Direct Numerical Simulation of 3D Salt Fingers: From Secondary Instability to Chaotic Convection

The amplification and equilibration of three-dimensional salt fingers in unbounded uniform vertical gradients of temperature and salinity is modeled with a Direct Numerical Simulation in a triply periodic computational domain. A fluid dynamics video of the simulation shows that the secondary instability of the fastest growing square-planform finger mode is a combination of the well-known vertical shear instability of two-dimensional fingers [Holyer, 1984] and a new horizontal shear mode.Comment: APS DFD Gallery of Fluid Motion 200

Dynamics of fingering convection I: Small-scale fluxes and large-scale instabilities

Double-diffusive instabilities are often invoked to explain enhanced transport in stably-stratified fluids. The most-studied natural manifestation of this process, fingering convection, commonly occurs in the ocean's thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion. Fingering convection is also often associated with structures on much larger scales, such as thermohaline intrusions, gravity waves and thermohaline staircases. In this paper, we present an exhaustive study of the phenomenon from small to large scales. We perform the first three-dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport. Our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions. We then develop a generalized mean-field theory to study the stability of fingering systems to large-scale perturbations, using our calculated turbulent fluxes to parameterize small-scale transport. The theory recovers the intrusive instability, the collective instability, and the gamma-instability as limiting cases. We find that the fastest-growing large-scale mode depends sensitively on the ratio of the background gradients of temperature and salinity (the density ratio). While only intrusive modes exist at high density ratios, the collective and gamma-instabilities dominate the system at the low density ratios where staircases are typically observed. We conclude by discussing our findings in the context of staircase formation theory.Comment: 23 pages, 9 figures, submitted to JF

Dynamics of fingering convection II: The formation of thermohaline staircases

Regions of the ocean's thermocline unstable to salt fingering are often observed to host thermohaline staircases, stacks of deep well-mixed convective layers separated by thin stably-stratified interfaces. Decades after their discovery, however, their origin remains controversial. In this paper we use 3D direct numerical simulations to shed light on the problem. We study the evolution of an analogous double-diffusive system, starting from an initial statistically homogeneous fingering state and find that it spontaneously transforms into a layered state. By analysing our results in the light of the mean-field theory developed in Paper I, a clear picture of the sequence of events resulting in the staircase formation emerges. A collective instability of homogeneous fingering convection first excites a field of gravity waves, with a well-defined vertical wavelength. However, the waves saturate early through regular but localized breaking events, and are not directly responsible for the formation of the staircase. Meanwhile, slower-growing, horizontally invariant but vertically quasi-periodic gamma-modes are also excited and grow according to the gamma-instability mechanism. Our results suggest that the nonlinear interaction between these various mean-field modes of instability leads to the selection of one particular gamma-mode as the staircase progenitor. Upon reaching a critical amplitude, this progenitor overturns into a fully-formed staircase. We conclude by extending the results of our simulations to real oceanic parameter values, and find that the progenitor gamma-mode is expected to grow on a timescale of a few hours, and leads to the formation of a thermohaline staircase in about one day with an initial spacing of the order of one to two metres.Comment: 18 pages, 9 figures, associated mpeg file at http://earth.uni-muenster.de/~stellma/movie_small.mp4, submitted to JF

Ukrainian artist-painter Yevgenia Gapchinska

Yevgenia Gennadievna Gapchinska (b. November 15, 1974, Kharkiv, Ukraine) is a Ukrainian artist-painter and an illustrator of children's literature

ВПЛИВ ТЕХНОЛОГІЧНОГО РОЗВИТКУ НА ЗДІЙСНЕННЯ ЕЛЕКТРОННОЇ КОМЕРЦІЇ

The article reflects Internet marketing as a modern and effective way to promote the company’s products at the market. The role of the media in the Internet has been highlighted and their polarity has been investigated for e-commerce. It is shown the role of smartphones when using information from the Internet. The necessity of using interactive technologies by Ukrainian producers to enter the European market is proved.В статье отражен интернет-маркетинг как современный и эффективный способ продвижения продукции компании на рынке. Выделенная роль средств массовой информации в сети Интернет и исследована их популярность для осуществления электронной коммерции. Показана роль смартфонов при использовании информации из Интернет-сети. Обоснована необходимость использования интерактивных технологий украинскими производителями для выхода на европейский рынок.У статті розглядається Інтернет-маркетинг як сучасний дієвий засіб просування продукції підприємства на ринку. Виділена роль засобів масової інформації в мережі Інтернет та досліджена їх популярність для здійснення електронної комерції. Показано роль смартфонів при використанні інформації з Інтернет-мережі. Обґрунтована необхідність використання інтерактивних технологій українськими виробниками для виходу на європейський ринок

Coexisting large and small vessel disease in patients with ischemic stroke of undetermined cause

Background and Purpose: Large artery atherosclerosis (LAA) and small vessel disease (SVD) share common risk factors for stroke. We aimed at investigating the association of SVD with cerebral LAA as well as with atherosclerosis in patients with stroke likely to originate from aortic plaques. Methods: We investigated 71 consecutive patients (48 men, mean age 64.2 +/- 13 years) with ischemic stroke of undetermined cause according to the ASCO classification, who received ECG-triggered CT angiography for best available atherosclerotic plaque detection in the aorta. Results: Aortic atherosclerotic plaques were detected in 54 patients (76.1%). The presence of SVD significantly correlated with the presence of aortic plaques (p < 0.001), as well as LAA (p < 0.001) and risk factors such as arterial hypertension (p = 0.032) and diabetes mellitus (p = 0.017). Conclusions: Aortic plaques are common in patients with stroke of undetermined cause. If so, SVD and LAA are often coexisting, which demonstrates the close link of macro- and microangiopathy, at least in cases of severe risk factors of atherosclerosis. Copyright © 2012 S. Karger AG, Base

Strong fuzzy subsethood measures and strong equalities via implication functions

In this work we present the definition of strong fuzzy subsethood measure as a unifiying concept for the different notions of fuzzy subsethood that can be found in the literature. We analyze the relations of our new concept with the definitions by Kitainik ( [20]), Young ( [26]) and Sinha and Dougherty ( [23]) and we prove that the most relevant properties of the latter are preserved. We show also several construction methods. &copy; 2014 Old City Publishing, Inc

Observation of the Magneto-Optic Voigt Effect in a Paramagnetic Diamond Membrane

The magneto-optic Voigt effect is observed in a synthetic diamond membrane with a substitutional nitrogen defect concentration in the order of 200 ppm and a nitrogen-vacancy defect sub-ensemble generated through neutron irradiation and annealing. The measured polarisation rotation in the reflected light is observed to be quadratically proportional to the applied magnetic field and to the incident reflection angle. Additionally, it is observed to be modifiable by illuminating the diamond with a 532 nm laser. Spectral analysis of the reflected light under 532 nm illumination shows a slow narrowing of the spectral distribution, indicating a small increase in the overall magnetisation, as opposed to magnetisation degradation caused by heating. Further analysis of the optical power dependence suggest this may be related to a shift in the spin ensembles charge state equilibrium and, by extension, the resulting ensemble magnetisation.Comment: 6 pages, 5 figure

CT angiography of the aorta is superior to transesophageal echocardiography for determining stroke subtypes in patients with cryptogenic ischemic stroke

Background: The etiology of ischemic strokes remains cryptogenic in about one third of patients, even after extensive workup in specialized centers. Atherosclerotic plaques in the aorta can cause thromboembolic events but are often overlooked. They can elude standard identification by transesophageal echocardiography (TEE), which is invasive or at best uncomfortable for many patients. CT angiography (CTA) can be used as an alternative or in addition to TEE if this technique fails to visualize every part of the aorta and in particular the aortic arch. Methods: We prospectively studied 64 patients (47 men, age 60 8 13 years) classified as having cryptogenic stroke after standard and full workup [including brain MRI and 24-hour electrocardiogram (ECG)] with ECG-triggered CTA of the aorta in search of plaques and compared the results with those of TEE. Investigators were blinded to the results of both techniques