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Nowadays, cloud computing is one of the important and rapidly growing services; its capabilities and applications have been extended to various areas of life. Cloud computing systems face many security issues, such as scalability, integrity, confidentiality, unauthorized access, etc. An illegitimate intruder may gain access to a sensitive cloud computing system and use the data for inappropriate purposes, which may lead to losses in business or system damage. This paper proposes a hybrid unauthorized data handling (HUDH) scheme for big data in cloud computing. The HUDH scheme aims to restrict illegitimate users from accessing the cloud and to provide data security provisions. The proposed HUDH consists of three steps: data encryption, data access, and intrusion detection. The HUDH scheme involves three algorithms: advanced encryption standards (AES) for encryption, attribute-based access control (ABAC) for data access control, and hybrid intrusion detection (HID) for unauthorized access detection. The proposed scheme is implemented using the Python and Java languages. The testing results demonstrated that the HUDH scheme can delegate computation overhead to powerful cloud servers. User confidentiality, access privilege, and user secret key accountability can be attained with more than 97% accuracy.

Nowadays, cloud computing is one of the important and rapidly growing paradigms that extend its capabilities and applications in various areas of life. The cloud computing system challenges many security issues, such as scalability, integrity, confidentiality, and unauthorized access, etc. An illegitimate intruder may gain access to the sensitive cloud computing system and use the data for inappropriate purposes that may lead to losses in business or system damage. This paper proposes a hybrid unauthorized data handling (HUDH) scheme for Big data in cloud computing. The HUDU aims to restrict illegitimate users from accessing the cloud and data security provision. The proposed HUDH consists of three steps: data encryption, data access, and intrusion detection. HUDH involves three algorithms; Advanced Encryption Standards (AES) for encryption, Attribute-Based Access Control (ABAC) for data access control, and Hybrid Intrusion Detection (HID) for unauthorized access detection. The proposed scheme is implemented using Python and Java language. Testing results demonstrate that the HUDH can delegate computation overhead to powerful cloud servers. User confidentiality, access privilege, and user secret key accountability can be attained with more than 97% high accuracy.

Time series data are significant and are derived from temporal data, which involve real numbers representing values collected regularly over time. Time series have a great impact on many types of data. However, time series have anomalies. We introduce hybrid algorithm named novel matrix profile (NMP) to solve the all-pairs similarity search problem for time series data. The proposed NMP inherits the features from two state-of-the art algorithms: similarity time-series automatic multivariate prediction (STAMP), and short text online microblogging protocol (STOMP). The proposed algorithm caches the output in an easy-to-access fashion for single- and multidimensional data. The proposed NMP algorithm can be used on large data sets and generates approximate solutions of high quality in a reasonable time. The proposed NMP can also handle several data mining tasks. It is implemented on a Python platform. To determine its effectiveness, it is compared with the state-of-the-art matrix profile algorithms i.e., STAMP and STOMP. The results confirm that the proposed NMP provides higher accuracy than the compared algorithms.

The Dark Web is known as a place triggering a variety of criminal activities. Anonymization techniques enable illegal operations, leading to the loss of confidential information and its further use as bait, a trade product or even a crime tool. Despite technical progress, there is still not enough awareness of the Dark Web and its secret activity. In this study, we introduced the Dark Web Enhanced Analysis (DWEA), in order to analyze and gather information about the content accessed on the Dark Net based on data characteristics. The research was performed to identify how the Dark Web has been influenced by recent global events, such as the COVID-19 epidemic. The research included the usage of a crawler, which scans the network and collects data for further analysis with machine learning. The result of this work determines the influence of the COVID-19 epidemic on the Dark Net.

Online social networks (OSNs) play an integral role in facilitating social interaction, however, these social networks increase antisocial behavior, such as cyberbullying, hate speech, and trolling. Aggression or hate speech that takes place through short message service (SMS) or the Internet (e.g., in social media platforms) is known as cyberbullying. Therefore, automatic detection utilizing natural language processing (NLP) is a necessary first step that helps prevent cyberbullying. This research proposes an automatic cyberbullying method to detect aggressive behavior using a consolidated deep learning model. This technique utilizes multichannel deep learning based on three models, namely, the bidirectional gated recurrent unit (BiGRU), transformer block, and convolutional neural network (CNN), to classify Twitter comments into two categories: aggressive and not aggressive. Three well-known hate speech datasets were combined to evaluate the performance of the proposed method. The proposed method achieved promising results. The accuracy of the proposed method was approximately 88%.

Background & Aim: Patients’ self-care management practice in diabetes is considered a critical element to keep diabetes under control and the disease management is usually conducted by the patients themselves and/or their families. The main aim of this study is to assess the level of self-care management practices of diabetic patients type 2 in Saudi Arabia. Materials & Methods: A cross-sectional study design was utilized in the Prince Sultan Military Medical City in Riyadh on a convenience sampling method consisted of 377 diabetic patients type 2. The researcher used a self-administered questionnaire (Summery of Diabetes Self-care Activities) which was adopted from Toobert et al. (2000). Results: The study results revealed that the level of self-care management practices among patients with type 2 DM is not satisfactory, except in the medication domain. Conclusion & Recommendations: Policymakers should revise the education strategy for diabetic patients and develop health education campaigns that focus on the patient’s family as well as the individual with type-2 DM.

Background: The absence of patient safety culture among nurses has been linked to increased errors and higher level of mortality and morbidity among patients. Higher culture of patient safety has been shown to be associated with better patient outcomes, and the implementation of improvements in organizational and safety culture enhances quality in healthcare. Aim: The main aim of this study is to assess the perception of nurses regarding patient safety among nurses at prince sultan military medical city in Saudi Arabia. Materials and Methods: Cross-sectional design was applied in this study among nurses who are working at prince sultan military medical city in Riyadh, Saudi Arabia. Sample was 215 nurses, selected by convenience sampling method. The Hospital Survey on Patient Safety Culture (HSOPS) survey was used in the current study to collect data. Data have been collected within seven weeks. Statistical package for social sciences has been used to analyze data using descriptive statistics and inferential statistics such as Independent sample t test and One-Way ANOVA. Results and Conclusion: The results can only be useful if data analysis is described. The highest domain of their perception was illustrated in “Hospital management support for patient safety” with a mean of 3.68 out of 5.0, while, the lowest mean for their perception was in the domain of “Teamwork across hospital units” with a mean 2.62. The total mean of nurses’ perception regarding patient safety was 3.19 out of 5.0. Also, there was a significant difference in the mean level of nurses’ perception of patient safety with regard to nurses’ gender. Encouraging patients’ safety culture among nurses is strongly recommended through effective communication and providing feedback.

The Internet of Things (IoT) is a wide network consisting of Internet-connected objects using installed software, such as home appliances, vehicles, and other entities embedded with sensors, actuators, radio-frequency identification (RFID), and electronics to exchange data. In the last two decades, numerous IoT solutions have been developed by small, medium-sized, and large enterprises to make our lives easier. Furthermore, private and academic researchers have extensively investigated some practical IoT solutions. The rapid expansion of IoT solutions accompanies numerous security concerns because the underlying IoT protocols and communication technologies have not considered security. Recently, blockchain has emerged to become one of the promising technologies that might overcome some of the IoT limitations (security limitations, in particular). Blockchain technology is a database ledger that uses a peer-to-peer (P2P) network and stores transactions and asset registries. Blockchain can be described as a mounting list of records (i.e., blocks) with the following properties: distributed, decentralized, immutable, and shared. This paper surveyed recent security advances to overcome IoT limitations using blockchain. In this article, the blockchain attempts to overcome IoT limitations that are related to cyber security have been classified into four categories: end-to-end traceability; data privacy and anonymity; identity verification and authentication; and confidentiality, data integrity, and availability (CIA). Intended as a guideline for future research, this paper also explores systematic processes.

Cloud computing has become a prominent technology due to its important utility service, this service concentrates on outsourcing data to organizations and individual consumers. Cloud computing has considerably changed the manner in which individuals or organizations store, retrieve, and organize their personal information. Despite the manifest development in cloud computing, there are still some concerns regarding the level of security and issues related to adopting cloud computing that prevent users from fully trusting this useful technology. Hence, for the sake of reinforcing the trust between cloud clients (CC) and cloud service providers (CSP), as well as safeguarding the CC’s data in the cloud, several security paradigms of cloud computing based on a third-party auditor (TPA) have been introduced. The TPA, as a trusted party, is responsible for checking the integrity of the CC’s data and all the critical information associated with it. However, the TPA could become an adversary and could aim to deteriorate the privacy of the CC’s data by playing a malicious role. In this paper, we present the state of the art of cloud computing’s privacy-preserving models (PPM) based on a TPA. Three TPA factors of paramount significance are discussed: TPA involvement, security requirements, and security threats caused by vulnerabilities. Moreover, TPA’s privacy preserving models are comprehensively analyzed and categorized into different classes with an emphasis on their dynamicity. Finally, we discuss the limitations of the models and present our recommendations for their improvement.

Thermal energy storage (TES) technologies are considered as enabling and supporting technologies for more sustainable and reliable energy generation methods such as solar thermal and concentrated solar power. A thorough investigation of the TES system using paraffin wax (PW) as a phase changing material (PCM) should be considered. One of the possible approaches for improving the overall performance of the TES system is to enhance the thermal properties of the energy storage materials of PW. The current study investigated some of the properties of PW doped with nano-additives, namely, multi-walled carbon nanotubes (MWCNs), forming a nanocomposite PCM. The paraffin/MWCNT composite PCMs were tailor-made for enhanced and efficient TES applications. The thermal storage efficiency of the current TES bed system was approximately 71%, which is significant. Scanning electron spectroscopy (SEM) with energy dispersive X-ray (EDX) characterization showed the physical incorporation of MWCNTs with PW, which was achieved by strong interfaces without microcracks. In addition, the FTIR (Fourier transform infrared) and TGA (thermogravimetric analysis) experimental results of this composite PCM showed good chemical compatibility and thermal stability. This was elucidated based on the observed similar thermal mass loss profiles as well as the identical chemical bond peaks for all of the tested samples (PW, CNT, and PW/CNT composites).

Currently, life cannot be imagined without the use of bank cards for purchases or money transfers, however, their use provides new opportunities for money launderers and terrorist organizations. This paper proposes a blockchain-enabled transaction scanning (BTS) method for the detection of anomalous actions. The BTS method specifies the rules for outlier detection and rapid movements of funds, which restrict anomalous actions in transactions. The specified rules determine the specific patterns of malicious activities in the transactions. Furthermore, the rules of the BTS method scan the transaction history and provide a list of entities that receive money suspiciously. Finally, the blockchain-enabled process is used to restrict money laundering. To validate the performance of the proposed BTS method, a Spring Boot application is built based on the Java programming language. Based on experimental results, the proposed BTS method automates the process of investigating transactions and restricts money laundering incidents.

The ignorance of or lack of knowledge about cybersecurity aspects causes a critical problem regarding confidentiality and privacy. This security problem will continue to exist even if the user possesses less expertise in information security. The modern IT technologies are well developed, and almost everyone uses the features of IT technologies and services within the Internet. However, people are being affected due to cybersecurity threats. People can adhere to the recommended cybersecurity guidelines, rules, adopted standards, and cybercrime preventive measures. However, it is not possible to entirely avoid cybercrimes. Cybercrimes often lead to sufficient business losses and spread forbidden themes (hatred, terrorism, child porn, etc.). Therefore, to reduce the risk of cybercrimes, a web-based Blockchain-enabled cybersecurity awareness program (WBCA) process is introduced in this paper. The proposed web-based cybersecurity awareness program trains users to improve their security skills. The proposed program helps with understanding the common behaviors of cybercriminals and improves user knowledge of cybersecurity hygiene, best cybersecurity practices, modern cybersecurity vulnerabilities, and trends. Furthermore, the proposed WBCA uses the Blockchain technology to protect the model from the potential threats. The proposed model is validated and tested using real-world cybersecurity topics with real users and cybersecurity experts. We anticipate that the proposed program can be extended to other domains, such as national or corporate courses, to increase the cybersecurity awareness level of users.

Herein, for the first time, the growth of ZnO nanorods directly on aluminum (Al) substrate via a low temperature (80 &deg, C) wet chemical method, and used as binder-free electrode for supercapacitors were reported. XRD pattern and HRTEM images showed that high crystalline nanorods grown on Al substrate with c-axis orientation. Morphological studies revealed that the nanorods possessed well defined hexagon phase with length and diameter of ~2 &micro, m and 100&ndash, 180 nm, respectively. Raman spectrum of ZnO nanorods showed that the characteristic E2H mode corresponds to the vibration associated with the oxygen atoms of ZnO. The optical properties of ZnO nanorods studied using Room-temperature PL spectra revealed a near-band-edge (NBE) peak at ~388 nm emission and deep level (DLE) at ~507 nm. Electrochemical measurements showed that ZnO nanorods on Al substrate exhibited remarkably enhanced performance as electrode for supercapacitors with a value of specific capacitance of 394 F g&minus, 1 measured with scan rate of 20 mV s&minus, 1. This unique nanorods structures also exhibited excellent stability of &gt, 98% capacitance retention for 1000 cycles that were measured at 1A g&minus, 1. The presented easy and cost-effective method might open up the possibility for the mass production of binder-free electrodes for efficient electrochemical energy storage devices.

The main technical challenge for the electrolytic production of hydrogen via water splitting lies in realizing a very stable material that effectively oxidizes water under low overpotential (η). Of all materials, metal oxides hold the greatest promise due to their inherited chemical stability in aqueous solutions; however, electrolytic effectiveness in water oxidation reactions (OERs) is limited to precious metals. In this study, we designed metal oxide/metal oxide (MO/MO) nanoparticle heterointerfaces to offer more active sites and enhance the overall performance of the OER. To demonstrate this improvement, we synthesized and characterized CeO2/Co3O4, CeO2/CuO, and CeO2/NiO nanoparticles. In these structures, onset potential and photoactivity were significantly improved relative to a single MO. A cathodic shift of onset potential as high as ~0.4 or 0.3 V was recorded for CeO2/Co3O4 relative to CeO2 or Co3O4, respectively. This improvement was further investigated using density functional theory calculations, upon which adsorption preferability and reaction free energy at the CeO2/Co3O4 heterointerface were found to play significant roles in OER enhancement.

Colon polyps might originate from the submucosa including lymphoid aggregates, carcinoids and lipomas. On the other hand, most polyps usually arise from the mucosa and include various types, whether neoplastic or not. The prognosis and treatment of these lesions depend on establishing an adequate diagnosis to rule out the presence of malignancy. Therefore, clinicians should be aware of each subclassification's different types and presentations to achieve the best outcomes. When conducting colonoscopy screening for colorectal cancer, colorectal polyps are commonly discovered. The prevalence of these lesions is high. However, most of them do not have any clinical significance. On the other hand, evidence shows that some polyps might have premalignant characteristics, which are usually challenging to manage in clinical practice. Therefore, evidence shows that the most appropriate approach to managing these lesions and achieving the best prognosis would be identifying and treating them as early as possible before complications appear to intervene against potential morbidities and mortality. Clinicians should consider the wide variations of colorectal cancer to establish the most appropriate diagnosis. A histological diagnosis is essential in these events to exclude malignancy and decide the most appropriate treatment plan.

Synergistic effect in alloys and plasmonic effect have both been explored for increasing the efficiency of water splitting. In depth understanding and comparison of their respective contributions in certain promising systems is highly desired for catalyst development, yet rarely investigated so far. We report herein our thorough investigations on a series of highly interesting nanocomposites composed of Pt, Au and C 3 N 4 nanocomponents, which are designed to benefit from both synergistic and plasmonic effects. Detailed analyses led to an important conclusion that the contribution from the synergistic effect was at least 3.5 times that from the plasmonic effect in the best performing sample, Pt 50 Au 50 alloy decorated C 3 N 4. It showed remarkable turnover frequency of >1.6 mmol h −1 g −1 at room temperature. Our work provides physical insights for catalyst development by rationally designing samples to compare long-known synergistic effect with recently emerging, attractive plasmonic effect and represents the first case study in the field.

Accurate detection of highly toxic aromatic nitro compounds in the water medium is urgent for the protection of human health and eco system. In the present study, we report the graphene oxide/ magnesium oxide nanocomposite (GO/MgO-NC) has been proposed for electrochemical analysis of nitrobenzene (NBZ) in water samples. The GO/MgO-NC was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscope, transmission electron microscopy, and energy dispersive X-ray analysis. Likewise, the electrochemical behaviour of NBZ was investigated through cyclic voltammetry and differential pulse voltammetry. The GO/MgO-NC electrode shows an excellent NBZ sensing properties compared to other electrodes. Under optimized conditions, the GO/MgO-NC/GCE can well measure the concentrations of NBZ in the range of 0.1–38.9 µM and 58.5–2333.5 µM with a low limit of detection of 0.01 µM. Besides, the GO/MgO-NC/GCE exhibits excellent selectivity, repeatability, reproducibility and stability. More importantly, the proposed GO/MgO-NC/GCE was further expanded to quantify NBZ in water samples with recoveries between 99.35–99.80%, providing an effective approach for the trace of NBZ in environmental medium.

Although existing membrane filtration technologies offer practical solutions for the removal of heavy metal ions from wastewater, there remains a great need for the realization of a membrane simultaneously possessing excellent selectivity, high permeability, and antifouling capability. Towards this end, novel buckypaper (BP) membranes were fabricated from multi-walled carbon nanotubes (MWCNTs) via vacuum filtration technique and the capability of two biopolymers (i.e. chitosan and carrageenan) to facilitate the formation of aqueous dispersions of MWCNTs was investigated alone and in combination of each other. For the first time, this study shows that the combination of BP membrane and both biopolymers (MWCNTs/chitosan-carrageenan) performs remarkably in terms of mechanical properties and high rejection of heavy metals. At an applied pressure of one bar, the removal of copper and lead reached 94% and 91%, respectively. The MWCNTs/chitosan-carrageenan membrane was also found to be mechanically robust, with a tensile strength and Young’s modulus of 30.69 ± 2.6 MPa and 3.78 ± 0.03 GPa, respectively. However, the MWCNTs/chitosan membrane showed superior water permeate flux, reaching up to 180 L/h.m2. The morphological properties and surface area (193 ± 3 to 285 ± 5 m2/g) of the three membrane types were also characterized using scanning electron microscopy and Brunauer, Emmett, and Teller analysis.

A solid oxide fuel cell (SOFC) is an energy converter device that directly converts the fuel's chemical energy into thermal and electrical energies. However, the performance of a SOFC is sensitive to the operating conditions, which indicates the need to control the operating parameters such as the operating temperature and inlet gas physical and chemical properties. In this paper, a three-dimensional (3-D) computational fluid dynamics (CFD) model of a button SOFC has been developed based on fluid flow, mass and heat transfer, and current and potential transport to study the performance of the button SOFC at different operating temperatures and flow rates. The results of all the investigated operating conditions have been validated with an in-house button SOFC. The results showed that the current density of the button SOFC increased significantly, to about 108.5% at average cell voltage 0.6 V and at oxygen flow rate of 1.8 L min−1 and hydrogen flow rate of 0.6 L min−1, when the operating temperature increased from 973 to 1023 K. However, less sensitivity has been found at the same average voltage of 0.6 V and an operating temperature of 973 K, the increase in the current density was about 9.7% when the flow rate of the oxygen increased from 0.4 to 0.6 L min−1, and the hydrogen flow rate increased from 1.2 to 1.8 L min−1, respectively; this was in good agreement with the experimental results.

The photochemical reduction of carbon dioxide (CO2) into energy-rich products can potentially address some of the critical challenges we face today, including energy resource shortages and greenhouse gas emissions. Our ab initio calculations show that CO2 molecules can be spontaneously activated on the clean nonpolar surfaces of wurtzite metal nitrides, for example, Ga(In)N. We have further demonstrated the photoreduction of CO2 into methanol (CH3OH) with sunlight as the only energy input. A conversion rate of CO2 into CH3OH (∼0.5 mmol gcat–1 h–1) is achieved under visible light illumination (>400 nm). Moreover, we have discovered that the photocatalytic activity for CO2 reduction can be drastically enhanced by incorporating a small amount of Mg dopant. The definitive role of Mg dopant in Ga(In)N, at both the atomic and device levels, has been identified. This study reveals the potential of III-nitride semiconductor nanostructures in solar-powered reduction of CO2 into hydrocarbon fuels.

A gallium nitride nanowire/silicon solar cell photocathode for the photoreduction of carbon dioxide (CO2 ) is demonstrated. Such a monolithically integrated nanowire/solar cell photocathode offers several unique advantages, including the absorption of a large part of the solar spectrum and highly efficient carrier extraction. With the incorporation of copper as the co-catalyst, the devices exhibit a Faradaic efficiency of about 19 % for the 8e(-) photoreduction to CH4 at -1.4 V vs Ag/AgCl, a value that is more than thirty times higher than that for the 2e(-) reduced CO (ca. 0.6 %).

A dual-photoelectrode device, consisting of a photoanode and photocathode with complementary energy bandgaps, has long been perceived as an ideal scheme for achieving high efficiency, unassisted solar-driven water splitting. Previously reported 2-photon tandem devices, however, generally exhibit an extremely low efficiency (0.1%), which has been largely limited by the incompatibility between the two photoelectrode materials. Here we show that the use of metal-nitride nanowire photoelectrodes, together with the scheme of parallel illumination by splitting the solar spectrum spatially and spectrally, can break the efficiency bottleneck of conventional 2-photon tandem devices. We have first investigated a dual-photoelectrode device consisting of a GaN nanowire photoanode and an InGaN nanowire photocathode, which exhibited an open circuit potential of 1.3 V and nearly 20-fold enhancement in the power conversion efficiency under visible light illumination (400-600 nm), compared to the individual photoelectrodes in 1 mol/L HBr. We have further demonstrated a dual-photoelectrode device consisting of parallel-connected metal-nitride nanowire photoanodes and a Si/InGaN nanowire photocathode, which can perform unassisted, direct solar-to-hydrogen conversion. A power conversion efficiency of 2% was measured under AM1.5G 1 sun illumination.

We report on the first demonstration of high-conversion-rate photochemical reduction of carbon dioxide (CO2) on gallium nitride (GaN) nanowire arrays into methane (CH4) and carbon monoxide (CO). It was observed that the reduction of CO2 to CO dominates on as-grown GaN nanowires under ultraviolet light irradiation. However, the production of CH4 is significantly increased by using the Rh/Cr2O3 core/shell cocatalyst, with an average rate of ∼3.5 μmol gcat–1 h–1 in 24 h. In this process, the rate of CO2 to CO conversion is suppressed by nearly an order of magnitude. The rate of photoreduction of CO2 to CH4 can be further enhanced and can reach ∼14.8 μmol gcat–1 h–1 by promoting Pt nanoparticles on the lateral m-plane surfaces of GaN nanowires, which is nearly an order of magnitude higher than that measured on as-grown GaN nanowire arrays. This work establishes the potential use of metal-nitride nanowire arrays as a highly efficient photocatalyst for the direct photoreduction of CO2 into chemical fuels. It al...

H2 generation under sunlight offers great potential for a sustainable fuel production system. To achieve high efficiency solar-to-hydrogen conversion, multijunction photoelectrodes have been commonly employed to absorb a large portion of the solar spectrum and to provide energetic charge carriers for water splitting. However, the design and performance of such tandem devices has been fundamentally limited by the current matching between various absorbing layers. Here, by exploiting the lateral carrier extraction scheme of one-dimensional nanowire structures, we have demonstrated that a dual absorber photocathode, consisting of p-InGaN/tunnel junction/n-GaN nanowire arrays and a Si solar cell wafer, can operate efficiently without the strict current matching requirement. The monolithically integrated photocathode exhibits an applied bias photon-to-current efficiency of 8.7% at a potential of 0.33 V versus normal hydrogen electrode and nearly unity Faradaic efficiency for H2 generation. Such an adaptive multijunction architecture can surpass the design and performance restrictions of conventional tandem photoelectrodes.

This article aims to build a misuse Wireless Local Area Network Intrusion Detection System (WIDS), and to discover some important fields in WLAN MAC-layer frame to differentiate the attackers from the legitimate devices. We tested several machine-learning algorithms, and found some promising ones to improve the accuracy and computation time on a public dataset. The best performing algorithms that we found are Extra Trees, Random Forests, and Bagging. We then used a majority voting technique to vote on these algorithms. The Bagging classifier and our customized voting technique have good results (about 96.25% and 96.32% respectively) when tested on all the features. We also used a data-mining technique based on Extra Trees ensemble method to find the most important features on Aegean WiFi Intrusion Dataset (AWID) public data-set. After selecting the most 20 important features, Extra Trees and our voting technique were the best performing classifiers in term of accuracy (96.31% and 96.32% respectively).

Investigation of the reliable operation of AlGaN/GaN HFETs at elevated temperatures is attempted. In this paper, a Monte Carlo-based temperature-dependent mobility model, with incorporation of steady-state velocity overshoot, is employed in modeling the drain current-voltage characteristics of AlGaN/GaN HFETs at 300, 400, and 500 K. One of the major merits of this model is that it employs a very small set of fitting parameters. The modeled drain current-voltage characteristics have been successfully matched to the experimental characteristics at the aforementioned temperatures. While confirming that a brief measurement at these temperatures is of no reliability concern on the quality of the metal-semiconductor contacts, this matching proves that the temperature dependency of the electron drift velocity is the cause of the degradation of drain current within the aforementioned range of temperature. In producing the aforementioned match for the long-gate AlGaN/GaN HFETs, it is also shown that the accurate modeling of the temperature dependency of the low-field drift transport is more consequential than the accurate representation of the transport in the medium-to-high electric fields.

The effects of the variation of the size of isolation mesa of AlGaN/GaN heterojunction field-effect transistors (HFETs) on the device characteristics are presented for the first time. Studies on the direct current and pulsed drain and gate current-voltage characteristics demonstrate a correlation between the pinchoff voltage and the size of the isolation mesa. In this paper, devices fabricated on narrow mesas (i.e., 16 × 40 μm2 fins) and also a device fabricated on an array of very small size mesas (i.e., 16 × 7 μm2 islands) are compared with AlGaN/GaN HFETs of traditionally sized mesas (i.e., 70 × 100 μm2). All these devices show maximum extrinsic gate transconductance greater than 220 mS/mm, whereas the pinchoff voltage is observed to become less negative by reducing the size of the individual mesas. The island-isolated HFETs also enjoy a relatively higher gate transconductance.

In article number 1500345, G. Zhao, A. Vomiero, F. Rosei, and co‐workers develop a new hybrid photoelectrochemical photoanode to generate H2 from water, composed of a TiO2 mesoporous frame functionalized by colloidal core@shell quantum dots (QDs) followed by CdS and ZnS capping layers. Saturated photocurrent density as high as 11.2 mA cm−2 is obtained in a solar‐cell‐driven PEC system using near infrared QDs.

Quantum dot (QD) sensitized TiO2 is considered as a highly promising photoanode material for photoelectrochemical (PEC) solar hydrogen production. However, due to its limited stability, the photoan ...

The aim of this paper is to detect Rogue Access Points (RAPs) that clone some of the characteristics of nearby legitimate Access Points (APs). A new passive approach that takes advantage of the first frame that the RAP sends (i.e., Beacon Frame (BF)) when it is planted in the Wireless Local Area Network (WLAN) is proposed. We apply the proposed fingerprint to detect RAPs to evaluate the fingerprint effectiveness. The proposed framework examines every beacon frame size, and compares it with a threshold value. The technique is implemented on a commercially available Wireless Network Interface Controller (WNIC) to evaluate its accuracy. The detection algorithm achieves 100 percent accuracy to determine the RAPs in a lightly loaded traffic environment. The detection time can be taken in approximately 100 ms and is scanned in real-time setting. The robustness and the efficiency of the detection algorithm are examined in two different locations.

Solar water splitting for hydrogen generation can be a potential source of renewable energy for the future. Here we show that efficient and stable stoichiometric dissociation of water into hydrogen and oxygen can be achieved under visible light by eradicating the potential barrier on nonpolar surfaces of indium gallium nitride nanowires through controlled p-type dopant incorporation. An apparent quantum efficiency of ∼12.3% is achieved for overall neutral (pH∼7.0) water splitting under visible light illumination (400-475 nm). Moreover, using a double-band p-type gallium nitride/indium gallium nitride nanowire heterostructure, we show a solar-to-hydrogen conversion efficiency of ∼1.8% under concentrated sunlight. The dominant effect of near-surface band structure in transforming the photocatalytic performance is elucidated. The stability and efficiency of this recyclable, wafer-level nanoscale metal-nitride photocatalyst in neutral water demonstrates their potential use for large-scale solar-fuel conversion.

Ferroelectric materials have been studied increasingly for solar energy conversion technologies due to the efficient charge separation driven by the polarization induced internal electric field. However, their insufficient conversion efficiency is still a major challenge. Here, a photocathode material of epitaxial double perovskite Bi(2) FeCrO(6) multiferroic thin film is reported with a suitable conduction band position and small bandgap (1.9-2.1 eV), for visible-light-driven reduction of water to hydrogen. Photoelectrochemical measurements show that the highest photocurrent density up to -1.02 mA cm(-2) at a potential of -0.97 V versus reversible hydrogen electrode is obtained in p-type Bi(2) FeCrO(6) thin film photocathode grown on SrTiO(3) substrate under AM 1.5G simulated sunlight. In addition, a twofold enhancement of photocurrent density is obtained after negatively poling the Bi(2) FeCrO(6) thin film, as a result of modulation of the band structure by suitable control of the internal electric field gradient originating from the ferroelectric polarization in the Bi(2) FeCrO(6) films. The findings validate the use of multiferroic Bi(2) FeCrO(6) thin films as photocathode materials, and also prove that the manipulation of internal fields through polarization in ferroelectric materials is a promising strategy for the design of improved photoelectrodes and smart devices for solar energy conversion.

We report on the photoelectrochemical water splitting and hydrogen generation under visible light on highly stable InGaN/GaN nanowire photoelectrodes. Keywords-water splitting; InGaN; nanowire; photoelectrochemical; hydrogen; solar fuel

We report on the first demonstration of stable photoelectrochemical water splitting and hydrogen generation on a double-band photoanode in acidic solution (hydrogen bromide), which is achieved by InGaN/GaN core/shell nanowire arrays grown on Si substrate using catalyst-free molecular beam epitaxy. The nanowires are doped n-type using Si to reduce the surface depletion region and increase current conduction. Relatively high incident-photon-to-current-conversion efficiency (up to ∼27%) is measured under ultraviolet and visible light irradiation. Under simulated sunlight illumination, steady evolution of molecular hydrogen is further demonstrated.

We have studied the photoelectrochemical properties of both undoped and Si-doped GaN nanowire arrays in 1 mol l 1 solutions of hydrogen bromide and potassium bromide, which were used separately as electrolytes. It is observed that variations of the photocurrent with bias voltage depend strongly on the n-type doping in GaN nanowires in both electrolytes, which are analyzed in the context of GaN surface band bending and its variation with the incorporation of Si-doping. Maximum incident-photon-to-current-conversion efficiencies of 15% and 18% are measured for undoped and Si-doped GaN nanowires under 350 nm light illumination, respectively. Stable hydrogen generation is also observed at a zero bias potential versus the counter-electrode. (Some figures may appear in colour only in the online journal)

A new hybrid photoelectrochemical photoanode is developed to generate H2 from water. The anode is composed of a TiO2 mesoporous frame functionalized by colloidal core@shell quantum dots (QDs) followed by CdS and ZnS capping layers. Saturated photocurrent density as high as 11.2 mA cm−2 in a solar‐cell‐driven photoelectrochemical system using near‐infrared QDs is obtained.

We report on the direct conversion of carbon dioxide (CO2) in a photoelectrochemical cell consisting of germanium doped gallium nitride nanowire anode and copper (Cu) cathode. Various products including methane (CH4), carbon monoxide (CO), and formic acid (HCOOH) were observed under light illumination. A Faradaic efficiency of ∼10% was measured for HCOOH. Furthermore, this photoelectrochemical system showed enhanced stability for 6 h CO2 reduction reaction on low cost, large area Si substrates.

In a photoelectrochemical (PEC) system, to harvest a wider wavelength range of sunlight, a relatively narrow bandgap photoelectrode is often used, which, however, requires an external bias to produce hydrogen, due to its insufficient photovoltage. One of the solutions to overcome the low photovoltage of single-photoelectrodes is to implement a buried junction below the photocatalyst (known as photovoltaic-PEC or PV-PEC). However, the design and performance of PV-PEC is severely limited by the stringent requirement of current matching between the buried PV and the top complementary light absorption photocatalyst. In this context, by exploiting the lateral carrier extraction scheme of 1-dimensional nanowire structures, we have developed an adaptive PV-PEC photocathode, consisting of monolithically integrated GaN/p-InGaN nanowire arrays on a planar Si solar cell wafer, that can surpass the current matching requirements of conventional tandem electrode. An applied bias photon-to-current efficiency of 8.7% is measured. The Si/GaN/p-InGaN PV-PEC device heterostructure consists of a planar n+-p Si solar cell wafer, ~ 150 nm n-GaN and ~ 600 nm p-InGaN nanowire segments along the axial direction. The top p-InGaN nanowire arrays are designed to absorb the ultraviolet and a large portion of the visible solar spectrum. The remaining photons with wavelengths up to 1.1 µm are absorbed by the underlying planar Si p-n junction. In contrary to conventional semiconductor photocatalysts, InGaN can uniquely straddle water oxidation and hydrogen reduction potentials under deep visible light irradiation. The n-GaN and p-InGaN are connected via an n++-GaN/InGaN/p++-GaN polarization-enhanced tunnel junction, which enables the transport of photo-excited holes from the p-InGaN to the n-GaN within each single nanowire. The presented device differs from conventional PV-PEC electrodes in that both the top p-InGaN and the bottom GaN/Si light absorbers can simultaneously drive proton reduction due to the lateral carrier extraction scheme of nanowires. That is, due to the relatively small offset between the n+ -Si and n-GaN conduction band edges, photo-excited electrons of the bottom Si solar cell can readily inject into the n-GaN nanowire segment. A large fraction of the injected electrons can drive proton reduction on GaN surfaces, with the rest recombining with holes from the p-InGaN in the tunnel junction. It is seen that such a novel design, with the use of Si/GaN-nanowire as the bottom light absorber, can surpass the restriction of current matching in conventional dual absorber devices and simultaneously provide energetic photo-excited electrons to the hydrogen-evolution-reaction (HER) catalyst. Compared to the conventional PEC-PV, such adaptive junction can reduce chemical loss by allowing charge carriers with different overpotentials to be utilized for HER. Such a monolithically integrated photocathode shows an applied bias photon-to-current efficiency of 8.7% at a potential of 0.33 V vs. normal hydrogen electrode. The Faradaic efficiency for hydrogen generation is also measured to be nearly unity.

Recently, III-nitride nanowire structures have been intensively investigated for applications in solar water splitting and hydrogen generation. Compared to the conventional oxide-based photoelectrodes, III-nitride nanowires offer distinct advantages including tunable energy bandgap across nearly the entire solar spectrum, conduction and valence band edges that can straddle water redox potentials under deep visible and near-infrared light irradiation, and high efficiency charge carrier separation and extraction. Spontaneous overall water splitting under UV, blue, and green light irradiation has been demonstrated on InGaN/GaN nanowire structures. Moreover, multi-band InGaN nanowire photocatalyst and photoanode have been developed to effectively harvest a large part of the solar spectrum. Such nanowire arrays also exhibit a high level of stability in aqueous solution. To further improve the efficiency of solar-to-hydrogen conversion, we have investigated the design, epitaxial growth, and testing of paired InGaN/GaN photoanode and photocathode. The devices exhibit relatively high incident photon-to-current conversion efficiency (up to 65%). The energy conversion efficiency in the wavelength range of 300-600 nm is also significantly improved, compared to a single electrode. Here, we report on the design principle and operation of such novel photoelectrodes. In this design, the photocathode and the photoanode are connected side by side, wherein the solar light can be split spectrally and spatially. Different split light spectra are spread out to strike the corresponding photoelectrodes. n-InGaN/GaN and p-InGaN/GaN decorated with Pt nanoparticles are used as the photoanode and photocathode, respectively. The design of paired InGaN nanowire photoelectrodes can provide high photovoltage without trading off on the harvesting of longer wavelength of sunlight. Catalyst-free, vertically aligned InGaN/GaN nanowire arrays were grown on n-type Si(111) substrate by radio frequency plasma-assisted molecular beam epitaxy under nitrogen rich conditions. After an in situ oxide desorption at ~ 770 °C, A GaN nanowire template with a height of ~ 200 nm was first grown on Si substrate. To enhance the carrier transport between the n-type Si substrate and p-InGaN nanowire, a tunnel junction consisting of n +-GaN/p +-InGaN/p +-GaN was implemented beneath the p-InGaN nanowire. The nanowires are doped n-type or p-type using silicon or magnesium, respectively. The photoelectrochemical (PEC) properties of the photocathode and the photoanodes were investigated separately using a cell with a three-electrode configuration in 1 mol/L HBr. A linear sweep voltammogram for n-InGaN/GaN photoanode was performed under both dark and illuminated conditions. The maximum incident photon-to-current conversion efficiency (IPCE) measured at 1 V vs. Ag/AgCl for the n-InGaN/GaN photoanode is ~ 50% at 350 nm, while the maximum IPCE for p-InGaN/GaN photocathode (at -0.6 V vs. Ag/AgCl) is ~ 65% at 350 nm. The IPCE shows a decreasing trend with increasing wavelength, limited by the effective light absorption of the nanowire structures. In the paired configuration, the incident light was split by using long- and short-pass optical filters. The parallel-connected photoanode was illuminated with light with wavelengths in the range of 300-480nm. The photocathode was illuminated with light with wavelengths of 485-600 nm. Using a two-electrode configuration, the photoanode was considered to be the working electrode, and the photocathode p-InGaN/GaN was connected as the counter electrode in 1 mol/L HCl. With this novel design, the power conversion efficiency in the range of 300-600 nm has been increased by nearly one order of magnitude, compared to efficiency of a single electrode. The maximum power conversion efficiency of this device can reach >5%. Work is currently in progress on the integration of InGaN nanowires with solar cells to achieve further increased efficiency for solar-to-hydrogen conversion.