Kinetic Energy (kinetic + energy)

Distribution by Scientific Domains

Kinds of Kinetic Energy

  • turbulent kinetic energy

  • Selected Abstracts

    The wealth of species: ecological communities, complex systems and the legacy of Frank Preston

    ECOLOGY LETTERS, Issue 3 2007
    Jeffrey C. Nekola
    Abstract General statistical patterns in community ecology have attracted considerable recent debate. Difficulties in discriminating among mathematical models and the ecological mechanisms underlying them are likely related to a phenomenon first described by Frank Preston. He noted that the frequency distribution of abundances among species was uncannily similar to the Boltzmann distribution of kinetic energies among gas molecules and the Pareto distribution of incomes among wage earners. We provide additional examples to show that four different ,distributions of wealth' (species abundance distributions, species,area and species,time relations, and distance decay of compositional similarity) are not unique to ecology, but have analogues in other physical, geological, economic and cultural systems. Because these appear to be general statistical patterns characteristic of many complex dynamical systems they are likely not generated by uniquely ecological mechanistic processes. [source]

    Correlated one-electron wave functions

    B. Weiner
    Abstract A one-electron theory of many-electron systems that explicitly describes electron,electron correlation may be based on the observation that antisymmetrized geminal power (AGP) states are completely characterized by the occupation numbers of their first-order reduced density operators (FORDO) and a set of canonical general spin,orbitals (CGSOs), which are in general distinct from the natural general spin,orbitals. Because the FORDO alone does not determine an AGP state, a density matrix functional may be defined. A generalization of the independent-particle Fock operator serves to express the total state energy in terms of ionization energies, kinetic energies, and potential energies of the CGSOs. A one-electron picture of chemical bonding emerges from this theory. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]

    Experimental investigation of the hydrodynamics in a liquid,solid riser

    AICHE JOURNAL, Issue 3 2005
    Shantanu Roy
    Abstract Liquid,solid fluid dynamics has been investigated in a 6-in. (0.15 m) "cold-flow" circulating fluidized bed riser using non-invasive flow monitoring methods. Gamma-ray computed tomography (CT) was used to measure the time-averaged cross-sectional solids volume fraction distributions at several elevations. The time-averaged mean and "fluctuating" solids velocity fields were quantified using the computer-automated radioactive particle tracking (CARPT) technique. The experimental equipment, protocol of implementation, and data analysis have been discussed briefly, with particular emphasis on the specific features in the use of these techniques for studying high-density turbulent flows as in a liquid,solid riser. The experimental study examines nine operating conditions, that is, three liquid superficial velocities and three solids flow rates. The solids holdup profile is found to be relatively uniform across the cross section of the riser, with marginal segregation near the walls. The time-averaged solids velocity profiles are found to have a negative component at the walls, indicating significant solids backmixing. Detailed characterization of the solids velocity fields in terms of RMS velocities, kinetic energies, Hurst exponents, residence time distributions, trajectory length distributions, dispersion coefficients, and so forth are presented. Comparative and symbiotic analyses of the results were used to develop a coherent picture of the solids flow field. In addition, the work also serves to demonstrate the power and versatility of these flow-imaging techniques in studying highly turbulent and opaque multiphase systems. © 2005 American Institute of Chemical Engineers AIChE J, 51: 802,835, 2005 [source]

    Energy transfer to phonons after photoexcitation in one-dimensional correlated electron-phonon systems

    Kenji Yonemitsu
    Abstract In order to study relaxation rates of photoexcited states in correlated electron systems, we calculate the time evolution of phonons' kinetic energies after photoexcitation of a one-dimensional half-filled Hubbard model coupled with different types of phonons, which modulate transfer integrals, site energies, and on-site repulsion strengths. Without or with weak dimerization, the energy transfer to phonons that modulate on-site repulsion strengths is the largest. It increases rapidly as a function of the corresponding displacement. This suggests that the rapid relaxation of photoexcited states in one-dimensional correlated electron systems is allowed without change in symmetry by phonons that modulate Coulomb repulsion strengths. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    On the high-resolution mass analysis of the product ions in tandem time-of-flight (TOF/TOF) mass spectrometers using a time-dependent re-acceleration technique

    Sergey Kurnosenko
    The time-dependent reacceleration of product ions produced as a result of dissociation of a single precursor ion in a tandem time-of-flight mass spectrometer is considered for the first time. Analytical expressions for the shapes of electric pulses bringing all the kinetic energies of the product ions to the same value are derived for two cases: forward acceleration mode and deceleration, followed by re-acceleration in the reversed direction (reversed mode). Secondary time-of-flight focusing resulting from the re-acceleration in the reversed mode is shown to be mass-dependent and, when averaged over a wide mass range, the focusing is tight enough to provide mass resolution exceeding 10,000. After time-dependent re-acceleration, additional compression of the ion packet width leading to better mass resolution can be obtained by decelerating the ions in a constant field. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    The Origin of Aromaticity: Important Role of the Sigma Framework in Benzene

    CHEMPHYSCHEM, Issue 9 2004
    Borislav Kova
    Abstract The physical nature of aromaticity is addressed at a high ab initio level. It is conclusively shown that the extrinsic aromatic stabilization energy of benzene E(ease)B, estimated relative to its linear polyene counterpart(s), is very well-reproduced at the Hartree,Fock (HF) level. This is a consequence of the fact that the contributions arising from the zero-point vibrational energy (ZPVE) and electron correlation are rather small. More specifically, they yield together 2.0 kcal,mol,1to the destabilization of benzene. A careful scrutiny of the HF energies by virial theorem shows further that the kinetic energies of the , and , electrons E(T) and E(T) are strictly additive in the gauge linear zig-zag polyenes, which also holds for their sum Et(T)HF. This finding has the important corollary that E(ease)Bis little dependent on the choice of the homodesmic reactions involving zig-zag polyenes. A detailed physical analysis of the ,- and ,-electron contributions to extrinsic aromaticity requires explicit introduction of the potential energy terms Vne, Vee, and Vnn, which signify Coulomb interactions between the electrons and the nuclei. The Veeterm involves repulsive interaction V between the , and , electrons, which cannot be unequivocally resolved into , and , contributions. The same holds for the Vnnenergy, which implicitly depends on the electron density distribution via the Born,Oppenheimer (BO) potential energy surface. Several possibilities for partitioning V and Vnnterms into , and , components are examined. It is argued that the stockholder principle is the most realistic, which strongly indicates that E(ease)Bis a result of favorable , -framework interactions. In contrast, the ,-electron framework prefers the open-chain linear polyenes. [source]

    Collapse of Reinforced Concrete Column by Vehicle Impact

    Hing-Ho Tsang
    The column slenderness ratio can be in the order of 6,9. Some of these buildings are right next to busy streets and hence continuously exposed to the potential hazard of a vehicle impacting on a column in an accident. In the early part of this study, the ultimate energy absorption capacity of a reinforced concrete column is compared to the kinetic energy embodied in the moving vehicle. The energy-absorption capacity is calculated from the force-displacement curve of the column as determined from a nonlinear static (push-over) analysis. The ultimate displacement of the column is defined at the point when the column fails to continue carrying the full gravitational loading. Results obtained from the nonlinear static analysis have been evaluated by computer simulations of the dynamic behavior of the column following the impact. Limitations in the static analysis procedure have been demonstrated. The effects of strain rate have been discussed and the sensitivity of the result to changes in the velocity function and stiffness of the impacting vehicle has also been studied. [source]

    Is Functional Capacity Related to Left Atrial Contractile Function in Nonobstructive Hypertrophic Cardiomyopathy?

    Yukitaka Shizukuda MD
    The mechanisms underlying reduced exercise capacity in patients with nonobstructive hypertrophic cardiomyopathy (NHCM) could include perturbations of ventricular relaxation, diastolic compliance, or compensatory atrial systolic function. We hypothesized that a loss of atrial contractility in NHCM patients leads to reduced functional capacity. To test this hypothesis, we compared resting noninvasive left atrial ejection phase indices in 49 consecutive patients with NHCM (ages 36±10 years; 41% female) and normal left ventricular ejection fraction (mean, 68%±8%) with objective metabolic exercise parameters. Left atrial active emptying fraction, ejection force, and kinetic energy failed to predict exercise capacity. Only left atrial total and active emptying volumes correlated weakly with minute volume/CO2 production slope (r=0.31 and r=0.33; p<0.05 for both). Furthermore, when subjects were stratified by New York Heart Association symptomatology, exercise parameters,but not atrial contractility,differed between groups. These data, obtained at rest, fail to suggest that NHCM-related heart failure symptoms are due to an atrial myopathy. [source]

    Wind erosion characteristics of Sahelian surface types

    Thomas Maurer
    Abstract The assessment of wind erosion magnitudes for a given area requires knowledge of wind erosion susceptibilities of the dominant local surface types. Relative wind erosion potentials of surfaces can hardly be compared under field conditions, as each erosion event is unique in terms of duration, intensity and extent. The objective of this study was to determine and compare relative wind erosion potentials of the most representative surface types over a transect comprising most parts of southwestern Niger. For this purpose, mobile wind tunnel experiments were run on 26 dominant surface types. The effects of surface disturbance were additionally determined for 13 of these surfaces. The results, namely measurements of wind fields and mass fluxes, can be classified according to specific surface characteristics. Three basic surface groups with similar emission behaviour and aerodynamic characteristics were identified: (1) sand surfaces, (2) rough stone surfaces and (3) flat crusted surfaces. Sand surfaces feature a turbulent zone close to the surface due to the development of a saltation layer. Their surface roughness is medium to high, as a consequence of the loss of kinetic energy of the wind field to saltating particles. Sand surfaces show the highest mass fluxes due to the abundance of loose particles, but also fairly high PM10 fluxes, as potential dust particles are not contained in stable crusts or aggregates. Rough stone surfaces, due to their fragmented and irregular surface, feature the highest surface roughness and the most intense turbulence. They are among the weakest emitters but, due to their relatively high share of potential dust particles, PM10 emissions are still average. Flat crusted surfaces, in contrast, show low turbulence and the lowest surface roughness. This group of surfaces shows rather heterogeneous mass fluxes, which range from moderate to almost zero, although the share of PM10 particles is always relatively high. Topsoil disturbance always results in higher total and PM10 emissions on sand surfaces and also on flat crusted surfaces. Stone surfaces regularly exhibit a decrease in emission after disturbance, which can possibly be attributed to a reorganization which protects finer particles from entrainment. The results are comparable with field studies of natural erosion events and similar wind tunnel field campaigns. The broad range of tested surfaces and the standardized methodology are a precondition for the future regionalization of the experimental point data. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Estimation of temporal variation in splash detachment in two Japanese cypress plantations of contrasting age

    Y. Wakiyama
    Abstract To elucidate splash erosion processes under natural rainfall conditions, temporal variations in splash detachment were observed using a piezoelectric saltation sensor (H11B; Sensit Co., Portland, ND, USA). Preliminary laboratory tests of Sensit suggested that they were suitable for field observations. Field observations were conducted between July and September 2006 in 21- and 36-year-old Japanese cypress (Chamaecyparis obtusa) plantations with mean stand heights of 9·2,m and 17·4,m, respectively. Splash detachment (in g m,2) was measured seven times using splash cups, and raindrop kinetic energy (in J,m,2,mm,1) in both stands was measured using laser drop-sizing (LD) gauges. Sensit was installed to record saltation counts, which were converted to temporal data of splash detachment (splash rate; in g m,2 10,min,1) using the relationship between splash detachment and saltation counts. Surface runoff was monitored using runoff plots of 0·5,m width and 2·0,m length to obtain temporal data of flow depth (in millimeters). Both total splash detachment and raindrop kinetic energy were larger in the older stand. Increased splash rates per unit throughfall were found in both stands after rainless durations longer than approximately one day in both stands. However, a lower splash rate was found in the 21-year stand after rainfall events. During extreme rainstorms, the 21-year stand showed a low runoff rate and a decline in the splash rate, while the 36-year stand showed a higher splash rate and increased flow depth. The piezoelectric sensor proved to be a useful means to elucidate splash erosion processes in field conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Interrill erosion on cultivated Greek soils: modelling sediment delivery

    D. Dimoyiannis
    Abstract For interrill erosion, raindrop-induced detachment and transport of sediment by rainfall-disturbed sheet flow are the predominant processes, while detachment by sheet flow and transport by raindrop impact are negligible. In general, interrill subprocesses are inter-actively affected by rainfall, soil and surface properties. The objective of this work was to study the relationships among interrill runoff and sediment loss and some selected para-meters, for cultivated soils in central Greece, and also the development of a formula for predicting single storm sediment delivery. Runoff and soil loss measurement field experiments have been conducted for a 3·5-year period, under natural storms. The soils studied were developed on Tertiary calcareous materials and Quaternary alluvial deposits and were textured from sandy loam to clay. The second group of soils showed greater susceptibility to sealing and erosion than the first group. Single storm sediment loss was mainly affected by rain and runoff erosivity, being significantly correlated with rain kinetic energy (r = 0·64***), its maximum 30-minute intensity (r = 0·64***) and runoff amount (r = 0·56***). Runoff had the greatest correlation with rain kinetic energy (r = 0·64***). A complementary effect on soil loss was detected between rain kinetic energy and its maximum 30-minute intensity. The same was true for rain kinetic energy and topsoil aggregate instability, on surface seal formation and thus on infiltration characteristics and overland flow rate. Empirical analysis showed that the following formula can be used for the successful prediction of sediment delivery (Di): Di = 0·638,EI30tan(,) (R2 = 0·893***), where , is a topsoil aggregate instability index, E the rain kinetic energy, I30 the maximum 30-minute rain intensity and , the slope angle. It describes soil erodibility using a topsoil aggregate instability index, which can be determined easily by a simple laboratory technique, and runoff through the product of this index and rain kinetic energy. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Turbulent flow over a dune: Green River, Colorado

    Jeremy G. Venditti
    Abstract Detailed echo-sounder and acoustic Doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide, low-gradient, alluvial reach of the Green River. Based on the geometric position of the sensor over the bedforms, measurements were taken in the wake, in transitional flow at the bedform crest, and in the internal boundary layer. Spatial distributions of Reynolds shear stress, turbulent kinetic energy, turbulence intensity, and correlation coefficient are qualitatively consistent with those over fixed, two-dimensional bedforms in laboratory flows. Spectral and cospectral analysis demonstrates that energy levels in the lee of the crest (i.e. wake) are two to four times greater than over the crest itself, with minima over the stoss slope (within the developing internal boundary layer). The frequency structure in the wake is sharply defined with single, dominant peaks. Peak and total spectral and cross-spectral energies vary over the bedform in a manner consistent with wave-like perturbations that ,break' or ,roll up' into vortices that amalgamate, grow in size, and eventually diffuse as they are advected downstream. Fluid oscillations in the lee of the dune demonstrate Strouhal similarity between laboratory and field environments, and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Wind effects on sediment transport by raindrop-impacted shallow flow: a wind-tunnel study

    G. Erpul
    Abstract In wind-driven rains, wind velocity and direction are expected to affect not only energy input of rains but also shallow ,ow hydraulics by changing roughness induced by raindrop impacts with an angle on ,ow and the unidirectional splashes in the wind direction. A wind-tunnel study under wind-driven rains was conducted to determine the effects of horizontal wind velocity and direction on sediment transport by the raindrop-impacted shallow ,ow. Windless rains and the rains driven by horizontal wind velocities of 6 m s,1, 10 m s,1, and 14 m s,1 were applied to three agricultural soils packed into a 20 by 55 cm soil pan placed on both windward and leeward slopes of 7 per cent, 15 per cent, and 20 per cent. During each rainfall application, sediment and runoff samples were collected at 5-min intervals at the bottom edge of the soil pan with wide-mouth bottles and were determined gravimetrically. Based on the interrill erosion mechanics, kinetic energy ,ux (Ern) as a rainfall parameter and product of unit discharge and slope in the form of qbSco as a ,ow parameter were used to explain the interactions between impact and ,ow parameters and sediment transport (qs). The differential sediment transport rates occurred depending on the variation in raindrop trajectory and rain intensity with the wind velocity and direction. Flux of rain energy computed by combining the effects of wind on the velocity, frequency, and angle of raindrop impact reasonably explained the characteristics of wind-driven rains and acceptably accounted for the differences in sediment delivery rates to the shallow ,ow transport (R2 , 0·78). Further analysis of the Pearson correlation coef,cients between Ern and qSo and qs also showed that wind velocity and direction signi,cantly affected the hydraulics of the shallow ,ow. Ern had a smaller correlation coef,cient with the qs in windward slopes where not only reverse splashes but also reverse lateral raindrop stress with respect to the shallow ,ow direction occurred. However, Ern was as much effective as qSo in the sediment transport in the leeward slopes where advance splashes and advance lateral raindrop stress on the ,ow occurred. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Sediment production in large gullies of the Mediterranean area (NE Spain) from high-resolution digital elevation models and geographical information systems analysis

    J. A. Martínez-Casasnovas
    Abstract Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedčs vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully-wall retreat seems to be an ongoing process. Multi-date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up-to-date, usual global standards. Here, we present a study carried out using large-scale multi-date (1975 and 1995) aerial photographs (1 : 5000 and 1 : 7000) to monitor sediment yield caused by large gullies in the Penedčs region (NE Spain). High-resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha,1 year,1, a sediment deposition rate of 270 ± 18 Mg ha,1 year,1 and a sediment delivery ratio of 68·1% were computed for a gully area of 0·10 km2. The average net erosion within the study period (1975,95) was 576 ± 58 Mg ha,1 year,1. In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Computational fluid dynamics modelling of boundary roughness in gravel-bed rivers: an investigation of the effects of random variability in bed elevation

    A.P. Nicholas
    Abstract Results from a series of numerical simulations of two-dimensional open-channel flow, conducted using the computational fluid dynamics (CFD) code FLUENT, are compared with data quantifying the mean and turbulent characteristics of open-channel flow over two contrasting gravel beds. Boundary roughness effects are represented using both the conventional wall function approach and a random elevation model that simulates the effects of supra-grid-scale roughness elements (e.g. particle clusters and small bedforms). Results obtained using the random elevation model are characterized by a peak in turbulent kinetic energy located well above the bed (typically at y/h,=,0·1,0·3). This is consistent with the field data and in contrast to the results obtained using the wall function approach for which maximum turbulent kinetic energy levels occur at the bed. Use of the random elevation model to represent supra-grid-scale roughness also allows a reduction in the height of the near-bed mesh cell and therefore offers some potential to overcome problems experienced by the wall function approach in flows characterized by high relative roughness. Despite these benefits, the results of simulations conducted using the random elevation model are sensitive to the horizontal and vertical mesh resolution. Increasing the horizontal mesh resolution results in an increase in the near-bed velocity gradient and turbulent kinetic energy, effectively roughening the bed. Varying the vertical resolution of the mesh has little effect on simulated mean velocity profiles, but results in substantial changes to the shape of the turbulent kinetic energy profile. These findings have significant implications for the application of CFD within natural gravel-bed channels, particularly with regard to issues of topographic data collection, roughness parameterization and the derivation of mesh-independent solutions. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Seismic base-isolation by use of a telescoping stepping mechanism

    Maria D. Martinez-Rodrigo
    Abstract A new base-isolation mechanism corresponding to a variance of the stepping A-shaped frame is proposed and its seismic performance is investigated numerically for strong ground accelerations with peak values in the range from 0.5 to 1g. In its simplest two-dimensional form, the system consists of a frame with two telescoping legs pinned at the apex at a sharp angle. The legs are attached to the foundation through a spring and a damper acting in parallel. Both the springs and viscous dampers have bilinear characteristics that make them very stiff in compression but very soft in tension. As the structure rocks sideways, the length of the loaded leg remains essentially constant while the length of the unloaded leg increases. When the ground acceleration changes direction, the process is reversed. The resulting system has three main characteristics: (i) as the structure steps on a rigid leg, the maximum acceleration that can be transmitted to the superstructure is limited to a value which is approximately independent of the amplitude of the ground motion; (ii) there is a systematic lifting of the superstructure with kinetic energy being systematically transformed into potential energy during the strong phase of the ground motion; and (iii) the system is slowly self-centering at the end of the earthquake. The seismic performance of the system is evaluated for a tall bridge pier and for a smaller frame that could be used in a multi-story building. The results obtained for the 1940 El Centro ground motion scaled to 1g and for the near-field Rinaldi ground motion recorded during the Northridge earthquake show that substantial reductions of the absolute acceleration can be obtained with reasonable relative displacements of the superstructure and small strokes in the isolation devices. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Response of a double-wedge base-isolation device

    J. Enrique Luco
    Abstract A novel base-isolation device is described and its performance is compared with that of a friction pendulum bearing. In its simplest form, the device consists of two wedges sliding on a horizontal plane in opposite directions and constrained from retreating by ratchets or bilinear dampers. The superstructure rests at the intersection of the two wedges. For a sufficiently large horizontal acceleration of the base, the structure starts to move up the inclined plane of one of the wedges, which remains fixed while the second wedge is slaved to follow the structure. As the direction of the base acceleration reverses, the process is reversed and the structure starts to climb on the second inclined plane while the first wedge follows. The overall result is that the horizontal acceleration of the structure is reduced with respect to that of the base and that kinetic energy associated with horizontal velocities is systematically transformed into potential energy. In the case of motion in a vertical plane, the device has the following advantages over a friction pendulum: (i) the sliding surface is linear instead of curved, (ii) kinetic energy is systematically transformed into potential energy during the strong ground motion, and (iii) the device is slowly self-centering. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Is the Presence of Mitral Annular Calcification Associated with Poor Left Atrial Function?

    ECHOCARDIOGRAPHY, Issue 8 2009
    Vignendra Ariyarajah M.D.
    Introduction: Mitral annular calcification (MAC) is characterized by calcium and lipid deposition in the annular fibrosa of the mitral valve. MAC is associated with cardiovascular events but little is known of its association with left atrial (LA) function. Methods: We prospectively obtained 12-lead electrocardiograms (ECGs) and transthoracic echocardiograms (TTE) on patients scheduled for nonemergent echocardiographic assessment at a tertiary care hospital. MAC was graded as 0 = none, 1 = mild, 2 = moderate, 3 = severe. LA linear and volume measurements (stroke volume, LA passive emptying fraction, LA active emptying fraction and LA kinetic energy) were done specifically in addition to commonly measured TTE parameters. Results: From the 124 considered for the study, 72 patients remained (aged 68±18 years; 44% male) after excluding those with poor ECG tracings and/or poor TTE images. Eighteen patients had MAC; mild MAC = 14, moderate MAC = 3, severe MAC = 1. When patients with MAC were compared to those without MAC, no significant difference was noted, except for LA linear dimension index (2.1±0.4 vs. 1.9±0.3 cm/m2; P = 0.03). For those with mild and moderate MAC, a trend was noted toward lower LA function with increasing MAC severity. In addition, significant differences were noted between those with and without interatrial conduction delay, where those with such delay had significantly impaired LA stroke volume (9.8±3 vs. 19.93±4 ml; P < 0.0001), LA active emptying fraction (18.83±8 vs. 65.71±9%; P < 0.0001) and LA total/reservoir fraction (39.54±6 vs. 75.1±6%; P < 0.0001). Conclusions: MAC is associated with increase in LA linear dimension on TTE and may be equally represented with lower overall LA function. Further study in a much larger cohort is warranted to delineate these and other potential associations of MAC. [source]

    Vegetation impacts on near bank flow

    ECOHYDROLOGY, Issue 4 2009
    Leslie Hopkinson
    Abstract Vegetation is an important component of stream restoration designs used to control streambank retreat, but vegetation effects on near bank flows need to be quantified. The goal of this research was to evaluate how three-dimensional velocity structure and turbulence characteristics vary with three vegetation treatments: tree, shrub and grass. A second order prototype stream (Tom's Creek in Blacksburg, Virginia, USA) with individual reaches dominated by each vegetation treatment was modelled in a research flume using a fixed-bed Froude-scale modelling technique. One model streambank of the prototype stream was constructed for each vegetation type and compared to a bare control (only grain roughness). Velocity profiles perpendicular to the flume model boundary were measured using a three-dimensional acoustic Doppler velocimeter. Three-dimensional velocity records, turbulent kinetic energy characteristics, and Reynolds stresses were analysed. The addition of vegetation on a sloping streambank increased the free stream streamwise velocity as compared to a bare streambank. Velocity in the downstream direction decreased in the area close to the streambank boundary for all vegetation treatments. Tree turbulence intensity and Reynolds stress distributions were similar to the bare condition due to the sparse tree placement characteristic of mature forests. The turbulence caused by the upright shrub treatment increased turbulent kinetic energy and Reynolds stresses near the streambank, particularly at the toe. The flexible grass vegetation folded and protected the streambank, reducing shear stress near the boundary. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Low-energy irradiation effects of gas cluster ion beams

    Shingo Houzumi
    Abstract A cluster-ion irradiation system with cluster-size selection has been developed to study the effects of the cluster size for surface processes using cluster ions. A permanent magnet with a magnetic field of 1.2 T is installed for size separation of large cluster ions. Trace formations at HOPG surface by the irradiation with size-selected Ar-cluster ions under an acceleration energy of 30 keV were investigated by scanning tunneling microscopy. Generation behavior of the craterlike traces is strongly affected by the number of constituent atoms (cluster size) of the irradiating cluster ion. When the incident cluster ion is composed of 100 to 3000 atoms, craterlike traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster ions composed of over 5000 atoms. Such behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion. To study GCIB irradiation effects on macromolecules, GCIB was irradiated on DNA molecules absorbed on graphite surface. Using GCIB irradiation, many more DNA molecules were sputtered away compared with the monomer-ion irradiation. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(2): 40,45, 2008; Published online in Wiley InterScience ( DOI 10.1002/eej.10031 [source]

    Development of equine upper airway fluid mechanics model for Thoroughbred racehorses

    Summary Reason for performing study: Computational fluid dynamics (CFD) models provide the means to evaluate airflow in the upper airways without requiring in vivo experiments. Hypothesis: The physiological conditions of a Thoroughbred racehorse's upper airway during exercise could be simulated. Methods: Computed tomography scanned images of a 3-year-old intact male Thoroughbred racehorse cadaver were used to simulate in vivo geometry. Airway pressure traces from a live Thoroughbred horse, during exercise was used to set the boundary condition. Fluid-flow equations were solved for turbulent flow in the airway during inspiratory and expiratory phases. The wall pressure turbulent kinetic energy and velocity distributions were studied at different cross-sections along the airway. This provided insight into the general flow pattern and helped identify regions susceptible to dynamic collapse. Results: The airflow velocity and static tracheal pressure were comparable to data of horses exercising on a high-speed treadmill reported in recent literature. The cross-sectional area of the fully dilated rima glottidis was 7% greater than the trachea. During inspiration, the area of highest turbulence (i.e. kinetic energy) was in the larynx, the rostral aspect of the nasopharynx was subjected to the most negative wall pressure and the highest airflow velocity is more caudal on the ventral aspect of the nasopharynx (i.e. the soft palate). During exhalation, the area of highest turbulence was in the rostral and mid-nasopharynx, the maximum positive pressure was observed at the caudal aspect of the soft palate and the highest airflow velocity at the front of the nasopharynx. Conclusions and clinical relevance: In the equine upper airway collapsible area, the floor of the rostral aspect of the nasopharynx is subjected to the most significant collapsing pressure with high average turbulent kinetic during inhalation, which may lead to palatal instability and explain the high prevalence of dorsal displacement of the soft palate (DDSP) in racehorses. Maximal abduction of the arytenoid cartilage may not be needed for optimal performance, since the trachea cross-sectional area is 7% smaller than the rima glottidis. [source]

    Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development

    D. N. Warrington
    Summary Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 × 40 × 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m,3; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures. [source]

    Relationships among vertically structured in situ measures of turbulence, larval fish abundance and feeding success and copepods on Western Bank, Scotian Shelf

    Using vertically stratified data of the abundance of silver hake (Merluccius bilinearis) larvae and concentrations of copepods collected in the field, we examine relationships among the vertical distribution of larval fish, their potential prey, feeding success and water column turbulence. Water column turbulence and associated stratification parameters were estimated from: (i) in situ measures of turbulent kinetic energy dissipation (,) provided by an EPSONDE profiler; (ii) in situ wind speed; (iii) the Richardson number (Ri); and (iv) the buoyancy frequency (N2). Small (< 5 mm total length) silver hake were more abundant in the least turbulent waters (i.e. at a minimum in the rate of dissipation of turbulent kinetic energy, , < 10,7 W kg,1; Ri > 0.25; N2 > 0.001 (rad s,1)2). Partial correlations amongst ,, N2 and small hake larvae were significant only for N2. The abundance of larger (> 5 mm total length) hake larvae was positively correlated with depth and was not associated with either , or N2. Vertical distributions of three potential prey (classified by stage) were variable. Early stage copepodids were positively correlated with N2 and negatively correlated with ,. We found no evidence of diel distribution patterns for small (< 5 mm total length) hake larvae or for any of the developmental stages of the copepods examined. Neither estimate of water column turbulence inferred from wind speed nor from Ri was meaningfully related to in situ estimates of , or to larval fish abundance. Feeding success, measured either as prey items (gut),1, average prey length, or total prey volume (gut),1, was not related to predicted encounter rates between days. However, the average prey length (gut),1 was significantly (P < 0.01) related to water column turbulence. These conflicting results suggest that the relationship between larval feeding and the environment is more complicated than assumed. We conclude that without substantial high resolution in situ examination of the relationship between the vertical distributions of turbulence, larvae and their prey, the growing acceptance in the secondary literature that turbulence has a positive and biologically meaningful effect on trophic interactions between fish and their zooplankton prey (a generalization based largely on modelling and laboratory experiments) is premature. [source]

    Origins of Improved Hole-Injection Efficiency by the Deposition of MoO3 on the Polymeric Semiconductor Poly(dioctylfluorene- alt -benzothiadiazole)

    Yasuo Nakayama
    Abstract The electronic structure of the interfaces formed after deposition of MoO3 hole-injection layers on top of a polymer light-emitting material, poly(dioctylfluorene- alt -benzothiadiazole) (F8BT), is studied by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy and metastable atom electron spectroscopy. Significant band bending is induced in the F8BT film by MoO3 "acceptors" that spontaneously diffuse into the F8BT "host" probably driven by kinetic energy of the deposited hot MoO3. Further deposition leads to the saturation of the band bending accompanied by the formation of MoO3 overlayers. Simultaneously, a new electronic state in the vicinity of the Fermi level appears on the UPS spectra. Since this peak does not appear in the bulk MoO3 film, it can be assigned as an interface state between the MoO3 overlayer and underlying F8BT film. Both band bending and the interface state should result from charge transfer from F8BT to MoO3, and they appear to be the origin of the hole-injection enhancement by the insertion of MoO3 layers between the F8BT light-emitting diodes and top anodes. [source]

    A Closed Form Slug Test Theory for High Permeability Aquifers

    GROUND WATER, Issue 1 2005
    David W. Ostendorf
    We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and under-damped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 × 10,3 m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as muchas 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction. [source]

    Bifurcation and second-order work in geomaterials

    François Nicot
    Abstract In this paper, the ability of a material rate-independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second-order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate-independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well-known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Free vibration analysis of arches using curved beam elements

    Jong-Shyong Wu
    Abstract The natural frequencies and mode shapes for the radial (in-plane) bending vibrations of the uniform circular arches were investigated by means of the finite arch (curved beam) elements. Instead of the complicated explicit shape functions of the arch element given by the existing literature, the simple implicit shape functions associated with the tangential, radial (or normal) and rotational displacements of the arch element were derived and presented in matrix form. Based on the relationship between the nodal forces and the nodal displacements of a two-node six-degree-of-freedom arch element, the elemental stiffness matrix was derived, and based on the equation of kinetic energy and the implicit shape functions of an arch element the elemental consistent mass matrix with rotary inertia effect considered was obtained. Assembly of the foregoing elemental property matrices yields the overall stiffness and mass matrices of the complete curved beam. The standard techniques were used to determine the natural frequencies and mode shapes for the curved beam with various boundary conditions and subtended angles. In addition to the typical circular arches with constant curvatures, a hybrid beam constructed by using an arch segment connected with a straight beam segment at each of its two ends was also studied. For simplicity, a lumped mass model for the arch element was also presented. All numerical results were compared with the existing literature or those obtained from the finite element method based on the conventional straight beam element and good agreements were achieved. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    A simplified v2,f model for near-wall turbulence

    M. M. Rahman
    Abstract A simplified version of the v2,f model is proposed that accounts for the distinct effects of low-Reynolds number and near-wall turbulence. It incorporates modified C,(1,2) coefficients to amplify the level of dissipation in non-equilibrium flow regions, thus reducing the kinetic energy and length scale magnitudes to improve prediction of adverse pressure gradient flows, involving flow separation and reattachment. Unlike the conventional v2,f, it requires one additional equation (i.e. the elliptic equation for the elliptic relaxation parameter fµ) to be solved in conjunction with the k,, model. The scaling is evaluated from k in collaboration with an anisotropic coefficient Cv and fµ. Consequently, the model needs no boundary condition on and avoids free stream sensitivity. The model is validated against a few flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    An eddy viscosity model with near-wall modifications

    M. M. Rahman
    Abstract An extended version of the isotropic k,, model is proposed that accounts for the distinct effects of low-Reynolds number (LRN) and wall proximity. It incorporates a near-wall correction term to amplify the level of dissipation in nonequilibrium flow regions, thus reducing the kinetic energy and length scale magnitudes to improve prediction of adverse pressure gradient flows, involving flow separation and reattachment. The eddy viscosity formulation maintains the positivity of normal Reynolds stresses and the Schwarz' inequality for turbulent shear stresses. The model coefficients/functions preserve the anisotropic characteristics of turbulence. The model is validated against a few flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data. Comparisons indicate that the present model is a significant improvement over the standard eddy viscosity formulation. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    A new symmetry-preserving Cartesian-grid method for computing flow past arbitrarily shaped objects

    Marc Dröge
    Abstract This paper deals with a numerical method for solving the unsteady, incompressible Navier,Stokes equations in domains of arbitrarily shaped boundaries, where the boundary is represented using the Cartesian-grid approach. We introduce a novel cut-cell discretization, which preserves the symmetry of convection and diffusion. That is, convection is discretized by a skew-symmetric operator and diffusion is approximated by a symmetric, positive-definite coefficient matrix. The resulting semi-discrete (continuous in time) system conserves the kinetic energy if the dissipation is turned off; the energy decreases if dissipation is turned on. The method is successfully tested for an incompressible, unsteady flow around a circular cylinder at Re=100. Copyright © 2005 John Wiley & Sons, Ltd. [source]