Absence Of Cusp Research Articles

New Small Bunodont Metatherian from the Late Eocene of the Argentinean Puna

We describe here a new small bunodont metatherian from Priabonian deposits of the Geste Formation exposed in the Puna of Catamarca Province (Argentina). The material, an isolated right M2?, was recovered by screen-washing techniques and allows us to erect the new species Apeirodon sorianoi. The combination of diagnostic characters includes triangular occlusal pattern, bunoid, with an equally developed stylocone and cusp D, absence of cusp C, protoconal base wide, preparacrista and postmetacrista short, well-developed paracingulum, presence of double rank postvallum-prevallid shear, and presence of small paraconule and larger metaconule that is distolingually located. The overall morphology of Apeirodon more closely resembles Glasbius (particularly G. ) than any other Cretaceous-Paleogene American metatherian, supporting the largely accepted hypothesis proposing a common origin for some North and South American metatherian lineages. Apeirodon also resembles Reigia punae (another small metatherian recovered from the same stratigraphic levels), Chulpasia, Palangania, and specimens referred to Bobbschaefferia. Tentatively, we propose the inclusion of Apeirodon and Reigia as early divergent members of Polydolopimorphia based on the presence of bunodonty, enlarged stylocone and cusp D, and a distolingually-shifted metaconule. These features, incipiently developed in these late Eocene taxa, are emphasized in later representatives of the order. The presence of a generalized putative polydolopimorphian in Priabonian deposits of northwestern Argentina highlights the key temporal and spatial position of the region in the context of the evolution of Paleogene South American mammals.

THE DISTRIBUTION OF STARS AND STELLAR REMNANTS AT THE GALACTIC CENTER

Motivated by recent observations that suggest a low density of old stars around the Milky Way supermassive black hole, models for the nuclear star cluster are considered that have not yet reached a steady state under the influence of gravitational encounters. A core of initial radius 1-1.5 pc evolves to a size of approximately 0.5 pc after 10 Gyr, roughly the size of the observed core. The absence of a Bahcall-Wolf cusp is naturally explained in these models, without the need for fine-tuning or implausible initial conditions. In the absence of a cusp, the time for a 10-solar-mass black hole to spiral in to the Galactic center from an initial distance of 5 pc can be much greater than 10 Gyr. Assuming that the stellar black holes had the same phase-space distribution initially as the stars, their density after 5-10 Gyr is predicted to rise very steeply going into the stellar core, but could remain substantially below the densities inferred from steady-state models that include a steep density cusp in the stars. Possible mechanisms for the creation of the parsec-scale initial core include destruction of stars on centrophilic orbits in a pre-existing triaxial nucleus, inhibited star formation near the supermassive black hole, or ejection of stars by a massive binary. The implications of these models are discussed for the rates of gravitational-wave inspiral events, as well as other physical processes that depend on a high density of stars or stellar mass black holes near Sagittarius A*.

Analyse morphométrique comparée des dents humaines de Gran Dolina (TD6) et de Sima de los Huesos d'Atapuerca

Comparative Morphometric Analysis of the Human Dental Samples of Gran Dolina (TD6) and Sima de los Huesos caves sites at Atapuerca. We present a comparative morphometric study of the human dental samples yielded by the Lower Pleistocene site of Gran Dolina (TD6 Aurora Stratum) and the Middle Pleistocene site of Sima de los Huesos (SH) from the Sierra de Atapuerca (Burgos, Spain). The remarkable size and shape differences between the TD6 and SH sample concern, especially, to the anterior vs. posterior size relationship. In the SH hominids, the strong size reduction of the posterior teeth, which reached a degree similar to that of the modern populations, implied the appearance of a set of derived traits, such as the crown and root simplification of the lower premolars, the absence of cingulum, the relative greater size reduction of the lower second premolar and second molar, or the reduction and absence of cusps of the upper and lower molars (hypocone and hypoconulid). The TD6 hominids, in contrast, exhibit a size balance between the anterior dentition and the posterior one, together with the retention of most plesiomorphies for the genus Homo. These observations imply important differences for certain dental development parameters of the two hominid populations, which justifies their taxonomical distinction. On the other hand, the SH hominids and the Neandertalians exhibit a similarity of most dental traits examined, which supports the hypothesis of a reproductive continuity (phyletic evolution) in Europe during the Middle and early Upper Pleistocene.

Sparking potentials in cusp and magnetic mirror fields

Abstract Magnetic field geometries containing cusps are widely used in laboratory devices for basic plasma physics studies. The present paper reports the influence of a cusped magnetic field on the sparking potentials in dry air, investigated experimentally using pressure variation technique (0.15–0.375 torr) and distance variation technique (2–30mm). The sparking voltages were determined, and hence the Paschen curves obtained in the presence and absence of cusp and magnetic mirror field configurations. The effect of B on the break-down voltage is opposite in the two regions before and after the Paschen minimum. For a magnetic field current of 250 A, the sparking voltage was 90 V less than that in the absence of cusp at pd = 0.03 torr cm. The effect of cusp is similar to the results obtained in long-itudinal fields to the left of the Paschen minimum and that of the crossed fields to the right of the Paschen minimum. The effect of cusp to decrease the breakdown potential may have good application potential wherever gas discharges find use. The results are reported and discussed.