The evolution of energy in flow driven by rising bubbles

We investigate by direct numerical simulations the flow that rising bubbles cause in an originally quiescent fluid. We employ the Eulerian-Lagrangian method with two-way coupling and periodic boundary conditions. In order to be able to treat up to 288000 bubbles, the following approximations and simplifications had to be introduced: (i) The bubbles were treated as point-particles, thus (ii) disregarding the near-field interactions among them, and (iii) effective force models for the lift and the drag forces were used. In particular, the lift coefficient was assumed to be 1/2, independent of the bubble Reynolds number and the local flow field. The results suggest that large scale motions are generated, owing to an inverse energy cascade from the small to the large scales. However, as the Taylor-Reynolds number is only in the range of 1, the corresponding scaling of the energy spectrum with an exponent of -5/3 cannot develop over a pronounced range. In the long term, the property of local energy transfer, characteristic of real turbulence, is lost and the input of energy equals the viscous dissipation at all scales. Due to the lack of strong vortices the bubbles spread rather uniformly in the flow. The mechanism for uniform spreading is as follows: Rising bubbles induce a velocity field behind them that acts on the following bubbles. Owing to the shear, those bubbles experience a lift force which make them spread to the left or right, thus preventing the formation of vertical bubble clusters and therefore of efficient forcing. Indeed, when the lift is artifically put to zero in the simulations, the flow is forced much more efficiently and a more pronounced energy accumulates at large scales is achieved.Comment: 9 pages, 7 figure

Traces of Thermalization from Transverse Momentum Fluctuations in Nuclear Collisions

Scattering of particles produced in Au+Au collisions at RHIC can wrestle the system into a state near local thermal equilibrium. I illustrate how measurements of the centrality dependence of the mean transverse momentum and its fluctuations can exhibit this thermalization.Comment: 4 pages, 2 eps figures, final version to appear in PR

WOOD JAMS OR BEAVER DAMS? PLIOCENE LIFE, SEDIMENT AND LANDSCAPE INTERACTIONS IN THE CANADIAN HIGH ARCTIC

ABSTRACT During the mid-Pliocene (Zanclean, ca. ∼ 3.9 Ma), parts of the Canadian High Arctic experienced mean annual temperatures that were 14–22°C warmer than today and supported diverse boreal-type forests. The landscapes of this vegetated polar region left behind a fragmented sedimentary record that crops out across several islands in the Canadian Arctic Archipelago as the Beaufort Formation and correlative strata. Paleoecological information from these strata provides a high-fidelity window onto Pliocene environments, and prominent fossil sites yield unparalleled insights into Cenozoic mammal evolution. Significantly, many of the strata reveal evidence for life-sediment interactions in a warm-climate Arctic, most notably in the form of extensive woody debris and phytoclast deposits. This paper presents original field data that refines the sedimentological context of plant debris accumulations from the anactualistic High Arctic forests, most notably at the ‘Fyles Leaf Beds' and ‘Beaver Pond' fossil-bearing sites in the ‘high terrace deposits' of central Ellesmere Island. The former is a remarkably well-preserved, leaf-rich deposit that is part of a complex of facies associations representing lacustrine, fluvio-deltaic and mire deposition above a paleotopographic unconformity. The latter yields tooth-marked woody debris within a peat layer that also contains a rich assemblage of vertebrate and plant fossils including abundant remains from the extinct beaver-group Dipoides. Here we present sedimentological data that provide circumstantial evidence that the woody debris deposit at Beaver Pond could record dam-building in the genus, by comparing the facies motif with new data from known Holocene beaver dam facies in England. Across the Pliocene of the High Arctic region, woody debris accumulations are shown to represent an array of biosedimentary deposits and landforms including mires, driftcretions, woody bedforms, and possible beaver dams, which help to contextualize mammal fossil sites, provide facies models for high-latitude forests, and reveal interactions between life and sedimentation in a vanished world that may be an analogue to that of the near-future.</jats:p

Perspectives on the revised Ghent criteria for the diagnosis of Marfan syndrome

Three international nosologies have been proposed for the diagnosis of Marfan syndrome (MFS): the Berlin nosology in 1988; the Ghent nosology in 1996 (Ghent-1); and the revised Ghent nosology in 2010 (Ghent-2). We reviewed the literature and discussed the challenges and concepts of diagnosing MFS in adults. Ghent-1 proposed more stringent clinical criteria, which led to the confirmation of MFS in only 32%-53% of patients formerly diagnosed with MFS according to the Berlin nosology. Conversely, both the Ghent-1 and Ghent-2 nosologies diagnosed MFS, and both yielded similar frequencies of MFS in persons with a causative FBN1 mutation (90% for Ghent-1 versus 92% for Ghent-2) and in persons not having a causative FBN1 mutation (15% versus 13%). Quality criteria for diagnostic methods include objectivity, reliability, and validity. However, the nosology-based diagnosis of MFS lacks a diagnostic reference standard and, hence, quality criteria such as sensitivity, specificity, or accuracy cannot be assessed. Medical utility of diagnosis implies congruency with the historical criteria of MFS, as well as with information about the etiology, pathogenesis, diagnostic triggers, prognostic triggers, and potential complications of MFS. In addition, social and psychological utilities of diagnostic criteria include acceptance by patients, patient organizations, clinicians and scientists, practicability, costs, and the reduction of anxiety. Since the utility of a diagnosis or exclusion of MFS is context-dependent, prioritization of utilities is a strategic decision in the process of nosology development. Screening tests for MFS should be used to identify persons with MFS. To confirm the diagnosis of MFS, Ghent-1 and Ghent-2 perform similarly, but Ghent-2 is easier to use. To maximize the utility of the diagnostic criteria of MFS, a fair and transparent process of nosology development is essential

Mean Annual Precipitation Explains Spatiotemporal Patterns of Cenozoic Mammal Beta Diversity and Latitudinal Diversity Gradients in North America

Spatial diversity patterns are thought to be driven by climate-mediated processes. However, temporal patterns of community composition remain poorly studied. We provide two complementary analyses of North American mammal diversity, using (i) a paleontological dataset (2077 localities with 2493 taxon occurrences) spanning 21 discrete subdivisions of the Cenozoic based on North American Land Mammal Ages (36 Ma – present), and (ii) climate space model predictions for 744 extant mammals under eight scenarios of future climate change. Spatial variation in fossil mammal community structure (b diversity) is highest at intermediate values of continental mean annual precipitation (MAP) estimated from paleosols (,450 mm/year) and declines under both wetter and drier conditions, reflecting diversity patterns of modern mammals. Latitudinal gradients in community change (latitudinal turnover gradients, aka LTGs) increase in strength through the Cenozoic, but also show a cyclical pattern that is significantly explained by MAP. In general, LTGs are weakest when continental MAP is highest, similar to modern tropical ecosystems in which latitudinal diversity gradients are weak or undetectable. Projections under modeled climate change show no substantial change in b diversity or LTG strength for North American mammals. Our results suggest that similar climate-mediated mechanisms might drive spatial and temporal patterns of community composition in both fossil and extant mammals. We also provide empirical evidence that the ecological processes on which climate space models are based are insufficient for accurately forecasting long-term mammalian response to anthropogenic climate change and inclusion of historical parameters may be essential

Trapping of strangelets in the geomagnetic field

Strangelets coming from the interstellar medium (ISM) are an interesting target to experiments searching for evidence of this hypothetic state of hadronic matter. We entertain the possibility of a {\it trapped} strangelet population, quite analogous to ordinary nuclei and electron belts. For a population of strangelets to be trapped by the geomagnetic field, these incoming particles would have to fulfill certain conditions, namely having magnetic rigidities above the geomagnetic cutoff and below a certain threshold for adiabatic motion to hold. We show in this work that, for fully ionized strangelets, there is a narrow window for stable trapping. An estimate of the stationary population is presented and the dominant loss mechanisms discussed. It is shown that the population would be substantially enhanced with respect to the ISM flux (up to two orders of magnitude) due to quasi-stable trapping.Comment: 10 pp., 5 figure

Ascending aortic aneurysm and aortic valve dysfunction in bicuspid aortic valve disease

BACKGROUND: The relationship of aortic valve dysfunction and ascending aortic aneurysm is unclear in adults with bicuspid aortic valve disease. METHODS: We retrospectively studied 134 consecutive out-patients (98 men, 36 women aged 43+/-18years) with bicuspid aortic valve disease. To investigate the relationship of ascending aortic aneurysm and aortic valve dysfunction we exclusively considered severe pathologies that required treatment by surgical or percutaneous intervention. RESULTS: Of 134 patients, 39 had aortic valve dysfunction without concomitant ascending aortic aneurysm which had been treated previously with isolated valve surgery or percutaneous valvuloplasty comprising 25 patients with aortic stenosis (19%) and 14 patients with aortic regurgitation (10%). Conversely, 26 patients had ascending aortic aneurysm which had been treated previously with aortic surgery (19%). Of these, ascending aortic aneurysm was associated with severe aortic stenosis in 13 patients and with severe aortic regurgitation in 7 patients, whereas aneurysm was unrelated to severe aortic valve dysfunction in the remaining 6 patients including 2 without any degree of aortic valve dysfunction. The maximal aortic diameters were similar at the time of aortic surgery irrespective of presence of severe aortic valve dysfunction (P=.527). Other characteristics of patients with ascending aortic aneurysm were also similar irrespective of presence or type of aortic valve dysfunction. CONCLUSION: The majority of patients with bicuspid aortic valve disease exhibit ascending aortic aneurysm in conjunction with severe aortic valve dysfunction. However, in our study 6 of 134 (5%) of persons with bicuspid aortic valve disease developed ascending aortic aneurysm without aortic valve dysfunction

A basal ursine bear (Protarctos abstrusus) from the Pliocene High Arctic reveals Eurasian affinities and a diet rich in fermentable sugars

The skeletal remains of a small bear (Protarctos abstrusus) were collected at the Beaver Pond fossil site in the High Arctic (Ellesmere I., Nunavut). This mid-Pliocene deposit has also yielded 12 other mammals and the remains of a boreal-forest community. Phylogenetic analysis reveals this bear to be basal to modern bears. It appears to represent an immigration event from Asia, leaving no living North American descendants. The dentition shows only modest specialization for herbivory, consistent with its basal position within Ursinae. However, the appearance of dental caries suggest a diet high in fermentable-carbohydrates. Fossil plants remains, including diverse berries, suggests that, like modern northern black bears, P. abstrusus may have exploited a high-sugar diet in the fall to promote fat accumulation and facilitate hibernation. A tendency toward a sugar-rich diet appears to have arisen early in Ursinae, and may have played a role in allowing ursine lineages to occupy cold habitats

Conformal oxide coating of Carbon Nanotubes

The International Roadmap for Ferroelectric Memories requires three-dimensional integration of high-dielectric materials onto metal interconnects or bottom electrodes by 2010. We report the first integration of high-dielectric oxide films onto carbon nanotube electrodes with an aim of ultra-high integration density of FeRAMs (Tb/in2).Comment: 4 pages, 3 figure