570 research outputs found
Self-Organized Discrimination of Resources
When selecting a resource to exploit, an insect colony must take into account at least two constraints: the resource must be abundant enough to sustain the whole group, but not too large to limit exploitation costs, and risks of conflicts with other colonies. Following recent results on cockroaches and ants, we introduce here a behavioral mechanism that satisfies these two constraints. Individuals simply modulate their probability to switch to another resource as a function of the local density of conspecifics locally detected. As a result, the individuals gather at the smallest resource that can host the whole group, hence reducing competition and exploitation costs while fulfilling the overall group's needs. Our analysis reveals that the group becomes better at discriminating between similar resources as it grows in size. Also, the discrimination mechanism is flexible and the group readily switches to a better suited resource as it appears in the environment. The collective decision emerges through the self-organization of individuals, that is, in absence of any centralized control. It also requires a minimal individual cognitive investment, making the proposed mechanism likely to occur in other social species and suitable for the development of distributed decision making tools
Longitudinal associations between adolescent dating violence victimization and adverse outcomes: A systematic review
Evidence on the outcomes of adolescent dating violence (ADV) victimization mainly derives from cross-sectional studies, which have limitations in suggesting causal relationships. Furthermore, the complexity of factors and overlapping dimensions in dating violence research, such as the forms of violence experienced, may have contributed to the variability of findings across the literature. To address these gaps and provide a more comprehensive understanding of the impact of ADV, this study reviews findings from prospective cohort studies, with a focus on the type of violence experienced and the gender of the victim. A systematic search was conducted in nine electronic databases and additional relevant journals. Prospective longitudinal studies were included if dating violence victimization occurred during adolescence and chronologically preceded the outcomes. A quality assessment was conducted using the Mixed Methods Appraisal Tool. A narrative approach was used to synthesize findings. After screening 1,838 records, 14 publications met the selection criteria and were included in this review. Our findings suggest that experiencing ADV is longitudinally associated with many adverse outcomes, including higher internalizing symptoms and externalizing behaviors, poorer well being, increased substance use, and increased revictimization. However, the associations are not consistently reported across studies when considering the type of ADV experienced and the gender of the victim. This review highlights the limited number of longitudinal studies examining the outcomes of ADV victimization, the unbalanced approach in investigating different forms of violence, and the lack of diverse samples examining this subject. Implications for research, policy, and practice are outlined
diagnostics on the nature of dark energy
The two dominant components of the cosmic budget today, pressureles matter
and dark energy, may or may not be interacting with each other. Currently, both
possibilities appear compatible with observational data. We propose several
criteria based on the history of the Hubble factor that can help discern
whether they are interacting and whether dark energy is phantom or quintessence
in nature.Comment: 22 pages, 7 figures. Accepted for publication in IJMP
Artificial Pheromone for Path Selection by a Foraging Swarm of Robots
Foraging robots involved in a search and retrieval task may create paths to navigate faster in their environment. In this context, a swarm of robots that has found several resources and created different paths may benefit strongly from path selection. Path selection enhances the foraging behavior by allowing the swarm to focus on the most profitable resource with the possibility for unused robots to stop participating in the path maintenance and to switch to another task. In order to achieve path selection, we implement virtual ants that lay artificial pheromone inside a network of robots. Virtual ants are local messages transmitted by robots; they travel along chains of robots and deposit artificial pheromone on the robots that are literally forming the chain and indicating the path. The concentration of artificial pheromone on the robots allows them to decide whether they are part of a selected path. We parameterize the mechanism with a mathematical model and provide an experimental validation using a swarm of 20 real robots. We show that our mechanism favors the selection of the closest resource is able to select a new path if a selected resource becomes unavailable and selects a newly detected and better resource when possible. As robots use very simple messages and behaviors, the system would be particularly well suited for swarms of microrobots with minimal abilitie
Explicit processing of verbal and spatial features during letter-location binding modulates oscillatory activity of a fronto-parietal network.
The present study investigated the binding of verbal and spatial features in immediate memory. In a recent study, we demonstrated incidental and asymmetrical letter-location binding effects when participants attended to letter features (but not when they attended to location features) that were associated with greater oscillatory activity over prefrontal and posterior regions during the retention period. We were interested to investigate whether the patterns of brain activity associated with the incidental binding of letters and locations observed when only the verbal feature is attended differ from those reflecting the binding resulting from the controlled/explicit processing of both verbal and spatial features. To achieve this, neural activity was recorded using magnetoencephalography (MEG) while participants performed two working memory tasks. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the task instructions. One of the tasks required participants to process both letters and locations. In the other, participants were instructed to memorize only the letters, regardless of their location. Time–frequency representation of MEG data based on the wavelet transform of the signals was calculated on a single trial basis during the maintenance period of both tasks. Critically, despite equivalent behavioural binding effects in both tasks, single and dual feature encoding relied on different neuroanatomical and neural oscillatory correlates. We propose that enhanced activation of an anterior–posterior dorsal network observed in the task requiring the processing of both features reflects the necessity for allocating greater resources to intentionally process verbal and spatial features in this task
Bottom-up hierarchical self-assembly of chiral porphyrins through coordination and hydrogen bonds
A series of chiral synthetic compounds is reported that show intricate but specific hierarchical assembly because of varying positions of coordination and hydrogen bonds. The evolution of the aggregates (followed by absorption spectroscopy and temperature-dependent circular dichroism studies in solution) reveal the influence of the proportion of stereogenic centers in the side groups connected to the chromophore ring in their optical activity and the important role of pyridyl groups in the self-assembly of these chiral macrocycles. The optical activity spans two orders of magnitude depending on composition and constitution. Two of the aggregates show very high optical activity even though the isolated chromophores barely give a circular dichroism signal. Molecular modeling of the aggregates, starting from the pyridine-zinc(II) porphyrin interaction and working up, and calculation of the circular dichroism signal confirm the origin of this optical activity as the chiral supramolecular organization of the molecules. The aggregates show a broad absorption range, between approximately 390 and 475 nm for the transitions associated with the Soret region alone, that spans wavelengths far more than the isolated chromophore. The supramolecular assemblies of the metalloporphyrins in solution were deposited onto highly oriented pyrolitic graphite in order to study their hierarchy in assembly by atomic force microscopy. Zero and one-dimensional aggregates were observed, and a clear dependence on deposition temperature was shown, indicating that the hierarchical assembly took place largely in solution. Moreover, scanning electron microscopy images of porphyrins and metalloporphyrins precipitated under out-of-equilibrium conditions showed the dependence of the number and position of chiral amide groups in the formation of a fibrillar nanomaterial. The combination of coordination and hydrogen bonding in the complicated assembly of these molecules - where there is a clear hierarchy for zinc(II)-pyridyl interaction followed by hydrogen-bonding between amide groups, and then van der Waals interactions - paves the way for the preparation of molecular materials with multiple chromophore environments
A tachyonic scalar field with mutually interacting components
We investigate the tachyonic cosmological potential in two
different cases of the quasi-exponential expansion of universe and discuss
various forms of interaction between the two components---matter and the
cosmological constant--- of the tachyonic scalar field, which leads to the
viable solutions of their respective energy densities. The distinction among
the interaction forms is shown to appear in the diagnostic. Further,
the role of the high- and low-redshift observations of the Hubble parameter is
discussed to determine the proportionality constants and hence the correct form
of matter--cosmological constant interaction.Comment: 14 page
Observational constraints on the dark energy and dark matter mutual coupling
We examine different phenomenological interaction models for Dark Energy and
Dark Matter by performing statistical joint analysis with observational data
arising from the 182 Gold type Ia supernova samples, the shift parameter of the
Cosmic Microwave Background given by the three-year Wilkinson Microwave
Anisotropy Probe observations, the baryon acoustic oscillation measurement from
the Sloan Digital Sky Survey and age estimates of 35 galaxies. Including the
time-dependent observable, we add sensitivity of measurement and give
complementary results for the fitting. The compatibility among three different
data sets seem to imply that the coupling between dark energy and dark matter
is a small positive value, which satisfies the requirement to solve the
coincidence problem and the second law of thermodynamics, being compatible with
previous estimates.Comment: 9 pages, 4 figures, accepted for publication in Phys. Lett.
Sequential Electron Transport and Vibrational Excitations in an Organic Molecule Coupled to Few-Layer Graphene Electrodes
Graphene electrodes are promising candidates to improvereproducibility and stability in molecular electronics through new electrode−molecule anchoring strategies. Here we report sequentialelectron transport in few-layer graphene transistors containing individualcurcuminoid-based molecules anchored to the electrodes via π −π orbital bonding. We show the coexistence of inelastic co-tunneling excitations with single-electron transport physics due to an intermediate molecule−electrode coupling; we argue that an intermediate electron−phononcoupling is the origin of these vibrational-assisted excitations. Theseexperimental observations are complemented with density functionaltheory calculations to model electron transport and the interaction between electrons and vibrational modes of thecurcuminoid molecule. We find that the calculated vibrational modes of the molecule are in agreement with theexperimentally observed excitation
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