2,381 research outputs found
A solute gradient in the tear meniscus I. A hypothesis to explain Marx's line
Marx's line is a line of mucosal staining behind the mucocutaneous junction. It can be demonstrated throughout life in all normal lids by staining with lissamine green and related dyes. Of all the body orifices, only the mucosae of the eye and mouth are directly exposed to the atmosphere. In this paper, we suggest that for the eye, this exposure leads to the formation of Marx's line. The tear meniscus thins progressively toward its apex, where it is pinned at the mucocutaneous junction of the lid. It also thins toward the black line, which segregates the meniscus from the tear film after the blink. We predict that, because of the geometry of the tear meniscus, evaporation generates a solute gradient across the meniscus profile in the anteroposterior plane, which peaks at the meniscus apices at the end of the interblink. One outcome would be to amplify the level of tear molarity at these sites so that they reach hyperosmolar proportions. Preliminary mathematical modeling suggests that dilution of this effect by advection and diffusion of solute away from the meniscus apex at the mucocutaneous junction will be restricted by spatial constraints, the presence of tear and surface mucins at this site, and limited fluid flow. We conclude that evaporative water loss from the tear meniscus may result in a physiological zone of hyperosmolar and related stresses to the occlusal conjunctiva, directly behind the mucocutaneous junction. We hypothesize that this stimulates a high epithelial cell turnover at this site, incomplete epithelial maturation, and a failure to express key molecules such as MUC 16 and galectin-3, which, with the tight junctions between surface epithelial cells, are necessary to seal the ocular surface and prevent penetration of dyes and other molecules into the epithelium. This is proposed as the basis for Marx's line. In Part II of this paper (also published in this issue of The Ocular Surface), we address additional pathophysiological consequences of this mechanism, affecting lid margins
A solute gradient in the tear meniscus II. implications for lid margin disease, including meibomian gland dysfunction
We have hypothesized previously that evaporation from the tears generates a solute gradient across the tear meniscus, which delivers hyperosmolar stress to the mucocutaneous junction (MCJ) of the lid margin. This is proposed as the basis for Marx's line, a line of staining with topically applied dyes that lies directly behind the MCJ. In this article, we consider the implications of this hypothesis for progressive damage to the lid margin as an age-related phenomenon, its amplification in dry eye states, and its possible role in the etiology of meibomian gland dysfunction (MGD). It is suggested that a hyperosmolar or related stimulus, acting behind the MCJ over a lifetime, promotes the anterior migration of the MCJ, which is a feature of the aging lid margin. This mechanism would be amplified in dry eye states, not only by reason of increased tear molarity at the meniscus apex but also by raising the concentration of inflammatory peptides at this site. This could explain the increased width and irregularity of Marx's line in dry eye. While the presence of stem cells at the lid margin may equip this region to respond to such stress, their depletion could be the basis of irreversible lid margin damage. It is further proposed, given the proximity of the MCJ to the meibomian gland orifices, that the solute gradient mechanism could play a role in the initiation of MGD by delivering hyperosmolar and inflammatory stresses to the terminal ducts and orifices of the glands. By the same token, the presence of a zone of increased epithelial permeability in this region may provide a back door route for the delivery of drugs in the treatment of MGD
A mass and solute balance model for tear volume & osmolarity in the normal and the dry eye
Tear hyperosmolarity is thought to play a key role in the mechanism of dry eye, a common symptomatic condition accompanied by visual disturbance, tear film instability, inflammation and damage to the ocular surface. We have constructed a model for the mass and solute balance of the tears, with parameter estimation based on extensive data from the literature which permits the influence of tear evaporation, lacrimal flux and blink rate on tear osmolarity to be explored. In particular the nature of compensatory events has been estimated in aqueous-deficient (ADDE) and evaporative (EDE) dry eye.\ud
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The model reproduces observed osmolarities of the tear meniscus for the healthy eye and predicts a higher concentration in the tear film than meniscus in normal and dry eye states. The differential is small in the normal eye, but is significantly increased in dry eye, especially for the simultaneous presence of high meniscus concentration and low meniscus radius. This may influence the interpretation of osmolarity values obtained from meniscus samples since they need not fully reflect potential damage to the ocular surface caused by tear film hyperosmolarity.\ud
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Interrogation of the model suggests that increases in blink rate may play a limited role in compensating for a rise in tear osmolarity in ADDE but that an increase in lacrimal flux, together with an increase in blink rate, may delay the development of hyperosmolarity in EDE. Nonetheless, it is predicted that tear osmolarity may rise to much higher levels in EDE than ADDE before the onset of tear film breakup, in the absence of events at the ocular surface which would independently compromise tear film stability. Differences in the predicted responses of the pre-ocular tears in ADDE compared to EDE or hybrid disease to defined conditions suggest that no single, empirically-accessible variable can act as a surrogate for tear film concentration and the potential for ocular surface damage. This emphasises the need to measure and integrate multiple diagnostic indicators to determine outcomes and prognosis. Modelling predictions in addition show that further studies concerning the possibility of a high lacrimal flux phenotype in EDE are likely to be profitable
Random-energy model in random fields
The random-energy model is studied in the presence of random fields.
The problem is solved exactly both in the microcanonical ensemble, without
recourse to the replica method, and in the canonical ensemble using the replica
formalism. The phase diagrams for bimodal and Gaussian random fields are
investigated in detail. In contrast to the Gaussian case, the bimodal random
field may lead to a tricritical point and a first-order transition. An
interesting feature of the phase diagram is the possibility of a first-order
transition from paramagnetic to mixed phase.Comment: 18 pages, 5 figures (included
Observations of gravity waves in the mesosphere with the MU radar
Wind motions were observed at 60 to 90 km altitudes with the MU radar during daylight hours (0800 to 1600 LT) from 13 to 31 October 1986. Quasi-monochromatic gravity waves were evident on 16 of the 19 days of observations. They were characterized by typical vertical wavelength of 5 to 15 km and intrinsic periods centered at about 9 hours. The propagation direction of the gravity waves, determined by the gravity wave dispersion relation, was mostly equatorward. The vertical wave number spectra of the horizontal components of the mesoscale wind fluctuations are explained well by saturated gravity wave theory. The frequency spectrum of vertical wind component has a slope of + 1/3, while the oblique spectra have a slope of -5/3 up to 4 x 10(-3) (c/s); these agree fairly well with model gravity wave spectra. Doppler shift effects on the frequency spectra are recognized at higher frequencies. Upward flux was determined of horizontal momentum flux induced by waves with periods from 10 min to 8 hours, and westward and northward body forces of 5.1 and 4.0 m/s/day, were estimated respectively
Spectral-Function Sum Rules in Supersymmetry Breaking Models
The technique of Weinberg's spectral-function sum rule is a powerful tool for
a study of models in which global symmetry is dynamically broken. It enables us
to convert information on the short-distance behavior of a theory to relations
among physical quantities which appear in the low-energy picture of the theory.
We apply such technique to general supersymmetry breaking models to derive new
sum rules.Comment: 18 pages, 1 figur
Relationships between a roller and a dynamic pressure distribution in circular hydraulic jumps
We investigated numerically the relation between a roller and the pressure
distribution to clarify the dynamics of the roller in circular hydraulic jumps.
We found that a roller which characterizes a type II jump is associated with
two high pressure regions after the jump, while a type I jump (without the
roller) is associated with only one high pressure region. Our numerical results
show that building up an appropriate pressure field is essential for a roller.Comment: 10 pages, 7 PS files. To appear in PR
Re(\gamm,n) cross section close to and above the neutron threshold
The neutron capture cross section of the unstable nucleus Re is
studied by investigating the inverse photodisintegration reaction
Re(,n). The special interest of the {\it s}-process branching
point Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}^{186}\gamma^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres
Susceptibility Amplitude Ratios Near a Lifshitz Point
The susceptibility amplitude ratio in the neighborhood of a uniaxial Lifshitz
point is calculated at one-loop level using field-theoretic and
-expansion methods. We use the Schwinger parametrization of the
propagator in order to split the quadratic and quartic part of the momenta, as
well as a new special symmetry point suitable for renormalization purposes. For
a cubic lattice (d = 3), we find the result .Comment: 7 pages, late
Specific heat amplitude ratios for anisotropic Lifshitz critical behaviors
We determine the specific heat amplitude ratio near a -axial Lifshitz
point and show its universal character. Using a recent renormalization group
picture along with new field-theoretical -expansion techniques,
we established this amplitude ratio at one-loop order. We estimate the
numerical value of this amplitude ratio for and . The result is in
very good agreement with its experimental measurement on the magnetic material
. It is shown that in the limit it trivially reduces to the
Ising-like amplitude ratio.Comment: 8 pages, RevTex, accepted as a Brief Report in Physical Review
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