Anirban Mondal

Bio: Anirban Mondal is an academic researcher from Ashoka University. The author has contributed to research in topics: Revenue & Markov chain Monte Carlo. The author has an hindex of 22, co-authored 140 publications receiving 1819 citations. Previous affiliations of Anirban Mondal include Indian Institute of Science & Indraprastha Institute of Information Technology.

Keyword Search in Spatial Databases: Towards Searching by Document

Abstract: This work addresses a novel spatial keyword query called the m-closest keywords (mCK) query. Given a database of spatial objects, each tuple is associated with some descriptive information represented in the form of keywords. The mCK query aims to find the spatially closest tuples which match m user-specified keywords. Given a set of keywords from a document, mCK query can be very useful in geotagging the document by comparing the keywords to other geotagged documents in a database. To answer mCK queries efficiently, we introduce a new index called the bR*-tree, which is an extension of the R*-tree. Based on bR*-tree, we exploit a priori-based search strategies to effectively reduce the search space. We also propose two monotone constraints, namely the distance mutex and keyword mutex, as our a priori properties to facilitate effective pruning. Our performance study demonstrates that our search strategy is indeed efficient in reducing query response time and demonstrates remarkable scalability in terms of the number of query keywords which is essential for our main application of searching by document.

Colloidal Synthesis and Photophysics of M3Sb2I9 (M=Cs and Rb) Nanocrystals: Lead‐Free Perovskites

Abstract: Herein we report the colloidal synthesis of Cs3Sb2I9 and Rb3Sb2I9 perovskite nanocrystals, and explore their potential for optoelectronic applications. Different morphologies, such as nanoplatelets and nanorods of Cs3Sb2I9, and spherical Rb3Sb2I9 nanocrystals were prepared. All these samples show band-edge emissions in the yellow–red region. Exciton many-body interactions studied by femtosecond transient absorption spectroscopy of Cs3Sb2I9 nanorods reveals characteristic second-derivative-type spectral features, suggesting red-shifted excitons by as much as 79 meV. A high absorption cross-section of ca. 10−15 cm2 was estimated. The results suggest that colloidal Cs3Sb2I9 and Rb3Sb2I9 nanocrystals are potential candidates for optical and optoelectronic applications in the visible region, though a better control of defect chemistry is required for efficient applications.

Palladium‐Catalyzed Directed para C−H Functionalization of Phenols

Abstract: Various practical methods for the selective C-H functionalization of the ortho and recently also of the meta position of an arene have already been developed. Following our recent development of the directing-group-assisted para C-H functionalization of toluene derivatives, we herein report the first remote para C-H functionalization of phenol derivatives by using a recyclable silicon-containing biphenyl-based template. The effectiveness of this strategy was illustrated with different synthetic elaborations and by the synthesis of various phenol-based natural products.

P2PR-Tree: an R-tree-based spatial index for peer-to-peer environments

Abstract: The unprecedented growth and increased importance of geographically distributed spatial data has created a strong need for efficient sharing of such data Interestingly, the ever-increasing popularity of peer-to-peer (P2P) systems has opened exciting possibilities for such sharing This motivates our investigation into spatial indexing in P2P systems While much work has been done towards expediting search in file-sharing P2P systems, issues concerning spatial indexing in P2P systems are significantly more complicated due to overlaps between spatial objects and the complexity of spatial queries Incidentally, existing R-tree-based structures for distributed environments (e.g., the MC-Rtree) are not adequate for addressing the sheer scale, dynamism and heterogeneity of P2P environments Hence, we propose the P2PR-tree (Peer-to-Peer R-tree), which is a new spatial index specifically designed for P2P systems The main features of P2PR-tree are two-fold First, it is hierarchical and performs efficient pruning of the search space by maintaining minimal amount of information concerning peers that are far away and storing more information concerning nearby peers, thereby optimizing disk space usage Second, it is completely decentralized, scalable and robust to peers joining/leaving the system The results of our performance evaluation demonstrate that it is indeed practically feasible to share spatial data in a P2P system and that P2PR-tree is able to outperform MC-Rtree significantly.

Ultrafast exciton many-body interactions and hot-phonon bottleneck in colloidal cesium lead halide perovskite nanocrystals

Abstract: Defect-tolerant perovskite nanocrystals of the general formula Cs-Pb-${X}_{3}$ (where $X=\mathrm{Cl}$, Br, and I) have shown exceptional potential in fundamental physics as well as in novel optoelectronic applications as the next generation of solar cells Although exciton many-body interactions such as biexciton Stark shift, state filling, and Auger recombination are studied extensively, other important correlated effects, such as band gap renormalization (BGR) and hot-phonon bottleneck, are not explored in these nanocrystals Here we experimentally demonstrate the carrier density dependence of the BGR and an effective hot-phonon bottleneck in $\mathrm{CsPb}{(\mathrm{C}{\mathrm{l}}_{020}\mathrm{B}{\mathrm{r}}_{080})}_{3}$ mixed-halide nanocrystals The results are compared with two other halide compositions, namely, ${\mathrm{CsPbBr}}_{3}$ and $\mathrm{CsPb}{(\mathrm{B}{\mathrm{r}}_{055}{\mathrm{I}}_{045})}_{3}$ nanocrystals with varying band gaps The optical response of the nanocrystals changes dramatically across the spectral range of many hundreds of meV at high carrier density due to large BGR We have calculated the BGR constant $\ensuremath{\approx}(60\ifmmode\pm\else\textpm\fi{}03)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{016em}{0ex}}\mathrm{eV}$ cm for $\mathrm{CsPb}{(\mathrm{C}{\mathrm{l}}_{020}\mathrm{B}{\mathrm{r}}_{080})}_{3}$ nanocrystals that provides the amount of band gap shift as a function of carrier density In these nanocrystals, an efficient hot-phonon bottleneck is observed at a carrier density of $31\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{016em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ that slows down the thermalization by 1 order of magnitude Our findings reveal that the complex kinetic profile of the exciton dynamics can be analyzed by the global target analysis using the sequential model with increasing lifetimes

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry.

Abstract: The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure The schemes feature typical substrates used, the products obtained as well as the required reaction conditions Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them Accordingly, this review should be of particular interest also for scientists from industrial R&D sector Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date

Designing an Super-Peer Network

Abstract: A super-peer is a node in a peer-to-peer network that operates both as a server to a set of clients, and as an equal in a network of super-peers. Super-peer networks strike a balance between the efficiency of centralized search, and the autonomy, load balancing and robustness to attacks provided by distributed search. Furthermore, they take advantage of the heterogeneity of capabilities (e.g., bandwidth, processing power) across peers, which recent studies have shown to be enormous. Hence, new and old P2P systems like KaZaA and Gnutella are adopting super-peers in their design. Despite their growing popularity, the behavior of super-peer networks is not well understood. For example, what are the potential drawbacks of super-peer networks? How can super-peers be made more reliable? How many clients should a super-peer take on to maximize efficiency? we examine super-peer networks in detail, gaming an understanding of their fundamental characteristics and performance tradeoffs. We also present practical guidelines and a general procedure for the design of an efficient super-peer network.