Primary Station Research Articles

Redox-Switchable Calix[6]arene-Based Isomeric Rotaxanes.

Operating molecular machines are based on switchable systems whose components can be set in motion in a controllable fashion. The presence of nonsymmetrical elements is a mandatory requirement to obtain and demonstrate the unidirectionality of motion. Calixarene-based macrocycles have proved to be very efficient hosts in the design of oriented rotaxanes and of pseudorotaxanes with strict control over the direction of complexation. A series of two-station rotaxanes based on bipyridinium-ammonium axles was synthesized and characterized. A recently reported supramolecularly assisted strategy for the synthesis of different orientational isomers was exploited, and the ammonium unit was identified as a proper secondary station for the calixarene. Displacement of the macrocycle was triggered by electrochemical reduction of the bipyridinium primary station, and it was shown that the shuttling is influenced both by the length of the chain of the axle component and by the position of the secondary station with respect to the calixarene rims.

Multi-user rate and power analysis in a cognitive radio network with massive multi-input multi-output

This paper discusses transmission performance and power allocation strategies in an underlay cognitive radio (CR) network that contains relay and massive multi-input multi-output (MIMO). The downlink transmission performance of a relay-aided massive MIMO network without CR is derived. By using the power distribution criteria, the kth user’s asymptotic signal to interference and noise ratio (SINR) is independent of fast fading. When the ratio between the base station (BS) antennas and the relay antennas becomes large enough, the transmission performance of the whole system is independent of BS-to-relay channel parameters and relates only to the relay-to-users stage. Then cognitive transmission performances of primary users (PUs) and secondary users (SUs) in an underlay CR network with massive MIMO are derived under perfect and imperfect channel state information (CSI), including the end-to-end SINR and achievable sum rate. When the numbers of primary base station (PBS) antennas, secondary base station (SBS) antennas, and relay antennas become infinite, the asymptotic SINR of the kth PU and SU is independent of fast fading. The interference between the primary network and secondary network can be canceled asymptotically. Transmission performance does not include the interference temperature. The secondary network can use its peak power to transmit signals without causing any interference to the primary network. Interestingly, when the antenna ratio becomes large enough, the asymptotic sum rate equals half of the rate of a single-hop single-antenna K-user system without fast fading. Next, the PUs’ utility function is defined. The optimal relay power is derived to maximize the utility function. The numerical results verify our analysis. The relationships between the transmission rate and the antenna number, relay power, and antenna ratio are simulated. We show that the massive MIMO with linear pre-coding can mitigate asymptotically the interference in a multi-user underlay CR network. The primary and secondary networks can operate independently.

Effect of Short‐Term Theta Frequency Stimulation of the Vagus Nerve on Cognition among Patients with Refractory Epilepsy: A Pilot Study

ObjectiveThe purpose of this investigation is to collect preliminary data on the effect of theta frequency vagus nerve stimulation on cognitive measures, including memory retention, in patients with refractory epilepsy.BackgroundVagus nerve stimulation (VNS) was approved by the FDA in 1997 as an adjunctive treatment for medically refractory epilepsy. VNS provides intermittent high frequency stimulation to the left vagus nerve, resulting in retrograde stimulation to centers in the brainstem. Research interest into alternative uses of VNS has increased in popularity over the past decade, including its effect on cognition.Initial short‐term studies (3–24 hours of stimulation) have provided information on how it may be working to alter cognitive function. Two pre‐clinical studies showed that rats displayed increased memory retention after 24 hours of VNS. Clinical studies have also demonstrated a significant increase in cognitive performance when VNS is administered during the memory consolidation period of a list learning task.The nucleus of the solitary tract (NST) in the brain stem is the primary relay station for afferent vagal nerve fibers. The NST has numerous projections to various areas of the forebrain and brain stem, including the hippocampus. Stimulation of the vagus nerve has been shown to alter the electrophysiological and metabolic profiles of the hippocampus, an area that plays a critical role in learning and memory functions. The hippocampus generates and maintains high amplitude oscillations in the theta frequency range (4–8 Hz), which play an important role in memory tasks. Furthermore, there is pre‐clinical evidence that theta oscillations are depressed in rodent models with temporal lobe epilepsy, and that reduced theta activity correlates with memory deficits. We hypothesize that theta frequency VNS will have a positive effect on memory retention.MethodsPatients with implanted VNS devices were identified in the medical records, consented, and screened via the Beck Depression Inventory (excluded if score > 20) and the Montreal Cognitive Assessment (excluded if score < 24). Participants then practiced cognitive tasks for 30 minutes, followed by three rounds of neurocognitive testing with different VNS settings (Figure 1). Only VNS frequency (theta: 5 Hz, beta: 25–30 Hz, and control: 0 Hz) was altered. Each round of neurocognitive testing included two tasks. The first was a memory encoding/retrieval task (California Verbal Learning Test, CVLT). The second was an executive function task administered between the encoding and retrieval portions of CVLT. Both participants and test administrators were blinded to VNS parameters.Results & DiscussionOver the course of one year, data was only collected from one patient. This was due to a combination of factors, including stringent exclusion criteria, difficult patient recruitment, and an understaffed research team. However, this patient did display a 23% increase in delayed free recall performance when treated with theta frequency stimulation (Figure 2). Furthermore, accuracy and reaction time decreased by 5% and >15% for both beta and theta stimulation (as compared to the control) during the executive function task (Stroop test). While generalizable conclusions are impossible to draw from this data, the preliminary results support our hypothesis. While we are in the process of collecting more data, we hope that this study can serve as a platform for researchers to build from.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Access Control Attacks on PLC Vulnerabilities

In Industrial Control Systems (ICS), security issues are getting more and more attention. The number of hacking attacks per year is endless, and the attacks on industrial control systems are numerous. Programmable Logic Controller (PLC) is one of the main controllers of industrial processes. Since the industrial control system network is isolated from the external network, many people think that PLC is a safety device. However, virus attacks in recent years, such as Stuxnet, have confirmed the erroneousness of this idea. In this paper, we use the vulnerability of Siemens PLC to carry out a series of attacks, such as S7-200, S7-300, S7-400, S7-1200 and so on. We read the data from the PLC output and then rewrite the data and write it to the PLC. We tamper with the writing of data to achieve communication chaos. When we attack the primary station, all slave devices connected to the primary station will be in a state of communication confusion. The attack methods of us can cause delay or even loss of data in the communications from the Phasor Data Concentrator (PMU) to the data concentrator. The most important thing is that our attack method generates small traffic and short attack time, which is difficult to be identified by traditional detection methods.

Interference Compensation for Smart Grid Communications: A Distributed Power Control Approach

The co-tier and cross-tier interferences become serious when the electric power communication networks are deployed densely in the coverage area of the primary network base station (PBS). To reduce the co-tier interference in the electric power communication networks and guarantee the quality of service of the primary networks users (PUEs), we propose a distributed power control method. First, a reasonable interference threshold of the PBS is chosen to guarantee the PUE’s transmission requirement. Then, a fictitious power-price game with interference compensation is employed to update the power of gateways in smart grid on the condition of the interference threshold. Finally, a modified distributed power control method is proposed to protect the primary network link. Simulation results show that the co-tier interference among gateways is reduced efficiently, the target signal-to-interference plus noise ratio of the PUEs can be achieved, and the network performance is improved.

Role of Imaging in Diagnosis, Predicting Biological Activity and in Treatment Plan of Hydatid Disease

Cystic Echinococcosis (CE) is a zoonotic parasitic disease caused by the larval stage of the cestode Echinococcus granulosus. Hydatid cyst is a significant universal medical problem. In human cestode involves any organ and develops to hydatid cyst. Liver is the first and most frequently involved organ as the liver is the primary filter station of portal circulation. Though hydatid disease is benign disease, traditionally surgery is the treatment of choice for complete elimination of infective focus, which is associated with considerable mortality, morbidity. Systemic chemotherapy and percutaneous drainage have evolved in the recent past as an alternative to conventional surgery. The safety and success rate of these methods is influenced by the size, stage, location of the cysts and associated complications. Benzimidazoles can be considered in multiple, small hydatid cysts, but large cysts (cysts > 6 cm), bone marrow depression, pregnancy are contraindications of pharmacotherapy. Percutaneous drainage combined with ALB is a safe and effective treatment in liver hydatid patients with a surgical contraindication and younger cysts, but the presence of certain radiological signs (pericystic ducts and exophytic components) is a contraindication to non-surgical management because of the danger of biliary obstruction. However, the surgical treatment technique also cannot be standardized, should be tailored according to the cyst relation to the Broncho, biliary, vascular structures and associated complications if any. This review will focus on role of imaging in establishing the diagnosis, in determining cyst location, size, stage of the cyst and in identifying any associated complications, so that enable the clinician to perform recommended therapeutic procedures for the different cyst types and tailor the procedure performed based on cyst relation to broncho, biliary, vascular structures and associated complications.

Power and Bandwidth Allocation for Cognitive Heterogeneous Multi-Homing Networks

In this paper, an uplink power and bandwidth allocation problem for multiple services with multi-homing technology is formulated for cognitive heterogeneous networks. The joint power and bandwidth allocation with multiple services is subject to constraints in system available bandwidth, proportional fairness transmission rate for non-real-time secondary mobile terminals (MTs), minimum required transmission rate for real-time secondary MTs, interference power for primary base station, and total power consumption for each secondary MT. The joint power and bandwidth allocation problem with multiple services based on risk-return model is formulated as a bargaining game framework, first. Then, an optimal power and bandwidth allocation algorithm utilizing a dual decomposition method is proposed to obtain Nash bargaining solution. Finally, a heuristic algorithm is proposed to reduce computational complexity. Simulation results demonstrate the optimal and heuristic algorithms not only improve the spectrum efficiency, but also guarantee the fairness for secondary MTs with non-real-time service.

Distributed Energy-Spectrum Trading in Green Cognitive Radio Cellular Networks

Reducing the power consumption of base stations is crucial to enhancing the energy efficiency of cellular networks. As the number of mobile users increases exponentially, enhancing the spectrum efficiency is also critical in order to accommodate more users. In this paper, by exploiting the cooperation between secondary base stations (SBSs) and primary base stations (PBSs), we propose a new energy spectrum trading model to enhance the energy as well as spectrum efficiency of cellular networks. In our scheme, by leveraging cognitive radio, PBSs share some portion of their licensed spectrum with SBSs, and SBSs, in exchange, provide data service to the primary users under their coverage. We first prove that the power consumption minimization problem is NP-hard. Then, to decrease the computational complexity, we design an efficient distributed auction model including green energy aware bidding (GEAB) and adaptive bid selection (ABS) algorithms, to achieve a good approximation of the optimal solution in less time. Our simulation results show that the cooperation between PBS and SBSs via ABS and GEAB algorithms can significantly improve the energy and spectral efficiency of cellular networks by nearly doubling the number of offloaded users and reducing the PBS power consumption by up to 40% as compared to existing approaches. Furthermore, green energy utilization among SBSs is increased by nearly 25%.

Uplink Spectral Efficiency Analysis for a Massive MIMO Primary Network

Faster development of smart electronic devices in recent years along with significant increase in demanding higher data rates has made cognitive radio networks (CRNs) to be taken into consideration as a promising technology. A CRN has the ability to increase spectral efficiency (SE) of communication systems by opportunistically using unused spectrums. Furthermore, Massive multiple-input multiple-output is a major candidate to be used in next generation cellular systems in light of its great capabilities to improve system performance from spectral as well as energy efficiency standpoint. In this paper, we propose a CRN whose base station, as well as the primary base station (PBS) are equipped with large numbers of antennas. We derive closed-form expressions for SE in the uplink of primary users for three different scenarios. In these scenarios perfect and imperfect channel state information are considered separately. In addition, the impact of pilot contamination due to the correlation among users’ pilot signals on sum SE of primary network is examined. For the first two scenarios, minimum number of antennas (MNA) at the PBS to achieve a specified SE is derived in a closed-form expression. MNA is analyzed numerically for the third scenario.

Massive MIMO in Spectrum Sharing Networks: Achievable Rate and Power Efficiency

Massive multiple input multiple output (MIMO) is one of the key technologies for fifth generation and can substantially improve energy and spectrum efficiencies. This paper explores the potential benefits of massive MIMO in spectrum sharing networks. We consider a multiuser MIMO primary network, with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -antenna primary base station (PBS) and K single-antenna primary users (PUs), and a multiple-input-single-output secondary network, with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> -antenna secondary base station and a single-antenna secondary user. Using the proposed model, we derive a tight closed-form expression for the lower bound on the average achievable rate, which is applicable to arbitrary system parameters. By performing large-system analysis, we examine the impact of large number of PBS antennas and large number of PUs on the secondary network. It is shown that, when N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> and K grow large, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> must be proportional to ln K or larger, to enable successful secondary transmission. In addition, we examine the impact of imperfect channel state information on the secondary network. It is shown that the detrimental effect of channel estimation errors is significantly mitigated as N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> grows large.

Joint Video Packet Scheduling, Subchannel Assignment and Power Allocation for Cognitive Heterogeneous Networks

In this paper, a joint video scheduling, subchannel assignment, and power allocation problem in cognitive heterogeneous networks are modeled as a mixed integer non-linear programming (MINLP), which maximizes the minimum video transmission quality among different secondary mobile terminals (MTs) subject to the total available energy at each secondary, the total interference power at each primary base station, the total available capacity at each radio interface of each secondary MTs, and the video sequence encoding characteristic. In order to solve it, we decompose the original MINLP as joint subchannel and power allocation problem and video packet scheduling problem. Then, we model the joint subchannel and power allocation problem as a max–min fractional programming, and transform it as a convex optimization problem. Finally, we utilize dual decomposition method to design a joint subchannel and power allocation algorithm, and propose a video packet scheduling scheme based on auction theory to maximize the video quality for each secondary MT. Simulation results demonstrate that the proposed framework not only improves the video transmission quality significantly, but also guarantees the fairness among different secondary MTs.

Novel sensing and joint beam and null steering based resource allocation for cross-tier interference mitigation in cognitive femtocell networks

Cognitive radios and femtocell networks are gaining much popularity due to the formers ability to carry out unlicensed transmission in licensed bands and the latter’s ability to increase the indoor capacity by bringing the transmitter and receiver closer to each other. The combination of the two provides us with a joint benefit of unlicensed transmission and increased system capacity. However, deployments of such cognitive radio based femtocell networks (CRFN) can pose some severe cross-tier interference towards the primary system. In this paper, we propose a novel spectrum sensing technique based on Uniform Linear array (ULA) combined with Genetic Algorithm to detect not only the presence of a Primary user but also estimate its parameters such as range, frequency, angle of arrival and amplitude. Furthermore, a joint beamforming and null steering technique is proposed to maximize the signal to interference plus noise ratio (SINR) towards the secondary user equipment (SUE) while minimizing the interference towards the primary Base Station (PBS). We are reutilizing the sensed uplink (UL) frequency of the Primary users for the downlink (DL) transmission; the cognitive femtocell base station (CFBS) calculates such weight vector that aims at sending the maximum signal power towards the femto user and null in the direction of PBS.

Secure Communication in OFDMA-Based Cognitive Radio Networks: An Incentivized Secondary Network Coexistence Approach

In this paper, we propose a secure cooperative communications scheme for orthogonal frequency-division multiple-access (OFDMA) cognitive radio networks (CRNs), where a primary base station (PBS) wants to transmit information to some distant primary users (PUs) in the presence of a set of passive eavesdroppers. In our model, the transmission is performed in two consecutive time slots; in the first time slot, the PBS transmits while the secondary users (SUs) and the eavesdroppers listen. In the second time slot, the SUs transmit while the PUs, the secondary base station (SBS), and the eavesdroppers listen. We consider two schemes for eavesdropping; in the first scheme, the eavesdroppers listen to transmissions from the PBS to the SUs, and in the second scheme, we assume that the eavesdroppers apply the maximal ratio combining approach on the received signals in the first and second time slots for the primary network. In the proposed model, the SUs are allowed to use the licensed spectrum of the PUs, as long as they help the PUs to satisfy their secrecy rate requirement. We assume a frame-based transmission where each frame is divided into two consecutive time slots of equal duration. In the first time slot, the PBS transmits while the SUs and the eavesdroppers listen. In the second time slot, the selected SUs relay the PBS information to the distant PUs. Meanwhile, the SUs use the remaining resources to transmit their own information to the SBS while the eavesdroppers listen to this transmission. We formulate our proposed schemes as an optimization problem and solve it by dual Lagrange approach. We evaluate our proposed scheme in various situations using simulations and show the efficiency of the proposed scheme. An important aspect of the proposed paradigm is that replacing the conventional average interference threshold constraint by the primary secrecy rate constraint does not only decrease the secondary average secrecy rate with respect to the conventional case but can actually provide significantly higher secondary average secrecy rate as well.

Non-Orthogonal Random Access in MIMO Cognitive Radio Networks: Beamforming, Power Allocation, and Opportunistic Transmission.

We study secondary random access in multi-input multi-output cognitive radio networks, where a slotted ALOHA-type protocol and successive interference cancellation are used. We first introduce three types of transmit beamforming performed by secondary users, where multiple antennas are used to suppress the interference at the primary base station and/or to increase the received signal power at the secondary base station. Then, we show a simple decentralized power allocation along with the equivalent single-antenna conversion. To exploit the multiuser diversity gain, an opportunistic transmission protocol is proposed, where the secondary users generating less interference are opportunistically selected, resulting in a further reduction of the interference temperature. The proposed methods are validated via computer simulations. Numerical results show that increasing the number of transmit antennas can greatly reduce the interference temperature, while increasing the number of receive antennas leads to a reduction of the total transmit power. Optimal parameter values of the opportunistic transmission protocol are examined according to three types of beamforming and different antenna configurations, in terms of maximizing the cognitive transmission capacity. All the beamforming, decentralized power allocation, and opportunistic transmission protocol are performed by the secondary users in a decentralized manner, thus resulting in an easy implementation in practice.

Spectrum Sharing Based on a Bertrand Game in Cognitive Radio Sensor Networks.

In the study of power control and allocation based on pricing, the utility of secondary users is usually studied from the perspective of the signal to noise ratio. The study of secondary user utility from the perspective of communication demand can not only promote the secondary users to meet the maximum communication needs, but also to maximize the utilization of spectrum resources, however, research in this area is lacking, so from the viewpoint of meeting the demand of network communication, this paper designs a two stage model to solve spectrum leasing and allocation problem in cognitive radio sensor networks (CRSNs). In the first stage, the secondary base station collects the secondary network communication requirements, and rents spectrum resources from several primary base stations using the Bertrand game to model the transaction behavior of the primary base station and secondary base station. The second stage, the subcarriers and power allocation problem of secondary base stations is defined as a nonlinear programming problem to be solved based on Nash bargaining. The simulation results show that the proposed model can satisfy the communication requirements of each user in a fair and efficient way compared to other spectrum sharing schemes.

Simultaneous wireless energy transfer and spectrum sharing with primary data relaying in cognitive radio networks

Spectrum sharing and energy harvesting (EH) are promising techniques to enhance the spectrum and energy efficiency of wireless networks. In this paper, we propose a spectrum sharing scheme based on the cooperative energy and data transfer in both the time and space domains. When the primary base station (PB) transfers energy to the primary user (PU), the secondary user (SU) can transmit its own data simultaneously, and the interference of secondary data transmission becomes beneficial to improve the EH efficiency of the PU. Furthermore, the SU can assist the primary data relaying using the Alamouti coding technique to improve the link robustness through introducing the space diversity. With the energy and data cooperation from the SU, the primary data can be more quickly and reliably delivered, and hence more opportunities can be achieved for the spectrum sharing. Considering the dependence of the energy and data transfer, the throughput of both systems is investigated. The time allocation between EH and data transmission can be numerically determined by maximizing the throughput of secondary system under the throughput constraint of primary system. Performance results are presented to validate our theoretical analysis and provide some guidelines for the network configuration.

Achievable Rates of UAV-Relayed Cooperative Cognitive Radio MIMO Systems

We study the achievable rate of an uplink MIMO cognitive radio system where the primary user (PU) and the secondary user (SU) aim to communicate to the closest primary base station (BS) via a multi-access channel through the same unmanned aerial vehicle (UAV) relay. The SU message is then forwarded from the primary BS to the secondary network with a certain incentive reward as a part of the cooperation protocol between both the networks. A special linear precoding scheme is proposed to enable the SU to exploit the PU free eigenmodes. We analyze two scenarios in which the UAV relay gain matrix is either fixed or optimized. We derive the optimal power allocation that maximizes the achievable rate of the SU respecting power budget, interference, and relay power constraints. Numerical results highlight the cognitive rate gain of our proposed scheme with respect to various problem parameters. We also highlight the effect of UAV altitude on the SU and PU rates. Finally, when the relay matrix is optimized, we show that the PU rate is remarkably enhanced and that the SU rate is only improved at high-power regime.

Modified hybrid interference cancellation algorithm for uplink cognitive radio transmission based on overloaded DS-CDMA

In this paper, cognitive radio network architecture based on overloaded direct sequence code division multiple access (O-DS-CDMA) is proposed. In this method, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. Orthogonality between the spreading codes is lost due to non-zero cross correlation between the codes and timing synchronisation error in the uplink transmission, which causes interference among primary and secondary users. In this paper, a modified hybrid parallel/successive interference cancellation algorithm is proposed for the primary and secondary user base station receivers with multiple antennas, to suppress the interference among the users. Interferences among same group users are cancelled using parallel interference cancellation and the interferences between groups are cancelled using successive interference cancellation. The simulation results show that, the proposed modified interference cancellation algorithm improves the BER performance of the system significantly.

Securing cognitive radio with a combined approach of beamforming and cooperative jamming

The authors consider secret communication through a relay-assisted cognitive interference channel in which primary and secondary base stations (SBSs), respectively, communicate with the primary and secondary receivers (PU-Rx and SU-Rx) in the presence of multiple eavesdroppers. An SBS is allowed to transmit simultaneously with the primary base station (PBS). They propose three cooperative jamming (CJ) schemes based on the available channel state information at the base stations and the relay. The proposed CJ schemes are designed to create additional interference in the direction of eavesdroppers without creating any interference to the PU-Rx and the SU-Rx. A combined approach of beamforming and zero-forcing precoding is developed at the PBS, the SBS and the relay to cancel out jamming interference at the PU-Rx and the SU-Rx. The secrecy rate of SU-Rx is calculated with the constraint of maintaining interference temperature at the PU-Rx under a certain threshold. Compared with the direct transmission schemes that are available in the literature, the authors’ results show that the approach which combined beamforming and CJ significantly improves the secrecy rate of the cognitive interference channel.

Nonrandomized Trial of Feasibility and Acceptability of Strategies for Promotion of Soapy Water as a Handwashing Agent in Rural Bangladesh.

We conducted a nonrandomized trial of strategies to promote soapy water for handwashing in rural Bangladesh and measured uptake. We enrolled households with children < 3 years for three progressively intensive study arms: promotion of soapy water (N = 120), soapy water promotion plus handwashing stations (N = 103), and soapy water promotion, stations plus detergent refills (N = 90); we also enrolled control households (N = 72). Our handwashing stations included tap-fitted buckets and soapy water bottles. Community promoters visited households and held community meetings to demonstrate soapy water preparation and promote handwashing at key times. Field workers measured uptake 4 months later. In-depth interviews and focus group discussions assessed factors associated with uptake. More households had soapy water at the handwashing place in progressively intensive arms: 18% (promotion), 60% (promotion plus station), and 71% (promotion, station with refills). Compared with the promotion-only arm, more households that received stations had soapy water at the primary handwashing station (44%, P ≤ 0.001; 71%, P < 0.001 with station plus detergent refill). Qualitative findings highlighted several dimensions that affected use: contextual (shared courtyard), psychosocial (perceived value), and technology dimensions (ease of use, convenience). Soapy water may increase habitual handwashing by addressing barriers of cost and availability of handwashing agents near water sources. Further research should inform optimal strategies to scale-up soapy water as a handwashing agent to study health impact.