37,087 research outputs found
Verification of Liveness Properties in Distributed Systems
No full textThis paper presents liveness properties that need to be preserved by Event-B models of distributed systems. Event-B is a formal technique for development of models of distributed systems related via refinement. In this paper we outline how enabledness preservation and non-divergence are related to the liveness properties of the B models of the distributed systems. We address the liveness issues related to our model of distributed transactions and outline the construction of proof obligations that need to be discharged to ensure liveness
First person – Shweta Yadav
No full textABSTRACT
First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Shweta Yadav is the first author on ‘RDGBα localization and function at membrane contact sites is regulated by FFAT–VAP interactions’, published in Journal of Cell Science. Shweta is a post-doctoral associate in the laboratory of Prof. Juan Botas at Baylor College of Medicine, Texas, USA, investigating neurodegenerative diseases.</jats:p
Formal Development of a Total Order Broadcast for Distributed Transactions using Event-B
No full textAbstract. In a replicated database system, copies of the database are kept across several sites for fault-tolerance and availability. Data access in such systems is usually done within a transactional framework. A read-only transaction accesses data locally and an update transaction modifies the database at all sites. Total order broadcast primitives have been proposed to support transactions and allow fault-tolerant cooperation between the sites in a distributed system. In this paper, we identify and analyze the problem of formation of deadlocks among conflicting update transactions due to race conditions and outline how a system of total order broadcast prevents deadlocks and transaction failures. Later we outline how a refinement based approach with Event-B can be used for formal development of the models of total order broadcast. In this approach we begin with the abstract model of a total order broadcast and verify that the required ordering properties are preserved by the system. total order can correctly be implemented by using a notion of sequence number. This technique requires us to discharge proof obligations due to consistency and refinement checking. To discharge the proof obligations we are required to discover invariants that describes the relationship between the abstract total order and the underlying mechanism.
Eriocaulon goaense Kolte, I. Yadav & Janarth. 2022, sp. nov.
No full text<p> <i>Eriocaulon goaense</i> Kolte, I.Yadav & Janarth., <i>sp. nov</i>. (Fig 1 & 2)</p> <p> Allied to <i>Eriocaulon cuspidatum</i> Dalzell, but differs in its broadly cuneate floral bracts that are densely hoary dorsally towards apex (vs. oblanceolate, sparsely hoary dorsally towards apex), narrowly keeled sepals of male flowers (vs. not keeled), obovate, conduplicate, broadly keeled sepals of female flowers that are smooth along margin, densely hairy along keel and on dorsal side (vs. oblanceolate, conduplicate, acuminate, keeled, scarious, glabrous), and unequal, linear to lanceolate petals of female flowers that are hoary at apex in odd petal (vs. subequal, spathulate, sparsely hoary at apex in all the petals).</p> <p> <b>Type</b>:— INDIA. <b>Goa</b>: North Goa, Goa University Campus, 15027 ’43.09”N 73049 ’ 59.77” E, 53m, 14 September 2019, <i>R. R. Kolte RRK 1890</i> (holo BSI!; iso SUK!).</p> <p>Acaulescent herb. Rootstock absent. Leaves 6–10 × 0.7–1 cm, rosulate, glabrous, entire along margin, cuspidate at apex. Sheaths up to 10 cm long, glabrous; limb ovate, acute, entire. Peduncles many, up to 35 cm high, 9–11 ridged. Heads ca. 7 mm across, hemispherical, straw coloured. Receptacles convex, glabrous. Involucral bracts 1.6–1.8 × 1.4–1.5 mm, chartaceous, oblong, spreading, obtuse, straw coloured. Floral bracts 1.4–1.5 × 1.1–1.2 mm, hyaline, broadly cuneate, obtuse, densely hoary dorsally towards apex. Male flowers: Sessile, sepals 2, ca. 2 mm long, hyaline, free, spathulate, narrowly keeled, densely hairy along keel and on dorsal side. Stipe of corolla 1.2–1.5 mm long. Petals 3, subequal, pubescent, dotted with black glands; odd one ca. 1 mm long, remaining 2 of same size, smaller than odd petal; anthers black. Female flowers: Shortly pedicelled. Sepals 2, free, similar, 1.4–1.5 × ca. 1 mm, obovate, conduplicate, broadly keeled, smooth along margin, hoary outside towards apex. Petals 3, unequal; odd one ca. 2 × 0.4 mm, lanceolate, hoary towards apex, black gland dotted; 2 petals similar, ca. 1.5 mm long, linear to narrow lanceolate, glabrous, black gland dotted. Ovary sessile, ellipsoid; style 3-fid. Seeds ca. 1 × 0.5 mm, ovoid, apiculate; cells of seed coat transversely elongated, arranged in vertical rows, appendage 1 from transverse radial walls.</p> <p> <b>Distribution</b>:—Scattered in distribution at low level lateritic plateaus of Goa.</p> <p> <b>Habitat</b>:—Shallow seasonal ponds of lateritic plateaus in association with <i>Eriocaulon fysonii</i> R.Ansari & N.P.Balakr. (1994: 89), <i>Oryza rufipogon</i> Griff. (1851: 5) and <i>Wiesneria triandra</i> (Dalzell 1850: 144) Micheli (1881: 82).</p> <p> <b>Flowering & Fruiting</b>:—July to November.</p> <p> <b>Etymology</b>:—Specific epithet ‘ <i>goaense</i> ’ refers to the state of Goa, wherein it is distributed.</p> <p> <b>Additional specimens examined (Paratypes)</b>:— INDIA. <b>Goa</b>: North Goa, Goa University Campus, 16 July 2010, <i>I. Yadav 1</i>; 24 July, 2010, <i>I. Yadav 2</i>; 31 July 2010, <i>I. Yadav 5</i>; 17 August 2010, <i>I. Yadav 8</i>; Succoro (Sukor) plateau, 18 September 2010, <i>I. yadav & M. K. Janarthanam 64</i>; South Goa, Farmagudi (Ponda), IIT Campus, 28 August 2010, <i>I. Yadav & M. K. Janarthanam 32</i>; 18 September, 2010, <i>I. Yadav & M. K. Janarthanam 35</i>; Loliem, 5 September 2010, <i>M. K. Janarthanam & I. Yadav 47</i>; 1 September 2018, <i>R. R. Kolte RRK 1710</i> (All at BSI!)</p> <p> <b>Note</b>:—This species is closely allied to <i>E. cuspidatum</i> which is occasionally found in wet or marshy places from sea level to 250 m altitude in Western Peninsular India, especially in Karnataka, Kerala and Maharashtra (Ansari & Balakrishnan, 2009). <i>Eriocaulon goaense</i> is so far known from shallow seasonal ponds of low level lateritic plateaus of Goa.</p>Published as part of <i>Kolte, Rutuja R., Yadav, Indu & Janarthanam, Malapati K., 2022, Eriocaulon goaense (Eriocaulaceae), a new species from lateritic plateaus of Goa, India, pp. 188-191 in Phytotaxa 532 (2)</i> on pages 189-190, DOI: 10.11646/phytotaxa.532.2.8, <a href="http://zenodo.org/record/5912666">http://zenodo.org/record/5912666</a>
Supporting data for Effects of Segment Length Asymmetry in Ternary Diblock Co-polymer-Homopolymer Mixtures
No full textThis data set contains data files and scripts to generate results reported in "Effects of Segment Length Asymmetry in Ternary Diblock Copolymer−Homopolymer Mixtures" by Yadav et al. Self-consistent field theory was used to study the effect of asymmetry between A and B statistical segment lengths on interfacial properties and phase behavior in ternary mixtures of AB diblock co-polymers, A homopolymers, and B homopolymers. We consider systems with volumetrically symmetric homopolymers and co-polymer, in which a difference between A and B statistical segment length is the only source of asymmetry between A and B monomers. The sign of the spontaneous curvature of monolayer interfaces between A- and B-rich homopolymer domains is shown to depend on the ratio of co-polymer to homopolymer chain lengths: Interfaces preferentially curve toward the component with a higher statistical segment length when the homopolymer lengths are greater than or comparable to the co- polymer length (as also found in diblock co-polymer melts) but curve away from this component when the homopolymers are much shorter than the co-polymer.National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013Yadav, Mridul; Morse, David C; Bates, Frank S. (2020). Supporting data for Effects of Segment Length Asymmetry in Ternary Diblock Co-polymer-Homopolymer Mixtures. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/abap-1q69
Formal Specifications and Verification of Message Ordering Properties in a Broadcasting System using Event B
No full textCausal and total order broadcast has been proposed as a mechanism to provide fault tolerance for constructing reliable distributed systems. The use of formal methods to develop a model of a system, specifying critical properties and the verification of them is a way of obtaining better design of dependable services. Event B is a formal technique which provides a framework for developing mathematical models of distributed systems by rigorous description of the problem, gradually introducing solutions in the refinement steps, and verification of solutions by discharge of proof obligations. In this paper, we present a formal development of a system in Event B where processes communicate by broadcast and the messages are delivered following a causal and a total order. We first present separate models of a broadcast system each for a causal order and a total order. Subsequently, we verify that the models of the system preserves the required ordering properties. Further, we develop a model of a system satisfying both causal and a total order on the messages. Later in the refinement, we outline how these ordering properties can correctly be implemented by the vector clocks. In this approach we discover some interesting invariant properties which describes the relationship of abstract causal and total order with the vector clocks and the sequence numbers
Rigorous Design of Fault-Tolerant Transactions for Replicated Database Systems using Event B
No full textSystem availability is improved by the replication of data objects in a distributed database system. However, during updates, the complexity of keeping replicas identical arises due to failures of sites and race conditions among conflicting transactions. Fault tolerance and reliability are key issues to be addressed in the design and architecture of these systems. Event B is a formal technique which provides a framework for developing mathematical models of distributed systems by rigorous description of the problem, gradually introducing solutions in refinement steps, and verification of solutions by discharge of proof obligations. In this paper, we present a formal development of a distributed system using Event B that ensures atomic commitment of distributed transactions consisting of communicating transaction components at participating sites. This formal approach carries the development of the system from an initial abstract specification of transactional updates on a one copy database to a detailed design containing replicated databases in refinement. Through refinement we verify that the design of the replicated database confirms to the one copy database abstraction
Srdja Popović in conversation with Yogendra Yadav: “Every non-violent struggle supports the same principle – it becomes efficient the moment people take it personally”
No full textThe first LSE India Summit took place in Goa 28-30 January 2016, and featured a wide range of panellists exploring topics from civil society to infrastructure challenges in India. During a pause in the conference, speakers Srdja Popović and Yogendra Yadav met to discuss political theory and the practicalities of fostering non-violent mass movements in the 21st Century
Fast Estimator of Primordial Non-Gaussianity from Temperatureand Polarization Anisotropies in the Cosmic Microwave Background II: Partial Sky Coverage and Inhomogeneous Noise
No full textIn the recent paper by Yadav and coworkers we described a fast cubic (bispectrum) estimator of the amplitude of primordial non-Gaussianity of local type, fNL, from a combined analysis of the cosmic microwave background (CMB) temperature and E-polarization observations. In this paper we generalize the estimator to deal with a partial sky coverage as well as inhomogeneous noise. Our generalized estimator is still computationally efficient, scaling as O(N3/2pix) compared to the O(N5/2pix) scaling of the brute-force bispectrum calculation for sky maps with Npix pixels. Upcoming CMB experiments are expected to yield high-sensitivity temperature and E-polarization data. Our generalized estimator will allow us to optimally utilize the combined CMB temperature and E-polarization information from these realistic experiments and to constrain primordial non-Gaussianity
Rigorous Design of Distributed Transactions
No full textDatabase replication is traditionally envisaged as a way of increasing fault-tolerance and availability. It is advantageous to replicate the data when transaction workload is predominantly read-only. However, updating replicated data within a transactional framework is a complex affair due to failures and race conditions among conflicting transactions. This thesis investigates various mechanisms for the management of replicas in a large distributed system, formalizing and reasoning about the behavior of such systems using Event-B. We begin by studying current approaches for the management of replicated data and explore the use of broadcast primitives for processing transactions. Subsequently, we outline how a refinement based approach can be used for the development of a reliable replicated database system that ensures atomic commitment of distributed transactions using ordered broadcasts. Event-B is a formal technique that consists of describing rigorously the problem in an abstract model, introducing solutions or design details in refinement steps to obtain more concrete specifications, and verifying that the proposed solutions are correct. This technique requires the discharge of proof obligations for consistency checking and refinement checking. The B tools provide significant automated proof support for generation of the proof obligations and discharging them. The majority of the proof obligations are proved by the automatic prover of the tools. However, some complex proof obligations require interaction with the interactive prover. These proof obligations also help discover new system invariants. The proof obligations and the invariants help us to understand the complexity of the problem and the correctness of the solutions. They also provide a clear insight into the system and enhance our understanding of why a design decision should work. The objective of the research is to demonstrate a technique for the incremental construction of formal models of distributed systems and reasoning about them, to develop the technique for the discovery of gluing invariants due to prover failure to automatically discharge a proof obligation and to develop guidelines for verification of distributed algorithms using the technique of abstraction and refinement
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