Showing papers on "Water environment published in 2017"

A Survey of Underwater Optical Wireless Communications

Abstract: Underwater wireless communications refer to data transmission in unguided water environment through wireless carriers, i.e., radio-frequency (RF) wave, acoustic wave, and optical wave. In comparison to RF and acoustic counterparts, underwater optical wireless communication (UOWC) can provide a much higher transmission bandwidth and much higher data rate. Therefore, we focus, in this paper, on the UOWC that employs optical wave as the transmission carrier. In recent years, many potential applications of UOWC systems have been proposed for environmental monitoring, offshore exploration, disaster precaution, and military operations. However, UOWC systems also suffer from severe absorption and scattering introduced by underwater channels. In order to overcome these technical barriers, several new system design approaches, which are different from the conventional terrestrial free-space optical communication, have been explored in recent years. We provide a comprehensive and exhaustive survey of the state-of-the-art UOWC research in three aspects: 1) channel characterization; 2) modulation; and 3) coding techniques, together with the practical implementations of UOWC.

The importance of small waterbodies for biodiversity and ecosystem services: implications for policy makers

Abstract: Small waterbodies, including ponds and small lakes, low-order streams, ditches and springs, are the most numerous freshwater environments globally, are critical for freshwater biodiversity and are increasingly recognised for their role in ecosystem service delivery Small waters often represent the best remaining examples of intact freshwater habitats and are the most likely to remain unpolluted, often being a refuge for species which have disappeared from larger, more damaged, waterbodies Practically all water-related ecosystem services are initially mediated by small waters and some, such as carbon cycling, may be dominated by them Small waters are exposed to all the threats affecting larger waters, and some experienced only by small waters Despite this, small waters remain the least investigated part of the water environment and are largely excluded from water management planning We identify the priorities for research to underpin better protection of small waters and recommend policy actions needed to better integrate small waters into the management of catchments and landscapes The primary requirements are to identify reliable monitoring programmes for small waters, develop effective measures to protect the biodiversity and ecosystem services they provide and ensure that regulators take full account of this critical part of the water environment

The Hospital Water Environment as a Reservoir for Carbapenem-Resistant Organisms Causing Hospital-Acquired Infections-A Systematic Review of the Literature.

Abstract: Over the last 20 years there have been 32 reports of carbapenem-resistant organisms in the hospital water environment, with half of these occurring since 2010. The majority of these reports have described associated clinical outbreaks in the intensive care setting, affecting the critically ill and the immunocompromised. Drains, sinks, and faucets were most frequently colonized, and Pseudomonas aeruginosa the predominant organism. Imipenemase (IMP), Klebsiella pneumoniae carbapenemase (KPC), and Verona integron-encoded metallo-β-lactamase (VIM) were the most common carbapenemases found. Molecular typing was performed in almost all studies, with pulse field gel electrophoresis being most commonly used. Seventy-two percent of studies reported controlling outbreaks, of which just more than one-third eliminated the organism from the water environment. A combination of interventions seems to be most successful, including reinforcement of general infection control measures, alongside chemical disinfection. The most appropriate disinfection method remains unclear, however, and it is likely that replacement of colonized water reservoirs may be required for long-term clearance.

Evaluation of Phi6 Persistence and Suitability as an Enveloped Virus Surrogate.

Abstract: Recent outbreaks involving enveloped viruses, such as Ebola virus, have raised questions regarding the persistence of enveloped viruses in the water environment. Efforts have been made to find enveloped virus surrogates due to challenges investigating viruses that require biosafety-level 3 or 4 handling. In this study, the enveloped bacteriophage Phi6 was evaluated as a surrogate for enveloped waterborne viruses. The persistence of Phi6 was tested in aqueous conditions chosen based on previously published viral persistence studies. Our results demonstrated that the predicted T90 (time for 90% inactivation) of Phi6 under the 12 evaluated conditions varied from 24 min to 117 days depending on temperature, biological activity, and aqueous media composition. Phi6 persistence was then compared with persistence values from other enveloped viruses reported in the literature. The apparent suitability of Phi6 as an enveloped virus surrogate was dependent on the temperature and composition of the media tested. Of e...

Robust construction of a graphene oxide barrier layer on a nanofibrous substrate assisted by the flexible poly(vinylalcohol) for efficient pervaporation desalination

Abstract: Here, a novel thin-film nanofibrous composite (TFNC) membrane consisting of an electrospun polyacrylonitrile (PAN) nanofibrous substrate and a robust graphene oxide barrier layer was developed through a facile vacuum filtration method for pervaporation desalination application. The exfoliated hydrophilic graphene oxide (GO) nanosheets were sturdily integrated together onto the PAN nanofibrous support with the aid of a flexible connector poly(vinylalcohol) (PVA) and a crosslinking agent glutaraldehyde (GA) via vacuum filtration. The hydrophilic PVA chains acting as the spacing bridges ensured that the stacked GO nanosheets were interlinked successfully with sufficient bonding by GA to provide adequate stability in a water environment. Benefiting from the superiority of an ultra-thin hydrophilic peculiar GO skin layer and a fully interconnected porous nanofibrous substrate, the resultant optimized robust GO/PAN TFNC membranes displayed an excellent permeate flux of 69.1 L m−2 h−1 and a stable high rejection (99.9%) over a testing period of 24 h from aqueous salt solution with NaCl concentrations of 35 g L−1 at 70 °C. This separation performance was superior to those of homogeneous membranes and composite membranes used in pervaporation desalination reported so far, indicating that this work may facilitate the development of pervaporation in practical desalination application.

Generation of Subsurface Voids, Incubation Effect, and Formation of Nanoparticles in Short Pulse Laser Interactions with Bulk Metal Targets in Liquid: Molecular Dynamics Study.

Abstract: The ability of short pulse laser ablation in liquids to produce clean colloidal nanoparticles and unusual surface morphology has been employed in a broad range of practical applications In this paper, we report the results of large-scale molecular dynamics simulations aimed at revealing the key processes that control the surface morphology and nanoparticle size distributions by pulsed laser ablation in liquids The simulations of bulk Ag targets irradiated in water are performed with an advanced computational model combining a coarse-grained representation of liquid environment and an atomistic description of laser interaction with metal targets For the irradiation conditions that correspond to the spallation regime in vacuum, the simulations predict that the water environment can prevent the complete separation of the spalled layer from the target, leading to the formation of large subsurface voids stabilized by rapid cooling and solidification The subsequent irradiation of the laser-modified surface

Improving the detection limit for on-chip photonic sensors based on subwavelength grating racetrack resonators

Abstract: Compared to the conventional strip waveguide microring resonators, subwavelength grating (SWG) waveguide microring resonators have better sensitivity and lower detection limit due to the enhanced photon-analyte interaction. As sensors, especially biosensors, are usually used in absorptive ambient environment, it is very challenging to further improve the detection limit of the SWG ring resonator by simply increasing the sensitivity. The high sensitivity resulted from larger mode-analyte overlap also brings significant absorption loss, which deteriorates the quality factor of the resonator. To explore the potential of the SWG ring resonator, we theoretically and experimentally optimize an ultrasensitive transverse magnetic mode SWG racetrack resonator to obtain maximum quality factor and thus lowest detection limit. A quality factor of 9800 around 1550 nm and sensitivity of 429.7 ± 0.4nm/RIU in water environment are achieved. It corresponds to a detection limit (λ/S·Q) of 3.71 × 10-4 RIU, which marks a reduction of 32.5% compared to the best value reported for SWG microring sensors.

Water salinity detection using a smartphone

Abstract: This paper demonstrates the operation of a smartphone based platform salinity sensor for accurate and reliable monitoring of salinity level in oceanic water environment. To measure water salinity level using the smartphone, two different approaches have been proposed and their sensing performances have been compared. The first approach is based on Beer-Lambert principle where collimated light beam from an optical source while passing through the medium gets attenuated due to absorption by the medium which can be detected and analyzed by the smartphone. The second approach is based on evanescent field absorption from an uncladed U-bent sensing region of an optical fiber. Variation in salinity level of the surrounding medium of the fiber sensing region affects the absorption of evanescent field and this can be monitored by the smartphone. Two freely available android applications have been used for detection and analysis of salinity level. The designed smartphone sensor has an ability to measure salinity level variation as low as 0.1 parts per thousand (ppt) with high accuracy and repeatability. We envision that owing to its compact size, low-cost and truly user-friendly in nature, the sensing techniques could emerge as potential alternative to existing salinity sensors that would be useful for different in-field applications.

Hierarchically self-morphing structure through 4D printing

Abstract: Hierarchical self-morphing refers to the concurrent global and local changes in shape or structure. Previous research works have demonstrated 3D printed self-morphing structures and the sequential folding/unfolding behaviours. However, the shape change events occurred mainly at the global level in a water environment either through absorbing moisture or through heating. Concurrent global and local shape changes in an ambient environment have not been reported. In this paper, we report a hierarchically blooming flower that blossoms in an ambient environment. Our design considers the strain limit through understanding the effect of thickness on the local strain to avoid fracture and the appropriate allocation of multiple materials to achieve predefined global and local shape changes. This design approach of hierarchical 4D printing may be useful for a variety of applications that involve controlled self-morphing structures with complex geometries.