Liquid Polymorphism and Density Anomaly in a Lattice Gas Model

We present a simple model for an associating liquid in which polymorphism and density anomaly are connected. Our model combines a two dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom represented through thermal \char`\"{}ice variables\char`\"{} . The competition between the directional attractive forces and the soft core potential leads to a phase diagram in which two liquid phases and a density anomaly are present. The coexistence line between the low density liquid and the high density liquid has a positive slope contradicting the surmise that the presence of a density anomaly implies that the high density liquid is more entropic than the low density liquid

Coexistence Curve Singularities at Critical End Points

We report an extensive Monte Carlo study of critical end point behaviour in a symmetrical binary fluid mixture. On the basis of general scaling arguments, singular behaviour is predicted in the diameter of the liquid-gas coexistence curve as the critical end point is approached. The simulation results show clear evidence for this singularity, as well as confirming a previously predicted singularity in the coexistence chemical potential. Both singularities should be detectable experimentally.Comment: 9 pages Revtex, 3 figures. To appear in Phys. Rev. Let

Enumerating Cyclic Orientations of a Graph

Acyclic and cyclic orientations of an undirected graph have been widely studied for their importance: an orientation is acyclic if it assigns a direction to each edge so as to obtain a directed acyclic graph (DAG) with the same vertex set; it is cyclic otherwise. As far as we know, only the enumeration of acyclic orientations has been addressed in the literature. In this paper, we pose the problem of efficiently enumerating all the \emph{cyclic} orientations of an undirected connected graph with $n$ vertices and $m$ edges, observing that it cannot be solved using algorithmic techniques previously employed for enumerating acyclic orientations.We show that the problem is of independent interest from both combinatorial and algorithmic points of view, and that each cyclic orientation can be listed with $\tilde{O}(m)$ delay time. Space usage is $O(m)$ with an additional setup cost of $O(n^2)$ time before the enumeration begins, or $O(mn)$ with a setup cost of $\tilde{O}(m)$ time

Diffusion behavior of water confined in deformed carbon nanotubes

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes, with different degrees of eccentricity at 300K. We found a water structural transition between tubular-like to single-file for the (7,7) nanotubes associated with a change from a high to low mobility regimes. The water which in the undeformed (9,9) nanotubes is frozen, becomes liquid for the distortion above a certain threshold. These water diffusion enhancement (suppresion) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is a particularly important ingredient when considering the dynamical and structural properties of confined water.Comment: 16 pages, 9 figure

Danos provocados por Amblycerus dispar Sharp, 1885 (Coleoptera: Bruchidae) a semente de imbuzeiro (Spondias tuberosa Arruda).

O objetivo deste foi identificar o inseto que estava atacando as sementes de plantas nativas de imbuzeiro, como também avaliar os danos causados as sementes e a existência de plantas jovens na área de estudo

Anatomia foliar de maracujazeiros infectados por vírus do endurecimento dos frutos e tratados com fertilizante foliar.

Um dos principais problemas enfrentados pelos produtores de maracujazeiro amarelo, Passiflora edulis Sims. f. flavicarpa Deg., são as doenças virais, destacando-se a do endurecimento dos frutos, provocada, principalmente, pelo vírus Cowpea aphid-borne mosaic virus (CABMV). Fertilizantes foliares têm sido utilizados na tentativa de reduzir os danos causados pelo vírus, mas nenhum estudo foi desenvolvido buscando elucidar os efeitos destes produtos sobre as alterações estruturais em plantas infectadas. Este trabalho teve como objetivo uma análise anatômica das folhas de indivíduos de maracujazeiro amarelo infectados pelo vírus CABMV e tratados com fertilizante foliar

Syphilitic Coronary Artery Ostial Stenosis Resulting in Acute Myocardial Infarction Treated by Percutaneous Coronary Intervention

Cardiovascular abnormalities are well-known manifestations of tertiary syphilis infections which although not frequent, are still causes of morbidity and mortality. A less common manifestation of syphilitic aortitis is coronary artery ostial narrowing related to aortic wall thickening. We report a case of a 46-year-old male admitted due to acute anterior ST elevation myocardial infarction submitted to primary percutaneous coronary intervention successfully. Coronary angiography showed a suboccluded ostial lesion of left main coronary artery. VDRL was titrated to 1/512. The patient was discharged with treatment including benzathine penicillin. Previous case reports of acute myocardial infarction in association with syphilitic coronary artery ostial stenosis have been reported, but the fact that the patient was treated by percutaneous coronary intervention is unique in this case