Top-N Recommendation on Graphs

Recommender systems play an increasingly important role in online applications to help users find what they need or prefer. Collaborative filtering algorithms that generate predictions by analyzing the user-item rating matrix perform poorly when the matrix is sparse. To alleviate this problem, this paper proposes a simple recommendation algorithm that fully exploits the similarity information among users and items and intrinsic structural information of the user-item matrix. The proposed method constructs a new representation which preserves affinity and structure information in the user-item rating matrix and then performs recommendation task. To capture proximity information about users and items, two graphs are constructed. Manifold learning idea is used to constrain the new representation to be smooth on these graphs, so as to enforce users and item proximities. Our model is formulated as a convex optimization problem, for which we need to solve the well-known Sylvester equation only. We carry out extensive empirical evaluations on six benchmark datasets to show the effectiveness of this approach.Comment: CIKM 201

A statistical approach to persistent homology

Assume that a finite set of points is randomly sampled from a subspace of a metric space. Recent advances in computational topology have provided several approaches to recovering the geometric and topological properties of the underlying space. In this paper we take a statistical approach to this problem. We assume that the data is randomly sampled from an unknown probability distribution. We define two filtered complexes with which we can calculate the persistent homology of a probability distribution. Using statistical estimators for samples from certain families of distributions, we show that we can recover the persistent homology of the underlying distribution.Comment: 30 pages, 2 figures, minor changes, to appear in Homology, Homotopy and Application

Effect of physical and chemical doping on optical spectra of SWNT's

We discuss the use of far-infrared spectroscopy in the characterization of doped and functionalized nanotube derivatives

A novel oligoribonuclease of Escherichia coli. I. Isolation and properties

A new ribonuclease has been isolated from Escherichia coli. The enzyme is present in the 100,000 times g supernatant fraction and has been purified over 200-fold. Studies of the enzyme reveal that: 1. The enzyme shows a marked preference for oligoribonucleotides; indeed, the reaction rate is inversely proportional to the chain length of the substrate. The enzyme does not attack polynucleotides even at high concentrations of enzyme and has no detectable DNase activity. 2. The enzyme is stimulated strongly by Mn2+, less strongly by Mg2+, and not at all by Ca2+ and monovalent cations. 3. The enzyme is purified free of RNase I, RNase II, RNase III, polynucleotide phosphorylase, and other known ribonucleases of E. coli. The enzyme displays identical properties when isolated from mutants of E. coli that are deficient in the above ribonucleases. 4. The enzyme has a marked thermostability, a point of further distinction from RNase II

Dust composition and mass-loss return from the luminous blue variable R71 in the LMC

We present an analysis of mid-and far-infrared (IR) spectrum and spectral energy distribution (SED) of the LBV R71 in the LMC.This work aims to understand the overall contribution of high-mass LBVs to the total dust-mass budget of the interstellar medium (ISM) of the LMC and compare this with the contribution from low-mass asymptotic giant branch (AGB) stars. As a case study, we analyze the SED of R71. We compiled all the available photometric and spectroscopic observational fluxes from various telescopes for a wide wavelength range (0.36 -- 250\,$\mu$m). We determined the dust composition from the spectroscopic data, and derived the ejected dust mass, dust mass-loss rate, and other dust shell properties by modeling the SED of R71. We noted nine spectral features in the dust shell of R71 by analyzing Spitzer spectroscopic data. Among these, we identified three new crystalline silicate features. We computed our model spectrum by using 3D radiative transfer code MCMax. Our model calculation shows that dust is dominated by amorphous silicates, with some crystalline silicates, metallic iron, and a very tiny amount of polycyclic aromatic hydrocarbon (PAH) molecules. The presence of both silicates and PAHs indicates that the dust has a mixed chemistry. We derived a dust mass of 0.01 M$_\odot$, from which we arrive at a total ejected mass of $\approx$ 5 M$_\odot$. This implies a time-averaged dust mass-loss rate of 2.5$\times$10$^{-6}$ M$_\odot$\,yr$^{-1}$ with an explosion about 4000 years ago. We assume that the other five confirmed dusty LBVs in the LMC loose mass at a similar rate, and estimate the total contribution to the mass budget of the LMC to be $\approx$ 10$^{-5}$ M$_\odot$\,yr$^{-1}$, which is comparable to the contribution by all the AGB stars in the LMC. Based on our analysis on R71, we speculate that LBVs as a class may be an important dust source in the ISM of the LMC.Comment: 10 pages, 6 figures, 2 table

Development of an Advanced Engineering Polymer from the Modification of Nylon 66 by e-Beam Irradiation

When Nylon 66 was irradiated by an optimum dose of e-beam in presence of polyurethane as impact modifierin combination with triallyl isocyanurate as cross-linker, a superior performance was observed for the irradiatednylon 66. Significant improvement of properties, such as hardness, tensile strength, flexural modulus and impactstrength was obtained on radiation processing of nylon 66 by e-beam. More interestingly, percent water absorptionof such irradiated nylon 66 was reduced substantially. Improvement of mechanical properties and reduction of waterabsorption of irradiated nylon 66 were due to the cross-linking of the polymer system. Increase of cross-linkingwith dose of e-beam was verified by the increased gel content at higher doses. Irradiated nylon 66 showed betterdimensional stability than those achieved with pristine nylon 66. The increase in dimensional stability may beattributed to reduction in crystallinity with increasing dose of e-beam as revealed by DSC studies.Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 281-289, DOI:http://dx.doi.org/10.14429/dsj.64.732

Application of three-dimensional triple nested mesoscale model for assessing the transport and boundary layer variability over the Indian Ocean during INDOEX

A three-dimensional triple nested domain version of MM5 was applied for INDOEX region (40.12°N- 32.04°S; 32.10°E-117.90°E) to study the regional flow patterns and associated transport using backward and forward trajectories. The model was integrated for 48- h period starting 00 UTC 5 March 1999. From the simulations a mapping of the temporal and spatial variations in the marine boundary layer (MBL) heights were obtained. The boundary layer heights were verified using actual ship-based sounding from RV Ronald H. Brown and a good agreement was found. The model simulated significant variability in the MBL heights both spatially and temporally. During the daytime, the continental boundary layer was ~ 1500 m deep while over the ocean, the MBL was shallow (~ 300 m) near the coast, and it increased steadily towards the ITCZ where MBL heights of ~ 1000 m were encountered. During night there was a reversal with the continental boundary layer heights averaging less than 500 m while over the ocean, particularly over the ITCZ, the MBL heights were ~ 1000 to 1500 m. This variability in the MBL heights significantly affected the transport pattern over the INDOEX region. Both the backward and forward trajectories showed distinct characteristics depending on the source region (eastern or western coastal landmass, equator, or near ITCZ). Near the coast, there was an evidence for localized circulation in which the air parcels were trapped along the coast. For the open oceans (both near the ITCZ as well as equator) the air parcel trajectories continued over a significant distance. Results suggest that MM5 can be successfully applied for diagnostic studies related to INDOEX, and that the boundary layer heights and the variations in the air parcel transport need to be considered for interpreting the surface measurements

Hexokinase is necessary for glucose-mediated photosynthesis repression and lipid accumulation in a green alga.

Global primary production is driven largely by oxygenic photosynthesis, with algae as major contributors. The green alga Chromochloris zofingiensis reversibly switches off photosynthesis in the presence of glucose in the light and augments production of biofuel precursors (triacylglycerols) and the high-value antioxidant astaxanthin. Here we used forward genetics to reveal that this photosynthetic and metabolic switch is mediated by the glycolytic enzyme hexokinase (CzHXK1). In contrast to wild-type, glucose-treated hxk1 mutants do not shut off photosynthesis or accumulate astaxanthin, triacylglycerols, or cytoplasmic lipid droplets. We show that CzHXK1 is critical for the regulation of genes related to photosynthesis, ketocarotenoid synthesis and fatty acid biosynthesis. Sugars play fundamental regulatory roles in gene expression, physiology, metabolism, and growth in plants and animals, and we introduce a relatively simple, emerging model system to investigate conserved eukaryotic sugar sensing and signaling at the base of the green lineage

Numerical study of the role of land-air-sea interactions for the northeasterly monsoon circulations over Indian Ocean during INDOEX

One of the principal objectives of the Indian Ocean Experiment (INDOEX) was to study the aerosol transport from the Indian subcontinent to the pristine oceanic environment. The underlying hypothesis for INDOEX is that, during the northeasterly monsoon, the intruding aerosols and other anthropogenic pollutants can entrain into the Inter Tropical Convergence Zone (ITCZ) and the Equatorial Indian Ocean and finally into the clouds. The altered clouds influence the radiative transfer processes at the regional and possibly global scale. The driving mechanism for the regional transport was the boundary layer circulation. In this study, it was hypothesized that the circulation pattern, which affects the regional transport, was strongly influenced by the land-air-sea interactions. To test this, a zonally symmetric version of a primitive equation numerical weather prediction model, called the Advanced Regional Prediction System (ARPS), was used. A number of numerical experiments were performed for a 2-D domain ranging from 14°N to 16°S centered over 76°E. In the experiments, the influence of land-sea interaction (differential heating), topography (Western Ghats), and the thermal gradients (SST and land surface temperature) on the coastal circulations over Equatorial Indian Ocean were studied. Results indicated a strong land-air-sea interaction and feedback teleconnection between the local and large scale features. Interestingly, the model generated land influence to the order of 1000 km offshore in the simulation domain, consistent with different observations. Results suggest that the oceanic environment in the northeast monsoon over Arabian Sea and the Indian Ocean can display significant diurnal variability and heterogeneity due to topography and surface temperature gradients, and that the local features have interactive feedback on the large scale circulations and transport

Roles of atmospheric and land surface data in dynamic regional downscaling

In studies dealing with the impact of land use changes on atmospheric processes, a key methodological step is the validation of simulated current conditions. However, regions lacking detailed atmospheric and land use data provide limited information with which to accurately generate control simulations. In this situation, the difference between baseline control simulations and different land use change simulations can be quite different owing to the quality of the atmospheric and land use data sets. Using multiple simulations at the Monteverde cloud forest region of Costa Rica as an example, we show that when a regional climate model is used to study the effect of land use change, it can produce distinctly different results at regional scales, depending on the amount of data available to run the climate simulations. We show that for the specific case of land use change impact studies, the simulation results are very sensitive to the prescribed atmospheric information (e.g., lateral boundary conditions) compared to the land use (surface boundary) information