Solar stills:a comprehensive review of designs, performance and material advances

The demand for fresh water production is growing day by day with the increase in world population and with industrial growth. Use of desalination technology is increasing to meet this demand. Among desalination technologies, solar stills require low maintenance and are readily affordable; however their productivity is limited. This paper aims to give a detailed review about the various types of solar stills, covering passive and active designs, single- and multi-effect types, and the various modifications for improved productivity including reflectors, heat storage, fins, collectors, condensers, and mechanisms for enhancing heat and mass transfer. Photovoltaic-thermal and greenhouse type solar stills are also covered. Material advances in the area of phase change materials and nanocomposites are very promising to enhance further performance; future research should be carried out in these and other areas for the greater uptake of solar still technology

Effects of nanoparticle-enhanced phase change material (NPCM) on solar still productivity

This paper investigates the effects of nanoparticle-enhanced phase change material (NPCM) on solar still operation and performance. Technical and economic aspects were considered, to show an advance on earlier works using virgin phase-change materials (PCM). Three types of nanoparticle (TiO2, CuO and GO) were impregnated individually at 0.3 weight% in paraffin to form NPCM-1, NPCM-2 and NPCM-3 respectively. Experiments were conducted with four solar stills (SS) each of 0.5 m2 area using respectively paraffin (SSPCM), paraffin-TiO2 (SSNPCM-1), paraffin-CuO (SSNPCM-2) and paraffin-GO (SSNPCM-3). There was observed an increase in thermal conductivity and a reduction in melting and solidification temperatures, with NPCM compared to PCM. The effects of NPCM on water temperature, storage temperature, hourly and annual productivity were determined. SSPCM, SSNPCM-1, SSNPCM-2 and SSNPCM-3 yielded 3.92, 4.94, 5.28 and 3.66 l/m2/day respectively, corresponding to 26 and 35% increases in productivity of SSNPCM-1 and 2 respectively over SSPCM. Economic analysis showed cost per liter (CPL) of water of $0.035,$0.028, $0.026 and$0.13 for SSPCM, SSNPCM-1, 2 and 3 respectively. Considering the advantages in productivity and CPL, SSNPCM-2 can be recommended as the best solar still compared to SSPCM, SSNPCM-1 and 3, providing clean water at less than half the cost of bottled water in India

A cross sectional study of prevalence of depression among patients with cerebrovascular accident

Background: Depression is one of the most common neuropsychiatric condition in patients with stroke. Early identification of depression for stroke patients can improve the outcome leading to better quality of life. Prevalence and determinants of post stroke depression are highly variable and there is paucity of data in Indian literature.Methods: This cross-sectional study was conducted at neurology department of Saveetha Medical College, Chennai. All patients with history of stroke within past one month attending neurology department who fulfilled the inclusion criteria were taken up for the study after getting consent. Neurological examination and CT brain findings were noted with the site of lesion. All patients were evaluated for depression using ICD 10 criteria. MADRS score was used to assess the severity of depression. Chi square was used for statistical analysis.Results: The mean age of subjects in the study was 56.54±10.82 years. The prevalence of depression among patients with stroke in our study was 75.8%. Among classifying those with depression based on severity using MADRS score, 35% had mild depression and 65% had moderate depression. There was no severe depression in our sample. There was no statistically significant difference between prevalence of depression based on side of lesion.Conclusions: In this study the prevalence of depression among patients with cerebrovascular accident was found to be 75.8%. From this study we learn that the prevalence of depression in patients with stroke is high and this shows that regular screening of patients with stroke for depression might help in earlier detection and management of depression

Nanoparticles Enhanced Phase Change Material (NPCM) as Heat Storage in Solar Still Application for Productivity Enhancement

Whereas other researchers used various active and passive techniques to improve the productivity of solar still, this paper uses nanoparticles impregnated in phase change material (NPCM) for productivity enhancement. The solar still is fabricated individually with phase change material (PCM) and NPCM and analyzed both experimentally and theoretically. It is found that the solar still with PCM yielded 1.96 kg/0.5m2 whereas the solar still with NPCM yielded 2.64 kg/0.5m2. There was 35% improvement in productivity observed in solar still with NPCM as against solar still with PCM. The experimental results were validated with the predicted results and the discrepancy was found to be ±10%. Hence it is concluded that NPCM has better potential than PCM for solar still application

Techno-economic analysis of solar stills using integrated fuzzy analytical hierarchy process and data envelopment analysis

Desalination using solar stills is an ancient economic method for water desalination. Over the years, research and development in the area of solar still has resulted in increased distillate yield by means of integration of PCM (phase change material), photo-voltaic thermal (PVT), etc with the still. Nano-PCM is an upcoming technology which modifies the thermal performance of PCM. The aim of this research is to analyze the efficiency of 20 solar stills including nano-PCM based solar stills considering various input and output criteria using integrated fuzzy analytical hierarchy process (AHP) and data envelopment analysis (DEA). The efficiency derived here is relative with regard to the parameters and stills considered in this study. The result infers that, even though the productivity of stepped solar still with sun tracking system was high, but when techno-economic aspects were considered it is not among the top solar stills. The analysis indicated pyramid type solar still, single slope solar still with PVT, solar still with NPCM (paraffin + copper oxide), solar still with NPCM (paraffin + titanium dioxide) and solar still with PCM (paraffin) occupies the top five positions with relative efficiency of 100, 100, 88.47, 88.46 and 76.93% respectively

Widespread polycistronic gene expression in green algae

Polycistronic gene expression, common in prokaryotes, was thought to be extremely rare in eukaryotes. The development of long-read sequencing of full-length transcript isomers (Iso-Seq) has facilitated a reexamination of that dogma. Using Iso-Seq, we discovered hundreds of examples of polycistronic expression of nuclear genes in two divergent species of green algae: Chlamydomonas reinhardtii and Chromochloris zofingiensis Here, we employ a range of independent approaches to validate that multiple proteins are translated from a common transcript for hundreds of loci. A chromatin immunoprecipitation analysis using trimethylation of lysine 4 on histone H3 marks confirmed that transcription begins exclusively at the upstream gene. Quantification of polyadenylated [poly(A)] tails and poly(A) signal sequences confirmed that transcription ends exclusively after the downstream gene. Coexpression analysis found nearly perfect correlation for open reading frames (ORFs) within polycistronic loci, consistent with expression in a shared transcript. For many polycistronic loci, terminal peptides from both ORFs were identified from proteomics datasets, consistent with independent translation. Synthetic polycistronic gene pairs were transcribed and translated in vitro to recapitulate the production of two distinct proteins from a common transcript. The relative abundance of these two proteins can be modified by altering the Kozak-like sequence of the upstream gene. Replacement of the ORFs with selectable markers or reporters allows production of such heterologous proteins, speaking to utility in synthetic biology approaches. Conservation of a significant number of polycistronic gene pairs between C. reinhardtii, C. zofingiensis, and five other species suggests that this mechanism may be evolutionarily ancient and biologically important in the green algal lineage

Low mass fraction impregnation with graphene oxide (GO) enhances thermo-physical properties of paraffin for heat storage applications

Whereas previous researchers analyzed the thermal behavior of paraffin waxes impregnated with graphene oxide nanoparticles (P-GONP) at high mass fraction ( > 1%), this paper analyzes behavior and stability at only 0.3% mass fraction. GONP was prepared by Hummer’s method. The morphology was studied using scanning electron microscope (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD) and Fourier Transformation-Infrared (FT-IR) Spectrometer and the thermal properties were measured using laser flash analyser (LFA), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and thermal cycling. LFA showed a 101.2% and 94.5% increase in the thermal conductivity of P-GONP compared to pure paraffin (P) in solid and liquid state respectively. Melting and solidifying temperatures and latent heat were found to be 63.5, 59 °C & 102 kJ/kg and 57.5, 56 °C & 64.7 kJ/kg for P and P-GONP respectively. Thermal cycling over 4000 cycles showed that P-GONP was 27% more stable than P. The latent heat was 64.7 kJ/kg, a 36.5% deterioration compared to virgin paraffin. Compared against higher mass fraction impregnation, lower mass fraction P-GONP was found to have almost equivalent thermo-physical properties (namely thermal conductivity, melting and solidifying characteristics, thermo-chemical stability and reliability) while providing considerable cost saving

SYMBA: An end-to-end VLBI synthetic data generation pipeline: Simulating Event Horizon Telescope observations of M 87

Context. Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are the most important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a direct comparison with observational data. Aims. We present the SYnthetic Measurement creator for long Baseline Arrays (SYMBA), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations. SYMBA takes into account several realistic atmospheric, instrumental, and calibration effects. Methods. We used SYMBA to create synthetic observations for the Event Horizon Telescope (EHT), a millimetre VLBI array, which has recently captured the first image of a black hole shadow. After testing SYMBA with simple source and corruption models, we study the importance of including all corruption and calibration effects, compared to the addition of thermal noise only. Using synthetic data based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M 87, we performed case studies to assess the image quality that can be obtained with the current and future EHT array for different weather conditions. Results. Our synthetic observations show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of our GRMHD source models can be recovered robustly with the EHT2017 array after performing calibration steps, which include fringe fitting, a priori amplitude and network calibration, and self-calibration. With the planned addition of new stations to the EHT array in the coming years, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images

THEMIS: A Parameter Estimation Framework for the Event Horizon Telescope

The Event Horizon Telescope (EHT) provides the unprecedented ability to directly resolve the structure and dynamics of black hole emission regions on scales smaller than their horizons. This has the potential to critically probe the mechanisms by which black holes accrete and launch outflows, and the structure of supermassive black hole spacetimes. However, accessing this information is a formidable analysis challenge for two reasons. First, the EHT natively produces a variety of data types that encode information about the image structure in nontrivial ways; these are subject to a variety of systematic effects associated with very long baseline interferometry and are supplemented by a wide variety of auxiliary data on the primary EHT targets from decades of other observations. Second, models of the emission regions and their interaction with the black hole are complex, highly uncertain, and computationally expensive to construct. As a result, the scientific utilization of EHT observations requires a flexible, extensible, and powerful analysis framework. We present such a framework, Themis, which defines a set of interfaces between models, data, and sampling algorithms that facilitates future development. We describe the design and currently existing components of Themis, how Themis has been validated thus far, and present additional analyses made possible by Themis that illustrate its capabilities. Importantly, we demonstrate that Themis is able to reproduce prior EHT analyses, extend these, and do so in a computationally efficient manner that can efficiently exploit modern high-performance computing facilities. Themis has already been used extensively in the scientific analysis and interpretation of the first EHT observations of M87