1,721,221 research outputs found
The influence of hemodialysis on intraocular pressure: III. Aqueous humor dynamics and tissue hydration
No full textTheoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes
Full text linkThe Nernst equilibrium potential calculates the theoretical OCV, which estimates the best performance achievable by an electrochemical cell. When multiple semi-reactions (or multiple ionic species) are active in one of the electrodes, the calculation of the theoretical OCV is not straightforward, since different Nernst potentials are associated to each semi-reaction. In this paper, analytical equations for calculation of the theoretical OCV are developed, using the mixed potential theory. The case of H2 and CO co-oxidation (or H2O and CO2 co-reduction) in solid oxide cells is used as a reference case, but similar conclusions can be drawn for other equivalent cases. OCV data from literature are used to calibrate and validate the model. The relative reaction rate of H2 and CO semi-reactions is estimated within the calibration process, and the result is in line with assumptions and suggestions given by other authors. The validation procedure shows predicted OCV values in line with experimental literature data, except for mixtures with relatively large CH4 concentration (e.g., 8%), for which the OCV is significantly underestimated. This is expected when thermochemical reactions, in parallel to electrochemical reactions occur, since the additional H2 produced by internal steam methane reforming is not accounted within the local mixed potential model. A fuel cell polarization model is developed based on the results from the calibration procedure, and it is used to predict the polarization behavior of an SOFC fed with a H2-H2O-CO-CO2 fuel mixture. It is found that either H2 or CO may be reduced rather than oxidized via an equivalent electrochemical water-gas-shift reaction
Structural and molecular tear film changes in glaucoma
No full textThe tear film (TF) is a trilaminar and dynamic fluid covering the entire ocular surface (OS), consisting of a mucus, aqueous, and lipid layer deeply interacting between them. Because of its structure and functions, TF plays a pivotal role in the preservation of the OS integrity and the quality of vision. Medical therapy for glaucoma is recognized to profoundly disturb the OS homeostasis by altering all components of the ocular surface unit, including TF. The presence of preservatives, the number of daily eye drops instillations, and the duration of therapy are the main contributors to TF changes. From the physio-pathological side, TF alterations are induced by toxic and allergic mechanisms, and result from goblet cell and Meibomian gland loss, dysfunction of accessory lacrimal glands, and epithelial disruption. In detail, TF changes are represented by mucus layer thinning, reduced mucin concentration, aqueous layer volume reduction, and lipid layer thinning with increased tear evaporation. Hyper-osmolarity and instability represent the main hallmarks of these changes and are expression of a iatrogenic form of dry eye. TF undergoes also molecular modifications that primarily reflect a therapy- or disease-induced inflammatory status of the OS. Over the last years, this field of research gained a progressively growing interest since molecular variations may be considered as potential candidate biomarkers of glaucoma. The aim of this review is to report the main TF changes occurring during glaucoma, exploring the relationship they may have with the glaucoma-related ocular surface disease and the patient quality of life, and their utility as potential biomarkers of disease
Anterior segment optical coherence tomography imaging of conjunctival filtering blebs after glaucoma surgery
Full text linkTime domain (TD) and spectral domain (SD) optical coherence tomography (OCT) are cross-sectional, noncontact, high-resolution diagnostic modalities for posterior and anterior segment (AS) imaging. The AS-OCT provides tomographic imaging of the cornea, iris, lens, and anterior chamber (AC) angle in several ophthalmic diseases. In glaucoma, AS-OCT is utilized to evaluate the morphology of AS structures involved in the pathogenesis of the disease, to obtain morphometric measures of the AC, to evaluate the suitability for laser or surgical approaches, and to assess modifications after treatment. In patients undergoing surgery, AS-OCT is crucial in the evaluation of the filtering bleb functionality, permitting a combined qualitative and quantitative analysis. In this field, AS-OCT may help clinicians in distinguishing between functioning and nonfunctioning blebs by classifying their macroscopic morphology, describing bleb-wall features, bleb cavity, and scleral opening. This information is critical in recognizing signs of filtration failure earlier than the clinical approach and in planning the appropriate timing for management procedures in failing blebs. In this review, we summarize the applications of AS-OCT in the conjunctival bleb assessment
Solid oxide fuel cell short stack performance testing - Part A: Experimental analysis and micro-combined heat and power unit comparison
Full text linkThe need to experimentally understand the detailed performance of SOFC stacks under operating conditions typical of commercial SOFC systems has prompted this two-part study. The steady state performance of a 6-cell short stack of yttria (Y2O3) stabilised zirconia (YSZ) with Ni/YSZ anodes and composite Sr-doped lanthanum manganite (LaMnO3, LSM)/YSZ cathodes is experimentally evaluated. In Part A, the stack characterisation is carried out by means of sensitivity analyses on the fuel utilisation factor and the steam-to-carbon ratio. Electrical and environmental performances are assessed and the results are compared with a commercial full-scale micro-CHP system, which comprises the same cells. The results show that the measured temperature dynamics of the short stack in a test stand environment are on the order of many minutes; therefore, one cannot neglect temperature dynamics for a precise measurement of the steady state polarisation behaviour. The overall polarisation performance is comparable to that of the full stack employed in the micro-CHP system, confirming the good representation that short-stack analyses can give of the entire SOFC module. The environmental performance is measured verifying the negligible values of NO emissions (<10 ppb) across the whole polarisation curve
Solar hydrogen production: Techno-economic analysis of a parabolic dish-supported high-temperature electrolysis system
Full text linkThe roadmap for the hydrogen uptake passes through the development of near-zero emission and/or renewable technologies for hydrogen production. This is the rationale for the investigation of renewable power-to-fuel, namely the coupling between high temperature electrolysis and concentrating solar power. The proposed plant is conceived to supply hydrogen for a small refuelling station. It is based on solid oxide electrolyser cell technology, which performs water electrochemical reduction, in order to produce a target of 150 kg d−1 of hydrogen. The plant is integrated with a parabolic dish solar field designed to provide both electricity and thermal energy, necessary for the electrolysis reaction to take place. Specifically, a modular multi-dish configuration is selected, in which electric power is produced by 30 kWel solarized micro-gas turbines placed in the dishes’ focus. In addition to considering a pure renewable power input, a hybridization with natural gas is considered to face the variability of solar resource. Once a yearly H2 yield is estimated, a preliminary economic analysis is carried out and the levelised cost of hydrogen is subsequently obtained. It is found that the system can be operated at a nominal solar-to-hydrogen efficiency above 30%, with a solid oxide electrolysis cell efficiency around 80%. In hybrid conditions, 10 parabolic dishes (9 generating electricity through the micro-gas turbines, 1 supplying heat to the solid oxide electrolysis cell) are needed to produce the target 150 kg d−1 of hydrogen. In conclusion, the competitiveness of the plant is evaluated in comparison with other solar fuels technologies
Femtosecond Laser-Assisted Stromal Lenticule Addition Keratoplasty for the Treatment of Advanced Keratoconus: A Preliminary Study
No full textPURPOSE: To investigate the in vivo effect of a novel femtosecond laser-assisted procedure termed stromal lenticule addition keratoplasty for advanced keratoconus.
METHODS:
Ten patients with stage III and IV stable keratoconus were included. Negative meniscus-shaped stromal lenticules were produced from corneoscleral eye bank buttons with a refractive lenticule extraction procedure with a 500-kHz VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). Recipient corneas underwent a modified femtosecond laser flap-cut procedure to produce an intrastromal pocket and lenticules were implanted. Patients were followed up for 6 months after surgery with determination of uncorrected (UDVA) and corrected (CDVA) distance visual acuity, subjective refraction and topographic corneal curvature changes, anterior segment optical coherence tomography (AS-OCT), and in vivo confocal microscopy.
RESULTS:
Comparison of preoperative and 6-month postoperative UDVA and CDVA showed statistically significant improvements (P = .024 and .007, respectively) from 1.58 ± 0.36 to 1.22 ± 0.37 and from 1.07 ± 0.17 to 0.70 ± 0.23 logMAR. Eight of 10 eyes showed an improvement in UDVA (P < .001) that ranged between one and three lines, whereas all but one eye presented improved CDVA. Corneal topography documented a decrease between preoperative and 6-month postoperative anterior mean curvature (AVG-K at 3 mm) and anterior Q values (P = .005). AS-OCT showed a significant increase in thickness of the central and mid-peripheral cornea produced by the lenticule implantation (P = .005).
CONCLUSIONS:
The stromal lenticule addition keratoplasty procedure was clinically efficient in improving the corneal shape and vision in patients with keratoconus. Negative meniscus-shaped lenticule addition induced a flattening of the cone while increasing corneal thickness
Conjunctival modifications induced by medical and surgical therapies in patients with glaucoma
No full textLowering intra-ocular pressure, either medically or surgically, is the proven strategy to control glaucoma, though profound changes to the ocular surface and conjunctiva are caused. Toxicity and allergy initiated by medical therapy induce modifications, which progressively worsen with the length of treatment and number of drugs. Conjunctival changes lead to symptoms of ocular surface disease, reduced quality of life, reduced therapeutic compliance and increased risk of surgical failure. Surgery modifies conjunctiva by inducing bleb formation in fistulizing techniques, and by activating secondary aqueous humour outflow pathways, such as trans-scleral routes, in both filtration and bleb-less approaches. The use of unpreserved medications, limitation of intra-operative conjunctival damage and development of bleb-less surgery are advisable
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