162,214 research outputs found
Oscillatory and steady streaming flow in the anterior chamber of the moving eye
No full textWe study the flow induced by eye rotations in the anterior chamber (AC) of the eye,
the region between the cornea and the iris. We model the geometry of the AC as
a thin domain sitting on the surface of a sphere, and study both the simpler case
of a constant-height domain as well as a more realistic AC shape. We model eye
rotations as harmonic in time with prescribed frequency ω f and amplitude β, and use
lubrication theory to simplify the governing equations. We write the equations in a
reference frame moving with the domain and show that fluid motion is governed by
three dimensionless parameters: the aspect ratio of the AC, the angular amplitude
β and the Womersley number α. We simplify the equations under the physiologically
realistic assumptions that is small and α large, leading to a linear system that can be
decomposed into three harmonics: a dominant frequency component, with frequency
ω f , and a steady streaming component and a third component with frequency 2ω f .
We solve the problem analytically for the constant-height domain and numerically as
the solution of ordinary differential equations in the more realistic geometry. Both the
primary flow and the steady streaming are shown to have a highly three-dimensional
structure, which has not been highlighted in previous numerical works. We show
that the steady streaming is particularly relevant from the clinical point of view, as
it induces fluid mixing in the AC. Furthermore, the steady flow component is the
dominant mixing mechanism during the night, when the thermal flow induced by
temperature variations across the AC is suppressed
High-resolution extreme ultraviolet spectroscopy of G191-B2B: structure of the stellar photosphere and the surrounding interstellar medium
No full textWe have continued our detailed analysis of the high-resolution (R= 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized He ii present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this He ii resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components
Christian work as a vocation,
No full text"Available literature on the Association vocation": p. 44 (at end)The ministry, by H. H. Tweedy.--The foreign missionary's calling, by H. P. Beach.--The Young men's Christian association, by J. J. McKim.Mode of access: Internet
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
Mathematical Models of Aqueous Production, Flow and Drainage
No full textThe aqueous humour (AH) is a transparent fluid with water-like properties that fills the anterior chamber (AC, the region between the cornea and the iris) and the posterior chamber (PC, the region between the iris and the lens) of the eye, which are connected at the pupil. AH is produced at ciliary processes, and it flows from the PC to the AC, where it is drained in the trabecular meshwork. AH flow is important physiologically, as it governs intraocular pressure and delivers nutrients to avascular ocular tissues. Disruption of AH flow may lead to multiple pathological conditions, such as glaucoma and nutrient depletion. Studying aqueous production, flow and drainage is thus relevant to understand eye physiology and pathophysiology. Mathematical modelling has proven to be a very useful tool for studying AH, as it allows one to understand the mechanisms of the flow by studying them separately. In this chapter we outline the mathematical models of AH production, different AH flow mechanisms and drainage, subsequently. We focus on analytical works and briefly mention the main conclusions of numerical ones
Aqueous humour flow in the posterior chamber of the eye and its modifications due to pupillary block and iridotomy
No full textThe anterior chamber (AC) and posterior chamber (PC) of the eye are connected through the pupil and are filled with aqueous humour. The aqueous flows from the posterior to the AC at an approximately constant rate, and the intraocular pressure is governed by this rate and the resistance to aqueous outflow. In some patients the iris and lens come into contact, leading to pressure build-up in the PC, peripheral axial shallowing of the AC and, possibly, to angle-closure glaucoma. This can lead to blindness, which may be prevented by surgically creating an iridotomy, that is a hole through the iris to facilitate the flow from the posterior to the AC. The problem of optimal size and location of an iridotomy is still poorly understood. In this article, we study aqueous flow in the PC and investigate how it is modified in the presence of an iridotomy. Our approach is based on the lubrication theory, which allows us to solve the problem semi-analytically. We treat the iridotomy as a point sink and assume that the flux through it is proportional to the pressure. We find that the ideal size and location of an iridotomy are influenced by various geometrical and fluid mechanical factors, the most relevant of which are the size of the hole and the length and height of the iris-lens channel. For certain iridotomy diameters, we find that the jet velocity through the iridotomy might be large enough to cause possible corneal damage
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