Decline in extinction rates and scale invariance in the fossil record

We show that the decline in the extinction rate during the Phanerozoic can be accurately parameterized by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results which previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.Comment: 11 pages including 3 postscript figures, typeset in LaTeX 2e using the Elsevier macro package elsart.cl

Hole spin dephasing time associated to hyperfine interaction in quantum dots

The spin interaction of a hole confined in a quantum dot with the surrounding nuclei is described in terms of an effective magnetic field. We show that, in contrast to the Fermi contact hyperfine interaction for conduction electrons, the dipole-dipole hyperfine interaction is anisotropic for a hole, for both pure or mixed hole states. We evaluate the coupling constants of the hole-nuclear interaction and demonstrate that they are only one order of magnitude smaller than the coupling constants of the electron-nuclear interaction. We also study, theoretically, the hole spin dephasing of an ensemble of quantum dots via the hyperfine interaction in the framework of frozen fluctuations of the nuclear field, in absence or in presence of an applied magnetic field. We also discuss experiments which could evidence the dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table

Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.Comment: Phys Rev B (in press

Etiology of pure tricuspid regurgitation based on anular circumference and leaflet area: Analysis of 45 necropsy patients with clinical and morphologic evidence of pure tricuspid regurgitation

Despite recent renewed interest in the detection of tricuspid valve regurgitation by echocardiographic and Doppler techniques, little morphologic information is available on dysfunctioning tricuspid valves. This report describes 45 necropsy patients with clinical and morphologic evidence of pure(no element of stenosis) tricuspid regurgitation and provides morphometric observations (anular circumference, leaflet area) of the tricuspid valve useful in determining the etiology of pure tricuspid regurgitation. Of 45 patients, 24 (53%) had pure tricuspid regurgitation resulting from an anatomically abnormal valve (prolap9e in 7, papillary muscle dysfunction in 6, rheumatic disease in 5, Ebstein's anomaly in 3, infective endocarditis in 2, carcinoid tumor in 1), and 21(47%) had an anatomically normal valve with systolic pulmonary artery hypertension (cor pulmonary in 12, mitral stenosis in 9). Anular circumference was dilated (> 12 cm) in patients with various causes of pulmonary hypertension, floppy valve and Ebstein's tricuspid anomaly. Leaflet area was increased in floppy valve and Ebstein's anomaly.Of the 45 patients, 24 had pulmonary systolic artery pressure measurements available for correlation with tricuspid valve morphology. Pulmonary artery pressures accurately predicted morphologically normal from abnormal valves in 16 patients (89 %). Morphologic overlap occurred in six patients with pulmonary pressures of 41 to 54 mm Hg. Of these six, the additional knowledge of normal or dilated anular circumference correctly separated valves with normal and abnormal leaflets

An Exhumed Late Paleozoic Canyon in the Rocky Mountains

Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite‐flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator

Evidence of a dual histogenetic pathway of sacrococcygeal teratomas

Aims Sacrococcygeal teratomas are rare tumours that occur most frequently in neonates, although adult cases also occur. The molecular pathogenesis of these tumours and their long-term prognosis is uncertain. We investigated the i(12p) status of a large number of primary sacrococcygeal teratomas in both children and adults, including cases with malignant germ cell tumour elements. Methods and results Fifty-four sacrococcygeal teratoma specimens from 52 patients were identified, and available follow-up information was obtained. Fluorescence in-situ hybridization analysis was performed to identify isochromosome 12p [i(12p)] abnormalities on paraffin blocks of the tumours. Among the 48 paediatric patients, there were 44 teratomas and four tumours with combined teratoma and yolk sac tumour (one of whom also had primitive neuroectodermal tumour). The teratomas included 37 mature teratomas and 11 immature teratomas (four grade 1, two grade 2, and five grade 3). The 44 teratomas lacking a yolk sac tumour component were all negative for i(12p). The four tumours with a yolk sac tumour component were all positive for i(12p). The four adult cases all lacked non-teratomatous germ cell tumour components, immature elements, and i(12p). Follow-up information was available for 32 patients. Two patients with teratoma had recurrence, but were alive with no evidence of disease after long-term follow-up. One patient with combined teratoma and yolk sac tumour had recurrence 7 months after resection. The other patients were alive with no evidence of disease at last follow-up. Conclusions Our data suggest that paediatric sacrococcygeal teratomas should be considered as two distinct groups with divergent histogenetic pathways. The prognosis of these tumours is excellent, despite rare recurrence

Full coherent control of nuclear spins in an optically pumped single quantum dot

Highly polarized nuclear spins within a semiconductor quantum dot (QD) induce effective magnetic (Overhauser) fields of up to several Tesla acting on the electron spin or up to a few hundred mT for the hole spin. Recently this has been recognized as a resource for intrinsic control of QD-based spin quantum bits. However, only static long-lived Overhauser fields could be used. Here we demonstrate fast redirection on the microsecond time-scale of Overhauser fields of the order of 0.5 T experienced by a single electron spin in an optically pumped GaAs quantum dot. This has been achieved using full coherent control of an ensemble of 10^3-10^4 optically polarized nuclear spins by sequences of short radio-frequency (rf) pulses. These results open the way to a new class of experiments using rf techniques to achieve highly-correlated nuclear spins in quantum dots, such as adiabatic demagnetization in the rotating frame leading to sub-micro K nuclear spin temperatures, rapid adiabatic passage, and spin squeezing

Niche as a determinant of word fate in online groups

Patterns of word use both reflect and influence a myriad of human activities and interactions. Like other entities that are reproduced and evolve, words rise or decline depending upon a complex interplay between {their intrinsic properties and the environments in which they function}. Using Internet discussion communities as model systems, we define the concept of a word niche as the relationship between the word and the characteristic features of the environments in which it is used. We develop a method to quantify two important aspects of the size of the word niche: the range of individuals using the word and the range of topics it is used to discuss. Controlling for word frequency, we show that these aspects of the word niche are strong determinants of changes in word frequency. Previous studies have already indicated that word frequency itself is a correlate of word success at historical time scales. Our analysis of changes in word frequencies over time reveals that the relative sizes of word niches are far more important than word frequencies in the dynamics of the entire vocabulary at shorter time scales, as the language adapts to new concepts and social groupings. We also distinguish endogenous versus exogenous factors as additional contributors to the fates of words, and demonstrate the force of this distinction in the rise of novel words. Our results indicate that short-term nonstationarity in word statistics is strongly driven by individual proclivities, including inclinations to provide novel information and to project a distinctive social identity.Comment: Supporting Information is available here: http://www.plosone.org/article/fetchSingleRepresentation.action?uri=info:doi/10.1371/journal.pone.0019009.s00