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Recently deep learning has made a great progress in the image classification and video object tracking. However the speed of traditional region proposal algorithms is too slow and become a bottleneck. Researchers have proposed a lot of neural networks for the improvements. With the region proposal network proposed, neural network can finish the computation enabling cost-free region proposals, which make it possible to do real-time detection and tracking. This paper will set up a system which can detect and track drone by using neural networks such as Faster R-CNN and Siamese-RPN.

In the modern age of smartphone penetration, the application market is also changing. People who regularly use native only applications are not happy with the operability of WEB applications. In this research, we aim to improve usability by using PWA to solve the web application user’s dissatisfaction.

In this study, we concentrated on the longitudinal magnetic field effect in critical current densities and investigated the enhancement of the electrical conduction properties in a commercial Bi-2223 superconducting tape. Since the samples used in this study were polycrystalline and tape-shaped, the variation of the critical current density caused by the longitudinal magnetic field effect and anisotropy of the upper critical magnetic field was expected to be clarified. Therefore, the critical current characteristics at a magnetic field of up to 5 T as well as at various angles between the magnetic field and current were measured in detail. Through investigation, more detailed electrical characteristics of Bi-2223 were clarified which can provide superconducting cable developer with more useful information. The results demonstrate the longitudinal magnetic field effect is obvious at the high magnetic field rather than that at the low magnetic field and the upper critical magnetic field is decreasing gradually with the increase of the temperature. It also can be known that the difference between the value of upper critical magnetic field and that of applied magnetic field will exert an influence on the critical current density of Bi-2223 superconducting tape.

In this study, we designed a power cable based on the longitudinal magnetic field (LMF) effect using an iterative approximation method. An evaluation of the cable shows that it is more efficient than conventional-design power cables. A cable with four inner layers and four shield layers and a maximum winding angle of 30° had a current capacity of more than 10 kA. Based on calculation results, we fabricated a 2-m-long LMF power cable and a conventional-design power cable. Experimental results show that the proposed power cable can carry more current (8.8% more current per tape and 18% more current overall) than a conventional-design power cable due to the LMF effect. These results well agree with the theoretical calculation results.

Due to the diversity of human behavior, scene noise, camera view angle and other characteristics, the difficulty of recognizing human behavior has increased. Nowadays, there are more and more problems, such as low learning efficiency or excessive mental pressure. To a large extent, these problems are caused by an unreasonable distribution of work and rest. Therefore, this paper proposes a learning behavior recognition method based on the structure of 3D convolutional neural networks (CNN). This involves taking several continuous frames of video as a group, through effective training, after the convolution and pooling operation to extract the action information in the features. Finally, the recognition and classification results are obtained through the full connection layer and the classifier. The experimental results show that this method is accurate and fast. Taking the KTH dataset as an example, the methods of improving test accuracy under different parameters were compared and discussed, which provided a theoretical basis for learning behavior dataset recognition.

Web technology is revolutionizing traditional education pattern [1], to manage the senior students efficiently and conveniently and improve the speed of response, this paper will set up management system which uses recent technology such as Node.js and React.js, contain the specific realization and application. The data collecting function is also implemented for further analysis.

AC susceptibilities (real χ ′ and imaginary χ ″) of Sr 0.6 K 0.4 Fe 2 As 2 (122 type) polycrystalline with Ag addition are analysed by the grained Bean model. A variety of characteristics, double peak in χ ″ and shoulder transition in χ ′, appear in the model simulation. Comparing the measured χ ′ and χ ″ with the model allows more clear insight on the polycrystalline structure. Estimated critical current densities J cg and J cl of the grain and the link in the iron-based pnictides show that the addition of 20 wt.% Ag increases J cl 9 times larger. Improvement of intergrain characteristics with Ag addition is clearly indicated.

```  Abstract-- In this review paper, we report the characteristics of the critical current density in FeAs based superconductors which is newly discovered by Hosono group of Tokyo Institute of Technology on 2008. Since the many specimens in present stage are not single crystals, there are two kinds of critical current density observed in the specimens which are so-called local and global critical current densities. Therefore, it is necessary to evaluate both kinds of critical current densities. The history effect in which the global critical current density shows different values in increasing and decreasing magnetic field is also observed when the specimens have the local and the global critical current densities. The wire which critical current is 180 A is successfully developed with using the knowledge of abovementioned characteristics of two kinds of critical current densities and the history effect. kinds of critical current density in the specimens. They are so-called local and global critical currents. That is, the connection between the grains in specimen is too week to carry large current, and the global critical current density is far lower than the local critical current density which flows only inside the grain. They are also called intra- and inter-grain shielding current density. It is essential to measure both local and global critical current densities, because the local critical current density will be achieved when the specimen will be prepared as single crystalline in near future which is already done in RE-123 (RE: Rare Earth) superconducting coated wire. Moreover, the global critical current is corresponding to transport critical current density which is usually measured by four probe method. In the present study, the local and the global critical current

It is important to investigate condensation energy density of superconducting material, since it determines its pinning property. According to the heavy-ion irradiation, the columnar defects are introduced to the superconductor which act as the strong pinning centers, and the critical current density is enhanced by the new pinning centers. Since the number density and the size of the columnar defects can be observed, the condensation energy density is estimated by using the pinning summation theory. In the present study, we prepared Ba(Fe0.93Co0.07)2As2 (Ba-122) pnictide superconductors by self-flux method. 200 MeV Au ions were irradiated into the specimens along c-axis and the matching field was 2 T. After the irradiation, the critical current density was 6 times larger than that before the irradiation. The estimated condensation energy density is in the order of 104 J/m3 and is slightly smaller than those of cuprate superconductors. The temperature dependence is similar to that of YBa2Cu3Ox oxide superconductors, since the anisotropy parameter is small in Ba-122. Therefore, it is expected to use Ba-122 at high temperatures near the critical temperature., Superconductivity Centennial Conference 2011 - EUCAS–ISEC–ICMC, Sep 18 - 23, 2011, Hague, Netherlands

In this study, we focused on the longitudinal magnetic field effect in critical current densities and investigated the enhancement of the electrical conduction properties in a commercial Bi-2223 superconducting tape. Since the samples used in this study were polycrystalline and tape-shaped, the longitudinal magnetic field effect was expected to differ from that in single crystals or conventional superconducting alloys. Therefore, the critical current characteristics at magnetic fields of up to 5 T as well as at various angles between the magnetic field and current were measured in detail.

In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB2 bulks prepared by a modified PIT (powder in tube) method. Campbell's method was applied for the purpose of acquiring the penetrating AC magnetic flux profile and the characteristic of AC magnetic field vs. penetration depth from the specimen's surface. A computer simulation on the penetrating AC flux profile in MgB2 bulks with certain amount of randomly distributed voids, oxidized grains and other faults was also carried out. The global critical current density obtained by Campbell's method turned out to be smaller than that obtained from the SQUID measurement, implying that the global super-current was reduced by the existence of various kinds of faults and the lack of the electrical connectivity between grains. It was verified that the relationship between the global critical current characteristics and the faults contained in MgB2 specimens can be quantitatively clarified by comparing the simulated critical current densities and other factors with the experimental results.

A practical Bi-2223 superconducting magnet, working in liquid nitrogen (L.N 2 ), was designed and fabricated. Bi-2223 tape with a critical current of 147 A was prepared by a controlled overpressure (CT-OP) process at 77.3 K in self-field. Ten double-pancake coils were resistively connected by copper terminals. The bore diameter was 54 mm ϕ , the magnet outer diameter was 122 mm ϕ , the height of the magnet was 124 mm, and the weight of the magnet was about 3 kg. The maximum magnetic field at the center of the bore was 0.48 T with an operating current of 50 A. The experimental results agree well with design predictions calculated by finite element method. AC operation was also performed, and no distortion of the voltage waveform was observed. Therefore, this Bi-2223 superconducting magnet is a suitable replacement for copper magnets designed for applications in science and technology.

In order to substitute cheaper sheath materials for Ag, Bi-2212 superconducting thick films grown on oxidized Ni substrates were prepared by using a normal partial melt process. 0-5 vol% of fine MgO particles were doped in Bi-2212 phase during the fabrication for the purpose of enhancement of the critical current density (J/sub c/) in Bi-2212. The samples were analyzed with the assistances of X-ray diffractometer (XRD) and electron probe microanalyzer (EPMA). The critical temperature and J/sub c/ were measured by using the conventional resistive method (4-probe method). An apparent improvement in J/sub c/ characteristic was observed in the samples with fine MgO particles doped. The J/sub c/ value in the 5 vol% MgO doped sample reached to the level comparable with that in other Ag-sheathed samples. Furthermore, the irreversibility field was confirmed to be largely enhanced by the addition of MgO particles. The pin parameters derived from the scaling behavior of pinning force density turned out to be similar to those predicted in the case of normal precipitate flux pinning, indicating that MgO particles in Bi-2212 act as effective pinning centers.

A Bi-2223 superconducting magnet for practical use in liquid nitrogen is designed and fabricated. Bi-2223 tapesprepared by ConTrolled Over Pressure (CT-OP) process are used for the winding, and the critical current at 77.3 K and self-field is in the range of 174–185 A. 28 double-pancake coils are resistively connected in series by copper terminals. Highcritical current tape is used for top and bottom double-pancake coils, since the magnetic field normal to the tape surface ishighest at the top and bottom of the magnet. Two iron plates at top and bottom of the magnet are used for reduction of thenormal component of magnetic field to the Bi-2223 tape, since the total performance of the magnet is determined by theminimum critical current at maximum normal magnetic field component to the tape. The inner bore diameter of the magnetis 92 mm. And the homogeneity of magnetic field of long-axis direction in 50 mmφ × 100 mm length is within 3%. Themaximum magnetic field at the center of the bore is over 1.0 T at 77.3 K., Proceedings of the Cryogenic Engineering Conference (2013) , June 17–21, 2013, Anchorage, Alaska, USA

In order to introduce effective pinning centers into Bi-2212 superconducting bulk, the addition of small MgO particles to Bi-2212 bulk and its effect on flux pinning were studied. Bi-2212 bulk samples were prepared by employing a normal partial-melting process, with a 0-8 vol.% of MgO particles addition. The morphology of Bi-2212 with MgO doping was investigated by means of XRD and EPMA. The magnetization and critical current densities (J/sub c/'s) in various magnetic fields and temperatures were measured by using a SQUID magnetometer. It was found that J/sub c/ in samples with relatively large MgO particles introduced shows a larger value than that in MgO-free sample, which implies that the MgO particles act as effective pinning centers and enhance the flux pinning characteristic in Bi-2212 bulk. A qualitative agreement between the experimental results and theoretical estimation was obtained.

The characteristics of electric field E vs. current density J at various magnetic fields and temperatures in superconducting PbBi samples with different pinning strength were measured by using a usual resistive method. The obtained E-J curves show a nonlinear behavior similar to that in high T/sub c/ superconductors (HTSC). With a scaling generally used in HTSC, E-J curves collapse onto one of the two universal branches, with the exponents of /spl nu/ and z similar to those reported in HTSC. It was found that the stronger flux pinning strength leads to the higher transition points of T/sub g/ and B/sub g/ in the E-J characteristic. The nonlinear E-J curves and the enhancement of the transition points were explained and reproduced by using the flux creep and flux flow theory.

Estimation of irreversibility fields in pinning-strength-controlled metallic superconductor is carried out for superconducting Pb - Bi alloys. The magnitude and temperature dependence of the irreversibility field depend only slightly on the flux pinning strength. The difference between the irreversibility field and the upper critical field remains finite in specimens with a strong pinning force. The experimental result is compared with the flux creep theory and found to be explained well by the theory.

The irreversibility line was obtained in terms of the imaginary a.c. susceptibility measurement for a melt-processed superconducting Bi-2212 single grain with fine non-superconducting particles. This line showed different temperature dependences in high and low temperature regions. The one in the low temperature region agrees approximately with the prediction from the flux creep theory with experimentally observed pinning parameters. On the other hand, the one in the high temperature region is close to the well known characteristics in Y-based superconductors, suggesting flux pinning by boundaries such as the surfaces of non-superconducting particles. A quantitative discussion is also given on flux bundle size.

The irreversibility line was measured for three silver-sheathed Bi-2223 tape wires with different critical current densities. It was found that the irreversibility line was shifted to a higher temperature region according to an increasing critical current density. The temperature dependence of the irreversibility line was divided into two regions. In the lower temperature region the irreversibility line strongly depends on the temperature, while the dependence at higher temperatures is weaker and is similar to that observed for Y-Ba-Cu-O. Such a difference is considered to be due to different pinning mechanisms. Nonsuperconducting particles observed microscopically are expected to be responsible for a pinning interaction, contributing to the enhancement of the irreversibility line at high temperatures. This possibility is clarified by comparison of the observed irreversibility line with theoretical prediction.

The imaginary part of the AC susceptibility was measured as a function of temperature under various AC field amplitudes for a powder of sintered Y-Ba-Cu-O and melt-processed bulk Y-B-Cu-O with and without cracks. Its peak value was found to reduce from the prediction of the critical state model with a shift of the position to higher temperature for powder and cracked specimens, in agreement with the AC field amplitude being decreased. This deviation from the model is attributed to reversible fluxoid motion. This motion is prominent for superconductors with an effective size comparable to or smaller than Campbell's Ac penetration depth. The experimental results agree with the theoretical analysis based on Campbell's model for the reversible fluxoid motion. This analysis is useful to estimate the effective size of superconducting specimens and hence, to infer causative defects for percolative superconducting currents.

The effect of flux creep is noticeable on the critical current density, Jc, of oxide superconductors especially at high temperatures. One of the remarkable features of the phenomenon is that the irreversibility line, i.e., the boundary of zero and nonzero Jc's, is far below the phase boundary, Bc2(T). The irreversibility line was observed for bulk oxide Bi-2223 and ordinary Nb-Ti tapes with different pinning strength. These results and results on Y-based superconductors given in literatures are compared with the collective flux pinning theory.

A rapid decrease in Jc with elevating temperature was recently observed in melt-processed Y-Ba-Cu-O at low temperatures. This suggests an existence of weak links in this material. In order to investigate weak link property in this material, the history effect of Jc and Jc in the longitudinal field geometry were measured. These measurements suggest that weak link property in this material is quite different from those at grain boundaries in polycrystalline materials.

Defects such as cracks and weak link regions are considered to be the causes for the low critical current densities in melt-processed Y-Ba-Cu-O in comparison with those in single-crystalline thin films. In order to understand the influence of those factors on the critical current density, the measurement of the imaginary ac susceptibility was carried out for two melt-processed Y-Ba-Cu-O specimens; one specimen contained fairly large number density of cracks and the other did not. The imaginary ac susceptibility was found to deviate from the prediction from the critical state model near the critical temperature due to the reversible motion of fluxoids only for the specimen with cracks. From the comparison of the experimental result with the theoretical calculation based on Campbell's model for the reversible fluxoid motion, the effective width of the channels of current paths was found to be comparable to the mean spacing of cracks. This shows that the cracks are the dominant factors which limit the critical current density. Such an effect of the reversible fluxoid motion was not observed in the specimen without the cracks. That is, the influence of weak link region was not appreciable in the present experiments at the do magnetic field of 1.0 T. This is attributed to a large size of the domains in comparison with Campbell's ac penetration depth.

Critical current density and its history effect in Bi-based high Tc superconducting tapes were measured using an a.c. inductive method with various magnetic fields and temperatures. A rapid decrease in the critical current density with increasing temperature and the history effect were observed in the same low temperature region between 4.2 and 30 K. This suggests that the two phenomena are caused by low temperature weak links in the specimens. A weak link region is considered to lose superconductivity at temperatures higher than 30 K. Above 30 K, a strongly bonded area retains superconductivity and the Jc changes slowly with increasing temperature, showing no history effect.

It has been found in measurements of AC susceptibility versus temperature for high temperature superconductors that, with decreasing AC magnetic field amplitude, the peak value of the imaginary part, χ decreases remarkably accompanied by a shift of its position to higher temperatures, while the height of the transition of the real part, χ does not change appreciably. This behavior contradicts the prediction by the critical state model in which the flux pinning phenomenon is assumed to be completely irreversible. It is shown that this anomalous magnetic behavior originates from reversible fluxoid motion in pinning potentials. The AC susceptibility is calculated on the basis of the Campbell model for the reversible fluxoid motion. The result obtainained warns us against incorrect use of the critical state model for analysis of experimental data.

Significantly broad resistive transition has been observed in high temperature superconductors under a magnetic field. A similar broad transition was observed by French et al. in resistance versus magnetic field characteristics in low temperature superconductors for various current densities. In this case, the critical current density and the flow resistivity completely determine the overall resistive characteristics. This suggests that the resistive characteristics in high temperature superconductors may also be determined by these two quantities alone. In fact, the procedure outlined reproduces the commonly observed resistive characteristics. A notable feature determined from this procedure is that a knee exists in the resistance versus temperature curve. This projection corresponds to the irreversibility point, i.e. the temperature at which the critical current density is reduced to zero.

A significantly broad resistive transition has been observed in high-temperature superconductors in magnetic fields, and its mechanism has been extensively discussed. A similar broad transition was observed by French et al. in 1967 even for low-temperature superconductors, where a variation in the magnetic field dependence of the resistance was measured for various current densities. The resistive properties in low-temperature superconductors are mainly determined by the fluxoid motion. Hence, this suggests that the resistive properties of high-temperature superconductors are similarly determined. In this paper, the broad resistive transition in high-temperature superconductors expected from the simple flux flow is estimated. The fluxoid motion in the longitudinal field geometry where the Lorentz force does not work is also discussed.

In this study, we constructed a distance education system for foreign graduate students who remotely take lessons, teach themselves and have a bidirectional communication with teachers or instructors. The system was configured with the necessary modules for the student's learning, such as giving live type lectures, presenting the on-demand type learning contents and managing the learning processes by using the general purpose technology, such as the Internet, recent data-streaming technology, and the general purpose hardware and software. The system has the function of remote operation of the video camera set in the classroom by the remote learners. With this function, the remote learner can not only recognize the characters and figures written on the blackboard, but also experience more active lessons with less boredom. In this system, It is possible to provide the bidirectional communications between all of the learners and instructors during the live type lecture. The practices of giving the regular graduate school courses of Fukuoka Institute of Technology to the foreign graduate students in China were carried out.

The electric field E vs. current density J in two superconducting PbBi samples with quite different J c were measured at various magnetic fields and temperatures by using a usual resistive method. A nonlinear E-J characteristic similar to that in high T c superconductors was observed. Each E-J curve collapsed onto one of the two universal branches and a scaling behavior was recognized. It turned out that the flux pinning characteristic influences E-J curve and the scaling significantly. The stronger flux pinning makes T g or B g higher.

Ac inductive measurement on critical current densities, Jc’s, and flux motions was carried out for two Pb-Bi alloy specimens with different flux pinning strength. The interaction distance, di, was evaluated by fitting the numerically obtained flux profile with the experimental result. It was found that di depends more strongly on temperature in the specimen with weaker flux pinning strength. A discussion was given on the effect of flux creep on the temperature dependence of di.

Irreversibility line was studied for superconducting Pb-Bi alloys with different pinning strength. It was found that the magnitude and temperature dependence of the irreversibility field depend rather slightly on the flux pinning strength. The difference between the irreversibility field and the upper critical field remains finite even in specimens with very strong pinning force. The experimental result is compared with the flux creep theory and found to be explained well by the theory.

The temperature and magnetic field dependence of the critical current density, Jc, in the melt processed Bi2Sr2Ca1Cu2Oy superconductors, (2212), with normal particles was measured. Although Jc at 4.2K was about one order of magnitude larger than in the polycrystalline (Bi,Pb)2Sr2Ca2Cu3Oz, its temperature dependence seemed to be enhanced by the existance of weak links. The irreversibility magnetic fields were represented as [1-(T/Tc)2]n with the exponent n=5.44 at low temperatures and n=1.5 in high temperatures. Discussion is given on the dominant pinning centers by comparing the results and the theoretical predictions based on the flux creep.

The anisotropy of the irreversibility field was measured for QMG processed Y-Ba-Cu-O and the irreversibility field in the a-b plane was larger by a factor of 4.2 than that in the c-axis at 85 K. The result was compared with the collective flux creep theory and a good agreement was obtained. It is concluded that large values of the irreversibility field in this material is determined by the flux pinning strength but its anisotropy comes from the anisotropic upper critical field.

Critical current densities, J c , in bulk Bi-Pb-Sr-Ca-Cu-O have been measured ac inductively under various magnetic fields and temperatures. The J c drops abruptly at high fields and high temperatures and such a significant reduction seems to be attributed to thermally activated flux creep. The irreversibility field at which J c goes to zero is investigated and compared with a theoretical prediction using observed macroscopic pinning force density. The mechanism of flux pinning in Bi-based superconductors is also argued.

The critical current density, J c , of bulk Y-Ba-Cu-O samples prepared with MPMG (Melt-Powder-Melt-Growth) method was investigated by an ac inductive measurement. A significant anisotropy was observed between J c ’s parallel and perpendicular to the c-axis under a magnetic field parallel to the a-b plane. The temperature dependence of J c was also measured. The results were discussed in terms of pinning mechanism by nonsuperconducting 211 particles and background pinning centers such as point defects.

Magnetic field dependence of Jc and its history effect were measured at various temperatures by ac inductive method for silver sheathed BiPbSrCaCuO high-Tc superconducting wires. It was revealed that the result was consistent with the 4 probe dc method. It was found that the Jc was influenced by weak links at very low temperature region, where the history effect was observed. This suggests that the history effect is caused by weak links.

Critical current characteristics in quench and melt growth (QMG) processed Y-Ba-Cu-O are investigated by ac inductive measurements. The critical current in these samples is percolative as is observed in sintered materials. However, this percolative behavior is not caused by weak-link grain boundaries but seems to be mainly attributed to layers of nonsuperconducting solidified melt. The experimental result of magnetization critical current density is compared with the theoretical estimate from the effective medium theory. It is also found that the shielding current with very high density flows locally inside the sample. Candidates for the dominant pinning centers in QMG processed samples are also discussed.

It has been observed in measurements of imaginary ac susceptibility, χ″, of oxide superconductors vs temperature that a peak is shifted to higher temperature with a reduction in its value according to decreasing ac field amplitude. The anomalous reduction in the peak value contradicts the theoretical prediction by the critical state model and is caused by a reversible motion of fluxoids in pinning potential. In this paper χ″ is calculated on the basis of the Campbell model.

The intergrain critical current densities, Jc, parallel and perpendicular to c-axis were measured as a function of the magnetic field at 4.2 and 77.3K by an ac inductive method for the fairly oriented Bi1.6Pb0.4Sr2Ca2Cu3Oy specimens. The Jc's perpendicular to c-axis were higher than those parallel c-axis, about ten times within 5T at 4.2K, and about three times within 0.1T at 77.3K. Our results suggect the orientation of each grain to be especially worthwhile for performing the high Jc at the low temperature.