Dependability where the mobile world meets the enterprise world

As we move toward increasingly larger scales of computing, complexity of systems and networks has increased manifold leading to massive failures of cloud providers (Amazon Cloudfront, November 2014) and geographically localized outages of cellular services (T-Mobile, June 2014). In this dissertation, we investigate the dependability aspects of two of the most prevalent computing platforms today, namely, smartphones and cloud computing. These two seemingly disparate platforms are part of a cohesive story—they interact to provide end-to-end services which are increasingly being delivered over mobile platforms, examples being iCloud, Google Drive and their smartphone counterparts iPhone and Android. ^ In one of the early work on characterizing failures in dominant mobile OSes, we analyzed bug repositories of Android and Symbian and found similarities in their failure modes [ISSRE2010]. We also presented a classification of root causes and quantified the impact of ease of customizing the smartphones on system reliability. Our evaluation of Inter-Component Communication in Android [DSN2012] show an alarming number of exception handling errors where a phone may be crashed by passing it malformed component invocation messages, even from unprivileged applications. In this work, we also suggest language extensions that can mitigate these problems. ^ Mobile applications today are increasingly being used to interact with enterprise-class web services commonly hosted in virtualized environments. Virutalization suffers from the problem of imperfect performance isolation where contention for low-level hardware resources can impact application performance. Through a set of rigorous experiments in a private cloud testbed and in EC2, we show that interference induced performance degradation is a reality. Our experiments have also shown that optimal configuration settings for web servers change during such phases of interference. Based on this observation, we design and implement the IC 2engine which can mitigate effects of interference by reconfiguring web server parameters [MW2014]. We further improve IC 2 by incorporating it into a two-level configuration engine, named ICE, for managing web server clusters [ICAC2015]. Our evaluations show that, compared to an interference agnostic configuration, IC 2 can improve response time of web servers by upto 40%, while ICE can improve response time by up to 94% during phases of interference

Expected Length of the Longest Chain in Linear Hashing

Hash table with chaining is a data structure that chains objects with identical hash values together with an entry or a memory address. It works by calculating a hash value from an input then placing the input in the hash table entry. When we place two inputs in the same entry, they chain together in a linear linked list. We are interested in the expected length of the longest chain in linear hashing and methods to reduce the length because the worst-case look-up time is directly proportional to it. The linear hash function used to calculate hash value is defined by ax+b mod p mod m, for any x ∈ {0,1, . . . , p−1} and a, b chosen uniformly at random from the set {0,1, . . . , p−1}, where p is a prime and p≥m. This class of hash functions is a 2-wise independent hash function family. For any 2-wise independent hash functions, the expected length of the longest chain is O(n1/2). Additionally, Alon et al. (JACM 1999) proved that when using a similar class of 2-wise independent hash function, the expected length of the longest chain has a tight lower bound of Ω(n1/2). Recently, in 2016, Knudsen (FOCS 2016) showed that the upper bound of the expected length of the longest chain of the linear hashing function is surprisingly n1/3+o(1). This bound is strictly better than O(n1/2), which, due to Alon et al.’s result, is already known to be tight for 2-wise independent hash functions. Consequently, there are exclusive properties of the linear hashing function, in addition to being 2-wise independent, that results in this phenomenon. Even though Knudsen’s upper bound on the expected length of the longest chain is remarkable, it is still unknown whether it is tight. In other words, does there exist a set of n inputs such that, when hashed using the linear hash function, the expected length of the longest chain is roughly n1/3. If Knudsen’s bound is not tight, then there is an additional motivation to study further and tighten the upper bound. Another focus of our research is to reduce the expected length of the longest chain by using the load balancing power of “two choices.” The idea is, instead of choosing one bin (hash table entry) for a ball (input), to choose two or more bins and put the ball in the bin with the least load at that moment. Mitzenmacher et al. proved that the power of two choices exponentially improves the expected max-load (from Θ(log n/log log n)) to Θ(log log n)) for the hash table that uses two truly random hash functions. We shall conduct an empirical study by simulation with SageMath (System for Algebra and Geometry Experimentation) to verify whether similar improvements are observed for the linear hash function as well. We anticipate that the length of the longest chain of our linear hash table can be significantly improved when used with two linear hash functions

Modification of Softwood by Monomers and Nanofillers

Technological development of wood polymer composites (WPC) is a very promising approach to overcome most of the disadvantageous properties of wood products, for example their poor mechanical strength, poor dimensional stability, susceptibility to fungal attack, weathering and the like. To find the substitute for costly items of hard wood, suitable technologies have been developed to modify softwood to meet specific end-use requirements. Various vinyl monomers and/or copolymers or thermosetting resin in combination with different types of cross linking agents, flameretarding agents have been used to improve the properties of wood. Nanotechnology is a new area of science andtechnology which opens up new opportunities to develop wood based products with desired properties. Now-a-days government is making strict legislations to promote green technology for the protection of environment worldwide.With the depletion of petroleum resources at alarming rate, it is high time to replace petroleum-based products by some sustainable alternative products based on vegetable biomass. The bio-based resins obtained from renewablefeedstock have been widely utilized by taking the advantages of easy availability, renewable nature and low cost.The green route of modification of wood is widely encouraged. With the progress of technological development,now it is possible to avoid the hazardous influence of organic solvents by using water as solvent or diluents formodification of wood. WPC has got tremendous scope for use in diverse areas of applications.Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 262-272, DOI:http://dx.doi.org/10.14429/dsj.64.732

Magnetic and electrical properties of RCo2Mn (R=Ho, Er) compounds

The RCo2Mn (R= Ho and Er) alloys, crystallizing in the cubic MgCu2-type structure, are isostructural to RCo2 compounds. The excess Mn occupies both the R and the Co atomic positions. Magnetic, electrical and heat capacity measurements have been done in these comounds. The Curie temperature is found to be 248 K and 222 K for HoCo2Mn and ErCo2Mn respectively, which are considerably higher than that of the corresponding RCo2 compounds. Saturation magnetization values calculated in these samples are less compared to that of the corresponding RCo2 compounds. Heat capacity data have been fitted with the nonmagnetic contribution with Debye temperature =250 K and electronic coefficient=26 mJ mol^-1K^-2.Comment: 13 pages, 5 figures, 2 table