Raising the Bar: Increased Hydraulic Pressure Allows Unprecedented High Power Densities in Pressure-Retarded Osmosis

Pressure-retarded osmosis (PRO) has the potential to generate sustainable energy from salinity gradients. PRO is typically considered for operation with river water and seawater, but a far greater energy of mixing can be harnessed from hypersaline solutions. This study investigates the power density that can be obtained in PRO from such concentrated solutions. Thin-film composite membranes with an embedded woven mesh were supported by tricot fabric feed spacers in a specially designed crossflow cell to maximize the operating pressure of the system, reaching a stable applied hydraulic pressure of 48 bar (700 psi) for more than 10 h. Operation at this increased hydraulic pressure allowed unprecedented power densities, up to 60 W/m2 with a 3 M (180 g/L) NaCl draw solution. Experimental power densities demonstrate reasonable agreement with power densities modeled using measured membrane properties, indicating high-pressure operation does not drastically alter membrane performance. Our findings exhibit the promise of the generation of power from high-pressure PRO with concentrated solutions

Harvesting low-grade heat energy using thermo-osmotic vapour transport through nanoporous membranes

Low-grade heat from sources below 100 ∘C offers a vast quantity of energy. The ability to extract this energy, however, is limited with existing technologies as they are not well-suited to harvest energy from sources with variable heat output or with a small temperature difference between the source and the environment. Here, we present a process for extracting energy from low-grade heat sources utilizing hydrophobic, nanoporous membranes that trap air within their pores when submerged in a liquid. By driving a thermo-osmotic vapour flux across the membrane from a hot reservoir to a pressurized cold reservoir, heat energy can be converted to mechanical work. We demonstrate operation of air-trapping membranes under hydraulic pressures up to 13 bar, show that power densities as high as 3.53 ± 0.29 W m−2 are achievable with a 60 ∘C heat source and a 20 ∘C heat sink, and estimate the efficiency of a full-scale system. The results demonstrate a promising process to harvest energy from low-temperature differences (<40 ∘C) and fluctuating heat sources

Generating on-the-fly large samples of theoretical spectra through N-dimensional grid

Many analyses and parameter estimations undertaken in astronomy require a large set (> 10^5) of non-analytical, theoretical spectra, each of these defined by multiple parameters. We describe the construction of an N-dimensional grid which is suitable for generating such spectra. The theoretical spectra are designed to correspond to a targeted parameter grid but otherwise to random positions in the parameter space, and they are interpolated on-the-fly through a pre-calculated grid of spectra. The initial grid is designed to be relatively low in parameter resolution and small in occupied hard disk space and therefore can be updated efficiently when a new model is desired. In a pilot study of stellar population synthesis of galaxies, the mean square errors on the estimated parameters are found to decrease with the targeted grid resolution. This scheme of generating a large model grid is general for other areas of studies, particularly if they are based on multi-dimensional parameter space and are focused on contrasting model differences.Comment: 7 pages, 5 figures, 1 table. Accepted for publication in A

A method for the simultaneous determination of transport and structural parameters of forward osmosis membranes

We present a simple and rapid methodology to characterize the water and solute permeability coefficients (A and B, respectively) and structural parameter (S) of forward osmosis (FO) membranes. The methodology comprises a single FO experiment divided into four stages, each using a different concentration of draw solution. The experimental water and reverse salt fluxes measured in each stage are fitted to the corresponding FO transport equations by performing a least-squares non-linear regression, using A, B, and S as regression parameters. Hand-cast thin-film composite (TFC) FO membranes and commercial TFC FO, TFC reverse osmosis (RO), and cellulose acetate-based asymmetric FO membranes are evaluated following this protocol. We compare the membrane properties obtained with our FO-based methodology with those derived from existing protocols based on an RO experiment followed by an FO experiment. For all membranes, the FO-based protocol gives more accurate predictions of the water and salt fluxes than the existing method. The numerical robustness of the method and the sensitivity of the regression parameters to random errors in the measured quantities are thoroughly analyzed. The assessment shows that confidence in the accuracy of the determined membrane parameters can be enhanced by simultaneously achieving close fitting of the predicted fluxes to experimental measurements (i.e., high R2 values) and constant water to salt flux ratios in each stage. Additionally, the existing and proposed approaches yield consistently dissimilar results for some of the analyzed membranes, indicating a discrepancy that might be attributed to the different driving forces utilized in RO and in FO that should be further investigated

Pathways and challenges for efficient solar-thermal desalination

Solar-thermal desalination (STD) is a potentially low-cost, sustainable approach for providing high-quality fresh water in the absence of water and energy infrastructures. Despite recent efforts to advance STD by improving heat-absorbing materials and system designs, the best strategies for maximizing STD performance remain uncertain. To address this problem, we identify three major steps in distillation-based STD: (i) light-to-heat energy conversion, (ii) thermal vapor generation, and (iii) conversion of vapor to water via condensation. Using specific water productivity as a quantitative metric for energy efficiency, we show that efficient recovery of the latent heat of condensation is critical for STD performance enhancement, because solar vapor generation has already been pushed toward its performance limit. We also demonstrate that STD cannot compete with photovoltaic reverse osmosis desalination in energy efficiency. We conclude by emphasizing the importance of factors other than energy efficiency, including cost, ease of maintenance, and applicability to hypersaline waters

Presynaptic Localization of Sodium/Calcium Exchangers in Neuromuscular Preparations

Calcium ions play a critical role in neurotransmitter release. The cytosolic Ca 2+ concentration ([Ca2+]cyt) at nerve terminals must therefore be carefully controlled. Several different mechanisms, including a plasmalemmal Na/Ca exchanger, are involved in regulating [Ca2+]cyta We employed immunofluorescence microscopy with polyclonal antiserum raised against dog cardiac sarcolemmal Na/Ca exchanger to determine the distribution of the exchanger in vertebrate neuromuscular preparations. Our data indicate that the Na/Ca exchanger is concentrated at the neuromuscular junctions of the rat diaphragm. The exchanger is also present in the nonjunctional sarcolemma, but at a much lower concentration than in the junctional regions. Denervation markedly lowers the concentration of the exchanger in the junctional regions; this implies that the Na/Ca exchanger is concentrated in the presynaptic nerve terminals. In Xenopus laevis nerve and muscle cell cocultures, high concentrations of the exchanger are observed along the neurites as well as at the nerve terminals. The high concentrations of Na/Ca exchanger at presynaptic nerve terminals in vertebrate neuromuscular preparations suggest that the exchanger may participate in the Ca-dependent regulation of neurotransmitter release. The Na/Ca exchanger is also abundant in developing neurites and growth cones, where it may also be important for Ca2+ homeostasis

Renal outcomes of suprarenal vs. infrarenal endograft fixation in endovascular abdominal aortic aneurysm repair: a narrative review

BACKGROUND AND OBJECTIVE: Abdominal aortic aneurysm (AAA) is a common pathology with a prevalence of 4.8%. AAA rupture is associated with significant mortality and so early diagnosis followed by regular monitoring is needed until treatment might be considered and plan intervention. Endovascular aneurysm repair (EVAR) is an established and effective alternative to open surgical repair (OSR) in the treatment of AAAs. Key parameters in defining conventional EVAR suitability include the infrarenal neck length and angulation for the fixation of the proximal graft component. Endograft fixation can be either suprarenal or infrarenal and much debate exists as to which approach is associated with optimum renal outcomes. This study aims to review the current literature with respect to the renal outcomes associated with conventional EVAR using suprarenal fixation (SRF) vs. infrarenal fixation (IRF). METHODS: A search was conducted from major search indices (PubMed, Google Scholar and EMBASE) to identify relevant literature pertaining to renal outcomes in EVAR. Recent papers comparing SRF and IRF were evaluated and their findings discussed. KEY CONTENT AND FINDINGS: The mechanism of renal function decline (RFD) following EVAR is uncertain and likely multifactorial. Aortic morphology, endograft type and surgical technique may all contribute to RFD. There is a significant degree of heterogeneity within the literature regarding study design and definitions of RFD. Recent literature suggests that RFD is more acute for SRF than IRF in the first post-operative year, but the clinical significance of this decline in patients with normal kidney function is questionable. Studies indicate that SRF is associated with accelerated RFD at 5 years, and that the RFD is worse in patients who are female and who have pre-existing renal insufficiency. CONCLUSIONS: SRF is associated with a greater decline in renal function than IRF in both short- and long-terms. Although clinically insignificant in the short-term, the limited available long-term evidence suggests that SRF results in a relatively accelerated decline in renal function when compared to IRF, but it is possibly partially explained by the higher prevalence of advanced degenerative/atherosclerotic disease in SRF cohorts. These trends are noted particularly in female patients and in patients with baseline renal insufficiency

Topical Beta-Blockers and Cardiovascular Mortality: Systematic Review and Meta-Analysis with Data from the EPIC-Norfolk Cohort Study.

PURPOSE: To determine if topical beta-blocker use is associated with increased cardiovascular mortality, particularly among people with self-reported glaucoma. METHODS: All participants who participated in the first health check (N = 25,639) of the European Prospective Investigation into Cancer (EPIC) Norfolk cohort (1993-2013) were included in this prospective cohort study, with a median follow-up of 17.0 years. We determined use of topical beta-blockers at baseline through a self-reported questionnaire and prescription check at the first clinical visit. Cardiovascular mortality was ascertained through data linkage with the Office for National Statistics mortality database. Hazard ratios (HRs) were estimated using multivariable Cox regression models. Meta-analysis of the present study's results together with other identified literature was performed using a random effects model. RESULTS: We did not find an association between the use of topical beta-blockers and cardiovascular mortality (HR 0.93, 95% confidence interval, CI, 0.67-1.30). In the 514 participants with self-reported glaucoma, no association was found between the use of topical beta-blockers and cardiovascular mortality (HR 0.89, 95% CI 0.56-1.40). In the primary meta-analysis of four publications, there was no evidence of an association between the use of topical beta-blockers and cardiovascular mortality (pooled HR estimate 1.10, 95% CI 0.84-1.36). CONCLUSION: Topical beta-blockers do not appear to be associated with excess cardiovascular mortality. This evidence does not indicate that a change in current practice is warranted, although clinicians should continue to assess individual patients and their cardiovascular risk prior to commencing topical beta-blockers.EPIC-Norfolk infrastructure and core functions are supported by grants from the Medical Research Council (G1000143) and Cancer Research UK (C864/A14136). The clinic for the third health examination was funded by Age UK Research into Ageing (262). Mr Khawaja is a Wellcome Trust Clinical Research Fellow. Mr Foster has received additional support from the Richard Desmond Charitable Trust (via Fight for Sight) and the Department for Health through the award made by the National Institute for Health Research to Moorfields Eye Hospital and the UCL Institute of Ophthalmology for a specialist Biomedical Research Centre for Ophthalmology.This is the final version of the article. It first appeared from Taylor & Francis via http://dx.doi.org/10.1080/09286586.2016.1213301