section of Weihe River Watershed is a provincial section between Shaanxi Province and Henan Province, China. Weihe River Watershed above TongGuan Section is taken as the research objective in this paper and COD is chosen as the water quality parameter. According to the discharge characteristics of point source pollutions and non-point source pollutions, a method—characteristic section load (CSLD) method is suggested and point and non-point source pollution loads of Weihe River Watershed above TongGuan Section are calculated in the rainy, normal and dry season in 2013. The results show that the monthly point source pollution loads of Weihe River Watershed above TongGuan Section discharge stably and the monthly non-point source pollution loads of Weihe River Watershed above TongGuan Section change greatly and the non-point source pollution load proportions of total pollution load of COD decrease in the rainy, wet and normal period in turn.

Using CSLD Method to Calculate COD Pollution Load of Wei River Watershed above Huaxian Section, China

NASA Astrophysics Data System (ADS)

Zhu, Lei; Song, JinXi; Liu, WanQing

2017-12-01

Huaxian Section is the last hydrological and water quality monitoring section of Weihe River Watershed. Weihe River Watershed above Huaxian Section is taken as the research objective in this paper and COD is chosen as the water quality parameter. According to the discharge characteristics of point source pollutions and non-point source pollutions, a new method to estimate pollution loads—characteristic section load(CSLD) method is suggested and point source pollution and non-point source pollution loads of Weihe River Watershed above Huaxian Section are calculated in the rainy, normal and dry season in the year 2007. The results show that the monthly point source pollution loads of Weihe River Watershed above Huaxian Section discharge stably and the monthly non-point source pollution loads of Weihe River Watershed above Huaxian Section change greatly and the non-point source pollution load proportions of total pollution load of COD decrease in the normal, rainy and wet period in turn.

Calculating NH3-N pollution load of wei river watershed above Huaxian section using CSLD method

NASA Astrophysics Data System (ADS)

Zhu, Lei; Song, JinXi; Liu, WanQing

2018-02-01

Huaxian Section is the last hydrological and water quality monitoring section of Weihe River Watershed. So it is taken as the research objective in this paper and NH3-N is chosen as the water quality parameter. According to the discharge characteristics of point source pollutions and non-point source pollutions, a new method to estimate pollution loads—characteristic section load (CSLD)method is suggested and point source pollution and non-point source pollution loads of Weihe River Watershed above Huaxian Section are calculated in the rainy, normal and dry season in the year 2007. The results show that the monthly point source pollution loads of Weihe River Watershed above Huaxian Section discharge stably and the monthly non-point source pollution loads of Weihe River Watershed above Huaxian Section change greatly. The non-point source pollution load proportions of total pollution load of NH3-N decrease in the normal, rainy and wet period in turn.

Simultaneous saccharification and co-fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222--Part I: kinetic modeling and parameters.

PubMed

Zhang, Jiayi; Shao, Xiongjun; Townsend, Oliver V; Lynd, Lee R

2009-12-01

A kinetic model was developed to predict batch simultaneous saccharification and co-fermentation (SSCF) of paper sludge by the xylose-utilizing yeast Saccharomyces cerevisiae RWB222 and the commercial cellulase preparation Spezyme CP. The model accounts for cellulose and xylan enzymatic hydrolysis and competitive uptake of glucose and xylose. Experimental results show that glucan and xylan enzymatic hydrolysis are highly correlated, and that the low concentrations of xylose encountered during SSCF do not have a significant inhibitory effect on enzymatic hydrolysis. Ethanol is found to not only inhibit the specific growth rate, but also to accelerate cell death. Glucose and xylose uptake rates were found to be competitively inhibitory, but this did not have a large impact during SSCF because the sugar concentrations are low. The model was used to evaluate which constants had the greatest impact on ethanol titer for a fixed substrate loading, enzyme loading, and fermentation time. The cellulose adsorption capacity and cellulose hydrolysis rate constants were found to have the greatest impact among enzymatic hydrolysis related constants, and ethanol yield and maximum ethanol tolerance had the greatest impact among fermentation related constants.

Comparison of Deterministic and Probabilistic Radial Distribution Systems Load Flow

NASA Astrophysics Data System (ADS)

Gupta, Atma Ram; Kumar, Ashwani

2017-12-01

Distribution system network today is facing the challenge of meeting increased load demands from the industrial, commercial and residential sectors. The pattern of load is highly dependent on consumer behavior and temporal factors such as season of the year, day of the week or time of the day. For deterministic radial distribution load flow studies load is taken as constant. But, load varies continually with a high degree of uncertainty. So, there is a need to model probable realistic load. Monte-Carlo Simulation is used to model the probable realistic load by generating random values of active and reactive power load from the mean and standard deviation of the load and for solving a Deterministic Radial Load Flow with these values. The probabilistic solution is reconstructed from deterministic data obtained for each simulation. The main contribution of the work is: Finding impact of probable realistic ZIP load modeling on balanced radial distribution load flow. Finding impact of probable realistic ZIP load modeling on unbalanced radial distribution load flow. Compare the voltage profile and losses with probable realistic ZIP load modeling for balanced and unbalanced radial distribution load flow.

The role of grain boundary chemistry and structure in the environmentally-assisted intergranular cracking of nickel-base alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Was, G.S.

1992-07-01

Stress corrosion cracking tests in constant extension rate tensile (CERT) and constant load tensile (CLT) tests were conducted on Ni-xCr- 9Fe-yC in Ar, water, and a LiOH-boric acid solution. Cr and C improve the resistance of Ni-base alloys to IG cracking in both Ar and water at 360C. Since creep plays a role in IG cracking, one possible explanation for the role of the environment involves its effect on the creep. Experiments were conducted on the role of C in the deformation behavior and failure mode of Ni-16Cr-9Fe. Constant load experiments were conducted on Ni-16Cr-9Fe to determine if the CLTmore » test is more aggressive than CERT. The electron backscattering technique in a SEM is being developed in order to extend the IG cracking studies to grain sizes typical of commercial alloys, 20-30 microns.« less

The role of grain boundary chemistry and structure in the environmentally-assisted intergranular cracking of nickel-base alloys. Progress report, August 1, 1991--July 31, 1992

DOE Office of Scientific and Technical Information (OSTI.GOV)

Was, G.S.

1992-07-01

Stress corrosion cracking tests in constant extension rate tensile (CERT) and constant load tensile (CLT) tests were conducted on Ni-xCr- 9Fe-yC in Ar, water, and a LiOH-boric acid solution. Cr and C improve the resistance of Ni-base alloys to IG cracking in both Ar and water at 360C. Since creep plays a role in IG cracking, one possible explanation for the role of the environment involves its effect on the creep. Experiments were conducted on the role of C in the deformation behavior and failure mode of Ni-16Cr-9Fe. Constant load experiments were conducted on Ni-16Cr-9Fe to determine if the CLTmore » test is more aggressive than CERT. The electron backscattering technique in a SEM is being developed in order to extend the IG cracking studies to grain sizes typical of commercial alloys, 20-30 microns.« less

Trajectories of BMI change impact glucose and insulin metabolism.

PubMed

Walsh, E I; Shaw, J; Cherbuin, N

2018-03-01

The aim of this study was to examine, in a community setting, whether trajectory of weight change over twelve years is associated with glucose and insulin metabolism at twelve years. Participants were 532 community-living middle-aged and elderly adults from the Personality and Total Health (PATH) Through Life study. They spanned the full weight range (underweight/normal/overweight/obese). Latent class analysis and multivariate generalised linear models were used to investigate the association of Body Mass Index (BMI, kg/m 2 ) trajectory over twelve years with plasma insulin (μlU/ml), plasma glucose (mmol/L), and HOMA2 insulin resistance and beta cell function at follow-up. All models were adjusted for age, gender, hypertension, pre-clinical diabetes status (normal fasting glucose or impaired fasting glucose) and physical activity. Four weight trajectories were extracted; constant normal (mean baseline BMI = 25; follow-up BMI = 25), constant high (mean baseline BMI = 36; follow-up BMI = 37), increase (mean baseline BMI = 26; follow-up BMI = 32) and decrease (mean baseline BMI = 34; follow-up BMI = 28). At any given current BMI, individuals in the constant high and increase trajectories had significantly higher plasma insulin, greater insulin resistance, and higher beta cell function than those in the constant normal trajectory. Individuals in the decrease trajectory did not differ from the constant normal trajectory. Current BMI significantly interacted with preceding BMI trajectory in its association with plasma insulin, insulin resistance, and beta cell function. The trajectory of preceding weight has an independent effect on blood glucose metabolism beyond body weight measured at any given point in time. Copyright © 2017 The Italian Society of Diabetology, the Italian Society for the Study of Atherosclerosis, the Italian Society of Human Nutrition, and the Department of Clinical Medicine and Surgery, Federico II University. Published by Elsevier B.V. All rights reserved.

Speed And Power Control Of An Engine By Modulation Of The Load Torque

DOEpatents

Ziph, Benjamin; Strodtman, Scott; Rose, Thomas K

1999-01-26

A system and method of speed and power control for an engine in which speed and power of the engine is controlled by modulation of the load torque. The load torque is manipulated in order to cause engine speed, and hence power to be changed. To accomplish such control, the load torque undergoes a temporary excursion in the opposite direction of the desired speed and power change. The engine and the driven equipment will accelerate or decelerate accordingly as the load torque is decreased or increased, relative to the essentially fixed or constant engine torque. As the engine accelerates or decelerates, its power increases or decreases in proportion.

Sensorless Load Torque Estimation and Passivity Based Control of Buck Converter Fed DC Motor

PubMed Central

Kumar, S. Ganesh; Thilagar, S. Hosimin

2015-01-01

Passivity based control of DC motor in sensorless configuration is proposed in this paper. Exact tracking error dynamics passive output feedback control is used for stabilizing the speed of Buck converter fed DC motor under various load torques such as constant type, fan type, propeller type, and unknown load torques. Under load conditions, sensorless online algebraic approach is proposed, and it is compared with sensorless reduced order observer approach. The former produces better response in estimating the load torque. Sensitivity analysis is also performed to select the appropriate control variables. Simulation and experimental results fully confirm the superiority of the proposed approach suggested in this paper. PMID:25893208

Optimal Topology of Aircraft Rib and Spar Structures under Aeroelastic Loads

NASA Technical Reports Server (NTRS)

Stanford, Bret K.; Dunning, Peter D.

2014-01-01

Several topology optimization problems are conducted within the ribs and spars of a wing box. It is desired to locate the best position of lightening holes, truss/cross-bracing, etc. A variety of aeroelastic metrics are isolated for each of these problems: elastic wing compliance under trim loads and taxi loads, stress distribution, and crushing loads. Aileron effectiveness under a constant roll rate is considered, as are dynamic metrics: natural vibration frequency and flutter. This approach helps uncover the relationship between topology and aeroelasticity in subsonic transport wings, and can therefore aid in understanding the complex aircraft design process which must eventually consider all these metrics and load cases simultaneously.

Numerical investigation of contact stresses for fretting fatigue damage initiation

NASA Astrophysics Data System (ADS)

Bhatti, N. A.; Abdel Wahab, M.

2017-05-01

Fretting fatigue phenomena occurs due to interaction between contacting bodies under application of cyclic and normal loads. In addition to environmental conditions and material properties, the response at the contact interface highly depends on the combination of applied loads. High stress concentration is present at the contact interface, which can start the damage nucleation process. At the culmination of nucleation process several micro cracks are initiated, ultimately leading to the structural failure. In this study, effect of ratio of tangential to normal load on contact stresses, slip amplitude and damage initiation is studied using finite element analysis. The results are evaluated for Ruiz parameter as it involves the slip amplitude which in an important factor in fretting fatigue conditions. It is observed that tangential to normal load ratio influences the stick zone size and damage initiation life. Furthermore, it is observed that tensile stress is the most important factor that drives the damage initiation to failure for the cases where failure occurs predominantly in mode I manner.

Loading of PAX3 to Mitotic Chromosomes Is Mediated by Arginine Methylation and Associated with Waardenburg Syndrome*

PubMed Central

Wu, Tsu-Fang; Yao, Ya-Li; Lai, I-Lu; Lai, Chien-Chen; Lin, Pei-Lun; Yang, Wen-Ming

2015-01-01

PAX3 is a transcription factor critical to gene regulation in mammalian development. Mutations in PAX3 are associated with Waardenburg syndrome (WS), but the mechanism of how mutant PAX3 proteins cause WS remains unclear. Here, we found that PAX3 loads on mitotic chromosomes using its homeodomain. PAX3 WS mutants with mutations in homeodomain lose the ability to bind mitotic chromosomes. Moreover, loading of PAX3 on mitotic chromosomes requires arginine methylation, which is regulated by methyltransferase PRMT5 and demethylase JMJD6. Mutant PAX3 proteins that lose mitotic chromosome localization block cell proliferation and normal development of zebrafish. These results reveal the molecular mechanism of PAX3s loading on mitotic chromosomes and the importance of this localization pattern in normal development. Our findings suggest that PAX3 WS mutants interfere with the normal functions of PAX3 in a dominant negative manner, which is important to the understanding of the pathogenesis of Waardenburg syndrome. PMID:26149688

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.

Code of Federal Regulations, 2014 CFR

2014-01-01

... combination of structural analysis and static load tests to limit load; or (3) Static load tests to ultimate... OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY... resulting from the ultimate static load factors prescribed in § 23.561(b)(2) of this part. Each occupant...

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.

Code of Federal Regulations, 2011 CFR

2011-01-01

... combination of structural analysis and static load tests to limit load; or (3) Static load tests to ultimate... OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY... resulting from the ultimate static load factors prescribed in § 23.561(b)(2) of this part. Each occupant...

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.

Code of Federal Regulations, 2010 CFR

2010-01-01

... combination of structural analysis and static load tests to limit load; or (3) Static load tests to ultimate... OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY... resulting from the ultimate static load factors prescribed in § 23.561(b)(2) of this part. Each occupant...

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.

Code of Federal Regulations, 2012 CFR

2012-01-01

... combination of structural analysis and static load tests to limit load; or (3) Static load tests to ultimate... OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY... resulting from the ultimate static load factors prescribed in § 23.561(b)(2) of this part. Each occupant...

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.

Code of Federal Regulations, 2013 CFR

2013-01-01

... combination of structural analysis and static load tests to limit load; or (3) Static load tests to ultimate... OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY... resulting from the ultimate static load factors prescribed in § 23.561(b)(2) of this part. Each occupant...

Scalar field and time varying cosmological constant in f(R,T) gravity for Bianchi type-I universe

NASA Astrophysics Data System (ADS)

Singh, G. P.; Bishi, Binaya K.; Sahoo, P. K.

2016-04-01

In this article, we have analysed the behaviour of scalar field and cosmological constant in $f(R,T)$ theory of gravity. Here, we have considered the simplest form of $f(R,T)$ i.e. $f(R,T)=R+2f(T)$, where $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor and explored the spatially homogeneous and anisotropic Locally Rotationally Symmetric (LRS) Bianchi type-I cosmological model. It is assumed that the Universe is filled with two non-interacting matter sources namely scalar field (normal or phantom) with scalar potential and matter contribution due to $f(R,T)$ action. We have discussed two cosmological models according to power law and exponential law of the volume expansion along with constant and exponential scalar potential as sub models. Power law models are compatible with normal (quintessence) and phantom scalar field whereas exponential volume expansion models are compatible with only normal (quintessence) scalar field. The values of cosmological constant in our models are in agreement with the observational results. Finally, we have discussed some physical and kinematical properties of both the models.

Emulating DC constant power load: a robust sliding mode control approach

NASA Astrophysics Data System (ADS)

Singh, Suresh; Fulwani, Deepak; Kumar, Vinod

2017-09-01

This article presents emulation of a programmable power electronic, constant power load (CPL) using a dc/dc step-up (boost) converter. The converter is controlled by a robust sliding mode controller (SMC). A novel switching surface is proposed to ensure a required power sunk by the converter. The proposed dc CPL is simple in design, has fast dynamic response and high accuracy, and offers an inexpensive alternative to study converters for cascaded dc distribution power system applications. Furthermore, the proposed CPL is sufficiently robust against the input voltage variations. A laboratory prototype of the proposed dc CPL has been developed and validated with SMC realised through OPAL-RT platform. The capability of the proposed dc CPL is confirmed via experimentations in varied scenarios.

Microscopic modeling of confined crystal growth and dissolution.

PubMed

Høgberget, Jørgen; Røyne, Anja; Dysthe, Dag K; Jettestuen, Espen

2016-08-01

We extend the (1+1)-dimensional fluid solid-on-solid (SOS) model to include a confining flat surface opposite to the SOS surface subject to a constant load. This load is balanced by a repulsive surface-surface interaction given by an ansatz which agrees with known analytical solutions in the limit of two separated flat surfaces. Mechanical equilibrium is imposed at all times by repositioning the confining surface. By the use of kinetic Monte Carlo (KMC) we calculate how the equilibrium concentration (deposition rate) depends on the applied load, and find it to reproduce analytical thermodynamics independent of the parameters of the interaction ansatz. We also study the dependency between the surface roughness and the saturation level as we vary the surface tension, and expand on previous analyses of the asymmetry between growth and dissolution by parametrizing the linear growth rate constant for growth and dissolution separately. We find the presence of a confining surface to affect the speed of growth and dissolution equally.

Effect of Shock Waves on Dielectric Properties of KDP Crystal

NASA Astrophysics Data System (ADS)

Sivakumar, A.; Suresh, S.; Pradeep, J. Anto; Balachandar, S.; Martin Britto Dhas, S. A.

2018-05-01

An alternative non-destructive approach is proposed and demonstrated for modifying electrical properties of crystal using shock-waves. The method alters dielectric properties of a potassium dihydrogen phosphate (KDP) crystal by loading shock-waves generated by a table-top shock tube. The experiment involves launching the shock-waves perpendicular to the (100) plane of the crystal using a pressure driven table-top shock tube with Mach number 1.9. Electrical properties of dielectric constant, dielectric loss, permittivity, impedance, AC conductivity, DC conductivity and capacitance as a function of spectrum of frequency from 1 Hz to 1 MHz are reported for both pre- and post-shock wave loaded conditions of the KDP crystal. The experimental results reveal that dielectric constant of KDP crystal is sensitive to the shock waves such that the value decreases for the shock-loaded KDP sample from 158 to 147. The advantage of the proposed approach is that it is an alternative to the conventional doping process for tailoring dielectric properties of this type of crystal.

The application of Newman crack-closure model to predicting fatigue crack growth

NASA Astrophysics Data System (ADS)

Si, Erjian

1994-09-01

Newman crack-closure model and the relevant crack growth program were applied to the analysis of crack growth under constant amplitude and aircraft spectrum loading on a number of aluminum alloy materials. The analysis was performed for available test data of 2219-T851, 2024-T3, 2024-T351, 7075-T651, 2324-T39, and 7150-T651 aluminum materials. The results showed that the constraint factor is a significant factor in the method. The determination of the constraint factor is discussed. For constant amplitude loading, satisfactory crack growth lives could be predicted. For the above aluminum specimens, the ratio of predicted to experimental lives, Np/Nt, ranged from 0.74 to 1.36. The mean value of Np/Nt was 0.97. For a specified complex spectrum loading, predicted crack growth lives are not in very good agreement with the test data. Further effort is needed to correctly simulate the transition between plane strain and plane stress conditions, existing near the crack tip.

RF power recovery feedback circulator

DOEpatents

Sharamentov, Sergey I [Bolingbrook, IL

2011-03-29

A device and method for improving the efficiency of RF systems having a Reflective Load. In the preferred embodiment, Reflected Energy from a superconducting resonator of a particle accelerator is reintroduced to the resonator after the phase of the Reflected Energy is aligned with the phase of the Supply Energy from a RF Energy Source. In one embodiment, a Circulator is used to transfer Reflected Energy from the Reflective Load into a Phase Adjuster which aligns the phase of the Reflected Energy with that of the Supply Energy. The phase-aligned energy is then combined with the Supply Energy, and reintroduced into the Reflective Load. In systems having a constant phase shift, the Phase Adjuster may be designed to shift the phase of the Reflected Energy by a constant amount using a Phase Shifter. In systems having a variety (variable) phase shifts, a Phase Shifter controlled by a phase feedback loop comprising a Phase Detector and a Feedback Controller to account for the various phase shifts is preferable.

Microscopic modeling of confined crystal growth and dissolution

NASA Astrophysics Data System (ADS)

Høgberget, Jørgen; Røyne, Anja; Dysthe, Dag K.; Jettestuen, Espen

2016-08-01

We extend the (1+1)-dimensional fluid solid-on-solid (SOS) model to include a confining flat surface opposite to the SOS surface subject to a constant load. This load is balanced by a repulsive surface-surface interaction given by an ansatz which agrees with known analytical solutions in the limit of two separated flat surfaces. Mechanical equilibrium is imposed at all times by repositioning the confining surface. By the use of kinetic Monte Carlo (KMC) we calculate how the equilibrium concentration (deposition rate) depends on the applied load, and find it to reproduce analytical thermodynamics independent of the parameters of the interaction ansatz. We also study the dependency between the surface roughness and the saturation level as we vary the surface tension, and expand on previous analyses of the asymmetry between growth and dissolution by parametrizing the linear growth rate constant for growth and dissolution separately. We find the presence of a confining surface to affect the speed of growth and dissolution equally.

Spatial cues serving the tactile directional sensibility of the human forearm.

PubMed Central

Norrsell, U; Olausson, H

1994-01-01

1. Tactile directional sensibility is considered to rely on the parallel processing of direction-contingent sensory data that depend on skin stretching caused by friction, and spatial cues that vary with time. A temperature-controlled airstream stimulus that prevented the activation of stretch receptors was used to investigate directional sensibility for the skin of the forearm. 2. The dependence on contact load and distance of movement was determined for normal subjects with a two-alternative forced-choice method. Testing was performed under two conditions, elbow bent or straight. Bracing the skin by straightening the arm did not alter the accuracy of the directional sensibility, in contrast to previous findings with stimuli that caused friction. 3. The accuracy of directional sensibility was correlated linearly to the logarithm of the distance of movement of the air jet. No correlation was found between accuracy and contact load, unlike findings with stimuli that cause friction. 4. Measurements were made with different subjects to determine the threshold distance at constant load. On average, subjects were able to distinguish direction with movements of < or = 8 mm. This acuity is sharper than has been reported with static stimuli. There was no correlation between subjects' threshold distances for judging direction and spatial acuity measured with absolute point localization. 5. The ability to distinguish direction was poor for the airstream stimulus compared with stimuli causing frictional contact with hairy skin. Nevertheless, the present findings are consistent with the suggestion that cutaneous spatial acuity is better for dynamic than for static stimuli. Images Figure 1 PMID:7965863

Caffeine, an anthropogenic marker for wastewater comtamination of surface waters.

PubMed

Buerge, Ignaz I; Poiger, Thomas; Müller, Markus D; Buser, Hans-Rudolf

2003-02-15

The suitability of caffeine as a chemical marker for surface water pollution by domestic wastewaters was assessed in this study. Caffeine concentrations in influents and effluents of Swiss wastewater treatment plants (WWTPs, 7-73 and 0.03-9.5 microg/L, respectively) indicated an efficient elimination of 81-99.9%. Corresponding loads in untreated wastewater showed small variations when normalized forthe population discharging to the WWTPs (15.8 +/- 3.8 mg person(-1) d(-1)), reflecting a rather constant consumption. WWTP effluent loads were considerably lower (0.06 +/- 0.03 mg person(-1) d(-1)), apart from installations with low sludge age (< or = 5 d, loads up to 4.4 mg person(-1) d(-1)). Despite the efficient removal in most WWTPs, caffeine was ubiquitously found in Swiss lakes and rivers (6-250 ng/ L), except for remote mountain lakes (<2 ng/L; analytical procedure for wastewater and natural waters: SPE, GC-MS-SIM or GC-MS-MS-MRM, internal standard 13C3-labeled caffeine). Caffeine concentrations in lakes correlated with the anthropogenic burden by domestic wastewaters, demonstrating the suitability of caffeine as a marker. A mass balance for Greifensee revealed that approximately 1-4% of the wastewaters had been discharged without treatment, presumably on rainy days when the capacity of WWTPs had been exceeded. For Zürichsee, it could be shown that the monthly inputs of caffeine correlated with precipitation data. The depth- and seasonal-dependent concentrations in this lake were adequately rationalized by a numerical model considering flushing, biodegradation, and indirect photodegradation via HO. radicals as elimination processes and caffeine inputs as fitting variables.

Continuous fluidized-bed contactor with recycle of sorbent

DOEpatents

Scott, Charles D.; Petersen, James N.; Davison, Brian H.

1996-01-01

A continuous fluidized-bed contactor containing sorbent particles is used to remove solutes from liquid solvents. As the sorbent particles, for example gel beads, sorb the solute, for example metal ion species, the sorbent particles tend to decrease in diameter. These smaller loaded sorbent particles rise to the top of the contactor, as larger sorbent particles remain at the bottom of the contactor as a result of normal hydraulic forces. The smaller loaded sorbent particles are then recovered, regenerated, and reintroduced into the contactor. Alternatively, the loaded sorbent particles may also slightly increase in diameter, or exhibit no change in diameter but an increase in density. As a result of normal hydraulic forces the larger loaded sorbent particles fall to the bottom of the contactor. The larger loaded sorbent particles are then recovered, regenerated, and reintroduced into the contactor.

Continuous fluidized-bed contactor with recycle of sorbent

DOEpatents

Scott, C.D.; Petersen, J.N.; Davison, B.H.

1996-07-09

A continuous fluidized-bed contactor containing sorbent particles is used to remove solutes from liquid solvents. As the sorbent particles, for example gel beads, sorb the solute, for example metal ion species, the sorbent particles tend to decrease in diameter. These smaller loaded sorbent particles rise to the top of the contactor, and larger sorbent particles remain at the bottom of the contactor as a result of normal hydraulic forces. The smaller loaded sorbent particles are then recovered, regenerated, and reintroduced into the contactor. Alternatively, the loaded sorbent particles may also slightly increase in diameter, or exhibit no change in diameter but an increase in density. As a result of normal hydraulic forces the larger loaded sorbent particles fall to the bottom of the contactor. The larger loaded sorbent particles are then recovered, regenerated, and reintroduced into the contactor. 8 figs.

Contact area of rough spheres: Large scale simulations and simple scaling laws

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pastewka, Lars, E-mail: lars.pastewka@kit.edu; Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218; Robbins, Mark O., E-mail: mr@pha.jhu.edu

2016-05-30

We use molecular simulations to study the nonadhesive and adhesive atomic-scale contact of rough spheres with radii ranging from nanometers to micrometers over more than ten orders of magnitude in applied normal load. At the lowest loads, the interfacial mechanics is governed by the contact mechanics of the first asperity that touches. The dependence of contact area on normal force becomes linear at intermediate loads and crosses over to Hertzian at the largest loads. By combining theories for the limiting cases of nominally flat rough surfaces and smooth spheres, we provide parameter-free analytical expressions for contact area over the wholemore » range of loads. Our results establish a range of validity for common approximations that neglect curvature or roughness in modeling objects on scales from atomic force microscope tips to ball bearings.« less

Determination Instructions Efficiency of Teaching Methods in Teaching Physics in the Case of Teaching Unit "Viscosity. Newtonian and Stokes Law"

ERIC Educational Resources Information Center

Radulovic, Branka; Stojanovic, Maja

2015-01-01

The use of different teaching methods has resulted in different quality and quantity of students' knowledge. For this reason, it is important to constantly review the teaching methods and applied most effectively. One way of determining instruction efficiency is by using cognitive load and student achievement. Cognitive load can be generally…

Holographic Determination Of Demineralization Of Bones

NASA Astrophysics Data System (ADS)

Ebbeni, J.; Huybrecht, A.; Orloff, S.

1980-05-01

Patients with osteomalacia often complain of back pain or diffuse peripheral bone aches where a mechanical component warrants closer investigations. In order to study the stress-strain patterns in whole human bones and the influence of the degree of calcification upon these patterns, normal bones are submitted to stress and holographic studies are performed prior to and after demineralization. Interpretation of fringes is delicate because the type of loading must be the same in all the experiments with the same bone. Or the demineralization can change non uniformaly the nature of the osseous inhomogeneous structure and caution must be taken to avoid resulting change namely in momentum. Displacements components must be determined in each face of the bone and the calcul of stresses is made in a first step with assumption of equivalent homogeneous material. The problems arrizing in the machanical behaviour of bones are studied experimentally with the various stress analysis techniques. Among these holographical interferometry proved to be particularly well suited because of its high sensitivity, the rough bone surface needs no preparation and it yields the whole deformation field of the surface. Unfortunately the mechanical comportment of the osseous material depends of many factors and the demineralization namely can change non uniformaly the nature of the inhomogeneous structures like bones and caution must be taken for the interpretation of holographic fringes : because of structural variations in bones, apparently similar types of loading can be different namely by evolution of the position of the neutral axis for momentum. Those phenomena will be analysed in different examples. If estimation of demineralization effect is desired, for instance by measurement of appropriated change in elastic modulus, it is important to know any variation in the loading conditions due to specific changes of the material. The first problem considered concerned the measure of Young's modulus E and Poisson's ration of a tigh-bone or tibia. Small test specimens of constant rectangular section are cut out and submitted to pure bending. Classical double exposure holograms are recorded, with the directions of lighting n1 and observation n2 of the specimen nearly parallel to the normal Oz by use of a mirror. (cfr Figure 1).

Effect of emplaced nZVI mass and groundwater velocity on PCE dechlorination and hydrogen evolution in water-saturated sand.

PubMed

Kim, Hye-Jin; Leitch, Megan; Naknakorn, Bhanuphong; Tilton, Robert D; Lowry, Gregory V

2017-01-15

The effect of nZVI mass loading and groundwater velocity on the tetrachloroethylene (PCE) dechlorination rate and the hydrogen evolution rate for poly(maleic acid-co-olefin) (MW=12K) coated nZVI was examined. In batch reactors, the PCE reaction rate constant (3.7×10 -4 Lhr -1 m -2 ) and hydrogen evolution rate constant (1.4 nanomolLhr -1 m -2 ) were independent of nZVI concentration above 10g/L, but the PCE dechlorination rate decreased and the hydrogen evolution rate increased for nZVI concentration below 10g/L. The nonlinearity between nZVI mass loading and PCE dechlorination and H 2 evolution was explained by differences in pH and E h at each nZVI mass loading; PCE reactivity increased when solution E h decreased, and the H 2 evolution rate increased with decreasing pH. Thus, nZVI mass loading of <5g/L yields lower reactivity with PCE and lower efficiency of Fe° utilization than for higher nZVI mass loading. The PCE dechlorination rate increased with increasing pore-water velocity, suggesting that mass transfer limits the reaction at low porewater velocity. Overall, this work suggests that design of nZVI-based reactive barriers for groundwater treatment should consider the non-linear effects of both mass loading and flow velocity on performance and expected reactive lifetime. Copyright © 2016 Elsevier B.V. All rights reserved.

Distribution Development for STORM Ingestion Input Parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulton, John

The Sandia-developed Transport of Radioactive Materials (STORM) code suite is used as part of the Radioisotope Power System Launch Safety (RPSLS) program to perform statistical modeling of the consequences due to release of radioactive material given a launch accident. As part of this modeling, STORM samples input parameters from probability distributions with some parameters treated as constants. This report described the work done to convert four of these constant inputs (Consumption Rate, Average Crop Yield, Cropland to Landuse Database Ratio, and Crop Uptake Factor) to sampled values. Consumption rate changed from a constant value of 557.68 kg / yr tomore » a normal distribution with a mean of 102.96 kg / yr and a standard deviation of 2.65 kg / yr. Meanwhile, Average Crop Yield changed from a constant value of 3.783 kg edible / m 2 to a normal distribution with a mean of 3.23 kg edible / m 2 and a standard deviation of 0.442 kg edible / m 2 . The Cropland to Landuse Database ratio changed from a constant value of 0.0996 (9.96%) to a normal distribution with a mean value of 0.0312 (3.12%) and a standard deviation of 0.00292 (0.29%). Finally the crop uptake factor changed from a constant value of 6.37e -4 (Bq crop /kg)/(Bq soil /kg) to a lognormal distribution with a geometric mean value of 3.38e -4 (Bq crop /kg)/(Bq soil /kg) and a standard deviation value of 3.33 (Bq crop /kg)/(Bq soil /kg)« less

14 CFR 27.337 - Limit maneuvering load factor.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Limit maneuvering load factor. 27.337 Section 27.337 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Strength Requirements Flight Loads § 27.337...

14 CFR 27.427 - Unsymmetrical loads.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Unsymmetrical loads. 27.427 Section 27.427 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Strength Requirements Control Surface and System Loads § 27.427...

Structural evaluation of the 2736Z Building for seismic loads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giller, R.A.

The 2736Z building structure is evaluated for high-hazard loads. The 2736Z building is analyzed herein for normal and seismic loads and is found to successfully meet the guidelines of UCRL-15910 along with the related codes requirements.

The Inclusion of Arbitrary Load Histories in the Strength Decay Model for Stress Rupture

NASA Technical Reports Server (NTRS)

Reeder, James R.

2014-01-01

Stress rupture is a failure mechanism where failures can occur after a period of time, even though the material has seen no increase in load. Carbon/epoxy composite materials have demonstrated the stress rupture failure mechanism. In a previous work, a model was proposed for stress rupture of composite overwrap pressure vessels (COPVs) and similar composite structures based on strength degradation. However, the original model was limited to constant load periods (holds) at constant load. The model was expanded in this paper to address arbitrary loading histories and specifically the inclusions of ramp loadings up to holds and back down. The broadening of the model allows for failures on loading to be treated as any other failure that may occur during testing instead of having to be treated as a special case. The inclusion of ramps can also influence the length of the "safe period" following proof loading that was previously predicted by the model. No stress rupture failures are predicted in a safe period because time is required for strength to decay from above the proof level to the lower level of loading. Although the model can predict failures during the ramp periods, no closed-form solution for the failure times could be derived. Therefore, two suggested solution techniques were proposed. Finally, the model was used to design an experiment that could detect the difference between the strength decay model and a commonly used model for stress rupture. Although these types of models are necessary to help guide experiments for stress rupture, only experimental evidence will determine how well the model may predict actual material response. If the model can be shown to be accurate, current proof loading requirements may result in predicted safe periods as long as 10(13) years. COPVs design requirements for stress rupture may then be relaxed, allowing more efficient designs, while still maintaining an acceptable level of safety.

Subepidermal moisture detection of heel pressure injury: The pressure ulcer detection study outcomes.

PubMed

Bates-Jensen, Barbara M; McCreath, Heather E; Nakagami, Gojiro; Patlan, Anabel

2018-04-01

We examined subepidermal moisture (SEM) and visual skin assessment of heel pressure injury (PrI) among 417 nursing home residents in 19 facilities over 16 weeks. Participants were older (mean age 77 years), 58% were female, over half were ethnic minorities (29% African American, 12% Asian American, 21% Hispanic), and at risk for PrI (mean Braden Scale Risk score = 15.6). Blinded concurrent visual assessments and SEM measurements were obtained at heels weekly. Visual skin damage was categorised as normal, erythema, stage 1 PrI, deep tissue injury (DTI) or stage 2 or greater PrI. PrI incidence was 76%. Off-loading occurred with pillows (76% of residents) rather than heel boots (21%) and often for those with DTI (91%). Subepidermal moisture was measured with a device where higher readings indicate greater moisture (range: 0-70 tissue dielectric constant), with normal skin values significantly different from values in the presence of skin damage. Subepidermal moisture was associated with concurrent damage and damage 1 week later in generalised multinomial logistic models adjusting for age, diabetes and function. Subepidermal moisture detected DTI and differentiated those that resolved, remained and deteriorated over 16 weeks. Subepidermal moisture may be an objective method for detecting PrI. © 2017 Medicalhelplines.com Inc and John Wiley & Sons Ltd.

The impact of constant light on the estrous cycle of the rat.

PubMed

Campbell, C S; Schwartz, N B

1980-04-01

The initial effects of constant bright light on the events of the rat estrous cycle were monitored in order to examine the interdependence of the hormonal and behavioral rhythms which comprise the cycle. Females exposed to constant bright light for only one cycle either failed to ovulate or showed a delay in the hormonal and behavioral events of the cycle as well as in ovulation. Females exposed to constant light for two cycles 1) failed to ovulate, 2) showed an advancement, or 3) showed a delay in the hormonal events of the estrous cycle and ovulation. Vaginal cytology and the onset of locomotor activity did not maintain their normal temporal relationships with the other events of the estrous cycle in constant light. In spite of the absence of an external timing signal, the majority of hormonal rhythms maintained their normal phase relationships and showed little sign of internal desynchrony. Ovaries in many animals showed high rates of follicular atresia early in the cycle, suggesting that the effects of bright constant light are far more complex than can be attributed to a simple absence of an external timing signal.

FRACTURE BEHAVIOR OF ALLOY 600, ALLOY 690, EN82H WELDS AND EN52 WELDS IN WATER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mills, W.J., Brown, C.M. and Burke, M.G.

2000-01-11

The cracking resistance of Alloy 600, Alloy 690 and their welds, EN82H and EN52, was characterized by conducting J{sub IC} rising load tests in air and hydrogenated water and cooldown testing in water under constant-displacement conditions. All test materials displayed excellent toughness in air and high temperature water, but Alloy 690 and the two welds were severely embrittled in low temperature water. In 54 C water with 150 cc H{sub 2}/kg H{sub 2}O, J{sub IC} values were reduced by 70% to 95%, relative to their air counterpart. The toughness degradation was associated with a fracture mechanism transition from microvoid coalescencemore » to intergranular fracture. Comparison of the cracking response in water with that for hydrogen-precharged specimens tested in air demonstrated that susceptibility to low temperature crack propagation (LTCP) is due to hydrogen embrittlement of grain boundaries. The effects of water temperature, hydrogen content and loading rate on LTCP were studied. In addition, testing of specimens containing natural weld defects and as-machined notches was performed to determine if low temperature cracking can initiate at these features. Unlike the other materials, Alloy 600 is not susceptible to LTCP as the toughness in 54 C water remained high and a microvoid coalescence mechanism was operative in both air and water. Cooldown testing of EN82H welds under constant-displacement conditions was performed to determine if LTCP data from rising load J{sub IC}/K{sub Pmax} tests predict the onset of LTCP for other load paths. In these tests, bolt-loaded CT specimens were subjected to 288 C water for up to 1 week, cooled to 54 C and held in 54 C hydrogenated water for 1 week. This cycle was repeated up to 6 times. For two of the three welds tested, critical K{sub I} levels for LTCP under constant-displacement conditions were much higher than rising load K{sub Pmax} values. Bolt-loaded specimens from a third weld were found to exhibit LTCP at K{sub I} levels comparable to K{sub Pmax} values. Although work to date indicates that rising load tests either accurately or conservatively predict the critical conditions for LTCP under constant displacement conditions, the potential for LTCP at K{sub I} levels less than K{sub Pmax} has not been fully evaluated. Annealing at 1093 C reduces or eliminates LTCP susceptibility. The microstructure and mechanical properties for susceptible and nonsusceptible EN82H welds were characterized to identify the key material parameters responsible for LTCP in the as-welded condition. The key microstructural feature associated with LTCP appears to be fine Nb- and Ti-rich carbonitrides decorating grain boundaries. In addition, the higher yield strength for the as-fabricated weld also promotes LTCP because it increases stresses and local hydrogen concentrations ahead of a crack.« less

Quantifying the effects of external shear loads on arterial and venous blood flow: implications for pressure ulcer development.

PubMed

Manorama, Abinand; Meyer, Ronald; Wiseman, Robert; Bush, Tamara Reid

2013-06-01

Forces applied to the skin cause a decrease in regional blood flow. This decrease in blood flow can cause tissue necrosis and lead to the formation of deep, penetrating wounds called pressure ulcers. These wounds are detrimental to individuals with compromised health, such as the elderly and spinal-cord injured. Although surface pressure is known to be a primary risk factor for developing a pressure ulcer, a seated individual rarely experiences pressure alone but rather combined loading which includes pressure as well as shear force on the skin. However, little research has been conducted to quantify the effects of shear forces on blood flow. Fifteen men were tested in a magnetic resonance imaging scanner under no load, a normal load, and a combination of normal and shear loads. Changes in arterial and venous blood flow in the forearm were measured using magnetic resonance angiography phase-contrast imaging. The blood flow in the anterior interosseous artery and basilic vein of the forearm decreased with the application of normal loads, and decreased further with the addition of shear loads. Marginal to significant differences at a 90% confidence level (P=0.08, 0.10) were observed, and medium to high effect sizes (0.3 to 0.5) were obtained. Based on these results, shear force is an important factor to consider in relation to pressure ulcer propagation and prevention, and hence, future prevention approaches should also focus on mitigating shear loads. Copyright © 2013 Elsevier Ltd. All rights reserved.

Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale.

PubMed

Tian, Kaiwen; Gosvami, Nitya N; Goldsby, David L; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W

2017-02-17

Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale

NASA Astrophysics Data System (ADS)

Tian, Kaiwen; Gosvami, Nitya N.; Goldsby, David L.; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W.

2017-02-01

Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

An in vitro biomechanical comparison of two fixation methods for transverse osteotomies of the medial proximal forelimb sesamoid bones in horses.

PubMed

Wilson, D A; Keegan, K G; Carson, W L

1999-01-01

This study compared the mechanical properties of the normal intact suspensory apparatus and two methods of fixation for repair of transverse, midbody fractures of the proximal sesamoid bones of adult horses: transfixation wiring (TW) and screws placed in lag fashion (LS). An in vitro, paired study using equine cadaver limbs mounted in a loading apparatus was used to test the mechanical properties of TW and LS. Seventeen paired (13 repaired, 4 normal) equine cadaver limbs consisting of the suspensory apparatus third metacarpal bone, and first and second phalanges. The two methods of repair and normal intact specimens were evaluated in single cycle-to-failure loading. Yield failure was defined to occur at the first notable discontinuity (>50 N) in the load-displacement curve, the first visible failure as evident on the videotape, or a change in the slope of the moment-fetlock angle curve. Ultimate failure was defined to occur at the highest load resisted by the specimen. Corresponding resultant force and force per kg of body weight on the suspensory apparatus, fetlock joint moment, and angle of fetlock dorsiflexion were calculated by use of specimen dimensions and applied load. These were compared along with specimen stiffness, and ram displacement. Load on the suspensory apparatus, load on the suspensory apparatus per kg of body weight, moment, applied load, and angle of fetlock dorsiflexion at yield failure were significantly greater for the TW-repaired than for the LS-repaired specimens. A 3 to 5 mm gap was observed before yield failure in most TW-repaired osteotomies. Transfixation wiring provided greater strength to yield failure than screws placed in lag fashion in single cycle load-to-failure mechanical testing of repaired transverse osteotomized specimens of the medial proximal forelimb sesamoid bone.

Cytoskeletal mechanics in pressure-overload cardiac hypertrophy

NASA Technical Reports Server (NTRS)

Tagawa, H.; Wang, N.; Narishige, T.; Ingber, D. E.; Zile, M. R.; Cooper, G. 4th

1997-01-01

We have shown that the cellular contractile dysfunction characteristic of pressure-overload cardiac hypertrophy results not from an abnormality intrinsic to the myofilament portion of the cardiocyte cytoskeleton but rather from an increased density of the microtubule component of the extramyofilament portion of the cardiocyte cytoskeleton. To determine how, in physical terms, this increased microtubule density mechanically overloads the contractile apparatus at the cellular level, we measured cytoskeletal stiffness and apparent viscosity in isolated cardiocytes via magnetic twisting cytometry, a technique by which magnetically induced force is applied directly to the cytoskeleton through integrin-coupled ferromagnetic beads coated with Arg-Gly-Asp (RGD) peptide. Measurements were made in two groups of cardiocytes from cats with right ventricular (RV) hypertrophy induced by pulmonary artery banding: (1) those from the pressure-overloaded RV and (2) those from the normally loaded same-animal control left ventricle (LV). Cytoskeletal stiffness increased almost twofold, from 8.53 +/- 0.77 dyne/cm2 in the normally loaded LV cardiocytes to 16.46 +/- 1.32 dyne/cm2 in the hypertrophied RV cardiocytes. Cytoskeletal apparent viscosity increased almost fourfold, from 20.97 +/- 1.92 poise in the normally loaded LV cardiocytes to 87.85 +/- 6.95 poise in the hypertrophied RV cardiocytes. In addition to these baseline data showing differing stiffness and, especially, apparent viscosity in the two groups of cardiocytes, microtubule depolymerization by colchicine was found to return both the stiffness and the apparent viscosity of the pressure overload-hypertrophied RV cells fully to normal. Conversely, microtubule hyperpolymerization by taxol increased the stiffness and apparent viscosity values of normally loaded LV cardiocytes to the abnormal values given above for pressure-hypertrophied RV cardiocytes. Thus, increased microtubule density constitutes primarily a viscous load on the cardiocyte contractile apparatus in pressure-overload cardiac hypertrophy.

(1)H magnetic resonance spectroscopy of preinvasive and invasive cervical cancer: in vivo-ex vivo profiles and effect of tumor load.

PubMed

Mahon, Marrita M; Cox, I Jane; Dina, Roberto; Soutter, W Patrick; McIndoe, G Angus; Williams, Andreanna D; deSouza, Nandita M

2004-03-01

To compare in vivo (1)H magnetic resonance (MR) spectra of preinvasive and invasive cervical lesions with ex vivo magic angle spinning (MAS) spectra of intact biopsies from the same subjects and to establish the effects of tumor load in the tissue sampled on the findings. A total of 51 subjects (nine with normal cervix, 10 with cervical intraepithelial neoplasia [CIN], and 32 with cervical cancer) underwent endovaginal MR at 1.5 T. Single-voxel (3.4 cm(3)) (1)H MR spectra were acquired and voxel tumor load was calculated (tumor volume within voxel as a percentage of voxel volume). Resonances from triglycerides -CH(2) and -CH(3) and choline-containing compounds (Cho) were correlated with voxel tumor load. Biopsies analyzed by (1)H MAS-MR spectroscopy (MRS) had metabolite levels correlated with tumor load in the sample at histology. In vivo studies detected Cho in normal, CIN, and cancer patients with no significant differences in levels (P = 0.93); levels were independent of voxel tumor load. Triglyceride -CH(2) and -CH(3) signals in-phase with Cho were present in 77% and 29%, respectively, of cancer subjects (but not in normal women or those with CIN), but did not correlate with voxel tumor load. Ex vivo cancer biopsies showed levels of triglycerides -CH(2) and -CH(3) and of Cho that were significantly greater than in normal or CIN biopsies (P < 0.05); levels were independent of the tumor load in the sample. The presence of -CH(2) in vivo predicted the presence of cancer with a sensitivity and specificity of 77.4% and 93.8% respectively, positive (PPV) and negative (NPV) predictive values were 96% and 68.2%; for -CH(2) ex vivo, sensitivity was 100%; specificity, 69%; PPV, 82%; and NPV, 100%. Elevated lipid levels are detected by MRS in vivo and ex vivo in cervical cancer and are independent of tumor load in the volume of tissue sampled. Copyright 2004 Wiley-Liss, Inc.

Hierarchical damage mechanisms in composite materials subjected to fatigue loadings

NASA Astrophysics Data System (ADS)

D'Amore, Alberto; Grassia, Luigi

2018-02-01

The strength degradation of fiber reinforced composites subjected to constant amplitude (CA) fatigue loadings can be described by a two-parameter residual strength model. From the analytical approach it results that under moderate loadings the multiple damage mechanisms develop with different kinetics and manifest their effectiveness at different time scales highlighting the three-Stage hierarchical nature of damage accumulation in composites. The model captures the sequence of damage accumulation mechanisms from diffuse matrix cracking (I), to fiber/matrix interface failure (II) to fiber and ply rupture and delamination (III). Further, by increasing the loading severity it appears that the different mechanisms superpose witnessing their simultaneous co-existence.

On optimization of energy harvesting from base-excited vibration

NASA Astrophysics Data System (ADS)

Tai, Wei-Che; Zuo, Lei

2017-12-01

This paper re-examines and clarifies the long-believed optimization conditions of electromagnetic and piezoelectric energy harvesting from base-excited vibration. In terms of electromagnetic energy harvesting, it is typically believed that the maximum power is achieved when the excitation frequency and electrical damping equal the natural frequency and mechanical damping of the mechanical system respectively. We will show that this optimization condition is only valid when the acceleration amplitude of base excitation is constant and an approximation for small mechanical damping when the excitation displacement amplitude is constant. To this end, a two-variable optimization analysis, involving the normalized excitation frequency and electrical damping ratio, is performed to derive the exact optimization condition of each case. When the excitation displacement amplitude is constant, we analytically show that, in contrast to the long-believed optimization condition, the optimal excitation frequency and electrical damping are always larger than the natural frequency and mechanical damping ratio respectively. In particular, when the mechanical damping ratio exceeds a critical value, the optimization condition is no longer valid. Instead, the average power generally increases as the excitation frequency and electrical damping ratio increase. Furthermore, the optimization analysis is extended to consider parasitic electrical losses, which also shows different results when compared with existing literature. When the excitation acceleration amplitude is constant, on the other hand, the exact optimization condition is identical to the long-believed one. In terms of piezoelectric energy harvesting, it is commonly believed that the optimal power efficiency is achieved when the excitation and the short or open circuit frequency of the harvester are equal. Via a similar two-variable optimization analysis, we analytically show that the optimal excitation frequency depends on the mechanical damping ratio and does not equal the short or open circuit frequency. Finally, the optimal excitation frequencies and resistive loads are derived in closed-form.

The interactive effect of dietary water-soluble vitamin levels on the depression of gonadal development in growing male rats kept under disturbed daily rhythm.

PubMed

Hanai, Miho; Esashi, Takatoshi

2012-01-01

The purpose of this study was to clarify the effects of nutrients on the gonadal development of male rats kept under constant darkness as a model of disturbed daily rhythm. In the present study we examined the effects of nine water-soluble vitamins. We selected 7 water-soluble vitamins (choline, nicotinic acid (NA), pantothenic acid (PA), vitamin B6 (VB6), vitamin B1 (VB1), vitamin B2 (VB2) and folic acid (FA)) as experimental factors for the first experiment (Ex. 1) and biotin and vitamin B12 (VB12) as experimental factors for the second experiment (Ex. 2). The dietary content of these vitamins was normal or six times the normal content. Lighting condition (L.C.) was also added as a factor. Four-week-old male rats (Fischer 344 strain) were kept under constant darkness or normal lighting (12-h light/dark cycle) for 4 wk. The depression of gonadal development in the constant darkness groups (D-groups) was shown. The L.C., PA, VB6 and VB1 influenced testes development, and these three vitamins had interactions with L.C. Among the normal lighting groups (N-groups), the highest value for testes weight was observed under the normal-PA, high-VB6 and high-B1 diet; on the other hand, among the D-groups, it was observed under the high-PA, normal-VB6 and normal-VB1 diet. The results showed that the depression of gonadal development in rats kept under disturbed daily rhythm was improved by getting a high amount of PA and normal amount of VB6 and VB1.

Design and develop speed/pressure regulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasanul Basher, A.M.

1993-09-01

The Physics Division at Oak Ridge National Laboratory has several recirculating water cooling systems. One of them supplies deionized water at 150 psi, which is mainly used for cooling magnet windings at the Oak Ridge Isochronous Cyclotron (ORIC). The system has three 125-hp water pumps, each of which is capable of supplying water at the rate of 1000 gpm. One of the major requirements of this water supply system is that the supply pressure must be kept constant. An adjustable-frequency speed controller was recently installed to control the speed of one of the pump motors. A servo-system was provided withmore » the adjustable-frequency controller for regulating motor speed and, subsequently, the water pressure. After unsuccessful attempts to operate the servo, it was concluded that the regulator may not work for the existing system. Prior to installation of the variable-frequency controller, pressure regulation was accomplished with a pneumatically controlled load by-pass valve. To maintain constant pressure in the system, it is necessary to run always at full load, even if full load is not on the system. Hence, there is a waste of energy when full load is not connected to the system. So, designing and implementing one regulator that works at any load condition has become necessary. This report discusses the design of such a pressure regulator.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobsen, A. J.

In a method of the type where petrol is recovered from a mixture of petrol vapor and air by absorption of the petrol in a cooled petroleum distillate, a petroleum distillate having a boiling point range higher than that of the petrol is used, and this petroleum distillate is in sequence cooled by heat exchange with a cold reservoir, brought into direct contact with the petrol/air mixture to absorb petrol, transferred to a buffer tank and transferred from the buffer tank to a stripping means which may be a distillation column. By combining cooling condensation and absorption of the petrolmore » vapor and controlling the amount of cooled petroleum distillate brought into contact with the petrol/air mixture so that the petrol concentration in the petroleum distillate transferred to the buffer tank is substantially constant, an unprecedented optimum control of the petrol absorbing process can be obtained both in peak load and in average load operations. A system for carrying out the method is advantageous in that only the absorption means need be dimensioned for peak load operation, while the other components, such as the distillation column or a heat exchanger with associated conduits can be dimensioned for average loads, a buffer tank being provided to temporarily receive the petroleum distillate which owing to the above-mentioned control has a substantially constant, maximum petrol concentration so that the system can cope with peak loads with a surprisingly small buffer tank.« less

Modelling of Fiber/Matrix Debonding of Composites Under Cyclic Loading

NASA Technical Reports Server (NTRS)

Naghipour, Paria; Pineda, Evan J.; Bednarcyk, Brett A.; Arnold, Steven M.

2013-01-01

The micromechanics theory, generalized method of cells (GMC), was employed to simulate the debonding of fiber/matrix interfaces, within a repeating unit cell subjected to global, cyclic loading, utilizing a cyclic crack growth law. Cycle dependent, interfacial debonding was implemented as a new module to the available GMC formulation. The degradation of interfacial stresses, with applied load cycles, was achieved via progressive evolution of the interfacial compliance. A periodic repeating unit cell, representing the fiber/matrix architecture of a composite, was subjected to combined normal and shear loadings, and degradation of the global transverse stress in successive cycles was monitored. The obtained results were compared to values from a corresponding finite element model. Reasonable agreement was achieved for combined normal and shear loading conditions, with minimal variation for pure loading cases. The local effects of interfacial debonding, and fatigue damage will later be combined as sub-models to predict the experimentally obtained fatigue life of Ti-15-3/Sic composites at the laminate level.

Force control compensation method with variable load stiffness and damping of the hydraulic drive unit force control system

NASA Astrophysics Data System (ADS)

Kong, Xiangdong; Ba, Kaixian; Yu, Bin; Cao, Yuan; Zhu, Qixin; Zhao, Hualong

2016-05-01

Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit (HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.

Time- & Load-Dependence of Triboelectric Effect.

PubMed

Pan, Shuaihang; Yin, Nian; Zhang, Zhinan

2018-02-06

Time- and load-dependent friction behavior is considered as important for a long time, due to its time-evolution and force-driving characteristics. However, its electronic behavior, mainly considered in triboelectric effect, has almost never been given the full attention and analyses from the above point of view. In this paper, by experimenting with fcc-latticed aluminum and copper friction pairs, the mechanical and electronic behaviors of friction contacts are correlated by time and load analyses, and the behind physical understanding is provided. Most importantly, the difference of "response lag" in force and electricity is discussed, the extreme points of coefficient of friction with the increasing normal loads are observed and explained with the surface properties and dynamical behaviors (i.e. wear), and the micro and macro theories linking tribo-electricity to normal load and wear (i.e. the physical explanation between coupled electrical and mechanical phenomena) are successfully developed and tested.

Cy5 total protein normalization in Western blot analysis.

PubMed

Hagner-McWhirter, Åsa; Laurin, Ylva; Larsson, Anita; Bjerneld, Erik J; Rönn, Ola

2015-10-01

Western blotting is a widely used method for analyzing specific target proteins in complex protein samples. Housekeeping proteins are often used for normalization to correct for uneven sample loads, but these require careful validation since expression levels may vary with cell type and treatment. We present a new, more reliable method for normalization using Cy5-prelabeled total protein as a loading control. We used a prelabeling protocol based on Cy5 N-hydroxysuccinimide ester labeling that produces a linear signal response. We obtained a low coefficient of variation (CV) of 7% between the ratio of extracellular signal-regulated kinase (ERK1/2) target to Cy5 total protein control signals over the whole loading range from 2.5 to 20.0μg of Chinese hamster ovary cell lysate protein. Corresponding experiments using actin or tubulin as controls for normalization resulted in CVs of 13 and 18%, respectively. Glyceraldehyde-3-phosphate dehydrogenase did not produce a proportional signal and was not suitable for normalization in these cells. A comparison of ERK1/2 signals from labeled and unlabeled samples showed that Cy5 prelabeling did not affect antibody binding. By using total protein normalization we analyzed PP2A and Smad2/3 levels with high confidence. Copyright © 2015 Elsevier Inc. All rights reserved.

Hip contact forces in asymptomatic total hip replacement patients differ from normal healthy individuals: Implications for preclinical testing.

PubMed

Li, Junyan; Redmond, Anthony C; Jin, Zhongmin; Fisher, John; Stone, Martin H; Stewart, Todd D

2014-08-01

Preclinical durability testing of hip replacement implants is standardised by ISO-14242-1 (2002) which is based on historical inverse dynamics analysis using data obtained from a small sample of normal healthy individuals. It has not been established whether loading cycles derived from normal healthy individuals are representative of loading cycles occurring in patients following total hip replacement. Hip joint kinematics and hip contact forces derived from multibody modelling of forces during normal walking were obtained for 15 asymptomatic total hip replacement patients and compared to 38 normal healthy individuals and to the ISO standard for pre-clinical testing. Hip kinematics in the total hip replacement patients were comparable to the ISO data and the hip contact force in the normal healthy group was also comparable to the ISO cycles. Hip contact forces derived from the asymptomatic total hip replacement patients were comparable for the first part of the stance period but exhibited 30% lower peak loads at toe-off. Although the ISO standard provides a representative kinematic cycle, the findings call into question whether the hip joint contact forces in the ISO standard are representative of those occurring in the joint following total hip replacement. Copyright © 2014. Published by Elsevier Ltd.

WEST-3 wind turbine simulator development

NASA Technical Reports Server (NTRS)

Hoffman, J. A.; Sridhar, S.

1985-01-01

The software developed for WEST-3, a new, all digital, and fully programmable wind turbine simulator is given. The process of wind turbine simulation on WEST-3 is described in detail. The major steps are, the processing of the mathematical models, the preparation of the constant data, and the use of system software generated executable code for running on WEST-3. The mechanics of reformulation, normalization, and scaling of the mathematical models is discussed in detail, in particulr, the significance of reformulation which leads to accurate simulations. Descriptions for the preprocessor computer programs which are used to prepare the constant data needed in the simulation are given. These programs, in addition to scaling and normalizing all the constants, relieve the user from having to generate a large number of constants used in the simulation. Also given are brief descriptions of the components of the WEST-3 system software: Translator, Assembler, Linker, and Loader. Also included are: details of the aeroelastic rotor analysis, which is the center of a wind turbine simulation model, analysis of the gimbal subsystem; and listings of the variables, constants, and equations used in the simulation.

Ball Bearing Mechanics

NASA Technical Reports Server (NTRS)

Hamrock, Bernard J.; Dowson, Duncan

1981-01-01

Load-deflection relationships for different types of elliptical contacts such as those found in a ball bearing are developed. Simplified expressions that allow quick calculations of deformation to be made simply from a knowledge of the applied load, the material properties, and the geometry of the contacting elements are presented. Ball bearings subjected to radial, thrust and combined ball loads are analyzed. A design criterion for fatigue life of ball bearings is developed. The section of a satisfactory lubricant, as well as describing systems that provide a constant flow of lubricant to the contact, is considered.

A crack-closure model for predicting fatigue-crack growth under aircraft spectrum loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1981-01-01

The development and application of an analytical model of cycle crack growth is presented that includes the effects of crack closure. The model was used to correlate crack growth rates under constant amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy sheet material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted to experimental lives ranged from 0.66 to 1.48. These predictions were made using data from an ASTM E24.06.01 Round Robin.

Improved Indentation Test for Measuring Nonlinear Elasticity

NASA Technical Reports Server (NTRS)

Eldridge, Jeffrey I.

2004-01-01

A cylindrical-punch indentation technique has been developed as a means of measuring the nonlinear elastic responses of materials -- more specifically, for measuring the moduli of elasticity of materials in cases in which these moduli vary with applied loads. This technique offers no advantage for characterizing materials that exhibit purely linear elastic responses (constant moduli of elasticity, independent of applied loads). However, the technique offers a significant advantage for characterizing such important materials as plasma-sprayed thermal-barrier coatings, which, in cyclic loading, exhibit nonlinear elasticity with hysteresis related to compaction and sliding within their microstructures.

[The links between learning load and well-being of high school seniors].

PubMed

Petrauskiene, Ausra; Matuleviciūte, Deimante

2007-01-01

To evaluate the links between learning overload and psychoemotional well-being of 12th grade students. In April 2006, an anonymous survey of 184 high school seniors was conducted in six secondary schools and one gymnasium of Kaunas. The total learning load of students was too high and made up 54.79+/-0.98 hours on average. The learning load of 61.4% of children was too high; girls mentioned this problem two times more often than boys did. Students suffered from psychoemotional problems: about half of them felt stress at school; every fifth fell asleep with difficulties. Students whose total learning load was too high (more than 48 hours per week) felt stress, tiredness, stomach or abdominal, head or back pains, vertigo or weakness significantly more often in comparison with those who had normal learning load. The total learning load of the majority of investigated high school seniors was too high. The psychoemotional well-being of 12th graders was unsatisfactory; girls complained about worse well-being than boys more frequently, they used medicine more frequently in comparison to the students whose learning load was normal.

Preliminary weight and costs of sandwich panels to distribute concentrated loads

NASA Technical Reports Server (NTRS)

Belleman, G.; Mccarty, J. E.

1976-01-01

Minimum mass honeycomb sandwich panels were sized for transmitting a concentrated load to a uniform reaction through various distances. The form skin gages were fully stressed with a finite element computer code. The panel general stability was evaluated with a buckling computer code labeled STAGS-B. Two skin materials were considered; aluminum and graphite-epoxy. The core was constant thickness aluminum honeycomb. Various panel sizes and load levels were considered. The computer generated data were generalized to allow preliminary least mass panel designs for a wide range of panel sizes and load intensities. An assessment of panel fabrication cost was also conducted. Various comparisons between panel mass, panel size, panel loading, and panel cost are presented in both tabular and graphical form.

Steady-state force-velocity relation in the ATP-dependent sliding movement of myosin-coated beads on actin cables in vitro studied with a centrifuge microscope.

PubMed Central

Oiwa, K; Chaen, S; Kamitsubo, E; Shimmen, T; Sugi, H

1990-01-01

To eliminate the gap between the biochemistry of actomyosin in solution and the physiology of contracting muscle, we developed an in vitro force-movement assay system in which the steady-state force-velocity relation in the actin-myosin interaction can be studied. The assay system consists of the internodal cells of an alga, Nitellopsis obtusa, containing well-organized actin filament arrays (actin cables); tosyl-activated polystyrene beads (diameter, 2.8 microns; specific gravity, 1.3) coated with skeletal muscle myosin; and a centrifuge microscope equipped with a stroboscopic light source and a video system. The internodal cell preparation was mounted on the rotor of the centrifuge microscope, so that centrifugal forces were applied to the myosin-coated beads moving along the actin cables in the presence of ATP. Under constant centrifugal forces directed opposite to the bead movement ("positive" loads), the beads continued to move with constant velocities, which decreased with increasing centrifugal forces. The steady-state force-velocity curve thus obtained was analogous to the double-hyperbolic force-velocity curve of single muscle fibers. The unloaded velocity of bead movement was 1.6-3.6 microns/s (20-23 degrees C), while the maximum "isometric" force generated by the myosin molecules on the bead was 1.9-39 pN. If, on the other hand, the beads were subjected to constant centrifugal forces in the direction of bead movement ("negative" loads), the bead also moved with constant velocities. Unexpectedly, the velocity of bead movement did not increase with increasing negative loads but first decreased by 20-60% and then increased towards the initial unloaded velocity until the beads were eventually detached from the actin cables. Images PMID:2236007

Steady-state force-velocity relation in the ATP-dependent sliding movement of myosin-coated beads on actin cables in vitro studied with a centrifuge microscope.

PubMed

Oiwa, K; Chaen, S; Kamitsubo, E; Shimmen, T; Sugi, H

1990-10-01

To eliminate the gap between the biochemistry of actomyosin in solution and the physiology of contracting muscle, we developed an in vitro force-movement assay system in which the steady-state force-velocity relation in the actin-myosin interaction can be studied. The assay system consists of the internodal cells of an alga, Nitellopsis obtusa, containing well-organized actin filament arrays (actin cables); tosyl-activated polystyrene beads (diameter, 2.8 microns; specific gravity, 1.3) coated with skeletal muscle myosin; and a centrifuge microscope equipped with a stroboscopic light source and a video system. The internodal cell preparation was mounted on the rotor of the centrifuge microscope, so that centrifugal forces were applied to the myosin-coated beads moving along the actin cables in the presence of ATP. Under constant centrifugal forces directed opposite to the bead movement ("positive" loads), the beads continued to move with constant velocities, which decreased with increasing centrifugal forces. The steady-state force-velocity curve thus obtained was analogous to the double-hyperbolic force-velocity curve of single muscle fibers. The unloaded velocity of bead movement was 1.6-3.6 microns/s (20-23 degrees C), while the maximum "isometric" force generated by the myosin molecules on the bead was 1.9-39 pN. If, on the other hand, the beads were subjected to constant centrifugal forces in the direction of bead movement ("negative" loads), the bead also moved with constant velocities. Unexpectedly, the velocity of bead movement did not increase with increasing negative loads but first decreased by 20-60% and then increased towards the initial unloaded velocity until the beads were eventually detached from the actin cables.

Active Flap Control of the SMART Rotor for Vibration Reduction

NASA Technical Reports Server (NTRS)

Hall, Steven R.; Anand, R. Vaidyanathan; Straub, Friedrich K.; Lau, Benton H.

2009-01-01

Active control methodologies were applied to a full-scale active flap rotor obtained during a joint Boeing/ DARPA/NASA/Army test in the Air Force National Full-Scale Aerodynamic Complex 40- by 80-foot anechoic wind tunnel. The active flap rotor is a full-scale MD 900 helicopter main rotor with each of its five blades modified to include an on-blade piezoelectric actuator-driven flap with a span of 18% of radius, 25% of chord, and located at 83% radius. Vibration control demonstrated the potential of active flaps for effective control of vibratory loads, especially normal force loads. Active control of normal force vibratory loads using active flaps and a continuous-time higher harmonic control algorithm was very effective, reducing harmonic (1-5P) normal force vibratory loads by 95% in both cruise and approach conditions. Control of vibratory roll and pitch moments was also demonstrated, although moment control was less effective than normal force control. Finally, active control was used to precisely control blade flap position for correlation with pretest predictions of rotor aeroacoustics. Flap displacements were commanded to follow specific harmonic profiles of 2 deg or more in amplitude, and the flap deflection errors obtained were less than 0.2 deg r.m.s.

Experimental study on ignition mechanisms of wet granulation sulfur caused by friction.

PubMed

Dai, Haoyuan; Fan, Jianchun; Wu, Shengnan; Yu, Yanqiu; Liu, Di; Hu, Zhibin

2018-02-15

It is common to see fire accidents caused by friction during the storage and transportation of wet granulation sulfur. To study the sulfur ignition mechanism under friction conditions, a new rotating test apparatus is developed to reproduce friction scenes at lab scale. A series of experiments are performed under different normal loads. The SEM-EDS and the XRD were utilized to examine the morphologies and compositions of the tested specimens and the friction products. Experimental results show that these two methods are mostly in agreement with each other. The iron-sulfide compounds are produced and the proportion of iron-sulfide compounds is reduced with normal loads increasing, compared to the total number of the friction products. The facts implied by the integration analysis of friction products with the temperature changes of the near friction surface unveil an underlying mechanism that may explain sulfur ignition by friction in real scenarios. The sulfur ignition may be mainly caused by the spontaneous combustion of iron sulfide compounds produced by friction under low normal load with 200N. With the increase of normal loads, the resulting iron-sulfide compounds are decreasing and the high temperature from friction heat begins to play a major role in causing fire. Copyright © 2017 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schultz, Bradley M.; Li, Nan; Economy, David R.

Mathematical models suggest that the strain along the film formed by parallel passes of a nanoindentation probe in contact with the film can be either homogenous or heterogeneous, depending on contact pressure and spacing between passes. Here, in this study, a 1 µm copper thin film was worn with a cono-spherical diamond probe with normal loads ranging from 25 to 800 µN and wear box edge lengths of 40, 60, and 80 µm. The nanoindenter counterface was rastered across the surface to mimic dry sliding wear. To determine potential strain field changes, 10-step quasi-static indents (200–2000 µN) were performed usingmore » nanoindentation inside the wear boxes created at various loads to determine if a strain field alteration could be observed in changes in hardness of the copper thin film. It was shown that there was a softening effect in the hardness for normal loads < 400 µN used during nanowear compared to the as-deposited copper. Normal loads ≥ 400 µN had a similar or higher hardness than the as-deposited copper. This is believed to have occurred due to a relaxation in the residual stresses created during deposition in the copper thin films at lower loads, which caused a decrease in hardness. Conversely, at the higher loads, increased deformation leads to an increase in hardness. Lastly, all of the wear boxes displayed a higher estimated strain hardening exponent than the as-deposited material.« less

Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model

PubMed Central

Koh, Y-G.; Son, J.; Kwon, S-K.; Kim, H-J.; Kang, K-T.

2017-01-01

Objectives Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA. Methods We developed the validated models to evaluate the post-operative kinematics in patient-specific bicruciate-retaining, standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under gait and deep knee bend loading conditions using numerical simulation. Results Tibial posterior translation and internal rotation in patient-specific bicruciate-retaining prostheses preserved near-normal kinematics better than other standard off-the-shelf prostheses under gait loading conditions. Differences from normal kinematics were minimised for femoral rollback and internal-external rotation in patient-specific bicruciate-retaining, followed by standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under deep knee bend loading conditions. Moreover, the standard off-the-shelf posterior cruciate-retaining TKA in this study showed the most abnormal performance in kinematics under gait and deep knee bend loading conditions, whereas patient-specific bicruciate-retaining TKA led to near-normal kinematics. Conclusion This study showed that restoration of the normal geometry of the knee joint in patient-specific bicruciate-retaining TKA and preservation of the anterior cruciate ligament can lead to improvement in kinematics compared with the standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining TKA. Cite this article: Y-G. Koh, J. Son, S-K. Kwon, H-J. Kim, O-R. Kwon, K-T. Kang. Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model. Bone Joint Res 2017;6:557–565. DOI: 10.1302/2046-3758.69.BJR-2016-0250.R1. PMID:28947604

14 CFR 23.787 - Baggage and cargo compartments.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and... critical load distributions at the appropriate maximum load factors corresponding to the flight and ground...

Activity vs. rest in the treatment of bone, soft tissue and joint injuries.

PubMed

Buckwalter, J A

1995-01-01

One of the most important advances in the treatment of musculoskeletal injuries has come from understanding that controlled early resumption of activity can promote restoration of function, and that treatment of injuries with prolonged rest may delay recovery and adversely affect normal tissues. In the last decade of the nineteenth century two widely respected orthopaedists with extensive clinical experience strongly advocated opposing treatments of musculoskeletal injuries. Hugh Owen Thomas in Liverpool believed that enforced, uninterrupted prolonged rest produced the best results. He noted that movement of injured tissues increased inflammation, and that, "It would indeed be as reasonable to attempt to cure a fever patient by kicking him out of bed, as to benefit joint disease by a wriggling at the articulation." Just Lucas-Championnier in Paris took the opposite position. He argued that early controlled active motion accelerated restoration of function, although he noted that mobility had to be given in limited doses. In general, Thomas' views met with greater acceptance in the early part of this century, but experimental studies of the last several decades generally support Lucas-Championneir. They confirm and help explain the deleterious effects of prolonged rest and the beneficial effects of activity on the musculoskeletal tissues. They have shown that maintenance of normal bone, tendon and ligament, articular cartilage and muscle structure and composition require repetitive use, and that changes in the patterns of tissue loading can strengthen or weaken normal tissues. Although all the musculoskeletal tissues can respond to repetitive loading, they vary in the magnitude and type of response to specific patterns of activity. Furthermore, their responsiveness may decline with increasing age. Skeletal muscle and bone demonstrate the most apparent response to changes in activity in individuals of any age. Cartilage and dense fibrous tissues also can respond to loading, but the responses are more difficult to measure. The effects of loading on injured tissues have been less extensively studied, but the available evidence indicates that repair tissues respond to loading and, like immature normal tissues, may be more sensitive to cyclic loading and motion than mature normal tissues. However, early motion and loading of injured tissues is not without risks. Premature or excessive loading and motion of repair tissue can inhibit or stop repair. Unfortunately, the optimal methods of facilitating healing by early application of loading and motion have not been defined.(ABSTRACT TRUNCATED AT 400 WORDS)

Variability of Slip Behavior in Simulations of Dynamic Rupture Interaction With Stronger Fault Patches Over Long-Term Deformation Histories

NASA Astrophysics Data System (ADS)

Lapusta, N.; Liu, Y.

2007-12-01

Heterogeneity in fault properties can have significant effect on dynamic rupture propagation and aseismic slip. It is often assumed that a fixed heterogeneity would have similar effect on fault slip throughout the slip history. We investigate dynamic rupture interaction with a fault patch of higher normal stress over several earthquake cycles in a three-dimensional model. We find that the influence of the heterogeneity on dynamic events has significant variation and depends on prior slip history. We consider a planar strike-slip fault governed by rate and state friction and driven by slow tectonic loading on deeper extension of the fault. The 30 km by 12 km velocity-weakening region, which is potentially seismogenic, is surrounded by steady-state velocity-strengthening region. The normal stress is constant over the fault, except in a circular patch of 2 km in diameter located in the seismogenic region, where normal stress is higher than on the rest of the fault. Our simulations employ the methodology developed by Lapusta and Liu (AGU, 2006), which is able to resolve both dynamic and quasi-static stages of spontaneous slip accumulation in a single computational procedure. The initial shear stress is constant on the fault, except in a small area where it is higher and where the first large dynamic event initiates. For patches with 20%, 40%, 60% higher normal stress, the first event has significant dynamic interaction with the patch, creating a rupture speed decrease followed by a supershear burst and larger slip around the patch. Hence, in the first event, the patch acts as a seismic asperity. For the case of 100% higher stress, the rupture is not able to break the patch in the first event. In subsequent dynamic events, the behavior depends on the strength of heterogeneity. For the patch with 20% higher normal stress, dynamic rupture in subsequent events propagates through the patch without any noticeable perturbation in rupture speed or slip. In particular, supershear propagation and additional slip accumulation around the patch are never repeated in the simulated history of the fault, and the patch stops manifesting itself as a seismic asperity. This is due to higher shear stress that is established at the patch after the first earthquake cycle. For patches with higher normal stress, shear stress redistribution also occurs, but it is less effective. The patches with 40% and 60% higher normal stress continue to affect rupture speed and fault slip in some of subsequent events, although the effect is much diminished with respect to the first event. For example, there are no supershear bursts. The patch with 100% higher normal stress is first broken in the second large event, and it retains significant influence on rupture speed and slip throughout the fault history, occasionally resulting in supershear bursts. Additional slip complexity emerges for patches with 40% and higher normal stress contrast. Since higher normal stress corresponds to a smaller nucleation size, nucleation of some events moves from the rheological transitions (where nucleation occurs in the cases with no stronger patch and with the patch of 20% higher normal stress) to the patches of higher normal stress. The patches nucleate both large, model-spanning, events, and small events that arrest soon after exiting the patch. Hence not every event that originates at the location of a potential seismic asperity is destined to be large, as its subsequent propagation is significantly influenced by the state of stress outside the patch.

In vivo and in vitro binding of fatty acids to genetic variants of human serum albumin.

PubMed

Kragh-Hansen, U; Nielsen, H; Pedersen, A O

1995-01-01

The effect of genetic variation on the fatty-acid binding properties of human serum albumin was studied by two methods involving the use of sequenced albumin variants isolated from bisalbuminaemic persons. First, the amount of total fatty acid and of several individuals fatty acids bound to eighteen different variants and to their normal counterpart (Alb A) were determined by a gas-chromatographic micromethod. Pronounced effects on total fatty acid binding were found for the glycosylated variants Alb Redhill (modified in domain II) and Alb Casebrook (domain III) in which cases a 1.7- and 8.6-fold increment, respectively, was found. By contrast, Alb Malm0 (glycosylated in domain I) carried the same amount of fatty acid as Alb A. The fatty acid loads on three chain-termination variants were normal. Finally, eight albumins with single amino-acid substitutions bound normal amounts of fatty acid, whereas one bound increased (1.7-fold) and three albumins bound diminished amounts (0.5-0.6-fold). Information on nineteen individual fatty acids was also obtained. It was possible, based on the type of changes in their relative amounts, to group the fatty acids as follows: (a) = C6:0 - C14:0, (b) = C15:0 - C18:0, (c) = C16:1 - C18:1, and (d) a group composed of essential and conditionally essential fatty acids. For nine variants, in most cases modified in domain III, large changes in one or more of these groups were observed. The changes were not related to any changes in total fatty acid load. Second, the binding of laurate, as a representative of the group (a) fatty acids, to delipidated albumin preparations was studied at pH 7.4 by a kinetic dialysis technique. The first stoichiometric association constant for binding to Alb Redhill (0.7-fold) and Alb Casebrook (0.6-fold) was diminished as compared with binding to their corresponding Alb A, whereas binding to one chain-termination variant and three single amino-acid substitutions were all unaffected by the mutation.

ZERODUR®: new stress corrosion data improve strength fatigue prediction

NASA Astrophysics Data System (ADS)

Hartmann, Peter; Kleer, Günter; Rist, Tobias

2015-09-01

The extremely low thermal expansion glass ceramic ZERODUR® finds more and more applications as sophisticated light weight structures with thin ribs or as thin shells. Quite often they will be subject to higher mechanical loads such as rocket launches or modulating wobbling vibrations. Designing such structures requires calculation methods and data taking into account their long term fatigue. With brittle materials fatigue is not only given by the material itself but to a high extent also by its surface condition and the environmental media especially humidity. This work extends the latest data and information gathered on the bending strength of ZERODUR® with new results concerning its long term behavior under tensile stress. The parameter needed for prediction calculations which combines the influences of time and environmental media is the stress corrosion constant n. Results of the past differ significantly from each other. In order to obtain consistent data the stress corrosion constant has been measured with the method comparing the breakage statistical distributions at different stress increase rates. For better significance the stress increase rate was varied over four orders of magnitude from 0.004 MPa/s to 40 MPa/s. Experiments were performed under normal humidity for long term earth bound applications and under nitrogen atmosphere as equivalent to dry environment occurring for example with telescopes in deserts and also equivalent to vacuum for space applications. As shown earlier the bending strength of diamond ground surfaces of ZERODUR® can be represented with a three parameter Weibull distribution. Predictions on the long term strength change of ZERODUR® structures under tensile stress are possible with reduced uncertainty if Weibull threshold strength values are considered and more reliable stress corrosion constant data are applied.

The crack and wedging problem for an orthotropic strip

NASA Technical Reports Server (NTRS)

Cinar, A.; Erdogan, F.

1982-01-01

The plane elasticity problem for an orthotropic strip containing a crack parallel to its boundaries is considered. The problem is formulated under general mixed mode loading conditions. The stress intensity factors depend on two dimensionless orthotropic constants only. For the crack problem the results are given for a single crack and two collinear cracks. The calculated results show that of the two orthotropic constants the influence of the stiffness ratio on the stress intensity factors is much more significant than that of the shear parameter. The problem of loading the strip by a rigid rectangular lengths continuous contact is maintained along the wedge strip interface; at a certain critical wedge length the separation starts at the midsection of the wedge, and the length of the separation zone increases rapidly with increasing wedge length.

Variable gas spring for matching power output from FPSE to load of refrigerant compressor

DOEpatents

Chen, Gong; Beale, William T.

1990-01-01

The power output of a free piston Stirling engine is matched to a gas compressor which it drives and its stroke amplitude is made relatively constant as a function of power by connecting a gas spring to the drive linkage from the engine to the compressor. The gas spring is connected to the compressor through a passageway in which a valve is interposed. The valve is linked to the drive linkage so it is opened when the stroke amplitude exceeds a selected limit. This allows compressed gas to enter the spring, increase its spring constant, thus opposing stroke increase and reducing the phase lead of the displacer ahead of the piston to reduce power output and match it to a reduced load power demand.

Variable gas spring for matching power output from FPSE to load of refrigerant compressor

DOEpatents

Chen, G.; Beale, W.T.

1990-04-03

The power output of a free piston Stirling engine is matched to a gas compressor which it drives and its stroke amplitude is made relatively constant as a function of power by connecting a gas spring to the drive linkage from the engine to the compressor. The gas spring is connected to the compressor through a passageway in which a valve is interposed. The valve is linked to the drive linkage so it is opened when the stroke amplitude exceeds a selected limit. This allows compressed gas to enter the spring, increase its spring constant, thus opposing stroke increase and reducing the phase lead of the displacer ahead of the piston to reduce power output and match it to a reduced load power demand. 6 figs.