Important functions of cornea in the eye include protecting the structures inside the eye, contributing to the refractive power of the eye, and focusing light rays on the retina with minimum scatter ...and optical degradation. Considerable advances have taken place in understanding the organization of collagen in the corneal stroma and its clinical significance. In this review, the structure and function of various components of cornea and ocular surface are presented.
Spiral structure in disk galaxies could arise from transient modes that create conditions conducive for their regeneration; this is the proposal of Sellwood and Carlberg, based on simulations of ...stellar disks. The linear response of an axisymmetric stellar disk, to an adiabatic nonaxisymmetric transient mode, gives a final distribution function (DF) that is equal to the initial DF everywhere in phase space, except at the Lindblad and corotation resonances where the final DF is singular. We use the nonlinear theory of adiabatic capture into resonance to resolve the singularities and calculate the finite changes in the DF. These take the form of axisymmetric "scars" concentrated around resonances, whose DFs have simple general forms. Global changes in the physical properties are explored for a cool Mestel disk: we calculate the DFs of scars and estimate the changes in the disk angular momentum, surface density, and orbital frequencies leading to shifts in resonances. Resonant torques between disk stars and any new linear nonaxisymmetric mode are suppressed within a scar, as is epicyclic heating. Because all resonances of a linear mode with the same angular wavenumber and pattern speed as its precursor lie inside the scars of the precursor, it suffers less damping. Hence, scars filter the spectrum of noise-generated modes, promoting the renewal of a few select modes. Relic scars sustained by a galaxy disk, due to past tidal interaction with a passing companion, may still be active enablers of nonaxisymmetric modes, such as the two-armed "grand design" spiral patterns.
We apply the Tremaine-Weinberg theory of dynamical friction to compute the orbital decay of a globular cluster (GC) on an initially circular orbit inside a cored spherical galaxy with isotropic ...stellar velocities. The retarding torque on the GC, , is a function of its orbital radius . The torque is exerted by stars whose orbits are resonant with the GC's orbit and given as a sum over the infinitely many possible resonances by the Lynden-Bell-Kalnajs (LBK) formula. We calculate the LBK torque and determine for a GC of mass and an isochrone galaxy of core mass and core radius . (i) When , many strong resonances are active, and as expected, , the classical Chandrasekhar torque. (ii) For , comes mostly from stars nearly corotating with the GC, trailing or leading it slightly; trailing resonances exert stronger torques. (iii) As decreases, the number and strength of resonances drop, so also decreases, with at , a characteristic "filtering" radius. (iv) Many resonances cease to exist inside this includes all leading and low-order trailing ones. (v) The higher-order trailing resonances inside are very weak, with at . (vi) Inspiral times for to decay from to far exceed .
•Facile separation of methanol/toluene azeotrope using a novel TEOS crossed composite chitosan/PTFE membrane.•TEOS cross-linking improved separation factor and thermal stability.•A combination of ...Molecular Dynamics and CFD simulations enabled performance prediction of commercial pervaporation systems.•High potential for membrane scale up owing to its composite structure.
Present work reports the synthesis of a novel Chitosan-Polytetrafluoroethylene composite membrane with solvent resistant property for efficient separation of methanol/toluene mixture by pervaporation. The composite was crossed with tetraethyl orthosilicate (TEOS) to prevent or reduce membrane swelling and improve the separation factor. The synthesized membranes were characterized by SEM, FTIR and DSC analysis. Molecular dynamics (MD) simulation and computational fluid dynamics were coupled to predict the structural and diffusive properties besides concentration profile inside the membrane. Diffusion coefficients of methanol and toluene were found to be 1.7 × 10−9 and 1.8 × 10−12 m2/s, respectively. The effect of crosslinking on process parameters such as flux and separation factor was analyzed. The study confirmed that increasing TEOS concentration reduced the methanol flux but enhanced separation factor with respect to this alcohol. The membranes exhibited a flux of 0.13 kg/m2 h and separation factor of 58.4 for azeotropic feed composition of 68 wt% methanol.
Mitochondrial function is critical to maintain high rates of oxidative metabolism supporting energy demands of both spontaneous and evoked neuronal activity in the brain. Mitochondria not only ...regulate energy metabolism, but also influence neuronal signaling. Regulation of “energy metabolism” and “neuronal signaling” (i.e. neurometabolic coupling), which are coupled rather than independent can be understood through mitochondria’s integrative functions of calcium ion (Ca2+) uptake and cycling. While mitochondrial Ca2+ do not affect hemodynamics directly, neuronal activity changes are mechanistically linked to functional hyperemic responses (i.e. neurovascular coupling). Early in vitro studies lay the foundation of mitochondrial Ca2+ homeostasis and its functional roles within cells. However, recent in vivo approaches indicate mitochondrial Ca2+ homeostasis as maintained by the role of mitochondrial Ca2+ uniporter (mCU) influences system-level brain activity as measured by a variety of techniques. Based on earlier evidence of subcellular cytoplasmic Ca2+ microdomains and cellular bioenergetic states, a mechanistic model of Ca2+ mobilization is presented to understand systems-level neurovascular and neurometabolic coupling. This integrated view from molecular and cellular to the systems level, where mCU plays a major role in mitochondrial and cellular Ca2+ homeostasis, may explain the wide range of activation-induced coupling across neuronal activity, hemodynamic, and metabolic responses.
Seawater intrusion promotes the salinity of groundwater, and it poses a great environmental impact on a global scale. The present study was carried out to determine the hydrogeochemical processes and ...influence of seawater intrusion in the coastal aquifers using geophysical, geochemical, and stable isotope techniques. The true resistivity value ranges from 0.5 to 8008.5 Ω-m which has been measured using vertical electrical sounding (VES) based on the Schlumberger method. About 33 groundwater samples were collected during post-monsoon (POM) (January 2012) and pre-monsoon (PRM) (June 2012) seasons from open and bore wells and were analyzed for major ions and stable isotopes. EC, Na
+
, and Cl
−
were high in groundwater of wells near salt pan, the Buckingham Canal, and backwater regions. Around 45% of the groundwater of this study area is of Na
+
-Cl
−
type due to salinisation. Reverse ion exchange and silicate weathering are the dominant processes controlling the geochemistry of groundwater. Saturation indexes (SI) of halite (SI
halite
) and gypsum (SI
gypsum
) versus sulfate show an increasing trend line from > 0 to < 0, which implies higher dissolution of minerals and hints increasing salinization during both seasons. The value of Na
+
/Cl
−
ranges between 0.7 and 2.4 (POM) and from 0.6 to 2.8 (PRM). The molar ratio suggested that around 25% of the groundwater samples are with values similar to those of seawater. Further, the groundwater is also affected by saline backwater, salt pan activities, and Buckingham Canal. Some locations are also are affected by anthropogenic, agricultural activities and geochemical processes. Heavy stable isotopes were found to be dominant in the coastal region due to seawater intrusion. Stable isotopes of δ
18
O range from − 5.6 to − 2.9‰ during both periods. About 201 km
2
of this area is affected by salinization. It is necessary to reduce pumping and plan for physical barriers to create freshwater ridges for controling the seawater intrusion.
In healthy hearts myocytes are typically coupled to nearest neighbours through gap junctions. Under pathological conditions such as fibrosis, or in scar tissue, or across ablation lines myocytes can ...uncouple from their neighbours. Electrical conduction may still occur via fibroblasts that not only couple proximal myocytes but can also couple otherwise unconnected regions. We hypothesise that such coupling can alter conduction between myocytes via introduction of delays or by initiation of premature stimuli that can potentially result in reentry or conduction blocks. To test this hypothesis we have developed several 2-cell motifs and investigated the effect of fibroblast mediated electrical coupling between uncoupled myocytes. We have identified various regimes of myocyte behaviour that depend on the strength of gap-junctional conductance, connection topology, and parameters of the myocyte and fibroblast models. These motifs are useful in developing a mechanistic understanding of long-distance coupling on myocyte dynamics and enable the characterisation of interaction between different features such as myocyte and fibroblast properties, coupling strengths and pacing period. They are computationally inexpensive and allow for incorporation of spatial effects such as conduction velocity. They provide a framework for constructing scar tissue boundaries and enable linking of cellular level interactions with scar induced arrhythmia.
Growth of highly dense ZnO nanowires (ZnO NWs) is demonstrated on three-dimensional graphene foam (GF) using resistive thermal evaporation technique. Photoresponse of the as-grown hybrid structure of ...ZnO NWs on GF (ZnO NWs/GF) is evaluated for ultraviolet (UV) detection. Excellent photoresponse with fast response and recovery times of 9.5 and 38 s with external quantum efficiency of 2490.8% is demonstrated at low illumination power density of 1.3 mW/cm2. In addition, due to excellent charge carrier transport, mobility of graphene reduces the recombination rate of photogenerated charge carriers, hence the lifetime of photogenerated free charge carriers enhances in the photodetectors.
We present a first-principles theory of resonant relaxation (RR) of a low-mass stellar system orbiting a more massive black hole (MBH). We first extend the kinetic theory of Gilbert to include the ...Keplerian field of a black hole of mass M
•. Specializing to a Keplerian stellar system of mass M ≪ M
•, we use the orbit-averaging method of Sridhar & Touma to derive a kinetic equation for RR. This describes the collisional evolution of a system of N ≫ 1 Gaussian rings in a reduced 5-dim space, under the combined actions of self-gravity, 1 post-Newtonian (PN) and 1.5 PN relativistic effects of the MBH and an arbitrary external potential. In general geometries, RR is driven by both apsidal and nodal resonances, so the distinction between scalar RR and vector RR disappears. The system passes through a sequence of quasi-steady secular collisionless equilibria, driven by irreversible two-ring correlations that accrue through gravitational interactions, both direct and collective. This correlation function is related to a ‘wake function’, which is the linear response of the system to the perturbation of a chosen ring. The wake function is easier to appreciate, and satisfies a simpler equation, than the correlation function. We discuss general implications for the interplay of secular dynamics and non-equilibrium statistical mechanics in the evolution of Keplerian stellar systems towards secular thermodynamic equilibria, and set the stage for applications to the RR of axisymmetric discs in Paper III.
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