Abstract

We consider the problem of probabilistic reliable communication (PRC) over synchronous networks modeled as directed graphs in the presence of a Byzantine adversary when players’ knowledge of the network topology is not complete. We show that possibility of PRC is extremely sensitive to the changes in players’ knowledge of the topology. This is in complete contrast with earlier known results on the possibility of perfectly reliable communication over undirected graphs where the case of each player knowing only its neighbours gives the same result as the case where players have complete knowledge of the network. Specifically, in either case,(2t+ 1)-vertex connectivity is necessary and sufficient, where t is the number of nodes that can be corrupted by the adversary [DDWY93, SKR+05]. We introduce a novel model for quantifying players’ knowledge of network topology, denoted by T K. Given a directed graph G, influenced by a Byzantine adversary that can corrupt up to any t players, we give a necessary and sufficient condition for possibility of PRC over G for any arbitrary topology knowledge T K. It follows from our main characterization theorem that knowledge of up to d=⌊ n− 2t

Abstract

Computational approaches are being successfully utilized for the design of small molecules that could be potential substrates for various biological targets both in academia and pharmaceutical industry. Over the past two decades or so, various computational techniques have been developed and improvements on the existing methodologies were proposed to accomplish high accuracy/ predictability of molecular properties. Consideration of the flexible nature of proteins in structure based drug design studies has been a bottleneck mainly due to the huge demand of computational and actual time. Hence most of the docking studies consider the biological macromolecules to be rigid and allow only the conformational changes of the small molecules. Similarly, the ligand based drug design approaches tend to focus more on the global minima of the small molecules. This could lead to incorrect model and hence false predictions since this approximation may not be true in cases where the global minima essentially is not the bioactive conformer – the conformer that binds to the target. Recently, advanced methods have been proposed to consider the flexible nature of the molecules. Molecular dynamics (MD) simulations have been shown to be a straightforward means to include the flexibility of both ligands and biomolecular targets. MD simulations are invaluable computational methods that are extensively used for deriving information of the structure, dynamics and energetic properties of various biomolecules including proteins, nucleic acids and lipids. The need for consideration of dynamic nature of the biomolecular targets will be demonstrated and the advantages of MD simulations to overcome this limitation will be discussed. Basic principles of MD simulations will be discussed and an introduction to biomolecular force fields will be given. Illustrated examples of the applications of MD simulations to ligand based and structure based drug design approaches will be presented.

Abstract

A Special Economic Zone (SEZ) is a geographical region that has economic laws more liberal than a country's typical economic laws. In the recent years, India has witnessed a confrontation between farmers and the state, the reason being use of highly productive land for setting up SEZs with some of the cases occupying a centre stage in the World fora (Nandigram violence). In this paper, we propose an integrated solution for identifying nonagricultural lands for setting up SEZs using MODIS NDVI product and remote sensing techniques. The study also identifies multi- cropping practices and reinforces the potential of time-series MODIS data for mapping and land cover classification at regional scales.

Abstract

The present study outlines an approach to classify forest density and to estimate canopy closure of the forest of the Andaman and Nicobar archipelago. The vector layers generated for the study area using satellite data was validated with the field knowledge of the surveyed ground control points. The methodology adopted in this present analysis is three-tiered. First, the density stratification into five zones using visual

Abstract

In this paper, we study the inherent tradeoff between the network connectivity, phase complexity and communication complexity of perfectly reliable message transmission (PRMT) problem in undirected synchronous network, tolerating a mixed adversary A^ b, t,) i who has unbounded computing power and can corrupt£(, and tf nodes in the network in Byzantine and fail-stop fashion respectively.

Abstract

In the problem of USMT [1, 2] 1, a sender S and a receiver R. are connected by n= 2t+ 1 bi-directional synchronous channels (also called as wires) such that any t out of the n channels are corrupted in Byzantine fashion by an adversary jA. t, having unbounded computing power. S intends to communicate a message m to R (where m£ F and I> 1 with F being a finite field) by executing a protocol such that after interacting in terms of phases, 2 R outputs m with probability at least (1—2~") and At gets no information about m. In [2], it shown that in any single phase USMT protocol with n= 2t+ 1,Xi>'J'+ 1, where 5 denotes the message space of S, X, denotes the set of possible data sent through the ith wire and 0< 6<^ is the error probability. 4 In [2], a single phase inefficient USMT protocol with communication complexity approximately matching the above bound has been proposed. We present a single phase polynomial time USMT protocol whose communication complexity is

Abstract

Protocols for Generalized Oblivious Transfer(GOT) were introduced by Ishai and Kushilevitz [10]. They built it by reducing GOT protocols to standard 1-out-of-2 oblivious transfer protocols based on private protocols. In our protocols, we provide alternative reduction by using secret sharing schemes instead of private protocols. We therefore show that there exist a natural correspondence between GOT and general secret sharing schemes and thus the techniques and tools developed for the latter can be applied equally well to the former.

Abstract

(URMT) problem, two non-faulty players, the sender S and the receiver R are part of a synchronous network modeled as a directed graph. S has a message that he wishes to send to R; the challenge is to design a protocol such that after exchanging messages as per the protocol, the receiver R should correctly obtain S’s message with arbitrarily small error probability δ, in spite of the influence of a Byzantine adversary that may actively corrupt up to t nodes in the network (we denote such a URMT protocol as (t,(1− δ))-reliable). While it is known that (2t+ 1) vertex disjoint directed paths from S to R are necessary and sufficient for (t, 1)-reliable URMT (that is with zero error probability), we prove that a strictly weaker condition, which we define and denote as (2t, t)-special-connectivity, together with just (t+ 1) vertex disjoint directed paths from S to R, is necessary and sufficient for (t,(1− δ))-reliable URMT with arbitrarily small (but non-zero) error probability, δ. Thus, we demonstrate the power of randomization in the context of reliable message transmission. In fact, for any positive integer k> 0, we show that there always exists a digraph Gk such that (k, 1)-reliable URMT is impossible over Gk whereas there exists a (2k,(1− δ))-reliable URMT protocol, δ> 0 in Gk. In a digraph G on which (t,(1− δ))-reliable URMT is possible, an edge is called critical if the deletion of that edge renders (t,(1− δ))-reliable URMT impossible. We give an example of a digraph G on n vertices such that G has Ω (n2) critical edges. This is quite baffling since no such graph exists for the case of perfect reliable message transmission (or equivalently (t, 1)-reliable URMT) or when the underlying graph is undirected. Such is the anomalous behavior of URMT protocols (when “randomness meet directedness”) that it makes it extremely hard to design efficient protocols over arbitrary digraphs. However, if URMT is possible between every pair of vertices in the network, then we present efficient protocols for the same.

Abstract

For content level access, very often database needs the query as a sample image. However, the image may contain private information and hence the user does not wish to reveal the image to the database. Private content based image retrieval (PCBIR) deals with retrieving similar images from an image database without revealing the content of the query image - not even to the database server. We propose algorithms for PCBIR, when the database is indexed using hierarchical index structure or hash based indexing scheme. Experiments are conducted on real datasets with popular features and state of the art data structures. It is observed that specialty and subjectivity of image retrieval (unlike SQL queries to a relational database) enables in computationally efficient yet private solutions.

Abstract

In this paper we present an automatic Keyphrase extraction technique for English documents of scientific domain. The devised algorithm uses n-gram filtration technique, which filters sophisticated n-grams {1dnd4} along with their weight from the words of input document. To develop n-gram filtration technique, we have used (1) LZ78 data compression based technique, (2) a simple refinement step, (3) A simple Pattern Filtration algorithm and, (4) a term weighting scheme. In term weighting scheme, we have introduced the importance of position of sentence (where given phrase occurs first) in document and position of phrase in sentence for documents of scientific domain (which is literally more organized than other domains). The entire system is based upon statistical observations, simple grammatical facts, heuristics, and lexical information of English language. We remark that the devised system does not require a learning phase. Our experimental results with publically available text dataset, shows that the devised system is comparable with other known algorithms.