Gaurav Sharma

Bio: Gaurav Sharma is an academic researcher from Shenzhen University. The author has contributed to research in topics: Medicine & Photocatalysis. The author has an hindex of 82, co-authored 1244 publications receiving 31482 citations. Previous affiliations of Gaurav Sharma include Northeastern University & D. E. Shaw & Co..

Content authentication for printed images utilizing high capacity data hiding

Abstract: Authentication of content in printed images poses a challenge that cannot be addressed by conventional digital signature schemes because under the analog transport provided by the printing channel the verifier does not have access to the original digital content in pristine form. We present a method for cryptography-based authentication of the content in printed images that also provides the capability for identifying localized changes made by informed malicious attackers—key functionality that is missing in print scan robust hashes that have traditionally been used for print content authentication. The proposed method operates by embedding, within the printed image, an authentication signature that consists of an encrypted thumbnail of the image using a high capacity data hiding method for halftone images. To authenticate the content, the embedded signature is extracted from a scan of the printed image and, after decryption, compared with the printed content. An implementation of the method that incorporates human or automated verification and identifies potential local tampering by informed malicious attackers is developed and successfully demonstrated.

Numerical Modelling of Wire-EDM for Predicting Erosion Rate of Silicon

Abstract: Recently, a lot of work is carried out in photovoltaic industry for slicing Si ingots using non-conventional technique like wire-EDM apart from conventional techniques like inner diameter saw and multi-wire saw. It is an emerging technology in field of Si wafer slicing and has a potential to be cost efficient. It reduces the kerf-loss and produces crack-free Si wafers. In general, the process of Si wafer cutting using wire-EDM is less understood due to its complex nature. In this work, the complex phenomena like formation of plasma channel, melting and erosion of Si material has been modelled mathematically. Further, the effect of input energy parameters like current, open voltage and pulse on-time on plasma and plasma-ingot interface temperature has been studied. The model is further extended along the length of the wire to evaluate the erosion depth and rate. The effect of process parameters on erosion depth and rate was validated experimentally. The model considers variation in material removal through the ‘plasma flushing efficiency’.

Clustered-dot color halftone watermarks using spatial frequency and color separability

Abstract: A framework for clustered-dot color halftone watermarking is proposed. Watermark patterns are embedded in the color halftone on per-separation basis. For typical CMYK printing systems, common desktop RGB color scanners are unable to provide the individual colorant halftone separations, which confounds per-separation detection methods. Not only does the K colorant consistently appear in the scanner channels as it absorbs uniformly across the spectrum, but cross-couplings between CMY separations are also observed in the scanner color channels due to unwanted absorptions. We demonstrate that by exploiting spatial frequency and color separability of clustered-dot color halftones, estimates of the individual colorant halftone separations can be obtained from scanned RGB images. These estimates, though not perfect, allow per-separation detection to operate efficiently. The efficacy of this methodology is demonstrated using continuous phase modulation for the embedding of per-separation watermarks.

On the optimality of de-synchronized demand response with stochastic renewables and inertial thermal loads

Abstract: We consider the problem of optimally supporting a collection of thermostatically controlled inertial loads in a smart microgrid environment. One key consideration is to reduce the need for costly nonrenewable reserves, while also meeting the consumer requirements specific to inertial thermal loads at the same time. Several models studied for optimal demand response leads to a response that is synchronized over the collection of loads, which is undesirable since synchronized response entails high demand fluctuations. We propose a model with an additional feature of stochastic variations in end user requirements. We show that employing a cost function that additionally penalizes the error in adhering to end user requirements leads to an optimal demand response that is de-synchronized over the collection of homogeneous loads. That is, identical thermal loads are intentionally staggered so as to hedge against future uncertainty of consumer preferences. We show that such desynchronization is related to the concavity of the cost-to-go function in the Hamilton-Jacobi-Bellman equation. We provide a simple heuristic to approximate the optimal policy. We also illustrate the results on a simple numerical example.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

SPAdes, a new genome assembly algorithm and its applications to single-cell sequencing ( 7th Annual SFAF Meeting, 2012)

Abstract: The lion's share of bacteria in various environments cannot be cloned in the laboratory and thus cannot be sequenced using existing technologies. A major goal of single-cell genomics is to complement gene-centric metagenomic data with whole-genome assemblies of uncultivated organisms. Assembly of single-cell data is challenging because of highly non-uniform read coverage as well as elevated levels of sequencing errors and chimeric reads. We describe SPAdes, a new assembler for both single-cell and standard (multicell) assembly, and demonstrate that it improves on the recently released E+V-SC assembler (specialized for single-cell data) and on popular assemblers Velvet and SoapDeNovo (for multicell data). SPAdes generates single-cell assemblies, providing information about genomes of uncultivatable bacteria that vastly exceeds what may be obtained via traditional metagenomics studies. SPAdes is available online ( http://bioinf.spbau.ru/spades ). It is distributed as open source software.