Net Displacement Research Articles

Movements vary according to dispersal stage, group size, and rainfall: the case of the African lion

Dispersal is one of the most important life‐history traits affecting species persistence and evolution and is increasingly relevant for conservation biology as ecosystems become more fragmented. However, movement during different dispersal stages has been difficult to study and remains poorly understood. We analyzed movement metrics and patterns of autocorrelation from GPS data for 20 lions (Panthera leo) over a five‐year period. We compared movement among different stages of natal dispersal (departure, transience, and settlement), in addition to that of territorial adults of both sexes. The movement of lions differed according to dispersal stage, sex, group size, and rainfall. As expected, during dispersal lions moved faster and further and in a more directional manner than pre‐ or post‐dispersal. Transient movement was more directional than adult movement, but somewhat surprisingly, was slower with less net displacement than that of territorial males. Interestingly, the effect of group size on movement differed between transient males and territorial males; solitary dispersers moved faster and further than individuals in bigger groups, while territorial males had the opposite trend. Although our sample size is limited, our results suggest a transition from directional movement during transience to random or periodic use of a fixed territory after settlement. In addition, group size may affect the search and settlement strategies of dispersers while seeking a territory in which to settle.

Home range and social analyses in a mouth brooding frog: testing the coexistence of paternal care and male territoriality

AbstractA link between paternal care and territoriality has been described in several anuran species. The southern Darwin's frog (Rhinoderma darwinii) has developed a highly specialized form of paternal care known as neomelia, in which males ingest developing embryos and transport them in their vocal sacs until metamorphosis is completed. Based on the main components of territoriality described in amphibians: site fidelity, resource limitation and defence (e.g. of oviposition sites and egg clutches), we hypothesized that R. darwinii males exhibit territoriality. To investigate this, we used a multi‐method approach that involved estimating home range and movements, performing social network analyses and monitoring potential egg attendance. Forty‐five individual frogs and three egg clutches were monitored in a population from southern Chile between December 2010 and February 2011. Site fidelity was found across all groups (juveniles, females, non‐brooding males and brooding males) based on small movements between captures (mean ±1 se; 0.96 ± 0.11 m) and small net displacement (2.95 ± 0.55 m). Home ranges were small (1.82 ± 0.54 m; range: 0.1–16 m2) and did not differ significantly among groups. We did not find evidence of male territoriality, instead male frogs exhibited high home range overlapping and intra‐group association. No frogs of either sex were ever seen attending eggs. This evidence supports Wells' suggestion; territoriality in anuran species with parental care should be expected only if males defend oviposition sites. Conversely, females did not exhibit home range overlapping and showed evidence of very low intra‐group association. This study has thrown up a range of additional questions with regard to temporal segregation between non‐brooding males, the roles of male and female calls during reproduction, potential female territoriality and what kind of signals triggers egg ingestion by males.

Photoinduced pure spin-current injection in graphene with Rashba spin-orbit interaction

We propose a photoexcitation scheme for pure spin current generation in graphene subject to a Rashba spinorbit coupling. Although excitation using circularly-polarized light does not result in optical orientation of spins in graphene unless an additional magnetic field is present, we show that excitation with linearly-polarized light at normal incidence yields spin current injection without magnetic field. Spins are polarized within the graphene plane and are displaced in opposite directions, with no net charge displacement. The direction of the spin current is determined by the linear polarization axis of the light, and the injection rate is proportional to the intensity. The technique is tunable via an applied bias voltage and is accessible over a wide frequency range. We predict a spin current polarization as high as 75% for photon frequencies comparable to the Rashba frequency. Spin current injection via optical methods removes the need for ferromagnetic contacts, which have been identified as a possible source of spin scattering in electrical spin injection in graphene.

The response of striped surfperch Embiotoca lateralis to progressive hypoxia: Swimming activity, shoal structure, and estimated metabolic expenditure

When exposed to moderately low O2 conditions (75–30% O2 saturation), shoaling striped surfperch Embiotoca lateralis show no changes in swimming activity, uniform levels of metabolic expenditure and an unchanging shoal structure. As O2 levels become more hypoxic surfperch reduce their locomotor activity, initially with a decrease in turning rate at 20% O2 saturation, followed by a reduction in swimming speed at 15% O2 saturation. Reductions in activity occur in combination with individuals adopting more uniform turning behaviors, which translate into an increase in the distance traveled per unit time (i.e. net displacement). This increase in net displacement may enhance the ability of surfperch to distance themselves from discrete zones of hypoxia. Measures of shoal structure, including nearest neighbor distances and shoal polarity, were constant throughout low O2 exposure despite changes in swimming activity. Estimation of the energetic costs of these behaviors reveals that metabolic expenditure (routine metabolic rate) remained steady at ~120mgO2kg−1h−1 between 100 and 30% O2 saturation, dropping to ~108mgO2kg−1h−1 at 20 and 15% O2 saturation. Given that surfperch possess a critical oxygen saturation (Scrit) of 15.2%, reductions in swimming activity and metabolic energy expenditure clearly occur as individuals reach their aerobic metabolic limits. These results identify that surfperch demonstrate a multi-faceted coping strategy when exposed to low oxygen conditions, which may prove advantageous when the species experience hypoxic episodes in their natural habitat.

Twinning Behaviour in the Intermetallic Compound Al18Cr2Mg3

The twinning in the intermetallic compound Al18Cr2Mg3 was observed and identified by transmission electron microscopy. The geometric description of the twinning in Al18Cr2Mg3 with 184 atoms per unit cell was investigated at atomic level. The classical theory of deformation twinning states that the net atomic displacements are divided into shear and shuffles during twinning. Based on the theory and the hypothesis of full mirror reflection symmetry, the displacement and angle of shuffle were calculated for each atom. The geometric calculation results show that all of the atoms in single crystal Al18Cr2Mg3 have to shuffle. Moreover, the calculation results can be divided into 22 groups, which do not show obvious regularity.

Analysis of the chemotactic behaviour of Leptospira using microscopic agar-drop assay.

Chemotaxis allows bacterial cells to migrate towards or away from chemical compounds. In the present study, we developed a microscopic agar-drop assay (MAA) to investigate the chemotactic behaviour of a coiled spirochete, Leptospira biflexa. An agar drop containing a putative attractant or repellent was placed around the centre of a flow chamber and the behaviour of free-swimming cells was analysed under a microscope. MAA showed that L. biflexa cells gradually accumulated around an agar drop that contained an attractant such as glucose. Leptospira cells often spin without migration by transformation of their cell body. The frequency at which cells showed no net displacement decreased with a higher glucose concentration, suggesting that sensing an attractive chemical allows these cells to swim more smoothly. Investigation of the chemotactic behaviour of these cells in response to different types of sugars showed that fructose and mannitol induced negative chemotactic responses, whereas xylose and lactose were non-chemotactic for L. biflexa. The MAA developed in this study can be used to investigate other chemoattractants and repellents.

Tillage erosion and controlling factors in traditional farming systems in Pinar del Río, Cuba

Traditionally, research on soil degradation focused on water erosion. Recent studies, however, point to the importance of tillage operations as a source of soil translocation in traditional animal-powered farming systems comparable to those applied in the Cuyaguateje watershed, Cuba. Together with the effect of some controlling factors, the extent of tillage erosion on a Ferralsol (Ferralítico Rojo) caused by the traditional ox-drawn mouldboard plough, the ‘arado americano’, and a harrow, the ‘rastrillo’, were studied with a tracer experiment on a Ferralsol with 30 plots on moderate slopes ranging from 4% to 16.5%. Two tillage directions were considered: (i) parallel to the contour and (ii) up and down the slope. Due to the shallow average tillage depth of tillage with the ‘rastrillo’ (3.8cm), net mean downslope displacement could not be observed. Average tillage depth with the ‘arado americano’ was relatively shallow (11.5cm) as well and resulted only in the up and downslope direction in a significant downslope soil flux. This downward movement showed no significant relation with the slope gradient, nor with tillage depth, tillage speed and plant cover. While the potential for tillage erosion is considerable with the ‘arado americano’, actual erosion rates in our study were low compared to previous tillage erosion studies. Single soil movements up to 44cm were detected, but taking crop rotation and tillage frequencies into account, soil transportation rates of accumulated tillage operations only ranged from 8.78 to 26.34kgm−1yr−1. This is mainly due to the moderate slope range, the low tillage depth and the good farmers' practice of tilling alternately in opposing direction.

Structural kinematics based damage zone prediction in gradient structures using vibration database

To explore the applications of functionally graded materials (FGMs) in dynamic structures, structural kinematics based health monitoring technique becomes an important problem. Depending upon the displacements in three dimensions, the health of the material to withstand dynamic loads is inferred in this paper, which is based on the net compressive and tensile displacements that each structural degree of freedom takes. These net displacements at each finite element node predicts damage zones of the FGM where the material is likely to fail due to a vibration response which is categorized according to loading condition. The damage zone prediction of a dynamically active FGMs plate have been accomplished using Reddy's higher-order theory. The constituent material properties are assumed to vary in the thickness direction according to the power-law behavior. The proposed C0finite element model (FEM) is applied to get net tensile and compressive displacement distributions across the structures. A plate made of Aluminum/Ziconia is considered to illustrate the concept of structural kinematics-based health monitoring aspects of FGMs.

Instantaneous movement of krill swarms in the Antarctic Circumpolar Current

Antarctic krill are known to have strong swimming capabilities, but direct observations of the speed and direction of krill‐swarm movement within their natural environment are rare. We identified and examined 4060 swarms within the main flow of the Antarctic Circumpolar Current (Scotia Sea) using a combination of an EK60 echosounder, a 153.6 kHz acoustic Doppler current profiler, and ground‐truthing nets. Net displacement magnitude (m) and net angle of deviation (d) were determined by vector subtraction from the background flow immediately below them. Values were compared against control data sets in which swarms were absent. With greater background flow, m became increasingly lower than predicted, which suggests that drag influences swarm movement. The characteristics of the flow regime influenced swarm behavior, given that both m and d varied according to the direction of background flow. Furthermore, multiple‐regression analysis indicated that swarm area, the vicinity of the sea‐ice edge, and salinity had a significant influence on m, with levels of displacement being greatest in larger swarms and in low‐salinity regions close to the ice edge. The ice edge is a key environment for Antarctic krill and swarm behavior may assist in retaining this location. Only fluorescence was found to have a significant influence on d, with deviations being greatest in regions of highest fluorescence. This agrees with laboratory observations of krill turning more frequently within food patches. We demonstrate that it is possible to measure instantaneous movement patterns in Antarctic krill swarms and, at large scales, these movements are consistent with current understanding of responses of krill to local stimuli such as sea‐ice and patches of food.

Abstract 658: Macrophage Dynamics in Inflammation: Tree Ring--Like Growth of Macrophages in Layers Within Atherosclerotic Plaques

The mechanisms that control macrophage accumulation and retraction from plaques are fervently debated. We had earlier wondered if monocyte-derived cells might be driven to become motile cells resembling dendritic cells, capable of leaving plaque, under conditions when macrophage content in plaques waned. Thus, our laboratory developed a technique that allows the use of fluorescent phagocytic tracers to quantitatively monitor macrophage influx into plaques as well as the potential emigration of macrophages out of plaques. The phagocytic tracer was not removed from plaques when plaque macrophage content receded in conjunction with a stark lowering of plasma cholesterol, arguing that macrophage loss does not result from robust emigration of macrophages out of plaques. Nonetheless, here we show that the distribution of the phagocytic tracer was very different under conditions when macrophage content wanes, as the tracer is distributed near the arterial lumen in this case, versus conditions when macrophages increase, when the tracer is located deep within plaques. Under all conditions and time points, the tracer remained equidistant from the internal elastic lamina that defined the border of the inflammatory plaque, indicating that tracer-bearing macrophages underwent no net displacement. Indeed, we could generate a tree-ring like appearance in plaques by labeling a second wave of monocytes with fluorescent particles of a different color than the first and show that they created a second layer, resembling growth of rings on an aging tree. Preliminary data from multiphoton imaging in atherosclerotic plaques supports the concept of restricted territories for plaque macrophages following recruitment. Under conditions when monocyte recruitment continues, previously recruited macrophages that get buried would likely be subjected to increasing hypoxia and related signals that are pro-inflammatory. This layering of macrophages on macrophages may itself drive a vicious cycle that perpetuates inflammation beyond through signals other than the signal that initiated plaque development in the first place.

Coupling of lever arm swing and biased Brownian motion in actomyosin.

An important unresolved problem associated with actomyosin motors is the role of Brownian motion in the process of force generation. On the basis of structural observations of myosins and actins, the widely held lever-arm hypothesis has been proposed, in which proteins are assumed to show sequential structural changes among observed and hypothesized structures to exert mechanical force. An alternative hypothesis, the Brownian motion hypothesis, has been supported by single-molecule experiments and emphasizes more on the roles of fluctuating protein movement. In this study, we address the long-standing controversy between the lever-arm hypothesis and the Brownian motion hypothesis through in silico observations of an actomyosin system. We study a system composed of myosin II and actin filament by calculating free-energy landscapes of actin-myosin interactions using the molecular dynamics method and by simulating transitions among dynamically changing free-energy landscapes using the Monte Carlo method. The results obtained by this combined multi-scale calculation show that myosin with inorganic phosphate (Pi) and ADP weakly binds to actin and that after releasing Pi and ADP, myosin moves along the actin filament toward the strong-binding site by exhibiting the biased Brownian motion, a behavior consistent with the observed single-molecular behavior of myosin. Conformational flexibility of loops at the actin-interface of myosin and the N-terminus of actin subunit is necessary for the distinct bias in the Brownian motion. Both the 5.5–11 nm displacement due to the biased Brownian motion and the 3–5 nm displacement due to lever-arm swing contribute to the net displacement of myosin. The calculated results further suggest that the recovery stroke of the lever arm plays an important role in enhancing the displacement of myosin through multiple cycles of ATP hydrolysis, suggesting a unified movement mechanism for various members of the myosin family.

Water Permeation Drives Tumor Cell Migration in Confined Microenvironments

Cell migration is a critical process for diverse (patho)physiological phenomena. Intriguingly, cell migration through physically confined spaces can persist even when typical hallmarks of 2D planar migration, such as actin polymerization and myosin II-mediated contractility, are inhibited. Here, we present an integrated experimental and theoretical approach ("Osmotic Engine Model") and demonstrate that directed water permeation is a major mechanism of cell migration in confined microenvironments. Using microfluidic and imaging techniques along with mathematical modeling, we show that tumor cells confined in a narrow channel establish a polarized distribution of Na+/H+ pumps and aquaporins in the cell membrane, which creates a net inflow of water and ions at the cell leading edge and a net outflow of water and ions at the trailing edge, leading to net cell displacement. Collectively, this study presents an alternate mechanism of cell migration in confinement that depends on cell-volume regulation via water permeation.

Boundary Adherence during Place-based Policing Evaluations

Objectives: This note explores complications with standard methods to evaluate place-based policing interventions. It identifies and explains issues of boundary misspecification during evaluation as a result of boundary adjustment by police during an intervention. Method: Using geographic data gathered during post-experiment focus groups with officers involved in the Philadelphia Foot Patrol Experiment, we highlight the practice of boundary adjustment on the part of officers and we explain why such adjustments occurred. Results: Officers involved in the focus groups who identified the active boundaries of their hot spot assignments ( n = 124) all reported policing outside of their delineated beats. On average, their active beats were 0.13 square miles larger than the originally delineated treatment beats. Some active beats overlapped catchment and control locations. Conclusion: Boundary misspecification could cause researchers to (1) incorrectly label a direct benefit of receiving treatment as a diffusion of crime control benefits; (2) underestimate immediate spatial crime displacement; and (3) underestimate treatment effects. Future place-based experiments should take into account the various pressures on officers to adjust the boundaries of their assignments by incorporating measures that track boundary adherence over time (and reporting them) in order to optimize assessments of net effects, diffusion and displacement.

1D-1D Coulomb Drag Signature of a Luttinger Liquid

One-dimensional (1D) interacting electronic systems exhibit distinct properties when compared to their counterparts in higher dimensions. We report Coulomb drag measurements between vertically integrated quantum wires separated by a barrier only 15 nanometers wide. The temperature dependence of the drag resistance is measured in the true 1D regime where both wires have less than one 1D subband occupied. As a function of temperature, an upturn in the drag resistance is observed below a temperature T* ~ 1.6 kelvin. This crossover in Coulomb drag behavior is consistent with Tomonaga-Luttinger liquid models for the 1D-1D drag between quantum wires.

The orientation of the neuronal growth process can be directed via magnetic nanoparticles under an applied magnetic field

There is a growing body of evidence indicating the importance of physical stimuli for neuronal growth and development. Specifically, results from published experimental studies indicate that forces, when carefully controlled, can modulate neuronal regeneration. Here, we validate a non-invasive approach for physical guidance of nerve regeneration based on the synergic use of magnetic nanoparticles (MNPs) and magnetic fields (Ms). The concept is that the application of a tensile force to a neuronal cell can stimulate neurite initiation or axon elongation in the desired direction, the MNPs being used to generate this tensile force under the effect of a static external magnetic field providing the required directional orientation. In a neuron-like cell line, we have confirmed that MNPs direct the neurite outgrowth preferentially along the direction imposed by an external magnetic field, by inducing a net angle displacement (about 30°) of neurite direction. From the Clinical EditorThis study validates that non-invasive approaches for physical guidance of nerve regeneration based on the synergic use of magnetic nanoparticles and magnetic fields are possible. The hypothesis was confirmed by observing preferential neurite outgrowth in a cell culture system along the direction imposed by an external magnetic field.

Pairwise hydrodynamic interactions and diffusion in a vesicle suspension

The hydrodynamic interaction of two deformable vesicles in shear flow induces a net displacement, in most cases an increase of their distance in the transverse direction. The statistical average of these interactions leads to shear-induced diffusion in the suspension, both at the level of individual particles which experience a random walk made of successive interactions, and at the level of suspension where a nonlinear down-gradient diffusion takes place, an important ingredient in the structuring of suspension flows. We make an experimental and computational study of the interaction of a pair of lipid vesicles in shear flow by varying physical parameters, and investigate the decay of the net lateral displacement with the distance between the streamlines on which the vesicles are initially located. This decay and its dependency upon vesicle properties can be accounted for by a simple model based on the well established law for the lateral drift of a vesicle in the vicinity of a wall. In the semi-dilute regime, a determination of self-diffusion coefficients is presented.

Mechanical Ageing Protocol Selection Affects Macroscopic Performance and Molecular Level Properties of Ethylene Vinyl Acetate (EVA) Running Shoe Midsole Foam

Existing attempts to evaluate footwear via cyclic compression fail to sufficiently represent biofidelic force-time curves or provide the underlying mechanism of EVA foam fatigue. A uniaxial biofidelic waveform was compared to a sine wave of the same frequency to examine differences in (1) net displacement, (2) absorbed energy, and (3) peak force from ASTM F1614. A non-destructive molecular-level technique (ATR-FTIR) recorded differences in hydroxyl, ester, and unsaturated moieties due to EVA degradation. It was concluded that (1) biofidelic waveforms may better simulate human running, (2) material degradation is discernible, and (3) inferences regarding polymeric degradation and macroscopic performance require further investigation.

Quasisteady Particle Transport in Slowly Varying Periodic Streaming Flows

When a cylindrical probe vibrates laterally in a fluid at a Reynolds number of order 10, a circulatory pattern of flow is established in the fluid near the probe. In a plane transverse to the probe, a symmetric arrangement of four streaming cells is maintained by the probe's vibration. A computational model has shown that inertial particles introduced to such a flow will be attracted to the centers of the streaming cells. We present preliminary experimental data supporting this prediction and outline a strategy whereby particles captured in this way can be transported from place to place as a result of periodic variations in the excitation of a fluid containing two independent probes. Specifically, we model the time-averaged flow around two probes by superposing two copies of a velocity field obtained analytically for the single-probe case and demonstrate that a cyclic change in the two-probe flow can engender acyclic variations in the positions and character of fixed points. A fixed point that's initially attractive to inertial particles can be moved from the vicinity of one probe to the vicinity of another and then annihilated or altered via bifurcation so that it will surrender the particles it carries. If parametric variations in such a flow are slow relative to the dynamics of particles migrating to attracting points, then the net displacement of inertial particles from one trapping point to another as a result of a cyclic change in the flow exhibits certain features of a geometric phase.

Shear behaviour of prestressed steel fibre concrete box-beams

Six full-scale prestressed concrete box-beams are tested to study the effects of steel fibres on the increase in shear strength of beams. Beams are cast with no traditional transverse steel reinforcement. The amount of steel fibres and shear span-to-effective depth ratio are the main variables studied. The beams are subjected to concentrated vertical loads up to their maximum shear capacity using two actuators in load and displacement control mode. During the load tests linear voltage displacement transducers (LVDTs) are used to measure displacements at several critical points on the web in the end zone of the beams. Several LVDTs are also placed under the beams at the points of loading to measure the actual total and net displacements of the beams. From the load tests it is observed that the shear capacities of the beams increase with an increase in the amount of steel fibres and decrease as the shear span-to-effective depth ratio increases.

Software for determining the true displacement of faults

One of the most important parameters of faults is the true (or net) displacement, which is measured by restoring two originally adjacent points, called “piercing points”, to their original positions. This measurement is not typically applicable because it is rare to observe piercing points in natural outcrops. Much more common is the measurement of the apparent displacement of a marker. Methods to calculate the true displacement of faults using descriptive geometry, trigonometry or vector algebra are common in the literature, and most of them solve a specific situation from a large amount of possible combinations of the fault parameters. True displacements are not routinely calculated because it is a tedious and tiring task, despite their importance and the relatively simple methodology. We believe that the solution is to develop software capable of performing this work. In a previous publication, our research group proposed a method to calculate the true displacement of faults by solving most combinations of fault parameters using simple trigonometric equations. The purpose of this contribution is to present a computer program for calculating the true displacement of faults. The input data are the dip of the fault; the pitch angles of the markers, slickenlines and observation lines; and the marker separation. To prevent the common difficulties involved in switching between operative systems, the software is developed using the Java programing language. The computer program could be used as a tool in education and will also be useful for the calculation of the true fault displacement in geological and engineering works. The application resolves the cases with known direction of net slip, which commonly is assumed parallel to the slickenlines. This assumption is not always valid and must be used with caution, because the slickenlines are formed during a step of the incremental displacement on the fault surface, whereas the net slip is related to the finite slip.