Mountain river meanders and typhoon strike frequency in the western Pacific

NASA Astrophysics Data System (ADS)

Stark, C. P.; Barbour, J.; Hsieh, M.; Hovius, N.; Jen, C.; Chen, M.

2004-12-01

Bedrock-floored mountain rivers are shaped by erosion processes that ultimately control the evolution of the landscape on geological time scales. In mountains across the western Pacific, meanders in bedrock channels are common and often emerge during incision rather than inherit their sinuosity from a past alluvial form. Incising emergent meanders are important because they reveal a process of lateral channel erosion at least as fast as the vertical rate erosion. Here we report a remarkable link between incised meander development and typhoon strike frequency, a good proxy for extreme rainfall and flood discharge. Using satellite imagery, shuttle-radar topographic data and a 58~year inventory of typhoon tracks, we mapped meander abundance and quantified regional densities of mountain river sinuosity and typhoon strikes. Our analysis shows that eroding meanders are most common in the typhoon-prone islands of Japan, Taiwan and the Philippines, and in rivers incising weak lithologies. One might expect that the faster the erosion rate, the greater the meandering, but we have found that monthly mean rainfall - and therefore mean discharge - correlates very poorly with sinuosity. Instead, the variability of rainfall, and presumably discharge, about the mean explains bedrock meander development much better. Mountain river sinuosity, for geologically similar bedrock, increases in a roughly linear fashion with typhoon strike frequency. The coefficient of variation of monthly rainfall (standard deviation normalized by the mean) exhibits a similar trend. We deduce that extreme flood discharge, e.g. driven by typhoon rainfall, accelerates lateral erosion rates and spurs meander development in mountain rivers.

Paleohydrological methods and some examples from Swedish fluvial environments. II - River meanders.

USGS Publications Warehouse

Williams, G.P.

1984-01-01

Empirical relations are developed between river-meander features and water-discharge characteristics for 19 reaches along Swedish rivers. In these relations, either average channel width or average radius of curvature of meander arcs can be used to estimate average annual peak discharge and average daily discharge. By accepting certain assumptions, the relations can be applied to other meandering Swedish rivers, present or ancient. The Oster-Dalalven River near Mora is used as an example.-Author

Distributed meandering waveguides (DMWs) for novel photonic circuits (Conference Presentation)

NASA Astrophysics Data System (ADS)

Dag, Ceren B.; Anil, Mehmet Ali; Serpengüzel, Ali

2017-05-01

Meandering waveguide distributed feedback structures are novel integrated photonic lightwave and microwave circuit elements. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave and microwave circuit element functions. Distributed meandering waveguide (DMW) structures [1] show a variety of spectral behaviors with respect to the number of meandering loop mirrors (MLMs) [2] used in their composition as well as their internal coupling constants (Cs). DMW spectral behaviors include Fano resonances, coupled resonator induced transparency (CRIT), notch, add-drop, comb, and hitless filters. What makes the DMW special is the self-coupling property intrinsic to the DMW's nature. The basic example of DMW's nature is motivated through the analogy between the so-called symmetric meandering resonator (SMR), which consists of two coupled MLMs, and the resonator enhanced Mach-Zehnder interferometer (REMZI) [3]. A SMR shows the same spectral characteristics of Fano resonances with its self-coupling property, similar to the single, distributed and binary self coupled optical waveguide (SCOW) resonators [4]. So far DMWs have been studied for their electric field intensity, phase [5] and phasor responses [6]. The spectral analysis is performed using the coupled electric field analysis and the generalization of single meandering loop mirrors to multiple meandering distributed feedback structures is performed with the transfer matrix method. The building block of the meandering waveguide structures, the meandering loop mirror (MLM), is the integrated analogue of the fiber optic loop mirrors. The meandering resonator (MR) is composed of two uncoupled MLM's. The meandering distributed feedback (MDFB) structure is the DFB of the MLM. The symmetric MR (SMR) is composed of two coupled MLM's, and has the characteristics of a Fano resonator in the general case, and tunable power divider or tunable hitless filter in special cases. The antisymmetric MR (AMR) is composed of two coupled MLM's. The AMR has the characteristics of an add-drop filter in the general case, and coupled resonator induced transparency (CRIT) filter in a special case. The symmetric MDFB (SMDFB) is composed of multiple coupled MLM's. The antisymmetric MDFB (AMDFB) is composed of multiple coupled MLM's. The SMDFB and AMDFB can be utilized as band-pass, Fano, or Lorentzian filters, or Rabi splitters. Distributed meandering waveguide elements with extremely rich spectral and phase responses can be designed with creative combinations of distributed meandering waveguides structures for various novel photonic circuits. References [1 ] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Meandering Waveguide Distributed Feedback Lightwave Circuits," J. Lightwave Technol, vol. 33, no. 9, pp. 1691-1702, May 2015. [2] N. J. Doran and D. Wood, "Nonlinear-optical loop mirror," Opt. Lett. vol. 13, no. 1, pp. 56-58, Jan. 1988. [3] L. Zhou and A. W. Poon, "Fano resonance-based electrically reconfigurable add-drop filters in silicon microring resonator-coupled Mach-Zehnder interferometers," Opt. Lett. vol. 32, no. 7, pp. 781-783, Apr. 2007. [4] Z. Zou, L. Zhou, X. Sun, J. Xie, H. Zhu, L. Lu, X. Li, and J. Chen, "Tunable two-stage self-coupled optical waveguide resonators," Opt. Lett. vol. 38, no. 8, pp. 1215-1217, Apr. 2013. [5] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Novel distributed feedback lightwave circuit elements," in Proc. SPIE, San Francisco, 2015, vol. 9366, p. 93660A. [6] C. B. Dağ, M. A. Anıl, and A. Serpengüzel, "Meandering Waveguide Distributed Feedback Lightwave Elements: Phasor Diagram Analysis," in Proc. PIERS, Prague, 1986-1990 (2015).

Stream-power model of meander cutoff in gravel beds

NASA Astrophysics Data System (ADS)

Pannone, M.; De Vincenzo, A.

2016-12-01

In the present study we propose a one-dimensional model for the prediction of the large-time evolution of river meanders (pre-cutoff conditions) characterized by gravel bed and negligible suspended load. Due to its relatively simple structure, it may be a fast and easy tool to forecast the time evolution of a bend when the symptoms of an incipient instability suggest quantifying the time left for river exploitation as a naturalistic or a commercial resource and timely planning, if needed, the site management and restoration. Most of the previous research on meandering rivers focused on linearized theories that apply to very small bend amplitudes and very large radii of curvature. The dynamics of meander growth and cutoff was typically afforded by case-sensitive numerical simulations or by descriptive methods aimed at deriving purely empirical laws relating the hydraulics to some geomorphological parameters. The present approach combines the immediacy of a general analytical model with the accuracy of a fluid-mechanical background. The model focuses on energetic principles and interprets the mechanism of meander cutoff as the achievement of limit conditions in terms of river stream power. The corresponding analytical solution, which consists in a 1-D deterministic integro-differential equation governing the meander pre-cutoff phase, accounts for the influence of the morphological and sedimentological parameters by the downstream migration rate and the radius of the meander osculating circle. The results, expressed in terms of instable meander lifetime, are in good agreement with the data obtained from a number of field surveys documented in literature. Additionally, the proposed fluid-mechanical model allows identifying the physical mechanisms responsible for some peculiarities of large-time meander evolution like the decreasing skewness and asymmetry.

Meandering down to the Sea: The Wandering Ways of Rivers.

ERIC Educational Resources Information Center

Aslamazov, Lev

1992-01-01

Discusses the hydrodynamic reasons why a riverbed meanders through a plain. Describes how water movement at a bend in a river causes erosion and changes in the riverbed. Provides a mathematical model to explain the periodic shape of meanders of a river in a plain. (MDH)

Secondary Circulation Asymmetry in a Meandering, Partially Stratified Estuary

NASA Astrophysics Data System (ADS)

Pein, J.; Valle-Levinson, A.; Stanev, E. V.

2018-03-01

Numerical model experiments are used to study the effects of multiple channel bends on estuarine dynamics and, in particular, on secondary flows. These effects are demonstrated by comparing experiments with two different idealized trumpet-shaped estuaries, one straight and another one with a ˜8 km meandering section in the middle of the estuary. Meanders complicate the flow field by introducing secondary processes. For instance, meanders increase turbulence and associated mixing locally within the water column, as well as outside the meandering portion. Furthermore, meanders transform up to 30% of the along-channel momentum into secondary circulation. Production of turbulence and secondary currents is different at flood and ebb tidal phases. At flood, meanders lead to unstable stratification and increased turbulence. At ebb, the flow develops a helical pattern and adjusts to the channel curvature with minimal decrease in density stability. The secondary circulation asymmetry is caused by an interplay between the across-channel baroclinic pressure gradient force and the centrifugal force. During ebb both forces enhance each other, whereas they oppose during flood. As a consequence of this interaction between baroclinic forcing and curving morphology, ebb flows and horizontal buoyancy fluxes increase relative to flood. The enhanced ebb dominance shifts a density front toward the mouth of the estuary, thus reducing salt intrusion.

A Cultural Resources LIterature Search, Record Review and Cultural Resources Survey of the Belle Fountain Ditch Enlargement Project within Pemiscot and Dunklin Counties, Missouri

DTIC Science & Technology

1986-06-01

Introduction I Project Location 1 Project History 3 Environment 3 The Relict Braided Surface 3 The Old Meander Belt 5 Soils and Biotic Communities 6 Macrobiotic...Project Area and the Sunk Lands (after Saucier 1970 and USGS Evadale Quad) 4 The Old Meander Belt The Old Meander Belt was incised into the Relict Braided...that the silting of the Old Meander Belt by the Mississippi River started in the Late Archaic period (ca. 3000 - 500 BC). It appears likely that this

Laboratory Experiments on Meandering Meltwater Channels

NASA Astrophysics Data System (ADS)

Fernandez, R.; Berens, J.; Parker, G.; Stark, C. P.

2017-12-01

Meandering channels of all scales and flowing over a wide variety of media have common planform patterns. Although the analogy in planform suggests there is a common underlying framework, the constitutive relations driving planform evolution through vertical incision/deposition and lateral migration differ from medium to medium. The driving processes in alluvial and mixed bedrock-alluvial meandering channels have been studied substantially over the last decades. However, this is not the case for meandering channels in other media such as ice or soluble rock. Here we present results from experiments conducted at the Ven Te Chow Hydrosystems Laboratory of the University of Illinois at Urbana-Champaign on meltwater meandering channels. A rivulet is carved into an ice block and water is allowed to flow at a constant discharge. Planform evolution is analyzed with time lapse imaging and complemented with rubber molds of the channel once the experiment is over. These molds give us the full 3D structure of the meandering, including incisional overhang. Vertical incision rates are measured throughout the run by taking elevations along the channel, and these measurements are complemented with analysis from the molds. We show examples of meandering of intense amplitude with deep overhangs. Features resembling scroll bars document cyclically punctuated melting. We report on lateral migration rates, incision rates, sinuosity, channel depths, channel widths, reach averaged velocities, bend wavelengths and amplitudes and compare them to values reported in the literature for alluvial rivers.

76 FR 63951 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-14

... meanders of the former left bank of the Tongue River, downstream, through sections 27, 28, and 29, and the adjusted original meanders of the former right bank of the Tongue River, downstream, through sections 21... Tongue River, downstream, through sections 27 and 28, and a portion of section 29, the meanders of the...

Designing and Assessing Restored Meandering River Planform Using RVR Meander

NASA Astrophysics Data System (ADS)

Langendoen, E. J.; Abad, J. D.; Motta, D.; Frias, C. E.; Wong, M.; Barnes, B. J.; Anderson, C. D.; Garcia, M. H.; MacDonald, T. E.

2013-12-01

The ongoing modification and resulting reduction in water quality of U.S. rivers have led to a significant increase in river restoration projects over the last two decades. The increased interest in restoring degraded streams, however, has not necessarily led to improved stream function. Palmer and Allan (2005) found that many restoration projects fail to achieve their objectives due to the lack of policies to support restoration standards, to promote proven methods and to provide basic data needed for planning and implementation. Proven models of in-stream and riparian processes could be used not only to guide the design of restoration projects but also to assess both pre- and post-project indicators of ecological integrity. One of the most difficult types of river restoration projects concern reconstructing a new channel, often with an alignment and channel form different from those of the degraded pre-project channel. Recreating a meandering planform to provide longitudinal and lateral variability of flow and bed morphology to improve in-stream aquatic habitat is often desired. Channel meander planform is controlled by a multitude of variables, for example channel width to depth ratio, radius of curvature to channel width ratio, bankfull discharge, roughness, bed-material physical characteristics, bed material transport, resistance to erosion of the floodplain soils, riparian vegetation, etc. Therefore, current practices that use simple, empirically based relationships or reference reaches have led to failure in several instances, for example a washing out of meander bends or a highly unstable planform, because they fail to address the site-specific conditions. Recently, progress has been made to enhance a physically- and process-based model, RVR Meander, for rapid analysis of meandering river morphodynamics with reduced empiricism. For example, lateral migration is based on measurable physical properties of the floodplain soils and riparian vegetation versus the driving forces of the river hydrodynamics. The model can also be used in a Monte Carlo framework to statistically describe the long-term evolution of the meander planform. RVR Meander has been successfully used to evaluate migration rates of restored meandering streams and bends on the Big Sioux River, SD and Trout Creek, CA at engineering time scales. It has also been used to assess the uncertainty and risk associated with the alignment of the meandering low-flow channel of the planned diversion of the Red River of the North around the metropolitan area of Fargo, ND and Moorhead, MN. Palmer MA, Allan JD. 2005. Restoring rivers, Issues in Science and Technology, Winter 2006, Published by National Academy of Sciences, 22: 40-48.

Meander morphodynamics over self-formed floodplains: can the migration history affect the future morphology of the river?

NASA Astrophysics Data System (ADS)

Bogoni, M.; Lanzoni, S.; Putti, M.

2017-12-01

Floodplains, and rivers therein, constitute complex systems whose simulation involves modeling of hydrodynamic, morphodynamic, chemical, and biological processes which act over a wide range of time scales (from days to centuries) and affect each other. Self-formed floodplains are produced by the sedimentary processes associated with the migration of river bends and the formation of abandoned oxbow lakes consequent to the cutoff of mature meanders. The erosion and deposition processes at the banks lead to heterogeneities in the surface composition, thus the river may experience faster or slower migration rates depending on the spatial distribution of the erosional resistance. As a consequence, the past spatial configurations of the river (i.e. the migration history) play a key role in shaping the successive river paths.We recently published a paper addressing the modeling of meander morphodynamics over self-formed heterogeneous floodplain. Results show that the heterogeneity in floodplain composition associated with the formation of geomorphic units (i.e., scroll bars and oxbow lakes) and the choice of a reliable flow field model to drive channel migration are two fundamental ingredients for reproducing correctly the long-term morphodynamics of alluvial meanders. We compare numerically generated planforms obtained for different scenarios of floodplain heterogeneity to natural meandering paths, through half meander metrics and spatial distribution of channel curvatures. Statistical and spectral tools disclose the complexity embedded in meandering geometry and the crucial differences between apparently similar configurations.Floodplain heterogeneity affects both the temporal and spatial distributions of meander geometry, and eventually leads to a closer statistical similarity between simulated and natural planform shapes when scroll bars and oxbow lakes left behind are harder to erode than the surrounding floodplain.

Understanding Single-Thread Meandering Rivers with High Sinuosity on Mars through Chemical Precipitation Experiments

NASA Astrophysics Data System (ADS)

Lim, Y.; Kim, W.

2015-12-01

Meandering rivers are extremely ubiquitous on Earth, yet it is only recently that single-thread experimental channels with low sinuosity have been created. In these recent experiments, as well as in natural rivers, vegetation plays a crucial role in maintaining a meandering pattern by adding cohesion to the bank and inhibiting erosion. The ancient, highly sinuous channels found on Mars are enigmatic because presumably vegetation did not exist on ancient Mars. Under the hypothesis that Martian meandering rivers formed by chemical precipitation on levees and flood plain deposits, we conducted carbonate flume experiments to investigate the formation and evolution of a single-thread meander pattern without vegetation. The flow recirculating in the flume is designed to accelerate chemical reactions - dissolution of limestone using CO2 gas to produce artificial spring water and precipitation of carbonates to increase cohesion- with precise control of water discharge, sediment discharge, and temperature. Preliminary experiments successfully created a single-thread meandering pattern through chemical processes. Carbonate deposits focused along the channel sides improved the bank stability and made them resistant to erosion, which led to a stream confined in a narrow path. The experimental channels showed lateral migration of the bend through cut bank and point bar deposits; intermittent floods created overbank flow and encouraged cut bank erosion, which enhanced lateral migration of the channel, while increase in sediment supply improved lateral point bar deposition, which balanced erosion and deposition rates. This mechanism may be applied to terrestrial single-thread and/or meandering rivers with little to no vegetation or before its introduction to Earth and also provide the link between meandering river records on Mars to changes in Martian surface conditions.

Fluvial bar dynamics in large meandering rivers with different sediment supply in the Amazon River basin

NASA Astrophysics Data System (ADS)

Monegaglia, Federico; Zolezzi, Guido; Tubino, Marco; Henshaw, Alex

2017-04-01

Sediments in the large meandering rivers of the Amazon basin are known to be supplied by sources providing highly different magnitudes of sediment input and storage, ranging from the sediment-rich Andean region to the sediment-poor Central Trough. Recent observations have highlighted how such differences in sediment supply have an important, net effect on the rates of planform activity of meandering rivers in the basin, in terms of meander migration and frequency of cutoffs. In this work we quantify and discuss the effect of sediment supply on the organization of macroscale sediment bedforms on several large meandering rivers in the Amazon basin, and we link our findings with those regarding the rates of planform activity. Our analysis is conducted through the newly developed software PyRIS, which enables us to perform extensive multitemporal analysis of river morphodynamics from multispectral remotely sensed Landsat imagery in a fully automated fashion. We show that large rivers with low sediment supply tend to develop alternate bars that consistently migrate through long reaches, characterized at the same time by limited planform development. On the contrary, high sediment supply is associated with the development of point bars that are well-attached to the evolving meander bends and that follow temporal oscillations around the bend apexes, which in turn show rapid evlution towards complex meander shapes. Finally, rivers with intermediate rates of sediment supply develop rather steady point bars associated with slowly migrating, regular meanders. We finally discuss the results of the image analysis in the light of the properties of river planform metrics (like channel curvature and width) for the examined classes of river reaches with different sediment supply rates.

Complexity, self-organisation and variation in behaviour in meandering rivers

NASA Astrophysics Data System (ADS)

Hooke, J. M.

2007-11-01

River meanders are natural features on the surface of Earth that present some degree of regularity of form. They range from being highly dynamic to being stable under present conditions. Conventional theory is that meanders develop to an equilibrium form which is related to discharge and sediment load. Other research has demonstrated that many highly active meanders exhibit a continuous evolution over time and a non-linearity in rate of development. Ideas of autogenesis and of self-organised criticality as being an explanation of some meander changes have been proposed. In this paper data from rivers around the world are examined for further evidence of autogenic, self-organised or non-linear behaviour through analysis of change in sinuosity over time for reaches and change in individual bend form, particularly bend curvature and bend elongation. Some examples do exhibit trends of increasing sinuosity over time and a few show limits from which large decreases occur. Several case studies show non-linearity of behaviour and increasing complexity of form. Other case studies, however, do not exhibit such trends. Phase space plots are used to help uncover emergent behaviour but show a variety of patterns. The example of a reach in which multiple cut-offs occurred is analysed for mechanisms of self-organisation of the planform and in the pool-riffle pattern. Riffles are more closely spaced and also more transient in the more rapidly changing and higher sinuosity parts of the channel. Hypothetical trajectories of different meander behaviour, including for bedrock meanders, are plotted but the challenge remains to uncover the conditions for occurrence and for divergence of tendencies to stability and instability. Identification of attractors and phase space of behaviour of different meandering systems offer the potential for application to sustainable channel management.

Modeling the Long-term Planform Evolution of Meandering Rivers in Confined Alluvial Valleys: Etsch-Adige River, NE Italy.

NASA Astrophysics Data System (ADS)

Zen, S.; Bogoni, M.; Zolezzi, G.; Lanzoni, S.; Scorpio, V.

2016-12-01

We combine the use of a morphodynamic model for river meander planform evolution with a geological dataset to investigate the influence of external confinements on the long-term evolution of a meandering river flowing in an Alpine valley. The analysis focuses on a 100 km reach of the Adige River, NE Italy, which had several sinuous/meandering sections before being extensively channelized in the 1800s. Geological surveys and historical maps revealed that many sections of the study reach impinge on the borders of the valley during its evolution. Moreover, a marked spatial heterogeneity in floodplain vertical accretion rates likely reflects preferential positions of the river channel in the floodplain. Valley confinements are represented by bedrock outcrops and by alluvial fans created by lateral tributaries, and were extracted from the geological and historical maps to build the computational domain for the meander morphodynamic model. The model predicts the long-term planform evolution of a meandering river based on a linear solution of the 2D De St Venant-Exner differential system and can manage changes in floodplain erodibility. Model applications allow to isolate the effects of valley bedrock and of alluvial fans in constraining the lateral channel migration. Modeled river channel persistence maps are compared with the available geological information. The present work allows further insights into the role of external confinements to river meander belts, which have been conducted so far mostly assuming the channel to evolve in unconfined floodplains. Future research shall incorporate model components for floodplain vertical accretion rates and for the advancement of alluvial fans occurring at the same time scale considered for meander evolution.

Development of an analytical Lagrangian model for passive scalar dispersion in low-wind speed meandering conditions

NASA Astrophysics Data System (ADS)

Stefanello, M. B.; Degrazia, G. A.; Mortarini, L.; Buligon, L.; Maldaner, S.; Carvalho, J. C.; Acevedo, O. C.; Martins, L. G. N.; Anfossi, D.; Buriol, C.; Roberti, D.

2018-02-01

Describing the effects of wind meandering motions on the dispersion of scalars is a challenging task, since this type of flow represents a physical state characterized by multiple scales. In this study, a Lagrangian stochastic diffusion model is derived to describe scalar transport during the horizontal wind meandering phenomenon that occurs within a planetary boundary layer. The model is derived from the linearization of the Langevin equation, and it employs a heuristic functional form that represents the autocorrelation function of meandering motion. The new solutions, which describe the longitudinal and lateral wind components, were used to simulate tracer experiments that were performed in low-wind speed conditions. The results of the comparison indicate that the new model can effectively reproduce the observed concentrations of the contaminants, and therefore, it can satisfactorily describe enhanced dispersion effects due to the presence of meandering.

A numerical study of the complex flow structure in a compound meandering channel

NASA Astrophysics Data System (ADS)

Moncho-Esteve, Ignacio J.; García-Villalba, Manuel; Muto, Yasu; Shiono, Koji; Palau-Salvador, Guillermo

2018-06-01

In this study, we report large eddy simulations of turbulent flow in a periodic compound meandering channel for three different depth conditions: one in-bank and two overbank conditions. The flow configuration corresponds to the experiments of Shiono and Muto (1998). The predicted mean streamwise velocities, mean secondary motions, velocity fluctuations, turbulent kinetic energy as well as mean flood flow angle to meandering channel are in good agreement with the experimental measurements. We have analyzed the flow structure as a function of the inundation level, with particular emphasis on the development of the secondary motions due to the interaction between the main channel and the floodplain flow. Bed shear stresses have been also estimated in the simulations. Floodplain flow has a significant impact on the flow structure leading to significantly different bed shear stress patterns within the main meandering channel. The implications of these results for natural compound meandering channels are also discussed.

Methodology for calculating shear stress in a meandering channel

Treesearch

Kyung-Seop Sin

2010-01-01

Shear stress in meandering channels is the key parameter to predict bank erosion and bend migration. A representative study reach of the Rio Grande River in central New Mexico has been modeled in the Hydraulics Laboratory at CSU. To determine the shear stress distribution in a meandering channel, the large scale (1:12) physical modeling study was conducted in the...

General mechanism for the meandering instability of rivulets of Newtonian fluids.

PubMed

Daerr, A; Eggers, J; Limat, L; Valade, N

2011-05-06

A rivulet flowing down an inclined plane often does not follow a straight path, but starts to meander spontaneously. Here we show that this instability is the result of two key ingredients: fluid inertia and anisotropy of the friction between rivulet and substrate. Meandering only occurs if the motion normal to the instantaneous flow direction is more difficult than parallel to it. We give a quantitative criterion for the onset of meandering and confirm it by comparing to the flow of a rivulet between two glass plates which are wetted completely. Above the threshold, the rivulet follows an irregular pattern with a typical wavelength of a few cm.

Interactions between hyporheic flow produced by stream meanders, bars, and dunes

USGS Publications Warehouse

Stonedahl, Susa H.; Harvey, Judson W.; Packman, Aaron I.

2013-01-01

Stream channel morphology from grain-scale roughness to large meanders drives hyporheic exchange flow. In practice, it is difficult to model hyporheic flow over the wide spectrum of topographic features typically found in rivers. As a result, many studies only characterize isolated exchange processes at a single spatial scale. In this work, we simulated hyporheic flows induced by a range of geomorphic features including meanders, bars and dunes in sand bed streams. Twenty cases were examined with 5 degrees of river meandering. Each meandering river model was run initially without any small topographic features. Models were run again after superimposing only bars and then only dunes, and then run a final time after including all scales of topographic features. This allowed us to investigate the relative importance and interactions between flows induced by different scales of topography. We found that dunes typically contributed more to hyporheic exchange than bars and meanders. Furthermore, our simulations show that the volume of water exchanged and the distributions of hyporheic residence times resulting from various scales of topographic features are close to, but not linearly additive. These findings can potentially be used to develop scaling laws for hyporheic flow that can be widely applied in streams and rivers.

How Do River Meanders Change with Sea Level Rise and Fall?

NASA Astrophysics Data System (ADS)

Scamardo, J. E.; Kim, W.

2016-12-01

River meander patterns are controlled by numerous factors, including variations in water discharge, sediment input, and base level. However, the effect of sea level rise and fall on meandering rivers has not been thoroughly quantified. This study examines geomorphic changes to meandering rivers as a result of sea level rise and fall. Twenty experimental runs using coarse-grained walnut shell sediment (D50= 500 microns) in a flume tank (2.4m x 0.6m x 0.1m) tested the optimal initial conditions for creating meandering rivers in a laboratory setting as well as variations in base level rise and fall rates. Geomorphic changes were recorded by camera images every 20 seconds for a duration of 4 hours per experiment. Seventeen experiments tested the effects of changes in initial base levels, water discharge between 200 and 400 mL/min, and sediment to water input ratios between 1:1000 and 1:250 while measuring sinuosity, channel geometry, and the timescale of the channel to reach a stable form. Sinuosity and channel activity increased with increasing water discharge, initial base level, and the sediment to water ratio to a point after which the activity decreased with increasing sediment input. Base-level change experiments used initial conditions of 400 mL/min, a 1:750 sediment to water input ratio, and a 6 cm initial base-level to induce river meanders for the initial 2 hours before base-level change occurred. Three separate experiments investigated the effects of increasing rates of sea level change: 0.07 cm/min, 0.1 cm/min, and 0.2 cm/min. Experimental sea level was decreased constantly from a high-stand of 6 cm to a low-stand of 2 cm back to the high-stand base-level in each experiment. The rates of change in the experiments scale roughly from central to glacial cycles. In all three experiments, sea level fall induced meander cut-off while sea level rise prompted greater rates of meander bend erosion and meander growth. Sinuosity increased by 12%, 13.5%, and 24%, respectively in the three experiments, with most sinuosity changes occurring in the downstream reach of the channel. These experiments could provide insight into long term effects of sea level change on modern meandering fluvial systems as well as provide a key to interpreting past fluvial changes in the stratigraphic record.

Meandering channels without vegetation: Examples from Nevada and Chile

NASA Astrophysics Data System (ADS)

Matsubara, Y.; Howard, A. D.; Burr, D. M.; Williams, R. M.; Moore, J. M.

2012-12-01

We report on a study motivated by the occurrence of highly sinuous, actively migrating paleochannels on Mars. Highly sinuous, unconfined meanders require small aspect ratios, which in turn require cohesive channel banks. This cohesion is obtained most commonly by vegetation cover coupled with high suspended sediment loading. The dominant role of vegetation in meandering is reflected in the difficulty in creating highly sinuous channels in flume experiment without introduction of vegetation. The occurrence of strongly meandering channels on Mars suggests meanders can develop in the absence of vegetation. The main objective of our study is to understand the processes of meander evolution in non-vegetated surfaces. We have studied two terrestrial sites in which meandering channels form where vegetation is sparse and has little influence on bank erodibility or point-bar deposition, indicating that there must be other mechanisms creating bank cohesion. One mechanism is stabilization of point-bar deposits by mud drapes. The Quinn River in Nevada is a sinuous channel that flows through fine lacustrine sediments on the floor of paleolake Lahontan resulting in the river having both bed and bank composed of sediment containing least 40% silt/clay. In addition to abundant mud, high salt content of the river water encourages flocculation and settling of fine sediment; thus both high clay/silt content and salt work together at the Quinn River to maintain a small aspect ratio. In contrast to the Quinn River, meandering channels on alluvial fans in the Atacama Desert in northern Chile are deposited by flows originating from the foothills of the Andes Mountains where sediments are coarser and more variable in size. Like Quinn River both fine sediments and salts contribute to meandering. The bank cohesion is provided by mudflows or hyperconcentrated flows creating bank drapes as well as extensive overbank levees which harden to adobe-like consistency. The Atacama Desert is rich in precipitated salts forming salt crusted deposits, and because grains are coarser, we speculate that these salts may possibly be playing a much more direct role in providing the cohesion than they do in the Quinn River. We are using chemical analyses and Scanning Electron Microscope (SEM) images of sediment samples to investigate cementation mechanisms.

Competing growth processes induced by next-nearest-neighbor interactions: Effects on meandering wavelength and stiffness

NASA Astrophysics Data System (ADS)

Blel, Sonia; Hamouda, Ajmi BH.; Mahjoub, B.; Einstein, T. L.

2017-02-01

In this paper we explore the meandering instability of vicinal steps with a kinetic Monte Carlo simulations (kMC) model including the attractive next-nearest-neighbor (NNN) interactions. kMC simulations show that increase of the NNN interaction strength leads to considerable reduction of the meandering wavelength and to weaker dependence of the wavelength on the deposition rate F. The dependences of the meandering wavelength on the temperature and the deposition rate obtained with simulations are in good quantitative agreement with the experimental result on the meandering instability of Cu(0 2 24) [T. Maroutian et al., Phys. Rev. B 64, 165401 (2001), 10.1103/PhysRevB.64.165401]. The effective step stiffness is found to depend not only on the strength of NNN interactions and the Ehrlich-Schwoebel barrier, but also on F. We argue that attractive NNN interactions intensify the incorporation of adatoms at step edges and enhance step roughening. Competition between NNN and nearest-neighbor interactions results in an alternative form of meandering instability which we call "roughening-limited" growth, rather than attachment-detachment-limited growth that governs the Bales-Zangwill instability. The computed effective wavelength and the effective stiffness behave as λeff˜F-q and β˜eff˜F-p , respectively, with q ≈p /2 .

Exploring the role of trees in the evolution of meander bends: The Tagliamento River, Italy

NASA Astrophysics Data System (ADS)

Zen, Simone; Gurnell, Angela M.; Zolezzi, Guido; Surian, Nicola

2017-07-01

To date, the role of riparian trees in the formation of scroll bars, ridges, and swales during the evolution of meandering channels has been inferred largely from field observations with support from air photographs. In situ field observations are usually limited to relatively short periods of time, whereas the evolution of these morphological features may take decades. By combining field observations of inner bank morphology and overlying riparian woodland structure with a detailed historical analysis of airborne LiDAR data, panchromatic, and color images, we reconstruct the spatial and temporal evolution of the morphology and vegetation across four meander bends of the Tagliamento River, Italy. Specifically we reveal (i) the appearance of deposited trees and elongated vegetated patches on the inner bank of meander bends following flood events; (ii) temporal progression from deposited trees, through small to larger elongated vegetated patches (pioneer islands), to their coalescence into long, linear vegetated features that eventually become absorbed into the continuous vegetation cover of the riparian forest; and (iii) a spatial correspondence between the resulting scrolls and ridge and swale topography, and tree cover development and persistence. We provide a conceptual model of the mechanisms by which vegetation can contribute to the formation of sequence of ridges and swales on the convex bank of meander bends. We discuss how these insights into the biomorphological processes that control meander bends advance can inform modeling activities that aim to describe the lateral and vertical accretion of the floodplain during the evolution of vegetated river meanders.

Temporal variation of meandering intensity and domain-wide lateral oscillations of the Gulf Stream

NASA Technical Reports Server (NTRS)

Lee, Tong; Cornillon, Peter

1995-01-01

The path of the Gulf Stream exhibits two modes of variability: wavelike spatial meanders associated with instability processes and large-sale lateral shifts of the path presumably due to atmospheric forcing. The objectives of this study are to examine the temporal variation of the intensity of spatial meandering in the stream, to characterize large-scale lateral oscillations in the stream's path, and to study the correlation betwen these two dynamically distinct modes of variability. The data used for this analysis are path displacemets ofthe Gulf Stream between 75 deg and 60 deg W obtained from AVHRR-derived (Advanced Very High Resolution Radiometer) infrared images for the period April 1982 through December 1989. Meandering intensity, measured by the spatial root-mean-sqaure displacement of the stream path, displays a 9-month dominant periodicity which is persistent through the study period. The 9-month fluctuation in meandering intensity may be related to the interaction of Rosseby waves with the stream. Interannual variation of meandering intensity is also found to be significant, with meandering being mich more intense during 1985 than it was in 1987. Annual variation, however,is weak and not well-defined.The spatially averaged position of the stream, which reflects nonmeandering large-scale lateral oscillations of the stream path, is dominated by an annual cycle. On average, the mean position is farthest north in November and farthest south in April. The first empirical orthogonal function mode of the space-time path displacements represents lateral oscillatins that are in-phase over the space-time domain. Interannual oscillations are also observed and are found to be weaker than the annual oscillation. The eigenvalue of the first mode indicates that about 21.5% of the total space-time variability of the stream path can be attibuted to domain-wide lateral oscillation. The correlation between meandering intensity and domain-wide lateral oscillations is very weak.

Evolution of cutoffs across meander necks in Powder River, Montana, USA

USGS Publications Warehouse

Gay, G.R.; Gay, H.H.; Gay, W.H.; Martinson, H.A.; Meade, R.H.; Moody, J.A.

1998-01-01

Over a period of several decades, gullies have been observed in various stages of forming, growing and completing the cutoff of meander necks in Powder River. During one episode of overbank flow, water flowing over the down-stream bank of the neck forms a headctu. The headcut migrates up-valley, forming a gully in its wake, until it has traversed the entire neck, cutting off the meander. The river then follows the course of the gully, which is subsequently enlarged as the river develops its new channel. The complete process usually requires several episodes of high water: in only one of the five cases described herein was a meander cutoff initiated and completed during a single large flood.

The Spatial Structure of Planform Migration - Curvature Relation of Meandering Rivers

NASA Astrophysics Data System (ADS)

Guneralp, I.; Rhoads, B. L.

2005-12-01

Planform dynamics of meandering rivers have been of fundamental interest to fluvial geomorphologists and engineers because of the intriguing complexity of these dynamics, the role of planform change in floodplain development and landscape evolution, and the economic and social consequences of bank erosion and channel migration. Improved understanding of the complex spatial structure of planform change and capacity to predict these changes are important for effective stream management, engineering and restoration. The planform characteristics of a meandering river channel are integral to its planform dynamics. Active meandering rivers continually change their positions and shapes as a consequence of hydraulic forces exerted on the channel banks and bed, but as the banks and bed change through sediment transport, so do the hydraulic forces. Thus far, this complex feedback between form and process is incompletely understood, despite the fact that the characteristics and the dynamics of meandering rivers have been studied extensively. Current theoretical models aimed at predicting planform dynamics relate rates of meander migration to local and upstream planform curvature where weighting of the influence of curvature on migration rate decays exponentially over distance. This theoretical relation, however, has not been rigorously evaluated empirically. Furthermore, although models based on exponential-weighting of curvature effects yield fairly realistic predictions of meander migration, such models are incapable of reproducing complex forms of bend development, such as double heading or compound looping. This study presents the development of a new methodology based on parametric cubic spline interpolation for the characterization of channel planform and the planform curvature of meandering rivers. The use of continuous mathematical functions overcomes the reliance on bend-averaged values or piece-wise discrete approximations of planform curvature - a major limitation of previous studies. Continuous curvature series can be related to measured rates of lateral migration to explore empirically the relationship between spatially extended curvature and local bend migration. The methodology is applied to a study reach along a highly sinuous section of the Embarras River in Illinois, USA, which contains double-headed asymmetrical loops. To identify patterns of channel planform and rates of lateral migration for a study reach along Embarrass River in central Illinois, geographical information systems analysis of historical aerial photography over a period from 1936 to 1998 was conducted. Results indicate that parametric cubic spline interpolation provides excellent characterization of the complex planforms and planform curvatures of meandering rivers. The findings also indicate that the spatial structure of migration rate-curvature relation may be more complex than a simple exponential distance-decay function. The study represents a first step toward unraveling the spatial structure of planform evolution of meandering rivers and for developing models of planform dynamics that accurately relate spatially extended patterns of channel curvature to local rates of lateral migration. Such knowledge is vital for improving the capacity to accurately predict planform change of meandering rivers.

Rapid replacement of riparian rainforest habitat and the impacts on the meandering dynamics of the Kinabatangan River, Borneo

NASA Astrophysics Data System (ADS)

Horton, Alexander J.; Constantine, José A.

2014-05-01

Meandering rivers are defined by their nature to migrate, remobilising floodplain sediment and constructing new surfaces for riparian vegetation to colonise. The presence of riparian vegetation has long been known to limit the ability of rivers to erode riverbanks, but it has remained unclear the principal means by which vegetation provides this function. As a result, most models that predict meandering behaviour do not fully incorporate vegetation, thereby limiting their utility where forest is rapidly replaced. The problem is particularly acute along the Kinabatangan River of Sabah in Malaysian Borneo, where oil palm plantations are replacing one of the oldest riparian rainforests on the planet. The area of Sabah has seen rapid and extensive land use change in the last 40 years, as virgin rainforest has been systematically cleared for logging, and to make way for oil palm plantations. In the 18 years from 1990 to 2008, Sabah lost half of its intact rainforest, which equates to more than 1.85 million hectares. Using Landsat imagery dating back to 1973, we report here the impacts of this rapid land-use change on rates of meander migration on a 280-km reach of the Kinabatangan River. The river planform has been remarkably stable throughout the time period of study, but individual meanders show a rapid response to large discharge events, migrating over an order of magnitude faster than nearby reaches. Rapidly migrating meanders generally occur along portions of floodplain that have been artificially cleared of riparian vegetation, potentially resulting in significant increases in sediment load and within-channel bar development. A field campaign is planned to investigate the mechanisms by which riparian vegetation effect meander migration in these tropical regions.

Flow Structure and Channel Morphology at a Confluent-Meander Bend

NASA Astrophysics Data System (ADS)

Riley, J. D.; Rhoads, B. L.

2009-12-01

Flow structure and channel morphology in meander bends have been well documented. Channel curvature subjects flow through a bend to centrifugal acceleration, inducing a counterbalancing pressure-gradient force that initiates secondary circulation. Transverse variations in boundary shear stress and bedload transport parallel cross-stream movement of high velocity flow and determine spatial patterns of erosion along the outer bank and deposition along the inner bank. Laboratory experiments and numerical modeling of confluent-meander bends, a junction planform that develops when a tributary joins a meandering river along the outer bank of a bend, suggest that flow and channel morphology in such bends deviate from typical patterns. The purpose of this study is to examine three-dimensional (3-D) flow structure and channel morphology at a natural confluent-meander bend. Field data were collected in southeastern Illinois where Big Muddy Creek joins the Little Wabash River near a local maximum of curvature along an elongated meander loop. Measurements of 3-D velocity components were obtained with an acoustic Doppler current profiler (ADCP) for two flow events with differing momentum ratios. Channel bathymetry was also resolved from the four-beam depths of the ADCP. Analysis of velocity data reveals a distinct shear layer flanked by dual helical cells within the bend immediately downstream of the confluence. Flow from the tributary confines flow from the main channel along the inner part of the channel cross section, displacing the thalweg inward, limiting the downstream extent of the point bar, protecting the outer bank from erosion and enabling bar-building along this bank. Overall, this pattern of flow and channel morphology is quite different from typical patterns in meander bends, but is consistent with a conceptual model derived from laboratory experiments and numerical modeling.

Testing the Role of Meander Cutoff in Promoting Gene Flow across a Riverine Barrier in Ground Skinks (Scincella lateralis)

PubMed Central

Jackson, Nathan D.; Austin, Christopher C.

2013-01-01

Despite considerable attention, the long-term impact of rivers on species diversification remains uncertain. Meander loop cutoff (MLC) is one river phenomenon that may compromise a river’s diversifying effects by passively transferring organisms from one side of the river to the other. However, the ability of MLC to promote gene flow across rivers has not been demonstrated empirically. Here, we test several predictions of MLC-mediated gene flow in populations of North American ground skinks (Scincella lateralis) separated by a well-established riverine barrier, the Mississippi River: 1) individuals collected from within meander cutoffs should be more closely related to individuals across the river than on the same side, 2) individuals within meander cutoffs should contain more immigrants than individuals away from meander cutoffs, 3) immigration rates estimated across the river should be highest in the direction of the cutoff event, and 4) the distribution of alleles native to one side of the river should be better predicted by the historical rather than current path of the river. To test these predictions we sampled 13 microsatellite loci and mitochondrial DNA from ground skinks collected near three ancient meander loops. These predictions were generally supported by genetic data, although support was stronger for mtDNA than for microsatellite data. Partial support for genetic divergence of samples within ancient meander loops also provides evidence for the MLC hypothesis. Although a role for MLC-mediated gene flow was supported here for ground skinks, the transient nature of river channels and morphologies may limit the long-term importance of MLC in stemming population divergence across major rivers. PMID:23658778

The life of a meander bend: Connecting shape and dynamics via analysis of a numerical model

NASA Astrophysics Data System (ADS)

Schwenk, Jon; Lanzoni, Stefano; Foufoula-Georgiou, Efi

2015-04-01

Analysis of bend-scale meandering river dynamics is a problem of theoretical and practical interest. This work introduces a method for extracting and analyzing the history of individual meander bends from inception until cutoff (called "atoms") by tracking backward through time the set of two cutoff nodes in numerical meander migration models. Application of this method to a simplified yet physically based model provides access to previously unavailable bend-scale meander dynamics over long times and at high temporal resolutions. We find that before cutoffs, the intrinsic model dynamics invariably simulate a prototypical cutoff atom shape we dub simple. Once perturbations from cutoffs occur, two other archetypal cutoff planform shapes emerge called long and round that are distinguished by a stretching along their long and perpendicular axes, respectively. Three measures of meander migration—growth rate, average migration rate, and centroid migration rate—are introduced to capture the dynamic lives of individual bends and reveal that similar cutoff atom geometries share similar dynamic histories. Specifically, through the lens of the three shape types, simples are seen to have the highest growth and average migration rates, followed by rounds, and finally longs. Using the maximum average migration rate as a metric describing an atom's dynamic past, we show a strong connection between it and two metrics of cutoff geometry. This result suggests both that early formative dynamics may be inferred from static cutoff planforms and that there exists a critical period early in a meander bend's life when its dynamic trajectory is most sensitive to cutoff perturbations. An example of how these results could be applied to Mississippi River oxbow lakes with unknown historic dynamics is shown. The results characterize the underlying model and provide a framework for comparisons against more complex models and observed dynamics.

Rotor meandering contributes to irregularity in electrograms during atrial fibrillation.

PubMed

Zlochiver, Sharon; Yamazaki, Masatoshi; Kalifa, Jérôme; Berenfeld, Omer

2008-06-01

Radiofrequency ablation therapy of atrial fibrillation (AF) recently incorporated the analysis of dominant frequency (DF) and/or electrogram fractionation for guidance. However, the relationships between DF, fractionation, and spatiotemporal characteristics of the AF source remain unclear. We hypothesize that a meandering reentrant AF source contributes to the wave fractionation and is reflected in the power spectrum of local electrograms elsewhere in the rotor's surroundings. Meandering rotors as AF sources were simulated in 2-dimensional models of human atrial tissue and recorded in isolated sheep hearts. Nondominant elements of the signals were differentiated from the dominant elements using singular value decomposition, whereby the purely periodic constituent (PC) relating to the rotor's DF was eliminated rendering a residual constituent (RC) that consisted of all other activity. Spectral analysis of the decomposed constituents revealed peaks corresponding to the meandering frequency of the rotor tip, the magnitudes of which were proportional to the size of and the distance to the rotor core. Similar analyses on epicardial optical signals and electrograms from isolated sheep hearts, as well as human complex fractionated atrial electrograms, showed applicability of the approach. Increased meandering of the rotor driving AF reduces activation periodicity and increases fractionation. The spectral manifestation of the rotor activity beyond the meandering region makes it possible to characterize AF source stability, as well as DF in humans using electrode mapping.

Rotor Meandering Contributes to Irregularity in Electrograms during Atrial Fibrillation

PubMed Central

Zlochiver, Sharon; Yamazaki, Masatoshi; Kalifa, Jerome; Berenfeld, Omer

2010-01-01

Radiofrequency ablation therapy of atrial fibrillation (AF) recently incorporated the analysis of dominant frequency (DF) and/or electrogram fractionation for guidance. However, the relationships between DF, fractionation and spatio-temporal characteristics of the AF source remain unclear. We hypothesize that meandering reentrant AF source contributes to the wave fractionation and is reflected in the power spectrum of local electrograms elsewhere in the rotor’s surroundings. Methods Meandering rotors as AF sources were simulated in 2D models of human atrial tissue and recorded in isolated sheep hearts. Non-dominant elements of the signals were differentiated from the dominant elements using singular value decomposition, whereby the purely periodic constituent (PC) relating to the rotor’s DF was eliminated rendering a residual constituent (RC) that consisted of all other activity. Results Spectral analysis of the decomposed constituents revealed peaks corresponding to the meandering frequency of the rotor tip, the magnitudes of which were proportional to the size of, and the distance to the rotor core. Similar analyses on epicardial optical signals and electrograms from isolated sheep hearts, as well as human complex fractionated atrial electrograms demonstrated applicability of the approach. Conclusion Increased meandering of the rotor driving AF reduces activation periodicity and increases fractionation. The spectral manifestation of the rotor activity beyond the meandering region makes it possible to characterize AF source stability, as well as DF in humans using electrode mapping. PMID:18534369

Modeling meander morphodynamics over self-formed heterogeneous floodplains

NASA Astrophysics Data System (ADS)

Bogoni, Manuel; Putti, Mario; Lanzoni, Stefano

2017-06-01

This work addresses the signatures embedded in the planform geometry of meandering rivers consequent to the formation of floodplain heterogeneities as the river bends migrate. Two geomorphic features are specifically considered: scroll bars produced by lateral accretion of point bars at convex banks and oxbow lake fills consequent to neck cutoffs. The sedimentary architecture of these geomorphic units depends on the type and amount of sediment, and controls bank erodibility as the river impinges on them, favoring or contrasting the river migration. The geometry of numerically generated planforms obtained for different scenarios of floodplain heterogeneity is compared to that of natural meandering paths. Half meander metrics and spatial distribution of channel curvatures are used to disclose the complexity embedded in meandering geometry. Fourier Analysis, Principal Component Analysis, Singular Spectrum Analysis and Multivariate Singular Spectrum Analysis are used to emphasize the subtle but crucial differences which may emerge between apparently similar configurations. A closer similarity between observed and simulated planforms is attained when fully coupling flow and sediment dynamics (fully-coupled models) and when considering self-formed heterogeneities that are less erodible than the surrounding floodplain.

Vortex coupling in trailing vortex-wing interactions

NASA Astrophysics Data System (ADS)

Chen, C.; Wang, Z.; Gursul, I.

2018-03-01

The interaction of trailing vortices of an upstream wing with rigid and flexible downstream wings has been investigated experimentally in a wind tunnel, using particle image velocimetry, hot-wire, force, and deformation measurements. Counter-rotating upstream vortices exhibit increased meandering when they are close to the tip of the downstream wing. The upstream vortex forms a pair with the vortex shed from the downstream wing and then exhibits large displacements around the wing tip. This coupled motion of the pair has been found to cause large lift fluctuations on the downstream wing. The meandering of the vortex pair occurs at the natural meandering frequency of the isolated vortex, with a low Strouhal number, and is not affected by the frequency of the large-amplitude wing oscillations if the downstream wing is flexible. The displacement of the leading vortex is larger than that of the trailing vortex; however, it causes highly correlated variations of the core radius, core vorticity, and circulation of the trailing vortex with the coupled meandering motion. In contrast, co-rotating vortices do not exhibit any increased meandering.

Highly Sinuous Meanders on Mars: Morphology, Hydrology and Terrestrial Analogs (Invited)

NASA Astrophysics Data System (ADS)

Howard, A. D.; Burr, D. M.; Williams, R.

2009-12-01

Of the rare preserved channel features on Mars, perhaps the most exciting are highly sinuous channels found, to date, in only three locations. We discuss the most extensive of these channel systems in the Aeolis/Zephyra Plana region. The channel features stand in positive relief (as inverted channels). The morphological assemblage of the sinuous ridges [Burr et al., 2009] presents a compelling case for their origin through persistent fluvial meandering within branching networks of preserved channels and associated meander belts. High resolution images reveal narrow sinuous ridges which can often be traced over tens of torturous loops. Wavelengths of these sinuous plateaus range from about 200-500 m and the width of the superposed or embedded ridges ranges from about 20-100 m where well preserved. The flat-topped plateaus exhibit irregular outer edges, often with lobate planforms with about the same size and curvature as bends in the associated sinuous ridges. We interpret these to be cutoff meander loops. In some cases parallel lineations occur interior to the sinuous ridges that appear to be analogs to point bar scars in terrestrial meandering channels. We interpret the sinuous ridges and associated sinuous plateaus featuring lobate scarps to be remnants of floodplains and associated channels formed by meandering streams. These have subsequently been eroded into positive relief by aeolian deflation of weaker surrounding deposits. At the time of fluvial activity the valleys would have been surrounded by uplands (probably with low relief). The dendritic pattern of the floodplain deposits and the considerable period of time required to sculpt the wide floodplains through lateral meander migration with cutoffs indicates a water source from distributed precipitation as rain or snow followed by runoff. The primary geomorphic issue with the martian meanders is the mechanism providing bank cohesion and a low aspect ratio. Terrestrial highly sinuous, unconfined meanders require small aspect ratios, γ (the ratio of channel width, W, to average depth, H). These in turn require resistant stream banks and generally low rates of bedload transport relative to fine, suspended sediment. On earth, resistance generally is conferred either by cohesive, clay-rich sediment deposited from suspension or a dense vegetation cover. Discounting vegetation control on Mars, cohesive banks might have been favored by high clay content, cohesion from ice in permafrost or from post-deposition cementation. The importance of bank cohesion in producing meandering channel patterns is illustrated by the difficulty in producing highly sinuous channels in a laboratory setting. We are presently investigating potential terrestrial analogs in the western US, Alaska, and Australia where bank cohesion may be provided by mechanisms other than vegetation.

Time-Frequency Variability of Kuroshio Meanders in Tokara Strait

NASA Astrophysics Data System (ADS)

Nakamura, H.; Yamashiro, T.; Nishina, A.; Ichikawa, H.

2006-12-01

The Kuroshio path in the northern Okinawa Trough, Japan, located between the continental slope and Tokara Strait, exhibits meandering motions with largest displacements in the East China Sea; these motions have dominant periods in the broad range of 30-90 days. Understanding the dynamic nature of such meanders is crucial to predicting small and large meanders of the Kuroshio path off the south coast of Japan. Previous numerical simulations suggest that the Kuroshio path meanders in the northern Okinawa Trough become nonstationary in variance because of changes in background states of the Kuroshio in the northern Okinawa Trough, but a detailed analysis based on observed data has yet to be performed. The purpose of the present study is to provide a detailed description of the time-frequency variability of Kuroshio path meanders observed in Tokara Strait. Three Kuroshio indicators were subjected to wavelet analysis for the period 1984-2004: the Kuroshio Position Index (KPI) in Tokara Strait, Kuroshio Volume Transport (KVT) in Tokara Strait, and the basal current velocity of the Kuroshio on the continental slope in the northern Okinawa Trough. The 30-90 day variance of the KPI shows a season-fixed nature, with larger amplitudes in the period December-July. The amplitude of the variance in this phenomenon is also modulated by interannual variations, with small variance recorded during 1989-1992, large variance during 1993-1998, and a return to small variance from 1999-2003. This interannual variation is positively correlated with that of the KVT. The largest variance of the KPI during February-April precedes the largest volume transport in April-May by about 1 month, suggesting that eddy vorticity flux strengthens the mean current field. Previous numerical simulations reproduce the recirculation gyre as a cyclonic eddy in the area between the continental slope and Tokara Strait; this gyre is analogous to the northern recirculation gyre associated with the eastward jet. On the basis of data from a moored current-meter situated on the continental slope, the genesis of the 30-90 day meanders within Tokara Strait is ascribed to nonlinear energy transfer from 8-25 day meanders on the continental slope.

River meanders

USGS Publications Warehouse

Leopold, Luna Bergere; Langbein, Walter Basil

1966-01-01

The striking geometric regularity of a winding river is no accident. Meanders appear to be the form in which a river does the least work in turning; hence they are the most probable form a river can take

Absolute and convective instabilities and their roles in the forecasting of large frontal meanderings

NASA Astrophysics Data System (ADS)

Liang, X. San; Robinson, Allan R.

2013-10-01

Frontal meanderings are generally difficult to predict. In this study, we demonstrate through an exercise with the Iceland-Faeroe Front (IFF) that satisfactory predictions may be achieved with the aid of hydrodynamic instability analysis. As discovered earlier on, underlying the IFF meandering is a convective instability in the western boundary region followed by an absolute instability in the interior; correspondingly the disturbance growth reveals a switch of pattern from spatial amplification to temporal amplification. To successfully forecast the meandering, the two instability processes must be faithfully reproduced. This sets stringent constraints for the tunable model parameters, e.g., boundary relaxation, temporal relaxation, eddy diffusivity, etc. By analyzing the instability dispersion properties, these parameters can be rather accurately set and their respective ranges of sensitivity estimated. It is shown that too much relaxation inhibits the front from varying; on the other hand, too little relaxation may have the model completely skip the spatial growth phase, leading to a meandering way more upstream along the front. Generally speaking, dissipation/diffusion tends to stabilize the simulation, but unrealistically large dissipation/diffusion could trigger a spurious absolute instability, and hence a premature meandering intrusion. The belief that taking in more data will improve the forecast does not need to be true; it depends on whether the model setup admits the two instabilities. This study may help relieve modelers from the laborious and tedious work of parameter tuning; it also provides us criteria to distinguish a physically relevant forecast from numerical artifacts.

Application of meandering centreline migration modelling and object-based approach of Long Nab member

NASA Astrophysics Data System (ADS)

Saadi, Saad

2017-04-01

Characterizing the complexity and heterogeneity of the geometries and deposits in meandering river system is an important concern for the reservoir modelling of fluvial environments. Re-examination of the Long Nab member in the Scalby formation of the Ravenscar Group (Yorkshire, UK), integrating digital outcrop data and forward modelling approaches, will lead to a geologically realistic numerical model of the meandering river geometry. The methodology is based on extracting geostatistics from modern analogous, meandering rivers that exemplify both the confined and non-confined meandering point bars deposits and morphodynamics of Long Nab member. The parameters derived from the modern systems (i.e. channel width, amplitude, radius of curvature, sinuosity, wavelength, channel length and migration rate) are used as a statistical control for the forward simulation and resulting object oriented channel models. The statistical data derived from the modern analogues is multi-dimensional in nature, making analysis difficult. We apply data mining techniques such as parallel coordinates to investigate and identify the important relationships within the modern analogue data, which can then be used drive the development of, and as input to the forward model. This work will increase our understanding of meandering river morphodynamics, planform architecture and stratigraphic signature of various fluvial deposits and features. We will then use these forward modelling based channel objects to build reservoir models, and compare the behaviour of the forward modelled channels with traditional object modelling in hydrocarbon flow simulations.

Wake meandering of a model wind turbine operating in two different regimes

NASA Astrophysics Data System (ADS)

Foti, Daniel; Yang, Xiaolei; Campagnolo, Filippo; Maniaci, David; Sotiropoulos, Fotis

2018-05-01

The flow behind a model wind turbine under two different turbine operating regimes (region 2 for turbine operating at optimal condition with the maximum power coefficient and 1.4-deg pitch angle and region 3 for turbine operating at suboptimal condition with a lower power coefficient and 7-deg pitch angle) is investigated using wind tunnel experiments and numerical experiments using large-eddy simulation (LES) with actuator surface models for turbine blades and nacelle. Measurements from the model wind turbine experiment reveal that the power coefficient and turbine wake are affected by the operating regime. Simulations with and without a nacelle model are carried out for each operating condition to study the influence of the operating regime and nacelle on the formation of the hub vortex and wake meandering. Statistics and energy spectra of the simulated wakes are in good agreement with the measurements. For simulations with a nacelle model, the mean flow field is composed of an outer wake, caused by energy extraction by turbine blades, and an inner wake directly behind the nacelle, while for the simulations without a nacelle model, the central region of the wake is occupied by a jet. The simulations with the nacelle model reveal an unstable helical hub vortex expanding outward toward the outer wake, while the simulations without a nacelle model show a stable and columnar hub vortex. Because of the different interactions of the inner region of the wake with the outer region of the wake, a region with higher turbulence intensity is observed in the tip shear layer for the simulation with a nacelle model. The hub vortex for the turbine operating in region 3 remains in a tight helical spiral and intercepts the outer wake a few diameters further downstream than for the turbine operating in region 2. Wake meandering, a low-frequency large-scale motion of the wake, commences in the region of high turbulence intensity for all simulations with and without a nacelle model, indicating that neither a nacelle model nor an unstable hub vortex is a necessary requirement for the existence of wake meandering. However, further analysis of the wake meandering and instantaneous flow field using a filtering technique and dynamic mode decomposition show that the unstable hub vortex energizes the wake meandering. The turbine operating regime affects the shape and expansion of the hub vortex, altering the location of the onset of the wake meandering and wake meander oscillating intensity. Most important, the unstable hub vortex promotes a high-amplitude energetic meandering which cannot be predicted without a nacelle model.

Investigation of fluvial landforms in the north-eastern Pannonian Basin, using cartographic materials from the XIX-XXI Centuries

NASA Astrophysics Data System (ADS)

Robu, Delia; Niga, Bogdan; Perşoiu, Ioana

2015-04-01

The study area is located in the north-eastern Pannonian Basin, and covers approximately 3700 km2. Using cartographic materials for the last 155 years, we analyzed and defined river network and relict fluvial morphologies created by the rivers Tur, Someş, Homorod and Crasna. Database extraction from each set of historical maps was performed by field verification and validation, associated to GIS techniques. Relict fluvial morphologies on the Someş alluvial cone comprise a wide variety of channel typologies and sizes, drainage directions and their consequent typology, which indicates a complex fluvial evolution. The dominant category of relict fluvial morphology is represented by the meander loop. Following the quantitative analysis on the successive sets of maps we identified and delimited meander loops and meandering paths formed prior to the reference year 1860. Generally, the post-1860 relict fluvial morphologies are secondary morphologies, as the keynote is given by those formed previous to the reference moment 1860. An analysis of the share of the relict fluvial morphologies on the three sets of reference cartographic materials (the second Austro-Hungarian topographic survey, Google Earth and orthophotoplans) highlights that most relict fluvial morphologies were identified on the second Austro-Hungarian topographic survey, followed by those identified in Google Earth and orthophotoplans. The map of fluvial morphologies constructed in this study enables a discussion on drainage directions, based on the observation that a series of abandoned meander loops and segments follow clear directions. We applied several quantitative indices in assessing the relict fluvial morphology (radius of curvature, paleochannel width). Consequently, we identified underfit stream sectors with meander loops larger than the modern ones Someş meanders (on the Racta River), uncharacteristic features such as braided riverbed reaches, a high frequency of meander scrolls present on the right bank of Crasna at its entrance in the plain, or the occurrence of wetlands in an area affected by subsidence (the Ecedeea Plain). Despite the ample human intervention in our study area through sewers, dams, meander cuts, the river network evolution trend remained the same between 1860 and 2005, with evolution and formation of meanders, although the change rate has diminished. "ACKNOWLEDGMENT This paper has been financially supported within the project entitled "SOCERT. Knowledge society, dynamism through research", contract number POSDRU/159/1.5/S/132406. This project is co-financed by European Social Fund through Sectoral Operational Programme for Human Resources Development 2007-2013. Investing in people!"

Low-frequency meandering piezoelectric vibration energy harvester.

PubMed

Berdy, David F; Srisungsitthisunti, Pornsak; Jung, Byunghoo; Xu, Xianfan; Rhoads, Jeffrey F; Peroulis, Dimitrios

2012-05-01

The design, fabrication, and characterization of a novel low-frequency meandering piezoelectric vibration energy harvester is presented. The energy harvester is designed for sensor node applications where the node targets a width-to-length aspect ratio close to 1:1 while simultaneously achieving a low resonant frequency. The measured power output and normalized power density are 118 μW and 5.02 μW/mm(3)/g(2), respectively, when excited by an acceleration magnitude of 0.2 g at 49.7 Hz. The energy harvester consists of a laser-machined meandering PZT bimorph. Two methods, strain-matched electrode (SME) and strain-matched polarization (SMP), are utilized to mitigate the voltage cancellation caused by having both positive and negative strains in the piezoelectric layer during operation at the meander's first resonant frequency. We have performed finite element analysis and experimentally demonstrated a prototype harvester with a footprint of 27 x 23 mm and a height of 6.5 mm including the tip mass. The device achieves a low resonant frequency while maintaining a form factor suitable for sensor node applications. The meandering design enables energy harvesters to harvest energy from vibration sources with frequencies less than 100 Hz within a compact footprint.

Mechanical Stress Effects on Electromigration Voiding in a Meandering Test Stripe

NASA Technical Reports Server (NTRS)

Lowry, L. E.; Tai, B. H.; Mattila, J.; Walsh, L. H.

1993-01-01

Earlier experimental findings concluded that electromigratin voids in these meandering stripe test structures were not randomly distributed and that void nucleation frequenly occurred sub-surface at the metal/thermal oxide interface.

Earth Observations taken by Expedition 38 crewmember

NASA Image and Video Library

2013-12-30

ISS038-E-023651 (26 Dec. 2013) --- Lake Sharpe near Lower Brule, South Dakota is featured in this image photographed by an Expedition 38 crew member on the International Space Station. The Missouri River rises in the Rocky Mountains of western Montana, and flows generally to the southeast for approximately 3,767 kilometers (2,341 miles) to its confluence with the Mississippi River north of St. Louis, Missouri -- making it the longest river in North America. The river does not follow a straight southeasterly course along this distance, but includes may meander bends such as illustrated in this photograph. This particular bend is occupied by Lake Sharpe, an approximately 130-kilometer (80 miles) long reservoir formed behind the Big Bend Dam on the Missouri River. The lake surface is frozen and covered with snow, presenting a uniform white appearance in the image. As meander bends develop, they tend to assume a distinctive U-shape when viewed from above. Over time, the river channel can continue to cut into the ends of the "U", eventually bringing them so close together that the river then cuts across the gap to achieve a shorter flow path, essentially short-circuiting or cutting off the meander bend. When this happens and the meander ceases to be part of the active river channel, it may become an oxbow lake. The distance across the narrow neck of land (lower right) associated with this meander near Lower Brule, South Dakota is approximately one kilometer (0.62 miles); however, as the river flow is controlled by the Big Bend Dam downstream, the natural process of meander cutoff has been significantly slowed. The snow cover also highlights circular agricultural fields on the small peninsula within the meander bend. This type of field indicates center-pivot irrigation, where water is distributed from a central point radially outwards using sprinklers to cover the field area. Crops grown here include corn and soybeans according to data from the US Department of Agriculture's CropScape database.

Stereo Anaglyphs of River Meanders in Eberswalde Delta

NASA Image and Video Library

2007-01-10

This anaglyph from NASA Mars Reconnaissance Orbiter spacecraft, shows that Eberswalde Delta contains river meanders, which indicate that flowing water was present for an extended period of time. 3D glasses are necessary to view this image.

Oxbows and Cutoffs in Idaeus Fossae

NASA Image and Video Library

2013-08-21

As rivers age they can meander and occasionally these meanders get so pronounced that the river cuts off these curving loops at their narrow end leaving them as isolated as oxbow lakes. Image from NASA Mars Reconnaissance Orbiter.

Plane mixing layer vortical structure kinematics

NASA Technical Reports Server (NTRS)

Leboeuf, Richard L.

1993-01-01

The objective of the current project was to experimentally investigate the structure and dynamics of the streamwise vorticity in a plane mixing layer. The first part of this research program was intended to clarify whether the observed decrease in mean streamwise vorticity in the far-field of mixing layers is due primarily to the 'smearing' caused by vortex meander or to diffusion. Two-point velocity correlation measurements have been used to show that there is little spanwise meander of the large-scale streamwise vortical structure. The correlation measurements also indicate a large degree of transverse meander of the streamwise vorticity which is not surprising since the streamwise vorticity exists in the inclined braid region between the spanwise vortex core regions. The streamwise convection of the braid region thereby introduces an apparent transverse meander into measurements using stationary probes. These results corroborated with estimated secondary velocity profiles in which the streamwise vorticity produces a signature which was tracked in time.

Wake meandering statistics of a model wind turbine: Insights gained by large eddy simulations

NASA Astrophysics Data System (ADS)

Foti, Daniel; Yang, Xiaolei; Guala, Michele; Sotiropoulos, Fotis

2016-08-01

Wind tunnel measurements in the wake of an axial flow miniature wind turbine provide evidence of large-scale motions characteristic of wake meandering [Howard et al., Phys. Fluids 27, 075103 (2015), 10.1063/1.4923334]. A numerical investigation of the wake, using immersed boundary large eddy simulations able to account for all geometrical details of the model wind turbine, is presented here to elucidate the three-dimensional structure of the wake and the mechanisms controlling near and far wake instabilities. Similar to the findings of Kang et al. [Kang et al., J. Fluid Mech. 744, 376 (2014), 10.1017/jfm.2014.82], an energetic coherent helical hub vortex is found to form behind the turbine nacelle, which expands radially outward downstream of the turbine and ultimately interacts with the turbine tip shear layer. Starting from the wake meandering filtering used by Howard et al., a three-dimensional spatiotemporal filtering process is developed to reconstruct a three-dimensional meandering profile in the wake of the turbine. The counterwinding hub vortex undergoes a spiral vortex breakdown and the rotational component of the hub vortex persists downstream, contributing to the rotational direction of the wake meandering. Statistical characteristics of the wake meandering profile, along with triple decomposition of the flow field separating the coherent and incoherent turbulent fluctuations, are used to delineate the near and far wake flow structures and their interactions. In the near wake, the nacelle leads to mostly incoherent turbulence, while in the far wake, turbulent coherent structures, especially the azimuthal velocity component, dominate the flow field.

Field Investigation of Flow Structure and Channel Morphology at Confluent-Meander Bends

NASA Astrophysics Data System (ADS)

Riley, J. D.; Rhoads, B. L.

2007-12-01

The movement of water and sediment through drainage networks is inevitably influenced by the convergence of streams and rivers at channel confluences. These focal components of fluvial systems produce a complex hydrodynamic environment, where rapid changes in flow structure and sediment transport occur to accommodate the merging of separate channel flows. The inherent geometric and hydraulic change at confluences also initiates the development of distinct geomorphic features, reflected in the bedform and shape of the channel. An underlying assumption of previous experimental and theoretical models of confluence dynamics has been that converging streams have straight channels with angular configurations. This generalized conceptualization was necessary to establish confluence planform as symmetrical or asymmetrical and to describe subsequent flow structure and geomorphic features at confluences. However, natural channels, particularly those of meandering rivers, curve and bend. This property and observation of channel curvature at natural junctions have led to the hypothesis that natural stream and river confluences tend to occur on the concave outer bank of meander bends. The resulting confluence planform, referred to as a confluent-meander bend, was observed over a century ago but has received little scientific attention. This paper examines preliminary data on three-dimensional flow structure and channel morphology at two natural confluent-meander bends of varying size and with differing tributary entrance locations. The large river confluence of the Vermilion River and Wabash River in west central Indiana and the comparatively small junction of the Little Wabash River and Big Muddy Creek in southeastern Illinois are the location of study sites for field investigation. Measurements of time-averaged three-dimensional velocity components were obtained at these confluences with an acoustic Doppler current profiler for flow events with differing momentum ratios. Bed and channel morphology were also surveyed with a digital fathometer to document geomorphic change. Preliminary analysis of the velocity data reveals the presence of a well-defined shear layer between the converging flows and secondary circulation in the main channel. The tributary channel appears to oppose high velocity flow directed toward the outer bank by centrifugal acceleration through the meander bend of the main channel, thereby diminishing erosion along the cut bank and possibly stabilizing the meander bend channel. The flow structure and channel morphology of the study sites are compared to consider the effect of spatial scale and geometric characteristics on confluent-meander bend dynamics.

Integration of fluvial erosion factors for predicting landslides along meandering rivers

NASA Astrophysics Data System (ADS)

Chen, Yi-chin; Chang, Kang-tsung; Ho, Jui-yi

2015-04-01

River incision and lateral erosion are important geomorphologic processes in mountainous areas of Taiwan. During a typhoon or storm event, the increase of water discharge, flow velocity, and sediment discharge enhances the power of river erosion on channel bank. After the materials on toe of hillslope were removed by river erosion, landslides were triggered at outer meander bends. Although it has been long expected that river erosion can trigger landslide, studies quantifying the effects of river erosion on landslide and the application of river erosion index in landslide prediction are still overlooked. In this study, we investigated the effect of river erosion on landslide in a particular meanders landscape of the Jhoukou River, southern Taiwan. We developed a semi-automatic model to separate meandering lines into several reach segments based on the inflection points and to calculate river erosion indexes, e.g. sinuosity of meander, stream power, and stream order, for each reach segment. This model, then, built the spatial relationship between the reaches and its corresponding hillslopes, of which the toe was eroded by the reach. Based on the spatial relationship, we quantified the correlations between these indexes and landslides triggered by Typhoon Morakot in 2009 to examine the effects of river erosion on landslide. The correlated indexes were then used as landslide predictors in logistic regression model. Results of the study showed that there is no significant correlation between landslide density and meander sinuosity. This may be a result of wider channel dispersing the erosion at a meandering reach. On the other hand, landslide density at concave bank is significantly higher than that at convex bank in the downstream (stream order > 3), but that is almost the same in the upstream (stream order < 3). This may imply that river sediment play different roles between down- and upstream segments. River sediment in the upstream is an erosion agent vertically scouring the river bed, resulting in a symmetrical effect on both concave and convex bank. In contrast, river sediment in the downstream is an erosion agent eroding the concave bank laterally, but also depositing on the concave side and protecting the bank from erosion. Finally, the results also showed that the integration of fluvial erosion factors can improve the performance in predicting landsliding along meandering rivers.

Observation method to predict meander migration and vertical degradation of rivers.

DOT National Transportation Integrated Search

2014-05-01

Meander migration and vertical degradation of river bed are processes that have been studied for years. : Different methods have been proposed to make predictions of the behavior of rivers with respect to these : processes. These two erosion controll...

The Amateur Scientist.

ERIC Educational Resources Information Center

Walker, Jearl

1985-01-01

Discusses forces that shape the behavior of water as a drop meanders down a windowpane. A homemade apparatus for studying meanders is described along with several experiments. Contact angles, molecule attraction, surface area, air tension, and gravity drag forces are some of the topics addressed. (DH)

Microelectromechanical power generator and vibration sensor

DOEpatents

Roesler, Alexander W [Tijeras, NM; Christenson, Todd R [Albuquerque, NM

2006-11-28

A microelectromechanical (MEM) apparatus is disclosed which can be used to generate electrical power in response to an external source of vibrations, or to sense the vibrations and generate an electrical output voltage in response thereto. The MEM apparatus utilizes a meandering electrical pickup located near a shuttle which holds a plurality of permanent magnets. Upon movement of the shuttle in response to vibrations coupled thereto, the permanent magnets move in a direction substantially parallel to the meandering electrical pickup, and this generates a voltage across the meandering electrical pickup. The MEM apparatus can be fabricated by LIGA or micromachining.

Influences of Relative Sea-Level Rise and Mississippi River Delta Plain Evolution on the Holocene Middle Amite River, Southeastern Louisiana

USGS Publications Warehouse

Autin, W.J.

1993-01-01

The Holocene geomorphic history of southeastern Louisiana's middle Amite River is recorded in the stratigraphy of three alloformations, identified in decreasing age as the Watson (WAT), Denham Springs (DS), and Magnolia Bridge (MAG). The WAT meander belt formed by at least 9000 yr B.P., when sea level was lower and the Amite River was tributary to a larger ancestral drainage basin. The DS became an active meander belt by at least 3000 yr B.P., in response to relative sea-level rise and eastward progradation of the Mississippi River delta plain. The MAG developed its meander belt, in part, during the European settlement of the drainage basin, and is now attempting to adjust to modern anthropogenic influences. Geomorphic influences on the middle Amite River floodplain have temporal and spatial components that induce regional- and local-scale effects. Regional extrinsic influences caused meander belt avulsion that produced alloformations. However, local influences produced intrinsic geomorphic thresholds that modified channel morphology within a meander belt but did not induce alloformation development. Base-level influences of the relative sea-level rise and the Mississippi River delta plain were so dominant that the effects of possible climate change were not recognized in the Holocene Amite River system.

Impact of different meander sizes on the RF transmit performance and coupling of microstrip line elements at 7 T.

PubMed

Rietsch, Stefan H G; Quick, Harald H; Orzada, Stephan

2015-08-01

In this work, the transmit performance and interelement coupling characteristics of radio frequency (RF) antenna microstrip line elements are examined in simulations and measurements. The initial point of the simulations is a microstrip line element loaded with a phantom. Meander structures are then introduced at the end of the element. The size of the meanders is increased in fixed steps and the magnetic field is optimized. In continuative simulations, the coupling between identical elements is evaluated for different element spacing and loading conditions. Verification of the simulation results is accomplished in measurements of the coupling between two identical elements for four different meander sizes. Image acquisition on a 7 T magnetic resonance imaging (MRI) system provides qualitative and quantitative comparisons to confirm the simulation results. Simulations point out an optimum range of meander sizes concerning coupling in all chosen geometric setups. Coupling measurement results are in good agreement with the simulations. Qualitative and quantitative comparisons of the acquired MRI images substantiate the coupling results. The coupling between coil elements in RF antenna arrays consisting of the investigated element types can be optimized under consideration of the central magnetic field strength or efficiency depending on the desired application.

Determination of real-time predictors of the wind turbine wake meandering

NASA Astrophysics Data System (ADS)

Muller, Yann-Aël; Aubrun, Sandrine; Masson, Christian

2015-03-01

The present work proposes an experimental methodology to characterize the unsteady properties of a wind turbine wake, called meandering, and particularly its ability to follow the large-scale motions induced by large turbulent eddies contained in the approach flow. The measurements were made in an atmospheric boundary layer wind tunnel. The wind turbine model is based on the actuator disc concept. One part of the work has been dedicated to the development of a methodology for horizontal wake tracking by mean of a transverse hot wire rake, whose dynamic response is adequate for spectral analysis. Spectral coherence analysis shows that the horizontal position of the wake correlates well with the upstream transverse velocity, especially for wavelength larger than three times the diameter of the disc but less so for smaller scales. Therefore, it is concluded that the wake is actually a rather passive tracer of the large surrounding turbulent structures. The influence of the rotor size and downstream distance on the wake meandering is studied. The fluctuations of the lateral force and the yawing torque affecting the wind turbine model are also measured and correlated with the wake meandering. Two approach flow configurations are then tested: an undisturbed incoming flow (modelled atmospheric boundary layer) and a disturbed incoming flow, with a wind turbine model located upstream. Results showed that the meandering process is amplified by the presence of the upstream wake. It is shown that the coherence between the lateral force fluctuations and the horizontal wake position is significant up to length scales larger than twice the wind turbine model diameter. This leads to the conclusion that the lateral force is a better candidate than the upstream transverse velocity to predict in real time the meandering process, for either undisturbed (wake free) or disturbed incoming atmospheric flows.

Alluvial cover controlling the width, slope and sinuosity of bedrock channels

NASA Astrophysics Data System (ADS)

Turowski, Jens Martin

2018-02-01

Bedrock channel slope and width are important parameters for setting bedload transport capacity and for stream-profile inversion to obtain tectonics information. Channel width and slope development are closely related to the problem of bedrock channel sinuosity. It is therefore likely that observations on bedrock channel meandering yields insights into the development of channel width and slope. Active meandering occurs when the bedrock channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments. Here, this idea is taken up by postulating that the rate of change of both width and sinuosity over time is dependent on bed cover only. Based on the physics of erosion by bedload impacts, a scaling argument is developed to link bedrock channel width, slope and sinuosity to sediment supply, discharge and erodibility. This simple model built on sediment-flux-driven bedrock erosion concepts yields the observed scaling relationships of channel width and slope with discharge and erosion rate. Further, it explains why sinuosity evolves to a steady-state value and predicts the observed relations between sinuosity, erodibility and storm frequency, as has been observed for meandering bedrock rivers on Pacific Arc islands.

Numerical modeling of dune progression in a high amplitude meandering channel

USDA-ARS?s Scientific Manuscript database

Laboratory experiments carried out by Abad and Garcia (2009) in a high-amplitude Kinoshita meandering channel show bed morphodynamics to comprise steady (local scour and deposition) and unsteady (migrating bedforms) components. The experiments are replicated with a numerical model. The sediment tran...

High speed curved position sensitive detector

DOEpatents

Hendricks, Robert W.; Wilson, Jack W.

1989-01-01

A high speed curved position sensitive porportional counter detector for use in x-ray diffraction, the detection of 5-20 keV photons and the like. The detector employs a planar anode assembly of a plurality of parallel metallic wires. This anode assembly is supported between two cathode planes, with at least one of these cathode planes having a serpentine resistive path in the form of a meander having legs generally perpendicular to the anode wires. This meander is produced by special microelectronic fabrication techniques whereby the meander "wire" fans outwardly at the cathode ends to produce the curved aspect of the detector, and the legs of the meander are small in cross-section and very closely spaced whereby a spatial resolution of about 50 .mu.m can be achieved. All of the other performance characteristics are about as good or better than conventional position sensitive proportional counter type detectors. Count rates of up to 40,000 counts per second with 0.5 .mu.s shaping time constants are achieved.

Fronts, meanders and eddies in Drake Passage during the ANT-XXIII/3 cruise in January-February 2006: A satellite perspective

NASA Astrophysics Data System (ADS)

Barré, Nicolas; Provost, Christine; Renault, Alice; Sennéchael, Nathalie

2011-12-01

We used satellite altimetric data to provide a context for the results of the ANT-XXIII/3 cruise in January-February 2006 both in time (16 years) and space (the whole of Drake Passage). The repeat of the hydrographical section within 3 weeks permitted different comparisons between the in-situ datasets and the satellite data products. Comparisons suggested that the multi-satellite product improved the temporal resolution on a Jason-1 track. A detailed analysis of the four absolute dynamic topography maps contemporaneous with the ANT-XXIII/3 cruise permitted identification of the location of the frontal branches of the Antarctic Circumpolar Current, of the major meanders and eddies. This spatial context proved particularly valuable for the interpretation of the in-situ data (see companion papers of Provost et al., 2011; Renault et al., 2011; Sudre et al., 2011). The altimetric time-series documented the long-term trends in sea-surface height, the recurrence of major frontal meanders and eddies and the statistical links between them. Negative trends in the Yaghan Basin indicated that both the Subantarctic Front and the Polar Front have shifted to the north of their climatological location. This northward shift in the Yaghan Basin contrasts with the large-scale southward shift in the Polar Front current core described in the literature, and is probably related to the local bottom topography in Drake Passage. Sea-level anomaly patterns observed during the cruise were related to statistical modes of the corresponding variations in Drake Passage. For example, the southward meander of the Subantarctic Front at the entrance to Drake Passage was part of a dipole comprising an adjacent Polar Front meander and occurred with a close to annual periodicity. A census of eddies in the Ona Basin revealed that the spatial distribution of anticyclonic eddies was consistent with generation from a meander of the Polar and Southern ACC Fronts over the Ona Seafloor Depression, while cyclonic eddies mostly originated from meanders of southern fronts associated with two rises on the continental slope: the Ona Rise and the Terror Rise.

Meandered-line antenna with integrated high-impedance surface.

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

Forman, Michael A.

2010-09-01

A reduced-volume antenna composed of a meandered-line dipole antenna over a finite-width, high-impedance surface is presented. The structure is novel in that the high-impedance surface is implemented with four Sievenpiper via-mushroom unit cells, whose area is optimized to match the meandered-line dipole antenna. The result is an antenna similar in performance to patch antenna but one fourth the area that can be deployed directly on the surface of a conductor. Simulations demonstrate a 3.5 cm ({lambda}/4) square antenna with a bandwidth of 4% and a gain of 4.8 dBi at 2.5 GHz.

Missouri: St. Louis

Atmospheric Science Data Center

2014-05-15

... side, are highlighted with green vegetation. Meandering rivers in the verdant Ozark Plateau appear to the south and west. This ... data were obtained from the NASA Langley Research Center Atmospheric Science Data Center in Hampton, VA. Image credit: ... October 15, 2005 - Green vegetation and meandering rivers. project:  MISR category:  gallery ...

Reductionist versus holistic approaches to the study of river meandering: An ideal dialogue

NASA Astrophysics Data System (ADS)

Seminara, G.; Pittaluga, M. Bolla

2012-08-01

We discuss some recent attempts to apply the theory of nonlinear dynamical systems to the interpretation of the long term morphodynamic evolution of meandering rivers. To make the discussion attractive for the reader, we employ the method of a Socratic dialogue between a member of the so called 'reductionist community', who is inclined to support only theories based on physical principles and who is skeptical about fashionable new paradigms, and a member of the 'holistic community', who supports the idea that new paradigms are needed because rivers are complex systems, whose response can only be interpreted using tools that analyze the system "as a whole". The dialogue focuses on a selection of recent contributions which assesses the progress in understanding of meander dynamics achieved by the use of the above new paradigms. The discussion suggests that some consensus has been reached on the fractal nature of meandering patterns, with the fractal dimension playing the role of a morphometric parameter. On the contrary, despite different early suggestions, recent thorough analysis has been unable to detect any clear evidence that the evolution of meanders displays the characters of either a chaotic or a self organized critical process. The dialogue is concluded with some consensus on the perspective that well founded cellular models may possibly help reconciling the reductionist and holistic viewpoints.

Superconducting properties of NbN film, bridge and meanders

NASA Astrophysics Data System (ADS)

Joshi, Lalit M.; Verma, Apoorva; Gupta, Anurag; Rout, P. K.; Husale, Sudhir; Budhani, R. C.

2018-05-01

The transport properties of superconducting NbN nanostructures in the form of thin film, bridge of width (w) = 50 μm and three meanders of w = 500, 250 and 100 nm have been investigated by resistance (R) measurements in temperature (T) range = 2 -300 K and magnetic field (B) range = 0 - 7 Tesla. The nanostructuring was carried out using Focused Ion Beam (FIB) milling. Reduction of sample width results in significant changes in the normal and superconducting state properties. For instance, the observed metallic behavior in the thin film sample is lost and the normal state resistance increases drastically from 2.4 Ω to 418 kΩ for the 100 nm meander. In the superconducting state, the value of critical temperature Tc (upper critical field Bc2 at T = 0 K) reduces gradually with width reduction, it changes from 13.15 K (42.8 Tesla) in the case of thin film sample to 5.7 K (12.7 Tesla) for the 100 nm meander sample. The superconducting transitions are found to get broader for the bridge sample and the meanders additionally show low-temperature resistive tails. In case of all the samples with reduced width, the transition onsets are found to be rounded at surprisingly high values of T ˜ 25 K >> Tc. These results are discussed in terms of the possible effects of FIB processing and weak localization in our samples.

High-temperature superconducting nano-meanders made by ion irradiation

NASA Astrophysics Data System (ADS)

Amari, P.; Feuillet-Palma, C.; Jouan, A.; Couëdo, F.; Bourlet, N.; Géron, E.; Malnou, M.; Méchin, L.; Sharafiev, A.; Lesueur, J.; Bergeal, N.

2018-01-01

In this article, we report on the fabrication of very long {{YBa}}2{{Cu}}3{{{O}}}7 nanowires in a meander shape patterned in a {{CeO}}2-capped thin film by high-energy oxygen ion irradiation. DC and RF characterizations outline the good superconducting properties of the nanowires whose geometry approaches the one used in single photon detectors. Their inductance, which mainly sets the maximum speed of these devices, has been measured on a wide range of temperature by mean of a resonant method. The extracted values are in agreement with the ones calculated from the geometry of the meanders and from the known London penetration depth in {{YBa}}2{{Cu}}3{{{O}}}7 thin films.

27 CFR 9.189 - High Valley.

Code of Federal Regulations, 2014 CFR

2014-04-01

...; then (4) Proceed easterly 2.7 miles along the meandering 2,000-foot elevation line to its first... mile along the north branch of the Salt Canyon Creek to its intersection with the 1,600-foot elevation...) Proceed westerly 15.2 miles along the meandering 1,600-foot elevation line, crossing the Clearlake Oaks...

27 CFR 9.189 - High Valley.

Code of Federal Regulations, 2010 CFR

2010-04-01

...; then (4) Proceed easterly 2.7 miles along the meandering 2,000-foot elevation line to its first... mile along the north branch of the Salt Canyon Creek to its intersection with the 1,600-foot elevation...) Proceed westerly 15.2 miles along the meandering 1,600-foot elevation line, crossing the Clearlake Oaks...

27 CFR 9.189 - High Valley.

Code of Federal Regulations, 2011 CFR

2011-04-01

...; then (4) Proceed easterly 2.7 miles along the meandering 2,000-foot elevation line to its first... mile along the north branch of the Salt Canyon Creek to its intersection with the 1,600-foot elevation...) Proceed westerly 15.2 miles along the meandering 1,600-foot elevation line, crossing the Clearlake Oaks...

27 CFR 9.189 - High Valley.

Code of Federal Regulations, 2013 CFR

2013-04-01

...; then (4) Proceed easterly 2.7 miles along the meandering 2,000-foot elevation line to its first... mile along the north branch of the Salt Canyon Creek to its intersection with the 1,600-foot elevation...) Proceed westerly 15.2 miles along the meandering 1,600-foot elevation line, crossing the Clearlake Oaks...

27 CFR 9.189 - High Valley.

Code of Federal Regulations, 2012 CFR

2012-04-01

...; then (4) Proceed easterly 2.7 miles along the meandering 2,000-foot elevation line to its first... mile along the north branch of the Salt Canyon Creek to its intersection with the 1,600-foot elevation...) Proceed westerly 15.2 miles along the meandering 1,600-foot elevation line, crossing the Clearlake Oaks...

76 FR 63952 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-14

... Bighorn River, downstream, through section 18, the limits of erosion, the medial lines of two relicted... subdivisional lines, the adjusted original meanders of the former left bank of the Bighorn River, downstream, through section 18, a portion of the meanders of the present right bank of the Bighorn River, downstream...

76 FR 27661 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-12

... sections 7 and 8, the adjusted original meanders of the former left bank of the Missouri River, downstream, through section 18, the meanders of the 2002-2005 left bank of the Missouri River, downstream, through section 18, the limits of erosion, downstream, through section 18, and a certain division of accretion...

Meanders in Ridge Form in the Zephyria Region

NASA Image and Video Library

2015-11-05

In this image from NASA Mars Reconnaissance Orbiter spacecraft, an ancient sinuous meandering river system is surrounded by features called yardangs. The yardangs are the ridge-like landforms that align approximately north-south. These features were created as the wind scoured and eroded the bedrock. The raised relief of the meandering river suggests inverted topography, likely due to lithification and cementation of the riverbed sediment. The cemented channel deposits were resistant, and thus less susceptible to erosion over time. However, the area surrounding the riverbed suggests that this area was a floodplain of weaker lithology that was subsequently eroded and shaped to the yardangs. The main meandering inverted riverbed within the image has a length of about 13 kilometers. The elevation of the channel at the top of the image is on the order of 113 meters higher than the bottom, based on Mars Orbiter Laser Altimeter (MOLA) data. This elevation difference and the increase in sinuosity of the channel shape in the southerly direction implies that the flow of the ancient river may have been heading south-southwest. http://photojournal.jpl.nasa.gov/catalog/PIA20047

Plume meander and dispersion in a stable boundary layer

NASA Astrophysics Data System (ADS)

Hiscox, April L.; Miller, David R.; Nappo, Carmen J.

2010-11-01

Continuous lidar measurements of elevated plume dispersion and corresponding micrometeorology data are analyzed to establish the relationship between plume behavior and nocturnal boundary layer dynamics. Contrasting nights of data from the JORNADA field campaign in the New Mexico desert are analyzed. The aerosol lidar measurements were used to separate the plume diffusion (plume spread) from plume meander (displacement). Mutiresolution decomposition was used to separate the turbulence scale (<90 s) from the submesoscale (>90 s). Durations of turbulent kinetic energy stationarity and the wind steadiness were used to characterize the local scale and submesoscale turbulence. Plume meander, driven by submesoscale wind motions, was responsible for most of the total horizontal plume dispersion in weak and variable winds and strong stability. This proportion was reduced in high winds (i.e., >4 m s-1), weakly stable conditions but remained the dominant dispersion mechanism. The remainder of the plume dispersion in all cases was accounted for by internal spread of the plume, which is a small eddy diffusion process driven by turbulence. Turbulence stationarity and the wind steadiness are demonstrated to be closely related to plume diffusion and plume meander, respectively.

Power law time dependence of river flood decay and its relationship to long term discharge frequency distribution. [California

NASA Technical Reports Server (NTRS)

Schubert, G.; Lingenfelter, R. E.

1973-01-01

Investigations have continued into the possibility that significant information on stream flow rates can be obtained from aerial and satellite imagery of river meander patterns by seeking a correlation between the meander and discharge spectra of rivers. Such a correlation could provide the basis for a simple and inexpensive technique for remote sensing of the water resources of large geographical areas, eliminating the need for much hydrologic recording. The investigation of the nature of the meander and discharge spectra and their interrelationship can also contribute to a more fundamental understanding of the processes of both river meander formation and drainage of large basins. It has been found that floods decay with an inverse power law dependence on time. The exponent of this dependence varies from river to river and even from station to station along the same river. This power law time dependence makes possible the forecasting of river discharge with an uncertainty of about 5% for as long as a month following the flood peak.

The use of GIS tools in determining the intensity of meandering of rivers based on the example of Noteć River (Poland)

NASA Astrophysics Data System (ADS)

Szatten, Dawid; Rabant, Hubert; Nadolny, Grzegorz

2017-11-01

The study used the tools of Geographic Information System (GIS) in the analysis of the intensity of meandering of Noteć River, calculated using indicators proposed by Brice [16], Leopold et al. [17], Rust [15] and Rosgen [18]. In this work the emphasis is placed on showing the suitability of using modelling software and spatial data. The study was based on archival cartographic materials and orthophotomap presenting the current course of the river channel. The software of geographic information system used for analysis was ArcMap v.10.0. The rate of meandering of the river in a multiyear period 1876-2013 and four typical scenarios of the development of river channel were determined. Comparing them with the types of human intervention in the fluvial system, the dynamics of transformation channel in the analysed period of time was specified. These types are characteristic for all the meandering rivers. These scenarios can determine the amount of anthropopressure and to evaluate the usefulness of GIS in the analysis of transformations of the fluvial system.

Modeling the stratigraphy and preservation potential of meandering stream deposits

NASA Astrophysics Data System (ADS)

Tucker, G. E.; Clevis, Q.; Lock, G.; Lancaster, S.; Desitter, A.

2003-12-01

Both natural and human-induced modes of river and floodplain behavior have the potential to obscure, expose, or even destroy portions of the archaeological record. In valley systems with actively meandering channels much material can be lost to lateral bank erosion. Conversely, floodplain aggradation can bury and therefore obscure sites. In this study we aim to quantify the preservation potential of fluvial units containing archaeological sites as a function of the natural process of meandering, climate change and increased land-use during the Holocene. We used the CHILD simulation model of landscape evolution to explore alternative scenarios in which these three factors are both varied independently and combined. Boundary and initial conditions for the model scenarios are based on the Holocene evolution of the archaeologically-rich Upper Thames Valley, which is known to have witnessed variations in flood frequency, land-clearance, episodic alluviation and river entrenchment. The CHILD model is set up to combine four components that simulate the development of valley and floodplain system: hillslope and channel erosion, lateral stream meandering, overbank deposition, and the accumulation of a 3D stratigraphy. The landscape is represented by an adaptable triangular mesh of nodes, especially suited for simulating the gradual shifting of meander bends. The new stratigraphic layering routine recently added to the model in improves the resolution of the stratigraphic record accumulated by the model. Simulation results reveal systematic controls on preservation potential, and suggest potential sources of bias in the archaeological record.

Controls on cutoff formation along a tropical meandering river in the Amazon Basin

NASA Astrophysics Data System (ADS)

Ahmed, J.; Constantine, J. A.

2016-12-01

The termination of meander bends is an inherent part of the evolution of meandering rivers. Cutoffs are produced by one of two mechanisms: neck cutoffs occur when two adjacent meanders converge, while chute cutoffs are generated by flood-driven floodplain incision, resulting in a shorter, steeper channel path. Here we use an annually-resolved record of Landsat imagery, coupled with daily discharge data to assess the role of high-magnitude discharges (Q ≥ QBF) on cutoff formation along the Rio Beni, Bolivia. Our results suggest that despite numerous above-bankfull events, the dominant cutoff mechanism operating on the Beni is neck cutoff. Evaluating the formation of these cutoffs reveals that migration rates accelerate during years of high discharge, and eventually cause the migrating bends to breach. The density of floodplain vegetation and the medium into which the channel migrated was also responsible for the patterns of cutoff documented along this river. The presence of existing floodplain channels permitted the river to divert its flow along shorter courses thereby facilitating cutoff, and limiting sinuosity growth. Understanding the long-term evolution of meandering channels is important since their morphodynamics are responsible for the creation of highly biodiverse riparian habitats, as well as the store and release of alluvial material. Moreover, the interactions between discharge and the channel-floodplain system are integral for the functioning and long-term evolution of these landscapes, particularly in the face of global climate change.

Experimental Study on the Wake Meandering Within a Scale Model Wind Farm Subject to a Wind-Tunnel Flow Simulating an Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Coudou, Nicolas; Buckingham, Sophia; Bricteux, Laurent; van Beeck, Jeroen

2017-12-01

The phenomenon of meandering of the wind-turbine wake comprises the motion of the wake as a whole in both horizontal and vertical directions as it is advected downstream. The oscillatory motion of the wake is a crucial factor in wind farms, because it increases the fatigue loads, and, in particular, the yaw loads on downstream turbines. To address this phenomenon, experimental investigations are carried out in a wind-tunnel flow simulating an atmospheric boundary layer with the Coriolis effect neglected. A 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models is subject to a neutral boundary layer over a slightly-rough surface, i.e. corresponding to offshore conditions. Particle-image-velocimetry measurements are performed in a horizontal plane at hub height in the wakes of the three wind turbines occupying the wind-farm centreline. These measurements allow determination of the wake centrelines, with spectral analysis indicating the characteristic wavelength of the wake-meandering phenomenon. In addition, measurements with hot-wire anemometry are performed along a vertical line in the wakes of the same wind turbines, with both techniques revealing the presence of wake meandering behind all three turbines. The spectral analysis performed with the spatial and temporal signals obtained from these two measurement techniques indicates a Strouhal number of ≈ 0.20 - 0.22 based on the characteristic wake-meandering frequency, the rotor diameter and the flow speed at hub height.

Experimental Study on the Wake Meandering Within a Scale Model Wind Farm Subject to a Wind-Tunnel Flow Simulating an Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Coudou, Nicolas; Buckingham, Sophia; Bricteux, Laurent; van Beeck, Jeroen

2018-04-01

The phenomenon of meandering of the wind-turbine wake comprises the motion of the wake as a whole in both horizontal and vertical directions as it is advected downstream. The oscillatory motion of the wake is a crucial factor in wind farms, because it increases the fatigue loads, and, in particular, the yaw loads on downstream turbines. To address this phenomenon, experimental investigations are carried out in a wind-tunnel flow simulating an atmospheric boundary layer with the Coriolis effect neglected. A 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models is subject to a neutral boundary layer over a slightly-rough surface, i.e. corresponding to offshore conditions. Particle-image-velocimetry measurements are performed in a horizontal plane at hub height in the wakes of the three wind turbines occupying the wind-farm centreline. These measurements allow determination of the wake centrelines, with spectral analysis indicating the characteristic wavelength of the wake-meandering phenomenon. In addition, measurements with hot-wire anemometry are performed along a vertical line in the wakes of the same wind turbines, with both techniques revealing the presence of wake meandering behind all three turbines. The spectral analysis performed with the spatial and temporal signals obtained from these two measurement techniques indicates a Strouhal number of ≈ 0.20 - 0.22 based on the characteristic wake-meandering frequency, the rotor diameter and the flow speed at hub height.

Sediment supply as a driver of river evolution in the Amazon Basin

NASA Astrophysics Data System (ADS)

Ahmed, Joshua; Constantine, José Antonio; Dunne, Thomas; Legleiter, Carl; Lazarus, Eli D.

2015-04-01

The Amazon represents the only large river basin in the world where there is a sufficient range of sediment supplies and a lack of engineering controls to assess how sediment supply drives the evolution of meandering rivers. Despite recent analytical advances (Asahi et al., 2013; Pittaluga and Seminara, 2011), modern theory does not yet identify or explain the effects of externally imposed sediment supplies, a fundamental river characteristic, on meandering river evolution. These sediment supplies would be radically reduced by the construction of large dams proposed for the Amazon Basin (Finer and Jenkins, 2012). Here, we demonstrate that the sediment loads imposed by their respective drainage basins determine planform changes in lowland rivers across the Amazon. Our analysis, based on Landsat image sequences, indicates that rivers with high sediment loads draining the Andes and associated foreland basin experience annual migration rates that are on average four times faster than rivers with lower sediment loads draining the Central Amazon Trough and shields. Incidents of meander cutoff also occur more frequently along the rivers of the Andes and foreland basin, where the number of oxbows in the floodplains is more than twice that observed in the floodplains of the Central Amazon Trough and shields. Our results, which cannot be explained by differences in channel slope or hydrology, highlight the importance of sediment supply in modulating the ability of meandering alluvial rivers to reshape the floodplain environment through river migration. Asahi, K., Shimizu, Y., Nelson, J., Parker, G., 2013. Numerical simulation of river meandering with self-evolving banks. Journal of Geophysical Research: Earth Surface, 118(4), 2013JF002752. Finer, M., Jenkins, C.N., 2012. Proliferation of hydroelectric dams in the Andean Amazon and implications for Andes-Amazon connectivity. PLOS One, 7(4), e35126. Pittaluga, M.B., Seminara, G., 2011. Nonlinearity and unsteadiness in river meandering: a review of progress in theory and modelling. Earth Surface Processes and Landforms, 36(1), 20-38.

The Middle Sacramento River: Human Impacts on Physical and Ecological Processes Along a Meandering River

Treesearch

Koll Buer; Dave Forwalter; Mike Kissel; Bill Stohlert

1989-01-01

Native plant and wildlife communities along Northern California's middle Sacramento River (Red Bluff to Colusa) originally adapted to a changing pattern of erosion and deposition across a broad meander belt. The erosion-deposition process was in balance, with the river alternately building and eroding terraces. Human-induced changes to the Sacramento River,...

78 FR 23952 - Notice of Filing of Plats of Survey; North Dakota

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-23

..., and the adjusted original meanders of the former left and right banks of the Little Missouri River... meanders of the present left and right banks of the Little Missouri River through sections 29, 31, and 32.... Steve L. Toth, Acting Chief Cadastral Surveyor, Division of Resources. [FR Doc. 2013-09488 Filed 4-22-13...

Electro-optic phase matching in a Si photonic crystal slow light modulator using meander-line electrodes.

PubMed

Hinakura, Yosuke; Terada, Yosuke; Arai, Hiroyuki; Baba, Toshihiko

2018-04-30

We demonstrate a Si photonic crystal waveguide Mach-Zehnder modulator that incorporates meander-line electrodes to compensate for the phase mismatch between slow light and RF signals. We first employed commonized ground electrodes in the modulator to suppress undesired fluctuations in the electro-optic (EO) response due to coupled slot-line modes of RF signals. Then, we theoretically and experimentally investigated the effect of the phase mismatch on the EO response. We confirmed that meander-line electrodes improve the EO response, particularly in the absence of internal reflection of the RF signals. The cut-off frequency of this device can reach 27 GHz, which allows high-speed modulation up to 50 Gbps.

Analysis of river planforms in the New Madrid region and possible relations to tectonic warping across the loess bluffs and within the meander belt of the Mississippi River

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

Johnson, K.A.; Mayer, L.

1993-03-01

Stream channel planforms measured from such streams as the Hatchie (H), L'Anguille (LA), St. Francis, White (W) and Little Red (LR) rivers provide a way to study influences of topographic warping between the loess bluffs that bound the Mississippi river valley. Planforms are analyzed using sinuosity, Richardson analysis, and pattern. Pattern changes include transitions from braided to meandering and meandering to straight. Sinuosities of the W and LR rivers show a transition from low sinuosity, [1.3, 1.4] to higher sinuosity [2.6, 2.8], over a short distance, as they cross the bluffs from the uplands to the Western Lowlands. On themore » east, the Hatchie changes from a braided to meandering pattern upon crossing the bluffs. Its sinuosity varies from a low of about 1.4 to a high of 2.2, coincident with a marsh area. The LA river flows on the west side of Crowley's Ridge and is paralleled by the St. Francis river on the east. These rivers, with very different drainage areas and sinuosities, show matching meander bends at similar wavelengths along Crowley's Ridge. The bends are about 10 km in 1/2 wavelength suggesting some extraordinary influence on pattern perpendicular to the ridge. Richardson analysis indicates that features with a 1/2 wavelength of 2 km may control several rivers' bending patterns. These features are analyzed to determine their spatial relations with one another.« less

Enhanced sediment loading facilitates point bar growth and accelerates bank erosion along a modelled meander bend on the Sacramento River, USA

NASA Astrophysics Data System (ADS)

Ahmed, J.; Constantine, J. A.; Hales, T. C.

2017-12-01

Meandering channels provide a conduit through which sediment and water is routed from the uplands to the sea. Alluvial material is periodically stored and transported through the channel network as permitted by the prevailing hydrologic conditions. The lowlands are typically characterised by accumulations of sediment attached to the inner banks of meander bends (point bars). These bedforms have been identified as important for facilitating a link between in-stream sediment supplies and channel dynamism. A 2D curvilinear hydrodynamic model (MIKE 21C) was used to perform a number of experiments in which the sediment load was adjusted to investigate how changes in alluvial material fluxes affect the development of point bars and the resultant patterns of bank erosion. A doubling of the sediment load caused a longitudinal increase in the bar in the upstream direction and caused a coeval doubling of the transverse channel slope at the meander apex. The upstream growth of the point bar was accompanied by an increase in length over which lateral migration took place at the outer bank. The magnitude of outer bank erosion was 9-times greater for the high-sediment simulation. These results suggest that enhanced sediment loads (potentially the result of changes in land use or climate) can trigger greater rates of bank erosion and channel change through the sequestration of alluvial material on point bars, which encourage high-velocity fluid deflection towards the outer bank of the meander. This controls riparian habitat development and exchanges of sediment and nutrients across the channel-floodplain interface.

On the characteristics and scales of outer bank roughness on large meander bends: the influence of bank material properties, floodplain vegetation and flow inundation

USDA-ARS?s Scientific Manuscript database

This paper explores the scales and characteristics of form roughness along the outer banks of two bends on a large meandering river through investigation of irregularities in bank contours and local topographic variability on the bank face. The analysis also examines how roughness varies over the ve...

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

Churchfield, M. J.; Moriarty, P. J.; Hao, Y.

The focus of this work is the comparison of the dynamic wake meandering model and large-eddy simulation with field data from the Egmond aan Zee offshore wind plant composed of 36 3-MW turbines. The field data includes meteorological mast measurements, SCADA information from all turbines, and strain-gauge data from two turbines. The dynamic wake meandering model and large-eddy simulation are means of computing unsteady wind plant aerodynamics, including the important unsteady meandering of wakes as they convect downstream and interact with other turbines and wakes. Both of these models are coupled to a turbine model such that power and mechanicalmore » loads of each turbine in the wind plant are computed. We are interested in how accurately different types of waking (e.g., direct versus partial waking), can be modeled, and how background turbulence level affects these loads. We show that both the dynamic wake meandering model and large-eddy simulation appear to underpredict power and overpredict fatigue loads because of wake effects, but it is unclear that they are really in error. This discrepancy may be caused by wind-direction uncertainty in the field data, which tends to make wake effects appear less pronounced.« less

Hydrodynamics and sediment transport in a meandering channel with a model axial-flow hydrokinetic turbine

NASA Astrophysics Data System (ADS)

Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele

2016-02-01

An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.

Channel-pattern adjustments and geomorphic characteristics of Elkhead Creek, Colorado, 1937-97

USGS Publications Warehouse

Elliott, John G.; Gyetvai, Stevan

1999-01-01

Onsite channel surveys and sediment measurements made in 1997, aerial photographs taken from 1937 through 1993, and streamflowgaging- station record from 1954 to 1996 were used to determine the probable cause of accelerated streambed and streambank erosion in the lower reaches of Elkhead Creek, a perennial, meandering tributary of the Yampa River. Concern about the possible effects of Elkhead Reservoir, constructed in 1974, has been expressed by landowners living downstream. Evidence cited as an indication of reservoirrelated effects include the trapping of bedloadtransported sediment in the reservoir, vertical incision of the streambed, and lateral erosion causing loss of agricultural land. A large deltaic deposit composed of approximately 163 acre-ft of bedload-transported sediment formed in Elkhead Reservoir between 1974 and 1993, the contemporary bankfull stage of Elkhead Creek is several feet below the elevation of a broad terrace that previously was the flood plain, and lateral erosion at meander bends occurs at a higher rate than in previous periods at some locations.Elkhead Creek meander migration rates were used as a measure of lateral instability in the study reaches. Meander migration rates based on changes in channel centerline position were calculated for three periods from five sets of rectified aerial photographs for reaches upstream and downstream from the reservoir. The creek upstream from Elkhead Reservoir was unaffected by impoundment and was used as the control reach. Mean meander migration rates in the downstream study reach were 1.2 ft/yr from 1938 to 1953, 2.5 ft/yr from 1954 to 1970, and 4.8 ft/yr from 1978 to 1993, compared to rates of 0.5 ft/yr, 1.6 ft/yr, and 6.6 ft/yr for the same periods in the upstream study reach. Sediment and channel-geometry measurements and estimated hydraulic conditions at eight cross sections indicate that most of the sediment sizes represented in the streambed are mobile at frequently occurring streamflows; those streamflows are less than or equal to the bankfull discharge of approximately 1,800 to 2,200 cubic feet per second. Discharge data from 1954 through 1996 recorded at a site upstream from the reservoir were examined to determine the effect of hydrology on meander migration rates. The discharge data were assumed to be representative of the total streamflow and flood hydrology of both the upstream and downstream reaches because Elkhead Reservoir normally has a full pool. Mean annual streamflow increased 122 percent, and the mean annual flood increased 130 percent from the pre-regulation period (1954 to 1970) to the post-regulation period (1978 to 1993), a possible explanation for much of the increase observed in meander migration rate in both the upstream and downstream reaches in the period after reservoir construction. Channel instability, quantified by meander migration rates, has increased throughout Elkhead Creek since 1977. The most probable cause is a combination of external factors affecting the 2 Channel-Pattern Adjustments and Geomorphic Characteristics of Elkhead Creek, Colorado, 1937-97 entire watershed, such as changes in annual runoff and flood magnitude and sedimentation in Elkhead Reservoir. Local land-use practices, such as intentional meander cutoff and riparian vegetation removal, also can decrease channel stability, but these factors were not addressed in this study.

Degree of contamination and sources of polychlorinated biphenyls in Meandering Road Creek and Woods Inlet of Lake Worth, Fort Worth, Texas, 2004 and 2006-07

USGS Publications Warehouse

Braun, Christopher L.; Wilson, Jennifer T.; Van Metre, Peter C.

2008-01-01

Lake Worth is a reservoir on the West Fork Trinity River on the western edge of Fort Worth, Texas. Air Force Plant 4 (AFP4) is on the eastern shore of Woods Inlet, an arm of Lake Worth that extends south from the main body of the lake. Two previous reports documented ele-vated polychlorinated biphenyl (PCB) concentrations in surficial sediment in Woods Inlet relative to those in surficial sediment in other parts of Lake Worth. This report presents the results of another USGS study, done in cooperation with the U.S. Air Force, to indicate the degree of PCB contamination of Meandering Road Creek and Woods Inlet and to identify possible sources of PCBs in Meandering Road Creek and Woods Inlet on the basis of suspended, streambed, and lake-bottom sediment samples collected there in 2004 and 2006-07. About 40 to 80 percent of total PCB concentrations (depending on how total PCB concentration is computed) in suspended sediment exceed the threshold effect concentration, a concentration below which adverse effects to benthic biota rarely occur. About 20 percent of total PCB concentrations (computed as sum of three Aroclors) in suspended sediment exceed the probable effect concentration, a concentration above which adverse effects to benthic biota are expected to occur frequently. About 20 to 30 percent of total PCB concentrations in streambed sediment exceed the threshold effect concentration; and about 6 to 20 percent of total PCB concentrations in lake-bottom (Woods Inlet) sediment exceed the threshold effect concentration. No streambed or lake-bottom sediment concentrations exceed the probable effect concentration. The sources of PCBs to Meandering Road Creek and Woods Inlet were investigated by comparing the relative distributions of PCB congeners of suspended sediment to those of streambed and lake-bottom sediment. The sources of PCBs were identified using graphical analysis of normalized concentrations (congener ratios) of 11 congeners. For graphical analysis, the sampling sites were divided into three groups with each group associated with one of the three outfalls sampled: SSO, OF4, and OF5. The variations of normalized PCB congener concentrations from Woods Inlet, from outfalls along Meandering Road Creek, and from streambed sediment sampling sites along Meandering Road Creek generally form similar patterns within sample groups, which is indicative of a common source of PCBs to each group. Overall, the variations in congener ratios indicate that PCBs in surficial lake-bottom sediment of Woods Inlet probably entered Woods Inlet primarily from Meandering Road Creek, and that runoff from AFP4 is a prominent source of PCBs in Meandering Road Creek. Sixteen of the 20 box core sites in Woods Inlet had lower PCB concentrations in the 2006 cores compared to those in the 2003 cores.

Jet meandering by a foil pitching in quiescent fluid

NASA Astrophysics Data System (ADS)

Shinde, Sachin Y.; Arakeri, Jaywant H.

2013-04-01

The flow produced by a rigid symmetric NACA0015 airfoil purely pitching at a fixed location in quiescent fluid (the limiting case of infinite Strouhal number) is studied using visualizations and particle image velocimetry. A weak jet is generated whose inclination changes continually with time. This meandering is observed to be random and independent of the initial conditions, over a wide range of pitching parameters.

Transposition of a Process-Based Model, Flumy: from Meandering Fluvial Systems to Channelized Turbidite Systems

NASA Astrophysics Data System (ADS)

Lemay, M.; Cojan, I.; Rivoirard, J.; Grimaud, J. L.; Ors, F.

2017-12-01

Channelized turbidite systems are among the most important hydrocarbon reservoirs. Yet building realistic turbidite reservoir models is still a challenge. Flumy has been firstly developed to simulate the long-term evolution of aggrading meandering fluvial systems in order to build facies reservoir models. In this study, Flumy has been transposed to channelized turbidite systems. The channel migration linear model of Imran et al. (1999) dedicated to subaqueous flows has been implemented. The whole model has been calibrated taking into account the differences on channel morphology, avulsion frequency, and aggradation and migration rates. This calibration and the comparison of the model to natural systems rely on: i) the channel planform morphology characterized by the meander wavelength, amplitude, and sinuosity; ii) the channel trajectory and the resulting stratigraphic architecture described using Jobe et al. (2016) indexes. Flumy succeeds in reproducing turbidite channel planform morphology as shown by the mean sinuosity of 1.7, the wavelength to width and amplitude to width ratios around 4 and 1 respectively. First-order meander architecture, characterized by the ratios meander belt width versus channel width, meander belt thickness versus channel depth, and the deduced stratigraphic mobility number (the ratio between lateral versus vertical channel displacements), is also well reproduced: 2.5, 3.8, and 0.6 respectively. Both lateral and downstream channel normalized migrations are around 3.5 times lower than in fluvial systems. All these values are absolutely coherent with the observations. In the other hand, the channel trajectory observed on seismic cross sections (hockey stick geometry) is not fully reproduced: the local stratigraphic mobility number is divided upward by 3 whereas up to 10 is expected. This behavior is generally explained in the literature by an increasing aggradation rate through time and/or flow stripping at outer bend that decreases lateral migration rate (Peakall et al., 2000). These processes are not currently simulated in Flumy, and need to be implemented. This study shows that Flumy model reproduces quite well the first order characteristics observed in the nature and can be used to simulate channelized turbidite reservoirs.

Creating self-formed meandering channels in laboratory flumes (Invited)

NASA Astrophysics Data System (ADS)

Braudrick, C. A.

2009-12-01

Our ability to construct predictive numerical models for meandering rivers is hampered by the inability to create meandering channels in the laboratory where individual variables can be isolated and controlled. Typically, experimental channels braid, straighten, or cease migration once they develop curvature. By using alfalfa sprouts to provide bank strength and fine sediment to attach point bars to the floodplain, we have successfully created and maintained meandering morphology in a laboratory flume. The 6.1 by 17 m flume has a floodplain slope of approximately 0.005 with a sandy bed and banks that scales as a gravel bed river. The alfalfa sprouts slow bank erosion allowing time for the bars to create new floodplain deposits. The sprouts also increase floodplain roughness, armor new bar deposits, and promote deposition of overbank sediment. The fine sediment, a lightweight plastic that scaled as sand, was crucial for blocking chutes formed between the bar and the floodplain, isolating cut-off channels from the main flow, and creating levees. During this 136-hour long experiment, the channel width stabilized as the channel migrated across the floodplain, and the curvature was recreated following cutoffs. Although the sinuosity (about 1.2) was low relative to meandering channels observed in the field, the spacing of bends was within the upper bounds of field examples. Subsequent experiments with higher bank strength had more limited chute development were able to generate a sinuosity of about 1.4. Scaling analysis indicates that the bank migration rates in the lower sinuosity experiment were approximately 10 times faster than migration rates in the field. A particular challenge in these experiments is maintaining a healthy alfalfa crop. After 15-20 hours of flood flows, the alfalfa begins to die off and new emergent bars need to be seeded. It then takes about 7 days for the alfalfa to grow to the size used in these experiments. The 15-20 hours scale to about one year of flood flows in the field. Therefore experiments that replicate the long-term evolution of meandering rivers would be prohibitively long with alfalfa. Future experiments should therefore focus on developing and testing models that to examine longer-term channel evolution.

Influence of Tectonics on the Channel Pattern of Alaknanda River in Srinagar Valley (Garhwal Himalaya)

NASA Astrophysics Data System (ADS)

Datt, Devi

2017-04-01

This paper describes the results of a continuing investigation of tectonic influence on channel pattern and morphology of Alaknanda River in Lesser Garhwal Himalaya, Uttarakhand, India. Extensive field investigations using conventional methods supported by topographical sheets and remote sensing data (LISS IV), were undertaken.The results are classified into three sections :- tectonics, channel pattern and impact of tectonics on channel pattern. The channel length is divided into 8 meanders sets of 3 segments from Supana to Kirtinagar. Thereafter, a litho-tectonic map of the Srinagar valley was prepared. The style of active tectonics on deformation and characterization of fluvial landscape was investigated on typical strike-slip transverse faults near the zone of North Almora Thrust (NAT). NAT is a major tectonic unit of the Lesser Himalaya which passes through the northern margin from NW to SE direction.. The structural and lithological controls on the Alaknanda River system in Srinagar valley are reflected on distinct drainage patterns, abrupt change in flow direction, incised meandering, offset river channels, straight river lines, palaeo-channels, multi levels of terraces, knick points and pools in longitudinal profile. The results of the study show that the sinuosity index of the river is 1.35. Transverse faulting is very common along the NAT. An earlier generation of linear tectonic features were displaced by the latter phase of deformation. Significant deviations were observed in river channel at deformation junctions. Moreover, all 8 sets of meanders are strongly influenced by tectonic features. The meandering course is, thereby, correlated with tectonic features. It is shown that the river channel is strongly influenced by the tectonic features in the study area. Key Words: Tectonic, Meander, Channel pattern, deformation, Knick point.

Geodiversity of a large meander bend in the Little Belt strait in the inner Danish waters

NASA Astrophysics Data System (ADS)

Brandbyge Ernstsen, Verner; Øbro Hansen, Lars; Becker, Marius; Brivio, Lara; Vang, Torben; Lynnerup Trinhammer, Per; Andresen, Katrine Juul; Seidenkrantz, Marit-Solveig; Boldreel, Lars Ole; Bartholdy, Jesper

2017-04-01

The Little Belt strait in the inner Danish waters is characterised by a high biodiversity, and continuous monitoring of flora and fauna and the water quality is undertaken by the authorities. However, the surface sedimentology and geomorphology, i.e. elements of the geodiversity, are less well-constrained. The aim of this study is to investigate the surface sediment and morphology of a large meander bend (with a channel width of 1 km) located between the two bridges crossing the strait (a channel reach of 4 km) in order to assess a potential coupling between geodiversity and biodiversity. More specifically, the objectives are 1) to identify and classify morphological units for creating a geomorphological map, 2) to quantify surface material characteristics for creating a surface material map, and 3) to develop a conceptual model of the substrate and the morphology and morphodynamics in the meander bend between the two bridges in the strait. Preliminary results reveal a diverse morphology in the meander bend; and the annual morphological changes reveal complex sediment transport patterns along and across the bend. Likewise significant sediment sorting trends exist along and across the meander bend. Hence, the preliminary results indicate a high geodiversity in the strait. Acknowledgements The data were collected as part of the MSc course Marine Geoscience, a joint MSc course between the Department of Geosciences and Natural Resource Management at the University of Copenhagen and the Department of Geoscience at Aarhus University. Additional data were included from the research project Control in the Danish Straits 1 (CiDS-1) funded by the Danish Centre for Marine Research (PI Morten Holtegaard). Thanks to the crew on board RV Aurora.

Simulation of Helical Flow Hydrodynamics in Meanders and Advection-Turbulent Diffusion Using Smoothed Particle Hydrodynamics

NASA Astrophysics Data System (ADS)

Gusti, T. P.; Hertanti, D. R.; Bahsan, E.; Soeryantono, H.

2013-12-01

Particle-based numerical methods, such as Smoothed Particle Hydrodynamics (SPH), may be able to simulate some hydrodynamic and morphodynamic behaviors better than grid-based numerical methods. This study simulates hydrodynamics in meanders and advection and turbulent diffusion in straight river channels using Microsoft Excel and Visual Basic. The simulators generate three-dimensional data for hydrodynamics and one-dimensional data for advection-turbulent diffusion. Fluid at rest, sloshing, and helical flow are simulated in the river meanders. Spill loading and step loading are done to simulate concentration patterns associated with advection-turbulent diffusion. Results indicate that helical flow is formed due to disturbance in morphology and particle velocity in the stream and the number of particles does not have a significant effect on the pattern of advection-turbulent diffusion concentration.

Directivity analysis of meander-line-coil EMATs with a wholly analytical method.

PubMed

Xie, Yuedong; Liu, Zenghua; Yin, Liyuan; Wu, Jiande; Deng, Peng; Yin, Wuliang

2017-01-01

This paper presents the simulation and experimental study of the radiation pattern of a meander-line-coil EMAT. A wholly analytical method, which involves the coupling of two models: an analytical EM model and an analytical UT model, has been developed to build EMAT models and analyse the Rayleigh waves' beam directivity. For a specific sensor configuration, Lorentz forces are calculated using the EM analytical method, which is adapted from the classic Deeds and Dodd solution. The calculated Lorentz force density are imported to an analytical ultrasonic model as driven point sources, which produce the Rayleigh waves within a layered medium. The effect of the length of the meander-line-coil on the Rayleigh waves' beam directivity is analysed quantitatively and verified experimentally. Copyright © 2016 Elsevier B.V. All rights reserved.

Meandering Right Pulmonary Vein to the Left Atrium and Inferior Vena Cava

PubMed Central

Tortoriello, Tia A.; Vick, G. Wesley; Chung, Taylor; Bezold, Louis I.; Vincent, Julie A.

2002-01-01

We report a case of a healthy, asymptomatic 6-year-old boy in whom an anomalous right pulmonary vein was noted to drain into both the inferior vena cava and left atrium in association with findings consistent with scimitar syndrome. The anomalous pulmonary vein took a very circuitous route through the lungs before draining into the left atrium, a condition previously termed “meandering pulmonary vein.” To aid in the diagnosis, cardiovascular magnetic resonance imaging and magnetic resonance angiography were used to delineate this complex course and the connection of the anomalous pulmonary vein. To our knowledge, this is the 1st reported case of a meandering pulmonary vein with dual drainage to the inferior vena cava and left atrium in association with other anomalies. (Tex Heart Inst J 2002;29:319–23) PMID:12484618

Simulation Comparisons of Three Different Meander Line Dipoles

DTIC Science & Technology

2015-01-01

Paez C I. Design formulas for a meandered dipole. IEEE Xplore Digital Library, 2014: n. pag. Web. 2 September 2014. 2. Nguyen, VH, Phan, HP, Hoang...MH. Improving radiation characteristics of UHF RFID antennas by zigzag structures. IEEE Xplore Digital Library, 2014: n. pag. Web. 2 September 2014...geometry-based, frequency-independent lumped element model. IEEE Xplore Digital Library, 2014: n. pag. Web. 2 September 2014. 5. Olaode OO, Palmer WD

Meandering Brownian Donkeys

NASA Astrophysics Data System (ADS)

Eichhorn, R.; Reimann, P.

2004-04-01

We consider a Brownian particle whose motion is confined to a ``meandering'' pathway and which is driven away from thermal equilibrium by an alternating external force. This system exhibits absolute negative mobility, i.e. when an external static force is applied the particle moves in the direction opposite to that force. We reveal the physical mechanism behind this ``donkey-like'' behavior, and derive analytical approximations that are in excellent agreement with numerical results.

River meanders and channel size

USGS Publications Warehouse

Williams, G.P.

1986-01-01

This study uses an enlarged data set to (1) compare measured meander geometry to that predicted by the Langbein and Leopold (1966) theory, (2) examine the frequency distribution of the ratio radius of curvature/channel width, and (3) derive 40 empirical equations (31 of which are original) involving meander and channel size features. The data set, part of which comes from publications by other authors, consists of 194 sites from a large variety of physiographic environments in various countries. The Langbein-Leopold sine-generated-curve theory for predicting radius of curvature agrees very well with the field data (78 sites). The ratio radius of curvature/channel width has a modal value in the range of 2 to 3, in accordance with earlier work; about one third of the 79 values is less than 2.0. The 40 empirical relations, most of which include only two variables, involve channel cross-section dimensions (bankfull area, width, and mean depth) and meander features (wavelength, bend length, radius of curvature, and belt width). These relations have very high correlation coefficients, most being in the range of 0.95-0.99. Although channel width traditionally has served as a scale indicator, bankfull cross-sectional area and mean depth also can be used for this purpose. ?? 1986.

A geomorphic explanation for a meander cutoff following channel relocation of a coarse-bedded river.

PubMed

Thompson, Douglas M

2003-03-01

The Veteran's Fishing section of the Blackledge River in central Connecticut was relocated in the late 1950s. The relocation resulted in an unstable channel despite extensive efforts to prevent erosion. Overbank erosion and meander cutoffs were investigated using detailed survey data, characterizations of sediment deposits, flow modeling, and a moment-stability analysis. Limited reworking of revetment boulders indicate that riprap bank material was immobile during a 1979 flood event responsible for the formation of the cutoff channel. A moment-stability analysis factor-of-safety value of 1.1 supports the conclusion that riprap was not directly eroded from the banks. Alluvial particles with d(95) values ranging up to 120 mm were deposited along a bar downstream from the cutoff channel at flows estimated to be below a 1.5-year recurrence interval flow. Development of the bar deposit resulted in locally elevated water surfaces at high flow. The resulting overbank flow across the meander neck to the adjacent downstream bend led to the creation of an upstream migrating knickpoint, the erosion of approximately 16,000-year-old sediments, and the subsequent meander cutoff. The results of the study indicate that traditional erosion-control measures cannot prevent extreme channel adjustments if the geomorphic processes that control sediment continuity also are not considered.

Effect of nucleation on instability of step meandering during step-flow growth on vicinal 3C-SiC (0001) surfaces

NASA Astrophysics Data System (ADS)

Li, Yuan; Chen, Xuejiang; Su, Juan

2017-06-01

A three-dimensional kinetic Monte Carlo (KMC) model has been developed to study the step instability caused by nucleation during the step-flow growth of 3C-SiC. In the model, a lattice mesh was established to fix the position of atoms and bond partners based on the crystal lattice of 3C-SiC. The events considered in the model were adsorption and diffusion of adatoms on the terraces, attachment, detachment and interlayer transport of adatoms at the step edges, and nucleation of adatoms. Then the effects of nucleation on the instability of step meandering and the coalescence of both islands and steps were simulated by the model. The results showed that the instability of step meandering caused by nucleation was affected by the growth temperature. And the effects of nucleation on the instability was also analyzed. Moreover, the surface roughness as a function of time for different temperatures was discussed. Finally, a phase diagram was presented to predict in which conditions the effects of nucleation on step meandering become significant and the three different regimes, the step-flow (SF), 2D nucleation (2DN), and 3D layer by layer (3DLBL) were determined.

Multiple focused EMAT designs for improved surface breaking defect characterization

NASA Astrophysics Data System (ADS)

Thring, C. B.; Fan, Y.; Edwards, R. S.

2017-02-01

Ultrasonic Rayleigh waves can be employed for the detection of surface breaking defects such as rolling contact fatigue and stress corrosion cracking. Electromagnetic Acoustic Transducers (EMATs) are well suited to this technique as they can directly generate Rayleigh waves within the sample without the requirement for wedges, and they are robust and inexpensive compared to laser ultrasonics. Three different EMAT coil types have been developed, and these are compared to assess their ability to detect and characterize small (down to 0.5 mm depth, 1 mm diameter) surface breaking defects in aluminium. These designs are: a pair of linear meander coils used in a pseudo-pulse-echo mode, a pair of focused meander coils also used in pseudo-pulse-echo mode, and a pair of focused racetrack coils used in pitch-catch mode. The linear meander coils are able to detect most of the defects tested, but have a much lower signal to noise ratio and give limited sizing information. The focused meander coils and the focused racetrack coils can detect all defects tested, but have the advantage that they can also characterize the defect sizes on the sample surface, and have a stronger sensitivity at their focal point. Measurements using all three EMAT designs are presented and compared for high resolution imaging of surface-breaking defects.

Characterization and prediction of meandering channel migration in the GIS environment: a case study of the Sabine River in the USA.

PubMed

Heo, Joon; Duc, Trinh Anh; Cho, Hyung-Sik; Choi, Sung-Uk

2009-05-01

This study focused on the prediction of a 22 km meandering channel migration of the Sabine River between the states of Texas and Louisiana. The meander characteristics of 12 bends, identified from seven orthophotos taken between 1974 and 2004, were acquired in a GIS environment. Based on that earlier years' data acquisition, channel prediction was performed for the two years 1996 and 2004 using least squares estimation and linear extrapolations, yielding a satisfactory agreement with the observations (the median predicted and observed migration rates were 3.1 and 3.6 [m/year], respectively). The best-predicted migration rate was found to be associated with the longest orthophoto-recorded interval. The study confirmed that channel migration is strongly correlated with bend curvature and that the maximum migration rate of the bend corresponded to a radius of curvature [bend radius (R(C))/channel width (W(C))] of 2.5. In tight bends of a smaller radius of curvature than 1.6, secondary flow scouring near the bend apex increases bend curvature. The stability index of the dimensionless bend radius was determined to be 2.45. Overall, this study proves the effectiveness of least squares estimation with historical orthophotography for characterization of meandering channel migration.

Swimming of Paramecium in confined channels

NASA Astrophysics Data System (ADS)

Jung, Sunghwan

2012-02-01

Many living organisms in nature have developed a few different swimming modes, presumably derived from hydrodynamic advantage. Paramecium is a ciliated protozoan covered by thousands of cilia with a few nanometers in diameter and tens of micro-meters in length and is able to exhibit both ballistic and meandering motions. First, we characterize ballistic swimming behaviors of ciliated microorganisms in glass capillaries of different diameters and explain the trajectories they trace out. We develop a theoretical model of an undulating sheet with a pressure gradient and discuss how it affects the swimming speed. Secondly, investigation into meandering swimmings within rectangular PDMS channels of dimension smaller than Paramecium length. We find that Paramecium executes a body-bend (an elastic buckling) using the cilia while it meanders. By considering an elastic beam model, we estimate and show the universal profile of forces it exerts on the walls. Finally, we discuss a few other locomotion of Paramecium in other extreme environments like gel.

Dielectric-based subwavelength metallic meanders for wide-angle band absorbers.

PubMed

Shen, Su; Qiao, Wen; Ye, Yan; Zhou, Yun; Chen, Linsen

2015-01-26

We propose nano-meanders that can achieve wide-angle band absorption in visible regime. The nano-meander consists of a subwavelength dielectric grating covered by continuous ultra-thin Aluminum film (less than one tenth of the incident wavelength). The excited photonic resonant modes, such as cavity mode, surface plasmonic mode and Rayleigh-Wood anomaly, are discussed in detail. Nearly total resonant absorption due to funneling mechanism in the air nano-groove is almost invariant with large incident angle in transverse magnetic polarization. From both the structural geometry and the nanofabrication point of view, the light absorber has a very simple geometrical structure and it is easy to be integrated into complex photonic devices. The highly efficient angle-robust light absorber can be potential candidate for a range of passive and active photonic applications, including solar-energy harvesting as well as producing artificial colors on a large scale substrate.

Stability of a dragged viscous thread: Onset of ``stitching'' in a fluid-mechanical ``sewing machine''

NASA Astrophysics Data System (ADS)

Ribe, Neil M.; Lister, John R.; Chiu-Webster, Sunny

2006-12-01

A thin thread of viscous fluid that falls on a moving belt acts like a fluid-mechanical "sewing machine," exhibiting a rich variety of "stitch" patterns including meanders, translated coiling, slanted loops, braiding, figures-of-eight, W-patterns, side kicks, and period-doubled patterns. Using a numerical linear stability analysis, we determine the critical belt speed and oscillation frequency of the first bifurcation, at which a steady dragged viscous thread becomes unstable to transverse oscillations or "meandering." The predictions of the stability analysis agree closely with the experimental measurements of Chiu-Webster and Lister [J. Fluid Mech. 569, 89 (2006)]. Moreover, the critical belt speed and onset frequency for meandering are nearly identical to the contact-point migration speed and angular frequency, respectively, of steady coiling of a viscous thread on a stationary surface, implying a remarkable degree of dynamical similarity between the two phenomena.

Onset of `stitching' in the fluid mechanical `sewing machine'

NASA Astrophysics Data System (ADS)

Ribe, Neil; Lister, John; Chiu-Webster, Sunny

2006-11-01

A thin thread of viscous fluid that falls on a moving belt acts like a fluid mechanical `sewing machine', exhibiting a rich variety of `stitch' patterns including meanders, side kicks, slanted loops, braiding, figures-of-eight, W-patterns, and period-doubled patterns (Chiu-Webster and Lister, J. Fluid Mech., in press). Using a numerical linear stability analysis based on asymptotic `slender thread' theory, we determine the critical belt speed and frequency of the first bifurcation, at which a steady dragged viscous thread becomes unstable to sideways oscillations (`meanders'). The predictions of the stability analysis agree closely with experimental measurements. Moreover, we find that the critical belt speed and frequency for meandering are nearly identical to the contact point migration speed and the frequency, respectively, of steady coiling of a viscous thread on a stationary surface, implying a remarkable degree of dynamical similarity between the two phenomena.

Electron Energization and Mixing Observed by MMS in the Vicinity of an Electron Diffusion Region During Magnetopause Reconnection

NASA Technical Reports Server (NTRS)

Chen, Li-Jen; Hesse, Michael; Wang, Shan; Gershman, Daniel; Ergun, Robert; Pollock, Craig; Torbert, Roy; Bessho, Naoki; Daughton, William; Dorelli, John;

Electron energization and mixing observed by MMS in the vicinity of an electron diffusion region during magnetopause reconnection

NASA Astrophysics Data System (ADS)

Chen, Li-Jen; Hesse, Michael; Wang, Shan; Gershman, Daniel; Ergun, Robert; Pollock, Craig; Torbert, Roy; Bessho, Naoki; Daughton, William; Dorelli, John; Giles, Barbara; Strangeway, Robert; Russell, Christopher; Khotyaintsev, Yuri; Burch, Jim; Moore, Thomas; Lavraud, Benoit; Phan, Tai; Avanov, Levon

2016-06-01

Measurements from the Magnetospheric Multiscale (MMS) mission are reported to show distinct features of electron energization and mixing in the diffusion region of the terrestrial magnetopause reconnection. At the ion jet and magnetic field reversals, distribution functions exhibiting signatures of accelerated meandering electrons are observed at an electron out-of-plane flow peak. The meandering signatures manifested as triangular and crescent structures are established features of the electron diffusion region (EDR). Effects of meandering electrons on the electric field normal to the reconnection layer are detected. Parallel acceleration and mixing of the inflowing electrons with exhaust electrons shape the exhaust flow pattern. In the EDR vicinity, the measured distribution functions indicate that locally, the electron energization and mixing physics is captured by two-dimensional reconnection, yet to account for the simultaneous four-point measurements, translational invariant in the third dimension must be violated on the ion-skin-depth scale.

Why do seif dunes meander?

NASA Astrophysics Data System (ADS)

Kryger, Mateusz; Bubenzer, Olaf; Parteli, Eric

2017-04-01

Seif dunes - which develop in the absence of vegetation and elongate in the resultant sand transport direction - are the prevailing dune type in many deserts of Earth and Mars and display a meandering shape that has challenged geomorphologists for decades. Understanding the factors controlling seif dune morphology may have impact for a broad range of scientific areas, in particular in the investigation of planetary wind regimes, as dune shape is primarily affected by wind directionality. Sand roses of areas hosting seif dunes display, in general, two main wind directions that form a divergence angle larger than 90˚ . Indeed, theory of dune formation predicts that longitudinal alignment of aeolian bedforms occurs under obtuse bimodal winds, a prediction that has been confirmed by field observations and numerical simulations of aeolian dunes, as well as by experiments on subaqueous bedforms. However, numerical simulations and water tank experiments performed under conditions of bimodal flows could never reproduce one of the most salient characteristics of the seif dune shape, which is its meandering. Instead, longitudinal dunes produced in such simulations and experiments display an unrealistic straight shape, which elongates into the resultant transport trend without developing the sinuous morphology of the seif dunes. Here we show, by means of morphodynamic modeling of aeolian sediment transport and dune formation under directionally varying flows, that the meandering shape of seif dunes can be explained by the action of subordinated sand-moving winds, which occur in addition to both main wind components of the bimodal wind. Because such subordinated winds - inherent to most measured sand roses of seif dune fields - are associated with transport rates much smaller than the sand flux values of the main bimodal wind components - they have been long thought to be negligible for dune shape. However, our simulations show that meandering may be caused by a single secondary wind component in the sand rose with transport rate of about 1/5 of the flux due to the bimodal wind components. To verify our model we calculate dune formation using the sand rose of the seif dune field in Bir Lahfan, Sinai, and find good quantitative agreement between the shape of seif dunes in this field and the dune morphology obtained in the simulations. Our simulations suggest that meandering seif dunes constitute a dune type produced by multimodal wind systems and cannot form under (strictly) bimodal wind regimes.

The influence of tributary flow density differences on the hydrodynamic behavior of a confluent meander bend and implications for flow mixing

NASA Astrophysics Data System (ADS)

Herrero, Horacio S.; Díaz Lozada, José M.; García, Carlos M.; Szupiany, Ricardo N.; Best, Jim; Pagot, Mariana

2018-03-01

The goal of this study is to evaluate the influence of tributary flow density differences on hydrodynamics and mixing at a confluent meander bend. A detailed field characterization is performed using an Acoustic Doppler Current Profiler (ADCP) for quantification of the 3D flow field, flow discharge and bathymetry, as well as CTD measurements (conductivity, temperature, depth) to characterize the patterns of mixing. Satellite images of the confluence taken at complementary times to the field surveys were analyzed to evaluate the confluence hydrodynamics at different flow conditions. The results illustrate the differences in hydrodynamics and mixing length in relation to confluences with equal density tributaries. At low-density differences, and higher discharge ratio (Qr) between the two rivers, the flow is similar to equi-density confluent meander bends. In contrast, at high-density differences (low Qr), the tributary flow is confined to near the confluence but the density difference causes the flow to move across channel. In this case, the density difference causes the lateral spread of the tributary flow to be greater than at a greater Qr when the density difference is less. These results illustrate the potential importance of density differences between tributaries in determining the rate and spatial extent of mixing and sediment dispersal at confluent meander bends.

Bathymetric surveys of the Kootenai River near Bonners Ferry, Idaho, water year 2011

USGS Publications Warehouse

Fosness, Ryan L.

2013-01-01

In 2009, the Kootenai Tribe of Idaho released and implemented the Kootenai River Habitat Restoration Master Plan. This plan aimed to restore, enhance, and maintain the Kootenai River habitat and landscape to support and sustain habitat conditions for aquatic species and animal populations. In support of these restoration efforts, the U.S. Geological Survey, in cooperation with the Kootenai Tribe of Idaho, conducted high-resolution multibeam echosounder bathymetric surveys in May, June, and July 2011, as a baseline bathymetric monitoring survey on the Kootenai River near Bonners Ferry, Idaho. Three channel patterns or reaches exist in the study area—braided, meander, and a transitional zone connecting the braided and meander reaches. Bathymetric data were collected at three study areas in 2011 to provide: (1) surveys in unmapped portions of the meander reach; (2) monitoring of the presence and extent of sand along planned lines within a section of the meander reach; and (3) monitoring aggradation and degradation of the channel bed at specific cross sections within the braided reach and transitional zone. The bathymetric data will be used to update and verify flow models, calibrate and verify sediment transport modeling efforts, and aid in the biological assessment in support of the Kootenai River Habitat Restoration Master Plan. The data and planned lines for each study reach were produced in ASCII XYZ format supported by most geospatial software.

Meandering instability of a viscous thread

NASA Astrophysics Data System (ADS)

Morris, Stephen W.; Dawes, Jonathan H. P.; Ribe, Neil M.; Lister, John R.

2008-06-01

A viscous thread falling from a nozzle onto a surface exhibits the famous rope-coiling effect, in which the thread buckles to form loops. If the surface is replaced by a belt moving with speed U , the rotational symmetry of the buckling instability is broken and a wealth of interesting states are observed [see S. Chiu-Webster and J. R. Lister, J. Fluid Mech. 569, 89 (2006)]. We experimentally studied this “fluid-mechanical sewing machine” in a more precise apparatus. As U is reduced, the steady catenary thread bifurcates into a meandering state in which the thread displacements are only transverse to the motion of the belt. We measured the amplitude and frequency ω of the meandering close to the bifurcation. For smaller U , single-frequency meandering bifurcates to a two-frequency “figure-8” state, which contains a significant 2ω component and parallel as well as transverse displacements. This eventually reverts to single-frequency coiling at still smaller U . More complex, highly hysteretic states with additional frequencies are observed for larger nozzle heights. We propose to understand this zoology in terms of the generic amplitude equations appropriate for resonant interactions between two oscillatory modes with frequencies ω and 2ω . The form of the amplitude equations captures both the axisymmetry of the U=0 coiling state and the symmetry-breaking effects induced by the moving belt.

Meandering instability of a viscous thread.

PubMed

Morris, Stephen W; Dawes, Jonathan H P; Ribe, Neil M; Lister, John R

2008-06-01

A viscous thread falling from a nozzle onto a surface exhibits the famous rope-coiling effect, in which the thread buckles to form loops. If the surface is replaced by a belt moving with speed U , the rotational symmetry of the buckling instability is broken and a wealth of interesting states are observed [see S. Chiu-Webster and J. R. Lister, J. Fluid Mech. 569, 89 (2006)]. We experimentally studied this "fluid-mechanical sewing machine" in a more precise apparatus. As U is reduced, the steady catenary thread bifurcates into a meandering state in which the thread displacements are only transverse to the motion of the belt. We measured the amplitude and frequency omega of the meandering close to the bifurcation. For smaller U , single-frequency meandering bifurcates to a two-frequency "figure-8" state, which contains a significant 2omega component and parallel as well as transverse displacements. This eventually reverts to single-frequency coiling at still smaller U . More complex, highly hysteretic states with additional frequencies are observed for larger nozzle heights. We propose to understand this zoology in terms of the generic amplitude equations appropriate for resonant interactions between two oscillatory modes with frequencies omega and 2omega . The form of the amplitude equations captures both the axisymmetry of the U=0 coiling state and the symmetry-breaking effects induced by the moving belt.

Martian Meanders and Scroll-Bars

NASA Image and Video Library

2017-03-01

This is a portion of an inverted fluvial channel in the region of Aeolis/Zephyria Plana, at the Martian equator. Channels become inverted when the sediments filling them become more resistant to erosion than the surrounding material. Here, the most likely process leading to hardening of the channel material is chemical cementation by precipitation of minerals. Once the surrounding material erodes, the channel is left standing as a ridge. The series of curvilinear lineations are ancient scroll-bars, which are features typical of river meanders (bends) in terrestrial fluvial channels. Scroll-bars are series of ridges that result from the continuous lateral migration of a meander. On Earth, they are more common in mature rivers. The presence of scroll bars suggests that the water flow in this channel may have been sustained for a relatively long time. Measuring characteristics of these scroll-bars and meanders may help to estimate the amount of water that once flowed in this channel, aiding our understanding of the history of water on Mars. The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 29.3 centimeters (11.5 inches) per pixel (with 1 x 1 binning); objects on the order of 88 centimeters (29.6 inches) across are resolved.] North is up. http://photojournal.jpl.nasa.gov/catalog/PIA21551

Biogeochemical reactive transport of carbon, nitrogen and iron in the hyporheic zone

NASA Astrophysics Data System (ADS)

Dwivedi, D.; Steefel, C. I.; Newcomer, M. E.; Arora, B.; Spycher, N.; Hammond, G. E.; Moulton, J. D.; Fox, P. M.; Nico, P. S.; Williams, K. H.; Dafflon, B.; Carroll, R. W. H.

2017-12-01

To understand how biogeochemical processes in the hyporheic zone influence carbon and nitrogen cycling as well as stream biogeochemistry, we developed a biotic and abiotic reaction network and integrated it into a reactive transport simulator - PFLOTRAN. Three-dimensional reactive flow and transport simulations were performed to describe the hyporheic exchange of fluxes from and within an intra-meander region encompassing two meanders of East River in the East Taylor watershed, Colorado. The objectives of this study were to quantify (1) the effect of transience on the export of carbon, nitrogen, and iron; and (2) the biogeochemical transformation of nitrogen and carbon species as a function of the residence time. The model was able to capture reasonably well the observed trends of nitrate and dissolved oxygen values that decreased as well as iron (Fe (II)) values that increased along the meander centerline away from the stream. Hyporheic flow paths create lateral redox zonation within intra-meander regions, which considerably impact nitrogen export into the stream system. Simulation results further demonstrated that low water conditions lead to higher levels of dissolved iron in groundwater, which (Fe (II)> 80%) is exported to the stream on the downstream side during high water conditions. An important conclusion from this study is that reactive transport models representing spatial and temporal heterogeneities are required to identify important factors that contribute to the redox gradients at riverine scales.

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

Laitinen, T.; Dalla, S., E-mail: tlmlaitinen@uclan.ac.uk

Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short timescales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in nondiffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and we quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. Wemore » show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1–10 MeV protons in turbulence conditions typical of the solar wind at 1 au. Subsequently, particles decouple from their initial field lines and after hundreds to thousands of Larmor periods reach time-asymptotic diffusive behavior consistent with particle diffusion across the mean field caused by the meandering of the field lines. We show that the typical duration of the prediffusive phase, hours to tens of hours for 10 MeV protons in 1 au solar wind turbulence conditions, is significant for SEP propagation to 1 au and must be taken into account when modeling SEP propagation in the interplanetary space.« less

Exploring Controls on Sinuousity, Terraces and River Capture in the Upper Dajia River, Taiwan

NASA Astrophysics Data System (ADS)

Belliveau, L. C.; Ouimet, W. B.; Chan, Y. C.; Byrne, T. B.

2015-12-01

Taiwan is one of the most tectonically active regions in the world and is prone to landslides due to steep topography, large earthquakes and frequent typhoons. Landslides often affect and alter the river valleys beneath them, producing knickpoints on longitudinal river profiles, segmenting valleys into mixed bedrock-alluvial rivers and affecting river incision for tens to thousands of years. This study investigates the origin and evolution of complex channel morphologies, terraces and river capture along a 20km stretch of the Upper Da-Jia River in the Heping area of Taiwan. Through GIS analysis and field studies, we explore controls on river channel sinuousity, terrace development and river capture in relation to tectonic and climatic forcing, rock erodibility and landslides. High channel sinuousity is proposed as the result of a coupling between bank erosion and landslides. We discuss three types of landslide-induced meanders and increased sinuousity: (a) depositional-push meanders, (b) failure-zone erosional meanders, and (c) complex-erosional meanders. We also investigate spatial variation in channel morphology (slope, width) and the distribution and heights of river terraces within the Upper Da-Jia watershed associated with periods of widespread valley filling from landslide activity. Examples of river capture provide further evidence of the dynamic interactions between river incision, landslides and associated changes in channel morphology and terrace development within steep rapidly uplift, eroding and evolving mountain belts.

Morphology and spacing of river meander scrolls

NASA Astrophysics Data System (ADS)

Strick, Robert J. P.; Ashworth, Philip J.; Awcock, Graeme; Lewin, John

2018-06-01

Many of the world's alluvial rivers are characterised by single or multiple channels that are often sinuous and that migrate to produce a mosaicked floodplain landscape of truncated scroll (or point) bars. Surprisingly little is known about the morphology and geometry of scroll bars despite increasing interest from hydrocarbon geoscientists working with ancient large meandering river deposits. This paper uses remote sensing imagery, LiDAR data-sets of meandering scroll bar topography, and global coverage elevation data to quantify scroll bar geometry, anatomy, relief, and spacing. The analysis focuses on preserved scroll bars in the Mississippi River (USA) floodplain but also compares attributes to 19 rivers of different scale and depositional environments from around the world. Analysis of 10 large scroll bars (median area = 25 km2) on the Mississippi shows that the point bar deposits can be categorised into three different geomorphological units of increasing scale: individual 'scrolls', 'depositional packages', and 'point bar complexes'. Scroll heights and curvatures are greatest near the modern channel and at the terminating boundaries of different depositional packages, confirming the importance of the formative main channel on subsequent scroll bar relief and shape. Fourier analysis shows a periodic variation in signal (scroll bar height) with an average period (spacing) of 167 m (range 150-190 m) for the Mississippi point bars. For other rivers, a strong relationship exists between the period of scroll bars and the adjacent primary channel width for a range of rivers from 55 to 2042 mis 50% of the main channel width. The strength of this correlation over nearly two orders of magnitude of channel size indicates a scale independence of scroll bar spacing and suggests a strong link between channel migration and scroll bar construction with apparent regularities despite different flow regimes. This investigation of meandering river dynamics and floodplain patterns shows that it is possible to develop a suite of metrics that describe scroll bar morphology and geometry that can be valuable to geoscientists predicting the heterogeneity of subsurface meandering deposits.

Bifurcation and stability analysis of rotating chemical spirals in circular domains: Boundary-induced meandering and stabilization

NASA Astrophysics Data System (ADS)

Bär, Markus; Bangia, Anil K.; Kevrekidis, Ioannis G.

2003-05-01

Recent experimental and model studies have revealed that the domain size may strongly influence the dynamics of rotating spirals in two-dimensional pattern forming chemical reactions. Hartmann et al. [Phys. Rev. Lett. 76, 1384 (1996)], report a frequency increase of spirals in circular domains with diameters substantially smaller than the spiral wavelength in a large domain for the catalytic NO+CO reaction on a microstructured platinum surface. Accompanying simulations with a simple reaction-diffusion system reproduced the behavior. Here, we supplement these studies by a numerical bifurcation and stability analysis of rotating spirals in a simple activator-inhibitor model. The problem is solved in a corotating frame of reference. No-flux conditions are imposed at the boundary of the circular domain. At large domain sizes, eigenvalues and eigenvectors very close to those corresponding to infinite medium translational invariance are observed. Upon decrease of domain size, we observe a simultaneous change in the rotation frequency and a deviation of these eigenvalues from being neutrally stable (zero real part). The latter phenomenon indicates that the translation symmetry of the spiral solution is appreciably broken due to the interaction with the (now nearby) wall. Various dynamical regimes are found: first, the spiral simply tries to avoid the boundary and its tip moves towards the center of the circular domain corresponding to a negative real part of the “translational” eigenvalues. This effect is noticeable at a domain radius of R

Hyporheic Exchange Flows and Biogeochemical Patterns near a Meandering Stream: East Fork of the Jemez River, Valles Caldera National Preserve, New Mexico

NASA Astrophysics Data System (ADS)

Christensen, H.; Wooten, J. P.; Swanson, E.; Senison, J. J.; Myers, K. D.; Befus, K. M.; Warden, J.; Zamora, P. B.; Gomez, J. D.; Wilson, J. L.; Groffman, A.; Rearick, M. S.; Cardenas, M. B.

2012-12-01

A study by the 2012 Hydrogeology Field Methods class of the University of Texas at Austin implemented multiple approaches to evaluate and characterize local hyporheic zone flow and biogeochemical trends in a highly meandering reach of the of the East Fork of the Jemez River, a fourth order stream in northwestern New Mexico. This section of the Jemez River is strongly meandering and exhibits distinct riffle-pool morphology. The high stream sinuosity creates inter-meander hyporheic flow that is also largely influenced by local groundwater gradients. In this study, dozens of piezometers were used to map the water table and flow vectors were then calculated. Surface water and ground water samples were collected and preserved for later geochemical analysis by ICPMS and HPLC, and unstable parameters and alkalinity were measured on-site. Additionally, information was collected from thermal monitoring of the streambed, stream gauging, and from a series of electrical resistivity surveys forming a network across the site. Hyporheic flow paths are suggested by alternating gaining and losing sections of the stream as determined by stream gauging at multiple locations along the reach. Water table maps and calculated fluxes across the sediment-water interface also indicate hyporheic flow paths. We find variability in the distribution of biogeochemical constituents (oxidation-reduction potential, nitrate, ammonium, and phosphate) along interpreted flow paths which is partly consistent with hyporheic exchange. The variability and heterogeneity of reducing and oxidizing conditions is interpreted to be a result of groundwater-surface water interaction. Two-dimensional mapping of biogeochemical parameters show redox transitions along interpreted flow paths. Further analysis of various measured unstable chemical parameters results in observable trends strongly delineated along these preferential flow paths that are consistent with the direction of groundwater flow and the assumed direction of inter-meander hyporheic flow.

A nonlinear model of flow in meandering submarine and subaerial channels

NASA Astrophysics Data System (ADS)

Imran, Jasim; Parker, Gary; Pirmez, Carlos

1999-12-01

A generalized model of flow in meandering subaqueous and subaerial channels is developed. The conservation equations of mass and momentum are depth/layer integrated, normalized, and represented as deviations from a straight base state. This allows the determination of integrable forms which can be solved at both linear and nonlinear levels. The effects of various flow and geometric parameters on the flow dynamics are studied. Although the model is not limited to any specific planform, this study focuses on sine-generated curves. In analysing the flow patterns, the turbidity current of the subaqueous case is simplified to a conservative density flow with water entrainment from above neglected. The subaqueous model thus formally corresponds to a subcritical or only mildly supercritical mud-rich turbidity current. By extension, however the analysis can be applied to a depositional or erosional current carrying sand that is changing only slowly in the streamwise direction. By bringing the subaqueous and subaerial cases into a common form, flow behaviour in the two environments can be compared under similar geometric and boundary conditions. A major difference between the two cases is the degree of superelevation of channel flow around bends, which is modest in the subaerial case but substantial in the subaqueous case. Another difference concerns Coriolis effects: some of the largest subaqueous meandering systems are so large that Coriolis effects can become important. The model is applied to meander bends on the youngest channel in the mid-fan region of the Amazon Fan and a mildly sinuous bend of the North-West Atlantic Mid-Ocean Channel. In the absence of specific data on the turbid flows that created the channel, the model can be used to make inferences about the flow, and in particular the range of values of flow velocity and sediment concentration that would allow the growth and downfan migration of meander bends.

Vegetative impacts upon bedload transport capacity and channel stability for differing alluvial planforms in the Yellow River source zone

NASA Astrophysics Data System (ADS)

Li, Zhi Wei; Yu, Guo An; Brierley, Gary; Wang, Zhao Yin

2016-07-01

The influence of vegetation upon bedload transport and channel morphodynamics is examined along a channel stability gradient ranging from meandering to anabranching to anabranching-braided to fully braided planform conditions along trunk and tributary reaches of the Upper Yellow River in western China. Although the regional geology and climate are relatively consistent across the study area, there is a distinct gradient in the presence and abundance of riparian vegetation for these reaches atop the Qinghai-Tibet Plateau (elevations in the study area range from 2800 to 3400 m a.s.l.). To date, the influence of vegetative impacts upon channel planform and bedload transport capacity of alluvial reaches of the Upper Yellow River remains unclear because of a lack of hydrological and field data. In this region, the types and pattern of riparian vegetation vary with planform type as follows: trees exert the strongest influence in the anabranching reach, the meandering reach flows through meadow vegetation, the anabranching-braided reach has a grass, herb, and sparse shrub cover, and the braided reach has no riparian vegetation. A non-linear relation between vegetative cover on the valley floor and bedload transport capacity is evident, wherein bedload transport capacity is the highest for the anabranching reach, roughly followed by the anabranching-braided, braided, and meandering reaches. The relationship between the bedload transport capacity of a reach and sediment supply from upstream exerts a significant influence upon channel stability. Bedload transport capacity during the flood season (June-September) in the braided reach is much less than the rate of sediment supply, inducing bed aggradation and dynamic channel adjustments. Rates of channel adjustment are less pronounced for the anabranching-braided and anabranching reaches, while the meandering reach is relatively stable (i.e., this is a passive meandering reach).

Transport of Solar Energetic Particles across the Parker field direction due to field line meandering

NASA Astrophysics Data System (ADS)

Laitinen, T. L.; Kopp, A.; Effenberger, F.; Dalla, S.; Marsh, M. S.

2014-12-01

Multi-spacecraft observations of Solar Energetic Particles (SEPs) show that the SEPs can spread large distances across the mean Parker spiral field. The SEPs accelerated during a solar eruption can be observed 360° around the Sun, and the dependence of SEP peak intensity on heliographic longitude at 1 AU has been fitted with Gaussian profiles with σ=30-50° for several events (e.g., Dresing et al 2014; Richardson et al 2014). SEP anisotropy measurements suggest that interplanetary transport is an important factor to the SEP cross-field extent (Dresing et al 2014). However, the currently used diffusive Fokker Planck (FP) description of SEP transport, with realistic diffusion coefficients, has been found insufficient to explain the SEP event cross-field extents. Recently Laitinen et al (2013) emphasised the importance of particle propagation along meandering field lines, which cannot be described as diffusion. They showed that early in an event field line meandering dominates particle cross-field transport and produces events wider than the FP description. They also introduced a new FP model that incorporates both field line meandering and SEP cross-field diffusion using stochastic differential equations and a constant background magnetic field. In this work, we implement the new FP model into Parker field geometry, to study the evolution of an SEP event in the interplanetary space. We compare the new model to the traditional FP approach by using particle and field line diffusion coefficients that are calculated consistently for both models using an assumed radial and spectral description of the turbulence evolution. We find that while the traditional SEP propagation modelling gives typically longitudinal extent with σ=10-20°, the new model results in values σ=30-50°, which is consistent with SEP observations. We conclude that field line meandering must be taken into account when modelling SEP propagation in the interplanetary space.

A generalised model of secondary circulation for a wide range of geophysical flows from direct observations of natural turbidity currents

NASA Astrophysics Data System (ADS)

Azpiroz, M.; Cartigny, M.; Sumner, E. J.; Talling, P.; Parsons, D. R.; Clare, M. A.; Cooper, C.

2017-12-01

Turbidity currents transport sediment through submarine channel systems for hundreds of kilometres to form vast deposits of sediment in the deep sea called submarine fans. The largest submarine fans are fed by meandering channels suggesting that bends may enhance sediment transport distances. The interaction between meander bends and turbidity currents has been a topic of intense debate. Due to the absence of observations of deep-sea turbidity currents flowing through meander bends, our understanding has been based on experimental and numerical models. Measurements of geophysical flows demonstrate a common helical flow structure around meanders. Previous work has demonstrated that helical circulation in rivers is dominated by a single helix that rotates towards the inner bend at near-bed depths. In contrast, initial numerical and experimental models for turbidity currents found both river-like and river-reversed circulations. Saline flows in well-mixed estuaries show a river-like basal helical circulation, while stratified estuaries and saline flows are river-reversed. The existence of lateral stratification in stratified flows is thought to be the key factor in the change of direction of rotation. Stratification causes lateral pressure gradients that can govern the rotation of the flow helix. Turbidity currents are stratified due to their upwards-decreasing sediment load. It has therefore been proposed that stratified turbidity currents behave like stratified saline flow, but this hypothesis remains so far untested. Here we present the first observations of the helical flow in turbidity currents, which occurred within the deep-sea Congo Canyon. The measurements show a consistent river-reversed pattern downstream of the bend apex. Those results lead us to develop a new generalised model for a wide range of flows around meanders. Our conclusions have implications for understanding the flow erosional and depositional patterns, the evolution of channel systems and the architecture of the depositional record.

Nutrient Pumping/Advection by Propagating Rossby Waves in the Kuroshio Extension

DTIC Science & Technology

2010-01-01

sea-elevation changes or SLA variance levels are a maximum as eddies and meanders cross a mean route. This boundary in terms of Chl- a levels (lower...and elevated Chl- a levels ) is south of the KE jet. Kuroshio Extension meanders and rings carry different water types across a mean Kuroshio Extension...Fig. 5A). The ring or eddy currents may also redistribute the surface Chl- a levels , drawing out plumes of locally increased Chl-a from regions of

Archaeological Investigations of the Tiptonville Levee Project Area along Old Graveyard Slough in Lake County, Tennessee.

DTIC Science & Technology

1987-09-01

Reelfoot Lake was formed in a series of meander scars after the earthquake. Most recent active channels have affected only the western margin of the...with a few prominent meander loop scars, and the lower eastern margin as essentially a collective backswamp. Subsidence of Reelfoot Lake itself as a...open river with the various bankline and sandbar habitats involved there. Open water may well have existed dt various times in part of the Reelfoot Lake

Two case studies in river naturalization: planform migration and bank erosion control

NASA Astrophysics Data System (ADS)

Abad, J. D.; Guneralp, I.; Rhoads, B. L.; Garcia, M. H.

2005-05-01

A sound understanding of river planform evolution and bank erosion control, along with integration of expertise from several disciplines is required for the development of predictive models for river naturalization. Over the last few years, several methodologies have been presented for naturalization projects, from purely heuristic to more advanced methods. Since the time and space scales of concern in naturalization vary widely, there is a need for appropriate tools at a variety of time and space scales. This study presents two case studies at different scales. The first case study describes the prediction of river planform evolution for a remeandering project based on a simplified two-dimensional hydrodynamic model. The second case study describes the applicability of a Computational Fluid Dynamics (CFD) model for evaluating the effectiveness of bank-erosion control structures in individual meander bends. Understanding the hydrodynamic influence of control structures on flow through bends allows accurate prediction of depositional and erosional distribution patterns, resulting in better assessment on river planform stability, especially for the case of natural complex systems. The first case study introduces a mathematical model for evolution of meandering rivers that can be used in remeandering projects. In United States in particular, several rivers have been channelized in the past causing environmental and ecological problems. Following Newton's third law, "for every action, there is a reaction", naturalization techniques evolve as natural reactive solutions to channelization. This model (herein referred as RVR Meander) can be used as a stand-alone Windows application or as module in a Geographic Information System. The model was applied to the Poplar Creek re-meanderization project and used to evaluate re-meandering alternatives for an approximately 800-meter long reach of Poplar Creek that was straightened in 1938. The second case study describes a streambank protection project using bendway weirs. In the State of Illinois, bendway weirs constructed of rock have been installed at hundreds of sites, especially on small streams, to control streambank erosion. Bendway weirs are low hard structures installed in the concave bank of a meander bend. Design criteria for these weirs are approximate and have not been rigorously evaluated for overall effectiveness at low-, medium- and high flows. This initial step of the study attempted to describe the hydrodynamics around the weirs and the influence of the hydrodynamic patterns on sediment transport (near-field and far-field). To do that, a state-of-the-art three-dimensional CFD model was used to simulate flow through meander bends where 3D velocity measurements have been obtained to validate model predictions at low stages. Results indicate that the weirs produce highly complex patterns of flow around the weirs, which in some cases may actually increase erosional potential near the outer bank. These two case studies represent components of an emerging initiative to develop predictive tools for naturalization over a range of spatial and temporal scales

Rate estimates for lateral bedrock erosion based on radiocarbon ages, Duck River, Tennessee

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

Brakenridge, G.R.

Rates of bedrock erosion in ingrown meandering rivers can be inferred from the location of buried relict flood-plain and river-bank surfaces, associated paleosols, and radiocarbon dates. Two independent methods are used to evaluate the long-term rates of limestone bedrock erosion by the Duck River. Radiocarbon dates on samples retrieved from buried Holocene flood-plain and bank surfaces indicate lateral migration of the river bank at average rates of 0.6-1.9 m/100 yr. Such rates agree with lateral bedrock cliff erosion rates of 0.5-1.4 m/100 yr, as determined from a comparison of late Pleistocene and modern bedrock cliff and terrace scarp positions. Thesemore » results show that lateral bedrock erosion by this river could have occurred coevally with flood-plain and terrace formation and that the resulting evolution of valley meander bends carved into bedrock is similar in many respects to that of channel meanders cut into alluvium. 11 references, 5 figures.« less

Experimental Research on Boundary Shear Stress in Typical Meandering Channel

NASA Astrophysics Data System (ADS)

Chen, Kai-hua; Xia, Yun-feng; Zhang, Shi-zhao; Wen, Yun-cheng; Xu, Hua

2018-06-01

A novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor was used to study the boundary shear stress distribution in the generalized natural meandering open channel, and the mean sidewall shear stress distribution along the meandering channel, and the lateral boundary shear stress distribution in the typical cross-section of the meandering channel was analysed. Based on the measurement of the boundary shear stress, a semi-empirical semi-theoretical computing approach of the boundary shear stress was derived including the effects of the secondary flow, sidewall roughness factor, eddy viscosity and the additional Reynolds stress, and more importantly, for the first time, it combined the effects of the cross-section central angle and the Reynolds number into the expressions. Afterwards, a comparison between the previous research and this study was developed. Following the result, we found that the semi-empirical semi-theoretical boundary shear stress distribution algorithm can predict the boundary shear stress distribution precisely. Finally, a single factor analysis was conducted on the relationship between the average sidewall shear stress on the convex and concave bank and the flow rate, water depth, slope ratio, or the cross-section central angle of the open channel bend. The functional relationship with each of the above factors was established, and then the distance from the location of the extreme sidewall shear stress to the bottom of the open channel was deduced based on the statistical theory.

Physically Modeling Stream Channel Adjustment to Woody Riparian Vegetation

NASA Astrophysics Data System (ADS)

Bennett, S. J.; Alonso, C. V.

2003-12-01

Stream restoration designs often use vegetation to promote bank and channel stability, to facilitate point-bar development, and to encourage natural colonization of riparian species. Here we examine the adjustment of an alluvial channel to in-stream and riparian vegetation using a distorted Froude-scale flume model with a movable boundary. A decimeter-scale trapezoidal channel comprised of 0.8-mm diameter sand was systematically vegetated with emergent, rigid dowels (3-mm in diameter) in rectangular and hemispherical patterns with varying vegetation densities while conserving the shape of the zone and the geometry of the vegetal patterns. Alternate sides of the channel were vegetated at the prescribed spacing of equilibrium alternate bars, ca. 5 to 7 times the channel width. Using flow conditions just below the threshold of sediment motion, flow obstruction, deflection, and acceleration caused bed erosion, bank failure, and morphologic channel adjustments that were wholly attributable to the managed plantings. As vegetation density increased, the magnitude and rate of scaled channel adjustment increased, which included increased channel widths, bankline steepening and meandering, and thalweg meandering. As the modeled channel began to meander, the stream bed aggraded and flow depth decreased markedly, creating a continuously connected, inter-reach complex of mid-channel bars. This study demonstrates the utility of using managed vegetations in stream corridor design and meander development, and it provides the practitioner with guidance on the magnitude of channel adjustment as it relates to vegetation density, shape, and spacing.

All-Printed Differential Temperature Sensor for the Compensation of Bending Effects.

PubMed

Ali, Shawkat; Hassan, Arshad; Bae, Jinho; Lee, Chong Hyun; Kim, Juho

2016-11-08

Because printed resistance temperature detectors (RTDs) are affected by tension and compression of metallic patterns on flexible or curved surfaces, a significant temperature-sensing error occurs in general. Hence, we propose a differential temperature sensor (DTS) to compensate the bending effect of the printed RTDs, which is composed of two serially connected similar meander patterns fabricated back-to-back on a polyimide polyethylene terephthalate substrate through a Dimatix DMP-3000 inkjet printer using silver nanoparticles. Under mechanical deformation, the resistance of the proposed DTS is not varied significantly under the same temperature environment because its patterns vary differentially as one side experiences tension while the opposite side experiences compression. A single meander pattern of the proposed DTS has a total length of 75 mm and device dimensions of 7 × 7 mm 2 . The total resistance variation is observed to be 15.5 Ω against the temperature variation from 0 to 100 °C, and the temperature coefficient of resistance is 1.076 × 10 -3 °C -1 . The proposed DTS exhibits no significant resistance change on bendability testing down to 2 mm diameter because of mechanical deformation. In addition, it is also used to detect the curvature of a body shape down to 2 mm diameter because its resistance changes by ±8.22% using a single meander pattern of DTS. The proposed sensor can be applied on a curved or flexible surface to measure relatively accurate temperature when compared to a single meander pattern.

Energetic Particle Transport across the Mean Magnetic Field: Before Diffusion

NASA Astrophysics Data System (ADS)

Laitinen, T.; Dalla, S.

2017-01-01

Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short timescales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in nondiffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and we quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. We show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1-10 MeV protons in turbulence conditions typical of the solar wind at 1 au. Subsequently, particles decouple from their initial field lines and after hundreds to thousands of Larmor periods reach time-asymptotic diffusive behavior consistent with particle diffusion across the mean field caused by the meandering of the field lines. We show that the typical duration of the prediffusive phase, hours to tens of hours for 10 MeV protons in 1 au solar wind turbulence conditions, is significant for SEP propagation to 1 au and must be taken into account when modeling SEP propagation in the interplanetary space.

Misssissippi River and St. Louis, MO

NASA Image and Video Library

1973-06-22

SL2-81-189 (22 June 1973) --- The well defined meanderings of the Mississippi River, just to the south of St. Louis, MO (38.5N, 90.5W) can easily be seen as curved lines and loops roughly paralleling the present river in this view showing the former water channels. The vegetated bluffs on either side of the river define the limits of the meanders where the rich river flood plain offers some of the most fertile land for agriculture although flooding remains a constant threat. Photo credit: NASA

Mass conservation: 1-D open channel flow equations

USGS Publications Warehouse

DeLong, Lewis L.

1989-01-01

Unsteady flow simulation in natural rivers is often complicated by meandering channels of compound section. Hydraulic properties and the length of the wetted channel may vary significantly as a meandering river inundates its adjacent floodplain. The one-dimensional, unsteady, open-channel flow equations can be extended to simulate floods in channels of compound section. It will be shown that equations derived from the addition of differential equations individually describing flow in main and overbank channels do not in general conserve mass when overbank and main channels are of different lengths.

Effects of the reconnection electric field on crescent electron distribution functions in asymmetric guide field reconnection

NASA Astrophysics Data System (ADS)

Bessho, N.; Chen, L. J.; Hesse, M.; Wang, S.

2017-12-01

In asymmetric reconnection with a guide field in the Earth's magnetopause, electron motion in the electron diffusion region (EDR) is largely affected by the guide field, the Hall electric field, and the reconnection electric field. The electron motion in the EDR is neither simple gyration around the guide field nor simple meandering motion across the current sheet. The combined meandering motion and gyration has essential effects on particle acceleration by the in-plane Hall electric field (existing only in the magnetospheric side) and the out-of-plane reconnection electric field. We analyze electron motion and crescent-shaped electron distribution functions in the EDR in asymmetric guide field reconnection, and perform 2-D particle-in-cell (PIC) simulations to elucidate the effect of reconnection electric field on electron distribution functions. Recently, we have analytically expressed the acceleration effect due to the reconnection electric field on electron crescent distribution functions in asymmetric reconnection without a guide field (Bessho et al., Phys. Plasmas, 24, 072903, 2017). We extend the theory to asymmetric guide field reconnection, and predict the crescent bulge in distribution functions. Assuming 1D approximation of field variations in the EDR, we derive the time period of oscillatory electron motion (meandering + gyration) in the EDR. The time period is expressed as a hybrid of the meandering period and the gyro period. Due to the guide field, electrons not only oscillate along crescent-shaped trajectories in the velocity plane perpendicular to the antiparallel magnetic fields, but also move along parabolic trajectories in the velocity plane coplanar with magnetic field. The trajectory in the velocity space gradually shifts to the acceleration direction by the reconnection electric field as multiple bounces continue. Due to the guide field, electron distributions for meandering particles are bounded by two paraboloids (or hyperboloids) in the velocity space. We compare theory and PIC simulation results of the velocity shift of crescent distribution functions based on the derived time period of bounce motion in a guide field. Theoretical predictions are applied to electron distributions observed by MMS in magnetopause reconnection to estimate the reconnection electric field.

The storage time, age, and erosion hazard of laterally accreted sediment on the floodplain of a simulated meandering river

USGS Publications Warehouse

Bradley, D. Nathan; Tucker, Gregory E.

2013-01-01

A sediment particle traversing the fluvial system may spend the majority of the total transit time at rest, stored in various sedimentary deposits. Floodplains are among the most important of these deposits, with the potential to store large amounts of sediment for long periods of time. The virtual velocity of a sediment grain depends strongly on the amount of time spent in storage, but little is known about sediment storage times. Measurements of floodplain vegetation age have suggested that storage times are exponentially distributed, a case that arises when all the sediment on a floodplain is equally vulnerable to erosion in a given interval. This assumption has been incorporated into sediment routing models, despite some evidence that younger sediment is more likely to be eroded from floodplains than older sediment. We investigate the relationship between sediment age and erosion, which we term the “erosion hazard,” with a model of a meandering river that constructs its floodplain by lateral accretion. We find that the erosion hazard decreases with sediment age, leading to a storage time distribution that is not exponential. We propose an alternate model that requires that channel motion is approximately diffusive and results in a heavy tailed distribution of storage time. The model applies to timescales over which the direction of channel motion is uncorrelated. We speculate that the lower end of this range of time is set by the meander cutoff timescale and the upper end is set by processes that limit the width of the meander belt.

Lateral migration of the Middle Sacramento River, California

USGS Publications Warehouse

Brice, James Coble

1977-01-01

Rates and processes of lateral erosion were studied for the middle Sacramento River between Chico Landing and Colusa, Calif. , a river distance of about 50 miles which is bordered by valuable agricultural land. The study is based on comparison of maps made during 1867-1949 and on aerial photographs made during 1924-74. Meander loops migrate by downstream translation in a direction nearly perpendicular to the loop axis. Loops are cut off by straight or diagonal chutes across the meander neck. The sinuosity of the river has gradually decreased from a value of 1.56 in 1896 to 1.35 in 1974. The morphology and curvature of meander loops cut off before white settlers came to the area indicate that the river was more stable, as well as more sinuous , then than now; subsequent morphologic changes are attributed mainly to the clearing of riparian vegetation and the effects of levees in reducing the area of overflow. The bank-erosion is 1.82 acres per year per stream mile or about 15 feet per year per stream foot for the period 1896-1974. (Woodard-USGS)

Measuring Plume Meander in the Nighttime Stable Boundary Layer with Lidar

NASA Astrophysics Data System (ADS)

Hiscox, A.; Miller, D. R.; Nappo, C. J.

2009-12-01

Complex dynamics of the stable planetary boundary layer (PBL), such as the effects of density currents, intermittent turbulence, surface-layer decoupling, internal gravity waves, cold air pooling, and katabatic flows affect plume transport and diffusion. A better understanding of these effects is needed for nighttime transport model development. The JORNADA (Joint Observational Research on Nocturnal Atmospheric Dispersion of Aerosols) field campaign, conducted in the New Mexico desert during April 2005, sought to address some of these issues The JORNADA data set includes simultaneous micrometeorological measurements of the boundary layer structure, turbulence, and wave activity along with continuous lidar measurement of aerosol plume releases. What makes JORNADA unique is the real-time monitoring of an elevated plume with a lidar. The quantification of plume meander will be presented in this paper. The application of these techniques to the JORNADA data allows for a more complete understanding of the nocturnal boundary layer (NBL). We will present an in-depth analysis of lidar measurements of plume meander and dispersion and their relationship to the complexities of NBL structure.

Design and simulation of MEMS vector hydrophone with reduced cross section based meander beams

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

Kumar, Manoj; Dutta, S.; Pal, Ramjay

MEMS based vector hydrophone is being one of the key device in the underwater communications. In this paper, we presented a bio-inspired MEMS vector hydrophone. The hydrophone structure consists of a proof mass suspended by four meander type beams with reduced cross-section. Modal patterns of the structure were studied. First three modal frequencies of the hydrophone structure were found to be 420 Hz, 420 Hz and 1646 Hz respectively. The deflection and stress of the hydrophone is found have linear behavior in the 1 µPa – 1Pa pressure range.

Defect images by planar ECT probe of meander-mesh coils

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

Yamada, Sotoshi; Katou, Masaki; Iwahara, Masayoshi

1996-09-01

This paper presents results pertaining to image data obtained from a planar meander-mesh coupled coil type ECT probe. The image data makes it possible to detect not only the existence of a defect but also to extract detailed information regarding the nature of the defect, such as its position, shape, length, and direction. In order to recognize a defect distinctly, the authors have fabricated the high sensitive planar coil which can be used to image a 2-D representation of the ECT signal. The relationships between the image pattern and defect shape are discussed.

Self-Formed Meanders (With Cutoffs) in a Laboratory Flume

NASA Astrophysics Data System (ADS)

Braudrick, C. A.; Leverich, G. T.; Sklar, L. S.; Dietrich, W. E.

2005-12-01

The development of a mechanistic understanding of channel geometry and morphodynamics has been inhibited by the inability to create self-formed, freely meandering, single thread channels in a laboratory flume. By being able to reliably generate such channels, studies of the influence of sediment supply and flow dynamics as well as bank strength on channel morphology can be experimentally explored. We have found that the key experimental controls are: 1) ratio of bank strength to boundary shear stress exerted on the bank; 2) bedload and suspended load rates; and 3) variable flow discharge. We have been able to create meandering channels in a sand bedded laboratory flume using alfalfa sprouts. The alfalfa sprouts decrease the bank erosion rate so that bank erosion would occur at approximately the same pace as bar growth. The addition of coarse suspended load was necessary to cause deposition on bars to grow to the floodplain height. The sprouts contributed to deposition by creating a rough floodplain surface. Steady discharge failed to produced meandering, apparently due to the lack of suspended load deposition on the bar surface. The channels were created in a 3.6-m wide and 6.1-m long flume with an adjustable slope set at 0.01. We introduced both bedload (sand) and suspended load (crushed silica) into the top of the flume, which has an initial channel with either one or two bends carved into the floodplain. Runs lasted between 1 and 4 hours and occurred once per week. Alfalfa seeds were spread evenly outside the low flow channel following each run and are allowed to grow between runs. With the same material and flow conditions, the channel rapidly braided without the alfalfa sprouts. Braided was also favored under steady flow conditions. Under dynamic flows with banks strengthened by sprouts, the resulting experimental channels had many of the features observed in meandering streams such as oxbow lakes and meander cutoffs. The cutoffs occurred during overbank flows when high flow channels were reoccupied. As the portion of the flow passing through the reoccupied channel increased, an upstream-propagating headcut was initiated. Once the headcut propagated past the upstream junction with the main channel, sediment deposition blocked the upstream end of a secondary channel. The cutoffs became oxbow lakes when rapid bar growth promoted lateral channel migration away from the downstream junction with the cutoff channel. With these results in hand we are completing the construction of a larger flume in which we will set forth experiments on the influence of sediment supply, discharge magnitude and duration, grain size and bank strength on channel geometry.

Relationship Between Vortex Meander and Ambient Turbulence

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.; Hardy, Gordon H.; Meyn, Larry A.

2006-01-01

Efforts are currently underway to increase the capacity of airports by use of closely-spaced parallel runways. If such an objective is to be achieved safely and efficiently during both visual and instrument flight conditions, it will be necessary to develop more precise methods for the prediction of the motion and spread of the hazard posed by the lift-generated vortex-wakes of aircraft, and their uncertainties. The purpose of the present study is to relate the motion induced in vortex filaments by turbulence in the ambient flow field to the measured turbulence in the flow field. The problem came about when observations made in the two largest NASA wind tunnels indicated that extended exposure of vortex wakes to the turbulence in the wind tunnel air stream causes the centers of the vortices to meander about with time at a given downstream station where wake measurements are being made. Although such a behavior was expected, the turbulence level based on the maximum amplitude of meander was much less than the root-mean-squared value measured in the free-stream of the wind tunnel by use of hot-film anemometers. An analysis of the time-dependent motion of segments of vortex filaments as they interact with an eddy, indicates that the inertia of the filaments retards their motion enough in the early part of their travel to account for a large part of the difference in the two determinations of turbulence level. Migration of vortex filaments from one turbulent eddy to another (probably with a different orientation), is believed to account for the remainder of the difference. Methods that may possibly be developed for use in the measurement of the magnitude of the more intense eddies in turbulent flow fields and how they should be adjusted to predict vortex meander are then discussed.

The Surface Velocity Structure of the Florida Current in a Jet Coordinate Frame

NASA Astrophysics Data System (ADS)

Archer, Matthew R.; Shay, Lynn K.; Johns, William E.

2017-11-01

The structure and variability of the Florida Current between 25° and 26°N are investigated using HF radar ocean current measurements to provide the most detailed view of the surface jet to date. A 2-D jet coordinate analysis is performed to define lateral displacements of the jet in time (meandering), and associated structural variations over a 2 year period (2005-2006). In the jet coordinate frame, core speed has a median value of ˜160 cm s-1 at the central latitude of the array (25.4°N), with a standard deviation (STD) of 35 cm s-1. The jet meanders at timescales of 3-30 days, with a STD of 8 km, and a downstream phase speed of ˜80 km d-1. Meandering accounts for ˜45% of eddy kinetic energy computed in a fixed (geographical) reference frame. Core speed, width, and shear undergo the same dominant 3-30 day variability, plus an annual cycle that matches seasonality of alongshore wind stress. Jet transport at 25.4°N exhibits a different seasonality to volume transport at 27°N, most likely driven by input from the Northwest Providence Channel. Core speed correlates inversely with Miami sea level fluctuations such that a 40 cm s-1 deceleration is associated with a ˜10 cm elevation in sea level, although there is no correlation of sea level to jet meandering or width. Such accurate quantification of the Florida Current's variability is critical to understand and forecast future changes in the climate system of the North Atlantic, as well as local impacts on coastal circulation and sea level variability along south Florida's coastline.

Lateral movement and stability of channel banks near four highway crossings in southwestern Mississippi

USGS Publications Warehouse

Turnipseed, D. Phil

1994-01-01

Channel meandering in alluvial streams has caused localized channel instability that has resulted in bridge failure and loss of human life in Mississippi. The U.S. Geological Survey, in coopera- tion with the Mississippi Department of Transpor- tation, conducted a study to develop a better methodology for defining and estimating channel meandering. For this report, river reaches near four bridge sites with current lateral movement of channel banks were selected for study. The lateral movement of channel banks was studied by mapping meanders from aerial photographs taken at various times, evaluating available discharge measurements, and measuring existing channel geometry and soil strength properties at these sites. Rapid, unre- stricted meander cuts and sandy banks are charac- teristic of the sites. Lateral movement was signi- ficant upstream from all four sites, and only one bridge site did not have significant lateral channel-bank movement during the study period. The development of cutbanks and localized channel-bank erosion have caused unstable conditions at three of the sites. Maps of tops of channel indicate significant lateral movement of channel banks upstream and downstream of all four sites and near the bridges at three of four sites. No significant movement occurred at the U.S. Highway 98 crossing of the Bogue Chitto near Tylertown from 1941 to 1991 despite large floods in 1983 and 1990. Slope stability analyses indicated this site to be marginally stable. The maximum lateral movement indicated from maps of tops of channel banks was 680 feet of northward movement of the right (north) bank of the Homochitto River near the State Highway 33 crossing at Rosetta from 1941 to 1983.

Errors in Martian paleodischarges skew interpretations of hydrologic history: Case study of the Aeolis Dorsa, Mars, with insights from the Quinn River, NV

NASA Astrophysics Data System (ADS)

Jacobsen, Robert E.; Burr, Devon M.

2018-03-01

Changes in Martian fluvial geomorphology with time-stratigraphic age, including decreases in paleochannel widths, suggest waning paleodischarges through time. Where fluvial landforms do not preserve paleochannel widths (e.g., meander deposits), other landform dimensions (i.e., radius of curvature) may be used to estimate paleodischarges. In the Aeolis Dorsa region, topographically inverted and stacked fluvial deposits - wide meander point bars overlain by thin channel fills - preserve ostensible evidence of decreasing paleodischarges through time. However, a robust paleohydraulic analysis of these distinct deposits requires knowledge of the accuracy of a terrestrial-based empirical relationship that estimates channel width from point-bar radius of curvature. We assess the accuracy of this radius-width relationship by applying it to a well-studied terrestrial analog, the Quinn River, Nevada. We find that radii of curvature from the Quinn River exceed the values predicted from the empirical relationship. These anomalously high radii are associated with greater resistance in the channel cut banks, indicating that bank strength is a confounding factor in the radius-width relationship. Some deposits in the Aeolis Dorsa include irregular meander morphologies, suggesting variably resistant channel banks and overestimates of both paleochannel widths and paleodischarges. Furthermore, the morphometry of the overlying thin channel fills suggests their widths have been eroded, such that their paleodischarges are underestimates. These overestimates and underestimates, when considered together, suggest little change in paleodischarge during the stratigraphic transition from meander deposits to channel fills. This work demonstrates the importance of terrestrial analog studies for revealing confounding factors in Martian fluvial systems and cautions against simplistic interpretations of Martian fluvial history. The discovered inaccuracies of paleodischarge estimates expose sources of uncertainty in the extant paleodischarge data that bias inferences toward waning hydrologic activity through time.

Fabrication of Metallic Magnetic Calorimeter for Radionuclide Analysis

NASA Astrophysics Data System (ADS)

Yoon, W. S.; Kim, G. B.; Lee, H. J.; Lee, J. Y.; Lee, J. H.; Jang, Y. S.; Lee, S. J.; Lee, M. K.; Kim, Y. H.

2014-09-01

We present a detailed report on the fabrication process of a metallic magnetic calorimeter (MMC). The MMC is configured in a planar geometry with a meander-shaped pickup coil covered with a Au:Er temperature sensor layer. The meander coil is used to apply a magnetic field to magnetize the erbium ions and to measure the magnetization change of the spin system. The MMC is designed to have a large area (1 mm) and 3 m thickness Au:Er layer, which is suited for large metal absorbers with a few nJ/K heat capacity in radionuclide analysis applications. The completed devices are used in alpha and Q spectrometries.

Two-dimensional periodic texture of actin filaments formed upon drying

PubMed Central

Honda, Hajime; Ishiwata, Shin’ichi

2011-01-01

We found that a solution of actin filaments can form a periodic texture in the process of drying on a flat glass surface in the air; the periodic texture was composed of smooth meandering bundles of actin filaments. We also found that a branched salt crystal grows in the space between the meandering bundles of actin filaments. The distance between the adjacent striae (striation period) in the resulting dried two-dimensional pattern of striation decreased from about 50 to 2 μm, as the ambient temperature was increased from 4 to 40°C at 1 mg/ml actin, and showed an increasing tendency from a few to several tens μm with the increase in the initial concentration of actin filaments from 0.6 to 2.0mg/ml at room temperature. As the speed of drying is increased at a certain temperature, the striation period was also found to decrease. We propose that the formation of the two-dimensional striation pattern of bundles of actin filaments is the result of condensation of proteins due to dehydration, and suggest that the solvent flow from the center to the periphery of the sample causes the meandering of actin filaments. PMID:27857588

Fueling plankton production by a meandering frontal jet: a case study for the Alboran Sea (Western Mediterranean).

PubMed

Oguz, Temel; Macias, Diego; Garcia-Lafuente, Jesus; Pascual, Ananda; Tintore, Joaquin

2014-01-01

A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15-20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

Birth, life and death of an Anticyclonic eddy in the Southern Ocean

NASA Astrophysics Data System (ADS)

Torres, R.; Sallee, J. B.; Schwarz, J.; Hosegood, P. J.; Taylor, J. R.; Adams, K.; Bachman, S.; Stamper, M. A.

2016-02-01

The Antarctic Circumpolar Current (ACC) is a climatically relevant frontal structure of global importance, which regularly develops instabilities growing into meanders, and eventually evolving into long-lived anticyclonic eddies. These eddies exhibit sustained primary productivity that can last several months fuelled by local resupply of nutrients. During April-May 2015 we conducted an intensive field experiment in the Southern Ocean where we sampled and tracked an ACC meander as it developed into an eddy and later vanished some 90 days later. The physical characteristics of the meander and eddy were observed with a combination of high resolution hydrography, ADCP and turbulence observations, in addition to biogeochemical observations of nutrients and phytoplankton. The life and death of the eddy was subsequently tracked through Argo, BIO-Argo Lagrangian profilers and remote sensing. In this presentation we will use observations and ecosystem modelling to discuss the physical processes that sustain the observed high Chlorophyll levels in the eddy and explore how the eddy evolution impacts the rate of nutrient supply and how this translates into the observed changes in chlorophyll. We will discuss the relevance of eddy formation to Chlorophyll and productivity in the region.

Bandwidth enhancement of a dual band planar monopole antenna using meandered microstrip feeding.

PubMed

Ahsan, M R; Islam, M T; Habib Ullah, M; Misran, N

2014-01-01

A meandered-microstrip fed circular shaped monopole antenna loaded with vertical slots on a high dielectric material substrate (ε r = 15) is proposed in this paper. The performance criteria of the proposed antenna have been experimentally verified by fabricating a printed prototype. The experimental results show that the proposed antenna has achieved wider bandwidth with satisfactory gain by introducing meandered-microstrip feeding in assistant of partial ground plane. It is observed that, the -10 dB impedance bandwidth of the proposed antenna at lower band is 44.4% (600 MHz-1 GHz) and at upper band is 28% (2.25 GHz-2.95 GHz). The measured maximum gains of -1.18 dBi and 4.87 dBi with maximum radiation efficiencies have been observed at lower band and upper band, respectively. The antenna configuration and parametric study have been carried out with the help of commercially available computer-aided EM simulator, and a good accordance is perceived in between the simulated and measured results. The analysis of performance criteria and almost consistent radiation pattern make the proposed antenna a suitable candidate for UHF RFID, WiMAX, and WLAN applications.

Bandwidth Enhancement of a Dual Band Planar Monopole Antenna Using Meandered Microstrip Feeding

PubMed Central

Ahsan, M. R.; Islam, M. T.; Habib Ullah, M.; Misran, N.

2014-01-01

A meandered-microstrip fed circular shaped monopole antenna loaded with vertical slots on a high dielectric material substrate (ε r = 15) is proposed in this paper. The performance criteria of the proposed antenna have been experimentally verified by fabricating a printed prototype. The experimental results show that the proposed antenna has achieved wider bandwidth with satisfactory gain by introducing meandered-microstrip feeding in assistant of partial ground plane. It is observed that, the −10 dB impedance bandwidth of the proposed antenna at lower band is 44.4% (600 MHz–1 GHz) and at upper band is 28% (2.25 GHz–2.95 GHz). The measured maximum gains of −1.18 dBi and 4.87 dBi with maximum radiation efficiencies have been observed at lower band and upper band, respectively. The antenna configuration and parametric study have been carried out with the help of commercially available computer-aided EM simulator, and a good accordance is perceived in between the simulated and measured results. The analysis of performance criteria and almost consistent radiation pattern make the proposed antenna a suitable candidate for UHF RFID, WiMAX, and WLAN applications. PMID:24723832

Ocean-Atmosphere Interaction Over Agulhas Extension Meanders

NASA Technical Reports Server (NTRS)

Liu, W. Timothy; Xie, Xiaosu; Niiler, Pearn P.

2007-01-01

Many years of high-resolution measurements by a number of space-based sensors and from Lagrangian drifters became available recently and are used to examine the persistent atmospheric imprints of the semi-permanent meanders of the Agulhas Extension Current (AEC), where strong surface current and temperature gradients are found. The sea surface temperature (SST) measured by the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and the chlorophyll concentration measured by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) support the identification of the meanders and related ocean circulation by the drifters. The collocation of high and low magnitudes of equivalent neutral wind (ENW) measured by Quick Scatterometer (QuikSCAT), which is uniquely related to surface stress by definition, illustrates not only the stability dependence of turbulent mixing but also the unique stress measuring capability of the scatterometer. The observed rotation of ENW in opposition to the rotation of the surface current clearly demonstrates that the scatterometer measures stress rather than winds. The clear differences between the distributions of wind and stress and the possible inadequacy of turbulent parameterization affirm the need of surface stress vector measurements, which were not available before the scatterometers. The opposite sign of the stress vorticity to current vorticity implies that the atmosphere spins down the current rotation through momentum transport. Coincident high SST and ENW over the southern extension of the meander enhance evaporation and latent heat flux, which cools the ocean. The atmosphere is found to provide negative feedback to ocean current and temperature gradients. Distribution of ENW convergence implies ascending motion on the downwind side of local SST maxima and descending air on the upwind side and acceleration of surface wind stress over warm water (deceleration over cool water); the convection may escalate the contrast of ENW over warm and cool water set up by the dependence of turbulent mixing on stability; this relation exerts a positive feedback to the ENW-SST relation. The temperature sounding measured by the Atmospheric Infrared Sounder(AIRS) is consistent with the spatial coherence between the cloud-top temperature provided by the International Satellite Cloud Climatology Project (ISCCP) and SST. Thus ocean mesoscale SST anomalies associated with the persistent meanders may have a long-term effect well above the midlatitude atmospheric boundary layer, an observation not addressed in the past.

Distribution and sources of polychlorinated biphenyls in Woods Inlet, Lake Worth, Fort Worth, Texas, 2003

USGS Publications Warehouse

Besse, Richard E.; Van Metre, Peter C.; Wilson, Jennifer T.

2005-01-01

Woods Inlet is a flooded stream channel on the southern shore of Lake Worth along the western boundary of Air Force Plant 4 in Fort Worth, Texas, where elevated polychlorinated biphenyl (PCB) concentrations in sediment were detected in a previous study. In response, the U.S. Geological Survey, in cooperation with the U.S. Air Force, conducted a study in 2003 to map the extent of elevated PCB concentrations in Woods Inlet and to identify possible sources (or more specifically, source areas) of PCBs in the watershed of Woods Inlet. Three gravity cores (penetration to pre-reservoir sediment at three sites) and 17 box cores (surficial bottom sediment samples) were collected in Woods Inlet. Suspended sediment in stormwater runoff and streambed sediment were sampled in tributaries to Woods Inlet following storms. Assemblages of PCB congeners in surficial inlet sediments and suspended and streambed sediments were analyzed to indicate sources of PCBs in the inlet sediments on the basis of chemical signatures of PCBs. Woods Inlet receives runoff primarily from three tributaries: (1) Gruggs Park Creek, (2) the small unnamed creek that drains a Texas National Guard maintenance facility, called TNG Creek for this report, and (3) Meandering Road Creek. Twenty-seven of 209 possible PCB congeners were analyzed. The sum of the congeners was used as a measure of total PCB. The spatial distribution of total PCB concentrations in the inlet indicates that most PCBs are originating in the Meandering Road Creek watershed. Peak total PCB concentrations in the three gravity cores occurred at depths corresponding to sediment deposition dates of about 1960 for two of the cores and about 1980 for the third core. The magnitudes of peak total PCB concentrations in the gravity cores followed a spatial distribution generally similar to that of surficial bottom sediment concentrations. Total PCB concentrations in suspended and streambed sediment varied greatly between sites and indicated a likely source of PCBs associated with a sampling site that receives runoff from Air Force Plant 4. Three approaches to the analyses of congener assemblages indicate that PCBs in surficial bottom sediment of Woods Inlet primarily enter Lake Worth from Meandering Road Creek and that runoff from Air Force Plant 4 is a source of the PCBs in Meandering Road Creek. Although current (2003) transport of PCBs from Air Force Plant 4 to the creek is occurring, large decreases in PCB concentrations with decreasing age in two cores indicate that PCB loading to the inlet has decreased greatly since the 1960s. Because runoff entering Meandering Road Creek from some parts of Air Force Plant 4 was not measured or sampled in this study, it cannot be said with certainty that the Air Force Plant 4 site sampled is the only source of PCBs to Meandering Road Creek.

Critical current and electric transport properties of superconducting epitaxial Nb(Ti)N submicron structures

NASA Astrophysics Data System (ADS)

Klimov, A.; Słysz, W.; Guziewicz, M.; Kolkovsky, V.; Wegrzecki, M.; Bar, J.; Marchewka, M.; Seredyński, B.

2016-12-01

Critical current and current-voltage characteristics of epitaxial Nb(Ti)N submicron ultrathin structures were measured as function of temperature. For 700-nm-wide bridge we found current-driven vortex de-pinning at low temperatures and thermally activated flux flow closer to the transition temperature, as the limiting factors for the critical current density. For 100-nm-wide meander we observed combination of phase-slip activation and vortex-anti-vortex pair (VAP) thermal excitation. Our Nb(Ti)N meander structure demonstrates high de-pairing critical current densities 107 A/cm2 at low temperatures, but the critical currents are much smaller due to presence of the local constrictions.

Inverted Meandering Rivers at a Possible Future Mars Landing Site

NASA Image and Video Library

2015-11-27

This image from NASA Mars Reconnaissance Orbiter spacecraft contains interesting examples of crosscutting, sinuous and straight ridges. The ridge in the lower left of the image (orange) has gradual bends and well-defined positive relief, while the ridge in the upper right (blue) exhibits a degree of high sinuosity. Both ridges may be ancient river deposits. In the southern part of the image, there are also possible cut bank and point bar deposition scars (green), but these do not possess visible positive relief. Although lacking relief, the sinuosity of these scars implies an ancient, mature, and low-gradient meandering river. The upper right ridge exhibits a sinuous geometry with positive relief reminiscent of a mature meandering river. Cementation of by underground fluids may have given the river deposits a higher resistance to erosion compared to the surrounding flood plain. Subsequent weathering removed the deposits in the flood plain, leaving behind the river channel positive relief. Offsets of the lower left ridge along possible fault scarps (red) suggest that the area was cut by faults either during or after deposition of the river deposits. There also appears to be a less pronounced fault at the terminus of the upper right ridge. http://photojournal.jpl.nasa.gov/catalog/PIA20160

Fluvial process and the establishment of bottomland trees

USGS Publications Warehouse

Scott, Michael L.; Friedman, Jonathan M.; Auble, Gregor T.

1996-01-01

The relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream. For successful establishment, cottonwoods, poplars, and willows require bare, moist surfaces protected from disturbance. Channel narrowing, channel meandering, and flood deposition promote different spatial and temporal patterns of establishment. During channel narrowing, the site requirements are met on portions of the bed abandoned by the stream, and establishment is associated with a period of low flow lasting one to several years. During channel meandering, the requirements are met on point bars following moderate or higher peak flows. Following flood deposition, the requirements are met on flood deposits ;high above the channel bed. Flood deposition can occur along most streams, but where a channel is constrained by a narrow valley, this process may be the only mechanism that can produce a bare, moist surface high enough to be safe from future disturbance. Because of differences in local bedrock, tributary influence, or geologic history, two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees. We illustrate this phenomenon with examples from forests of plains cottonwood (Populus deltoides ssp. monilifera) along meandering and constrained reaches of the Missouri River in Montana.

Numerical Estimation of the Outer Bank Resistance Characteristics in AN Evolving Meandering River

NASA Astrophysics Data System (ADS)

Wang, D.; Konsoer, K. M.; Rhoads, B. L.; Garcia, M. H.; Best, J.

2017-12-01

Few studies have examined the three-dimensional flow structure and its interaction with bed morphology within elongate loops of large meandering rivers. The present study uses a numerical model to simulate the flow pattern and sediment transport, especially the flow close to the outer-bank, at two elongate meandering loops in Wabash River, USA. The numerical grid for the model is based on a combination of airborne LIDAR data on floodplains and the multibeam data within the river channel. A Finite Element Method (FEM) is used to solve the non-hydrostatic RANS equation using a K-epsilon turbulence closure scheme. High-resolution topographic data allows detailed numerical simulation of flow patterns along the outer bank and model calibration involves comparing simulated velocities to ADCP measurements at 41 cross sections near this bank. Results indicate that flow along the outer bank is strongly influenced by large resistance elements, including woody debris, large erosional scallops within the bank face, and outcropping bedrock. In general, patterns of bank migration conform with zones of high near-bank velocity and shear stress. Using the existing model, different virtual events can be simulated to explore the impacts of different resistance characteristics on patterns of flow, sediment transport, and bank erosion.

Fueling Plankton Production by a Meandering Frontal Jet: A Case Study for the Alboran Sea (Western Mediterranean)

PubMed Central

Oguz, Temel; Macias, Diego; Garcia-Lafuente, Jesus; Pascual, Ananda; Tintore, Joaquin

2014-01-01

A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15–20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive. PMID:25372789

Insights on surface-water/groundwater exchange in the upper Floridan aquifer, north-central Florida (USA), from streamflow data and numerical modeling

NASA Astrophysics Data System (ADS)

Sutton, James E.; Screaton, Elizabeth J.; Martin, Jonathan B.

2015-03-01

Surface-water/groundwater exchange impacts water quality and budgets. In karst aquifers, these exchanges also play an important role in dissolution. Five years of river discharge data were analyzed and a transient groundwater flow model was developed to evaluate large-scale temporal and spatial variations of exchange between an 80-km stretch of the Suwannee River in north-central Florida (USA) and the karstic upper Floridan aquifer. The one-layer transient groundwater flow model was calibrated using groundwater levels from 59 monitoring wells, and fluxes were compared to the exchange calculated from discharge data. Both the numerical modeling and the discharge analysis suggest that the Suwannee River loses water under both low- and high-stage conditions. River losses appear greatest at the inside of a large meander, and the former river water may continue across the meander within the aquifer rather than return to the river. In addition, the numerical model calibration reveals that aquifer transmissivity is elevated within this large meander, which is consistent with enhanced dissolution due to river losses. The results show the importance of temporal and spatial variations in head gradients to exchange between streams and karst aquifers and dissolution of the aquifers.

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2010-01-04

ISS022-E-019513 (4 Jan. 2010) --- The Rio Negro floodplain in Patagonia, Argentina is featured in this image photographed by an Expedition 22 crew member on the International Space Station. The Rio Negro is recognizable by astronaut crews from orbit as one of the most meandering rivers in South America. This is well illustrated in this view, where the entire river floodplain (approximately 10 kilometers wide) is covered with curved relics of channels known as meander scars. The main channel of the river, flowing south at this point?60 kilometers south of the city of Choele Choel (not shown)?appears in partial sun glint at right. Sun glint occurs when light is reflected off a water surface directly back towards the viewer, imparting a silvery sheen to those areas. When meander scars contain water they are known as oxbow lakes, some of which are also highlighted by sun glint in the image. Meander scars show the numerous past positions of river bends, produced as the river snaked across the plain in the very recent geological past. The Rio Negro is a dramatic example of how mobile a river can be. The orange tint to the water in one of the oxbow lakes (center) could result from orange salt-loving algae. Their appearance here would be unusual since floodplain lakes are usually too fresh for algae blooms. But an explanation may lie in the location of the Rio Negro on the margin of Argentina?s arid Patagonian region with annual rainfall less than 12 inches (300 mm). Evaporation in this cloudless region could be high enough for some lakes to become salty. The Rio Negro flows generally southeast from the Andes Mts. to the Atlantic Ocean. Its floodplain supports the biggest pear- and apple-growing region of Argentina. Rectangular farm boundaries can be seen at bottom center. The river also hosts the world?s longest kayak regatta (653 kilometers), which lasts six days.

Three-dimensional flow structure and patterns of bed shear stress in an evolving compound meander bend

USGS Publications Warehouse

Engel, Frank; Rhoads, Bruce L.

2016-01-01

Compound meander bends with multiple lobes of maximum curvature are common in actively evolving lowland rivers. Interaction among spatial patterns of mean flow, turbulence, bed morphology, bank failures and channel migration in compound bends is poorly understood. In this paper, acoustic Doppler current profiler (ADCP) measurements of the three-dimensional (3D) flow velocities in a compound bend are examined to evaluate the influence of channel curvature and hydrologic variability on the structure of flow within the bend. Flow structure at various flow stages is related to changes in bed morphology over the study timeframe. Increases in local curvature within the upstream lobe of the bend reduce outer bank velocities at morphologically significant flows, creating a region that protects the bank from high momentum flow and high bed shear stresses. The dimensionless radius of curvature in the upstream lobe is one-third less than that of the downstream lobe, with average bank erosion rates less than half of the erosion rates for the downstream lobe. Higher bank erosion rates within the downstream lobe correspond to the shift in a core of high velocity and bed shear stresses toward the outer bank as flow moves through the two lobes. These erosion patterns provide a mechanism for continued migration of the downstream lobe in the near future. Bed material size distributions within the bend correspond to spatial patterns of bed shear stress magnitudes, indicating that bed material sorting within the bend is governed by bed shear stress. Results suggest that patterns of flow, sediment entrainment, and planform evolution in compound meander bends are more complex than in simple meander bends. Moreover, interactions among local influences on the flow, such as woody debris, local topographic steering, and locally high curvature, tend to cause compound bends to evolve toward increasing planform complexity over time rather than stable configurations.

In-channel Restoration Structures and the Implications on Hyporheic Exchange: a Laboratory Experiment

NASA Astrophysics Data System (ADS)

Han, B.; Chu, H. H.; Endreny, T. A.

2014-12-01

In-channel structures, i.e. cross-vanes and J-hooks, are commonly installed in river restoration projects to modify the streambed morphology and stream water surface profile, and are known to change hyporhiec exchange flux and habitats for riverine animals. However, few studies have continuous and accurate pre- and post-treatment data to evaluate the impact of these structures on channel hydraulic gradients and morphology. To quantify the effects of in-channel structures, we developed a scaled physical model of a meandering stream with a cross-vane and 6 J-hooks on a mobile-bed river table. Close-range photogrammetry technique was applied to obtain 3-D water and ground surface profiles with sub-millimeter vertical accuracy and horizontal resolution. The experiment was compared with a control experiment without structures while maintaining the same initial conditions of river bed, floodplain and stream flow. Results indicated that the cross-vane caused an average local head loss that represented 16% of the total stream reach head loss, and a 74% increase in channel load in the entire stream reach. Most J-hooks can create stepwise patterns in stream longitudinal profile, and cross-vane can create even more significant ones. Hydraulic gradients across the intra-meander zone also increased with in-channel structures, i.e. from 2.5% to 3.5% at the meander neck. Scour pools developed downstream of the cross-vane, and mostly around the 4 meander apex J-hooks at their hooked tip. Backwater caused by the cross-vane steepened the local water table profile by an additional 4.2%, and was the primary driver of statistically significant hydraulic gradient increase. Reach scale water and streambed surface profiles from our study provided detailed data to improve the understanding of in-channel structure effects, and may serve as reliable data source in computational modeling of hyporheic exchange.

The interaction between vegetation and channel dynamics based on experimental findings

NASA Astrophysics Data System (ADS)

Teske, R.; Van Dijk, W. M.; Van De Lageweg, W.; Kleinhans, M. G.

2012-12-01

Strong feedbacks exist between river channel dynamics, floodplain development and riparian vegetation. Several experimental studies showed how uniformly sown vegetation causes a shift from a braided river to a single-thread and sometimes meandering river. The objective of this study is to test what the effect of fluvially distributed seeds and vegetation settling is on channel pattern change and channel dynamics. The experiments were carried out in a flume of 3 m wide and 10 m long. We tested where the vegetation deposited in a braided and meandering river and how the morphology changed. We used a simple hydrograph of 0.25 hour high flow and 3.75 hour low flow, where alfalfa seeds were added during high flow. The bed sediment consisted of a poorly sorted sediment mixture ranging from fine sand to fine gravel. The evolution was recorded by a high-resolution laser-line scanner and a Digital Single Lens Reflex (DSLR) camera used for channel floodplain segmentation, water depth approximation and vegetation distribution. In an initially braided river, vegetation settled on the higher banks and stabilized the banks. In an initially meandering river, vegetation settled in the inner scrolls, and also on the outer banks when water level exceeded bankfull conditions. In agreement with earlier work, the outer bank was stabilized; erosion rate decreased and bends became sharper. The inner bend vegetation stabilized a part of the point bar and hydraulic resistance of the vegetation steered water in the channel and to the non-vegetated part of the inner bend. As result the meander bend became braided as water flows along the vegetation. Vegetation formed patches that grew over time and reduced channel dynamics. We conclude that self-settling vegetation decreased local bank erosion and that vegetated islands leads to a multi-thread system instead of single-threaded.

Riparian zone hydrology and biogeochemistry as a function of stream evolution stage in glaciated landscapes of the US Northeast

NASA Astrophysics Data System (ADS)

Rook, S. P.; Vidon, P.; Walter, M. T.

2011-12-01

The management of riparian buffer strips is often regarded as one of the most economical and sustainable methods of managing non-point source pollution and water quality. However, current riparian management often follows a 'one size fits all' design, which fails to recognize the complexity of the many biogeochemical processes that regulate pollutant transformation and retention in these systems. This study addresses two critical gaps in knowledge: (1) How carbon, nitrogen, phosphorous, and iron cycles interact with one another (rather than individually). (2) How stream channel geometry and evolution regulate these nutrient cycles and greenhouse gas (GHG) dynamics in the near stream zone. This project specifically explores the hydrological and biogeochemical functioning of riparian zones across a gradient of stream meander evolution stages, with the primary goal of understanding and predicting potential interactions between nutrient dynamics in these systems. Key research questions include: (1) How does stream meander curvature affect riparian zone hydrology? (2) How does stream meander curvature influence riparian zone biogeochemistry? (3) What relationships exist among N, P, Fe, and GHG dynamics? We instrumented three riparian sites near Ithaca, NY, with a dense network of wells, piezometers, and static chambers. These sites represent three riparian zones along three evolution stages of stream meanders: an inner meander, a straight stream section, and an outer bend of the stream with an oxbow lake formation. In spring through fall 2011, water samples and gas samples were collected at a tri-weekly bases at each of the three sites. Water samples were analyzed for oxidation-reduction potential, dissolved oxygen, temperature, FeII/FeIII, nutrients (NO3-, NH4+, PO43-) and dissolved organic carbon (DOC). GHG fluxes at the soil-atmosphere interface were measured for N2O, CO2, and CH4 gases. We predict that stream curvature will significantly affect groundwater flow direction in the riparian zones. Owing to more prolonged saturation, we expect that the oxbow setting will exhibit anoxic conditions, and associated biogeochemistry. Finally, we hypothesize clear relationships among N, P, Fe, and GHG dynamics. In areas of significant denitrification, we expect to see an increase in Fe reduction, PO43- release, N2O emission, and CH4 emission, and a decrease in CO2 emission. Quantifying these interactions will enhance our ability to model riparian biogeochemical processes, promote water quality, and comprehend to what extent the promotion of riparian zones for nitrate removal is done at the expense of air quality (with respect to GHG emissions) and/or water quality (with respect to P).

Integrating remote sensing and subsurface geological data to characterize a tidally-influenced paleodrainage from the mid-late Holocene succession of the Po Delta Plain (Italy)

NASA Astrophysics Data System (ADS)

Giacomelli, Serena; Rossi, Veronica; Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno; Ciampalini, Andrea; Civa, Andrea; de Souza Filho, Roberto Carlos; Sgavetti, Maria

2017-04-01

A tidally-influenced, mid-late Holocene paleodrainage system from the Po Delta Plain (N Adriatic Sea, Italy) is reconstructed coupling remote sensing (RS) and subsurface geological data. Optical satellite images, DTM LiDAR, soil reflectance spectral features and core stratigraphy were combined in a GIS environment following a fully integrated methodological approach. The stratigraphic significance of RS-derived data (traces) was defined in terms of both depositional facies and depth, furnishing new insights on the role of RS in reconstructing the recent evolution of paleodrainages in coastal-deltaic settings. Sixteen images from Landsat 7 ETM+ (Enhanced Thematic Mapper Plus), Landsat 8 OLI (Operational Land Imager), Sentinel-2 MSI (Multispectral Instruments), and Hyperion satellites were collected from the USGS and the Scientific Hub ESA-Copernicus on-line databases, and integrated with Google Earth imagery. The visual interpretation of the images, mostly based on the brightness contrast (high and low reflectance values) and aimed to the recognition of traces, has been facilitated by the RGB combinations of the spectral bands most sensitive to lithology and moisture content and supported by a semi-automatic processing, including unsupervised classification and the spectral bands Principal Component Analysis (PCA). Multitemporal analysis of satellite imagery have been also performed. Two main traces, interpreted as meanders, have been analyzed for their sedimentological and stratigraphic characteristics. Following a field survey aimed to describe the morphology, grain-size, colors, and accessory materials of surface deposits, 11 soil samples have been collected for the extraction of the reflectance spectral signature and coring along the traces and in adjacent areas (bright and dark portions). Cores have been sampled for benthic foraminifer/ostracod analysis (42 samples) and stratigraphic cross-sections were constructed transversal to the meandering traces. Nine radiocarbon ages allowed to set the depositional evolution of the two meanders into a definite chronological framework. The integrated, RS-stratigraphic methodological approach revealed a meandering paleodrainage system buried > 2 m below the ground level. Its surface visibility is guided by the spatial distribution of surface moisture, which mainly depends on subsurface stratigraphic architecture and, in particular, on the distribution of organic-rich deposits laterally to the migrating meanders. The formation and activity of the buried paleochannels dates back to the early Holocene highstand (6000-2500 cal yr BP), when a drainage system likely developed under tide-influenced conditions.

Two-Scale Ion Meandering Caused by the Polarization Electric Field During Asymmetric Reconnection

NASA Technical Reports Server (NTRS)

Wang, Shan; Chen, Li-Jen; Hesse, Michael; Bessho, Naoki; Gershman, Daniel J.; Dorelli, John; Giles, Barbara L.; Torbert, Roy B.; Pollock, Craig J.; Strangeway, Robert;

Design of a Miniaturized Meandered Line Antenna for UHF RFID Tags

PubMed Central

Islam, Mohammad Tariqul; Rowe, Wayne S. T.; Kibria, Salehin; Jit Singh, Mandeep; Misran, Norbahiah

2016-01-01

A semi-circle looped vertically omnidirectional radiation (VOR) patterned tag antenna for UHF (919–923 MHz for Malaysia) frequency is designed to overcome the impedance mismatch issue in this paper. Two impedance matching feeding strips are used in the antenna structure to tune the input impedance of the antenna. Two dipole shaped meandered lines are used to achieve a VOR pattern. The proposed antenna is designed for 23-j224 Ω chip impedance. The antenna is suitable for ‘place and tag’ application. A small size of 77.68×35.5 mm2 is achieved for a read range performance of 8.3 meters using Malaysia regulated maximum power transfer of 2.0 W effective radiated power (ERP). PMID:27533470

Two-scale ion meandering caused by the polarization electric field during asymmetric reconnection

NASA Astrophysics Data System (ADS)

Wang, Shan; Chen, Li-Jen; Hesse, Michael; Bessho, Naoki; Gershman, Daniel J.; Dorelli, John; Giles, Barbara; Torbert, Roy B.; Pollock, Craig J.; Strangeway, Robert; Ergun, Robert E.; Burch, James L.; Avanov, Levon; Lavraud, Benoit; Moore, Thomas E.; Saito, Yoshifumi

2016-08-01

Ion velocity distribution functions (VDFs) from a particle-in-cell simulation of asymmetric reconnection are investigated to reveal a two-scale structure of the ion diffusion region (IDR). Ions bouncing in the inner IDR are trapped mainly by the electric field normal to the current sheet (N direction), while those reaching the outer IDR are turned back mainly by the magnetic force. The resulting inner layer VDFs have counter-streaming populations along N with decreasing counter-streaming speeds away from the midplane while maintaining the out-of-plane speed, and the outer layer VDFs exhibit crescent shapes toward the out-of-plane direction. Observations of the above VDF features and the normal electric fields provide evidence for the two-scale meandering motion.

Sediment Transport Dynamic in a Meandering Fluvial System: Case Study of Chini River

NASA Astrophysics Data System (ADS)

Nazir, M. H. M.; Awang, S.; Shaaban, A. J.; Yahaya, N. K. E. M.; Jusoh, A. M.; Arumugam, M. A. R. M. A.; Ghani, A. A.

2016-07-01

Sedimentation in river reduces the flood carrying capacity which lead to the increasing of inundation area in the river basin. Basic sediment transport can predict the fluvial processes in natural rivers and stream through modeling approaches. However, the sediment transport dynamic in a small meandering and low-lying fluvial system is considered scarce in Malaysia. The aim of this study was to analyze the current riverbed erosion and sedimentation scenarios along the Chini River, Pekan, Pahang. The present study revealed that silt and clay has potentially been eroded several parts of the river. Sinuosity index (1.98) indicates that Chini River is very unstable and continuous erosion process in waterways has increase the riverbank instability due to the meandering factors. The riverbed erosional and depositional process in the Chini River is a sluggish process since the lake reduces the flow velocity and causes the deposited particles into the silt and clay soil at the bed of the lake. Besides, the bed layer of the lake comprised of cohesive silt and clayey composition that tend to attach the larger grain size of sediment. The present study estimated the total sediment accumulated along the Chini River is 1.72 ton. The HEC-RAS was employed in the simulations and in general the model performed well, once all parameters were set within their effective ranges.

The Au modified Ge(1 1 0) surface

NASA Astrophysics Data System (ADS)

Zhang, L.; Kabanov, N. S.; Bampoulis, P.; Saletsky, A. M.; Zandvliet, H. J. W.; Klavsyuk, A. L.

2018-05-01

The pristine Ge(1 1 0) surface is composed of Ge pentagons, which are arranged in relatively large (16 × 2) and c(8 × 10) unit cells. The deposition of sub-monolayer amounts of Au and mild annealing results into de-reconstructed Ge(1 1 0) regions completely free of Ge pentagons and regions composed of nanowires that are aligned along the high symmetry [ 1 1 bar 0 ] direction of the Ge(1 1 0) surface. The de-reconstructed Ge(1 1 0) regions consist of atomic rows that are aligned along the [ 1 1 bar 0 ] direction. A substantial fraction of these substrate rows are straight and resemble the atom rows of the unreconstructed, i.e. bulk terminated, Ge(1 1 0) surface, whereas the other substrate rows have a meandering appearance. These meandering atom rows are comprised of two types of atoms, one type that appears dim, whereas the other type appears bright in filled-state scanning tunneling microscopy images. Using density functional theory calculations, we have tested more than 20 different atomic models for the meandering atom rows. The density functional theory calculations reveal that it is energetically favorable for the deposited Au atoms to exchange position with Ge atoms in the first layer. Based on these findings we conclude that the bright atoms are Ge atoms, whereas the dim atoms are Au atoms.

Thread amplitudes and frequencies in a fluid mechanical `sewing machine'

NASA Astrophysics Data System (ADS)

Morris, Stephen W.; Dawes, J. H. P.; Lister, John; Dalziel, Stuart

2006-11-01

A viscous thread falling on a surface exhibits the famous rope- coiling effect, in which the thread buckles to form loops. If the surface is replaced by a belt moving at speed U, the rotational symmetry of the buckling instability is broken and a wealth of interesting states are observed (1). We experimentally studied this fluid mechanical `sewing machine' in a new, more precise apparatus. As U is reduced, the stretched thread bifurcates into a meandering state in which the thread displacements are only transverse to the motion of the belt. We measured the amplitudes A and frequency φ of the meandering close to the bifurcation. For small U, single- frequency meandering bifurcates to a two-frequency `figure 8' state, which contains a significant 2φ component and parallel as well as transverse displacements. This eventually reverts to single-frequency coiling at smaller U. More complex, highly hysteretic states with additional harmonics are observed for larger nozzle heights. We propose to understand this zoology in terms of the generic amplitude equations appropriate for resonant interactions between three oscillatory modes with frequencies φ, 2φ and 3φ. The form of the amplitude equations captures both the axisymmetry of the U=0 coiling state and the symmetry-breaking effects induced by the moving belt.(1) Chiu-Webster and Lister, J. Fluid Mech., in press.

Geologic Tests for Snowmelt Runoff on Early Mars

NASA Astrophysics Data System (ADS)

Kite, E. S.; Sneed, J.; Mayer, D. P.

2017-12-01

Data from the Curiosity rover have sharpened the question: was Early Mars climate warm enough for rainfall, or was the climate cold? The hypothesis of a cold (snow-and-ice melt) climate on Early Mars can be tested using runoff production. Runoff production cannot exceed snowmelt rate in a cold climate. Therefore, high runoff production would rule out cold conditions, and would suggest rain (or catastrophic melting of snow). How can runoff production be reliably measured? To constrain runoff production, the lead author is measuring paleochannel widths and meander wavelengths for Early Mars watersheds with well-defined drainage area. The measurement method is the same as in Kite et al., EPSL, 2015. >250 channel-width measurements and 89 meander wavelength measurements are included, representing 158 drainage areas. The catalog emphasizes better-preserved (post-Noachian) paleochannels, but includes a re-survey of previously-reported paleochannel width and wavelength measurement sites. Channel widths and wavelengths are a proxy for paleodischarge. Discharge (m3/s) can be divided by drainage area (m2) to obtain a lower bound on runoff-production (mm/hr). If runoff production >(1-3) mm/hr, then a seasonal melting snow-and-ice climate is strongly disfavored. However, high runoff production would be consistent with rainfall. Initial results will be reported at the conference. The figure shows the locations of measurement sites for Early Mars channel width (black) and meander wavelength (red).

Ocean Bottom Pressure Variation Associated with the Large Meander of the Kuroshio South of Japan in 2004-2005

NASA Astrophysics Data System (ADS)

Nagano, A.; Hasegawa, T.; Matsumoto, H.; Ariyoshi, K.

2016-02-01

The Kuroshio, the western boundary current of the North Pacific subtropical gyre, takes a stable meandering path off the southern coast of Japan, called the large meander (LM), on interannual to decadal timescales. The LM of the Kuroshio formed in July 2004 associated with the intensified anticyclonic recirculation gyre south of the Kuroshio, and gradually decayed in the latter half of 2005. The variations of the Kuroshio and the southern recirculating currents may be related to deep currents, which are expected to be associated with bottom pressure (BP) variation. In order to examine the variation of BP associated with the variations of the sea surface currents, we analyzed data of eleven pressure sensors equipped to inverted echo sounders deployed from July 2004 to October 2006. An abrupt enhancement of BP is found on the continental slope off Shikoku, lagging a few months behind an elevation of sea surface height (SSH) due to the onshore shift of the recirculation gyre associated with the LM formation. Subsequently, BP beneath the recirculation gyre dwindles, leading the gradual depression of SSH due to the decay of the LM. The relationship between BP and SSH may suggest that the occurrence and decay of the LM depend on the extension of the recirculation gyre current down to the ocean bottom.

River channel patterns: Braided, meandering, and straight

USGS Publications Warehouse

Leopold, Luna Bergere; Wolman, M. Gordon

1957-01-01

Channel pattern is used to describe the plan view of a reach of river as seen from an airplane, and includes meandering, braiding, or relatively straight channels.Natural channels characteristically exhibit alternating pools or deep reaches and riffles or shallow reaches, regardless of the type of pattern. The length of the pool or distance between riffles in a straight channel equals the straight line distance between successive points of inflection in the wave pattern of a meandering river of the same width. The points of inflection are also shallow points and correspond to riffles in the straight channel. This distance, which is half the wavelength of the meander, varies approximately as a linear function of channel width. In the data we analysed the meander wavelength, or twice the distance between successive riffles, is from 7 to 12 times the channel width. It is concluded that the mechanics which may lead to meandering operate in straight channels.River braiding is characterized by channel division around alluvial islands. The growth of an island begins as the deposition of a central bar which results from sorting and deposition of the coarser fractions of the load which locally cannot be transported. The bar grows downstream and in height by continued deposition on its surface, forcing the water into the flanking channels, which, to carry the flow, deepen and cut laterally into the original banks. Such deepening locally lowers the water surface and the central bar emerges as an island which becomes stabilized by vegetation. Braiding was observed in a small river in a laboratory. Measurements of the adjustments of velocity, depth, width, and slope associated with island development lead to the conclusion that braiding is one of the many patterns which can maintain quasi-equilibrium among discharge, load, and transporting ability. Braiding does not necessarily indicate an excess of total load.Channel cross section and pattern are ultimately controlled by the discharge and load provided by the drainage basin. It is important, therefore, to develop a picture of how the several variables involved in channel shape interact to result in observed channel characteristics. Such a rationale is summarized as follows:Channel width appears to be primarily a function of near-bankfull discharge, in conjunction with the inherent resistance of bed and bank to scour. Excessive width increases the shear on the bed at the expense of that on the bank and the reverse is true for very narrow widths. Because at high stages width adjustment can take place rapidly and with the evacuation or deposition of relatively small volumes of debris, achievement of a ,relatively stable width at high flow is a primary adjustment to which the further interadjustments between depth, velocity, slope, and roughness tend to accommodate.Channel roughness, to the extent that it is determined by particle size, is an independent factor related to the drainage basin rather than to the channel. Roughness in streams carrying fine material, however, is also a function of the dunes or other characteristics of bed configuration. Where roughness is independently determined as well as discharge and load, these studies indicate that a particular slope is associated with the roughness. At the width determined by the discharge, velocity and depth must be adjusted to satisfy quasi-equilibrium in accord with the particular slope. But if roughness also is variable, depending on the transitory configuration of the bed, then a number of combinations of velocity, depth, and slope will satisfy equilibrium.An increase in load at constant discharge, width, and caliber of load tends to be associated with an increasing slope if the roughness (dune or bed configuration) changes with the load. In the laboratory river an increase of load at constant discharge, width, and caliber resulted in progressive aggradation of long reaches of channel at constant slope.The adjustments of several variables tending toward the establishment of quasi-equilibrium in river channels lead to the different channel patterns observed in nature. For example, the data indicate that at a given discharge, meanders occur at smaller values of slope than do’ braids. Further, at the same slope braided channels are associated with higher bankfull discharges than are meanders. An additional example is provided by the division of discharge around islands in braided rivers which produces numerous small channels. The changes in slope, roughness, and channel shape which accompany this division are in accord with quasi-equilibrium adjustments observed in the comparison of large and small rivers.

Physical mechanisms of timing jitter in photon detection by current-carrying superconducting nanowires

NASA Astrophysics Data System (ADS)

Sidorova, Mariia; Semenov, Alexej; Hübers, Heinz-Wilhelm; Charaev, Ilya; Kuzmin, Artem; Doerner, Steffen; Siegel, Michael

2017-11-01

We studied timing jitter in the appearance of photon counts in meandering nanowires with different fractional amount of bends. Intrinsic timing jitter, which is the probability density function of the random time delay between photon absorption in current-carrying superconducting nanowire and appearance of the normal domain, reveals two different underlying physical mechanisms. In the deterministic regime, which is realized at large photon energies and large currents, jitter is controlled by position-dependent detection threshold in straight parts of meanders. It decreases with the increase in the current. At small photon energies, jitter increases and its current dependence disappears. In this probabilistic regime jitter is controlled by Poisson process in that magnetic vortices jump randomly across the wire in areas adjacent to the bends.

Flexural plate wave devices fabricated from silicon carbide membrane

NASA Astrophysics Data System (ADS)

Diagne, Ndeye Fama

Flexural Plate Wave (FPW) devices fabricated from Silicon Carbide (SiC) membranes are presented here which exhibit electrical and mechanical characteristics in its transfer functions that makes it very useful as a low voltage probe device capable of functioning in small areas that are commonly inaccessible to ordinary devices. The low input impedance characteristic of this current driven device makes it possible for it to operate at very low voltages, thereby reducing the hazards for flammable or explosive areas to be probed. The Flexural Plate Wave (FPW) devices are of a family of gravimetric type sensors that permit direct measurements of the mass of the vibrating element. The primary objective was to study the suitability of Silicon Carbide (SiC) membranes as a replacement of Silicon Nitride (SiN) membrane in flexural plate wave devices developed by Sandia National Laboratories. Fabrication of the Flexural Plate Wave devices involves the overlaying a silicon wafer with membranes of 3C-SiC thin film upon which conducting meander lines are placed. The input excitation energy is in the form of an input current. The lines of current along the direction of the conducting Meander Lines Transducer (MLTs) and the applied perpendicular external magnetic field set up a mechanical wave perpendicular to both, exciting the membrane by means of a Lorentz force, which in turn sets up flexural waves that propagate along the thin membrane. The physical dimensions, the mass density, the tension in the membrane and the meander spacing are physical characteristics that determine resonance frequency of the Flexural Plate Wave (FPW) device. Of primary interest is the determination of the resonant frequency of the silicon carbide membrane as functions of the device physical characteristic parameters. The appropriate transduction scheme with Meander Line Transducers (IDTs) are used to excite the membrane. Equivalent circuit models characterizing the reflection response S11 (amplitude and phase) for a one-port Flexural PlateWave device and the transmission response S21 of a two-port device are used for the development of the equivalent mechanical characteristics.

Coupling MAST-1D, a sediment routing model for channel-floodplain complexes, with channel migration relationships to predict reach-averaged river morphodynamics. Preliminary results

NASA Astrophysics Data System (ADS)

Viparelli, E.; Eke, E. C.; Lauer, J. W.

2017-12-01

Sediment exchange between the channel and floodplain can occur via meander migration, overbank deposition or erosion, and changes in channel geometry. Depending on channel and floodplain history, floodplains can act either as sources or sinks of bed material and/or wash load. Here we present preliminary modeling results that explicitly account for the feedbacks between the changes in floodplain geometry and sediment size distribution and the changes in channel geometry and migration. These results are obtained by coupling the Morphodynamics And Sediment Tracers in 1D (MAST-1D) program with the results of meander migration studies linking the bankfull flow depth and mean velocity to channel migration, sinuosity and channel geometry. MAST-1D is a numerical model built to describe grain size specific transport of sediment and tracers and the long-term - i.e. decadal and longer - evolution of channel floodplain complexes. MAST-1D differs from other 1D numerical models because it allows for 1) uneven exchange of sediment and tracers between the river channel and the floodplain, 2) temporal changes in channel geometry, bed elevation and floodplain thickness, which result in changes in the channel hydraulic capacity, and 3) temporal changes of size distribution and tracer content in the floodplain, in the load and in the underlying substrate. Under conditions of constant base level, water and sediment supply, the system evolves toward a steady state wherein the amount of sediment deposited through point bar deposition and overbank sedimentation is balanced by the erosion of sediment from the floodplain through lateral migration. The current formulation couples MAST-1D with empirical channel migration relationships that link bankfull flow depth and mean velocity to channel migration, sinuosity and channel geometry. Future development of this preliminary work will involve a fully coupled MAST-1D model with a standard meander migration model that will allow for the building of floodplain stratigraphy and tracking of the position of the meandering channel in space and time.

Wind tunnel study of the wind turbine interaction with a boundary-layer flow: Upwind region, turbine performance, and wake region

NASA Astrophysics Data System (ADS)

Bastankhah, M.; Porté-Agel, F.

2017-06-01

Comprehensive wind tunnel experiments were carried out to study the interaction of a turbulent boundary layer with a wind turbine operating under different tip-speed ratios and yaw angles. Force and power measurements were performed to characterize the variation of thrust force (both magnitude and direction) and generated power of the wind turbine under different operating conditions. Moreover, flow measurements, collected using high-resolution particle-image velocimetry as well as hot-wire anemometry, were employed to systematically study the flow in the upwind, near-wake, and far-wake regions. These measurements provide new insights into the effect of turbine operating conditions on flow characteristics in these regions. For the upwind region, the results show a strong lateral asymmetry under yawed conditions. For the near-wake region, the evolution of tip and root vortices was studied with the use of both instantaneous and phase-averaged vorticity fields. The results suggest that the vortex breakdown position cannot be determined based on phase-averaged statistics, particularly for tip vortices under turbulent inflow conditions. Moreover, the measurements in the near-wake region indicate a complex velocity distribution with a speed-up region in the wake center, especially for higher tip-speed ratios. In order to elucidate the meandering tendency of far wakes, particular focus was placed on studying the characteristics of large turbulent structures in the boundary layer and their interaction with wind turbines. Although these structures are elongated in the streamwise direction, their cross sections are found to have a size comparable to the rotor area, so that they can be affected by the presence of the turbine. In addition, the study of spatial coherence in turbine wakes reveals that any statistics based on streamwise velocity fluctuations cannot provide reliable information about the size of large turbulent structures in turbine wakes due to the effect of wake meandering. The results also suggest that the magnitude of wake meandering does not depend on turbine-operating conditions. Finally, the suitability of the proper orthogonal decomposition for studying wake meandering is examined.

The effect of bedload transport rates on bedform and planform morphological development in a laboratory meandering stream under varying flow conditions

NASA Astrophysics Data System (ADS)

Sullivan, C.; Good, R. G. R.; Binns, A. D.

2017-12-01

Sediment transport processes in streams provides valuable insight into the temporal evolution of planform and bedform geometry. The majority of previous experimental research in the literature has focused on bedload transport and corresponding bedform development in rectangular, confined channels, which does not consider planform adjustment processes in streams. In contrast, research conducted with laboratory streams having movable banks can investigate planform development in addition to bedform development, which is more representative of natural streams. The goal of this research is to explore the relationship between bedload transport rates and the morphological adjustments in meandering streams. To accomplish this, a series of experimental runs were conducted in a 5.6 m by 1.9 m river basin flume at the University of Guelph to analyze the bedload impacts on bed formations and planform adjustments in response to varying flow conditions. In total, three experimental runs were conducted: two runs using steady state conditions and one run using unsteady flow conditions in the form of a symmetrical hydrograph implementing quasi steady state flow. The runs were performed in a series of time-steps in order to monitor the evolution of the stream morphology and the bedload transport rates. Structure from motion (SfM) was utilized to capture the channel morphology after each time-step, and Agisoft PhotoScan software was used to produce digital elevation models to analyze the morphological evolution of the channel with time. Bedload transport rates were quantified using a sediment catch at the end of the flume. Although total flow volumes were similar for each run, the morphological evolution and bedload transport rates in each run varied. The observed bedload transport rates from the flume are compared with existing bedload transport formulas to assess their accuracy with respect to sediment transport in unconfined meandering channels. The measured sediment transport rates varied from the existing equations, which can be attributed to the sediment characteristics, planform morphology and bed formations. The results from this research provide greater knowledge of morphological processes in natural meandering streams to improve the capabilities of computational modelling and river engineering practice.

Data assimilation in the low noise regime

NASA Astrophysics Data System (ADS)

Weare, J.; Vanden-Eijnden, E.

2012-12-01

On-line data assimilation techniques such as ensemble Kalman filters and particle filters tend to lose accuracy dramatically when presented with an unlikely observation. Such observation may be caused by an unusually large measurement error or reflect a rare fluctuation in the dynamics of the system. Over a long enough span of time it becomes likely that one or several of these events will occur. In some cases they are signatures of the most interesting features of the underlying system and their prediction becomes the primary focus of the data assimilation procedure. The Kuroshio or Black Current that runs along the eastern coast of Japan is an example of just such a system. It undergoes infrequent but dramatic changes of state between a small meander during which the current remains close to the coast of Japan, and a large meander during which the current bulges away from the coast. Because of the important role that the Kuroshio plays in distributing heat and salinity in the surrounding region, prediction of these transitions is of acute interest. { Here we focus on a regime in which both the stochastic forcing on the system and the observational noise are small. In this setting large deviation theory can be used to understand why standard filtering methods fail and guide the design of the more effective data assimilation techniques. Motivated by our large deviations analysis we propose several data assimilation strategies capable of efficiently handling rare events such as the transitions of the Kuroshio. These techniques are tested on a model of the Kuroshio and shown to perform much better than standard filtering methods.Here the sequence of observations (circles) are taken directly from one of our Kuroshio model's transition events from the small meander to the large meander. We tested two new algorithms (Algorithms 3 and 4 in the legend) motivated by our large deviations analysis as well as a standard particle filter and an ensemble Kalman filter. The parameters of each algorithm are chosen so that their costs are comparable. The particle filter and an ensemble Kalman filter fail to accurately track the transition. Algorithms 3 and 4 maintain accuracy (and smaller scale resolution) throughout the transition.

27 CFR 9.227 - Ancient Lakes of Columbia Valley.

Code of Federal Regulations, 2013 CFR

2013-04-01

... County, 1965; (10) Vantage, Washington, 1965, photorevised 1978; (11) Ginkgo, Washington, 1953... meandering Columbia River for approximately 23.3 miles, crossing over the Ginkgo and Cape Horn SE maps, and...

27 CFR 9.227 - Ancient Lakes of Columbia Valley.

Code of Federal Regulations, 2014 CFR

2014-04-01

... County, 1965; (10) Vantage, Washington, 1965, photorevised 1978; (11) Ginkgo, Washington, 1953... meandering Columbia River for approximately 23.3 miles, crossing over the Ginkgo and Cape Horn SE maps, and...

77 FR 27245 - Big Stone National Wildlife Refuge, Big Stone and Lac Qui Parle Counties, MN

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-09

... include habitat management, sedimentation, invasive species, and demand for additional recreation... the Refuge. Alternative 2 Under this alternative the natural alignment, channel capacity, and meander...

Contributions of the stochastic shape wake model to predictions of aerodynamic loads and power under single wake conditions

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

Doubrawa, P.; Barthelmie, R. J.; Wang, H.

The contribution of wake meandering and shape asymmetry to load and power estimates is quantified by comparing aeroelastic simulations initialized with different inflow conditions: an axisymmetric base wake, an unsteady stochastic shape wake, and a large-eddy simulation with rotating actuator-line turbine representation. Time series of blade-root and tower base bending moments are analyzed. We find that meandering has a large contribution to the fluctuation of the loads. Moreover, considering the wake edge intermittence via the stochastic shape model improves the simulation of load and power fluctuations and of the fatigue damage equivalent loads. Furthermore, these results indicate that the stochasticmore » shape wake simulator is a valuable addition to simplified wake models when seeking to obtain higher-fidelity computationally inexpensive predictions of loads and power.« less

Aeromagnetic search for Cenozoic magmatism over the Admiralty Mountains Block (East Antarctica)

USGS Publications Warehouse

,; ,; Ferraccioli, F.; Zunino, A.; Bozzo, E.; Rocchi, S.; Armienti, P.

2007-01-01

Cenozoic magmatic rocks of the Transantarctic Mountains provide an important window on the tectonic and magmatic processes of the West Antarctic Rift System. Previous aeromagnetic investigations in northern Victoria Land have delineated Cenozoic volcanic and intrusive complexes assigned to the McMurdo Volcanic Group and Meander Intrusives over the Transantarctic Mountains. We present a new aeromagnetic anomaly map for the region north of the Mariner Glacier to study the extent and spatial distribution of these Cenozoic rocks over the previously unexplored Admiralty Mountains. The new map shows that the Meander Intrusives are restricted to the coastal region between the Malta Plateau and the Daniell Peninsula. However, the McMurdo Volcanic Group rocks extend further inland, and may delineate a hitherto unrecognised volcano-tectonic rift zone, extending as far north as the Trafalgar Glacier.

Textile inspired flexible metamaterial with negative refractive index

NASA Astrophysics Data System (ADS)

Burgnies, L.; Lheurette, É.; Lippens, D.

2015-04-01

This work introduces metallo-dielectric woven fabric as a metamaterial for phase-front manipulation. Dispersion diagram as well as effective medium parameters retrieved from reflection and transmission coefficients point out negative values of refractive index. By numerical simulations, it is evidenced that a pair of meandered metallic wires, arranged in a top to bottom configuration, can yield to a textile metamaterial with simultaneously negative permittivity and permeability. While the effective negative permittivity stems from the metallic grid arrangement, resonating current loop resulting from the top to bottom configuration of two meandered metallic wires in near proximity produces magnetic activity with negative permeability. By adjusting the distance between pairs of metallic wires, the electric plasma frequency can be shifted to overlap the magnetic resonance. Finally, it is shown that the woven metamaterial is insensitive to the incident angle up to around 60°.

Contributions of the stochastic shape wake model to predictions of aerodynamic loads and power under single wake conditions

DOE PAGES

Doubrawa, P.; Barthelmie, R. J.; Wang, H.; ...

2016-10-03

The contribution of wake meandering and shape asymmetry to load and power estimates is quantified by comparing aeroelastic simulations initialized with different inflow conditions: an axisymmetric base wake, an unsteady stochastic shape wake, and a large-eddy simulation with rotating actuator-line turbine representation. Time series of blade-root and tower base bending moments are analyzed. We find that meandering has a large contribution to the fluctuation of the loads. Moreover, considering the wake edge intermittence via the stochastic shape model improves the simulation of load and power fluctuations and of the fatigue damage equivalent loads. Furthermore, these results indicate that the stochasticmore » shape wake simulator is a valuable addition to simplified wake models when seeking to obtain higher-fidelity computationally inexpensive predictions of loads and power.« less

New technique for excitation of bulk and surface spin waves in ferromagnets

NASA Astrophysics Data System (ADS)

Bogacz, S. A.; Ketterson, J. B.

1985-09-01

A meander-line magnetic transducer is discussed in the context of bulk and surface spin-wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self-consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon-Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.

Morphological change on the River Towy, Wales assessed using aerial photogrammetry

NASA Astrophysics Data System (ADS)

Ahmed, Joshua; Hodge, Michael

2017-04-01

The dynamic nature of meandering channels has fascinated geomorphologists for decades; with the onset of remote sensing, and technological advances in field equipment, scientists are able to capture high-resolution data from the Earth's surface using cost-effective techniques that require minimal manual labour. Here we present a morphological assessment of three meander bends on the River Towy, Wales, using aerial photography captured by the Welsh Assembly Government and supplemented by data captured by a UAV. Migration rates and changes in channel length were measured between 1969 and 2016 and compared to a coupled discharge record to quantify the effects of discharge variability on the morphological evolution of the channel. A short-term (seasonal) assessment of channel change was conducted by comparing sub-metre resolution 3D point cloud and digital elevation models, generated using a UAV and Structure-from-Motion (SfM) photogrammetry. Our results suggest that discharge variability plays a crucial role in controlling the evolution of meandering planforms and can be an effective means of excavating floodplain material over relatively short timescales, although erosion rates can be suppressed by bankline roughness, which effectively disrupts outwardly directed flow momentum. These findings have implications for land managers and those modelling the effects of climate change on hydrological regimes which are ultimately used to forecast channel planform changes. Additionally, our results demonstrate the potential of low-cost field surveying techniques in producing high resolution models of landscape change.

Natural change and human impact in a present-day fluvial catchment: The Geul River, Southern Netherlands

NASA Astrophysics Data System (ADS)

Vandenberghe, J.; de Moor, J. J. W.; Spanjaard, G.

2012-07-01

The Geul River has a long history of channel straightening and bank protection, but also has several natural meandering parts. In addition, some formerly 'fixed' or 'protected' stretches of the river have been allowed to meander freely since 1988. Therefore, it represents an ideal case for evaluating the contribution of human interference to the intrinsic evolution of the river. In this paper, we compare the response of selected (not protected) reaches of the present-day river to different human modifications. The river banks were labelled as "stable", "unstable" or "erosive". As might be expected, stretches with a high sinuosity have a high percentage of erosive and unstable bank length, while low-sinuosity stretches experience hardly any erosion. The amount of lateral erosion and sedimentation in natural situations is compared with that in situations with different bank protection and stabilization types. Erosion rates may locally attain up to 2 m per year. Detailed grain-size analysis of point-bar sections enable distinction of successive fining-up sequences. Vertical aggradation rates within the point-bars are up to 0.15 m yr- 1. The highest rates are found in the youngest point-bars. Collectively, the results of this study show that when bank protection is removed, the freely meandering river creates its own specific ecosystems and retention capacity increases. Such a return to natural environmental and ecological conditions is in accordance with the objectives of the European Water Framework Directive.

Historical contingency in fluviokarst landscape evolution

NASA Astrophysics Data System (ADS)

Phillips, Jonathan D.

2018-02-01

Lateral and vertical erosion at meander bends in the Kentucky River gorge area has created a series of strath terraces on the interior of incised meander bends. These represent a chronosequence of fluviokarst landscape evolution from the youngest valley side transition zone near the valley bottom to the oldest upland surface. This five-part chronosequence (not including the active river channel and floodplain) was analyzed in terms of the landforms that occur at each stage or surface. These include dolines, uvalas, karst valleys, pocket valleys, unincised channels, incised channels, and cliffs (smaller features such as swallets and shafts also occur). Landform coincidence analysis shows higher coincidence indices (CI) than would be expected based on an idealized chronosequence. CI values indicate genetic relationships (common causality) among some landforms and unexpected persistence of some features on older surfaces. The idealized and two observed chronosequences were also represented as graphs and analyzed using algebraic graph theory. The two field sites yielded graphs more complex and with less historical contingency than the idealized sequence. Indeed, some of the spectral graph measures for the field sites more closely approximate a purely hypothetical no-historical-contingency benchmark graph. The deviations of observations from the idealized expectations, and the high levels of graph complexity both point to potential transitions among landform types as being the dominant phenomenon, rather than canalization along a particular evolutionary pathway. As the base level of both the fluvial and karst landforms is lowered as the meanders expand, both fluvial and karst denudation are rejuvenated, and landform transitions remain active.

Turning the Tide: Estuaries Shaped by Channel-Shoal Interactions, Eco-engineers and Inherited Landscapes

NASA Astrophysics Data System (ADS)

Kleinhans, M. G.; Braat, L.; Leuven, J.; Baar, A. W.; van der Vegt, M.; Van Maarseveen, M. C. G.; Markies, H.; Roosendaal, C.; van Eijk, A.

2015-12-01

Estuaries exhibit correlations between inlet dimensions, tidal prism and intertidal area, but to what extent estuary planform shape and shoal patterns resulted from biomorphological processes or from inherited conditions such as coastal plain and drowned valley dimensions remains unclear. We explore the hypothesis that mud flats and vegetation as a self-formed lateral confinement have effects analogous to that of river floodplain on braided versus meandering river patterns. Here we use the Delft3D numerical model and a novel tidal flume setup, the Metronome, to create estuaries from idealized initial conditions, with and without mud supply at the fluvial boundary. Experimental mud was simulated by crushed nutshell. Both the numerical and experimental estuaries were narrower with increasing mud, and had a lower degree of channel braiding. The experimental estuaries developed meanders at the river boundary with floodplain developing on the pointbar whereas cohesionless cases were more dynamic.

Method for detection and imaging over a broad spectral range

DOEpatents

Yefremenko, Volodymyr; Gordiyenko, Eduard; Pishko, legal representative, Olga; Novosad, Valentyn; Pishko, deceased; Vitalii

2007-09-25

A method of controlling the coordinate sensitivity in a superconducting microbolometer employs localized light, heating or magnetic field effects to form normal or mixed state regions on a superconducting film and to control the spatial location. Electron beam lithography and wet chemical etching were applied as pattern transfer processes in epitaxial Y--Ba--Cu--O films. Two different sensor designs were tested: (i) a 3 millimeter long and 40 micrometer wide stripe and (ii) a 1.25 millimeters long, and 50 micron wide meandering-like structure. Scanning the laser beam along the stripe leads to physical displacement of the sensitive area, and, therefore, may be used as a basis for imaging over a broad spectral range. Forming the superconducting film as a meandering structure provides the equivalent of a two-dimensional detector array. Advantages of this approach are simplicity of detector fabrication, and simplicity of the read-out process requiring only two electrical terminals.

On the recent destabilization of the Gulf Stream path downstream of Cape Hatteras

NASA Astrophysics Data System (ADS)

Andres, M.

2016-09-01

Mapped satellite altimetry reveals interannual variability in the position of initiation of Gulf Stream meanders downstream of Cape Hatteras. The longitude where the Gulf Stream begins meandering varies by 1500 km. There has been a general trend for the destabilization point to shift west, and 5 of the last 6 years had a Gulf Stream destabilization point upstream of the New England Seamounts. Independent in situ data suggest that this shift has increased both upper-ocean/deep-ocean interaction events at Line W and open-ocean/shelf interactions across the Middle Atlantic Bight (MAB) shelf break. Mooring data and along-track altimetry indicate a recent increase in the number of deep cyclones that stir Deep Western Boundary Current waters from the MAB slope into the deep interior. Temperature profiles from the Oleander Program suggest that recent enhanced warming of the MAB shelf may be related to shifts in the Gulf Stream's destabilization point.

Evolution of fluvial styles in the Eocene Wasatch Formation, Powder River Basin, Wyoming

USGS Publications Warehouse

Warwick, Peter D.; Flores, Romeo M.; Ethridge, Frank G.; Flores, Romeo M.

1987-01-01

Vertical and lateral facies changes in the lower part of the Eocene Wasatch Formation in the Powder River Basin, Wyoming represent an evolution of fluvial systems that varied from meandering to anastomosing. The meandering facies in the lower part of the study interval formed in a series of broad meanderbelts in a northnorthwestflowing system. Upon abandonment this meanderbelt facies served as a topographic high on which a raised or ombrotrophic Felix peat swamp developed. Peat accumulated until compaction permitted encroachment of crevasse splays from an adjoining transitional facies which consists of deposits of a slightly sinuous fluvial system. Crevasse splays eventually prograded over the peat swamp that was partly covered by lakes. Bifurcation, reunification, and transformation of crevasse channels into major conduits produced an anastomosing system that was characterized by diverging and converging channels separated by floodbasins drowned by lakes and partly covered swamps.

Partial transpose of random quantum states: Exact formulas and meanders

NASA Astrophysics Data System (ADS)

Fukuda, Motohisa; Śniady, Piotr

2013-04-01

We investigate the asymptotic behavior of the empirical eigenvalues distribution of the partial transpose of a random quantum state. The limiting distribution was previously investigated via Wishart random matrices indirectly (by approximating the matrix of trace 1 by the Wishart matrix of random trace) and shown to be the semicircular distribution or the free difference of two free Poisson distributions, depending on how dimensions of the concerned spaces grow. Our use of Wishart matrices gives exact combinatorial formulas for the moments of the partial transpose of the random state. We find three natural asymptotic regimes in terms of geodesics on the permutation groups. Two of them correspond to the above two cases; the third one turns out to be a new matrix model for the meander polynomials. Moreover, we prove the convergence to the semicircular distribution together with its extreme eigenvalues under weaker assumptions, and show large deviation bound for the latter.

Improving the signal amplitude of meandering coil EMATs by using ribbon soft magnetic flux concentrators (MFC).

PubMed

Dhayalan, R; Satya Narayana Murthy, V; Krishnamurthy, C V; Balasubramaniam, Krishnan

2011-08-01

This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials. Copyright © 2011 Elsevier B.V. All rights reserved.

The fall of a viscous thread onto a moving surface: a ‘fluid-mechanical sewing machine’

NASA Astrophysics Data System (ADS)

Chiu-Webster, S.; Lister, J. R.

2006-12-01

A viscous thread falling onto a steadily moving horizontal belt shows a surprisingly complex range of behaviour in experiments. Low belt speeds produce coiling, as might be expected from the behaviour of a thread falling onto a stationary surface. High belt speeds produce a steady thread, whose shape is predicted well by theory developed to describe a stretching viscous catenary with surface tension and inertia. Intermediate belt speeds show several novel modes of oscillation, which lay down a wide variety of patterns on the belt. The patterns include meanders, side kicks, slanted loops, braiding, figures-of-eight, Ws, and also period-doubled versions of figures-of-eight, meanders and coiling. The experimental boundary between steady and unsteady behaviour occurs at a slightly lower belt speed than the loss of the steady solution for a stretching catenary.

Mechanisms for Enhanced Supercurrent Across Meandered Grain Boundaries in High-Temperature Superconductors

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

Feldmann, D. M.; Holesinger, T. G.; Feenstra, Roeland

2007-01-01

It has been well established that the critical current density J{sub c} across grain boundaries (GBs) in high-temperature superconductors decreases exponentially with misorientation angle {theta} beyond {approx}2-3 degrees. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson (AJ) vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced J{sub c} values: up to six times at 0 T and four times at 1 T at {theta}{approx}4-6 degrees. This enhancement is due to an increase in the current-carryingmore » cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov (A) vortices in the grains.« less

Estimation of annual energy production using dynamic wake meandering in combination with ambient CFD solutions

NASA Astrophysics Data System (ADS)

Hahn, S.; Machefaux, E.; Hristov, Y. V.; Albano, M.; Threadgill, R.

2016-09-01

In the present study, combination of the standalone dynamic wake meandering (DWM) model with Reynolds-averaged Navier-Stokes (RANS) CFD solutions for ambient ABL flows is introduced, and its predictive performance for annual energy production (AEP) is evaluated against Vestas’ SCADA data for six operating wind farms over semi-complex terrains under neutral conditions. The performances of conventional linear and quadratic wake superposition techniques are also compared, together with the in-house implemention of successive hierarchical merging approaches. As compared to our standard procedure based on the Jensen model in WindPRO, the overall results are promising, leading to a significant improvement in AEP accuracy for four of the six sites. While the conventional linear superposition shows the best performance for the improved four sites, the hierarchical square superposition shows the least deteriorated result for the other two sites.

The role of magnetic loops in particle acceleration at nearly perpendicular shocks

NASA Technical Reports Server (NTRS)

Decker, R. B.

1993-01-01

The acceleration of superthermal ions is investigated when a planar shock that is on average nearly perpendicular propagates through a plasma in which the magnetic field is the superposition of a constant uniform component plus a random field of transverse hydromagnetic fluctuations. The importance of the broadband nature of the transverse magnetic fluctuations in mediating ion acceleration at nearly perpendicular shocks is pointed out. Specifically, the fluctuations are composed of short-wavelength components which scatter ions in pitch angle and long-wavelength components which are responsible for a spatial meandering of field lines about the mean field. At nearly perpendicular shocks the field line meandering produces a distribution of transient loops along the shock. As an application of this model, the acceleration of a superthermal monoenergetic population of seed protons at a perpendicular shock is investigated by integrating along the exact phase-space orbits.

Modulation of frontogenetic plankton production along a meandering jet by zonal wind forcing: An application to the Alboran Sea

NASA Astrophysics Data System (ADS)

Oguz, Temel; Mourre, Baptiste; Tintoré, Joaquin

2017-08-01

We present a coupled physical-biological modeling study to elucidate the changes in ageostrophic frontal dynamics and the frontogenetic plankton production characteristics of a meandering jet under the impacts of successive westerly/easterly wind events combined with seasonal variations in the upstream transport and buoyancy flux characteristics of the jet, using a case study for the Alboran Sea (Western Mediterranean). Their nonlinear coupling is shown to result in different forms of physical and biological characteristics of the background jet structure that follows a meandering path around two anticyclonic gyres in the western and eastern basins and a cyclonic eddy in between. The westerly, downfront wind events broaden the jet, and result in stronger cross-frontal density contrast and intensify ageostrophic cross-frontal secondary circulation. Thus, they improve the frontogenetic plankton production with respect to the no-wind case. They also support higher production along the northern coast in response to wind-induced coastal upwelling and spreading of resulting nutrient-rich, productive water by mesoscale stirring. These features weaken gradually as the jet transport reduces. In contrast, stronger and longer-lasting easterlies during the reduced jet transport phase weaken the currents and frontal density structure, change the circular Western Alboran Gyre to an elongated form, and shift the main axis of the jet towards the southern basin. Then, frontogenesis fails to contribute to phytoplankton production that becomes limited to the eddy pumping within cyclones. Apart from the frontogenetic production, eddy pumping, mesoscale stirring, and diapycnal mixing of nutrients support intermittent and localized phytoplankton patches over the basin.

Morphology and growth pattern of Amazon deep-sea fan: a computer-processed GLORIA side-scan mosaic

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

Flood, R.D.; Damuth, J.E.

1984-04-01

Deep-sea fans have become increasingly important targets for exploration because of their favorable facies associations. A better understanding of deep-sea fans is needed to successfully exploit these complex sediment bodies. Recent studies of the Amazon fan, using long-range side-scan sonar (GLORIA) and single-channel seismic data, provide an overall view of channel patterns of this fan and demonstrate the relationship between successive channel/levee systems. The digitally collected GLORIA data have been computer processed to produce a mosaic of the fan. Computer processing has corrected the records for slant range and ship navigation, and targets have been enhanced. Many features of themore » modern fan system are readily apparent on the sonar mosaic. The 1.5 to 0.5-km (5000 to 1600-ft) wide channels meander intensely across the fan with sinuosities up to 2.5. Because of these meanders, the channel gradients decrease regularly across the fan despite changes in regional slope. Other channel-related targets include cutoff meanders, overbank deposits (especially small debris flows), and channel branchings. Other debris flows cover large areas of the fan and override channel/levee systems. Air-gun records show that this fan is built of a series of channel/levee systems that overlay one another. Channels from at least 6 of these systems are visible at the surface now, but apparently only one channel at a time has been active. The length of time needed to build a single channel/levee system is not known, but it appears to be rapid.« less

Experimental study on the wind-turbine wake meandering inside a scale model wind farm placed in an atmospheric-boundary-layer wind tunnel

NASA Astrophysics Data System (ADS)

Coudou, N.; Buckingham, S.; van Beeck, J.

2017-05-01

Increasing use of wind energy over the years results in more and larger clustered wind farms. It is therefore fundamental to have an in-depth knowledge of wind-turbine wakes, and especially a better understanding of the well-known but less understood wake-meandering phenomenon which causes the wake to move as a whole in both horizontal and vertical directions as it is convected downstream. This oscillatory motion of the wake is crucial for loading on downstream turbines because it increases fatigue loads and in particular yaw loads. In order to address this phenomenon, experimental investigations were carried out in an atmospheric-boundary-layer wind tunnel using a 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models subject to a neutral atmospheric boundary layer (ABL) corresponding to a slightly rough terrain, i.e. to offshore conditions. Particle Image Velocimetry (PIV) measurements were performed in a horizontal plane, at hub height, in the wake of the three wind turbines in the wind-farm centreline. From the PIV velocity fields obtained, the wake-centrelines were determined and a spectral analysis was performed to obtain the characteristics of the wake-meandering phenomenon. In addition, Hot-Wire Anemometry (HWA) measurements were performed in the wakes of the same wind turbines to validate the PIV results. The spectral analysis performed with the spatial and temporal signals obtained from PIV and HWA measurements respectively, led to Strouhal numbers St = fD/Uhub ≃ 0.20 - 0.22.

Optimal Design of a Planar Textile Antenna for Industrial Scientific Medical (ISM) 2.4 GHz Wireless Body Area Networks (WBAN) with the CRO-SL Algorithm.

PubMed

Sánchez-Montero, Rocío; Camacho-Gómez, Carlos; López-Espí, Pablo-Luís; Salcedo-Sanz, Sancho

2018-06-21

This paper proposes a low-profile textile-modified meander line Inverted-F Antenna (IFA) with variable width and spacing meanders, for Industrial Scientific Medical (ISM) 2.4-GHz Wireless Body Area Networks (WBAN), optimized with a novel metaheuristic algorithm. Specifically, a metaheuristic known as Coral Reefs Optimization with Substrate Layer (CRO-SL) is used to obtain an optimal antenna for sensor systems, which allows covering properly and resiliently the 2.4⁻2.45-GHz industrial scientific medical bandwidth. Flexible pad foam has been used to make the designed prototype with a 1.1-mm thickness. We have used a version of the algorithm that is able to combine different searching operators within a single population of solutions. This approach is ideal to deal with hard optimization problems, such as the design of the proposed meander line IFA. During the optimization phase with the CRO-SL, the proposed antenna has been simulated using CST Microwave Studio software, linked to the CRO-SL by means of MATLAB implementation and Visual Basic Applications (VBA) code. We fully describe the antenna design process, the adaptation of the CRO-SL approach to this problem and several practical aspects of the optimization and details on the algorithm’s performance. To validate the simulation results, we have constructed and measured two prototypes of the antenna, designed with the proposed algorithm. Several practical aspects such as sensitivity during the antenna manufacturing or the agreement between the simulated and constructed antenna are also detailed in the paper.

Quantifying Process-Based Mitigation Strategies in Historical Context: Separating Multiple Cumulative Effects on River Meander Migration

PubMed Central

Fremier, Alexander K.; Girvetz, Evan H.; Greco, Steven E.; Larsen, Eric W.

2014-01-01

Environmental legislation in the US (i.e. NEPA) requires defining baseline conditions on current rather than historical ecosystem conditions. For ecosystems with long histories of multiple environmental impacts, this baseline method can subsequently lead to a significantly altered environment; this has been termed a ‘sliding baseline’. In river systems, cumulative effects caused by flow regulation, channel revetment and riparian vegetation removal significantly impact floodplain ecosystems by altering channel dynamics and precluding subsequent ecosystem processes, such as primary succession. To quantify these impacts on floodplain development processes, we used a model of river channel meander migration to illustrate the degree to which flow regulation and riprap impact migration rates, independently and synergistically, on the Sacramento River in California, USA. From pre-dam conditions, the cumulative effect of flow regulation alone on channel migration is a reduction by 38%, and 42–44% with four proposed water diversion project scenarios. In terms of depositional area, the proposed water project would reduce channel migration 51–71 ha in 130 years without current riprap in place, and 17–25 ha with riprap. Our results illustrate the utility of a modeling approach for quantifying cumulative impacts. Model-based quantification of environmental impacts allow scientists to separate cumulative and synergistic effects to analytically define mitigation measures. Additionally, by selecting an ecosystem process that is affected by multiple impacts, it is possible to consider process-based mitigation scenarios, such as the removal of riprap, to allow meander migration and create new floodplains and allow for riparian vegetation recruitment. PMID:24964145

Identifying sensitive areas of adaptive observations for prediction of the Kuroshio large meander using a shallow-water model

NASA Astrophysics Data System (ADS)

Zou, Guang'an; Wang, Qiang; Mu, Mu

2016-09-01

Sensitive areas for prediction of the Kuroshio large meander using a 1.5-layer, shallow-water ocean model were investigated using the conditional nonlinear optimal perturbation (CNOP) and first singular vector (FSV) methods. A series of sensitivity experiments were designed to test the sensitivity of sensitive areas within the numerical model. The following results were obtained: (1) the eff ect of initial CNOP and FSV patterns in their sensitive areas is greater than that of the same patterns in randomly selected areas, with the eff ect of the initial CNOP patterns in CNOP sensitive areas being the greatest; (2) both CNOP- and FSV-type initial errors grow more quickly than random errors; (3) the eff ect of random errors superimposed on the sensitive areas is greater than that of random errors introduced into randomly selected areas, and initial errors in the CNOP sensitive areas have greater eff ects on final forecasts. These results reveal that the sensitive areas determined using the CNOP are more sensitive than those of FSV and other randomly selected areas. In addition, ideal hindcasting experiments were conducted to examine the validity of the sensitive areas. The results indicate that reduction (or elimination) of CNOP-type errors in CNOP sensitive areas at the initial time has a greater forecast benefit than the reduction (or elimination) of FSV-type errors in FSV sensitive areas. These results suggest that the CNOP method is suitable for determining sensitive areas in the prediction of the Kuroshio large-meander path.

Medium fidelity modelling of loads in wind farms under non-neutral ABL stability conditions - a full-scale validation study

NASA Astrophysics Data System (ADS)

Larsen, G. C.; Larsen, T. J.; Chougule, A.

2017-05-01

The aim of the present paper is to demonstrate the capability of medium fidelity modelling of wind turbine component fatigue loading, when the wind turbines are subjected to wake affected non-stationary flow fields under non-neutral atmospheric stability conditions. To accomplish this we combine the classical Dynamic Wake Meandering model with a fundamental conjecture stating: Atmospheric boundary layer stability affects primary wake meandering dynamics driven by large turbulent scales, whereas wake expansion in the meandering frame of reference is hardly affected. Inclusion of stability (i.e. buoyancy) in description of both large- and small scale atmospheric boundary layer turbulence is facilitated by a generalization of the classical Mann spectral tensor, which consistently includes buoyancy effects. With non-stationary wind turbine inflow fields modelled as described above, fatigue loads are obtained using the state-of-the art aeroelastic model HAWC2. The Lillgrund offshore wind farm (WF) constitute an interesting case study for wind farm model validation, because the WT interspacing is small, which in turn means that wake effects are significant. A huge data set, comprising 5 years of blade and tower load recordings, is available for model validation. For a multitude of wake situations this data set displays a considerable scatter, which to a large degree seems to be caused by atmospheric boundary layer stability effects. Notable is also that rotating wind turbine components predominantly experience high fatigue loading for stable stratification with significant shear, whereas high fatigue loading of non-rotating wind turbine components are associated with unstable atmospheric boundary layer stratification.

77 FR 53906 - Notice of Filing of Plats of Survey; South Dakota

Federal Register 2010, 2011, 2012, 2013, 2014

2012-09-04

... section 18, and the survey of a portion of the meanders of the present left bank of Chouteau Creek... they have become final, including decisions or appeals. Authority: 43 U.S.C. chapter 3. Steve L. Toth...

Earth meandering

NASA Astrophysics Data System (ADS)

Asadiyan, H.; Zamani, A.

2009-04-01

In this paper we try to put away current Global Tectonic Model to look the tectonic evolution of the earth from new point of view. Our new dynamic model is based on study of river meandering (RM) which infer new concept as Earth meandering(EM). In a universal gravitational field if we consider a clockwise spiral galaxy model rotate above Ninety East Ridge (geotectonic axis GA), this system with applying torsion field (likes geomagnetic field) in side direction from Rocky Mt. (west geotectonic pole WGP) to Tibetan plateau TP (east geotectonic pole EGP),it seems that pulled mass from WGP and pushed it in EGP due to it's rolling dynamics. According to this idea we see in topographic map that North America and Green land like a tongue pulled from Pacific mouth toward TP. Actually this system rolled or meander the earth over itself fractaly from small scale to big scale and what we see in the river meandering and Earth meandering are two faces of one coin. River transport water and sediments from high elevation to lower elevation and also in EM, mass transport from high altitude-Rocky Mt. to lower altitude Himalaya Mt. along 'S' shape geodetic line-optimum path which connect points from high altitude to lower altitude as kind of Euler Elastica(EE). These curves are responsible for mass spreading (source) and mass concentration (sink). In this regard, tiltness of earth spin axis plays an important role, 'S' are part of sigmoidal shape which formed due to intersection of Earth rolling with the Earth glob and actual feature of transform fault and river meandering. Longitudinal profile in mature rivers as a part of 'S' curve also is a kind of EE. 'S' which bound the whole earth is named S-1(S order 1) and cube corresponding to this which represent Earth fracturing in global scale named C-1(cube order 1 or side vergence cube SVC), C-1 is a biggest cycle of spiral polygon, so it is not completely closed and it has separation about diameter of C-7. Inside SVC we introduce cone vergence cube (CVC or geotectonic equator GE) which rotate 45 degree counterclockwise with respect to SVC. Every cube from big scale to small scale fractalize in order of 23 and every '8' shape from big scale to small scale also fractalize in the same order. Three dimensional and fractoscopic imagination about understanding the changing on earth is very important so we should imagine '8' as curved surface, sea floor spreading happened in maximum curvature of these surfaces. '8' formed from pair 'S' string with opposite direction. '8' oscillate in Pole-Pole and Side-Side direction and have saddle geometry with two 'U' path along perpendicular saddle (e.g. Lut/Jazmurian and Helmand/Mashkal basin in Iran actually intersection of this saddle shape with the earth surface and Iceland /Black Sea and CapeVerde/Victoria Lake are also In/Out (small scale polygon) of 'U' shape conduit which followed axial saddle of Side-'S-2' and Okhotsk Sea /Balkhash Lake followed axial saddle conduit of Pole-'S-2' actually intersection of this perpendicular conduit with surface make spot-like-lakes/volcanoes or basin. Global EM in Side-S-1 bounded compression region-TP inside and tension region-East African Rift offside).This is a interesting competing between two kinematic geometry - spherical and isometrical geometry by using the interaction of them we can analyze the earth face in past, present and future apart of the forces that cause this face. C-1 in two dimensional look like six sided big tent which speared over Tibet and main rod driven along GA. Pair S-1 curve. have seven component(fold) and six segment in between,S-7 exactly located on TP(center of S-1). Between two successive fold we have complex geology(e.g. eastern Iran and Afghanistan)mass dragged from North America and Siberian and accumulated gradually during six step in Earth Foundation(Tibet),S-7 bounded Takla Makan Desert (in smaller loop) and TP (in bigger loop) S-7 alter the earth balance and responsible for earth disturbing, another sample of 'S' curve we see around Australia and Kermadec/Tonga Trench, Aleutian ridge and Mackenzie Mt. and central Iran which are well obvious in topographic map, we find many samples converge in to this unified model.

Polychlorinated Biphenyls in suspended-sediment samples from outfalls to Meandering Road Creek at Air Force Plant 4, Fort Worth, Texas, 2003-08

USGS Publications Warehouse

Braun, Christopher L.; Wilson, Jennifer T.

2010-01-01

Meandering Road Creek is an intermittent stream and tributary to Lake Worth, a reservoir on the West Fork Trinity River on the western edge of Fort Worth, Texas. U.S. Air Force Plant 4 (AFP4) is on the eastern shore of Woods Inlet, an arm of Lake Worth. Meandering Road Creek gains inflow from several stormwater outfalls as it flows across AFP4. Several studies have characterized polychlorinated biphenyls (PCBs) in the water and sediments of Lake Worth and Meandering Road Creek; sources of PCBs are believed to originate primarily from AFP4. Two previous U.S. Geological Survey (USGS) reports documented elevated PCB concentrations in surficial sediment samples from Woods Inlet relative to concentrations in surficial sediment samples from other parts of Lake Worth. The second of these two previous reports also identified some of the sources of PCBs to Lake Worth. These reports were followed by a third USGS report that documented the extent of PCB contamination in Meandering Road Creek and Woods Inlet and identified runoff from outfalls 4 and 5 at AFP4 as prominent sources of these PCBs. This report describes the results of a fourth study by the USGS, in cooperation with the Lockheed Martin Corporation, to investigate PCBs in suspended-sediment samples in storm runoff from outfalls 4 and 5 at AFP4 following the implementation of engineering controls designed to potentially alleviate PCB contamination in the drainage areas of these outfalls. Suspended-sediment samples collected from outfalls 4 and 5 during storms on March 2 and November 10, 2008, were analyzed for selected PCBs. Sums of concentrations of 18 reported PCB congeners (Sigma PCBc) in suspended-sediment samples collected before and after implementation of engineering controls are compared. At both outfalls, the Sigma PCBc before engineering controls was higher than the Sigma PCBc after engineering controls. The Sigma PCBc in suspended-sediment samples collected at AFP4 before and after implementation of engineering controls also is compared to the threshold effect concentration (TEC), the concentration below which adverse effects to benthic biota rarely occur. Sigma PCBc exceeded the TEC for 75 percent of the samples collected at outfall 4 and 67 percent of the samples collected at outfall 5 before the implementation of engineering controls. Sigma PCBc did not exceed the TEC in samples collected at either outfall 4 or outfall 5 after the implementation of engineering controls. The relative prominence of 10 selected PCB congeners was evaluated by graphical analysis of ratios of individual concentrations of the 10 PCB congeners to the sum of these PCB congeners. An overall decrease in concentrations of PCB congeners at outfalls 4 and 5 after implementation of engineering controls, as well as a shift in prominence from lighter, less chlorinated congeners to a heavier, more chlorinated congener might have resulted from the implementation of engineering controls. Because of the small number of samples collected and lack of runoff and precipitation data to evaluate comparability of sampling conditions before and after implementation of engineering controls, all conclusions are preliminary.

MWM-Array Characterization of Mechanical Damage and Corrosion

DOT National Transportation Integrated Search

2011-02-09

The MWM-Array is an inductive sensor that operates like a transformer in a plane. The MWMArray is based on the original MWM(R) (Meandering Winding Magnetometer) developed at MIT in the 1980s. A rapid multivariate inverse method converts impedance dat...

WATER QUALITY STATUS REPORT, CROOKED RIVER, IDAHO COUNTY IDAHO, 1987

EPA Science Inventory

Crooked River (17060305), a primary anadromous fisheries resource, is located approximately 120 miles southeast of Lewiston, Idaho. Dredging operations between 1936 and 1948 left large piles of gravel in the natural watercourse, causing the river to meander. Impoundments of wat...

Improved numerical modelling of morphodynamics of rivers with steep banks

USDA-ARS?s Scientific Manuscript database

The flow and sediment transport processes near steep streambanks, which are commonly found in meandering, braided, and anastomosing stream systems, exhibit complex patterns. The interactions between bed and bank morphologic adjustment, and their governing processes are still not well understood. Inc...

27 CFR 9.200 - Mokelumne River.

Code of Federal Regulations, 2011 CFR

2011-04-01

... significance. (b) Approved maps. The seven United States Geological Survey, 1:24,000 scale, topographic... South, Calif., 1968, photorevised 1976; (2) Terminous, Calif., 1978, minor revision 1993; (3) Thornton... Quadrangle); then (2) Proceed southeast (upstream) 5 miles along the meandering Mokelumne River to its...

27 CFR 9.200 - Mokelumne River.

Code of Federal Regulations, 2010 CFR

2010-04-01

... significance. (b) Approved maps. The seven United States Geological Survey, 1:24,000 scale, topographic... South, Calif., 1968, photorevised 1976; (2) Terminous, Calif., 1978, minor revision 1993; (3) Thornton... Quadrangle); then (2) Proceed southeast (upstream) 5 miles along the meandering Mokelumne River to its...

An Ice-and-Snow Hypothesis for Early Mars, and the Runoff-Production Test

NASA Astrophysics Data System (ADS)

Kite, E. S.

2017-10-01

Cold (snowmelt) models for Early Mars climate can be tested by measuring paleochannel widths and meander wavelengths for Early Mars watersheds with well-defined drainage area. I will review snowmelt models, and report results of these tests.

Apollo 15 at Hadley Base.

ERIC Educational Resources Information Center

National Aeronautics and Space Administration, Washington, DC.

This publication highlights the mission of Apollo 15 and includes many detailed black and white and color photographs taken near the lunar Apennine Mountains and the mile-wide, meandering Hadley Rille. Some of the photographs are full page (9 by 12 inch) reproductions. (Author/PR)

Hydrological and dynamical characterization of Meddies in the Azores region: A paradigm for baroclinic vortex dynamics

NASA Astrophysics Data System (ADS)

Tychensky, A.; Carton, X.

1998-10-01

The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Expérimentale (SEMAPHORE) oceanographic experiment surveyed a 500 × 500 km2 domain south of the Azores from June to November 1993 and collected hydrological data, float trajectories, and current meter recordings. This data exhibited three intrathermocline eddies of Mediterranean water (Meddies), two of them being repeatedly sampled. Their hydrological and dynamical properties are quantified here by an isopycnic analysis. For the three Meddies, intense temperature and salinity anomalies (up to 4°C and 1.1 practical salinity units (psu)) are observed extending vertically over up to 1000 m and centered around 1000 m. Horizontally, these anomalies spread out to radii of 50-60 km, while the maximum azimuthal velocities (30 cm s-1, as computed by geostrophy) lie only at 35-40 km from the central axis. These Meddies followed curved trajectories, with drift velocities up to 7.5 cm s-1, under the influence of the neighboring mesoscale features (cyclonic vortices or Azores Current meanders). The three-dimensional structure of potential vorticity in and around these features evidences their complex interactions. Northwest of the domain, a Meddy was coupled to a subsurface anticyclone, forming an "aligned" vortex. It later interacted with the Azores Current, creating a large-amplitude northward meander by vertical alignment of vorticity. In the southeastern part of the domain, another Meddy was vertically aligned with an anticyclonic meander of the Azores Current and horizontally coupled with a cyclone of large vertical extent. These two features, as well as a small warm and salty fragment in their vicinity, seem to result from the southward crossing of the Meddy under the Azores Current. These observations illustrate previous theoretical studies of baroclinic vortex dynamics.

River capture controlling changes in the drainage pattern and river slope

NASA Astrophysics Data System (ADS)

Castelltort, Xavier; Colombo, Ferran

2016-04-01

The crystalline block of Les Guilleries, in the northeast of the Iberian Peninsula, is part of the Hercynian basement over which Palaeogene materials of the Ebro basinwere deposited . This massif is affected by a family of basement fractures of NW-SE direction which continue under the Paleogene cover. This is evident in the areas of contact between the two units. One of these areas affected by fractures was used by the primitive river Ter to transition, through a process of river capture, from the crystal unit Guilleries, with a rectangular drainage pattern, toward the sedimentary cover of the Ebro basin, with a meander drainage pattern. The fractured material that the river Ter used to deepen against the dip of the layers is more evident due to it being rigid and resistant to erosion, the Sandstones of Folgueroles Fm. The use of fractures resulted in a course of the river Ter that can be divided into three subparallel reaches with a shape of Z, which can be described as structural pseudomeanders. The change in the drainage pattern of the river between its passage accross the basement and the cover can never be the product of a process of antecedence or superimposition as has been proclaimed earlier. The rectangular pattern fits the structure of the crystalline massif. The meandering pattern on the cover is due to the difficulty of flowing through the Sandstones of Folgueroles Fm, and to the subsequent pressure loss affecting the current of the river that moves upstream beyond the Bellmunt Anticline. Up to the point where the pattern meander is conserved, river slope is below 1%. Upstream, the river slope increases significantly due to the adaptation of the river to a new layout.

Measuring the Timing, Magnitude, and Rate of Rock uplift of Sierra Madre Mountains with CRN Analysis of Relict Landscapes and Strath Terraces

NASA Astrophysics Data System (ADS)

Schoettle, E.; Burbank, D. W.; Bookhagen, B.

2014-12-01

California's Sierra Madre Mountains lie at the junction of the Coast and Transverse Ranges, where they form an arcuate range crest with peak elevations of nearly 1,800 m. Near the range crest, a gently sloping paleovalley in the Southern Sierra Madre is being consumed by the headward migration of a prominent knickpoint, with an ~250-m-high headwall abutting below the gently sloped paleovalley. This paleovalley at 1400 m elevation and other low-relief, high-elevation remnants in the Sierra Madres at elevations from 800-1400 m show that the range is young enough to have regions not yet in equilibrium with the modern base level and uplift rate. Toward the western end of the Sierra Madre, the Cuyama River cuts a bedrock canyon through the range. The canyon planform describes a meandering river that has now incised ~400 m into the range. The combination of (i) high-altitude, low-relief surfaces in the Sierra Madre including the paleovalley with (ii) a meandering planform that has been incised into bedrock by a transverse river suggests (1) a low-altitude meandering proto-Cuyama river preceded significant rock uplift, and (2) the river's incision records the rock uplift of the range. Using cosmogenic nuclides to measure both the bedrock-lowering rate of the high-elevation paleovalley and the erosion rate of the steep catchment eroding into it, we can place some limits on the timing and magnitude of rock uplift in the range. By dating bedrock straths along the river canyon's walls, we can directly quantify the pace of channel incision. Together these new estimates will yield an improved reconstruction of the timing, magnitude, and rate of rock uplift of the Sierra Madre.

Dual-band LTCC antenna based on 0.95Zn2SiO4-0.05CaTiO3 ceramics for GPS/UMTS applications

NASA Astrophysics Data System (ADS)

Dou, Gang; Li, Yu-Xia; Guo, Mei

2015-10-01

In this paper, we present a compact low-temperature co-fired ceramic (LTCC) dual-band antenna by using the electromagnetic coupling effect concept for global positioning system (GPS) and universal mobile telecommunication system (UMTS) applications. The overall dimension of the antenna is 8.6 mm × 13.0 mm × 1.1 mm. It consists of double meander lines and a via hole line. The top meander line operates at the upper band, and the bottom radiating patch is designed for the lower band. The via-hole line is employed to connect the double meander lines. Because of the effect of the coupled line, total dimension of the proposed antenna is greatly reduced. With the 2.5: voltage standing wave ratio (VSWR) impedance bandwidth definition, the lower and upper bands have the bandwidths of 110 MHz and 150 MHz, respectively. The proposed antenna is successfully designed, simulated, and analyzed by a high frequency structure simulator (HFSS). And the antenna is manufactured by using the 0.95Zn2SiO4-0.05CaTiO3 ceramics (εr = 7.1, tanδ = 0.00038) that is prepared by ourselves. The results show that the antenna is compact, efficient, and of near omnidirectional radiation pattern. Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20133718120009), the Natural Science Foundation of Shandong Provence, China (Grant Nos. ZR2013FQ002 and ZR2014FQ006), the China Postdoctoral Science Foundation (Grant No. 2014M551935), the Qingdao Municipality Postdoctoral Science Foundation, China, and the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents, China (Grant Nos. 2013RCJJ042 and 2014RCJJ052).

The Morphodynamic Signature of Rivers in the Ucamara Depression: A Habitat for Formative Rivers and the Scavenger Meandering Channels they Feed

NASA Astrophysics Data System (ADS)

Abad, J. D.; Escobar, C.; Shan, J.

2017-12-01

The Pacaya Samiria National Reserve, located in Loreto, Peru, is a region of incomparable biodiversity resulting from the consistent annual climate patterns (little seasonal variability), and more importantly, the dynamics of the freshwater rivers that surround and traverse it. The Ucamara Depression, where the Pacaya Samiria National Reserve is located, presently has a myriad of active and abandoned fluvial landforms. The exploration of the geologic and tectonic history that fabricated this exceptional fluvial system is the foundation for researching and understanding further phenomena of the region. The interpretation of the history of the geologic events that occurred to form this region and the inspection of the river belts, or areas of active river migration, of these fluvial landforms, facilitate the understanding of 1) how the Ucayali and Maranon rivers interact with one another and with the streams and bodies of water in the Ucamara Depression, 2) the role of wetlands, hydrodynamics, and sediment transport mechanisms in the movement of rivers and the extent of mixing before the rivers reach their confluence, and 3) how the water chemistry, flooding, and sediment transport processes of rivers create an environment capable of fostering an unimaginable array of life and how changes in these processes affect the flora and fauna that inhabit the region. This study will discuss field measurements (hydrodynamic and bed morphodynamic) and remote sensing analysis of scavenger meandering channels (Pacaya and Samiria) and discuss confluence dynamics of the two tributaries that form the Amazon River. Morphometric parameters show that these meandering rivers do not achieve typical planform-based conditions.

Stratigraphy and paleohydrology of delta channel deposits, Jezero crater, Mars

NASA Astrophysics Data System (ADS)

Goudge, Timothy A.; Mohrig, David; Cardenas, Benjamin T.; Hughes, Cory M.; Fassett, Caleb I.

2018-02-01

The Jezero crater open-basin lake contains two well-exposed fluvial sedimentary deposits formed early in martian history. Here, we examine the geometry and architecture of the Jezero western delta fluvial stratigraphy using high-resolution orbital images and digital elevation models (DEMs). The goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position. The delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret, from oldest to youngest, as: (1) point bar strata deposited by repeated flood events in meandering channels; (2) inverted channel-filling deposits formed by avulsive distributary channels; and (3) a valley that incises the deposit. We use DEMs to quantify the geometry of the channel deposits and estimate flow depths of ∼7 m for the meandering channels and ∼2 m for the avulsive distributary channels. Using these estimates, we employ a novel approach for assessing paleohydrology of the formative channels in relative terms. This analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four-fold decrease in the water to sediment discharge ratio. We use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the Jezero western delta. The delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin, followed by outlet breaching, and eventual erosion of the delta. Our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the Jezero basin without major drops in lake level, but also with discrete flooding events at non-orbital (e.g., annual to decadal) timescales.

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

NASA Astrophysics Data System (ADS)

Archer, Matthew R.; Roughan, Moninya; Keating, Shane R.; Schaeffer, Amandine

2017-11-01

Given the importance of western boundary currents over a wide range of scales in the ocean, it is crucial that we understand their dynamics to accurately predict future changes. For this, we need detailed knowledge of their structure and variability. Here we investigate the jet structure of the East Australian Current (EAC), using observations from HF radars and moorings deployed at 30°S-31°S. Meandering, core velocity, width, and eddy kinetic energy (EKE) are quantified from 4 years of hourly 1.5 km resolution surface current maps (2012-2016), to obtain the most detailed representation of the surface EAC jet to date. The EAC flows predominantly over the ˜1,500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65-100 days—the time scale associated with mesoscale eddy shedding at the EAC separation. Smaller-amplitude, higher-frequency meanders occur every 20-45 days. Using a coordinate frame that follows the jet, we show core velocity and EKE exhibit seasonality in both magnitude and variance, being maximum in summer (1.55 m s-1 mean core velocity), minimum in winter (0.8 m s-1). However, it is the eddy-shedding time scale that dominates jet variability. As the EAC moves shoreward, shelf temperature and along-stream velocity vary linearly with jet movement, within ˜35 km of the core. The EAC is within this range 75% of the time, demonstrating its importance to the shelf circulation. Temperature and velocity fluctuations at the 70 m (100 m) isobath are more influenced by wind (EAC encroachment), with the strongest response occurring when wind and EAC act constructively.

Meandered conformal antenna for ISM-band ingestible capsule communication systems.

PubMed

Arefin, Md Shamsul; Redoute, Jean-Michel; Yuce, Mehmet Rasit

2016-08-01

The wireless capsule has been used to measure physiological parameters in the gastrointestinal tract where communication from in-body to external receiver is necessary using a miniaturized antenna with high gain and onmidirectional radiation pattern. This paper presents a meandered conformal antenna with center frequency of 433 MHz for a wireless link between an in-body capsule system and an ex-body receiver system. The antenna is wrapped around the wireless capsule, which provides extra space for other circuits and sensors inside the capsule as well as allows it having larger dimensions compared to inner antennas. This paper analyses return loss, radiation pattern, antenna gain, and propagation loss using pork as the gastrointestinal tissue simulating medium. From the radiation pattern and return loss results, the antenna shows an omni-directional radiation pattern and an ultrawide bandwidth of 124.4 MHz (371.6 to 496 MHz) for VSWR <; 2. Experimental results shows that the path loss is 17.24 dB for an in-body propagation distance of 140 mm.

Inverted Streams in the Aeolis Region

NASA Image and Video Library

2015-12-10

The sinuous ridges in this image display strong characteristics of ancient meandering riverbeds that are preserved as inverted topography (blue). The ancient river sediments that make up the ridges might have allowed fluids to produce cements (e.g., calcite or iron oxides) to make the channel lithology resistant to weathering and erosion. Later, physical and/or chemical processes removed the weaker surrounding flood plain material and left inverted river channels, or "positive relief." On closer inspection, degradation along sections of some inverted channels display large blocks of cemented sediment that were transported downslope by mass wasting. The sinuous character of the ridges resembles multi-thread river branches, implying that the ancient river flowed down a gentle to nearly horizontal slope (i.e., a moderate to low stream gradient). This ancient river was a mature meandering system, with flow from south to north. Multiple branches that diverted from the main flow later converged back with it. http://photojournal.jpl.nasa.gov/catalog/PIA20210

The Spacing of Strongly Meandering Jets in Quasigeostrophic Turbulence

NASA Astrophysics Data System (ADS)

Scott, R.

2017-12-01

Based on an assumption of inhomogeneous potential vorticity mixing,estimates are obtained for kinetic and potential energies inquasigeostrophic β -plane turbulence with strongly meanderingjets and in the limit of small Rossby deformation length. Theestimates provide, inter alia, a means to predict the jetspacing based on knowledge of either the kinetic or potential energy,which, in situations where the flow is forced with a uniform totalenergy input, are known a priori in the case of frictional orthermal damping, respectively. The estimates are lower bounds for thejet spacing, achieved in the limit of perfect mixing between regularlyspaced jets with simple meanders. These lower bounds are sharp in astrict mathematical sense but are likely to substantiallyunderestimate jet spacing in actual flows, which exhibit a remarkablediversity of structures and irregularities. The latter areillustrated numerically in direct integrations of the forced system.A convenient description of the forced system is presented in terms ofa number of independent length scales of the problem, anddimensionless ratios of these.

A Passive Temperature-Sensing Antenna Based on a Bimetal Strip Coil.

PubMed

Shi, Xianwei; Yang, Fan; Xu, Shenheng; Li, Maokun

2017-03-23

A passive temperature-sensing antenna is presented in this paper, which consists of a meandering dipole, a bimetal strip and a back cavity. The meandering dipole is divided into two parts: the lower feeding part and the upper radiating part, which maintain electric contact during operation. As a sensing component, a bimetal strip coil offers a twisting force to rotate the lower feeding part of the antenna when the temperature varies. As a result, the effective length of the dipole antenna changes, leading to a shift of the resonant frequency. Furthermore, a metal back cavity is added to increase the antenna's quality factor Q, which results in a high-sensitivity design. An antenna prototype is designed, fabricated, and measured, which achieves a sensitivity larger than 4.00 MHz/°C in a temperature range from 30 °C to 50 °C and a read range longer than 4 m. Good agreement between the simulation and measurement results is obtained.

Erosional and depositional changes wrought by the flood of May 1978 in the channels of Powder River, southeastern Montana

USGS Publications Warehouse

Meade, Robert H.; Moody, John A.

2013-01-01

Powder River’s second largest flood of record (1919–2012) moved through northeastern Wyoming and southeastern Montana during May 1978. Within a ninety-kilometer reach of the channel in southeastern Montana, the most prominent planform effects of the flood were the growth of meander bends by bank erosion (this was most intense just downriver of bend apexes, causing 1–2 channel widths of lateral displacement) and the erosion of new cutoff channels through the necks of two large and two small meanders. Surveys of cross sections, made before and after the flood, show the responses of the channel to the flood waters, which ranged from minimal (bedrock control) to large (maximum channel curvature in unconsolidated bank and terrace deposits). Geomorphic work done during two weeks of extreme flooding in May 1978, as measured by cross-channel erosion and new sediment deposition, was approximately equal in magnitude to the work done during the two decades (1978–1998) that followed the flood.

Reduced size dual band pass filters for RFID applications with excellent bandpass/bandstop characteristics

NASA Astrophysics Data System (ADS)

Abdalla, M. A.; Choudhary, D. Kumar; Chaudhary, R. Kumar

2018-02-01

This paper presents the design of two reduced size dual-band metamaterial bandpass filters and its simulation followed by measurements of proposed filters. These filters are supporting different frequency bands and primarily could be utilize in radio frequency identification (RFID) application. The filter includes three cells in which two are symmetrical and both inductively coupled with the third cell which is present in between them. In the proposed designs, three different metamaterial composite right/left handed (CRLH) cell resonators have been analysed for compactness. The CRLH cell consists of an interdigital capacitor, a stub/meander line/spiral inductor and a via to connect the top of the structure and ground plane. Finally, the proposed dual band bandpass filters (using meander line and spiral inductor) are showing size reduction by 65% and 50% (with 25% operating frequency reduction), respectively, in comparison with reference filter using stub inductor. More than 30 dB attenuation has been achieved between the two passbands.

A new planar broadband antenna based on meandered line loops for portable wireless communication devices

NASA Astrophysics Data System (ADS)

Alibakhshi-Kenari, Mohammad; Naser-Moghadasi, Mohammad; Sadeghzadeh, R. A.; Virdee, Bal S.; Limiti, Ernesto

2016-07-01

This article presents the design of a novel planar antenna structure comprising two pairs of interconnected meandered line loops that are grounded to a truncated T-shaped ground plane through two via holes. The T-shaped ground plane is used as a reflector to enhance the performance of the antenna. The resulting antenna is compact occupying an area of 38.5 × 36.6 mm2 (0.070λo × 0.067λo), where free-space wavelength is 550 MHz. The antenna radiates omnidirectionally in the E plane across its operational bandwidth (550 MHz to 3.85 GHz) with peak gain and efficiency of 5.5 dBi and 90.1%, respectively, at 2.35 GHz and reflection coefficient better than -10 dB. These characteristics make the antenna suitable for numerous applications, in particular, JCDMA, UHF RFID, GSM 900, GPS, KPCS, DCS, IMT-2000, WiMAX, WiFi, and Bluetooth.

Origin choice and petal loss in the flower garden of spiral wave tip trajectories

PubMed Central

Gray, Richard A.; Wikswo, John P.; Otani, Niels F.

2009-01-01

Rotating spiral waves have been observed in numerous biological and physical systems. These spiral waves can be stationary, meander, or even degenerate into multiple unstable rotating waves. The spatiotemporal behavior of spiral waves has been extensively quantified by tracking spiral wave tip trajectories. However, the precise methodology of identifying the spiral wave tip and its influence on the specific patterns of behavior remains a largely unexplored topic of research. Here we use a two-state variable FitzHugh–Nagumo model to simulate stationary and meandering spiral waves and examine the spatiotemporal representation of the system’s state variables in both the real (i.e., physical) and state spaces. We show that mapping between these two spaces provides a method to demarcate the spiral wave tip as the center of rotation of the solution to the underlying nonlinear partial differential equations. This approach leads to the simplest tip trajectories by eliminating portions resulting from the rotational component of the spiral wave. PMID:19791998

Origin choice and petal loss in the flower garden of spiral wave tip trajectories.

PubMed

Gray, Richard A; Wikswo, John P; Otani, Niels F

2009-09-01

Rotating spiral waves have been observed in numerous biological and physical systems. These spiral waves can be stationary, meander, or even degenerate into multiple unstable rotating waves. The spatiotemporal behavior of spiral waves has been extensively quantified by tracking spiral wave tip trajectories. However, the precise methodology of identifying the spiral wave tip and its influence on the specific patterns of behavior remains a largely unexplored topic of research. Here we use a two-state variable FitzHugh-Nagumo model to simulate stationary and meandering spiral waves and examine the spatiotemporal representation of the system's state variables in both the real (i.e., physical) and state spaces. We show that mapping between these two spaces provides a method to demarcate the spiral wave tip as the center of rotation of the solution to the underlying nonlinear partial differential equations. This approach leads to the simplest tip trajectories by eliminating portions resulting from the rotational component of the spiral wave.

Potential for Small Unmanned Aircraft Systems applications for identifying groundwater-surface water exchange in a meandering river reach

USGS Publications Warehouse

Pai, H.; Malenda, H.; Briggs, Martin A.; Singha, K.; González-Pinzón, R.; Gooseff, M.; Tyler, S.W.; ,

2017-01-01

The exchange of groundwater and surface water (GW-SW), including dissolved constituents and energy, represents a critical yet challenging characterization problem for hydrogeologists and stream ecologists. Here, we describe the use of a suite of high spatial-resolution remote-sensing techniques, collected using a small unmanned aircraft system (sUAS), to provide novel and complementary data to analyze GW-SW exchange. sUAS provided centimeter-scale resolution topography and water surface elevations, which are often drivers of exchange along the river corridor. Additionally, sUAS-based vegetation imagery, vegetation-top elevation, and normalized difference vegetation index (NDVI) mapping indicated GW-SW exchange patterns that are difficult to characterize from the land surface and may not be resolved from coarser satellite-based imagery. We combined these data with estimates of sediment hydraulic conductivity to provide a direct estimate of GW “shortcutting” through meander necks, which was corroborated by temperature data at the riverbed interface.

Neutron detection using the superconducting Nb-based current-biased kinetic inductance detector

NASA Astrophysics Data System (ADS)

Shishido, Hiroaki; Yamaguchi, Hiroyuki; Miki, Yuya; Miyajima, Shigeyuki; Oikawa, Kenichi; Harada, Masahide; Hidaka, Mutsuo; Oku, Takayuki; Arai, Masatoshi; Fujimaki, Akira; Ishida, Takekazu

2017-09-01

We demonstrate neutron detection using a solid-state 3He-free superconducting current-biased kinetic inductance detector (CB-KID), which consists of a superconducting Nb meander line and 10B neutron absorption layer. The CB-KID is based on the transient process of kinetic inductance of Cooper pairs induced by the nuclear reaction between 10B and neutrons. Therefore, the CB-KID can be operated in a wide superconducting region in the bias current-temperature diagram, as demonstrated in this paper. The transient change of the kinetic inductance induces the electromagnetic wave pulse under a DC bias current. The signal propagates along the meander line toward both sides with opposite polarity, where the signal polarity is dominated by the bias current direction. The full width at half maximum of the signals remains on the order of a few tens of ns, which confirms the high-speed operation of our detectors. We determine the neutron incident position within 1.3 mm accuracy in one dimension using the multichannel CB-KIDs.

Potential for Small Unmanned Aircraft Systems Applications for Identifying Groundwater-Surface Water Exchange in a Meandering River Reach

NASA Astrophysics Data System (ADS)

Pai, H.; Malenda, H. F.; Briggs, M. A.; Singha, K.; González-Pinzón, R.; Gooseff, M. N.; Tyler, S. W.

2017-12-01

The exchange of groundwater and surface water (GW-SW), including dissolved constituents and energy, represents a critical yet challenging characterization problem for hydrogeologists and stream ecologists. Here we describe the use of a suite of high spatial resolution remote sensing techniques, collected using a small unmanned aircraft system (sUAS), to provide novel and complementary data to analyze GW-SW exchange. sUAS provided centimeter-scale resolution topography and water surface elevations, which are often drivers of exchange along the river corridor. Additionally, sUAS-based vegetation imagery, vegetation-top elevation, and normalized difference vegetation index mapping indicated GW-SW exchange patterns that are difficult to characterize from the land surface and may not be resolved from coarser satellite-based imagery. We combined these data with estimates of sediment hydraulic conductivity to provide a direct estimate of GW "shortcutting" through meander necks, which was corroborated by temperature data at the riverbed interface.

A Passive Temperature-Sensing Antenna Based on a Bimetal Strip Coil

PubMed Central

Shi, Xianwei; Yang, Fan; Xu, Shenheng; Li, Maokun

2017-01-01

A passive temperature-sensing antenna is presented in this paper, which consists of a meandering dipole, a bimetal strip and a back cavity. The meandering dipole is divided into two parts: the lower feeding part and the upper radiating part, which maintain electric contact during operation. As a sensing component, a bimetal strip coil offers a twisting force to rotate the lower feeding part of the antenna when the temperature varies. As a result, the effective length of the dipole antenna changes, leading to a shift of the resonant frequency. Furthermore, a metal back cavity is added to increase the antenna’s quality factor Q, which results in a high-sensitivity design. An antenna prototype is designed, fabricated, and measured, which achieves a sensitivity larger than 4.00 MHz/°C in a temperature range from 30 °C to 50 °C and a read range longer than 4 m. Good agreement between the simulation and measurement results is obtained. PMID:28333076

The Meandering Margin of the Meteorological Moist Tropics

NASA Astrophysics Data System (ADS)

Mapes, Brian E.; Chung, Eui Seok; Hannah, Walter M.; Masunaga, Hirohiko; Wimmers, Anthony J.; Velden, Christopher S.

2018-01-01

Bimodally distributed column water vapor (CWV) indicates a well-defined moist regime in the Tropics, above a margin value near 48 kg m-2 in current climate (about 80% of column saturation). Maps reveal this margin as a meandering, sinuous synoptic contour bounding broad plateaus of the moist regime. Within these plateaus, convective storms of distinctly smaller convective and mesoscales occur sporadically. Satellite data composites across the poleward most margin reveal its sharpness, despite the crude averaging: precipitation doubles within 100 km, marked by both enhancement and deepening of cloudiness. Transported patches and filaments of the moist regime cause consequential precipitation events within and beyond the Tropics. Distinguishing synoptic flows that cross the margin from flows that move the margin is made possible by a novel satellite-based Lagrangian CWV tendency estimate. Climate models do not reliably reproduce the observed bimodal distribution, so studying the moist mode's maintenance processes and the margin-zone air mass transformations, guided by the Lagrangian tendency product, might importantly constrain model moist process treatments.

27 CFR 9.215 - Lake Chelan.

Code of Federal Regulations, 2010 CFR

2010-04-01

... purposes of part 4 of this chapter, “Lake Chelan” and “Chelan” are terms of viticultural significance. (b... Co., 1968, photorevised 1987; (2) Cooper Ridge Quadrangle—Washington, 1968, photorevised 1987; (3... meandering 2,000-foot elevation line generally southeast onto the Cooper Ridge map, crossing Purtterman Gulch...

27 CFR 9.215 - Lake Chelan.

Code of Federal Regulations, 2011 CFR

2011-04-01

... purposes of part 4 of this chapter, “Lake Chelan” and “Chelan” are terms of viticultural significance. (b... Co., 1968, photorevised 1987; (2) Cooper Ridge Quadrangle—Washington, 1968, photorevised 1987; (3... meandering 2,000-foot elevation line generally southeast onto the Cooper Ridge map, crossing Purtterman Gulch...

The Stream Table in Physical Geography Instruction.

ERIC Educational Resources Information Center

Wikle, Thomas A.; Lightfoot, Dale R.

1997-01-01

Outlines a number of activities to be conducted with a stream table (large wooden box filled with sediment and designed for water to pass through) in class. Activities illustrate such fluvial processes as stream meandering, erosion, transportation, and deposition. Includes a diagram for constructing a stream table. (MJP)

Assessment of the effects of regional channel stability and sediment transport on roadway hydraulic structures : final report.

DOT National Transportation Integrated Search

2014-06-01

Rivers and streams evolve all the time. As a result, no stream channel is absolutely stable. Channels evolve at various speeds both vertically (degradation/aggradation) and horizontally (meander : migration). They also respond to man-made changes ran...

Boundary shear stress along rigid trapezoidal bends

Treesearch

Christopher I. Thornton; Kyung-Seop Sin; Paul Sclafani; Steven R. Abt

2012-01-01

The migration of alluvial channels through the geologic landform is an outcome of the natural erosive processes. Mankind continually attempts to stabilize channel meandering processes, both vertically and horizontally, to reduce sediment discharge, provide boundary definition, and enable economic development along the river's edge. A critical component in the...

27 CFR 9.225 - Middleburg Virginia.

Code of Federal Regulations, 2013 CFR

2013-04-01

... (downstream) for approximately 8.2 miles, crossing onto the Point of Rocks map, to the mouth of Catoctin Creek; then (2) Proceed southwesterly (upstream) along the meandering Catoctin Creek for approximately 4 miles... State Route 663 for approximately 0.1 mile to State Route 665 (locally known as Loyalty Road) in...

27 CFR 9.225 - Middleburg Virginia.

Code of Federal Regulations, 2014 CFR

2014-04-01

... (downstream) for approximately 8.2 miles, crossing onto the Point of Rocks map, to the mouth of Catoctin Creek; then (2) Proceed southwesterly (upstream) along the meandering Catoctin Creek for approximately 4 miles... State Route 663 for approximately 0.1 mile to State Route 665 (locally known as Loyalty Road) in...

27 CFR 9.183 - Yamhill-Carlton.

Code of Federal Regulations, 2014 CFR

2014-04-01

...) Proceed northerly then southerly for approximately 5 miles along the 200-foot elevation line, crossing... turning northerly along the 200-foot elevation line, continue along the elevation line for about 6 miles... Quadrangle); then (15) Proceed easterly and then northerly for 4.1 miles along the meandering 1,000-foot...

27 CFR 9.183 - Yamhill-Carlton.

Code of Federal Regulations, 2012 CFR

2012-04-01

...) Proceed northerly then southerly for approximately 5 miles along the 200-foot elevation line, crossing... turning northerly along the 200-foot elevation line, continue along the elevation line for about 6 miles... Quadrangle); then (15) Proceed easterly and then northerly for 4.1 miles along the meandering 1,000-foot...

27 CFR 9.183 - Yamhill-Carlton.

Code of Federal Regulations, 2013 CFR

2013-04-01

...) Proceed northerly then southerly for approximately 5 miles along the 200-foot elevation line, crossing... turning northerly along the 200-foot elevation line, continue along the elevation line for about 6 miles... Quadrangle); then (15) Proceed easterly and then northerly for 4.1 miles along the meandering 1,000-foot...

27 CFR 9.183 - Yamhill-Carlton.

Code of Federal Regulations, 2011 CFR

2011-04-01

...) Proceed northerly then southerly for approximately 5 miles along the 200-foot elevation line, crossing... turning northerly along the 200-foot elevation line, continue along the elevation line for about 6 miles... Quadrangle); then (15) Proceed easterly and then northerly for 4.1 miles along the meandering 1,000-foot...

Seeing the Unseen: Molecular Visualization in Biology

ERIC Educational Resources Information Center

Finnan, Jeff; Taylor-Papp, Kim; Duran, Mesut

2005-01-01

In high school biology, students are challenged by many molecular concepts and structures. They meander through a number of molecular structures, some in macromolecular form: carbohydrates, amino acids, fatty acids, nucleotides. Student difficulties arise in part from inability to visualize what they can't easily see. Students struggle moving from…

Magnetically excited flexural plate wave apparatus

DOEpatents

Martin, Stephen J.; Butler, Michael A.; Frye, Gregory C.; Smith, James H.

1998-01-01

A non-piezoelectric flexural plate wave apparatus having meander-line transducers mounted on a non-piezoelectric membrane. A static magnetic field is directed perpendicularly to the conductive legs of the transducers in the plane of the membrane. Single-port, two-port, resonant, non-resonant, eigenmode, and delay-line modes may be employed.

Instructor Gallery. Homage to the Laborer.

ERIC Educational Resources Information Center

Vanelli, Jill

1991-01-01

Discusses the life and paintings of Vincent van Gogh, focusing on "The Road Meanders," and describes how to teach students through the painting (e.g., analyzing colors, discussing feelings it evokes, and writing poems that speak to the people in the painting). A copy of the painting is included. (SM)

Hydrology, geomorphology, and vegetation of Coastal Plain rivers in the southeastern United States

Treesearch

Cliff R. Hupp

2000-01-01

Rivers of the Coastal Plain of the southeastern United States are characteristically low-gradient meandering systems that develop broad floodplains subjected to frequent and prolonged flooding. These floodplains support a relatively unique forested wetland (Bottomland Hardwoods), which have received considerable ecological study, but distinctly less hydrogeomorphic...

43 CFR 2545.3 - Publication and protests.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Publication and protests. 2545.3 Section... Erroneously Meandered Lands: Wisconsin § 2545.3 Publication and protests. (a) The applicant will be required..., accompanied by a copy of the notice published, showing that publication has been had for the required time. ...

43 CFR 2544.4 - Publication and posting.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Publication and posting. 2544.4 Section... Erroneously Meandered Lands: Louisiana § 2544.4 Publication and posting. Upon payment of the appraised price of the land the Bureau will issue notice of publication. Such notice shall be published at the...

Morphodynamics structures induced by variations of the channel width

NASA Astrophysics Data System (ADS)

Duro, Gonzalo; Crosato, Alessandra; Tassi, Pablo

2014-05-01

In alluvial channels, forcing effects, such as a longitudinally varying width, can induce the formation of steady bars (Olesen, 1984). The type of bars that form, such as alternate, central or multiple, will mainly depend on the local flow width-to-depth ratio and on upstream conditions (Struiksma et al., 1985). The effects on bar formation of varying the channel width received attention only recently and investigations, based on flume experiments and mathematical modelling, are mostly restricted to small longitudinal sinusoidal variations of the channel width (e.g. Repetto et al., 2002; Wu and Yeh, 2005, Zolezzi et al., 2012; Frascati and Lanzoni, 2013). In this work, we analyze the variations in equilibrium bed topography in a longitudinal width-varying channel with characteristic scales of the Waal River (The Netherlands) using two different 2D depth-averaged morphodynamic models, one based on the Delft3D code and one on Telemac-Mascaret system. In particular, we explore the effects of changing the wavelength of sinusoidal width variations in a straight channel, focusing on the effects of the spatial lag between bar formation and forcing that is observed in numerical models and laboratory experiments (e.g. Crosato et al, 2011). We extend the investigations to finite width variations in which longitudinal changes of the width-to-depth ratio are such that they may affect the type of bars that become unstable (alternate, central or multiple bars). Numerical results are qualitatively validated with field observations and the resulting morphodynamic pattern is compared with the physics-based predictor of river bar modes by Crosato and Mosselman (2009). The numerical models are finally used to analyse the experimental conditions of Wu and Yeh (2005). The study should be seen as merely exploratory. The aim is to investigate possible approaches for future research aiming at assessing the effects of artificial river widening and narrowing to control bar formation in alluvial rivers. References Crosato A. and Mosselman E., 2009. Simple physics-based predictor for the number of river bars and the transition between meandering and braiding. Water Resources Research, 45, W03424, doi: 10.1029/2008WR007242. Crosato A., Mosselman E., Desta F.B. and Uijttewaal W.S.J., 2011. Experimental and numerical evidence for intrinsic nonmigrating bars in alluvial channels. Water Resources Research, AGU, 47(3), W03511, doi 10.1029/2010WR009714. Frascati A. and Lanzoni S., 2013. A mathematical model for meandering rivers with varying width. J. Geophys. Res.Earth Surf., 118, doi:10.1002/jgrf.20084. Olesen K.W., 1984. Alternate bars in and meandering of alluvial rivers. In: River Meandering, Proc. of the Conf. Rivers '83, 24-26 Oct. 1983, New Orleans, Louisiana, U.S.A., ed. Elliott C.M., pp. 873-884, ASCE, New York. ISBN 0-87262-393-9. Repetto R., Tubino, M. and Paola C., 2002. Planimetric instability of channels with variable width. J. Fluid Mech., 457, 79-109. Struiksma N., Olesen K.W., Flokstra C. and De Vriend H.J., 1985. Bed deformation in curved alluvial channels. J. Hydraul. Res., 23(1), 57- 79. Wu F.-C. and Yeh T.-H., 2005. Forced bars induced by variations of channel width: Implications for incipient bifurcation. J. Geophys. Res., 110, F02009, doi:10.1029/2004JF000160. Zolezzi, G., R. Luchi, and M. Tubino (2012), Modeling morphodynamic processes in meandering rivers with spatial width variations, Rev. Geophys., 50, RG4005, doi:10.1029/2012RG000392.

Channel movement of meandering Indiana streams

USGS Publications Warehouse

Daniel, James F.

1971-01-01

Because of the consistency of yearly above-average discharge volumes, it was possible to develop a general relation between path-length increase per thousand cubic-feet-per-second-days per square mile of drainage area above average discharge and the width-depth ratio of the channel. Little progress was made toward defining relationships for rotation and translation.

Dynamical Analysis of the Boundary Layer and Surface Wind Responses to Mesoscale SST Perturbations

DTIC Science & Technology

2010-02-01

latitude (e.g., Gille and Romero 2003; Lumpkin and Pazos 2007). We thus expect that inclusion of ocean current effects in the surface stress computations...Niiler, 2007: Ocean–atmosphere interaction over Agulhas Extension meanders. J. Climate, 20, 5784–5797. Lumpkin, R., and M. Pazos , 2007: Measuring surface

Pollock without Paint?

ERIC Educational Resources Information Center

Sutley, Jane

2011-01-01

This article describes how the author exposes her students to the world of Jackson Pollock, the artist who brings to mind dripping, meandering, splashing puddles of paint. Pollock's action paintings of the late 1940s-'50s call out for unfettered movement, fluidity, and freedom of application. Is it even possible to capture the action, rhythm and…

27 CFR 9.181 - McMinnville.

Code of Federal Regulations, 2012 CFR

2012-04-01

... this point follow the meandering 200-foot contour line westerly for about 2 miles to its intersection... is as described below— (1) The beginning point is on the McMinnville, Oregon, map where the 200-foot... Road west about 2 miles through Happy Valley to the road's intersection with Power House Hill Road in...

27 CFR 9.204 - Tracy Hills.

Code of Federal Regulations, 2012 CFR

2012-04-01

... miles generally northwest along the meandering 500-foot elevation line to section 18, T4S/R6E, where the... point, proceed 0.4 mile generally southeast along the Delta-Mendota Canal to its intersection with the...) Proceed 5.6 miles straight east along the Western Pacific Railway line and then along Linne Road to the...

27 CFR 9.106 - North Yuba.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 1,900-foot contour line, approximately 0.75 mile north of Finley Ranch; (11) Then north along said... indiana Creek, approximately 0.87 mile, to the point where Indiana Creek meets the 2,000-foot contour line.... 17 N., R. 6 E., the boundary proceeds northeasterly in a meandering line approximately 1.5 miles...

27 CFR 9.204 - Tracy Hills.

Code of Federal Regulations, 2014 CFR

2014-04-01

... miles generally northwest along the meandering 500-foot elevation line to section 18, T4S/R6E, where the... point, proceed 0.4 mile generally southeast along the Delta-Mendota Canal to its intersection with the...) Proceed 5.6 miles straight east along the Western Pacific Railway line and then along Linne Road to the...

27 CFR 9.106 - North Yuba.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 1,900-foot contour line, approximately 0.75 mile north of Finley Ranch; (11) Then north along said... indiana Creek, approximately 0.87 mile, to the point where Indiana Creek meets the 2,000-foot contour line.... 17 N., R. 6 E., the boundary proceeds northeasterly in a meandering line approximately 1.5 miles...

27 CFR 9.181 - McMinnville.

Code of Federal Regulations, 2013 CFR

2013-04-01

... this point follow the meandering 200-foot contour line westerly for about 2 miles to its intersection... is as described below— (1) The beginning point is on the McMinnville, Oregon, map where the 200-foot... Road west about 2 miles through Happy Valley to the road's intersection with Power House Hill Road in...

27 CFR 9.204 - Tracy Hills.

Code of Federal Regulations, 2013 CFR

2013-04-01

... miles generally northwest along the meandering 500-foot elevation line to section 18, T4S/R6E, where the... point, proceed 0.4 mile generally southeast along the Delta-Mendota Canal to its intersection with the...) Proceed 5.6 miles straight east along the Western Pacific Railway line and then along Linne Road to the...

27 CFR 9.204 - Tracy Hills.

Code of Federal Regulations, 2011 CFR

2011-04-01

... miles generally northwest along the meandering 500-foot elevation line to section 18, T4S/R6E, where the... point, proceed 0.4 mile generally southeast along the Delta-Mendota Canal to its intersection with the...) Proceed 5.6 miles straight east along the Western Pacific Railway line and then along Linne Road to the...

27 CFR 9.106 - North Yuba.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 1,900-foot contour line, approximately 0.75 mile north of Finley Ranch; (11) Then north along said... indiana Creek, approximately 0.87 mile, to the point where Indiana Creek meets the 2,000-foot contour line.... 17 N., R. 6 E., the boundary proceeds northeasterly in a meandering line approximately 1.5 miles...

27 CFR 9.181 - McMinnville.

Code of Federal Regulations, 2014 CFR

2014-04-01

... this point follow the meandering 200-foot contour line westerly for about 2 miles to its intersection... is as described below— (1) The beginning point is on the McMinnville, Oregon, map where the 200-foot... Road west about 2 miles through Happy Valley to the road's intersection with Power House Hill Road in...

Meandering toward Graduation: Transcript Outcomes of High School Graduates

ERIC Educational Resources Information Center

Bromberg, Marni; Theokas, Christina

2016-01-01

Graduation rates have reached an all-time high and postsecondary enrollment rates are steadily rising in this country. However, thousands of those new college students are testing into remedial reading, writing, or math courses because they don't have the foundation to perform at the levels demanded in college classes. Employers, too, report that…

27 CFR 9.169 - Red Hills Lake County.

Code of Federal Regulations, 2010 CFR

2010-04-01

... intersection with the 1,400-foot contour line, section 3, T12N, R7W (Clearlake Highlands Quadrangle); then (2) Proceed east-southeasterly along the meandering 1,400-foot contour line onto the Lower Lake map south of Anderson Flat, then reverse direction with the contour line and continue westerly, leaving the Lower Lake...

27 CFR 9.169 - Red Hills Lake County.

Code of Federal Regulations, 2011 CFR

2011-04-01

... intersection with the 1,400-foot contour line, section 3, T12N, R7W (Clearlake Highlands Quadrangle); then (2) Proceed east-southeasterly along the meandering 1,400-foot contour line onto the Lower Lake map south of Anderson Flat, then reverse direction with the contour line and continue westerly, leaving the Lower Lake...

27 CFR 9.201 - Sloughhouse.

Code of Federal Regulations, 2012 CFR

2012-04-01

... estuary and Alta Mesa Road, on the western boundary of section 4, T5N, R7E. From the beginning point... Dorado and Sacramento-Amador County line to the County line's intersection with the Laguna estuary, 0.75...) 17.5 miles along the meandering Laguna estuary, crossing over the Sloughhouse map, and return to the...

27 CFR 9.201 - Sloughhouse.

Code of Federal Regulations, 2013 CFR

2013-04-01

... estuary and Alta Mesa Road, on the western boundary of section 4, T5N, R7E. From the beginning point... Dorado and Sacramento-Amador County line to the County line's intersection with the Laguna estuary, 0.75...) 17.5 miles along the meandering Laguna estuary, crossing over the Sloughhouse map, and return to the...

27 CFR 9.201 - Sloughhouse.

Code of Federal Regulations, 2014 CFR

2014-04-01

... estuary and Alta Mesa Road, on the western boundary of section 4, T5N, R7E. From the beginning point... Dorado and Sacramento-Amador County line to the County line's intersection with the Laguna estuary, 0.75...) 17.5 miles along the meandering Laguna estuary, crossing over the Sloughhouse map, and return to the...

Wind-Forced Modeling Studies of Currents, Meanders, Eddies, and Filaments of the Canary Current System

DTIC Science & Technology

1997-06-01

infra-red images from NOAA7 and NOAA9 and numerous in- situ measurements reveal the existence of a surface poleward flow off the northern coast of...dinamica das Aguas costeiras de Portugal. Dissertacao apresentada a Universidade de Lisboa para obtencao do grau de Doutor em Fisica, especializacao

76 FR 17443 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-29

... original meanders of the former left bank of the Missouri River, downstream through sections 28 and 29, and... of the present left bank of the Missouri River, downstream through a portion of sections 28 and 29, an informative traverse and the limits of erosion, through a portion of section 29, and certain...

43 CFR 2543.4 - Publication and posting.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Publication and posting. 2543.4 Section... Erroneously Meandered Lands: Arkansas § 2543.4 Publication and posting. Upon payment of the appraised price a notice of publication will be issued. Such notice shall be published at the expense of the applicant in a...

77 FR 53905 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2012-09-04

... original meanders of the former left bank of the Missouri River, downstream, through section [[Page 53906... present left bank of the Missouri River, downstream, through sections 29 and 30 and certain division of... final, including decisions or appeals. Authority: 43 U.S.C. Chap. 3. Steve L. Toth, Acting Chief...

Meandering worms: mechanics of undulatory burrowing in muds

PubMed Central

Dorgan, Kelly M.; Law, Chris J.; Rouse, Greg W.

2013-01-01

Recent work has shown that muddy sediments are elastic solids through which animals extend burrows by fracture, whereas non-cohesive granular sands fluidize around some burrowers. These different mechanical responses are reflected in the morphologies and behaviours of their respective inhabitants. However, Armandia brevis, a mud-burrowing opheliid polychaete, lacks an expansible anterior consistent with fracturing mud, and instead uses undulatory movements similar to those of sandfish lizards that fluidize desert sands. Here, we show that A. brevis neither fractures nor fluidizes sediments, but instead uses a third mechanism, plastically rearranging sediment grains to create a burrow. The curvature of the undulating body fits meander geometry used to describe rivers, and changes in curvature driven by muscle contraction are similar for swimming and burrowing worms, indicating that the same gait is used in both sediments and water. Large calculated friction forces for undulatory burrowers suggest that sediment mechanics affect undulatory and peristaltic burrowers differently; undulatory burrowing may be more effective for small worms that live in sediments not compacted or cohesive enough to extend burrows by fracture. PMID:23446526

Field Distribution and Coupling Investigation of an Eight-Channel RF Coil Consisting of Different Dipole Coil Elements for 7 T MRI.

PubMed

Chen, Zhichao; Solbach, Klaus; Erni, Daniel; Rennings, Andreas

2017-06-01

In this contribution, we investigate the [Formula: see text] distribution and coupling characteristics of a multichannel radio frequency (RF) coil consisting of different dipole coil elements for 7 T MRI, and explore the feasibility to achieve a compromise between field distribution and decoupling by combining different coil elements. Two types of dipole elements are considered here: the meander dipole element with a chip-capacitor-based connection to the RF shield which achieves a sufficient decoupling between the neighboring elements; and the open-ended meander dipole element which exhibits a broader magnetic field distribution. By nesting the open-ended dipole elements in between the ones with end-capacitors, the [Formula: see text] distribution, in terms of field penetration depth and homogeneity, is improved in comparison to the dipole coil consisting only of the elements with end-capacitors, and at the same time, the adjacent elements are less coupled to each other in comparison to the dipole coil consisting only of the open-ended elements. The proposed approach is validated by both full-wave simulation and experimental results.

Numerical modeling of gravel bed river response to meander straightening: The coupling between the evolution of bed pavement and long profile

NASA Astrophysics Data System (ADS)

Talbot, Tracey; Lapointe, Michel

2002-06-01

Artificial meander straightening (rectification) was conducted in the early 1960s along the Sainte-Marguerite River, Canada, in order to facilitate highway construction along the valley. Previous studies [Talbot and Lapointe, 2002] confirm that vertical reprofiling, coupled with pavement coarsening in the degrading reach, were the main responses counteracting the disequilibrium in gravel transport rates triggered at rectification of this system. Numerical simulations, using SEDROUT2.0, a one-dimensional hydraulic and sediment transport model, and validated against the observed channel response, show the important role played by an advancing wave of pavement coarsening down the rectified reach in modulating the bed degradation response. Simulations extending into the future reveal an asymptotically slowing approach to equilibrium in the middle of the 21st century, with a response half-time of the order of 10 years. In near-threshold gravel bed systems like the Sainte-Marguerite River, pavement coarsening after rectification buffers the system against extreme degradation. Most significantly for watershed management, this also appears to severely limit the extent of propagation of degradation upstream of the rectification.

Integration of Low-Power ASIC and MEMS Sensors for Monitoring Gastrointestinal Tract Using a Wireless Capsule System.

PubMed

Arefin, Md Shamsul; Redoute, Jean-Michel; Yuce, Mehmet Rasit

2018-01-01

This paper presents a wireless capsule microsystem to detect and monitor the pH, pressure, and temperature of the gastrointestinal tract in real time. This research contributes to the integration of sensors (microfabricated capacitive pH, capacitive pressure, and resistive temperature sensors), frequency modulation and pulse width modulation based interface IC circuits, microcontroller, and transceiver with meandered conformal antenna for the development of a capsule system. The challenges associated with the system miniaturization, higher sensitivity and resolution of sensors, and lower power consumption of interface circuits are addressed. The layout, PCB design, and packaging of a miniaturized wireless capsule, having diameter of 13 mm and length of 28 mm, have successfully been implemented. A data receiver and recorder system is also designed to receive physiological data from the wireless capsule and to send it to a computer for real-time display and recording. Experiments are performed in vitro using a stomach model and minced pork as tissue simulating material. The real-time measurements also validate the suitability of sensors, interface circuits, and meandered antenna for wireless capsule applications.

Methods for monitoring the effects of grazing management on bank erosion and channel morphology, Fever River, Pioneer Farm, Wisconsin, 2004

USGS Publications Warehouse

Peppler, Marie C.; Fitzpatrick, Faith A.

2005-01-01

Bank erosion is a natural process that occurs in meandering streams (Leopold and others, 1964); however, in the Midwestern United States, historical and present agricultural activities in uplands, riparian areas, and channels have increased erosion (Waters, 1995; Lyons and others, 2000; Simon and Rinaldi, 2000; and Knox, 2001). Reducing streambank erosion is important because sediment carried by streams has adverse environmental effects; for example, sediment carried by streams is a major source of phosphorus (Waters, 1995). Continuous cattle grazing in riparian areas may increase local erosion processes in a meandering stream by removal or trampling of bank vegetation, which in turn affects channel morphology, water chemistry, and fish and aquatic-insect habitat (Kauffman and Krueger, 1984; Fitch and Adams, 1998). However, studies of livestock exclusion from riparian corridors have shown mixed results in reducing bank erosion (Trimble, 1994; Sarr, 2002). Some studies have shown reduced bank erosion after row-cropped or continuously grazed riparian areas are converted to managed grazing (see inset box) (Lyons and others, 2000; Sovell and others, 2000; and Zaimes and others, 2004).

Inspecting Friction Stir Welding using Electromagnetic Probes

NASA Technical Reports Server (NTRS)

Kinchen, David G.

2004-01-01

A report describes the use of advanced electromagnetic probes to measure the dimensions, the spatial distribution of electrical conductivity, and related other properties of friction stir welds (FSWs) between parts made of the same or different aluminum alloy(s). The probes are of the type described in in another Tech Brief. To recapitulate: A probe of this type is essentially an eddy-current probe that includes a primary (driver) winding that meanders and multiple secondary (sensing) windings that meander along the primary winding. Electrical conductivity is commonly used as a measure of heat treatment and tempering of aluminum alloys, but prior to the development of these probes, the inadequate sensitivity and limited accuracy of electrical-conductivity probes precluded such use on FSWs between different aluminum alloys, and the resolution of those probes was inadequate for measurement of FSW dimensions with positions and metallurgical properties. In contrast, the present probes afford adequate accuracy and spatial resolution for the purposes of measuring the dimensions of FSW welds and correlating spatially varying electrical conductivities with metallurgical properties, including surface defects.

The effect of chordwise flexibility on flapping foil propulsion in quiescent fluid

NASA Astrophysics Data System (ADS)

Shinde, Sachin; Arakeri, Jaywant

2010-11-01

Motivated to understand the role of wing flexibility of flying creatures during hovering, we experimentally study the effect of chordwise flexibility on the flow generated in quiescent fluid by a sinusoidally pitching rigid symmetrical foil with a flexible flap attached at the trailing edge. This foil produces a narrow, coherent jet containing reverse Karman vortex street, and a corresponding thrust. The thrust and flow is similar to that produced by a hovering bird or insect, however the mechanism seems to be different from known hovering mechanisms. Novelty of the present hovering mechanism is that the thrust generation is due to the coordinated pushing action of rigid foil and flexible flap. We identify the flow and vortex generation mechanism. This foil produces jet flows over a range of flapping frequencies and amplitudes. In contrast, the foil without flap i.e. with rigid trailing edge produces a weak, divergent jet that meanders randomly. Appending a flexible flap to the foil suppresses jet-meandering and strengthens the jet. Flexibility of flap is crucial in determining the flow structure. This study is useful in designing MAVs and thrusters.

Translational Symmetry-Breaking for Spiral Waves

NASA Astrophysics Data System (ADS)

LeBlanc, V. G.; Wulff, C.

2000-10-01

Spiral waves are observed in numerous physical situations, ranging from Belousov-Zhabotinsky (BZ) chemical reactions, to cardiac tissue, to slime-mold aggregates. Mathematical models with Euclidean symmetry have recently been developed to describe the dynamic behavior (for example, meandering) of spiral waves in excitable media. However, no physical experiment is ever infinite in spatial extent, so the Euclidean symmetry is only approximate. Experiments on spiral waves show that inhomogeneities can anchor spirals and that boundary effects (for example, boundary drifting) become very important when the size of the spiral core is comparable to the size of the reacting medium. Spiral anchoring and boundary drifting cannot be explained by the Euclidean model alone. In this paper, we investigate the effects on spiral wave dynamics of breaking the translation symmetry while keeping the rotation symmetry. This is accomplished by introducing a small perturbation in the five-dimensional center bundle equations (describing Hopf bifurcation from one-armed spiral waves) which is SO(2)-equivariant but not equivariant under translations. We then study the effects of this perturbation on rigid spiral rotation, on quasi-periodic meandering and on drifting.

Meandering and material accumulation in the alcove on present day gully evolution

NASA Astrophysics Data System (ADS)

Pasquon, K.; Gargani, J.; Masse, M.; Vincendon, M.; Conway, S. J.; Séjourné, A.

2016-12-01

Since their first observation by Malin and Edgett (2000) [1], martian gullies have been abundantly studied, but their formation mechanism is still under debate [e.g. 2, 3, 4, 5, 6]. Gullies are generally composed of an alcove, a channel and an apron [1, 7] and some of them are active today [8]. Here, we show for the first time active martian meanders. This study was performed using HiRISE images at 25-30 cm/pix and 1 m/pix HiRISE elevation data. We found that this gully has been extremely active over the last 4 martian years. Each year, we observe an accumulation of material in the alcove and then its subsequent mobilisation - causing meander growth, extension of the channel, and growth of the debris apron. Over one martian year the debris apron expanded by almost 150 meters from an initial size of 900 meters. Two different pulses of activity are observed: 1) in the middle of winter when CO2 frost is still present and 2) at the beginning of spring when the seasonal defrosting is coming to an end. This phenomenon is observed on a moderate east-facing slope ( 13°). A correlation between seasonal frost and this gully could be consistent with its development timing. Laboratory experiments have been performed at low pressure to better constrain the potential range of processes involved in such seasonal mobilisation of material on Mars. [1] Malin and Edgett, 2000 Science 288, 2330-2335 ; [2] Costard et al.; 2002. Science 295, 110-113 ; [3] Treiman, 2003. J. Geophys. Res. Planets, 108 (E4), 8031; [4] Heldmann et al., 2005. J. Geophys. Res. Planets, 110 (E5), 004; [5] Hugenholtz et al., 2008. Icarus 197, 65-72 ; [6] Cedillo-Flores et al., 2011. Geophys. Res. Lett. 38, L21202; [7] Harrison et al., 2015. Icarus 252, 236-254; [8] Diniega et al., 2010. Geology 38, 1047-1050.

Evaluating Predictive Uncertainty of Hyporheic Exchange Modelling

NASA Astrophysics Data System (ADS)

Chow, R.; Bennett, J.; Dugge, J.; Wöhling, T.; Nowak, W.

2017-12-01

Hyporheic exchange is the interaction of water between rivers and groundwater, and is difficult to predict. One of the largest contributions to predictive uncertainty for hyporheic fluxes have been attributed to the representation of heterogeneous subsurface properties. This research aims to evaluate which aspect of the subsurface representation - the spatial distribution of hydrofacies or the model for local-scale (within-facies) heterogeneity - most influences the predictive uncertainty. Also, we seek to identify data types that help reduce this uncertainty best. For this investigation, we conduct a modelling study of the Steinlach River meander, in Southwest Germany. The Steinlach River meander is an experimental site established in 2010 to monitor hyporheic exchange at the meander scale. We use HydroGeoSphere, a fully integrated surface water-groundwater model, to model hyporheic exchange and to assess the predictive uncertainty of hyporheic exchange transit times (HETT). A highly parameterized complex model is built and treated as `virtual reality', which is in turn modelled with simpler subsurface parameterization schemes (Figure). Then, we conduct Monte-Carlo simulations with these models to estimate the predictive uncertainty. Results indicate that: Uncertainty in HETT is relatively small for early times and increases with transit times. Uncertainty from local-scale heterogeneity is negligible compared to uncertainty in the hydrofacies distribution. Introducing more data to a poor model structure may reduce predictive variance, but does not reduce predictive bias. Hydraulic head observations alone cannot constrain the uncertainty of HETT, however an estimate of hyporheic exchange flux proves to be more effective at reducing this uncertainty. Figure: Approach for evaluating predictive model uncertainty. A conceptual model is first developed from the field investigations. A complex model (`virtual reality') is then developed based on that conceptual model. This complex model then serves as the basis to compare simpler model structures. Through this approach, predictive uncertainty can be quantified relative to a known reference solution.

Numerical simulation and prediction of coastal ocean circulation

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

Chen, P.

1992-01-01

Numerical simulation and prediction of coastal ocean circulation have been conducted in three cases. 1. A process-oriented modeling study is conducted to study the interaction of a western boundary current (WBC) with coastal water, and its responses to upstream topographic irregularities. It is hypothesized that the interaction of propagating WBC frontal waves and topographic Rossby waves are responsible for upstream variability. 2. A simulation of meanders and eddies in the Norwegian Coastal Current (NCC) for February and March of 1988 is conducted with a newly developed nested dynamic interactive model. The model employs a coarse-grid, large domain to account formore » non-local forcing and a fine-grid nested domain to resolve meanders and eddies. The model is forced by wind stresses, heat fluxes and atmospheric pressure corresponding Feb/March of 1988, and accounts for river/fjord discharges, open ocean inflow and outflow, and M[sub 2] tides. The simulation reproduced fairly well the observed circulation, tides, and salinity features in the North Sea, Norwegian Trench and NCC region in the large domain and fairly realistic meanders and eddies in the NCC in the nested region. 3. A methodology for practical coastal ocean hindcast/forecast is developed, taking advantage of the disparate time scales of various forcing and considering wind to be the dominant factor in affecting density fluctuation in the time scale of 1 to 10 days. The density field obtained from a prognostic simulation is analyzed by the empirical orthogonal function method (EOF), and correlated with the wind; these information are then used to drive a circulation model which excludes the density calculation. The method is applied to hindcast the circulation in the New York Bight for spring and summer season of 1988. The hindcast fields compare favorably with the results obtained from the prognostic circulation model.« less

Scroll-Wave Dynamics in Human Cardiac Tissue: Lessons from a Mathematical Model with Inhomogeneities and Fiber Architecture

PubMed Central

Majumder, Rupamanjari; Nayak, Alok Ranjan; Pandit, Rahul

2011-01-01

Cardiac arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF), are among the leading causes of death in the industrialized world. These are associated with the formation of spiral and scroll waves of electrical activation in cardiac tissue; single spiral and scroll waves are believed to be associated with VT whereas their turbulent analogs are associated with VF. Thus, the study of these waves is an important biophysical problem. We present a systematic study of the combined effects of muscle-fiber rotation and inhomogeneities on scroll-wave dynamics in the TNNP (ten Tusscher Noble Noble Panfilov) model for human cardiac tissue. In particular, we use the three-dimensional TNNP model with fiber rotation and consider both conduction and ionic inhomogeneities. We find that, in addition to displaying a sensitive dependence on the positions, sizes, and types of inhomogeneities, scroll-wave dynamics also depends delicately upon the degree of fiber rotation. We find that the tendency of scroll waves to anchor to cylindrical conduction inhomogeneities increases with the radius of the inhomogeneity. Furthermore, the filament of the scroll wave can exhibit drift or meandering, transmural bending, twisting, and break-up. If the scroll-wave filament exhibits weak meandering, then there is a fine balance between the anchoring of this wave at the inhomogeneity and a disruption of wave-pinning by fiber rotation. If this filament displays strong meandering, then again the anchoring is suppressed by fiber rotation; also, the scroll wave can be eliminated from most of the layers only to be regenerated by a seed wave. Ionic inhomogeneities can also lead to an anchoring of the scroll wave; scroll waves can now enter the region inside an ionic inhomogeneity and can display a coexistence of spatiotemporal chaos and quasi-periodic behavior in different parts of the simulation domain. We discuss the experimental implications of our study. PMID:21483682

Sedimentology of the fluvial and fluvio-marine facies of the Bahariya Formation (Early Cenomanian), Bahariya Oasis, Western Desert, Egypt

NASA Astrophysics Data System (ADS)

Khalifa, M. A.; Catuneanu, O.

2008-05-01

The Lower Cenomanian Bahariya Formation in the Bahariya Oasis, Western Desert, Egypt, was deposited under two coeval environmental conditions. A fully fluvial system occurs in the southern portion of the Bahariya Oasis, including depositional products of meandering and braided streams, and a coeval fluvio-marine setting is dominant to the north. These deposits are organized into four unconformity-bounded depositional sequences, whose architecture is shaped by a complex system of incised valleys. The fluvial portion of the lower two depositional sequences is dominated by low-energy, meandering systems with a tabular geometry, dominated by overbank facies. The fluvial deposits of the upper two sequences represent the product of sedimentation within braided streams, and consist mainly of amalgamated channel-fills. The braided fluvial systems form the fill of incised valleys whose orientation follows a southeast-northwest trending direction, and which truncate the underlying sequences. Four sedimentary facies have been identified within the braided-channel systems, namely thin-laminated sandstones (Sh), cross-bedded sandstones (Sp, St), massive ferruginous sandstones (Sm) and variegated mudstones (Fm). The exposed off-channel overbank facies of the meandering systems include floodplain (Fm) and crevasse splay (Sl) facies. The fluvio-marine depositional systems consist of interbedded floodplain, coastal and shallow-marine deposits. The floodplain facies include fine-grained sandstones (Sf), laminated siltstones (Stf) and mudstones (Mf) that show fining-upward cycles. The coastal to shallow-marine facies consist primarily of mudstones (Mc) and glauconitic sandstones (Gc) organized vertically in coarsening-upward prograding cyclothems topped by thin crusts of ferricrete (Fc). The four depositional sequences are present across the Bahariya Oasis, albeit with varying degrees of preservation related to post-depositional erosion associated with the formation of sequence boundaries. These unconformities may be overlain by braided-stream channel sandstones at the base of incised valleys, or marked by ferricrete paleosols (lithofacies Fc) in the interfluve areas.

Fluvial responses to tectonics and climate change during the Late Weichselian in the eastern part of the Pannonian Basin (Hungary)

NASA Astrophysics Data System (ADS)

Nádor, Annamária; Thamó-Bozsó, Edit; Magyari, Árpád; Babinszki, Edit

2007-11-01

Fine-grained sandy-silty channel-belt and floodplain deposits of the Berettyó-Körös Rivers, a main eastern transverse tributary system of the modern Tisza River in the eastern part of the Pannonian Basin, were deposited during the Late Pleistocene under net subsiding conditions. The palaeo-drainage network pattern of a 2500 km 2 large part of the alluvial plain was reconstructed based on interpretation of airborne photographs and analysis of 18th century topographic maps, which show the natural river patterns that predate the introduction of river regulation schemes. The investigation showed that a large meandering river system, with two main channel belts surrounding a floodbasin, entered the alluvial plain from the northeast, and a braided river entered the alluvial plain from the southeast. Detailed sedimentary logs of seven continuous corings and several sand and clay-pit sections were used to characterize different alluvial units. Optical luminescence dating (OSL) of 25 quartz samples and four 14C datings showed that the sediments are of Late Pleniglacial to Late Glacial age. Transport directions inferred from heavy mineral analyses combined with the OSL ages strongly suggest that the large meandering system represents the palaeo-Tisza River, which supposedly flowed along the northeast-southwest striking Érmellék depression during the Late Pleniglacial. The braided river can be regarded as a precursor to the Fekete and Fehér-Körös Rivers, which entered the alluvial plain from the southeast during the Late Glacial. The interpretation of seismic profiles, field measurements of neotectonic activity, and variations in thickness of sediments along the studied profile revealed that river development was largely controlled by subsidence along the Érmellék depression until 14 to 16 ky, and by uplift of the southeastern part of the catchment area. The studied fluvial successions also document the response of the palaeo-Tisza and Körös system to the climate changes of the Weichselian Late Pleniglacial-Late Glacial period. Much of the sand from the meandering zones was deposited during the Bølling-Allerød and Ságvár-Lascaux interstadials, whereas some dated sand units from the braided zone represent the Older and Younger Dryas. The error ranges of OSL dates, which often exceed the duration of Weichselian substages and subdivisions, prevented an unambiguous correlation of the studied sections with the millennial-scale climate changes of the last 25 ky. Meandering and braided river activity coexisted under different climate conditions, whereas locations of the main channel belts are related to subsidence anomalies. The results of our study thus clearly indicate that tectonics was the primary control on river development.

Detection and monitoring of invasive exotic plants: a comparison of four sampling methods

Treesearch

Cynthia D. Huebner

2007-01-01

The ability to detect and monitor exotic invasive plants is likely to vary depending on the sampling method employed. Methods with strong qualitative thoroughness for species detection often lack the intensity necessary to monitor vegetation change. Four sampling methods (systematic plot, stratified-random plot, modified Whittaker, and timed meander) in hemlock and red...

Hydrogeology and water quality in the Cedar Rapids area, Iowa, 1992-96

USGS Publications Warehouse

Schulmeyer, P.M.; Schnoebelen, D.J.

1998-01-01

Several areas in the Cedar River alluvial aquifer with large iron and manganese concentrations could be related to the original depositional environment of the sediment. In general, large iron and manganese concentrations in ground water are often associated with abundant organic and argillaceous material in sediment near old meander channels and sloughs.

A dynamical systems approach to actin-based motility in Listeria monocytogenes

NASA Astrophysics Data System (ADS)

Hotton, S.

2010-11-01

A simple kinematic model for the trajectories of Listeria monocytogenes is generalized to a dynamical system rich enough to exhibit the resonant Hopf bifurcation structure of excitable media and simple enough to be studied geometrically. It is shown how L. monocytogenes trajectories and meandering spiral waves are organized by the same type of attracting set.

Quantification of shear stress in a meandering native topographic channel using a physical hydraulic model

Treesearch

Michael E. Ursic

2011-01-01

Current guidelines for predicting increases in shear stress in open-channel bends were developed from investigations that were primarily prismatic in cross section. This study provides possible increases in shear stress relative to approach flow conditions resulting from planimetric and topographic geometric features. Boundary shear stress estimates were determined by...

Hydraulic modeling and meander migration of the Middle Rio Grande, New Mexico

Treesearch

Michael J. Sixta

2004-01-01

The dynamic characteristics of the Middle Rio Grande (MRG) in central New Mexico have been of both interest and concern for the regulatory agencies involved with its management. The MRG has experienced sedimentation problems, prompting the development and implementation of sediment detention and flood control features, including the construction of Cochiti Dam in 1973...

Development and testing of a physically based model of streambank erosion for coupling with a basin-scale hydrologic model SWAT

USDA-ARS?s Scientific Manuscript database

A comprehensive stream bank erosion model based on excess shear stress has been developed and incorporated in the hydrological model Soil and Water Assessment Tool (SWAT). It takes into account processes such as weathering, vegetative cover, and channel meanders to adjust critical and effective str...

Methodology for calculating shear stress in a meandering channel

Treesearch

Kyung-Seop Sin; Christopher I. Thornton; Amanda L. Cox; Steven R. Abt

2012-01-01

Natural channels never stop changing their geomorphic characteristics. Natural alluvial streams are similar to living creatures because they generate water flow, develop point bars, alter bed profile, scour the bed, erode the bank, and cause other phenomena in the stream system. The geomorphic changes in a natural system lead to a wide array of research worldwide,...

Riverbed formation

NASA Technical Reports Server (NTRS)

Skinner, M.

1972-01-01

The general fluvial processes that work to form a riverbed and produce the characteristic pattern of either meandering, braided, or straight are reviewed. A method for quantification of river pattern and correlation, with the basic hydraulic characteristics of discharge and slope, is presented. Additional characteristics of a river system may be deduced from high-quality photography and imagery obtained from either aircraft or space platforms.

75 FR 5342 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-02

... 27, the adjusted original meanders of the former left bank of the Missouri River, downstream, through... of the Missouri River, downstream, through sections 21, 22, 23, 24, 25, 26, and 27, the limits of erosion in section 16, the left bank and informative traverse of the left bank of an abandoned channel of...

76 FR 37372 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-27

... Missouri River, downstream, through sections 4, 5, 7, and 8, the subdivision of sections 5, 7, and 8, and the survey of the meanders of the present left bank of the Missouri River and informative traverse, downstream, through sections 4, 5, 7, and 8, the limits of erosion, through a portion of sections 7 and 8...

A multifaceted approach to prioritize and design bank stabilization measures along the Big Sioux River, South Dakota, USA

USDA-ARS?s Scientific Manuscript database

A multifaceted approach was used to manage fine-grained sediment loadings from river bank erosion along the Big Sioux River between Dell Rapids and Sioux Falls, South Dakota, USA. Simulations with the RVR Meander and CONCEPTS river-morphodynamics computer models were conducted to identify stream-ban...

Impacts of non-native plant removal on vertebrates along the Middle Rio Grande (New Mexico)

Treesearch

Heather L. Bateman; Alice Chung-MacCoubrey; Deborah M. Finch; Howard L. Snell; David L. Hawksworth

2008-01-01

The Middle Rio Grande and its riparian forest in central New Mexico are the focus of restoration activities to reverse or lessen negative anthropogenic impacts. The riparian forest is the largest gallery cottonwood (Populus deltoides) forest in the Southwest (Hink and Ohmart 1984). Historically, the river was free to meander across the floodplain,...

A Half-Century of Change on College Hill: Institutional Growth, Historic Preservation, and the College Hill Study

ERIC Educational Resources Information Center

Gast, Frances M.

2011-01-01

One of the epicenters of the historic preservation movement in the United States, the east side of Providence is also home to Brown University and Rhode Island School of Design. Preservation leaders and institutional leaders--sometimes adversaries, sometimes partners--took a meandering path toward the expansive notion of Historic Providence that…

Navigating the Kokosing: A Comparison between Honors and Private Liberal Arts Colleges

ERIC Educational Resources Information Center

Carnicom, Scott

2014-01-01

The Kokosing is a small river, barely a stream after a storm, which meanders its way through the gently undulating hills and farmland of central Ohio. Kenyon College is nestled among the trees atop a hill near the Kokosing. Kenyon is a private, selective, liberal arts college of about 1600 undergraduate students founded by an Episcopal bishop…

Quantification of shear stress in a meandering native topographic channel using a physical hydraulic model

Treesearch

Michael E. Ursic; Christopher I. Thornton; Amanda L. Cox; Steven R. Abt

2012-01-01

Fluvial systems respond to changes in boundary conditions in order to sustain the flow and sediment supplied to the system. Local channel responses are typically difficult to predict due to possible affects from upstream, downstream, or local boundary conditions that cause changes in channel or planform geometry. Changes to the system can threaten riverside...

Maximum outer-bank velocity reduction for vane-dike fields installed in channel bends

Treesearch

S. Michael Scurlock; Amanda L. Cox; Christopher I. Thornton; Drew C. Baird

2011-01-01

Hydraulic conditions associated with channel bends in meandering rivers include secondary, helical currents, mass shift of flow to the outside of the bend, and increased erosion along the outer streambank. Such outer-bank erosion may result in undesired plan-form migration of the stream course, placing valuable land holdings or infrastructure in jeopardy. A type of in-...

KSC-04pd0661

NASA Image and Video Library

2004-03-26

CAPE CANAVERAL, Fla. -- The 525-foot high Vehicle Assembly Building dominates the Launch Complex 39 Area. On the right is the Launch Control Center. To the left are the Orbiter Processing Facility Bays 1, 2 and 3. At lower left is the Operation Support Building at lower right is the construction area for Operations Support Building 2. Behind the VAB meanders the Banana Creek. Photo credit: NASA

Modeling of High Capacity Passive Cooling System

DTIC Science & Technology

2009-03-01

Pulsating Heat Pipes : Closed Loop Pulsating Heat Pipes , which is also known as Meandering Capillary Tube Heat Pipe or Closed Loop Oscillating Heat ... Pipe , has emerged in the recent years as a new electronics cooling technology. The Pulsating Heat Pipe is an innovating technology that has gained...horizontal orientation, the operating temperatures are lower. Pulsating heat pipes are capable of higher heat

THE GAPS BETWEEN AN INTEGRATED UNDERSTANDING OF CHANNELIZATION, HYDROLOGY AND WATER QUALITY VERSUS HOLISTIC FUTURE MANAGEMENT: A CASE STUDY OF THE WILLAMETTE RIVER, OREGON

EPA Science Inventory

Over the last 150 years the main channel of the Willamette River has been drastically altered by human activity. It has changed from a generally meandering and anastamosing river with extensive reaches of broad, active and connected flood plain features to a river with 13 major ...

Soil and water characteristics in restored canebrake and forest riparian zones

Treesearch

Danielle M. Andrews; Christopher D. Barton; Randy Kolka; Charles C. Rhoades; Adam J. Dattilo

2011-01-01

The degradation of streams has been widespread in the United States. In Kentucky, for instance, almost all of its large streams have been impounded or channelized. A restoration project was initiated in a channelized section of Wilson Creek (Nelson Co., Kentucky) to return its predisturbance meandering configuration. A goal of the project was to restore the native...

U.S. Universities Negotiate Tricky Terrain in the Middle East

ERIC Educational Resources Information Center

Mills, Andrew

2008-01-01

A herd of camels meanders through the 115-degree heat as sand billows across the abandoned stretch of desert that once was to be a branch campus of George Mason University. Nearby, alongside the road that leads into the tall sand dunes is a sign that reads: "REDUCE SPEED: MOVING SANDS AHEAD." The sign is intended for motorists, of…

33 CFR 334.640 - Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Bay, Fla.; Air Force rocket firing range. 334.640 Section 334.640 Navigation and Navigable Waters... REGULATIONS § 334.640 Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range. (a) The... meanderings of the shore to the point of beginning. (b) The regulations. (1) The fact that aerial rocket...

33 CFR 334.640 - Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Bay, Fla.; Air Force rocket firing range. 334.640 Section 334.640 Navigation and Navigable Waters... REGULATIONS § 334.640 Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range. (a) The... meanderings of the shore to the point of beginning. (b) The regulations. (1) The fact that aerial rocket...

33 CFR 334.640 - Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Bay, Fla.; Air Force rocket firing range. 334.640 Section 334.640 Navigation and Navigable Waters... REGULATIONS § 334.640 Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range. (a) The... meanderings of the shore to the point of beginning. (b) The regulations. (1) The fact that aerial rocket...

33 CFR 334.640 - Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Bay, Fla.; Air Force rocket firing range. 334.640 Section 334.640 Navigation and Navigable Waters... REGULATIONS § 334.640 Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range. (a) The... meanderings of the shore to the point of beginning. (b) The regulations. (1) The fact that aerial rocket...

33 CFR 334.640 - Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Bay, Fla.; Air Force rocket firing range. 334.640 Section 334.640 Navigation and Navigable Waters... REGULATIONS § 334.640 Gulf of Mexico south of Apalachee Bay, Fla.; Air Force rocket firing range. (a) The... meanderings of the shore to the point of beginning. (b) The regulations. (1) The fact that aerial rocket...

Botanical reconnaissance of The Bowl Research Natural Area.

Treesearch

Lee E. Carbonneau; Sarah D. Allen

1995-01-01

The Bowl Research Natural Area is a 206-ha old-growth forest in the White Mountain National Forest of New Hampshire. Elevations range from approximately 580 m along Wonalancet Brook to 1,215 m at the summit of Mt. Whiteface. Vascular vegetation in four Ecological Land Types (ELT's) of the Bowl was characterized on 12 plots and during qualitative meander surveys....

Harvesting Social Change: A Peace Education Program in Three Acts

ERIC Educational Resources Information Center

Cann, Colette N.

2012-01-01

This article narrates the story of how a peace education program, over the course of a year, shifts from a more traditional form of peace education as conflict resolution skill building to a critical form of peace education. The path of this journey was neither straight nor direct; rather it meandered through an iteration of itself that actually…

77 FR 24513 - Notice of Filing of Plats of Survey; North Dakota

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-24

... the former left and right banks of the Little Missouri River through sections 4, 5, and 6, the subdivision of sections 5 and 6, and the survey of the meanders of the present left and right banks of the... have become final, including decisions or appeals. Authority: 43 U.S.C. Chap. 3. Steve L. Toth, Acting...

76 FR 44946 - Notice of Filing of Plats of Survey; Montana

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-27

... former left bank of the Missouri River, downstream, through sections 21, 29, and 30, the subdivision of sections 21, 28, and 29, and the survey of the meanders of the present left bank of the Missouri River and... informative traverse in sections 28 and 29, the left bank and the medial line of a relicted channel of the...

New Perspectives on Southern Ocean Frontal Variability

NASA Astrophysics Data System (ADS)

Chapman, Christopher

2017-04-01

The frontal structure of the Southern Ocean is investigated using a the Wavelet/Higher Order Statistics Enhancement (WHOSE) frontal detection method, introduced in Chapman (2014). This methodology is applied to 21 years of daily gridded sea-surface height (SSH) data to obtain daily maps of the locations of the fronts. By forming frontal occurrence frequency maps and then approximating these occurrence-maps by a superposition of simple functions, the time-mean locations of the fronts, as well as a measure of their capacity to meander, are obtained and related to the frontal locations found by previous studies. The spatial and temporal variability of the frontal structure is then considered. The number of fronts is found to be highly variable throughout the Southern Ocean, increasing (`splitting') downstream of large bathymetric features and decreasing (`merging') in regions where the fronts are tightly controlled by the underlying topography. In contrast, frontal meandering remains relatively constant. Contrary to many previous studies, little no southward migration of the fronts over the 1993-2014 time period is found, and there is only weak sensitivity to atmospheric forcing related to SAM or ENSO. Finally, the implications of splitting and merging for the flux of tracers will be discussed.

Optimization of an electrokinetic mixer for microfluidic applications.

PubMed

Bockelmann, Hendryk; Heuveline, Vincent; Barz, Dominik P J

2012-06-01

This work is concerned with the investigation of the concentration fields in an electrokinetic micromixer and its optimization in order to achieve high mixing rates. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component, which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house finite-element-method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of the complex flow topology found in simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e., frequency and amplitude, for a given waveform. Two optimized electrical excitations featuring a discrete and a continuous waveform are discussed with respect to characteristic time scales of our mixing problem. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly.

Optimization of an electrokinetic mixer for microfluidic applications

PubMed Central

Bockelmann, Hendryk; Heuveline, Vincent; Barz, Dominik P. J.

2012-01-01

This work is concerned with the investigation of the concentration fields in an electrokinetic micromixer and its optimization in order to achieve high mixing rates. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component, which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house finite-element-method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of the complex flow topology found in simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e., frequency and amplitude, for a given waveform. Two optimized electrical excitations featuring a discrete and a continuous waveform are discussed with respect to characteristic time scales of our mixing problem. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly. PMID:22712034

Somersault of Paramecium in extremely confined environments.

PubMed

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-08-19

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young's modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces.

Somersault of Paramecium in extremely confined environments

PubMed Central

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-01-01

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young’s modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces. PMID:26286234

Somersault of Paramecium in extremely confined environments

NASA Astrophysics Data System (ADS)

Jana, Saikat; Eddins, Aja; Spoon, Corrie; Jung, Sunghwan

2015-08-01

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young’s modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces.

Development of Aluminum LEKIDs for Balloon-Borne Far-IR Spectroscopy

NASA Astrophysics Data System (ADS)

Hailey-Dunsheath, S.; Barlis, A. C. M.; Aguirre, J. E.; Bradford, C. M.; Redford, J. G.; Billings, T. S.; LeDuc, H. G.; McKenney, C. M.; Hollister, M. I.

2018-04-01

We are developing lumped-element kinetic inductance detectors (LEKIDs) designed to achieve background-limited sensitivity for far-infrared (FIR) spectroscopy on a stratospheric balloon. The spectroscopic terahertz airborne receiver for far-infrared exploration will study the evolution of dusty galaxies with observations of the [CII] 158 μm and other atomic fine-structure transitions at z=0.5 -1.5, both through direct observations of individual luminous infrared galaxies, and in blind surveys using the technique of line intensity mapping. The spectrometer will require large format (˜ 1800 detectors) arrays of dual-polarization sensitive detectors with NEPs of 1 × 10^{-17} W Hz^{-1/2} . The low-volume LEKIDs are fabricated with a single layer of aluminum (20-nm-thick) deposited on a crystalline silicon wafer, with resonance frequencies of 100-250 MHz. The inductor is a single meander with a linewidth of 0.4 μm , patterned in a grid to absorb optical power in both polarizations. The meander is coupled to a circular waveguide, fed by a conical feedhorn. Initial testing of a small array prototype has demonstrated good yield and a median NEP of 4 × 10^{-18} W Hz^{-1/2}.

Hub vortex helical instability as the origin of wake meandering in the lee of a model wind-turbine

NASA Astrophysics Data System (ADS)

Viola, Francesco; Iungo, Giacomo Valerio; Camarri, Simone; Porte-Agel, Fernando; Gallaire, Francois

2012-11-01

Wind tunnel measurements were performed for the wake produced by a three-bladed wind turbine immersed in uniform flow. These tests show the presence of a vorticity structure in the near wake region mainly oriented along the streamwise direction, which is denoted as hub vortex. The hub vortex is characterized by oscillations with frequencies lower than the one connected to the rotational velocity of the rotor, which are ascribed to wake meandering by previous works. This phenomenon consists in transversal oscillations of the wind turbine wake, which are excited by the shedding of vorticity structures from the rotor disc acting as a bluff body. In this work temporal and spatial linear stability analyses of a wind turbine wake are performed on a base flow obtained through time-averaged wind tunnel velocity measurements. This study shows that the low frequency spectral component detected experimentally is the result of a convective instability of the hub vortex, which is characterized by a counter-winding single-helix structure. Simultaneous hot-wire measurements confirm the presence of a helicoidal unstable mode of the hub vortex with a streamwise wavenumber roughly equal to the one predicted from the linear instability analysis.

Denitrification in the Mississippi River network controlled by flow through river bedforms

USGS Publications Warehouse

Gomez-Velez, Jesus D.; Harvey, Judson W.; Cardenas, M. Bayani; Kiel, Brian

2015-01-01

Increasing nitrogen concentrations in the world’s major rivers have led to over-fertilization of sensitive downstream waters. Flow through channel bed and bank sediments acts to remove riverine nitrogen through microbe-mediated denitrification reactions. However, little is understood about where in the channel network this biophysical process is most efficient, why certain channels are more effective nitrogen reactors, and how management practices can enhance the removal of nitrogen in regions where water circulates through sediment and mixes with groundwater - hyporheic zones. Here we present numerical simulations of hyporheic flow and denitrification throughout the Mississippi River network using a hydrogeomorphic model. We find that vertical exchange with sediments beneath the riverbed in hyporheic zones, driven by submerged bedforms, has denitrification potential that far exceeds lateral hyporheic exchange with sediments alongside river channels, driven by river bars and meandering banks. We propose that geomorphic differences along river corridors can explain why denitrification efficiency varies between basins in the Mississippi River network. Our findings suggest that promoting the development of permeable bedforms at the streambed - and thus vertical hyporheic exchange - would be more effective at enhancing river denitrification in large river basins than promoting lateral exchange through induced channel meandering.

Refernce Conditions for Streams in the Grand Prairie Natural Division of Illinois

NASA Astrophysics Data System (ADS)

Sangunett, B.; Dewalt, R.

2005-05-01

As part of the Critical Trends Assessment Program (CTAP) of the Illinois Department of Natural Resources (IDNR), 12 potential reference quality stream sites in the Grand Prairie Natural Division were evaluated in May 2004. This agriculturally dominated region, located in east central Illinois, is the most highly modified in the state. The quality of these sites was assessed using a modified Hilsenhoff Biotic Index and species richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) insect orders and a 12 parameter Habitat Quality Index (HQI). Illinois EPA high quality fish stations, Illinois Natural History Survey insect collection data, and best professional knowledge were used to choose which streams to evaluate. For analysis, reference quality streams were compared to 37 randomly selected meandering streams and 26 randomly selected channelized streams which were assessed by CTAP between 1997 and 2001. The results showed that the reference streams exceeded both taxa richness and habitat quality of randomly selected streams in the region. Both random meandering sites and reference quality sites increased in taxa richness and HQI as stream width increased. Randomly selected channelized streams had about the same taxa richness and HQI regardless of width.

Analysing the meandering rivers responses to the slope-changes, depending on their bankfull discharge - Case study in the Pannonian Basin

NASA Astrophysics Data System (ADS)

Petrovszki, Judit; Timár, Gábor; Molnár, Gábor

2014-05-01

The multi-variable connection between the channel slope, bankfull discharge and sinuosity values were analysed to get a mathematical formula, which describes the responses of the rivers, and gives the probable sinuosity values for every slope and discharge values. Timár (2003) merged two planar diagrams into a quasi 3D graph. One of them displayed how the river pattern changes, according to the slope and bankfull discharge values (Leopold and Wolmann, 1957; Ackers and Charlton, 1971); the other based on flume experiments, and gives a connection between the slope and sinuosity (Schumm and Khan, 1972). The result graph suggests that the slope-sinuosity connection also works along the natural rivers, for every discharge values. The aim of this work was to prove this relation, and describe it numerically. The sinuosity values were calculated along the natural, meandering river beds, using historical maps (2nd Military Survey of the Habsburg Empire, from the 19th century). The available slope and discharge values were imported from a database measured after the main river control works, at the beginning of the 20th century (Viczián, 1905). Analysing the reports of the river control works, the natural slope could be computed for every river sections. The mean discharges were also converted to bankfull discharges. Neither long time series, nor cross sectional areas were obtainable, so other method was used to generate the bankfull discharge. After the above mentioned corrections a quadratic polynomial surface was fitted onto these points with least squares regression. The cross section of this surface follows the theoretical slope-sinuosity graph, verifying that the flume experiments and natural rivers behave similarly. The differences between the fitted surface and the original points were caused by other river parameters, which also affect the natural rivers (e.g. the sediment discharge). Furthermore, this graph confirms the connection between the slope and sinuosity, so the sinuosity is a useable parameter to detect the changing slope. The research is made in the frame of project OTKA-NK83400 (SourceSink Hungary). The European Union and the European Social Fund also have provided financial support to the project under the grant agreement no. TÁMOP 4.2.1./B-09/1/KMR-2010-0003. References: Ackers, P., Charlton, F. G. (1971): The slope and resistance of small meandering channels. Inst. Civil Engineers Proc. Supp. XV, Paper 73625. Leopold, L. B., Wolman, M. G. (1957): River chanel patterns; braided, meandering and straight. USGS Prof. Paper 282B: 1-73. Schumm, S. A., Khan, H. R. (1972): Experimental study of channel patterns. Geol. Soc. Am. Bull. 83:1755-1770. Timár, G. (2003): Controls on channel sinuosity changes: a case study of the Tisza River, the Great Hungarian Plain. Quaternary Science Reviews 22: 2199-2207. Viczián E. (1905): Magyarország vízierői. Pallas, Budapest, 349 o.

The Importance of Precise Digital Elevation Models (DEM) in Modelling Floods

NASA Astrophysics Data System (ADS)

Demir, Gokben; Akyurek, Zuhal

2016-04-01

Digital elevation Models (DEM) are important inputs for topography for the accurate modelling of floodplain hydrodynamics. Floodplains have a key role as natural retarding pools which attenuate flood waves and suppress flood peaks. GPS, LIDAR and bathymetric surveys are well known surveying methods to acquire topographic data. It is not only time consuming and expensive to obtain topographic data through surveying but also sometimes impossible for remote areas. In this study it is aimed to present the importance of accurate modelling of topography for flood modelling. The flood modelling for Samsun-Terme in Blacksea region of Turkey is done. One of the DEM is obtained from the point observations retrieved from 1/5000 scaled orthophotos and 1/1000 scaled point elevation data from field surveys at x-sections. The river banks are corrected by using the orthophotos and elevation values. This DEM is named as scaled DEM. The other DEM is obtained from bathymetric surveys. 296 538 number of points and the left/right bank slopes were used to construct the DEM having 1 m spatial resolution and this DEM is named as base DEM. Two DEMs were compared by using 27 x-sections. The maximum difference at thalweg of the river bed is 2m and the minimum difference is 20 cm between two DEMs. The channel conveyance capacity in base DEM is larger than the one in scaled DEM and floodplain is modelled in detail in base DEM. MIKE21 with flexible grid is used in 2- dimensional shallow water flow modelling. The model by using two DEMs were calibrated for a flood event (July 9, 2012). The roughness is considered as the calibration parameter. From comparison of input hydrograph at the upstream of the river and output hydrograph at the downstream of the river, the attenuation is obtained as 91% and 84% for the base DEM and scaled DEM, respectively. The time lag in hydrographs does not show any difference for two DEMs and it is obtained as 3 hours. Maximum flood extents differ for the two DEMs, larger flooded area is simulated from scaled DEM. The main difference is observed for the braided and meandering parts of the river. For the meandering part of the river, additional 1.82 106 m3 water (5% of the total volume) is calculated as the flooded volume simulated by using the scaled DEM. For the braided stream part 0.187 106 m3 more water is simulated as the flooded volume by the scaled DEM. The flood extent around the braided part of the river is 27.6 ha larger in the simulated flood map obtained from scaled DEM compared to the one obtained from base DEM. Around the meandering part of the river scaled DEM gave 59.8 ha more flooded area. The importance of correct topography of the braided and meandering part of the river in flood modelling and the uncertainty it brings to modelling are discussed in detail.

Joint Observational Research on Nocturnal Atmospheric Dispersion of Aerosols (JORNADA)

DTIC Science & Technology

2009-02-01

physical processes in NBL . Research Progress: July 2008-January 2009 Objective 1. Analysis of the Stationarity of Mesoscale Turbulence in the...data allows for a more complete understanding of the nocturnal boundary layer ( NBL ). We have analyzed lidar measurements of plume meander and...dispersion and their relationship to the complexities of NBL structure. Plume Dispersion: Vertical plume dispersion parameters (σz) were derived

Cultural Resources Survey at Selected Locations, Table Rock Lake, Missouri and Arkansas,

DTIC Science & Technology

1986-12-01

terrace along the river banks, and this alluvial material interfingers with fine-grained colluvium (redeposited loess) and cherty residuum washed fran...by block nhstber) Archaic Period Interfluve Meander Core Rice Complex Bluff Shelter James River Complex Mississippian Sprfld Plteu Cultural Resource...Invt Jefferson City Chert Osage Table Rock Lake Dalton Kings River Ozark Highlands White River Geomorphology Long Creek Paleo-Indian Basin 20

77 FR 32979 - Notice of Filing of Plats of Survey; North Dakota

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-04

... Little Missouri River, through sections 3, 4, 9, 10, 15, 21, 22, 28, and 33, the subdivision of certain sections, and the survey of the meanders of the present left and right banks of the Little Missouri River, through sections 3, 4, 9, 10, 15, 21, 22, 27, 28, and 33, the limits of erosion in sections 3, 4, 9, 15...

Processes Leading to Beaded Channels Formation in Central Yakutia

NASA Astrophysics Data System (ADS)

Tarbeeva, A. M.; Lebedeva, L.; Efremov, V. S.; Krylenko, I. V.; Surkov, V. V.

2017-12-01

Beaded channels, consisting of deepened and widened pools and connecting narrow runs, are common fluvial forms in permafrost regions. Recent studies have shown that beaded channels are very important for connecting alluvial rivers with headwater lakes allowing fish passage and foraging habitats, as well as regulating river runoff. Beaded channels are known as typical thermokarst landforms; however, there is no evidence of their origin and formative processes. Geomorphological analyzes of beaded channels have been completed in several permafrost regions including field observations of Shestakovka River in Central Yakutia. The study aims to recognize the modern exogenic processes and formative mechanisms of beaded river channels. We show that beaded channel of Shestakovka River form in the perennially frozen sand with low ice content, leading us to hypothesize that thermokarst is not the main process of formation. Due to the significant volume of water, the pools don't freeze over entirely during winters, even under harsh climatic conditions. As a result, lenses of pressurized water remain under surface ice underlain by perennially thawed sediments. The presence of thawed sediments under the pools and frozen sediments under the runs leads to uneven thermoerosion of the riverbed during floods, providing the beaded form of the channel. In addition, freezing of pools during winter leads to pressure increasing under ice cover and formation of ice mounds, which crack several times during winter leading to disturbance of riverbanks. Many 1st to 3rd order streams have a specific transitional meandering-to-beaded form resembling the shape of unconfined meandering rivers, but consisting of pools and runs. However, such channels exhibit no evidences of present-day erosion of concave banks and sediment accumulation at the convex banks as typically being observed in normally meandering rivers. Such forms of channels indicates that their formation occurred by the greater channel-forming flow discharges in the past. Transition to the beaded channel planform took place only later, presumably as a result of climate changes. Reduction of water runoff and freezing over of taliks leaded to activation of cryogenic processes (thermokarst, uneven thermoerosion, disturbance of riverbanks during the cracking of ice mounds).

Link between Neogene and modern sedimentary environments in the Zagros foreland basin

NASA Astrophysics Data System (ADS)

Pirouz, Mortaza; Simpson, Guy; Bahroudi, Abbas

2010-05-01

The Zagros mountain belt, with a length of 1800 km, is located in the south of Iran and was produced by collision between the Arabian plate and the Iran micro plate some time in the early Tertiary. After collision, the Zagros carbonate-dominated sedimentary basin has been replaced by a largely clastic system. The Neogene Zagros foreland basin comprises four main depositional environments which reflect the progressive southward migration of the deformation front with time. The oldest unit - the Gachsaran formation - is clastic in the northern part of the basin, but is dominated by evaporates in southern part, being deposited in a supratidal Sabkha-type environment. Overlying the Gachsaran is the Mishan formation, which is characterized by the Guri limestone member at the base, overlain by marine green marls. The thickness of the Guri member increases dramatically towards the southeast. The next youngest unit is the Aghajari Formation which consists of well sorted lenticular sandstone bodies in a red silty-mudstone. This formation is interpreted as representing the floodplain of dominantly meandering rivers. Finally, the Bakhtiari formation consists of mainly coarse-grained gravel sheets which are interpreted to represent braided river deposits. Each of these Neogene depositional environments has a modern day equivalent. For example, the braided rivers presently active in the Zagros mountains are modern analogues of the Bakhtiari. In the downstream direction, these braided rivers become meandering systems, which are equivalents of the Aghajari. Eventually, the meandering rivers meet the Persian gulf which is the site of the ‘modern day' Mishan shallow marine marls. Finally, the modern carbonate system on the southern margin of Persian Gulf represents the Guri member paleo-environment, behind which Sabkha-type deposits similar to the Gachsaran are presently being deposited. One important implication of this link between the Neogene foreland basin deposits and the modern environments is that all formation boundaries are strongly diachronous. Thus, for example, although the Mishan is Burdigalian-Messinian in regions where it is currently undergoing subaerial erosion in the Fars zone, it is presumably still forming today in the modern Persian gulf foredeep.

Refining fault slip rates using multiple displaced terrace risers-An example from the Honey Lake fault, NE California, USA

NASA Astrophysics Data System (ADS)

Gold, Ryan D.; Briggs, Richard W.; Crone, Anthony J.; DuRoss, Christopher B.

2017-11-01

Faulted terrace risers are semi-planar features commonly used to constrain Quaternary slip rates along strike-slip faults. These landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces. However, substantial differences in the ages of the upper and lower terrace surfaces (a factor of 2.4 difference observed globally) produce large uncertainties in the slip-rate estimate. In this investigation, we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate. We use 0.25-m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right-laterally by the Honey Lake fault in NE California, USA. We use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation: an upper surface is the bed of abandoned Lake Lahontan having an age of 15.8 ± 0.6 ka and a lower surface is a fluvial terrace abandoned at 4.7 ± 0.1 ka. We estimate lateral offsets of the risers ranging between 6.6 and 28.3 m (median values), a greater than fourfold difference in values. The amount of offset corresponds to the riser's position relative to modern stream meanders: the smallest offset is in a meander cutbank position, whereas the larger offsets are in straight channel or meander point-bar positions. Taken in isolation, the individual terrace-riser offsets yield slip rates ranging from 0.3 to 7.1 mm/a. However, when the offset values are collectively assessed in a probabilistic framework, we find that a uniform (linear) slip rate of 1.6 mm/a (1.4-1.9 mm/a at 95% confidence) can satisfy the data, within their respective uncertainties. This investigation demonstrates that integrating observations of multiple offset elements (crest, midpoint, and base) from numerous faulted and dated terrace risers at closely spaced sites can refine slip-rate estimates on strike-slip faults.

Dynamics of floodplain lakes in the Upper Amazon Basin during the late Holocene

NASA Astrophysics Data System (ADS)

Quintana-Cobo, Isabel; Moreira-Turcq, Patricia; Cordeiro, Renato C.; Aniceto, Keila; Crave, Alain; Fraizy, Pascal; Moreira, Luciane S.; Duarte Contrera, Julia Maria de Aguiar; Turcq, Bruno

2018-01-01

To better understand the impact of channel migration processes and climate change on the depositional dynamics of floodplain lakes of the upper Amazon Basin during the late Holocene, we collected three sediment cores from floodplain lakes of the Ucayali River and one from the Marañón River. The cores were dated with 14C, radiographed and described. Bulk density, grain size analysis and total organic carbon (TOC) were determined. The results show that sedimentation in Ucayali floodplain lakes was marked by variations during the late Holocene, with periods of intense hydrodynamic energy and abrupt accumulations, a gap in the record between about 2870 and 690 cal yr BP, and periods of more lacustrine conditions. These changes in sedimentation were associated with variations in the river's influence related to changes in its meandering course (2870 cal yr BP) and a period of severe flooding between 3550 and 3000 cal yr BP. Lake Lagarto on the Marañón River floodplain exhibits a different sedimentary environment of low hydrodynamics with palm trees and macrophytes. Apparently, the lake has not experienced intense migration processes during the last 600 cal yr BP (base of the core). Nevertheless, the river sediment flux to the lake was important from 600 to 500 cal yr BP, although it decreased thereafter until the present. This decrease in the mineral accumulation rate indicates a decrease in river discharge since 500 cal yr BP, which coincides with precipitation records from the central Andes. In the upper part of the three Ucayali floodplain cores, a 30- to 250-cm-thick layer of reworked sediments has been deposited since 1950 AD (post-bomb). In Lake Carmen, this layer is associated with invasion of the lake by the levee of a migrating meander of the Ucayali. In Lakes Hubos and La Moringa, however, the river is still far away and the deposition must be interpreted as the result of extreme flooding. The beginning of the Ucayali meander migration is dated back to 2000 AD, suggesting that these extreme floods could be very recent and linked to hydrologic extremes registered instrumentally in the Amazon Basin.

Refining fault slip rates using multiple displaced terrace risers—An example from the Honey Lake fault, NE California, USA

USGS Publications Warehouse

Gold, Ryan D.; Briggs, Richard; Crone, Anthony J.; Duross, Christopher

2017-01-01

Faulted terrace risers are semi-planar features commonly used to constrain Quaternary slip rates along strike-slip faults. These landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces. However, substantial differences in the ages of the upper and lower terrace surfaces (a factor of 2.4 difference observed globally) produce large uncertainties in the slip-rate estimate. In this investigation, we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate. We use 0.25-m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right-laterally by the Honey Lake fault in NE California, USA. We use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation: an upper surface is the bed of abandoned Lake Lahontan having an age of 15.8 ± 0.6 ka and a lower surface is a fluvial terrace abandoned at 4.7 ± 0.1 ka. We estimate lateral offsets of the risers ranging between 6.6 and 28.3 m (median values), a greater than fourfold difference in values. The amount of offset corresponds to the riser's position relative to modern stream meanders: the smallest offset is in a meander cutbank position, whereas the larger offsets are in straight channel or meander point-bar positions. Taken in isolation, the individual terrace-riser offsets yield slip rates ranging from 0.3 to 7.1 mm/a. However, when the offset values are collectively assessed in a probabilistic framework, we find that a uniform (linear) slip rate of 1.6 mm/a (1.4–1.9 mm/a at 95% confidence) can satisfy the data, within their respective uncertainties. This investigation demonstrates that integrating observations of multiple offset elements (crest, midpoint, and base) from numerous faulted and dated terrace risers at closely spaced sites can refine slip-rate estimates on strike-slip faults.

Variational Data Assimilation for the Global Ocean

DTIC Science & Technology

2013-01-01

ocean includes the Geoid (a fixed gravity equipotential surface ) as well as the MDT, which is not known accurately enough relative to the centimeter...scales, including processes that control the surface mixed layer, the formation of ocean eddies, meandering ocean J.A. Cummings (E3) nography Division...variables. Examples of this in the ocean are integral quantities, such as acous^B travel time and altimeter measures of sea surface height, and direct

What is Required to Model the Global Ocean Circulation?

DTIC Science & Technology

2011-01-01

eddy kinetic energy (EKE) in the upper-ocean, encompassed by mesoscale eddies, meanders and rings of the boundary currents [ Stammer , 1997; Ferrari...Resolution studies [Bryan, et al., 2007 ; Smith, et al., 2000; Hogan and Hurlburt, 2000; Oschlies, 2002] show that increasing the horizontal resolution...energy estimates from surface drifter observations [Lumpkin and Pazos, 2007 ], satellite altimetry (150 m) [Ducet, et al., 2000], ARGO floats at 1,000

Spaceborne Microwave Imagers

NASA Technical Reports Server (NTRS)

Stacey, J. M.

1991-01-01

Monograph presents comprehensive overview of science and technology of spaceborne microwave-imaging systems. Microwave images used as versatile orbiting, remote-sensing systems to investigate atmospheres and surfaces of planets. Detect surface objects through canopies of clouds, measure distributions of raindrops in clouds that their views penetrate, find meandering rivers in rain forests and underground water in arid regions, and provide information on ocean currents, wakes, ice/water boundaries, aircraft, ships, buoys, and bridges.

Imaging and locating paleo-channels using geophysical data from meandering system of the Mun River, Khorat Plateau, Northeastern Thailand

NASA Astrophysics Data System (ADS)

Nimnate, P.; Thitimakorn, T.; Choowong, M.; Hisada, K.

2017-12-01

The Khorat Plateau from northeast Thailand, the upstream part of the Mun River flows through clastic sedimentary rocks. A massive amount of sand was transported. We aimed to understand the evolution of fluvial system and to discuss the advantages of two shallow geophysical methods for describing subsurface morphology of modern and paleo-channels. We applied Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to characterize the lateral, vertical morphological and sedimentary structures of paleo-channels, floodplain and recent point bars. Both methods were interpreted together with on-sites boreholes to describe the physical properties of subsurface sediments. As a result, we concluded that four radar reflection patterns including reflection free, shingled, inclined and hummocky reflections were appropriated to apply as criteria to characterize lateral accretion, the meandering rivers with channel-filled sequence and floodplain were detected from ERT profiles. The changes in resistivity correspond well with differences in particle size and show relationship with ERT lithological classes. Clay, silt, sand, loam and bedrock were classified by the resistivity data. Geometry of paleo-channel embayment and lithological differences can be detected by ERT, whereas GPR provides detail subsurface facies for describing point bar sand deposit better than ERT.

Unravelling the Drivers of Chute Cutoff and the Commonality of Oxbow Production

NASA Astrophysics Data System (ADS)

Constantine, J. A.; Edmonds, D. A.; David, S.

2017-12-01

Chute cutoff is the principal means of channel shortening along steep, sparsely vegetated, or perturbed meandering river floodplains. Although flood waters are capable of unravelling the floodplain in a variety of ways, only a small number of mechanisms of chute cutoff have been observed in nature, each with seemingly different controls on their occurrence. The complexity of these controls partly explains the difficulty of deterministically incorporating chute cutoff into channel evolution models. Despite the challenges, recent field observations have allowed us not only to identify particular mechanisms but also to highlight first-order controls. We provide a summary of these findings and describe the processes that drive the various mechanisms of cutoff and their resulting oxbow lakes. For example, many agricultural floodplains show evidence of pervasive gully incision as a precursor to chute cutoff. And perhaps surprising given the diversity of cutoff mechanisms, oxbows globally share characteristic dimensions that are a function of the sinuosity and width of the rivers from which they are derived. Our results suggest that, in spite of the many processes involved, aspects of the mechanisms of chute cutoff can be generalised, providing a means for improving cutoff prediction and for assessing the impacts of cutoffs on the meandering river floodplain.

Rotor termination is critically dependent on kinetic properties of I kur inhibitors in an in silico model of chronic atrial fibrillation.

PubMed

Scholz, Eberhard P; Carrillo-Bustamante, Paola; Fischer, Fathima; Wilhelms, Mathias; Zitron, Edgar; Dössel, Olaf; Katus, Hugo A; Seemann, Gunnar

2013-01-01

Inhibition of the atrial ultra-rapid delayed rectifier potassium current (I Kur) represents a promising therapeutic strategy in the therapy of atrial fibrillation. However, experimental and clinical data on the antiarrhythmic efficacy remain controversial. We tested the hypothesis that antiarrhythmic effects of I Kur inhibitors are dependent on kinetic properties of channel blockade. A mathematical description of I Kur blockade was introduced into Courtemanche-Ramirez-Nattel models of normal and remodeled atrial electrophysiology. Effects of five model compounds with different kinetic properties were analyzed. Although a reduction of dominant frequencies could be observed in two dimensional tissue simulations for all compounds, a reduction of spiral wave activity could be only be detected in two cases. We found that an increase of the percent area of refractory tissue due to a prolongation of the wavelength seems to be particularly important. By automatic tracking of spiral tip movement we find that increased refractoriness resulted in rotor extinction caused by an increased spiral-tip meandering. We show that antiarrhythmic effects of I Kur inhibitors are dependent on kinetic properties of blockade. We find that an increase of the percent area of refractory tissue is the underlying mechanism for an increased spiral-tip meandering, resulting in the extinction of re-entrant circuits.

Rotor Termination Is Critically Dependent on Kinetic Properties of I Kur Inhibitors in an In Silico Model of Chronic Atrial Fibrillation

PubMed Central

Scholz, Eberhard P.; Carrillo-Bustamante, Paola; Fischer, Fathima; Wilhelms, Mathias; Zitron, Edgar; Dössel, Olaf; Katus, Hugo A.; Seemann, Gunnar

2013-01-01

Inhibition of the atrial ultra-rapid delayed rectifier potassium current (I Kur) represents a promising therapeutic strategy in the therapy of atrial fibrillation. However, experimental and clinical data on the antiarrhythmic efficacy remain controversial. We tested the hypothesis that antiarrhythmic effects of I Kur inhibitors are dependent on kinetic properties of channel blockade. A mathematical description of I Kur blockade was introduced into Courtemanche-Ramirez-Nattel models of normal and remodeled atrial electrophysiology. Effects of five model compounds with different kinetic properties were analyzed. Although a reduction of dominant frequencies could be observed in two dimensional tissue simulations for all compounds, a reduction of spiral wave activity could be only be detected in two cases. We found that an increase of the percent area of refractory tissue due to a prolongation of the wavelength seems to be particularly important. By automatic tracking of spiral tip movement we find that increased refractoriness resulted in rotor extinction caused by an increased spiral-tip meandering. We show that antiarrhythmic effects of I Kur inhibitors are dependent on kinetic properties of blockade. We find that an increase of the percent area of refractory tissue is the underlying mechanism for an increased spiral-tip meandering, resulting in the extinction of re-entrant circuits. PMID:24376659

A Planar Microfluidic Mixer Based on Logarithmic Spirals

PubMed Central

Scherr, Thomas; Quitadamo, Christian; Tesvich, Preston; Park, Daniel Sang-Won; Tiersch, Terrence; Hayes, Daniel; Choi, Jin-Woo; Nandakumar, Krishnaswamy

2013-01-01

A passive, planar micromixer design based on logarithmic spirals is presented. The device was fabricated using polydimethylsiloxane soft photolithography techniques, and mixing performance was characterized via numerical simulation and fluorescent microscopy. Mixing efficiency initially declined as Reynolds number increased, and this trend continued until a Reynolds number of 15 where a minimum was reached at 53%. Mixing efficiency then began to increase reaching a maximum mixing efficiency of 86% at Re = 67. Three-dimensional simulations of fluid mixing in this design were compared to other planar geometries such as the Archimedes spiral and Meandering-S mixers. The implementation of logarithmic curvature offers several unique advantages that enhance mixing, namely a variable cross-sectional area and a logarithmically varying radius of curvature that creates 3-D Dean vortices. These flow phenomena were observed in simulations with multilayered fluid folding and validated with confocal microscopy. This design provides improved mixing performance over a broader range of Reynolds numbers than other reported planar mixers, all while avoiding external force fields, more complicated fabrication processes, and the introduction of flow obstructions or cavities that may unintentionally affect sensitive or particulate-containing samples. Due to the planar design requiring only single-step lithographic features, this compact geometry could be easily implemented into existing micro-total analysis systems requiring effective rapid mixing. PMID:23956497

A planar microfluidic mixer based on logarithmic spirals

NASA Astrophysics Data System (ADS)

Scherr, Thomas; Quitadamo, Christian; Tesvich, Preston; Sang-Won Park, Daniel; Tiersch, Terrence; Hayes, Daniel; Choi, Jin-Woo; Nandakumar, Krishnaswamy; Monroe, W. Todd

2012-05-01

A passive, planar micromixer design based on logarithmic spirals is presented. The device was fabricated using polydimethylsiloxane soft photolithography techniques, and mixing performance was characterized via numerical simulation and fluorescent microscopy. Mixing efficiency initially declined as the Reynolds number increased, and this trend continued until a Reynolds number of 15 where a minimum was reached at 53%. Mixing efficiency then began to increase reaching a maximum mixing efficiency of 86% at Re = 67. Three-dimensional (3D) simulations of fluid mixing in this design were compared to other planar geometries such as the Archimedes spiral and Meandering-S mixers. The implementation of logarithmic curvature offers several unique advantages that enhance mixing, namely a variable cross-sectional area and a logarithmically varying radius of curvature that creates 3D Dean vortices. These flow phenomena were observed in simulations with multilayered fluid folding and validated with confocal microscopy. This design provides improved mixing performance over a broader range of Reynolds numbers than other reported planar mixers, all while avoiding external force fields, more complicated fabrication processes and the introduction of flow obstructions or cavities that may unintentionally affect sensitive or particulate-containing samples. Due to the planar design requiring only single-step lithographic features, this compact geometry could be easily implemented into existing micro-total analysis systems requiring effective rapid mixing.

The potential for dams to impact lowland meandering river floodplain geomorphology.

PubMed

Marren, Philip M; Grove, James R; Webb, J Angus; Stewardson, Michael J

2014-01-01

The majority of the world's floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We review studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, and interactions with floodplain vegetation. The results are synthesized into a conceptual model of the effects of dams on the major geomorphic influences on floodplain development. This model is used to assess the likely consequences of eight dam and flow regulation scenarios for floodplain geomorphology. Sediment starvation downstream of dams has perhaps the greatest potential to impact on floodplain development. Such effects will persist further downstream where tributary sediment inputs are relatively low and there is minimal buffering by alluvial sediment stores. We can identify several ways in which floodplains might potentially be affected by dams, with varying degrees of confidence, including a distinction between passive impacts (floodplain disconnection) and active impacts (changes in geomorphological processes and functioning). These active processes are likely to have more serious implications for floodplain function and emphasize both the need for future research and the need for an "environmental sediment regime" to operate alongside environmental flows.

Characteristics of Helical Flow through Neck Cutoffs

NASA Astrophysics Data System (ADS)

Richards, D.; Konsoer, K. M.; Turnipseed, C.; Willson, C. S.

2017-12-01

Meander cutoffs and oxbows lakes are a ubiquitous feature of riverine landscapes yet there is a paucity of detailed investigations concentrated on the three-dimensional flow structure through evolving neck cutoffs. The purpose of this research is to investigate and characterize helical flow through neck cutoffs with two different planform configurations: elongate meander loops and serpentine loops. Three-dimensional velocity measurements was collected with an acoustic Doppler current profiler for five cutoffs on the White River, Arkansas. Pronounced helical flow was found through all elongate loop cutoff sites, formed from the balance between centrifugal force resulting from the curving of flow through the cutoff channel and pressure gradient force resulting from water surface super-elevation between primary flow and flow at the entrance and exit of the abandoned loop. The sense of motion of the helical flow caused near-surface fluid to travel outward toward the abandoned loop while near-bed fluid was redirected toward the downstream channel. Another characteristic of the helical flow structure for elongate loop cutoffs was the reversal of helical flow over a relatively short distance, causing patterns of secondary circulation that differed from typical patterns observed through curved channels with point bars. Lastly, helical flow was revealed within zones of strong flow recirculation, enhanced by an exchange of streamwise momentum between shear layers.

The Potential for Dams to Impact Lowland Meandering River Floodplain Geomorphology

PubMed Central

Marren, Philip M.; Grove, James R.; Webb, J. Angus; Stewardson, Michael J.

2014-01-01

The majority of the world's floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We review studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, and interactions with floodplain vegetation. The results are synthesized into a conceptual model of the effects of dams on the major geomorphic influences on floodplain development. This model is used to assess the likely consequences of eight dam and flow regulation scenarios for floodplain geomorphology. Sediment starvation downstream of dams has perhaps the greatest potential to impact on floodplain development. Such effects will persist further downstream where tributary sediment inputs are relatively low and there is minimal buffering by alluvial sediment stores. We can identify several ways in which floodplains might potentially be affected by dams, with varying degrees of confidence, including a distinction between passive impacts (floodplain disconnection) and active impacts (changes in geomorphological processes and functioning). These active processes are likely to have more serious implications for floodplain function and emphasize both the need for future research and the need for an “environmental sediment regime” to operate alongside environmental flows. PMID:24587718

Denitrification in the Mississippi River network controlled by flow through river bedforms

USGS Publications Warehouse

Gomez-Velez, Jesus D.; Harvey, Judson W.; Cardenas, M. Bayani; Kiel, Brian

2015-01-01

Increasing nitrogen concentrations in the world’s major rivers have led to over-fertilization of sensitive downstream waters1, 2, 3, 4. Flow through channel bed and bank sediments acts to remove riverine nitrogen through microbe-mediated denitrification reactions5, 6, 7, 8, 9, 10. However, little is understood about where in the channel network this biophysical process is most efficient, why certain channels are more effective nitrogen reactors, and how management practices can enhance the removal of nitrogen in regions where water circulates through sediment and mixes with groundwater - hyporheic zones8, 11, 12. Here we present numerical simulations of hyporheic flow and denitrification throughout the Mississippi River network using a hydrogeomorphic model. We find that vertical exchange with sediments beneath the riverbed in hyporheic zones, driven by submerged bedforms, has denitrification potential that far exceeds lateral hyporheic exchange with sediments alongside river channels, driven by river bars and meandering banks. We propose that geomorphic differences along river corridors can explain why denitrification efficiency varies between basins in the Mississippi River network. Our findings suggest that promoting the development of permeable bedforms at the streambed - and thus vertical hyporheic exchange - would be more effective at enhancing river denitrification in large river basins than promoting lateral exchange through induced channel meandering. 

A hydrogeomorphic river network model predicts where and why hyporheic exchange is important in large basins

USGS Publications Warehouse

Gomez-Velez, Jesus D.; Harvey, Judson

2014-01-01

Hyporheic exchange has been hypothesized to have basin-scale consequences; however, predictions throughout river networks are limited by available geomorphic and hydrogeologic data and by models that can analyze and aggregate hyporheic exchange flows across large spatial scales. We developed a parsimonious but physically based model of hyporheic flow for application in large river basins: Networks with EXchange and Subsurface Storage (NEXSS). We applied NEXSS across a broad range of geomorphic diversity in river reaches and synthetic river networks. NEXSS demonstrates that vertical exchange beneath submerged bed forms rather than lateral exchange through meanders dominates hyporheic fluxes and turnover rates along river corridors. Per kilometer, low-order streams have a biogeochemical potential at least 2 orders of magnitude larger than higher-order streams. However, when biogeochemical potential is examined per average length of each stream order, low- and high-order streams were often found to be comparable. As a result, the hyporheic zone's intrinsic potential for biogeochemical transformations is comparable across different stream orders, but the greater river miles and larger total streambed area of lower order streams result in the highest cumulative impact from low-order streams. Lateral exchange through meander banks may be important in some cases but generally only in large rivers.

A hydrogeomorphic river network model predicts where and why hyporheic exchange is important in large basins

NASA Astrophysics Data System (ADS)

Gomez-Velez, Jesus D.; Harvey, Judson W.

2014-09-01

Hyporheic exchange has been hypothesized to have basin-scale consequences; however, predictions throughout river networks are limited by available geomorphic and hydrogeologic data and by models that can analyze and aggregate hyporheic exchange flows across large spatial scales. We developed a parsimonious but physically based model of hyporheic flow for application in large river basins: Networks with EXchange and Subsurface Storage (NEXSS). We applied NEXSS across a broad range of geomorphic diversity in river reaches and synthetic river networks. NEXSS demonstrates that vertical exchange beneath submerged bed forms rather than lateral exchange through meanders dominates hyporheic fluxes and turnover rates along river corridors. Per kilometer, low-order streams have a biogeochemical potential at least 2 orders of magnitude larger than higher-order streams. However, when biogeochemical potential is examined per average length of each stream order, low- and high-order streams were often found to be comparable. As a result, the hyporheic zone's intrinsic potential for biogeochemical transformations is comparable across different stream orders, but the greater river miles and larger total streambed area of lower order streams result in the highest cumulative impact from low-order streams. Lateral exchange through meander banks may be important in some cases but generally only in large rivers.

Morphology of a Wetland Stream

PubMed

Jurmu; Andrle

1997-11-01

/ Little attention has been paid to wetland stream morphology in the geomorphological and environmental literature, and in the recently expanding wetland reconstruction field, stream design has been based primarily on stream morphologies typical of nonwetland alluvial environments. Field investigation of a wetland reach of Roaring Brook, Stafford, Connecticut, USA, revealed several significant differences between the morphology of this stream and the typical morphology of nonwetland alluvial streams. Six morphological features of the study reach were examined: bankfull flow, meanders, pools and riffles, thalweg location, straight reaches, and cross-sectional shape. It was found that bankfull flow definitions originating from streams in nonwetland environments did not apply. Unusual features observed in the wetland reach include tight bends and a large axial wavelength to width ratio. A lengthy straight reach exists that exceeds what is typically found in nonwetland alluvial streams. The lack of convex bank point bars in the bends, a greater channel width at riffle locations, an unusual thalweg location, and small form ratios (a deep and narrow channel) were also differences identified. Further study is needed on wetland streams of various regions to determine if differences in morphology between alluvial and wetland environments can be applied in order to improve future designs of wetland channels.KEY WORDS: Stream morphology; Wetland restoration; Wetland creation; Bankfull; Pools and riffles; Meanders; Thalweg

Wave effects on ocean-ice interaction in the marginal ice zone

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Hakkinen, Sirpa; Peng, Chih Y.

1993-01-01

The effects of wave train on ice-ocean interaction in the marginal ice zone are studied through numerical modeling. A coupled two-dimensional ice-ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics. The sea ice model is coupled to the reduced-gravity ocean model through interfacial stresses. The main dynamic balance in the ice momentum is between water-ice stress, wind stress, and wave radiation stresses. By considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves, a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed. The numerical results show significant effects from wave action. The ice edge is sharper, and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days. Upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action; wave action sharpens the ice edge and can produce ice meandering, which enhances local Ekman pumping and pycnocline anomalies. The resulting ice concentration, pycnocline changes, and flow velocity field are shown to be consistent with previous observations.

To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual-Acoustic Survey

PubMed Central

Richman, Nadia I.; Gibbons, James M.; Turvey, Samuel T.; Akamatsu, Tomonari; Ahmed, Benazir; Mahabub, Emile; Smith, Brian D.; Jones, Julia P. G.

2014-01-01

Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista gangetica gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring. PMID:24805782

To see or not to see: investigating detectability of Ganges River dolphins using a combined visual-acoustic survey.

PubMed

Richman, Nadia I; Gibbons, James M; Turvey, Samuel T; Akamatsu, Tomonari; Ahmed, Benazir; Mahabub, Emile; Smith, Brian D; Jones, Julia P G

2014-01-01

Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista gangetica gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring.

Nonlinear Gulf Stream Interaction with the Deep Western Boundary Current System: Observations and a Numerical Simulation

NASA Technical Reports Server (NTRS)

Dietrich, David E.; Mehra, Avichal; Haney, Robert L.; Bowman, Malcolm J.; Tseng, Yu-Heng

2003-01-01

Gulf Stream (GS) separation near its observed Cape Hatteras (CH) separation location, and its ensuing path and dynamics, is a challenging ocean modeling problem. If a model GS separates much farther north than CH, then northward GS meanders, which pinch off warm core eddies (rings), are not possible or are strongly constrained by the Grand Banks shelfbreak. Cold core rings pinch off the southward GS meanders. The rings are often re-absorbed by the GS. The important warm core rings enhance heat exchange and, especially, affect the northern GS branch after GS bifurcation near the New England Seamount Chain. This northern branch gains heat by contact with the southern branch water upstream of bifurcation, and warms the Arctic Ocean and northern seas, thus playing a major role in ice dynamics, thermohaline circulation and possible global climate warming. These rings transport heat northward between the separated GS and shelf slope/Deep Western Boundary Current system (DWBC). This region has nearly level time mean isopycnals. The eddy heat transport convergence/divergence enhances the shelfbreak and GS front intensities and thus also increases watermass transformation. The fronts are maintained by warm advection by the Florida Current and cool advection by the DWBC. Thus, the GS interaction with the DWBC through the intermediate eddy field is climatologically important.

Scales of variability of bio-optical properties as observed from near-surface drifters

NASA Technical Reports Server (NTRS)

Abbott, Mark R.; Brink, Kenneth H.; Booth, C. R.; Blasco, Dolors; Swenson, Mark S.; Davis, Curtiss O.; Codispoti, L. A.

1995-01-01

A drifter equipped with bio-optical sensors and an automated water sampler was deployed in the California Current as part of the coastal transition zone program to study the biological, chemical, and physical dynamics of the meandering filaments. During deployments in 1987 and 1988, measurements were made of fluorescence, downwelling irradiance, upwelling radiance, and beam attenuation using several bio-optical sensors. Samples were collected by an automated sampler for later analysis of nutrients and phytoplankton species compositon. Large-scale spatial and temporal changes in the bio-optical and biological properties of the region were driven by changes in phytoplankton species composition which, in turn, were associated with the meandering circulation. Variance spectra of the bio-optical paramenters revealed fluctuations on both diel and semidiurnal scales, perhaps associated with solar variations and internal tides, respectively. Offshore, inertial-scale fluctuations were apparent in the variance spectra of temperature, fluorescence, and beam attenuation. Although calibration samples can help remove some of these variations, these results suggest that the use of bio-optical data from unattended platforms such as moorings and drifters must be analyzed carefully. Characterization of the scaled of phytoplankton variability must account for the scales of variability in the algorithms used to convert bio-optical measurments into biological quantities.

Bus network redesign for inner southeast suburbs of Melbourne, Australia

NASA Astrophysics Data System (ADS)

Pandangwati, S. T.; Milyanab, N. A.

2017-06-01

Public transport is the most effective mode of transport in the era of climate change and oil depletion. It can address climate change issues by reducing urban greenhouse gas emission and oil consumption while at the same time improving mobility. However, many public transport networks are not effective and instead create high operating costs with low frequencies and occupancy. Melbourne is one example of a metropolitan area that faces this problem. Even though the city has well-integrated train and tram networks, Melbourne’s bus network still needs to be improved. This study used network planning approach to redesign the bus network in the City of Glen Eira, a Local Government Area (LGA) in the southeastern part of Metropolitan Melbourne. The study area is the area between Gardenvale North and Oakleigh Station, as well as between Caulfield and Patterson Stations. This area needs network improvement mainly because of the meandering bus routes that run within it. This study aims to provide recommendations for improving the performance of bus services by reducing meandering routes, improving transfer point design and implementing coordinated timetables. The recommendations were formulated based on a ‘ready-made’ concept to increase bus occupancy. This approach can be implemented in other cities with similar problems and characteristics including those in Indonesia.

Near Earth Current Meander (Necm) Model of Substorms

NASA Astrophysics Data System (ADS)

Heikkila, W. J.; Chen, T.; Liu, Z. X.; Pu, Z. Y.; Pellinen, R. J.; Pulkkinen, T. I.

2001-01-01

We propose that the appropriate instability to trigger a substorm is a tailward meander (in the equatorial plane) of the strong current filament that develops during the growth phase. From this single assumption follows the entire sequence of events for a substorm. The main particle acceleration mechanism in the plasma sheet is curvature drift with a dawn-dusk electric field, leading to the production of auroral arcs. Eventually the curvature becomes so high that the ions cannot negotiate the sharp turn at the field-reversal region, locally, at a certain time. The particle motion becomes chaotic, causing a local outward meander of the cross-tail current. An induction electric field is produced by Lenz's law, E^ind=-∂A/∂t. An outward meander with B_z>0 will cause E×B flow everywhere out from the disturbance; this reaction is a macroscopic instability which we designate the electromotive instability. The response of the plasma is through charge separation and a scalar potential, E^es=-∇φ. Both types of electric fields have components parallel to B in a realistic magnetic field. For MHD theory to hold the net E_∥ must be small; this usually seems to happen (because MHD often does hold), but not always. Part of the response is the formation of field-aligned currents producing the well-known substorm current diversion. This is a direct result of a strong E_∥^ind (the cause) needed to overcome the mirror force of the current carriers; this enables charge separation to produce an opposing electrostatic field E_∥^es (the effect). Satellite data confirm the reality of a strong E_∥ in the plasma sheet by counter-streaming of electrons and ions, and by the inverse ion time dispersion, up to several 100 keV. The electron precipitation is associated with the westward traveling surge (WTS) and the ion with omega (Ω) bands, respectively. However, with zero curl, E^es cannot modify the emf ɛ=∮E.dl=-dΦ^M/dt of the inductive electric field E^ind (a property of vector fields); the charge separation that produces a reduction of E_∥ must enhance the transverse component E_⊥. The new plasma flow becomes a switch for access to the free energy of the stressed magnetotail. On the tailward side the dusk-dawn electric field with E.J<0 will cause tailward motion of the plasma and a plasmoid may be created; it will move in the direction of least magnetic pressure, tailward. On the earthward side the enhanced dawn-dusk induction electric field with E.J>0 will cause injection into the inner plasma sheet, repeatedly observed at moderate energies of 1-50 keV. This same electric field near the emerging X-line will accelerate particles non-adiabatically to moderate energies. With high magnetic moments in a weak magnetic field, electrons (ions) can benefit from gradient and curvature drift to attain high energies (by the ratio of the magnetic field magnitude) in seconds (minutes).

Panoramic Okavango Swamp, Botswana and Fires in Angola, Africa

NASA Image and Video Library

1991-08-11

In this panoramic view of the Okavango Swamp, Botswana, (19.0S, 22.0E), the Okavango River, seen in sunglint, flows into a topographic trough to form an inland delta. Water, trapped in the meandering delta distributaries is evaporated or transpired by vegetation. In Angola to the north, the many fires of the seasonal burning of savannah vegetation for land clearing, in preparation for agriculture, has filled the atmosphere with haze and smoke.

Louisville, KY, USA

NASA Technical Reports Server (NTRS)

1973-01-01

The meandering Ohio River bisecting this image is the border between Kentucky and Indiana. Louisville, KY (38.5N, 86.0W) on the south shore, is the main city seen in this predominately agricultural region where much of the native hardwood forests have been preserved in the hilly terrain. The main crops in this region include corn, alfalfa, wheat and soybeans. The dark rectangle in south Indiana near the river is The U.S. Army's Jefferson Proving Ground.

A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Functions of Forested Wetlands in the Mississippi Alluvial Valley

DTIC Science & Technology

2013-07-01

Definition Depression Depressional wetlands occur in topographic depressions (i.e., closed elevation contours) that allow the accumulation of surface water... depression . The predominant hydrodynamics are vertical fluctuations that may occur over a range of time, from a few days to many months. Depressional ... depression in dunefields ............................... 3b. Depressional feature in abandoned meander features (oxbows or swales) not subject to 5-year

Public Use Land Requirements, Tennessee Colony Lake.

DTIC Science & Technology

1972-03-30

source of pollution by oil and oil field brines. If these and existing gas fields continue to operate, oil -pumping and storage stations and oil and gas ...the lake and large numbers can be expected to visit this area. The land is in the middle of the Cayuga oil field and there are many oil and gas ...Project Area Geographic boundary and physiographic classification The Trinity River meanders south- southeast through Freestone, Anderson, Navarro and

Investigating historical changes in morphodynamic processes associated with channelization of a large Alpine river: the Etsch/Adige River, NE Italy

NASA Astrophysics Data System (ADS)

Zen, Simone; Scorpio, Vittoria; Mastronunzio, Marco; Proto, Matteo; Zolezzi, Guido; Bertoldi, Walter; Comiti, Francesco; Surian, Nicola; Prà, Elena Dai

2016-04-01

River channel management within the last centuries has largely modified fluvial processes and morphodynamic evolution of most large European rivers. Several river systems experienced extensive channelization early in the 19th century, thus strongly challenging our present ability to detect their morphodynamic functioning with contemporary photogrammetry or cartographical sources. This consequently leaves open questions about their potential future response, especially to management strategies that "give more room" to the river, aiming at partially rehabilitating their natural functioning. The Adige River (Etsch in German), the second longest Italian river, is an exemplary case where channelization occurred more than 150 years ago, and is the focus of the present work. This work aims (i) to explore changes in fundamental morphodynamic processes associated with massive channelization of the Adige River and (ii) to quantify the alteration in river bars characteristics, by using morphodynamic models of bars and meandering. To fulfil our aims we combine the analysis of historical data with morphodynamic mathematical modelling. Historical sources (recovered in a number of European archives), such as hydrotopographical maps, airborne photogrammetry and hydrological datasets were collected to investigate channel morphology before and after the channelization. Information extracted from this analysis was combined with morphodynamic linear models of free migrating and forced steady bars, to investigate river bars and bend stability properties under different hydromorphological scenarios. Moreover, a morphodynamic model for meandering channel was applied to investigate the influence of river channel planform on the evolution of the fluvial bars. Results from the application of morphodynamic models allowed to predict the type, position and geometry of bars characterizing the channelized configuration of the river, and to explain the presently observed relative paucity of bars if compared to the previous, less confined, river planform. The application of a meander model allows insight into the properties of bars that were observed in the old historical maps. A threshold range of the imposed channel width can be predicted above which the river may partially restore conditions for bar instability to occur and for their further development, with direct management implications. Overall the conducted analysis confirms the potential of integrating morphodynamic models with geomorphological and time-series analysis of historical large-scale maps and airborne photogrammetry to increase our understanding and predictive ability of the evolution of rivers with a long-lasting record of morphological regulation.

Are Streams in the Southwestern Ozarks Underfit? Applying Dury's model to the Illinois River Watershed in Arkansas.

NASA Astrophysics Data System (ADS)

Shepherd, S. L.; Davis, R. K.; Dixon, J. C.; Cothren, J. D.

2008-12-01

George H. Dury (1964) proposed eight theoretical combinations of stream pattern and valley pattern that represent underfit streams; claiming underfit is a climate induced condition caused by a significant decrease in channel forming discharge. One combination was defined by the Osage River in the northeastern Ozark Plateaus of Missouri. Osage underfit streams fail to meander within a meandering valley. The mean channel meander wavelength and channel width of the stream is much less than the valley resulting in valley-stream ratios of up to 40:1 in contrast to his expected values of approximately 11:1. Dury's model is generally applied to the entire Ozarks including the Illinois River watershed without field data support. The Illinois River is located on the western flank of the Ozark Plateaus physiographic region on the Springfield Plateau which has different lithology than the Salem Plateau where the Osage River is located. To test the assumption that streams in the Illinois River watershed are underfit a combination of field, map, and GIS data were collected. Geomorphic surveys of ten reaches along eight first order streams were completed. The average stream widths of the ten reaches were compared to valley widths measured from USGS 1:24000 Quadrangle maps. The valley to stream ratios ranged from 1 to 15. Forested watersheds exhibited the highest width ratios, ranging from 12 to 15, while ratios in urban and agricultural watersheds were less than 2. This finding is consistent with observed changes in stream morphology caused by anthropogenic influences. To extrapolate to the larger watershed thirteen valley and stream widths along the Illinois River and two higher order tributaries, Osage Creek and Clear Creek, were measured from USGS maps. These ratios ranged from 2.8 to 5.7. Additionally, stream and valley wavelengths are being analyzed in a GIS using the USGS medium resolution hydrology data set and a LiDAR derived 8 m DEM for the watershed. These data suggest it is invalid to apply the Osage underfit model to this watershed. These findings are being validated with additional stream and valley width measurements in the field along the first order streams, Osage Creek, Clear Creek, and the Illinois River.

Heat waves and jet stream relations - nature of dry and wet shifts around the 2.8 kyr BP event in Central Europe

NASA Astrophysics Data System (ADS)

Slowinski, M. M.; Persoiu, A.; Slowinska, S.; Marcisz, K.; Ionita, M.; Lamentowicz, M.

2017-12-01

Solar insolation was the main driver of N Hemisphere storm tracks changes, with significant impacts on European climate variability during the Holocene. Consequently, the Homeric solar minimum, which occurred between 2,750 and 2,550 cal BP, was characterized by cooling and increase in wind strength and humidity in W Europe. In contrast, environmental reconstructions from Central and E Europe show that the climatic changes during this period were often more complex, with increased hydrological instability and a shift towards drier conditions. These contrasting conditions could be explained by the blocking in a stationary position of a high-pressure system above Central and E Europe as a result of the behavior of the jet stream. In order to understand how these changes in the behavior of the jet stream were acting in the past, we have analyzed a modern analogue to better understand the climatic map of Europe during the Homeric minimum of the 9th century BC. Thus, in summer 2015, a northward extending meander of the jet stream led to dry and hot conditions in C Europe, blocking the transport of Atlantic-sourced moisture eastwards and leading to increased precipitation in W Europe. Contrary, in 2013, the position of the high-pressure cells associated with the meandering of the jet-stream was located over W Russia and E Europe (both affected by heat waves resulting from meridional advection of dry/hot air), leading to more Rossby waves breaking over C Europe and delivering record amounts of precipitation. To test whether a similar mechanism could act on longer times scales, we have analyzed two high-resolution palaeoclimate datasets from E Europe (Rąbień peatbog, Poland and Scăriloara Ice Cave, Romania), located in areas with both N Atlantic and Mediterranean climatic influences. At the time of the Homeric Solar Minimum, warm climatic conditions dominated in SE Europe, with advection of warm and dry air from the Mediterranean. W Europe was rather wet around that time and these contrasting conditions could have been the result of blocking conditions over C Europe, induced by a solar-influenced strongly meandering jet-stream. Our recent monitoring observation and paleoclimate data support studies that presents link between arctic polar vortex, jet streams, sea-ice formation in the Arctic and climate variability in Europe.

Lake Murray, Fly and Strickland River Basins, Papua, New Guinea

NASA Image and Video Library

1991-12-01

Lake Murray, a manmade reservoir, lies between the Fly and Strickland River Basins, Papua, New Guinea (7.0S, 141.5E). The region, photographed in sunglint, shows the water level in the reservoir and the full extent of the drainage basins of both river systems as the rivers meander through wide alluvial floodplains. Some forest clearing can be seen in places throughout the region, but most of the area remains in closed canopy forest.

Placement insensitive antenna for RFID, sensing, and/or communication systems

DOEpatents

Bernhard, Jennifer T.; Ruyle, Jessica E.

2014-06-10

An antenna includes a ground plane having a slot. The slot may be miniaturized using a meandered slot structure or other appropriate reactive loading method as an end load to one or both ends of the slot. An edge treatment may be included on one or more edges of the ground plane or a closely spaced reflecting plane. The antenna is structured to transmit or receive a signal independently or in response to electromagnetic radiation.

Canyonlands National Park, UT, USA

NASA Image and Video Library

1973-06-22

SL2-81-014 (22 June 1973) --- Desert and mountain scenery along the Utah/Colorado border are displayed in this scene of the Canyonlands National Park, UT (39.0N, 110.0W). The park occupies the near center of the image, displaying spectacular incised meanders and the bulls-eye structure of Upheaval Dome (a salt dome). The Green River and the Colorado River flow southward to join (off scene) before flowing through the Grand Canyon National Park. Photo credit: NASA

A Cultural Resource Inventory of 13 Proposed Waterfowl Ponds and a Sample of the Prairie Dog Arm, Harlan County Lake, Nebraska

DTIC Science & Technology

1988-01-01

information derived from surrounding areas, this cultural period was characterized by intensive hunting of Pleistocene megafauna augmented by some gathering...migratory patterns of the Pleistocene megafauna brought about by the Altithermal climatic shifts. Archaic period sites contain nebulous house floors...surpassed the erosional and gradient stages. In the project area streams with mature beds have low gradients and are slow moving through wide meander

New Orleans area as seen from the Apollo 7 spacecraft

NASA Image and Video Library

1968-10-19

The greater New Orleans area, including portions of Louisiana and Mississippi, as seen from the Apollo 7 spacecraft during its 120th revolution of the earth. Photographed from an altitude of 95 nautical miles, at ground elapsed time of 190 hours and 45 minutes. The largest body of water in the picture is Lake Pontchartrain. The Mississippi River is clearly visible as it meanders past New Orleans. Note highway network, and 25-mile causeway across lake.

Generic theory for channel sinuosity.

PubMed

Lazarus, Eli D; Constantine, José Antonio

2013-05-21

Sinuous patterns traced by fluid flows are a ubiquitous feature of physical landscapes on Earth, Mars, the volcanic floodplains of the Moon and Venus, and other planetary bodies. Typically discussed as a consequence of migration processes in meandering rivers, sinuosity is also expressed in channel types that show little or no indication of meandering. Sinuosity is sometimes described as "inherited" from a preexisting morphology, which still does not explain where the inherited sinuosity came from. For a phenomenon so universal as sinuosity, existing models of channelized flows do not explain the occurrence of sinuosity in the full variety of settings in which it manifests, or how sinuosity may originate. Here we present a generic theory for sinuous flow patterns in landscapes. Using observations from nature and a numerical model of flow routing, we propose that flow resistance (representing landscape roughness attributable to topography or vegetation density) relative to surface slope exerts a fundamental control on channel sinuosity that is effectively independent of internal flow dynamics. Resistance-dominated surfaces produce channels with higher sinuosity than those of slope-dominated surfaces because increased resistance impedes downslope flow. Not limited to rivers, the hypothesis we explore pertains to sinuosity as a geomorphic pattern. The explanation we propose is inclusive enough to account for a wide variety of sinuous channel types in nature, and can serve as an analytical tool for determining the sinuosity a landscape might support.

Cycloidal meandering of a mesoscale anticyclonic eddy

NASA Astrophysics Data System (ADS)

Kizner, Ziv; Shteinbuch-Fridman, Biana; Makarov, Viacheslav; Rabinovich, Michael

2017-08-01

By applying a theoretical approach, we propose a hypothetical scenario that might explain some features of the movement of a long-lived mesoscale anticyclone observed during 1990 in the Bay of Biscay [R. D. Pingree and B. Le Cann, "Three anticyclonic slope water oceanic eddies (SWODDIES) in the southern Bay of Biscay in 1990," Deep-Sea Res., Part A 39, 1147 (1992)]. In the remote-sensing infrared images, at the initial stage of observations, the anticyclone was accompanied by two cyclonic eddies, so the entire structure appeared as a tripole. However, at later stages, only the anticyclone was seen in the images, traveling generally west. Unusual for an individual eddy were the high speed of its motion (relative to the expected planetary beta-drift) and the presence of almost cycloidal meanders in its trajectory. Although surface satellites seem to have quickly disappeared, we hypothesize that subsurface satellites continued to exist, and the coherence of the three vortices persisted for a long time. A significant perturbation of the central symmetry in the mutual arrangement of three eddies constituting a tripole can make reasonably fast cycloidal drift possible. This hypothesis is tested with two-layer contour-dynamics f-plane simulations and with finite-difference beta-plane simulations. In the latter case, the interplay of the planetary beta-effect and that due to the sloping bottom is considered.

Seaglider surveys at Ocean Station Papa: Circulation and water mass properties in a meander of the North Pacific Current

NASA Astrophysics Data System (ADS)

Pelland, Noel A.; Eriksen, Charles C.; Cronin, Meghan F.

2016-09-01

A Seaglider autonomous underwater vehicle augmented the Ocean Station Papa (OSP; 50°N, 145°W) surface mooring, measuring spatial structure on scales relevant to the monthly evolution of the moored time series. During each of three missions from June 2008 to January 2010, a Seaglider made biweekly 50 km × 50 km surveys in a bowtie-shaped survey track. Horizontal temperature and salinity gradients measured by these surveys were an order of magnitude stronger than climatological values and sometimes of opposite sign. Geostrophically inferred circulation was corroborated by moored acoustic Doppler current profiler measurements and AVISO satellite altimetry estimates of surface currents, confirming that glider surveys accurately resolved monthly scale mesoscale spatial structure. In contrast to climatological North Pacific Current circulation, upper-ocean flow was modestly northward during the first half of the 18 month survey period, and weakly westward during its latter half, with Rossby number O>(0.01>). This change in circulation coincided with a shift from cool and fresh to warm, saline, oxygen-rich water in the upper-ocean halocline, and an increase in vertical fine structure there and in the lower pycnocline. The anomalous flow and abrupt water mass transition were due to the slow growth of an anticyclonic meander within the North Pacific Current with radius comparable to the scale of the survey pattern, originating to the southeast of OSP.

Interactions of a co-rotating vortex pair at multiple offsets

NASA Astrophysics Data System (ADS)

Forster, Kyle J.; Barber, Tracie J.; Diasinos, Sammy; Doig, Graham

2017-05-01

Two NACA0012 vanes at various lateral offsets were investigated by wind tunnel testing to observe the interactions between the streamwise vortices. The vanes were separated by nine chord lengths in the streamwise direction to allow the upstream vortex to impact on the downstream geometry. These vanes were evaluated at an angle of incidence of 8° and a Reynolds number of 7 ×104 using particle image velocimetry. A helical motion of the vortices was observed, with rotational rate increasing as the offset was reduced to the point of vortex merging. Downstream meandering of the weaker vortex was found to increase in magnitude near the point of vortex merging. The merging process occurred more rapidly when the upstream vortex was passed on the pressure side of the vane, with the downstream vortex being produced with less circulation and consequently merging into the upstream vortex. The merging distance was found to be statistical rather than deterministic quantity, indicating that the meandering of the vortices affected their separations and energies. This resulted in a fluctuation of the merging location. A loss of circulation associated with the merging process was identified, with the process of achieving vortex circularity causing vorticity diffusion, however all merged cases maintained higher circulation than a single vortex condition. The presence of the upstream vortex was found to reduce the strength of the downstream vortex in all offsets evaluated.

Wide-Band, High-Quantum-Efficiency Photodetector

NASA Technical Reports Server (NTRS)

Jackson, Deborah; Wilson, Daniel; Stern, Jeffrey

2007-01-01

A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of optiA design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of opti-

Structure of the Head of the Bartonella Adhesin BadA

PubMed Central

Szczesny, Pawel; Linke, Dirk; Ursinus, Astrid; Bär, Kerstin; Schwarz, Heinz; Riess, Tanja M.; Kempf, Volkhard A. J.; Lupas, Andrei N.; Martin, Jörg; Zeth, Kornelius

2008-01-01

Trimeric autotransporter adhesins (TAAs) are a major class of proteins by which pathogenic proteobacteria adhere to their hosts. Prominent examples include Yersinia YadA, Haemophilus Hia and Hsf, Moraxella UspA1 and A2, and Neisseria NadA. TAAs also occur in symbiotic and environmental species and presumably represent a general solution to the problem of adhesion in proteobacteria. The general structure of TAAs follows a head-stalk-anchor architecture, where the heads are the primary mediators of attachment and autoagglutination. In the major adhesin of Bartonella henselae, BadA, the head consists of three domains, the N-terminal of which shows strong sequence similarity to the head of Yersinia YadA. The two other domains were not recognizably similar to any protein of known structure. We therefore determined their crystal structure to a resolution of 1.1 Å. Both domains are β-prisms, the N-terminal one formed by interleaved, five-stranded β-meanders parallel to the trimer axis and the C-terminal one by five-stranded β-meanders orthogonal to the axis. Despite the absence of statistically significant sequence similarity, the two domains are structurally similar to domains from Haemophilus Hia, albeit in permuted order. Thus, the BadA head appears to be a chimera of domains seen in two other TAAs, YadA and Hia, highlighting the combinatorial evolutionary strategy taken by pathogens. PMID:18688279

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

Zhao Hanqing; Fu Zhiguo; Lu Xiaoguang

Guided by the sedimentation theory and knowledge of modern and ancient fluvial deposition and utilizing the abundant information of sedimentary series, microfacies type and petrophysical parameters from well logging curves of close spaced thousands of wells located in a large area. A new method for establishing detailed sedimentation and permeability distribution models for fluvial reservoirs have been developed successfully. This study aimed at the geometry and internal architecture of sandbodies, in accordance to their hierarchical levels of heterogeneity and building up sedimentation and permeability distribution models of fluvial reservoirs, describing the reservoir heterogeneity on the light of the river sedimentarymore » rules. The results and methods obtained in outcrop and modem sedimentation studies have successfully supported the study. Taking advantage of this method, the major producing layers (PI{sub 1-2}), which have been considered as heterogeneous and thick fluvial reservoirs extending widely in lateral are researched in detail. These layers are subdivided into single sedimentary units vertically and the microfacies are identified horizontally. Furthermore, a complex system is recognized according to their hierarchical levels from large to small, meander belt, single channel sandbody, meander scroll, point bar, and lateral accretion bodies of point bar. The achieved results improved the description of areal distribution of point bar sandbodies, provide an accurate and detailed framework model for establishing high resolution predicting model. By using geostatistic technique, it also plays an important role in searching for enriched zone of residual oil distribution.« less

Comparing Transition-Edge Sensor Response Times in a Modified Contact Scheme with Different Support Beams

NASA Technical Reports Server (NTRS)

Beyer, A. D.; Kenyon, M. E.; Bumble, B.; Runyan, M. C.; Echternach, P. E.; Holmes, W. A.; Bock, J. J.; Bradford, C. M.

2013-01-01

We present measurements of the thermal conductance, G, and effective time constants, tau, of three transition-edge sensors (TESs) populated in arrays operated from 80-87mK with T(sub C) approximately 120mK. Our TES arrays include several variations of thermal architecture enabling determination of the architecture that demonstrates the minimum noise equivalent power (NEP), the lowest tau and the trade-offs among designs. The three TESs we report here have identical Mo/Cu bilayer thermistors and wiring structures, while the thermal architectures are: 1) a TES with straight support beams of 1mm length, 2) a TES with meander support beams of total length 2mm and with 2 phononfilter blocks per beam, and 3) a TES with meander support beams of total length 2mm and with 6 phonon-filter blocks per beam. Our wiring scheme aims to lower the thermistor normal state resistance R(sub N) and increase the sharpness of the transition alpha=dlogR/dlogT at the transition temperature T(sub C). We find an upper limit of given by (25+/-10), and G values of 200fW/K for 1), 15fW/K for 2), and 10fW/K for 3). The value of alpha can be improved by slightly increasing the length of our thermistors.

Neotectonic effects on sinuosity and channel migration, Belle Fourche River, Western South Dakota

USGS Publications Warehouse

Gomez, Basil; Marron, Donna C.

1991-01-01

Short-term instability in the behaviour of a small, meandering alluvial channel is identified from the relation between sinuosity and either floodplain slope or channel slope within 17 reaches along an 81-kilometre section of the Belle Fourche River in western South Dakota. In reaches 1 to 4 and 11 to 17 the channel is relatively stable and sinuosity varies inversely with channel slope. In reaches 5 to 10, sinuosity is positively related to floodplain slope. Sinuosity increases markedly in reaches 5, 6, and 7 (which are immediately downstream from a discontinuity in the long profile of the floodplain) in association with an increase in floodplain slope. Immediately upstream from the discontinuity, bankfull channel depth and sinuosity decrease and the area of the floodplain reworked by meander migration between 1939 and 1981 increases, in association with a decrease in floodplain slope. Channel behaviour in reaches 5 to 10 is best explained as a consequence of neotectonic activity, as indicated by changes in elevation recorded along geodetic survey lines that cross lineaments that may delimit the eastern boundary of the Black Hills uplift. Sinuosity acts as a barometer of the effects of neotectonic activity on alluvial channels. Initial indications of channel and floodplain instability due to neotectonic activity may be derived from evidence of anomalously active channel migration, as documented from photographic or topographic sources.

Identifying Variations in Hydraulic Conductivity on the East River at Crested Butte, CO

NASA Astrophysics Data System (ADS)

Ulmer, K. N.; Malenda, H. F.; Singha, K.

2016-12-01

Slug tests are a widely used method to measure saturated hydraulic conductivity, or how easily water flows through an aquifer, by perturbing the piezometric surface and measuring the time the local groundwater table takes to re-equilibrate. Saturated hydraulic conductivity is crucial to calculating the speed and direction of groundwater movement. Therefore, it is important to document data variance from in situ slug tests. This study addresses two potential sources of data variability: different users and different types of slug used. To test for user variability, two individuals slugged the same six wells with water multiple times at a stream meander on the East River near Crested Butte, CO. To test for variations in type of slug test, multiple water and metal slug tests were performed at a single well in the same meander. The distributions of hydraulic conductivities of each test were then tested for variance using both the Kruskal-Wallis test and the Brown-Forsythe test. When comparing the hydraulic conductivity distributions gathered by the two individuals, we found that they were statistically similar. However, we found that the two types of slug tests produced hydraulic conductivity distributions for the same well that are statistically dissimilar. In conclusion, multiple people should be able to conduct slug tests without creating any considerable variations in the resulting hydraulic conductivity values, but only a single type of slug should be used for those tests.

A Dual Band Frequency Reconfigurable Origami Magic Cube Antenna for Wireless Sensor Network Applications.

PubMed

Shah, Syed Imran Hussain; Lim, Sungjoon

2017-11-20

In this paper, a novel dual band frequency reconfigurable antenna using an origami magic cube is proposed for wireless sensor network (WSN) applications. The proposed origami antenna consists of a meandered monopole folded onto three sides of the magic cube. A microstrip open-ended stub is loaded on the meandered monopole. The proposed origami magic cube can be mechanically folded and unfolded. The proposed antenna operates at 1.57 GHZ and 2.4 GHz in the folded state. In the unfolded state, the proposed antenna operates at 900 MHz and 2.3 GHz. The resonant frequency of the second band can be tunable by varying the length and position of the open stub. The origami magic cube is built on paper. Its performance is numerically and experimentally demonstrated from S-parameters and radiation patterns. The measured 10 dB impedance bandwidth of the proposed origami antenna is 18% (900-1120 MHz) and 15% (2.1-2.45 GHz) for the unfolded state and 20% (1.3-1.6 GHz) and 14% (2.3-2.5 GHz) for the folded state. The measured peak gain at 900 MHz and 2.3 GHz are 1.1 dBi and 2.32 dBi, respectively, in the unfolded state. The measured peak gain at 1.5 GHz and 2.4 GHz are 3.28 dBi and 1.98 dBi, respectively, in the folded state.

Wild, scenic, and transcendental rivers

NASA Astrophysics Data System (ADS)

Showstack, Randy

“A more lovely stream than this has never flowed on Earth,” 19th century American author Nathaniel Hawthorne wrote about the confluence of the Assabet and Concord Rivers, streams that meander about 40 km west of Boston, Massachusetts.Segments of these streams as well as the Assabet River became the newest additions to the U.S. National Wild and Scenic Rivers System, when President Bill Clinton signed into law the “Sudbury, Assabet, and Concord Wild and Scenic River Act” on April 9.

Louisville, KY, USA

NASA Image and Video Library

1973-06-22

SL2-10-260 (22 June 1973) --- The meandering Ohio River bisecting this image is the border between Kentucky and Indiana. Louisville, KY (38.5N, 86.0W) on the south shore, is the main city seen in this predominately agricultural region where much of the native hardwood forests have been preserved in the hilly terrain. The main crops in this region include corn, alfalfa, wheat and soybeans. The dark rectangle in south Indiana near the river is The U.S. Army's Jefferson Proving Ground. Photo credit: NASA

Impacts of Woody Debris on Fluvial Processes and Channel Morphology in Stable and Unstable Streams

DTIC Science & Technology

1997-06-01

the channel, 4 through erosion and flotation of emergent and riparian trees (Hogan, 1987) (Figuie 2.1). Fetherston et al. (1995) suggest that debris...the CEM or is actively meandering. Jams tend to form where the key debris elements fall into the river and, hence, ar,- commonly located at bend apices ... flotation force due to the pressure on the under surface of a submerged or partially submerged body is given by: Ff - p•,gLA (5.1) where, Ft. - flotation

Proceedings of the Gulf Stream Workshop Held at West Greenwich, Rhode Island on 23-26 April 1985,

DTIC Science & Technology

1985-04-01

complex. We now realize that a correct dytiamical description must intrinsically couple the mass-, momentum -, energy-, and vorticity-fluxes of a strong mean...path and structure, and the mass- and momentum transport. 2. Meander dynamics "intrinsic" to the Gulf Stream, such as growth and propagation of...contribute to the dissipation of momentum through wave and form drag. A general study of the influence of the seamounts seems more appropriate for the

HF Meander-Line Antenna Simulations and Investigations for NVIS on a HMMV

DTIC Science & Technology

2016-09-28

power   transfer  at  frequencies  of   interests  [10].       Graph  1.  Conventional  MLA  input  impedance...the  ratio  of  accepted   power  versus  the  radiated   power  of  a   simulated  antenna  after  the  equation...the  antenna  (x,  y,  z   coordinates)  and  !""=  the  accepted  

System design of a remotely operated, program controlled measurement table for the calibration of the Egret experiment. Part A: Program control

NASA Technical Reports Server (NTRS)

1984-01-01

The structure of the program, the five priority levels, the drive routines, the stepwise drive plan, the figure routines, meander X and y, the range of measurement table, the optimization of figure drive, the figure drive plan, dialogue routines, stack processing, the drive for the main terminal, the protocol routines, the drive for the microterminal, the drive for the experiment computer, and the main program are discussed.

Global Bifurcation of Periodic Solutions with Symmetry,

DTIC Science & Technology

1987-07-01

C4-family of sectorial operators on a real Hilbert (2.32.a) space X, with dense domain D(A(A)) which is independent of A E E, and with compact...Vanl, theorem 2.5.91. If .F and E’ are both Hilbert spaces with orthogonal action of r, we may drop the assumption that 1 is compact. Just take...some meandering. Let us define a limit for any sequence Si of subsets of some metric space . Following Whyburn [Why], we define lir sup Si {z: z

Evidence for persistent flow and aqueous sedimentation on early Mars.

PubMed

Malin, Michael C; Edgett, Kenneth S

2003-12-12

Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.

Essays on War: 1. The Inconsequence of Superpower War, 2. Quarantine, 3. The Quagmire of Self-Defense,

DTIC Science & Technology

1981-01-01

prestige will no longer be tolerated internationally. The rewards of exploration are minimal, the claims of manifest destiny absurd, and the discovery of... embryo , many pious platitudes meandered into the finished product. Article 51 was an exception, however; it was considered objectively and composed...which is to say that they are unhappy with the power which other nations may have to control their destinies . Perhaps national security is a cat’s paw

Recent (circa 1998 to 2011) channel-migration rates of selected streams in Indiana

USGS Publications Warehouse

Robinson, Bret A.

2013-01-01

An investigation was completed to document recent (circa 1998 to 2011) channel-migration rates at 970 meander bends along 38 of the largest streams in Indiana. Data collection was completed by using the Google Earth™ platform and, for each selected site, identifying two images with capture dates separated by multiple years. Within each image, the position of the meander-bend cutbank was measured relative to a fixed local landscape feature visible in both images, and an average channel-migration rate was calculated at the point of maximum cutbank displacement. From these data it was determined that 65 percent of the measured sites have recently been migrating at a rate less than 1 ft/yr, 75 percent of the sites have been migrating at a rate less than 10 ft/yr, and while some sites are migrating in excess of 20 ft/yr, these occurrences are rare. In addition, it is shown that recent channel-migration activity is not evenly distributed across Indiana. For the stream reaches studied, far northern and much of far southern Indiana are drained by streams that recently have been relatively stationary. At the same time, this study shows that most of the largest streams in west-central Indiana and many of the largest streams in east-central Indiana have shown significant channel-migration activity during the recent past. It is anticipated that these results will support several fluvial-erosion-hazard mitigation activities currently being undertaken in Indiana.

Long-term morphological evolution of a morphologically active man-made stream in the Netherlands

NASA Astrophysics Data System (ADS)

Eekhout, J.; Hoitink, T.

2010-12-01

Around 1770, a straight artificial canal (Gelderns-Nierskanaal) has been constructed between the River Niers and the River Meuse, crossing the border between Germany and the Netherlands, with the purpose of reducing flood risk in the downstream reaches of the River Niers. Whereas the German part of the canal is kept straight throughout time, the Dutch part was left unprotected and developed into a morphodynamically active stream featuring a meandering planform. The current planform and in-channel morphology are analyzed using airborne LiDAR data and historical topographic maps. Around the turn of the 18th century, the first attempts were made to make detailed topographic maps. From this time on, at least 16 topographic maps of the area around the stream were made. With the use of these historical topographic maps, a reconstruction is made of the planimetric shape of the stream over a period of 240 years. The LiDAR data show old meander belts at several places around the stream. Those belts compare well with the topographic maps. The sinuosity increases from upstream to downstream. This could be a consequence of the valley slope, where the upper part is flat and the slope increases in downstream direction. Besides, the LiDAR data show that erosion resulted in an incised valley, with dimensions to 50 m in width and 6 m in depth. Both the datasets are combined to make an estimate of the historical sediment budget of the stream.

Application of sub-micrometer patterned permalloy thin film in tunable radio frequency inductors

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

Rahman, B.M. Farid; Divan, Ralu; Rosenmann, Daniel

Electrical tunable meander line inductor using coplanar waveguide structures with patterned permalloy (Py) thin film has been designed and implemented in this paper. High resistivity Si substrate is used to reduce the dielectric loss from the substrate. Inductor is implemented with a 60 nm thick Py deposited and patterned on top of the gold meander line, and Py film is patterned with dimension of 440 nm 10 lm to create the shape anisotropy field, which in turn increases the FMR frequency. Compared to a regular meanderline inductor without the application of sub-micrometer patterned Py thin film, the inductance density hasmore » been increased to 20% for the implemented inductor with patterned Py. Measured FMR frequency of the patterned Py is 4.51 GHz without the application of any external magnetic field. This has enabled the inductor application in the practical circuit boards, where the large external magnet is unavailable. Inductance tunability of the implemented inductor is demonstrated by applying a DC current. Applied DC current creates a magnetic field along the hard axis of the patterned Py thin film, which changes the magnetic moment of the thin film and thus, decreases the inductance of the line. Measured results show that the inductance density of the inductor can be varied 5% by applying 300 mA DC current, larger inductance tunability is achievable by increasing the thickness of Py film. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4918766]« less

Moth-inspired navigation algorithm in a turbulent odor plume from a pulsating source.

PubMed

Liberzon, Alexander; Harrington, Kyra; Daniel, Nimrod; Gurka, Roi; Harari, Ally; Zilman, Gregory

2018-01-01

Some female moths attract male moths by emitting series of pulses of pheromone filaments propagating downwind. The turbulent nature of the wind creates a complex flow environment, and causes the filaments to propagate in the form of patches with varying concentration distributions. Inspired by moth navigation capabilities, we propose a navigation strategy that enables a flier to locate an upwind pulsating odor source in a windy environment using a single threshold-based detection sensor. This optomotor anemotaxis strategy is constructed based on the physical properties of the turbulent flow carrying discrete puffs of odor and does not involve learning, memory, complex decision making or statistical methods. We suggest that in turbulent plumes from a pulsating point source, an instantaneously measurable quantity referred as a "puff crossing time", improves the success rate as compared to the navigation strategies based on temporally regular zigzags due to intermittent contact, or an "internal counter", that do not use this information. Using computer simulations of fliers navigating in turbulent plumes of the pulsating point source for varying flow parameters such as turbulent intensities, plume meandering and wind gusts, we obtained statistics of navigation paths towards the pheromone sources. We quantified the probability of a successful navigation as well as the flight parameters such as the time spent searching and the total flight time, with respect to different turbulent intensities, meandering or gusts. The concepts learned using this model may help to design odor-based navigation of miniature airborne autonomous vehicles.

River banks and channel axis curvature: Effects on the longitudinal dispersion in alluvial rivers

NASA Astrophysics Data System (ADS)

Lanzoni, Stefano; Ferdousi, Amena; Tambroni, Nicoletta

2018-03-01

The fate and transport of soluble contaminants released in natural streams are strongly dependent on the spatial variations of the flow field and of the bed topography. These variations are essentially related to the presence of the channel banks and to the planform configuration of the channel. Large velocity gradients arise near to the channel banks, where the flow depth decreases to zero. Moreover, single thread alluvial rivers are seldom straight, and usually exhibit meandering planforms and a bed topography that deviates from the plane configuration. Channel axis curvature and movable bed deformations drive secondary helical currents which enhance both cross sectional velocity gradients and transverse mixing, thus crucially influencing longitudinal dispersion. The present contribution sets up a rational framework which, assuming mild sloping banks and taking advantage of the weakly meandering character often exhibited by natural streams, leads to an analytical estimate of the contribution to longitudinal dispersion associated with spatial non-uniformities of the flow field. The resulting relationship stems from a physics-based modeling of the flow in natural rivers, and expresses the bend averaged longitudinal dispersion coefficient as a function of the relevant hydraulic and morphologic parameters. The treatment of the problem is river specific, since it relies on an explicit spatial description, although linearized, of the flow field that establishes in the investigated river. Comparison with field data available from tracer tests supports the robustness of the proposed framework, given also the complexity of the processes that affect dispersion dynamics in real streams.

Anatomy and growth pattern of Amazon deep-sea fan as revealed by long-range side-scan sonar (GLORIA) and high-resolution seismic studies

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

Damuth, J.E.; Flood, R.D.; Kowsmann, R.O.

1988-08-01

Imaging of the Amazon deep-sea fan with long-range side-scan sonar (GLORIA) has, for the first time, revealed the anatomy, trends, and growth pattern of distributary channels on this fan. Only one channel-levee system was active at any given time and extended from the Amazon Submarine Canyon downslope onto the lower fan (> 4,200 m). Formation of new channel-levee systems occurred when a currently active channel-levee system was cut off and abandoned through avulsion, and a new channel-levee system was established nearby. Through time, successive channel-levee formation and abandonment built two broad levee complexes consisting of groups of overlapping, coalescing segmentsmore » of channel-levee systems across the present fan surface. These, plus older, now buried levee complexes, indicate that fan growth is radially outward and downslope through development of successive levee complexes. The most striking characteristic of the distributary channels is their intricate, often recurving, meanders with sinuosities of up to 2.5. Cutoffs and abandoned meander loops indicate that the channels migrate laterally through time. Channel bifurcation results predominantly from avulsion when flows breach a channel levee, thereby abandoning the present channel and establishing a new channel-levee segment nearby. No clear evidence of channel branching (i.e., division of a single channel into two active segments) or braiding was observed. 22 figs.« less

Reproductive indices in natural nests of giant Amazon river turtles Podocnemis expansa (Schweigger, 1812) (Testudines, Podocnemididae) in the Environmental Protection Area Meanders of the Araguaia River.

PubMed

Alves-Júnior, J R F; Lustosa, A P G; Bosso, A C S; Balestra, R A M; Bastos, L F; Miranda, L B; Santos, A L Q

2012-02-01

A count was made of unhatched eggs and hatchling live and dead Podocnemis expansa turtles in 327 natural nests located on the beaches of the Environmental Protection Area (EPA) Meanders of the Araguaia River, to determine the percentage of hatching (94.63%), non-hatching (5.37%), survival (94.24%) and hatchling mortality (5.76%), and the average percentage of dead hatchlings during the 15 days in the nursery (0.97%). The mean number of hatchlings per nest was determined from the sum of the number of live and dead hatchlings divided by the total number of nests, while the mean number of eggs per nest was determined from the sum of live and dead hatchlings and unhatched eggs divided by the number of nests. These calculations yielded the following mean values: live hatchlings (88.98 ± 23.94), dead hatchlings (0.37 ± 0.93), unhatched eggs (5.07 ± 9.57), and total number of eggs (94.42 ± 21.30). The reproductive efficiency of the wild population of P. expansa can be affected by many environmental factors such as temperature, humidity and rainfall. In addition, man-made factors like the presence of chemicals in the water and the potential for infectious disease also have significant impact. The reproductive indices data obtained from this study are indispensable for future investigations of hatching anomalies.

Packing, Scheduling and Covering Problems in a Game-Theoretic Perspective

NASA Astrophysics Data System (ADS)

Karlstrom, Leif

Magma transport pathways through Earth's crust span 12--15 orders of magnitude in time and space, with unsteadiness at all scales. However emergent organization of this system is widespread, recorded by spatial loci of volcanism at the surface and large-scale, rapid outpourings of magma throughout the geologic record. This thesis explores several mechanisms for the organization and time evolution of magma transport, from the deep crust to the surface. A primary focus (Chapters 2--5) is the filling, stability and drainage of magma chambers, structures which function both as reservoirs feeding individual volcanic eruptions and as stalling points in the crust where magma accumulates and differentiation occurs. We show that magma chambers may dictate the spatio-temporal organization of magma rising through crust (Chapters 2--3), control the surface eruptive progression of extreme mantle melting events (Chapter 4), and actively set the size of calderas that form during shallow, crystal rich eruptions (Chapter 5). Each of these chapters explores variations on a hypothesis: interactions between magma chamber stresses and the rheology of surrounding crustal materials evolve during magma transport and this unsteady process helps determine the magnitude, location, and timing of surface eruptions. The last part of this thesis (Chapters 6--7) focuses on surface transport processes, the meandering of melt channels on the surface of glaciers and lava flows. We show that the meandering instability is a generic feature of flow over an erodable substrate, despite significantly different fluid characteristics and erosion mechanics.

Depositional environments of the uranium-bearing Cutler Formations, Lisbon Valley, Utah

USGS Publications Warehouse

Campbell, John A.; Steele-Mallory, Brenda A.

1979-01-01

The Cutler Formation in Lisbon Valley, San Juan County, Utah, is composed predominantly of fluvial arkosic sandstones, siltstones, shales, and mudstones that were deposited by meandering streams that flowed across a flood plain and tidal flat close to sea level. Two types of channel deposits are recognized from their sedimentary structures: meandering and distributary. The flood plain was occasionally transgressed by a shallow sea from the west, resulting in the deposition of several thin limestones and marine sandstones. The marine sandstones were deposited as longshore bars. Wind transported sand along the shoreline of the shallow sea, forming a coastal dune field. Marine sandstones and eolian sandstones are more common in the upper Cutler in the southern part of the area, whereas in the central and northern part of the area the formation is predominantly fluvial. Crossbed orientation indicates that Cutler streams flowed S. 67? W. on the the average, whereas marine currents moved sediment S. 36? E. and N. 24? W., and wind transported sand S. 800 E. The uranium in the Cutler is found in the central and northern part of the area, in the upper part of the formation, in small fluvial sandstone bodies that were deposited predominantly in a distributary environment. No uranium is known in the marine or eolian sandstones. Petrographically, the uranium-bearing sandstones are identical to other Cutler fluvial sandstones except that they contain less calcite and more clay and are slightly coarser grained. Ore formation has modified the host sandstones very little.

A Dual Band Frequency Reconfigurable Origami Magic Cube Antenna for Wireless Sensor Network Applications

PubMed Central

Shah, Syed Imran Hussain

2017-01-01

In this paper, a novel dual band frequency reconfigurable antenna using an origami magic cube is proposed for wireless sensor network (WSN) applications. The proposed origami antenna consists of a meandered monopole folded onto three sides of the magic cube. A microstrip open-ended stub is loaded on the meandered monopole. The proposed origami magic cube can be mechanically folded and unfolded. The proposed antenna operates at 1.57 GHZ and 2.4 GHz in the folded state. In the unfolded state, the proposed antenna operates at 900 MHz and 2.3 GHz. The resonant frequency of the second band can be tunable by varying the length and position of the open stub. The origami magic cube is built on paper. Its performance is numerically and experimentally demonstrated from S-parameters and radiation patterns. The measured 10 dB impedance bandwidth of the proposed origami antenna is 18% (900–1120 MHz) and 15% (2.1–2.45 GHz) for the unfolded state and 20% (1.3–1.6 GHz) and 14% (2.3–2.5 GHz) for the folded state. The measured peak gain at 900 MHz and 2.3 GHz are 1.1 dBi and 2.32 dBi, respectively, in the unfolded state. The measured peak gain at 1.5 GHz and 2.4 GHz are 3.28 dBi and 1.98 dBi, respectively, in the folded state. PMID:29156654

Topographic Signatures of Meandering Rivers with Differences in Outer Bank Cohesion

NASA Astrophysics Data System (ADS)

Kelly, S. A.; Belmont, P.

2014-12-01

Within a given valley setting, interactions between river hydraulics, sediment, topography, and vegetation determine attributes of channel morphology, including planform, width and depth, slope, and bed and bank properties. These feedbacks also govern river behavior, including migration and avulsion. Bank cohesion, from the addition of fine sediment and/or vegetation has been recognized in flume experiments as a necessary component to create and maintain a meandering channel planform. Greater bank cohesion slows bank erosion, limiting the rate at which a river can adjust laterally and preventing so-called "runaway widening" to a braided state. Feedbacks of bank cohesion on channel hydraulics and sediment transport may thus produce distinct topographic signatures, or patterns in channel width, depth, and point bar transverse slope. We expect that in bends of greater outer bank cohesion the channel will be narrower, deeper, and bars will have greater transverse slopes. Only recently have we recognized that biotic processes may imprint distinct topographic signatures on the landscape. This study explores topographic signatures of three US rivers: the lower Minnesota River, near Mankato, MN, the Le Sueur River, south central MN, and the Fall River, Rocky Mountain National Park, CO. Each of these rivers has variability in outer bank cohesion, quantified based on geotechnical and vegetation properties, and in-channel topography, which was derived from rtkGPS and acoustic bathymetry surveys. We present methods for incorporating biophysical feedbacks into geomorphic transport laws so that models can better simulate the spatial patterns and variability of topographic signatures.

Linking hydro-morphology with invertebrate ecology in diverse morphological units of a large river-floodplain system

NASA Astrophysics Data System (ADS)

Blettler, Martín. C. M.; Amsler, Mario L.; Eberle, Eliana G.; Szupiany, Ricardo; Latosinski, Francisco G.; Abrial, Elie; Oberholster, Paul J.; Espinola, Luis A.; Paira, Aldo; Poza, Ailen; Rodrigues Capítulo, Alberto

2016-12-01

Interdisciplinary research in the fields of ecohydrology and ecogeomorphology is becoming increasingly important as a way to understand how biological and physical processes interact with each other in river systems. The objectives of the current study were 1) to determine changes in invertebrate community due to hydrological stages, 2) to link local physical features [flow configuration, sediment composition and morphological feature) with the ecological structure between and within dissimilar morphological units (meander and confluence), and 3) to determine the existence and the origin of bed hydro-geomorphic patches, determining their ecological structure. Results were discussed in the frame of prevailing ecological models and concepts. The study site extends over a floodplain area of the large Paraná River (Argentina), including minor and major secondary channels as well as the main channel. Overall results suggested that hydrodynamics was the driving force determining distribution patterns of benthic assemblages in the floodplain. However, while the invertebrates living in minor secondary channels seem to benefit from flooding, this hydrological phase had the opposite effect on organisms from the main and major secondary channels. We also found a clear linkage between physical features and invertebrate ecology, which caused a dissimilar fauna structure between and within the meander and the confluence. Furthermore, several sandy-patches were recorded in the confluence. These patches were colonized by the particular benthic assemblage recorded in the main channel, supported the view of rivers as patchy discontinua, under uncertain ecological equilibrium.

River morphodynamics from space: the Landsat frontier

NASA Astrophysics Data System (ADS)

Schwenk, Jon; Khandelwal, Ankush; Fratkin, Mulu; Kumar, Vipin; Foufoula-Georgiou, Efi

2017-04-01

NASA's Landsat family of satellites have been observing the entire globe since 1984, providing over 30 years of snapshots with an 18 day frequency and 30 meter resolution. These publicly-available Landsat data are particularly exciting to researchers interested in river morphodynamics, who are often limited to use of historical maps, aerial photography, and field surveys with poor and irregular time resolutions and limited spatial extents. Landsat archives show potential for overcoming these limitations, but techniques and tools for accurately and efficiently mining the vault of scenes must first be developed. In this PICO presentation, we detail the problems we encountered while mapping and quantifying planform dynamics of over 1,300 km of the actively-migrating, meandering Ucayali River in Peru from Landsat imagery. We also present methods to overcome these obstacles and introduce the Matlab-based RivMAP (River Morphodynamics from Analysis of Planforms) toolbox that we developed to extract banklines and centerlines, compute widths, curvatures, and angles, identify cutoffs, and quantify planform changes via centerline migration and erosion/accretion over large spatial domains with high temporal resolution. Measurement uncertainties were estimated by analyzing immobile, abandoned oxbow lakes. Our results identify hotspots of planform changes, and combined with limited precipitation, stage, and topography data, we parse three simultaneous controls on river migration: climate, sediment, and meander cutoff. Overall, this study demonstrates the vast potential locked within Landsat archives to identify multi-scale controls on river migration, observe the co-evolution of width, curvature, discharge, and migration, and discover and develop new geomorphic insights.

Geomorphic and vegetation changes in a meandering dryland river regulated by a large dam, Sauce Grande River, Argentina

NASA Astrophysics Data System (ADS)

Casado, Ana; Peiry, Jean-Luc; Campo, Alicia M.

2016-09-01

This paper investigates post-dam geomorphic and vegetation changes in the Sauce Grande River, a meandering dryland river impounded by a large water-conservation dam. As the dam impounds a river section with scarce influence of tributaries, sources for fresh water and sediment downstream are limited. Changes were inspected based on (i) analysis of historical photographs/imagery spanning pre- (1961) and post-dam (1981, 2004) channel conditions for two river segments located above and below the dam, and (ii) field survey of present channel conditions for a set of eight reference reaches along the river segments. Whilst the unregulated river exhibited active lateral migration with consequent adjustments of the channel shape and size, the river section below the dam was characterized by (i) marked planform stability (93 to 97%), and by (ii) vegetation encroachment leading to alternating yet localized contraction of the channel width (up to 30%). The present river displays a moribund, stable channel where (i) redistribution of sediment along the river course no longer occurs and (ii) channel forms constitute a remnant of a fluvial environment created before closing the dam, under conditions of higher energy. In addition to providing new information on the complex geomorphic response of dryland rivers to impoundment, this paper represents the very first geomorphic assessment of the regulated Sauce Grande and therefore provides an important platform to underpin further research assessing the geomorphic state of this highly regulated dryland river.

Morphology and sediment dynamics of the Capbreton canyon (Bay of Biscay, SW France)

NASA Astrophysics Data System (ADS)

Gaudin, M.; Umr 5805; Ifremer Team

2003-04-01

The Canyon of Capbreton extending in the Bay of Biscay (SW France) is the deepest canyon in the world. Its structure and morphology was studied using new multibeam bathymetry, acoustic imagery and high-resolution seismic data. The canyon head appears only 250 m away from the coast line and runs westward parallel to the north coast of Spain for 160 km due to structural control, then turns northward, widens and abruptly disappears in the continental rise by 3500 m water depth. Its northern margin is flat and progrades clearly westward. Conversely the southern margin is steep and progrades towards the north (i.e. towards the canyon). Down to 800 m water depth, the canyon deeply incises the continental shelf and the axial channel is meandering (sinuosity of 1.9). The canyon shows both major and minor stream beds, perched tributary valleys, nested terraces and abandoned meanders. The terraces have three morphologies: (1) flat, (2) with a raised side or (3) with a horseshoe structure. These morphologies have been interpreted as overbank deposits or nested levees (1 and 2) or as the result of meander abandon (3). Terraces of types (1) and (2) contain mainly fine deposits resulting from decantation of the top of turbulent surges that flow in the canyon. Westward (800 to 2000 m water depth) the main talweg remains sinuous (1.7). On the southern margin, several straight or slightly sinuous S-N tributary valleys are followed by alignments of pockmarks that also indicate a structural control. On the northern margin, a single large tributary valley with a sinuous central talweg, flowing from the upper Aquitaine continental slope, is interpreted as a giant slump scar due to sediment instability. This valley is bordered to the west by a topographic high with sediment waves on the external flank that might be interpreted as a sedimentary levee. The canyon recorded a recent turbidite activity. An 18 cm-thick turbidite was deposited at 650 m water depth by a turbidity current triggered by the storm which affected the French Atlantic coast on 27.12.1999. These present sedimentary processes contribute to maintain the freshness of the canyon morphology. However, the present frequency (in the range of one event every ten years) of gravity processes is too low to explain the incision. This suggests an increased activity when the canyon head was connected to the Adour River (previous to 1310 AD).

Sinuosity change of the Po River near Cremona (Northern Italy) - a result of neotectonic activity?

NASA Astrophysics Data System (ADS)

Petrovszki, Judit; Timár, Gábor

2010-05-01

In the map sheets of the Second Military Survey of the Habsburg Empire, Lombardia, Parma, Modena and Venice also can be seen (Timár et al., 2006). This area was surveyed between 1818 and 1829. In these map sheets, we can also follow the river Po from Vaccarizza to the delta. This river reach is about 350 km long. This river reach was digitized and sinuosity values were calculated with different window sizes, and displayed in a spectrum-like diagram (sinuosity spectra; after van Balen et al., 2008). At Cremona, a significante sinuosity change were identified. The sinuosity increasing, and we have high sinuosity values. In the summarizing geological map of Italy (Compagnoni and Calluzzo, 2004), at this place, a tectonic line was identified. So probably this fault line invokes the sinuosity change on the river. The vertical movements indicated on the maps are just the opposite like they would be according to the flume experiments of Ouchi (1985). In the case of the Po River at Cremona, the decrease of the channel slope results higher sinuosity. The reason is that the rate of the slope and water discharge is higher than it is required by the self-organized meandering and the river parameters fell to the range of the unorganized meandering (cf. Timár, 2003). Another possible explanation could be that the northern tributary, the Adda River has significant sediment load that lowers the sinuosity of the trunk river at the confluence. Compagnoni, B., Galluzzo, F. (eds., 2004): Geological Map of Italy. Agenzia per la Protezione dell'Ambiente per I Servizi Tecnici - Dipartimento Difesa del Suolo, Servizio Geologico d'Italia, Rome-Florence-Genoa. Map, scale=1:1250000, especially printed for the 32nd International Geological Congress. Ouchi, S. (1985): Response of alluvial rivers to slow active tectonic movement. Geol. Soc. Am. Bull. 96: 504-515. Timár, G. (2003): Controls on channel sinuosity changes: a case study of the Tisza River, the Great Hungarian Plain. Quaternary Science Reviews 22: 2199-2207. Timár, G., Molnár, G., Székely, B., Biszak, S., Varga, J., Jankó, A. (2006): Digitized maps of the Habsburg Empire - The map sheets of the second military survey and their georeferenced version. Arcanum, Budapest, 59 p. van Balen, R. T., Kasse, C., Moor, J. (2008): Impact of groundwater flow on meandering; example from the Geul river, the Netherlands. Earth Surf. Process. and Landf. 33(13): 2010-2028.

A systematic overview of the coincidences of river sinuosity changes and tectonically active structures in the Pannonian Basin

NASA Astrophysics Data System (ADS)

Petrovszki, Judit; Székely, Balázs; Timár, Gábor

2012-12-01

As tectonic movements change the valley slope (low-gradient reaches of valleys, in sedimentary basins), the alluvial rivers, as sensitive indicators, respond to these changes, by varying their courses to accommodate this forcing. In our study sinuosity values, a commonly used characteristic parameter to detect river pattern changes, were studied for the major rivers in the Pannonian Basin in order to reveal neotectonic influence on their planform shape. Our study area comprises the entire Pannonian Basin (330,000 km2) located in eastern Central-Europe, bounded by the Alps, Carpathians and Dinarides. The studied rivers were mostly in their natural meandering state before the main river regulations of the 19th century. The last quasi-natural, non-regulated river planforms were surveyed somewhat earlier, during the Second Military Survey of the Habsburg Empire. Using the digitized river sections of that survey, the sinuosities of the rivers were calculated with different sample section sizes ranging from 5 km to 80 km. Depending on the bank-full discharge, also a 'most representative' section size is given, which can be connected to the neotectonic activity. In total, the meandering reaches of 28 rivers were studied; their combined length is 7406 km. The places where the river sinuosity changed were compared to the structural lines of the "Atlas of the present-day geodynamics of the Pannonian Basin" (Horváth et al., 2006). 36 junctions along 26 structural lines were identified where the fault lines of this neotectonic map crossed the rivers. Across these points the mean sinuosity changed. Depending on the direction of the relative vertical movements, the sinuosity values increased or decreased. There were some points, where the sinuosity changed in an opposite way. Along these sections, the rivers belong to the range of unorganized meandering or there are lithological margins. Assuming that the rivers indicate on-going faulting accurately, some places were found, where positioning of the faults of the neotectonic map could be improved according to the sinuosity jumps. However, some significant sinuosity changes cannot be correlated to known faults. In these cases other factors may play a role (e.g., hydrological changes, increase of sediment discharge also can modify sinuosity). In order to clarify the origin of these changes seismic sections and other geodynamical information should be analyzed to prove or disprove tectonic relationship if hydrological reasons can be excluded.

Two-dimensional metamaterial transparent metal electrodes for infrared optoelectronics.

PubMed

Clark, Samuel M; Han, Sang Eon

2014-06-15

We examine the optical properties of two-dimensionally nanostructured metals in the metamaterial regime for infrared applications. Compared with straight nanowires and nanogrids, serpentine structures exhibit much lower optical losses of less than 7% even at a large metal area fraction of 0.3. The low loss is primarily due to a small effective conductivity of the meandering structures, and self-inductance plays a modest role in reducing losses in these structures. The high transparency at a large metal area coverage would be useful for transparent electrodes in optoelectronic devices.

Accessing the scientific literature. The reality of virtual scholarship.

PubMed

Birrer, R B; Doherty, M

1997-01-01

The age-honored practice of plowing through the Index Medicus in a good medical library to meander through citations for treasured finds is an anachronism. Today, clinicians have the astonishing capacity to bring to bear existing knowledge almost effortlessly. Virtual scholarship makes available up-to-date medical citations and their abstracts. There can be access around the clock on any topic in the office, at the bedside, or from home. Computerized searches of the medical literature promote directed continuing education and may enhance clinical care of patients.

Atlantis on Approach to ISS during the STS-132 Mission

NASA Image and Video Library

2010-05-16

ISS023-E-044528 (16 May 2010) --- Flying above coastal dunes along the Brazilian coast, the space shuttle Atlantis is shown making its relative approach to the International Space Station, from which this photo was taken. The city of Rutoia is close to the bay near the center of the image and the sandy meanders of the Rio Parnaiba. Center point coordinates of the image are 2.9 degrees south latitude and 42.2 degrees west longitude. Photo credit: NASA or National Aeronautics and Space Administration

Metallic Bead Detection by Using Eddy-Current Probe with SV-GMR Sensor

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

Yamada, S.; Chomsuwan, K.; Hagino, T.

2005-04-09

The progress of the ECT probe with micro magnetic sensor becomes possible to apply to various applications. The detection of micro metallic bead used for electric packaging has been reported in this paper. We proposed micro ECT probes with meander coil as exciter and spin-valve giant magneto-resistance (SV-GMR) as receiver. Micro metallic bead(solder ball) with the diameter of 0.25 to 0.76 mm is used as a measuring object. We discuss the detection and alignment of metallic bead by using ECT technique.

Satellite altitude determination uncertainties

NASA Technical Reports Server (NTRS)

Siry, J. W.

1972-01-01

Satellite altitude determination uncertainties will be discussed from the standpoint of the GEOS-C satellite, from the longer range viewpoint afforded by the Geopause concept. Data are focused on methods for short-arc tracking which are essentially geometric in nature. One uses combinations of lasers and collocated cameras. The other method relies only on lasers, using three or more to obtain the position fix. Two typical locales are looked at, the Caribbean area, and a region associated with tracking sites at Goddard, Bermuda and Canada which encompasses a portion of the Gulf Stream in which meanders develop.

Eddies and Filaments of the Western Adriatic Current near Cape Gargano: Analysis and Prediction

DTIC Science & Technology

2008-10-21

circulation in the lee of the cape. By 4 Sep. (Fig. 7b), the winds have relaxed, and the meanders are larger in amplitude. The anti-cyclone in the lee of...branch, which forms an anti- cyclonic ‘ lee ’ eddy near the cape, and an eastward branch, which forms a matching cyclonic eddy further downstream. In some...separation of the resulting combined flow and its subsequent point of impingement on the coast vary from frame to frame. The lee eddy resembles one described

Geology of the Molina Member of the Wasatch Formation, Piceance Basin, Colorado

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

Lorenz, J.; Nadon, G.; LaFreniere, L.

1996-06-01

The Molina Member of the Wasatch Formation has been cored in order to assess the presence/absence and character of microbial communities in the deep subsurface. Geological study of the Molina Member was undertaken in support of the microbiological tasks of this project, for the purposes of characterizing the host strata and of assessing the potential for post-depositional introduction of microbes into the strata. The Molina Member comprises a sandy fluvial unit within a formation dominated by mudstones. Sandy to conglomeratic deposits of braided and meandering fluvial systems are present on the western and eastern margins of the basin respectively, althoughmore » the physical and temporal equivalence of these systems cannot be proven. Distal braided facies of planar-horizontal bedded sandstones are recognized on the western margin of the basin. Natural fractures are present in all Molina sandstones, commonly as apparent shear pairs. Core from the 1-M-18 well contains natural fractures similar to those found in outcrops, and has sedimentological affinities to the meandering systems of the eastern margin of the basin. The hydrologic framework of the Molina, and thus any potential post-depositional introduction of microbes into the formation, should have been controlled by approximately east-west flow through the natural fracture system, the geometries and extent of the sandstones in which the fractures occur, and hydraulic gradient. Migration to the well site, from outcropping recharge areas at the edge of the basin, could have started as early as 40 million years ago if the cored strata are connected to the eastern sedimentary system.« less

Thinking outside the Box: Rotor Modulation in the Treatment of Atrial Fibrillation.

PubMed

Sehra, Ruchir; Narayan, Sanjiv M; Hummel, John

2013-01-01

Ablation for atrial fibrillation (AF) is an important and exciting therapy whose results remain suboptimal. Although most clinical trials show that ablation eliminates AF more effectively than medications, it is disappointing that the continued single procedural success remains ≈50% despite the substantial advances that have taken place in imaging, catheter positioning and energy delivery. Focal impulse and rotor modulation (FIRM), on the other hand, offers the opportunity to precisely define and then ablate patient-specific sustaining mechanisms for AF, rather than trying to eliminate all possible AF triggers. For over a decade, electrophysiologists have described cases in which AF terminates after only limited ablation - usually that cannot be explained by 'random' meandering wavelets. Indeed, recent studies from several laboratories show that all forms of clinical AF are typically 'driven' by stable electrical rotors and focal sources, not by multiple meandering waves. FIRM mapping enables an operator to place a catheter at typically 1-3 predicted sites in the atria, and with <5-10 minutes of RF ablation, terminate AF and potentially render it non-inducible. Several independent laboratories have now shown that such FIRM ablation alone can terminate or substantially slow AF in >80% of patients with persistent and paroxysmal AF and increase the single procedure rate of AF elimination from 50% with PV isolation alone to >80%. Ongoing studies hint that FIRM only ablation, enabling ablation times in the range observed for typical atrial flutter, may also achieve these high success rates without subsequent trigger ablation. This review summarizes the current state-of-the-art on FIRM mapping and ablation.

Defibrillation depends on conductivity fluctuations and the degree of disorganization in reentry patterns.

PubMed

Plank, Gernot; Leon, L Joshua; Kimber, Shane; Vigmond, Edward J

2005-02-01

Defibrillation depends on conductivity and disorganization. Cardiac fibrillation is the deterioration of the heart's normally well-organized activity into one or more meandering spiral waves, which subsequently break up into many meandering wave fronts. Delivery of an electric shock (defibrillation) is the only effective way of restoring the normal rhythm. This study focuses on examining whether higher degrees of disorganization requires higher shock strengths to defibrillate and whether microscopic conductivity fluctuations favor shock success. We developed a three-dimensional computer bidomain model of a block of cardiac tissue with straight fibers immersed in a conductive bath. The membrane behavior was described by the Courtemanche human atrial action potential model incorporating electroporation and an acetylcholine- (ACh) dependent potassium current. Intracellular conductivities were varied stochastically around nominal values with variations of up to 50%. A single rotor reentry was initiated and, by adjusting the spatial ACh variation, the level of organization could be controlled. The single rotor could be stabilized or spiral wave breakup could be provoked leading to fibrillatory-like activity. For each level of organization, multiple shock timings and strengths were applied to compute the probability of shock success as a function of shock strength. Our results suggest that the level of the small-scale conductivity fluctuations is a very important factor in defibrillation. A higher variation significantly lowers the required shock strength. Further, we demonstrated that success also heavily depends on the level of organization of the fibrillatory episode. In general, higher levels of disorganization require higher shock strengths to defibrillate.

Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs, North Slope, Alaska

USGS Publications Warehouse

Flores, Romeo M.; Myers, Mark D.; Houseknecht, David W.; Stricker, Gary D.; Brizzolara, Donald W.; Ryherd, Timothy J.; Takahashi, Kenneth I.

2007-01-01

Stratigraphic and sedimentologic studies of facies of the Upper Cretaceous rocks along the Colville River Bluffs in the west-central North Slope of Alaska identified barrier shoreface deposits consisting of vertically stacked, coarsening-upward parasequences in the Schrader Bluff Formation. This vertical stack of parasequence deposits represents progradational sequences that were affected by shoaling and deepening cycles caused by fluctuations of sea level. Further, the vertical stack may have served to stabilize accumulation of voluminous coal deposits in the Prince Creek Formation, which formed braided, high-sinuosity meandering, anastomosed, and low-sinuosity meandering fluvial channels and related flood plain deposits. The erosional contact at the top of the uppermost coarsening-upward sequence, however, suggests a significant drop of base level (relative sea level) that permitted a semiregional subaerial unconformity to develop at the contact between the Schrader Bluff and Prince Creek Formations. This drop of relative sea level may have been followed by a relative sea-level rise to accommodate coal deposition directly above the unconformity. This rise was followed by a second drop of relative sea level, with formation of incised valley topography as much as 75 ft deep and an equivalent surface of a major marine erosion or mass wasting, or both, either of which can be traced from the Colville River Bluffs basinward to the subsurface in the west-central North Slope. The Prince Creek fluvial deposits represent late Campanian to late Maastrichtian depositional environments that were affected by these base level changes influenced by tectonism, basin subsidence, and sea-level fluctuations.

Characterizing frontal eddies along the East Australian Current from HF radar observations

NASA Astrophysics Data System (ADS)

Schaeffer, Amandine; Gramoulle, A.; Roughan, M.; Mantovanelli, A.

2017-05-01

The East Australian Current (EAC) dominates the ocean circulation along south-eastern Australia, however, little is known about the submesoscale frontal instabilities associated with this western boundary current. One year of surface current measurements from HF radars, in conjunction with mooring and satellite observations, highlight the occurrence and propagation of meanders and frontal eddies along the inshore edge of the EAC. Eddies were systematically identified using the geometry of the high spatial resolution (˜1.5 km) surface currents, and tracked every hour. Cyclonic eddies were observed irregularly, on average every 7 days, with inshore radius ˜10 km. Among various forms of structures, frontal eddies associated with EAC meanders were characterized by poleward advection speeds of ˜0.3-0.4 m/s, migrating as far as 500 km south, based on satellite imagery. Flow field kinematics show that cyclonic eddies have high Rossby numbers (0.6-1.9) and enhance particle dispersion. Patches of intensified surface divergence at the leading edge of the structures are expected to generate vertical uplift. This is confirmed by subsurface measurements showing temperature uplift of up to 55 m over 24 h and rough estimates of vertical velocities of 10s of meters per day. While frontal eddies propagate through the radar domain independently of local wind stress, upfront wind can influence their stalling and growth, and can also generate large cold core eddies through intense shear. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal or deep waters, influencing physical and biological dynamics, and connectivity over large distances.

Stretchable multilayer self-aligned interconnects fabricated using excimer laser photoablation and in situ masking

NASA Astrophysics Data System (ADS)

Lin, Kevin L.; Jain, Kanti

2009-02-01

Stretchable interconnects are essential to large-area flexible circuits and large-area sensor array systems, and they play an important role towards the realization of the realm of systems which include wearable electronics, sensor arrays for structural health monitoring, and sensor skins for tactile feedback. These interconnects must be reliable and robust for viability, and must be flexible, stretchable, and conformable to non-planar surfaces. This research describes the design, modeling, fabrication, and testing of stretchable interconnects on polymer substrates using metal patterns both as functional interconnect layers and as in-situ masks for excimer laser photoablation. Excimer laser photoablation is often used for patterning of polymers and thin-film metals. The fluences for photoablation of polymers are generally much lower than the threshold fluence for removal or damage of high-thermallyconductive metals; thus, metal thin films can be used as in-situ masks for polymers if the proper fluence is used. Selfaligned single-layer and multi-layer interconnects of various designs (rectilinear and 'meandering') have been fabricated, and certain 'meandering' interconnect designs can be stretched up to 50% uniaxially while maintaining good electrical conductivity and structural integrity. These results are compared with Finite Element Analysis (FEA) models and are observed to be in good accordance with them. This fabrication approach eliminates masks and microfabrication processing steps as compared to traditional fabrication approaches; furthermore, this technology is scalable for large-area sensor arrays and electronic circuits, adaptable for a variety of materials and interconnects designs, and compatible with MEMS-based capacitive sensor technology.

Investigating spatial variability of vertical water fluxes through the streambed in distinctive stream morphologies using temperature and head data

NASA Astrophysics Data System (ADS)

Wang, Liping; Jiang, Weiwei; Song, Jinxi; Dou, Xinyi; Guo, Hongtao; Xu, Shaofeng; Zhang, Guotao; Wen, Ming; Long, Yongqing; Li, Qi

2017-08-01

Investigating the interaction of groundwater and surface water is key to understanding the hyporheic processes. The vertical water fluxes through a streambed were determined using Darcian flux calculations and vertical sediment temperature profiles to assess the pattern and magnitude of groundwater/surface-water interaction in Beiluo River, China. Field measurements were taken in January 2015 at three different stream morphologies including a meander bend, an anabranching channel and a straight stream channel. Despite the differences of flux direction and magnitude, flux directions based on vertical temperature profiles are in good agreement with results from Darcian flux calculations at the anabranching channel, and the Kruskal-Wallis tests show no significant differences between the estimated upward fluxes based on the two methods at each site. Also, the upward fluxes based on the two methods show similar spatial distributions on the streambed, indicating (1) that higher water fluxes at the meander bend occur from the center of the channel towards the erosional bank, (2) that water fluxes at the anabranching channel are higher near the erosional bank and in the center of the channel, and (3) that in the straight channel, higher water fluxes appear from the center of the channel towards the depositional bank. It is noted that higher fluxes generally occur at certain locations with higher streambed vertical hydraulic conductivity ( K v) or where a higher vertical hydraulic gradient is observed. Moreover, differences of grain size, induced by stream morphology and contrasting erosional and depositional conditions, have significant effects on streambed K v and water fluxes.

Chaos in a restricted problem of rotation of a rigid body with a fixed point

NASA Astrophysics Data System (ADS)

Borisov, A. V.; Kilin, A. A.; Mamaev, I. S.

2008-06-01

In this paper, we consider the transition to chaos in the phase portrait of a restricted problem of rotation of a rigid body with a fixed point. Two interrelated mechanisms responsible for chaotization are indicated: (1) the growth of the homoclinic structure and (2) the development of cascades of period doubling bifurcations. On the zero level of the area integral, an adiabatic behavior of the system (as the energy tends to zero) is noted. Meander tori induced by the break of the torsion property of the mapping are found.

Through the microcirculatory maze with machete, molecule, and minicomputer (1986 Alza lecture).

PubMed

Bassingthwaighte, J B

1987-01-01

This is a personal historical essay on meanderings through the jungle of the microcirculatory swamp. Because one pretends that the wandering was purposefully exploratory, a few guideposts are placed at positions where one could discern blaze-marks from earlier wanderers, and the path cut a little wider along some of the routes that may be enjoyed by investigators wanting to put their blazes along more distant paths. Naturally, one starts by coming up the broad rivers, then branching into the little streams. Each of us chooses to seek a different "mother lode," up a different stream.

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

Milyaev, M. A., E-mail: milyaev@imp.uran.ru; Naumova, L. I.; Kamenskii, I. Yu.

Using the example of spin valves of the Ta(50 Å)/Ni{sub 80}Fe{sub 20}(30 Å)/Co{sub 90}Fe{sub 10}(15 Å)/Cu(28 Å)/Co{sub 90}Fe{sub 10}(20 Å)/Mn{sub 75}Ir{sub 25}(50 Å)/Ta(20 Å) composition, factors controlling the hysteresis properties are studied for the case of macro- and microscopic sizes of an experimental sample. It is shown that a linear change in the magnetoresistance with small hysteresis while retaining the giant magnetoresistance effect at a level of 8% can be obtained in a micro-object (meander) using thermomagnetic treatment.

Two-stage bulk electron heating in the diffusion region of anti-parallel symmetric reconnection

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

Le, Ari Yitzchak; Egedal, Jan; Daughton, William Scott

2016-10-13

Electron bulk energization in the diffusion region during anti-parallel symmetric reconnection entails two stages. First, the inflowing electrons are adiabatically trapped and energized by an ambipolar parallel electric field. Next, the electrons gain energy from the reconnection electric field as they undergo meandering motion. These collisionless mechanisms have been described previously, and they lead to highly structured electron velocity distributions. Furthermore, a simplified control-volume analysis gives estimates for how the net effective heating scales with the upstream plasma conditions in agreement with fully kinetic simulations and spacecraft observations.

On the recovery of gravity anomalies from high precision altimeter data

NASA Technical Reports Server (NTRS)

Lelgemann, D.

1976-01-01

A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

Two cases of scimitar variant.

PubMed

Takeda, S; Imachi, T; Arimitsu, K; Minami, M; Hayakawa, M

1994-01-01

The scimitar sign is characteristic of partial anomalous pulmonary venous drainage into the inferior vena cava (IVC). We encountered two variant cases of scimitar sign. In one case, the scimitar vein entered both the IVC and the left atrium (LA) without any intracardiac shunts. Surgical repair was made by simple ligation of the scimitar vein to correct the left to right shunt. Retrograde balloon occlusion angiography of the scimitar vein was diagnostic. In the other case, the scimitar vein showed a meandering course, and then drained into the LA without any connection with the IVC, and surgical intervention was not required.

An experimental study of secondary vortex structure in mixing layers

NASA Technical Reports Server (NTRS)

Bell, J. H.; Mehta, Rabindra D.

1990-01-01

This report covers the first eight months of an experimental research project on the secondary vortex structure in plane mixing layers. The aim of the project is to obtain quantitative data on the behavior of the secondary structure in a turbulent mixing layer at reasonable reynolds numbers (Re(sub delta(sub w)) approx. 50,000). In particular, we hope to resolve the questions of how the scale of the secondary vortex structure changes with the scale of the mixing layer, and whether the structures are fixed in space, or whether they 'meander' in the spanwise direction.

Electromagnetic interference reduction using electromagnetic bandgap structures in packages, enclosures, cavities, and antennas

NASA Astrophysics Data System (ADS)

Mohajer Iravani, Baharak

Electromagnetic interference (EMI) is a source of noise problems in electronic devices. The EMI is attributed to coupling between sources of radiation and components placed in the same media such as package or chassis. This coupling can be either through conducting currents or through radiation. The radiation of electromagnetic (EM) fields is supported by surface currents. Thus, minimizing these surface currents is considered a major and critical step to suppress EMI. In this work, we present novel strategies to confine surface currents in different applications including packages, enclosures, cavities, and antennas. The efficiency of present methods of EM noise suppression is limited due to different drawbacks. For example, the traditional use of lossy materials and absorbers suffers from considerable disadvantages including mechanical and thermal reliability leading to limited life time, cost, volume, and weight. In this work, we consider the use of Electromagnetic Band Gap (EBG) structures. These structures are suitable for suppressing surface currents within a frequency band denoted as the bandgap. Their design is straight forward, they are inexpensive to implement, and they do not suffer from the limitations of the previous methods. A new method of EM noise suppression in enclosures and cavity-backed antennas using mushroom-type EBG structures is introduced. The effectiveness of the EBG as an EMI suppresser is demonstrated using numerical simulations and experimental measurements. To allow integration of EBGs in printed circuit boards and packages, novel miniaturized simple planar EBG structures based on use of high-k dielectric material (epsilonr > 100) are proposed. The design consists of meander lines and patches. The inductive meander lines serve to provide current continuity bridges between the capacitive patches. The high-k dielectric material increases the effective capacitive load substantially in comparison to commonly used material with much lower dielectric constant. Meander lines can increase the effective inductive load which pushes down the lower edge of bandgap, thus resulting in a wider bandgap. Simulation results are included to show that the proposed EBG structures provide very wide bandgap (˜10GHz) covering the multiple harmonics of of currently available microprocessors and its harmonics. To speed up the design procedure, a model based on combination of lumped elements and transmission lines is proposed. The derived model predicts accurately the starting edge of bandgap. This result is verified with full-wave analysis. Finally, another novel compact wide band mushroom-type EBG structure using magneto-dielectric materials is designed. Numerical simulations show that the proposed EBG structure provides in-phase reflection bandgap which is several times greater than the one obtained from a conventional EBG operating at the same frequency while its cell size is smaller. This type of EBG structure can be used efficiently as a ground plane for low-profile wideband antennas.

Morphological assessment of reconstructed lowland streams in the Netherlands

NASA Astrophysics Data System (ADS)

Eekhout, Joris P. C.; Hoitink, Antonius J. F.; de Brouwer, Jan H. F.; Verdonschot, Piet F. M.

2015-07-01

Channelisation measures taken halfway the 20th century have had destructive consequences for the diversity of the ecology in the majority of the lowland streams in countries such as the Netherlands. Re-meandering is the common practice in restoring these lowland streams. Three reconstructed streams were monitored during the initial two years after construction of a new channel. The monitoring program included morphological surveys, sediment sampling, habitat pattern surveys, and discharge and water level measurements. Adjustments of the longitudinal bed profile formed the main morphological response. These adjustments were most likely caused by a lack of longitudinal connectivity of the streams as a whole, interrupting transport of sediment at locations of weirs and culverts. Bank erosion was observed only in a limited number of channel bends, and was often related to floodplain heterogeneity. Longitudinal channel bed adjustments and bank erosion were mainly caused by exogenous influences. In channel bends, the cross-sectional shape transformed from trapezoidal to the typical asymmetrical shape as found in meandering rivers. This behaviour can be attributed to an autogenous response to the prevailing flow conditions. Due to the prevailing fine sediment characteristics, bed material is readily set in motion and is being transported during the entire year. The existing design principles fail to address the initial morphological development after reconstruction. An evaluation of pre-set targets to realise water depth and flow velocity ranges shows the current procedures to be deficient. Based on this unfavourable evaluation, and the two-dimensional nature of habitat patterns needed to improve the conditions for stream organisms, we recommend to predict morphological developments as part of the design procedures for lowland stream restoration in the Netherlands.

Morphological Assessment of Reconstructed Lowland Streams in the Netherlands

NASA Astrophysics Data System (ADS)

Hoitink, T.; Eekhout, J.; de Brouwer, J.; Verdonschot, P.

2014-12-01

Channelisation measures taken halfway the 20th century have had destructive consequences for the diversity of the ecology in the majority of the lowland streams in countries such as the Netherlands. Re-meandering is the common practice in restoring these lowland streams. Three lowland streams were monitored during the initial two years after construction of a new channel. The monitoring program included morphological surveys, sediment sampling, habitat pattern surveys, and discharge and water level measurements. Adjustments of the longitudinal bed profile formed the main morphological response. These adjustments were most likely caused by a lack of longitudinal connectivity of the streams as a whole, interrupting transport of sediment at locations of weirs and culverts. Bank erosion was observed only in a limited number of channel bends, and was often related to floodplain heterogeneity. Longitudinal channel bed adjustments and bank erosion were mainly caused by exogenous influences. In channel bends, the cross-sectional shape transformed from trapezoidal to the typical asymmetrical shape as found in meandering rivers. This behaviour can be attributed to an autogenous response to the prevailing flow conditions. Due to the prevailing fine sediment characteristics, bed material is readily set in motion and is being transported during the entire year. The existing design principles fail to address the initial morphological development after reconstruction. An evaluation of pre-set targets to realize water depth and flow velocity ranges shows the current procedures to be deficient. Based on this unfavourable evaluation, and the two-dimensional nature of habitat patterns needed to improve the conditions for stream organisms, we recommend to predict morphological developments as part of the design procedures for lowland stream restoration in the Netherlands.

Spiral wave classification using normalized compression distance: Towards atrial tissue spatiotemporal electrophysiological behavior characterization.

PubMed

Alagoz, Celal; Guez, Allon; Cohen, Andrew; Bullinga, John R

2015-08-01

Analysis of electrical activation patterns such as re-entries during atrial fibrillation (Afib) is crucial in understanding arrhythmic mechanisms and assessment of diagnostic measures. Spiral waves are a phenomena that provide intuitive basis for re-entries occurring in cardiac tissue. Distinct spiral wave behaviors such as stable spiral waves, meandering spiral waves, and spiral wave break-up may have distinct electrogram manifestations on a mapping catheter. Hence, it is desirable to have an automated classification of spiral wave behavior based on catheter recordings for a qualitative characterization of spatiotemporal electrophysiological activity on atrial tissue. In this study, we propose a method for classification of spatiotemporal characteristics of simulated atrial activation patterns in terms of distinct spiral wave behaviors during Afib using two different techniques: normalized compressed distance (NCD) and normalized FFT (NFFTD). We use a phenomenological model for cardiac electrical propagation to produce various simulated spiral wave behaviors on a 2D grid and labeled them as stable, meandering, or breakup. By mimicking commonly used catheter types, a star shaped and a circular shaped both of which do the local readings from atrial wall, monopolar and bipolar intracardiac electrograms are simulated. Virtual catheters are positioned at different locations on the grid. The classification performance for different catheter locations, types and for monopolar or bipolar readings were also compared. We observed that the performance for each case differed slightly. However, we found that NCD performance is superior to NFFTD. Through the simulation study, we showed the theoretical validation of the proposed method. Our findings suggest that a qualitative wavefront activation pattern can be assessed during Afib without the need for highly invasive mapping techniques such as multisite simultaneous electrogram recordings.

Experiments on tip vortices interacting with downstream wings

NASA Astrophysics Data System (ADS)

Chen, C.; Wang, Z.; Gursul, I.

2018-05-01

The interaction of meandering tip vortices shed from a leading wing with a downstream wing was investigated experimentally in a water tunnel using flow visualization, particle image velocimetry measurements, and volumetric velocity measurements. Counter-rotating upstream vortices may exhibit sudden variations of the vortex core location when the wing-tip separation is within approximately twice the vortex core radius. This is caused by the formation of vortex dipoles near the wing tip. In contrast, co-rotating upstream vortices do not exhibit such sensitivity. Large spanwise displacement of the trajectory due to the image vortex is possible when the incident vortex is further inboard. For both co-rotating and counter-rotating vortices, as long as there is no direct impingement upon the wing, there is a little change in the structure of the time-averaged vortex past the wing, even though the tip vortex shed from the downstream wing may be substantially weakened or strengthened. In the absence of the downstream wing, as well as for weak interactions, the most energetic unsteady modes represent the first helical mode | m| = 1, which is estimated from the three-dimensional Proper Orthogonal Decomposition modes and has a very large wavelength, on the order of 102 times the vortex core radius, λ/ a = O(102). Instantaneous vorticity measurements as well as flow visualization suggest the existence of a smaller wavelength, λ/ a = 5-6, which is not among the most energetic modes. These two-orders of magnitude different wavelengths are in agreement with the previous measurements of tip vortices and also exhibit qualitative agreement with the transient energy growth analysis. The very long wavelength mode in the upstream vortex may persist during the interaction, and reveal coupling with the trailing vortex as well as increased meandering.

Dryland anabranching river morphodynamics: Río Capilla, Salar de Uyuni, Bolivia

NASA Astrophysics Data System (ADS)

Li, Jiaguang; Bristow, Charlie S.; Luthi, Stefan M.; Donselaar, Marinus E.

2015-12-01

The dryland anabranching river Río Capilla is characterized by nonvegetated and vegetated reaches with prominent channel morphology. To identify the morphodynamics of such dryland anabranching systems and their controls, we investigated the Río Capilla of the southern Altiplano Plateau using high-resolution satellite imagery and field measurements. Comparison of high-resolution satellite data reveals that erosion exceeds deposition for the main channel, accompanied by changes in channel planform, such as meander and channel morphology. On-site surveys combined with high-precision GPS and high-resolution satellite imagery show that channels are characterized by shallowness and poor development of levees. The study area of the Río Capilla is divided into two zones of different slopes: zone 1 with a high slope and zone 2 with a low slope. Zone 1 has a relatively straight main channel with few anabranches and grass-covered banks that are stable despite the high gradient; whereas zone 2 is typified by more anabranches with nonvegetated banks, and the main channel experiences prominent bank accretion and erosion. Excavations show that point-bar deposits are fine-sand-dominated in two reaches and that river banks primarily consist of silt and clay. The limited vegetation cover and abundance of desiccation cracks and macropores make the river bank more erodible leading to pronounced lateral migration in this low-gradient dryland river system. Shallow channels and poor development of levees in combination with in-channel accretionary benches result in frequent overbank flooding, which results in a high density of crevasse splays over unconsolidated river banks and accretionary benches. Connection of headcuts and crevasse channels together with lateral migration and chute channels and reactivation of partially abandoned meanders produces an anabranching pattern in such dryland river systems.

Origin and characteristics of high Shannon entropy at the pivot of locally stable rotors: insights from computational simulation.

PubMed

Ganesan, Anand N; Kuklik, Pawel; Gharaviri, Ali; Brooks, Anthony; Chapman, Darius; Lau, Dennis H; Roberts-Thomson, Kurt C; Sanders, Prashanthan

2014-01-01

Rotors are postulated to maintain cardiac fibrillation. Despite the importance of bipolar electrograms in clinical electrophysiology, few data exist on the properties of bipolar electrograms at rotor sites. The pivot of a spiral wave is characterized by relative uncertainty of wavefront propagation direction compared to the periphery. The bipolar electrograms used in electrophysiology recording encode information on both direction and timing of approaching wavefronts. To test the hypothesis that bipolar electrograms from the pivot of rotors have higher Shannon entropy (ShEn) than electrograms recorded at the periphery due to the spatial dynamics of spiral waves. We studied spiral wave propagation in 2-dimensional sheets constructed using a simple cell automaton (FitzHugh-Nagumo), atrial (Courtemanche-Ramirez-Nattel) and ventricular (Luo-Rudy) myocyte cell models and in a geometric model spiral wave. In each system, bipolar electrogram recordings were simulated, and Shannon entropy maps constructed as a measure of electrogram information content. ShEn was consistently highest in the pivoting region associated with the phase singularity of the spiral wave. This property was consistently preserved across; (i) variation of model system (ii) alterations in bipolar electrode spacing, (iii) alternative bipolar electrode orientation (iv) bipolar electrogram filtering and (v) in the presence of rotor meander. Directional activation plots demonstrated that the origin of high ShEn at the pivot was the directional diversity of wavefront propagation observed in this location. The pivot of the rotor is consistently associated with high Shannon entropy of bipolar electrograms despite differences in action potential model, bipolar electrode spacing, signal filtering and rotor meander. Maximum ShEn is co-located with the pivot for rotors observed in the bipolar electrogram recording mode, and may be an intrinsic property of spiral wave dynamic behaviour.

A 184-year record of river meander migration from tree rings, aerial imagery, and cross sections

NASA Astrophysics Data System (ADS)

Schook, Derek M.; Rathburn, Sara L.; Friedman, Jonathan M.; Wolf, J. Marshall

2017-09-01

Channel migration is the primary mechanism of floodplain turnover in meandering rivers and is essential to the persistence of riparian ecosystems. Channel migration is driven by river flows, but short-term records cannot disentangle the effects of land use, flow diversion, past floods, and climate change. We used three data sets to quantify nearly two centuries of channel migration on the Powder River in Montana. The most precise data set came from channel cross sections measured an average of 21 times from 1975 to 2014. We then extended spatial and temporal scales of analysis using aerial photographs (1939-2013) and by aging plains cottonwoods along transects (1830-2014). Migration rates calculated from overlapping periods across data sets mostly revealed cross-method consistency. Data set integration revealed that migration rates have declined since peaking at 5 m/year in the two decades after the extreme 1923 flood (3000 m3/s). Averaged over the duration of each data set, cross section channel migration occurred at 0.81 m/year, compared to 1.52 m/year for the medium-length air photo record and 1.62 m/year for the lengthy cottonwood record. Powder River peak annual flows decreased by 48% (201 vs. 104 m3/s) after the largest flood of the post-1930 gaged record (930 m3/s in 1978). Declining peak discharges led to a 53% reduction in channel width and a 29% increase in sinuosity over the 1939-2013 air photo record. Changes in planform geometry and reductions in channel migration make calculations of floodplain turnover rates dependent on the period of analysis. We found that the intensively studied last four decades do not represent the past two centuries.

Bank Erosion Vulnerability Zonation (BEVZ) -A Proposed Method of Preparing Bank Erosion Zonation and Its Application on the River Haora, Tripura, India

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Shreya; de, Sunil Kumar

2014-05-01

In the present paper an attempt has been made to propose RS-GIS based method for erosion vulnerability zonation for the entire river based on simple techniques that requires very less field investigation. This method consist of 8 parameters, such as, rainfall erosivity, lithological factor, bank slope, meander index, river gradient, soil erosivity, vegetation cover and anthropogenic impact. Meteorological data, GSI maps, LISS III (30m resolution), SRTM DEM (56m resolution) and Google Images have been used to determine rainfall erosivity, lithological factor, bank slope, meander index, river gradient, vegetation cover and anthropogenic impact; Soil map of the NBSSLP, India has been used for assessing Soil Erosivity index. By integrating the individual values of those six parameters (the 1st two parameters are remained constant for this particular study area) a bank erosion vulnerability zonation map of the River Haora, Tripura, India (23°37' - 23°53'N and 91°15'-91°37'E) has been prepared. The values have been compared with the existing BEHI-NBS method of 60 spots and also with field data of 30 cross sections (covering the 60 spots) taken along 51 km stretch of the river in Indian Territory and found that the estimated values are matching with the existing method as well as with field data. The whole stretch has been divided into 5 hazard zones, i.e. Very High, High, Moderate, Low and Very Low Hazard Zones and they are covering 5.66 km, 16.81 km, 40.82km, 29.67 km and 9.04 km respectively. KEY WORDS: Bank erosion, Bank Erosion Hazard Index (BEHI), Near Bank Stress (NBS), Erosivity, Bank Erosion Vulnerability Zonation.

Channel formation by flow stripping: large-scale scour features along the Monterey East Channel and their relation to sediment waves

USGS Publications Warehouse

Fildani, A.; Normark, W.R.; Kostic, S.; Parker, G.

2006-01-01

The Monterey East system is formed by large-scale sediment waves deposited as a result of flows stripped from the deeply incised Monterey fan valley (Monterey Channel) at the apex of the Shepard Meander. The system is dissected by a linear series of steps that take the form of scour-shaped depressions ranging from 3·5 to 4·5 km in width, 3 to 6 km in length and from 80 to 200 m in depth. These giant scours are aligned downstream from a breech in the levee on the southern side of the Shepard Meander. The floor of the breech is only 150 m above the floor of the Monterey fan valley but more than 100 m below the levee crests resulting in significant flow stripping. Numerical modeling suggests that the steps in the Monterey East system were created by Froude-supercritical turbidity currents stripped from the main flow in the Monterey channel itself. Froude-supercritical flow over an erodible bed can be subject to an instability that gives rise to the formation of cyclic steps, i.e. trains of upstream-migrating steps bounded upstream and downstream by hydraulic jumps in the flow above them. The flow that creates these steps may be net-erosional or net-depositional. In the former case it gives rise to trains of scours such as those in the Monterey East system, and in the latter case it gives rise to the familiar trains of upstream-migrating sediment waves commonly seen on submarine levees. The Monterey East system provides a unique opportunity to introduce the concept of cyclic steps in the submarine environment to study processes that might result in channel initiation on modern submarine fans.

Impact of debris dams on hyporheic interaction along a semi-arid stream

NASA Astrophysics Data System (ADS)

Lautz, Laura K.; Siegel, Donald I.; Bauer, Robert L.

2006-01-01

Hyporheic exchange increases the potential for solute retention in streams by slowing downstream transport and increasing solute contact with the substrate. Hyporheic exchange may be a major mechanism to remove nutrients in semi-arid watersheds, where livestock have damaged stream riparian zones and contributed nutrients to stream channels. Debris dams, such as beaver dams and anthropogenic log dams, may increase hyporheic interactions by slowing stream water velocity, increasing flow complexity and diverting water to the subsurface.Here, we report the results of chloride tracer injection experiments done to evaluate hyporheic interaction along a 320 m reach of Red Canyon Creek, a second order stream in the semi-arid Wind River Range of Wyoming. The study site is part of a rangeland watershed managed by The Nature Conservancy of Wyoming, and used as a hydrologic field site by the University of Missouri Branson Geologic Field Station. The creek reach we investigated has debris dams and tight meanders that hypothetically should enhance hyporheic interaction. Breakthrough curves of chloride measured during the field experiment were modelled with OTIS-P, a one-dimensional, surface-water, solute-transport model from which we extracted the storage exchange rate and cross-sectional area of the storage zone As for hyporheic exchange. Along gaining reaches of the stream reach, short-term hyporheic interactions associated with debris dams were comparable to those associated with severe meanders. In contrast, along the non-gaining reach, stream water was diverted to the subsurface by debris dams and captured by large-scale near-stream flow paths. Overall, hyporheic exchange rates along Red Canyon Creek during snowmelt recession equal or exceed exchange rates observed during baseflow at other streams.

Relationship of fluviodeltaic facies to coal deposition in the lower Fort Union formation (Palaeocene), south-western North Dakota

USGS Publications Warehouse

Belt, Edward S.; Flores, Romeo M.; Warwick, Peter D.; Conway, Kevin M.; Johnson, Kirk R.; Waskowitz, Robert S.; Rahmani, R.A.; Flores, Romeo M.

1984-01-01

Facies analysis of the Ludlow and Tongue River Members of the Palaeocene Fort Union Formation provides an understanding of the relationship between fluviodeltaic environments and associated coal deposition in the south-western Williston Basin. The Ludlow Member consists of high-constructive delta facies that interfinger with brackish-water tongues of the Cannonball Member of the Fort Union Formation. The lower part of the Ludlow Member was deposited on a lower delta plain that consisted of interdistributary crevasse and subdelta lobes. The upper part of the Ludlow Member was deposited in meander belts of the upper delta plain. The delta plain facies of the Ludlow Member is overlain by alluvial plain facies consisting of swamp, crevasse-lobe, lacustrine, and trunk meander belt deposits of the Tongue River Member. The Ludlow delta is believed to have been fed by fluvial systems that probably flowed from the Powder River Basin to the Williston Basin undeterred by the Cedar Creek Anticline. However, the evidence indicates that the Cedar Creek Anticline was prominent enough, during early Tongue River Member deposition, to cause the obstruction of the regional fluvial system flowing from the SW, and the formation of local drainage.The Ludlow Member contains 18 coal beds in the area studied, of which the T-Cross and Yule coals are as thick as 4 m (12 ft). Abandoned delta lobes served as platforms where coals formed, which in turn, were drowned by mainly fresh water and subordinate brackish water. Repetition of deltaic sedimentation, abandonment, and occupation by swamp led to preservation of the T-Cross and Oyster coals in areas as extensive as 260 km2 (< 100 miles2).

A theoretical study of topographic effects on coastal upwelling and cross-shore exchange

NASA Astrophysics Data System (ADS)

Song, Y. Tony; Chao, Yi

The effects of topographic variations on coastal upwelling and cross-shore exchange are examined with a theoretical, continuously stratified, three-dimensional coastal ocean model. The model takes into account topographic variations in both alongshore and cross-shore directions and allows analytical solutions with an Ekman surface layer that faithfully represents the physical nature of the coastal upwelling system. Theoretical solutions with any analytical form of alongshore-varying topography can be solved based on the perturbation method of Killworth [J. Phys. Oceanogr. 8 (1978) 188]. Analyses of the model solutions lead to the following conclusions: The variation of upwelling fronts and currents is shown to be caused by the combined effect of topography and stratification. Topographic variation causes uneven upwelling distribution and leads to density variation, which results in a varying horizontal pressure gradient field that causes the meandering currents. The variation index is dependent upon a bilinear function of their physical parameters--the ratio of the topographic variation depth to the total depth and Burger's number of stratification. Cross-shore slope is found to play a role in maintaining the meandering structure of the alongshore currents. The anticyclonic circulations can further induce downwelling on the offshore side of the current, while the cyclonic circulations enhance upwelling and form upwelling centers on the inshore side of the current. Alongshore topography does not change the total upwelled water, i.e., the total Ekman pumping is conserved. However, it increases cross-exchange of water masses by transporting inshore (offshore) water near topographic features far offshore (inshore) from the mean position of the front. The applicability and limitations of the theory are also discussed.

How Do Morphodynamic Signatures Vary Along the Ucayali, a Large Transitional River?

NASA Astrophysics Data System (ADS)

Dauer, K.; Frias, C. E.; Abad, J. D.; Paredes, J.; Vizcarra, J.; Holguin, C.

2013-12-01

The Ucayali River, with an average discharge of 11, 260 m3 ● s-1 at the Requena station, is one of the largest rivers in Peru, and at its confluence with the Maranon River, the Amazon River is born. The Ucayali River transitions from purely meandering to quasi-anabranching planform near the confluence with the Marañon River. In addition, it carries large amounts of suspended sediment and has been shown to display high rates of migration. Prompted by evidence of changing trends in rainfall and discharge in the Amazon basin, where the Ucayali is located, we have performed a baseline characterization of the planform metrics, thus to determine if effects of climatic change on the morphodynamics are happening in this transitional river, which is a vital transportation route for cities in the jungle such as Iquitos, Peru. Herein, the morphodynamics of the Ucayali River are characterized from its upstream end in Atalaya, Peru to its confluence with the Marañon near Nauta City. First, the migration rates along the Ucayali River are calculated from temporal Landsat images. Then migration rates and planform characteristics, such as wavelength and sinuosity, along the river are compared with the slope along the river to distinguish spatial dominant scales. In addition, bathymetry and velocity measurements taken in 2013 along the Ucayali River help us to understand the complex morphodynamics of the river. Specific case studies have been done at Pucallpa and Jenaro-Herrera, Peru using hydrodynamic and bathymetric measurements complemented with high-resolution shallow water modeling to understand the process of cutoff formation in different locations along the river. This study discusses the frequency at which meanders along the Ucayali River shift from low sinuosity to complete maturity in order to produce cutoffs.

Metabolic heterogeneity in human calf muscle during maximal exercise

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

Vandenborne, K.; McCully, K.; Kakihira, H.

1991-07-01

Human skeletal muscle is composed of various muscle fiber types. The authors hypothesized that differences in metabolism between fiber types could be detected noninvasively with {sup 31}P nuclear magnetic resonance spectroscopy during maximal exercise. This assumes that during maximal exercise all fiber types are recruited and all vary in the amount of acidosis. The calf muscles of seven subjects were studied. Two different coils were applied: an 11-cm-diameter surface coil and a five-segment meander coil. The meander coil was used to localize the {sup 31}P signal to either the medial or the lateral gastrocnemius. Maximal exercise, consisting of rapid plantarmore » flexions, resulted in an 83.7% {plus minus} 7.8% decrease of the phosphocreatine pool and an 8-fold increase of the inorganic phosphate (P{sub i}) pool. At rest the P{sub i} pool was observed as a single resonance (pH 7.0). Toward the end of the first minute of exercise, three subjects showed three distinct P{sub i} peaks. During the second minute of exercise the pH values stabilized. The same pattern was seen when the signal was collected from the medial or lateral gastrocnemius. In four subjects only two distinct P{sub i} peaks were observed. The P{sub i} peaks had differing relative areas in different subjects, but they were reproducible in each individual. This method allowed is to study the appearance and disappearance of the different P{sub i} peaks, together with the changes in pH. Because multiple P{sub i} peaks were seen in single muscles they most likely identify different muscle fiber types.« less

A 184-year record of river meander migration from tree rings, aerial imagery, and cross sections

USGS Publications Warehouse

Schook, Derek M.; Rathburn, Sara L.; Friedman, Jonathan M.; Wolf, J. Marshall

2017-01-01

Channel migration is the primary mechanism of floodplain turnover in meandering rivers and is essential to the persistence of riparian ecosystems. Channel migration is driven by river flows, but short-term records cannot disentangle the effects of land use, flow diversion, past floods, and climate change. We used three data sets to quantify nearly two centuries of channel migration on the Powder River in Montana. The most precise data set came from channel cross sections measured an average of 21 times from 1975 to 2014. We then extended spatial and temporal scales of analysis using aerial photographs (1939–2013) and by aging plains cottonwoods along transects (1830–2014). Migration rates calculated from overlapping periods across data sets mostly revealed cross-method consistency. Data set integration revealed that migration rates have declined since peaking at 5 m/year in the two decades after the extreme 1923 flood (3000 m3/s). Averaged over the duration of each data set, cross section channel migration occurred at 0.81 m/year, compared to 1.52 m/year for the medium-length air photo record and 1.62 m/year for the lengthy cottonwood record. Powder River peak annual flows decreased by 48% (201 vs. 104 m3/s) after the largest flood of the post-1930 gaged record (930 m3/s in 1978). Declining peak discharges led to a 53% reduction in channel width and a 29% increase in sinuosity over the 1939–2013 air photo record. Changes in planform geometry and reductions in channel migration make calculations of floodplain turnover rates dependent on the period of analysis. We found that the intensively studied last four decades do not represent the past two centuries

A geomorphological characterisation of river systems in South Africa: A case study of the Sabie River

NASA Astrophysics Data System (ADS)

Eze, Peter N.; Knight, Jasper

2018-06-01

Fluvial geomorphology affects river character, behaviour, evolution, trajectory of change and recovery potential, and as such affects biophysical interactions within a catchment. Water bodies in South Africa, in common with many other water-stressed parts of the world, are generally under threat due to increasing natural and anthropogenic influences including aridity, siltation and pollution, as well as climate and environmental change. This study reports on a case study to characterise the geomorphology of different river systems in South Africa, with the aim of better understanding their properties, controls, and implications for biophysical interactions including water quality, biodiversity (aquatic and riparian), and human activity within the catchment. The approach adopted is based on the River Styles® framework (RSF), a geomorphology-based approach developed for rivers in New Zealand and Australia, but applied here for the first time to South Africa. Based on analysis of remote sensing imagery, SRTM-2 digital topographic data and field observations on sites through the entire river system, six geomorphic elements were identified along the Sabie River, northeast South Africa (gorge, bedrock-forced meander, low-moderate sinuosity planform controlled sand bed, meandering sand bed, low sinuosity fine grained sand bed, and floodouts), using the RSF classification scheme and based on the RSF procedural tree of Brierley and Fryirs (2005). Previous geomorphological studies along the Sabie River have shown that different reaches respond differently to episodic floods; we use these data to link river geomorphological character (as defined by the RSF) to the hydrodynamic conditions and processes giving rise to such character. This RSF approach can be used to develop a new management approach for river systems that considers their functional biophysical behaviour within individual reaches, rather than considering them as homogeneous and uniform systems.

Internal flow patterns on heat transfer characteristics of a closed-loop oscillating heat-pipe with check valves using ethanol and a silver nano-ethanol mixture

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

Bhuwakietkumjohn, N.; Rittidech, S.

The aim of this research was to investigate the internal flow patterns and heat transfer characteristics of a closed-loop oscillating heat-pipe with check valves (CLOHP/CV). The ratio of number of check valves to meandering turns was 0.2. Ethanol and a silver nano-ethanol mixture were used as working fluids with a filling ratio of 50% by total volume of tube. The CLOHP/CV was made of a glass tube with an inside diameter of 2.4 mm. The evaporator section was 50 mm and 100 mm in length and there were 10 meandering turns. An inclination angle of 90 from horizontal axis wasmore » established. The evaporator section was heated by an electric heater and the condenser section was cooled by distilled water. Temperature at the evaporator section was controlled at 85 C, 105 C and 125 C. The inlet and outlet temperatures were measured. A digital camera and video camera were used to observe the flow patterns at the evaporator. The silver nano-ethanol mixture gave higher heat flux than ethanol. When the temperature at the evaporator section was increased from 85 C to 105 C and 125 C. It was found that, the flow patterns occurred as annular flow + slug flow, slug flow + bubble flow and dispersed bubble flow + bubble flow respectively. The main regime of each flow pattern can be determined from the flow pattern map ethanol and a silver nano-ethanol mixture. Each of the two working fluids gave corresponding flow patterns. (author)« less

Channel-shoal morphodynamics in response to distinct hydrodynamic drivers at the outer Weser estuary

NASA Astrophysics Data System (ADS)

Herrling, Gerald; Benninghoff, Markus; Zorndt, Anna; Winter, Christian

2017-04-01

The interaction of tidal, wave and wind forces primarily governs the morphodynamics of intertidal channel-shoal systems. Typical morphological changes comprise tidal channel meandering and/or migration with related shoal erosion or accretion. These intertidal flat systems are likely to response to accelerated sea level rise and to potential changes in storm frequency and direction. The aim of the ongoing research project is an evaluation of outer estuarine channel-shoal dynamics by combining the analysis of morphological monitoring data with high-resolution morphodynamic modelling. A focus is set on their evolution in reaction to different hydrodynamic forcings like tides, wind driven currents, waves under fair-weather and high energy conditions, and variable upstream discharges. As an example the Outer Weser region was chosen, and a tidal channel system serves as a reference site: Availability of almost annual bathymetrical observations of an approx. 10 km long tidal channel (Fedderwarder Priel) and its morphological development largely independent from maintenance dredging of the main Weser navigational channel make this tributary an ideal study area. The numerical modelling system Delft3D (Deltares) is applied to run real-time annual scenario simulations aiming to evaluate and to differentiate the morphological responses to distinct hydrodynamic drivers. A comprehensive morphological analysis of available observations at the FWP showed that the channel migration trends and directions are persistent at particular channel bends and meanders for the considered period of 14 years. Migration trends and directions are well reproduced by one-year model simulations. Morphodynamic modelling is applied to interpolate between observations and relate sediment dynamics to different forcing scenarios in the outer Weser estuary as a whole and at the scale of local tributary channels and flats.

Controls on sinuosity in the sparsely vegetated Fossálar River, southern Iceland

NASA Astrophysics Data System (ADS)

Ielpi, Alessandro

2017-06-01

Vegetation exerts strong controls on fluvial sinuosity, providing bank stability and buffering surface runoff. These controls are manifest in densely vegetated landscapes, whereas sparsely vegetated fluvial systems have been so far overlooked. This study integrates remote sensing and gauging records of the meandering to wandering Fossálar River, a relatively steep-sloped (< 2.5%) Icelandic river featuring well-developed point bars (79%-85% of total active bar surface) despite the lack of thick, arborescent vegetation. Over four decades, fluctuations in the sinuosity index (1.15-1.43) and vegetation cover (63%-83%) are not significantly correlated (r = 0.28, p > 0.05), suggesting that relationships between the two are mediated by intervening variables and uncertain lag times. By comparison, discharge regime and fluvial planform show direct correlation over monthly to yearly time scales, with stable discharge stages accompanying the accretion of meander bends and peak floods related to destructive point-bar reworking. Rapid planform change is aided by the unconsolidated nature of unrooted alluvial banks, with recorded rates of lateral channel-belt migration averaging 18 m/yr. Valley confinement and channel mobility also control the geometry and evolution of individual point bars, with the highest degree of spatial geomorphic variability recorded in low-gradient stretches where lateral migration is unimpeded. Point bars in the Fossálar River display morphometric values comparable to those of other sparsely vegetated rivers, suggesting shared scalar properties. This conjecture prompts the need for more sophisticated integrations between remote sensing and gauging records on modern rivers lacking widespread plant life. While a large volume of experimental and field-based work maintains that thick vegetation has a critical role in limiting braiding, thus favouring sinuosity, this study demonstrates the stronger controls of discharge regime and alluvial morphology on sparsely vegetated sinuous rivers.

Far-infrared-induced magnetoresistance oscillations in GaAs/AlxGa1-xAs -based two-dimensional electron systems

NASA Astrophysics Data System (ADS)

Wirthmann, André; McCombe, Bruce D.; Heitmann, Detlef; Holland, Steffen; Friedland, Klaus-Jürgen; Hu, Can-Ming

2007-11-01

We report on photoresistance and magnetotransport measurements in a moderate mobility two-dimensional electron system subject to far-infrared (terahertz) radiation. The photoresistance shows radiation induced 1/B -periodic oscillations, which we identify as the terahertz analog of microwave-induced resistance oscillations (MIROs). The MIRO-analog oscillations show a sign reversal in the low-field, high current regime. We simultaneously observe magnetoplasmons and MIRO-analog oscillations with no apparent coupling between them. Using a meandering Hall-bar geometry allows us to greatly enhance sensitivity and detect these oscillations even at elevated temperatures and moderate mobilities.

Applications of space technology to developing nations

NASA Technical Reports Server (NTRS)

Freden, S. C.

1976-01-01

The use of imagery from the Landsat spacecraft for the monitoring and management of natural resources in developing countries is discussed. The Landsat imagery can be used to make cartographic maps at scales of 1:250,000 which meet the US National Map Accuracy Standards, providing a means of map updating to correct for river meanders or changing shorelines. The Landsat data can also be used in defining and measuring agricultural areas, identifying pest breeding areas, and monitoring irrigation practices and crop performance. Total volume estimates can be obtained in many cases for surface bodies of water, and subsurface water supplies can be detected from changes in vegetation in some instances.

Morphodynamic modeling of erodible laminar channels.

PubMed

Devauchelle, Olivier; Josserand, Christophe; Lagrée, Pierre-Yves; Zaleski, Stéphane

2007-11-01

A two-dimensional model for the erosion generated by viscous free-surface flows, based on the shallow-water equations and the lubrication approximation, is presented. It has a family of self-similar solutions for straight erodible channels, with an aspect ratio that increases in time. It is also shown, through a simplified stability analysis, that a laminar river can generate various bar instabilities very similar to those observed in natural rivers. This theoretical similarity reflects the meandering and braiding tendencies of laminar rivers indicated by F. Métivier and P. Meunier [J. Hydrol. 27, 22 (2003)]. Finally, we propose a simple scenario for the transition between patterns observed in experimental erodible channels.

Quasiperiodicity and chaos in cardiac fibrillation.

PubMed Central

Garfinkel, A; Chen, P S; Walter, D O; Karagueuzian, H S; Kogan, B; Evans, S J; Karpoukhin, M; Hwang, C; Uchida, T; Gotoh, M; Nwasokwa, O; Sager, P; Weiss, J N

1997-01-01

In cardiac fibrillation, disorganized waves of electrical activity meander through the heart, and coherent contractile function is lost. We studied fibrillation in three stationary forms: in human chronic atrial fibrillation, in a stabilized form of canine ventricular fibrillation, and in fibrillation-like activity in thin sheets of canine and human ventricular tissue in vitro. We also created a computer model of fibrillation. In all four studies, evidence indicated that fibrillation arose through a quasiperiodic stage of period and amplitude modulation, thus exemplifying the "quasiperiodic transition to chaos" first suggested by Ruelle and Takens. This suggests that fibrillation is a form of spatio-temporal chaos, a finding that implies new therapeutic approaches. PMID:9005999

Quasiperiodicity and chaos in cardiac fibrillation.

PubMed

Garfinkel, A; Chen, P S; Walter, D O; Karagueuzian, H S; Kogan, B; Evans, S J; Karpoukhin, M; Hwang, C; Uchida, T; Gotoh, M; Nwasokwa, O; Sager, P; Weiss, J N

1997-01-15

In cardiac fibrillation, disorganized waves of electrical activity meander through the heart, and coherent contractile function is lost. We studied fibrillation in three stationary forms: in human chronic atrial fibrillation, in a stabilized form of canine ventricular fibrillation, and in fibrillation-like activity in thin sheets of canine and human ventricular tissue in vitro. We also created a computer model of fibrillation. In all four studies, evidence indicated that fibrillation arose through a quasiperiodic stage of period and amplitude modulation, thus exemplifying the "quasiperiodic transition to chaos" first suggested by Ruelle and Takens. This suggests that fibrillation is a form of spatio-temporal chaos, a finding that implies new therapeutic approaches.

Impact of the natural Fe-fertilization on the magnitude, stoichiometry and efficiency of particulate biogenic silica, nitrogen and iron export fluxes

NASA Astrophysics Data System (ADS)

Lemaitre, N.; Planquette, H.; Dehairs, F.; van der Merwe, P.; Bowie, A. R.; Trull, T. W.; Laurenceau-Cornec, E. C.; Davies, D.; Bollinger, C.; Le Goff, M.; Grossteffan, E.; Planchon, F.

2016-11-01

The Kerguelen Plateau is characterized by a naturally Fe-fertilized phytoplankton bloom that extends more than 1000 km downstream in the Antarctic Circumpolar Current. During the KEOPS2 study, in austral spring, we measured particulate nitrogen (PN), biogenic silica (BSi) and particulate iron (PFe) export fluxes in order to investigate how the natural fertilization impacts the stoichiometry and the magnitude of export fluxes and therefore the efficiency of the biological carbon pump. At 9 stations, we estimated elemental export fluxes based on element concentration to 234Th activity ratios for particulate material collected with in-situ pumps and 234Th export fluxes (Planchon et al., 2015). This study revealed that the natural Fe-fertilization increased export fluxes but to variable degrees. Export fluxes for the bloom impacted area were compared with those of a high-nutrient, low-chlorophyll (HNLC), low-productive reference site located to the south-west of Kerguelen and which had the lowest BSi and PFe export fluxes (2.55 mmol BSi m-2 d-1 and 1.92 μmol PFem-2 d-1) and amongst the lowest PN export flux (0.73 mmol PN m-2 d-1). The impact of the Fe fertilization was the greatest within a meander of the polar front (PF), to the east of Kerguelen, with fluxes reaching 1.26 mmol PN m-2 d-1; 20.4 mmol BSi m-2 d-1 and 22.4 μmol PFe m-2 d-1. A highly productive site above the Kerguelen Plateau, on the contrary, was less impacted by the fertilization with export fluxes reaching 0.72 mmol PN m-2 d-1; 4.50 mmol BSi m-2 d-1 and 21.4 μmol PFe m-2 d-1. Our results suggest that ecosystem features (i.e. type of diatom community) could play an important role in setting the magnitude of export fluxes of these elements. Indeed, for the PF meander, the moderate productivity was sustained by the presence of large and strongly silicified diatom species while at the higher productivity sites, smaller and slightly silicified diatoms dominated. Interestingly, our results suggest that PFe export fluxes can be driven by the lithogenic pool of particles, especially over the Plateau where such inputs from the sediments are important. Finally, for the Plateau and the PF meander, the comparison between PFe export and the particulate PFe stock integrated over the mixed layer depth revealed an efficient PFe export out of the mixed layer at these sites. Export efficiencies (i.e. the ratio between export and uptake) exhibit a very efficient silica pump especially at the HNLC reference station where heavily silicified diatoms were present. On the contrary, the increase with depth of the C:N ratio and the low nitrogen export efficiencies support the idea of a strong remineralization and nitrification activity.

Investigation of watercourses by comparison of successive historical map surveys of Western Hungary

NASA Astrophysics Data System (ADS)

Kovács, Gábor

2010-05-01

The Second (Timár et al., 2006) and Third Military Survey (Biszak et al., 2007) of the Habsburg Empire, completed in the 19th century (1806-69 and 1869-87), can be very useful in different scientific investigations because of their accuracy and data content. The mapmakers used geodetic projections and survey technologies provided high accuracy. Therefore, scientists can use these maps and the represented objects in retrospective studies. The streams were drawn with very thin lines that also ascertain the high accuracy of their location. Previous study used the Second Military Survey to examine the neotectonic evaluation of the western part of the Pannonian Basin, bordered by Pinka, Rába and Répce Rivers (Kovács, 2010). The watercourses, especially alluvial ones, react very sensitively to tectonic forcing (Schumm & Khan, 1972; Ouchi, 1985). However, the present-day course of the creeks and rivers are mostly regulated, therefore they are unsuitable for such studies. The watercourses have reconstructed from maps surveyed prior to the main water control measures. The Second Military Survey was a perfect source for such studies. The investigated streams were free meandering ones. They could flood their banks, and only natural levees were present. After georeferencing the maps of the area, the streams were digitized, and their sinuosity values were computed. Where significant sinuosity changes have been detected along the streams, it can be considered as indicators of differential uplift or subsidence of the bedrock/alluvium. The goal of this study is to decide the character of several stream sections: were they free meandering ones or not? Some of the sections are antecedent ones, especially at the Vas Mountain at the present Austrian-Hungarian border. If the shapes of the watercourses on the different surveys are almost the same, the sinuosity refers to a prior, forced state of the stream. After digitizing the watercourses on the Third Military Survey sheets, some newly regulated sections are recognized as well as forced and free meandering ones. Thus, the neotectonic evaluation of the study area can be made more accurate. References - Biszak, S., Timár, G., Molnár, G., Jankó, A. (2007): Digitized maps of the Habsburg Empire - The third military survey, Ungarn, Siebenbürgen, Kroatien-Slawonien, 1867-1887, 1:25000. Arcanum, Budapest, DVD-issue. - Kovács, G. (2010): The advantages of using the Second Military Survey maps in fluvial studies. Acta Geodaetica et Geophysica Hungarica 45(1): 64-70. - Ouchi, S. (1985): Response of alluvial rivers to slow active tectonic movement. Geol. Soc. Am. Bull. 96: 504-515. - Schumm, S. A., Khan, H. R. (1972): Experimental study of channel patterns. Geol. Soc. Am. Bull. 83: 1755-1770. - Timár, G., Molnár, G., Székely, B., Biszak, S., Varga, J., Jankó, A. (2006): Digitized maps of the Habsburg Empire - The map sheets of the second military survey and their georeferenced version. Arcanum, Budapest, 59 p.

An Explanation for Saturn's Hexagon

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

For over three decades, weve been gathering observations of the mysterious hexagonal cloud pattern encircling Saturns north pole. Now, researchers believe they have a model that can better explain its formation.Fascinating GeometrySaturns northern Hexagon is a cloud band circling Saturns north pole at 78 N, first observed by the Voyager flybys in 198081. This remarkable pattern has now persisted for more than a Saturn year (29.5 Earth years).Eight frames demonstrating the motion within Saturns Hexagon. Click to watch the animation! The view is from a reference frame rotating with Saturn. [NASA/JPL-Caltech/SSI/Hampton University]Observations by Voyager and, more recently, Cassini have helped to identify many key characteristics of this bizarre structure. Two interesting things weve learned are:The Hexagon is associated with an eastward zonal jet moving at more than 200 mph.The cause of the Hexagon is believed to be a jet stream, similar to the ones that we experience on Earth. The path of the jet itself appears to follow the hexagons outline.The Hexagon rotates at roughly the same rate as Saturns overall rotation.While we observe individual storms and cloud patterns moving at different speeds within the Hexagon, the vertices of the Hexagon move at almost exactly the same rotational speed as that of Saturn itself.Attempts to model the formation of the Hexagon with a jet stream have yet to fully reproduce all of the observed features and behavior. But now, a team led by Ral Morales-Juberas of the New Mexico Institute of Mining and Technology believes they have created a model that better matches what we see.Simulating a Meandering JetThe team ran a series of simulations of an eastward, Gaussian-profile jet around Saturns pole. They introduced small perturbations to the jet and demonstrated that, as a result of the perturbations, the jet can meander into a hexagonal shape. With the initial conditions of the teams model, the meandering jet is able to settle into a stable hexagonal shape that rotates with very nearly the same period as Saturns rotational period.The formation of this hexagon depends on factors such as the initial amplitude and curvature of the jet. The models treatment of the wind profile within Saturns atmosphere is another key component that allowed them to match the observed characteristics of the Hexagon, such as its shape, vorticity behavior, temperature gradient, and seasonal stability.BonusThe gif below shows part of an animation the authors produced of the jet evolution in their model. You can see a hexagon begin to develop at around 230 days into the simulation, and by about 400 days it becomes stable and non-rotating (were looking at it from a reference frame rotating with Saturn). The full animation can be viewed here. [Morales-Juberas et al., 2015]CitationR. Morales-Juberas et al.2015 ApJ 806 L18 doi:10.1088/2041-8205/806/1/L18

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

Doubrawa Moreira, Paula; Annoni, Jennifer; Jonkman, Jason

FAST.Farm is a medium-delity wind farm modeling tool that can be used to assess power and loads contributions of wind turbines in a wind farm. The objective of this paper is to undertake a calibration procedure to set the user parameters of FAST.Farm to accurately represent results from large-eddy simulations. The results provide an in- depth analysis of the comparison of FAST.Farm and large-eddy simulations before and after calibration. The comparison of FAST.Farm and large-eddy simulation results are presented with respect to streamwise and radial velocity components as well as wake-meandering statistics (mean and standard deviation) in the lateral andmore » vertical directions under different atmospheric and turbine operating conditions.« less

Sedimentology, stratigraphy, and extinctions during the Cretaceous-Paleogene transition at Bug Creek, Montana

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

Fastovsky, D.E.; Dott, R.H. Jr.

1986-04-01

Bug Creek Valley, the source of an unusual and controversial Cretaceous-Paleogene coincidence of mammals, dinosaurs, pollen, and iridium, exemplifies the importance of depositional process in the reconstruction of evolutionary events. Five sedimentary facies are recognized at Bug Creek: a cross-stratified sandstone, a green and purple siltstone, a lateral accretionary sandstone, a coal, and a variegated siltstone. Repeated fluvial channeling restricts the accuracy of lateral correlations, and the relationship of the fossil assemblage to the presumed Cretaceous-Paleogene boundary cannot be established. Sedimentologically, the Cretaceous-Paleogene transition is represented here by Cretaceous meandering channels that gave way initially to Paleogene swamp deposition. 13more » references, 4 figures.« less

Meandering Musings by Linus Pauling: "American Scientists and the Spirit of the Frontier".

PubMed

Bause, George S

2016-04-01

Hoping to raise funds in 1975 for his namesake institute, Linus Pauling submitted to Esquire magazine a 32-page handwritten manuscript, "American Scientists and the Spirit of the Frontier." Angered when his submission for publication was declined, Pauling eventually gifted the original manuscript in 1986 to his friend, Linus Pauling Institute fundraiser Stephen Maddox, who would sell it in 2004 to the Wood Library-Museum of Anesthesiology. Published accurately here for the first time, the manuscript captures not only Pauling's sweeping metaphor of scientists as frontiersmen but also the creative process by which Pauling formulated his hydrate microcrystal theory of general anesthesia. Copyright © 2015 Elsevier Inc. All rights reserved.

Cannabis and psychopathology: The meandering journey of the last decade

PubMed Central

Ghosh, Abhishek; Basu, Debasish

2015-01-01

Since its inception cannabis has been observed to be associated with various psycho-pathology. In this paper, the authors have reviewed the advancement made in this area over the last decade. The association between cannabis and schizophrenia has been researched more intensively. The controversy regarding the reliability, clinical utility, and the existence of a cannabis withdrawal syndrome has also been settled. Recent studies also buttressed the possibility of acute and chronic effect of cannabis on various cognitive functions. There has been a plethora of research regarding the treatment for cannabis use disorders. But the new and most interesting area of research is concentrated on the endocannabinoid system and its contribution in various psychiatric disorders. PMID:26124519

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Multi-mode Spiral Wave in a Coupled Oscillatory Medium

NASA Astrophysics Data System (ADS)

Wang, Qun; Gao, Qing-Yu; Lü, Hua-Ping; Zheng, Zhi-Gang

2010-05-01

Multi-mode spiral wave and its breakup in 1-d and 2-d coupled oscillatory media is studied here by theoretic analysis and numerical simulations. The analysis in 1-d system shows that the dispersion relation curve could be non-monotonic depending on the coupling strength. It may also lead to the coexistence of different wave numbers within one system. Direct numerical observations in 1-d and 2-d systems conform to the prediction of dispersion relation analysis. Our findings indicate that the wave grouping can also be observed in oscillatory media without tip meandering and waves with negative group velocity can occur without inhomogeneity.

GEOS-3 ocean current investigation using radar altimeter profiling. [Gulf Stream surface topography

NASA Technical Reports Server (NTRS)

Leitao, C. D.; Huang, N. E.; Parra, C. G.

1978-01-01

Both quasi-stationary and dynamic departures from the marine geoid were successfully detected using altitude measurements from the GEOS-3 radar altimeter. The quasi-stationary departures are observed either as elevation changes in single pass profiles across the Gulf Stream or at the crowding of contour lines at the western and northern areas of topographic maps generated using altimeter data spanning one month or longer. Dynamic features such as current meandering and spawned eddies can be monitored by comparing monthly mean maps. Comparison of altimeter inferred eddies with IR detected thermal rings indicates agreement of the two techniques. Estimates of current velocity are made using derived slope estimates in conjunction with the geostrophic equation.

Feedbacks Between Bioclogging and Infiltration in Losing River Systems

NASA Astrophysics Data System (ADS)

Newcomer, M. E.; Hubbard, S. S.; Fleckenstein, J. H.; Schmidt, C.; Maier, U.; Thullner, M.; Ulrich, C.; Rubin, Y.

2014-12-01

Reduction in riverbed permeability due to biomass growth is a well-recognized yet poorly understood process associated with losing connected and disconnected rivers. Although several studies have focused on riverbed bioclogging processes at the pore-scale, few studies have quantified bioclogging feedback cycles at the scale relevant for water resources management, or at the meander-scale. At this scale, often competing hydrological-biological processes influence biomass dynamics and infiltration. Disconnection begins when declines in the water table form an unsaturated zone beneath the river maximizing seepage. Simultaneously, bioclogging reduces the point-scale infiltration flux and can either limit the nutrient flux and reduce bioclogging, or preferentially focus infiltration elsewhere and enhance bioclogging. These feedbacks are highly dependent on geomorphology and seasonal patterns of discharge and water temperature. To assess the mutual influences of disconnection, biomass growth, and temperature changes on infiltration in a geomorphologically complex river system, we built a 3D numerical model, conditioned on field data, using the reactive-transport simulator MIN3P. Results show that in disconnected regions of the river, biomass growth reduced vertical seepage downward and extended the unsaturated zone length; however these changes were contingent upon disconnection. Mid-way through the seasonal cycle, biomass declined in these same regions due to limited nutrient flux. Seepage and biomass continued to oscillate with a lag correlation of 1 month. Connected regions, however, showed the largest infiltration rates, nutrient fluxes, and concentrations of biomass. Despite the reduction in conductivity from biomass, flow remains high in connected regions because the feedback between bioclogging and infiltration is not as pronounced due to the sharpening hydraulic gradient. Bioclogging ultimately shapes the pattern of flow, however geomorphology dominates the strength of connection. Recognition of the feedbacks between geomorphological patterns and heterogeneous biomass on meander scale hydrological processes can lead to better estimates of local water volumes and capacities, especially when these systems are used as municipal and public water supply sources.

The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

NASA Astrophysics Data System (ADS)

Laitinen, Timo; Effenberger, Frederic; Kopp, Andreas; Dalla, Silvia

2018-02-01

Insights into the processes of Solar Energetic Particle (SEP) propagation are essential for understanding how solar eruptions affect the radiation environment of near-Earth space. SEP propagation is influenced by turbulent magnetic fields in the solar wind, resulting in stochastic transport of the particles from their acceleration site to Earth. While the conventional approach for SEP modelling focuses mainly on the transport of particles along the mean Parker spiral magnetic field, multi-spacecraft observations suggest that the cross-field propagation shapes the SEP fluxes at Earth strongly. However, adding cross-field transport of SEPs as spatial diffusion has been shown to be insufficient in modelling the SEP events without use of unrealistically large cross-field diffusion coefficients. Recently, Laitinen et al. [ApJL 773 (2013b); A&A 591 (2016)] demonstrated that the early-time propagation of energetic particles across the mean field direction in turbulent fields is not diffusive, with the particles propagating along meandering field lines. This early-time transport mode results in fast access of the particles across the mean field direction, in agreement with the SEP observations. In this work, we study the propagation of SEPs within the new transport paradigm, and demonstrate the significance of turbulence strength on the evolution of the SEP radiation environment near Earth. We calculate the transport parameters consistently using a turbulence transport model, parametrised by the SEP parallel scattering mean free path at 1 AU, λ∥*, and show that the parallel and cross-field transport are connected, with conditions resulting in slow parallel transport corresponding to wider events. We find a scaling σφ,max∝(1/λ∥*)1/4 for the Gaussian fitting of the longitudinal distribution of maximum intensities. The longitudes with highest intensities are shifted towards the west for strong scattering conditions. Our results emphasise the importance of understanding both the SEP transport and the interplanetary turbulence conditions for modelling and predicting the SEP radiation environment at Earth.

Integrated multi-stratigraphic study of the Coll de Terrers late Permian-Early Triassic continental succession from the Catalan Pyrenees (NE Iberian Peninsula): A geologic reference record for equatorial Pangaea

NASA Astrophysics Data System (ADS)

Mujal, Eudald; Fortuny, Josep; Pérez-Cano, Jordi; Dinarès-Turell, Jaume; Ibáñez-Insa, Jordi; Oms, Oriol; Vila, Isabel; Bolet, Arnau; Anadón, Pere

2017-12-01

The most severe biotic crisis on Earth history occurred during the Permian-Triassic (PT) transition around 252 Ma. Whereas in the marine realm such extinction event is well-constrained, in terrestrial settings it is still poorly known, mainly due to the lack of suitable complete sections. This is utterly the case along the Western Tethys region, located at Pangaea's equator, where terrestrial successions are typically build-up of red beds often characterised by a significant erosive gap at the base of the Triassic strata. Henceforth, documenting potentially complete terrestrial successions along the PT transition becomes fundamental. Here, we document the exceptional Coll de Terrers area from the Catalan Pyrenees (NE Iberian Peninsula), for which a multidisciplinary research is conducted along the PT transition. The red-bed succession, located in a long E-W extended narrow rift system known as Pyrenean Basin, resulted from a continuous sedimentary deposition evolving from meandering (lower Upper Red Unit) to playa-lake/ephemeral lacustrine (upper Upper Red Unit) and again to meandering settings (Buntsandstein facies). Sedimentary continuity is suggested by preliminary cyclostratigraphic analysis that warrants further analysis. Our combined sedimentological, mineralogical and geochemical data infer a humid-semiarid-humid climatic trend across the studied succession. The uppermost Permian strata, deposited under an orbitally controlled monsoonal regime, yields a relatively diverse ichnoassemblage mainly composed of tetrapod footprints and arthropod trace fossils. Such fossils indicate appropriate life conditions and water presence in levels that also display desiccation structures. These levels alternate with barren intervals formed under dry conditions, being thus indicative of strong seasonality. All these features are correlated with those reported elsewhere in Gondwana and Laurasia, and suggest that the Permian-Triassic boundary might be recorded somewhere around the Buntsandstein base. Consequently, Coll de Terrers and the whole Catalan Pyrenees become key regions to investigate in detail the Permian extinction event and the Triassic ecosystems recovery.

Hydrodynamics and Connectivity of Channelized Floodplains: Insights from the Meandering East Fork White River, Indiana, USA

NASA Astrophysics Data System (ADS)

Czuba, J. A.; David, S. R.; Edmonds, D. A.

2017-12-01

High resolution topography reveals that meandering river floodplains in Indiana commonly have networks of channels. These floodplain channel networks are most prevalent in agricultural, low-gradient, wide floodplains. It appears that these networks are formed when floodplain channels connect oxbows to each other and the main river channel. Collectively, the channels in the floodplain create an interconnected network of pathways that convey water beginning at flows less than bankfull, and as stage increases, more of the floodplain becomes dissected by floodplain channels. In this work, we quantify the hydrodynamics and connectivity of the flow on the floodplain and in the main channel of the East Fork White River near Seymour, Indiana, USA. We constructed a two-dimensional numerical model using HECRAS of the river-floodplain system from LiDAR data and from main-channel river bathymetry to elucidate the behaviour of these floodplain channels across a range of flows. Model calibration and verification data included stage from a USGS gage, high-water marks at a high and medium flow, and an aerial photograph of inundation in the floodplain channels. The numerical model simulated flow depth and velocity, which was used to quantify connectivity of the floodplain channels, exchange between the main channel and floodplain channels, and residence time of water on the floodplain. Model simulations suggest that the floodplain channels convey roughly 50% of the total flow at what is typically considered "bankfull" flow. Overall, we present a process-based approach for analyzing complex floodplain-river systems where an individual floodplain-river system can be distilled down to a set of characteristic curves. Notably, we map the East Fork White River system to exchange-residence time space and argue that this characterization forms the basis for thinking about morphologic evolution (e.g., sediment deposition and erosion) and biogeochemistry (e.g., nitrate removal) in floodplain-river systems.

Experiments on Bedrock Cover in a Highly Sinuous Channel

NASA Astrophysics Data System (ADS)

Parker, G.; Fernandez, R.; Stark, C. P.

2015-12-01

One of several mechanisms by which bedrock rivers can incise is abrasion of the bedrock surface by colliding sediment particles. This effect has been captured in terms of a "cover factor" corresponding to the areal fraction p of the bed that is covered with sediment. According to this formulation, a value of p equal to 1 corresponds to complete alluvial cover: sediment particles strike each other and no bedrock abrasion is accomplished. Correspondingly, a value of p equal to 0 corresponds to the absence of sediment: no particles are available to strike the bed, and again no bedrock abrasion is accomplished. Thus the condition 0 < p < 1 is hypothesized to be the condition for incision driven by abrasion. At the microscopic level, however, p can take only the binary values 0 and 1: either a point on the bedrock surface is covered or is not covered. Therefore, the value of p that enters into any morphodynamic formulation of cover must represent an average over some spatiotemporal window. Here we consider the case of a highly sinuous meandering flume. The bed is set in concrete to take the topography corresponding to purely alluvial mobile-bed equilibrium. The recirculation of sediment over this bed at below-capacity conditions leads to a complex pattern of free and forced bars that only partially cover the bed. At certain locations, such as near the inside of bends, the bed is always covered, where at other locations, such as right near the apexes of the very tight bends in the flume, the bed is almost never covered. At other locations, the instantaneous cover fluctuates between the binary values 0 and 1, reflecting the migration of bars of various sizes over the bedrock surface. The averaging of these binary values over appropriate time windows allows determination of the local spatial variation of p that can serve as input to a numerical model of the evolution of bedrock meandering channels.