Net Displacement Research Articles

Volume displacement effects during bubble entrainment in a travelling vortex ring

AbstractWhen a few bubbles are entrained in a travelling vortex ring, it has been shown that, even at extremely low volume loadings, their presence can significantly affect the structure of the vortex core (Sridhar & Katz, J. Fluid Mech., vol. 397, 1999, pp. 171–202). A typical Euler–Lagrange point-particle model with two-way coupling for this dilute system, wherein the bubbles are assumed subgrid and momentum point sources are used to model their effect on the flow, is shown to be unable to capture accurately the experimental trends of bubble settling location, bubble escape and vortex distortion for a range of bubble parameters and vortex strengths. The bubbles experience significant amounts of drag, lift, added mass, pressure and gravity forces. However, these forces are in balance with each other as the bubbles reach a mean settling location away from the vortex core. The reaction force on the fluid due to the net summation of these forces alone is thus very small and is unable to affect the vortex core. By accounting for fluid volume displacement due to bubble motion, experimental trends on vortex distortion and bubble settling location are captured accurately. The fluid displacement effects are studied by computing various contributions to an effective volume displacement force and are found to be important even at low volume loadings. As the bubble size and hence bubble Reynolds number increase, the bubbles settle further away from the vortex centre and have strong potential for vortex distortion. The net volume displacement force depends on the radial pressure force, the radial settling location of the bubble, as well as the vortex Reynolds number. The resultant of the volume displacement force is found to be roughly at $4{5}^{\circ } $ with the vortex travel direction, resulting in wakes directed towards the vortex centre. Finally, a simple modification to the standard point-particle two-way coupling approach is developed wherein the interphase reaction source terms are consistently altered to account for the fluid displacement effects and reactions due to bubble accelerations.

Intrafraction displacement of prone versus supine prostate positioning monitored by real‐time electromagnetic tracking

Implanted radiofrequency transponders were used for real‐time monitoring of the intrafraction prostate displacement between patients in the prone position and the same patients in the supine position. Thirteen patients had three transponders implanted transperineally and were treated prone with a custom‐fitted thermoplastic immobilization device. After collecting data from the last fraction, patients were realigned in the supine position and the displacements of the transponders were monitored for 5–7 minutes. Fourier transforms were applied to the data from each patient to determine periodicity and its amplitude. To remove auto correlation from the stream of displacement data, the distribution of short‐term and long‐term velocity components were calculated from Poincaré plots of paired sequential vector displacements. The mean absolute displacement was significantly greater prone than supine in the superior–inferior (SI) plane (1.2±0.6mm vs. 0.6±0.4mm, p=0.015), but not for the lateral or anterior–posterior (AP) planes. Displacements were least in the lateral direction. Fourier analyses showed the amplitude of respiratory oscillations was much greater for the SI and AP planes in the prone versus the supine position. Analysis of Poincaré plots confirmed greater short‐term variance in the prone position, but no difference in the long‐term variance. The centroid of the implanted transponders was offset from the treatment isocenter by > 5 mm for 1.9% of the time versus 0.8% of the time for supine. These results confirmed significantly greater net intrafraction prostate displacement of patients in the prone position than in the supine position, but most of the difference was due to respiration‐induced motion that was most pronounced in the SI and AP directions. Because the respiratory motion remained within the action threshold and also within our 5 mm treatment planning margins, there is no compelling reason to choose one treatment position over the other.PACS number: 87.50.st

Affluence drives the global displacement of land use

Increasing affluence is often postulated as a main driver for the human footprint on biologically productive areas, identified among the main causes of biodiversity loss, but causal relationships are obscured by international trade. Here, we trace the use of land and ocean area through international supply chains to final consumption, modeling agricultural, food, and forestry products on a high level of resolution while also including the land requirements of manufactured goods and services. In 2004, high-income countries required more biologically productive land per capita than low-income countries, but this connection could only be identified when land used to produce internationally traded products was taken into account, because higher-income countries tend to displace a larger fraction of land use. The equivalent land and ocean area footprint of nations increased by a third for each doubling of income, with all variables analyzed on a per capita basis. This increase came largely from imports, which increased proportionally to income. Export depended mostly on the capacity of countries to produce useful biomass, the biocapacity. Our analysis clearly shows that countries with a high biocapacity per capita tend to spare more land for nature. Biocapacity per capita can be increased through more intensive production or by reducing population density. The net displacement of land use from high-income to low-income countries amounted to 6% of the global land demand, even though high-income countries had more land available per capita than low-income countries. In particular, Europe and Japan placed high pressure on ecosystems in lower-income countries.

Quantification of Patient Migration in Bed

The study objective was to quantify the movement of hospital bed occupants relative to the bed in typical bed articulations. Movement of a patient in bed results in two common adverse events: (a) increase in shear and friction forces between the patient and bed, which are extrinsic pressure ulcer risk factors, and (b) musculoskeletal injuries to nurses, resulting from repositioning patients who have migrated down in bed. The study involved 12 participants who lay supine in three hospital beds, which were articulated to common positions. Body movement relative to the bed was quantified with the use of motion capture. Cumulative movement, net displacement, and torso compression (shoulder to trochanter distance) were calculated for different bed types and bed movements. Bed design and bed movement had a significant effect on most of the dependent variables. Bed design (e.g., type) influenced cumulative movement by up to 115%, net displacement by up to 70%, and torso compression by about 20%. Bed movement (e.g., knee elevation) reduced cumulative migration by up to 35%. The quantification of patient migration provides a metric for evaluating the interaction between body and bed surfaces. Overall, the measures were sensitive to design changes in bed frames, bed articulations, and mattress inflation. Documentation of the cumulative movement, net displacement, and torso compression provides hospital bed designers quantifiable measures for reducing migration and potentially shear and friction forces when designing bed frames, bed articulations, and mattresses. Optimization of these metrics may ultimately have an impact on patient and caregiver health.

Ratchet effect and amplitude dependence of phase locking in a two-dimensional Frenkel-Kontorova model

We demonstrate the ratchet and phase locking effects in a two-dimensional overdamped Frenkel-Kontorova model with a square symmetric periodic substrate when both a longitudinal dc drive and a circular ac drive are applied. Besides the harmonic steps, the large half integer steps can also clearly be seen in the longitudinal (x) direction. These half integer steps are directly correlated to the appearance of positive and negative ratchet effects in the transverse (y) direction due to the symmetry breaking in the combination of the dc and ac drives. The angle between the net displacement and the longitudinal direction is analytically obtained in a single period of the ac drive. In the examination of the amplitude dependence of the ac drive, the maxima decrease monotonically with the amplitude, while the anomalies occur for the critical depinning force and the harmonic steps due to the spatial symmetry breaking of orbits in the presence of the ac drive.

Trajectory and distribution of suspended non-Brownian particles moving past a fixed spherical or cylindrical obstacle

AbstractWe investigate the motion of a suspended non-Brownian sphere past a fixed cylindrical or spherical obstacle in the limit of zero Reynolds number for arbitrary particle–obstacle aspect ratios. We consider both a suspended sphere moving in a quiescent fluid under the action of a uniform force as well as a uniform ambient velocity field driving a freely suspended particle. We determine the distribution of particles around a single obstacle and solve for the individual particle trajectories to comment on the transport of dilute suspensions past an array of fixed obstacles. First, we obtain an expression for the probability density function governing the distribution of a dilute suspension of particles around an isolated obstacle, and we show that it is isotropic. We then present an analytical expression – derived using both Eulerian and Lagrangian approaches – for the minimum particle–obstacle separation attained during the motion, as a function of the incoming impact parameter, i.e. the initial offset between the line of motion far from the obstacle and a parallel line that goes through its centre. Further, we derive the asymptotic behaviour for small initial offsets and show that the minimum separation decays exponentially. Finally we use this analytical expression to define an effective hydrodynamic surface roughness based on the net lateral displacement experienced by a suspended sphere moving past an obstacle.

Ultrafast Energy Migration in Porphyrin-based Metal Organic Frameworks (MOFs)

ABSTRACTIn this paper, we have studied the energy transport properties of two porphyrincontaining metal organic frameworks (MOFs) for light-harvesting applications. The photoinduced singlet exciton migration is investigated using fluorescence quenching experiments, whereas details on exciton transport anisotropy and net displacements are obtained using a Förster theory analysis. The striking difference in the energy-transport properties for the two MOFs, albeit for similar molecular organization, is attributed to dissimilar spatial expanse and difference in the electronic structure of their porphyrin struts. The observed exciton displacements, of up to 60 nm, provides motivation to explore new MOF materials. Several new linkers are considered, leading to predictions of MOF structures, which provide both broadwavelength harvesting and unidirectional energy transporting MOFs with selected examples.

Life Cycle Water Usage in CdTe Photovoltaics

Life cycle water withdrawal for cadmium telluride photovoltaics (CdTe PV) ranges from approximately 382-425 L/MWh, with only ~12% from direct on-site usage. The remainder is related to indirect water withdrawal from the use of grid electricity and raw materials throughout the product life cycle. Approximately half of life cycle water withdrawal is associated with module manufacturing, one-third from balance of systems (BOS), and the remainder from takeback and recycling. Primary contributors to life cycle water withdrawal are the use of grid electricity, glass, and on-site water during manufacturing; steel, copper, inverters, and on-site water in the BOS; and electricity, chemical use, and transport during takeback and recycling. During manufacturing, water consumption is approximately one quarter of withdrawal and is due to cooling tower water evaporation and site irrigation. When deployed in the U.S. Southwest, a CdTe PV array can provide net displacement of life cycle water withdrawal of over 1700-5600 L/MWh relative to grid electricity.

Self-employment and Conflict in Colombia

Many Colombians are confronted with the ongoing conflict that influences their decision making in everyday life, including their behavior in labor markets. This study focuses on the impact of violent conflict on self-employment, enlarging the usual determinants with a set of conflict variables. Our estimation strategy compares three different estimates: one from fixed-effects panel data (OLS-FE), estimates using lagged conflict indicators instead of contemporaneous regressors, and instrumental variables (IV-FE) estimates. Our results show that a one standard deviation increase in net displacement rates increases the rate of self-employment by about 7 percent points. Dividing the self-employed into different sectors (services and agriculture), we find that net displacement increases self-employment in the services sector but has no effect in agriculture that is affected by attacks by rebel and paramilitary groups, instead. Looking at the income of self-employed individuals, an influx of displaced reduces sharply hourly income in the self-employment sector.

Vegetation dynamics drive segregation by body size in Galapagos tortoises migrating across altitudinal gradients

Seasonal migration has evolved in many taxa as a response to predictable spatial and temporal variation in the environment. Individual traits, physiology and social state interact with environmental factors to increase the complexity of migratory systems. Despite a huge body of research, the ultimate causes of migration remain unclear. A relatively simple, tractable system - giant tortoises on Santa Cruz Island, Galapagos, was studied to elucidate the roles of environmental variation and individual traits in a partial migratory system. Specifically, we asked: (i) do Galapagos tortoises undergo long-distance seasonal migrations? (ii) is tortoise migration ultimately driven by gradients in forage quality or temperature; and (iii) how do sex and body size influence migration patterns? We recorded the daily locations of 17 GPS-tagged tortoises and walked a monthly survey along the altitudinal gradient to characterize the movements and distribution of tortoises of different sizes and sexes. Monthly temperature and rainfall data were obtained from weather stations deployed at various altitudes, and the Normalized Difference Vegetation Index was used as a proxy for forage quality. Analyses using net displacement or daily movement characteristics did not agree on assigning individuals as either migratory or non-migratory; however, both methods suggested that some individuals were migratory. Adult tortoises of both sexes move up and down an altitudinal gradient in response to changes in vegetation dynamics, not temperature. The largest tagged individuals all moved, whereas only some mid-sized individuals moved, and the smallest individuals never left lowland areas. The timing of movements varied with body size: large individuals moved upward (as lowland forage quality declined) earlier in the year than did mid-sized individuals, while the timing of downward movements was unrelated to body size and occurred as lowland vegetation productivity peaked. Giant tortoises are unlikely candidates for forage-driven migration as they are well buffered against environmental fluctuations by large body size and a slow metabolism. Notably the largest, and presumably most dominant, individuals were most likely to migrate. This characteristic and the lack of sex-based differences in movement behaviour distinguish Galapagos tortoise movement from previously described partial migratory systems.

Strain localization associated with channelized melt migration in upper mantle lithosphere: Insights from the Twin Sisters ultramafic complex, Washington, USA

We present results of field, microstructural, and textural studies in the Twin Sisters ultramafic complex (Washington State) that document localized deformation associated with the formation of dunite channels in naturally deformed upper mantle. The Twin Sisters complex is a well-exposed, virtually unaltered section of upper mantle lithosphere comprised largely of dunite and harzburgite (in cm- to m-scale primary compositional layers), and variably deformed orthopyroxenite and clinopyroxenite dikes. A series of ∼N–S striking, m-scale dunite bands (typically with porphyroclastic texture) occur throughout the study area and crosscut both the primary compositional layers and older orthopyroxenite dikes. Structural relationships suggest that these dunite bands represent former zones of channelized melt migration (i.e., dunite channels), and that strain localization was associated with melt migration. Early formed orthopyroxenite dikes are either absent within cross-cutting dunite channels, or have been displaced within channels relative to their position in the adjacent host rocks. These pre-existing orthopyroxenite dikes provide strain markers illustrating that displacement was localized primarily along channel margins, which have opposite senses of shear. In all cases where offsets were noted, the center of the channel was moved southward relative to its margins. Material flow and strain was, therefore, partitioned within channels during melt migration, and dunite channels did not accommodate net shear displacement of the adjacent host peridotites. Primary compositional layers adjacent to dunite channels document opposite rotation of olivine [100] crystallographic axes on either side of channel margins, consistent with the kinematic reversal inferred from offset markers at the outcrop scale, suggesting that the formation of dunite channels also induced host rock deformation proximal to channels. Strain localization that was focused at the margin of the bands was likely facilitated by melt-induced weakening. Channelized movement within the dunite bands may have resulted from matrix compaction within channels, pressure gradients during melt migration, or a combination of these processes during coaxial deformation.

Long-Distance and Frequent Movements of the Flying-Fox Pteropus poliocephalus: Implications for Management

Flying-foxes (Pteropodidae) are large bats capable of long-distance flight. Many species are threatened; some are considered pests. Effective conservation and management of flying-foxes are constrained by lack of knowledge of their ecology, especially of movement patterns over large spatial scales. Using satellite telemetry, we quantified long-distance movements of the grey-headed flying-fox Pteropus poliocephalus among roost sites in eastern Australia. Fourteen adult males were tracked for 2–40 weeks (mean 25 weeks). Collectively, these individuals utilised 77 roost sites in an area spanning 1,075 km by 128 km. Movement patterns varied greatly between individuals, with some travelling long distances. Five individuals travelled cumulative distances >1,000 km over the study period. Five individuals showed net displacements >300 km during one month, including one movement of 500 km within 48 hours. Seasonal movements were consistent with facultative latitudinal migration in part of the population. Flying-foxes shifted roost sites frequently: 64% of roost visits lasted <5 consecutive days, although some individuals remained at one roost for several months. Modal 2-day distances between consecutive roosts were 21–50 km (mean 45 km, range 3–166 km). Of 13 individuals tracked for >12 weeks, 10 moved >100 km in one or more weeks. Median cumulative displacement distances over 1, 10 and 30 weeks were 0 km, 260 km and 821 km, respectively. On average, over increasing time-periods, one additional roost site was visited for each additional 100 km travelled. These findings explain why culling and relocation attempts have had limited success in resolving human-bat conflicts in Australia. Flying-foxes are highly mobile between camps and regularly travel long distances. Consequently, local control actions are likely to have only temporary effects on local flying-fox populations. Developing alternative methods to manage these conflicts remains an important challenge that should be informed by a better understanding of the species’ movement patterns.

Effect of Body Mass Index on Intrafraction Prostate Displacement Monitored by Real-Time Electromagnetic Tracking

To evaluate, using real-time monitoring of implanted radiofrequency transponders, the intrafraction prostate displacement of patients as a function of body mass index (BMI). The motions of Beacon radiofrequency transponders (Calypso Medical Technologies, Seattle, WA) implanted in the prostate glands of 66 men were monitored throughout the course of intensity modulated radiation therapy. Data were acquired at 10 Hz from setup to the end of treatment, but only the 1.7 million data points with a "beam on" tag were used in the analysis. There were 21 obese patients, with BMI ≥ 30 and 45 nonobese patients in the study. Mean displacements were least in the left-right lateral direction (0.56 ± 0.24 mm) and approximately twice that magnitude in the superior-inferior and anterior-posterior directions. The net vector displacement was larger still, 1.95 ± 0.47 mm. Stratified by BMI cohort, the mean displacements per patient in the 3 Cartesian axes as well as the net vector for patients with BMI ≥ 30 were slightly less (<0.2 mm) but not significantly different than the corresponding values for patients with lower BMIs. As a surrogate for the magnitude of oscillatory noise, the standard deviation for displacements in all measured planes showed no significant differences in the prostate positional variability between the lower and higher BMI groups. Histograms of prostate displacements showed a lower frequency of large displacements in obese patients, and there were no significant differences in short-term and long-term velocity distributions. After patients were positioned accurately using implanted radiofrequency transponders, the intrafractional displacements in the lateral, superior-inferior, and anterior-posterior directions as well as the net vector displacements were smaller, but not significantly so, for obese men than for those with lower BMI.

Physical confinement alters tumor cell adhesion and migration phenotypes

Cell migration on planar surfaces is driven by cycles of actin protrusion, integrin-mediated adhesion, and myosin-mediated contraction; however, this mechanism may not accurately describe movement in 3-dimensional (3D) space. By subjecting cells to restrictive 3D environments, we demonstrate that physical confinement constitutes a biophysical stimulus that alters cell morphology and suppresses mesenchymal motility in human breast carcinoma (MDA-MB-231). Dorsoventral polarity, stress fibers, and focal adhesions are markedly attenuated by confinement. Inhibitors of myosin, Rho/ROCK, or β1-integrins do not impair migration through 3-μm-wide channels (confinement), even though these treatments repress motility in 50-μm-wide channels (unconfined migration) by ≥50%. Strikingly, confined migration persists even when F-actin is disrupted, but depends largely on microtubule (MT) dynamics. Interfering with MT polymerization/depolymerization causes confined cells to undergo frequent directional changes, thereby reducing the average net displacement by ≥80% relative to vehicle controls. Live-cell EB1-GFP imaging reveals that confinement redirects MT polymerization toward the leading edge, where MTs continuously impact during advancement of the cell front. These results demonstrate that physical confinement can induce cytoskeletal alterations that reduce the dependence of migrating cells on adhesion-contraction force coupling. This mechanism may explain why integrins can exhibit reduced or altered function during migration in 3D environments.

Ship-borne contour integration for flux determination

The consumption of nutrients by mussel beds can be monitored by measuring the net nutrient flux across a circumscribing vertical surface. Measuring this nutrient flux not only requires resolving the spatial (and temporal) distribution of nutrients at the bounding contour, but also an ability to unambiguously measure net water motion across it. As a prerequisite for future application to nutrient flux determination, we here describe results of a field campaign in the inland Wadden Sea in which we aim to measure just the latter water balance. This is done by comparing the water transport across a vertical surface, spanned by the closed contour and the bottom, to the net tidal displacement of the free surface enclosed by this contour. The former is obtained by measuring currents while traversing the contour repeatedly within one tidal cycle. The latter is estimated using sea-level observations at nearby tidal stations as well as by means of direct sea-level observations at the location of measurements. The current measurements are used to reveal the spatial structure of the tidal and tidally rectified fields, which are divided into cross and along contour currents. These measurements show how the presence of a steep slope in the bathymetry has an impact on the presence of circulation cells that are relevant for the mixing and flushing of water. A neat closure of the water budget is obstructed since it is dominated by the difference between a strong inflow and a concurrent, nearly equally strong outflow. For future application we recommend using observed tidal elevations within the closed contour as a constraint in determining the best estimates for cross-contour water fluxes, thus opening the route to genuine nutrient flux measurements by ‘contour integration’.

Differential patterns of home-range, net displacement and resting sites use of Conepatus chinga in southern Brazil

Studies on the spatial ecology of Molina's hog-nosed skunk were conducted in southern Brazil. Between April 2008 and April 2009, 18 individuals were tagged with radio collars and monitored by radio-telemetry (VHF). The average home-range estimated for 12 skunks was 1.63km2±1.17km2. Males had home-ranges 2.5 times larger than females, and also showed significantly larger patterns of displacement. These differences in space probably were related not only to sexual size dimorphism, but also to differential behavior between sexes. We identified six basic types of resting sites, among which holes in the ground were the most common and comprised more than 50% of the total. Reuse of resting sites was high (32%), especially for females, which had a significantly higher rate than males. Although they showed a large proportion of home-range overlap even in the core areas, skunks exhibited a solitary life style, rarely sharing resting sites and maintaining relatively long distances from each other, equivalent to twice the distance of daily movements. The almost strictly nocturnal activity pattern observed in this study is a common characteristic of the family. Among practically all of the ecological features analyzed, males and females showed significant differences, denoting the importance of a sex-specific approach in ecological studies regarding this species.

Physical Analysis of a Biomimetic Microphone With a Central-Supported (C-S) Circular Diaphragm for Sound Source Localization

This paper presents a physical analysis of the biomimetic microphone designed with a central-supported (C-S) diaphragm for the sound source localization. A clover-stem-like C-S design is proposed and achieving 47% improvement of net diaphragm displacement in comparison with the conventional C-S diaphragm design. The new design can effectively not only compensate undesired deformation of sensing diaphragm due to gravity and residual stresses but also make the diaphragm more flexible for better sound pressure sensitivity.

Spherical‐Earth finite element model of short‐term postseismic deformation following the 2004 Sumatra earthquake

Decadal‐scale postseismic deformation of subduction earthquakes has been widely modeled using a Maxwell viscoelastic Earth with a mantle‐wedge viscosity of about 1019 Pa s. Short‐term postseismic deformation within a few years after the earthquake remains a more challenging problem because of the predominance of afterslip of the megathrust and the potentially more complex mantle rheology. Questions include the necessity of invoking the transient rheology and the relative importance of contributions from afterslip and viscoelastic relaxation. In this work, we address these questions by developing a spherical‐Earth viscoelastic finite element model for the short‐term postseismic deformation following the magnitude 9.2 Sumatra earthquake of 2004. The model consists of elastic overriding and subducting plates and a viscoelastic mantle of bi‐viscous Burgers rheology, with the continental mantle (mantle wedge) being less viscous than the oceanic mantle by a factor of ten. Primary observational constraints for the short‐term postseismic deformation include ∼1 year net displacements of nine near‐field GPS sites and ∼3 year time series from three far‐field sites several hundred kilometers from the 2004 rupture zone. Model results indicate that the afterslip of the fault must be at work within the first few years after the earthquake. The observed deformation is best explained with a model that includes both the afterslip and transient rheology. In the preferred model, the transient and steady state viscosities of the mantle wedge are 5 × 1017 Pa s and 1019 Pa s, respectively.

Postcapture movement rates can inform data-censoring protocols for GPS-collared animals

Wildlife research often requires the capture, chemical immobilization, and handling of free-ranging animals. These activities have been documented to yield detrimental effects among some study subjects and may bias study results. We developed an empirical censoring protocol that investigated the postcapture movement rates of 89 white-tailed deer (Odocoileus virginianus) outfitted with global positioning system (GPS) collars to identify data that should be censored from analyses due to postcapture recovery and acclimation. Average daily postcapture movement rates were significantly lower than average daily movement rates for a given calendar day for approximately 14 days postcapture. We tested the influence of biased data in a simple random walk simulation and found that net displacement values were significantly lower after 1,000 iterations when an uncensored data set was used than for data sets that did not include the first 2 weeks of GPS locations. Our results indicate that study animals exhibited sublethal effects of capture, handling, and instrument acclimation (reduced movement rates) for approximately 14 days postcapture. We recommend that all studies involving marked animals assess the influence of capture, handling, and instrumentation on postcapture movements to guard against data sets that are not representative of normal movement behavior. Inclusion of these data in movement analyses may bias results, especially when data sets are small (,90 days).

Experimental study of the particle paths in solitary water waves

We provide experiments that had been conducted to investigate the particle trajectory beneath a solitary water wave. Experimental results show that the surface drift is larger than the bottom drift. Meanwhile, the ratio of the net horizontal displacement to the total height of the trajectory at the free surface and subsurface will decrease with the initial vertical position and increase with the relative wave height.