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Search Results: 1 - 10 of 8052 matches for " Akash Das Sarma "
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Multi-Armed Bandit Mechanisms for Multi-Slot Sponsored Search Auctions
Akash Das Sarma,Sujit Gujar,Y. Narahari
Computer Science , 2010,
Abstract: In pay-per click sponsored search auctions which are currently extensively used by search engines, the auction for a keyword involves a certain number of advertisers (say k) competing for available slots (say m) to display their ads. This auction is typically conducted for a number of rounds (say T). There are click probabilities mu_ij associated with each agent-slot pairs. The goal of the search engine is to maximize social welfare of the advertisers, that is, the sum of values of the advertisers. The search engine does not know the true values advertisers have for a click to their respective ads and also does not know the click probabilities mu_ij s. A key problem for the search engine therefore is to learn these click probabilities during the T rounds of the auction and also to ensure that the auction mechanism is truthful. Mechanisms for addressing such learning and incentives issues have recently been introduced and are aptly referred to as multi-armed-bandit (MAB) mechanisms. When m = 1, characterizations for truthful MAB mechanisms are available in the literature and it has been shown that the regret for such mechanisms will be O(T^{2/3}). In this paper, we seek to derive a characterization in the realistic but non-trivial general case when m > 1 and obtain several interesting results.
Globally Optimal Crowdsourcing Quality Management
Akash Das Sarma,Aditya Parameswaran,Jennifer Widom
Computer Science , 2015,
Abstract: We study crowdsourcing quality management, that is, given worker responses to a set of tasks, our goal is to jointly estimate the true answers for the tasks, as well as the quality of the workers. Prior work on this problem relies primarily on applying Expectation-Maximization (EM) on the underlying maximum likelihood problem to estimate true answers as well as worker quality. Unfortunately, EM only provides a locally optimal solution rather than a globally optimal one. Other solutions to the problem (that do not leverage EM) fail to provide global optimality guarantees as well. In this paper, we focus on filtering, where tasks require the evaluation of a yes/no predicate, and rating, where tasks elicit integer scores from a finite domain. We design algorithms for finding the global optimal estimates of correct task answers and worker quality for the underlying maximum likelihood problem, and characterize the complexity of these algorithms. Our algorithms conceptually consider all mappings from tasks to true answers (typically a very large number), leveraging two key ideas to reduce, by several orders of magnitude, the number of mappings under consideration, while preserving optimality. We also demonstrate that these algorithms often find more accurate estimates than EM-based algorithms. This paper makes an important contribution towards understanding the inherent complexity of globally optimal crowdsourcing quality management.
A Mechanism of Virus-Induced Demyelination
Jayasri Das Sarma
Interdisciplinary Perspectives on Infectious Diseases , 2010, DOI: 10.1155/2010/109239
Abstract: Myelin forms an insulating sheath surrounding axons in the central and peripheral nervous systems and is essential for rapid propagation of neuronal action potentials. Demyelination is an acquired disorder in which normally formed myelin degenerates, exposing axons to the extracellular environment. The result is dysfunction of normal neuron-to-neuron communication and in many cases, varying degrees of axonal degeneration. Numerous central nervous system demyelinating disorders exist, including multiple sclerosis. Although demyelination is the major manifestation of most of the demyelinating diseases, recent studies have clearly documented concomitant axonal loss to varying degrees resulting in long-term disability. Axonal injury may occur secondary to myelin damage (outside-in model) or myelin damage may occur secondary to axonal injury (inside-out model). Viral induced demyelination models, has provided unique imminent into the cellular mechanisms of myelin destruction. They illustrate mechanisms of viral persistence, including latent infections, virus reactivation and viral-induced tissue damage. These studies have also provided excellent paradigms to study the interactions between the immune system and the central nervous system (CNS). In this review we will discuss potential cellular and molecular mechanism of central nervous system axonal loss and demyelination in a viral induced mouse model of multiple sclerosis. 1. Introduction Demyelination is the process by which axons lose their normal insulating myelin. Several central nervous system demyelinating disorders have been described in humans including multiple sclerosis, neuromyelitis optica (Devic’s disease), acute disseminated encephalomyelitis, and osmotic demyelination (central pontine myelinolysis, extrapontine myelinolysis). Multiple sclerosis (MS) is a chronic, progressive, or relapsing and remitting demyelinating disorder that affects the central nervous system (CNS) specifically and ranks as a major cause of nervous system disability in young adults aged 20 to 45 [1–3]. It has long been hypothesized that oligodendrocytes (OLGs) and/or the myelin sheath are the target of immune system-mediated destruction in MS. Recent studies have demonstrated that axonal damage [4, 5] also occurs and is likely to be a major component of long-term disability observed in MS. The etiology of MS is not very clearly known but the process of demyelination is believed to involve a Tcell-mediated phenomenon that may be triggered by one or more viral infections. Clinical studies show that infectious agents
γδ T cells and IL-17/IL-17R signaling axis in CNS inflammation
Jayasri Das Sarma
International Journal of Interferon, Cytokine and Mediator Research , 2010, DOI: http://dx.doi.org/10.2147/IJICMR.S7066
Abstract: ells and IL-17/IL-17R signaling axis in CNS inflammation Review (3193) Total Article Views Authors: Jayasri Das Sarma Published Date November 2010 Volume 2010:2 Pages 149 - 155 DOI: http://dx.doi.org/10.2147/IJICMR.S7066 Jayasri Das Sarma Department of Biological Sciences, Indian Institute of Science Education and Research – Kolkata, Mohanpur, Nadia, West Bengal, India Abstract: Lymphocytes expressing γδ T-cell receptors constitute an entire system of functionally specialized subsets that have been implicated in the regulation of immune responses, including responses to pathogens and allergens, and in tissue repair. γδ T cells represent a small subpopulation of T cells that, unlike aβ T cells, function more as cells of the innate immune system. γδ T cells are known to mediate the production of inflammatory cytokines, including interferon-γ, tumor necrosis factor-a, and interleukin (IL)-17, and thus enable the activation of other subsets of infiltrating effector cells. However, not much attention was paid to γδ T cells until the recent discovery of a distinct CD4+ T helper (TH) cell, TH17 cell. CD4+ T cells, upon activation and expansion, develop into different TH-cell subsets with different cytokine profiles and distinct effector functions. T cells were earlier divided into TH1 or TH2 cells, depending on the cytokines they produce. A third subset of IL-17-producing effector TH cells, called TH17 cells, has been discovered and characterized recently. Since then the literature on IL-17-producing cells has grown steadily, and several studies have focused on γδ T cells. Cytokine-mediated modulation of central nervous system (CNS) inflammatory diseases by γδ T cells in humans or in animal models is currently the subject of many studies. IL-17 and its receptor IL-17R have been implicated in the pathogenesis of immune-mediated CNS diseases, and attention has been paid to understand the mechanisms by which IL-17 cytokines and it receptor (IL-17R) family mediate the effects at a molecular level. This article reviews the studies that cover earlier aspects of γδ T cell/IL-17 biology and the new dimension of γδ T cells, IL-17, and IL-17/IL-17R signaling axis in CNS inflammation. Understanding the role of γδ T cells, IL-17, and IL-17/IL-17R signaling axis in infection and immunity could open a new avenue for immunomodulation.
Dynamic Scaling in Epitaxial Growth
S. Das Sarma
Physics , 1997,
Abstract: A review is provided of our current theoretical understanding of dynamic scaling in nonequilibrium interface growth as, for example, in MBE growth under ultrahigh vacuum deposition conditions.
Spindle Cell Carcinoma of the Head and Neck: A Clinicopathological and Immunohistochemical Study of 40 Cases  [PDF]
Anupam Sarma, Rajjyoti Das, J. D. Sharma, A. C. Kataki
Journal of Cancer Therapy (JCT) , 2012, DOI: 10.4236/jct.2012.36137
Abstract: Spindle cell carcinoma of head and neck, a subtype of squamous cell carcinoma is a unique and rare neoplasm. It has a more aggressive behavior as compared to classical squomous cell carcinoma warranting surgical interventions with wider surgical margins. Immunohistochemistry along with routine histopathology is essential in establishing the diagnosis of spindle cell carcinoma. We at Dr. B. Borooah Cancer Institute, Guwahati, a regional institute for treatment and research, hereby report 40 cases of such lesion with clinicopathological and immunohistochemical study. Out of total 40 cases included in the study group most of the cases were in the age group of 40 to 60 years. Commonest site of presentation was nasopharynx and buccal mucosa. 14 cases of the oral cavity (buccal mucosa, alveolus, oral tongue and hard palate) were treated with surgery. All the cases with disease of the larynx and hypopharynx were treated with radiotherapy and cases involving the nasopharynx received radiotherapy and chemotherapy. In the surgery group recurrence rate was found to be 71.4% and metastasis rate was 21.4%. Biopsy specimens were subjected to histopathological examination followed by immunohistochemistry. Immunohistochemical analysis show concurrent presence of malignant epithelial and sarcomatoid spindle cell components by co-expression of cytokeratin (CK) and vimentin to various degrees.
Synthesis, Spectroscopy, Thermal Analysis, Electrochemistry and Superoxide Scavenging Activity of a New Bimetallic Copper(II) Complex
Babita Sarma,Diganta Kumar Das
Journal of Chemistry , 2013, DOI: 10.1155/2013/349580
Abstract:
An exchange-correlation energy for a two-dimensional electron gas in a magnetic field
Rodney Price,S. Das Sarma
Physics , 1995, DOI: 10.1103/PhysRevB.54.8033
Abstract: We present the results of a variational Monte Carlo calculation of the exchange-correlation energy for a spin-polarized two-dimensional electron gas in a perpendicular magnetic field. These energies are a necessary input to the recently developed current-density functional theory. Landau-level mixing is included in a variational manner, which gives the energy at finite density at finite field, in contrast to previous approaches. Results are presented for the exchange-correlation energy and excited-state gap at $\nu =$ 1/7, 1/5, 1/3, 1, and 2. We parameterize the results as a function of $r_s$ and $\nu$ in a form convenient for current-density functional calculations.
Comment on ``Energy Dependence of Electron Lifetime in Graphite Observed with Femtosecond Photoemission Spectroscopy'' (PRL 76, 483(1996).)
Lian Zheng,S. Das Sarma
Physics , 1996, DOI: 10.1103/PhysRevLett.77.1410
Abstract: We comment on the theoretical interpretations applied to a recent experiment on electron lifetime in graphite. We point out that the acoustic-plasmon excitations in a layered two-dimensional electron system do not produce a linear energy dependence for the Coulomb scattering rate.
Inelastic lifetimes of confined two-component electron systems in semiconductor quantum wire and quantum well structures
Lian Zheng,S. Das Sarma
Physics , 1996, DOI: 10.1103/PhysRevB.54.13908
Abstract: We calculate Coulomb scattering lifetimes of electrons in two-subband quantum wires and in double-layer quantum wells by obtaining the quasiparticle self-energy within the framework of the random-phase approximation for the dynamical dielectric function. We show that, in contrast to a single-subband quantum wire, the scattering rate in a two-subband quantum wire contains contributions from both particle-hole excitations and plasmon excitations. For double-layer quantum well structures, we examine individual contributions to the scattering rate from quasiparticle as well as acoustic and optical plasmon excitations at different electron densities and layer separations. We find that the acoustic plasmon contribution in the two-component electron system does not introduce any qualitatively new correction to the low energy inelastic lifetime, and, in particular, does not produce the linear energy dependence of carrier scattering rate as observed in the normal state of high-$T_c$ superconductors.
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