21,726 research outputs found
The Life of a Vortex Knot
The idea that the knottedness (hydrodynamic Helicity) of a fluid flow is
conserved has a long history in fluid mechanics. The quintessential example of
a knotted flow is a knotted vortex filament, however, owing to experimental
difficulties, it has not been possible until recently to directly generate
knotted vortices in real fluids. Using 3D printed hydrofoils and high-speed
laser scanning tomography, we generate vortex knots and links and measure their
subsequent evolution. In both cases, we find that the vortices deform and
stretch until a series of vortex reconnections occurs, eventually resulting
several disjoint vortex rings.
This article accompanies a fluid dynamics video entered into the Gallery of
Fluid Motion at the 66th Annual Meeting of the APS Division of Fluid Dynamics.Comment: Videos are included; this submission is part of the DFD Gallery of
Fluid Motio
Density functional theory study of the nematic-isotropic transition in an hybrid cell
We have employed the Density Functional Theory formalism to investigate the
nematic-isotropic capillary transitions of a nematogen confined by walls that
favor antagonist orientations to the liquid crystal molecules (hybrid cell). We
analyse the behavior of the capillary transition as a function of the
fluid-substrate interactions and the pore width. In addition to the usual
capillary transition between isotropic-like to nematic-like states, we find
that this transition can be suppressed when one substrate is wet by the
isotropic phase and the other by the nematic phase. Under this condition the
system presents interface-like states which allow to continuously transform the
nematic-like phase to the isotropic-like phase without undergoing a phase
transition. Two different mechanisms for the disappearance of the capillary
transition are identified. When the director of the nematic-like state is
homogeneously planar-anchored with respect to the substrates, the capillary
transition ends up in a critical point. This scenario is analogous to the
observed in Ising models when confined in slit pores with opposing surface
fields which have critical wetting transitions. When the nematic-like state has
a linearly distorted director field, the capillary transition continuously
transforms in a transition between two nematic-like states.Comment: 31 pages, 10 figures, submitted to J. Chem. Phy
Kointegrasi Harga Jagung Pipil Impor, Harga Jagung Pipil Sumatera Utara dan Kabupaten Karo
Penelitian bertujuan untuk menganalisis kointegrasi harga jagung pipil impor dengan harga jagung pipil Sumatera Utara, untuk menganalisis kointegrasi harga jagung pipil impor dengan harga jagung pipil Kabupaten Karo, dan untuk menganalisis kointegrasi harga jagung pipil Sumatera Utara dengan harga jagung pipil Kabupaten Karo. Alat analisis yang digunakan adalah uji kointegrasi Johansen dengan bantuan perangkat lunak Eviews, dengan melakukan 3 langkah uji yaitu uji akar unit, uji kointegrasi dan Error Correction Model (ECM). Data yang digunakan adalah data harga bulanan time series selama periode 4 tahun (2009-2012). Hasil analisis menyimpulkan bahwa ada kointegrasi antara harga jagung pipil impor, harga jagung pipil Sumatera Utara dan harga jagung pipil Kabupaten Karo. Perubahan harga jagung pipil yang terjadi di pasar Internasional akan diikuti dengan Perubahan harga jagung pipil di pasar domestik (Sumatera Utara dan Kabupaten Karo). Harga jagung pipil di pasar Internasional berfluktuasi, maka harga jagung pipil di pasar domestik baik Sumatera Utara maupun Kabupaten Karo juga akan mengalami fluktuasi. Pasar Internasional, Sumatera Utara dan Kabupaten Karo perlahan-lahan akan menuju pada titik keseimbangan, hal ini berarti pasar terintegrasi dalam jangka panjang. Ada hubungan positif antara harga jagung pipil Internasional (harga ekspor) dan harga jagung pipil Sumatera Utara (harga domestik) dengan volume produksi jagung pipil Sumatera Utara
The feasibility of wireless capsule endoscopy in detecting small intestinal pathology in children under the age of 8 years: a multicentre European study.
Objective: To systematically evaluate the feasibility and methodology to carry out wireless capsule endoscopy (WCE) in children <8 years to define small intestinal pathology.
Design: Prospective European multicentre study with negative prior investigation.
Patients and interventions: 83 children aged 1.5â7.9 years were recruited. Initially, all were offered âswallowingâ (Group 1) for capsule introduction. If this failed endoscopic placement (Group 2) was used and the Roth net, Advance or custom-made introducers were compared.
Outcome measures: Primary endpoint: to determine pathology; secondary endpoint: comparison of capsule introduction methods.
Results: Capsule introduction: 20 (24%) children aged 4.0â7.9 years (mean, 6.9 years; 14 male) comprising Group 1 were older (p<0.025) than 63 (76%) aged 1.5â7.9 years (mean, 5.25 years; 30 male) forming Group 2. Complications: Roth net mucosal trauma in 50%; no others occurred. The available recording apparatus was inappropriate for those <3 years. Indications: gastrointestinal bleeding: nâ=â30 (16 positive findings: four ulcerative jejunitis, four polyps, two angiodysplasia, two blue rubber blebs, two Meckelâs diverticula, one anastomotic ulcer, one reduplication); suspected Crohnâs disease: nâ=â20 (11 had Crohnâs disease); abdominal pain: nâ=â12 (six positive findings: three Crohnâs disease, two lymphonodular hyperplasia, one blue rubber bleb); protein loss: nâ=â9 (four lymphangectasia); malabsorption: nâ=â12 (seven positive findings: six enteropathy, one ascaris). No abnormalities overall: 45%.
Conclusion: WCE is feasible and safe down to the age of 1.5 years. 20 children >4 years swallowed the capsule. The Advance introducer proved superior for endoscopic placement. The pathologies encountered showed age specificity and, unlike in adolescents, obscure gastrointestinal bleeding was the commonest indication
The nuclear spectrum of the radio galaxy NGC 5128 (Centaurus A)
We present near-infrared spectra of the nuclear disk in the nearby radio
galaxy NGC 5128 (Centaurus A). On the basis of the observed strengths of the [S
III] 0.9532um and [Fe II] 1.2567um lines, we classify NGC 5128 as a LINER.
Modeling of the strengths of these and additional lines suggests that the
nuclear region is powered by shocks rather than photoionization.Comment: 12 pages including 2 figures, accepted by ApJ Letter
Ground state of a large number of particles on a frozen topography
Problems consisting in finding the ground state of particles interacting with
a given potential constrained to move on a particular geometry are surprisingly
difficult. Explicit solutions have been found for small numbers of particles by
the use of numerical methods in some particular cases such as particles on a
sphere and to a much lesser extent on a torus. In this paper we propose a
general solution to the problem in the opposite limit of a very large number of
particles M by expressing the energy as an expansion in M whose coefficients
can be minimized by a geometrical ansatz. The solution is remarkably universal
with respect to the geometry and the interaction potential. Explicit solutions
for the sphere and the torus are provided. The paper concludes with several
predictions that could be verified by further theoretical or numerical work.Comment: 9 pages, 9 figures, LaTeX fil
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