Joy Ghosh - Academia.edu (original) (raw)

Papers by Joy Ghosh

Investigative Ophthalmology & Visual Science, 2011

Wireless Communications and Networking, IEEE Conference, 2004

A major challenge faced in mobile ad hoc networks (MANET) is locating the devices for communicati... more A major challenge faced in mobile ad hoc networks (MANET) is locating the devices for communication, especially with high node mobility and sparse node density. Present solutions provided by the ad hoc routing protocols range from flooding the entire network with route requests, to deploying a separate location management scheme to maintain a device location database. In this work, we

Our problem formulation is as follows. Given a probabilistic graph G and routing algorithm A, we ... more Our problem formulation is as follows. Given a probabilistic graph G and routing algorithm A, we wish to determine a delivery subgraph G[A] of G with at most k edges, such that the probability Conn2(G[A]) that there is a path from source s to destination t in a graph H chosen randomly from the probability space defined by G[A] is maximized. To the best of our knowledge, this problem and its complexity has not been addressed in the literature. Also, there is the corresponding distributed version of the problem where the delivery subgraph G[A] is to be constructed distributively, yielding a routing protocol. Our proposed solution to this routing problem is multi-fold: First, we prove the hardness of our optimization problem of finding a delivery subgraph that maximizes the delivery probability and discuss the hardness of computing the objective function Conn2(G[A]) (which is not the hardness of Conn2(G[A]) itself); Second, we present an algorithm to approximate Conn2(G[A]) and compare it with an optimal algorithm; Third, we model mobility using a Semi-Markov Chain to estimate the pairwise user contact probabilities; and Fourth, we propose an edgeconstrained routing protocol (EC-SOLAR-KSP) for intermittently connected networks based on the insights obtained from the first step and the contact probabilities computed in the third step. We then highlight the protocol's novelty and effectiveness by comparing it with a probabilistic routing protocol, and an epidemic routing protocol proposed in literature for intermittently connected networks.

Proceedings of the 2nd international workshop on Multi-hop ad hoc networks: from theory to reality, 2006

In this paper, we analyze a year long wireless network users' mobility trace data collected on ET... more In this paper, we analyze a year long wireless network users' mobility trace data collected on ETH Zurich campus. Unlike earlier work in [4, 19], we profile the movement pattern of wireless users and predict their locations. More specifically, we show that each network user regularly visits a list of places such as a building (also referred to as "hubs") with some probability. The daily list of hubs, along with their corresponding visit probabilities, are referred to as a mobility profile. We also show that over a period of time (e.g., a week), a user may repeatedly follow a mixture of mobility profiles with certain probabilities associated with each of the profiles. Our analysis of the mobility trace data not only validate the existence of our so-called sociological orbits [8], but also demonstrate the advantages of exploiting it in performing hub-level location predictions. In particular, we show that such profile based location predictions are more precise than common statistical approaches based on observed hub visitation frequencies alone.

2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733)

With the availability of location based services, applications that use locations for optimal per... more With the availability of location based services, applications that use locations for optimal performance will require efficient location management algorithms, where user locations are kept track with minimal system overhead. Geography based routing in mobile ad hoc networks is one such application that uses location information of nodes in a network to route data packets. Previous work in this area has shown that the selection of location management protocol is critical to the performance of such routing algorithms. Many location management schemes have been proposed in literature, and in an effort to quantitatively compare the performance of some of these schemes, we carry out extensive simulations to study SLURP, SLALoM and HGRID, three grid based protocols described in literature. Our study is two pronged-to compare the performance of location management with network mobility as well as traffic load, and to evaluate the effect these protocols have on the performance of geographic routing in mobile ad hoc networks. Our results show that the Hierarchical Grid Location Management protocol (HGRID) achieves steady performance for data throughput and delay, and minimally affects the performance of geographic routing.

IEEE Globecom 2006, 2006

Geometric routing using source-destination locations has been widely suggested as a scalable alte... more Geometric routing using source-destination locations has been widely suggested as a scalable alternative to conventional routing approaches in mobile ad hoc networks. Recently, there has been considerable attention on face routing in planar graphs constructed from overlay graphs in wireless networks. Given a plane tiled into an infinite mesh of polygons, an overlay graph is defined as one in which a graph edge is defined between two adjacent polygons if a radio link exists between any two nodes located in these polygons. We consider the problem of constructing a connected planar graph from the overlay graph, and geometric routing in such graphs. We prove a specific property of such graphs known as the redundancy property and propose a distributed routing algorithm called Grid Traversal Algorithm (GTA) based on the redundancy property of overlay graphs. The algorithm is both localized and energy efficient, but may not guarantee connectivity in pathological cases. Simulations show that such disconnections are rare in practise and that GTA performs very well in terms of percentage of data delivered, data delay and overhead compared to GPSR, a geometric routing protocol that routes on a planar graph extracted from the unit disk graph.

The Journal of Neuroscience, 2009

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause autosomal-dominant familial Parkinson&#39... more Mutations in leucine-rich repeat kinase 2 (LRRK2) cause autosomal-dominant familial Parkinson's disease. We generated lines ofCaenorhabditis elegansexpressing neuronally directed human LRRK2. Expressing human LRRK2 increased nematode survival in response to rotenone or paraquat, which are agents that cause mitochondrial dysfunction. Protection by G2019S, R1441C, or kinase-dead LRRK2 was less than protection by wild-type LRRK2. Knockdown of lrk-1, the endogenous ortholog of LRRK2 inC. elegans, reduced survival associated with mitochondrial dysfunction.C. elegansexpressing LRRK2 showed rapid loss of dopaminergic markers (DAT::GFP fluorescence and dopamine levels) beginning in early adulthood. Loss of dopaminergic markers was greater for the G2019S LRRK2 line than for the wild-type line. Rotenone treatment induced a larger loss of dopamine markers inC. elegansexpressing G2019S LRRK2 than inC. elegansexpressing wild-type LRRK2; however, loss of dopaminergic markers in the G2019S LRR...

Cell Stress & Chaperones, 2005

Cell Stress & Chaperones, 2006

Knowledge of the interactive domains on the surface of small heat shock proteins (sHSPs) is neces... more Knowledge of the interactive domains on the surface of small heat shock proteins (sHSPs) is necessary for understanding the assembly of complexes and the activity as molecular chaperones. The primary sequences of 26 sHSP molecular chaperones were aligned and compared. In the interactive ␤3 sequence, 73 DRFSVNLDVKHFS 85 of human ␣B crystallin, Ser-76, Asn-78, Lys-82, and His-83 were identified as nonconserved residues on the exposed surface of the ␣ crystallin core domain. Site-directed mutagenesis produced the mutant ␣B crystallins: S76E, N78G, K82Q, and H83F. Domain swapping with homologous ␤3 sequences, 32 EKFEVGLDVQFFT 44 from Caenorhabditis elegans sHSP12.2 or 69 DKFVIFLDVKHFS 81 from ␣A crystallin, resulted in the mutant ␣B crystallins, CE1 and ␣A1, respectively. Decreased chaperone activity was observed with the point mutants N78G, K82Q, and H83F and with the mutant, CE1, in aggregation assays using ␤ L crystallin, alcohol dehydrogenase (ADH), or citrate synthase (CS). The S76E mutant had minimal effect on chaperone activity, and domain swapping with ␣A crystallin had no effect on chaperone activity. The mutations that resulted in altered chaperone activity, produced minimal modification to the secondary, tertiary, and quaternary structure of human ␣B crystallin as determined by ultraviolet circular dichroism spectroscopy, chymotrypsin proteolysis, and size exclusion chromatography. Chaperone activity was influenced by the amount of unfolding of the target proteins and independent of complex size. The results characterized the importance of the exposed side chains of Glu-78, Lys-82, and His-83 in the interactive ␤3 sequence of the ␣ crystallin core domain in ␣B crystallin for chaperone function.

Analytical Biochemistry, 2006

The molecular chaperone activity of B crystallin, an important stress protein in humans, is regul... more The molecular chaperone activity of B crystallin, an important stress protein in humans, is regulated by physiological factors, including temperature, pH, Ca 2+ , and ATP. In this study, the role of these factors in regulating the subunit dynamics of human B crystallin was investigated using surface plasmon resonance (SPR). SPR experiments indicate that at temperatures above 37°C, where B crystallin has been reported to have higher chaperone activity, the subunit dynamics of B crystallin were increased with faster association and dissociation rates. SPR experiments also indicate that interactions between B crystallin subunits were enhanced with much faster association and slower dissociation rates at pH values below 7.0, where B crystallin has been reported to have lower chaperone activity. The results suggest that the dynamic and rapid subunit exchange rate may regulate the chaperone activity of B crystallin. The eVect of Ca 2+ and ATP on the subunit dynamics of B crystallin was minimal, suggesting that Ca 2+ and ATP modulate the chaperone activity of B crystallin without altering the subunit dynamics. Based on the SPR results and previously reported biochemical data for the chaperone activity of B crystallin under diVerent conditions of temperature and pH, a model for the relationship between the subunit dynamics and chaperone activity of B crystallin is established. The model is consistent with previous biochemical data for the chaperone activity and subunit dynamics of small heat shock proteins (sHSPs) and establishes a working hypothesis for the relationship between complex assembly and chaperone activity for sHSPs.

Routing in Intermittently Connected Networks (ICN) is a challenging problem due to the uncertaint... more Routing in Intermittently Connected Networks (ICN) is a challenging problem due to the uncertainty and time varying nature of network connectivity. In this work, we focus on a special class of ICN formed by mobile ad hoc users called ICMAN. We first consider a new and practical probabilistic mobility model where the nodes move between a set of "hubs" in a partially repetitive and nondeterministic pattern to form the so-called "sociological orbits". Second, to leverage the sociological orbit based mobility pattern in routing within ICMAN, we propose a series of multi-path Sociological Orbit aware Location Approximation and Routing (SOLAR) protocols. We present theoretical analysis of the mobility model and routing algorithms under consideration, and show that the proposed routing algorithms can outperform other conventional routing approaches in an ICN by taking advantage of the sociological orbit based mobility pattern.

Alzheimer's & Dementia, 2009

No abstract is available. To read the body of this article, please view the Full Text online. ...... more No abstract is available. To read the body of this article, please view the Full Text online. ... © 2009 The Alzheimer's Association. Published by Elsevier Inc. All rights reserved. ... Visit SciVerse ScienceDirect to see if you have access via your institution. ... Advertisements on this site ...

Alzheimer's & Dementia, 2010

Down syndrome (DS, trisomy 21) is the most common chromosomal disorder and the leading genetic ca... more Down syndrome (DS, trisomy 21) is the most common chromosomal disorder and the leading genetic cause of intellectual disability in humans. In DS, triplication of chromosome 21 invariably includes the APP gene (21q21) encoding the Alzheimer's disease (AD) amyloid precursor protein (APP). Triplication of the APP gene accelerates APP expression leading to cerebral accumulation of APP-derived amyloid-b peptides (Ab), early-onset AD neuropathology, and age-dependent cognitive sequelae. The DS phenotype complex also includes distinctive early-onset cerulean cataracts of unknown etiology. Previously, we reported increased Ab accumulation, co-localizing amyloid pathology, and disease-linked supranuclear cataracts in the ocular lenses of subjects with AD. Here, we investigate the hypothesis that related AD-linked Ab pathology underlies the distinctive lens phenotype associated with DS. Ophthalmological examinations of DS subjects were correlated with phenotypic, histochemical, and biochemical analyses of lenses obtained from DS, AD, and normal control subjects. Evaluation of DS lenses revealed a characteristic pattern of supranuclear opacification accompanied by accelerated supranuclear Ab accumulation, co-localizing amyloid pathology, and fiber cell cytoplasmic Ab aggregates (,5 to 50 nm) identical to the lens pathology identified in AD. Peptide sequencing, immunoblot analysis, and ELISA confirmed the identity and increased accumulation of Ab in DS lenses. Incubation of synthetic Ab with human lens protein promoted protein aggregation, amyloid formation, and light scattering that recapitulated the molecular pathology and clinical features observed in DS lenses. These results establish the genetic etiology of the distinctive lens phenotype in DS and identify the molecular origin and pathogenic mechanism by which lens pathology is expressed in this common chromosomal disorder. Moreover, these findings confirm increased Ab accumulation as a key pathogenic determinant linking lens and brain pathology in both DS and AD.

Ad Hoc Networks, 2007

Routing in delay tolerant networks poses a challenging problem compared to a conventional data ne... more Routing in delay tolerant networks poses a challenging problem compared to a conventional data network due to the uncertainty and time varying nature of network connectivity. Initial research in this area has considered algorithms based on deterministic mobility of the nodes in DTN. While the assumption of deterministic mobility can lay the groundwork for a theoretical understanding of DTN, such knowledge may not be applicable to mobile ad hoc networks. In this work, we introduce a novel concept of a partially repetitive "orbital" pattern of mobile users (nodes) involving a set of "hubs", that may be better suited for a semi-deterministic mobility modeling of DTN users. This partially deterministic movement pattern is both practical as well as useful in the sense that the hub list information can be useful for locating nodes and routing packets to them in a DTN.