Polarization Layer Research Articles

Optimal intermittent ultrasound-assisted ultrafiltration for membrane fouling remediation

One of the most critical issues encountered in membrane-based separation processes is the permeate flux decline over a long period of operation. This study considered the potential advantages of applying intermittent ultrasound (US) to the ultrafiltration (UF) processes to control long term membrane fouling. The particles in the feed solution tend to attach to the membrane's internal pores and accumulate on the membrane surface, which impedes the filtration process and limits separation efficiency and significantly increases the power consumption. US-generated microbubbles create local turbulence and shear effect near the membrane surface, which disrupt the concentration polarization and fouling layer, resulting in flux improvement. In this regard, remediation of ceramic membrane fouling by an in-line intermittent US system was investigated. Bubble generation under different frequencies (20 kHz, 28 kHz, and 40 kHz), power intensities (50 W, 60 W, and 100 W) and time intervals were evaluated to determine the optimal US condition for enhanced filtration. A real time in-situ imaging of US-generated bubbles was employed, using a synchrotron propagation-based imaging (PBI) at the Canadian Light Source (CLS). A novel non-invasive method was employed to improve the contrast between the liquid and gas inside the bubble (interface of liquid and gas) facilitating the qualitative and quantitative analysis of US-generated bubbles. In addition, a piezoelectric ultrasonic transducer was integrated into a UF unit that was used to filter a 0.5 wt% latex paint solution. The microbubble dynamics at different US conditions were analyzed in order to correlate it with latex particles’ detachment, cake formation control and flux enhancement from data obtained with filtration experiments. It was found that the flux enhancement at 20 kHz and 28 kHz were significant, while the flux enhancement at 100 kHz was not noticeable. It was also observed that the amount of deposited particles on the membrane decreased when the frequency was increased. Oscillation of large bubbles leads to liquid movement around the bubbles and reduces the probability of the particle-membrane attachment. Our results showed that the bubble velocity increased as the frequency was increased from 20 kHz to 40 kHz. In addition, more bubbles were created when the US irradiation was turned on; however, the bubbles did not disappear when the US was off, which represent the long lifetime of the bubbles. The optimal flux was achieved when the ultrasound was set at a frequency of 28 kHz and power intensity of 50 W, while the interval of intermittent ultrasound was set at 60 s.

Theory of nematic and polar active fluid surfaces

We derive a fully covariant theory of the hydrodynamics of nematic and polar active surfaces, subjected to internal and external forces and torques. We study the symmetries of polar and nematic surfaces and find that in addition to 5 different types of in-plane isotropic surfaces, polar and nematic surfaces can be classified into 5 polar, 2 pseudopolar, 5 nematic and 2 pseudonematic types of surfaces. We give examples of physical realisations of the different types of surfaces we have identified. We obtain expressions for the equilibrium tensions, moments, and external forces and torques acting on a passive polar or nematic surface. We calculate the entropy production rate using the framework of thermodynamics close to equilibrium and find constitutive equations for polar and nematic active surfaces with different symmetries. We study the instabilities of a confined flat planar-chiral polar active layer and of a confined deformable polar active surface with broken up-down symmetry.

Impact of the Polarization Layer on the Hydrodynamics and Mechanical Performance of a Filtering Hydrocyclone Applied to Oily Water Separation

The growing concern with the environment has driven the development of new technologies for the treatment of produced water. In this context, the filtering hydrocyclone appears as an interesting alternative for the treatment of these waters contaminated with oil from the petroleum industry. This research addresses the flow of fluids inside a hydrocyclone equipped with a porous wall (membrane) containing two tangential inlets and two concentric outlets, with the aim of study the impact of the formation of the polarization layer by concentration on the oily water separation process using CFD. Concentration fields and transmembrane pressure, concentration, and permeate flux profiles are presented and analyzed. The results show that the proposed filtering cyclonic separator concentrates the oil in the central region of the equipment, however, for high oil concentrations; the core expands and approaches the porous wall. Furthermore, the increase in the oil volume fraction causes a decline in the permeate flux, and an increase in feed velocity causes a decrease in the polarization layer.

Separation of oil–water emulsion by disc ceramic membrane under dynamic membrane filtration mode

The disc ceramic membrane under a dynamic membrane filtration is applied to separate oil–water emulsion. The dynamic membrane filtration means that the membrane is rotating to obtain the flow velocity of membrane surface but the feed solution is almost still. In this case, the trans-membrane pressure (TMP) and the flow velocity of membrane surface can be controlled separately. Here, the effects of operation parameters on the separation performance and re-generation of disc ceramic membrane are studied. The membrane fouling and stability and practicability of disc ceramic membrane are evaluated. The results show that the permeate flux of disc ceramic membrane increases with the increment of rotating speed and the rejection increases with the TMP decreases. Furthermore, the rejection efficiency of oil achieved up to ＞99.9% during a 90 min continuous separation if the TMP was only 0.2 bar. High flow velocity but low TMP of disc ceramic membrane alleviates the membrane fouling caused by concentration polarization layer and gel layer, and reduces the deformation and penetration of oil droplets. This work provides a new method to separate the high-concentration of oil–water emulsion.

A novel Cu-BTC@PVA/PVDF Janus membrane with underwater-oleophobic/hydrophobic asymmetric wettability for anti-fouling membrane distillation

In this study, a novel Janus membrane was developed by constructing Cu-1,3,5-benzenetricarboxylic acid (Cu-BTC) metal–organic frameworks (MOFs) hydrophilic coating on polyvinylidene fluoride (PVDF) membrane. The Cu-BTC@PVA/PVDF Janus membrane showed a rougher surface with an in-air water contact angle of 27.4˚ and an underwater oil contact angle of 152.8°. The Cu-BTC had minimal impact on mass transfer efficiency in MD process, and the Janus membrane exhibited excellent anti-oil-fouling and anti-NOM-fouling properties. The formation of the hydration layer, the slip boundary effect, and the electrostatic repulsion by the hydrophilic serrated interface were the main antifouling mechanisms. The hydrophobic-hydrophobic interaction was the main fouling mechanism of PVDF membrane for both oil and NOM. Sodium alginate (SA) displayed severe fouling with a compacted fouling layer in PVDF membrane due to the concentration polarization (CP) and gel layer formation. Inorganic fouling was the predominant fouling for the high CP and inorganic–organic coupling. While humic acid (HA) surpassed SA in Cu-BTC@PVA/PVDF Janus membrane for the stronger hydrogen bond, hydrophobic-hydrophobic interaction was significantly alleviated. Inorganic fouling was also significantly alleviated due to the strong electrostatic repulsion effect. The prepared Janus membrane has great potential to promote MD dealing with hypersaline industrial wastewaters containing complex organic matters.

Urea-ZrP nanoparticle-enabled electro-responsivity

In this research, we discovered the electro-responsive behavior of Zirconium phosphate (α -ZrP) two-dimensional (2D) nanomaterials, which was enabled by modifying the surface chemistry of ZrP. The urea molecules were utilized to modify the 2D ZrP nanoparticles. The evolution of shear stress in the fluid against an electric field was observed. The nanofluid's viscosity change under an electric field was observed due to the generation of dipoles in urea-modified ZrP particles. The formation of dipoles affected the fluidic behavior through the transition between Newtonian behavior and Bingham fluids. Such transition is attributed to the reorganization of those particles after applying the electric field. Their functionalization through urea rapidly transforms on the microsecond scale after applying the field. The high permittivity of urea provided a polar layer, which attains electric response. This research opens the possibility of using functionalized nanoparticles in fluids for improving their damping performance.

High‐Performance Organic Solar Modules via Bilayer‐Merged‐Annealing Assisted Blade Coating

Although encouraging progresses being made on the spin-coated prototype cells, organic solar cells still face significant challenges, yet to be explored, for up-scaling the multi-stacked photoactive layers in the construction of large area modules. Herein, high-performance opaque and semitransparent organic solar modules are developed via a bilayer-merged-annealing (BMA) assisted blade-coating strategy, achieving the impressive efficiencies of 14.79% and 12.01% with respect to active area of 18.73 cm2 , which represent the best organic solar minimodules so far. It is revealed that BMA strategy effectively resolves the de-wetting issues between polar charge transport layer solution and non-polar bulk heterojunction blends, hence improving the film coverage, along with electronic and electric contacts of multi-stacked photoactive layers. As results, organic solar modules coated under ambient condition successfully retain the high-efficiency of small area cells upon 312 times area scaling-up. Overall, this work provides a facile and effective method to fabricate high-performance organic solar modules under ambient condition. This article is protected by copyright. All rights reserved.

Distribution, Sources, and Dynamics of Particulate Matter Along Trans‐Arctic Sections

AbstractIn order to better understand the sources, sinks, and hydrodynamic influences on particulate matter distribution and variability in Arctic basins, we combined transmissometer data from two 2015 fall expeditions: one from Bering Strait (USCGC Healy) and the other from Barents Sea (R/V Polarstern) meeting at the North Pole. These first trans‐Arctic sections of beam attenuation were overlain by salinity, temperature, and chlorophyll‐a fluorescence (Chl‐a) contours. Chl‐a sections were overlain by nitrate contours. Particle composition analyzed from filtered samples throughout the full water column aided significantly in discerning sources, distribution, and dynamics of particles. Dense Pacific water moving swiftly through Bering Strait erodes and carries sediment‐laden waters onto the Chukchi Shelf and into the Canada Basin. This nutrient‐rich Pacific water sinks below a low‐salinity, nutrient‐poor polar mixed layer, forming a thick lens of high salinity water known as Pacific halocline water (salinity 31–33). Ice and the nutrient‐poor mixed layer inhibit photosynthesis in surface waters of Canada and Makarov Basins, but subsurface chlorophyll‐a maxima are observed if nutrients and light are available. Surface‐water biomass is greater in the Barents Sea than in the Beaufort Gyre because nutrient‐rich Atlantic water entering Barents Sea is not isolated from surface waters by ice or strong stratification. Surface water cools, creating high‐density water that cascades into ∼400 m basins in Barents Sea and into deep Nansen Basin, eroding sediment that creates patches of nepheloid layers in the shallow basins. Intense nepheloid layers in the deep basins are rare, suggesting weak bottom currents.

Simultaneous Observations of a Polar Cap Sporadic‐E Layer by Twin Incoherent Scatter Radars at Resolute

AbstractAt high latitudes, the Sporadic‐E layer (Es layer) is a common phenomenon but is still poorly understood due to sparse measurements and the difficulty of conventional mechanisms to operate. In this study, an interesting case of polar cap Es layer is first studied by using the twin incoherent scatter radars (northward‐looking face of Resolute Incoherent‐Scatter Radar and Resolute Incoherent‐Scatter Radar‐Canada), a Canadian Advanced Digital Ionosonde, and a Magnetometer, all at Resolute, Canada. From several electron density profiles of the twin radars, the horizontal scale of the polar cap Es layer is found to be greater than 350 km. Moreover, the polar cap Es layer is determined to be drifting from the bottom F region (>150 km) to the lower E region. Furthermore, a unique appearance of double polar cap Es layers is observed. As a result, these peculiar signatures inspire a newly proposed process that involves the combination of localized electric fields and gravity waves.

Insights into the Chemistry of Iodine New Particle Formation: The Role of Iodine Oxides and the Source of Iodic Acid.

Iodine chemistry is an important driver of new particle formation in the marine and polar boundary layers. There are, however, conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that the photooxidation of iodine produces iodine oxides (IxOy), which are well-known particle precursors. By contrast, nitrate anion chemical ionization mass spectrometry (CIMS) observations in field and environmental chamber studies have been interpreted as evidence of a dominant role of iodic acid (HIO3) in iodine-driven particle formation. Here, we report flow tube laboratory experiments that solve these discrepancies by showing that both IxOy and HIO3 are involved in atmospheric new particle formation. I2Oy molecules (y = 2, 3, and 4) react with nitrate core ions to generate mass spectra similar to those obtained by CIMS, including the iodate anion. Iodine pentoxide (I2O5) produced by photolysis of higher-order IxOy is hydrolyzed, likely by the water dimer, to yield HIO3, which also contributes to the iodate anion signal. We estimate that ∼50% of the iodate anion signals observed by nitrate CIMS under atmospheric water vapor concentrations originate from I2Oy. Under such conditions, iodine-containing clusters and particles are formed by aggregation of I2Oy and HIO3, while under dry laboratory conditions, particle formation is driven exclusively by I2Oy. An updated mechanism for iodine gas-to-particle conversion is provided. Furthermore, we propose that a key iodine reservoir species such as iodine nitrate, which we observe as a product of the reaction between iodine oxides and the nitrate anion, can also be detected by CIMS in the atmosphere.

Geologic Context of the Bright MARSIS Reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars

AbstractRadar‐bright basal reflectors have been detected below the South Polar Layered Deposits (SPLD), using Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data and have an exciting but controversial interpretation: liquid water from subglacial lakes. We mapped the surface of the SPLD immediately above and surrounding the putative lakes (1:2M map scale) in order to provide a geologic context for the interpretation of bright basal reflectors. We use Thermal Emission Imaging System daytime IR (100 m/pixel), Context Camera (6 m/pixel), and High Resolution Imaging Science Experiment (25 cm/pixel) data to characterize geologic units and typical surface roughness. We find evidence for multiple geologic units with features due to CO2 and aeolian‐related processes. We do not find evidence for surface modification linked to postulated lake locations. This is not consistent with the interpretation of the MARSIS basal radar reflector as subglacial lakes.

Competing orders and cascade of degeneracy lifting in doped Bernal bilayer graphene

Motivated by recent experiments [H. Zhou et al., Science 375, 774 (2022) and S. C. de la Barrera et al., arXiv:2110.13907], here we propose a general mechanism for valley and/or spin degeneracy lifting of the electronic bands in doped Bernal bilayer graphene, subject to electric displacement ($D$) fields. A $D$-field induced layer polarization (LP), when accompanied by a Hubbard repulsion-driven layer antiferromagnet (LAF) and next-nearest-neighbor repulsion-driven quantum anomalous Hall (QAH) orders, lifts the fourfold degeneracy of electronic bands, yielding a quarter metal for small doping, as also observed in ABC trilayer graphene. With the disappearance of the QAH order, electronic bands recover twofold valley degeneracy, thereby forming a conventional or compensated (with majority and minority carriers) half metal at moderate doping, depending on the relative strength of LP and LAF. At even higher doping and for a weak $D$ field only LAF survives and the Fermi surface recovers fourfold degeneracy. We also show that a pure repulsive electronic interaction mediated triplet $f$-wave pairing emerges from a parent correlated nematic liquid or compensated half metal when an in-plane magnetic field is applied to the system.

An ultra‐wideband dual‐band hybrid frequency‐selective rasorber

A hybrid frequency-selective rasorber (HFSR) with two broadband passbands and high selectivity based on serpentine line resonator (SLR) is proposed, which has low insertion loss (IL) in two passbands. The HFSR is constituted by a polarization layer, lossy layer, and lossless layer. The polarization layer is formed by a pair of arrows to realize the polarization conversion at the high-frequency band. The lossy layer is composed of the SLR and metallic strips with four resistors, and it is adopted to absorb the electromagnetic waves and supply two broadband transparent windows. The lossless layer is a second-order bandstop frequency-selective surface, which consists of three metal layers of the patches and square rings. A four-port equivalent circuit model with absorbing function is excavated to interpret the working principle of the designed HFSR. The simulation results indicate that the transmission window with 1 dB IL is achieved in 4.57–5.86 GHz and 10.65–14.43 GHz corresponding to a 24.7% and 30.1% fractional bandwidth (FBW), respectively. Besides, the co-polarized reflection coefficients less than −10 dB are obtained from 4.57 GHz to 17.37 GHz, which has a 116.6% FBW. In addition, the physical sample of the proposed HFSR is fabricated and tested. The test results are consistent with the simulation results.

Three-Dimensional Quantification of Copepods Predictive Distributions in the Ross Sea: First Data Based on a Machine Learning Model Approach and Open Access (FAIR) Data

Zooplankton is a fundamental group in aquatic ecosystems representing the base of the food chain. It forms a link between the lower trophic levels with secondary consumers and shows marked fluctuations in populations with environmental change, especially reacting to heating and water acidification. Marine copepods account for approx. 70% of the abundance of zooplankton and are a target of monitoring activities in key areas such as the Southern Ocean. In this study, we have used FAIR-inspired legacy data (dating back to the 1980s) collected in the Ross Sea by the Italian National Antarctic Program at GBIF.org. Together with other open-access GIS data sources and tools, it allows one to generate, for the first time, three-dimensional predictive distribution maps for twenty-six copepod species. These predictive maps were obtained by applying machine learning techniques to grey literature data, which were visualized in open-source GIS platforms. In a Species Distribution Modeling (SDM) framework, we used machine learning with three types of algorithms (TreeNet, RandomForest, and Ensemble) to analyze the presence and absence of copepods in different areas and depth classes as a function of environmental descriptors obtained from the Polar Macroscope Layers present in Quantartica. The models allow, for the first time, to map-predict the food chain per depth class in quantitative terms, showing the relative index of occurrence (RIO) in 3Dimensions and identifying the presence of each copepod species analyzed in the Ross Sea, a globally-relevant wilderness area of conservation concern. Our results show marked geographical preferences that vary with species and trophic strategy. This study demonstrates that machine learning is a successful method in accurately predicting the Antarctic copepod presence, also providing useful data to orient future sampling and the management of wildlife and conservation.

Sediments Within the Icy North Polar Deposits of Mars Record Recent Impacts and Volcanism

AbstractThe North Polar Layered Deposits (NPLD) of Mars are ice‐rich sedimentary layers that formed under the influence of Mars' modern climate and thus record the recent climatic history of Mars, analogous to terrestrial ice sheets. The 2013–2023 Planetary Science Decadal Survey recommends a lander mission to sample the NPLD for climatic records; however, linking the geologic record to the climatic history will require quantitative dating of the NPLD. In this study we use orbital reflectance spectroscopy to show for the first time that dateable mafic lithics are present throughout the NPLD. We find significant glass as well as diverse crystalline minerals, which suggests that surface processes like impacts and volcanism were active during the late Amazonian and transported sediments from across the planet to the north pole. In situ investigation of the NPLD will thus provide critical quantitative constraints on both the recent geologic and climatic histories of Mars.

Nanofiltration of aquatic weed hydrolysate: Diafiltration versus concentration mode for separating saccharides from phenolics

The study deals with nanofiltration for separating saccharides from phenolics and considers permeation of each individual sugar (mono- or disaccharide) from a plant hydrolysate compared to a model sugar solution. Experiments are carried out in a cross-flow flat-sheet cell (MaxiMem, Prozesstechnik GmbH) equipped with Nadir® NP030 P membrane. Nanofiltration in concentration and diafiltration mode has been investigated. It has been found that diafiltration mode ensures the appropriate conditions in the concentration polarization layer of the membrane that favors the sugar diffusion but prevents critical deposition and fouling. Due to the different mass transfer rates of sugars, a stepwise purification of phenolics in the retentate is obtained. Phenolics are first purified from galactose and mannose due to the negative rejections of these sugars at the beginning of diafiltration. Then purification from disaccharides increases with the increase in concentration polarization effect on diffusive transport of disaccharides through the membrane. At the same time purification from glucose also increases and becomes significant. Purification factors achieved in diafiltration mode vary from 3.9 to 10.2 and are up to 6.4-fold higher than in concentration mode.

Modelling the effect of submarine iceberg melting on glacier-adjacent water properties

Abstract. The rate of ocean-driven retreat of Greenland's tidewater glaciers remains highly uncertain in predictions of future sea level rise, in part due to poorly constrained glacier-adjacent water properties. Icebergs and their meltwater contributions are likely important modifiers of fjord water properties, yet their effect is poorly understood. Here, we use a 3-D ocean circulation model, coupled to a submarine iceberg melt module, to investigate the effect of submarine iceberg melting on glacier-adjacent water properties in a range of idealised settings. Submarine iceberg melting can modify glacier-adjacent water properties in three principal ways: (1) substantial cooling and modest freshening in the upper ∼50 m of the water column; (2) warming of Polar Water at intermediate depths due to iceberg melt-induced upwelling of warm Atlantic Water and; (3) warming of the deeper Atlantic Water layer when vertical temperature gradients through this layer are steep (due to vertical mixing of warm water at depth) but cooling of the Atlantic Water layer when vertical temperature gradients are shallow. The overall effect of iceberg melt is to make glacier-adjacent water properties more uniform with depth. When icebergs extend to, or below, the depth of a sill at the fjord mouth, they can cause cooling throughout the entire water column. All of these effects are more pronounced in fjords with higher iceberg concentrations and deeper iceberg keel depths. These iceberg melt-induced changes to glacier-adjacent water properties will reduce rates of glacier submarine melting near the surface, increase them in the Polar Water layer, and cause typically modest impacts in the Atlantic Water layer. These results characterise the important role of submarine iceberg melting in modifying ice sheet-ocean interaction and highlight the need to improve representations of fjord processes in ice sheet scale models.

Mars’s polar ice layers signal climate changes

Mars’s polar ice layers signal climate changes

Tutorial review of reverse osmosis and electrodialysis

Reverse osmosis (RO) and electrodialysis (ED) are the two most important membrane technologies for water desalination and treatment. Their desalination and transport mechanisms are very different, but on a closer look also have many similarities. In this tutorial review, we describe state-of-the-art theory for both processes, focusing on simple examples that are helpful for the non-specialist and for classroom teaching. We describe relevant theory for ion and water transport and the coupling with theory for chemical and mechanical equilibrium on membrane/solution interfaces. For RO of neutral solutes, we explain the solution-friction (SF) model which is closely related to the classical sieving or pore flow model. The SF model includes advection, diffusion, and solute partitioning, and leads to simple relationships for the coupled fluxes of water and solutes (and thus for solute retention as well), also when a diffusion boundary (or concentration polarization) layer is included in the model. Subsequently this theory is extended to describe RO for symmetric salt solutions with charged membranes. For the desalination of salt solutions, both for RO and ED we present two-dimensional module-scale calculations which lead to a characteristic curve that determines optimum operational conditions based on a simple cost calculation that offsets energy and material costs. We discuss the two-fluid model (TFM) that comprehensively describes ion and water flow both in RO and ED, and we explain how this theory also accurately describes osmosis experiments where water and ions are transported in opposite directions through a membrane. Finally, we present results of optimization studies of the combination of multiple modules for RO and ED, and we evaluate the relevance of concentration polarization by using a 3D model for cross-current flow in an ED module.

Effect of the polar cap ionospheric sporadic-E layer on GNSS-based positioning: a case study at Resolute Bay, Canada, September 5, 2012

Effect of the polar cap ionospheric sporadic-E layer on GNSS-based positioning: a case study at Resolute Bay, Canada, September 5, 2012