scholarly journals A Class of Probability Models for Littoral Drift

1970 ◽  
Vol 1 (12) ◽  
pp. 52
Author(s):  
William R. James
Keyword(s):  
Average Rate ◽  
Accurate Method ◽  
Sediment Flux ◽  
Transport Rate ◽  
Constant Thickness ◽  
Burial Depth ◽  
Tracer Transport ◽  
Probability Models ◽  
Littoral Drift ◽  
Tracer Concentration

The major goal in the development of sediment tracer technology is to produce an accurate method for the field measurement of short term volume littoral rate Many of the technical difficulties involved in tagging, injecting, and sensing the movement of radioisotope sand tracers in the littoral zone have been overcome by the RIST project However, quantitative determination of volume drift rate requires more than knowledge of tracer position in time and space A mathematical model is required to relate the flux of tracer material to the sediment flux A linear (or average) rate of tracer transport along the coastline can be measured to a fair degree of accuracy with tracers These measurements, when determined from tracers injected along a line source which span the transport zone, can be used to provide an estimate of an areal transport rate However, it is not obvious how to measure the third dimension, depth of transport This, of course, is needed to provide the desired estimate of volume transport rate This problem arises, even if the relation of tracer concentration to burial depth is everywhere known without error Sediment transport does not occur as a sheet of constant thickness moving at a constant rate If this were so tracer concentration would rapidly attain a uniform concentration over a fixed depth and no tracers would appear below that depth In fact no observations of the relation between tracer concentration and burial depth support this model as even a first approximation Studies such as those of Courtois and Monaco (1969) and Hubble and Sayre (1964) suggest that the concentration of tracers is related to burial depth in a complex fashion The concentration on the surface is finite, but not maximal The concentration increases with depth to some point where a maximum is reached and diminishes in a "long tailed" fashion.

scholarly journals Measurement of Blood—Brain Hexose Transport with Dynamic PET: Comparison of [18F]2-Fluoro-2-Deoxyglucose and [11C]O-Methylglucose

1989 ◽  
Vol 9 (1) ◽  
pp. 104-110 ◽  
Author(s):  
K. Herholz ◽  
K. Wienhard ◽  
U. Pietrzyk ◽  
G. Pawlik ◽  
W.-D. Heiss
Keyword(s):  
Blood Volume ◽  
Rate Constants ◽  
Regional Analysis ◽  
Close Correlation ◽  
Transport Rate ◽  
Hexose Transport ◽  
Tracer Transport ◽  
Parametric Images ◽  
Positron Emission ◽  
Regional Blood Volume

Blood-to-tissue transport of [18F]2-fluoro-2-deoxyglucose (FDG) and [11C]O-methylglucose (CMG) was compared by dynamic positron emission tomography in four patients with recent ischemic infarcts and in three patients with intracerebral tumors. Local blood volume, tracer transport from tissue to blood, and FDG phosphorylation rates were also determined. A regional analysis of parametric images showed a close correlation of FDG and CMG transport rate constants in pathological tissue. Transport rates of FDG and CMG showed correspondingly less asymmetric remote effects than FDG phosphorylation rates. Transport rate constants were consistently higher for FDG than for CMG in pathological and normal tissue, in accordance with the higher affinity of carrier enzymes to FDG. There was a significant correlation between fitted regional blood volume values and correspondence of average absolute values with both tracers. It is concluded that dynamic FDG PET for measurement of cerebral glucose metabolism is also useful to measure alterations of hexose transport and local blood volume in pathological tissue.

scholarly journals SEDIMENT TRANSPORT UNDER SHEET FLOW CONDITION

1982 ◽  
Vol 1 (18) ◽  
pp. 82 ◽  
Author(s):  
Kiyoshi Horikawa ◽  
Akira Watanabe ◽  
Sadakazu Katori
Keyword(s):  
Sediment Transport ◽  
Flow Condition ◽  
Average Rate ◽  
Empirical Relationship ◽  
Sediment Concentration ◽  
Transport Rate ◽  
Sheet Flow ◽  
Load Transport ◽  
Bed Load Transport ◽  
Moving Layer

A series of laboratory experiments in an oscillatory tank was carried out to investigate the sheet flow of sediment. Objectives of the study were to determine the criterion for inception of sheet flow, and to evaluate the sediment transport rate under the sheet flow condition. In order to proceed with the investigation, it was necessary to develop devices appropriate for tracing the sediment particle movement, and for measuring the extremely dense sediment concentration in the moving layer of sheet flow. The chief results are: 1) the criteria for the inception of sheet flow given by Manohar C1955) and by Komar and Miller (1974) are both applicable to materials composed of spheroidal particles, and 2) the average rate of sediment transport for sheet flow is well described by an empirical relationship given by Madsen and Grant (1976) for the bed load transport rate on a plane bed in oscillatory flow.

scholarly journals Adaptive stochastic trajectory modelling in the chaotic advection regime

2015 ◽  
Vol 769 ◽  
pp. 1-25 ◽  
Author(s):  
J. G. Esler
Keyword(s):  
Turbulent Flows ◽  
Numerical Estimate ◽  
Accurate Method ◽  
Particle Dispersion ◽  
Transport Problem ◽  
Chaotic Advection ◽  
Back Trajectory ◽  
Tracer Transport ◽  
Lagrangian Simulation ◽  
Main Challenge

Motivated by the goal of improving and augmenting stochastic Lagrangian models of particle dispersion in turbulent flows, techniques from the theory of stochastic processes are applied to a model transport problem. The aim is to find an efficient and accurate method to calculate the total tracer transport between a source and a receptor when the flow between the two locations is weak, rendering direct stochastic Lagrangian simulation prohibitively expensive. Importance sampling methods that combine information from stochastic forward and back trajectory calculations are proposed. The unifying feature of the new methods is that they are developed using the observation that a perfect strategy should distribute trajectories in proportion to the product of the forward and adjoint solutions of the transport problem, a quantity here termed the ‘density of trajectories’ $D(\boldsymbol{x},t)$. Two such methods are applied to a ‘hard’ model problem, in which the prescribed kinematic flow is in the large-Péclet-number chaotic advection regime, and the transport problem requires simulation of a complex distribution of well-separated trajectories. The first, Milstein’s measure transformation method, involves adding an artificial velocity to the trajectory equation and simultaneously correcting for the weighting given to each particle under the new flow. It is found that, although a ‘perfect’ artificial velocity $\boldsymbol{v}^{\ast }$ exists, which is shown to distribute the trajectories according to $D$, small errors in numerical estimates of $\boldsymbol{v}^{\ast }$ cumulatively lead to difficulties with the method. A second method is Grassberger’s ‘go-with-the-winners’ branching process, where trajectories found unlikely to contribute to the net transport (losers) are periodically removed, while those expected to contribute significantly (winners) are split. The main challenge of implementation, which is finding an algorithm to select the winners and losers, is solved by a choice that explicitly forces the distribution towards a numerical estimate of $D$ generated from a previous back trajectory calculation. The result is a robust and easily implemented algorithm with typical variance up to three orders of magnitude lower than the direct approach.

scholarly journals The neurofilament middle molecular mass subunit carboxyl-terminal tail domains is essential for the radial growth and cytoskeletal architecture of axons but not for regulating neurofilament transport rate

2003 ◽  
Vol 163 (5) ◽  
pp. 1021-1031 ◽  
Author(s):  
Mala V. Rao ◽  
Jabbar Campbell ◽  
Aidong Yuan ◽  
Asok Kumar ◽  
Takahiro Gotow ◽  
...  
Keyword(s):  
Radial Growth ◽  
Average Rate ◽  
Embryonic Stem ◽  
Transport Rate ◽  
Tail Domain ◽  
Neurofilament Protein ◽  
Carboxyl Terminal ◽  
Cross Bridges ◽  
Neurofilament Transport

The phosphorylated carboxyl-terminal “tail” domains of the neurofilament (NF) subunits, NF heavy (NF-H) and NF medium (NF-M) subunits, have been proposed to regulate axon radial growth, neurofilament spacing, and neurofilament transport rate, but direct in vivo evidence is lacking. Because deletion of the tail domain of NF-H did not alter these axonal properties (Rao, M.V., M.L. Garcia, Y. Miyazaki, T. Gotow, A. Yuan, S. Mattina, C.M. Ward, N.S. Calcutt, Y. Uchiyama, R.A. Nixon, and D.W. Cleveland. 2002. J. Cell Biol. 158:681–693), we investigated possible functions of the NF-M tail domain by constructing NF-M tail–deleted (NF-MtailΔ) mutant mice using an embryonic stem cell–mediated “gene knockin” approach that preserves normal ratios of the three neurofilament subunits. Mutant NF-MtailΔ mice exhibited severely inhibited radial growth of both motor and sensory axons. Caliber reduction was accompanied by reduced spacing between neurofilaments and loss of long cross-bridges with no change in neurofilament protein content. These observations define distinctive functions of the NF-M tail in regulating axon caliber by modulating the organization of the neurofilament network within axons. Surprisingly, the average rate of axonal transport of neurofilaments was unaltered despite these substantial effects on axon morphology. These results demonstrate that NF-M tail–mediated interactions of neurofilaments, independent of NF transport rate, are critical determinants of the size and cytoskeletal architecture of axons, and are mediated, in part, by the highly phosphorylated tail domain of NF-M.

scholarly journals A GROSS LONGSHORE TRANSPORT RATE FORMULA

1972 ◽  
Vol 1 (13) ◽  
pp. 47 ◽  
Author(s):  
Cyril J. Galvin
Keyword(s):  
Current Velocity ◽  
Empirical Relation ◽  
Field Measurements ◽  
Transport Rate ◽  
Longshore Current ◽  
Physical Explanation ◽  
Littoral Drift ◽  
Longshore Transport ◽  
Term Field

Gross longshore transport rates for 11 long-term field measurements are predicted reasonably well by the empirical relation, Q=2H2, where Q is longshore transport rate in 100,000 yd3/yr, and H is a mean breaker height in feet. A physical explanation of this empirical relation assumes: (1) most littoral drift is transported in suspension; (2) longshore current velocity is predicted by V-gmTsin28j,; (3) the empirical relation is an equation for conservation of suspended sediment in the longshore current.

Steady streaming and sediment transport at the bottom of sea waves

2012 ◽  
Vol 697 ◽  
pp. 115-149 ◽  
Author(s):  
Paolo Blondeaux ◽  
Giovanna Vittori ◽  
Antonello Bruschi ◽  
Francesco Lalli ◽  
Valeria Pesarino
Keyword(s):  
Boundary Layer ◽  
Sediment Transport ◽  
Empirical Relationship ◽  
Sediment Concentration ◽  
Sediment Flux ◽  
Transport Rate ◽  
Sea Waves ◽  
Steady Streaming ◽  
Sediment Transport Rate ◽  
Advection Diffusion Equation

AbstractThe flow and sediment transport in the boundary layer at the sea bottom due to the passage of surface waves are determined by considering small values of the wave steepness and of the ratio between the thickness of the boundary layer and the local water depth. Both the velocity field and the sediment transport rate are determined up to the second order of approximation thus evaluating both the steady streaming and the net (wave-averaged) flux of sediment induced by nonlinear effects. The flow regime is assumed to be turbulent and a two-equation turbulence model is used to close the problem. The bed load is evaluated by means of an empirical relationship as function of the bed shear stress. The suspended load is determined by computing the sediment flux, once the sediment concentration is determined by solving an appropriate advection–diffusion equation. The decay of the wave amplitude, which is due to the energy dissipation taking place in the boundary layer, is taken into account. The steady streaming and the sediment transport rate at the bottom of sea waves turn out to be different from those which are observed in a wave tunnel (U-tube), because of the dependence on the streamwise coordinate of the former flow. In particular, in the range of the parameters presently investigated, the sediment transport rate at the bottom of sea waves is found to be always onshore directed while, in a water tunnel (U-tube), the sediment transport rate can be onshore or offshore directed.

scholarly journals ACCURACY OF HYDROGRAPHIC SURVEYING IN AND NEAR THE SURF ZONE

2000 ◽  
Vol 1 (3) ◽  
pp. 3
Author(s):  
Thorndike Saville, Jr. ◽  
Joseph M. Caldwell
Keyword(s):  
Surf Zone ◽  
Average Rate ◽  
Significant Degree ◽  
Beach Erosion ◽  
Littoral Drift ◽  
Depth Measurement ◽  
Average Change ◽  
Sand Movement ◽  
Quantitative Changes ◽  
Dominant Direction

The analysis and solution of most beach erosion problems are based to a significant degree on the quantitative changes in the bottom hydrography as observed in successive surveys. Critical decisions as to the dominant direction of littoral drift, the average rate of this drift, and the onshore-offshore movement of material are based largely on such hydrographic surveys. As the net changes between successive surveys are usually small compared to the area being studied, the degree of accuracy or comparability of the hydrographic surveys is of considerable importance. For instance, a net change of 100,000 cubic yards over one square mile of beach represents an average change in depth of only about 0.1 feet. Thus, it can be seen that uncompensated errors in depth measurement of as little as 0.1 feet can produce indications of significant littoral sand movement which might not exist in reality.

Contemporary Squamish River sediment flux to Howe Sound, British Columbia

1989 ◽  
Vol 26 (10) ◽  
pp. 1953-1963 ◽  
Author(s):  
Edward J. Hickin
Keyword(s):  
British Columbia ◽  
River Sediment ◽  
Sediment Load ◽  
Average Rate ◽  
Sediment Concentration ◽  
Sediment Flux ◽  
Large Magnitude ◽  
Delta Front ◽  
Coast Mountains

Squamish River drains 3600 km2 in the southern Coast Mountains of British Columbia to Howe Sound at Squamish, some 50 km north of Vancouver. This study uses differencing of digitized bathymetric surfaces based on the Canadian Hydrographic Services surveys of 1930, 1973, and 1984 at the head of Howe Sound to yield a long-term sedimentation rate for Squamish River delta. The sediment flux from Squamish River to Howe Sound is determined to be 1.29 × 106 m3 a−1 or 1.81 × 109 kg a−1, rates consistent with loads calculated from flow and sediment-concentration regimes measured in the estuary in 1973 – 1975 and 1987 – 1988. The latter data indicate that the modal discharge-effectiveness class is 600 – 700 m3 s−1, moving 13% of the annual suspended-sediment load. Discharges up to 1400 m3 s−1 constitute 99.8% of all flows and are responsible for transporting 81.5% of the annual load. A very significant 18.5% of the load is moved by large-magnitude floods (> 1400 m3 s−1), which occur less than 0.2% of the time.Squamish Delta is prograding downfjord at an average rate of 3.86 m a−1 although local extensions of the delta front in a given year may approach 20 m. Some of the geomorphic implications of extrapolating these contemporary rates of fjord infilling over the Holocene are discussed briefly.

scholarly journals STUDY OF SHELF WAVES VS SAND DRIFT IN NW COAST OF TAIWAN

1988 ◽  
Vol 1 (21) ◽  
pp. 86
Author(s):  
Ho-Shong Hou
Keyword(s):  
Wave Energy ◽  
Coastal Engineering ◽  
Transport Rate ◽  
Western Coast ◽  
Littoral Drift ◽  
The North ◽  
Planning And Design ◽  
Shelf Waves ◽  
The Relationship ◽  
North Western

For the planning and design of harbor and coastal Engineering, most important affected factors are waves and Littoral drift. This research deals with analysis of the measured waves and the budget of the beach material whether it is deposited or scoured in the North-western coast of Taiwan; and the relationship between wave energy and littoral transport rate. For processing this research the field Survey wave measurement, sand sampling, and echo sounding is necessitated. The objective of this research is to establish the model of waves and littoral transport budget. Therefore, the results of this research are planned to submit to the planning and design of harbor and coastal engineering works of the Taiwan west sandy coast. The main contains of this research are consisted of (1) Analysis, observations and investigations of the field oceanographic data, winds, waves, coastal geomorphology and littoral drift of the North-western coast of Taiwan. (2) Analysis of the shelf waves from the actual measured wave records. (3) Research of the wave decaying process of the continental shelf waves. (4) Statistical research of the measured waves and establishment of the practical model of the relationship between the shelf wave energy and the littoral transport rate in the north-west coast of Taiwan.

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