Modeling Dry-Snow Densification without Abrupt Transition

An empirical model for the densification of dry snow has been calibrated using strain-rate data from Pine Island Glacier basin, Antarctica. The model provides for a smooth transition between Stage 1 and Stage 2 densification, and leads to an analytical expression for density as a function of depth. It introduces two new parameters with a simple physical basis: transition density ρ T and a scaling factor, M, which controls the extent of the transition zone. The standard (Herron and Langway) parameterization is used for strain rates away from the transition zone. Calibration, though tentative, produces best parameter values of ρ T = 580 kg m − 3 and M = 7 for the region. Using these values, the transition model produces better simulations of snow profiles from Pine Island Glacier basin than the well-established Herron and Langway and Ligtenberg models, both of which postulate abrupt transition. Simulation of density profiles from other sites using M = 7 produces the best values of ρ T = 550 kg m − 3 for a high accumulation site and 530 kg m − 3 for a low accumulation site, suggesting that transition density may vary with climatic conditions. The variation of bubble close-off depth and depth-integrated porosity with mean annual accumulation predicted by the transition model is similar to that predicted by the Simonsen model tuned for Greenland.

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Modelling the transition from grain-boundary sliding to power-law creep in dry snow densification

Journal of Glaciology ◽

10.1017/jog.2021.95 ◽

2021 ◽

pp. 1-14

Author(s):

Elizabeth M. Morris ◽

Lynn N. Montgomery ◽

Robert Mulvaney

Keyword(s):

Grain Boundary ◽

Transition Zone ◽

Power Law ◽

Transition Density ◽

Grain Boundary Sliding ◽

Smooth Transition ◽

Physically Based ◽

Boundary Sliding ◽

Power Law Creep ◽

Stage 1

Abstract This paper presents a physics-based macroscale model for the densification of dry snow which provides for a smooth transition between densification by grain-boundary sliding (stage 1) and densification by power-law creep (stage 2). The model uses established values of the stage 1 and 2 densification rates away from the transition zone and two transition parameters with a simple physical basis: the transition density and the half-width of the transition zone. It has been calibrated using density profiles from the SUMup database and physically based expressions for the transition parameters have been derived. The transition model produces better predictions of the depth of the nominal bubble close-off horizon than the Herron and Langway model, both in its classical form and in a recent version with re-optimised densification rates.

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Engineered Semi-Flexible Composite Mixture Design and Its Implementation Method at Railroad Bridge Approach

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/03611981211004981 ◽

2021 ◽

pp. 036119812110049

Author(s):

Shuai Yu ◽

Shihui Shen ◽

Hai Huang ◽

Cheng Zhang

Keyword(s):

Transition Zone ◽

Structural Adjustment ◽

Asphalt Mixture ◽

Vertical Displacement ◽

Smooth Transition ◽

Railway Track ◽

Dynamic Force ◽

Entire Structure ◽

Bridge Approach ◽

Composite Mixture

Considerable variation in the vertical displacement can cause railway tracks’ transition problems at the bridge approach. The vertical displacement gaps can result in amplification of the dynamic force and frequency, and gradually degrade the serviceability of the railway track. Many strategies, focusing on either modifying the track component or making changes to the entire structure, were used to mitigate transition problems. In particular, asphalt concrete underlayment as a structural adjustment method provides additional support to the ballast and protects the subgrade. However, its effect of reducing dynamic impact at the bridge approach is limited because asphalt mixture has a limited range of modulus and cannot make enough adjustments to the entire structure. Therefore, this paper aims to develop an engineered semi-flexible composite mixture (SFCM) design to mitigate the transition problem. The experiment showed that SFCM is a viscoelastic material with a wider modulus range, and its modulus can adjust with its air voids and the concrete slurry content. Track analysis using a 2.5D sandwich model was conducted to simulate the effects of the structure and material on the responses of the railway track under the dynamic loads and determine the arrangement of the transition zone. A four-segment transition zone design was eventually proposed for a special case of bridge approach. This method can be used to develop transition zones for achieving a smooth transition at the bridge approaches.

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Stability of model performance and parameter values on two catchments facing changes in climatic conditions

Hydrological Sciences Journal ◽

10.1080/02626667.2014.978333 ◽

2015 ◽

Vol 60 (7-8) ◽

pp. 1317-1330 ◽

Cited By ~ 15

Author(s):

Hong Li ◽

Stein Beldring ◽

Chong-Yu Xu

Keyword(s):

Model Performance ◽

Climatic Conditions ◽

Parameter Values

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Pleistocene stratigraphy, paleopedology, and paleoecology of a multiple till sequence exposed on the Little Bear River, Western District of Mackenzie, N.W.T., Canada

Canadian Journal of Earth Sciences ◽

10.1139/e93-071 ◽

1993 ◽

Vol 30 (4) ◽

pp. 851-866 ◽

Cited By ~ 5

Author(s):

O. L. Hughes ◽

C. Tarnocai ◽

C. E. Schweger

Keyword(s):

Transition Zone ◽

Ice Sheet ◽

Climatic Conditions ◽

Canadian Shield ◽

Laurentide Ice Sheet ◽

Spruce Forest ◽

River Section ◽

Valley Glacier ◽

Bear River ◽

Late Wisconsinan

The Little Bear River section lies in a transition zone between Mackenzie Lowland and Canyon Ranges of Mackenzie Mountains. Within the transition zone, the maximum extent of the Laurentide ice sheet overlaps the former extent of montane glaciers that emanated from the higher parts of Canyon Ranges or from the still higher Backbone Ranges to the southwest. Five montane tills, each with a paleosol developed in its upper part, indicate five separate glaciations during each of which a valley glacier emanating from the headwaters of Little Bear River extended eastward into the transition zone. The uppermost of the montane tills is overlain by boulder gravel containing rocks of Canadian Shield origin deposited by the Laurentide ice sheet.Solum and B horizon depths, red colours, and lack of leaching and cryoturbation indicate that although each successive interglacial interval was cooler than the preceding one, even the last of the intervals was warmer than the Holocene. Climatic conditions during one of the intervals inferred from the paleobotanic data, particularly spruce forest development, are consistent with conditions inferred from the associated paleosol.The uppermost of the montane tills is thought to correlate with till of Reid (Illinoian) age in central Yukon. The paleosol developed on that till is, accordingly, thought to correlate with the Diversion Creek paleosol developed on drift of Reid age. The Laurentide boulder gravel is assigned to a stade of Hungry Creek Glaciation of Late Wisconsinan age. The Laurentide ice sheet reached its apparent all-time western limit during the Hungry Creek Glaciation maximum.

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Parameter Selection in the Parameter Estimation of Grade Transitions in a Polyethylene Plant

Studies in Engineering and Technology ◽

10.11114/set.v3i1.887 ◽

2015 ◽

Vol 3 (1) ◽

pp. 1

Author(s):

Niklas Andersson ◽

Per-Ola Larsson ◽

Johan Åkesson ◽

Niclas Carlsson ◽

Staffan Skålén ◽

...

Keyword(s):

Parameter Estimation ◽

Steady State ◽

State Parameter ◽

Parameter Selection ◽

Selection Algorithm ◽

Parameter Estimations ◽

Dynamic Case ◽

Nominal Parameter ◽

Best Parameter ◽

Parameter Values

A polyethylene plant at Borealis AB is modelled in the Modelica language and considered for parameter estimations at grade transitions. Parameters have been estimated for both the steady-state and the dynamic case using the JModelica.org platform, which offers tools for steady-state parameter estimation and supports simulation with parameter sensitivies. The model contains 31 candidate parameters, giving a huge amount of possible parameter combinations. The best parameter sets have been chosen using a parameter-selection algorithm that identified parameter sets with poor numerical properties. The parameter-selection algorithm reduces the number of parameter sets that is necessary to explore. The steady-state differs from the dynamic case with respect to parameter selection. Validations of the parameter estimations in the dynamic case show a significant reduction in an objective value used to evaluate the quality of the solution from that of the nominal reference, where the nominal parameter values are used.

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Non-linear cointegration and adjustment: an asymmetric exponential smooth-transition model for US interest rates

Empirical Economics ◽

10.1007/s00181-007-0180-z ◽

2008 ◽

Vol 35 (3) ◽

pp. 591-606 ◽

Cited By ~ 6

Author(s):

David G. McMillan

Keyword(s):

Interest Rates ◽

Smooth Transition ◽

Transition Model ◽

Non Linear

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Comparison and Supervised Learning of Segmentation Methods Dedicated to Specular Microscope Images of Corneal Endothelium

International Journal of Biomedical Imaging ◽

10.1155/2014/704791 ◽

2014 ◽

Vol 2014 ◽

pp. 1-13 ◽

Cited By ~ 4

Author(s):

Yann Gavet ◽

Jean-Charles Pinoli

Keyword(s):

Image Segmentation ◽

Cell Layer ◽

Spatial Density ◽

Specular Microscopy ◽

Main Criterion ◽

Segmentation Methods ◽

Best Parameter ◽

Good Transparency ◽

Parameter Values

The cornea is the front of the eye. Its inner cell layer, called the endothelium, is important because it is closely related to the light transparency of the cornea. An in vivo observation of this layer is performed by using specular microscopy to evaluate the health of the cells: a high spatial density will result in a good transparency. Thus, the main criterion required by ophthalmologists is the cell density of the cornea endothelium, mainly obtained by an image segmentation process. Different methods can perform the image segmentation of these cells, and the three most performing methods are studied here. The question for the ophthalmologists is how to choose the best algorithm and to obtain the best possible results with it. This paper presents a methodology to compare these algorithms together. Moreover, by the way of geometric dissimilarity criteria, the algorithms are tuned up, and the best parameter values are thus proposed to the expert ophthalmologists.

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A Feature-Based Morphing Methodology for Biological Structures Applied to the Spatial Organization of Cardiomyocytes in the Left Atrium

ASME 2011 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2011-53762 ◽

2011 ◽

Author(s):

Alessandro Satriano ◽

Edward J. Vigmond ◽

Elena S. Di Martino

Keyword(s):

Spatial Organization ◽

Experimental Tests ◽

Smooth Transition ◽

Patient Specific ◽

Clinical Environment ◽

Individual Values ◽

Tissue Properties ◽

Biological Structures ◽

Critical Issues ◽

Parameter Values

When complex biological structures are modeled, one of the most critical issues is the assignment of geometrical, mechanical and electrical properties to the meshed surfaces. Properties of interest are commonly obtained from diagnostic imaging, experimental tests or anatomical observation. These parameters are usually lumped into individual values assigned to a specific region after subdividing the structure in sub-regions. This practice simplifies the problem avoiding the cumbersome assignment of parameter values to each element. However, sub-regions may not adequately represent the smooth transition between regions thus resulting in artificial discontinuities. In addition, some parameters, such as for example the organization of cardiomyocytes, which is the objective of our research, may be obtained through destructive tests or through sophisticated methods that can only be performed on a limited number of samples. Or else, data structure obtained for one animal species could be applied on a different species. Furthermore, in a clinical environment the need for fast turnout of patient-specific models would benefit from the assignment of tissue properties in a semi-automatic manner.

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