Joint beamforming design for secure RIS-assisted IoT networks

This paper studies secure communication in an internet-of-things (IoT) network, where the confidential signal is sent by an active refracting reconfigurable intelligent surface (RIS)-based transmitter, and a passive reflective RIS is utilized to improve the secrecy performance of users in the presence of multiple eavesdroppers. Specifically, we aim to maximize the weighted sum secrecy rate by jointly designing the power allocation, transmit beamforming (BF) of the refracting RIS, and the phase shifts of the reflective RIS. To solve the non-convex optimization problem, we propose a linearization method to approximate the objective function into a linear form. Then, an alternating optimization (AO) scheme is proposed to jointly optimize the power allocation factors, BF vector and phase shifts, where the first one is found using the Lagrange dual method, while the latter two are obtained by utilizing the penalty dual decomposition method. Moreover, considering the demands of green and secure communications, by applying the Dinkelbach’s method, we extend our proposed scheme to solving a secrecy energy maximization problem. Finally, simulation results demonstrate the effectiveness of the proposed design

Attitudes toward health, healthcare, and eHealth of people with a low socioeconomic status: a community-based participatory approach

Health and self-regulatio

An overview of facilitators and barriers in the development of eHealth interventions for people of low socioeconomic position: a Delphi study

Objective: eHealth interventions can improve the health outcomes of people with a low socioeconomic position (SEP) by promoting healthy lifestyle behaviours. However, developing and implementing these interventions among the target group can be challenging for professionals. To facilitate the uptake of effective interventions, this study aimed to identify the barriers and facilitators anticipated or experienced by professionals in the development, reach, adherence, implementation and evaluation phases of eHealth interventions for people with a low SEP.Method: We used a Delphi method, consisting of two online questionnaires, to determine the consensus on barriers and facilitators anticipated or experienced during eHealth intervention phases and their importance. Participants provided open-ended responses in the first round and rated statements in the second round. The interquartile range was used to calculate consensus, and the (totally) agree ratings were used to assess importance. Results: Twenty-seven professionals participated in the first round, and 19 (70.4%) completed the second round. We found a consensus for 34.8% of the 46 items related to highly important rated barriers, such as the lack of involvement of low-SEP people in the development phase, lack of knowledge among professionals about reaching the target group, and lack of knowledge among lower-SEP groups about using eHealth interventions. Additionally, we identified a consensus for 80% of the 60 items related to highly important rated facilitators, such as rewarding people with a low SEP for their involvement in the development phase and connecting eHealth interventions to the everyday lives of lower-SEP groups to enhance reach.Conclusion: Our study provides valuable insights into the barriers and facilitators of developing eHealth interventions for people with a low SEP by examining current practices and offering recommendations for future improvements. Strengthening facilitators can help overcome these barriers. To achieve this, we recommend defining the roles of professionals and lower-SEP groups in each phase of eHealth intervention and disseminating this study's findings to professionals to optimize the impact of eHealth interventions for this group.NWOPublic Health and primary carePrevention, Population and Disease management (PrePoD

Factors associated with spontaneous stone passage in a contemporary cohort of patients presenting with acute ureteric colic. Results from the MIMIC Study (A Multi-centre cohort study evaluating the role of Inflammatory Markers in patients presenting with acute ureteric Colic)

Objectives There is conflicting data on the role of white blood cell count (WBC) and other inflammatory markers in spontaneous stone passage in patients with acute ureteric colic. The aim of the study was to assess the relationship of WBC and other routinely collected inflammatory and clinical markers including stone size, stone position and Medically Expulsive Therapy use (MET) with spontaneous stone passage (SSP) in a large contemporary cohort of patients with acute ureteric colic. Subjects and Methods Multi‐centre retrospective cohort study coordinated by the British Urology Researchers in Surgical Training (BURST) Research Collaborative at 71 secondary care hospitals across 4 countries (United Kingdom, Republic of Ireland, Australia and New Zealand). 4170 patients presented with acute ureteric colic and a computer tomography confirmed single ureteric stone. Our primary outcome measure was SSP as defined by the absence of need for intervention to assist stone passage. Multivariable mixed effects logistic regression was used to explore the relationship between key patient factors and SSP. Results 2518 patients were discharged with conservative management and had further follow up with a SSP rate of 74% (n = 1874/2518). Sepsis after discharge with conservative management was reported in 0.6% (n = 16/2518). On multivariable analysis neither WBC, Neutrophils or CRP were seen to predict SSP, with an adjusted OR of 0.97 [95% CI 0.91 to 1.04, p = 0.38], 1.06 [95% CI 0.99 to 1.13, p = 0.1] and 1.00 [95% CI 0.99 to 1.00, p = 0.17], respectively. Medical expulsive therapy (MET) also did not predict SSP [adjusted OR 1.11 [95% CI 0.76 to 1.61]). However, stone size and stone position were significant predictors. SSP for stones 7mm. For stones in the upper ureter the SSP rate was 52% [95% CI 48 to 56], middle ureter was 70% [95% CI 64 to 76], and lower ureter was 83% [95% CI 81 to 85]. Conclusion In contrast to the previously published literature, we found that in patients with acute ureteric colic who are discharged with initial conservative management, neither WBC, Neutrophil count or CRP help determine the likelihood of spontaneous stone passage. We also found no overall benefit from the use of MET. Stone size and position are important predictors and our findings represent the most comprehensive stone passage rates for each mm increase in stone size from a large contemporary cohort adjusting for key potential confounders. We anticipate that these data will aid clinicians managing patients with acute ureteric colic and help guide management decisions and the need for intervention

Exploiting extrinsic passivation on thin film dielectrics for high efficiency solar cells

The development of high efficiency solar cells is critical for the expansion of solar power capacity across the world. A major limitation to achieving high efficiency is the recombination of electrons and holes at the silicon surface. A common method to reduce recombination is to deposit a dielectric thin film, such as SiO2 or SiNx, upon the silicon surface. This serves to chemically passivate the surface, while the dielectric’s intrinsic charge provides a surface electric field to control the charge carrier population. The passivation performance of such dielectrics can be further improved by extrinsic methods that modify the film properties after deposition. This thesis explores how the intrinsic properties of dielectrics can be supplemented by extrinsic methods to provide enhanced surface passivation. Dielectric thin films are a fundamental part of solid-state devices providing the means for advanced structures and enhanced operation. Ion-charged dielectrics are a particular kind of thin film in which ions are embedded to create a static electric field. Such charge can add functionality and improve the performance of electronic devices. To date, the electric field has been primarily demonstrated using embedded potassium and sodium cations. While the field effect provided by such ions have shown promising results in surface passivation, it is possible that alternative ions can provide greater long-term durability while enabling fine tailoring of the electric fields. Alongside potassium ions, this work demonstrates the migration kinetics, passivation performance, and stability of two new alkali ions, rubidium and caesium, inside of a SiO2 thin film. A comprehensive model of ion injection and transport has been developed, and a detailed investigation of the kinetics of potassium, rubidium and caesium ions is presented. It is shown that the concentration of charged ions within the film can be tuned by controlling the embedding process, leading to charge densities between 0.1-10 x 1012 q cm-2. Through the use of ion-charged SiO2, this thesis demonstrates that the effective surface recombination velocities can be reduced from ∼100 cm s-1 to as a low as 2.23 cm s-1 on 1 Ω cm n-type FZ silicon. The role of dielectric charge in producing high efficiency solar cells is demonstrated through Sentaurus TCAD modelling of PERC, IBC, TOPCon cell architectures. It is shown that by optimising the charge concentration within the dielectric, the recombination activity at defect-heavy interfaces can be successfully mitigated by field effect passivation. The exploitation of dielectric charge is predicted to achieve efficiencies >24% in PERC and TOPCon cells, and >25 % in IBC cells. Additionally, this thesis demonstrates that surface electric fields can influence the chemical passivation provided by a SiO2 + SiNx dielectric stack. It is shown that an electric field present within a dielectric not only modifies the charge carrier concentrations at the silicon surface, but also induces a chemical change in the interface properties upon annealing. By tailoring the surface electric field in the dielectric stack prior to annealing, it is shown that the capture rates at the Si-SiO2 interface can be modified depending on the field polarity and magnitude. Understanding the effect of surface electric fields on chemical passivation can lead to novel and unexplored methods of surface passivation.</p

Charge fluctuations at the Si-SiO2 interface and its effect on surface recombination in solar cells

The Si–SiO2 interface has and will continue to play a major role in the development of silicon photovoltaic devices. This work presents a detailed examination of how charge at or near this interface influences device performance. New understanding is identified on the effect of charge-induced potential fluctuations at the silicon surface. Such fluctuations have been considered in Si–SiO2 recombination models previously, where a universal value of electrical potential deviation was used to represent the effect. However, the approach disregards that the variation occurs in the charge concentration rather than the potential. We modify the models to accurately reflect fluctuations in external charge, allowing a precise representation of surface recombination velocity, with self-consistent Dit, δp, and δn parameters. Correctly accounting for these parameters can provide insights into the passivation mechanisms which can aid the development of future devices. Using the corrected model, we find that the effect of charge fluctuation at the Si–SiO2 interface is significant for the depletion regime to the weak inversion regime. This indicates that surface passivation dielectrics must operate with charge concentrations in excess of 2x1012 q/cm2 to avoid these effects. TCAD device simulations show that the efficiency of future PERC cells can improve up to 1% absolute when optimally charged dielectric coatings are applied both at the front and rear surfaces

Extracting band-tail interface state densities from measurements and modelling of space charge layer resistance

Dielectric-silicon interfaces are becoming ever more important to device performance. Charge inside a surface dielectric layer is neutralized in Si leading to an accumulation or inversion layer of free carriers. Additionally, states at the interface are occupied by charges via Shockley-Read-Hall carrier statistics. It is accepted that the density of interface charge near midgap, which can only reach a concentration as high as the density of states, Dit, has a minor effect on band bending compared to the charges in the dielectric for a well passivated interface. Here, we show that it is the state density near the band edge what plays the major role. We conclude this by comparing our measurements with device modelling of a Si/SiO2 interface. We measure the wafer sheet resistance while applying various amounts of positive charge to the passivating dielectric on an n-type Si wafer, and then reproduce the measured resistance values using simulations. This modelling indicates that Dit at midgap has indeed a minor effect on sheet resistance change, while the total amount of tail states has a significant impact on the distribution of induced carriers. We test this model to detect the amount of acceptor-like states at the band-tails of oxide passivated silicon with different processing. We discuss and analyse the limitations of this technique. While we report on the Si/SiO2 interface due to its relevance in photovoltaics, our method can be used to study the properties of other semiconductor-dielectric interfaces. As such this work is of importance across various optoelectronic devices

Electrostatic tuning of ionic charge in SiO2 dielectric thin films

Dielectric thin films are a fundamental part of solid-state devices providing the means for advanced structures and enhanced operation. Charged dielectrics are a particular kind in which embedded charge is used to create a static electric field which can add functionality and improve the performance of adjacent electronic materials. To date, the charge concentration has been limited to intrinsic defects present after dielectric synthesis, unstable corona charging, or complex implantation processes. While such charging mechanisms have been exploited in silicon surface passivation and energy harvesters, an alternative is presented here. Solid-state cations are migrated into SiO2 thin films using a gateless and implantation-free ion injecting method, which can provide greater long-term durability and enable fine charge tailoring. We demonstrate the migration kinetics and the stability of potassium, rubidium, and caesium cations inside of SiO2 thin films, showing that the ion concentration within the film can be tuned, leading to charge densities between 0.1-10 x 1012 qcm-2 . A comprehensive model of ion injection and transport is presented along a detailed investigation of the kinetics of alkali cations. Integrating ionic charge into dielectrics to produce controlled electric fields can enable new architectures where field effect is exploited for improved electron devices

Alternative dielectrics for hole selective passivating contacts and the influence of nanolayer built-in charge

Highly passivating, hole selective contacts are required for future high efficiency silicon solar cells. This work investigates selected dielectrics as potential SiOx replacements to act as hole selective contacts. AlOx and SiNx were identified as good candidates due to their low valence band offsets to silicon and proven surface passivation capabilities. Simulated J-V curves show AlOx and SiNx maintain acceptable contact resistivities at thicknesses below 1.4 and 1.7 nm, respectively. The SiOx hole contact was found to become extremely resistive even at thicknesses &lt;1 nm, suggesting that either pinholes dominate conduction, or the band offset parameters differ from those in real TOPCon structures. The passivation of the dielectrics was also simulated, with SiOx outperforming both AlOx and SiNx primarily due to the excellent interface. Additionally, the effect of nanolayer built in charge was investigated. Charges below 1012 q/cm2 were found to have little effect, while negative charges above 1012 q/cm2 resulted in reductions in the contact resistivity and recombination current. The calculated selectivity for a 1.4 nm layer of AlOx was 12.9, while a value of 13.8 was calculated for SiNx at typical intrinsic charge levels