Modeling Virus Transport and Removal during Storage and Recovery in Heterogeneous Aquifers

A quantitative understanding of virus removal during aquifer storage and recovery (ASR) in physically and geochemically heterogeneous aquifers is needed to accurately assess human health risks from viral infections. A two-dimensional axisymmetric numerical model incorporating processes of virus attachment, detachment, and inactivation in aqueous and solid phases was developed to systematically evaluate the virus removal performance of ASR schemes. Physical heterogeneity was considered as either layered or randomly distributed hydraulic conductivities (with selected variance and horizontal correlation length). Geochemical heterogeneity in the aquifer was accounted for using Colloid Filtration Theory to predict the spatial distribution of attachment rate coefficient. Simulation results demonstrate that the combined effects of aquifer physical heterogeneity and spatial variability of attachment rate resulted in higher virus concentrations in the recovered water at the ASR well (i.e. reduced virus removal). While the sticking efficiency of viruses to aquifer sediments was found to significantly influence virus concentration in the recovered water, the solid phase inactivation under realistic field conditions combined with the duration of storage phase had a predominant influence on the overall virus removal. The relative importance of physical heterogeneity increased under physicochemical conditions that reduced virus removal (e.g. lower value of sticking efficiency or solid phase inactivation rate). This study provides valuable insight on site selection of ASR projects and an approach to optimize ASR operational parameters (e.g. storage time) for virus removal and to minimize costs associated with post-recovery treatment

PASA: A Priori Adaptive Splitting Algorithm for the Split Delivery Vehicle Routing Problem

The split delivery vehicle routing problem (SDVRP) is a relaxed variant of the capacitated vehicle routing problem (CVRP) where the restriction that each customer is visited precisely once is removed. Compared with CVRP, the SDVRP allows a reduction in the cost of the routes traveled by vehicles. The exact methods to solve the SDVRP are computationally expensive. Moreover, the complexity and difficult implementation of the state-of-the-art heuristic approaches hinder their application in real-life scenarios of the SDVRP. In this paper, we propose an easily understandable and effective approach to solve the SDVPR based on an a priori adaptive splitting algorithm (PASA). The idea of a priori split strategy was first introduced in Chen et al. (2017). In this approach, the demand of the customers is split into smaller values using a fixed splitting rule in advance. Consequently, the original SDVRP instance is converted to a CVRP instance which is solved using an existing CVRP solver. While the proposed a priori splitting rule in Chen et al. (2017) is fixed for all customers regardless of their demand and location, we suggest an adaptive splitting rule that takes into account the distance of the customers to the depot and their demand values. Our experiments show that PASA can generate solutions comparable to the state-of-the-art but much faster. Furthermore, our algorithm outperforms the fixed a priori splitting rule proposed by Chen et al. (2017)

Joint Satellite Gateway Placement and Routing for Integrated Satellite-Terrestrial Networks

With the increasing attention to the integrated satellite-terrestrial networks (ISTNs), the satellite gateway placement problem becomes of paramount importance. The resulting network performance may vary depending on the different design strategies. In this paper, a joint satellite gateway placement and routing strategy for the terrestrial network is proposed to minimize the overall cost of gateway deployment and traffic routing, while adhering to the average delay requirement for traffic demands. Although traffic routing and gateway placement can be solved independently, the dependence between the routing decisions for different demands makes it more realistic to solve an aggregated model instead. We develop a mixed-integer linear program (MILP) formulation for the problem. We relax the integrality constraints to achieve a linear program (LP) which reduces time-complexity at the expense of a sub-optimal solution. We further propose a variant of the proposed model to balance the load between the selected gateways.Comment: 6 pages, In Proceedings of IEEE ICC 2020. https://ieeexplore.ieee.org/document/9149175 N. Torkzaban, A. Gholami, J. S. Baras and C. Papagianni, "Joint Satellite Gateway Placement and Routing for Integrated Satellite-Terrestrial Networks," ICC 2020 - 2020 IEEE International Conference on Communications (ICC), Dublin, Ireland, 2020, pp. 1-6. doi: 10.1109/ICC40277.2020.914917

Colloid Release and Clogging in Porous Media: Effects of Solution Ionic Strength and Flow Velocity

The release and retention of in-situ colloids in aquifers play an important role in the sustainable operation of managed aquifer recharge (MAR) schemes. The processes of colloid release, retention, and associated permeability changes in consolidated aquifer sediments were studied by displacing native groundwater with reverse osmosis-treated (RO) water at various flow velocities. Significant amounts of colloid release occurred when: (i) the native groundwater was displaced by RO-water with a low ionic strength (IS), and (ii) the flow velocity was increased in a stepwise manner. The amount of colloid release and associated permeability reduction upon RO-water injection depended on the initial clay content of the core. The concentration of released colloids was relatively low and the permeability reduction was negligible for the core sample with a low clay content of about 1.3%. In contrast, core samples with about 6 and 7.5% clay content exhibited: (i) close to two orders of magnitude increase in effluent colloid concentration and (ii) more than 65% permeability reduction. Incremental improvement in the core permeability was achieved when the flow velocity increased, whereas a short flow interruption provided a considerable increase in the core permeability.This dependence of colloid release and permeability changes on flow velocity and colloid concentration was consistent with colloid retention and release at pore constrictions due to the mechanism of hydrodynamic bridging. A mathematical model was formulated to describe the processes of colloid release, transport, retention at pore constrictions, and subsequent permeability changes. Our experimental and modeling results indicated that only a small fraction of the in-situ colloids was released for any given change in the IS or flow velocity. Comparison of the fitted and experimentally measured effluent colloid concentrations and associated changes in the core permeability showed good agreement, indicating that the essential physics were accurately captured by the model

Design and Performance of a Novel Low Energy Multi-Species Beamline for the ALPHA Antihydrogen Experiment

The ALPHA Collaboration, based at the CERN Antiproton Decelerator, has recently implemented a novel beamline for low-energy ($\lesssim$ 100 eV) positron and antiproton transport between cylindrical Penning traps that have strong axial magnetic fields. Here, we describe how a combination of semianalytical and numerical calculations were used to optimise the layout and design of this beamline. Using experimental measurements taken during the initial commissioning of the instrument, we evaluate its performance and validate the models used for its development. By combining data from a range of sources, we show that the beamline has a high transfer efficiency, and estimate that the percentage of particles captured in the experiments from each bunch is (78 $\pm$ 3)% for up to $10^{5}$ antiprotons, and (71 $\pm$ 5)% for bunches of up to $10^{7}$ positrons.Comment: 15 pages, 15 figure

Fate and transport of viruses and colloids in saturated and unsaturated porous media

The fundamental mechanisms involved in fate and transport of colloidal particles (viruses and latex microspheres) in saturated and unsaturated porous media were systematically examined. Two different bacteriophages were used as surrogate for pathogenic viruses to investigate the effects of various water contents and solution chemistries in terms of pH and ionic strength (IS) on virus transport. The experiments were complimented by utilizing a transport model that accounts for virus interaction with the solid-water interfaces (SWI) and air-water interfaces (AWI). It was found that under saturated conditions virus retention enhanced with decreasing the pH and increasing the IS. Under unsaturated conditions, viruses exhibited a high affinity to the AWI only when the pH was lower than 7. In contrast with the saturated experiments that a one-site kinetic model was sufficient to fit the breakthrough curves, a two-site kinetic model was needed to produce a good fit to the breakthrough curves obtained from unsaturated columns. To complement the previous work, packed column and mathematical modeling studies were conducted to explore the influence of water saturation, IS, and grain size on the transport of larger colloids (latex microspheres; 1.1 μm) in porous media. Experiments were carried out under chemically unfavorable conditions for colloid attachment to both SWI and AWI. The breakthrough curve and final deposition profile in each experiment indicated that colloid retention was highly dependent on IS, water content, and sand grain size. Experimental and modeling results suggested that straining – the retention of colloids in low velocity regions of porous media such as grain junctions – was the primary mechanism of colloid retention under both saturated and unsaturated conditions. Increasing the solution ionic strength is believed to increase the depth of secondary minimum in the DLVO interaction energy profile and as a result, increase the adhesive force between colloids and the SWI by increasing. These weakly associated colloids can be funneled to small regions of the pore space formed adjacent to grain-grain junctions. For select systems, the IS of the influent was decreased to a low solution IS following the obtaining of the effluent concentration data. In this case, only a small portion of the deposited colloids was recovered in the effluent and the majority was still retained in the sand. These observations suggest that the extent of colloid removal by straining is strongly coupled to solution chemistry. This research established that colloid retention in porous media is a coupled process that strongly depends on solution chemistry, pore structure, and system hydrodynamics. Therefore, modeling colloid transport through porous media will require nontraditional approaches which account for the abovementioned factors

Uterine Septum Dimensions in Patients with Infertility and Recurrent Abortion and the Outcomes of Hystroscopic Metroplasty

Abstract: Background & Aims: It is believed that uterine septum, because of its effect on infertility and recurrent abortion is very important and pregnancy outcome is obviously improved by hysteroscopic metroplasty (HM). In this study, the probable relationship of uterine septum dimensions (length and width) with infertility and recurrent abortion has been investigated. Methods: This clinical trial was carried out from Jan. 2004 to Feb. 2007 on all patients referred to Ahwaz educational hospitals for evaluation of infertility and recurrent abortion and underwent hysterosalpingography (HSG). Patients with suspected uterine septum were referred to Imam Khomeyni Hospital and underwent simultaneous hysteroscopy and laparoscopy. After that hysteroscopic metroplasy was done. The participants were checked by new HSG after one month and were evaluated for pregnancy outcome after one year. Results: In whole, 50 patients (28 cases with infertility and 22 cases with recurrent abortion) were studied. In 62.5% septum width was equal or less than 3cm and in 48% length of septum occupied two thirds of uterine cavity and there was no significant difference between the tow groups in regard to septum's width and length. Rate of pregnancy occurrence was 71.4% in patients with infertility and 76.5% in patients with recurrent abortion and no significant difference was found between the two groups in this regard. Conclusion: According to the findings, it seems that septum dimensions (width and length) have no role in infertility and abortion. Therefore, resection of uterine septum regardless of its size is recommended. In patients with uterine septum who suffer from infertility and recurrent abortion, HM is an appropriate approach. Keywords: Infertility, Hysteroscopy, Recurrent abortion, Septate uteru

Fate and transport of viruses and colloids in saturated and unsaturated porous media

The fundamental mechanisms involved in fate and transport of colloidal particles (viruses and latex microspheres) in saturated and unsaturated porous media were systematically examined. Two different bacteriophages were used as surrogate for pathogenic viruses to investigate the effects of various water contents and solution chemistries in terms of pH and ionic strength (IS) on virus transport. The experiments were complimented by utilizing a transport model that accounts for virus interaction with the solid-water interfaces (SWI) and air-water interfaces (AWI). It was found that under saturated conditions virus retention enhanced with decreasing the pH and increasing the IS. Under unsaturated conditions, viruses exhibited a high affinity to the AWI only when the pH was lower than 7. In contrast with the saturated experiments that a one-site kinetic model was sufficient to fit the breakthrough curves, a two-site kinetic model was needed to produce a good fit to the breakthrough curves obtained from unsaturated columns. To complement the previous work, packed column and mathematical modeling studies were conducted to explore the influence of water saturation, IS, and grain size on the transport of larger colloids (latex microspheres; 1.1 μm) in porous media. Experiments were carried out under chemically unfavorable conditions for colloid attachment to both SWI and AWI. The breakthrough curve and final deposition profile in each experiment indicated that colloid retention was highly dependent on IS, water content, and sand grain size. Experimental and modeling results suggested that straining – the retention of colloids in low velocity regions of porous media such as grain junctions – was the primary mechanism of colloid retention under both saturated and unsaturated conditions. Increasing the solution ionic strength is believed to increase the depth of secondary minimum in the DLVO interaction energy profile and as a result, increase the adhesive force between colloids and the SWI by increasing. These weakly associated colloids can be funneled to small regions of the pore space formed adjacent to grain-grain junctions. For select systems, the IS of the influent was decreased to a low solution IS following the obtaining of the effluent concentration data. In this case, only a small portion of the deposited colloids was recovered in the effluent and the majority was still retained in the sand. These observations suggest that the extent of colloid removal by straining is strongly coupled to solution chemistry. This research established that colloid retention in porous media is a coupled process that strongly depends on solution chemistry, pore structure, and system hydrodynamics. Therefore, modeling colloid transport through porous media will require nontraditional approaches which account for the abovementioned factors