bluuebunny/crossref_metadata_2025 huggingface dataset:
Secure cognitive radio networks with source selection and unreliable backhaul connections
Authors: Truong Tien‐Vu , Nguyen Minh‐Nghia , Kundu Chinmoy , Nguyen Long D.
Published: December 2017

In this study, the secrecy performance of cooperative half‐duplex cognitive relay networks (CRNs) comprised of multiple primary users (PUs) and multiple eavesdroppers under the effect of unreliable wireless backhauls is studied. The authors consider relay networks with single relay assisting multiple sources under power constraints at PUs and secondary transmitters, and based on the availability of channel‐state information at the sources, they propose two best source selection schemes, namely: (i) optimal source selection (OSS) and (ii) sub‐optimal source selection (SoSS). For both scenarios, they obtain exact closed‐form and asymptotic expressions for the system's outage probability and carry out numerical simulations to justify their analyses. From the results, source selection is proven to be capable of counteracting the negative impact of unreliable backhaul on CRNs. The secrecy performance limitations are also verified to be influenced by the backhaul reliability. Furthermore, OSS is more desirable compared to SoSS in low signal‐to‐noise ratio (SNR) regime, while the secrecy performance for both schemes converge to an asymptotic limit in high‐SNR ranges.
Fairness aware multiple drone base station deployment
Authors: Akarsu Alper , Girici Tolga
Published: December 2017

The recent advances in drone technology significantly improved the effectiveness of applications such as border surveillance, disaster management, seismic surveying, and precision agriculture. The use of drones as base stations to improve communication in the next generation wireless networks is another attractive application. However, the deployment of drone base stations (DBSs) is not an easy task and requires a carefully designed strategy. Fairness is one of the most important metrics of tactical communications or a disaster‐affected network and must be considered for the efficient deployment of DBSs. In this study, a fairness‐aware multiple DBS deployment algorithm is proposed. As the proposed algorithm uses particle swarm optimisation (PSO) that requires significant processing power, simpler algorithms with faster execution times are also proposed and the results are compared. The simulations are performed to evaluate the performance of the algorithms in two different network scenarios. The simulation results show that the proposed PSO‐based method finds the three‐dimensional locations of DBSs, achieving the best fairness performance with a minimum number of DBSs for deployment. However, it is shown that the proposed suboptimal algorithm performs very close to the PSO‐based solution and requires significantly less processing time.
Hybrid adaptive framework for coordinated control of distributed generators in cyber‐physical energy systems
Authors: Korukonda Meher Preetam , Mishra Swaroop R. , Rajawat Ketan , Behera Laxmidhar
Published: December 2017

With the development of information and communications technology (ICT) and inundation of sensing devices, the control of smart grid is undergoing a paradigm shift from centralised/decentralised to a more distributed nature allowing each distributed generator to receive information from sensors at distant buses. In such systems, there is much interdependency between various power, control and communication parameters due to which the control of parameters from one domain gets affected by other. The central idea of this study is to develop a generic, hybrid and customised framework to jointly model the multi‐disciplinary variables and their interactions present in the smart grid and to develop controllers in an adaptive manner to ensure better control of physical variables such as voltage irrespective of the changes in operating point brought about by changes in physical/cyber parameters. Hence, the different operating conditions of the power system have been modelled as multiple subsystems of a hybrid switching system and controller design is carried out by solving the optimisation formulations developed for delay‐free and delay‐existent cases using the theory of common Lyapunov function. The optimisation is carried out using the block coordinate descent methodology by converting the non‐convex formulation into a series of convex problems to obtain a solution.
Performance of dual‐band AMC antenna for wireless local area network applications
Authors: Mersani Ameni , Osman Lotfi , Ribero Jean‐Marc
Published: December 2017

This study focuses on the design, simulation, and fabrication of a coplanar waveguide miniaturised wearable antenna that is fully implemented in textile materials and operable at 2.45/5.8 GHz for wireless local area network applications. This antenna is assumed to be placed near the human body, so that it needs to be miniaturised with excellent performances. To increase the performance of the short‐distance textile antenna and to control the specific absorption rate, an artificial magnetic conductor (AMC) is preferred as a reflector plane. The volume of the proposed antenna with AMC is 75 × 50 × 6 mm3, the simulation and measurement results are in good agreement and show that the antenna performances perform better results in comparison with the one reported so far in the literature while having a smaller volume. AMC significantly improves the performance of the antenna. The gains of the antenna are 8.2 and 9.95 dBi at 2.45 and 5.8 GHz, respectively (an increase of 3 dB compared with an antenna without AMC).
One to 40 GHz ultra‐wideband RF MEMS direct‐contact switch based on GaAs MMIC technique
Authors: Chu Chenlei , Liao Xiaoping
Published: December 2017

This study presents a 1–40 GHz ultra‐wideband radio frequency (RF) micro‐electro‐mechanical systems (MEMS) direct‐contact switch based on a GaAs microwave monolithic integrated circuit (MMIC) process. The proposed switch utilises an inline cantilever membrane and a pull‐in electrode to achieve ‘off’ and ‘on’ states. It has been manufactured by micro‐machining, which is completely compatible with the GaAs MMIC process. An equivalent distributed parameter circuit model of the switch is established to analyse the microwave performances. The measured S‐parameters show that the isolation (S21) in the ‘off’ state is better than 22.5 dB from 1 to 40 GHz. In the ‘on’ state, the input reflection coefficient (S11) is less than −20.9 dB and the forward transmission coefficient (S21) is better than −0.25 dB over the complete band. In addition, the measured pull‐in voltage is ∼17.5 V. The measured maximum power handling capacity is 36.5 dBm. A lifetime of 2.4 × 107 switching cycles is also verified by this design. The whole structure is designed with the purpose of expanding its working bandwidth and achieving higher microwave performances over current state of art.
Wideband microstrip antenna array with simultaneously low sidelobe level in both sum and difference patterns
Authors: Atamanesh Mehran , Abbasi Arand Bijan , Zahedi Amir
Published: December 2017

An X‐band microstrip antenna array is fully designed. A multilayer structure is chosen for the antenna and the radiating elements are fed by the aperture‐coupled patch technique. A mono‐pulse feeding network is also designed which distributes the power to the radiating elements in a way that low sidelobe level is created in the sum pattern and both difference patterns. The measurement and simulation results coincide well in the whole bandwidth.
Metallic inductive coupling frame‐based HF RFID cards
Authors: Rizkalla Shrief , Prestros Ralph , Mecklenbräuker Christoph F.
Published: December 2017

A coupling frame (CF)‐based high‐frequency radio‐frequency identification (HF RFID) card is composed of a metallic CF with a slot and a module (contains a small coil and an integrated circuit). This provides higher coupling and better performance in comparison to the standalone module. Such design eliminates the need for a mechanical connection between the module and card body (metal frame) which leads to reduced manufacturing costs. Further, it enhances the card's robustness against mechanical stress. The authors explain the operation of such a design from first principles and highlight the effect of the slot on the performance. In addition, a circuit model for the card is derived. Furthermore, they propose an enhancement to the card design which improves the card's performance with two variations either in terms of better transferred voltage (up to three times higher) or more bandwidth (up to double). The enhancement is shown by HFSS simulations, circuit simulations and corresponding measurements including the HF RFID integrated circuit. Finally, a double CF‐based design is proposed and analysed which simultaneously achieves increased bandwidth and higher transferred voltage. The results are compared to those of conventional HF RFID cards with galvanic coupling to the integrated circuit.
Cylindrical to rectangular coordinate transformation for planar phase front synthesis
Authors: Sedighy Seyed Hassan , Guclu Caner , Amirhosseini Mohammad Khalaj , Capolino Filippo
Published: December 2017

Coordinate transformation technique is employed to engineer a metamaterial slab that enables planar wave emission from a planar or line localised source. First a rigorous cylindrical to rectangular coordinate transformation is applied resulting in with a sheet current generating a plane wave with impedance matching at the boundary between the device and the surrounding medium. Then, based on physical reasoning, the material constitutive parameters are further reduced to having only one entry of the spatially varying permeability tensor instead of two entries as discussed in the references. This further reduction is equivalent to modifying the near field in the transformed domain. Finally, due to a specific mu‐near‐zero condition near the origin, the sheet source is transformed to a localised one in the transformed domain and via full‐wave simulations, the authors show that the field is still propagating as a plane wave. Moreover, the transmission line (TL) metamaterial implementation with discretised spatially varying permeability is designed. The capacitor‐ and inductor‐loaded two‐dimensional TL grid is used to synthesise the required spatially varying relative permeability in the wavefront converter metamaterial slab. The TL metamaterial design is proven to successfully synthesise a planar wave front using a microwave circuit simulator.
Comparative study between different optimisation techniques for finding precise switching angle for SHE‐PWM of three‐phase seven‐level cascaded H‐bridge inverter
Authors: Kundu Sourabh , Burman Arka Deb , Giri Santu K. , Mukherjee Sarbani , Banerjee Subrata
Published: December 2017

Selective harmonic elimination pulse‐width modulation (SHE‐PWM) works at low‐frequency switching, which reduces switching losses, device stress, and increases energy conversion efficiency. So, it can be an effective control strategy for multilevel inverter working on medium‐voltage, high‐power industrial energy conversion application. It provides desired output voltage by retaining the requested fundamental component as well as eliminating some low‐order harmonics. The application of SHE‐PWM in industries is having an influence on precise solvability of complex and non‐linear equations. This study presents two recently reported optimisation techniques, namely backtracking search algorithm and differential search algorithm (DSA) for obtaining a more accurate solution of the harmonics elimination problem. The superiority of the proposed optimisation algorithms over the well known ancient algorithm such as genetic algorithm, BEE algorithm and particle swarm optimisation have been established by a comparative study with respect to the possibility of attaining global minima, the rank of convergence rate, and inverter performance analysis. Simulation and experimental results validate the efficacy of the DSA optimisation technique for calculating more precise switching angles that totally eliminate 5th‐ and 7th‐order harmonics with fulfilling the requested fundamental component.
Ultraviolet differential spectroscopy quantitative analysis of SF6 decomposition component SO2
Authors: Zhang Xiaoxing , Xiao Hanyan , Li Xin , Zhang Jun
Published: December 2017

SO2 is a symbolic gas that can indicate the insulation status of SF6 insulation electrical equipment. Its accurate quantitative measurement is of the great significance for the judgement of the type and severity of faults inside the insulation equipment. For this reason, a detection system of trace SO2 based on ultraviolet (UV) spectrometry was presented. The measured UV absorption spectra of SO2 were processed using the wavelet analysis to remove useless spectra information and get the UV differential absorption spectra of SO2. The fast Fourier transform (FFT) was used to analyse UV differential spectra in the band of 190–230 and 290–310 nm and extract the feature information. The results show that there is a good linear relationship between the FFT characteristic peak value and the concentration of trace SO2 in the two wave bands. The detection limit in the band of 190–230 nm was even lower than that in the band of 290–310 nm. Besides, the differential absorption cross section of SO2 decreases with the increase of temperature. The study has laid a foundation for the application of the UV differential absorption spectroscopy in the online monitoring and fault diagnosis of SF6 insulation electrical equipment.
Influence of back‐to‐back VSC‐HVDC project on the operation characteristics of Hubei power grid
Authors: Cai Defu , Zhou Kunpeng , Wang Wenna , Liu Haiguang , Cao Kan , Wang Ying
Published: December 2017

The synchronous interconnection between Chongqing and Hubei power grid is planned to be unsynchronised by back‐to‐back voltage source converter based high‐voltage direct current (VSC‐HVDC) project, which has great impact on the operation characteristics of Hubei power grid. In this study, the basic information of back‐to‐back VSC‐HVDC project was introduced. The influence of this project on the operation characteristics of Hubei power grid was analysed in detail, including power flow, short‐circuit current, transient stability and frequency characteristic. The corresponding grid reinforcement measures were proposed to solve power flow over‐limit and transient instability problems caused by this project. The study has some reference value for the planning and operation of Hubei power grid and the design of other similar HVDC transmission projects.
Research on fault protection of DC grid based on hybrid MMC
Authors: Zhang Junjie , Xiang Wang , Lin Weixing , Wen Jinyu
Published: December 2017

The protection strategy of overhead direct current (DC) grid is studied based on the hybrid modular multilevel converter (MMC), which is composed of half bridge sub‐modules and full bridge SMs (FBSMs). First, the topology, operating principle and DC voltage operating region of the hybrid MMC are analysed. Then, a control framework embedding three‐channel control freedom and DC fault ride through control strategy are presented. Two protection schemes based on DC disconnectors and mechanical DC circuit breakers (DC CBs) are designed. In the first scheme, the hybrid MMC controls the DC fault to zero and a current injection method is adopted to restart the DC grid. In the second scheme, the mechanical DC CBs can block the DC fault current and has the ability to reclose for three attempts. At last, the feasibility of two schemes is validated in power systems computer‐aided design/electro‐magnetic transient design and control.
Method to determine the maximum generation capacity of distribution generation in low‐voltage distribution feeders
Authors: Fan Shixiong , Li Chen , Wei Zechen , Pu Tianjiao , Liu Xingwei
Published: December 2017

This study presents a simple applicable methodology to directly calculate maximum distribution generation (DG) capacity in radial low‐voltage (LV) feeder without leading to steady‐state voltage and current violations. The proposed methodology considers the phase mutual inductance and line losses to ensure the accuracy of the results. In order to validate the accuracy and feasibility of the proposed approach, the comparative analysis of power flow tool and proposed algorithm is carried out based on the three‐phase radial LV feeder. The calculated value of maximum DG capacity can be used to support the DG planning and grid safety operation with DG integration.
Equivalencing‐tracking‐based method for incorporating distributed energy resources in transmission system economic dispatch
Authors: Li Zhengshuo , Guo Qinglai , Sun Hongbin , Xu Tong
Published: December 2017

This paper proposes an equivalencing‐tracking‐based (ETB) method to incorporate distributed energy resources (DERs) in transmission system economic dispatch (TED). This method has three key steps. The first is a ‘dispatch model equivalencing’ step in which an equivalent dispatch model is created by an aggregator or a distribution system operator (DSO) to represent the aggregate operational features of the numerous DERs on the distribution side. In the second step, the equivalent dispatch model is sent to the transmission system operator (TSO) who then solves a DER‐equivalent‐included TED problem. The optimal solution regarding the DERs' equivalent dispatch model is returned to the aggregator, who will, in the third step, solve an optimal tracking problem to provide each DER with an optimal dispatch scheme that best tracks the optimal solution regarding the equivalent model. Case studies on a real power system confirm that the transmission system operation benefits from DERs' being incorporated in TED, and also that the proposed method can attain a nearly optimal solution without repeated iterations between TSOs and DSOs, which is a notable advantage over mathematical decomposition methods.
Power grid planning based on differential abandoned wind rate
Authors: Song Zhuoran , Shen Fang , Nan Zhe , Zhang Yibo , Zhao Lin , Deng Xinyang , Zhang Na , Li Hua , Zhang Zixin , Ye Wang , Lu Tianqi
Published: December 2017

With the rapid development of wind power, the abandoned wind phenomenon is becoming increasingly serious. In order to study the reasonable scale of wind power development in the region, it is necessary to study the power grid construction and operation cost in different areas. In this paper, the optimal operation model of wind power is established, which is based on the abandoned wind rate. The model takes into account the generation cost, the penalty cost of the abandoned wind and the investment cost of the new line. The generating cost of the unit includes the cost of starting and stopping of the thermal power unit and the cost of the wind turbine. Abandoned wind penalty cost refers to the reduction of abandoned wind power, with certain amount of wind power curtailment of wind field punishment. The investment cost of the new line is obtained by multiplying the length of the unit length of the line by the length of the new line, and converting the cost to the level of the year. Finally, the reasonability and feasibility of the proposed method are verified by a provincial power grid case.
Renewable energy integration capacity assessment in regional power grid based on an enhanced sequential production simulation
Authors: Zhang Yan , Dai Xianzhong , Han Xinyang
Published: December 2017

As the scale of renewable energy increases significantly, the renewable energy integration will gradually become the key issue in urgent need of a solution for Shaanxi power system. To tackle such a new situation, this study proposes an innovative method for accessing the renewable energy integration capacity of Shaanxi power system during the next ‘Five‐Year Plan’ period. First, an in‐depth study of the power demand, load characteristics, renewable energy as well as their output characteristics is performed. Then, the maximum wind and solar power integration capacity is simultaneously calculated based on an enhanced sequential stochastic production simulation in consideration of several boundary conditions of Shaanxi power system such as power supply, network constraints and future load. Finally, the influence of electric heating scale in Yulin region on the renewable energy integration capacity of Shaanxi power system is further studied. Through such analysis, this study attempts to provide decision support for a reasonable renewable energy development scale and power grid plan.
Optimised recovery strategy for microgrid with distributed generations
Authors: Jiehui Chen , Haiqiang Zhou , Dayan Sun , Jizu Guo
Published: December 2017

Microgrids with a variety of distributed generations (DGs) are very common in modern power system. When a fault occurs in the power system, the microgrid will operate as an isolated grid to ensure security. Then DGs were separated from the microgrid and the measures of load shedding were taken accordingly. When the fault is cleared, it is important to restore the whole network and as much load as it can. An optimal restoration strategy for the microgrid is proposed here. Firstly, the objective for the network recovery is to have a shorter recovery time and the mathematical model is to seek the shortest path. The Dijkstra's algorithm is a classical method to solve the optimal path problem which can be applied in the microgrid network restoration to find the shortest path from a given source node to every other node. Also, analytic hierarchy process method, which is a structured technique for organising and analysing complex decisions, can help select the source node. Then, when a bus is recovered in the microgrid, the load on the relevant bus should be considered to recover. Finally, a microgrid including DGs and diverse energy storages is used to illustrate the effectiveness of the proposed method.
Quantitative method to pre‐assess vulnerability for microgrid based on probability theory
Authors: He Weiguo , Hua Guanghui , Zheng Hao , Fang Wanliang , Liu Haoming
Published: December 2017

Along with the advance of smart grid and power system resilience, there has been a growing interest in the vulnerability of power grid. In this study, our focus is on a microgrid, and a probability theory based quantitative method to pre‐assess vulnerability for microgrid is proposed. Firstly, the concept of vulnerability for microgrid is introduced. Then, several key indices for vulnerability pre‐assessment is presented, mainly including generation capacity adequacy and power supply vulnerability, and five important indices of power supply vulnerability are addressed, they are loss of load risk, overload risk, overvoltage risk, low load power factor risk and three‐phase unbalance risk. Finally, the detailed implementation of the comprehensive vulnerability pre‐assessment is discussed, followed by a case study, the results demonstrate the validity of proposed method.
Siloxane injection technology for extending the lifetime of the operating cable
Authors: Tao Wenbiao , Song Shuyong , Ma Zhenguo , Sun Ruihao , Zhang Yifan , Zhao Jin
Published: December 2017

To promote the insulation level of running cable, the siloxane injection technology is utilised. In this study, the siloxane liquid was injected into cable samples and penetrated into the insulation to react with the water in water tree. At the same time, the microvoids were filled with the organic compounds created by chemical reaction. Then the electron microscopy energy spectrum was detected and the experiments of driving large current and industrial frequency breakdown were performed. Moreover, the electric field of water tree area was simulated simultaneously. The result showed that the repair liquid could rapidly penetrate into the insulation of the cross‐linked polyethylene cables, reacting with water and inhibiting the growth of water tree, thus greatly enhanced the insulation performance. Based on the analysis, the authors found that the siloxane liquid can promote the industrial running cable's insulation safely quickly and effectively.
Online electromechanical and electromagnetic hybrid simulation system
Authors: Dongyu Shi , Xujiang Chen , Yalou Li , Feng Wang , Dechao Xu , Chunjiang He , Gang Li
Published: December 2017

In China, most of the renewable energy resources are reserved in the West, like wind and solar power in the Northwest and hydraulic power in the Southwest, but the load center is in the East; therefore, a safe and stable long‐distance transmission system is necessary. Along with the development of UHV technology, an extra‐large‐scaled AC/DC hybrid power grid has been accomplished in China, the characteristics of the power system are facing profound changes and the techs of stability analysis and control are needed to be improved as well. An online electromechanical and electromagnetic hybrid simulation system is proposed, in which electromagnetism models are adopted for the DC system and electromechanical models for the rest. The key issue is to speed up the simulation for the need of online analysis. First, the system architecture is introduced, which is followed by several key technologies, such as adaptive electromagnetic model of DC system, fault screening method and scheduling policy of parallel computing. Finally, the validity of the proposed system is verified using online data. The hybrid simulation could promote the accuracy of online analysis and ensure stable operation of a power grid, and then improve the utilization of renewable energy resources.
Improved extreme‐scenario extraction method for the economic dispatch of active distribution networks
Authors: Zhang Yipu , Ai Xiaomeng , Fang Jiakun , Wen Jinyu
Published: December 2017

Optimisation techniques with good characterisation of the uncertainties in modern power system enable the system operators well trade‐off between security and sustainability. This study proposes the extreme‐scenario extraction‐based robust optimisation method for the economic dispatch of active distribution network with renewables. The extreme scenarios are selected from the historical data using the improved minimum volume enclosing ellipsoid (MVEE) algorithm to guarantee the security of system operation while avoid frequently switching the transformer tap. It is theoretically proved that if the decision can be adaptive to the selected extreme scenarios, it can be robust to all the possible scenarios. Simulation results demonstrate that the proposed improved MVEE algorithm significantly reduces the number of scenarios, so that the computational burden is dramatically cut down. Additionally, compared to the existing robust optimisation approach, the proposed method is less conservative for the smaller size of the uncertainty set.
New massive members of Cygnus OB2
Authors: Berlanas S. R. , Herrero A. , Comerón F. , Pasquali A. , Bertelli Motta C. , Sota A.
Published: December 2017

Context.The Cygnus complex is one of the most powerful star forming regions at a close distance from the Sun (~1.4 kpc). Its richest OB association Cygnus OB2 is known to harbor many tens of O-type stars and hundreds of B-type stars, providing a large homogeneous population of OB stars that can be analyzed. Many studies of its massive population have been developed in the last decades, although the total number of OB stars is still incomplete.

Aim.Our aim is to increase the sample of O and B members of Cygnus OB2 and its surroundings by spectroscopically classifying 61 candidates as possible OB-type members of Cygnus OB2, using new intermediate resolution spectroscopy.

Methods.We have obtained intermediate resolution (R ~ 5000) spectra for all of the OB-type candidates between 2013 and 2017. We thus performed a spectral classification of the sample using HeI-II and metal lines rates, as well as the Marxist Ghost Buster (MGB) software for O-type stars and the IACOB standards catalog for B-type stars.

Results.From the whole sample of 61 candidates, we have classified 42 stars as new massive OB-type stars, earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The other candidates are discarded as they display later spectral types inconsistent with membership in the association. We have also obtained visual extinctions for all the new confirmed massive OB members, placing them in a Hertzsprung-Russell Diagram using calibrations forTeffand luminosity. Finally, we have studied the age and extinction distribution of our sample within the region.

Conclusions.We have obtained new blue intermediate-resolution spectra suitable for spectral classification of 61 OB candidates in Cygnus OB2 and surroundings. The confirmation of 42 new OB massive stars (earlier than B3) in the region allows us to increase the young massive population known in the field. We have also confirmed the correlation between age and Galactic longitude previously found in the region. We conclude that many O and early B stars atB> 16 mag are still undiscovered in Cygnus.
Imaging for Epilepsy Surgery
Authors: Cosgrove G. , Chavakula Vamsidhar
Published: December 2017

Successful epilepsy surgery requires accurate localization of the zone of seizure onset and its complete removal without causing any permanent neurological deficits. While clinical semiology, ictal EEG recordings, and neuropsychological testing are all useful in defining the seizure focus, advanced neuroimaging has emerged as the most important localizing tool. Structural and metabolic imaging can now identify subtle cortical abnormalities that if consistent with other presurgical evaluation investigations, can improve surgical outcomes. Functional imaging can also be helpful in defining eloquent cortex and its relationship to planned surgical resection sites to reduce the risk of neurological impairment. This article explores several advanced neuroimaging techniques and their role in the surgical treatment of epilepsy.
Neuroimaging of Brain Tumors: Pseudoprogression, Pseudoresponse, and Delayed Effects of Chemotherapy and Radiation
Authors: Winter Sebastian , Klein Joshua , Dietrich Jörg
Published: December 2017

Management of patients with brain cancer critically depends on an accurate interpretation of imaging findings that will guide treatment decisions. Treatment with chemotherapy and radiation can affect the imaging characteristics of a tumor and therefore cause misinterpretation of treatment response. Specifically, radiotherapy or chemotherapy may result in distinctive imaging abnormalities that can be challenging to differentiate from tumor itself. Moreover, cancer therapy can be associated with unique adverse effects on the brain, which need to be appropriately recognized by the treating physician to guide patient management. Specific imaging findings, such as radiation-induced tissue necrosis, leukoencephalopathy, pseudoprogression, and pseudoresponse represent treatment-related phenomena that can complicate interpretation of imaging studies and clinical decision making. The aim of this review is to describe these phenomena and improve clinician familiarity as to how these appear on structural (MRI) and functional (perfusion, spectroscopy, PET) imaging studies.
Neuroimaging in Dementia
Authors: Staffaroni Adam , Elahi Fanny , McDermott Dana , Marton Kacey , Karageorgiou Elissaios , Sacco Simone , Paoletti Matteo , Caverzasi Eduardo , Hess Christopher , Rosen Howard , Geschwind Michael
Published: December 2017

Although the diagnosis of dementia still is primarily based on clinical criteria, neuroimaging is playing an increasingly important role. This is in large part due to advances in techniques that can assist with discriminating between different syndromes. Magnetic resonance imaging remains at the core of differential diagnosis, with specific patterns of cortical and subcortical changes having diagnostic significance. Recent developments in molecular PET imaging techniques have opened the door for not only antemortem but early, even preclinical, diagnosis of underlying pathology. This is vital, as treatment trials are underway for pharmacological agents with specific molecular targets, and numerous failed trials suggest that earlier treatment is needed. This article provides an overview of classic neuroimaging findings as well as new and cutting-edge research techniques that assist with clinical diagnosis of a range of dementia syndromes, with an emphasis on studies using pathologically proven cases.
Three lessons from evidence-based medicine and policy: increase transparency, balance inputs and understand power
Authors: Oliver Kathryn , Pearce Warren
Published: December 2017

Evidence-based medicine is often described as the ‘template’ for evidence-based policymaking. EBM has evolved over the last 70 years, and now tends to be methodologically pluralistic, operates through specific structures to promote EBM, and is inclusive of a wide range of stakeholders. These strategies allow EBM practitioners to effectively draw on useful evidence, be transparent, and be inclusive; essentially, to share power. We identify three lessons EBP could learn from EBM. Firstly, to be more transparent about the processes and structures used to find and use evidence. Secondly, to consider how to balance evidence and other interests, and how to assemble the evidence jigsaw. Finally–and this is a lesson for EBM too–that understanding power is vital, and how it shapes how knowledge is produced and used. We suggest that advocates of evidence use, and commentators, should focus on thinking about how the type of problem faced by decision-makers should influence what evidence is produced, sought, and used.
Two-body perturbation theory versus first order perturbation theory: A comparison based on the square-well fluid
Authors: Mercier Franco Luís Fernando , Castier Marcelo , Economou Ioannis G.
Published: December 2017

We show that the Zwanzig first-order perturbation theory can be obtained directly from a truncated Taylor series expansion of a two-body perturbation theory and that such truncation provides a more accurate prediction of thermodynamic properties than the full two-body perturbation theory. This unexpected result is explained by the quality of the resulting approximation for the fluid radial distribution function. We prove that the first-order and the two-body perturbation theories are based on different approximations for the fluid radial distribution function. To illustrate the calculations, the square-well fluid is adopted. We develop an analytical expression for the two-body perturbed Helmholtz free energy for the square-well fluid. The equation of state obtained using such an expression is compared to the equation of state obtained from the first-order approximation. The vapor-liquid coexistence curve and the supercritical compressibility factor of a square-well fluid are calculated using both equations of state and compared to Monte Carlo simulation data. Finally, we show that the approximation for the fluid radial distribution function given by the first-order perturbation theory provides closer values to the ones calculated via Monte Carlo simulations. This explains why such theory gives a better description of the fluid thermodynamic behavior.
In-depth porosity control of mesoporous silicon layers by an anodization current adjustment
Authors: Lascaud J. , Defforge T. , Certon D. , Valente D. , Gautier G.
Published: December 2017

The formation of thick mesoporous silicon layers in P+-type substrates leads to an increase in the porosity from the surface to the interface with silicon. The adjustment of the current density during the electrochemical etching of porous silicon is an intuitive way to control the layer in-depth porosity. The duration and the current density during the anodization were varied to empirically model porosity variations with layer thickness and build a database. Current density profiles were extracted from the model in order to etch layer with in-depth control porosity. As a proof of principle, an 80 μm-thick porous silicon multilayer was synthetized with decreasing porosities from 55% to 35%. The results show that the assessment of the in-depth porosity could be significantly enhanced by taking into account the pure chemical etching of the layer in the hydrofluoric acid-based electrolyte.
Study of Li atom diffusion in amorphous Li3PO4 with neural network potential
Authors: Li Wenwen , Ando Yasunobu , Minamitani Emi , Watanabe Satoshi
Published: December 2017

To clarify atomic diffusion in amorphous materials, which is important in novel information and energy devices, theoretical methods having both reliability and computational speed are eagerly anticipated. In the present study, we applied neural network (NN) potentials, a recently developed machine learning technique, to the study of atom diffusion in amorphous materials, using Li3PO4 as a benchmark material. The NN potential was used together with the nudged elastic band, kinetic Monte Carlo, and molecular dynamics methods to characterize Li vacancy diffusion behavior in the amorphous Li3PO4 model. By comparing these results with corresponding DFT calculations, we found that the average error of the NN potential is 0.048 eV in calculating energy barriers of diffusion paths, and 0.041 eV in diffusion activation energy. Moreover, the diffusion coefficients obtained from molecular dynamics are always consistent with those from ab initio molecular dynamics simulation, while the computation speed of the NN potential is 3–4 orders of magnitude faster than DFT. Lastly, the structure of amorphous Li3PO4 and the ion transport properties in it were studied with the NN potential using a large supercell model containing more than 1000 atoms. The formation of P2O7 units was observed, which is consistent with the experimental characterization. The Li diffusion activation energy was estimated to be 0.55 eV, which agrees well with the experimental measurements.
Doping properties of cadmium-rich arsenic-doped CdTe single crystals: Evidence of metastable AX behavior
Authors: Nagaoka Akira , Kuciauskas Darius , Scarpulla Michael A.
Published: December 2017

Cd-rich composition and group-V element doping are of interest for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe, but the critical details concerning point defects are not yet fully established. Herein, we report on the properties of arsenic doped CdTe single crystals grown from Cd solvent by the travelling heater method. The photoluminescence spectra and activation energy of 74 ± 2 meV derived from the temperature-dependent Hall effect are consistent with AsTe as the dominant acceptor. Doping in the 1016 to 1017/cm3 range is achieved for measured As concentrations between 1016 and 1020/cm3 with the highest doping efficiency of 40% occurring near 1017 As/cm3. We observe persistent photoconductivity, a hallmark of light-induced metastable configuration changes consistent with AX behavior. Additionally, quenching experiments reveal at least two mechanisms of increased p-type doping in the dark, one decaying over 2–3 weeks and the other persisting for at least 2 months. These results provide essential insights for the application of As-doped CdTe in thin film solar cells.
Nuclear quantum effects of light and heavy water studied by all-electron first principles path integral simulations
Authors: Machida Masahiko , Kato Koichiro , Shiga Motoyuki
Published: December 2017

The isotopologs of liquid water, H2O, D2O, and T2O, are studied systematically by first principles PIMD simulations, in which the whole entity of the electrons and nuclei are treated quantum mechanically. The simulation results are in reasonable agreement with available experimental data on isotope effects, in particular, on the peak shift in the radial distributions of H2O and D2O and the shift in the evaporation energies. It is found that, due to differences in nuclear quantum effects, the H atoms in the OH bonds more easily access the dissociative region up to the hydrogen bond center than the D (T) atoms in the OD (OT) bonds. The accuracy and limitation in the use of the current density-functional-theory-based first principles PIMD simulations are also discussed. It is argued that the inclusion of the dispersion correction or relevant improvements in the density functionals are required for the quantitative estimation of isotope effects.
Anti-reflective coating for visible light using a silver nanodisc metasurface with a refractive index of less than 1.0
Authors: Yasuda Hideki , Matsuno Ryo , Koito Naoki , Hosoda Hidemasa , Tani Takeharu , Naya Masayuki
Published: December 2017

Suppression of visible-light reflection from material surfaces is an important technology for many applications such as flat-panel displays, camera lenses, and solar panels. In this study, we developed an anti-reflective coating design based on a silver nanodisc metasurface. The effective refractive index of a 10-nm-thick monolayer of silver nanodiscs was less than 1.0, which enabled strong suppression of reflection from the underlying substrate. The nanodisc structure was easy to fabricate using a conventional roll-to-roll wet-coating method. The anti-reflective structure was fabricated over a large area.
Effect of capping layer on formation and magnetic properties of MnBi thin films
Authors: Quarterman P. , Zhang Delin , Schliep Karl B. , Peterson Thomas J. , Lv Yang , Wang Jian-Ping
Published: December 2017

We report on the effect of varied capping layers on the formation of thin film MnBi, and the associated magnetic and crystalline properties for use in magnetic memory. MnBi thin films with a capping layer of either Ta, SiO2, Cr, or Au were grown, and it was observed that the magnetic properties vary significantly depending on the capping layer. Continuous 20 nm MnBi thin films capped with Ta and SiO2 show ferromagnetism with large perpendicular magnetocrystalline anisotropy, however, films capped with Cr and Au show no ferromagnetic behavior. In this work, MnBi thin films have been characterized utilizing magnetization vs. field, x-ray diffraction, cross-section transmission electron microscopy, and optical microscopy. We show that the capping layer plays a significant role in the formation of the low temperature phase MnBi structure and propose that the underlying cause is due to a surface energy difference for the MnBi//Au and MnBi//Cr interface, which allows for Mn oxidation, and prevents the formation of the low temperature phase. This work demonstrates that continuous ultra-thin film MnBi can achieve large magnetocrystalline anisotropy and theoretical magnetization. We also show that film delamination causes a significant variation in the magnetic performance, and leads to a large surface roughness.
σ-SCF: A direct energy-targeting method to mean-field excited states
Authors: Ye Hong-Zhou , Welborn Matthew , Ricke Nathan D. , Van Voorhis Troy
Published: December 2017

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry—a problem known as “variational collapse.” In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states—ground or excited—are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.
Effects of gas flow rate on the structure and elemental composition of tin oxide thin films deposited by RF sputtering
Authors: Al-Mansoori Muntaser , Al-Shaibani Sahar , Al-Jaeedi Ahlam , Lee Jisung , Choi Daniel , Hasoon Falah S.
Published: December 2017

Photovoltaic technology is one of the key answers for a better sustainable future. An important layer in the structure of common photovoltaic cells is the transparent conductive oxide. A widely applied transparent conductive oxide is tin oxide (SnO2). The advantage of using tin oxide comes from its high stability and low cost in processing. In our study, we investigate effects of working gas flow rate and oxygen content in radio frequency (RF)-sputtering system on the growth of intrinsic SnO2 (i-SnO2) layers. X-ray diffraction results showed that amorphous-like with nano-crystallite structure, and the surface roughness varied from 1.715 to 3.936 nm. X-Ray photoelectron spectroscopy analysis showed different types of point defects, such as tin interstitials and oxygen vacancies, in deposited i-SnO2 films.
Dielectric and energy storage performances of PVDF-based composites with colossal permittivitied Nd-doped BaTiO3 nanoparticles as the filler
Authors: Wang Jing , Hu Juntao , Sun Qiaomei , Zhu Kongjun , Li Bao-Wen , Qiu Jinhao
Published: December 2017

The energy storage density of pure polymers is usually limited by their low intrinsic dielectric constants (εeff). Integrating polymer matrix with ceramic particles with high εeff values has been one powerful approach to enhance the εeff values of polymer composites and thus their energy storage density. In this study, we report a flexible polymer-based composite by introducing Nd-doped BaTiO3 (NBT) nanoparticles (εeff over 3×105) into the poly(vinylidene fluoride) (PVDF). The phase of PVDF and its dielectric behavior could be adjusted by varying the NBT loadings. Composites including less than 5 vol.% NBT loading exhibited enhanced dielectric constants and maintained high breakdown strength. With a quenching process, the composite delivers a discharged energy density up to 7.91 J/cm3 at an electric field of 350 kV/mm with 2.5 vol.% NBT loading, which is 140% more than that of pure PVDF at the same electric field.
Noise reduction in heat-assisted magnetic recording of bit-patterned media by optimizing a high/low Tc bilayer structure
Authors: Muthsam O. , Vogler C. , Suess D.
Published: December 2017

It is assumed that heat-assisted magnetic recording is the recording technique of the future. For pure hard magnetic grains in high density media with an average diameter of 5 nm and a height of 10 nm, the switching probability is not sufficiently high for the use in bit-patterned media. Using a bilayer structure with 50% hard magnetic material with low Curie temperature and 50% soft magnetic material with high Curie temperature to obtain more than 99.2% switching probability leads to very large jitter. We propose an optimized material composition to reach a switching probability of Pswitch > 99.2% and simultaneously achieve the narrow transition jitter of pure hard magnetic material. Simulations with a continuous laser spot were performed with the atomistic simulation program VAMPIRE for a single cylindrical recording grain with a diameter of 5 nm and a height of 10 nm. Different configurations of soft magnetic material and different amounts of hard and soft magnetic material were tested and discussed. Within our analysis, a composition with 20% soft magnetic and 80% hard magnetic material reaches the best results with a switching probability Pswitch > 99.2%, an off-track jitter parameter σoff,80∕20 = 0.46 nm and a down-track jitter parameter σdown,80∕20 = 0.49 nm.