Biomedical subjects

S S Manna

Publications and source records attributed to S S Manna.

16 recordsLinked to original sources

PubMed2006

Weighted scale-free networks in Euclidean space using local selection rule.

A spatial scale-free network is introduced and studied, whose motivation originated in the growing Internet as well as airport networks. We argue that in these real-world networks a new node necessarily selects one of its neighboring local nodes for connection and is not controlled by preferential attachment as in the Barabási-Albert (BA) model. This observation is mimicked in our model where the nodes pop up at randomly located positions in the Euclidean space and are connected to one end of the nearest link. In spite of this crucial difference it is observed that the leading behavior of our network is like that of the BA model. Defining the link weight as an algebraic power of its Euclidean length, the weight distribution and the nonlinear dependence of the nodal strength on the degree are analytically calculated. It is claimed that a power law decay of the link weights with time ensures such nonlinear behavior. Switching off the Euclidean space from the same model yields a much simpler definition of the BA model where numerical effort grows linearly with N.

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PubMed2005

Phase transition in a directed traffic flow network.

The generic feature of traffic in a network of flowing electronic data packets is a phase transition from a stationary free-flow phase to a continuously growing congested nonstationary phase. In the most simple network of directed oriented square lattice we have been able to observe all crucial features of such flow systems having nontrivial critical behavior near the critical point of transition. The network here is in the shape of a square lattice and data packets are randomly posted with a rate rho at one side of the lattice. Each packet executes a directed diffusive motion toward the opposite boundary where it is delivered. Packets accumulated at a particular node form a queue and a maximum of m such packets randomly jump out of this node at every time step to its neighbors on a first-in-first-out basis. The phase transition occurs at rho(c) = m. The distribution of travel times through the system is found to have a log-normal behavior and the power spectrum of the load time series shows 1/f-like noise similar to the scenario of Internet traffic.

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PubMed2005

Precise toppling balance, quenched disorder, and universality for sandpiles.

A single sandpile model with quenched random toppling matrices captures the crucial features of different models of self-organized criticality. With symmetric matrices avalanche statistics falls in the multiscaling Bak-Tang-Wiesenfeld universality class. In the asymmetric case the simple scaling of the Manna model is observed. The presence or absence of a precise toppling balance between the amount of sand released by a toppling site and the total quantity the same site receives when all its neighbors topple once determines the appropriate universality class.

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PubMed2005

Sandpile model on a quenched substrate generated by kinetic self-avoiding trails.

Kinetic self-avoiding trails are introduced and used to generate a substrate of randomly quenched flow vectors. A sandpile model is studied on such a substrate with asymmetric toppling matrices where the precise balance between the net outflow of grains from a toppling site, and the total inflow of grains to the same site when all its neighbors topple once, is maintained at all sites. Within numerical accuracy this model behaves in the same way as the multiscaling Bak, Tang, and Wiesenfeld model.

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PubMed2004

Directed fixed energy sandpile model.

We numerically study the directed version of the fixed energy sandpile. On a closed square lattice, the dynamical evolution of a fixed density of sand grains is studied. The activity of the system shows a continuous phase transition around a critical density. While the deterministic version has the set of nontrivial exponents, the stochastic model is characterized by mean field like exponents.

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PubMed2004

Scale-free network on a vertical plane.

A scale-free network is grown in the Euclidean space with a global directional bias. On a vertical plane, nodes are introduced at unit rate at randomly selected points and a node is allowed to be connected only to the subset of nodes which are below it using the attachment probability, pi(i)(t) approximately k(i)(t)l(alpha). Our numerical results indicate that the directed scale-free network for alpha=0 belongs to a different universality class compared to the isotropic scale-free network. For alpha - infinity. The link length distribution is calculated analytically for all values of alpha.

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PubMed2003

Scale-free networks from a Hamiltonian dynamics.

Contrary to many recent models of growing networks, we present a model with fixed number of nodes and links, where a dynamics favoring the formation of links between nodes with degree of connectivity as different as possible is introduced. By applying a local rewiring move, the network reaches equilibrium states assuming broad degree distributions, which have a power-law form in an intermediate range of the parameters used. Interestingly, in the same range we find nontrivial hierarchical clustering.

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PubMed2003

Diffusion-limited friendship network: a model for six degrees of separation.

A dynamic model of a society is studied where each person is an uncorrelated and noninteracting random walker. A dynamical random graph represents the acquaintance network of the society whose nodes are the individuals and links are the pairs of mutual friendships. This network exhibits a different percolationlike phase transition in all dimensions. On introducing simultaneous death and birth rates in the population, we show that the friendship network shows the six degrees of separation for ever after where the precise value of the network diameter depends on the death/birth rate. A susceptible-infected-susceptible-type model of disease spreading shows that this society always remains healthy if the population density is less than certain threshold value.

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PubMed2003

Clustering properties of a generalized critical Euclidean network.

Many real-world networks exhibit a scale-free feature, have a small diameter, and a high clustering tendency. We study the properties of a growing network, which has all these features, in which an incoming node is connected to its ith predecessor of degree k(i) with a link of length l using a probability proportional to k(beta)(i)l(alpha). For alpha>-0.5, the network is scale-free at beta=1 with the degree distribution P(k) proportional to k(-gamma) and gamma=3.0 as in the Barabási-Albert model (alpha=0,beta=1). We find a phase boundary in the alpha-beta plane along which the network is scale-free. Interestingly, we find a scale-free behavior even for beta>1 for alpha<-0.5, where the existence of a different universality class is indicated from the behavior of the degree distribution and the clustering coefficients. The network has a small diameter in the entire scale-free region. The clustering coefficients emulate the behavior of most real networks for increasing negative values of alpha on the phase boundary.

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PubMed2003

Small-world properties of the Indian railway network.

Structural properties of the Indian railway network is studied in the light of recent investigations of the scaling properties of different complex networks. Stations are considered as "nodes" and an arbitrary pair of stations is said to be connected by a "link" when at least one train stops at both stations. Rigorous analysis of the existing data shows that the Indian railway network displays small-world properties. We define and estimate several other quantities associated with this network.

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PubMed2003

Quasistatic scale-free networks.

A network is formed using the N sites of a one-dimensional lattice in the shape of a ring as nodes and each node with the initial degree k(in)=2. N links are then introduced to this network, each link starts from a distinct node, the other end being connected to any other node with degree k randomly selected with an attachment probability proportional to k(alpha). Tuning the control parameter alpha, we observe a transition where the average degree of the largest node changes its variation from N0 to N at a specific transition point of alpha(c). The network is scale free, i.e., the nodal degree distribution has a power law decay for alpha> or = alpha(c).

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PubMed2003

Treatment of plastic bronchitis in acute chest syndrome of sickle cell disease with intratracheal rhDNase.

Plastic bronchitis, a condition associated with widespread mucous plugging of the tracheobronchial tree, is an increasingly recognised bronchoscopic finding in acute chest syndrome of sickle cell disease. Removal of casts by bronchoscopy is technically challenging. We describe a child with acute chest syndrome where bronchoscopic removal of extensive tracheobronchial plastic casts was facilitated by intratracheal rhDNase.

Acute Disease↗

PubMed2002

Percolation in models of thin film depositions.

We have studied the percolation behavior of deposits for different (2+1)-dimensional models of surface layer formation. The mixed model of deposition was used, where particles were deposited selectively according to the random (RD) and ballistic (BD) deposition rules. In the mixed one-component models with deposition of only conducting particles, the mean height of the percolation layer (measured in monolayers) grows continuously from 0.898 32 for the pure RD model to 2.605 for the pure BD model, but the percolation transition belongs to the same universality class, as in the two-dimensional (2D) random percolation problem. In two-component models with deposition of conducting and isolating particles, the percolation layer height approaches infinity as concentration of the isolating particles becomes higher than some critical value. The crossover transition from 2D to 3D percolation was observed with increase of the percolation layer height.

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PubMed2002

Modulated scale-free network in Euclidean space.

A random network is grown by introducing at unit rate randomly selected nodes on the Euclidean space. A node is randomly connected to its ith predecessor of degree k(i) with a directed link of length l using a probability proportional to k(i)l(alpha). Our numerical study indicates that the network is scale free for all values of alpha>alpha(c) and the degree distribution decays stretched exponentially for the other values of alpha. The link length distribution follows a power law: D(l) approximately l(delta), where delta is calculated exactly for the whole range of values of alpha.

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PubMed2001

Infantile null cell acute lymphoblastic leukaemia (ALL) presenting with cerebellar tonsillar herniation.

We report a child with ALL who presented with acute neurological collapse and coning of the cerebellar tonsils as a result of massive brain infiltration by leukaemic cells. Such severe involvement of cerebral parenchyma by leukaemic cells is rare and cerebellar tonsillar herniation has not been reported. CNS parenchymal involvement with leukaemia is demonstrated using MRI and, for the first time, cranial US.

Cerebellar Diseases↗

PubMed1999

Critical states in a dissipative sandpile model.

A directed dissipative sandpile model is studied in two dimensions. Numerical results indicate that the long time steady states of this model are critical when grains are dropped only at the top, or everywhere. The critical behavior is mean-field-like. We discuss the role of infinite avalanches of dissipative models in periodic systems in determining the critical behavior of same models in open systems.

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