bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal control of microalgae growth using linear quadratic regulator method with firefly algorithm optimization
Authors: Setyowati Suci Yongki , Mardlijah  
Published: June 2020

Abstract
Microalgae is an important potential resource for various industrial applications. In the industry, there are a variety of processed products from algae biomass. Lipids from microalgae used for biofuell, humans and animals in food supplements while in the pharmaceutical, lipids used as a vitamin or protein. The other application of microalgae captures CO
2 and wastewater treatment. This research discusses the optimal control of microalgae growth with variable control are carbon dioxide and nutrients. In this case, the methodology is the Linear Quadratic Regulator method. In the Linear Quadratic Regulator method, there are weights in which the value is determined by trial and error in the matrices Q and R. The method of optimizing the weight value is required to optimize the weight. In this paper, the firefly algorithm is used to optimize the matrix values for Q and R. Application of firefly algorithm is able to optimally increase microalgae growth, so that the biomass produced is also abundant. The using of Firefly Algorithms optimization in the LQR method can increase algal concentration by 63.3% of the initial concentration.
The base matrix of hermitian operator order n<4
Authors: Epiningtiyas S , Supriadi B , Prihandono T , Saputra B H , Makmun M S , Antono B H 
Published: June 2020

Abstract
The Eigen problem is a problem that exists when there is an operator that is affected by the function, then that function does not change except being multipled by the constant in the form of an eigenvalue. In general, the eigenvalue problem uses the Hermitian operators by using observable variable in the form of mathematical operations. Hermitian operator is an operator that happens when the Hermit conjugation is performed, then the operator will return to its original condition. This research aims to determine the base matrix of Hermitian operators with order n ≤ 4 (size 2 × 2, 3 × 3 and 4 × 4). Entry element of the hermitian matrix operator uses complex numbers of which each order consists of few Hermitian operators. The method used is an analytical method by inserting problems into the eigen equation then normalized to obtain a diagonal matrix, so as to obtain a complete solution of the eigen problem on form of a matrix (including eigenvalues, normalized eigenvectors, and base matrix). Base matrix that has been obtained will be a diagonal matrix with diagonal elements of the eigenvalue. The results of this research indicate that the base matrix obtained in each order forms a square matrix that has entry elements in the form of complex numbers.
Students’ creative-innovative thinking skill in solving rainbow antimagic coloring under research based learning model
Authors: Sulistiyono B , Slamin  , Dafik  , Wangguway Y , Al Jabbar Z L 
Published: June 2020

Abstract
The study aims to investigate students’ creative-innovative thinking skill in solving rainbow antimagic coloring on research based learning model. The method used in this study is a mixed method, i.e. combining the qualitative and quantitative methods. The research subjects were 4th semester of students of higher education consisting of 41 students of experimental class and 30 students of control class. The instruments of this research are test, an observation, and an interview. Qualitative method is applied to analyze observation and development research, while quantitative method is applied to analysis the difference in student achievment result among two classes. The result show that there are significant difference between the two classes that applied research based learning and conventional learning models. The statistical result indicates that the (2-tailed) significance of the independent sample t-test in the post-test was 0.000 or p < 0.05. It implies that the implementation of RBL, significantly influenced the students’ creative-innovative thinking skill in solving rainbow antimagic coloring.
The effect of comic-based realistic mathematics approach on students’ learning motivation and conceptual understanding
Authors: Sipayung T N , Simanjuntak S D , Wijaya A , Sugiman S 
Published: June 2020

Abstract
Comics are reading material that is generally more desirable than textbooks by children, especially teenagers. Based on its characteristics, comics contain stories in the form of pictures and text which is contained in the balloons of text and presented in the panels. If the comic is presented in line with the application of a realistic mathematical approach, especially in learning mathematics, it hopes to create an interesting learning atmosphere for students. However, in this case, the contents of the comic story presented are in the form of learning about integers that are connected with a realistic mathematical approach. Therefore, this study aims to determine the effect of learning with comic-based realistic mathematical approaches on learning motivation and students’ understanding of mathematical concepts. This research is a quasi-experimental study. The population in this study was all the students of class VII of Junior High School of RK Serdang Murni Lubuk Pakam in the Academic Year of 2019/2020. While the sample was the class VII-1 as a control class of 31 students and class VII-2 as an experimental class of 32 students. The instruments in this study were two tests of the ability to understand the mathematical concepts and a learning motivation questionnaire. The normality test uses Liliefors test and the homogeneity test uses the Levene’s test with significance. The data were analyzed using the Manova test. Based on the data analysis, the results show that there was a significant effect of comic-based realistic mathematical approaches on students’ learning motivation and conceptual understanding of integer’s material.
Submicron-sized MoRe-doped Si-MoRe Josephson junctions with a low specific capacitance
Authors: Kalenyuk A , Shapovalov A , Shnyrkov V , Shaternik V , Belogolovskii M , Febvre P , Schmidl F , Seidel P 
Published: June 2020

Abstract
We start with a short look at the problem of low-capacitance Josephson junctions, its history, and actual state-of-the-art. It is argued that such devices are important for applications requiring nonhysteretic current-voltage characteristics since reduction of capacitance by several times makes it possible to increase the device resistance by the same amount while keeping the McCumber-Stewart damping parameter unaltered. Moreover, at very high frequencies the capacitance in the RCSJ circuit with a parallel connection starts to shunt the superconducting current component due to reduction of the corresponding reactance inversely proportional to C. Hence, to extend the operating frequency range of a Josephson junction its capacitance should be as small as possible. As a solution of a new type of the Josephson device, less resistive and with smaller capacitance, we propose and realize a submicron-sized trilayer with tens nm-thick Si interlayer doped by metallic ultra-small inclusions and superconducting Mo-Re alloy electrodes.
A superconducting flux-flow oscillator of terahertz range
Authors: Kinev N V , Rudakov K I , Filippenko L V , Fominskiy M Yu , Baryshev A M , Koshelets V P 
Published: June 2020

Abstract
We have elaborated, fabricated and tested a THz source radiating to open space based on the superconducting flux-flow oscillator (FFO). In this concept, the oscillator is integrated with the transmitting lens antenna based on a slot structure in Nb film with a thickness of ~200 nm located on the same chip. The slot planar antenna is matched to the oscillator (by input) and to the semielliptical Si lens with a diameter of 10 mm (by output) providing a narrow output beam of THz emission. A harmonic mixer based on the superconductor-insulator-superconductor junction embedded in the “FFO and antenna” integrated structure has been used for the phase locking of the oscillator. Several designs of antenna coupled with the oscillator by microstrip lines have been numerically simulated, and the batches of experimental samples based on Nb-AlN-NbN superconducting trilayers with Rn
·A ~ 20 Ω·μm2 (jc
~ 10 kA/cm2) have been fabricated and tested. Two different setups were used for experimental study: a THz spectrometer based on the SIS receiver with a high spectral resolution (better than 0.1 MHz) and a Si bolometer. The overall operating range of 250 to 700 GHz is covered by all the developed designs.
Modeling the Resonance Shifts Due to Coupling Between HTS Coils in NMR Probes
Authors: Thomas J N , Ramaswamy V , Johnston T L , Belc D C , Freytag N , Hornak L A , Edison A S , Brey W W 
Published: June 2020

Abstract
Nuclear magnetic resonance (NMR) probes using thin-film HTS coils offer high sensitivity and are particularly suitable for small-sample applications. Typically, HTS probes are optimized for the detection of multiple nuclei and require several coils to be located within a small volume near the sample. Coupling between the coils shifts coil resonances and complicates coil trimming when tuning HTS probes. We have modeled the magnetic coupling between the coils of a 1.5-mm all-HTS NMR probe with 13C, 1H, and 2H channels. By measuring the magnetic coupling coefficients between individual coils, we solve the general coupling matrix given by KVL for six coupled resonators. Our results indicate that required trims can be accurately predicted by applying single coil trimming simulations to this magnetic coupling model. Use of the magnetic coupling model significantly improves the efficiency of tuning HTS probes.
Comparison of the Effect of Graphene and Graphene Oxide Doping on YBCO
Authors: Gaffoor M Z , Jarvis A L L , Young E A , Dorrell D 
Published: June 2020

Abstract
Weak-links in high temperature superconductors (HTS) are a result of an incorrect stoichiometric ratio found in grain boundaries and misaligned planes. These weak-links severely decrease the critical transport current of the bulk HTS material (such as YBCO) and increase resistance in the normal state. Bulk YBCO was doped with graphene oxide (GO) and reduced graphene oxide (rGO) in the following dopant concentrations: 0, 0.1, 0.5, 0.7, 0.9 and 1 % wt. Through mechanical hardness testing, it was observed that the hardness of the samples increased as the GO and rGO concentration increased. The 1 % wt. doped GO and rGO samples was observed to be hardest, with a true hardness of 2.630 GPa and 2.405 GPa respectively, compared to the control sample with a true hardness of 1.499 GPa. Critical transition temperature (TC
) of the GO doped YBCO samples are greater than rGO doped samples and is presumably related to the higher oxygen content found in GO. The 0.7 % wt. doping for GO and rGO samples had the highest critical transition temperature of 98 K and 91 K, respectively. Both GO and rGO samples showed a decrease in normal resistance up to 0.7 % wt. doping, compared to the control sample. The weak-link effect was most improved in the 0.7 % wt. doped samples for GO and rGO.
Improvement of trapped magnetic field in GdBCO by waveform control pulse magnetization at 70 K
Authors: Ida Tetsuya , Watanabe Shunya , Watasaki Masahiro , Izumi Mitsuru 
Published: June 2020

Abstract
We attempted to trap a strong magnetic field with a single pulsed magnetic field by applying waveform control pulse magnetization (WCPM) method to a high-temperature superconductor (HTS) bulk sandwiched between two vortex-type copper coils at less than 77 K. The GM cryocooler conductively cooled the GdBCO bulk to 70 K in an arrangement similar to the internal structure of our axial gap type HTS motor. The HTS bulk showed no flux jump, while the duty ratio of WCPM was small. When we increased the duty ratio, we found a flux jump without looking at any prior signs and the trapped magnetic flux density increased twice. Hence we attempted a negative feedback WCPM with the control target at the highest trapped magnetic flux density while no flux jump was found. After trial and error of control conditions, the HTS bulk sample trapped a maximum magnetic flux density of 1.79 T by a single pulse magnetic field. If the WCPM technique is used, a single pulse magnetic field will cause the HTS bulk to obtain a higher trapped field at lower temperatures.
Modifying the critical current anisotropy of YBCO films via buffering layers on IBAD-MgO based templates
Authors: Khan M. Z. , Rivasto E. , Wu Y. , Zhao Y. , Chen C. , Zhu J. , Palonen H. , Tikkanen J. , Huhtinen H. , Paturi P. 
Published: June 2020

Abstract
The role of variations in the buffer layer structure of IBAD-MgO based templates on the critical current anisotropy has been investigated in undoped and BaZrO3 (BZO) doped YBa2Cu3O6+x
(YBCO) films. Not only do the natural defects grow distinct within the undoped YBCO lattice but also due to the different lengths of BZO induced nanorods within the YBCO matrix, the flux pinning properties are greatly affected by the underlying layers which in turn has a great impact on the angular dependent critical current density J
c(θ). This has been verified by transport measurements where the shape of the J
c (θ) varies in accordance with the substrates. Based on our results, the template having a cap layer with the minimum lattice mismatch and a good chemical compatibility with deposited YBCO is proven to be the best for growing both the undoped and BZO doped YBCO films. Furthermore, a model we can present based on the shapes of J
c(θ) curves depicts how the formation of nanosized defects affects the flux pinning anisotropy.
Superconducting properties and surface roughness of thin Nb samples fabricated for SRF applications
Authors: Ries R , Seiler E , Gömöry F , Medvids A , Pira C , Malyshev O B 
Published: June 2020

Abstract
Using a thin Nb layer on Copper substrate has several advantages compared with the bulk Nb in construction of Superconducting Radiofrequency accelerating cavities (SRF) for particle accelerators. We were evaluating the properties of two series of Nb layers deposited on Cu substrate, mainly by determining the start of magnetic flux penetration into the sample – the first magnetic flux entry field B
en, proportional to the B
c1. The values of B
en are compared with the surface roughness and surface morphology of the Nb layers, which have a strong influence on B
en. The surfaces of the samples were also treated by Nd:YAG laser depending on laser irradiation dose. The results of B
en and surface roughness before and after laser polishing are compared.
Effect of non-uniform proton irradiation on the critical current of REBCO tapes
Authors: Yamamoto H , Ito S , Miwa M , Matsuyama S , Hashizume H 
Published: June 2020

Abstract
Generally, uniformly-distributed irradiation defects such as artificial pinning centers improve the critical current, I
c, of REBCO tapes in strong external field. On the other hand, at self-field or low field, irradiation is not effective for improving I
c. However, if non-uniform pinning center distribution similar to vortex profile is assumed, this would increase I
c at selffield. Therefore, in this study, we experimentally investigated the effect of partial irradiation on I
c based on the assumption. We prepared REBCO tapes irradiated with trihydrogen cations in the c-axis direction. Three different patterns of defects were examined; overall, edge-only and center-only irradiations. We measured I
c at 77 K, 25 K and 15 K using the four terminal method. Results showed that, while I
c was not improved after the irradiations for each pattern, I
c behaviour depends on the patterns; edge-only-irradiated tapes showed the highest I
c and overall irradiation caused the largest I
c degradation at 77 K. However, center-only-irradiated tapes showed the lowest critical current at 25 K and 15 K which may be due to enhancement of flux pinning effect at lower temperature. Moreover, pinning centers in the edge region might be more effective to increase I
c, though further investigation on the effect of non-uniform pinning centers is required.
Influence of local deformation on critical current of high temperature superconductor tape
Authors: Kujovič Tomáš , Gömöry Fedor 
Published: June 2020

Abstract
In many applications, high temperature superconductor (HTS) tapes are placed on top of uneven surfaces. Because the electrical properties of HTS tapes are sensitive to mechanical loading, mechanical stress generated at such local imperfections can considerably decrease the critical current of a HTS tape. Then a method of predicting degradation of critical current from a numerical simulation would be helpful.
We present the results of 3D mechanical finite element model analysis, using the software ANSYS for optimising the geometry of a round CORT (Conductor-On-Round-Tube) cable. In these simulations, the HTS tape is bent around a circular former of certain diameter with a surface imperfection. We used three parameters to characterize the imperfection geometry: diameter of the former, the height and the width of imperfection. In order to validate the mechanical simulation results, we performed in-situ measurement of critical current of HTS tape.
Superconducting Properties of a Prototype Pancake Coil using a MgB2 Rutherford-type Stranded Conductor
Authors: Onji T , Ishihara A , Kobayashi Y , Tomita M , Hira M , Yagai T , Takao T , Makida Y , Shintomi T , Hirano N , Komagome T , Tsukada K , Hamajima T 
Published: June 2020

Abstract
Our group has developed a coil using MgB2 wires for SMES. In this paper, a prototype coil using a MgB2 Rutherford-type stranded conductor was fabricated based on react-and-wind (R&W) method. In the R&W method, a Rutherford-type conductor in which nine MgB2 wires were wound at pitch of 450 mm around a copper former were manufactured using reacted wires (performed by Columbus Superconductors SpA), and then coiling was performed. The coil was cooled by conduction cooling and the I-V properties were evaluated under magnetic field. As a result, in the R&W method, critical current of a coil was degraded, since making a coil by hand would cause the strain beyond the scope of the assumption which was the marginally allowable bending strain. This result suggests the coil for SMES proposed in ASPCS is difficult to react before twisting, and Rutherford-type conductors should be fabricated before reacting, which means that coil processing should be performed based on the React after making stranded conductors and Wind method, or the wind-and-react method.
Geometrical surface pinning in the nonlinear AC susceptibility of HTS tapes
Authors: Smith A P , Raine M J , Surrey E , Hampshire D P 
Published: June 2020

Abstract
The analytic expression for the nonlinear magnetic susceptibility of a thin disk derived from Bean’s model with a uniform J
C for

B
∥

n
^

predicts a peak-peak ratio of 7.1 (5.4) for the real (imaginary) components of the third harmonic χ
3 susceptibility. Our measurements show a peak-peak ratio closer to 1.1 in the real component and a noise limited lower estimate of ≈ 7 in the imaginary component. The anomalous third harmonic can be explained by the presence of a geometrical surface barrier for flux entry and exit which we have included as a small region of enhanced current density, J
C,G, close to the surface of the disk. The geometrical surface current density is predicted to be approximately equal to J
C,G ≈ 2B
C1/μ
0
d. In 2G HTS tapes with d ≈ 1μm and B
C1 ≈ 5mT this is J
C,G ≈ 8GAm−2. We have measured both J
C,B and J
C,G using the nonlinear susceptibility of a Superpower tape without artificial pinning in fields orthogonal to the tape up to 35T. We find a geometrical surface current of J
C,G ≈ 10GAm−2 and an average critical current density J
C which is in good agreement with transport measurements performed on material from the same reel of tape.
Feasibility Study of a Novel Superconducting DC Induction Heater Structure
Authors: Yan X F , Dai S T , Zhang J , Xu Y 
Published: June 2020

Abstract
A novel superconducting DC induction heater which can heat more than two aluminum billets at a time is proposed. The workpiece can rotate on its axis and move around the center cylinder of the iron core. In order to evaluate the effect of the movement speed and the rotation speed on the heating the aluminum billet, a 2D simulation model has been built by the finite element software. And the magnetic flux density distribution and the temperature distribution under different movement speed for different rotation speed has also been evaluated. Results show that the movement can improve the temperature uniformity of the aluminum billet at the cost of increasing the heating time. What is more, the new superconducting DC induction heating structure is feasible.
Dielectric strength of insulating material in LN2 with thermally induced bubbles
Authors: Gromoll D , Schumacher R , Humpert C 
Published: June 2020

Abstract
To realize a reliable and cost-effective application of high-temperature superconductive (HTS) equipment at high-voltage (HV) levels, the influence of thermally induced gas bubbles on the dielectric strength of different solid insulating materials in liquid nitrogen (LN2) was investigated. A heatable copper tape electrode arrangement was developed simulating HTS tapes with insulation in between. AC breakdown measurements were performed without and with forced boiling on insulating papers, polypropylene laminated paper (PPLP) and polyimide (PI) films. Under nucleate boiling the influence of bubbles on the dielectric strength of all materials was not significant. However under film boiling the dielectric strength of the insulating papers decreased to a level comparable to their dielectric strength in air, demonstrating the insufficient impregnation of porous materials under film boiling. For PI there was no degradation at all. PPLP retained about 70% of its basic dielectric strength in LN2.
Simulation of the Thermal Performance of HTS Coated Conductors for HVDC SFCL
Authors: de Sousa W T B , Kudymow A , Strauss S , Palasz S , Elschner S , Noe M 
Published: June 2020

Abstract
Within the EU-funded project FastGrid a resistive superconducting fault current limiter for DC-application is actually under development. To reduce substantially the amount of deployed superconducting tape an increase of voltage per length in the limitation case is needed. Moreover, the resistive transition (quench) should be fast and uniform. In the present work, the thermal behavior of three different architectures of coated conductors are investigated by means of transient simulations. The first architecture is composed by an additional Hastelloy shunt layer, which is supposed to avoid overheating of the conductor during fault limitation. The other architectures include layers of silver and copper as stabilizers. Our parameter study including the geometries of the different layers and the inhomogeneity of the critical current density of the superconducting tape shall lead to an optimized tape layout. First comparisons with experiment indicate, that, with the first architecture, electric field strength up to 100 V/m should be within reach.