Stellar structure and compact objects before 1940: Towards relativistic astrophysics

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal

Restricted three body problems at the nanoscale

In this paper, we investigate some of the classical restricted three body problems at the nanoscale, such as the circular planar restricted problem for three C60 fullerenes, and a carbon atom and two C60 fullerenes. We model the van der Waals forces between the fullerenes by the Lennard-Jones potential. In particular, the pairwise potential energies between the carbon atoms on the fullerenes are approximated by the continuous approach, so that the total molecular energy between two fullerenes can be determined analytically. Since we assume that such interactions between the molecules occur at sufficiently large distance, the classical three body problems analysis is legitimate to determine the collective angular velocity of the two and three C60 fullerenes at the nanoscale. We find that the maximum angular frequency of the two and three fullerenes systems reach the terahertz range and we determine the stationary points and the points which have maximum velocity for the carbon atom for the carbon atom and the two fullerenes system

Enterotoxemia em caprinos no Rio Grande do Sul Caprine enterotoxaemia in Rio Grande do Sul, Brazil

São descritos surtos de enterotoxemia em caprinos em cinco propriedades no Estado do Rio Grande do Sul. Os animais afetados eram, normalmente, encontrados mortos ou apresentavam evolução aguda de 2 a 3 horas com acentuada depressão, cólicas abdominais e diarréia profusa com fibrina. Em duas propriedades relataram-se casos com a evolução de até 12 horas. Em treze animais necropsiados observaram-se aumento de líquidos nas cavidades abdominal, torácica e pericárdica, congestão e hiperemia da serosa e mucosa do intestino, conteúdo do cólon líquido com fibrina além de hemorragias de serosa e fibrina. Em um animal constatou-se microangiopatia cerebral caracterizada por acúmulo de material homogêneo e eosinofílico no espaço perivascular. No conteúdo intestinal, colônias com bastonetes morfológica e bioquimicamente sugestivos de Clostridium perfringens foram caracterizadas no estudo bacteriológico. A soroneutralização em camundongos com conteúdo intestinal dos animais afetados, revelou a presença da toxina épsilon. Estes achados evidenciam a enterotoxemia como doença de importância para criação de caprinos no Rio Grande do Sul.<br>Five outbreaks of caprine enterotoxaemia in Rio Grande do Sul, Brazil, were studied. The animals were found dead or had a clinical course that usually lasted 2-3 hours. From two farms a clinical manifestation period of 12 hours was reported. Clinical signs were characterized by depression, marked abdominal discomfort, profuse watery diarrhea with fibrin clots, and death. Thirteen necropsies were performed and hydropericardium, hydrothorax and hydroperitoneum were commonly found. The mucosa and serosa of the colon were congested, and its contents was watery with multiple fibrin clots. Serosal hemorrhages and fibrin clots in the gallbladder were also seen. Fibrinous colitis and thyphilitis were the most frequent histological changes. Cerebral microangiopathy was observed in one case, which was characterized by acute perivascular proteinaceous edema around arterioles of the nucleus caudatus and thalamus. Large numbers of Gram-positive rods, often in clumps and with morphology consistent with Clostridium perfringens, were seen in intestinal smears. The intestinal contents of six goats were positive for epsilon toxin by mouse neutralization test. These findings suggest that enterotoxaemia is an important disease of goat flocks in southern Brazil