Rounding Algorithms for a Geometric Embedding of Minimum Multiway Cut

The multiway-cut problem is, given a weighted graph and k >= 2 terminal nodes, to find a minimum-weight set of edges whose removal separates all the terminals. The problem is NP-hard, and even NP-hard to approximate within 1+delta for some small delta > 0. Calinescu, Karloff, and Rabani (1998) gave an algorithm with performance guarantee 3/2-1/k, based on a geometric relaxation of the problem. In this paper, we give improved randomized rounding schemes for their relaxation, yielding a 12/11-approximation algorithm for k=3 and a 1.3438-approximation algorithm in general. Our approach hinges on the observation that the problem of designing a randomized rounding scheme for a geometric relaxation is itself a linear programming problem. The paper explores computational solutions to this problem, and gives a proof that for a general class of geometric relaxations, there are always randomized rounding schemes that match the integrality gap.Comment: Conference version in ACM Symposium on Theory of Computing (1999). To appear in Mathematics of Operations Researc

A Compilation of Global Bio-Optical in Situ Data for Ocean-Colour Satellite Applications

A compiled set of in situ data is important to evaluate the quality of ocean-colour satellite-data records. Here we describe the data compiled for the validation of the ocean-colour products from the ESA Ocean Colour Climate Change Initiative (OC-CCI). The data were acquired from several sources (MOBY, BOUSSOLE, AERONET-OC, SeaBASS, NOMAD, MERMAID, AMT, ICES, HOT, GePandCO), span between 1997 and 2012, and have a global distribution. Observations of the following variables were compiled: spectral remote-sensing reflectances, concentrations of chlorophyll α, spectral inherent optical properties and spectral diffuse attenuation coefficients. The data were from multi-project archives acquired via the open internet services or from individual projects, acquired directly from data providers. Methodologies were implemented for homogenisation, quality control and merging of all data. No changes were made to the original data, other than averaging of observations that were close in time and space, elimination of some points after quality control and conversion to a standard format. The final result is a merged table designed for validation of satellite-derived ocean-colour products and available in text format. Metadata of each in situ measurement (original source, cruise or experiment, principal investigator) were preserved throughout the work and made available in the final table. Using all the data in a validation exercise increases the number of matchups and enhances the representativeness of different marine regimes. By making available the metadata, it is also possible to analyse each set of data separately. The compiled data are available at doi:10.1594/PANGAEA.854832 (Valente et al., 2015)

Mechanical and abrasion wear properties of hydrogenated nitrile butadiene rubber of identical hardness filled with carbon black and silica

The mechanical and abrasive wear properties of a hydrogenated nitrile butadiene rubber filled with 35 part per hundred rubber carbon black or silica with and without silane surface treatment (SI-si and SI, respectively), were investigated. Specimens were subjected to dynamic mechanical thermal analysis (also to study the Payne effect), mechanical (hardness, tensile modulus, ultimate tensile strength and strain, Mullins effect and tear strength), and fracture mechanical (J-integral) tests. The abrasive coefficient of friction and wear (specific wear rate, Ws) of the hydrogenated nitrile butadiene rubbers of identical hardness were measured against abrasive papers of different grit sizes (P600-P5000).The worn surface of the HNBR systems was inspected in scanning electron microscopy and the typical wear mechanisms deduced and discussed. Coefficient of friction did not change with the grit size by contrast to Ws which was markedly reduced with decreasing surface roughness of the abrasive paper. Ws of the compounds did not vary when wearing against P3000 and P5000 abrasive papers, representing mean surface roughness values of 7 and 5  μm, respectively. This was attributed to a change from abrasion to sliding type wear. hydrogenated nitrile butadiene rubber- carbon black outperformed the silica filled versions with respect to Ws though exhibited the highest coefficient of friction. No definite correlation could be found between the abrasive wear and the studied dynamic mechanical thermal analysis and (fracture) mechanical properties. </jats:p

Satellite sensor requirements for monitoring essential biodiversity variables of coastal ecosystems

The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satellite‐based sensors can repeatedly record the visible and near‐infrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100‐m pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the short‐wave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14‐bit digitization, absolute radiometric calibration temporal resolution of hours to days. We refer to these combined specifications as H4 imaging. Enabling H4 imaging is vital for the conservation and management of global biodiversity and ecosystem services, including food provisioning and water security. An agile satellite in a 3‐d repeat low‐Earth orbit could sample 30‐km swath images of several hundred coastal habitats daily. Nine H4 satellites would provide weekly coverage of global coastal zones. Such satellite constellations are now feasible and are used in various applications

"Ultralow" sliding wear polytetrafluoro ethylene nanocomposites with functionalized graphene

The dry friction and sliding wear behavior of sintered polytetrafluoro ethylene containing various amounts of functionalized graphene were studied in this work. Graphene was incorporated in 0, 0.25, 0.75, 1, 2 and 4 vol.%, respectively. Sliding wear tests were performed in ring(metal)-on-plate(polytetrafluoro ethylene) test rig under ambient temperature setting 1 m/s sliding speed and 1 MPa contact pressure. The dynamic coefficient of friction and specific wear rate (ws) data were determined. Very low coefficient of frictions (0.12–0.14) were measured for polytetrafluoro ethylene containing 2 or 4 vol.% graphene, which was attributed to the formation of a tribofilm on the countersurface. Specific wear rate went through a maximum (peaked at doubling that of the unmodified polytetrafluoro ethylene at about 0.75 vol.% graphene) as a function of graphene content. Ultralow wear rate data in the range of 10−6 mm3/(N.m) were measured for the polytetrafluoro ethylene nanocomposites with 2 and 4 vol.% graphene. This was reasoned by the formation of a robust tribofilm, the development of which was followed by scanning electron microscopy by inspecting the worn surface of polytetrafluoro ethylene nanocomposites and that of the steel ring of the ring(metal)-on-plate(polytetrafluoro ethylene) test rig. Fourier transform infrared spectroscopic results confirmed the formation of carboxyl groups in the tribofilm. They were supposed to react with the functional groups of graphene and to create complexes with the metal countersurface ensuring the tribofilm with high adhesion and cohesion strengths. </jats:p

Variability of the Sea Surface Temperature Around Cuba

Space and time variability of sea surface temperature in oceanic and shelf waters of Cuba were examined using the Advanced Very High Resolution Radiometer (AVHRR) sensors flown on satellites operated by the National Oceanic and Atmospheric Administration from February 1995 to August 2001. Statistics at 90 specific time series stations around Cuba were extracted from the AVHRR images to characterize shelf and oceanic waters using the long-term overall mean, minimum, and maximum sea surface temperature (SST) values. Shelf and oceanic waters reached SST maxima (29.5-30.5°C) in August. Waters off southern and western Cuba reached slightly higher temperatures than those off the northeast in the Old Bahamas Channel; waters along the northern coast of Cuba were about 1°C cooler on average than those along the southern coast. Oceanic waters around Cuba experienced minima (24.5-25.5°C) in February-March, about a month after shelf waters. Only minor regional differences in maximum temperatures were observed in shelf areas. Shelf regions around Cuba have lower annual average SSTs than adjacent oceanic waters, and the range of monthly average SST of shelf waters exceeded that of oceanic waters by 3°C, with the largest differences observed during winter. Shelf waters also cooled down at \u3e0.04°C/d, or twice as fast as oceanic waters (0.02°C/d) by action of sensible heat and evaporative losses. Shelf waters also warmed up at rates exceeding 0.06°C/d, which was two to three times faster than oceanic waters (0.02-0.03°C/d). SST anomalies were slightly positive between February 1995 and February 1999 and slightly negative from October 1999 to August 2001. In summer of 1995, 1997, and 1998, coral bleaching was observed in northern and southern reefs of Cuba. Summer anomalies \u3e1°C occurred in May 1995 and August 1997, which may have contributed to the coral bleaching

Physical environments of the Caribbean Sea

The Caribbean Sea encompasses a vast range of physical environmental conditions that have a profound influence on the organisms that live there. Here we utilize a range of satellite and in situ products to undertake a region-wide categorization of the physical environments of the Caribbean Sea (PECS). The classification approach is hierarchical and focuses on physical constraints that drive many aspects of coastal ecology, including species distributions, ecosystem function, and disturbance. The first level represents physicochemical properties including metrics of satellite sea surface temperature, water clarity, and in situ salinity. The second level considers mechanical disturbance and includes both chronic disturbance from wind-driven wave exposure and acute disturbance from hurricanes. The maps have a spatial resolution of 1 km. An unsupervised neural network classification produced 16 physicochemical provinces that can be categorized into six broad groups: (1) low water clarity and low salinity and average temperatures; (2) low water clarity but average salinity and temperature, broadly distributed in the basin; (3) low salinity but average water clarity and temperature; (4) upwelling; (5) high latitude; and (6) offshore waters of the inner Caribbean. Additional mechanical disturbance layers impose additional pattern that operates over different spatial scales. Because physical environments underpin so much of coastal ecosystem structure and function, we anticipate that the PECS classification, which will be freely distributed as geographic information system layers, will facilitate comparative analyses and inform the stratification of studies across environmental provinces in the Caribbean basin

Imaging Granulomatous Lesions with Optical Coherence Tomography

www.karger.com/cde This is an Open Access article licensed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (www.karger.com/OA-license), applicable to the online version of the article only. Distribution for non-commercial purposes only