Preventing Atomicity Violations with Contracts

Software developers are expected to protect concurrent accesses to shared regions of memory with some mutual exclusion primitive that ensures atomicity properties to a sequence of program statements. This approach prevents data races but may fail to provide all necessary correctness properties.The composition of correlated atomic operations without further synchronization may cause atomicity violations. Atomic violations may be avoided by grouping the correlated atomic regions in a single larger atomic scope. Concurrent programs are particularly prone to atomicity violations when they use services provided by third party packages or modules, since the programmer may fail to identify which services are correlated. In this paper we propose to use contracts for concurrency, where the developer of a module writes a set of contract terms that specify which methods are correlated and must be executed in the same atomic scope. These contracts are then used to verify the correctness of the main program with respect to the usage of the module(s). If a contract is well defined and complete, and the main program respects it, then the program is safe from atomicity violations with respect to that module. We also propose a static analysis based methodology to verify contracts for concurrency that we applied to some real-world software packages. The bug we found in Tomcat 6.0 was immediately acknowledged and corrected by its development team

Model-independent constraints on the shape parameters of dilepton angular distributions

The coefficients determining the dilepton decay angular distribution of vector particles obey certain positivity constraints and a rotation-invariant identity. These relations are a direct consequence of the covariance properties of angular momentum eigenstates and are independent of the production mechanism. The Lam-Tung relation can be derived as a particular case, simply recognizing that the Drell-Yan dilepton is always produced transversely polarized with respect to one or more quantization axes. The dilepton angular distribution continues to be characterized by a frame-independent identity also when the Lam-Tung relation is violated. Moreover, the violation can be easily characterized by measuring a one-dimensional distribution depending on one shape coefficient.Comment: 7 page

It's about THYME: On the design and implementation of a time-aware reactive storage system for pervasive edge computing environments

This work was partially supported by Fundacao para a Ciencia e a Tecnologia (FCT-MCTES) through project DeDuCe (PTDC/CCI-COM/32166/2017), NOVA LINCS UIDB/04516/2020, and grant SFRH/BD/99486/2014; and by the European Union through project LightKone (grant agreement n. 732505).Nowadays, smart mobile devices generate huge amounts of data in all sorts of gatherings. Much of that data has localized and ephemeral interest, but can be of great use if shared among co-located devices. However, mobile devices often experience poor connectivity, leading to availability issues if application storage and logic are fully delegated to a remote cloud infrastructure. In turn, the edge computing paradigm pushes computations and storage beyond the data center, closer to end-user devices where data is generated and consumed, enabling the execution of certain components of edge-enabled systems directly and cooperatively on edge devices. In this article, we address the challenge of supporting reliable and efficient data storage and dissemination among co-located wireless mobile devices without resorting to centralized services or network infrastructures. We propose THYME, a novel time-aware reactive data storage system for pervasive edge computing environments, that exploits synergies between the storage substrate and the publish/subscribe paradigm. We present the design of THYME and elaborate a three-fold evaluation, through an analytical study, and both simulation and real world experimentations, characterizing the scenarios best suited for its use. The evaluation shows that THYME allows the notification and retrieval of relevant data with low overhead and latency, and also with low energy consumption, proving to be a practical solution in a variety of situations.publishersversionpublishe

Al-containing MCM-41 type materials prepared by different synthesis methods: hydrothermal stability and catalytic properties

Al-containing MCM-41 type materials were prepared by three different synthesis methods (aluminum grafting on the calcined MCM-41, pH adjustment during the crystallization period and crystallization in the presence of zeolite seeds). The samples were characterized by powder XRD, nitrogen adsorption, 27Al MAS NMR and FTIR with pyridine as probe molecule. All the samples exhibit a high hydrothermal stability at high temperature just with a minor structural degradation. N2 adsorption data obtained for the sample prepared from a gel containing zeolite seeds suggest a higher structural resistance to the hydrothermal treatment in comparison with the samples prepared by other methods. A different type of pyridine adsorbed, probably interacting simultaneously with a Brönsted and a Lewis acid site, is observed upon pyridine adsorption. This type of adsorption is stronger for the sample prepared in the presence of zeolite seeds and is not observed on Al-grafted MCM-41. 2 The catalytic activity towards the isomerization of α-pinene depends mainly on the number of Brönsted acid sites. The data obtained in this study strongly indicate that for this type of materials, the Lewis acid sites do not influence the selectivity for the isomerization products

Aluminum containing dendrimeric silica nanoparticles as promising metallocene catalyst supports for ethylene polymerization

Several aluminum containing dendrimeric silica nanospheres, DSAl materials, were prepared using different synthesis and post-synthetic procedures. These materials were used for the immobilization of Cp2ZrCl2 via direct impregnation. The support materials were rigorously characterized by TEM, N2 adsorption, FTIR (using pyridine as probe molecule) and SS-NMR to assess their morphological, textural and surface acidic properties. Supported catalysts were tested in ethylene homopolymerization using methylaluminoxane (MAO) as co-catalyst and scavenger. The relationships between the types and strength of acid sites, as well as the textural and morphological parameters of DSAl materials with the behavior of catalytic systems are explored in this work. The results analyzed in this paper confirm the importance that support surface acidity plays in the formation of the active species for ethylene polymerization and in its activity without neglecting the contribution of support textural properties as well.info:eu-repo/semantics/publishedVersio

Gas-phase conversion of glycerol to allyl alcohol over vanadium-supported zeolite beta

Vanadium oxide supported beta zeolite (Si/Al=25, 4% V) was used as catalyst for the one-pass gas-phase conversion of glycerol to allyl alcohol without any external reductant. The catalytic data strongly suggest a consecutive reactions path involving the dehydration to acrolein over the zeolite acid sites followed by a selective reduction through a hydrogen-transfer reaction. Acidity is expected to play a major role in what concerns the selectivity, as demonstrated by the catalytic results obtained by the impregnation of vanadium on a previously Cs-exchanged sample that achieved ca. 30% selectivity to allyl alcohol at ca. 20% glycerol conversion.info:eu-repo/semantics/publishedVersio

Avaliação do comportamento de ligações estruturais em madeira lamelada colada por meio de parafusos autoperfurantes

Neste artigo é avaliado o comportamento de ligações autoperfurantes em madeira glulam, utilizando a metodologia de cálculo preconizada pelo Eurocódigo 5 para o cálculo da força estimada e para a identificação dos modos de rotura. O programa experimental e os cálculos para o coeficiente de deslizamento foram definidos pela Norma Europeia EN 26891:1991. Os resultados experimentais obtidos são discutidos e comparados com a metodologia proposta por Tomasi. Os resultados indicam que o modo de rotura, neste tipo de ligação, é o modo f. Os valores de capacidade de carga obtidos pelo Eurocódigo 5, quando comparados com os experimentais, são conservadores e os obtidos pelo método proposto por Tomasi superestima.In this paper we evaluated the behavior of self-drilling wood glulam connections, using the calculation methodology recommended by the Eurocode 5 for calculating the estimated strength and the identification of failure modes. The experimental program and the calculations for the coefficient of slip defined by the European standard EN 26891:1991. The experimental results are discussed and compared with the methodology proposed by Tomasi. The results indicate that the mode of failure in this type of connection is the way f. The load capacity values obtained by the Eurocode 5 when compared with the experimental, are conservative and those obtained by the method proposed by Tomasi overestimates

Structural joints of cross laminated timber (CLT) with self-drilling

A madeira laminada colada cruzada (CLT) é composta por laminas com espessura máxima de 20 mm, colados transversalmente com um adesivo estrutural. Como as laminas são coladas com as fibras intercaladas, as características mecânicas ficam homogeneizadas. Neste artigo foi avaliado o comportamento de ligações estruturais de elementos de CLT e MLC, utilizando várias tipologias de parafusos autoperfurantes. Foi ensaiado um total de 20 corpos-de-prova de ligações divididos em 4 grupos de acordo com o tipo de parafuso usado: HBS 8x140, VGZ 7x140, SFS 8.2x190 e VGZ 7x180. A campanha experimental, a determinação da força máxima e o módulo de deslizamento obedeceram aos requisitos da EN-26891:1991. Os resultados experimentais são discutidos e comparados com a metodologia de cálculo preconizada pelo Eurocódigo 5, em particular, no que refere-se à previsão da força máxima, modo de ruptura e módulo de deslizamento. Os resultados são ainda confrontados com as conclusões de trabalhos semelhantes. Conclui-se que os sistemas de ligações dispostos com uma inclinação de penetração de 45º apresentam valores de resistência ao corte superiores aos dos sistemas de ligações com inclinação de penetração de 90º. Os deslocamentos relativos também são menores. Os módulos de deslizamentos calculados revelam-se conservadores quando comparados com os resultados experimentais, apresentado uma diferença de 22% a 30%. Quando comparamos os tipos de parafusos, constatou-se que é mais vantajoso utilizar parafusos VGZ a 45º do que SFS, pois, além de apresentarem uma relação muito próxima em termos de força máxima e deslocamento, os parafusos VGZ 7x180 são uma solução economicamente favorávelThe Cross Laminated Timber (CLT) is composed of lamina with a 20 mm maximum thickness transversally glued with a structural adhesive. Because these laminas are bonded with the fibers interspersed, the mechanical characteristics are homogenized. The aim of this paper was to evaluate the behavior CLT and GLULAM structural connections, using many types of self-drillings screws. It was tested a total of 20 test pieces divided into 4 groups according to the used screw: HBS 8x140, VGZ 7x140, SFS 8.2x190 and VGZ 7x180. The experimental program, the maximum strength calculations and slip modulus met the European Standard requirements EN 26891:1991. Experimental results are discussed and compared with the calculation methodology indicated by the Eurocode 5, in particular for the estimation of maximum strength, failure modes and slip modulus. The results are also confronted with findings of similar studies. We conclude that the connections system arranged at 45° inclination have shear values higher than those with connections system at 90° inclination. The relative displacements are also smaller. The slips modulus calculated revealed to be conservative when compared with experimental results, presenting 22% to 30% difference. When comparing the screw types, it was noted that it is more advantageous to use screws VGZ at 45 ° than screws SFS because they have a close relation in terms of maximum force and displacement. In addition, the screws VGZ 7x180 are an economically favorable solution

Determination of chi_c and chi_b polarizations from dilepton angular distributions in radiative decays

The angular distributions of the decay products in the successive decays chi_c (chi_b) to J/psi (Upsilon) gamma and J/psi (Upsilon) to l+l- are calculated as a function of the angular momentum composition of the decaying chi meson and of the multipole structure of the photon radiation, using a formalism independent of production mechanisms and polarization frames. The polarizations of the chi states produced in high energy collisions can be derived from the dilepton decay distributions of the daughter J/psi or Upsilon mesons, with a reduced dependence on the details of the photon reconstruction or simulation. Moreover, this method eliminates the dependence of the polarization measurement on the actual details of the multipole structure of the radiative transition. Problematic points in previous calculations of the chi_c decay angular distributions are identified and clarified.Comment: Submitted to Phys Rev