Winding Modes Research Articles

Time Heals All Wounds: Obstacles in Glaucoma Surgery from an Asian Perspective

Glaucoma is the leading cause of irreversible blindness worldwide and is a particular burden on the Asian population. Glaucoma surgeries such as trabeculectomy and glaucoma drainage implants are routinely performed to lower intraocular pressure (IOP) to prevent disease progression. However, scarring of the filtering bleb limits their long-term success and Asian eyes are more at risk. Although this is so, many existing studies have been done on Caucasian patients, but few have focused solely on Asian patients. Intraoperative anti-metabolites such as Mitomycin-C (MMC) and 5-Fluorouracil (5-FU) are the current mainstay of adjunctive treatments to reduce scarring, and in this review, we evaluate the evolution, benefits and side effects of these agents. Recently, newer methods of wound modulation including anti-vascular endothelial growth factor (VEGF) agents and collagen implants are also being investigated as part of a multi-pronged approach to tackle this problem. Some opportunities exist to limit scarring post-operatively, but it is an ongoing battle.

Foulant characterization and distribution in spiral wound reverse osmosis membranes from different pressure vessels

In this study, the origin and extent of membrane fouling on spiral wound module (SWM) elements from different pressure vessels and the distribution of membrane foulants inside the SWM elements were systematically investigated using the membrane autopsy methods. Three fouled SWM elements from different pressure vessels were examined for a quantitative and qualitative comparison of membrane foulants. Results obtained indicate that a major contributor to membrane fouling were fulvic acid components, consisting of small, hydrophilic compounds from the raw groundwater. A small amount of inorganic components such as Fe and Al, which can form a complex structure with fulvic acid, also partially contributed to the membrane fouling of lead elements in first pass RO vessels. In particular, through the elemental comparisons of two sheets (both sides) of fouled membranes obtained from identical positions of a membrane leaf, the distribution of membrane foulants inside the SWM elements was fully evaluated. Based on the data obtained, much more organic and inorganic foulants were accumulated on the back side of the membrane leaf than on the front side. Overall, these results would help improve understanding of fouling behavior inside membrane modules and pressure vessels.

Removal of thiophene from n-heptane/thiophene mixtures by spiral wound pervaporation module: Modelling, validation and influence of operating conditions

In recent years, pervaporation has been investigated rigorously for separation of thiophene and its derivatives from the fluid catalytic cracker (FCC) gasoline. Like other membrane-based processes, the scale up and commercialization of this process require the study of the separation performance at the membrane module scale. In this study, a suitable mathematical model is obtained to predict the performance of a spiral wound pervaporative module for the removal of thiophene from n-heptane/thiophene mixtures. The experiments were performed on a Polydimethylsiloxane (PDMS) based spiral wound module for a variety of operating conditions. The model predictions showed good agreement with the experiment results. Results indicate that the module performance may be improved with higher permeate pressures and the lower feed temperatures. However, this trend may not be universal and may be altered for some different feed systems or membranes, which shows the necessity to analyse every feed system and membrane material for determining the optimum operating conditions. Simulations also demonstrated that the variations in flow variables along the feed and permeate channels may also have profound effects on the module performances. Finally, the performance of a pervaporation process was simulated by using a number of spiral wound modules in series, which demonstrated that the pervaporation might successfully remove thiophene from FCC gasoline up to any desired limit.

Online monitor for the reverse osmosis spiral wound module — Development of the canary cell

The development of a side-stream reverse osmosis cell, called the ‘canary cell’, to simulate the spiral wound module (SWM) is described. Representative fouling rates and ex-situ membrane autopsies show the capability of the canary cell to simulate the SWM under controlled hydrodynamics and flux conditions. The development of a dimensionless calibration curve allows the canary cell to act as an early warning system with respect to the SWM. The rate of cake thickness increase was also measured by ultrasonic time domain reflectometry coupled to the canary cell and used to monitor membrane fouling and cleaning.

Solar signals in CMIP‐5 simulations: the stratospheric pathway

The 11 year solar‐cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP‐5). Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period ∼1850–2005. The analysis is performed on all CMIP‐5 models but focuses on the 13 CMIP‐5 models that resolve the stratosphere (high‐top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (∼70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response.A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short‐wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modelled response is more consistent with observations when only data from 1979–2005 are considered. The observed North Pacific high‐pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high‐ and low‐top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations.

Conformal perturbation theory and higher spin entanglement entropy on the torus

We study the free fermion theory in 1+1 dimensions deformed by chemical potentials for holomorphic, conserved currents at finite temperature and on a spatial circle. For a spin-three chemical potential \mu, the deformation is related at high temperatures to a higher spin black hole in hs[0] theory on AdS_3 spacetime. We calculate the order \mu^2 corrections to the single interval Renyi and entanglement entropies on the torus using the bosonized formulation. A consistent result, satisfying all checks, emerges upon carefully accounting for both perturbative and winding mode contributions in the bosonized language. The order \mu^2 corrections involve integrals that are finite but potentially sensitive to contact term singularities. We propose and apply a prescription for defining such integrals which matches the Hamiltonian picture and passes several non-trivial checks for both thermal corrections and the Renyi entropies at this order. The thermal corrections are given by a weight six quasi-modular form, whilst the Renyi entropies are controlled by quasi-elliptic functions of the interval length with modular weight six. We also point out the well known connection between the perturbative expansion of the partition function in powers of the spin-three chemical potential and the Gross-Taylor genus expansion of large-N Yang-Mills theory on the torus. We note the absence of winding mode contributions in this connection, which suggests qualitatively different entanglement entropies for the two systems.

Effects of membrane characteristics on performances of pressure retarded osmosis power system

Effects of the characteristics of membrane such as water permeability-coefficient, solute permeability-coefficient, and membrane resistivity on the performances of the spiral wound module in the PRO system have been studied numerically. Fluxes of water and solute through membrane, and concentrations and flow rates in the channels were obtained. The water flux through membrane increases almost linearly with the water permeability-coefficient, but it is insensitive to the solute permeability-coefficient. Decreasing the membrane resistivity makes the water flux through membrane and the power density increase. Effects of the membrane resistivity on the water flux through membrane and flow rates in the channels are small when the difference between the inlet-pressures of draw- and feed-channel is large and vice versa. The power density increases and then decreases as the channel-inlet pressure difference increases. The maximum power density is 16 W/m2 at 14 atm of the channel-inlet pressure difference in our system.

Osmotically driven membrane processes by using a spiral wound module — Modeling, experimentation and numerical parameter estimation

Pressure retarded osmosis (PRO) and forward osmosis (FO) are osmotically driven membrane processes and emerging as viable methods for capturing clean energy and producing fresh water from sea water, respectively. The critical problems restricting the application of these processes are the accurate design and analysis of the membrane module or module configurations. Hence, a mathematical model is obtained to predict the performance of a spiral wound membrane module for osmotically driven membrane processes. Transport phenomena through the membrane are described by the previously proposed solution diffusion based model. In the current work, this model is coupled with the differential mass balances on the feed and permeate sides of the module. In addition, the Darcy's theory is used in the model to incorporate the pressure drop in the channels of module. The finite difference method is employed to solve coupled algebraic and ordinary differential equations. Here, we also employ a combination of two optimization techniques (Univariate and Fibonacci three point methods) with laboratory scale experimental data points to estimate the unknown parameters of the model. These estimated parameters are then used to predict the performance of FO and PRO at some other operating conditions and validate the mathematical model. Relatively lower maximum power density is observed at a lower draw side hydraulic pressure in the spiral wound module as compared to power density in a membrane test cell. The experimental results obtained by this module matched well with the model predictions.

Dune deformation in a multi‐directional wind regime: White Sands Dune Field, New Mexico

AbstractAs with most dune fields, the White Sands Dune Field in New Mexico forms in a wind regime that is not unimodal. In this study, crescentic dune shape change (deformation) with migration at White Sands was explored in a time series of five LiDAR‐derived digital elevation models (DEMs) and compared to a record of wind direction and speed during the same period. For the study period of June 2007 to June 2010, 244 sand‐transporting wind events occurred and define a dominant wind mode from the SW and lesser modes from the NNW and SSE. Based upon difference maps and tracing of dune brinklines, overall dune behavior consists of crest‐normal migration to the NE, but also along‐crest migration of dune sinuosity and stoss superimposed dunes to the SE. The SW winds are transverse to dune orientations and cause most forward migration. The NNW winds cause along‐crest migration of dune sinuosity and stoss bedforms, as well as SE migration of NE‐trending dune terminations. The SSE winds cause ephemeral dune deformation, especially crestal slipface reversals. The dunes deform with migration because of differences in dune‐segment size, and differences in the lee‐face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation. Each wind event deforms dune shape, this new shape then serves as the boundary condition for the next wind event. Shared incidence‐angle control on dune deformation and lee‐face stratification types allows for an idealized model for White Sands dunes. Copyright © 2015 John Wiley & Sons, Ltd.

Modernization of conventional spiral wound module—principles to design RO without pretreatment and concentrate effluents

The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. The described techniques enable us to remove calcium carbonate from RO concentrate by means of “seed” crystallization. These proposed techniques use “open channel” spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The driving force for crystal growth was constantly created by RO process due to increase in calcium and carbonate ion concentration values. Fouling control is achieved by providing sufficient cross-flow velocities, flushings and cleanings. Coagulated suspended matter after membrane flushes is collected, sedimented and finally dewatered. The concentrated solution that contains rejected salts and impurities constitutes not more than 1% of initial feed water volume and can be withdrawn together with wet sludge as sludge moisture. The described technical procedure enables us to completely utilize concentrate and produce quality product water, softened water and sludge.

Nanofiltration for dextrose recovery from crystallization mother liquors: A feasibility study

A wide experimentation was carried out to test performances of industrial NF modules for dextrose (DX) recovery from crystallization mother liquors, coming from dextrose manufacturing by saccharification of starch hydrolizates. Real solutions were processed containing total Dry Substance (DS) in the range from 17 to 43wt% and DX content close to 80–83%; impurities being mainly maltose and other sugars with higher degree of polymerization.Aim of the work was to achieve at least a DX purity of 95% in correspondence with average transmembrane fluxes higher than 4dm3/(hm2).Four commercial spiral wound modules with polyamide membranes were tested, manufactured by KOCH-Membrane Systems and by GE Power&Water (well-known as DESAL membrane products). Module performances were measured at temperatures from 30 to 50°C, at pressures from 15 to 30bar.Nanofiltration is confirmed as a feasible technique to get preferential permeation of dextrose.For all the modules tested many analogies were observed in their behavior as a function of operative conditions. In spite of the complexity of the solutions investigated, module performances can be easily described by using few simple quantities (DS wt%, DX purity, total flux, DX rejection and Impurities Rejection). DX purity in the Permeate is strictly dependent on the DX purity in the module feed and on the total volume flux.Results give a general indication about the experimentation protocol to be performed in order to obtain basic data useful both to test the process feasibility and to scale-up the process.Membranes tested showed different separation efficiencies; only the module GE-DL4040C1025 fitted the industrial requirements for the process application. Modules GE-DL can be used with confidence at 50°C and 30bar, in a range of feed flow rates from 2300 to 3600L/h, achieving DX purity in the Permeate higher than 97%; correspondingly, the NF plant can be designed to work with a DS content in the feed stream from 22wt% to 35wt%, obtaining total fluxes from 16 to 6dm3/(hm2) and a DS content in the Permeate from 11.5wt% to 22.5wt%, correspondingly.

Experimental characterization and numerical simulation of the anti-biofuling activity of nanosilver-modified feed spacers in membrane filtration

The antibiofouling activity of nanosilver-coated feed spacers was investigated in a crossflow membrane filtration-cell system simulating the conditions in spiral wound modules. Silver ions distribution in the feed channel and near the membrane was estimated by numerical simulation. Nanosilver was embedded into the polypropylene network using sonochemical deposition. The ability of the modified spacer to hinder biofilm development on the adjacent membranes was studied at 0.15ms−1 crossflow velocity, using polysulfone ultrafiltration membrane exposed to a mixed microbial enrichment. The physical properties of the modified spacer and biofilm development were evaluated using scanning electron microscopy and confocal laser scanning microscopy imaging (HRSEM and CLSM). HRSEM images depicted significantly less bacteria attached to the membranes near the modified spacer, mainly scattered with a sporadic monolayer structure. Dead/live staining assay by CLSM indicated a significantly higher percentage of dead bacteria cells attached to the membranes adjacent to the modified spacer in comparison to untreated spacers (control). The silver modified spacers displayed improved and steadier permeate flux along the 10 days of the run compared to the control. Flow and mass transfer simulations showed increased silver ions concentration near the membrane as a function of the spacer configuration. The life span of the modified spacer was evaluated as well.

Energetics of East Pacific Easterly Waves during Intraseasonal Events

Abstract The background atmospheric state of the east Pacific warm pool in which easterly waves develop varies dramatically on intraseasonal time scales. East Pacific intraseasonal variability is well known to modulate local convective and circulation patterns. Westerly (easterly) intraseasonal phases are associated with westerly (easterly) low-level wind and positive (negative) convective anomalies. This study investigates the perturbation available potential energy (PAPE) and perturbation kinetic energy (PKE) budgets of easterly waves composited during westerly, easterly, and neutral intraseasonal phases, respectively. The mechanisms, magnitudes, locations, and vertical structures of easterly waves are shown to strongly vary as a function of intraseasonal phase. Easterly waves draw energy from low-level barotropic conversion, regardless of phase, although the location and magnitude of the conversion varies strongly. During neutral and westerly intraseasonal phases, the generation of PAPE associated with perturbation diabatic heating that is subsequently converted to PKE is the dominant energy source for easterly waves. A novel and previously unrecognized result is the detection of strong barotropic generation of PKE at midlevels during westerly intraseasonal phases. This previously unidentified source of PKE at midlevels is in part due to strong intraseasonal modulation of the background midlevel winds.

The Potential Roles of Background Surface Wind in the SST Variability Associated with Intraseasonal Oscillations

Abstract The current study is aimed at exploring the potential roles of the seasonally altering background surface wind in the seasonality of the intraseasonal oscillations (ISOs) with a focus on the sea surface temperature (SST) variability. A composite analysis of the ocean mixed layer heat budget in term of ISO phases with various satellite data is performed for boreal winter and summer. The scalar wind is found to be a dominant factor that accounts for the ocean surface heat budget, implying that the background surface wind as well as its anomaly is important for the SST variability. An easterly anomaly to the east of convection diminishes scalar wind, and thus latent heat flux, when superposed onto a background westerly wind, implying that the presence of basic westerly wind is important for the development of a warm SST anomaly ahead of the ISO convection. On the other hand, an easterly anomaly in combination with basic easterly wind magnifies scalar wind and latent heat flux and cancels out the shortwave heat flux anomaly. The seasonal migration of the background westerly wind, which is confined to a southern equatorial belt in boreal winter but spread across the northern Indian Ocean in boreal summer, may offer a mechanism that partly accounts for the seasonal characteristics of ISO propagation. The northward propagation of the SST variability associated with the boreal summer ISO is found to also involve a similar mechanism with the meridional wind modulation of scalar wind.

Comparative study of red grape must nanofiltration: Laboratory and pilot plant scales

A consequence of global warming is the early ripening of grapes which promotes, among others, a higher fermentable sugar (glucose and fructose) content. This leads to wines with an alcoholic degree higher than desired.In this work, the main differences between red grape must nanofiltration at laboratory and pilot plant scale were studied in order to perform the scale-up of a nanofiltration process to reduce the sugar content. For this, previous results of the nanofiltration of commercial red must using the SR3 membrane in a flat sheet crossflow module were compared with those obtained for the filtration of natural red must using the same membrane in a spiral wound module at two different applied pressures.The aim of this publication is to analyze the main differences between red grape must nanofiltration at laboratory and at pilot plant scale. Resultsshowed that the flow destabilization and eddy promotion caused by spacers in the spiral wound module mitigate the rate at which the cake thickens and compacts on the membrane surface. This causes a less sharp flux decrease, less variable sugars rejection and osmotic pressure difference. Moreover, higher applied pressure promotes a higher membrane fouling and osmotic pressure that worsen the flux decay.

Do regions outside the tropical Pacific influence ENSO through atmospheric teleconnections?

This paper aims at identifying oceanic regions outside the tropical Pacific, which may influence the El Nino Southern Oscillation (ENSO) through interannual modulation of equatorial Pacific winds. An Atmospheric General Circulation Model (AGCM) 7-members ensemble experiment forced by climatological sea surface temperature (hereafter, SST) in the tropical Pacific Ocean and observed interannually varying SST elsewhere produces ensemble-mean equatorial zonal wind stress interannual anomalies (ZWSA) over the equatorial Pacific. These ZWSA are largest during boreal winter in the western Pacific, and induce a ~0.5 °C response in the central Pacific during the following spring in a simple ocean model, that weakly but significantly correlates with the following ENSO peak amplitude. When correlated with global SST, the residual western equatorial Pacific ZWSA yield SST patterns that are reminiscent of ENSO teleconnections in the Indian, North and South Pacific, and Atlantic Oceans. We further design 20-members ensemble sensitivity experiments forced by typical SST patterns of the main climate modes for each of these regions, in order to identify regions that influence equatorial Pacific ZWSA most. In our experiments, only the Indian Ocean Basin-wide SST warming in late boreal winter produces a statistically significant ZWSA in the western equatorial Pacific, resulting in a weak but significant ~0.35 °C SST response in the central Pacific (i.e. ~35 % of the observed standard deviation) during the following spring, the season when the Bjerkness coupled feedback is particularly efficient. This paper hence agrees with previous studies, which suggest that ENSO-induced basin-wide SST signals in the Indian Ocean may contribute to the phase transition of ENSO. Our results suggest that studies exploring external influences on ENSO should adopt a global approach rather than focus on a specific region. Designing coupled model simulations would also allow investigating air–sea interactions-mediated teleconnection mechanisms, which we can’t reproduce in our forced AGCM framework.

Tropical response to stratospheric sudden warmings and its modulation by the QBO

Major Stratospheric Sudden Warmings (SSWs) are characterized by a reversal of the zonal mean zonal wind and an anomalous warming in the polar stratosphere that proceeds downward to the lower stratosphere. In the tropical stratosphere, a downward propagating cooling is observed. However, the strong modulation of tropical winds and temperatures by the quasi-biennial oscillation (QBO) renders accurate characterization of the tropical response to SSWs challenging. A novel metric based on temperature variations relative to the central date of the SSW using ERA-Interim data is presented. It filters most of the temperature structure related to the phase of the QBO and provides proper characterization of the SSW cooling amplitude and downward propagation tropical signal. Using this new metric, a large SSW-related cooling is detected in the tropical upper stratosphere that occurs almost simultaneously with the polar cap warming. The tropical cooling weakens as it propagates downward, reaching the lower stratosphere in a few days. Substantial differences are found in the response to SSWs depending on the QBO phase. Similar to what is observed in the polar stratosphere, tropical SSW-associated temperatures persist longer during the west QBO phase at levels above about 40 hPa, suggesting that the signal is mainly controlled by changes in the residual mean meridional circulation associated with SSWs. Conversely, in the lower stratosphere, around 50–70 hPa, enhanced cooling occurs only during QBO east phase. This behavior seems to be driven by anomalous subtropical wave breaking related to changes in the zero-wind line position with the QBO phase.

Critical role of boreal summer North Pacific subtropical highs in ENSO transition

The quasi-biennial (QB)-type El Nino-Southern Oscillation (ENSO), showing a fast phase transition from El Nino to La Nina, is closely related to the variability of the North Pacific subtropical high (NPSH) and western North Pacific subtropical high (WNPSH) during summer. Here, we show that the NPSH plays a key role in the fast ENSO transition. The QB-type ENSO is associated with both strengthened WNPSH and NPSH during the boreal summer. By contrast, the low-frequency-type ENSO, which occurs in a typical period of 3–7 years, displays an enhanced WNPSH but weakened NPSH. The stronger El Nino tends to generate a more intensified WNPSH from spring to summer, leading to the initial decay of El Nino via the modulation of easterly wind in the western Pacific. On the contrary, the NPSH has greater linkage with the decaying El Nino process after the boreal summer. Therefore, the coupled pattern of WNPSH–NPSH is important in changing ENSO phase from El Nino to La Nina. The NPSH causes sea surface temperature cooling over the subtropical Northeastern Pacific. The resultant subtropical cooling induces anomalous anticyclone west of the reduced heating, which generates the strengthening of trade winds south of the anticyclone. Consequently, this process contributes to tropical central Pacific cooling and the rapid transition of El Nino to La Nina. This study hints that the QB-type ENSO could be significantly linked to a tropics-midlatitudes coupled system such as an in-phase pattern between WNPSH and NPSH. The results are useful for improvement of ENSO prediction.

Laser-supported joining of SiC-fiber/SiCN ceramic matrix composites fabricated by precursor infiltration

Abstract SiC-fiber/SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. The fiber preform was made by slurry infiltration and winding using a computer-controlled winding module. Multiple infiltration steps using a Si–C–N precursor were included to increase the density. The influence of the sintering conditions on the microstructure of the CMC was demonstrated. Pipe sections made of the CMC materials were joined using a laser-supported heating technology with an Y–Al–Si–O glass–ceramic filler. The thermal response of the CMC components was controlled by the anisotropic thermal conductivity. Fast heating by laser beam was achieved for elements rotating in the direction of the fiber winding. SEM micrographs of the joints showed the good wettability of the CMC by the glass–ceramic filler. Nearly defect-free joints were obtained using a nitrogen process atmosphere. The laser-supported technology was shown to be promising for the joining of CMC components.

Evaluation of pretreatments for a blowdown stream to feed a filtration system with discarded reverse osmosis membranes

In reverse osmosis demineralization processes, spiral wound modules are used and after approximately 5years are discarded, since they lose their performance. These modules could be reused for other treatments that do not require a final permeate with so high quality, but still have limitations for feed water quality. The aim of this study is to propose a pretreatment configuration to a membrane filtration system that uses discarded membranes to treat the stream of a cooling tower for reuse as make-up water. Steps of coagulation/flocculation, sand filtration, sorption with GAC and combinations of these were proposed. Parameters as pH, electrical conductivity, turbidity, total hardness, COD, silica content and SDI were analyzed. The pretreated effluent was tested in a bench scale membrane filtration system. Permeate flux, salt retention and hydraulic permeability were evaluated to identify fouling. The best results were obtained coupling coagulation/flocculation with sand filtration. The RO discarded membranes presented high salt retention, about 97% and analysis of permeates indicates the possibility of reuse. MEV and EDS of SDI membranes showed a decrease of silica and total hardness scale, which are the main causes of fouling and the pretreated stream seems to present suitable characteristics to feed the RO filtration system.