Showing papers by "Indian Institute of Technology Bombay published in 2006"

ALICE: Physics Performance Report, Volume II

Abstract: ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes.

Record linkage: similarity measures and algorithms

Abstract: This tutorial provides a comprehensive and cohesive overview of the key research results in the area of record linkage methodologies and algorithms for identifying approximate duplicate records, and available tools for this purpose. It encompasses techniques introduced in several communities including databases, information retrieval, statistics and machine learning. It aims to identify similarities and differences across the techniques as well as their merits and limitations.

Emissions from open biomass burning in India: Integrating the inventory approach with high-resolution Moderate Resolution Imaging Spectroradiometer (MODIS) active-fire and land cover data

Abstract: [1] Climatological mean estimates of forest burning and crop waste burning based on broad assumptions of the amounts burned have so far been used for India in global inventories. Here we estimate open biomass burning representative of 1995–2000 from forests using burned area and biomass density specific for Indian ecosystems and crop waste burning as a balance between generation and known uses as fuel and fodder. High-resolution satellite data of active fires and land cover classification from MODIS, both on a scale of 1 km × 1 km, were used to capture the seasonal variability of forest and crop waste burning and in conjunction with field reporting. Correspondence in satellite-detected fire cycles with harvest season was used to identify types crop waste burned in different regions. The fire season in forest areas was from February to May, and that in croplands varied with geographical location, with peaks in April and October, corresponding to the two major harvest seasons. Spatial variability in amount of forest biomass burned differed from corresponding forest fire counts with biomass burned being largest in central India but fire frequency being highest in the east-northeast. Unutilized crop waste and MODIS cropland fires were predominant in the western Indo-Gangetic plain. However, the amounts of unutilized crop waste in the four regions were not strictly proportional to the fire counts. Fraction crop waste burned in fields ranged from 18 to 30% on an all-India basis and had a strong regional variation. Open burning contributes importantly (about 25%) to black carbon, organic matter, and carbon monoxide emissions, a smaller amount (9–13%) to PM2.5 (particulate mass in particles smaller than 2.5 micron diameter) and CO2 emissions, and negligibly to SO2 emissions (1%). However, it cannot explain a large “missing source” of BC or CO from India.

Identified baryon and meson distributions at large transverse momenta from Au plus Au collisions at root(S)(NN)=200 GeV

Abstract: Transverse momentum spectra of pi(+/-), p, and (p) over bar p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at root s(NN) = 200 GeV are presented. In central Au + Au collisions, both pi(+/-) and p((p) over bar) show significant suppression with respect to binary scaling at p(T) greater than or similar to 4 GeV/c. Protons and antiprotons are less suppressed than pi(+/-), in the range 1.5 less than or similar to p(T) less than or similar to 6 GeV/c. The pi(-)/pi(+) and (p) over bar /p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at p(T) greater than or similar to 5 GeV/c. The results at high p(T) indicate that the partonic sources of pi(+/-), p, and (p) over bar have similar energy loss when traversing the nuclear medium

SYNERGY: a new algorithm for property checking

Abstract: We consider the problem if a given program satisfies a specified safety property. Interesting programs have infinite state spaces, with inputs ranging over infinite domains, and for these programs the property checking problem is undecidable. Two broad approaches to property checking are testing and verification. Testing tries to find inputs and executions which demonstrate violations of the property. Verification tries to construct a formal proof which shows that all executions of the program satisfy the property. Testing works best when errors are easy to find, but it is often difficult to achieve sufficient coverage for correct programs. On the other hand, verification methods are most successful when proofs are easy to find, but they are often inefficient at discovering errors. We propose a new algorithm, Synergy, which combines testing and verification. Synergy unifies several ideas from the literature, including counterexample-guided model checking, directed testing, and partition refinement.This paper presents a description of the Synergy algorithm, its theoretical properties, a comparison with related algorithms, and a prototype implementation called Yogi.

Pseudo-dynamic approach of seismic active earth pressure behind retaining wall

Abstract: Knowledge of seismic active earth pressure behind rigid retaining wall is very important in the design of retaining wall in earthquake prone region. Commonly used Mononobe-Okabe method considers pseudo-static approach, which gives the linear distribution of seismic earth pressure in an approximate way. In this paper, the pseudo-dynamic method is used to compute the distribution of seismic active earth pressure on a rigid retaining wall supporting cohesionless backfill in more realistic manner by considering time and phase difference within the backfill. Planar rupture surface is considered in the analysis. Effects of a wide range of parameters like wall friction angle, soil friction angle, shear wave velocity, primary wave velocity and horizontal and vertical seismic accelerations on seismic active earth pressure have been studied. Results are provided in tabular and graphical non-dimensional form with a comparison to pseudo-static method to highlight the realistic non-linearity of seismic active earth pressures distribution.

Direct observation of dijets in central Au+Au collisions at sNN=200GeV

Abstract: The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum (p(T)) charged hadrons in Au+Au collisions at higher p(T) than reported previously. As p(T) is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter.

Minijet deformation and charge-independent angular correlations on momentum subspace (eta, phi) in Au-Au collisions at root S-NN=130 GeV

Abstract: Measurements of two-particle correlations on angular difference variables η1 − η2 (pseudorapidity) and φ1 − φ2 (azimuth) are presented for all primary charged hadrons with transverse momentum 0.15 ≤ p_t ≤ 2 GeV/c and |η| ≤ 1.3 from Au-Au collisions at √s_(NN) = 130 GeV. Large-amplitude correlations are observed over a broad range in relative angles where distinct structures appear on the same-side and away-side (i.e., relative azimuth less than π/2 or greater than π/2). The principal correlation structures include that associated with elliptic flow plus a strong, same-side peak. It is hypothesized that the latter results from correlated hadrons associated with semi-hard parton scattering in the early stage of the heavy-ion collision which produces a jet-like correlation peak at small relative angles. The width of the jet-like peak on η1 − η2 increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. The new methods of jet analysis introduced here provide access to scattered partons at low transverse momentum well below the kinematic range where perturbative quantum chromodynamics and standard fragmentation models are applicable.

Forward neutral pion production in p+p and d+Au collisions at root(S)(NN)=200 GeV

Abstract: Measurements of the production of forward pi(0) mesons from p+p and d+Au collisions at root s(NN) = 200 GeV are reported. The p+p yield generally agrees with next-to-leading order perturbative QCD calculations. The d+Au yield per binary collision is suppressed as eta increases, decreasing to similar to 30% of the p+p yield at =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward pi(0) with charged hadrons at eta approximate to 0 show a recoil peak in p+p that is suppressed in d+Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei.

Creating probabilistic databases from information extraction models

Abstract: Many real-life applications depend on databases automatically curated from unstructured sources through imperfect structure extraction tools. Such databases are best treated as imprecise representations of multiple extraction possibli-ties. State-of-the-art statistical models of extraction provide a sound probability distribution over extractions but are not easy to represent and query in a relational framework. In this paper we address the challenge of approximating such distributions as imprecise data models. In particular, we investigate a model that captures both row-level and column-level uncertainty and show that this representation provides significantly better approximation compared to models that use only row or only column level uncertainty. We present efficient algorithms for finding the best approximating parameters for such a model: our algorithm exploits the structure of the model to avoid enumerating the exponential number of extraction possibilities.

Dietary antioxidant curcumin inhibits microtubule assembly through tubulin binding

Abstract: Curcumin, a component of turmeric, has potent antitumor activity against several tumor types. However, its molecular target and mechanism of antiproliferative activity are not clear. Here, we identified curcumin as a novel antimicrotubule agent. We have examined the effects of curcumin on cellular microtubules and on reconstituted microtubules in vitro. Curcumin inhibited HeLa and MCF-7 cell proliferation in a concentration-dependent manner with IC(50) of 13.8 +/- 0.7 microm and 12 +/- 0.6 microm, respectively. At higher inhibitory concentrations (> 10 microm), curcumin induced significant depolymerization of interphase microtubules and mitotic spindle microtubules of HeLa and MCF-7 cells. However, at low inhibitory concentrations there were minimal effects on cellular microtubules. It disrupted microtubule assembly in vitro, reduced GTPase activity, and induced tubulin aggregation. Curcumin bound to tubulin at a single site with a dissociation constant of 2.4 +/- 0.4 microm and the binding of curcumin to tubulin induced conformational changes in tubulin. Colchicine and podophyllotoxin partly inhibited the binding of curcumin to tubulin, while vinblastine had no effect on the curcumin-tubulin interactions. The data together suggested that curcumin may inhibit cancer cells proliferation by perturbing microtubule assembly dynamics and may be used to develop efficacious curcumin analogues for cancer chemotherapy.

Optimization approach to real power tracing: an application to transmission fixed cost allocation

Abstract: Megawatt (MW) power flow tracing can assess the extent of network usage by the participants that can be effectively used for multiple objectives like transmission pricing, loss allocation, etc. MW power tracing, a post-facto analysis of power flow solution, is amenable to multiple solutions. This implies multiplicity of solution space of transmission cost and loss allocation problems. The conventional tracing methods enforce a "proportionate sharing rule" to calculate the shares. These shares are sensitive to quantity and distance as against the postage stamp method, which is immune to distance. Any of these methods will result in penalizing a set of constituents, which raises a fairness issue. This is evident from the experiences of developing countries like India. In this paper, a new paradigm is suggested that attempts to capture the best of the two methodologies by exploring multiplicity of the solution space of the tracing problem, within the given constraints. We show that the tracing problem can be formulated as a linear constrained optimization problem. We propose a tracing compliant modified postage stamp allocation method that computes a traceable solution that minimizes overall deviation from the postage stamp allocation. Results on actual data of central transmission utility of Western Regional Grid of India demonstrate the claims

Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at s=200GeV

Abstract: We report a measurement of the longitudinal double-spin asymmetry A(LL) and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at s=200 GeV. The cross section data cover transverse momenta 5 < p(T)< 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A(LL) data cover 5 < p(T)< 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.

Broken-symmetry density functional theory investigation on bis-nitronyl nitroxide diradicals: influence of length and aromaticity of couplers.

Abstract: A series of nitronyl nitroxide (NN) diradicals with linear conjugated couplers and another series with aromatic couplers have been investigated by the broken-symmetry (BS) DFT approach. The overlap integral between the magnetically active orbitals in the BS state has been explicitly computed and used for the evaluation of the magnetic exchange coupling constant (J). The calculated J values are in very good agreement with the observed values in the literature. The magnitude of J depends on the length of the coupler as well as the conformation of the radical units. The aromaticity of the spacer decreases the strength of the exchange coupling constant. The SOMO−SOMO energy splitting analysis, where SOMO stands for the singly occupied molecular orbital, and the calculation of electron paramagnetic resonance (EPR) parameters have also been carried out. The computed hyperfine coupling constants support the intramolecular magnetic interactions. The nature of magnetic exchange coupling constant can also be predic...

Numerical simulation of flow through microchannels with designed roughness

Abstract: A three-dimensional numerical simulation of flow through serpentine microchannels with designed roughness in form of obstructions placed along the channels walls is conducted here. CFD-ACE+ is used for the numerical simulations. The effect of the roughness height (surface roughness), geometry, Reynolds number on the friction factor is investigated. It is found that the friction factor increases in a nonlinear fashion with the increase in obstruction height. The friction factor is more for rectangular and triangular obstructions and it decreases as the obstruction geometry is changed to trapezoidal. It is observed that the obstruction geometry, i.e., aspect ratio plays an important role in prediction of friction factor in rough channels. It is also found that the pressure drop decreases with the increase in the roughness pitch. Hence, the roughness pitch is an important design parameter for microchannels.