An improved model to analyze the partial molar entropy step between stage II and stage I for lithium intercalation in graphite, based in statistical mechanics, is presented. At difference with our ...previous formulation, which assumed a priori heterogeneities, the present model considers the more realistic case of induced heterogeneities. The present work shows that, similarly to considerations made in the literature with intercalation cathode materials, most of the partial molar entropy changes for Li insertion into graphite may be explained on a configurational basis.
The interaction between ions intercalated in a same layer of graphite can be inferred to be strongly attractive, as was assumed in the literature for the simulation of voltammetric profiles.
3D morphometry of the human optic nerve head Sigal, Ian A.; Flanagan, John G.; Tertinegg, Inka ...
Experimental eye research,
2010, 2010-Jan, 2010-01-00, 20100101, Letnik:
90, Številka:
1
Journal Article
Recenzirano
Human optic nerve head (ONH) anatomy is of interest in glaucoma. Our goal was to carry out a morphometric study of the human ONH based on 3D reconstructions from histologic sections. A set of 10 ...human ONHs (from four pairs of eyes plus two singles) were reconstructed in an iterative procedure that required the resulting geometries to satisfy a set of quality control criteria. Five models corresponded to eyes fixed at 5 mmHg and the other five models to eyes fixed at 50 mmHg. Several aspects of ONH morphology were measured based on surface and point landmarks: the thicknesses of the lamina cribrosa (LC), the peripapillary sclera and the pre-laminar neural tissue (peripapillary and within the cup); the minimum distance between the anterior surface of the LC and the subarachnoid space; the surface area of the anterior and posterior surfaces of the LC; and the diameter of the scleral canal opening. Our results showed that about one third of the anterior LC surface was obscured from view from the front by the sclera. In all eyes the LC inserted into the pia mater, and not only into the sclera. The variations in ONH morphology between eyes of a pair exceeded, or were of the same order as, changes in morphology due to acute changes in IOP. The reconstruction and morphometry techniques introduced are suitable for application to the ONH. Comparison of measurements in eyes fixed at different pressures suggested small effects on geometry of the increase in IOP. A large variability in ONH morphology, even between contralateral eyes of different IOP, was observed. We conclude that reconstruction of human ONH anatomy from 3D histology is possible, but that large inter-individual anatomic variations make morphometric analysis of the ONH very difficult in the absence of large sample numbers. The insertion of the pia mater into the LC may have biomechanical implications and should be further investigated. Emerging clinical imaging techniques such as deep-scanning OCT will be limited to investigation of the central and mid-peripheral regions of the LC due to optical “occluding” by the peripapillary sclera.
Optic nerve head (ONH) tissue properties and biomechanics remain mostly unmeasurable in the experiment. We hypothesized that these can be estimated numerically from ocular parameters measurable in ...vivo with optical coherence tomography (OCT). Using parametric models representing human ONHs we simulated acute intraocular pressure (IOP) increases (10 mmHg). Statistical models were fit to predict, from OCT-measurable parameters, 15 outputs, including ONH tissue properties, stresses, and deformations. The calculations were repeated adding parameters that have recently been proposed as potentially measurable with OCT. We evaluated the sensitivity of the predictions to variations in the experimental parameters. Excellent fits were obtained to predict all outputs from the experimental parameters, with cross-validated R2s between 0.957 and 0.998. Incorporating the potentially measurable parameters improved fits significantly. Predictions of tissue stiffness were accurate to within 0.66 MPa for the sclera and 0.24 MPa for the lamina cribrosa. Predictions of strains and stresses were accurate to within 0.62% and 4.9 kPa, respectively. Estimates of ONH biomechanics and tissue properties can be obtained quickly from OCT measurements using an applet that we make freely available. These estimates may improve understanding of the eye sensitivity to IOP and assessment of patient risk for development or progression of glaucoma.
Density functional theory (DFT) calculations are performed for the adsorption energy of hydrogen and oxygen on graphene decorated with a wide set of metals (Li, Na, K, Al, Ti, V, Ni, Cu, Pd, Pt). It ...is found that oxygen interferes with hydrogen adsorption by either blocking the adsorption site or by the irreversible oxidation of the metal decoration. The most promising decorations are Ni, Pd, and Pt due to a reasonable relationship of adsorption energies which minimize the oxygen interference. The DFT results are used to parametrize a statistical mechanical model which allows evaluation of the effect of partial pressures in the gas phase during storage. According to this model, even in the most promising case, it is necessary to reduce the oxygen partial pressure close to ultrahigh vacuum conditions to allow hydrogen storage.
To investigate gold nanorods (GNRs) as a contrast agent to enhance Doppler optical coherence tomography (OCT) imaging of the intrascleral aqueous humor outflow.
A serial dilution of GNRs was scanned ...with a spectral-domain OCT device (Bioptigen, Durham, NC) to visualize Doppler signal. Doppler measurements using GNRs were validated using a controlled flow system. To demonstrate an application of GNR enhanced Doppler, porcine eyes were perfused at constant pressure with mock aqueous alone or 1.0×10(12) GNR/mL mixed with mock aqueous. Twelve Doppler and volumetric SD-OCT scans were obtained from the limbus in a radial fashion incremented by 30°, forming a circular scan pattern. Volumetric flow was computed by integrating flow inside non-connected vessels throughout all 12 scans around the limbus.
At the GNR concentration of 0.7×10(12) GNRs/mL, Doppler signal was present through the entire depth of the testing tube without substantial attenuation. A well-defined laminar flow profile was observed for Doppler images of GNRs flowing through the glass capillary tube. The Doppler OCT measured flow profile was not statistically different from the expected flow profile based upon an autoregressive moving average model, with an error of -0.025 to 0.037 mm/s (p = 0.6435). Cross-sectional slices demonstrated the ability to view anterior chamber outflow ex-vivo using GNR-enhanced Doppler OCT. Doppler volumetric flow measurements were comparable to flow recorded by the perfusion system.
GNRs created a measureable Doppler signal within otherwise silent flow fields in OCT Doppler scans. Practical application of this technique was confirmed in a constant pressure ex-vivo aqueous humor outflow model in porcine eyes.
Scleral structure and biomechanics Boote, Craig; Sigal, Ian A.; Grytz, Rafael ...
Progress in retinal and eye research,
01/2020, Letnik:
74
Journal Article
Recenzirano
Odprti dostop
As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide ...stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.
•Reviews the state of the art in structural, biomechanical and in silico techniques for characterising the sclera.•Presents a comprehensive view of physiological biomechanical loads on the sclera , including fluid pressures and eye movements.•Discusses recent findings on scleral changes in ageing, glaucoma and myopia.•Challenges current thinking about the relationship between scleral structure and biomechanical function.•Summarises recent therapeutic breakthroughs and predicts future areas of progress.
The purpose of this study was to leverage polarized light microscopy (PLM) to visualize the collagen fiber architecture of posterior pole and optic nerve head with micrometer-scale resolution and to ...identify and quantify major organizational components.
Eight sheep posterior poles were cryosectioned and imaged using PLM. Collagen fiber orientation was determined by using custom scripts, and the resulting orientation maps were inspected and quantified to identify major structural elements and tested for differences in mean fiber orientation and anisotropy, using linear mixed effect models.
Images revealed an intricate organization of collagen fibers in the posterior pole. In the lamina cribrosa, interweaving fibers formed large knots and wrapped around nerve fiber pores, with beam insertions into the scleral canal wall that were either narrow and straight or wide. In the peripapillary sclera, three significantly different (P < 0.0001) components were identified: fibers oriented circumferentially proximal to the canal, radially in the innermost sclera, and unaligned with interweaving fibers. The radial fibers were between 60 and 180 μm thick, extending at least 3 mm from the canal.
PLM revealed structural aspects of the lamina cribrosa and sclera that may have important biomechanical roles but that were previously unreported or not characterized quantitatively. In the lamina cribrosa, these roles included wide and narrow beam insertions and details of collagen fibers interweaving and wrapping around the pores. In the sclera, we described regions of circumferential, radial, and unaligned "random" fibers. Although there is consensus that circumferential fibers protect neural tissues by resisting canal expansion, the role of the radial fibers remains unclear.
Aqueous humor (AH) exiting the eye via the trabecular meshwork and Schlemm’s canal (SC) passes through the deep and intrascleral venous plexus (ISVP) or directly through aqueous veins. The purpose of ...this study was to visualize the human AH outflow system 360° in three dimensions (3D) during active AH outflow in a virtual casting.
The conventional AH outflow pathways of 7 donor eyes were imaged with a modified Bioptigen spectral-domain optical coherence tomography system (Bioptigen Inc, USA; SuperLum LTD, Ireland) at a perfusion pressure of 20 mmHg (
N = 3), and 10 mmHg (
N = 4). In all eyes, 36 scans (3 equally distributed in each clock hour), each covering a 2 × 3 × 2 mm volume (512 frames, each 512 × 1024 pixels), were obtained. All image data were black/white inverted, and the background subtracted (ImageJ 1.40 g,
http://rsb.info.nih.gov/ij/). Contrast was adjusted to isolate the ISVP.
SC, collector channels, the deep and ISVP, and episcleral veins were observed throughout the limbus. Aqueous veins could be observed extending into the episcleral veins. Individual scan ISVP castings were rendered and assembled in 3D space in Amira 4.1 (Visage Imaging Inc. USA). A 360-degree casting of the ISVP was obtained in all perfused eyes. The ISVP tended to be dense and overlapping in the superior and inferior quadrants, and thinner in the lateral quadrants.
The human AH outflow pathway can be imaged using SD-OCT. The more superficial structures of the AH outflow pathway present with sufficient contrast as to be optically isolated and cast in-situ 360° in cadaver eye perfusion models. This approach may be useful as a model in future studies of human AH outflow.
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► OCT can be used to non-invasively visualize the conventional aqueous outflow system. ► By using image processing, the aqueous channels from Schlemm’s canal to the episcleral vasculature can be isolated. ► A virtual casting can be created from the isolated aqueous outflow channels. ► The virtual casting can be viewed 360° in three dimensions. ► This approach may serve as a model in future studies of the conventional aqueous outflow system.
The main objective of this article is to analyze the feasibility of producing ammonia as main component for the synthesis of nitrogen fertilizers in the state of Ceará – Brazil. The potential for the ...ammonia production, via the Haber–Bosch process with electrolytic wind and solar photovoltaic hydrogen, is described with maps showing it per unit area in each municipal division of the state. Thus, by using high resolution solar radiation digital databases and average wind regimes databases (speed, Weibull factor, terrain roughness) available for Ceará, news maps of the potentials for solar and wind hydrogen are developed. Then a map of renewable hydrogen as the sum of both was created along with the corresponding potential for ammonia production with this renewable hydrogen. Land use and environmental externalities were considered as areas where energy development would be restricted.
•A proposal of an electrolytic ammonia production system is presented.•The feasibility of ammonia production for the synthesis of nitrogen fertilizers is analyzed.•Eventual ammonia produced in the state of Ceará can meet the required demand of such commodity in Brazil.
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