Accelerated testing of composites

NASA Technical Reports Server (NTRS)

Papazian, H. A.

1983-01-01

It is shown that the Zhurkov method for testing the strength of solids can be applied to dynamic tension and to cyclic loading and provides a viable approach to accelerated testing of composites. Data from the literature are used to demonstrate a straightforward application of the method to dynamic tension of glass fiber and cyclic loading for glass/polymer, metal matrix, and graphite/epoxy composites. Zhurkov's equation can be used at relatively high loads to obtain failure times at any temperature of interest. By taking a few data points at one or two other temperatures the spectrum of failure times can be expanded to temperatures not easily accessible.

Development of a subway operation incident delay model using accelerated failure time approaches.

PubMed

Weng, Jinxian; Zheng, Yang; Yan, Xuedong; Meng, Qiang

2014-12-01

This study aims to develop a subway operational incident delay model using the parametric accelerated time failure (AFT) approach. Six parametric AFT models including the log-logistic, lognormal and Weibull models, with fixed and random parameters are built based on the Hong Kong subway operation incident data from 2005 to 2012, respectively. In addition, the Weibull model with gamma heterogeneity is also considered to compare the model performance. The goodness-of-fit test results show that the log-logistic AFT model with random parameters is most suitable for estimating the subway incident delay. First, the results show that a longer subway operation incident delay is highly correlated with the following factors: power cable failure, signal cable failure, turnout communication disruption and crashes involving a casualty. Vehicle failure makes the least impact on the increment of subway operation incident delay. According to these results, several possible measures, such as the use of short-distance and wireless communication technology (e.g., Wifi and Zigbee) are suggested to shorten the delay caused by subway operation incidents. Finally, the temporal transferability test results show that the developed log-logistic AFT model with random parameters is stable over time. Copyright © 2014 Elsevier Ltd. All rights reserved.

Volcanic Eruption Forecasts From Accelerating Rates of Drumbeat Long-Period Earthquakes

NASA Astrophysics Data System (ADS)

Bell, Andrew F.; Naylor, Mark; Hernandez, Stephen; Main, Ian G.; Gaunt, H. Elizabeth; Mothes, Patricia; Ruiz, Mario

2018-02-01

Accelerating rates of quasiperiodic "drumbeat" long-period earthquakes (LPs) are commonly reported before eruptions at andesite and dacite volcanoes, and promise insights into the nature of fundamental preeruptive processes and improved eruption forecasts. Here we apply a new Bayesian Markov chain Monte Carlo gamma point process methodology to investigate an exceptionally well-developed sequence of drumbeat LPs preceding a recent large vulcanian explosion at Tungurahua volcano, Ecuador. For more than 24 hr, LP rates increased according to the inverse power law trend predicted by material failure theory, and with a retrospectively forecast failure time that agrees with the eruption onset within error. LPs resulted from repeated activation of a single characteristic source driven by accelerating loading, rather than a distributed failure process, showing that similar precursory trends can emerge from quite different underlying physics. Nevertheless, such sequences have clear potential for improving forecasts of eruptions at Tungurahua and analogous volcanoes.

Using a cross correlation technique to refine the accuracy of the Failure Forecast Method: Application to Soufrière Hills volcano, Montserrat

NASA Astrophysics Data System (ADS)

Salvage, R. O.; Neuberg, J. W.

2016-09-01

Prior to many volcanic eruptions, an acceleration in seismicity has been observed, suggesting the potential for this as a forecasting tool. The Failure Forecast Method (FFM) relates an accelerating precursor to the timing of failure by an empirical power law, with failure being defined in this context as the onset of an eruption. Previous applications of the FFM have used a wide variety of accelerating time series, often generating questionable forecasts with large misfits between data and the forecast, as well as the generation of a number of different forecasts from the same data series. Here, we show an alternative approach applying the FFM in combination with a cross correlation technique which identifies seismicity from a single active source mechanism and location at depth. Isolating a single system at depth avoids additional uncertainties introduced by averaging data over a number of different accelerating phenomena, and consequently reduces the misfit between the data and the forecast. Similar seismic waveforms were identified in the precursory accelerating seismicity to dome collapses at Soufrière Hills volcano, Montserrat in June 1997, July 2003 and February 2010. These events were specifically chosen since they represent a spectrum of collapse scenarios at this volcano. The cross correlation technique generates a five-fold increase in the number of seismic events which could be identified from continuous seismic data rather than using triggered data, thus providing a more holistic understanding of the ongoing seismicity at the time. The use of similar seismicity as a forecasting tool for collapses in 1997 and 2003 greatly improved the forecasted timing of the dome collapse, as well as improving the confidence in the forecast, thereby outperforming the classical application of the FFM. We suggest that focusing on a single active seismic system at depth allows a more accurate forecast of some of the major dome collapses from the ongoing eruption at Soufrière Hills volcano, and provides a simple addition to the well-used methodology of the FFM.

An accelerating precursor to predict "time-to-failure" in creep and volcanic eruptions

NASA Astrophysics Data System (ADS)

Hao, Shengwang; Yang, Hang; Elsworth, Derek

2017-09-01

Real-time prediction by monitoring of the evolution of response variables is a central goal in predicting rock failure. A linear relation Ω˙Ω¨-1 = C(tf - t) has been developed to describe the time to failure, where Ω represents a response quantity, C is a constant and tf represents the failure time. Observations from laboratory creep failure experiments and precursors to volcanic eruptions are used to test the validity of the approach. Both cumulative and simple moving window techniques are developed to perform predictions and to illustrate the effects of data selection on the results. Laboratory creep failure experiments on granites show that the linear relation works well during the final approach to failure. For blind prediction, the simple moving window technique is preferred because it always uses the most recent data and excludes effects of early data deviating significantly from the predicted trend. When the predicted results show only small fluctuations, failure is imminent.

Using Seismic Signals to Forecast Volcanic Processes

NASA Astrophysics Data System (ADS)

Salvage, R.; Neuberg, J. W.

2012-04-01

Understanding seismic signals generated during volcanic unrest have the ability to allow scientists to more accurately predict and understand active volcanoes since they are intrinsically linked to rock failure at depth (Voight, 1988). In particular, low frequency long period signals (LP events) have been related to the movement of fluid and the brittle failure of magma at depth due to high strain rates (Hammer and Neuberg, 2009). This fundamentally relates to surface processes. However, there is currently no physical quantitative model for determining the likelihood of an eruption following precursory seismic signals, or the timing or type of eruption that will ensue (Benson et al., 2010). Since the beginning of its current eruptive phase, accelerating LP swarms (< 10 events per hour) have been a common feature at Soufriere Hills volcano, Montserrat prior to surface expressions such as dome collapse or eruptions (Miller et al., 1998). The dynamical behaviour of such swarms can be related to accelerated magma ascent rates since the seismicity is thought to be a consequence of magma deformation as it rises to the surface. In particular, acceleration rates can be successfully used in collaboration with the inverse material failure law; a linear relationship against time (Voight, 1988); in the accurate prediction of volcanic eruption timings. Currently, this has only been investigated for retrospective events (Hammer and Neuberg, 2009). The identification of LP swarms on Montserrat and analysis of their dynamical characteristics allows a better understanding of the nature of the seismic signals themselves, as well as their relationship to surface processes such as magma extrusion rates. Acceleration and deceleration rates of seismic swarms provide insights into the plumbing system of the volcano at depth. The application of the material failure law to multiple LP swarms of data allows a critical evaluation of the accuracy of the method which further refines current understanding of the relationship between seismic signals and volcanic eruptions. It is hoped that such analysis will assist the development of real time forecasting models.

Integrated condition monitoring of a fleet of offshore wind turbines with focus on acceleration streaming processing

NASA Astrophysics Data System (ADS)

Helsen, Jan; Gioia, Nicoletta; Peeters, Cédric; Jordaens, Pieter-Jan

2017-05-01

Particularly offshore there is a trend to cluster wind turbines in large wind farms, and in the near future to operate such a farm as an integrated power production plant. Predictability of individual turbine behavior across the entire fleet is key in such a strategy. Failure of turbine subcomponents should be detected well in advance to allow early planning of all necessary maintenance actions; Such that they can be performed during low wind and low electricity demand periods. In order to obtain the insights to predict component failure, it is necessary to have an integrated clean dataset spanning all turbines of the fleet for a sufficiently long period of time. This paper illustrates our big-data approach to do this. In addition, advanced failure detection algorithms are necessary to detect failures in this dataset. This paper discusses a multi-level monitoring approach that consists of a combination of machine learning and advanced physics based signal-processing techniques. The advantage of combining different data sources to detect system degradation is in the higher certainty due to multivariable criteria. In order to able to perform long-term acceleration data signal processing at high frequency a streaming processing approach is necessary. This allows the data to be analysed as the sensors generate it. This paper illustrates this streaming concept on 5kHz acceleration data. A continuous spectrogram is generated from the data-stream. Real-life offshore wind turbine data is used. Using this streaming approach for calculating bearing failure features on continuous acceleration data will support failure propagation detection.

Accelerated life testing and reliability of high K multilayer ceramic capacitors

NASA Technical Reports Server (NTRS)

Minford, W. J.

1981-01-01

The reliability of one lot of high K multilayer ceramic capacitors was evaluated using accelerated life testing. The degradation in insulation resistance was characterized as a function of voltage and temperature. The times to failure at a voltage-temperature stress conformed to a lognormal distribution with a standard deviation approximately 0.5.

Viscoelastic behavior and life-time predictions

NASA Technical Reports Server (NTRS)

Dillard, D. A.; Brinson, H. F.

1985-01-01

Fiber reinforced plastics were considered for many structural applications in automotive, aerospace and other industries. A major concern was and remains the failure modes associated with the polymer matrix which serves to bind the fibers together and transfer the load through connections, from fiber to fiber and ply to ply. An accelerated characterization procedure for prediction of delayed failures was developed. This method utilizes time-temperature-stress-moisture superposition principles in conjunction with laminated plate theory. Because failures are inherently nonlinear, the testing and analytic modeling for both moduli and strength is based upon nonlinear viscoelastic concepts.

Accelerated fatigue durability of a high performance composite

NASA Technical Reports Server (NTRS)

Rotem, A.

1982-01-01

The fatigue behavior of multidirectional graphite-epoxy laminates was analyzed theoretically and experimentally in an effort to establish an accelerated testing methodology. Analysis of the failure mechanism in fatigue of the laminates led to the determination of the failure mode governing fracture. The nonlinear, cyclic-dependent shear modulus was used to calculate the changing stress field in the laminate during the fatigue loading. Fatigue tests were performed at three different temperatures: 25 C, 74 C, and 114 C. The prediction of the S-N curves was made based on the artificial static strength artificial static strength at a reference temperature and the fatigue functions associated with them. The prediction of an S-N curve at other temperatures was performed using shifting factors determined for the specific failure mode. For multidirectional laminates, different S-N curves at different temperatures could be predicted using these shifting factors. Different S-N curves at different temperatures occur only when the fatigue failure mode is matrix dominated. It was found that whenever the fatigue failure mode is fiber dominated, temperature, over the range investigated, had no influence on the fatigue life. These results permit the prediction of long-time, low temperature fatigue behavior from data obtained in short time, high temperature testing, for laminates governed by a matrix failure mode.

Analysis of Weibull Grading Test for Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2010-01-01

Weibull grading test is a powerful technique that allows selection and reliability rating of solid tantalum capacitors for military and space applications. However, inaccuracies in the existing method and non-adequate acceleration factors can result in significant, up to three orders of magnitude, errors in the calculated failure rate of capacitors. This paper analyzes deficiencies of the existing technique and recommends more accurate method of calculations. A physical model presenting failures of tantalum capacitors as time-dependent-dielectric-breakdown is used to determine voltage and temperature acceleration factors and select adequate Weibull grading test conditions. This, model is verified by highly accelerated life testing (HALT) at different temperature and voltage conditions for three types of solid chip tantalum capacitors. It is shown that parameters of the model and acceleration factors can be calculated using a general log-linear relationship for the characteristic life with two stress levels.

Reliability of High-Voltage Tantalum Capacitors. Parts 3 and 4)

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2010-01-01

Weibull grading test is a powerful technique that allows selection and reliability rating of solid tantalum capacitors for military and space applications. However, inaccuracies in the existing method and non-adequate acceleration factors can result in significant, up to three orders of magnitude, errors in the calculated failure rate of capacitors. This paper analyzes deficiencies of the existing technique and recommends more accurate method of calculations. A physical model presenting failures of tantalum capacitors as time-dependent-dielectric-breakdown is used to determine voltage and temperature acceleration factors and select adequate Weibull grading test conditions. This model is verified by highly accelerated life testing (HALT) at different temperature and voltage conditions for three types of solid chip tantalum capacitors. It is shown that parameters of the model and acceleration factors can be calculated using a general log-linear relationship for the characteristic life with two stress levels.

Failure Mode Classification for Life Prediction Modeling of Solid-State Lighting

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

Sakalaukus, Peter Joseph

2015-08-01

Since the passing of the Energy Independence and Security Act of 2007, the U.S. government has mandated greater energy independence which has acted as a catalyst for accelerating and facilitating research efforts toward the development and deployment of market-driven solutions for energy-saving homes, buildings and manufacturing, as well as sustainable transportation and renewable electricity generation. As part of this effort, an emphasis toward advancing solid-state lighting technology through research, development, demonstration, and commercial applications is assisting in the phase out of the common incandescent light bulb, as well as developing a more economical lighting source that is less toxic thanmore » compact fluorescent lighting. This has led lighting manufacturers to pursue SSL technologies for a wide range of consumer lighting applications. An SSL luminaire’s lifetime can be characterized in terms of lumen maintenance life. Lumen maintenance or lumen depreciation is the percentage decrease in the relative luminous flux from that of the original, pristine luminous flux value. Lumen maintenance life is the estimated operating time, in hours, when the desired failure threshold is projected to be reached at normal operating conditions. One accepted failure threshold of SSL luminaires is lumen maintenance of 70% -- a 30% reduction in the light output of the luminaire. Currently, the only approved lighting standard that puts forth a recommendation for long-term luminous flux maintenance projections towards a specified failure threshold of an SSL luminaire is the IES TM-28-14 (TM28) standard. iii TM28 was derived as a means to compare luminaires that have been tested at different facilities, research labs or companies. TM28 recommends the use of the Arrhenius equation to determine SSL device specific reaction rates from thermally driven failure mechanisms used to characterize a single failure mode – the relative change in the luminous flux output or “light power” of the SSL luminaire. The use of the Arrhenius equation necessitates two different temperature conditions, 25°C and 45°C are suggested by TM28, to determine the SSL lamp specific activation energy. One principal issue with TM28 is the lack of additional stresses or parameters needed to characterize non-temperature dependent failure mechanisms. Another principal issue with TM28 is the assumption that lumen maintenance or lumen depreciation gives an adequate comparison between SSL luminaires. Additionally, TM28 has no process for the determination of acceleration factors or lifetime estimations. Currently, a literature gap exists for established accelerated test methods for SSL devices to assess quality, reliability and durability before being introduced into the marketplace. Furthermore, there is a need for Physics-of-Failure based approaches to understand the processes and mechanisms that induce failure for the assessment of SSL reliability in order to develop generalized acceleration factors that better represent SSL product lifetime. This and the deficiencies in TM28 validate the need behind the development of acceleration techniques to quantify SSL reliability under a variety of environmental conditions. The ability to assess damage accrual and investigate reliability of SSL components and systems is essential to understanding the life time of the SSL device itself. The methodologies developed in this work increases the understanding of SSL devices iv through the investigation of component and device reliability under a variety of accelerated test conditions. The approaches for suitable lifetime predictions through the development of novel generalized acceleration factors, as well as a prognostics and health management framework, will greatly reduce the time and effort needed to produce SSL acceleration factors for the development of lifetime predictions.« less

Some practical observations on the accelerated testing of Nickel-Cadmium Cells

NASA Technical Reports Server (NTRS)

Mcdermott, P. P.

1979-01-01

A large scale test of 6.0 Ah Nickel-Cadmium Cells conducted at the Naval Weapons Support Center, Crane, Indiana has demonstrated a methodology for predicting battery life based on failure data from cells cycled in an accelerated mode. After examining eight variables used to accelerate failure, it was determined that temperature and depth of discharge were the most reliable and efficient parameters for use in accelerating failure and for predicting life.

Lamp reliability studies for improved satellite rubidium frequency standard

NASA Technical Reports Server (NTRS)

Frueholz, R. P.; Wun-Fogle, M.; Eckert, H. U.; Volk, C. H.; Jones, P. F.

1982-01-01

In response to the premature failure of Rb lamps used in Rb atomic clocks onboard NAVSTAR GPS satellites experimental and theoretical investigations into their failure mechanism were initiated. The primary goal of these studies is the development of an accelerated life test for future GPS lamps. The primary failure mechanism was identified as consumption of the lamp's Rb charge via direct interaction between Rb and the lamp's glass surface. The most effective parameters to accelerate the interaction between the Rb and the glass are felt to be RF excitation power and lamp temperature. Differential scanning calorimetry is used to monitor the consumption of Rb within a lamp as a function of operation time. This technique yielded base line Rb consumption data for GPS lamps operating under normal conditions.

Scaled CMOS Technology Reliability Users Guide

NASA Technical Reports Server (NTRS)

White, Mark

2010-01-01

The desire to assess the reliability of emerging scaled microelectronics technologies through faster reliability trials and more accurate acceleration models is the precursor for further research and experimentation in this relevant field. The effect of semiconductor scaling on microelectronics product reliability is an important aspect to the high reliability application user. From the perspective of a customer or user, who in many cases must deal with very limited, if any, manufacturer's reliability data to assess the product for a highly-reliable application, product-level testing is critical in the characterization and reliability assessment of advanced nanometer semiconductor scaling effects on microelectronics reliability. A methodology on how to accomplish this and techniques for deriving the expected product-level reliability on commercial memory products are provided.Competing mechanism theory and the multiple failure mechanism model are applied to the experimental results of scaled SDRAM products. Accelerated stress testing at multiple conditions is applied at the product level of several scaled memory products to assess the performance degradation and product reliability. Acceleration models are derived for each case. For several scaled SDRAM products, retention time degradation is studied and two distinct soft error populations are observed with each technology generation: early breakdown, characterized by randomly distributed weak bits with Weibull slope (beta)=1, and a main population breakdown with an increasing failure rate. Retention time soft error rates are calculated and a multiple failure mechanism acceleration model with parameters is derived for each technology. Defect densities are calculated and reflect a decreasing trend in the percentage of random defective bits for each successive product generation. A normalized soft error failure rate of the memory data retention time in FIT/Gb and FIT/cm2 for several scaled SDRAM generations is presented revealing a power relationship. General models describing the soft error rates across scaled product generations are presented. The analysis methodology may be applied to other scaled microelectronic products and their key parameters.

Voltage stress effects on microcircuit accelerated life test failure rates

NASA Technical Reports Server (NTRS)

Johnson, G. M.

1976-01-01

The applicability of Arrhenius and Eyring reaction rate models for describing microcircuit aging characteristics as a function of junction temperature and applied voltage was evaluated. The results of a matrix of accelerated life tests with a single metal oxide semiconductor microcircuit operated at six different combinations of temperature and voltage were used to evaluate the models. A total of 450 devices from two different lots were tested at ambient temperatures between 200 C and 250 C and applied voltages between 5 Vdc and 15 Vdc. A statistical analysis of the surface related failure data resulted in bimodal failure distributions comprising two lognormal distributions; a 'freak' distribution observed early in time, and a 'main' distribution observed later in time. The Arrhenius model was shown to provide a good description of device aging as a function of temperature at a fixed voltage. The Eyring model also appeared to provide a reasonable description of main distribution device aging as a function of temperature and voltage. Circuit diagrams are shown.

A relation to predict the failure of materials and potential application to volcanic eruptions and landslides.

PubMed

Hao, Shengwang; Liu, Chao; Lu, Chunsheng; Elsworth, Derek

2016-06-16

A theoretical explanation of a time-to-failure relation is presented, with this relationship then used to describe the failure of materials. This provides the potential to predict timing (tf - t) immediately before failure by extrapolating the trajectory as it asymptotes to zero with no need to fit unknown exponents as previously proposed in critical power law behaviors. This generalized relation is verified by comparison with approaches to criticality for volcanic eruptions and creep failure. A new relation based on changes with stress is proposed as an alternative expression of Voight's relation, which is widely used to describe the accelerating precursory signals before material failure and broadly applied to volcanic eruptions, landslides and other phenomena. The new generalized relation reduces to Voight's relation if stress is limited to increase at a constant rate with time. This implies that the time-derivatives in Voight's analysis may be a subset of a more general expression connecting stress derivatives, and thus provides a potential method for forecasting these events.

Failure Engineering Study and Accelerated Stress Test Results for the Mars Global Surveyor Spacecraft's Power Shunt Assemblies

NASA Technical Reports Server (NTRS)

Gibbel, Mark; Larson, Timothy

2000-01-01

An Engineering-of-Failure approach to designing and executing an accelerated product qualification test was performed to support a risk assessment of a "work-around" necessitated by an on-orbit failure of another piece of hardware on the Mars Global Surveyor spacecraft. The proposed work-around involved exceeding the previous qualification experience both in terms of extreme cold exposure level and in terms of demonstrated low cycle fatigue life for the power shunt assemblies. An analysis was performed to identify potential failure sites, modes and associated failure mechanisms consistent with the new use conditions. A test was then designed and executed which accelerated the failure mechanisms identified by analysis. Verification of the resulting failure mechanism concluded the effort.

Mechanical loading of bovine pericardium accelerates enzymatic degradation.

PubMed

Ellsmere, J C; Khanna, R A; Lee, J M

1999-06-01

Bioprosthetic heart valves fail as the result of two simultaneous processes: structural deterioration and calcification. Leaflet deterioration and perforation have been correlated with regions of highest stress in the tissue. The failures have long been assumed to be due to simple mechanical fatigue of the collagen fibre architecture; however, we have hypothesized that local stresses-and particularly dynamic stresses-accelerate local proteolysis, leading to tissue failure. This study addresses that hypothesis. Using a novel, custom-built microtensile culture system, strips of bovine pericardium were subjected to static and dynamic loads while being exposed to solutions of microbial collagenase or trypsin (a non-specific proteolytic enzyme). The time to extend to 30% strain (defined here as time to failure) was recorded. After failure, the percentage of collagen solubilized was calculated based on the amount of hydroxyproline present in solution. All data were analyzed by analysis of variance (ANOVA). In collagenase, exposure to static load significantly decreased the time to failure (P < 0.002) due to increased mean rate of collagen solubilization. Importantly, specimens exposed to collagenase and dynamic load failed faster than those exposed to collagenase under the same average static load (P = 0.02). In trypsin, by contrast, static load never led to failure and produced only minimal degradation. Under dynamic load, however, specimens exposed to collagenase, trypsin, and even Tris/CaCl2 buffer solution, all failed. Only samples exposed to Hanks' physiological solution did not fail. Failure of the specimens exposed to trypsin and Tris/CaCl2 suggests that the non-collagenous components and the calcium-dependent proteolytic enzymes present in pericardial tissue may play roles in the pathogenesis of bioprosthetic heart valve degeneration.

Degradation of Leakage Currents and Reliability Prediction for Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2016-01-01

Two types of failures in solid tantalum capacitors, catastrophic and parametric, and their mechanisms are described. Analysis of voltage and temperature reliability acceleration factors reported in literature shows a wide spread of results and requires more investigation. In this work, leakage currents in two types of chip tantalum capacitors were monitored during highly accelerated life testing (HALT) at different temperatures and voltages. Distributions of degradation rates were approximated using a general log-linear Weibull model and yielded voltage acceleration constants B = 9.8 +/- 0.5 and 5.5. The activation energies were Ea = 1.65 eV and 1.42 eV. The model allows for conservative estimations of times to failure and was validated by long-term life test data. Parametric degradation and failures are reversible and can be annealed at high temperatures. The process is attributed to migration of charged oxygen vacancies that reduce the barrier height at the MnO2/Ta2O5 interface and increase injection of electrons from the MnO2 cathode. Analysis showed that the activation energy of the vacancies' migration is 1.1 eV.

Bounded influence function based inference in joint modelling of ordinal partial linear model and accelerated failure time model.

PubMed

Chakraborty, Arindom

2016-12-01

A common objective in longitudinal studies is to characterize the relationship between a longitudinal response process and a time-to-event data. Ordinal nature of the response and possible missing information on covariates add complications to the joint model. In such circumstances, some influential observations often present in the data may upset the analysis. In this paper, a joint model based on ordinal partial mixed model and an accelerated failure time model is used, to account for the repeated ordered response and time-to-event data, respectively. Here, we propose an influence function-based robust estimation method. Monte Carlo expectation maximization method-based algorithm is used for parameter estimation. A detailed simulation study has been done to evaluate the performance of the proposed method. As an application, a data on muscular dystrophy among children is used. Robust estimates are then compared with classical maximum likelihood estimates. © The Author(s) 2014.

Controlling Electron Backstreaming Phenomena Through the Use of a Transverse Magnetic Field

NASA Technical Reports Server (NTRS)

Foster, John E.; Patterson, Michael J.

2002-01-01

DEEP-SPACE mission propulsion requirements can be satisfied by the use of high specific impulse systems such as ion thrusters. For such missions. however. the ion thruster will be required to provide thrust for long periods of time. To meet the long operation time and high-propellant throughput requirements, thruster lifetime must be increased. In general, potential ion thruster failure mechanisms associated with long-duration thrusting can be grouped into four areas: (1) ion optics failure; (2) discharge cathode failure; (3) neutralizer failure; and (4) electron backstreaming caused by accelerator grid aperture enlargement brought on by accelerator grid erosion. The work presented here focuses on electron backstreaming. which occurs when the potential at the center of an accelerator grid aperture is insufficient to prevent the backflow of electrons into the ion thruster. The likelihood of this occurring depends on ion source operation time. plasma density, and grid voltages, as accelerator grid apertures enlarge as a result of erosion. Electrons that enter the gap between the high-voltage screen and accelerator grids are accelerated to the energies approximately equal to the beam voltage. This energetic electron beam (typically higher than 1 kV) can damage not only the ion source discharge cathode assembly. but also any of the discharge surfaces upstream of the ion acceleration optics that the electrons happen to impact. Indeed. past backstreaming studies have shown that near the backstreaming limit, which corresponds to the absolute value of the accelerator grid voltage below which electrons can backflow into the thruster, there is a rather sharp rise in temperature at structures such as the cathode keeper electrode. In this respect operation at accelerator grid voltages near the backstreaming limit is avoided. Generally speaking, electron backstreaming is prevented by operating the accelerator grid at a sufficiently negative voltage to ensure a sufficiently negative aperture center potential. This approach can provide the necessary margin assuming an expected aperture enlargement. Operation at very negative accelerator grid voltages, however, enhances ion charge-exchange and direct impingement erosion of the accelerator grid. The focus of the work presented here is the mitigation of electron backstreaming by the use of a magnetic field. The presence of a magnetic field oriented perpendicular to the thruster axis can significantly decrease the magnitude of the backflowing electron current by significantly reducing the electron diffusion coefficient. Negative ion sources utilize this principle to reduce the fraction of electrons in the negative ion beam. The focus of these efforts has been on the attenuation of electron current diffusing from the discharge plasma into the negative ion extraction optics by placing the transverse magnetic field upstream of the extraction electrodes. In contrast. in the case of positive ion sources such as ion thrusters, the approach taken in the work presented here is to apply the transverse field downstream of the ion extraction system so as to prevent electrons from flowing back into the source. It was found in the work presented here that the magnetic field also reduces the absolute value of the electron backstreaming limit voltage. In this respect. the applied transverse magnetic field provides two mechanisms for electron backstreaming mitigation: (1) electron current attenuation and (2) backstreaming limit voltage shift. Such a shift to less negative voltages can lead to reduced accelerator grid erosion rates.

Accelerated life testing effects on CMOS microcircuit characteristics

NASA Technical Reports Server (NTRS)

1977-01-01

Accelerated life tests were performed on CMOS microcircuits to predict their long term reliability. The consistency of the CMOS microcircuit activation energy between the range of 125 C to 200 C and the range 200 C to 250 C was determined. Results indicate CMOS complexity and the amount of moisture detected inside the devices after testing influences time to failure of tested CMOS devices.

Accelerated Degradation Test and Predictive Failure Analysis of B10 Copper-Nickel Alloy under Marine Environmental Conditions

PubMed Central

Sun, Bo; Ye, Tianyuan; Feng, Qiang; Yao, Jinghua; Wei, Mumeng

2015-01-01

This paper studies the corrosion behavior of B10 copper-nickel alloy in marine environment. Accelerated degradation test under marine environmental conditions was designed and performed based on the accelerated testing principle and the corrosion degradation mechanism. With the prolongation of marine corrosion time, the thickness of Cu2O film increased gradually. Its corrosion product was Cu2(OH)3Cl, which increased in quantity over time. Cl− was the major factor responsible for the marine corrosion of copper and copper alloy. Through the nonlinear fitting of corrosion rate and corrosion quantity (corrosion weight loss), degradation data of different corrosion cycles, the quantitative effects of two major factors, i.e., dissolved oxygen (DO) and corrosion medium temperature, on corrosion behavior of copper alloy were analyzed. The corrosion failure prediction models under different ambient conditions were built. One-day corrosion weight loss under oxygenated stirring conditions was equivalent to 1.31-day weight loss under stationary conditions, and the corrosion rate under oxygenated conditions was 1.31 times higher than that under stationary conditions. In addition, corrosion medium temperature had a significant effect on the corrosion of B10 copper sheet. PMID:28793549

Accelerated Degradation Test and Predictive Failure Analysis of B10 Copper-Nickel Alloy under Marine Environmental Conditions.

PubMed

Sun, Bo; Ye, Tianyuan; Feng, Qiang; Yao, Jinghua; Wei, Mumeng

2015-09-10

This paper studies the corrosion behavior of B10 copper-nickel alloy in marine environment. Accelerated degradation test under marine environmental conditions was designed and performed based on the accelerated testing principle and the corrosion degradation mechanism. With the prolongation of marine corrosion time, the thickness of Cu₂O film increased gradually. Its corrosion product was Cu₂(OH)₃Cl, which increased in quantity over time. Cl - was the major factor responsible for the marine corrosion of copper and copper alloy. Through the nonlinear fitting of corrosion rate and corrosion quantity (corrosion weight loss), degradation data of different corrosion cycles, the quantitative effects of two major factors, i.e. , dissolved oxygen (DO) and corrosion medium temperature, on corrosion behavior of copper alloy were analyzed. The corrosion failure prediction models under different ambient conditions were built. One-day corrosion weight loss under oxygenated stirring conditions was equivalent to 1.31-day weight loss under stationary conditions, and the corrosion rate under oxygenated conditions was 1.31 times higher than that under stationary conditions. In addition, corrosion medium temperature had a significant effect on the corrosion of B10 copper sheet.

A relation to predict the failure of materials and potential application to volcanic eruptions and landslides

PubMed Central

Hao, Shengwang; Liu, Chao; Lu, Chunsheng; Elsworth, Derek

2016-01-01

A theoretical explanation of a time-to-failure relation is presented, with this relationship then used to describe the failure of materials. This provides the potential to predict timing (tf − t) immediately before failure by extrapolating the trajectory as it asymptotes to zero with no need to fit unknown exponents as previously proposed in critical power law behaviors. This generalized relation is verified by comparison with approaches to criticality for volcanic eruptions and creep failure. A new relation based on changes with stress is proposed as an alternative expression of Voight’s relation, which is widely used to describe the accelerating precursory signals before material failure and broadly applied to volcanic eruptions, landslides and other phenomena. The new generalized relation reduces to Voight’s relation if stress is limited to increase at a constant rate with time. This implies that the time-derivatives in Voight’s analysis may be a subset of a more general expression connecting stress derivatives, and thus provides a potential method for forecasting these events. PMID:27306851

Failure Forecasting in Triaxially Stressed Sandstones

NASA Astrophysics Data System (ADS)

Crippen, A.; Bell, A. F.; Curtis, A.; Main, I. G.

2017-12-01

Precursory signals to fracturing events have been observed to follow power-law accelerations in spatial, temporal, and size distributions leading up to catastrophic failure. In previous studies this behavior was modeled using Voight's relation of a geophysical precursor in order to perform `hindcasts' by solving for failure onset time. However, performing this analysis in retrospect creates a bias, as we know an event happened, when it happened, and we can search data for precursors accordingly. We aim to remove this retrospective bias, thereby allowing us to make failure forecasts in real-time in a rock deformation laboratory. We triaxially compressed water-saturated 100 mm sandstone cores (Pc= 25MPa, Pp = 5MPa, σ = 1.0E-5 s-1) to the point of failure while monitoring strain rate, differential stress, AEs, and continuous waveform data. Here we compare the current `hindcast` methods on synthetic and our real laboratory data. We then apply these techniques to increasing fractions of the data sets to observe the evolution of the failure forecast time with precursory data. We discuss these results as well as our plan to mitigate false positives and minimize errors for real-time application. Real-time failure forecasting could revolutionize the field of hazard mitigation of brittle failure processes by allowing non-invasive monitoring of civil structures, volcanoes, and possibly fault zones.

Landslide triggering by rain infiltration

USGS Publications Warehouse

Iverson, Richard M.

2000-01-01

Landsliding in response to rainfall involves physical processes that operate on disparate timescales. Relationships between these timescales guide development of a mathematical model that uses reduced forms of Richards equation to evaluate effects of rainfall infiltration on landslide occurrence, timing, depth, and acceleration in diverse situations. The longest pertinent timescale is A/D0, where D0 is the maximum hydraulic diffusivity of the soil and A is the catchment area that potentially affects groundwater pressures at a prospective landslide slip surface location with areal coordinates x, y and depth H. Times greater than A/D0 are necessary for establishment of steady background water pressures that develop at (x, y, H) in response to rainfall averaged over periods that commonly range from days to many decades. These steady groundwater pressures influence the propensity for landsliding at (x, y, H), but they do not trigger slope failure. Failure results from rainfall over a typically shorter timescale H2/D0 associated with transient pore pressure transmission during and following storms. Commonly, this timescale ranges from minutes to months. The shortest timescale affecting landslide responses to rainfall is √(H/g), where g is the magnitude of gravitational acceleration. Postfailure landslide motion occurs on this timescale, which indicates that the thinnest landslides accelerate most quickly if all other factors are constant. Effects of hydrologic processes on landslide processes across these diverse timescales are encapsulated by a response function, R(t*) = √(t*/π) exp (-1/t*) - erfc (1/√t*), which depends only on normalized time, t*. Use of R(t*) in conjunction with topographic data, rainfall intensity and duration information, an infinite-slope failure criterion, and Newton's second law predicts the timing, depth, and acceleration of rainfall-triggered landslides. Data from contrasting landslides that exhibit rapid, shallow motion and slow, deep-seated motion corroborate these predictions.

A Statistical Perspective on Highly Accelerated Testing

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

Thomas, Edward V.

Highly accelerated life testing has been heavily promoted at Sandia (and elsewhere) as a means to rapidly identify product weaknesses caused by flaws in the product's design or manufacturing process. During product development, a small number of units are forced to fail at high stress. The failed units are then examined to determine the root causes of failure. The identification of the root causes of product failures exposed by highly accelerated life testing can instigate changes to the product's design and/or manufacturing process that result in a product with increased reliability. It is widely viewed that this qualitative use ofmore » highly accelerated life testing (often associated with the acronym HALT) can be useful. However, highly accelerated life testing has also been proposed as a quantitative means for "demonstrating" the reliability of a product where unreliability is associated with loss of margin via an identified and dominating failure mechanism. It is assumed that the dominant failure mechanism can be accelerated by changing the level of a stress factor that is assumed to be related to the dominant failure mode. In extreme cases, a minimal number of units (often from a pre-production lot) are subjected to a single highly accelerated stress relative to normal use. If no (or, sufficiently few) units fail at this high stress level, some might claim that a certain level of reliability has been demonstrated (relative to normal use conditions). Underlying this claim are assumptions regarding the level of knowledge associated with the relationship between the stress level and the probability of failure. The primary purpose of this document is to discuss (from a statistical perspective) the efficacy of using accelerated life testing protocols (and, in particular, "highly accelerated" protocols) to make quantitative inferences concerning the performance of a product (e.g., reliability) when in fact there is lack-of-knowledge and uncertainty concerning the assumed relationship between the stress level and performance. In addition, this document contains recommendations for conducting more informative accelerated tests.« less

Ultra-accelerated natural sunlight exposure testing

DOEpatents

Jorgensen, Gary J.; Bingham, Carl; Goggin, Rita; Lewandowski, Allan A.; Netter, Judy C.

2000-06-13

Process and apparatus for providing ultra accelerated natural sunlight exposure testing of samples under controlled weathering without introducing unrealistic failure mechanisms in exposed materials and without breaking reciprocity relationships between flux exposure levels and cumulative dose that includes multiple concurrent levels of temperature and relative humidity at high levels of natural sunlight comprising: a) concentrating solar flux uniformly; b) directing the controlled uniform sunlight onto sample materials in a chamber enclosing multiple concurrent levels of temperature and relative humidity to allow the sample materials to be subjected to accelerated irradiance exposure factors for a sufficient period of time in days to provide a corresponding time of about at least a years worth of representative weathering of the sample materials.

Real-time eruption forecasting using the material Failure Forecast Method with a Bayesian approach

NASA Astrophysics Data System (ADS)

Boué, A.; Lesage, P.; Cortés, G.; Valette, B.; Reyes-Dávila, G.

2015-04-01

Many attempts for deterministic forecasting of eruptions and landslides have been performed using the material Failure Forecast Method (FFM). This method consists in adjusting an empirical power law on precursory patterns of seismicity or deformation. Until now, most of the studies have presented hindsight forecasts based on complete time series of precursors and do not evaluate the ability of the method for carrying out real-time forecasting with partial precursory sequences. In this study, we present a rigorous approach of the FFM designed for real-time applications on volcano-seismic precursors. We use a Bayesian approach based on the FFM theory and an automatic classification of seismic events. The probability distributions of the data deduced from the performance of this classification are used as input. As output, it provides the probability of the forecast time at each observation time before the eruption. The spread of the a posteriori probability density function of the prediction time and its stability with respect to the observation time are used as criteria to evaluate the reliability of the forecast. We test the method on precursory accelerations of long-period seismicity prior to vulcanian explosions at Volcán de Colima (Mexico). For explosions preceded by a single phase of seismic acceleration, we obtain accurate and reliable forecasts using approximately 80% of the whole precursory sequence. It is, however, more difficult to apply the method to multiple acceleration patterns.

Latent Subgroup Analysis of a Randomized Clinical Trial Through a Semiparametric Accelerated Failure Time Mixture Model

PubMed Central

Altstein, L.; Li, G.

2012-01-01

Summary This paper studies a semiparametric accelerated failure time mixture model for estimation of a biological treatment effect on a latent subgroup of interest with a time-to-event outcome in randomized clinical trials. Latency is induced because membership is observable in one arm of the trial and unidentified in the other. This method is useful in randomized clinical trials with all-or-none noncompliance when patients in the control arm have no access to active treatment and in, for example, oncology trials when a biopsy used to identify the latent subgroup is performed only on subjects randomized to active treatment. We derive a computational method to estimate model parameters by iterating between an expectation step and a weighted Buckley-James optimization step. The bootstrap method is used for variance estimation, and the performance of our method is corroborated in simulation. We illustrate our method through an analysis of a multicenter selective lymphadenectomy trial for melanoma. PMID:23383608

Reduced withdrawal and failure rates of accelerated nursing students enrolled in pharmacology is associated with a supportive intervention.

PubMed

Doggrell, Sheila Anne; Schaffer, Sally

2016-02-01

To reduce nursing shortages, accelerated nursing programs are available for domestic and international students. However, the withdrawal and failure rates from these programs may be different than for the traditional programs. The main aim of our study was to improve the retention and experience of accelerated nursing students. The academic background, age, withdrawal and failure rates of the accelerated and traditional students were determined. Data from 2009 and 2010 were collected prior to intervention. In an attempt to reduce the withdrawal of accelerated students, we set up an intervention, which was available to all students. The assessment of the intervention was a pre-post-test design with non-equivalent groups (the traditional and the accelerated students). The elements of the intervention were a) a formative website activity of some basic concepts in anatomy, physiology and pharmacology, b) a workshop addressing study skills and online resources, and c) resource lectures in anatomy/physiology and microbiology. The formative website and workshop was evaluated using questionnaires. The accelerated nursing students were five years older than the traditional students (p < 0.0001). The withdrawal rates from a pharmacology course are higher for accelerated nursing students, than for traditional students who have undertaken first year courses in anatomy and physiology (p = 0.04 in 2010). The withdrawing students were predominantly the domestic students with non-university qualifications or equivalent experience. The failure rates were also higher for this group, compared to the traditional students (p = 0.05 in 2009 and 0.03 in 2010). In contrast, the withdrawal rates for the international and domestic graduate accelerated students were very low. After the intervention, the withdrawal and failure rates in pharmacology for domestic accelerated students with non-university qualifications were not significantly different than those of traditional students. The accelerated international and domestic graduate nursing students have low withdrawal rates and high success rates in a pharmacology course. However, domestic students with non-university qualifications have higher withdrawal and failure rates than other nursing students and may be underprepared for university study in pharmacology in nursing programs. The introduction of an intervention was associated with reduced withdrawal and failure rates for these students in the pharmacology course.

Delayed Diagnosis and Treatment among Children with Autism Who Experience Adversity

ERIC Educational Resources Information Center

Berg, Kristin L.; Acharya, Kruti; Shiu, Cheng-Shi; Msall, Michael E.

2018-01-01

The effects of family adverse childhood experiences (ACEs) on timing of ASD diagnoses and receipt of therapies were measured using data from the 2011-2012 National Survey of Children's Health. Parametric accelerated failure time models estimated the relationship between family ACEs and both timing of ASD diagnosis and receipt of therapies among US…

A novel approach on accelerated ageing towards reliability optimization of high concentration photovoltaic cells

NASA Astrophysics Data System (ADS)

Tsanakas, John A.; Jaffre, Damien; Sicre, Mathieu; Elouamari, Rachid; Vossier, Alexis; de Salins, Jean-Edouard; Bechou, Laurent; Levrier, Bruno; Perona, Arnaud; Dollet, Alain

2014-09-01

This paper presents a preliminary study upon a novel approach proposed for highly accelerated ageing and reliability optimization of high concentrating photovoltaic (HCPV) cells and assemblies. The intended approach aims to overcome several limitations of some current accelerated ageing tests (AAT) adopted up today, proposing the use of an alternative experimental set-up for performing faster and more realistic thermal cycles, under real sun, without the involvement of environmental chamber. The study also includes specific characterization techniques, before and after each AAT sequence, which respectively provide the initial and final diagnosis on the condition of the tested sample. The acquired data from these diagnostic/characterization methods are then used as indices to determine both quantitatively and qualitatively the severity of degradation and, thus, the ageing level for each tested HCPV assembly or cell sample. Ultimate goal of such "initial diagnosis - AAT - final diagnosis" sequences is to provide the basis for a future work on the reliability analysis of the main degradation mechanisms and confident prediction of failure propagation in HCPV cells, by means of acceleration factor (AF) and mean-time-to-failure (MTTF) estimations.

Accelerated Stress-Corrosion Testing

NASA Technical Reports Server (NTRS)

1986-01-01

Test procedures for accelerated stress-corrosion testing of high-strength aluminum alloys faster and provide more quantitative information than traditional pass/fail tests. Method uses data from tests on specimen sets exposed to corrosive environment at several levels of applied static tensile stress for selected exposure times then subsequently tensile tested to failure. Method potentially applicable to other degrading phenomena (such as fatigue, corrosion fatigue, fretting, wear, and creep) that promote development and growth of cracklike flaws within material.

Management of Mediastinal Relapse after Treatment with Stereotactic Body Radiotherapy or Accelerated Hypofractionated Radiotherapy for Stage I/II Non–Small-Cell Lung Cancer

PubMed Central

Kilburn, Jeremy M.; Lester, Scott C.; Lucas, John T.; Soike, Michael H.; Blackstock, A. William; Kearns, William T.; Hinson, William H.; Miller, Antonius A.; Petty, William J.; Munley, Michael T.; Urbanic, James J.

2014-01-01

Purpose/Objective(s) Regional failures occur in up to 15% of patients treated with stereotactic body radiotherapy (SBRT) for stage I/II lung cancer. This report focuses on the management of the unique scenario of isolated regional failures. Methods Patients treated initially with SBRT or accelerated hypo-fractionated radiotherapy were screened for curative intent treatment of isolated mediastinal failures (IMFs). Local control, regional control, progression-free survival, and distant control were estimated from the date of salvage treatment using the Kaplan–Meier method. Results Among 160 patients treated from 2002 to 2012, 12 suffered IMF and were amenable to salvage treatment. The median interval between treatments was 16 months (2–57 mo). Median salvage dose was 66 Gy (60–70 Gy). With a median follow-up of 10 months, the median overall survival was 15 months (95% confidence interval, 5.8–37 mo). When estimated from original treatment, the median overall survival was 38 months (95% confidence interval, 17–71 mo). No subsequent regional failures occurred. Distant failure was the predominant mode of relapse following salvage for IMF with a 2-year distant control rate of 38%. At the time of this analysis, three patients have died without recurrence while four are alive and no evidence of disease. High-grade toxicity was uncommon. Conclusions To our knowledge, this is first analysis of salvage mediastinal radiation after SBRT or accelerated hypofractionated radiotherapy in lung cancer. Outcomes appear similar to stage III disease at presentation. Distant failures were common, suggesting a role for concurrent or sequential chemotherapy. A standard full course of external beam radiotherapy is advisable in this unique clinical scenario. PMID:24736084

Forecasting volcanic eruptions and other material failure phenomena: An evaluation of the failure forecast method

NASA Astrophysics Data System (ADS)

Bell, Andrew F.; Naylor, Mark; Heap, Michael J.; Main, Ian G.

2011-08-01

Power-law accelerations in the mean rate of strain, earthquakes and other precursors have been widely reported prior to material failure phenomena, including volcanic eruptions, landslides and laboratory deformation experiments, as predicted by several theoretical models. The Failure Forecast Method (FFM), which linearizes the power-law trend, has been routinely used to forecast the failure time in retrospective analyses; however, its performance has never been formally evaluated. Here we use synthetic and real data, recorded in laboratory brittle creep experiments and at volcanoes, to show that the assumptions of the FFM are inconsistent with the error structure of the data, leading to biased and imprecise forecasts. We show that a Generalized Linear Model method provides higher-quality forecasts that converge more accurately to the eventual failure time, accounting for the appropriate error distributions. This approach should be employed in place of the FFM to provide reliable quantitative forecasts and estimate their associated uncertainties.

Accelerated Thermal Cycling and Failure Mechanisms for BGA and CSP Assemblies

NASA Technical Reports Server (NTRS)

Ghaffarian, Reza

2000-01-01

This paper reviews the accelerated thermal cycling test methods that are currently used by industry to characterize the interconnect reliability of commercial-off-the-shelf (COTS) ball grid array (BGA) and chip scale package (CSP) assemblies. Acceleration induced failure mechanisms varied from conventional surface mount (SM) failures for CSPs. Examples of unrealistic life projections for other CSPs are also presented. The cumulative cycles to failure for ceramic BGA assemblies performed under different conditions, including plots of their two Weibull parameters, are presented. The results are for cycles in the range of -30 C to 100 C, -55 C to 100 C, and -55 C to 125 C. Failure mechanisms as well as cycles to failure for thermal shock and thermal cycling conditions in the range of -55 C to 125 C were compared. Projection to other temperature cycling ranges using a modified Coffin-Manson relationship is also presented.

An accelerated test design for use with synchronous orbit. [on Ni-Cd cell degradation behavior

NASA Technical Reports Server (NTRS)

Mcdermott, P. P.; Vasanth, K. L.

1980-01-01

The Naval Weapons Support Center at Crane, Indiana has conducted a large scale accelerated test of 6.0 Ah Ni-Cd cells. Data from the Crane test have been used to develop an equation for the description of Ni-Cd cell behavior in geosynchronous orbit. This equation relates the anticipated time to failure for a cell in synchronous orbit to temperature and overcharge rate sustained by the cell during the light period. A test design is suggested which uses this equation for setting test parameters for future accelerated testing.

Modelling accelerated degradation data using Wiener diffusion with a time scale transformation.

PubMed

Whitmore, G A; Schenkelberg, F

1997-01-01

Engineering degradation tests allow industry to assess the potential life span of long-life products that do not fail readily under accelerated conditions in life tests. A general statistical model is presented here for performance degradation of an item of equipment. The degradation process in the model is taken to be a Wiener diffusion process with a time scale transformation. The model incorporates Arrhenius extrapolation for high stress testing. The lifetime of an item is defined as the time until performance deteriorates to a specified failure threshold. The model can be used to predict the lifetime of an item or the extent of degradation of an item at a specified future time. Inference methods for the model parameters, based on accelerated degradation test data, are presented. The model and inference methods are illustrated with a case application involving self-regulating heating cables. The paper also discusses a number of practical issues encountered in applications.

Mechanism of electromigration failure in Damascene processed copper interconnects

NASA Astrophysics Data System (ADS)

Michael, Nancy Lyn

2002-11-01

A major unresolved issue in Cu interconnect reliability is the interface role in the failure mechanism of real structures. The present study investigates failure in single-level damascene Cu interconnects with variations in interface condition, passivation and barrier, and linewidth. In the first phase, accelerated electromigration testing of 0.25mum Cu interconnects capped with SiN or SiCN, shows that lifetime and failure mode vary with capping layer. The first mode, seen primarily in SiN samples, is characterized by gradual resistance increase and extensive interface damage, believed to result from failure led by interface electromigration. The competing failure mode, found in SiCN capped samples, is characterized by abrupt resistance increase and localized voiding. The second phase fixes SiCN as the capping material and varies barrier material and line width. The three barrier materials, Ta, TaN, and Ta/TaN, produce similar lifetime statistics and failure is abrupt. Line width, however, does have a strong influence on failure time. The line width/grain size ratio ranged from 0.53 to 2.2 but does not correlate with mean time to failure (MTF). The strong dependence on interface fraction, combined with the conclusion from phase one that interface electromigration is not rate controlling, suggests another mechanism related to the interface is a controlling factor. The possibility that contamination and defects at the interface are key to this failure mode was investigated using electro-thermal fatigue (ETF). In ETF, where lines are simultaneously subjected to thermal cycling and constant current, damage caused by thermal stress is accelerated. Tests reveal that in 80 nm lines, transient failure occurs at times far below MTF in electromigration tests at higher temperatures. Failure found in ETF is clearly a result of damage growth due to thermal/mechanical stress rather than electromigration. At the stress levels created by the moderate ETF test conditions, the only place voids are likely to nucleate and grow is at pre-existing defects and impurities. In narrower lines, where smaller voids can cause catastrophic damage, defects have a greater effect on MTF. Results from this investigation suggest that impurities and defects in the Cu and at the interface, must be carefully controlled to make reliable narrow Cu interconnects.

Understanding How Kurtosis Is Transferred from Input Acceleration to Stress Response and Its Influence on Fatigue Llife

NASA Technical Reports Server (NTRS)

Kihm, Frederic; Rizzi, Stephen A.; Ferguson, Neil S.; Halfpenny, Andrew

2013-01-01

High cycle fatigue of metals typically occurs through long term exposure to time varying loads which, although modest in amplitude, give rise to microscopic cracks that can ultimately propagate to failure. The fatigue life of a component is primarily dependent on the stress amplitude response at critical failure locations. For most vibration tests, it is common to assume a Gaussian distribution of both the input acceleration and stress response. In real life, however, it is common to experience non-Gaussian acceleration input, and this can cause the response to be non-Gaussian. Examples of non-Gaussian loads include road irregularities such as potholes in the automotive world or turbulent boundary layer pressure fluctuations for the aerospace sector or more generally wind, wave or high amplitude acoustic loads. The paper first reviews some of the methods used to generate non-Gaussian excitation signals with a given power spectral density and kurtosis. The kurtosis of the response is examined once the signal is passed through a linear time invariant system. Finally an algorithm is presented that determines the output kurtosis based upon the input kurtosis, the input power spectral density and the frequency response function of the system. The algorithm is validated using numerical simulations. Direct applications of these results include improved fatigue life estimations and a method to accelerate shaker tests by generating high kurtosis, non-Gaussian drive signals.

Accelerated Aging Experiments for Capacitor Health Monitoring and Prognostics

NASA Technical Reports Server (NTRS)

Kulkarni, Chetan S.; Celaya, Jose Ramon; Biswas, Gautam; Goebel, Kai

2012-01-01

This paper discusses experimental setups for health monitoring and prognostics of electrolytic capacitors under nominal operation and accelerated aging conditions. Electrolytic capacitors have higher failure rates than other components in electronic systems like power drives, power converters etc. Our current work focuses on developing first-principles-based degradation models for electrolytic capacitors under varying electrical and thermal stress conditions. Prognostics and health management for electronic systems aims to predict the onset of faults, study causes for system degradation, and accurately compute remaining useful life. Accelerated life test methods are often used in prognostics research as a way to model multiple causes and assess the effects of the degradation process through time. It also allows for the identification and study of different failure mechanisms and their relationships under different operating conditions. Experiments are designed for aging of the capacitors such that the degradation pattern induced by the aging can be monitored and analyzed. Experimental setups and data collection methods are presented to demonstrate this approach.

Effect of High Temperature Storage in Vacuum, Air, and Humid Conditions on Degradation of Gold/Aluminum Wire Bonds in PEMs

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2006-01-01

Microcircuits encapsulated in three plastic package styles were stored in different environments at temperatures varying from 130 C to 225 C for up to 4,000 hours in some cases. To assess the effect of oxygen, the parts were aged at high temperatures in air and in vacuum chambers. The effect of humidity was evaluated during long-term highly accelerated temperature and humidity stress testing (HAST) at temperatures of 130 C and 150 C. High temperature storage testing of decapsulated microcircuits in air, vacuum, and HAST chambers was carried out to evaluate the role of molding compounds in the environmentally-induced degradation and failure of wire bonds (WB). This paper reports on accelerating factors of environment and molding compound on WB failures. It has been shown that all environments, including oxygen, moisture, and the presence of molding compounds reduce time-to-failures compared to unencapsulated devices in vacuum conditions. The mechanism of the environmental effect on KB degradation is discussed.

Retaining Residual Ovarian Tissue following Ovarian Failure Has Limited Influence on Bone Loss in Aged Mice

PubMed Central

Craig, Zelieann R.; Marion, Samuel L.; Funk, Janet L.; Bouxsein, Mary L.; Hoyer, Patricia B.

2010-01-01

Previous work showed that retaining residual ovarian tissue protects young mice from accelerated bone loss following ovarian failure. The present study was designed to determine whether this protection is also present in aged animals. Aged (9–12 months) C57BL/6Hsd female mice were divided into: CON (vehicle), VCD (160 mg/kg; 15d), or OVX (ovariectomized). Lumbar BMD was monitored by DXA and μCT used to assess vertebral microarchitecture. BMD was not different between VCD and CON at any time point but was lower (P < .05) than baseline, starting 1 month after ovarian failure in VCD and OVX mice. Following μCT analysis there were no differences between CON and VCD, but OVX mice had lower bone volume fraction, trabecular thickness, and a trend for decreased connectivity density. These findings provide evidence that retention of residual ovarian tissue may protect aged follicle-depleted mice from accelerated bone loss to a lesser extent than that observed in young mice. PMID:20948577

Implications of Secondary Aftershocks for Failure Processes

NASA Astrophysics Data System (ADS)

Gross, S. J.

2001-12-01

When a seismic sequence with more than one mainshock or an unusually large aftershock occurs, there is a compound aftershock sequence. The secondary aftershocks need not have exactly the same decay as the primary sequence, with the differences having implications for the failure process. When the stress step from the secondary mainshock is positive but not large enough to cause immediate failure of all the remaining primary aftershocks, failure processes which involve accelerating slip will produce secondary aftershocks that decay more rapidly than primary aftershocks. This is because the primary aftershocks are an accelerated version of the background seismicity, and secondary aftershocks are an accelerated version of the primary aftershocks. Real stress perturbations may be negative, and heterogeneities in mainshock stress fields mean that the real world situation is quite complicated. I will first describe and verify my picture of secondary aftershock decay with reference to a simple numerical model of slipping faults which obeys rate and state dependent friction and lacks stress heterogeneity. With such a model, it is possible to generate secondary aftershock sequences with perturbed decay patterns, quantify those patterns, and develop an analysis technique capable of correcting for the effect in real data. The secondary aftershocks are defined in terms of frequency linearized time s(T), which is equal to the number of primary aftershocks expected by a time T, $ s ≡ ∫ t=0T n(t) dt, where the start time t=0 is the time of the primary aftershock, and the primary aftershock decay function n(t) is extrapolated forward to the times of the secondary aftershocks. In the absence of secondary sequences the function s(T)$ re-scales the time so that approximately one event occurs per new time unit; the aftershock sequence is gone. If this rescaling is applied in the presence of a secondary sequence, the secondary sequence is shaped like a primary aftershock sequence, and can be fit by the same modeling techniques applied to simple sequences. The later part of the presentation will concern the decay of Hector Mine aftershocks as influenced by the Landers aftershocks. Although attempts to predict the abundance of Hector aftershocks based on stress overlap analysis are not very successful, the analysis does do a good job fitting the decay of secondary sequences.

Product Reliability Trends, Derating Considerations and Failure Mechanisms with Scaled CMOS

NASA Technical Reports Server (NTRS)

White, Mark; Vu, Duc; Nguyen, Duc; Ruiz, Ron; Chen, Yuan; Bernstein, Joseph B.

2006-01-01

As microelectronics is scaled into the deep sub-micron regime, space and aerospace users of advanced technology CMOS are reassessing how scaling effects impact long-term product reliability. The effects of electromigration (EM), time-dependent-dielectric-breakdown (TDDB) and hot carrier degradation (HCI and NBTI) wearout mechanisms on scaled technologies and product reliability are investigated, accelerated stress testing across several technology nodes is performed, and FA is conducted to confirm the failure mechanism(s).

Promotion at Canadian Universities: The Intersection of Gender, Discipline, and Institution

ERIC Educational Resources Information Center

Ornstein, Michael; Stewart, Penni; Drakich, Janice

2007-01-01

Statistics Canada's annual census of full-time faculty at all Canadian universities, between 1984 to 1999, is used to measure the effect of gender, discipline, and institution on promotion from assistant to associate professor and from associate to full professor. Accelerated failure time models show that gender has some effect on rates of…

A late and failure of airbag deployment case study for drivers of passenger cars in rear-end collisions

NASA Astrophysics Data System (ADS)

Toganel, George-Radu; Ovidiu Soica, Adrian

2017-10-01

The presented study was directed at two types of airbag miss-deployments: late deployment and non-deployment. Late deployment can be a product of override or underride road traffic accidents. Non-deployment can be a product of technical failure or trigger algorithm’s inability to correctly assume the state of the accident to happen. In order to analyse the phenomena through physical tests, a specialized test device was used for a series of 8 non-deployment tests and a series of 4 airbag firing tests, totalling 12 tests. Acceleration based data was recorded and analysed for the movement of the device part simulating the driver head. High speed video recording was used to analyse the mechanics of airbag deployment and correlate with the acceleration based data. It has been determined, in the limitations of the laboratory testing environment, a significant variation of the time frame for the airbag deployments, despite using similar testing conditions and identical tested products. Also, the initial time frame for airbag deployment delay was overshadowed by other factors such as time to impact.

Seismic precursory patterns before a cliff collapse and critical point phenomena

USGS Publications Warehouse

Amitrano, D.; Grasso, J.-R.; Senfaute, G.

2005-01-01

We analyse the statistical pattern of seismicity before a 1-2 103 m3 chalk cliff collapse on the Normandie ocean shore, Western France. We show that a power law acceleration of seismicity rate and energy in both 40 Hz-1.5 kHz and 2 Hz-10kHz frequency range, is defined on 3 orders of magnitude, within 2 hours from the collapse time. Simultaneously, the average size of the seismic events increases toward the time to failure. These in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane. They mimic the "critical point" like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures. Our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse. Copyright 2005 by the American Geophysical Union.

Basis for the power supply reliability study of the 1 MW neutron source

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

McGhee, D.G.; Fathizadeh, M.

1993-07-01

The Intense Pulsed Neutron Source (IPNS) upgrade to 1 MW requires new power supply designs. This paper describes the tools and the methodology needed to assess the reliability of the power supplies. Both the design and operation of the power supplies in the synchrotron will be taken into account. To develop a reliability budget, the experiments to be conducted with this accelerator are reviewed, and data is collected on the number and duration of interruptions possible before an experiment is required to start over. Once the budget is established, several accelerators of this type will be examined. The budget ismore » allocated to the different accelerator systems based on their operating experience. The accelerator data is usually in terms of machine availability and system down time. It takes into account mean time to failure (MTTF), time to diagnose, time to repair or replace the failed components, and time to get the machine back online. These estimated times are used as baselines for the design. Even though we are in the early stage of design, available data can be analyzed to estimate the MTTF for the power supplies.« less

Lifetime validation of high-reliability (>30,000hr) rotary cryocoolers for specific customer profiles

NASA Astrophysics Data System (ADS)

Cauquil, Jean-Marc; Seguineau, Cédric; Vasse, Christophe; Raynal, Gaetan; Benschop, Tonny

2018-05-01

The cooler reliability is a major performance requested by the customers, especially for 24h/24h applications, which are a growing market. Thales has built a reliability policy based on accelerate ageing and tests to establish a robust knowledge on acceleration factors. The current trend seems to prove that the RM2 mean time to failure is now higher than 30,000hr. Even with accelerate ageing; the reliability growth becomes hardly manageable for such large figures. The paper focuses on these figures and comments the robustness of such a method when projections over 30,000hr of MTTF are needed.

Lifetime assessment of atomic-layer-deposited Al2O3-Parylene C bilayer coating for neural interfaces using accelerated age testing and electrochemical characterization.

PubMed

Minnikanti, Saugandhika; Diao, Guoqing; Pancrazio, Joseph J; Xie, Xianzong; Rieth, Loren; Solzbacher, Florian; Peixoto, Nathalia

2014-02-01

The lifetime and stability of insulation are critical features for the reliable operation of an implantable neural interface device. A critical factor for an implanted insulation's performance is its barrier properties that limit access of biological fluids to the underlying device or metal electrode. Parylene C is a material that has been used in FDA-approved implantable devices. Considered a biocompatible polymer with barrier properties, it has been used as a substrate, insulation or an encapsulation for neural implant technology. Recently, it has been suggested that a bilayer coating of Parylene C on top of atomic-layer-deposited Al2O3 would provide enhanced barrier properties. Here we report a comprehensive study to examine the mean time to failure of Parylene C and Al2O3-Parylene C coated devices using accelerated lifetime testing. Samples were tested at 60°C for up to 3 months while performing electrochemical measurements to characterize the integrity of the insulation. The mean time to failure for Al2O3-Parylene C was 4.6 times longer than Parylene C coated samples. In addition, based on modeling of the data using electrical circuit equivalents, we show here that there are two main modes of failure. Our results suggest that failure of the insulating layer is due to pore formation or blistering as well as thinning of the coating over time. The enhanced barrier properties of the bilayer Al2O3-Parylene C over Parylene C makes it a promising candidate as an encapsulating neural interface. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Quantile Regression with Censored Data

ERIC Educational Resources Information Center

Lin, Guixian

2009-01-01

The Cox proportional hazards model and the accelerated failure time model are frequently used in survival data analysis. They are powerful, yet have limitation due to their model assumptions. Quantile regression offers a semiparametric approach to model data with possible heterogeneity. It is particularly powerful for censored responses, where the…

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

Puskar, Joseph David; Quintana, Michael A.; Sorensen, Neil Robert

A program is underway at Sandia National Laboratories to predict long-term reliability of photovoltaic (PV) systems. The vehicle for the reliability predictions is a Reliability Block Diagram (RBD), which models system behavior. Because this model is based mainly on field failure and repair times, it can be used to predict current reliability, but it cannot currently be used to accurately predict lifetime. In order to be truly predictive, physics-informed degradation processes and failure mechanisms need to be included in the model. This paper describes accelerated life testing of metal foil tapes used in thin-film PV modules, and how tape jointmore » degradation, a possible failure mode, can be incorporated into the model.« less

On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

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

Dennis H. LeMieux

2004-10-01

Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land -based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCsmore » have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems; a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization.« less

Durability of building joint sealants

Treesearch

Christopher C. White; Kar Tean Tan; Donald L. Hunston; R. Sam Williams

2009-01-01

Predicting the service life of building joint sealants exposed to service environments in less than real time has been a need of the sealant community for many decades. Despite extensive research efforts to design laboratory accelerated tests to duplicate the failure modes occurring in field exposures, little success has been achieved using conventional durability...

Cell and gene therapy for severe heart failure patients: The time and place for Pim-1 Kinase

PubMed Central

Siddiqi, Sailay; Sussman, Mark A

2014-01-01

Regenerative therapy in severe heart failure patients presents a challenging set of circumstances including a damaged myocardial environment that accelerates senescence in myocytes and cardiac progenitor cells. Failing myocardium suffers from deterioration of contractile function coupled with impaired regenerative potential that drives the heart toward decompensation. Efficacious regenerative cell therapy for severe heart failure requires disruption of this vicious circle that can be accomplished by alteration of the compromised myocyte phenotype and rejuvenation of progenitor cells. This review focuses upon potential for Pim-1 kinase to mitigate chronic heart failure by improving myocyte quality through preservation of mitochondrial integrity, prevention of hypertrophy and inhibition of apoptosis. In addition, cardiac progenitors engineered with Pim-1 possess enhanced regenerative potential, making Pim-1 an important player in future treatment of severe heart failure. PMID:23984924

Validation of accelerated ageing of Thales rotary Stirling cryocoolers for the estimation of MTTF

NASA Astrophysics Data System (ADS)

Seguineau, C.,; Cauquil, J.-M.; Martin, J.-Y.; Benschop, T.

2016-05-01

The cooled IR detectors are used in a wide range of applications. Most of the time, the cryocoolers are one of the components dimensioning the lifetime of the system. The current market needs tend to reliability figures higher than 15,000hrs in "standard conditions". Field returns are hardly useable mostly because of the uncertain environmental conditions of use, or the differences in user profiles. A previous paper explains how Thales Cryogenics has developed an approach based on accelerated ageing and statistical analysis [1]. The aim of the current paper is to compare results obtained on accelerated ageing on one side, and on the other side, specific field returns where the conditions of use are well known. The comparison between prediction and effective failure rate is discussed. Moreover, a specific focus is done on how some new applications of cryocoolers (continuous operation at a specific temperature) can increase the MTTF. Some assumptions are also exposed on how the failure modes, effects and criticality analysis evolves for continuous operation at a specific temperature and compared to experimental data.

Accelerated approval of oncology products: the food and drug administration experience.

PubMed

Johnson, John R; Ning, Yang-Min; Farrell, Ann; Justice, Robert; Keegan, Patricia; Pazdur, Richard

2011-04-20

We reviewed the regulatory history of the accelerated approval process and the US Food and Drug Administration (FDA) experience with accelerated approval of oncology products from its initiation in December 11, 1992, to July 1, 2010. The accelerated approval regulations allowed accelerated approval of products to treat serious or life-threatening diseases based on surrogate endpoints that are reasonably likely to predict clinical benefit. Failure to complete postapproval trials to confirm clinical benefit with due diligence could result in removal of the accelerated approval indication from the market. From December 11, 1992, to July 1, 2010, the FDA granted accelerated approval to 35 oncology products for 47 new indications. Clinical benefit was confirmed in postapproval trials for 26 of the 47 new indications, resulting in conversion to regular approval. The median time between accelerated approval and regular approval of oncology products was 3.9 years (range = 0.8-12.6 years) and the mean time was 4.7 years, representing a substantial time savings in terms of earlier availability of drugs to cancer patients. Three new indications did not show clinical benefit when confirmatory postapproval trials were completed and were subsequently removed from the market or had restricted distribution plans implemented. Confirmatory trials were not completed for 14 new indications. The five longest intervals from receipt of accelerated approval to July 1, 2010, without completion of trials to confirm clinical benefit were 10.5, 6.4, 5.5, 5.5, and 4.7 years. The five longest intervals between accelerated approval and successful conversion to regular approval were 12.6, 9.7, 8.1, 7.5, and 7.4 years. Trials to confirm clinical benefit should be part of the drug development plan and should be in progress at the time of an application seeking accelerated approval to prevent an ineffective drug from remaining on the market for an unacceptable time.

The use of test structures for reliability prediction and process control of integrated circuits and photovoltaics

NASA Astrophysics Data System (ADS)

Trachtenberg, I.

How a reliability model might be developed with new data from accelerated stress testing, failure mechanisms, process control monitoring, and test structure evaluations is illustrated. The effects of the acceleration of temperature on operating life is discussed. Test structures that will further accelerate the failure rate are discussed. Corrosion testing is addressed. The uncoated structure is encapsulated in a variety of mold compounds and subjected to pressure-cooker testing.

Vibrational fatigue failures in short cantilevered piping with socket-welding fittings

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

Smith, J.K.

1996-12-01

Approximately 80% of the vibrational fatigue failures in nuclear power plants have been caused by high cycle vibrational fatigue. Many of these failures have occurred in short, small bore (2 in. nominal diameter and smaller), unbraced, cantilevered piping with socket-welding fittings. The fatigue failures initiated in the socket welds. These failures have been unexpected, and have caused costly, unscheduled outages in some cases. In order to reduce the number of vibrational fatigue failures in these short cantilevered pipes, an acceleration based vibrational fatigue screening criteria was developed under Electric Power Research Institute (EPRI) sponsorship. In this paper, the acceleration basedmore » criteria will be compared to the results obtained from detailed dynamic modeling of a short, cantilevered pipe.« less

SU-E-T-495: Neutron Induced Electronics Failure Rate Analysis for a Single Room Proton Accelerator

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

Knutson, N; DeWees, T; Klein, E

2014-06-01

Purpose: To determine the failure rate as a function of neutron dose of the range modulator's servo motor controller system (SMCS) while shielded with Borated Polyethylene (BPE) and unshielded in a single room proton accelerator. Methods: Two experimental setups were constructed using two servo motor controllers and two motors. Each SMCS was then placed 30 cm from the end of the plugged proton accelerator applicator. The motor was then turned on and observed from outside of the vault while being irradiated to known neutron doses determined from bubble detector measurements. Anytime the motor deviated from the programmed motion a failuremore » was recorded along with the delivered dose. The experiment was repeated using 9 cm of BPE shielding surrounding the SMCS. Results: Ten SMCS failures were recorded in each experiment. The dose per monitor unit for the unshielded SMCS was 0.0211 mSv/MU and 0.0144 mSv/MU for the shielded SMCS. The mean dose to produce a failure for the unshielded SMCS was 63.5 ± 58.3 mSv versus 17.0 ±12.2 mSv for the shielded. The mean number of MUs between failures were 2297 ± 1891 MU for the unshielded SMCS and 2122 ± 1523 MU for the shielded. A Wilcoxon Signed Ranked test showed the dose between failures were significantly different (P value = 0.044) while the number of MUs between failures were not (P value = 1.000). Statistical analysis determined a SMCS neutron dose of 5.3 mSv produces a 5% chance of failure. Depending on the workload and location of the SMCS, this failure rate could impede clinical workflow. Conclusion: BPE shielding was shown to not reduce the average failure of the SMCS and relocation of the system outside of the accelerator vault was required to lower the failure rate enough to avoid impeding clinical work flow.« less

Rapid behavioral maturation accelerates failure of stressed honey bee colonies

PubMed Central

Perry, Clint J.; Myerscough, Mary R.; Barron, Andrew B.

2015-01-01

Many complex factors have been linked to the recent marked increase in honey bee colony failure, including pests and pathogens, agrochemicals, and nutritional stressors. It remains unclear, however, why colonies frequently react to stressors by losing almost their entire adult bee population in a short time, resulting in a colony population collapse. Here we examine the social dynamics underlying such dramatic colony failure. Bees respond to many stressors by foraging earlier in life. We manipulated the demography of experimental colonies to induce precocious foraging in bees and used radio tag tracking to examine the consequences of precocious foraging for their performance. Precocious foragers completed far fewer foraging trips in their life, and had a higher risk of death in their first flights. We constructed a demographic model to explore how this individual reaction of bees to stress might impact colony performance. In the model, when forager death rates were chronically elevated, an increasingly younger forager force caused a positive feedback that dramatically accelerated terminal population decline in the colony. This resulted in a breakdown in division of labor and loss of the adult population, leaving only brood, food, and few adults in the hive. This study explains the social processes that drive rapid depopulation of a colony, and we explore possible strategies to prevent colony failure. Understanding the process of colony failure helps identify the most effective strategies to improve colony resilience. PMID:25675508

Rapid behavioral maturation accelerates failure of stressed honey bee colonies.

PubMed

Perry, Clint J; Søvik, Eirik; Myerscough, Mary R; Barron, Andrew B

2015-03-17

Many complex factors have been linked to the recent marked increase in honey bee colony failure, including pests and pathogens, agrochemicals, and nutritional stressors. It remains unclear, however, why colonies frequently react to stressors by losing almost their entire adult bee population in a short time, resulting in a colony population collapse. Here we examine the social dynamics underlying such dramatic colony failure. Bees respond to many stressors by foraging earlier in life. We manipulated the demography of experimental colonies to induce precocious foraging in bees and used radio tag tracking to examine the consequences of precocious foraging for their performance. Precocious foragers completed far fewer foraging trips in their life, and had a higher risk of death in their first flights. We constructed a demographic model to explore how this individual reaction of bees to stress might impact colony performance. In the model, when forager death rates were chronically elevated, an increasingly younger forager force caused a positive feedback that dramatically accelerated terminal population decline in the colony. This resulted in a breakdown in division of labor and loss of the adult population, leaving only brood, food, and few adults in the hive. This study explains the social processes that drive rapid depopulation of a colony, and we explore possible strategies to prevent colony failure. Understanding the process of colony failure helps identify the most effective strategies to improve colony resilience.

Lifetime prediction and reliability estimation methodology for Stirling-type pulse tube refrigerators by gaseous contamination accelerated degradation testing

NASA Astrophysics Data System (ADS)

Wan, Fubin; Tan, Yuanyuan; Jiang, Zhenhua; Chen, Xun; Wu, Yinong; Zhao, Peng

2017-12-01

Lifetime and reliability are the two performance parameters of premium importance for modern space Stirling-type pulse tube refrigerators (SPTRs), which are required to operate in excess of 10 years. Demonstration of these parameters provides a significant challenge. This paper proposes a lifetime prediction and reliability estimation method that utilizes accelerated degradation testing (ADT) for SPTRs related to gaseous contamination failure. The method was experimentally validated via three groups of gaseous contamination ADT. First, the performance degradation model based on mechanism of contamination failure and material outgassing characteristics of SPTRs was established. Next, a preliminary test was performed to determine whether the mechanism of contamination failure of the SPTRs during ADT is consistent with normal life testing. Subsequently, the experimental program of ADT was designed for SPTRs. Then, three groups of gaseous contamination ADT were performed at elevated ambient temperatures of 40 °C, 50 °C, and 60 °C, respectively and the estimated lifetimes of the SPTRs under normal condition were obtained through acceleration model (Arrhenius model). The results show good fitting of the degradation model with the experimental data. Finally, we obtained the reliability estimation of SPTRs through using the Weibull distribution. The proposed novel methodology enables us to take less than one year time to estimate the reliability of the SPTRs designed for more than 10 years.

Investigation of accelerated stress factors and failure/degradation mechanisms in terrestrial solar cells

NASA Technical Reports Server (NTRS)

Lathrop, J. W.

1983-01-01

Results of an ongoing research program into the reliability of terrestrial solar cells are presented. Laboratory accelerated testing procedures are used to identify failure/degradation modes which are then related to basic physical, chemical, and metallurgical phenomena. In the most recent tests, ten different types of production cells, both with and without encapsulation, from eight different manufacturers were subjected to a variety of accelerated tests. Results indicated the presence of a number of hitherto undetected failure mechanisms, including Schottky barrier formation at back contacts and loss of adhesion of grid metallization. The mechanism of Schottky barrier formation is explained by hydrogen, formed by the dissociation of water molecules at the contact surface, diffusing to the metal semiconductor interface. This same mechanism accounts for the surprising increase in sensitivity to accelerated stress conditions that was observed in some cells when encapsulated.

Accelerated stress testing of terrestrial solar cells

NASA Technical Reports Server (NTRS)

Lathrop, J. W.; Hawkins, D. C.; Prince, J. L.; Walker, H. A.

1982-01-01

The development of an accelerated test schedule for terrestrial solar cells is described. This schedule, based on anticipated failure modes deduced from a consideration of IC failure mechanisms, involves bias-temperature testing, humidity testing (including both 85-85 and pressure cooker stress), and thermal-cycle thermal-shock testing. Results are described for 12 different unencapsulated cell types. Both gradual electrical degradation and sudden catastrophic mechanical change were observed. These effects can be used to discriminate between cell types and technologies relative to their reliability attributes. Consideration is given to identifying laboratory failure modes which might lead to severe degradation in the field through second quadrant operation. Test results indicate that the ability of most cell types to withstand accelerated stress testing depends more on the manufacturer's design, processing, and worksmanship than on the particular metallization system. Preliminary tests comparing accelerated test results on encapsulated and unencapsulated cells are described.

Irradiation performance of HTGR recycle fissile fuel

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

Homan, F.J.; Long, E.L. Jr.

1976-08-01

The irradiation performance of candidate HTGR recycle fissile fuel under accelerated testing conditions is reviewed. Failure modes for coated-particle fuels are described, and the performance of candidate recycle fissile fuels is discussed in terms of these failure modes. The bases on which UO/sub 2/ and (Th,U)O/sub 2/ were rejected as candidate recycle fissile fuels are outlined, along with the bases on which the weak-acid resin (WAR)-derived fissile fuel was selected as the reference recycle kernel. Comparisons are made relative to the irradiation behavior of WAR-derived fuels of varying stoichiometry and conclusions are drawn about the optimum stoichiometry and the rangemore » of acceptable values. Plans for future testing in support of specification development, confirmation of the results of accelerated testing by real-time experiments, and improvement in fuel performance and reliability are described.« less

Measuring the Impact of Technology on Nurse Workflow: A Mixed Methods Approach

ERIC Educational Resources Information Center

Cady, Rhonda Guse

2012-01-01

Background. Investment in health information technology (HIT) is rapidly accelerating. The absence of contextual or situational analysis of the environment in which HIT is incorporated makes it difficult to measure success or failure. The methodology introduced in this paper combines observational research with time-motion study to measure the…

Durability of adhesives in plywood

Treesearch

Robert H. Gillespie; Bryan H. River

1976-01-01

Seven different adhesives were evaluated for durability as plywood adhesives by exposing panels and shear-test specimens to weathering at the Madison exposure site for nearly 8 years. Wet-strength loss and wood-failure changes were measured as a function of exposure time. The method of exposure accelerated the degradation that would have resulted from exposure in most...

Life Assessment for Cr-Mo Steel Dissimilar Joints by Various Filler Metals Using Accelerated Creep Testing

NASA Astrophysics Data System (ADS)

Petchsang, S.; Phung-on, I.; Poopat, B.

2016-12-01

Accelerated creep rupture tests were performed on T22/T91 dissimilar metal joints to determine the fracture location and rupture time of different weldments. Four configurations of deposited filler metal were tested using gas tungsten arc welding to estimate the service life for Cr-Mo steel dissimilar joints at elevated temperatures in power plants. Results indicated that failure in all configurations occurred in the tempered original microstructure and tempered austenite transformation products (martensite or bainite structure) as type IV cracking at the intercritical area of the heat-affected zone (ICHAZ) for both T22 and T91 sides rather than as a consequence of the different filler metals. Creep damage occurred with the formation of precipitations and microvoids. The correlation between applied stress and the Larson-Miller parameter (PLM) was determined to predict the service life of each material configuration. Calculated time-to-failure based on the PLM and test results for both temperature and applied stress parameters gave a reasonable fit. The dissimilar joints exhibited lower creep rupture compared to the base material indicating creep degradation of the weldment.

Lifetime Prediction for Degradation of Solar Mirrors using Step-Stress Accelerated Testing (Presentation)

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

Lee, J.; Elmore, R.; Kennedy, C.

This research is to illustrate the use of statistical inference techniques in order to quantify the uncertainty surrounding reliability estimates in a step-stress accelerated degradation testing (SSADT) scenario. SSADT can be used when a researcher is faced with a resource-constrained environment, e.g., limits on chamber time or on the number of units to test. We apply the SSADT methodology to a degradation experiment involving concentrated solar power (CSP) mirrors and compare the results to a more traditional multiple accelerated testing paradigm. Specifically, our work includes: (1) designing a durability testing plan for solar mirrors (3M's new improved silvered acrylic "Solarmore » Reflector Film (SFM) 1100") through the ultra-accelerated weathering system (UAWS), (2) defining degradation paths of optical performance based on the SSADT model which is accelerated by high UV-radiant exposure, and (3) developing service lifetime prediction models for solar mirrors using advanced statistical inference. We use the method of least squares to estimate the model parameters and this serves as the basis for the statistical inference in SSADT. Several quantities of interest can be estimated from this procedure, e.g., mean-time-to-failure (MTTF) and warranty time. The methods allow for the estimation of quantities that may be of interest to the domain scientists.« less

Pulse Generator Exchange Does Not Accelerate the Rate of Electrical Failure in a Recalled Small Caliber ICD Lead.

PubMed

Lovelock, Joshua D; Premkumar, Ajay; Levy, Mathew R; Mengistu, Andenet; Hoskins, Michael H; El-Chami, Mikhael F; Lloyd, Michael S; Leon, Angel R; Langberg, Jonathan J; Delurgio, David B

2015-12-01

St. Jude Riata/Riata ST defibrillator leads (St. Jude Medical, Sylmar, CA, USA) were recalled by the Food and Drug Administration in 2011 for an increased rate of failure. More than 227,000 leads were implanted and at least 79,000 patients still have active Riata leads. Studies have examined clinical predictors of lead failure in Riata leads, but none have addressed the effect of implantable cardioverter defibrillator (ICD) generator exchange on lead failure. The purpose of this study is to assess the effect of ICD generator exchange on the rate of electrical failure in the Riata lead at 1 year. A retrospective chart review was conducted in patients who underwent implantation of a Riata/Riata ST lead at one center. Patients with a functioning Riata lead (with/without externalized conductor) at the time of ICD exchange were compared to controls with Riata leads implanted for a comparable amount of time who did not undergo generator replacement. Riata leads were implanted in 1,042 patients prior to the recall and 153 of these patients underwent generator exchange without lead replacement. Conductor externalization was noted in 21.5% of Riata leads in the ICD exchange cohort, which was not different from the control group (19.2%; P = 0.32). Two leads failed in the first year after generator replacement (1.5%) which did not significantly differ from the control group (2.0%; P = 0.57). At change-out, 54% received a commanded shock (18.6 ± 0.9 J) that did not result in any change in the high-voltage lead impedance (46.1 ± 1.1 ohms). Conductor externalization was seen frequently in our cohort of patients. ICD generator exchange did not accelerate the rate of Riata lead failure at 1 year. Although both the control and the change-out cohorts failed at a rate much greater than nonrecalled leads, generator exchange did not appear to add to the problem. ©2015 Wiley Periodicals, Inc.

Failure Modes in Capacitors When Tested Under a Time-Varying Stress

NASA Technical Reports Server (NTRS)

Liu, David (Donhang)

2011-01-01

Steady step surge testing (SSST) is widely applied to screen out potential power-on failures in solid tantalum capacitors. The test simulates the power supply's on and off characteristics. Power-on failure has been the prevalent failure mechanism for solid tantalum capacitors for decoupling applications. On the other hand, the SSST can also be reviewed as an electrically destructive test under a time-varying stress. It consists of rapidly charging the capacitor with incremental voltage increases, through a low resistance in series, until the capacitor under test is electrically shorted. Highly accelerated life testing (HALT) is usually a time-efficient method for determining the failure mechanism in capacitors; however, a destructive test under a time-varying stress like SSST is even more effective. It normally takes days to complete a HALT test, but it only takes minutes for a time-varying stress test to produce failures. The advantage of incorporating specific time-varying stress into a statistical model is significant in providing an alternative life test method for quickly revealing the failure modes in capacitors. In this paper, a time-varying stress has been incorporated into the Weibull model to characterize the failure modes. The SSST circuit and transient conditions to correctly test the capacitors is discussed. Finally, the SSST was applied for testing polymer aluminum capacitors (PA capacitors), Ta capacitors, and multi-layer ceramic capacitors with both precious metal electrode (PME) and base-metal-electrodes (BME). It appears that testing results are directly associated to the dielectric layer breakdown in PA and Ta capacitors and are independent on the capacitor values, the way the capacitors being built, and the manufactures. The testing results also reveal that ceramic capacitors exhibit breakdown voltages more than 20 times the rated voltage, and the breakdown voltages are inverse proportional to the dielectric layer thickness. The possibility of ceramic capacitors in front-end decoupling applications to block the surge noise from a power supply is also discussed.

On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

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

Dennis H. LeMieux

2005-04-01

Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs havemore » been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.« less

ON-LINE THERMAL BARRIER COATING MONITORING FOR REAL-TIME FAILURE PROTECTION AND LIFE MAXIMIZATION

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

Dennis H. LeMieux

2003-10-01

Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCsmore » have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.« less

ON-LINE THERMAL BARRIER COATING MONITORING FOR REAL-TIME FAILURE PROTECTION AND LIFE MAXIMIZATION

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

Dennis H. LeMieux

2003-07-01

Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCsmore » have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.« less

On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

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

Dennis H. LeMieux

2005-10-01

Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Power Generation, Inc proposed a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs havemore » been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Power Generation, Inc. has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.« less

Characterization of wear debris generated in accelerated rolling-element fatigue tests

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.; Parker, R. J.

1978-01-01

A ferrographic analysis was used to determine the types and quantities of wear debris generated during accelerated rolling contact fatigue tests. The five-ball rolling contact fatigue tester was used. Ball specimens were made of a corrosion resistant, high-temperature bearing steel. The lubricant was a superrefined naphthenic mineral oil. Conditions included a maximum Hertz stress of 5.52 10 to the 9th power Pa and a shaft speed of 10,000 rpm. Four types of wear debris were observed: (1) normal rubbing wear particles, (2) fatigue microspall particles, (3) spheres, and (4) friction polymer deposits. The characterization of wear debris as a function of time was of limited use in predicting fatigue failures in these accelerated tests.

Reliability and failure modes of implant-supported zirconium-oxide fixed dental prostheses related to veneering techniques

PubMed Central

Baldassarri, Marta; Zhang, Yu; Thompson, Van P.; Rekow, Elizabeth D.; Stappert, Christian F. J.

2011-01-01

Summary Objectives To compare fatigue failure modes and reliability of hand-veneered and over-pressed implant-supported three-unit zirconium-oxide fixed-dental-prostheses(FDPs). Methods Sixty-four custom-made zirconium-oxide abutments (n=32/group) and thirty-two zirconium-oxide FDP-frameworks were CAD/CAM manufactured. Frameworks were veneered with hand-built up or over-pressed porcelain (n=16/group). Step-stress-accelerated-life-testing (SSALT) was performed in water applying a distributed contact load at the buccal cusp-pontic-area. Post failure examinations were carried out using optical (polarized-reflected-light) and scanning electron microscopy (SEM) to visualize crack propagation and failure modes. Reliability was compared using cumulative-damage step-stress analysis (Alta-7-Pro, Reliasoft). Results Crack propagation was observed in the veneering porcelain during fatigue. The majority of zirconium-oxide FDPs demonstrated porcelain chipping as the dominant failure mode. Nevertheless, fracture of the zirconium-oxide frameworks was also observed. Over-pressed FDPs failed earlier at a mean failure load of 696 ± 149 N relative to hand-veneered at 882 ± 61 N (profile I). Weibull-stress-number of cycles-unreliability-curves were generated. The reliability (2-sided at 90% confidence bounds) for a 400N load at 100K cycles indicated values of 0.84 (0.98-0.24) for the hand-veneered FDPs and 0.50 (0.82-0.09) for their over-pressed counterparts. Conclusions Both zirconium-oxide FDP systems were resistant under accelerated-life-time-testing. Over-pressed specimens were more susceptible to fatigue loading with earlier veneer chipping. PMID:21557985

Anterior Cruciate Ligament-Derived Stem Cells Transduced With BMP2 Accelerate Graft-Bone Integration After ACL Reconstruction.

PubMed

Kawakami, Yohei; Takayama, Koji; Matsumoto, Tomoyuki; Tang, Ying; Wang, Bing; Mifune, Yutaka; Cummins, James H; Warth, Ryan J; Kuroda, Ryosuke; Kurosaka, Masahiro; Fu, Freddie H; Huard, Johnny

2017-03-01

Strong graft-bone integration is a prerequisite for successful graft remodeling after reconstruction of the anterior cruciate ligament (ACL) using soft tissue grafts. Novel strategies to accelerate soft tissue graft-bone integration are needed to reduce the need for bone-tendon-bone graft harvest, reduce patient convalescence, facilitate rehabilitation, and reduce total recovery time after ACL reconstruction. The application of ACL-derived stem cells with enhanced expression of bone morphogenetic protein 2 (BMP2) onto soft tissue grafts in the form of cell sheets will both accelerate and improve the quality of graft-bone integration after ACL reconstruction in a rat model. Controlled laboratory study. ACL-derived CD34+ cells were isolated from remnant human ACL tissues, virally transduced to express BMP2, and embedded within cell sheets. In a rat model of ACL injury, bilateral single-bundle ACL reconstructions were performed, in which cell sheets were wrapped around tendon autografts before reconstruction. Four groups containing a total of 48 rats (96 knees) were established (n = 12 rats; 24 knees per group): CD34+BMP2 (100%), CD34+BMP2 (25%), CD34+ (untransduced), and a control group containing no cells. Six rats from each group were euthanized 2 and 4 weeks after surgery, and each graft was harvested for immunohistochemical and histological analyses. The remaining 6 rats in each group were euthanized at 4 and 8 weeks to evaluate in situ tensile load to failure in each femur-graft-tibia complex. In vitro, BMP2 transduction promoted the osteogenic differentiation of ACL-derived CD34+ cells while retaining their intrinsic multipotent capabilities. Osteoblast densities were greatest in the BMP2 (100%) and BMP2 (25%) groups. Bone tunnels in the CD34+BMP2 (100%) and CD34+BMP2 (25%) groups had the smallest cross-sectional areas according to micro-computed tomography analyses. Graft-bone integration occurred most rapidly in the CD34+BMP2 (25%) group. Tensile load to failure was significantly greater in the groups containing stem cells at 4 and 8 weeks after surgery. Tensile strength was greatest in the CD34+BMP2 (100%) group at 4 weeks, and in the CD34+BMP2 (25%) group at 8 weeks. ACL-derived CD34+ cells transduced with BMP2 accelerated graft-bone integration after ACL reconstruction using soft tissue autografts in a rat model, as evidenced by improved histological appearance and graft-bone interface biology along with tensile load to failure at each time point up to 8 weeks after surgery. A primary disadvantage of using soft tissue grafts for ACL reconstruction is the prolonged time required for bony ingrowth, which delays the initiation of midsubstance graft remodeling. The lack of consistent correlation between the appearance of a "healed" ACL on postoperative magnetic resonance imaging and readiness to return to sport results in athletes being released to sport before the graft is ready to handle high-intensity loading. Therefore, it is desirable to identify strategies that accelerate graft-bone integration, which would reduce the time to biologic fixation, improve the reliability of biologic fixation, allow for accelerated rehabilitation, and potentially reduce the incidence of early graft pullout and late midsubstance failure.

Economic Shocks and Children's Dropout from Primary School: Implications for Education Policy in Ethiopia

ERIC Educational Resources Information Center

Woldehanna, Tassew; Hagos, Adiam

2015-01-01

This paper investigates the impact of idiosyncratic and covariate economic shocks, on the likelihood of children dropping out of primary school. In this endeavour, an Accelerated Failure Time Hazard model was estimated using data from the Young Lives study of childhood poverty. The estimated results indicate that both idiosyncratic shocks and…

High Pressure Hydrogen Pressure Relief Devices: Accelerated Life Testing and Application Best Practices

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

Burgess, Robert M.; Post, Matthew B.; Buttner, William J.

Pressure relief devices (PRDs ) are used to protect high pressure systems from burst failure caused by overpressurization. Codes and standards require the use of PRDs for the safe design of many pressurized systems. These systems require high reliability due to the risks associated with a burst failure. Hydrogen service can increase the risk of PRD failure due to material property degradation caused by hydrogen attack. The National Renewable Energy Laboratory (NREL) has conducted an accelerated life test on a conventional spring loaded PRD. Based on previous failures in the field, the nozzles specific to these PRDs are of particularmore » interest. A nozzle in a PRD is a small part that directs the flow of fluid toward the sealing surface to maintain the open state of the valve once the spring force is overcome. The nozzle in this specific PRD is subjected to the full tensile force of the fluid pressure. These nozzles are made from 440C material, which is a type of hardened steel that is commonly chosen for high pressure applications because of its high strength properties. In a hydrogen environment, however, 440C is considered a worst case material since hydrogen attack results in a loss of almost all ductility and thus 440C is prone to fatigue and material failure. Accordingly, 440C is not recommended for hydrogen service. Conducting an accelerated life test on a PRD with 440C material provides information on necessary and sufficient conditions required to produce crack initiation and failure. The accelerated life test also provides information on other PRD failure modes that are somewhat statistically random in nature.« less

Linking Seismicity at Depth to the Mechanics of a Lava Dome Failure - a Forecasting Approach

NASA Astrophysics Data System (ADS)

Salvage, R. O.; Neuberg, J. W.; Murphy, W.

2014-12-01

Soufriere Hills volcano (SHV), Montserrat has been in a state of ongoing unrest since 1995. Prior to eruptions, an increase in the number of seismic events has been observed. We use the Material Failure Law (MFL) (Voight, 1988) to investigate how an accelerating number of low frequency seismic events are related to the timing of a large scale dome collapse in June 1997. We show that although the forecasted timing of a dome collapse may coincide with the known timing, the accuracy of the application of the MFL to the data is poor. Using a cross correlation technique we show how characterising seismicity into similar waveform "families'' allows us to focus on a single process at depth and improve the reliability of our forecast. A number of families are investigated to assess their relative importance. We show that despite the timing of a forecasted dome collapse ranging between several hours of the known timing of collapse, each of the families produces a better forecast in terms of fit to the seismic acceleration data than when using all low frequency seismicity. In addition, we investigate the stability of such families between major dome collapses (1997 and 2003), assessing their potential for use in real-time forecasting. Initial application of Grey's Incidence Analysis suggests that a key parameter influencing the potential for a large scale slumping on the dome of SHV is the rate of low frequency seismicity associated with magma movement and dome growth. We undertook numerical modelling of an andesitic dome with a hydrothermally altered layer down to 800m. The geometry of the dome is based on SHV prior to the collapse of 2003. We show that a critical instability is reached once slope angles exceed 25°, corresponding to a summit height of just over 1100m a.s.l.. The geometry of failure is in close agreement with the identified failure plane suggesting that the input mechanical properties are broadly consistent with reality. We are therefore able to compare different failure geometries based on edifice geomorphology and determine a Factor of Safety associated with such scenarios. This modelling would be extremely useful in a holistic forecasting approach within a volcanic environment. Reference: Voight, B. (1988). A method for prediction of volcanic eruptions. Nature, 332: 125-130.

Dietary Salt Exacerbates Isoproterenol-induced Cardiomyopathy in Rats

EPA Science Inventory

Spontaneously Hypertensive Heart Failure rats (SHHFs) take far longer to develop compensated heart failure and congestive decompensation than common surgical models of heart failure. Isoproterenol (ISO) infusion can accelerate cardiomyopathy in young SHHFs, while dietary salt loa...

Predicting drowsy driving in real-time situations: Using an advanced driving simulator, accelerated failure time model, and virtual location-based services.

PubMed

Wang, Junhua; Sun, Shuaiyi; Fang, Shouen; Fu, Ting; Stipancic, Joshua

2017-02-01

This paper aims to both identify the factors affecting driver drowsiness and to develop a real-time drowsy driving probability model based on virtual Location-Based Services (LBS) data obtained using a driving simulator. A driving simulation experiment was designed and conducted using 32 participant drivers. Collected data included the continuous driving time before detection of drowsiness and virtual LBS data related to temperature, time of day, lane width, average travel speed, driving time in heavy traffic, and driving time on different roadway types. Demographic information, such as nap habit, age, gender, and driving experience was also collected through questionnaires distributed to the participants. An Accelerated Failure Time (AFT) model was developed to estimate the driving time before detection of drowsiness. The results of the AFT model showed driving time before drowsiness was longer during the day than at night, and was longer at lower temperatures. Additionally, drivers who identified as having a nap habit were more vulnerable to drowsiness. Generally, higher average travel speeds were correlated to a higher risk of drowsy driving, as were longer periods of low-speed driving in traffic jam conditions. Considering different road types, drivers felt drowsy more quickly on freeways compared to other facilities. The proposed model provides a better understanding of how driver drowsiness is influenced by different environmental and demographic factors. The model can be used to provide real-time data for the LBS-based drowsy driving warning system, improving past methods based only on a fixed driving. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

Burnham, A K; Weese, R K; Adrzejewski, W J

Accelerated aging tests play an important role in assessing the lifetime of manufactured products. There are two basic approaches to lifetime qualification. One tests a product to failure over range of accelerated conditions to calibrate a model, which is then used to calculate the failure time for conditions of use. A second approach is to test a component to a lifetime-equivalent dose (thermal or radiation) to see if it still functions to specification. Both methods have their advantages and limitations. A disadvantage of the 2nd method is that one does not know how close one is to incipient failure. Thismore » limitation can be mitigated by testing to some higher level of dose as a safety margin, but having a predictive model of failure via the 1st approach provides an additional measure of confidence. Even so, proper calibration of a failure model is non-trivial, and the extrapolated failure predictions are only as good as the model and the quality of the calibration. This paper outlines results for predicting the potential failure point of a system involving a mixture of two energetic materials, HMX (nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and CP (2-(5-cyanotetrazalato) pentaammine cobalt (III) perchlorate). Global chemical kinetic models for the two materials individually and as a mixture are developed and calibrated from a variety of experiments. These include traditional thermal analysis experiments run on time scales from hours to a couple days, detonator aging experiments with exposures up to 50 months, and sealed-tube aging experiments for up to 5 years. Decomposition kinetics are determined for HMX (nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and CP (2-(5-cyanotetrazalato) pentaammine cobalt (III) perchlorate) separately and together. For high levels of thermal stress, the two materials decompose faster as a mixture than individually. This effect is observed both in high-temperature thermal analysis experiments and in long-term thermal aging experiments. An Arrhenius plot of the 10% level of HMX decomposition by itself from a diverse set of experiments is linear from 120 to 260 C, with an apparent activation energy of 165 kJ/mol. Similar but less extensive thermal analysis data for the mixture suggests a slightly lower activation energy for the mixture, and an analogous extrapolation is consistent with the amount of gas observed in the long-term detonator aging experiments, which is about 30 times greater than expected from HMX by itself for 50 months at 100 C. Even with this acceleration, however, it would take {approx}10,000 years to achieve 10% decomposition at {approx}30 C. Correspondingly, negligible decomposition is predicted by this kinetic model for a few decades aging at temperatures slightly above ambient. This prediction is consistent with additional sealed-tube aging experiments at 100-120 C, which are estimated to have an effective thermal dose greater than that from decades of exposure to temperatures slightly above ambient.« less

Sensitivity analysis of tall buildings in Semarang, Indonesia due to fault earthquakes with maximum 7 Mw

NASA Astrophysics Data System (ADS)

Partono, Windu; Pardoyo, Bambang; Atmanto, Indrastono Dwi; Azizah, Lisa; Chintami, Rouli Dian

2017-11-01

Fault is one of the dangerous earthquake sources that can cause building failure. A lot of buildings were collapsed caused by Yogyakarta (2006) and Pidie (2016) fault source earthquakes with maximum magnitude 6.4 Mw. Following the research conducted by Team for Revision of Seismic Hazard Maps of Indonesia 2010 and 2016, Lasem, Demak and Semarang faults are three closest earthquake sources surrounding Semarang. The ground motion from those three earthquake sources should be taken into account for structural design and evaluation. Most of tall buildings, with minimum 40 meter high, in Semarang were designed and constructed following the 2002 and 2012 Indonesian Seismic Code. This paper presents the result of sensitivity analysis research with emphasis on the prediction of deformation and inter-story drift of existing tall building within the city against fault earthquakes. The analysis was performed by conducting dynamic structural analysis of 8 (eight) tall buildings using modified acceleration time histories. The modified acceleration time histories were calculated for three fault earthquakes with magnitude from 6 Mw to 7 Mw. The modified acceleration time histories were implemented due to inadequate time histories data caused by those three fault earthquakes. Sensitivity analysis of building against earthquake can be predicted by evaluating surface response spectra calculated using seismic code and surface response spectra calculated from acceleration time histories from a specific earthquake event. If surface response spectra calculated using seismic code is greater than surface response spectra calculated from acceleration time histories the structure will stable enough to resist the earthquake force.

Ceramic capacitor insulation resistance failures accelerated by low voltage

NASA Technical Reports Server (NTRS)

Brennan, T. F.

1978-01-01

Ceramic capacitors failed insulation resistance testing at less than one-tenth their rated voltage. Many failures recovered as the voltage was increased. Comprehensive failure analysis techniques, some of which are unprecedented, were used to examine these failures. It was determined that there was more than one failure mechanism, and the results indicate a need for special additional screening.

The role of shear and tensile failure in dynamically triggered landslides

USGS Publications Warehouse

Gipprich, T.L.; Snieder, R.K.; Jibson, R.W.; Kimman, W.

2008-01-01

Dynamic stresses generated by earthquakes can trigger landslides. Current methods of landslide analysis such as pseudo-static analysis and Newmark's method focus on the effects of earthquake accelerations on the landslide mass to characterize dynamic landslide behaviour. One limitation of these methods is their use Mohr-Coulomb failure criteria, which only accounts for shear failure, but the role of tensile failure is not accounted for. We develop a limit-equilibrium model to investigate the dynamic stresses generated by a given ground motion due to a plane wave and use this model to assess the role of shear and tensile failure in the initiation of slope instability. We do so by incorporating a modified Griffith failure envelope, which combines shear and tensile failure into a single criterion. Tests of dynamic stresses in both homogeneous and layered slopes demonstrate that two modes of failure exist, tensile failure in the uppermost meters of a slope and shear failure at greater depth. Further, we derive equations that express the dynamic stress in the near-surface in the acceleration measured at the surface. These equations are used to approximately define the depth range for each mechanism of failure. The depths at which these failure mechanisms occur suggest that shear and tensile failure might collaborate in generating slope failure. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Accelerated life assessment of coating on the radar structure components in coastal environment.

PubMed

Liu, Zhe; Ming, ZhiMao

2016-07-04

This paper aimed to build an accelerated life test scheme and carry out quantitative analysis between accelerated life test in the laboratory and actual service for the coating composed of epoxy primer and polyurethane paint on structure components of some kind of radar served in the coastal environment of South China Sea. The accelerated life test scheme was built based on the service environment and failure analysis of the coating. The quantitative analysis between accelerated life test and actual service was conducted by comparing the gloss loss, discoloration, chalking, blistering, cracking and electrochemical impedance spectroscopy of the coating. The main factors leading to the coating failure were ultraviolet radiation, temperature, moisture, salt fog and loads, the accelerated life test included ultraviolet radiation, damp heat, thermal shock, fatigue and salt spray. The quantitative relationship was that one cycle of the accelerated life test was equal to actual service for one year. It was established that one cycle of the accelerated life test was equal to actual service for one year. It provided a precise way to predict actual service life of newly developed coatings for the manufacturer.

Coexisting Frailty, Cognitive Impairment, and Heart Failure: Implications for Clinical Care

PubMed Central

Butts, Brittany; Gary, Rebecca

2015-01-01

Objective To review some of the proposed pathways that increase frailty risk in older persons with heart failure and to discuss tools that may be used to assess for changes in physical and cognitive functioning in this population in order to assist with appropriate and timely intervention. Methods Review of the literature. Results Heart failure is the only cardiovascular disease that is increasing by epidemic proportions, largely due to an aging society and therapeutic advances in disease management. Because heart failure is largely a cardiogeriatric syndrome, age-related syndromes such as frailty and cognitive impairment are common in heart failure patients. Compared with age-matched counterparts, older adults with heart failure 4 to 6 times more likely to be frail or cognitively impaired. The reason for the high prevalence of frailty and cognitive impairment in this population is not well known but may likely reflect the synergistic effects of heart failure and aging, which may heighten vulnerability to stressors and accelerate loss of physiologic reserve. Despite the high prevalence of frailty and cognitive impairment in the heart failure population, these conditions are not routinely screened for in clinical practice settings and guidelines on optimal assessment strategies are lacking. Conclusion Persons with heart failure are at an increased risk for frailty, which may worsen symptoms, impair self-management, and lead to worse heart failure outcomes. Early detection of frailty and cognitive impairment may be an opportunity for intervention and a key strategy for improving clinical outcomes in older adults with heart failure. PMID:26594103

Final Report: System Reliability Model for Solid-State Lighting (SSL) Luminaires

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

Davis, J. Lynn

2017-05-31

The primary objectives of this project was to develop and validate reliability models and accelerated stress testing (AST) methodologies for predicting the lifetime of integrated SSL luminaires. This study examined the likely failure modes for SSL luminaires including abrupt failure, excessive lumen depreciation, unacceptable color shifts, and increased power consumption. Data on the relative distribution of these failure modes were acquired through extensive accelerated stress tests and combined with industry data and other source of information on LED lighting. This data was compiled and utilized to build models of the aging behavior of key luminaire optical and electrical components.

The Revolution Starts Now: Why It Is Time to Reclaim Education's Connection to Our Democracy

ERIC Educational Resources Information Center

Coleman, Elizabeth

2011-01-01

This author contends that, during the past decade, people have witnessed escalating crises in the most vital areas of their public life, including: (1) a relentless acceleration in the awesome failure to effectively educate vast numbers of the young; (2) a no-less-relentless increase in the spectacular inequities in the distribution of wealth; (3)…

Prognostics of Power Electronics, Methods and Validation Experiments

NASA Technical Reports Server (NTRS)

Kulkarni, Chetan S.; Celaya, Jose R.; Biswas, Gautam; Goebel, Kai

2012-01-01

Abstract Failure of electronic devices is a concern for future electric aircrafts that will see an increase of electronics to drive and control safety-critical equipment throughout the aircraft. As a result, investigation of precursors to failure in electronics and prediction of remaining life of electronic components is of key importance. DC-DC power converters are power electronics systems employed typically as sourcing elements for avionics equipment. Current research efforts in prognostics for these power systems focuses on the identification of failure mechanisms and the development of accelerated aging methodologies and systems to accelerate the aging process of test devices, while continuously measuring key electrical and thermal parameters. Preliminary model-based prognostics algorithms have been developed making use of empirical degradation models and physics-inspired degradation model with focus on key components like electrolytic capacitors and power MOSFETs (metal-oxide-semiconductor-field-effect-transistor). This paper presents current results on the development of validation methods for prognostics algorithms of power electrolytic capacitors. Particularly, in the use of accelerated aging systems for algorithm validation. Validation of prognostics algorithms present difficulties in practice due to the lack of run-to-failure experiments in deployed systems. By using accelerated experiments, we circumvent this problem in order to define initial validation activities.

ACCELERATED FAILURE TIME MODELS PROVIDE A USEFUL STATISTICAL FRAMEWORK FOR AGING RESEARCH

PubMed Central

Swindell, William R.

2009-01-01

Survivorship experiments play a central role in aging research and are performed to evaluate whether interventions alter the rate of aging and increase lifespan. The accelerated failure time (AFT) model is seldom used to analyze survivorship data, but offers a potentially useful statistical approach that is based upon the survival curve rather than the hazard function. In this study, AFT models were used to analyze data from 16 survivorship experiments that evaluated the effects of one or more genetic manipulations on mouse lifespan. Most genetic manipulations were found to have a multiplicative effect on survivorship that is independent of age and well-characterized by the AFT model “deceleration factor”. AFT model deceleration factors also provided a more intuitive measure of treatment effect than the hazard ratio, and were robust to departures from modeling assumptions. Age-dependent treatment effects, when present, were investigated using quantile regression modeling. These results provide an informative and quantitative summary of survivorship data associated with currently known long-lived mouse models. In addition, from the standpoint of aging research, these statistical approaches have appealing properties and provide valuable tools for the analysis of survivorship data. PMID:19007875

Accelerated failure time models provide a useful statistical framework for aging research.

PubMed

Swindell, William R

2009-03-01

Survivorship experiments play a central role in aging research and are performed to evaluate whether interventions alter the rate of aging and increase lifespan. The accelerated failure time (AFT) model is seldom used to analyze survivorship data, but offers a potentially useful statistical approach that is based upon the survival curve rather than the hazard function. In this study, AFT models were used to analyze data from 16 survivorship experiments that evaluated the effects of one or more genetic manipulations on mouse lifespan. Most genetic manipulations were found to have a multiplicative effect on survivorship that is independent of age and well-characterized by the AFT model "deceleration factor". AFT model deceleration factors also provided a more intuitive measure of treatment effect than the hazard ratio, and were robust to departures from modeling assumptions. Age-dependent treatment effects, when present, were investigated using quantile regression modeling. These results provide an informative and quantitative summary of survivorship data associated with currently known long-lived mouse models. In addition, from the standpoint of aging research, these statistical approaches have appealing properties and provide valuable tools for the analysis of survivorship data.

Earthquake and failure forecasting in real-time: A Forecasting Model Testing Centre

NASA Astrophysics Data System (ADS)

Filgueira, Rosa; Atkinson, Malcolm; Bell, Andrew; Main, Ian; Boon, Steven; Meredith, Philip

2013-04-01

Across Europe there are a large number of rock deformation laboratories, each of which runs many experiments. Similarly there are a large number of theoretical rock physicists who develop constitutive and computational models both for rock deformation and changes in geophysical properties. Here we consider how to open up opportunities for sharing experimental data in a way that is integrated with multiple hypothesis testing. We present a prototype for a new forecasting model testing centre based on e-infrastructures for capturing and sharing data and models to accelerate the Rock Physicist (RP) research. This proposal is triggered by our work on data assimilation in the NERC EFFORT (Earthquake and Failure Forecasting in Real Time) project, using data provided by the NERC CREEP 2 experimental project as a test case. EFFORT is a multi-disciplinary collaboration between Geoscientists, Rock Physicists and Computer Scientist. Brittle failure of the crust is likely to play a key role in controlling the timing of a range of geophysical hazards, such as volcanic eruptions, yet the predictability of brittle failure is unknown. Our aim is to provide a facility for developing and testing models to forecast brittle failure in experimental and natural data. Model testing is performed in real-time, verifiably prospective mode, in order to avoid selection biases that are possible in retrospective analyses. The project will ultimately quantify the predictability of brittle failure, and how this predictability scales from simple, controlled laboratory conditions to the complex, uncontrolled real world. Experimental data are collected from controlled laboratory experiments which includes data from the UCL Laboratory and from Creep2 project which will undertake experiments in a deep-sea laboratory. We illustrate the properties of the prototype testing centre by streaming and analysing realistically noisy synthetic data, as an aid to generating and improving testing methodologies in imperfect conditions. The forecasting model testing centre uses a repository to hold all the data and models and a catalogue to hold all the corresponding metadata. It allows to: Data transfer: Upload experimental data: We have developed FAST (Flexible Automated Streaming Transfer) tool to upload data from RP laboratories to the repository. FAST sets up data transfer requirements and selects automatically the transfer protocol. Metadata are automatically created and stored. Web data access: Create synthetic data: Users can choose a generator and supply parameters. Synthetic data are automatically stored with corresponding metadata. Select data and models: Search the metadata using criteria design for RP. The metadata of each data (synthetic or from laboratory) and models are well-described through their respective catalogues accessible by the web portal. Upload models: Upload and store a model with associated metadata. This provide an opportunity to share models. The web portal solicits and creates metadata describing each model. Run model and visualise results: Selected data and a model to be submitted to a High Performance Computational resource hiding technical details. Results are displayed in accelerated time and stored allowing retrieval, inspection and aggregation. The forecasting model testing centre proposed could be integrated into EPOS. Its expected benefits are: Improved the understanding of brittle failure prediction and its scalability to natural phenomena. Accelerated and extensive testing and rapid sharing of insights. Increased impact and visibility of RP and GeoScience research. Resources for education and training. A key challenge is to agree the framework for sharing RP data and models. Our work is provocative first step.

Seismic energy data analysis of Merapi volcano to test the eruption time prediction using materials failure forecast method (FFM)

NASA Astrophysics Data System (ADS)

Anggraeni, Novia Antika

2015-04-01

The test of eruption time prediction is an effort to prepare volcanic disaster mitigation, especially in the volcano's inhabited slope area, such as Merapi Volcano. The test can be conducted by observing the increase of volcanic activity, such as seismicity degree, deformation and SO2 gas emission. One of methods that can be used to predict the time of eruption is Materials Failure Forecast Method (FFM). Materials Failure Forecast Method (FFM) is a predictive method to determine the time of volcanic eruption which was introduced by Voight (1988). This method requires an increase in the rate of change, or acceleration of the observed volcanic activity parameters. The parameter used in this study is the seismic energy value of Merapi Volcano from 1990 - 2012. The data was plotted in form of graphs of seismic energy rate inverse versus time with FFM graphical technique approach uses simple linear regression. The data quality control used to increase the time precision employs the data correlation coefficient value of the seismic energy rate inverse versus time. From the results of graph analysis, the precision of prediction time toward the real time of eruption vary between -2.86 up to 5.49 days.

Seismic energy data analysis of Merapi volcano to test the eruption time prediction using materials failure forecast method (FFM)

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

Anggraeni, Novia Antika, E-mail: novia.antika.a@gmail.com

The test of eruption time prediction is an effort to prepare volcanic disaster mitigation, especially in the volcano’s inhabited slope area, such as Merapi Volcano. The test can be conducted by observing the increase of volcanic activity, such as seismicity degree, deformation and SO2 gas emission. One of methods that can be used to predict the time of eruption is Materials Failure Forecast Method (FFM). Materials Failure Forecast Method (FFM) is a predictive method to determine the time of volcanic eruption which was introduced by Voight (1988). This method requires an increase in the rate of change, or acceleration ofmore » the observed volcanic activity parameters. The parameter used in this study is the seismic energy value of Merapi Volcano from 1990 – 2012. The data was plotted in form of graphs of seismic energy rate inverse versus time with FFM graphical technique approach uses simple linear regression. The data quality control used to increase the time precision employs the data correlation coefficient value of the seismic energy rate inverse versus time. From the results of graph analysis, the precision of prediction time toward the real time of eruption vary between −2.86 up to 5.49 days.« less

Fatigue Behavior of Computer-Aided Design/Computer-Assisted Manufacture Ceramic Abutments as a Function of Design and Ceramics Processing.

PubMed

Kelly, J Robert; Rungruanganunt, Patchnee

2016-01-01

Zirconia is being widely used, at times apparently by simply copying a metal design into ceramic. Structurally, ceramics are sensitive to both design and processing (fabrication) details. The aim of this work was to examine four computer-aided design/computer-assisted manufacture (CAD/CAM) abutments using a modified International Standards Organization (ISO) implant fatigue protocol to determine performance as a function of design and processing. Two full zirconia and two hybrid (Ti-based) abutments (n = 12 each) were tested wet at 15 Hz at a variety of loads to failure. Failure probability distributions were examined at each load, and when found to be the same, data from all loads were combined for lifetime analysis from accelerated to clinical conditions. Two distinctly different failure modes were found for both full zirconia and Ti-based abutments. One of these for zirconia has been reported clinically in the literature, and one for the Ti-based abutments has been reported anecdotally. The ISO protocol modification in this study forced failures in the abutments; no implant bodies failed. Extrapolated cycles for 10% failure at 70 N were: full zirconia, Atlantis 2 × 10(7) and Straumann 3 × 10(7); and Ti-based, Glidewell 1 × 10(6) and Nobel 1 × 10(21). Under accelerated conditions (200 N), performance differed significantly: Straumann clearly outperformed Astra (t test, P = .013), and the Glidewell Ti-base abutment also outperformed Atlantis zirconia at 200 N (Nobel ran-out; t test, P = .035). The modified ISO protocol in this study produced failures that were seen clinically. The manufacture matters; differences in design and fabrication that influence performance cannot be discerned clinically.

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

DiCostanzo, D; Ayan, A; Woollard, J

Purpose: To predict potential failures of hardware within the Varian TrueBeam linear accelerator in order to proactively replace parts and decrease machine downtime. Methods: Machine downtime is a problem for all radiation oncology departments and vendors. Most often it is the result of unexpected equipment failure, and increased due to lack of in-house clinical engineering support. Preventative maintenance attempts to assuage downtime, but often is ineffective at preemptively preventing many failure modes such as MLC motor failures, the need to tighten a gantry chain, or the replacement of a jaw motor, among other things. To attempt to alleviate downtime, softwaremore » was developed in house that determines the maximum value of each axis enumerated in the Truebeam trajectory log files. After patient treatments, this data is stored in a SQL database. Microsoft Power BI is used to plot the average maximum error of each day of each machine as a function of time. The results are then correlated with actual faults that occurred at the machine with the help of Varian service engineers. Results: Over the course of six months, 76,312 trajectory logs have been written into the database and plotted in Power BI. Throughout the course of analysis MLC motors have been replaced on three machines due to the early warning of the trajectory log analysis. The service engineers have also been alerted to possible gantry issues on one occasion due to the aforementioned analysis. Conclusion: Analyzing the trajectory log data is a viable and effective early warning system for potential failures of the TrueBeam linear accelerator. With further analysis and tightening of the tolerance values used to determine a possible imminent failure, it should be possible to pinpoint future issues more thoroughly and for more axes of motion.« less

Application of Failure Mode and Effects Analysis to Intraoperative Radiation Therapy Using Mobile Electron Linear Accelerators

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

Ciocca, Mario, E-mail: mario.ciocca@cnao.it; Cantone, Marie-Claire; Veronese, Ivan

2012-02-01

Purpose: Failure mode and effects analysis (FMEA) represents a prospective approach for risk assessment. A multidisciplinary working group of the Italian Association for Medical Physics applied FMEA to electron beam intraoperative radiation therapy (IORT) delivered using mobile linear accelerators, aiming at preventing accidental exposures to the patient. Methods and Materials: FMEA was applied to the IORT process, for the stages of the treatment delivery and verification, and consisted of three steps: 1) identification of the involved subprocesses; 2) identification and ranking of the potential failure modes, together with their causes and effects, using the risk probability number (RPN) scoring system,more » based on the product of three parameters (severity, frequency of occurrence and detectability, each ranging from 1 to 10); 3) identification of additional safety measures to be proposed for process quality and safety improvement. RPN upper threshold for little concern of risk was set at 125. Results: Twenty-four subprocesses were identified. Ten potential failure modes were found and scored, in terms of RPN, in the range of 42-216. The most critical failure modes consisted of internal shield misalignment, wrong Monitor Unit calculation and incorrect data entry at treatment console. Potential causes of failure included shield displacement, human errors, such as underestimation of CTV extension, mainly because of lack of adequate training and time pressures, failure in the communication between operators, and machine malfunctioning. The main effects of failure were represented by CTV underdose, wrong dose distribution and/or delivery, unintended normal tissue irradiation. As additional safety measures, the utilization of a dedicated staff for IORT, double-checking of MU calculation and data entry and finally implementation of in vivo dosimetry were suggested. Conclusions: FMEA appeared as a useful tool for prospective evaluation of patient safety in radiotherapy. The application of this method to IORT lead to identify three safety measures for risk mitigation.« less

Earthquake Prediction in Large-scale Faulting Experiments

NASA Astrophysics Data System (ADS)

Junger, J.; Kilgore, B.; Beeler, N.; Dieterich, J.

2004-12-01

We study repeated earthquake slip of a 2 m long laboratory granite fault surface with approximately homogenous frictional properties. In this apparatus earthquakes follow a period of controlled, constant rate shear stress increase, analogous to tectonic loading. Slip initiates and accumulates within a limited area of the fault surface while the surrounding fault remains locked. Dynamic rupture propagation and slip of the entire fault surface is induced when slip in the nucleating zone becomes sufficiently large. We report on the event to event reproducibility of loading time (recurrence interval), failure stress, stress drop, and precursory activity. We tentatively interpret these variations as indications of the intrinsic variability of small earthquake occurrence and source physics in this controlled setting. We use the results to produce measures of earthquake predictability based on the probability density of repeating occurrence and the reproducibility of near-field precursory strain. At 4 MPa normal stress and a loading rate of 0.0001 MPa/s, the loading time is ˜25 min, with a coefficient of variation of around 10%. Static stress drop has a similar variability which results almost entirely from variability of the final (rather than initial) stress. Thus, the initial stress has low variability and event times are slip-predictable. The variability of loading time to failure is comparable to the lowest variability of recurrence time of small repeating earthquakes at Parkfield (Nadeau et al., 1998) and our result may be a good estimate of the intrinsic variability of recurrence. Distributions of loading time can be adequately represented by a log-normal or Weibel distribution but long term prediction of the next event time based on probabilistic representation of previous occurrence is not dramatically better than for field-observed small- or large-magnitude earthquake datasets. The gradually accelerating precursory aseismic slip observed in the region of nucleation in these experiments is consistent with observations and theory of Dieterich and Kilgore (1996). Precursory strains can be detected typically after 50% of the total loading time. The Dieterich and Kilgore approach implies an alternative method of earthquake prediction based on comparing real-time strain monitoring with previous precursory strain records or with physically-based models of accelerating slip. Near failure, time to failure t is approximately inversely proportional to precursory slip rate V. Based on a least squares fit to accelerating slip velocity from ten or more events, the standard deviation of the residual between predicted and observed log t is typically 0.14. Scaling these results to natural recurrence suggests that a year prior to an earthquake, failure time can be predicted from measured fault slip rate with a typical error of 140 days, and a day prior to the earthquake with a typical error of 9 hours. However, such predictions require detecting aseismic nucleating strains, which have not yet been found in the field, and on distinguishing earthquake precursors from other strain transients. There is some field evidence of precursory seismic strain for large earthquakes (Bufe and Varnes, 1993) which may be related to our observations. In instances where precursory activity is spatially variable during the interseismic period, as in our experiments, distinguishing precursory activity might be best accomplished with deep arrays of near fault instruments and pattern recognition algorithms such as principle component analysis (Rundle et al., 2000).

Maximal blood flow acceleration analysis in the early diastolic phase for aortocoronary artery bypass grafts: a new transit-time flow measurement predictor of graft failure following coronary artery bypass grafting.

PubMed

Handa, Takemi; Orihashi, Kazumasa; Nishimori, Hideaki; Yamamoto, Masaki

2016-11-01

Maximal graft flow acceleration (max df/dt) determined using transit-time flowmetry (TTFM) in the diastolic phase was assessed as a potential predictor of graft failure for aortocoronary artery (AC) bypass grafts in coronary artery bypass patients. Max df/dt was retrospectively measured in 114 aortocoronary artery bypass grafts. TTFM data were fitted to a 9-polynomial curve, which was derived from the first-derivative curve, to measure max df/dt (9-polynomial max df/dt). Abnormal TTFM was defined as a mean flow of <15 ml/min, a pulsatility index of >5 or a diastolic filling ratio of <50 %. Postoperative assessments were routinely performed by coronary artery angiography (CAG) at 1 year after surgery. Using TTFM, 68 grafts were normal, 4 of which were failing on CAG, and 46 grafts were abnormal, 21 of which were failing on CAG. 9-polynomial max df/dt was significantly lower in abnormal TTFM/failing by the CAG group compared with abnormal TTFM/patent by the CAG group (1.08 ± 0.89 vs. 2.05 ± 1.51 ml/s(2), respectively; P < 0.01, Mann-Whitney U test, Holm adjustment). TTFM 9-polynomial max df/dt in the early diastolic phase may be a promising predictor of future graft failure for AC bypass grafts, particularly in abnormal TTFM grafts.

Flow-accelerated corrosion in power plants. Revision 1

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

Chexal, B.; Horowitz, J.; Dooley, B.

1998-07-01

Flow-Accelerated Corrosion (FAC) is a phenomenon that results in metal loss from piping, vessels, and equipment made of carbon steel. FAC occurs only under certain conditions of flow, chemistry, geometry, and material. Unfortunately, those conditions are common in much of the high-energy piping in nuclear and fossil-fueled power plants. Undetected, FAC will cause leaks and ruptures. Consequently, FAC has become a major issue, particularly for nuclear plants. Although major failures are rare, the consequences can be severe. In 1986, four men in the area of an FAC-induced pipe rupture were killed. Fossil plants too, are subject to FAC. In 1995,more » a failure at a fossil-fired plant caused two fatalities. In addition to concerns about personnel safety, FAC failures can pose challenges to plant safety. Regulatory agencies have therefore required nuclear utilities to institute formal programs to address FAC. Finally, a major FAC failure (like the one that happened in 1997 at a US nuclear power plant) can force a plant to shutdown and purchase replacement power at a price approaching a million dollars per day depending upon the MWe rating of the plant. A great deal of time and money has been spent to develop the technology to predict, detect, and mitigate FAC in order to prevent catastrophic failures. Over time, substantial progress has been made towards understanding and preventing FAC. The results of these efforts include dozens of papers, reports, calculations, and manuals, as well as computer programs and other tools. This book is written to provide a detailed treatment of the entire subject in a single document. Any complex issue requires balancing know-how, the risk of decision making, and a pragmatic engineering solution. This book addresses these by carrying out the necessary R and D and engineering along with plant knowledge to cover all quadrants of Chexal`s four quadrant known-unknown diagram, as seen in Figure i.« less

Two critical tests for the Critical Point earthquake

NASA Astrophysics Data System (ADS)

Tzanis, A.; Vallianatos, F.

2003-04-01

It has been credibly argued that the earthquake generation process is a critical phenomenon culminating with a large event that corresponds to some critical point. In this view, a great earthquake represents the end of a cycle on its associated fault network and the beginning of a new one. The dynamic organization of the fault network evolves as the cycle progresses and a great earthquake becomes more probable, thereby rendering possible the prediction of the cycle’s end by monitoring the approach of the fault network toward a critical state. This process may be described by a power-law time-to-failure scaling of the cumulative seismic release rate. Observational evidence has confirmed the power-law scaling in many cases and has empirically determined that the critical exponent in the power law is typically of the order n=0.3. There are also two theoretical predictions for the value of the critical exponent. Ben-Zion and Lyakhovsky (Pure appl. geophys., 159, 2385-2412, 2002) give n=1/3. Rundle et al. (Pure appl. geophys., 157, 2165-2182, 2000) show that the power-law activation associated with a spinodal instability is essentially identical to the power-law acceleration of Benioff strain observed prior to earthquakes; in this case n=0.25. More recently, the CP model has gained support from the development of more dependable models of regional seismicity with realistic fault geometry that show accelerating seismicity before large events. Essentially, these models involve stress transfer to the fault network during the cycle such, that the region of accelerating seismicity will scale with the size of the culminating event, as for instance in Bowman and King (Geophys. Res. Let., 38, 4039-4042, 2001). It is thus possible to understand the observed characteristics of distributed accelerating seismicity in terms of a simple process of increasing tectonic stress in a region already subjected to stress inhomogeneities at all scale lengths. Then, the region of accelerating seismic release is associated with the region defined by the stress field required to rupture a fault with a specified orientation and rake; it is thus possible to incorporate tectonic information into the analysis. Recent analysis of Greek seismicity shows definite power-law acceleration in two areas along the Hellenic Arc, with critical exponents in the expected range of 0.2-0.3. The first area is in the west Hellenic Arc, (Ionian Sea). The projected time of failure is in the interval 2003.05-2003.19 and the projected magnitude is of the order M=7. Tectonic modeling of the accelerating sequence shows that this may be interpreted in terms of stress transfer from two fault geometries generating very similar patterns of stress increase and stress shadows. The first scenario calls for a right-lateral oblique-slip fault of NE-SW orientation at the west boundary of the Aegean microplate, just east of the island of Kefallinia (Kefallinia Fault Zone). The second scenario predicts rupture in a slightly left-lateral inverse fault of NW-SE orientation, underlying Kefallinia, with mechanisms consisted with that of McKenzie (Geophys. J. R. astr. Soc., 30, 109-185, 1972) for the destructive M=7.3 earthquake of 12 August 1953. Both scenaria are consistent with the regional tectonics and kinematics and both are consistent with fault zones known to have generated large earthquakes in the past. The second area is in the SW Hellenic Arc (Mediterranean Sea). The projected time of failure is 2003.6 +/- 0.6 and the projected magnitude is M=7.1 +/- 0.4. Tectonic modelling of this sequence leads to a unique rupture scenario, on a left-lateral oblique-slip fault, probably lying at intermediate depths between Crete and the Peloponnesus, to the SW of the island of Antikythira. In both cases, the tectonic modeling has revealed the existence of a region of accelerating seismicity at the areas of positive stress transfer and, importantly, a region of power-law decelerating seismicity at the areas of negative stress transfer (stress shadows), i.e. the reverse effect which should be observed if energy was extracted from a fault system. In both cases the critical exponent of the accelerating sequence at the positive-stress-transfer regions is very close 0.25, consistent with the view of the fault network as a Self-Organizing Spinodal moving toward a first order phase transition. The reported observations are consistent with almost all of the theoretical predictions and expectations made in terms of the critical point / stress transfer model of seismogenesis. However, there are reservations as to whether they comprise bona-fide predictions. Time-to-failure modelling of accelerated seismicity is a relatively new field of study with few cases-histories whence to draw experience, most of which in fact comprise retrospective analyses of past earthquakes. Still, very little is known as to the development of real-time situations and their probability of success or failure. Also, the power-law scaling is essentially the result of a renormalisation, in which the process of failure at a small spatial scale and temporarily far from a global event can be remapped to the process of failure at a larger scale and closer to the global event. In consequence, when new elements are added, (i.e. large foreschocks), the sequence is renormalized and the predicted parameters may change, sometimes significantly. Yet another difficulty arises from the fact that even if a full-scale self-organising process is active in the critical area, it is not at all necessary that a large earthquake will occur as soon as the system enters the critical state. The critical point model merely predicts that past this time an earthquake is possible but not certain. The time of the large event may depend on several uncertain factors pertaining to the nucleation process, which may have significant time dependence of their own. Moreover, the stored energy may be dissipated with aseismic (low moment release rate) event(s). Again, the absence of a concrete case history complicates anyone’s ability to make solid inferences. In conclusion, our observations can be considered to be critical tests of the critical point / stress transfer earthquake model. If the expected earthquakes occur, then it is possible that we have a powerful tool. If not, we should contemplate the possibility that this approach has limited predictive capacity and is unsafe in evaluating seismic hazard. The answer is pending and the question is open for discussion.

Accelerated Aging System for Prognostics of Power Semiconductor Devices

NASA Technical Reports Server (NTRS)

Celaya, Jose R.; Vashchenko, Vladislav; Wysocki, Philip; Saha, Sankalita

2010-01-01

Prognostics is an engineering discipline that focuses on estimation of the health state of a component and the prediction of its remaining useful life (RUL) before failure. Health state estimation is based on actual conditions and it is fundamental for the prediction of RUL under anticipated future usage. Failure of electronic devices is of great concern as future aircraft will see an increase of electronics to drive and control safety-critical equipment throughout the aircraft. Therefore, development of prognostics solutions for electronics is of key importance. This paper presents an accelerated aging system for gate-controlled power transistors. This system allows for the understanding of the effects of failure mechanisms, and the identification of leading indicators of failure which are essential in the development of physics-based degradation models and RUL prediction. In particular, this system isolates electrical overstress from thermal overstress. Also, this system allows for a precise control of internal temperatures, enabling the exploration of intrinsic failure mechanisms not related to the device packaging. By controlling the temperature within safe operation levels of the device, accelerated aging is induced by electrical overstress only, avoiding the generation of thermal cycles. The temperature is controlled by active thermal-electric units. Several electrical and thermal signals are measured in-situ and recorded for further analysis in the identification of leading indicators of failures. This system, therefore, provides a unique capability in the exploration of different failure mechanisms and the identification of precursors of failure that can be used to provide a health management solution for electronic devices.

Foil Bearing Starting Considerations and Requirements for Rotorcraft Engine Applications

NASA Technical Reports Server (NTRS)

Radil, Kevin C.; DellaCorte, Christopher

2009-01-01

Foil gas bearings under development for rotorcraft-sized, hot core engine applications have been susceptible to damage from the slow acceleration and rates typically encountered during the pre-ignition stage in conventional engines. Recent laboratory failures have been assumed to be directly linked to operating foil bearings below their lift-off speed while following conventional startup procedures for the engines. In each instance, the continuous sliding contact between the foils and shaft was believed to thermally overload the bearing and cause the engines to fail. These failures highlight the need to characterize required acceleration rates and minimum operating speeds for these applications. In this report, startup experiments were conducted with a large, rotorcraft engine sized foil bearing under moderate load and acceleration rates to identify the proper start procedures needed to avoid bearing failure. The results showed that a bearing under a 39.4 kPa static load can withstand a modest acceleration rate of 500 rpm/s and excessive loitering below the bearing lift-off speed provided an adequate solid lubricant is present.

Failure Modes in Capacitors When Tested Under a Time-Varying Stress

NASA Technical Reports Server (NTRS)

Liu, David (Donhang)

2011-01-01

Power-on failure has been the prevalent failure mechanism for solid tantalum capacitors in decoupling applications. A surge step stress test (SSST) has been previously applied to identify the critical stress level of a capacitor batch to give some predictability to the power-on failure mechanism [1]. But SSST can also be viewed as an electrically destructive test under a time-varying stress (voltage). It consists of rapidly charging the capacitor with incremental voltage increases, through a low resistance in series, until the capacitor under test is electrically shorted. When the reliability of capacitors is evaluated, a highly accelerated life test (HALT) is usually adopted since it is a time-efficient method of determining the failure mechanism; however, a destructive test under a time-varying stress such as SSST is even more time efficient. It usually takes days or weeks to complete a HALT test, but it only takes minutes for a time-varying stress test to produce failures. The advantage of incorporating a specific time-varying stress profile into a statistical model is significant in providing an alternative life test method for quickly revealing the failure mechanism in capacitors. In this paper, a time-varying stress that mimics a typical SSST has been incorporated into the Weibull model to characterize the failure mechanism in different types of capacitors. The SSST circuit and transient conditions for correctly surge testing capacitors are discussed. Finally, the SSST was applied for testing Ta capacitors, polymer aluminum capacitors (PA capacitors), and multi-layer ceramic (MLC) capacitors with both precious metal electrodes (PME) and base metal electrodes (BME). The test results are found to be directly associated with the dielectric layer breakdown in Ta and PA capacitors and are independent of the capacitor values, the way the capacitors were built, and the capacitors manufacturers. The test results also show that MLC capacitors exhibit surge breakdown voltages much higher than the rated voltage and that the breakdown field is inversely proportional to the dielectric layer thickness. The SSST data can also be used to comparatively evaluate the voltage robustness of capacitors for decoupling applications.

Vascular toxicity of urea, a new "old player" in the pathogenesis of chronic renal failure induced cardiovascular diseases.

PubMed

Giardino, Ida; D'Apolito, Maria; Brownlee, Michael; Maffione, Angela Bruna; Colia, Anna Laura; Sacco, Michele; Ferrara, Pietro; Pettoello-Mantovani, Massimo

2017-12-01

Chronic kidney disease in children is an irreversible process that may lead to end-stage renal disease. The mortality rate in children with end-stage renal disease who receive dialysis increased dramatically in the last decade, and it is significantly higher compared with the general pediatric population. Furthermore, dialysis and transplant patients, who have developed end-stage renal disease during childhood, live respectively far less as compared with age/race-matched populations. Different reports show that cardiovascular disease is the leading cause of death in children with end-stage renal disease and in adults with childhood-onset chronic kidney disease, and that children with chronic kidney disease are in the highest risk group for the development of cardiovascular disease. Urea, which is generated in the liver during catabolism of amino acids and other nitrogenous metabolites, is normally excreted into the urine by the kidneys as rapidly as it is produced. When renal function is impaired, increasing concentrations of blood urea will steadily accumulate. For a long time, urea has been considered to have negligible toxicity. However, the finding that plasma urea is the only significant predictor of aortic plaque area fraction in an animal model of chronic renal failure -accelerated atherosclerosis, suggests that the high levels of urea found in chronic dialysis patients might play an important role in accelerated atherosclerosis in this group of patients. The aim of this review was to provide novel insights into the role played by urea in the pathogenesis of accelerated cardiovascular disease in renal failure.

Vascular toxicity of urea, a new “old player” in the pathogenesis of chronic renal failure induced cardiovascular diseases

PubMed Central

D’Apolito, Maria; Brownlee, Michael; Maffione, Angela Bruna; Colia, Anna Laura; Sacco, Michele; Ferrara, Pietro; Pettoello-Mantovani, Massimo

2017-01-01

Chronic kidney disease in children is an irreversible process that may lead to end-stage renal disease. The mortality rate in children with end-stage renal disease who receive dialysis increased dramatically in the last decade, and it is significantly higher compared with the general pediatric population. Furthermore, dialysis and transplant patients, who have developed end-stage renal disease during childhood, live respectively far less as compared with age/race-matched populations. Different reports show that cardiovascular disease is the leading cause of death in children with end-stage renal disease and in adults with childhood-onset chronic kidney disease, and that children with chronic kidney disease are in the highest risk group for the development of cardiovascular disease. Urea, which is generated in the liver during catabolism of amino acids and other nitrogenous metabolites, is normally excreted into the urine by the kidneys as rapidly as it is produced. When renal function is impaired, increasing concentrations of blood urea will steadily accumulate. For a long time, urea has been considered to have negligible toxicity. However, the finding that plasma urea is the only significant predictor of aortic plaque area fraction in an animal model of chronic renal failure -accelerated atherosclerosis, suggests that the high levels of urea found in chronic dialysis patients might play an important role in accelerated atherosclerosis in this group of patients. The aim of this review was to provide novel insights into the role played by urea in the pathogenesis of accelerated cardiovascular disease in renal failure. PMID:29483797

Mediation Analysis with Survival Outcomes: Accelerated Failure Time vs. Proportional Hazards Models.

PubMed

Gelfand, Lois A; MacKinnon, David P; DeRubeis, Robert J; Baraldi, Amanda N

2016-01-01

Survival time is an important type of outcome variable in treatment research. Currently, limited guidance is available regarding performing mediation analyses with survival outcomes, which generally do not have normally distributed errors, and contain unobserved (censored) events. We present considerations for choosing an approach, using a comparison of semi-parametric proportional hazards (PH) and fully parametric accelerated failure time (AFT) approaches for illustration. We compare PH and AFT models and procedures in their integration into mediation models and review their ability to produce coefficients that estimate causal effects. Using simulation studies modeling Weibull-distributed survival times, we compare statistical properties of mediation analyses incorporating PH and AFT approaches (employing SAS procedures PHREG and LIFEREG, respectively) under varied data conditions, some including censoring. A simulated data set illustrates the findings. AFT models integrate more easily than PH models into mediation models. Furthermore, mediation analyses incorporating LIFEREG produce coefficients that can estimate causal effects, and demonstrate superior statistical properties. Censoring introduces bias in the coefficient estimate representing the treatment effect on outcome-underestimation in LIFEREG, and overestimation in PHREG. With LIFEREG, this bias can be addressed using an alternative estimate obtained from combining other coefficients, whereas this is not possible with PHREG. When Weibull assumptions are not violated, there are compelling advantages to using LIFEREG over PHREG for mediation analyses involving survival-time outcomes. Irrespective of the procedures used, the interpretation of coefficients, effects of censoring on coefficient estimates, and statistical properties should be taken into account when reporting results.

Real-Time Adaptive Control Allocation Applied to a High Performance Aircraft

NASA Technical Reports Server (NTRS)

Davidson, John B.; Lallman, Frederick J.; Bundick, W. Thomas

2001-01-01

Abstract This paper presents the development and application of one approach to the control of aircraft with large numbers of control effectors. This approach, referred to as real-time adaptive control allocation, combines a nonlinear method for control allocation with actuator failure detection and isolation. The control allocator maps moment (or angular acceleration) commands into physical control effector commands as functions of individual control effectiveness and availability. The actuator failure detection and isolation algorithm is a model-based approach that uses models of the actuators to predict actuator behavior and an adaptive decision threshold to achieve acceptable false alarm/missed detection rates. This integrated approach provides control reconfiguration when an aircraft is subjected to actuator failure, thereby improving maneuverability and survivability of the degraded aircraft. This method is demonstrated on a next generation military aircraft Lockheed-Martin Innovative Control Effector) simulation that has been modified to include a novel nonlinear fluid flow control control effector based on passive porosity. Desktop and real-time piloted simulation results demonstrate the performance of this integrated adaptive control allocation approach.

Experimental Evidence of Accelerated Seismic Release without Critical Failure in Acoustic Emissions of Compressed Nanoporous Materials

NASA Astrophysics Data System (ADS)

Baró, Jordi; Dahmen, Karin A.; Davidsen, Jörn; Planes, Antoni; Castillo, Pedro O.; Nataf, Guillaume F.; Salje, Ekhard K. H.; Vives, Eduard

2018-06-01

The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based (SiO2 ) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary, and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by mechanisms of transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models.

Deformation and failure of single- and multi-phase silicate liquids: seismic precursors and mechanical work

NASA Astrophysics Data System (ADS)

Vasseur, Jeremie; Lavallée, Yan; Hess, Kai-Uwe; Wassermann, Joachim; Dingwell, Donald B.

2013-04-01

Along with many others, volcanic unrest is regarded as a catastrophic material failure phenomenon and is often preceded by diverse precursory signals. Although a volcanic system intrinsically behave in a non-linear and stochastic way, these precursors display systematic evolutionary trends to upcoming eruptions. Seismic signals in particular are in general dramatically increasing prior to an eruption and have been extensively reported to show accelerating rates through time, as well as in the laboratory before failure of rock samples. At the lab-scale, acoustic emissions (AE) are high frequency transient stress waves used to track fracture initiation and propagation inside a rock sample. Synthesized glass samples featuring a range of porosities (0 - 30%) and natural rock samples from volcán de Colima, Mexico, have been failed under high temperature uniaxial compression experiments at constant stresses and strain rates. Using the monitored AEs and the generated mechanical work during deformation, we investigated the evolutionary trends of energy patterns associated to different degrees of heterogeneity. We observed that the failure of dense, poorly porous glasses is achieved by exceeding elevated strength and thus requires a significant accumulation of strain, meaning only pervasive small-scale cracking is occurring. More porous glasses as well as volcanic samples need much lower applied stress and deformation to fail, as fractures are nucleating, propagating and coalescing into localized large-scale cracks, taking the advantage of the existence of numerous defects (voids for glasses, voids and crystals for volcanic rocks). These observations demonstrate that the mechanical work generated through cracking is efficiently distributed inside denser and more homogeneous samples, as underlined by the overall lower AE energy released during experiments. In contrast, the quicker and larger AE energy released during the loading of heterogeneous samples shows that the mechanical work tends to concentrate in specific weak regions facilitating dynamical failure of the material through dissipation of the accumulated strain energy. Applying a statistical Global Linearization Method (GLM) in multi-phase silicate liquids samples leads to a maximum likelihood power-law fit of the accelerating rates of released AEs. The calculated α exponent of the famous empirical Failure Forecast Method (FFM) tends to decrease from 2 towards 1 with increasing porosity, suggesting a shift towards an idealized exponential-like acceleration. Single-phase silicate liquids behave more elastically during deformation without much cracking and suddenly releasing their accumulated strain energy at failure, implying less clear trends in monitored AEs. In a predictive prospective, these results support the fact that failure forecasting power is enhanced by the presence of heterogeneities inside a material.

The Remote Detection of Incipient Catastrophic Failure in Large Landslides

NASA Astrophysics Data System (ADS)

Petley, D.; Bulmer, M. H.; Murphy, W.; Mantovani, F.

2001-12-01

Landslide movement is commonly associated with brittle failure and ductile deformation. Kilburn and Petley (2001) proposed that cracking in landslides occurs due to downslope stress acting on the deforming horizon. If the assumption that a given crack event breaks a fixed distance of unbroken rock or soil the rate of cracking becomes equivalent to the number of crack events per unit time. Where crack growth (not nucleation) is occurring, the inverse rate of displacement changes linearly with time. Failure can be assumed to be the time at which displacement rates become infinitely large. Thus, for a slope heading towards catastrophic failure due to the development of a failure plane, this relationship would be linear, with the point at which failure will occur being the time when the line intercepts the x-axis. Increasing rates of deformation associated with ductile processes of crack nucleation would yield a curve with a negative gradient asymptopic to the x-axis. This hypothesis is being examined. In the 1960 movement of the Vaiont slide, Italy, although the rate of movement was accelerating, the plot of 1/deformation against time shows that it was increasing towards a steady state deformation. This movement has been associated with a low accumulated strain ductile phase of movement. In the 1963 movement event, the trend is linear. This was associated with a brittle phase of movement. A plot of 1/deformation against time for movement of the debris flow portion of the Tessina landslide (1998) shows a curve with a negative gradient asymptopic to the x-axis. This indicates that the debris flow moved as a result of ductile deformation processes. Plots of movement data for the Black Ven landslide over 1999 and 2001 also show curves that correlate with known deformation and catastrophic phases. The model results suggest there is a definable deformation pattern that is diagnostic of landslides approaching catastrophic failure. This pattern can be differentiated from landslides that are undergoing ductile deformation and those that are suffering crack nucleation.

Estimation of lifetime distributions on 1550-nm DFB laser diodes using Monte-Carlo statistic computations

NASA Astrophysics Data System (ADS)

Deshayes, Yannick; Verdier, Frederic; Bechou, Laurent; Tregon, Bernard; Danto, Yves; Laffitte, Dominique; Goudard, Jean Luc

2004-09-01

High performance and high reliability are two of the most important goals driving the penetration of optical transmission into telecommunication systems ranging from 880 nm to 1550 nm. Lifetime prediction defined as the time at which a parameter reaches its maximum acceptable shirt still stays the main result in terms of reliability estimation for a technology. For optoelectronic emissive components, selection tests and life testing are specifically used for reliability evaluation according to Telcordia GR-468 CORE requirements. This approach is based on extrapolation of degradation laws, based on physics of failure and electrical or optical parameters, allowing both strong test time reduction and long-term reliability prediction. Unfortunately, in the case of mature technology, there is a growing complexity to calculate average lifetime and failure rates (FITs) using ageing tests in particular due to extremely low failure rates. For present laser diode technologies, time to failure tend to be 106 hours aged under typical conditions (Popt=10 mW and T=80°C). These ageing tests must be performed on more than 100 components aged during 10000 hours mixing different temperatures and drive current conditions conducting to acceleration factors above 300-400. These conditions are high-cost, time consuming and cannot give a complete distribution of times to failure. A new approach consists in use statistic computations to extrapolate lifetime distribution and failure rates in operating conditions from physical parameters of experimental degradation laws. In this paper, Distributed Feedback single mode laser diodes (DFB-LD) used for 1550 nm telecommunication network working at 2.5 Gbit/s transfer rate are studied. Electrical and optical parameters have been measured before and after ageing tests, performed at constant current, according to Telcordia GR-468 requirements. Cumulative failure rates and lifetime distributions are computed using statistic calculations and equations of drift mechanisms versus time fitted from experimental measurements.

Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends

NASA Astrophysics Data System (ADS)

Coyle, Richard J.; Sweatman, Keith; Arfaei, Babak

2015-09-01

Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. The electronic packaging industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu alloys first established as replacements for eutectic SnPb. This paper discusses the results from Pb-free solder joint reliability programs sponsored by two industry consortia. The characteristic life in accelerated thermal cycling is reported for 12 different Pb-free solder alloys and a SnPb control in 9 different accelerated thermal cycling test profiles in terms of the effects of component type, accelerated thermal cycling profile and dwell time. Microstructural analysis on assembled and failed samples was performed to investigate the effect of initial microstructure and its evolution during accelerated thermal cycling test. A significant finding from the study is that the beneficial effect of Ag on accelerated thermal cycling reliability (measured by characteristic lifetime) diminishes as the severity of the accelerated thermal cycling, defined by greater ΔT, higher peak temperature, and longer dwell time increases. The results also indicate that all the Pb-free solders are more reliable in accelerated thermal cycling than the SnPb alloy they have replaced. Suggestions are made for future work, particularly with respect to the continued evolution of alloy development for emerging application requirements and the value of using advanced analytical methods to provide a better understanding of the effect of microstructure and its evolution on accelerated thermal cycling performance.

The role of resting duration in the kinematic pattern of two consecutive bench press sets to failure in elite sprint kayakers.

PubMed

García-López, D; Herrero, J A; Abadía, O; García-Isla, F J; Ualí, I; Izquierdo, M

2008-09-01

This study aimed to investigate the role of rest period duration (RP) on the time course of the acceleration portion (AP) and mean velocity of the concentric phase across two bench press sets to failure with a submaximal load (60% of the 1RM) using different RP. Ten elite junior kayakers performed, on four different days, two consecutive bench press sets to failure, allowing randomly 1-, 2-, 3- and 4-min RP between sets. AP reached a maximal value of 66% of the concentric movement time. This maximal AP was observed in repetition number 2 or 3, and then AP declined during the set, with a significant decrease when the number of repetitions was over 80% of the total number of repetitions performed. AP and lifting velocity patterns of the concentric phase were not altered during a second set to failure, regardless of RP. However, when velocity was expressed in absolute terms, 1-min RP was insufficient to maintain the average lifting velocity during the second set, compared to the first one. These results may be of use in selecting number of repetitions and resting duration in order to ensure optimal maintenance of the accelerative portion of concentric movement time with different resting-period durations.

Generalized Accelerated Failure Time Spatial Frailty Model for Arbitrarily Censored Data

PubMed Central

Zhou, Haiming; Hanson, Timothy; Zhang, Jiajia

2017-01-01

Flexible incorporation of both geographical patterning and risk effects in cancer survival models is becoming increasingly important, due in part to the recent availability of large cancer registries. Most spatial survival models stochastically order survival curves from different subpopulations. However, it is common for survival curves from two subpopulations to cross in epidemiological cancer studies and thus interpretable standard survival models can not be used without some modification. Common fixes are the inclusion of time-varying regression effects in the proportional hazards model or fully non-parametric modeling, either of which destroys any easy interpretability from the fitted model. To address this issue, we develop a generalized accelerated failure time model which allows stratification on continuous or categorical covariates, as well as providing per-variable tests for whether stratification is necessary via novel approximate Bayes factors. The model is interpretable in terms of how median survival changes and is able to capture crossing survival curves in the presence of spatial correlation. A detailed Markov chain Monte Carlo algorithm is presented for posterior inference and a freely available function frailtyGAFT is provided to fit the model in the R package spBayesSurv. We apply our approach to a subset of the prostate cancer data gathered for Louisiana by the Surveillance, Epidemiology, and End Results program of the National Cancer Institute. PMID:26993982

Risk factors associated with rural water supply failure: A 30-year retrospective study of handpumps on the south coast of Kenya.

PubMed

Foster, Tim; Willetts, Juliet; Lane, Mike; Thomson, Patrick; Katuva, Jacob; Hope, Rob

2018-06-01

An improved understanding of failure risks for water supplies in rural sub-Saharan Africa will be critical to achieving the global goal of safe water for all by 2030. In the absence of longitudinal biophysical and operational data, investigations into water point failure risk factors have to date been limited to cross-sectional research designs. This retrospective cohort study applies survival analysis to identify factors that predict failure risks for handpumps installed on boreholes along the south coast of Kenya from the 1980s. The analysis is based on a unique dataset linking attributes of >300 water points at the time of installation with their operational lifespan over the following decades. Cox proportional hazards and accelerated failure time models suggest water point failure risks are higher and lifespans are shorter when water supplied is more saline, static water level is deeper, and groundwater is pumped from an unconsolidated sand aquifer. The risk of failure also appears to grow as distance to spare part suppliers increases. To bolster the sustainability of rural water services and ensure no community is left behind, post-construction support mechanisms will need to mitigate heterogeneous environmental and geographical challenges. Further studies are needed to better understand the causal pathways that underlie these risk factors in order to inform policies and practices that ensure water services are sustained even where unfavourable conditions prevail. Copyright © 2018 Elsevier B.V. All rights reserved.

Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

NASA Astrophysics Data System (ADS)

Sun, Huarui; Bajo, Miguel Montes; Uren, Michael J.; Kuball, Martin

2015-01-01

Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage "hot spots" at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7-0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Degradation phenomena in laser diodes

NASA Astrophysics Data System (ADS)

Beister, G.; Krispin, P.; Maege, J.; Richter, G.; Weber, H.; Rechenberg, I.

1988-11-01

Accelerated tests on GaAlAs/GaAs double heterostructure laser diodes showed, in agreement with earlier results on light-emitting diodes, that ageing appeared in three distinct forms: initial and slow degradation stages, both obeying a logarithmic time dependence, and a superimposed "gradation" (enhancement of the output power). Measurements made by the method of deep level transient spectroscopy during the accelerated tests on these lasers, operated as light-emitting diodes, revealed the appearance right from the beginning of B levels attributed to the antisite GaAs defects. The B levels appeared again in diodes tested in the lasing mode. In the case of a group of 21 laser diodes the mean time-to-failure was 9000 h at 70°C for 5 mW (in accordance with the Weibull statistics of degradation rates).

Accelerated life testing effects on CMOS microcircuit characteristics, phase 1

NASA Technical Reports Server (NTRS)

Maximow, B.

1976-01-01

An accelerated life test of sufficient duration to generate a minimum of 50% cumulative failures in lots of CMOS devices was conducted to provide a basis for determining the consistency of activation energy at 250 C. An investigation was made to determine whether any thresholds were exceeded during the high temperature testing, which could trigger failure mechanisms unique to that temperature. The usefulness of the 250 C temperature test as a predictor of long term reliability was evaluated.

Accelerated graft dysfunction in heart transplant patients with persistent atrioventricular conduction block.

PubMed

Lee, William; Tay, Andre; Walker, Bruce D; Kuchar, Dennis L; Hayward, Christopher S; Spratt, Phillip; Subbiah, Rajesh N

2016-12-01

Bradyarrhythmia following heart transplantation is common-∼7.5-24% of patients require permanent pacemaker (PPM) implantation. While overall mortality is similar to their non-paced counterparts, the effects of chronic right ventricular pacing (CRVP) in heart transplant patients have not been studied. We aim to examine the effects of CRVP on heart failure and mortality in heart transplant patients. Records of heart transplant recipients requiring PPM at St Vincent's Hospital, Sydney, Australia between January 1990 and January 2015 were examined. Patient's without a right ventricular (RV) pacing lead or a follow-up time of <1 year were excluded. Patients with pre-existing abnormal left ventricular function (<50%) were analysed separately. Patients were grouped by pacing dependence (100% pacing dependent vs. non-pacing dependent). The primary endpoint was clinical or echocardiographic heart failure (<35%) in the first 5 years post-PPM. Thirty-three of 709 heart transplant recipients were studied. Two patients had complete RV pacing dependence, and the remaining 31 patients had varying degrees of pacing requirement, with an underlying ventricular escape rhythm. The primary endpoint occurred significantly more in the pacing-dependent group; 2 (100%) compared with 2 (6%) of the non pacing dependent group (P < 0.0001 by log-rank analysis, HR = 24.58). Non-pacing-dependent patients had reversible causes for heart failure, unrelated to pacing. In comparison, there was no other cause of heart failure in the pacing-dependent group. Permanent atrioventricular block is rare in the heart transplant population. We have demonstrated CRVP as a potential cause of accelerated graft failure in pacing-dependent heart transplant patients. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.

Accelerated Thermal Cycling and Failure Mechanisms

NASA Technical Reports Server (NTRS)

Ghaffarian, R.

1999-01-01

This paper reviews the accelerated thermal cycling test methods that are currently used by industry to characterize the interconnect reliability of commercial-off-the-shelf (COTS) ball grid array (BGA) and chip scale package (CSP) assemblies.

Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

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

Cabet, Celine; Carroll, Laura; Wright, Richard

Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degreesmore » C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.« less

A Validation Study of the Rank-Preserving Structural Failure Time Model: Confidence Intervals and Unique, Multiple, and Erroneous Solutions.

PubMed

Ouwens, Mario; Hauch, Ole; Franzén, Stefan

2018-05-01

The rank-preserving structural failure time model (RPSFTM) is used for health technology assessment submissions to adjust for switching patients from reference to investigational treatment in cancer trials. It uses counterfactual survival (survival when only reference treatment would have been used) and assumes that, at randomization, the counterfactual survival distribution for the investigational and reference arms is identical. Previous validation reports have assumed that patients in the investigational treatment arm stay on therapy throughout the study period. To evaluate the validity of the RPSFTM at various levels of crossover in situations in which patients are taken off the investigational drug in the investigational arm. The RPSFTM was applied to simulated datasets differing in percentage of patients switching, time of switching, underlying acceleration factor, and number of patients, using exponential distributions for the time on investigational and reference treatment. There were multiple scenarios in which two solutions were found: one corresponding to identical counterfactual distributions, and the other to two different crossing counterfactual distributions. The same was found for the hazard ratio (HR). Unique solutions were observed only when switching patients were on investigational treatment for <40% of the time that patients in the investigational arm were on treatment. Distributions other than exponential could have been used for time on treatment. An HR equal to 1 is a necessary but not always sufficient condition to indicate acceleration factors associated with equal counterfactual survival. Further assessment to distinguish crossing counterfactual curves from equal counterfactual curves is especially needed when the time that switchers stay on investigational treatment is relatively long compared to the time direct starters stay on investigational treatment.

Disparity between online and offline tests in accelerated aging tests of LED lamps under electric stress.

PubMed

Wang, Yao; Jing, Lei; Ke, Hong-Liang; Hao, Jian; Gao, Qun; Wang, Xiao-Xun; Sun, Qiang; Xu, Zhi-Jun

2016-09-20

The accelerated aging tests under electric stress for one type of LED lamp are conducted, and the differences between online and offline tests of the degradation of luminous flux are studied in this paper. The transformation of the two test modes is achieved with an adjustable AC voltage stabilized power source. Experimental results show that the exponential fitting of the luminous flux degradation in online tests possesses a higher fitting degree for most lamps, and the degradation rate of the luminous flux by online tests is always lower than that by offline tests. Bayes estimation and Weibull distribution are used to calculate the failure probabilities under the accelerated voltages, and then the reliability of the lamps under rated voltage of 220 V is estimated by use of the inverse power law model. Results show that the relative error of the lifetime estimation by offline tests increases as the failure probability decreases, and it cannot be neglected when the failure probability is less than 1%. The relative errors of lifetime estimation are 7.9%, 5.8%, 4.2%, and 3.5%, at the failure probabilities of 0.1%, 1%, 5%, and 10%, respectively.

Failure Scenarios and Mitigations for the BABAR Superconducting Solenoid

NASA Astrophysics Data System (ADS)

Thompson, EunJoo; Candia, A.; Craddock, W. W.; Racine, M.; Weisend, J. G.

2006-04-01

The cryogenic department at the Stanford Linear Accelerator Center is responsible for the operation, troubleshooting, and upgrade of the 1.5 Tesla superconducting solenoid detector for the BABAR B-factory experiment. Events that disable the detector are rare but significantly impact the availability of the detector for physics research. As a result, a number of systems and procedures have been developed over time to minimize the downtime of the detector, for example improved control systems, improved and automatic backup systems, and spares for all major components. Together they can prevent or mitigate many of the failures experienced by the utilities, mechanical systems, controls and instrumentation. In this paper we describe various failure scenarios, their effect on the detector, and the modifications made to mitigate the effects of the failure. As a result of these modifications the reliability of the detector has increased significantly with only 3 shutdowns of the detector due to cryogenics systems over the last 2 years.

HALT to qualify electronic packages: a proof of concept

NASA Astrophysics Data System (ADS)

Ramesham, Rajeshuni

2014-03-01

A proof of concept of the Highly Accelerated Life Testing (HALT) technique was explored to assess and optimize electronic packaging designs for long duration deep space missions in a wide temperature range (-150°C to +125°C). HALT is a custom hybrid package suite of testing techniques using environments such as extreme temperatures and dynamic shock step processing from 0g up to 50g of acceleration. HALT testing used in this study implemented repetitive shock on the test vehicle components at various temperatures to precipitate workmanship and/or manufacturing defects to show the weak links of the designs. The purpose is to reduce the product development cycle time for improvements to the packaging design qualification. A test article was built using advanced electronic package designs and surface mount technology processes, which are considered useful for a variety of JPL and NASA projects, i.e. (surface mount packages such as ball grid arrays (BGA), plastic ball grid arrays (PBGA), very thin chip array ball grid array (CVBGA), quad flat-pack (QFP), micro-lead-frame (MLF) packages, several passive components, etc.). These packages were daisy-chained and independently monitored during the HALT test. The HALT technique was then implemented to predict reliability and assess survivability of these advanced packaging techniques for long duration deep space missions in much shorter test durations. Test articles were built using advanced electronic package designs that are considered useful in various NASA projects. All the advanced electronic packages were daisychained independently to monitor the continuity of the individual electronic packages. Continuity of the daisy chain packages was monitored during the HALT testing using a data logging system. We were able to test the boards up to 40g to 50g shock levels at temperatures ranging from +125°C to -150°C. The HALT system can deliver 50g shock levels at room temperature. Several tests were performed by subjecting the test boards to various g levels ranging from 5g to 50g, test durations of 10 minutes to 60 minutes, hot temperatures of up to +125°C and cold temperatures down to -150°C. During the HALT test, electrical continuity measurements of the PBGA package showed an open-circuit, whereas the BGA, MLF, and QFPs showed signs of small variations of electrical continuity measurements. The electrical continuity anomaly of the PBGA occurred in the test board within 12 hours of commencing the accelerated test. Similar test boards were assembled, thermal cycled independently from -150°C to +125°C and monitored for electrical continuity through each package design. The PBGA package on the test board showed an anomalous electrical continuity behavior after 959 thermal cycles. Each thermal cycle took around 2.33 hours, so that a total test time to failure of the PBGA was 2,237 hours (or ~3.1 months) due to thermal cycling alone. The accelerated technique (thermal cycling + shock) required only 12 hours to cause a failure in the PBGA electronic package. Compared to the thermal cycle only test, this was an acceleration of ~186 times (more than 2 orders of magnitude). This acceleration process can save significant time and resources for predicting the life of a package component in a given environment, assuming the failure mechanisms are similar in both the tests. Further studies are in progress to make systematic evaluations of the HALT technique on various other advanced electronic packaging components on the test board. With this information one will be able to estimate the number of mission thermal cycles to failure with a much shorter test program. Further studies are in progress to make systematic study of various components, constant temperature range for both the tests. Therefore, one can estimate the number of hours to fail in a given thermal and shock levels for a given test board physical properties.

Creep rupture of polymer-matrix composites

NASA Technical Reports Server (NTRS)

Brinson, H. F.; Morris, D. H.; Griffith, W. I.

1981-01-01

The time-dependent creep-rupture process in graphite-epoxy laminates is examined as a function of temperature and stress level. Moisture effects are not considered. An accelerated characterization method of composite-laminate viscoelastic modulus and strength properties is reviewed. It is shown that lamina-modulus master curves can be obtained using a minimum of normally performed quality-control-type testing. Lamina-strength master curves, obtained by assuming a constant-strain-failure criterion, are presented along with experimental data, and reasonably good agreement is shown to exist between the two. Various phenomenological delayed failure models are reviewed and two (the modified rate equation and the Larson-Miller parameter method) are compared to creep-rupture data with poor results.

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

Willen, E.

The development of superconducting wire and cable in the late 20th century enabled high field magnets and thus much higher beam collision energies in accelerators. These higher collision energies have allowed experiments to probe further into the structure of matter at the most fundamental, subatomic level. The behavior of the early universe, where these high energies prevailed, and its evolution over time are what these experiments seek to investigate. The subject has aroused the curiosity of not only scientists but of the public as well and has facilitated the support needed to build and operate such expensive machines and experiments.more » The path forward has not been easy, however. Success in most projects has been mixed with failure, progress with ineptitude. The building of high energy accelerators is mostly a story of capable people doing their best to develop new and unusual technology toward some defined goal, with success and failure in uneven measure along the way. It is also a story of administrative imperatives that have had unpredictable effects on a project’s success, depending mostly on the people in the administrative roles and the decisions that they have made.« less

Building Magnets at Brookhaven National Laboratory: A Condensed Account

NASA Astrophysics Data System (ADS)

Willen, Erich

2017-09-01

The development of superconducting wire and cable in the late twentieth century enabled high-field magnets and thus much higher beam-collision energies in accelerators. These higher collision energies have allowed experimentalists to probe further into the structure of matter at the most fundamental, subatomic level. The behavior of the early universe, where these high energies prevailed, and its evolution over time are the realm their experiments seek to investigate. The subject has aroused the curiosity of the public as well as scientists and has facilitated the support needed to build and operate such expensive machines and experiments. The path forward has not been easy, however. Success in most projects has been mixed with failure, progress with ineptitude. The building of high energy accelerators is mostly a story of capable people doing their best to develop new and unusual technology toward some defined goal, facing both success and failure along the way. It is also a story of administrative imperatives that had unpredictable effects on a project's success, depending mostly on the people in the administrative roles and the decisions that they made.

Mediation Analysis with Survival Outcomes: Accelerated Failure Time vs. Proportional Hazards Models

PubMed Central

Gelfand, Lois A.; MacKinnon, David P.; DeRubeis, Robert J.; Baraldi, Amanda N.

2016-01-01

Objective: Survival time is an important type of outcome variable in treatment research. Currently, limited guidance is available regarding performing mediation analyses with survival outcomes, which generally do not have normally distributed errors, and contain unobserved (censored) events. We present considerations for choosing an approach, using a comparison of semi-parametric proportional hazards (PH) and fully parametric accelerated failure time (AFT) approaches for illustration. Method: We compare PH and AFT models and procedures in their integration into mediation models and review their ability to produce coefficients that estimate causal effects. Using simulation studies modeling Weibull-distributed survival times, we compare statistical properties of mediation analyses incorporating PH and AFT approaches (employing SAS procedures PHREG and LIFEREG, respectively) under varied data conditions, some including censoring. A simulated data set illustrates the findings. Results: AFT models integrate more easily than PH models into mediation models. Furthermore, mediation analyses incorporating LIFEREG produce coefficients that can estimate causal effects, and demonstrate superior statistical properties. Censoring introduces bias in the coefficient estimate representing the treatment effect on outcome—underestimation in LIFEREG, and overestimation in PHREG. With LIFEREG, this bias can be addressed using an alternative estimate obtained from combining other coefficients, whereas this is not possible with PHREG. Conclusions: When Weibull assumptions are not violated, there are compelling advantages to using LIFEREG over PHREG for mediation analyses involving survival-time outcomes. Irrespective of the procedures used, the interpretation of coefficients, effects of censoring on coefficient estimates, and statistical properties should be taken into account when reporting results. PMID:27065906

Accelerated testing for studying pavement design and performance (FY 2004) : research summary.

DOT National Transportation Integrated Search

2009-03-01

The thirteenth full-scale Accelerated Pavement Test (APT) experiment at the Civil Infrastructure Laboratory (CISL) of Kansas State University aimed to determine the response and the failure mode of thin concrete overlays.

Membrane Accelerated Stress Test Development for Polymer Electrolyte Fuel Cell Durability Validated Using Field and Drive Cycle Testing

DOE PAGES

Mukundan, Rangachary; Baker, Andrew M.; Kusoglu, Ahmet; ...

2018-03-01

A combined chemical/mechanical accelerated stress test (AST) was developed for proton exchange membrane (PEM) fuel cells based on relative humidity cycling (RHC) between dry and saturated gases at open circuit voltage (OCV). Membrane degradation and failure were investigated using scanning electron microscopy and small- and wide-angle X-ray scattering. Changes to membrane thickness, hydrophilic domain spacing, and crystallinity were observed to be most similar between field-operated cells and OCV RHC ASTs, where local thinning and divot-type defects are the primary failure modes. While RHC in air also reproduces these failure modes, it is not aggressive enough to differentiate between different membranemore » types in >1,333 hours (55 days) of testing. Conversely, steady-state OCV tests result in significant ionomer morphology changes and global thinning, which do not replicate field degradation and failure modes. It is inferred that during the OCV RHC AST, the decay of the membrane's mechanical properties is accelerated such that materials can be evaluated in hundreds, instead of thousands, of hours, while replicating the degradation and failure modes of field operation; associated AST protocols are recommended as OCV RHC at 90°C for 500 hours with wet/dry cycle durations of 30s/45s and 2m/2m for automotive and bus operation, respectively.« less

Fatigue Failure of External Hexagon Connections on Cemented Implant-Supported Crowns.

PubMed

Malta Barbosa, João; Navarro da Rocha, Daniel; Hirata, Ronaldo; Freitas, Gileade; Bonfante, Estevam A; Coelho, Paulo G

2018-01-17

To evaluate the probability of survival and failure modes of different external hexagon connection systems restored with anterior cement-retained single-unit crowns. The postulated null hypothesis was that there would be no differences under accelerated life testing. Fifty-four external hexagon dental implants (∼4 mm diameter) were used for single cement-retained crown replacement and divided into 3 groups: (3i) Full OSSEOTITE, Biomet 3i (n = 18); (OL) OEX P4, Osseolife Implants (n = 18); and (IL) Unihex, Intra-Lock International (n = 18). Abutments were torqued to the implants, and maxillary central incisor crowns were cemented and subjected to step-stress-accelerated life testing in water. Use-level probability Weibull curves and probability of survival for a mission of 100,000 cycles at 200 N (95% 2-sided confidence intervals) were calculated. Stereo and scanning electron microscopes were used for failure inspection. The beta values for 3i, OL, and IL (1.60, 1.69, and 1.23, respectively) indicated that fatigue accelerated the failure of the 3 groups. Reliability for the 3i and OL (41% and 68%, respectively) was not different between each other, but both were significantly lower than IL group (98%). Abutment screw fracture was the failure mode consistently observed in all groups. Because the reliability was significantly different between the 3 groups, our postulated null hypothesis was rejected.

Membrane Accelerated Stress Test Development for Polymer Electrolyte Fuel Cell Durability Validated Using Field and Drive Cycle Testing

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

Mukundan, Rangachary; Baker, Andrew M.; Kusoglu, Ahmet

A combined chemical/mechanical accelerated stress test (AST) was developed for proton exchange membrane (PEM) fuel cells based on relative humidity cycling (RHC) between dry and saturated gases at open circuit voltage (OCV). Membrane degradation and failure were investigated using scanning electron microscopy and small- and wide-angle X-ray scattering. Changes to membrane thickness, hydrophilic domain spacing, and crystallinity were observed to be most similar between field-operated cells and OCV RHC ASTs, where local thinning and divot-type defects are the primary failure modes. While RHC in air also reproduces these failure modes, it is not aggressive enough to differentiate between different membranemore » types in >1,333 hours (55 days) of testing. Conversely, steady-state OCV tests result in significant ionomer morphology changes and global thinning, which do not replicate field degradation and failure modes. It is inferred that during the OCV RHC AST, the decay of the membrane's mechanical properties is accelerated such that materials can be evaluated in hundreds, instead of thousands, of hours, while replicating the degradation and failure modes of field operation; associated AST protocols are recommended as OCV RHC at 90°C for 500 hours with wet/dry cycle durations of 30s/45s and 2m/2m for automotive and bus operation, respectively.« less

Linear accelerator-based stereotactic radiosurgery for brainstem metastases: the Dana-Farber/Brigham and Women's Cancer Center experience.

PubMed

Kelly, Paul J; Lin, Yijie Brittany; Yu, Alvin Y C; Ropper, Alexander E; Nguyen, Paul L; Marcus, Karen J; Hacker, Fred L; Weiss, Stephanie E

2011-09-01

To review the safety and efficacy of linear accelerator-based stereotactic radiosurgery (SRS) for brainstem metastases. We reviewed all patients with brain metastases treated with SRS at DF/BWCC from 2001 to 2009 to identify patients who had SRS to a single brainstem metastasis. Overall survival and freedom-from-local failure rates were calculated from the date of SRS using the Kaplan-Meier method. Prognostic factors were evaluated using the log-rank test and Cox proportional hazards model. A total of 24 consecutive patients with brainstem metastases had SRS. At the time of SRS, 21/24 had metastatic lesions elsewhere within the brain. 23/24 had undergone prior WBRT. Primary diagnoses included eight NSCLC, eight breast cancer, three melanoma, three renal cell carcinoma and two others. Median dose was 13 Gy (range, 8-16). One patient had fractionated SRS 5 Gy ×5. Median target volume was 0.2 cc (range, 0.02-2.39). The median age was 57 years (range, 42-92). Follow-up information was available in 22/24 cases. At the time of analysis, 18/22 patients (82%) had died. The median overall survival time was 5.3 months (range, 0.8-21.1 months). The only prognostic factor that trended toward statistical significance for overall survival was the absence of synchronous brain metastasis at the time of SRS; 1-year overall survival was 31% with versus 67% without synchronous brain metastasis (log rank P = 0.11). Non-significant factors included primary tumor histology and status of extracranial disease (progressing vs. stable/absent). Local failure occurred in 4/22 cases (18%). Actuarial freedom from local failure for all cases was 78.6% at 1 year. RTOG grade 3 toxicities were recorded in two patients (ataxia, confusion). Linac-based SRS for small volume brainstem metastases using a median dose of 13 Gy is associated with acceptable local control and low morbidity.

Time-Dependent Behavior of High-Strength Kevlar and Vectran Webbing

NASA Technical Reports Server (NTRS)

Jones, Thomas C.; Doggett, William R.

2014-01-01

High-strength Kevlar and Vectran webbings are currently being used by both NASA and industry as the primary load-bearing structure in inflatable space habitation modules. The time-dependent behavior of high-strength webbing architectures is a vital area of research that is providing critical material data to guide a more robust design process for this class of structures. This paper details the results of a series of time-dependent tests on 1-inch wide webbing including an initial set of comparative tests between specimens that underwent realtime and accelerated creep at 65 and 70% of their ultimate tensile strength. Variability in the ultimate tensile strength of the webbings is investigated and compared with variability in the creep life response. Additional testing studied the effects of load and displacement rate, specimen length and the time-dependent effects of preconditioning the webbings. The creep test facilities, instrumentation and test procedures are also detailed. The accelerated creep tests display consistently longer times to failure than their real-time counterparts; however, several factors were identified that may contribute to the observed disparity. Test setup and instrumentation, grip type, loading scheme, thermal environment and accelerated test postprocessing along with material variability are among these factors. Their effects are discussed and future work is detailed for the exploration and elimination of some of these factors in order to achieve a higher fidelity comparison.

Service Life Extension of the Propulsion System of Long-Term Manned Orbital Stations

NASA Technical Reports Server (NTRS)

Kamath, Ulhas; Kuznetsov, Sergei; Spencer, Victor

2014-01-01

One of the critical non-replaceable systems of a long-term manned orbital station is the propulsion system. Since the propulsion system operates beginning with the launch of station elements into orbit, its service life determines the service life of the station overall. Weighing almost a million pounds, the International Space Station (ISS) is about four times as large as the Russian space station Mir and about five times as large as the U.S. Skylab. Constructed over a span of more than a decade with the help of over 100 space flights, elements and modules of the ISS provide more research space than any spacecraft ever built. Originally envisaged for a service life of fifteen years, this Earth orbiting laboratory has been in orbit since 1998. Some elements that have been launched later in the assembly sequence were not yet built when the first elements were placed in orbit. Hence, some of the early modules that were launched at the inception of the program were already nearing the end of their design life when the ISS was finally ready and operational. To maximize the return on global investments on ISS, it is essential for the valuable research on ISS to continue as long as the station can be sustained safely in orbit. This paper describes the work performed to extend the service life of the ISS propulsion system. A system comprises of many components with varying failure rates. Reliability of a system is the probability that it will perform its intended function under encountered operating conditions, for a specified period of time. As we are interested in finding out how reliable a system would be in the future, reliability expressed as a function of time provides valuable insight. In a hypothetical bathtub shaped failure rate curve, the failure rate, defined as the number of failures per unit time that a currently healthy component will suffer in a given future time interval, decreases during infant-mortality period, stays nearly constant during the service life and increases at the end when the design service life ends and wear-out phase begins. However, the component failure rates do not remain constant over the entire cycle life. The failure rate depends on various factors such as design complexity, current age of the component, operating conditions, severity of environmental stress factors, etc. Development, qualification and acceptance test processes provide rigorous screening of components to weed out imperfections that might otherwise cause infant mortality failures. If sufficient samples are tested to failure, the failure time versus failure quantity can be analyzed statistically to develop a failure probability distribution function (PDF), a statistical model of the probability of failure versus time. Driven by cost and schedule constraints however, spacecraft components are generally not tested in large numbers. Uncertainties in failure rate and remaining life estimates increase when fewer units are tested. To account for this, spacecraft operators prefer to limit useful operations to a period shorter than the maximum demonstrated service life of the weakest component. Running each component to its failure to determine the maximum possible service life of a system can become overly expensive and impractical. Spacecraft operators therefore, specify the required service life and an acceptable factor of safety (FOS). The designers use these requirements to limit the life test duration. Midway through the design life, when benefits justify additional investments, supplementary life test may be performed to demonstrate the capability to safely extend the service life of the system. An innovative approach is required to evaluate the entire system, without having to go through an elaborate test program of propulsion system elements. Evaluating every component through a brute force test program would be a cost prohibitive and time consuming endeavor. ISS propulsion system components were designed and built decades ago. There are no representative ground test articles for some of the components. A 'test everything' approach would require manufacturing new test articles. The paper outlines some of the techniques used for selective testing, by way of cherry picking candidate components based on failure mode effects analysis, system level impacts, hazard analysis, etc. The type of testing required for extending the service life depends on the design and criticality of the component, failure modes and failure mechanisms, life cycle margin provided by the original certification, operational and environmental stresses encountered, etc. When specific failure mechanism being considered and the underlying relationship of that mode to the stresses provided in the test can be correlated by supporting analysis, time and effort required for conducting life extension testing can be significantly reduced. Exposure to corrosive propellants over long periods of time, for instance, lead to specific failure mechanisms in several components used in the propulsion system. Using Arrhenius model, which is tied to chemically dependent failure mechanisms such as corrosion or chemical reactions, it is possible to subject carefully selected test articles to accelerated life test. Arrhenius model reflects the proportional relationship between time to failure of a component and the exponential of the inverse of absolute temperature acting on the component. The acceleration factor is used to perform tests at higher stresses that allow direct correlation between the times to failure at a high test temperature to the temperatures to be expected in actual use. As long as the temperatures are such that new failure mechanisms are not introduced, this becomes a very useful method for testing to failure a relatively small sample of items for a much shorter amount of time. In this article, based on the example of the propulsion system of the first ISS module Zarya, theoretical approaches and practical activities of extending the service life of the propulsion system are reviewed with the goal of determining the maximum duration of its safe operation.

Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

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

Sun, Huarui, E-mail: huarui.sun@bristol.ac.uk; Bajo, Miguel Montes; Uren, Michael J.

2015-01-26

Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage “hot spots” at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7–0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which ismore » consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.« less

Forecasting the brittle failure of heterogeneous, porous geomaterials

NASA Astrophysics Data System (ADS)

Vasseur, Jérémie; Wadsworth, Fabian; Heap, Michael; Main, Ian; Lavallée, Yan; Dingwell, Donald

2017-04-01

Heterogeneity develops in magmas during ascent and is dominated by the development of crystal and importantly, bubble populations or pore-network clusters which grow, interact, localize, coalesce, outgas and resorb. Pore-scale heterogeneity is also ubiquitous in sedimentary basin fill during diagenesis. As a first step, we construct numerical simulations in 3D in which randomly generated heterogeneous and polydisperse spheres are placed in volumes and which are permitted to overlap with one another, designed to represent the random growth and interaction of bubbles in a liquid volume. We use these simulated geometries to show that statistical predictions of the inter-bubble lengthscales and evolving bubble surface area or cluster densities can be made based on fundamental percolation theory. As a second step, we take a range of well constrained random heterogeneous rock samples including sandstones, andesites, synthetic partially sintered glass bead samples, and intact glass samples and subject them to a variety of stress loading conditions at a range of temperatures until failure. We record in real time the evolution of the number of acoustic events that precede failure and show that in all scenarios, the acoustic event rate accelerates toward failure, consistent with previous findings. Applying tools designed to forecast the failure time based on these precursory signals, we constrain the absolute error on the forecast time. We find that for all sample types, the error associated with an accurate forecast of failure scales non-linearly with the lengthscale between the pore clusters in the material. Moreover, using a simple micromechanical model for the deformation of porous elastic bodies, we show that the ratio between the equilibrium sub-critical crack length emanating from the pore clusters relative to the inter-pore lengthscale, provides a scaling for the error on forecast accuracy. Thus for the first time we provide a potential quantitative correction for forecasting the failure of porous brittle solids that build the Earth's crust.

The Environmental Qualification Specification as a Technical Management Tool,

DTIC Science & Technology

1981-11-01

CommuentI The dwell test for fatigue of the isolation system in a container is intended to be an accelerated test, in order to save test time and...diagnostic purposes * Response computation is not the only possible design approach. In the development of control system or servomechanism theory , emphasis...seldom aborts a mission in the same way as a complete failure of any function, and properly influences system effectiveness through a different type of

SMART empirical approaches for predicting field performance of PV modules from results of reliability tests

NASA Astrophysics Data System (ADS)

Hardikar, Kedar Y.; Liu, Bill J. J.; Bheemreddy, Venkata

2016-09-01

Gaining an understanding of degradation mechanisms and their characterization are critical in developing relevant accelerated tests to ensure PV module performance warranty over a typical lifetime of 25 years. As newer technologies are adapted for PV, including new PV cell technologies, new packaging materials, and newer product designs, the availability of field data over extended periods of time for product performance assessment cannot be expected within the typical timeframe for business decisions. In this work, to enable product design decisions and product performance assessment for PV modules utilizing newer technologies, Simulation and Mechanism based Accelerated Reliability Testing (SMART) methodology and empirical approaches to predict field performance from accelerated test results are presented. The method is demonstrated for field life assessment of flexible PV modules based on degradation mechanisms observed in two accelerated tests, namely, Damp Heat and Thermal Cycling. The method is based on design of accelerated testing scheme with the intent to develop relevant acceleration factor models. The acceleration factor model is validated by extensive reliability testing under different conditions going beyond the established certification standards. Once the acceleration factor model is validated for the test matrix a modeling scheme is developed to predict field performance from results of accelerated testing for particular failure modes of interest. Further refinement of the model can continue as more field data becomes available. While the demonstration of the method in this work is for thin film flexible PV modules, the framework and methodology can be adapted to other PV products.

Application of accelerated failure time models for breast cancer patients' survival in Kurdistan Province of Iran.

PubMed

Karimi, Asrin; Delpisheh, Ali; Sayehmiri, Kourosh

2016-01-01

Breast cancer is the most common cancer and the second common cause of cancer-induced mortalities in Iranian women. There has been a rapid development in hazard models and survival analysis in the last decade. The aim of this study was to evaluate the prognostic factors of overall survival (OS) in breast cancer patients using accelerated failure time models (AFT). This was a retrospective-analytic cohort study. About 313 women with a pathologically proven diagnosis of breast cancer who had been treated during a 7-year period (since January 2006 until March 2014) in Sanandaj City, Kurdistan Province of Iran were recruited. Performance among AFT was assessed using the goodness of fit methods. Discrimination among the exponential, Weibull, generalized gamma, log-logistic, and log-normal distributions was done using Akaik information criteria and maximum likelihood. The 5 years OS was 75% (95% CI = 74.57-75.43). The main results in terms of survival were found for the different categories of the clinical stage covariate, tumor metastasis, and relapse of cancer. Survival time in breast cancer patients without tumor metastasis and relapse were 4, 2-fold longer than other patients with metastasis and relapse, respectively. One of the most important undermining prognostic factors in breast cancer is metastasis; hence, knowledge of the mechanisms of metastasis is necessary to prevent it so occurrence and treatment of metastatic breast cancer and ultimately extend the lifetime of patients.

Tertiary creep test by ring shear apparatus in predicting initiation time of rainfall-induced-shallow landslide

NASA Astrophysics Data System (ADS)

Dok, A.; Fukuoka, H.

2010-12-01

Landslides are complex geo-disaters that frequently occur due to certain causes, but only one trigger such as earthquake or heavy rainfall or other related natural phenomenas. A slope failure seldom occurs without any creep deformation. Failure time of a slope as found by Fukuzono (1985) and Siato (1965) based on graphical analysis of extensometer monitoring data through large scale flume test for landslide studies, logarithm of acceleration is proportional to the logarithm of velocity of surface displacement immediately before the failure. It is expressed as d2x/dt2 = A(dx/dt)α, where x is surface displacement, t is time, and A and α are constant. And, Fukuzono (1985, 1989) proposed a simple method of predicting the time of falure by the inverse velocity (1/v) mean. The curve of inverse velocity is concave at 1< α<2, linear at α=2, and convex at α>2. Recently, Minamitani (2007) have researched on mechanism of Tertiary Creep deformation for landslide failure time prediction by increasing shear-stress development in order to understand the story behind the empirical relationship found by senior researcher Fukozono. He found a strong relationshp between constants A and α, expressed as α = 0.1781A+ 1.814. For deeper understanding, this study aims at learning in more detail on mechanism of landslides in tropical soils by ring shear apparatus (invented by DPRI, Disaster Prevention Research Institute) based on Tertiary Creep deformation theory in help issue warning on rainfall-induced landslides through back (pore-water) pressure control tests under combined conditions of particular normal stress and shear stress with pore-water pressure changes to simulate the potential sliding surface condition in the heavy rainfall, which no body experiences conducting such a test series, particularly by applying cyclic and actual groundwater change pattern to the soils. To reach the archivement, serie of back pressure control test were implemented by utilising stress-controlled ring shear apparatus which can control pore pressure, as well as monotonic increase of pore pressure at constant rate. Mixture of sand and clay materials was used to simulate actual landslide potential sliding surface. Repeated 1~5 time shear test for a specimen was also additionally conducted to produce reactivated motion landsliding. As a result, the tests were succeeded to reproduce tertiary creep to failure, through which the logarithm of acceleration-logarithm of velicity relation was found to be concave feature of 1/v trend (of safer side), and alpha value is much smaller than Fukuzono and Minamitani's works (0.3~0.7) by unknown reason. Moreover, trial repeated shear found a scatter of alpha values and the value itself did not show any significant trend of change.

Optimization of salt fog conditions for organic zinc paints : final report.

DOT National Transportation Integrated Search

1981-10-01

Although Louisiana has been testing and using organic zinc coatings since 1963, premature failures have occurred on bridges within the state recently. These failures were not predicted by accelerated testing which included salt fog exposure. the resu...

Update of the NEXT Ion Thruster Service Life Assessment with Post-Test Correlation to the Long Duration Test

NASA Technical Reports Server (NTRS)

Yim, John T.; Soulas, George C.; Shastry, Rohit; Choi, Maria; Mackey, Jonathan A.; Sarver-Verhey, Timothy R.

2017-01-01

The service life assessment for NASA's Evolutionary Xenon Thruster is updated to incorporate the results from the successful and voluntarily early completion of the 51,184 hour long duration test which demonstrated 918 kg of total xenon throughput. The results of the numerous post-test investigations including destructive interrogations have been assessed against all of the critical known and suspected failure mechanisms to update the life and throughput expectations for each major component. Analysis results of two of the most acute failure mechanisms, namely pit-and-groove erosion and aperture enlargement of the accelerator grid, are not updated in this work but will be published at a future time after analysis completion.

Determination of failure limits for sterilizable solid rocket motor

NASA Technical Reports Server (NTRS)

Lambert, W. L.; Mastrolia, E. J.; Mcconnell, J. D.

1974-01-01

A structural evaluation to establish probable failure limits and a series of environmental tests involving temperature cycling, sustained acceleration, and vibration were conducted on an 18-inch diameter solid rocket motor. Despite the fact that thermal, acceleration and vibration loads representing a severe overtest of conventional environmental requirements were imposed on the sterilizable motor, no structural failure of the grain or flexible support system was detected. The following significant conclusions are considered justified. It is concluded that: (1) the flexible grain retention system, which permitted heat sterilization at 275 F on the test motor, can readily be adopted to meet the environmental requirements of an operational motor design, and (2) if further substantiation of structural integrity is desired, the motor used is considered acceptable for static firing.

Characterization of Tantalum Polymer Capacitors

NASA Technical Reports Server (NTRS)

Spence, Penelope

2012-01-01

Overview Reviewed data Caution must be taken when accelerating test conditions Data not useful to establish an acceleration model Introduction of new failure mechanism skewing results Evidence of Anti-Wear-Out De-doping of polymer Decreased capacitance Increased ESR Not dielectric breakdown Needs further investigation Further investigation into tantalum polymer capacitor technology Promising acceleration model for Manufacturer A Possibility for use in high-reliability space applications with suitable voltage derating.

Dynamic Response of Metal-Polymer Bilayers - Viscoelasticity, Adhesion and Failure

DTIC Science & Technology

2013-11-25

polymers, particularly at large stretches. In the method developed for this purpose, a gas gun is used to impact a flange and impart a known velocity...Mott in his fragmentation model. Winter (1979) developed a method based on a gas - gun launched projectile in order to generate a rapidly...6061-O a The steady ring expansion speed reached in the time interval 15-50 | xs is quoted. There is a brief period of acceleration for about 15

Analogue modelling of the rupture process of vulnerable stalagmites in an earthquake simulator

NASA Astrophysics Data System (ADS)

Gribovszki, Katalin; Bokelmann, Götz; Kovács, Károly; Hegymegi, Erika; Esterhazy, Sofi; Mónus, Péter

2017-04-01

Earthquakes hit urban centers in Europe infrequently, but occasionally with disastrous effects. Obtaining an unbiased view of seismic hazard is therefore very important. In principle, the best way to test Probabilistic Seismic Hazard Assessments (PSHA) is to compare them with observations that are entirely independent of the procedure used to produce PSHA models. Arguably, the most valuable information in this context should be information on long-term hazard, namely maximum intensities (or magnitudes) occurring over time intervals that are at least as long as a seismic cycle. Long-term information can in principle be gained from intact and vulnerable stalagmites in natural caves. These formations survived all earthquakes that have occurred, over thousands of years - depending on the age of the stalagmite. Their "survival" requires that the horizontal ground acceleration has never exceeded a certain critical value within that time period. To determine this critical value for the horizontal ground acceleration more precisely we need to understand the failure process of these intact and vulnerable stalagmites. More detailed information of the vulnerable stalagmites' rupture is required, and we have to know how much it depends on the shape and the substance of the investigated stalagmite. Predicting stalagmite failure limits using numerical modelling is faced with a number of approximations, e.g. from generating a manageable digital model. Thus it seemed reasonable to investigate the problem by analogue modelling as well. The advantage of analogue modelling among other things is that nearly real circumstances can be produced by simple and quick laboratory methods. The model sample bodies were made from different types of concrete and were cut out from real broken stalagmites originated from the investigated caves. These bodies were reduced-scaled with similar shape as the original, investigated stalagmites. During the measurements we could change both the shape and the material and the time series of acting horizontal acceleration. Comparing the results from analogue to numerical modelling could improve the accuracy of long-term seismic hazard assessment.

Accelerating policy decisions to adopt haemophilus influenzae type B vaccine: a global, multivariable analysis.

PubMed

Shearer, Jessica C; Stack, Meghan L; Richmond, Marcie R; Bear, Allyson P; Hajjeh, Rana A; Bishai, David M

2010-03-16

Adoption of new and underutilized vaccines by national immunization programs is an essential step towards reducing child mortality. Policy decisions to adopt new vaccines in high mortality countries often lag behind decisions in high-income countries. Using the case of Haemophilus influenzae type b (Hib) vaccine, this paper endeavors to explain these delays through the analysis of country-level economic, epidemiological, programmatic and policy-related factors, as well as the role of the Global Alliance for Vaccines and Immunisation (GAVI Alliance). Data for 147 countries from 1990 to 2007 were analyzed in accelerated failure time models to identify factors that are associated with the time to decision to adopt Hib vaccine. In multivariable models that control for Gross National Income, region, and burden of Hib disease, the receipt of GAVI support speeded the time to decision by a factor of 0.37 (95% CI 0.18-0.76), or 63%. The presence of two or more neighboring country adopters accelerated decisions to adopt by a factor of 0.50 (95% CI 0.33-0.75). For each 1% increase in vaccine price, decisions to adopt are delayed by a factor of 1.02 (95% CI 1.00-1.04). Global recommendations and local studies were not associated with time to decision. This study substantiates previous findings related to vaccine price and presents new evidence to suggest that GAVI eligibility is associated with accelerated decisions to adopt Hib vaccine. The influence of neighboring country decisions was also highly significant, suggesting that approaches to support the adoption of new vaccines should consider supply- and demand-side factors.

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

Lall, Pradeep; Wei, Junchao; Sakalaukus, Peter

A new method has been developed for assessment of the onset of degradation in solid state luminaires to classify failure mechanisms by using metrics beyond lumen degradation that are currently used for identification of failure. Luminous Flux output, Correlated Color Temperature Data on Philips LED Lamps has been gathered under 85°C/85%RH till lamp failure. Failure modes of the test population of the lamps have been studied to understand the failure mechanisms in 85°C/85%RH accelerated test. Results indicate that the dominant failure mechanism is the discoloration of the LED encapsulant inside the lamps which is the likely cause for the luminousmore » flux degradation and the color shift. The acquired data has been used in conjunction with Bayesian Probabilistic Models to identify luminaires with onset of degradation much prior to failure through identification of decision boundaries between lamps with accrued damage and lamps beyond the failure threshold in the feature space. In addition luminaires with different failure modes have been classified separately from healthy pristine luminaires. The α-λ plots have been used to evaluate the robustness of the proposed methodology. Results show that the predicted degradation for the lamps tracks the true degradation observed during 85°C/85%RH during accelerated life test fairly closely within the ±20% confidence bounds. Correlation of model prediction with experimental results indicates that the presented methodology allows the early identification of the onset of failure much prior to development of complete failure distributions and can be used for assessing the damage state of SSLs in fairly large deployments. It is expected that, the new prediction technique will allow the development of failure distributions without testing till L70 life for the manifestation of failure.« less

Precursory changes in seismic velocity for the spectrum of earthquake failure modes

PubMed Central

Scuderi, M.M.; Marone, C.; Tinti, E.; Di Stefano, G.; Collettini, C.

2016-01-01

Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes, tremor and low frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2, however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3. Here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults. We systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick-slip and monitored ultrasonic wave speed during frictional sliding. We find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure, which suggests that real time monitoring of active faults may be a means to detect earthquake precursors. PMID:27597879

PV Degradation Curves: Non-Linearities and Failure Modes

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

Jordan, Dirk C.; Silverman, Timothy J.; Sekulic, Bill

Photovoltaic (PV) reliability and durability have seen increased interest in recent years. Historically, and as a preliminarily reasonable approximation, linear degradation rates have been used to quantify long-term module and system performance. The underlying assumption of linearity can be violated at the beginning of the life, as has been well documented, especially for thin-film technology. Additionally, non-linearities in the wear-out phase can have significant economic impact and appear to be linked to different failure modes. In addition, associating specific degradation and failure modes with specific time series behavior will aid in duplicating these degradation modes in accelerated tests and, eventually,more » in service life prediction. In this paper, we discuss different degradation modes and how some of these may cause approximately linear degradation within the measurement uncertainty (e.g., modules that were mainly affected by encapsulant discoloration) while other degradation modes lead to distinctly non-linear degradation (e.g., hot spots caused by cracked cells or solder bond failures and corrosion). The various behaviors are summarized with the goal of aiding in predictions of what may be seen in other systems.« less

Photometric and Colorimetric Assessment of LED Chip Scale Packages by Using a Step-Stress Accelerated Degradation Test (SSADT) Method.

PubMed

Qian, Cheng; Fan, Jiajie; Fang, Jiayi; Yu, Chaohua; Ren, Yi; Fan, Xuejun; Zhang, Guoqi

2017-10-16

By solving the problem of very long test time on reliability qualification for Light-emitting Diode (LED) products, the accelerated degradation test with a thermal overstress at a proper range is regarded as a promising and effective approach. For a comprehensive survey of the application of step-stress accelerated degradation test (SSADT) in LEDs, the thermal, photometric, and colorimetric properties of two types of LED chip scale packages (CSPs), i.e., 4000 °K and 5000 °K samples each of which was driven by two different levels of currents (i.e., 120 mA and 350 mA, respectively), were investigated under an increasing temperature from 55 °C to 150 °C and a systemic study of driving current effect on the SSADT results were also reported in this paper. During SSADT, junction temperatures of the test samples have a positive relationship with their driving currents. However, the temperature-voltage curve, which represents the thermal resistance property of the test samples, does not show significant variance as long as the driving current is no more than the sample's rated current. But when the test sample is tested under an overdrive current, its temperature-voltage curve is observed as obviously shifted to the left when compared to that before SSADT. Similar overdrive current affected the degradation scenario is also found in the attenuation of Spectral Power Distributions (SPDs) of the test samples. As used in the reliability qualification, SSADT provides explicit scenes on color shift and correlated color temperature (CCT) depreciation of the test samples, but not on lumen maintenance depreciation. It is also proved that the varying rates of the color shift and CCT depreciation failures can be effectively accelerated with an increase of the driving current, for instance, from 120 mA to 350 mA. For these reasons, SSADT is considered as a suitable accelerated test method for qualifying these two failure modes of LED CSPs.

Photometric and Colorimetric Assessment of LED Chip Scale Packages by Using a Step-Stress Accelerated Degradation Test (SSADT) Method

PubMed Central

Yu, Chaohua; Fan, Xuejun; Zhang, Guoqi

2017-01-01

By solving the problem of very long test time on reliability qualification for Light-emitting Diode (LED) products, the accelerated degradation test with a thermal overstress at a proper range is regarded as a promising and effective approach. For a comprehensive survey of the application of step-stress accelerated degradation test (SSADT) in LEDs, the thermal, photometric, and colorimetric properties of two types of LED chip scale packages (CSPs), i.e., 4000 °K and 5000 °K samples each of which was driven by two different levels of currents (i.e., 120 mA and 350 mA, respectively), were investigated under an increasing temperature from 55 °C to 150 °C and a systemic study of driving current effect on the SSADT results were also reported in this paper. During SSADT, junction temperatures of the test samples have a positive relationship with their driving currents. However, the temperature-voltage curve, which represents the thermal resistance property of the test samples, does not show significant variance as long as the driving current is no more than the sample’s rated current. But when the test sample is tested under an overdrive current, its temperature-voltage curve is observed as obviously shifted to the left when compared to that before SSADT. Similar overdrive current affected the degradation scenario is also found in the attenuation of Spectral Power Distributions (SPDs) of the test samples. As used in the reliability qualification, SSADT provides explicit scenes on color shift and correlated color temperature (CCT) depreciation of the test samples, but not on lumen maintenance depreciation. It is also proved that the varying rates of the color shift and CCT depreciation failures can be effectively accelerated with an increase of the driving current, for instance, from 120 mA to 350 mA. For these reasons, SSADT is considered as a suitable accelerated test method for qualifying these two failure modes of LED CSPs. PMID:29035300

Prediction of the Critical Curvature for LX-17 with the Time of Arrival Data from DNS

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

Yao, Jin; Fried, Laurence E.; Moss, William C.

2017-01-10

We extract the detonation shock front velocity, curvature and acceleration from time of arrival data measured at grid points from direct numerical simulations of a 50mm rate-stick lit by a disk-source, with the ignition and growth reaction model and a JWL equation of state calibrated for LX-17. We compute the quasi-steady (D, κ) relation based on the extracted properties and predicted the critical curvatures of LX-17. We also proposed an explicit formula that contains the failure turning point, obtained from optimization for the (D, κ) relation of LX-17.

Biomechanical tolerance of whole lumbar spines in straightened posture subjected to axial acceleration.

PubMed

Stemper, Brian D; Chirvi, Sajal; Doan, Ninh; Baisden, Jamie L; Maiman, Dennis J; Curry, William H; Yoganandan, Narayan; Pintar, Frank A; Paskoff, Glenn; Shender, Barry S

2018-06-01

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12-L5) were dynamically loaded using a custom-built drop tower. Twenty-three specimens were tested at sub-failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p < 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty-percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9-5.2 kN), and 16 (13-19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2-L5 spinal levels. In general, force-based tolerance was consistent with previous shorter-segment lumbar spine testing (3-5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:1747-1756, 2018. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Enhanced switching stability in Ta2O5 resistive RAM by fluorine doping

NASA Astrophysics Data System (ADS)

Sedghi, N.; Li, H.; Brunell, I. F.; Dawson, K.; Guo, Y.; Potter, R. J.; Gibbon, J. T.; Dhanak, V. R.; Zhang, W. D.; Zhang, J. F.; Hall, S.; Robertson, J.; Chalker, P. R.

2017-08-01

The effect of fluorine doping on the switching stability of Ta2O5 resistive random access memory devices is investigated. It shows that the dopant serves to increase the memory window and improve the stability of the resistive states due to the neutralization of oxygen vacancies. The ability to alter the current in the low resistance state with set current compliance coupled with large memory window makes multilevel cell switching more favorable. The devices have set and reset voltages of <1 V with improved stability due to the fluorine doping. Density functional modeling shows that the incorporation of fluorine dopant atoms at the two-fold O vacancy site in the oxide network removes the defect state in the mid bandgap, lowering the overall density of defects capable of forming conductive filaments. This reduces the probability of forming alternative conducting paths and hence improves the current stability in the low resistance states. The doped devices exhibit more stable resistive states in both dc and pulsed set and reset cycles. The retention failure time is estimated to be a minimum of 2 years for F-doped devices measured by temperature accelerated and stress voltage accelerated retention failure methods.

Solder joint aging characteristics from the MC2918 firing set of a B61 accelerated aging unit (AAU)

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

Vianco, P.T.; Rejent, J.A.

1997-10-01

The B61 accelerated aging unit (AAU) provided a unique opportunity to document the effects of a controlled, long-term thermal cycling environment on the aging of materials used in the device. This experiment was of particular interest to solder technologists because thermal cycling environments are a predominant source of solder joint failures in electronic assemblies. Observations of through hole solder joints in the MC2918 Firing Set from the B61 AAU did not reveal signs of catastrophic failure. Quantitative analyses of the microstructural metrics of intermetallic compound layer thickness and Pb-rich phase particle distributions indicated solder joint aging that was commensurate withmore » the accelerated aging environment. The effects of stress-enhanced coarsening of the Pb-rich phase were also documented.« less

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

NASA Technical Reports Server (NTRS)

Fasanella, Edwin L.; Billings, Marcus D.

2001-01-01

The nonlinear finite element program MSC.Dytran was used to predict the impact pulse for (he drop test of an energy absorbing cellular structure. This pre-test simulation was performed to aid in the design of an energy absorbing concept for a highly reliable passive Earth Entry Vehicle (EEV) that will directly impact the Earth without a parachute. In addition, a goal of the simulation was to bound the acceleration pulse produced and delivered to the simulated space cargo container. EEV's are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the enter of the EEV's cellular structure. The material models and failure criteria were varied to determine their effect on the resulting acceleration pulse. Pre-test analytical predictions using MSC.Dytran were compared with the test results obtained from impact test #4 using bungee accelerator located at the NASA Langley Research Center Impact Dynamics Research Facility. The material model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAMI model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for drop test #4.

The use of accelerated radiation testing for avionics

NASA Astrophysics Data System (ADS)

Quinn, Heather

2013-04-01

In recent years, the use of unmanned aerial vehicles (UAVs) for military and national security applications has been increasing. One possible use of these vehicles is as remote sensing platforms, where the UAV carries several sensors to provide real-time information about biological, chemical or radiological agents that might have been released into the environment. One such UAV, the Global Hawk, has a payload space that can carry nearly one ton of sensing equipment, which makes these platforms significantly larger than many satellites. Given the size of the potential payload and the heightened radiation environment at high altitudes, these systems could be affected by the radiation-induced failure mechanisms from the naturally occurring terrestrial environment. In this paper, we will explore the use of accelerated radiation testing to prepare UAV payloads for deployment.

Reliability of constricted double-heterojunction AlGaAs diode lasers

NASA Technical Reports Server (NTRS)

Botez, D.; Connolly, J. C.; Ettenberg, M.; Gilbert, D. B.; Hughes, J. J.

1983-01-01

Constricted double-heterojunction diode lasers have been life tested at 70 C heatsink temperature and 3-4 mW/facet in CW operation. A median life of 7800 h is obtained at 70 C, which extrapolates to 400,000 h median life at room temperature. The extrapolated mean time to failure at room temperature is in excess of 1,000,000 h. Single-longitudinal-mode CW operation is maintained after 10,000 h of accelerated aging at 70 C.

Reliability assessment of multiple quantum well avalanche photodiodes

NASA Technical Reports Server (NTRS)

Yun, Ilgu; Menkara, Hicham M.; Wang, Yang; Oguzman, Isamil H.; Kolnik, Jan; Brennan, Kevin F.; May, Gray S.; Wagner, Brent K.; Summers, Christopher J.

1995-01-01

The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

Hepatitis C and liver transplantation

NASA Astrophysics Data System (ADS)

Brown, Robert S.

2005-08-01

Liver transplantation is a life-saving therapy to correct liver failure, portal hypertension and hepatocellular carcinoma arising from hepatitis C infection. But despite the successful use of living donors and improvements in immunosuppression and antiviral therapy, organ demand continues to outstrip supply and recurrent hepatitis C with accelerated progression to cirrhosis of the graft is a frequent cause of graft loss and the need for retransplantation. Appropriate selection of candidates and timing of transplantation, coupled with better pre- and post-transplant antiviral therapy, are needed to improve outcomes.

Peter Hacke | NREL

Science.gov Websites

photovoltaic (PV) modules, inspections for root cause of module failures in the field, and accelerated lifetime delamination. His research interests are in modeling of degradation processes of PV modules, module integrated analysis of PV degradation data. He also explores accelerated multi-stress and combined stress testing to

Finite element simulation of structural performance on flexible pavements with stabilized base/treated sub-base materials under accelerated loading : research project capsule.

DOT National Transportation Integrated Search

2008-12-01

PROBLEM: The full-scale accelerated pavement testing (APT) provides a unique tool for pavement : engineers to directly collect pavement performance and failure data under heavy : wheel loading. However, running a full-scale APT experiment is very exp...

Accelerated testing for studying pavement design and performance (FY 2004) : thin bonded rigid overlay on PCCP and HMA (CISL experiment no. 13).

DOT National Transportation Integrated Search

2009-03-01

The thirteenth full-scale Accelerated Pavement Test (APT) experiment at the Civil Infrastructure Laboratory (CISL) : of Kansas State University aimed to determine the response and the failure mode of thin concrete overlays. Four : pavement structures...

How to Stop Disagreeing and Start Cooperatingin the Presence of Asymmetric Packet Loss.

PubMed

Morales-Ponce, Oscar; Schiller, Elad M; Falcone, Paolo

2018-04-22

We consider the design of a disagreement correction protocol in multi-vehicle systems. Vehicles broadcast in real-time vital information such as position, direction, speed, acceleration, intention, etc. This information is then used to identify the risks and adapt their trajectory to maintain the highest performance without compromising the safety. To minimize the risk due to the use of inconsistent information, all cooperating vehicles must agree whether to use the exchanged information to operate in a cooperative mode or use the only local information to operate in an autonomous mode. However, since wireless communications are prone to failures, it is impossible to deterministically reach an agreement. Therefore, any protocol will exhibit necessary disagreement periods. In this paper, we investigate whether vehicles can still cooperate despite communication failures even in the scenario where communication is suddenly not available. We present a deterministic protocol that allows all participants to either operate a cooperative mode when vehicles can exchange all the information in a timely manner or operate in autonomous mode when messages are lost. We show formally that the disagreement time is bounded by the time that the communication channel requires to deliver messages and validate our protocol using NS-3 simulations. We explain how the proposed solution can be used in vehicular platooning to attain high performance and still guarantee high safety standards despite communication failures.

How to Stop Disagreeing and Start Cooperatingin the Presence of Asymmetric Packet Loss

PubMed Central

2018-01-01

We consider the design of a disagreement correction protocol in multi-vehicle systems. Vehicles broadcast in real-time vital information such as position, direction, speed, acceleration, intention, etc. This information is then used to identify the risks and adapt their trajectory to maintain the highest performance without compromising the safety. To minimize the risk due to the use of inconsistent information, all cooperating vehicles must agree whether to use the exchanged information to operate in a cooperative mode or use the only local information to operate in an autonomous mode. However, since wireless communications are prone to failures, it is impossible to deterministically reach an agreement. Therefore, any protocol will exhibit necessary disagreement periods. In this paper, we investigate whether vehicles can still cooperate despite communication failures even in the scenario where communication is suddenly not available. We present a deterministic protocol that allows all participants to either operate a cooperative mode when vehicles can exchange all the information in a timely manner or operate in autonomous mode when messages are lost. We show formally that the disagreement time is bounded by the time that the communication channel requires to deliver messages and validate our protocol using NS-3 simulations. We explain how the proposed solution can be used in vehicular platooning to attain high performance and still guarantee high safety standards despite communication failures. PMID:29690572

Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

2002-01-01

Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

Snow fracture: From micro-cracking to global failure

NASA Astrophysics Data System (ADS)

Capelli, Achille; Reiweger, Ingrid; Schweizer, Jürg

2017-04-01

Slab avalanches are caused by a crack forming and propagating in a weak layer within the snow cover, which eventually causes the detachment of the overlying cohesive slab. The gradual damage process leading to the nucleation of the initial failure is still not entirely understood. Therefore, we studied the damage process preceding snow failure by analyzing the acoustic emissions (AE) generated by bond failure or micro-cracking. The AE allow studying the ongoing progressive failure in a non-destructive way. We performed fully load-controlled failure experiments on snow samples presenting a weak layer and recorded the generated AE. The size and frequency of the generated AE increased before failure revealing an acceleration of the damage process with increased size and frequency of damage and/or microscopic cracks. The AE energy was power-law distributed and the exponent (b-value) decreased approaching failure. The waiting time followed an exponential distribution with increasing exponential coefficient λ before failure. The decrease of the b-value and the increase of λ correspond to a change in the event distribution statistics indicating a transition from homogeneously distributed uncorrelated damage producing mostly small AE to localized damage, which cause larger correlated events which leads to brittle failure. We observed brittle failure for the fast experiment and a more ductile behavior for the slow experiments. This rate dependence was reflected also in the AE signature. In the slow experiments the b value and λ were almost constant, and the energy rate increase was moderate indicating that the damage process was in a stable state - suggesting the damage and healing processes to be balanced. On a shorter time scale, however, the AE parameters varied indicating that the damage process was not steady but consisted of a sum of small bursts. We assume that the bursts may have been generated by cascades of correlated micro-cracks caused by localization of stresses at a small scale. The healing process may then have prevented the self-organization of this small scale damage and, therefore, the total failure of the sample.

The comparison of proportional hazards and accelerated failure time models in analyzing the first birth interval survival data

NASA Astrophysics Data System (ADS)

Faruk, Alfensi

2018-03-01

Survival analysis is a branch of statistics, which is focussed on the analysis of time- to-event data. In multivariate survival analysis, the proportional hazards (PH) is the most popular model in order to analyze the effects of several covariates on the survival time. However, the assumption of constant hazards in PH model is not always satisfied by the data. The violation of the PH assumption leads to the misinterpretation of the estimation results and decreasing the power of the related statistical tests. On the other hand, the accelerated failure time (AFT) models do not assume the constant hazards in the survival data as in PH model. The AFT models, moreover, can be used as the alternative to PH model if the constant hazards assumption is violated. The objective of this research was to compare the performance of PH model and the AFT models in analyzing the significant factors affecting the first birth interval (FBI) data in Indonesia. In this work, the discussion was limited to three AFT models which were based on Weibull, exponential, and log-normal distribution. The analysis by using graphical approach and a statistical test showed that the non-proportional hazards exist in the FBI data set. Based on the Akaike information criterion (AIC), the log-normal AFT model was the most appropriate model among the other considered models. Results of the best fitted model (log-normal AFT model) showed that the covariates such as women’s educational level, husband’s educational level, contraceptive knowledge, access to mass media, wealth index, and employment status were among factors affecting the FBI in Indonesia.

Lumen degradation and chromaticity shift in glass and silicone based high-power phosphor-converted white-emitting diodes under thermal tests

NASA Astrophysics Data System (ADS)

Cheng, Wood-Hi; Tsai, Chun-Chin; Wang, Jimmy

2011-10-01

The lumen degradation and chromaticity shift in glass and silicone based high-power phosphor-converted white-emitting diodes (PC-WLEDs) under accelerated thermal tests at 150°C, 200°C, and 250°C are presented and compared. The glass based PC-WLEDs exhibited better thermal stability than the silicone by 4.8 time reductions in lumen loss 6.8 time reductions in chromaticity shift at 250°C, respectively. The mean-time-to-failure (MTTF) evaluation of glass and silicone based high-power PC-WLEDs in accelerated thermal tests is also presented and compared. The results showed that the glass based PC-WLEDs exhibited higher MTTF than the silicone by 7.53 times in lumen loss and 14.4 times in chromaticity shift at 250°C, respectively. The thermal performance of lumen, chromaticity, and MTTF investigations demonstrated that the thermal stability of the glass based PC-WLEDs were better than the silicone. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.

neutron-Induced Failures in semiconductor Devices

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

Wender, Stephen Arthur

2017-03-13

Single Event Effects are a very significant failure mode in modern semiconductor devices that may limit their reliability. Accelerated testing is important for semiconductor industry. Considerable more work is needed in this field to mitigate the problem. Mitigation of this problem will probably come from Physicists and Electrical Engineers working together

Adaptation to vestibular disorientation. III, Influence on adaptation of interrupting nystagmic eye movements with opposing stimuli.

DOT National Transportation Integrated Search

1966-09-01

Failure of adaptation of nystagmic eye movements to occur under certain conditions of stimulation by angular acceleration has been ascribed to a failure to allow the eye-movement response to run its course. In this study, 3 groups of subjects were te...

Mechanical Ventilation during Extracorporeal Membrane Oxygenation in Patients with Acute Severe Respiratory Failure.

PubMed

Zhang, Zhongheng; Gu, Wan-Jie; Chen, Kun; Ni, Hongying

2017-01-01

Conventionally, a substantial number of patients with acute respiratory failure require mechanical ventilation (MV) to avert catastrophe of hypoxemia and hypercapnia. However, mechanical ventilation per se can cause lung injury, accelerating the disease progression. Extracorporeal membrane oxygenation (ECMO) provides an alternative to rescue patients with severe respiratory failure that conventional mechanical ventilation fails to maintain adequate gas exchange. The physiology behind ECMO and its interaction with MV were reviewed. Next, we discussed the timing of ECMO initiation based on the risks and benefits of ECMO. During the running of ECMO, the protective ventilation strategy can be employed without worrying about catastrophic hypoxemia and carbon dioxide retention. There is a large body of evidence showing that protective ventilation with low tidal volume, high positive end-expiratory pressure, and prone positioning can provide benefits on mortality outcome. More recently, there is an increasing popularity on the use of awake and spontaneous breathing for patients undergoing ECMO, which is thought to be beneficial in terms of rehabilitation.

Mechanical Ventilation during Extracorporeal Membrane Oxygenation in Patients with Acute Severe Respiratory Failure

PubMed Central

Gu, Wan-Jie; Chen, Kun; Ni, Hongying

2017-01-01

Conventionally, a substantial number of patients with acute respiratory failure require mechanical ventilation (MV) to avert catastrophe of hypoxemia and hypercapnia. However, mechanical ventilation per se can cause lung injury, accelerating the disease progression. Extracorporeal membrane oxygenation (ECMO) provides an alternative to rescue patients with severe respiratory failure that conventional mechanical ventilation fails to maintain adequate gas exchange. The physiology behind ECMO and its interaction with MV were reviewed. Next, we discussed the timing of ECMO initiation based on the risks and benefits of ECMO. During the running of ECMO, the protective ventilation strategy can be employed without worrying about catastrophic hypoxemia and carbon dioxide retention. There is a large body of evidence showing that protective ventilation with low tidal volume, high positive end-expiratory pressure, and prone positioning can provide benefits on mortality outcome. More recently, there is an increasing popularity on the use of awake and spontaneous breathing for patients undergoing ECMO, which is thought to be beneficial in terms of rehabilitation. PMID:28127231

Life test of the InGaAs focal plane arrays detector for space applications

NASA Astrophysics Data System (ADS)

Zhu, Xian-Liang; Zhang, Hai-Yan; Li, Xue; Huang, Zhang-Cheng; Gong, Hai-Mei

2017-08-01

The short-wavelength infrared (SWIR) InGaAs focal plane array (FPA) detector consists of infrared detector chip, readout integrated circuit (ROIC), and flip-chip bonding interconnection by Indium bump. In order to satisfy space application requirements for failure rates or Mean Time to Failure (MTTF), which can only be demonstrated with the large number of detectors manufactured, the single pixel in InGaAs FPAs was chosen as the research object in this paper. The constant-stress accelerated life tests were carried out at 70°C 80°C 90°C and100°C. The failed pixels increased gradually during more than 14000 hours at each elevated temperatures. From the random failure data the activation energy was estimated to be 0.46eV, and the average lifetime of a single pixel in InGaAs FPAs was estimated to be longer than 1E+7h at the practical operating temperature (5°C).

Strain corrosion cracking in rpm sewer piping

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

Hopkins, S.W.; Wachob, H.F.; Duffner, D.H.

1993-12-31

Long term, aggressive environmental exposure can result in localized failure of large diameter, glass reinforced plastic mortar (RPM) piping. In order to evaluate the performance of the liner and glass reinforced matrix polyester resin, accelerated strain corrosion tests were performed on samples of RPM piping that had already experienced almost 15 years of service. To assess the sensitivity of RPM pipe to acidic environments and to correlate the fractography of the laboratory produced failures with the excavated crack, short segments of 8-inch and 48-inch diameter piping were statically loaded to produce various known surface strains. After preloading the specimens tomore » fixed strain levels, these samples were then exposed to sulfuric acid solutions having pH values of 2.7 and 4.7 and monitored as a function of time until failure. The resulting lifetimes were related to initial surface strains and showed a decreasing logarithmic relationship. Fractographic examination of the excavated crack revealed the typical strain corrosion fractography of glass fibers after almost a 1000 hour exposure at 1.3 % strain; similar fractographic observations were obtained from failed laboratory samples. At shorter times, failure appeared to be overload in nature and exhibited little, if any, timedependent fracture features. Fractographic examination of the excavated crack strongly indicated that the crack had been present for a significant time. The extremely aggressive environment had totally dissolved the exposed glass reinforcement. Based on the laboratory strain corrosion performance, the nature of the contained cracking, and fractography of the failed surface, cracking of the excavated RPM pipe was believed to be the result of an early overload failure that subsequently propagated slowly via strain corrosion in an extremely aggressive environment.« less

Overview of Fabrication Techniques and Lessons Learned with Accelerator Vacuum Windows

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

Ader, C. R.; McGee, M. W.; Nobrega, L. E.

Vacuum thin windows have been used in Fermilab's accelerators for decades and typically have been overlooked in terms of their criticality and fragility. Vacuum windows allow beam to pass through while creating a boundary between vacuum and air or high vacuum and low vacuum areas. The design of vacuum windows, including Titanium and Beryllium windows, will be discussed as well as fabrication, testing, and operational concerns. Failure of windows will be reviewed as well as safety approaches to mitigating failures and extending the lifetimes of vacuum windows. Various methods of calculating the strengths of vacuum windows will be explored, includingmore » FEA.« less

High-power UV-LED degradation: Continuous and cycled working condition influence

NASA Astrophysics Data System (ADS)

Arques-Orobon, F. J.; Nuñez, N.; Vazquez, M.; Segura-Antunez, C.; González-Posadas, V.

2015-09-01

High-power (HP) UV-LEDs can replace UV lamps for real-time fluoro-sensing applications by allowing portable and autonomous systems. However, HP UV-LEDs are not a mature technology, and there are still open issues regarding their performance evolution over time. This paper presents a reliability study of 3 W UV-LEDs, with special focus on LED degradation for two working conditions: continuous and cycled (30 s ON and 30 s OFF). Accelerated life tests are developed to evaluate the influence of temperature and electrical working conditions in high-power LEDs degradation, being the predominant failure mechanism the degradation of the package. An analysis that includes dynamic thermal and optical HP UV-LED measurements has been performed. Static thermal and stress simulation analysis with the finite element method (FEM) identifies the causes of package degradation. Accelerated life test results prove that HP UV-LEDs working in cycled condition have a better performance than those working in continuous condition.

Impact of accelerated plant growth on seed variety development

NASA Astrophysics Data System (ADS)

Christophersen, Eric

1998-01-01

The commercial lives of agricultural seed products have steadily declined in recent years. The introduction of genetically engineered crop seeds in 1966 has accentuated that trend. Widespread grower demand for genetically engineered seed requires competitive response by industry followers in order to avert market share losses to the industry leaders. Limitations on plant transformation technology, regulatory requirements and patent impediments require companies to rapidly convert transformed lines into elite commercial products. Massive multigenerational backcrossing efforts are required to distribute genetically engineered traits into a broad product mix. Significant incidents of expression failures, or ``gene silencing,'' have occurred unexpectedly, requiring product substitution strategies. First-to-market strategies, competitive response, broad germplasm conversion and rescue of product failures all share the element of urgency. Technologies which reliably accelerate product development rates can expect favorable reception by commercial seed developers. A growth chamber which dramatically accelerates the rate of plant growth is described.

Performance and Reliability of Bonded Interfaces for High-Temperature Packaging

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

Paret, Paul P

2017-08-02

Sintered silver has proven to be a promising candidate for use as a die-attach and substrate-attach material in automotive power electronics components. It holds promise of greater reliability than lead-based and lead-free solders, especially at higher temperatures (>200 degrees C). Accurate predictive lifetime models of sintered silver need to be developed and its failure mechanisms thoroughly characterized before it can be deployed as a die-attach or substrate-attach material in wide-bandgap device-based packages. Mechanical characterization tests that result in stress-strain curves and accelerated tests that produce cycles-to-failure result will be conducted. Also, we present a finite element method (FEM) modeling methodologymore » that can offer greater accuracy in predicting the failure of sintered silver under accelerated thermal cycling. A fracture mechanics-based approach is adopted in the FEM model, and J-integral/thermal cycle values are computed.« less

Evaluating the Performance of the NASA LaRC CMF Motion Base Safety Devices

NASA Technical Reports Server (NTRS)

Gupton, Lawrence E.; Bryant, Richard B., Jr.; Carrelli, David J.

2006-01-01

This paper describes the initial measured performance results of the previously documented NASA Langley Research Center (LaRC) Cockpit Motion Facility (CMF) motion base hardware safety devices. These safety systems are required to prevent excessive accelerations that could injure personnel and damage simulator cockpits or the motion base structure. Excessive accelerations may be caused by erroneous commands or hardware failures driving an actuator to the end of its travel at high velocity, stepping a servo valve, or instantly reversing servo direction. Such commands may result from single order failures of electrical or hydraulic components within the control system itself, or from aggressive or improper cueing commands from the host simulation computer. The safety systems must mitigate these high acceleration events while minimizing the negative performance impacts. The system accomplishes this by controlling the rate of change of valve signals to limit excessive commanded accelerations. It also aids hydraulic cushion performance by limiting valve command authority as the actuator approaches its end of travel. The design takes advantage of inherent motion base hydraulic characteristics to implement all safety features using hardware only solutions.

MAGNETAR OUTBURSTS FROM AVALANCHES OF HALL WAVES AND CRUSTAL FAILURES

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

Li, Xinyu; Levin, Yuri; Beloborodov, Andrei M.

2016-12-20

We explore the interaction between Hall waves and mechanical failures inside a magnetar crust, using detailed one-dimensional models that consider temperature-sensitive plastic flow, heat transport, and cooling by neutrino emission, as well as the coupling of the crustal motion to the magnetosphere. We find that the dynamics is enriched and accelerated by the fast, short-wavelength Hall waves that are emitted by each failure. The waves propagate and cause failures elsewhere, triggering avalanches. We argue that these avalanches are the likely sources of outbursts in transient magnetars.

Nonlinear interaction of strong S-waves with the rupture front in the shallow subsurface

NASA Astrophysics Data System (ADS)

Sleep, N. H.

2017-12-01

Shallow deformation in moderate to large earthquakes is sometimes distributed rather than being concentrated on a single fault plane. Strong high-frequency S-waves interact with the rupture front to produce this effect. For strike-slip faults, the rupture propagation velocity is a fraction of the S-wave velocity. The rupture propagation vector refracts essentially vertically in the low (S-wave) velocity shallow subsurface. So does the propagation direction of S-waves. The shallow rupture front is essentially mode 3 near the surface. Strong S-waves arrive before the rupture front. They continue to arrive for several seconds in a large event. There are simple scaling relationships. The dynamic Coulomb stress ratio of horizontal stress on horizontal planes from S-waves is the normalized acceleration in g's. For fractured rock and gravel, frictional failure occurs when the normalized acceleration exceeds the effective coefficient of friction. Acceleration tends to saturate at that level as the anelastic strain rate increases rapidly with stress. For muddy materials, failure begins at a low normalized acceleration but increases slowly with dynamic stress. Dynamic accelerations sometimes exceed 1 g. In both cases, the rupture tip finds the shallow subsurface already in nonlinear failure down to a few to tens of meters depth. The material does not distinguish between S-wave and rupture tip stresses. Both stresses add to the stress invariant and hence to the anelastic strain rate tensor. Surface anelastic strain from fault slip is thus distributed laterally over a distance scaling to the depth of nonlinearity from S-waves. The environs of the fault anelastically accommodate the fault slip at depth. This process differs from blind faults where the shallow coseismic strain is mostly elastic and interseismic anelastic processes accommodate the long-term shallow deformation.

Seismic Signals reveal Precursors, Force History and Runout Dynamics of the Tsunami-creating Askja Caldera Landslide, July 21, 2014

NASA Astrophysics Data System (ADS)

Schöpa, A.; Chao, W. A.; Burtin, A.; Hovius, N.

2016-12-01

We have analysed signals from a network of 52 seismic stations that recorded a large landslide at the steep-sided Askja caldera, Central Iceland, on 21 July 2014. As no direct observations where made, the seismic signals are a very valuable record not only to describe the landslide dynamics in great detail but also to identify triggers and precursors of the slide useful for early warning purposes. This study is motivated by the high hazard potential of the side as the landslide created a tsunami in the caldera lake with waves up to 60 m high reaching famous tourist spots at the northern lake shore. Analysis of the high frequencies reveals that the main slope failure started at 23.24UTC. The relatively long rise time of 40 s until the maximum peak ground velocity was reached points towards cascading failure of the caldera wall. The high seismic energies recorded during the first two minutes of the slide are the result of colliding and impacting blocks. Velocity peaks in the seismic signals following the main failure are indicative for subsequent slope failures that occur less frequent, with shorter duration and lower amplitude during the twelve hours after the main event. The high frequency records of the stations up to 30 km away from the landslide source area show that the background noise level started to increase 20 min before the main failure, with amplitudes up to three times the background level about seven minutes before the main slide. Five minutes before the main failure, amplitudes decreased back to the background level. The characteristic increase and decrease in ground velocities before the main landslide could be implemented in a monitoring and early warning system of the caldera walls at Askjas. Inversion of the long-period signals (0.025-0.05 Hz) enables us to describe the history of the forces acting on the Earth during the landslide. The maximum acceleration of the moving mass was reached 40 s after the start of the slide with unloading forces directed to the SE, in the opposite direction of the landslide path. After the transition from acceleration to deceleration, the force vectors strike to the NW, the reloading direction of the Earth. Calculated horizontal and vertical total displacements of 1258 m and 411 m as well as the inverted location of the landslide at the SE side of the caldera lake are consistent with field observations.

Omnibus Risk Assessment via Accelerated Failure Time Kernel Machine Modeling

PubMed Central

Sinnott, Jennifer A.; Cai, Tianxi

2013-01-01

Summary Integrating genomic information with traditional clinical risk factors to improve the prediction of disease outcomes could profoundly change the practice of medicine. However, the large number of potential markers and possible complexity of the relationship between markers and disease make it difficult to construct accurate risk prediction models. Standard approaches for identifying important markers often rely on marginal associations or linearity assumptions and may not capture non-linear or interactive effects. In recent years, much work has been done to group genes into pathways and networks. Integrating such biological knowledge into statistical learning could potentially improve model interpretability and reliability. One effective approach is to employ a kernel machine (KM) framework, which can capture nonlinear effects if nonlinear kernels are used (Scholkopf and Smola, 2002; Liu et al., 2007, 2008). For survival outcomes, KM regression modeling and testing procedures have been derived under a proportional hazards (PH) assumption (Li and Luan, 2003; Cai et al., 2011). In this paper, we derive testing and prediction methods for KM regression under the accelerated failure time model, a useful alternative to the PH model. We approximate the null distribution of our test statistic using resampling procedures. When multiple kernels are of potential interest, it may be unclear in advance which kernel to use for testing and estimation. We propose a robust Omnibus Test that combines information across kernels, and an approach for selecting the best kernel for estimation. The methods are illustrated with an application in breast cancer. PMID:24328713

Debris-flow initiation from large, slow-moving landslides

USGS Publications Warehouse

Reid, M.E.; Brien, D.L.; LaHusen, R.G.; Roering, J.J.; de la Fuente, J.; Ellen, S.D.; ,

2003-01-01

In some mountainous terrain, debris flows preferentially initiate from the toes and margins of larger, deeper, slower-moving landslides. During the wet winter of 1997, we began real-time monitoring of the large, active Cleveland Corral landslide complex in California, USA. When the main slide is actively moving, small, shallow, first-time slides on the toe and margins mobilize into debris flows and travel down adjacent gullies. We monitored the acceleration of one such failure; changes in velocity provided precursory indications of rapid failure. Three factors appear to aid the initiation of debris flows at this site: 1) locally steepened ground created by dynamic landslide movement, 2) elevated pore-water pressures and abundant soil moisture, and 3) locally cracked and dilated materials. This association between debris flows and large landslides can be widespread in some terrain. Detailed photographic mapping in two watersheds of northwestern California illustrates that the areal density of debris-flow source landsliding is about 3 to 7 times greater in steep geomorphically fresher landslide deposits than in steep ground outside landslide deposits. ?? 2003 Millpress.

Transient and steady-state performance of a single turbojet combustor with four different fuel nozzles

NASA Technical Reports Server (NTRS)

Mccafferty, Richard J; Donlon, Richard H

1955-01-01

Acceleration and steady-state performance of a tubular combustor was evaluated at two simulated altitudes with four different fuel nozzles. Temperature response lag was observed with all the nozzles. Except for rich-limit blowout, the only combustion failures observed during acceleration were with a fuel nozzle that gave an interrupted flow delivery during the acceleration. This same nozzle, because of superior fuel atomization, gave the highest steady-state combustion efficiencies.

Scintillation Breakdowns in Chip Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2008-01-01

Scintillations in solid tantalum capacitors are momentarily local breakdowns terminated by a self-healing or conversion to a high-resistive state of the manganese oxide cathode. This conversion effectively caps the defective area of the tantalum pentoxide dielectric and prevents short-circuit failures. Typically, this type of breakdown has no immediate catastrophic consequences and is often considered as nuisance rather than a failure. Scintillation breakdowns likely do not affect failures of parts under surge current conditions, and so-called "proofing" of tantalum chip capacitors, which is a controllable exposure of the part after soldering to voltages slightly higher than the operating voltage to verify that possible scintillations are self-healed, has been shown to improve the quality of the parts. However, no in-depth studies of the effect of scintillations on reliability of tantalum capacitors have been performed so far. KEMET is using scintillation breakdown testing as a tool for assessing process improvements and to compare quality of different manufacturing lots. Nevertheless, the relationship between failures and scintillation breakdowns is not clear, and this test is not considered as suitable for lot acceptance testing. In this work, scintillation breakdowns in different military-graded and commercial tantalum capacitors were characterized and related to the rated voltages and to life test failures. A model for assessment of times to failure, based on distributions of breakdown voltages, and accelerating factors of life testing are discussed.

Moisture-Induced TBC Spallation on Turbine Blade Samples

NASA Technical Reports Server (NTRS)

Smialek, James

2011-01-01

Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. The weekend effect or DeskTop Spallation (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond coat are reported. Cut sections were intermittently oxidized at 1100, 1150, and 1200 C and monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that embrittle the interface. A negative synergistic effect with interfacial sulfur is also invoked.

Moisture-Induced TBC Spallation on Turbine Blade Samples

NASA Technical Reports Server (NTRS)

Smialek, James L.

2011-01-01

Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. "The weekend effect" or "DeskTop Spallation" (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that 'embrittle' the interface. A negative synergistic effect with interfacial sulfur is also invoked.

Mass failures and other processes of sediment production in Pacific northwest forest landscapes

Treesearch

Frederick J. Swanson; Lee E. Benda; Stanley H. Duncan; Gordon E. Grant; Walter F. Megahan; Leslie M. Reid; Robert R. Ziemer

1987-01-01

Abstract - Accelerated sediment production by mass failures and other erosion processes is an important link between management of forest resources and fish resources. Dominant processes and the rates of sediment production vary greatly throughout the Pacific Northwest in response to geologic and climatic factors. The complex sediment routing systems characteristic...

Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives

Treesearch

B.H. River; R.O. Ebewele; G.E. Myers

1994-01-01

Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mechanisms in UF-bonded joints, specimens were bonded with unmodified, modified (amine), or phenol formaldehyde adhesive and subjected to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear...

Field measurements and modeling of wave propagation and subsequent weak layer failure in snow due to explosive loading

NASA Astrophysics Data System (ADS)

Simioni, Stephan; Sidler, Rolf; Dual, Jürg; Schweizer, Jürg

2015-04-01

Avalanche control by explosives is among the key temporary preventive measures. Yet, little is known about the mechanism involved in releasing avalanches by the effect of an explosion. Here, we test the hypothesis that the stress induced by acoustic waves exceeds the strength of weak snow layers. Consequently the snow fails and the onset of rapid crack propagation might finally lead to the release of a snow slab avalanche. We performed experiments with explosive charges over a snowpack. We installed microphones above the snowpack to measure near-surface air pressure and accelerometers within three snow pits. We also recorded pit walls of each pit with high speed cameras to detect weak layer failure. Empirical relationships and a priori information from ice and air were used to characterize a porous layered model from density measurements of snow profiles in the snow pits. This model was used to perform two-dimensional numerical simulations of wave propagation in Biot-type porous material. Locations of snow failure were identified in the simulation by comparing the axial and deviatoric stress field of the simulation to the corresponding snow strength. The identified snow failure locations corresponded well with the observed failure locations in the experiment. The acceleration measured in the snowpack best correlated with the modeled acceleration of the fluid relative to the ice frame. Even though the near field of the explosion is expected to be governed by non-linear effects as for example the observed supersonic wave propagation in the air above the snow surface, the results of the linear poroelastic simulation fit well with the measured air pressure and snowpack accelerations. The results of this comparison are an important step towards quantifying the effectiveness of avalanche control by explosives.

Acceleration of recovery in acute renal failure: from cellular mechanisms of tubular repair to innovative targeted therapies.

PubMed

Abbate, M; Remuzzi, G

1996-05-01

Kidney repair from injury is a major focus of interest for research, both clinical and basic, in the field of acute renal failure. This is so because very little progress has been made during the past several years to improve mortality in hospitalized patients with acute renal failure despite the unique potential of the kidney for complete structural and functional recovery. Novel therapeutic options have recently emerged from the knowledge of molecular mechanisms of tissue injury after ischemia, including pathways of endothelial-leukocyte interaction and epithelial cell aggregation mediated by integrin molecules. These strategies are promising because they may target early mechanisms of leukocyte infiltration and tubular obstruction. However, it seems clear that additional interventions should address the reparative program that potentially leads to the full restoration of kidney structure and function. Thus, acceleration of repair from acute renal failure is achieved experimentally by growth factors which besides different renal actions seem to have in common the ability to stimulate proliferation of surviving tubular epithelial cells. We direct attention to cellular processes which characterize, and possibly have role in, renal repair from acute tubular injury as potential targets of therapy. In addition to proliferation, they include epithelial differentiation and apoptosis. Further investigation in the biology of repair should set the stage for rational design of targeted therapies which may accelerate the pace of recovery and hopefully decrease mortality in such a dramatic and potentially reversible setting.

Reliability and Failure Modes of Solid-State Lighting Electrical Drivers Subjected to Accelerated Aging

DOE PAGES

Lall, Pradeep; Sakalaukus, Peter; Davis, Lynn

2015-02-19

An investigation of an off-the-shelf solid-state lighting device with the primary focus on the accompanied light-emitting diode (LED) electrical driver (ED) has been conducted. A set of 10 EDs were exposed to temperature humidity life testing of 85% RH and 85 C (85/85) without an electrical bias per the JEDEC standard JESD22-A101C in order to accelerate the ingress of moisture into the aluminum electrolytic capacitor (AEC) and the EDs in order to assess the reliability of the LED drivers for harsh environment applications. The capacitance and equivalent series resistance for each AEC inside the ED were measured using a handheldmore » LCR meter as possible leading indications of failure. The photometric quantities of a single pristine light engine were monitored in order to investigate the interaction between the light engine and the EDs. These parameters were used in assessing the overall reliability of the EDs. In addition, a comparative analysis has been conducted between the 85/85 accelerated test data and a previously published high-temperature storage life accelerated test of 135°C. The results of the 85/85 acceleration test and the comparative analysis are presented in this paper.« less

Service contract with periodic preventive maintenance for a dump truck sold with a two-dimensional warranty

NASA Astrophysics Data System (ADS)

Nasrum, A.; Pasaribu, U. S.; Husniah, H.

2016-02-01

This paper deals with maintenance service contract for a dump truck sold with a two-dimensional warranties. We consider a situation where an agent offers two maintenance contract options and the owner of the equipment has to select the optimal option either the OEM carried out all repairs and preventive maintenance activities (option one) or the OEM only carries out failure while the costumer undertakes preventive maintenance action in-house (option two). As the number of preventive maintenance and corrective maintenance that occurs in the area of servicing contracts is very influential in determining the value of the contract, we have to determine the optimal time between preventive maintenance that can minimize the cost of repair in the contract area. Moreover, we also study the maintenance service contract considering reduction of the intensity function after preventive maintenance from both the owner and OEM point of views. In this paper, we use a Weibull intensity function to consider a product with increasing failure intensity. We use a non-cooperative game formulation to determine the optimal price structure (i.e., the contract price and repair cost) for the OEM and the owner. A numerical example derived from the model has shown that if the owner choose option one then the owner obtain a higher profit compared with the profit resulted from option two. The result agree with earlier work which uses the accelerated failure time (AFT) for the failure modeling, while here we model the failure of the dump truck without the use of the AFT.

SU-E-T-627: Failure Modes and Effect Analysis for Monthly Quality Assurance of Linear Accelerator

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

Xie, J; Xiao, Y; Wang, J

2014-06-15

Purpose: To develop and implement a failure mode and effect analysis (FMEA) on routine monthly Quality Assurance (QA) tests (physical tests part) of linear accelerator. Methods: A systematic failure mode and effect analysis method was performed for monthly QA procedures. A detailed process tree of monthly QA was created and potential failure modes were defined. Each failure mode may have many influencing factors. For each factor, a risk probability number (RPN) was calculated from the product of probability of occurrence (O), the severity of effect (S), and detectability of the failure (D). The RPN scores are in a range ofmore » 1 to 1000, with higher scores indicating stronger correlation to a given influencing factor of a failure mode. Five medical physicists in our institution were responsible to discuss and to define the O, S, D values. Results: 15 possible failure modes were identified and all RPN scores of all influencing factors of these 15 failue modes were from 8 to 150, and the checklist of FMEA in monthly QA was drawn. The system showed consistent and accurate response to erroneous conditions. Conclusion: The influencing factors of RPN greater than 50 were considered as highly-correlated factors of a certain out-oftolerance monthly QA test. FMEA is a fast and flexible tool to develop an implement a quality management (QM) frame work of monthly QA, which improved the QA efficiency of our QA team. The FMEA work may incorporate more quantification and monitoring fuctions in future.« less

Amnion-Derived Multipotent Progenitor Cells Increase Gain of Incisional Breaking Strength and Decrease Incidence and Severity of Acute Wound Failure

PubMed Central

Xing, Liyu; Franz, Michael G.; Marcelo, Cynthia L.; Smith, Charlotte A.; Marshall, Vivienne S.; Robson, Martin C.

2007-01-01

Objective: Acute wound failure is a common complication following surgical procedures and trauma. Laparotomy wound failure leads to abdominal dehiscence and incisional hernia formation. Delayed recovery of wound-breaking strength is one mechanism for laparotomy wound failure. Early fascial wounds are relatively acellular, and there is a delay in the appearance of acute wound growth factors and cytokines. The objective of this study was to accelerate and improve laparotomy wound healing using amnion-derived multipotent cells (AMPs). AMPs' nonimmunogenic phenotype and relative abundance support its role as a cell therapy. Methods: AMPs were injected into the load-bearing layer of rat abdominal walls prior to laparotomy, and cell viability was confirmed. Wound mechanical properties were measured over 28 days. The incidence and severity of laparotomy wound failure was measured in an incisional hernia model. Results: AMP cells were viable in laparotomy wounds for at least 28 days and did not migrate to other tissues. Laparotomy wound-breaking strength was increased by postoperative day 7 following AMP therapy. AMP therapy reduced the incidence of hernia formation and the size of hernia defects. Histology suggested stimulated wound fibroplasia and angiogenesis. Conclusions: AMP cell therapy reduces the incidence of laparotomy wound failure by accelerating the recovery of wound-breaking strength. This results in fewer incisional hernias and smaller hernia defects. PMID:18091982

FMEA on the superconducting torus for the Jefferson Lab 12 GeV accelerator upgrade

DOE PAGES

Ghoshal, Probir K.; Biallas, George H.; Fair, Ruben J.; ...

2015-01-16

As part of the Jefferson Lab 12GeV accelerator upgrade project, Hall B requires two conduction cooled superconducting magnets. One is a magnet system consisting of six superconducting trapezoidal racetrack-type coils assembled in a toroidal configuration and the second is an actively shielded solenoidal magnet system consisting of 5 coils. Both magnets are to be wound with Superconducting Super Collider-36 NbTi strand Rutherford cable soldered into a copper channel. This paper describes the various failure modes in torus magnet along with the failure modes that could be experienced by the torus and its interaction with the solenoid which is located inmore » close proximity.« less

Reliability study of Piezoelectric Structures Dedicated to Energy Harvesting by the Way of Blocking Force Investigation

NASA Astrophysics Data System (ADS)

Maaroufi, S.; Parrain, F.; Lefeuvre, E.; Boutaud, B.; Dal Molin, R.

2015-12-01

In this paper we propose an approach to study the reliability of piezoelectric structures and more precisely energy harvesting micro-devices dedicated to autonomous active medical implants (new generation pacemakers). The structure under test is designed as a bimorph piezoelectric cantilever with a seismic mass at its tip. Good understanding of material aging and mechanical failure is critical for this kind of system. To study the reliability and durability of the piezoelectric part we propose to establish a new accelerated methodology and an associated test bench where the environment and stimuli can be precisely controlled over a wide period of time. This will allow the identification of potential failure modes and the study of their impacts by the way of direct mechanical investigation based on stiffness and blocking force measurements performed periodically.

Pre-conditioning procedure suitable for internal-RF-antenna of J-PARC RF-driven H{sup −} ion source

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

Ueno, A., E-mail: akira.ueno@j-parc.jp; Ohkoshi, K.; Ikegami, K.

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H{sup −} ion source has been successfully operated for about 1 yr. By the world brightest level beam, the J-PARC design beam power of 1 MW was successfully demonstrated. Although no internal-RF-antenna failure, except for the once caused by an excess cesium due to a misoperation, occurred in the operation, many antennas failed in pre-conditionings for the first hundred days. The antenna failure rate was drastically decreased by using an antenna with coating thicker than a standard value and the pre-conditioning procedure repeating 15 min 25 kW RF-power operation and impurity-gasmore » evacuation a few times, before the full power (50 kW) operation.« less

A Low-Pressure Oxygen Storage System for Oxygen Supply in Low-Resource Settings.

PubMed

Rassool, Roger P; Sobott, Bryn A; Peake, David J; Mutetire, Bagayana S; Moschovis, Peter P; Black, Jim Fp

2017-12-01

Widespread access to medical oxygen would reduce global pneumonia mortality. Oxygen concentrators are one proposed solution, but they have limitations, in particular vulnerability to electricity fluctuations and failure during blackouts. The low-pressure oxygen storage system addresses these limitations in low-resource settings. This study reports testing of the system in Melbourne, Australia, and nonclinical field testing in Mbarara, Uganda. The system included a power-conditioning unit, a standard oxygen concentrator, and an oxygen store. In Melbourne, pressure and flows were monitored during cycles of filling/emptying, with forced voltage fluctuations. The bladders were tested by increasing pressure until they ruptured. In Mbarara, the system was tested by accelerated cycles of filling/emptying and then run on grid power for 30 d. The low-pressure oxygen storage system performed well, including sustaining a pressure approximately twice the standard working pressure before rupture of the outer bag. Flow of 1.2 L/min was continuously maintained to a simulated patient during 30 d on grid power, despite power failures totaling 2.9% of the total time, with durations of 1-176 min (mean 36.2, median 18.5). The low-pressure oxygen storage system was robust and durable, with accelerated testing equivalent to at least 2 y of operation revealing no visible signs of imminent failure. Despite power cuts, the system continuously provided oxygen, equivalent to the treatment of one child, for 30 d under typical power conditions for sub-Saharan Africa. The low-pressure oxygen storage system is ready for clinical field trials. Copyright © 2017 by Daedalus Enterprises.

NASA's Evolutionary Xenon Thruster (NEXT) Long-Duration Test as of 736 kg of Propellant Throughput

NASA Technical Reports Server (NTRS)

Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Patterson, Michael J.

2012-01-01

The NASA s Evolutionary Xenon Thruster (NEXT) program is developing the next-generation solar-electric ion propulsion system with significant enhancements beyond the state-of-the-art NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) ion propulsion system to provide future NASA science missions with enhanced mission capabilities. A Long-Duration Test (LDT) was initiated in June 2005 to validate the thruster service life modeling and to qualify the thruster propellant throughput capability. The thruster has set electric propulsion records for the longest operating duration, highest propellant throughput, and most total impulse demonstrated. At the time of this publication, the NEXT LDT has surpassed 42,100 h of operation, processed more than 736 kg of xenon propellant, and demonstrated greater than 28.1 MN s total impulse. Thruster performance has been steady with negligible degradation. The NEXT thruster design has mitigated several lifetime limiting mechanisms encountered in the NSTAR design, including the NSTAR first failure mode, thereby drastically improving thruster capabilities. Component erosion rates and the progression of the predicted life-limiting erosion mechanism for the thruster compare favorably to pretest predictions based upon semi-empirical ion thruster models used in the thruster service life assessment. Service life model validation has been accomplished by the NEXT LDT. Assuming full-power operation until test article failure, the models and extrapolated erosion data predict penetration of the accelerator grid grooves after more than 45,000 hours of operation while processing over 800 kg of xenon propellant. Thruster failure due to degradation of the accelerator grid structural integrity is expected after groove penetration.

NASA's Evolutionary Xenon Thruster (NEXT) Long-Duration Test as of 736 kg of Propellant Throughput

NASA Technical Reports Server (NTRS)

Shastry, Rohit; Herman, Daniel A.; Soulas, George C.; Patterson, Michael J.

2012-01-01

The NASA s Evolutionary Xenon Thruster (NEXT) program is developing the next-generation solar-electric ion propulsion system with significant enhancements beyond the state-of-the-art NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) ion propulsion system to provide future NASA science missions with enhanced mission capabilities. A Long-Duration Test (LDT) was initiated in June 2005 to validate the thruster service life modeling and to qualify the thruster propellant throughput capability. The thruster has set electric propulsion records for the longest operating duration, highest propellant throughput, and most total impulse demonstrated. At the time of this publication, the NEXT LDT has surpassed 42,100 h of operation, processed more than 736 kg of xenon propellant, and demonstrated greater than 28.1 MN s total impulse. Thruster performance has been steady with negligible degradation. The NEXT thruster design has mitigated several lifetime limiting mechanisms encountered in the NSTAR design, including the NSTAR first failure mode, thereby drastically improving thruster capabilities. Component erosion rates and the progression of the predicted life-limiting erosion mechanism for the thruster compare favorably to pretest predictions based upon semi-empirical ion thruster models used in the thruster service life assessment. Service life model validation has been accomplished by the NEXT LDT. Assuming full-power operation until test article failure, the models and extrapolated erosion data predict penetration of the accelerator grid grooves after more than 45,000 hours of operation while processing over 800 kg of xenon propellant. Thruster failure due to degradation of the accelerator grid structural integrity is expected after

A Mechanistic Thermal Fatigue Model for SnAgCu Solder Joints

NASA Astrophysics Data System (ADS)

Borgesen, Peter; Wentlent, Luke; Hamasha, Sa'd.; Khasawneh, Saif; Shirazi, Sam; Schmitz, Debora; Alghoul, Thaer; Greene, Chris; Yin, Liang

2018-02-01

The present work offers both a complete, quantitative model and a conservative acceleration factor expression for the life span of SnAgCu solder joints in thermal cycling. A broad range of thermal cycling experiments, conducted over many years, has revealed a series of systematic trends that are not compatible with common damage functions or constitutive relations. Complementary mechanical testing and systematic studies of the evolution of the microstructure and damage have led to a fundamental understanding of the progression of thermal fatigue and failure. A special experiment was developed to allow the effective deconstruction of conventional thermal cycling experiments and the finalization of our model. According to this model, the evolution of damage and failure in thermal cycling is controlled by a continuous recrystallization process which is dominated by the coalescence and rotation of dislocation cell structures continuously added to during the high-temperature dwell. The dominance of this dynamic recrystallization contribution is not consistent with the common assumption of a correlation between the number of cycles to failure and the total work done on the solder joint in question in each cycle. It is, however, consistent with an apparent dependence on the work done during the high-temperature dwell. Importantly, the onset of this recrystallization is delayed by pinning on the Ag3Sn precipitates until these have coarsened sufficiently, leading to a model with two terms where one tends to dominate in service and the other in accelerated thermal cycling tests. Accumulation of damage under realistic service conditions with varying dwell temperatures and times is also addressed.

Computational Failure Modeling of Accelerative Injuries to the Lower Leg Below the Knee

DTIC Science & Technology

2013-03-01

accelerations in the lower extremities in the range of 155 to 217 G [Nilakantan and Tabiei, 2009]. During an underbody blast event, within 0.5 ms of the... acceleration and subsequent deformations of the plate which apply significant loads to the soldier’s lower extremities [NATO HFM-090, Task Group 25, 2007... acceleration of the vehicle and the collisions that follow are also a significant source of injury, especially if the soldier is not properly restrained. In

Solid-state lighting life prediction using extended Kalman filter

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

Lall, Pradeep; Wei, Junchao; Davis, Lynn

2013-07-16

Solid-state lighting (SSL) luminaires containing light emitting diodes (LEDs) have the potential of seeing excessive temperatures when being transported across country or being stored in non-climate controlled warehouses. They are also being used in outdoor applications in desert environments that see little or no humidity but will experience extremely high temperatures during the day. This makes it important to increase our understanding of what effects high temperature exposure for a prolonged period of time will have on the usability and survivability of these devices. The U.S. Department of Energy has made a long term commitment to advance the efficiency, understandingmore » and development of solid-state lighting (SSL) and is making a strong push for the acceptance and use of SSL products to reduce overall energy consumption attributable to lighting. Traditional light sources “burn out” at end-of-life. For an incandescent bulb, the lamp life is defined by B50 life. However, the LEDs have no filament to “burn”. The LEDs continually degrade and the light output decreases eventually below useful levels causing failure. Presently, the TM-21 test standard is used to predict the L70 life of SSL Luminaires from LM-80 test data. The TM-21 model uses an Arrhenius Equation with an Activation Energy, Pre-decay factor and Decay Rates. Several failure mechanisms may be active in a luminaire at a single time causing lumen depreciation. The underlying TM-21 Arrhenius Model may not capture the failure physics in presence of multiple failure mechanisms. Correlation of lumen maintenance with underlying physics of degradation at system-level is needed. In this paper, a Kalman Filter and Extended Kalman Filters have been used to develop a 70% Lumen Maintenance Life Prediction Model for a LEDs used in SSL luminaires. This model can be used to calculate acceleration factors, evaluate failure-probability and identify ALT methodologies for reducing test time. Ten-thousand hour LM-80 test data for various LEDs have been used for model development. System state has been described in state space form using the measurement of the feature vector, velocity of feature vector change and the acceleration of the feature vector change. System state at each future time has been computed based on the state space at preceding time step, system dynamics matrix, control vector, control matrix, measurement matrix, measured vector, process noise and measurement noise. The future state of the lumen depreciation has been estimated based on a second order Kalman Filter model and a Bayesian Framework. The measured state variable has been related to the underlying damage using physics-based models. Life prediction of L70 life for the LEDs used in SSL luminaires from KF and EKF based models have been compared with the TM-21 model predictions and experimental data.« less

Time-dependent Brittle Deformation in Etna Basalt

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2008-12-01

Mt Etna is the largest and most active volcano in Europe. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). Pre-eruptive patterns of flank eruptions, closely monitored by means of ground deformation and seismicity, revealed the slow development of fracture systems at different altitudes, marked by repeated bursts of seismicity and accelerating/decelerating deformation patterns acting over the scale of months to days. The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as 'brittle creep'. Stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short- term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data demonstrate that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time- to-failure properties of the basaltic volcanic pile.

Human growth hormone may be detrimental when used to accelerate recovery from acute tendon-bone interface injuries.

PubMed

Baumgarten, Keith M; Oliver, Harvey A; Foley, Jack; Chen, Ding-Geng; Autenried, Peter; Duan, Shanzhong; Heiser, Patrick

2013-05-01

There have been few scientific studies that have examined usage of human growth hormone to accelerate recovery from injury. The hypothesis of this study was that human growth hormone would accelerate tendon-to-bone healing compared with control animals treated with placebo in a rat model of acute rotator cuff injury repair. Seventy-two rats underwent repair of acute rotator cuff injuries and were randomized into the following postoperative dosing regimens: placebo, and human growth hormone at 0.1, 1, 2, 5, and 10 mg/kg/day, administered subcutaneously once per day for fourteen days (Protocol 1). An additional twenty-four rats were randomized to receive either (1) placebo or (2) human growth hormone at 5 mg/kg, administered subcutaneously twice per day for seven days preoperatively and twenty-eight days postoperatively (Protocol 2). All rats were killed twenty-eight days postoperatively. Mechanical testing was performed. Ultimate stress, ultimate force, stiffness, energy to failure, and ultimate distension were determined. For Protocol 1, analysis of variance testing showed no significant difference between the groups with regard to ultimate stress, ultimate force, stiffness, energy to failure, or ultimate distension. In Protocol 2, ultimate force to failure was significantly worse in the human growth hormone group compared with the placebo group (21.1 ± 5.85 versus 26.3 ± 5.47 N; p = 0.035). Failure was more likely to occur through the bone than the tendon-bone interface in the human growth hormone group compared with the placebo group (p = 0.001). No significant difference was found for ultimate stress, ultimate force, stiffness, energy to failure, or ultimate distension between the groups in Protocol 2. In this rat model of acute tendon-bone injury repair, daily subcutaneous postoperative human growth hormone treatment for fourteen days failed to demonstrate a significant difference in any biomechanical parameter compared with placebo. Furthermore, subcutaneous administration of 5 mg/kg of human growth hormone twice daily from seven days preoperatively until twenty-eight days postoperatively demonstrated lower loads to ultimate failure and a higher risk of bone fracture failure compared with placebo.

Assessing the Causes of Encapsulant Delamination in PV Modules

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

Wohlgemuth, John H.; Hacke, Peter; Bosco, Nick

Delamination of the encapsulant is one of the most prevalent PV module field failures. This paper will present examples of various types of delaminations that have been observed in the field. It will then discuss the development of accelerated stress tests designed to duplicate those field failures and thus provide tools for avoiding them in the future.

Molding compound trends in a denser packaging world: Qualification tests and reliability concerns

NASA Astrophysics Data System (ADS)

Nguyen, L. T.; Lo, R. H. Y.; Chen, A. S.; Belani, J. G.

1993-12-01

Molding compound development has traditionally been driven by the memory market, then subsequent applications filter down to other IC technologies such as logic, analog, and ASIC. However, this strategy has changed lately with the introduction of thin packages such as PQFP & TSOP. Rather than targeting a compound for a family of IC such as DRAM or SRAM, compound development efforts are now focused at specific classes of packages. The configurations of these thin packages impose new functional requirements that need to be revisited to provide the optimized combination of properties. The evolution of qualification tests mirrors the advances in epoxy and compounding technologies. From the first standard novolac-based epoxies of the 1970s to the latest 3(sup rd)-generation ultra-low stress materials, longer test times at increasingly harsher environments were achieved. This paper benchmarks the current reliability tests used by the electronic industry, examines those tests that affect and are affected by the molding compounds, discusses the relevance of accelerated testing, and addresses the major reliability issues facing current molding compound development efforts. Six compound-related reliability concerns were selected: moldability, package stresses, package cracking, halogen-induced intermetallic growth at bond pads, moisture-induced corrosion, and interfacial delamination. Causes of each failure type are surveyed and remedies are recommended. Accelerated tests are designed to apply to a limited quantity of devices, bias, or environmental conditions larger than usual ratings, to intensify failure mechanisms that would occur under normal operating conditions. The observed behavior is then extrapolated from the lot to the entire population. Emphasis is on compressing the time necessary to obtain reliability data. This approach has two main drawbacks. With increasingly complex devices, even accelerated tests are expensive. And with new technologies, it becomes difficult to ascertain that the applied stress 1) induces the failure phenomenon linked with usual field conditions, and 2) does not create any new ones. Technology evolution and reliability testing are interdependent. Devices get larger with increasingly smaller features and more complex geometries. Molding compounds have evolved considerably over the past decade to provide ultra-low stress levels and moldability for thin packages.

Chapter 3: Photovoltaic Module Stability and Reliability

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

Jordan, Dirk; Kurtz, Sarah

2017-01-01

Profits realized from investment in photovoltaic will benefit from decades of reliable operation. Service life prediction through accelerated tests is only possible if indoor tests duplicate power loss and failure modes observed in fielded systems. Therefore, detailing and quantifying power loss and failure modes is imperative. In the first section, we examine recent trends in degradation rates, the gradual power loss observed for different technologies, climates and other significant factors. In the second section, we provide a summary of the most commonly observed failure modes in fielded systems.

Electromigration failures under bidirectional current stress

NASA Astrophysics Data System (ADS)

Tao, Jiang; Cheung, Nathan W.; Hu, Chenming

1998-01-01

Electromigration failure under DC stress has been studied for more than 30 years, and the methodologies for accelerated DC testing and design rules have been well established in the IC industry. However, the electromigration behavior and design rules under time-varying current stress are still unclear. In CMOS circuits, as many interconnects carry pulsed-DC (local VCC and VSS lines) and bidirectional AC current (clock and signal lines), it is essential to assess the reliability of metallization systems under these conditions. Failure mechanisms of different metallization systems (Al-Si, Al-Cu, Cu, TiN/Al-alloy/TiN, etc.) and different metallization structures (via, plug and interconnect) under AC current stress in a wide frequency range (from mHz to 500 MHz) has been study in this paper. Based on these experimental results, a damage healing model is developed, and electromigration design rules are proposed. It shows that in the circuit operating frequency range, the "design-rule current" is the time-average current. The pure AC component of the current only contributes to self-heating, while the average (DC component) current contributes to electromigration. To ensure longer thermal-migration lifetime under high frequency AC stress, an additional design rule is proposed to limit the temperature rise due to self-joule heating.

Accelerated Strength Testing of Thermoplastic Composites

NASA Technical Reports Server (NTRS)

Reeder, J. R.; Allen, D. H.; Bradley, W. L.

1998-01-01

Constant ramp strength tests on unidirectional thermoplastic composite specimens oriented in the 90 deg. direction were conducted at constant temperatures ranging from 149 C to 232 C. Ramp rates spanning 5 orders of magnitude were tested so that failures occurred in the range from 0.5 sec. to 24 hrs. (0.5 to 100,000 MPa/sec). Below 204 C, time-temperature superposition held allowing strength at longer times to be estimated from strength tests at shorter times but higher temperatures. The data indicated that a 50% drop in strength might be expected for this material when the test time is increased by 9 orders of magnitude. The shift factors derived from compliance data applied well to the strength results. To explain the link between compliance and strength, a viscoelastic fracture model was investigated. The model, which used compliance as input, was found to fit the strength data only if the critical fracture energy was allowed to vary with temperature reduced stress rate. This variation in the critical parameter severely limits its use in developing a robust time-dependent strength model. The significance of this research is therefore seen as providing both the indication that a more versatile acceleration method for strength can be developed and the evidence that such a method is needed.

Application of Vibration and Oil Analysis for Reliability Information on Helicopter Main Rotor Gearbox

NASA Astrophysics Data System (ADS)

Murrad, Muhamad; Leong, M. Salman

Based on the experiences of the Malaysian Armed Forces (MAF), failure of the main rotor gearbox (MRGB) was one of the major contributing factors to helicopter breakdowns. Even though vibration and oil analysis are the effective techniques for monitoring the health of helicopter components, these two techniques were rarely combined to form an effective assessment tool in MAF. Results of the oil analysis were often used only for oil changing schedule while assessments of MRGB condition were mainly based on overall vibration readings. A study group was formed and given a mandate to improve the maintenance strategy of S61-A4 helicopter fleet in the MAF. The improvement consisted of a structured approach to the reassessment/redefinition suitable maintenance actions that should be taken for the MRGB. Basic and enhanced tools for condition monitoring (CM) are investigated to address the predominant failures of the MRGB. Quantitative accelerated life testing (QALT) was considered in this work with an intent to obtain the required reliability information in a shorter time with tests under normal stress conditions. These tests when performed correctly can provide valuable information about MRGB performance under normal operating conditions which enable maintenance personnel to make decision more quickly, accurately and economically. The time-to-failure and probability of failure information of the MRGB were generated by applying QALT analysis principles. This study is anticipated to make a dramatic change in its approach to CM, bringing significant savings and various benefits to MAF.

Decreased brain sigma-1 receptor contributes to the relationship between heart failure and depression.

PubMed

Ito, Koji; Hirooka, Yoshitaka; Matsukawa, Ryuichi; Nakano, Masatsugu; Sunagawa, Kenji

2012-01-01

Depression often coexists with cardiovascular disease, such as hypertension and heart failure, in which sympathetic hyperactivation is critically involved. Reduction in the brain sigma-1 receptor (S1R) functions in depression pathogenesis via neuronal activity modulation. We hypothesized that reduced brain S1R exacerbates heart failure, especially with pressure overload via sympathetic hyperactivation and worsening depression. Male Institute of Cancer Research mice were treated with aortic banding and, 4 weeks thereafter, fed a high-salt diet for an additional 4 weeks to accelerate cardiac dysfunction (AB-H). Compared with sham-operated controls (Sham), AB-H showed augmented sympathetic activity, decreased per cent fractional shortening, increased left ventricular dimensions, and significantly lower brain S1R expression. Intracerebroventricular (ICV) infusion of S1R agonist PRE084 increased brain S1R expression, lowered sympathetic activity, and improved cardiac function in AB-H. ICV infusion of S1R antagonist BD1063 increased sympathetic activity and decreased cardiac function in Sham. Tail suspension test was used to evaluate the index of depression-like behaviour, with immobility time and strain amplitude recorded as markers of struggle activity using a force transducer. Immobility time increased and strain amplitude decreased in AB-H compared with Sham, and these changes were attenuated by ICV infusion of PRE084. These results indicate that decreased brain S1R contributes to the relationship between heart failure and depression in a mouse model of pressure overload.

Graves' Disease

MedlinePlus

... blood to the body (congestive heart failure). Thyroid storm. A rare, but life-threatening complication of Graves' disease is thyroid storm, also known as accelerated hyperthyroidism or thyrotoxic crisis. ...

Statistical study of the reliability of oxide-defined stripe cw lasers of (AlGa)As

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

Ettenberg, M.

1979-03-01

In this report, we describe a statistical study of the reliability of oxide-defined stripe-contact cw injection lasers of (AlGa)As. These devices have one facet coated with Al/sub 2/O/sub 3/ and one facet coated with an Al/sub 2/O/sub 3//Si dichroic reflector; the lasers are optimized for cw low-threshold currents at room temperature, with values typically about 50 mA. Lifetests were carried out at 70 /sup 0/C ambient, in the cw mode of operation with about 5 mW output. Previous lifetests showed that the degradation rate followed a 0.95-eV activation energy so the 70 /sup 0/C environment provides a degradation acceleration factormore » of 190 over that at room temperature. We have found that the device failures follow a log-normal distribution, characterized by a mean time before failure of 4200 h and a standard deviation of 1.3. This corresponds to a mean time to failure (MTTF) of 10/sup 6/ h at room temperature. Failure is defined here as the inability of the device to emit 1 mW of stimulated cw output at 70 /sup 0/C, and assumes that optical feedback will be employed to adjust the laser current during operation. If a constant-current drive is envisioned, the failures for a 3-dB drop in light output also follow a log-normal distribution with a similar slope (standard deviation=1.1) and a MTTF of 2000 h at 70 /sup 0/C (500 000 h at room temperature). The failures were found to be mainly due to bulk gradual degradation and not facet or contact failure. Careful study of lasers before and after lifetest showed a significant increase in contact thermal resistance. However, this increase accounts for only a small portion of the nearly 70% increase in room-temperature cw threshold after failure at 70 /sup 0/C. After failure at 70 /sup 0/C, we also noted a degradation in the near-field and associated far-field pattern of the laser.« less

Interset stretching does not influence the kinematic profile of consecutive bench-press sets.

PubMed

García-López, David; Izquierdo, Mikel; Rodríguez, Sergio; González-Calvo, Gustavo; Sainz, Nuria; Abadía, Olaia; Herrero, Azael J

2010-05-01

This study was undertaken to examine the role of interset stretching on the time course of acceleration portion AP and mean velocity profile during the concentric phase of 2 bench-press sets with a submaximal load (60% of the 1 repetition maximum). Twenty-five college students carried out, in 3 different days, 2 consecutive bench-press sets leading to failure, performing between sets static stretching, ballistic stretching, or no stretching. Acceleration portion and lifting velocity patterns of the concentric phase were not altered during the second set, regardless of the stretching treatment performed. However, when velocity was expressed in absolute terms, static stretching reduced significantly (p <0.05) the average lifting velocity during the second set compared to the first one. Therefore, if maintenance of a high absolute velocity over consecutive sets is important for training-related adaptations, static stretching should be avoided or replaced by ballistic stretching.

Application of failure mode and effects analysis to intracranial stereotactic radiation surgery by linear accelerator.

PubMed

Masini, Laura; Donis, Laura; Loi, Gianfranco; Mones, Eleonora; Molina, Elisa; Bolchini, Cesare; Krengli, Marco

2014-01-01

The aim of this study was to analyze the application of the failure modes and effects analysis (FMEA) to intracranial stereotactic radiation surgery (SRS) by linear accelerator in order to identify the potential failure modes in the process tree and adopt appropriate safety measures to prevent adverse events (AEs) and near-misses, thus improving the process quality. A working group was set up to perform FMEA for intracranial SRS in the framework of a quality assurance program. FMEA was performed in 4 consecutive tasks: (1) creation of a visual map of the process; (2) identification of possible failure modes; (3) assignment of a risk probability number (RPN) to each failure mode based on tabulated scores of severity, frequency of occurrence and detectability; and (4) identification of preventive measures to minimize the risk of occurrence. The whole SRS procedure was subdivided into 73 single steps; 116 total possible failure modes were identified and a score of severity, occurrence, and detectability was assigned to each. Based on these scores, RPN was calculated for each failure mode thus obtaining values from 1 to 180. In our analysis, 112/116 (96.6%) RPN values were <60, 2 (1.7%) between 60 and 125 (63, 70), and 2 (1.7%) >125 (135, 180). The 2 highest RPN scores were assigned to the risk of using the wrong collimator's size and incorrect coordinates on the laser target localizer frame. Failure modes and effects analysis is a simple and practical proactive tool for systematic analysis of risks in radiation therapy. In our experience of SRS, FMEA led to the adoption of major changes in various steps of the SRS procedure.

Chronic Heart Failure Follow-up Management Based on Agent Technology.

PubMed

Mohammadzadeh, Niloofar; Safdari, Reza

2015-10-01

Monitoring heart failure patients through continues assessment of sign and symptoms by information technology tools lead to large reduction in re-hospitalization. Agent technology is one of the strongest artificial intelligence areas; therefore, it can be expected to facilitate, accelerate, and improve health services especially in home care and telemedicine. The aim of this article is to provide an agent-based model for chronic heart failure (CHF) follow-up management. This research was performed in 2013-2014 to determine appropriate scenarios and the data required to monitor and follow-up CHF patients, and then an agent-based model was designed. Agents in the proposed model perform the following tasks: medical data access, communication with other agents of the framework and intelligent data analysis, including medical data processing, reasoning, negotiation for decision-making, and learning capabilities. The proposed multi-agent system has ability to learn and thus improve itself. Implementation of this model with more and various interval times at a broader level could achieve better results. The proposed multi-agent system is no substitute for cardiologists, but it could assist them in decision-making.

Accidental Beam Losses and Protection in the LHC

NASA Astrophysics Data System (ADS)

Schmidt, R.; Working Group On Machine Protection

2005-06-01

At top energy (proton momentum 7 TeV/c) with nominal beam parameters, each of the two LHC proton beams has a stored energy of 350 MJ threatening to damage accelerator equipment in case of accidental beam loss. It is essential that the beams are properly extracted onto the dump blocks in case of failure since these are the only elements that can withstand full beam impact. Although the energy stored in the beams at injection (450 GeV/c) is about 15 times smaller compared to top energy, the beams must still be properly extracted in case of large accidental beam losses. Failures must be detected at a sufficiently early stage and initiate a beam dump. Quenches and power converter failures will be detected by monitoring the correct functioning of the hardware systems. In addition, safe operation throughout the cycle requires the use of beam loss monitors, collimators and absorbers. Ideas of detection of fast beam current decay, monitoring of fast beam position changes and monitoring of fast magnet current changes are discussed, to provide the required redundancy for machine protection.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate ('dynamic fatigue') testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rate in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate (dynamic fatigue) testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rates in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

The effect of accelerated aging on the wear of UHMWPE.

PubMed

Sakoda, H; Fisher, J; Lu, S; Buchanan, F

2001-01-01

Oxidative degradation of UHMWPE has been found to be a cause of elevated wear rate of the polymer in total joint replacement leading to failure of these devices. In order to evaluate long term stability of polymers, various accelerated aging methods have been developed. In this study, wear rates of shelf aged UHMWPE and "accelerated aged" UHMWPE were compared using a multi-directional pin-on-plate wear test machine in order to evaluate the effect of the accelerated aging on wear. Wear factors of the aged materials were found to depend on their density, which is a measure of oxidation level. Finally, accelerated aging was calibrated against shelf aging in terms of wear rate. Copyright 2001 Kluwer Academic Publishers

Flying qualities design criteria applicable to supersonic cruise aircraft

NASA Technical Reports Server (NTRS)

Chalk, C. R.

1980-01-01

A comprehensive set of flying qualities design criteria was prepared for use in the supersonic cruise research program. The framework for stating the design criteria is established and design criteria are included which address specific failures, approach to dangerous flight conditions, flight at high angle of attack, longitudinal and lateral directional stability and control, the primary flight control system, and secondary flight controls. Examples are given of lateral directional design criteria limiting lateral accelerations at the cockpit, time to roll through 30 deg of bank, and time delay in the pilot's command path. Flight test data from the Concorde certification program are used to substantiate a number of the proposed design criteria.

New understandings of failure modes in SSL luminaires

NASA Astrophysics Data System (ADS)

Shepherd, Sarah D.; Mills, Karmann C.; Yaga, Robert; Johnson, Cortina; Davis, J. Lynn

2014-09-01

As SSL products are being rapidly introduced into the market, there is a need to develop standard screening and testing protocols that can be performed quickly and provide data surrounding product lifetime and performance. These protocols, derived from standard industry tests, are known as ALTs (accelerated life tests) and can be performed in a timeframe of weeks to months instead of years. Accelerated testing utilizes a combination of elevated temperature and humidity conditions as well as electrical power cycling to control aging of the luminaires. In this study, we report on the findings of failure modes for two different luminaire products exposed to temperature-humidity ALTs. LEDs are typically considered the determining component for the rate of lumen depreciation. However, this study has shown that each luminaire component can independently or jointly influence system performance and reliability. Material choices, luminaire designs, and driver designs all have significant impacts on the system reliability of a product. From recent data, it is evident that the most common failure modes are not within the LED, but instead occur within resistors, capacitors, and other electrical components of the driver. Insights into failure modes and rates as a result of ALTs are reported with emphasis on component influence on overall system reliability.

Accelerated Aging Experiments for Prognostics of Damage Growth in Composite Materials

NASA Technical Reports Server (NTRS)

Saxena, Abhinav; Goebel, Kai Frank; Larrosa, Cecilia C.; Janapati, Vishnuvardhan; Roy, Surajit; Chang, Fu-Kuo

2011-01-01

Composite structures are gaining importance for use in the aerospace industry. Compared to metallic structures their behavior is less well understood. This lack of understanding may pose constraints on their use. One possible way to deal with some of the risks associated with potential failure is to perform in-situ monitoring to detect precursors of failures. Prognostic algorithms can be used to predict impending failures. They require large amounts of training data to build and tune damage model for making useful predictions. One of the key aspects is to get confirmatory feedback from data as damage progresses. These kinds of data are rarely available from actual systems. The next possible resource to collect such data is an accelerated aging platform. To that end this paper describes a fatigue cycling experiment with the goal to stress carbon-carbon composite coupons with various layups. Piezoelectric disc sensors were used to periodically interrogate the system. Analysis showed distinct differences in the signatures of growing failures between data collected at conditions. Periodic X-radiographs were taken to assess the damage ground truth. Results after signal processing showed clear trends of damage growth that were correlated to damage assessed from the X-ray images.

Omnibus risk assessment via accelerated failure time kernel machine modeling.

PubMed

Sinnott, Jennifer A; Cai, Tianxi

2013-12-01

Integrating genomic information with traditional clinical risk factors to improve the prediction of disease outcomes could profoundly change the practice of medicine. However, the large number of potential markers and possible complexity of the relationship between markers and disease make it difficult to construct accurate risk prediction models. Standard approaches for identifying important markers often rely on marginal associations or linearity assumptions and may not capture non-linear or interactive effects. In recent years, much work has been done to group genes into pathways and networks. Integrating such biological knowledge into statistical learning could potentially improve model interpretability and reliability. One effective approach is to employ a kernel machine (KM) framework, which can capture nonlinear effects if nonlinear kernels are used (Scholkopf and Smola, 2002; Liu et al., 2007, 2008). For survival outcomes, KM regression modeling and testing procedures have been derived under a proportional hazards (PH) assumption (Li and Luan, 2003; Cai, Tonini, and Lin, 2011). In this article, we derive testing and prediction methods for KM regression under the accelerated failure time (AFT) model, a useful alternative to the PH model. We approximate the null distribution of our test statistic using resampling procedures. When multiple kernels are of potential interest, it may be unclear in advance which kernel to use for testing and estimation. We propose a robust Omnibus Test that combines information across kernels, and an approach for selecting the best kernel for estimation. The methods are illustrated with an application in breast cancer. © 2013, The International Biometric Society.

Effect of surface finish on the failure mechanisms of flip-chip solder joints under electromigration

NASA Astrophysics Data System (ADS)

Lin, Y. L.; Lai, Y. S.; Tsai, C. M.; Kao, C. R.

2006-12-01

Two substrate surface finishes, Au/Ni and organic solderable preservative (OSP), were used to study the effect of the surface finish on the reliability of flip-chip solder joints under electromigration at 150°C ambient temperature. The solder used was eutectic PbSn, and the applied current density was 5×103 A/cm2 at the contact window of the chip. The under bump metallurgy (UBM) on the chip was sputtered Cu/Ni. It was found that the mean-time-to-failure (MTTF) of the OSP joints was six times better than that of the Au/Ni joints (3080 h vs. 500 h). Microstructure examinations uncovered that the combined effect of current crowding and the accompanying local Joule heating accelerated the local Ni UBM consumption near the point of electron entrance. Once Ni was depleted at a certain region, this region became nonconductive, and the flow of the electrons was diverted to the neighboring region. This neighboring region then became the place where electrons entered the joint, and the local Ni UBM consumption was accelerated. This process repeated itself, and the Ni-depleted region extended further on, creating an ever-larger nonconductive region. The solder joint eventually, failed when the nonconductive region became too large, making the effective current density very high. Accordingly, the key factor determining the MTTF was the Ni consumption rate. The joints with the OSP surface finish had a longer MTTF because Cu released from the substrate was able to reduce the Ni consumption rate.

Rate-weakening friction characterizes both slow sliding and catastrophic failure of landslides.

PubMed

Handwerger, Alexander L; Rempel, Alan W; Skarbek, Rob M; Roering, Joshua J; Hilley, George E

2016-09-13

Catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually, whereas slow-moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes. Surprisingly, both failure modes are displayed by nearby landslides (and individual landslides in different years) subjected to almost identical environmental conditions. Such observations have motivated the search for mechanisms that can cause slow-moving landslides to transition via runaway acceleration to catastrophic failure. A similarly diverse range of sliding behavior, including earthquakes and slow-slip events, occurs along tectonic faults. Our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions. Here, we describe landslide motion using a rate- and state-dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip. Our idealized, one-dimensional model reproduces both the displacement patterns observed in slow-moving landslides and the acceleration toward failure exhibited by catastrophic events. Catastrophic failure occurs only when the slip surface is characterized by rate-weakening friction and its lateral dimensions exceed a critical nucleation length [Formula: see text] that is shorter for higher effective stresses. However, landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure. Our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments.

Rate-weakening friction characterizes both slow sliding and catastrophic failure of landslides

PubMed Central

Handwerger, Alexander L.; Rempel, Alan W.; Skarbek, Rob M.; Roering, Joshua J.; Hilley, George E.

2016-01-01

Catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually, whereas slow-moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes. Surprisingly, both failure modes are displayed by nearby landslides (and individual landslides in different years) subjected to almost identical environmental conditions. Such observations have motivated the search for mechanisms that can cause slow-moving landslides to transition via runaway acceleration to catastrophic failure. A similarly diverse range of sliding behavior, including earthquakes and slow-slip events, occurs along tectonic faults. Our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions. Here, we describe landslide motion using a rate- and state-dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip. Our idealized, one-dimensional model reproduces both the displacement patterns observed in slow-moving landslides and the acceleration toward failure exhibited by catastrophic events. Catastrophic failure occurs only when the slip surface is characterized by rate-weakening friction and its lateral dimensions exceed a critical nucleation length h* that is shorter for higher effective stresses. However, landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure. Our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments. PMID:27573836

NWSC nickel cadmium spacecraft cell accelerated life test program data analysis

NASA Technical Reports Server (NTRS)

Lander, J.

1980-01-01

An analysis of the data leading to a proposed accelerated life test scheme to test a nickel cadmium cell under spacecraft usage conditions is described. The amount and concentration of electrolyte and the amount of precharge in the cell are discussed in relation to the design of the cell and the accelerated test design. A failure analysis of the cell is summarized. The analysis included such environmental test variables as the depth of discharge, the temperature, the amount of recharge and the charge and discharge rate.

Experimental evaluation of the Battelle accelerated test design for the solar array at Mead, Nebraska

NASA Technical Reports Server (NTRS)

Frickland, P. O.; Repar, J.

1982-01-01

A previously developed test design for accelerated aging of photovoltaic modules was experimentally evaluated. The studies included a review of relevant field experience, environmental chamber cycling of full size modules, and electrical and physical evaluation of the effects of accelerated aging during and after the tests. The test results indicated that thermally induced fatigue of the interconnects was the primary mode of module failure as measured by normalized power output. No chemical change in the silicone encapsulant was detectable after 360 test cycles.

High Altitude Plasma Instrument (HAPI) data analysis

NASA Technical Reports Server (NTRS)

Burch, J. L.

1994-01-01

The objectives of the Dynamics Explorer mission are to investigate the coupling of energy, mass, and momentum among the earth's magnetosphere, ionosphere, and upper atmosphere. At launch, on August 3, 1981, DE-1 was placed into an elliptical polar orbit having an apogee of 23,130 km to allow global auroral imaging and crossings of auroral field lines at altitudes of several thousand kilometers. At the same time DE-2 was placed into a polar orbit, coplanar with that of DE-1 but with a perigee altitude low enough (309 km) for neutral measurements and an apogee altitude of 1012 km. The DE-1 High Altitude Plasma Instrument (HAPI) provided data on low and medium energy electrons and ions from August 13, 1981 until December 1, 1981, when a high-voltage failure occured. Analysis of HAPI data for the time period of this contract has produced new results on the source mechanisms for electron conical distributions, particle acceleration phenomena in auroral acceleration regions, Birkeland currents throughout the nightside auroral regions, the source region for auroral kilometric radiation (AKR), and plasma injection phenomena in the polar cusp.

Evaluation of Data Retention and Imprint Characteristics of FRAMs Under Environmental Stresses for NASA Applications

NASA Technical Reports Server (NTRS)

Sharma, Ashok K.; Teverovsky, Alexander; Dowdy, Terry W.; Hamilton, Brett

2000-01-01

A major reliability issue for all advanced nonvolatile memory (NVM) technology devices including FRAMs (Ferroelectric random access memories) is the data retention characteristics over extended period of time, under environmental stresses and exposure to total ionizing dose (TID) radiation effects. For this testing, 256 Kb FRAMs in 28-pin plastic DIPS, rated for industrial grade temperature range of -40 C to +85 C, were procured. These are two-transistor, two-capacitor (2T-2C) design FRAMs. In addition to data retention characteristics, the parts were also evaluated for imprint failures, which are defined as the failure of cells to change from a "preferred" state, where it has been for a significant period of time to an opposite state (e.g., from 1 to 0, or 0 to 1). These 256 K FRAMs were subjected to scanning acoustic microscopy (C-SAM); 1,000 temperature cycles from -65 C to +150 C; high temperature aging at 150 C, 175 C, and 200 C for 1,000 hours; highly accelerated stress test (HAST) for 500 hours; 1,000 hours of operational life test at 125 C; and total ionizing dose radiation testing. As a preconditioning, 10 K read/write cycles were performed on all devices. Interim electrical measurements were performed throughout this characterization, including special imprint testing and final electrical testing. Some failures were observed during high temperature aging test at 200 C, during HAST testing, and during 1,000 hours of operational life at 125 C. The parts passed 10 Krad exposure, but began showing power supply current increases during the dose increment from 10 Krad to 30 Krad, and at 40 Krad severe data retention and parametric failures were observed. Failures from various environmental group testing are currently being analyzed.

Evaluation of Data Retention and Imprint Characteristics of FRAMs Under Environmental Stresses for NASA Applications

NASA Technical Reports Server (NTRS)

Sharma, Asbok K.; Teverovsky, Alexander; Dowdy, Terry W.; Hamilton, Brett

2002-01-01

A major reliability issue for all advanced nonvolatile memory (NVM) technology devices including FRAMs is the data retention characteristics over extended period of time, under environmental stresses and exposure to total ionizing dose (TID) radiation effects. For this testing, 256 Kb FRAMs in 28-pin plastic DIPS, rated for industrial grade temperature range of -40 C to +85 C, were procured. These are two-transistor, two-capacitor (2T-2C) design FRAMs. In addition to data retention characteristics, the parts were also evaluated for imprint failures, which are defined as the failure of cells to change from a "preferred" state, where it has been for a significant period of time to an opposite state (e.g., from 1 to 0, or 0 to 1). These 256 K FRAMs were subjected to scanning acoustic microscopy (C-SAM); 1,000 temperature cycles from -65 C to +150 C; high temperature aging at 150 C, 175 C, and 200 C for 1,000 hours; highly accelerated stress test (HAST) for 500 hours; 1,000 hours of operational life test at 125 C; and total ionizing dose radiation testing. As a preconditioning, 10 K read/write cycles were performed on all devices. Interim electrical measurements were performed throughout this characterization, including special imprint testing and final electrical testing. Some failures were observed during high temperature aging test at 200 C, during HAST testing, and during 1,000 hours of operational life at 125 C. The parts passed 10 Krad exposure, but began showing power supply current increases during the dose increment from 10 Krad to 30 Krad, and at 40 Krad severe data retention and parametric failures were observed. Failures from various environmental group testing are currently being analyzed.

Failure Engineering Study and Accelerated Stress Test Results for the Mars Global Surveyor Spacecraft's Power Shunt Assemblies

NASA Technical Reports Server (NTRS)

Gibbel, Mark; Larson, Tim

1999-01-01

Due to a post launch failure of a part a new plan for the Mars Global Surveyor was developed. This new plan involved the addition of many deep thermal cycles to the Power Shunt Assemblies (PSA's). This new plan exceeds the previous acceptance cold level, and fatigue life on packaging design. This presentation reviews the experiments that were used to test the capabilities of the PSA to function in the new situation. It also reviews the analyses preformed to verify the most likely failure mechanism, and the likelihood that these failures would impact the new mission requirements.

Slow, fast, and post-collapse displacements of the Mud Creek landslide in California from UAVSAR and satellite SAR analysis

NASA Astrophysics Data System (ADS)

Fielding, E. J.; Handwerger, A. L.; Burgmann, R.; Liu, Z.

2017-12-01

Landslides display a wide variety of behaviors ranging from slow steady or seasonal motion to runaway acceleration and catastrophic failure. In some cases, a single landslide moves slowly for a period of weeks to years before it rapidly accelerates into a catastrophic failure. Measurement of the spatio-temporal patterns of landslide motion in response to changes in environmental parameters such as rainfall, snowmelt, and nearby earthquakes will help us to constrain the mechanisms that control these landslide behaviors. Here, we use synthetic aperture radar interferometry (InSAR) from satellite and airborne platforms to measure the kinematics of several landslides along the coast of Central California, including the large Mud Creek landslide near Big Sur that catastrophically collapsed in May 2017 and led to the destruction of a major highway and millions of dollars in damages. We use InSAR and pixel offset data from NASA/JPL UAVSAR, JAXA ALOS1/2, and Copernicus Sentinel 1A/B to quantify the displacement time series and 3D motion. Our data show that the Mud Creek landslide has been active for at least 2.5 years and displayed persistent motion (average rate of 10 cm/yr in LOS) with seasonal variations in velocity driven by rainfall-induced changes in pore pressure. We find that each year the landslide accelerated approximately 60-90 days after the onset of seasonal precipitation, which provides constraints on the hillslope hydrology. Before its ultimate collapse, the landslide displayed a large increase in velocity due to the above average rainfall during the 2017 water year. It appears a series of major storms in January and February 2017, some fed by atmospheric rivers, triggered a sufficient increase in pore-water pressure that led to the runaway failure. We model this behavior using a rate-and-state friction model developed to capture this range of landslide behaviors. This model will allow us to explore how different landslide properties (e.g., material properties, geometry, stress changes) can control the behavior of these types of landslides. We observe additional motion of the landslide deposits after the catastrophic collapse.

Monitoring and Early Warning of the 2012 Preonzo Catastrophic Rockslope Failure

NASA Astrophysics Data System (ADS)

Loew, Simon; Gschwind, Sophie; Keller-Signer, Alexandra; Valenti, Giorgio

2015-04-01

In this contribution we describe the accelerated creep stage and early warning system of a 210'000 m3 rock slope failure that occurred in May 2012 above the village of Preonzo (Swiss Alps). The very rapid failure occurred from a larger and retrogressive instability in high-grade metamorphic ortho-gneisses and amphibolites with a total volume of about 350'000 m3 located at an alpine meadow called Alpe di Roscioro. This instability showed clearly visible signs of movements since 1989 and accelerated creep with significant hydro-mechanical forcing since about 1999. Because the instability at Preonzo threatened a large industrial facility and important transport routes a cost-effective early warning system was installed in 2010. The alarm thresholds for pre-alarm, general public alarm and evacuation were derived from 10 years of continuous displacement monitoring with crack extensometers and an automated total station. These thresholds were successfully applied to evacuate the industrial facility and close important roads a few days before the catastrophic slope failure of May 15th, 2012. The rock slope failure occurred in two events, exposing a planar rupture plane dipping 42° and generating deposits in the mid-slope portion with a travel angle of 38°. Two hours after the second rockslide, the fresh colluvial deposits became reactivated in a devastating de-bris avalanche reaching the foot of the slope.

Parabens Accelerate Ovarian Dysfunction in a 4-Vinylcyclohexene Diepoxide-Induced Ovarian Failure Model

PubMed Central

Lee, Jae-Hwan; Lee, Myeongho; Ahn, Changhwan; Kang, Hee Young; Tran, Dinh Nam; Jeung, Eui-Bae

2017-01-01

Parabens are widely used preservatives in basic necessities such as cosmetic and pharmaceutical products. In previous studies, xenoestrogenic actions of parabens were reported in an immature rat model and a rat pituitary cell line (GH3 cells). The relationship between parabens and ovarian failure has not been described. In the present study, the influence of parabens on ovarian folliculogenesis and steroidogenesis was investigated. A disruptor of ovarian small pre-antral follicles, 4-vinylcyclohexene diepoxide (VCD, 40 mg/kg), was used to induce premature ovarian failure (POF). Methylparaben (MP, 100 mg/kg), propylparaben (PP, 100 mg/kg), and butylparaben (BP, 100 mg/kg) dissolved in corn oil were treated in female 8-week-old Sprague-Dawley rat for 5 weeks. Estrus cycle status was checked daily by vaginal smear test. Ovarian follicle development and steroid synthesis were investigated through real-time PCR and histological analyses. Diestrus phases in the VCD, PP, and BP groups were longer than that in the vehicle group. VCD significantly decreased mRNA level of folliculogenesis-related genes (Foxl2, Kitl and Amh). All parabens significantly increased the Amh mRNA level but unchanged Foxl2 and Kitlg acting in primordial follicles. VCD and MP slightly increased Star and Cyp11a1 levels, which are related to an initial step in steroidogenesis. VCD and parabens induced an increase in FSH levels in serum and significantly decreased the total number of follicles. Increased FSH implies impairment in ovarian function due to VCD or parabens. These results suggest that VCD may suppress both formation and development of follicles. In particular, combined administration of VCD and parabens accelerated inhibition of the follicle-developmental process through elevated AMH level in small antral follicles. PMID:28208728

Reliability demonstration test for load-sharing systems with exponential and Weibull components

PubMed Central

Hu, Qingpei; Yu, Dan; Xie, Min

2017-01-01

Conducting a Reliability Demonstration Test (RDT) is a crucial step in production. Products are tested under certain schemes to demonstrate whether their reliability indices reach pre-specified thresholds. Test schemes for RDT have been studied in different situations, e.g., lifetime testing, degradation testing and accelerated testing. Systems designed with several structures are also investigated in many RDT plans. Despite the availability of a range of test plans for different systems, RDT planning for load-sharing systems hasn’t yet received the attention it deserves. In this paper, we propose a demonstration method for two specific types of load-sharing systems with components subject to two distributions: exponential and Weibull. Based on the assumptions and interpretations made in several previous works on such load-sharing systems, we set the mean time to failure (MTTF) of the total system as the demonstration target. We represent the MTTF as a summation of mean time between successive component failures. Next, we introduce generalized test statistics for both the underlying distributions. Finally, RDT plans for the two types of systems are established on the basis of these test statistics. PMID:29284030

Reliability demonstration test for load-sharing systems with exponential and Weibull components.

PubMed

Xu, Jianyu; Hu, Qingpei; Yu, Dan; Xie, Min

2017-01-01

Conducting a Reliability Demonstration Test (RDT) is a crucial step in production. Products are tested under certain schemes to demonstrate whether their reliability indices reach pre-specified thresholds. Test schemes for RDT have been studied in different situations, e.g., lifetime testing, degradation testing and accelerated testing. Systems designed with several structures are also investigated in many RDT plans. Despite the availability of a range of test plans for different systems, RDT planning for load-sharing systems hasn't yet received the attention it deserves. In this paper, we propose a demonstration method for two specific types of load-sharing systems with components subject to two distributions: exponential and Weibull. Based on the assumptions and interpretations made in several previous works on such load-sharing systems, we set the mean time to failure (MTTF) of the total system as the demonstration target. We represent the MTTF as a summation of mean time between successive component failures. Next, we introduce generalized test statistics for both the underlying distributions. Finally, RDT plans for the two types of systems are established on the basis of these test statistics.

The ac and dc performance of polymeric insulating materials under accelerated aging in a fog chamber

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

Gorur, R.S.; Cherney, E.A.; Hackam, R.

1988-10-01

The paper presents the results of the dc performance of polymeric insulating materials in a fog chamber. The materials evaluated in fog produced from low (250 ..mu..S/cm) and high (1000 ..mu..S/cm) conductivity water include cylindrical rod samples of high temperature vulcanized (HTV) silicone rubber and ethylene propylene diene monomer (EPDM) rubber containing various amounts of either alumina trihydrate (ATH) or silica fillers, or both. Comparison is made of material performance obtained with ac which was reported in an earlier study. In both low and high conductivity fog, the time to failure with ac and +dc was very similar, but amore » reduction by a factor of about four was observed in the time to failure with -dc. For both ac and dc, silicone rubber performed better than EPDM samples in low conductivity fog, while the order of performance was reversed in high conductivity fog. A theoretical model to determine the effect of dry band discharges on material is presented. Good agreement of the predicted behavior of materials with the experimental findings is shown.« less

Time-Temperature Superposition to Determine the Stress-Rupture of Aramid Fibres

NASA Astrophysics Data System (ADS)

Alwis, K. G. N. C.; Burgoyne, C. J.

2006-07-01

Conventional creep testing takes a long time to obtain stress-rupture data for aramid fibres at the low stress levels likely to be used in practical applications. However, the rate of creep of aramid can be accelerated by a thermally activated process to obtain the failure of fibres within a few hours. It is possible to obtain creep curves at different temperature levels which can be shifted along the time axis to generate a single curve know as a master curve, from which stress-rupture data can be obtained. This technique is known as the time-temperature superposition principle and will be applied to Kevlar 49 yarns. Important questions relating to the techniques needed to obtain smooth master curves will be discussed, as will the validity the resulting curves and the corresponding stress-rupture lifetime.

Sepsis and Septic Shock Strategies.

PubMed

Armstrong, Bracken A; Betzold, Richard D; May, Addison K

2017-12-01

Three therapeutic principles most substantially improve organ dysfunction and survival in sepsis: early, appropriate antimicrobial therapy; restoration of adequate cellular perfusion; timely source control. The new definitions of sepsis and septic shock reflect the inadequate sensitivity, specify, and lack of prognostication of systemic inflammatory response syndrome criteria. Sequential (sepsis-related) organ failure assessment more effectively prognosticates in sepsis and critical illness. Inadequate cellular perfusion accelerates injury and reestablishing perfusion limits injury. Multiple organ systems are affected by sepsis and septic shock and an evidence-based multipronged approach to systems-based therapy in critical illness results in improve outcomes. Copyright © 2017 Elsevier Inc. All rights reserved.

Effects of Near Field Pyroshock on the Performance of a Nitramine Nitrocellulose Propellant

NASA Technical Reports Server (NTRS)

Baca, Arcenio B.

2016-01-01

The overall purpose of this study is to investigate the effects of a pyroshock environment on the performance characteristics of a propellant used in pyrotechnic devices such as guillotine cutters. Near field pyroshock which is defined by acceleration amplitudes in excess of 10,000g at a frequency of greater than 10,000 Hz is a highly transient environment that has a known potential to cause failure in both structural and electronic components. A heritage pressure cartridge assembly which uses a nitramine nitrocellulose propellant with a known performance baseline will be exposed to a near field pyroshock event. The pressure cartridge will then be fired in an ambient closed bomb firing to collect pressure time history. The two performance characteristics that will be evaluated are the pressure amplitude and time to peak pressure. This data will be compared to the base-lined ambient closed bomb data to evaluate the effects of the shock on the performance of the propellant. It is expected that the pyroshock environment will cause brittle failures of the propellant increasing the surface area of said propellant. This increase of surface area should result in increased combustion rate which should show as an increased pressure peak and decreased time to peak pressure in the pressure time data.

Investigation of accelerated stress factors and failure/degradation mechanisms in terrestrial solar cells

NASA Technical Reports Server (NTRS)

Lathrop, J. W.

1984-01-01

Research on the reliability of terrestrial solar cells was performed to identify failure/degradation modes affecting solar cells and to relate these to basic physical, chemical, and metallurgical phenomena. Particular concerns addressed were the reliability attributes of individual single crystalline, polycrystalline, and amorphous thin film silicon cells. Results of subjecting different types of crystalline cells to the Clemson accelerated test schedule are given. Preliminary step stress results on one type of thin film amorphous silicon (a:Si) cell indicated that extraneous degradation modes were introduced above 140 C. Also described is development of measurement procedures which are applicable to the reliability testing of a:Si solar cells as well as an approach to achieving the necessary repeatability of fabricating a simulated a:Si reference cell from crystalline silicon photodiodes.

Heterogeneity: The key to forecasting material failure?

NASA Astrophysics Data System (ADS)

Vasseur, J.; Wadsworth, F. B.; Lavallée, Y.; Dingwell, D. B.

2014-12-01

Empirical mechanistic models have been applied to the description of the stress and strain rate upon failure for heterogeneous materials. The behaviour of porous rocks and their analogous two-phase viscoelastic suspensions are particularly well-described by such models. Nevertheless, failure cannot yet be predicted forcing a reliance on other empirical prediction tools such as the Failure Forecast Method (FFM). Measurable, accelerating rates of physical signals (e.g., seismicity and deformation) preceding failure are often used as proxies for damage accumulation in the FFM. Previous studies have already statistically assessed the applicability and performance of the FFM, but none (to the best of our knowledge) has done so in terms of intrinsic material properties. Here we use a rheological standard glass, which has been powdered and then sintered for different times (up to 32 hours) at high temperature (675°C) in order to achieve a sample suite with porosities in the range of 0.10-0.45 gas volume fraction. This sample suite was then subjected to mechanical tests in a uniaxial press at a constant strain rate of 10-3 s-1 and a temperature in the region of the glass transition. A dual acoustic emission (AE) rig has been employed to test the success of the FFM in these materials of systematically varying porosity. The pore-emanating crack model describes well the peak stress at failure in the elastic regime for these materials. We show that the FFM predicts failure within 0-15% error at porosities >0.2. However, when porosities are <0.2, the forecast error associated with predicting the failure time increases to >100%. We interpret these results as a function of the low efficiency with which strain energy can be released in the scenario where there are few or no heterogeneities from which cracks can propagate. These observations shed light on questions surrounding the variable efficacy of the FFM applied to active volcanoes. In particular, they provide a systematic demonstration of the fact that a good understanding of the material properties is required. Thus, we wish to emphasize the need for a better coupling of empirical failure forecasting models with mechanical parameters, such as failure criteria for heterogeneous materials, and point to the implications of this for a broad range of material-based disciplines.

Capacitor Technologies, Applications and Reliability

NASA Technical Reports Server (NTRS)

1981-01-01

Various aspects of capacitor technologies and applications are discussed. Major emphasis is placed on: the causes of failures; accelerated testing; screening tests; destructive physical analysis; applications techniques; and improvements in capacitor capabilities.

Rate-weakening friction characterizes both slow sliding and catastrophic failure of landslides

NASA Astrophysics Data System (ADS)

Handwerger, Alexander L.; Rempel, Alan W.; Skarbek, Rob M.; Roering, Joshua J.; Hilley, George E.

2016-09-01

Catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually, whereas slow-moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes. Surprisingly, both failure modes are displayed by nearby landslides (and individual landslides in different years) subjected to almost identical environmental conditions. Such observations have motivated the search for mechanisms that can cause slow-moving landslides to transition via runaway acceleration to catastrophic failure. A similarly diverse range of sliding behavior, including earthquakes and slow-slip events, occurs along tectonic faults. Our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions. Here, we describe landslide motion using a rate- and state-dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip. Our idealized, one-dimensional model reproduces both the displacement patterns observed in slow-moving landslides and the acceleration toward failure exhibited by catastrophic events. Catastrophic failure occurs only when the slip surface is characterized by rate-weakening friction and its lateral dimensions exceed a critical nucleation length h*h* that is shorter for higher effective stresses. However, landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure. Our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments.

Predictive factors of tumor control and survival after radiosurgery for local failures of nasopharyngeal carcinoma.

PubMed

Chua, Daniel T T; Sham, Jonathan S T; Hung, Kwan-Ngai; Leung, Lucullus H T; Au, Gordon K H

2006-12-01

Stereotactic radiosurgery has been employed as a salvage treatment of local failures of nasopharyngeal carcinoma (NPC). To identify patients that would benefit from radiosurgery, we reviewed our data with emphasis on factors that predicted treatment outcome. A total of 48 patients with local failures of NPC were treated by stereotactic radiosurgery between March 1996 and February 2005. Radiosurgery was administered using a modified linear accelerator with single or multiple isocenters to deliver a median dose of 12.5 Gy to the target periphery. Median follow-up was 54 months. Five-year local failure-free probability after radiosurgery was 47.2% and 5-year overall survival rate was 46.9%. Neuroendocrine complications occurred in 27% of patients but there were no treatment-related deaths. Time interval from primary radiotherapy, retreatment T stage, prior local failures and tumor volume were significant predictive factors of local control and/or survival whereas age was of marginal significance in predicting survival. A radiosurgery prognostic scoring system was designed based on these predictive factors. Five-year local failure-free probabilities in patients with good, intermediate and poor prognostic scores were 100%, 42.5%, and 9.6%. The corresponding five-year overall survival rates were 100%, 51.1%, and 0%. Important factors that predicted tumor control and survival after radiosurgery were identified. Patients with good prognostic score should be treated by radiosurgery in view of the excellent results. Patients with intermediate prognostic score may also be treated by radiosurgery but those with poor prognostic score should receive other salvage treatments.

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

NASA Technical Reports Server (NTRS)

Fasanella, Edwin L.; Billings, Marcus D.

2001-01-01

The nonlinear, transient dynamic finite element code, MSC.Dytran, was used to simulate an impact test of an energy absorbing Earth Entry Vehicle (EEV) that will impact without a parachute. EEVOs are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the center of the EEVOs cellular structure. Pre-test analytical predictions were compared with the test results from a bungee accelerator. The model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAM1 model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for cellular impact.

Monitoring the corrosion process of reinforced concrete using BOTDA and FBG sensors.

PubMed

Mao, Jianghong; Chen, Jiayun; Cui, Lei; Jin, Weiliang; Xu, Chen; He, Yong

2015-04-15

Expansion and cracking induced by the corrosion of reinforcement concrete is the major factor in the failure of concrete durability. Therefore, monitoring of concrete cracking is critical for evaluating the safety of concrete structures. In this paper, we introduce a novel monitoring method combining Brillouin optical time domain analysis (BOTDA) and fiber Bragg grating (FBG), based on mechanical principles of concrete expansion cracking. BOTDA monitors concrete expansion and crack width, while FBG identifies the time and position of cracking. A water-pressure loading simulation test was carried out to determine the relationship between fiber strain, concrete expansion and crack width. An electrical accelerated corrosion test was also conducted to evaluate the ability of this novel sensor to monitor concrete cracking under practical conditions.

Effect of Al-trace dimension on Joule heating and current crowding in flip-chip solder joints under accelerated electromigration

NASA Astrophysics Data System (ADS)

Liang, S. W.; Chang, Y. W.; Chen, Chih

2006-04-01

Three-dimensional thermoelectrical simulation was conducted to investigate the influence of Al-trace dimension on Joule heating and current crowding in flip-chip solder joints. It is found that the dimension of the Al-trace effects significantly on the Joule heating, and thus directly determines the mean time to failure (MTTF). Simulated at a stressing current of 0.6A at 70°C, we estimate that the MTTF of the joints with Al traces in 100μm width was 6.1 times longer than that of joints with Al traces in 34μm width. Lower current crowding effect and reduced hot-spot temperature are responsible for the improved MTTF.

Lifetime Extension Report: Progress on the SAVY-4000 Lifetime Extension Program

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

Welch, Cynthia F.; Smith, Paul Herrick; Weis, Eric M.

The 3-year accelerated aging study of the SAVY-4000 O-ring shows very little evidence of significant degradation to samples subjected to aggressive elevated temperature and radiation conditions. Whole container thermal aging studies followed by helium leakage testing and compression set measurements were used to establish an estimate for a failure criterion for O-ring compression set of ≥65 %. The whole container aging studies further show that the air flow and efficiency functions of the filter do not degrade significantly after thermal aging. However, the degradation of the water-resistant function leads to water penetration failure after four months at 210°C, but doesmore » not cause failure after 10 months at 120°C (130°C is the maximum operating temperature for the PTFE membrane). The thermal aging data for O-ring compression set do not meet the assumptions of standard time-temperature superposition analysis for accelerated aging studies. Instead, the data suggest that multiple degradation mechanisms are operative, with a reversible mechanism operative at low aging temperatures and an irreversible mechanism dominating at high aging temperatures. To distinguish between these mechanisms, we have measured compression set after allowing the sample to physically relax, thereby minimizing the effect of the reversible mechanism. The resulting data were analyzed using two distinct mathematical methods to obtain a lifetime estimate based on chemical degradation alone. Both methods support a lifetime estimate of greater than 150 years at 80°C. Although the role of the reversible mechanism is not fully understood, it is clear that the contribution to the total compression set is small in comparison to that due to the chemical degradation mechanism. To better understand the chemical degradation mechanism, thermally aged O-ring samples have been characterized by Fourier Transform Infrared (FTIR), Electron Paramagnetic Resonance (EPR), Gel Permeation Chromatography (GPC), and Differential Scanning Calorimetry (DSC). These experiments detect no significant O-ring degradation below 80°C. Furthermore, durometer measurements indicate that there is no significant change in O-ring hardness at all aging conditions examined. Therefore, our current conservative lifetime estimate for the O-ring and the filter is 10 years at 80°C. In FY17, we will continue to probe the chemical degradation mechanism using oxygen consumption measurements under accelerated aging conditions to reveal temperatures at which oxidation occurs, along with any differences in oxidation rate at the low vs. high aging temperatures. We will also refine the failure criteria and finalize the radiation/thermal synergistic studies to determine a final design lifetime.« less

Characteristics of Landslides Triggered by Mw 7.8 2015 Gorkha Earthquake

NASA Astrophysics Data System (ADS)

Dhital, Smriti

The Mw 7.8 Gorkha earthquake struck central Nepal on April 25, 2015 and brought about a huge loss of life and property. The quake was also responsible for the generation of a large number of landslides. They blocked highways, devastated villages, and temporarily dammed some rivers. About 14,670 landslips were triggered off by the main shock and its numerous large aftershocks. Among the detected failures, about 23% had an area greater than 100 m2. Since such failures can directly affect people's life and property, they are considered for further investigation in this study. A comparison of these coseismic landslides with the 29 historical failures reveals that these landslides slightly exceed in number from those expected for the peak ground acceleration observed due to these earthquakes. The landslides seem to be concentrated within the area of the fault rupture surface. About 90% of the detected landslips could be classified as earth falls. The areas having relatively soft rocks, such as slates, shales, schists and phyllites of the Lesser Himalaya, suffered from a greater number of failures. The landslides had a strong correlation with the peak ground acceleration and they also showed a positive correlation with some landslide-susceptible geological formations composing the study area.

Accelerated Creep Testing of High Strength Aramid Webbing

NASA Technical Reports Server (NTRS)

Jones, Thomas C.; Doggett, William R.; Stnfield, Clarence E.; Valverde, Omar

2012-01-01

A series of preliminary accelerated creep tests were performed on four variants of 12K and 24K lbf rated Vectran webbing to help develop an accelerated creep test methodology and analysis capability for high strength aramid webbings. The variants included pristine, aged, folded and stitched samples. This class of webbings is used in the restraint layer of habitable, inflatable space structures, for which the lifetime properties are currently not well characterized. The Stepped Isothermal Method was used to accelerate the creep life of the webbings and a novel stereo photogrammetry system was used to measure the full-field strains. A custom MATLAB code is described, and used to reduce the strain data to produce master creep curves for the test samples. Initial results show good correlation between replicates; however, it is clear that a larger number of samples are needed to build confidence in the consistency of the results. It is noted that local fiber breaks affect the creep response in a similar manner to increasing the load, thus raising the creep rate and reducing the time to creep failure. The stitched webbings produced the highest variance between replicates, due to the combination of higher local stresses and thread-on-fiber damage. Large variability in the strength of the webbings is also shown to have an impact on the range of predicted creep life.

Preparation and comparative testing of advanced diamond-like carbon foils for tandem accelerators and time-of-flight spectrometers

NASA Astrophysics Data System (ADS)

Liechtenstein, V. Kh.; Ivkova, T. M.; Olshanski, E. D.; Baranov, A. M.; Repnow, R.; Hellborg, R.; Weller, R. A.; Wirth, H. L.

1999-12-01

The sputter preparation technique for thin diamond-like carbon (DLC) foils, advantageously used for ion-beam stripping and timing in accelerator experiments, has been optimized to improve the quality and the performance of the foils. Irradiation lifetimes of 5 μg/cm 2 DLC foils prepared by this technique have been compared with those for foils of approximately the same thickness, prepared by laser plasma ablation and for ethylene cracked foils when bombarded by 11 MeV Cu - - and Au --ion beams of ˜1 μA beam current at the Heidelberg MP-tandem. Standard carbon arc-evaporated foils were used as references. In these experiments, DLC stripper foils appeared to have a mean lifetime approximately two times longer than ethylene-cracked foils regardless of ion species, and compared favorably with foils prepared by laser ablation method. All these foils lasted at least, 10 times longer than standard carbon foils, when irradiated in the MP terminal. Approximately, the same improvement factor was confirmed with 3 μg/cm 2 DLC stripper foils irradiated with 2.3 MeV Ni-beams at the Pelletron accelerator in Lund. Unlike standard carbon foils, most of the advanced lifetime foils exhibited thinning during long irradiation, under clean vacuum. This suggests that sputtering of the foil by the heavy-ion beam might be a dominant process, responsible for the observed failure of these long-lived strippers. Along with specifically corrugated self-supporting DLC beam strippers, we succeeded in the fabrication of very smooth and ultra thin (˜0.5 μg/cm 2) DLC foils, mounted on grids and used as start foils for the ToF spectrometers applied in ion beam analysis.

A comparison between standard methods and structural nested modelling when bias from a healthy worker survivor effect is suspected: an iron-ore mining cohort study.

PubMed

Björ, Ove; Damber, Lena; Jonsson, Håkan; Nilsson, Tohr

2015-07-01

Iron-ore miners are exposed to extremely dusty and physically arduous work environments. The demanding activities of mining select healthier workers with longer work histories (ie, the Healthy Worker Survivor Effect (HWSE)), and could have a reversing effect on the exposure-response association. The objective of this study was to evaluate an iron-ore mining cohort to determine whether the effect of respirable dust was confounded by the presence of an HWSE. When an HWSE exists, standard modelling methods, such as Cox regression analysis, produce biased results. We compared results from g-estimation of accelerated failure-time modelling adjusted for HWSE with corresponding unadjusted Cox regression modelling results. For all-cause mortality when adjusting for the HWSE, cumulative exposure from respirable dust was associated with a 6% decrease of life expectancy if exposed ≥15 years, compared with never being exposed. Respirable dust continued to be associated with mortality after censoring outcomes known to be associated with dust when adjusting for the HWSE. In contrast, results based on Cox regression analysis did not support that an association was present. The adjustment for the HWSE made a difference when estimating the risk of mortality from respirable dust. The results of this study, therefore, support the recommendation that standard methods of analysis should be complemented with structural modelling analysis techniques, such as g-estimation of accelerated failure-time modelling, to adjust for the HWSE. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Accelerated failure time models for semi-competing risks data in the presence of complex censoring.

PubMed

Lee, Kyu Ha; Rondeau, Virginie; Haneuse, Sebastien

2017-12-01

Statistical analyses that investigate risk factors for Alzheimer's disease (AD) are often subject to a number of challenges. Some of these challenges arise due to practical considerations regarding data collection such that the observation of AD events is subject to complex censoring including left-truncation and either interval or right-censoring. Additional challenges arise due to the fact that study participants under investigation are often subject to competing forces, most notably death, that may not be independent of AD. Towards resolving the latter, researchers may choose to embed the study of AD within the "semi-competing risks" framework for which the recent statistical literature has seen a number of advances including for the so-called illness-death model. To the best of our knowledge, however, the semi-competing risks literature has not fully considered analyses in contexts with complex censoring, as in studies of AD. This is particularly the case when interest lies with the accelerated failure time (AFT) model, an alternative to the traditional multiplicative Cox model that places emphasis away from the hazard function. In this article, we outline a new Bayesian framework for estimation/inference of an AFT illness-death model for semi-competing risks data subject to complex censoring. An efficient computational algorithm that gives researchers the flexibility to adopt either a fully parametric or a semi-parametric model specification is developed and implemented. The proposed methods are motivated by and illustrated with an analysis of data from the Adult Changes in Thought study, an on-going community-based prospective study of incident AD in western Washington State. © 2017, The International Biometric Society.

Accelerated Aging with Electrical Overstress and Prognostics for Power MOSFETs

NASA Technical Reports Server (NTRS)

Saha, Sankalita; Celaya, Jose Ramon; Vashchenko, Vladislav; Mahiuddin, Shompa; Goebel, Kai F.

2011-01-01

Power electronics play an increasingly important role in energy applications as part of their power converter circuits. Understanding the behavior of these devices, especially their failure modes as they age with nominal usage or sudden fault development is critical in ensuring efficiency. In this paper, a prognostics based health management of power MOSFETs undergoing accelerated aging through electrical overstress at the gate area is presented. Details of the accelerated aging methodology, modeling of the degradation process of the device and prognostics algorithm for prediction of the future state of health of the device are presented. Experiments with multiple devices demonstrate the performance of the model and the prognostics algorithm as well as the scope of application. Index Terms Power MOSFET, accelerated aging, prognostics

Analysis of lead-acid battery accelerated testing data

NASA Astrophysics Data System (ADS)

Clifford, J. E.; Thomas, R. E.

1983-06-01

Battelle conducted an independent review and analysis of the accelerated test procedures and test data obtained by Exide in the 3 year Phase 1 program to develop advanced lead acid batteries for utility load leveling. Of special importance is the extensive data obtained in deep discharge cycling tests on 60 cells at elevated temperatures over a 2-1/2 year period. The principal uncertainty in estimating cell life relates to projecting cycle life data at elevated temperature to the lower operating temperatures. The accelerated positive grid corrosion test involving continuous overcharge at 500C provided some indication of the degree of grid corrosion that might be tolerable before failure. The accelerated positive material shedding test was not examined in any detail. Recommendations are made for additional studies.

Accelerated Implantable Defibrillator Battery Depletion Secondary to Lithium Cluster Formation: A Case Series.

PubMed

Aggarwal, Ashim; Sarmiento, Joseph J; Charles, David R; Parr, Alan R; Baman, Timir S

2016-04-01

Device failure from unanticipated and precipitous battery depletion is uncommon but can be life-threatening. Multiple mechanisms of battery failure have been previously described in the medical literature. However, in this current case series, we describe the largest cohort of patients (n = 4) with St. Jude (St. Paul, MN, USA) early implantable defibrillator battery depletion attributable to lithium cluster formation causing short circuit and high current drain. Clinicians must be aware of this occult cause of device failure and more studies are needed to determine its true prevalence. © 2015 Wiley Periodicals, Inc.

Chronic Heart Failure Follow-up Management Based on Agent Technology

PubMed Central

Safdari, Reza

2015-01-01

Objectives Monitoring heart failure patients through continues assessment of sign and symptoms by information technology tools lead to large reduction in re-hospitalization. Agent technology is one of the strongest artificial intelligence areas; therefore, it can be expected to facilitate, accelerate, and improve health services especially in home care and telemedicine. The aim of this article is to provide an agent-based model for chronic heart failure (CHF) follow-up management. Methods This research was performed in 2013-2014 to determine appropriate scenarios and the data required to monitor and follow-up CHF patients, and then an agent-based model was designed. Results Agents in the proposed model perform the following tasks: medical data access, communication with other agents of the framework and intelligent data analysis, including medical data processing, reasoning, negotiation for decision-making, and learning capabilities. Conclusions The proposed multi-agent system has ability to learn and thus improve itself. Implementation of this model with more and various interval times at a broader level could achieve better results. The proposed multi-agent system is no substitute for cardiologists, but it could assist them in decision-making. PMID:26618038

Updated azca (Farallon)—South America relative motions during the last 40 My: implications for mountain building in the central Andean region

NASA Astrophysics Data System (ADS)

Somoza, R.

1998-05-01

Recently published seafloor data around the Antarctica plate boundaries, as well as calibration of the Cenozoic Magnetic Polarity Time Scale, allow a reevaluation of the Nazca (Farallon)-South America relative convergence kinematics since late Middle Eocene time. The new reconstruction parameters confirm the basic characteristics determined in previous studies. However, two features are notable in the present data set: a strong increase in convergence rate in Late Oligocene time, and a slowdown during Late Miocene time. The former is coeval with the early development of important tectonic characteristics of the present Central Andes, such as compressional failure in wide areas of the region, and the establishment of Late Cenozoic magmatism. This supports the idea that a relationship exists between strong acceleration of convergence and mountain building in the Central Andean region.

Risk-adjusted monitoring of survival times

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

Sego, Landon H.; Reynolds, Marion R.; Woodall, William H.

2009-02-26

We consider the monitoring of clinical outcomes, where each patient has a di®erent risk of death prior to undergoing a health care procedure.We propose a risk-adjusted survival time CUSUM chart (RAST CUSUM) for monitoring clinical outcomes where the primary endpoint is a continuous, time-to-event variable that may be right censored. Risk adjustment is accomplished using accelerated failure time regression models. We compare the average run length performance of the RAST CUSUM chart to the risk-adjusted Bernoulli CUSUM chart, using data from cardiac surgeries to motivate the details of the comparison. The comparisons show that the RAST CUSUM chart is moremore » efficient at detecting a sudden decrease in the odds of death than the risk-adjusted Bernoulli CUSUM chart, especially when the fraction of censored observations is not too high. We also discuss the implementation of a prospective monitoring scheme using the RAST CUSUM chart.« less

Development of Acceleration Sensor and Acceleration Evaluation System for Super-Low-Range Frequencies

NASA Astrophysics Data System (ADS)

Asano, Shogo; Matsumoto, Hideki

2001-05-01

This paper describes the development process for acceleration sensors used on automobiles and an acceleration evaluation system designed specifically for acceleration at super-low-range frequencies. The features of the newly developed sensor are as follows. 1) Original piezo-bimorph design based on a disc-center-fixed structure achieves pyroeffect cancelling and stabilization of sensor characteristics and enables the detection of the acceleration of 0.0009 G at the super-low-range-frequency of 0.03 Hz. 2) The addition of a self-diagnostic function utilizing the characteristics of piezoceramics enables constant monitoring of sensor failure. The frequency range of acceleration for accurate vehicle motion control is considered to be from DC to about 50 Hz. However, the measurement of acceleration in the super-low-range frequency near DC has been difficult because of mechanical and electrical noise interruption. This has delayed the development of the acceleration sensor for automotive use. We have succeeded in the development of an acceleration evaluation system for super-low-range frequencies from 0.015 Hz to 2 Hz with detection of the acceleration range from 0.0002 G (0.2 gal) to 1 G, as well as the development of a piezoelectric-type acceleration sensor for automotive use.

RADC (Rome Air Development Center) Guide to Environmental Stress Screening

DTIC Science & Technology

1986-08-01

and the processes which are used in their manufacture. ESS is the vehicle by which latent defects are accelerated to early failure in the factory. ESS...structured as part of a production 2 reliability assurance program, is the vehicle through which product reliability in manufacture can be maintained...mechanical, electrical and/or thermal stresses to an equipment item for the purpose of precipitating latent part and workmanship defects to early failure

Analysis of EDZ Development of Columnar Jointed Rock Mass in the Baihetan Diversion Tunnel

NASA Astrophysics Data System (ADS)

Hao, Xian-Jie; Feng, Xia-Ting; Yang, Cheng-Xiang; Jiang, Quan; Li, Shao-Jun

2016-04-01

Due to the time dependency of the crack propagation, columnar jointed rock masses exhibit marked time-dependent behaviour. In this study, in situ measurements, scanning electron microscope (SEM), back-analysis method and numerical simulations are presented to study the time-dependent development of the excavation damaged zone (EDZ) around underground diversion tunnels in a columnar jointed rock mass. Through in situ measurements of crack propagation and EDZ development, their extent is seen to have increased over time, despite the fact that the advancing face has passed. Similar to creep behaviour, the time-dependent EDZ development curve also consists of three stages: a deceleration stage, a stabilization stage, and an acceleration stage. A corresponding constitutive model of columnar jointed rock mass considering time-dependent behaviour is proposed. The time-dependent degradation coefficient of the roughness coefficient and residual friction angle in the Barton-Bandis strength criterion are taken into account. An intelligent back-analysis method is adopted to obtain the unknown time-dependent degradation coefficients for the proposed constitutive model. The numerical modelling results are in good agreement with the measured EDZ. Not only that, the failure pattern simulated by this time-dependent constitutive model is consistent with that observed in the scanning electron microscope (SEM) and in situ observation, indicating that this model could accurately simulate the failure pattern and time-dependent EDZ development of columnar joints. Moreover, the effects of the support system provided and the in situ stress on the time-dependent coefficients are studied. Finally, the long-term stability analysis of diversion tunnels excavated in columnar jointed rock masses is performed.

Factors and processes causing accelerated decomposition in human cadavers - An overview.

PubMed

Zhou, Chong; Byard, Roger W

2011-01-01

Artefactually enhanced putrefactive and autolytic changes may be misinterpreted as indicating a prolonged postmortem interval and throw doubt on the veracity of witness statements. Review of files from Forensic Science SA and the literature revealed a number of external and internal factors that may be responsible for accelerating these processes. Exogenous factors included exposure to elevated environmental temperatures, both outdoors and indoors, exacerbated by increased humidity or fires. Situations indoor involved exposure to central heating, hot water, saunas and electric blankets. Deaths within motor vehicles were also characterized by enhanced decomposition. Failure to quickly or adequately refrigerate bodies may also lead to early decomposition. Endogenous factors included fever, infections, illicit and prescription drugs, obesity and insulin-dependent diabetes mellitus. When these factors or conditions are identified at autopsy less significance should, therefore, be attached to changes of decomposition as markers of time since death. Copyright © 2010 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.

Stochastic Modeling and Analysis of Multiple Nonlinear Accelerated Degradation Processes through Information Fusion

PubMed Central

Sun, Fuqiang; Liu, Le; Li, Xiaoyang; Liao, Haitao

2016-01-01

Accelerated degradation testing (ADT) is an efficient technique for evaluating the lifetime of a highly reliable product whose underlying failure process may be traced by the degradation of the product’s performance parameters with time. However, most research on ADT mainly focuses on a single performance parameter. In reality, the performance of a modern product is usually characterized by multiple parameters, and the degradation paths are usually nonlinear. To address such problems, this paper develops a new s-dependent nonlinear ADT model for products with multiple performance parameters using a general Wiener process and copulas. The general Wiener process models the nonlinear ADT data, and the dependency among different degradation measures is analyzed using the copula method. An engineering case study on a tuner’s ADT data is conducted to demonstrate the effectiveness of the proposed method. The results illustrate that the proposed method is quite effective in estimating the lifetime of a product with s-dependent performance parameters. PMID:27509499

Stochastic Modeling and Analysis of Multiple Nonlinear Accelerated Degradation Processes through Information Fusion.

PubMed

Sun, Fuqiang; Liu, Le; Li, Xiaoyang; Liao, Haitao

2016-08-06

Accelerated degradation testing (ADT) is an efficient technique for evaluating the lifetime of a highly reliable product whose underlying failure process may be traced by the degradation of the product's performance parameters with time. However, most research on ADT mainly focuses on a single performance parameter. In reality, the performance of a modern product is usually characterized by multiple parameters, and the degradation paths are usually nonlinear. To address such problems, this paper develops a new s-dependent nonlinear ADT model for products with multiple performance parameters using a general Wiener process and copulas. The general Wiener process models the nonlinear ADT data, and the dependency among different degradation measures is analyzed using the copula method. An engineering case study on a tuner's ADT data is conducted to demonstrate the effectiveness of the proposed method. The results illustrate that the proposed method is quite effective in estimating the lifetime of a product with s-dependent performance parameters.

Interfacial Reaction and IMC Growth of an Ultrasonically Soldered Cu/SAC305/Cu Structure during Isothermal Aging

PubMed Central

Long, Weifeng; Hu, Xiaowu; Fu, Yanshu

2018-01-01

In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i) Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii) The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii) The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv) Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time. PMID:29316625

Limitations of predicting in vivo biostability of multiphase polyurethane elastomers using temperature-accelerated degradation testing.

PubMed

Padsalgikar, Ajay; Cosgriff-Hernandez, Elizabeth; Gallagher, Genevieve; Touchet, Tyler; Iacob, Ciprian; Mellin, Lisa; Norlin-Weissenrieder, Anna; Runt, James

2015-01-01

Polyurethane biostability has been the subject of intense research since the failure of polyether polyurethane pacemaker leads in the 1980s. Accelerated in vitro testing has been used to isolate degradation mechanisms and predict clinical performance of biomaterials. However, validation that in vitro methods reproduce in vivo degradation is critical to the selection of appropriate tests. High temperature has been proposed as a method to accelerate degradation. However, correlation of such data to in vivo performance is poor for polyurethanes due to the impact of temperature on microstructure. In this study, we characterize the lack of correlation between hydrolytic degradation predicted using a high temperature aging model of a polydimethylsiloxane-based polyurethane and its in vivo performance. Most notably, the predicted molecular weight and tensile property changes from the accelerated aging study did not correlate with clinical explants subjected to human biological stresses in real time through 5 years. Further, DMTA, ATR-FTIR, and SAXS experiments on samples aged for 2 weeks in PBS indicated greater phase separation in samples aged at 85°C compared to those aged at 37°C and unaged controls. These results confirm that microstructural changes occur at high temperatures that do not occur at in vivo temperatures. In addition, water absorption studies demonstrated that water saturation levels increased significantly with temperature. This study highlights that the multiphase morphology of polyurethane precludes the use of temperature accelerated biodegradation for the prediction of clinical performance and provides critical information in designing appropriate in vitro tests for this class of materials. © 2014 Wiley Periodicals, Inc.

Empirical membrane lifetime model for heavy duty fuel cell systems

NASA Astrophysics Data System (ADS)

Macauley, Natalia; Watson, Mark; Lauritzen, Michael; Knights, Shanna; Wang, G. Gary; Kjeang, Erik

2016-12-01

Heavy duty fuel cells used in transportation system applications such as transit buses expose the fuel cell membranes to conditions that can lead to lifetime-limiting membrane failure via combined chemical and mechanical degradation. Highly durable membranes and reliable predictive models are therefore needed in order to achieve the ultimate heavy duty fuel cell lifetime target of 25,000 h. In the present work, an empirical membrane lifetime model was developed based on laboratory data from a suite of accelerated membrane durability tests. The model considers the effects of cell voltage, temperature, oxygen concentration, humidity cycling, humidity level, and platinum in the membrane using inverse power law and exponential relationships within the framework of a general log-linear Weibull life-stress statistical distribution. The obtained model is capable of extrapolating the membrane lifetime from accelerated test conditions to use level conditions during field operation. Based on typical conditions for the Whistler, British Columbia fuel cell transit bus fleet, the model predicts a stack lifetime of 17,500 h and a membrane leak initiation time of 9200 h. Validation performed with the aid of a field operated stack confirmed the initial goal of the model to predict membrane lifetime within 20% of the actual operating time.

An accelerated technique for irradiation of malignant canine nasal and paranasal sinus tumors.

PubMed

Adams, W M; Miller, P E; Vail, D M; Forrest, L J; MacEwen, E G

1998-01-01

Tumor and normal tissue response was assessed in 21 dogs with malignant nasal tumors given 42 Gy cobalt radiation in 9 or 10 fractions over 11 to 13 days. Local tumor/clinical relapse recurred in 68% of dogs, with a median relapse free interval (RFI) of 270 days. Median survival was 428 days. One year survival for all dogs was 60%. RFI and survival times are better than, or similar to, previous reports of dogs treated with radiotherapy only. Acute radiation effects were severe in one dog. Late effects were severe in six of 15 dogs (40%) with durable tumor control. Late effects included bilateral blindness (3), osteoradionecrosis (3), and seizures (1). These six dogs had a median survival of 705 days. Loss of vision occurred in at least one eye in nine dogs (47%). Tumor staging based on CT findings was predictive for survival duration. Tumor histology was not predictive of outcome. Labrador Retrievers were significantly over-represented. Despite comparable or improved tumor control and survival times provided by this accelerated protocol, relative to other radiotherapy reports, local failure remains the major cause of death, and late radiation effects can be severe in dogs with durable tumor control.

Angular velocity and acceleration meter

NASA Technical Reports Server (NTRS)

Melamed, L.

1972-01-01

Meter uses a liquid crystalline film which changes coloration due to shear-stresses produced by a rotating disk. Device is advantageous in that it is not subject to bearing failure or electrical burnouts as are conventional devices.

10 CFR 820.34 - Accelerated decision.

Code of Federal Regulations, 2010 CFR

2010-01-01

... upon such limited additional evidence as he requires, on the basis of failure to establish a prima facie case or other grounds that show no right to relief on the part of the Director. (b) Effect of...

Study of the damage evolution function of tin silver copper in cycling

NASA Astrophysics Data System (ADS)

Qasaimeh, Awni

The present research focused on the assessment of solder joint fatigue life in microelectronics assemblies. A general concern of any reliability engineer is whether accelerated tests are relevant to field conditions. The risk of this was minimized by developing an approach to reduce the duration of an accelerated thermal cycling test, thus allowing for the use of less accelerated test conditions. For this purpose the conventional dye and pry technique was improved and used together with artificial neural networks to measure and characterize very early stages of crack growth. The same work also demonstrated a quantitative link between thermal cycling induced recrystallization and a strong acceleration of the subsequent fatigue crack growth and failure. A new study was conducted in which different combinations of annealing and isothermal cycling provided a systematic characterization of the effects of a range of individual parameters on the recrystallization. Experiments showed the ongoing coarsening of secondary precipitates to have a clear effect on recrystallization. The rate of recrystallization was also shown not to scale with the inelastic energy deposition. This means that the most popular current thermal cycling model cannot apply to SnAgCu solder joints. Recrystallization of the Sn grains is usually not the rate limiting mechanism in isothermal cycling. The crack initiation stage often takes up a much greater fraction of the overall life, and the eventual failure of BGA joints tends to involve transgranular crack growth instead. Cycling of individual solder joints allowed for monitoring of the evolution of the solder properties and the rate of inelastic energy deposition. Both the number of cycles to crack initiation and the subsequent number of cycles to failure were shown to be determined by the inelastic energy deposition. This provides for a simple model for the extrapolation of accelerated test results to the much milder cycling amplitudes characteristic of long term service conditions based on conventional Finite Element Modeling. It also offers a critical basis for the ongoing development of a practical model to account for the often dramatic break-down of Miner's rule of linear damage accumulation under variable cycling amplitudes as expected in realistic applications.

Optimal Aircraft Control Upset Recovery With and Without Component Failures

NASA Technical Reports Server (NTRS)

Sparks, Dean W.; Moerder, Daniel D.

2002-01-01

This paper treats the problem of recovering sustainable nondescending (safe) flight in a transport aircraft after one or more of its control effectors fail. Such recovery can be a challenging goal for many transport aircraft currently in the operational fleet for two reasons. First, they have very little redundancy in their means of generating control forces and moments. These aircraft have, as primary control surfaces, a single rudder and pairwise elevators and aileron/spoiler units that provide yaw, pitch, and roll moments with sufficient bandwidth to be used in stabilizing and maneuvering the airframe. Beyond this, throttling the engines can provide additional moments, but on a much slower time scale. Other aerodynamic surfaces, such as leading and trailing edge flaps, are only intended to be placed in a position and left, and are, hence, very slow-moving. Because of this, loss of a primary control surface strongly degrades the controllability of the vehicle, particularly when the failed effector becomes stuck in a non-neutral position where it exerts a disturbance moment that must be countered by the remaining operating effectors. The second challenge in recovering safe flight is that these vehicles are not agile, nor can they tolerate large accelerations. This is of special importance when, at the outset of the recovery maneuver, the aircraft is flying toward the ground, as is frequently the case when there are major control hardware failures. Recovery of safe flight is examined in this paper in the context of trajectory optimization. For a particular transport aircraft, and a failure scenario inspired by an historical air disaster, recovery scenarios are calculated with and without control surface failures, to bring the aircraft to safe flight from the adverse flight condition that it had assumed, apparently as a result of contact with a vortex from a larger aircraft's wake. An effort has been made to represent relevant airframe dynamics, acceleration limits, and actuator limits faithfully, since these contribute to the lack of agility and control power that plays an important role in defining what can be achieved with the vehicle when it is in extremis.

Effect of the amount of Na2SO4 on the high temperature corrosion of Udimet-700

NASA Technical Reports Server (NTRS)

Misra, A. K.; Kohl, F. J.

1983-01-01

The corrosion of Udimet-700, coated with different doses of Na2SO4, was studied in an isothermal thermogravimetric test in the temperature range 900 to 950 C. The weight gain curve is characterized by five distinct stages: an initial period of linear corrosion; an induction period; a period of accelerated corrosion; a period of decelerating corrosion; and a period of parabolic oxidation. The time required for the failure of the alloy increases with an increase in the amount of Na2SO4, reaches a peak and then decreases with further increase in the amount of Na2SO4. For low and intermediate doses (0.3 to 2.0 mg/sq cm), the catastrophic failure of the material occurs by the formation of Na2MoO4 and interaction of the liquid Na2MoO4 with the alloy. For heavy doses, the degradation of the material is due to the formation of large amounts of sulfides.

A Model-Based Fast Protection System for High-Power RF Tube Amplifiers Used at the European XFEL Accelerator

NASA Astrophysics Data System (ADS)

Butkowski, Łukasz; Vogel, Vladimir; Schlarb, Holger; Szabatin, Jerzy

2017-06-01

The driving engine of the superconducting accelerator of the European X-ray free electron laser (XFEL) is a set of 27 radio frequency (RF) stations. Each of the underground RF stations consists of a multibeam horizontal klystron that can provide up to 10 MW of power at 1.3 GHz. Klystrons are sensitive devices with a limited lifetime and a high mean time between failures. In real operation, the lifetime of the tube can be significantly reduced because of failures. The special fast protection klystron lifetime management (KLM) system has been developed to minimize the influence of service conditions on the lifetime of klystrons. The main task of this system is to detect all events which can destroy the tube as quickly as possible, and switch off the driving RF signal or the high voltage. Detection of events is based on a comparison of the value of the real signal obtained at the system output with the value estimated on the basis of a high-power RF amplifier model and input signals. The KLM system has been realized in field-programmable gate array (FPGA) and implemented in XFEL. Implementation is based on the standard low-level RF micro telecommunications computing architecture (MTCA.4 or xTCA). The main part of the paper focuses on an estimation of the klystron model and the implementation of KLM in FPGA. The results of the performance of the KLM system will also be presented.

Structural loads preliminary results

NASA Technical Reports Server (NTRS)

Alfaro-Bou, E.

1986-01-01

From a total of 351 instrumentation channels, 341 channels (97%) were in operation during the initial impact of the airplane. Both NASA seats, the energy absorbing seat and the standard seat, maintained their integrity during the impact. The floor accelerations at the seat locations were lower than the accelerations required for the energy absorbers to stroke; consequently, the energy absorbing seat did not stroke. The two seats remained firm in place during the crash and no seat attachment failures were observed. Due to the low accelerations experienced during the crash, both seats performed as standard seats. In the airplane structure, the accelerations were higher at both the point of impact in the left wing and at the forward end of the fuselage. The accelerations on the floor were higher toward the front than toward the rear and the floor accelerations on the left side were higher than on the right side at the front of the fuselage, but toward the rear they evened out.

Insulation Resistance Degradation in Ni-BaTiO3 Multilayer Ceramic Capacitors

NASA Technical Reports Server (NTRS)

Liu, Donhang (David)

2015-01-01

Insulation resistance (IR) degradation in Ni-BaTiO3 multilayer ceramic capacitors has been characterized by the measurement of both time to failure and direct-current (DC) leakage current as a function of stress time under highly accelerated life test conditions. The measured leakage current-time dependence data fit well to an exponential form, and a characteristic growth time ?SD can be determined. A greater value of tau(sub SD) represents a slower IR degradation process. Oxygen vacancy migration and localization at the grain boundary region results in the reduction of the Schottky barrier height and has been found to be the main reason for IR degradation in Ni-BaTiO3 capacitors. The reduction of barrier height as a function of time follows an exponential relation of phi (??)=phi (0)e(exp -2?t), where the degradation rate constant ??=??o??(????/????) is inversely proportional to the mean time to failure (MTTF) and can be determined using an Arrhenius plot. For oxygen vacancy electromigration, a lower barrier height phi(0) will favor a slow IR degradation process, but a lower phi(0) will also promote electronic carrier conduction across the barrier and decrease the insulation resistance. As a result, a moderate barrier height phi(0) (and therefore a moderate IR value) with a longer MTTF (smaller degradation rate constant ??) will result in a minimized IR degradation process and the most improved reliability in Ni-BaTiO3 multilayer ceramic capacitors.

Factors Affecting the Development of an Antibody Response to Hepatitis B Immunization in Children With Intestinal Failure: Before and After Small Bowel Transplantation (With and Without Liver Graft).

PubMed

Craggs, Helen M; Jackson, Phoebe; Gupte, Girish; Hartley, Jane; Abdel-Hady, Mona; Morton, Rachael; Beath, Sue; Hogg, Lindsay

2017-08-01

Small bowel transplant with or without a liver graft (SBTx ± LTx) for children with intestinal failure involves checking their immunity to a range of microorganisms, including hepatitis B virus (HBV), at the time of assessment. HBV vaccination in the United Kingdom is recommended for transplant candidates. The aim of this audit was to find out how many SBTx ± LTx candidates received HBV vaccination before transplantation and how the timing of vaccination influenced the development of immunity. Retrospective review of case notes and hospital microbiology database formed the basis of the study. Vaccination history and serology were available in 56 of 87 subjects who had SBTx ± LTx. All patients were seronegative for HBV when assessed for transplant. HBV vaccination was started before transplant in 25 children and after transplant in 31. Eight children died posttransplant before their immunity could be checked, but of the 48 survivors, 20 children developed immunity, of whom 13 (65%) received at least 1 vaccination before SBTx ± LTx ( P = .008). Lack of response to HBV vaccine was significantly associated with isolated bowel transplantation and intensification of immune suppression. Of 11 children, 5 lost hepatitis B surface antibody (HbsAb), and 28 never made HBsAb, despite repeated vaccinations. Our study clearly shows that HBV vaccine before transplant is more effective. In line with renal failure patients, we suggest that children with chronic intestinal failure receive HBV vaccine when clinically stable, before referral for transplant. Higher-dose vaccines, accelerated schedules, and more frequent booster vaccinations are also strategies that may improve HBsAb levels after transplant.

Supersonic Localized Excitations Mediate Microscopic Dynamic Failure

NASA Astrophysics Data System (ADS)

Ghaffari, H. O.; Griffith, W. A.; Pec, M.

2017-12-01

A moving rupture front activates a fault patch by increasing stress above a threshold strength level. Subsequent failure yields fast slip which releases stored energy in the rock. A fraction of the released energy is radiated as seismic waves carrying information about the earthquake source. While this simplified model is widely accepted, the detailed evolution from the onset of dynamic failure to eventual re-equilibration is still poorly understood. To study dynamic failure of brittle solids we indented thin sheets of single mineral crystals and recorded the emitted ultrasound signals (high frequency analogues to seismic waves) using an array of 8 to 16 ultrasound probes. The simple geometry of the experiments allows us to unravel details of dynamic stress history of the laboratory earthquake sources. A universal pattern of failure is observed. First, stress increases over a short time period (1 - 2 µs), followed by rapid weakening (≈ 15 µs). Rapid weakening is followed by two distinct relaxation phases: a temporary quasi-steady state phase (10 µs) followed by a long-term relaxation phase (> 50 µs). We demonstrate that the dynamic stress history during failure is governed by formation and interaction of local non-dispersive excitations, or solitons. The formation and annihilation of solitons mediates the microscopic fast weakening phase, during which extreme acceleration and collision of solitons lead to non-Newtonian behavior and Lorentz contraction, i.e. shortening of solitons' characteristic length. Interestingly, a soliton can propagate as fast as 37 km/s, much faster than the p-wave velocity, implying that a fraction of the energy transmits through soliton excitations. The quasi-steady state phase delays the long-term ageing of the damaged crystal, implying a potentially weaker material. Our results open new horizons for understanding the complexity of earthquake sources, and, more generally, non-equilibrium relaxation of many body systems.

Analysis of L-band Multi-Channel Sea Clutter

DTIC Science & Technology

2010-08-01

Some researchers found that the use of a hybrid algorithm of PS and GA could accelerate the convergence for array beamforming designs (Yeo and Lu...to be shown is array failure correction using the PS algorithm . Assume element 5 of a 32 half-wavelength spacing linear array is in failure. The goal... algorithm . The blue one is the 20 dB Chebyshev pattern and the template in red is the goal pattern to achieve. Two corrected beam patterns are

Monitoring the Corrosion Process of Reinforced Concrete Using BOTDA and FBG Sensors

PubMed Central

Mao, Jianghong; Chen, Jiayun; Cui, Lei; Jin, Weiliang; Xu, Chen; He, Yong

2015-01-01

Expansion and cracking induced by the corrosion of reinforcement concrete is the major factor in the failure of concrete durability. Therefore, monitoring of concrete cracking is critical for evaluating the safety of concrete structures. In this paper, we introduce a novel monitoring method combining Brillouin optical time domain analysis (BOTDA) and fiber Bragg grating (FBG), based on mechanical principles of concrete expansion cracking. BOTDA monitors concrete expansion and crack width, while FBG identifies the time and position of cracking. A water-pressure loading simulation test was carried out to determine the relationship between fiber strain, concrete expansion and crack width. An electrical accelerated corrosion test was also conducted to evaluate the ability of this novel sensor to monitor concrete cracking under practical conditions. PMID:25884790

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

Daniel, Isaac M.

To facilitate and accelerate the process of introducing, evaluating and adopting of new material systems, it is important to develop/establish comprehensive and effective procedures of characterization, modeling and failure prediction of structural laminates based on the properties of the constituent materials, e. g., fibers, matrix, and the single ply or lamina. A new failure theory, the Northwestern (NU-Daniel) theory, has been proposed for predicting lamina yielding and failure under multi-axial states of stress including strain rate effects. It is primarily applicable to matrix-dominated interfiber/interlaminar failures. It is based on micromechanical failure mechanisms but is expressed in terms of easily measuredmore » macroscopic lamina stiffness and strength properties. It is presented in the form of a master failure envelope incorporating strain rate effects. The theory was further adapted and extended to the prediction of in situ first ply yielding and failure (FPY and FPF) and progressive failure of multi-directional laminates under static and dynamic loadings. The significance of this theory is that it allows for rapid screening of new composite materials without very extensive testing and offers easily implemented design tools.« less

Deformation behavior and spall fracture of the Hadfield steel under shock-wave loading

NASA Astrophysics Data System (ADS)

Gnyusov, S. F.; Rotshtein, V. P.; Polevin, S. D.; Kitsanov, S. A.

2011-03-01

Comparative studies of regularities in plastic deformation and fracture of the Hadfield polycrystalline steel upon quasi-static tension, impact failure, and shock-wave loading with rear spall are performed. The SINUS-7 accelerator was used as a shock-wave generator. The electron beam parameters of the accelerator were the following: maximum electron energy was 1.35 MeV, pulse duration at half-maximum was 45 ns, maximum energy density on a target was 3.4·1010 W/cm2, shock-wave amplitude was ~20 GPa, and strain rate was ~106 s-1. It is established that the failure mechanism changes from ductile transgranular to mixed ductile-brittle intergranular one when going from quasi-static tensile and Charpy impact tests to shock-wave loading. It is demonstrated that a reason for the intergranular spallation is the strain localization near the grain boundaries containing a carbide interlayer.

The Prognostic Importance of Changes in Renal Function during Treatment for Acute Heart Failure Depends on Admission Renal Function

PubMed Central

Reid, Ryan; Ezekowitz, Justin A.; Brown, Paul M.; McAlister, Finlay A.; Rowe, Brian H.; Braam, Branko

2015-01-01

Background Worsening and improving renal function during acute heart failure have been associated with adverse outcomes but few studies have considered the admission level of renal function upon which these changes are superimposed. Objectives The objective of this study was to evaluate definitions that incorporate both admission renal function and change in renal function. Methods 696 patients with acute heart failure with calculable eGFR were classified by admission renal function (Reduced [R, eGFR<45 ml/min] or Preserved [P, eGFR≥45 ml/min]) and change over hospital admission (worsening [WRF]: eGFR ≥20% decline; stable [SRF]; and improving [IRF]: eGFR ≥20% increase). The primary outcome was all-cause mortality. The prevalence of Pres and Red renal function was 47.8% and 52.2%. The frequency of R-WRF, R-SRF, and R-IRF was 11.4%, 28.7%, and 12.1%, respectively; the incidence of P-WRF, P-SRF, and P-IRF was 5.7%, 35.3%, and 6.8%, respectively. Survival was shorter for patients with R-WRF compared to R-IRF (median survival times 13.9 months (95%CI 7.7–24.9) and 32.5 months (95%CI 18.8–56.1), respectively), resulting in an acceleration factor of 2.3 (p = 0.016). Thus, an increase compared with a decrease in renal function was associated with greater than two times longer survival among patients with Reduced renal function. PMID:26380982

Effects of hydromechanical loading history and antecedent soil mechanical damage on shallow landslide triggering

NASA Astrophysics Data System (ADS)

Fan, Linfeng; Lehmann, Peter; Or, Dani

2015-10-01

Evidence suggests that the sudden triggering of rainfall-induced shallow landslides is preceded by accumulation of local internal failures in the soil mantle before their abrupt coalescence into a landslide failure plane. The mechanical status of a hillslope at any given time reflects competition between local damage accumulated during antecedent rainfall events and rates of mechanical healing (e.g., rebonding of microcracks and root regrowth). This dynamic interplay between damage accumulation and healing rates determines the initial mechanical state for landslide modeling. We evaluated the roles of these dynamic processes on landslide characteristics and patterns using a hydromechanical landslide-triggering model for a sequence of rainfall scenarios. The progressive nature of soil failure was represented by the fiber bundle model formalism that considers threshold strength of mechanical bonds linking adjacent soil columns and bedrock. The antecedent damage induced by prior rainfall events was expressed by the fraction of broken fibers that gradually regain strength or mechanically heal at rates specific to soil and roots. Results indicate that antecedent damage accelerates landslide initiation relative to pristine (undamaged) hillslopes. The volumes of first triggered landslides increase with increasing antecedent damage; however, for heavily damaged hillslopes, landslide volumes tend to decrease. Elapsed time between rainfall events allows mechanical healing that reduces the effects of antecedent damage. This study proposed a quantitative framework for systematically incorporating hydromechanical loading history and information on precursor events (e.g., such as recorded by acoustic emissions) into shallow landslide hazard assessment.

EEMD-based multiscale ICA method for slewing bearing fault detection and diagnosis

NASA Astrophysics Data System (ADS)

Žvokelj, Matej; Zupan, Samo; Prebil, Ivan

2016-05-01

A novel multivariate and multiscale statistical process monitoring method is proposed with the aim of detecting incipient failures in large slewing bearings, where subjective influence plays a minor role. The proposed method integrates the strengths of the Independent Component Analysis (ICA) multivariate monitoring approach with the benefits of Ensemble Empirical Mode Decomposition (EEMD), which adaptively decomposes signals into different time scales and can thus cope with multiscale system dynamics. The method, which was named EEMD-based multiscale ICA (EEMD-MSICA), not only enables bearing fault detection but also offers a mechanism of multivariate signal denoising and, in combination with the Envelope Analysis (EA), a diagnostic tool. The multiscale nature of the proposed approach makes the method convenient to cope with data which emanate from bearings in complex real-world rotating machinery and frequently represent the cumulative effect of many underlying phenomena occupying different regions in the time-frequency plane. The efficiency of the proposed method was tested on simulated as well as real vibration and Acoustic Emission (AE) signals obtained through conducting an accelerated run-to-failure lifetime experiment on a purpose-built laboratory slewing bearing test stand. The ability to detect and locate the early-stage rolling-sliding contact fatigue failure of the bearing indicates that AE and vibration signals carry sufficient information on the bearing condition and that the developed EEMD-MSICA method is able to effectively extract it, thereby representing a reliable bearing fault detection and diagnosis strategy.

Applicability of out-of-pile fretting wear tests to in-reactor fretting wear-induced failure time prediction

NASA Astrophysics Data System (ADS)

Kim, Kyu-Tae

2013-02-01

In order to investigate whether or not the grid-to-rod fretting wear-induced fuel failure will occur for newly developed spacer grid spring designs for the fuel lifetime, out-of-pile fretting wear tests with one or two fuel assemblies are to be performed. In this study, the out-of-pile fretting wear tests were performed in order to compare the potential for wear-induced fuel failure in two newly-developed, Korean PWR spacer grid designs. Lasting 20 days, the tests simulated maximum grid-to-rod gap conditions and the worst flow induced vibration effects that might take place over the fuel life time. The fuel rod perforation times calculated from the out-of-pile tests are greater than 1933 days for 2 μm oxidized fuel rods with a 100 μm grid-to-rod gap, whereas those estimated from in-reactor fretting wear failure database may be about in the range of between 60 and 100 days. This large discrepancy in fuel rod perforation may occur due to irradiation-induced cladding oxide microstructure changes on the one hand and a temperature gradient-induced hydrogen content profile across the cladding metal region on the other hand, which may accelerate brittleness in the grid-contacting cladding oxide and metal regions during the reactor operation. A three-phase grid-to-rod fretting wear model is proposed to simulate in-reactor fretting wear progress into the cladding, considering the microstructure changes of the cladding oxide and the hydrogen content profile across the cladding metal region combined with the temperature gradient. The out-of-pile tests cannot be directly applicable to the prediction of in-reactor fretting wear-induced cladding perforations but they can be used only for evaluating a relative wear resistance of one grid design against the other grid design.

Gender Differences in Adherence and Response to Antiretroviral Treatment in the Stratall Trial in Rural District Hospitals in Cameroon.

PubMed

Boullé, Charlotte; Kouanfack, Charles; Laborde-Balen, Gabrièle; Boyer, Sylvie; Aghokeng, Avelin F; Carrieri, Maria P; Kazé, Serge; Dontsop, Marlise; Mben, Jean-Marc; Koulla-Shiro, Sinata; Peytavin, Gilles; Spire, Bruno; Delaporte, Eric; Laurent, Christian

2015-07-01

Evidence of gender differences in antiretroviral treatment (ART) outcomes in sub-Saharan Africa is conflicting. Our objective was to assess gender differences in (1) adherence to ART and (2) virologic failure, immune reconstitution, mortality, and disease progression adjusting for adherence. Cohort study among 459 ART-naive patients followed up 24 months after initiation in 2006-2010 in 9 rural district hospitals. Adherence to ART was assessed using (1) a validated tool based on multiple patient self-reports and (2) antiretroviral plasma concentrations. The associations between gender and the outcomes were assessed using multivariate mixed models or accelerated time failure models. One hundred thirty-five patients (29.4%) were men. At baseline, men were older, had higher body mass index and hemoglobin level, and received more frequently efavirenz than women. Gender was not associated with self-reported adherence (P = 0.872, 0.169, and 0.867 for moderate adherence, low adherence, and treatment interruption, respectively) or with antiretroviral plasma concentrations (P = 0.549 for nevirapine/efavirenz). In contrast, male gender was associated with virologic failure [odds ratio: 2.18, 95% confidence interval (CI): 1.31 to 3.62, P = 0.003], lower immunologic reconstitution (coefficient: -58.7 at month 24, 95% CI: -100.8 to -16.6, P = 0.006), and faster progression to death (time ratio: 0.30, 95% CI: 0.12 to 0.78, P = 0.014) and/or to World Health Organization stage 4 event (time ratio: 0.27, 95% CI: 0.09 to 0.79, P = 0.017). Our study provides important evidence that African men are more vulnerable to ART failure than women and that the male vulnerability extends beyond adherence issues. Additional studies are needed to determine the causes for this vulnerability to optimize HIV care. However, personalized adherence support remains crucial.

Prognostics Approach for Power MOSFET Under Thermal-Stress

NASA Technical Reports Server (NTRS)

Galvan, Jose Ramon Celaya; Saxena, Abhinav; Kulkarni, Chetan S.; Saha, Sankalita; Goebel, Kai

2012-01-01

The prognostic technique for a power MOSFET presented in this paper is based on accelerated aging of MOSFET IRF520Npbf in a TO-220 package. The methodology utilizes thermal and power cycling to accelerate the life of the devices. The major failure mechanism for the stress conditions is dieattachment degradation, typical for discrete devices with leadfree solder die attachment. It has been determined that dieattach degradation results in an increase in ON-state resistance due to its dependence on junction temperature. Increasing resistance, thus, can be used as a precursor of failure for the die-attach failure mechanism under thermal stress. A feature based on normalized ON-resistance is computed from in-situ measurements of the electro-thermal response. An Extended Kalman filter is used as a model-based prognostics techniques based on the Bayesian tracking framework. The proposed prognostics technique reports on preliminary work that serves as a case study on the prediction of remaining life of power MOSFETs and builds upon the work presented in [1]. The algorithm considered in this study had been used as prognostics algorithm in different applications and is regarded as suitable candidate for component level prognostics. This work attempts to further the validation of such algorithm by presenting it with real degradation data including measurements from real sensors, which include all the complications (noise, bias, etc.) that are regularly not captured on simulated degradation data. The algorithm is developed and tested on the accelerated aging test timescale. In real world operation, the timescale of the degradation process and therefore the RUL predictions will be considerable larger. It is hypothesized that even though the timescale will be larger, it remains constant through the degradation process and the algorithm and model would still apply under the slower degradation process. By using accelerated aging data with actual device measurements and real sensors (no simulated behavior), we are attempting to assess how such algorithm behaves under realistic conditions.

The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington

NASA Astrophysics Data System (ADS)

Kendrick, Jackie Evan; Smith, Rosanna; Sammonds, Peter; Meredith, Philip G.; Dainty, Matthew; Pallister, John S.

2013-07-01

Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young's modulus and Poisson's ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions.

Fracture analysis of tube boiler for physical explosion accident.

PubMed

Kim, Eui Soo

2017-09-01

Material and failure analysis techniques are key tools for determining causation in case of explosive and bursting accident result from material and process defect of product in the field of forensic science. The boiler rupture generated by defect of the welding division, corrosion, overheating and degradation of the material have devastating power. If weak division of boiler burner is fractured by internal pressure, saturated vapor and water is vaporized suddenly. At that time, volume of the saturated vapor and water increases up to thousands of volume. This failure of boiler burner can lead to a fatal disaster. In order to prevent an explosion and of the boiler, it is critical to introduce a systematic investigation and prevention measures in advance. In this research, the cause of boiler failure is investigated through forensic engineering method. Specifically, the failure mechanism will be identified by fractography using scanning electron microscopes (SEM) and Optical Microscopes (OM) and mechanical characterizations. This paper presents a failure analysis of household welding joints for the water tank of a household boiler burner. Visual inspection was performed to find out the characteristics of the fracture of the as-received material. Also, the micro-structural changes such as grain growth and carbide coarsening were examined by optical microscope. Detailed studies of fracture surfaces were made to find out the crack propagation on the weld joint of a boiler burner. It was concluded that the rupture may be caused by overheating induced by insufficient water on the boiler, and it could be accelerated by the metal temperature increase. Copyright © 2017 Elsevier B.V. All rights reserved.

Development of Safety Analysis Code System of Beam Transport and Core for Accelerator Driven System

NASA Astrophysics Data System (ADS)

Aizawa, Naoto; Iwasaki, Tomohiko

2014-06-01

Safety analysis code system of beam transport and core for accelerator driven system (ADS) is developed for the analyses of beam transients such as the change of the shape and position of incident beam. The code system consists of the beam transport analysis part and the core analysis part. TRACE 3-D is employed in the beam transport analysis part, and the shape and incident position of beam at the target are calculated. In the core analysis part, the neutronics, thermo-hydraulics and cladding failure analyses are performed by the use of ADS dynamic calculation code ADSE on the basis of the external source database calculated by PHITS and the cross section database calculated by SRAC, and the programs of the cladding failure analysis for thermoelastic and creep. By the use of the code system, beam transient analyses are performed for the ADS proposed by Japan Atomic Energy Agency. As a result, the rapid increase of the cladding temperature happens and the plastic deformation is caused in several seconds. In addition, the cladding is evaluated to be failed by creep within a hundred seconds. These results have shown that the beam transients have caused a cladding failure.

Prognostics of Power Mosfets Under Thermal Stress Accelerated Aging Using Data-Driven and Model-Based Methodologies

NASA Technical Reports Server (NTRS)

Celaya, Jose; Saxena, Abhinav; Saha, Sankalita; Goebel, Kai F.

2011-01-01

An approach for predicting remaining useful life of power MOSFETs (metal oxide field effect transistor) devices has been developed. Power MOSFETs are semiconductor switching devices that are instrumental in electronics equipment such as those used in operation and control of modern aircraft and spacecraft. The MOSFETs examined here were aged under thermal overstress in a controlled experiment and continuous performance degradation data were collected from the accelerated aging experiment. Dieattach degradation was determined to be the primary failure mode. The collected run-to-failure data were analyzed and it was revealed that ON-state resistance increased as die-attach degraded under high thermal stresses. Results from finite element simulation analysis support the observations from the experimental data. Data-driven and model based prognostics algorithms were investigated where ON-state resistance was used as the primary precursor of failure feature. A Gaussian process regression algorithm was explored as an example for a data-driven technique and an extended Kalman filter and a particle filter were used as examples for model-based techniques. Both methods were able to provide valid results. Prognostic performance metrics were employed to evaluate and compare the algorithms.

A quantitative model of honey bee colony population dynamics.

PubMed

Khoury, David S; Myerscough, Mary R; Barron, Andrew B

2011-04-18

Since 2006 the rate of honey bee colony failure has increased significantly. As an aid to testing hypotheses for the causes of colony failure we have developed a compartment model of honey bee colony population dynamics to explore the impact of different death rates of forager bees on colony growth and development. The model predicts a critical threshold forager death rate beneath which colonies regulate a stable population size. If death rates are sustained higher than this threshold rapid population decline is predicted and colony failure is inevitable. The model also predicts that high forager death rates draw hive bees into the foraging population at much younger ages than normal, which acts to accelerate colony failure. The model suggests that colony failure can be understood in terms of observed principles of honey bee population dynamics, and provides a theoretical framework for experimental investigation of the problem.

Failure mechanisms of thermal barrier coatings exposed to elevated temperatures

NASA Technical Reports Server (NTRS)

Miller, R. A.; Lowell, C. E.

1982-01-01

The failure of a ZrO2-8%Y2O3/Ni-14% Al-0.1% Zr coating system on Rene 41 in Mach 0.3 burner rig tests was characterized. High flame and metal temperatures were employed in order to accelerate coating failure. Failure by delamination was shown to precede surface cracking or spalling. This type of failure could be duplicated by cooling down the specimen after a single long duration isothermal high temperature cycle in a burner rig or a furnace, but only if the atmosphere was oxidizing. Stresses due to thermal expansion mismatch on cooling coupled with the effects of plastic deformation of the bond coat and oxidation of the irregular bond coat are the probable life limiting factors. Heat up stresses alone could not fail the coating in the burner rig tests. Spalling eventually occurs on heat up but only after the coating has already failed through delamination.

Ditching Investigation of a 1/18-Scale Model of the North American B-45 Airplane

NASA Technical Reports Server (NTRS)

Fisher, Lloyd J.; Thompson, William C.

1949-01-01

An investigation of a 1/18-scale dynamically similar model of the North American B-45 airplane was made to observe the ditching behavior and determine the proper landing technique to be used in an emergency water landing. Various conditions of damage were simulated to determine the behavior which probably would occur in a full-scale ditching. The behavior of the model was determined from high-speed motion-picture records, time-history acceleration records, and visual observations. It was concluded that the airplane should be ditched at the maximum nose-high attitude with the landing flaps full down for minimum landing speed. During the ditching, the nose-wheel and bomb-bay doors probably will be torn away and the rear of the fuselage flooded. A violent dive will very likely occur. Longitudinal decelerations of approximately 5g and vertical accelerations of approximately -6g (including gravity) will be experienced near the pilots' compartment. Ditching braces installed in the bomb bay will tend to improve the behavior slightly but will be torn away along with the bomb-bay doors. A hydroflap installed ahead of the nose-wheel doors will eliminate the dive and failure of the nose-wheel doors, and substantially reduce the motions and accelerations.

Impingement-Current-Erosion Characteristics of Accelerator Grids on Two-Grid Ion Thrusters

NASA Technical Reports Server (NTRS)

Barker, Timothy

1996-01-01

Accelerator grid sputter erosion resulting from charge-exchange-ion impingement is considered to be a primary cause of failure for electrostatic ion thrusters. An experimental method was developed and implemented to measure erosion characteristics of ion-thruster accel-grids for two-grid systems as a function of beam current, accel-grid potential, and facility background pressure. Intricate accelerator grid erosion patterns, that are typically produced in a short time (a few hours), are shown. Accelerator grid volumetric and depth-erosion rates are calculated from these erosion patterns and reported for each of the parameters investigated. A simple theoretical volumetric erosion model yields results that are compared to experimental findings. Results from the model and experiments agree to within 10%, thereby verifying the testing technique. In general, the local distribution of erosion is concentrated in pits between three adjacent holes and trenches that join pits. The shapes of the pits and trenches are shown to be dependent upon operating conditions. Increases in beam current and the accel-grid voltage magnitude lead to deeper pits and trenches. Competing effects cause complex changes in depth-erosion rates as background pressure is increased. Shape factors that describe pits and trenches (i.e. ratio of the average erosion width to the maximum possible width) are also affected in relatively complex ways by changes in beam current, ac tel-grid voltage magnitude, and background pressure. In all cases, however, gross volumetric erosion rates agree with theoretical predictions.

The Los Alamos Neutron Science Center Spallation Neutron Sources

NASA Astrophysics Data System (ADS)

Nowicki, Suzanne F.; Wender, Stephen A.; Mocko, Michael

The Los Alamos Neutron Science Center (LANSCE) provides the scientific community with intense sources of neutrons, which can be used to perform experiments supporting civilian and national security research. These measurements include nuclear physics experiments for the defense program, basic science, and the radiation effect programs. This paper focuses on the radiation effects program, which involves mostly accelerated testing of semiconductor parts. When cosmic rays strike the earth's atmosphere, they cause nuclear reactions with elements in the air and produce a wide range of energetic particles. Because neutrons are uncharged, they can reach aircraft altitudes and sea level. These neutrons are thought to be the most important threat to semiconductor devices and integrated circuits. The best way to determine the failure rate due to these neutrons is to measure the failure rate in a neutron source that has the same spectrum as those produced by cosmic rays. Los Alamos has a high-energy and a low-energy neutron source for semiconductor testing. Both are driven by the 800-MeV proton beam from the LANSCE accelerator. The high-energy neutron source at the Weapons Neutron Research (WNR) facility uses a bare target that is designed to produce fast neutrons with energies from 100 keV to almost 800 MeV. The measured neutron energy distribution from WNR is very similar to that of the cosmic-ray-induced neutrons in the atmosphere. However, the flux provided at the WNR facility is typically 5×107 times more intense than the flux of the cosmic-ray-induced neutrons. This intense neutron flux allows testing at greatly accelerated rates. An irradiation test of less than an hour is equivalent to many years of neutron exposure due to cosmic-ray neutrons. The low-energy neutron source is located at the Lujan Neutron Scattering Center. It is based on a moderated source that provides useful neutrons from subthermal energies to ∼100 keV. The characteristics of these sources, and ongoing industry program are described in this paper.

Acoustic emission monitoring of tensile testing of corroded and un-corroded clad aluminum 2024-T3 and characterization of effects of corrosion on AE source events and material tensile properties

NASA Astrophysics Data System (ADS)

Okafor, A. Chukwujekwu; Natarajan, Shridhar

2014-02-01

Corrosion damage affects structural integrity and deteriorates material properties of aluminum alloys in aircraft structures. Acoustic Emission (AE) is an effective nondestructive evaluation (NDE) technique for monitoring such damages and predicting failure in large structures of an aircraft. For successful interpretation of data from AE monitoring, sources of AE and factors affecting it need to be identified. This paper presents results of AE monitoring of tensile testing of corroded and un-corroded clad Aluminum 2024-T3 test specimens, and characterization of the effects of strain-rate and corrosion damage on material tensile properties and AE source events. Effect of corrosion was studied by inducing corrosion in the test specimens by accelerated corrosion testing in a Q-Fog accelerated corrosion chamber for 12 weeks. Eight (8) masked dog-bone shaped specimens were placed in the accelerated corrosion chamber at the beginning of the test. Two (2) dog-bone shaped specimens were removed from the corrosion chamber after exposure time of 3, 6, 9, and 12 weeks respectively, and subjected to tension testing till specimen failure along with AE monitoring, as well as two (2) reference samples not exposed to corrosion. Material tensile properties (yield strength, ultimate tensile strength, toughness, and elongation) obtained from tension test and AE parameters obtained from AE monitoring were analyzed and characterized. AE parameters increase with increase in exposure period of the specimens in the corrosive environment. Aluminum 2024-T3 is an acoustically silent material during tensile deformation without any damage. Acoustic emission events increase with increase of corrosion damage and with increase in strain rate above a certain value. Thus AE is suitable for structural health monitoring of corrosion damage. Ultimate tensile strength, toughness and elongation values decrease with increase of exposure period in corrosion chamber.

Predicting, examining, and evaluating FAC in US power plants

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

Cohn, M.J.; Garud, Y.S.; Raad, J. de

1999-11-01

There have been many pipe failures in fossil and nuclear power plant piping systems caused by flow-accelerated corrosion (FAC). In some piping systems, this failure mechanism maybe the most important type of damage to mitigate because FAC damage has led to catastrophic failures and fatalities. Detecting the damage and mitigating the problem can significantly reduce future forced outages and increase personnel safety. This article discusses the implementation of recent developments to select FAC inspection locations, perform cost-effective examinations, evaluate results, and mitigate FAC failures. These advances include implementing the combination of software to assist in selecting examination locations and anmore » improved pulsed eddy current technique to scan for wall thinning without removing insulation. The use of statistical evaluation methodology and possible mitigation strategies also are discussed.« less

Predictors of nursing home residents' time to hospitalization.

PubMed

O'Malley, A James; Caudry, Daryl J; Grabowski, David C

2011-02-01

To model the predictors of the time to first acute hospitalization for nursing home residents, and accounting for previous hospitalizations, model the predictors of time between subsequent hospitalizations. Merged file from New York State for the period 1998-2004 consisting of nursing home information from the minimum dataset and hospitalization information from the Statewide Planning and Research Cooperative System. Accelerated failure time models were used to estimate the model parameters and predict survival times. The models were fit to observations from 50 percent of the nursing homes and validated on the remaining observations. Pressure ulcers and facility-level deficiencies were associated with a decreased time to first hospitalization, while the presence of advance directives and facility staffing was associated with an increased time. These predictors of the time to first hospitalization model had effects of similar magnitude in predicting the time between subsequent hospitalizations. This study provides novel evidence suggesting modifiable patient and nursing home characteristics are associated with the time to first hospitalization and time to subsequent hospitalizations for nursing home residents. © Health Research and Educational Trust.

Next-generation foundations for special trackwork : phase I.

DOT National Transportation Integrated Search

2013-02-01

This report reviews the dynamic load environment and failure modes of special trackwork frog foundations. Key measurements taken under a 39,000-pound wheel load traffic at the Facility for Accelerated Service Testing were used to develop and calibrat...

Failure rates for accelerated acceptance testing of silicon transistors

NASA Technical Reports Server (NTRS)

Toye, C. R.

1968-01-01

Extrapolation tables for the control of silicon transistor product reliability have been compiled. The tables are based on a version of the Arrhenius statistical relation and are intended to be used for low- and medium-power silicon transistors.

Accelerated battery-life testing - A concept

NASA Technical Reports Server (NTRS)

Mccallum, J.; Thomas, R. E.

1971-01-01

Test program, employing empirical, statistical and physical methods, determines service life and failure probabilities of electrochemical cells and batteries, and is applicable to testing mechanical, electrical, and chemical devices. Data obtained aids long-term performance prediction of battery or cell.

Toward a more efficient and scalable checkpoint/restart mechanism in the Community Atmosphere Model

NASA Astrophysics Data System (ADS)

Anantharaj, Valentine

2015-04-01

The number of cores (both CPU as well as accelerator) in large-scale systems has been increasing rapidly over the past several years. In 2008, there were only 5 systems in the Top500 list that had over 100,000 total cores (including accelerator cores) whereas the number of system with such capability has jumped to 31 in Nov 2014. This growth however has also increased the risk of hardware failure rates, necessitating the implementation of fault tolerance mechanism in applications. The checkpoint and restart (C/R) approach is commonly used to save the state of the application and restart at a later time either after failure or to continue execution of experiments. The implementation of an efficient C/R mechanism will make it more affordable to output the necessary C/R files more frequently. The availability of larger systems (more nodes, memory and cores) has also facilitated the scaling of applications. Nowadays, it is more common to conduct coupled global climate simulation experiments at 1 deg horizontal resolution (atmosphere), often requiring about 103 cores. At the same time, a few climate modeling teams that have access to a dedicated cluster and/or large scale systems are involved in modeling experiments at 0.25 deg horizontal resolution (atmosphere) and 0.1 deg resolution for the ocean. These ultrascale configurations require the order of 104 to 105 cores. It is not only necessary for the numerical algorithms to scale efficiently but the input/output (IO) mechanism must also scale accordingly. An ongoing series of ultrascale climate simulations, using the Titan supercomputer at the Oak Ridge Leadership Computing Facility (ORNL), is based on the spectral element dynamical core of the Community Atmosphere Model (CAM-SE), which is a component of the Community Earth System Model and the DOE Accelerated Climate Model for Energy (ACME). The CAM-SE dynamical core for a 0.25 deg configuration has been shown to scale efficiently across 100,000 cpu cores. At this scale, there is an increased risk that the simulation could be terminated due to hardware failures, resulting in a loss that could be as high as 105 - 106 titan core hours. Increasing the frequency of the output of C/R files could mitigate this loss but at the cost of additional C/R overhead. We are testing a more efficient C/R mechanism in CAM-SE. Our early implementation has demonstrated a nearly 3X performance improvement for a 1 deg CAM-SE (with CAM5 physics and MOZART chemistry) configuration using nearly 103 cores. We are in the process of scaling our implementation to 105 cores. This would allow us to run ultra scale simulations with more sophisticated physics and chemistry options while making better utilization of resources.

Development of an Accelerated Hydrogen Embrittlement Test for Manganese Phosphated Steels

DTIC Science & Technology

2011-05-01

from the same vendor (RSL Testing Systems) and lot (HT/ HTP ) were used. See Appendix B for the certifications for lots HT/ HTP . Note: lot HTP is...Based on the vendor certification of the notched tensile specimens from RSL lot HT/ HTP , the NTS was 373 ksi and the average load at failure was...Systems Lot HT/ HTP ). Note that use of a higher reference NTS and load to failure is a conservative approach since the specimens will experience

Yield and failure criteria for composite materials under static and dynamic loading

DOE PAGES

Daniel, Isaac M.

2015-12-23

To facilitate and accelerate the process of introducing, evaluating and adopting of new material systems, it is important to develop/establish comprehensive and effective procedures of characterization, modeling and failure prediction of structural laminates based on the properties of the constituent materials, e. g., fibers, matrix, and the single ply or lamina. A new failure theory, the Northwestern (NU-Daniel) theory, has been proposed for predicting lamina yielding and failure under multi-axial states of stress including strain rate effects. It is primarily applicable to matrix-dominated interfiber/interlaminar failures. It is based on micromechanical failure mechanisms but is expressed in terms of easily measuredmore » macroscopic lamina stiffness and strength properties. It is presented in the form of a master failure envelope incorporating strain rate effects. The theory was further adapted and extended to the prediction of in situ first ply yielding and failure (FPY and FPF) and progressive failure of multi-directional laminates under static and dynamic loadings. The significance of this theory is that it allows for rapid screening of new composite materials without very extensive testing and offers easily implemented design tools.« less

Academic and Demographic Predictors of NCLEX-RN Pass Rates in First- and Second-Degree Accelerated BSN Programs.

PubMed

Kaddoura, Mahmoud A; Flint, Elizabeth P; Van Dyke, Olga; Yang, Qing; Chiang, Li-Chi

Relatively few studies have addressed predictors of first-attempt outcomes (pass-fail) on the National Council Licensure Examination-Registered Nurses (NCLEX-RN) for accelerated BSN programs. The purpose of this study was to compare potential predictors of NCLEX outcomes in graduates of first-degree accelerated (FDA; n=62) and second-degree accelerated (SDA; n=173) BSN programs sharing a common nursing curriculum. In this retrospective study, bivariate analyses and multiple logistic regression assessed significance of selected demographic and academic characteristics as predictors of NCLEX-RN outcomes. FDA graduates were more likely than SDA graduates to fail the NCLEX-RN (P=.0013). FDA graduates were more likely to speak English as a second or additional language (P<.0001), have lower end-of-program GPA and HESI Exit Exam scores (both P<.0001), and have a higher proportions of grades ≤ C (P=.0023). All four variables were significant predictors of NCLEX-RN outcomes within both FDA and SDA programs. The only significant predictors in adjusted logistic regression of NCLEX-RN outcome for the pooled FDA+SDA graduate sample were proportion of grades ≤ C (a predictor of NCLEX-RN failure) and HESI Exit Exam score (a predictor of passing NCLEX-RN). Grades of C or lower on any course may indicate inadequate mastery of critical NCLEX-RN content and increased risk of NCLEX-RN failure. Copyright © 2016 Elsevier Inc. All rights reserved.

The application of the detection filter to aircraft control surface and actuator failure detection and isolation

NASA Technical Reports Server (NTRS)

Bonnice, W. F.; Wagner, E.; Motyka, P.; Hall, S. R.

1985-01-01

The performance of the detection filter in detecting and isolating aircraft control surface and actuator failures is evaluated. The basic detection filter theory assumption of no direct input-output coupling is violated in this application due to the use of acceleration measurements for detecting and isolating failures. With this coupling, residuals produced by control surface failures may only be constrained to a known plane rather than to a single direction. A detection filter design with such planar failure signatures is presented, with the design issues briefly addressed. In addition, a modification to constrain the residual to a single known direction even with direct input-output coupling is also presented. Both the detection filter and the modification are tested using a nonlinear aircraft simulation. While no thresholds were selected, both filters demonstrated an ability to detect control surface and actuator failures. Failure isolation may be a problem if there are several control surfaces which produce similar effects on the aircraft. In addition, the detection filter was sensitive to wind turbulence and modeling errors.

Accelerated Fatigue Resistance of Thick CAD/CAM Composite Resin Overlays Bonded with Light- and Dual-polymerizing Luting Resins.

PubMed

Goldberg, Jack; Güth, Jan-Frederik; Magne, Pascal

To evaluate the accelerated fatigue resistance of thick CAD/CAM composite resin overlays luted with three different bonding methods. Forty-five sound human second mandibular molars were organized and distributed into three experimental groups. All teeth were restored with a 5-mm-thick CAD/CAM composite resin overlay. Group A: immediate dentin sealing (IDS) with Optibond FL and luted with light-polymerizing composite (Herculite XRV). Group B: IDS with Optibond FL and luted with dual-polymerizing composite (Nexus 3). Group C: direct luting with Optibond FL and dual-polymerizing composite (Nexus 3). Masticatory forces at a frequency of 5 Hz were simulated using closed-loop servo-hydraulics and forces starting with a load of 200 N for 5000 cycles, followed by steps of 400, 600, 800, 1000, 1200 and 1400 N for a maximum of 30,000 cycles. Each step was applied through a flat steel cylinder at a 45-degree angle under submerged conditions. The fatigue test generated one failure in group A, three failures in group B, and no failures in group C. The survival table analysis for the fatigue test did not demonstrate any significant difference between the groups (p = 0.154). The specimens that survived the fatigue test were set up for the load-to-failure test with a limit of 4600 N. The survival table analysis for the load-to-failure test demonstrates an average failure load of 3495.20 N with survival of four specimens in group A, an average failure load of 4103.60 N with survival of six specimens in group B, and an average failure load of 4075.33 N with survival of nine specimens in group C. Pairwise comparisons revealed no significant differences (p < 0.016 after Bonferroni correction). Within the limitations of this in vitro study, it can be concluded that although the dual-polymerizing luting material seems to provide better results under extreme conditions, light-polymerizing luting composites in combination with IDS are not contraindicated with thick restorations.

SELF-MANAGEMENT COUNSELING IN PATIENTS WITH HEART FAILURE: PRIMARY RESULTS FROM THE HEART FAILURE ADHERENCE AND RETENTION TRIAL (HART)

PubMed Central

Powell, Lynda H.; Calvin, James E.; Richardson, Dejuran; Janssen, Imke; Mendes de Leon, Carlos F.; Flynn, Kristin J.; Grady, Kathleen L.; Rucker-Whitaker, Cheryl S.; Eaton, Claudia; Avery, Elizabeth

2013-01-01

Context Activating patients with heart failure (HF) to adhere to physician advice has not translated into clinical benefit, but past trials have had methodologic limitations. Objective To determine the value of self-management counseling plus HF education, over HF education alone, on the primary endpoint of death or HF hospitalization. Design, Setting, and Patients A single center behavioral efficacy trial in 902 patients with mild to moderate systolic or diastolic dysfunction, randomized between 2001–2004. Interventions All patients were offered 18 contacts and 18 HF educational tip sheets over the course of 1 year. Patients randomized to education received tip sheets in the mail and phone calls to check comprehension. Patients randomized to self-management received tip sheets in groups and were taught self-management skills to implement the advice. Main Outcome Measure Death or HF hospitalization, blindly adjudicated by cardiologists. Intent-to-treat results were analyzed as time-to-event and accelerated failure time models were used for non-proportional hazards. Results Patients were an average of 63.6 years, 47% female, 40% minority, 52% with family income <$30,000/year, and 23% with diastolic dysfunction. The self-management arm was no different from the education arm on the primary endpoint (Wilcoxon p=0.58). Post-hoc analyses on pre-specified subgroups revealed a significant income x treatment interaction (log-logistic estimate=0.64, p=0.02). Patients with income <$30,000 in self-management had a slower time to event than those in education (p=0.05) and were no different than higher income patients in either treatment arm. Conclusions The addition of self-management counseling to HF education does not reduce death or HF hospitalizations in patients with mild to moderate HF. Future trials should evaluate tailored outpatient HF management featuring ongoing education and comprehension checks for all, augmented by group-based skill development for those more economically disadvantaged. Such an approach may be a cost-effective, timely, and simple option for reducing HF costs. PMID:20858878

TU-FG-201-09: Predicting Accelerator Dysfunction

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

Able, C; Nguyen, C; Baydush, A

Purpose: To develop an integrated statistical process control (SPC) framework using digital performance and component data accumulated within the accelerator system that can detect dysfunction prior to unscheduled downtime. Methods: Seven digital accelerators were monitored for twelve to 18 months. The accelerators were operated in a ‘run to failure mode’ with the individual institutions determining when service would be initiated. Institutions were required to submit detailed service reports. Trajectory and text log files resulting from a robust daily VMAT QA delivery were decoded and evaluated using Individual and Moving Range (I/MR) control charts. The SPC evaluation was presented in amore » customized dashboard interface that allows the user to review 525 monitored parameters (480 MLC parameters). Chart limits were calculated using a hybrid technique that includes the standard SPC 3σ limits and an empirical factor based on the parameter/system specification. The individual (I) grand mean values and control limit ranges of the I/MR charts of all accelerators were compared using statistical (ranked analysis of variance (ANOVA)) and graphical analyses to determine consistency of operating parameters. Results: When an alarm or warning was directly connected to field service, process control charts predicted dysfunction consistently on beam generation related parameters (BGP)– RF Driver Voltage, Gun Grid Voltage, and Forward Power (W); beam uniformity parameters – angle and position steering coil currents; and Gantry position accuracy parameter: cross correlation max-value. Control charts for individual MLC – cross correlation max-value/position detected 50% to 60% of MLCs serviced prior to dysfunction or failure. In general, non-random changes were detected 5 to 80 days prior to a service intervention. The ANOVA comparison of BGP determined that each accelerator parameter operated at a distinct value. Conclusion: The SPC framework shows promise. Long term monitoring coordinated with service will be required to definitively determine the effectiveness of the model. Varian Medical System, Inc. provided funding in support of the research presented.« less

Survival Data and Regression Models

NASA Astrophysics Data System (ADS)

Grégoire, G.

2014-12-01

We start this chapter by introducing some basic elements for the analysis of censored survival data. Then we focus on right censored data and develop two types of regression models. The first one concerns the so-called accelerated failure time models (AFT), which are parametric models where a function of a parameter depends linearly on the covariables. The second one is a semiparametric model, where the covariables enter in a multiplicative form in the expression of the hazard rate function. The main statistical tool for analysing these regression models is the maximum likelihood methodology and, in spite we recall some essential results about the ML theory, we refer to the chapter "Logistic Regression" for a more detailed presentation.

Reliability systems for implantable cardiac defibrillator batteries

NASA Astrophysics Data System (ADS)

Takeuchi, Esther S.

The reliability of the power sources used in implantable cardiac defibrillators is critical due to the life-saving nature of the device. Achieving a high reliability power source depends on several systems functioning together. Appropriate cell design is the first step in assuring a reliable product. Qualification of critical components and of the cells using those components is done prior to their designation as implantable grade. Product consistency is assured by control of manufacturing practices and verified by sampling plans using both accelerated and real-time testing. Results to date show that lithium/silver vanadium oxide cells used for implantable cardiac defibrillators have a calculated maximum random failure rate of 0.005% per test month.

Correlation between mechanical and chemical degradation after outdoor and accelerated laboratory aging for multilayer photovoltaic backsheets

NASA Astrophysics Data System (ADS)

Lin, Chiao-Chi; Lyu, Yadong; Yu, Li-Chieh; Gu, Xiaohong

2016-09-01

Channel cracking fragmentation testing and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were utilized to study mechanical and chemical degradation of a multilayered backsheet after outdoor and accelerated laboratory aging. A model sample of commercial PPE backsheet, namely polyethylene terephthalate/polyethylene terephthalate/ethylene vinyl acetate (PET/PET/EVA) was investigated. Outdoor aging was performed in Gaithersburg, Maryland, USA for up to 510 days, and complementary accelerated laboratory aging was conducted on the NIST (National Institute of Standards and Technology) SPHERE (Simulated Photodegradation via High Energy Radiant Exposure). Fracture energy, mode I stress intensity factor and film strength were analyzed using an analytical model based on channel cracking fragmentation testing results. The correlation between mechanical and chemical degradation was discussed for both outdoor and accelerated laboratory aging. The results of this work provide preliminary understanding on failure mechanism of backsheets after weathering, laying the groundwork for linking outdoor and indoor accelerated laboratory testing for multilayer photovoltaic backsheets.

On the dynamical behaviour of low-frequency earthquake swarms prior to a dome collapse of Soufrière Hill volcano, Montserrat

NASA Astrophysics Data System (ADS)

Hammer, C.; Neuberg, J. W.

2009-03-01

A series of low-frequency earthquake swarms prior to a dome collapse on Soufrière Hills volcano, Montserrat, are investigated with the emphasis on event rate and amplitude behaviour. In a single swarm, the amplitudes of consecutive events tend to increase with time, while the rate of event occurrence accelerates initially and then decelerates toward the end of the swarm. However, when consecutive swarms are considered, the average event rates seem to follow the material failure law, and the time of the dome collapse can be successfully estimated using the inverse event rate. These patterns in amplitude and event rate are interpreted as fluctuations in magma ascent velocity, which result in both the generation of low-frequency events as well as cyclic ground deformation accompanying the swarm activity.

Creep and slip: Seismic precursors to the Nuugaatsiaq landslide (Greenland)

NASA Astrophysics Data System (ADS)

Poli, Piero

2017-09-01

Precursory signals to material's failure are predicted by numerical models and observed in laboratory experiments or using field data. These precursory signals are a marker of slip acceleration on weak regions, such as crustal faults. Observation of these precursory signals of catastrophic natural events, such as earthquakes and landslides, is necessary for improving our knowledge about the physics of the nucleation process. Furthermore, observing such precursory signals may help to forecast these catastrophic events or reduce their hazard. I report here the observation of seismic precursors to the Nuugaatsiaq landslide in Greenland. Time evolution of the detected precursors implies that an aseismic slip event is taking place for hours before the landslide, with an exponential increase of slip velocity. Furthermore, time evolution of the precursory signals' amplitude sheds light on the evolution of the fault physics during the nucleation process.

Forecasting slope failures from space-based synthetic aperture radar (SAR) measurements

NASA Astrophysics Data System (ADS)

Wasowski, J.; Bovenga, F.; Nutricato, R.; Nitti, D. O.; Chiaradia, M. T.; Tijani, K.; Morea, A.

2017-12-01

New space-borne radar sensors enable multi-scale monitoring of potentially unstable slopes thanks to wide-area coverage (tens of thousands km2), regular long-term image acquisition schedule with increasing re-visit frequency (weekly to daily), and high measurement precision (mm). In particular, the recent radar satellite missions e.g., COSMO-SkyMed (CSK), Sentinel-1 (S-1) and improved multi-temporal interferometry (MTI) processing techniques allow timely delivery of information on slow ground surface displacements. Here we use two case study examples to show that it is possible to capture pre-failure slope strains through long-term MTI-based monitoring. The first case is a retrospective investigation of a huge 500ML m3 landslide, which occurred in Sept. 2016 in a large, active open-cast coal mine in central Europe. We processed over 100 S-1 images acquired since Fall 2014. The MTI results showed that the slope that failed had been unstable at least since 2014. Importantly, we detected consistent displacement trends and trend changes, which can be used for slope failure forecasting. Specifically, we documented significant acceleration in slope surface displacement in the two months preceding the catastrophic failure. The second case of retrospectively captured pre-failure slope strains regards our earlier study of a small 50 m long landslide, which occurred on Jan. 2014 and caused the derailment of a train on the railway line connecting NW Italy to France. We processed 56 CSK images acquired from Fall 2008 to Spring 2014. The MTI results revealed pre-failure displacements of the engineering structures on the slope subsequently affected by the 2014 slide. The analysis of the MTI time series further showed that the displacements had been occurring since 2009. This information could have been used to forewarn the railway authority about the slope instability hazard. The above examples indicate that more frequent and consistent image acquisitions by the new radar satellites represent the key improvement for MTI-based slope monitoring. The forecasting of potential slope failures from space is now more feasible. ACKNOWLEDGEMENTS We thank European (ESA) and Italian (ASI) space agencies for S-1 and CSK® Products. We also acknowledge the IT resources made available by ReCaS, a project financed by the MIUR.

Heterogeneity: The key to failure forecasting

PubMed Central

Vasseur, Jérémie; Wadsworth, Fabian B.; Lavallée, Yan; Bell, Andrew F.; Main, Ian G.; Dingwell, Donald B.

2015-01-01

Elastic waves are generated when brittle materials are subjected to increasing strain. Their number and energy increase non-linearly, ending in a system-sized catastrophic failure event. Accelerating rates of geophysical signals (e.g., seismicity and deformation) preceding large-scale dynamic failure can serve as proxies for damage accumulation in the Failure Forecast Method (FFM). Here we test the hypothesis that the style and mechanisms of deformation, and the accuracy of the FFM, are both tightly controlled by the degree of microstructural heterogeneity of the material under stress. We generate a suite of synthetic samples with variable heterogeneity, controlled by the gas volume fraction. We experimentally demonstrate that the accuracy of failure prediction increases drastically with the degree of material heterogeneity. These results have significant implications in a broad range of material-based disciplines for which failure forecasting is of central importance. In particular, the FFM has been used with only variable success to forecast failure scenarios both in the field (volcanic eruptions and landslides) and in the laboratory (rock and magma failure). Our results show that this variability may be explained, and the reliability and accuracy of forecast quantified significantly improved, by accounting for material heterogeneity as a first-order control on forecasting power. PMID:26307196

Heterogeneity: The key to failure forecasting.

PubMed

Vasseur, Jérémie; Wadsworth, Fabian B; Lavallée, Yan; Bell, Andrew F; Main, Ian G; Dingwell, Donald B

2015-08-26

Elastic waves are generated when brittle materials are subjected to increasing strain. Their number and energy increase non-linearly, ending in a system-sized catastrophic failure event. Accelerating rates of geophysical signals (e.g., seismicity and deformation) preceding large-scale dynamic failure can serve as proxies for damage accumulation in the Failure Forecast Method (FFM). Here we test the hypothesis that the style and mechanisms of deformation, and the accuracy of the FFM, are both tightly controlled by the degree of microstructural heterogeneity of the material under stress. We generate a suite of synthetic samples with variable heterogeneity, controlled by the gas volume fraction. We experimentally demonstrate that the accuracy of failure prediction increases drastically with the degree of material heterogeneity. These results have significant implications in a broad range of material-based disciplines for which failure forecasting is of central importance. In particular, the FFM has been used with only variable success to forecast failure scenarios both in the field (volcanic eruptions and landslides) and in the laboratory (rock and magma failure). Our results show that this variability may be explained, and the reliability and accuracy of forecast quantified significantly improved, by accounting for material heterogeneity as a first-order control on forecasting power.

Heterogeneity: The key to failure forecasting

NASA Astrophysics Data System (ADS)

Vasseur, Jérémie; Wadsworth, Fabian B.; Lavallée, Yan; Bell, Andrew F.; Main, Ian G.; Dingwell, Donald B.

2015-08-01

Elastic waves are generated when brittle materials are subjected to increasing strain. Their number and energy increase non-linearly, ending in a system-sized catastrophic failure event. Accelerating rates of geophysical signals (e.g., seismicity and deformation) preceding large-scale dynamic failure can serve as proxies for damage accumulation in the Failure Forecast Method (FFM). Here we test the hypothesis that the style and mechanisms of deformation, and the accuracy of the FFM, are both tightly controlled by the degree of microstructural heterogeneity of the material under stress. We generate a suite of synthetic samples with variable heterogeneity, controlled by the gas volume fraction. We experimentally demonstrate that the accuracy of failure prediction increases drastically with the degree of material heterogeneity. These results have significant implications in a broad range of material-based disciplines for which failure forecasting is of central importance. In particular, the FFM has been used with only variable success to forecast failure scenarios both in the field (volcanic eruptions and landslides) and in the laboratory (rock and magma failure). Our results show that this variability may be explained, and the reliability and accuracy of forecast quantified significantly improved, by accounting for material heterogeneity as a first-order control on forecasting power.

Design for dependability: A simulation-based approach. Ph.D. Thesis, 1993

NASA Technical Reports Server (NTRS)

Goswami, Kumar K.

1994-01-01

This research addresses issues in simulation-based system level dependability analysis of fault-tolerant computer systems. The issues and difficulties of providing a general simulation-based approach for system level analysis are discussed and a methodology that address and tackle these issues is presented. The proposed methodology is designed to permit the study of a wide variety of architectures under various fault conditions. It permits detailed functional modeling of architectural features such as sparing policies, repair schemes, routing algorithms as well as other fault-tolerant mechanisms, and it allows the execution of actual application software. One key benefit of this approach is that the behavior of a system under faults does not have to be pre-defined as it is normally done. Instead, a system can be simulated in detail and injected with faults to determine its failure modes. The thesis describes how object-oriented design is used to incorporate this methodology into a general purpose design and fault injection package called DEPEND. A software model is presented that uses abstractions of application programs to study the behavior and effect of software on hardware faults in the early design stage when actual code is not available. Finally, an acceleration technique that combines hierarchical simulation, time acceleration algorithms and hybrid simulation to reduce simulation time is introduced.

Overview of the SHIELDS Project at LANL

NASA Astrophysics Data System (ADS)

Jordanova, V.; Delzanno, G. L.; Henderson, M. G.; Godinez, H. C.; Jeffery, C. A.; Lawrence, E. C.; Meierbachtol, C.; Moulton, D.; Vernon, L.; Woodroffe, J. R.; Toth, G.; Welling, D. T.; Yu, Y.; Birn, J.; Thomsen, M. F.; Borovsky, J.; Denton, M.; Albert, J.; Horne, R. B.; Lemon, C. L.; Markidis, S.; Young, S. L.

2015-12-01

The near-Earth space environment is a highly dynamic and coupled system through a complex set of physical processes over a large range of scales, which responds nonlinearly to driving by the time-varying solar wind. Predicting variations in this environment that can affect technologies in space and on Earth, i.e. "space weather", remains a big space physics challenge. We present a recently funded project through the Los Alamos National Laboratory (LANL) Directed Research and Development (LDRD) program that is developing a new capability to understand, model, and predict Space Hazards Induced near Earth by Large Dynamic Storms, the SHIELDS framework. The project goals are to specify the dynamics of the hot (keV) particles (the seed population for the radiation belts) on both macro- and micro-scale, including important physics of rapid particle injection and acceleration associated with magnetospheric storms/substorms and plasma waves. This challenging problem is addressed using a team of world-class experts in the fields of space science and computational plasma physics and state-of-the-art models and computational facilities. New data assimilation techniques employing data from LANL instruments on the Van Allen Probes and geosynchronous satellites are developed in addition to physics-based models. This research will provide a framework for understanding of key radiation belt drivers that may accelerate particles to relativistic energies and lead to spacecraft damage and failure. The ability to reliably distinguish between various modes of failure is critically important in anomaly resolution and forensics. SHIELDS will enhance our capability to accurately specify and predict the near-Earth space environment where operational satellites reside.

Measuring unsteady pressure on rotating compressor blades

NASA Technical Reports Server (NTRS)

Englund, D. R.; Grant, H. P.; Lanati, G. A.

1979-01-01

Miniature semiconductor strain gage pressure transducers mounted in several arrangements were studied. Both surface mountings and recessed flush mountings were tested. Test parameters included mounting arrangement, blade material, temperature, local strain in the acceleration normal to the transducer diaphragm, centripetal acceleration, and pressure. Test results show no failures of transducers or mountings and indicate an uncertainty of unsteady pressure measurement of approximately + or - 6 percent + 0.1 kPa for a typical application. Two configurations were used on a rotating fan flutter program. Examples of transducer data and correction factors are presented.

Failure of metoclopramide to control emesis or nausea due to stressful angular or linear acceleration

NASA Technical Reports Server (NTRS)

Kohl, Randall Lee

1987-01-01

Orally administered metoclopramide (REGLAN) at doses of 10 or 20 mg, 75 min prior to either stressful linear acceleration (parabolic flight) or cross-coupled accelerative semicircular canal stimulation in a rotating chair was evaluated for its ability to prevent emesis or nausea II, respectively. Although metoclopramide is an effective antiemetic agent that enhances gastric emptying and prevents cancer chemotherapy-induced emesis, it was not possible to demonstrate any significant (p less than 0.05) effects of this drug on motion sickness.

Analysis of Tsunamigenic Coastal Rock Slope Failures Triggered by the 2007 Earthquake in the Chilean Fjordland

NASA Astrophysics Data System (ADS)

Sepulveda, S. A.; Serey, A.; Hermanns, R. L.; Redfield, T. F.; Oppikofer, T.; Duhart, P.

2011-12-01

The fjordland of the Chilean Patagonia is subject to active tectonics, with large magnitude subduction earthquakes, such as the M 9.5 1960 earthquake, and shallow crustal earthquakes along the regional Liquiñe-Ofqui Fault Zone (LOFZ). One of the latter (M 6.2) struck the Aysen Fjord region (45.5 S) on the 21st of April 2007, triggering dozens of landslides in the epicentral area along the fjord coast and surroundings. The largest rock slides and rock avalanches induced a local tsunami that together with debris flows caused ten fatalities and severely damaged several salmon farms, the most important economic activity of the area. Multi-scale studies of the landslides triggered during the Aysen earthquake have been carried out, including landslide mapping and classification, slope stability back-analyses and structural and geomorphological mapping of the largest failures from field surveys and high-resolution digital surface models created from terrestrial laser scanning. The failures included rock slides, rock avalanches, rock-soil slides, soil slides and debris flows. The largest rock avalanche had a volume of over 20 million cubic metres. The landslides affected steep slopes of intrusive rocks of the North Patagonian batholith covered by a thin layer of volcanic soils, which supports a high forest. The results of geotechnical analyses suggest a site effect due to topographic amplification on the generation of the landslides, with peak ground accelerations that may have reached between about 1.0 and 2.0 g for rock avalanches and between 0.6 and 1.0 g for shallow rock-soil slides, depending on the amount of assumed vertical acceleration and the applied method (limit equilibrium and Newmark). Attenuation relationships for shallow crustal seismicity indicate accelerations below 0.5 g for earthquakes of a similar magnitude and epicentral distances. Detailed field structural analyses of the largest rock avalanche in Punta Cola indicate a key role in the failure mechanics of brittle faults and jointing related to the LOFZ. The basal failure plane closely followed an older (epidote chlorite facies) thrust fault. Later fracture patterns suggest the thrust relaxed under gravitational stress following rock column uplift. Failure probably utilized a combination of these structures. Digital geomorphic models allowed establishing a sequence of events during failure which together make up the complex rock avalanche deposit. The volume of each individual slide could be more accurately determined. These and ongoing studies will allow a unique characterization of earthquake-induced slope failures in fjord coastal environments, providing new tools for landslide, seismic and tsunami hazard assessment in Patagonia and similar geomorphological settings around the world. This work was funded by Fondecyt project 11070107, the International Center for Geohazards, the Millenium Nucleus 'International Earthquake Research Center Montessus de Ballore', FNDR-Project 'Geological-Mining Environmental Research in Aysen' of the Chilean Government and the Andean Geothermal Center of Excellence.

Preliminary control law and hardware designs for a ride quality augmentation system for commuter aircraft. Phase 2

NASA Technical Reports Server (NTRS)

Davis, D. J.; Linse, D. J.; Suikat, R.; Entz, D. P.

1986-01-01

The continued investigation of the design of Ride Quality Augmentation Systems (RQAS) for commuter aircraft is described. The purpose of these RQAS is the reduction of the vertical and lateral acceleration response of the aircraft due to atmospheric turbulence by the application of active control. The current investigations include the refinement of the sample data feedback control laws based on the control-rate-weighting and output-weighting optimal control design techniqes. These control designs were evaluated using aircraft time simulations driven by Dryden spectra turbulence. Fixed gain controllers were tested throughout the aircrft operating envelope. The preliminary design of the hardware modifications necessary to implement and test the RQAS on a commuter aircraft is included. These include a separate surface elevator and the flap modifications to provide both direct lift and roll control. A preliminary failure mode investigation was made for the proposed configuration. The results indicate that vertical acceleration reductions of 45% and lateral reductions of more than 50% are possible. A fixed gain controller appears to be feasible with only minor response degradation.

Preliminary floor, seat, and dummy data

NASA Technical Reports Server (NTRS)

Cannon, M. R.; Zimmerman, R. E.

1986-01-01

According to preliminary examination of the data, out of 179 data channels that were onboard the aircraft in support of the seat experiments, there is data from 168. There was somewhat more severe environment imposed in the structure of the obstacles than by the ground impact. Therefore, both ground impact and obstacle impact are of interest for crashworthiness experiments. Most of the data channels that were studied are fairly consistent with the physical evidence: they show acceleration levels that are reasonable, and in many cases these integrate out to a reasonable velocity change. Finally, from observation thus far, the ground impact did not fail or significantly damage any seat. Nor did any of the energy absorbers in the modified seats extend. The accelerations do not appear high enough and/or energetic enough to cause this to happen. At this time, the onboard films have not been studied; only some videotape have been viewed. Some of the seats were so badly damaged by the fire that any failures which might have occurred were obscured. A close examination of the onboard films using a stop-action projector will allow a more thorough evaluation.

Finite element analyses of a linear-accelerator electron gun

NASA Astrophysics Data System (ADS)

Iqbal, M.; Wasy, A.; Islam, G. U.; Zhou, Z.

2014-02-01

Thermo-structural analyses of the Beijing Electron-Positron Collider (BEPCII) linear-accelerator, electron gun, were performed for the gun operating with the cathode at 1000 °C. The gun was modeled in computer aided three-dimensional interactive application for finite element analyses through ANSYS workbench. This was followed by simulations using the SLAC electron beam trajectory program EGUN for beam optics analyses. The simulations were compared with experimental results of the assembly to verify its beam parameters under the same boundary conditions. Simulation and test results were found to be in good agreement and hence confirmed the design parameters under the defined operating temperature. The gun is operating continuously since commissioning without any thermal induced failures for the BEPCII linear accelerator.

Finite element analyses of a linear-accelerator electron gun.

PubMed

Iqbal, M; Wasy, A; Islam, G U; Zhou, Z

2014-02-01

Thermo-structural analyses of the Beijing Electron-Positron Collider (BEPCII) linear-accelerator, electron gun, were performed for the gun operating with the cathode at 1000 °C. The gun was modeled in computer aided three-dimensional interactive application for finite element analyses through ANSYS workbench. This was followed by simulations using the SLAC electron beam trajectory program EGUN for beam optics analyses. The simulations were compared with experimental results of the assembly to verify its beam parameters under the same boundary conditions. Simulation and test results were found to be in good agreement and hence confirmed the design parameters under the defined operating temperature. The gun is operating continuously since commissioning without any thermal induced failures for the BEPCII linear accelerator.

Adverse remodeling of the electrophysiological response to ischemia-reperfusion in human heart failure is associated with remodeling of metabolic gene expression.

PubMed

Ng, Fu Siong; Holzem, Katherine M; Koppel, Aaron C; Janks, Deborah; Gordon, Fabiana; Wit, Andrew L; Peters, Nicholas S; Efimov, Igor R

2014-10-01

Ventricular arrhythmias occur more frequently in heart failure during episodes of ischemia-reperfusion although the mechanisms underlying this in humans are unclear. We assessed, in explanted human hearts, the remodeled electrophysiological response to acute ischemia-reperfusion in heart failure and its potential causes, including the remodeling of metabolic gene expression. We optically mapped coronary-perfused left ventricular wedge preparations from 6 human end-stage failing hearts (F) and 6 donor hearts rejected for transplantation (D). Preparations were subjected to 30 minutes of global ischemia, followed by 30 minutes of reperfusion. Failing hearts had exaggerated electrophysiological responses to ischemia-reperfusion, with greater action potential duration shortening (P<0.001 at 8-minute ischemia; P=0.001 at 12-minute ischemia) and greater conduction slowing during ischemia, delayed recovery of electric excitability after reperfusion (F, 4.8±1.8 versus D, 1.0±0 minutes; P<0.05), and incomplete restoration of action potential duration and conduction velocity early after reperfusion. Expression of 46 metabolic genes was probed using custom-designed TaqMan arrays, using extracted RNA from 15 failing and 9 donor hearts. Ten genes important in cardiac metabolism were downregulated in heart failure, with SLC27A4 and KCNJ11 significantly downregulated at a false discovery rate of 0%. We demonstrate, for the first time in human hearts, that the electrophysiological response to ischemia-reperfusion in heart failure is accelerated during ischemia with slower recovery after reperfusion. This can enhance spatial conduction and repolarization gradients across the ischemic border and increase arrhythmia susceptibility. This adverse response was associated with downregulation of expression of cardiac metabolic genes. © 2014 American Heart Association, Inc.

Reliability and Characteristics of Wafer-Level Chip-Scale Packages under Current Stress

NASA Astrophysics Data System (ADS)

Chen, Po-Ying; Kung, Heng-Yu; Lai, Yi-Shao; Hsiung Tsai, Ming; Yeh, Wen-Kuan

2008-02-01

In this work, we present a novel approach and method for elucidating the characteristics of wafer-level chip-scale packages (WLCSPs) for electromigration (EM) tests. The die in WLCSP was directly attached to the substrate via a soldered interconnect. The shrinking of the area of the die that is available for power, and the solder bump also shrinks the volume and increases the density of electrons for interconnect efficiency. The bump current density now approaches to 106 A/cm2, at which point the EM becomes a significant reliability issue. As known, the EM failure depends on numerous factors, including the working temperature and the under bump metallization (UBM) thickness. A new interconnection geometry is adopted extensively with moderate success in overcoming larger mismatches between the displacements of components during current and temperature changes. Both environments and testing parameters for WLCSP are increasingly demanded. Although failure mechanisms are considered to have been eliminated or at least made manageable, new package technologies are again challenging its process, integrity and reliability. WLCSP technology was developed to eliminate the need for encapsulation to ensure compatibility with smart-mount technology (SMT). The package has good handing properties but is now facing serious reliability problems. In this work, we investigated the reliability of a WLCSP subjected to different accelerated current stressing conditions at a fixed ambient temperature of 125 °C. A very strong correlation exists between the mean time to failure (MTTF) of the WLCSP test vehicle and the mean current density that is carried by a solder joint. A series of current densities were applied to the WLCSP architecture; Black's power law was employed in a failure mode simulation. Additionally, scanning electron microscopy (SEM) was adopted to determine the differences existing between high- and low-current-density failure modes.

Accelerated life-test methods and results for implantable electronic devices with adhesive encapsulation.

PubMed

Huang, Xuechen; Denprasert, Petcharat May; Zhou, Li; Vest, Adriana Nicholson; Kohan, Sam; Loeb, Gerald E

2017-09-01

We have developed and applied new methods to estimate the functional life of miniature, implantable, wireless electronic devices that rely on non-hermetic, adhesive encapsulants such as epoxy. A comb pattern board with a high density of interdigitated electrodes (IDE) could be used to detect incipient failure from water vapor condensation. Inductive coupling of an RF magnetic field was used to provide DC bias and to detect deterioration of an encapsulated comb pattern. Diodes in the implant converted part of the received energy into DC bias on the comb pattern. The capacitance of the comb pattern forms a resonant circuit with the inductor by which the implant receives power. Any moisture affects both the resonant frequency and the Q-factor of the resonance of the circuitry, which was detected wirelessly by its effects on the coupling between two orthogonal RF coils placed around the device. Various defects were introduced into the comb pattern devices to demonstrate sensitivity to failures and to correlate these signals with visual inspection of failures. Optimized encapsulation procedures were validated in accelerated life tests of both comb patterns and a functional neuromuscular stimulator under development. Strong adhesive bonding between epoxy and electronic circuitry proved to be necessary and sufficient to predict 1 year packaging reliability of 99.97% for the neuromuscular stimulator.

Stressor-induced increase in muscle fatigability of young men and women is predicted by strength but not voluntary activation

PubMed Central

Pereira, Hugo M.; Pruse, Jaclyn; Yoon, Tejin; Schlinder-DeLap, Bonnie; Nielson, Kristy A.; Hunter, Sandra K.

2014-01-01

This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P < 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P < 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P > 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties. PMID:24526582

Experimental investigation of detonation waves instabilities in liquid high explosives

NASA Astrophysics Data System (ADS)

Sosikov, V. A.; Torunov, S. I.; Utkin, A. V.; Mochalova, V. M.; Rapota, D. Yu

2018-01-01

Experimental investigation of unstable detonation front structure in mixtures of liquid high explosives (nitromethane and FEFO—bis-(2-fluor-2.2-dinitroethyl)-formal) with inert diluents (acetone, methanol, DETA—diethylene triamine) has been carried out. Inhomogeneities have been registered by electro-optical camera NANOGATE 4BP allowing to make 4 frames with the exposure time 10 ns. According to experimental results the detonation front in nitromethane-acetone mixture is unstable. It is evident that pulsations on detonation front do not form spatial periodic structure and their dimensions differ several times. But mean longitudinal size of pulsation is about 500 μm at 20 wt% of acetone concentration. This means that the typical size of cell equals to reaction zone width. The same structure of cellular front have been registered in 70/30 FEFO-methanol mixture. Second kind of instability, failure waves, was observed in neat nitromethane at the free surface. In this case the stability loss result in turbulent flow which is clearly detected in the shots obtained. Adding small amount of DETA (0.5 wt%) results in disappearance of the failure waves and flow stabilization. The effect is caused by the fact that DETA sharply accelerates initial rate of chemical reaction because it is sensitizer for nitromethane.

Fundamental mechanisms of failure in polyethylene gas pipes. Final report, January 1, 1992-December 31, 1995

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

Brown, N.; Lu, X.

1996-07-30

The reseach objectives were: to provide a fundamental understanding of the primary long term failure process which occurs in gas pipe systems, notably slow crack growth (SCG)s; to develop methods for the accelerated testing of the resistance of polyethylene piping systems to SCG; to obtain experimental results on current materials being used or considered for use by the gas industry; and to measure the effects on SCG of processing variables in the production of pipe and fittings and compositional variables in the production of resin.

Operation and postirradiation examination of ORR capsule OF-2: accelerated testing of HTGR fuel

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

Tiegs, T.N.; Thoms, K.R.

1979-03-01

Irradiation capsule OF-2 was a test of High-Temperature Gas-Cooled Reactor fuel types under accelerated irradiation conditions in the Oak Ridge Research Reactor. The results showed good irradiation performance of Triso-coated weak-acid-resin fissile particles and Biso-coated fertile particles. These particles had been coated by a fritted gas distributor in the 0.13-m-diam furnace. Fast-neutron damage (E > 0.18 MeV) and matrix-particle interaction caused the outer pyrocarbon coating on the Triso-coated particles to fail. Such failure depended on the optical anisotropy, density, and open porosity of the outer pyrocarbon coating, as well as on the coke yield of the matrix. Irradiation of specimensmore » with values outside prescribed limits for these properties increased the failure rate of their outer pyrocarbon coating. Good irradiation performance was observed for weak-acid-resin particles with conversions in the range from 15 to 75% UC/sub 2/.« less

Aging and failure mode of electrochemical double layer capacitors during accelerated constant load tests

NASA Astrophysics Data System (ADS)

Kötz, R.; Ruch, P. W.; Cericola, D.

Electrochemical double layer capacitors of the BCAP0350 type (Maxwell Technologies) were tested under constant load conditions at different voltages and temperatures. The aging of the capacitors was monitored during the test in terms of capacitance, internal resistance and leakage current. Aging was significantly accelerated by elevated temperature or increased voltage. Only for extreme conditions at voltages of 3.5 V or temperatures above 70 °C the capacitors failed due to internal pressure build-up. No other failure events such as open circuit or short circuit were detected. Impedance measurements after the tests showed increased high frequency resistance, an increased distributed resistance and most likely an increase in contact resistance between electrode and current collector together with a loss of capacitance. Capacitors aged at elevated voltages (3.3 V) exhibited a tilting of the low frequency component, which implies an increase in the heterogeneity of the electrode surface. This feature was not observed upon aging at elevated temperatures (70 °C).

Experimental Insights into the Mechanisms of Particle Acceleration by Shock Waves

NASA Astrophysics Data System (ADS)

Scolamacchia, T.; Scheu, B.; Dingwell, D. B.

2011-12-01

The generation of shock waves is common during explosive volcanic eruptions. Particles acceleration following shock wave propagation has been experimentally observed suggesting the potential hazard related to this phenomenon. Experiments and numerical models focused on the dynamics of formation and propagation of different types of shock waves when overpressurized eruptive mixtures are suddenly released in the atmosphere, using a pseudo-gas approximation to model those mixtures. Nevertheless, the results of several studies indicated that the mechanism of coupling between a gas and solid particles is valid for a limited grain-size range, which at present is not well defined. We are investigating particle acceleration mechanisms using a vertical shock tube consisting of a high-pressure steel autoclave (450 mm long, 28 mm in diameter), pressurized with argon, and a low-pressure 140 mm long acrylic glass autoclave, with the same internal diameter of the HP reservoir. Shock waves are generated by Ar decompression at atmospheric pressures at Pres/Pamb 100:1 to 150:1, through the failure of a diaphragm. Experiments were performed either with empty autoclave or suspending solid analogue particles 150 μm in size inside the LP autoclave. Incident Mach number varied from 1.7 to 2.1. Absolute and relative pressure sensors monitored P histories during the entire process, and a high-speed camera recorded particles movement at 20,000 to 30,000 fps. Preliminary results indicate pressure multiplication at the contact between shock waves and the particles in a time lapse of 100s μs, suggesting a possible different mechanism with respect to gas-particle coupling for particle acceleration.

Sensory Constraints on Birdsong Syntax: Neural Responses to Swamp Sparrow Songs with Accelerated Trill Rates

PubMed Central

Prather, JF; Peters, S; Mooney, R; Nowicki, S

2013-01-01

Both sensory and motor mechanisms can constrain behavioral performance. Sensory mechanisms may be especially important for constraining behaviors that depend on experience, such as learned birdsongs. Swamp sparrows learn to sing by imitating the song of a tutor, but sparrows fail to accurately imitate artificial tutor songs with abnormally accelerated trills, instead singing brief and rapid trills interrupted by silent gaps. This “broken syntax” has been proposed to arise from vocal-motor limitations. Here we consider whether sensory limitations exist that could also contribute to broken syntax. We tested this idea by recording auditory-evoked activity of sensorimotor neurons in the swamp sparrow’s brain that are known to be important for the learning, performance and perception of song. In freely behaving adult sparrows that sang songs with normal syntax, neurons were detected that exhibited precisely time-locked activity to each repetition of the syllable in a trill when presented at a natural rate. Those cells failed to faithfully follow syllables presented at an accelerated rate, however, and their failure to respond to consecutive syllables increased as a function of trill rate. This “flickering” auditory representation in animals performing normal syntax reveals a central constraint on the sensory processing of rapid trills. Furthermore, because these neurons are implicated in both song learning and perception, and because auditory flickering began to occur at accelerated trill rates previously associated with the emergence of broken song syntax, these sensory constraints may contribute to the emergence of broken syntax. PMID:23976787

Operating Experience and Reliability Improvements on the 5 kW CW Klystron at Jefferson Lab

NASA Astrophysics Data System (ADS)

Nelson, R.; Holben, S.

1997-05-01

With substantial operating hours on the RF system, considerable information on reliability of the 5 kW CW klystrons has been obtained. High early failure rates led to examination of the operating conditions and failure modes. Internal ceramic contamination caused premature failure of gun potting material and ultimate tube demise through arcing or ceramic fracture. A planned course of repotting and reconditioning of approximately 300 klystrons, plus careful attention to operating conditions and periodic analysis of operational data, has substantially reduced the failure rate. It is anticipated that implementation of planned supplemental monitoring systems for the klystrons will allow most catastrophic failures to be avoided. By predicting end of life, tubes can be changed out before they fail, thus minimizing unplanned downtime. Initial tests have also been conducted on this same klystron operated at higher voltages with resultant higher output power. The outcome of these tests will provide information to be considered for future upgrades to the accelerator.

Comparative Reliability Studies and Analysis of Au, Pd-Coated Cu and Pd-Doped Cu Wire in Microelectronics Packaging

PubMed Central

Chong Leong, Gan; Uda, Hashim

2013-01-01

This paper compares and discusses the wearout reliability and analysis of Gold (Au), Palladium (Pd) coated Cu and Pd-doped Cu wires used in fineline Ball Grid Array (BGA) package. Intermetallic compound (IMC) thickness measurement has been carried out to estimate the coefficient of diffusion (Do) under various aging conditions of different bonding wires. Wire pull and ball bond shear strengths have been analyzed and we found smaller variation in Pd-doped Cu wire compared to Au and Pd-doped Cu wire. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of Cu. The obtained weibull slope, β of three bonding wires are greater than 1.0 and belong to wearout reliability data point. Pd-doped Cu wire exhibits larger time-to-failure and cycles-to-failure in both wearout reliability tests in Highly Accelerated Temperature and Humidity (HAST) and Temperature Cycling (TC) tests. This proves Pd-doped Cu wire has a greater potential and higher reliability margin compared to Au and Pd-coated Cu wires. PMID:24244344

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

Unneberg, L.

The main features of the 16 core grids (top guides) designed by ABB ATOM AB are briefly described and the evolution of the design is discussed. One important characteristic of the first nine grids is the existence of bolts securing guide bars to the core grid plates. These bolts are made of precipitation hardened or solution annealed stainless steel. During operation, bolts in all none grids have cracked. The failure analyses indicate that intergranular stress corrosion cracking (IGSCC), possibly accelerated by crevice conditions and/or irradiation, was the cause of failure. Fast neutron fluences approaching or exceeding the levels considered asmore » critical for irradiation assisted stress corrosion cracking (IASCC) will be reached in a few cases only. Temporary measures were taken immediately after the discovery of the cracking. For five of the nine reactors affected, it was decided to replace the complete grids. Two of these replacements have been successfully carried out to date. IASCC as a potential future problem is discussed and it is pointed out that, during their life times, the ABB ATOM core grids will be exposed to sufficiently high fast neutron fluences to cause some concern.« less

A new yield and failure theory for composite materials under static and dynamic loading

DOE PAGES

Daniel, Isaac M.; Daniel, Sam M.; Fenner, Joel S.

2017-09-12

In order to facilitate and accelerate the process of introducing, evaluating and adopting new material systems, it is important to develop/establish comprehensive and effective procedures of characterization, modeling and failure prediction of composite structures based on the properties of the constituent materials, e. g., fibers, matrix, and the single ply or lamina. A new yield/failure theory is proposed for predicting lamina yielding and failure under multi-axial states of stress including strain rate effects. It is based on the equivalent stress concept derived from energy principles and is expressed in terms of a single criterion. It is presented in the formmore » of master yield and failure envelopes incorporating strain rate effects. The theory can be further adapted and extended to the prediction of in situ first ply yielding and failure (FPY and FPF) and progressive damage of multi-directional laminates under static and dynamic loadings. The significance of this theory is that it allows for rapid screening of new composite materials without extensive testing and offers easily implemented design tools.« less

A new yield and failure theory for composite materials under static and dynamic loading

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

Daniel, Isaac M.; Daniel, Sam M.; Fenner, Joel S.

In order to facilitate and accelerate the process of introducing, evaluating and adopting new material systems, it is important to develop/establish comprehensive and effective procedures of characterization, modeling and failure prediction of composite structures based on the properties of the constituent materials, e. g., fibers, matrix, and the single ply or lamina. A new yield/failure theory is proposed for predicting lamina yielding and failure under multi-axial states of stress including strain rate effects. It is based on the equivalent stress concept derived from energy principles and is expressed in terms of a single criterion. It is presented in the formmore » of master yield and failure envelopes incorporating strain rate effects. The theory can be further adapted and extended to the prediction of in situ first ply yielding and failure (FPY and FPF) and progressive damage of multi-directional laminates under static and dynamic loadings. The significance of this theory is that it allows for rapid screening of new composite materials without extensive testing and offers easily implemented design tools.« less

Simulations of the failure scenarios of the crab cavities for the nominal scheme of the LHC

NASA Astrophysics Data System (ADS)

Yee, B.; Calaga, R.; Zimmermann, F.; Lopez, R.

2012-02-01

The Crab Cavity (CC) represents a possible solution to the problem of the reduction in luminosity due to the impact angle of two colliding beams. The CC is a Radio Frequency (RF) superconducting cavity which applies a transversal kick into a bunch of particles producing a rotation in order to have a head-on collision to improve the luminosity. For this reason people at the Beams Department-Accelerators & Beams Physics of CERN (BE-ABP) have studied the implementation of the CC scheme at the LHC. It is essential to study the failure scenarios and the damage that can be produced to the lattice devices. We have performed simulations of these failures for the nominal scheme.

Raman spectral observation of a new phase observed in nickel electrodes cycled to failure

NASA Technical Reports Server (NTRS)

Loyselle, Patricia L.; Shan, X.; Cornilsen, B. C.; Reid, Margaret A.

1991-01-01

A new phase is reported in nickel electrodes from Ni/H2 boilerplate cells which were cycled to failure in electrolyte of variable KOH concentration (21 to 36 percent). Raman spectra clearly show the presence of this phase, and these spectra have been used to estimate the amounts present on these electrodes. Ten of 12 electrodes examined contain this new phase. The cycle life at higher KOH concentrations (31 and 36 percent) was greatly reduced, and nickel electrodes from these cells exhibited extensive amounts of this new phase. The presence of this new phase correlates with cell failure defined by low end of discharge voltages. It is proposed that the lowered capacity and failure of these electrodes was caused by loss of active mass and formation of a phase with reduced electrochemical activity. These results indicate that formation of the new phase is accelerated at higher KOH concentrations.

The clinical course of diabetic nephropathy.

PubMed

Kussman, M J; Goldstein, H; Gleason, R E

1976-10-18

A retrospective record analysis of 112 juvenile-onset diabetics with nephropathy was conducted in order to determine their clinical course. The mean duration of diabetes at the onset of proteinuria was 17.3+/-6.0 years. Early renal failure appeared two years after the onset of protein-uria, and severe renal failure (mean serum creatinine level, 8.5+/-3.9 mg/100 ml) four years after the onset of proteinuria. The mean duration of life after the onset of severe renal failure was six months. The mortality was 53%, with 59% of the deaths attributable to renal failure and 36% to cardiovascular disease. All patients experienced progressive deterioration of renal function as well as the other complications of diabetes, the rate of progression being accelerated toward the end of the course. Juvenile onset diabetics should be considered for renal transplantation before the serum creatinine level reaches 8.5 mg/100 ml.

Estimation of the lower and upper bounds on the probability of failure using subset simulation and random set theory

NASA Astrophysics Data System (ADS)

Alvarez, Diego A.; Uribe, Felipe; Hurtado, Jorge E.

2018-02-01

Random set theory is a general framework which comprises uncertainty in the form of probability boxes, possibility distributions, cumulative distribution functions, Dempster-Shafer structures or intervals; in addition, the dependence between the input variables can be expressed using copulas. In this paper, the lower and upper bounds on the probability of failure are calculated by means of random set theory. In order to accelerate the calculation, a well-known and efficient probability-based reliability method known as subset simulation is employed. This method is especially useful for finding small failure probabilities in both low- and high-dimensional spaces, disjoint failure domains and nonlinear limit state functions. The proposed methodology represents a drastic reduction of the computational labor implied by plain Monte Carlo simulation for problems defined with a mixture of representations for the input variables, while delivering similar results. Numerical examples illustrate the efficiency of the proposed approach.

Visual Processing of Object Velocity and Acceleration

DTIC Science & Technology

1994-02-04

A failure of motion deblurring in the human visual system. Investigative Opthalmology and Visual Sciences (Suppl),34, 1230 Watamaniuk, S.N.J. and...McKee, S.P. Why is a trajectory more detectable in noise than correlated signal dots? Investigative Opthalmology and Visual Sciences (Suppl),34, 1364

Investigation into the vibration of metro bogies induced by rail corrugation

NASA Astrophysics Data System (ADS)

Ling, Liang; Li, Wei; Foo, Elbert; Wu, Lei; Wen, Zefeng; Jin, Xuesong

2017-01-01

The current research of rail corrugation mainly focuses on the mechanisms of its formation and development. Compared with the root causes and development mechanisms, the wheel-rail impacts, the fatigue failure of vehicle-track parts, and the loss of ride comfort due to rail corrugation should also be taken into account. However, the influences of rail corrugation on vehicle and track vibration, and failure of vehicle and track structural parts are barely discussed in the literature. This paper presents an experimental and numerical investigation of the structural vibration of metro bogies caused by rail corrugation. Extensive experiments are conducted to investigate the effects of short-pitch rail corrugation on the vibration accelerations of metro bogies. A dynamic model of a metro vehicle coupled with a concrete track is established to study the influence of rail corrugation on the structural vibration of metro bogies. The field test results indicate that the short-pitch rail corrugation generates strong vibrations on the axle-boxes and the bogie frames, therefore, accelerates the fatigue failure of the bogie components. The numerical results show that short-pitch rail corrugation may largely reduce the fatigue life of the coil spring, and improving the damping value of the primary vertical dampers is likely to reduce the strong vibration induced by short-pitch rail corrugation. This research systematically studies the effect of rail corrugation on the vibration of metro bogies and proposes some remedies for mitigating strong vibrations of metro bogies and reducing the incidence of failure in primary coil springs, which would be helpful in developing new metro bogies and track maintenance procedures.

Cu-Induced Dielectric Breakdown of Porous Low-Dielectric-Constant Film

NASA Astrophysics Data System (ADS)

Cheng, Yi-Lung; Lee, Chih-Yen; Huang, Yao-Liang; Sun, Chung-Ren; Lee, Wen-Hsi; Chen, Giin-Shan; Fang, Jau-Shiung; Phan, Bach Thang

2017-06-01

Dielectric breakdown induced by Cu ion migration in porous low- k dielectric films has been investigated in alternating-polarity bias conditions using a metal-insulator-metal capacitor with Cu top metal electrode. The experimental results indicated that Cu ions migrated into the dielectric film under stress with positive polarity, leading to weaker dielectric strength and shorter time to failure (TTF). In the alternating-polarity test, the measured TTFs increased with decreasing stressing frequency, implying backward migration of Cu ions during reverse-bias stress. Additionally, compared with a direct-current stress condition, the measured TTFs were higher as the frequency was decreased to 10-2 Hz. The electric-field acceleration factor for porous low- k dielectric film breakdown in the alternating-polarity test was also found to increase. This Cu backward migration effect is effective when the stressing time under negative polarity is longer than 0.1 s.

Research on stratified evolution of composite materials under four-point bending loading

NASA Astrophysics Data System (ADS)

Hao, M. J.; You, Q. J.; Zheng, J. C.; Yue, Z.; Xie, Z. P.

2017-12-01

In order to explore the effect of stratified evolution and delamination on the load capacity and service life of the composite materials under the four-point bending loading, the artificial tectonic defects of the different positions were set up. The four-point bending test was carried out, and the whole process was recorded by acoustic emission, and the damage degree of the composite layer was judged by the impact accumulation of the specimen - time-amplitude history chart, load-time-relative energy history chart, acoustic emission impact signal positioning map. The results show that the stratified defects near the surface of the specimen accelerate the process of material failure and expansion. The location of the delamination defects changes the bending performance of the composites to a great extent. The closer the stratification defects are to the surface of the specimen, the greater the damage, the worse the service capacity of the specimen.

Testing homogeneity in Weibull-regression models.

PubMed

Bolfarine, Heleno; Valença, Dione M

2005-10-01

In survival studies with families or geographical units it may be of interest testing whether such groups are homogeneous for given explanatory variables. In this paper we consider score type tests for group homogeneity based on a mixing model in which the group effect is modelled as a random variable. As opposed to hazard-based frailty models, this model presents survival times that conditioned on the random effect, has an accelerated failure time representation. The test statistics requires only estimation of the conventional regression model without the random effect and does not require specifying the distribution of the random effect. The tests are derived for a Weibull regression model and in the uncensored situation, a closed form is obtained for the test statistic. A simulation study is used for comparing the power of the tests. The proposed tests are applied to real data sets with censored data.

Comparison of hypertabastic survival model with other unimodal hazard rate functions using a goodness-of-fit test.

PubMed

Tahir, M Ramzan; Tran, Quang X; Nikulin, Mikhail S

2017-05-30

We studied the problem of testing a hypothesized distribution in survival regression models when the data is right censored and survival times are influenced by covariates. A modified chi-squared type test, known as Nikulin-Rao-Robson statistic, is applied for the comparison of accelerated failure time models. This statistic is used to test the goodness-of-fit for hypertabastic survival model and four other unimodal hazard rate functions. The results of simulation study showed that the hypertabastic distribution can be used as an alternative to log-logistic and log-normal distribution. In statistical modeling, because of its flexible shape of hazard functions, this distribution can also be used as a competitor of Birnbaum-Saunders and inverse Gaussian distributions. The results for the real data application are shown. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

SHORT ACCELERATION TIMES FROM SUPERDIFFUSIVE SHOCK ACCELERATION IN THE HELIOSPHERE

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

Perri, S.; Zimbardo, G., E-mail: silvia.perri@fis.unical.it

2015-12-10

The analysis of time profiles of particles accelerated at interplanetary shocks allows particle transport properties to be inferred. The frequently observed power-law decay upstream, indeed, implies a superdiffusive particle transport when the level of magnetic field variance does not change as the time interval from the shock front increases. In this context, a superdiffusive shock acceleration (SSA) theory has been developed, allowing us to make predictions of the acceleration times. In this work we estimate for a number of interplanetary shocks, including the solar wind termination shock, the acceleration times for energetic protons in the framework of SSA and wemore » compare the results with the acceleration times predicted by standard diffusive shock acceleration. The acceleration times due to SSA are found to be much shorter than in the classical model, and also shorter than the interplanetary shock lifetimes. This decrease of the acceleration times is due to the scale-free nature of the particle displacements in the framework of superdiffusion. Indeed, very long displacements are possible, increasing the probability for particles far from the front of the shock to return, and short displacements have a high probability of occurrence, increasing the chances for particles close to the front to cross the shock many times.« less

Finite element analyses of a linear-accelerator electron gun

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

Iqbal, M., E-mail: muniqbal.chep@pu.edu.pk, E-mail: muniqbal@ihep.ac.cn; Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049; Wasy, A.

Thermo-structural analyses of the Beijing Electron-Positron Collider (BEPCII) linear-accelerator, electron gun, were performed for the gun operating with the cathode at 1000 °C. The gun was modeled in computer aided three-dimensional interactive application for finite element analyses through ANSYS workbench. This was followed by simulations using the SLAC electron beam trajectory program EGUN for beam optics analyses. The simulations were compared with experimental results of the assembly to verify its beam parameters under the same boundary conditions. Simulation and test results were found to be in good agreement and hence confirmed the design parameters under the defined operating temperature. The gunmore » is operating continuously since commissioning without any thermal induced failures for the BEPCII linear accelerator.« less

Forecasting giant, catastrophic slope collapse: lessons from Vajont, Northern Italy

NASA Astrophysics Data System (ADS)

Kilburn, Christopher R. J.; Petley, David N.

2003-08-01

Rapid, giant landslides, or sturzstroms, are among the most powerful natural hazards on Earth. They have minimum volumes of ˜10 6-10 7 m 3 and, normally preceded by prolonged intervals of accelerating creep, are produced by catastrophic and deep-seated slope collapse (loads ˜1-10 MPa). Conventional analyses attribute rapid collapse to unusual mechanisms, such as the vaporization of ground water during sliding. Here, catastrophic collapse is related to self-accelerating rock fracture, common in crustal rocks at loads ˜1-10 MPa and readily catalysed by circulating fluids. Fracturing produces an abrupt drop in resisting stress. Measured stress drops in crustal rock account for minimum sturzstrom volumes and rapid collapse accelerations. Fracturing also provides a physical basis for quantitatively forecasting catastrophic slope failure.

Life prediction for white OLED based on LSM under lognormal distribution

NASA Astrophysics Data System (ADS)

Zhang, Jianping; Liu, Fang; Liu, Yu; Wu, Helen; Zhu, Wenqing; Wu, Wenli; Wu, Liang

2012-09-01

In order to acquire the reliability information of White Organic Light Emitting Display (OLED), three groups of OLED constant stress accelerated life tests (CSALTs) were carried out to obtain failure data of samples. Lognormal distribution function was applied to describe OLED life distribution, and the accelerated life equation was determined by Least square method (LSM). The Kolmogorov-Smirnov test was performed to verify whether the white OLED life meets lognormal distribution or not. Author-developed software was employed to predict the average life and the median life. The numerical results indicate that the white OLED life submits to lognormal distribution, and that the accelerated life equation meets inverse power law completely. The estimated life information of the white OLED provides manufacturers and customers with important guidelines.

Tyrosinase kinetics: failure of acceleration in oxidation of ring-blocked monohydric phenol substrate.

PubMed

Naish-Byfield, S; Riley, P A

1998-04-01

When 2,5,6-trimethyl-4-hydroxyanisole is used as substrate for mushroom tyrosinase the oxidation rate is slow and the kinetics do not exhibit an initial acceleration (lag period), in contrast to the kinetics of oxidation of the parent compound, 4-hydroxyanisole. This finding is interpreted as evidence that the acceleration of oxidation of 4-hydroxyanisole is indirectly contingent on a reductive nucleophile addition to the orthoquinone product of the monohydric phenol, which is prevented by ring methylation. Such a view is consistent with the proposal that the lag-phase characteristic of the kinetics of monohydric phenol oxidation by tyrosinase is due to the activation of previously inactive enzyme by electron donation from an orthodiphenol substrate formed from the orthoquinone oxidation product.

Error-Rate Estimation Based on Multi-Signal Flow Graph Model and Accelerated Radiation Tests

PubMed Central

Wang, Yueke; Xing, Kefei; Deng, Wei; Zhang, Zelong

2016-01-01

A method of evaluating the single-event effect soft-error vulnerability of space instruments before launched has been an active research topic in recent years. In this paper, a multi-signal flow graph model is introduced to analyze the fault diagnosis and meantime to failure (MTTF) for space instruments. A model for the system functional error rate (SFER) is proposed. In addition, an experimental method and accelerated radiation testing system for a signal processing platform based on the field programmable gate array (FPGA) is presented. Based on experimental results of different ions (O, Si, Cl, Ti) under the HI-13 Tandem Accelerator, the SFER of the signal processing platform is approximately 10−3(error/particle/cm2), while the MTTF is approximately 110.7 h. PMID:27583533

Error-Rate Estimation Based on Multi-Signal Flow Graph Model and Accelerated Radiation Tests.

PubMed

He, Wei; Wang, Yueke; Xing, Kefei; Deng, Wei; Zhang, Zelong

2016-01-01

A method of evaluating the single-event effect soft-error vulnerability of space instruments before launched has been an active research topic in recent years. In this paper, a multi-signal flow graph model is introduced to analyze the fault diagnosis and meantime to failure (MTTF) for space instruments. A model for the system functional error rate (SFER) is proposed. In addition, an experimental method and accelerated radiation testing system for a signal processing platform based on the field programmable gate array (FPGA) is presented. Based on experimental results of different ions (O, Si, Cl, Ti) under the HI-13 Tandem Accelerator, the SFER of the signal processing platform is approximately 10-3(error/particle/cm2), while the MTTF is approximately 110.7 h.

Non-destructive measurement and role of surface residual stress monitoring in residual life assessment of a steam turbine blading material

NASA Astrophysics Data System (ADS)

Prabhu-Gaunkar, Gajanana; Rawat, M. S.; Prasad, C. R.

2014-02-01

Steam turbine blades in power generation equipment are made from martensitic stainless steels having high strength, good toughness and corrosion resistance. However, these steels are susceptible to pitting which can promote early failures of blades in the turbines, particularly in the low pressure dry/wet areas by stress corrosion and corrosion fatigue. Presence of tensile residual stresses is known to accelerate failures whereas compressive stresses can help in delaying failures. Shot peening has been employed as an effective tool to induce compressive residual stresses which offset a part of local surface tensile stresses in the surface layers of components. Maintaining local stresses at stress raisers, such as pits formed during service, below a threshold level can help in preventing the initiation microcracks and failures. The thickness of the layer in compression will, however, depend of the shot peening parameters and should extend below the bottom of corrosion pits. The magnitude of surface compressive drops progressively during service exposure and over time the effectiveness of shot peening is lost making the material susceptible to micro-crack initiation once again. Measurement and monitoring of surface residual stress therefore becomes important for assessing residual life of components in service. This paper shows the applicability of surface stress monitoring to life assessment of steam turbine blade material based on data generated in laboratory on residual surface stress measurements in relation to fatigue exposure. An empirical model is proposed to calculate the remaining life of shot peened steam turbine blades in service.

Real Time On-line Space Research Laboratory Environment Monitoring with Off-line Trend and Prediction Analysis

NASA Technical Reports Server (NTRS)

Jules, Kenol; Lin, Paul P.

2006-01-01

One of the responsibilities of the NASA Glenn Principal Investigator Microgravity Services is to support NASA sponsored investigators in the area of reduced-gravity acceleration data analysis, interpretation and the monitoring of the reduced-gravity environment on-board various carriers. With the International Space Station currently operational, a significant amount of acceleration data is being down-linked and processed on ground for both the space station onboard environment characterization (and verification) and scientific experiments. Therefore, to help principal investigator teams monitor the acceleration level on-board the International Space Station to avoid undesirable impact on their experiment, when possible, the NASA Glenn Principal Investigator Microgravity Services developed an artificial intelligence monitoring system, which detects in near real time any change in the environment susceptible to affect onboard experiments. The main objective of the monitoring system is to help research teams identify the vibratory disturbances that are active at any instant of time onboard the International Space Station that might impact the environment in which their experiment is being conducted. The monitoring system allows any space research scientist, at any location and at any time, to see the current acceleration level on-board the Space Station via the World Wide Web. From the NASA Glenn s Exploration Systems Division web site, research scientists can see in near real time the active disturbances, such as pumps, fans, compressor, crew exercise, re-boost, extra-vehicular activity, etc., and decide whether or not to continue operating or stopping (or making note of such activity for later correlation with science results) their experiments based on the g-level associated with that specific event. A dynamic graphical display accessible via the World Wide Web shows the status of all the vibratory disturbance activities with their degree of confidence as well as their g-level contribution to the environment. The system can detect both known and unknown vibratory disturbance activities. It can also perform trend analysis and prediction by analyzing past data over many Increments of the space station for selected disturbance activities. This feature can be used to monitor the health of onboard mechanical systems to detect and prevent potential system failure as well as for use by research scientists during their science results analysis. Examples of both real time on-line vibratory disturbance detection and off-line trend analysis are presented in this paper. Several soft computing techniques such as Kohonen s Self-Organizing Feature Map, Learning Vector Quantization, Back-Propagation Neural Networks, and Fuzzy Logic were used to design the system.

Protection of the CERN Large Hadron Collider

NASA Astrophysics Data System (ADS)

Schmidt, R.; Assmann, R.; Carlier, E.; Dehning, B.; Denz, R.; Goddard, B.; Holzer, E. B.; Kain, V.; Puccio, B.; Todd, B.; Uythoven, J.; Wenninger, J.; Zerlauth, M.

2006-11-01

The Large Hadron Collider (LHC) at CERN will collide two counter-rotating proton beams, each with an energy of 7 TeV. The energy stored in the superconducting magnet system will exceed 10 GJ, and each beam has a stored energy of 362 MJ which could cause major damage to accelerator equipment in the case of uncontrolled beam loss. Safe operation of the LHC will therefore rely on a complex system for equipment protection. The systems for protection of the superconducting magnets in case of quench must be fully operational before powering the magnets. For safe injection of the 450 GeV beam into the LHC, beam absorbers must be in their correct positions and specific procedures must be applied. Requirements for safe operation throughout the cycle necessitate early detection of failures within the equipment, and active monitoring of the beam with fast and reliable beam instrumentation, mainly beam loss monitors (BLM). When operating with circulating beams, the time constant for beam loss after a failure extends from apms to a few minutes—failures must be detected sufficiently early and transmitted to the beam interlock system that triggers a beam dump. It is essential that the beams are properly extracted on to the dump blocks at the end of a fill and in case of emergency, since the beam dump blocks are the only elements of the LHC that can withstand the impact of the full beam.

In Defense of an Accelerating Universe: Model Insensitivity of the Hubble Diagram

NASA Astrophysics Data System (ADS)

Ringermacher, Harry I.; Mead, Lawrence R.

2018-01-01

A recently published paper by Nielsen, Guffanti & Sarkar (. Sci. Rep. 6, 35596, Oct. 2016) argues that the evidence for cosmic acceleration is marginal and that a coasting universe - the “Milne Universe” - fits the same supernovae data in a Hubble diagram nearly as well. Other papers have since jumped on the bandwagon. The Milne Universe has negative spatial curvature, but is Riemann-flat. Nevertheless, we confirm that the Milne model fits the data just as well as LCDM. We show that this unexpected result points to a weakness in the Hubble diagram rather than to a failure in LCDM. It seems the Hubble diagram is insensitive to spatial curvature. To be specific, the spatial curvature dependences of the comoving radius in the luminosity distance nearly exactly cancel the energy density differences. That is, r(LCDM) = sinh[r(Milne)]. By transforming the distance modulus vs. redshift data to scale factor vs. cosmological time data, for each curvature, k = {+1, 0, -1}, the curvature dependence of the data is effectively separated thus permitting a more precise fit of the Omega parameters to the scale factor data to decide the correct model. Here we present the data and both models in a scale factor vs. cosmological time plot. The difference of the means of the k = 0 and k =-1 data separate at a 2-sigma confidence level. The LCDM fit to the k = 0 data are consistent with an accelerating universe to 99% confidence. The Milne universe fits the k =-1 data to no better than about 70% confidence. This is consistent with independent CMB and BAO observations supporting a flat universe.

The Great Leap Forward: Anatomy of a Central Planning Disaster

ERIC Educational Resources Information Center

Li, Wei; Yang, Dennis Tao

2005-01-01

The Great Leap Forward disaster, characterized by a collapse in grain production and a widespread famine in China between 1959 and 1961, is found attributable to a systemic failure in central planning. Wishfully expecting a great leap in agricultural productivity from collectivization, the Chinese government accelerated its aggressive…

Depression and Delinquency Covariation in an Accelerated Longitudinal Sample of Adolescents

ERIC Educational Resources Information Center

Kofler, Michael J.; McCart, Michael R.; Zajac, Kristyn; Ruggiero, Kenneth J.; Saunders, Benjamin E.; Kilpatrick, Dean G.

2011-01-01

Objectives: The current study tested opposing predictions stemming from the failure and acting out theories of depression-delinquency covariation. Method: Participants included a nationwide longitudinal sample of adolescents (N = 3,604) ages 12 to 17. Competing models were tested with cohort-sequential latent growth curve modeling to determine…

When Triple Helix Unravels: A Multi-Case Analysis of Failures in Industry-University Cooperative Research Centres

ERIC Educational Resources Information Center

Gray, Denis; Sundstrom, Eric; Tornatzky, Louis G.; McGowen, Lindsey

2011-01-01

Cooperative research centres (CRCs) increasingly foster Triple Helix (industry-university-government) collaboration and represent significant vehicles for cooperation across sectors, the promotion of knowledge and technology transfer and ultimately the acceleration of innovation. A growing social science literature on CRCs focuses on their…

Module performance and failure analysis area: Flat-plate solar array project

NASA Technical Reports Server (NTRS)

Tornstrom, E.

1984-01-01

A redesign of the initial (Group I) Mobile Solar Block V module was done and documented. Manufacturing experience and accelerated test data from Group I formed the basis for the redesign. Ten Block V Group II modules were submitted for evaluation and the results are presented.

Interpreting Space-Mission LET Requirements for SEGR in Power MOSFETs

NASA Technical Reports Server (NTRS)

Lauenstein, J. M.; Ladbury, R. L.; Batchelor, D. A.; Goldsman, N.; Kim, H. S.; Phan, A. M.

2010-01-01

A Technology Computer Aided Design (TCAD) simulation-based method is developed to evaluate whether derating of high-energy heavy-ion accelerator test data bounds the risk for single-event gate rupture (SEGR) from much higher energy on-orbit ions for a mission linear energy transfer (LET) requirement. It is shown that a typical derating factor of 0.75 applied to a single-event effect (SEE) response curve defined by high-energy accelerator SEGR test data provides reasonable on-orbit hardness assurance, although in a high-voltage power MOSFET, it did not bound the risk of failure.

Load-Unload Response Ratio (LURR), Accelerating Moment/Energy Release (AM/ER) and State Vector Saltation as Precursors to Failure of Rock Specimens

NASA Astrophysics Data System (ADS)

Yin, Xiang-Chu; Yu, Huai-Zhong; Kukshenko, Victor; Xu, Zhao-Yong; Wu, Zhishen; Li, Min; Peng, Keyin; Elizarov, Surgey; Li, Qi

2004-12-01

In order to verify some precursors such as LURR (Load/Unload Response Ratio) and AER (Accelerating Energy Release) before large earthquakes or macro-fracture in heterogeneous brittle media, four acoustic emission experiments involving large rock specimens under tri-axial stress, have been conducted. The specimens were loaded in two ways: monotonous or cycling. The experimental results confirm that LURR and AER are precursors of macro-fracture in brittle media. A new measure called the state vector has been proposed to describe the damage evolution of loaded rock specimens.

Highly reliable oxide VCSELs for datacom applications

NASA Astrophysics Data System (ADS)

Aeby, Ian; Collins, Doug; Gibson, Brian; Helms, Christopher J.; Hou, Hong Q.; Lou, Wenlin; Bossert, David J.; Wang, Charlie X.

2003-06-01

In this paper we describe the processes and procedures that have been developed to ensure high reliability for Emcore"s 850 nm oxide confined GaAs VCSELs. Evidence from on-going accelerated life testing and other reliability studies that confirm that this process yields reliable products will be discussed. We will present data and analysis techniques used to determine the activation energy and acceleration factors for the dominant wear-out failure mechanisms for our devices as well as our estimated MTTF of greater than 2 million use hours. We conclude with a summary of internal verification and field return rate validation data.

A Monotonic Degradation Assessment Index of Rolling Bearings Using Fuzzy Support Vector Data Description and Running Time

PubMed Central

Shen, Zhongjie; He, Zhengjia; Chen, Xuefeng; Sun, Chuang; Liu, Zhiwen

2012-01-01

Performance degradation assessment based on condition monitoring plays an important role in ensuring reliable operation of equipment, reducing production downtime and saving maintenance costs, yet performance degradation has strong fuzziness, and the dynamic information is random and fuzzy, making it a challenge how to assess the fuzzy bearing performance degradation. This study proposes a monotonic degradation assessment index of rolling bearings using fuzzy support vector data description (FSVDD) and running time. FSVDD constructs the fuzzy-monitoring coefficient ε̄ which is sensitive to the initial defect and stably increases as faults develop. Moreover, the parameter ε̄ describes the accelerating relationships between the damage development and running time. However, the index ε̄ with an oscillating trend disagrees with the irreversible damage development. The running time is introduced to form a monotonic index, namely damage severity index (DSI). DSI inherits all advantages of ε̄ and overcomes its disadvantage. A run-to-failure test is carried out to validate the performance of the proposed method. The results show that DSI reflects the growth of the damages with running time perfectly. PMID:23112591

A monotonic degradation assessment index of rolling bearings using fuzzy support vector data description and running time.

PubMed

Shen, Zhongjie; He, Zhengjia; Chen, Xuefeng; Sun, Chuang; Liu, Zhiwen

2012-01-01

Performance degradation assessment based on condition monitoring plays an important role in ensuring reliable operation of equipment, reducing production downtime and saving maintenance costs, yet performance degradation has strong fuzziness, and the dynamic information is random and fuzzy, making it a challenge how to assess the fuzzy bearing performance degradation. This study proposes a monotonic degradation assessment index of rolling bearings using fuzzy support vector data description (FSVDD) and running time. FSVDD constructs the fuzzy-monitoring coefficient ε⁻ which is sensitive to the initial defect and stably increases as faults develop. Moreover, the parameter ε⁻ describes the accelerating relationships between the damage development and running time. However, the index ε⁻ with an oscillating trend disagrees with the irreversible damage development. The running time is introduced to form a monotonic index, namely damage severity index (DSI). DSI inherits all advantages of ε⁻ and overcomes its disadvantage. A run-to-failure test is carried out to validate the performance of the proposed method. The results show that DSI reflects the growth of the damages with running time perfectly.

AGFATL- ACTIVE GEAR FLEXIBLE AIRCRAFT TAKEOFF AND LANDING ANALYSIS

NASA Technical Reports Server (NTRS)

Mcgehee, J. R.

1994-01-01

The Active Gear, Flexible Aircraft Takeoff and Landing Analysis program, AGFATL, was developed to provide a complete simulation of the aircraft takeoff and landing dynamics problem. AGFATL can represent an airplane either as a rigid body with six degrees of freedom or as a flexible body with multiple degrees of freedom. The airframe flexibility is represented by the superposition of up to twenty free vibration modes on the rigid-body motions. The analysis includes maneuver logic and autopilots programmed to control the aircraft during glide slope, flare, landing, and takeoff. The program is modular so that performance of the aircraft in flight and during landing and ground maneuvers can be studied separately or in combination. A program restart capability is included in AGFATL. Effects simulated in the AGFATL program include: (1) flexible aircraft control and performance during glide slope, flare, landing roll, and takeoff roll under conditions of changing winds, engine failures, brake failures, control system failures, strut failures, restrictions due to runway length, and control variable limits and time lags; (2) landing gear loads and dynamics for up to five gears; (3) single and multiple engines (maximum of four) including selective engine reversing and failure; (4) drag chute and spoiler effects; (5) wheel braking (including skid-control) and selective brake failure; (6) aerodynamic ground effects; (7) aircraft carrier operations; (8) inclined runways and runway perturbations; (9) flexible or rigid airframes; 10) rudder and nose gear steering; and 11) actively controlled landing gear shock struts. Input to the AGFATL program includes data which describe runway roughness; vehicle geometry, flexibility and aerodynamic characteristics; landing gear(s); propulsion; and initial conditions such as attitude, attitude change rates, and velocities. AGFATL performs a time integration of the equations of motion and outputs comprehensive information on the airframe, state-of-maneuver logic, autopilots, control response, and aircraft loads from impact, runway roll-out, and ground operations. Flexible-body and total (elastic plus rigid-body) displacements, velocities, and accelerations are also output in the flexible-body option for up to twenty points on the aircraft. The AGFATL program is written in FORTRAN IV for batch execution and has been implemented on a CDC CYBER 170 series computer with an overlayed central memory requirement of approximately 141 (octal) of 60 bit words. The AGFATL program was last updated in 1984.

[Chronic heart failure and depression].

PubMed

Herrmann-Lingen, C

2018-05-01

Depression is a frequent comorbidity in chronic heart failure. It can be triggered by the experience of suffering from heart disease, but it can also play a causal role in accelerated development and poor prognosis of heart failure. The aim of this study was to investigate the interrelationships between heart failure and depression and the psychophysiological and behavioral mechanisms involved in this association. The effects of comorbid depression on quality of life in patients with heart failure were also examined and therapeutic options reviewed. A narrative review of the literature was undertaken. Several psychophysiological and behavioral mechanisms have been identified as mediators of the association between depression and heart failure and the adverse prognostic effects of this comorbidity. Comorbid depression leads to substantial reductions in health-related quality of life. These effects are only incompletely antagonized by exercise training and cognitive behavioral therapy. No specific effect of antidepressant medication has been demonstrated as yet in patients with heart failure. While current guidelines recommend the identification and treatment of depressive comorbidity in patients with heart failure, the available evidence provides no convincing rationale for specific treatment recommendations beyond the guideline-based treatment of heart failure itself, lifestyle interventions and patient-centered medical care. If available, psychotherapy should be offered, ideally cognitive behavioral therapy. For patients that do not improve sufficiently under outpatient treatment, the German health care system offers dedicated psychocardiological inpatient treatment programs.

Mathematics and science acceleration in grade eight: School leaders' perceptions and satisfaction

NASA Astrophysics Data System (ADS)

Graham, Kenneth

Shifts in attitudes regarding academic program accessibility to provide the most rigorous academic opportunities to all students will not occur smoothly without departmental level leaders who believe in the potential benefits of accelerating larger numbers of students. Without the support and the belief of the department level leadership, practices such as open enrollment and universal acceleration that target school equity will be doomed to failure. This study was conducted using a questionnaire developed by the researcher called the Perceptions of Acceleration and Leadership Survey. The survey was distributed to all math and science department leaders within a suburban region of New York. The survey sought to determine how the perceptions of acceleration, job satisfaction, self-efficacy, and role longevity for the department level leaders are impacted by their personal demographics, professional characteristics, and community characteristics. The study did not reveal any statistically significant differences among department level leaders' personal, professional, and community characteristics with respect to perceptions of acceleration. There were significant differences for job satisfaction, self-efficacy, and role longevity for several intervening and independent variables within the study. Statistically significant correlations were found between beliefs in college preparation and perceptions of acceleration as well as relationships with the community and perceptions of acceleration. The results indicate the importance of hiring department leaders who recognize the potential for accelerating more students, hiring more ethnically diverse candidates for these leadership positions, affording department level leaders with significant professional development, and evaluation of administrative structures to maximize student success.

Simvastatin Exposure and Rotator Cuff Repair in a Rat Model.

PubMed

Deren, Matthew E; Ehteshami, John R; Dines, Joshua S; Drakos, Mark C; Behrens, Steve B; Doty, Stephen; Coleman, Struan H

2017-03-01

Simvastatin is a common medication prescribed for hypercholesterolemia that accelerates local bone formation. It is unclear whether simvastatin can accelerate healing at the tendon-bone interface after rotator cuff repair. This study was conducted to investigate whether local and systemic administration of simvastatin increased tendon-bone healing of the rotator cuff as detected by maximum load to failure in a controlled animal-based model. Supraspinatus tendon repair was performed on 120 Sprague-Dawley rats. Sixty rats had a polylactic acid membrane overlying the repair site. Of these, 30 contained simvastatin and 30 did not contain medication. Sixty rats underwent repair without a polylactic acid membrane. Of these, 30 received oral simvastatin (25 mg/kg/d) and 30 received a regular diet. At 4 weeks, 5 rats from each group were killed for histologic analysis. At 8 weeks, 5 rats from each group were killed for histologic analysis and the remaining 20 rats were killed for biomechanical analysis. One rat that received oral simvastatin died of muscle necrosis. Average maximum load to failure was 35.2±6.2 N for those receiving oral simvastatin, 36.8±9.0 N for oral control subjects, 39.5±12.8 N for those receiving local simvastatin, and 39.1±9.3 N for control subjects with a polylactic acid membrane. No statistically significant differences were found between any of the 4 groups (P>.05). Qualitative histologic findings showed that all groups showed increased collagen formation and organization at 8 weeks compared with 4 weeks, with no differences between the 4 groups at each time point. The use of systemic and local simvastatin offered no benefit over control groups. [Orthopedics. 2017; 40(2):e288-e292.]. Copyright 2016, SLACK Incorporated.

JBP485 improves gentamicin-induced acute renal failure by regulating the expression and function of Oat1 and Oat3 in rats

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

Guo, Xinjin; Meng, Qiang; Liu, Qi

2013-09-01

We investigated the effects of JBP485 (an anti-inflammatory dipeptide and a substrate of OAT) on regulation of the expression and function of renal Oat1 and Oat3, which can accelerate the excretion of accumulated uremic toxins (e.g. indoxyl sulfate) in the kidney to improve gentamicin-induced ARF in rats. JBP485 caused a significant decrease in the accumulation of endogenous substances (creatinine, blood urea nitrogen and indoxyl sulfate) in vivo, an increase in the excretion of exogenous compounds (lisinopril and inulin) into urine, and up-regulation of the expressions of renal Oat1 and Oat3 in the kidney tissues and slices via substrate induction. Tomore » determine the effect of JBP485 on the accelerated excretion of uremic toxins mediated by Oat1 and Oat3, the mRNA and protein expression levels of renal basolateral Oats were assessed by quantitative real-time PCR, western blot, immunohistochemical analysis and an immunofluorescence method. Gentamicin down-regulated the expression of Oats mRNA and protein in rat kidney, and these effects were reversed after administration of JBP485. In addition, JBP485 caused a significant decrease in MPO and MDA levels in the kidney, and improved the pathological condition of rat kidney. These results indicated that JBP485 improved acute renal failure by increasing the expression and function of Oat1 and Oat3, and by decreasing overoxidation of the kidney in gentamicin-induced ARF rats. - Highlights: • JBP485 could up-regulate function and expression of Oat1 and Oat3 in kidney. • Effects of JBP485 on ARF are mediated by stimulating excretion of uremic toxins. • JBP485 protected against gentamicin-induced ARF by decreasing MPO and MDA.« less

Mucosal immunity to poliovirus.

PubMed

Ogra, Pearay L; Okayasu, Hiromasa; Czerkinsky, Cecil; Sutter, Roland W

2011-10-01

The Global Polio Eradication Initiative (GPEI) currently based on use of oral poliovirus vaccine (OPV) has identified suboptimal immunogenicity of this vaccine as a major impediment to eradication, with a failure to induce protection against paralytic poliomyelitis in certain population segments in some parts of the world. The Mucosal Immunity and Poliovirus Vaccines: Impact on Wild Poliovirus Infection, Transmission and Vaccine Failure conference was organized to obtain a better understanding of the current status of global control of poliomyelitis and identify approaches to improve the immune responsiveness and effectiveness of the orally administered poliovirus vaccines in order to accelerate the global eradication of paralytic poliomyelitis.

Power Cycle Testing of Power Switches: A Literature Survey

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

GopiReddy, Lakshmi Reddy; Tolbert, Leon M.; Ozpineci, Burak

Reliability of power converters and lifetime prediction has been a major topic of research in the last few decades, especially for traction applications. The main failures in high power semiconductors are caused by thermomechanical fatigue. Power cycling and temperature cycling are the two most common thermal acceleration tests used in assessing reliability. The objective of this paper is to study the various power cycling tests found in the literature and to develop generalized steps in planning application specific power cycling tests. A comparison of different tests based on the failures, duration, test circuits, and monitored electrical parameters is presented.

Power Cycle Testing of Power Switches: A Literature Survey

DOE PAGES

GopiReddy, Lakshmi Reddy; Tolbert, Leon M.; Ozpineci, Burak

2014-09-18

Reliability of power converters and lifetime prediction has been a major topic of research in the last few decades, especially for traction applications. The main failures in high power semiconductors are caused by thermomechanical fatigue. Power cycling and temperature cycling are the two most common thermal acceleration tests used in assessing reliability. The objective of this paper is to study the various power cycling tests found in the literature and to develop generalized steps in planning application specific power cycling tests. A comparison of different tests based on the failures, duration, test circuits, and monitored electrical parameters is presented.

Reliability improvement of wire bonds subjected to fatigue stresses.

NASA Technical Reports Server (NTRS)

Ravi, K. V.; Philofsky, E. M.

1972-01-01

The failure of wire bonds due to repeated flexure when semiconductor devices are operated in an on-off mode has been investigated. An accelerated fatigue testing apparatus was constructed and the major fatigue variables, aluminum alloy composition, and bonding mechanism, were tested. The data showed Al-1% Mg wires to exhibit superior fatigue characteristics compared to Al-1% Cu or Al-1% Si and ultrasonic bonding to be better than thermocompression bonding for fatigue resistance. Based on these results highly reliable devices were fabricated using Al-1% Mg wire with ultrasonic bonding which withstood 120,000 power cycles with no failures.

Advantages, Disadvantages, and Trend of Integrative Medicine in the Treatment of Heart Failure.

PubMed

Zhang, PeiYing

2015-06-01

Integrative medicine therapy using traditional Chinese medicine (TCM) combined with western medicine has shown some advantages in treating heart failure (HF), such as holistic concept; multi-target treatment; dialectical logic; personalized therapy; formulae compatibility; and reduction of side effects of western medicine. However, problems still exist in TCM treatment of HF, including non-uniformed categorization of TCM, lack of standardized syndrome differentiation and lack of an evidence base. The future of treatment of HF seems to be focused on reversing ventricular remodeling, improving cardiac rehabilitation, and accelerating experimental research and drug discovery in TCM.

The Los Alamos Neutron Science Center Spallation Neutron Sources

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

Nowicki, Suzanne F.; Wender, Stephen A.; Mocko, Michael

The Los Alamos Neutron Science Center (LANSCE) provides the scientific community with intense sources of neutrons, which can be used to perform experiments supporting civilian and national security research. These measurements include nuclear physics experiments for the defense program, basic science, and the radiation effect programs. This paper focuses on the radiation effects program, which involves mostly accelerated testing of semiconductor parts. When cosmic rays strike the earth's atmosphere, they cause nuclear reactions with elements in the air and produce a wide range of energetic particles. Because neutrons are uncharged, they can reach aircraft altitudes and sea level. These neutronsmore » are thought to be the most important threat to semiconductor devices and integrated circuits. The best way to determine the failure rate due to these neutrons is to measure the failure rate in a neutron source that has the same spectrum as those produced by cosmic rays. Los Alamos has a high-energy and a low-energy neutron source for semiconductor testing. Both are driven by the 800-MeV proton beam from the LANSCE accelerator. The high-energy neutron source at the Weapons Neutron Research (WNR) facility uses a bare target that is designed to produce fast neutrons with energies from 100 keV to almost 800 MeV. The measured neutron energy distribution from WNR is very similar to that of the cosmic-ray-induced neutrons in the atmosphere. However, the flux provided at the WNR facility is typically 5×107 times more intense than the flux of the cosmic-ray-induced neutrons. This intense neutron flux allows testing at greatly accelerated rates. An irradiation test of less than an hour is equivalent to many years of neutron exposure due to cosmic-ray neutrons. The low-energy neutron source is located at the Lujan Neutron Scattering Center. It is based on a moderated source that provides useful neutrons from subthermal energies to ~100 keV. The characteristics of these sources, and ongoing industry program are described in this paper.« less

The Los Alamos Neutron Science Center Spallation Neutron Sources

DOE PAGES

Nowicki, Suzanne F.; Wender, Stephen A.; Mocko, Michael

2017-10-26

The Los Alamos Neutron Science Center (LANSCE) provides the scientific community with intense sources of neutrons, which can be used to perform experiments supporting civilian and national security research. These measurements include nuclear physics experiments for the defense program, basic science, and the radiation effect programs. This paper focuses on the radiation effects program, which involves mostly accelerated testing of semiconductor parts. When cosmic rays strike the earth's atmosphere, they cause nuclear reactions with elements in the air and produce a wide range of energetic particles. Because neutrons are uncharged, they can reach aircraft altitudes and sea level. These neutronsmore » are thought to be the most important threat to semiconductor devices and integrated circuits. The best way to determine the failure rate due to these neutrons is to measure the failure rate in a neutron source that has the same spectrum as those produced by cosmic rays. Los Alamos has a high-energy and a low-energy neutron source for semiconductor testing. Both are driven by the 800-MeV proton beam from the LANSCE accelerator. The high-energy neutron source at the Weapons Neutron Research (WNR) facility uses a bare target that is designed to produce fast neutrons with energies from 100 keV to almost 800 MeV. The measured neutron energy distribution from WNR is very similar to that of the cosmic-ray-induced neutrons in the atmosphere. However, the flux provided at the WNR facility is typically 5×107 times more intense than the flux of the cosmic-ray-induced neutrons. This intense neutron flux allows testing at greatly accelerated rates. An irradiation test of less than an hour is equivalent to many years of neutron exposure due to cosmic-ray neutrons. The low-energy neutron source is located at the Lujan Neutron Scattering Center. It is based on a moderated source that provides useful neutrons from subthermal energies to ~100 keV. The characteristics of these sources, and ongoing industry program are described in this paper.« less

Metallization failures

NASA Technical Reports Server (NTRS)

Beatty, R.

1971-01-01

Metallization-related failure mechanisms were shown to be a major cause of integrated circuit failures under accelerated stress conditions, as well as in actual use under field operation. The integrated circuit industry is aware of the problem and is attempting to solve it in one of two ways: (1) better understanding of the aluminum system, which is the most widely used metallization material for silicon integrated circuits both as a single level and multilevel metallization, or (2) evaluating alternative metal systems. Aluminum metallization offers many advantages, but also has limitations particularly at elevated temperatures and high current densities. As an alternative, multilayer systems of the general form, silicon device-metal-inorganic insulator-metal, are being considered to produce large scale integrated arrays. The merits and restrictions of metallization systems in current usage and systems under development are defined.

Towards Prognostics of Power MOSFETs: Accelerated Aging and Precursors of Failure

NASA Technical Reports Server (NTRS)

Celaya, Jose R.; Saxena, Abhinav; Wysocki, Philip; Saha, Sankalita; Goebel, Kai

2010-01-01

This paper presents research results dealing with power MOSFETs (metal oxide semiconductor field effect transistor) within the prognostics and health management of electronics. Experimental results are presented for the identification of the on-resistance as a precursor to failure of devices with die-attach degradation as a failure mechanism. Devices are aged under power cycling in order to trigger die-attach damage. In situ measurements of key electrical and thermal parameters are collected throughout the aging process and further used for analysis and computation of the on-resistance parameter. Experimental results show that the devices experience die-attach damage and that the on-resistance captures the degradation process in such a way that it could be used for the development of prognostics algorithms (data-driven or physics-based).

Long term real-time monitoring of large alpine rockslides by GB-InSAR: mechanisms, triggers, scenario assessment and Early Warning

NASA Astrophysics Data System (ADS)

Crosta, G. B.; Agliardi, F.; Sosio, R.; Rivolta, C.; Leva, D.; Dei Cas, L.

2012-04-01

Large rockslides in alpine valleys can undergo catastrophic evolution, posing extraordinary risks to settlements, lives and critical infrastructures. These phenomena are controlled by a complex interplay of lithological, structural, hydrological and meteo-climatic factors, which eventually result in: complex triggering mechanisms and kinematics, highly variable activity, regressive to progressive trends with superimposed acceleration and deceleration periods related to rainfall and snowmelt. Managing large rockslide risk remains challenging, due the high uncertainty related to their geological model and dynamics. In this context, the most promising approach to constrain rockslide kinematics, establish correlations with triggering factors, and predict future displacements, velocity and acceleration, and eventually possible final collapse is based on the analysis and modelling of long-term series of monitoring data. More than traditional monitoring activities, remote sensing represents an important tool aimed at describing local rockslide displacements and kinematics, at distinguishing rates of activity, and providing real time data suitable for early warning. We analyze a long term monitoring dataset collected for a deep-seated rockslide (Ruinon, Lombardy, Italy), actively monitored since 1997 through an in situ monitoring network (topographic and GPS, wire extensometers and distometer baselines) and since 2006 by a ground based radar (GB-InSAR). Monitoring allowed to set-up and update the geological model, identify rockslide extent and geometry, analyze its sensitivity to seasonal changes and their impact on the reliability and EW potential of monitoring data. GB-InSAR data allowed to identify sub-areas with different behaviors associated to outcropping bedrock and thick debris cover, and to set-up a "virtual monitoring network" by a posteriori selection of critical locations. Resulting displacement time series provide a large amount of information even in debris-covered areas, where traditional monitoring fails. Such spatially-distributed, improved information, validated by selected ground-based measurements, allowed to establish new velocity thresholds for EW purposes. Relationships between rainfall and displacement rates allowed to identify different possible failure mechanisms and to constrain the applicability of rainfall EW thresholds. Comparison with temperature and snow melting time series allowed to clarify the sensitivity of the rockslide movement to these controlling factors. Finally, the recognition of the sensitivity to all these factors allowed us to accomplish a more complete hazard assessment by defining different failure scenarios and the associated triggering thresholds.

Multicenter, dose-ranging study of efegatran sulfate versus heparin with thrombolysis for acute myocardial infarction: The Promotion of Reperfusion in Myocardial Infarction Evolution (PRIME) trial.

PubMed

2002-01-01

Adjunctive therapies that increase the incidence of normal reperfusion after thrombolysis for acute myocardial infarction (MI) could enhance clinical outcomes. Direct thrombin inhibitors may offer an advantage over standard adjunctive therapies. We randomized 336 patients with acute MI at 33 sites to receive 1 of 5 doses of efegatran sulfate, a direct thrombin inhibitor, or heparin for 72 to 96 hours, both with accelerated alteplase and aspirin. The primary end point was the incidence of thrombolytic failure (death, reinfarction, or TIMI grade 0-2 flow in the infarct artery from 90 minutes to discharge or 30 days, whichever occurred earlier). Significantly more patients randomized to efegatran had evidence of heart failure at admission. The lowest-dose efegatran arm was terminated at 15 patients because of unacceptably increased thrombolytic failure. The primary end point occurred in 53.0% of patients treated with heparin, in 53.8% of patients treated with efegatran overall (P =.90), and in 55.4% of patients given intermediate-dose efegatran (P =.74). These findings were unaffected after adjustment was done for baseline differences. Most bleeding was minor; major bleeding and the use of blood transfusions did not differ significantly by treatment. Three patients in the high-dose efegatran group had intracranial hemorrhage, as did 1 patient in the heparin group. Continuous ST monitoring showed a shorter time to recovery for the efegatran group (median 107 minutes) compared with the heparin group (154 minutes; P =.025). Efegatran sulfate appeared to offer no clear advantage over heparin as an adjunct to thrombolysis for acute myocardial infarction, although there may be a modest improvement in time to reperfusion.

Evaluation of Current Consensus Statement Recommendations for Accelerated Partial Breast Irradiation: A Pooled Analysis of William Beaumont Hospital and American Society of Breast Surgeon MammoSite Registry Trial Data

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

Wilkinson, J. Ben; Beitsch, Peter D.; Shah, Chirag

Purpose: To determine whether the American Society for Radiation Oncology (ASTRO) Consensus Statement (CS) recommendations for accelerated partial breast irradiation (APBI) are associated with significantly different outcomes in a pooled analysis from William Beaumont Hospital (WBH) and the American Society of Breast Surgeons (ASBrS) MammoSite® Registry Trial. Methods and Materials: APBI was used to treat 2127 cases of early-stage breast cancer (WBH, n=678; ASBrS, n=1449). Three forms of APBI were used at WBH (interstitial, n=221; balloon-based, n=255; or 3-dimensional conformal radiation therapy, n=206), whereas all Registry Trial patients received balloon-based brachytherapy. Patients were divided according to the ASTRO CS intomore » suitable (n=661, 36.5%), cautionary (n=850, 46.9%), and unsuitable (n=302, 16.7%) categories. Tumor characteristics and clinical outcomes were analyzed according to CS group. Results: The median age was 65 years (range, 32-94 years), and the median tumor size was 10.0 mm (range, 0-45 mm). The median follow-up time was 60.6 months. The WBH cohort had more node-positive disease (6.9% vs 2.6%, P<.01) and cautionary patients (49.5% vs 41.8%, P=.06). The 5-year actuarial ipsilateral breast tumor recurrence (IBTR), regional nodal failure (RNF), and distant metastasis (DM) for the whole cohort were 2.8%, 0.6%, 1.6%. The rate of IBTR was not statistically higher between suitable (2.5%), cautionary (3.3%), or unsuitable (4.6%) patients (P=.20). The nonsignificant increase in IBTR for the cautionary and unsuitable categories was due to increased elsewhere failures and new primaries (P=.04), not tumor bed recurrence (P=.93). Conclusions: Excellent outcomes after breast-conserving surgery and APBI were seen in our pooled analysis. The current ASTRO CS guidelines did not adequately differentiate patients at an increased risk of IBTR or tumor bed failure in this large patient cohort.« less

Extended (5-year) Outcomes of Accelerated Partial Breast Irradiation Using MammoSite Balloon Brachytherapy: Patterns of Failure, Patient Selection, and Dosimetric Correlates for Late Toxicity

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

Vargo, John A.; Verma, Vivek; Kim, Hayeon

2014-02-01

Purpose: Accelerated partial breast irradiation (APBI) with balloon and catheter-based brachytherapy has gained increasing popularity in recent years and is the subject of ongoing phase III trials. Initial data suggest promising local control and cosmetic results in appropriately selected patients. Long-term data continue to evolve but are limited outside of the context of the American Society of Breast Surgeons Registry Trial. Methods and Materials: A retrospective review of 157 patients completing APBI after breast-conserving surgery and axillary staging via high-dose-rate {sup 192}Ir brachytherapy from June 2002 to December 2007 was made. APBI was delivered with a single-lumen MammoSite balloon-based applicatormore » to a median dose of 34 Gy in 10 fractions over a 5-day period. Tumor coverage and critical organ dosimetry were retrospectively collected on the basis of computed tomography completed for conformance and symmetry. Results: At a median follow-up time of 5.5 years (range, 0-10.0 years), the 5-year and 7-year actuarial incidences of ipsilateral breast control were 98%/98%, of nodal control 99%/98%, and of distant control 99%/99%, respectively. The crude rate of ipsilateral breast recurrence was 2.5% (n=4); of nodal failure, 1.9% (n=3); and of distant failure, 0.6% (n=1). The 5-year and 7-year actuarial overall survival rates were 89%/86%, with breast cancer–specific survival of 100%/99%, respectively. Good to excellent cosmetic outcomes were achieved in 93.4% of patients. Telangiectasia developed in 27% of patients, with 1-year, 3-year, and 5-year actuarial incidence of 7%/24%/33%; skin dose >100% significantly predicted for the development of telangiectasia (50% vs 14%, P<.0001). Conclusions: Long-term single-institution outcomes suggest excellent tumor control, breast cosmesis, and minimal late toxicity. Skin toxicity is a function of skin dose, which may be ameliorated with dosimetric optimization afforded by newer multicatheter brachytherapy applicators and a more rigorous skin dose constraint of ≤100%.« less

Accelerometer Data Analysis and Presentation Techniques

NASA Technical Reports Server (NTRS)

Rogers, Melissa J. B.; Hrovat, Kenneth; McPherson, Kevin; Moskowitz, Milton E.; Reckart, Timothy

1997-01-01

The NASA Lewis Research Center's Principal Investigator Microgravity Services project analyzes Orbital Acceleration Research Experiment and Space Acceleration Measurement System data for principal investigators of microgravity experiments. Principal investigators need a thorough understanding of data analysis techniques so that they can request appropriate analyses to best interpret accelerometer data. Accelerometer data sampling and filtering is introduced along with the related topics of resolution and aliasing. Specific information about the Orbital Acceleration Research Experiment and Space Acceleration Measurement System data sampling and filtering is given. Time domain data analysis techniques are discussed and example environment interpretations are made using plots of acceleration versus time, interval average acceleration versus time, interval root-mean-square acceleration versus time, trimmean acceleration versus time, quasi-steady three dimensional histograms, and prediction of quasi-steady levels at different locations. An introduction to Fourier transform theory and windowing is provided along with specific analysis techniques and data interpretations. The frequency domain analyses discussed are power spectral density versus frequency, cumulative root-mean-square acceleration versus frequency, root-mean-square acceleration versus frequency, one-third octave band root-mean-square acceleration versus frequency, and power spectral density versus frequency versus time (spectrogram). Instructions for accessing NASA Lewis Research Center accelerometer data and related information using the internet are provided.

Changing impact of modifiable risk factors on the incidence of major outcomes of type 1 diabetes: the Pittsburgh Epidemiology of Diabetes Complications Study.

PubMed

Miller, Rachel G; Secrest, Aaron M; Ellis, Demetrius; Becker, Dorothy J; Orchard, Trevor J

2013-12-01

The incidence of type 1 diabetes complications appears to be decreasing, but relative contributions of risk factors are unclear. We thus estimated the effect of modifiable risk factors on the incidence of a composite end point, major outcomes of diabetes (MOD). The Pittsburgh Epidemiology of Diabetes Complications (EDC) Study was used to derive two cohorts based on diabetes diagnosis year (1960-1969 and 1970-1980). Baseline exam data in the current analysis for the 1960s group were collected in 1986-1988 and for the 1970s in 1996-1998. Each group was followed for 8 years for MOD incidence (diabetes-related death, myocardial infarction, revascularization procedure/blockage ≥50%, stroke, end-stage renal disease, blindness, and amputation). Assessed risk factors include the following: HbA1c, hypertension, microalbuminuria, BMI, hypercholesterolemia, and smoking. Accelerated failure time models were used to estimate the acceleration factor. MOD incidence decreased in the 1970s cohort (15.8% [95% CI 11.6-21.4]) compared with the 1960s (22.6% [17.0-29.1]) over the 8-year follow-up (P = 0.06). Hypertension and microalbuminuria were associated with significantly accelerated MOD incidence in both cohorts (P < 0.01 for both). High HbA1c (P = 0.0005), hypercholesterolemia (P = 0.01), and current smoking (P = 0.003) significantly accelerated the incidence of MOD in the 1960s but not 1970s cohort. BMI was not associated with MOD in either cohort. These results suggest that hypertension and microalbuminuria remain important predictors of complications that are not being adequately addressed.

NASA's Evolutionary Xenon Thruster (NEXT) Power Processing Unit (PPU) Capacitor Failure Root Cause Analysis

NASA Technical Reports Server (NTRS)

Soeder, James F.; Pinero, Luis; Schneidegger, Robert; Dunning, John; Birchenough, Art

2012-01-01

The NASA's Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. A critical element of the propulsion system is the Power Processing Unit (PPU) which supplies regulated power to the key components of the thruster. The PPU contains six different power supplies including the beam, discharge, discharge heater, neutralizer, neutralizer heater, and accelerator supplies. The beam supply is the largest and processes up to 93+% of the power. The NEXT PPU had been operated for approximately 200+ hours and has experienced a series of three capacitor failures in the beam supply. The capacitors are in the same, nominally non-critical location the input filter capacitor to a full wave switching inverter. The three failures occurred after about 20, 30, and 135 hours of operation. This paper provides background on the NEXT PPU and the capacitor failures. It discusses the failure investigation approach, the beam supply power switching topology and its operating modes, capacitor characteristics and circuit testing. Finally, it identifies root cause of the failures to be the unusual confluence of circuit switching frequency, the physical layout of the power circuits, and the characteristics of the capacitor.

NASA's Evolutionary Xenon Thruster (NEXT) Power Processing Unit (PPU) Capacitor Failure Root Cause Analysis

NASA Technical Reports Server (NTRS)

Soeder, James F.; Scheidegger, Robert J.; Pinero, Luis R.; Birchenough, Arthur J.; Dunning, John W.

2012-01-01

The NASA s Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. A critical element of the propulsion system is the Power Processing Unit (PPU) which supplies regulated power to the key components of the thruster. The PPU contains six different power supplies including the beam, discharge, discharge heater, neutralizer, neutralizer heater, and accelerator supplies. The beam supply is the largest and processes up to 93+% of the power. The NEXT PPU had been operated for approximately 200+ hr and has experienced a series of three capacitor failures in the beam supply. The capacitors are in the same, nominally non-critical location-the input filter capacitor to a full wave switching inverter. The three failures occurred after about 20, 30, and 135 hr of operation. This paper provides background on the NEXT PPU and the capacitor failures. It discusses the failure investigation approach, the beam supply power switching topology and its operating modes, capacitor characteristics and circuit testing. Finally, it identifies root cause of the failures to be the unusual confluence of circuit switching frequency, the physical layout of the power circuits, and the characteristics of the capacitor.

Choice reaction time to visual motion during prolonged rotary motion in airline pilots

NASA Technical Reports Server (NTRS)

Stewart, J. D.; Clark, B.

1975-01-01

Thirteen airline pilots were studied to determine the effect of preceding rotary accelerations on the choice reaction time to the horizontal acceleration of a vertical line on a cathode-ray tube. On each trial, one of three levels of rotary and visual acceleration was presented with the rotary stimulus preceding the visual by one of seven periods. The two accelerations were always equal and were presented in the same or opposite directions. The reaction time was found to increase with increases in the time the rotary acceleration preceded the visual acceleration, and to decrease with increased levels of visual and rotary acceleration. The reaction time was found to be shorter when the accelerations were in the same direction than when they were in opposite directions. These results suggest that these findings are a special case of a general effect that the authors have termed 'gyrovisual modulation'.

GIS-based seismic shaking slope vulnerability map of Sicily (Central Mediterranean)

NASA Astrophysics Data System (ADS)

Nigro, Fabrizio; Arisco, Giuseppe; Perricone, Marcella; Renda, Pietro; Favara, Rocco

2010-05-01

Earthquakes often represent very dangerouses natural events in terms of human life and economic losses and their damage effects are amplified by the synchronous occurrence of seismically-induced ground-shaking failures in wide regions around the seismogenic source. In fact, the shaking associated with big earthquakes triggers extensive landsliding, sometimes at distances of more than 100 km from the epicenter. The active tectonics and the geomorphic/morphodinamic pattern of the regions affected by earthquakes contribute to the slopes instability tendency. In fact, earthquake-induced groun-motion loading determines inertial forces activation within slopes that, combined with the intrinsic pre-existing static forces, reduces the slope stability towards its failure. Basically, under zero-shear stress reversals conditions, a catastrophic failure will take place if the earthquake-induced shear displacement exceeds the critical level of undrained shear strength to a value equal to the gravitational shear stress. However, seismic stability analyses carried out for various infinite slopes by using the existing Newmark-like methods reveal that estimated permanent displacements smaller than the critical value should also be regarded as dangerous for the post-earthquake slope safety, in terms of human activities use. Earthquake-induced (often high-speed) landslides are among the most destructive phenomena related to slopes failure during earthquakes. In fact, damage from earthquake-induced landslides (and other ground-failures), sometimes exceeds the buildings/infrastructures damage directly related to ground-shaking for fault breaking. For this matter, several hearthquakes-related slope failures methods have been developed, for the evaluation of the combined hazard types represented by seismically ground-motion landslides. The methodologies of analysis of the engineering seismic risk related to the slopes instability processes is often achieved through the evaluation of the permanent displacement potentially induced by an seismic scenario. Such methodologies found on the consideration that the conditions of seismic stability and the post-seismic functionality of engineering structures are tightly related to the entity of the permanent deformations that an earthquake can induce. Regarding the existing simplified procedures among slope stability models, Newmark's model is often used to derive indications about slope instabilities due to earthquakes. In this way, we have evaluated the seismically-induced landslides hazard in Sicily (Central Mediterranean) using the Newmark-like model. In order to determine the map distribution of the seismic ground-acceleration from an earthquake scenario, the attenuation-law of Sabetta & Pugliese has been used, analyzing some seismic recordings occurred in Italy. Also, by evaluating permanent displacements, the correlation of Ambraseys & Menu has been assumed. The seismic shaking slope vulnerability map of Sicily has been carried out using GIS application, also considering max seismic ground-acceleration peak distribution (in terms of exceedance probability for fixed time), slope acclivity, cohesion/angle of internal friction of outcropping rocks, allowing the zoning of the unstable slopes under seismic forces.

Stripper foil failure modes and cures at the Spallation Neutron Source

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

Cousineau, Sarah M; Galambos, John D; Kim, Sang-Ho

2011-01-01

The Spallation Neutron Source comprises a 1 GeV, 1.4 MW linear accelerator followed by an accumulator ring and a liquid mercury target. To manage the beam loss caused by the $H^0$ excited states created during the $H^-$ charge exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming $H^-$ beam, which circled around to strike the foilmore » bracket and cause bracket failure. Another consequence is that convoy electrons can reflect back up from the electron catcher and strike the foil and bracket. An additional contributor to foil system failure is vacuum breakdown due to the charge developed on the foil by secondary electron emission. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them.« less

Stripper foil failure modes and cures at the Oak Rdige Spallation Neutron Source

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

Plum, M.A.; Raparia, D.; Cousineau, S.M.

2011-03-28

The Oak Ridge Spallation Neutron Source comprises a 1 GeV, 1.5 MW linear accelerator followed by an accumulator ring and a liquid mercury target. To manage the beam loss caused by the H{sup 0} excited states created during the H{sup -} charge-exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming H{sup -} beam, which circled aroundmore » to strike the foil bracket and cause bracket failure. Another consequence is that convoy electrons can reflect back up from the electron catcher and strike the foil and bracket. An additional contributor to foil system failure is vacuum breakdown due to the charge developed on the foil by secondary electron emission. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them.« less

Visual reaction times during prolonged angular acceleration parallel the subjective perception of rotation

NASA Technical Reports Server (NTRS)

Mattson, D. L.

1975-01-01

The effect of prolonged angular acceleration on choice reaction time to an accelerating visual stimulus was investigated, with 10 commercial airline pilots serving as subjects. The pattern of reaction times during and following acceleration was compared with the pattern of velocity estimates reported during identical trials. Both reaction times and velocity estimates increased at the onset of acceleration, declined prior to the termination of acceleration, and showed an aftereffect. These results are inconsistent with the torsion-pendulum theory of semicircular canal function and suggest that the vestibular adaptation is of central origin.

Towards Accelerated Aging Methodologies and Health Management of Power MOSFETs (Technical Brief)

NASA Technical Reports Server (NTRS)

Celaya, Jose R.; Patil, Nishad; Saha, Sankalita; Wysocki, Phil; Goebel, Kai

2009-01-01

Understanding aging mechanisms of electronic components is of extreme importance in the aerospace domain where they are part of numerous critical subsystems including avionics. In particular, power MOSFETs are of special interest as they are involved in high voltage switching circuits such as drivers for electrical motors. With increased use of electronics in aircraft control, it becomes more important to understand the degradation of these components in aircraft specific environments. In this paper, we present an accelerated aging methodology for power MOSFETs that subject the devices to indirect thermal overstress during high voltage switching. During this accelerated aging process, two major modes of failure were observed - latch-up and die attach degradation. In this paper we present the details of our aging methodology along with details of experiments and analysis of the results.

Comment on ‘Poynting flux in the neighbourhood of a point charge in arbitrary motion and radiative power losses’

NASA Astrophysics Data System (ADS)

Rowland, David R.

2018-01-01

Based on a calculation of the Poynting vector flux in the neighbourhood of an accelerating point charge, Singal (2016 Eur. J. Phys. 37 045210) has claimed that the instantaneous rate of energy radiated by the charge differs from the Larmor formula. It is argued in this comment that Singal’s proposed formula for the radiated power is physically untenable because it predicts a negative rate of energy loss in physically realisable situations. The cause of Singal’s erroneous conclusion is identified as being a failure to realise that the bound electromagnetic field energy of an accelerating charge differs by the Schott energy from the bound field energy of a charge moving at a constant velocity equal to the current velocity of the accelerating charge. References to the salient literature are provided.

Stabilization of Landslides for the Improvement of Aquatic Habitat

Treesearch

Michael J. Furniss

1989-01-01

Chronic surface and mass erosion from recent landslides often prevents the recovery of productive stream habitats following initial mass failure events. Low-cost methods that can accelerate recovery and stabilization processes have been employed on numerous failed slopes in the Six Rivers National Forest in the northwest corner of California, with notable success. Two...

Composite-Unit Accelerated Life Testing (CUALT) of Sonar Transducers

DTIC Science & Technology

1979-09-01

Developed and technically defended the Texas Research Institute CUALT plan, Helped prepare sections 5 and 7. Edward Hobaica and Ray Haworth - Developed...le2--Te- TT-Sonar 3R. A. Larmi, E. C. Hobaica , Failure Modes & Effects Analysis for the DT-308’ (now called the DT-605) Hydrophone, EB Div Report No.: U

Application of the NEXT Ion Thruster Lifetime Assessment to Thruster Throttling

NASA Technical Reports Server (NTRS)

VanNoord, Jonathan L.; Herman, Daniel A.

2010-01-01

Ion thrusters are low thrust, high specific impulse devices with typical operational lifetimes of 10,000 to 30,000 hr over a range of throttling conditions. The NEXT ion thruster is the latest generation of ion thrusters under development. The NEXT ion thruster currently has a qualification level propellant throughput requirement of 450 kg of xenon, which corresponds to roughly 22,000 hr of operation at the highest input power throttling point. This paper will provide a brief review the previous life assessment predictions for various throttling conditions. A further assessment will be presented examining the anticipated accelerator grid hole wall erosion and related electron backstreaming limit. The continued assessment of the NEXT ion thruster indicates that the first failure mode across the throttling range is expected to be in excess of 36,000 hr of operation from charge exchange induced groove erosion. It is at this duration that the groove is predicted to penetrate the accelerator grid possibly resulting in structural failure. Based on these lifetime and mission assessments, a throttling approach is presented for the Long Duration Test to demonstrate NEXT thruster lifetime and validate modeling.

Sleep Disturbance Preceding Suicide Among Veterans

PubMed Central

Britton, Peter C.; Ilgen, Mark A.; Chapman, Ben; Conner, Kenneth R.

2012-01-01

Objectives. We examined the role of sleep disturbance in time to suicide since the last treatment visit among veterans receiving Veterans Health Administration (VHA) services. Methods. Among 423 veteran suicide decedents from 2 geographic areas, systematic chart reviews were conducted on the 381 (90.1%) who had a VHA visit in the last year of life. Veteran suicides with a documented sleep disturbance (45.4%) were compared with those without sleep disturbance (54.6%) on time to death since their last VHA visit using an accelerated failure time model. Results. Veterans with sleep disturbance died sooner after their last visit than did those without sleep disturbance, after we adjusted for the presence of mental health or substance use symptoms, age, and region. Conclusions. Findings indicated that sleep disturbance was associated with time to suicide in this sample of veterans who died by suicide. The findings had implications for using the presence of sleep disturbance to detect near-term risk for suicide and suggested that sleep disturbance might provide an important intervention target for a subgroup of at-risk veterans. PMID:22390611

“Smooth” Semiparametric Regression Analysis for Arbitrarily Censored Time-to-Event Data

PubMed Central

Zhang, Min; Davidian, Marie

2008-01-01

Summary A general framework for regression analysis of time-to-event data subject to arbitrary patterns of censoring is proposed. The approach is relevant when the analyst is willing to assume that distributions governing model components that are ordinarily left unspecified in popular semiparametric regression models, such as the baseline hazard function in the proportional hazards model, have densities satisfying mild “smoothness” conditions. Densities are approximated by a truncated series expansion that, for fixed degree of truncation, results in a “parametric” representation, which makes likelihood-based inference coupled with adaptive choice of the degree of truncation, and hence flexibility of the model, computationally and conceptually straightforward with data subject to any pattern of censoring. The formulation allows popular models, such as the proportional hazards, proportional odds, and accelerated failure time models, to be placed in a common framework; provides a principled basis for choosing among them; and renders useful extensions of the models straightforward. The utility and performance of the methods are demonstrated via simulations and by application to data from time-to-event studies. PMID:17970813

Breaking Off of Large Ice Masses From Hanging Glaciers

NASA Astrophysics Data System (ADS)

Pralong, A.; Funk, M.

In order to reduce damage to settlements or other installations (roads, railway, etc) and avoid loss of life, a forecast of the final failure time of ice masses is required. At present, the most promising approach for such a prediction is based on the regularity by which certain large ice masses accelerate prior to the instant of collapse. The lim- itation of this forecast lies in short-term irregularities and in the difficulties to obtain sufficiently accurate data. A better physical understanding of the breaking off process is required, in order to improve the forecasting method. Previous analyze has shown that a stepwise crack extension coupling with a viscous flow leads to the observed acceleration function. We propose another approach by considering a local damage evolution law (gener- alized Kachanow's law) coupled with Glen's flow law to simulate the spatial evolu- tion of damage in polycristalline ice, using a finite element computational model. The present study focuses on the transition from a diffuse to a localised damage reparti- tion occurring during the damage evolution. The influence of inhomogeneous initial conditions (inhomogeneity of the mechanical properties of ice, damage inhomogene- ity) and inhomogeneous boundary conditions on the damage repartition are especially investigated.

Reshocks, rarefactions, and the generalized Layzer model for hydrodynamic instabilities

NASA Astrophysics Data System (ADS)

Mikaelian, Karnig O.

2009-02-01

We report numerical simulations and analytic modeling of shock tube experiments on Rayleigh-Taylor and Richtmyer-Meshkov instabilities. We examine single interfaces of the type A /B where the incident shock is initiated in A and the transmitted shock proceeds into B. Examples are He/air and air/He. In addition, we study finite-thickness or double-interface A /B/A configurations such as air/SF6/air gas-curtain experiments. We first consider conventional shock tubes that have a "fixed" boundary: A solid endwall which reflects the transmitted shock and reshocks the interface(s). Then we focus on new experiments with a "free" boundary—a membrane disrupted mechanically or by the transmitted shock, sending back a rarefaction toward the interface(s). Complex acceleration histories are achieved, relevant for inertial confinement fusion implosions. We compare our simulation results with a generalized Layzer model for two fluids with time-dependent densities and derive a new freeze-out condition whereby accelerating and compressive forces cancel each other out. Except for the recently reported failures of the Layzer model, the generalized Layzer model and hydrocode simulations for reshocks and rarefactions agree well with each other and remain to be verified experimentally.

The effects of simulated bone loss on the implant-abutment assembly and likelihood of fracture: an in vitro study.

PubMed

Manzoor, Behzad; Suleiman, Mahmood; Palmer, Richard M

2013-01-01

The crestal bone level around a dental implant may influence its strength characteristics by offering protection against mechanical failures. Therefore, the present study investigated the effect of simulated bone loss on modes, loads, and cycles to failure in an in vitro model. Different amounts of bone loss were simulated: 0, 1.5, 3.0, and 4.5 mm from the implant head. Forty narrow-diameter (3.0-mm) implant-abutment assemblies were tested using compressive bending and cyclic fatigue testing. Weibull and accelerated life testing analysis were used to assess reliability and functional life. Statistical analyses were performed using the Fisher-Exact test and the Spearman ranked correlation. Compressive bending tests showed that the level of bone loss influenced the load-bearing capacity of implant-abutment assemblies. Fatigue testing showed that the modes, loads, and cycles to failure had a statistically significant relationship with the level of bone loss. All 16 samples with bone loss of 3.0 mm or more experienced horizontal implant body fractures. In contrast, 14 of 16 samples with 0 and 1.5 mm of bone loss showed abutment and screw fractures. Weibull and accelerated life testing analysis indicated a two-group distribution: the 0- and 1.5-mm bone loss samples had better functional life and reliability than the 3.0- and 4.5-mm samples. Progressive bone loss had a significant effect on modes, loads, and cycles to failure. In addition, bone loss influenced the functional life and reliability of the implant-abutment assemblies. Maintaining crestal bone levels is important in ensuring biomechanical sustainability and predictable long-term function of dental implant assemblies.

Geological hazards associated with intense rain and flooding in Natal

NASA Astrophysics Data System (ADS)

Thomas, M. A.; van Schalkwyk, A.

1993-02-01

The combination of rugged topography and climate predisposes the province of Natal to severe floods. Information available since 1856 shows that bridge and slope failures have been recorded in twenty out of twenty-five flood episodes. Bridge failures are caused mostly by geological factors. The mechanism of failure can be classified broadly into foundation failures and changes of river course. Scour and debris build-up have led to failures of foundations located in rock and alluvial sediments. In preparing and replacing bridges the aims have been to increase the area of waterway, increase foundation depths to reach more competent strata and lay protection along banks and abutments to counteract scour. Historically, slope failures have not been well documented but following the 1987/88 storms 223 slope failures were recorded. The classification of the failures allowed the mechanisms of failure to be ascertained, and general design considerations to be reviewed. In areas adjacent to the Drakensberg Mountains slope failures are part of a natural erosion cycle which may be accelerated in periods of heavy rain. Throughout Natal, hummocky ground adjacent to dolerite intrusions reveals the on-going history of failure caused by water ingress and the generation of high pore water pressures on the slip planes. Classic flows occurred throughout the Greater Durban area where residual sandy soils of the Natal Group sandstone became supersaturated. Slumping was common on steep terrain underlain by granite-gneiss in the Kwa-Zulu area. Shales of the Pietermaritzburg Formation are notoriously unstable, yet few failures occurred during the summer storms of 1987/88. Inadequate drainage was responsible for many failures, this was particularly so along the railways.

Bayes Analysis and Reliability Implications of Stress-Rupture Testing a Kevlar/Epoxy COPV Using Temperature and Pressure Acceleration

NASA Technical Reports Server (NTRS)

Phoenix, S. Leigh; Kezirian, Michael T.; Murthy, Pappu L. N.

2009-01-01

Composite Overwrapped Pressure Vessels (COPVs) that have survived a long service time under pressure generally must be recertified before service is extended. Flight certification is dependent on the reliability analysis to quantify the risk of stress rupture failure in existing flight vessels. Full certification of this reliability model would require a statistically significant number of lifetime tests to be performed and is impractical given the cost and limited flight hardware for certification testing purposes. One approach to confirm the reliability model is to perform a stress rupture test on a flight COPV. Currently, testing of such a Kevlar49 (Dupont)/epoxy COPV is nearing completion. The present paper focuses on a Bayesian statistical approach to analyze the possible failure time results of this test and to assess the implications in choosing between possible model parameter values that in the past have had significant uncertainty. The key uncertain parameters in this case are the actual fiber stress ratio at operating pressure, and the Weibull shape parameter for lifetime; the former has been uncertain due to ambiguities in interpreting the original and a duplicate burst test. The latter has been uncertain due to major differences between COPVs in the database and the actual COPVs in service. Any information obtained that clarifies and eliminates uncertainty in these parameters will have a major effect on the predicted reliability of the service COPVs going forward. The key result is that the longer the vessel survives, the more likely the more optimistic stress ratio model is correct. At the time of writing, the resulting effect on predicted future reliability is dramatic, increasing it by about one "nine," that is, reducing the predicted probability of failure by an order of magnitude. However, testing one vessel does not change the uncertainty on the Weibull shape parameter for lifetime since testing several vessels would be necessary.

49 CFR 563.8 - Data format.

Code of Federal Regulations, 2012 CFR

2012-10-01

... the first acceleration data point; (3) The number of the last point (NLP), which is an integer that...; and (4) NLP—NFP + 1 acceleration values sequentially beginning with the acceleration at time NFP * TS and continue sampling the acceleration at TS increments in time until the time NLP * TS is reached...

Detection of linear ego-acceleration from optic flow.

PubMed

Festl, Freya; Recktenwald, Fabian; Yuan, Chunrong; Mallot, Hanspeter A

2012-07-20

Human observers are able to estimate various ego-motion parameters from optic flow, including rotation, translational heading, time-to-collision (TTC), time-to-passage (TTP), etc. The perception of linear ego-acceleration or deceleration, i.e., changes of translational velocity, is less well understood. While time-to-passage experiments indicate that ego-acceleration is neglected, subjects are able to keep their (perceived) speed constant under changing conditions, indicating that some sense of ego-acceleration or velocity change must be present. In this paper, we analyze the relation of ego-acceleration estimates and geometrical parameters of the environment using simulated flights through cylindrical and conic (narrowing or widening) corridors. Theoretical analysis shows that a logarithmic ego-acceleration parameter, called the acceleration rate ρ, can be calculated from retinal acceleration measurements. This parameter is independent of the geometrical layout of the scene; if veridical ego-motion is known at some instant in time, acceleration rate allows updating of ego-motion without further depth-velocity calibration. Results indicate, however, that subjects systematically confuse ego-acceleration with corridor narrowing and ego-deceleration with corridor widening, while veridically judging ego-acceleration in straight corridors. We conclude that judgments of ego-acceleration are based on first-order retinal flow and do not make use of acceleration rate or retinal acceleration.

Particle Acceleration and Fractional Transport in Turbulent Reconnection

NASA Astrophysics Data System (ADS)

Isliker, Heinz; Pisokas, Theophilos; Vlahos, Loukas; Anastasiadis, Anastasios

2017-11-01

We consider a large-scale environment of turbulent reconnection that is fragmented into a number of randomly distributed unstable current sheets (UCSs), and we statistically analyze the acceleration of particles within this environment. We address two important cases of acceleration mechanisms when particles interact with the UCS: (a) electric field acceleration and (b) acceleration by reflection at contracting islands. Electrons and ions are accelerated very efficiently, attaining an energy distribution of power-law shape with an index 1-2, depending on the acceleration mechanism. The transport coefficients in energy space are estimated from test-particle simulation data, and we show that the classical Fokker-Planck (FP) equation fails to reproduce the simulation results when the transport coefficients are inserted into it and it is solved numerically. The cause for this failure is that the particles perform Levy flights in energy space, while the distributions of the energy increments exhibit power-law tails. We then use the fractional transport equation (FTE) derived by Isliker et al., whose parameters and the order of the fractional derivatives are inferred from the simulation data, and solving the FTE numerically, we show that the FTE successfully reproduces the kinetic energy distribution of the test particles. We discuss in detail the analysis of the simulation data and the criteria that allow one to judge the appropriateness of either an FTE or a classical FP equation as a transport model.

Particle Acceleration and Fractional Transport in Turbulent Reconnection

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

Isliker, Heinz; Pisokas, Theophilos; Vlahos, Loukas

We consider a large-scale environment of turbulent reconnection that is fragmented into a number of randomly distributed unstable current sheets (UCSs), and we statistically analyze the acceleration of particles within this environment. We address two important cases of acceleration mechanisms when particles interact with the UCS: (a) electric field acceleration and (b) acceleration by reflection at contracting islands. Electrons and ions are accelerated very efficiently, attaining an energy distribution of power-law shape with an index 1–2, depending on the acceleration mechanism. The transport coefficients in energy space are estimated from test-particle simulation data, and we show that the classical Fokker–Planckmore » (FP) equation fails to reproduce the simulation results when the transport coefficients are inserted into it and it is solved numerically. The cause for this failure is that the particles perform Levy flights in energy space, while the distributions of the energy increments exhibit power-law tails. We then use the fractional transport equation (FTE) derived by Isliker et al., whose parameters and the order of the fractional derivatives are inferred from the simulation data, and solving the FTE numerically, we show that the FTE successfully reproduces the kinetic energy distribution of the test particles. We discuss in detail the analysis of the simulation data and the criteria that allow one to judge the appropriateness of either an FTE or a classical FP equation as a transport model.« less

Using performance measurement to drive improvement: a road map for change.

PubMed

Galvin, Robert S; McGlynn, Elizabeth A

2003-01-01

Performance measures and reporting have not been adopted throughout the US health care system despite their central role in encouraging increased participation by consumers in decision-making. Understanding whether the failure of measurement and reporting to diffuse throughout the health system can be overcome is critical for determining future policy in this area. To create a conceptual framework for analyzing the current rate of adoption and evaluating alternatives for accelerating adoption, and to recommend a set of concrete steps that can be taken to increase the use of performance measurement and reporting. Review of three theoretic models (Rogers, Prochaska/DiClemente, Gladwell), examination of the literature on previous experiences with quality measurement and reporting, and interviews with select stakeholders. The three theoretic models provide a valuable framework for understanding why the use of performance measures is stalled ("the circle of unaccountability") and for generating ideas about concrete steps that could be taken to accelerate adoption. Six steps are recommended: (1) raise public awareness, (2) redesign measures and reports, (3) make the delivery of information timely, (4) require public reporting, (5) develop and implement systems to reward quality, and (6) actively court leaders. The recommended six steps are interconnected; action on all will be required to drive significant acceleration in rates of adoption of performance measurement and reporting. Leadership and coordination are necessary to ensure these steps are taken and that they work in concert with one another.

IMPULSIVE ACCELERATION OF CORONAL MASS EJECTIONS. II. RELATION TO SOFT X-RAY FLARES AND FILAMENT ERUPTIONS

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

Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.

2012-08-10

Using high time cadence images from the STEREO EUVI, COR1, and COR2 instruments, we derived detailed kinematics of the main acceleration stage for a sample of 95 coronal mass ejections (CMEs) in comparison with associated flares and filament eruptions. We found that CMEs associated with flares reveal on average significantly higher peak accelerations and lower acceleration phase durations, initiation heights, and heights, at which they reach their peak velocities and peak accelerations. This means that CMEs that are associated with flares are characterized by higher and more impulsive accelerations and originate from lower in the corona where the magnetic fieldmore » is stronger. For CMEs that are associated with filament eruptions we found only for the CME peak acceleration significantly lower values than for events that were not associated with filament eruptions. The flare rise time was found to be positively correlated with the CME acceleration duration and negatively correlated with the CME peak acceleration. For the majority of the events the CME acceleration starts before the flare onset (for 75% of the events) and the CME acceleration ends after the soft X-ray (SXR) peak time (for 77% of the events). In {approx}60% of the events, the time difference between the peak time of the flare SXR flux derivative and the peak time of the CME acceleration is smaller than {+-}5 minutes, which hints at a feedback relationship between the CME acceleration and the energy release in the associated flare due to magnetic reconnection.« less

Voltage Fluctuation in a Supercapacitor During a High-g Impact

PubMed Central

Dai, Keren; Wang, Xiaofeng; Yin, Yajiang; Hao, Chenglong; You, Zheng

2016-01-01

Supercapacitors (SCs) are a type of energy storage device with high power density and long lifecycles. They have widespread applications, such as powering electric vehicles and micro scale devices. Working stability is one of the most important properties of SCs, and it is of significant importance to investigate the operational characteristics of SCs working under extreme conditions, particularly during high-g acceleration. In this paper, the failure mechanism of SCs upon high-g impact is thoroughly studied. Through an analysis of the intrinsic reaction mechanism during the high-g impact, a multi-faceted physics model is established. Additionally, a multi-field coupled kinetics simulation of the SC failure during a high-g impact is presented. Experimental tests are conducted that confirm the validity of the proposed model. The key factors of failure, such as discharge currents and discharging levels, are analyzed and discussed. Finally, a possible design is proposed to avoid the failure of SCs upon high-g impact. PMID:27958309

Property Values Associated with the Failure of Individual Links in a System with Multiple Weak and Strong Links.

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

Helton, Jon C.; Brooks, Dusty Marie; Sallaberry, Cedric Jean-Marie.

Representations are developed and illustrated for the distribution of link property values at the time of link failure in the presence of aleatory uncertainty in link properties. The following topics are considered: (i) defining properties for weak links and strong links, (ii) cumulative distribution functions (CDFs) for link failure time, (iii) integral-based derivation of CDFs for link property at time of link failure, (iv) sampling-based approximation of CDFs for link property at time of link failure, (v) verification of integral-based and sampling-based determinations of CDFs for link property at time of link failure, (vi) distributions of link properties conditional onmore » time of link failure, and (vii) equivalence of two different integral-based derivations of CDFs for link property at time of link failure.« less

A Study of Longitudinal Control Problems at Low and Negative Damping and Stability with Emphasis on Effects of Motion Cues

NASA Technical Reports Server (NTRS)

Sadoff, Melvin; McFadden, Norman M.; Heinle, Donovan R.

1961-01-01

As part of a general investigation to determine the effects of simulator motions on pilot opinion and task performance over a wide range of vehicle longitudinal dynamics, a cooperative NASA-AMAL program was conducted on the centrifuge at Johnsville, Pennsylvania. The test parameters and measurements for this program duplicated those of earlier studies made at Ames Research Center with a variable-stability airplane and with a pitch-roll chair flight simulator. Particular emphasis was placed on the minimum basic damping and stability the pilots would accept and on the minimum dynamics they considered controllable in the event of stability-augmentation system failure. Results of the centrifuge-simulator program indicated that small positive damping was required by the pilots over most of the frequency range covered for configurations rated acceptable for emergency conditions only (e.g., failure of a pitch damper). It was shown that the pilot's tolerance for unstable dynamics was dependent primarily on the value of damping. For configurations rated acceptable for emergency operation only, the allowable instability and damping corresponded to a divergence time to double amplitude of about 1 second. Comparisons were made of centrifuge, pitch-chair and fixed-cockpit simulator tests with flight tests. Pilot ratings indicated that the effects of incomplete or spurious motion cues provided by these three modes of simulation were important only for high-frequency, lightly damped dynamics or unstable, moderately damped dynamics. The pitch- chair simulation, which provided accurate angular-acceleration cues to the pilot, compared most favorably with flight. For the centrifuge simulation, which furnished accurate normal accelerations but spurious pitching and longitudinal accelerations, there was a deterioration of pilots' opinion relative to flight results. Results of simulator studies with an analog pilot replacing the human pilot illustrated the adaptive capability of human pilots in coping with the wide range of vehicle dynamics and the control problems covered in this study. It was shown that pilot-response characteristics, deduced by the analog-pilot method, could be related to pilot opinion. Possible application of these results for predicting flight-control problems was illustrated by means of an example control-problem analysis. The results of a brief evaluation of a pencil-type side-arm controller in the centrifuge showed a considerable improvement in the pilots' ability to cope with high-frequency, low-damping dynamics, compared to results obtained with the center stick. This improvement with the pencil controller was attributed primarily to a marked reduction in the adverse effects of large and exaggerated pitching and longitudinal accelerations on pilot control precision.

Accelerated superfractionated radiotherapy for inflammatory breast carcinoma: complete response predicts outcome and allows for breast conservation.

PubMed

Arthur, D W; Schmidt-Ullrich, R K; Friedman, R B; Wazer, D E; Kachnic, L A; Amir, C; Bear, H D; Hackney, M H; Smith, T J; Lawrence, W

1999-05-01

Chemotherapy and accelerated superfractionated radiotherapy were prospectively applied for inflammatory breast carcinoma with the intent of breast conservation. The efficacy, failure patterns, and patient tolerance utilizing this approach were analyzed. Between 1983 and 1996, 52 patients with inflammatory breast carcinoma presented to the Medical College of Virginia Hospitals of VCU and the New England Medical Center. Thirty-eight of these patients were jointly evaluated in multidisciplinary breast clinics and managed according to a defined prospectively applied treatment policy. Patients received induction chemotherapy, accelerated superfractionated radiotherapy, selected use of mastectomy, and concluded with additional chemotherapy. The majority were treated with 1.5 Gy twice daily to field arrangements covering the entire breast and regional lymphatics. An additional 18-21 Gy was then delivered to the breast and clinically involved nodal regions. Total dose to clinically involved areas was 63-66 Gy. Following chemoradiotherapy, patients were evaluated with physical examination, mammogram, and fine needle aspiration x 3. Mastectomy was reserved for those patients with evidence of persistent or progressive disease in the involved breast. All patients received additional chemotherapy. Median age was 51 years. Median follow-up was 23.9 months (6-86) months. The breast preservation rate at the time of last follow-up was 74%. The treated breast or chest wall as the first site of failure occurred in only 13%, and the ultimate local control rate with the selected use of mastectomy was 74%. Ten patients underwent mastectomy, 2 of which had pathologically negative specimens despite a clinically palpable residual mass. Response to chemotherapy was predictive of treatment outcome. Of the 15 patients achieving a complete response, 87% remain locoregionally controlled without the use of mastectomy. Five-year overall survival for complete responders was 68%. This is in contrast to the 14% 5-year overall survival observed with incomplete responders. The 5-year actuarial disease-free survival and overall survival for the entire patient cohort was 11% and 33%, respectively. All patients tolerated irradiation with limited acute effects, of which all were managed conservatively. Our experience demonstrates that induction chemotherapy, accelerated superfractionated radiotherapy, and the selected use of mastectomy results in excellent locoregional control rates, is well tolerated, and optimizes breast preservation. Based on our present results, we recommend that a patient's response to induction chemotherapy guide the treatment approach used for locoregional disease, such that mastectomy be reserved for incomplete responders and avoided in those achieving a complete response.

The Pulse of the Crust: Slow fracture and rapid healing during the seismic cycle (Louis Néel Medal Lecture)

NASA Astrophysics Data System (ADS)

Meredith, Philip

2016-04-01

Earthquake ruptures and volcanic eruptions are the most dramatic manifestations of the dynamic failure of a critically stressed crust. However, these are actually very rare events in both space and time; and most of the crust spends most of its time in a highly stressed but subcritical state. Under upper crustal conditions most rocks accommodate applied stresses in a brittle manner through cracking, fracturing and faulting. Cracks can grow at all scales from the grain scale to the crustal scale, and under different stress regimes. Under tensile stresses, single, long cracks tend to grow at the expense of shorter ones; while under all-round compressive, multiple microcracks tend to coalesce to form macroscopic fractures or faults. Deformation in the crust also occurs over a wide range of strain rates, from the very slow rates associated with tectonic loading up to the very fast rates occurring during earthquake rupture. It is now well-established that reactions between chemically-active pore fluids and the rock matrix can lead to time-dependent, subcritical crack propagation and failure in rocks. In turn, this can allow them to deform and fail over extended periods of time at stresses well below their short-term strength, and even at constant stress; a process known as brittle creep. Such cracking at constant stress eventually leads to accelerated deformation and critical, dynamic failure. However, in the period between sequential dynamic failure events, fractures can become subject to chemically-enhanced time-dependent strength recovery processes such as healing or the growth of mineral veins. We show that such strengthening can be much faster than previously suggested and can occur over geologically very short time-spans. These observations of ultra-slow cracking and ultra-fast healing have profound implications for the evolution and dynamics of the Earth's crust. To obtain a complete understanding of crustal dynamics we require a detailed knowledge of all these time-dependent mechanisms. Such knowledge should be based on micromechanics, but also provide an adequate description at the macroscopic or crustal scale. One way of moving towards this is to establish a relationship between the internal, microstructural state of the rock and the macroscopically observable external quantities. Here, we present a number of examples of attempts to reconcile these ideas through external measurements of stress and strain evolution during deformation with simultaneous measurements of the evolution of key internal variables such as elastic wave speeds, acoustic emission output, porosity and permeability. Overall, the combined data are able to explain both the complexity of stress-strain relations during constant strain rate loading and the shape of creep curves during constant stress loading, thus providing a unifying framework to describe the time-dependent mechanical behaviour of crustal rocks.

Efficient SRAM yield optimization with mixture surrogate modeling

NASA Astrophysics Data System (ADS)

Zhongjian, Jiang; Zuochang, Ye; Yan, Wang

2016-12-01

Largely repeated cells such as SRAM cells usually require extremely low failure-rate to ensure a moderate chi yield. Though fast Monte Carlo methods such as importance sampling and its variants can be used for yield estimation, they are still very expensive if one needs to perform optimization based on such estimations. Typically the process of yield calculation requires a lot of SPICE simulation. The circuit SPICE simulation analysis accounted for the largest proportion of time in the process yield calculation. In the paper, a new method is proposed to address this issue. The key idea is to establish an efficient mixture surrogate model. The surrogate model is based on the design variables and process variables. This model construction method is based on the SPICE simulation to get a certain amount of sample points, these points are trained for mixture surrogate model by the lasso algorithm. Experimental results show that the proposed model is able to calculate accurate yield successfully and it brings significant speed ups to the calculation of failure rate. Based on the model, we made a further accelerated algorithm to further enhance the speed of the yield calculation. It is suitable for high-dimensional process variables and multi-performance applications.

Reliability of Beam Loss Monitor Systems for the Large Hadron Collider

NASA Astrophysics Data System (ADS)

Guaglio, G.; Dehning, B.; Santoni, C.

2005-06-01

The increase of beam energy and beam intensity, together with the use of super conducting magnets, opens new failure scenarios and brings new criticalities for the whole accelerator protection system. For the LHC beam loss protection system, the failure rate and the availability requirements have been evaluated using the Safety Integrity Level (SIL) approach. A downtime cost evaluation is used as input for the SIL approach. The most critical systems, which contribute to the final SIL value, are the dump system, the interlock system, the beam loss monitors system, and the energy monitor system. The Beam Loss Monitors System (BLMS) is critical for short and intense particles losses at 7 TeV and assisted by the Fast Beam Current Decay Monitors at 450 GeV. At medium and higher loss time it is assisted by other systems, such as the quench protection system and the cryogenic system. For BLMS, hardware and software have been evaluated in detail. The reliability input figures have been collected using historical data from the SPS, using temperature and radiation damage experimental data as well as using standard databases. All the data has been processed by reliability software (Isograph). The analysis spaces from the components data to the system configuration.

High Reliability of 0.1 μm InGaAs/InAlAs/InP High Electron Mobility Transistors Microwave Monolithic Integrated Circuit on 3-inch InP Substrates

NASA Astrophysics Data System (ADS)

Chou, Yeong-Chang; Leung, Denise; Lai, Richard; Grundbacher, Ron; Scarpulla, John; Barsky, Mike; Nishimoto, Matt; Eng, David; Liu, Po-Hsin; Oki, Aaron; Streit, Dwight

2002-02-01

The high-reliability performance of K-band microwave monolithic integrated circuit (MMIC) amplifiers fabricated with 0.1 μm gate length InGaAs/InAlAs/InP high electron mobility transistors (HEMTs) on 3-inch wafers using a high volume production process technology is reported. Operating at an accelerated life test condition of Vds=1.5 V and Ids=150 mA/mm, two-stage balanced amplifiers were lifetested at two-temperatures (T1=230°C, and T2=250°C) in nitrogen ambient. The activation energy (Ea) is as high as 1.5 eV, achieving a projected median-time-to-failure (MTTF) >1× 106 h at a 125°C of junction temperature. MTTF was determined by 2-temperature constant current stress using |Δ S21|>1.0 dB as the failure criteria. This is the first report of high reliability 0.1 μm InGaAs/InAlAs/InP HEMT MMICs based on small-signal microwave characteristics. This result demonstrates a reliable InGaAs/InAlAs/InP HEMT production technology.

Space Mechanisms Lessons Learned and Accelerated Testing Studies

NASA Technical Reports Server (NTRS)

Fusaro, Robert L.

1997-01-01

A number of mechanism (mechanical moving component) failures and anomalies have recently occurred on satellites. In addition, more demanding operating and life requirements have caused mechanism failures or anomalies to occur even before some satellites were launched (e.g., during the qualification testing of GOES-NEXT, CERES, and the Space Station Freedom Beta Joint Gimbal). For these reasons, it is imperative to determine which mechanisms worked in the past and which have failed so that the best selection of mechanically moving components can be made for future satellites. It is also important to know where the problem areas are so that timely decisions can be made on the initiation of research to develop future needed technology. To chronicle the life and performance characteristics of mechanisms operating in a space environment, a Space Mechanisms Lessons Learned Study was conducted. The work was conducted by the NASA Lewis Research Center and by Mechanical Technologies Inc. (MTI) under contract NAS3-27086. The expectation of the study was to capture and retrieve information relating to the life and performance of mechanisms operating in the space environment to determine what components had operated successfully and what components had produced anomalies.

Three-dimensional conformal radiation therapy for esophageal squamous cell carcinoma: is elective nodal irradiation necessary?

PubMed

Zhao, Kuai-le; Ma, Jin-bo; Liu, Guang; Wu, Kai-liang; Shi, Xue-hui; Jiang, Guo-liang

2010-02-01

To evaluate the local control, survival, and toxicity associated with three-dimensional conformal radiotherapy (3D-CRT) for squamous cell carcinoma (SCC) of the esophagus, to determine the appropriate target volumes, and to determine whether elective nodal irradiation is necessary in these patients. A prospective study of 3D-CRT was undertaken in patients with esophageal SCC without distant metastases. Patients received 68.4 Gy in 41 fractions over 44 days using late-course accelerated hyperfractionated 3D-CRT. Only the primary tumor and positive lymph nodes were irradiated. Isolated out-of-field regional nodal recurrence was defined as a recurrence in an initially uninvolved regional lymph node. All 53 patients who made up the study population tolerated the irradiation well. No acute or late Grade 4 or 5 toxicity was observed. The median survival time was 30 months (95% confidence interval, 17.7-41.8). The overall survival rate at 1, 2, and 3 years was 77%, 56%, and 41%, respectively. The local control rate at 1, 2, and 3 years was 83%, 74%, and 62%, respectively. Thirty-nine of the 53 patients (74%) showed treatment failure. Seventeen of the 39 (44%) developed an in-field recurrence, 18 (46%) distant metastasis with or without regional failure, and 3 (8%) an isolated out-of-field nodal recurrence only. One patient died of disease in an unknown location. In patients treated with 3D-CRT for esophageal SCC, the omission of elective nodal irradiation was not associated with a significant amount of failure in lymph node regions not included in the planning target volume. Local failure and distant metastases remained the predominant problems. Copyright 2010 Elsevier Inc. All rights reserved.

The Frank-Starling mechanism involves deceleration of cross-bridge kinetics and is preserved in failing human right ventricular myocardium.

PubMed

Milani-Nejad, Nima; Canan, Benjamin D; Elnakish, Mohammad T; Davis, Jonathan P; Chung, Jae-Hoon; Fedorov, Vadim V; Binkley, Philip F; Higgins, Robert S D; Kilic, Ahmet; Mohler, Peter J; Janssen, Paul M L

2015-12-15

Cross-bridge cycling rate is an important determinant of cardiac output, and its alteration can potentially contribute to reduced output in heart failure patients. Additionally, animal studies suggest that this rate can be regulated by muscle length. The purpose of this study was to investigate cross-bridge cycling rate and its regulation by muscle length under near-physiological conditions in intact right ventricular muscles of nonfailing and failing human hearts. We acquired freshly explanted nonfailing (n = 9) and failing (n = 10) human hearts. All experiments were performed on intact right ventricular cardiac trabeculae (n = 40) at physiological temperature and near the normal heart rate range. The failing myocardium showed the typical heart failure phenotype: a negative force-frequency relationship and β-adrenergic desensitization (P < 0.05), indicating the expected pathological myocardium in the right ventricles. We found that there exists a length-dependent regulation of cross-bridge cycling kinetics in human myocardium. Decreasing muscle length accelerated the rate of cross-bridge reattachment (ktr) in both nonfailing and failing myocardium (P < 0.05) equally; there were no major differences between nonfailing and failing myocardium at each respective length (P > 0.05), indicating that this regulatory mechanism is preserved in heart failure. Length-dependent assessment of twitch kinetics mirrored these findings; normalized dF/dt slowed down with increasing length of the muscle and was virtually identical in diseased tissue. This study shows for the first time that muscle length regulates cross-bridge kinetics in human myocardium under near-physiological conditions and that those kinetics are preserved in the right ventricular tissues of heart failure patients. Copyright © 2015 the American Physiological Society.

Reliability evaluation of CMOS RAMs

NASA Astrophysics Data System (ADS)

Salvo, C. J.; Sasaki, A. T.

The results of an evaluation of the reliability of a 1K x 1 bit CMOS RAM and a 4K x 1 bit CMOS RAM for the USAF are reported. The tests consisted of temperature cycling, thermal shock, electrical overstress-static discharge and accelerated life test cells. The study indicates that the devices have high reliability potential for military applications. Use-temperature failure rates at 100 C were 0.54 x 10 to the -5th failures/hour for the 1K RAM and 0.21 x 10 to the -5th failures/hour for the 4K RAM. Only minimal electrostatic discharge damage was noted in the devices when they were subjected to multiple pulses at 1000 Vdc, and redesign of the 7 Vdc quiescent parameter of the 4K RAM is expected to raise its field threshold voltage.

From experiment to design -- Fault characterization and detection in parallel computer systems using computational accelerators

NASA Astrophysics Data System (ADS)

Yim, Keun Soo

This dissertation summarizes experimental validation and co-design studies conducted to optimize the fault detection capabilities and overheads in hybrid computer systems (e.g., using CPUs and Graphics Processing Units, or GPUs), and consequently to improve the scalability of parallel computer systems using computational accelerators. The experimental validation studies were conducted to help us understand the failure characteristics of CPU-GPU hybrid computer systems under various types of hardware faults. The main characterization targets were faults that are difficult to detect and/or recover from, e.g., faults that cause long latency failures (Ch. 3), faults in dynamically allocated resources (Ch. 4), faults in GPUs (Ch. 5), faults in MPI programs (Ch. 6), and microarchitecture-level faults with specific timing features (Ch. 7). The co-design studies were based on the characterization results. One of the co-designed systems has a set of source-to-source translators that customize and strategically place error detectors in the source code of target GPU programs (Ch. 5). Another co-designed system uses an extension card to learn the normal behavioral and semantic execution patterns of message-passing processes executing on CPUs, and to detect abnormal behaviors of those parallel processes (Ch. 6). The third co-designed system is a co-processor that has a set of new instructions in order to support software-implemented fault detection techniques (Ch. 7). The work described in this dissertation gains more importance because heterogeneous processors have become an essential component of state-of-the-art supercomputers. GPUs were used in three of the five fastest supercomputers that were operating in 2011. Our work included comprehensive fault characterization studies in CPU-GPU hybrid computers. In CPUs, we monitored the target systems for a long period of time after injecting faults (a temporally comprehensive experiment), and injected faults into various types of program states that included dynamically allocated memory (to be spatially comprehensive). In GPUs, we used fault injection studies to demonstrate the importance of detecting silent data corruption (SDC) errors that are mainly due to the lack of fine-grained protections and the massive use of fault-insensitive data. This dissertation also presents transparent fault tolerance frameworks and techniques that are directly applicable to hybrid computers built using only commercial off-the-shelf hardware components. This dissertation shows that by developing understanding of the failure characteristics and error propagation paths of target programs, we were able to create fault tolerance frameworks and techniques that can quickly detect and recover from hardware faults with low performance and hardware overheads.

Heroic Reliability Improvement in Manned Space Systems

NASA Technical Reports Server (NTRS)

Jones, Harry W.

2017-01-01

System reliability can be significantly improved by a strong continued effort to identify and remove all the causes of actual failures. Newly designed systems often have unexpected high failure rates which can be reduced by successive design improvements until the final operational system has an acceptable failure rate. There are many causes of failures and many ways to remove them. New systems may have poor specifications, design errors, or mistaken operations concepts. Correcting unexpected problems as they occur can produce large early gains in reliability. Improved technology in materials, components, and design approaches can increase reliability. The reliability growth is achieved by repeatedly operating the system until it fails, identifying the failure cause, and fixing the problem. The failure rate reduction that can be obtained depends on the number and the failure rates of the correctable failures. Under the strong assumption that the failure causes can be removed, the decline in overall failure rate can be predicted. If a failure occurs at the rate of lambda per unit time, the expected time before the failure occurs and can be corrected is 1/lambda, the Mean Time Before Failure (MTBF). Finding and fixing a less frequent failure with the rate of lambda/2 per unit time requires twice as long, time of 1/(2 lambda). Cutting the failure rate in half requires doubling the test and redesign time and finding and eliminating the failure causes.Reducing the failure rate significantly requires a heroic reliability improvement effort.

Microseismic Signature of Magma Failure: Testing Failure Forecast in Heterogeneous Material

NASA Astrophysics Data System (ADS)

Vasseur, J.; Lavallee, Y.; Hess, K.; Wassermann, J. M.; Dingwell, D. B.

2012-12-01

Volcanoes exhibit a range of seismic precursors prior to eruptions. This range of signals derive from different processes, which if quantified, may tell us when and how the volcano will erupt: effusively or explosively. This quantification can be performed in laboratory. Here we investigated the signals associated with the deformation and failure of single-phase silicate liquids compare to mutli-phase magmas containing pores and crystals as heterogeneities. For the past decades, magmas have been simplified as viscoelastic fluids with grossly predictable failure, following an analysis of the stress and strain rate conditions in volcanic conduits. Yet it is clear that the way magmas fail is not unique and evidences increasingly illustrate the role of heterogeneities in the process of magmatic fragmentation. In such multi-phase magmas, failure cannot be predicted using current rheological laws. Microseismicity, as detected in the laboratory by analogous Acoustic Emission (AE), can be used to monitor fracture initiation and propagation, and thus provides invaluable information to characterise the process of brittle failure underlying explosive eruptions. Tri-axial press experiments on different synthetised and natural glass samples have been performed to investigate the acoustic signature of failure. We observed that the failure of single-phase liquids occurs without much strain and is preceded by the constant nucleation, propagation and coalescence of cracks as demonstrated by the monitored AE. In contrast, the failure of multi-phase magmas depends on the applied stress and is strain dependent. The path dependence of magma failure is nonetheless accompanied by supra exponential acceleration in released AEs. Analysis of the released AEs following material Failure Forecast Method (FFM) suggests that the predicability of failure is enhanced by the presence of heterogeneities in magmas. We discuss our observations in terms of volcanic scenarios.

Electromagnetic guided couch and multileaf collimator tracking on a TrueBeam accelerator

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

Hansen, Rune; Ravkilde, Thomas; Worm, Esben Schjødt

2016-05-15

Purpose: Couch and MLC tracking are two promising methods for real-time motion compensation during radiation therapy. So far, couch and MLC tracking experiments have mainly been performed by different research groups, and no direct comparison of couch and MLC tracking of volumetric modulated arc therapy (VMAT) plans has been published. The Varian TrueBeam 2.0 accelerator includes a prototype tracking system with selectable couch or MLC compensation. This study provides a direct comparison of the two tracking types with an otherwise identical setup. Methods: Several experiments were performed to characterize the geometric and dosimetric performance of electromagnetic guided couch and MLCmore » tracking on a TrueBeam accelerator equipped with a Millennium MLC. The tracking system latency was determined without motion prediction as the time lag between sinusoidal target motion and the compensating motion of the couch or MLC as recorded by continuous MV portal imaging. The geometric and dosimetric tracking accuracies were measured in tracking experiments with motion phantoms that reproduced four prostate and four lung tumor trajectories. The geometric tracking error in beam’s eye view was determined as the distance between an embedded gold marker and a circular MLC aperture in continuous MV images. The dosimetric tracking error was quantified as the measured 2%/2 mm gamma failure rate of a low and a high modulation VMAT plan delivered with the eight motion trajectories using a static dose distribution as reference. Results: The MLC tracking latency was approximately 146 ms for all sinusoidal period lengths while the couch tracking latency increased from 187 to 246 ms with decreasing period length due to limitations in the couch acceleration. The mean root-mean-square geometric error was 0.80 mm (couch tracking), 0.52 mm (MLC tracking), and 2.75 mm (no tracking) parallel to the MLC leaves and 0.66 mm (couch), 1.14 mm (MLC), and 2.41 mm (no tracking) perpendicular to the leaves. The motion-induced gamma failure rate was in mean 0.1% (couch tracking), 8.1% (MLC tracking), and 30.4% (no tracking) for prostate motion and 2.9% (couch), 2.4% (MLC), and 41.2% (no tracking) for lung tumor motion. The residual tracking errors were mainly caused by inadequate adaptation to fast lung tumor motion for couch tracking and to prostate motion perpendicular to the MLC leaves for MLC tracking. Conclusions: Couch and MLC tracking markedly improved the geometric and dosimetric accuracies of VMAT delivery. However, the two tracking types have different strengths and weaknesses. While couch tracking can correct perfectly for slowly moving targets such as the prostate, MLC tracking may have considerably larger dose errors for persistent target shift perpendicular to the MLC leaves. Advantages of MLC tracking include faster dynamics with better adaptation to fast moving targets, the avoidance of moving the patient, and the potential to track target rotations and deformations.« less

Reliability Technology to Achieve Insertion of Advanced Packaging (RELTECH) program

NASA Astrophysics Data System (ADS)

Fayette, Daniel F.; Speicher, Patricia; Stoklosa, Mark J.; Evans, Jillian V.; Evans, John W.; Gentile, Mike; Pagel, Chuck A.; Hakim, Edward

1993-08-01

A joint military-commercial effort to evaluate multichip module (MCM) structures is discussed. The program, Reliability Technology to Achieve Insertion of Advanced Packaging (RELTECH), has been designed to identify the failure mechanisms that are possible in MCM structures. The RELTECH test vehicles, technical assessment task, product evaluation plan, reliability modeling task, accelerated and environmental testing, and post-test physical analysis and failure analysis are described. The information obtained through RELTECH can be used to address standardization issues, through development of cost effective qualification and appropriate screening criteria, for inclusion into a commercial specification and the MIL-H-38534 general specification for hybrid microcircuits.

Increased Surface Fatigue Lives of Spur Gears by Application of a Coating

NASA Technical Reports Server (NTRS)

Krantz, Timothy L.; Cooper, Clark V.; Townsend, Dennis P.; Hansen, Bruce D.

2003-01-01

Hard coatings have potential for increasing gear surface fatigue lives. Experiments were conducted using gears both with and without a metal-containing, carbonbased coating. The gears were case-carburized AISI 9310 steel spur gears. Some gears were provided with the coating by magnetron sputtering. Lives were evaluated by accelerated life tests. For uncoated gears, all of fifteen tests resulted in fatigue failure before completing 275 million revolutions. For coated gears, eleven of the fourteen tests were suspended with no fatigue failure after 275 million revolutions. The improved life owing to the coating, approximately a six-fold increase, was a statistically significant result.

Utilization of operating experience to prevent piping failures at steam plants

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

Adams, T.S.; Dietrich, E.B.

1999-11-01

The key to preventing flow-accelerated corrosion (FAC) induced piping failures in steam plants is the development and implementation of a methodical program for assessing plant susceptibility to FAC and managing the effects of FAC. One of the key elements of an effective FAC program is the accurate and comprehensive utilization of plant-specific and industry-wide operating experience. Operating experience should be used to develop the program to identify specific areas for inspection or replacement, and to maintain an effective program. This paper discusses the utilization of operating experience in FAC programs at nuclear power plants, fossil plants and other steam plants.

Reliability Technology to Achieve Insertion of Advanced Packaging (RELTECH) program

NASA Technical Reports Server (NTRS)

Fayette, Daniel F.; Speicher, Patricia; Stoklosa, Mark J.; Evans, Jillian V.; Evans, John W.; Gentile, Mike; Pagel, Chuck A.; Hakim, Edward

1993-01-01

A joint military-commercial effort to evaluate multichip module (MCM) structures is discussed. The program, Reliability Technology to Achieve Insertion of Advanced Packaging (RELTECH), has been designed to identify the failure mechanisms that are possible in MCM structures. The RELTECH test vehicles, technical assessment task, product evaluation plan, reliability modeling task, accelerated and environmental testing, and post-test physical analysis and failure analysis are described. The information obtained through RELTECH can be used to address standardization issues, through development of cost effective qualification and appropriate screening criteria, for inclusion into a commercial specification and the MIL-H-38534 general specification for hybrid microcircuits.

A bivariate model for analyzing recurrent multi-type automobile failures

NASA Astrophysics Data System (ADS)

Sunethra, A. A.; Sooriyarachchi, M. R.

2017-09-01

The failure mechanism in an automobile can be defined as a system of multi-type recurrent failures where failures can occur due to various multi-type failure modes and these failures are repetitive such that more than one failure can occur from each failure mode. In analysing such automobile failures, both the time and type of the failure serve as response variables. However, these two response variables are highly correlated with each other since the timing of failures has an association with the mode of the failure. When there are more than one correlated response variables, the fitting of a multivariate model is more preferable than separate univariate models. Therefore, a bivariate model of time and type of failure becomes appealing for such automobile failure data. When there are multiple failure observations pertaining to a single automobile, such data cannot be treated as independent data because failure instances of a single automobile are correlated with each other while failures among different automobiles can be treated as independent. Therefore, this study proposes a bivariate model consisting time and type of failure as responses adjusted for correlated data. The proposed model was formulated following the approaches of shared parameter models and random effects models for joining the responses and for representing the correlated data respectively. The proposed model is applied to a sample of automobile failures with three types of failure modes and up to five failure recurrences. The parametric distributions that were suitable for the two responses of time to failure and type of failure were Weibull distribution and multinomial distribution respectively. The proposed bivariate model was programmed in SAS Procedure Proc NLMIXED by user programming appropriate likelihood functions. The performance of the bivariate model was compared with separate univariate models fitted for the two responses and it was identified that better performance is secured by the bivariate model. The proposed model can be used to determine the time and type of failure that would occur in the automobiles considered here.

Principal Investigator Microgravity Services Role in ISS Acceleration Data Distribution

NASA Technical Reports Server (NTRS)

McPherson, Kevin

1999-01-01

Measurement of the microgravity acceleration environment on the International Space Station will be accomplished by two accelerometer systems. The Microgravity Acceleration Measurement System will record the quasi-steady microgravity environment, including the influences of aerodynamic drag, vehicle rotation, and venting effects. Measurement of the vibratory/transient regime comprised of vehicle, crew, and equipment disturbances will be accomplished by the Space Acceleration Measurement System-II. Due to the dynamic nature of the microgravity environment and its potential to influence sensitive experiments, Principal Investigators require distribution of microgravity acceleration in a timely and straightforward fashion. In addition to this timely distribution of the data, long term access to International Space Station microgravity environment acceleration data is required. The NASA Glenn Research Center's Principal Investigator Microgravity Services project will provide the means for real-time and post experiment distribution of microgravity acceleration data to microgravity science Principal Investigators. Real-time distribution of microgravity environment acceleration data will be accomplished via the World Wide Web. Data packets from the Microgravity Acceleration Measurement System and the Space Acceleration Measurement System-II will be routed from onboard the International Space Station to the NASA Glenn Research Center's Telescience Support Center. Principal Investigator Microgravity Services' ground support equipment located at the Telescience Support Center will be capable of generating a standard suite of acceleration data displays, including various time domain and frequency domain options. These data displays will be updated in real-time and will periodically update images available via the Principal Investigator Microgravity Services web page.

Minimum-Time and Vibration Avoidance Attitude Maneuver for Spacecraft with Torque and Momentum Limit Constraints in Redundant Reaction Wheel Configuration

NASA Technical Reports Server (NTRS)

Ha, Kong Q.; Femiano, Michael D.; Mosier, Gary E.

2004-01-01

In this paper, we present an optimal open-loop slew trajectory algorithm developed at GSFC for the so-called "Yardstick design" of the James Webb Space Telescope (JWST). JWST is an orbiting infrared observatory featuring a lightweight, segmented primary mirror approximately 6 meters in diameter and a sunshield approximately the size of a tennis court. This large, flexible structure will have significant number of lightly damped, dominant flexible modes. With very stringent requirements on pointing accuracy and image quality, it is important that slewing be done within the required time constraint and with minimal induced vibration in order to maximize observing efficiency. With reaction wheels as control actuators, initial wheel speeds as well as individual wheel torque and momentum limits become dominant constraints in slew performance. These constraints must be taken into account when performing slews to ensure that unexpected reaction wheel saturation does not occur, since such saturation leads to control failure in accurately tracking commanded motion and produces high frequency torque components capable of exciting structural modes. A minimum-time constraint is also included and coupled with reaction wheel limit constraints in the optimization to minimize both the effect of the control torque on the flexible body motion and the maneuver time. The optimization is on slew command parameters, such as maximum slew velocity and acceleration, for a given redundant reaction wheel configuration and is based on the dynamic interaction between the spacecraft and reaction wheel motion. Analytical development of the slew algorithm to generate desired slew position, rate, and acceleration profiles to command a feedback/feed forward control system is described. High-fidelity simulation and experimental results are presented to show that the developed slew law achieves the objectives.

Sex differences in the return-to-work process of cancer survivors 2 years after diagnosis: results from a large French population-based sample.

PubMed

Marino, Patricia; Teyssier, Luis Sagaon; Malavolti, Laetitia; Le Corroller-Soriano, Anne-Gaelle

2013-04-01

To investigate the effects of clinical, sociodemographic, and occupational factors on time to return to work (RTW) during the 2 years after cancer diagnosis and to analyze whether sex differences exist. This study was based on a French national cross-sectional survey involving 4,270 cancer survivors. Time to RTW was estimated through the duration of sick leave of 801 cancer survivors younger than 58 years who were employed during the 2-year survey. Multivariate analysis of the RTW after sick leave was performed using a Weibull accelerated failure time model. We found some sex differences in the RTW process. Older men returned to work more slowly than older women (P = .013), whereas married men returned to work much faster than married women (P = .019). Duration dependence was also sex-specific. In men, the time spent on sick leave was independent of the probability of returning to work, whereas in women, this duration dependence was positive (P < .001). For both men and women, clinical factors including chemotherapy, adverse effects, and cancer severity were found to delay RTW (P = .035, P = .001, and P < .001, respectively). Survivors investing most strongly in their personal lives also delayed their RTW (P = .006), as did those with a permanent work contract (P = .042). The factor found to accelerate RTW was a higher educational level (P = .014). The RTW process 2 years after cancer diagnosis differed between men and women. A better knowledge of this process should help the national implementation of more cost-effective strategies for managing the RTW of cancer survivors.

Acceleration characteristics of human ocular accommodation.

PubMed

Bharadwaj, Shrikant R; Schor, Clifton M

2005-01-01

Position and velocity of accommodation are known to increase with stimulus magnitude, however, little is known about acceleration properties. We investigated three acceleration properties: peak acceleration, time-to-peak acceleration and total duration of acceleration to step changes in defocus. Peak velocity and total duration of acceleration increased with response magnitude. Peak acceleration and time-to-peak acceleration remained independent of response magnitude. Independent first-order and second-order dynamic components of accommodation demonstrate that neural control of accommodation has an initial open-loop component that is independent of response magnitude and a closed-loop component that increases with response magnitude.

Dual Pathways from Reactive Aggression to Depressive Symptoms in Children: Further Examination of the Failure Model.

PubMed

Evans, Spencer C; Fite, Paula J

2018-04-13

The failure model posits that peer rejection and poor academic performance are dual pathways in the association between early aggressive behavior and subsequent depressive symptoms. We examined this model using an accelerated longitudinal design while also incorporating proactive and reactive aggression and gender moderation. Children in 1st, 3rd, and 5th grades (n = 912; ages 6-12; 48% female) were rated three times annually by their primary teachers on measures of proactive and reactive aggression, peer rejection, academic performance, and depressive symptoms. Using Bayesian cross-classified estimation to account for nested and planned-missing data, path models were estimated to examine whether early reactive aggression predicted subsequent peer rejection and academic performance, and whether these, in turn, predicted subsequent depressive symptoms. From 1st to 3rd grade, reactive aggression predicted peer rejection (not academic performance), proactive aggression predicted academic performance (not peer rejection), and academic performance and peer rejection both predicted depressive symptoms. From 3rd to 5th grade, however, neither peer rejection nor academic performance predicted subsequent depressive symptoms. Results were not moderated by gender. Overall, these findings provide mixed and limited support for the failure model among school-age children. Early reactive aggression may be a key risk factor for social problems, whereas proactive aggression may be linked to improved academic functioning. The "dual pathways" of peer rejection and academic performance may operate during early but not later elementary school. Limitations and implications are discussed.

Antimicrobial resistance and biological governance: explanations for policy failure.

PubMed

Wallinga, D; Rayner, G; Lang, T

2015-10-01

The paper reviews the state of policy on antimicrobial use and the growth of antimicrobial resistance (AMR). AMR was anticipated at the time of the first use of antibiotics by their originators. For decades, reports and scientific papers have expressed concern about AMR at global and national policy levels, yet the problem, first exposed a half-century ago, worsened. The paper considers the explanations for this policy failure and the state of arguments about ways forward. These include: a deficit of economic incentivisation; complex interventions in behavioural dynamics; joint and separate shifts in medical and animal health regimes; consumerism; belief in technology; and a narrative that in a 'war on bugs' nature can be beaten by human ingenuity. The paper suggests that these narratives underplay the biological realities of the human-animal-biosphere being in constant flux, an understanding which requires an ecological public health analysis of AMR policy development and failure. The paper suggests that effective policy change requires simultaneous actions across policy levels. No single solution is possible, since AMR is the result of long-term human intervention which has accelerated certain trends in the evolution of a microbial ecosystem shared by humans, animals and other biological organisms inhabiting that ecosystem. Viewing the AMR crisis today through an ecological public health lens has the advantage of reuniting the social-ecological and bio-ecological perspectives which have been separated within public health. Copyright © 2015 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.

Schwann cell glycogen selectively supports myelinated axon function.

PubMed

Brown, Angus M; Evans, Richard D; Black, Joel; Ransom, Bruce R

2012-09-01

Interruption of energy supply to peripheral axons is a cause of axon loss. We determined whether glycogen was present in mammalian peripheral nerve, and whether it supported axon conduction during aglycemia. We used biochemical assay and electron microscopy to determine the presence of glycogen, and electrophysiology to monitor axon function. Glycogen was present in sciatic nerve, its concentration varying directly with ambient glucose. Electron microscopy detected glycogen granules primarily in myelinating Schwann cell cytoplasm, and these diminished after exposure to aglycemia. During aglycemia, conduction failure in large myelinated axons (A fibers) mirrored the time course of glycogen loss. Latency to compound action potential (CAP) failure was directly related to nerve glycogen content at aglycemia onset. Glycogen did not benefit the function of slow-conducting, small-diameter unmyelinated axons (C fibers) during aglycemia. Blocking glycogen breakdown pharmacologically accelerated CAP failure during aglycemia in A fibers, but not in C fibers. Lactate was as effective as glucose in supporting sciatic nerve function, and was continuously released into the extracellular space in the presence of glucose and fell rapidly during aglycemia. Our findings indicated that glycogen is present in peripheral nerve, primarily in myelinating Schwann cells, and exclusively supports large-diameter, myelinated axon conduction during aglycemia. Available evidence suggests that peripheral nerve glycogen breaks down during aglycemia and is passed, probably as lactate, to myelinated axons to support function. Unmyelinated axons are not protected by glycogen and are more vulnerable to dysfunction during periods of hypoglycemia. . Copyright © 2012 American Neurological Association.

Reduction in pediatric identification band errors: a quality collaborative.

PubMed

Phillips, Shannon Connor; Saysana, Michele; Worley, Sarah; Hain, Paul D

2012-06-01

Accurate and consistent placement of a patient identification (ID) band is used in health care to reduce errors associated with patient misidentification. Multiple safety organizations have devoted time and energy to improving patient ID, but no multicenter improvement collaboratives have shown scalability of previously successful interventions. We hoped to reduce by half the pediatric patient ID band error rate, defined as absent, illegible, or inaccurate ID band, across a quality improvement learning collaborative of hospitals in 1 year. On the basis of a previously successful single-site intervention, we conducted a self-selected 6-site collaborative to reduce ID band errors in heterogeneous pediatric hospital settings. The collaborative had 3 phases: preparatory work and employee survey of current practice and barriers, data collection (ID band failure rate), and intervention driven by data and collaborative learning to accelerate change. The collaborative audited 11377 patients for ID band errors between September 2009 and September 2010. The ID band failure rate decreased from 17% to 4.1% (77% relative reduction). Interventions including education of frontline staff regarding correct ID bands as a safety strategy; a change to softer ID bands, including "luggage tag" type ID bands for some patients; and partnering with families and patients through education were applied at all institutions. Over 13 months, a collaborative of pediatric institutions significantly reduced the ID band failure rate. This quality improvement learning collaborative demonstrates that safety improvements tested in a single institution can be disseminated to improve quality of care across large populations of children.

Schwann Cell Glycogen Selectively Supports Myelinated Axon Function

PubMed Central

Brown, Angus M; Evans, Richard D; Black, Joel; Ransom, Bruce R

2012-01-01

Objectives Interruption of energy supply to peripheral axons is a cause of axon loss. We determined if glycogen was present in mammalian peripheral nerve, and if it supported axon conduction during aglycemia. Methods We used biochemical assay and electron microscopy to determine the presence of glycogen, and electrophysiology to monitor axon function. Results Glycogen was present in sciatic nerve, its concentration varying directly with ambient [glucose]. Electron microscopy detected glycogen granules primarily in myelinating Schwann cell cytoplasm and these diminished after exposure to aglycemia. During aglycemia, conduction failure in large myelinated axons (A fibers) mirrored the time-course of glycogen loss. Latency to CAP failure was directly related to nerve glycogen content at aglycemia onset. Glycogen did not benefit the function of slow-conducting, small diameter unmyelinated axons (C fibers) during aglycemia. Blocking glycogen breakdown pharmacologically accelerated CAP failure during aglycemia in A fibers, but not in C fibers. Lactate was as effective as glucose in supporting sciatic nerve function, and was continuously released into the extracellular space in the presence of glucose and fell rapidly during aglycemia. Interpretation Our findings indicated that glycogen is present in peripheral nerve, primarily in myelinating Schwann cells, and exclusively supports large diameter, myelinated axon conduction during aglycemia. Available evidence suggests that peripheral nerve glycogen breaks down during aglycemia and is passed, probably as lactate, to myelinated axons to support function. Unmyelinated axons are not protected by glycogen and are more vulnerable to dysfunction during periods of hypoglycemia. PMID:23034913

A Computer Code for Dynamic Stress Analysis of Media-Structure Problems with Nonlinearities (SAMSON). Volume III. User’s Manual.

DTIC Science & Technology

NONLINEAR SYSTEMS, LINEAR SYSTEMS, SUBROUTINES , SOIL MECHANICS, INTERFACES, DYNAMICS, LOADS(FORCES), FORCE(MECHANICS), DAMPING, ACCELERATION, ELASTIC...PROPERTIES, PLASTIC PROPERTIES, CRACKS , REINFORCING MATERIALS , COMPOSITE MATERIALS , FAILURE(MECHANICS), MECHANICAL PROPERTIES, INSTRUCTION MANUALS, DIGITAL COMPUTERS...STRESSES, *COMPUTER PROGRAMS), (*STRUCTURES, STRESSES), (*DATA PROCESSING, STRUCTURAL PROPERTIES), SOILS , STRAIN(MECHANICS), MATHEMATICAL MODELS

Safety assessment of historical masonry churches based on pre-assigned kinematic limit analysis, FE limit and pushover analyses

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

Milani, Gabriele, E-mail: milani@stru.polimi.it; Valente, Marco, E-mail: milani@stru.polimi.it

2014-10-06

This study presents some results of a comprehensive numerical analysis on three masonry churches damaged by the recent Emilia-Romagna (Italy) seismic events occurred in May 2012. The numerical study comprises: (a) pushover analyses conducted with a commercial code, standard nonlinear material models and two different horizontal load distributions; (b) FE kinematic limit analyses performed using a non-commercial software based on a preliminary homogenization of the masonry materials and a subsequent limit analysis with triangular elements and interfaces; (c) kinematic limit analyses conducted in agreement with the Italian code and based on the a-priori assumption of preassigned failure mechanisms, where themore » masonry material is considered unable to withstand tensile stresses. All models are capable of giving information on the active failure mechanism and the base shear at failure, which, if properly made non-dimensional with the weight of the structure, gives also an indication of the horizontal peak ground acceleration causing the collapse of the church. The results obtained from all three models indicate that the collapse is usually due to the activation of partial mechanisms (apse, façade, lateral walls, etc.). Moreover the horizontal peak ground acceleration associated to the collapse is largely lower than that required in that seismic zone by the Italian code for ordinary buildings. These outcomes highlight that structural upgrading interventions would be extremely beneficial for the considerable reduction of the seismic vulnerability of such kind of historical structures.« less

Seismically induced rock slope failures resulting from topographic amplification of strong ground motions: The case of Pacoima Canyon, California

USGS Publications Warehouse

Sepulveda, S.A.; Murphy, W.; Jibson, R.W.; Petley, D.N.

2005-01-01

The 1994 Northridge earthquake (Mw = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (Mw = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses. ?? 2005 Elsevier B.V. All rights reserved.

Time-dependent brittle deformation (creep) at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2009-04-01

Mt. Etna is the largest and most active volcano in Europe. Time-dependent weakening mechanisms, leading to slow fracturing, have been shown to act during pre-eruptive patterns of flank eruptions at Mt. Etna volcano. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Time-dependent brittle deformation at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Baud, Patrick; Heap, Michael; Meredith, Philip; Vinciguerra, Sergio; Bell, Andrew; Main, Ian

2010-05-01

Time-dependent weakening mechanisms, leading to slow fracturing, are likely to act during the build up to flank eruptions at Mt. Etna volcano and are potentially a primary control on pre-eruptive patterns of seismicity and deformation. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts a large water reservoir (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations and inverse seismicity plots using our experimental AE data. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Torque-based optimal acceleration control for electric vehicle

NASA Astrophysics Data System (ADS)

Lu, Dongbin; Ouyang, Minggao

2014-03-01

The existing research of the acceleration control mainly focuses on an optimization of the velocity trajectory with respect to a criterion formulation that weights acceleration time and fuel consumption. The minimum-fuel acceleration problem in conventional vehicle has been solved by Pontryagin's maximum principle and dynamic programming algorithm, respectively. The acceleration control with minimum energy consumption for battery electric vehicle(EV) has not been reported. In this paper, the permanent magnet synchronous motor(PMSM) is controlled by the field oriented control(FOC) method and the electric drive system for the EV(including the PMSM, the inverter and the battery) is modeled to favor over a detailed consumption map. The analytical algorithm is proposed to analyze the optimal acceleration control and the optimal torque versus speed curve in the acceleration process is obtained. Considering the acceleration time, a penalty function is introduced to realize a fast vehicle speed tracking. The optimal acceleration control is also addressed with dynamic programming(DP). This method can solve the optimal acceleration problem with precise time constraint, but it consumes a large amount of computation time. The EV used in simulation and experiment is a four-wheel hub motor drive electric vehicle. The simulation and experimental results show that the required battery energy has little difference between the acceleration control solved by analytical algorithm and that solved by DP, and is greatly reduced comparing with the constant pedal opening acceleration. The proposed analytical and DP algorithms can minimize the energy consumption in EV's acceleration process and the analytical algorithm is easy to be implemented in real-time control.

Catastrophic optical bulk degradation in high-power single- and multi-mode InGaAs-AlGaAs strained QW lasers: part II

NASA Astrophysics Data System (ADS)

Sin, Yongkun; Ayvazian, Talin; Brodie, Miles; Lingley, Zachary

2018-03-01

High-power single-mode (SM) and multi-mode (MM) InGaAs-AlGaAs strained quantum well (QW) lasers are critical components for both terrestrial and space satellite communications systems. Since these lasers predominantly fail by catastrophic and sudden degradation due to catastrophic optical damage (COD), it is especially crucial for space satellite applications to investigate reliability, failure modes, precursor signatures of failure, and degradation mechanisms of these lasers. Our group reported a new failure mode in MM and SM InGaAs-AlGaAs strained QW lasers in 2009 and 2016, respectively. Our group also reported in 2017 that bulk failure due to catastrophic optical bulk damage (COBD) is the dominant failure mode of both SM and MM lasers that were subject to long-term life-tests. For the present study, we continued our physics of failure investigation by performing long-term life-tests followed by failure mode analysis (FMA) using nondestructive and destructive micro-analytical techniques. We performed long-term accelerated life-tests on state-of-the-art SM and MM InGaAs- AlGaAs strained QW lasers under ACC mode. Our life-tests have accumulated over 25,000 test hours for SM lasers and over 35,000 test hours for MM lasers. We first employed electron beam induced current (EBIC) technique to identify failure modes of degraded SM lasers by observing dark line defects. All the SM failures that we studied showed catastrophic and sudden degradation and all of these failures were bulk failures. Since degradation mechanisms responsible for COBD are still not well understood, we also employed other techniques including focused ion beam (FIB) and high-resolution TEM to further study dark line defects and dislocations in post-aged lasers. Keywor

Time series analysis of tool wear in sheet metal stamping using acoustic emission

NASA Astrophysics Data System (ADS)

Vignesh Shanbhag, V.; Pereira, P. Michael; Rolfe, F. Bernard; Arunachalam, N.

2017-09-01

Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stamping tools represent significant economic cost, even a slight improvement in maintenance cost is of high importance for the stamping industry. In other manufacturing industries, online tool condition monitoring has been used to prevent tool wear-related failure. However, monitoring the acoustic emission signal from a stamping process is a non-trivial task since the acoustic emission signal is non-stationary and non-transient. There have been numerous studies examining acoustic emissions in sheet metal stamping. However, very few have focused in detail on how the signals change as wear on the tool surface progresses prior to failure. In this study, time domain analysis was applied to the acoustic emission signals to extract features related to tool wear. To understand the wear progression, accelerated stamping tests were performed using a semi-industrial stamping setup which can perform clamping, piercing, stamping in a single cycle. The time domain features related to stamping were computed for the acoustic emissions signal of each part. The sidewalls of the stamped parts were scanned using an optical profilometer to obtain profiles of the worn part, and they were qualitatively correlated to that of the acoustic emissions signal. Based on the wear behaviour, the wear data can be divided into three stages: - In the first stage, no wear is observed, in the second stage, adhesive wear is likely to occur, and in the third stage severe abrasive plus adhesive wear is likely to occur. Scanning electron microscopy showed the formation of lumps on the stamping tool, which represents galling behavior. Correlation between the time domain features of the acoustic emissions signal and the wear progression identified in this study lays the basis for tool diagnostics in stamping industry.

Capturing pre-failure signs of slope instability using multi-temporal interferometry and Sentinel-1 data

NASA Astrophysics Data System (ADS)

Wasowski, Janusz; Bovenga, Fabio; Nitti, Davide Oscar; Tijani, Khalid; Morea, Alberto; Nutricato, Raffaele; Chiaradia, Maria Teresa

2017-04-01

The shorter repeat cycle (6 days since October 2016) and regularity of acquisitions of Sentinel-1A/B with respect to earlier European Space Agency (ESA) satellites with C-band sensors (ERS1/2, ENVISAT) represent the key advantages for the research-oriented and practical applications of multi-temporal interferometry (MTI). The applicability of the Interferometric Wide Swath acquisition mode of Sentinel-1 (images covering a 250 km swath on the ground) to regional scale slope instability detection through MTI has already been demonstrated, e.g., via studies of landslide-prone areas in Italy. Here we focus on the potential of Sentinel-1 data for local (site-specific), MTI-based monitoring and capturing pre-failure signs of slope instability, by exploiting the Persistent and Distributed Scatterers processing capability of the SPINUA algorithm. In particular, we present an example of a retrospective study of a large (over 2 km long) landslide, which took place in 2016 in an active open-cast coal mine in central Europe. This seemingly sudden failure caused destruction of the mining equipment, blocked the mining operations thereby resulting in significant economic losses. For the study, we exploited over 60 Sentinel-1A/B images acquired since November 2014. The MTI results furnished a valuable overview of the ground instability/stability conditions within and around the active mine, even though considerable spatial gaps in information were encountered due to surface disturbance by mining operations. Significantly, the ground surface displacement time series revealed that the 2016 slope failure was preceded by very slow (generally 1-3 cm/yr) creep-like deformations, already present in 2014. The MTI results also indicated that the slope experienced a phase of accelerated movement several weeks prior to the landslide event. Furthermore, the spatio-temporal analysis of interferometric coherence changes in the unstable area (mapped on Sentinel-2 Bottom Of Atmosphere reflectance images processed by using the ESA Sen2Cor processor), indicated a sharp coherence loss in the last few weeks before the slope collapse. The availability of more frequent measurements represents a key improvement for MTI-based ground surface displacement monitoring and this will better support research on slope destabilization processes over time and, ultimately, on slope failure forecasting. Acknowledgments We thank ESA for Sentinel-1 & Sentinel-2 images.

Desirable limits of accelerative forces in a space-based materials processing facility

NASA Technical Reports Server (NTRS)

Naumann, Robert J.

1990-01-01

There are three categories of accelerations to be encountered on orbiting spacecraft: (1) quasi-steady accelerations, caused by atmospheric drag or by gravity gradients, 10(exp -6) to 10(exp -7) g sub o; (2) transient accelerations, caused by movements of the astronauts, mass translocations, landing and departure of other spacecraft, etc.; and (3) oscillary accelerations, caused by running machinery (fans, pumps, generators). Steady accelerations cause continuing displacements; transients cause time-limited displacements. The important aspect is the area under the acceleration curve, measured over a certain time interval. Note that this quantity is not equivalent to a velocity because of friction effects. Transient motions are probably less important than steady accelerations because they only produce constant displacements. If the accelerative forces were not equal and opposite, the displacement would increase with time. A steady acceleration will produce an increasing velocity of a particle, but eventually an equilibrium value will be reached where drag and acceleration forces are equal. From then on, the velocity will remain constant, and the displacement will increase linearly with time.