Expression templates implementation of continuous and discontinuous Galerkin methods

Efficiency and flexibility are often mutually exclusive features in a code. This still prompts a large part of the Scientific Computing community to use traditional procedural languages. In the last years, however, new programming techniques have been introduced allowing for a high level of abstraction without loss of performance. In this paper we present an application of the Expression Templates technique introduced in (Veldhuizen in Expression templates. C++ Report magazine, vol 7, pp 26–31, 1995) to the assembly step of a finite element computation. We show that a suitable implementation, such that the compiler has the role of parsing abstract operations, allows for user-friendliness. Moreover, it gains in performance with respect to more traditional techniques for achieving this kind of abstraction. Both the cases of conforming and discontinuous Galerkin finite element discretization are considered. The proposed implementation is finally applied to a number of problems entailing different kind of complications.     

Near real-time parallel processing and advanced data management of SAR images in grid environments

In this paper, we describe the process of parallelizing an existing, production level, sequential Synthetic Aperture Radar (SAR) processor based on the Range-Doppler algorithmic approach. We show how, taking into account the constraints imposed by the software architecture and related software engineering costs, it is still possible with a moderate programming effort to parallelize the software and present an message-passing interface (MPI) implementation whose speedup is about 8 on 9 processors, achieving near real-time processing of raw SAR data even on a moderately aged parallel platform. Moreover, we discuss a hybrid two-level parallelization approach that involves the use of both MPI and OpenMP. We also present GridStore, a novel data grid service to manage raw, focused and post-processed SAR data in a grid environment. Indeed, another aim of this work is to show how the processed data can be made available in a grid environment to a wide scientific community, through the adoption of a data grid service providing both metadata and data management functionalities. In this way, along with near real-time processing of SAR images, we provide a data grid-oriented system for data storing, publishing, management, etc.

Interactive multi-user video retrieval systems

In this paper we present two interactive multi-user systems for video search and browsing. The first is composed by web applications which allows multiuser interaction in a distributed environment; such applications are based on the Rich Internet Application paradigm, designed to obtain the levels of responsiveness and interactivity typical of a desktop application. The second system implements a multi-user collaborative application within a single location, exploiting multi-touch devices. Both systems use the same backend, based on a service oriented architecture (SOA) that provides services for automatic and manual annotation, and an ontology-based video search and browsing engine. Ontology-based browsing let users to inspect the content of video collections; user queries are expanded through ontology reasoning. User-centered field trials of the systems, conducted to assess the user experience and satisfaction, have shown that the approach followed to design these interfaces is extremely appreciated by professional archivists and people working on multimedia.     

Comparison of algorithms that detect drug side effects using electronic healthcare databases

The electronic healthcare databases are starting to become more readily available and are thought to have excellent potential for generating adverse drug reaction signals. The Health Improvement Network (THIN) database is an electronic healthcare database containing medical information on over 11 million patients that has excellent potential for detecting ADRs. In this paper we apply four existing electronic healthcare database signal detecting algorithms (MUTARA, HUNT, Temporal Pattern Discovery and modified ROR) on the THIN database for a selection of drugs from six chosen drug families. This is the first comparison of ADR signalling algorithms that includes MUTARA and HUNT and enabled us to set a benchmark for the adverse drug reaction signalling ability of the THIN database. The drugs were selectively chosen to enable a comparison with previous work and for variety. It was found that no algorithm was generally superior and the algorithms’ natural thresholds act at variable stringencies. Furthermore, none of the algorithms perform well at detecting rare ADRs.     

<Emphasis Type="SmallCaps">COVER</Emphasis>: a linguistic resource combining common sense and lexicographic information

Lexical resources are fundamental to tackle many tasks that are central to present and prospective research in Text Mining, Information Retrieval, and connected to Natural Language Processing. In this article we introduce COVER, a novel lexical resource, along with COVERAGE, the algorithm devised to build it. In order to describe concepts, COVER proposes a compact vectorial representation that combines the lexicographic precision characterizing BabelNet and the rich common-sense knowledge featuring ConceptNet. We propose COVER as a reliable and mature resource, that has been employed in as diverse tasks as conceptual categorization, keywords extraction, and conceptual similarity. The experimental assessment is performed on the last task: we report and discuss the obtained results, pointing out future improvements. We conclude that COVER can be directly exploited to build applications, and coupled with existing resources, as well.     

In situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst

The Journal of Supercomputing - In situ visualization on high-performance computing systems allows us to analyze simulation results that would otherwise be impossible, given the size of the...     

Carrier Tunneling from Charge Transfer States in Organic Photovoltaic Cells

Charge transfer (CT) states play a key role in the functioning of organic solar cells; however, understanding the mechanism by which CT states dissociate efficiently into free charges remain a conceptual challenge. Here, the electric field dependent dynamics of charge generation in planar cyanine/fullerene photovoltaic cells is probed over a wide temperature range using time-resolved Stark effect experiments, transient absorption, and photocurrent measurements. Results indicate that dissociation of thermalized CT states is the rate-limiting step for all temperatures. The dissociation rate strongly depends on the field, but is temperature independent. The results also suggest that the yield of generated charges is temperature independent. Model electrostatic calculations illustrate that specific orientations of the cyanine crystal relative to C₆₀ create a repulsive potential for an electron near the interface that is largely due to the quadrupole moment of the unit cell. In combination with the electron-hole coulomb attraction and the electric field-induced barrier lowering, a high-energy potential barrier forms with a narrow width of a few nanometers. It is proposed that charge separation occurs via a field-dependent electron tunneling mechanism through that barrier, which is temperature independent. The results support a thus far overlooked pathway for CT state dissociation via carrier tunneling.     

Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene

Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.     

Structure of Se–Te glasses by Raman spectroscopy and DFT modeling

For the first time, the Raman spectra of bulk Se_xTe_1‐x glasses, 0.5 ≤ x ≤ 1.0, have been measured over the entire glass‐forming range. The spectra exhibit three broad spectral features between 150 and 300 cm^?1, attributed to Te–Te, Se–Te, and Se–Se stretching modes according to DFT simulations. The observed weak chemical ordering in the glasses is discussed on the basis of heteropolar and homopolar bond fractions derived from integrated intensity of the Raman modes and DFT cross‐sections. The underlying structural model of the glasses suggests a random distribution of the Se–Se, Se–Te, and Te–Te chemical bonds with some preference for heteropolar bonding within Se–Te–Se structural units.     

Larval Diet Affects Male Pheromone Blend in a Laboratory Strain of the Medfly, <Emphasis Type="Italic">Ceratitis capitata</Emphasis> (Diptera: Tephritidae)

The Mediterranean fruit fly (medfly) Ceratitis capitata is a polyphagous pest of fruits and crops with a worldwide distribution. Its ability to use different larval hosts may have multiple effects, including impacts on adult reproductive biology. The male sex pheromone, which plays a key role in attracting both other males to lekking arenas and females for mating, is a mixture of chemical compounds including esters, acids, alkanes and terpenes known to differ between laboratory strains and wild-type populations. The relationship between larval diet and adult pheromone composition remains unexplored. Here, we investigated the effect of larval diet, including laboratory media and fresh fruits, on the composition of the male pheromone mixture. Using Headspace Solid Phase Microextraction we collected the pheromone emitted by males reared as larvae on different substrates and found both qualitative and quantitative differences. A number of alkanes appeared to be typical of the pheromone of males reared on wheat bran-based larval medium, and these may be cuticular hydrocarbons involved in chemical communication. We also detected differences in pheromone composition related to adult male age, suggesting that variations in hormonal levels and/or adult diet could also play a role in determining the chemical profile emitted. Our findings highlight the plasticity of dietary responses of C. capitata, which may be important in determining the interactions of this pest with the environment and with conspecifics. These results also have applied relevance to increase the mating competitiveness of mass-reared C. capitata used in Sterile Insect Technique programs.