Semi-analytical solution of time-dependent thermomechanical creep behavior of FGM hollow spheres
NASA Astrophysics Data System (ADS)
Jafari Fesharaki, J.; Loghman, A.; Yazdipoor, M.; Golabi, S.
2014-02-01
By using a method of successive elastic solution, the time-dependent creep behavior of a functionally graded hollow sphere under thermomechanical loads has been investigated. Based on volume percentage, the mechanical and thermal properties of material, except for the Poisson's ratio, are assumed to be radially dependent. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are temperature-, stress- and time-dependent. Using the Prandtl-Reuss relations and Sherby's law, histories of stresses and strains are presented from their initial elastic values at zero time up to 30 years after loading. The results show that the creep stresses and strains change with time and material inhomogeneity has influence on thermomechanical creep behavior. The aim of this work was to understand the effect of creep behavior on a functionally graded hollow sphere subjected to thermomechanical load.
Time-Dependent Behaviors of Granite: Loading-Rate Dependence, Creep, and Relaxation
NASA Astrophysics Data System (ADS)
Hashiba, K.; Fukui, K.
2016-07-01
To assess the long-term stability of underground structures, it is important to understand the time-dependent behaviors of rocks, such as their loading-rate dependence, creep, and relaxation. However, there have been fewer studies on crystalline rocks than on tuff, mudstone, and rock salt, because the high strength of crystalline rocks makes the detection of their time-dependent behaviors much more difficult. Moreover, studies on the relaxation, temporal change of stress and strain (TCSS) conditions, and relations between various time-dependent behaviors are scarce for not only granites, but also other rocks. In this study, previous reports on the time-dependent behaviors of granites were reviewed and various laboratory tests were conducted using Toki granite. These tests included an alternating-loading-rate test, creep test, relaxation test, and TCSS test. The results showed that the degree of time dependence of Toki granite is similar to other granites, and that the TCSS resembles the stress-relaxation curve and creep-strain curve. A viscoelastic constitutive model, proposed in a previous study, was modified to investigate the relations between the time-dependent behaviors in the pre- and post-peak regions. The modified model reproduced the stress-strain curve, creep, relaxation, and the results of the TCSS test. Based on a comparison of the results of the laboratory tests and numerical simulations, close relations between the time-dependent behaviors were revealed quantitatively.
A novel time dependent gamma evaluation function for dynamic 2D and 3D dose distributions
NASA Astrophysics Data System (ADS)
Podesta, Mark; CGG Persoon, Lucas; Verhaegen, Frank
2014-10-01
Modern external beam radiotherapy requires detailed verification and quality assurance so that confidence can be placed on both the delivery of a single treatment fraction and on the consistency of delivery throughout the treatment course. To verify dose distributions, a comparison between prediction and measurement must be made. Comparisons between two dose distributions are commonly performed using a Gamma evaluation which is a calculation of two quantities on a pixel by pixel basis; the dose difference, and the distance to agreement. By providing acceptance criteria (e.g. 3%, 3 mm), the function will find the most appropriate match within its two degrees of freedom. For complex dynamic treatments such as IMRT or VMAT it is important to verify the dose delivery in a time dependent manner and so a gamma evaluation that includes a degree of freedom in the time domain via a third parameter, time to agreement, is presented here. A C++ (mex) based gamma function was created that could be run on either CPU and GPU computing platforms that would allow a degree of freedom in the time domain. Simple test cases were created in both 2D and 3D comprising of simple geometrical shapes with well-defined boundaries varying over time. Changes of varying magnitude in either space or time were introduced and repeated gamma analyses were performed varying the criteria. A clinical VMAT case was also included, artificial air bubbles of varying size were introduced to a patient geometry, along with shifts of varying magnitude in treatment time. For all test cases where errors in distance, dose or time were introduced, the time dependent gamma evaluation could accurately highlight the errors. The time dependent gamma function presented here allows time to be included as a degree of freedom in gamma evaluations. The function allows for 2D and 3D data sets which are varying over time to be compared using appropriate criteria without penalising minor offsets of subsequent radiation
A novel time dependent gamma evaluation function for dynamic 2D and 3D dose distributions.
Podesta, Mark; Persoon, Lucas C G G; Verhaegen, Frank
2014-10-21
Modern external beam radiotherapy requires detailed verification and quality assurance so that confidence can be placed on both the delivery of a single treatment fraction and on the consistency of delivery throughout the treatment course. To verify dose distributions, a comparison between prediction and measurement must be made. Comparisons between two dose distributions are commonly performed using a Gamma evaluation which is a calculation of two quantities on a pixel by pixel basis; the dose difference, and the distance to agreement. By providing acceptance criteria (e.g. 3%, 3 mm), the function will find the most appropriate match within its two degrees of freedom. For complex dynamic treatments such as IMRT or VMAT it is important to verify the dose delivery in a time dependent manner and so a gamma evaluation that includes a degree of freedom in the time domain via a third parameter, time to agreement, is presented here. A C++ (mex) based gamma function was created that could be run on either CPU and GPU computing platforms that would allow a degree of freedom in the time domain. Simple test cases were created in both 2D and 3D comprising of simple geometrical shapes with well-defined boundaries varying over time. Changes of varying magnitude in either space or time were introduced and repeated gamma analyses were performed varying the criteria. A clinical VMAT case was also included, artificial air bubbles of varying size were introduced to a patient geometry, along with shifts of varying magnitude in treatment time. For all test cases where errors in distance, dose or time were introduced, the time dependent gamma evaluation could accurately highlight the errors.The time dependent gamma function presented here allows time to be included as a degree of freedom in gamma evaluations. The function allows for 2D and 3D data sets which are varying over time to be compared using appropriate criteria without penalising minor offsets of subsequent radiation fields
Visual Analysis of time-dependent 2D Uncertainties in Decadal Climate Predictions
NASA Astrophysics Data System (ADS)
Böttinger, Michael; Röber, Niklas; Meier-Fleischer, Karin; Pohlmann, Holger
2016-04-01
Climate prediction systems used today for investigating the climate predictability on a decadal time scale are based on coupled global climate models. First, ensembles of hindcast experiments are carried out in order to derive the predictive skill of the prediction system. Then, in a second step, the prediction system is initialized with observations and actual future predictions are computed. The ensemble simulation techniques applied enable issuing of probabilistic information along with the quantities predicted. Different aspects of the uncertainty can be derived: The ensemble standard deviation (or ensemble spread) is a measure for the internal variability of the simulation, while the predictive skill is an inverse measure for the uncertainty in the prediction. In this work, we focus on the concurrent visualization of three related time-dependent 2D fields: the forecast variable itself, here the 2m temperature anomaly, along with the corresponding predictive skill and the ensemble spread which is given through the ensemble standard deviation. On the basis of temporally filtered data, animations are used to visualize the mean spatio-temporal development of the three quantities. Furthermore, seasonal analyses are similarly visualized in order to identify seasonal patterns. We show exemplary solutions produced with three different visualization systems: NCL, Avizo Green and ParaView. As example data set, we have used a decadal climate prediction carried out within the German research project "MiKlip - Decadal Predictions" using the MPI-M Earth System Model (MPI-ESM) from the Max Planck Institute for Meteorology in Hamburg.
WREM--TOODEE2--MOD3. 2d Time-Dependent Fuel Element Study
Lauben, G.N.
1992-03-05
WREM-TOODEE2 is a two dimensional, time-dependent, fuel-element thermal analysis program. Its primary purpose is to evaluate fuel-element thermal response during post-LOCA refill and reflood in a pressurized water reactor (PWR).
NASA Astrophysics Data System (ADS)
Brzesowsky, R. H.; Hangx, S. J. T.; Brantut, N.; Spiers, C. J.
2014-10-01
Time-dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production-induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical behavior of gouge-rich faults. We performed uniaxial creep experiments on sand to investigate the effects of chemical environment (dry versus solution flooded), grain size (d = 196-378 µm), and applied effective stress (σa up to 30 MPa), at room temperature conditions favoring grain-scale brittle processes. Creep measurements were complemented with acoustic emission (AE) detection and microstructural analysis to characterize the main creep mechanism. Wet samples showed much higher creep strains than dry-tested samples. AE event counts showed a direct relation between grain failure and creep strain, with higher AE rates occurring in the wet samples. Therefore, we inferred that time-dependent deformation was dominated by subcritical crack growth, resulting in grain failure accompanied by intergranular sliding rearrangements, and that crack growth in the presence of chemically active fluids was controlled by stress corrosion. The sensitivity of the compaction rate of the sands to d and σa can be expressed as ɛ˙∝diσaj where i ≈ 6 and j ≈ 21 under dry conditions and i ≈ 9 and j ≈ 15 under wet conditions. Our results were compared to a simple model based on Hertzian contact theory, linear elastic fracture mechanics, and subcritical crack growth. This model showed agreement between the observed stress and grain size sensitivities of creep, within a factor of 2.
2-D Time-Dependent Fuel Element, Thermal Analysis Code System.
2001-09-24
Version 00 WREM-TOODEE2 is a two dimensional, time-dependent, fuel-element thermal analysis program. Its primary purpose is to evaluate fuel-element thermal response during post-LOCA refill and reflood in a pressurized water reactor (PWR). TOODEE2 calculations are carried out in a two-dimensional mesh region defined in slab or cylindrical geometry by orthogonal grid lines. Coordinates which form order pairs are labeled x-y in slab geometry, and those in cylindrical geometry are labeled r-z for the axisymmetric casemore » and r-theta for the polar case. Conduction and radiation are the only heat transfer mechanisms assumed within the boundaries of the mesh region. Convective and boiling heat transfer mechanisms are assumed at the boundaries. The program numerically solves the two-dimensional, time-dependent, heat conduction equation within the mesh region. KEYWORDS: FUEL MANAGEMENT; HEAT TRANSFER; LOCA; PWR« less
NASA Astrophysics Data System (ADS)
Shirzaei, M.; Bürgmann, R.
2013-04-01
Spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults. To solve for a time-dependent model of creep on the Hayward fault, we invert 18 years of surface deformation data (1992-2010), obtained by interferometric processing of 52 and 50 SAR images acquired by the ERS1/2 and Envisat satellites, respectively, and surface creep data obtained at 19 alinement and 4 creepmeter stations. For multi-temporal analysis of the SAR data we developed a method for identifying stable pixels using wavelet multi-resolution analysis. We also implement a variety of wavelet-based filters for reducing the effects of environmental artifacts. Using a reweighted least squares approach, we inverted the interferometric data to generate a time series of surface deformation over the San Francisco Bay Area with a precision of better than a few millimeters. To jointly invert the InSAR displacement time series and the surface creep data for a time-dependent model of fault creep, we use a robust inversion approach combined with a Kalman filter. The time-dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future M≈7 earthquakes. We identify several additional temporal variations in creep rate along the Hayward fault, the most important one being a zone of accelerating slip just northwest of the major locked zone. We estimate that a slip-rate deficit equivalent to Mw 6.3-6.8 has accumulated on the fault, since the last event in 1868.
2D simulations based on general time-dependent reciprocal relation for LFEIT.
Karadas, Mursel; Gencer, Nevzat Guneri
2015-08-01
Lorentz field electrical impedance tomography (LFEIT) is a newly proposed technique for imaging the conductivity of the tissues by measuring the electromagnetic induction under the ultrasound pressure field. In this paper, the theory and numerical simulations of the LFEIT are reported based on the general time dependent formulation. In LFEIT, a phased array ultrasound probe is used to introduce a current distribution inside a conductive body. The velocity current occurs, due to the movement of the conductive particles under a static magnetic field. In order to sense this current, a receiver coil configuration that surrounds the volume conductor is utilized. Finite Element Method (FEM) is used to carry out the simulations of LFEIT. It is shown that, LFEIT can be used to reconstruct the conductivity even up to 50% perturbation in the initial conductivity distribution. PMID:26736569
A time dependent 2D divertor code with TVD scheme for complex divertor configurations
NASA Astrophysics Data System (ADS)
Shimizu, K.; Takizuka, T.; Hirayama, T.
1999-11-01
In order to study the transport of heat and particles in the SOL and divertor plasmas, a two-dimensional divertor code, SOLDOR has been developed. The model used in this code is identical to the B2-code. Fluid equations are discretized in space under a non orthogonal mesh to treat accurately the W shape divertor configuration of JT-60U. The total variation diminishing scheme (TVD), which is a most familiar one in computational fluid dynamics, is applied for convective terms. The equations obtained by a finite volume method (FVM) are discretized in time with a full implicit scheme and are solved time-dependently using the Newton-Raphson method. The discretized equations are solved efficiently using approximate factorization method (AF). Test calculations in the slab geometry successfully reproduced the B2 results (B.J. Braams, NET report 1987) . We are going to apply this code to JT-60U divertor plasma and investigate the flow reversal and impurity transport.
Time dependent inflow-outflow boundary conditions for 2D acoustic systems
NASA Technical Reports Server (NTRS)
Watson, Willie R.; Myers, Michael K.
1989-01-01
An analysis of the number and form of the required inflow-outflow boundary conditions for the full two-dimensional time-dependent nonlinear acoustic system in subsonic mean flow is performed. The explicit predictor-corrector method of MacCormack (1969) is used. The methodology is tested on both uniform and sheared mean flows with plane and nonplanar sources. Results show that the acoustic system requires three physical boundary conditions on the inflow and one on the outflow boundary. The most natural choice for the inflow boundary conditions is judged to be a specification of the vorticity, the normal acoustic impedance, and a pressure gradient-density gradient relationship normal to the boundary. Specification of the acoustic pressure at the outflow boundary along with these inflow boundary conditions is found to give consistent reliable results. A set of boundary conditions developed earlier, which were intended to be nonreflecting is tested using the current method and is shown to yield unstable results for nonplanar acoustic waves.
Time-dependent fifth-order bands in nominally third-order 2D IR vibrational echo spectra.
Thielges, Megan C; Fayer, Michael D
2011-09-01
Progress in the field of 2D IR vibrational spectroscopy has been bolstered by the production of intense mid-IR laser pulses. As higher-energy pulses are employed, a concomitant increase occurs in the likelihood of fifth-order contributions to the 2D IR spectra. We report the appearance of fifth-order signals in 2D IR spectra of CO bound to the active site of the enzyme cytochrome P450(cam) with the substrate norcamphor. Two bands with novel time dependences, one on the diagonal and one off-diagonal, are not accounted for by normal third-order interactions. These bands are associated with a ν = 1-2 vibrational transition frequency. Both bands decay to 0 and then grow back in with opposite sign. The diagonal band is positive at short time, decays to 0, reappears with negative sign, before eventually decaying to 0. The off-diagonal band is negative at short time, decays to 0, reappears positive, and then decays to 0. The appearance and time dependence of these bands are characterized. Understanding these fifth-order bands is useful because they may be misidentified with time-dependent bands that arise from other processes, such as chemical exchange, vibrational coupling, or energy transfer. The presence and unusual time dependences of the fifth-order bands are reproduced with model calculations that account for the fact that vibrational relaxation from the ν = 2 to 1 level is approximately a factor of 2 faster than that from the ν = 1 to 0 level.
NASA Astrophysics Data System (ADS)
Marketos, George; Govers, Rob; Spiers, Chris
2015-04-01
Rocksalt is the caprock for a large number of hydrocarbon reservoirs. Understanding its response to extraction-induced stress perturbations can therefore be very important when calculating the resulting deformation and associated subsidence above such fields. We investigate how flow in the rocksalt leads to time-dependent deformation of the ground surface using numerical models that simulate the mechanical response of the subsurface. Rock mechanical experiments have demonstrated that rocksalt can flow by linear creep or power-law creep, depending on stress and grain size among others. Given that we often do not have data from cores that constrain these quantities, we investigate the two rocksalt flow laws as alternatives. Here, we focus specifically on differences in the surface imprints of these two types of flow. Mechanical models for linear creep show that the rocksalt exhibits two time scales in response to the reservoir pumping. The first, and shortest, time scale reflects flow that is driven by relaxation of stresses in the vicinity of the reservoir. At the surface, this results in maximum subsidence that is increasing with time. The second time scale reflects closed-conduit flow within the rocksalt layer that is driven by mean stresses equilibration. Interestingly, this results in a decrease in the maximum subsidence above the reservoir.
NASA Astrophysics Data System (ADS)
Noda, H.; Okazaki, K.; Katayama, I.
2013-12-01
During diagenesis, incohesive sediments are compacted and gain strength against shear deformation for a geologically long time scale. The evolution of shear strength as well as the change in the mechanical and hydraulic characteristics under shear deformation is of significant importance in considering deformation at shallow part of the subduction zones and in accretionary prisms. Sediments after induration due to time-dependent diagenesis process probably deform with increases in porosity and permeability much more significantly than normally compacted incohesive sediments. An active fault in a shallow incohesive medium may favor thermal pressurization of pore fluid when slid rapidly, while the lack of time-dependent healing effect may cause stable (e.g., rate-strengthening) frictional property there. On the other hand, indurated sediments may deform with significant post-failure weakening, and thus exhibit localization of deformation or unstable behavior. In order to investigate how the time-dependent compaction and induration affect the mechanical and hydraulic characteristics of sediments under deformation, we have conducted a series of compaction experiments under hydrothermal conditions (at temperatures from R.T. to 500 °C, 200 MPa confining pressure, 100 MPa pore water pressure, and for various time), and following triaxial deformation experiments for the compacted samples, with monitoring permeability and storage capacity with pore pressure oscillation method [Fischer and Paterson, 1992]. Previous work [e.g., Niemeijer et at., 2003] reported that under the adopted conditions, quartz aggregate deforms by pressure solution-precipitation creep. The initial synthetic sediments have been prepared by depositing commercially available crushed quartzite the grain size of which is about 6 μm on average. 4 cm long samples have been extracted from the middle of 10 cm long deposited columns. The experiments have been performed with a gas-medium apparatus in Hiroshima
NASA Astrophysics Data System (ADS)
Koyanagi, Jun; Nagayama, Hideo; Yoneyama, Satoru; Aoki, Takahira
2016-06-01
This paper presents the time dependence of the mesoscopic strain of a triaxial woven carbon-fiber-reinforced polymer under creep loading measured using digital image correlation (DIC). Two types of DIC techniques were employed for the measurement: conventional subset DIC and mesh DIC. Static tensile and creep tests were carried out, and the time dependence of the mesoscopic strain distribution was investigated by applying these techniques. The ultimate failure of this material is dominated by inter-bundle decohesion caused by relative rigid rotation and relating shear stress. Therefore, these were focused on in the present study. During the creep tests, the fiber directional strain, shear strain, and rotation were monitored using the DIC, and the mechanism for the increase in the specimen's macro-strain over time was investigated based on the results obtained by the DIC measurement.
NASA Astrophysics Data System (ADS)
Lowry, Thomas; Li, Shu-Guang
2005-02-01
Difficulty in solving the transient advection-diffusion equation (ADE) stems from the relationship between the advection derivatives and the time derivative. For a solution method to be viable, it must account for this relationship by being accurate in both space and time. This research presents a unique method for solving the time-dependent ADE that does not discretize the derivative terms but rather solves the equation analytically in the space-time domain. The method is computationally efficient and numerically accurate and addresses the common limitations of numerical dispersion and spurious oscillations that can be prevalent in other solution methods. The method is based on the improved finite analytic (IFA) solution method [Lowry TS, Li S-G. A characteristic based finite analytic method for solving the two-dimensional steady-state advection-diffusion equation. Water Resour Res 38 (7), 10.1029/2001WR000518] in space coupled with a Laplace transformation in time. In this way, the method has no Courant condition and maintains accuracy in space and time, performing well even at high Peclet numbers. The method is compared to a hybrid method of characteristics, a random walk particle tracking method, and an Eulerian-Lagrangian Localized Adjoint Method using various degrees of flow-field heterogeneity across multiple Peclet numbers. Results show the IFALT method to be computationally more efficient while producing similar or better accuracy than the other methods.
Creeping motion and deformation of liquid drops in flow through 2D model porous media
Fong, I. )
1988-01-01
The motion, deformation and breakup of immiscible drops suspended in low Reynolds number flow through cylinder arrays has been studied experimentally to assess the applicability of the 2D model as a prototype for 2-phase flow through porous media. Both Newtonian and non-Newtonian fluid systems are considered. The relationship between key flow and geometric parameters and the critical condition for breakup, the resulting drop site distribution and the drop mobility is investigated. It is observed that the headon impact of a drop with a cylinder is an effective precursor to severe drop deformation and even breakup. The sequence of flow leading to impact is also important in determining the effectiveness of impact to result in breakup. When many drops fragments are present, the interaction between nearby drops strongly influences the final disposition of the fragments. Fluid elasticity appears to enhance the elongation of drops to form strands, but also to stabilize the strand against breakup.
Okunishi, Takuma; Clark, Richard; Takeda, Kyozaburo; Kusakabe, Kouichi; Tomita, Norikazu
2013-12-04
We extend the static multi-reference description (resonant UHF) to the dynamic system in order to include the correlation effect over time, and simplify the TD Schrödinger equation (TD-CI) into a time-developed rate equation where the TD external field Ĥ′(t) is then incorporated directly in the Hamiltonian without any approximations. We apply this TD-CI method to the two-electron ground state of a 2D quantum dot (QD) under photon injection and study the resulting two-electron Rabi oscillation.
NASA Astrophysics Data System (ADS)
Zhao, Juan
2013-04-01
We investigated spin-orbit-induced intersystem crossing effects in the title reaction by the time-dependent wave-packet method combined with an extended split operator scheme. We performed non-adiabatic calculations of the fine-structure-resolved cross section and adiabatic calculations of integral cross section. The calculations are based on the potential energy surfaces of 3A' and the two degenerate 3A'' states [S. Rogers, D. Wang, A. Kuppermann, and S. Walch, J. Phys. Chem. A 104, 2308 (2000)], 10.1021/jp992985g, together with the spin-orbit coupling matrix [B. Maiti and G. C. Schatz, J. Chem. Phys. 119, 12360 (2003)], 10.1063/1.1623481 and singlet 1A' potential energy surface [J. Dobbyn and P. J. Knowles, Faraday Discuss. 110, 247 (1998)]. The results of the O(3P) + D2 are similar to those of the O(3P) + H2 reaction. The product spin state-resolved reaction cross section and the total reaction cross section both show that the adiabatic channel is dominant in all cases, and the non-adiabatic channels have cross sections of several orders of magnitude smaller than the adiabatic channels at high collision energy. Although the cross sections caused by the intersystem crossing effects in the O(3P) + D2 reaction are larger than those in the O(3P) + H2 reaction, the differences in non-adiabaticity between these two reaction systems are quite modest. Based on the results of the O(3P) + H2 reaction, we can predict that the influence of spin-orbit on the total reaction cross sections of the O(3P) + D2 reaction is also insignificant. However, these non-adiabatic effects can be reflected in the presence of some forward-scattering in the angular distribution for the OD product.
Spatial fluctuations in transient creep deformation
NASA Astrophysics Data System (ADS)
Laurson, Lasse; Rosti, Jari; Koivisto, Juha; Miksic, Amandine; Alava, Mikko J.
2011-07-01
We study the spatial fluctuations of transient creep deformation of materials as a function of time, both by digital image correlation (DIC) measurements of paper samples and by numerical simulations of a crystal plasticity or discrete dislocation dynamics model. This model has a jamming or yielding phase transition, around which power law or Andrade creep is found. During primary creep, the relative strength of the strain rate fluctuations increases with time in both cases—the spatially averaged creep rate obeys the Andrade law epsilont ~ t - 0.7, while the time dependence of the spatial fluctuations of the local creep rates is given by Δepsilont ~ t - 0.5. A similar scaling for the fluctuations is found in the logarithmic creep regime that is typically observed for lower applied stresses. We review briefly some classical theories of Andrade creep from the point of view of such spatial fluctuations. We consider these phenomenological, time-dependent creep laws in terms of a description based on a non-equilibrium phase transition separating evolving and frozen states of the system when the externally applied load is varied. Such an interpretation is discussed further by the data collapse of the local deformations in the spirit of absorbing state/depinning phase transitions, as well as deformation-deformation correlations and the width of the cumulative strain distributions. The results are also compared with the order parameter fluctuations observed close to the depinning transition of the 2d linear interface model or the quenched Edwards-Wilkinson equation.
ERIC Educational Resources Information Center
Collyer, A. A.
1974-01-01
Discusses the flow characteristics of thixotropic and negative thixotropic fluids; various theories underlying the thixotropic behavior; and thixotropic phenomena exhibited in drilling muds, commercial paints, pastes, and greases. Inconsistencies in the terminology used to label time dependent effects are revealed. (CC)
Progress Report on Alloy 617 Time Dependent Allowables
Wright, Julie Knibloe
2015-06-01
Time dependent allowable stresses are required in the ASME Boiler and Pressure Vessel Code for design of components in the temperature range where time dependent deformation (i.e., creep) is expected to become significant. There are time dependent allowable stresses in Section IID of the Code for use in the non-nuclear construction codes, however, there are additional criteria that must be considered in developing time dependent allowables for nuclear components. These criteria are specified in Section III NH. St is defined as the lesser of three quantities: 100% of the average stress required to obtain a total (elastic, plastic, primary and secondary creep) strain of 1%; 67% of the minimum stress to cause rupture; and 80% of the minimum stress to cause the initiation of tertiary creep. The values are reported for a range of temperatures and for time increments up to 100,000 hours. These values are determined from uniaxial creep tests, which involve the elevated temperature application of a constant load which is relatively small, resulting in deformation over a long time period prior to rupture. The stress which is the minimum resulting from these criteria is the time dependent allowable stress St. In this report data from a large number of creep and creep-rupture tests on Alloy 617 are analyzed using the ASME Section III NH criteria. Data which are used in the analysis are from the ongoing DOE sponsored high temperature materials program, form Korea Atomic Energy Institute through the Generation IV VHTR Materials Program and historical data from previous HTR research and vendor data generated in developing the alloy. It is found that the tertiary creep criterion determines St at highest temperatures, while the stress to cause 1% total strain controls at low temperatures. The ASME Section III Working Group on Allowable Stress Criteria has recommended that the uncertainties associated with determining the onset of tertiary creep and the lack of significant
Time-Dependent Erosion of Ion Optics
NASA Technical Reports Server (NTRS)
Wirz, Richard E.; Anderson, John R.; Katz, Ira; Goebel, Dan M.
2008-01-01
The accurate prediction of thruster life requires time-dependent erosion estimates for the ion optics assembly. Such information is critical to end-of-life mechanisms such as electron backstreaming. CEX2D was recently modified to handle time-dependent erosion, double ions, and multiple throttle conditions in a single run. The modified code is called "CEX2D-t". Comparisons of CEX2D-t results with LDT and ELT post-tests results show good agreement for both screen and accel grid erosion including important erosion features such as chamfering of the downstream end of the accel grid and reduced rate of accel grid aperture enlargement with time.
Further Developments in Modeling Creep Effects Within Structural SiC/SiC Components
NASA Technical Reports Server (NTRS)
Lang, Jerry; DiCarlo, James A.
2008-01-01
Anticipating the implementation of advanced SiC/SiC composites into turbine section components of future aero-propulsion engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly manipulate constituent materials and processes in order to minimize these effects. Focusing on SiC/SiC components experiencing through-thickness stress gradients (e.g., airfoil leading edge), prior NASA creep modeling studies showed that detrimental residual stress effects can develop globally within the component walls which can increase the risk of matrix cracking. These studies assumed that the SiC/SiC composites behaved as isotropic viscoelastic continuum materials with creep behavior that was linear and symmetric with stress and that the creep parameters could be obtained from creep data as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The present study expands on those prior efforts by including constituent behavior with non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.
Creep and creep-rupture behavior of Alloy 718
Brinkman, C.R.; Booker, M.K.; Ding, J.L.
1991-01-01
Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forgoing material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760{degree}C ad at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis and two based on the Minimum Commitment Method. A master'' curve approach was used to develop and equation for estimating creep deformation up to the onset of tertiary creep. 11 refs., 13 figs.
Time-dependent rheological behaviour of bacterial cellulose hydrogel.
Gao, Xing; Shi, Zhijun; Kuśmierczyk, Piotr; Liu, Changqing; Yang, Guang; Sevostianov, Igor; Silberschmidt, Vadim V
2016-01-01
This work focuses on time-dependent rheological behaviour of bacterial cellulose (BC) hydrogel. Due to its ideal biocompatibility, BC hydrogel could be employed in biomedical applications. Considering the complexity of loading conditions in human body environment, time-dependent behaviour under relevant conditions should be understood. BC specimens are produced by Gluconacetobacter xylinus ATCC 53582 at static-culture conditions. Time-dependent behaviour of specimens at several stress levels is experimentally determined by uniaxial tensile creep tests. We use fraction-exponential operators to model the rheological behaviour. Such a representation allows combination of good accuracy in analytical description of viscoelastic behaviour of real materials and simplicity in solving boundary value problems. The obtained material parameters allow us to identify time-dependent behaviour of BC hydrogel at high stress level with sufficient accuracy. PMID:26478298
Time-dependent rheological behaviour of bacterial cellulose hydrogel.
Gao, Xing; Shi, Zhijun; Kuśmierczyk, Piotr; Liu, Changqing; Yang, Guang; Sevostianov, Igor; Silberschmidt, Vadim V
2016-01-01
This work focuses on time-dependent rheological behaviour of bacterial cellulose (BC) hydrogel. Due to its ideal biocompatibility, BC hydrogel could be employed in biomedical applications. Considering the complexity of loading conditions in human body environment, time-dependent behaviour under relevant conditions should be understood. BC specimens are produced by Gluconacetobacter xylinus ATCC 53582 at static-culture conditions. Time-dependent behaviour of specimens at several stress levels is experimentally determined by uniaxial tensile creep tests. We use fraction-exponential operators to model the rheological behaviour. Such a representation allows combination of good accuracy in analytical description of viscoelastic behaviour of real materials and simplicity in solving boundary value problems. The obtained material parameters allow us to identify time-dependent behaviour of BC hydrogel at high stress level with sufficient accuracy.
Modeling Creep Effects within SiC/SiC Turbine Components
NASA Technical Reports Server (NTRS)
DiCarlo, J. A.; Lang, J.
2008-01-01
Anticipating the implementation of advanced SiC/SiC ceramic composites into the hot section components of future gas turbine engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly select and manipulate constituent materials, processes, and geometries in order to minimize these effects. In initial studies aimed at SiC/SiC components experiencing through-thickness stress gradients, creep models were developed that allowed an understanding of detrimental residual stress effects that can develop globally within the component walls. It was assumed that the SiC/SiC composites behaved as isotropic visco-elastic materials with temperature-dependent creep behavior as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The creep models and their key results are discussed assuming state-of-the-art SiC/SiC materials within a simple cylindrical thin-walled tubular structure, which is currently being employed to model creep-related effects for turbine airfoil leading edges subjected to through-thickness thermal stress gradients. Improvements in the creep models are also presented which focus on constituent behavior with more realistic non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.
Time-dependent Brittle Deformation in Darley Dale Sandstone
NASA Astrophysics Data System (ADS)
Baud, P.; Heap, M. J.; Meredith, P. G.; Bell, A. F.; Main, I. G.
2008-12-01
The characterization of time-dependent brittle rock deformation is fundamental to understanding the long- term evolution and dynamics of the Earth's upper crust. The chemical influence of water promotes time- dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here we report results from a study of time-dependent brittle creep in water- saturated samples of Darley Dale sandstone (initial porosity of 13%). Conventional creep experiments (or 'static fatigue' tests) show that time to failure decreases dramatically with the imposed deviatoric stress. They also suggest the existence of a critical level of damage beyond which localized failure develops. Sample variability results however in significant scattering in the experimental data and numerous tests are needed to clearly define a relation between the strain rate and the applied stress. We show here that stress-stepping experiments provide a means to overcome this problem and that it is possible this way to obtain the strain rate dependence on applied stress with a single test. This allows to study in details the impact of various thermodynamical conditions on brittle creep. The influence of effective stress was investigated in stress-stepping experiments with effective confining pressures of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the expected purely mechanical influence of an elevated effective stress our results also demonstrate that stress corrosion appears to be inhibited at higher effective stresses. The influence of doubling the pore fluid pressure however, whilst maintaining a constant effective stress, is shown to have no effect on the rate of stress corrosion. We then discuss the results in light of acoustic emission hypocentre location data and optical microscope analysis and use our experimental data to validate proposed macroscopic creep laws. Finally, using
A Unified Constitutive Relationship for the Time-dependent Behavior of Fast Breeder Alloys
NASA Technical Reports Server (NTRS)
Robinson, D. N.
1983-01-01
Constitutive equations based on classical concepts of creep and plasticity generally rest on the assumption that the inelastic strain can be decomposed into two distinct and additive contributions, one time dependent (creep) and the other time dependent (plastic). It is suggested that an approach is to adopt a unified representation in which creep and plasticity are characterized as occurring simultaneously and interactively and time is an essential ingredient throughout. Examples of the inherent time dependency exhibited by some fast breeder alloys at elevated temperature are rate dependency under monotonic and cyclic straining, thermal recovery and strong creep-elasticity interaction. The stron influence of the recent history of plastic straining on stress relaxation is shown.
Time dependent view factor methods
Kirkpatrick, R.C.
1998-03-01
View factors have been used for treating radiation transport between opaque surfaces bounding a transparent medium for several decades. However, in recent years they have been applied to problems involving intense bursts of radiation in enclosed volumes such as in the laser fusion hohlraums. In these problems, several aspects require treatment of time dependence.
Creep-Fatigue Interaction Testing
NASA Technical Reports Server (NTRS)
Halford, Gary R.
2001-01-01
Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.
Spike-timing-dependent construction.
Lightheart, Toby; Grainger, Steven; Lu, Tien-Fu
2013-10-01
Spike-timing-dependent construction (STDC) is the production of new spiking neurons and connections in a simulated neural network in response to neuron activity. Following the discovery of spike-timing-dependent plasticity (STDP), significant effort has gone into the modeling and simulation of adaptation in spiking neural networks (SNNs). Limitations in computational power imposed by network topology, however, constrain learning capabilities through connection weight modification alone. Constructive algorithms produce new neurons and connections, allowing automatic structural responses for applications of unknown complexity and nonstationary solutions. A conceptual analogy is developed and extended to theoretical conditions for modeling synaptic plasticity as network construction. Generalizing past constructive algorithms, we propose a framework for the design of novel constructive SNNs and demonstrate its application in the development of simulations for the validation of developed theory. Potential directions of future research and applications of STDC for biological modeling and machine learning are also discussed.
Time-Dependent Reliability Analysis
1999-10-27
FRANTIC-3 was developed to evaluate system unreliability using time-dependent techniques. The code provides two major options: to evaluate standby system unavailability or, in addition to the unavailability to calculate the total system failure probability by including both the unavailability of the system on demand as well as the probability that it will operate for an arbitrary time period following the demand. The FRANTIC-3 time dependent reliability models provide a large selection of repair and testingmore » policies applicable to standby or continously operating systems consisting of periodically tested, monitored, and non-repairable (non-testable) components. Time-dependent and test frequency dependent failures, as well as demand stress related failure, test-caused degradation and wear-out, test associated human errors, test deficiencies, test override, unscheduled and scheduled maintenance, component renewal and replacement policies, and test strategies can be prescribed. The conditional system unavailabilities associated with the downtimes of the user specified failed component are also evaluated. Optionally, the code can perform a sensitivity study for system unavailability or total failure probability to the failure characteristics of the standby components.« less
Time-Dependent Reliability Analysis
Sartori, Enrico
1999-10-27
FRANTIC-3 was developed to evaluate system unreliability using time-dependent techniques. The code provides two major options: to evaluate standby system unavailability or, in addition to the unavailability to calculate the total system failure probability by including both the unavailability of the system on demand as well as the probability that it will operate for an arbitrary time period following the demand. The FRANTIC-3 time dependent reliability models provide a large selection of repair and testing policies applicable to standby or continously operating systems consisting of periodically tested, monitored, and non-repairable (non-testable) components. Time-dependent and test frequency dependent failures, as well as demand stress related failure, test-caused degradation and wear-out, test associated human errors, test deficiencies, test override, unscheduled and scheduled maintenance, component renewal and replacement policies, and test strategies can be prescribed. The conditional system unavailabilities associated with the downtimes of the user specified failed component are also evaluated. Optionally, the code can perform a sensitivity study for system unavailability or total failure probability to the failure characteristics of the standby components.
Nanogranular origin of concrete creep.
Vandamme, Matthieu; Ulm, Franz-Josef
2009-06-30
Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium-silicate-hydrates (C-S-H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C-S-H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C-S-H forms: low density, high density, ultra-high density. We demonstrate that the creep rate ( approximately 1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years.
Nanogranular origin of concrete creep
Vandamme, Matthieu; Ulm, Franz-Josef
2009-01-01
Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652
Selfsimilar time dependent shock structures
NASA Technical Reports Server (NTRS)
Beck, R.; Drury, L. O.
1985-01-01
Diffusive shock acceleration as an astrophysical mechanism for accelerating charged particles has the advantage of being highly efficient. This means however that the theory is of necessity nonlinear; the reaction of the accelerated particles on the shock structure and the acceleration process must be self-consistently included in any attempt to develop a complete theory of diffusive shock acceleration. Considerable effort has been invested in attempting, at least partially, to do this and it has become clear that in general either the maximum particle energy must be restricted by introducing additional loss processes into the problem or the acceleration must be treated as a time dependent problem (Drury, 1984). It is concluded that stationary modified shock structures can only exist for strong shocks if additional loss processes limit the maximum energy a particle can attain. This is certainly possible and if it occurs the energy loss from the shock will lead to much greater shock compressions. It is however equally possible that no such processes exist and we must then ask what sort of nonstationary shock structure develops. The ame argument which excludes stationary structures also rules out periodic solutions and indeed any solution where the width of the shock remains bounded. It follows that the width of the shock must increase secularly with time and it is natural to examine the possibility of selfsimilar time dependent solutions.
Creep behavior of uranium carbide-based alloys
NASA Technical Reports Server (NTRS)
Seltzer, M. S.; Wright, T. R.; Moak, D. P.
1975-01-01
The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.
Network-timing-dependent plasticity
Delattre, Vincent; Keller, Daniel; Perich, Matthew; Markram, Henry; Muller, Eilif B.
2015-01-01
Bursts of activity in networks of neurons are thought to convey salient information and drive synaptic plasticity. Here we report that network bursts also exert a profound effect on Spike-Timing-Dependent Plasticity (STDP). In acute slices of juvenile rat somatosensory cortex we paired a network burst, which alone induced long-term depression (LTD), with STDP-induced long-term potentiation (LTP) and LTD. We observed that STDP-induced LTP was either unaffected, blocked or flipped into LTD by the network burst, and that STDP-induced LTD was either saturated or flipped into LTP, depending on the relative timing of the network burst with respect to spike coincidences of the STDP event. We hypothesized that network bursts flip STDP-induced LTP to LTD by depleting resources needed for LTP and therefore developed a resource-dependent STDP learning rule. In a model neural network under the influence of the proposed resource-dependent STDP rule, we found that excitatory synaptic coupling was homeostatically regulated to produce power law distributed burst amplitudes reflecting self-organized criticality, a state that ensures optimal information coding. PMID:26106298
Room temperature creep in metals and alloys
Deibler, Lisa Anne
2014-09-01
Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 T_{m} for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.
Time-dependent deformations on marine clays on submarine slopes
Silva, A.J.; Brandes, H.; Sadd, M.H.; Tian, W.M. )
1990-06-01
Evidence from geological and geophysical records indicates that time-dependent deformations occur on or within many submarine slopes. Laboratory studies on marine clays from the slope/rise and the ocean's basin have shown that these clays are generally quite viscous and therefore can be expected to deform in the field even under such small stresses as those caused by the downslope component of gravity on relatively gentle slopes. The nature and extent of these deformations has important geologic and engineering applications and depends on a number of factors. A research program at the University of Rhode Island is under way to study these factors, make predictions on rates of displacement, and identify environmental conditions that may lead to catastrophic mass failures. A laboratory testing program on the time-dependent characteristics of marine clays has been under way for a number of years. The data include, among others, long-term drained triaxial, one-dimensional, and direct simple shear creep tests. These results along with practical considerations are used to select a constitutive model for inclusion in the numerical code. Sediment deposits encountered on the continental slope and rise can vary substantially both in composition and behavior over relatively short distances. To analyze the integrated behavior of such a continuum, the authors have selected the finite element method. The code being developed will initially include a numerical model proposed by other investigators. With the aid of the developed methodology, creep deformations can be studied for a number of field cases of interest.
Time-dependent damage in predictions of fatigue behaviour of normal and healing ligaments
NASA Astrophysics Data System (ADS)
Thornton, Gail M.; Bailey, Soraya J.; Schwab, Timothy D.
2015-08-01
Ligaments are dense fibrous tissues that connect bones across a joint and are exposed daily to creep and fatigue loading. Ligaments are tensile load-bearing tissues; therefore, fatigue loading will have a component of time-dependent damage from the non-zero mean stress and cycle-dependent damage from the oscillating stress. If time-dependent damage is not sufficient to completely predict the fatigue response, then cycle-dependent damage could be an important contributor. Using data from normal ligaments (current study and Thornton et al., Clin. Biomech. 22:932-940, 2007a) and healing ligaments (Thornton and Bailey, J. Biomech. Eng. 135:091004-1-091004-6, 2013), creep data was used to predict the fatigue response considering time-dependent damage. Relationships between creep lifetime and test stress or initial strain were modelled using exponential or power-law regression. In order to predict fatigue lifetimes, constant rates of damage were assumed and time-varying stresses were introduced into the expressions for time-dependent damage from creep. Then, the predictions of fatigue lifetime were compared with curvefits to the fatigue data where exponential or power-law regressions were used to determine the relationship between fatigue lifetime and test stress or initial strain. The fatigue prediction based on time-dependent damage alone greatly overestimated fatigue lifetime suggesting that time-dependent damage alone cannot account for all of the damage accumulated during fatigue and that cycle-dependent damage has an important role. At lower stress and strain, time-dependent damage was a greater relative contributor for normal ligaments than healing ligaments; however, cycle-dependent damage was a greater relative contributor with incremental increases in stress or strain for normal ligaments than healing ligaments.
Remaining Creep Life Assessment Techniques Based on Creep Cavitation Modeling
NASA Astrophysics Data System (ADS)
Ankit, Kumar
2009-05-01
The boiler and its components are built with assumed nominal design and reasonable life of operation about two to three decades (one or two hundred thousand hours). These units are generally replaced or life is extended at the end of this period. Under normal operating conditions, after the initial period of teething troubles, the reliability of these units remains fairly constant up to about two decades of normal operation. The failure rate then increases as a result of their time-dependent material damage. Further running of these units may become uneconomical and dangerous in some cases. In the following article, step-by-step methodology to quantify creep cavitation based on statistical probability analysis and continuum damage mechanics has been described. The concepts of creep cavity nucleation have also been discussed with a special emphasis on the need for development of a model based on creep cavity growth kinetics.
Impression Creep Behavior of 316LN Stainless Steel
NASA Astrophysics Data System (ADS)
Mathew, M. D.; Naveena; Vijayanand, D.
2013-02-01
Impression creep tests have been carried out at 923 K on 316LN SS containing 0.07, 0.14, and 0.22 wt.% nitrogen, under different applied stress levels. It was observed that the impression creep depth versus time curves were similar to the creep curves obtained from conventional uniaxial creep tests. The impression creep curves were characterized by a loading strain and primary and secondary creep stages similar to uniaxial creep curves. The tertiary stage observed in uniaxial creep curves was absent. The steady-state impression velocity was found to increase with increasing applied stress. The equivalent steady-state creep rates calculated from impression velocities were found to be in good agreement with the steady-state creep rates obtained from conventional uniaxial creep tests. Equivalence between applied stress and steady-state impression velocity with uniaxial creep stress and steady-state creep rate, respectively, has been established based on the laws of mechanics for time-dependent plasticity. It was found that impression velocity was sensitive to the variation in nitrogen content in the steel; impression velocity decreased with increasing nitrogen content, and the results obtained in this study were in agreement with those obtained from uniaxial creep tests.
Characterization and modeling time-dependent behavior in PZT fibers and active fiber composites
NASA Astrophysics Data System (ADS)
Dridi, Mohamed A.; Atitallah, Hassene B.; Ounaies, Zoubeida; Muliana, Anastasia
2015-04-01
Active fiber composites (AFC) are comprised of lead zirconate titanate (PZT) fibers embedded in a polymer. This paper presents an experimental characterization of the PZT fibers and a constitutive model focused on their time-dependent, nonlinear response. The experiments herein focus on characterizing time dependence of various properties by conducting creep, relaxation, mechanical and electric field-cyclic loading at different frequencies. The constitutive model is a time-dependent polarization model that predicts nonlinear polarization and electro-mechanical strain responses of the fibers. The model of PZT fibers is used in the FEM simulation of AFCs and results of the model are compared to experiments for validation.
Spectral methods for time dependent problems
NASA Technical Reports Server (NTRS)
Tadmor, Eitan
1990-01-01
Spectral approximations are reviewed for time dependent problems. Some basic ingredients from the spectral Fourier and Chebyshev approximations theory are discussed. A brief survey was made of hyperbolic and parabolic time dependent problems which are dealt with by both the energy method and the related Fourier analysis. The ideas presented above are combined in the study of accuracy stability and convergence of the spectral Fourier approximation to time dependent problems.
Time-dependent behavior of flax/starch composites
NASA Astrophysics Data System (ADS)
Varna, J.; Spārniņš, E.; Joffe, R.; Nättinen, K.; Lampinen, J.
2012-02-01
The time-dependent mechanical response of flax fiber-reinforced thermoplastic starch matrix composite and neat starch is analyzed. It is demonstrated that the response is highly sensitive to the relative humidity (with specific saturation moisture content in the composite) and special effort has to be made to keep it constant. It was found that the accumulation of micro-damage and the resulting reduction of the elastic modulus in this type of composite is limited. The highly nonlinear behavior of composites is related to the nonlinear viscoelasticity and viscoplasticity. These phenomena are accounted for by simple material models, as suggested in this study. The stress-dependent nonlinearity descriptors in these models are determined in creep and strain recovery tests at low as well as by high stresses.
Time-Dependent Neutral Particle Transport Benchmarks in Two and Three Dimensions
Barry D. Ganapol
2007-10-12
The main objective of NEER grant was to generate highly accurate 2D and 3D time-dependent neutral particle intensity maps from 3D pulsed wire sources through integration of the analytical representation of a time-dependent point source.
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.
Time-dependent mechanical response of HDPE geomembranes
Merry, S.M.; Bray, J.D.
1997-01-01
Geomembranes are used extensively in the construction of base liners and cover systems for both hazardous and municipal waste-containment facilities. Characterization of the long-term mechanical response of geomembranes used in waste-containment facilities is crucial to designing base liner and over systems that perform satisfactorily. To investigate the long-term mechanical response, strain-controlled multiaxial tension testing was performed over a fourfold variation of strain rate using a newly developed multiaxial tension-test apparatus capable of performing constant strain rate and constant stress creep tests. This device subjects a geomembrane specimen to multiaxial stress states and allows for the development of strain conditions that vary from plane strain at the clamped edges to balanced biaxial at the center. Results from testing high-density polyethylene (HDPE) specimens indicate that the secant modulus and strength decreases considerably at strain rates appropriate for long-term field applications. The strength of HDPE measured at a typical laboratory strain rate of 1% per minute can be more than twice the strength predicted at a strain rate of 1E-6% per minute, which may be representative of field performance for a typical 30-year design life. A hyperbolic model and the Singh-Mitchell creep model (which was originally formulated for soils) are shown to capture the time-dependent mechanical response of HDPE well.
Bohr Hamiltonian with time-dependent potential
NASA Astrophysics Data System (ADS)
Naderi, L.; Hassanabadi, H.; Sobhani, H.
2016-04-01
In this paper, Bohr Hamiltonian has been studied with the time-dependent potential. Using the Lewis-Riesenfeld dynamical invariant method appropriate dynamical invariant for this Hamiltonian has been constructed and the exact time-dependent wave functions of such a system have been derived due to this dynamical invariant.
Computer program for predicting creep behavior of bodies of revolution
NASA Technical Reports Server (NTRS)
Adams, R.; Greenbaum, G.
1971-01-01
Computer program, CRAB, uses finite-element method to calculate creep behavior and predict steady-state stresses in an arbitrary body of revolution subjected to a time-dependent axisymmetric load. Creep strains follow a time hardening law and a Prandtl-Reuss stress-strain relationship.
Creep-rupture of polymer-matrix composites. [graphite-epoxy laminates
NASA Technical Reports Server (NTRS)
Brinson, H. F.; Griffith, W. I.; Morris, D. H.
1980-01-01
An accelerated characterization method for resin matrix composites is reviewed. Methods for determining modulus and strength master curves are given. Creep rupture analytical models are discussed as applied to polymers and polymer matrix composites. Comparisons between creep rupture experiments and analytical models are presented. The time dependent creep rupture process in graphite epoxy laminates is examined as a function of temperature and stress level.
Time-dependent photoelectron angular distributions
NASA Astrophysics Data System (ADS)
Wang, Xiangyang
1999-09-01
I show that the angular distribution of electrons photoionized from gas phase targets by short light pulses is time-dependent, when the orbital momentum composition of the photocurrent changes with excitation energy so evolves with the time of detection. A theory of time- dependent photoionization is outlined and general formulas of time-dependent photoelectron flux and angular distribution are given. Two general propagator methods suitable to describe the time-dependent photoionization and scattering processes are developed. The photoionization process is viewed as a local excitation followed by a half scattering. The local excitation process is solved theoretically in a small region around the target core. This approach has been generalized to describe the evolution of a wavepacket in an unbound system. An asymptotic propagator theorem is discovered and used to derive analytic expressions for asymptotic propagators. The origin of the time dependence is explored by parameterizing the time delay and orbital momentum coupling in a two channel model. K-shell photoionization of N2 and CO are calculated with this time- dependent photoionization theory, implemented using a multiple scattering model. Numerical results demonstrate that the time dependence of photoelectron angular distributions is a realistic effect.
Birefringence in time-dependent moving media
NASA Astrophysics Data System (ADS)
Lin, Shirong; Zhang, Ruoyang; Zhai, Yanwang; Wei, Jianye; Zhao, Qing
2016-08-01
Electromagnetic wave propagation in one- and two-dimensional time-dependent moving media is investigated in this paper. We identify another origin of linear birefringence caused by the component of the flow perpendicular to the wave vector. Previously, birefringence is induced by applying external electric and magnetic fields to non-crystalline material. Here it is shown that the time-varying velocity field also contributes to such a phenomenon. Our results indicate that the parallel component, time-dependent or not, will not yield birefringence. Furthermore, the time-dependent flow also results in a frequency shift. One-dimensional simulation is conducted to demonstrate these effects.
Time-dependent Deformation in Porous Rocks Driven by Chemo-mechanical Coupling
NASA Astrophysics Data System (ADS)
Meredith, P. G.; Brantut, N.; Heap, M. J.; Baud, P.
2015-12-01
We report results from triaxial deformation of porous sandstone and limestone conducted to determine the time-dependency of deformation. Experiments were run on water-saturated samples under constant differential stress (creep) conditions. In sandstone, the deformation is entirely brittle for all levels of stress and for all resulting strain rates. The strain rate during creep is very stress sensitive, with a change of only 20 MPa in differential stress producing three orders of magnitude change in strain rate. Failure occurs by localized shear faulting after an extended period of dilatant microcracking, as evidenced by the output of acoustic emissions. By contrast, the behaviour of limestone is more complex. At low effective pressure, the creep behavior is brittle and characterised by the same features as observed for sandstone; a decelerating phase of creep, followed by an inflection and then an accelerating creep phase leading to macroscopic failure. Similarly, only a small amount of inelastic strain is accommodated before failure, and P wave speeds measured throughout deformation decrease continuously, indicating a continuous increase in dilatant crack damage. At higher effective pressure, brittle creep still occurs, but the details of the time-dependent deformation behavior are quite different. First, the total amount of accumulated creep strain increases dramatically with decreasing strain rate, and no localized failure occurs even at these higher strains. Second, the rate of decrease in P wave speeds during deformation decreases with decreasing strain rate; indicating that less damage is accumulated per unit strain when the strain rate is lower. Third, complementary strain rate stepping experiments indicate that the deformation becomes more compactant at lower strain rates. Taken together, these observations suggest that rate-dependent compactive deformation mechanisms compete with dilatant subcritical crack growth during creep in limestone under low
Topic 5: Time-Dependent Behavior
Pfeiffer, P.A.; Tanabe, Tada-aki
1991-12-31
This chapter is a report of the material presented at the International Workshop on Finite Element Analysis of Reinforced Concrete, Session 4 -- Time Dependent Behavior, held at Columbia University, New York on June 3--6, 1991. Dr. P.A. Pfeiffer presented recent developments in time-dependent behavior of concrete and Professor T. Tanabe presented a review of research in Japan on time-dependent behavior of concrete. The chapter discusses the recent research of time-dependent behavior of concrete in the past few years in both the USA-European and Japanese communities. The author appreciates the valuable information provided by Zdenek P. Bazant in preparing the USA-European Research section.
Time dependent breakdown in silicon dioxide films
NASA Technical Reports Server (NTRS)
Svensson, C.; Shumka, A.
1975-01-01
An investigation was conducted regarding the possible existence of a time-dependent breakdown mechanism in thermal oxides of the type used as gate oxide in MOS circuits. Questions of device fabrication are discussed along with details concerning breakdown measurements and the determination of C-V characteristics. A relatively large prebreakdown current observed in one of the cases is related to the time-dependent breakdown.
NASA Technical Reports Server (NTRS)
Gates, Thomas S.; Feldman, Mark
1995-01-01
Experimental studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. Isothermal tensile creep/aging test techniques developed for polymers were adapted for testing of the composite material. Time dependent transverse and shear compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(8) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress.
Deterministic methods for time-dependent stochastic neutron transport
Baker, Randal S
2009-01-01
A numerical method is presented for solving the time-dependent survival probability equation in general (lD/2D/3D) geometries using the multi group SNmethod. Although this equation was first formulated by Bell in the early 1960's, it has only been applied to stationary systems (for other than idealized point models) until recently, and detailed descriptions of numerical solution techniques are lacking in the literature. This paper presents such a description and applies it to a dynamic system representative of a figurative criticality accident scenario.
2002-01-31
This program solves the two-dimensional mechanical equilbrium configuration of a core restraint system, which is subjected to radial temperature and flux gradients, on a time increment basis. At each time increment, the code calculates the irradiation creep and swelling strains for each duct from user-specified creep and swelling correlations. Using the calculated thermal bowing, inelastic bowing and the duct dilation, the corresponding equilibrium forces, beam deflections, total beam displacements, and structural reactivity changes are calculated.
A multilayer model of time dependent deformation following an earthquake on a strike-slip fault
NASA Technical Reports Server (NTRS)
Cohen, S. C.
1981-01-01
A multilayer model of the Earth to calculate finite element of time dependent deformation and stress following an earthquake on a strike slip fault is discussed. The model involves shear properties of an elastic upper lithosphere, a standard viscoelastic linear solid lower lithosphere, a Maxwell viscoelastic asthenosphere and an elastic mesosphere. Systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations are analyzed. Both the creep of the lower lithosphere and astenosphere contribute to the postseismic deformation. The magnitude of the deformation is enhanced by a short distance between the bottom of the fault (slip zone) and the top of the creep region but is less sensitive to the thickness of the creeping layer. Postseismic restressing is increased as the lower lithosphere becomes more viscoelastic, but the tendency for the width of the restressed zone to growth with time is retarded.
Postseismic relaxation and transient creep
Savage, J.C.; Svarc, J.L.; Yu, S.-B.
2005-01-01
Postseismic deformation has been observed in the epicentral area following the 1992 Landers (M = 7.3), 1999 Chi-Chi (M = 7.6), 1999 Hector Mine (M = 7.1), 2002 Denali (M = 7.9), 2003 San Simeon (M = 6.5), and 2004 Parkfield (M = 6.0) earthquakes. The observations consist of repeated GPS measurements of the position of one monument relative to another (separation ???100 km). The early observations (t < 0.1 year) are well fit by the function a' + c'log(t), where t is the time after the earthquake and a' and c' are constants chosen to fit the data. Because a log(t) time dependence is characteristic of transient (primary) creep, the early postseismic response may be governed by transient creep as Benioff proposed in 1951. That inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments. The observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause.
Time-dependent behaviour of high performance concrete: influence of coarse aggregate characteristics
NASA Astrophysics Data System (ADS)
Makani, A.; Vidal, T.; Pons, G.; Escadeillas, G.
2010-06-01
This paper examines the influence of coarse aggregate characteristics on the time-dependent deformations of High Performances Concretes (HPC). Four concretes made using the same cement paste but incorporating different types of aggregate (rolled siliceous gravel, crushed granite, crushed limestone and crushed siliceous gravels) were studied in order to investigate the effect of aggregate properties on the compressive strength, modulus of elasticity, shrinkage and creep. The results indicate that the aggregate type has a significant effect on creep and shrinkage deformations of HPC. An influence of the shape of aggregate on time-dependent deformations has also been observed. On the basis of these results, long-term behaviour seems to be correlated to the characteristics of the Interfacial Transition Zone (ITZ) strongly depending on the mineralogical nature and properties of aggregates. The experimental results are compared with the values calculated using the current Eurocode 2 model in order to assess the accuracy of the predictions.
Time dependence of adiabatic particle number
NASA Astrophysics Data System (ADS)
Dabrowski, Robert; Dunne, Gerald V.
2016-09-01
We consider quantum field theoretic systems subject to a time-dependent perturbation, and discuss the question of defining a time-dependent particle number not just at asymptotic early and late times, but also during the perturbation. Naïvely, this is not a well-defined notion for such a nonequilibrium process, as the particle number at intermediate times depends on a basis choice of reference states with respect to which particles and antiparticles are defined, even though the final late-time particle number is independent of this basis choice. The basis choice is associated with a particular truncation of the adiabatic expansion. The adiabatic expansion is divergent, and we show that if this divergent expansion is truncated at its optimal order, a universal time dependence is obtained, confirming a general result of Dingle and Berry. This optimally truncated particle number provides a clear picture of quantum interference effects for perturbations with nontrivial temporal substructure. We illustrate these results using several equivalent definitions of adiabatic particle number: the Bogoliubov, Riccati, spectral function and Schrödinger picture approaches. In each approach, the particle number may be expressed in terms of the tiny deviations between the exact and adiabatic solutions of the Ermakov-Milne equation for the associated time-dependent oscillators.
NASA Technical Reports Server (NTRS)
Wilson, D. J.
1974-01-01
Time dependent notch sensitivity was observed in Udimet 700 sheet, bar, and investment castings between 1000 and 1400 F (538 -760 C), but not at 1600 F (871 C). As was the case for modified Waspaloy, Waspaloy and Inconel 718, it occurred in notched specimens loaded below the yield strength when the creep deformation was localized. For each alloy and notched specimen geometry, a stress-average particle size zone can be defined that characterizes the notch sensitive behavior.
Micromechanics effects in creep of metal-matrix composites
NASA Astrophysics Data System (ADS)
Davis, L. C.; Allison, J. E.
1995-12-01
The creep of metal-matrix composites is analyzed by finite element techniques. An axisymmetric unit-cell model with spherical reinforcing particles is used. Parameters appropriate to TiC particles in a precipitation-hardened (2219) Al matrix are chosen. The effects of matrix plasticity and residual stresses on the creep of the composite are calculated. We confirm (1) that the steady-state rate is independent of the particle elastic moduli and the matrix elastic and plastic properties, (2) that the ratio of composite to matrix steady-state rates depends only on the volume fraction and geometry of the reinforcing phase, and (3) that this ratio can be determined from a calculation of the stress-strain relation for the geometrically identical composite (same phase volume and geometry) with rigid particles in the appropriate power-law hardening matrix. The values of steady-state creep are compared to experimental ones (Krajewski et al.). Continuum mechanics predictions give a larger reduction of the composite creep relative to the unreinforced material than measured, suggesting that the effective creep rate of the matrix is larger than in unreinforced precipitation-hardened Al due to changes in microstructure, dislocation density, or creep mechanism. Changes in matrix creep properties are also suggested by the comparison of calculated and measured creep strain rates in the primary creep regime, where significantly different time dependencies are found. It is found that creep calculations performed for a timeindependent matrix creep law can be transformed to obtain the creep for a time-dependent creep law.
Micromechanics of brittle creep in rocks
NASA Astrophysics Data System (ADS)
Brantut, N.; Baud, P.; Heap, M. J.; Meredith, P. G.
2012-08-01
In the upper crust, the chemical influence of pore water promotes time dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail at stresses well below their short-term failure strength, and even at constant applied stress (“brittle creep”). Here we provide a micromechanical model describing time dependent brittle creep of water-saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model of Ashby and Sammis (1990), and the crack length evolution is computed from Charles' law. The macroscopic strains and strain rates computed from the model are non linear, and compare well with experimental results obtained on granite, low porosity sandstone and basalt rock samples. Primary creep (decelerating strain) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as an inflexion between those two end-member phases. The minimum strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature, which provides an approximate creep law for the process. The creep law is used to infer the long term strain rate as a function of depth in the upper crust due to the action of the applied stresses: in this way, sub-critical cracking reduces the failure stress in a manner equivalent to a decrease in cohesion. We also investigate the competition with pressure solution in porous rocks, and show that the transition from sub
Time-dependent corona models - Scaling laws
NASA Technical Reports Server (NTRS)
Korevaar, P.; Martens, P. C. H.
1989-01-01
Scaling laws are derived for the one-dimensional time-dependent Euler equations that describe the evolution of a spherically symmetric stellar atmosphere. With these scaling laws the results of the time-dependent calculations by Korevaar (1989) obtained for one star are applicable over the whole Hertzsprung-Russell diagram and even to elliptic galaxies. The scaling is exact for stars with the same M/R-ratio and a good approximation for stars with a different M/R-ratio. The global relaxation oscillation found by Korevaar (1989) is scaled to main sequence stars, a solar coronal hole, cool giants and elliptic galaxies.
Investigations of Low Temperature Time Dependent Cracking
Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J
2002-09-30
The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.
Time-Dependent Molecular Reaction Dynamics
NASA Astrophysics Data System (ADS)
Öhrn, Yngve
2007-11-01
This paper is a brief review of a time-dependent, direct, nonadiabatic theory of molecular processes called Electron Nuclear Dynamics (END). This approach to the study of molecular reaction dynamics is a hierarchical theory that can be applied at various levels of approximation. The simplest level of END uses classical nuclei and represents all electrons by a single, complex, determinantal wave function. The wave function parameters such as average nuclear positions and momenta, and molecular orbital coefcients carry the time dependence and serve as dynamical variables. Examples of application are given of the simplest level of END to ion-atom and ion-molecule reactions.
Time-dependent mechanical-electrical coupled behavior in single crystal ZnO nanorods
Kim, Yong-Jae; Yun, Tae Gwang; Choi, In-Chul; Kim, Sungwoong; Park, Won Il; Han, Seung Min; Jang, Jae-il
2015-01-01
Nanoscale time-dependent mechanical-electrical coupled behavior of single crystal ZnO nanorods was systematically explored, which is essential for accessing the long-term reliability of the ZnO nanorod-based flexible devices. A series of compression creep tests combined with in-situ electrical measurement was performed on vertically-grown single crystal ZnO nanorods. Continuous measurement of the current (I)-voltage (V) curves before, during, after the creep tests revealed that I is non-negligibly increased as a result of the time-dependent deformation. Analysis of the I-V curves based on the thermionic emission-diffusion theory allowed extraction of nanorod resistance, which was shown to decrease as time-dependent deformation. Finally, based on the observations in this study, a simple analytical model for predicting the reduction in nanorod resistance as a function of creep strain that is induced from diffusional mechanisms is proposed, and this model was demonstrated to be in an excellent agreement with the experimental results. PMID:25982962
Brittle and compaction creep in porous sandstone
NASA Astrophysics Data System (ADS)
Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip
2015-04-01
Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate
Wave function for time-dependent harmonically confined electrons in a time-dependent electric field.
Li, Yu-Qi; Pan, Xiao-Yin; Sahni, Viraht
2013-09-21
The many-body wave function of a system of interacting particles confined by a time-dependent harmonic potential and perturbed by a time-dependent spatially homogeneous electric field is derived via the Feynman path-integral method. The wave function is comprised of a phase factor times the solution to the unperturbed time-dependent Schrödinger equation with the latter being translated by a time-dependent value that satisfies the classical driven equation of motion. The wave function reduces to that of the Harmonic Potential Theorem wave function for the case of the time-independent harmonic confining potential. PMID:24070284
Shin, U.; Miller, W.F. Jr. |; Morel, J.E.
1994-10-01
Using conventional diffusion limit analysis, we asymptotically compare three competitive time-dependent equations (the telegrapher`s equation, the time-dependent Simplified P{sub 2} (SP{sub 2}) equation, and the time-dependent Simplified Evcn-Parity (SEP) equation). The time-dependent SP{sub 2} equation contains higher order asymptotic approximations of the time-dependent transport equation than the other equations in a physical regime in which the time-dependent diffusion equation is the leading order approximation. In addition, we derive the multigroup modified time-dependent SP{sub 2} equation from the multigroup time-dependent transport equation by means of an asymptotic expansion in which the multigroup time-dependent diffusion equation is the leading, order approximation. Numerical comparisons of the timedependent diffusion, the telegrapher`s, the time-dependent SP{sub 2}, and S{sub 8} solutions in 2-D X-Y geometry show that, in most cases, the SP{sub 2} solutions contain most of the transport corrections for the diffusion approximation.
In-situ Creep Testing Capability Development for Advanced Test Reactor
B. G. Kim; J. L. Rempe; D. L. Knudson; K. G. Condie; B. H. Sencer
2010-08-01
Creep is the slow, time-dependent strain that occurs in a material under a constant strees (or load) at high temperature. High temperature is a relative term, dependent on the materials being evaluated. A typical creep curve is shown in Figure 1-1. In a creep test, a constant load is applied to a tensile specimen maintained at a constant temperature. Strain is then measured over a period of time. The slope of the curve, identified in the figure below, is the strain rate of the test during Stage II or the creep rate of the material. Primary creep, Stage I, is a period of decreasing creep rate due to work hardening of the material. Primary creep is a period of primarily transient creep. During this period, deformation takes place and the resistance to creep increases until Stage II, Secondary creep. Stage II creep is a period with a roughly constant creep rate. Stage II is referred to as steady-state creep because a balance is achieved between the work hardening and annealing (thermal softening) processes. Tertiary creep, Stage III, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation; that is, the creep rate increases due to necking of the specimen and the associated increase in local stress.
Time-dependent species sensitivity distributions.
Fox, David R; Billoir, Elise
2013-02-01
Time is a central component of toxicity assessments. However, current ecotoxicological practice marginalizes time in concentration-response (C-R) modeling and species sensitivity distribution (SSD) analyses. For C-R models, time is invariably fixed, and toxicity measures are estimated from a function fitted to the data at that time. The estimated toxicity measures are used as inputs to the SSD modeling phase, which similarly avoids explicit recognition of the temporal component. The present study extends some commonly employed probability models for SSDs to derive theoretical results that characterize the time-dependent nature of hazardous concentration (HCx) values. The authors' results show that even from very simple assumptions, more complex patterns in the SSD time dependency can be revealed.
Landauer Approach to Time-Dependent Transport
NASA Astrophysics Data System (ADS)
Chen, L. Y.; Nash, P. L.
Based upon the nonequilibrium Green's function formalism, we present a time-dependent Landauer approach to transport through a mesoscopic system under an ac bias voltage. The system is modeled as an elastic scatterer coupled to large electron reservoirs through perfect conducting wires (leads). The chemical potentials of the reservoirs are driven apart by the bias and, consequently, current flows through the leads from one reservoir to another. We examine the nonequilibrium statistical processes of electrons in the leads. The electronic waves are quantized on the basis of orthonormal wave packets moving along the leads, scattered by the scatterer, and coupled to the reservoirs. The time for an electron to traverse the leads between the source and the drain reservoirs plus the phase delay time caused by the scatterer is found to be the relevant time scale in the time-dependent transport. The frequency dependence of the admittance is fully investigated.
Transformation of time dependence to linear algebra
NASA Astrophysics Data System (ADS)
Menšík, Miroslav
2005-10-01
Reduced density matrix and memory function in the Nakajima-Zwanzig equation are expanded in properly chosen basis of special functions. This trick completely transforms time dependence to linear algebra. Then, the master equation for memory function is constructed and expanded in the same basis functions. For the model of a simple harmonic oscillator it is shown that this trick introduces infinite partial summation of the memory function in the system-bath interaction.
Time-dependent oral absorption models
NASA Technical Reports Server (NTRS)
Higaki, K.; Yamashita, S.; Amidon, G. L.
2001-01-01
The plasma concentration-time profiles following oral administration of drugs are often irregular and cannot be interpreted easily with conventional models based on first- or zero-order absorption kinetics and lag time. Six new models were developed using a time-dependent absorption rate coefficient, ka(t), wherein the time dependency was varied to account for the dynamic processes such as changes in fluid absorption or secretion, in absorption surface area, and in motility with time, in the gastrointestinal tract. In the present study, the plasma concentration profiles of propranolol obtained in human subjects following oral dosing were analyzed using the newly derived models based on mass balance and compared with the conventional models. Nonlinear regression analysis indicated that the conventional compartment model including lag time (CLAG model) could not predict the rapid initial increase in plasma concentration after dosing and the predicted Cmax values were much lower than that observed. On the other hand, all models with the time-dependent absorption rate coefficient, ka(t), were superior to the CLAG model in predicting plasma concentration profiles. Based on Akaike's Information Criterion (AIC), the fluid absorption model without lag time (FA model) exhibited the best overall fit to the data. The two-phase model including lag time, TPLAG model was also found to be a good model judging from the values of sum of squares. This model also described the irregular profiles of plasma concentration with time and frequently predicted Cmax values satisfactorily. A comparison of the absorption rate profiles also suggested that the TPLAG model is better at prediction of irregular absorption kinetics than the FA model. In conclusion, the incorporation of a time-dependent absorption rate coefficient ka(t) allows the prediction of nonlinear absorption characteristics in a more reliable manner.
Time-dependent nucleation in partitioning systems
Kelton, K.F.; Narayan, K.L.
1998-12-31
Nucleation in multi-component systems is poorly understood, particularly when the rates of long-range diffusion are comparable with the rates of attachment at the cluster interface. For illustration, measurements of the time-dependent nucleation rates in silicate and metallic glasses are discussed. A new model for nucleation in partitioning systems, which explains many of devitrification microstructural features in bulk metallic glasses, is presented.
Time-dependent projected Hartree-Fock
Tsuchimochi, Takashi; Van Voorhis, Troy
2015-03-28
Projected Hartree-Fock (PHF) has recently emerged as an alternative approach to describing degenerate systems where static correlation is abundant, when the spin-symmetry is projected. Here, we derive a set of linearized time-dependent equations for PHF in order to be able to access excited states. The close connection of such linear-response time-dependent PHF (TDPHF) to the stability condition of a PHF wave function is discussed. Expanding this analysis also makes it possible to give analytical expressions for the projected coupling terms of Hamiltonian and overlaps between excited Slater determinants. TDPHF with spin-projection (TDSUHF) and its Tamm-Dancoff approximation are benchmarked for several electronically degenerate molecules including the dissociating H{sub 2}, F{sub 2} and O{sub 3} at equilibrium, and the distorted ethylene. It is shown that they give consistently better descriptions of excited states than does time-dependent HF (TDHF). Furthermore, we demonstrate that they offer not only singly but also doubly excited states, which naturally arise upon spin-projection. We also address the thermodynamic limit of TDSUHF, using non-interacting He gas. While TDPHF singly excited states tend to converge to those of HF with the size of the system due to the lack of size-extensivity of PHF, doubly excited states remain reasonable even at the thermodynamic limit. We find that the overall performance of our method is systematically better than the regular TDHF in many cases at the same computational scaling.
Dissipative time-dependent quantum transport theory.
Zhang, Yu; Yam, Chi Yung; Chen, GuanHua
2013-04-28
A dissipative time-dependent quantum transport theory is developed to treat the transient current through molecular or nanoscopic devices in presence of electron-phonon interaction. The dissipation via phonon is taken into account by introducing a self-energy for the electron-phonon coupling in addition to the self-energy caused by the electrodes. Based on this, a numerical method is proposed. For practical implementation, the lowest order expansion is employed for the weak electron-phonon coupling case and the wide-band limit approximation is adopted for device and electrodes coupling. The corresponding hierarchical equation of motion is derived, which leads to an efficient and accurate time-dependent treatment of inelastic effect on transport for the weak electron-phonon interaction. The resulting method is applied to a one-level model system and a gold wire described by tight-binding model to demonstrate its validity and the importance of electron-phonon interaction for the quantum transport. As it is based on the effective single-electron model, the method can be readily extended to time-dependent density functional theory.
Time Dependent Behavior in the Weissenberg Effect
NASA Astrophysics Data System (ADS)
Degen, Michael M.; Andereck, C. David
1997-03-01
The Weissenberg effect is the climb of a non-Newtonian fluid up a rotating rod. We have found novel transitional effects in the behavior of a particular climbing fluid, STP(STP Oil Treatment distributed by First Brands Corporation.). The first state is a time-independent axisymmetric concave climb. As the rotation rate of the rod is increased, the first transition is to an axisymmetric climb with an ``onion dome'' shape. At higher rotation rates, the flow undergoes a symmetry breaking bifurcation to a time-dependent state. This time-dependent state exhibits an oscillation with a single frequency. Upon further increase of the rod rotation rate, the oscillation becomes modulated by a second frequency. The nature of each transition will be characterized, including the measurement of oscillation amplitudes and the frequency (or frequencies) of the time dependent states. These results will be compared with previous work.(G.S. Beavers, D.D. Joseph, J. Fluid Mech. 69), 475 (1975).(D.D. Joseph, R.L. Fosdick, Arch. Rational Mech. 49), 321 (1973).
Creep of plain weave polymer matrix composites
NASA Astrophysics Data System (ADS)
Gupta, Abhishek
Polymer matrix composites are increasingly used in various industrial sectors to reduce structural weight and improve performance. Woven (also known as textile) composites are one class of polymer matrix composites with increasing market share mostly due to their lightweight, their flexibility to form into desired shape, their mechanical properties and toughness. Due to the viscoelasticity of the polymer matrix, time-dependent degradation in modulus (creep) and strength (creep rupture) are two of the major mechanical properties required by engineers to design a structure reliably when using these materials. Unfortunately, creep and creep rupture of woven composites have received little attention by the research community and thus, there is a dire need to generate additional knowledge and prediction models, given the increasing market share of woven composites in load bearing structural applications. Currently, available creep models are limited in scope and have not been validated for any loading orientation and time period beyond the experimental time window. In this thesis, an analytical creep model, namely the Modified Equivalent Laminate Model (MELM), was developed to predict tensile creep of plain weave composites for any orientation of the load with respect to the orientation of the fill and warp fibers, using creep of unidirectional composites. The ability of the model to predict creep for any orientation of the load is a "first" in this area. The model was validated using an extensive experimental involving the tensile creep of plain weave composites under varying loading orientation and service conditions. Plain weave epoxy (F263)/ carbon fiber (T300) composite, currently used in aerospace applications, was procured as fabrics from Hexcel Corporation. Creep tests were conducted under two loading conditions: on-axis loading (0°) and off-axis loading (45°). Constant load creep, in the temperature range of 80-240°C and stress range of 1-70% UTS of the
Algorithms for elasto-plastic-creep postbuckling
NASA Technical Reports Server (NTRS)
Padovan, J.; Tovichakchaikul, S.
1984-01-01
This paper considers the development of an improved constrained time stepping scheme which can efficiently and stably handle the pre-post-buckling behavior of general structure subject to high temperature environments. Due to the generality of the scheme, the combined influence of elastic-plastic behavior can be handled in addition to time dependent creep effects. This includes structural problems exhibiting indefinite tangent properties. To illustrate the capability of the procedure, several benchmark problems employing finite element analyses are presented. These demonstrate the numerical efficiency and stability of the scheme. Additionally, the potential influence of complex creep histories on the buckling characteristics is considered.
Singular boundary method using time-dependent fundamental solution for scalar wave equations
NASA Astrophysics Data System (ADS)
Chen, Wen; Li, Junpu; Fu, Zhuojia
2016-11-01
This study makes the first attempt to extend the meshless boundary-discretization singular boundary method (SBM) with time-dependent fundamental solution to two-dimensional and three-dimensional scalar wave equation upon Dirichlet boundary condition. The two empirical formulas are also proposed to determine the source intensity factors. In 2D problems, the fundamental solution integrating along with time is applied. In 3D problems, a time-successive evaluation approach without complicated mathematical transform is proposed. Numerical investigations show that the present SBM methodology produces the accurate results for 2D and 3D time-dependent wave problems with varied velocities c and wave numbers k.
Singular boundary method using time-dependent fundamental solution for scalar wave equations
NASA Astrophysics Data System (ADS)
Chen, Wen; Li, Junpu; Fu, Zhuojia
2016-07-01
This study makes the first attempt to extend the meshless boundary-discretization singular boundary method (SBM) with time-dependent fundamental solution to two-dimensional and three-dimensional scalar wave equation upon Dirichlet boundary condition. The two empirical formulas are also proposed to determine the source intensity factors. In 2D problems, the fundamental solution integrating along with time is applied. In 3D problems, a time-successive evaluation approach without complicated mathematical transform is proposed. Numerical investigations show that the present SBM methodology produces the accurate results for 2D and 3D time-dependent wave problems with varied velocities c and wave numbers k.
NASA Astrophysics Data System (ADS)
Khoshmanesh, M.; Shirzaei, M.; Nadeau, R. M.
2015-09-01
The Central segment of San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. However, observations of the creep rate obtained using small characteristically repeating earthquakes (CREs) show pulses of creep along the CSAF, which may indicate spatially and temporally variable seismic hazard along the CSAF. Therefore, the goal of this study is to obtain a high-resolution time-dependent model of creep along the CSAF to examine this hypothesis. To this end, we apply a time-dependent creep modeling approach, which combines interferometric synthetic aperture radar (InSAR) surface deformation time series and observations of fault creep obtained from CREs. The SAR data set includes C band scenes acquired by the ERS-2 and Envisat satellites between 2003 and 2011. The resulting creep rate distribution implies a peak rate up to 32 mm/yr along the central part of the CSAF. Afterslip due to the 2004 Parkfield earthquake on the southeastern segment of the CSAF is also manifest in the model, and there is clear evidence of creep pulsing along strike and depth of the CSAF. Estimated annual rate of slip deficit accumulation is equivalent to a magnitude 5.6-5.7 earthquake. Taking advantage of the time-dependence of our model, we also refine the scaling relationship, which associates the released seismic moment due to a CRE event with the amount of creep on the fault, surrounding the CRE patches. This study provides the first kinematic model of creep pulsing, constrained using geodetic and seismic data, which can enhance time-dependent seismic hazard maps and improve earthquake operational forecast models.
Time-dependent Dyson orbital theory.
Gritsenko, O V; Baerends, E J
2016-08-21
Although time-dependent density functional theory (TDDFT) has become the tool of choice for real-time propagation of the electron density ρ(N)(t) of N-electron systems, it also encounters problems in this application. The first problem is the neglect of memory effects stemming from the, in TDDFT virtually unavoidable, adiabatic approximation, the second problem is the reliable evaluation of the probabilities P(n)(t) of multiple photoinduced ionization, while the third problem (which TDDFT shares with other approaches) is the reliable description of continuum states of the electrons ejected in the process of ionization. In this paper time-dependent Dyson orbital theory (TDDOT) is proposed. Exact TDDOT equations of motion (EOMs) for time-dependent Dyson orbitals are derived, which are linear differential equations with just static, feasible potentials of the electron-electron interaction. No adiabatic approximation is used, which formally resolves the first TDDFT problem. TDDOT offers formally exact expressions for the complete evolution in time of the wavefunction of the outgoing electron. This leads to the correlated probability of single ionization P(1)(t) as well as the probabilities of no ionization (P(0)(t)) and multiple ionization of n electrons, P(n)(t), which formally solves the second problem of TDDFT. For two-electron systems a proper description of the required continuum states appears to be rather straightforward, and both P(1)(t) and P(2)(t) can be calculated. Because of the exact formulation, TDDOT is expected to reproduce a notorious memory effect, the "knee structure" of the non-sequential double ionization of the He atom. PMID:26987972
Pulsar Electrodynamics: a Time-dependent View
Spitkovsky, Anatoly; /KIPAC, Menlo Park
2006-04-10
Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the formation of the magnetosphere and its response to perturbations, opening a qualitatively new window on pulsar phenomena. Applications of the method to other magnetized rotators, such as magnetars and accretion disks, are also discussed.
The time-dependent Gutzwiller approximation
NASA Astrophysics Data System (ADS)
Fabrizio, Michele
2015-03-01
The time-dependent Gutzwiller Approximation (t-GA) is shown to be capable of tracking the off-equilibrium evolution both of coherent quasiparticles and of incoherent Hubbard bands. The method is used to demonstrate that the sharp dynamical crossover observed by time-dependent DMFT in the quench-dynamics of a half-filled Hubbard model can be identified within the t-GA as a genuine dynamical transition separating two distinct physical phases. This result, strictly variational for lattices of infinite coordination number, is intriguing as it actually questions the occurrence of thermalization. Next, we shall present how t-GA works in a multi-band model for V2O3 that displays a first-order Mott transition. We shall show that a physically accessible excitation pathway is able to collapse the Mott gap down and drive off-equilibrium the insulator into a metastable metal phase. Work supported by the European Union, Seventh Framework Programme, under the project GO FAST, Grant Agreement No. 280555.
Two-parameter Failure Model Improves Time-independent and Time-dependent Failure Predictions
Huddleston, R L
2004-01-27
A new analytical model for predicting failure under a generalized, triaxial stress state was developed by the author and initially reported in 1984. The model was validated for predicting failure under elevated-temperature creep-rupture conditions. Biaxial data for three alloy steels, Types 304 and 316 stainless steels and Inconel 600, demonstrated two to three orders of magnitude reduction in the scatter of predicted versus observed creep-rupture times as compared to the classical failure models of Mises, Tresca, and Rankine. In 1990, the new model was incorporated into American Society of Mechanical Engineers (ASME) Code Case N47-29 for design of components operating under creep-rupture conditions. The current report provides additional validation of the model for predicting failure under time-independent conditions and also outlines a methodology for predicting failure under cyclic, time-dependent, creep-fatigue conditions. The later extension of the methodology may have the potential to improve failure predictions there as well. These results are relevant to most design applications, but they have special relevance to high-performance design applications such as components for high-pressure equipment, nuclear reactors, and jet engines.
Pseudospectral time-dependent density functional theory
NASA Astrophysics Data System (ADS)
Ko, Chaehyuk; Malick, David K.; Braden, Dale A.; Friesner, Richard A.; Martínez, Todd J.
2008-03-01
Time-dependent density functional theory (TDDFT) is implemented within the Tamm-Dancoff approximation (TDA) using a pseudospectral approach to evaluate two-electron repulsion integrals. The pseudospectral approximation uses a split representation with both spectral basis functions and a physical space grid to achieve a reduction in the scaling behavior of electronic structure methods. We demonstrate here that exceptionally sparse grids may be used in the excitation energy calculation, following earlier work employing the pseudospectral approximation for determining correlation energies in wavefunction-based methods with similar conclusions. The pseudospectral TDA-TDDFT method is shown to be up to ten times faster than a conventional algorithm for hybrid functionals without sacrificing chemical accuracy.
Time-dependent landslide probability mapping
Campbell, Russell H.; Bernknopf, Richard L.; ,
1993-01-01
Case studies where time of failure is known for rainfall-triggered debris flows can be used to estimate the parameters of a hazard model in which the probability of failure is a function of time. As an example, a time-dependent function for the conditional probability of a soil slip is estimated from independent variables representing hillside morphology, approximations of material properties, and the duration and rate of rainfall. If probabilities are calculated in a GIS (geomorphic information system ) environment, the spatial distribution of the result for any given hour can be displayed on a map. Although the probability levels in this example are uncalibrated, the method offers a potential for evaluating different physical models and different earth-science variables by comparing the map distribution of predicted probabilities with inventory maps for different areas and different storms. If linked with spatial and temporal socio-economic variables, this method could be used for short-term risk assessment.
Time-dependent Benioff strain release diagrams
NASA Astrophysics Data System (ADS)
Frid, V.; Goldbaum, J.; Rabinovitch, A.; Bahat, D.
2011-04-01
New time-dependent Benioff strain (TDBS) release diagrams were analyzed for acoustic emission during various loading tests and for electromagnetic (EM) radiation emanating during compression and, tension, which end in failure. TDBS diagrams are Benioff diagrams that are built consecutively, each time using a greater number of events (acoustic or EM emissions) using the last event as if it were associated with the 'actual failure'. An examination of such TDBS diagrams shows that at a certain time point (this time point is denoted by the term 'alarm' time), a comparatively short interval prior to actual collapse, their decreasing part is broken by a positive 'bulge'. This 'bulge' is quantified and an algorithm proposed for its assessment. Using the alarm time and other parameters of the failure process (fall, bulge size and escalation factors, bulge slope and slope fall time), a criterion for estimating the time of the actual collapse is developed and shown to agree well with laboratory experimental results.
Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear?
NASA Astrophysics Data System (ADS)
Anssari-Benam, Afshin
2014-05-01
The widely popular quasi-linear viscoelasticity (QLV) theory has been employed extensively in the literature for characterising the time-dependent behaviour of many biological tissues, including the aortic valve (AV). However, in contrast to other tissues, application of QLV to AV data has been met with varying success, with studies reporting discrepancies in the values of the associated quantified parameters for data collected from different timescales in experiments. Furthermore, some studies investigating the stress-relaxation phenomenon in valvular tissues have suggested discrete relaxation spectra, as an alternative to the continuous spectrum proposed by the QLV. These indications put forward a more fundamental question: Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear? In other words, can the inherent characteristics of the tissue that govern its biomechanical behaviour facilitate a quasi-linear time-dependent behaviour? This paper attempts to address these questions by presenting a mathematical analysis to derive the expressions for the stress-relaxation G( t) and creep J( t) functions for the AV tissue within the QLV theory. The principal inherent characteristic of the tissue is incorporated into the QLV formulation in the form of the well-established gradual fibre recruitment model, and the corresponding expressions for G( t) and J( t) are derived. The outcomes indicate that the resulting stress-relaxation and creep functions do not appear to voluntarily follow the observed experimental trends reported in previous studies. These results highlight that the time-dependent behaviour of the AV may not be quasi-linear, and more suitable theoretical criteria and models may be required to explain the phenomenon based on tissue's microstructure, and for more accurate estimation of the associated material parameters. In general, these results may further be applicable to other planar soft tissues of the same class, i.e. with the same
Solid-phase creep during the expression of palm-oil filter cakes
Kamst, G.F.; Bruinsma, O.S.L.; Graauw, J. de
1997-03-01
For an adequate model of the processes of compressible cake filtration and mechanical expression, permeability and compressibility data are required. Experimental and modeling results of the creep behavior of palm-oil filter cakes at constant and time-dependent pressures are presented. Creep curves of palm-oil cakes at constant pressures cannot be modeled with linear viscoelastic models. Modeling with a modified form of the empirical equation of Nutting gives satisfactory results. This modification does not lead to unrealistic values of the porosity at extreme conditions, contrary to the original form of the equation of Nutting. Creep curves at time-dependent pressures were modeled with two nonlinear viscoelastic models, which describe the time-dependent creep behavior as a function of the pressure history and creep curves at constant pressures. Modeling with the strain-hardening model provides the best porosity predictions.
GEOMETRY, TIME DEPENDENT AND FAILURE PROPERTIES OF HUMAN MENISCAL ATTACHMENTS
Hauch, Karen N.; Villegas, Diego F.; Donahue, Tammy L. Haut
2009-01-01
Meniscectomies have been shown to lead to osteoarthritis and the success of meniscal replacements remains questionable. It has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau at the horn locations. To aid in the development of meniscal replacements, the objectives of the current study were to determine the time-dependent and failure properties of human meniscal attachments. In contrast to the time-dependent tests, during uniaxial failure testing a charge-coupled video camera was used to document the local strain and linear modulus distribution across the surface of the attachments. The lateral attachments were statistically smaller in cross-sectional area and longer than the medial attachments. The anterior attachments were statistically longer and had a smaller cross-sectional area than the posterior attachments. From the stress relaxation tests, the load and stress relaxation rates of the medial anterior attachment were statistically greater than the medial posterior attachment. There were no significant differences in the creep, structural properties or the ultimate stress between the different attachments. Ultimate strain varied between attachments as well as along the length of the attachment. Ultimate strain in the meniscus region (10.4±6.9%) and mid-substance region (12.7±16.4%) was smaller than the bony insertion region (32.2±21.5%). The lateral and anterior attachments were also found to have statistically greater strain than the medial and posterior attachments, respectively. The linear modulus was statistically weaker in the bony insertion region (69.7±33.7 MPa) compared to the meniscus region (153±123 MPa) and mid-substance region (195±121 MPa). Overall the anterior attachments (169±130 MPa) were also found to be statistically stronger than the posterior attachments (90.8±64.9 MPa). These results can be used
Endochronic theory of transient creep and creep recovery
NASA Technical Reports Server (NTRS)
Wu, H. C.; Chen, L.
1979-01-01
Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ber derived from the general constitutive equation by imposing appropriate constraints. In this unified approach, the effect of strain-hardening is naturally accounted for when describing creep and creep recovery. The theory predicts with reasonable accuracy the creep and creep recovery behaviors for Aluminum 1100-0 at 150 C. It was found that the strain-rate history at prestraining stage affects the subsequent creep. A critical stress was also established for creep recovery. The theory predicts a forward creep for creep recovery stress greater than the critical stress. For creep recovery stress less than the critical stress, the theory then predicts a normal strain recovery.
Static & Dynamic Response of 2D Solids
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surfacemore » contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.« less
Static & Dynamic Response of 2D Solids
Lin, Jerry
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.
Unified creep-plasticity model for halite
Krieg, R. D.
1980-11-01
There are two national energy programs which are considering caverns in geological salt (NaCl) as a storage repository. One is the disposal of nuclear wastes and the other is the storage of oil. Both short-time and long-time structural deformations and stresses must be predictable for these applications. At 300K, the nominal initial temperature for both applications, the salt is at 0.28 of the melting temperature and exhibits a significant time dependent behavior. A constitutive model has been developed which describes the behavior observed in an extensive set of triaxial creep tests. Analysis of these tests showed that a single deformation mechanism seems to be operative over the stress and temperature range of interest so that the secondary creep data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified creep-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and creep strains yet models the total inelastic strain reasonably well including primary and secondary creep and reverse loadings. A multiaxial formulation is applied with a back stress. A Bauschinger effect is exhibited as a consequence and is present regardless of the time scale over which the loading is applied. The model would be interpreted as kinematic hardening in the sense of classical plasticity. Comparisons are made between test data and model behavior.
NASA Technical Reports Server (NTRS)
Wilson, D. J.
1975-01-01
Time-dependent notch sensitivity of Udimet 700 sheet, bar, and investment castings was observed between 1000 and 1400 F (538-760 C) but not at 1600 F (871 C). As was the case for Modified Waspaloy, Waspaloy, Rene 41, Inconel 718, and TD-NiCr, it occurred when notched specimens were loaded below the yield strength and when creep deformation was localized. For each gamma-prime strengthened alloy and notched specimen geometry, a stress-average particle size zone can be defined to characterize the notch-sensitive behavior.
Instabilities in Time Dependent Boundary Layers
NASA Astrophysics Data System (ADS)
Otto, Stephen Robert
Available from UMI in association with The British Library. The work in this thesis is concerned with instabilities known to occur in boundary layers. The boundary layers considered herein are of a temporal nature; that is they are time dependent. In Chapter 1 a general overview of the subject is given. In Chapter 2, we consider two Stokes layers found to occur on a sphere. Firstly, the case where the sphere oscillates along a radius, referred to as transverse oscillations, and secondly where the sphere oscillates about its axis, referred to as torsional oscillations. We also consider the oscillations to be of such an amplitude and frequency so that the resulting boundary layer is thin compared to the sphere's radius. Chapter 3, is concerned with the development of vortices in a temporally growing boundary layer occurring on an infinite flat plate, the fluid above which is started to move impulsively. Here we take account of the fact that the boundary layer is growing with time, in a similar manner as has been used for the Blasius layer to grow with a downstream coordinate. In Chapter 4, we consider a boundary layer found to occur outside a cylinder, which at a certain instant has a torsional velocity imparted to it, this layer grows with time. The development of vortices in considered in this layer, and certain parameter regimes are investigated namely those appropriate to the right hand branch of the neutral curve, and those appropriate to the development of inviscid Gortler modes.
Time dependent friction in a free gas
NASA Astrophysics Data System (ADS)
Fanelli, Cristiano; Sisti, Francesco; Stagno, Gabriele V.
2016-03-01
We consider a body moving in a perfect gas, described by the mean-field approximation and interacting elastically with the body, we study the friction exerted by the gas on the body fixed at constant velocities. The time evolution of the body in this setting was studied in Caprino et al. [Math. Phys. 264, 167-189 (2006)], Caprino et al. [Math. Models Methods Appl. Sci. 17, 1369-1403 (2007)], and Cavallaro [Rend. Mat. Appl. 27, 123-145 (2007)] for object with simple shape; the first study where a simple kind of concavity was considered was in Sisti and Ricciuti [SIAM J. Math. Anal. 46, 3759-3611 (2014)], showing new features in the dynamic but not in the friction term. The case of more general shape of the body was left out for further difficulties, and we believe indeed that there are actually non-trivial issues to be faced for these more general cases. To show this and in the spirit of getting a more realistic perspective in the study of friction problems, in this paper, we focused our attention on the friction term itself, studying its behavior on a body with a more general kind of concavity and fixed at constant velocities. We derive the expression of the friction term for constant velocities, we show how it is time dependent, and we give its exact estimate in time. Finally, we use this result to show the absence of a constant velocity in the actual dynamic of such a body.
Heating liquid dielectrics by time dependent fields
NASA Astrophysics Data System (ADS)
Khalife, A.; Pathak, U.; Richert, R.
2011-10-01
Steady state and time-resolved dielectric relaxation experiments are performed at high fields on viscous glycerol and the effects of energy absorption from the electric field are studied. Time resolution is obtained by a sinusoidal field whose amplitude is switched from a low to a high level and by recording voltage and current traces with an oscilloscope during this transition. Based on their distinct time and frequency dependences, three sources of modifying the dynamics and dielectric loss via an increase in the effective temperature can be distinguished: electrode temperature, real sample temperature, and configurational temperatures of the modes that absorbed the energy. Isothermal conditions that are desired for focusing on the configurational temperature changes (as in dielectric hole burning and related techniques) are maintained only for very thin samples and for moderate power levels. For high frequencies, say ν > 1 MHz, changes of the real temperature will exceed the effects of configurational temperatures in the case of macroscopic samples. Regarding microwave chemistry, heating via cell phone use, and related situations in which materials are subject to fields involving frequencies beyond the MHz regime, we conclude that changes in the configurational (or fictive) temperatures remain negligible compared with the increase of the real temperature. This simplifies the assessment of how time dependent electric fields modify the properties of materials.
Time dependence of Hawking radiation entropy
Page, Don N.
2013-09-01
If a black hole starts in a pure quantum state and evaporates completely by a unitary process, the von Neumann entropy of the Hawking radiation initially increases and then decreases back to zero when the black hole has disappeared. Here numerical results are given for an approximation to the time dependence of the radiation entropy under an assumption of fast scrambling, for large nonrotating black holes that emit essentially only photons and gravitons. The maximum of the von Neumann entropy then occurs after about 53.81% of the evaporation time, when the black hole has lost about 40.25% of its original Bekenstein-Hawking (BH) entropy (an upper bound for its von Neumann entropy) and then has a BH entropy that equals the entropy in the radiation, which is about 59.75% of the original BH entropy 4πM{sub 0}{sup 2}, or about 7.509M{sub 0}{sup 2} ≈ 6.268 × 10{sup 76}(M{sub 0}/M{sub s}un){sup 2}, using my 1976 calculations that the photon and graviton emission process into empty space gives about 1.4847 times the BH entropy loss of the black hole. Results are also given for black holes in initially impure states. If the black hole starts in a maximally mixed state, the von Neumann entropy of the Hawking radiation increases from zero up to a maximum of about 119.51% of the original BH entropy, or about 15.018M{sub 0}{sup 2} ≈ 1.254 × 10{sup 77}(M{sub 0}/M{sub s}un){sup 2}, and then decreases back down to 4πM{sub 0}{sup 2} = 1.049 × 10{sup 77}(M{sub 0}/M{sub s}un){sup 2}.
Time-dependence in mixture toxicity prediction
Dawson, Douglas A.; Allen, Erin M.G.; Allen, Joshua L.; Baumann, Hannah J.; Bensinger, Heather M.; Genco, Nicole; Guinn, Daphne; Hull, Michael W.; Il'Giovine, Zachary J.; Kaminski, Chelsea M.; Peyton, Jennifer R.; Schultz, T. Wayne; Pöch, Gerald
2014-01-01
The value of time-dependent toxicity (TDT) data in predicting mixture toxicity was examined. Single chemical (A and B) and mixture (A + B) toxicity tests using Microtox® were conducted with inhibition of bioluminescence (Vibrio fischeri) being quantified after 15, 30 and 45-min of exposure. Single chemical and mixture tests for 25 sham (A1:A2) and 125 true (A:B) combinations had a minimum of seven duplicated concentrations with a duplicated control treatment for each test. Concentration/response (x/y) data were fitted to sigmoid curves using the five-parameter logistic minus one parameter (5PL-1P) function, from which slope, EC25, EC50, EC75, asymmetry, maximum effect, and r2 values were obtained for each chemical and mixture at each exposure duration. Toxicity data were used to calculate percentage-based TDT values for each individual chemical and mixture of each combination. Predicted TDT values for each mixture were calculated by averaging the TDT values of the individual components and regressed against the observed TDT values obtained in testing, resulting in strong correlations for both sham (r2 = 0.989, n = 25) and true mixtures (r2 = 0.944, n = 125). Additionally, regression analyses confirmed that observed mixture TDT values calculated for the 50% effect level were somewhat better correlated with predicted mixture TDT values than at the 25 and 75% effect levels. Single chemical and mixture TDT values were classified into five levels in order to discern trends. The results suggested that the ability to predict mixture TDT by averaging the TDT of the single agents was modestly reduced when one agent of the combination had a positive TDT value and the other had a minimal or negative TDT value. PMID:25446331
Time dependence of Hawking radiation entropy
NASA Astrophysics Data System (ADS)
Page, Don N.
2013-09-01
If a black hole starts in a pure quantum state and evaporates completely by a unitary process, the von Neumann entropy of the Hawking radiation initially increases and then decreases back to zero when the black hole has disappeared. Here numerical results are given for an approximation to the time dependence of the radiation entropy under an assumption of fast scrambling, for large nonrotating black holes that emit essentially only photons and gravitons. The maximum of the von Neumann entropy then occurs after about 53.81% of the evaporation time, when the black hole has lost about 40.25% of its original Bekenstein-Hawking (BH) entropy (an upper bound for its von Neumann entropy) and then has a BH entropy that equals the entropy in the radiation, which is about 59.75% of the original BH entropy 4πM02, or about 7.509M02 ≈ 6.268 × 1076(M0/Msolar)2, using my 1976 calculations that the photon and graviton emission process into empty space gives about 1.4847 times the BH entropy loss of the black hole. Results are also given for black holes in initially impure states. If the black hole starts in a maximally mixed state, the von Neumann entropy of the Hawking radiation increases from zero up to a maximum of about 119.51% of the original BH entropy, or about 15.018M02 ≈ 1.254 × 1077(M0/Msolar)2, and then decreases back down to 4πM02 = 1.049 × 1077(M0/Msolar)2.
Mechanical behavior of low porosity carbonate rock: from brittle creep to ductile creep
NASA Astrophysics Data System (ADS)
Nicolas, A.; Fortin, J.; Gueguen, Y.
2013-12-01
Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were deformed in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room temperature. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a creep steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different creep behaviors: (1) brittle creep is observed at low confining pressures, whereas (2) ductile creep is observed at higher confining pressures. These two creep behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary creep is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary creep is observed. In the ductile domain, the primary creep
NASA Technical Reports Server (NTRS)
Duffy, Stephen F.; Gyekenyesi, John P.
1989-01-01
Presently there are many opportunities for the application of ceramic materials at elevated temperatures. In the near future ceramic materials are expected to supplant high temperature metal alloys in a number of applications. It thus becomes essential to develop a capability to predict the time-dependent response of these materials. The creep rupture phenomenon is discussed, and a time-dependent reliability model is outlined that integrates continuum damage mechanics principles and Weibull analysis. Several features of the model are presented in a qualitative fashion, including predictions of both reliability and hazard rate. In addition, a comparison of the continuum and the microstructural kinetic equations highlights a strong resemblance in the two approaches.
Impact of time-dependency on long-term material testing and modeling of polyethylene
NASA Astrophysics Data System (ADS)
Bischoff, Jeffrey E.
2008-09-01
Ultra-high molecular weight polyethylene (UHMWPE) has an important role in orthopaedic implants because of its favorable properties as an articulating surface. UHMWPE component testing often focuses on measuring the long-term fatigue or wear response of the material that could be realized during many years of use. However, the impact of time-dependent properties of UHMWPE on such tests is not well characterized. In particular, altering the frequency of loading and allowing for material creep or relaxation can significantly alter the stress/strain state of the material, and therefore affect long-term mechanical properties (e.g. wear, fatigue) that are dependent on the constitutive state. The goal of this work is to use advanced, validated material modeling of UHMPWE that incorporates time-dependent properties to explore the effects of frequency and rest time on the mechanical response of UHMWPE.
Time-Dependent, Parallel Neutral Particle Transport Code System.
2009-09-10
Version 00 PARTISN (PARallel, TIme-Dependent SN) is the evolutionary successor to CCC-547/DANTSYS. The PARTISN code package is a modular computer program package designed to solve the time-independent or dependent multigroup discrete ordinates form of the Boltzmann transport equation in several different geometries. The modular construction of the package separates the input processing, the transport equation solving, and the post processing (or edit) functions into distinct code modules: the Input Module, the Solver Module, and themore » Edit Module, respectively. PARTISN is the evolutionary successor to the DANTSYSTM code system package. The Input and Edit Modules in PARTISN are very similar to those in DANTSYS. However, unlike DANTSYS, the Solver Module in PARTISN contains one, two, and three-dimensional solvers in a single module. In addition to the diamond-differencing method, the Solver Module also has Adaptive Weighted Diamond-Differencing (AWDD), Linear Discontinuous (LD), and Exponential Discontinuous (ED) spatial differencing methods. The spatial mesh may consist of either a standard orthogonal mesh or a block adaptive orthogonal mesh. The Solver Module may be run in parallel for two and three dimensional problems. One can now run 1-D problems in parallel using Energy Domain Decomposition (triggered by Block 5 input keyword npeg>0). EDD can also be used in 2-D/3-D with or without our standard Spatial Domain Decomposition. Both the static (fixed source or eigenvalue) and time-dependent forms of the transport equation are solved in forward or adjoint mode. In addition, PARTISN now has a probabilistic mode for Probability of Initiation (static) and Probability of Survival (dynamic) calculations. Vacuum, reflective, periodic, white, or inhomogeneous boundary conditions are solved. General anisotropic scattering and inhomogeneous sources are permitted. PARTISN solves the transport equation on orthogonal (single level or block-structured AMR) grids in 1-D
Mechanisms of time-dependent crack growth at elevated temperature
Saxena, A.; Stock, S.R.
1990-04-15
Objective of this 3-y study was to conduct creep and creep-fatigue crack growth experiments and to characterize the crack tip damage mechanisms in a model material (Cu-1wt%Sb), which is known to cavitate at grain boundaries under creep deformation. Results were: In presence of large scale cavitation damage and crack branching, time rate of creep crack growth da/dt does not correlate with C[sub t] or C[sup *]. When cavitation damage is constrained, da/dt is characterized by C[sub t]. Area fraction of grain boundary cavitated is the single damage parameter for the extent of cavitation damage ahead of crack tips. C[sub t] is used for the creep-fatigue crack growth behavior. In materials prone to rapid cavity nucleation, creep cracks grow faster initially and then reach a steady state whose growth rate is determined by C[sub t]. Percent creep life exhausted correlates with average cavity diameter and fraction of grain boundary area occupied by cavities. Synchrotron x-ray tomographic microscopy was used to image individual cavities in Cu-1wt% Sb. A methodology was developed for predicting the remaining life of elevated temperature power plant components; (C[sub t])[sub avg] was used to correlate creep-fatigue crack growth in Cr-Mo and Cr-Mo-V steel and weldments.
Analysis of available creep and creep-rupture data for commercially heat-treated alloy 718
Booker, M.K.; Booker, B.L.P.
1980-03-01
The Ni-Cr-Fe-Nb alloy 718 is a widely used material in elevated- temperature applications. Currently, it is approved by the American Society of Mechanical Engineers ASME Boiler and Pressure Vessel Code only as a bolting material for elevated-temperature nuclear service. This report presents analyses of available creep and creep-rupture data for commercially heat-treated alloy 718 toward the development of allowable stress levels for this material in general elevated-temperature nuclear service. Available data came from 14 heats of bar, plate, and forging material over the temperature range from 538 to 704{degrees}C. The longest rupture time encompassed by the data was almost 87,000 h. Generalized regression analyses were performed to yield an analytical expression for rupture life as a function of stress and temperature. Heat-to-heat variations were accounted for by lot-centering'' the data. Effects of different solution heat treatment temperatures (T{sub s}) were accounted for by normalizing the creep stresses to the data for T{sub s} = 954{degrees}C. Thus, the results are strictly applicable only for material with this solution treatment. Time and strain to tertiary creep were predicted as functions of rupture life. Creep strain-time data were represented by normalization to the time and strain to tertiary creep and development of master creep curves.'' The results allow estimation of time-dependent allowable stress per American Society of Mechanical Engineers Code Class N-47, and the creep strain-time relationships can be used to develop isochronous stress-strain curves. 29 refs., 44 figs., 14 tabs.
Accelerated characterization for long-term creep behavior of polymer
NASA Astrophysics Data System (ADS)
Zhao, Rongguo; Chen, Chaozhong; Li, Qifu; Luo, Xiyan
2008-11-01
Based on the observation that high stress results in increasing creep rate of polymeric material, which is analogous to the time-temperature equivalence, where high temperature accelerates the process of creep or relaxation of polymer, the time-stress equivalence is investigated. The changes of intrinsic time in polymer induced by temperature and stress are studied using the free volume theory, and a clock model based on the time-temperature and time-stress equivalence is constructed to predict the long-term creep behavior of polymer. Polypropylene is used for this work. The specimens with shape of dumbbell are formed via injection molding. The short-term creep tests under various stress levels are carried out at ambient temperature. The creep strains of specimens are modeled according to the concept of time-stress equivalence, and the corresponding stress shift factors are calculated. A master creep curve is built by the clock model. The result indicates that the time-stress superposition principle provides an accelerated characterization method in the laboratory. Finally, the time-dependent axial elongations at sustained stress levels, whose values are close to the tensile strength of polypropylene, are measured. The three phases of creep, i.e., the transient, steady state and accelerated creep phases, are studied, and the application and limitation of the time-stress superposition principle are discussed.
Blacic, J.D.; Andersen, R.
1983-01-01
We have established a methodology to determine the time dependence of strength and transport properties of tuff under conditions appropriate to a nuclear waste repository. Exploratory tests to determine the approximate magnitudes of thermomechanical property changes are nearly complete. In this report we describe the capabilities of an apparatus designed to precisely measure the time-dependent deformation and permeability of tuff at simulated repository conditions. Preliminary tests with this new apparatus indicate that microclastic creep failure of tuff occurs over a narrow strain range with little precursory Tertiary creep behavior. In one test, deformation under conditions of slowly decreasing effective pressure resulted in failure, whereas some strain indicators showed a decreasing rate of strain.
NASA Astrophysics Data System (ADS)
Fakpan, Kittichai; Otsuka, Yuichi; Miyashita, Yukio; Mutoh, Yoshiharu; Nagata, Kohsoku
2013-12-01
In the present study, fatigue crack growth tests of Pb-containing [Sn-37Pb (wt.%)] and Pb-free [Sn-3.0Ag-0.5Cu (wt.%)] solders were performed under cycle/time-dependent step loading at a constant J-integral range (Δ J). The C * parameter was also estimated for discussing time-dependent crack growth behavior. The experimental results indicated that acceleration of the crack growth rate at the beginning of the second loading step was induced when the C * value for the first loading step was high, regardless of time- or cycle-dependent crack growth and for both Sn-37Pb and Sn-3.0Ag-0.5Cu solders. The length of the acceleration region of the crack growth rate for both solders was in good agreement with the creep damage zone size estimated by the creep zone model proposed by Riedel and Rice.
Time-dependent statistical failure of fiber networks
NASA Astrophysics Data System (ADS)
Mattsson, Amanda; Uesaka, Tetsu
2015-10-01
Numerical simulations of time-dependent stochastic failure of fiber network have been performed by using a central-force, triangular lattice model. This two-dimensional (2D) network can be seen as the next level of structural hierarchy to fiber bundles, which have been investigated for many years both theoretically and numerically. Unlike fiber bundle models, the load sharing of the fiber network is determined by the network mechanics rather than a preassigned rule, and its failure is defined as the point of avalanche rather than the total fiber failure. We have assumed that the fiber in the network follows Coleman's probabilistic failure law [B. D. Coleman, J. Appl. Phys. 29, 968 (1958), 10.1063/1.1723343] with the Weibull shape parameter β =1 (memory less fiber). Our interests are how the fiber-level probabilistic failure law is transformed into the one for the network and how the failure characteristics and disorders on the fiber level influence the network failure response. The simulation results showed that, with increasing the size of the network (N ), weakest-link scaling (WLS) appeared and each lifetime distribution at a given size approximately followed Weibull distribution. However, the scaling behavior of the mean and the Weibull shape parameter clearly deviate from what we can predict from the WLS of Weibull distribution. We have found that a characteristic distribution function has, in fact, a double exponential form, not Weibull form. Accordingly, for the 2D network system, Coleman's probabilistic failure law holds but only approximately. Comparing the fiber and network failure properties, we found that the network structure induces an increase of the load sensitivity factor ρ (more brittle than fiber) and Weibull shape parameter β (less uncertainty of lifetime). Superimposed disorders on the fiber level reduce all these properties for the network.
Time-dependent statistical failure of fiber networks.
Mattsson, Amanda; Uesaka, Tetsu
2015-10-01
Numerical simulations of time-dependent stochastic failure of fiber network have been performed by using a central-force, triangular lattice model. This two-dimensional (2D) network can be seen as the next level of structural hierarchy to fiber bundles, which have been investigated for many years both theoretically and numerically. Unlike fiber bundle models, the load sharing of the fiber network is determined by the network mechanics rather than a preassigned rule, and its failure is defined as the point of avalanche rather than the total fiber failure. We have assumed that the fiber in the network follows Coleman's probabilistic failure law [B. D. Coleman, J. Appl. Phys. 29, 968 (1958)] with the Weibull shape parameter β=1 (memory less fiber). Our interests are how the fiber-level probabilistic failure law is transformed into the one for the network and how the failure characteristics and disorders on the fiber level influence the network failure response. The simulation results showed that, with increasing the size of the network (N), weakest-link scaling (WLS) appeared and each lifetime distribution at a given size approximately followed Weibull distribution. However, the scaling behavior of the mean and the Weibull shape parameter clearly deviate from what we can predict from the WLS of Weibull distribution. We have found that a characteristic distribution function has, in fact, a double exponential form, not Weibull form. Accordingly, for the 2D network system, Coleman's probabilistic failure law holds but only approximately. Comparing the fiber and network failure properties, we found that the network structure induces an increase of the load sensitivity factor ρ (more brittle than fiber) and Weibull shape parameter β (less uncertainty of lifetime). Superimposed disorders on the fiber level reduce all these properties for the network. PMID:26565219
Time-Dependent Rate Phenomenon in Viruses
Aiewsakun, Pakorn
2016-01-01
ABSTRACT Among the most fundamental questions in viral evolutionary biology are how fast viruses evolve and how evolutionary rates differ among viruses and fluctuate through time. Traditionally, viruses are loosely classed into two groups: slow-evolving DNA viruses and fast-evolving RNA viruses. As viral evolutionary rate estimates become more available, it appears that the rates are negatively correlated with the measurement timescales and that the boundary between the rates of DNA and RNA viruses might not be as clear as previously thought. In this study, we collected 396 viral evolutionary rate estimates across almost all viral genome types and replication strategies, and we examined their rate dynamics. We showed that the time-dependent rate phenomenon exists across multiple levels of viral taxonomy, from the Baltimore classification viral groups to genera. We also showed that, by taking the rate decay dynamics into account, a clear division between the rates of DNA and RNA viruses as well as reverse-transcribing viruses could be recovered. Surprisingly, despite large differences in their biology, our analyses suggested that the rate decay speed is independent of viral types and thus might be useful for better estimation of the evolutionary time scale of any virus. To illustrate this, we used our model to reestimate the evolutionary timescales of extant lentiviruses, which were previously suggested to be very young by standard phylogenetic analyses. Our analyses suggested that these viruses are millions of years old, in agreement with paleovirological evidence, and therefore, for the first time, reconciled molecular analyses of ancient and extant viruses. IMPORTANCE This work provides direct evidence that viral evolutionary rate estimates decay with their measurement timescales and that the rate decay speeds do not differ significantly among viruses despite the vast differences in their molecular features. After adjustment for the rate decay dynamics, the
2005-07-01
Aniso2d is a two-dimensional seismic forward modeling code. The earth is parameterized by an X-Z plane in which the seismic properties Can have monoclinic with x-z plane symmetry. The program uses a user define time-domain wavelet to produce synthetic seismograms anrwhere within the two-dimensional media.
NASA Astrophysics Data System (ADS)
Jang, Hyun-Sook; Yu, Changqian; Hayes, Robert; Granick, Steve
2015-03-01
Polymer vesicles (``polymersomes'') are an intriguing class of soft materials, commonly used to encapsulate small molecules or particles. Here we reveal they can also effectively incorporate nanoparticles inside their polymer membrane, leading to novel ``2D nanocomposites.'' The embedded nanoparticles alter the capacity of the polymersomes to bend and to stretch upon external stimuli.
Analysis of time-dependent deformation of a CFRP mirror under hot and humid conditions
NASA Astrophysics Data System (ADS)
Arao, Yoshihiko; Koyanagi, Jun; Utsunomiya, Shin; Takeda, Shin-Ichi; Kawada, Hiroyuki
2009-05-01
The long-term micro-dimensional stability of a carbon fiber reinforced plastic (CFRP) mirror was investigated in terms of creep deformation, moisture swelling and self-shrinkage. A 4-point bending creep test was carried out using specimens made from pitch-based high-modulus CFRP laminates to obtain a creep constant based on linear viscoelasticity, and we then investigated the weight change and geometrical change during a moisture absorption test using a CFRP specimen. The anisotropic diffusivities and coefficients of moisture expansion (CMEs) in CFRP laminates were obtained by fitting analytical data into the experimental data. Finally, the shrinkage behavior caused by physical aging of the polymeric material was examined using a fiber Bragg grating (FBG) sensor embedded in the neat resin specimen. Applying these results, we analyzed the geometrical changes in a CFRP mirror that resulted from time-dependent deformation by the mirror’s weight, moisture absorption and physical aging, respectively. We discuss which factor is dominant in the deformation of CFRP mirrors under various conditions.
NASA Astrophysics Data System (ADS)
Benyoucef, S.; Tounsi, A.; Benrahou, K. H.; Adda Bedia, E. A.
2007-12-01
External bonding of fibre reinforced polymer (FRP) composites has becomes a popular technique for strengthening concrete structures all over the world. An important failure mode of such strengthened members is the debonding of the FRP plate from the concrete due to high interfacial stresses near the plate ends. For correctly installed FRP plate, failure will occur within the concrete. Accurate predictions of the interfacial stresses are prerequisite for designing against debonding failures. In particular, the interfacial stresses between a beam and soffit plate within the linear elastic range have been addressed by numerous analytical investigations. In this study, the time-dependent behavior of RC beams bonded with thin composite plate was investigated theoretically by including the effect of the adherend shear deformations. The time effects considered here are those that arise from shrinkage and creep deformations of the concrete. This paper presents an analytical model for the interfacial stresses between RC beam and a thin FRP plate bonded to its soffit. The influence of creep and shrinkage effect relative to the time of the casting and the time of the loading of the beams is taken into account. Numerical results from the present analysis are presented to illustrate the significance of time-dependent of adhesive stresses.
Differences in time-dependent mechanical properties between extruded and molded hydrogels.
Ersumo, N; Witherel, C E; Spiller, K L
2016-01-01
The mechanical properties of hydrogels used in biomaterials and tissue engineering applications are critical determinants of their functionality. Despite the recent rise of additive manufacturing, and specifically extrusion-based bioprinting, as a prominent biofabrication method, comprehensive studies investigating the mechanical behavior of extruded constructs remain lacking. To address this gap in knowledge, we compared the mechanical properties and swelling properties of crosslinked gelatin-based hydrogels prepared by conventional molding techniques or by 3D bioprinting using a BioBots Beta pneumatic extruder. A preliminary characterization of the impact of bioprinting parameters on construct properties revealed that both Young's modulus and optimal extruding pressure increased with polymer content, and that printing resolution increased with both printing speed and nozzle gauge. High viability (>95%) of encapsulated NIH 3T3 fibroblasts confirmed the cytocompatibility of the construct preparation process. Interestingly, the Young's moduli of extruded and molded constructs were not different, but extruded constructs did show increases in both the rate and extent of time-dependent mechanical behavior observed in creep. Despite similar polymer densities, extruded hydrogels showed greater swelling over time compared to molded hydrogels, suggesting that differences in creep behavior derived from differences in microstructure and fluid flow. Because of the crucial roles of time-dependent mechanical properties, fluid flow, and swelling properties on tissue and cell behavior, these findings highlight the need for greater consideration of the effects of the extrusion process on hydrogel properties. PMID:27550945
Micromechanics of Brittle Creep Under Triaxial Loading Conditions
NASA Astrophysics Data System (ADS)
Meredith, P. G.; Brantut, N.; Baud, P.; Heap, M. J.
2011-12-01
In the upper crust, the chemical influence of pore water promotes time-dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail (i) at stresses far below their short-term failure strength, and (ii) even at constant applied stress ("brittle creep"). Here we provide a micromechanical model and experimental results describing time-dependent brittle creep of water-saturated granite under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of microcracks in compression are derived from the sliding wing-crack model of Ashby and Sammis (1990). Crack length evolution is computed from Charles' law. The macroscopic strain and strain rates are then computed from the change in energy potential due to microcrack growth. They are non-linear, and compare well with complementary experimental results obtained on granite samples. Primary creep (decelerating strain) corresponds to decreasing crack growth rate , due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as merely an inflexion between the two end-member phases.
TIME DEPENDENT BIAXIAL MECHANICAL BEHAVIOR OF THE AORTIC HEART VALVE LEAFLET
Stella, John A.; Liao, Jun; Sacks, Michael S.
2007-01-01
Despite continued progress in the treatment of aortic valve (AV) disease, current treatments continue to be challenged to consistently restore AV function for extended durations. Improved approaches toward AV repair and replacement rests upon our ability to more fully comprehend and simulate AV function. While the elastic behavior the AV leaflet (AVL) has been previously investigated, time dependent behaviors under physiological biaxial loading states have yet to be quantified. In the current study, we performed strain rate, creep, and stress relaxation experiments using porcine AVL under planar biaxial stretch and loaded to physiological levels (60 N/m equi-biaxial tension), with strain rates ranging from quasi-static to physiologic. The resulting stress-strain responses were found to be independent of strain rate, as was the observed low level of hysteresis (∼17%). Stress relaxation and creep results indicated that while the AVL exhibited significant stress relaxation, it exhibited negligible creep over the three hour test duration. These results are all in accordance with our previous findings for the mitral valve anterior leaflet (MVAL) (Grashow et al., 2006, ABME vol. 34, pp. 315-25; Grashow et al., ABME, Vol. 34, pp. 1509-18, 2006), and support our observations that valvular tissues are functionally anisotropic, quasi-elastic biological materials. These results appear to be unique to valvular tissues, and indicate an ability to withstand loading without time-dependent effects under physiologic loading conditions. Based on a recent study that suggested valvular collagen fibrils are not intrinsically viscoelastic (Liao, et al., JBME, vol. 129, 2007), we speculate that the mechanisms underlying this quasi-elastic behavior may be attributed to supra-fibrillar structure unique to valvular tissue. These mechanisms are an important functional aspect of native valvular tissues, and are likely critical to improve our understanding of valvular disease and help guide
NASA Technical Reports Server (NTRS)
Dillard, D. A.; Morris, D. H.; Brinson, H. F.
1981-01-01
An incremental numerical procedure based on lamination theory is developed to predict creep and creep rupture of general laminates. Existing unidirectional creep compliance and delayed failure data is used to develop analytical models for lamina response. The compliance model is based on a procedure proposed by Findley which incorporates the power law for creep into a nonlinear constitutive relationship. The matrix octahedral shear stress is assumed to control the stress interaction effect. A modified superposition principle is used to account for the varying stress level effect on the creep strain. The lamina failure model is based on a modification of the Tsai-Hill theory which includes the time dependent creep rupture strength. A linear cumulative damage law is used to monitor the remaining lifetime in each ply.
Creep and recovery behavior analysis of space mesh structures
NASA Astrophysics Data System (ADS)
Tang, Yaqiong; Li, Tuanjie; Ma, Xiaofei
2016-11-01
The Schapery's nonlinear viscoelastic theory and nonlinear force-density method have been investigated to analyze the creep and recovery behaviors of space deployable mesh reflectors in this paper. Based on Schapery's nonlinear viscoelastic theory, we establish the creep and recovery constitutive model for cables whose pretensions were applied stepwise in time. This constitutive model has been further used for adjustment of cables' elongation rigidity. In addition, the time-dependent tangent stiffness matrix is calculated by the partial differentiation of the corresponding load vector with respect to the nodal coordinate vector obtained by the nonlinear force-density method. An incremental-iterative solution based on the Newton-Raphson method is adopted for solving the time-dependent nonlinear statics equations. Finally, a hoop truss reflector antenna is presented as a numerical example to illustrate the efficiency of the proposed method for the creep and recovery behavior analysis of space deployable mesh structures.
2011-12-31
Mesh2d is a Fortran90 program designed to generate two-dimensional structured grids of the form [x(i),y(i,j)] where [x,y] are grid coordinates identified by indices (i,j). The x(i) coordinates alone can be used to specify a one-dimensional grid. Because the x-coordinates vary only with the i index, a two-dimensional grid is composed in part of straight vertical lines. However, the nominally horizontal y(i,j0) coordinates along index i are permitted to undulate or otherwise vary. Mesh2d also assignsmore » an integer material type to each grid cell, mtyp(i,j), in a user-specified manner. The complete grid is specified through three separate input files defining the x(i), y(i,j), and mtyp(i,j) variations.« less
Elevated time-dependent strengthening rates observed in San Andreas Fault drilling samples
NASA Astrophysics Data System (ADS)
Ikari, Matt J.; Carpenter, Brett M.; Vogt, Christoph; Kopf, Achim J.
2016-09-01
The central San Andreas Fault in California is known as a creeping fault, however recent studies have shown that it may be accumulating a slip deficit and thus its seismogenic potential should be seriously considered. We conducted laboratory friction experiments measuring time-dependent frictional strengthening (healing) on fault zone and wall rock samples recovered during drilling at the San Andreas Fault Observatory at Depth (SAFOD), located near the southern edge of the creeping section and in the direct vicinity of three repeating microearthquake clusters. We find that for hold times of up to 3000 s, frictional healing follows a log-linear dependence on hold time and that the healing rate is very low for a sample of the actively shearing fault core, consistent with previous results. However, considering longer hold times up to ∼350,000 s, the healing rate accelerates such that the data for all samples are better described by a power law relation. In general, samples having a higher content of phyllosilicate minerals exhibit low log-linear healing rates, and the notably clay-rich fault zone sample also exhibits strong power-law healing when longer hold times are included. Our data suggest that weak faults, such as the creeping section of the San Andreas Fault, can accumulate interseismic shear stress more rapidly than expected from previous friction data. Using the power-law dependence of frictional healing on hold time, calculations of recurrence interval and stress drop based on our data accurately match observations of discrete creep events and repeating Mw = 2 earthquakes on the San Andreas Fault.
Application Of Elastic Perfectly Plastic Cyclic Analysis To Assessment Of Creep Strain
Carter, Peter; Jetter, Robert I; Sham, Sam
2012-01-01
A cyclic elastic-perfectly plastic analysis method is proposed which provides a conservative estimate to cyclic creep strain accumulation within the ratchet boundary. The method is to check for ratcheting based on an elastic-perfectly material with a temperature-dependent pseudo yield stress defined by temperature, time and stress to give 1% creep strain. It does not require stress classification and is also applicable to a full range of temperature above and below the creep regime. This simplified method could be used as a rapid screening calculation, with full time-dependent creep analysis used if necessary.
NASA Technical Reports Server (NTRS)
Morscher, Gregory N.; Pujar, Vijay
2004-01-01
Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.
Time-dependent biaxial mechanical behavior of the aortic heart valve leaflet.
Stella, John A; Liao, Jun; Sacks, Michael S
2007-01-01
Despite continued progress in the treatment of aortic valve (AV) disease, current treatments continue to be challenged to consistently restore AV function for extended durations. Improved approaches for AV repair and replacement rests upon our ability to more fully comprehend and simulate AV function. While the elastic behavior the AV leaflet (AVL) has been previously investigated, time-dependent behaviors under physiological biaxial loading states have yet to be quantified. In the current study, we performed strain rate, creep, and stress-relaxation experiments using porcine AVL under planar biaxial stretch and loaded to physiological levels (60 N/m equi-biaxial tension), with strain rates ranging from quasi-static to physiologic. The resulting stress-strain responses were found to be independent of strain rate, as was the observed low level of hysteresis ( approximately 17%). Stress relaxation and creep results indicated that while the AVL exhibited significant stress relaxation, it exhibited negligible creep over the 3h test duration. These results are all in accordance with our previous findings for the mitral valve anterior leaflet (MVAL) [Grashow, J.S., Sacks, M.S., Liao, J., Yoganathan, A.P., 2006a. Planar biaxial creep and stress relaxatin of the mitral valve anterior leaflet. Annals of Biomedical Engineering 34 (10), 1509-1518; Grashow, J.S., Yoganathan, A.P., Sacks, M.S., 2006b. Biaxial stress-stretch behavior of the mitral valve anterior leaflet at physiologic strain rates. Annals of Biomedical Engineering 34 (2), 315-325], and support our observations that valvular tissues are functionally anisotropic, quasi-elastic biological materials. These results appear to be unique to valvular tissues, and indicate an ability to withstand loading without time-dependent effects under physiologic loading conditions. Based on a recent study that suggested valvular collagen fibrils are not intrinsically viscoelastic [Liao, J., Yang, L., Grashow, J., Sacks, M.S., 2007
Irradiation Induced Creep of Graphite
Burchell, Timothy D; Murty, Prof K.L.; Eapen, Dr. Jacob
2010-01-01
The current status of graphite irradiation induced creep strain prediction is reviewed and the major creep models are described. The ability of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work is made and the need for improved creep models across multi-scales is highlighted.
Time-dependent deformation of gas shales - role of rock framework versus reservoir fluids
NASA Astrophysics Data System (ADS)
Hol, Sander; Zoback, Mark
2013-04-01
Hydraulic fracturing operations are generally performed to achieve a fast, drastic increase of permeability and production rates. Although modeling of the underlying short-term mechanical response has proven successful via conventional geomechanical approaches, predicting long-term behavior is still challenging as the formation interacts physically and chemically with the fluids present in-situ. Recent experimental work has shown that shale samples subjected to a change in effective stress deform in a time-dependent manner ("creep"). Although the magnitude and nature of this behavior is strongly related to the composition and texture of the sample, also the choice of fluid used in the experiments affects the total strain response - strongly adsorbing fluids result in more, recoverable creep. The processes underlying time-dependent deformation of shales under in-situ stresses, and the long-term impact on reservoir performance, are at present poorly understood. In this contribution, we report triaxial mechanical tests, and theoretical/thermodynamic modeling work with the aim to identify and describe the main mechanisms that control time-dependent deformation of gas shales. In particular, we focus on the role of the shale solid framework versus the type and pressure of the present pore fluid. Our experiments were mainly performed on Eagle Ford Shale samples. The samples were subjected to cycles of loading and unloading, first in the dry state, and then again after equilibrating them with (adsorbing) CO2 and (non-adsorbing) He at fluid pressures of 4 MPa. Stresses were chosen close to those persisting under in-situ conditions. The results of our tests demonstrate that likely two main types of deformation mechanisms operate that relate to a) the presence of microfractures as a dominating feature in the solid framework of the shale, and b) the adsorbing potential of fluids present in the nanoscale voids of the shale. To explain the role of adsorption in the observed
Biaxial Creep Specimen Fabrication
JL Bump; RF Luther
2006-02-09
This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.
Ubic, Rick; Butt, Darryl; Windes, William
2014-03-13
An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.
Frank E. Goodwin
2002-12-31
This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.
Studies of time dependence of fields in TEVATRON superconducting dipole magnets
Hanft, R.W.; Brown, B.C.; Herrup, D.A.; Lamm, M.J.; McInturff, A.D.; Syphers, M.J.
1988-08-22
The time variation in the magnetic field of a model Tevatron dipole magnet at constant excitation current has been studied. Variations in symmetry allowed harmonic components over long time ranges show a log t behavior indicative of ''flux creep.'' Both short time range and long time range behavior depend in a detailed way on the excitation history. Similar effects are seen in the remnant fields present in full-scale Tevatron dipoles following current ramping. Both magnitudes and time dependences are observed to depend on details for the ramps, such as ramp rate, flattop duration, and number of ramps. In a few magnets, variations are also seen in symmetry unallowed harmonics. 9 refs., 10 figs.
NASA Astrophysics Data System (ADS)
Heeter, Ann E.
Gas turbine engines are an important part of power generation in modern society, especially in the field of aerospace. Aerospace engines are design to last approximately 30 years and the engine components must be designed to survive for the life of the engine or to be replaced at regular intervals to ensure consumer safety. Fatigue crack growth analysis is a vital component of design for an aerospace component. Crack growth modeling and design methods date back to an origin around 1950 with a high rate of accuracy. The new generation of aerospace engines is designed to be efficient as possible and require higher operating temperatures than ever seen before in previous generations. These higher temperatures place more stringent requirements on the material crack growth performance under creep and time dependent conditions. Typically the types of components which are subject to these requirements are rotating disk components which are made from advanced materials such as nickel base superalloys. Traditionally crack growth models have looked at high temperature crack growth purely as a function of temperature and assumed that all crack growth was either controlled by a cycle dependent or time dependent mechanism. This new analysis is trying to evaluate the transition between cycle-dependent and time-dependent mechanism and the microstructural markers that characterize this transitional behavior. The physical indications include both the fracture surface morphology as well as the shape of the crack front. The research will evaluate whether crack tunneling occurs and whether it consistently predicts a transition from cycle-dependent crack growth to time-dependent crack growth. The study is part of a larger research program trying to include the effects of geometry, mission profile and environmental effects, in addition to temperature effects, as a part of the overall crack growth system. The outcome will provide evidence for various transition types and correlate those
Tensile creep of dental amalgam.
Greener, E H; Szurgot, K; Lautenschlager, E P
1982-04-01
Rather than the usual compressive dental creep, various types of one week old dental amalgams were continuously monitored in tensile creep. Testing was done at 37, 45 and 50 degrees C, in a specially designed apparatus capable of 0 to 60 degrees C while maintaining a constant true tensile stress of 17 MPa. For the first time, the classical four stages of creep were observed at elevated temperatures in the low Cu amalgams, including creep rupture. The high Cu systems displayed only transient creep up to 50 degrees C and no rupture. Approximately one half the stress was needed in tension to provide the equivalent creep in compression. PMID:7082735
Vectran Fiber Time-Dependent Behavior and Additional Static Loading Properties
NASA Technical Reports Server (NTRS)
Fette, Russell B.; Sovinski, Marjorie F.
2004-01-01
Vectran HS appears from literature and testing to date to be an ideal upgrade from Kevlar braided cords for many long-term, static-loading applications such as tie-downs on solar arrays. Vectran is a liquid crystalline polymer and exhibits excellent tensile properties. The material has been touted as a zero creep product. Testing discussed in this report does not support this statement, though the creep is on the order of four times slower than with similar Kevlar 49 products. Previous work with Kevlar and new analysis of Vectran testing has led to a simple predictive model for Vectran at ambient conditions. The mean coefficient of thermal expansion (negative in this case) is similar to Kevlar 49, but is not linear. A positive transition in the curve occurs near 100 C. Out-gassing tests show that the material performs well within parameters for most space flight applications. Vectran also offers increased abrasion resistance, minimal moisture regain, and similar UV degradation. The effects of material construction appear to have a dramatic effect in stress relaxation for braided Vectran. To achieve the improved relaxation rate, upgrades must also examine alternate construction or preconditioning methods. This report recommends Vectran HS as a greatly improved replacement material for applications where time-dependent relaxation is a major factor.
Review of time-dependent fatigue behavior and life prediction for 2 1/4 Cr-1 Mo steel. [LMFBR
Booker, M.K.; Majumdar, S.
1982-01-01
Available data on creep-fatigue life and fracture behavior of 2 1/4 Cr-1 Mo steel are reviewed. Whereas creep-fatigue interaction is important for Type 304 stainless steel, oxidation effects appear to dominate the time-dependent fatigue behavior of 2 1/4 Cr-1 Mo steel. Four of the currently available predictive methods - the Linear Damage Rule, Frequency Separation Equation, Strain Range Partitioning Equation, and Damage Rate Equation - are evaluated for their predictive capability. Variations in the parameters for the various predictive methods with temperature, heat of material, heat treatment, and environment are investigated. Relative trends in the lives predicted by the various methods as functions of test duration, waveshape, etc., are discussed. The predictive methods will need modification in order to account for oxidation and aging effects in the 2 1/4 Cr-1 Mo steel. Future tests that will emphasize the difference between the various predictive methods are proposed.
A time-dependent vector field topology based on streak surfaces.
Uffinger, Markus; Sadlo, Filip; Ertl, Thomas
2013-03-01
It was shown recently how the 2D vector field topology concept, directly applicable to stationary vector fields only, can be generalized to time-dependent vector fields by replacing the role of stream lines by streak lines. The present paper extends this concept to 3D vector fields. In traditional 3D vector field topology separatrices can be obtained by integrating stream lines from 0D seeds corresponding to critical points. We show that in our new concept, in contrast, 1D seeding constructs are required for computing streak-based separatrices. In analogy to the 2D generalization we show that invariant manifolds can be obtained by seeding streak surfaces along distinguished path surfaces emanating from intersection curves between codimension-1 ridges in the forward and reverse finite-time Lyapunov exponent (FTLE) fields. These path surfaces represent a time-dependent generalization of critical points and convey further structure in time-dependent topology of vector fields. Compared to the traditional approach based on FTLE ridges, the resulting streak manifolds ease the analysis of Lagrangian coherent structures (LCS) with respect to visual quality and computational cost, especially when time series of LCS are computed. We exemplify validity and utility of the new approach using both synthetic examples and computational fluid dynamics results.
NASA Astrophysics Data System (ADS)
Hoffman, Adam J.; Lee, John C.
2016-02-01
A new time-dependent Method of Characteristics (MOC) formulation for nuclear reactor kinetics was developed utilizing angular flux time-derivative propagation. This method avoids the requirement of storing the angular flux at previous points in time to represent a discretized time derivative; instead, an equation for the angular flux time derivative along 1D spatial characteristics is derived and solved concurrently with the 1D transport characteristic equation. This approach allows the angular flux time derivative to be recast principally in terms of the neutron source time derivatives, which are approximated to high-order accuracy using the backward differentiation formula (BDF). This approach, called Source Derivative Propagation (SDP), drastically reduces the memory requirements of time-dependent MOC relative to methods that require storing the angular flux. An SDP method was developed for 2D and 3D applications and implemented in the computer code DeCART in 2D. DeCART was used to model two reactor transient benchmarks: a modified TWIGL problem and a C5G7 transient. The SDP method accurately and efficiently replicated the solution of the conventional time-dependent MOC method using two orders of magnitude less memory.
ORNL irradiation creep facility
Reiley, T.C.; Auble, R.L.; Beckers, R.M.; Bloom, E.E.; Duncan, M.G.; Saltmarsh, M.J.; Shannon, R.H.
1980-09-01
A machine was developed at ORNL to measure the rates of elongation observed under irradiation in stressed materials. The source of radiation is a beam of 60 MeV alpha particles from the Oak Ridge Isochronous Cyclotron (ORIC). This choice allows experiments to be performed which simulate the effects of fast neutrons. A brief review of irradiation creep and experimental constraints associated with each measurement technique is given. Factors are presented which lead to the experimental choices made for the Irradiation Creep Facility (ICF). The ICF consists of a helium-filled chamber which houses a high-precision mechanical testing device. The specimen to be tested must be thermally stabilized with respect to the temperature fluctuations imposed by the particle beam which passes through the specimen. Electrical resistance of the specimen is the temperature control parameter chosen. Very high precision in length measurement and temperature control are required to detect the small elongation rates relevant to irradiation creep in the test periods available (approx. 1 day). The apparatus components and features required for the above are presented in some detail, along with the experimental procedures. The damage processes associated with light ions are discussed and displacement rates are calculated. Recent irradiation creep results are given, demonstrating the suitability of the apparatus for high resolution experiments. Also discussed is the suitability of the ICF for making high precision thermal creep measurements.
Plasmon excitations in sodium atomic planes: a time-dependent density functional theory study.
Wang, Bao-Ji; Xu, Yuehua; Ke, San-Huang
2012-08-01
The collective electronic excitation in planar sodium clusters is studied by time-dependent density functional theory calculations. The formation and development of the resonances in photoabsorption spectra are investigated in terms of the shape and size of the two-dimensional (2D) systems. The nature of these resonances is revealed by the frequency-resolved induced charge densities present on a real-space grid. For long double chains, the excitation is similar to that in long single atomic chains, showing longitudinal modes, end and central transverse modes. However, for 2D planes consisting of (n × n) atoms with n being up to 16, new 2D characteristic modes emerge regardless of the symmetries considered. For in-plane excitations, besides the equivalent end mode, mixed modes with contrary polarity occur. The relation between the frequency of the primary modes and the system size is similar to the case of a 2D electron gas but with a correction due to the realistic atomic structure. For excitations perpendicular to the plane there are corner, side center, bulk center, and circuit modes. Our calculation reveals the importance of dimensionality for plasmon excitation and how it evolves from 1D to 2D.
Time-dependent potential-functional embedding theory.
Huang, Chen; Libisch, Florian; Peng, Qing; Carter, Emily A
2014-03-28
We introduce a time-dependent potential-functional embedding theory (TD-PFET), in which atoms are grouped into subsystems. In TD-PFET, subsystems can be propagated by different suitable time-dependent quantum mechanical methods and their interactions can be treated in a seamless, first-principles manner. TD-PFET is formulated based on the time-dependent quantum mechanics variational principle. The action of the total quantum system is written as a functional of the time-dependent embedding potential, i.e., a potential-functional formulation. By exploiting the Runge-Gross theorem, we prove the uniqueness of the time-dependent embedding potential under the constraint that all subsystems share a common embedding potential. We derive the integral equation that such an embedding potential needs to satisfy. As proof-of-principle, we demonstrate TD-PFET for a Na4 cluster, in which each Na atom is treated as one subsystem and propagated by time-dependent Kohn-Sham density functional theory (TDDFT) using the adiabatic local density approximation (ALDA). Our results agree well with a direct TDDFT calculation on the whole Na4 cluster using ALDA. We envision that TD-PFET will ultimately be useful for studying ultrafast quantum dynamics in condensed matter, where key regions are solved by highly accurate time-dependent quantum mechanics methods, and unimportant regions are solved by faster, less accurate methods.
Time-dependent potential-functional embedding theory
Huang, Chen; Libisch, Florian; Carter, Emily A.
2014-03-28
We introduce a time-dependent potential-functional embedding theory (TD-PFET), in which atoms are grouped into subsystems. In TD-PFET, subsystems can be propagated by different suitable time-dependent quantum mechanical methods and their interactions can be treated in a seamless, first-principles manner. TD-PFET is formulated based on the time-dependent quantum mechanics variational principle. The action of the total quantum system is written as a functional of the time-dependent embedding potential, i.e., a potential-functional formulation. By exploiting the Runge-Gross theorem, we prove the uniqueness of the time-dependent embedding potential under the constraint that all subsystems share a common embedding potential. We derive the integral equation that such an embedding potential needs to satisfy. As proof-of-principle, we demonstrate TD-PFET for a Na{sub 4} cluster, in which each Na atom is treated as one subsystem and propagated by time-dependent Kohn-Sham density functional theory (TDDFT) using the adiabatic local density approximation (ALDA). Our results agree well with a direct TDDFT calculation on the whole Na{sub 4} cluster using ALDA. We envision that TD-PFET will ultimately be useful for studying ultrafast quantum dynamics in condensed matter, where key regions are solved by highly accurate time-dependent quantum mechanics methods, and unimportant regions are solved by faster, less accurate methods.
Deterministic Multiaxial Creep and Creep Rupture Enhancements for CARES/Creep Integrated Design Code
NASA Technical Reports Server (NTRS)
Jadaan, Osama M.
1998-01-01
High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep rupture criterion. However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of sum, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of Ns methodology and the
NASA Astrophysics Data System (ADS)
Khoshmanesh, M.; Shirzaei, M.; Nadeau, R. M.
2014-12-01
The Central segment of the San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. Geodetic observations of surface deformation along CSAF indicate interseismic strain accumulation with a rate of about 10 mm/yr. The creep rates obtained using Characteristic Repeating Earthquakes (CRE) show pulses of creep affecting most of the CSAF, suggesting spatiotemporal variability of seismic hazard. Therefore, a high resolution time-dependent model of creep on the CSAF can greatly enhance the knowledge of aseismic and seismic faulting processes as well as the seismic hazard estimates. We used InSAR surface deformation time series in conjunction with observations of fault creep obtained from CRE. The SAR data set includes C-band scenes acquired by the ERS-2 and Envisat during period 2003-2011, comprising 46 images, resulted in about 150 interferograms. Within the same observation period, the CRE data set includes more than 630 repeating sequences. Understanding the spatiotemporal distribution of creep, we implement a time-dependent modeling scheme, allowing us to jointly invert the surface deformation time series and CRE estimates of the fault creep.The distribution of obtained creep rate on the CSAF includes features similar to that reported in earlier works. The map of long-term slip rate reveals that fastest creep rate occurs at the central part of CSAF with an average rate of 27 mm/yr, which is less than the long-term shearing rate. Moving northwestward, the slip rate gradually drops to less than half of its long-term rate. The spatiotemporal map of the creep includes unique features such as afterslip due to the 2004 Parkfield earthquake affecting the southeastern part of the CSAF and the clear evidence of creep pulsing along strike and depth of the CSAF with a period of 1.5 to 2 years. Considering 34.5 mm/yr as the long-term shearing rate, the zone of afterslip is characterized by relaxation time of about 16.35 years. The moment
Functional differentiability in time-dependent quantum mechanics
Penz, Markus Ruggenthaler, Michael
2015-03-28
In this work, we investigate the functional differentiability of the time-dependent many-body wave function and of derived quantities with respect to time-dependent potentials. For properly chosen Banach spaces of potentials and wave functions, Fréchet differentiability is proven. From this follows an estimate for the difference of two solutions to the time-dependent Schrödinger equation that evolve under the influence of different potentials. Such results can be applied directly to the one-particle density and to bounded operators, and present a rigorous formulation of non-equilibrium linear-response theory where the usual Lehmann representation of the linear-response kernel is not valid. Further, the Fréchet differentiability of the wave function provides a new route towards proving basic properties of time-dependent density-functional theory.
On the time-dependent Lagrangian approach in quantum chemistry
NASA Astrophysics Data System (ADS)
Pedersen, Thomas Bondo; Koch, Henrik
1998-04-01
We formulate the time-dependent variational principle in the form of the Euler-Lagrange equations, and demonstrate that standard variational as well as nonvariational wave functions may be obtained from these. We also demonstrate how inherently real expectation values of Hermitian operators can be constructed for nonvariational wave functions by using the time-dependent Hellmann-Feynman theorem which, in turn, is a simple consequence of the Euler-Lagrange equations. The procedure is illustrated by derivation of time-dependent Hartree-Fock and of time-dependent coupled cluster theory. Finally we give the fundamental equations for molecular dynamics within semiclassical electron nuclear dynamics (END) with a classical description of the nuclei and coupled cluster description of the electrons.
Cosmological evolution of cosmic strings with time-dependent tension
Yamaguchi, Masahide
2005-08-15
We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling solution: the characteristic scale of the string network grows with the time. But due to the time dependence of the tension, the ratio of the energy density of infinite strings to that of the background universe is not necessarily constant.
Time-dependent evolution of rock slopes by a multi-modelling approach
NASA Astrophysics Data System (ADS)
Bozzano, F.; Della Seta, M.; Martino, S.
2016-06-01
This paper presents a multi-modelling approach that incorporates contributions from morpho-evolutionary modelling, detailed engineering-geological modelling and time-dependent stress-strain numerical modelling to analyse the rheological evolution of a river valley slope over approximately 102 kyr. The slope is located in a transient, tectonically active landscape in southwestern Tyrrhenian Calabria (Italy), where gravitational processes drive failures in rock slopes. Constraints on the valley profile development were provided by a morpho-evolutionary model based on the correlation of marine and river strath terraces. Rock mass classes were identified through geomechanical parameters that were derived from engineering-geological surveys and outputs of a multi-sensor slope monitoring system. The rock mass classes were associated to lithotechnical units to obtain a high-resolution engineering-geological model along a cross section of the valley. Time-dependent stress-strain numerical modelling reproduced the main morpho-evolutionary stages of the valley slopes. The findings demonstrate that a complex combination of eustatism, uplift and Mass Rock Creep (MRC) deformations can lead to first-time failures of rock slopes when unstable conditions are encountered up to the generation of stress-controlled shear zones. The multi-modelling approach enabled us to determine that such complex combinations may have been sufficient for the first-time failure of the S. Giovanni slope at approximately 140 ka (MIS 7), even without invoking any trigger. Conversely, further reactivations of the landslide must be related to triggers such as earthquakes, rainfall and anthropogenic activities. This failure involved a portion of the slope where a plasticity zone resulted from mass rock creep that evolved with a maximum strain rate of 40% per thousand years, after the formation of a river strath terrace. This study demonstrates that the multi-modelling approach presented herein is a useful
Time-dependent {P} {T}-symmetric quantum mechanics
NASA Astrophysics Data System (ADS)
Gong, Jiangbin; Wang, Qing-hai
2013-12-01
The parity-time-reversal ( {P} {T})-symmetric quantum mechanics (QM) (PTQM) has developed into a noteworthy area of research. However, to date, most known studies of PTQM focused on the spectral properties of non-Hermitian Hamiltonian operators. In this work, we propose an axiom in PTQM in order to study general time-dependent problems in PTQM, e.g., those with a time-dependent {P} {T}-symmetric Hamiltonian and with a time-dependent metric. We illuminate our proposal by examining a proper mapping from a time-dependent Schrödinger-like equation of motion for PTQM to the familiar time-dependent Schrödinger equation in conventional QM. The rich structure of the proper mapping hints that time-dependent PTQM can be a fruitful extension of conventional QM. Under our proposed framework, we further study in detail the Berry-phase generation in a class of {P} {T}-symmetric two-level systems. It is found that a closed path in the parameter space of PTQM is often associated with an open path in a properly mapped problem in conventional QM. In one interesting case, we further interpret the Berry phase as the flux of a continuously tunable fictitious magnetic monopole, thus highlighting the difference between PTQM and conventional QM despite the existence of a proper mapping between them.
Numerical solution of the two-dimensional time-dependent incompressible Euler equations
NASA Technical Reports Server (NTRS)
Whitfield, David L.; Taylor, Lafayette K.
1994-01-01
A numerical method is presented for solving the artificial compressibility form of the 2D time-dependent incompressible Euler equations. The approach is based on using an approximate Riemann solver for the cell face numerical flux of a finite volume discretization. Characteristic variable boundary conditions are developed and presented for all boundaries and in-flow out-flow situations. The system of algebraic equations is solved using the discretized Newton-relaxation (DNR) implicit method. Numerical results are presented for both steady and unsteady flow.
NASA Astrophysics Data System (ADS)
Wang, Jin; Ma, Jianyong; Zhou, Changhe
2014-11-01
A 3×3 high divergent 2D-grating with period of 3.842μm at wavelength of 850nm under normal incidence is designed and fabricated in this paper. This high divergent 2D-grating is designed by the vector theory. The Rigorous Coupled Wave Analysis (RCWA) in association with the simulated annealing (SA) is adopted to calculate and optimize this 2D-grating.The properties of this grating are also investigated by the RCWA. The diffraction angles are more than 10 degrees in the whole wavelength band, which are bigger than the traditional 2D-grating. In addition, the small period of grating increases the difficulties of fabrication. So we fabricate the 2D-gratings by direct laser writing (DLW) instead of traditional manufacturing method. Then the method of ICP etching is used to obtain the high divergent 2D-grating.
ERIC Educational Resources Information Center
Kennerknecht, Norbert J.; Scarnati, James T.
1998-01-01
Discusses how to keep school district capital-improvement projects within budget. Examines areas where runaway costs creep into a project and ways of cutting or lessening these costs, such as using standard agreements, controlling architect's expense reimbursements, developing a quality-control process, and reducing document duplication. (GR)
Creep behaviour and creep mechanisms of normal and healing ligaments
NASA Astrophysics Data System (ADS)
Thornton, Gail Marilyn
Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep
Creep avalanches on the Central San Andreas Fault: Clues and Causes
NASA Astrophysics Data System (ADS)
Khoshmanesh, M.; Shirzaei, M.; Nadeau, R. M.
2015-12-01
The Central segment of San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. However, observations of the creep rate obtained using Characteristically Repeating Earthquakes (CREs) show a quasi-periodic temporal variation, which is recently confirmed using both InSAR surface deformation time series and geodetic-based time-dependent kinematic model of creep along the CSAF. Here, we show that the statistical analysis of creep fronts along the CSAF indicates a sporadic behavior, signature of a burst-like creep dynamics. Moreover, the probability of creep velocities follows a Gumbel distribution characterized by longer tail toward the extreme positive rates. Fourier analysis of the time series of surface creep rate indicates a self-affine regime with Hurst exponent altering between 0.6 and 0.9 during the observation period of 2003-2011. The variable Hurst component is an indicator for temporal variation in the roughness of the fault zone. To explain the causes of creep avalanches, two possible mechanisms are considered, including temporal variation in: 1) fault geometry, and 2) Ambient normal stress. We find that the overall statistical dependence between the pattern of surface creep rate and the fault geometry is insignificant. To investigate the effect of ambient normal stress, primarily due to variation in pore pressure, we implement a rate and state friction law to link the time-dependent kinematic creep model to the spatiotemporal variations of the normal stress on the velocity-strengthening fault zones. These observations and models help to understand the driving mechanisms that govern the creep rate variations at short spatial length and low velocities. Under these circumstances, the other mechanisms such as thermal pressurization are not feasible.
Watching excitons move: the time-dependent transition density matrix
NASA Astrophysics Data System (ADS)
Ullrich, Carsten
2012-02-01
Time-dependent density-functional theory allows one to calculate excitation energies and the associated transition densities in principle exactly. The transition density matrix (TDM) provides additional information on electron-hole localization and coherence of specific excitations of the many-body system. We have extended the TDM concept into the real-time domain in order to visualize the excited-state dynamics in conjugated molecules. The time-dependent TDM is defined as an implicit density functional, and can be approximately obtained from the time-dependent Kohn-Sham orbitals. The quality of this approximation is assessed in simple model systems. A computational scheme for real molecular systems is presented: the time-dependent Kohn-Sham equations are solved with the OCTOPUS code and the time-dependent Kohn-Sham TDM is calculated using a spatial partitioning scheme. The method is applied to show in real time how locally created electron-hole pairs spread out over neighboring conjugated molecular chains. The coupling mechanism, electron-hole coherence, and the possibility of charge separation are discussed.
Effect of Time-dependent Rupture on Tsunami Generation
NASA Astrophysics Data System (ADS)
Arcas, D.; Kanoglu, U.; Moore, C. W.; Aydin, B.
2013-12-01
Differential GPS data from the recent Chile 2009 and Japan 2011 seismic events have unveiled complex time-dependent ground motion dynamics during seismic rupture. Current tsunami modeling techniques usually ignore this time-dependent behavior in tsunami sources by assuming an instantaneous initial deformation field. Initial attempts to include time-dependent rupture behavior have motivated scientists to simulate this phenomenon as a series of instantaneous changes in the sea-floor. The present study investigates the effect of dynamic ground motion rupture on tsunami generation by including the time-dependent initial conditions in the derivation of the linear shallow-water wave equations. We then study the sensitivity of initial water surface deformation to time-dependent seafloor rupture by performing a parametric study of varying speed and rupture direction, while assuming a monotonic deformation from an initial pre-rupture state to a post-rupture final state. Numerical results for some selected scenarios are validated by comparing with analytical solutions of the non-homogeneous linear shallow-water equations.
Radiation and temperature effects on the time-dependent response of T300/934 graphite/epoxy
NASA Technical Reports Server (NTRS)
Yancey, Robert N.; Pindera, Marek-Jerzy
1988-01-01
A time-dependent characterization study was performed on T300/934 graphite/epoxy in a simulated space environment. Creep tests on irradiated and nonirradiated graphite/epoxy and bulk resin specimens were carried out at temperatures of 72 and 250 F. Irradiated specimens were exposed to dosages of penetrating electron radiation equal to 30 years exposure at GEO-synchronous orbit. Radiation was shown to have little effect on the creep response of both the composite and bulk resin specimens at 72 F while radiation had a significant effect at 250 F. A healing process was shown to be present in the irradiated specimens where broken bonds in the epoxy due to radiation recombined over time to form cross-links in the 934 resin structure. An analytical micromechanical model was also developed to predict the viscoelastic response of fiber reinforced composite materials. The model was shown to correlate well with experimental results for linearly viscoelastic materials with relatively small creep strains.
Time-dependent bridging and life prediction of SiC/SiC in a hypothetical fusion environment
Henager, C.H. Jr.; Lewinsohn, C.A.; Windisch, C.F. Jr.; Jones, R.H.
1996-10-01
Growth of subcritical cracks in SiC/SiC composites of CG-Nicalon fibers with a {approximately}1 {mu}m C-interphase has been measured on a related Basic Energy Sciences program using environments of purified argon and mixtures of argon and oxygen at 1073K to 1373K. Companion thermo-gravimetric (TGA) testing measured mass loss in identical environments. The TGA mass loss was from C-interphase oxidation to CO and CO{sub 2}, which was undetectable in argon and linear with oxygen concentration in argon-oxygen mixtures, and was converted into an interphase linear recession rate. Crack growth in pure argon indicated that fiber creep was causing time-dependent crack bridging to occur, while crack growth in argon-oxygen mixtures indicated that time-dependent C-interphase recession was also causing time-dependent bridging with different kinetics. A model of time-dependent bridging was used to compute crack growth rates in argon and in argon-oxygen mixtures and gave an estimate of useable life of about 230 days at 1073K in a He + 1.01 Pa O{sub 2} (10 ppm) environment.
The computational foundations of time dependent density functional theory
NASA Astrophysics Data System (ADS)
Whitfield, James
2014-03-01
The mathematical foundations of TDDFT are established through the formal existence of a fictitious non-interacting system (known as the Kohn-Sham system), which can reproduce the one-electron reduced probability density of the actual system. We build upon these works and show that on the interior of the domain of existence, the Kohn-Sham system can be efficiently obtained given the time-dependent density. Since a quantum computer can efficiently produce such time-dependent densities, we present a polynomial time quantum algorithm to generate the time-dependent Kohn-Sham potential with controllable error bounds. Further, we find that systems do not immediately become non-representable but rather become ill-representable as one approaches this boundary. A representability parameter is defined in our work which quantifies the distance to the boundary of representability and the computational difficulty of finding the Kohn-Sham system.
Computational complexity of time-dependent density functional theory
NASA Astrophysics Data System (ADS)
Whitfield, J. D.; Yung, M.-H.; Tempel, D. G.; Boixo, S.; Aspuru-Guzik, A.
2014-08-01
Time-dependent density functional theory (TDDFT) is rapidly emerging as a premier method for solving dynamical many-body problems in physics and chemistry. The mathematical foundations of TDDFT are established through the formal existence of a fictitious non-interacting system (known as the Kohn-Sham system), which can reproduce the one-electron reduced probability density of the actual system. We build upon these works and show that on the interior of the domain of existence, the Kohn-Sham system can be efficiently obtained given the time-dependent density. We introduce a V-representability parameter which diverges at the boundary of the existence domain and serves to quantify the numerical difficulty of constructing the Kohn-Sham potential. For bounded values of V-representability, we present a polynomial time quantum algorithm to generate the time-dependent Kohn-Sham potential with controllable error bounds.
NASA Technical Reports Server (NTRS)
Gates, Thomas S.; Feldman, Mark
1993-01-01
Two complimentary studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. The first of these studies, experimental in nature, used isothermal tensile creep/aging test techniques developed for polymers and adapted them for testing of the composite material. From these tests, the time dependent transverse (S22) and shear (S66) compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(sub g) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress. The second part of the study relied upon isothermal uniaxial tension tests of IM7/8320 to determine the effects of physical aging on the nonlinear material behavior at elevated temperature. An elastic/viscoplastic constitutive model was used to quantify the effects of aging on the rate-independent plastic and rate-dependent viscoplastic response. Sensitivity of the material constants required by the model to aging time were determined for aging times up to 65 hours. Verification of the analytical model indicated that the effects of prior aging on the nonlinear stress/strain/time data of matrix dominated laminates can be predicted.
Exact response functions within the time-dependent Gutzwiller approach
NASA Astrophysics Data System (ADS)
Bünemann, J.; Wasner, S.; Oelsen, E. v.; Seibold, G.
2015-02-01
We investigate the applicability of the two existing versions of a time-dependent Gutzwiller approach (TDGA) beyond the frequently used limit of infinite spatial dimensions. To this end, we study the two-particle response functions of a two-site Hubbard model where we can compare the exact results and those derived from the TDGA. It turns out that only the more recently introduced version of the TDGA can be combined with a diagrammatic approach which allows for the evaluation of Gutzwiller wave functions in finite dimensions. For this TDGA method, we derive the time-dependent Lagrangian for general single-band Hubbard models.
Choice of Variables and Preconditioning for Time Dependent Problems
NASA Technical Reports Server (NTRS)
Turkel, Eli; Vatsa, Verr N.
2003-01-01
We consider the use of low speed preconditioning for time dependent problems. These are solved using a dual time step approach. We consider the effect of this dual time step on the parameter of the low speed preconditioning. In addition, we compare the use of two sets of variables, conservation and primitive variables, to solve the system. We show the effect of these choices on both the convergence to a steady state and the accuracy of the numerical solutions for low Mach number steady state and time dependent flows.
Time dependent nucleation in a bulk metallic glass forming alloy
Croat, T.K.; Kelton, K.F.
1998-12-31
The effect of composition on the time-dependent nucleation rates in Zr{sub 65}Al{sub 7.5}Ni{sub 10}Cu{sub 17.5} glasses is investigated to better understand nucleation processes in partitioning systems. As-quenched glasses were annealed to produce a homogeneous dispersion of nanocrystals within the amorphous matrix. The nucleation rates were estimated from the number of crystallites produced as function of annealing time, using scanning and transmission electron microscopy. Experimental results for single and multiple-step annealing treatments are presented. The nucleation results are discussed briefly within the time-dependent model of the classical theory of nucleation.
Two-stream instability with time-dependent drift velocity
Qin, Hong; Davidson, Ronald C.
2014-06-26
The classical two-stream instability driven by a constant relative drift velocity between two plasma components is extended to the case with time-dependent drift velocity. A solution method is developed to rigorously define and calculate the instability growth rate for linear perturbations relative to the time-dependent unperturbed two-stream motions. The stability diagrams for the oscillating two-stream instability are presented over a large region of parameter space. It is shown that the growth rate for the classical two-stream instability can be significantly reduced by adding an oscillatory component to the relative drift velocity.
Time-Dependent Collective Neutrino Oscillations in Supernovae
NASA Astrophysics Data System (ADS)
Abbar, Sajad; Duan, Huaiyu
2015-10-01
Neutrinos can experience self-induced flavor conversion in core-collapse supernovae due to neutrino-neutrino forward scattering. Previously a stationary supernova model, the so called ``neutrino bulb model,'' was used exclusively to study collective neutrino oscillations in the core-collapse supernova. We show that even a small time-dependent perturbation in neutrino fluxes on the surface of the proto-neutron star can lead to fast varying collective oscillations at large radii. This result calls for time-dependent supernova models for the study of collective neutrino oscillations. This work was supported by DOE EPSCoR Grant DE-SC0008142 at UNM.
Two-stream instability with time-dependent drift velocity
Qin, Hong; Davidson, Ronald C.
2014-06-15
The classical two-stream instability driven by a constant relative drift velocity between two plasma components is extended to the case with time-dependent drift velocity. A solution method is developed to rigorously define and calculate the instability growth rate for linear perturbations relative to the time-dependent unperturbed two-stream motions. Stability diagrams for the oscillating two-stream instability are presented over a large region of parameter space. It is shown that the growth rate for the classical two-stream instability can be significantly reduced by adding an oscillatory component to the relative drift velocity.
Key, S.W.; Krieg, R.D.
1980-01-01
A number of complex issues are addressed which will allow the incorporation of finite strain, inelastic material behavior into the piecewise numerical construction of solutions in solid mechanics. Without recourse to extensive continuum mechanics preliminaries, an elementary time independent plasticity model, an elementary time dependent creep model, and a viscoelastic model are introduced as examples of constitutive equations which are routinely used in engineering calculations. The constitutive equations are all suitable for problems involving large deformations and finite strains. The plasticity and creep models are in rate form and use the symmetric part of the velocity gradient or the stretching to compute the co-rotational time derivative of the Cauchy stress. The viscoelastic model computes the current value of the Cauchy stress from a hereditary integral of a materially invariant form of the stretching history. The current configuration is selected for evaluation of equilibrium as opposed to either the reference configuration or the last established equilibrium configuration. The process of strain incrementation is examined in some depth and the stretching evaluated at the midinterval multiplied by the time step is identified as the appropriate finite strain increment to use with the selected form of the constitutive equations. Discussed is the conversion of rotation rates based on the spin into incremental orthogonal rotations which are then used to update stresses and state variables due to rigid body rotation during the load increment. Comments and references to the literature are directed at numerical integration of the constitutive equations with an emphasis on doing this accurately, if not exactly, for any time step and stretching. This material taken collectively provides an approach to numerical implementation which is marked by its simplicity.
NASA Astrophysics Data System (ADS)
Petruk, O.; Kopytko, B.
2016-11-01
Three approaches are considered to solve the equation which describes the time-dependent diffusive shock acceleration of test particles at the non-relativistic shocks. At first, the solution of Drury for the particle distribution function at the shock is generalized to any relation between the acceleration time-scales upstream and downstream and for the time-dependent injection efficiency. Three alternative solutions for the spatial dependence of the distribution function are derived. Then, the two other approaches to solve the time-dependent equation are presented, one of which does not require the Laplace transform. At the end, our more general solution is discussed, with a particular attention to the time-dependent injection in supernova remnants. It is shown that, comparing to the case with the dominant upstream acceleration time-scale, the maximum momentum of accelerated particles shifts towards the smaller momenta with increase of the downstream acceleration time-scale. The time-dependent injection affects the shape of the particle spectrum. In particular, (i) the power-law index is not solely determined by the shock compression, in contrast to the stationary solution; (ii) the larger the injection efficiency during the first decades after the supernova explosion, the harder the particle spectrum around the high-energy cutoff at the later times. This is important, in particular, for interpretation of the radio and gamma-ray observations of supernova remnants, as demonstrated on a number of examples.
Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei
2014-01-01
We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear “one beam” geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments. PMID:25089490
Time dependent solution for acceleration of tau-leaping
NASA Astrophysics Data System (ADS)
Fu, Jin; Wu, Sheng; Petzold, Linda R.
2013-02-01
The tau-leaping method is often effective for speeding up discrete stochastic simulation of chemically reacting systems. However, when fast reactions are involved, the speed-up for this method can be quite limited. One way to address this is to apply a stochastic quasi-steady state assumption. However we must be careful when using this assumption. If the fast subsystem cannot reach a steady distribution fast enough, the quasi-steady-state assumption will propagate error into the simulation. To avoid these errors, we propose to use the time dependent solution rather than the quasi-steady-state. Generally speaking, the time dependent solution is not easy to derive for an arbitrary network. However, for some common motifs we do have time dependent solutions. We derive the time dependent solutions for these motifs, and then show how they can be used with tau-leaping to achieve substantial speed-ups, including for a realistic model of blood coagulation. Although the method is complicated, we have automated it.
Time dependent solution for acceleration of tau-leaping
Fu, Jin; Wu, Sheng; Petzold, Linda R.
2013-02-15
The tau-leaping method is often effective for speeding up discrete stochastic simulation of chemically reacting systems. However, when fast reactions are involved, the speed-up for this method can be quite limited. One way to address this is to apply a stochastic quasi-steady state assumption. However we must be careful when using this assumption. If the fast subsystem cannot reach a steady distribution fast enough, the quasi-steady-state assumption will propagate error into the simulation. To avoid these errors, we propose to use the time dependent solution rather than the quasi-steady-state. Generally speaking, the time dependent solution is not easy to derive for an arbitrary network. However, for some common motifs we do have time dependent solutions. We derive the time dependent solutions for these motifs, and then show how they can be used with tau-leaping to achieve substantial speed-ups, including for a realistic model of blood coagulation. Although the method is complicated, we have automated it.
Dynamic structure evolution of time-dependent network
NASA Astrophysics Data System (ADS)
Zhang, Beibei; Zhou, Yadong; Xu, Xiaoyan; Wang, Dai; Guan, Xiaohong
2016-08-01
In this paper, we research the long-voided problem of formulating the time-dependent network structure evolution scheme, it focus not only on finding new emerging vertices in evolving communities and new emerging communities over the specified time range but also formulating the complex network structure evolution schematic. Previous approaches basically applied to community detection on time static networks and thus failed to consider the potentially crucial and useful information latently embedded in the dynamic structure evolution process of time-dependent network. To address these problems and to tackle the network non-scalability dilemma, we propose the dynamic hierarchical method for detecting and revealing structure evolution schematic of the time-dependent network. In practice and specificity, we propose an explicit hierarchical network evolution uncovering algorithm framework originated from and widely expanded from time-dependent and dynamic spectral optimization theory. Our method yields preferable results compared with previous approaches on a vast variety of test network data, including both real on-line networks and computer generated complex networks.
Time-Dependent Effects of Cardiovascular Exercise on Memory.
Roig, Marc; Thomas, Richard; Mang, Cameron S; Snow, Nicholas J; Ostadan, Fatemeh; Boyd, Lara A; Lundbye-Jensen, Jesper
2016-04-01
We present new evidence supporting the hypothesis that the effects of cardiovascular exercise on memory can be regulated in a time-dependent manner. When the exercise stimulus is coupled temporally with specific phases of the memory formation process, a single bout of cardiovascular exercise may be sufficient to improve memory. PMID:26872291
Shoulder pain and time dependent structure in wheelchair propulsion variability.
Jayaraman, Chandrasekaran; Moon, Yaejin; Sosnoff, Jacob J
2016-07-01
Manual wheelchair propulsion places considerable repetitive mechanical strain on the upper limbs leading to shoulder injury and pain. While recent research indicates that the amount of variability in wheelchair propulsion and shoulder pain may be related. There has been minimal inquiry into the fluctuation over time (i.e. time-dependent structure) in wheelchair propulsion variability. Consequently the purpose of this investigation was to examine if the time-dependent structure in the wheelchair propulsion parameters are related to shoulder pain. 27 experienced wheelchair users manually propelled their own wheelchair fitted with a SMARTWheel on a roller at 1.1m/s for 3min. Time-dependent structure of cycle-to-cycle fluctuations in contact angle and inter push time interval was quantified using sample entropy (SampEn) and compared between the groups with/without shoulder pain using non-parametric statistics. Overall findings were, (1) variability observed in contact angle fluctuations during manual wheelchair propulsion is structured (Z=3.15;p<0.05), (2) individuals with shoulder pain exhibited higher SampEn magnitude for contact angle during wheelchair propulsion than those without pain (χ(2)(1)=6.12;p<0.05); and (3) SampEn of contact angle correlated significantly with self-reported shoulder pain (rs (WUSPI) =0.41;rs (VAS)=0.56;p<0.05). It was concluded that the time-dependent structure in wheelchair propulsion may provide novel information for tracking and monitoring shoulder pain.
Acceleration in a nonplanar time-dependent billiard
NASA Astrophysics Data System (ADS)
Raeisi, Sedighe; Eslami, Parvin
2016-08-01
We study the dynamical properties of a particle in a nonplanar square billiard. The plane of the billiard has a sinusoidal shape. We consider both the static and time-dependent plane. We study the affect of different parameters that control the geometry of the billiard in this model. We consider variations of different parameters of the model and describe how the particle trajectory is affected by these parameters. We also investigate the dynamical behavior of the system in the static condition using its reduced phase plot and show that the dynamics of the particle inside the billiard may be regular, mixed, or chaotic. Finally, the problem of the particle energy growth is studied in the billiard with the time-dependent plane. We show that when in the static case, the billiard is chaotic, then the particle energy in the time-dependent billiard grows for a small number of collisions, and then it starts to saturate. But when the dynamics of the static case is regular, then the particle average energy in the time-dependent situation stays constant.
Acceleration in a nonplanar time-dependent billiard.
Raeisi, Sedighe; Eslami, Parvin
2016-08-01
We study the dynamical properties of a particle in a nonplanar square billiard. The plane of the billiard has a sinusoidal shape. We consider both the static and time-dependent plane. We study the affect of different parameters that control the geometry of the billiard in this model. We consider variations of different parameters of the model and describe how the particle trajectory is affected by these parameters. We also investigate the dynamical behavior of the system in the static condition using its reduced phase plot and show that the dynamics of the particle inside the billiard may be regular, mixed, or chaotic. Finally, the problem of the particle energy growth is studied in the billiard with the time-dependent plane. We show that when in the static case, the billiard is chaotic, then the particle energy in the time-dependent billiard grows for a small number of collisions, and then it starts to saturate. But when the dynamics of the static case is regular, then the particle average energy in the time-dependent situation stays constant. PMID:27627308
Student Understanding of Time Dependence in Quantum Mechanics
ERIC Educational Resources Information Center
Emigh, Paul J.; Passante, Gina; Shaffer, Peter S.
2015-01-01
The time evolution of quantum states is arguably one of the more difficult ideas in quantum mechanics. In this article, we report on results from an investigation of student understanding of this topic after lecture instruction. We demonstrate specific problems that students have in applying time dependence to quantum systems and in recognizing…
Time-Dependent Interfacial Properties and DNAPL Mobility
Tuck, D.M.
1999-03-10
Interfacial properties play a major role in governing where and how dense nonaqueous phase liquids (DNAPLs) move in the subsurface. Interfacial tension and contact angle measurements were obtained for a simple, single component DNAPL (tetrachloroethene, PCE), complex laboratory DNAPLs (PCE plus Sudan IV dye), and a field DNAPL from the Savannah River Site (SRS) M-Area DNAPL (PCE, trichloroethene [TCE], and maching oils). Interfacial properties for complex DNAPLs were time-dependent, a phenomenon not observed for PCE alone. Drainage capillary pressure-saturation curves are strongly influenced by interfacial properties. Therefore time-dependence will alter the nature of DNAPL migration and penetration. Results indicate that the time-dependence of PCE with relatively high Sudan IV dye concentrations is comparable to that of the field DNAPL. Previous DNAPL mobility experiments in which the DNAPL was dyed should be reviewed to determine whether time-dependent properties influenced the resutls. Dyes appear to make DNAPL more complex, and therefore a more realistic analog for field DNAPLs than single component DNAPLs.
Solving time-dependent operator equations for nanoscale physics
Rau, A. Ravi P.
2007-08-27
This is the final technical report on an Office of Basic Energy Sciences Grant, detailing the work accomplished on solving time-dependent operator equations of interest in nanoscale physics. A summary of the results and list of publications is given.
Rate and time dependent failure of structural adhesives
NASA Technical Reports Server (NTRS)
Brinson, H. F.; Renieri, M. P.; Herakovich, C. T.
1975-01-01
Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having important applications in the bonding of composite materials are presented. A testing program to ascertain stress-strain, strain-rate, time, yield, and/or failure behavior of these materials in bulk form using uniaxial tensile constant strain-rate, creep, and relaxation tests is described. The stress-strain behavior of each material is shown to be significantly rate dependent. A rate dependent stress whitening (crazing) phenomenon occurs prior to either yield or fracture. A region of linear elasticity, a region of viscoelasticity, and the onset of yielding are identified in the stress-strain behavior. The linear elastic limit and the yield point are shown to be rate dependent and agree well with an empirical equation proposed by Ludwik. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Analytical predictions based on a modified Bingham model are shown to agree well with experimental stress-strain strain-rate data. Analytical predictions based on a modified Ramberg-Osgood equation are also shown for comparison purposes.
2004-08-01
AnisWave2D is a 2D finite-difference code for a simulating seismic wave propagation in fully anisotropic materials. The code is implemented to run in parallel over multiple processors and is fully portable. A mesh refinement algorithm has been utilized to allow the grid-spacing to be tailored to the velocity model, avoiding the over-sampling of high-velocity materials that usually occurs in fixed-grid schemes.
Time-dependent magnetohydrodynamic simulations of the inner heliosphere
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Lyon, J. G.; Lario, D.; Arge, C. N.; Henney, C. J.
2016-04-01
This paper presents results from a simulation study exploring heliospheric consequences of time-dependent changes at the Sun. We selected a 2 month period in the beginning of year 2008 that was characterized by very low solar activity. The heliosphere in the equatorial region was dominated by two coronal holes whose changing structure created temporal variations distorting the classical steady state picture of the heliosphere. We used the Air Force Data Assimilate Photospheric Flux Transport (ADAPT) model to obtain daily updated photospheric magnetograms and drive the Wang-Sheeley-Arge (WSA) model of the corona. This leads to a formulation of a time-dependent boundary condition for our three-dimensional (3-D) magnetohydrodynamic (MHD) model, LFM-helio, which is the heliospheric adaptation of the Lyon-Fedder-Mobarry MHD simulation code. The time-dependent coronal conditions were propagated throughout the inner heliosphere, and the simulation results were compared with the spacecraft located near 1 astronomical unit (AU) heliocentric distance: Advanced Composition Explorer (ACE), Solar Terrestrial Relations Observatory (STEREO-A and STEREO-B), and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft that was in cruise phase measuring the heliospheric magnetic field between 0.35 and 0.6 AU. In addition, during the selected interval MESSENGER and ACE aligned radially allowing minimization of the effects of temporal variation at the Sun versus radial evolution of structures. Our simulations show that time-dependent simulationsreproduce the gross-scale structure of the heliosphere with higher fidelity, while on smaller spatial and faster time scales (e.g., 1 day) they provide important insights for interpretation of the data. The simulations suggest that moving boundaries of slow-fast wind transitions at 0.1 AU may result in the formation of inverted magnetic fields near pseudostreamers which is an intrinsically time-dependent process
Time-dependent ion transport in heterogeneous permselective systems
NASA Astrophysics Data System (ADS)
Green, Yoav; Yossifon, Gilad
2015-06-01
The current study extends previous analytical and numerical solutions of chronopotentiometric response of one-dimensional systems consisting of three layers to the more realistic two-dimensional (2D) heterogeneous ion-permselective medium. An analytical solution for the transient concentration-polarization problem, under the local electroneutrality approximation and assumption of ideal permselectivity, was obtained using the Laplace transform and separation of variables technique. Then the 2D electric potential was obtained numerically and was compared to the full Poisson-Nernst-Planck solution. It was then shown that the resultant voltage drop across the system varies between the initial Ohmic response and that of the steady state accounting for concentration polarization. Also, the field-focusing effect in a 2D system is shown to result in a faster depletion of ions at the permselective interface.
Time-dependent ion transport in heterogeneous permselective systems.
Green, Yoav; Yossifon, Gilad
2015-06-01
The current study extends previous analytical and numerical solutions of chronopotentiometric response of one-dimensional systems consisting of three layers to the more realistic two-dimensional (2D) heterogeneous ion-permselective medium. An analytical solution for the transient concentration-polarization problem, under the local electroneutrality approximation and assumption of ideal permselectivity, was obtained using the Laplace transform and separation of variables technique. Then the 2D electric potential was obtained numerically and was compared to the full Poisson-Nernst-Planck solution. It was then shown that the resultant voltage drop across the system varies between the initial Ohmic response and that of the steady state accounting for concentration polarization. Also, the field-focusing effect in a 2D system is shown to result in a faster depletion of ions at the permselective interface.
Generating time dependent conformally coupled Einstein-scalar solutions
NASA Astrophysics Data System (ADS)
Sultana, Joseph
2015-07-01
Using the correspondence between a minimally coupled scalar field and an effective stiff perfect fluid with or without a cosmological constant, we present a simple method for generating time dependent Einstein-scalar solutions with a conformally coupled scalar field that has vanishing or non-vanishing potential. This is done by using Bekenstein's transformation on Einstein-scalar solutions with minimally coupled massless scalar fields, and its later generalization by Abreu et al. to massive fields. In particular we obtain two new spherically symmetric time dependent solutions to the coupled system of Einstein's and the conformal scalar field equations, with one of the solutions having a Higgs' type potential for the scalar field, and we study their properties.
Statistical time-dependent model for the interstellar gas
NASA Technical Reports Server (NTRS)
Gerola, H.; Kafatos, M.; Mccray, R.
1974-01-01
We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.
A time-dependent approach to electron-atom scattering
NASA Astrophysics Data System (ADS)
Buffington, Gavin Douglas
1997-08-01
This time-dependent approach utilizes a fully correlated two electron wave function developed by Bottcher, Schultz and Madison. A finite element spline basis is employed with the principle of collocation in order to express the wave function and Hamiltonian numerically. An initial state, composed of a wavepacket for the projectile and an isolated atomic wave function, is evolved in time according to the time-dependent Schrodinger equation. Probabilities for excitation and ionization are computed as a function of time by taking projections onto states and pseudostates of the target atom. The wavepacket approach obviates the need for consideration of three- body boundary conditions and the asymptotic form of the wave function. Cross sections for electron impact excitation and ionization are obtained and compared with results from other theoretical methods.
Boosting thermoelectric efficiency using time-dependent control.
Zhou, Hangbo; Thingna, Juzar; Hänggi, Peter; Wang, Jian-Sheng; Li, Baowen
2015-01-01
Thermoelectric efficiency is defined as the ratio of power delivered to the load of a device to the rate of heat flow from the source. Till date, it has been studied in presence of thermodynamic constraints set by the Onsager reciprocal relation and the second law of thermodynamics that severely bottleneck the thermoelectric efficiency. In this study, we propose a pathway to bypass these constraints using a time-dependent control and present a theoretical framework to study dynamic thermoelectric transport in the far from equilibrium regime. The presence of a control yields the sought after substantial efficiency enhancement and importantly a significant amount of power supplied by the control is utilised to convert the wasted-heat energy into useful-electric energy. Our findings are robust against nonlinear interactions and suggest that external time-dependent forcing, which can be incorporated with existing devices, provides a beneficial scheme to boost thermoelectric efficiency.
A time dependent theory of crazing behavior in polymers
NASA Technical Reports Server (NTRS)
Chern, S. S.; Hsiao, C. C.
1982-01-01
The development of crazing is not only a function of stress, but also a function of time. Under a simple state of tension, a craze opening displacement is closely associated with the viscoelastic behavior of the original bulk polymer medium in which individual crazes initiate and develop. Within each craze region, molecular orientation takes place when conditions permit, and a new phase of rearranged molecules governs its local behavior. Based upon a time-dependent viscoelastic two-dimensional model, using a computer program the craze opening displacement field has been calculated, time-dependent craze length was also computed by taking into consideration the molecular orientation mechanism and large deformations in the craze region. Examples are given for simple viscoelastic media with simplified stress distributions. It is interesting to find out that the occurrence of crazing may be interpreted in terms of the stability or instability of the constitutive behavior of the bulk polymer.
Sublinear scaling for time-dependent stochastic density functional theory
Gao, Yi; Neuhauser, Daniel; Baer, Roi; Rabani, Eran
2015-01-21
A stochastic approach to time-dependent density functional theory is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy. The core idea of the approach involves time-propagation of a small set of stochastic orbitals which are first projected on the occupied space and then propagated in time according to the time-dependent Kohn-Sham equations. The evolving electron density is exactly represented when the number of random orbitals is infinite, but even a small number (≈16) of such orbitals is enough to obtain meaningful results for absorption spectrum and the RPA correlation energy per electron. We implement the approach for silicon nanocrystals using real-space grids and find that the overall scaling of the algorithm is sublinear with computational time and memory.
Chromospheric extents predicted by time-dependent acoustic wave models
NASA Technical Reports Server (NTRS)
Cuntz, Manfred
1990-01-01
Theoretical models for chromospheric structures of late-type giant stars are computed, including the time-dependent propagation of acoustic waves. Models with short-period monochromatic shock waves as well as a spectrum of acoustic waves are discussed, and the method is applied to the stars Arcturus, Aldebaran, and Betelgeuse. Chromospheric extent, defined as the monotonic decrease with height of the time-averaged electron densities, are found to be 1.12, 1.13, and 1.22 stellar radii for the three stars, respectively; this corresponds to a time-averaged electron density of 10 to the 7th/cu cm. Predictions of the extended chromospheric obtained using a simple scaling law agree well with those obtained by the time-dependent wave models; thus, the chromospheres of all stars for which the scaling law is valid consist of the same number of pressure scale heights.
Boosting thermoelectric efficiency using time-dependent control.
Zhou, Hangbo; Thingna, Juzar; Hänggi, Peter; Wang, Jian-Sheng; Li, Baowen
2015-01-01
Thermoelectric efficiency is defined as the ratio of power delivered to the load of a device to the rate of heat flow from the source. Till date, it has been studied in presence of thermodynamic constraints set by the Onsager reciprocal relation and the second law of thermodynamics that severely bottleneck the thermoelectric efficiency. In this study, we propose a pathway to bypass these constraints using a time-dependent control and present a theoretical framework to study dynamic thermoelectric transport in the far from equilibrium regime. The presence of a control yields the sought after substantial efficiency enhancement and importantly a significant amount of power supplied by the control is utilised to convert the wasted-heat energy into useful-electric energy. Our findings are robust against nonlinear interactions and suggest that external time-dependent forcing, which can be incorporated with existing devices, provides a beneficial scheme to boost thermoelectric efficiency. PMID:26464021
Nonlinear time-dependent simulation of helix traveling wave tubes
NASA Astrophysics Data System (ADS)
Peng, Wei-Feng; Yang, Zhong-Hai; Hu, Yu-Lu; Li, Jian-Qing; Lu, Qi-Ru; Li, Bin
2011-07-01
A one-dimensional nonlinear time-dependent theory for helix traveling wave tubes is studied. A generalized electromagnetic field is applied to the expression of the radio frequency field. To simulate the variations of the high frequency structure, such as the pitch taper and the effect of harmonics, the spatial average over a wavelength is substituted by a time average over a wave period in the equation of the radio frequency field. Under this assumption, the space charge field of the electron beam can be treated by a space charge wave model along with the space charge coefficient. The effects of the radio frequency and the space charge fields on the electrons are presented by the equations of the electron energy and the electron phase. The time-dependent simulation is compared with the frequency-domain simulation for a helix TWT, which validates the availability of this theory.
Boosting thermoelectric efficiency using time-dependent control
Zhou, Hangbo; Thingna, Juzar; Hänggi, Peter; Wang, Jian-Sheng; Li, Baowen
2015-01-01
Thermoelectric efficiency is defined as the ratio of power delivered to the load of a device to the rate of heat flow from the source. Till date, it has been studied in presence of thermodynamic constraints set by the Onsager reciprocal relation and the second law of thermodynamics that severely bottleneck the thermoelectric efficiency. In this study, we propose a pathway to bypass these constraints using a time-dependent control and present a theoretical framework to study dynamic thermoelectric transport in the far from equilibrium regime. The presence of a control yields the sought after substantial efficiency enhancement and importantly a significant amount of power supplied by the control is utilised to convert the wasted-heat energy into useful-electric energy. Our findings are robust against nonlinear interactions and suggest that external time-dependent forcing, which can be incorporated with existing devices, provides a beneficial scheme to boost thermoelectric efficiency. PMID:26464021
Boosting thermoelectric efficiency using time-dependent control
NASA Astrophysics Data System (ADS)
Zhou, Hangbo; Thingna, Juzar; Hänggi, Peter; Wang, Jian-Sheng; Li, Baowen
2015-10-01
Thermoelectric efficiency is defined as the ratio of power delivered to the load of a device to the rate of heat flow from the source. Till date, it has been studied in presence of thermodynamic constraints set by the Onsager reciprocal relation and the second law of thermodynamics that severely bottleneck the thermoelectric efficiency. In this study, we propose a pathway to bypass these constraints using a time-dependent control and present a theoretical framework to study dynamic thermoelectric transport in the far from equilibrium regime. The presence of a control yields the sought after substantial efficiency enhancement and importantly a significant amount of power supplied by the control is utilised to convert the wasted-heat energy into useful-electric energy. Our findings are robust against nonlinear interactions and suggest that external time-dependent forcing, which can be incorporated with existing devices, provides a beneficial scheme to boost thermoelectric efficiency.
Clean Time-Dependent String Backgrounds from Bubble Baths
Silverstein, Eva M
2002-08-08
We consider the set of controlled time-dependent backgrounds of general relativity and string theory describing ''bubbles of nothing'', obtained via double analytic continuation of black hole solutions. We analyze their quantum stability, uncover some novel features of their dynamics, identify their causal structure and observables, and compute their particle production spectrum. We present a general relation between squeezed states, such as those arising in cosmological particle creation, and nonlocal theories on the string worldsheet. The bubble backgrounds have various aspects in common with de Sitter space, Rindler space, and moving mirror systems, but constitute controlled solutions of general relativity and string theory with no external forces. They provide a useful theoretical laboratory for studying issues of observables in systems with cosmological horizons, particle creation, and time-dependent string perturbation theory.
Time-dependent response of filamentary composite spherical pressure vessels
NASA Technical Reports Server (NTRS)
Dozier, J. D.
1983-01-01
A filamentary composite spherical pressure vessel is modeled as a pseudoisotropic (or transversely isotropic) composite shell, with the effects of the liner and fill tubes omitted. Equations of elasticity, macromechanical and micromechanical formulations, and laminate properties are derived for the application of an internally pressured spherical composite vessel. Viscoelastic properties for the composite matrix are used to characterize time-dependent behavior. Using the maximum strain theory of failure, burst pressure and critical strain equations are formulated, solved in the Laplace domain with an associated elastic solution, and inverted back into the time domain using the method of collocation. Viscoelastic properties of HBFR-55 resin are experimentally determined and a Kevlar/HBFR-55 system is evaluated with a FORTRAN program. The computed reduction in burst pressure with respect to time indicates that the analysis employed may be used to predict the time-dependent response of a filamentary composite spherical pressure vessel.
Time-dependent first-principles approaches to PV materials
Miyamoto, Yoshiyuki
2013-12-10
Computational scheme for designing photovoltaic (PV) materials is presented. First-principles electron dynamics of photo-excitation and subsequent electron-hole splitting is performed based on the time-dependent density functional theory. Photo-induced enhancement of dipole moment was observed in a polar crystal and a donor-acceptor molecular pair. These experiences will pave a way to design PV material from first-principles simulations.
Shoulder pain and time dependent structure in wheelchair propulsion variability.
Jayaraman, Chandrasekaran; Moon, Yaejin; Sosnoff, Jacob J
2016-07-01
Manual wheelchair propulsion places considerable repetitive mechanical strain on the upper limbs leading to shoulder injury and pain. While recent research indicates that the amount of variability in wheelchair propulsion and shoulder pain may be related. There has been minimal inquiry into the fluctuation over time (i.e. time-dependent structure) in wheelchair propulsion variability. Consequently the purpose of this investigation was to examine if the time-dependent structure in the wheelchair propulsion parameters are related to shoulder pain. 27 experienced wheelchair users manually propelled their own wheelchair fitted with a SMARTWheel on a roller at 1.1m/s for 3min. Time-dependent structure of cycle-to-cycle fluctuations in contact angle and inter push time interval was quantified using sample entropy (SampEn) and compared between the groups with/without shoulder pain using non-parametric statistics. Overall findings were, (1) variability observed in contact angle fluctuations during manual wheelchair propulsion is structured (Z=3.15;p<0.05), (2) individuals with shoulder pain exhibited higher SampEn magnitude for contact angle during wheelchair propulsion than those without pain (χ(2)(1)=6.12;p<0.05); and (3) SampEn of contact angle correlated significantly with self-reported shoulder pain (rs (WUSPI) =0.41;rs (VAS)=0.56;p<0.05). It was concluded that the time-dependent structure in wheelchair propulsion may provide novel information for tracking and monitoring shoulder pain. PMID:27134151
Time-dependent HF approach to SHE dynamics
NASA Astrophysics Data System (ADS)
Umar, A. S.; Oberacker, V. E.
2015-12-01
We employ the time-dependent Hartree-Fock (TDHF) method to study various aspects of the reactions utilized in searches for superheavy elements. These include capture cross-sections, quasifission, prediction of PCN, and other interesting dynamical quantities. We show that the microscopic TDHF approach provides an important tool to shed some light on the nuclear dynamics leading to the formation of superheavy elements.
Relating Time-Dependent Acceleration and Height Using an Elevator
ERIC Educational Resources Information Center
Kinser, Jason M.
2015-01-01
A simple experiment in relating a time-dependent linear acceleration function to height is explored through the use of a smartphone and an elevator. Given acceleration as a function of time, a(t), the velocity function and position functions are determined through integration as in v(t)=? a(t) dt (1) and x(t)=? v(t) dt. Mobile devices such as…
Autoionization in time-dependent density-functional theory
NASA Astrophysics Data System (ADS)
Kapoor, V.
2016-06-01
We compute the exact exchange-correlation potential of the time-dependent density-functional theory (TDDFT) for the correlated process of autoionization. The potential develops barriers which regulate the autoionization rate. TDDFT employing known and practicable exchange-correlation potentials does not capture any autoionization dynamics. Approximate exchange-correlation potentials capturing such dynamics would necessarily require memory effects and are unlikely to be developed, as will be illustrated.
Time dependence of the reaction of water with glass
Doremus, R.H.
1980-01-01
Equations for the time-dependence of release of constituents from glass during reaction with water are discussed. Values of linear dissolution rates of different glasses are compared. Models for the reaction of water with glass are discussed. It is concluded that extrapolation of constant dissolution rates for durable glasses such as commercial soda-limes is reliable, but such extrapolation for borosilicate glass for waste disposal is less reliable because the mechanisms involved in their reaction with water are unclear. 25 refs.
Quasinormal modes in a time-dependent black hole background
Shao Chenggang; Wang Bin; Abdalla, Elcio; Su Rukeng
2005-02-15
We have studied the evolution of the massless scalar field propagating in a time-dependent charged Vaidya black hole background. A generalized tortoise coordinate transformation was used to study the evolution of the massless scalar field. It is shown that, for the slowest damped quasinormal modes, the approximate formulas in the stationary Reissner-Nordstroem black hole turn out to be a reasonable prescription, showing that results from quasinormal mode analysis are rather robust.
Quasinormal modes in a time-dependent black hole background
NASA Astrophysics Data System (ADS)
Shao, Cheng-Gang; Wang, Bin; Abdalla, Elcio; Su, Ru-Keng
2005-02-01
We have studied the evolution of the massless scalar field propagating in a time-dependent charged Vaidya black hole background. A generalized tortoise coordinate transformation was used to study the evolution of the massless scalar field. It is shown that, for the slowest damped quasinormal modes, the approximate formulas in the stationary Reissner-Nordström black hole turn out to be a reasonable prescription, showing that results from quasinormal mode analysis are rather robust.
Gamma time-dependency in Blaxter's compartmental model.
NASA Technical Reports Server (NTRS)
Matis, J. H.
1972-01-01
A new two-compartment model for the passage of particles through the gastro-intestinal tract of ruminants is proposed. In this model, a gamma distribution of lifetimes is introduced in the first compartment; thereby, passage from that compartment becomes time-dependent. This modification is strongly suggested by the physical alteration which certain substances, e.g. hay particles, undergo in the digestive process. The proposed model is applied to experimental data.
Stochastic protein production and time-dependent current fluctuations
NASA Astrophysics Data System (ADS)
Gorissen, Mieke; Vanderzande, Carlo
2011-03-01
Translation is the cellular process in which ribosomes make proteins from information encoded on messenger RNA. We model this process using driven lattice gases and take into account the finite lifetime of mRNA. The stochastic properties of the translation process can then be determined from the time-dependent current fluctuations of the lattice gas model. We illustrate our ideas with a totally asymmetric exclusion process with extended objects.
Time-Dependent 5D Solutions of the Einstein Equations
Lopez, L. A.
2010-07-12
In this work are obtained 5D time-dependent solutions of Einstein equations, one is obtained by means of equiping a cylindrically symmetry solution (JEKK) with a scalar field, then lifting it to a fifth dimension. The other is obtained transforming the Myers-Perry solution via Wick rotation. The two solutions can be interpreted as gravitational waves in some cases. The singularities and C-energy are addressed.
Designing for time-dependent material response in spacecraft structures
NASA Technical Reports Server (NTRS)
Hyer, M. W.; Oleksuk, Lynda L. S.; Bowles, D. E.
1992-01-01
To study the influence on overall deformations of the time-dependent constitutive properties of fiber-reinforced polymeric matrix composite materials being considered for use in orbiting precision segmented reflectors, simple sandwich beam models are developed. The beam models include layers representing the face sheets, the core, and the adhesive bonding of the face sheets to the core. A three-layer model lumps the adhesive layers with the face sheets or core, while a five-layer model considers the adhesive layers explicitly. The deformation response of the three-layer and five-layer sandwich beam models to a midspan point load is studied. This elementary loading leads to a simple analysis, and it is easy to create this loading in the laboratory. Using the correspondence principle of viscoelasticity, the models representing the elastic behavior of the two beams are transformed into time-dependent models. Representative cases of time-dependent material behavior for the facesheet material, the core material, and the adhesive are used to evaluate the influence of these constituents being time-dependent on the deformations of the beam. As an example of the results presented, if it assumed that, as a worst case, the polymer-dominated shear properties of the core behave as a Maxwell fluid such that under constant shear stress the shear strain increases by a factor of 10 in 20 years, then it is shown that the beam deflection increases by a factor of 1.4 during that time. In addition to quantitative conclusions, several assumptions are discussed which simplify the analyses for use with more complicated material models. Finally, it is shown that the simpler three-layer model suffices in many situations.
Time-dependent MOS breakdown. [of Na contaminated capacitors
NASA Technical Reports Server (NTRS)
Li, S. P.; Bates, E. T.; Maserjian, J.
1976-01-01
A general model for time-dependent breakdown in metal-oxide-silicon (MOS) structures is developed and related to experimental measurements on samples deliberately contaminated with Na. A statistical method is used for measuring the breakdown probability as a function of log time and applied field. It is shown that three time regions of breakdown can be explained respectively in terms of silicon surface defects, ion emission from the metal interface, and lateral ion diffusion at the silicon interface.
Time-dependent global modeling of the inner heliosphere
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Lyon, J.; Arge, C. N.; Lario, D.; Linker, J.; Lionello, R.
2015-12-01
We present results of time-dependent modeling of the inner heliosphere using the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamic (MHD). Two types of simulations are performed: one concentrates on the background solar wind specification, while the other deals with the propagation of coronal mass ejections (CMEs). For simulations of the first type we coupled the LFM-helio code with the ADAPT-driven WSA model. We present some details of the coupling machinery and then simulate selected periods characterized by very low solar activity with no significant energetic particle events or CMEs. The results of the model are compared with MESSENGER, ACE, STEREO A and B spacecraft to probe both radial and temporal evolution of solar wind structure. The results indicate, in particular, the importance of time-dependent modeling for more accurate prediction of high-speed streams and heliospheric current sheet structure when the spacecraft skim its surface. We will comment on the formation of magnetic field reversals in pseudostreamer regions, which is an intrinsically time-dependent phenomenon, and on the current sheet corrugation caused by solar wind momentum shears. For the second type of time-dependent inner heliosphere simulations we have coupled LFM-helio with the MAS MHD model of the corona. We first present results of idealized coupled MAS/LFM-helio simulations with symmetric solar wind background and no rotation intended to test the interface for seamless propagation of transients from the corona into the inner heliosphere domain. We then simulate an event with a CME propagating through a realistic heliosphere background including corotating interaction regions. We show details of propagation of flux-rope CMEs through the boundary between MAS and LFM-helio and compare the results between the two codes in the heliospheric domain. The results indicate that the coupling works well, although some differences in the solutions are observed probably due to differences in numerical
Quantum anholonomies in time-dependent Aharonov-Bohm rings
Tanaka, Atushi; Cheon, Taksu
2010-08-15
Anholonomies in eigenstates are studied through time-dependent variations of a magnetic flux in an Aharonov-Bohm ring. The anholonomies in the eigenenergy and the expectation values of eigenstates are shown to persist beyond the adiabatic regime. The choice of the gauge of the magnetic flux is shown to be crucial to clarify the relationship of these anholonomies to the eigenspace anholonomy, which is described by a non-Abelian connection in the adiabatic limit.
Time dependent turbulence modeling and analytical theories of turbulence
NASA Technical Reports Server (NTRS)
Rubinstein, R.
1993-01-01
By simplifying the direct interaction approximation (DIA) for turbulent shear flow, time dependent formulas are derived for the Reynolds stresses which can be included in two equation models. The Green's function is treated phenomenologically, however, following Smith and Yakhot, we insist on the short and long time limits required by DIA. For small strain rates, perturbative evaluation of the correlation function yields a time dependent theory which includes normal stress effects in simple shear flows. From this standpoint, the phenomenological Launder-Reece-Rodi model is obtained by replacing the Green's function by its long time limit. Eddy damping corrections to short time behavior initiate too quickly in this model; in contrast, the present theory exhibits strong suppression of eddy damping at short times. A time dependent theory for large strain rates is proposed in which large scales are governed by rapid distortion theory while small scales are governed by Kolmogorov inertial range dynamics. At short times and large strain rates, the theory closely matches rapid distortion theory, but at long times it relaxes to an eddy damping model.
Time-dependent dynamic behavior of light diffraction in ferrofluid
NASA Astrophysics Data System (ADS)
Chung, Min-Feng; Chou, S. E.; Fu, Chao-Ming
2012-04-01
The time-dependent dynamic behavior of diffraction patterns induced by external magnetic field in a suspension of nano-sized magnetic particles (Fe3O4) in a water-based magnetic fluid was investigated. It was observed that the diffraction pattern changed with time as the magnetic field was applied. In the absence of applied magnetic field, there was no diffraction pattern in the screen. When the magnetic field was applied, the transmitted light was perpendicular to the magnetic field, and the diffraction pattern was unstable. There were many small lines and points moving with time. After one minute, the diffraction pattern turned stable, and the small lines became longer. This time-dependent behavior helps us to understand the evolution of the forming chains of magnetic nanoparticles. Moreover, we have measured the other diffraction pattern, the transmitted light propagating parallel to the applied field. These time-dependent diffraction patterns give a new point to understand the dynamic three-dimensional structure of magnetic fluid under a dc magnetic field.
The multi-configurational time-dependent Hartree approach revisited
Manthe, Uwe
2015-06-28
The multi-configurational time-dependent Hartree (MCTDH) approach facilitates accurate high-dimensional quantum dynamics simulations. In the approach, the wavefunction is expanded in a direct product of self-adapting time-dependent single-particle functions (SPFs). The equations of motion for the expansion coefficients and the SPFs are obtained via the Dirac-Frenkel variational principle. While this derivation yields well-defined differential equations for the motion of occupied SPFs, singularities in the working equations resulting from unoccupied SPFs have to be removed by a regularization procedure. Here, an alternative derivation of the MCTDH equations of motion is presented. It employs an analysis of the time-dependence of the single-particle density matrices up to second order. While the analysis of the first order terms yields the known equations of motion for the occupied SPFs, the analysis of the second order terms provides new equations which allow one to identify optimal choices for the unoccupied SPFs. The effect of the optimal choice of the unoccupied SPFs on the structure of the MCTDH equations of motion and their regularization is discussed. Generalized equations applicable in the multi-layer MCTDH framework are presented. Finally, the effects resulting from the initial choice of the unoccupied SPFs are illustrated by a simple numerical example.
Time-dependent neutron and photon dose-field analysis
NASA Astrophysics Data System (ADS)
Wooten, Hasani Omar
2005-11-01
A unique tool is developed that allows the user to model physical representations of complicated glovebox facilities in two dimensions and determine neutral-particle flux and ambient dose-equivalent fields throughout that geometry. The code Pandemonium, originally designed to determine flux and dose rates only, has been improved to include realistic glovebox geometries, time-dependent source and detector positions, time-dependent shielding thickness calculations, time-integrated doses, a representative criticality accident scenario based on time-dependent reactor kinetics, and more rigorous photon treatment. The photon model has been significantly enhanced by expanding the energy range to 10 MeV to include fission photons, and by including a set of new buildup factors, the result of an extensive study into the previously unknown "purely-angular effect" on photon buildup. Purely-angular photon buildup factors are determined using discrete ordinates and coupled electron-photon cross sections to account for coherent and incoherent scattering and secondary photon effects of bremsstrahlung and florescence. Improvements to Pandemonium result in significant modeling capabilities for processing facilities using intense neutron and photon sources, and the code obtains comparable results to Monte Carlo calculations but within a fraction of the time required to run such codes as MCNPX.
Eisenhart lifts and symmetries of time-dependent systems
NASA Astrophysics Data System (ADS)
Cariglia, M.; Duval, C.; Gibbons, G. W.; Horváthy, P. A.
2016-10-01
Certain dissipative systems, such as Caldirola and Kannai's damped simple harmonic oscillator, may be modelled by time-dependent Lagrangian and hence time dependent Hamiltonian systems with n degrees of freedom. In this paper we treat these systems, their projective and conformal symmetries as well as their quantisation from the point of view of the Eisenhart lift to a Bargmann spacetime in n + 2 dimensions, equipped with its covariantly constant null Killing vector field. Reparametrisation of the time variable corresponds to conformal rescalings of the Bargmann metric. We show how the Arnold map lifts to Bargmann spacetime. We contrast the greater generality of the Caldirola-Kannai approach with that of Arnold and Bateman. At the level of quantum mechanics, we are able to show how the relevant Schrödinger equation emerges naturally using the techniques of quantum field theory in curved spacetimes, since a covariantly constant null Killing vector field gives rise to well defined one particle Hilbert space. Time-dependent Lagrangians arise naturally also in cosmology and give rise to the phenomenon of Hubble friction. We provide an account of this for Friedmann-Lemaître and Bianchi cosmologies and how it fits in with our previous discussion in the non-relativistic limit.
Time-Dependent Delayed Signatures From Energetic Photon Interrogations
D. R. Norman; J. L. Jones; B. W. Blackburn; S. M. Watson; K. J. Haskell
2006-08-01
A pulsed photonuclear interrogation environment is rich with time-dependent, material specific, radiation signatures. Exploitation of these signatures in the delayed time regime (>1us after the photon flash) has been explored through various detection schemes to identify both shielded nuclear material and nitrogen-based explosives. Prompt emission may also be invaluable for these detection methods. Numerical and experimental results, which utilize specially modified neutron and HpGe detectors, are presented which illustrate the efficacy of utilizing these time-dependent signatures. Optimal selection of the appropriate delayed time window is essential to these pulsed inspection systems. For explosive (ANFO surrogate) detection, both numerical models and experimental results illustrate that nearly all 14N(n,y) reactions have occurred within l00 us after the flash. In contrast, however, gamma-ray and neutron signals for nuclear material detection require a delay of several milliseconds after the photon pulse. In this case, any data collected too close to the photon flash results in a spectrum dominated by high energy signals which make it difficult to discern signatures from nuclear material. Specifically, two short-lived, high-energy fission fragments (97Ag(T1/2=5.1 s) and 94Sr(T1/2=75.2 s)) were measured and identified as indicators of the presence of fissionable material. These developments demonstrate that a photon inspection environment can be exploited for time-dependent, material specific signatures through the proper operation of specially modified detectors.
Creep Measurement Video Extensometer
NASA Technical Reports Server (NTRS)
Jaster, Mark; Vickerman, Mary; Padula, Santo, II; Juhas, John
2011-01-01
Understanding material behavior under load is critical to the efficient and accurate design of advanced aircraft and spacecraft. Technologies such as the one disclosed here allow accurate creep measurements to be taken automatically, reducing error. The goal was to develop a non-contact, automated system capable of capturing images that could subsequently be processed to obtain the strain characteristics of these materials during deformation, while maintaining adequate resolution to capture the true deformation response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.
Creep anomaly in electrospun fibers made of globular proteins
NASA Astrophysics Data System (ADS)
Regev, Omri; Arinstein, Arkadii; Zussman, Eyal
2013-12-01
The anomalous responses of electrospun nanofibers and film fabricated of unfolded bovine serum albumin (BSA) under constant stress (creep) is observed. In contrast to typical creep behavior of viscoelastic materials demonstrating (after immediate elastic response) a time-dependent elongation, in case of low applied stresses (<1 MPa) the immediate elastic response of BSA samples is followed by gradual contraction up to 2%. Under higher stresses (2-6 MPa) the contraction phase changes into elongation; and in case of stresses above 7 MPa only elongation was observed, with no initial contraction. The anomalous creep behavior was not observed when the BSA samples were subjected to additional creep cycles independently on the stress level. The above anomaly, which was not observed before either for viscoelastic solids or for polymers, is related to specific protein features, namely, to the ability to fold. We hypothesize that the phenomenon is caused by folding of BSA macromolecules into dry molten globule states, feasible after cross-linked bonds break up, resulting from the applied external force.
Creep fatigue life prediction for engine hot section materials (isotropic)
NASA Technical Reports Server (NTRS)
Moreno, Vito; Nissley, David; Lin, Li-Sen Jim
1985-01-01
The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.
Creep anomaly in electrospun fibers made of globular proteins.
Regev, Omri; Arinstein, Arkadii; Zussman, Eyal
2013-12-01
The anomalous responses of electrospun nanofibers and film fabricated of unfolded bovine serum albumin (BSA) under constant stress (creep) is observed. In contrast to typical creep behavior of viscoelastic materials demonstrating (after immediate elastic response) a time-dependent elongation, in case of low applied stresses (<1 MPa) the immediate elastic response of BSA samples is followed by gradual contraction up to 2%. Under higher stresses (2-6 MPa) the contraction phase changes into elongation; and in case of stresses above 7 MPa only elongation was observed, with no initial contraction. The anomalous creep behavior was not observed when the BSA samples were subjected to additional creep cycles independently on the stress level. The above anomaly, which was not observed before either for viscoelastic solids or for polymers, is related to specific protein features, namely, to the ability to fold. We hypothesize that the phenomenon is caused by folding of BSA macromolecules into dry molten globule states, feasible after cross-linked bonds break up, resulting from the applied external force. PMID:24483479
NASA Astrophysics Data System (ADS)
Wang, Q.; Yang, M.; Song, X. L.; Jia, J.; Xiang, Z. D.
2016-07-01
The conventional power law creep equation (Norton equation) relating the minimum creep rate to creep stress and temperature cannot be used to predict the long-term creep strengths of creep-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of creep determined on the basis of this equation depend on creep temperature and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law creep equation can be resolved if the new power law equation is used to rationalize the creep data. The new power law creep equation takes a form similar to the conventional power law creep equation but has a radically different capability not only in rationalizing creep data but also in predicting the long-term creep strengths from short-term test data. These capabilities of the new power law creep equation are demonstrated using the tensile strength and creep test data measured for both pipe and tube grades of the creep-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).
Time dependence of fast electron beam divergence in ultraintense laser-plasma interactions.
Akli, K U; Storm, M J; McMahon, M; Jiang, S; Ovchinnikov, V; Schumacher, D W; Freeman, R R; Dyer, G; Ditmire, T
2012-08-01
We report on the measurement and computer simulation of the divergence of fast electrons generated in an ultraintense laser-plasma interaction (LPI) and the subsequent propagation in a nonrefluxing target. We show that, at Iλ(2) of 10(20) Wcm(-2)μm(2), the time-integrated electron beam full divergence angle is (60±5)°. However, our time-resolved 2D particle-in-cell simulations show the initial beam divergence to be much smaller (≤30°). Our simulations show the divergence to monotonically increase with time, reaching a final value of (68±7)° after the passage of the laser pulse, consistent with the experimental time-integrated measurements. By revealing the time-dependent nature of the LPI, we find that a substantial fraction of the laser energy (~7%) is transported up to 100 μm with a divergence of 32°.
Time-dependent radiation dose estimations during interplanetary space flights
NASA Astrophysics Data System (ADS)
Dobynde, M. I.; Shprits, Y.; Drozdov, A.
2015-12-01
Time-dependent radiation dose estimations during interplanetary space flights 1,2Dobynde M.I., 2,3Drozdov A.Y., 2,4Shprits Y.Y.1Skolkovo institute of science and technology, Moscow, Russia 2University of California Los Angeles, Los Angeles, USA 3Lomonosov Moscow State University Skobeltsyn Institute of Nuclear Physics, Moscow, Russia4Massachusetts Institute of Technology, Cambridge, USASpace radiation is the main restriction for long-term interplanetary space missions. It induces degradation of external components and propagates inside providing damage to internal environment. Space radiation particles and induced secondary particle showers can lead to variety of damage to astronauts in short- and long- term perspective. Contribution of two main sources of space radiation- Sun and out-of-heliosphere space varies in time in opposite phase due to the solar activity state. Currently the only habituated mission is the international interplanetary station that flights on the low Earth orbit. Besides station shell astronauts are protected with the Earth magnetosphere- a natural shield that prevents significant damage for all humanity. Current progress in space exploration tends to lead humanity out of magnetosphere bounds. With the current study we make estimations of spacecraft parameters and astronauts damage for long-term interplanetary flights. Applying time dependent model of GCR spectra and data on SEP spectra we show the time dependence of the radiation in a human phantom inside the shielding capsule. We pay attention to the shielding capsule design, looking for an optimal geometry parameters and materials. Different types of particles affect differently on the human providing more or less harm to the tissues. Incident particles provide a large amount of secondary particles while propagating through the shielding capsule. We make an attempt to find an optimal combination of shielding capsule parameters, namely material and thickness, that will effectively decrease
Time-Dependent Neutron and Photon Dose-Field Analysis
Wooten, Hasani Omar
2005-08-01
A unique tool is developed that allows the user to model physical representations of complicated glovebox facilities in two dimensions and determine neutral-particle flux and ambient dose-equivalent fields throughout that geometry. The Pandemonium code, originally designed to determine flux and dose-rates only, is improved to include realistic glovebox geometries, time-dependent source and detector positions, time-dependent shielding thickness calculations, time-integrated doses, a representative criticality accident scenario based on time-dependent reactor kinetics, and more rigorous photon treatment. A primary benefit of this work has been an extensive analysis and improvement of the photon model that is not limited to the application described in this thesis. The photon model has been extended in energy range to 10 MeV to include photons from fission and new photon buildup factors have been included that account for the effects of photon buildup at slant-path thicknesses as a function of angle, where the mean free path thickness has been preserved. The overall system of codes is user-friendly and it is directly applicable to facilities such as the plutonium facility at Los Alamos National Laboratory, where high-intensity neutron and photon emitters are regularly used. The codes may be used to determine a priori doses for given work scenarios in an effort to supply dose information to process models which will in turn assist decision makers on ensuring as low as reasonably achievable (ALARA) compliance. In addition, coupling the computational results of these tools with the process model visualization tools will help to increase worker safety and radiological safety awareness.
Recent results on time-dependent Hamiltonian oscillators
NASA Astrophysics Data System (ADS)
Robnik, M.
2016-09-01
Time-dependent Hamilton systems are important in modeling the nondissipative interaction of the system with its environment. We review some recent results and present some new ones. In time-dependent, parametrically driven, one-dimensional linear oscillator, the complete analysis can be performed (in the sense explained below), also using the linear WKB method. In parametrically driven nonlinear oscillators extensive numerical studies have been performed, and the nonlinear WKB-like method can be applied for homogeneous power law potentials (which e.g. includes the quartic oscillator). The energy in time-dependent Hamilton systems is not conserved, and we are interested in its evolution in time, in particular the evolution of the microcanonical ensemble of initial conditions. In the ideal adiabatic limit (infinitely slow parametric driving) the energy changes according to the conservation of the adiabatic invariant, but has a Dirac delta distribution. However, in the general case the initial Dirac delta distribution of the energy spreads and we follow its evolution, especially in the two limiting cases, the slow variation close to the adiabatic regime, and the fastest possible change - a parametric kick, i.e. discontinuous jump (of a parameter), where some exact analytic results are obtained (the so-called PR property, and ABR property). For the linear oscillator the distribution of the energy is always, rigorously, the arcsine distribution, whose variance can in general be calculated by the linear WKB method, while in nonlinear systems there is no such universality. We calculate the Gibbs entropy for the ensembles of noninteracting nonlinear oscillator, which gives the right equipartition and thermostatic laws even for one degree of freedom.
Time-dependent tomographic reconstruction of the solar corona
NASA Astrophysics Data System (ADS)
Vibert, D.; Peillon, C.; Lamy, P.; Frazin, R. A.; Wojak, J.
2016-10-01
Solar rotational tomography (SRT) applied to white-light coronal images observed at multiple aspect angles has been the preferred approach for determining the three-dimensional (3D) electron density structure of the solar corona. However, it is seriously hampered by the restrictive assumption that the corona is time-invariant which introduces significant errors in the reconstruction. We first explore several methods to mitigate the temporal variation of the corona by decoupling the "fast-varying" inner corona from the "slow-moving" outer corona using multiple masking (either by juxtaposition or recursive combination) and radial weighting. Weighting with a radial exponential profile provides some improvement over a classical reconstruction but only beyond ≈ 3R⊙. We next consider a full time-dependent tomographic reconstruction involving spatio-temporal regularization and further introduce a co-rotating regularization aimed at preventing concentration of reconstructed density in the plane of the sky. Crucial to testing our procedure and properly tuning the regularization parameters is the introduction of a time-dependent MHD model of the corona based on observed magnetograms to build a time-series of synthetic images of the corona. Our procedure, which successfully reproduces the time-varying model corona, is finally applied to a set of 53 LASCO-C2 pB images roughly evenly spaced in time from 15 to 29 March 2009. Our procedure paves the way to a time-dependent tomographic reconstruction of the coronal electron density to the whole set of LASCO-C2 images presently spanning 20 years.
TIME-DEPENDENT MODELS OF FLARES FROM SAGITTARIUS A*
Dodds-Eden, Katie; Genzel, Reinhard; Gillessen, Stefan; Eisenhauer, Frank; Sharma, Prateek; Quataert, Eliot; Porquet, Delphine
2010-12-10
The emission from Sgr A*, the supermassive black hole in the Galactic Center, shows order of magnitude variability ('flares') a few times a day that is particularly prominent in the near-infrared (NIR) and X-rays. We present a time-dependent model for these flares motivated by the hypothesis that dissipation of magnetic energy powers the flares. We show that episodic magnetic reconnection can occur near the last stable circular orbit in time-dependent magnetohydrodynamic simulations of black hole accretion-the timescales and energetics of these events are broadly consistent with the flares from Sgr A*. Motivated by these results, we present a spatially one-zone time-dependent model for the electron distribution function in flares, including energy loss due to synchrotron cooling and adiabatic expansion. Synchrotron emission from transiently accelerated particles can explain the NIR/X-ray light curves and spectra of a luminous flare observed on 2007 April 4. A significant decrease in the magnetic field strength during the flare (coincident with the electron acceleration) is required to explain the simultaneity and symmetry of the simultaneous light curves. Our models predict that the NIR and X-ray spectral indices are related by {Delta}{alpha} {approx_equal} 0.5 (where {nu}F{sub {nu}} {proportional_to} {nu}{sup {alpha}}) and that there is only modest variation in the spectral index during flares. We also explore implications of this model for longer wavelength (radio-submillimeter) emission seemingly associated with X-ray and NIR flares; we argue that a few hour decrease in the submillimeter emission is a more generic consequence of large-scale magnetic reconnection than delayed radio emission from adiabatic expansion.
Timing-Dependent Actions of NGF Required for Cell Differentiation
Chung, Jaehoon; Kubota, Hiroyuki; Ozaki, Yu-ichi; Uda, Shinsuke; Kuroda, Shinya
2010-01-01
Background Continuous NGF stimulation induces PC12 cell differentiation. However, why continuous NGF stimulation is required for differentiation is unclear. In this study, we investigated the underlying mechanisms of the timing-dependent requirement of NGF action for cell differentiation. Methodology/Principal Findings To address the timing-dependency of the NGF action, we performed a discontinuous stimulation assay consisting of a first transient stimulation followed by an interval and then a second sustained stimulation and quantified the neurite extension level. Consequently, we observed a timing-dependent action of NGF on cell differentiation, and discontinuous NGF stimulation similarly induced differentiation. The first stimulation did not induce neurite extension, whereas the second stimulation induced fast neurite extension; therefore, the first stimulation is likely required as a prerequisite condition. These observations indicate that the action of NGF can be divided into two processes: an initial stimulation-driven latent process and a second stimulation-driven extension process. The latent process appears to require the activities of ERK and transcription, but not PI3K, whereas the extension-process requires the activities of ERK and PI3K, but not transcription. We also found that during the first stimulation, the activity of NGF can be replaced by PACAP, but not by insulin, EGF, bFGF or forskolin; during the second stimulation, however, the activity of NGF cannot be replaced by any of these stimulants. These findings allowed us to identify potential genes specifically involved in the latent process, rather than in other processes, using a microarray. Conclusions/Significance These results demonstrate that NGF induces the differentiation of PC12 cells via mechanically distinct processes: an ERK-driven and transcription-dependent latent process, and an ERK- and PI3K-driven and transcription-independent extension process. PMID:20126402
DYNA2D96. Explicit 2-D Hydrodynamic FEM Program
Whirley, R.G.
1992-04-01
DYNA2D is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
Time Dependence of Correlation Functions Following a Quantum Quench
Calabrese, Pasquale; Cardy, John
2006-04-07
We show that the time dependence of correlation functions in an extended quantum system in d dimensions, which is prepared in the ground state of some Hamiltonian and then evolves without dissipation according to some other Hamiltonian, may be extracted using methods of boundary critical phenomena in d+1 dimensions. For d=1 particularly powerful results are available using conformal field theory. These are checked against those available from solvable models. They may be explained in terms of a picture, valid more generally, whereby quasiparticles, entangled over regions of the order of the correlation length in the initial state, then propagate classically through the system.
Time dependent modeling of non-LTE plasmas: Final report
Not Available
1988-06-01
During the period of performance of this contract Science Applications International Corporation (SAIC) has aided Lawrence Livermore National Laboratory (LLNL) in the development of an unclassified modeling tool for studying time evolution of high temperature ionizing and recombining plasmas. This report covers the numerical code developed, (D)ynamic (D)etailed (C)onfiguration (A)ccounting (DDCA), which was written to run on the National Magnetic Fusion Energy Computing Center (NMFECC) network as well as the classified Livermore Computer Center (OCTOPUS) network. DDCA is a One-Dimensional (1D) time dependent hydrodynamic model which makes use of the non-LTE detailed atomic physics ionization model DCA. 5 refs.
Optimal moving grids for time-dependent partial differential equations
NASA Technical Reports Server (NTRS)
Wathen, A. J.
1989-01-01
Various adaptive moving grid techniques for the numerical solution of time-dependent partial differential equations were proposed. The precise criterion for grid motion varies, but most techniques will attempt to give grids on which the solution of the partial differential equation can be well represented. Moving grids are investigated on which the solutions of the linear heat conduction and viscous Burgers' equation in one space dimension are optimally approximated. Precisely, the results of numerical calculations of optimal moving grids for piecewise linear finite element approximation of partial differential equation solutions in the least squares norm.
Time Dependent Hartree Fock Equation: Gateway to Nonequilibrium Plasmas
James W. Dufty
2007-04-28
This is the Final Technical Report for DE-FG02-2ER54677 award “Time Dependent Hartree Fock Equation - Gateway to Nonequilibrium Plasmas”. Research has focused on the nonequilibrium dynamics of electrons in the presence of ions, both via basic quantum theory and via semi-classical molecular dynamics (MD) simulation. In addition, fundamental notions of dissipative dynamics have been explored for models of grains and dust, and for scalar fields (temperature) in turbulent edge plasmas. The specific topics addressed were Quantum Kinetic Theory for Metallic Clusters, Semi-classical MD Simulation of Plasmas , and Effects of Dissipative Dynamics.
Advances in time-dependent current-density functional theory
NASA Astrophysics Data System (ADS)
Berger, Arjan
In this work we solve the problem of the gauge dependence of molecular magnetic properties (magnetizabilities, circular dichroism) using time-dependent current-density functional theory [1]. We also present a new functional that accurately describes the optical absorption spectra of insulators, semiconductors and metals [2] N. Raimbault, P.L. de Boeij, P. Romaniello, and J.A. Berger Phys. Rev. Lett. 114, 066404 (2015) J.A. Berger, Phys. Rev. Lett. 115, 137402 (2015) This study has been partially supported through the Grant NEXT No. ANR-10-LABX-0037 in the framework of the Programme des Investissements d'Avenir.
Brownian motion of electrons in time-dependent magnetic fields.
NASA Technical Reports Server (NTRS)
Iverson, G. J.; Williams, R. M.
1973-01-01
The behavior of a weakly ionized plasma in slowly varying time-dependent magnetic fields is studied through an extension of Williamson's stochastic theory. In particular, attention is focused on the properties of electron diffusion in the plane perpendicular to the direction of the magnetic field, when the field strength is large. It is shown that, in the strong field limit, the classical 1/B-squared dependence of the perpendicular diffusion coefficient is obtained for two models in which the field B(t) is monotonic in t and for two models in which B(t) possesses at least one turning point.
Optimal moving grids for time-dependent partial differential equations
NASA Technical Reports Server (NTRS)
Wathen, A. J.
1992-01-01
Various adaptive moving grid techniques for the numerical solution of time-dependent partial differential equations were proposed. The precise criterion for grid motion varies, but most techniques will attempt to give grids on which the solution of the partial differential equation can be well represented. Moving grids are investigated on which the solutions of the linear heat conduction and viscous Burgers' equation in one space dimension are optimally approximated. Precisely, the results of numerical calculations of optimal moving grids for piecewise linear finite element approximation of PDE solutions in the least-squares norm are reported.
The Nonlinear Dynamics of Time Dependent Subcritical Baroclinic Currents
NASA Astrophysics Data System (ADS)
Pedlosky, J.; Flierl, G. R.
2006-12-01
The nonlinear dynamics of baroclinically unstable waves in a time dependent zonal shear flow is considered in the framework of the two-layer Phillips model on the beta plane. In most cases considered in this study the amplitude of the shear is well below the critical value of the steady shear version of the model. Nevertheless, the time dependent problem in which the shear oscillates periodically is unstable, and the unstable waves grow to substantial amplitudes, in some cases with strongly nonlinear and turbulent characteristics. For very small values of the shear amplitude in the presence of dissipation an analytical, asymptotic theory predicts a self-sustained wave whose amplitude undergoes a nonlinear oscillation whose period is amplitude dependent. There is a sensitive amplitude dependence of the wave on the frequency of the oscillating shear when the shear amplitude is small. This behavior is also found in a truncated model of the dynamics, and that model is used to examine larger shear amplitudes. When there is a mean value of the shear in addition to the oscillating component, but such that the total shear is still subcritical, the resulting nonlinear states exhibit a rectified horizontal buoyancy flux with a nonzero time average as a result of the instability of the oscillating shear. For higher, still subcritical, values of the shear we have detected a symmetry breaking in which a second cross-stream mode is generated through an instability of the unstable wave although this second mode would by itself be stable on the basic time dependent current. For shear values that are substantially subcritical but of order of the critical shear, calculations with a full quasi-geostrophic numerical model reveal a turbulent flow generated by the instability. If the beta effect is disregarded the inviscid, linear problem is formally stable. However, our calculations show that a small degree of nonlinearity is enough to destabilize the flow leading to large amplitude
Perspective: Fundamental aspects of time-dependent density functional theory
NASA Astrophysics Data System (ADS)
Maitra, Neepa T.
2016-06-01
In the thirty-two years since the birth of the foundational theorems, time-dependent density functional theory has had a tremendous impact on calculations of electronic spectra and dynamics in chemistry, biology, solid-state physics, and materials science. Alongside the wide-ranging applications, there has been much progress in understanding fundamental aspects of the functionals and the theory itself. This Perspective looks back to some of these developments, reports on some recent progress and current challenges for functionals, and speculates on future directions to improve the accuracy of approximations used in this relatively young theory.
Time-dependent Kohn-Sham approach to quantum electrodynamics
Ruggenthaler, M.; Mackenroth, F.; Bauer, D.
2011-10-15
We prove a generalization of the van Leeuwen theorem toward quantum electrodynamics, providing the formal foundations of a time-dependent Kohn-Sham construction for coupled quantized matter and electromagnetic fields. We circumvent the symmetry-causality problems associated with the action-functional approach to Kohn-Sham systems. We show that the effective external four-potential and four-current of the Kohn-Sham system are uniquely defined and that the effective four-current takes a very simple form. Further we rederive the Runge-Gross theorem for quantum electrodynamics.
Efficient auxiliary-mode approach for time-dependent nanoelectronics
NASA Astrophysics Data System (ADS)
Popescu, Bogdan Stefan; Croy, Alexander
2016-09-01
A new scheme for numerically solving the equations arising in the time-dependent non-equilibrium Green's function formalism is developed. It is based on an auxiliary-mode expansion of the self-energies which convert the complicated set of integro-differential equations into a set of ordinary differential equations. In the new scheme all auxiliary matrices are replaced by vectors or scalars. This drastically reduces the computational effort and memory requirements of the method, rendering it applicable to topical problems in electron quantum optics and molecular electronics. As an illustrative example we consider the dynamics of a Leviton wave-packet in a 1D wire.
Creep-strengthening of steel at high temperatures using nano-sized carbonitride dispersions.
Taneike, Masaki; Abe, Fujio; Sawada, Kota
2003-07-17
Creep is a time-dependent mechanism of plastic deformation, which takes place in a range of materials under low stress-that is, under stresses lower than the yield stress. Metals and alloys can be designed to withstand creep at high temperatures, usually by a process called dispersion strengthening, in which fine particles are evenly distributed throughout the matrix. For example, high-temperature creep-resistant ferritic steels achieve optimal creep strength (at 923 K) through the dispersion of yttrium oxide nanoparticles. However, the oxide particles are introduced by complicated mechanical alloying techniques and, as a result, the production of large-scale industrial components is economically unfeasible. Here we report the production of a 9 per cent Cr martensitic steel dispersed with nanometre-scale carbonitride particles using conventional processing techniques. At 923 K, our dispersion-strengthened material exhibits a time-to-rupture that is increased by two orders of magnitude relative to the current strongest creep-resistant steels. This improvement in creep resistance is attributed to a mechanism of boundary pinning by the thermally stable carbonitride precipitates. The material also demonstrates enough fracture toughness. Our results should lead to improved grades of creep-resistant steels and to the economical manufacture of large-scale steel components for high-temperature applications. PMID:12867976
Curtin, W.A.; Fabeny, B.; Ibnabdeljalil, M.; Iyengar, N.; Reifsnider, K.L.
1996-07-31
The models developed, contain explicit dependences on constituent material properties and their changes with time, so that composite performance can be predicted. Three critical processes in ceramic composites at elevated temperatures have been modeled: (1) creep deformation of composite vs stress and time-dependent creep of fibers and matrix, and failure of these components; (2) creep deformation of ``interface`` around broken fibers; and (3) lifetime of the composite under conditions of fiber strength loss over time at temperature. In (1), general evolution formulas are derived for relaxation time of matrix stresses and steady-state creep rate of composite; the model is tested against recent data on Ti-MMCs. Calculations on a composite of Hi-Nicalon fibers in a melt-infiltrated SiC matrix are presented. In (2), numerical simulations of composite failure were made to map out time-to-failure vs applied load for several sets of material parameters. In (3), simple approximate relations are obtained between fiber life and composite life that should be useful for fiber developers and testers. Strength degradation data on Hi-Nicalon fibers is used to assess composite lifetime vs fiber lifetime for Hi-Nicalon fiber composites.
NASA Astrophysics Data System (ADS)
Maurer, J.; Segall, P.
2015-12-01
Understanding and predicting earthquake magnitudes from injection-induced seismicity is critically important for estimating hazard due to injection operations. A particular problem has been that the largest event often occurs post shut-in. A rigorous analysis would require modeling all stages of earthquake nucleation, propagation, and arrest, and not just initiation. We present a simple conceptual model for predicting the distribution of earthquake magnitudes during and following injection, building on the analysis of Segall & Lu (2015). The analysis requires several assumptions: (1) the distribution of source dimensions follows a Gutenberg-Richter distribution; (2) in environments where the background ratio of shear to effective normal stress is low, the size of induced events is limited by the volume perturbed by injection (e.g., Shapiro et al., 2013; McGarr, 2014), and (3) the perturbed volume can be approximated by diffusion in a homogeneous medium. Evidence for the second assumption comes from numerical studies that indicate the background ratio of shear to normal stress controls how far an earthquake rupture, once initiated, can grow (Dunham et al., 2011; Schmitt et al., submitted). We derive analytical expressions that give the rate of events of a given magnitude as the product of three terms: the time-dependent rate of nucleations, the probability of nucleating on a source of given size (from the Gutenberg-Richter distribution), and a time-dependent geometrical factor. We verify our results using simulations and demonstrate characteristics observed in real induced sequences, such as time-dependent b-values and the occurrence of the largest event post injection. We compare results to Segall & Lu (2015) as well as example datasets. Future work includes using 2D numerical simulations to test our results and assumptions; in particular, investigating how background shear stress and fault roughness control rupture extent.
Lattice continuum and diffusional creep
NASA Astrophysics Data System (ADS)
Mesarovic, Sinisa Dj.
2016-04-01
Diffusional creep is characterized by growth/disappearance of lattice planes at the crystal boundaries that serve as sources/sinks of vacancies, and by diffusion of vacancies. The lattice continuum theory developed here represents a natural and intuitive framework for the analysis of diffusion in crystals and lattice growth/loss at the boundaries. The formulation includes the definition of the Lagrangian reference configuration for the newly created lattice, the transport theorem and the definition of the creep rate tensor for a polycrystal as a piecewise uniform, discontinuous field. The values associated with each crystalline grain are related to the normal diffusional flux at grain boundaries. The governing equations for Nabarro-Herring creep are derived with coupled diffusion and elasticity with compositional eigenstrain. Both, bulk diffusional dissipation and boundary dissipation accompanying vacancy nucleation and absorption, are considered, but the latter is found to be negligible. For periodic arrangements of grains, diffusion formally decouples from elasticity but at the cost of a complicated boundary condition. The equilibrium of deviatorically stressed polycrystals is impossible without inclusion of interface energies. The secondary creep rate estimates correspond to the standard Nabarro-Herring model, and the volumetric creep is small. The initial (primary) creep rate is estimated to be much larger than the secondary creep rate.
Sandia/Stanford Unified Creep Plasticity Damage Model for ANSYS
2006-09-03
A unified creep plasticity (UCP) model was developed, based upon the time-dependent and time-independent deformation properties of the 95.5Sn-3.9Ag-0.6Cu (wt.%) soldier that were measured at Sandia. Then, a damage parameter, D, was added to the equation to develop the unified creep plasticity damage (UCPD) model. The parameter, D, was parameterized, using data obtained at Sandia from isothermal fatigue experiments on a double-lap shear test. The softwae was validated against a BGA solder joint exposed tomore » thermal cycling. The UCPD model was put into the ANSYS finite element as a subroutine. So, the softwae is the subroutine for ANSYS 8.1.« less
Analytical simulation of weld effects in creep range
NASA Technical Reports Server (NTRS)
Dhalla, A. K.
1985-01-01
The inelastic analysis procedure used to investigate the effect of welding on the creep rupture strength of a typical Liquid Metal Fast Breeder Reactor (LMFBR) nozzle is discussed. The current study is part of an overall experimental and analytical investigation to verify the inelastic analysis procedure now being used to design LMFBR structural components operating at elevated temperatures. Two important weld effects included in the numerical analysis are: (1) the residual stress introduced in the fabrication process; and (2) the time-independent and the time-dependent material property variations. Finite element inelastic analysis was performed on a CRAY-1S computer using the ABAQUS program with the constitutive equations developed for the design of LMFBR structural components. The predicted peak weld residual stresses relax by as much as 40% during elevated temperature operation, and their effect on creep-rupture cracking of the nozzle is considered of secondary importance.
Mesoscopic structure of neuronal tracts from time-dependent diffusion.
Burcaw, Lauren M; Fieremans, Els; Novikov, Dmitry S
2015-07-01
Interpreting brain diffusion MRI measurements in terms of neuronal structure at a micrometer level is an exciting unresolved problem. Here we consider diffusion transverse to a bundle of fibers, and show theoretically, as well as using Monte Carlo simulations and measurements in a phantom made of parallel fibers mimicking axons, that the time dependent diffusion coefficient approaches its macroscopic limit slowly, in a (ln t)/t fashion. The logarithmic singularity arises due to short range disorder in the fiber packing. We identify short range disorder in axonal fibers based on histological data from the splenium, and argue that the time dependent contribution to the overall diffusion coefficient from the extra-axonal water dominates that of the intra-axonal water. This dominance may explain the bias in measuring axon diameters in clinical settings. The short range disorder is also reflected in the asymptotically linear frequency dependence of the diffusion coefficient measured with oscillating gradients, in agreement with recent experiments. Our results relate the measured diffusion to the mesoscopic structure of neuronal tissue, uncovering the sensitivity of diffusion metrics to axonal arrangement within a fiber tract, and providing an alternative interpretation of axonal diameter mapping techniques.
Transient Orthogonality Catastrophe in a Time Dependent Nonequilibrium Environment
NASA Astrophysics Data System (ADS)
Schiro, Marco; Mitra, Aditi; 0 Team
2015-03-01
We study the response of a highly-excited time dependent quantum many-body state to a sudden local perturbation, a sort of orthogonality catastrophe problem in a transient non-equilibrium environment. To this extent we consider, as key quantity, the overlap between time dependent wave-functions, that we write in terms of a novel two-time correlator generalizing the standard Loschmidt Echo. We discuss its physical meaning, general properties, and its connection with experimentally measurable quantities probed through non-equilibrium Ramsey interferometry schemes. Then we present explicit calculations for a one dimensional interacting Fermi system brought out of equilibrium by a sudden change of the interaction, and perturbed by the switching on of a local static potential. We show that different scattering processes give rise to remarkably different behaviors at long times, quite opposite from the equilibrium situation. In particular, while the forward scattering contribution retains its power law structure even in the presence of a large non-equilibrium perturbation, with an exponent that is strongly affected by the transient nature of the bath, the backscattering term is a source of non-linearity which generates an exponential decay in time of the Loschmidt Echo, reminiscent of
Transient Orthogonality Catastrophe in a Time-Dependent Nonequilibrium Environment
NASA Astrophysics Data System (ADS)
Schiró, Marco; Mitra, Aditi
2014-06-01
We study the response of a highly excited time-dependent quantum many-body state to a sudden local perturbation, a sort of orthogonality catastrophe problem in a transient nonequilibrium environment. To this extent we consider, as a key quantity, the overlap between time-dependent wave functions, which we write in terms of a novel two-time correlator generalizing the standard Loschmidt echo. We discuss its physical meaning, general properties, and its connection with experimentally measurable quantities probed through nonequilibrium Ramsey interferometry schemes. Then we present explicit calculations for a one-dimensional interacting Fermi system brought out of equilibrium by a sudden change of the interaction, and perturbed by the switching on of a local static potential. We show that different scattering processes give rise to remarkably different behaviors at long times, quite opposite from the equilibrium situation. In particular, while the forward scattering contribution retains its power-law structure even in the presence of a large nonequilibrium perturbation, with an exponent that is strongly affected by the transient nature of the bath, the backscattering term is a source of nonlinearity which generates an exponential decay in time of the Loschmidt Echo, reminiscent of an effective thermal behavior.
Time-dependent behavior of passive skeletal muscle
NASA Astrophysics Data System (ADS)
Ahamed, T.; Rubin, M. B.; Trimmer, B. A.; Dorfmann, L.
2016-03-01
An isotropic three-dimensional nonlinear viscoelastic model is developed to simulate the time-dependent behavior of passive skeletal muscle. The development of the model is stimulated by experimental data that characterize the response during simple uniaxial stress cyclic loading and unloading. Of particular interest is the rate-dependent response, the recovery of muscle properties from the preconditioned to the unconditioned state and stress relaxation at constant stretch during loading and unloading. The model considers the material to be a composite of a nonlinear hyperelastic component in parallel with a nonlinear dissipative component. The strain energy and the corresponding stress measures are separated additively into hyperelastic and dissipative parts. In contrast to standard nonlinear inelastic models, here the dissipative component is modeled using an evolution equation that combines rate-independent and rate-dependent responses smoothly with no finite elastic range. Large deformation evolution equations for the distortional deformations in the elastic and in the dissipative component are presented. A robust, strongly objective numerical integration algorithm is used to model rate-dependent and rate-independent inelastic responses. The constitutive formulation is specialized to simulate the experimental data. The nonlinear viscoelastic model accurately represents the time-dependent passive response of skeletal muscle.
Time-dependent countermeasure considerations in industrial protection. Final report
Spogen, L.
1984-05-01
Protecting industrial capability from nuclear attack may be done by employing various countermeasures intended to accomplish specific protective goals. Many potential countermeasures have previously been recommended without an appropriate consideration of their implementation times. A countermeasure's effectiveness in accomplishing a prescribed goal depends on the times when various actions associated with it are executed, and on the times required for their execution. We must therefore know about any time dependencies in the countermeasures. A countermeasure's effectiveness is also influenced by the level of protection needed by specific industries and the characteristics of those industries. An overview of basic interdependencies allows us to properly characterize the time dependencies existing in countermeasures. Considerations in this report include: dispersal, survivability requirements for critical industries, enhanced recovery measures, the characterization of industries, and the characterization of countermeasures. Based on these considerations, this report also describes a general method for providing a required post-attack industrial capability at a minimum cost. However, the development and collection of detailed information is needed before the method can be applied. 5 refs., 21 figs.
Time Circular Birefringence in Time-Dependent Magnetoelectric Media
Zhang, Ruo-Yang; Zhai, Yan-Wang; Lin, Shi-Rong; Zhao, Qing; Wen, Weijia; Ge, Mo-Lin
2015-01-01
Light traveling in time-dependent media has many extraordinary properties which can be utilized to convert frequency, achieve temporal cloaking, and simulate cosmological phenomena. In this paper, we focus on time-dependent axion-type magnetoelectric (ME) media, and prove that light in these media always has two degenerate modes with opposite circular polarizations corresponding to one wave vector , and name this effect “time circular birefringence” (TCB). By interchanging the status of space and time, the pair of TCB modes can appear simultaneously via “time refraction” and “time reflection” of a linear polarized incident wave at a time interface of ME media. The superposition of the two TCB modes causes the “time Faraday effect”, namely the globally unified polarization axes rotate with time. A circularly polarized Gaussian pulse traversing a time interface is also studied. If the wave-vector spectrum of a pulse mainly concentrates in the non-traveling-wave band, the pulse will be trapped with nearly fixed center while its intensity will grow rapidly. In addition, we propose an experimental scheme of using molecular fluid with external time-varying electric and magnetic fields both parallel to the direction of light to realize these phenomena in practice. PMID:26329928
Bayesian latent structure models with space-time-dependent covariates.
Cai, Bo; Lawson, Andrew B; Hossain, Md Monir; Choi, Jungsoon
2012-04-01
Spatial-temporal data requires flexible regression models which can model the dependence of responses on space- and time-dependent covariates. In this paper, we describe a semiparametric space-time model from a Bayesian perspective. Nonlinear time dependence of covariates and the interactions among the covariates are constructed by local linear and piecewise linear models, allowing for more flexible orientation and position of the covariate plane by using time-varying basis functions. Space-varying covariate linkage coefficients are also incorporated to allow for the variation of space structures across the geographical location. The formulation accommodates uncertainty in the number and locations of the piecewise basis functions to characterize the global effects, spatially structured and unstructured random effects in relation to covariates. The proposed approach relies on variable selection-type mixture priors for uncertainty in the number and locations of basis functions and in the space-varying linkage coefficients. A simulation example is presented to evaluate the performance of the proposed approach with the competing models. A real data example is used for illustration.
Time-dependent strains and stresses in a pumpkin balloon
NASA Astrophysics Data System (ADS)
Gerngross, T.; Xu, Y.; Pellegrino, S.
This paper presents a study of pumpkin-shaped superpressure balloons consisting of gores made from a thin polymeric film attached to high stiffness meridional tendons This type of design is being used for the NASA ULDB balloons The gore film shows considerable time-dependent stress relaxation whereas the behaviour of the tendons is essentially time-independent Upon inflation and pressurization the instantaneous i e linear-elastic strain and stress distributions in the film show significantly higher values in the meridional direction However over time and due to the biaxial visco-elastic stress relaxation of the the gore material the em hoop strains increase and the em meridional stresses decrease whereas the em remaining strain and stress components remain substantially unchanged These results are important for a correct assessment of the structural integrity of a pumpkin balloon in a long-duration mission both in terms of the material performance and the overall stability of the shape of the balloon An experimental investigation of the time dependence of the biaxial strain distribution in the film of a 4 m diameter 48 gore pumpkin balloon is presented The inflated shape of selected gores has been measured using photogrammetry and the time variation in strain components at some particular points of these gores has been measured under constant pressure and temperature The results show good correlation with a numerical study using the ABAQUS finite-element package that includes a widely used model of
Inverse problem of quadratic time-dependent Hamiltonians
NASA Astrophysics Data System (ADS)
Guo, Guang-Jie; Meng, Yan; Chang, Hong; Duan, Hui-Zeng; Di, Bing
2015-08-01
Using an algebraic approach, it is possible to obtain the temporal evolution wave function for a Gaussian wave-packet obeying the quadratic time-dependent Hamiltonian (QTDH). However, in general, most of the practical cases are not exactly solvable, for we need general solutions of the Riccatti equations which are not generally known. We therefore bypass directly solving for the temporal evolution wave function, and study its inverse problem. We start with a particular evolution of the wave-packet, and get the required Hamiltonian by using the inverse method. The inverse approach opens up a new way to find new exact solutions to the QTDH. Some typical examples are studied in detail. For a specific time-dependent periodic harmonic oscillator, the Berry phase is obtained exactly. Project supported by the National Natural Science Foundation of China (Grant No. 11347171), the Natural Science Foundation of Hebei Province of China (Grant No. A2012108003), and the Key Project of Educational Commission of Hebei Province of China (Grant No. ZD2014052).
Time-Dependent CP Asymmetries in b {yields} s Penguins
Miyake, H.
2006-07-11
We present measurements of time-dependent CP asymmetry parameters in B{sup 0} {yields} {phi}(1020)K{sup 0}, {eta}'K{sup 0}, K{sub S}{sup 0}K{sub S}{sup 0}K{sub S}{sup 0} K{sub S}{sup 0}, K{sub S}{sup 0}{pi}{sup 0}, f{sub 0}(980)K{sub S}{sup 0}, {omega}(782)K{sub S}{sup 0} and K{sup +}K{sup -}K{sub S}{sup 0} decays based on a sample of 386 x 106BB(bar sign) pairs collected at the {upsilon}(4S) resonance with the Belle detector at the KEKB energy asymmetric e+e- collider. These decays are dominated by the b {yields} s gluonic penguin transition and are sensitive to new CP-violating phases from physics beyond the standard model. One neutral meson is fully reconstructed in one of the specified decay channels, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. We also perform measurement of time-dependent CP asymmetry parameters in B{sup 0} {yields} K{sub S}{sup 0}{gamma} decay that is dominated by the b {yields} s radiative penguin.
Time-dependent response of dissipative electron systems
Tremblay, Jean Christophe; Krause, Pascal; Klamroth, Tillmann; Saalfrank, Peter
2010-06-15
We present a systematic study of the influence of energy and phase relaxation on dynamic polarizability simulations in the linear response regime. The nonperturbative approach is based on explicit electron dynamics using short laser pulses of low intensities. To include environmental effects on the property calculation, we use the time-dependent configuration-interaction method in its reduced density matrix formulation. Both energy dissipation and nonlocal pure dephasing are included. The explicit treatment of time-resolved electron dynamics gives access to the phase shift between the electric field and the induced dipole moment, which can be used to define a useful uncertainty measure for the dynamic polarizability. The nonperturbative treatment is compared to perturbation theory expressions, as applied to a simple model system, the rigid H{sub 2} molecule. It is shown that both approaches are equivalent for low field intensities, but the time-dependent treatment provides complementary information on the phase of the induced dipole moment, which allows for the definition of an uncertainty associated with the computation of the dynamic polarizability in the linear response regime.
Mesoscopic structure of neuronal tracts from time-dependent diffusion
Burcaw, Lauren M.; Fieremans, Els; Novikov, Dmitry S.
2015-01-01
Interpreting brain diffusion MRI measurements in terms of neuronal structure at a micrometer level is an exciting unresolved problem. Here we consider diffusion transverse to a bundle of fibers, and show theoretically, as well as using Monte Carlo simulations and measurements in a phantom made of parallel fibers mimicking axons, that the time dependent diffusion coefficient approaches its macroscopic limit slowly, in a (lnt)/t fashion. The logarithmic singularity arises due to short range disorder in the fiber packing. We identify short range disorder in axonal fibers based on histological data from the splenium, and argue that the time dependent contribution to the overall diffusion coefficient from the extra-axonal water dominates that of the intra-axonal water. This dominance may explain the bias in measuring axon diameters in clinical settings. The short range disorder is also reflected in the linear frequency dependence of the diffusion coefficient measured with oscillating gradients, in agreement with recent experiments. Our results relate the measured diffusion to the mesoscopic structure of neuronal tissue, uncovering the sensitivity of diffusion metrics to axonal arrangement within a fiber tract, and providing an alternative interpretation of axonal diameter mapping techniques. PMID:25837598
Efficient photoheating algorithms in time-dependent photoionization simulations
NASA Astrophysics Data System (ADS)
Lee, Kai-Yan; Mellema, Garrelt; Lundqvist, Peter
2016-02-01
We present an extension to the time-dependent photoionization code C2-RAY to calculate photoheating in an efficient and accurate way. In C2-RAY, the thermal calculation demands relatively small time-steps for accurate results. We describe two novel methods to reduce the computational cost associated with small time-steps, namely, an adaptive time-step algorithm and an asynchronous evolution approach. The adaptive time-step algorithm determines an optimal time-step for the next computational step. It uses a fast ray-tracing scheme to quickly locate the relevant cells for this determination and only use these cells for the calculation of the time-step. Asynchronous evolution allows different cells to evolve with different time-steps. The asynchronized clocks of the cells are synchronized at the times where outputs are produced. By only evolving cells which may require short time-steps with these short time-steps instead of imposing them to the whole grid, the computational cost of the calculation can be substantially reduced. We show that our methods work well for several cosmologically relevant test problems and validate our results by comparing to the results of another time-dependent photoionization code.
Time-dependent strains and stresses in a pumpkin balloon
NASA Technical Reports Server (NTRS)
Gerngross, T.; Xu, Y.; Pellegrino, S.
2006-01-01
This paper presents a study of pumpkin-shaped superpressure balloons, consisting of gores made from a thin polymeric film attached to high stiffness, meridional tendons. This type of design is being used for the NASA ULDB balloons. The gore film shows considerable time-dependent stress relaxation, whereas the behaviour of the tendons is essentially time-independent. Upon inflation and pressurization, the "instantaneous", i.e. linear-elastic strain and stress distribution in the film show significantly higher values in the meridional direction. However, over time, and due to the biaxial visco-elastic stress relaxation of the the material, the hoop strains increase and the meridional stresses decrease, whereas the remaining strain and stress components remain substantially unchanged. These results are important for a correct assessment of the structural integrity of a pumpkin balloon in a long-duration mission, both in terms of the material performance and the overall stability of the shape of the balloon. An experimental investigation of the time dependence of the biaxial strain distribution in the film of a 4 m diameter, 48 gore pumpkin balloon is presented. The inflated shape of selected gores has been measured using photogrammetry and the time variation in strain components at some particular points of these gores has been measured under constant pressure and temperature. The results show good correlation with a numerical study, using the ABAQUS finite-element package, that includes a widely used model of the visco-elastic response of the gore material:
Time Dependent Relative Risks in Life Insurance Medical Underwriting.
Kneepkens, Robert F
2015-01-01
Introduction .- Life insurance medicine focuses on mortality hazards in specified periods. People are free to insure their lives for shorter or longer terms. Because the chosen terms range from 1 year to a life time, life insurers have to take into account the fact that the predictive value of risk indicators can and will change over time. The time a risk indicator keeps its predictive value, will be dependent on its biological effects, volatility, and treatability. For a given applicant this implies that the relative hazard (RH) calculated for his/her medical condition should be dependent on the term of the insurance. The main objective of this study is to determine if some commonly used risk indicators - previously used to study age dependency of relative risks - have a predictive value that increases with the observation period. (1) Methods .- This population-based cohort study uses NHANES-data files from the Third National Health and Nutrition Examination Survey (NHANES III) and the NHANES Linked Mortality Files 2010. Only participants aged 20 to 69 that were examined in mobile examination centers, without a history of some prevalent high risk diseases were included. The observed mortality was compared to the expected mortality in a Generalized Linear Model (GLM) with Poisson error structure with two reference populations, which both can serve as preferred reference for life insurers: The United States Life Tables 2008 (USLT) and the 2008 Valuation Basic Tables (VBT) based on the insured population of 35 US Life insurers. The time dependency of the RHs of the systolic blood pressure (SBP), aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), serum albumin and albuminuria, was assessed, with correction for ethnicity, household income, history of diabetes mellitus, BMI and serum cholesterol. To be able to compare the results with the results of the Age Dependency Study (ADS), the same data, risk indicators, statistical analysis method, and the
Endocannabinoids mediate bidirectional striatal spike-timing-dependent plasticity
Cui, Yihui; Paillé, Vincent; Xu, Hao; Genet, Stéphane; Delord, Bruno; Fino, Elodie; Berry, Hugues; Venance, Laurent
2015-01-01
Key points Although learning can arise from few or even a single trial, synaptic plasticity is commonly assessed under prolonged activation. Here, we explored the existence of rapid responsiveness of synaptic plasticity at corticostriatal synapses in a major synaptic learning rule, spike-timing-dependent plasticity (STDP). We found that spike-timing-dependent depression (tLTD) progressively disappears when the number of paired stimulations (below 50 pairings) is decreased whereas spike-timing-dependent potentiation (tLTP) displays a biphasic profile: tLTP is observed for 75–100 pairings, is absent for 25–50 pairings and re-emerges for 5–10 pairings. This tLTP induced by low numbers of pairings (5–10) depends on activation of the endocannabinoid system, type-1 cannabinoid receptor and the transient receptor potential vanilloid type-1. Endocannabinoid-tLTP may represent a physiological mechanism operating during the rapid learning of new associative memories and behavioural rules characterizing the flexible behaviour of mammals or during the initial stages of habit learning. Abstract Synaptic plasticity, a main substrate for learning and memory, is commonly assessed with prolonged stimulations. Since learning can arise from few or even a single trial, synaptic strength is expected to adapt rapidly. However, whether synaptic plasticity occurs in response to limited event occurrences remains elusive. To answer this question, we investigated whether a low number of paired stimulations can induce plasticity in a major synaptic learning rule, spike-timing-dependent plasticity (STDP). It is known that 100 pairings induce bidirectional STDP, i.e. spike-timing-dependent potentiation (tLTP) and depression (tLTD) at most central synapses. In rodent striatum, we found that tLTD progressively disappears when the number of paired stimulations is decreased (below 50 pairings) whereas tLTP displays a biphasic profile: tLTP is observed for 75–100 pairings, absent for 25
Time Dependent Relative Risks in Life Insurance Medical Underwriting.
Kneepkens, Robert F
2015-01-01
Introduction .- Life insurance medicine focuses on mortality hazards in specified periods. People are free to insure their lives for shorter or longer terms. Because the chosen terms range from 1 year to a life time, life insurers have to take into account the fact that the predictive value of risk indicators can and will change over time. The time a risk indicator keeps its predictive value, will be dependent on its biological effects, volatility, and treatability. For a given applicant this implies that the relative hazard (RH) calculated for his/her medical condition should be dependent on the term of the insurance. The main objective of this study is to determine if some commonly used risk indicators - previously used to study age dependency of relative risks - have a predictive value that increases with the observation period. (1) Methods .- This population-based cohort study uses NHANES-data files from the Third National Health and Nutrition Examination Survey (NHANES III) and the NHANES Linked Mortality Files 2010. Only participants aged 20 to 69 that were examined in mobile examination centers, without a history of some prevalent high risk diseases were included. The observed mortality was compared to the expected mortality in a Generalized Linear Model (GLM) with Poisson error structure with two reference populations, which both can serve as preferred reference for life insurers: The United States Life Tables 2008 (USLT) and the 2008 Valuation Basic Tables (VBT) based on the insured population of 35 US Life insurers. The time dependency of the RHs of the systolic blood pressure (SBP), aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), serum albumin and albuminuria, was assessed, with correction for ethnicity, household income, history of diabetes mellitus, BMI and serum cholesterol. To be able to compare the results with the results of the Age Dependency Study (ADS), the same data, risk indicators, statistical analysis method, and the
Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.
2000-04-27
High-temperature creep measurements combined with microstructural investigations can be used to elucidate deformation mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.
Time-dependent, irreversible entropy production and geodynamics.
Regenauer-Lieb, Klaus; Karrech, Ali; Chua, Hui Tong; Horowitz, Franklin G; Yuen, Dave
2010-01-13
We present an application of entropy production as an abstraction tool for complex processes in geodynamics. Geodynamic theories are generally based on the principle of maximum dissipation being equivalent to the maximum entropy production. This represents a restriction of the second law of thermodynamics to its upper bound. In this paper, starting from the equation of motion, the first law of thermodynamics and decomposition of the entropy into reversible and irreversible terms,(1) we come up with an entropy balance equation in an integral form. We propose that the extrema of this equation give upper and lower bounds that can be used to constrain geodynamics solutions. This procedure represents an extension of the classical limit analysis theory of continuum mechanics, which considers only stress and strain rates. The new approach, however, extends the analysis to temperature-dependent problems where thermal feedbacks can play a significant role. We apply the proposed procedure to a simple convective/conductive heat transfer problem such as in a planetary system. The results show that it is not necessary to have a detailed knowledge of the material parameters inside the planet to derive upper and lower bounds for self-driven heat transfer processes. The analysis can be refined by considering precise dissipation processes such as plasticity and viscous creep. PMID:19948557
Wawersik, W.R.; Zimmerer, D.J.
1994-05-01
Tejas Power Company requested that facilities in the Rock Mechanics Laboratory at Sandia National Laboratories be used to assess the time-dependent properties of rock salt from the Jennings dome in Acadia Parish, Louisiana. Nominally 2.5-inch diameter slat core from borehole LA-1, core 8 (depth 3924.8 to 3837.8 ft; 1196.8--1197.1 m) was provided to accomplish two tasks: (1) Using the smallest possible number of experiments, evaluate the tendency of Jennings salt to undergo time-dependent deformation (creep) under constant applied stresses, and compare the creep of Jennings salt with creep data for rock salt from other locations. (2) Assess the applicability of published laboratory-derived creep properties for rock salt from several bedded and domal sites in finite element analyses concerning the design of new gas storage caverns in the Jennings dome. The characterization of Jennings salt followed the same strategy that was applied in earlier laboratory experiments on core from the Moss Bluff dome near Houston, Texas. This report summarizes the relevant details of five creep experiments on a sample from depth 3927.5 ft, the results obtained, and how these results compared with laboratory creep measurements gathered on rock salt from other locations including the West Hackberry, Bryan Mound and Moss Bluff domes. The report also considers the estimates of specific creep parameters commonly used in numerical engineering design analyses.
2001-01-31
This software reduces the data from two-dimensional kSA MOS program, k-Space Associates, Ann Arbor, MI. Initial MOS data is recorded without headers in 38 columns, with one row of data per acquisition per lase beam tracked. The final MOSS 2d data file is reduced, graphed, and saved in a tab-delimited column format with headers that can be plotted in any graphing software.
Time-dependent radiation hazard estimations during space flights
NASA Astrophysics Data System (ADS)
Dobynde, Mikhail; Shprits, Yuri; Drozdov, Alexander
Cosmic particle radiation is a limiting factor for the out of magnetosphere crewed flights. The cosmic radiation uncrewed flights inside heliosphere and crewed flights inside of magnetosphere tend to become a routine procedure, whereas there have been only few shot time flights out of it (Apollo missions 1969-1972) with maximum duration less than a month. Long term crewed missions set much higher requirements to the radiation shielding, primarily because of long exposition term. Inside the helosphere there are two main sources of cosmic radiation: galactic cosmic rays (GCR) and coronal mass ejections (CME). GCR come from the outside of heliosphere forming a background of overall radiation that affects the spacecraft. The intensity of GCR is varied according to solar activity, increasing with solar activity decrease and backward, with the modulation time (time between nearest maxima) of 11 yeas. CME are shot term events, comparing to GCR modulation time, but are much more energetic. The probability of CME increases with the increase of solar activity. Time dependences of the intensity of these two components encourage looking for a time window of flight, when intensity and affection of CME and GCR would be minimized. Applying time dependent models of GCR spectra [1] and estimations of CME we show the time dependence of the radiation dose in a realistic human phantom [2] inside the shielding capsule. We pay attention to the shielding capsule design, looking for an optimal geometry parameters and materials. Different types of particles affect differently on the human providing more or less harm to the tissues. Incident particles provide a large amount of secondary particles while propagating through the shielding capsule. We make an attempt to find an optimal combination of shielding capsule parameters, namely material and thickness, that will effectively decrease the incident particle energy, at the same time minimizing flow of secondary induced particles and
Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya
2014-10-30
The research built upon a prior investigation to develop a unified constitutive model for design-by-analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-fatigue and creep-ratcheting tests were conducted on the nickel-base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-fatigue and creep-ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched
Ultrafast 2D-IR spectroelectrochemistry of flavin mononucleotide
NASA Astrophysics Data System (ADS)
El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Bredenbeck, Jens
2015-06-01
We demonstrate the coupling of ultrafast two-dimensional infrared (2D-IR) spectroscopy to electrochemistry in solution and apply it to flavin mononucleotide, an important cofactor of redox proteins. For this purpose, we designed a spectroelectrochemical cell optimized for 2D-IR measurements in reflection and measured the time-dependent 2D-IR spectra of the oxidized and reduced forms of flavin mononucleotide. The data show anharmonic coupling and vibrational energy transfer between different vibrational modes in the two redox species. Such information is inaccessible with redox-controlled steady-state FTIR spectroscopy. The wide range of applications offered by 2D-IR spectroscopy, such as sub-picosecond structure determination, IR band assignment via energy transfer, disentangling reaction mixtures through band connectivity in the 2D spectra, and the measurement of solvation dynamics and chemical exchange can now be explored under controlled redox potential. The development of this technique furthermore opens new horizons for studying the dynamics of redox proteins.
Ultrafast 2D-IR spectroelectrochemistry of flavin mononucleotide.
El Khoury, Youssef; Van Wilderen, Luuk J G W; Bredenbeck, Jens
2015-06-01
We demonstrate the coupling of ultrafast two-dimensional infrared (2D-IR) spectroscopy to electrochemistry in solution and apply it to flavin mononucleotide, an important cofactor of redox proteins. For this purpose, we designed a spectroelectrochemical cell optimized for 2D-IR measurements in reflection and measured the time-dependent 2D-IR spectra of the oxidized and reduced forms of flavin mononucleotide. The data show anharmonic coupling and vibrational energy transfer between different vibrational modes in the two redox species. Such information is inaccessible with redox-controlled steady-state FTIR spectroscopy. The wide range of applications offered by 2D-IR spectroscopy, such as sub-picosecond structure determination, IR band assignment via energy transfer, disentangling reaction mixtures through band connectivity in the 2D spectra, and the measurement of solvation dynamics and chemical exchange can now be explored under controlled redox potential. The development of this technique furthermore opens new horizons for studying the dynamics of redox proteins.
Shortcuts to adiabaticity in a time-dependent box
Campo, A. del; Boshier, M. G.
2012-01-01
A method is proposed to drive an ultrafast non-adiabatic dynamics of an ultracold gas trapped in a time-dependent box potential. The resulting state is free from spurious excitations associated with the breakdown of adiabaticity, and preserves the quantum correlations of the initial state up to a scaling factor. The process relies on the existence of an adiabatic invariant and the inversion of the dynamical self-similar scaling law dictated by it. Its physical implementation generally requires the use of an auxiliary expulsive potential. The method is extended to a broad family of interacting many-body systems. As illustrative examples we consider the ultrafast expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in different dimensions, where the method exhibits an excellent robustness against different regimes of interactions and the features of an experimentally realizable box potential. PMID:22970340
Histogram bin width selection for time-dependent Poisson processes
NASA Astrophysics Data System (ADS)
Koyama, Shinsuke; Shinomoto, Shigeru
2004-07-01
In constructing a time histogram of the event sequences derived from a nonstationary point process, we wish to determine the bin width such that the mean squared error of the histogram from the underlying rate of occurrence is minimized. We find that the optimal bin widths obtained for a doubly stochastic Poisson process and a sinusoidally regulated Poisson process exhibit different scaling relations with respect to the number of sequences, time scale and amplitude of rate modulation, but both diverge under similar parametric conditions. This implies that under these conditions, no determination of the time-dependent rate can be made. We also apply the kernel method to these point processes, and find that the optimal kernels do not exhibit any critical phenomena, unlike the time histogram method.
Large blue isocurvature spectral index signals time-dependent mass
NASA Astrophysics Data System (ADS)
Chung, Daniel J. H.
2016-08-01
We show that if a spectator linear isocurvature dark matter field degree of freedom has a constant mass through its entire evolution history, the maximum measurable isocurvature spectral index that is consistent with the current tensor-to-scalar ratio bound of about r ≲0.1 is about nI≲2.4 , even if experiments can be sensitive to a 10-6 contamination of the predominantly adiabatic power spectrum with an isocurvature power spectrum at the shortest observable length scales. Hence, any foreseeable future measurement of a blue isocurvature spectral index larger than ˜2.4 may provide nontrivial evidence for dynamical degrees of freedom with time-dependent masses during inflation. The bound is not sensitive to the details of the reheating scenario and can be made mildly smaller if r is better constrained in the future.
Relating Time-Dependent Acceleration and Height Using an Elevator
NASA Astrophysics Data System (ADS)
Kinser, Jason M.
2015-04-01
A simple experiment in relating a time-dependent linear acceleration function to height is explored through the use of a smartphone and an elevator. Given acceleration as a function of time1, a(t), the velocity function and position functions are determined through integration as in v (t ) =∫ a (t ) d t (1) and x (t ) =∫ v (t ) dt. Mobile devices such as smartphones or tablets have accelerometers that capture slowly evolving acceleration with respect to time and can deliver those measurements as a CSV file. A recent example measured the oscillations of the elevator as it starts its motion.2 In the application presented here the mobile device is used to estimate the height of the elevator ride. By estimating the functional form of the acceleration of an elevator ride, it is possible to estimate the height of the ride through Eqs. (1) and (2).
Time-dependent reliability analysis and condition assessment of structures
Ellingwood, B.R.
1997-01-01
Structures generally play a passive role in assurance of safety in nuclear plant operation, but are important if the plant is to withstand the effect of extreme environmental or abnormal events. Relative to mechanical and electrical components, structural systems and components would be difficult and costly to replace. While the performance of steel or reinforced concrete structures in service generally has been very good, their strengths may deteriorate during an extended service life as a result of changes brought on by an aggressive environment, excessive loading, or accidental loading. Quantitative tools for condition assessment of aging structures can be developed using time-dependent structural reliability analysis methods. Such methods provide a framework for addressing the uncertainties attendant to aging in the decision process.
Light pressure of time-dependent fields in plasmas
Zeidler, A.; Schnabl, H.; Mulser, P.
1985-01-01
An expression of the light pressure Pi is derived for the case of a nearly monochromatic electromagnetic wave with arbitrarily time-dependent amplitude. Thereby Pi is defined as the time-averaged force density exerted on a plasma by the wave. The resulting equations are valid for both transverse and longitudinal waves. The light pressure turns out to consist of two components: the well-known gradient-type term and a new nonstationary solenoidal term. This is true for warm as well as cold plasmas. The importance of the new term for the generation of static magnetic fields is shown, and a model in which shear forces may result is given. Formulas for the nonstationary light pressure developed previously are discussed.
Two-dimensional time dependent Riemann solvers for neutron transport
Brunner, Thomas A. . E-mail: tabrunn@sandia.gov; Holloway, James Paul
2005-11-20
A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P{sub 1} equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem.
Time-dependent Corotation Resonance in Barred Galaxies
NASA Astrophysics Data System (ADS)
Wu, Yu-Ting; Pfenniger, Daniel; Taam, Ronald E.
2016-10-01
The effective potential neighboring the corotation resonance region in barred galaxies is shown to be strongly time-dependent in any rotating frame, due to the competition of nearby perturbations of similar strengths with differing rotation speeds. Contrary to the generally adopted assumption that in the bar rotating frame the corotation region should possess four stationary equilibrium points (Lagrange points), with high quality N-body simulations, we localize the instantaneous equilibrium points (EPs) and find that they circulate or oscillate broadly in azimuth with respect to the pattern speeds of the inner or outer perturbations. This implies that at the particle level the Jacobi integral is not well conserved around the corotation radius. That is, angular momentum exchanges decouple from energy exchanges, enhancing the chaotic diffusion of stars through the corotation region.
Time-dependent variation of composition of SC1 solution
NASA Astrophysics Data System (ADS)
Takahashi, Isao; Kobayashi, Hideyuki; Ryuta, Jiro; Kishimoto, Mikio; Shingyouji, Takayuki
1993-09-01
We investigated the time-dependent variation of composition of NH4OH/H2O2/H2O mixture, the standard cleaning 1 (SC1) solution in the RCA cleaning process. The NH4OH concentration decreased with time and that of H2O2 was almost constant. It was clarified that the decrease rate of NH4OH concentration depended on the temperature and H2O2 concentration in the SC1 solution. As the temperature was raised, the decrease rate accelerated. Conversely, as H2O2 concentration was raised, the rate decelerated. It is concluded that the hydrogen bond between NH3 and H2O2 prevents NH3 evaporation.
Origin of the spike-timing-dependent plasticity rule
NASA Astrophysics Data System (ADS)
Cho, Myoung Won; Choi, M. Y.
2016-08-01
A biological synapse changes its efficacy depending on the difference between pre- and post-synaptic spike timings. Formulating spike-timing-dependent interactions in terms of the path integral, we establish a neural-network model, which makes it possible to predict relevant quantities rigorously by means of standard methods in statistical mechanics and field theory. In particular, the biological synaptic plasticity rule is shown to emerge as the optimal form for minimizing the free energy. It is further revealed that maximization of the entropy of neural activities gives rise to the competitive behavior of biological learning. This demonstrates that statistical mechanics helps to understand rigorously key characteristic behaviors of a neural network, thus providing the possibility of physics serving as a useful and relevant framework for probing life.
Measuring time-dependent diffusion in polymer matrix composites
Pilli, Siva Prasad; Smith, Lloyd V.; Shutthanandan, V.
2014-11-01
Moisture plays a significant role in influencing the mechanical behavior and long-term durability of polymer matrix composites (PMC’s). The common methods used to determine the moisture diffusion coefficients of PMCs are based on the solution of Fickian diffusion in the one-dimensional domain. Fick’s Law assumes that equilibrium between the material surface and the external vapor is established instantaneously. A time dependent boundary condition has been shown to improve correlation with some bulk diffusion measurements, but has not been validated experimentally. The surface moisture content in a Toray 800S/3900-2B toughened quasi-isotropic laminate system, [0/±60]s, was analyzed experimentally using Nuclear Reaction Analysis (NRA). It was found that the surface moisture content showed a rapid increase to an intermediate concentration C0, followed by a slow linear increase to the saturation level.
Time dependent electronic transport in chiral edge channels
NASA Astrophysics Data System (ADS)
Fève, G.; Berroir, J.-M.; Plaçais, B.
2016-02-01
We study time dependent electronic transport along the chiral edge channels of the quantum Hall regime, focusing on the role of Coulomb interaction. In the low frequency regime, the a.c. conductance can be derived from a lumped element description of the circuit. At higher frequencies, the propagation equations of the Coulomb coupled edge channels need to be solved. As a consequence of the interchannel coupling, a charge pulse emitted in a given channel fractionalized in several pulses. In particular, Coulomb interaction between channels leads to the fractionalization of a charge pulse emitted in a given channel in several pulses. We finally study how the Coulomb interaction, and in particular the fractionalization process, affects the propagation of a single electron in the circuit. All the above-mentioned topics are illustrated by experimental realizations.
Reprint of : Time dependent electronic transport in chiral edge channels
NASA Astrophysics Data System (ADS)
Fève, G.; Berroir, J.-M.; Plaçais, B.
2016-08-01
We study time dependent electronic transport along the chiral edge channels of the quantum Hall regime, focusing on the role of Coulomb interaction. In the low frequency regime, the a.c. conductance can be derived from a lumped element description of the circuit. At higher frequencies, the propagation equations of the Coulomb coupled edge channels need to be solved. As a consequence of the interchannel coupling, a charge pulse emitted in a given channel fractionalized in several pulses. In particular, Coulomb interaction between channels leads to the fractionalization of a charge pulse emitted in a given channel in several pulses. We finally study how the Coulomb interaction, and in particular the fractionalization process, affects the propagation of a single electron in the circuit. All the above-mentioned topics are illustrated by experimental realizations.
Shortcuts to adiabaticity in a time-dependent box.
del Campo, A; Boshier, M G
2012-01-01
A method is proposed to drive an ultrafast non-adiabatic dynamics of an ultracold gas trapped in a time-dependent box potential. The resulting state is free from spurious excitations associated with the breakdown of adiabaticity, and preserves the quantum correlations of the initial state up to a scaling factor. The process relies on the existence of an adiabatic invariant and the inversion of the dynamical self-similar scaling law dictated by it. Its physical implementation generally requires the use of an auxiliary expulsive potential. The method is extended to a broad family of interacting many-body systems. As illustrative examples we consider the ultrafast expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in different dimensions, where the method exhibits an excellent robustness against different regimes of interactions and the features of an experimentally realizable box potential.
Shortcuts to adiabaticity in a time-dependent box
NASA Astrophysics Data System (ADS)
Del Campo, A.; Boshier, M. G.
2012-09-01
A method is proposed to drive an ultrafast non-adiabatic dynamics of an ultracold gas trapped in a time-dependent box potential. The resulting state is free from spurious excitations associated with the breakdown of adiabaticity, and preserves the quantum correlations of the initial state up to a scaling factor. The process relies on the existence of an adiabatic invariant and the inversion of the dynamical self-similar scaling law dictated by it. Its physical implementation generally requires the use of an auxiliary expulsive potential. The method is extended to a broad family of interacting many-body systems. As illustrative examples we consider the ultrafast expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in different dimensions, where the method exhibits an excellent robustness against different regimes of interactions and the features of an experimentally realizable box potential.
Spin-orbit torque induced spike-timing dependent plasticity
Sengupta, Abhronil Al Azim, Zubair; Fong, Xuanyao; Roy, Kaushik
2015-03-02
Nanoelectronic devices that mimic the functionality of synapses are a crucial requirement for performing cortical simulations of the brain. In this work, we propose a ferromagnet-heavy metal heterostructure that employs spin-orbit torque to implement spike-timing dependent plasticity. The proposed device offers the advantage of decoupled spike transmission and programming current paths, thereby leading to reliable operation during online learning. Possible arrangement of such devices in a crosspoint architecture can pave the way for ultra-dense neural networks. Simulation studies indicate that the device has the potential of achieving pico-Joule level energy consumption (maximum 2 pJ per synaptic event) which is comparable to the energy consumption for synaptic events in biological synapses.
String pair production in a time-dependent gravitational field
Tolley, Andrew J.; Wesley, Daniel H.
2005-12-15
We study the pair creation of point particles and strings in a time-dependent, weak gravitational field. We find that, for massive string states, there are surprising and significant differences between the string and point-particle results. Central to our approach is the fact that a weakly curved spacetime can be represented by a coherent state of gravitons, and therefore we employ standard techniques in string perturbation theory. String and point-particle pairs are created through tree-level interactions between the background gravitons. In particular, we focus on the production of excited string states and perform explicit calculations of the production of a set of string states of arbitrary excitation level. The differences between the string and point-particle results may contain important lessons for the pair production of strings in the strong gravitational fields of interest in cosmology and black hole physics.
Time Dependence of Joy's Law for Emerging Active Regions
NASA Astrophysics Data System (ADS)
Chintzoglou, Georgios; Zhang, J.; Liu, Y.
2013-07-01
Joy's law governs the tilt of Active Regions (ARs) with respect to their absolute heliographic latitude. Together with Hale's law of hemispheric polarity, it is essential in constraining solar dynamo models. However, previous studies on Joy's law show only a weak positive trend between AR tilt angles and latitudes. In this study, we are focusing on the time dependence of Joy's law, for the cases of emerging ARs of Solar Cycle 24. We selected 40 ARs that emerge on the East hemisphere, effectively maximizing the observing time for each AR. Then, by converting the helioprojective maps into heliographic, we determine the geometrical as well as the magnetic-flux-weighted centroids for each emergence case. That way we are able to track the temporal evolution of their physical properties, including locations, fluxes of positive and negative polarities, as well as the tilt angles of these regions in a continuous manner until emergence stops and the ARs assume their final state.
SYMTRAN - A Time-dependent Symmetric Tandem Mirror Transport Code
Hua, D; Fowler, T
2004-06-15
A time-dependent version of the steady-state radial transport model in symmetric tandem mirrors in Ref. [1] has been coded up and first tests performed. Our code, named SYMTRAN, is an adaptation of the earlier SPHERE code for spheromaks, now modified for tandem mirror physics. Motivated by Post's new concept of kinetic stabilization of symmetric mirrors, it is an extension of the earlier TAMRAC rate-equation code omitting radial transport [2], which successfully accounted for experimental results in TMX. The SYMTRAN code differs from the earlier tandem mirror radial transport code TMT in that our code is focused on axisymmetric tandem mirrors and classical diffusion, whereas TMT emphasized non-ambipolar transport in TMX and MFTF-B due to yin-yang plugs and non-symmetric transitions between the plugs and axisymmetric center cell. Both codes exhibit interesting but different non-linear behavior.
Multiaxial Temperature- and Time-Dependent Failure Model
NASA Technical Reports Server (NTRS)
Richardson, David; McLennan, Michael; Anderson, Gregory; Macon, David; Batista-Rodriquez, Alicia
2003-01-01
A temperature- and time-dependent mathematical model predicts the conditions for failure of a material subjected to multiaxial stress. The model was initially applied to a filled epoxy below its glass-transition temperature, and is expected to be applicable to other materials, at least below their glass-transition temperatures. The model is justified simply by the fact that it closely approximates the experimentally observed failure behavior of this material: The multiaxiality of the model has been confirmed (see figure) and the model has been shown to be applicable at temperatures from -20 to 115 F (-29 to 46 C) and to predict tensile failures of constant-load and constant-load-rate specimens with failure times ranging from minutes to months..
A time dependent anatomically detailed model of cardiac conduction
NASA Technical Reports Server (NTRS)
Saxberg, B. E.; Grumbach, M. P.; Cohen, R. J.
1985-01-01
In order to understand the determinants of transitions in cardiac electrical activity from normal patterns to dysrhythmias such as ventricular fibrillation, we are constructing an anatomically and physiologically detailed finite element simulation of myocardial electrical propagation. A healthy human heart embedded in paraffin was sectioned to provide a detailed anatomical substrate for model calculations. The simulation of propagation includes anisotropy in conduction velocity due to fiber orientation as well as gradients in conduction velocities, absolute and relative refractory periods, action potential duration and electrotonic influence of nearest neighbors. The model also includes changes in the behaviour of myocardial tissue as a function of the past local activity. With this model, we can examine the significance of fiber orientation and time dependence of local propagation parameters on dysrhythmogenesis.
A gauge invariant theory for time dependent heat current
NASA Astrophysics Data System (ADS)
Chen, Jian; ShangGuan, Minhui; Wang, Jian
2015-05-01
In this work, we develop a general gauge-invariant theory for AC heat current through multi-probe systems. Using the non-equilibrium Green’s function, a general expression for time-dependent electrothermal admittance is obtained where we include the internal potential due to the Coulomb interaction explicitly. We show that the gauge-invariant condition is satisfied for heat current if the self-consistent Coulomb interaction is considered. It is known that the Onsager relation holds for dynamic charge conductance. We show in this work that the Onsager relation for electrothermal admittance is violated, except for a special case of a quantum dot system with a single energy level. We apply our theory to a nano capacitor where the Coulomb interaction plays an essential role. We find that, to the first order in frequency, the heat current is related to the electrochemical capacitance as well as the phase accumulated in the scattering event.
Time-dependent reliability analysis of ceramic engine components
NASA Technical Reports Server (NTRS)
Nemeth, Noel N.
1993-01-01
The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing either the power or Paris law relations. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating proof testing and fatigue parameter estimation are given.
Equation-free analysis of spike-timing-dependent plasticity.
Laing, Carlo R; Kevrekidis, Ioannis G
2015-12-01
Spike-timing-dependent plasticity is the process by which the strengths of connections between neurons are modified as a result of the precise timing of the action potentials fired by the neurons. We consider a model consisting of one integrate-and-fire neuron receiving excitatory inputs from a large number-here, 1000-of Poisson neurons whose synapses are plastic. When correlations are introduced between the firing times of these input neurons, the distribution of synaptic strengths shows interesting, and apparently low-dimensional, dynamical behaviour. This behaviour is analysed in two different parameter regimes using equation-free techniques, which bypass the explicit derivation of the relevant low-dimensional dynamical system. We demonstrate both coarse projective integration (which speeds up the time integration of a dynamical system) and the use of recently developed data mining techniques to identify the appropriate low-dimensional description of the complex dynamical systems in our model.
Translation invariant time-dependent solutions to massive gravity
Mourad, J.; Steer, D.A. E-mail: steer@apc.univ-paris7.fr
2013-12-01
Homogeneous time-dependent solutions of massive gravity generalise the plane wave solutions of the linearised Fierz-Pauli equations for a massive spin-two particle, as well as the Kasner solutions of General Relativity. We show that they also allow a clear counting of the degrees of freedom and represent a simplified framework to work out the constraints, the equations of motion and the initial value formulation. We work in the vielbein formulation of massive gravity, find the phase space resulting from the constraints and show that several disconnected sectors of solutions exist some of which are unstable. The initial values determine the sector to which a solution belongs. Classically, the theory is not pathological but quantum mechanically the theory may suffer from instabilities. The latter are not due to an extra ghost-like degree of freedom.
Fermion Mass Renormalization Using Time-dependent Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Kutnink, Timothy; Santrach, Amelia; Hocket, Sarah; Barcus, Scott; Petridis, Athanasios
2015-10-01
The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the staggered-leap-frog algorithm with refcecting boundary conditions. The stability region of the method versus the interaction strength and the spatial-grid size over time-step ratio is established. The expectation values of several dynamic operators are then evaluated as functions of time. These include the fermion and electromagnetic energies and the fermion dynamic mass, as the self-interacting spinors are no longer mass-eigenfunctions. There is a characteristic, non-exponential, oscillatory dependence leading to asymptotic constants of these expectation values. In the case of the fermion mass this amounts to renormalization. The dependence of the expectation values on the spatial-grid size is evaluated in detail. Statistical regularization is proposed to remove the grid-size dependence.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Time-dependent local density measurements in unsteady flows
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.; Monson, D. J.; Exberger, R. J.
1979-01-01
A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm-diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.
Retroactive modulation of spike timing-dependent plasticity by dopamine
Brzosko, Zuzanna; Schultz, Wolfram; Paulsen, Ole
2015-01-01
Most reinforcement learning models assume that the reward signal arrives after the activity that led to the reward, placing constraints on the possible underlying cellular mechanisms. Here we show that dopamine, a positive reinforcement signal, can retroactively convert hippocampal timing-dependent synaptic depression into potentiation. This effect requires functional NMDA receptors and is mediated in part through the activation of the cAMP/PKA cascade. Collectively, our results support the idea that reward-related signaling can act on a pre-established synaptic eligibility trace, thereby associating specific experiences with behaviorally distant, rewarding outcomes. This finding identifies a biologically plausible mechanism for solving the ‘distal reward problem’. DOI: http://dx.doi.org/10.7554/eLife.09685.001 PMID:26516682
Time-dependent, optically thick accretion onto a black hole
NASA Technical Reports Server (NTRS)
Gilden, D. L.; Wheeler, J. C.
1980-01-01
A fully relativistic hydrodynamics code which incorporates diffusive radiation transport is used to study time-dependent, spherically symmetric, optically thick accretion onto a black hole. It is found that matter free-falls into the hole regardless of whether the diffusion time scale is longer or shorter than the dynamical time. Nonadiabatic heating due to magnetic field reconnection is included. The internal energy thus generated affects the flow in a purely relativistic way, again ensuring free-fall collapse of the inflowing matter. Any matter enveloping a black hole will thus be swallowed on a dynamical time scale with relatively small net release of energy. The inclusion of angular momentum will not necessarily affect this conclusion.
Image charge dynamics in time-dependent quantum transport
NASA Astrophysics Data System (ADS)
Myöhänen, Petri; Tuovinen, Riku; Korhonen, Topi; Stefanucci, Gianluca; van Leeuwen, Robert
2012-02-01
In this work, we investigate the effects of the electron-electron interaction between a molecular junction and the metallic leads in time-dependent quantum transport. We employ the recently developed embedded Kadanoff-Baym method [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.80.115107 80, 115107 (2009)] and show that the molecule-lead interaction changes substantially the transient and steady-state transport properties. We first show that the mean-field Hartree-Fock (HF) approximation does not capture the polarization effects responsible for the renormalization of the molecular levels neither in nor out of equilibrium. Furthermore, due to the time-local nature of the HF self-energy, there exists a region in parameter space for which the system does not relax after the switch-on of a bias voltage. These and other artifacts of the HF approximation disappear when including correlations at the second-Born or GW levels. Both these approximations contain polarization diagrams, which correctly account for the screening of the charged molecule. We find that by changing the molecule-lead interaction, the ratio between the screening and relaxation time changes, an effect which must be properly taken into account in any realistic time-dependent simulation. Another important finding is that while in equilibrium the molecule-lead interaction is responsible for a reduction of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap and for a substantial redistribution of the spectral weight between the main spectral peaks and the induced satellite spectrum, in the biased system it can have the opposite effect, i.e., it sharpens the spectral peaks and opens the HOMO-LUMO gap.
Time-dependent changes in altruistic punishment following stress.
Vinkers, Christiaan H; Zorn, Jelle V; Cornelisse, Sandra; Koot, Susanne; Houtepen, Lotte C; Olivier, Berend; Verster, Joris C; Kahn, René S; Boks, Marco P M; Kalenscher, Tobias; Joëls, Marian
2013-09-01
Decisions are rarely made in social isolation. One phenomenon often observed in social interactions is altruistic punishment, i.e. the punishment of unfair behavior by others at a personal cost. The tendency for altruistic punishment is altered by affective states including those induced by stress exposure. Stress is thought to exert bi-directional effects on behavior: immediately after stress, reflex-like and habitual behavior is promoted while later on more far-sighted, flexible and goal-directed behavior is enhanced. We hypothesized that such time-dependent effects of stress would also be present in the context of altruistic punishment behavior. Healthy male participants (N=80) were exposed to either a grouped stress test or a control condition. Participants were tested in prosocial decision making tasks either directly after stress or 75 min later. Altruistic punishment was assessed using the Ultimatum Game. General altruism was assessed with a one-shot version of the Dictator Game in which an anonymous donation could be offered to a charitable organization. We found that stress caused a bi-directional effect on altruistic punishment, with decreased rejection rates in the late aftermath of stress in response to ambiguous 30% offers. In the Dictator Game, stressed participants were less generous than controls, but no time-dependent effect was observed, indicating that the general reward sensitivity remained unchanged at various time-points after stress. Overall, during the late aftermath after acute stress exposure (i.e. 75 min later), participants acted more consistent with their own material self-interest, and had a lower propensity for altruistic punishment, possibly through upregulation of cognitive self-control mechanisms. Thus, our findings underscore the importance of time as a factor in simple, real-life economic decisions in a stressful social context.
Time-Dependent Rock Failure in a Heterogeneous Limestone
NASA Astrophysics Data System (ADS)
Roth, K.; Kemeny, J.
2015-12-01
Time-dependent rock failure is an important aspect in the analysis of long-term rock stability for slopes, dam and bridge foundations, and underground storage facilities. An on-going project at the University of Arizona is using Kartchner Caverns in Benson, Arizona as a natural analog to study such failure by reconstructing the process of natural cave breakdown with subcritical crack growth modeling. Breakdown is thought to occur along joints through the time-dependent failure of rock bridges: sections of intact rock separating discontinuities in a rock mass. The Escabrosa limestone composing the caverns ranges from a more homogenous, even-grained texture to a more heterogeneous texture consisting of coarse-grained veins and solution cavities set in a fine-grained matrix. To determine if the veined regions are more susceptible to fracturing and act as the nuclei of rock bridge failure, fracture toughness tests were conducted for both textures. The subcritical crack growth parameters were calculated using the constant stress-rate method. Results indicate that the more heterogeneous limestone has a higher fracture strength, fracture toughness, and subcritical crack growth index n than the more homogeneous limestone. This is in agreement with previous studies which found that a more complex and heterogeneous microstructure produces a larger microcrack process zone, leading to higher fracture energies and lower susceptibility to subcritical crack growth. Thus, despite their solution cavities, the calcite veins do not localize failure or act as planes of weakness; instead, rock bridges fail through the more homogeneous limestone matrix.
Creep of posterior dental composites.
Papadogianis, Y; Boyer, D B; Lakes, R S
1985-01-01
The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.
The creep behavior of acrylic denture base resins.
Sadiku, E R; Biotidara, F O
1996-01-01
The creep behavior of acrylic dental base resins, at room temperature and at different loading conditions, has been examined. The behaviors of these resins are similar to that of "commercial perspex" at room temperature over a period of 1000 seconds. The pseudo-elastic moduli of the blends of PMMA VC show a significant increase compared with PMMA alone. The addition of the PVC powder to the heat-cured acrylic resin increased the time-dependent elastic modulus. This increase in elastic modulus is advantageous in the production of denture based resins of improv mechanical properties.
Tavernelli, Ivano; Curchod, Basile F. E.; Rothlisberger, Ursula
2010-05-15
A mixed quantum-classical method aimed at the study of nonadiabatic dynamics in the presence of external electromagnetic fields is developed within the framework of time-dependent density functional theory. To this end, we use a trajectory-based description of the quantum nature of the nuclear degrees of freedom according to Tully's fewest switches trajectories surface hopping, where both the nonadiabatic coupling elements between the different potential energy surfaces, and the coupling with the external field are given as functionals of the ground-state electron density or, equivalently, of the corresponding Kohn-Sham orbitals. The method is applied to the study of the photodissociation dynamics of some simple molecules in gas phase.
NASA Astrophysics Data System (ADS)
Voth, Greg A.; Perez, John A.; Son, Reuben
2009-06-01
We experimentally measure time-dependent velocity statistics in a quasi-2D granular gas under gravity. High resolution video particle tracking measurements show that the vibration induced shock waves have a serrated substructure on the scale of a particle diameter. We identify this substructure as an experimental visualization of collisional transport. Collisional transport is non-local in granular variables and is the mechanism for increased sound speed at higher densities. We also measure the time-dependent statistical properties of the gas after the energy input has been halted. The cooling occurs in two distinct stages separated by a high temperature settling shock. In the final stage, the temperature of a fluid packet decreases as a power law until the gas reaches a static state in agreement with recent theoretical work on this problem. However, the measured power law exponent is significantly larger than the theoretical value.
Room Temperature Creep Of SiC/SiC Composites
NASA Technical Reports Server (NTRS)
Morscher, Gregory N.; Gyekenyesi, Andrew; Levine, Stanley (Technical Monitor)
2001-01-01
During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time dependent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the interfacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interfacial shear stress with time at room temperature as measured by fiber push-in experiments.
(Irradiation creep of graphite)
Kennedy, C.R.
1990-12-21
The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.
Estimation of time-dependent input from neuronal membrane potential.
Kobayashi, Ryota; Shinomoto, Shigeru; Lansky, Petr
2011-12-01
The set of firing rates of the presynaptic excitatory and inhibitory neurons constitutes the input signal to the postsynaptic neuron. Estimation of the time-varying input rates from intracellularly recorded membrane potential is investigated here. For that purpose, the membrane potential dynamics must be specified. We consider the Ornstein-Uhlenbeck stochastic process, one of the most common single-neuron models, with time-dependent mean and variance. Assuming the slow variation of these two moments, it is possible to formulate the estimation problem by using a state-space model. We develop an algorithm that estimates the paths of the mean and variance of the input current by using the empirical Bayes approach. Then the input firing rates are directly available from the moments. The proposed method is applied to three simulated data examples: constant signal, sinusoidally modulated signal, and constant signal with a jump. For the constant signal, the estimation performance of the method is comparable to that of the traditionally applied maximum likelihood method. Further, the proposed method accurately estimates both continuous and discontinuous time-variable signals. In the case of the signal with a jump, which does not satisfy the assumption of slow variability, the robustness of the method is verified. It can be concluded that the method provides reliable estimates of the total input firing rates, which are not experimentally measurable. PMID:21919789
Complexities in gauging time-dependency of proliferation resistance
Avens, L. R.; Eller, P. G.; Stanbro, W. D.
2004-01-01
To a considerable extent, policy decisions on nuclear fuel cycle issues depend upon how decision makers recognize and weigh 'long-term' and 'short-term' nuclear proliferation risk factors. Priorities and structures of advanced fuel cycle and safeguards research and development programs are affected similarly. Unfortunately, there is a diversity of understanding of the precise meanings of these proliferation risk terms, leading to lack of precision in their usage. In addition, proliferation risk evaluation fundamentally involves value judgments on the relative importance of time-dependent risks. Poor communication and diverse conclusions often result. This paper explores some complexities in gauging 'long-term' and 'short-term' proliferation risk in the context of advanced nuclear fuel cycles. A convenient vehicle for this purpose is a commonly used notional plot of some proliferation resistance attribute of spent fuel or separated plutonium versus years from reactor discharge, often overlain with similar notional curves denoting multiple fuel irradiation and recycle. A common basis for misuse of such plots is failure to clearly define the range of proliferation threats being evaluated, as illustrated by several common examples of such omissions. Partial arguments of this type can be misleading and provide a disservice to policy makers who must have a clear picture of the tradeoffs being made. This paper concludes with a call for much greater care to avoid overly simplistic interpretations of notional proliferation-related concepts and greater precision in general in use of proliferation-related terminology.
Immersion Freezing of Clay Minerals and its Time Dependence
NASA Astrophysics Data System (ADS)
Hiranuma, N.; Moehler, O.; Bundke, U.; Cziczo, D. J.; Danielczok, A.; Ebert, M.; Garimella, S.; Hoffmann, N.; Kanji, Z. A.; Kiselev, A. A.; Raddatz, M.; Stetzer, O.
2012-12-01
Immersion ice nucleation efficiency of clay minerals has been investigated using the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber. Various clay dust samples, including two illite as well as three kaolinite standards, have been examined in the temperature range between 238 K and 255 K. We observed two trends in immersion ice nucleation properties as cloud expansion conditions in the AIDA are varied. First, as previously described in the literature, the supersaturation required for the immersion freezing of clay minerals decreased with decreasing temperature and increasing inferred ice-active surface site densities. Second, the ice nucleation activity of clay minerals strongly depended on the solo-parameter, which is the rate change in temperature (i.e., dNice/dT = ∂Nice/∂t ÷ ∂T/∂t). Further time dependence of ice formation is investigated and discussed as a function of cooling rates, ice nuclei (IN), and aerosol concentrations. Ice residuals collected through a pumped counterflow virtual impactor are examined by electron microprobe analyses to seek the true chemical and physical identity of IN in clay minerals. Brief comparisons of AIDA measurement to the measurements with other ice nucleation chambers (e.g., ETH-PINC, FINCH, and commercially available DMT-SPIN) are also presented.
A time-dependent model for improved biogalvanic tissue characterisation.
Chandler, J H; Culmer, P R; Jayne, D G; Neville, A
2015-10-01
Measurement of the passive electrical resistance of biological tissues through biogalvanic characterisation has been proposed as a simple means of distinguishing healthy from diseased tissue. This method has the potential to provide valuable real-time information when integrated into surgical tools. Characterised tissue resistance values have been shown to be particularly sensitive to external load switching direction and rate, bringing into question the stability and efficacy of the technique. These errors are due to transient variations observed in measurement data that are not accounted for in current electrical models. The presented research proposes the addition of a time-dependent element to the characterisation model to account for losses associated with this transient behaviour. Influence of switching rate has been examined, with the inclusion of transient elements improving the repeatability of the characterised tissue resistance. Application of this model to repeat biogalvanic measurements on a single ex vivo human colon tissue sample with healthy and cancerous (adenocarcinoma) regions showed a statistically significant difference (p < 0.05) between tissue types. In contrast, an insignificant difference (p > 0.05) between tissue types was found when measurements were subjected to the current model, suggesting that the proposed model may allow for improved biogalvanic tissue characterisation. PMID:26298197
Time-dependent simulations of disk-embedded planetary atmospheres
NASA Astrophysics Data System (ADS)
Stökl, A.; Dorfi, E. A.
2014-03-01
At the early stages of evolution of planetary systems, young Earth-like planets still embedded in the protoplanetary disk accumulate disk gas gravitationally into planetary atmospheres. The established way to study such atmospheres are hydrostatic models, even though in many cases the assumption of stationarity is unlikely to be fulfilled. Furthermore, such models rely on the specification of a planetary luminosity, attributed to a continuous, highly uncertain accretion of planetesimals onto the surface of the solid core. We present for the first time time-dependent, dynamic simulations of the accretion of nebula gas into an atmosphere around a proto-planet and the evolution of such embedded atmospheres while integrating the thermal energy budget of the solid core. The spherical symmetric models computed with the TAPIR-Code (short for The adaptive, implicit RHD-Code) range from the surface of the rocky core up to the Hill radius where the surrounding protoplanetary disk provides the boundary conditions. The TAPIR-Code includes the hydrodynamics equations, gray radiative transport and convective energy transport. The results indicate that diskembedded planetary atmospheres evolve along comparatively simple outlines and in particular settle, dependent on the mass of the solid core, at characteristic surface temperatures and planetary luminosities, quite independent on numerical parameters and initial conditions. For sufficiently massive cores, this evolution ultimately also leads to runaway accretion and the formation of a gas planet.
Determination of the time dependence of colored afterimages
NASA Astrophysics Data System (ADS)
Reidenbach, H.-D.
2008-02-01
Investigations have been done with high-brightness LEDs in order to determine the flight of colors for these high-intensity light sources. By simply glancing into such a device for time durations of less than 10 seconds a long-lasting afterimage that slowly changes colors was observed. A computer assisted measuring system was developed in order to determine the dependency on various parameters like color, optical power, exposure duration of the stimulating LED. For that a specially designed color wheel diagram has been designed and used which contains the necessary information on hue, saturation, and brightness. The time-dependent process and changes of the afterimage colors were determined for 4 different dominant wavelengths, i.e. 455 nm, 530 nm, 590 nm and 625 nm, in the optical power range between 0.05 mW and 0.5 mW for exposure durations between 0.5 s and 5 s. The results obtained with 5 test persons will be reported and especially the time course of the color fractions is given in an 8-bit color space with the respective RGB values. The progression of the afterimage colors as a function of the applied optical energy will be shown in the CIE chromaticity diagram together with the respective total afterimage duration.
Time-dependent numerical simulation of vertical cavity lasers
Thode, L.E.; Csanak, G.; So, L.L.; Kwan, T.J.T.; Campbell, M.
1994-12-31
To simulate vertical cavity surface emitting lasers (VCSELs), the authors are developing a three-dimensional, time-dependent field-gain model with absorption in bulk dielectric regions and gain in quantum well regions. Since the laser linewidth is narrow, the bulk absorption coefficient is assumed to be independent of frequency with a value determined by the material and the lattice temperature. In contrast, the frequency-dependent gain regions must be solved consistently in the time domain. Treatment of frequency-dependent media in a finite-difference time-domain code is computationally intensive. However, because the volume of the quantum well regions is small relative to the volume of the multilayer dielectric (MLD) mirror regions, the computational overhead is reasonable. A key issue is the calculation of the fields in the MLD mirror regions. Although computationally intensive, good agreement has been obtained between simulation results and matrix equation solutions for the reflection coefficient, transmission coefficient, and bandwidth of MLD mirrors. The authors discuss the development and testing of the two-dimensional field-gain model. This field-gain model will be integrated with a carrier transport model to form the self-consistent laser code, VCSEL.
The Out-of-Equilibrium Time-Dependent Gutzwiller Approximation
NASA Astrophysics Data System (ADS)
Fabrizio, Michele
We review the recently proposed extension of the Gutzwiller approximation (Schirò and Fabrizio, Phys Rev Lett 105:076401, 2010), designed to describe the out-of-equilibrium time-evolution of a Gutzwiller-type variational wave function for correlated electrons. The method, which is strictly variational in the limit of infinite lattice-coordination, is quite general and flexible, and it is applicable to generic non-equilibrium conditions, even far beyond the linear response regime. As an application, we discuss the quench dynamics of a single-band Hubbard model at half-filling, where the method predicts a dynamical phase transition above a critical quench that resembles the sharp crossover observed by time-dependent dynamical mean field theory. We next show that one can actually define in some cases a multi-configurational wave function combination of a whole set of mutually orthogonal Gutzwiller wave functions. The Hamiltonian projected in that subspace can be exactly evaluated and is equivalent to a model of auxiliary spins coupled to non-interacting electrons, closely related to the slave-spin theories for correlated electron models. The Gutzwiller approximation turns out to be nothing but the mean-field approximation applied to that spin-fermion model, which displays, for any number of bands and integer fillings, a spontaneous Z 2 symmetry breaking that can be identified as the Mott insulator-to-metal transition.
Translation invariant time-dependent solutions to massive gravity II
Mourad, J.; Steer, D.A. E-mail: steer@apc.univ-paris7.fr
2014-06-01
This paper is a sequel to JCAP 12 (2013) 004 and is also devoted to translation-invariant solutions of ghost-free massive gravity in its moving frame formulation. Here we consider a mass term which is linear in the vielbein (corresponding to a β{sub 3} term in the 4D metric formulation) in addition to the cosmological constant. We determine explicitly the constraints, and from the initial value formulation show that the time-dependent solutions can have singularities at a finite time. Although the constraints give, as in the β{sub 1} case, the correct number of degrees of freedom for a massive spin two field, we show that the lapse function can change sign at a finite time causing a singular time evolution. This is very different to the β{sub 1} case where time evolution is always well defined. We conclude that the β{sub 3} mass term can be pathological and should be treated with care.
Time-dependent buoyant puff model for explosive sources
Kansa, E.J.
1997-10-01
This paper presents a new model for explosive puff rise histories that is derived from the strong conservative form of the partial differential equations of mass, momenta, and total energy that are integrated over space to yield a coupled system of time dependent nonlinear ordinary differential equations (ODEs). By allowing the dimensions of the puff to evolve laterally and horizontally, the initial rising spherical shaped puff evolves into a rising ellipsoidal shaped mushroom cloud. This model treats the turbulence that is generated by the puff itself and the ambient atmospheric turbulence as separate mechanisms in determining the puff history. The puff rise history was found to depend not only upon the mass and initial temperature of the explosion, but also upon the local stability conditions of the ambient atmosphere through which the puff rises. This model was calibrated by comparison with the Roller Coaster experiments, ranging from unstable to very stable atmospheric conditions; the agreement of the model history curves with these experimental curves was within 10%.
Learning Probabilistic Inference through Spike-Timing-Dependent Plasticity123
Pecevski, Dejan
2016-01-01
Abstract Numerous experimental data show that the brain is able to extract information from complex, uncertain, and often ambiguous experiences. Furthermore, it can use such learnt information for decision making through probabilistic inference. Several models have been proposed that aim at explaining how probabilistic inference could be performed by networks of neurons in the brain. We propose here a model that can also explain how such neural network could acquire the necessary information for that from examples. We show that spike-timing-dependent plasticity in combination with intrinsic plasticity generates in ensembles of pyramidal cells with lateral inhibition a fundamental building block for that: probabilistic associations between neurons that represent through their firing current values of random variables. Furthermore, by combining such adaptive network motifs in a recursive manner the resulting network is enabled to extract statistical information from complex input streams, and to build an internal model for the distribution p* that generates the examples it receives. This holds even if p* contains higher-order moments. The analysis of this learning process is supported by a rigorous theoretical foundation. Furthermore, we show that the network can use the learnt internal model immediately for prediction, decision making, and other types of probabilistic inference. PMID:27419214
Distributed energy storage: Time-dependent tree flow design
NASA Astrophysics Data System (ADS)
Bejan, A.; Ziaei, S.; Lorente, S.
2016-05-01
This article proposes "distributed energy storage" as a basic design problem of distributing energy storage material on an area. The energy flows by fluid flow from a concentrated source to points (users) distributed equidistantly on the area. The flow is time-dependent. Several scenarios are analyzed: sensible-heat storage, latent-heat storage, exergy storage vs energy storage, and the distribution of a finite supply of heat transfer surface between the source fluid and the distributed storage material. The chief conclusion is that the finite amount of storage material should be distributed proportionally with the distribution of the flow rate of heating agent arriving on the area. The total time needed by the source stream to "invade" the area is cumulative (the sum of the storage times required at each storage site) and depends on the energy distribution paths and the sequence in which the users are served by the source stream. Directions for future designs of distributed storage and retrieval are outlined in the concluding section.
Recovery of time-dependent volatility in option pricing model
NASA Astrophysics Data System (ADS)
Deng, Zui-Cha; Hon, Y. C.; Isakov, V.
2016-11-01
In this paper we investigate an inverse problem of determining the time-dependent volatility from observed market prices of options with different strikes. Due to the non linearity and sparsity of observations, an analytical solution to the problem is generally not available. Numerical approximation is also difficult to obtain using most of the existing numerical algorithms. Based on our recent theoretical results, we apply the linearisation technique to convert the problem into an inverse source problem from which recovery of the unknown volatility function can be achieved. Two kinds of strategies, namely, the integral equation method and the Landweber iterations, are adopted to obtain the stable numerical solution to the inverse problem. Both theoretical analysis and numerical examples confirm that the proposed approaches are effective. The work described in this paper was partially supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region (Project No. CityU 101112) and grants from the NNSF of China (Nos. 11261029, 11461039), and NSF grants DMS 10-08902 and 15-14886 and by Emylou Keith and Betty Dutcher Distinguished Professorship at the Wichita State University (USA).
The time-dependent one-zone hadronic model
NASA Astrophysics Data System (ADS)
Mastichiadis, A.
2012-01-01
We investigate the radiative signatures of the one zone hadronic model, solving five space averaged, time-dependent coupled kinetic equations which describe the evolution of relativistic protons, electrons, photons, neutrons and neutrinos in a spherical volume containing a magnetic field. Protons are injected and lose energy by synchrotron, photopair and photopion production. We model photopair and photopion using the results of relevant MC codes, like the SOPHIA code in the case of photopion, which give accurate description for the injection of secondaries which then become source functions in their respective equations. Using these we model the corresponding proton losses and thus the code is self-consistent in the sense that the amount of energy lost by the protons is given to the secondaries. Furthermore, we treat the leptonic part of the system by including all relevant processes of the leptonic one-zone models. This approach allows us to examine questions like the efficiency of proton conversion to secondaries in addition to calculating self consistently the neutrino and photon spectra. We also show that the hadronic models are inherently unstable due to various supercriticalities which explosively transfer energy from protons to secondaries leading the system to a very rich temporal and spectral behavior.
Time-dependent radiation dose simulations during interplanetary space flights
NASA Astrophysics Data System (ADS)
Dobynde, Mikhail; Shprits, Yuri; Drozdov, Alexander; Hoffman, Jeffrey; Li, Ju
2016-07-01
Space radiation is one of the main concerns in planning long-term interplanetary human space missions. There are two main types of hazardous radiation - Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR). Their intensities and evolution depend on the solar activity. GCR activity is most enhanced during solar minimum, while the most intense SEPs usually occur during the solar maximum. SEPs are better shielded with thick shields, while GCR dose is less behind think shields. Time and thickness dependences of the intensity of these two components encourage looking for a time window of flight, when radiation intensity and dose of SEP and GCR would be minimized. In this study we combine state-of-the-art space environment models with GEANT4 simulations to determine the optimal shielding, geometry of the spacecraft, and launch time with respect to the phase of the solar cycle. The radiation environment was described by the time-dependent GCR model, and the SEP spectra that were measured during the period from 1990 to 2010. We included gamma rays, electrons, neutrons and 27 fully ionized elements from hydrogen to nickel. We calculated the astronaut's radiation doses during interplanetary flights using the Monte-Carlo code that accounts for the primary and the secondary radiation. We also performed sensitivity simulations for the assumed spacecraft size and thickness to find an optimal shielding. In conclusion, we present the dependences of the radiation dose as a function of launch date from 1990 to 2010, for flight durations of up to 3 years.
Nuclear inertia from the time dependent pairing equations
NASA Astrophysics Data System (ADS)
Mirea, M.
2016-10-01
In a dynamical system, the momenta of inertia and the effective masses are not adiabatic quantities, but are dynamical ones that depend on the dissipated energy accumulated during motion. However, these parameters are calculated for adiabatic nuclear systems, leaving no room for dissipated energy. In this work, a formalism is elaborated in order to derive simultaneously the nuclear momenta of inertia and the effective masses by taking into account the appearance of dissipated energy for large amplitude motion of the nuclear system. The expressions that define the inertia are obtained from the variational principle. The same principle manages the time dependent pairing equations, offering estimations of the averaged dissipation energy for large amplitude motions. The model is applied to 232Th fission. The fission barrier was calculated along the least action trajectory. The dissipation energy, effective mass and moment of inertia are determined for different values of the collective velocities. The dissipation increases with the internuclear velocity in binary disintegration processes and modifies the effective mass parameters. We observed that the inertia decreases as long as the collective velocity increases to some moderate values and begins to grow for larger collective velocities. So, a dependence between the cranking mass parameters and the intrinsic excitation energy is evidenced. In order to investigate the overall effect, the half-lives are predicted for adiabatic and dynamics simulations.
Time-dependent motor properties of multipedal molecular spiders
NASA Astrophysics Data System (ADS)
Samii, Laleh; Blab, Gerhard A.; Bromley, Elizabeth H. C.; Linke, Heiner; Curmi, Paul M. G.; Zuckermann, Martin J.; Forde, Nancy R.
2011-09-01
Molecular spiders are synthetic biomolecular walkers that use the asymmetry resulting from cleavage of their tracks to bias the direction of their stepping motion. Using Monte Carlo simulations that implement the Gillespie algorithm, we investigate the dependence of the biased motion of molecular spiders, along with binding time and processivity, on tunable experimental parameters, such as number of legs, span between the legs, and unbinding rate of a leg from a substrate site. We find that an increase in the number of legs increases the spiders’ processivity and binding time but not their mean velocity. However, we can increase the mean velocity of spiders with simultaneous tuning of the span and the unbinding rate of a spider leg from a substrate site. To study the efficiency of molecular spiders, we introduce a time-dependent expression for the thermodynamic efficiency of a molecular motor, allowing us to account for the behavior of spider populations as a function of time. Based on this definition, we find that spiders exhibit transient motor function over time scales of many hours and have a maximum efficiency on the order of 1%, weak compared to other types of molecular motors.
Time dependent sorption behavior of dinotefuran, imidacloprid and thiamethoxam.
Kurwadkar, Sudarshan T; Dewinne, Dustan; Wheat, Remington; McGahan, Donald G; Mitchell, Forrest L
2013-01-01
Dinetofuran (DNT), imidacloprid (IMD) and thiamethoxam (THM) are among the neonicotinoid insecticides widely used for managing insect pests of agricultural and veterinary importance. Environmental occurrence of neonicotinoid in post-application scenario poses unknown issues to human health and ecology. A sorption kinetic study provides much needed information on physico-chemical interaction of neonicotinoid with soil material. In this research study, time-dependent sorption behavior of DNT, IMD and THM in vineyard soil was studied. Sorption kinetics studies were conducted over a period of 96 hours with sampling duration varying from 0, 2, 4, 8, 12, 24, 60 and 96 hours. All three neonicotinoids exhibited very low sorption potential for the soil investigated. Overall percent sorption for all three neonicotinoids was below 20.04 ± 2.03% with highest percent sorption being observed for IMD followed by DNT and THM. All three neonicotinoids are highly soluble with solubility increasing with IMD < THM < DNT. Although, DNT has the highest solubility among all three neonicotinoids investigated, it exhibited higher percent sorption compared to THM, indicating factors other than solubility influenced the sorption kinetics. Low sorption potential of neonicotinoids indicates greater leaching potential with regard to groundwater and surface water contamination.
Time-dependent Magnetohydrodynamic Self-similar Extragalactic Jets
NASA Astrophysics Data System (ADS)
Tsui, K. H.; Serbeto, A.
2007-04-01
Extragalactic jets are visualized as dynamic eruptive events modeled by time-dependent magnetohydrodynamic (MHD) equations. The jet structure comes from the temporally self-similar solutions in two-dimensional axisymmetric spherical geometry. The two-dimensional magnetic field is solved in the finite plasma pressure regime, or finite-β regime, and it is described by an equation where plasma pressure plays the role of an eigenvalue. This allows a structure of magnetic lobes in space, among which the polar axis lobe is strongly peaked in intensity and collimated in angular spread compared to the others. For this reason, the polar lobe overwhelms the other lobes, and a jet structure naturally arises in the polar direction. Furthermore, within each magnetic lobe in space, there are small secondary regions with closed two-dimensional field lines embedded along this primary lobe. In these embedded magnetic toroids, plasma pressure and mass density are accordingly much higher. These are termed secondary plasmoids. The magnetic field lines in these secondary plasmoids circle in alternating sequence such that adjacent plasmoids have opposite field lines. In particular, along the polar primary lobe, such periodic plasmoid structure happens to be compatible with radio observations in which islands of high radio intensities are mapped.
Hot Jupiter breezes: time-dependent outflows from extrasolar planets
NASA Astrophysics Data System (ADS)
Owen, James E.; Adams, Fred C.
2016-03-01
We explore the dynamics of magnetically controlled outflows from hot Jupiters, where these flows are driven by UV heating from the central star. In these systems, some of the open field lines do not allow the flow to pass smoothly through the sonic point, so that steady-state solutions do not exist in general. This paper focuses on this type of magnetic field configuration, where the resulting flow becomes manifestly time-dependent. We consider the case of both steady heating and time-variable heating, and find the time-scales for the corresponding time variations of the outflow. Because the flow cannot pass through the sonic transition, it remains subsonic and leads to so-called breeze solutions. One manifestation of the time variability is that the flow samples a collection of different breeze solutions over time, and the mass outflow rate varies in quasi-periodic fashion. Because the flow is subsonic, information can propagate inwards from the outer boundary, which determines, in part, the time-scale of the flow variability. This work finds the relationship between the outer boundary scale and the time-scale of flow variations. In practice, the location of the outer boundary is set by the extent of the sphere of influence of the planet. The measured time variability can be used, in principle, to constrain the parameters of the system (e.g. the strengths of the surface magnetic fields).
Endocannabinoid dynamics gate spike-timing dependent depression and potentiation
Cui, Yihui; Prokin, Ilya; Xu, Hao; Delord, Bruno; Genet, Stephane; Venance, Laurent; Berry, Hugues
2016-01-01
Synaptic plasticity is a cardinal cellular mechanism for learning and memory. The endocannabinoid (eCB) system has emerged as a pivotal pathway for synaptic plasticity because of its widely characterized ability to depress synaptic transmission on short- and long-term scales. Recent reports indicate that eCBs also mediate potentiation of the synapse. However, it is not known how eCB signaling may support bidirectionality. Here, we combined electrophysiology experiments with mathematical modeling to question the mechanisms of eCB bidirectionality in spike-timing dependent plasticity (STDP) at corticostriatal synapses. We demonstrate that STDP outcome is controlled by eCB levels and dynamics: prolonged and moderate levels of eCB lead to eCB-mediated long-term depression (eCB-tLTD) while short and large eCB transients produce eCB-mediated long-term potentiation (eCB-tLTP). Moreover, we show that eCB-tLTD requires active calcineurin whereas eCB-tLTP necessitates the activity of presynaptic PKA. Therefore, just like glutamate or GABA, eCB form a bidirectional system to encode learning and memory. DOI: http://dx.doi.org/10.7554/eLife.13185.001 PMID:26920222
Time-dependent, multimode interaction analysis of the gyroklystron amplifier
NASA Astrophysics Data System (ADS)
Swati, M. V.; Chauhan, M. S.; Jain, P. K.
2016-08-01
In this paper, a time-dependent multimode nonlinear analysis for the gyroklystron amplifier has been developed by extending the analysis of gyrotron oscillators by employing the self-consistent approach. The nonlinear analysis developed here has been validated by taking into account the reported experimental results for a 32.3 GHz, three cavity, second harmonic gyroklystron operating in the TE02 mode. The analysis has been used to estimate the temporal RF growth in the operating mode as well as the nearby competing modes. Device gain and bandwidth have been computed for different drive powers and frequencies. The effect of various beam parameters, such as beam voltage, beam current, and pitch factor, has also been studied. The computational results have estimated the gyroklystron saturated RF power ˜319 kW at 32.3 GHz with efficiency ˜23% and gain ˜26.3 dB with device bandwidth ˜0.027% (8 MHz) for a 70 kV, 20 A electron beam. The computed results are found to be in agreement with the experimental values within 10%.
Some Consequences of a Time Dependent Speed of Light
NASA Astrophysics Data System (ADS)
Smith, Felix T.
2007-06-01
For reasons connected with both cosmology (the flatness and horizon problems) and atomic physics (n-body Dirac equation, etc.), various proposals have been made to modify general or special relativity(SR) to accommodate a cosmologically decreasing light speed [J. Magueijo, Rep. Prog. Phys. 66, 2025 (2003)]. Two such theories, projective SR [S.N. Manida, gr-qc/9905046; S. S. Stepanov, physics/9909009 and Phys. Rev. D, 62, 023507 (2000)] and symmetric SR [F.T. Smith, Ann. Fond. L. de Broglie, 30, 179 (2005)] adapt special relativity to in different ways to an expanding, hyperbolically curved position space and predict time-dependences of c within reach of measurement but differing by a factor of two. Both theories bring in a new constant λ-1=σ=c^2H0-1. As Magueijo points, out the role of c in physics and cosmology is so profound that many deep changes must follow if is not absolutely invariant in space and time. In particular, symmetric SR brings a new light to the Dirac large-number relationship between the constants of gravitation and atomic physics.
Aspects of time-dependent solutions of string theory
NASA Astrophysics Data System (ADS)
Fabinger, Michal
Most of our present knowledge of string theory pertains to time-independent backgrounds. Time-dependent backgrounds are in general much harder to understand, and pose a number of interesting questions. In the first part of this dissertation, we study light-like singularities in string theory. We discuss physical properties of the parabolic orbifold and the null-brane orbifold of Minkowski space, and we show how a large class of light-like singularities gets repaired by string worldsheet instantons. The second part of the dissertation is devoted to the study of physical systems related to double analytic continuations of black holes. In particular, we discuss M-theory compactified on a non-supersymmetric interval, which can decay by nucleation of bubbles of nothing. We also study the evolution of spacetimes obtained by a double analytic continuation of Kerr black holes. We compute particle creation in these spacetimes, and explain its relation to non-local deformations of the string worldsheet action. The main motivation for the work presented in the last part of the dissertation is to gain information about a possible holographic description of de Sitter space. We study the entropy of de Sitter flux compactifications, and the entropy of their deformations containing D-brane domain walls. We find a string scale correspondence point at which the thermodynamic entropy of the spacetime and the statistical entropy on the D-brane domain walls agree up to coefficients of order one.
Time-dependent corticosteroid modulation of prefrontal working memory processing
Henckens, Marloes J. A. G.; van Wingen, Guido A.; Joëls, Marian; Fernández, Guillén
2011-01-01
Corticosteroids are potent modulators of human higher cognitive function. They are released in response to stress, and are thought to be involved in the modulation of cognitive function by inducing distinct rapid nongenomic, and slow genomic changes, affecting neural plasticity throughout the brain. However, their exact effects on the neural correlates of higher-order cognitive function as performed by the prefrontal cortex at the human brain system level remain to be elucidated. Here, we targeted these time-dependent effects of corticosteroids on prefrontal cortex processing in humans using a working memory (WM) paradigm during functional MRI scanning. Implementing a randomized, double-blind, placebo-controlled design, 72 young, healthy men received 10 mg hydrocortisone either 30 min (rapid corticosteroid effects) or 240 min (slow corticosteroid effects), or placebo before a numerical n-back task with differential load (0- to 3-back). Corticosteroids’ slow effects appeared to improve working memory performance and increased neuronal activity during WM performance in the dorsolateral prefrontal cortex depending on WM load, whereas no effects of corticosteroids’ rapid actions were observed. Thereby, the slow actions of corticosteroids seem to facilitate adequate higher-order cognitive functioning, which may support recovery in the aftermath of stress exposure. PMID:21436038
A two-scale time-dependent damage model based on non-planar growth of micro-cracks
NASA Astrophysics Data System (ADS)
François, Bertrand; Dascalu, Cristian
2010-11-01
This paper presents the theoretical developments and the numerical applications of a time-dependent damage law. This law is deduced from considerations at the micro-scale where non-planar growth of micro-cracks, following a subcritical propagation criterion, is assumed. The orientation of the crack growth is governed by the maximum energy release rate at the crack tips and the introduction of an equivalent straight crack. The passage from micro-scale to macro-scale is done through an asymptotic homogenization approach. The model is built in two steps. First, the effective coefficients are calculated at the micro-scale in finite periodical cells, with respect to the micro-cracks length and their orientation. Then, a subcritical damage law is developed in order to establish the evolution of damage. This damage law is obtained as a differential equation depending on the microscopic stress intensity factors, which are a priori calculated for different crack lengths and orientations. The developed model enables to reproduce not only the classical short-term stress-strain response of materials (in tension and compression) but also the long-term behavior encountering relaxation and creep effects. Numerical simulations show the ability of the developed model to reproduce this time-dependent damage response of materials.
Fiber creep rate and high-temperature properties of SiC/SiC composites
Lewinsohn, C.A.; Jones, R.H.; Youngblood, G.E.; Henager, C.H. Jr.
1998-03-01
Results of studies aimed at relating the fiber creep rate to the subcritical crack growth rate and fracture properties of SiC/SiC composites have demonstrated that the crack growth rate in a bulk composite is controlled by the fiber creep rate. This result was demonstrated for Nicalon-CG and Hi-Nicalon fiber reinforced material where a 50--75 c shift in the creep strength of the fiber resulted in a similar shift in the crack growth rate of the composite. Irradiation enhanced creep of SiC fibers and matrix must also be considered in the performance assessment of SiC/SiC composites. The shape of the displacement versus time curve for composites containing Hi-Nicalon fibers were similar to those of the previously tested materials, containing Ceramic-grade fibers, that exhibited subcritical crack growth controlled by time-dependent relaxation of the fiber-bridging stresses due to fiber creep. The crack velocity in the CG-C composites at 1100 C in argon was very close to that of the Hi-C materials at 1150--1175 C, this roughly corresponds to the temperature differential shown by DiCarlo et al. to obtain the same relaxation in 1 hour bend stress relaxation (BSR) tests in the two fibers. This supports the hypothesis that subcritical crack growth in SiC/SiC composites is controlled by fiber creep.
NASA Technical Reports Server (NTRS)
Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac
2009-01-01
The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.
Georgi, Howard; Kats, Yevgeny
2008-09-26
We discuss what can be learned about unparticle physics by studying simple quantum field theories in one space and one time dimension. We argue that the exactly soluble 2D theory of a massless fermion coupled to a massive vector boson, the Sommerfield model, is an interesting analog of a Banks-Zaks model, approaching a free theory at high energies and a scale-invariant theory with nontrivial anomalous dimensions at low energies. We construct a toy standard model coupling to the fermions in the Sommerfield model and study how the transition from unparticle behavior at low energies to free particle behavior at high energies manifests itself in interactions with the toy standard model particles.
Unitary quantum evolution for time-dependent quasi-Hermitian systems with nonobservable Hamiltonians
NASA Astrophysics Data System (ADS)
Fring, Andreas; Moussa, Miled H. Y.
2016-04-01
It has been argued that it is incompatible to maintain unitary time evolution for time-dependent non-Hermitian Hamiltonians when the metric operator is explicitly time dependent. We demonstrate here that the time-dependent Dyson equation and the time-dependent quasi-Hermiticity relation can be solved consistently in such a scenario for a time-dependent Dyson map and time-dependent metric operator, respectively. These solutions are obtained at the cost of rendering the non-Hermitian Hamiltonian to be a nonobservable operator as it ceases to be quasi-Hermitian when the metric becomes time dependent.
Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.
NASA Astrophysics Data System (ADS)
Nicolas, A.; Fortin, J.; Gueguen, Y.
2014-12-01
Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry
NASA Technical Reports Server (NTRS)
Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.
1998-01-01
High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and
Reconsolidation of Motor Memories Is a Time-Dependent Process.
de Beukelaar, Toon T; Woolley, Daniel G; Alaerts, Kaat; Swinnen, Stephan P; Wenderoth, Nicole
2016-01-01
Reconsolidation is observed when a consolidated stable memory is recalled, which renders it transiently labile and requires re-stabilization. Motor memory reconsolidation has previously been demonstrated using a three-day design: on day 1 the memory is encoded, on day 2 it is reactivated and experimentally manipulated, and on day 3 memory strength is tested. The aim of the current study is to determine specific boundary conditions in order to consistently degrade motor memory through reconsolidation paradigms. We investigated a sequence tapping task (n = 48) with the typical three-day design and confirmed that reactivating the motor sequence briefly (10 times tapping the learned motor sequence) destabilizes the memory trace and makes it susceptible to behavioral interference. By systematically varying the time delay between memory reactivation and interference while keeping all other aspect constant we found that a short delay (i.e., 20 s) significantly decreased performance on day 3, whereas performance was maintained or small (but not significant) improvements were observed for longer delays (i.e., 60 s). We also tested a statistical model that assumed a linear effect of the different time delays (0 s, 20 s, 40 s, 60 s) on the performance changes from day 2 to day 3. This linear model revealed a significant effect consistent with the interpretation that increasing time delays caused a gradual change from performance degradation to performance conservation across groups. These findings indicate that re-stabilizing motor sequence memories during reconsolidation does not solely rely on additional motor practice but occurs with the passage of time. This study provides further support for the hypothesis that reconsolidation is a time-dependent process with a transition phase from destabilization to re-stabilization. PMID:27582698
Pharmacokinetics: time-dependent changes--autoinduction of carbamazepine epoxidation
Bertilsson, L.; Tomson, T.; Tybring, G.
1986-07-01
Drugs labeled with stable isotopes have been useful to study time-dependent changes in kinetics. Early studies suggested that carbamazepine (CBZ) may induce its own metabolism, but this could not be proved until tetradeuterium-labeled CBZ (CBZ-D4) was synthesized and then given to patients. CBZ-D4 was administered to three children during long-term treatment of epilepsy with CBZ. After 17 to 32 days of treatment, the plasma clearance of CBZ-D4 was doubled, but during the next four months, there was no further increase, indicating that autoinduction was complete within one month. Two patients with chronic alcoholism were treated with CBZ for five days. Half of the first dose of 600 mg was comprised of CBZ-D4. The half-life of this CBZ-D4 dose in the two patients (20 and 26 hr, respectively) was similar to the post-steady-state half-life of CBZ (23 hr in both patients) measured later. A single dose of CBZ given one week after the last maintenance dose had a longer half-life (46 and 45 hr, respectively), which probably is close to the disposition of the drug before starting the treatment with CBZ. This shows that autoinduction of CBZ metabolism was completed during the very first doses of CBZ. Autoinduction also disappeared rapidly after stopping the treatment. We have shown that it is mainly the epoxide-diol pathway that is induced, both during autoinduction and after induction with other antiepileptic agents.
Solving the time dependent vehicle routing problem by metaheuristic algorithms
NASA Astrophysics Data System (ADS)
Johar, Farhana; Potts, Chris; Bennell, Julia
2015-02-01
The problem we consider in this study is Time Dependent Vehicle Routing Problem (TDVRP) which has been categorized as non-classical VRP. It is motivated by the fact that multinational companies are currently not only manufacturing the demanded products but also distributing them to the customer location. This implies an efficient synchronization of production and distribution activities. Hence, this study will look into the routing of vehicles which departs from the depot at varies time due to the variation in manufacturing process. We consider a single production line where demanded products are being process one at a time once orders have been received from the customers. It is assumed that order released from the production line will be loaded into scheduled vehicle which ready to be delivered. However, the delivery could only be done once all orders scheduled in the vehicle have been released from the production line. Therefore, there could be lateness on the delivery process from awaiting all customers' order of the route to be released. Our objective is to determine a schedule for vehicle routing that minimizes the solution cost including the travelling and tardiness cost. A mathematical formulation is developed to represent the problem and will be solved by two metaheuristics; Variable Neighborhood Search (VNS) and Tabu Search (TS). These algorithms will be coded in C ++ programming and run using 56's Solomon instances with some modification. The outcome of this experiment can be interpreted as the quality criteria of the different approximation methods. The comparison done shown that VNS gave the better results while consuming reasonable computational efforts.
Reconsolidation of Motor Memories Is a Time-Dependent Process
de Beukelaar, Toon T.; Woolley, Daniel G.; Alaerts, Kaat; Swinnen, Stephan P.; Wenderoth, Nicole
2016-01-01
Reconsolidation is observed when a consolidated stable memory is recalled, which renders it transiently labile and requires re-stabilization. Motor memory reconsolidation has previously been demonstrated using a three-day design: on day 1 the memory is encoded, on day 2 it is reactivated and experimentally manipulated, and on day 3 memory strength is tested. The aim of the current study is to determine specific boundary conditions in order to consistently degrade motor memory through reconsolidation paradigms. We investigated a sequence tapping task (n = 48) with the typical three-day design and confirmed that reactivating the motor sequence briefly (10 times tapping the learned motor sequence) destabilizes the memory trace and makes it susceptible to behavioral interference. By systematically varying the time delay between memory reactivation and interference while keeping all other aspect constant we found that a short delay (i.e., 20 s) significantly decreased performance on day 3, whereas performance was maintained or small (but not significant) improvements were observed for longer delays (i.e., 60 s). We also tested a statistical model that assumed a linear effect of the different time delays (0 s, 20 s, 40 s, 60 s) on the performance changes from day 2 to day 3. This linear model revealed a significant effect consistent with the interpretation that increasing time delays caused a gradual change from performance degradation to performance conservation across groups. These findings indicate that re-stabilizing motor sequence memories during reconsolidation does not solely rely on additional motor practice but occurs with the passage of time. This study provides further support for the hypothesis that reconsolidation is a time-dependent process with a transition phase from destabilization to re-stabilization. PMID:27582698
Time-dependent computational studies of flames in microgravity
NASA Technical Reports Server (NTRS)
Oran, Elaine S.; Kailasanath, K.
1989-01-01
The research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of the NASA Microgravity Science and Applications Program is described. The primary focus was on investigating fundamental questions concerning the propagation and extinction of premixed flames in Earth gravity and in microgravity environments. The approach was to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. A combination of one-dimensional and two-dimensional simulations was used to investigate the effects of curvature and dilution on ignition and propagation of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the mechanism leading to cellular instability, and to study the effects of gravity on the transition to cellular structure. A flame in a microgravity environment can be extinguished without external losses, and the mechanism leading to cellular structure is not preferential diffusion but a thermo-diffusive instability. The simulations have also lead to a better understanding of the interactions between buoyancy forces and the processes leading to thermo-diffusive instability.
Time dependence of energy storage across multiple ecosystems
NASA Astrophysics Data System (ADS)
Reed, D. E.; Frank, J. M.; Ewers, B. E.; Desai, A. R.
2015-12-01
Energy flow through ecosystems plays a critical role in processes at multiple spatial and temporal scales, from monthly growing season length of landscapes to sub-diurnal responses of soil respiration to temperature, photosynthesis and water inputs. The interaction of solar radiation and ecosystems is complex with terrestrial canopies and aquatic structure both connecting above- and below-ground processes via energy fluxes. Previous work by Leuning et al has shown that at 30-minute timescales, only 8% of eddy covariance sites in the La Thuile dataset observe energy closure and when averaged to 24-hour timescales, this goes up to 45%. This work examines the effect of temporal lags in energy storage in both terrestrial (shrub and forest) and aquatic (lake) ecosystems. Analyses show energy storage terms have unique temporal lags that vary between ecosystem and time of year, from having zero lag to several hour timescales within terrestrial ecosystems, depending primarily on water content. Large differences between ecosystem types are also highlighted as aquatic ecosystems have lags that range between daily and monthly timescales. Furthermore, ecosystem disturbance can alter time lags as well and results from a native bark beetle disturbance show vegetation lag decreasing while soil lag increasing following changes in water content. Energy storage lags can improve site energy closure by several percent, and these results will lead to a better understanding of surface energy budget closure, an as-of-yet unresolved issue in the flux community, as well as highlighting the importance of time-dependency of ecosystem energy fluxes as a unique method to examine ecosystem processes.
A History of Spike-Timing-Dependent Plasticity
Markram, Henry; Gerstner, Wulfram; Sjöström, Per Jesper
2011-01-01
How learning and memory is achieved in the brain is a central question in neuroscience. Key to today’s research into information storage in the brain is the concept of synaptic plasticity, a notion that has been heavily influenced by Hebb's (1949) postulate. Hebb conjectured that repeatedly and persistently co-active cells should increase connective strength among populations of interconnected neurons as a means of storing a memory trace, also known as an engram. Hebb certainly was not the first to make such a conjecture, as we show in this history. Nevertheless, literally thousands of studies into the classical frequency-dependent paradigm of cellular learning rules were directly inspired by the Hebbian postulate. But in more recent years, a novel concept in cellular learning has emerged, where temporal order instead of frequency is emphasized. This new learning paradigm – known as spike-timing-dependent plasticity (STDP) – has rapidly gained tremendous interest, perhaps because of its combination of elegant simplicity, biological plausibility, and computational power. But what are the roots of today’s STDP concept? Here, we discuss several centuries of diverse thinking, beginning with philosophers such as Aristotle, Locke, and Ribot, traversing, e.g., Lugaro’s plasticità and Rosenblatt’s perceptron, and culminating with the discovery of STDP. We highlight interactions between theoretical and experimental fields, showing how discoveries sometimes occurred in parallel, seemingly without much knowledge of the other field, and sometimes via concrete back-and-forth communication. We point out where the future directions may lie, which includes interneuron STDP, the functional impact of STDP, its mechanisms and its neuromodulatory regulation, and the linking of STDP to the developmental formation and continuous plasticity of neuronal networks. PMID:22007168
Brain activity during interval timing depends on sensory structure.
Pfeuty, Micha; Ragot, Richard; Pouthas, Viviane
2008-04-14
Precise timing is crucial for accurate perception and action in the range of hundreds of milliseconds. One still unresolved question concerns the influence of sensory information content on timing mechanisms. Numerous studies have converged to suggest that the CNV (Contingent Negative Variation), a slow negative wave that develops between two events, notably reflects temporal processing of the interval between these two events. The present study aimed at investigating CNV activity in duration discrimination tasks using either filled (continuous tones) or empty intervals (silent periods bounded by two brief tones). Participants had to compare a test duration with a 600-ms standard. Time perception was markedly better in the 'empty' than in the 'filled' condition. Electrophysiological analyses performed on the longest test duration (794 ms) of the comparison phase revealed an effect of the sensory structure on both the CNV amplitude and CNV time-course. The CNV amplitude was larger for filled than for empty intervals, suggesting a superimposition of timing-dependent activity and sensory sustained activity. Furthermore, the CNV time-course paralleled the temporal structure of the memorized sensory event: for filled intervals, the CNV amplitude stopped increasing at 600 ms, i.e. the expected end of the continuous tone; for empty intervals, in contrast, the CNV amplitude precisely increased at 600 ms, i.e. the expected onset of the second brief tone. These results suggest that the CNV reflects the mental rehearsal of the memorized sensory event, in line with the idea that temporal processing in the sub-second range is based on sensory information.
Time dependent processing in a parallel pipeline architecture.
Biddiscombe, John; Geveci, Berk; Martin, Ken; Moreland, Kenneth; Thompson, David
2007-01-01
Pipeline architectures provide a versatile and efficient mechanism for constructing visualizations, and they have been implemented in numerous libraries and applications over the past two decades. In addition to allowing developers and users to freely combine algorithms, visualization pipelines have proven to work well when streaming data and scale well on parallel distributed-memory computers. However, current pipeline visualization frameworks have a critical flaw: they are unable to manage time varying data. As data flows through the pipeline, each algorithm has access to only a single snapshot in time of the data. This prevents the implementation of algorithms that do any temporal processing such as particle tracing; plotting over time; or interpolation, fitting, or smoothing of time series data. As data acquisition technology improves, as simulation time-integration techniques become more complex, and as simulations save less frequently and regularly, the ability to analyze the time-behavior of data becomes more important. This paper describes a modification to the traditional pipeline architecture that allows it to accommodate temporal algorithms. Furthermore, the architecture allows temporal algorithms to be used in conjunction with algorithms expecting a single time snapshot, thus simplifying software design and allowing adoption into existing pipeline frameworks. Our architecture also continues to work well in parallel distributed-memory environments. We demonstrate our architecture by modifying the popular VTK framework and exposing the functionality to the ParaView application. We use this framework to apply time-dependent algorithms on large data with a parallel cluster computer and thereby exercise a functionality that previously did not exist.
Creep of laminated aluminum composites
NASA Astrophysics Data System (ADS)
Moore, W.; Davies, T. J.
1980-08-01
The creep behavior of a laminate system consisting of alternate layers of pure aluminum and SAP (sintered aluminum powder) sheet has been examined in the temperature range 323 to 473 K and in the stress range 35 to 68 MN m-2. It was observed that secondary creep strain in the laminates was greater than in elemental SAP; the secondary creep strain rate in laminates was lower than that in pure aluminum and the creep rate decreased with increasing fracture of SAP. A stress exponent ( n) value of ˜20 was observed for most of the laminates and was reasonably constant for 3, 5, 7, and 9 ply laminates and volume fractions V f ) in the range 0.3 < V f < 0.65. For higher volume fractions of SAP the mechanical behavior of the laminates was similar to that of SAP. The experimental activation energy for creep of 30.5 ± 5 Kcal mol-1 correlates well with that for self-diffusion in aluminum. Laminating induced appreciable ductility to the SAP.
Creep of plasma sprayed zirconia
NASA Technical Reports Server (NTRS)
Firestone, R. F.; Logan, W. R.; Adams, J. W.
1982-01-01
Specimens of plasma-sprayed zirconia thermal barrier coatings with three different porosities and different initial particle sizes were deformed in compression at initial loads of 1000, 2000, and 3500 psi and temperatures of 1100 C, 1250 C, and 1400 C. The coatings were stabilized with lime, magnesia, and two different concentrations of yttria. Creep began as soon as the load was applied and continued at a constantly decreasing rate until the load was removed. Temperature and stabilization had a pronounced effect on creep rate. The creep rate for 20% Y2O3-80% ZrO2 was 1/3 to 1/2 that of 8% Y2O3-92% ZrO2. Both magnesia and calcia stabilized ZrO2 crept at a rate 5 to 10 times that of the 20% Y2O3 material. A near proportionality between creep rate and applied stress was observed. The rate controlling process appeared to be thermally activated, with an activation energy of approximately 100 cal/gm mole K. Creep deformation was due to cracking and particle sliding.
Investigating the Creeping Segment of the San Andreas Fault using InSAR time series analysis
NASA Astrophysics Data System (ADS)
Rolandone, Frederique; Ryder, Isabelle; Agram, Piyush S.; Burgmann, Roland; Nadeau, Robert M.
2010-05-01
We exploit the advanced Interferometric Synthetic Aperture Radar (InSAR) technique referred to as the Small BAseline Subset (SBAS) algorithm to analyze the creeping section of the San Andreas Fault in Central California. Various geodetic creep rate measurements along the Central San Andreas Fault (CSAF) have been made since 1969 including creepmeters, alignment arrays, geodolite, and GPS. They show that horizontal surface displacements increase from a few mm/yr at either end to a maximum of up to ~34 mm/yr in the central portion. They also indicate some discrepancies in rate estimates, with the range being as high as 10 mm/yr at some places along the fault. This variation is thought to be a result of the different geodetic techniques used and of measurements being made at variable distances from the fault. An interferometric stack of 12 interferograms for the period 1992-2001 shows the spatial variation of creep that occurs within a narrow (<2 km) zone close to the fault trace. The creep rate varies spatially along the fault but also in time. Aseismic slip on the CSAF shows several kinds of time dependence. Shallow slip, as measured by surface measurements across the narrow creeping zone, occurs partly as ongoing steady creep, along with brief episodes with slip from mm to cm. Creep rates along the San Juan Bautista segment increased after the 1989 Loma Prieta earthquake and slow slip transients of varying duration and magnitude occurred in both transition segments The main focus of this work is to use the SBAS technique to identify spatial and temporal variations of creep on the CSAF. We will present time series of line-of-sight (LOS) displacements derived from SAR data acquired by the ASAR instrument, on board the ENVISAT satellite, between 2003 and 2009. For each coherent pixel of the radar images we compute time-dependent surface displacements as well as the average LOS deformation rate. We compare our results with characteristic repeating microearthquakes that
Time dependent weak localization of a 2DEG in the presence of Andreev reflections
Drexler, H.; Harris, J.; Yuh, E.L.
1995-12-31
Experiments on superconducting-normal-superconducting, SNS, junctions, comprised of Nb-2D InAs - Nb, exhibit AC currents at v = 4eV/h, twice the Josephson frequency. These currents can be ascribed to time dependent weak localization in the 2D InAs electron gas modulated by the presence of superconducting electrodes. The change of the current-voltage characteristic of a SNS structure under far-infrared (FIR) illumination (180GHz, 300GHz) has been investigated as a function of temperature, FIR power and magnetic field. The sample is an InAs/AlSb quantum well with a 1{mu}m-period Nb grating contacting the InAs. In the experiments a series connection of N = 300 junctions is measured. The differential resistance of the sample shows a very clear subharmonic gap structure, indicating multiple Andreev reflections between the SN-interfaces. Below a temperature of about T = 5K the sample is superconductive. At sufficiently high temperatures (T > 6K) the photoresponse of the sample under FIR illumination exhibits only a single resonance. This resonance is at V = Nhv/4e, that is half the voltage at which the first step of the AC Josephson effect would occur. B.Z. Spivak and D.E. Khmel`nitskii predicted this effect which arises from the quantum correction of the conductivity of a normal state electron gas due to Andreev reflections. Electrons and holes that are Andreev reflected at the superconductor interface acquire a phase shift that is determined by the phase {Phi} of the superconductor. Interference terms of time reversed paths that include Andreev reflections on adjacent superconductor stripes oscillate with 2({Phi}{sub 2}-{Phi}{sub 1}) = 4eVt/h and therefore lead to a time-dependent conductivity. The manifestation of the oscillating conductivity in the experiments is similar to the Shapiro steps of the AC Josephson effect but with twice the frequency. The experiments show that this effect is very sensitive to an applied magnetic field.
Implosion Robustness, Time-Dependent Flux Asymmetries and Big Data
NASA Astrophysics Data System (ADS)
Peterson, J. L.; Field, J. E.; Spears, B. K.; Brandon, S. T.; Gaffney, J. A.; Hammer, J.; Kritcher, A.; Nora, R. C.; Springer, P. T.
2015-11-01
Both direct and indirect drive inertial confinement fusion rely on the formation of spherical implosions, which can be a challenge under temporal and spatial drive variations (either from discrete laser beams, a complex hohlraum radiation environment, or both). To that end, we examine the use of large simulation databases of 2D capsule implosions to determine the sensitivity of indirectly driven NIF designs to time-varying low-mode radiation drive asymmetries at varying convergence ratios. In particular, we define and calculate a large number of extensive quantities for the simulations within the database and compare with the equivalent quantities extracted from fully 3D simulations and those used in 1D hydrodynamic models. Additionally, we discuss some of the practical challenges of searching for physical insight in multi-petabyte datasets. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, Lawrence Livermore National Security, LLC. LLNL-ABS-674884.
A model for the stability and creep of organic materials.
Jäger, Ingomar L
2005-07-01
A model is presented for the thermally assisted breaking of a number of bonds arranged in parallel and stressed by an individual soft spring each. Using a simplified potential for the bond it is shown that in equilibrium there are two definite regions of elastic behavior: one with all bonds intact, the other with a variable fraction of bonds broken, therefore with a tangent modulus steadily decreasing with applied stress. Criteria are given for the existence of these regions. Beyond these regions time-dependent creep to rupture is found, limited, in turn, by the theoretical fracture strength, the stress necessary for fracture without any thermal assistance, beyond which a bound state is impossible. The time-to-fracture for creep rupture is calculated and an example of the time evolution of the accelerating creep given. The results of the calculations are applied to experimental data on Wallaby tendons by Wang and Ker (J. Exp. Biol. 198 (1995) 831) and data estimated for the bond potential depth, the theoretical fracture strength and the number density of bonds involved as well as the elastic modulus of the ensemble. Values are derived under the assumption of one deformation mechanism being dominant--e.g., (sub-)fibril sliding or sliding of collagen molecules along one another--but the model cannot definitely distinguish between mechanisms. PMID:15922757
Presynaptic Spike Timing-Dependent Long-Term Depression in the Mouse Hippocampus
Andrade-Talavera, Yuniesky; Duque-Feria, Paloma; Paulsen, Ole; Rodríguez-Moreno, Antonio
2016-01-01
Spike timing-dependent plasticity (STDP) is a Hebbian learning rule important for synaptic refinement during development and for learning and memory in the adult. Given the importance of the hippocampus in memory, surprisingly little is known about the mechanisms and functions of hippocampal STDP. In the present work, we investigated the requirements for induction of hippocampal spike timing-dependent long-term potentiation (t-LTP) and spike timing-dependent long-term depression (t-LTD) and the mechanisms of these 2 forms of plasticity at CA3-CA1 synapses in young (P12–P18) mouse hippocampus. We found that both t-LTP and t-LTD can be induced at hippocampal CA3-CA1 synapses by pairing presynaptic activity with single postsynaptic action potentials at low stimulation frequency (0.2 Hz). Both t-LTP and t-LTD require NMDA-type glutamate receptors for their induction, but the location and properties of these receptors are different: While t-LTP requires postsynaptic ionotropic NMDA receptor function, t-LTD does not, and whereas t-LTP is blocked by antagonists at GluN2A and GluN2B subunit-containing NMDA receptors, t-LTD is blocked by GluN2C or GluN2D subunit-preferring NMDA receptor antagonists. Both t-LTP and t-LTD require postsynaptic Ca2+ for their induction. Induction of t-LTD also requires metabotropic glutamate receptor activation, phospholipase C activation, postsynaptic IP3 receptor-mediated Ca2+ release from internal stores, postsynaptic endocannabinoid (eCB) synthesis, activation of CB1 receptors and astrocytic signaling, possibly via release of the gliotransmitter d-serine. We furthermore found that presynaptic calcineurin is required for t-LTD induction. t-LTD is expressed presynaptically as indicated by fluctuation analysis, paired-pulse ratio, and rate of use-dependent depression of postsynaptic NMDA receptor currents by MK801. The results show that CA3-CA1 synapses display both NMDA receptor-dependent t-LTP and t-LTD during development and identify a
Quantum Drude friction for time-dependent density functional theory.
Neuhauser, Daniel; Lopata, Kenneth
2008-10-01
sophisticated description of the coupling, and to memory functionals. Our results open the way to very simple finite grid description of scattering and multistage conductance using time-dependent density functional theory away from the linear regime, just as absorbing potentials and self-energies are useful for noninteracting systems and leads. PMID:19045077
Time-dependent fiber bundles with local load sharing
NASA Astrophysics Data System (ADS)
Newman, W. I.; Phoenix, S. L.
2001-02-01
Fiber bundle models, where fibers have random lifetimes depending on their load histories, are useful tools in explaining time-dependent failure in heterogeneous materials. Such models shed light on diverse phenomena such as fatigue in structural materials and earthquakes in geophysical settings. Various asymptotic and approximate theories have been developed for bundles with various geometries and fiber load-sharing mechanisms, but numerical verification has been hampered by severe computational demands in larger bundles. To gain insight at large size scales, interest has returned to idealized fiber bundle models in 1D. Such simplified models typically assume either equal load sharing (ELS) among survivors, or local load sharing (LLS) where a failed fiber redistributes its load onto its two nearest flanking survivors. Such models can often be solved exactly or asymptotically in increasing bundle size, N, yet still capture the essence of failure in real materials. The present work focuses on 1D bundles under LLS. As in previous works, a fiber has failure rate following a power law in its load level with breakdown exponent ρ. Surviving fibers under fixed loads have remaining lifetimes that are independent and exponentially distributed. We develop both new asymptotic theories and new computational algorithms that greatly increase the bundle sizes that can be treated in large replications (e.g., one million fibers in thousands of realizations). In particular we develop an algorithm that adapts several concepts and methods that are well-known among computer scientists, but relatively unknown among physicists, to dramatically increase the computational speed with no attendant loss of accuracy. We consider various regimes of ρ that yield drastically different behavior as N increases. For 1/2<=ρ<=1, ELS and LLS have remarkably similar behavior (they have identical lifetime distributions at ρ=1) with approximate Gaussian bundle lifetime statistics and a finite limiting
Numerical Simulations of Time-dependent Herbig-Haro Jets
NASA Astrophysics Data System (ADS)
Biro, Susana
1994-11-01
Recent observations of Herbig-Haro jets (or optical jets) show evidence that these highly collimated, supersonic flows associated with young stellar objects are not steady, but rather show many types of variations. The string of shock excited nebulae that make up such jets have highly supersonic proper motions, substantial variations of radial velocity along the length of the jet and often several working surfaces. Several models (both analytic and numerical) exist which explain some of the observed properties of optical jets. However, these jets have a wide variety of shapes, sizes and velocities, so a general model for them is not possible. Three simple time-dependent effects have been simulated for this thesis using the approximate Riemann solver, Flux-Vector-Splitting. A periodic variation in the magnitude of the velocity of the flow produces a straight jet with a head (or working surface) and several regularly spaced pairs of shocks (internal working surfaces, IWS). This structure is similar to that of the HH34 and HH111 jets. Special attention is given to a single IWS. The evolution and emission properties of this structure are determined. A periodic variation in the direction of the flow produces a jet with a sinuous body and a complex working surface. Pairs of shocks appear at the bends of this sinuous beam. An adiabatic simulation of the complete jet serves to illustrate the general structure of the flow. The sinuous body and knotty working surface are similar to the HH46/47 jet. A non-adiabatic simulation of the body of the jet (excluding the head) permits the calculation of emission maps which show a structure similar to that observed in HH46/47. By combining the variations in magnitude and direction of the velocity, a jet is created which eventually breaks-up into independent knots (or ``bullets''). Maps of the emission obtained from this simulation present a structure reminiscent of the flow in L1551+IRS5. In general, groups of bow-shaped HH objects
Time-dependent Computational Studies of Premixed Flames in Microgravity
NASA Technical Reports Server (NTRS)
Kailasanath, K.; Patnaik, Gopal; Oran, Elaine S.
1993-01-01
This report describes the research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of NASA Microgravity Science and Applications Program. The primary focus of this research is on investigating fundamental questions concerning the propagation and extinction of premixed flames in earth gravity and in microgravity environments. Our approach is to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. Recently more advanced wall boundary conditions such as isothermal and no-slip have been added to the model. This enables the simulation of flames propagating in more practical systems than before. We have used the numerical simulations to investigate the effects of heat losses and buoyancy forces on the structure and stability of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the interaction between the various processes leading to flame instabilities and extinguishment, and to study the dynamics of cell formation and splitting. Our studies have been able to bring out the differences between upward- and downward-propagating flames and predict the zero-gravity behavior of these flames. The simulations have also highlighted the dominant role of wall heat losses in the case of downward-propagating flames. The simulations have been able to qualitatively predict the
Fluid Creep and Over-resuscitation.
Saffle, Jeffrey R
2016-10-01
Fluid creep is the term applied to a burn resuscitation, which requires more fluid than predicted by standard formulas. Fluid creep is common today and is linked to several serious edema-related complications. Increased fluid requirements may accompany the appropriate resuscitation of massive injuries but dangerous fluid creep is also caused by overly permissive fluid infusion and the lack of colloid supplementation. Several strategies for recognizing and treating fluid creep are presented. PMID:27600130
Fortran programs for the time-dependent Gross-Pitaevskii equation in a fully anisotropic trap
NASA Astrophysics Data System (ADS)
Muruganandam, P.; Adhikari, S. K.
2009-10-01
Here we develop simple numerical algorithms for both stationary and non-stationary solutions of the time-dependent Gross-Pitaevskii (GP) equation describing the properties of Bose-Einstein condensates at ultra low temperatures. In particular, we consider algorithms involving real- and imaginary-time propagation based on a split-step Crank-Nicolson method. In a one-space-variable form of the GP equation we consider the one-dimensional, two-dimensional circularly-symmetric, and the three-dimensional spherically-symmetric harmonic-oscillator traps. In the two-space-variable form we consider the GP equation in two-dimensional anisotropic and three-dimensional axially-symmetric traps. The fully-anisotropic three-dimensional GP equation is also considered. Numerical results for the chemical potential and root-mean-square size of stationary states are reported using imaginary-time propagation programs for all the cases and compared with previously obtained results. Also presented are numerical results of non-stationary oscillation for different trap symmetries using real-time propagation programs. A set of convenient working codes developed in Fortran 77 are also provided for all these cases (twelve programs in all). In the case of two or three space variables, Fortran 90/95 versions provide some simplification over the Fortran 77 programs, and these programs are also included (six programs in all). Program summaryProgram title: (i) imagetime1d, (ii) imagetime2d, (iii) imagetime3d, (iv) imagetimecir, (v) imagetimesph, (vi) imagetimeaxial, (vii) realtime1d, (viii) realtime2d, (ix) realtime3d, (x) realtimecir, (xi) realtimesph, (xii) realtimeaxial Catalogue identifier: AEDU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data
Creep and Creep-Fatigue of Alloy 617 Weldments
Wright, Jill K.; Carroll, Laura J.; Wright, Richard N.
2014-08-01
Alloy 617 is the primary candidate material for the heat exchanger of a very high temperature gas cooled reactor intended to operate up to 950°C. While this alloy is currently qualified in the ASME Boiler and Pressure Vessel Code for non-nuclear construction, it is not currently allowed for use in nuclear designs. A draft Code Case to qualify Alloy 617 for nuclear pressure boundary applications was submitted in 1992, but was withdrawn prior to approval. Prior to withdrawal of the draft, comments were received indicating that there was insufficient knowledge of the creep and creep-fatigue behavior of Alloy 617 welds. In this report the results of recent experiments and analysis of the creep-rupture behavior of Alloy 617 welds prepared using the gas tungsten arc process with Alloy 617 filler wire. Low cycle fatigue and creep-fatigue properties of weldments are also discussed. The experiments cover a range of temperatures from 750 to 1000°C to support development of a new Code Case to qualify the material for elevated temperature nuclear design. Properties of the welded material are compared to results of extensive characterization of solution annealed plate base metal.
Development and validation of a predictive technology for creep closure of underground rooms in salt
Munson, D.E. ); DeVries, K.L. )
1991-07-01
Because of the concern for public health and safety, when compared to normal engineering practice, radioactive waste repositories have quite unusual requirements governing performance assessment. In part, performance assessment requires prediction of time-dependent or creep response of the repository hundreds to thousands of years into the future. In salt, one specific need is to predict, with confidence, the time at which the repository rooms creep closed sufficiently to encapsulate the waste and seal the repository. Thus, a major task of the Waste Isolation Pilot Plant (WIPP) Program is to develop and validate this predictive technology to calculate creep of repository rooms in the bedded salt deposits of Southeastern New Mexico. 19 refs., 15 figs., 2 tabs.
Network Structures Arising from Spike-Timing Dependent Plasticity
NASA Astrophysics Data System (ADS)
Babadi, Baktash
Spike-timing dependent plasticity (STDP), a widespread synaptic modification mechanism, is sensitive to correlations between presynaptic spike trains, and organizes neural circuits in functionally useful ways. In this dissertation, I study the structures arising from STDP in a population of synapses with an emphasis on the interplay between synaptic stability and Hebbian competition, explained in Chapter 1. Starting from the simplest description of STDP which relates synaptic modification to the intervals between pairs of pre- and postsynaptic spikes, I show in Chapter 2 that stability and Hebbian competition are incompatible in this class of "pair-based" STDP models, either when hard bounds or soft bounds are imposed to the synapses. In chapter 3, I propose an alternative biophysically inspired method for imposing bounds to synapses, i.e. introducing a small temporal shift in the STDP window. Shifted STDP overcomes the incompatibility of synaptic stability and competition and can implement both Hebbian and anti-Hebbian forms of competitive plasticity. In light of experiments the explored a variety of spike patterns, STDP models have been augmented to account for interactions between multiple pre- and postsynaptic action potentials. In chapter 4, I study the stability/competition interplay in three different proposed multi-spike models of STDP. I show that the "triplet model" leads to a partially steady-state distribution of synaptic weights and induces Hebbian competition. The "suppression model" develops a stable distribution of weights when the average weight is high and shows predominantly anti-Hebbian competition. The "NMDAR-based" model can lead to either stable or partially stable synaptic weight distribution and exhibits both Hebbian and anti-Hebbian competition, depending on the parameters. I conclude that multi-spike STDP models can produce radically different effects at the population level depending on how they implement multi-spike interactions
Analysis of Accelerometer Data from a Woven Inflatable Creep Burst Test
NASA Technical Reports Server (NTRS)
James, George H.; Grygier, Michael; Selig, Molly M.
2015-01-01
Accelerometers were used to montor an inflatable test article during a creep test to failure. The test article experienced impulse events that were classified based on the response of the sensors and their time-dependent manifestation. These impulse events required specialized techniques to process the structural dynamics data. However, certain phenomena were defined as worthy of additional study. An assessment of one phenomena (a frequency near 1000Hz) showed a time dependent frequency and an amplitude that increased significantly near the end of the test. Hence, these observations are expected to drive future understanding of and utility in inflatable space structures.
ERIC Educational Resources Information Center
Dubrow, Greg; Moseley, Bryan; Dustin, Daniel
2006-01-01
The term "mission creep" was originally coined nearly a hundred years ago to describe the gradual process by which a military mission's stated methods and goals change, and recently the term has been applied to incremental organizational changes. In this article, the term is used to describe what happens when a teaching-oriented college or…
Experimental Creep Life Assessment for the Advanced Stirling Convertor Heater Head
NASA Technical Reports Server (NTRS)
Krause, David L.; Kalluri, Sreeramesh; Shah, Ashwin R.; Korovaichuk, Igor
2010-01-01
The United States Department of Energy is planning to develop the Advanced Stirling Radioisotope Generator (ASRG) for the National Aeronautics and Space Administration (NASA) for potential use on future space missions. The ASRG provides substantial efficiency and specific power improvements over radioisotope power systems of heritage designs. The ASRG would use General Purpose Heat Source modules as energy sources and the free-piston Advanced Stirling Convertor (ASC) to convert heat into electrical energy. Lockheed Martin Corporation of Valley Forge, Pennsylvania, is integrating the ASRG systems, and Sunpower, Inc., of Athens, Ohio, is designing and building the ASC. NASA Glenn Research Center of Cleveland, Ohio, manages the Sunpower contract and provides technology development in several areas for the ASC. One area is reliability assessment for the ASC heater head, a critical pressure vessel within which heat is converted into mechanical oscillation of a displacer piston. For high system efficiency, the ASC heater head operates at very high temperature (850 C) and therefore is fabricated from an advanced heat-resistant nickel-based superalloy Microcast MarM-247. Since use of MarM-247 in a thin-walled pressure vessel is atypical, much effort is required to assure that the system will operate reliably for its design life of 17 years. One life-limiting structural response for this application is creep; creep deformation is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the deformation eventually results in creep rupture. Since creep material properties are not available in the open literature, a detailed creep life assessment of the ASC heater head effort is underway. This paper presents an overview of that creep life assessment approach, including the reliability-based creep criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also
Physical aging effects on the compressive linear viscoelastic creep of IM7/K3B composite
NASA Technical Reports Server (NTRS)
Veazie, David R.; Gates, Thomas S.
1995-01-01
An experimental study was undertaken to establish the viscoelastic behavior of 1M7/K3B composite in compression at elevated temperature. Creep compliance, strain recovery and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(g)). The IM7/K3B composite is a graphite reinforced thermoplastic polyimide with a T(g) of approximately 240 C. In a composite, the two matrix dominated compliance terms associated with time dependent behavior occur in the transverse and shear directions. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. Creep strain was converted to compliance and measured as a function of test time and aging time. Results included creep compliance master curves, physical aging shift factors and shift rates. The description of the unique experimental techniques required for compressive testing is also given.
Chen, Zhong-hua; Zhang, Su-xing; Long, Na; Lin, Li-shan; Chen, Tao; Zhang, Fei-peng; Lv, Xue-qin; Ye, Pei-zhen; Li, Ning; Zhang, Ke-zhi
2016-01-01
Aim: The substrate cocktail is frequently used to evaluate cytochrome P450 (CYP) enzyme-mediated drug interactions and potential interactions among the probe substrates. Here, we re-optimized the substrate cocktail method to increase the reliability and accuracy of screening for candidate compounds and expanded the method from a direct CYP inhibition assay to a time-dependent inhibition (TDI) assay. Methods: In the reaction mixtures containing human liver microsome (0.1 mg/mL), both the concentrations of a substrate cocktail (phenacetin for 1A2, coumarin for 2A6, bupropion for 2B6, diclofenac for 2C9, dextromethorphan for 2D6, and testosterone for 3A4) and the incubation time were optimized. Metabolites of the substrate probes were simultaneously analyzed by multiple-reaction monitoring (MRM) using a routine LC/MS/MS. Direct CYP inhibition was validated using 7 inhibitors (α-naphthoflavone, tranylcypromine, ticlopidine, fluconazole, quinidine, ketoconazole and 1-ABT). The time-dependent inhibition was partially validated with 5 inhibitors (ketoconazole, verapamil, quinidine, paroxetine and 1-ABT). Results: The inhibition curve profiles and IC50 values of 7 CYP inhibitors were approximate when a single substrate and the substrate cocktail were tested, and were consistent with the previously reported values. Similar results were obtained in the IC50 shifts of 5 inhibitors when a single substrate and the substrate cocktail were tested in the TDI assay. Conclusion: The 6-in-1 substrate cocktail (for 1A2, 2A6, 2B6, 2C9, 2D6 and 3A) is reliable for assessing CYP inhibition and time-dependent inhibition of drug candidates. PMID:27063220
Micromechanics of brittle creep and implications for the strength of the upper crust
NASA Astrophysics Data System (ADS)
Brantut, N.; Baud, P.; Heap, M. J.; Meredith, P. G.
2012-04-01
In the upper crust, the chemical influence of pore water or other aqueous solutions promotes time dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail at stresses far below their short-term failure strength, and even at constant applied stress ("brittle creep"). Here we present a new micromechanical model describing time dependent brittle creep of water-saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modelled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model of Ashby and Sammis (1990). Crack length evolution is computed from Charles' power law description of stress corrosion crack growth. The macroscopic strains and strain rates computed from the model are non-linear and compare well with experimental results obtained on granite, low porosity sandstone and basalt samples. Primary creep (decelerating strain rate) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain rate as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep, with apparently constant strain rate, arises as merely an inflexion between these two end-member phases. The strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature conditions, which provides an approximate creep law for the process. The creep law is used to infer the long term differential stress as a function of depth in the upper crust for tectonic loading rates: sub-critical cracking induces an offset of the rock strength, which is equivalent to a decrease in cohesion. For porous rocks, the competition between sub
Creep Deformation of Allvac 718Plus
Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam
2014-11-11
The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.
Creep Deformation of Allvac 718Plus
Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam
2014-11-11
The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics aremore » common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.« less
Dislocation Creep in Magnesium Calcite
NASA Astrophysics Data System (ADS)
Xu, L.; Xiao, X.; Evans, B. J.
2003-12-01
To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800° C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is ˜200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.
Tensile creep behavior of polycrystalline alumina fibers
NASA Technical Reports Server (NTRS)
Yun, H. M.; Goldsby, J. C.
1993-01-01
Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.
Exact solution of a quantum forced time-dependent harmonic oscillator
NASA Technical Reports Server (NTRS)
Yeon, Kyu Hwang; George, Thomas F.; Um, Chung IN
1992-01-01
The Schrodinger equation is used to exactly evaluate the propagator, wave function, energy expectation values, uncertainty values, and coherent state for a harmonic oscillator with a time dependent frequency and an external driving time dependent force. These quantities represent the solution of the classical equation of motion for the time dependent harmonic oscillator.
NASA Astrophysics Data System (ADS)
Jung, Katinka; Richter, J.; Kabrodt, K.; Lücke, I. M.; Schellenberg, I.; Herrling, Th.
2006-03-01
In the last decade, naturally occurring antioxidants continue to play an important role in the food-supplement industry. The content of antioxidants in a plant depends on the species, temperature, humidity, period of growth, harvest month, part of the plant used and many other variables. Herein, we present a new method able to determine the all over antioxidative power (AP) of plant extracts or lyophilised plant parts based on the reducing activity against a stable test radical. The method is performed by ESR spectroscopy and is based on the well-known 1,1-diphenyl-2-picryl-hydrazil (DPPH) method with the major difference that both the antioxidative capacity and the antioxidative activity are used to characterise an antioxidant. The resulting antioxidative power is expressed in antioxidative units (AU), where 1 AU corresponds to the activity of a 1 ppm solution of Vitamin C as a benchmark. This method allows a rapid, unexpensive and general applicable technique for the measurement of the antioxidative power of very different kinds of substances. The inclusion of the kinetic behaviour of the reducing process of the antioxidant for the determination of the AP allows the identification of the main antioxidant present in a sample. Herein, we present the application example of seeds, sprouts and adult parts of dandelion, amaranth, quinoa, fenugreek, broccoli, red clover and mugwort, where the AP method permits to characterise the plants with the highest antioxidant capacity and reaction velocity. The method permits to select active plant extracts for the food and nutrition industry.
Creep in Topopah Spring Member welded tuff. Yucca Mountain Site Characterization Project
Martin, R.J. III; Boyd, P.J.; Noel, J.S.; Price, R.H.
1995-06-01
A laboratory investigation has been carried out to determine the effects of elevated temperature and stress on the creep deformation of welded tuffs recovered from Busted Butte in the vicinity of Yucca Mountain, Nevada. Water saturated specimens of tuff from thermal/mechanical unit TSw2 were tested in creep at a confining pressure of 5.0 MPa, a pore pressure of 4.5 MPa, and temperatures of 25 and 250 C. At each stress level the load was held constant for a minimum of 2.5 {times} 10{sup 5} seconds and for as long as 1.8 {times} 10{sup 6} seconds. One specimen was tested at a single stress of 80 MPa and a temperature of 250 C. The sample failed after a short time. Subsequent experiments were initiated with an initial differential stress of 50 or 60 MPa; the stress was then increased in 10 MPa increments until failure. The data showed that creep deformation occurred in the form of time-dependent axial and radial strains, particularly beyond 90% of the unconfined, quasi-static fracture strength. There was little dilatancy associated with the deformation of the welded tuff at stresses below 90% of the fracture strength. Insufficient data have been collected in this preliminary study to determine the relationship between temperature, stress, creep deformation to failure, and total failure time at a fixed creep stress.
Development of a simplified procedure for rocket engine thrust chamber life prediction with creep
NASA Technical Reports Server (NTRS)
Badlani, M. L.; Porowski, J. S.; Odonnell, W. J.; Peterson, D. B.
1983-01-01
An analytical method for predicting engine thrust chamber life is developed. The method accounts for high pressure differentials and time-dependent creep effects both of which are significant in limiting the useful life of the shuttle main engine thrust chamber. The hot-gas-wall ligaments connecting adjacent cooling channels ribs and separating the coolant flow from the combustion gas are subjected to a high pressure induced primary stress superimposed on an alternating cyclic thermal strain field. The pressure load combined with strain-controlled cycling produces creep ratcheting and consequent bulging and thinning of these ligaments. This mechanism of creep-enhanced ratcheting is analyzed for determining the hot-gas-wall deformation and accumulated strain. Results are confirmed by inelastic finite element analysis. Fatigue and creep rupture damage as well as plastic tensile instability are evaluated as potential failure modes. It is demonstrated for the NARloy Z cases analyzed that when pressure differentials across the ligament are high, creep rupture damage is often the primary failure mode for the cycle times considered.
Effect of temperature on the time-dependent behavior of geomaterials
NASA Astrophysics Data System (ADS)
Zhang, Sheng; Xu, Shuo; Teng, Jidong; Xiong, Yonglin
2016-08-01
In many geotechnical engineering applications, such as nuclear waste disposal and geothermal extraction and storage, it is necessary to consider the long-term mechanical properties. The effect of temperature could have a complicated influence on the creep damage behavior of soft rock. As a consequence, it is meaningful, both in theory and in practice, to establish a constitutive model that can describe the creep damage behavior. Within the framework of continuum mechanics, a thermo-visco-elastoplastic model is proposed on the basis of a sub-loading Cam-clay model and the concept of equivalent stress. Triaxial creep tests under different confining pressures for Tage stone were conducted to validate the proposed model. The experimental results show that an optimum temperature exists for a certain stress state, and this temperature significantly slows down the creep damage rate. In addition, both the retarding and accelerating effects on creep rupture due to limited warming are observed for the same material, and this phenomenon can be predicted well by the proposed model. Finally, a parametric analysis is performed, and the influence of the material parameter on creep regularity is discussed in detail.
Perspectives for spintronics in 2D materials
NASA Astrophysics Data System (ADS)
Han, Wei
2016-03-01
The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
Modeling Creep Effects in Advanced SiC/SiC Composites
NASA Technical Reports Server (NTRS)
Lang, Jerry; DiCarlo, James
2006-01-01
Because advanced SiC/SiC composites are projected to be used for aerospace components with large thermal gradients at high temperatures, efforts are on-going at NASA Glenn to develop approaches for modeling the anticipated creep behavior of these materials and its subsequent effects on such key composite properties as internal residual stress, proportional limit stress, ultimate tensile strength, and rupture life. Based primarily on in-plane creep data for 2D panels, this presentation describes initial modeling progress at applied composite stresses below matrix cracking for some high performance SiC/SiC composite systems recently developed at NASA. Studies are described to develop creep and rupture models using empirical, mechanical analog, and mechanistic approaches, and to implement them into finite element codes for improved component design and life modeling
Proton Irradiation Creep in Pyrocarbon
Was, Gary S.; Campbell, Anne
2011-10-01
This project aims to understand irradiation creep in pyrocarbon using proton irradiation under controlled stresses and temperatures. Experiments will be conducted over a range of temperatures and stresses per the proposal submitted. The work scope will include the preparation of samples, measurement of deposition thickness, thickness uniformity, and anisotropy. The samples produced will be made in strips, which will be used for the creep experiments. Materials used will include pyrolytic carbon (PyC), Highly Oriented Pyrolytic Graphite (HOPG), or graphite strip samples in that order depending upon success. Temperatures tested under will range from 800°C to 1200°C, and stresses from 6MPa to 20.7MPa. Optional testing may occur at 900°C and 1100°C and stresses from 6MPa to 20.7MPa if funding is available.
Creep of Structural Nuclear Composites
Will Windes; R.W. Lloyd
2005-09-01
A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600º C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.
NASA Astrophysics Data System (ADS)
Cabriolu, Raffaela
Detecting any precursors of failure in Soft Matter Systems (SMS) is an inter-disciplinary topic with important applications (e.g. prediction of failure in engineering processes). Further, it provides an ideal benchmark to understand how mechanical stress and failure impacts the flow properties of amorphous condensed matter. Furthermore, some SMS are viscoelastic, flowing like viscous liquids or deforming like a solid according to applied forces. Often SMS are fragile and local rearrangements trigger catastrophic macroscopic failure. Despite the importance of the topic little is known on the local creep dynamics before the occurrence of such catastrophic events. To study creep and failure at an atomic/molecular level and at time scales that are not easily accessible by experiments we chose to carry out microscopic simulations. In this work we present the response of a colloidal system to uniaxial tensile stress applied and we compare our results to experimental works [8].
Quantitative 2D liquid-state NMR.
Giraudeau, Patrick
2014-06-01
Two-dimensional (2D) liquid-state NMR has a very high potential to simultaneously determine the absolute concentration of small molecules in complex mixtures, thanks to its capacity to separate overlapping resonances. However, it suffers from two main drawbacks that probably explain its relatively late development. First, the 2D NMR signal is strongly molecule-dependent and site-dependent; second, the long duration of 2D NMR experiments prevents its general use for high-throughput quantitative applications and affects its quantitative performance. Fortunately, the last 10 years has witnessed an increasing number of contributions where quantitative approaches based on 2D NMR were developed and applied to solve real analytical issues. This review aims at presenting these recent efforts to reach a high trueness and precision in quantitative measurements by 2D NMR. After highlighting the interest of 2D NMR for quantitative analysis, the different strategies to determine the absolute concentrations from 2D NMR spectra are described and illustrated by recent applications. The last part of the manuscript concerns the recent development of fast quantitative 2D NMR approaches, aiming at reducing the experiment duration while preserving - or even increasing - the analytical performance. We hope that this comprehensive review will help readers to apprehend the current landscape of quantitative 2D NMR, as well as the perspectives that may arise from it.
Compression creep of filamentary composites
NASA Technical Reports Server (NTRS)
Graesser, D. L.; Tuttle, M. E.
1988-01-01
Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis.
Controlling surface plasmon polaritons by a static and/or time-dependent external magnetic field
NASA Astrophysics Data System (ADS)
Kuzmiak, V.; Eyderman, S.; Vanwolleghem, M.
2012-07-01
We have demonstrated numerically by using of Fourier modal method (FMM) that the interface between a metal and a uniformly magnetized two-dimensional photonic crystal fabricated from a transparent dielectric magneto-optical (MO) material possesses a one-way frequency range in which a surface plasmon polariton (SPP) is allowed to propagate only in one direction. The time-reversal symmetry breaking is implied by the MO properties of the photonic crystal material, namely, bismuth iron garnet (BIG), which may be magnetically saturated by fields of the order of tens of milli tesla. The results obtained by FMM have been validated by a theoretical model and a standard plane-wave method that yield separately a nonreciprocal dispersion relation for the SPP and the band structure of the two-dimensional magneto-optical photonic crystal (2D MOPhC), respectively. These spectra represent the key characteristics assuring the functionality of the one-way waveguide associated with the both underlying mechanisms, namely, time-reversal symmetry breaking and a suppression of disorder-induced backscattering. By using a generalized finite-difference time-domain (FDTD) method, which allows studying the propagation of electromagnetic (EM) waves through media with a tensor MO permittivity, we studied transport properties of the one-way waveguide. We examined the influence of specific types of boundary conditions on one-way functionality in the presence of a static external magnetic field and have shown that the SPP can be dynamically controlled by applying a time-dependent magnetic field. By evaluating the Fourier transform of the energy density, we have analyzed the behavior of the field patterns observed in the waveguide in the case of ac magnetic field, and have interpreted new and interesting features associated with the redistribution of the EM field that may offer new mechanisms for dynamical control of SPP flow.
Experimental identification of diffusive coupling using 2D NMR.
Song, Y-Q; Carneiro, G; Schwartz, L M; Johnson, D L
2014-12-01
Spin relaxation based nuclear magnetic resonance (NMR) methods have been used extensively to determine pore size distributions in a variety of materials. This approach is based on the assumption that each pore is in the fast diffusion limit but that diffusion between pores can be neglected. However, in complex materials these assumptions may be violated and the relaxation time distribution is not easily interpreted. We present a 2D NMR technique and an associated data analysis that allow us to work directly with the time dependent experimental data without Laplace inversion to identify the signature of diffusive coupling between different pores. Measurements on microporous glass beads and numerical simulations are used to illustrate the technique. PMID:25526135
Empirical law for fault-creep events
Crough, S.T.; Burford, R.O.
1977-01-01
Fault-creep events measured on the San Andreas and related faults near Hollister, California, can be described by a rheological model consisting of a spring, power-law dashpotand sliding block connected in series. An empirical creep-event law, derived from many creep-event records analyzed within the constraints of the model, provides a remarkably simple and accurate representation of creep-event behavior. The empirical creep law is expressed by the equation: D(t)= Df [1-1/{ct(n-1)Dfn-1+1}/(n-1)] where D is the value of displacement at time t following the onset of an event, Df is the final equilibrium value of the event displacementand C is a proportionality constant. This discovery should help determine whether the time-displacement character of creep events is controlled by the material properties of fault gouge, or by other parameters. ?? 1977.
Cumulative creep damage for polycarbonate and polysulfone
NASA Technical Reports Server (NTRS)
Zhang, M.; Brinson, H. F.
1985-01-01
The literature for creep to failure cumulative damage laws are reviewed. Creep to failure tests performed on polycarbonate and polysulfone under single and two step loadings are discussed. A cumulative damage law or modified time fraction rule is developed using a power law for transient creep response as the starting point. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested.
NASA Astrophysics Data System (ADS)
Oberson, P. Gregory
Titanium alloys are used for many applications due to their desirable properties, including its high strength-to-weight ratio, corrosion resistance, and biocompatibility. Titanium alloys are used extensively for aerospace, chemical, nuclear, industrial, biomedical, and consumer applications. In many applications, titanium components may be subject to stresses for extended periods of time. It has long been known that single-phase hexagonally close-packed (HCP) alpha and body-centered cubic (BCC) beta titanium alloys deform over time, or creep, at low temperatures (<0.25*Tm). As such, creep is an important factor to consider when assessing the structural reliability of titanium components. However, the factors that affect creep behavior such as grain size and alloy chemistry and the deformation mechanisms associated with creep such as slip and twinning are not well understood. The aim of this investigation is to experimentally and theoretically study the creep deformation behavior of single-phase alpha and beta titanium alloys. The first part of the investigation concerns alpha-Ti alloys. The low temperature creep behavior was studied experimentally, using alpha-Ti-1.6wt.%V as the model alloy. Creep testing was performed at a range of temperatures and slip and twinning were identified as creep deformation mechanisms by optical, SEM and TEM microscopy. The activation energy for creep was measured for the first time for an alpha-Ti than deforms by twinning. The activation energy was found to increase as a function of creep strain, suggesting that there is a change in the predominant deformation mechanism from slip at low strain to twinning at high strain. The reason for this change is explained by a model for twin nucleation caused by dislocation pileups. The theoretical aspect of the study of alpha-Ti, concerns the phenomenon of slow twin growth (time-dependent twinning) during low temperature creep. This phenomenon is unusual and poorly understood as twins in bulk
Staring 2-D hadamard transform spectral imager
Gentry, Stephen M.; Wehlburg, Christine M.; Wehlburg, Joseph C.; Smith, Mark W.; Smith, Jody L.
2006-02-07
A staring imaging system inputs a 2D spatial image containing multi-frequency spectral information. This image is encoded in one dimension of the image with a cyclic Hadamarid S-matrix. The resulting image is detecting with a spatial 2D detector; and a computer applies a Hadamard transform to recover the encoded image.
Electrochemical control of creep in nanoporous gold
Ye, Xing-Long; Jin, Hai-Jun
2013-11-11
We have investigated the mechanical stability of nanoporous gold (npg) in an electrochemical environment, using in situ dilatometry and compression experiments. It is demonstrated that the gold nano-ligaments creep under the action of surface stress which leads to spontaneous volume contractions in macroscopic npg samples. The creep of npg, under or without external forces, can be controlled electrochemically. The creep rate increases with increasing potential in double-layer potential region, and deceases to almost zero when the gold surface is adsorbed with oxygen. Surprisingly, we also noticed a correlation between creep and surface diffusivity, which links the deformation of nanocrystals to mobility of surface atoms.
Creep Deformation of B2 Alumindes
NASA Technical Reports Server (NTRS)
Nathal, M. V.
1991-01-01
The creep resistance and elevated temperature deformation mechanisms in CoAl, FeAl, and NiAl are reviewed. The stress and temperature dependencies of the steady state creep rate, the primary creep behavior, the dislocation substructure, and the response during transient tests are used as the main indicators of the deformation processes. In single phase intermetallics, the influence of grain size, stoichiometry, and solid solution hardening have been examined. In addition, the effect of adding dispersoids, precipitates, and other types of reinforcements to improve creep strength are compared.
Model for transient creep of southeastern New Mexico rock salt
Herrmann, W; Wawersik, W R; Lauson, H S
1980-11-01
In a previous analysis, existing experimental data pertaining to creep tests on rock salt from the Salado formation of S.E. New Mexico were fitted to an exponential transient creep law. While very early time portions of creep strain histories were not fitted very well for tests at low temperatures and stresses, initial creep rates in particular generally being underestimated, the exponential creep law has the property that the transient creep strain approaches a finite limit with time, and is therefore desirable from a creep modelling point of view. In this report, an analysis of transient creep is made. It is found that exponential transient creep can be related to steady-state creep through a universal creep curve. The resultant description is convenient for creep analyses where very early time behavior is not important.
NASA Astrophysics Data System (ADS)
Kazil, J.; Kopp, E.
2001-12-01
The University of Bern Atmospheric Ion Model (UBAIM) is a time-dependent, pseudo-2D model of the ion chemistry in the earth atmosphere. It covers the latitudes between 85oS and 85oN and the (log-p) altitudes between 20 and 120km. On this grid, the system of differential equations describing the ion chemistry is integrated numerically until a dynamic equilibrium, governed by the diurnal changes in the incident radiation, is reached. Densities of main and minor atmospheric constituents are taken from the NCAR two-dimensional neutral SOCRATES model, the solar flux data are computed by the SOLAR2000 model. With this combination of models, it is possible to investigate the diurnal changes of the ion densities in the stratosphere, mesosphere, and lower thermosphere.
NASA Astrophysics Data System (ADS)
Vanaja, J.; Laha, Kinkar; Mathew, M. D.
2014-10-01
Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, , considering minimum creep rate instead of steady-state creep rate . The relationships between (i) rate of exhaustion of transient creep r' with minimum creep rate, (ii) rate of exhaustion of transient creep r' with time to reach minimum creep rate, and (iii) initial creep rate with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r' and minimum creep rate decreased, whereas the transient strain ɛ T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of with . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.
2D materials for nanophotonic devices
NASA Astrophysics Data System (ADS)
Xu, Renjing; Yang, Jiong; Zhang, Shuang; Pei, Jiajie; Lu, Yuerui
2015-12-01
Two-dimensional (2D) materials have become very important building blocks for electronic, photonic, and phononic devices. The 2D material family has four key members, including the metallic graphene, transition metal dichalcogenide (TMD) layered semiconductors, semiconducting black phosphorous, and the insulating h-BN. Owing to the strong quantum confinements and defect-free surfaces, these atomically thin layers have offered us perfect platforms to investigate the interactions among photons, electrons and phonons. The unique interactions in these 2D materials are very important for both scientific research and application engineering. In this talk, I would like to briefly summarize and highlight the key findings, opportunities and challenges in this field. Next, I will introduce/highlight our recent achievements. We demonstrated atomically thin micro-lens and gratings using 2D MoS2, which is the thinnest optical component around the world. These devices are based on our discovery that the elastic light-matter interactions in highindex 2D materials is very strong. Also, I would like to introduce a new two-dimensional material phosphorene. Phosphorene has strongly anisotropic optical response, which creates 1D excitons in a 2D system. The strong confinement in phosphorene also enables the ultra-high trion (charged exciton) binding energies, which have been successfully measured in our experiments. Finally, I will briefly talk about the potential applications of 2D materials in energy harvesting.
Internal Photoemission Spectroscopy of 2-D Materials
NASA Astrophysics Data System (ADS)
Nguyen, Nhan; Li, Mingda; Vishwanath, Suresh; Yan, Rusen; Xiao, Shudong; Xing, Huili; Cheng, Guangjun; Hight Walker, Angela; Zhang, Qin
Recent research has shown the great benefits of using 2-D materials in the tunnel field-effect transistor (TFET), which is considered a promising candidate for the beyond-CMOS technology. The on-state current of TFET can be enhanced by engineering the band alignment of different 2D-2D or 2D-3D heterostructures. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band alignments of various 2-D materials, in particular SnSe2 and WSe2, which have been proposed for new TFET designs. The metal-oxide-2-D semiconductor test structures are fabricated and characterized by IPE, where the band offsets from the 2-D semiconductor to the oxide conduction band minimum are determined by the threshold of the cube root of IPE yields as a function of photon energy. In particular, we find that SnSe2 has a larger electron affinity than most semiconductors and can be combined with other semiconductors to form near broken-gap heterojunctions with low barrier heights which can produce a higher on-state current. The details of data analysis of IPE and the results from Raman spectroscopy and spectroscopic ellipsometry measurements will also be presented and discussed.
NASA Astrophysics Data System (ADS)
Majorosi, Szilárd; Czirják, Attila
2016-11-01
We present a novel numerical method and algorithm for the solution of the 3D axially symmetric time-dependent Schrödinger equation in cylindrical coordinates, involving singular Coulomb potential terms besides a smooth time-dependent potential. We use fourth order finite difference real space discretization, with special formulae for the arising Neumann and Robin boundary conditions along the symmetry axis. Our propagation algorithm is based on merging the method of the split-operator approximation of the exponential operator with the implicit equations of second order cylindrical 2D Crank-Nicolson scheme. We call this method hybrid splitting scheme because it inherits both the speed of the split step finite difference schemes and the robustness of the full Crank-Nicolson scheme. Based on a thorough error analysis, we verified both the fourth order accuracy of the spatial discretization in the optimal spatial step size range, and the fourth order scaling with the time step in the case of proper high order expressions of the split-operator. We demonstrate the performance and high accuracy of our hybrid splitting scheme by simulating optical tunneling from a hydrogen atom due to a few-cycle laser pulse with linear polarization.
2D materials: to graphene and beyond.
Mas-Ballesté, Rubén; Gómez-Navarro, Cristina; Gómez-Herrero, Julio; Zamora, Félix
2011-01-01
This review is an attempt to illustrate the different alternatives in the field of 2D materials. Graphene seems to be just the tip of the iceberg and we show how the discovery of alternative 2D materials is starting to show the rest of this iceberg. The review comprises the current state-of-the-art of the vast literature in concepts and methods already known for isolation and characterization of graphene, and rationalizes the quite disperse literature in other 2D materials such as metal oxides, hydroxides and chalcogenides, and metal-organic frameworks.
NASA Astrophysics Data System (ADS)
Froger, Jean-Luc; Famin, Vincent; Cayol, Valérie; Augier, Aurélien; Michon, Laurent; Lénat, Jean-François
2015-04-01
From March 30 to May 1 2007, Piton de la Fournaise, La Réunion Island, experienced a major eruptive crisis, characterized by the largest emitted lava volume (210 × 106 m3) of the 20th and 21st centuries, and by a 340 m deep caldera collapse. The event was captured by InSAR data from the ENVISAT and ALOS-1 satellites. From this data, we computed the EW and vertical components of the displacement that occurred on the entire edifice during the co-eruptive period and in the following months. Our results reveal unusually large and time-dependent displacements of the Central Cone and the Eastern Flank of Piton de la Fournaise, both of which continued to deform for at least a year after the end of the eruption. The analysis of InSAR displacement combined with other geophysical and field observations allows us to propose conceptual models to explain the Central Cone and the Eastern Flank displacements. We propose that the April 2007 caldera collapse induced a sudden decompression of the hydrothermal system, which had been previously pressurized and heated by temporary sealing of its upper part. This sudden decompression resulted in a strong centripetal subsidence. This then decreased exponentially as poro-elastic compaction and creep of the Central Cone propagated from the collapsed rock column to more distal parts of the hydrothermal system. For the Eastern Flank, we propose that the displacement is related to an intrusion within the Grandes Pentes. While propagating to the surface, the intrusion may have encountered a pre-existing structural discontinuity, intruded it and activated it as a detachment surface. It is likely that the detachment slip, by reducing the minimum principal stress close to the summit, allowed the injection of the dyke that fed the brief March 30-31 eruption. Then it may have promoted the migration of magma from the main magma storage zone, beneath the Central Cone, to the distal April 2 eruption site. The EW extensional stress field resulting
Cumulative creep damage for polycarbonate and polysulfone
NASA Technical Reports Server (NTRS)
Zhang, M. J.; Straight, M. R.; Brinson, H. F.
1985-01-01
Creep to failure tests performed on polycarbonate and polysulfone under single and two step loadings are discussed. A cumulative damage law or modified time fraction rule is developed using a power law for transient creep response as the starting point. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested.
NASA Astrophysics Data System (ADS)
mallet, celine; quintal, beatriz; caspari, eva; holliger, klaus
2016-04-01
The seismic and hydraulic characterization of fractured rocks is an important objective for reservoir development in general and the production of geothermal energy in particular. The attenuation of seismic waves in saturated fractured media is governed by local displacements of the fluid relative to the solid induced by the compressions and extensions associated with the passing wavefield. This phenomenon is generally referred to as wave-induced fluid flow (WIFF). Recent evidence suggests that this energy dissipation mechanism is sensitive to the interconnectivity of the fractures, which offers the perspective of linking seismic observations to the hydraulic properties of fractured rocks. Here, we consider the results of laboratory experiments, which are referred to as creep tests. Such tests consist of applying a constant stress to a water-saturated thermally cracked glass sample and recording the resulting strain response as a function of time. The primary advantages of the considered material are (i) that the fracture network is well documented and (ii) that the homogeneous and non-porous glass matrix limits WIFF to the fracture network. Due to the high stress levels as well as other technical issues, creep tests are not commonly used for laboratory-based measurements of energy dissipation. Therefore, an objective of this study is to explore whether and to what extent such data can be interpreted in terms of the seismic attenuation characteristics of the probed samples, as this might open access to a vast reservoir of corresponding data, notably for cracked materials. Transforming the observed time-dependent stress-strain relation into the Fourier domain, allows us to infer the corresponding frequency-dependent attenuation characteristics, which we then seek to interpret through numerical simulations based on Biot's quasi-static poroelastic equations. The 2D geometry of the fracture network considered in these simulations is derived from a scanning electron
2-d Finite Element Code Postprocessor
1996-07-15
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forcesmore » along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.« less
Ginsparg, P.
1991-01-01
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Ginsparg, P.
1991-12-31
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
Creep-assisted slow crack growth in bio-inspired dental multilayers.
Du, Jing; Niu, Xinrui; Soboyejo, Wole
2015-06-01
Ceramic crown structures under occlusal contact are often idealized as flat multilayered structures that are deformed under Hertzian contact loading. Previous models treated each layer as linear elastic materials and resulted in differences between the measured and predicted critical loads. This paper examines the combined effects of creep (in the adhesive and substrate layers) and creep-assisted slow crack growth (in the ceramic layer) on the contact-induced deformation of bio-inspired, functionally graded multilayer (FGM) structures and the conventional tri-layers. The time-dependent moduli of each of the layers were determined from constant load creep tests. The resulting modulus-time characteristics were modeled using Prony series. These were then incorporated into a finite element model for the computation of stress distributions in the sub-surface regions of the top ceramic layer, in which sub-surface radial cracks, are observed as the clinical failure mode. The time-dependent stresses are incorporated into a slow crack growth (SCG) model that is used to predict the critical loads of the dental multilayers under Hertzian contact loading. The predicted loading rate dependence of the critical loads is shown to be consistent with experimental results. The implications of the results are then discussed for the design of robust dental multilayers.
First integrals for time-dependent higher-order Riccati equations by nonholonomic transformation
NASA Astrophysics Data System (ADS)
Guha, Partha; Ghose Choudhury, A.; Khanra, Barun
2011-08-01
We exploit the notion of nonholonomic transformations to deduce a time-dependent first integral for a (generalized) second-order nonautonomous Riccati differential equation. It is further shown that the method can also be used to compute the first integrals of a particular class of third-order time-dependent ordinary differential equations and is therefore quite robust.
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology. PMID:27478083
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology.
Creep resistant high temperature martensitic steel
Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.
2015-11-13
The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6 carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.
Irradiation creep of vanadium-base alloys
Tsai, H.; Billone, M.C.; Strain, R.V.; Smith, D.L.; Matsui, H.
1998-03-01
A study of irradiation creep in vanadium-base alloys is underway with experiments in the Advanced Test Reactor (ATR) and the High Flux Isotope Reactor (HFIR) in the United States. Test specimens are thin-wall sealed tubes with internal pressure loading. The results from the initial ATR irradiation at low temperature (200--300 C) to a neutron damage level of 4.7 dpa show creep rates ranging from {approx}0 to 1.2 {times} 10{sup {minus}5}/dpa/MPa for a 500-kg heat of V-4Cr-4Ti alloy. These rates were generally lower than reported from a previous experiment in BR-10. Because both the attained neutron damage levels and the creep strains were low in the present study, however, these creep rates should be regarded as only preliminary. Substantially more testing is required before a data base on irradiation creep of vanadium alloys can be developed and used with confidence.
Creep and relaxation behavior of Inconel-617
Osthoff, W.; Ennis, P.J.; Nickel, H.; Schuster, H.
1984-08-01
The static and dynamic creep behavior of Inconel alloy 617 has been determined in constant load creep tests, relaxation tests, and stress reduction tests in the temperature range 1023 to 1273 K. The results have been interpreted using the internal stress concept: The dependence of the internal stress on the applied stress and test temperature was determined. In a few experiments, the influence of cold deformation prior to the creep test on the magnitude of the internal stress was also investigated. It was found that the experimentally observed relaxation behavior could be more satisfactorily described using the Norton creep equation modified by incorporation of the internal stress than by the conventional Norton creep equation.
Yang, Li-Ming; Dornfeld, Matthew; Frauenheim, Thomas; Ganz, Eric
2015-10-21
We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.
2d index and surface operators
NASA Astrophysics Data System (ADS)
Gadde, Abhijit; Gukov, Sergei
2014-03-01
In this paper we compute the superconformal index of 2d (2, 2) supersymmetric gauge theories. The 2d superconformal index, a.k.a. flavored elliptic genus, is computed by a unitary matrix integral much like the matrix integral that computes the 4d superconformal index. We compute the 2d index explicitly for a number of examples. In the case of abelian gauge theories we see that the index is invariant under flop transition and under CY-LG correspondence. The index also provides a powerful check of the Seiberg-type duality for non-abelian gauge theories discovered by Hori and Tong. In the later half of the paper, we study half-BPS surface operators in = 2 super-conformal gauge theories. They are engineered by coupling the 2d (2, 2) supersymmetric gauge theory living on the support of the surface operator to the 4d = 2 theory, so that different realizations of the same surface operator with a given Levi type are related by a 2d analogue of the Seiberg duality. The index of this coupled system is computed by using the tools developed in the first half of the paper. The superconformal index in the presence of surface defect is expected to be invariant under generalized S-duality. We demonstrate that it is indeed the case. In doing so the Seiberg-type duality of the 2d theory plays an important role.
Squeezing in a 2-D generalized oscillator
NASA Technical Reports Server (NTRS)
Castanos, Octavio; Lopez-Pena, Ramon; Manko, Vladimir I.
1994-01-01
A two-dimensional generalized oscillator with time-dependent parameters is considered to study the two-mode squeezing phenomena. Specific choices of the parameters are used to determine the dispersion matrix and analytic expressions, in terms of standard hermite polynomials, of the wavefunctions and photon distributions.
Integrated Design Software Predicts the Creep Life of Monolithic Ceramic Components
NASA Technical Reports Server (NTRS)
1996-01-01
Significant improvements in propulsion and power generation for the next century will require revolutionary advances in high-temperature materials and structural design. Advanced ceramics are candidate materials for these elevated-temperature applications. As design protocols emerge for these material systems, designers must be aware of several innate features, including the degrading ability of ceramics to carry sustained load. Usually, time-dependent failure in ceramics occurs because of two different, delayedfailure mechanisms: slow crack growth and creep rupture. Slow crack growth initiates at a preexisting flaw and continues until a critical crack length is reached, causing catastrophic failure. Creep rupture, on the other hand, occurs because of bulk damage in the material: void nucleation and coalescence that eventually leads to macrocracks which then propagate to failure. Successful application of advanced ceramics depends on proper characterization of material behavior and the use of an appropriate design methodology. The life of a ceramic component can be predicted with the NASA Lewis Research Center's Ceramics Analysis and Reliability Evaluation of Structures (CARES) integrated design programs. CARES/CREEP determines the expected life of a component under creep conditions, and CARES/LIFE predicts the component life due to fast fracture and subcritical crack growth. The previously developed CARES/LIFE program has been used in numerous industrial and Government applications.
Creep fatigue life prediction for engine hot section materials (isotropic). Annual report
Moreno, V.; Nissley, D.; Lin, L.J.
1985-03-01
The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.
SIMULATIONS OF 2D AND 3D THERMOCAPILLARY FLOWS BY A LEAST-SQUARES FINITE ELEMENT METHOD. (R825200)
Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matri...
Second quantized scalar QED in homogeneous time-dependent electromagnetic fields
Kim, Sang Pyo
2014-12-15
We formulate the second quantization of a charged scalar field in homogeneous, time-dependent electromagnetic fields, in which the Hamiltonian is an infinite system of decoupled, time-dependent oscillators for electric fields, but it is another infinite system of coupled, time-dependent oscillators for magnetic fields. We then employ the quantum invariant method to find various quantum states for the charged field. For time-dependent electric fields, a pair of quantum invariant operators for each oscillator with the given momentum plays the role of the time-dependent annihilation and the creation operators, constructs the exact quantum states, and gives the vacuum persistence amplitude as well as the pair-production rate. We also find the quantum invariants for the coupled oscillators for the charged field in time-dependent magnetic fields and advance a perturbation method when the magnetic fields change adiabatically. Finally, the quantum state and the pair production are discussed when a time-dependent electric field is present in parallel to the magnetic field.
NASA Astrophysics Data System (ADS)
Gholamhoseini, Alireza
2016-03-01
Relatively little research has been reported on the time-dependent in-service behavior of composite concrete slabs with profiled steel decking as permanent formwork and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, and this has only recently been quantified. This paper presents the results of long-term laboratory tests on composite slabs subjected to both drying shrinkage and sustained loads. Based on laboratory measurements, a design model for the shrinkage strain profile through the thickness of a slab is proposed. The design model is based on some modifications to an existing creep and shrinkage prediction model B3. In addition, an analytical model is developed to calculate the time-dependent deflection of composite slabs taking into account the time-dependent effects of creep and shrinkage. The calculated deflections are shown to be in good agreement with the experimental measurements.
Non-Abelian Aharonov-Bohm effect with the time-dependent gauge fields
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz
2016-04-01
We investigate the non-Abelian Aharonov-Bohm (AB) effect for time-dependent gauge fields. We prove that the non-Abelian AB phase shift related to time-dependent gauge fields, in which the electric and magnetic fields are written in the adjoint representation of SU (N) generators, vanishes up to the first order expansion of the phase factor. Therefore, the flux quantization in a superconductor ring does not appear in the time-dependent Abelian or non-Abelian AB effect.
A TIME-DEPENDENT RADIATIVE MODEL FOR THE ATMOSPHERE OF THE ECCENTRIC EXOPLANETS
Iro, N.; Deming, L. D. E-mail: leo.d.deming@nasa.go
2010-03-20
We present a time-dependent radiative model for the atmosphere of extrasolar planets that takes into account the eccentricity of their orbit. In addition to the modulation of stellar irradiation by the varying planet-star distance, the pseudo-synchronous rotation of the planets may play a significant role. We include both of these time-dependent effects when modeling the planetary thermal structure. We investigate the thermal structure and spectral characteristics for time-dependent stellar heating for two highly eccentric planets. Finally, we discuss observational aspects for those planets suitable for Spitzer measurements and investigate the role of the rotation rate.
Time-dependent scalar fields in modified gravities in a stationary spacetime
NASA Astrophysics Data System (ADS)
Zhong, Yi; Gu, Bao-Ming; Wei, Shao-Wen; Liu, Yu-Xiao
2016-07-01
Most no-hair theorems involve the assumption that the scalar field is independent of time. Recently in Graham and Jha (Phys. Rev. D90: 041501, 2014) the existence of time-dependent scalar hair outside a stationary black hole in general relativity was ruled out. We generalize this work to modified gravities and non-minimally coupled scalar field with the additional assumption that the spacetime is axisymmetric. It is shown that in higher-order gravity such as metric f( R) gravity the time-dependent scalar hair does not exist. In Palatini f( R) gravity and the non-minimally coupled case the time-dependent scalar hair may exist.
Nonequilibrium itinerant-electron magnetism: A time-dependent mean-field theory
NASA Astrophysics Data System (ADS)
Secchi, A.; Lichtenstein, A. I.; Katsnelson, M. I.
2016-08-01
We study the dynamical magnetic susceptibility of a strongly correlated electronic system in the presence of a time-dependent hopping field, deriving a generalized Bethe-Salpeter equation that is valid also out of equilibrium. Focusing on the single-orbital Hubbard model within the time-dependent Hartree-Fock approximation, we solve the equation in the nonequilibrium adiabatic regime, obtaining a closed expression for the transverse magnetic susceptibility. From this, we provide a rigorous definition of nonequilibrium (time-dependent) magnon frequencies and exchange parameters, expressed in terms of nonequilibrium single-electron Green's functions and self-energies. In the particular case of equilibrium, we recover previously known results.
On the dynamics of a time-dependent mesoscopic LC circuit with a negative inductance
NASA Astrophysics Data System (ADS)
Pedrosa, I. A.; Nogueira, E.; Guedes, I.
2016-05-01
We discuss the problem of a mesoscopic LC circuit with a negative inductance ruled by a time-dependent Hermitian Hamiltonian. Classically, we find unusual expressions for the Faraday’s law and for the inductance of a solenoid. Quantum mechanically, we solve exactly the time-dependent Schrödinger equation through the Lewis and Riesenfeld invariant operator method and construct Gaussian wave packet solutions for this time-dependent LC circuit. We also evaluate the expectation values of the charge and the magnetic flux in these Gaussian states, their quantum fluctuations and the corresponding uncertainty product.
A Time-Dependent Radiative Model for the Atmosphere of the Eccentric Exoplanets
NASA Astrophysics Data System (ADS)
Iro, N.; Deming, L. D.
2010-03-01
We present a time-dependent radiative model for the atmosphere of extrasolar planets that takes into account the eccentricity of their orbit. In addition to the modulation of stellar irradiation by the varying planet-star distance, the pseudo-synchronous rotation of the planets may play a significant role. We include both of these time-dependent effects when modeling the planetary thermal structure. We investigate the thermal structure and spectral characteristics for time-dependent stellar heating for two highly eccentric planets. Finally, we discuss observational aspects for those planets suitable for Spitzer measurements and investigate the role of the rotation rate.
Davydov-Chaban Hamiltonian in presence of time-dependent potential
NASA Astrophysics Data System (ADS)
Sobhani, Hadi; Hassanabadi, Hassan
2016-09-01
In this article, we have investigated collective effects of atomic nuclei in presence of a time-dependent potential in Davydov-Chaban Hamiltonian. Since such potential has an explicit time-dependency, in order to obtain the wave function of considered system, we should face with time-dependent Schrödinger equation. Obtaining the wave function could be possible using Lewis-Riesenfeld dynamical invariant method. Appropriate dynamical invariant has been constructed after determining the wave functions and values, the wave function will obtain.
Irradiation creep of dispersion strengthened copper alloy
Pokrovsky, A.S.; Barabash, V.R.; Fabritsiev, S.A.
1997-04-01
Dispersion strengthened copper alloys are under consideration as reference materials for the ITER plasma facing components. Irradiation creep is one of the parameters which must be assessed because of its importance for the lifetime prediction of these components. In this study the irradiation creep of a dispersion strengthened copper (DS) alloy has been investigated. The alloy selected for evaluation, MAGT-0.2, which contains 0.2 wt.% Al{sub 2}O{sub 3}, is very similar to the GlidCop{trademark} alloy referred to as Al20. Irradiation creep was investigated using HE pressurized tubes. The tubes were machined from rod stock, then stainless steel caps were brazed onto the end of each tube. The creep specimens were pressurized by use of ultra-pure He and the stainless steel caps subsequently sealed by laser welding. These specimens were irradiated in reactor water in the core position of the SM-2 reactors to a fluence level of 4.5-7.1 x 10{sup 21} n/cm{sup 2} (E>0.1 MeV), which corresponds to {approx}3-5 dpa. The irradiation temperature ranged from 60-90{degrees}C, which yielded calculated hoop stresses from 39-117 MPa. A mechanical micrometer system was used to measure the outer diameter of the specimens before and after irradiation, with an accuracy of {+-}0.001 mm. The irradiation creep was calculated based on the change in the diameter. Comparison of pre- and post-irradiation diameter measurements indicates that irradiation induced creep is indeed observed in this alloy at low temperatures, with a creep rate as high as {approx}2 x 10{sup {minus}9}s{sup {minus}1}. These results are compared with available data for irradiation creep for stainless steels, pure copper, and for thermal creep of copper alloys.
NASA Astrophysics Data System (ADS)
Cortez, Jerónimo; Mena Marugán, Guillermo A.; Olmedo, Javier; Velhinho, José M.
2012-11-01
We consider the quantization of scalar fields in spacetimes such that, by means of a suitable scaling of the field by a time dependent function, the field equation can be regarded as that of a field with a time dependent mass propagating in an auxiliary ultrastatic static background. For Klein-Gordon fields, it is well known that there exist an infinite number of nonequivalent Fock representations of the canonical commutation relations and, therefore, of inequivalent quantum theories. A context in which this kind of ambiguities arises and prevents the derivation of robust results is, e.g., in the quantum analysis of cosmological perturbations. In these situations, typically, a suitable scaling of the field by a time dependent function leads to a description in an auxiliary static background, though the nonstationarity still shows up in a time dependent mass. For such a field description, and assuming the compactness of the spatial sections, we recently proved in three or less spatial dimensions that the criteria of a natural implementation of the spatial symmetries and of a unitary time evolution are able to select a unique class of unitarily equivalent vacua, and hence of Fock representations. In this work, we succeed to extend our uniqueness result to the consideration of all possible field descriptions that can be reached by a time dependent canonical transformation which, in particular, involves a scaling of the field by a function of time. These kinds of canonical transformations modify the dynamics of the system and introduce a further ambiguity in its quantum description, exceeding the choice of a Fock representation. Remarkably, for any compact spatial manifold in less than four dimensions, we show that our criteria eliminate any possible nontrivial scaling of the field other than that leading to the description in an auxiliary static background. Besides, we show that either no time dependent redefinition of the field momentum is allowed or, if this may
Orthotropic Piezoelectricity in 2D Nanocellulose
NASA Astrophysics Data System (ADS)
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-10-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V‑1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
Orthotropic Piezoelectricity in 2D Nanocellulose
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-01-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V−1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies. PMID:27708364
2D microwave imaging reflectometer electronics
Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.
2014-11-15
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
Optical modulators with 2D layered materials
NASA Astrophysics Data System (ADS)
Sun, Zhipei; Martinez, Amos; Wang, Feng
2016-04-01
Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this Review, we cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also take a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.
Kinematic hardening in creep of Zircaloy
NASA Astrophysics Data System (ADS)
Sedláček, Radan; Deuble, Dietmar
2016-10-01
Results of biaxial creep tests with stress changes on Zircaloy-2 tube samples are presented. A Hollomon-type viscoplastic strain hardening model is extended by the Armstrong-Frederic nonlinear kinematic hardening law, resulting in a mixed (i.e. isotropic and kinematic) strain hardening model. The creep tests with stress changes and similar tests published in the literature are simulated by the models. It is shown that introduction of the kinematic strain hardening in the viscoplastic strain hardening model is sufficient to describe the creep transients following stress drops, stress reversals and stress removals.
Prediction of creep of polymer concrete
Khristova, Yu.; Aniskevich, K.
1995-11-01
We studied the applicability of the phenomenological approach to the prediction of long-time creep of polymer concrete consisting of polyester binder with diabase filler and diabase aggregate. We discovered that the principles of temperature-time analogy, of moisture-time analogy, and of temperature-moisture-time analogy are applicable to the description of the diagrams of short-time creep and to the prediction of long-time creep of polymer concrete at different temperatures and constant moisture content of the material.
Thermodynamic approach to creep and plasticity
Loefstedt, R.
1997-06-01
A solid subjected to a small load distorts rapidly in the manner predicted by elasticity theory. On a much longer time scale, the solid will creep. This dissipative motion is an important consideration in the engineering design of, for example, aircraft engines, but the macroscopic equations of motion describing this deformation are based on empirical observations. The principles of thermodynamics specify the dissipative fluxes appropriate to the classical equations of elasticity, which include one, unique to solids, which describes creep. The thermodynamic theory is presented, and the insights into the underlying microscopic mechanisms of creep, gleaned from the macroscopic formalism, are also discussed. {copyright} {ital 1997} {ital The American Physical Society}
Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior
NASA Technical Reports Server (NTRS)
Tewari, S.N.
1995-01-01
Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.
NASA Technical Reports Server (NTRS)
Raj, S. V.; Pharr, G. M.
1989-01-01
Creep tests conducted on NaCl single crystals in the temperature range from 373 to 1023 K show that true steady state creep is obtained only above 873 K when the ratio of the applied stress to the shear modulus is less than or equal to 0.0001. Under other stress and temperature conditions, corresponding to both power law and exponential creep, the creep rate decreases monotonically with increasing strain. The transition from power law to exponential creep is shown to be associated with increases in the dislocation density, the cell boundary width, and the aspect ratio of the subgrains along the primary slip planes. The relation between dislocation structure and creep behavior is also assessed.
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials. PMID:25169938
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials.
On Noether's Theorem for the Invariant of the Time-Dependent Harmonic Oscillator
ERIC Educational Resources Information Center
Abe, Sumiyoshi; Itto, Yuichi; Matsunaga, Mamoru
2009-01-01
The time-dependent oscillator describing parametric oscillation, the concept of invariant and Noether's theorem are important issues in physics education. Here, it is shown how they can be interconnected in a simple and unified manner.
Time-dependent intensity and phase measurements of ultrashort laser pulses as short as 10 fs
DeLong, K.W.; Fittinghoff, D.N.; Ladera, C.L.; Trebino, R.; Taft, G.; Rundquist, A.; Murnane, M.M.; Kapteyn, H.C.; Christov, I.P.
1995-05-01
Frequency-Resolved Optical Gating (FROG) measures the time-dependent intensity and phase of an ultrashort laser pulse. Using FROG, we have tested theories for the operation of sub{minus}10 fs laser oscillators.
Experimental Quantum-Walk Revival with a Time-Dependent Coin
NASA Astrophysics Data System (ADS)
Xue, P.; Zhang, R.; Qin, H.; Zhan, X.; Bian, Z. H.; Li, J.; Sanders, Barry C.
2015-04-01
We demonstrate a quantum walk with time-dependent coin bias. With this technique we realize an experimental single-photon one-dimensional quantum walk with a linearly ramped time-dependent coin flip operation and thereby demonstrate two periodic revivals of the walker distribution. In our beam-displacer interferometer, the walk corresponds to movement between discretely separated transverse modes of the field serving as lattice sites, and the time-dependent coin flip is effected by implementing a different angle between the optical axis of half-wave plate and the light propagation at each step. Each of the quantum-walk steps required to realize a revival comprises two sequential orthogonal coin-flip operators, with one coin having constant bias and the other coin having a time-dependent ramped coin bias, followed by a conditional translation of the walker.
Experimental quantum-walk revival with a time-dependent coin.
Xue, P; Zhang, R; Qin, H; Zhan, X; Bian, Z H; Li, J; Sanders, Barry C
2015-04-10
We demonstrate a quantum walk with time-dependent coin bias. With this technique we realize an experimental single-photon one-dimensional quantum walk with a linearly ramped time-dependent coin flip operation and thereby demonstrate two periodic revivals of the walker distribution. In our beam-displacer interferometer, the walk corresponds to movement between discretely separated transverse modes of the field serving as lattice sites, and the time-dependent coin flip is effected by implementing a different angle between the optical axis of half-wave plate and the light propagation at each step. Each of the quantum-walk steps required to realize a revival comprises two sequential orthogonal coin-flip operators, with one coin having constant bias and the other coin having a time-dependent ramped coin bias, followed by a conditional translation of the walker. PMID:25910099
Time-dependent Pauli equation in the presence of the Aharonov-Bohm effect
Bouguerra, Y.; Bounames, A.; Maamache, M.; Saadi, Y.
2008-04-15
We use the Lewis-Riesenfeld theory to determine the exact form of the wavefunctions of a two-dimensional Pauli equation of a charged spin 1/2 particle with time-dependent mass and frequency in the presence of the Aharonov-Bohm effect and a two-dimensional time-dependent harmonic oscillator. We find that the irregular solution at the origin as well as the regular one contributes to the phase of the wavefunction.
Dynamic acoustics for the STAR-100. [computer algorithms for time dependent sound waves in jet
NASA Technical Reports Server (NTRS)
Bayliss, A.; Turkel, E.
1979-01-01
An algorithm is described to compute time dependent acoustic waves in a jet. The method differs from previous methods in that no harmonic time dependence is assumed, thus permitting the study of nonharmonic acoustical behavior. Large grids are required to resolve the acoustic waves. Since the problem is nonstiff, explicit high order schemes can be used. These have been adapted to the STAR-100 with great efficiencies and permitted the efficient solution of problems which would not be feasible on a scalar machine.
Performance of Time-Dependent Propensity Scores: A Pharmacoepidemiology Case Study
Ray, Wayne A.; Liu, Qi; Shepherd, Bryan E.
2014-01-01
Purpose Pharmacoepidemiologic studies of acute effects of episodic exposures often must control for many time-dependent confounders. Marginal structural models permit this and provide unbiased estimates when confounders are on the causal pathway. However, if causal pathway confounding is minimal, analyses with time-dependent propensity scores, calculated for time-periods defined by individual drug prescriptions, may have better efficiency. We justify time-dependent propensity scores and compare the performance of these methods in a case study from a previous investigation of the risk of medication toxicity death in current users of propoxyphene and hydrocodone, with both substantial time-dependent confounding and a large number of covariates. Methods The cohort included Tennessee Medicaid enrollees who filled a qualifying study opioid prescription between 1992 and 2007. We identified 22 time-dependent covariates that accounted for most of the confounding in the original study. We compared analyses with all covariates in the regression model with those based on time-dependent propensity scores and those from marginal structural models. Results We identified 489,008 persons with 1,771,295 propoxyphene and 4,088,754 hydrocodone prescriptions. The unadjusted HR (propoxyphene:hydrocodone) was 0.70 (95% CI, 0.46–1.07). Estimates from inclusion of all covariates in the model, time-dependent propensity score analysis with inverse probability of treatment weighting, and marginal structural models were 1.63 (1.04–2.57), 1.65 (1.01–2.72), and 1.64 (0.83–3.27), respectively. Findings varied little with use of alternative propensity score methods, time origin, or techniques for marginal structural model estimation. Conclusions Time-dependent propensity scores may be useful for pharmacoepidemiologic studies with time-varying exposures when causal pathway confounding is limited. PMID:25408360
The Numerical Solution of the Time-Dependent Nernst-Planck Equations
Cohen, H.; Cooley, J. W.
1965-01-01
Calculations are reported of the time-dependent Nernst-Planck equations for a thin permeable membrane between electrolytic solutions. Charge neutrality is assumed for the time-dependent case. The response of such a membrane system to step current input is measured in terms of the time and space changes in concentration, electrical potential, and effective conductance. The report also includes discussion of boundary effects that occur when charge neutrality does not hold in the steady-state case. PMID:14268950
Extending quantum control of time-independent systems to time-dependent systems
Wang Zhenyu; Liu Renbao
2011-06-15
We establish that if a scheme can control a time-independent system arbitrarily coupled to a generic finite bath over a short period of time T with control precision O(T{sup N+1}), it can also realize the control with the same order of precision on smoothly time-dependent systems. This result extends the validity of various universal dynamical control schemes to arbitrary analytically time-dependent systems.
Amplitude and phase representation of quantum invariants for the time-dependent harmonic oscillator
Fernandez Guasti, M.; Moya-Cessa, H.
2003-06-01
The correspondence between classical and quantum invariants is established. The Ermakov-Lewis quantum invariant of the time-dependent harmonic oscillator is translated from the coordinate and momentum operators into amplitude and phase operators. In doing so, Turski's phase operator as well as Susskind-Glogower operators are generalized to the time-dependent harmonic-oscillator case. A quantum derivation of the Manley-Rowe relations is shown as an example.
NASA Astrophysics Data System (ADS)
Heßelmann, Andreas; Görling, Andreas
2011-01-01
A recently introduced time-dependent exact-exchange (TDEXX) method, i.e., a response method based on time-dependent density-functional theory that treats the frequency-dependent exchange kernel exactly, is reformulated. In the reformulated version of the TDEXX method electronic excitation energies can be calculated by solving a linear generalized eigenvalue problem while in the original version of the TDEXX method a laborious frequency iteration is required in the calculation of each excitation energy. The lowest eigenvalues of the new TDEXX eigenvalue equation corresponding to the lowest excitation energies can be efficiently obtained by, e.g., a version of the Davidson algorithm appropriate for generalized eigenvalue problems. Alternatively, with the help of a series expansion of the new TDEXX eigenvalue equation, standard eigensolvers for large regular eigenvalue problems, e.g., the standard Davidson algorithm, can be used to efficiently calculate the lowest excitation energies. With the help of the series expansion as well, the relation between the TDEXX method and time-dependent Hartree-Fock is analyzed. Several ways to take into account correlation in addition to the exact treatment of exchange in the TDEXX method are discussed, e.g., a scaling of the Kohn-Sham eigenvalues, the inclusion of (semi)local approximate correlation potentials, or hybrids of the exact-exchange kernel with kernels within the adiabatic local density approximation. The lowest lying excitations of the molecules ethylene, acetaldehyde, and pyridine are considered as examples.
Linking the fractional derivative and the Lomnitz creep law to non-Newtonian time-varying viscosity
NASA Astrophysics Data System (ADS)
Pandey, Vikash; Holm, Sverre
2016-09-01
Many of the most interesting complex media are non-Newtonian and exhibit time-dependent behavior of thixotropy and rheopecty. They may also have temporal responses described by power laws. The material behavior is represented by the relaxation modulus and the creep compliance. On the one hand, it is shown that in the special case of a Maxwell model characterized by a linearly time-varying viscosity, the medium's relaxation modulus is a power law which is similar to that of a fractional derivative element often called a springpot. On the other hand, the creep compliance of the time-varying Maxwell model is identified as Lomnitz's logarithmic creep law, making this possibly its first direct derivation. In this way both fractional derivatives and Lomnitz's creep law are linked to time-varying viscosity. A mechanism which yields fractional viscoelasticity and logarithmic creep behavior has therefore been found. Further, as a result of this linking, the curve-fitting parameters involved in the fractional viscoelastic modeling, and the Lomnitz law gain physical interpretation.
Creep relaxation and fully reversible creep of foam core sandwich composites in seawater
NASA Astrophysics Data System (ADS)
de la Paz, Ismael; Shafiq, Basir
2015-12-01
Foam core sandwich composites were subjected to (i) creep to failure, (ii) cyclic creep-relaxation and (iii) fully reversible cyclic creep loading in seawater in order to mimic an actual ship hull's service lifetime scenario. The results indicate a strong dependence of lifetime on the mode of loading. A significant reduction in the overall life was observed under cyclic creep as compared with the conventional creep to failure. Creep relaxation (R=1) tests were performed at loading-relaxation periods of 24/24, 24/12, 24/6, 12/12 and 6/6 h, while the fully reversible (R=-1) creep tests were conducted at loading-reversed loading times of 36/36, 24/24, 12/12, 6/6, and 3/3 h. The results suggest that creep-relaxation lifetime characteristics depend predominantly on the relaxation time as opposed to loading times, i.e. longer relaxation periods lead to shorter life. Whereas, fully reversible creep appears to be dependent upon the number of reversals whereby, life is observed to reduce as the number of reversals increase. These significant observations are explained in terms of various possible paths to interface cell wall collapse. Modes of failure were predominantly indentation and core compression in the vicinity of the loading site.
Long-Term Creep and Creep Rupture Behavior of Woven Ceramic Matrix Composites
NASA Technical Reports Server (NTRS)
Haque, A.; Rahman, M.; Mach, A.; Jeelani, S.; Verrilli, Michael J. (Technical Monitor)
2001-01-01
Tensile creep behavior of SiC/SiNC ceramic matrix composites at elevated temperatures and at various stress levels have been investigated for turbine engine applications. The objective of this research is to present creep behavior of SiC/SiCN composites at stress levels above and below the monotonic proportional limit strength and predict the life at creep rupture conditions. Tensile creep-rupture tests were performed on an Instron 8502 servohydraulic testing machine at constant load conditions up to a temperature limit of 1000 C. Individual creep curves indicate three stages such as primary, secondary, and tertiary. The creep rate increased linearly at an early stage and then gradually became exponential at higher strains. The stress exponent and activation energy were also obtained at 700 and 1000 C. The specimen lifetime was observed to be 55 hrs at 121 MPa and at 700 C. The life span reduced to 35 hrs at 143 MPa and at 1000 C. Scanning electron microscopy observations revealed significant changes in the crystalline phases and creep damage development. Creep failures were accompanied by extensive fiber pullout, matrix cracking, and debonding along with fiber fracture. The creep data was applied to Time-Temperature-Stress superposition model and the Manson-Haferd parametric model for long-time life prediction.
Photodetachment of the H‑ ion in a linear time-dependent electric field
NASA Astrophysics Data System (ADS)
Wang, De-Hua; Chen, Zhaohang; Cheng, Shaohao
2016-10-01
Using the time-dependent closed orbit theory, we study the photodetachment of the H‑ ion in a linear time-dependent electric field for the first time. An analytical formula for calculating the time-dependent photodetachment cross section of this system has been put forward. It is found when the external electric field changes very slowly with time, there is only one closed orbit of the detached electron and the photodetachment cross section is quite stable. However, when the electric field changes quickly with time, three different types of closed orbits are found and the photodetachment cross section oscillates in a much more complex way. The connection of each type of closed orbit with the oscillatory structure in the photodetachment cross section is analyzed quantitatively. In addition, the photon energy and the laser field parameters can also have great influence on the time-dependent photodetachment cross section of this system. This study provides a clear and intuitive picture for the photodetachment dynamics of a negative ion in the presence of a time-dependent electric field and may guide future experimental studies exploring the quantum effect in the photodetachment dynamics of negative ions from a time-dependent viewpoint.
Understanding the Origins of Time-Dependent Inhibition by Polypeptide Deformylase Inhibitors
Totoritis, Rachel; Duraiswami, Chaya; Taylor, Amy N.; Kerrigan, John J.; Campobasso, Nino; Smith, Katherine J.; Ward, Paris; King, Bryan W.; Murrayz-Thompson, Monique; Jones, Amber D.; Van Aller, Glenn S.; Aubart, Kelly M.; Zalacain, Magdalena; Thrall, Sara H.; Meek, Thomas D.; Schwartz, Benjamin
2012-03-15
The continual bacterial adaptation to antibiotics creates an ongoing medical need for the development of novel therapeutics. Polypeptide deformylase (PDF) is a highly conserved bacterial enzyme, which is essential for viability. It has previously been shown that PDF inhibitors represent a promising new area for the development of antimicrobial agents, and that many of the best PDF inhibitors demonstrate slow, time-dependent binding. To improve our understanding of the mechanistic origin of this time-dependent inhibition, we examined in detail the kinetics of PDF catalysis and inhibition by several different PDF inhibitors. Varying pH and solvent isotope led to clear changes in time-dependent inhibition parameters, as did inclusion of NaCl, which binds to the active site metal of PDF. Quantitative analysis of these results demonstrated that the observed time dependence arises from slow binding of the inhibitors to the active site metal. However, we also found several metal binding inhibitors that exhibited rapid, non-time-dependent onset of inhibition. By a combination of structural and chemical modification studies, we show that metal binding is only slow when the rest of the inhibitor makes optimal hydrogen bonds within the subsites of PDF. Both of these interactions between the inhibitor and enzyme were found to be necessary to observe time-dependent inhibition, as elimination of either leads to its loss.
An MHD simulation model of time-dependent co-rotating solar wind
NASA Astrophysics Data System (ADS)
Hayashi, K.
2012-08-01
We present a treatment of observation-based time-dependent boundary conditions for the inner boundary sphere in the time-dependent three-dimensional MHD simulations of the global solar wind. With this boundary treatment, we obtain super-Alfvenic MHD solutions of time-dependent co-rotating solar wind structures. The boundary variables on the inner boundary sphere, at 50 solar radii in this study, are assumed to change linearly from one instant to the next. A new feature is that, in order to maintain the divergence-free condition of the magnetic field, the changes of the time-dependent boundary magnetic field are expressed as the potential field in a thin shell volume. The solar magnetic field data from the Wilcox Solar Observatory (WSO) and the solar wind speed data from the interplanetary scintillation (IPS) observations at Nagoya University, Japan, are used as the input boundary data. The solar wind simulated with the time-dependent boundary condition is compared with the near-Earth and Ulysses in situ measurement data and the solar wind simulated with the fixed boundary condition over a 7-month period in 1991. Reasonable agreements with the in situ measurements are obtained. The differences between the two simulations in the interplanetary field line paths are significant. The three-dimensional time-dependent MHD solution of the global solar wind will help enhance space weather models and other fields in heliophysics.
A time-dependent probabilistic seismic-hazard model for California
Cramer, C.H.; Petersen, M.D.; Cao, T.; Toppozada, Tousson R.; Reichle, M.
2000-01-01
For the purpose of sensitivity testing and illuminating nonconsensus components of time-dependent models, the California Department of Conservation, Division of Mines and Geology (CDMG) has assembled a time-dependent version of its statewide probabilistic seismic hazard (PSH) model for California. The model incorporates available consensus information from within the earth-science community, except for a few faults or fault segments where consensus information is not available. For these latter faults, published information has been incorporated into the model. As in the 1996 CDMG/U.S. Geological Survey (USGS) model, the time-dependent models incorporate three multisegment ruptures: a 1906, an 1857, and a southern San Andreas earthquake. Sensitivity tests are presented to show the effect on hazard and expected damage estimates of (1) intrinsic (aleatory) sigma, (2) multisegment (cascade) vs. independent segment (no cascade) ruptures, and (3) time-dependence vs. time-independence. Results indicate that (1) differences in hazard and expected damage estimates between time-dependent and independent models increase with decreasing intrinsic sigma, (2) differences in hazard and expected damage estimates between full cascading and not cascading are insensitive to intrinsic sigma, (3) differences in hazard increase with increasing return period (decreasing probability of occurrence), and (4) differences in moment-rate budgets increase with decreasing intrinsic sigma and with the degree of cascading, but are within the expected uncertainty in PSH time-dependent modeling and do not always significantly affect hazard and expected damage estimates.
Time-Dependent Effects of Prognostic Factors in Advanced Gastric Cancer Patients
Kwon, Jin-Ok; Min, Jae-Seok; Kim, Min-Suk; Lee, Hae-Won; Park, Sunhoo; Yu, Hang-Jong; Bang, Ho-Yoon; Lee, Jong-Inn
2015-01-01
Purpose This study aimed to identify time-dependent prognostic factors and demonstrate the time-dependent effects of important prognostic factors in patients with advanced gastric cancer (AGC). Materials and Methods We retrospectively evaluated 3,653 patients with AGC who underwent curative standard gastrectomy between 1991 and 2005 at the Korea Cancer Center Hospital. Multivariate survival analysis with Cox proportional hazards regression was used in the analysis. A non-proportionality test based on the Schoenfeld residuals (also known as partial residuals) was performed, and scaled Schoenfeld residuals were plotted over time for each covariate. Results The multivariate analysis revealed that sex, depth of invasion, metastatic lymph node (LN) ratio, tumor size, and chemotherapy were time-dependent covariates violating the proportional hazards assumption. The prognostic effects (i.e., log of hazard ratio [LHR]) of the time-dependent covariates changed over time during follow-up, and the effects generally diminished with low slope (e.g., depth of invasion and tumor size), with gentle slope (e.g., metastatic LN ratio), or with steep slope (e.g., chemotherapy). Meanwhile, the LHR functions of some covariates (e.g., sex) crossed the zero reference line from positive (i.e., bad prognosis) to negative (i.e., good prognosis). Conclusions The time-dependent effects of the prognostic factors of AGC are clearly demonstrated in this study. We can suggest that time-dependent effects are not an uncommon phenomenon among prognostic factors of AGC. PMID:26819803
Time-dependent plane-wave spectrum representations for radiation from volume source distributions
NASA Astrophysics Data System (ADS)
Heyman, Ehud
1996-02-01
A new time-domain spectral theory for radiation from a time-dependent source distribution, is presented. The full spectral representation is based on a Radon transform of the source distribution in the four-dimensional space-time domain and consists of time-dependent plane waves that propagate in all space directions and with all (spectral) propagation speeds vκ. This operation, termed the slant stack transform, involves projection of the time-dependent source distribution along planes normal to the spectral propagation direction and stacking them with a progressive delay corresponding to the spectral propagation speed vκ along this direction. Outside the source domain, this three-fold representation may be contracted into a two-fold representation consisting of time-dependent plane waves that satisfy the spectral constraint vκ=c with c being the medium velocity. In the two-fold representation, however, the complete spectral representation involves both propagating time-dependent plane waves and evanescent time-dependent plane waves. We explore the separate role of these spectral constituents in establishing the causal field, and determine the space-time regions where the field is described only by the propagating spectrum. The spectral theory is presented here for scalar wave fields, but it may readily be extended to vector electromagnetic fields.
NASA Astrophysics Data System (ADS)
Lode, Axel U. J.; Bruder, Christoph
2016-07-01
We apply the multiconfigurational time-dependent Hartree method for indistinguishable particles (MCTDH-X) to systems of bosons or fermions in lattices described by Hubbard-type Hamiltonians with long-range or short-range interparticle interactions. The wave function is expanded in a variationally optimized time-dependent many-body basis generated by a set of effective creation operators that are related to the original particle creation operators by a time-dependent unitary transform. We use the time-dependent variational principle for the coefficients of this transform and the expansion coefficients of the wave function expressed in the time-dependent many-body basis as variational parameters to derive equations of motion. The convergence of MCTDH-X is shown by comparing its results to the exact diagonalization of one-, two-, and three-dimensional lattices filled with bosons with contact interactions. We use MCTDH-X to study the buildup of correlations in the long-time splitting dynamics of a Bose-Einstein condensate loaded into a large two-dimensional lattice subject to a barrier that is ramped up in the center. We find that the system is split into two parts with emergent time-dependent correlations that depend on the ramping time—for most barrier-raising times the system becomes twofold fragmented, but for some of the very fast ramps, the system shows revivals of coherence.
Tensile creep and creep-recovery behavior of a SiC-fiber-Si3N4-matrix composite
NASA Technical Reports Server (NTRS)
Holmes, John W.; Park, Yong H.; Jones, J. W.
1993-01-01
The tensile creep and creep-recovery behavior of a hot-pressed unidirectional SiC-fiber/Si3N4-matrix composite was investigated at 1200 C in air, in order to determine how various sustained and cyclic creep loading histories would influence the creep rate, accumulated creep strain, and the amount of strain recovered upon specimen unloading. The data accumulated indicate that the fundamental damage mode for sustained tensile creep at stresses of 200 and 250 MPa was periodic fiber fracture and that the creep life and the failure mode at 250 MPa were strongly influenced by the rate at which the initial creep stress was applied. Cyclic loading significantly lowered the duration of primary creep and the overall creep-strain accumulation. The implications of the results for microstructural and component design are discussed.
Parallel stitching of 2D materials
Ling, Xi; Wu, Lijun; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; et al
2016-01-27
Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. Lastly, the methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Parallel Stitching of 2D Materials.
Ling, Xi; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; Hsu, Allen L; Bie, Yaqing; Lee, Yi-Hsien; Zhu, Yimei; Wu, Lijun; Li, Ju; Jarillo-Herrero, Pablo; Dresselhaus, Mildred; Palacios, Tomás; Kong, Jing
2016-03-23
Diverse parallel stitched 2D heterostructures, including metal-semiconductor, semiconductor-semiconductor, and insulator-semiconductor, are synthesized directly through selective "sowing" of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Rate and time dependent behavior of structural adhesives. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Renieri, M. P.; Herakovich, C. T.; Brinson, H. F.
1976-01-01
Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having applications in the bonding of composite materials are presented. Constitutive equations capable of describing changes in material behavior with strain rate are derived from various theoretical approaches. It is shown that certain unique relationships exist between these approaches. It is also shown that the constitutive equation derived from mechanical models can be used for creep and relaxation loading. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Loading-unloading results are presented and are shown to correlate well with the proposed form of the loading-unloading equations for the modified Bingham model. Experimental results obtained for relaxation tests above and below the glass transition temperature are presented. It is shown that the adhesives obey the time-temperature superposition principle.
Creep behavior of niobium alloy PWC-11
NASA Technical Reports Server (NTRS)
Titran, R. H.; Moore, T. J.; Grobstein, T. L.
1987-01-01
The high vacuum creep and creep-rupture behavior of a Nb-1Zr-.1C alloy (PWC 11) was investigated at 1350 and 1400 K with an applied stress of 40 MPa. The material was tested in the following four conditions: annealed (1 hr 1755 K/2 hr 1475 K); annealed plus EB welded; annealed plus aged for 1000 hr at 1350 or 1400 K; and annealed, welded, and aged. It was found that the material in the annealed state was the most creep-resistant condition tested, and that aging the alloy for 1000 hr without an applied stress greatly reduced that strength; however, it was still approximately three times as creep resistant as Nb-1Zr. Additionally, the EB weld region was stronger than the base metal in each condition tested, and phase extraction of the dispersed precipitate revealed the presence of a 70%ZrC-30%NbC cubic monocarbide phase.
Creep-fatigue of low cobalt superalloys
NASA Technical Reports Server (NTRS)
Halford, G. R.
1982-01-01
Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.
Modeling Stepped Leaders Using a Time Dependent Multi-dipole Model and High-speed Video Data
NASA Astrophysics Data System (ADS)
Karunarathne, S.; Marshall, T.; Stolzenburg, M.; Warner, T. A.; Orville, R. E.
2012-12-01
In summer of 2011, we collected lightning data with 10 stations of electric field change meters (bandwidth of 0.16 Hz - 2.6 MHz) on and around NASA/Kennedy Space Center (KSC) covering nearly 70 km × 100 km area. We also had a high-speed video (HSV) camera recording 50,000 images per second collocated with one of the electric field change meters. In this presentation we describe our use of these data to model the electric field change caused by stepped leaders. Stepped leaders of a cloud to ground lightning flash typically create the initial path for the first return stroke (RS). Most of the time, stepped leaders have multiple complex branches, and one of these branches will create the ground connection for the RS to start. HSV data acquired with a short focal length lens at ranges of 5-25 km from the flash are useful for obtaining the 2-D location of these multiple branches developing at the same time. Using HSV data along with data from the KSC Lightning Detection and Ranging (LDAR2) system and the Cloud to Ground Lightning Surveillance System (CGLSS), the 3D path of a leader may be estimated. Once the path of a stepped leader is obtained, the time dependent multi-dipole model [ Lu, Winn,and Sonnenfeld, JGR 2011] can be used to match the electric field change at various sensor locations. Based on this model, we will present the time-dependent charge distribution along a leader channel and the total charge transfer during the stepped leader phase.
Analysis of shell-type structures subjected to time-dependent mechanical and thermal loading
NASA Technical Reports Server (NTRS)
Simitses, G. J.; Riff, R.
1987-01-01
A general mathematical model and solution methodologies for analyzing structural response of thin, metallic shell-type structures under large transient, cyclic, or static thermomechanical loads are developed. Among the system responses, which are associated with these load conditions, are thermal buckling, creep buckling and ratcheting. Thus, geometric as well as material type nonlinearities (of high order) can be anticipated and must be considered in the development of the mathematical model. Furthermore, this must also be accommodated in the solution procedures.
Analysis of shell-type structures subjected to time-dependent mechanical and thermal loading
NASA Technical Reports Server (NTRS)
Simitses, G. J.; Carlson, R. L.; Riff, R.
1987-01-01
A general mathematical model and solution methodologies are being developed for analyzing structural response of thin, metallic shell-type structures under large transient, cyclic, or static thermomechanical loads. Among the system responses, which were associated with these load conditions, were thermal buckling, creep buckling, and ratcheting. Thus, geometric as well as material-type nonlinearities (of high order) can be anticipated and must be considered in the development of the mathematical model. Furthermore, this must also be accommodated in the solution process.
Analysis of shell type structures subjected to time dependent mechanical and thermal loading
NASA Technical Reports Server (NTRS)
Simitses, G. J.; Carlson, R. L.; Riff, R.
1985-01-01
A general mathematical model and solution methodologies for analyzing structural response of thin, metallic shell-type structures under large transient, cyclic or static thermomechanical loads is considered. Among the system responses, which are associated with these load conditions, are thermal buckling, creep buckling and ratchetting. Thus, geometric as well as material-type nonlinearities (of high order) can be anticipated and must be considered in the development of the mathematical model.
C programs for solving the time-dependent Gross-Pitaevskii equation in a fully anisotropic trap
NASA Astrophysics Data System (ADS)
Vudragović, Dušan; Vidanović, Ivana; Balaž, Antun; Muruganandam, Paulsamy; Adhikari, Sadhan K.
2012-09-01
We present C programming language versions of earlier published Fortran programs (Muruganandam and Adhikari (2009) [1]) for calculating both stationary and non-stationary solutions of the time-dependent Gross-Pitaevskii (GP) equation. The GP equation describes the properties of dilute Bose-Einstein condensates at ultra-cold temperatures. C versions of programs use the same algorithms as the Fortran ones, involving real- and imaginary-time propagation based on a split-step Crank-Nicolson method. In a one-space-variable form of the GP equation, we consider the one-dimensional, two-dimensional, circularly-symmetric, and the three-dimensional spherically-symmetric harmonic-oscillator traps. In the two-space-variable form, we consider the GP equation in two-dimensional anisotropic and three-dimensional axially-symmetric traps. The fully-anisotropic three-dimensional GP equation is also considered. In addition to these twelve programs, for six algorithms that involve two and three space variables, we have also developed threaded (OpenMP parallelized) programs, which allow numerical simulations to use all available CPU cores on a computer. All 18 programs are optimized and accompanied by makefiles for several popular C compilers. We present typical results for scalability of threaded codes and demonstrate almost linear speedup obtained with the new programs, allowing a decrease in execution times by an order of magnitude on modern multi-core computers. New version program summary Program title: GP-SCL package, consisting of: (i) imagtime1d, (ii) imagtime2d, (iii) imagtime2d-th, (iv) imagtimecir, (v) imagtime3d, (vi) imagtime3d-th, (vii) imagtimeaxial, (viii) imagtimeaxial-th, (ix) imagtimesph, (x) realtime1d, (xi) realtime2d, (xii) realtime2d-th, (xiii) realtimecir, (xiv) realtime3d, (xv) realtime3d-th, (xvi) realtimeaxial, (xvii) realtimeaxial-th, (xviii) realtimesph. Catalogue identifier: AEDU_v2_0. Program Summary URL: http://cpc.cs.qub.ac.uk/summaries/AEDU_v2_0.html
Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions
Julian K. Benz; Richard N. Wright
2013-10-01
The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650
A creep-rupture model of filament-wound spherical pressure vessels
NASA Technical Reports Server (NTRS)
Dozier, Jan D.; Hackett, Robert M.
1987-01-01
The creep-rupture model is that of a quasi-isotropic filament-wound spherical pressure vessel, subjected to internal pressurization. The matrix material of the composite system is assumed to be linearly viscoelastic. Internal damage resulting from the relaxation of the matrix and the corresponding increase in microcracks is represented by a functional relationship between circumferential strain and transverse modulus. The numerical solution to this nonlinear problem is an iterative technique, whereby the elastic-viscoelastic correspondence principle is employed. In the Laplace domain, the associated elastic solution is obtained and this solution is inverted by the multidata method to yield the time-dependent solution.
Saxena, A.; Stock, S.R.
1990-04-15
Objective of this 3-y study was to conduct creep and creep-fatigue crack growth experiments and to characterize the crack tip damage mechanisms in a model material (Cu-1wt%Sb), which is known to cavitate at grain boundaries under creep deformation. Results were: In presence of large scale cavitation damage and crack branching, time rate of creep crack growth da/dt does not correlate with C{sub t} or C{sup *}. When cavitation damage is constrained, da/dt is characterized by C{sub t}. Area fraction of grain boundary cavitated is the single damage parameter for the extent of cavitation damage ahead of crack tips. C{sub t} is used for the creep-fatigue crack growth behavior. In materials prone to rapid cavity nucleation, creep cracks grow faster initially and then reach a steady state whose growth rate is determined by C{sub t}. Percent creep life exhausted correlates with average cavity diameter and fraction of grain boundary area occupied by cavities. Synchrotron x-ray tomographic microscopy was used to image individual cavities in Cu-1wt% Sb. A methodology was developed for predicting the remaining life of elevated temperature power plant components; (C{sub t}){sub avg} was used to correlate creep-fatigue crack growth in Cr-Mo and Cr-Mo-V steel and weldments.
Review of recent irradiation-creep results
Coghlan, W.A.
1982-05-01
Materials deform faster under stress in the presence of irradiation by a process known as irradiation creep. This phenomenon is important to reactor design and has been the subject of a large number of experimental and theoretical investigations. The purpose of this work is to review the recent experimental results to obtain a summary of these results and to determine those research areas that require additional information. The investigations have been classified into four subgroups based on the different experimental methods used. These four are: (1) irradiation creep using stress relaxation methods, (2) creep measurements using pressurized tubes, (3) irradiation creep from constant applied load, and (4) irradiation creep experiments using accelerated particles. The similarity and the differences of the results from these methods are discussed and a summary of important results and suggested areas for research is presented. In brief, the important results relate to the dependence of creep on swelling, temperature, stress state and alloying additions. In each of these areas new results have been presented and new questions have arisen which require further research to answer. 65 references.
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials. PMID:26861346
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology.
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.
Stochastic Inversion of 2D Magnetotelluric Data
Chen, Jinsong
2010-07-01
The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function is explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows