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Appl. Sci., Volume 7, Issue 6 (June 2017)

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Cover Story (view full-size image) Foamed concrete contains numerous pores which strongly affect the material characteristics and [...] Read more.
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Open AccessFeature PaperArticle
Arginine-Mediated Self-Assembly of Porphyrin on Graphene: A Photocatalyst for Degradation of Dyes
Appl. Sci. 2017, 7(6), 643; https://doi.org/10.3390/app7060643
Received: 17 May 2017 / Revised: 9 June 2017 / Accepted: 13 June 2017 / Published: 21 June 2017
Cited by 3 | Viewed by 2072 | PDF Full-text (3675 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Porphyrin nanostructures with well-controlled size, shape and functionality can be used for visible-light photocatalysis. In this work, a graphene@porphyrin nanofibre composite was successfully fabricated via arginine-mediated self-assembly of tetrakis (4-carboxyphenyl) porphyrin (TCPP) on graphene nanoplates (GNPs). The formation and crystallisation of the graphene@porphyrin [...] Read more.
Porphyrin nanostructures with well-controlled size, shape and functionality can be used for visible-light photocatalysis. In this work, a graphene@porphyrin nanofibre composite was successfully fabricated via arginine-mediated self-assembly of tetrakis (4-carboxyphenyl) porphyrin (TCPP) on graphene nanoplates (GNPs). The formation and crystallisation of the graphene@porphyrin nanofibre composite was fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared (FTIR), ultraviolet-visible (UV-vis) and fluorescence spectroscopy. The assembled TCPP nanofibers were 50–200 nm in diameter with length in micrometers long, which were densely and uniformly distributed on the surface of graphene. The GNPs@TCPP nanofibers showed enhanced visible-light photocatalytic activity in comparison with free-standing TCPP nanorods for the degradation of Rhodamine B (RhB) and methyl orange (MO). The possible photodegradation mechanism of these dyes by the GNPs@TCPP nanofiber photocatalyst was proposed. Full article
(This article belongs to the Section Nanotechnology and Applied Nanosciences)
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Open AccessArticle
Computational Analysis and Artificial Neural Network Optimization of Dry Turning Parameters—AA2024-T351
Appl. Sci. 2017, 7(6), 642; https://doi.org/10.3390/app7060642
Received: 26 April 2017 / Revised: 8 June 2017 / Accepted: 9 June 2017 / Published: 21 June 2017
Cited by 2 | Viewed by 2026 | PDF Full-text (2800 KB) | HTML Full-text | XML Full-text
Abstract
In dry turning operation, various parameters influence the cutting force and contribute in machining precision. Generally, the numerical cutting models are adopted to establish the optimum cutting parameters and results are substantiated with the experimental findings. In this paper, the optimal turning parameters [...] Read more.
In dry turning operation, various parameters influence the cutting force and contribute in machining precision. Generally, the numerical cutting models are adopted to establish the optimum cutting parameters and results are substantiated with the experimental findings. In this paper, the optimal turning parameters of AA2024-T351 alloy are determined through Abaqus/Explicit numerical cutting simulations by employing the Johnson-Cook thermo-viscoplastic-damage material model. Turning simulations were verified with published experimental data. Considering the constrained and nonlinear optimization problem, the artificial neural networks (ANN) were executed for training, testing, and performance evaluation of the numerical simulations data. Two feedforward backpropagation neural networks were developed with ten hidden neutrons in each hidden layer. The Log-Sigmoid transfer function and the Levenberg-Marquardt algorithm were applied in the model. The ANN models were studied with four input parameters: the cutting speed (200, 400, and 800 m/min), tool rake angle (5°, 10°, 14.8°, and 17.5°), cutting feed (0.3 and 0.4 mm), and the contact friction coefficients (0.1 and 0.15).The two target parameters include the tool-chip interface temperature and the cutting reaction force. The performance of the trained data was evaluated using root-mean-square error and correlation coefficients. The ANN predicted values were compared both with the Abaqus simulations and the published experimental findings. All of the results are found in good approximation to each other. The performance of the ANN models demonstrated the fidelity of solving and predicting the optimum process parameters. Full article
(This article belongs to the Section Mechanical Engineering)
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Open AccessArticle
Design and Implementation of an Interactive Interface for Demand Response and Home Energy Management Applications
Appl. Sci. 2017, 7(6), 641; https://doi.org/10.3390/app7060641
Received: 24 April 2017 / Revised: 1 June 2017 / Accepted: 16 June 2017 / Published: 21 June 2017
Cited by 4 | Viewed by 1892 | PDF Full-text (6972 KB) | HTML Full-text | XML Full-text
Abstract
Demand response (DR) implementations have recently found wide application areas in the context of smart grids. The effectiveness of these implementations is primarily based on the willingness of end-users to be involved in such programs. In this paper, an interactive and user-friendly interface [...] Read more.
Demand response (DR) implementations have recently found wide application areas in the context of smart grids. The effectiveness of these implementations is primarily based on the willingness of end-users to be involved in such programs. In this paper, an interactive and user-friendly interface is presented in order to facilitate and accordingly to increase the participation of end-users in DR programs. The proposed interface has the capability of providing the targeted information about the DR events to end-users and system operators, as well as allowing end-users to interactively monitor and control the progress of their appliances. In addition to its benefits to system operators and thus to the improved operation of power systems, the proposed interface particularly aims to exploit the potential energy-related cost savings by providing the required information and resources to end-users via mobile phone. A separate interface apart from the mentioned end-user oriented interface has also been developed for the system operator to more effectively check the status of DR applications in detail. The capabilities of the proposed concept are evaluated in a real smart home in terms of various aspects. Full article
(This article belongs to the Special Issue Smart Home and Energy Management Systems)
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Open AccessFeature PaperArticle
FERMI: Present and Future Challenges
Appl. Sci. 2017, 7(6), 640; https://doi.org/10.3390/app7060640
Received: 12 May 2017 / Revised: 12 June 2017 / Accepted: 12 June 2017 / Published: 21 June 2017
Cited by 4 | Viewed by 1382 | PDF Full-text (3206 KB) | HTML Full-text | XML Full-text
Abstract
We present an overview of the FERMI (acronym of Free Electron laser Radiation for Multidisciplinary Investigations) seeded free electron laser (FEL) facility located at the Elettra laboratory in Trieste. FERMI is now in user operation with both the FEL lines FEL-1 and FEL-2, [...] Read more.
We present an overview of the FERMI (acronym of Free Electron laser Radiation for Multidisciplinary Investigations) seeded free electron laser (FEL) facility located at the Elettra laboratory in Trieste. FERMI is now in user operation with both the FEL lines FEL-1 and FEL-2, covering the wavelength range between 100 nm and 4 nm. The seeding scheme adopted for photon pulse production makes FERMI unique worldwide and allows the extension of table top laser experiments in the extreme ultraviolet/soft X-ray region. In this paper, we discuss how advances in the performance of the FELs, with respect to coherent control and multi-colour pulse production, may push the development of original experimental strategies to study non-equilibrium behaviour of matter at the attosecond-nanometer time-length scales. This will have a tremendous impact as an experimental tool to investigate a large array of phenomena ranging from nano-dynamics in complex materials to phenomena that are at the heart of the conversion of light into other forms of energy. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser) Printed Edition available
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Open AccessArticle
Multidisciplinary Aerodynamic Design of a Rotor Blade for an Optimum Rotor Speed Helicopter
Appl. Sci. 2017, 7(6), 639; https://doi.org/10.3390/app7060639
Received: 16 May 2017 / Revised: 9 June 2017 / Accepted: 13 June 2017 / Published: 20 June 2017
Cited by 1 | Viewed by 1779 | PDF Full-text (11695 KB) | HTML Full-text | XML Full-text
Abstract
The aerodynamic design of rotor blades is challenging, and is crucial for the development of helicopter technology. Previous aerodynamic optimizations that focused only on limited design points find it difficult to balance flight performance across the entire flight envelope. This study develops a [...] Read more.
The aerodynamic design of rotor blades is challenging, and is crucial for the development of helicopter technology. Previous aerodynamic optimizations that focused only on limited design points find it difficult to balance flight performance across the entire flight envelope. This study develops a global optimum envelope (GOE) method for determining blade parameters—blade twist, taper ratio, tip sweep—for optimum rotor speed helicopters (ORS-helicopters), balancing performance improvements in hover and various freestream velocities. The GOE method implements aerodynamic blade design by a bi-level optimization, composed of a global optimization step and a secondary optimization step. Power loss as a measure of rotor performance is chosen as the objective function, referred to as direct power loss (DPL) in this study. A rotorcraft comprehensive code for trim simulation with a prescribed wake method is developed. With the application of the GOE method, a DPL reduction of as high as 16.7% can be achieved in hover, and 24% at high freestream velocity. Full article
(This article belongs to the Section Mechanical Engineering)
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Open AccessArticle
Levels of Organic Pollution Indicators in Groundwater at the Old Landfill and Waste Management Site
Appl. Sci. 2017, 7(6), 638; https://doi.org/10.3390/app7060638
Received: 19 May 2017 / Revised: 15 June 2017 / Accepted: 16 June 2017 / Published: 20 June 2017
Cited by 14 | Viewed by 1303 | PDF Full-text (5227 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this paper was to assess groundwater quality in a landfill and waste management site, with special regard to levels of organic pollution indicators: chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC). Analysis of specific indicators [...] Read more.
The aim of this paper was to assess groundwater quality in a landfill and waste management site, with special regard to levels of organic pollution indicators: chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC). Analysis of specific indicators was conducted for piezometers located in the area of the Radiowo landfill, the composting plant and the facilities adjacent to the landfill. The article discusses the temporal and spatial changes of selected organic pollution indicators. Based on the results of groundwater monitoring, several maps of COD, BOD and TOC areal distribution were provided. Statistical distribution of monitoring data was presented using box-and-whisker plots. Pearson’s correlation coefficients between selected pollution indicators were measured with a significance level set at p < 0.01 and p < 0.05. The strongest correlation was observed between BOD and COD. The maximum BOD/COD ratio was observed at the level of 1.561 before the closure of the vertical barrier, whereas, at present, average values of this ratio are below 0.18. The results indicate significant improvement of groundwater quality in the landfill site after the closure of the vertical barrier. In particular, this refers to BOD values, which decreased even 160 times in the 1998–2016 monitoring period. Full article
(This article belongs to the Section Chemistry)
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Open AccessArticle
Functionalization of a Hydrophilic Commercial Membrane Using Inorganic-Organic Polymers Coatings for Membrane Distillation
Appl. Sci. 2017, 7(6), 637; https://doi.org/10.3390/app7060637
Received: 3 May 2017 / Revised: 13 June 2017 / Accepted: 16 June 2017 / Published: 20 June 2017
Cited by 4 | Viewed by 1584 | PDF Full-text (7234 KB) | HTML Full-text | XML Full-text
Abstract
Membrane distillation is a thermal separation technique using a microporous hydrophobic membrane. One of the concerns with respect to the industrialization of the technique is the development of novel membranes. In this paper, a commercially available hydrophilic polyethersulfone membrane with a suitable structure [...] Read more.
Membrane distillation is a thermal separation technique using a microporous hydrophobic membrane. One of the concerns with respect to the industrialization of the technique is the development of novel membranes. In this paper, a commercially available hydrophilic polyethersulfone membrane with a suitable structure for membrane distillation was modified using available hydrophobic coatings using ORMOCER® technology to obtain a hydrophobic membrane that can be applied in membrane distillation. The surface modification was performed using a selection of different components, concentrations, and application methods. The resulting membranes can have two hydrophobic surfaces or a hydrophobic and hydrophilic surface depending on the application method. An extensive characterization procedure confirmed the suitability of the coating technique and the obtained membranes for membrane distillation. The surface contact angle of water could be increased from 27° up to 110°, and fluxes comparable to membranes commonly used for membrane distillation were achieved under similar process conditions. A 100 h test demonstrated the stability of the coating and the importance of using sufficiently stable base membranes. Full article
(This article belongs to the Special Issue Wastewater Treatment and Reuse Technologies) Printed Edition available
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Open AccessArticle
Random Forest Prediction of IPO Underpricing
Appl. Sci. 2017, 7(6), 636; https://doi.org/10.3390/app7060636
Received: 2 May 2017 / Revised: 12 June 2017 / Accepted: 15 June 2017 / Published: 20 June 2017
Cited by 7 | Viewed by 1088 | PDF Full-text (927 KB) | HTML Full-text | XML Full-text
Abstract
The prediction of initial returns on initial public offerings (IPOs) is a complex matter. The independent variables identified in the literature mix strong and weak predictors, their explanatory power is limited, and samples include a sizable number of outliers. In this context, we [...] Read more.
The prediction of initial returns on initial public offerings (IPOs) is a complex matter. The independent variables identified in the literature mix strong and weak predictors, their explanatory power is limited, and samples include a sizable number of outliers. In this context, we suggest that random forests are a potentially powerful tool. In this paper, we benchmark this algorithm against a set of eight classic machine learning algorithms. The results of this comparison show that random forests outperform the alternatives in terms of mean and median predictive accuracy. The technique also provided the second smallest error variance among the stochastic algorithms. The experimental work also supports the potential of random forests for two practical applications: IPO pricing and IPO trading. Full article
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Open AccessFeature PaperReview
Soliton Content of Fiber-Optic Light Pulses
Appl. Sci. 2017, 7(6), 635; https://doi.org/10.3390/app7060635
Received: 11 May 2017 / Revised: 8 June 2017 / Accepted: 11 June 2017 / Published: 19 June 2017
Cited by 4 | Viewed by 1908 | PDF Full-text (3704 KB) | HTML Full-text | XML Full-text
Abstract
This is a review of fiber-optic soliton propagation and of methods to determine the soliton content in a pulse, group of pulses or a similar structure. Of central importance is the nonlinear Schrödinger equation, an integrable equation that possesses soliton solutions, among others. [...] Read more.
This is a review of fiber-optic soliton propagation and of methods to determine the soliton content in a pulse, group of pulses or a similar structure. Of central importance is the nonlinear Schrödinger equation, an integrable equation that possesses soliton solutions, among others. Several extensions and generalizations of this equation are customary to better approximate real-world systems, but this comes at the expense of losing integrability. Depending on the experimental situation under discussion, a variety of pulse shapes or pulse groups can arise. In each case, the structure will contain one or several solitons plus small amplitude radiation. Direct scattering transform, also known as nonlinear Fourier transform, serves to quantify the soliton content in a given pulse structure, but it relies on integrability. Soliton radiation beat analysis does not suffer from this restriction, but has other limitations. The relative advantages and disadvantages of the methods are compared. Full article
(This article belongs to the Special Issue Guided-Wave Optics) Printed Edition available
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Open AccessArticle
Optimized Design of Thermoelectric Energy Harvesting Systems for Waste Heat Recovery from Exhaust Pipes
Appl. Sci. 2017, 7(6), 634; https://doi.org/10.3390/app7060634
Received: 1 June 2017 / Revised: 14 June 2017 / Accepted: 15 June 2017 / Published: 19 June 2017
Cited by 2 | Viewed by 2022 | PDF Full-text (5116 KB) | HTML Full-text | XML Full-text
Abstract
With the increasing interest in energy efficiency and resource protection, waste heat recovery processes have gained importance. Thereby, one possibility is the conversion of the heat energy into electrical energy by thermoelectric generators. Here, a thermoelectric energy harvesting system is developed to convert [...] Read more.
With the increasing interest in energy efficiency and resource protection, waste heat recovery processes have gained importance. Thereby, one possibility is the conversion of the heat energy into electrical energy by thermoelectric generators. Here, a thermoelectric energy harvesting system is developed to convert the waste heat from exhaust pipes, which are very often used to transport the heat, e.g., in automobiles, in industrial facilities or in heating systems. That is why a mockup of a heating is built-up, and the developed energy harvesting system is attached. To build-up this system, a model-based development process is used. The setup of the developed energy harvesting system is very flexible to test different variants and an optimized system can be found in order to increase the energy yield for concrete application examples. A corresponding simulation model is also presented, based on previously developed libraries in Modelica®/Dymola®. In the end, it can be shown—with measurement and simulation results—that a thermoelectric energy harvesting system on the exhaust pipe of a heating system delivers extra energy and thus delivers a contribution for a more efficient usage of the inserted primary energy carrier. Full article
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Open AccessArticle
Experimental Investigation on the Effects of DBD Plasma on the Film Cooling Effectiveness of a 30-Degree Slot
Appl. Sci. 2017, 7(6), 633; https://doi.org/10.3390/app7060633
Received: 22 March 2017 / Revised: 22 May 2017 / Accepted: 15 June 2017 / Published: 19 June 2017
Cited by 1 | Viewed by 1341 | PDF Full-text (6411 KB) | HTML Full-text | XML Full-text
Abstract
The effects of dielectric barrier discharge (DBD) plasma on the film cooling effectiveness of a 30-degree slot was experimentally investigated in a low-speed wind tunnel. The pressure sensitive paint (PSP) technique was used to measure the film cooling effectiveness, and two blowing ratios [...] Read more.
The effects of dielectric barrier discharge (DBD) plasma on the film cooling effectiveness of a 30-degree slot was experimentally investigated in a low-speed wind tunnel. The pressure sensitive paint (PSP) technique was used to measure the film cooling effectiveness, and two blowing ratios (0.5 and 1.0) were tested. A sinusoidal waveform with a 1-kHz frequency was supplied to the exposed electrode. Two input voltages (6 and 7 kV) and two exposed electrode locations were considered. The results showed that the film cooling effectiveness of the slot was higher for the blowing ratio of the 1.0 case than that for the blowing ratio of the 0.5 case regardless of plasma operation. The higher input voltage case (7 kV) showed higher film cooling effectiveness than the lower input voltage case (6 kV). The improvement in film cooling effectiveness facilitated by the DBD plasma was more significant when the coolant had less momentum. The maximum improvement of the area averaged film cooling effectiveness was 2.3% for the case with the exposed electrode located at the slot exit and a blowing ratio of 0.5. Full article
(This article belongs to the Special Issue Advances in Thermal System Analysis and Optimization)
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Open AccessArticle
Supercritical Transesterification of Waste Vegetable Oil: Characteristic Comparison of Ethanol and Methanol as Solvents
Appl. Sci. 2017, 7(6), 632; https://doi.org/10.3390/app7060632
Received: 15 May 2017 / Revised: 9 June 2017 / Accepted: 12 June 2017 / Published: 17 June 2017
Cited by 1 | Viewed by 1414 | PDF Full-text (739 KB) | HTML Full-text | XML Full-text
Abstract
Transesterification of waste vegetable oil is one of the promising partial substitutes for fossil fuels. The degradation characteristics of waste vegetable oil using supercritical alcohols (ethanol and methanol) have been studied in this research. The elementary target was to conduct comparative analysis of [...] Read more.
Transesterification of waste vegetable oil is one of the promising partial substitutes for fossil fuels. The degradation characteristics of waste vegetable oil using supercritical alcohols (ethanol and methanol) have been studied in this research. The elementary target was to conduct comparative analysis of the effect of supercritical methanol and supercritical ethanol as solvents on the transesterification along with the analysis of product obtained in terms of carbon number. The experiments were carried out at transesterification temperatures of 250, 270 and 290 °C, retention time of 0 to 60 min at an interval of 15 min and oil to alcohol molar ratios of 1:6, 1:12 and 1:18 for both alcohols. The conversion increased with increase in transesterification temperature and retention time. At 290 °C, almost 99% conversion was achieved for 60-min holding time for both alcohols. Increase in conversion of waste vegetable oil was observed as the molar ratio increased. Supercritical transesterification resulted into ester yield higher than 95% with non-ester composition and glycerol collectively less than 5%. Full article
(This article belongs to the Section Energy)
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Open AccessArticle
Demonstration of High-Speed Optical Transmission at 2 µm in Titanium Dioxide Waveguides
Appl. Sci. 2017, 7(6), 631; https://doi.org/10.3390/app7060631
Received: 16 May 2017 / Revised: 12 June 2017 / Accepted: 15 June 2017 / Published: 17 June 2017
Cited by 9 | Viewed by 1681 | PDF Full-text (2276 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate the transmission of a 10-Gbit/s optical data signal in the 2 µm waveband into titanium dioxide waveguides. Error-free transmissions have been experimentally achieved taking advantage of a 23-dB insertion loss fiber-to-fiber grating-based injection test-bed platform. Full article
(This article belongs to the Special Issue Guided-Wave Optics) Printed Edition available
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Open AccessArticle
Comparative Study of Stator Configurations of a Permanent Magnet Linear Oscillating Actuator for Orbital Friction Vibration Actuator
Appl. Sci. 2017, 7(6), 630; https://doi.org/10.3390/app7060630
Received: 8 April 2017 / Revised: 20 May 2017 / Accepted: 5 June 2017 / Published: 17 June 2017
Cited by 2 | Viewed by 1432 | PDF Full-text (5789 KB) | HTML Full-text | XML Full-text
Abstract
A PM orbital friction vibration actuator (OFVA) which composes four linear oscillating actuators (LOA) is proposed in this paper. This paper presents the design, analysis, and experimental validation of stator configuration of a permanent magnet LOA to improve its thrust force characteristics. First, [...] Read more.
A PM orbital friction vibration actuator (OFVA) which composes four linear oscillating actuators (LOA) is proposed in this paper. This paper presents the design, analysis, and experimental validation of stator configuration of a permanent magnet LOA to improve its thrust force characteristics. First, the magnetized topology and the coil configuration are interpreted. The optimization design goal of the LOA was established and the end effects of the actuator are illustrated. The influences of stator design parameters on the performance of LOA were investigated and the optimal parameters have been identified with reference to the thrust force density and thrust force ripple. Results showed that a quasi‐Halbach magnetized E‐cored LOA with obtrapezoid teeth has the best electromagnetic performances of all the LOAs examined here. Finally, the predicted thrust force characteristics were validated by measurements on a prototype actuator. Full article
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Open AccessArticle
Experimental Study and Numerical Simulation of a Laminated Reinforced Concrete Shear Wall with a Vertical Seam
Appl. Sci. 2017, 7(6), 629; https://doi.org/10.3390/app7060629
Received: 10 April 2017 / Revised: 2 June 2017 / Accepted: 13 June 2017 / Published: 17 June 2017
Cited by 10 | Viewed by 1871 | PDF Full-text (4848 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, 12 laminated reinforced concrete shear walls are designed for cyclic loading tests. Seismic performance of laminated reinforced concrete shear walls with vertical seams are evaluated by the failure mode, deformability, hysteresis curve, stiffness degradation, and energy dissipation capacity. In addition, [...] Read more.
In this paper, 12 laminated reinforced concrete shear walls are designed for cyclic loading tests. Seismic performance of laminated reinforced concrete shear walls with vertical seams are evaluated by the failure mode, deformability, hysteresis curve, stiffness degradation, and energy dissipation capacity. In addition, two different construction measures and construction techniques are designed to study their influence on the wall behavior, which provides a reference for the construction of laminated reinforced concrete shear walls. The numerical simulation of the specimen is carried out with ABAQUS, which is in good agreement with the experimental results. These results provide a technical basis for the design, application, and construction of the laminated reinforced concrete shear wall structure. Full article
(This article belongs to the Special Issue The Industrialization of the Building Construction Process)
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Open AccessArticle
Entropy Analysis for Damage Quantification of Hysteretic Dampers Used as Seismic Protection of Buildings
Appl. Sci. 2017, 7(6), 628; https://doi.org/10.3390/app7060628
Received: 7 May 2017 / Revised: 1 June 2017 / Accepted: 13 June 2017 / Published: 17 June 2017
Cited by 6 | Viewed by 2078 | PDF Full-text (3253 KB) | HTML Full-text | XML Full-text
Abstract
Relative wavelet energy entropy (RWEE) is proposed to detect and quantify damage to hysteretic dampers used for the passive seismic control of building structures. Hysteretic dampers have the role of dissipating most of the energy input of an earthquake. Minor or moderate earthquakes [...] Read more.
Relative wavelet energy entropy (RWEE) is proposed to detect and quantify damage to hysteretic dampers used for the passive seismic control of building structures. Hysteretic dampers have the role of dissipating most of the energy input of an earthquake. Minor or moderate earthquakes do not exhaust the energy dissipation capacity of the dampers, yet they damage them. For this reason, continuous or periodic damper-health evaluation is required to decide if they need to be replaced. Such evaluation calls for the application of efficient structural health monitoring techniques (SHM). This paper focuses on the well-known vibration technique, which is applied to a particular type of hysteretic damper called Web Plastifying Damper (WPD), patented by the University of Granada. Vibration signals, properly recorded by piezoelectric sensors attached around the damaged area of the dampers, are decomposed by means of wavelet packet analysis. Then, the relative wavelet energy entropy of these decompositions is used to calculate the proposed index. Validation of RWEE for this particular application involved dampers installed in two different specimens of reinforced concrete structures subjected to earthquake sequences of increasing intensity. When compared with a well-established mechanical energy-based damage index, results demonstrate that RWEE is a successful and low-cost technique for reliable in-situ monitoring of dampers. Full article
(This article belongs to the Section Mechanical Engineering)
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Open AccessFeature PaperReview
Spatial Audio for Soundscape Design: Recording and Reproduction
Appl. Sci. 2017, 7(6), 627; https://doi.org/10.3390/app7060627
Received: 29 March 2017 / Revised: 2 June 2017 / Accepted: 9 June 2017 / Published: 16 June 2017
Cited by 6 | Viewed by 1746 | PDF Full-text (2430 KB) | HTML Full-text | XML Full-text
Abstract
With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools [...] Read more.
With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools for sound capture and 3D sound rendering over headphones and speaker arrays. In this paper, we outline a list of available state-of-the-art spatial audio recording techniques and devices, spatial audio physical and perceptual reproduction techniques, emerging spatial audio techniques for virtual and augmented reality, followed by a discussion on the degree of perceptual accuracy of recording and reproduction techniques in representing the acoustic environment. Full article
(This article belongs to the Special Issue Spatial Audio) Printed Edition available
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Open AccessArticle
A Wireless Sensor Network Using GNSS Receivers for a Short-Term Assessment of the Modal Properties of the Neckartal Bridge
Appl. Sci. 2017, 7(6), 626; https://doi.org/10.3390/app7060626
Received: 31 March 2017 / Revised: 30 May 2017 / Accepted: 8 June 2017 / Published: 16 June 2017
Cited by 8 | Viewed by 1472 | PDF Full-text (5265 KB) | HTML Full-text | XML Full-text
Abstract
In this article, we present a novel structural health monitoring system based on a wireless sensor network for GNSS (global navigation satellite system) receivers. The GNSS network presented here consists of three GNSS rover stations and one base station that are deployed at [...] Read more.
In this article, we present a novel structural health monitoring system based on a wireless sensor network for GNSS (global navigation satellite system) receivers. The GNSS network presented here consists of three GNSS rover stations and one base station that are deployed at the Neckartal bridge on the Autobahn A81 in southwest Germany. The newly-developed GNSS sensor nodes support satellite data logging up to a sampling rate of 20 Hz. Due to the ultra-low-power consumption achieved by the wake-up receiver during inactive periods, the nodes offer a lifetime from 20 to almost 200 days, without energy harvesting and depending on the satellite data logging period. By performing differential post-processing, precise positioning information in the millimeter range could be achieved. Using the GNSS sensors, we determined resonant frequencies at 0.33 Hz and 1.31 Hz, mainly in the lateral direction of the bridge. To verify the GNSS results, we placed an accelerometer on the bridge. The frequencies detected by the acceleration sensor correspond well to the frequencies found by the GNSS sensors, although the accelerometer measured further higher frequencies as it is probably more sensitive to small amplitudes. Full article
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Open AccessArticle
Large Earthquake Magnitude Prediction in Chile with Imbalanced Classifiers and Ensemble Learning
Appl. Sci. 2017, 7(6), 625; https://doi.org/10.3390/app7060625
Received: 19 April 2017 / Revised: 31 May 2017 / Accepted: 13 June 2017 / Published: 16 June 2017
Cited by 5 | Viewed by 928 | PDF Full-text (992 KB) | HTML Full-text | XML Full-text
Abstract
This work presents a novel methodology to predict large magnitude earthquakes with horizon of prediction of five days. For the first time, imbalanced classification techniques are applied in this field by attempting to deal with the infrequent occurrence of such events. So far, [...] Read more.
This work presents a novel methodology to predict large magnitude earthquakes with horizon of prediction of five days. For the first time, imbalanced classification techniques are applied in this field by attempting to deal with the infrequent occurrence of such events. So far, classical classifiers were not able to properly mine these kind of datasets and, for this reason, most of the methods reported in the literature were only focused on moderate magnitude prediction. As an additional step, outputs from different algorithms are combined by applying ensemble learning. Since false positives are quite undesirable in this field, due to the social impact that they might cause, ensembles have been designed in order to reduce these situations. The methodology has been tested on different cities of Chile, showing very promising results in terms of accuracy. Full article
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Open AccessArticle
Efficiency Evaluation of Operation Analysis Systems Based on Dynamic Data Envelope Analysis Models from a Big Data Perspective
Appl. Sci. 2017, 7(6), 624; https://doi.org/10.3390/app7060624
Received: 14 April 2017 / Revised: 12 June 2017 / Accepted: 12 June 2017 / Published: 16 June 2017
Cited by 4 | Viewed by 1267 | PDF Full-text (1718 KB) | HTML Full-text | XML Full-text
Abstract
The operating environment of power grid enterprises is complex with a range of monitoring indicators. To grasp the overall operational status in time and find the key affecting factors, Balanced Scorecard Card (BSC), Interpretive Structural Model (ISM), Principal component analysis (PCA) should be [...] Read more.
The operating environment of power grid enterprises is complex with a range of monitoring indicators. To grasp the overall operational status in time and find the key affecting factors, Balanced Scorecard Card (BSC), Interpretive Structural Model (ISM), Principal component analysis (PCA) should be applied. This paper proposed several grid enterprise operators and monitoring indicator systems (which include achievement indicators and driver indicators), and applied PCA for verification and evaluation. The achievement indicators mainly reflected the effectiveness of business operations, which included corporate value, social value, customer value, and so on. Driver indicators mainly reflected the core resources and operations process management of business operations, which have a direct impact on the achievement indicators. The driver and achievement indicators were used as input and output indicators for the provinces to assess the efficiency of operations, and appropriate measures were proposed for improvement. The results showed that the dynamic data envelopment analysis (DEA) model could reflect the time lag of the grid enterprises operating investment and income much better than the other two methods, and the static changes compared to assess efficiency had an average around 4%. Full article
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Open AccessFeature PaperArticle
Combined CFD-Stochastic Analysis of an Active Fluidic Injection System for Jet Noise Reduction
Appl. Sci. 2017, 7(6), 623; https://doi.org/10.3390/app7060623
Received: 3 May 2017 / Revised: 13 June 2017 / Accepted: 14 June 2017 / Published: 16 June 2017
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Abstract
In the framework of DANTE project (Development of Aero-Vibroacoustics Numerical and Technical Expertise), funded under the Italian Aerospace Research Program (PRORA), the prediction and reduction of noise from subsonic jets through the reconstruction of turbulent fields from Reynolds Averaged Navier Stokes (RANS) calculations [...] Read more.
In the framework of DANTE project (Development of Aero-Vibroacoustics Numerical and Technical Expertise), funded under the Italian Aerospace Research Program (PRORA), the prediction and reduction of noise from subsonic jets through the reconstruction of turbulent fields from Reynolds Averaged Navier Stokes (RANS) calculations are addressed. This approach, known as Stochastic Noise Generation and Radiation (SNGR), reconstructs the turbulent velocity fluctuations by RANS fields and calculates the source terms of Vortex Sound acoustic analogy. In the first part of this work, numerical and experimental jet-noise test cases have been reproduced by means RANS simulations and with different turbulence models in order to validate the approach for its subsequent use as a design tool. The noise spectra, predicted with SNGR, are in good agreement with both the experimental data and the results of Large-Eddy Simulations (LES). In the last part of this work, an active fluid injection technique, based on extractions from turbine and injections of high-pressure gas into the main stream of exhausts, has been proposed and finally assessed with the aim of reducing the jet-noise through the mixing and breaking of the turbulent eddies. Some tests have been carried out in order to set the best design parameters in terms of mass flow rate and injection velocity and to design the system functionalities. The SNGR method is, therefore, suitable to be used for the early design phase of jet-noise reduction technologies and a right combination of the fluid injection design parameters allows for a reduction of the jet-noise to 3.5 dB, as compared to the baseline case without injections. Full article
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Open AccessArticle
Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers
Appl. Sci. 2017, 7(6), 621; https://doi.org/10.3390/app7060621
Received: 27 April 2017 / Revised: 6 June 2017 / Accepted: 9 June 2017 / Published: 16 June 2017
Cited by 1 | Viewed by 1492 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, [...] Read more.
Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, scans of the pump-probe delay is preferable to a single long-lasting scan. The limited availability of beamtime makes it impractical to repeat measurements indiscriminately, and the large, rapid flow of single-shot data that need to be processed and aggregated into a dataset, makes it difficult to assess the quality of a measurement in real time. In post-analysis it is then necessary to devise unbiased criteria to select or reject datasets, and to assign the weight with which they enter the analysis. One such case was the measurement of the lifetime of Intermolecular Coulombic Decay in the weakly-bound neon dimer. We report on the method we used to accomplish this goal for the pump-probe delay scans that constitute the core of the measurement; namely we report on the use of simple auto- and cross-correlation techniques based on the general concept of “matched filter”. We are able to unambiguously assess the signal-to-noise ratio (SNR) of each scan, which then becomes the weight with which a scan enters the average of multiple scans. We also observe a clear gap in the values of SNR, and we discard all the scans below a SNR of 0.45. We are able to generate an average delay scan profile, suitable for further analysis: in our previous work we used it for comparison with theory. Here we argue that the method is sufficiently simple and devoid of human action to be applicable not only in post-analysis, but also for the real-time assessment of the quality of a dataset. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser) Printed Edition available
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Open AccessArticle
ANN Sizing Procedure for the Day-Ahead Output Power Forecast of a PV Plant
Appl. Sci. 2017, 7(6), 622; https://doi.org/10.3390/app7060622
Received: 4 May 2017 / Revised: 5 June 2017 / Accepted: 12 June 2017 / Published: 15 June 2017
Cited by 16 | Viewed by 1654 | PDF Full-text (2790 KB) | HTML Full-text | XML Full-text
Abstract
Since the beginning of this century, the share of renewables in Europe’s total power capacity has almost doubled, becoming the largest source of its electricity production. In 2015 alone, photovoltaic (PV) energy generation rose with a rate of more than 5%; nowadays, Germany, [...] Read more.
Since the beginning of this century, the share of renewables in Europe’s total power capacity has almost doubled, becoming the largest source of its electricity production. In 2015 alone, photovoltaic (PV) energy generation rose with a rate of more than 5%; nowadays, Germany, Italy, and Spain account together for almost 70% of total European PV generation. In this context, the so-called day-ahead electricity market represents a key trading platform, where prices and exchanged hourly quantities of energy are defined 24 h in advance. Thus, PV power forecasting in an open energy market can greatly benefit from machine learning techniques. In this study, the authors propose a general procedure to set up the main parameters of hybrid artificial neural networks (ANNs) in terms of the number of neurons, layout, and multiple trials. Numerical simulations on real PV plant data are performed, to assess the effectiveness of the proposed methodology on the basis of statistical indexes, and to optimize the forecasting network performance. Full article
(This article belongs to the Special Issue Computational Intelligence in Photovoltaic Systems)
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Open AccessArticle
Experimental Investigations of Composite Adsorbent 13X/CaCl2 on an Adsorption Cooling System
Appl. Sci. 2017, 7(6), 620; https://doi.org/10.3390/app7060620
Received: 7 April 2017 / Revised: 23 May 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
Cited by 2 | Viewed by 1296 | PDF Full-text (5667 KB) | HTML Full-text | XML Full-text
Abstract
A new experimental device which tests the adsorption performance of the 13X/CaCl2 composite adsorbent under vacuum conditions was established. In this device, heat transfer characteristics in the adsorbent bed have a great influence on the adsorbent performance, the temperature of the bottom [...] Read more.
A new experimental device which tests the adsorption performance of the 13X/CaCl2 composite adsorbent under vacuum conditions was established. In this device, heat transfer characteristics in the adsorbent bed have a great influence on the adsorbent performance, the temperature of the bottom outside bed is very close to the temperature of the bottom inside bed and the temperature difference between them at the end of heating and cooling are 5.66 °C and 0.303 °C, respectively. The following conclusions could be drawn: the equilibrium water uptake of composite adsorbent CA10X (zeolite 13X impregnated with 10 wt % CaCl2 solution) was increased 5.7% compared with that of 13X, and the water uptake was 0.37 g/g. The composite adsorbent CA10X has a better performance in the adsorption refrigeration system. Full article
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Open AccessArticle
Simulation Investigation on Combustion Characteristics in a Four-Point Lean Direct Injection Combustor with Hydrogen/Air
Appl. Sci. 2017, 7(6), 619; https://doi.org/10.3390/app7060619
Received: 5 May 2017 / Revised: 5 June 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
Cited by 3 | Viewed by 2299 | PDF Full-text (10063 KB) | HTML Full-text | XML Full-text
Abstract
To investigate the combustion characteristics in multi-point lean direct injection (LDI) combustors with hydrogen/air, two swirl–venturi 2 × 2 array four-point LDI combustors were designed. The four-point LDI combustor consists of injector assembly, swirl–venturi array and combustion chamber. The injector, swirler and venturi [...] Read more.
To investigate the combustion characteristics in multi-point lean direct injection (LDI) combustors with hydrogen/air, two swirl–venturi 2 × 2 array four-point LDI combustors were designed. The four-point LDI combustor consists of injector assembly, swirl–venturi array and combustion chamber. The injector, swirler and venturi together govern the rapid mixing of hydrogen and air to form the mixture for combustion. Using clockwise swirlers and anticlockwise swirlers, the co-swirling and count-swirling swirler arrays LDI combustors were achieved. Using Reynolds-Averaged Navier–Stokes (RANS) code for steady-state reacting flow computations, the four-point LDI combustors with hydrogen/air were simulated with an 11 species and 23 lumped reaction steps H2/Air reaction mechanism. The axial velocity, turbulence kinetic energy, total pressure drop coefficient, outlet temperature, mass fraction of OH and emission of pollutant NO of four-point LDI combustors, with different equivalence ratios, are here presented and discussed. As the equivalence ratios increased, the total pressure drop coefficient became higher because of increasing heat loss. Increasing equivalence ratios also corresponded with the rise in outlet temperature of the four-point LDI combustors, as well as an increase in the emission index of NO EINO in the four-point LDI combustors. Along the axial distance, the EINO always increased and was at maximum at the exit of the dump. Along the chamber, the EINO gradually increased, maximizing at the exit of chamber. The total temperature of four-point LDI combustors with different equivalence ratios was identical to the theoretical equilibrium temperature. The EINO was an exponential function of the equivalence ratio. Full article
(This article belongs to the Special Issue Clean Energy and Fuel (Hydrogen) Storage)
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Open AccessFeature PaperArticle
Iridescent Perfect Absorption in Critically-Coupled Acoustic Metamaterials Using the Transfer Matrix Method
Appl. Sci. 2017, 7(6), 618; https://doi.org/10.3390/app7060618
Received: 31 May 2017 / Revised: 7 June 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
Cited by 2 | Viewed by 1388 | PDF Full-text (1122 KB) | HTML Full-text | XML Full-text
Abstract
The absorption performance of a locally-reacting acoustic metamaterial under oblique incidence is studied. The metamaterial is composed of a slotted panel, each slit being loaded by an array of Helmholtz resonators. The system is analytically studied using the transfer matrix method, accounting for [...] Read more.
The absorption performance of a locally-reacting acoustic metamaterial under oblique incidence is studied. The metamaterial is composed of a slotted panel, each slit being loaded by an array of Helmholtz resonators. The system is analytically studied using the transfer matrix method, accounting for the viscothermal losses both in the resonator elements and in the slits, allowing the representation of the reflection coefficient in the complex frequency plane. We show that by tuning the geometry of the metamaterial, perfect absorption peaks can be obtained on demand at selected frequencies and different angles of incidence. When tilting the incidence angle, the peaks of perfect absorption are shifted in frequency, producing an acoustic iridescence effect similar to the optic iridescence achieved by incomplete band gap. Effectively, we show that in this kind of locally-reacting metamaterial, perfect and omnidirectional absorption for a given frequency is impossible to achieve because the metamaterial impedance does not depend on the incidence angle (i.e., the impedance is a locally reacting one). The system is interpreted in the complex frequency plane by analysing the trajectories of the zeros of the reflection coefficient. We show that the trajectories of the zeros do not overlap under oblique incidence, preventing the observation of perfect and omnidirectional absorption in locally reacting metamaterials. Moreover, we show that for any locally resonant material, the absorption in diffuse field takes a maximal value of 0.951, which is achieved by a material showing perfect absorption for an incidence angle of 50.34 degrees. Full article
(This article belongs to the Section Acoustics and Vibrations)
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Open AccessArticle
Synthesis and Biophysical Insights into the Binding of a Potent Anti-Proliferative Non-symmetric Bis-isatin Derivative with Bovine Serum Albumin: Spectroscopic and Molecular Docking Approaches
Appl. Sci. 2017, 7(6), 617; https://doi.org/10.3390/app7060617
Received: 21 May 2017 / Revised: 11 June 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
Cited by 2 | Viewed by 1320 | PDF Full-text (5945 KB) | HTML Full-text | XML Full-text
Abstract
As part of the research endeavors to combat cancer, a non-symmetric bis-isatin derivative (compound 3) was synthesized and showed a significant anti-proliferative potency. The current study provides a comprehensive characterization of the interaction of compound 3 with the drug-transporting protein bovine serum [...] Read more.
As part of the research endeavors to combat cancer, a non-symmetric bis-isatin derivative (compound 3) was synthesized and showed a significant anti-proliferative potency. The current study provides a comprehensive characterization of the interaction of compound 3 with the drug-transporting protein bovine serum albumin (BSA) via the use of spectroscopic tools along with molecular docking studies. Fluorescence spectral measurements showed that the BSA intrinsic fluorescence can be significantly quenched by the addition of compound 3 and the formation of a non-fluorescent complex. Further measurements revealed a static type of quenching with Stern–Volmer and Linweaver–Burk constants of 105. The thermodynamic parameters of the binding were calculated to be ΔS° 105.09 ± 5.32 with ΔH° of −0.72 ± 0.71 and negative ΔG° values. In addition, synchronous fluorescence and 3D fluorescence spectroscopy suggested that compound 3 did not induce conformational changes in BSA. Site competition experiments revealed that compound 3 competes with warfarin within the BSA binding domain (Sudlow site I). This was further confirmed by the molecular docking results showing a binding energy of −25.93 kJ/mol for compound 3-BSA. Hence, the observed results in the present study assumed that the compound 3-BSA binding is spontaneous, involving electrostatic forces and hydrogen bonding. Full article
(This article belongs to the Section Chemistry)
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Open AccessArticle
Smartphones as a Light Measurement Tool: Case of Study
Appl. Sci. 2017, 7(6), 616; https://doi.org/10.3390/app7060616
Received: 25 April 2017 / Revised: 29 May 2017 / Accepted: 7 June 2017 / Published: 14 June 2017
Cited by 8 | Viewed by 1411 | PDF Full-text (2325 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In recent years, smartphones have become the main computing tool for most of the population, making them an ideal tool in many areas. Most of these smartphones are equipped with cutting-edge hardware on their digital cameras, sensors and processors. For this reason, this [...] Read more.
In recent years, smartphones have become the main computing tool for most of the population, making them an ideal tool in many areas. Most of these smartphones are equipped with cutting-edge hardware on their digital cameras, sensors and processors. For this reason, this paper discusses the possibility of using smartphones as an accessible and accurate tool, focusing on the measurement of light, which is an element that has a high impact on human behavior, which promotes conformance and safety, or alters human physiology when it is inappropriate. To carry out this study, three different ways to measure light through smartphones have been checked: the ambient light sensor, the digital camera and an external Bluetooth luxmeter connected with the smartphone. As a result, the accuracy of these methods has been compared to check if they can be used as accurate measurement tools. Full article
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Open AccessArticle
Non-Pulse-Leakage 100-kHz Level, High Beam Quality Industrial Grade Nd:YVO4 Picosecond Amplifier
Appl. Sci. 2017, 7(6), 615; https://doi.org/10.3390/app7060615
Received: 27 April 2017 / Revised: 22 May 2017 / Accepted: 26 May 2017 / Published: 14 June 2017
Cited by 2 | Viewed by 1639 | PDF Full-text (2203 KB) | HTML Full-text | XML Full-text
Abstract
A non-pulse-leakage optical fiber pumped 100-kHz level high beam quality Nd:YVO4 picosecond amplifier has been developed. An 80 MHz, 11.5 ps mode-locked picosecond laser is used as the seed with single pulse energy of 1 nJ. By harnessing the double β-BaB2 [...] Read more.
A non-pulse-leakage optical fiber pumped 100-kHz level high beam quality Nd:YVO4 picosecond amplifier has been developed. An 80 MHz, 11.5 ps mode-locked picosecond laser is used as the seed with single pulse energy of 1 nJ. By harnessing the double β-BaB2O4 (BBO) crystal Pockels cells in both the pulse picker and regenerative amplifier, the seed pulse leakage of the output is suppressed effectively with an adjustable repetition rate from 200 to 500 kHz. Through one stage traveling-wave amplifier, a maximum output power of 24.5 W is generated corresponding to the injected regenerative amplified power of 9.73 W at 500 kHz. The output pulse duration is 16.9 ps, and the beam quality factor M2 is measured to be 1.25 with near-field roundness higher than 99% at the full output power. Full article
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Open AccessArticle
Terawatt-Isolated Attosecond X-ray Pulse Using a Tapered X-ray Free Electron Laser
Appl. Sci. 2017, 7(6), 614; https://doi.org/10.3390/app7060614
Received: 30 March 2017 / Revised: 29 May 2017 / Accepted: 8 June 2017 / Published: 13 June 2017
Cited by 2 | Viewed by 1446 | PDF Full-text (3536 KB) | HTML Full-text | XML Full-text
Abstract
High power attosecond (as) X-ray pulses are in great demand for ultrafast dynamics and high resolution microscopy. We numerically demonstrate the generation of a ~230 attosecond, 1.5 terawatt (TW) pulse at a photon energy of 1 keV, and a 115 attosecond, 1.2 TW [...] Read more.
High power attosecond (as) X-ray pulses are in great demand for ultrafast dynamics and high resolution microscopy. We numerically demonstrate the generation of a ~230 attosecond, 1.5 terawatt (TW) pulse at a photon energy of 1 keV, and a 115 attosecond, 1.2 TW pulse at a photon energy of 12.4 keV, using the realistic electron beam parameters such as those of Korean X-ray free electron laser (XFEL) in a tapered undulator configuration. To compensate the energy loss of the electron beam and maximize its radiation power, a tapering is introduced in the downstream section of the undulator. It is found that the tapering helps in not only amplifying a target radiation pulse but also suppressing the growth of satellite radiation pulses. Tapering allows one to achieve a terawatt-attosecond pulse only with a 60 m long undulator. Such an attosecond X-ray pulse is inherently synchronized to a driving optical laser pulse; hence, it is well suited for the pump-probe experiments for studying the electron dynamics in atoms, molecules, and solids on the attosecond time-scale. For the realization of these experiments, a high level of synchronization up to attosecond precision between optical laser and X-ray pulse is demanded, which can be possible by using an interferometric feedback loop. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser) Printed Edition available
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