Restricted Connectivity Research Articles

Convergence time analysis of quantized gossip consensus on digraphs

We have recently proposed quantized gossip algorithms which solve the consensus and averaging problems on directed graphs with the least restrictive connectivity requirements. In this paper we study the convergence time of these algorithms. To this end, we investigate the shrinking time of the smallest interval that contains all states for the consensus algorithm, and the decay time of a suitable Lyapunov function for the averaging algorithm. The investigation leads us to characterize the convergence time by the hitting time in certain special Markov chains. We simplify the structures of state transition by considering the special case of complete graphs, where every edge can be activated with an equal probability, and derive polynomial upper bounds on convergence time.

Subtle genetic structure reveals restricted connectivity among populations of a coral reef fish inhabiting remote atolls

We utilized a spatial and temporal analyses of genetic structure, supplemented with ecological and oceanographic analysis, to assess patterns of population connectivity in a coral reef fish Chromis margaritifer among the unique and remote atolls in the eastern Indian Ocean. A subtle, but significant genetic discontinuity at 10 microsatellite DNA loci was detected between atoll systems corresponding with a low (≤ 1%) probability of advection across the hundreds of kilometers of open ocean that separates them. Thus, although genetic connections between systems are likely maintained by occasional long-distance dispersal of C. margaritifer larvae, ecological population connectivity at this spatial scale appears to be restricted. Further, within one of these atoll systems, significant spatial differentiation among samples was accompanied by a lack of temporal pairwise differentiation between recruit and adult samples, indicating that restrictions to connectivity also occur at a local scale (tens of kilometers). In contrast, a signal of panmixia was detected at the other atoll system studied. Lastly, greater relatedness and reduced genetic diversity within recruit samples was associated with relatively large differences among them, indicating the presence of sweepstakes reproduction whereby a small proportion of adults contributes to recruitment in the next generation. These results are congruent with earlier work on hard corals, suggesting that local production of larvae drives population replenishment in these atoll systems for a range of coral reef species.

Phase precession through acceleration of local theta rhythm: a biophysical model for the interaction between place cells and local inhibitory neurons

Phase precession is one of the most well known examples within the temporal coding hypothesis. Here we present a biophysical spiking model for phase precession in hippocampal CA1 which focuses on the interaction between place cells and local inhibitory interneurons. The model's functional block is composed of a place cell (PC) connected with a local inhibitory cell (IC) which is modulated by the population theta rhythm. Both cells receive excitatory inputs from the entorhinal cortex (EC). These inputs are both theta modulated and space modulated. The dynamics of the two neuron types are described by integrate-and-fire models with conductance synapses, and the EC inputs are described using non-homogeneous Poisson processes. Phase precession in our model is caused by increased drive to specific PC/IC pairs when the animal is in their place field. The excitation increases the IC's firing rate, and this modulates the PC's firing rate such that both cells precess relative to theta. Our model implies that phase coding in place cells may not be independent from rate coding. The absence of restrictive connectivity constraints in this model predicts the generation of phase precession in any network with similar architecture and subject to a clocking rhythm, independently of the involvement in spatial tasks.

ANATOMY OF EINSTEIN'S THEORY: ABELIAN DECOMPOSITION OF GENERAL RELATIVITY

Treating Einstein's theory as a gauge theory of Lorentz group, we decompose the gravitational connection (the gauge potential of Lorentz group) Γμ into the restricted connection of the maximal Abelian subgroup of Lorentz group and the valence connection which transforms covariantly under Lorentz gauge transformation. With this decomposition we show that the Einstein's theory can be decomposed into the restricted part made of the restricted connection which has the full Lorentz gauge invariance and the valence part made of the valence connection which plays the role of gravitational source of the restricted gravity. We show that there are two different Abelian decomposition of Einstein's theory, the light-like (or null) decomposition and the non light-like (or non-null) decomposition. In this decomposition the role of the metric gμν is replaced by a four-index metric tensor gμν which transforms covariantly under the Lorentz group, and the metric-compatibility condition ∇αgμν = 0 of the connection is replaced by the gauge and generally covariant condition [Formula: see text]. The decomposition shows the existence of a restricted theory of gravitation which has the full general invariance but is much simpler and has less physical degrees of freedom than Einstein's theory. Moreover, it tells that the restricted gravity can be written as an Abelian gauge theory, which implies that the graviton can be described by a massless spin-one field.

Restricted dispersal of the reef fish Myripristis berndti at the scale of the SW Indian Ocean

The reef fish Myripristis berndti (Jordan & Everman 1903) is a pantropical species. A genetic analysis was conducted on 353 individuals from 10 localities distributed across the SW Indian Ocean (SWIO) in order to determine patterns of connectivity in the SWIO. Both the mtDNA sequences (711-bp cytochrome b sequences) and the microsatellites (8 newly developed loci) reveal spatial patterns of differentiation within the SWIO. There is, however, a discrepancy between the structure observed with each kind of marker. MtDNA revealed that 3 peripheral populations (NW Kenya, SE Reunion, and SW Europa) were isolated from the 7 more central populations, which form a more densely connected population network, while microsatellite data indicated a more restricted connectivity with significant differentiation between most pairs of localities. Higher genetic differences between Reunion and Europa were found, which might be explained by geography and isolation by distance pattern. In contrast, the genetic signature of Kenya-the most divergent locality identified by mtDNA basis but not with microsatellite-was probably the consequence of a particular colonisation history. These results indicate a much more restricted connectivity than previously thought for this species.

Respuesta barotrópica de los golfos norpatagónicos argentinos forzados por mareas y vientos

This work presents the results of a high resolution three dimensional non-linear barotropic hydrodynamic model used to examine the response of three north Patagonian gulfs in Argentina (San Matias, SMG; Nuevo, NG; and San Jose, SJG) forced by tides and idealized patterns of surface winds. The structure of the circulation induced by the dominant winds (Westerly) in all three gulfs consists of two independent gyres: one anticyclonic gyre in the west with an intense southward coastal flow and weaker return flow in the middle of the gulfs and one cyclonic gyre in the east that, in the SMG's case, connects with the shelf. The other two gulfs (NG and SJG) have much more restricted connections with the exterior. The inclusion of tidal dissipation effects reduces the intensity of the gyres, but the general spatial pattern of the circulation remains. Increasing the wind magnitude mainly intensifies the anticyclonic gyre and the cross-shelf transport through the SMG mouth and deepens the surface Ekman layer. If the gulfs are forced with meridional winds, the circulation splits into two gyres whose sense of circulation depends on the wind direction: a northern cyclonic (anticyclonic) gyre and a southern anticyclonic (cyclonic) gyre for Southerly (Northerly) winds. When the gulfs are forced simultaneously by tides and winds, the residual tidal currents dominates the general circulation and contributes to a greater dynamical isolation of the gulfs from the exterior shelf.

Group-size effects on the evolution of cooperation in the spatial public goods game

We study the evolution of cooperation in public goods games on the square lattice, focusing on the effects that are brought about by different sizes of groups where individuals collect their payoffs and search for potential strategy donors. We find that increasing the group size does not necessarily lead to mean-field behavior, as is traditionally observed for games governed by pairwise interactions, but rather that public cooperation may be additionally promoted by means of enhanced spatial reciprocity that sets in for very large groups. Our results highlight that the promotion of cooperation due to spatial interactions is not rooted solely in having restricted connections among players, but also in individuals having the opportunity to collect payoffs separately from their direct opponents. Moreover, in large groups the presence of a small number of defectors is bearable, which makes the mixed-phase region expand with increasing group size. Having a chance of exploiting distant players, however, offers defectors a different way to break the phalanx of cooperators and even to resurrect from small numbers to eventually completely invade the population.

An efficient and secure mobile payment protocol for restricted connectivity scenarios in vehicular ad hoc network

Value-added applications in vehicular ad hoc network (VANET) come with the emergence of electronic trading. The restricted connectivity scenario in VANET, where the vehicle cannot communicate directly with the bank for authentication due to the lack of internet access, opens up new security challenges. Hence a secure payment protocol, which meets the additional requirements associated with VANET, is a must. In this paper, we propose an efficient and secure payment protocol that aims at the restricted connectivity scenario in VANET. The protocol applies self-certified key agreement to establish symmetric keys, which can be integrated with the payment phase. Thus both the computational cost and communication cost can be reduced. Moreover, the protocol can achieve fair exchange, user anonymity and payment security.

Efficient unicast in bijective connection networks with the restricted faulty node set

The connectivity is an important criteria to measure the fault-tolerant performance of a graph. However, the connectivity based on the condition of the set of arbitrary faulty nodes is generally lower. In this paper, in order to heighten this measure, we introduce the restricted connectivity into bijective connection networks. First, we prove that the probability that all the neighbors of an arbitrary node becomes faulty in any n-dimensional bijective connection network X n is very low when n becomes sufficient large. Then, we give a constructive proof that under the condition that each node of an n-dimensional bijective connection network X n has at least one fault-free neighbor, its restricted connectivity is 2 n − 2, about half of the connectivity of X n . Finally, by our constructive proof, we give an O( n) algorithm to get a reliable path of length at most n + 3⌈log 2∣ F∣⌉ + 1 between any two fault-free nodes in an n-dimensional bijective connection network. In particular, since the family of BC networks contains hypercubes, crossed cubes, Möbius cubes, etc., our algorithm is appropriate for these cubes.

Neural Network based System for Real-time Organ Recognition during Surgical Operation

AbstractIn this paper we propose (based on testing results) a Neural Network structures that can be used for recognition of presence and absence of internal organ on images received from endoscope. Based on selected NN structure we design two NN-based systems for distinguishing and real-time recognition of internal organs on sequence of endoscopic images during abdominal surgery. First NN-based system proposed in this paper is designed for recognition of several different internal organs on color endoscopic images. Second NN-based system is designed for real-time recognition of presence of a particular internal organ on a sequence of color images (video stream) from endoscope. Restricted connectivity structure of the network makes possible decomposition of the image during the analysis and significantly reduces the number of parameters thus making training easier, faster and more accurate. The algorithms proposed in the paper are implemented in software application and their effectiveness is demonstrated on simulations.

Edge neighbor connectivity of Cartesian product graph [formula omitted

Let G be a k-regular graph with girth at least 4, connectivity k, and restricted connectivity 2k-2. We prove in this paper that the edge neighbor connectivity of G×K2 is k. As a consequence, the edge neighbor connectivity of n-dimensional hypercube is n-1. Furthermore, we prove that the edge neighbor connectivity of Kn×K2 is ⌈n/2⌉.

One-to-one communication in twisted cubes under restricted connectivity

The dimensions of twisted cubes are only limited to odd integers. In this paper, we first extend the dimensions of twisted cubes to all positive integers. Then, we introduce the concept of the restricted faulty set into twisted cubes. We further prove that under the condition that each node of the n-dimensional twisted cube TQ n has at least one fault-free neighbor, its restricted connectivity is 2n ? 2, which is almost twice as that of TQ n under the condition of arbitrary faulty nodes, the same as that of the n-dimensional hypercube. Moreover, we provide an O(NlogN) fault-free unicast algorithm and simulations result of the expected length of the fault-free path obtained by our algorithm, where N denotes the node number of TQ n . Finally, we propose a polynomial algorithm to check whether the faulty node set satisfies the condition that each node of the n-dimensional twisted cube TQ n has at least one fault-free neighbor.

The role of life-history and location of barriers to migration in the spatial distribution and conservation of fish assemblages in a coastal river system

Water resource development in coastal river catchments contributes to poor fish assemblage health due to the effects of barriers to migration and altered flow regimes. Impacts of migration barriers on fish assemblages depend primarily on the location of each barrier within the river network and migration needs of regional fish fauna. This study examined how temporal and spatial patterns in the distribution and composition of fish assemblages was associated with varying estuarine connectivity and migration barriers in higher altitude reaches in the eastern Hunter River catchment, temperate Australia. Species richness and abundances of diadromous species were expected to be greater in a tributary catchment with unrestricted connectivity to the Hunter River estuary when compared to a neighbouring tributary catchment with restricted connectivity. Six diadromous species were sampled only, or in greater abundances, in the unrestricted tributary when compared to the restricted tributary. As a consequence, assemblage composition in the restricted tributary was dominated by non-diadromous species. Greater abundances of the amphidromous Cox’s gudgeon ( Gobiomorphus coxii) were sampled in the unrestricted tributary following their estuarine-freshwater upstream juvenile migration period when compared to the restricted tributary. Differences in the accumulations of migratory species immediately downstream of upland barriers between the two levels of estuary connectivity indicate that migration barriers in lowland reaches have significant effects throughout the entire catchment. Results of this study indicate that the location of each barrier to migration within river networks has varying consequences for catchment-scale connectivity loss and assessing the impacts of multiple barriers. Determining the effects and most appropriate management of migration barriers requires that all obstructions within a river network are recognised, as multiple barriers can have cumulative and interacting consequences for freshwater fish fauna, especially diadromous species.

Paleoenvironmental conditions preceding the Messinian Salinity Crisis in the Central Mediterranean: Integrated data from the Upper Miocene Trave section (Italy)

Integrated data of calcareous plankton and benthic foraminifers from the pre-evaporitic interval of Trave section (Central Italy) allowed the reconstruction of surface and bottom-water conditions in the Central Mediterranean during the interval from 7.61 to 6.33 Ma, preceding the Messinian Salinity Crisis. Our data point out a three-step paleoenvironmental evolution. During the first stage (7.61–7.02 Ma) benthic foraminiferal assemblages depict stable, well-oxygenated and ventilated bottom-water conditions, while the surface water records variable temperature and high nutrient conditions, probably associated with strong seasonality. The second stage (7.02–6.70 Ma) points to unfavourable bottom-water condition, triggered by deep-sea stagnation. This is witnessed by a significant decrease in oxygen concentration and biotic diversity, and by the presence of stress-tolerant taxa. A general warming of the surface water and a strongly stratified water column, characterized by an expanded mixed layer, are also recorded. From 6.70 Ma onwards (third stage), a prominent change to more restricted, low-oxygenated, hypersaline conditions at the sea floor is testified by the total disappearance of deep-dwelling planktonic foraminifers and the increasing abundance of stress-tolerant species. Calcareous plankton reflects high instability of the surface water in terms of nutrients, temperature and salinity. During this stage the environmental deterioration reaches intermediate depths in the water column. The initial change toward a step-wise isolation of the Central Mediterranean bottom-waters is probably related to a general warming, responsible for a first slowing-down of the vertical circulation, favouring stratification of surface and intermediate waters and stagnation of bottom-waters. This warming is related to the restricted connection between the Mediterranean Sea and the Atlantic Ocean, which occurred since 7.146 Ma. In the Trave section, the isolation of bottom-waters most likely occurred at the same time as in other Mediterranean sections. However, due to the presence of a hiatus it cannot be excluded that it occurred with a delay of ~ 100 kyr, probably related to the shallower paleodepth of the basin.

Access to Digital Libraries from low speed Disconnected Environments

Digital libraries provide an important tool for expanding and improving access to knowledge, so their services must be affordable even for people in remote areas with restricted connectivity. This paper describes an architecture for accessing services and contents of digital libraries in the program EHAS (Enlace Hispano Americano de Salud) (Hispano American Health Link), which for the case of deployments in Alto Amazonas (Peru) and Cauca (Colombia), uses connectivity solutions based on VHF and HF radios, which provide intermittent (20 min max.) and low bandwidth (9600 bps max.) connections. The HTTP protocol is used to consult the contents of the library, but for downloading files the email is used through a segmentation and reassemble mechanism. In field tests conducted at 9600 bps, response times were the order of 35 s for consultation, 40 minutes for downloading a file of 100 KB and 4 hours for downloading a 1MB file.

Spatial and Temporal Patterns in Fish Assemblages Following an Artificially Extended Floodplain Inundation Event, Northern Murray-Darling Basin, Australia

Water extraction from dryland rivers is often associated with declines in the health of river and floodplain ecosystems due to reduced flooding frequency and extent of floodplain inundation. Following moderate flooding in early 2008 in the Narran River, Murray-Darling Basin, Australia, 10,423 ML of water was purchased from agricultural water users and delivered to the river to prolong inundation of its terminal lake system to improve the recruitment success of colonial waterbirds that had started breeding in response to the initial flooding. This study examined the spatial and temporal patterns of fish assemblages in river and floodplain habitats over eight months following flooding to assess the possible ecological benefits of flood extension. Although the abundances of most fish species were greater in river channel habitats, the fish assemblage used floodplain habitats when inundated. Young-of-the-year (4-12 months age) golden perch (Macquaria ambigua) and bony bream (Nematalosa erebi) were consistently sampled in floodplain sites when inundated, suggesting that the floodplain provides rearing habitat for these species. Significant differences in the abundances of fish populations between reaches upstream and downstream of a weir in the main river channel indicates that the effectiveness of the environmental water release was limited by restricted connectivity within the broader catchment. Although the seasonal timing of flood extension may have coincided with sub-optimal primary production, the use of the environmental water purchase is likely to have promoted recruitment of fish populations by providing greater access to floodplain nursery habitats, thereby improving the ability to persist during years of little or no flow.

The existence and upper bound for two types of restricted connectivity

In this paper, we study two types of restricted connectivity: κ k ( G ) is the cardinality of a minimum vertex cut S such that every component of G − S has at least k vertices; κ k ′ ( G ) is the cardinality of a minimum vertex cut S such that there are at least two components in G − S of order at least k . In this paper, we give some sufficient conditions for the existence and upper bound of κ k ( G ) and/or κ k ′ ( G ) , and study some properties of these two parameters.

Super p-restricted edge connectivity of line graphs

Super restricted connectivity and super restricted edge connectivity are more refined network reliability indices than connectivity and edge connectivity. In this paper, we first introduce the concepts of super restricted connectivity and super restricted edge connectivity and then give a property of graphs with equal p-restricted edge connectivity and 1–p-restricted connectivity. Applying this property, we show a sufficient condition for a line graph to be super p-restricted edge-connected and a relationship between super 1–p-restricted connected graphs and super p-restricted edge-connected graphs.

A distributed minimum restrictive connectivity maintenance algorithm

The dynamic character of autonomous mobile multi-agent networks makes the control of the individual agent's movement a challenging task when certain properties or conditions concerning the global network state must be fulfilled. Many distributed algorithms require that the communication topology of the regarded multi-agent network is connected at all times to execute properly. Since particularly motion control algorithms directly influence the connectivity itself, the fundamental question how connectivity of the network can be maintained is raised. As an additional difficulty, individual agents often have only access to local information, whereas connectivity is a property of the global network. In this work, a distributed hybrid connectivity maintenance algorithm is proposed, which guarantees global connectivity of the network based on local information. The algorithm is divided in two components: First, a discrete topology control algorithm determines periodically the structure of a minimum cost spanning tree on the network communication graph. Second, a continuous connectivity motion control algorithm constrains the location of each individual agent such that the determined spanning tree is preserved. This combined algorithm effectively maintains connectivity under the presence of any finite-valued primary motion control law.

Restricted connections among distinguished players support cooperation

We study the evolution of cooperation within the spatial prisoner's dilemma game on a square lattice where a fraction of players mu can spread their strategy more easily than the rest due to a predetermined larger teaching capability. In addition, players characterized by the larger teaching capability are allowed to temporarily link with distant opponents of the same kind with probability p , thus introducing shortcut connections among the distinguished players. We show that these additional temporary connections are able to sustain cooperation throughout the whole range of the temptation to defect. Remarkably, we observe that, as the temptation to defect increases the optimal mu decreases, and moreover only minute values of p warrant the best promotion of cooperation. Our study thus indicates that influential individuals must be few and sparsely connected in order for cooperation to thrive in a defection-prone environment.