Size Selection Mechanism Research Articles

Low predator and conspecific density lead to larger juveniles

Predation is a key size-selective mechanism structuring juvenile fish populations, given typically greater susceptibility of small juveniles in a population to predation compared to larger individuals. We tested the hypothesis that greater predator abundance selectively removes the smallest age 0 Atlantic cod (Gadus morhua) in nearshore habitat, truncating their size distribution in nursery habitats. We tested this hypothesis using fifteen years of historical data on nearshore fish abundance in Newman Sound, Newfoundland. Using skewness to estimate size-frequency distribution asymmetry, our analyses showed smaller age 0 cod were least prevalent under low predator and low conspecific densities. In contrast, high predator abundances corresponded to weak, size-selective removal of the smallest juveniles. Age 0 cod reached the largest sizes under lower predator and conspecific densities. Our analyses link size of individual juvenile fish in the wild with their survival, where predator abundance modulates the advantages gained by attaining larger size.

Single-Step Control of Liquid-Liquid Crystalline Phase Separation by Depletion Gradients.

Fine-tuning nucleation and growth of colloidal liquid crystalline (LC) droplets, also known as tactoids, is highly desirable in both fundamental science and technological applications. However, the tactoid structure results from the trade-off between thermodynamics and nonequilibrium kinetics effects, and controlling liquid-liquid crystalline phase separation (LLCPS) in these systems is still a work in progress. Here, a single-step strategy is introduced to obtain a rich palette of morphologies for tactoids formed via nucleation and growth within an initially isotropic phase exposed to a gradient of depletants. The simultaneous appearance is shown of rich LC structures along the depleting potential gradient, where the position of each LC structure is correlated with the magnitude of the depleting potential. Changing the size (nanoparticles) or the nature (polymers) of the depleting agent provides additional, precise control over the resulting LC structures through a size-selective mechanism, where the depletant may be found both within and outside the LC droplets. The use of depletion gradients from depletants of varying sizes and nature offers a powerful toolbox for manipulation, templating, imaging, and understanding heterogeneous colloidal LC structures.

Selectivity in snow crab (Chionoecetes opilio) pot fishery: Effect of escape gap shape and size for conservation of fishery resources

Conical pots are commonly used fishing gear for capturing snow crab (Chionoecetes opilio). In these fisheries, optimal snow crab size selection is important for reducing unintended mortality of undersized individuals aiming at conserving fisheries resources and reducing sorting time onboard fishing vessels. Size selection in snow crab pot fisheries commonly takes place through pot netting meshes during deployment. The diamond mesh netting has varying opening angles affecting retention of snow crab of different sizes, and often large proportions of catches consist of undersized crab challenging natural resource conservation. Some commercial snow crab fisheries use rigid escape gaps in addition to mesh selection to improve size selectivity. In this study, we predict the size selection potential of escape gaps with different shape and size and investigated whether such additional size selection mechanism can have a potential to improve selectivity compared to mesh selection. Results showed that circular escape gaps have potential to provide sharper size selection compared to netting meshes and thus could be used to limit the capture of undersized snow crab which is relevant for management and conservation of snow crab resources. However, a similar positive effect cannot be obtained to the same extent with elliptical and rectangular escape gaps.

Multiobjective trajectory optimization algorithms for solving multi-UAV-assisted mobile edge computing problem

The Internet of Things (IoT) devices are not able to execute resource-intensive tasks due to their limited storage and computing power. Therefore, Mobile edge computing (MEC) technology has recently been utilized to provide computing and storage capabilities to those devices, enabling them to execute these tasks with less energy consumption and low latency. However, the edge servers in the MEC network are located at fixed positions, which makes them unable to be adjusted according to the requirements of end users. As a result, unmanned aerial vehicles (UAVs) have recently been used to carry the load of these edge servers, making them mobile and capable of meeting the desired requirements for IoT devices. However, the trajectories of the UAVs need to be accurately planned in order to minimize energy consumption for both the IoT devices during data transmission and the UAVs during hovering time and mobility between halting points (HPs). The trajectory planning problem is a complicated optimization problem because it involves several factors that need to be taken into consideration. This problem is considered a multiobjective optimization problem since it requires simultaneous optimization of both the energy consumption of UAVs and that of IoT devices. However, existing algorithms in the literature for this problem have been based on converting it into a single objective, which may give preference to some objectives over others. Therefore, in this study, several multiobjective trajectory planning algorithms (MTPAs) based on various metaheuristic algorithms with variable population size and the Pareto optimality theory are presented. These algorithms aim to optimize both objectives simultaneously. Additionally, a novel mechanism called the cyclic selection mechanism (CSM) is proposed to manage the population size accurately, optimizing the number of HPs and the maximum function evaluations. Furthermore, the HPs estimated by each MTPA are associated with multiple UAVs using the k-means clustering algorithm. Then, a low-complexity greedy mechanism is used to generate the order of HPs assigned to each UAV, determining its trajectory. Several experiments are conducted to assess the effectiveness of the MTPAs with variable population size and cyclic selection mechanisms. The experimental findings demonstrate that the MTPAs with the cyclic selection mechanism outperform all competing algorithms, achieving better outcomes.

Anthropogenic and natural size-related selection act in concert during brown trout (Salmo trutta) smolt river descent

By hindering migration and inducing direct turbine mortality during downstream migration, hydropower is regarded as one of the most serious threats to anadromous salmonids. Yet, little attention has been paid to long-term turbine-induced selection mechanisms effecting fish populations. This work evaluates turbine and post-turbine survival of PIT-tagged wild brown trout smolts. By estimating individual river and sea survival rates, we were able to compare survival rates of smolts that had migrated through the turbine with smolts that had bypassed the turbine, as well as investigate both natural and anthropogenic size-selective mechanisms operative on the population. Total river-descent survival probability was 0.20 for turbine migrants and 0.44 for bypass migrants. The surviving turbine migrants were significantly smaller than their bypass counterparts and more exposed to predation from Northern pike. The estimated mean-adjusted selection gradient was − 0.76 for turbine migrants and + 1.85 for the bypass migrants. The resulting disruptive selection may ultimately lead to increased phenotypic smolt size variation provided sufficient additive genetic variance associated with smolt size. Mitigation measures at hydropower plants are thus essential for preserving sustainable populations of anadromous fish and maintaining population genetic variation.

Nesterov acceleration of alternating least squares for canonical tensor decomposition: Momentum step size selection and restart mechanisms

SummaryWe present Nesterov‐type acceleration techniques for alternating least squares (ALS) methods applied to canonical tensor decomposition. While Nesterov acceleration turns gradient descent into an optimal first‐order method for convex problems by adding a momentum term with a specific weight sequence, a direct application of this method and weight sequence to ALS results in erratic convergence behavior. This is so because ALS is accelerated instead of gradient descent for our nonconvex problem. Instead, we consider various restart mechanisms and suitable choices of momentum weights that enable effective acceleration. Our extensive empirical results show that the Nesterov‐accelerated ALS methods with restart can be dramatically more efficient than the stand‐alone ALS or Nesterov's accelerated gradient methods, when problems are ill‐conditioned or accurate solutions are desired. The resulting methods perform competitively with or superior to existing acceleration methods for ALS, including ALS acceleration by nonlinear conjugate gradient, nonlinear generalized minimal residual method, or limited‐memory Broyden‐Fletcher‐Goldfarb‐Shanno, and additionally enjoy the benefit of being much easier to implement. We also compare with Nesterov‐type updates where the momentum weight is determined by a line search (LS), which are equivalent or closely related to existing LS methods for ALS. On a large and ill‐conditioned 71×1,000×900 tensor consisting of readings from chemical sensors to track hazardous gases, the restarted Nesterov‐ALS method shows desirable robustness properties and outperforms any of the existing methods we compare with by a large factor. There is clear potential for extending our Nesterov‐type acceleration approach to accelerating other optimization algorithms than ALS applied to other nonconvex problems, such as Tucker tensor decomposition.

Empirical Shipment Size Model for Urban Freight and its Implications

Modeling shipment size for intra-city shipments is a subject that has not been sufficiently addressed in past research, despite its growing importance in disaggregate freight modeling. While past research on shipment size estimation mainly focuses on inter-city shipments, intra-city shipments differ from them in various aspects. In filling this research gap, this study estimates shipment size models using the records of intra-city shipments, identifying the effects of factors and heterogeneity on the shipment size selection mechanism. The estimated coefficients are also compared against their theoretical values derived from a conceptual economic order quantity model. The estimated empirical models highlight the characteristics of intra-city shipments and indicate the importance of both receiver function and commodity type, and also vehicle operation type, in capturing the nuances of the selection mechanism among intra-city shipments.

A data cleaning method for heterogeneous attribute fusion and record linkage

In big data era, massive heterogeneous data are generated from various data sources, the cleaning of dirty data is critical for reliable data analysis. Existing rule-based methods are generally developed in single data source environment, issues like data standardisation and duplication detection for different data type attributes, are not fully studied. In order to address these challenges, we introduce a method based on dynamic configurable rules which can integrate data detection, modification and transformation together. Secondly, we propose a type-based blocking and a varying window size selection mechanism based on classic sorted-neighbourhood algorithm. We present a reference implementation of our method in a real-life data fusion system and validate its effectiveness and efficiency using recall and precision metrics. Experimental results indicate that our method is suitable in the scenario of multiple data sources with heterogeneous attribute properties.

Design and evaluation of glomerulus mesangium-targeted PEG-PLGA nanoparticles loaded with dexamethasone acetate.

Mesangial proliferative glomerulonephritis (MsPGN), one of the most common glomerulonephritis pathological types, often leads to end-stage renal disease over a prolonged period. But the current treatment of MsPGN is non-specific and causes serious side effects, thus novel therapeutics and targeting strategies are urgently demanded. By combining the advantages of PEG-PLGA nanoparticles and the size selection mechanism of renal glomerulus, we designed and developed a novel PEG-PLGA nanoparticle delivery system capable of delivering dexamethasone acetate (A-DEX) into glomerular mesangium. We determined that 90 nm was the optimum size to encapsulate A-DEX for glomerular mesangium targeting based on the size-selection mechanism of glomerulus. After intravenous administration in rats, 90 nm DiD-loaded NPs were found to accumulate to a greater extent in the kidney and kidney cortex compared with the free DiD solution. The 90 nm A-DEX NPs are also more stable at room temperature and showed a sustained release pattern. In rat glomerular mesangial cells (HBZY-1) in vitro, we found that the uptake of 90 nm A-DEX NPs was both temperature-dependent and energe-dependent, and they were mostly engulfed via clathrin-dependent endocytosis pathways. In summary, we have successfully developed a glomerular mesangium-targeted PEG-PLGA NPs, which is potential for the treatment of MsPGN.

Pipelined set-membership approach to adaptive Volterra filtering

Due to the high computational complexity required by Volterra filter, some of its practical implementations consider pipelined adaptive Volterra filter architecture with two layers structure. However, its main challenges are the poor robustness against impulsive noise, slow convergence and high computational complexity for long memory high order expansion on each module. In this paper, we firstly extend the pipelined second-order adaptive Volterra filter to its high order version. Then, to reduce the computational complexity and improve the robust performance of pipelined adaptive Volterra filter architecture, the pipelined adaptive Volterra set-membership (PAVF-SM) algorithm and its robust version (PAVF-RSM) are proposed, which are derived from the least-perturbation property and adaptive approximation principle. Due to the inherent variable step size and nonlinear selective update mechanisms, the proposed PAVF-SM and PAVF-RSM algorithms achieve lower complexity and improved convergence performance. Simulations also verify the improved performance of the PAVF-SM and PAVF-RSM algorithms under Gaussian noise and impulsive noise environments.

Microplastics in the Terrestrial Ecosystem: Implications for Lumbricus terrestris (Oligochaeta, Lumbricidae).

Plastic debris is widespread in the environment, but information on the effects of microplastics on terrestrial fauna is completely lacking. Here, we studied the survival and fitness of the earthworm Lumbricus terrestris (Oligochaeta, Lumbricidae) exposed to microplastics (Polyethylene, <150 μm) in litter at concentrations of 7, 28, 45, and 60% dry weight, percentages that, after bioturbation, translate to 0.2 to 1.2% in bulk soil. Mortality after 60 days was higher at 28, 45, and 60% of microplastics in the litter than at 7% w/w and in the control (0%). Growth rate was significantly reduced at 28, 45, and 60% w/w microplastics, compared to the 7% and control treatments. Due to the digestion of ingested organic matter, microplastic was concentrated in cast, especially at the lowest dose (i.e., 7% in litter) because that dose had the highest proportion of digestible organic matter. Whereas 50 percent of the microplastics had a size of <50 μm in the original litter, 90 percent of the microplastics in the casts was <50 μm in all treatments, which suggests size-selective egestion by the earthworms. These concentration-transport and size-selection mechanisms may have important implications for fate and risk of microplastic in terrestrial ecosystems.

Soft repulsive interactions, particle rearrangements and size selection in the self-assembly of nanoparticles at liquid interfaces.

In the adsorption of nanoparticles at liquid interfaces, soft and short ranged repulsive effective interactions between the nanoparticles at the interface may eventually induce crowding, slow dynamics and jamming at high surface coverage. These phenomena can interfere during the adsorption process, significantly slowing down its kinetics. Here, by means of numerical simulations, we find that modifying the effective interactions, which can be achieved for example by grafting differently functionalized polymer shells on the bare nanoparticles, may qualitatively change such interplay. In particular our results suggest that, in the presence of ultrasoft particle interactions such as the ones described by a Gaussian Core Model potential, a small size polydispersity can be sufficient to decouple the adsorption kinetics from the slow dynamics that develops at the interface, due to a qualitative change from an irreversible adsorption controlled by particle rearrangements at the interface to one dominated by size selection mechanisms. These findings may be useful to achieve higher surface coverages and faster adsorption kinetics.

Mechanisms of prey size selection in a suspension-feeding copepod, Temora longicornis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 517:61-74 (2014) - DOI: https://doi.org/10.3354/meps11039 Mechanisms of prey size selection in a suspension-feeding copepod, Temora longicornis Rodrigo J. Gonçalves1,2,3,*, Hans van Someren Gréve1, Damien Couespel1, Thomas Kiørboe1 1Centre for Ocean Life, DTU Aqua, Technical University of Denmark, Kavalergården 6, 2920 Charlottenlund, Denmark 2Estación de Fotobiología Playa Unión, Casilla de Correos N° 15 (9103) Rawson, Chubut, Argentina 3Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Rivadavia 1917, Caba, Argentina *Corresponding author: rodrigo@efpu.org.ar ABSTRACT: We examined size-dependent prey detection and prey capture in free-swimming Temora longicornis using video observations, particle image velocimetry (PIV), and bottle incubations with phytoplankton prey sizes within the range 6-60 µm equivalent spherical diameter (ESD). T. longicornis generates feeding currents by oscillating its appendages at about 25 Hz. Prey cells >10 µm ESD are perceived and captured individually. A capture response was elicited when prey was touched by (or within a few cell radii from) the setae on the feeding appendages. The extension of the setae defines the prey encounter cross section, which is therefore independent of prey size. The flux of water through the encounter area, estimated from PIV, was ca. 150 ml ind.-1 d-1, which represents the maximum possible clearance rates and was similar to that estimated in incubation experiments. However, while the detection probability was nearly 100% for cells >10-15 µm, it declined rapidly for smaller cells. Conversely, the probability that a cell which elicited a capture response was actually ingested declined with increased cell size, from nearly 100% for small cells, to ~0% for the largest cells examined. The resulting prey size spectrum, predicted as the product of the cell-size-specific encounter rates and capture probabilities, was dome-shaped, with a maximum around 20-30 µm ESD. The prey size spectrum from incubation experiments had a similar shape and an optimum range of 30-50 µm ESD. The mechanistic underpinning of the prey size spectrum suggested here deviates from previous descriptions mainly in the mechanism and range of prey detection. KEY WORDS: Temora longicornis · Calanoid copepods · Prey detection · Feeding currents · Prey capture · Zooplankton · Size spectrum · Prey size Full text in pdf format Supplementary material PreviousNextCite this article as: Gonçalves RJ, van Someren Gréve H, Couespel D, Kiørboe T (2014) Mechanisms of prey size selection in a suspension-feeding copepod, Temora longicornis. Mar Ecol Prog Ser 517:61-74. https://doi.org/10.3354/meps11039 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 517. Online publication date: December 15, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Multiplex fluorometric assessment of nutrient limitation as a strategy for enhanced lipid enrichment and harvesting of Neochloris oleoabundans

Detailed in this study are the results of fluorometric assays used to assess the impact of gradual nutrient limitation versus punctuated nitrate limitation on the lipid content and morphology of Neochloris oleoabundans cells in batch culture. Punctuated nitrate limitation was imposed during pre-log, log, late-log, stationary, and senescent growth phases, and the cells were analyzed by bulk fluorescence emission, flow cytometry, and hyperspectral fluorescence imaging. In addition to intrinsic spectroscopic signatures provided by scatter and endogenous fluorescence, Nile Red staining was employed to monitor relative changes in lipid concentration. Analysis of the fluorescence images and temporal data sets was performed using multivariate curve resolution and fitting to logistic growth models to extract parameters of interest. The spectral components independently isolated from the image and temporal data sets showed close agreement with one another, especially relating to chlorophylls and Nile Red in polar and neutral lipid fractions, respectively. The fastest accumulation and highest total neutral lipid per cell and per chlorophyll were obtained with punctuated nitrate limitation during log phase growth on day 4 of culture. The presence of unbound chlorophyll in the resulting lipid bodies supports a membrane recycling TAG accumulation mechanism mediated by chloropolast-ER lipid exchange. Furthermore, an increase in cell size, indicated by forward scatter, was also found to correlate with increased neutral lipid, providing a size selection mechanism for passive harvest of algal cells at peak lipid enrichment.

Two size-selective mechanisms specifically trap bacteria-sized food particles in Caenorhabditis elegans

Caenorhabditis elegans is a filter feeder: it draws bacteria suspended in liquid into its pharynx, traps the bacteria, and ejects the liquid. How pharyngeal pumping simultaneously transports and filters food particles has been poorly understood. Here, we use high-speed video microscopy to define the detailed workings of pharyngeal mechanics. The buccal cavity and metastomal flaps regulate the flow of dense bacterial suspensions and exclude excessively large particles from entering the pharynx. A complex sequence of contractions and relaxations transports food particles in two successive trap stages before passage into the terminal bulb and intestine. Filtering occurs at each trap as bacteria are concentrated in the central lumen while fluids are expelled radially through three apical channels. Experiments with microspheres show that the C. elegans pharynx, in combination with the buccal cavity, is tuned to specifically catch and transport particles of a size range corresponding to most soil bacteria.

Dendrimers as size selective inhibitors to protein–protein binding

This communication describes how the "quantized" size effect of dendrimers can be exploited towards a size selective binding mechanism for the inhibition of protein-protein binding.

A new adaptive Runge–Kutta method for stochastic differential equations

In this paper, we will present a new adaptive time stepping algorithm for strong approximation of stochastic ordinary differential equations. We will employ two different error estimation criteria for drift and diffusion terms of the equation, both of them based on forward and backward moves along the same time step. We will use step size selection mechanisms suitable for each of the two main regimes in the solution behavior, which correspond to domination of the drift-based local error estimator or diffusion-based one. Numerical experiments will show the effectiveness of this approach in the pathwise approximation of several standard test problems.

Hybrid Organic−Inorganic Membrane: Solving the Tradeoff between Permeability and Selectivity

To solve the tradeoff between permeability and selectivity of polymeric membranes, organic−inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and γ-glycidyloxypropyltrimethoxysilane (GPTMS) were prepared by an in situ sol−gel approach for pervaporative separation of benzene/ cyclohexane mixtures. The structure of PVA-GPTMS hybrid membranes was characterized with FTIR, 29Si NMR, SEM, TEM, and XRD. Energy-dispersive X-ray Si-mapping analysis demonstrated homogeneous dispersion of silica in the PVA matrix. Compared with pure PVA membranes, the hybrid membranes exhibited high thermal stability and lower Tg, and in particular improved pervaporation properties. Permeation flux increased from 20.3 g/(m2 h) for pure PVA membrane to 137.1 g/(m2 h) for PVA-GPTMS hybrid membrane with 28 wt % GPTMS content, and separation factor increased from 9.6 to 46.9 correspondingly. The pervaporation results of PVA-GPTMS hybrid membranes are all above the upper bound tradeoff curve (Lue, S. J.; Peng, S. H. J. Membr. Sci. 2003, 222, 203), while that of pure PVA membrane is obviously below the curve. Positron annihilation lifetime spectroscopy (PALS) was employed to elucidate the enhancement of permeation flux in polymer-based pervaporation membranes, and a size-selective mechanism was proposed to explain the enhancement of the separation factor.

Separating particles according to their physical properties: Transverse drift of over-damped interacting particles through two-dimensional ratchets

We study the transverse net current of particles moving through two-dimensional square arrays or chains of potential energy hills or wells when driven perpendicularly to their spatial symmetry axis (i.e., the mirror-symmetry axis). Although unrelated to the usual Hall effect, such a zero-applied-magnetic-field Hall-like particle current can be observed for vortices, electrons, colloidal particles, and other interacting particles. This effect is quite general and occurs for non-zero inertia, and/or interaction, and/or temperature. We focus on two-dimensional ratchets and we also study the transverse rectification with particle interactions. The transverse rectification of interacting particles moving through 2D asymmetric potential landscapes can drop to zero if their interaction length is smaller than a certain characteristic geometric length. This size-selective rectification mechanism could be used for developing new particle separation devices. Ratchets of interacting particles could also be used to separate these based on either their spin, mass, or charge.

Erratum: Shear-induced formation of vesicles in membrane phases: Kinetics and size selection mechanisms, elasticity versus surface tension [Phys. Rev. E69, 021504 (2004)

Erratum: Shear-induced formation of vesicles in membrane phases: Kinetics and size selection mechanisms, elasticity versus surface tension [Phys. Rev. E<b>69</b>, 021504 (2004)