Vacancy Diffusion with Time-Dependent Length Scale: An Insightful New Model for Physical Aging in Polymers

2010 ◽  
Vol 49 (23) ◽  
pp. 12119-12124 ◽  
Author(s):  
Aaron W. Thornton ◽  
Anita J. Hill
Keyword(s):  
Physical Aging ◽  
Time Dependent ◽  
Length Scale ◽  
Vacancy Diffusion ◽  
New Model

Application of a Viscoelastic Model for Polyester Mooring

2010 ◽  
Author(s):  
J. W. Kim ◽  
J. H. Kyoung ◽  
A. Sablok
Keyword(s):  
Material Properties ◽  
Viscoelastic Model ◽  
Practical Method ◽  
Time Dependent ◽  
Mooring Line ◽  
New Model ◽  
Global Performance ◽  
Excitation Period ◽  
Linear Viscoelastic ◽  
Floating Platforms

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.

Boundary Layers on Characteristic Surfaces for Time-Dependent Rotating Flows

1983 ◽  
Vol 50 (2) ◽  
pp. 251-254 ◽  
Author(s):  
R. F. Gans
Keyword(s):  
Boundary Layers ◽  
Kinematic Viscosity ◽  
Normal Component ◽  
Rotating Flows ◽  
Rotation Vector ◽  
Time Dependent ◽  
Normal Vector ◽  
Length Scale ◽  
Rotation Vectors ◽  
Typical Length

Time-dependent motion of a fluid in a container rotating at Ω is characterized by boundary layers on the container surfaces if ν/Ω, where ν denotes kinematic viscosity, is small compared to the square of a typical length of the container. Let the frequency of the motion, measured in a corotating coordinate system, be ωΩ. If ω ~ 1, then the length scale of the boundary layer is (ν/Ω)1/2, unless |ω| is equal to twice the normal component of the unit rotation vector. If |ω| does equal twice the normal component of the unit rotation vector, scales of (ν/ΩL2)1/3 L and (ν/ΩL2)1/4 L are possible. If the normal vector and rotation vectors are parallel, the former scale vanishes.

ENTROPY OF A NONSTATIC BLACK HOLE

2000 ◽  
Vol 15 (28) ◽  
pp. 1739-1747 ◽  
Author(s):  
LI XIANG ◽  
ZHAO ZHENG
Keyword(s):  
Black Hole ◽  
Black Hole Entropy ◽  
Time Dependent ◽  
Brick Wall ◽  
Two Dimensional ◽  
De Sitter ◽  
Wall Model ◽  
New Model ◽  
Brick Wall Model ◽  
Dynamical Degrees

We point out that the brick-wall model cannot be applied to the nonstatic black hole. In the case of a static hole, we propose a new model where the black hole entropy is attributed to the dynamical degrees of the field covering the two-dimensional membrane just outside the horizon. A cutoff different from the model of 't Hooft is necessarily introduced. It can be treated as an increase in horizon because of the space–time fluctuations. We also apply our model to the nonequilibrium and nonstatic cases, such as Schwarzschild–de Sitter and Vaidya space–times. In the nonstatic case, the entropy relies on a time-dependent cutoff.

scholarly journals New models for the time dependent toxicity of individual and combined toxicants

2019 ◽  
Vol 8 (4) ◽  
pp. 509-521 ◽  
Author(s):  
Ronald J. W. Lambert ◽  
Douglas A. Dawson
Keyword(s):  
Time Dependent ◽  
New Model ◽  
Combination Effects ◽  
New Models

A new model for combination effects gives descriptions of additivity, independence, synergy and antagonism and explains the multiple shapes of isoboles.

Fractals to Model Hierarchical Biomaterials

2008 ◽  
Vol 58 ◽  
pp. 54-59 ◽  
Author(s):  
Alberto Carpinteri ◽  
Pietro Cornetti ◽  
Nicola Maria Pugno ◽  
Alberto Sapora
Keyword(s):  
Mechanical Properties ◽  
Hierarchical Structure ◽  
Length Scale ◽  
Primary Concern ◽  
New Materials ◽  
New Model ◽  
Hierarchical Materials ◽  
Fractal Approach ◽  
Recursive Formulas ◽  
Strength And Stiffness

Many biological materials exhibit a hierarchical structure over more than one length scale. Understanding how hierarchy affects their mechanical properties emerges as a primary concern, since it can guide the synthesis of new materials to be tailored for specific applications. In this paper the strength and stiffness of hierarchical materials are investigated by means of a fractal approach. A new model is proposed, based both on geometric and material considerations and involving simple recursive formulas.

The Effect of Physical Aging on the Time-Dependent Properties of Carbon-Fiber-Reinforced Epoxy Composites

1982 ◽  
Vol 4 (3) ◽  
pp. 97 ◽  
Author(s):  
TT Chiao ◽  
KL Reifsnider ◽  
GP Sendeckyj ◽  
RJ Morgan ◽  
PL Lien ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Physical Aging ◽  
Time Dependent ◽  
Epoxy Composites ◽  
Fiber Reinforced ◽  
Carbon Fiber Reinforced

8. Mover-Stayer Models for Analyzing Event Nonoccurrence and Event Timing with Time-Dependent Covariates: An Application to an Analysis of Remarriage

1998 ◽  
Vol 28 (1) ◽  
pp. 327-361 ◽  
Author(s):  
Kazuo Yamaguchi
Keyword(s):  
Black Women ◽  
White Women ◽  
Time Dependent ◽  
Regression Equations ◽  
New Model ◽  
American Women ◽  
Duration Data ◽  
Covariate Effects ◽  
Event Timing ◽  
Time Dependent Covariates

This paper introduces a novel extension of mover-stayer models for duration data that allows time-dependent covariates to be used for both a pair of regression equations, one that identifies the determinants of event timing and one that identifies the determinants of the probability of ultimate event nonoccurrence. Existing models intended to distinguish covariate effects on event timing from those on event nonoccurrence cannot use time-dependent covariates in the equation for the probability of ultimate event nonoccurrence. This paper applies the new model to an analysis of remarriage among American women. The analysis generally demonstrates that some covariates effect remarriage timing while others affect the probability of ultimate remarriage nonoccurrence. Some differences in patterns of remarriage between black women and white women are also reported. Theoretical implications of these findings are discussed.

scholarly journals A new exponentially-decaying error correlation model for assimilating OCO-2 column-average CO<sub>2</sub> data, using a length scale computed from airborne lidar measurements

2021 ◽  
Author(s):  
David F. Baker ◽  
Emily Bell ◽  
Kenneth J. Davis ◽  
Joel F. Campbell ◽  
Bing Lin ◽  
...  
Keyword(s):  
Correlation Length ◽  
Error Model ◽  
Airborne Lidar ◽  
Length Scale ◽  
Correlation Model ◽  
Correlation Lengths ◽  
New Model ◽  
The Mean ◽  
Error Correlation ◽  
Along Track

Abstract. To check the accuracy of column-average dry air CO2 mole fractions (XCO2) retrieved from Orbiting Carbon Overvatory (OCO-2) data, a similar quantity has been measured from the Multi-functional Fiber Laser Lidar (MFLL) aboard aircraft flying underneath OCO-2 as part of the Atmospheric Carbon and Transport (ACT)-America flight campaigns. Here we do a lagged correlation analysis of these MFLL-OCO-2 column CO2 differences and find that their correlation spectrum falls off rapidly at along-track separation distances of under 10 km, with a correlation length scale of about 10 km, and less rapidly at longer separation distances, with a correlation length scale of about 20 km. The OCO-2 satellite takes many CO2 measurements with small (~3 km2) fields of view (FOVs) in a thin (<10 km wide) swath running parallel to its orbit: up to 24 separate FOVs may be obtained per second (across a ~6.75 km distance on the ground), though clouds, aerosols, and other factors cause considerable data dropout. Errors in the CO2 retrieval method have long been thought to be correlated at these fine scales, and methods to account for these when assimilating these data into top-down atmospheric CO2 flux inversions have been developed. A common approach has been to average the data at coarser scales (e.g., in 10-second-long bins) along-track, then assign an uncertainty to the averaged value that accounts for the error correlations. Here we outline the methods used up to now for computing these 10-second averages and their uncertainties, including the constant-correlation-with-distance error model currently being used to summarize the OCO-2 version 9 XCO2 retrievals as part of the OCO-2 flux inversion model intercomparison project. We then derive a new one-dimensional error model using correlations that decay exponentially with separation distance, apply this model to the OCO-2 data using the correlation length scales derived from the MFLL-OCO-2 differences, and compare the results (for both the average and its uncertainty) to those given by the current constant-correlation error model. To implement this new model, the data are averaged first across 2-second spans, to collapse the cross-track distribution of the real data onto the 1-D path assumed by the new model. A small percentage of the data that cause nonphysical negative averaging weights in the model are thrown out. The correlation lengths over the ocean, which the land-based MFLL data do not clarify, are assumed to be twice those over the land. The new correlation model gives 10-second XCO2 averages that are only a few tenths of a ppm different from the constant-correlation model. Over land, the uncertainties in the mean are also similar, suggesting that the +0.3 constant correlation coefficient currently used in the model there is accurate. Over the oceans, the twice-the-land correlation lengths that we assume here result in a significantly lower uncertainty on the mean than the +0.6 constant correlation currently gives – measurements similar to the MFLL ones are needed over the oceans to do better. Finally, we show how our 1-D exponential error correlation model may be used to account for correlations in those inversion methods that choose to assimilate each XCO2 retrieval individually, and to account for correlations between separate 10-second averages when these are assimilated instead.

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