Structure and phase behavior of colloidal dumbbells with tunable attractive interactions

We investigate thermodynamic and structural properties of colloidal dumbbells in the framework provided by the Reference Interaction Site Model (RISM) theory of molecular fluids and Monte Carlo simulations. We consider two different models: in the first one we set identical square-well attractions on the two tangent spheres composing the molecule (SW-SW model); in the second scheme, one of square-well interactions is switched off (HS-SW model). Appreciable differences emerge between the physical properties of the two models. Specifically, the $k \to 0$ behavior of SW-SW structure factors $S(k)$ points to the presence of a gas-liquid coexistence, as confirmed by subsequent fluid phase equilibria calculations. Conversely, the HS-SW $S(k)$ develops a low-$k$ peak, signaling the presence of aggregates; such a process destabilizes the gas-liquid phase separation, promoting at low temperatures the formation of a cluster phase, whose structure depends on the system density. We further investigate such differences by studying the phase behavior of a series of intermediate models, obtained from the original SW-SW by progressively reducing the depth of one square-well interaction. RISM structural predictions positively reproduce the simulation data, including the rise of $S(k \to 0$) in the SW-SW model and the low-$k$ peak in the HS-SW structure factor. As for the phase behavior, RISM agrees with Monte Carlo simulations in predicting a gas-liquid coexistence for the SW-SW model (though the critical parameters appears overestimated by the theory) and its progressive disappearance moving toward the HS-SW model.Comment: 12 pages, 13 figures, 1 table, 78 reference

Magnetized electron-positron plasmas

Electrostatic oscillations in cold electron-positron plasmas can be coupled to a propagating electromagnetic mode if the background magnetic field is inhomogeneous. Previous work considered this coupling in the quasi-linear regime, successfully simulating the electromagnetic mode. Here we present a stability analysis of the non-linear problem, perturbed from dynamical equilibrium, in order to gain some insight into the modes present in the system.Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.145-14

Labels for non-individuals

Quasi-set theory is a first order theory without identity, which allows us to cope with non-individuals in a sense. A weaker equivalence relation called ``indistinguishability'' is an extension of identity in the sense that if $x$ is identical to $y$ then $x$ and $y$ are indistinguishable, although the reciprocal is not always valid. The interesting point is that quasi-set theory provides us a useful mathematical background for dealing with collections of indistinguishable elementary quantum particles. In the present paper, however, we show that even in quasi-set theory it is possible to label objects that are considered as non-individuals. We intend to prove that individuality has nothing to do with any labelling process at all, as suggested by some authors. We discuss the physical interpretation of our results.Comment: 11 pages, no figure

A systematic review of life cycle sustainability assessment: current state, methodological challenges, and implementation issues

The life cycle sustainability assessment (LCSA) is a tool to assess sustainability from a life cycle perspective, which has been receiving increased attention over the years. This work presents a systematic review of the current application of LCSA, presenting the foundations, main methods, current operationalization state, and major challenges to its broad implementation. The review protocol considered the search of keywords in Scopus and Web of Science databases. The search has considered the literature published or in the press until December 2018, resulting in the selection of 144 articles written in English. Of those, 71 articles operationalize LCSA in real case studies, while the remaining consist of review, viewpoint, and methodological development articles. This review demonstrates that the use of LCSA has been increasing in recent years. Today, the most applied approach is to consider LCSA as the sum of life cycle assessment, life cycle costing, and social life cycle assessment because it is built on the methodologies that already exist and are under continuous development. However, the lack of harmonization of the methodology is a central challenge to its operationalization. Therefore, LCSA still requires further improvement in, among others, definition of coherent system boundaries, the development of robust databases to allow the assessment of economic and social perspectives, definition of impact categories that allow comparability between studies, development of impact assessment methods, development of methods to carry out uncertainty analysis, and communication strategies. Besides, further case studies should be developed to support the improvement of the methodology and a better understanding of the interaction of the environmental, economic, and social aspects.publishe

Levantamento de nematóides fitoparasitas associados a pomares de videira em declínio da serra gaúcha.

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Collective secondary cremation in a pit grave: a unique funerary context in Portuguese Chalcolithic burial practices

Perdigões is a large site with a set of ditched enclosures located at Reguengos de Monsaraz, Alentejo, South Portugal. Recently at the central area of this site burnt human remains were found in a pit (#16). This structure had inside human remains, animal bones (namely pig, sheep or goat, cattle, dog, deer and rabbit), shards, ivory idols and arrowheads. All have been subjected to fire and later deposited in that pit, resulting in a secondary disposal of human bones. The recovered fragmented human bones (4845.18 g) correspond to a minimal number of 9 individuals: 6 adults and 3 sub-adults. The aim of this work is to document and interpret this funerary context based on the study of the recovered human remains. For that purpose, observations of all alterations due to fire, such as colour change and type of bone distortion, as well as anthropological data were collected. The data obtained suggest that these human remains were probably intentionally cremated, carefully collected and finally deposited in this pit. The cremation was conducted on probably complete corpses, some of them still fairly fresh and fleshed, as some bones presented thumbnail fractures. The collective cremation of the pit 16 represents an unprecedented funerary context for Portuguese, and Iberian Peninsula, Chalcolithic burial practices. Moreover, it is an example of the increasing diversity of mortuary practices of Chalcolithic human populations described in present Portuguese territory, as well as, in the Iberian Peninsula.O recinto dos Perdigões, localizado em Reguengos de Monsaraz, no sul de Portugal, tem revelado desde 1997 diversos contextos funerários do Neolítico final e Calcolítico. Na sua área central foi identificado uma fossa (16), contendo restos ósseos humanos, cerâmica e fauna diversa. A respectiva escavação veio revelar tratar-se de um depósito secundário correspondendo ao despejo de restos de ossos humanos cremados, restos faunísticos (porco, ovelha ou cabra, vaca, cão, cervo e coelho) e cerca de meia centena de pontas de seta e fragmentos de ídolos em marfim, material que se apresentava também intensamente queimado. Neste trabalho serão apresentados os resultados do estudo laboratorial dos restos ósseos humanos. Este revelou que todo o espólio ósseo humano (4845.18 gr) esteve sujeito à acção de fogo, de diversa intensidade. Predominam os vestígios ósseos sujeitos a altas temperaturas (> 900°), revelado pelas alterações registadas em termos de cor, tipo de fracturas e deformações. Este espólio terá pertencido a um mínimo de 9 indivíduos, 3 dos quais faleceram antes de atingir a idade adulta. A fossa 16, um contexto secundário e colectivo de cremação representa um contexto funerário único do Calcolítico Português, bem como de toda a Península Ibérica. Constitui mais um exemplo da crescente diversidade de práticas funerárias descritas para esta região da Europa

Formation energy and interaction of point defects in two-dimensional colloidal crystals

The manipulation of individual colloidal particles using optical tweezers has allowed vacancies to be created in two-dimensional (2d) colloidal crystals, with unprecedented possibility of real-time monitoring the dynamics of such defects (Nature {\bf 413}, 147 (2001)). In this Letter, we employ molecular dynamics (MD) simulations to calculate the formation energy of single defects and the binding energy between pairs of defects in a 2d colloidal crystal. In the light of our results, experimental observations of vacancies could be explained and then compared to simulation results for the interstitial defects. We see a remarkable similarity between our results for a 2d colloidal crystal and the 2d Wigner crystal (Phys. Rev. Lett. {\bf 86}, 492 (2001)). The results show that the formation energy to create a single interstitial is $12$ lower than that of the vacancy. Because the pair binding energies of the defects are strongly attractive for short distances, the ground state should correspond to bound pairs with the interstitial bound pairs being the most probable.Comment: 5 pages, 2 figure

Experimental tests for seismic assessment and strengthening of adobe structures

Adobe structures present very appealing characteristics regarding a more sustainable practice with the preservation of our natural resources. However, when subjected to cyclic horizontal actions, such as earthquakes, they can present a deficient behaviour. With the purpose of evaluating the seismic vulnerability of adobe structures, a series of tests were conducted on a full-scale adobe wall considering constant dead and live loads combined with cyclic horizontal actions with rising amplitude. A structural strengthening solution was tested on the repaired wall after its assessment test. The adopted repair solution, based on cracks injection, combined with the strengthening solution, proved to be very efficient in improving the performance of the adobe wall. With the study conducted, it was possible to contribute to the characterization of adobe structural walls in terms of deformation capacity and failure modes, establishing the basis for the calibration of numerical models for adobe structures