Small-scale Behavior Research Articles

Small-Scale Plastic Deformation of Nanocrystalline High Entropy Alloy.

High entropy alloys (HEAs) have attracted widespread interest due to their unique properties at many different length-scales. Here, we report the fabrication of nanocrystalline (NC) Al0.1CoCrFeNi high entropy alloy and subsequent small-scale plastic deformation behavior via nano-pillar compression tests. Exceptional strength was realized for the NC HEA compared to pure Ni of similar grain sizes. Grain boundary mediated deformation mechanisms led to high strain rate sensitivity of flow stress in the nanocrystalline HEA.

Influence of behavioral plasticity and foraging strategy on starvation tolerance of planktonic copepods

Starvation is considered a major cause of non-predatory mortality in zooplankton. Planktonic copepods display behavioral plasticity and small-scale behaviors associated with different foraging strategies that can affect starvation tolerance. However, little is still known about the influence of behavior on starvation tolerance in zooplankton. Here, we experimentally investigated behavioral changes and survival of planktonic copepods (adults and nauplii) with different foraging strategies under prolonged starvation. The behavioral response to starvation varied depending on the foraging strategy. The strict ambusher Oithona nana showed a low and, almost constant, motile activity (relocation jumps, <4% of the time) whereas the feeding-current feeder Temora longicornis swam for most of the time (~100%) without reducing their activity under prolonged starvation. The switching-behavior feeder Acartia tonsa move actively in the presence of food but had a low motile activity in absence of food (~12%) and decreased its motile activity during starvation (from ~12% to 3%). The observed behavioral responses to the absence of food can be broadly classified in terms of motility as: (i) “sit-and-wait” strategy for copepods with low motile activity under starvation (mostly relocation jumps) and (ii) “searching” strategy for copepods with high motility activity (swimming/cruising) under starvation. Median survival time in absence of food increased with increasing copepod body weight and it was ~1.75 fold lower in active feeders (“searching” strategy under starvation) than in ambush and switching-behavior feeders (“sit-and-wait” strategy under starvation). Thus, copepods with foraging strategies linked to a low motility (ambush feeders) and/or with behavioral plasticity to reduce motility in absence of food (switching -behavior feeders) would cope better with resource limitation/fluctuation than some active feeders. We demonstrate that behavioral plasticity and motile activity associated with foraging strategy significantly influences starvation tolerance in planktonic copepods. These results help to quantify the main trade-offs (gain vs costs) of the main zooplankton foraging strategies and emphasize that behavior is a key trait to understand the distribution of planktonic copepods in marine environments depending on trophic conditions.

Experimentally validated multi-scale modeling of 3D printed hyper-elastic lattices

This work deals with mechanical analysis of hyper-elastic lattices in the finite-strain range through multi-scale simulations and experimental testing. It describes designing appropriate unit cells (UCs) and mode-shapes to accurately predict mechanical behaviors of soft lattices in the finite-strain range. Lattices are based on three different types of repeating UCs in triangular, square and hexagonal shapes. Generic planar UCs consisting of beam-like structures are simulated to determine overall constitutive behaviors. In this respect, periodic boundary conditions are introduced in the finite-strain regime. Deformations of the unit cells and lattice are described on the basis of non-linear Green strains. Finite element (FE) solutions coupled with the Mooney–Rivlin constitutive equations are developed and solved using an iterative Newton–Raphson method and a multi-scale strategy. Then, the computational tool is applied to analyze lattice structures fabricated by three-dimensional (3D) printing technology. Samples are tested in tension and compression modes in different directions revealing strong non-linear, directional and load-dependent responses. A detailed analysis of small-scale behavior of unit cells is presented. Large-scale and multi-scale FE models are also implemented to simulate experimental results with high accuracy and computational efficiency. Due to the absence of similar results in the literature, this paper would contribute to understanding of hyper-elastic behaviors of lattices at small-scale and be instrumental in the large-scale design and analysis of soft lattice structures.

Nanomechanics to 1000 °C for high temperature mechanical properties of bulk materials and hard coatings

It is important to measure nanomechanical properties of materials for extreme environments at temperatures that match their operating conditions so that the data are more relevant than those obtained from room temperature measurements. Reliable high temperature mechanical property data improves our understanding of the linkage between the small-scale mechanical behaviour and the performance and design of advanced materials systems for increasingly extreme environments. Accurate high temperature nanomechanical measurements require significantly more careful instrumental and experimental design than at room temperature. It is important to consider (i) instrumental stability and thermal drift (ii) the test environment and its influence on the stability of the indenter and sample (iii) modifications to the experimental load history and analysis procedures to minimise the effect of greater time-dependency. In this review of best practice and published studies effective strategies for mitigating these effects and achieving reliable, validated data are discussed with illustrative examples on thin films and bulk materials operating in extreme environments in applications in the nuclear, aerospace, fuel cell and cutting tool industries to 1000 °C.

Weak field limit of infinite derivative gravity

A form of infinite derivative gravity is free from ghostlike instabilities with improved small scale behavior. In this theory, we calculate the tree-level scattering amplitude and the corresponding weak field potential energy between two localized covariantly conserved spinning pointlike sources that also have velocities and orbital motion. We show that the spin-spin and spin-orbit interactions take the same form as in Einstein's gravity at large separations, whereas at small separations, the results are different. We find that not only the usual Newtonian potential energy but also the spin-spin and spin-orbit interaction terms in the potential energy are nonsingular as one approaches $r\ensuremath{\rightarrow}0$.

Size effects on plasticity in high-entropy alloys

Abstract

Scalar dark matter clumps with angular momentum

The behavior of light scalar dark matter has been a subject of much interest recently as it can lead to interesting small scale behavior. In particular, this can lead to the formation of gravitationally bound clumps for these light scalars, including axions. In ref. [1] we analyzed the behavior of these clumps, assuming spherical symmetry, allowing for both attractive and repulsive self-interactions. There is a maximum allowed mass for the clumps in the case of attractive interactions, and a minimum radius for the clumps in the case of repulsive interactions, which is saturated at large mass. Here we extend this work to include non-spherically symmetric clumps. Since the system tries to re-organize into a BEC ground state, we consider configurations with a conserved non-zero angular momentum, and construct minimum energy configurations at fixed particle number and fixed angular momentum. We find generalizations of the previous spherically symmetric results. In particular, while there is still a maximum mass for the attractive case, its value increases with angular momentum. Also, the minimum radius in the repulsive case is raised to higher radii. We clarify how a recent claim in the literature of an upper bound on angular momentum is due to inaccurate numerics. In a forthcoming paper we shall investigate the possibility of resonance of axion clumps into both visible and hidden sector photons, and analyze how the altered mass and radius from non-zero angular momentum affects the resonance.

Using a benthic lander to explore and monitor vulnerable ecosystems in the Mediterranean Sea

&lt;p class="Abstract"&gt;The MEMO (Marine Environment MOnitoring system) baited lander is used to explore and monitor marine ecosystems in the Mediterranean Sea. MEMO is equipped with 2 video cameras, a multiparametric probe and a current meter, fully operative down to 1000 m in depth for 24 consecutive hours. Since 2010, the ecology team of the Department of Biology of the University of Bari (Italy) deployed the MEMO lander in some sensitive and vulnerable deep-sea habitats of the Mediterranean Sea, as part of national and international research projects. Data on environmental parameters (depth, salinity, temperature and current) and related to bentho-pelagic species, their small-scale distribution, size and behavior, have been recorded. MEMO has been also deployed in fragile and structurally complex habitats, such as coralligenous and cold-water corals, in order to monitor physico-chemical and biological variables as part of the EU Marine Strategy Framework Directive. Some practical applications of the MEMO lander are reported here, with indications of relative advantages and limitations.&lt;/p&gt;

Machine Learning of Spatiotemporal Bursting Behavior in Developing Neural Networks.

As with other modern sciences (and their computational counterparts), neuroscience experiments can now produce data that, in terms of both quantity and complexity, challenge our interpretative abilities. It is relatively common to be faced with datasets containing many millions of neural spikes collected from tens of thousands of neurons. Traditional data analysis methods can, in a relatively straightforward manner, identify large-scale features in such data (e.g., on the scale of entire networks). What these approaches often cannot do is to connect macroscopic activity to the relevant small-scale behaviors of individual cells, especially in the face of ongoing background activity that is not relevant. This communication presents an application of machine learning techniques to bridge the gap between microscopic and macroscopic behaviors and identify the small-scale activity that leads to large-scale behavior, reducing data complexity to a level that can be amenable to further analysis. A small number of spatiotemporal spikes (among many millions) were found to provide reliable information about if and where a burst will occur.

Influence of system aspects on fading at mm‐waves

This contribution presents propagation measurements at 60 GHz in indoor non-line of sight scenarios. Besides analysing the measurements, the authors have considered several system aspects, such as bandwidth and directivity in order to investigate the small-scale behaviour of the radio channel after beam-forming. The results show that due to the high resolution in the angular and time domain achievable by large antenna arrays and wideband signals, the fading is significantly reduced and the equivalent transmission channel becomes more sparse and deterministic. These insights represent an essential source of information for future systems design and the ongoing channel modelling activities for systems operating at mm-waves.

Using script analysis to understand the financial crimes involved in wildlife trafficking

Wildlife trafficking has evolved in the last few decades from a critical conservation concern to a global security threat. What was once thought to be small-scale opportunistic behavior has now become a large organized trade partly run by criminal networks. Most research on wildlife trafficking has focused on the drivers of the trade and its modus operandi for catching, moving, and selling wildlife. There has been little research on the financial aspects of wildlife trafficking, despite how useful financial laws could be to prosecute traffickers in countries where environmental laws are weak. This research uses the crime script model and Gottschalk’s (Journal of Financial Crime, 17(4), 441–458, 2010) financial crime classification to study the financial crimes committed by wildlife traffickers during the trafficking process. Results show that financial crimes, including corruption, fraud, and money laundering, are part of every stage of the trafficking process for every actor involved. This research locates “pinch points” where it is most effective to intervene to dismantle the financial networks involved in wildlife trafficking and suggests interventions based on situational crime prevention principles.

Behavioral response of the freshwater cyclopoid copepod Eucyclops serrulatus to hydropeaking and thermopeaking in a laboratory flume

ABSTRACTThe generation of electricity by hydropower plants meets the requirements for intermittent energy demand and for the production of renewable energy. However, the hydropower plant operation has important consequences for the biotic compartment of the river reaches downstream. Intermittent release of water causes sudden variations in discharge that increase bed shear stress and dislodge benthic organisms. Release from high-elevation reservoir can also affect the thermal regime of the river by causing sharp variations in water temperature. Because the hydrodynamic and thermal waves separate while propagating downstream, the benthic community is exposed to two distinct stressors that affect taxa differently based on their sensitivity and adaptations. We investigated separately the effects of a sudden variation in discharge or in water temperature on the small-scale swimming behavior of a widespread species of cyclopoid copepod in a laboratory flume that allows the tracking of organisms both in the water column and in a transparent sediment bed. We gradually varied the discharge or the temperature of the water to mimic the artificial changes caused by hydropower plants. We tracked copepods in three dimensions and quantified the kinematics of their motion. Copepods increased substantially their counter-current swimming effort in response to increasing flow velocity. This behavioral response seems to occur above a threshold in flow velocity of approx. 40 mm/s. It results in a substantial reduction in their downstream transport and hence opposes drift. Copepods reacted differently to warm and cold variations in temperature. Decreasing temperature resulted in a substantially lower counter-current swimming effort, which may therefore increase drift. Rising temperature had no clear effect on their behavior. Our study highlights the importance of understanding the behavioral traits that mediate the response of stream invertebrates to disturbances in the hydraulic and thermal regimes of their environment.

Discussions on the correspondence of dissipative particle dynamics and Langevin dynamics at small scales

We investigate the behavior of dissipative particle dynamics (DPD) within different scaling regimes by numerical simulations. The paper extends earlier analytical findings of Ripoll, M., Ernst, M. H., and Espa˜nol, P. (Large scale and mesoscopic hydrodynamics for dissipative particle dynamics. Journal of Chemical Physics, 115(15), 7271–7281 (2001)) by evaluation of numerical data for the particle and collective scaling regimes and the four different subregimes. DPD simulations are performed for a range of dynamic overlapping parameters. Based on analyses of the current auto-correlation functions (CACFs), we demonstrate that within the particle regime at scales smaller than its force cut-off radius, DPD follows Langevin dynamics. For the collective regime, we show that the small-scale behavior of DPD differs from Langevin dynamics. For the wavenumber-dependent effective shear viscosity, universal scaling regimes are observed in the microscopic and mesoscopic wavenumber ranges over the considered range of dynamic overlapping parameters.

Homogenization analysis of invasion dynamics in heterogeneous landscapes with differential bias and motility.

Animal movement behaviors vary spatially in response to environmental heterogeneity. An important problem in spatial ecology is to determine how large-scale population growth and dispersal patterns emerge within highly variable landscapes. We apply the method of homogenization to study the large-scale behavior of a reaction-diffusion-advection model of population growth and dispersal. Our model includes small-scale variation in the directed and random components of movement and growth rates, as well as large-scale drift. Using the homogenized model we derive simple approximate formulas for persistence conditions and asymptotic invasion speeds, which are interpreted in terms of residence index. The homogenization results show good agreement with numerical solutions for environments with a high degree of fragmentation, both with and without periodicity at the fast scale. The simplicity of the formulas, and their connection to residence index make them appealing for studying the large-scale effects of a variety of small-scale movement behaviors.

The effects of the small-scale behaviour of dark matter power spectrum on CMB spectral distortion

After numerous astronomical and experimental searches, the precise particle nature of dark matter is still unknown. The standard Weakly Interacting Massive Particle(WIMP) dark matter, despite successfully explaining the large-scale features of the universe, has long-standing small-scale issues. The spectral distortion in the Cosmic Microwave Background(CMB) caused by Silk damping in the pre-recombination era allows one to access information on a range of small scales 0.3 Mpc < k < 104 Mpc−1, whose dynamics can be precisely described using linear theory. In this paper, we investigate the possibility of using the Silk damping induced CMB spectral distortion as a probe of the small-scale power. We consider four suggested alternative dark matter candidates—Warm Dark Matter (WDM), Late Forming Dark Matter (LFDM), Ultra Light Axion (ULA) dark matter and Charged Decaying Dark Matter (CHDM); the matter power in all these models deviate significantly from the ΛCDM model at small scales. We compute the spectral distortion of CMB for these alternative models and compare our results with the ΛCDM model. We show that the main impact of alternative models is to alter the sub-horizon evolution of the Newtonian potential which affects the late-time behaviour of spectral distortion of CMB. The y-parameter diminishes by a few percent as compared to the ΛCDM model for a range of parameters of these models: LFDM for formation redshift zf = 105 (7%); WDM for mass mwdm = 1 keV (2%); CHDM for decay redshift zdecay = 105 (5%); ULA for mass ma = 10−24 eV (3%). This effect from the pre-recombination era can be masked by orders of magnitude higher y-distortions generated by late-time sources, e.g. the Epoch of Reionization and tSZ from the cluster of galaxies. We also briefly discuss the detectability of this deviation in light of the upcoming CMB experiment PIXIE, which might have the sensitivity to detect this signal from the pre-recombination phase.

Effect of diatom morphology on the small-scale behavior of the copepod Temora stylifera (Dana, 1849)

We explored the small-scale behavior of the calanoid copepod Temora stylifera in relation to the diatoms Chaetoceros socialis, Leptocylindrus aporus, Leptocylindrus danicus and Pseudo-nitzschia calliantha offered as monospecific diets at similar carbon concentrations. These four diatoms are characterized by distinct size, shape and colony forming ability and are important components of the autumnal bloom co-occurring with the seasonal peak of T. stylifera abundance in Mediterranean coastal waters. High-speed video recordings showed that T. stylifera acquired cells in a suspension feeding mode while creating feeding currents. Copepod behavior was quantified in terms of feeding, motion, and grooming activities. T. stylifera spent more time in hovering than cruising in presence of all diets. The solitary L. aporus and P. calliantha elicited longer feeding bouts, lower appendage beat frequency and shorter grooming events compared to the colonial L. danicus and C. socialis. Overall the present results indicate that the behavioral responses of T. stylifera to different diatom diets were species-specific. The observed behavioral plasticity may help T. stylifera to adjust rapidly to changes in the food environment and this can be advantageous in exploiting short-lived phytoplankton blooms.

Spatially resolved star formation relation in two HI-rich galaxies with central post-starburst signature

E+A galaxies are post-starburst systems that are identified from their optical spectra. These galaxies contain a substantial young A-type stellar component, but have only little ongoing star formation (SF). HI 21-cm line emission is found in approximately half of the nearby E+A galaxies, indicating that they contain a reservoir of gas that could fuel active SF. Here, we study two HI-rich galaxies, which show a typical E+A spectrum at the centre and SF at larger radii. We present new high spatial resolution radio interferometric observations of the HI 21-cm emission line using the VLA and of the CO(1-0) emission line using ALMA. We combine these data sets to predict the SFR and show that it does not correlate well with the SFR derived from H alpha on sub-kpc scales. We apply a recently developed statistical model for the small scale behaviour of the SF relation to predict and interpret the observed scatter. We find smoothly distributed, regularly rotating HI gas. The CO(1-0) emission line is not detected for both galaxies. The derived upper limit on the CO mass implies a molecular gas depletion time shorter than 20 Myr. However, due to the low metallicity, the CO-to-H2 conversion factor is highly uncertain. In the relations between the H alpha-based SFR and the HI mass, we observe a substantial scatter we demonstrate results from small-number statistics of independent star-forming regions on sub-kpc scales. This finding adds to the existing literature reporting a scale dependence of the molecular SF relation, showing that the atomic and molecular phases are both susceptible to the evolutionary 'cycling' of individual regions. This suggests that the atomic gas reservoirs host substantial substructure, which should be observable with future high-resolution observations. (abridged)

Small and large scale behavior of moments of Poisson cluster processes

Small and large scale behavior of moments of Poisson cluster processes

Small and large scale behavior of moments of Poisson cluster processes

Poisson cluster processes are special point processes that find use in modeling Internet traffic, neural spike trains, computer failure times and other real-life phenomena. The focus of this work is on the various moments and cumulants of Poisson cluster processes, and specifically on their behavior at small and large scales. Under suitable assumptions motivated by the multiscale behavior of Internet traffic, it is shown that all these various quantities satisfy scale free (scaling) relations at both small and large scales. Only some of these relations turn out to carry information about salient model parameters of interest, and consequently can be used in the inference of the scaling behavior of Poisson cluster processes. At large scales, the derived results complement those available in the literature on the distributional convergence of normalized Poisson cluster processes, and also bring forward a more practical interpretation of the so-called slow and fast growth regimes. Finally, the results are applied to a real data trace from Internet traffic.

Small-Scale Fading Analysis of the Vehicular-to-Vehicular Channel inside Tunnels

We present a small-scale fading analysis of the vehicular-to-vehicular (V2V) propagation channel at 5.9 GHz when both the transmitter (Tx) and the receiver (Rx) vehicles are inside a tunnel and are driving in the same direction. This analysis is based on channel measurements carried out at different tunnels under real road traffic conditions. The Rice distribution has been adopted to fit the empirical cumulative distribution function (CDF). A comparison of theKfactor values inside and outside the tunnels shows differences in the small-scale fading behavior, with theKvalues derived from the measurements being lower inside the tunnels. Since there are so far few published results for these confined environments, the results obtained can be useful for the deployment of V2V communication systems inside tunnels.