An algebraic semantics for MOF

In model-driven development, software artifacts are represented as models in order to improve productivity, quality, and cost effectiveness. In this area, the meta-object facility (MOF) standard plays a crucial role as a generic framework within which a wide range of modeling languages can be defined. The MOF standard aims at offering a good basis for model-driven development, providing some of the building concepts that are needed: what is a model, what is a metamodel, what is reflection in the MOF framework, and so on. However, most of these concepts are not yet fully formally defined in the current MOF standard. In this paper we define a reflective, algebraic, executable framework for precise metamodeling based on membership equational logic (mel) that supports the MOF standard. Our framework provides a formal semantics of the following notions: metamodel, model, and conformance of a model to its metamodel. Furthermore, by using the Maude language, which directly supports mel specifications, this formal semantics is executable. This executable semantics has been integrated within the Eclipse modeling framework as a plugin tool called MOMENT2. In this way, formal analyses, such as semantic consistency checks, model checking of invariants and LTL model checking, become available within Eclipse to provide formal support for model-driven development processes.     

An Algebraic Baseline for Automatic Transformations in MDA

Software evolution can be supported at two levels: models and programs. The model-based software development approach allows the application of a more abstract process of software evolution, in accordance with the OMG's MDA initiative. We describe a framework for model management, called MOMENT, that supports automatic formal model transformations in MDA. Our model transformation approach is based on the algebraic specification of models and benefits from mature term rewriting system technology to perform model transformation using rewriting logic. In this paper, we present how we apply this formal transformation mechanism between platformindependent models, such as UML models and relational schemas. Our approach enhances the integration between formal environments and industrial technologies such as .NET technology, and exploits the best features of both.     

Diffusion Monte Carlo for Excited States: Phonons and Rotons in Superfluid 4He

We have applied the fixed-node and the released-node Monte Carlo techniques to calculate the phonon-roton excitation spectrum ((q)) of superfluid ⁴ He. An excellent agreement with the experimental spectrum is achieved both at the equilibrium and near the freezing densities. The strength of the single excitation peak Z(q) in the dynamic structure function S(q, ) shows an overall agreement with experimental data. New results for (q) and Z(q) at a negative pressure close to the spinodal point are also reported.     

Binding energy of one4He impurity in liquid3He

A variational microscopic calculation of the binding energy of a⁴He impurity (_i) in homogeneous liquid³He at zero temperature is presented. Starting on an extended Jastrow-Slater wave function including three-body correlations, the expression for _I is derived and the appropriated FHNC formalism for this problem is reviewed. In the framework of the Average Correlation Approximation (ACA), it is proved that it is possible to obtain the chemical potential of the impurity only from liquid³He magnitudes with a good accuracy. Our results are consistent with both a recent experimental determination of _I at zero pressure and the non-solubility of⁴He in³He. However, numerical uncertainties preclude a firm conclusion about the latter property.     

A cross-technology benchmark for incremental graph queries

Software and Systems Modeling - To cope with the increased complexity of systems, models are used to capture what is considered the essence of a system. Such models are typically represented as a...     

Enhanced adaptive RTCP-based Inter-Destination Multimedia Synchronization approach for distributed applications

Newer social multimedia applications, such as Social TV or networked multi-player games, enable independent groups (or clusters) of users to interact among themselves and share services within the context of simultaneous media content consumption. In such scenarios, concurrently synchronized playout points must be ensured so as not to degrade the user experience on such interaction. We refer to this process as Inter-Destination Multimedia Synchronization (IDMS). This paper presents the design, implementation and evaluation of an evolved version of an RTCP-based IDMS approach, including an Adaptive Media Playout (AMP) scheme that aims to dynamically and smoothly adjust the playout timing of each one of the geographically distributed consumers in a specific cluster if an allowable asynchrony threshold between their playout states is exceeded. For that purpose, we previously had also to develop a full implementation of RTP/RTCP protocols for NS-2, in which we included the IDMS approach as an optional functionality. Simulation results prove the feasibility of such IDMS and AMP proposals, by adopting several dynamic master reference selection policies, to maintain an overall synchronization status (within allowable limits) in each cluster of participants, while minimizing the occurrence of long-term playout discontinuities (such as skips/pauses) which are subjectively more annoying and less tolerable to users than small variations in the media playout rate.     

Path Integral Monte Carlo Calculation of Momentum Distribution in Solid 4He

We perform calculations of the momentum distribution n(k) in solid ⁴He by means of path integral Monte Carlo methods. We see that, in perfect crystals, n(k) does not depend on temperature T and that is different from the classical Gaussian shape of the Maxwell-Boltzmann distribution, even though these discrepancies decrease when the density of the system increases. In crystals presenting vacancies, we see that for T??0.75 K, n(k) presents the same behavior as in the perfect crystal, but, at lower T, it presents a peak when k??0.     

Development of natural fiber‐reinforced plastics (NFRP) based on biobased polyethylene and waste fibers from Posidonia oceanica seaweed

In the present study the valorization of wastes from Posidonia oceanica (PO) has been carried out in order to obtain a fully biobased composite material in combination with a biobased polyethylene obtained from sugar cane as matrix. Morphological analysis by scanning electron microscopy (SEM) of the fractured surfaces from impact tests has revealed a homogenous distribution of particles of PO, as a consequence, good balanced properties have been obtained for composites with PO contents in the 5–40 wt%. Thermal properties of composites have been studied through differential scanning calorimetry (DSC) and thermogravymetric analysis (TGA); the obtained results show an improvement on the thermal degradation. With regard to thermomechanical properties, dynamic mechanical analysis (DMA) results have shown a much enhanced storage modulus (G′) as the Posidonia oceanica content increases. Tensile tests have shown a remarkable increase in stiffness with tensile modulus values about 60% higher for composites with 40 wt% with regard to unfilled material. In a similar way, the flexural modulus is more than twice with regard the unloaded polyethylene. Shore D hardness confirms this improvement on mechanical properties and Charpy impact test shows values very similar to sample without PO, so that the intrinsic high impact energy absorption of HDPE is maintained in HDPE‐PO composites. The water uptake test determines that the water absorption percent does not exceed 8%, which is relatively low for a high immersion time (5 months), which guarantees a dimensional stability in lifetime for these composites. POLYM. COMPOS., 36:1378–1385, 2015. © 2014 Society of Plastics Engineers     

Cloning and characterization of a gene from Escherichia coli encoding a transketolase-like enzyme that catalyzes the synthesis of D-1-deoxyxylulose 5-phosphate, a common precursor for isoprenoid, thiamin, and pyridoxol biosynthesis

For many years it was accepted that isopentenyl diphosphate, the common precursor of all isoprenoids, was synthesized through the well known acetate/mevalonate pathway. However, recent studies have shown that some bacteria, including Escherichia coli, use a mevalonate-independent pathway for the synthesis of isopentenyl diphosphate. The occurrence of this alternative pathway has also been reported in green algae and higher plants. The first reaction of this pathway consists of the condensation of (hydroxyethyl)thiamin derived from pyruvate with the C1 aldehyde group of D-glyceraldehyde 3-phosphate to yield D-1-deoxyxylulose 5-phosphate. In E. coli, D-1-deoxyxylulose 5-phosphate is also a precursor for the biosynthesis of thiamin and pyridoxol. Here we report the molecular cloning and characterization of a gene from E. coli, designated dxs, that encodes D-1-deoxyxylulose-5-phosphate synthase. The dxs gene was identified as part of an operon that also contains ispA, the gene that encodes farnesyl-diphosphate synthase. D-1-Deoxyxylulose-5-phosphate synthase belongs to a family of transketolase-like proteins that are highly conserved in evolution.