557 research outputs found
Chemistry of 2-(phenylazo)pyridine complexes of osmium: synthesis, characterization and reactivities
No full textOxidation of Rhodium(I) by Hydroxamic Acids. Synthesis, Structure, and Electrochemical Properties of Bis(hydroxamate) Complexes of Rhodium(III)
No full textChemistry of osmium in N2P2Br2 coordination sphere: Synthesis, structure and reactivities
No full textSynthesis, structure and electrochemical properties of a group of ruthenium(III) complexes of N-(aryl)picolinamide
No full textCoded sparse matrix computation schemes that leverage partial stragglers
Full text linkDistributed matrix computations over large clusters can suffer from the problem of slow or failed worker nodes (called stragglers) which can dominate the overall job execution time. Coded computation utilizes concepts from erasure coding to mitigate the effect of stragglers by running 'coded' copies of tasks comprising a job; stragglers are typically treated as erasures. While this is useful, there are issues with applying, e.g., MDS codes in a straightforward manner. Several practical matrix computation scenarios involve sparse matrices. MDS codes typically require dense linear combinations of submatrices of the original matrices which destroy their inherent sparsity. This is problematic as it results in significantly higher worker computation times. Moreover, treating slow nodes as erasures ignores the potentially useful partial computations performed by them. Furthermore, some MDS techniques also suffer from significant numerical stability issues. In this work we present schemes that allow us to leverage partial computation by stragglers while imposing constraints on the level of coding that is required in generating the encoded submatrices. This significantly reduces the worker computation time as compared to previous approaches and results in improved numerical stability in the decoding process. Exhaustive numerical experiments on Amazon Web Services (AWS) clusters support our findings.This is a pre-print of the article Das, Anindya Bijoy, and Aditya Ramamoorthy. "Coded sparse matrix computation schemes that leverage partial stragglers." arXiv preprint arXiv:2012.06065 (2020). Posted with permission.</p
C3LES: Codes for Coded Computation that Leverage Stragglers
Full text linkIn distributed computing systems, it is well recognized that worker nodes that are slow (called stragglers) tend to dominate the overall job execution time. Coded computation utilizes concepts from erasure coding to mitigate the effect of stragglers by running "coded" copies of tasks comprising a job. Stragglers are typically treated as erasures in this process. While this is useful, there are issues with applying, e.g., MDS codes in a straightforward manner. Specifically, several applications such as matrix-vector products deal with sparse matrices. MDS codes typically require dense linear combinations of submatrices of the original matrix which destroy their inherent sparsity. This is problematic as it results in significantly higher processing times for computing the submatrix-vector products in coded computation. Furthermore, it also ignores partial computations at stragglers. In this work, we propose a fine-grained model that quantifies the level of non-trivial coding needed to obtain the benefits of coding in matrix-vector computation. Simultaneously, it allows us to leverage partial computations performed by the straggler nodes. For this model, we propose and evaluate several code designs and discuss their properties.This is a pre-print of the article Das, Anindya B., Li Tang, and Aditya Ramamoorthy. "C3LES: Codes for Coded Computation that Leverage Stragglers." arXiv preprint arXiv:1809.06242 (2018). Posted with permission.</p
Random Convolutional Coding for Robust and Straggler Resilient Distributed Matrix Computation
Full text linkDistributed matrix computations (matrix-vector and matrix-matrix multiplications) are at the heart of several tasks within the machine learning pipeline. However, distributed clusters are well-recognized to suffer from the problem of stragglers (slow or failed nodes). Prior work in this area has presented straggler mitigation strategies based on polynomial evaluation/interpolation. However, such approaches suffer from numerical problems (blow up of round-off errors) owing to the high condition numbers of the corresponding Vandermonde matrices. In this work, we introduce a novel solution approach that relies on embedding distributed matrix computations into the structure of a convolutional code. This simple innovation allows us to develop a provably numerically robust and efficient (fast) solution for distributed matrix-vector and matrix-matrix multiplication.This is a pre-print of the article Das, Anindya B., Aditya Ramamoorthy, and Namrata Vaswani. "Random Convolutional Coding for Robust and Straggler Resilient Distributed Matrix Computation." arXiv preprint arXiv:1907.08064 (2019). Posted with permission.</p
First-principles study of electromechanical and polar properties in perovskite oxides and half-Heusler semiconductors
No full textThis thesis discusses electromechanical and polar properties in two well-known classes of materials, perovskite oxides and half-Heusler compounds, using first-principles calculations. Certain features of the ab initio codes, such as the capability to calculate polarization based on the modern theory of polarization, or to apply a finite electric field, are central to the problems presented in this thesis. Hence these formalisms are discussed, following a brief opening section on the basic methodology of density-functional theory. The first problem presented in this thesis concerns the nonlinear piezoelectric response of ferroelectric PbTiO₃ for the case of a polarization-enhancing electric field applied along the tetragonal axis. The dependence of the c/a ratio on electric field is found to be almost linear in the range up to 500 MV/m, contrary to what expected from Landau-Devonshire theory, but in qualitative agreement with a recent experiment. In the second problem we study the energy landscape and ferroelectric states of double perovskites of the form AA'BB'O₆ in which the atoms on both the A and B sites are arranged in rock-salt order. If a ferroelectric instability occurs, the energy landscape will tend to have minima with the polarization along tetrahedral directions, leading to a rhombohedral phase, or along Cartesian directions, leading to an orthorhombic phase. We are not aware of compounds naturally occurring in this structure, although they might be synthesized experimentally. In the final problem, we use a first-principles rational-design approach to search a large materials family, half-Heusler compounds to identify semiconductors, and then compute their piezoelectric properties. This previously-unrecognized class of piezoelectrics may benefit greatly from calculations such as those presented here. Our work may provide guidance for experimental verification of existing compounds and for the experimental realization of other potential candidates.Ph. D.Includes bibliographical referencesIncludes vitaby Anindya Ro
Straggler-Resistant Distributed Matrix Computation via Coding Theory: Removing a Bottleneck in Large-Scale Data Processing
No full textThe current BigData era routinely requires the processing of large scale data on massive distributed computing clusters. Such large scale clusters often suffer from the problem of "stragglers", which are defined as slow or failed nodes. The overall speed of a computational job on these clusters is typically dominated by stragglers in the absence of a sophisticated assignment of tasks to the worker nodes. In recent years, approaches based on coding theory (referred to as "coded computation") have been effectively used for straggler mitigation. Coded computation offers significant benefits for specific classes of problems such as distributed matrix computations (which play a crucial role in several parts of the machine learning pipeline). The essential idea is to create redundant tasks so that the desired result can be recovered as long as a certain number of worker nodes complete their tasks. In this survey article, we overview recent developments in the field of coding for straggler-resilient distributed matrix computations.This is a manuscript of an article published as Ramamoorthy, Aditya, Anindya Bijoy Das, and Li Tang. "Straggler-Resistant Distributed Matrix Computation via Coding Theory: Removing a Bottleneck in Large-Scale Data Processing." IEEE Signal Processing Magazine 37, no. 3 (2020): 136-145. DOI: 10.1109/MSP.2020.2974149.Posted with permission.</p
Quantum transport in Graphene Moire Superlattice and p-n junction
No full textThe discovery of graphene has revolutionized the field of mesoscopic condensed matter physics. It has started a new field of van-der Waals heterostructure in which different two-dimensional materials including graphene can be stacked on top of each other. In the last few years graphene based van-der Walls heterostructure has lead to many interesting physics like Hofstadter’s butterfly, Valley Hall effect, Mott insulator and superconductivity. In this thesis, two different kinds of graphene heterostructures, namely, graphene moiré superlattice (GMSL) and graphene p-n junction (GPNJ) have been studied extensively. The GMSL is realized by aligning and stacking graphene and hexagonal boron nitride with an accuracy of . This leads to additional set of Dirac cones known as cloned Dirac cones (CDC) which are placed symmetrically around the primary Dirac cone (PDC). As a part of the thesis, we have studied the magneto-conductance on GMSL devices as a function of carrier concentration and temperature, which reveals a transition from weak anti-localization (WAL) near the PDC to weak localization (WL) near the CDC. The transition is explained due to the shift of Berry phase, which is measured experimentally by probing the Shubnikov-de Haas oscillations. Furthermore, we study the low frequency 1/f noise at multiple Dirac cones in GMSL devices. Our results reveal that the low-frequency noise in GMSL devices can be tuned by more than two-orders of magnitude by changing carrier concentration as well as by modifying the band structure. We find that the noise is suppressed at the CDC compared to the PDC and understood in terms of screening. In the second part of the thesis, we study the equilibration of quantum Hall edges in GPNJ devices, which are realized in dual gated geometry. The equilibration of electron-like and hole-like edges in graphene p-n junction have been studied in single and bilayer graphene in both unipolar and bipolar regime, when the different symmetries likes valley, spin and orbital degrees of freedoms are broken. Our studies reveal the partial equilibration based on the spin polarization of the quantum Hall edges. Furthermore, we have carried out shot noise measurements to understand the dynamics and mixing of quantum Hall edges at the p-n junction, which could be used as an electronic beam splitte
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